Low temperature molten salt synthesis of porous La1-xSrxMn0.8Fe0.2O3 (0 ≤ x ≤ 0.6) microspheres with high catalytic activity for CO oxidation

Abstract

A molten salt method was developed to prepare porous La1-xSrxMn0.8Fe0.2O3 (0 ≤ x ≤ 0.6) microspheres using hierarchical porous δ-MnO2 microspheres as a template in eutectic NaNO3-KNO3. X-ray diffraction patterns showed that single phase LaMn0.8Fe0.2O3 with good crystallinity was synthesized at 450 °C after 4 h. Transmission electron microscope images exhibited that the LaMn0.8Fe0.2O3 sample obtained at 450 °C after 4 h possessed a porous spherical morphology composed of aggregated nanocrystallites. Field emission scanning electron microscope images indicated that the growth of the porous LaMn0.8Fe0.2O3 microspheres has two stages. SEM pictures showed that a higher calcination temperature than 450 °C had an adverse effect on the formation of a porous spherical structure. The LaMn0.8Fe0.2O3 sample obtained at 450 °C after 4 h displayed a high BET surface area of 55.73 m2/g with a pore size of 9.38 nm. Fourier transform infrared spectra suggested that Sr2+ ions entered the A sites and induced a decrease of the binding energy between Mn and O. The CO conversion with the La1-xSrxMn0.8Fe0.2O3 (0 ≤ x ≤ 0.6) samples indicated that the La0.4Sr0.6Mn0.8Fe0.2O3 sample had the best catalytic activity and stability. Further analysis by X-ray photoelectron spectroscopy demonstrated that Sr2+ doping altered the content of Mn4+ ions, oxygen vacancies and adsorbed oxygen species on the surface, which affected the catalytic performance for CO oxidation.