Insight into active sites of Pd–Au/TiO2 catalysts in hydrogen peroxide synthesis directly from H2 and O2

H2O2 synthesis directly from H2 and O2 and side reactions in this system over a variety of Pd–Au/TiO2 catalysts have been studied systemically. The effects of Pd/Au ratio on H2O2 synthesis and subsequent H2O2 hydrogenation were investigated. The catalysts were characterized using multiple techniques including transmission electron microscopy (TEM), in situ diffuse reflectance infrared Fourier transform spectroscopy of CO adsorption (CO-DRIFTS), X-rays photoelectron spectroscopy (XPS), and temperature-programmed desorption of H2/O2 (H2-/O2-TPD). By detailed analysis of these spectroscopies and the kinetics of this reaction, new insights into various active sites of Pd upon alloying with Au were elaborated. Pd monomer surrounded by Au atoms could be the primary active site for H2O2 formation. In addition, Pd ensembles were assumed to be more active for H2O2 hydrogenation than monomeric Pd sites; the over-oxidation of H2 to H2O likely occurred at the interface between Au and TiO2.