Flow reactor studies and kinetic modeling of the H-2/O-2/NOx and CO/H2O/O-2/NOx reactions

Flow reactor experiments were performed over wide ranges of pressure (0.5-1 4.0 atm) and temperature (750-1100 K) to study H-2/O-2 and CO/H2O/O-2 kinet ics in the presence of trace quantities of NO and NO,. The promoting and in hibiting effects of NO reported previously at near atmospheric pressures ex tend throughout the range of pressures explored in the present study. At co nditions where the recombination reaction H + O-2 (+M) = HO2 (+M) is favore d over the competing branching reaction, low concentrations of NO promote H -2 and CO oxidation by converting HO2 to OH. In high concentrations, NO can also inhibit oxidative processes by catalyzing the recombination of radica ls. The experimental data show that the overall effects of NO addition on f uel consumption and conversion of NO to NO2 depend strongly on pressure and stoichiometry. The addition of NO2 was also found to promote H, and CO oxi dation but only at conditions where the reacting mixture first promoted the conversion of NO2 to NO. Experimentally measured profiles of H-2, CO, CO2, NO, NO2, O-2, H2O, and te mperature were used to constrain the development of a detailed kinetic mech anism consistent with the previously studied H-2/O-2, CO/H2O/O-2, H-2/NO2, and CO/H2O/N2O systems. Model predictions generated using the reaction mech anism presented here are in good agreement with the experimental data over the entire range of conditions explored. (C) 1999 John Wiley & Sons, Inc.