Currently, the human race faces two important issues: energy and the environment. Obtaining energy and chemicals in a sustainable and environmentally friendly manner has been the target of many chemists. Among many potential approaches, biomass conversion has been considered as one of the most important ones because of its renewable and carbon-neutral properties. Cellulose is the most abundant source of biomass and generally accounts for 30-60 wt % of dried plants. Much effort has been devoted to the development of a green and effective process for cellulose conversion, such as fermentation with enzymes to produce ethanol, [1] thermo-pyrolysis to biooils [2] and syn-gas, [3] and hydrolysis with dilute acids in ionic liquids to yield oligomers, [4] glucose, [5] and HMF.[6]An alternative green process for cellulose conversion is to use solid catalysts to convert cellulose into polyols in an aqueous solution. Yan et al. [7] found that cellubiose, the simplest model molecule for cellulose, can be converted into sorbitol by using a Ru nanocatalyst in an aqueous solution. Fukuoka and Dhepe, [8] and Luo et al., [9] disclosed that cellulose can be converted into hexitols under hydrothermal and hydrogen conditions over noble-metal catalysts. These studies opened up a green route for the conversion of cellulose. On the other hand, the yields of polyols in these processes were not very high; generally less than 40 %. Furthermore, expensive noblemetal catalysts were used. Therefore, the development of lessexpensive but efficient catalysts for cellulose conversion is highly desirable.Recently, we successfully achieved the direct conversion of cellulose into ethylene glycol (EG) by a heterogeneous catalytic reaction under hydrogen atmosphere and hydrothermal conditions.[10] Over an active-carbon-supported tungsten carbide catalyst (W 2 C/AC), cellulose was completely depolymerized and EG was produced with a yield of 27 %. More importantly, upon the addition of a small amount of Ni to the W 2 C catalyst, the EG yield was significantly increased to as high as 61 %. EG is an important bulk chemical and sourced dominantly from petroleum resources.[11] Thus, this work provided a novel route for EG production as well as for cellulose conversion.However, there are some very intriguing questions about this novel process yet to be answered. For example, besides the W 2 C catalysts, are there any other catalysts effective for the conversion of cellulose into EG? With the Ni-modified W 2 C catalysts, a remarkable synergistic effect was observed. Which effect caused this synergy in the conversion process? Herein, based on the element W, we develop a series of bimetallic catalysts for the cellulose conversion, including Ni-W, Pd-W, Pt-W, Ru-W, and Ir-W, supported on different carriers. A remarkable synergy is observed between tungsten and metals of groups 8, 9, and 10 [M(8,9,10)]. Moreover, it is found that the product selectivity can be tuned effectively by changing the weight ratio of W to M(8,9,10). The maximum yield of EG, 75.4 %, was ...
