Promotional Catalytic Activity of Bifunctional Ru-Ce-Zr Catalysts forNH3-SCO by Deposition Order of Dual Active Components

The ammonia fuel injected into the combustion chamber cannot be completely combusted resulting in high levels of escaped ammonia in the ammonia-fueled engine exhaust. It is a feasible way to obtain ammonia selective catalytic oxidation (NH₃-SCO) catalysts with excellent performance using noble metal-transition metal catalysts. In this work, a series of Ru-Ce-Zr bifunctional catalysts were synthesized by precipitation and impregnation methods to investigate the influence of introduction methods of different active components (Ru and Ce) on their physicochemical properties and NH₃-SCO performance. Among them, the BET and NH₃-TPD results showed that Ru-Ce/ZrO₂ (RC/Z) catalyst had the largest specific surface area and NH₃ desorption amount, indicating that its surface could capture more NH₃. More importantly, compared to other catalysts, RC/Z catalyst exhibited highest relative concentration of Ce³⁺, which facilitated electron transfer via Ce⁴⁺ + Ru³⁺ ↔ Ce³⁺ + Ru⁴⁺. The Ru-Ce/ZrO₂ catalyst exhibited the best catalytic performance under the strong interaction between Ru and Ce species. its NH₃ conversion reached 100% and N₂ selectivity was 95.7% at 237 °C. The N₂ selectivity exceeded 70% over a wide temperature range of 150–400 °C. In situ diffuse reflectance infrared Fourier transform spectroscopy (in-situ DRIFTS) showed that the surface of RC/Z catalyst exhibited the highest amount of Lewis and Brønsted acid sites, which might be one of the reasons for its excellent N₂ selectivity. This work revealed the effect of the way of introduction of Ru and Ce active species on their NH₃-SCO performance.

Graphical Abstract