Lanthanum exchanged X and Y type zeolites were prepared by ion exchange and investigated as catalysts for isobutane/2-butene alkylation. With the reactions performed in a continuously operated stirred tank reactor under industrially relevant conditions (T = 348 K, p = 20 bar, paraffin/ olefin molar ratio = 10, olefin weight hourly space velocity = 0.2 h(-1)) the catalyst lifetime of LaX was nearly twice as long as that of LaY. Moreover, a much higher yield of octane isomers was observed with LaX. The product distributions showed that LaX had a high activity for hydride transfer and "self-alkylation" as well as a higher concentration of strong Bronsted acid sites. These differences are related to a higher residual concentration of sodium cations in LaY leading not only to less, but also weaker strong Bronsted acid sites in LaY than in LaX. The replacement of the residual sodium cations by lanthanum cations is less favorable in LaY due to the lower concentration of appropriate sites to accommodate multivalent cations. (c) 2007 Published by Elsevier B.V.