Core-shell structured, nano-Pd-embedded SiO2-Al2O3 catalyst (Pd@SiO2-Al2O3) for direct hydrogen peroxide synthesis from hydrogen and oxygen

Abstract

In our previous studies, we proved that core/shell-structured Pd/SiO2 catalysts are more active for direct hydrogen peroxide synthesis than the conventional, impregnated Pd/SiO2 catalysts. In this study, the topic of our previous studies was extended to core/shell Pd/SiO2-Al2O3 catalysts, through which we examined the influence of acidic shell oxides (SiO2-Al2O3) on the hydrogen peroxide formation activity. The catalysts were prepared based on the Stober method, and the reaction tests were performed by adding H3PO4 (0-0.03 M) and in the presence of KBr (0.9 mM). It was proved that the surface Bronsted acid sites promote hydrogen peroxide formation activity in a manner similar to protons dissolved in a reaction medium (ethanol-water). It was supposed that the influences of heterogeneous and homogeneous acids on catalytic activity are related to how much those acids promote the adsorption of Br- ions on the Pd surface. The highest H2O2 production rate was approximately 470 mmol H2O2/g(pd) h, which was obtained using core/shell Pd/SiO2-Al2O3 catalysts under specific H3PO4 concentrations. This rate was higher than the highest value (similar to 420 mmol H2O2/g(pd) h) achieved using core/shell Pd/SiO2 catalysts. (C) 2015 Elsevier B.V. All rights reserved.