On the Mechanism of the Decomposition of Acidic O₃ Solutions, Thermally or H₂O₂-Initiated

Thermal or hydrogen peroxide initiated decomposition of acidic aqueous ozone is described as a chain process propagated by OH and O 2 - /HO 2 radicals. In the absence of H 2 O 2 added, the chain is initiated by surface-catalyzed formation of H 2 O 2 . Surface-dependent formation of H 2 O 2 is experimentally verified. Since homogeneous radical−radical reactions are much too inefficient to account for the termination, a heterogeneous chain termination is strongly suggested. Without addition of H 2 O 2 no dependence of the decay on the surface-to-volume ratio could be observed. However, on initial addition of H 2 O 2 in amounts sufficient for homogeneous initiation to prevail, the rate of O 3 decay becomes proportional to the surface of the reaction vessel. These findings strongly suggest that the decomposition of acidic aqueous O 3 is governed by initiation and termination processes occurring at the reaction-vessel surface, while its apparent appearance of a homogeneous solution-phase reaction results from the counteractive nature of these two processes.