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

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 Bronsted-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. Volcano plot of NO oxidation using OH and O2 over TM-N4-C.