Soot and hydrocarbon oxidation over vanadia-based SCR catalysts

Abstract

The selective catalytic reduction (SCR) of NOx with NH3 and the oxidation of propylene and soot have been investigated on a series of V-W-TiO2 SCR catalysts prepared by incipient wetness impregnation, flame spray pyrolysis and a commercial reference sample. Depending on the preparation method, monomeric vanadly, polymeric vanadia and also two-dimensional vanadyl structures with vanadium in the +5 oxidation state on the catalyst surface were identified using Raman and X-ray photoelectron spectroscopy. The amount of acidic sites was highest if SiO2 was added to the catalyst. The SCR-performance of the catalysts prepared by incipient wetness impregnation was similar to those reported in literature and to that shown by the commercial catalyst. The catalysts were also very attractive for propylene and soot oxidation. The synthesis method had a strong effect on the SCR of NOx and on both the propylene and soot oxidation activity. In all cases, CO and CO2 were detected as oxidation products from propylene. Catalytic soot oxidation led predominantly to CO2 formation. The presence of propylene has a strong impact on the SCR activity particularly in the temperature range where C3H6 oxidation occurs.