Nature of the Exchange Site

In addition to ions of varying degrees of co-ordination, the presence of a number of different oxygen species such as 0 , OJ, O3, is well documented on oxide surfaces.Within the literature, relatively httle attention is devoted to the exact nature of the oxygen species undergoing exchange. The identity of the active species is likely to be highly dependent 

For the alkaline earth oxides. Winter originally suggested that R2 defect centres, i.e., pairs of associated F centres, were of considerable importance.It was proposed that the activation of oxygen by such centres was rapid and non-activated with the reverse reaction (i.e., the elimination of exchanged oxygen) being responsible for the observed kinetics  

At higher temperatures, additional pathways were suggested to be operative and it was observed that homomolecular exchange required the removal of most surface hydroxyls at high temperatures in order to proceed. In 

The active O involved was proposed to be generated via the decomposition of some of the hydroxyl groups (hence the relationship with H2 TPD), 

The evolution of hydrogen during the thermal decomposition of brucite has also been reported elsewhere.[ 1 

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