Statistical mechanics and semi-empirical molecular orbital theory (PM6) are used to calculate the surface coverage of CO 2 and H 2 molecular species chemically adsorbed on the surface of Cu and Zn micro clusters. The calculation shows that CO 2 is adsorbed well both on the surface of Cu and Zn micro clusters. Although H 2 is adsorbed well on the surface of Zn micro clusters, H 2 absorption on the surface of Cu micro clusters is much more limited in the pressure range of 20 -100 atm and temperature range of 200 -1000 K. Reaction rates are also estimated for some chemical adsorption process of H 2 gas using theory of absolute reaction rates. It is found that the values of the reaction rate calculated in the present paper agree reasonably well with the experimental values.