In metal-free ZSM-5, the decrease in the concentration of Bronsted and Lewis acid sites parallels the increase in the SiO2/Al2O3 ratio. Tn the presence of residual moisture, the adsorption of small alkanes does not markedly depend on the SiO2/Al2O3 ratio in the range from 30 to 150. The acidity is more important for the adsorption of alkenes (propene) which oligomerize following adsorption. The addition of 5 wt.% of La does nor significantly affect the strength of the surface acid sites but does decrease their concentration. It causes a transformation, in a part, of the Bronsted acid sites. These new centers could perhaps be assigned to LaO(OH) or La(OH)(2)(+) species which may be formed on the surface in La-containing ZSM-5. La could exchange only the strongest acidic sites without inducing large changes in their total concentration. La addition has a very small effect on the adsorption of small hydrocarbons. The exchange of the protons by Cu2+ decreases the concentration of Bronsted acid sites. At a sufficient loading of the ZSM-5 by Cu2+, i.e, at an atomic ratio Cu/Al > 1.0, the exchange can almost totally suppress the Bronsted acidity. Another effect of the ion exchange is the suppression of the adsorption capacity of small hydrocarbons due to lowered surface area and internal pore volume. The lowered available internal pore volume also limits the extent of the oligomerization of propene.