Synergistic roles of intrinsic and extrinsic iron in enhancing the activity and SO₂/H₂O resistance of a coal fly ash-supported VWTi SCR catalyst

Coal fly ash (CFA) is a solid waste discharged from coal-fired power plants. Here, a series of VWTi/CFA-Fe catalysts were prepared by high-speed ball milling the mixture of CFA, TiO₂ and Fe powder, followed by impregnation of vanadium (V) and tungsten (W) active components, where CFA accounts for 64.6 wt%, greatly reducing the cost of commercial V₂O₅-WO₃/TiO₂ (VWTi). The optimal VWTi/CFA-Fe presents excellent selective catalytic reduction (SCR) denitrification (de-NO_x) performance with above 90% NO_x conversion in the temperature of 300–450 °C under harsh conditions (1000 ppm NO, 1000 ppm NH₃, 5% O₂, GHSV (gas hourly space velocity) = 30,000 h⁻¹), and high tolerance to SO₂ and H₂O poisoning with above 90% NO_x conversion in the presence of 500 ppm SO₂ and 10% H₂O. Experimental and theoretical research reveal that the intrinsic iron (I-Fe) in CFA itself and the extrinsic iron (E-Fe) added afterwards play different important roles in improving de-NO_x activity and tolerance to SO₂ and H₂O poisoning. E-Fe is mainly presented as Fe³⁺, which plays crucial role in promoting NH₃ adsorption through electronic modulation, including d-band center elevation and strengthened Fe-3d/N-2p hybridization, thus enhancing de-NO_x activity. I-Fe is mainly presented as Fe²⁺, which helps inhibit SO₂ adsorption, thereby improving tolerance to SO₂ poisoning. Furthermore, both Fe³⁺ and Fe²⁺ can reduce the adsorption energy of H₂O, with Fe³⁺ being more prominent, which helps to enhance tolerance to H₂O poisoning. This study opens up a new path for the resource utilization of CFA, achieving the goal of “treating waste with waste”.