(Co‐)Oligomerization of Olefins to Hydrocarbon Fuels: Influence of Feed Composition and Pressure

Fuchs, Constantin; Arnold, Ulrich; Sauer, Jörg

doi:10.1002/cite.202200209

Cited by 4 publications

(1 citation statement)

References 44 publications

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“…For Cr/LTO, selectivity toward terminal olefins (67%) is higher than that observed at atmospheric pressure of ethylene (Figure S10), indicating that olefin isomerization is slower at higher pressures. 86,87 In contrast to the catalytic behavior of Cr/LTO, molecular organometallic chromium(II) complexes such as Cr(CH 2 SiMe 3 ) 2 (dippe) have been shown to polymerize ethylene slowly at 25 °C and 10 atm to produce polyethylene. 88 Such a dichotomy in product distributions and selectivities might plausibly be explained by the generation and highly electron-rich low-valent chromium sites on lithium titanium oxide lowering the energy required to bind two ethylene molecules and oxidatively cyclize them to provide metallacyclopentanes, bypassing the Cossee−Arlman insertion mechanisms which generally produce high molecular weight polyethylenes.…”

Section: ■ Introductionmentioning

confidence: 99%

Supported Organochromium Ethylene Oligomerization Enabled by Surface Lithiation

Kanbur,

Hall,

Kim

et al. 2024

ACS Catal.

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In this work, supported organochromium ethylene polymerization catalysts have been tuned to mediate ethylene oligomerization via surface lithiation, which provides a generalizable protocol to control stereoelectronics and redox states of surface organometallic active sites. The homoleptic chromium(IV) alkyl complex Cr(CH 2 SiMe 3 ) 4 was grafted on high-surface-area anatase titania (TiO 2 ) nanoparticles as well as on silica to produce Cr/TiO 2 and Cr/SiO 2 , respectively. Treatment of these materials with excess n-butyllithium led to the reduced chromium complexes Cr/Li x TiO 2 and Cr/Li/SiO 2 , each of which still retains one hydrocarbyl ligand on chromium. A set of heterogeneous complexes were studied by electron paramagnetic resonance and X-ray absorption spectroscopy, which indicate a reduction in the oxidation state of the major chromium species to Cr II upon lithiation. Cr/ Li x TiO 2 converts ethylene to hexenes with a high selectivity (>80%), which was persistent over 10 days at 80 °C, achieving >950 turnovers. The exclusive formation of C 4 and C 6 olefins, preferring the trimerization product, without a statistical (Flory−Schulz) distribution is characteristic of the oxidative cyclization oligomerization mechanism rather than the traditional Cossee−Arlman mechanism, whereas Cr/Li/SiO 2 produced a mixture of trimerization and polymerization products, suggesting site heterogeneity in the silica-based material. On the other hand, the unreduced chromium(IV) materials as well as low lithium-containing Cr/Li x TiO 2 (x < 0.16) exclusively produced ultrahigh molecular weight polyethylene, determined by differential scanning calorimetry and gel permeation chromatography analysis, likely formed via a linear-insertion mechanism, with a crossover from the polymerization to oligomerization regime observed at ∼16% Li intercalation.

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Section: ■ Introductionmentioning

confidence: 99%