Pore confinement effect of MoO3/Al2O3 catalyst for deep hydrodesulfurization

To investigate the pore confinement effect of MoO3/Al2O3 catalyst for deep hydrodesulfurization, a series of MoO3/gamma-Al2O3 catalysts were prepared via impregnation method. All catalysts had almost the same physicochemical properties, such as the specific surface area, apparent morphology, microstructure, coordination of Al atom and acidity, and differed in the pore size. The control experiments results showed that enlarging the pore size from 3.6 to 8.8 nm increased the desulfurization efficiency of 4,6-dimethyldibenzothiophene (4,6-DMDBT) from 62.6% to 95.0%, then decreased to 71.3%. The catalyst with a pore size of 5.9 nm displayed the optimum hydrodesulfurization performance. The larger pores weaken the effect of polarization of Al3+ on the van der Waals interactions between the layers of active phase and result in more stacking of MoS2. The more stacked MoS2 contribute to more edge and corner active sites for the catalysts with the pore size of 5.9 nm, which resulted that this catalyst exhibited the highest reaction rate and sulfidation degree of Mo species, lowest reduction temperature and largest amount of chemisorbed CO. The reaction and characterization results revealed that the smaller mesopores favored the accessibility of 4,6-DMDBT to the edge sites of MoS2 active phase, whereas the larger ones promoted the reactant molecules to the corner sites. Compared to the catalyst with mono-pore size, the catalyst with hierarchical mesopore structure had a higher hydrodesulfurization activity through the synergism of small and large pores. The larger pores enable 4,6-DMDBT to reach the active sites located in the small pores and promote the accessibility of the reactants to the corner sites of hexagonal shaped MoS2. This catalyst possessed a lower ratio of hydrodesulfurization products to direct desulfurization ones.