Redox behavior and catalytic activity of La–Fe–V–O mixed oxides Original Research Article

The mixed oxides of composition LaFexV1−xO4−δ (0.0≤x≤1.0) were characterized using XRD and FTIR techniques, and their redox behavior was examined by recording temperature-programmed reduction/oxidation profiles. The samples with x≤0.2 and x≥0.8 compositions were of monoclinic LaVO4 and orthorhombic LaFeO3 phase, respectively. The intermediate compositions consisted of a mix of these two phases in addition to small concentration of a non-stoichiometric LaV(Fe)O4−δ phase, where iron occupied some of the lattice positions of vanadium. Substitution of Fe at a small level resulted in considerable lowering of the reduction temperature and also in the lowering of the temperature required for subsequent re-oxidation. At the same time, these samples showed higher catalytic activity for CO oxidation reaction and demonstrated a greater stability during the repeated cycles of reduction interspersed by oxidation steps. Our results reveal that the lattice defects in the host matrix and the synergistic effect between the multiple oxide phases may together control the overall performance of a multi-component oxide sample. Also, the data of this study support the predominance of an ionic redox mechanism where the re-oxidation step is a rate-limiting process.