The role of promoters on the catalytic performance of MxV2O5 bronzes for the selective partial oxidation of H2S

Abstract

Metal-containing vanadium oxide bronzes (MxV2O5; M= Cu, Ag and Ca) have been prepared, characterized (before and after reaction) by various physicochemical techniques, and tested in the partial oxidation of H2S. The catalysts were prepared hydrothermally at 175 °C (from gels containing M/V molar ratios of 0.17 or 0.33) and heat-treated at 500 °C/2 h in N2. The most effective catalysts, showing a sulfur selectivity greater than 95 % for a H2S conversion beyond 90 %, were those presenting vanadium oxide bronze (β-Cu0.261V2O5 or Ag0.333V2O5) as the main crystalline phase. Cu- and Ag-containing vanadium oxide bronzes were stable under reaction conditions. For calcium containing materials (mainly presenting the Ca0.17V2O5 bronze phase), the formation of CaSO4 has been observed during the reaction, which resulted in a negative effect on both activity and selectivity. The nature of active and selective sites in this type of catalysts, as well as the role of promoters, are also discussed.