Insights into key parameters of MnO₂ catalyst toward high catalytic combustion performance

Controllable crystal phases (α-, β-, γ- and δ-) of MnO₂ materials were developed via tuning hydrothermal conditions and investigated in toluene catalytic combustion. Extensive characterization techniques such as XRD, BET, SEM, TEM, H₂-TPR and XPS were employed for analyzing the structure-performance relationship between physicochemical properties, such as specific surface area, vacancy/lattice oxygen and their mobility, reduction property and catalytic activity. Results indicated that the degradation activity of MnO₂ catalyst greatly hinges on materials intrinsic properties, namely the vacancy oxygen generation, lattice oxygen content and their reduction behaviors. α-MnO₂ exhibited the best catalytic activity (0.24 μmol/min @ 240 °C) among the obtained MnO₂ materials; however, its cycle stability was inferior to that of δ-MnO₂ catalyst owing to the different moderating effect of potassium ions remained within the tunnels or mezzanines structure. In addition, δ-MnO₂ showed an easiest reduction property among all the manganese oxides investigated. The findings will shed lights on designing of Mn-based catalysts with a higher VOCs combustion capacity.