Selective catalytic reduction of NO by NH3 over Fe2O3-promoted V2O5/TiO2-based catalysts with high Fe2O3-to-V2O5 ratios

Abstract

Fe2O3-promoted V2O5-WO3/TiO2 catalysts with high Fe2O3-to-V2O5 ratios (3.4-6) have been prepared for the selective reduction of NO with NH3 (NH3-SCR) and extensively characterized using various spectroscopic measurements. No crystalline iron oxides were indicated even for 8% Fe2O3-promoted V2O5-WO3/TiO2 but alpha-Fe2O3 crystallites were observed in a XRD pattern for 7.04 % Fe2O3-promoted WO3/TiO2. Both Raman and XPS measurements suggest the formation of Fe-O-V species which may make a better N-2 selectivity in NH3-SCR reaction at high temperatures. All Fe2O3-promoted catalysts showed a great depression on N2O formation. At temperatures > 400 degrees C, samples with 5.46 and 8% Fe2O3(Fe2O3/V2O5 ratio = 3.4 and 5) gave significantly lower N2O production levels compared with the unpromoted and lower Fe2O3 loading catalysts. However, increasing in Fe2O3 loading resulted in a decrease in high temperature deNO(x) activity due to the oxidation of NH3 into NO. All the 3.4 and 5 ratio catalysts after a hydrothermal aging at 550 degrees C for 10 h gave NO removal activity and N2O formation similar to those measured over non-aged ones. However, such an aging at 750 degrees C could lead to a considerable increase in N2O formation even for the 5.46 % Fe2O3-promoted catalyst. Fe2O3-promoted V2O5/TiO2-based catalysts could catalyze the reduction of gas-phase N2O by NH3 adsorbed strongly, suggesting that this reaction may be a major route to greatly suppress N2O formation, consistent with infrared studies showing a reaction between N2O and surface NH3 species strongly adsorbed on the catalysts. This surface reaction could readily occur from a temperature as low as 250 degrees C.