Abstract
Flow reactor experiments and XPS measurements were used to investigate the observed decrease in activity of Pt/Al 2O 3 and Pt/BaO/Al 2O 3 catalysts during reaction conditions. The reactions studied were NO ( g) +1/2O 2( g) ⇔NO 2( g) . The influence of platinum dispersion on activity and on the activity decrease with time was also studied. When the Pt/Al 2O 3 catalyst was exposed to NO 2 (350°C), the NO 2 dissociation rate decreased. This activity decrease with time was also studied with XPS and it is suggested that it was due to platinum oxide formation. Further, when the platinum dispersion was increased, the platinum activity decreased and the reason may be that small platinum particles more easily form oxides. According to XPS measurements platinum supported on BaO/Al 2O 3 gave a higher concentration of platinum oxide after NO 2 exposure compared to what was found for Pt supported on only Al 2O 3. Flow reactor experiments also showed that Pt/BaO/Al 2O 3 was less active, both for oxidation of NO and for reduction of NO 2, than Pt/Al 2O 3 was and one possible explanation for this is the fact that platinum on BaO/Al 2O 3 forms more oxides.
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