Effect of Ammonia on the Intermediates and Chemical Pathway of Selective Catalytic Reduction of NO by Ethanol over a Pt/Al₂O₃ Catalyst

Abstract

In order to effectively reduce NO x produced in diesel engine exhaust at low temperatures, synchrotron vacuum ultraviolet photoionization mass spectrometry (SVUV-PIMS) was used to study ethanol-selective catalytic reduction (SCR) and (ethanol + NH3)-SCR over a Pt/Al2O3 catalyst. The Pt/Al2O3 catalyst was prepared by the impregnation method. The intermediates produced in the catalytic reaction at different temperatures were identified by SVUV-PIMS and photoionization efficiency spectroscopy. The results show that compared with the ethanol-SCR process, NH3 as a coreductant can improve the conversion efficiency of NO. Moreover, coaddition of ethanol and NH3 over the Pt/Al2O3 catalyst would result in a significant reduction or disappearance of organic intermediates. With the increase in temperature, the types of organic intermediates increased at first and then decreased, and most of the intermediates could be identified at 250 °C. The addition of NH3 in ethanol-SCR can enhance the reduction efficiency of NO x and the oxidation of ethanol over the Pt/Al2O3 catalyst. NH3 reacts with enolic species over the Pt/Al2O3 to form isocyanate (−NCO), which will improve the deNO x efficiency in ethanol-SCR. At the same time, the H* species provided by ethanol facilitate the oxidation of NO to form intermediate nitrogen-containing species, such as HONO/HNO3, which creates favorable conditions for NH3 to achieve fast SCR (similar to a H2-assisted NH3-SCR process). The SCR of NO x by ethanol in cooperation with NH3 over Pt/Al2O3 catalysts creates the possibility to achieve high deNO x efficiency at low temperatures.