Understanding the Diffusion Properties of Sulfur-Containing Compounds in Mesoporous Alumina: A Molecular Dynamics Study

Enhancing the diffusion of reactants in catalysts is imperatively needed in the hydrodesulfurization process. However, diffusion properties of sulfur-containing compounds are poorly characterized owing to experimental limitations. Herein, molecular dynamics (MD) simulation was applied to explore diffusion properties of thiane, thiophene, dibenzothiophene, and 4,6-dimethyldibenzothiophene in mesoporous alumina with pore sizes of 11.8, 13.6, and 15.3 nm. It is found that larger pore size and higher temperature facilitate diffusion. In other words, with the increase of pore size and temperature, the self-diffusion coefficient increased while the average interaction energy dropped. Notably, the diffusion activation energy showed that diffusion of larger molecules was more sensitive to variations in pore size and temperature. Furthermore, the effect of the molecular structure on diffusion was also studied; the increase in the number of benzene rings and branched chains was detrimental to diffusion. The simulated results were demonstrated by our experimental findings and harbor tremendous guiding significance for the design of effective hydrodesulfurization catalysts.