Characterization of Surface Supported Organometallic Olefin Polymerization Catalysts by High Field Solid-State Multi-Nuclear Magnetic Resonance
EMSL Project ID
35590
Abstract
Metallocenes are a class of compounds which contain main group or transition metal elements bound to one or more cyclopentadienyl ligands (Cp). The "metallocene revolution" has been used to describe the increased use of transition metal metallocene catalysts in industrial olefin polymerization processes over the last fifteen years. In particular, the use of metallocenes as heterogeneous catalysts for production of polyolefins is of great interest, due to the ability of such systems to provide narrow molecular weight distributions, high activities and controlled stereospecificities and morphologies. Knowledge of the local structure at the metal sites would be invaluable in the rational design and tuning of heterogeneous catalysts; however, only 1H and 13C SSNMR experiments have been conducted on such systems. For the first time, we propose to apply solid-state 91Zr and 35Cl NMR experiments at high field (18.8 T) and low temperature (< 25 K) to examine the molecular structure of metallocenes supported on mesoporous silica. Since both 91Zr and 35Cl are unreceptive nuclei with broad second-order quadrupolar patterns, and the concentration of these nuclei is very diluted in the supported materials, specialized quadrupolar Carr-Purcell Meiboom-Gill (QCPMG) pulse sequences will be applied to enhance the signal-to-noise. Analysis of the 91Zr and 35Cl NMR spectra, and accompanying first principles calculations of the quadrupolar and chemical shift parameters, will provide insight into the identity and structures of surface-bound catalytic metallocene species.
Project Details
Project type
Large-Scale EMSL Research
Start Date
2009-10-01
End Date
2010-09-30
Status
Closed
Released Data Link
Team
Principal Investigator
Team Members