Applied Catalysis A: General, Vol.235, No.1-2, 61-69, 2002
Studies on sulfate formation during the conversion of H2S and SO2 to sulfur over activated alumina
A mechanism for the conversion of H2S and SO2 over alumina is proposed in which surface thiosulfate is formed and reacts with SO2 and H2S via a series of oxy-anions to form sulfur and H2O. In addition to thiosulfate being a key species of the catalytic cycle, it is proposed that sulfate is also formed as part of the catalytic cycle but that its surface concentration is limited to some steady-state concentration by virtue of its reduction by H2S. The initial formation of thiosulfate and sulfate on alumina probably occurs by two mechanisms. One pathway involves interaction of either H2S or SO2 with oxide sites on the alumina surface. Such oxide sites have been suggested by Sohlberg et al. to arise as a consequence of the interaction of vacant sites in the defect spinel structure of alumina with H2O [J. Phys. Chem. 100 (1996) 7550]. The other pathway, the first step of which has been referred to numerous times in the literature, likely involves the adsorption of SO2 at Lewis acid-base sites, and reaction with H2S to form sulfur oxy-anions and eventually, sulfur and water.