SKELETAL REACTIONS OF N-HEXANE OVER PT-NAY, PT SIO2, HY, AND MIXED PT/SIO2+HY CATALYSTS/

The activity and selectivity of three samples of 8% Pt-NaY calcined at 633, 723, and 823 K, respectively, have been probed with n-hexane as the model reactant at 603 K and subatmospheric pressures in a glass cl osed-loop reactor. These catalysts were compared with 6.3% Pt/SiO2 (EU ROPT-1), HY, and a physical mixture of the latter two. The activity of all Pt-NaY catalysts is superior to EUROPT-1 and they deactivate more slowly. The selectivity pattern of all Pt-NaY samples is closer to th at characteristic of monofunctional Pt catalysts, as opposed to the pr onounced acidic character of pure HY and the mechanical mixtures. The sample calcined at 633 K, which has the highest dispersion and probabl y contains Pt particles anchored to the support as [Pt-n - H-x](x+) en tities, shows the highest aromatization selectivity. The sample precal cined at 823 K with the lowest dispersion has a pronouncedly high skel etal isomerization selectivity. The isomerization pathway may be relat ed to the C-5 cyclic route on metal sites that are more abundant on th e larger crystallites of this catalyst and are more easily accessible with its partially collapsed zeolite framework. Characteristic differe nces between samples in the response of their catalytic performance to changes in hydrogen and hydrocarbon pressure are discussed. (C) 1995 Academic Press, Inc.