Superior Performance of Fe 1– x W x O δ for the Selective Catalytic Reduction of NO x with NH 3 : Interaction between Fe and W

Novel iron–tungsten catalysts were first developed for the selective catalytic reduction of NO x by NH 3 in diesel exhaust, achieving an excellent performance with a wide operating temperature window above 90% NO x conversion from 225 or 250 to 450 °C (GHSVs of 30 000 or 50 000 h –1 ). It also exhibited a pronounced stability and relatively high NO x conversion in the presence of H 2 O, SO 2 and CO 2 . The introduction of W resulted in the formation of α-Fe 2 O 3 and FeWO 4 species obtained by HRTEM directly. The synergic effect of two species contributed to the high SCR activity, because of the increased surface acidity and electronic property. The FeWO 4 with octahedral [FeO 6 ]/[WO 6 ] structure acted as the Brønsted acid sites to form highly active NH 4 + species. Combining DFT calculations with XPS and UV–vis results, it was found that the fine electron interaction between α-Fe 2 O 3 and FeWO 4 made the electron more easily transfer from W 6+ sites to Fe 3+ sites, which promoted the formation of NO 2 . Judging by the kinetics and SCR activity studies, the Fe 0.75 W 0.25 O δ with an appropriate W amount showed the strongest interaction, and thereby the lowest activation energy of 39 kJ•mol –1 and optimal catalytic activity. These findings would be conducive to the reasonable design of NH 3 –SCR catalysts by adjusting the fabrication.