New catalysts active for the mild oxidation of hydrogen sulfide to sulfur

Nickel iron phosphates were studied for the selective oxidation of hydrogen sulfide to sulfur, Nickel iron phosphate and Fe/Cr samples were more activ e than simple iron, chromium, and mixed iron-chromium oxides, which had bee n previously studied. Nickel iron phosphate catalyst prepared by solid-soli d method with, consequently, a very low specific surface area was intrinsic ally active and selective to sulfur(conversion 17%, S-n selectivity 97%); n o rapid deactivation was observed. Even though higher specific surface area samples, prepared according to a solution method at various calcination te mperatures, showed better performance (conversion 76%, S-n selectivity >90% ), the specific activity depended on the crystallinity of the samples. The reaction is apparently structure sensitive. The structure of the catalytic material must facilitate electronic exchange, evidenced by Mossbauer Charac terization. The establishment of the mixed valency Fe2+/Fe3+ under catalyti c feed was shown to be an essential factor in this reaction. (C) 1999 Acade mic Press.