Catalytic wet oxidation of reactive dyes with H2/O2 mixture on Pd–Pt/Al2O3 catalysts

Abstract

The Pd–Pt/Al2O3 bimetallic catalysts showed extremely high activities toward the wet oxidation of the reactive dyes in the presence of 1% H2 together with excess oxygen. Palladium acted as a promoter to spillover the adsorbed H2 onto the surface of the oxidized Pt surface, and thereby the reducibility of the Pt increased greatly. The organic dye molecule had higher chance to adsorb on the reduced Pt surface under the competition with excess oxygen, which is an essential step for the catalytic wet oxidation (CWO). The Pd–Pt/Al2O3 catalysts also produced H2O2 from H2/O2 mixture, and the hydroxyl radical was formed through the subsequent decomposition of H2O2. Additional oxidation of the reactive dyes was obtained with hydroxyl radical. The extremely high activities of the Pd–Pt/Al2O3 catalysts were believed to be due to the combined effects of the faster redox cycle resulting from the increased reducibility of Pt surface and the additional oxidation of the reactive dyes with hydroxyl radical.