Phosphate of transition elements A(3)M(4)(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 are
a, the catalysts develop a good activity (up to 17% of H2S conversion for s
urface area lower than 1 m(2) g(-1)) and an excellent sulphur selectivity (
always higher than 95%). Screening experiments show that the best systems a
lways contain Fe as element and, in these cases, Mossbauer characterisation
s 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 diva
lent A site to promote the redox mechanism between M2+/M3+ and H2S/S-0 and
to prevent sulphidation determines the catalytic activity. (C) 2000 Publish
ed by Elsevier Science B.V.