Mo-Doped Mesoporous Silica for Thiophene Hydrodesulfurization: Comparison of Materials and Methods

The mesoporous silica APMS-30 was compared to MCM-41 and MCM-48 as a substrate for the hydrodesulfurization (HDS) of thiophene with H2. Mo was introduced to these materials by four methods: dry impregnation of the calcined silica with MoO3, wet impregnation with aqueous (NH4)6Mo7O24·4H2O, "reactive" impregnation with MoCl3 in toluene, or in situ addition of (NH4) 6Mo7O24·4H2O to the reaction mixture (APMS-30 only). Mo loading was approximately 6 wt % (Si/Mo = 24). Samples were characterized by chemical analysis, XRD, N2 physisorption, SEM, and TEM. All samples were active for HDS and showed decreasing catalytic performance as a function of time, generally leveling out at total thiophene conversions between 22.8% and 57.4% after 75 min. Mo-APMS-30 showed the highest conversions, although Mo-MCM-48 synthesized by dry impregnation had slightly higher total conversion. Product distributions showed a shift from more hydrogenated to less hydrogenated C4 compounds as conversion decreased, and low amounts of C1, C2, and C3, compounds indicated that hydrocarbon cracking did not occur to a significant degree. Surface area did not appear to be a significant factor in catalytic performance.