Influence of Templates on the Overgrowth of MCM-41 over HY and the Hydrodesulfurization Performances of the Supported Ni-Mo Catalysts

Overgrowth of MCM-41 on HY zeolite was performed using different templates [cetyltrimethylammonium bromide (CTABr) and cetyltrimethylammonium chloride (CTACl)]. The hydrodesulfurization (HDS) performances of Ni-Mo sulfides supported over these synthesized composites were evaluated with dibenzothiophene (DBT) as the model sulfur-containing molecule. TEM and STEM images revealed that zeolite HY overgrown with an MCM-41 layer (less than 20 nm) was obtained using CTABr as the template [MY(Br)], and the MCM-41 pore channels were assumed to be oriented outward from the inner HY core. Nevertheless, for the samples synthesized using CTACl [MY(Cl)], the HY crystals were buried independently in the MCM-41 phase. Both Ni-Mo/MY(Br) and Ni-Mo/MY(Cl) showed higher HDS activity and reducibility than Ni-Mo/MCM-41. The hydrogenation activity of Ni-Mo/MCM-41 was enhanced more than the direct desulfurization activity by the introduction of HY zeolite. Ni-Mo/MY(Br) and Ni-Mo/MY(Cl) exhibited hydrocracking activities equivalent to that of Ni-Mo/MCM-41, indicating that the HDS of DBT predominantly takes place in the mesopores of Ni-Mo/MY(Br) and Ni-Mo/MY(Cl). Because the active species located in the mesopores cannot have close contact with the strong acid sites of the HY zeolite, it is suggested that the spillover hydrogen might play an essential role in the HDS reaction over the supported Ni-Mo sulfides.