Enhanced Catalytic Oxidation of Toluene over Manganese Oxide Modified by Lanthanum with a Coral-Like Hierarchical Structure Nanosphere

Coral-like lanthanum manganese oxides (LayMnOx) with a hierarchical structure nanosphere were successfully prepared using a simple method, which presented a high-efficiency catalytic performance for toluene combustion. Among them, La0.08MnOx with the Mn3O4 phase exhibits superior catalytic activity, such as a lower T95 value (218 °C), excellent H2O resistance, and catalytic stability. The effects of La addition on the bulk and surface physicochemical properties of LayMnOx were investigated by sorts of characterization including X-ray diffraction, scanning electron microscopy, transmission electron microscopy, N2 adsorption–desorption, temperature-programmed reduction with H2, temperature-programmed desorption of O2, X-ray photoelectron spectroscopy, and so forth. The results demonstrate that the doping of La can induce the variation of physicochemical properties and the formation of more surface oxygen species and high valence state amorphous manganese oxides, improving low-temperature reducibility, which facilitates good catalytic activity for La0.08MnOx. A series of in situ diffuse reflectance infrared Fourier transform spectroscopy experiments for toluene adsorption were performed on the La0.08MnOx catalyst pretreated under different atmosphere conditions to investigate the role of oxygen species and the reaction processes. The results indicate that the abundant surface oxygen species over La0.08MnOx can make the rapid formation of benzoic acid species, further transfer into CO2 and H2O, which is considered as the key factor in the activation and oxidation of toluene.