Effect of Pd Doping on the Cu0/Cu+ Ratio of Cu-Pd/SiO2 Catalysts for Ethylene Glycol Synthesis from Dimethyl Oxalate

The Cu-0/Cu+ ratio is very important in many copper-catalyzed reactions. A series of Cu-Pd/SiO2 catalysts were prepared by composite evaporation of ammonia with subsequent Pd impregnation. The Cu-0/Cu+ ratio could be controlled by changing the Pd content in the catalysts during reduction. The catalysts were applied to the hydrogenation of dimethyl oxalate, and experimental results showed that a suitable amount of Pd doping remarkably improved the activity and prolonged the lifetime of the catalyst. The optimized Cu-0.5% Pd/SiO2 catalyst showed complete conversion with 96.0% ethylene glycol selectivity over a lifetime of 300 h. Enhancements in the activity and stability of the Cu-Pd/SiO2 catalysts were ascribed to the stable generation of hydrogen spillover, which tended to adjust the Cu-0/Cu+ ratio with changes in Pd content in the reduced catalysts. Hydrogen spillover also promoted the release of intermediates in contact with Cu+ to inhibit copper sintering.