Origin of First-Order Kinetics during the Bimolecular Cracking of n-Hexane over H-ZSM-5 and H- Zeolites Academic Article uri icon

abstract

  • An in situ diffuse FTIR spectroscopy study of n-hexane cracking over H-ZSM-5 and H--zeolites was performed to elucidate the origin of first-order kinetics under bimolecular conditions. Contrary to an earlier proposal, the acidic protons were not extensively complexed with olefins during the reaction. A simple qualitative kinetic model consisting of six elementary reactions were used to rationalize the first-order rate law for n-hexane conversion with only a small fraction of the protons being complexed. Because of competing reactions, the olefin and the protonated-complex concentrations became constant as a function of residence time and was independent of the hexane concentration. The model provided a plausible explanation consistent with the kinetic and IR results. By considering a set of reactions including olefin adsorption/desorption, -scission, and oligomerization, the alkoxide concentration may be nearly independent of n-hexane concentration, even when most of the protons remain uncomplexed. Thus, during bimolecular cracking, first-order kinetics may prevail.

published proceedings

  • Journal of Catalysis

author list (cited authors)

  • Kotrel, S., Rosynek, M. P., & Lunsford, J. H.

citation count

  • 36

complete list of authors

  • Kotrel, Stefan||Rosynek, Michael P||Lunsford, Jack H

publication date

  • April 2000