Low temperature use of SiC-supported NiS2-based catalysts for selective H2S oxidation -: Role of SiC surface heterogeneity and nature of the active phase

High activity for the direct oxidation of H2S into elemental sulfur at low reaction temperature (40-60 degreesC) on medium surface area silicon carbide-supported nickel sulfide (NiS2/SiC) catalyst was attributed to the formation of a highly active superficial nickel oxysulfide. The hypothesis of the superficial formation of,either nickel oxide or nickel sulfate was rejected. The superiority of the SiC support in terms of performance as compared to silica, high surface area alumina and activated charcoal was evidenced. The high stability of the SiC-supported catalyst as a function of time and solid sulfur loading in the presence of water was explained by a peculiar mode of sulfur deposition, involving the role of water and the hydrophilic/hydrophobic duality of the SiC support surface. Water acts as a conveyor belt, continuously cleaning the active phase particles, located on the hydrophilic oxygen-containing surfaces of the support. Hydrophobic pure SiC, located outside the mesoporosity and exempt of active phase, remains as an available surface for the storage of high amounts of solid sulfur. (C) 2002 Elsevier Science B.V. All rights reserved.