The property tuning of NH3-SCR over iron-tungsten catalyst: Role of calcination temperature on surface defect and acidity

Abstract Iron-tungsten composite oxide catalysts have been prepared using a no-water grinding method followed by calcination from 400 to 800 °C. Treatment from 400 °C to 800 °C led to the crystallinity increase and weaker interaction between Fe and W. The catalyst calcined at low temperature (400°C) obtained ample lattice defect, more surface Fe2+ species and surface oxygen and showed the greatest low-temperature catalytic activity. At high calcination temperature, less surface oxygen-vacancies and weak reducibility of samples were found and correspond to decreased catalytic properties. The calcination at 500 °C for iron-tungsten catalyst was accompanied by the coexistence of surface defect and FeWO4 or WO3 species with an optimal ratio, prompting its best active window with more than 90% NOx conversion at 220-500 °C. More specially, the unsaturated cations (Fem+ and Wn+) about surface defect gave rise to form more Lewis acid sites, and the O-W-O and W-O-W in connection with hydrated tungsten species led to the formation of Bronsted acid sites. The reaction intermediate between NO3- and NH2 formed on the surface of FeOx-WO3 catalyst was such a crucial factor in improving the reaction performance of NH3-SCR and the difference of N2 selectivity.