Selective liquid-phase oxidation of glycerol over Au–Pd/C bimetallic catalysts prepared by electroless deposition

Abstract

Liquid phase oxidation of glycerol under basic conditions was examined for a series of Au–Pd/C bimetallic catalysts prepared by electroless deposition. Enhanced activity was observed for bimetallic compositions with θAu>0.30, with a maximum in activity at θAu=0.50 having a turnover frequency ∼20 times larger than for Pd and ∼4 times larger than for gold. A volcano shaped curve suggests the formation of bimetallic sites composed of Au–Pd in close contact, with the maximum at θAu=0.50 indicating the largest concentration of bimetallic sites at that coverage. Further increase in the coverage of Au on Pd lead to a catalytic surface approaching that of monometallic Au with lower TOF values. Selectivity to glyceric acid was 80% (±2%) for Pd and Au–Pd bimetallic catalysts below θAu<0.90. Selectivity to glycerate remained constant as long as there are sufficient Pd sites to rapidly decompose the non-selective H2O2 oxidant that is presumably produced on the Au sites. At the highest Au coverages, selectivity dropped to <60% due to further oxidation of glycerate to C1 and C2 oxygenated products.