Microcalorimetric, 13C NMR Spectroscopic, and Reaction Kinetic-Studies of Silica-Supported and L-Zeolite-Supported Platinum Catalysts for N-Hexane Conversion

• Published in: Journal of catalysis Vol. 150; no. 2; pp. 234 - 242
• Main Authors: Sharma, S.B., Ouraipyvan, P., Nair, H.A., Balaraman, P., Root, T.W., Dumesic, J.A.
• Format: Journal Article
• Language: English
• Published: Elsevier Inc 01.12.1994
• ISSN: 0021-9517; 1090-2694
• DOI: 10.1006/jcat.1994.1341

Reaction kinetics measurements of n-hexane conversion over 4% Pt/SiO 2 and 1% Pt/K(Ba)-L catalysts were made at a pressure of 3 atm and temperatures from 698 to 750 K. The rates of benzene and methylcyclopentane formation decrease with time during reaction over Pt/SiO 2, while 1% Pt/K(Ba)-L does not deactivate significantly. Microcalorimetric measurements at 353 K show that the heat of carbon monoxide adsorption is the same on freshly reduced Pt/SiO 2 and Pt/K(Ba)-L catalysts; however, carbonaceous species that accumulate on Pt/SiO 2 during n-hexane conversion decrease the total number of adsorption sites and the number of sites that adsorb carbon monoxide strongly. The 1% Pt/K(Ba)-L catalyst retains the adsorptive properties of the freshly reduced catalyst. Nuclear magnetic resonance studies of 13CO adsorption show that cluster-sized platinum particles are more resistant to deactivation by self-poisoning reactions than larger platinum particles. The greater catalyst stability and higher steady-state activity of L-zeolite-supported platinum catalysts may be attributed to the ability of L-zeolite to stabilize cluster-sized particles under reaction conditions. Differences in dehydrocyclization activity between catalysts may be related to differences in the number of strong adsorption sites that are present under reaction conditions.