Development of the HYD route of hydrodesulfurization of dibenzothiophenes over Pd-Pt/γ-Al_2O_3 catalysts

摘要

The hydrodesulfurization (HDS) of dibenzothiophene (DBT) on a series of Pd-Pt/γ-Al_2O_3 catalysts was studied as a function of the Pd/(Pd + Pt) molar ratio at different reaction conditions. It was determined that the catalytic performance in HDS is controlled by the Pd/(Pd + Pt) molar ratio. In particular, a synergetic effect exists rather in the development of the hydrogenation (HYD) route of HDS of dibenzothiophene than in the activity, but both can be controlled from the Pd/(Pd + Pt) molar ratio. An analysis of the relationship between the mechanism of HYD, analyzed here from a different perspective as that currently presented in the literature, and the surface properties of the bimetallic Pd-Pt alloyed particles indicated that: (i) the development of HYD is in correspondence with the capacity of Pd-Pt to hydrogenate aromatics under HDS environments; (ii) the dispersion of the active phase is not directly related to the performance in HDS. Consequently, other geometric effects are more important to the development of HYD over Pd-Pt; and (iii) Pd~(δ+) surface species of the Pd-Pt alloyed particles are responsible for the hydrogenation-dehydrogenation steps during HYD, whereas C-S-C bond scission mainly takes place on Pt sites.