Carbon Monoxide Oxidation over Chromium Sesquioxide. I. Nature of Oxygen Adsorbed on Cr2O3

The nature of oxygen species adsorbed on Cr2O3surface in the temperature range 131–163 °C was studied in detail by application of the transient response method with simultaneous measurements of the electrical conductivity of the catalyst as a p-type semiconductor. The distribution of oxidation power of the adsorbed oxygen species was also measured. The mode of the distribution curve of oxidation power indicates that the oxygen can be classified into two groups which differ in oxidation power as well as in the catalytic activity for the oxidation of CO. From the comparison between the results of the transient response and the oxidation power measurements, it is concluded that the rapidly and slowly adsorbed oxygen groups observed by the transient response method correspond to those of oxygen species of higher and lower oxidation power, respectively. Kinetic analysis of the conductivity response curve caused by the adsorption of oxygen leads to the conclusion that the dissociative adsorption of oxygen associated with electron transfer from the catalyst takes place simultaneously on two different kinds of adsorption sites at substantially different rates.