Hydrodesulfurization of Dibenzothiophene over MCM-41-Supported Pd and Pt Catalysts

Three series of aluminosilicate MCM-41 (Al-MCM-41) were synthesized using different aluminum sources, including aluminum isopropoxide (AIM-I), pseudoboehmite, and aluminum sulfate, by a hydrothermal method. The hydrodesulfurization (HDS) performance of the Al-MCM-41-supported Pd and Pt catalysts prepared with chlorided precursors were evaluated with dibenzothiophene (DBT) as the model sulfur-containing molecule, in comparison with those supported on a siliceous MCM-41 (SiM). Pd/SiM and Pt/SiM were not promising for DBT HDS because of their relatively low activities and the rapid irreversible deactivation. Pd and Pt supported on the acidic Al-MCM-41 materials showed higher dispersion and enhanced HDS performances. AIM-I, which possessed the strongest acidity, was the most promising among the mesoporous materials investigated. The deactivated Pd/AlM-I and Pt/AlM-I can be reversibly regenerated by H-2 reduction. DBT HDS over the Pd catalysts predominantly took the hydrogenation (HYD) pathway, whereas the direct desulfurization (DDS) pathway and HYD pathway were comparable for the Pt catalysts. Increasing the support acidity had no positive effect on the DDS activity of Pd but significantly enhanced its HYD activity, while the increase in the rate constant of DDS pathway was close to that of the HYD pathway for Al-MCM-41-supported Pt catalysts. The effect of the acid properties of the supports on the HDS performance of Pd and Pt catalysts was discussed by considering the formation of "electronic-deficient" particles and the hydrogen spillover process.