Insights into the reaction pathways of glycerol hydrogenolysis over Cu–Cr catalysts

Abstract

In order to well understand reaction pathways of glycerol hydrogenolysis over Cu–Cr catalysts, hydrogenolysis of glycerol was investigated as a function of the molar ratios of Cu to Cr, reaction time, reaction temperature, hydrogen pressure, and glycerol concentration. The intermediates in glycerol hydrogenolysis were identified under Ar atmosphere or relatively mild condition. Hydrogenolysis of propanediols was also investigated for understanding the formation of propanols as by-products. The structure of Cu–Cr catalysts, prepared by an epoxide-assisted route, was determined by X-ray diffraction and scanning transmission electron microscopy. The high conversion of 85.9% and high selectivity toward 1,2-propylene glycol of 98.5% was achieved over the CuCr(4) catalyst in the hydrogenolysis of glycerol. As expected, extending reaction time, or elevating temperature and hydrogen pressure favored the conversion of glycerol. Interestingly, the conversion of glycerol and the selectivity to 1,2-propanediol increased with increasing the glycerol concentration at the same ratio of catalyst to glycerol. It was found that the hydrogenolysis of glycerol not only involved glycerol directly dehydrated and hydrogenated to 1,2-propanediol (DH route), but also involved glycerol dehydrogenation to glyceraldehyde, which was subsequently dehydrated and hydrogenated to 1,2-propanediol (DDH route), while 1,2-propanediol was further converted to propanol through H+ transfer from alcohol compounds.