Selective catalytic reduction of NO with NH3 over Mn–Fe/USY under lean burn conditions

A series of catalysts of Mn/USY and Mn–Fe/USY prepared by impregnation were studied for selective catalytic reduction (SCR) of NO with NH3 under lean burn conditions. The most active 10%Mn–8%Fe/USY catalyst nearly reached 100% NO conversion with the space velocity of 36,000 h−1 in the wide temperature range of 423–573 K. Both manganese and iron oxides dispersed well, no visible manganese or iron oxide phase was observed in X-ray powder diffraction (XRD) spectra. In addition, Mn and Fe oxides on Mn–Fe/USY catalyst, which were prepared by impregnation, were mainly formed MnO2 and γ-Fe2O3 by X-ray photoelectron spectroscopy (XPS). Diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) results showed that Fe promoted NO oxidation and created more monodentate and bidentate nitrates adsorbed species on the catalyst surface. The addition of Fe enhanced the quantity and strength of the Brönsted and Lewis acid sites on the surface of 10%Mn–8%Fe/USY, which might promote the absorption of NH3 to form active intermediate and increase the catalytic performance at low temperature. FT-IR spectra of chemisorbed pyridine (Py-IR) results also demonstrated the increase in acidity of 10%Mn–8%Fe/USY catalyst by Fe promotion effect.