Significant Roles of Carbon Pore and Surface Structure in AuPd/C Catalyst for Achieving High Chemoselectivity in Direct Hydrogen Peroxide Synthesis

Abstract

Direct synthesis of hydrogen peroxide (H2O2) from hydrogen (H-2) and oxygen (O-2) has been widely investigated as an attractive way for small-scale/on-site H2O2 production. Among various catalysts, carbon -supported AuPd catalysts have been reported to exhibit the most promising H2O2 productivity and selectivity. In this work, to better understand the catalytic role of the surface properties and porous structures of the carbon supports, we systematically investigated AuPd catalysts supported on various nano structured carbons including activated carbon, carbon nano tube, carbon black, and ordered mesoporous carbons. The results showed that a high density of oxygen functional groups on the carbon surface was essential for synthesizing highly dispersed bimetallic catalysts with effective AuPd alloying, which is a prerequisite for achieving high H2O2 selectivity. Regarding porous structure, a solely mesoporous carbon support was superior to microporous ones. Microporous carbons such as activated carbon suffered from diffusion limitation, leading to significantly slower H-2 conversion than mesoporous catalysts. Furthermore, H2O2 produced from AuPd catalyst in the micropores was more prone to subsequent disproportionation/hydrogenation into H2O due to retarded diffusion of the H2O2 out of the microporous structure, which led to decreased H2O, selectivity. The present study showed that solely mesoporous carbons with high surface oxygen content are most desirable as a support for AuPd catalyst in order to achieve high H2O2 productivity and selectivity.