Relevant changes in the properties of Co(Ni)Mo/Al₂O₃HDS catalysts modified by small amounts of SiO₂

Abstract

The changes in hydrodesulfurization activity, selectivity, dispersion, sulfidation, and extent of promotion of Co(Ni)Mo catalysts were investigated when the alumina support surface is modified by grafting 4 wt% silica. Adding SiO 2 eliminates the most reactive hydroxyl groups on the alumina surface (IR band at 3775 cm À1 ) decreasing the possibility of generating tetrahedral Mo species difficult to sulfide in favor of octahedral ones capable of contributing to the sulfided active phase. The catalysts were evaluated in the hydrodesulfurization of 4,6-dimethyldibenzothiophene. Incorporating SiO 2 to alumina increases the hydrogenation rate constant and therefore the global hydrodesulfurization rate of 4,6-dimethyldibenzothiophene and enhances the promotion of Mo by Co (or Ni). The global sulfidation of Ni is not affected by the addition of silica but the sulfidation of cobalt is significantly improved. The extent of promotion of the NiMo/Al 2 O 3 and NiMo/SiO 2 / Al 2 O 3 catalysts was greater than the one achieved in their Co-promoted counterparts.

The Silicon on the Catalysis: Hydrodesulfurization of Petroleum Fractions

“…On the other hand, the catalysts NiW/MCM41 prepared at pH 7 with different Si/Al (10, 25 and 50) molar ratio presented bands in the range of 710-730 nm ascribed to octahedral nickel species [11,[49][50][51]. But also a band between 807 and 818 nm were detected, which was associated to nickel species with octahedral symmetry distorted; this latter may be related to an interaction Ni-W [41,42].…”

“…Recently, Romero-Galarza et al [50] carried out a systematic study of the change in activity, selectivity, dispersion, sulfidation, and extent of promotion for CoMo and NiMo HDS catalysts supported on Al2O3 and SiO2/Al2O3. They found for CoMo and NiMo catalysts that the grafting of the surface of alumina support with a 4.0 wt% of silica was enough to eliminate the most basic hydroxyl groups bonded to tetrahedral aluminum (IR band at 3767 cm À1 ), and thus, this induces to have a higher proportion of Mo and Co(Ni) in octahedral coordination (DRS-UVvis results), resulting in a better catalytic performance in the HDS of 4,6-DMDBT.…”