Application of Heteropolyacid H4SiMo3W9O40 for the Preparation of Bimetallic MoWS2/Al2O3 Hydrotreatment Catalysts

Abstract

The bimetallic MoWS₂/Al₂O₃ catalyst was synthesized using the Keggin-type mixed heteropolyacid H₄SiMo₃W₉O₄₀. The monometallic catalysts SiMo₁₂/Al₂O₃ and SiW₁₂/Al₂O₃ based on the H₄SiMo₁₂O₄₀ and H₄SiW₁₂O₄₀ acids are prepared as reference samples. The sulfidized catalysts are analyzed by temperature-programmed reduction with hydrogen, high-resolution transmission electron microscopy, and X-ray photoelectron spectroscopy. Their catalytic properties are studied in the cohydrotreatment of dibenzothiophene (DBT) and naphthalene on a flow-type setup. The introduction of three molybdenum atoms into the structure of an oxide precursor is shown to increase the degree of sulfidation of the tungsten particles by 20% in comparison with SiW₁₂/Al₂O₃. The DBT turnover frequency in the hydrodesulfurization (HDS) on the sites on the edges of the active phase of the SiMo₃W₉/Al₂O₃ catalyst is shown to be 5.5 times higher than in the presence of SiW₁₂/Al₂O₃. The bimetallic sample demonstrated the highest selectivity in the preliminary DBT hydrogenation route and activity in the prehydrogenation of naphthalene. The high level of activity of the SiMo₃W₉/Al₂O₃ catalyst was due to the formation of a mixed Mo_xW_(1–x)S₂ active phase with a MoW oxide precursor, whose structure contained both metals bonded at the molecular level.