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 NOx 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 degree celsius and the excellent N-2 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) (NH3(ads) + O-(ads)/O2-(ads) -> -NH2(ads) + -OH(ads)). The presence of Fe3+ was conducive to NO3- formation (NO3- + NO(ads) -> NO2(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.