Ds. Lafyatis et al., A TAP REACTOR INVESTIGATION OF C6 REFORMING ON NONACIDIC AND ACIDIC SUPPORTED METAL-CATALYSTS, Journal of catalysis, 147(2), 1994, pp. 552-566
The reforming of C6 hydrocarbons on Pt/Mg(Al)O, Pt/K-L, Pd/Mg(Al)O, an
d Pt-Re/Al2O3 (sulfided and unsulfided forms) has been investigated us
ing the temporal analysis of products (TAP) reactor. Pulse experiments
with several different pure C6 feeds were performed in a continuous f
low of H-2 at a pressure of 1 bar and temperatures between 400 and 510
-degrees-C. Under these conditions the reaction network for all of the
catalysts appeared to occur by a monofunctional metal pathway: methyl
pentane --> methylcyclopentane --> n-hexane --> benzene. Evidence of p
artially dehydrogenated linear C6 molecules as intermediates between n
-hexane and benzene was also obtained. Turnover frequencies and benzen
e selectivities for the Pt/Mg(Al)O and the Pt/KL catalysts were compar
able. For the Pd/Mg(Al)O catalyst the selectivity to benzene was highe
r and the turnover frequency was lower. Because the TAP technique refl
ects only the activity of truly active catalytic sites, the turnover f
requencies from this study (10(-12) sec-1 at 425-degrees-C on Pt) are
higher than generally reported in the literature. Previous investigati
ons of the Pt-Re/Al2O3 catalyst under industrial conditions have shown
that the bifunctional mechanism was dominant. The monofunctional mech
anism found here implies the existence of two dehydrocyclization pathw
ays on these catalysts: a monofunctional metal pathway favored at low
pressures, and a bifunctional pathway which is dominant at higher pres
sures. (C) 1994 Academic Press, Inc.