TEMPERATURE-PROGRAMMED REDUCTION OF OXIDIC AND SULFIDIC ALUMINA-SUPPORTED NIO, WO3, AND NIO-WO3 CATALYSTS

The reduction behaviour of oxidic and sulfidic alumina-supported Ni, W , and NiW catalysts has been studied using temperature-programmed redu ction (TPR). Besides giving structural information on the oxidic and s ulfidic state, the TPR patterns gave detailed information on the sulfi dability of the various oxidic species. From the oxidic species only d ispersed NiO was completely sulfidable at 673 K, whereas the other spe cies were partly sulfidable (mixed Ni-W phase, dispersed WO3, and Ni i n the surface alumina layer) or not sulfidable (Ni in subsurface alumi na layers and NiWO4). The sulfided catalysts contained at least four t ypes of sulfur, viz. stoichiometric sulfur behaving as S in a bulk ana logue (WS2, Ni3S2, NiS1+x) or in NiWS (NiWS is not directly observed u nder TPR conditions due to sintering into Ni3S2 and WS2), a reactive t ype of sulfur indicated as S(x), S-H groups, and adsorbed H2S. Except NiS1+x and S(x), no sulfided phase reduces under HDS conditions. Altho ugh hydrogenation of sulfur might well be an elementary step in the de sulfurisation reaction, only a weak correlation was observed between t he HDS activity and the reduction rate of the S. species. (C) 1994 Aca demic Press, Inc.