Understanding Zeolite Catalysis: Inverse Shape Selectivity Revised

Doing a stretch in zeolites: Usually molecular sieves selectively process and yield the fastest diffusing, least bulky molecule. When sieves were identified that seemed to selectively yield, adsorb, and stabilize isomers with a larger diameter, the term “inverse shape selectivity” was coined. Molecular simulations indicate that these sieves preferentially yield molecules because of entropic effects, which favor those molecules that have the shortest effective length. In narrow zeolite pores linear molecules are stretched whereas in wide pores they can be coiled (see diagram).