Single-atom iron as a promising low-temperature catalyst for selective catalytic reduction of NOx with NH3: A theoretical prediction

Abstract

Selective catalytic reduction of NOx with NH3 (NH3-SCR) is a dominant technology to reduce NOx (deNOx). However, there are two shortcomings for commercial deNOx catalysts (vanadium-titanium-based metal oxides), such as poor low-temperature efficiency and toxicity. Thus, it is urgent to develop environmentally friendly low-temperature catalysts with high deNOx efficiency. Therefore, we firstly proposed a single-atom iron coordinated with four N atoms (Fe1-N4) as a novel low-temperature NH3-SCR catalyst, due to its high coordination unsaturation and safety. The detailed reaction mechanisms are revealed via density functional theory calculations and microkinetic modeling. Seven possible reaction pathways were found in the NH3-SCR reaction. Different from metal oxides, special intermediates such as N2H and NHNO are found in the reaction pathway. The dominant pathway of the NH3-SCR reaction over the Fe1-N4 catalyst is a three-step process including NO oxidation, NO2 reduction, and NHNO decomposition. The suitable temperature window of the Fe1-N4 catalyst is <430 K due to its relatively low energy barrier of 0.99 eV. Different from other metal oxide catalysts, the fast oxidation of NO on Fe1-N4 catalyst significantly promotes the reaction rate of NH3-SCR on Fe1-N4 catalyst. Based on its outstanding performance, we believe that single Fe atom catalyst can provide new insights to design novel catalysts for NH3-SCR.