Highly dispersed Pd catalysts prepared by a sonochemical method for the direct synthesis of hydrogen peroxide

Abstract

Pd catalysts prepared by a sonochemical method that is known to be effective in metal dispersion are applied to direct H2O2 synthesis. To determine the effect of the preparation method on the catalytic performance, Pd catalysts were supported on TiO2 and SiO2 by a sonochemical method and general incipient wetness method (IWI), and supports were compared. The sonochemical preparation method achieved the highest Pd dispersion value of 16.6% in the TiO2 supported catalyst, which is attributed to a synergistic effect between the sonochemical method and TiO2 support. A near-homogeneous and small size nucleation is often reported in sonochemical methods, and oxygen vacancies in TiO2 are reported to be strong adsorption sites for Pd nucleation. However, SiO2 support has not been reported to have obvious oxygen vacancies, and sonochemically prepared Pd/SiO2 showed the lowest Pd dispersion in addition to a large Pd particle size. In the direct synthesis of H2O2, a remarkably high H2 conversion of 22% was achieved in sonochemical Pd/TiO2, which led to the highest H2O2 yield of 16% and H2O2 production rate of 729.0 mmol/gPd radical doth.