Abstract
The oxidation of CO by NO and by O 2 has been studied on a number of supported transition metal oxide catalysts. On supported chromia the oxidation of CO by NO is faster than by O 2; however, with mixtures of NO and O 2 the reaction is selective towards O 2. The application of continuous mass-spectrometer monitoring to the study of surface state changes in chromia catalysts is outlined. The method was extended to determine the oxidation state of the surface in situ during reaction. In the oxidation-reduction cycle involving alternate passage of HeCO and HeO 2 mixtures at 500 °, the majority of the surface atoms undergo a change of oxidation state from Cr 6+ to Cr 2+. The extent of this change diminishes with decreasing temperature. Mixtures of He and NO oxidize the surface of supported chromia to a lesser extent than HeO 2. During the CONO reaction the average surface oxidation state is lower than in the presence of oxygen. A tentative explanation is offered for the selectivity for oxygen over nitric oxide in the oxidation-reduction reactions on commonly employed catalysts.
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