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 t he 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 coefficie nts 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 coeffi cient and branching fraction that are in excellent agreement with experimen ts 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 i n 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 wit h the experiments of Kasuya et al. and discuss the results in some detail. (C) 1999 John Wiley & Sons, Inc.