Effect of the Addition of Au in Zirconia and Ceria Supported Pd Catalysts for the Direct Synthesis of Hydrogen Peroxide

Mono- and bimetallic palladium–gold catalysts supported on zirconia and ceria, both sulfated and nonsulfated, are tested for the direct synthesis of hydrogen peroxide under very mild (1 bar and 20◦C) and non-explosive conditions. Catalysts are characterized by N2 physisorption, sulfur content analysis, temperature programmed reduction (TPR), Fourier transmission infrared (FTIR) spectroscopy and high resolution transmission electron microscopy (HRTEM). Catalytic tests are carried out with different gas mixtures and after various pretreatments. Best catalytic results are observed using sulfate doped zirconia samples and H2/O2 mixtures containing a large excess of oxygen. Monometallic gold catalysts are completely inactive, while the addition of gold to palladium improves both the productivity and the selectivity of the process. Surface oxidized Pd and Pd–Au catalysts pretreated with hydrogen and oxygen show higher activity and selectivity with respect to non-pretreated samples. A mechanistic explanation is proposed