Pd and PdAu catalysts supported over 3-MPTES grafted HMS used in the HDS of thiophene

Abstract

Palladium and bimetallic palladium-gold catalysts were supported over mesoporous silica HMS grafted with variable amount of mercaptopropyl groups corresponding to different molar ratio of the SH group over the metal, molesSH/molesmetal=2, 4, 7, 9. The obtained catalysts, characterized by XRD and XPS techniques were tested in the hydrodesulphurization (HDS) reaction of thiophene. Generally speaking, all the bimetallic catalysts were more active as compared to the monometallic ones. The support modification affected the structure of the fresh (calcined) and reduced catalysts. Supporting the metals over the bare HMS, through deposition–precipitation with urea, produced a drastic decrease of the surface area at variance with the catalysts supported over the functionalized HMS which maintained fairly high surface areas. According to the XRD, the introduction of the SH groups contributed to the better dispersion of the PdO and metallic gold in the calcined samples. Upon hydrogen treatment the supported metals transformed into small particles of gold enriched alloy leading to high activity and lower catalyst deactivation. The promotion of the catalytic behaviour increased with the increase of the SH loading up to a molar ratio, molesSH/molesmetal=7. Above this value, the beneficial effect started diminishing. Based on the XPS and the XRD results, the catalytic behaviour was correlated with the structure and surface composition of the supported species, governed by the interaction between the metals and the mercaptogroups.