Hydrodesulfurization over PdMo/HY zeolite catalysts

Abstract

A series of palladium-promoted Mo catalysts was prepared by two-step impregnation procedure using an ultrastable HY zeolite carrier. The mutual effect of Pd and Mo phases and zeolitic support was investigated in hydrodesulfurization (HDS) of dibenzothiophene (DBT) and diesel oil (1.1 wt% S). Pd/HY was more active than its binary PdMo/HY counterparts, suggesting an inhibitory effect of Mo on Pd. The incorporation of Pd probably prevented deactivation of PdMo catalysts in HDS of DBT. The initial sulfur conversion in HDS of gas oil over Pd/HY was similar to that on a commercial CoMo/Al 2O 3 catalyst; however, both Pd/HY catalyst and the blank HY zeolite deactivated very fast at short times on-stream. On the basis of catalyst characterization by X-ray photoelectron spectroscopy, Fourier transform i.r. spectroscopy of adsorbed CO and pyridine, and temperature-programmed reduction, it is concluded that formation of H x MoS 2 and S[PdH +] hydride-like species in PdMo zeolites are probably responsible for the inhibitory effect on HDS activity.