Oxygen-deficient surfaces

The mechanism of CWO is complex until now and there is still no final conclusion. A common opinion is that an fi ee radical appears in the reaction [15,16]. Yang et al. [10] proved the free radical mechanism under supercritical conditions. The research of Li [15] and Pintar [16] indicates that TiOj may first interact with O2 to produce superoxide radical O2" These radicals can initiate a free radical reaction. The final products are CO2 and H2O. The surface of TiOj becomes an oxygen deficient surface when the superoxide radical 02 is derived from the stoichiometric composition, and the number of surface vacant sites for oxygen activation is a function of the specific area. This would explain the relationship between the specific area and the catalytic activity. The larger the specific... 

Liu et al studied the conversion of carbon dioxide in the nanocrystal form of titanium dioxide polymorphs and compared the activity using in situ DRIFT and photoactivity measurements [123]. It is found that defect free oxygen deficient surface of brookite showed the highest yield for CO and CH4 (Fig. 15). This shows that the surface interface showed a crucial role in photocatalytic reduc-... 

Partial oxidations over complex mixed metal oxides are far from ideal for singlecrystal like studies of catalyst structure and reaction mechanisms, although several detailed (and by no means unreasonable) catalytic cycles have been postulated. Successful catalysts are believed to have surfaces that react selectively vith adsorbed organic reactants at positions where oxygen of only limited reactivity is present. This results in the desired partially oxidized products and a reduced catalytic site, exposing oxygen deficiencies. Such sites are reoxidized by oxygen from the bulk that is supplied by gas-phase O2 activated at remote sites. 

Figure 1. Ball model illustrations of (a) the ideal, stoichiometric Cu20(lll) surface and (b) the oxygen-deficient Cu (lll)-(J3xJ3)R30 surface. The small filled ci xles represent Cu" cations, and the larger open circles represent O anions. For clarity, only the top four atomic layers are shown.

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