High energy ion irradiation-induced ordered macropores in zeolite crystals.

The present study demonstrated the possibility to form a secondary system of parallel macropores in zeolite crystals. The secondary pore formation was predetermined by the creation of defect zones in ZSM-5 crystals. A high energy (238)U ion beam was employed to form latent tracks in zeolite crystals, which were further subjected to attack with diluted HF solution and thus developed to uniformally sized macropores. The selective extraction of material from latent tracks was due to the higher etching velocity of highly agitated zones created by heavy ion bombardment. The combination of complementary methods unambiguously demonstrated the formation of hierarchical zeolite material comprising parallel macropores that extended through the entire crystal. The catalytic tests revealed improved activity at retained selectivity in the reaction of m-xylene conversion. The possibility to control the number of macropores per unit of crystal surface and thus the catalytic performance of the material was demonstrated. This model material is expected to bring better understanding to the effect of a secondary pore system in the catalytic performance of hierarchical zeolites obtained by the top-down or bottom-up approach.