Secondary-ion-promoted active site redistribution in molecular sieves: A strategy to enhance catalyst bifunctionality

As the frontier of environmental catalysis, mercury removal by deNO_x unit over bifunctional catalyst has emerged. However, it is fundamentally challenging to achieve simultaneous NO and mercury removal in industrial flue gas due to the commercial selective catalytic reduction (SCR) molecular sieves' lack of demercuration active centers. Herein, we demonstrate an active site in situ reconfiguration approach to enhance the oxidation of elemental mercury and immobilize divalent mercury by modified commercial SCR catalysts. Under extreme test conditions (mercury concentrations above 1200 μg/m³), the modified catalysts exhibited a 94 % and 183 % increase in mercury oxidation performance at 200 and 300°C, respectively, along with an expansion of the SCR reaction's T90 temperature window by 100 °C. Theoretical calculations and experimental characterization results indicate that the secondary introduction of high oxidation state ions induces a redistribution of the ratio and quantity of key active species ([ZCu²⁺(OH)]⁺, Z₂Cu²⁺, and CuO) through occupation and charge transfer. The increase of Cu species at the lowest energy site along the Hg transfer pathway, i.e., at the center of the eight-membered ring plane, enhances Hg oxidation performance. Correspondingly, the reduction of CuO and Cu⁺ species increases low-temperature NO reduction activity. Active species reconfiguration ensures significant bifunctional performance to increase the match of the temperature window of the synergistic reaction, offering potential for application in the next generation of flue gas treatment systems in industrial boilers.