Projects / Programmes
Design and Optimization of Zeolite Catalysts by Molecular Modeling Methods
| Code |
Science |
Field |
Subfield |
| 1.04.02 |
Natural sciences and mathematics |
Chemistry |
Structural chemistry |
| Code |
Science |
Field |
| P351 |
Natural sciences and mathematics |
Structure chemistry |
catalysis, epoxidation, zeolites, TS-1, molecular modeling, large-scale systems, crystal structure, ab initio calculations, QM/MM, periodic boundary conditions, hydrogen bonding
Researchers (1)
| no. |
Code |
Name and surname |
Research area |
Role |
Period |
No. of publicationsNo. of publications |
| 1. |
20393 |
PhD Jernej Stare |
Chemistry |
Head |
2007 - 2008 |
157 |
Organisations (1)
| no. |
Code |
Research organisation |
City |
Registration number |
No. of publicationsNo. of publications |
| 1. |
0104 |
National Institute of Chemistry |
Ljubljana |
5051592000 |
21,007 |
Abstract
This research project will provide new insights into structure of the active sites and the origin and nature of the catalytic activity of titanosilicalite zeolites (TSZs) with the use of the extensive studies based on advanced computational methods. A novel modeling strategy for the optimization of the existing TSZs and for the design of improved ones will be developed on the basis of our findings. The focus of this work will be the best known example of these catalysts, TS-1 (“titanosilicialite-1”) which catalyzes a number of important reactions which exceptionally high selectivity and efficiency, such as oxidations of small organic molecules. It does so with the use of hydrogen peroxide as the source of oxygen with the environmentally benign byproduct water.
The reason for the remarkable catalytic activity of TS-1 is thought to be the isolation of the active sites from one another, as only a small number (< 3 atomic %) of the Si sites in the MFI structure are isomorphously replaced by Ti. Because of this low concentration it has been difficult to obtain detailed experimental information on the structure of these active sites despite a large amount of experimental and computational effort. Molecular level details of reactions and their mechanisms catalyzed by TS-1 have similarly been exceedingly difficult to obtain.
Our new approach to these problems will be the use of advanced quantum chemical computational methods which include a number of accurate, size-consistent models for large systems, including the QM/MM embedding aproach dubbed ONIOM and fully periodic ab initio and DFT calculations. The latter will be carried out with a novel ab initio program package Mondo, developed at Los Alamos National Laboratory [C. J. Tymczak, V. T. Weber, E. Schwegler, M. Challacombe, J. Chem. Phys. 122, 124105-1 (2005)], which is unique for the linear scaling of required computer resources with system size, and thus suitable for periodic systems consisting of several hundreds of atoms. Results obtained by these size-consistent models should provide significant improvements in comparison with those from conventional cluster models, whch often fail to properly depict the active site because the effects of the surrounding zeolite framework are not properly included.
We have chosen the most important reaction catalyzed by TS-1, the epoxidation of propene by aqueous hydrogen peroxide, for modeling by our computational methods. This will include a detailed study on the formation of reactive precursors at the active site and an exploration of possible reaction pathways. We will evaluate the significance of the various possible reaction pathways by analysis of their respective transition states and activation barriers. A much simpler reference study of the propene epoxidation reaction in the gas phase will be performed in order to facilitate the search for possible reaction mechanisms. Special attention will be paid to the role of hydrogen bonds that may be established between the catalyst and reactants or products, which may provide sterical stabilization and/or proton transfer pathway that may well be relevant for reactions of this type. This aspect of our work will involve taking into account the effects that are common to hydrogen-bonded systems, such as anharmonicity and proton tunneling, and their impact on the reaction mechanism.
The main scope of the proposed research is to improve our understanding of the structure and catalytic activity of TSZs by using novel computational methods which will shift the forefront approach of research on large-scale systems. Our calculations will be at every step measured by reference to experimental results from crystallography, X-ray absorption spectroscopy, inelastic neutron scattering and optical vibrational spectroscopy, and will thus provide important feedback and links between computational and experimental work.
Finally, the ultimate goal of the proposed research is to i
Significance for science
This project considered a highly relevant scientific problem of the structure and catalytic activity of zeloite materials and was based on a first-class research methodology in the field of solid-state quantum mechanical simulations. Our results were published in high-quality scientific journals and were presented at various international meetings and at foreign universities. A special value of the project is the adoption of periodical quantum methods which are gaining importance in the computational treatment of crystalline matter, yet they have still not reached the mature stage as seen with gas-phase methods. Importantly, the employed methodologies are easily transferable to other relevant scientific problems in the solid state. Thus the application of the methods adopted in the course of this project to crystalline systems not directly related to the main scope of the project can also be listed as this project’s achievements. Namely, a considerable amount of work in which this project’s leader was involved, included periodical quantum methods, which significantly improved the scientific value of our studies, as reflected in high-quality publications. All in all, adoption of periodical quantum computational methodologies represents a permanent and universal achievement of the project.
Significance for the country
This project is highly relevant for the development of Slovenian science for several reasons. Firstly, it enriches the Slovenian research with new, high-quality and high-impact knowledge and techniques. Periodical quantum methodologies represent an important upgrade in the field of computational chemistry and are gaining importance as supporting tool to experimental studies of the crystalline matter. However, there is only little experience with these methods in Slovenia, hence any experience in this field is of a great value. Additional value of the project is in the fact that it stimulates interdisciplinary collaboration between complementary Slovenian research groups. With a rather novel field of quantum simulations of the crystalline matter being available in Slovenia, a number of new opportunities for joint experimental and theoretical research has emerged.
Apart form direct application for Slovenian science, this project features possible applications for industrial research. The topics considered in the project are of a high industrial relevance and can thus be transferred to actual industrial projects in Slovenia. Nevertheless it is likely that any application to industrial research can be established only at a longer timescale.
Most important scientific results
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Most important socioeconomically and culturally relevant results
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