Direct reduction of sulfur dioxide to elemental sulfur with hydrogen over Sn-Zr-based catalysts

We conducted the SO2 reduction with H-2 over Sn-Zr-based catalysts for the direct sulfur recovery process. The reaction temperature was varied from 250 to 550 degrees C while using SnO2-only, ZrO2-only, and SnO2-ZrO2 (Sn/Zr = 2/1) catalysts. The highest reactivity was obtained using the SnO2-ZrO2 (Sn/Zr = 2/1) catalyst at 550 degrees C, for which the SO2 conversion and sulfur selectivity were 98 and 55%, respectively. Also, the following mechanistic pathway was suggested: (1) The elemental sulfur is produced by the direct conversion of SO2 according to the redox mechanism (SO2 + 2H(2) -> S + 2H(2)O). (2) The produced sulfur is partially converted into H2S with the hydrogenation (H-2 + S -> H2S). (3) Finally, the Claus reaction proceeds through Lewis and Bronsted acidic sites (SO2 + 2H(2)S -> 3S + 2H(2)O). It was estimated that the lattice oxygen vacancies might be active sites for the redox mechanism and the Lewis and Bronsted acidic sites might be related to the pathway of the Claus reaction.