Abstract
A series of γ-alumina-supported tungsten sulfide catalysts containing up to ca. 10 μmol m −2 tungsten has been characterized by oxygen chemisorption (static) at −78°C, X-ray diffraction and surface area measurements. They have also been evaluated by two probe reactions, namely hydrodesulfurization (HDS) of thiophene and hydrogenation (HYD) of cyclohexene. HDS and HYD activities of these catalysts are found to correlate with their oxygen chemisorption capacities. Nickel is found to have considerable promotional effect on these reactions; however, cobalt shows no such effect on the HDS activity, and only marginal promotional effect on HYD activity of the W/Al 2O 3 catalysts. Based on the results, a surface structural model, showing a highly dispersed patchy monolayer of amorphous tungsten sulfide phase at lower tungsten loadings and a bulk WS 2 phase, in addition to the monolayer phase at higher tungsten loadings, is proposed.
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