Acid-activated coal fly ash as a partial substitute for TiO₂ in VW/Ti catalysts for enhanced SO₂/H₂O tolerance in NH₃-SCR

VW/Ti catalysts are widely used for NH₃-SCR, yet they readily deactivate in SO₂/H₂O-rich flue gas and depend on costly TiO₂ supports. Herein, coal fly ash (CFA) activated by wet ball milling with sulfuric acid was used to replace 35.3 wt% of the TiO₂ support, yielding VWTi/CFA-H₂SO₄. Compared with commercial VW/Ti, this catalyst substantially reduces TiO₂ consumption and lowers WO₃ usage while maintaining comparable V₂O₅ loading. The catalyst maintained above 90% NO_x conversion from 300 to 450 °C and remained above 92% after 12 h at 350 °C under harsh conditions with 500 ppm SO₂ and 10 vol% H₂O. Characterization and in-situ DRIFTS reveal that sulfuric-acid activation enhanced surface acidity and redox cycling, accompanied by increased oxygen vacancies and accelerated charge transfer. The reaction proceeds via parallel Eley-Rideal and Langmuir-Hinshelwood routes and readily triggers fast SCR. This work offers a scalable strategy to improve VW/Ti durability in complex flue gas while reducing TiO₂ and WO₃ usage and valorizing CFA as a functional support.