Synthesis, characterization, thermal stability and redox behavior of In³⁺₂Ti⁴⁺_1–xTm³⁺_xO_5–δ, (Tm = Fe³⁺ and Cr³⁺, 0.0 ≤ x ≤ 0.2) mixed-oxide catalysts

Mixed metal oxide catalysts with nominal compositions of In₂Ti_1–xFe_xO_5–δ, In₂Ti_1–xCr_xO_5–δ, where 0.0 ≤ x ≤ 0.2, have been synthesized by the ceramic route and characterized using the powder x-ray diffraction technique. The In₂Ti_1–xFe_xO_5–δ samples were single-phase compositions, isomorphic with In₂TiO₅ phase. The particle size of the In₂Ti_1–xFe_xO_5–δ samples was lower compared to the parent In₂TiO₅ oxide. Thermal stability (by thermogravimetry-differential thermal analysis) in varying atmospheres, and temperature-programmed reduction (TPR)/temperature-programmed oxidation cycles have been recorded to investigate their redox behavior as a function of the value of x in this study. The amount of H₂ consumed under TPR curves was correlated with the nonstoichiometry generated in the In₂Ti_1–xFe_xO_5–δ samples. Fe substitution induced ease in the reducibility (i.e., maximum temperature) of the substituted oxides compared to that in In₂TiO₅. X-ray photoelectron spectroscopy has been used to confirm the oxidation states of indium and other metal ions in fresh and reduced samples.