The role of group VIII metal promoter in MoS 2 and WS 2 hydrotreating catalysts : II. Catalytic and physicochemical properties of nickel-promoted catalysts

Abstract

The promotional effects of nickel on the catalytic activities of MoS 2 and WS 2 have been investigated. A series of unsupported NiW sulfides with a composition ratio, r = Ni Ni + W (atom), varying from 0.0 to 1.0, and two unsupported and fully sulfided nickel-molybdenum catalysts (one prepared by comaceration method and the other by homogeneous sulfide precipitation method) with r = 0.25 have been tested for cyclohexane isomerization, cyclohexene hydrogenation, and thiophene hydrogenolysis at 305 °C and 30 bars of hydrogen pressure. Surface area, X-ray diffraction, and ESR measurements on NiW samples show that in the low composition range, r < 0.05, the surface area decrease is associated with the formation of large crystallites. The ESR study shows the presence of W(V), W(III), and sulfur-containing paramagnetic species in the sample with r = 0.00. At the synergetic composition range, r = 0.15 to 0.40, the surface area versus composition plot shows a wide maximum, while the ESR results indicate the presence of certain ferromagnetic nickel-containing phase. It is shown that a strong electronic interaction takes place between two sulfide phases.