Abstract:
In the temperature range 440-540’C, the oxidation of HCHO in KCl-coated vessels is reproducible
and of short chain length for HCHO concentrations in the range 0.05-4 Torr. Interpretation of the
[CO] against time profile permits evaluation of the unknown parameters A'i, k7jk^ and ka.
HCHO + O2->HO2 + HCO
HO2 + HO2->H2O2 + O2
surface
HO2---->4H2O + JO2
surface
H2o2—>H2O + 4O2.
(1)
(4)
(7)
(8)
Comparison of the experimental values for k7/kf and ka with those calculated from diffusion theory
indicates that the destruction of HO2 at the surface is fully diffusion controlled, whereas the destruc
tion of H2O2, though moderately efficient, is not fully diffusion controlled. From measurements
at HCHO concentrations below 0.5 Torr, where the chain length is close to unity, effectively direct
measurements of ki have been obtained, the values being 7.65 x 10~’, 2.08 x 10-1, 8.50 x IO-2 and
2.20x 1CF2 dm3 moF* s_1 at 542.5, 500, 471 and 440.5°C, respectively. These values give the
Arrhenius parameters At = 2.04x 1010 dm3 moF1 s~l, £\ = 38.9 ± 1.5 kcal moF1. The absence
of any diameter effect on the value of k, confirms that the parameters refer to the homogeneous pro
cess.
