Gas Phase Homogeneous Catalysis in Shock Waves. II. The Oxidation of Carbon Monoxide by Oxygen in the Presence of Iron Pentacarbonyl

Abstract

The catalytic effect of iron pentacarbonyl on the oxidation of carbon monoxide was investigated in shock waves. Reaction mixtures, typically containing 200 ppm Fe(CO)5, 4% CO, 2% O2, and 94% Ar, were shock heated to between 1000 and 2400°K in incident shock waves. The rate of CO2 formation was followed by monitoring infrared emission at 4.20 μ. It was found that the rate of CO2 formation was greatly accelerated in the presence of small amounts of Fe(CO)5. The observation with a time-of-flight mass spectrometer coupled to a shock tube, to study the formation of intermediate species, suggested that the larger portion of Fe existed as polymeric iron oxides, although small mass peaks due to Fe+ and FeO+ were detected. A mechanism of the catalytic oxidation of CO by Fe(CO)5 in the homogeneous gas phase is discussed. The catalytic effect of Fe(CO)5 disappeared below about 1600°K where the Fe vapor pressure becomes supersaturated under the present conditions. This indicates the removal of Fe and Fe containing species from the gas phase by a condensation process. At temperatures below 1400°K evidence for the direct oxidation of CO in Fe(CO)n (n=1–5) was obtained.