Selective electro-oxidation of carbon monoxide with carbon-supported Rh- and Ir-porphyrins at low potentials in acid electrolyte

During our study of carbon-supported Group VIII metalloporphyrins as oxygen reduction electrocatalysts it was found that catalysts based on Rh and Ir are very active in the electrochemical oxidation of CO, particularly when pretreated at elevated temperatures in an inert atmosphere. The active site appears to be an isolated metal ion in a (thermally modified) porphyrin framework. During this CO-electro-oxidation reaction the following three stages can be envisaged: (i) adsorption of CO onto an isolated metal centre, (ii) nucleophilic attack of H2O on the adsorbed CO, and (III) decarboxylation. The Rh- and Ir-porphyrin-Norit BRX catalysts have the unique feature of selectively oxidizing the CO component of COH2 gas mixtures.