Comparison of the intraparticle diffusion of DBT and 4,6-DMDBT in HDS over different mesostructured silica-based catalysts

Achieving ultradeep hydrodesulfurization (HDS) of diesel necessitates HDS catalyst optimization. Understanding the catalyst pore structure effects on the diffusion behavior of the organosulfur compound benefits the proper design of the HDS catalysts with maximized apparent reactivities. In the present study, we controllably synthesized three mesoporous silica-based catalysts (NiMo/Zr-SBA-15, FDU-12, and MCFs) with similar intrinsic reactivities (-13 x 10(-4) and -5 x 10(-4 )mol.g(-1).h(- 1) for DBT and 4,6-DMDBT HDS) but different pore structures. The diffusion behaviors of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) in pore channels were systematically investigated via the reaction kinetic method. The pore channel/cage sizes rather than the pore mouth/win-dow sizes dominated the intraparticle diffusion. The effective diffusion coefficient (De) decreased in the order of NiMo/Zr-MCFs (19.7 cm(2).s(-1)) > NiMo/Zr-FDU-12 (18.2 cm(2).s(-1)) > NiMo/Zr-SBA-15 (8.2 cm(2).s(-1)) for DBT, while NiMo/Zr-MCFs (7.4 cm(2).s(-1)) > NiMo/Zr-FDU-12 (4.4 cm(2).s(-1)) > NiMo/Zr-SBA-15 (4.2 cm(2).s(-1)) for 4,6-DMDBT. The corresponding correlation with pore size suggested that the intraparticle diffusion resistance can be greatly relieved when the catalyst pore/cage size is > 25x larger than the molecule size of the organosulfur-containing compounds. The findings present fresh opportunities for designing silica-based HDS catalysts for efficient HDS reaction.

Automated summary

This study investigates the diffusion behavior of organosulfur compounds in catalyst pore channels and reveals that the pore channel/cage sizes dominate the intraparticle diffusion. The effective diffusion coefficient decreases with decreasing pore size, but the intraparticle diffusion resistance can be greatly relieved when the catalyst pore/cage size is larger than 25 times the molecule size of the compounds. These findings present new opportunities for designing efficient silica-based HDS catalysts.