Formation of molecularly chemisorbed oxygen on TiO2-supported gold nanoclusters and Au(111) from exposure to an oxygen plasma jet

We present results of an investigation into the low-temperature formation of molecularly chemisorbed oxygen on a Au/TiO2 model catalyst and on a Au(1 11) single crystal during exposure to a plasma jet of oxygen. Through the use of collision-induced desorption measurements and isotopic mixing experiments we show evidence suggesting that at least some of the molecular oxygen is formed as a result of recombination of oxygen atoms on the samples during the plasma exposure. Of course, adsorption of excited molecular oxygen directly from the gas phase may also take place. We also present evidence showing that the adsorption of oxygen atoms on the surface assists in the molecular chemisorption of oxygen on the Au/TiO2 model catalyst samples. Thus, oxygen molecules impinging on the samples during plasma-jet exposures (plasma jet has similar to 40% dissociation fraction) could have an enhanced probability of adsorption due to simultaneous oxygen atom adsorption.