Transient Characterization of Carbon Monoxide, Carbon Dioxide and Oxygen Adsorbed on MgO and MgCO_3*

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The dynamic adsorption behavior of O_2, CO and CO_2 on MgO and MgCO_3 has been studied in detail at temperatures ranging from 150 to 171℃, by using the transient response method. 0n MgCO_3 no CO adsorbs and no CO oxidation proceeds. CO_2 is reversibly adsorbed obeying the Langmuir isotherm and the heat of adsorption is evaluated to be 2.7kcal/mol. On MgO, on the other hand, no CO adsorbs whereas the oxidation of CO easily proceeds and the rate equation is expressed : γ=kPco^<0.63>Po_2^<0.29> The apparent activation energy of reaction is estimated to be 14.6 kcal/mol. CO_2, adsorbs on the surface in both the reversible and irreversible forms. The reversibly adsorbed CO_2 has 4.3 kcal/mol of activation energy for adsorption and 13 kcal/mol for desorption. The irreversibly adsorbed CO_2 can partly desorb by elevating the temperature. A large part of the surface is covered with the strongly adsorbed CO_2, the surface coverage of which is 0.86. Only a small part of the active sites (θ=4.2×10^<-4>) is available for the adsorption of oxygen and one fifth of the amount is irreversible. The mode of the transient response curves obtained in the oxidation of CO indicates a typical monotone type suggesting that the reaction rate is controlled by the surface reaction and the desorptipon of CO_2.　　
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