Selective hydrogenolysis of glycerol to 1,3-propanediol over egg-shell type Ir-ReOx catalysts

The selective liquid-phase hydrogenolysis of glycerol to 1,3-propanediol over egg-shell catalysts in which the loadings of Ir and Re were both 2 wt% is reported. The shell thickness could be tuned by impregnating a hydrophobic silanized support with an aqueous solution of precursors containing various concentrations of ethanol and using entrapped air to prevent the impregnation solution from entering into the support pellets. The conversion of glycerol for the target reaction over egg-shell catalysts was higher than that over a uniform catalyst and was accompanied by a high selectivity for 1,3-propanediol over 1,2-propanediol. Reacting over the catalyst for which the impregnation solution ethanol concentration was 20 vol% resulted in the highest glycerol conversion (60.9%) and the highest yield of secondary hydroxyl group removal (30.2%). The properties of the egg-shell and uniform catalysts were characterized by XRD, TEM, XPS, H-2-TPR, H-2-pulse chemisorption and NH3-TPD. An appropriate diffusion distance of the reactants for egg-shell catalysts might result in better catalytic performance because of the high viscosity of the glycerol aqueous solution.