ChemInform Abstract La3+ ions are introduced (ion-exchange) into a series of faujasite and ZSM-20 zeolites having a minimum amount of extraframework Al and a broad range of Si/Al ratios and the catalytic activity of the resulting materials in the hexane cracking reaction is measured. The cracking activity is found to increase with increasing La3+ loading up to a maximum and then decreases. Plots of the maximum activities of the different zeolites versus the framework Al content, Alf, show that the catalytic activity reaches a maximum at 35 Al/unit cell. The change in activity with respect to Alf parallels that observed with steam-dealuminated zeolites, but the absolute activities of the La-exchanged samples are lower. These results are consistent with a model of strong acidity in which both the Alf and the presence of polyvalent cations in the β-cage are important. Lanthanum ions in the form of (La(µ-OH)2La)4+ and La(OH)2+ appear to be responsible for a withdrawal of electrons from the framework hydroxyl groups resulting in a higher acidity of the protons.

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