Influence of binder on catalytic performance of Ni

Catalysis Communications 45 (2014) 109–113

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Short Communication

Influence of binder on catalytic performance of Ni/HZSM-5 for hydrodeoxygenation of cyclohexanone Xiaobao Du a, Xiangjin Kong b,⁎, Ligong Chen a a b

School of Chemical Engineering and Technology, Tianjin University, Tianjin 300072, PR China Shandong Provincial Key Laboratory of Chemical Energy Storage and Novel Cell Technology, School of Chemistry and Chemical Engineering, Liaocheng University, Liaocheng 252059, PR China

a r t i c l e

i n f o

Article history: Received 18 July 2013 Received in revised form 28 October 2013 Accepted 29 October 2013 Available online 11 November 2013 Keywords: Hydrodeoxygenation Cyclohexanone Alumina binder Ni/HZSM-5

a b s t r a c t The influences of binders (alumina, silica sol, kaolin) on the performance of Ni/H-ZSM-5 for hydrodeoxygenation of cyclohexanone were investigated in a fixed-bed reactor. N2 sorption, X-ray diffractions, H2-temperatureprogrammed reduction, transmission electron microscopy, 27Al MAS NMR, and temperature-programmed desorption of ammonia were used to characterize the catalysts. The obtained results exhibited that porosity and acidity of the catalysts were strongly influenced by the binders. The most outstanding catalytic performance was observed on catalyst with alumina binder, which bears a well-developed pore structure and more acid sites than the others. Thus, alumina was chosen as the optimum binder to Ni/HZSM-5. © 2013 Elsevier B.V. All rights reserved.

1. Introduction

2. Experimental

The reduction of carbonyls to corresponding methylenes is among the most important and prevalent transformations in pharmaceutical industry and in the production of bio-oils from biomass. Clemmensen [1] reaction and Wolff–Kishner–Huangminlon [2] reaction are the traditional procedures to complete this functional group manipulation. Recently, hydrodeoxygenation has drawn people's attentions as an alternative approach for this transformation [3–5]. In early studies, metal supported on solid acid especially on zeolite has proved to be an efficient catalytic system for this method [6]. Generally, if a zeolitebased catalyst is to be used in an industrial process, it must be pelletized with a binder [7,8]. It has been revealed that [9–11] the binder could have a key impact on the overall acidic properties and distribution of active metal particles on the catalyst, and thus leading to different catalytic performances. As presented in our previous works [6], Ni/HZSM-5 was developed and exhibited excellent performance for the hydrodeoxygenation of cyclohexanone (the catalytic process preceded as shown in Scheme 1). Nevertheless, the effect of binder on the catalytic performance has not been investigated yet. In this work, a series of Ni/ HZSM-5 with different binders (alumina, silica sol, and kaolin) was prepared and tested in a fixed-bed reactor. The aim of this work was to evaluate the influence of binder on the performance of Ni/HZSM-5 and to select a suitable binder for the application of this catalyst.

2.1. Materials and catalysts

⁎ Corresponding author. E-mail address: [email protected] (X. Kong). 1566-7367/$ – see front matter © 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.catcom.2013.10.042

The parent HZSM-5 powder (nominal Si/Al = 25) was provided by Nankai University catalyst Co., Ltd. All the other chemicals in the present study were reagent grade and were used without further purification. The supported monometallic catalysts with different binders were prepared by kneading the metal carbonates with HZSM-5 as well as the binder. The content of binder in the catalyst was 30 wt%. The detailed procedures for preparation of the catalyst were described in our previous work [6]. For example, Ni/HZSM-5-Al (the content of Ni in the catalyst was 20 wt.%; Al means that the binder of the catalyst is alumina) was prepared as follows: 16.18 g metal carbonates were kneaded with a mixture of 22.40 g HZSM-5 and 14.44 g pseudo-boehmite (alumina source), accompanied with deionized water as adhesive, and then molded to bars (diameter: about 3 mm) with an extruder. After being dried in air for 6 h at 110 °C, the bars were calcined for 4 h at 500 °C, and then Ni/HZSM-5-Al was obtained. Ni/HZSM-5-Si (silica sol as the binder) and Ni/HZSM-5-Ka (kaolin as the binder) were prepared in the same way as described above.

2.2. Catalysts characterization Brunner–Emmett–Teller (BET) surface area and pore volume were measured by N2 adsorption/desorption at 77 K with a NOVA 2000e surface and porosity analyzer (Quantachrome, US). Powder X-ray

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X. Du et al. / Catalysis Communications 45 (2014) 109–113

Scheme 1. The main reaction process for the reductive deoxygenation of cyclohexanone.

diffractions (XRD) were recorded on a Rigaka D/max 2500 X-ray diffractometer with Cu-Kα radiation (40 kV, 100 mA) in the range of 5–90°. H2-temperature programmed reduction (H2-TPR) was measured using a micromeritics 2910 apparatus equipped with a thermal conductivity detector (TCD). The calcined samples were heated from ambient temperature to 700 °C at a rate of 10 °C/min. High-resolution transmission electron microscopy (HR-TEM) images were observed using a JEOL electron microscope (JEM-2010), with an accelerating voltage of 200 keV. Solid-state 27Al MAS NMR spectra were collected in a BrukerDSX-400 spectrometer. The 27Al NMR spectra were obtained at 10.0 kHz, using 15° pulses and a 4 s delay, with a total of 2000 pulses being accumulated. The acid capacity was investigated via temperature-programmed desorption of ammonia (NH3-TPD) using a TP-5000 instrument at the atmospheric pressure with a thermal conductivity detector (TCD) device. 2.3. Catalytic reaction The reaction was carried out in a fixed-bed tubular reactor with an inner diameter of 15 mm and a length of 660 mm, which was loaded with 40.0 mL catalysts. All the catalysts were reduced at 360 °C for 4 h in a stream of hydrogen under 1.0 MPa before use. A solution of cyclohexanone (concentration in 1,4-dioxane: 20.0 wt.%. ) was dosed into the reactor at a flow rate of 0.2 mL/min by a syringe pump. The continuous reaction was conducted at 160 °C under H2 pressure of 2 MPa. The reaction mixture was collected using a cold trap (0–2 °C) and analyzed without preliminary separation by off-line gas chromatograph (OV-1701 capillary column: 30 m × 0.25 mm, 0.2 μm film thickness). The components of the reaction mixture were identified by GC/MS (HP-1 capillary column: 30 m × 0.25 mm, 0.2 μm film thickness) which was equipped with an ion-trap detector. 3. Results and discussion

a well-developed micropore structure. Moreover, it can be seen from Table 1, the surface area and pore volume of Ni/HZSM-5-Ka are the least. During reaction, a poor mechanical strength was also displayed by this catalyst. Clearly, these results are related to the special structure characteristic of kaolin. As reported [12], kaolin is a kind of laminar clay, the interlayer of which is combined with weak van der Waals force. When kaolin was used as binder, water can enter its interlayer and lead to cracking of its layer to layer structure. The cracked kaolin powders could wrap the metal carbonates and block the HZSM-5 pores during the catalyst preparation process. According to some previous researchers [13], alumina mainly contains mesopore structure. When it was used as binder, a welldeveloped mesopore structure may probably be formed over the catalyst. This is also confirmed by total mesopore volume and the average pore diameter of these catalysts in Table 1, from which we know the total pore volume of Ni/HZSM-5-Al is bigger than the others and 80% of the pores are mesopores. These results imply that Ni/HZSM-5-Al contains a well-developed mesopore structure which is helpful to the mass transfer during the reaction. 3.1.2. XRD The XRD patterns of the reduced catalysts are depicted in Fig. 1. The typical peaks of HZSM-5 (23 ∼ 24°) are shown in the patterns of all the catalysts, while no obvious peak of the binder is observed on these XRD curves, indicating that the structure of HZSM-5 did not changed after mixed with amounts of binder and the XRD intensities of the binder are very small or probably hided by those of HZSM-5. The diffraction lines (44.4°, 51.8° and 76.4°) of elementary nickel are displayed by the XRD curves of all catalysts; thus Ni0 could be confirmed as the hydrogenation active sites on these catalysts. It's noteworthy that, diffraction lines of NiO are also found on the patterns of Ni/HZSM-5-Si and Ni/HZSM-5-Ka, demonstrated that the catalysts with silica sol and kaolin binder are hard to be reduced completely. These results are in agreement with our above discussions that some of the metal carbonates were wrapped in the kaolin or silica sol binder. In other words,

3.1. Catalysts characterization

Table 1 The influences of binder to the N2 sorption characteristics of Ni/HZSM-5. Sample

SBETa (m2/g)

Vtotalb (cm3/g)

Vmicropc (cm3/g)

Vmesopd (cm3/g)

Daverage (nm)

Ni/HZSM-5 Ni/HZSM-5-Al Ni/HZSM-5-Si Ni/HZSM-5-Ka

284.9 264.4 242.2 197.1

0.1764 0.2855 0.2841 0.1692

0.0982 0.0631 0.0469 0.0763

0.07821 0.2224 0.2372 0.0929

1.2 4.3 4.5 3.4

a b c d

Calculated from BET function. Evaluated from N2 uptake at a relative N2 pressure of 0.99. T-method micro pore volume. Vmesop = Vtotal − Vmicrop.

o Ni * NiO

o

Intensity (CPS)

3.1.1. N2 sorption To understand the influences of binder on the texture properties, the surface area and pore volume of these catalysts were measured by nitrogen sorption. As described in Table 1, after addition of the binders, surface area and micropore volume of Ni/HZSM-5 are found to be less. This is a result of dilution of HZSM-5 which having

*

*

o

(d)

o

(c) (b) (a) 10

20

30

40

50

60

70

80

90

2-Theta (deg) Fig. 1. XRD patterns of reduced (a) Ni/HZSM-5, (b) Ni/HZSM-5-Al, (c) Ni/HZSM-5-Si, and (d) Ni/HZSM-5-Ka.


111

the metal active sites are distributed better on the catalyst with alumina binder than others. The diameters of Ni0 on these reduced catalysts were calculated via Scherrer equation and are summarized in Table 2. The average Ni particles diameter on these catalysts is about 20–40 nm, which means that the Ni particles are too large to enter the HZSM-5 channels. So we propose that the Ni particles located mainly on the external surface of the zeolite.

(d)

(c) 3.1.3. H2-TPR The influence of binder on the reducibility of nickel species in the catalysts was investigated by H2-TPR experiments and the results are described in Fig. 2. Normally, the area of a specific peak can be used to estimate the amount of H2 consumed during the reduction process, and can be taken as a standard to quantify the degree of reduction of the sample. All the unreduced catalysts curves displayed one broad peak from 300 to 450 °C, which contains a weak shoulder peak and a sharp peak. The shoulder peak and the main peak can be assigned to the reduction of highly dispersed nickel oxide and large NiO crystallites in contact with the support [14–16], respectively. The Tpeak and peak area of the broad peak are listed in Table S1. For the unreduced Ni/HZSM-5-Al, a slight shift of the reduction peak towards lower temperature is detected in comparison with other catalysts, and the area of the H2 consumed peak of Ni/HZSM-5-Al is the biggest (shown in Table S1). Based on the results above, a conclusion can be reached that the catalyst with alumina binder was reduced more completely than the others. These results agree well with the XRD results. 3.1.4. TEM TEM images of Ni/HZSM-5 with different binders are shown in Fig. 3. The images showed the different Ni particle distributions on the catalysts. For Ni/HSZM-5-Al, the mean particle size of Ni species is about 15.0 nm. Each other catalyst (Ni/HZSM-5, Ni/HSZM-5-Si or Ni/HSZM-5-Ka) has a much larger metal particle size of 20 nm due to the aggregation of Ni particles. The TEM images also prove that the binder, HZSM-5 and Ni species dispersed well on the Ni/HZSM5-Al. But for Ni/HZSM-5-Si and Ni/HZSM-5-Ka, wrapping of the Ni particles by binder and aggregation of binder are observed. These results well answered the question that why the unreduced catalyst with alumina as binder is easily to be reduced than other catalysts. 3.1.5. 27Al MAS NMR spectra To better understand the effect of binder on the structure of HZSM-5, 27 Al MAS NMR spectra of different samples were carried out and the results are shown in Fig. S1. In general, two Al species signals are in the spectra of HZSM-5 zeolite: one is at about 54 ppm corresponding to tetrahedrally coordinated framework aluminum and the other is at 0 ppm corresponding to octahedrally coordinated nonframework aluminum [10]. The spectra of Ni/HZSM-5 is characterized with an intense and sharp signal at 54 ppm and no signal at 0 ppm, which indicates that all of the aluminum species have been incorporated into the framework of HZSM-5. It may be attributed to the high silica-alumina ratio of zeolite used in the experiment. The peak at 54 ppm is broadened when the catalyst contains alumina or kaolin binder, and the peak area also increases. This may be due to the Al species in the binders enter into the framework of zeolite during the calcinations [10,11]. Furthermore, a new signal at about 0–3 ppm is observed, which can be assigned to

Table 2 The influence of binder on the size of the Ni0 particles on the catalysts. Sample

Ni/HZSM-5

Ni/HZSM-5-Al

Ni/HZSM-5-Si

Ni/HZSM-5-Ka

Sizea (nm)

24.6

23.9

25.1

38.1

a

Calculated via Scherrer equation.

(b) (a) 100

200

300

400

Temperature (

500

600

700

)

Fig. 2. H2 -TPR spectra of (a) Ni/HZSM-5, (b) Ni/HZSM-5-Al, (c) Ni/HZSM-5-Si, and (d) Ni/HZSM-5-Ka.

the Al species from binders. The above results displayed that part of Al species from the binder was incorporated into HZSM-5 framework during the catalyst preparation process. As to the catalyst with silica gel binder, the peak area at 54 ppm slightly decreased (Table S2). This is probably due to that the framework aluminum of HZSM-5 was diluted by the addition of binder. 3.1.6. NH3-TPD Extensive NH3-TPD studies were performed to compare the acidic strength of these catalysts with different binders (shown in Fig. S2). All these catalysts exhibited two desorption peaks, i.e., weak and strong acid sites, which give the peaks at around 150–250 °C, and 450–550 °C respectively. The acidic capacity of the samples is listed in Table 3. As seen in Table 3, the strong acid sites of Ni/HZSM-5 are lower than the pure HZSM-5 support, but more than those with binders. It means that the acid sites are neutralized by the supported Ni species and the binder has a big influence on the catalyst acidity. In general, the lowtemperature peak is assigned to ammonia desorbed from weak acid Lewis sites of Al species and the high-temperature peak is ascribed to desorption from the more strongly acidic Brønsted sites of the bridged OH groups [17]. Obviously, the Al species played an important role in the amount of weak acid sites of the catalyst. From the above 27Al MAS NMR characterization results, we know some Al species from the binder are migrated into the zeolite framework during the calcinations. Furthermore, it is well known that a slight of alkali metal cations are contained on silica sol (Na+) or kaolin (Na+, K+) binders, and of course these cations can easily neutralize the bridged OH groups on HZSM-5 and thus reduced the strong acid sites on the catalyst [18,19]. According to the above analysis, it can be deduced that the catalyst with alumina has more weak and strong acid sites than the others. 3.2. Catalytic performance of Ni/HZSM-5 with different binders During the catalytic test, Ni/HZSM-5 displayed a poor mechanical strength and the reaction cannot to be conducted, so only the catalytic performances of Ni/HZSM-5 with different binders are shown in Table 4. Compared with other catalysts, Ni/HZSM-5-Ka exhibited a lowest cyclohexanone conversion, indicating the weak hydrogenation ability of the catalyst, which may be caused by the poor metal dispersion on the catalyst as discussed before. More cyclohexanol were collected over this catalyst than Ni/HZSM-5-Si, which is opposite to the total acid sites sequence of these two catalysts. From Table 1, we know Ni/HZSM-5-Ka has the lowest mesopore volume in all catalysts. Thus, here we assumed that the considerable amount of cyclohexanol over Ni/HZSM-5-Ka may

112


(a)

50 nm

(b)

50 nm

(c)

50 nm

(d)

50 nm

Fig. 3. TEM images of (a) Ni/HZSM-5, (b) Ni/HZSM-5-Al, (c) Ni/HZSM-5-Si, and (d) Ni/HZSM-5-Ka.

4. Conclusion

be caused by the mass transfer limitations which restricted the diffusion of cyclohexanol from outside metal sites to inside acid sites. The most outstanding catalytic performance was observed on Ni/HZSM-5 with alumina binder, the conversion of cyclohexanone and selectivity of cyclohexane were 97.3% and 88.3%, respectively. As presented before, Ni/HZSM-5-Al bears a well-developed mesopore structures and much more acid sites than the others. These properties promised a better hydrogenation and dehydration ability for the catalyst. Therefore, the alumina is chosen as the optimum binder for Ni/HZSM-5.

The influences of different binders on the catalytic performance of Ni/HZSM-5 for reduction of cyclohexanone to cyclohexane were studied in a fixed-bed reactor. The obtained results demonstrated that the pore volume and the acid sites of catalysts were greatly influenced by the binders. The catalyst with alumina was found to have the biggest mesopore volume and the total acid sites, which could facilitate the mass transfer and promote the dehydration of the key intermediate cyclohexanol. Therefore, it exhibited exhibit excellent performance for the hydrodeoxygenation of cyclohexanone. Acknowledgment

Table 3 Temperature programmed desorption of NH3 for various catalysts. Sample

Weak acidity (mmol NH3/g)

Strong acidity (mmol NH3/g)

Total acidity (mmol NH3/g)

HZSM-5 Ni/HZSM-5 Ni/HZSM-5-Al Ni/HZSM-5-Si Ni/HZSM-5-Ka

0.60 0.46 0.44 0.37 0.41

0.22 0.19 0.10 0.09 0.08

0.82 0.65 0.54 0.46 0.49

This work is supported by the Natural Science Foundation of China (Under Grant No. 20976123). Appendix A. Supplementary data Supplementary data to this article can be found online at http://dx. doi.org/10.1016/j.catcom.2013.10.042.

Table 4 The influences of binder on catalytic performance for hydrodeoxygenation of cyclohexanone. Sample

Conversion/%

Ni/HZSM-5-Al Ni/HZSM-5-Si Ni/HZSM-5-Ka

97.3 96.5 92.2

Selectivity/% Low boilers

Cyclohexane

Cyclohexene

Cyclohexanol

Other

4.4 2.5 1.6

88.3 75.8 72.1

0.6 0.2 0.6

4.0 18.0 22.5

2.7 3.6 2.8


References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10]

J.H. Brewster, J. Am. Chem. Soc. 76 (1954) 6361. Huang Minlon, J. Am. Chem. Soc. 68 (1946) 2487. S. Liu, X.P. Fan, X.L. Yan, X.B. Du, L.G. Chen, Appl. Catal. A 400 (2011) 99. J.C. Ma, S. Liu, X.J. Kong, X.P. Fan, X.L. Yan, L.G. Chen, Res. Chem. Intermed. 38 (2012) 1341. F. Alvarez, P. Magnouxb, F. RarnBa Ribeiro, M. Guisnet, J. Mol. Catal. 92 (1994) 67. X.J. Kong, W.C. Lai, J. Tian, Y. Li, X.L. Yan, L.G. Chen, Chem. Cat. Chem. 5 (2013) 2009. M.W. Kasture, P.S. Niphadkar, V.V. Bokade, P.N. Joshi, Catal. Commun. 8 (2007) 1003. F. Dorado, R. Romero, P. Canizares, Appl. Catal. A 236 (2002) 235. K. Honda, X. Chen, Z.-G. Zhang, Appl. Catal. A 351 (2008) 122. H. Liu, Y.M. Zhou, Y.W. Zhang, L.Y. Bai, M.H. Tang, Ind. Eng. Chem. Res. 47 (2008) 8142.

113

[11] Y.W. Zhang, Y.M. Zhou, A.D. Qiu, Y. Wang, Y. Xu, P.C. Wu, Ind. Eng. Chem. Res. 45 (2006) 2213. [12] H.Y. Wang, C.S. Li, Z.J. Peng, S.J. Zhang, J. Therm. Anal. Calorim. 105 (2011) 157. [13] S.D. Kim, S.C. Baek, Y.J. Lee, K.W. Jun, M.J. Kim, I.S. Yoo, Appl. Catal. A 309 (2006) 139. [14] D.P. Upare, S.H. Yoon, C.W. Lee, J. Porous. Mater. 20 (2013) 1129. [15] Y.H. Yang, S.Y. Lim, G.A. Du, Y.A. Chen, D. Ciuparu, G.L. Haller, J. Phys. Chem. B 109 (2005) 13237. [16] A.M. Ruppert, M. Niewiadomski, J. Grams, W. Kwapiński, Appl. Catal. B 145 (2014) 85. [17] K.Y. Lee, H.K. Lee, S.K. Ihm, Top. Catal. 53 (2010) 247. [18] V.R. Choudhary, P. Devadas, A.K. Kinage, M. Guisnet, Appl. Catal. A 162 (1997) 223. [19] M.D. Romero, J.A. Calles, A. Rodr'ıguez, A. De Lucas, Microporous Mesoporous Mater. 9 (1997) 221.