Partial oxidation of hydrogen sulfide to sulfur over vanadium oxides bronzes
Abstract Me containing V 2 O 5 materials (Me Ag, Cu, Ca and Na) were prepared hydrothermally (from aqueous gels containing V 2 O 5 /H 2 O 2 /MeCl x mixtures, with Me/V ratios of 0.17) The samples were finally heat treated in air or in N 2 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 51 V NMR results, Ag 0.35 V 2 O 5 and Na 0.33 V 2 O 5 (or NaV 6 O 15 bronzes with a minority presence of V 2 O 5 were mainly obtained in the case of Ag and Na containing materials in samples both heat treated in air or in N 2 atmosphere. In the case of Cu and Ca containing samples, V 2 O 5 was mainly observed in samples calcined in air. However, Cu 0.26 V 2 O 5 and Ca 0.17 V 2 O 5 bronzes, with the minority presence of V 2 O 5 have been observed in Cu and Ca containing samples heat treated in N 2 On the other hand, the catalytic behavior strongly depends on the metal promoter. Thus catalysts presenting vanadium oxide bronzes, i.e. samples presenting Ag 0.35 V 2 O 5 NaV 6 O 15 Cu 0.26 V 2 O 5 or Ca 0.17 V 2 O 5 shows a catalytic activity during the partial oxidation of H 2 S to sulfur higher than that observed over pure V 2 O 5 or over promoted catalysts presenting mainly V 2 O 5 (i.e. Cu or Ca containing samples calcined in air) Moreover, some differences in the selectivity to sulfur were observed. A higher formation of SO 2 at high reaction temperature has been favored over Ag 0.35 V 2 O 5 containing catalyst. This different behavior between samples could be explained by the presence of metallic Ag on the surface of Ag 0.35 V 2 O 5 which was detected by XRD. Also, higher formation of SO 2 is favored in the case of catalyst heat treated in N 2 in which the presence of VO 2 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.