Kinetics of homogeneous nitrous oxide decomposition

The major uncertainties in the consumption mechanism for N2O are related to the efficiency of various components as collision partners in N2O dissociation and to the rate constant for the N2O + OH reaction. In this work thermal dissociation of N2O in different carrier gases has been measured at atmospheric pressure in the temperature range 1000-1400 K.

Based on these, as well as earlier data from this laboratory, collision efficiencies were determined for O2, CO2, N2 and H2O. The relative efficiencies compared to Ar were found to 1.4 ± 0.3, 3.0 ± 0.6, 1.7 ± 0.3, and 12 ± 3.5, respectively. The fast rate measured for N2O + H2O indicates that the commonly accepted rate constant for N2O dissociation at the high-pressure limit may be too low around 1300 K.

The reaction between N2O and OH was investigated by addition of N2O to moist CO oxidization experiments. The N2O + OH reaction was found to be very slow under the present conditions, with an upper limit of 3 · 109 cm3/mole-s for the rate constant at 1250 K. In agreement with recent theoretical studies, this makes the reaction more than one order of magnitude slower than estimates currently used in modeling.

The implications of the present results for modeling N2O chemistry in fluidized bed and other combustion systems are discussed.