Comparative study on K-tolerance performance of Fe/ZrO2 and Fe/ZrO2-W catalysts for NH3-SCR of NOx

BACKGROUND: Selective catalytic reduction (SCR) of nitrous oxides (NOx) with ammonia (NH3) as reductant is used worldwide in mobile and stationary sources to reach strict emission standards. It is a feasible strategy to modify support with acidic metal oxides to improve the alkali metal potassium (K) tolerance of SCR catalysts. Herein, a comparative investigation was conducted based on iron/zirconium dioxide (Fe/ZrO2)and Fe/ZrO2-tungsten (W) catalysts to reveal the correlation of support modification with W and K-tolerance performance. RESULTS: The NOx conversion for K-Fe/ZrO2 catalyst was <80% across the whole temperature range, and the catalyst was completely deactivated at approximate to 400 degrees C. As expected, the Fe/ZrO2-W catalyst exhibited a much superior anti-K-performance in comparison to the Fe/ZrO2 catalyst. The active temperature window for K-Fe/ZrO2-W catalyst was 285-485 degrees C (NOx conversion of >80%). CONCLUSION: According to the characterization results, it was found that K-species impose a negative impact on NH3 adsorption on the surface of the Fe/ZrO2 catalyst, especially drastically preventing the adsorption of NH3 species on Bronsted acid sites, thus inhibiting the occurrence of SCR reactions via the Langmuir-Hinshelwood (L-H) mechanism. By contrast, W modification resulted in more chemisorbed oxygen, stronger redox capacity and an increased Fe3+/(Fe3++Fe2+) ratio on the surface of the Fe/ZrO2-W catalyst. More importantly, W modification brought about abundant Bronsted acid sites, significantly promoting NH3 adsorption and activation. Wmodification also weakened the adsorption stability of NOx species to a certain extent. As a result, SCR reactions over the Fe/ZrO2-W catalyst could proceed via both Eley-Rideal (E-R) and L-H pathways. (c) 2023 Society of Chemical Industry (SCI).