NOx Reconstruction Triggered by Zeolite Reverses Alkali Metal Poisoning in NO Selective Catalytic Reduction

Alkali metal poisoning represents a formidable challenge for the effective utilization of ammonia selective catalytic reduction (NH3–SCR) technology. Herein, we propose a versatile strategy to radically circumvent the deactivation effect from alkali metals via regulated activation of surface NOx species. Activity test showed that after physical mixing with a series of zeolites (ZSM-5, MOR, and SAPO-34), the activity of the K-poisoned CeO2–MnOx catalyst achieved complete recovery, and the observed NO conversion was found to be even superior to that of the fresh catalyst. Mechanism analysis from in situ DRIFTS and TPSR revealed that K deposition shut off the transformation of surface NOx from chelating bidentate nitrites to bidentate nitrates (both bridging and chelating bidentate nitrates), leading to catalyst deactivation. Zeolite coupling introduced labile NO+ species, which interacted facilely with the chelating bidentate nitrites to generate chemically reactive bidentate nitrates, enabling a thorough regeneration of NH3–SCR performance. In addition to CeO2–MnOx, this strategy was also found to be valid for a variety of NH3–SCR catalysts, demonstrating great potential in reversing alkali metal poisoning.