Abstract.A model of the heterogeneous catalysis of a dissociated carbon dioxide mixture on high-temperature heat shield coating has been developed. The model takes into account both chemical and physical adsorption and desorption of oxygen atoms at vacant active sites on the surface; recombination of chemisorbed oxygen atoms with gas phase of O atoms and of CO molecules (Eley -Rideal recombination) and with physisorbed atoms (Langmuir -Hinshelwood recombination). Note that the physisorbed atoms either are desorbed from the surface or diffused to the nearest chemisorbed site. Therefore some of these diffusing atoms will be able either to occupy vacant active sites or to react with chemisorbed atoms.