Impact of γ-alumina pore structure on structure and performance of Ni-Mo/γ-Al2O3 catalyst for 4,6-dimethyldibenzothiophene desulfurization

The pore structure plays a vital role in material properties. Therefore, in this study, we prepared gamma-Al2O3 with various mesopore diameters to explore the impact of pore structure on the property of Ni-Mo/gamma-Al2O3 catalyst and hydrodesulfurization of 4,6-dimethyldibenzothiophene. It reveals that the pore size adjusts the reducibility of Mo species via affecting ammonium heptamolybdate adsorption. The Ni benefits the dispersion and reduction of Mo species. The larger pore imparts weaker polarization of Al3+, which less weakens the interactions between the MoS2 layers. The different polarization of Al3+ results in the diverse Ni-Mo-S structures over the catalysts with various pore sizes, and different active sites in edges and corners are obtained. The optimum pore size of Ni-Mo/gamma-Al2O3 catalyst for the desulfurization of 4,6-dimethyldibenzothiophene is 7.0 nm, rather than 5.9 nm for the MoO3/gamma-Al2O3 catalyst. The reaction pathway is regulated by the pore size and Ni-Mo-S structure. 4,6-dimethyldibenzothiophene reacts mainly via the hydrogenation pathway over 4.5 nm pore sized catalyst and high edge to corner ratio of the Ni-Mo-S slab (e.g. 2.63). Whereas, the sulfur in 4,6-dimethyldibenzothiophene is preferably eliminated by the direct desulfurization pathway in the pore size of 8.7 nm and low edge to corner ratio of the Ni-Mo-S slab (e.g. 2.04). All these can also be used to design deep desulfurization catalyst for environmental protection.