Catalytic\nActivity and Reaction Mechanism of Ru-Modified\nCe<sub>0.7</sub>Zr<sub>0.3</sub>O<sub><i>x</i></sub> Catalysts\nfor Selective Catalytic Oxidation of Ammonia

To solve the problem of the poor low-temperature NH<sub>3</sub> selective catalytic oxidation (NH<sub>3</sub>–SCO)\nperformance\nof CeZrO<sub><i>x</i></sub> catalysts, a series of Ru/CeZrO<sub><i>x</i></sub> catalysts with various Ru mass ratios were\nprepared via the impregnation–precipitation method. The introduction\nof Ru could significantly improve the low-temperature catalytic performance\nof CeZrO<sub><i>x</i></sub> catalysts from activity test\nresults. Among prepared catalysts, the catalyst with a Ru mass ratio\nof 0.5 wt % and a Ce/Zr molar ratio of 7:3 (denoted as Ru<sub>0.5</sub>/CZO) was considered to have an excellent NH<sub>3</sub>–SCO\nperformance; NH<sub>3</sub> conversion reached 100 and 91.2% N<sub>2</sub> selectivity at 237 °C. Physicochemical properties of\nRu<sub>0.5</sub>/CZO and CZO catalysts were compared through a series\nof characterization tests to investigate the relationship between\nthe introduction of Ru and the NH<sub>3</sub>–SCO performance.\nH<sub>2</sub>-TPR results revealed an interaction between the Ru and\nCe species. The introduction of Ru significantly shifted the reduction\npeak toward the lower-temperature direction, enhancing the low-temperature\nredox performance of the CZO catalyst. NH<sub>3</sub>-TPD results\nindicated that Ru<sub>0.5</sub>/CZO catalysts had abundant acid sites\non its surface, facilitating NH<sub>3</sub> adsorption and oxidation.\nIn situ DRIFTS characterization results indicated that the reaction\nmechanism of the Ru<sub>0.5</sub>/CZO catalyst might be both internal-selective\ncatalytic reduction (i-SCR) and imine (−NH) mechanisms.