Relayed Regeneration of Multiple Metals-Poisoned Catalysts for Elimination of NO_x from Flue Gases

Ammonia selective catalytic reduction (NH₃–SCR) technology is an essential method for reducing NO_x emissions from flue gases, but catalyst deactivation due to poisoning remains a significant challenge, leading to reduced lifespans and increased hazardous waste. To address this issue, we propose a novel relayed regeneration strategy combining “liquid” and “gas” phase treatments to restore V₂O₅–WO₃/TiO₂ (VWTi) catalysts copoisoned by alkaline and heavy metals. The “liquid” phase employs formic acid, chosen for its acid ionization constant similar to that of vanadic acid, to remove soluble alkaline metals while preserving active vanadium oxide (VO_x). The subsequent “gas” phase uses NO-mediated SO₂ as a regenerant to neutralize insoluble heavy metals, restore acidity, and promote the formation of highly active polymeric VO_x species, as revealed by in situ Raman spectroscopy. These processes work together to eliminate alkaline poisons, mask heavy metals, and reconstruct active catalytic sites, generating new high-activity components. This regeneration strategy fully restores the performance of copoisoned VWTi catalysts and even surpasses the activity of fresh catalysts. This study presents a sustainable and effective pathway for extending catalyst lifespans, reducing hazardous waste, and advancing the NH₃–SCR technology.