► Design of industrial catalysts based on first-principle calculations
Polyolefin, represented by polyethylene and polypropylene, is the most widely used resin over the world.
The industrial production of polyolefin greatly relies on heterogeneous olefin polymerization catalysts,
and the design of active surface structures is crucial on the structures of polyolefin, namely physical properties of resin.
However, as is usual for heterogeneous catalysts, the surface structures of the olefin polymerization catalysts
are highly complicated and heterogeneous to prevent the understandings of active site or surface structures
and their relationship with resultant polymer structures. Although computational approaches have been frequently attempted,
there is no conclusive model for the active surface structures of the olefin polymerization catalysts.
Our group have successfully established a highly-consistent model and clarified the above key issues,
by means on a combination approach of tailored model catalysts and systematic DFT calculations.
We further attempt to utilize the developed model for ab initio prediction of industrial catalysts.
Two interesting topics are highlighted below.
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- 1, Heterogeneous Ziegler-Natta catalyst
Heterogeneous Ziegler-Natta catalysts, exclusively responsible for the production of polypropylene,
consist of titanium chloride catalytic species and Lewis basic compounds as modifier co-supported on MgCl2 support.
The Lewis basic compounds called as donors (typically specific ester and ether molecules)
dramatically improve various catalytic properties (especially for the selectivity) and therefore,
the finding of new donor structures is the most important for the catalyst development.
We have successfully developed a highly-consistent “coadsorption model”, and uncovered the active surface structures
and the mechanism for donors to improve the catalytic properties [1,2].
The proposed model enables the ab initio prediction of new donor structures.
- 2, Phillips catalyst
The Phillips catalyst, comprising of chromate species supported on calcined SiO2, produces one of the most important grades of polyethylene featured with short & long chain branches and ultra broad molecular weight distribution. We believe that such the multi-functional nature of the catalyst results from the heterogeneity of the interaction between the chromate species and SiO2 surfaces. For example, our DFT calculations elucidated that the heterogeneity in the coordination environment around chromium species accounts for experimentally obtained broad molecular weight distribution, where the number and placements of bonding or coordinating oxygen play important roles in the activity and chain transfer properties of the chromium active center .
 “Coadsorption model for first-principle description of roles of donors in heterogeneous Ziegler-Natta propylene polymerization”, T. Taniike, M. Terano, J. Catal. 293, pp 39-50, 2012.
 “不均一系Ziegler-Natta触媒の性能発現機構に関する密度汎関数計算”, 谷池 俊明, 寺野 稔, 触媒 52, pp 547-552, 2010.
 “Origin of broad molecular weight distribution of polyethylene produced by Phillips-type silica-supported chromium catalyst”, K. Tonosaki, T. Taniike, M. Terano, J. Mol. Catal. A: Chem. 340, pp 33-38, 2011.
The research was
conducted by Taniike et. al. laboratory of the center.