Promoter role of tungsten in W-Pd/Al2O3 catalyst for direct synthesis of H2O2: Modification of Pd/PdO ratio

Abstract

The addition of non-precious-metal is a promising approach to develop Pd-based catalysts for the direct synthesis of H2O2. Herein, we prepare W modified Pd/Al2O3 for enhanced synthesis towards H2O2. With fixed Pd loading, the H2O2 productivity show a volcano relationship with increasing W addition, and reach up to peak value for slice W content. It is found that W species in the form of WO3 existing on the surface of Pd particles. The small addition of W optimizes the ratio between surface PdO and Pd, which simultaneously augments the productivity of H2O2 and hinders hydrogenation/decomposition of H2O2. Nevertheless, excess W addition not only leads to overmuch metallic state of Pd species, but also impedes the O2 adsorption on Pd particles surface, resulting in a decrease in H2O2 synthesis. This work demonstrates the promoter mechanism of W and offers a promising strategy developing Pd-based catalysts for the direct synthesis of H2O2.