Evolution of VO_<i>x</i> on TiO₂-ZSM-5 Composite Supports upon K Poisoning and Its Effects on Ultralow Temperature NH₃–SCR

Compared with V₂O₅/TiO₂, vanadia catalysts supported on TiO₂-ZSM-5 composite support possess excellent resistance to potassium poisoning in the selective catalytic reduction of NO by NH₃ (NH₃-SCR). Appropriate addition of ZSM-5 (10 wt %) enhances the low-temperature activity of NH₃-SCR with more than 80% NO_<i>x</i> conversion at 175-450 °C, as the combination of TiO₂ and ZSM-5 is conducive to the formation of more low-valent (polymeric) VO_<i>x</i> preferentially deposited on TiO₂. Compared with V₂O₅/TiO₂, the composite support catalysts effectively shield V₂O₅ as the main active species from K poisoning by preferential ion-exchange of K⁺ with Brønsted acid sites (Si-O(H)-Al) of ZSM-5. According to physicochemical characterizations, the mechanism of catalyst deactivation is mainly attributed to excessive aggregation of VO_<i>x</i> to form inactive crystalline V₂O₅ in addition to KVO₃. In situ diffuse reflectance infrared Fourier transform spectroscopy indicates that the presence of K leads to the formation of inactive bidentate nitrates instead of active bridged nitrates. A novel vanadium-based catalyst with high alkali poisoning resistance for ultralow temperature (<200 °C) denitration was developed.