Modeling the Thermal De-NOx Process:: Closing in on a final solution

We have extended our previous kinetic model for the Thermal De-NOx Process to include recent information about the branching fraction alpha(1)(T) of the NH2 + NO reaction, (R1a) NH2 + NO <-> N-2 + H2O (R1b) NH2 + NO <-> NNH + OH where alpha(1)(T) = k(1b)/(k(1a) + k(1b)). The values of the rate coefficients k(1a)(T) and k(1b)(T) used in the model are k(1a) = 2.77 x 10(20) T-2.65 exp(-1258/RT) cm(3)/mole-sec. and k(1b) = 2.29 x 10(10) T-0.425 exp(814/RT) cm(3)/mole-sec. These two rate coefficients combine to give values of the total rate coefficient and branching fraction that are in excellent agreement with experiments over a wide range of temperatures, 300 K < T < 1400 K for k(1) = k(1a) + k(1a) and 300 K < T < 2000 K for alpha(1)(T). The smaller values of alpha(1)(T) in the Thermal De-NOx temperature window, 1100 K < T < 1400 K, used in the model allow us to reduce the value of the NNH lifetime to 1.5 x 10(-8) sec, which is consistent both with the upper limit set by experiment and with the best theoretical predictions. We compare the model predictions with the experiments of Kasuya et al. and discuss the results in some detail. (C) 1999 John Wiley & Sons, Inc.