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Diss. ETH No 16399. Quantification of Evolved Species in. Hyphenated Thermal Analysis -. MS -. FTIR Spectroscopy Systems. A dissertation submitted to the.

Research Collection

Doctoral Thesis

Quantification of evolved species in hyphenated thermal analysis - MS-FTIR spectroscopy systems Author(s): Eigenmann, Florian Publication Date: 2005 Permanent Link: https://doi.org/10.3929/ethz-a-005124797

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ETH Library

Diss. ETH No 16399

Quantification of Evolved Species in

Hyphenated MS

-

FTIR

Thermal

Analysis

Spectroscopy Systems

A dissertation submitted Swiss Federal Institute of Technology Zurich

for the

-

degree

to

the

(ETH)

of Doctor of Technical Sciences

presented by

Florian

Eigenmann

Dipl. Chem.-Ing. born 5

ETH

July

1973

citizen of Waldkirch

(S G)

accepted on

the recommendation of

Prof. Dr. A. Baiker, examiner Prof. Dr. M. MorbidelU, co-examiner

2005

Seite Leer

/1

Blank leaf

\

dedicated to the

allowing to

reference samples

measure

the

difference...

Seite Leer / Blank leaf

Acknowledgment

I would like

Firstly,

for his support, both

plete port

express my sincere

to

gratitude

and this work whenever it

was

Prof. Dr. Alfons Baiker

and the

personally and scientifically,

my doctoral thesis in his group. I very much me

to

opportunity

appreciate no matter

necessary,

his efforts

to com¬

to

sup¬

how difficult the

circumstances.

Moreover, I would like

ing the duty of the

thank Prof. Dr. Massimo Morbidelli for accept¬

to

co-examiner in this thesis.

I furthermore thank Dr. Marek

his valuable like

suggestions

teacher and

a

and the

mentor

as

to

and very valuable

help

in

Special

Emmerich

Many Dr. Marco

during the being

acknowledge

generating

are

to

Burgener

Dr.

in

Andy Gisler,

by

turn

to

"ups

numerous

to me

(Bruker) and

settling

discussion and the

Rager (Bruker),

Netzsch GmbH

(Germany).

Dr. Wolf-Dieter

the TA-FTIR system.

Dr. Nikiaus

and Stefan Hannemann for

last years, but also the

friends I could

Gast

Jürgen

(Netzsch) for their support to

Dr. Albrecht

solutions offered

also due

thanks go

was

lots of fabulous ideas, which

the continuous interest,

suggestions given by

solving experimental thanks

the last years. He

big help during

well

for constructive discussions,

experimental investigations.

resulted in several successful I would like

Maciejewski

Künzle, Dr. Leo Schmid,

sharing

not

only

an

office

and downs" of a doctoral thesis and for

in order

to

discuss both scientific and

general

VI

topics. Additionally

sphere. Especially ing

members for

Frauchiger, Nils

van

I thank the whole

I would like

spending

Dr. Markus

a

Rohr,

to

my efforts

to

acknowledge

Ramin for the careful

rereading

ETH and

often

was

cial thank is due

to

Achter (Students

unforgettable joining

my

an

rowing

and

moments.

RowingClasses

Keresszegi, Erika Wolf,

sport

success

Zusammenfassung.

was an

contrast to

important

part of my time

scientific research, Therefore

to

a

thank also all the

in ASVZ and

lot

of

crew

World Record

hold in 2004

largest RowingClass,

spe¬

a

Poly-

times

and

members who

were

good

especially Kaspar Egger rowing ideas,

the

at

members of the GC-Achter 00-05 and the

Iten for their support in many of my crazy

with the

show

Jan-Dierk Grunwaldt and Micha

Professors) for sharing I wish

the follow¬

mates

Opre stop smoking will

also Dr.

of the

essential

the

atmo¬

Micha Ramin and Simon Diezi. In addition I

make Zsuzsanna

daily business,

pleasant

time in and outside the ETH: Dr. Simon

Dr. Reto Hess, Dr. Csilla

also in the future. I

Besides the

for the

mention besides my office

good

Vegten, Ronny Wirz,

whish, that

Baiker-group

such at

and Heiner

as

a

Guinness

the ETH

by

121

rowers.

Finally,

I would like

throughout all

to

thank my

family

these years of my education.

and my friends for their support

Seite Leer / Blank leaf

Seite Leer / Blank leaf

Table of Contents

1

Acknowledgment

v

Table of Contents

ix

Summary

xiii

Zusammenfassung

xvü

Introduction 1.1

General

1

Aspects

of Thermal

Analysis

1.1.1

Thermogravimetry (TG)

1.1.2

Differential Thermal

1 2

Analysis (DTA)

and Differential

Calorimetry (DSC) 1.2

2

3

Hyphenated Techniques

2

in Thermal

1.2.1

Mass

1.2.2

Fourier Transform Infrared

Analysis

Spectrometry (MS)

1.3

Pulse Thermal

1.4

Scope

1.5

References

Scanning 3 4

(FTIR) Spectroscopy

Analysis

6 7

of this Thesis

7 8

Experimental

15

2.1

Simultaneous Thermal

2.2

Hyphenated

2.3

Pulse Thermal

Analysis

Evolved Gas

Analysis

Analysis

Quantitative Calibration of

FTIR

15 17

19

Spectroscopic Signals

25

3-1

Introduction

25

3.2

Experimental

28

3.2.1

Pulse Calibration

29

X

3.3

3.2.2

Pinhole Calibration

30

3.2.3

Differential Calibration

30

Results and Discussion

31

3-3.1

Quantification

of FTIR

Signals Using

Gases

3-3.2

Quantification

of FTIR

Signals by Liquids

3.3.3

Quantification

of FTIR

Signals Using

3.3.4

Comparison

31 37

Solids

51

of the Calibration Methods

54

3.4

Conclusions

56

3.5

References

57

4 Influence of

Measuring

Conditionson the

Quantification of

FTIR

Signals

61

4.1

Introduction

61

4.2

Experimental

64

4.3

Results and Discussion

65

4.3.1

Influence of Sample Mass and Concentration of the Gas

4.3.2

Influence of Parameters of Data-Acquisition and Carrier Gas ..69

66

4.4

Conclusions

81

4.5

References

82

5 Gas

Adsorption

Studied

on

Zeolites

85

5.1

Introduction

85

5.2

Experimental

88

5.3

Results

89

5.3.1

Influence of Thickness of Adsorbent Bed

90

5.3.2

Influence of Temperature

92

5.3.3

Influence of Carrier Gas Flow

95

5.3.4

Determination of the

Adsorption

Heat

97

5.4

Discussion

100

5.5

Conclusions

104

5.6

References

105

6 Selective

Catalytic

Oxides 6.1

Introduction

Reduction of NO

by NH3

over

Manganese-Cerium

Mixed 109 109

XI

6.2

Experimental

Ill

6.3

Results and Discussion

113

Behavior

6.3.1

Adsorption

6.3.2

Redox Behavior

6.3.3

Catalytic Activity

114 119

in SCR

123

6.4

Conclusions

131

6.5

References

132

Final Remarks

135

List of Publications

139

Curriculum Vitae

143

Seite Leer / Blank leaf

Summary

In

thermoanalytical investigations

gas-solid

reactions

processes

or

potential

of simultaneous

species, such

of the

pulse

calibration

by relating

quantity of probe So to

thermogravimetry-mass

the

mass

was

only applied

quantitative

and

to

signals

FTIR was

or

FTIR

thermo-

or

the introduction

provides

qualitative analysis was

analyzed species,

concentration of the on

improved by

of

signals

a

to

quantitative

injected

the

combined TA-MS and its extension

thesis. Furthermore the influence of several

gas

spectrometry

This method

spectrometric

qualitative analysis

gas.

far, PulseTA®

TA-FTIR for

as

the

techniques, enabling

analysis (PulseTA®).

thermal

of the

systems. The

multi-component

in

occurring

spectroscopy has been further

gravimetry-FTIR

composition

important, especially when investigating decomposition

evolved gases is very

evolved

the determination of the

signals

checked

has been

them

experimental

parameters such

temperature and flow

investigated.

by relating

the main target of this

to

The

the

reliability

amount

rate

as

of the carrier

of quantifying FTIR

of evolved gases measured

bythermogravimetry. Comparisons zation of several

which as a

was not

with

a mass

important

significantly

reference for

spectrometer in tandem allowed

precise optimi¬

parameters for FTIR spectroscopy. MS

affected

assessing the

by

the

experimental conditions,

accuracy of quantification

by FTIR.

analysis, was

The

used

quanti-

XIV

fication

of the

(NaHC03)

or

spectroscopic signals

dehydration (CuS04

5



verified

was

the

by

decomposition

of compounds with well known

H20)

stoichiometry. The linear

dependence

tion of FTIR data.

vaporization

of

Systematic

tional calibration

studies

(varying

For the

stream.

several methods, of

pulse

calibration and

applying different organic liquids

applied tion of

on

nitrogen

by

studying adsorption

rier gas

provided

processes. The

of FTIR two

the

as a

and

as

probe

same

concentration of the

desorption

temperature

experimental

gases)

of

signals

methods based

to

gas

rate

of

to

at

either or,

as

conven¬

mentioned

liquids, the

on

we

car¬

applied

evaporation

were

studied

the

was

and selective reduc¬

atmospheric

investigate

analysis

acidity of a

widely applied.

cat¬

PulseTA

pressure. Continu¬

molecules in the

dynamics

physisorbed species

car¬

of physisorption

is shown

to

depend

on

bed. An

important advantage of

methods,

is that pretreatment of

sample

programmed desorption Integral

by

gas into the

determine the

pulsed probe

classical volumetric

set-up.

isothermal

on

thermal

adsorption

to

adsorbent, determination of the kind and as

possible

calibrating

molecule is

desorption

opportunity

PulseTA®, compared

well

is

quantifica¬

water.

such

carrier gas flow and thickness of the

the

of the

ammonia. In order

of ammonia

monitoring of the

ous

signals

and the

range of in situ calibra¬

quantification, pulse

catalytic studies,

oxides

alyst, adsorption allows

and

these methods of

in different

method based

concentrations of target

quantification

liquids

enabled easy

application

amount

of

amount

and differential calibrations. These methods

liquids: pinhole

Based

a new

of FTIR

quantification

above, by the injection of a known rier gas

on

further widen the

liquids

tions. For gases the

injected

spectroscopic signals (peak area)

of

integral intensity

between the

heats of

amount

can

of preadsorbed gases,

all be carried

adsorption

out

and the

using

amount

as

the of

XV

chemisorbed ammonia

were

found

agree well with values

to

in litera¬

reported

ture.

Finally gen oxides

TA-FTIR-MS

by

ammonia

responding metal their

catalytic ered

a

nitrates

using the

Mn/(Mn+Ce)

by NH3.

clear correlation between the

mixed oxide

catalyst

a

and

measurements

ments

(NOx, NH3)

NH3 of the

are

adsorbed

reactants

that there

on

showed similar

was

no

indicated that

at

concern¬

uncov¬

properties

and the

found for

adsorption

uptakes

was

studies indicated

adsorption

separate

measure¬

interference between adsorbed

reactants.

100-150 °C

NOx

cor¬

PulseTA

on

separate sites. Consecutive

investigations by changing the

whereas adsorbed

tions used.

investigated

of these

dependence

from the

behavior in the selective

These studies based

showed

no

as

sequence of admittance of reactants

nitrogen

Rideal type mechanism where adsorbed ammonia

phase,

prepared

molar ratio Mn/(Mn+Ce) of 0.25, whereas the activity

indicating

Mechanistic

were

composition. Highest activity to nitrogen formation was

with

NOx

reduction of nitro¬

mixed oxides. Mixed oxide

properties and

much lower for the pure constituent oxides. The that

catalytic

citric acid method and

redox

adsorption behavior, reduction of NOx

in selective

manganese-cerium

over

with different molar ratio

catalysts

ing

applied

was

formation follows

reacts

with

NOx

significant reactivity

an

Eley-

in the gas

under condi¬

Seite Leer / Blank leaf

Zusammenfassung

In

thermoanalytischen Untersuchungen

gas

analysis, EGA)

sehr

wichtig,

ist die

Analyse

der

Untersuchugen

insbesondere bei

setzungsvorgängen oder Gas-Feststoff-Reaktionen, die auftreten. Das Potential tative

Analyse

kombinierten trie-FTIR

von

gasförmigen

wurde durch die

erweitert. Diese Methode

Bisher wurde die PulseTA

wendet. Das

quantitative

quali¬

Produkte mit Hilfe der

Signale

Einführung

ermöglicht

mit der

Hauptziel und

nur

der

eine

Pulsthermoanalyse

quantitative

eingespritzten Menge

dieser Arbeit

qualitative Analyse.

in kombinierten TA-MS war

die

Temperatur

und der

Kalibri¬

des Prüf¬

der FTIR

Signale

wurde

der entwickelten Gase

wurden.

zu

bezog,

TA-FTIR für die

des

Trägergases

auf die

Zuverlässigkeit der Quantifi¬

indem

die durch

ange¬

analysierenden Komponenten,

untersucht. Die

überprüft,

zu

Systemen

einiger wichtiger experimen¬

Strömungsgeschwindigkeit

Signale wurde systematisch

zierung

Erweiterung

Der Einfluss

teller Parameter, wie der Konzentration der

Menge

Mehrstoffsystemen

in

Beziehung gebracht werden.

gases in

FTIR

Zer¬

Thermogravimetrie-Massenspektrometrie oder Thermogravime-

erung, indem MS oder FTIR

der

von

kombinierten Techniken, insbesondere die

der sich entwickelnden

Spektroskopie

(PulseTA®)

Gasphase (evolved

man

die

Signale

Thermogravimetrie

auf die

gemessen

XV111

Vergleiche

mierung einiger wichtiger experimenteller pie.

Die MS

Analyse,

gen beeinflusst

der

welche nicht

Signale

(Q1SO4

Die lineare

glichte

von

integralen

eine einfache

tifizierung

Für die

Signalen.

zwischen der

Signale

einer bekannten

Quantifizierung

thoden, die auf der

Quantifzierung oder

von

und die

der FTIR

Quan¬

Prüfgase) möglich, oder,

Signale

von

in den

der

basieren:

gezeigt,

die

dass die

wurden

Desorption

Zentren

die

zwei Me¬

am

Beispiel

wurde die Puls¬

angewandt,

von

Untersuchung

Stickoxiden der

Adsorp¬

Normaldruck. Die kontinuierliche Auf¬

injizierten

von

wie

Katalysatoroberflächen

Moleküle im

liefert die

Trägergas

Dynamik der Physisorptionsprozesse zu bestimmen. Desorptionrate

der

und Wasser getestet.

selektiven Reduktion

ermöglichte

unter

an

ver¬

Splintloch- (Pin¬

verschiedener Prozesse

katalytischen

der Konzentration der

Möglichkeit,

durch die Ein¬

Flüssigkeiten,

Quantifizierungsmethoden,

von sauren

durch Ammoniak. Die PulseTA

zeichnung

Kalibrierung

Trägergasstrom.

Diese Methoden wurden

Untersuchung

Bestimmung

tion als auch der

der Flüs¬

FTIR Daten. Für Gase ist die

Verdampfung von Flüssigkeiten

Verfolgung

überprüft.

untersucht, nämlich die Pulskalibrierung und

für die

die

Dehydratisierung

ermö¬

Menge des Kalibriergases

Basierend auf den getesteten

Beispiel

spektroskopi¬

eingespritzten Menge

Quantifizierung verschiedener organischen Flüssigkeiten

zum

der

entweder durch herkömmliche

hole-) und Differentialkalibrierung.

thermoanalyse

Genauigkeit

spektroskopischen Signale

Intensität der

Konzentrationen der

schiedene Methoden

Die

Opti¬

experimentelle Bedingun¬

Zersetzung (NaHC03)

Quantifizierung

der FTIR

(unterschiedliche

spritzung

durch

Substanzen mit bekannter Stöchiometrie

Abhängigkeit

und der

sigkeiten

FTIR

wurde durch die

H20)

5



signifikant

die

Spektrosko¬

Parameter für die FTIR

wurde, diente als Referenz für die Bestimmung der

Quanitifzierung von

schen

erlaubten

massenspektrometrischer Analyse

mit

physisorbierten Species

vom

Es wurde

Trägergas-

XIX

strom

und

PulseTA

,

von

der Schichtdicke der Probe

verglichen

bierten Gases, sowie die

werten

von

die

Vorteil der

und

Menge

des adsor¬

gleichen experimentellen

Einrich¬

und

Integrale Adsorptionswärmen

können.

die

chemisorbiertem Ammoniak stimmten gut mit den Literatur¬

überein, welche mit anderen Methoden ermittelt wurden.

Schliesslich wurde mit Hilfe Reduktion untersucht.

von

von

TA-FTIR-MS die selektive

Stickoxiden durch Ammoniak

Zitronensäuremethode

den

an

hergestellt

Redox-Eigenschaften

Mangan-Cer-Mischoxiden

an

entsprechenden

Metallnitraten mittels der

und hinsichtlich des

katalytischen

und des

katalytische

mit unterschiedlichem molarem Verhältnis

Mischoxidkatalysatoren

Mn/(Mn+Ce) wurden

der

in der

wichtiger

Methoden, ist, dass die

Bestimmung der Art

Desorption

untersucht werden

Mengen

Ein

mit klassischen volumetrischen

Vorbehandlung des Adsorbens,

tung

abhängt.

Adsorptionsvermögens,

Verhaltens untersucht. Diese

Studien, die auf der PulseTA® basierten, zeigten eine deutliche Korrelation zwischen der

dieser

Abhängigkeit

mensetzung auf. Höchste Aktivität wurde für den 0.25

Katalysator

gefunden,

niedriger

war.

Eigenschaften bezüglich

und der Mischoxidzusam¬

selektiver Stickstoff-Produktion

mit einem molaren Verhältnis

während die Aktivität für die reinen

Die

Adsorptionsstudien zeigten,

dass

Mn/(Mn+Ce)

Oxidkomponenten

NOx und NH3

an

von

viel

unter¬

schiedlichen Zentren adsorbiert werden. Konsekutive

Adsorptionsmessungen

zeigten ähnliche Adsorptionsmengen

wie sie durch separate

der Reaktanten

Messungen ausschloss.

erhalten

wurden,

Untersuchungen

Zuführungsreihenfolge 150 °C

bezüglich

eine Interferenz zwischen den Adsorbaten

was

zum

Reaktionsmechanismus

der Reaktanten

(NOx, NH3)

Stickstoff-Produktion auf einen

hin, wobei absorbiertes Ammoniak

mit

NOx

in der

unter

Variation der

wiesen zwischen 100-

Eley-Rideal-Mechanismus Gasphase reagiert,

während

XX

absorbiertes gungen

NOx

zeigte.

keine bedeutende Reaktivität

unter

den verwendeten Bedin¬

1

Chapter

Introduction

1.1 General

Thermal

and

Aspects of Thermal Analysis

analysis (TA)

is

well-known

a

quantitative information about

mainly

solid

materials, such

set

of

techniques enabling qualitative

the effects of various heat

catalysts, polymers, pharmaceuticals, clays

as

minerals, metals and alloys. The

change of the

formed under

conditions and

enthalpy

due

studied. A

techniques

strictly controlled to

physical

and chemical

widely accepted that

study

the

treatments

can

reveal

changes

phenomena occurring

between

and

temperature in the system is per¬

definition of thermal

relationship

on

mass

and

in the material

analysis (TA)

sample property

a

in

is:

group

a

of

and its tempera¬

ture.

There

are

different thermal methods

properties, including: ature

ning

difference

heat

(calorimetry),

(differential

calorimetry),

thermal

mass

allowing

the

temperature

analysis),

(thermometry),

heat flow

(thermogravimetry),

of several

measurement

rate

temper¬

(differential

mechanical

scan¬

properties

(thermomechanical analysis), electrical properties (dielectric thermal analysis) pressure

(thermomanometry

thermobarometry), optical properties (ther-

thermoluminescense),

moptometry

or

coustimetry)

or structure

most

or

acoustic

(thermosonimetry

(thermodiffractometry).

Here

important techniques: thermogravimetry (TG),

we

focus

or

thermoa-

on

the three

differential thermal anal¬

ysis (DTA) and differential scanning calorimetry (DSC).

2

Chapter

1.1.1

Thermogravimetry (TG)

1

The definition of TG

and

Analysis stance

given by

as

the International Confederation for Thermal

Calorimetry (ICTAC)

is measured as

a

is:

a

technique

function oftemperature

in which the

whilst the substance is

subjected to a

controlled temperature program. A controlled temperature program •

ing

the

mon



the

Heating or cooling mass

the

change

Therefore,

or

Additionally the

rate,

and monitor¬ most com¬

The DTG which the

or

data

are

usually presented

change

curve

be

can

(DTG),

curve

in

mass

which

also allows the

of mass loss has

teristic temperature

depicting

a

presented as

which is

temperature. The DTG

changes

rate

temperature and

monitoring

the

as

mass

a

of the

plot

loss

on

mass

the ordinate

gains plotted upwards.

mass

mass

thermogravimetric time

constant

some

temperature (the TG curve), with the

downwards and

subtle

at

thermogravimetric

plotted

ing

constant

function of time, called isothermal TG.

as a

time

against

defined

function of temperature. This is the

as a

sample

against

tial

at some

can mean:

mode of operation.

Holding mass

change

sample

sub-

of a

mass

curve

are not

ready

plot

a

point

rate

discernible

differen¬

or

of mass

useful in on

change

display¬

the TG

curve.

determination of the temperature

maximum and

the

of the

particularly

is

easily

the derivative

provides

an

at

additional charac¬

of inflection of the

investigated

TG

curve.

1.1.2 Differential Thermal

Analysis (DTA)

and Differential

Scanning

Calorimetry (DSC) Differential thermal

(DSC) have had ment

a

analysis (DTA)

great

impact

on

and differential

material science

of a great number of physical and chemical

scanning calorimetry

by enabling

properties.

the

These

measure¬

techniques

Introduction

have allowed elucidation of endothermic and exothermic processes in

temperature range. Some of the

analytical

methods include

these processes,

specific

measured

physical properties

melting, crystallizations

DTA state

lytic

are

temperatures,

enthalpy

which could be monitored

properties

transition

DSC and

by

oxidative and reductive reactions, solid

chemisorption, combustion, polymerization, curing

and

cata¬

reactions.

According

to

ICTAC:

difference

In DTA, the temperature

material is measured as material are

rial is measured material are

(DTA

as a

a

in energy

are

simultaneous thermal

to

of mass

while the substance and reference

into

a

substance and

a

reference

while the substance and

two

main thermal

(TG) and changes

measured

simultaneously.

mate¬

reference

analysis techniques

in heat

capacity of the sample

Such

combination is called

a

analysis (STA).

Hyphenated Techniques

The

success

of simultaneous

analytical

input

combine

1.2

ventional

reference

controlled temperature program.

advantageous

DSC),

a

controlled temperature program.

function of temperature,

measurements

or

between the substance and

function oftemperature,

difference

subjected to

It is often

that

a

subjected to a

In DSC, the

so

of

capacity, liquid crystal transitions, vaporization,

heat

dehydration, decomposition,

reactions,

wide

a

these thermal

by

sublimation, solid-solid transition, thermal conductivity and glass temperature. Chemical

3

in Thermal

techniques

methods with

an

has led

to

STA system.

Analysis the

coupling

Analytical

of other

con¬

methods such

as

MS, FTIR spectroscopy, GC, condensation of volatiles and their chemical

Chapter

4

1

have proven

analysis from

a

goals

of coupling these

sample

tem

and

to

data

sets

that

as

it

be suitable for

to

undergoes

thermal

techniques

eliminate the

problems

gas

have those which

the

monitor

can

most

Due

to

the

probably

is

universal

most

resulting

are

generally

course

done

taining key fragment

compounds.

Much

for

technique

currents

for

linking

et

are

but clear of the

develop¬ experi¬

al. [1-3].

of the

of the gas

MS is

systems

Their identification is the main

together with

thermal

investigated

reaction. The

qualitative MS

analysis

aids

anal¬

recorded spectrum with references

by comparing the

con¬

ions and their relative intensities for known elements and

more

and the

difficult, but

very

relationship

amount

published by Gohlke a mass

composition,

which

of the

One of the earliest reports of the was

samples

analyzing multicomponent

products.

technique,

i.e. the determination of the

(EGA)

sys¬

compare

from the first

by Materazzi

spectrometer

and

to a

is the

important

pretation of mass spectrometric data, which needs the

the ion

to

MS and FTIR. The

hyphenated techniques

in gaseous

of the TA-MS

interpreting the

ysis

trying

single

conditions. There

the gaseous

possibility of continuous monitoring

and reactions

in

of a

Spectrometry (MS)

the

application

evolved

continuously the composition

mental attempts has been reviewed in detail

1.2.1 Mass

specificity

experimental

useful methods

of TA-MS and TA-FTIR

product

STA system. The main

associated with

are

analyze

to

an

enhance the

collected under different

were

phase. Therefore,

ment

that

the gaseous in

treatment

are to

many detection methods available

advantage

analyzing

quantitative

inter¬

calibration of the system,

between the observed intensities of

analyzed species.

coupling

of MS with evolved gas

analysis

Over the years several

designs

Langer [4].

TG/DTA system have been

reported

in lit-

Introduction

Raemaeker and Bart

erature.

main

of TG-MS

development

Table 1 -1

:

Raemaekers

1965

[5]

a

gave

detailed review and summarized the

settings (cf.

Table

1-1). One of the pioneers of

History of thermogravimetry-mass spectrometry and Bart [5].

Usefulness of MS

TG

to

[29]; (Friedman [30] 1968

Zitomer [31]

1968

Wiedemann

al.

up

to

1996. Table taken from

coupling suggested by Wendlandt et al. [28] and Gohlke et al. Py-TOFMS for plastics thermal decomposition studies)

describes

designs unique et

5

TG-TOFMS instrument; first

application

to

polymers

[32] develop Mettler-Balzers TG-QMS instrument with direct

vacuum

coupling al. [33] describe

TG-CT-MS arrangement

1969

Stanton

1975

Advanced

1977

Critical review of simultaneous

et

coupling systems

Baumgartner 1979

a

et

al. [36];

for

TG-QMS [34] TG-QMS couplings [35];

high

temperature TG/DTG/DTA-MS

[38] with two-stage pressure reduction system (quantitative interface);

magnetic

sector

instrument

First Du Pont-Du Pont TG-MS apparatus

1982

Development of TG-APCI QMS [42]

>1982

Strong improvement

1983

Commercially

1984

Shushan

al.

in data

collection; software development [43,44]

[49] describe TG-APCI MS/MS; Holdiness [50] and Dollimore

1997

Development of simultaneous TG-modulated (STMMBA) by

Behrens

et

al. [51]

developments

Introduction of Stanton Redcroft-VG commercial apparatus [52,53]

et

molecular beam

mass

spectrometry appara¬

al. [54]

Reviews of application of TG-MS for

al.

to

[40,41]

1986/87

1987/88

coupling of TG

available TG-MS interface [45-48]

review TG-MS instrumental

tus

equipment

[39]

1980

et

by

of Linseis-Leybold-Heraeus TG-MS instrument [37]

development

Introduction of commercial Netzsch

introduction of TG-CIMS

polymer

characterization

by

Chiu [55] and Jones

et

[56] of capillary

1988/91

Optimization

1991

TG-MS,-FFIR Conference in

1993

Hi-Res TG-MS

1994

Development of high sensitivity orifice-skimmer coupling [62]

1997

Special

sampling

coupling by

system [57,58]

Würzburg [59]; application

Lever

et

of TG-LVMS

by Yun

al. [60]

al. [61]

commercial Netzsch-Balzers instrument with

issue of Thermochimica Acta

et

on

TG-MS

improved

Chapter

6

the

1

hyphenated

this system

on

TA-MS

technique

Netzsch, later other manufacturers put

was

(former

the marked: Mettler, Perkin Elmer, TA Instruments

Pont) and others.

Mass spectrometers used for

coupling mainly originate

Du

from

Balzers, VG, Finnigan and Sciex.

1.2.2 Fourier Transform Infrared

The

(FTIR) Spectroscopy

of FTIR spectroscopy with

coupling

a

thermal

EGA is another well-established method for the

Although

suggestion for using

the

FTIR in EGA

analysis

analysis

was

unit

to

perform

of gaseous

first made

by

species.

Low

[6]

in

1967, and while experimental results obtained from coupling of TA and FTIR spectroscopy

were

reported

in 1981

available until 1987 [8-10].

was not

[7], the commercial

Up

to

that time

cation of evolved gases from TG has been carried

reports

on

studies

introduced new



on

powerful

using hyphenated

the market

by

TA-FTIR

e.g. Netzsch in

method with the

work

most

out on

were rare.

coupling on

TA-FTIR

the identifi¬

TA-MS systems and

The TA-FTIR system

cooperation

with Bruker offers

a

following advantages:

Functional group identification and

specific compound analysis

on

the

basis of vibrational spectra. •

Simultaneous



Reference

spectral

spectral

information

libraries for

over

On the other hand it is rather difficult

pounds

with similar functional groups,

nuclear gases

not

showing

distinguish hydrocarbons

many

species.

250 000

species.

on

to use

moreover

IR absorbance

above

C3H6.

IR

to

analyze

FTIR

mixtures of

cannot

(e.g. 02, N2)

or

com¬

detect homo-

does

not

readily

Introduction

1.3 Pulse Thermal

Pulse Thermal increase the

Analysis

Analysis (PulseTA )

potential

was

developed

of conventional thermal

ket in 1997. The basis of the PulseTA

in 1996

analysis,

technique

of the desired gas into the inert carrier gas

changes

in the

progress. In

makes it

as

possible

well

injected,

enthalpy

addition, with

reactions caused MS

and

as

to

by

the

TA-MS

coupling

offers three

stream

the

of a

injection and

mar¬

specific

monitoring

or

TA-FTIR systems, PulseTA

phase composition changes resulting

injected pulses.

the FTIR

PulseTA

gas

on

to

which result from the incremental reaction

coupled

analyze

in order

[11]

and arrived

is the

amount

mass

7

The PulseTA

box

Depending

systems.

can

on

from the

be used with

the type of gas

primary options for the investigation

of gas-

solid reactions: •





Injection

of gas which

Injection

of gas which adsorbs

Injection

of inert gas in order

PulseTA

reacts

chemically with

nism of decomposition of solids

1.4

In

removal

Scope

recent

calibrate was

spectroscopic signals.

applied

for

investigation

of:

properties of gold catalyst [13,14],

catalytic mecha¬

[15,16], redox properties of ceria [17-20], and

of this Thesis

years

hyphenated techniques involving

more

situ

quantification

important.

exploring

the solid.

[16,21-27].

and

to

to

in combination with MS

combustion of methane [11,12],

NOx

on

solids.

The aim of this thesis

from TA-MS

PulseTA

and

to

thermal

was to

TA-FTIR.

analysis

extend the

Special

became

application

more

of in

effort has been devoted

finding optimal measuring conditions,

which allow

Chapter

8

quantification FTIR

1

of spectroscopic

complement

linking

of TA

series) enables Another

to

each other, for studies of

both

a

complete

more

important

the

sites

catalysts (Chapter 5)

as

(Chapter 6).

and the

on

parallel

in

application

investigation

over

or

in

the acidic

mixed oxides

to

by

of the evolved gases

crucial issue and lead

a

in

of the mechanism of the

quantification

results which would have been difficult

of PulseTA

assessing

manganese-cerium

catalyst was

the

the

of ammonia for

In both studies the

during reaction/adsorption esting

study was

adsorption

selective reduction of nitric oxides ammonia

(either

evaluations.

aspect of this

research such

reactions the

complex gas-solid

MS and FTIR spectrometer

catalytic on

in TA-FTIR-MS systems. Since MS and

signals

gain by

to

inter¬

experimental

other

methods.

1.5 References

[1]

S. Materazzi,

Appl. Spectrosc.

Rev. 32

(1997) 385.

[2]

S. Materazzi,

Appl. Spectrosc.

Rev. 33

(1998)

[3]

S. Materazzi, R. Curini,

[4]

R.S. Gohlke, H.G.

[5]

K.G.H.

[6]

MJ.D. Low, ker,

C.A.

[8]

D.A.C.

[9]

R.C. 1

Langer,

Rev. 36

(2001)

1.

Anal. Chim. Acta 36 (1966) 530.

Raemakers, J.C.J. Bart, Thermochim. Acta 295 (1997) In: W.

New York

[7]

Appl. Spectrosc.

189.

Cody,

L.

Lodding, Editor,

Analysis,

M. Dek-

(1967). DiCarlo, B.K. Faulsek, Am. Lab. 13 (1981) 93.

Compton,

Intl. Labmate 12 4

Wieboldt, G.E. Adams,

(1988) 70.

Gas Effluent

1.

S.R.

(1987)

37.

Lowry, RJ. Rosenthal,

Am. Lab. 20

Introduction

[10]

Solomon,

PR.

Charpenay, J. Whelan, J. [11]

M.

Maciejewski,

CA.

CA.

Müller,

19

(1991)

1

Tschan, W.D. Emmerich, A. Baiker,

R.

(1997) 167.

Maciejewski,

M.

Bassilakis, Z.Z. Yu, S.

R.

Appl. Pyrolysis

Anal.

Muller,

Thermochim. Acta 295

[12]

Carangelo,

M.A. Serio, R.M.

9

Koeppel,

R.

A.

Baiker, Catal. Today 47

(1999) 245. [13]

J.-D. Grunwaldt,

M.

Maciejewski,

O.S.

Becker,

P.

Fabrizioli, A. Baiker,

J. Catal. 186(1999)458. [14]

M.

Maciejewski,

Phys. [15]

P.

Chem. Chem.

Maciejewski,

M.

Fabrizioli, J-.D. Grunwaldt, O.S. Becker,

Phys.

Baiker,

(2001) 3846.

3

Ingier-Stocka,

E.

A.

W.-D.

Emmerich,

A.

Baiker, J.

Therm. Anal. Cal. 60 (2000) 735.

[16]

E.

Ingier-Stocka

E, M.

Maciejewski,

Thermochim. Acta 432

(2005)

56.

[17]

E.

Rocchini, A. Trovarelli, J. Llorca, G.W. Graham, WH. Weber, M.

Maciejewski, A. Baiker, J. [18]

WJ. Stark, L. Mädler,

M.

Catal. 194 (2000) 461.

Maciejewski,

S.E. Pratsinis and A.

Baiker, J.

Catal. 220 (2003) 35.

[19]

H. Schulz H,

WJ. Stark,

Mater. Chem. 13

[20]

C

Wögerbauer,

Maciejewski,

S.E. Pratsinis, A. Baiker,

J.

(2003) 2979.

WJ. Stark, J.D. Grunwaldt, Chem. Mater. 17

[21]

M.

M.

Maciejewski,

S.E. Pratsinis, A. Baiker,

(2005) 3352. Baiker, Top. Catal. 16/17 (2001)

M.

Maciejewski,

A.

M.

Maciejewski,

M.M.

181.

[22]

C

Wögerbauer,

74(2001)

1.

Schubert, A. Baiker, Cat.

Lett.

10

Chapter

[23]

C

1

Wögerbauer,

M.

Maciejewski,

A.

Baiker, U. Göbel, J. Catal.

201

(2001) 113. [24]

C

Appl.

Baiker,

Catal. B 34 (2001)

Wögerbauer,

M.

Maciejewski,

Wögerbauer,

M.

Maciejewski,

A.

Baiker, J. Catal. 205 (2002) 157.

Maciejewski,

T.

Burgi,

A.

11.

[25]

C

[26]

M. Piacentini, M.

(2004)

A. Baiker,

Top.

Catal. 30

71.

[27]

M. Piacentini, M.

[28]

WW

[29]

R.S.

[30]

H.L.

[31]

F.

[32]

R.

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H.L.

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Wendlandt,

Maciejewski, A. Baiker, Appl. TM.

Cat. B 59

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187.

Southern, Anal. Chim. Acta 32 ( 1965) 405.

Gohlke, H.G. Langer, Anal. Chem. 37 (1965) 25.

Friedman, J. Appl. Polym. Sei. 9 (1965) 651.

Zitomer, Anal. Chem. 40 ( 1968) 1091.

Giovanoli, H.G. Wiedemann, Helv. Chim. Acta 51 (1968) 1134. Friedman, Thermochim. Acta

Eppler,

In: I. Buzas,

1

(1970)

199.

Editor, Therm. Anal., Proc. ICTA,

4th, Mtg. date 1974 Vol. 3, Heyden and Son, London (1975) 1049.

Eppler,

Selhofer, Thermochim. Acta 20 (1977) 45.

H.

[35]

H.

[36]

E.

Baumgartner,

E.

[37]

W

Lampen and

G.

[38]

W.D.

Emmerich, E.

[39]

K.W

Smalldon, R.E. Ardrey, L.R. Mullings, Anal. Chim. Acta 107

(1979)

Nachbaur, Thermochim. Acta 19 (1977) 3.

Koopmann,

Keram. Ztschr. 29

Kaisersberger, J.

Therm. Anal. 17

p. 457.

(1979)

197.

327.

[40]

J. Chiu, AJ. Beattie, Thermochim.

[41]

R.L. Hassel

[42]

S.M.

1,

(1977),

(to

Dyszel,

Du

In: B.

Wiley Heyden,

Acta 40

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Pont), Appl. Brief TA 45 (n.d.). Miller, Editor, Therm. Anal., Proc. ICTA, 7th Vol.

Chichester (1982) 272.

[43]

H.K. Yuen, G.W.

Mappes,

Introduction

11

W.A. Grote, Thermochim. Acta 52

(1982)

143.

Till,

[44]

G.

Vârhegyi,

[45]

E.

Kaisersberger,

M.

[46]

E.

Kaisersberger,

Intl.

[47]

E.

Kaisersberger,

W-D.

[48]

E.

E

Kaisersberger,

T.

Székely,

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J.

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W.-D. Emmerich, H.

Pfaffenberger,

Thermochim.

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[49]

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[50]

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Dollimore, G.A. Gamlen, T.J. Taylor, Thermochim. Acta 75 (1984)

59.

[51]

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Warrington, Journ. Calorim.,

Anal.

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E.L.

Charsley, N.J. Manning,

Therm.

Thermodyn.

S.B.

Chim. 17 (1986) 164.

(1987) 451.

[54]

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[55]

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D.L.

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Schwanebeck, H.W. Wenz, Fresenius Z. Anal. Chem. 331 (1988)

61.

[58]

H. Wenz and H.

ellen trie.

Rohrbach, Fachtagung,

Analytik (TA, IR, MS) (1988) Würzburg

Kopplungen

der Instrument¬

für die Kunststoff- und Kautschukindus¬

12

Chapter

[59]

Fachtagung, Kopplungen

1

der Instrumentellen

für die Kunststoff- und Kautschukindustrie

[60]

Y Yun, H.L.C.

Analytik (TA,

(1972) Würzburg

IR, MS) .

Meuzelaar, N. Simmleit, H.-R. Schulten, Energy Fuels

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T.J. Lever,

[62]

E.

A.

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74.

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In: ACS

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Seite Leer / Blank leaf

Seite Leer / Blank leaf

Chapter

2

Experimental

This

chapter describes

of the the

analytical

the

methods.

experimental

of the

Specific descriptions

general

experiments

features

given

are

in

pertinent chapters.

2.1 Simultaneous Thermal

The heart of the is

setup used and reports

a

2-1.

calorimetry (DTA/DSC)

The results of both

reaction is

single

not

affected

by

measurements.

neously with

mass

changes

corrected for

mass

loss

nates

the uncertainties

caused

by

the

or

are

are

techniques

different

be

experimental

are

to

the

same

as

the target

conditions which

can occur

easier

to

interpret and enthalpy changes

gain. Moreover, simultaneous

inhomogenity

in

analysis/differen¬

directly compared,

arising with separate TG

investigated.

schematically presented

applied simultaneously

can

analysis

addition, the thermal effects measured simulta¬

In

temperature control. This is reactions

which is

and differential thermal

Thermogravimetry (TG)

tial thermal

sample.

thermal up used for the simultaneous

Jupiter®,

Netzsch STA 449 C

Figure

with

experimental set

Analysis

and geometry of

thermal

analysis

can

be

elimi¬

and DTA/DSC measurements,

samples

especially significant

and

when

inaccuracy

in the

complex multistage

16

Chapter 2

J DSC

sample

carrier

gas outlet

(MS-GC-FTIR)

/ furnace

TG

sample

carrier

sample

carrier

radiation shield

protective tube thermostatic control vacuum

seal

reactive gas

protective gas

(QH^

evacuation

inductive displacement transducer

system

electromagnetic compensation system

tight

vacuum

Fig.

2-1

Scheme of thermoanalyzer: Netzsch STA 449 C Jupiter

:

Characteristic for the instrument TG

(drift

ments

to


150 °C) in the

after the

liquids

a

very

and

narrow

FTIR

signal

injection before the thermoanalyzer.

through

due

sharp

to

a

much

larger volume (TA)

com¬

In that

and FTIR

prominent backmixing phenomena

occur¬

in the TA-chamber.

3.2.2 Pinhole Calibration This method with

was

used

organic liquids

placed

to

or

calibrate the FTIR spectra when

water.

in the crucible closed

(0.1, 0.5, 50 ml min"

25 mg of the

the lids with

calibration

investigated liquid

pinholes with

mm). The heating and flow

and 2

1

by

Usually

making

rate

was

different diameters

were

10 K

min"1 and

respectively.

,

3.2.3 Differential Calibration Last method allows

gation

of the

carrying

out

the calibration of the FTIR

decomposition (or desorption)

process

signal

during

and investi¬

one run.

up consists of two crucibles: the first contains the

liquid used for the

and the second

quantification

FTIR

signal

perature

one

the

obtained

(25-50 °C)

investigated sample.

during vaporization

or

during a

The

of the

non-isothermal

liquid

run

at

carried

The

set

calibration

is based

on

the

low,

constant tem¬

out

with low heat-

Quantitative

ing

rate

up

to

temperature of the solid

The

sample.

rate

of vaporization

very broad range

by varying

experiments

normally performed applying

30 min 10 K

were

followed

by

the

min"1. The sample

25 mg and the

overlapping

mass

the temperature and the

of the calibrated

of decomposed

of the calibration and

the

liquid

ing

the isothermal

sample was

with

liquid

was

The carrier gas flow

before

was set to

25-50 ml min'

in

a

diameter. The of about

period

of

rate

in the range of 10-

100-200 mg. In order

of the

beginning

changed

heating

a

processes, it

measuring

be

pinhole

reference material used for the calibration had run,

can

31

decomposition

isothermal

an

decomposition period

mass

Spectroscopic Signals below the

lying significantly

temperature

a

Calibration of FTIR

was

to

avoid

important that

fully evaporated

decomposition

dur¬

of the solid.

.

3.3 Results and Discussion

We

have

investigated

described above. The gases and

3.3.1 The

liquids

application

FTIR in

in the calibration

a

FTIR

of PulseTA

by comparing simultaneous

decomposed

position 2

presented examples

Quantification of

illustrated

was

the three methods of calibration

—>

results obtained

by

means

of

of FTIR

a

occurs

H20

+

heating

rate

according

C02

to

of 10 K

Eq.

signals

thermogravimetry

PulseTA®-FTIR experiment. 36.15

+

of both,

Gases

quantitative interpretation

under helium with

Na2C03

application

signals

procedure.

Signals Using

for

of sodium bicarbonate

NaHC03

describe the

of FTIR

mg of

is

and

NaHC03

min'1. The decom¬

1:

(1)

Chapter

32

In order

injected

to

3

the FTIR

quantify

before and after the

of C02,

signal

decomposition

of

of C02

were

NaHC03 (Figure 3-1A).

The

two

1 ml

pulses

B

12.34 mg

50-

30-

pulaa

20-

10-

//b.osII

at 50 *C

\

puis«

at 250 'C

// /4,5o\ll

V

HI/2-7s\\I

20

time / mln

2

4

amount of

Fig.

3-1

:

A: 3-D

the

FTIR-diagram of

6

C02

present

8

in the

10

sample

of the calibration

12

14

/ mg

(2 pulses) and the evolved

decomposition Relationship between amount NaHC03. and sample intensity of C02 traces recorded in TA-FTIR system. C: FTIR function of amount of C02 present in the sample. as by a

B:

of evolved

gases

during

C02

in the

Amount of C02 found

mean

the

value of the

perature of the

of the

injected pulses

of the evolved

signal

injected gas was

decomposition

of the

integral intensities

integral intensity

Spectroscopic Signals

Calibration of FTIR

Quantitative

28 °C. The

C02

amount

calculated from these data

quantification

intensity

of FTIR

NaHC03 Figure

were

method. In order

signals

and

amount

decomposed.

The

to

corresponds

check the

of evolved

9236

was

tem¬

the

during

confirming

the accuracy

dependence

between the

traces

amounts

presented

are

of in

3-IB.

Figure

3- 1C shows the relation between the

derived from FTIR obtained linear

(peak areas) presented

and

case

and the

signals

dependence amount

from 0.64

integral

12.34

milligrams

of evolved

a

intensity C02

of the FTIR

have been

(Eq. 2)

was

101/99

a.u.,

signals

injected

independent

=

investigated.

C02

The

traces

wide range: in the

C02. the

on

At each temperature

into the carrier gas stream; the

shape

and

pulses

two

integral intensity

of the temperature (50 °C: 101/100

950 °C: 101/98

/

was

C02

sample.

intensities of

of evolved gas has been hold in to

of evolved

of C02 present in the

amount

between the

amount

The influence of the temperature (in the TA chamber)

of

The

9.52 mg, which

to

species, different

resulting C02

while

a.u.,

a.u.

of C02 formed

agrees well with the stoichiometric value of 9.47 mg,

of the

1727

was

33

a.u.,

/

350 °C:

a.u.).

}[j^(v)

1

*

-r-

methanol

'^^T^

time / min

02

04 w

Fig.

3-4:

A: FTIR spectra of

B: methanol and

pendence

binary liquid

methylformate traces

between the

as a

integral intensity

D: resulted FTIR absorbance ratio

06

(methanol)

/

06

mgVmg

mixtures of methanol and

function of the mixtures

of the FTIR

vs. mass

ratio

signals

on

methylformate.

composition.

the mixture

(W) of methanol in the

C: The de¬

composition. binary mixtures.

Quantitative

is in

principle possible

to

limitation is the poor

ous

stirring As

liquids, the

is an

not

possible

example

we

Calibration of FTIR

obtain the

vapor-liquid equilibrium data,

mixing (natural

in the

commonly

convection

only).

but

Note, that

a

seri¬

sample

used TA-FTIR systems.

of quantification of FTIR spectra

present the determination of the

decomposition

41

Spectroscopic Signals

amount

of sodium bicarbonate and

by pulse of

water

dehydration

calibration with evolved

during

of copper sulfate

pentahydrate. Figure 3-5A and

shows the

decomposition

water traces

of 106.5 mg

recorded

during

NaHC03 according

20

30

two

to

calibration reaction

pulses

(1). The

40

time / min

during decomposition of 106.5 mg NaHC03 (A) and 48.9 mg CuS04 5 H20 (B). Heating rate: 10 K min"1, carrier gas: 50 ml min"1, Injected water volumes: 10 JLLl (A), 2.5 |ll (B). Fig.

3-5:

Pulse calibration:

water-traces •

recorded

42

Chapter

mean

the

3

value of the

integral

integral intensity of

amount

formed

injected

during

the

intensities of the

of the

water

of the evolved

signal

10.0 mg

was

decomposition

injected pulses

(ca.

10

was

H20

was

The

(4.1).

445

515

The

a.u.

of

amount

calculated from these data

while

a.u.,

H20

corresponded

to

10.87 wt.%, which agrees well with the stoichiometric value of 10.69 wt.%,

confirming the

the accuracy of the

decomposition

due

to

corroborated

the evolution of C02 and

ric value

and

was

amounts to

shows the

dehydration

of 48.9 mg

dration of the

sponded

to

During

firmed

of FTIR

the further

respectively).

The

the observed

mass

of

loss

36.85 wt%, while the stoichiomet¬

recorded

H20. two

calibration

pulses

At lower temperatures the

dehy¬

during

two

steps; the observed

well with the evolved

agreed

at

mass

loss

corre¬

of

water

amount

amount

(between

about 220 °C

(dehydration

and stoichiometric

mass

of

48 and 52 min)

monohydrate),

losses

(7.17 and

of water determined from the FTIR of the

injected

2.41 mg

decomposition peak was 7-24

results and the reaction

gravimetric

analysis:

stoichiometry

(26.35 wt.%).

paring the integral intensity of the

5



molecules evolved

water

TG

was

occurred in

dehydration

by experimental

intensity

CuS04

25.82 wt.% and

the residual

H20

water traces

pentahydrate

by means

by the

method. The

36.90 wt.%.

Figure 3-5B

found

quantification

(ca.

2.5

con¬

7.21 wt.%,

traces

pü)

as

by

water

com¬

and the

wt.% which is in accord with the

stoichiometry.

Pinhole Calibration

During

the

pinhole

gas stream, but

by

a

linear

calibration the

placed

heating

into the

ramp. For

compound

thermoanalyzer

liquid

mixtures

is

not

and

injected

into the carrier

vaporized isothermally

(cf. binary mixtures)

it is

or

impor-

tant

select

to

related

ization of

3-6 shows the

pinhole sizes.

nol remarkable

mass

In this case,

.

losses

40

Due were

the low

recorded

immediately

T-

'

1

SO

certain

a

amount

T—''"

'

1

60

70

accurate

an

t

80

'

—\

90

100

I"

1

1

1

40

1

SO

1

1

00

1

1

1

70

1

80

1

1

00

1

1

1

100

1

1

1

120

1

1

p

130

r~~\

1

140

150

'

Mi

'

40

30

I

3-6:

sample

indicated

on

25 mg,

the

heating

curves.

rate:

loss

during evaporation

1

'

"

'

50

i"



SO

'

1

1

1

40

1

1

60

1

1

80

1

1

p

100

'

'

'

'

100

r-

110

/ 'C

1

|

120

1

90

80

70

even

r,M-'

140

""T

160

'"

'

"I

160

'

200

temperature / °C

Pinhole calibration of

mass:

measure¬

using larger pinhole

temperature

110

starting

of the substance will evaporate

temperature / *C

Fig.

after or

lid

mass

pans

of acetone and etha¬

boiling points

temperature / *C

30

of

during vapor¬

(C) and hexanol (D) from the

water

to

determine

to

because

r——'—-r

30

overlapping

recorded

signals

especially when working without

sizes, it is difficult

(cf. Figure 3-6A)

losses and FTIR

mass

(A), ethanol (B),

acetone

with different

avoid

to

bands.

absorption

Figure

ment.

characteristic wavenumber interval

a

43

Spectroscopic Signals

Calibration of FTIR

Quantitative

acetone

(A), ethanol (B),

10 K min"

,

flow

rate:

water

50 ml min"

(C) and heaxanol (D), ,

pinhole

diameters

are

44

at

Chapter 3

room

temperature, which in turn, will disallow

between the with tion

a

amount

pinhole

at room

of

size of 0.1

sary

to

achieve

loss in the

pressure)

higher

accurate

water

beginning of the experiment

of

the

liquids,

some

than 25 mg.

amount

due

of the

mass

measurements were

loss of the

started

The detailed results of the relative standard deviation

boiling points ranging at

Table 3-3 :

can

and

was

from 56 °C at

introduce

the a

(acetone)

beginning

to

the

rate

mass

(vapor was

liq¬

mg.

listed in Table 3-3. The

liquids with

154 °C (hexanol). The vapor¬

of the

error

by

of the calibration

smaller than 4% for all four

significant

Pinhole calibration: FTIR

are

pinhole

recorded. The cali¬

precisely 25.0

calibrations

a

isothermal part of

some

mass

the base¬

substance used

was not

the

vaporiza¬

were neces¬

high evaporation

sample

was

lids

caused

calibrating

exactly when

pinhole

(RSD)

low temperatures

its start, which

the

at

For ethanol

uncertainty

During experiment settling

uid, measured by the internal TA balance,

ization

to

acetone

even no

A lid

traces.

which started

trace,

and hexanol

calibration. To avoid

the temperature ramp the

bration

and for

relationship

of FTIR

prevent the

integration of the recorded peak.

enough

mm was

intensity

to

necessary

mm was

temperature and obtain the FTIR

line and enabled proper size of 2.0

and

evaporated liquid

the

finding

experiment

during

integral intensity

the

recorded

or even

pinhole

before

calibration

during vaporization

of

liquids (acetone, ethanol, water and hexanol) from pans covered by lids with various pinhole sizes. Peak areas were determined at their characteristic wavenumber and 25 mg of different

normalized

Sample

to

an

average of 100

0.1

mm

a.u.

0.5

mm

acetone

98.7

-

ethanol

97.2

-

water

102.0

hexanol

104.2

1.0

mm

2.0

mm

no

lid

RSD / %

101.1

101.5

98.6

1.52

99.1

102.8

100.9

2.38

98.8

99.2

1.78

98.1

100.2

3.73

-

-

102.7

94.8

45

Quantitative Calibration of FTIR Spectroscopic Signals

procedure,

also

was

reported by Slager

highly volatile compounds (e.g. occurred before the TGA

affects

intensity of the

backmixing, resulting can cause

in

started.

actually

crucial factor in the calibration recorded

signals.

of the

does

desorption

or

spectroscopic signals

has been

MS-TA system

In order

[11].

pinhole method, experiments

to

study

were

The real progress of the

curve

(DTG) that indicates the

shape

carrier gas flow

carried

out

evaporation rate

of the

of the recorded

3-7 shows the

normalized in order

signals.

carrier gas flow

in

a

prominent

phenomenon

single

stage due

to

and intensity of

shape

on

some

of

us

the calibration

for the

by

the

with different carrier gas flow

is reflected

mass

change.

by

the derivative TG

This progress has been

spectroscopic signals

of the FTIR

quantification

to

heated with 10 K allow

to

as a

investigate

the

function of the

a

the

leads

to

presented

signals using pinhole

carrier gas flow

rate.

25 mg

min"1. All DTG and FTIR curves

comparison

The results

rate

and results in

backmixing (cf.

higher

rate.

sample of ethanol was

tem

the

this influence

(2.0 mm) calibration of ethanol when varying the

the FTIR

to

intensities of the recorded

not occur

on

This

the recorded FTIR spectra which allowed

of the

leads

to more

analyzed quantitatively by

rates.

Figure

rate

signals.

integral

The influence of the flow

overlapping signals.

to

Low flow

that

procedure,

observed spectra, but increases the residence time of

significant tailing

when the reaction

changes

methanol) significant evaporation

and

difficulties in the evaluation of the

compared

[21]. They found that for

molecules in the TA-FTIR system and leads

evaporated

signals

a

intensity and shape of the

maximum

the

acetone

run was

The carrier gas flow is

and Prozonic

of flow

in

rate

Figure

influence

3-7

clearly

on

the

were

shape

of

indicate that low

increase of the residence time in the TG-FTIR sys¬

long tailing of the

recorded FTIR

comparison of the real

rate

of the

traces

due

to

evaporation

prominent

process rep-

46

Chapter 3

'

A

5mlmln1

20 ml

mm

27

50 ml

mln1

65 ml

DTG

FTIR

5 min i

1

35 ml mln

mln1

JIJLJL 25000

0 00

0 01

0 03

0.02

flow"1

Fig.

3-7

heating rate: 10 K min'1, the integral intensity and

tween

the

(thin) and

DTG

the flow

to

resented 20 ml

by

mass

al.

(ml

to

min"

the

transfer

thermoanalytical

varying carrier FTIR (thick lines).

flow defined

), which

delayed a

linear

are

as

B:

sample size: The relationship be¬ rate,

the ratio of

marked

FTIR

flow

on

volume

the data.

for

traces

relationship

injected

the

flow

of

between FTIR absor-

and

(by

convection and

mass

spectrometric

diffusion) curves

on

was

the relation

reported by

[11].

Although, for the

ml"1

reciprocal values of the flow rate (Figure 3-7B). A detailed study

of the influence of

et

curve

reciprocal

However, there exists

bances and the

between

of carrier gas

rate

DTG

min'1).

Roduit

/ min

006

0 05

A: Pinhole calibration of ethanol with

:

25 mg,

(1 ml)

0 04

the best accordance between DTG and FTIR

highest flow rate

of 65 ml

min'1,

in further

traces was

found

experiments generally a flow

Quantitative

to

min"1

of 50 ml

rate

used. This flow

was

nation of different

TG-steps

in

a narrow

De la Guardia and coworkers

critical parameter in vapor

analytical sensitivity of 50 ml

[17] used

min'1,

stated that

The main

a

good compromise

temperature window.

spectrometric analysis which

which allows

a

20

(60 ml

rate

of the

carrier gas flow

TG

or

min"1)

of

one

this method temperatures up

of the FTIR peratures

to

obtain the

FTIR

the

run.

As shown

boiling point

for the calibration.

however, affect the process

low it in situ. Therefore

we

flow

in the carrier gas

al.

FTIR

same

it

et

can

be

requires

signals.

dependence between

signal required

can,

to

a

minimize the differences between ther¬

pinhole-calibration

experimental

is

affects the

nitrogen

in his studies with the

evolving species

rate to

DTG) and

disadvantage

be done in

necessary

a

rate

h"1 sampling frequency. Marsanich

beside uncontrolled

mentioned above, lies in the fact that the calibration and

can not

are

be

sampling frequency. They selected

higher diffusivity

a

moanalytical (e.g.

as

to

(8.7 ml) and FTIR path length (123 mm). Generally,

higher minimal

loss,

proved

[23] found that the carrier gas flow

FTIR

phase

and the

similar flow

a

gas cell volume

a

rate

47

Spectroscopic Signals

high analytical sensitivity and sampling frequency allowing discrimi¬

achieve

rate

Calibration of FTIR

developed

to

be

and

by Slager

of the

mass

Application

investigated,

applied

decomposition

at

al.

[21], using

calibrating

loss and

mass

substance

integral intensity

of such if one

high

tem¬

wants to

another method in

fol¬ our

laboratory, which will be discussed next.

Differential Calibration

The differential calibration is based ization of

a

liquid compound

and simultaneous

monitoring,

losses and intensities of FTIR

at

on

the isothermal

or

non-isothermal vapor¬

different temperatures, with low

in differential time

signals. Figure

heating

rates

periods, corresponding

mass

3-8A shows the

principle

of this

48

Chapter

3

ethanol i

1

0

20

specified

the

same

rate:

time

50 ml min"1. B: Linear

Crucible diameter

method

was

applied

for

mm

ing

time intervals

the

Figure the

same

on

the

are

indicated

mm

for

(5 min)

integral

and

by

plotted against

the TG

additionally the

time intervals

absorbances

on

water

(10 min)

signal.

same

is

were

the

This

mass

for

The very

over

liquids during

the temperature

curve.

calibration.

at

temperatures

measured

during

con¬

loss Am recorded dur¬

dependence

relationship

depicted.

of absorbance

of evolved

amount

isothermal calibration with ethanol

time intervals

3-8 B where

longer

dependence between the integral

for ethanol and 17-0

between 30 and 70 °C. The stant

r—

100

various temperatures. Interval time:

at

Corresponding temperatures 7.5

1

1

80

loss / mg

(5 min ethanol and 10 min water)

time interval.

1

SO mass

A: Differential calibration of ethanol

3-8:

5 min, flow a

loss / mg "i

40

HO

Fig.

mass "

r

is

presented

in

collected

during

good regression

coeffi-

water

Quantitative

(r2

cients obtained for ethanol accuracy of the

high

amount

periods

of

(observed

s

signals

signals

did

ml

of the reaction

course

14.1

to

significantly

period

and the

evaporation

is

this

During

are

the

experimental

(flow of 20

s

set-up.

beginning of the reaction

steady state

performed period of

the

this

of the

delay (flow:

in the

was

min'1). mass

Data

loss and

50 ml min"

)

placed

in

of the FTIR traces, but the

phenomenon. two

The target

in the isothermal mode

relationship

sam¬

separate pans which

thermogravimetric at

between the

evaporated liquid

can

are

The

runs.

relatively

low

intensity of the

be determined in

a

few

which increases the accuracy of the calibration. After

of the calibration

the TG

by

tailing

conventional

during

amount

periods

affected

sample

as

to some

curve,

liquid,

the second

which is indicated

experimental according

by

the end of the

stage is started, to

during

the chosen tempera¬

ramp. This in situ calibration is shown in

tion

chosen

(DTG curve) and that of measured

which the temperature in the system is raised ture

exact

influence the calibration results. At low flows the back-

not

prominent leading

differential time

on

one

had been reached. The 5.6 seconds

first calibration

loss

in

lag between

few minutes after

during a

weighed continuously

signal

species

ml

and the calibration

mass

arbitrarily

min"1)

was not

temperature.

the time

(for flow of 65

became

calibration

total

with the

signals

between the real

FTIR

signal

of the FTIR

DTG curve) and the appearance of the FTIR

collection occurred

ple

0.9975) indicate the

=

thermobalance in

by

of evolved

measurement

on

range of 4.3

mixing

(r2

water

of time allowed the extension of the method for the simultaneous cali¬

Depending on the flow rate,

FTIR

measured

49

Spectroscopic Signals

technique.

integral intensity

evaporated liquid

bration and

FTIR

0.99998) and

calibration

applied

The correlation of the

=

Calibration of FTIR

by FTIR of the

evolved

water

Figure

formed

3-9 which

depicts

during dehydration

the

quantifica¬

of sodium bicar-

Chapter

50

Fig.

3-9

Differential calibration:

:

NaHC03 (A) 50

(B)

3

and 200 mg

ml min'1. The

CuS04

mass

during decomposition of 200 mg H20 (B). Heating rate: 10 K min'1, carrier gas: 25 (A),

water-traces

5

recorded

of water used for the calibration

35 mg (B). Interval time: 10 min. Crucible diameter: 7.5

bonate and copper sulfate

pentahydrate. Figure

recorded

and

to

during calibration

reaction

10 min

H20 was

was

was

(Eq. 1). 2039

5045

The

a.u.,

a.u.

8.90 mg. The

integral

while the

The

amount

amount

lated from these data

decomposition

of

at

50 °C

3-9A shows the

of the

of evolved

during

corresponds

to

(A) and

water

during

the

water

trace

NaHC03 according

of 200 mg

integral intensity

formed

25 mg

mm.

of the FTIR absorbance

H20

was ca.

over

signal the

the interval of of the evolved

calibrating

decomposition

stage

calcu¬

10.98 wt.%, which agrees well with the

Quantitative Calibration of FTIR Spectroscopic Signals

stoichiometric value of 10.69 wt.%, the differential

Figure

quantification

3-9B shows

the observed evolved

amount

During

loss

mass

the

corresponding

CuS04

recorded •

5

corresponded

H20. to

decomposition starting

of

at

determined from FTIR

water

to

with

1071

3.3.3

integral intensity

Quantification of

At the first step of

decomposition

agreed

well with the

about 220 °C

(45 min), the

based

traces

loss agrees well

mass

7.21 wt.%,

vs.

on

applied

calibration data

was

signal

a.u).

FTIR

Solids

Signals Using

with solid calibration materials. In this

into the TG-FTIR system the calibration substance vent

The

respectively).

Some of the methods described above for the calibration of FTIR

also be

water

release of 12.68 mg of water results in FTIR

7.26 wt.% (mass loss due an

calibration and

24.90 wt.% and

with the stoichiometric value (7-35 wt.% amount

accuracy of

during differential

evolved: the observed

monohydrate

the

good

by FTIR (25.64 wt.%).

of water found

to

the very

method.

water traces

of 200 mg

decomposition

corroborating

51

case,

must

signals

before

could

injection

be dissolved in

a

sol¬

that possesses different characteristic FTIR bands than the calibration sub¬

stance.

Figure salicylic

3-10A shows the spectra recorded

acid

(ASA

or

spectra of the main and

phenol.

aspirin)

products

at

during decomposition

260 °C under

from

The bands used for the

of

dry and wet conditions,

IR-library:

acetic

quantification

acetyl-

and the

acid, salicylic acid (SA)

were

1800 cm"

(acetic acid)

and 3300 cm"1 (SA).

Figure

3-10B

position of 21.5

depicts

mg

the acetic acid and SA

aspirin

under

dry

and

wet

traces

recorded

during decom¬

(saturation of the

carrier gas

by

Chapter 3

52

JL

/\

phenol

salicylic acid acetic acid, (S

e o

É

.wet

-dry /*\-

m3500

3000

2500

1500

21

wavenumber /

1000

cm"1

wet. 29 wt.%

Jl

c

e

fV salicy|ic

FTIR

dry. acetic acid 100-

TG

80

I



8

20

E

o

25 wt.%

wet: 24 wt.%

43 wt.%

57 wt.%

temperature / °C

Fig.

3-10:

A: Extracted spectra recorded

260 °C under

wet

during decomposition

approximately

B: Acetic acid and

traces.

wave-

salicylic acid

during decomposition of 21.5 mg aspirin under wet and dry conditions and done after the TA, imme¬ pulses injected before decomposition: Injections

recorded

calibration

were

diately before

the FTIR-transfer-line.

purging through

water at

30

°C) conditions.

10 mg SA dissolved in 100 ml ethanol

\i\ of the SA/ethanol avoid the show

at

(thick line) and dry conditions. The window of the characteristic

number is marked and used for further time-resolved traces

of aspirin

mixture

crystallization

were

was

injected

For the calibration

used. Two after the

|xl

of acetic acid and

thermoanalyzer

of SA in the TA chamber. Gravimetric

clearly a two-step-decomposition

57 wt.% for the first and second step,

two

in order

traces

to

(TG)

dry

conditions

(43

whereas

during the

reaction

of aspirin under

respectively),

solution of

a

and

Quantitative Calibration of FTIR Spectroscopic Signals

under

conditions the

wet

acid is evolved main

mainly

in

decomposition a

first step,

decomposition product

tion of

phenol

FTIR under

wet

conditions

slightly higher

was

(24 and 25 wt.%) for both conditions. Robeiro

mass

loss in

to

which agrees with

our

tion of acetic acid and

a

loss of 42.8% followed

results.

evaporation

by means

of ASA and SA.

of chromatography but

TG-FTIR system,

same

different flow able

flow

rate

carrier flow

the SA

heated transfer-line

high (50 SA

on

ml

possible

flow

rate

acetic acid

by Jackson

because of the

generate

directly

dry

of

con¬

almost the

reported

also

a

57.2% in the second step, mass

They

were not

on

was

loss

to

the evolu¬

able

quantify

to

it.

the FTIR spectra of the SA

heated under

nitrogen

with

al. [25], who found consider¬

et

high boiling point narrower,

the top of the

to

identified the evapo¬

of

salicylic

acid. With

but in TGA system

instability problems of the balance.

on

(200 °C)

the FTIR spectrometer and

high

The fact, that

thermoanalyzer just

cold spots in the system. This

acquisition due

to

the

kept

before the

the flow

peaks

in

Figure 3-10B),

procedure slightly

sharpness

and the short distance between

would result in much ment.

means

rate

min"1), leads to accurate quantification and avoids condensation of

accuracy of the data

high

acid

the IR responses would be

rates can

injected

salicylic

and pressures

peak broadening

higher

we

rates

by

attributed the first

They

To characterize the influence of the gas flow in the

evolu¬

consecutive steps, between 120 and 400 °C. The first step up

260 °C occurred with

ration process

were

al. [24]

et

by

than under

of the acetic acid

amounts

°C) the

additionally the

of evolved SA found

same

two

260

(ca.

temperature

about 360 °C

amount

(29 wt.%)

ditions (23 wt.%). However, the

at

well resolved. Acetic

are not so

higher

at

is SA and

is observed. The

steps

53

of the

injection position

but condensation

larger error than

some

peaks

or

lowers the

caused

by the

and IR cell (cf.

resublimation of SA

peak cutting in

the calibration seg¬

Chapter 3

54

3.3.4

of the Calibration Methods

Comparison

Table 3-4 compares the results of the

quantification

using

methods, pulse calibration (PC) and differential calibration (DC).

two

in situ

The

comparison

is based

the

on

amounts

of water evolved

tion of sodium bicarbonate and copper sulfate

with well-known

decompose recorded

of the FTIR spectra

quantification between

Table 3-4:

Comparison

obtained by

pulse calibration (PC)

of the

gravimetric or

(RSD) is calculated based

Sample

on

compounds

thermogravimetric

accuracy of the

applied

curves

proce¬

spectroscopic signals. and

spectroscopic results

differential calibration (DC)

of sodium bicarbonate and copper sulfate

Both

pentahydrate.

and the

comparing the

allow

simultaneously

dures used for the

stoichiometry

during decomposi¬

pentahydrate.

of

water

evolution

during the decomposition

The relative standard deviation

TG and FTIR results.

method

step

stoich.

NaHC03

1

PC

10.69

NaHC03

1

DC

10.69

FTIR

TG

-

-

RSD / %

10.87

1.68*

10.98

2.71a

5

H20

1

PC

28.84

25.82

26.35

2.05

5

H20

1

DC

28.84

24.90

25.64

2.97

CuS04

5

H20

2

PC

7.21

7.17

7.24

0.98

CuS04

5

H20

2

DC

7.21

7.35

7.26

1.22

CuS04 CuS04



RSD is related

to

the stoichiometric

expected value.

The relative standard deviation FTIR

results

(RSD)

is calculated based

on

TG and

results, except the decomposition of sodium bicarbonate, where TG are

neously,

expected

not

taken into

i.e. in the

same

account

results

are

C02

and

water

evolved simulta¬

temperature range. Here the RSD is related

stoichiometric value

spectroscopic

because

only.

All deviations between

to

gravimetric

lower than 3% which corroborates the

good

the

and

accuracy

Quantitative Calibration of FTIR Spectroscopic Signals

of the situ, in

applied one

methods. The fact that both these methods could be

experimental

run,

calibration

time-consuming

of injecting the fluid before

hyphenated

range of the can react

underlines their

after the

TG-FTIR

sample (allowing

with the

investigation

less

application

before the TA,

of adsorption

or

gas-

anal¬

simple quantitative

TA allows

in

opportunity

the

technique. Fluids, injected

injection after the

solid reactions), whereas

The

thermoanalyzer widens

e.g. the

applied

potential. They offer a much

procedure than generally applied. or

55

ysis of the evolved species. The

pinhole

calibration. The results

quantification

pinhole

presented

of volatile

extends the scope of

significantly

calibration method

in this

compounds.

confirmed its

study

The

and different temperature ramps

use

liquid

applicability

of different diameters of the

during

calibration

provides

opportunity of calibrating FTIR signals with liquids having very different oration

(vapor pressure)

rate

at room

achieved calibrations for methanol, acetamid with this method

experimental the

amount

parameters

found

cal of the flow

(e.g.

by means

a

constant

dimethyl changing

We showed that

proportional to

pinhole

method is its e.g.

acetone.

already during sample handling

the relation between the

amount

and

the

recipro¬

of evaporated

application

with

Part of the calibra¬

experiment settling,

liquid

and the FTIR

inaccurate.

The differential method, described in this paper, further tunities of

[21]

rate.

tion agent evaporates

integral signal

formamide and

the

evap¬

and Prozonic

application.

of FTIR absorbance is

possessing very low boiling point as

substances

Slager

flow rate, however,

flow rate) limits this

Another serious limitation of the

rendering

temperature.

xylene, dimethyl

using

for

liquid

and Marsanich

calibrations

et

al.

by

the

vaporization

extents

the oppor¬

methods described

[18,21]. Especially high volatile materials (e.g.

by Slager acetone,

56

Chapter

ethanol)

can

3

applied

be

without any limitations for

method. For the calibration, the

chosen differential time interval

of the

experiment, where already significant are

are

only

a

certain, arbi¬

taken, omitting the ill-defined

trarily

TA-FTIR data

data from

experimental

with this

quantification

losses may

mass

occur

start

before the

collected.

3.4 Conclusions

The methods of quantification of FTIR

techniques,

less

time-consuming the

as

solid reactions

tages of the

monly very can

calibration

quantification (cf. chapter 6)

pulse

used

quantification

performed

procedure which

of

in

facts and minimizes

a

and

significantly

run

experimental

errors

application

range of the TG-FTIR

(e.g.

gas-

of solids. The main advan¬

are:

compared

simplicity,

to

the

com¬

accuracy and

experiment

decreases the influence of

arte¬

shift of the base-line in FTIR cell,

flow, etc.) which

technique,

which is

characterizing reactions involving solids reactions. The extension of the

solid-liquid

quantification

be used in different stud¬

can

bias the

quantifica¬

FTIR spectra. The described calibration methods widen the

on

uid and

and easy and

The fact that both the calibration and

tion based

decomposition

applications

can

decomposition

of the FTIR spectra

single

differen¬

pulse and

adsorption phenomena (cf. chapter 5),

influence of changes in the carrier gas

able tool for

the

on

and differential calibration methods

good reproducibility. be

based

described in this work, allow in situ

tial

ies, such

signals

signals

in

very sensitive and reli¬

and gases such

as

complex

quantification by applying liq¬

solutions opens up further

of spectroscopic

a

coupled

opportunities

in the

area

TG-FTIR-MS systems.

of

Quantitative Calibration of FTIR Spectroscopic Signals

57

3.5 References

[1]

Magri,

S. Materazzi, R. Curini, G. D'Ascenzo, A.D. Acta 264

(1995)

Thermochim.

75.

[2]

S. Materazzi,

Appl. Spectrosc.

Rev. 33

(1998)

[3]

S. Materazzi,

Appl. Spectrosc.

Rev. 32

(1997) 385.

[4]

A.B.

Kiss, Acta Chim.Acad. Sei. Hung. 61 (1969) 207.

[5]

CA.

Cody,

[6]

P.B.

[7]

J.O. Lephardt, Appl. Spectrosc.

[8]

M.

[9]

L.C.K. Liau, T.C.K.

189.

Dicarlo, B.K. Faulseit, Am. Lab. 13 (1981) 93.

L.

Roush, J.M. Luce, G.A. Totten, Am. Lab. 15 (1983) 90.

Mittleman, Thermochim.

Yang,

Rev. 18

Acta 166

D.S.

(1982) 265.

(1990)

301.

Viswanath, Appl. Spectrosc. 51 (1997)

905.

[10]

M.E Cai, R.B.

[11]

B.

Roduit, J.

Smart, Energy Fuels 7 (1993) 52.

Baldyga,

M.

Maciejewski,

A.

Baiker, Thermochim.

Acta

295 (1997) 59.

[12]

M.

Maciejewski,

[13]

M.

Maciejewski,

A.

Baiker, Thermochim. Acta 295 (1997) 95.

CA. Muller, R. Tschan, W.D. Emmerich, A. Baiker,

Thermochim. Acta 295

[14]

J. Wang,

[15]

E.

B.

McEnaney,

Lopez-Anreus,

S.

(1997) 167. Thermochim. Acta 190

Garrigues,

M. de la

(1991) 143.

Guardia, Analyst 123 (1998)

1247.

[16]

A. Perez-Ponce,

Guardia, Analyst [17]

K.

F.J. Rambla, J.M. Garrigues, 123

Garrigues,

M. de la

(1998) 1253.

Marsanich, F. Barontini,

390(2002) 153.

S.

V.

Cozzani, L. Petarca, Thermochim. Acta

58

Chapter 3

[18]

F. Barontini, K.

Marsanich, V. Cozzani, J. Therm. Anal. Cal. 78 (2004)

599.

[19]

M.

Muller-Vonmoos, G. Kahr, A. Rub, Thermochim. Acta

20

(1977)

387.

Gonzalez, Catal. Lett. 54 (1998) 5.

[20]

B.H. Li, R.D.

[21]

T.L.

[22]

F. Barontini, E. Brunazzi, V. Cozzani, in Proc. 5th SKT 2003,

Slager,

RM. Prozonic, Thermochim. Acta 426

(2005) 93. Netzsch,

Selb, Germany, 2003, p. 37. [23]

A. Perez-Ponce,

lyst [24]

123

J.M. Garrigues,

S.

Garrigues,

M. de la

Guardia,

(1998) 1817.

Y. Asakura

Ribeiro, A.C.F. Caires, N. Boralle, M. Ionashiro, Thermo¬

chim. Acta 279 (1996) 177.

[25]

R.S.

Ana¬

Jackson,

A.

Rager,

Thermochim. Acta 367 (2001) 415.

Seite Leer / Blank leaf

Seite Leer / Bl&nk leaf

Chapter

4

Influence of

Measuring Conditions on the Quantification of Spectroscopic Signals

FTIR

4.1 Introduction

A

disadvantage

of classical thermal

probe sample during coming can be

the

overcome

analysis (TA)

measurement are

is that gases released from the

normally

by coupling TA with

rier-Transform-Infrared (FTIR) spectroscopy,

mass

as

it

not

analyzed.

(MS)

spectrometry was

This short¬

shown in the

or

Fou¬

previous

chapter. Besides the identification of evolved gases, their

[1-6] of

or

MS

[4,7-9] spectrometry has been addressed. The

quantification

application

of

spectrometric signals

on

the

composition.

pulse technique

First

investigated

in

Chapter

stoichiometry

of the

decomposition

using ammonia,

et

al.

method

3

the

quantifi¬

combined with TA sys¬

al. [8,10]. The extension

was

FTIR

time-consuming and requires

et

into the TA-FTIR system. Marsanich tion

common

reported by Maciejewski

coupled technique known

is

of gaseous mixtures with well-defined

cation of evolved gases based tems was

quantification by

to

by decomposing

process and

FTIR-TA

solids with

by injection

of liquids

[11] applied the gas-pulse calibra¬

carbon monoxide and carbon dioxide.

They

introduced

Chapter 4

62

vaporization technique of liquid samples for calibration

the

procedure was applied

nals. Similar

Quantification using facilitated

by the

ties of the ion

also

MS combined with the

fact that the linear

current

by Slager

and the

relationship of the

amount

In contrast,

by

evolved gases

recording

quantification

calibration

ally

the data

MS when ters

must

such

high

amount

time in FTIR is

acquisition

choosing

the

of

match that evolved

closely

poor

spectral

only

injected

in

a

(e.g. are

32

the

concentra¬

single-point

with that

cm"1).

also

wide

complicated

small

by

gas

a

time resolution.

high

a

only comparable

resolution

is

generally

time is

acquisition

during decomposition.

e.g. residence time in the IR-cell

as

is hold in

analyzed species

of evolved gases in TA-FTIR systems is

consequently

technique

between the observed intensi¬

the fact that the Lambert-Beer's law is often valid

tion range, and

calibration

be achieved with

can

sig¬

and Prozonic [12].

pulse

concentration range. Furthermore the MS data

short and

of the FTIR

Addition¬

applied

in

The other parame¬ for

important

achieving

accuracy in data collection.

A closer look

reported

on

the

TA-FTIR studies indicates that in certain

significantly

from the

Table 4-1 [4,6,12-20]. describes the ratio below

used

tribute

to

or

equal

one

indicate that

the

which

of

indicate to

most

the

a

big

can

of FTIR

investigations

acquisition

the various

Some

traces.

are

listed

in

time and residence time

of the recorded

traces:

values of this

likelihood that each molecule could be

some

signal thereby lowering

in

the conditions deviate

cases

integral intensity

likely

applied

quantification

TA-FTIR

precision and completeness

especially important, peaks,

for

Comparison

detected and contributed one

for

optimal settings

conditions

experimental

above

conditions

experimental

of recorded

traces.

of the target molecules did

the accuracy of

if pulse calibration is

result in the situation that under

not con¬

quantification.

applied, resulting extreme

in

Values

This is

generally sharp

conditions

(high

Influence of Measuring Conditions

Table 4-1

:

Comparison

of TA-FTIR systems with different

Ref.

Apparatus

on

the

measuring conditions.

Reso-

Co-

Acq.

Flow

Vol. IR

Resid.

lution

adding

time

rate

cell

time

scans

s

min"1

ml

s

cm"1

ml

63

Quantification

Quot.

Acq.

Resid.

Bruker IFS 28

[13]

4

10

-10

15

8.7

34.8

0.3

Perkin Elmer

[14]

8

4

-4

89

-10

-7

0.6

Digilab

FTS 60

[4]

8

16

-5

50

6

7.2

0.7

Bruker

Equinox

[15]

4

16

9.5

60

8.7

8.7

1.1

Bruker

Equinox

[16]

4

17.5

35

8.7

14.9

1.2

556

25

1.2

-

[17]

-

-

[6]

8

16

Midac / Nicolet

[12]

4

Nicolet

[18]

16

Bruker Vector 22

[19]

Perkin Elmer

[20]

IBM IR 85

Digilab

FTS 7

Magna

quotient of acquisition

30

-

t/ t

13

10

6

7.2

1.8

60

100

30

18

3-3

3

-3

50

0.49

0.6

5

2

16

75

100

19.7

11.8

6.4

-

-

-60

95

4.8

3

20

are not

fully

32-45

time divided per residence

time) the pulses

recorded.

Preliminary investigations clearly improper experimental settings spectra

by

the

pulse technique.

on

The

indicated

a

the accuracy of the

importance of this

cation of FTIR in combined TA-FTIR systems has

tematically

the influence of the

interpretation of FTIR traces.

significant

experimental

influence

of

quantification

of IR

aspect for proper

appli¬

prompted

conditions

on

us to

the

study

sys¬

quantitative

64

Chapter 4

Experimental

4.2

Experiments

pulse

two

or

gases

were

devices

out on a

enabling injection

Netzsch STA 449 of a certain

gaseous mixtures into the carrier gas

(Figure 2-5

tem

carried

Additionally cies after the

the

of

option

bypassing

thermoanalyzer (into

calibration without

contact

of the

the

the

bration is less

model 5850E, based

(purity to

on

rate was

a

transfer-line)

calibrating pulse

200 ml min

.

The

to a

the FTIR spectrometer

with the

flow

mass

were

by

used

were

used

as

passed through mass

carrier gases with flow was

connected

by

a

rates

a

heated (ca. 200 °C)

from

heated

(ca.

leaving

capillary

to a

equipped

with

a

MCT detector and a

123

mm

an

espe¬

path length

and

the cell

was

compounds

temperature of 200 °C. The whole FTIR compartment

minimize the

water

and

additionally

and carbon dioxide

spectra. The resolution of the collected spectra and co-addition of 4

Helium and

spectrometer.

continuously purged by nitrogen to

sam¬

and therefore cali¬

sensing technique.

ZnSe windows. To avoid condensation of low volatile

was

spe¬

flow controllers, Brook's

mass

low-volume gas cell (8.7 ml) with

to a constant

investigated

Bruker Vector 22 FTIR spectrometer. Gases

The FTIR spectrometer is

heated

were

used, which enabled

was

sharper signals

thermoanalyzer

Pfeiffer Omni Star GSD 301 O

cially developed

controlled

thermal

99.999%, PanGas)

°C) transfer-line

200

the sys¬

flowing through

(vide infra).

accurate

The carrier gas flow

12.5

different

thermoanalyzer by injecting

This alternative method results in much

argon

or two

used.

mainly

ple.

of one

Volumes of 0.25, 0.5, 1.0 and 2.0 ml

Chapter 2).

in

amount

stream

with

analyzer equipped

scans

per spectrum

was

molecular sieves

background

was set

applied.

in the recorded

between 1 and 32

As

a

were

cm'1

consequence spectra

Influence of Measuring Conditions

recorded with

were

MS

ing

to

charge

monitored Data

temporal ratios

versus

FTIR

for

C02

temperature

acquisition

time

was

tion time could

only

be

or

and

H20

The few characteristic

species.

m/z=44 and 18,

time in the

cost

on

the inte¬

the FTIR chamber result¬

multiple

respectively)

were

ion detection mode.

relatively short, generally about

applied

on

65

resolution.

of the evolved

traces

(e.g.

spectral

performed directly after

measurements were

in similar

mass

applied

Quantification

depending

time resolution of about 2-20 s,

a

methods and

gration

the

on

2

s.

Such

acquisi¬

an

of low resolution i.e. 32 cm"

in the

FTIR system.

NaHC03 (p.a. Merck) ence

samples with

and

well known

CuS04

mass

of NaHC03

of CuS04

mass

5

For the gas

moanalyzer.

loop

of

a

H20

were

a

wide range of

home-made device valve

sample

In order

to

injected generally

A standard

used

C02

as

refer¬

In order

to

concentrations the

sample

50 mg.

which had been

composition.

known volume

a

were

varied between 2 and 420 mg, while the

rotary

a

given volume,

gated sample.

was

injections

It contains

gas of known

was

H20 (Fluka AG)

stoichiometry of the decomposition.

check the behavior of the system in

sample

5

heating

rate

was

placed

before the ther¬

enabling a carrier gas

previously

quantify

before the

to

purge the

filled with the calibration

the FTIR

signals, pulses

decomposition of the

of 10 K min'1

was

applied

of

a

investi¬

for all decom¬

positions.

4.3 Results and Discussion

From

preliminary investigations

parameters

can

it

emerged

affect the accuracy of the

that the

following experimental

quantification

of FTIR

signals:

sam-

Chapter 4

66

pie

mass,

place of the injection of the calibrating gas,

of the spectrometer and were

compared with

icant

optimization

of the FTIR

the

on

Sample

of PulseTA

increase of the accuracy

to

Mass and Concentration of the for

C02

Target

Gas

quantitative interpretation of FTIR signals

Figure

of C02 where different

TA-FTIR-MS system.

signif¬

method.

the Lambert-Beer's-Law.

example

MS data, which allowed

simultaneously gained

quantification

application

based

the

flow, resolution

time in the IR cell. FTIR data

of the various parameters and led

4.3.1 Influence of The

accordingly acquisition

carrier gas

traces

4-1 shows the of the gas

amounts

were

pulse

monitored

were

using

calibration

injected

two

is

using

into the

characteristic

50^ «

1

402350

,

3

cm"1

1 3600

CO ~~

30-

1

cm'' .

_

8

4000

3500

3000

2500

wavenumtwr /

n

20-

co

f-i—3600 cm"1 VV

()

2000

1500

cm''

A

1

LI

1 ml

0.5 ml

J

2 ml 1

cm"'

,

I

i

10-

0-

2350

IL. 0.25 ml

i

1

i

i

10

20

30

40

time / min

Fig.

4-1

:

intensity of C02 signals recorded in TA-FTIR system for the wavenumbers 2350 cm"1 and 3600 cm'1, respectively. Carrier gas:

Pulse calibration:

characteristic 100 ml min"

He, resolution: 4

cm"

.

Inset:

IR-spectrum of C02.

Influence of Measuring Conditions

), which

is

much lower FTIR

are

integral

shown in

intensity,

intensities /

Figure

(overtone band, peak-3600 and interferes with

(Eq.

2 in

4-2 :

F

1

1

1

0.0

0.5

1.0

1.5

Relationship cm"

between

injected

from

at

quantification

cm"

pur¬

), which shows

bands in the

same

region.

from calibration

pulses

1-

2.0

volume / ml

volume and

regions:

integral intensity

of evolved

C02

solid circles: 3600 cm" and open cir¬

.

The absorbance of the evolved recorded

67

4-2.

measured in TA-FTIR system for different IR cles: 2350

water

Chapter 3) resulting

injected

Fig.

Quantification

for identification and

widely applied

poses and 3780—3480 cm'

The

the

regions, namely 2450-2150 cm"1 (asymmetric stretch, peak-

wavenumber 2350 cm"

on

2350 cm"

than

at

was

much

3600 cm" and this led

linearity during injections

observed for 2 ml

C02

of higher

injections deviated by

amounts

larger

to a

for the

significant

of C02.

Integral

13.9% from the linear

traces

deviation

intensities

dependence

for

Chapter 4

68

the

traces

earity was

recorded for 2350 observed

Figure 4-3

whereas for 3600 cm"

relationship

and the

dependence

between

between the

traces

integral intensity

gained

of the

(13 mg of evolved C02). Quantification based ever,

could be achieved

spectral sample was

even

resolution of 4 cm" masses over

obtained

using

small non-lin¬

100 mg

the

up

and

at

2350

signal

C02

and

sample (ca. rate

mg of evolved

decomposed

as

determined

cm"1 show

the band

on

carrier flow

a

(ca. 26

signal

400 mg

to

at

of the

mass

of evolved

integral intensity

the TA-FTIR system. The

using

only

(-3.2%).

shows the

sample (NaHC03)

cm'1,

mass

up

to

3600 cm"

at

105 mg

C02)

of 50 ml min"

C02)

no

linear

linear

a

50 mg ,

how¬

with

a

He. For

relationship

cm"1 biasing quantification.

2350

80000

3 «

60000

o

(overflow)

200

sample

Relationship between the gral intensity of evolved C02 measured Fig.

4-3

:

open circles: 2350 cm"

mass

.

500

300 mass

of the

/ mg

investigated sample (NaHC03)

and inte¬

in TA-FTIR system: solid circles: 3600 cm"

Carrier gas: 50 ml min"

He, resolution: 4 cm"

.

and

Influence of Measuring Conditions

4.3.2 Influence of Parameters of

on

the

Data-Acquisition

Quantification

and Carrier Gas

Figure

4-4 illustrates the influence of the parameters of data

other

experimental

recorded shows tion

was

injected can

be

on

the

recorded with different

made before the gas with the

injected

thermoanalyzer,

investigated sample

into the carrier gas

resolutions.

but in the

has

by-passing

case

traces

C02. Figure

where

4-4a

the

injec¬

contact

of the

Generally

be avoided, the

to

calibrating

the TA chamber. This

,4cm1

100 ml

of 1 ml

injection

spectral

acquisition and

intensity of C02

and

shape

the TA-FTIR system after

using

pulses

conditions

69

gas

procedure

(6)

mm'1 (24) Ar (39) 50 ml

mln"1 (57) 25 ml

time /

Fig. es

4-4:

min1 (139)

time / mln

mm

Influence of the

experimental conditions

recorded in TA-FTIR system after

(> 1% of maximal intensity) before TA,

(C02

(C02

traces at

resolution 4

traces at

3600

cm"

,

cm"1).

(C02

the

on

shape and intensity of C02 trac¬

injection of 1 ml C02. Numbers of recorded data points

given in btackets. A: Carrier gas: 50 ml min" He, injection 2350 cm"1). B: Carrier gas: 50 ml min" He, injection after TA, are

C: Carrier gas: 100, 50 and 25 ml min"1 He,

traces at

tion before TA, resolution 4

cm"

injection

2350 cm" ). D: Carrier gas: 50 ml min" ,

(C02

traces at

2350

cm"

).

before TA,

He and Ar,

injec¬

4

Chapter

70

leads

much

to

which allows

the small distance between

points

the

at

much lower than in the

tively large

same

case

in

Figure

where the

broader

in

Figure

on

nificantly

data-points

of the evolved gas. Similar tative calibration of mass

zone

higher diffusivity

(marked

gas

Due

.

in

brackets)

passed through

points

increases with

not

concentra¬

only by low¬

in helium result in

to

of the

higher diffusivity

of helium enables the collection of sig¬

in helium

significantly

gas.

of different carrier gas. The

C02 pulses

which results in better

C02

was

the rela¬

injected

maximal

be caused

can

than in argon due

dependence was

of

to

the number of

in dilution of the

by the application

description

observed

of the real

by Roduit et al. by quanti¬

compared

increases to

traces

to

the

argon, the mixed-flow

to

leading

to

peak broadening.

of certain

injections

amount

of

into the carrier gas is smaller in helium than in argon.

illustrates the

relationship

tion time and the residence time of

between IR-resolution, the

injected

molecules.

and NO spectra recorded with different

and 32 cm"1. The

application

of high

spectral

e.g.

acetylene

and

hydrogen cyanide.

For

Figure 4-5A

spectral

resolution

tification of specific mixtures where the vibrational as

sensor

cm"

spectrometric signals [7]. They found that due

in the TA chamber

Figure 4-5

C02

3600

intensity

shape and intensity of FTIR signal

signal

However, the maximal concentration due

C02

at

lowering of the

to

of the

Application

gas in helium.

more

the

4-4D show that

peaks (larger tailing)

investigated

much

tailing

carrier gas flow but also

presented

signal

4-4C. The number of recorded data

tions in the FTIR cell. The

results

injected

maximal

huge

detecting

resulting

decreasing flow rate leading additionally

ering the

a

carrier gas flow

volume of the TA chamber

presented

and

injection

The influence of the carrier gas flow is

the weaker

quantification using only

recorded data

with

sharper peaks (Figure 4-4B)

NO,

at

acquisi¬

shows the

resolutions between 1

(2

signals

cm"

) allows

of both gases

higher resolution,

quan¬

overlap

even

dif-

Influence of Measuring Conditions

on

Quantification

the

71

c (0 o

2600

2200

2000

wavenumber /

flow / ml

1800

1600

cm'1

min1

a) d

9

resolution /

Fig.

4-5

:

Influence of selected

corded with different

spectral

centration of both gases:

ca.

spectral

resolution of FTIR: A:

1 % in He. B:

Relationship

chamber)

between

are

and NO spectra

re¬

scaled up (xlO). Con¬

acquisition time, spectral

in TA-FTIR system. Number of

averaged

4.

ferentiation between olution has

a

isotopes

significant

is

possible. However,

drawback in

increase the accuracy of quantification

has

C02

resolutions. Intensities of NO spectra

resolution and residence time (FTIR scans:

cm1

to

be decreased, which

can

dynamic at a

the

TA

given flow

application

experiments. rate,

the

only be achieved by lowering

of high

In order

acquisition

the

res¬

spectral

to

time

résolu-

Chapter 4

72

tion,

shown in

as

poral acquisition comparable

The

of 21.5

the

to

quantification

Figure 4-5B. High resolution, s,

and low resolution time of

acquisition

in this

as

be

to

quantify properly

to

in the gas cell estimated

strictly

by

the

Figure 4-5B (carrier

dependences presented required

for

the

when

example,

For

10.4

in this

using

a

or

1 cm"

,

data

through

allows

figure

of the traces,

not

be

The

needs

residence time it is

residence time

maximal resolution

a

quantification.

accurate

of 50 ml min" than 4

cm"1.

time

larger

a

(residence

For

higher

than 10.4

resolu¬

(11.7

s

min"1 part of the

target gas

species will not be accounted for, leading to erroneous quantification. investigating the influence of the experimental

integral intensity allowing

exact

of FTIR

to

the IR

experiments we compared previous

independent study.

signals

of the

apply

applied

we

the data obtained

integral

experimental conditions,

This observation allowed

pretation

to

an

us to use

intensity of IR signals

conditions

independent

obtained in different

technique,

studies [8,10] the of

has

one

comparison of signals

studies, parallel

our

ml

s

time

s,

When

using a flow of 50

upper

comparison of both

The

enabling

as an

and 21.5

respectively),

therefore when

mean

the system, is shown

choosing

rate

higher

acquisition

mean

long acquisition

too

reciprocal scale).

carrier flow

s), the resolution should

tions, i.e. 2

used for

between the volume of the IR cell

quotient

gas flow:

good description

a

a tem¬

in 2.1 s, the latter is

correlated with the

analyzed species.

compartment and the carrier gas flow line in

32 cm"

results in

spectrometric signals

mass

time of the evolved gas in the FTIR gas cell. For

impossible

cm"1,

e.g. 1

study.

time has

acquisition

as

mass

on

the

reference

experiments.

In

our

spectrometry. In all

by both techniques. As reported

intensities of MS as

signals

are

in

almost

also corroborated in the present

the MS

signal

as a

reference for inter¬

obtained under different conditions.

Influence of Measuring Conditions

In order

compare the FTIR results obtained

to

mental set-ups with the MS results,

signals

MS

and

tative FTIR

injected a

provides a reasonable

analysis. Figure

in He recorded

by

a

corresponding

4-6 shows the

that

acquisition

(2.1

s

times in this

for FTIR and 2

s

for

integral

signal

73

different

experi¬

integral

largest

correctness

case were

almost the

of the

quanti¬

intensities of 1 ml

C02

recorded

using

amount

the factor F is

illustrated in

as

intensities of FTIR and

FTIR and MS. For the FTIR

MS

Quantification

by using

criterion for the

low resolution of 32 cm"1 where the

lected and

the

introduced the ratio F

we

4-6. F is the normalized ratio between

Figure

on

signal

of data

points

deliberately set same

for both

are

to

col¬

1. Note

techniques

MS).

50-

3.5

-3.0

40-2.5

_o

ca

0.5-

0.0-

0

10

20

30

60

50

40

time / min

Fig.

4-9 :

calibration of the

Influence of the carrier gas flow

(injection

decomposition (ml min"1).

of 1 ml

C02)

traces are

and

on

the

shape

decomposition

of FTIR

of 20 mg

normalized. Carrier gas flow

signals

measured

NaHC03.

rates are

during

The intensities

indicated

on

the

curves

Influence of Measuring Conditions

traces are

normalized. With

increasing

compared to the decomposition ) show

50 cm"

decomposition

a

traces.

larger tailing, The

traces.

is shown in

Figure 4-9

Quantification

the calibration

as

On the other

clearly

quantification 4-10. This

Figure

intensities of the calibration and

integral

gas flow. The

ison of

rate

the

peaks

amount

integral

the upper part of the

plot.

emerges from

figure depicts

calibrating

the

sample

dependence on

determined

compar¬

amount can

E 13 CD C

rati0.^tomB2-94 25000: -2

cd -"

of the

is shown in

decomposition peaks

The deviation from the stoichiometric

in

the carrier

by

-4

^

and

presented

traces

decomposition signals

intensities of calibration and

become

hand, lower flow rates (25

of the FTIR

of C02 evolved from the

77

significantly

and the value of their maximal concentration increases

sharper

or

flow

on

CD T3

^decomposition

20000'

&

o O

1

S

15000'

S

10000"

-0 CO

S 5000'

-

100

12.5

200

flow / ml min"

Fig. nals

Dependence

4-10: on

of the

the carrier gas flow. The

integral amount

Figure.

tion of 1 ml

C02

The

of evolved

C02 determined

decomposition sig¬

from the

comparison of

decomposition (open circles) signals is presented in stoichiometric value for the sample mass 20 mg NaHC03

calibration (solid circles) and part of the

intensities of the calibration and

amounts to

2.94.

the upper and

injec¬

Chapter 4

78

easily

be

more

the

seen

when

narrow

increasing

However,

disadvantage, flow in

rate

e.g. when

visible also in

of the

tailing

reactions have

This

signal.

more

to

phenomenon the real

thermogravimetric

4-11

depicting

the

6

occurring

stages

25^

CO

50

difficulty

in

clearly

a

Lower

visible

of the reaction

(DTG, dotted line) This aspect is

multistage dehydration

The results illustrate the

dehydration

is

course

curve

also

cases,

investigated.

be

represented by spectrometric signals.

Figure

pentahydrate.

consecutive

multistage

the differential

differs from those

broad

relatively

of low carrier gas flows has, in certain

The lower the flow rate, the

represented by

influences much

decomposition.

application

increases the

Figure 4-9:

fate

the

course

calibration than the

during

obtained

peaks

signals resulting from

the flow rate, which of

clearly

of copper sul¬

separation

of the

in the range 60-120 °C. The

two

water

A

(\ ;V\

-_

iooJ

8 co

CO

co

3

t\V_^

„100E -

90-

change

o

8

70"

TG

CD

E

eo



50

i

'

100

150

250

200

3C

temperature / °C

Fig.

4-11

:

carrier gas flows. curves

during dehydration of 50 mg CuS04 5 H20 measured at different Heating rate: 10 K min"1, carrier gas: He, flow rates are indicated on the

Water

'

traces

(ml min"1). Corresponding TG

traces are

shown in the lower part.

Influence of Measuring Conditions

traces

fied

recorded

properly

due

to

partial ovetlap.

of these

splitting

heating

rate,

system and

79

be

quanti¬

In contrast,

can

can

using

cannot

carrier gas flow of

a

be determined. Note that

also be achieved

by

e.g.

decreasing

the

however that lowers the concentration of the detected gas in the

consequently the

by pulse

spectra

peaks

two

example indicating

An

Quantification

carrier gas flows of 25 and 50 ml min"

min"1 the contribution of these peaks

100 ml

better

using

the

on

accuracy of quantification.

how the

procedure

calibration with gases

mental parameter

settings

is

in

given

can

quantification

of the

be influenced

by

Figure 4-12, which

of FTIR

different

experi¬

presents the

C02

"

CO -

,

134.7%

S c ca

o CO

COSHB

(23)/

[(4)

V^

\

co

:

! v*>

99.8%

my

-

—i—

i

i

30

40

i

i

10

0

20

5

time / min

Example of quantification of FTIR traces by pulse technique during decomposi¬ tion of 20 mg NaHCOj. Numbers of recorded data points (> 1% of maximal intensity) are 4 given in brackets. A (open circles): Carrier gas 200 ml min"1 Ar, resolution 1 cm" (pulse: Fig.

4-12

:

,

points).

Calculated

amount

of C02 in the

sample amounted to

134.7% of the stoichiometric

value. B (solid circles): Carrier gas 50 ml min"1 He, resolution 4 99.8% of C02

was

determined.

cm'1, (pulse:

57

points).

Chapter

80

recorded

traces

according to

2

4

calibration

during

the

and

pulses

of

decomposition

NaHC03

following reaction (Eq. 1):

NaHC03 —> Na2C03

H20

+

(1)

C02

+

technique with different experimental set-ups A and B reported in Figure 4-12. C02 amounts (%) quantified by MS and FTIR related to sto¬ ichiometric value are given. F is the normalized ratio between integral intensity of FTIR and

Table 4-2 :

Results of the

MS calibration

pulse

calibration

signal (decomposition peaks

were

normalized). F/-

FTIR/%

MS / %

Set-up A

(open circles)

102.9

134.7

0.76

B

(solid circles)

99.2

99.8

0.99

Table 4-2 compares the results of the

Figure 4-12 using pulse

recorded

traces

different

experimental

amounts

of C02 evolved

to

quantification

shown in

parameters. The

the stoichiometric value.

Experiment

using high spectral

(200 ml min"1 Ar) led

temporal

low

high

to a

resolution

large

error

resolution (collection of

maximal

the calibration

intensity significantly

pulse

were

only

B

(solid circles)

regards quantification:

a

flow

was

rate

the calculated

shows the used: the

high

that

error

sharp pulse

carrier gas flow

quantification.

Due

rate

to

the

points during injection) and the

lower values of the

resulting

found

4

were

and

in the FTIR

C02 originating from the decomposition

Experiment

cm"1)

(1

on

of sodium bicarbonate related

had been introduced when unsuitable parameters observed

is based

(open circles)

A

significantly

calibration with

comparison

during decomposition

of the FTIR and MS

integral

intensities of amount

of

conditions

as

in overestimation of the

reaction.

performed

of 50 ml min"

under was

optimized

chosen and

spectral

reso-

Influence of Measuring Conditions

lution

was set to

and led

pulse

4

cm"1,

which

to a more accurate

and FTIR results obtained rated that

the

Quantification

proper

experimental

C02

trace.

MS

(B) corrobo¬

conditions

quantification of spectral signals

81

the calibration

points during

determination of the evolved

using

accuracy of the

high

57 data

provided

on

can

be achieved

with both TA-MS and TA-FTIR. We have shown the

tions, in order

to

such

data

acquisition

into

account

time

when

of FTIR

signals.

improve

the

Several param¬

quantify evolved gases by the pulse technique.

carrier flow rate,

eters

as

importance of choosing adequate experimental condi¬

resulting the

setting

We

injection location,

hope

quantification

from the

spectral

experimental

optimal the

study helps

gas and

injected

resolution have

conditions

that the present

of

amount

be taken

to

for calibration

practitioner

to

of evolved components in combined TA-FTIR

investigations.

4.4 Conclusions

Quantification MS

using

mental sen

or

of evolved gases

FTIR spectroscopy

settings. Quantification

experimental

most

are:

to

resolution leads

to

separation of the

shown for the

based

on

properly

spectral

the

analysis by

careful

FTIR is

pulse technique of the

optimization

strongly

analysis

is

affected

only

by

quantification by

of CuS04 chosen



5

the cho¬

means

resolution and carrier gas flow

reaction steps

experi¬

little affected. The

of TA-

rate.

flow poor time resolution. Low carrier gas

to

dehydration

MS system with

requires

be considered in gas

the choice of the

spectral poor

thermal

parameters, whereas MS

important factors

FTIR

during

rate

High leads

during multistage decompositions, H20.

experimental

The

application

as

of a TA-FTIR-

conditions allows

an

easy and

Chapter 4

82

less

time-consuming

ent

studies, such

as

in situ calibration

the

quantification

gas-solid reactions (cf. chapter 6)

and

procedure

which

of adsorption

can

be used in differ¬

phenomena (cf. chapter 5),

decomposition of solids (cf. chapter 3).

4.5 References

[1]

Magri, Thermochim.

S. Materazzi, R. Curini, G. D'Ascenzo, A.D.

Acta 264

(1995) 75.

[2]

S. Materazzi,

Appl. Spectrosc.

Rev. 33

(1998) 189.

[3]

S. Materazzi,

Appl. Spectrosc.

Rev. 32

(1997) 385.

[4]

M.

[5]

L.C.K. Liau, T.C.K.

Mittleman, Thermochim. Acta 166 (1990) 301.

Yang,

D.S.

Viswanath, Appl. Spectrosc. 51 (1997)

905.

[6]

M.F. Cai, R.B. Smart,

[7]

B.

Roduit, J.

Baldyga,

Energy M.

Fuels 7

(1993) 52.

Maciejewski,

A. Baiker, Thermochim. Acta

295 (1997) 59.

[8]

M.

Maciejewski,

CA.

Muller,

R.

Tschan, WD. Emmerich,

A.

Baiker,

Thermochim. Acta 295 (1997) 167.

[9]

J. Wang,

[10]

M.

[11]

K.

B.

McEnaney, Thermochim.

Maciejewski,

A.

Acta 190

(1991) 143.

Baiker, Thermochim. Acta 295 (1997) 95.

Marsanich, F. Barontini, V. Cozzani, L. Petarca, Thermochim. Acta

390(2002) 153.

Slager,

[12]

XL.

[13]

E. Post, S.

(1995)

1.

EM. Prozonic, Thermochim. Acta 426

(2005)

93.

Rahner, H. Mohler, A. Rager, Thermochim. Acta 263

Influence of Measuring Conditions

[14]

I.

on

the

Quantification

83

Pitkanen, J. Huttunen, H. Halttunen, R. Vesterinen, J. Therm. Anal.

Cal. 56 (1999) 1253.

[15]

F. Barontini, K.

Marsanich, V. Cozzani, J. Therm. Anal. Cal. 78 (2004)

599.

Jackson, A. Rager, Thermochim.

[16]

R.S.

[17]

R.

[18]

A. Perez-Ponce,

Bassilakis, R.M.

lyst [19]

A.I.

123

(1998)

Carangelo,

M.A.

J.M. Garrigues,

S.

Acta 367-368

Wojtowicz,

Garrigues,

(2001) 415.

Fuel 80 (2001) 1765.

M. de la Guardia, Ana¬

1817.

Balabanovich, A. Hornung, D. Merz, H. Seifert, Polym.

Degrad.

Stab. 85 (2004) 713.

[20]

WM.

Groenewoud, W de Jong, Thermochim. Acta 286 ( 1996) 341.

Seite Leer / Blank leaf

Chapter

Gas

Adsorption

5

Zeolites

Studied

on

PulseTA®

catalytic

5.1 Introduction

In this

chapter

described. try, the

an

Using hyphenated

quantity

gas

is

sion of

species

provide

sites. The selective

monolayer,

in the

(adsorp-

gas

and the various thermal effects combined with the

information

chemisorption,

atoms

a

is

The determination of the

on

the

and

amount

i.e. formation of a

nature

accessible

on

is

expressed

the surface

to

of active surface

strongly bound

allows the determination of the metal surface

number of metal

area

adsorbed

and metal

disper¬

the ratio of the total

as

the total number of metal

sample.

measurement

volumetry

spectrome¬

is studied.

supported catalysts. Dispersion

The

research is

with differential

adsorption

which includes the processes involved whenever

of adsorbed

above process

atoms

analysis-mass

brought into contact with a solid (adsorbent).

amount

in

frequently used method for characterizing heterogeneous catalysts

adsorption,

tive)

simultaneous thermal

of adsorbed gas and their heat of

scanning calorimetry (DSC) A very

of

important application

and

of gas

gravimetry,

chromatography

or

well

gas thermal

previously pretreated adsorbate gas. The

as

uptake as

is carried

with

out

dynamic

conductivity [1].

and evacuated, is contacted

amount

static methods such,

by

flow In

by

techniques

volumetry, a

known

of adsorbed gas is determined

such

the

as

as

gas

catalyst,

quantity

of the

by measuring

the

Chapter

86

5

pressure after the

versus

equilibrium

pressure.

understanding the method, the

Recently,

a

nature

amount

new,

so

of the

catalytically active sites [2-4].

of adsorbed gas is measured

called

element

tapered

technique has been developed that offers in

a

fixed bed

mass

reactor

is determined

element

probe

molecules

[7], the

In

bypass

the

contrast to

the

maximum adsorbed

Dynamic

methods of measuring

they

than static methods because tinuous flow

technique,

detector

stream

determined

adsorption

desorbing

(generally

a

thermal

An

been

on to

et

more

al.

well

convenient

systems. In the

by

is flushed

species.

inert gas

an

After

con¬

cooling

at a

to

the

the adsorbate gas until the down¬

conductivity cell) the

modification of the conventional

recently reported by

which

Rebo

shows

a

adsorptive

constant

is

gas

once more

investigate possible reversible adsorption.

interesting

instrument

faster and

vacuum

phase composition. After purging with an inert gas, switched

of the

systems.

all adsorbed to

none

reported by

as

oscil¬

tapered

of the

The

sample.

the

by TEOM correspond

are

require

temperature, the flow is switched

required

however,

pretreated catalyst

the

temperature sufficient for

frequency changes

not

sample.

measuring mass changes

passed through

gravimetric

do

gravimet¬

the

conventional microbalances,

amounts

with values obtained in conventional

In the

in

helps

oscillating microbalance (TEOM)

are

sample holder,

with calo¬

which

by weighing

method for

a

while reaction gases

by monitoring

[5,6].

lating

adsorption,

of

amount

Volumetry combined

allows the determination of the heat of

rimetry

ric

the

the

i.e.

adsorption isotherm,

allow the determination of the adsorbed gas

is established. Successive doses of gas

adsorption equilibrium

was

equipped

Brown and Rhodes

with

a

permitted switching between

tive gas in the carrier gas. The

gravimetric

method has

[8]. A combined TG-DSC

pneumatically operated three-way valve, a

sample

and pure carrier gas was

dosed with the

a

blend of 5%

adsorptive

in

reac¬

a con-

Gas

trolled

phase

stepwise

prerequisite irrespective

ena,

is

ture

always

involves

a

probe

lead

to a

tion

higher

temperatures

thermodynamic equilibrium

between the

not

not ensure

energetically

that

begin

to

that each dose of adsorptive

mobility

The

technique

for

of the

In

common

practice,

equipments.

makes it

possible

surements.

are

low

too

of physisorbed mole¬

stronger active sites would be

can

enough

interrogate

at

the

adsorption

tempera¬

all of the available

adsorbed molecules

adsorp¬

checked

be

can

which has become

amount

desorption

of desorbed

process, this

the determination of the

a

by

com¬

very

species

being

to

demonstrate that

we

study

all these

compared

to

amount

and indi¬

related

to

the

of adsorbed

species,

different

experi¬

study of the desorption require

Here

set-up. Results of ammonia

technique

mobility

hand,

between adsorbate and the surface.

the heat of adsorption and the mental

On the other

characterization [10]. The information collected

catalyst

the temperature range of the

energies

and low.

fill [9].

from TPD studies contains the type and

bond

[4].

allow sufficient

temperature-programmed desorption (TPD),

cates

gas

used. The choice of tempera¬

high

coverage of the surface

before weaker sites

sites.

mon

composition of the

High

Adsorbate molecules should be mobile ture so

87

molecules and the active surface sites, whereas low tempera¬

cules and thus do

populated

technique

between

achieve

to

temperatures do

adsorption

of the

compromise

reduce the time needed

tures

Zeolites

investigating adsorption phenom¬

selection of temperature, when

Proper

adsorbed

the

by repeatedly switching

on

the adsorbent.

over

a

fashion

Adsorption Studied

pulse

phenomena using

adsorption

measurements

corresponding

thermal the

same

by

means

analysis [11] experimental of the

data derived from volumetric

pulse mea¬

Chapter

88

Experimental

5.2

Experiments with two

a

carried

were

different pure gases

10 ml.

controlled mass

flow

200

by mass

flow

of injected gas could be

amount

amount

(Pt crucible, o.d.=6.8

from

a

remove

amount

these

mm,

on

the

out on

adsorption the

at

200

ammonia and

of chemisorbed ammonia

isotherms, according

to

the

a

through bridging

0.67

nm x

0.70

nm

20-400 mg

was

where

investigated.

with the

with those same

reac¬

measuring

evacuated in order was

to

measured. The

generally applied procedure [12].

tetrahedrally a

as

adsorbents,

are

coordinated Al and Si three-dimensional pore

interconnected channels of dimensions 0.53 a

to

experiments

process

was

heated

a

calculated from the difference between

was

oxygens. ZSM-5 has

Mordenite possesses

in the

second isotherm

The zeolites, ZSM-5 and mordenite, used minosilicates made up of

ml))

by the pulse technique

°C, the system

thermal

25-30 mg for DSC

ca.

measurements

to

spectrometer

mass

Micromeritics ASAP 2010 system. After

isotherm

physisorbed

ml)

by

0.01

rate was

on a

connected

quadrupole

adsorption

compare the results obtained

carried

was

or

flowing

stream

changed from

volume 0.085

o.d.= l6.4mm, volume 1.0

conventional method, volumetric

tants were

the first

to

Balzers

to a

of one

used. The flow

of the adsorbents varied from

the influence of the bed thickness In order

were

thermoanalyzer

The

°C) stainless steel capillary

(alumina crucible,

amount

controllers, Brooks's model 5850E, based

sensing technique.

measurements

certain

gaseous mixtures into the carrier gas

0.25, 0.50 and 1.0 ml volumes

420. The

QMG

or

the system. The

Mainly

thermoanalyzer equipped

Netzsch STA 409

out on

(Netzsch) enabling injection of a

device

pulse

through

(ca.

5

nm

x

0.57

nm

crystalline aluatoms

bonded

structure

with

and 0.55

nm.

two-dimensional channel system with dimensions

and small

perpendicular

pores with dimensions 0.29

nm x

Gas

0.57

nm

[13]. The zeolites were received

AG. After calcination

NH4N03

at

they

500 °C

and heated in air

to

the

the gases adsorbed

able.

were

used

Additionally,

as

silica-titania

Ni-5256 E3/64)

(Engelhard

used

89

90 °C with 1 M

at

thermoanalyzer

then

until

change

a

500 °C

was

to

detect¬

argon

(purity

commercial nickel

catalyst

and helium

and

to

cooled down

they were

no mass

and carrier gases,

aerogel [14]

were

Zeolites

obtain the H-form. Before the

heated in the

equilibrated

adsorptive

exchanged

to

(purity 99-98%, PanGas)

Ammonia

99.999%)

ion

during handling,

temperature and

measuring

were

were

on

in the Na form from Chemie Uetikon

500 °C for 2h

adsorption experiments samples to remove

Adsorption Studied

or

respectively.

adsorbents.

as

5.3 Results

Figure

5-1 shows the

from

series of ammonia

a

mass

changes

pulses,

technique. Strong, virtually

injected

ammonia occurred

and weak

of the H-ZSM-5 zeolite

and illustrates the

irreversible

weight water

by

6 in

loss

Figure 5-1,

amount

depicts at

features of the

pulse

of the

4 resulted in both strong

where

took

no

place.

further

The

mass

the temperature range of the

gain at steady state,

changes

desorption

temperatures above 550 °C is due

as

mass

6

were

detectable,

of chemisorbed ammonia. The second part of the exper¬

from the zeolite, the

205-550 °C, nal.

resulting

(reversible) adsorption phenomena, whereas during pulses 5 and

represents the iment

200 °C

adsorption (chemisorption)

during pulses 1-3, pulse

only weak adsorption (physisorption) indicated

typical

at

confirmed

desorption

to

(TPD). The

the evolution of residual

of ammonia

by monitoring the

process

m/z =15

occurs

mass

in

the range

spectrometric sig¬

Chapter

90

5

3.0

2.5

-

2.0

-

Ol

E

1.5

Ol Ol

1.0

«S .e u t/i

vi

nj

0.5

5

0.0

-0.5

Time / min

Fig.

5-1

monia

Mass

:

at

200 °C. The

10 K min"

.

The

In the ence

changes of H-ZSM-5

on

zeolite after exposure

desoiption after

amount

the 6th

was

initiated

of chemisorbed ammonia is marked

following, experimental

the

pulse

adsorption

series of pulses of 1 ml

to a

as

by heating

am¬

at a rate

of

0.

influ¬ parameters which have the greatest

process under

dynamic conditions,

were

investigated.

These parameters embrace: thickness of the adsorbent bed in the crucible,

tem¬

perature and carrier gas flow.

5.3.1 Influence of Thickness of Adsorbent Bed The conditions for mal for the not

flow

tion due

gas-solid

through to

effects and

mass

the

transport in the

experimental set-up

are not

typical thermoanalyzers

sample bed,

influence the kinetics of the

this

can

check the

reproducibility

to

study the

opti¬

the gas does

interaction. As in all

diffusional limitations. In order to

used

adsorp¬

influence of diffusion

of the method, the

sample

mass was

Adsorption

Gas

varied

over

amount

a

range from 10

to

independent of crucible

of the

was

sample

used

mass

at

°C, related

200

i.e. the bed

(open symbols

to

of zeolite, did

and lower

amount

The

ammonia

(solid symbols). However,

influence the

not

use

mass

100

_J

specific

the

same

kind

of the DTA cruci¬ in

amount

a

thicker bed

of chemisorbed

significantly

/ mg

i

l_

i

250

200

150

I

i

91

adsorbent, is

the thickness of the bed

Sample 50

that the

1 g of

(smaller diameter), resulting

ble with its different geometry

Zeolites

provided

thickness,

Figure 5-2A).

in

on

Figure 5-2A shows

400 mg.

of chemisorbed ammonia

Studied

500 o

£

•|



450



IL

O

-o

o

E Ë

a"

(0

"8 -S

400

o 1/1

£

4

N2

+

and NO, and the consump¬

catalysts

are

suitable for

temperature window 300-400 °C At

appli¬ higher

Chapter 6

110

temperatures (> 400 °C) nitrous oxide is formed [3]. One of the

leading

tions

to

nitrous oxide is: 4 NO

Catalysts working their

NH3

02

3

+

—>

4

significant

N20

+

6

have been shown




NH3 (a)

+

NO

(g)

NH2 (a) OH

(a)

O

SCR of NO

+

+

ions

on

transition metal

(1)

(2)

NH3 (a) (a)

—>

NH2 (a)

OH

+

N02 (a)

(g)

—>

NH2NO (a)

N02 (a)

—>

O

NO

and Mn

oxides [5] :

—>

+

support,

amide-nitrosoamide type mechanism for SCR of NO

Vi02 (g)

+

Ce02

FTIR studies and the knowl¬

02(g)—>20 NH3 (g)

the

MnOx(0.3)-

(a)

+

(3)

(a)

(4) _>

N2 (g)

HN02 (a)

+

H20 (g)

(5) (6)

Selective

NH3 (a)

N2 (g)

—>

They

HN02 (a)

+

—>

Catalytic

NH4N02 (a)

—>

+

the

on

H20 (7)

sorption

and

perature

NOx reduction

can

be

in

catalyst with

a

considerable

reactants, we

known

to

the

the

a

applied pulse

relationship

how the

properties,

to

thermal

analysis

further this

Best

sorptive NOx

content

between

for sorp¬

of 25%.

about manganese-

behavior of

adsorption

catalytic

combined with

knowledge.

content was

tem¬

in SCR, there is still rela¬

behavior in SCR.

varied from 0

spectroscopy

mass

In order

composition of the manganese-cerium the manganese

of low

properties

gained

properties

redox behavior of the mixed oxide and

have

them for

of

interactions

development

manganese

has been

knowledge

concerning

and FTIR spectroscopy

insight

to use

oxidizing atmosphere.

cerium mixed oxides and their favorable

tively little

[10-14] studied the

oxides

broadly applied

an

found for

were

al.

adsorption

(< 150 °C). The combination of nitrogen oxide

low temperatures

catalysis

et

manganese-cerium

at

Although,

Machida

catalyst [7-9].

removal

tion of NOx

111

2H20 (g)

+

of nitrogen oxides with

these

NH2NO (a)

by NH3

concluded that the initial step of the SCR process is the

ammonia

Here

Reduction of NO

to

gain

some

mixed oxides affect to

100 at.%.

Experimental

6.2

The

MnOx-Ce02 catalysts

from aqueous solutions [6,7]. were

dissolved in

ratio of citric acid

mixture

was

water

to

stirred

110 °C for 12

were

prepared by

Manganese nitrate,

a

cerium nitrate and citric acid

and mixed in the desired

metal components

at room

standard citric acid method

proportions and the

(manganese

and

cerium)

was

temperature for 1 hour. The solution

hours, resulting

in

a

was

molar

1.0. The

dried

at

porous, foam-like solid. The foam-like pre-

Chapter 6

112

calcined in air

cursor was

oxides

face

the

the

determined

instrument. Before

The

catalysts

are

measurement

the

samples

as

rep¬

The BET

sur¬

Micromeritics ASAP 2010

were

of the mixed oxide

area

a

denoted

Mn(0.25)

composition (MnOn)025(CeO2)075.

by N2 adsorption using

150 °C The BET surface

m2

procedure.

same

represents the molar ratio of Mn/(Mn+Ce), e.g.

x

catalyst with

area was

of 20-30

the

prepared using

were

Mn(x), where resents

500 °C for 2 hours. The pure manganese and ceria

at

was

degassed found

g"1, while that of the pure MnOx and Ce02

to

were

in

vacuum

at

be in the range

3 and 15

m

g'1,

respectively. reduction-oxidation behavior and SCR

Adsorption, were

carried

device

enabling injection

of

certain

a

gaseous mixtures into the carrier gas amount

of injected gas

controlled mass

(ca.

flow

200

by

was

1.0

to a

generally

50

or

step of 0.01° and 0.3

were

passed through mass

to

carried

s

rate was

thermal

on a

by

a

heated (ca. 200 °C) amount

heated

leaving

capillary to

of the

a

catalyst

out on a

Siemens D5000

powder X-ray diffracto-

in step mode between 10 and 80° 20 with

a

step4.

500 °C

cooled down

change was

a

or

the system. The

connected

was

spectrometer. The

adsorption experiments

thermoanalyzer

mass

flowing through

pulse

different gases

Bruker Vector 22 FTIR spectrometer. Gases

using the Cu-IC^ radiation

they were

one or two

a

100 mg.

analysis was

Before the

with

ml, if not otherwise specified. The flow

Pfeiffer Omni Star GSD 301 O

meter

stream

of

sensing technique. The thermoanalyzer

°C) capillary

XRD

amount

flow controllers, Brook's model 5850E, based

mass

the FTIR spectrometer

was

measurements

thermoanalyzer equipped

Netzsch STA 449

out on a

activity

to

to remove

the

the

the gases adsorbed

measuring

detectable (cf.

catalyst samples

Ammonia

heated in the

during handling,

temperature and

chapter 5).

were

then

equilibrated until

no

(purity 99.98%, PanGas)

Selective

nitric oxide

and helium

(purity 99-98%, Messer)

(purity 99-999%, PanGas)

were

Reduction of NO

Catalytic

used

113

5% oxygen in helium

or

adsorptive

as

by NH3

and carrier gases, respec¬

tively. Redox-experiments 1

3 K min was

were

and each 50 °C

injected

followed

by

a

performed

one

pulse

under helium with

of 1.0 ml

reoxidarion

pulse

a

heating

rate

of

hydrogen (99-999%, PanGas)

of 1.0 ml oxygen

(99.999%,

Pan-

Gas). SCR

activity

50 ml min' After the

using

02,

due

to

method

adsorption

the

pulse

method

nitrogen

the

cerning

stream

and the formed

evolution

applied

suitability

their

injected

was

of the

N02,

during

tested

pulse

NO and

NH3

of

was

and

changed

until

H20

was

down

uptake

no mass

injected

were

monitored

monitored

experiment,

the

5% NO,

to

were

to

by

allowed

FTIR.

quanti¬

[15,16]. The reliability of the

reaction

by repetitive method for

cooling

pulses (1 ml)

N2, N20

rate

following procedure:

equilibrated

the end of each

at

total gas flow

the

(He)

recorded. Then ammonia

was

of nitrogen,

fying

was

to

a

500 °C and

the carrier gas flow

while the evolution of

pulses

at

at

out

according

balance helium, and the system

by MS,

more,

pulse

temperature)

into the carrier gas

The

the

carried

were

preparation period (calcination

desired reaction

5%

measurements

runs

on

each

discriminating

activity was confirmed by corresponding

tests

sample. the

using

Further¬

samples a

con¬

continuous

microreactor.

6.3 Results and Discussion

Analysis

of the structural and textural

mixed oxides

by X-ray

diffraction and

properties

of the

nitrogen adsorption

manganese-cerium corroborated that

114

Chapter 6

the structural and textural

similar

6.3.1 In

a

and

to

those

NH3

on

of the

reported by Machida et

Adsorption

first step

properties

we

samples

al. in their

used in this studies

were

original work [10,11].

Behavior

have

investigated

selected

samples.

the

As

of the

adsorption

an

reactant

gases

NO/02

6-1 shows the

example, Figure

mass

20

A

1 5

„, en c m

1-0

NOx adsorption

2U2>N

Xs^"^

-

1 27 mg

.c

o us

05

/

NHj adsorption 1

i

00 0

07mg

20 min

B

10xNO„ 1 5

-

I

N.°.

NO,

NOi

Nt|^

NH,

.:::!:::....::

E

.-.i. 00 9mg

1 0

1 28 mg

u

05

«

-

(0

E 00

20 min,



-0 5

time /

Fig.

6-1

:

Change

of the

mass

due

adsorption of NOx and NH3 on Mn(0.75) at 100 °C, ml min'1, volume of the pulses: 1.0 ml, carrier gas: 5%

to

catalyst mass: 100 mg, flow rate: 50 02/He. A: separate adsorption of one

changes

of the

mm

gas. B: consecutive

sample containing

75% Mn

adsorption

(Mn(0.75))

-

first

at

NOx,

100 °C

then

NH3.

resulting

Selective

from 5%

carrier gas. It illustrates the

02/He

irreversible

Strong, virtually

during the

first

further

no

mass

adsorbed

versibly

into

pulse technique.

of the

injected

gas

3 and 4 resulted in both

The

steady

at

detectable, represents the

were

corresponding

listed in Table 6-1.

gain

mass

mg of

NOx

with

of irre¬

and 0.07 mg of with different

content

of 25-75 at.%

Mn

a

amount

samples

results for all

Samples

state, i.e.

NH3 adsorption on various manganese-ceria mixed oxides. Up¬ (coverages) determined by pulse thermogravimetry; NO pulses in helium (©nq)' NO

Table 6-1

takes

changes

occurred. The

(chemisorbed) species (1.27

NH3, Figure 6-lA). content are

features of the

pulses, subsequent pulses

115

pulses, respectively,

adsorption (chemisorption)

adsorption (physisorption)

when

Mn

two

typical

by NH3

(reversible) adsorption, whereas during further pulses only

strong and weak

weak

Reduction of NO

of a series of ammonia and nitric oxide

injection

occurred

Catalytic

pulses

NO,

:

in 5%

(0nh3 c)

and

N02

02,

and

balance helium

(6N02),

and ammonia

pulses

in

helium, chemisorbed

physisorbed (0NH3 c+p).

6NO / plmol g

Sample

l

6N02 / \lmo\ g'1 0NH3

c

/

plmol g'1

ÖNH3c+p/ Jlmol g'1

Mn(0.00)

77

196

0

6

Mn(0.10)

160

422

6

55

Mn(0.25)

197

559

41

135

Mn(0.50)

167

483

41

118

Mn(0.75)

70

276

41

106

Mn(1.00)

7

22

0

21

showed

highest uptakes

for chemisorbed ammonia, whereas

physisorbed ammonia, NO, ing 25

at.% Mn.

adsorbed

Generally on

compared

pure oxides

and

to

NH3.

NO/02

were

the mixed oxides

Lowest

Mn203 (Mn(1.00))

and

highest

for the

uptakes sample

due

to

contain¬

considerably more NO/02 was measured for the

adsorption uptakes

were

Ce02 (Mn(0)).The

total ammonia

uptake

Chapter

116

6

(physisorbed

and chemisorbed, cf.

Mn

seemed

14

content

(0);

(0.10);

23

27

to

correlate

(0.25);

Particularly interesting ments

of the

clearly

indicate that

and that

reactant

are

gases

NO/02

coadsorption

has

curve

adsorption

of ammonia. The

tion of both gases

Figure

the

are

(0.75);

20

the results of

presented

in

and

are

NH3

6-IB

mass

same as

Figure

gains

in the

on

(sample):

the

uptakes of

when the gases

NOx

measure¬

measurements

different surface sites

at

adsorption

Note the values of 1.27 and 1.28 mg for

arately.

6-IB. These

that resulted from case

g'

m

(1.00).

adsorbed

the

areas:

subsequent adsorption

influence

depicts

3

with different

samples

their BET-surface

virtually no

gases. The

in

to

(0.50);

24

of the

Figure 6-12A)

of the

reactant

NOx followed by

subsequent adsorp¬ were

adsorbed sep¬

and 0.07 and 0.09 mg

for ammonia for separate and consecutive

adsorption, respectively (Figure

and B).

of ammonia

ferent

Figure

6-2

catalysts

at

100 °C The

determined after 20 min small

all

on

of the

to

amount

desorption

of

the

on

irreversibly

into the carrier gas stream, is

to

the

adsorption uptake

measurements

programmed desorption Figure 6-3A.

The

is shown in

tored

NOx adsorption indicate

FTIR after

100-400 °C is due

traces

to

of

amount

representative example

ammonia

over

the dif¬

adsorbed ammonia,

relatively

weakly, reversibly

manganese-ceria catalysts depends

in situ temperature

by

adsorption

on

the Mn

con¬

investigated samples.

Subsequent

jected

curves

On the other hand, the

catalysts.

adsorbed ammonia tent

the TG

depicts

6-1A

occurs

to

the evolution of

in the range 100-250

(Figure 6-3B).

Note that the

N20 during desorption.

the

measurements

as

major part

were

that the

confirmed

mass

The

sub¬

(TPD).

desorption profiles

nitrogen dioxide.

°C,

samples

A

moni¬

loss between

desorption

by monitoring

of

FTIR

of adsorbed ammonia is oxidized

Selective

Catalytic

Reduction of NO

by NH3

117

0.4

0.3-

E 0.25 / 0.23 mg

0)

0.50 / 0.20 mg 0.75/0.18 mg

iz

CO

tn

w co

E

T"

40

20

60

time / min

Fig.

Mn(0.75) 1.0

ml,

versibly are

of the

Change

6-2:

°C,

100

at

catalyst

carrier gas: He.

due

mass:

Manganese

indicated

on

the

100 mg, flow

mass

of

adsorption rate:

maximal

change due

NH3

uptake

mass

to

by

,

due

volume of the to

irreversibly

pulses: and

irreversibly adsorbed ammonia only

the

pulse technique

is very similar

breakthrough

al. [12] showed

by

curves

DRIFT

for

on

to

the

catalyst composition

that found

determining

by

the

Machida

studies, that the NOx uptake increased

increased, suggesting chemisorption via oxidation of NO. The fact that observed in the desorbed gas

Based

et

on

is adsorbed

et

NOx uptake.

lower temperature and when the oxygen concentration in the gas feed

of Machida

re-

curves.

al. [13] who measured et

Mn(0.25), Mn(0.50),

on

50 ml min"

dependence of NOx (NO/02) adsorption

determined

Machida

to

content,

adsorbed ammonia and the

The

at

mass

only the presence of N02

was

we

confirms the conclusion

al. [11]. FTIR studies

on

Yang and coworkers [5,6] proposed

manganese-cerium mixed

oxides

on

that ammonia

Lewis acid sites subse-

Chapter 6

118

T"1 T'"

f—I—I—I—I—i—i—|—i—i—i—i

100

150

200

|

I

I

I

A: FTIR

6-3:

Mn(0.50) NH3

He,

at

traces

N02

10 °C, carrier gas: 5%

recorded

heating-rate:

during TPD

10 K min"

quently transforming nism

recorded

after

400

TPD after

during

NH3 adsorption

i.e.

NO/02

measurements

by

clearly

the

to

on

10 K

NOx adsorption

min"1.

Mn(0.50)

B: FTIR

at

step 3 of the

exposure leads

to

desorption profiles

indicate that

interfere, supporting that these species

sites.

350

02/He, heating-rate:

NH2 according

which is corroborated

adsorption

traces

I—?—I—I—|—i—i—i—r

N20

on

and

100 °C, carrier gas:

.

into

(cf. Introduction),

(N02)

not

and NO

|

300

/ °C

temperature

Fig.

I

250

proposed

adsorbed nitrite shown in

Fig.

mecha¬

species

3A. Our

NO/02 and NH3 adsorption do

are

adsorbed

at

different surface

Selective

Catalytic

Reduction of NO

by NH3

119

6.3.2 Redox Behavior In order

alysts

to

check the

and their

temperature

by

reactivity in

reoxidation. As

pulses

cant

at

between redox

SCR their redox behavior

programmed reduction (TPR) reducing agents

The behavior of nia

possible dependence

ammonia and

due

to

Figure

pulses, only

ammonia

cat¬

investigated by both,

hydrogen

Mn(l.OO) and Mn(0.50) during

occurs

of the

and differential reduction followed

100 °C and 300 °C is shown in

reduction

was

properties

were

applied.

interaction with

6-4. At 100 °C a

small

no

ammo¬

signifi¬

adsorption uptake

1.0300 °C

100 °C 0.8. +

0.6-

E

0.4-

0.00 mg

Mn(1.00)K.

\

H

Mn(1.00)

0.2 O) c

03 JO

0.0Mn

u

w

E

(0.50)

+

-0.2

0.07 mg

7*

Mn

(0.50)

-0.4. -0.6

-0.8-1.0-

—r~

—|—

50

100

—,—

200

150

250

time / min

Fig.

6-4:

changes resulting from 1 °C, sample mass: 100 mg.

Mass

100 °C and 300

is observed. However,

at

300 °C

(0.72%) which corresponds

to

an

ml

NH3 pulses

over

Mn(0.50) shows extent

a

Mn(1.00) and Mn(0.50)

weight

of reduction of

ca.

at

loss of 0.72 mg

68%, assuming

Chapter 6

120

that

Mn203

Mn(0.50)

at

ammonia

by

the lattice oxygen. After

due

monitored, with to

of the

change at

maximum

due

mass

not

this temperature

to a

lead no

to

any

that reoxidized the reduced

mixed oxides,

sponding observed

mass

a

catalyst

in the

followed

the initial

by

mass

loss observed

was

in formation

resulting

to

oxygen

mass

mass

by

an

oxygen

physisorption)

and

pulses

at

this

corroborating

and tem¬

that

at

ammonia exposure. At 200 °C,

by desorption

and reduction, both

loss indicated the reduction of

mass was

in

regained after an

hydrogen

TG. Mn

mass

of the

hydrogen pulses

and evolution of N20

oxygen

pulse

to

content

575 °C

are

of the

in the

indicated

manganese-cerium and

catalysts on

the

corre¬

curves.

The

reduction increased with the manganese content, for

negligible

reducibility

NH3/He. Beyond

for Mn(0.50) followed

species. Further

TPR-profiles

during

a

sample.

monitored

loss

into the carrier

shown). Figure 6-5B shows the

not

adsorption (chemi-

change

losses recorded up

only

differential and 1 ml

as

mass

pure ceria

the lattice oxygen

NH3 pulse

was

catalyst by ammonia and

6-6 shows the

pulses

in 5%

250 °C. Further

The observed

occurring simultaneously.

Figure

Mn(0.50)

reduction occurred due

however, weak adsorption

pulses

by

of physisorbed ammonia

perature did

the

at ca.

150 °C, which resulted in

desorption

of

nitrogen (observed by MS,

and

and oxidation of

of the process.

profile

the oxidation of ammonia

water

pulse

a

oxygen

catalyst by ammonia started

150 °C, reduction of the

was

injecting

catalyst

with

NH3

(before the reduction step) could be regained after

mass

shows the TPR

Figure 6-5A ca.

strong reduction of the

pulses, indicating the reversibility

few

of

to

Thus the interaction of

Mn304.

to

300 °C leads

the initial

stream

gas

reduced

is

catalyst,

were

which reoxidized the

change

was

the

injected

observed. In order

experimental

strategy

each 50 °C followed

catalyst (Figure 6-7).

by

Below 200 °C

to

check the

was

changed

1 ml oxygen no

reduction

Reduction of NO

Catalytic

Selective

by NH3

121

temperature / *C 100

50



150

200

250

t

i

i

....

....

.

300

350

400

450

i

i

i

i

...

....

....

....

.

500 .

200 "C

E

0.1-

0.034 mo

time / min

Fig.

A: FTIR

6-5:

Mn(0.50), carrier

N20, H20 and NH3 recorded during heating of 50 mg NH3/He, 10 K min"1; 50-150 °C desorption of NH3(a), above

traces

gas: 5%

of

due to NH3 pulse on 100 mg Mn(0.50) Change of the followed by 02 pulse at 150 °C (only NH3 adsorption and desorption of physisorbed species) and 200 °C (NH3 adsorption, desorption and catalyst reduction followed by reoxidation by

150 °C: reduction

by NH3.

B:

mass

oxygen).

observed but with

was

increased the

significantly.

Mn(1.00) did

not

increasing In

temperature

contrast to

show the

mass

loss due

to

hydrogen pulses

the total reduction shown in

largest

mass

loss

at

Figure 6-6,

temperatures below 400 °C.

Thus different reduction behaviors emerge when total and differential reduc¬ tion

are

considered, which

is

important when relating

catalytic activity of the samples,

as

will be done in the

the redox behavior next

chapter.

to

the

Chapter 6

122

0-

0.00 / 0.24 mg

ÏÏ.1Ô ;o.4fa fflg0.25 / 0.86 mg -1

-

E 0.50/2.11 mg

-2-

œ en c

co ^ o

-3-

ID to

CO

E -4-

1.00/5.27mg

-5-

100

400

300

200

temperature

Fig.

6-6:

TPR of Mn(x)

the

catalyst

and

mass

catalysts

in 5%

loss from 50 mg

in He,

H2

sample

600

500

/ °C

heating rate:

is indicated

on

the

5 K

min"1,

Mn

content

in

curves.

E CD US

m as

CO

E

0.5 mg

I

200

150

'

250

'

—TT—i—|—i—i—r-

i

300

temperature

Fig.

6-7:

Redox-behavior ofMn(x)

composition. 3 K

1 ml

min"1, sample

catalysts

H2 pulses followed by

mass:

100 mg. Mn

content

400

350

as a

450

500

550

/ "C

function of the temperature and

1 ml

02 pulses

in the

catalysts

each 50 °C.

is indicated

on

catalyst

heating the

rate:

curves.

Selective

6.3.3

Catalytic Activity

In order

oxides

to

by means

stream

gas

investigate the

123

by NH3

in SCR SCR

activity of the various manganese-cerium mixed

pulse technique, NH3 pulses were injected into

of the

5% NO/5%

containing

02,

balance helium.

continuous system corroborated that the

criminating

Reduction of NO

Catalytic

pulse

the SCR activities of the different

Activity

method

was

tests

a

carrier

using

a

suitable for dis¬

manganese-cerium

mixed oxide

catalysts. The influence of the temperature ucts

to

of the SCR reaction and the

ammonia

the

pulses

experiment

Above 100 °C but

at

are

were

shown in

50 °C there

change Figure

used for the

only negligible was

a

the

on

of the

mass

6-8. The

quantitative

mass

distinct

composition

gain

of catalyst

two

N2-pulses

due

the reactions to

prod¬

Mn(0.25) due at

the end of

calibration of the FTIR

change during mass

of the gaseous

was

formation of

signal.

observed,

NH4N03.

ci

3

time / min

Change of the mass (TG) of Mn(0.25) and spectroscopic signals of N2 and N20 recorded during pulses of NH3 at different temperatures. Catalyst mass: 100 mg, flow rate 50 ml min"1, carrier gas: 5% NO, 5% 02 balance He. Fig.

6-8:

Chapter 6

124

Ammonium nitrate formation showed also

mixed oxide

composition, showing

deposited NH4NO3 (sample):

on

0.15

100 mg

a

maximum for

samples

due

mg

0.19

(1.00). The formation of NH4N03

results of the fresh Results of this

to

analysis

of the

catalyst

are

depicted

in

Figure

the Mn-Ce

on

Mn(0.75). The

amounts

confirmed

after reaction

1.62

(0.75);

by comparing at

the

50 °C with TA

aqueous solution of

6-9.

of

of 1 ml reactive gas

injections

was

catalyst impregnated by

analysis

dependence

(0); 0.45 (0.10); 0.34 (0.25); 0.96 (0.50);

were:

results of the thermal

clear

a

Decomposition

NH4N03.

of NH4N03

3 CO

£> (=



8 c CO

e o

_o CO

350

temperature / °C

NH3, H20, NOx and N2 traces recorded during decomposi¬ tion of the deposited material on the catalyst (Mn(0.50)) after NH3 and NOx co-adsorption at 50 °C (thick lines) and during decomposition of the NH4N03 impregnated catalyst Fig.

Comparison

6-9:

of the

(Mn(0.50)).

shows that this salt is stable up

to

150-200 °C For the

with the aqueous solution of NH4N03 the evolution

H20

are

similar

as

those observed

catalyst impregnated of NOx,

N2 and

of the solid

deposit

profiles

during decomposition

Selective

formed

on

the

NOx profiles

catalyst

probe

model for temperature perature with

by NH3

lower temperatures. The small shift in the

at

explained by

the different

and reference

sample. According

could be

in the

NH4N03

Reduction of NO

Catalytic

programmed

increasing sample

mass

Table 6-2 lists the results of the

reactions

peaks

of

amount

are

to

shifted

a

to

125

N2 and

deposited

quantitative

higher

tem¬

[17].

comparative activity

tests

of the

catalysts

Catalytic Performance of Mn-Ce mixed oxides: N2 / N20 yield (%) at different temperatures. Catalyst mass: 100 mg, flow rate: 50 ml min" atmosphere: 5% NO, 5% 02

Table 6-2:

,

balance He.

100 °C

50 °C

Sample

200 °C

150 °C

250 °C

300 °C

Mn(0.00)

55/-

71/-

73/-

75/-

68/-

60/1

Mn(0.10)

59/-

85/-

88/-

89/-

87/1

76/7

Mn(0.25)

67/-

98/1

99/1

97/3

88/5

80/11

Mn(0.50)

65/-

91/2

95/5

93/7

87/13

75/23

Mn(0.75)

62/-

78/2

81/6

82/8

76/15

59/32

Mn(l.OO)

54/1

69/1

81/4

72/6

66/14

52/28

with different manganese ent

temperatures. The

cantly

with

increasing of

N20

content.

activity

manganese

is very low for pure

addition.

Selectivity

of nitrous oxide

were

differ¬

at

signifi¬

nitrogen decreases

with

to

nitrogen

was

°C, beside N2, only very small

dependence

of the

of the various Mn-Ce mixed oxides is shown

6-10. At all temperatures the best

selectivity

given

ceria, and increases

observed. The temperature

catalytic performance (N2-yield) Figure

to

are

reaction temperature and manganese content, whereas the formation

increases. At temperatures below 150

amounts

in

N2 and N20 yields (%)

Mn(0.25) and

catalyst concerning conversion the

highest N2-yield (99%)

and was

Chapter 6

126

Fig.

N2 yield

6-10:

function of the temperature and

as a

catalyst composition (marked

curves) obtained during pulsing of NH3, carrier gas: 5% NO, 5% 02 balance

found with this

catalyst

at

SCR-performance

150 °C The

lowing sequence: Mn(0.25)

>

Mn(0.50)

>

Mn(0.10)

>

on

He.

decreased in the fol¬

Mn(0.75)

>

Mn(0.00)

>

Mn(l.OO). In order over

these

gain

some

catalysts

sequence of

for

to

reactant

a

pulses

in oxygen

series of

pulses

catalyst Mn(0.50)

in

was

Figure

containing

further

phase

no

were

performed

6-11A. First the

were

catalyst

(5% 02/He) till

injected,

but

they

was

complete consumption

resulted

of the adsorbed ammonia

NOx pulses

be detected anymore and the

no

catalyst

mass

NO

to

in

was

NH3

injection

NOx

by

shown

by NOx

only

upon

significant nitrogen

are

exposed

saturation

the adsorbed ammonia reacted with the

tion occurred. After four

in which the

changed. Representative examples

nitrogen production was observed. However,

NOx pulses,

till

experiments

carrier gas

achieved, then NH3 pulses

adsorption,

into the mechanism of low-temperature SCR

insight

of

in the gas

the SCR

reac¬

formation could

(TG) reached the

same

value

as

Selective

Catalytic

Reduction of NO

by NH3

127

J3 CD

t T3 C

CD

1 'S

time /

Fig.

6-11

100 qC,

N2 production

:

catalyst mass:

due

to

pulses

100 mg, flow

rate:

mm

(NOx and NH3) over Mn(0.50) at min"1, carrier gas: 5% 02 balance He. A: cat¬

of reactive gas

50 ml

alyst was saturated first by NOx, then further NH3 pulses were injected and they resulted only in adsorption, no N2 production was observed, further NOx(g) pulses reacted with NH3(a) forming nitrogen (ER-mechanism) until NH3(a) is completely consumed. B: After saturation by NOx following pulses were injected: 1: 1 ml NH3 and 4 ml NOx simultaneously, N2 yield: 72% 2: 1 ml NH3, 3: 4 ml NOx, N2 yield: 37%, 4: 1 ml NH3, 5: 1 ml NH3 followed by 4 ml with

NOx

delay of 1

a

before ammonia with

min, N2

yield:

55%

that all adsorbed ammonia reacted

injection, corroborating

NOx.

To further elucidate the role of adsorbed ammonia in the SCR reaction,

several

NH3 pulses

oxidative

pulses

as

presented

of NOx

72%. The TG

were

curve

ammonia which was

removed in the

in

Figure

shows first

reacts

after

by

a

complete adsorption

6-1 IB. First,

distinct

mass

mass

loss due

with the gaseous

introduced

(pulse

No.

2)

preceding SCR reaction.

of NOx under

an excess

one

pulse

simultaneously injected resulting in

tion of both gases followed

ammonia

in the presence of

injected

atmosphere (5% 02/He),

and ammonia

four

were

to

gain the

a

to

NOx

of ammonia and

nitrogen yield

of

mainly physisorp¬

consumption of adsorbed

NOx species.

in order

As

due

a

of both,

an

to

Then

one

pulse

of

readsorb the ammonia

consequence the

mass

of the

cata-

Chapter 6

128

lyst

reached the

pulse

or

pulse (No.

phase does

in gas

3 in

but the

pulse

ammonia

adsorption. During

was

pulse

minute. This

ammonia

lower

by

ca.

was

the fifth

followed

by a

yield

was

still

a

the

in order

no

we can

conclude that

and lead

mixed oxides is

adsorbed ammonia

reacts

minor

importance

be attributed

with

that

to

investigations

presented

Eley-Rideal

with NOx from the gas

proposed by Yang and the

slow

HN02 (a) (step 7)

ments

an

in this

HN02 (a) can

not

study and

24%

originating

carried

on

out

NOx

coworkers is

applied.

formation

NOx (g).

in the

tem¬

in the gas

these observations

This

on

the

implies

that step

mainly contributing

type step 7

seems to

(step 6)

or

reaction of NH3 on

the

investigations.

to

be of

Whether this behavior has

be discriminated based

needs further

from

type mechanism, where

phase.

Langmuir-Hinshelwood

under the conditions

to too

to ca.

100—150 °C the dominant mechanism of SCR

at

N2 formation, whereas

physisorbed

of

simultaneous introduction of both

formation occurred. Based

manganese-cerium

5 of the mechanism

IB) injection

NOx delayed by

amount

desorption

of

equilibrium

adsorbed ammonia reacted with

series of analogous

significant nitrogen

1). Then the

6-1

of four ml

decrease of the to

Figure

indicated that in the absence of perature tange 100-150 °C

phase

significant

to

No.

reach

to

5 in

injection

due

(pulse

ammonia

higher compared

only irreversibly

and

injected leading

pulse (No.

during

obtained

In the third

NOx species.

half of that observed when the gaseous

physisorbed

resulted in

nitrogen yield than

experiment

was

(cf. Figure 6-2)

20%

No. 3, where

pulse

was

delay

gases. However, the

This

yield

NOx

repeated (pulse No.4)

ammonia

of an ammonia

with adsorbed

not react

reacted with chemi- and

NOx

observed, indicating that NH3 either

was

6-1 IB) 4 ml

Figure

nitrogen production,

one

before the SCR reaction. During the ammonia

as

nitrogen production

no

adsorbed

value

same

to

(a)

pulse experi¬

Catalytic Reduction

Selective

(a)

OH

N02 (a)

+

NH3 (a) ->

HN02 (a)

+

N2 (g)

+

interesting

It is

SCR is

an

—>

Yang [7]

and

zero

to

with respect

coverage of ammonia

NH3 species

et

+

at

120 °C

was

form

ER

through

a

react on

By

proceeds

an

NO

was

catalyst

of

reside

et

al.

[21]

tracer

tigation catalytic

of the

relationship

on

the main

between

behavior. The results in

and

Most of

V205

based

where

N02

studies

they

found that it is

with ammonia and

to react

et

al. [22]

aminooxy

with gaseous

suggested

reacts

species. They proposed or

groups

also

adsorption behavior, B and C

redox

two

different

are

involved. inves¬

properties

clearly

an

from the gas

objective of our study, namely the

Figure 6-12A,

to

reported a different mecha¬

species reacting

mechanism. Marban

SCR mechanisms, in which ammonium ions

Finally we come back to

that adsorbed

(Eley-Rideal mechanism)

the surface

with the surface active ammonia

pressure

surface in the presence of oxygen

isotopic

on

NO

to

proposed by Inomata et al. [19].

via adsorbed ammonia

Eley-Rideal

MnOx/Al203

Langmuir-Hinshelwood mechanism, the

of Qi

that the surface

investigated partial

in the over

imply

in the literature deal with SCR

mechanism

means

not

This would

mechanism, in which N02 (or the less reactive NO)

phase

study

(Langmuir-Hinshelwood mechanism).

reported

that NO does

that the SCR NO

phase

with both, gas

[20] proposed

nism of this reaction.

that the dominant mechanism of

for SCR

nitrogen and water, whereas Ozkan

possible

H20

reaction order of one with respect

virtually constant proposed

al. [18]

(ad) and NH3 (ad)

a

NH3, respectively.

to

can react

proposal

our

catalysts. An Eley-Rideal (ER) al.

+

type mechanism is in line with the kinetic

the mechanistic studies

et

NH2NO (a)

—>

(7)

reactive nitrite intermediates

Takagi

(6)

HN02 (a)

NH4N02 (a)

that

note

who found

Kijlstra

(a)

2H20 (g)

Eley-Rideal

and

range.

O

—>

129

by NH3

of NO

and

indicate that

Chapter 6

130

Fig.

6-12 :

Dependence of the amount of adsorbed N02 (NO puls¬ (NO pulses in He) and NH3 (NH3 pulses in He), chemi- and phys¬

A: Adsorption behavior:

02/He), NO isorbed or only chemisorbed, es

in 5%

catalyst composition, catalyst mass: 100 mg, flow rate: 50 ml min"1. B: Redox properties: Mass loss due to 1 ml H2 pulsed over 50 mg of function of catalyst as a function of temperature and catalyst composition. C: N2 yield as a the

catalyst composition

NO, 5% 02 balance He.

at

100 °C

on

the

and temperature obtained

during pulsing

of NH3, carrier gas: 5%

Selective

these

properties change strongly

cerium oxides and that there is

Catalytic

with the a

Reduction of NO

composition

by NH3

of the manganese-

correlation between

striking

131

adsorption

behavior, redox behavior and catalytic properties in SCR. Pulse thermal sis combined with

tool for

elucidating such

for all these

proved

spectroscopy and FTIR

mass

a

correlation because it

to

be

analy¬

very suitable

a

provides quantitative

measures

properties.

6.4 Conclusions

The selective reduction of NOx

catalysts

of different

combined with oxides Mn

content

their

on

to

composition, showing a

the

maximum for

Ce mixed oxide

proceeds

to

via

and the

catalytic

an

Eley-Rideal

an

Eley-Rideal mechanism,

with gaseous

adsorption

NOx

to

a

form

nitrogen

at

or a

100-150 °C

water.

of

similar

striking

cor¬

pulse

on

Mn-

Langmuir-Hin¬

where the adsorbed

and

a

behavior in SCR. The

mechanism

a

improved catalytic

discriminate whether the SCR reaction

shelwood mechanism. The studies indicate that via

of the mixed

samples with

composition of the mixed oxides, indicating

allowed

technique applied

reacts

activity

and NO, and of the redox behavior revealed

properties

analysis

thermal

the pure constituents oxides. Studies of the

relation between these

produced

using pulse

spectroscopy and FTIR. The SCR

NH3

reactants,

dependence

studied

of about 25 at.% Mn. All mixed oxides showed

activity compared both

manganese-cerium mixed oxides

over

composition has been

mass

depended on

by NH3

nitrogen

was

NH3 species

132

Chapter 6

6.5 References

Bosch,

F.

Janssen, Catal. Today

[1]

H.

[2]

V. I.

[3]

M.

[4]

K. Kawamura, A. Hirasawa, S.

(1988) 369.

2

Parvulescu, P. Grange, B. Delmon, Catal. Today 46 (1998) 233.

T.

Koebel, M. Elsener, M. Kleemann, Catal. Today 59 (2000) 335.

Higo,

R.

Aoki,

H.

5.

[5]

G.

R. T.

[6]

G. S.

[7]

G.

[8]

G. S.

[9]

G.

Qi,

[10]

M.

Machida, Catal. Lett. 5 (2002) 91.

[11]

M.

Qi,

Qi,

R. T.

R. T.

Qi,

Yang,

Chang, Appl.

Yang,

R.

217

Chang,

Yang, Appl. Catal.

Machida,

Catal. B 51 (2004) 93.

Yang, J. Phys. Chem.

Yang, J. Catal.

R. T.

R. T.

R.

M. Uto, D.

Chem. 13

Phys.

Ishikawa, K. Adachi, S. Hosoki, Rad.

(1979)

Qi,

Kimura, T Fujn, S. Mizutani,

B 108

(2004) 15738.

(2003) 434. Catal. Lett. 87 (2003) 67. B 44

Kurogi,

(2003) 217-

T.

Mater. Chem.

Kijima, J.

11

(2001) 900. [12]

M.

Machida, M. Uto, D. Kurogi, T. Kijima, Chem. Mater.

12

(2000)

3158.

(2000) 3165.

[13]

M.

Machida, D. Kurogi, T. Kijima, Chem. Mater.

[14]

M.

Machida, A. Yoshii, T. Kijima, Int. J. Inorg. Mater.

[15]

M.

Maciejewski, A. Baiker, Thermochim. Acta 295 (1997)

[16]

M.

Maciejewski,

C. A.

12

2

(2000) 413. 95.

Müller, R. Tschan, W. D. Emmerich, A. Baiker,

Thermochim. Acta 295 (1997) 167.

[17]

D. A. M. Monti, A.

[18]

W. S.

171

[19]

Kijlstra,

D. S.

Baiker, J. Catal. 83 (1983) 323. Brands, H. I. Smit,

E. K.

Poels,

A.

Bliek, J. Catal.

(1997)219.

M. Inomata, A.

Miyamoto,

Y.

Murakami, J. Catal. 62 (1980) 140.

Selective

[20]

M.

Takagi,

Catalytic

Reduction of NO

by NH3

T. Kawai, M. Soma, T. Onishi, K. Tamaru,

133

J. Catal.

(1977)441. [21]

U. S.

[22]

G.

Ozkan,

Y. P.

Cai, M. W. Kumthekar, J. Catal. 149 (1994) 390.

Marban, T. Valdes-Solis, A.

B.

Fuertes, J. Catal. 226 (2004) 138.

50

Seite Leer / Blank leaf

Final Remarks

The present

mal

analysis by

careful

the

FTIR is

strongly

analysis

is

gas

pulse technique using

optimization

only

by

Among

accurate

possibilities

the various

advantage

evolved or

sess

similar

severely

fragmentation

affect the

showed that

a

use

ions

of MS

Micro GC

packed columns,

strategy may be suitable four columns in

or

using

parallel,

identification of the evolved

resolu¬

spectral

poor time

reso¬

analysis

chromatography (GC).

The

the gases

identify

reactions, which is difficult when using

FTIR for

released

may pos¬

vibrational spectra which

extremely

efficiency every

provides

during TA,

quantification. Preliminary

short and

analysis

which

be considered in

to

separate and

one can

overlapping

increases the to run

gas

simultaneously or

to

of combining TA with evolved gas

parallel

FTIR. Gases and vapors,

MS

micro

or

on

quantification.

of this method is that

during multistage

factors

resolution leads

(EGA), another promising method would be great

based

parameters, whereas MS

the choice of the

are:

High spectral

rate.

lution, which is crucial for

important

of TA-FTIR

means

tion and carrier gas flow

most

requires

FTIR spectroscopy

or

experimental

the chosen

little affected. The

quantification by

MS

ther¬

during

experimental settings. Quantification

of the

affected

of evolved gases

quantification

showed that the

study

of the

two

the

species. However,

narrow

minutes with

opportunity a

limitation

for

results

capillaries

separation

can

and

process. This

two or

optional

separation

compared

to

and

FTIR

136

or

MS systems is that: the

method is less tems,

accurate

quantification

because of the

of the evolved gases with the

relatively poor time

which is discussed for FTIR and MS methods in

The extension of the present system

provide

further

where neither MS

resolution in GC sys¬

chapter

4.

TA-MS-FTIR-GC system would

analytical possibilities particular

adsorption phenomena, cal tool.

to a

pulse

nor

for

gas-solid

FTIR is the

reactions and

appropriate analyti¬

Seite Leer / Blank leaf

Seite Leer / Blank leaf

List of Publications

List of

The on

publications

related to the thesis

following list summarizes chronologically

pertinent chapters of the thesis

this thesis. The

Calibration of

"Quantitative

the

publications which are are

Spectroscopic Signals

given

based

in brackets.

in Combined TG-FTIR

System" F.

M.

Eigenmann,

Maciejewski,

A.

Baiker, Thermochim. Acta (in press)

(Chapter 3)

"Influence of

Signals F.

Measuring

in TA-FTIR-MS

Eigenmann,

M.

Conditions

on

the

Quantification

of

Spectroscopic

System"

Maciejewski,

A.

Baiker, J. Therm. Anal. Cal. (in press)

(Chapter 4)

"Gas F.

Adsorption

Eigenmann,

(Chapter 5)

Studied

M.

by

Pulse Thermal

Maciejewski, A. Baiker,

Analysis"

Thermochim. Acta 359 (2000) 131.

140

"Selective Reduction of NO

Relation between F.

Eigenmann,

by NH3

adsorption,

M.

over

redox and

Maciejewski,

A.

Manganese-Cerium

catalytic

Baiker,

Appl.

Mixed Oxides:

behavior"

Catal. B 62 (2005) 311.

(Chapter 6)

publications

List of other

Following publication research

G.

published during

the thesis but

covers

another

topic.

"Continuous Pt/TS-1

was

Epoxidation

of

Propylene

with

Oxygen

and

Hydrogen

on a

Pd-

Catalyst"

Jenzer,

T.

Gen. 5304

Mallat, M. Maciejewski, F. Eigenmann, A. Baiker,

(2000)

Appl.

Catal. A-

1.

Patents

"Process for the Production of Molybdenum Oxide,

Molybdenum

Oxide pro¬

duced from this Process and Use thereof" R.

Nesper,

Eur. Patent

F.

Krumeich,

Appl.

M.

Niederberger,

No. 01810072.7, 2001

Technology (ETH),

Zürich

(Switzerland)

A.

Baiker, F. Eigenmann

Applicant:

Swiss Federal Institute of

141

List of Conference Contributions

"Pulsthermoanalyse:

pling Days (2nd F.

Eigenmann,

proceedings,

Neue

SKT

M.

oral

1999) from

Maciejewski,

F.

M.

poster and oral

Maciejewski,

proceedings,

F.

M.

oral

Adsorption

Chemical

1999 in Selb

(Germany),

A. Baiker,

FTIR

a

workshop.

Signalen", Analytica,

28-31

Maciejewski,

presentation

Studied

Society 2000,

Eigenmann,

A.

13

April

2000 in

Baiker,

of Spectroscopic FTIR

2000) from

SKT

Eigenmann,

"Gas

April

presentation.

"Quantitative Calibration

F.

von

für STA-FTIR", 2nd Selber Cou¬

(Germany),

Eigenmann,

Days (3rd

18-22

presentation and leading

"Quantitative Kalibrierung München

Möglichkeiten

M.

A.

and

May

Signals", 3rd

2000 in Bad Orb

Coupling

(Germany),

Baiker,

leading a workshop.

by Pulse Thermal Analysis",

Fall

Meeting

of the Swiss

(Switzerland),

Lausanne

Maciejewski,

Selber

A.

Baiker,

poster.

"Methanol Oxidation Studied Swiss Chemical F.

Eigenmann,

poster.

by

Pulse Thermal

Analysis",

Society 2001, Zürich (Switzerland),

M.

Maciejewski,

A.

Baiker,

Fall

Meeting

of the

Curriculum Vitae

Name

Florian

Date of Birth

5

City

of Birth

July

Eigenmann

1973

Zürich

Citizen of

Waldkirch (SG)

Nationality

Swiss

Education

1986-1992

Kantonsschule Zürich-Wiedikon

Graduation with Matura

1993-1998

ETH

B

Zürich, Chemistry Department

Chemical

Engineering Studies

Graduation

1999-2005

Type

as

Dipl.

Chem.

Ing.

ETH

ETH Zürich, Institute for Chemical and Doctoral Thesis under the

Supervision

Bioengineering

of Prof. Dr. A. Baiker