Selective oxidation of H2S to elemental sulfur over VOx/SiO2 and V2O5 catalysts

The selective oxidation of H2S was investigated over VOx/SiO2 catalysts (1-100% V contents) using a packed-bed flow reactor in the temperature range 200-350 degreesC. When a stoichiometric ratio of O-2/H2S is used in the feed, high conversion of H2S 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 degreesC. About 10-30% decrease of the sulfur yield is observed in the presence of 30% water in the feed. The conversion of H,S and selectivity to sulfur exceed the equilibrium values. Reaction tests and characterization using XRD, XPS and XANES have revealed that during the reaction, the V2O5 catalysts are reduced severely to VO2 and/or V2O3, 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 H2S to SO2 (zero sulfur selectivity). As the reaction proceeds via redox mechanism, high space velocities: and low V loadings at low reaction temperatures (<250<degrees>C) result in eventual decrease of the conversion with time on stream due to depletion of labile oxygen on the surface. (C) 2001 Elsevier Science B.V. All rights reserved.