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The addition of NO (0 to 400ppm) to mixtures of Hz (ca. 1%) and 0 2 (0.7 to 22%) has been studied over the temperature range 700 to 825 K, in a flow reactor at atmospheric pressure. The overall effect of NO is to promote the oxidation of Hz but high concentrations of 0 2 actually inhibit the NO-promoted oxidation of Hz.A detailed kinetic mechanism has been constructed and found to describe the experimental observations. The promotion of the oxidation of HZ arises through the catalytic cycleThe ability of R.34 to reactivate chains normally terminated by the formation of HO2 is a key feature of this system. The predictions are highly sensitive to the rate of the reaction R.5 and the rate constants for this reaction is the only adjustable parameter required in the model. The value of h 5 ,~2 found to describe all the results K 5 ,~2 = 2.60 X lOI5 exp(+1350 cal.mol-l/RT) cm6.mol -'.s-l has an absolute uncertainty 135%. The uncertainty relative to other important rate constants in the Ha-02 system is less than 10%. 0 1995 John Wiley & Sons, Inc.

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