Abstract
The activity of Rh/Al 2O 3 catalysts for CO oxidation was investigated by transient isotopic pulse experiments using a packed-bed reactor. This transient experimental scheme revealed significant CO dissociation activity during CO oxidation over Rh/Al 2O 3 catalysts. Results indicate that the oxidation of CO proceeds via dissociative oxidation by its own oxygen as well as via direct oxidation by gas-phase oxygen on well-dispersed Rh/Al 2O 3 catalysts. The rate of CO dissociation is on the same order of magnitude as the rate of CO oxidation; under steady-state conditions at 300 °C, the rate of CO dissociation is approximately half that of direct oxidation. Differences in CO dissociation activity between single-crystal Rh surfaces and well-dispersed supported Rh particles are explained in terms of the molecular bonding and adsorption characteristics on these two different surfaces. The importance of CO dissociation kinetics in the overall CO oxidation activity of Rh/Al 2O 3 catalysts is further discussed in view of the reaction lightoff behavior.
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