Ultrasonic-assistance influence on the impregnation method for high metal loading CoMo/Ti-HMS catalysts

Abstract

Here, it reports the influence of ultrasonic assistance during the impregnation process using traditional precursor salts of cobalt nitrate, molybdenum heptamolybdate, and citric acid as a chelating agent. The variation in metal loading (CoO + MoO₃) from 16.1 wt% (12.7 wt% MoO₃, 3.4 wt% CoO) to 46.8 wt% (35.7 wt% MoO₃, 10.1 wt% CoO) was evaluated in the HDS of DBT. Ultrasonically-assisted impregnation demonstrated improved metal dispersion, improved the Co-Mo interactions and complete sulfidation of cobalt species, and enhanced the formation of well-dispersed CoMoS phase, unlike traditional impregnation catalysts that even exhibited non-sulfided Co species. Catalysts prepared using ultrasonic assistance exhibited a higher initial reaction rate for the HDS of DBT than their traditionally impregnated counterparts. Although the direct desulfurization pathway was the primary reaction route, the ultrasonic-assisted catalysts exhibited higher selectivity toward the hydrogenation pathway (higher HYD/DDS ratios), especially at higher metal loadings. The increased surface acidity, which correlated with rising metal content, enhanced the hydrogenation pathway during the HDS of DBT. Despite the superior catalytic performance of ultrasonic-assisted catalysts, the effectiveness of increasing metal content decreases at higher metal loadings, likely due to limitations in active site dispersion on the surface.