Partial oxidation of hydrogen sulfide to sulfur over vanadium oxides bronzes

Abstract

Me-containing V2O5 materials (Me=Ag, Cu, Ca and Na) were prepared hydrothermally (from aqueous gels containing V2O5/H2O2/MeClx mixtures, with Me/V ratios of 0.17). The samples were finally heat-treated in air or in N2 atmosphere. The heat-treated samples have been characterized by several physico-chemical techniques and tested in the partial oxidation of hydrogen sulfide. According to XRD, electron paramagnetic resonance and 51V NMR results, Ag0.35V2O5 and Na0.33V2O5 (or NaV6O15) bronzes with a minority presence of V2O5 were mainly obtained in the case of Ag- and Na-containing materials in samples both heat-treated in air or in N2 atmosphere. In the case of Cu- and Ca-containing samples, V2O5 was mainly observed in samples calcined in air. However, Cu0.26V2O5 and Ca0.17V2O5 bronzes, with the minority presence of V2O5, have been observed in Cu- and Ca-containing samples heat-treated in N2. On the other hand, the catalytic behavior strongly depends on the metal promoter. Thus catalysts presenting vanadium oxide bronzes, i.e. samples presenting Ag0.35V2O5, NaV6O15, Cu0.26V2O5 or Ca0.17V2O5 shows a catalytic activity during the partial oxidation of H2S to sulfur higher than that observed over pure V2O5 or over promoted catalysts presenting mainly V2O5 (i.e. Cu- or Ca-containing samples calcined in air). Moreover, some differences in the selectivity to sulfur were observed. A higher formation of SO2 at high reaction temperature has been favored over Ag0.35V2O5-containing catalyst. This different behavior between samples could be explained by the presence of metallic Ag on the surface of Ag0.35V2O5, which was detected by XRD. Also, higher formation of SO2 is favored in the case of catalyst heat-treated in N2, in which the presence of VO2, as minority, could have a role in combustion of sulfur. Accordingly, this work should be considered as a first approach to relate catalytic activity of the Me-containing vanadium oxide bronze (containing Ag, Cu, Ca and Na) for the selective oxidation of hydrogen sulfide.