Solid State Synthesis and Reversible Oxygen Capacity of Li/Mg Overstoichiometric Solid Solutions Based on the Spinel MgMnO3 – δ

Resumo

Series of spinel solid solutions with a specified cation composition, Mg_{1 +x}MnO_{3 – δ} and, for the first time, MgLi_xMnO_{3 – δ}, potential materials of catalytic systems for oxidation reactions such as oxidative conversion of methane and chemical looping combustion process were prepared by solid-state syntheses from mechanocomposites obtained by milling of ultra-high purity precursors (MgO, Mn₂O₃, MnO₂, and Li₂CO₃). Their homogeneity region was found to be up to 1573 K at p(O₂) = 0.21 atm. For both series of solid solutions, the synthesis from Mn₂O₃ and MnO₂ in air was investigated by the TG-DSC method and the oxygen content in the resulting materials was determined (TG-DSC, titration). The products of extensive reduction of spinels Mg_{1 +x}MnO_{3 – δ} and MgLi_xMnO_3–δ with an Ar + 4.8% H₂ mixture were investigated. Parameters of conversion of the reduction products to the initial single-phase spinels on treatment with air were determined. The obtained materials showed good reproducibility of reversible oxygen capacity over 20 reduction–oxidation cycles.