Coke and product profiles formed along the catalyst bed during n-heptane reforming .2. Influence of S on Pt/Al2O3 and Pt-Re/Al2O3

Studies of coke and product profiles along catalyst beds of Pt/Al2O3 and Pt-Re/Al2O3 during n-heptane reforming have provided insight into catalyst deactivation and reaction mechanisms. The addition of rhenium to a Pt catalyst changes coke and product profiles similar to those observed with an increase in pressure. Sulfur modifies these profiles in the opposite direction of rhenium. It affects the catalyst in a similar manner to a decrease in reactor pressure: a reduction in hydrogenolysis activity, an increase in dehydrogenation and coke-make, and a shift of the maximum in the coke profile toward the bottom of the reactor. Due to a slow stripping of sulfur during reforming reactions, an increasing sulfur concentration along the bed is observed at the end of several-days run. As a consequence, the coke profile does not match exactly with the C5-ring naphthene concentration profile, as was previously found on both unsulfided Pt and Pt-Re catalysts. The observed increase in coke-make and dehydrogenation activity, when sulfur is added to the Pt-Re catalyst, is probably due to a decrease in the hydrogen surface fugacity produced through electronic modifications of Pt by adsorbed sulfur atoms. (C) 1996 Academic Press, Inc.