Effect of Ag loading on Cu/Al2O3 catalyst in the production of 1,2-propanediol from glycerol

•Vapor-phase hydrogenolysis of glycerol into 1,2-propanediol was examined over silver-modified Cu/Al2O3 catalysts.•Ag was found to be efficient in inhibiting the decomposition of glycerol into ethylene glycol.•The highest 1,2-propanediol yield of 98.3% was obtained at a gradient temperature from 170 to 105 °C.

The vapor-phase hydrogenolysis of glycerol was performed at a gradient temperature and ambient hydrogen pressure over a commercial Cu/Al2O3 catalyst modified with silver. Addition of Ag into Cu/Al2O3 catalysts was found to be efficient in inhibiting the decomposition of glycerol to produce ethylene glycol and gave a yield of 1,2-propanediol higher than that of the original Cu/Al2O3 without Ag. To minimize the ethylene glycol formation, the suitable loading of Ag was 1 wt.%. Since the Ag loading decreases the hydrogenation ability of the Cu/Al2O3 catalyst, 1 wt.% Ag-loaded Cu/Al2O3 catalyst was placed on the upper layer of the fixed catalyst bed and the Cu/Al2O3 catalyst was placed on the bottom layer for achieving much higher 1,2-propanediol yield. The effect of temperatures of the top, the interlayer, and the bottom of the catalyst bed on the yield was also examined: a high 1,2-propanediol yield of 98.3%, which is the highest value under ambient H2 pressure conditions, was achieved at a gradient temperature from 170 to 105 °C and a glycerol concentration of 15 wt.%.

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