Pathway of the cycle between the oxidative adsorption of SO₂ and the reductive decomposition of sulfate on the MgAl(2-x)Fe(x)O₄ catalyst

The behaviors of the SO₂ oxidative adsorption and the reduction decomposition of formed sulfate over Mg-Fe-Al-O mixed spinel catalyst were studied by in situ IR, MR-GC-MS, Moessbauer spectroscopy and electrical conductivity measurement 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 ions. When the sulfated samples are reduced by hydrogen at 773 K, a large amount of H₂S along with a small part of SO₂ is produced. Different iron species, Fe³⁺, Fe^2.5+, Fe²⁺ and Fe⁰ are identified in the sulfated sample during the reduction process. In the half cycle of SO₂ oxidative adsorption and reaction, iron ions are directly involved in the formation of the mixed sulfate; in the half cycle of the reduction, due to the S-O-Fe bond being easily broken, the reducibility of the mixed sulfate hence is improved. A mechanism on the cycle between SO₂ oxidative adsorption and sulfate reductive decomposition is proposed.