Cu-OFF/ERI Zeolite: Intergrowth Structure Synergistically Boosting Selective Catalytic Reduction of NOx with NH3

Revealing the synergistic effect of InO+ and Brønsted acid on the superior activity of hybrid In/H-SSZ-39 in the selective catalytic reduction of NOx with CH4

Selective catalytic reduction of NOx with CH4 (CH4-SCR) is a promising strategy for NOx abatement that utilizes CH4 escaping from the incomplete combustion of liquefied natural gas (LNG) to reduce NOx. However, developing CH4-SCR catalysts with high efficiency at temperature < 450°C remains a significant challenge. Herein, this work reported an In/H-SSZ-39-Hy zeolite catalyst (Hy represents hybrid AEI/MOR topology) with superior activity by utilizing the synergistic effect of InO+ and Brønsted acid (BA). The maximum NOx conversion (74 %) achieved over the In/H-SSZ-39-Hy at 430°C with a gas hourly space velocity (GHSV) of 48,000 h-1, which was significantly higher than that over the commercial In/H-SSZ-39 and In/H-SSZ-13 catalysts. A series of characterizations revealed that abundant BA sites and surface adsorbed oxygen contributed to the formation of reactive InO+ and nitrate species, which played a critical role in facilitating CH4 activation and redox cycling. In situ DRIFTS confirmed that CH4 was activated at the InO+ site and reacted with nitrate at the BA sites to form the important intermediate CH3NO2, which further converted to N2, CO2 and H2O. This study elucidates the synergistic roles of InO+ and BA in CH4-SCR, and provides a deeper understanding of catalytic mechanism.

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

As the frontier of environmental catalysis, mercury removal by deNOx 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.