Identification of Surface Species on Titania-Supported Manganese, Chromium, and Copper Oxide Low-Temperature SCR Catalysts

Abstract

TiO2-supported transition metal oxides (Mn, Cr, and Cu) for the SCR of NO with NH3 have been synthesized by wet impregnation. The adsorption and coadsorption of NH3, NO, and O2, in conjunction with in situ FT-IR spectroscopy, was used to elucidate the reaction mechanism as the samples were heated from 323 to 673 K. While Cr was the only transition metal that generated significant amounts of Bronsted acidity, strong Lewis acid sites were present over all of the materials. The peak strength corresponding to the δs(NH3) coordinated to Lewis acid sites decreased in the following order: Ti > Mn > Cr ∼ Cu. Similarly, the peak strength corresponding to the δas(NH3) coordinated to Lewis acid sites decreased as follows: Mn > Cr ∼ Cu. Exposing the catalysts to oxygen before the introduction of NO did not impact the adsorption of NO as nitrates on the catalysts, suggesting that labile lattice oxygen plays an important role in the formation of nitrates. Three types of nitrates were observed after the adsorption of ...