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Methane production over the three-way catalyst has been observed for E85 (blend of 85% anhydrous ethanol and 15% gasoline)-fuelled vehicles. In order to understand the mechanisms of the methane production, the oxidations of ethanol and acetaldehyde were studied in laboratory flow reactor using commercial three-way catalysts containing Pd/Rh Ce-Zr-O. The influence of H₂O (absence/presence/concentration) and CO (absence/presence) in the gas feed was also studied. In this paper, a mechanism for the production of methane is proposed. As will be shown in the results section, ethanol oxidation over the TWC resulted in partial and total oxidation products (acetaldehyde, CH₄, CO, CO₂ and water), while acetaldehyde oxidation over the TWC resulted in partial and total oxidation products (CH₄, CO, CO₂ and water).

In this study, a speciation of organic gas emissions from E85-fuelled light duty vehicles was performed through mass spectrometric (MS) analysis of exhaust bag samples from a constant volume sampling (CVS) system. The objective was to identify and measure all organic species that gave a significant contribution to the Flame Ionization Detector (FID) response. It was concluded that the speciated concentration data that was obtained through the MS and a photoacoustic sensor was sufficient to predict the FID response for the CVS bag samples with a high degree of accuracy. Further on, it could be concluded that: methane, ethanol, ethene, acetylene (ethyne) and acetaldehyde all gave significant contributions to the FID response. Methane was the dominating contributor to the FID response in tests with relatively lower emissions and ethanol dominated in tests with relatively higher organic gas emissions.