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 AuxPdy 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.