OCR Text |
Show 1.6.11 P = \[N0]{2 + (3 - «>T0Hk3[NH3] + (2 - oc>THk4[NH3] • (3 - 2a)TQHk3THk4[NH3] 2} " [N^c,eq<l + THk4[NH3])>/S q = <-[N0]Cjeq[N0]{2 + <2 - oc>THk4[NH3]> [N0]2{1 + (1 - oc><THk4 + TQHk3>[NH3] + <1 - 2a)T0 Hk3THk4[NH3]2»/s r " - [N0]CjP.q[N0]2{l • <1 - «)THk4[HH3]}/s s = (1 + THk4[NH3])(l + 2TnHk3[NH3]> tN^c,eq=(k2/k1^0H]eq. Eqs. (21) and (22) were solved numerically by computer. This required specification of the values of TQHk3> THk4> kjk3/k2, [NO]c>eq • (k2/ki)[OH]eq and oc It was assumed that TQJJ can be represented by the expression C3exp(C4/T), while Tjjk4, k3 and k2/k^ were taken to be constant. The value of [OH] was calculated as indicated in the previous section. Next, values were chosen for k3 and oc Fitting the calculated results to the experimental data of [4] at 1076 K then yielded THk4 and TO H(1076 K). Finally, the values of k2/kA and TQH<1287 K) were adjusted to obtain optimal agreement with the data at temperatures other than 1076 K. Values taken for k3 included 2.6 x 1011 cm3gmole"is"i and 1.3 x 10i2 cm3gmole~1s'1. These choices were guided by the values mentioned in the previous section. Values taken for oc included 0.25, 0.4, 0.5 and 0.9; the value 0.4 is the choice made in [151 Some of the parameter combinations used are listed in columns a)-f) of Table I. Each of these combinations yielded essentially the same good fit to the experimental data of [41 An example of this fit is shown in Fig. 7, which is based on the values shown in column a) of Table I. It can be seen that the fit is better than that of Fig. 3. For decreasing values of A the theoretical curves show a downward shift of the optimum temperature for NO-reduction, in agreement with the data. The relatively small dependence on A of the reduction in NO observed at low temperatures also is correctly modeled. It is of interest to note that the results for [NO] at the higher temperatures drop below the value of [NOIQ. The values of [NO]/[NO]eq = [OH]/[OH]eq as a function of time for A = 1.6 and for various temperatures are shown in Fig. 8 a)-d), corresponding to columns a)-d) of Table L Except at the highest temperatures, |