Promoter effect of Pd in CuCr2O4catalysts on the hydrogenolysis of glycerol to 1,2-propanediol

Abstract

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 Cu⁰ 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 H₂ 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.