Catalytic Oxidation of NO over Fe-Doped MnO2 Catalyst

Fe-doped MnO2 (Fe-MnO2) generally exhibits higher NO oxidation activity than MnO2, which is widely attributed to the promoting effect of surface chemisorbed oxygen species (Oads) adsorbed on surface oxygen vacancies (SOVs) generated upon Fe doping. Whether the higher content of SOVs and thus higher content of Oads can be achieved by increasing the content of Fe precursor in synthesis and whether higher content of SOVs in MnO2 can lead to higher NO oxidation activity remain to be investigated. Herein, Fe-MnO2 catalysts with different Mn/Fe molar ratios were synthesized by a simple coprecipitation method based on the comproportionation reaction between Mn7+ and Mn2+ by adjusting the Mn/Fe molar ratio in precursor. Physicochemical characterization shows that Fe doping can not only increase the content of SOVs but also significantly influence the other physicochemical properties of MnO2, such as crystalline phase, textural property, and redox property, but increasing the content of Fe cannot monotonically increase the content of SOVs in Fe-MnO2 catalyst. NO oxidation test shows that the Fe-MnO2 catalyst with higher content of SOVs exhibits higher NO oxidation activity. The enhanced NO oxidation activity observed on MnO2 after Fe doping should result from its higher content of SOVs and Oads, improved oxygen mobility, and more adsorption sites resulting from its larger specific surface area and pore volume as well as the additional adsorption sites provided by Fe ions.