Taming NO oxidation efficiency by γ-MnO2 morphology regulation†
Abstract
Nitric oxide (NO) emitted from the combustion of fossil fuels has drawn global concern, and the oxidation of NO contributes greatly to the DeNOx process. Herein, single-crystal γ-MnO2 catalysts with well-defined hollow-sphere-, sea-urchin-, and flower-like morphologies (γ-MnO2-HS, γ-MnO2-SU, and γ-MnO2-F) were rationally designed and synthesized via an environmental-friendly template-free hydrothermal strategy. The physicochemical properties of the prepared materials were characterized by XRD, FE-SEM, TEM, BET, XPS, H2-TPR, O2/NO-TPD and in situ DRIFTS, and their catalytic activities in NO oxidation were evaluated. The results showed the γ-MnO2-HS sample possessed the highest activity and could oxidize 91.1% of NO at 275 °C, which was obviously higher than those of the γ-MnO2-SU and γ-MnO2-F catalysts. It was found that the presence of abundant surface-adsorbed oxygen and the largest quantity of Mn3+ over the γ-MnO2-HS material respectively accelerated the processes of NO adsorption and O2 activation, which greatly promoted the NO oxidation process. This work provides significant insights into NO oxidation over γ-MnO2 catalysts.