Construction of Surface Synergetic Oxygen Vacancies on CuMn2O4 Spinel for Enhancing NO Reduction with CO

The effectiveness of surface synergetic oxygen vacancy (SSOV) on a catalyst has been proposed in the selective reduction of NO to N 2 by CO. In this work, we prepared fresh CuMn 2 O 4 spinel catalyst using the freeze-assisted sol–gel method, and then engineered SSOVs through CO pretreatment (CO–CuMn 2 O 4 ) at 250 °C. The catalytic performance of the CO–CuMn 2 O 4 catalyst showed significant improvement, attributed to the presence of SSOVs, in comparison to that of the fresh CuMn 2 O 4 sample. Additionally, our findings elucidated the limited reactivity of surface oxygen vacancies (SOVs) on a single metal oxide, emphasizing the crucial role played by SSOVs. Experimental results, including NO temperature-programmed desorption-mass spectrometry and in situ diffuse reflectance infrared Fourier transform spectroscopy, provided further insights by suggesting that SSOVs facilitate the formation of N 2 O and its subsequent decomposition into N 2 . Density functional theory calculations have unveiled the pivotal role of SSOV in stabilizing the nitrogen atom derived from gaseous NO, facilitating the NO + CO → N* + CO 2 reaction. Notably, the energy barrier for this process is only 0.54 eV, which is the rate-determining step of the NO + CO reaction. In stark contrast, this reaction scarcely occurs on the SOVs of single CuO and Mn 2 O 3 surfaces. Furthermore, the presence of SSOVs considerably lowers the energy barrier for the conversion of N 2 O to N 2, with a minimal barrier of 0.12 eV. In contrast, the reduction of N 2 O by CO without SSOV assistance necessitates a significantly higher energy barrier of 2.77 eV. Extending our investigation, we engineered SSOVs on the CuFe 2 O 4 spinel catalyst and observed similar SSOV-mediated effects in the NO + CO reaction. Our research offers a comprehensive understanding of atomic-level role of SSOV, thereby offering valuable insights for the design of efficient NO + CO catalysts.