COKE AND PRODUCT PROFILES FORMED ALONG THE CATALYST BED DURING N-HEPTANE REFORMING .1. NONSULFIDED PT/AL2O3 AND PT-RE/AL2O3

Deactivation of Pt/Al2O3 and Pt-Re/Al2O3 during n-heptane reforming was studied using a multi-outlet reactor, which allows determination of gas-phase composition profiles and coke profiles along the catalyst bed. Coke profiles strongly depend on catalyst type and pressure. At low pressure, 105 kPa, the coke content on the Pt catalyst increases along the bed and at 1225 kPa decreases. Between these pressure values, a maximum in the coke profile is observed. Similar changes in C5 ring naphthene concentration profile with pressure are observed and a general correlation has been established between coke and C5 naphthenes covering variations in time on-oil, pressure, and location of catalyst. Therefore, C5 naphthenes appear as the dominant factor in the deactivation of these catalysts. The addition of Re to a Pt catalyst has a similar effect on the coke profile and on the C5 naphthene profile of the Pt catalyst as increasing its operation pressure, i.e., shifting the maximum of coke and C5 naphthene profile from bed outlet to inlet. Additionally, pressure at which coke is deposited affects TPO spectra. An increase in the total pressure of a Pt catalyst produces a TPO spectrum similar to that of Pt-Re. These results suggest that Re increases the hydrogen surface concentration on Pt-Re, and therefore, Re decreases the dehydrogenating capacity of this catalyst and increases its hydrogenating activity. The lower dehydrogenation activity of Pt-Re catalysts as compared with Pt catalysts results in forming less C5 ring diolefins and, thus, Pt-Re catalysts exhibit lower coke make and better stability. © 1993 Academic Press, Inc.