Structural, Magnetic and Catalytic Properties of Non-Stoichiometric Lanthanum Ferrite Nano-Perovskites in Carbon Monoxide Oxidation

Abstract

Perovskite-type oxides of LaFe(1+x)O(3+δ) (x = 0.0, 0.2, 0.5 and 0.7) were synthesized by citrate sol–gel method to ensure the formation of nanosized perovskites. The physicochemical properties of these LaFe(1+x)O(3+δ) materials were characterized by thermal gravimetric/differential analyses, Fourier transform infrared spectroscopy, X-ray powder diffraction, scanning electron and transmission electron microscopies, ultraviolet-visible spectroscopy, Brunauer Emmett Teller nitrogen absorption, electrical conductivity measurements and magnetic studies. Catalytic performances of the prepared materials were evaluated for the carbon monoxide oxidation. Trace of FeCO3 and Fe2O3 phases were detected over the perovskites of LaFe(1+x)O(3+δ) with excess iron (x > 0) using the XRD and FT-IR studies. The SEM results demonstrate the formation of non-spongy particles. The magnetic measurements show a charge ordering transition at ~230 K for LaFe1.2O(3+δ) perovskite. The weak long range charge ordering of Fe2+/Fe3+ destroys over an increase in the content of the phases other than LaFeO3 perovskite. The best σox/σRed and the lowest Ec is accounted for the more suitable path for catching and giving of the gas phase oxygen over LaFe1.2O(3+δ) nanoperovskite; meaning most favorable redox properties. The light off temperature of the CO oxidation in terms of reducibility studies is decreased about 70°C over crystalline LaFe1.2O(3+δ) catalyst.