The alcoholysis of cellulose into methyl levulinate (ML) in methanol media was investigated in the presence of several kinds of acid catalyst. One of the synthesized solid niobium-based phosphate catalysts was found to be highly efficient for the generation of ML, reaching an ML yield as high as 56%, higher than the LA yield (52%) in aqueous solution with the same reaction conditions as those used in our previous study (Green Chem., 2014, 16, 3846-3853). More interestingly, in water, very strong Lewis acid promoted the formation of LA; but in methanol, Brönsted acid enhanced the formation of ML. In-depth investigation showed that the mechanism and type of intermediates of cellulose alcoholysis in methanol were different from those in water and a high Brönsted/Lewis acid ratio (known as B/L acid ratio) of solid catalysts is needed to prevent the generation of by-products, namely, methyl lactate and 1,1,2-trimethoxyethane. This new-proposed reaction mechanism affected by the B/L acid ratio was very helpful for the design of efficient catalysts. † Electronic supplementary information (ESI) available. See
The efficient usage of lignocellulosic biomass is of great significance for large-scale low-cost biomass conversion to biofuels and other useful chemicals. Here, an interesting catalytic process was reported related to converting cellulose into ethylene glycol (EG) and ethylene glycol monoether (EGME) in methanol over a Ru/NbOPO 4 catalyst, with the cleavage of a C−C bond by NbOPO 4 and further hydrogenation by supported Ru particles. The influence of reaction temperature, hydrogen pressure, and reaction time was systematically investigated and showed that a 54.5% total yield of EG and EGME could be obtained at 220°C in 3 M Pa H 2 , which was an exciting result. Meanwhile, the effect of solvent was also studied in detail. It was shown that methanol played an important role in the production of EG and EGME, especially in the cleavage of the C−C bond. Methanol could protect the C O bond in glucose produced from cellulose through acetalization, thus prevent its hydrogenation, and led to the production of EG and EGME. Furthermore, the influence of dopants (W, Sn, Ni, Cu) was further investigated, and it was found that only the Ru−Ni/NbOPO 4 catalyst was more effective through limiting the further hydrogenolysis of products (EG and EGME) to CO and alkanes, and as high as 64% total yield of EG+EGME was achieved. Moreover, the Ru−Ni/NbOPO 4 catalyst showed good reusability, which can be reused at least four times with a little loss in EG and EGME yield.
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