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Nickel iron phosphates were studied for the selective oxidation of hydrogen sulfide to sulfur. Nickel iron phosphate and Fe/Cr samples were more active than simple iron, chromium, and mixed iron–chromium oxides, which had been previously studied. Nickel iron phosphate catalyst prepared by solid–solid method with, consequently, a very low specific surface area was intrinsically active and selective to sulfur (conversion 17%, Sn selectivity 97%); no rapid deactivation was observed. Even though higher specific surface area samples, prepared according to a solution method at various calcination temperatures, showed better performance (conversion 76%, Sn 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 Characterization. The establishment of the mixed valency Fe2+/Fe3+ under catalytic feed was shown to be an essential factor in this reaction. |
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