Unraveling the effects of the coordination number of Mn over α-MnO2 catalysts for toluene oxidation

Herein, nanorod-like a-MnO2 catalysts with 5-, 4-, and 3-coordinated Mn exposed on the surface (alpha-MnO2-Mn-5c, alpha-MnO2-Mn-4c, and alpha-MnO2-Mn-3c) were employed for toluene combustion. The toluene combustion performance followed an order of alpha-MnO2-Mn-4c > alpha-MnO2-Mn-3c > alpha-MnO2-Mn-5c. The effects of the coordination number of Mn over alpha-MnO2 catalysts for toluene oxidation were unraveled. The excellent activity of alpha-MnO2-Mn-4c was due to stronger interactions between Mn-4c with reactants and a larger amount of charge transfer from the Mn-4c to the adsorbed O-2, as evidenced by computational results. The results of operando diffuse reflectance infrared Fourier transform spectroscopy and gas chromatography-mass spectrometry revealed that toluene oxidation over alpha-MnO2 catalysts proceeded by coordination number-dependent rate-determining step. For alpha-MnO2-Mn-4c, the rate-determining step was the cleavage of benzene species, while decarboxylation of benzoic acid was more sluggish for alpha-MnO2-Mn-5c. These findings strongly pave a way for understanding the coordination number-induced improvement of catalytic performance of nanorod-like alpha-MnO2 catalysts for toluene oxidation and a deeper understanding of the mechanism of toluene degradation.