Promoter effect of Pd in CuCr2O4 catalysts on the hydrogenolysis of glycerol to 1,2-propanediol

CuCr2O4 catalysts containing various amounts of Pd (Pd-CuCr) were prepared by a co-precipitation method and examined for use in the conversion of glycerol to 1,2-propanediol (1,2-PDO). Pd was observed to be highly dispersed in a CuCr2O4 spinel structure and conferred unique reduction characteristics of a CuCr2O4 catalyst. After reduction, the amounts of surface exposed Cu-0 species and occluded hydrogen species were much larger in the case of added Pd, the Pd-CuCr catalyst, compared to a pure copper chromite catalyst. The Pd-CuCr catalyst utilized hydrogen very efficiently, resulting in an enhancement in the catalytic activity for the conversion of glycerol to 1,2-PDO, even at a relatively low hydrogen pressure. The Pd-0.5-CuCr catalyst (containing 0.5 wt% of Pd) showed a total yield of 93.9%, with a selectivity approaching 100% for 1,2-PDO at a hydrogen pressure of 4 MPa. In a kinetic study, the effects of H-2 pressure and the concentration of glycerol on the initial rate were examined. Based on the results, the palladium promoter (Pd-CuCr) enhanced the rate constant by about 1.7 times compared with copper chromite. The results provide a basis for the production of 1,2-PDO from glycerol using a process which is both environmentally benign and has improved economics.