4. Zeolite-Supported Noble Metal Catalysts for Low-Temperature Hydrogenation of Naphthalene

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Platinum and palladium catalysts supported on H-mordentine (HM) and HY zeolites have been prepared, characterized and tested in the hydrogenation of naphthalene at 25-200℃, with or without added organic sulfur-containing compound (benzothiophene). Catalytic behavior is compared with Pt and Pd on conventional Al_2O_3 and TiO_2 supports. The zeolite-supported catalysts had significantly higher activity. High selectivity for one of two possible decahydronaphthalene (DeHN) isomers was obtained with the zeolite catalysts. For example, at 200℃ and 100% naphthalene conversion, 80% selectivity for cis-DeHN was obtained with Pt/HY; whereas, Pd/HM can be made to give 95% selectivity for trans-DeHN. On HM support, Pt was found to catalyze both hydrogenation and isomerization of cis-DeHN to trans-DeHN, but on HY support, Pt catalyzes only hydrogenation. High DeHN isomer selectivity was not realized with catalysts based on the conventional supports. Addition of sulfur in the form of benzothiophene decreased the activity of all catalysts tested, but sulfur poisoning was much less severe for zeolite-supported catalysts.