Engineering the grain boundary and surface sites of binary Cu–Mn catalysts to boost CO oxidation†

The catalytic oxidation of CO over Cu-based catalysts has garnered significant interest due to their promising potential in addressing environmental pollution and enhancing industrial processes. Herein, we report a dual-stimuli strategy to boost the catalytic performance of CO oxidation via synergistically harnessing active Cu⁺ species with oxygen vacancies by engineering the grain boundary of Cu–Mn catalysts. Nanorod-like MnO₂ with a tunnel structure was prepared by a hydrothermal method and employed as the catalyst support, where different amounts of Cu were further introduced via impregnation to obtain Cu/MnO₂ catalysts. It is found that apart from the highly dispersed Cu species within the MnO₂ lattice to create lattice mismatch and distortion, some Cu are present as oxidized nanoparticles over the MnO₂ surface, thus sparking off increased dislocations and grain boundaries. A combination of characterization methods demonstrates that the proportion of active Cu⁺ species decreases with increasing amount of Cu, presenting an inverse relationship to the abundance of oxygen vacancies over the catalyst surface. Correspondingly, both Cu⁺ species and oxygen vacancies are identified as the main active sites for the adsorption and activation of CO and O₂, respectively. Therefore, a trade-off between the percentage of active Cu⁺ species and oxygen vacancies for the 15% Cu/MnO₂ catalyst with a moderate Cu introduction contributes to its highest catalytic activity, with T₅₀ and T₉₀ reaching 66 °C and 89 °C, respectively. This investigation highlights the potential of synergistically harnessing active Cu⁺ species with oxygen vacancies via grain boundary engineering for enhanced catalytic performance in CO oxidation applications.