The decomposition of nitric oxide on a heated platinum wire

Abstract

The catalytic rate of decomposition of pure nitric oxide on platinum (2NO → N 2 + O 2) was measured employing the batch, hot-wire technique at wire temperatures in the range 900–1200°C and at total pressures from 400–2260 torr. Chemisorbed oxygen is known to inhibit the rate of this reaction but very little surface oxygen is present at these elevated temperatures and thus an effectively clean platinum surface was realized. Also the experiments were limited to low conversions and thus low oxygen partial pressures ( P O 2 → O 2), again minimizing the likelihood of oxygen inhibition. A Rideal—Eley type rate expression: − r (moles NO reached/cm 2 . sec) = k 2 P 2 NO/(1 + K 1 P O 2 + K 2 P NO) describes quite well the dependence of the measured rate of the NO partial pressure on P NO. In contrast the data are not fit well by a Langmuir—Hinshelwood type rate-expression, similar to that above except for a unimolecular term P NO in the numerator. Owing to the large values of P NO and low conversions used in the present study with P O 2 → O, the study focused on the kinetics with respect to NO itself. For the above Rideal—Eley mechanism: k 2 ≊ 4·63 × 10 −4 exp (−8,600/ RT) mol/cm 2 . atm 2 . sec and K 2 ≊ 3 · 5 × 10 −2 exp (11,300/ RT) atm −1.