Effect of Temperature on Ethanol Reaction Pathways during the (Ethanol + NH₃)-SCR Process over Cu-SSZ-13 Catalyst: a Photoionization Mass Spectrometry Study

Abstract

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.