Efficient α-MnO2 with (2 1 0) facet exposed for catalytic oxidation of toluene at low temperature: A combined in-situ DRIFTS and theoretical investigation

The α-MnO2 catalysts with (1 1 0), (2 1 0) and (3 1 0) crystal facets exposed were prepared via hydrothermal method and studied for the catalytic oxidation of toluene. Some characterization technologies and DFT theoretical calculation were combined to analyze the as-synthesized catalysts. The α-MnO2 catalyst exposed with the (2 1 0) plane displayed best catalytic performance and attained complete toluene conversion at 140 °C. The O2-TPD and XPS results exhibited the amount of surface lattice oxygen on α-MnO2-210 catalyst was largest. Lower accumulation and faster disintegration of intermediates which was characterized by in-situ DRIFTS could be discovered on the surface of α-MnO2-210 catalyst. The results of DFT calculation showed that the unique atomic arrangement of α-MnO2-210 catalyst enhanced the charge separation and conversion, promoting the formation of active oxygen and the activation of toluene. The Ea of α-MnO2-210 catalyst was 24.75 kJ mol−1, lowest among the three catalysts. This work highlights the facet effects on catalytic property and provides new insight into the understanding of catalytic oxidation reaction mechanism of toluene.