Molecular models, Phillips chromium catalyst

Molecular modeling. To simulate the behavior of the real heterogeneous catalyst, a reasonable molecular model must be first built to mimic the active sites anchored on the support. Figure 3.3 shows some typical molecular models for the active sites of the Phillips chromium catalyst. Espehd and Borve had done a series of systematic density functional theory (DFT) investigations on the active sites of the Phillips chromium... 

Figure 3.3 Molecular models for Phillips chromium catalyst.

Although numerous experiments and spectroscopic characterizations have been conducted on the Phillips catalyst, the precise structure of the active site on the silica surface, reduction of the surface chromate species during the induction period, the formation of the first chromium-carbon bond, and the mechanism for ethylene polymerization still need to be further clarified [11]. In order to achieve more specific information, molecular modeling approaches could provide a useful complement to the experiments and enable us to study these obscure mechanistic problems directly at the atomic and molecular level. In the last decade, very precise mechanistic pictures of the Cr-based polymerization catalysts have been obtained using different theoretical methods, especially through a combination of the experimental findings with theoretical calculations. 

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