| OCR Text |
Show 1.6.12 [OH] is nearly constant, which supports the quasi-steady-state assumption made in deriving Eqs. (21) and (22), as well as the assumption [OH] = constant made in Sec. II. The value of [0H]/[0H3eq is well below unity, in agreement with one of the conclusions drawn from the results of Sec. III. The sudden drop from the initial value 1.0 is an approximate representation of the initial process leading to the quasi-steady state assumed in the computations. This initial process again is an "inner region" in the sense of perturbation theory (cf. Sec. II). Finally, Fig. 9 shows the corresponding values of the ratio k4[H3/(k3[OH3) of NH2 production by reaction 4 to that by reaction 3. These values again are nearly constant except at the highest temperatures. The maximum values of the curves shown range from 2 to 55%. The present extended model was used also to generate plots corresponding to Figs. 4 and 5. The results were found to be similar to those based on the model of Sec. II. However, the agreement with the experimental data could not be improved beyond that shown in Figs. 4 and 5. Finally, the extended model was applied to the data of [143 shown in Fig. 6. The fit that could be obtained is shown in Fig. 10. As was the case in Fig. 7, the agreement between the curves and the experimental data is quite satisfactory. The curves of Fig. 10 are based on the following parameter values: oc = 0.6, k^k3/k2 = 3.1 x 10i0 cn^gmole'^s"1, rjjk4 = 3.3 x 106 cm3gmole"1, [N03Cf6q/[OH3eq = 160, TOHk3<i!10 K) = 9.4 x 108 cm3gmole_1, T0Hk3<1263 K) = 4.8 x 108 cm3gmole"i, [OH]eq = 2.5 x 1010exp(-1.96 x 104/T). The corresponding value of k3 is 4.9 x 10*2 cm3gmole~*s~l, which is much larger than the values listed in Table I. It should be noted that the basic parameters TQjjk3, k^k3/k2 and [NO]c e q remain unchanged if both k3 and k2/k^ are divided by some factor, while T Q H and [OH]eq are multiplied by that factor. It seems plausible that the effective equilibrium concentration of OH in the experiments of [14] was significantly higher than follows from the procedure on which the present calculations are based. This would explain the main differences between the values of TOH^3> ^2^1 a nd ^3 Just listed, and those listed in Table I. In any case, the value of the basic parameter k^k3/k2 is in quite reasonable agreement. The model proposed can account at least qualitatively for the influence of the addition of hydrogen and of hydrogen peroxide on the NO reduction by NH3 reported in [2], [5] and [6]. In the context of the present model, the main effect of these additives is an increase in the rate of production of OH. This is equivalent to a decrease of T Q H and an increase of [OH]. As a consequence, the optimum temperature for NO reduction is moved to a lower value. The effect is illustrated in Fig. 11, which was obtained with the same parameter |
