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

Abstract

AbstractBACKGROUNDSelective 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.RESULTSThe NOx conversion for K‐Fe/ZrO2 catalyst was <80% across the whole temperature range, and the catalyst was completely deactivated at ≈400 °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 °C (NOx conversion of >80%).CONCLUSIONAccording 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 Brønsted 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 Brønsted acid sites, significantly promoting NH3 adsorption and activation. W modification 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. © 2023 Society of Chemical Industry (SCI).