Study of H2S selective oxidation on new model catalysts. Influence of composition

Phosphate of transition elements A3M4(PO4)6 (A = Fe, Ni, Zn, Mg, Cu, Cr and M = Fe, V, Cr) are prepared by solid methods, at 1223 K. Their activity in H2S selective oxidation are compared. In spite of their low specific area, the catalysts develop a good activity (up to 17% of H2S conversion for surface area lower than 1 m2g-1) and an excellent sulphur selectivity (always higher than 95%). Screening experiments show that the best systems always contain Fe as element and, in these cases, Mossbauer characterizations evidence the establishment of Fe2+/Fe3+ mixed valency during the reaction. As shown by XANES and XRD results, the ability of the element in the divalent A site to promote the redox mechanism between M2+/M3+and H2S/S° and to prevent sulphidation determines the catalytic activity.