Coordination engineering for single-atom catalysts in bifunctional oxidation NO and mercury

Abstract

Catalytic oxidation of NO and Hg0 in flue gas is essential for environmental protection. Some state-of-the-art single-atom catalysts (SACs) have shown good catalytic performance for NO and Hg0 in both theoretical and experimental aspects. However, the catalytic activity of currently reported catalysts for the oxidation NO and Hg0 still need to be promoted. Here, we report a method to reduce the reaction energy barrier via doping different p-block elements to regulate the coordination environment of single-atom cobalt catalysts. Through spin polarization density functional theory calculations, 64 stable structures were obtained from 122 SACs with different coordination environments. To analyze their catalytic activity performance for oxidation NO and Hg0, the adsorption energy for O2, O, and NO was calculated. The results show that the coordination environment can effectively regulate the adsorption energy of O2 (−0.24 to −1.98 eV) and O (0.40 to −3.65 eV). Four potentially high-activity catalysts were obtained based on their suitable adsorption energies for O2 and O atoms. Furthermore, the energy barriers for catalytic oxidation of NO and Hg0 over Co1P2C2-pen are 0.98 and 2.14 eV, respectively, which are 0.33 and 0.42 eV lower than Fe1N4 currently reported in the experiment. Moreover, by microkinetic modeling, the turnover frequency (TOF) of these four catalysts in the catalytic oxidation of NO and Hg0 were calculated. Finally, pCOHP and charge transfer characteristic of Co1P2C2-pen is calculated to reveal its origin of high activity from the electronic structure. Co1P2C2-pen can be used for the bifunctional catalytic oxidation of NO and Hg0. Most importantly, this study shows that adjusting the coordination environment of the active metal center can significantly improve the catalytic activity of SACs in the catalytic oxidation NO and Hg0.