Chinese Journal of Catalysis ›› 2014, Vol. 35 ›› Issue (5): 631-643.DOI: 10.1016/S1872-2067(14)60094-2

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Selective hydrogenolysis of glycerol to propylene glycol on hydroxycarbonate-derived Cu-ZnO-Al2O3 catalysts

Shuai Wang, Haichao Liu   

  1. Beijing National Laboratory for Molecular Sciences, State Key Laboratory for Structural Chemistry of Unstable and Stable Species, College of Chemistry and Molecular Engineering, Peking University, Beijing 100871, China
  • Received:2014-03-20 Revised:2014-03-27 Online:2014-04-18 Published:2014-04-24
  • Supported by:

    This work was supported by the National Basic Research Program of China (973 Program, 2011CB201400, 2011CB808700) and the National Natural Science Foundation of China (21173008, 21373019, 51121091).

Abstract:

Three Cu-ZnO-Al2O3 catalysts with similar compositions were prepared by homogeneous coprecipitation (CZA-HP), deposition-precipitation (CZA-DP), and conventional coprecipitation (CZA-CP). A Cu-ZnO catalyst was also prepared by homogeneous coprecipitation (CZ-HP) for reference. X-ray diffraction results showed that the degree of mixing of Cu2+, Zn2+, and Al3+ ions in the Cu-Zn-Al hydroxycarbonate precursor followed the order of CZA-DP < CZA-HP < CZA-CP. A more homogeneous aluminum distribution and intimate contact between Al2O3 and ZnO led to smaller CuO and ZnO crystallites in the CuO-ZnO-Al2O3 composite oxides, and consequently smaller Cu and ZnO crystallites in the final Cu-ZnO-Al2O3 catalysts. However, the intimate ZnO-Al2O3 contact hindered the interaction between Cu and ZnO in the Cu-ZnO-Al2O3 catalysts. As a result of these effects of Al2O3, for the samples other than CZA-CP, the Cu particles on CZA-HP showed the highest redox activity, which was characterized by N2O chemisorption-H2 temperature-programmed reduction. These catalysts catalyzed glycerol hydrogenolysis to propylene glycol with high selectivities above 90% at 30% glycerol conversion (473 K and 6.0 MPa H2). Their activities normalized per exposed surface Cu atom to give turnover frequencies increased in the order CZA-DP < CZA-CP < CZ-HP < CZA-HP, which was the order of the redox ability of the Cu particles. The addition of alumina increased the stability of Cu-ZnO catalysts. After six cycles (6 h per run), the activity of CZ-HP decreased by 45% accompanied by an increase of Cu crystallite size from 13.2 to 45.2 nm, while that of CZA-HP decreased only by 10% with an increase of the Cu crystallite size from 8.3 to 19.0 nm. These results demonstrated the promoting effects of Al2O3 on the activity and stability of Cu-ZnO catalysts derived from the hydroxycarbonates.

Key words: Glycerol, Selective hydrogenolysis, Propylene glycol, Copper, Zinc oxide, Alumina, Hydroxycarbonate precursor, Structure-activity relationship, Stability