CHARACTERIZATION OF NICKEL AND TUNGSTEN SPECIES SUPPORTED ON ALUMINA

The effect of thermal activation on NiW/Al2O3 catalyst in their oxide, reduced and sulfided forms has been studied by X-ray diffraction (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 reduced, whereas upon sulfiding 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 stabilizing function.