Catalytic dehydration of propan-2-ol has been investigated over the range 353 to 407 K on a series of LaY zeolites containing up to 9.5 lanthanum atoms per unit cell. Zero-order kinetics were obeyed, with mean activation energies of 128.5 and 139.5 kJ mol ^-1 , respectively, for diisopropyl ether and propene formation. These activation energies, which were independent of both the temperature of catalyst activation and the extent of lanthanum exchange, are identical to those for the reaction on HY zeolites made from the same NaY starting material. Reaction is thus considered in terms of the same single Brønsted acid-site mechanism, where differences in activity arise from differences in the concentration of active sites. Progressive poisoning experiments with pyridine assess the total concentration of acid sites, which generally exceeds that which is accessible to propan-2-ol and active in catalysis.