Abstract
The adsorption and reaction of CO, CO2 and O2 on TiO2 and Au/TiO2 have been studied using a mass spectrometric method which can detect processes occurring on a time scale of seconds. Adsorption of CO on TiO2 at 300 K is rapidly reversible and less on reduced samples than oxidised ones indicating that the adsorption sites are oxide ions. The amount adsorbed reversibly on reduced Au/TiO2 is less still, consistent with enhanced reduction, but additional amounts adsorb irreversibly at a slower rate. The amount of CO2 adsorbed under similar conditions is also greater on TiO2 than reduced Au/TiO2 and approximately one order of magnitude greater than that of CO. However, adsorption of O2 is undetectable on the time scale of the measurement. Exposure of Au/TiO2 to mixtures of CO and O2 results in near instantaneous generation of CO2 although its appearance is attenuated by adsorption. Adsorption of CO occurs concurrently in a way similar to that seen with CO alone except that the amount of the more slowly adsorbed form seems less. This suggests that it is the form utilised in catalysis. Oxygen uptake beyond that generating CO2 is appreciable during the initial stages of exposure to reaction mixtures and this capacity is enhanced if one or other reactant is removed and then reintroduced, possibly due to the generation of reducible interface sites. It is concluded that the remarkable activity of Au/TiO2 for CO oxidation at ambient temperature resides in a very high turnover frequency on sites at the interface between the metal and oxide.
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Ossipoff, N.J., Cant, N.W. Adsorption and reactivity during low temperature oxidation of carbon monoxide on Au/TiO2 catalysts studied by rapid response mass spectrometry. Topics in Catalysis 8, 161–169 (1999). https://doi.org/10.1023/A:1019161111188
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DOI: https://doi.org/10.1023/A:1019161111188