Issue |
J. Chim. Phys.
Volume 84, 1987
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Page(s) | 27 - 32 | |
DOI | https://doi.org/10.1051/jcp/1987840027 | |
Published online | 29 May 2017 |
Influence des traitements de parois. Réactions hétérogènes de haute et de basse température des radicaux HO2
Laboratoire de Chimie Générale, CNRS UA 40870. Université P. et M. Curie, Tour 54-55, 4 e etage, 4, Place Jussieu, 75252 Paris Cedex 05, France.
Il est montré par quelques exemples que la paroi du réacteur peut avoir une grande influence sur les réactions se produisant dans la phase gazeuse. Elle peut modifier considérablement la vitesse globale de la réaction, conduire à la formation préférentielle d’un produit, être source de radicaux ou être suffisamment inerte pour l’étude de réactions élémentaires, de radicaux HO2 par exemple. Les réactions hétérogènes de ceux-ci sont de nature différente, suivant qu’elles ont lieu à haute ou basse température.
Abstract
Each gas kinetics study begins by choosing vessel and coating, for these play a crucial role on the altogether reaction rate, the nature and the proportions of products obtained. For instance, the global reaction rate can be strongly modified; in boric acid coated vessels, the slow oxidation of hydrogen or formaldehyde was self-accelerated and large amounts of HO2 radicals and H2O2 were produced, whereas they were not observed in a KCI coated one. The reaction selectivity could be improved in order to produce a desired product; with rich propane-oxygen mixtures and a B2O3 treatment, 15% of the consumed C3H8 was transformed into H2O2. To study decomposition kinetics of peroxides, different treatments were investigated and we selected the most unreactive one. We have also observed a difference of nature between heterogeneous reactions of HO2 radicals according to the temperature range : reaction at high temperature depends strongly on the coating but its activation energy Ea remains always positive, whereas at low temperature Ea is negative and the phenomenon looks like a physisorption. Initiation of active centres at wall may be important and a few cases are presented.
© Paris : Société de Chimie Physique, 1987