IR KLTL ZEOLITES - STRUCTURAL CHARACTERIZATION AND CATALYSIS OF N-HEXANE REFORMING/

Ir/KLTL zeolite catalysts were prepared by incipient wetness impregnat ion of LTL zeolites with [Ir(NH3)(5)Cl]Cl-2. The catalysts were charac terized by extended X-ray absorption fine structure (EXAFS) spectrosco py, infrared spectroscopy, and H-2 chemisorption. EXAFS data show that the average Ir cluster size (after treatment at 300 degrees C in H-2) increased from about 7 to 20 Angstrom as the zeolite K:Al atomic rati o increased from 0.34 to 1.56. Infrared spectra of adsorbed CO show th at the electron donation to the Ir increased as the K:Al ratio increas ed. In contrast to the performance reported for Pt/KLTL zeolites with metal clusters as small as those observed in the present experiments, the Ir/KLTL catalyst has a low selectivity for dehydrocyclization of n -hexane at 440-480 degrees C and 1 atm with a H-2:n-hexane feed molar ratio of 6. Instead, the catalysts are selective for hydrogenolysis. T he selectivity is insensitive to the K:Al ratio, but the activity for dehydrocyclization is a maximum at a K:Al atomic ratio of about 1. The results show that even the smallest Ir clusters to which electron don ation is significant still behave essentially like metallic Ir in the catalytic reactions. (C) 1996 Academic Press, Inc.