Insight into the dynamic behaviors of reactants with temperature over a TiOx-based catalyst for NOx removal via NH3-SCR

Abstract

NH3-SCR has been an efficient technology for purifying NOx from industrial facilities. However, it is still a huge challenge to clearly understand the intrinsic mechanisms. Here, in situ DRIFTS was employed for elucidating the adsorption behaviors, active sites and reaction routes over the model catalyst of CuNbTiOx. The oxygen played a vital role in the reactant adsorption and reaction process, especially for NOx adsorbing, in which oxygen could promote monodentate and bidentate nitrates forming and bridged nitrate increasing. Then the correlation between DRIFTS peak locations and active sites for NH3 adsorption was further defined, thereinto, the bands at ca. 1604 cm−1 represented the coordinated NH3 species at Cu2+. Similar with most SCR catalysts, CuNbTiOx exhibited various catalytic activities among different temperature ranges. It was found that NH3-SCR reaction occurred mainly via Langmuir-Hinshelwood pathway at 200 °C, in which the relatively inert nitrates and NH3 adsorption species restricted the low temperature activity. Afterwards, the reaction mechanism transformed into Eley-Rideal when the temperature was elevating to a high temperature of 400 °C due to the weak adsorption of NOx. These new findings provide an innovative view for understanding the surface reaction on catalysts, further facilitate the development of NH3-SCR catalysts.