| With the depletion of fossil fuel reserves and the increase of energy demands, combined with the political and environmental concerns, it is imperative to develop efficient processes for the conversion of renewable biomass resources into non-petroleum-derived fuels and chemicals to avoid intensification of global warming and diversify energy sources.1,2-propanediol and ethylene glycol are important renewable chemicals due to their extensive applications. One of promising routes for their production is the catalytic conversion of biomass.High efficient Cu-Cr catalysts were prepared by an epoxide assisted sol-gel route. The surface areas of Cu-Cr xerogels were highly dependent on synthetic conditions like gelation temperature, amount of water in the solvent, and gel aging time. The xerogel surface area could reach up to230m2/g by adjusting the operating parameters. After heat treatment in20%O2/Ar, Cu-Cr catalyst with CuCr2O4and Cr2O3phases was obtained, while Cu and Cr2O3phases formed by calcinating in Ar. Due to the formation of CuCr2O4, the former had higher catalytic performance for the hydrogenolysis of glycerol. Besides, the Cu-Cr catalysts with the structure of CuCr2O4/CuO, CuCr2O4and CuCrO4/Cr2O3could be obtained by adjusting the Cu/Cr molar ratios. These catalysts with various structures exhibited excellent activity in the hydrogenolysis of solvent-free glycerol.Structural characterization of the Cu-Cr catalysts was performed by means of in situ XPS, N2O titration and so on. On the basis of the characterizations, the copper species in the calcined Cu-Cr catalysts and the reduced Cu-Cr catalysts were assigned. Reaction results indicated that a two-site (Cu0and Cu+) mechanism existed in the hydrogenolysis of glycerol over Cu-Cr catalysts. In addition, the synergetic effect between the Cu0and Cu+was considered to be responsible for the high catalytic activity. Under optimalizing reaction conditions, the high conversion of85.9%and high selectivity towards1,2-propanediol of98.5%were achieved. The formation of1,2-propanediol in the hydrogenolysis of glycerol under Ar atmosphere, indicating that the hydrogenolysis of glycerol not only involved glycerol directly dehydrated and hydrogenated to1,2-propanediol (DH route), but also involved glycerol dehydrogenation to glyceraldehyde, which was subsequently dehydrated and hydrogenated to1,2-propanediol (DDH route), while1,2-propanediol was further converted to propanol through H+transfer from alcohol compounds.For the hydrogenolysis of highly concentrated cellulose, the Cu-Cr catalyst exhibited excellence in anti-coking and a good catalytic performance. This provides a possibility for scale-up in industrial application. Adding base as co-catalyst, the yield of ethylene glycol significantly increased. Based on these results, the role of base was further investigated in the hydrogeno lysis of saccharide model molecule glucose. It was found that the performance of hydrogeno lysis was enhanced with increasing the concentration of OH-. Meanwhile, the appropriate ionic radius and electric charge were necessary for the formation of a relatively stable ring transitional state with glucose.In consideration of the toxicity of chromium and the magnetism of iron, similarly, the Cu-Fe catalyst was prepared by sol-gel route. Its structural properties were characterized by XRD, Mossbauer spectroscopy et al. These results indicated that a crystalline phase transformation from CuO-Fe2O3to CuFe2O4, and c-CuFe2O4to t-CuFe2O4occurred in elevating calcination temperature. The Cu-Fe catalyst exhibited higher catalytic activity for the hydrogeno lysis of glycerol compared to the Cu-Cr catalyst. |
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