Reduction of the Phillips catalyst by various olefins: Stoichiometry, thermochemistry, reaction products and polymerization activity

Reduction of the Phillips catalyst by various olefins: Stoichiometry, thermochemistry, reaction products and polymerization activity

[Display omitted] •Cr(VI)/SiO2 reduced by ethylene and hexenes.•Olefin oxidation products are retained on the surface of Cr/SiO2.•Thermal decomposition products CO2 and H2 suggest formation of formate.•Thermal decomposition products CO2 and CH4 suggest formation of acetate.•Reduction of Cr(VI) by he...

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Bibliographic Details
Published in:Journal of catalysis Vol. 344; pp. 657 - 668
Main Authors: Potter, Kelsey C., Beckerle, Connor W., Jentoft, Friederike C., Schwerdtfeger, Eric, McDaniel, Max P.
Format: Journal Article
Language:English
Published: San Diego Elsevier Inc 01-12-2016
Elsevier BV
Subjects:
Adsorbate
Catalysis
Catalysts
CrO3
Ligand
Polyethylene
Reaction enthalpy
Reaction kinetics
Reduction
Silica
Temperature-programmed desorption
Thermogravimetric analysis
Reduction
Polyethylene
CrO3
Adsorbate
Reaction enthalpy
Ligand
Silica
Temperature-programmed desorption
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Summary:[Display omitted] •Cr(VI)/SiO2 reduced by ethylene and hexenes.•Olefin oxidation products are retained on the surface of Cr/SiO2.•Thermal decomposition products CO2 and H2 suggest formation of formate.•Thermal decomposition products CO2 and CH4 suggest formation of acetate.•Reduction of Cr(VI) by hexenes does not necessarily produce active sites. The adsorption, reaction and desorption of ethylene or hexenes on Cr(VI)/SiO2 containing 1 or 3wt.% chromium were monitored by thermogravimetry, differential scanning calorimetry and mass spectrometry. Reaction of Cr(VI)/SiO2 with ethylene at a temperature of 200°C always included some oligomerization, making it impossible to identify the stoichiometry of the initial redox reaction. Reaction of Cr(VI)/SiO2 with 1-hexene or cyclohexene at 150°C indicated an adsorption stoichiometry of one olefin per chromium. Heats of reaction were consistent with oxidation of the olefin to an aldehyde or ketone, or even to a carboxylic acid or ester. Oxidation products were retained on the surface. Thermal desorption of surface products resulted in CO2 evolution at temperatures of 265–285 and 390–415°C, with the co-products indicating decomposition of formate and acetate species, respectively. Reduction of Cr(VI) with ethylene led to sites active for ethylene polymerization after thermal desorption of the redox products, whereas reduction with hexenes did not generate active sites irrespective of thermal desorption of products.
ISSN:0021-9517
1090-2694
DOI:10.1016/j.jcat.2016.10.031