Mechanisms for Modifying the Electronic and Spatial Distribution of the Single-Atom Ni/CeO₂ Surface to Enhance CO-SCR Reactivity: Density Functional Theory Study

Modulating the intrinsic activity of heterogeneous catalysts at the atomic level is an effective strategy to improve the low-temperature CO-SCR (selective catalytic reduction) reaction activity and N₂ selectivity, but it remains challenging by the experiment. In this paper, a single-atom-loaded surface generation strategy is developed to construct single-atom catalysts by density functional theory analysis, which will effectively reduce the reaction energy barriers in CO-SCR reaction. Specifically, the reaction of NO reduction by CO before and after Ni adsorption was thoroughly investigated and the reactivity was evaluated by using the CeO₂ (1 1 1) surface as a carrier, with the application of density functional theory, electronic structure analysis, and transition state theory. The loading of Ni increases the energy barrier for the generation of N₂O on the CeO₂ (1 1 1) surface by 1.498 eV and decreases the energy barrier for the generation of N₂ by 1.864 eV. This indicates that the adsorption of Ni inhibits the generation of N₂O and promotes the generation of N₂. After thermodynamics and kinetics analysis, the pathway of CeO₂ (1 1 1)-O_t-Ni via O atoms filling O vacancies to generate N₂ is a spontaneous unidirectional reaction when no nonvolumetric work is done at constant temperature and pressure. Theoretical calculations show that the modification of isolated Ni atoms on CeO₂ induces electronic coupling and redistribution, which leads to the activation of neighboring O sites around Ni atoms. This study provides the strategy mechanism to enhance the activity and N₂ selectivity of the low-temperature CO-SCR reaction at the atomic level and provides theoretical guidance for the theory of novel catalysts for synergistic removal of NO and CO.