Factors controlling the development of the HYD route of desulfurization of DBT over γ-alumina supported Pt and Pd catalysts

The influence of the metallic precursor and the pretreatment of γ-alumina supported Pt and Pd catalysts on the reactivity of dibenzothiophene (DBT) over these materials was studied. It was found that the use of chlorided precursors induces changes in the chemical state of the metals and in the acidic properties of the supported catalysts which are partly a function of the type of noble metal. Such changes were found to positively affect the conversion of DBT over both monometallic systems. Regardless of the preparation conditions, Pt possesses a high activity and a high selectivity to the direct route of desulfurization of DBT, whereas Pd is less active but performs HDS with a strong tendency to develop the hydrogenation route of desulfurization (HYD) when employing a chlorided precursor. The use of a low temperature pretreatment of the chlorided catalysts enhanced DBT conversion, and for Pd/γ-Al2O3 it doubled the selectivity to HYD. The registered trends were considered to be rather related to a change in the distribution of acidic sites of the catalysts and to changes in the chemical state of the noble metals than to the effect of dispersion.