Brønsted acid sites in MCM-22 zeolite as molecular "Grippers" to NH3 and potassium for boosting NH3-SCR performance and resistance to alkali.

The selective catalytic reduction of nitrogen oxides (NOx) with NH3 (NH3-SCR) in alkali-rich industrial flue gases (e.g., cement kilns) remains a pivotal challenge in environmental catalysis. Herein, we report a layered CeMoOx/MCM-22 catalyst that achieves > 80 % NOx conversion and > 95 % N2 selectivity over a broad temperature window of 250-530 °C, and crucially maintains > 80 % conversion even after exposure to 1 wt% K2O (a typical alkali metal poison in industrial flue gases). Combined in situ characterizations (X-ray absorption near-edge spectroscopy, diffuse reflectance infrared Fourier transform spectroscopy) and density functional theory (DFT) calculations reveal that the Brønsted acid sites of MCM-22 preferentially grip K⁺ ions with an adsorption energy (Ead) of -0.285 eV, effectively preserving the adjacent Ce3 + /Ce4+ redox centers in CeMoOx. The acidic sites of MCM-22 exhibit a strong affinity for NH3, with the captured NH3 species undergoing transfer to the oxide component in two distinct forms: molecular NH3 and protonated ammonium ions (NH4⁺). Notably, the NH4⁺ intermediate, characterized by its diagnostic infrared absorption band at 1450 cm-1, is effectively stabilized; this stabilization concomitantly suppresses parasitic NH3 over-oxidation under high-temperature conditions, a critical feature for maintaining robust catalytic performance in NH3-SCR. Compared with conventional V-based catalysts, CeMoOx/MCM-22 reduces NOx emissions by 40-60 % in cement kiln field tests, offering a sustainable catalyst design strategy for industrial NOx control with direct applicability to waste incineration and biomass energy sectors facing similar alkali poisoning issues.