Characterization of La1−xSrxMnO3 perovskite catalysts for hydrogen peroxide reduction

Abstract

We investigated the crystalline phase and electronic structure of perovskite-type La_1−xSr_xMnO₃ (0.0 ≤ x ≤ 1.0) (LSM_x) catalysts synthesized via the citric sol–gel route, for H₂O₂ reduction. The resulting materials were characterized by XRD, XANES, TR-XANES, and TPO and, after calcination, consisted of cubic perovskite for 0.0 ≤ x ≤ 0.8 and hexagonal perovskite for x = 1.0. Mn species in the precalcined catalysts were oxidized to Mn³⁺ for x = 0.0 to 0.6 and to Mn²⁺ for x = 0.8 and 1.0. After calcination, Mn species were present in a mixed oxidation state of Mn³⁺/Mn⁴⁺, while Sr²⁺ and La³⁺ were not altered. TR-XANES and TPO showed that Mn species were oxidized at 210–220 °C and formed active perovskites LSM_0.4 and LSM_0.0 at 580 °C and 640 °C. This shows that Sr doping can reduce the oxidation temperature of LSM_x with 0.2 ≤ x ≤ 0.4. However, the concentration of Mn⁴⁺ in LSM_x is increased which is useful for enhancing their catalytic activity and stability. When tested in an alkaline electrolyte, LSM_0.6 containing the optimum Mn⁴⁺/Mn³⁺ ratio promoted the formation of hydroxyl via the oxygen intercalation reaction and exhibited low polarization resistance and the highest catalytic activity for H₂O₂ reduction.