A cyclic reaction pathway triggered by ammonia for the selective catalytic reduction of NOx by ethanol over Ag/Al2O3

Alumina-supported silver catalysts (Ag/Al2O3) prepared using nordstrandite as a precursor exhibited excellent activity for the selective catalytic reduction of NOx by ethanol (ethanol-SCR). During the ethanol-SCR, the formation of NH3 was observed over all Ag/Al2O3 catalysts, the amount of which was related to silver loading, reaction temperature, and the concentration of ethanol used, even when water was excluded from the inlet gas. Transient activity testing and in situ diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) analysis showed that the reaction between isocyanate species (-NCO) and water is the main pathway of NH3 formation. Addition of NH3 enhanced the NOx conversion for ethanol-SCR and the oxidation of ethanol over 3 wt% Ag/Al2O3. DRIFTS analysis revealed for the first time that NH3 reacted with enolic species to form -NCO over Ag/Al2O3, thus resulting in a novel and cyclic reaction pathway for ethanol-SCR. (C) 2013 Elsevier B.V. All rights reserved.