The activity, stability, and selectivity of a series of bifunctional Pt/SAPO-5 and Pt/SAPO-11 catalysts containing 0.5 wt% platinum were compared for n-heptane transformation at 300-450 degrees C and atmospheric and 3 and 5 bars hydrogen pressures. Hydrogen pressure had a strong influence on the activity, iso-heptane selectivity, and time-on-stream deactivation. Isomerization of n-heptane to iso-heptanes was the major reaction with Pt/SAPO-5 catalyst, especially at lower conversions, whereas Pt/SAPO-11 shows high selectivity to isomers in all conversion range. The selectivity patterns found in these classes of molecular sieve catalysts are wed interpreted in terms of a series of reaction pathways that incorporate both confinement effects and shape selectivity factors as being important in determining the observed product distribution. Based on experimental results, the protonated cyclopropane appears as an intermediate in the mechanism of this reaction.