Characterization of Nickel and Tungsten species supported on alumina

Abstract

The effect of thermal activation on NiW/AI,03 catalyst in their oxide, reduced and sulfided forms has been studied by X-ray dsraction (XRD), differential thermal analysis (DTA), diffusion reflectance spectroscopy (DTS), infrared spectroscopy (IR), Raman spectroscopy (RS), electron paramagnetic resonance (EPR) and magnetic susceptibility measurements.Thermal activation in oxygen results in production of many species of the mono-, di-, and polymeric type. Upon activation in hydrogen they are partially r e d u d , whereas upon sulfding number of oxide ions are replaced by sulfide ones. Among others, formation of dithiotungstenates was proved, yet neither the exchange of hydroxyl groups for the thiol ones nor the exchange of bridge oxide ions for sulphur ions was indicated.The simultanous reduction and sulfiding process do not affect the spinel subsurface structure. With respect to the surface species, the catalyst's support takes on a stabiliing function.