Oxidation of Carbon Monoxide by Oxygen in Shock Waves

Abstract

The oxidation of CO by O2, with and without small amounts of added H2, was investigated in very dilute mixtures with argon at about 5.4 × 1017 particles/cc total concentration. The reaction was followed in incident shock waves by measuring CO and CO2 infrared emissions for about 2000 μsec particle time over the 1700–2600°K range. The reaction shows an initial accelerating rate followed, in H2 mixtures, by a period of constant rate. The observed [CO2]-time profiles were compared to those calculated numerically on an IBM 360/65 computer. These calculations used two branching-chain mechanisms proposed by others. The one involving hydrogenous impurities is CO+O2=CO2+O, O+H2=OH+H, O+H2O=OH+OH, OH+CO=CO2+H, OH+H2=H2O+H, H+O2=OH+O, which describes all of the observations if the assumption is made that the total hydrogenous impurity (H2 and H2O) is approximately 40 ppm. This figure is in the range of the experimentally estimated impurity concentrations. In the calculations, least-squares averages of literature values of k3, k5, and k6 were used and best fits were obtained with: k1 = 5.8 × 10+12exp(− 50 000 / RT) cc molecule−1·sec−1, k2 = 1.5 × 10−10exp(− 10 000 / RT) cc molecule−1·sec−1, k4 = 1.9 × 10−12exp(− 1030 / RT) cc molecule−1·sec−1. With these values, which are consistent with literature data referring to high temperatures, quantitative agreement was obtained between calculated and observed rates of CO2 formation. The observed rates could not be explained by the other proposed mechanism, which postulated electronically excited CO2 as a chain carrier.