SCR of NO with CH4 over Fe/Ga2O3-Al2O3 and the mechanism

Abstract

The selective catalytic reduction of NO with methane (SCR-CH4) is a very promising alternative method, however, the catalysts reported showed low catalytic activity for SCR-CH4. In order to improve the catalytic activity and resistance to H2O of the catalysts, Fe was introduced to modify the Ga2O3-Al2O3. The xFe/Ga2O3-Al2O3 catalysts were prepared with the co-precipitation method, and the SCR-CH4 performance was investigated. It was found that Fe improved the catalytic activity at medium and high temperatures, the N2 selectivity, and the resistance to H2O. Among all catalysts, the 5Fe/Ga2O3-Al2O3 catalyst achieved NO conversion of 76% and N2 selectivity of 100% at 500 ℃, and still maintained NO conversion of more than 60% in the presence of 5% H2O. Several characterization techniques, XRD, N2 adsorption-desorption, XPS, UV–Vis, H2-TPR, Py-IR, etc., were used to explore the relationship between the catalytic activity and structure. The results showed that after the doping of Fe, the pore diameter was increased, resulting in a promotion in the resistance to H2O. In addition, the redox properties and Lewis acid content of the catalysts were promoted by the Fe species, where the isolated Fe3+ species contribute to the catalytic activity at medium and high temperatures. In situ DRIFTS revealed that NO, CH4, and O2 were adsorbed and reacted on the catalyst surface to form various nitrates, formate, and R-NCO species, where O2 can promote the formation of bidentate nitrates.