Abstract Cyclopropane isomerization to propylene over various Eu 3+ loadings in NaX zeolite have been studied by measurements of steady-state and transient kinetics and by Fourier transform infrared spectroscopy. As Eu 3+ loading increases, the rate of deactivation increases, the conversion increases, apparent activation energies are lowered, and Brønsted acid site strength and amounts increase. Apparent activation energies of 13–15 kcal/mol for propylene formation have been observed for these systems, consistent with literature reports for other metal supported heterogeneous catalyst systems. Deactivation studies have shown that activity can be restored by heating in He at 380°C between various temperature runs, and that gases desorbed during regeneration are predominantly propylene. Poisoning studies of Brønsted sites with Na vapor lead to deactivation of these catalysts. A reaction mechanism scheme based on π allyl intermediates in the supercages of Eu +NaX has been proposed to account for the activity, selectivity, and stability of these catalysts.