Acid-etched defect engineering in spinel CoMn2O4: Synergizing oxygen and cation vacancies to unlock high NH3-SCR performance

Spinel oxides hold considerable potential for NH₃-SCR reaction, but poor inherent activity and untreatable surface defects restrict their practical application. Herein, we proposed a strategy to synergistically modulate oxygen vacancies and cation vacancies by acid etching in spinel CoMn₂O₄. Nitric acid selectively solubilizes weakly coordinated Co²⁺ to produce cobalt vacancies, while the destabilization of O^2- coordinated to Co²⁺ may induce the formation of oxygen vacancies. Oxygen vacancies contribute to the generation of reactive oxygen species to facilitate NO reduction, while cobalt vacancies increase the density of acid sites to improve the adsorption and activation of NO and NH₃. DFT calculations reveal that oxygen vacancies and cobalt vacancies optimize the electronic structure, especially the electron density and energy level distribution near the Co and Mn sites, enhancing the electron exchange and redox properties. In-situ DRIFTS analysis proves that this cooperative regulation improves NH₃-SCR performance by facilitating the adsorption and conversion of intermediates. Therefore, CoMn₂O₄/N_0.10 shows high efficiency and anti-poisoning capability at a wide operating temperature, with above 90 % NO conversion from 165 to 400 °C. These findings present new insights into designing spinel oxide with high wide-temperature NH₃-SCR activity, expected to break the limitated operating temperature.