Pd–Pt/Al2O3 bimetallic catalysts for the advanced oxidation of reactive dye solutions

The Pd–Pt/Al2O3 bimetallic catalysts showed high activities toward the wet oxidation of the reactive dyes in the presence of 1% H2 together with excess oxygen. Palladium was believed to act as a co-catalyst 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 adsorbed on the reduced Pt surface more easily than the oxidized 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 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.