Selective oxidation of H 2S to elemental sulfur over VO x/SiO 2 and V 2O 5 catalysts

Abstract

The selective oxidation of H 2S was investigated over VO x /SiO 2 catalysts (1–100% V contents) using a packed-bed flow reactor in the temperature range 200–350°C. When a stoichiometric ratio of O 2/H 2S is used in the feed, high conversion of H 2S and high selectivity to sulfur (>90%) can be achieved at various V loadings (5–100 wt.%) if the space velocity is kept below 4000 h −1 and the reaction temperature above 270°C. About 10–30% decrease of the sulfur yield is observed in the presence of 30% water in the feed. The conversion of H 2S and selectivity to sulfur exceed the equilibrium values. Reaction tests and characterization using XRD, XPS and XANES have revealed that during the reaction, the V 2O 5 catalysts are reduced severely to VO 2 and/or V 2O 3, resulting in changes in the surface area and pore size. The sulfur selectivity can be kept high (>90%) only at such a highly reduced condition. Oxidized catalyst (with O/V ratio>2.26) exhibits complete oxidation of H 2S to SO 2 (zero sulfur selectivity). As the reaction proceeds via redox mechanism, high space velocities and low V loadings at low reaction temperatures (<250°C) result in eventual decrease of the conversion with time on stream due to depletion of labile oxygen on the surface.