Operando Molecular Spectroscopy During Ethylene Polymerization by Supported CrO x /SiO2 Catalysts: Active Sites, Reaction Intermediates, and Structure-Activity Relationship

Chakrabarti, Anisha; Gierada, Maciej; Handzlik, Jarosław; Wachs, Israel E.

doi:10.1007/s11244-016-0546-6

Cited by 57 publications

(62 citation statements)

References 54 publications

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“…Thus,determining the true structure of the active sites in these catalysts remains ac hallenge. [267,268] Thef ormation of Cr III active sites is consistent with earlier reports that show that Cr III salts supported on silica, [269] or well-defined Cr III silicates (discussed below), [270,271] are active polymerization catalysts. [266,267] However,the Cr II sites further evolve to Cr III at longer reaction times.…”

Section: Phillips and Union Carbide Catalystssupporting

confidence: 90%

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

et al. 2018

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Many industrial catalysts contain isolated metal sites on the surface of oxide supports. Although such catalysts have been used in a broad range of processes for more than 40 years, there is often a very limited understanding about the structure of the catalytically active sites. This Review discusses how surface organometallic chemistry (SOMC) engineers surface sites with well-defined structures and provides insight into the nature of the active sites of industrial catalysts; the Review focuses in particular on olefin production and conversion processes.

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Section: Phillips and Union Carbide Catalystssupporting

confidence: 90%

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

et al. 2018

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“…Beside these two bands, another band at ~1574 cm -1 , was observed and assigned to (C=C) vibrations. [18] In our case, two bands at 1462 and Accordingly, the bands at 2931 and 2862 cm -1 , and 1462 cm -1 are assigned to C-H vibrations in R-CH 2 -R. [55] According to the literature database, the observed spectra suggest adsorption of butane/hexane molecules or the formation of butadiyl species. [56,57] The TPD spectrum obtained from this sample is depicted in Fig.…”

Section: Ethylene Adsorptionmentioning

confidence: 56%

“…The silicate film was grown using 18 Thermal stability of deposited Cr species was examined by measuring IRA spectra after the sample was flashed in UHV to the temperatures increased stepwise. The results presented in Fig.…”

Section: Preparation Of Cr/sio 2 Model Catalystsmentioning

confidence: 99%

“…Wachs and coworkers using operando spectroscopies. [17,18] They found that in the initial stage Cr(VI) is reduced to Cr(III) with a formation of Cr(III)-(CH 2 ) 2 CH=CH 2 and Cr(III)-CH=CH 2 intermediates, with the latter representing the catalytic active site. However, this active organo Cr(III) site develops through ethylene coordination with hydroxylated Cr(III)-OH, instead of Cr(II) site as suggested by Scott's group.…”

Section: Introductionmentioning

confidence: 99%

“…Albeit the absolute wavenumbers are higher as compared to those reported in the literature, [17,37,38] the deviation might be related to that our measurements were performed under clean, UHV conditions with no adventitious adsorbates commonly present if measured in low vacuum on powdered samples. In attempt to discriminate monoxo and dioxo species we performed isotopic experiments with 18 O in the film. Due to spectral broadening and overlapping, it was difficult to precisely deconvolute the spectra.…”

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confidence: 99%

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Planar model system of the Phillips (Cr/SiO2) catalyst based on a well-defined thin silicate film

Pan

Shaikhutdinov

et al. 2018

Journal of Catalysis

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The Phillips catalyst (Cr/SiO 2 ) is successfully used in the large-scale production of polyethylene and has attracted a great interest in catalytic community over the last sixty years.However, the atomic structure(s) of the active site(s) and the reaction mechanism remain controversial, in particular due to the structural complexity and surface heterogeneity of the amorphous silica. In this work, we used a well-defined, atomically flat silicate bilayer film grown on Ru(0001) as a support offering the opportunity to investigate mechanistic aspects at the atomic scale. To fabricate a planar Cr/SiO 2 model system suitable for surface science studies, chromium was deposited using physical vapor deposition onto the hydroxylated silica film surface. Structural characterization and adsorption studies were performed by infrared reflection absorption spectroscopy (IRAS) and temperature programmed desorption (TPD).Hydroxyls groups seem to serve as anchoring cites to Cr ad-atoms. As monitored by IRAS, hydroxyls consumption correlated with the appearance of the new band at ~ 1007 cm -1 typical for Cr=O vibrations. In addition, CO titration experiments suggested also the presence of "naked" Cr, which transforms into mono-and di-oxo chromyl species and their aggregation upon oxidation treatments. TPD experiments of ethylene adsorption at low temperatures under UHV conditions showed the formation of butane as one of the main products. The resultant surfaces are thermally stable, at least, up to 400 K which allows to investigate ethylene polymerization further under more realistic conditions.

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Computational Studies of Chromium/Silica Catalysts

Liu

2018

Handbook of Transition Metal Polymerization Catalysts

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Operando Molecular Spectroscopy During Ethylene Polymerization by Supported CrO x /SiO2 Catalysts: Active Sites, Reaction Intermediates, and Structure-Activity Relationship

Cited by 57 publications

References 54 publications

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

Bridging the Gap between Industrial and Well‐Defined Supported Catalysts

Planar model system of the Phillips (Cr/SiO2) catalyst based on a well-defined thin silicate film

Computational Studies of Chromium/Silica Catalysts

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