Design of single-atom catalysts for NO oxidation using OH radicals

Abstract

The catalytic oxidation of NO is an effective route for removing NO. However, achieving high oxidation efficiency of NO at a low temperature remains a great challenge. Therefore, the challenge for NO oxidation was addressed via adopting an advanced oxidation method of OH radicals over the emerging single-atom catalysts (SACs). Through spin-polarized density functional theory calculations, the reaction paths of NO oxidation with OH radicals over 8 types of TM–N₄–C SACs were explored. Based on the linear scaling relationship and Brønsted–Evans–Polanyi relationship, a kinetic volcano model of NO oxidation was established using OH adsorption energy as a descriptor. Through screening 3d, 4d, and 5d transition metals of SACs, Fe–N₄–C was found to have the highest reaction rate among them. The energy barrier is only 0.86 eV for the rate-determining step of NO oxidation over Fe–N₄–C, indicating that the catalytic oxidation of NO can efficiently take place at room temperature. Based on the linear relationship of adsorption energy between O and OH, the catalytic reactions of NO oxidation using O₂ and OH radicals were plotted in the unified volcano map with O adsorption energy as the descriptor. Obviously, the catalytic oxidation of NO using OH radicals has a higher activity than that using O₂ for the system of SACs. Furthermore, the catalytic activity origin was analyzed through the electronic properties of SACs, such as Bader charge, electronegativity, and d-band center. This study provides a new approach for the current NO oxidation, which can guide us in the screening of catalysts and experimental preparation work in the future.