The rate of redistribution of isotopic carbon between CO and COZ has been studied on An supported on MgO in the temperature range 300 to 4OO"C, Pw,/Pco ratios 9.1 to 1.2 and total pressure of 50 Torr. A few experiments were also carried out on supported Rn and Pt. The effect of Au concentration, temperature, and catalyst preparation method have been selected for investigation. In addition, determinations of the particle size of Au have been carried out by X-ray to illustrate the effect of the temperature of reduction and decomposition of the Au salt upon the particle size of the metal in the supported catalyst. Chemicai reduction of the Au salt at low temperature (

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The rate of the exchange reaction: *CO* + CO + *CO + COn was measured at atmospheric pressure in a flow reactor containing diBerent TiOz catalysts. The variables investigated and their range were as follows: ratio (p&p& 0.2 to 5.0; temperature, 450' to 575°C; flow rate, 10 to 50 cc min-1; additions of Fe, Cr, Nb, and P to TiOz. From the results, the influence of the (pcoJp& ratio on the rate of reaction was determined and compared to that of po, on the electronic conductivity of TiOt as gathered in previous investigations. From this information suggestions are advanced for the nature of the defect equilibrium reaction at the surface, the controlling step of the reaction rate, the nature of the adsorbed oxygen, and the influence of alterions upon the reactivity of TiOl. The results on TiOt + Cr indicated that a space-charge layer at the surface governed the reactivity of TiOt. In this instance, the thermodynamic derivations were modiied to take into account the influence of the surface space charge on the defect equilibrium. The values of the reaction rate constants were compared with those calculated with the help of the absolute rate theory and the experimental activation energies. Order of magnitude agreement was obtained assuming that the adsorption of CO2 was the controlling step of the isotope exchange reaction. On TiO, with low impurity levels a mobile configuration of the adsorption complex is in beet accord with the results. At higher impurity levels an immobile complex gives better agreement. The significance of the present results for the oxidation of CO on TiOn is pointed out. Finally, the diverse yet complementary, roles of electron and ion defects in governing surface reactivity and catalytic activity of TiOz and metal oxides in general is pointed out.