Electron paramagnetic resonance of heterogeneous chromium catalysts

Weckhuysen, Bert M.; Schoonheydt, Robert A.; Mabbs, Frank E.; Collison, David

doi:10.1039/ft9969202431

Cited by 103 publications

(108 citation statements)

References 22 publications

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“…The ESR spectra of the assynthesized Cr-containing samples were dominated by an isotropic signal and a broad signal with g of about 2 and 5.2, respectively. This is characteristic of Cr 3+ in a distorted octahedral coordination [3,24,25,31,35,36]. After calcination, a strong and narrow signal, attributed to isolated Cr 5+ , appeared with a g = 1.97, whereas the broad signal with the g % 2 disappeared.…”

Section: Catalyst Synthesis and Characterizationmentioning

confidence: 98%

Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)- and (Cr, V)APO-5 molecular sieves

Fan

Song

et al. 2006

Microporous and Mesoporous Materials

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Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)-and (Cr, V)APO-5 molecular sieves ) molecular sieves have been hydrothermally synthesized and characterized. The as-synthesized and calcined samples were investigated with XRD, ICP, DRS UV-vis spectroscopy, ESR, 27 Al MAS NMR techniques to explore the valence, coordination and location of the incorporated transition metal ions. It was shown that isomorphous substitution of Co 2+ for Al 3+ convincingly occurred, and V 4+ also anchored to the sample by coordinating to two framework oxygen atoms and most probably occupying P 5+ sites, while no unambiguous spectroscopic evidence was provided for the incorporation of Cr 3+ in the lattice, although chemical analysis suggests this possibility in the case that Co 2+ or V 4+ are added to the synthesis gel. The preferential sequence for the incorporation of these transition metal ions in the AFI framework is: Co 2+ > V 4+ > Cr 3+ . After calcination, almost all V 4+ ions were oxidized to V 5+ , whereas Cr 3+ ions were oxidized to Cr 5+ and Cr 6+ . As catalysts, the (M, N)APO-5 molecular sieves are highly active for the selective oxidation of cyclohexane with a high cyclohexanone/cyclohexanol ratio in the presence of H 2 O 2 . The reaction temperature and solvent significantly influenced the catalytic behavior. Although some leaching of the transition metal ions was observed, the catalytic performance remained stable at least within five repeated runs.

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Section: Catalyst Synthesis and Characterizationmentioning

confidence: 98%

Synthesis, characterization and catalysis of (Co, V)-, (Co, Cr)- and (Cr, V)APO-5 molecular sieves

Fan

Song

et al. 2006

Microporous and Mesoporous Materials

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“…(1) Infrared spectroscopy 47,78,65 and diffuse reflectance spectroscopy in the near-infrared region, 93 indicating the consumption of OH groups. This OH consumption is proportional to the quantity of deposited Cr, and Turek et al 96 have shown that on alumina this OH consumption starts from the more basic OH groups to the more acidic groups.…”

Section: +mentioning

confidence: 99%

Surface Chemistry and Spectroscopy of Chromium in Inorganic Oxides

1996

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“…For 3d TMIs the most popular techniques for direct probing of the oxidation state and coordination environments are X-ray photoelectron spectroscopy (XPS) (1-7), electron spin resonance (ESR) (8)(9)(10)(11)(12), X-ray absorption 1 To whom correspondence should be addressed. spectroscopy (EXAFS-XANES) (13,14), Raman spectroscopy (15)(16)(17)(18)(19)(20)(21), and diffuse reflectance spectroscopy (DRS) (22)(23)(24)(25)(26)(27)(28)(29)(30).…”

Section: Introductionmentioning

confidence: 99%