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Multinuclear solid-state NMR study of the coordinative nature of alkylaluminum cocatalyst on Phillips CrOx/SiO2 catalyst

Paper ID Volume ID Publish Year Pages File Format Full-Text
41896 45903 2010 9 PDF Available
Title
Multinuclear solid-state NMR study of the coordinative nature of alkylaluminum cocatalyst on Phillips CrOx/SiO2 catalyst
Abstract

Solid-state nuclear magnetic resonance (NMR) spectroscopy was used to investigate the coordinative states of surface Al species on various triethylaluminum (TEA)-modified Phillips CrOx/SiO2 catalysts under different Al/Cr molar ratios. 1H and 27Al MAS NMR spectra clearly demonstrated that the existing states of surface Al species in TEA modified catalysts strongly depended on the concentration of TEA and on the calcination temperature used during the catalyst preparation process. 1H MAS NMR spectra of TEA-modified Phillips CrOx/SiO2 catalysts calcined at three different temperatures exhibited similar trends in peak shifts with increasing Al/Cr molar ratios, but the sensitivity dependence of variation in chemical shift of the main peaks on Al/Cr molar ratios increases with increasing of calcinations temperature. This increased sensitivity might have been due to the relatively low amount of residual hydroxyl groups present on the silica support after catalyst calcination. 27Al MAS NMR spectra showed the presence of three different coordination states (6-, 5-, and 4-coordinated Al species) in the TEA-modified Phillips catalysts. At relatively low Al/Cr molar ratios, the 6-coordinated Al species was the dominant species observed in the catalysts. However, the 4-coordinated Al species became dominant at relatively high Al/Cr ratios for TEA-modified catalysts calcined at 600 and 800 °C, because the increase in TEA concentration might have decreased the amount of oxygen atoms surrounding each Al species. After a saturation state of Al species directly coordinated on the catalyst or silica surface reached, residual TEA coordinated with the Al species already coordinated on the catalyst or silica surface, thus increasing the coordination number of the Al species. Consequently, the 6-coordinated Al species became predominant again for the TEA-modified catalysts calcined at 600 and 800 °C.

Graphical abstractFigure optionsDownload full-size imageDownload high-quality image (40 K)Download as PowerPoint slideResearch highlights▶ Solid-state NMR was first used to investigate coordinative states of Al on Phillips catalysts. ▶ States of Al species strongly depended on the concentration of TEA and the calcination temperature. ▶ 4-Coordinated Al species seems related to the polymerization activity.

Keywords
Phillips catalyst; Al–alkyl cocatalyst; Ethylene polymerization; Solid-state NMR
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Multinuclear solid-state NMR study of the coordinative nature of alkylaluminum cocatalyst on Phillips CrOx/SiO2 catalyst
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Publisher
Database: Elsevier - ScienceDirect
Journal: Applied Catalysis A: General - Volume 389, Issues 1–2, 1 December 2010, Pages 186–194
Authors
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Subjects
Physical Sciences and Engineering Chemical Engineering Catalysis
Get Full-Text Now
Don't Miss Today's Special Offer
Price was $35.95
You save - $31
Price after discount Only $4.95
100% Money Back Guarantee
Full-text PDF Download
Online Support
Any Questions? feel free to contact us