Insight into the Potassium Poisoning Effect for Selective Catalytic Reduction of NOx with NH3 over Fe/Beta

Alkali metal poisoning has been a complex yet unresolved issue restricting the catalytic activity of NH3–SCR catalysts in industry to date. Herein, the effect of K deposition on the catalytic activity of Fe/beta catalysts for NH3–SCR of NOx was systematically investigated by a series of experimental characterizations and density functional theory (DFT) calculations. It has been determined that a lower K deposition could activate and facilitate the transfer of electrons and enhance the ratio of Fe2+/Fe3+ and reducible Fe species, thereafter promoting the NO and O2 adsorption and decreasing the activation energy of NO to NO2, and thereby significantly improving the catalytic activity of 0.25% K–Fe/Beta. To the best of our knowledge, this phenomenon has not been reported in the field of exhaust abatement. Nevertheless, excessive K deposition (≥0.50%) can not only occupy the Brönsted acid sites, leading to perceptible aggregation of the active Fe species and an increase in the activation energy for NO oxidation on Lewis acid sites, but also induce the generation of inactive nitrates, blocking the pore structure of the Beta molecular sieve, resulting in the distinctive reduction of catalytic active Fe species, thereby seriously restricting the catalytic performances of 0.50% K–Fe/beta and 1.0% K–Fe/beta catalysts. Thus, this study may shine light on the deep understanding of alkali metal poison during NH3–SCR of NOx and the design of advanced catalysts in heterogeneous catalysis in the future.