| The dwindling in finite energy sources and the accumulating of greenhouse gases drive the development of suitable replacements for substitute fossil by renewable energy sources. Transformation of biomass into commodity chemicals, which could relieve the bottle-neck of resource depletion and avoid greenhouse gas emissions by the utilization of fossil fuel, was proposed as a high potential in substituting fossil fuels. Cellulose, which is considered the most abundant and cheapest carbon source of biomass, could transform into many chemicals through hydrolyzation and subsequent hydrogenolysis. Wherein, various short-chain polyols originated from the hydrogenolysis of cellulose, such as ethylene glycol (EG) and 1,2-propanediol (1,2-PD), are widely used as starting monomers for the production of polyesters, polyethers and polyurethanes. Owing to the high atomic economy, value-added products and large market demand, catalytic hydrogenolysis of cellulose into short-chain polyols represents a particularly attractive process.The CuMgAl HT-like precursors with different molar ratio were prepared by co-precipitation. As a precursor, hydrotalcites compounds can be transformed into Cu-containing catalysts after calcination which was used for converting highly concentrated cellulose. The effect of metal molar ratio on crystalline phase and physicochemical property for the as-synthesized Cu-containing hydrotalcites as well as calcined or reduction catalysts was studied by a series of Characterization. Dissociative N2O adsorption and CO2-TPD were performed respectively in order to identify the surface Cu areas and basic properties in the reduced samples. It was found that the amount of the alkalinity sites decreased dramatically with the declining amount of Mg. Besides, the amount of Cu not only changed the alkalinity, but also had a remarkable effect on the surface Cu area. For the reaction of cellulose hydrogenolysis, the increase of alkalinity was beneficial to the conversion of cellulose and cleavage of C-C bond. On the other hand, the yield of EG and 1,2-PD raised with the content of Cu increasing. Therefore, the conversion of cellulose and the yield of polyols products could optimized through refined controlling the alkalinity and the surface Cu area.In addition, The Cu-containing catalysts with different crystalline phase were synthesized via thermal decomposition of the CuMgAl hydrotalcite under a series of calcination temperature. We systematically investigated the construction characterization of Cu-containing catalysts caused by different calcination temperature and the effect of structure transformation on the basicity or activities of catalyst were evaluated in detail. It was noted that the form of O2- in the mixed metal oxide was a critical factor in basicity of the catalysts during the transformation of structure. The surface Cu areas of the catalysts were identified by N2O titration. It could be seen that different Cu species had a significant effect on the surface Cu areas. In view of the cellulose hydrogenolysis, the alkalinity of the catalyst showed notable promotion effects not only on the hydrolyzation of cellulose but also on subsequent retro-aldol condensation, which was beneficial to acquisition of short-chain polyols. Besides, it was noteworthy that the surface Cu was main active for the hydrogenolysis reaction, which promoted the further hydrogenolysis and hydrogenation of the hydrolyzing substances. Also, the amount of surface Cu areas was an important role for the product distribution. It could be concluded that the surface Cu active sites along with the base sites of catalyst should exhibit a synergistic function on the hydrogenolysis of cellulose.Furthermore, for the purpose of gaining more insight into the catalytic performance, the effects of reaction conditions including reaction temperature, H2 pressure and the cellulose concentration were investigated. It was interesting to notice that no obvious decrease in the conversion with the scarce coke-like precipitates was observed even the concentration of cellulose reached up to 18%. It revealed that the catalyst possessed adequate activity to convert the highly concentrated cellulose. |
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