Synergistic regulation mechanism of WO3 on the resistance to thallium poisoned V2O5/TiO2 SCR catalysts

Tl poisons VTi catalysts by forming stable V-O-Tl bonds at V O active sites. • WO 3 provides steric shielding and acts as a sacrificial trap for Tl species. • WO 3 drives the electronic oxidation of highly toxic Tl + to less harmful Tl 3+ . • Optimized VWTi catalysts retain ~80% NO x conversion under cement kiln flue gas. Thallium (Tl), an extremely toxic and highly volatile heavy metal, has become the primary cause of rapid deactivation of V 2 O 5 /TiO 2 (VTi) SCR catalysts used in cement kilns. Industrial post-operation analyses consistently show exceptional Tl enrichment on catalyst surfaces—often 2–3 orders of magnitude higher than other heavy metals—resulting in a sharp decline in NO x removal efficiency and raising significant environmental and operational hazards. Motivated by real industrial observations that appropriate amounts of WO 3 substantially enhance the Tl tolerance of VTi catalysts, this study provides a mechanistic explanation for both the poisoning pathway and the mitigation effect. We demonstrate that Tl deactivation originates from its strong affinity for V O active sites, where it forms stable V-O-Tl bonds that collapse Lewis acidity, suppress oxygen-vacancy regeneration, and disrupt the V 5+ /V 4+ redox cycle essential for SCR activity. Through multi-scale characterization and DFT analysis, we reveal that WO₃ alleviates Tl toxicity through a dual synergistic mechanism: steric shielding that limits Tl access to vanadium centers, and oxidation of mobile Tl + to less reactive Tl 3+ , thereby weakening its ability to bind and deactivate V sites. This cooperative electronic-structural modulation preserves both acidity and redox functionality under realistic high-Tl exposure. The mechanistic insights presented here offer a rational foundation for developing durable, Tl-resistant SCR catalysts tailored for hazardous flue gas environments in cement and waste-incineration industries.