REACTIONS OF N-HEXANE OVER PT-ZEOLITE CATALYSTS OF DIFFERENT ACIDITY

Pt-HY, Pt-NaHY, Pt-NaY, and Pt-NaX catalysts, which possess decreasing acidity and increasing basicity in the above sequence, were tested at 603 K in n-hexane conversion as a model reaction. Pt-HY and Pt-NaHY, which are acidic, are more active by about an order of magnitude than the two non-acidic catalysts. Selectivities measured at different hydrocarbon and hydrogen pressures are presented as a function of the overall conversion. Pt-HY and Pt-NaHY produce mainly skeletal isomers, fragments and, at most, minor amounts of benzene. Fragment composition indicated that pronounced cracking occurs over Pt-HY only, together with minor hydrogenolysis on the metallic centers. This latter reaction is responsible for most fragments over the other three catalysts. Metal-catalyzed C5-cyclic isomerization, ring closure, and pronounced aromatization prevail over Pt-NaY and Pt-NaX. The latter behaves like a typical non-acidic metal catalyst. Pt-NaY exhibits an outstanding aromatization selectivity which can possibly be attributed to the interaction of basic centers of the framework with the Pt particles rather than to geometric reasons. (C) 1994 Academic Press, Inc.