Pathway of the cycle between the oxidative adsorption of SO2 and the reductive decomposition of sulfate on the MgAl2-xFexO4 catalyst

The behaviors of the SO2 oxidative adsorption and the reduction decompositi on of formed sulfate over Mg-Fe-Al-O mixed spinel catalyst were studied by in situ IR, MR-GC-MS, Mossbauer spectroscopy and electrical conductivity me asurement techniques. In the oxidative adsorption and/or reaction process, SO2 and oxygen molecules are adsorbed on the lattice oxygen ions and oxygen vacancies, respectively. During the SO2 adsorption and reaction, adsorbed sulfur species react with the lattice oxygen ions and form the sulfite-like species. When oxygen molecules are present in the feed mixture, sulfate is formed from the sulfite-like species reacting with the adsorbed oxygen ion s. When the sulfated samples are reduced by hydrogen at 773 K, a large amou nt of H2S along with a small part of SO2 is produced. Different iron specie s, Fe3+, Fe2.5+, Fe2+ and Fe-0 are identified in the sulfated sample during the reduction process. In the half cycle of SO2 oxidative adsorption and r eaction, iron ions are directly involved in the formation of the mixed sulf ate; in the half cycle of the reduction, due to the S-O-Fe bond being easil y broken, the reducibility of the mixed sulfate hence is improved. A mechan ism on the cycle between SO2 oxidative adsorption and sulfate reductive dec omposition is proposed. (C) 1999 Elsevier Science B.V. All rights reserved.