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The steady-state reduction of NOx at temperatures between 150-300°C has been investigated under simulated lean-burn conditions using a two-stage transient flow reactor system consisting of non-thermal plasma in combination with a sodium Y zeolite catalyst. Reactivity comparisons were made with and without plasma operation in order to identify the plasma-generated hydrocarbon species necessary for the selective catalytic reduction (SCR) of NOx. With propene as the hydrocarbon in the feed, NO is completely oxidized to NO2 in the plasma and the formation of oxidized carbon-containing species include formaldehyde, acetaldehyde, carbon monoxide, carbon dioxide, and methanol. Fourier transform infrared (FTIR) measurements indicate a close carbon balance between plasma inlet and outlet gas feed concentrations, signifying the major species have been identified.

The transient, one-dimensional monolith model previously developed for gasoline emission control applications has been extended to study converter warmup behavior in the exhaust from a variable-fuel vehicle (VFV) running on mixtures of methanol and gasoline by including the catalytic oxidation of methanol which involves the formation of stable gaseous formaldehyde as a reaction intermediate. The model calculations show that the aldehyde formation increases gradually at the early stages of converter lightoff (when methanol conversions are low), peaks at ∼50% methanol conversion, and then declines rapidly with a further increase in methanol conversion. Consequently, for all cases of practical interest, the total amount of aldehyde produced during the converter warmup period correlates well with the time to converter lightoff, with lower aldehyde emissions predicted at faster converter lightoff.