Reconciling the Paradox of SO ₂ in the High Temperature NH3‐SCR Reaction: The Role of SO ₄ ²⁻ in Electronic Structure

ABSTRACT

At present, the effect mechanism of SO ₂ on high‐temperature denitrification catalysts is unclear. In this study, 3DOM CeWTi _1‐x ‐Si _x O ₂ catalysts were constructed for high‐temperature NH ₃ ‐SCR reaction, and deeply explored the mechanism of SO ₂ on the catalyst. Among them, 3DOM CeWTi _0.7 ‐Si _0.3 O ₂ catalyst exhibited excellent NO _x removal efficiency at 500°C in SCR reaction due to its excellent specific surface area as well as three‐dimensional ordered macroporous‐mesoporous structure. Based on the series of analyses, we concluded that Si and SO ₄ ²⁻ played distinct roles in accelerating the NH ₃ ‐SCR reaction. Specifically, Si incorporated into the Ti matrix through elemental doping, forming a three‐dimensional framework structure that enhanced the catalyst's thermal stability under elevated temperature conditions. Through electron‐withdrawing effects, it altered the catalyst electronic structure and chemical environment. Meanwhile, SO ₄ ²⁻ formed on the catalyst surface reshaped the surface electronic structure through strong electron‐withdrawing effects. It modified Ce/W active sites, weakened the Ce‐O bond and activated lattice oxygen, and optimized surface acidity, thereby accelerating the SCR reaction. Combining DFT calculations with in situ DRIFTS results, we concluded that the 3DOM CeW‐SO ₄ ²⁻ /Ti _0.7 ‐Si _0.3 O ₂ catalyst primarily followed E‐R and MvK mechanisms. This mechanism reconciled the contradictory phenomena of SO ₂ poisoning and SO ₂ promotion in NH ₃ ‐SCR process.