Effect of Fe³⁺ or Fe²⁺ species on the catalytic performance and reaction pathway over CWK modified by iron sources in NH₃-SCR reaction

Developing high-performance catalysts for NO_x reduction was a significant challenge. CWK catalysts modified with iron sources were synthesized using co-precipitation and impregnation methods. The CWK-F₃C and CWK-F₃S catalysts exhibited the superior catalytic activity at 250–350 ℃ and the excellent N₂ selectivity. The key reasons for the enhanced catalytic activity of CWK-F₃C and CWK-F₃S catalysts could be attributed to the higher Fe³⁺ concentration, more surface chemisorbed oxygen species and bigger relative fraction of Ce³⁺. More significantly, the adsorption of NH₃ and redox capability were both strengthened by the Fe³⁺ doping. The DRIFTS experiment results showed that the E-R and L–H mechanism were followed by CWK-F₃C and CWK-F₂C catalysts. Furthermore, the introduction of Fe³⁺ generated more surface acidic sites, which could facilitate the formation of key intermediates (-NH₂) (NH_3(ads) + O_(ads)/O²⁻(ads) → -NH_2(ads) + -OH_(ads)). The presence of Fe³⁺ was conducive to NO₃⁻ formation (NO₃⁻ + NO_(ads) → NO_2(ads)), resulting in the presence of fast reaction, causing the excellent low temperature catalytic performance. Hence, the production of -NH₂ and NO₃⁻ species was responsible for the outstanding catalytic activity of CWK-F₃C.