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A multistep mechanism has been elucidated for the reduction of NOx in the presence of added ethanol over Ag/γ-Al2O3 at 320 °C. Under these conditions, ethanol principally reacts with oxygen to form acetaldehyde. Surface acetate ions, which are formed from adsorbed acetaldehyde, react with NO2 to yield nitromethane. Evidence is presented indicating that the aci-anion of nitromethane is an intermediate. In contrast, NOx reduction with ethanol over Ag/γ-Al2O3 at 200 °C is inefficient, because surface acetate ions are much less reactive at 200 °C than at 320 °C. At 200 °C, the dominant pathway for ethanol oxidation is reaction with NO2, producing ethyl nitrite, which decomposes into a number of products, including N2O, which is stable under reaction conditions. On the basis of these mechanistic data, conditions can be defined under which NOx reduction with ethanol may be viable. |
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