The steady-state kinetics of the reduction of nitrogen dioxide (NO2) with carbon monoxide (CO) on a polycrystalline platinum foil have been investigated using reactant pressures between 1 × 10-7 and 5 × 10-6 Torr. At temperatures less than 400 K, the primary products formed are carbon dioxide (CO2) and nitric oxide (NO). The CO2 formation rate at temperatures less than 400 K is at least an order of magnitude greater for this reaction than for those of either CO + O2 or CO + NO under similar reaction conditions. The reaction rate is first-order in CO pressure when PCO PNO2 < 0.25 and first-order in NO2 pressure when PCO PNO2 > 1. The activation energy when PCO PNO2 = 0.10 is 7.2 kcal mole-1 which is consistent with the activation energy for CO + O2 under similar conditions. However, when PCO PNO2 = 1.5, the activation energy is only 4.3 kcal mole-1. This value is 29 kcal mole-1 lower than the activation energy for CO + O2 at low temperatures when the reaction is first-order in the oxidant. Consistent reaction mechanisms for both regimes are proposed based upon recent reports of the chemisorption of NO2 on Pt surfaces.
All Science Journal Classification (ASJC) codes
- Physical and Theoretical Chemistry