Catalytic Activity and Reaction Mechanism of Ru-Modified Ce0.7Zr0.3Ox Catalysts for Selective Catalytic Oxidation of Ammonia

Abstract

To solve the problem of the poor low-temperature NH₃ selective catalytic oxidation (NH₃–SCO) performance of CeZrO_x catalysts, a series of Ru/CeZrO_x catalysts with various Ru mass ratios were prepared via the impregnation–precipitation method. The introduction of Ru could significantly improve the low-temperature catalytic performance of CeZrO_x catalysts from activity test results. Among prepared catalysts, the catalyst with a Ru mass ratio of 0.5 wt % and a Ce/Zr molar ratio of 7:3 (denoted as Ru_0.5/CZO) was considered to have an excellent NH₃–SCO performance; NH₃ conversion reached 100 and 91.2% N₂ selectivity at 237 °C. Physicochemical properties of Ru_0.5/CZO and CZO catalysts were compared through a series of characterization tests to investigate the relationship between the introduction of Ru and the NH₃–SCO performance. H₂-TPR results revealed an interaction between the Ru and Ce species. The introduction of Ru significantly shifted the reduction peak toward the lower-temperature direction, enhancing the low-temperature redox performance of the CZO catalyst. NH₃-TPD results indicated that Ru_0.5/CZO catalysts had abundant acid sites on its surface, facilitating NH₃ adsorption and oxidation. In situ DRIFTS characterization results indicated that the reaction mechanism of the Ru_0.5/CZO catalyst might be both internal-selective catalytic reduction (i-SCR) and imine (−NH) mechanisms.