Structure sensitivity of hydrogenolytic cleavage of endocyclic and exocyclic C-C bonds in methylcyclohexane over supported iridium particles

Hui Shi, Oliver Y. Gutiérrez, Gary L. Haller, Donghai Mei, Roger Rousseau, Johannes A. Lercher

Research output: Contribution to journalArticle

19 Citations (Scopus)

Abstract

Structure sensitivities, H2 pressure effects, and temperature dependencies for rates and selectivities of endo- and exocyclic C-C bond cleavage in methylcyclohexane were studied over supported Ir catalysts. The rate of endocyclic C-C bond cleavage first decreased and then increased with declining Ir dispersion from 0.65 to 0.035. The ring opening (RO) product distribution remained unchanged with varying H2 pressure on small Ir particles, while further shifting to methylhexanes with increasing H2 pressure on large particles. In contrast, the rate and selectivity of exocyclic C-C bond cleavage decreased monotonically with increasing H2 pressure and decreasing Ir particle size. The distinct dependencies of endocyclic and exocyclic C-C bond cleavage pathways on Ir dispersion and H 2 pressure suggest that they are mediated by surface species with different ensemble size requirements. DFT calculations were performed on an Ir50 cluster and an Ir(1 1 1) surface, with or without pre-adsorbed hydrogen atoms, to provide insight into the observed effects of particle size and H2 pressure on RO pathways. On small Ir particles, the calculated dehydrogenation enthalpies for all endocyclic bonds were similar and affected to similar extents by H2 pressure; on large particles, the selectivity to n-heptane (via substituted C-C bond cleavage) was even lower than on small particles as a result of the least favorable adsorption and dehydrogenation energetics for hindered bonds.

Original languageEnglish
Pages (from-to)70-78
Number of pages9
JournalJournal of Catalysis
Volume297
DOIs
Publication statusPublished - Jan 2013

Fingerprint

Iridium
iridium
cleavage
sensitivity
Dehydrogenation
selectivity
dehydrogenation
Particle size
Pressure effects
Heptane
Catalyst supports
rings
Discrete Fourier transforms
pressure effects
heptanes
methylcyclohexane
Hydrogen
Enthalpy
adatoms
hydrogen atoms

Keywords

  • Demethylation
  • Hydrogenolysis
  • Iridium
  • Methylcyclohexane
  • Ring opening
  • Structure sensitivity

ASJC Scopus subject areas

  • Catalysis
  • Physical and Theoretical Chemistry

Cite this

Structure sensitivity of hydrogenolytic cleavage of endocyclic and exocyclic C-C bonds in methylcyclohexane over supported iridium particles. / Shi, Hui; Gutiérrez, Oliver Y.; Haller, Gary L.; Mei, Donghai; Rousseau, Roger; Lercher, Johannes A.

In: Journal of Catalysis, Vol. 297, 01.2013, p. 70-78.

Research output: Contribution to journalArticle

Shi, Hui ; Gutiérrez, Oliver Y. ; Haller, Gary L. ; Mei, Donghai ; Rousseau, Roger ; Lercher, Johannes A. / Structure sensitivity of hydrogenolytic cleavage of endocyclic and exocyclic C-C bonds in methylcyclohexane over supported iridium particles. In: Journal of Catalysis. 2013 ; Vol. 297. pp. 70-78.
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