The pseudo-catalytic promotion of nitric oxide oxidation by ethane at low temperatures

Experimental work carried out in a flow reactor has shown that, from 700 to 750 K, low concentrations of ethane can act as a virtual catalyst in effecting the oxidation of NO to NO2. That is, while there is strong promotion of the oxidation of NO, there is very little concurrent degradation of the ethane. This contrasts with other experimental and modeling investigations, in which promotion by the hydrocarbon of NO oxidation has accompanied oxidation of a considerable fraction of the hydrocarbon. The rate of this pseudo-catalytic effect is significantly affected by the concentrations of both ethane and oxygen, which in this study ranged from 0 to 70% for [O2], 0 to 5000 ppm for [C2H6], and 0 to 350 ppm for [NO]. The level of reaction achieved under the various conditions was measured in terms of the rates of formation of NO2 and C2H4. Current kinetic mechanisms, though displaying good accuracy in other temperature regimes, fail to predict this pseudo-catalytic behavior of ethane, indicating that several elementary reactions important at the low temperatures are missing or poorly represented in such mechanisms. Mechanistic modifications are discussed and allow the measurements to be simulated more closely than with existing reaction schemes. It has been shown that the relative rates of the competing reactions C2H5 + O2 → C2H4 + HO2 and C2H5 + O2 (+M) → C2H5O2 + (M) are of critical importance in this situation.