Synthesis and Mössbauer spectroscopic investigation of copper-manganese ferrite catalysts for water-gas shift reaction and methanol decomposition

Abstract Copper-manganese ferrites with nominal compositions Cu 1-х Mn х Fe 2 O 4 , where x = 0; 0.2; 0.4; 0.6; 0.8 and 1 are synthesized by sol-gel auto-combustion method. Formation of ferrites with cubic spinel structure and crystallite size of 11–26 nm was observed. A decrease of iron located in tetrahedral positions with the increase of Mn content in ferrite structure was found. The prepared ferrite materials are tested as catalysts in water-gas shift reaction (WGSR) and methanol decomposition (MD). The samples are arranged according the WGS activity in following order: Cu 0.8 Mn 0.2 Fe 2 O 4  > Cu 0.5 Mn 0.5 Fe 2 O 4  > CuFe 2 O 4  > Cu 0.2 Mn 0.8 Fe 2 O 4  > MnFe 2 O 4 . All mixed copper-manganese ferrites exhibit higher catalytic activity in methanol decomposition as compared to single CuFe 2 O 4 and MnFe 2 O 4 ones. A significant phase transformation with ferrites under the reduction reaction medium which influences the formation of real catalytic active phase is registered. Formation of magnetite or Mn-substituted magnetite is registered during the WGSR, while iron carbides and Mn-rich oxides are the dominant phases during the MD reaction.