Catalytic oxidation of carbon monoxide on platinum deposited on alumina

The most effective way to clean car exhaust gases from carbon monoxide (“poison gas”) is its post-oxidation to CO₂. The highest catalytic activity in this reaction is exhibited by the supported platinum group metals.

The oxidation of CO on supported platinum both in the reduction and catalysis regimes can proceed through the interaction of CO with oxygen atoms of OH groups, however, the temperature ranges for the implementation of these regimes differ by more than 250°C. We see the reason for this difference in the fact that in the catalysis regime there is no breaking of bonds in OH groups, and the formation of CO₂ and the regeneration of OH groups are carried out by redistribution of bonds in the intermediate complex with the participation of adsorbed oxygen. Since, in the case under consideration, CO interacts directly with OH groups and not with oxygen under the reaction conditions, CO adsorption is accompanied by the formation of carboxyl-type structures. The formation of such structures is apparently the stage that determines the reaction rate. In this case, the role of adsorbed oxygen is reduced to the reoxidation of platinum atoms reduced in previous events and the initiation of the decomposition of carboxyl structures with the formation of CO₂ and the regeneration of OH groups. The possibility of such a mechanism is consistent with a similar phenomenon of initiation of the decomposition of surface structures of the carbonate-carboxylate type by molecular oxygen.

A similar mechanism has been proposed in the literature for the oxidation of CO with Pt/TiO₂ and Pd/Al₂O₃.