Isolated FeII on silica as a selective propane dehydrogenation catalyst

Bo Hu, Neil M. Schweitzer, Guanghui Zhang, Steven J. Kraft, David J. Childers, Michael P. Lanci, Jeffrey T. Miller*, Adam S. Hock

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

67 Scopus citations

Abstract

We report a comparative study of isolated FeII, iron oxide particles, and metallic nanoparticles on silica for non-oxidative propane dehydrogenation. It was found that the most selective catalyst was an isolated FeII species on silica prepared by grafting the open cyclopentadienide iron complex, bis(2,4-dimethyl-1,3-pentadienide) iron(II) or Fe(oCp)2. The grafting and evolution of the surface species was elucidated by 1H NMR, diffuse reflectance infrared Fourier transform spectroscopy and X-ray absorption spectroscopies. The oxidation state and local structure of surface Fe were characterized by X-ray absorption near-edge structure (XANES) and extended X-ray absorption fine structure. The initial grafting of iron proceeds by one surface hydroxyl Si-OH reacting with Fe(oCp)2 to release one diene ligand (oCpH), generating a SiO2-bound FeII(oCp) species, 1-FeoCp. Subsequent treatment with H2 at 400 °C leads to loss of the remaining diene ligand and formation of nanosized iron oxide clusters, 1-C. Dispersion of these Fe oxide clusters occurs at 650 °C, forming an isolated, ligand-free FeII on silica, 1-FeII, which is catalytically active and highly selective (∼99%) for propane dehydrogenation to propene. Under reaction conditions, there is no evidence of metallic Fe by in situ XANES. For comparison, metallic Fe nanoparticles, 2-NP-Fe0, were independently prepared by grafting Fe[N(SiMe3)2]2 onto silica, 2-FeN∗, and reducing it at 650 °C in H2. The Fe NPs were highly active for propane conversion but showed poor selectivity (∼14%) to propene. Independently prepared Fe oxide clusters on silica display a low activity. The sum of these results suggests that selective propane dehydrogenation occurs at isolated FeII sites.

Original languageEnglish (US)
Pages (from-to)3494-3503
Number of pages10
JournalACS Catalysis
Volume5
Issue number6
DOIs
StatePublished - Jun 5 2015

Keywords

  • EXAFS
  • Fe XANES
  • Fe nanoparticles on silica
  • dehydrogenation catalyst
  • isolated Fe catalysts
  • propane dehydrogenation

ASJC Scopus subject areas

  • Catalysis
  • Chemistry(all)

Fingerprint Dive into the research topics of 'Isolated Fe<sup>II</sup> on silica as a selective propane dehydrogenation catalyst'. Together they form a unique fingerprint.

Cite this