Evolution of VOx on TiO2-ZSM-5 Composite Supports upon K Poisoning and Its Effects on Ultralow Temperature NH3–SCR

Abstract

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_x conversion at 175–450 °C, as the combination of TiO₂ and ZSM-5 is conducive to the formation of more low-valent (polymeric) VO_x 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_x 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.