Influence of preparation methods on iron-tungsten composite catalyst for NH3-SCR of NO: The active sites and reaction mechanism

A series of iron-tungsten composite oxides catalysts prepared by grinding methods (FW-GR), incipient impregnation (FW-IM), sol-gel (FW-SG) and microemulsion (FW-ME) methods were used for selective catalytic reduction of NO by NH3 (NH3-SCR). The SCR activity was significantly depended on the preparation method, the NO conversions over different catalysts were following the order of FW-GR > FW-SG > FW-ME > FW-IM. The results indicated that the NO conversion was strongly related to the FeWO4 species. It also discovered that the catalyst with higher specific surface area, surface Fe2+ content, surface adsorbed oxygen species, redox potential, surface acidic sites and acidic strength showed better NO reduction activity among all catalysts. In situ DRIFTS results revealed that the main reaction mechanisms of iron-tungsten catalysts were L-H at low temperature and E-R at high temperature. The SCR reaction over FW-GR sample involved the formation of NH2 intermediate and subsequent reduction by NO, while the formation of NH4NO3 species over FW-IM was easily transformed into N2O species.