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)-Ot-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.