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.

The selective catalytic reduction (SCR) of NO x with ethanol and NH3 over Cu-SSZ-13 catalyst was studied by using the synchrotron vacuum ultraviolet photoionization mass spectrometry technique. The Cu-SSZ-13 catalyst was synthesized by an aqueous solution ion-exchange method and characterized using X-ray powder diffraction, scanning electron microscopy, and X-ray photoelectron spectroscopy techniques. The reaction intermediates at different temperatures were identified by photoionization mass spectrometry and photoionization efficiency spectra. The result showed that ethanol dehydration and the partial oxidation reaction occurred during the (ethanol + NH3)-SCR process. Diethyl ether was preferentially formed at low temperature, whereas high temperature was favorable to the formation of ethylene and acetic acid. The vinyloxy radical (CH2CHO), C2H3NO2, and CH3NO2 were detected at different temperatures. Based on the result, it was proposed that the ethanol-SCR pathway with C2H3NO2 as an intermediate was independent of reaction temperature and the CH3NO2 pathway only existed at high temperatures (250/350 °C). This work can provide new insights for unconventional emission control and the improvement of the SCR system.