The structure sensitivity of cyclohexane dehydrogenation and hydrogenolysis catalyzed by platinum single crystals at atmospheric pressure

• Published in: Journal of catalysis 1981-02, Vol.67 (2), p.371-386
• Main Authors: Herz, R.K., Gillespie, W.D., Petersen, E.E., Somorjai, G.A.
• Format: Article
• Language: English
• Subjects: INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1016/0021-9517(81)90297-9

The dehydrogenation and hydrogenolysis of cyclohexane catalyzed by platinum single-crystal surfaces has been investigated at total reactant pressures of 115 to 760 Torr and temperatures of 533 to 573 K. The flat (111), stepped (557), and kinked (25, 10, 7) and (10, 8, 7) surfaces used in this study were characterized in ultrahigh vacuum by low-energy electron diffraction and Auger electron spectroscopy, before and after reaction experiments. Benzene, cyclohexene, n-hexane, and alkane fragments with carbon number less than 6 were observed as reaction products. The rate of dehydrogenation to benzene on the four surfaces increased in the order (111) < (557) < (10, 8, 7) < (25, 10, 7). On the other and, the hydrogenolysis rates and the rate of cyclohexene production were highest on the (111) surface. In general, the reaction rates decreased with increasing reaction time. The decrease of the dehydrogenation rates was due to reversible product inhibition by benzene, as well as the irreversible adsorption of tightly bound carbonaceous deposits. The hydrogenolysis rates did not exhibit product inhibition and decreased solely as the result of the irreversibly adsorbed carbonaceous species. The strength of inhibition by benzene increased in the order (25, 10, 7) < (10, 8, 7) < (557) < (111). These high-pressure results using single-crystal catalysts are compared to similar studies previously performed at pressures of less than 10 −5 Torr. A comparison is also made to studies by others using dispersed platinum catalysts.