Synthesis of Ru-W/CeZrO catalyst with superior NH-SCO performance: Synergy between Ru and W species.

Ammonia selective catalytic oxidation (NH-SCO) is an effective method for NH removal. However, it is still a great challenge to develop catalysts with a wide operating temperature window, high catalytic activity and N selectivity, particularly for the removal of high-concentration NH from NH-fueled engine exhaust gas. Herein, a small amount of Ru (0.5 wt%) together with W were used to co-modify CeZrO through impregnation method to synthesize a novel NH-SCO catalyst. The as-prepared Ru-W/CeZrO catalyst could achieve a complete NH conversion at 300 °C, and a superior N 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 NH-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 catalyst, significantly enhancing the low-temperature activity. Besides, the co-existing W species could suppress the excessive oxidation of NH on catalyst surface, which was crucial for improving N selectivity. In-situ DRIFTS results suggested that Ru-W/CeZrO catalyst followed both the internal selective catalytic reduction (i-SCR) and amide (-NH) mechanisms during NH-SCO reaction. More importantly, the NH species adsorbed on Ru-W/CeZrO catalyst surface reacted more rapidly than that of W/CeZrO catalyst, and were mainly converted to N rather than NO or NO under the synergy of Ru and W species.