Catalytic Oxidation of NO over Fe-Doped MnO₂ Catalyst

Abstract

Fe-doped MnO 2 (Fe-MnO 2 ) generally exhibits higher NO oxidation activity than MnO 2 , which is widely attributed to the promoting effect of surface chemisorbed oxygen species (O ads ) adsorbed on surface oxygen vacancies (SOVs) generated upon Fe doping. Whether the higher content of SOVs and thus higher content of O ads can be achieved by increasing the content of Fe precursor in synthesis and whether higher content of SOVs in MnO 2 can lead to higher NO oxidation activity remain to be investigated. Herein, Fe-MnO 2 catalysts with different Mn/Fe molar ratios were synthesized by a simple coprecipitation method based on the comproportionation reaction between Mn 7+ and Mn 2+ 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 MnO 2 , such as crystalline phase, textural property, and redox property, but increasing the content of Fe cannot monotonically increase the content of SOVs in Fe-MnO 2 catalyst. NO oxidation test shows that the Fe-MnO 2 catalyst with higher content of SOVs exhibits higher NO oxidation activity. The enhanced NO oxidation activity observed on MnO 2 after Fe doping should result from its higher content of SOVs and O ads , 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.

Highly Active and Water-Resistant Cu-Doped OMS-2 Catalysts for CO Oxidation: The Importance of the OMS-2 Synthesis Method and Cu Doping

“…It is widely accepted that O ads is associated with the oxygen vacancy in Mn oxides. 21 The O ads /O latt ratio decreases in the following order: OMS-2 S (0.45) > OMS-2 R (0.41) > OMS-2 H (0.39). Figure 4c depicts the Mn 2p spectra of the three catalysts.…”

“…The H 2 -TPR profiles of the three catalysts shown in Figure c reveal that OMS-2 S has the lowest reduction temperature, followed by OMS-2 R and then OMS-2 H . This suggests that OMS-2 S has higher oxygen mobility compared to OMS-2 R and OMS-2 H as a lower reduction temperature indicates higher oxygen mobility . This higher oxygen mobility is advantageous for the CO oxidation reaction.…”

“…Two peaks, corresponding to lattice oxygen (O latt ) and chemisorbed oxygen (O ads ), can be observed in the deconvoluted O 1s spectra of all three catalysts. It is widely accepted that O ads is associated with the oxygen vacancy in Mn oxides . The O ads /O latt ratio decreases in the following order: OMS-2 S (0.45) > OMS-2 R (0.41) > OMS-2 H (0.39).…”

“…This suggests that OMS-2 S has higher oxygen mobility compared to OMS-2 R and OMS-2 H as a lower reduction temperature indicates higher oxygen mobility. 21 This higher oxygen mobility is advantageous for the CO oxidation reaction.…”

Highly Efficient Ce and Co Codoped OMS-2 Catalyst for NO Oxidation

“…Various catalysts, mainly including metal oxides, molecular sieves, carbon materials, noble metals, and perovskite oxides, have been investigated for NO oxidation . Among these catalysts, non-noble transition metal oxides, represented by MnO 2 , have stood out because of their low cost and relatively good NO oxidation performance. − It is reported that the surface-active oxygen species (chemisorbed oxygen especially) in MnO 2 play important roles in catalyzing NO oxidation, and improving the concentration of active oxygen species has been demonstrated to be effective in enhancing catalytic activity. , …”