The cyclization of terminal diols with ammonia was carried out over modified ZSM-5 catalyst, to obtain the desired saturated heterocyclic product in high yields and selectivity. In the reaction of 1,4-butanediol and ammonia at 250degreesC, >95% yield was obtained of pyrrolidine over FeZSM-5 and CuZSM-5 catalysts. The high yield of piperidine, >62-90% was obtained over NiZSM-5 and CuZSM-5 in the reaction of pentanediol and ammonia. Similarly, greater than or equal to88% yield was obtained of hexamethyleneimine over CeZSM-5 in the reaction of hexanediol and ammonia. (C) 2002 Published by Elsevier Science B.V.