Morphologically controlled synthesis of porous spherical and cubic LaMnO3 with high activity for the catalytic removal of toluene.

A morphology-controlled molten salt route was developed to synthesize porous spherical LaMnO3 and cubic LaMnO3 nanoparticles using the as-prepared porous Mn2O3 spheres as template. The porous LaMnO3 spheres with an average pore size of about 34.7 nm and the cubic LaMnO3 nanoparticles with a good dispersion were confirmed by scanning electron microscope, transmission electron microscope, and N2 adsorption-desorption measurements. The mechanism of morphological transformation from the porous spherical structure to the cubic particle in the molten salt was proposed. The porous spherical LaMnO3 and cubic LaMnO3 catalysts exhibited high catalytic performance for the combustion of toluene, and the latter performed better than the former. Under the conditions of toluene/oxygen molar ratio = 1/400 and space velocity = 20,000 h(-1), the temperature required for 10, 50, and 90% toluene conversion was 110, 170, and 220 °C over the cubic LaMnO3 catalyst, respectively. Based on the results of X-ray photoelectron spectroscopic and hydrogen temperature-programmed reduction characterization, we deduce that the higher surface Mn(4+)/Mn(3+) molar ratio and better low-temperature reducibility enhanced the catalytic performance of cubic LaMnO3. Taking the facile morphology-controlled synthesis and excellent catalytic performance into consideration, we believe that the well-defined morphological LaMnO3 samples are good candidate catalytic materials for the oxidative removal of toluene.