The nature of the sulfur tolerance of amorphous silica-alumina supported NiMo(W) sulfide and Pt hydrogenation catalysts

Abstract

Amorphous silica-aluminas (ASA) based NiMo and NiW sulfide and Pt hydrogenation catalysts were prepared and compared in toluene hydrogenation in the presence of H 2S to alumina- and silica-supported reference catalysts with the aim to elucidate the influence of (strong) Brønsted acidity of the support on the sulfur tolerance. Despite precautions to prepare NiMo sulfide catalysts with equal morphology, the stacking degree of the MoS 2 phase was found to decrease with alumina content of the ASA. Similar but more pronounced differences of the stacking degree were observed among the NiW sulfide catalysts. This variation in the stacking degree had a substantial effect on the catalytic activity of dibenzothiophene hydrodesulfurization. ASA-based catalysts show higher activity and improved sulfur tolerance in toluene hydrogenation compared to their alumina- and silica-based counterparts. However, the sulfur tolerance does not correlate with the number of strong Brønsted acid sites, nor, indeed, with total Brønsted acidity. Instead, it decreases with increasing Al content of the ASA support. The sulfur tolerance of the active metal sulfide phase is related to the electronegativity of the support. That silica itself does not follow this trend is surmised to be due to its lack of Lewis acid sites, necessary for introducing the active phase-support effect.