Structure and activity of Au-Pd/SiO2 bimetallic catalyst for thiophene hydrodesulfurization

Monometallic Au, Pd and bimetallic Au-Pd catalysts supported on SiO₂ were prepared by an impregnation method. Their activities on thiophene hydrodesulfurization (HDS) at atmospheric pressure are found to be as a function of calcination temperature of these catalysts. The bimetallic catalyst calcined in air at 400 °C gives the highest activity among them. The techniques including nitrogen physical adsorption, X-ray diffraction, transmission electron microscopy, and X-ray absorption near edge structure were employed to characterize the structure of these catalysts. The results indicate that the effect of gold particles in AuPd/SiO₂ catalyst can facilitate the reduction of PdO phase as well as inhibit the formation of less active Pd₄S phase. The promotional effect of partially oxidative gold and a little of Pd⁰ in AuPd/SiO₂ catalyst is suggested to enhance the HDS activity. The formation of Au_xPd_y alloy phase improves the resistance to sulfur-poisoning of the bimetallic catalyst. The presence of partially oxidized gold particles is considered to be due to the inter-atomic charge transfer from the Au 5d to the Pd 5d band.