SBA-15 catalysts

JOURNAL OF FUEL CHEMISTRY AND TECHNOLOGY Volume 41, Issue 8, Aug 2013 Online English edition of the Chinese language journal Cite this article as: J Fuel Chem Technol, 2013, 41(8), 943949

RESEARCH PAPER

Hydrolytic hydrogenation of cellulose over Ni-WO3/SBA-15 catalysts CAO Yue-ling1,2, WANG Jun-wei1,*, LI Qi-feng1, YIN Ning1, LIU Zhen-min1, KANG Mao-qing1, ZHU Yu-lei1 1

Institute of Coal Chemistry, Chinese Academy of Sciences, Taiyuan 030001, China;

2

University of Chinese Academy of Sciences, Beijing 100049, China

Abstract:

Series of non-precious metal catalysts Ni-WO3/SBA-15 were prepared by means of incipient impregnation and applied to

the hydrogenolysis of cellulose in aqueous solution. The effect of reaction temperature on the hydrolysis and morphology of cellulose, and the influence of Ni, WO3 loading on the conversion of cellulose were investigated. High crystalline cellulose was transformed gradually into amorphous state with the increase of reaction temperature. H2 temperature program reduction of the catalyst proved that a strong interaction existed between nickel and tungsten trioxide, which enhanced the ability of tungsten species to the cleavage of C-C bond and the activity of hydrogenation of nickel. Thus, the transformation of cellulose into ethylene glycol was strengthened markedly. The complete conversion of cellulose and 70.7% ethylene glycol yield were obtained over a 3% Ni-15% WO3/SBA-15 catalyst under the reaction condition of 230qC and 6.0 MPa H2 for 6.0 h. Keywords: cellulose; Ni-WO3/SBA-15; hydrogenolysis; ethylene glycol

Currently, it is urgent for people to seek a new way of synthetizing chemicals from renewable resources due to the gradual depletion of fossil resources and the growing seriousness of environmental pollution. Biomass is the only feedstock that can provide the chemicals as well as the energy, and therefore, its controllable transformation is becoming the hot field in the world. Moreover, among many components of biomass, the lignocellulose possesses the most large-scale development prospects because of its abundance and non-edibility. Recently, there have been a lot of research on the conversion of biomass derivatives to bio-fuels and high valued chemicals, such as glucose, polyols, 5-HMF, organic acid and hydrogen[1–5]. Among these products, polyols, such as ethylene glycol and propylene glycol, are widely used in chemical industries, such as food, coating, detergent, and pharmaceutical industries. At first, the noble metal catalysts ZHUHXVHGWRFRQYHUWFHOOXORVHLQWRSRO\ROVVXFKDV3WȖ-Al2O3, Ru/CNT and Pt/Na(H)-ZSM-5[6–8]. Later, to facilitate the hydrolysis of cellulose, some researchers proposed the combined system, such as heteropolyacids combined with Ru/C, mineral acid combined with Ru/C and mineral acid combined with Ru/USY[9–11]. Considering the high price of

noble metal catalysts, more researchers paid attention to the investigation of non-noble metal catalysts, such as Ni-W2C/AC, Ni-W/SBA-15, Ni-WxC/CMK-3, Ni2P/AC and Ni/ZnO[12–15]. Among the proposed non-noble metal catalyst systems, supported Ni-W catalysts were attracted lots of attention because of their higher activity and lower cost. It was found that various tungsten compounds were all efficient for the catalytic conversion of cellulose to ethylene glycol, such as W2C, W, WO3 and H2WO4. However, due to the complexity of reaction system and the limitation of in situ characterization techniques, it was far from comprehension concerning the study of Ni-WO3 catalysts, including the optimization of the types of catalysts, and the preparation technology and parameters of catalysts. On the other hand, there was a controversy and somewhere unknown concerning the real structure of tungsten-based catalysts and the catalytic mechanism, especially the reason for the high selectivity to ethylene glycol. Based on these problems, the effect of temperature on the conversion of cellulose and its morphology was investigated in this work. It was found that there was a strong interaction between the metal Ni and WO3, which could promote the hydrogenation activity of metal Ni as well

Received: 13-Apr-2013; Revised: 21-Jun-2013 * Corresponding author: E-mail: [email protected], Tel: 0351-4069680 Foundation item: Supported by the Major State Basic Research Development Program of China (973 Program, 2012CB215305). Copyright ” 2013, Institute of Coal Chemistry, Chinese Academy of Sciences. Published by Elsevier Limited. All rights reserved.

CAO Yue-ling et al. / Journal of Fuel Chemistry and Technology, 2013, 41(8): 943949

as the selective cleavage of C-C bond. Up to 70% ethylene glycol yield was obtained with complete conversion of cellulose under the reaction conditions of 230qC, 6 MPa and 6 h.

1

Experimental

1.1

Main materials

Cellulose (D-cellulose, particle size 25 µm) was supplied by Aladdin Chemistry Co. Ltd. Nickel nitrate hexahydrate [Ni(NO3)2·6H2O] and tungstophosphoric acid hydrate [H3O4PW12·xH2O] were purchased from Sinopharm Chemical Reagent Co., Ltd., AR. SBA-15 Zeolite was obtained from Shanghai Novel Chemical Technology Co., Ltd. 1.2

Preparation of catalysts

All catalysts were prepared using a conventional incipient impregnation method. Firstly, the support, SBA-15, was impregnated with an aqueous solution of tungstophosphoric acid hydrate [H3O40PW12·xH2O] and nickel nitrate hexahydrate [Ni(NO3)2·6H2O]. Then the catalyst was dried at 100qC for 12 h. Finally, it was calcined at 500qC for 3 h. Before the reaction, all of the catalysts were reduced at 500qC for 3 h in a hydrogen flow. 1.3

Catalytic experiments and product analysis

All catalytic experiments were carried out in a 100 mL stainless-steel autoclave. Firstly, 1.00 g cellulose, 40.0 g deionized water and 0.250 g catalysts were successively loaded in the autoclave, and then the reactor was purged with hydrogen to remove air. Secondly, the reactor was filled with 6 MPa hydrogen pressure at room temperature and finally heated to 230qC with a strong stirring. The zero reaction time was regarded as the time when the temperature reached the set temperature. After the reaction, the autoclave was cooled to room temperature by a water bath. The solid residues were separated from the liquid products by filtered with filter paper and the pH value of filtrate was measured by universal indicator paper. Table 1

a

Effect of temperature on the conversion of cellulosea

Temperature t/qC

Conversion x/%b

pH value

200

15

4.0

210

38

4.0

220

55

3.5

230

74

2.5

reaction conditions: cellulose: 1.00 g; deionized water: 40.0 g;

initial H2 pressure: 6.0 MPa; time: 6.0 h

The solid product was washed several times using deionized water and dried 12 h at 100qC in order to evaluate the cellulose conversion. The cellulose conversion and the polyol yield were calculated based on the following formulas: x(%)=(wweight of cellulose before the reaction-wweight of cellulose after the reaction)/ (1) wweight of cellulose before the reaction×100% w(%)=mweight of the products determined/mweight of cellulose charged into the (2) reactor×100% Products were quantified by both gas chromatograph (GC) and high performance liquid chromatography (HPLC). The polyols, including ethylene glycol, 1, 2-propylene glycol, 1, 2-butanediol, 1, 2-hexylene glycol and glycerol, were analyzed by a Shimadzu GC-2014 equipped with a flame ionization detector (FID). The hexitols were determined by HPLC with Ca-NP capillary chromatography column and evaporative light scattering detector. All the products were quantified using internal standard method. 1.4

Characterization

Scanning electron microscope (SEM) images were obtained on a KYKY-2800B thermal field emission scanning microscope with an acceleration voltage of 25 kV for all samples. The XRD patterns were obtained with a D8 ADVANCE instrument operated at 50 kV using Cu KD radiation. TPR experiments were carried out in a ChemBet 3000 equipped with a thermal conductivity detector (TCD). In the TPR experiments, the samples were pretreated in situ at 450qC for 1 h under N2 flow and then cooled to 40qC in an N2 stream. The reduction step was performed using an 10%H2/N2 mixture by heating the sample from 40qC to 700qC at a heating rate of 10qC /min.

2 2.1

Results and discussion Effect of temperature on conversion of cellulose

The effect of reaction temperature on conversion of cellulose in the absence of catalysts was investigated and the results are summarized in Table 1. As shown in Table 1, the conversion of cellulose increases from 15% to 74% with increasing reaction temperature from 200 to 230qC. This may result from the H3O+ produced from hot compressed water and the by-products—organic acids[16]. It was reported that hot compressed water could produce the H3O+ when the temperature of aqueous solution was above 190qC[17]. In addition, it was found that the pH value of filtrated solutions decreased with increase in the reaction temperature, indicating that more organic acids were produced under higher reaction temperature. In order to investigate the change of morphology and crystallinity of cellulose treated or not at different

CAO Yue-ling et al. / Journal of Fuel Chemistry and Technology, 2013, 41(8): 943949

temperatures, SEM and X-ray diffraction (XRD) were carried out and the results are shown in Figures 1 and 2, respectively. It is found that the temperature has a vast influence on the particle sizes and uniformity of cellulose. The particle sizes of cellulose decline and become more uniformity with the increase of processing temperature. The particle size of cellulose is reduced to about 20, 10, 4 and 2 Pm after treated at 200, 210, 220 and 230qC, respectively. Correspondingly, the crystallinity of cellulose also dramatically changes at different processing temperatures. As shown in Figure 2, the crystallinity of untreated cellulose is very high (roughly 80%), but that of treated cellulose gradually decreases with increase in processing temperature. Finally, amorphous cellulose is formed when treated temperature is up to 230qC. 2.2 Effect of Ni loading on the catalytic activity of Ni/SBA-15 For the monometallic Ni/SBA-15 catalysts, the Ni loading has a great impact on the conversion of cellulose and the product yield. The results are shown in Table 2. From Table 2, it can be seen that both cellulose conversion and product yield increase with the increase of Ni loading. It is interesting to note that when the Ni loading is 3%, the conversion of cellulose is 86%, which is higher than that with higher Ni loading. This might be because that the presence of Ni promotes the hydrogenalysis rate of cellulose. At the same time, some by-products such as organic acids, produced from the cellulose due to the low Ni loading having poor hydrogenation ability, also facilitate the conversion of

Fig. 1

cellulose. For the 3%Ni/SBA-15 catalysts, the products of conversion of cellulose is acidic (solution pH value around 3.5) and the conversion of cellulose reaches up to 86%, which might be resulted from the autocatalysis of organic acids (by-products). Meanwhile, it is also showed the catalyst with 3%Ni loading is not enough to hydrogenate the unsaturated intermediate products from cellulose hydrolysis. However, when the Ni loading increases from 5% to 20%, the colorless and neutral solutions are obtained, indicating the catalyst with these Ni loading has sufficient hydrogenation ability for the intermediates and prohibits them from being converted to acidic species. Shrotri et al[18] had found the similar phenomena that the hydrogenation of intermediates or precursors of acids was predominated in the conversion of cellulose with the Ni loading, which could restrain the acid catalysis of by-products. Thus, the conversion of cellulose is exhibited a decrease first and then increased with increasing Ni loading. It is also found that the pH value of resultant solutions increases with increasing Ni loading, indicating the presence of self-catalysis. From the distribution of products, it is found that there are hexitol and polyols produced from the cleavage of C-C bond. It is in line with previous report that metal Ni not only has the hydrogenation ability, but also possesses the hydrogenolysis ability, especially under high temperature[19]. Its hydrogenolysis ability can promote the conversion of cellulose and the cleavage of C-C bond in the sugar intermediates. This can also explain why metal Ni is the main active component in the methane reforming catalyst[20].

SEM images of treated cellulose at different temperatures (a): untreated; (b): 200qC; (c): 210qC; (d): 220qC; (e): 230qC

CAO Yue-ling et al. / Journal of Fuel Chemistry and Technology, 2013, 41(8): 943949

Fig. 2

XRD patterns of treated cellulose at different temperatures

It is worth noting that with the increase of Ni loading, the yield of hexitol (sorbitol and mannitol) increases; however, the yields of 1,2-alkanediols including EG, 1,2-PG, 1,2-BG, and 1,2-HG almost remain unchanged. This is because that saturated alcohol is more stable than unsaturated acid and aldehyde. To be more exact, part of products produced from hydrolysis of cellulose, such as glucose, are quickly transformed into alcohols. This, to some extent, inhabits the cleavage of C-C bond. Further increase the Ni loading to 20%, hexitol yield increases greatly and the polyols yields decline. Considering the fact that the goal products are the polyols and the catalysts should have enough hydrogenation and hydrogenolysis ability, the 15% Ni loading is chosen for the further study. 2.3 Effect of tungsten trioxide loading on catalytic activity of Ni-WO3/SBA-15 Liu et al[21] reported that the selectivity of ethylene glycol was 51.5% at 205qC, 6 MPa H2 for 30 min using WO3 combined with Ru/C as the catalyst, but under the same reaction conditions, the selectivity of ethylene glycol was only 7.5% when the Ru/C was adopted alone. These results indicated that WO3 could promote the conversion of cellulose into ethylene glycol. Ji et al[12] also reported that tungsten Table 2 Ni loading w/%

a

compounds were efficient to convert cellulose into ethylene glycol. In order to further understand the interaction between the metal Ni and WO3, and its influence on the conversion of cellulose, phosphotungstic acids were adopted as the tungsten source and introduced into catalysts to improve the selectivity of ethylene glycol. The effect of WO3 loading on the conversion of cellulose was investigated and the results are summarized in Table 3. As shown in Table 3, the yield of ethylene glycol increases with the increase of WO3 loading. When the WO3 loading is 15% and 20%, the yield of ethylene glycol was 40.3% and 40.9%, respectively, which might due to the total loading of Ni and WO3 (35%) is so high that the catalyst active species aggravate and their dispersities decrease. These results are in line with the XRD patterns of catalysts that the WO3 crystallite peaks appeared when the WO3 loading was up to 20%. Many researchers believed that the process of converting cellulose into ethylene glycol involved the hydrolysis of cellulose to glucose, and then the glucose being converted into ethylene glycol. Compared with Ni/SBA-15 catalysts, the yield of hexitol decreased to below 3% after the introduction of WO3, which revealed that the C-C bonds of glucose or hexitols were ruptured quickly, and this process facilitated the further hydrolysis of cellulose to achieve the complete conversion of cellulose under the same reaction conditions. Among the products, the change of the yields of 1,2-propylene glycol and 1,2-butanediol was very low with the increase of WO3 loading. Together with the low yield of 1,2-butanediol, it can be proposed that the producing of ethylene glycol may involve the process that C-C bond of C6ĺ&4ĺ&2 successively fractured. The presence of C3 alcohols and trace methanol showed that there were some processes involving non-selective cleavage of C-C bond in this reaction and the corresponding intermediates from these processes were hydrogenated into low molecular alcohols. In view of the total yield of alcohols and the price of WO3, 15% was chosen for further study.

Effect of Ni loading on the catalytic activity of Ni/SBA-15a Yieldb w/%

Conversion x/%

EG

1,2-PG

1,2-BG

1,2-HG

glycerol

hexitol

3

86

5.2

2.0

0.15

trace

trace

trace

5

70

5.7

6.0

0.85

0.5

0.3

10.7

10

76

5.1

6.4

0.70

trace

0.5

11.5

15

80

6.0

7.1

0.95

trace

2.5

13.7

20

91

3.0

4.8

0.70

trace

3.7

24.1

reaction conditions: cellulose: 1.00 g; catalyst: 0.250 g; deionized water: 40.0 g; temperature: 230qC; initial H2 pressure: 6.0 MPa; time: 6.0 h;

b

EG: ethylene glycol; 1,2-PG: 1,2-propylene glycol; 1,2-BG: 1,2-butanediol; 1,2-HG: 1,2-hexanediol; hexitol: sorbitol and mannitol

CAO Yue-ling et al. / Journal of Fuel Chemistry and Technology, 2013, 41(8): 943949 Effect of WO3 loading on catalytic activity of Ni-WO3/SBA-15a

Table 3

a

Yieldb w/%

WO3 loading w/%

Conversion x/%

EG

1,2-PG

1,2-BG

1,2-HG

5

100

14.6

8.1

2.2

trace

6.8

10

100

29.2

7.9

1.9

trace

6.9

15

100

40.3

8.9

2.6

trace

8.8

20

100

40.9

6.6

2.1

trace

3.3

glycerol

reaction conditions: cellulose: 1.00 g; catalyst: 0.250 g; deionized water: 40.0 g; temperature: 230qC; initial H2 pressure: 6.0 MPa; time: 6.0 h;

b

EG: ethylene glycol; 1,2-PG: 1,2-propylene glycol; 1,2-BG: 1,2-butanediol; 1,2-HG: 1,2-hexanediol; hexitol: sorbitol and mannitol

Table 4

a

Effect of Ni loading on catalytic activity of Ni-WO3/SBA-15a Yieldb w/%

Ni loading w/%

Conversion x/%

EG

1,2-PG

1,2-BG

1

100

28.3

2.7

3.3

trace

3

100

70.7

5.9

4.2

0.5

0.3

1,2-HG

glycerol trace

5

100

51.1

5.4

2.6

trace

trace

10

100

53.6

8.5

3.5

trace

3.7

15

100

40.3

8.9

2.6

trace

8.8

20

100

30.3

6.3

1.4

trace

5.9

reaction conditions: cellulose: 1.00 g; catalyst: 0.250 g; deionized water: 40.0 g; temperature: 230qC; initial H2 pressure: 6.0 MPa; time: 6.0 h;

b

EG: ethylene glycol; 1,2-PG: 1,2-propylene glycol; 1,2-BG: 1,2-butanediol; 1,2-HG: 1,2-hexanediol; hexitol: sorbitol and mannitol

Table 5

Effect of calcination temperature on catalytic activity of catalystsa Yieldb w/%

Calcination temperature t/qC

a

Conversion x/% EG

1,2-PG

1,2-BG

1,2-HG

glycerol

400

100

57.3

4.9

3.0

1.5

trace

450

100

59.6

4.7

2.8

1.0

trace

500

100

70.7

5.9

4.2

trace

trace

550

100

62.5

4.8

2.8

0.8

trace

600

100

53.3

3.5

2.0

0.5

trace

reaction conditions: cellulose: 1.00 g; catalyst: 0.250 g; deionized water: 40.0 g; temperature: 230qC; initial H2 pressure: 6.0 MPa; time: 6.0 h;

b

EG: ethylene glycol; 1,2-PG: 1,2-propylene glycol; 1,2-BG: 1,2-butanediol; 1,2-HG: 1,2-hexanediol; hexitol: sorbitol and mannitol

2.4 Effect of Ni loading on catalytic activity of Ni-WO3/SBA-15 Based on our experimental results and previous report, the hydrolysis hydrogenation of cellulose was a complex process that involved many reactions[22]. Therefore, to achieve a high selectivity to the desired product, promoting the target reactions and inhibiting the side reactions were proved to be very important. High Ni loading was beneficial to boost hydrogenation, but more importantly, it may cover part of active sites of WO3. Finally, it could weaken the catalytic activity of tungsten oxide species. Thus, the effect of Ni loading on the conversion of cellulose was further investigated and related experiment results are summarized in Table 4. As shown in Table 4, the yield of ethylene glycol increases with the rise in Ni loading and reaches the highest (70.7%) when the Ni loading is 3%. However, further increasing in Ni

loading to exceed 5% leads to a slight decline in yield toward ethylene glycol. The selectivity of ethylene glycol of catalysts with 5% and 10%Ni loading are 51.12% and 53.64%, respectively. These results are in line with the report by Zheng et al that for the Ni-W/SBA-15 catalysts, the yield of ethylene glycol was 76.1% when the ratio of Ni to W was 1/3, but its yield decreased to 17.2% when the ratio of Ni to W was 1/1[3]. Compared with the yield of ethylene glycol over the Ni/SBA-15 catalysts, it can be suggested that this phenomenon related with the fact that the active sites of WO3 were covered by the excessive Ni. It is interesting to note that some organic acids are obtained over 3%Ni/SBA-15 catalyst because of its poor hydrogenation ability. But the introduction of WO3 greatly enhances the hydrogenation reactions of acids or aldehydes with the yield of ethylene glycol is up to 28% when Ni loading is only 1%. On the other hand, Tai et al[23] reported that WO3 did not possess hydrogenation ability.

CAO Yue-ling et al. / Journal of Fuel Chemistry and Technology, 2013, 41(8): 943949

Fig. 3

H2-TPR patterns of different catalysts (a): bulk Ni and 3%Ni/SBA-15; (b): bulk WO3 and 15%WO3/SBA-15;

(c): 3% Ni/SBA-15, 15% WO3/SBA-15, physical mixture of A and B, 3% Ni-15%WO3/SBA-15

Fig. 4

XRD patterns of different catalysts (all of them were unreduced)

(a): 3% Ni-15% WO3/SBA-15; (b): 5% Ni-15% WO3/SBA-15; (c): 15% Ni-15% WO3/SBA-15; (d): 20% Ni-15% WO3/SBA-15

Therefore, it could be concluded that there is an interaction between the metal Ni and WO3, which enhances the hydrogenation ability of metal Ni as well as the yields of alcohols. However, further increasing the Ni loading might partly cover the active sites of WO3 and lower the cleavage of C-C bond ability of catalysts. Thus, the yield of ethylene glycol decreases while the yield of hexitols increases. 2.5 Effect of calcination temperature on catalytic activity of catalysts Table 5 give the effect of calcination temperature on the catalysts activity. As shown in Table 5, the calcination temperature of catalysts has a great impact on their activity. When the calcination temperature is only 400qC, the yield of ethylene glycol is 57.3%. This might be because that the HPW does not completely decompose at lower calcination temperature. The yield of ethylene glycol increases with the increase in calcination temperature of catalysts at first, and reaches the highest (70.7%) at 230qC, and then decreases with the further increase in calcination temperature of catalysts. This is because that sintering of Ni particles occurs at higher

calcination temperature, which lead to lower active sites of catalysts. According to our previous results that the conversion of cellulose changed dramatically after the introduction of metal Ni and WO3, H2-TPR was conducted to investigate the reduction behavior of catalysts. TPR characterization results for the prepared catalysts are shown in Figure 3. As shown in Figure 3, compared with bulk NiO samples, the initial reduction temperature of Ni/SBA-15 increases from 280qC to 300qC, indicating that there is an interaction between the SBA-15 and NiO. This interaction restrains the reduction of nickel oxides and make metal Ni be firmly loaded on the SBA-15. Compared with bulk WO3 samples, the reduction temperature of WO3/SBA-15 also shifts toward to higher temperature. As for the weak peak at 500qC, it might ascribe to the highly dispersed surface WO3 species. From Figure 3c, it can be seen that the H2-TPR pattern of mechanical mixture of 3%Ni/SBA-15 and 15%WO3/SBA-15 is almost the same as their H2-TPR patterns due to there is no interaction between them. On the contrary, the initial reduction temperature of the 3%Ni-15%WO3/SBA-15 catalyst prepared by co-impregnation increases from 300qC to 350qC. Moreover, the reduction peaks of NiO and WO3 were overlaid together and its reduction peak area is significantly bigger than that of Ni/SBA-15 catalysts, indicating that part of WO3 is reduced at lower temperature (500qC). These results that the initial reduction temperature of WO3 declines while that of NiO increases demonstrate that there is a strong interaction between NiO and WO3, which not only promotes the ability of tungsten species for the cleavage of C-C bond, but also enhances the hydrogenation ability of metal Ni. The XRD patterns of different catalysts are shown in Figure 4. From Figure 4, it is found that there is no manifest NiO and WO3 crystallite peaks when the Ni loading was 3%, indicating that both of them are well dispersed. However, crystalline NiO peaks appear when the Ni loading is 5%, showing the congregation of NiO. On the contrary, for the XRD patterns of catalysts with different WO3 loading (Figures 4(c) and 4(d)), there is no manifest WO3 crystallite peaks when the WO3

CAO Yue-ling et al. / Journal of Fuel Chemistry and Technology, 2013, 41(8): 943949

loading is 15%, while the WO3 crystallite peaks appear when the WO3 loading is up to 20%. These results reveal that compared with the WO3, the NiO is easier to aggregate.

2010, 46(20): 3577–3579. [10] Liang G F, Wu C Y, He L M, Ming J, Cheng H Y, Zhuo L H, Zhao F Y. Selective conversion of concentrated microcrystalline cellulose to isosorbide over Ru/C catalyst. Green Chem, 2011,

3

Conclusion

13(4): 839–842. [11] Geboers J, Van De Vyver S, Carpentier K, Jacobs P, Sels B.

In conclusion, supported Ni-WO3/SBA-15 catalysts were efficient to transform cellulose into ethylene glycol. The best result was obtained on 3%Ni-15%WO3/SBA-15, which exhibited complete conversion of cellulose with up to 70.7% ethylene glycol yield. It was found that there was a strong interaction between nickel oxide and tungsten trioxide, which not only facilitated the hydrogenation ability of metal Ni, but also enhanced the ability of tungsten species for the cleavage of C-C bond. To achieve high yield of ethylene glycol, the synergistic effect between the hydrogenation of metal Ni and the cleavage of C-C bond of tungsten species was proved to be important.

Efficient hydrolytic hydrogenation of cellulose in the presence of Ru-loaded zeolites and trace amounts of mineral acid. Catal Commun, 2011, 47(19): 5590–5592. [12] Ji N, Zhang T, Zheng M Y, Wang A Q, Wang H, Wang X D, Cheng J G. Direct catalytic conversion of cellulose into ethylene glycol using nickel-promoted tungsten carbide catalysts. Angew Chem, 2008, 120(44): 8638–8641. [13] Zhang Y H, Wang A Q, Zhang T. A new 3D mesoporous carbon replicated from commercial silica as a catalyst support for direct conversion of cellulose into ethylene glycol. Chem Comm, 2010, 46(6): 862–864. [14] Wang X C, Meng L Q, Wu F, Jiang Y J, Wang L, Mu X D. Efficient conversion of microcrystalline cellulose to 1,2-

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