Mixed‐Impurity Co‐Poisoning of NH ₃ ‐SCR Catalysts: Poisoning Mechanisms, Antagonistic Effects, and Anti‐Inactivation Strategies

ABSTRACT Industrial flue gases rarely contain only one type of toxic substance. Instead, alkali/alkaline‐earth metals, heavy metals, sulfur species, and phosphorus often coexist and interact with NH 3 ‐SCR catalysts in a nonadditive manner. This review mainly summarizes the research progress on various poisons exposure over the past 5 years, with a focus on combinations involving anion and alkali/heavy metals, SO 2 and alkali/heavy metals, alkali or alkaline‐earth metals and heavy metals, P and alkali/heavy metals, as well as combinations of heavy metals. Coexisting toxins often synergistically leads to catalyst deactivation. The main pathways include the concurrent loss of Brønsted and Lewis acidity of the catalyst, weakened redox ability, formation of chlorides or sulfates, pore blockage, and obstruction of electron and oxygen transport at the interface between the active phase and the support. Antagonistic effects also appear when toxic substances cross chelate into inert phases, such as Ca–As–O complexes or sulfates/phosphates of alkali/heavy metals. The active sites occupied by the toxic substances will be released and partially restore their adsorption and activation capabilities for reactants. From these cases, three practical strategies have emerged: establishing sacrificial capture domains for alkali and heavy metals, protecting the active phase with shells or layered porous carrier that intercepts deposit, and introducing co‐catalysts to enhance oxygen migration rate and acid‐site density, thereby maintaining the Langmuir–Hinshelwood and Eley–Rideal routes. These insights clarify the relationship between the structure and function of NH 3 ‐SCR catalysts, and outline strategies for maintaining strong NH 3 ‐SCR performance under typical mixed impurity conditions in sintering and other industrial flue gases.