EPR Study of CO and O2 Interaction with Supported Au Catalysts

The interaction of CO and O2 with Au/TiO2 and Au/Al2O3 catalysts is studied with EPR spectroscopy. Adsorption of CO and O2 can produce at room temperature in both fresh catalysts O2− radicals stabilized on support cations (suggesting a spillover process exists at least in Au/Al2O3); thus, O2− generation does not require a reducible support. These O2− species react upon CO addition giving diamagnetic species. CO adsorption at room temperature on freshly activated Au/TiO2 abstracts oxygen ions from the support surface producing Ti3+ anion vacancy centers, but after the specimen has interacted with both O2 and CO a new CO adsorption gives (reversibly, suggesting easy Au–titania electronic interaction) only fully coordinated Ti3+ unable to stabilize O2−; this indicates coverage of Ti active centers by reaction products (e.g., carbonate or peroxide species) which are not eliminated by CO or O2. The results indicate that steady state catalytic CO oxidation on Au/TiO2 may proceed without involving Ti-stabilized O2−.