Taming NO oxidation efficiency by γ-MnO2morphology regulation

Nitric oxide (NO) emitted from the combustion of fossil fuels has drawn global concern, and the oxidation of NO contributes greatly to the DeNO(x)process. Herein, single-crystal gamma-MnO(2)catalysts with well-defined hollow-sphere-, sea-urchin-, and flower-like morphologies (gamma-MnO2-HS, gamma-MnO2-SU, and gamma-MnO2-F) were rationally designed and synthesizedviaan environmental-friendly template-free hydrothermal strategy. The physicochemical properties of the prepared materials were characterized by XRD, FE-SEM, TEM, BET, XPS, H-2-TPR, O-2/NO-TPD andin situDRIFTS, and their catalytic activities in NO oxidation were evaluated. The results showed the gamma-MnO2-HS sample possessed the highest activity and could oxidize 91.1% of NO at 275 degrees C, which was obviously higher than those of the gamma-MnO2-SU and gamma-MnO2-F catalysts. It was found that the presence of abundant surface-adsorbed oxygen and the largest quantity of Mn(3+)over the gamma-MnO2-HS material respectively accelerated the processes of NO adsorption and O(2)activation, which greatly promoted the NO oxidation process. This work provides significant insights into NO oxidation over gamma-MnO(2)catalysts.