Promoting effect of Cu as electron transfer medium on NH-SCO reaction in asymmetric Ag-O-Ti-Sm-Cu ring active site.

Selective catalytic oxidation of ammonia (NH-SCO) has become an effective method to reduce ammonia (NH) emissions, and is a key part to solve the problem of NH pollution. Nevertheless, the optimization of this technology's performance relies heavily on innovation and the development of catalyst design. In this study, a SmCuAgTiO catalyst with an asymmetric Ag-O-Ti-Sm-Cu ring active site was prepared and applied to the NH-SCO reaction. The low conversion of Cu-based catalysts in NH at low temperature and the inherent low N₂ selectivity of Ag-based catalysts were solved. The successful creation of the asymmetric ring active site improved the catalyst's reduction performance. Additionally, Cu, acting as an electron transfer medium, plays a crucial role in enhancing electron transfer within the asymmetric ring active site, thus increasing the redox cycle of the catalyst during the reaction. In addition, some lattice oxygen is lost in the catalyst, resulting in the formation of a large number of oxygen vacancies. This process stimulates the adsorption and activation of surface-adsorbed oxygen, facilitating the conversion of NH to an amide (NH) intermediate during the reaction and reducing non-selective oxidation. The N selectivity was improved without significantly affecting the performance of Ag-based catalyst. In-situ diffuse reflectance fourier transform infrared spectroscopy (In-situ DRIFTS) analysis reveals that the SmCuAgTiO catalyst primarily follows an "internal" selective catalytic reduction (iSCR) mechanism in the NH-SCO reaction, complemented by the imide mechanism. The asymmetric Ag-O-Ti-Sm-Cu ring active site developed in this study provides a new perspective for efficiently solving NH pollution in the future.