Promotional effects of Sb on Pd-based catalysts for the direct synthesis of hydrogen peroxide at ambient pressure

TiO2-supported Pd-Sb bimetallic catalysts were prepared and evaluated for the direct synthesis of H2O2 at ambient pressure. The addition of Sb to Pd significantly enhanced catalytic performance, and a PdsoSb catalyst showed the greatest selectivity of up to 73%. Sb promoted the dispersion of Pd on TiO2, as evidenced by transmission electron microscopy and X-ray diffraction. X-ray photoelectron spectroscopy indicated that the oxidation of Pd was suppressed by Sb. In addition, Sb2O3 layers were formed and partially wrapped the surfaces of Pd catalysts, thus suppressing the activation of H-2 and subsequent hydrogenation of H2O2. In situ diffuse reflection infrared Fourier transform spectroscopy for CO adsorption suggested that Sb homogenously located on the surface of Pd-Sb catalysts and isolated contiguous Pd sites, resulting in the rise of the ratio of Pd monomer sites that are favorable for H2O2 formation. As a result, the Sb modified Pd surfaces significantly enhanced the non-dissociative activation of O-2 and H2O2 selectivity. (C) 2018, Dalian Institute of Chemical Physics, Chinese Academy of Sciences. Published by Elsevier B.V. All rights reserved.