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

Abstract

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