Development of the HYD route of hydrodesulfurization of dibenzothiophenes over Pd–Pt/γ-Al2O3 catalysts

The hydrodesulfurization (HDS) of dibenzothiophene (DBT) on a series of Pd–Pt/γ-Al2O3 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) Pdδ+ 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.