Mingyuan Zheng

Direct Catalytic Conversion of Cellulose into Ethylene Glycol Using Nickel-Promoted Tungsten Carbide Catalysts

Cellulose, the most abundant source of biomass, is currently regarded as a promising alternative for fossil fuels as it cannot be digested by human beings and thus its use, unlike corn and starch, will not impose a negative impact on food supplies. One of the most attractive routes for the reaction of cellulose utilization is its direct conversion into useful organic compounds. A recent example of the catalytic conversion of cellulose has been demonstrated by Fukuoka and Dhepe, who utilized Pt/Al2O3 as an effective catalyst to convert cellulose into sugar alcohols (Scheme 1, Route A). The product sugar alcohols can be used as chemicals in their own right or as new starting materials for the production of fuels, as demonstrated by Dumesic and co-workers. 6] Recently, Luo et al. have studied this process further. In their work, the reaction was conducted at elevated temperatures so that water could generate H ions to catalyze the hydrolysis reactions. The subsequent hydrogenation reaction was catalyzed by Ru/C. An increased sugar alcohol yield was obtained, which was attributed to the higher reaction temperatures and the wellknown high efficiency of Ru/C in the hydrogenation reaction. . A disadvantage of the above two studies is the use of precious-metal catalysts. The amount of precious metals needed for the degradation of cellulose was relatively high, 4– 10 mg per gram of cellulose. This is too expensive for the conversion of large quantities of cellulose, even though the solid catalyst could be reused. Therefore, it is highly desirable to develop a less expensive but efficient catalyst to replace precious-metal catalysts in this cellulose degradation process. The carbides of Groups 4–6 metals show catalytic performances similar to those of platinum-group metals in a variety of reactions involving hydrogen. In our previous work, tungsten and molybdenum carbides were found to exhibit excellent performances in the catalytic decomposition of hydrazine, which were comparable with those of expensive iridium catalysts. Tungsten carbides have been used as electrocatalysts because of their platinum-like catalytic behavior, stability in acidic solutions, and resistance to CO poisoning. 18] However, to the best of our knowledge, there have been no attempts so far to utilize metal carbides as catalysts for cellulose conversion. Herein we report the first observation that carbonsupported tungsten carbide (W2C/AC; AC = activated carbon) can effectively catalyze cellulose conversion into polyols (Scheme 1, Route B). More interestingly, when the catalyst is promoted with a small amount of nickel, the yield of polyols, especially ethylene glycol (EG) and sorbitol, can be significantly increased. These Ni-W2C/AC catalysts showed a remarkably higher selectivity for EG formation than Pt/Al2O3 [4] and Ru/C. After 30 minutes at 518 K and 6 MPa H2, the cellulose could be completely converted into polyols and the yield of EG was as high as 61 wt % with a 2% Ni-30% W2C/AC-973 catalyst. This value is the highest yield reported to date. Currently in the petrochemical industry, EG is mainly produced from ethylene via the intermediate ethylene oxide. The global production of EG in 2007 is estimated to be 17.8 million tonnes, an increase of Scheme 1. Catalytic conversion of cellulose into polyols.

One-pot catalytic hydrocracking of raw woody biomass into chemicals over supported carbide catalysts: simultaneous conversion of cellulose, hemicellulose and lignin.

Using raw lignocellulosic biomass as feedstock for sustainable production of chemicals is of great significance. Herein, we report the direct catalytic conversion of raw woody biomass into two groups of chemicals over a carbon supported Ni-W2C catalyst. The carbohydrate fraction in the woody biomass, i.e., cellulose and hemicellulose, were converted to ethylene glycol and other diols with a total yield of up to 75.6% (based on the amount of cellulose & hemicellulose), while the lignin component was converted selectively into monophenols with a yield of 46.5% (based on lignin). It was found that the chemical compositions and structures of different sources of lignocellulose exerted notable influence on the catalytic activity. The employment of small molecule alcohol as a solvent could increase the yields of phenols due to the high solubilities of lignin and hydrogen. Remarkably, synergistic effect in Ni-W2C/AC existed not only in the conversion of carbohydrate fractions, but also in lignin component degradation. For this reason, the cheap Ni-W2C/AC exhibited competitive activity in comparison with noble metal catalysts for the degradation of the wood lignin. Furthermore, the catalyst could be reused at least three times without the loss of activity. The direct conversion of the untreated lignocellulose drives our technology nearer to large-scale application for cost-efficient production of chemicals from biomass.

Temperature-controlled phase-transfer catalysis for ethylene glycol production from cellulose.

A temperature-controlled phase-transfer catalyst-tungsten acid, which in combination with a robust heterogeneous catalyst Ru/C shows a high activity and exceptional reusability for the one-pot conversion of cellulose to ethylene glycol. This binary system can be reused more than 20 times with ethylene glycol yield over 50%.

Catalytic conversion of cellulose to hexitols with mesoporous carbon supported Ni-based bimetallic catalysts

Robust and highly active Ni-based bimetallic catalysts supported on mesoporous carbon have been developed for catalytic conversion of cellulose to hexitols, over which the maximum hexitol yield reached 59.8%.

Catalytic Conversion of Cellulose to Ethylene Glycol over a Low‐Cost Binary Catalyst of Raney Ni and Tungstic Acid

Following our previous report on the selective transformation of cellulose to ethylene glycol (EG) over a binary catalyst composed of tungstic acid and Ru/C, we herein report a new low-cost but more effective binary catalyst by using Raney nickel in place of Ru/C (Raney Ni+H(2 WO(4) ). In addition to tungstic acid, other W compounds were also investigated in combination with Raney Ni. The results showed that the EG yield depended on the W compound: H(4)SiW(12)O(40) <H(3 PW(12)O(40) <WO(3) <H(2)WO(4) , but all the investigated W compounds were selective towards EG. Moreover, both WO(3) and H2 WO(4) were dissolved partially under the reaction conditions and transformed into Hx WO(3) , which is the genuinely active species for the C-C bond breakage of cellulose. This result further confirmed that the reaction that involves the selective breakage of the C-C bonds of cellulose with W species is homogenous. Among various binary catalysts, the combination of Raney Ni and H(2)WO(4) gave the highest yield of EG (65 %), which could be attributed to the high activity of Raney Ni for hydrogenation and its inertness for the further degradation of EG. Moreover, Raney Ni+H(2)WO(4) showed good reusability; it could be reused at least 17 times without any decay in the EG yield, which shows its great potential for industrial applications.

Synthesis of ethylene glycol and terephthalic acid from biomass for producing PET

There have been considerable efforts to produce renewable polymers from biomass. Poly(ethylene terephthalate) (PET) is one of the most versatile bulk materials used in our daily lives. Recent advances in the new catalytic process for conversion of biomass have allowed us to design more technically effective and cheaper methods for the synthesis of green PET monomers. This review analyses recent advances in the synthesis of PET monomers from biomass. Different routes for ethylene glycol (EG) and purified terephthalic acid (PTA) synthesis are systematically summarized. The advantages and drawbacks of each route are discussed in terms of feedstock, reaction pathway, catalyst, economic evaluation and technology status, trying to provide some state-of-the-art information on green PET monomer synthesis. Finally, an outlook is presented to highlight the challenges, opportunities and on-going trends, which may serve as guidelines for designing novel synthetic routes to green polymers from fundamental science to practical use.

Production of 5-hydroxymethylfurfural in ionic liquids under high fructose concentration conditions.

Acid-promoted, selective production of 5-hydroxymethylfurfural (HMF) under high fructose concentration conditions was achieved in ionic liquids (ILs) at 80 degrees C. A HMF yield up to 97% was obtained in 8min using 1-butyl-3-methylimidazolium chloride ([C(4)mim]Cl) catalyzed with 9mol% hydrochloric acid. More significantly, an HMF yield of 51% was observed when fructose was loaded at a high concentration of 67wt% in [C(4)mim]Cl. Water content below 15.4% in the system had little effect on HMF yield, whereas a higher water content was detrimental to both reaction rate and HMF yield. In situ NMR analysis suggested that the transformation of fructose to HMF was a highly selective reaction that proceeded through the cyclic fructofuranosyl intermediate pathway. This work increased our capacity to produce HMF, and should be valuable to facilitate cost-efficient conversion of biomass into biofuels and bio-based products.

One-pot catalytic conversion of cellulose to ethylene glycol and other chemicals: From fundamental discovery to potential commercialization

Abstract The one-pot catalytic conversion of cellulose to ethylene glycol (CEG) is a highly attractive way for biomass utilization to lessen the consumption of fossil energy resources. In this paper, we reviewed the disclosure of the CEG process and the rapid progress in the development of highly efficient and robust catalysts for it. Based on our study of tungstenic catalysts, we discuss the reaction mechanism, in which the reaction routes, catalyst states, and catalytic roles of the tungsten species and hydrogenation sites in the cascade reactions are understood clearly. With future applications in mind, the conversion of raw cellulosic biomass and the strategy to develop an efficient CEG process for commercialization are discussed, and a model where the CEG process is incorporated into a bio-refinery process of acetone- n -butanol-ethanol (ABE) production is presented.

Selective Production of 1,2‐Propylene Glycol from Jerusalem Artichoke Tuber using Ni–W2C/AC Catalysts

A series of Ni-promoted W(2) C/activated carbon (AC) catalysts were investigated for the catalytic conversion of Jerusalem artichoke tuber (JAT) under hydrothermal conditions and hydrogen pressure. Even a small amount of Ni could greatly promote the conversion of JAT to 1,2-propylene glycol (1,2-PG), whereas the pure W(2) C/AC catalyst resulted in the selective formation of acetol. The product distribution profiles involving the reaction temperature, time, and H(2) pressure indicated that 1,2-PG formed as a result of acetol hydrogenation, which was catalyzed by Ni. Thus, there was a synergy between W(2) C and Ni, and the best performance yielded 38.5% of 1,2-PG over a 4%Ni-20%W(2) C/AC catalyst at 245°C, 6 MPa H(2) , and 80 min. To understand the reaction process, some important intermediates, such as inulin, fructose, acetol, glyceraldehyde, and 1,3-dihydroxyacetone, were used as the feedstock. Based on the product distributions derived from these intermediates, a reaction pathway was proposed, where JAT was first hydrolyzed into a mixture of fructose and glucose under the catalysis of H(+) , then the sugars underwent a retro-aldol reaction followed by hydrogenation catalyzed by Ni-W(2) C.

Nickel‐Promoted Tungsten Carbide Catalysts for Cellulose Conversion: Effect of Preparation Methods

A series of Ni-promoted W(2) C catalysts was prepared by means of a post-impregnation method and evaluated for the catalytic conversion of cellulose into ethylene glycol (EG). Quite different from our previously reported Ni-W(2) C/AC catalysts, which were prepared by using the co-impregnation method, the introduction of Ni by the post-impregnation method did not cause catalyst sintering, but resulted in redispersion of the W component, which was identified and characterized by means of XRD, TEM, and CO chemisorption. The highly dispersed Ni-promoted W(2) C catalyst was very active and selective in cellulose conversion into EG, with a 100% conversion of cellulose and a 73.0% yield in EG. The underlying reason for the enhanced catalytic performance was most probably the significantly higher dispersion of active sites on the catalyst.