ON THE DEPENDENCE OF THE RATE OF MOIST CO OXIDATION ON O2 CONCENTRATION AT ATMOSPHERIC-PRESSURE

Counter-intuitively, moist CO oxidation is experimentally shown to be inhibited by the addition of oxygen to stoichiometric mixtures at 1000 K and atmospheric pressure. At these conditions, oxygen essentially r educes the ratio of [H]/[OH] such that the consumption of HO2 occurs t hrough chain-terminating rather than chain propagating reactions. Alth ough multiple sets of reactions are active in this transition, the pri ncipal effect results from a transition from HO2 + H --> OH + OH to HO 2 + OH --> H2O + O2 and HO2 + O --> OH + 02 as oxygen concentration is increased. As temperature is increased these reactions have a lesser influence on the 0, H and OH radical pool due to the reduced productio n of HO2. Near 1040 K, the inhibition effects cease to be observed and the reaction rate is essentially independent of oxygen concentration. At higher temperatures still, previous experiments have shown that ox ygen addition increases the rate of CO consumption. These experimental trends are qualitatively predicted by a comprehensive mechanism for C O/H-2/02 oxidation developed previously. Quantitative predictions can be obtained by updating the rate of HO2 + OH --> H2O + O2 to the value s given by recently published reviews of low temperature data and to n ew high temperature experimental data.