Characterization and hydrodesulfurization activity of CoMo catalysts supported on boron-doped sol–gel alumina

A series of hydrodesulfurization (HDS) catalysts was prepared by impregnation of Co and Mo on sol–gel B–Al2O3 supports with B/Al ratios of 0, 0.02, 0.04, 0.08, 0.20, 0.32, 0.49, and 0.61. The thiophene HDS and dibenzothiophene (DBT) HDS activities were both maximal for the catalyst with B/Al = 0.04, with respective values 70 and 42% higher than those for an industrial reference catalyst. These maxima in HDS activity correlated with the previously reported presence of isolated BO4 surface species. These BO4 species were responsible for a local maximum in the acidity of the B–Al2O3 supports when B/Al = 0.04. In contrast, the formation of mixed oxides (A9B2 and A2B) or B2O3 that also resulted in enhanced acidity of the B–Al2O3 supports had a detrimental effect on the HDS activity.The 4,6-dimethyldibenzothiophene (4,6-DMDBT) HDS activity over the CoMo/B–Al2O3 catalysts decreased when the B/Al ratio was increased. This was attributed to the strong direct desulfurization character of the CoMo catalysts supported on the B–Al2O3 supports, because high hydrogenation ability toward the CC double bonds is essential prior to sulfur removal from 4,6-DMDBT. The excellent performance in the thiophene and DBT HDS of the CoMo/B–Al2O3 catalysts is particularly useful for ultra-deep HDS of light fractions.

The thiophene and dibenzothiophene (DBT) HDS activities of the B-doped catalysts were maximal for B/Al = 0.04 and higher than those for an industrial reference catalyst. The 4,6-dimethyldibenzothiophene (DMDBT) HDS activities, however, were lower than that for the reference catalyst and decreased with increasing B/Al ratio. These were attributed to the strong direct desulfurization character of the B-doped catalysts. Figure optionsDownload as PowerPoint slide