Steady-state kinetics of the catalytic reduction of nitrogen dioxide by carbon monoxide on platinum

Abstract

The steady-state kinetics of the reduction of nitrogen dioxide (NO 2) 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 (CO 2) and nitric oxide (NO). The CO 2 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 + O 2 or CO + NO under similar reaction conditions. The reaction rate is first-order in CO pressure when P CO P NO2 < 0.25 and first-order in NO 2 pressure when P CO P NO2 > 1 . The activation energy when P CO P NO2 = 0.10 is 7.2 kcal mole −1 which is consistent with the activation energy for CO + O 2 under similar conditions. However, when P CO P NO2 = 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 + O 2 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 NO 2 on Pt surfaces.