Infra-red spectrophotometric study of the oxidation of nitric oxide

Abstract

The thermal oxidation of nitric oxide at concentrations of p.p.m. has been investigated under simulated atmospheric conditions by long-path infra-red spectrophotometry. At 20°C, the reaction follows pseudo second-order kinetics with a rate constant of (2.0±0.1)× 10⁴1.² mole^–2 sec^–1, defined by –d[NO]/dt=k[NO]²[O₂]. Excess water vapour and the presence of different surfaces have no apparent effect on the order and rate constant. Removal of nitrogen dioxide from the gas phase is attributed largely to adsorption on silicon monoxide and chromium-plated surfaces. The rate of adsorption is increased by the presence of nitric oxide and water vapour in the gas phase. The significance and mechanism of the adsorption effects are discussed together with the mechanism of the homogeneous reaction.