Synthesis of Ru-W/CeZrO_x catalyst with superior NH₃-SCO performance: Synergy between Ru and W species

Ammonia selective catalytic oxidation (NH₃-SCO) is an effective method for NH₃ removal. However, it is still a great challenge to develop catalysts with a wide operating temperature window, high catalytic activity and N₂ selectivity, particularly for the removal of high-concentration NH₃ from NH₃-fueled engine exhaust gas. Herein, a small amount of Ru (0.5 wt%) together with W were used to co-modify CeZrO_x through impregnation method to synthesize a novel NH₃-SCO catalyst. The as-prepared Ru-W/CeZrO_x catalyst could achieve a complete NH₃ conversion at 300 °C, and a superior N₂ selectivity, which exceeded 95.7 % over a wide temperature range of 225-400 °C. The physicochemical properties of the prepared catalysts were compared using various characterization techniques to reveal the possible roles of Ru and W species in NH₃-SCO reaction. XPS results showed that the introduction of Ru species was in favor of forming abundant surface adsorbed oxygen species on the surface of Ru-W/CeZrO_x catalyst, significantly enhancing the low-temperature activity. Besides, the co-existing W species could suppress the excessive oxidation of NH₃ on catalyst surface, which was crucial for improving N₂ selectivity. In-situ DRIFTS results suggested that Ru-W/CeZrO_x catalyst followed both the internal selective catalytic reduction (i-SCR) and amide (-NH) mechanisms during NH₃-SCO reaction. More importantly, the NH₃ species adsorbed on Ru-W/CeZrO_x catalyst surface reacted more rapidly than that of W/CeZrO_x catalyst, and were mainly converted to N₂ rather than NO_x or N₂O under the synergy of Ru and W species.