Revealing the influencing mechanism of CO2 on SCR of NOx with NH3 over FeW mixed oxide catalyst: interactions of carbonate-Fe2O3–FeWO4

Abstract

The effect of CO₂, a major component of the exhaust gas, on the elimination of NO_x over FeW oxide catalyst was studied. It reveals that the presence of CO₂ inhibits NO_x conversion and N₂ selectivity, which is due to the triple interactions of carbonate-Fe₂O₃–FeWO₄. CO₂ could be adsorbed to form carbonate species. The electron interactions between carbonate species and FeW oxides decrease the electron cloud density of Fe and W, leading to the increment of electrophilicity of metal species and thereby promoting the formation of nitrates. Meanwhile, a new reaction mechanism is proposed in which the NO₂ species formed on the catalyst surface can react with the adsorbed NH₃ or NH₄⁺ by following the E–R mechanism. Meanwhile, NO₃⁻ could combine with NH₄⁺ to form the NH₄NO₃ intermediate, which disciplines the L–H mechanism.