LaMnO3 perovskite oxides prepared by different methods for catalytic oxidation of toluene

Abstract

Perovskite-type oxides of LaMnO3 (LMO) were synthesized by citrate sol–gel (SG), glycine combustion (GC) and co-precipitation (CP) methods, respectively. The physicochemical properties of these LaMnO3 materials were characterized by XRD, N2 sorption, H2-TPR and O2-TPD. Their catalytic performances were evaluated for the oxidation of toluene. It was shown that well-formed perovskite structures were obtained over samples LMO-SG and LMO-GC. Traces of La2O3 phase were detected over sample LMO-CP. The ranking in terms of specific surface area, low-temperature reducibility and concentration of surface adsorbed oxygen species from the highest to the lowest value was LMO-SG>LMO-CP>LMO-GC, which was in good agreement with the catalytic activity order. Sample LMO-SG exhibited the optimum catalytic activity and durability without any deactivation observed during the steady state of 60h. Its superior catalytic performance could be greatly attributed to its higher specific surface area, better low-temperature reducibility and more available surface adsorbed oxygen species. The apparent activation energies of samples LMO-SG, LMO-GC and LMO-CP were 71, 84 and 76kJmol−1, respectively. The lowest apparent activation energy of sample LMO-SG was in good agreement with its better catalytic behavior for toluene oxidation.