Catalysts rational design

All mechanistic studies on activation by NHC complexes are of great interest (particularly when computations and experiments are combined) as they help rationalise catalytic behaviour, they allow catalyst improvement and nltimately they might allow rational catalyst design. 

Initially, most theoretical methods calculated the properties of molecules in the gas phase as isolated species, but chemical reactions are most often carried out in solution. Biochemical reactions normally take place in water. Consequently, there is increasing interest in methods for including solvents in the calculations. In the simplest approach, solvents are treated as a continuum, whose average properties are included in the calculation. Explicit inclusion of solvent molecules in the calculation greatly expands the size of the problem, but newer approaches do this for at least those solvent molecules next to the dissolved species of interest. The detailed structures and properties of these solvent molecules affect their direct interaction with the dissolved species. Reactions at catalytic surfaces present an additional challenge, as the theoretical techniques must be able to handle the reactants and the atoms in the surface, as well as possible solvent species. The first concrete examples of computationally based rational catalyst design have begun to appear in publications and to have impact in industry. 

The above achievements depend highly on both the recent advances in rational catalyst design with the aid of computational science represented by DFT calculations and the wide range of catalyst design possibilities that are afforded by FI catalysts. These possibilities are derived from the readily varied steric and electronic properties of the phenoxy-imine ligands. It is expected that future research on FI catalysts will provide opportunities to produce additional polyolefin-based materials with unique microstructures and a chance to study catalysis and mechanisms for olefin polymerization. 

M. E. Davis, A. Katz, W. R. Ahmad, Rational catalyst design via imprinted nanostructured materials , Chem. Mater. 1996, 8,1820-1839. 

Due to the frequently observed chemical memory of a working catalyst, reproducible synthesis of the active mass with respect to all synthetic steps is a basic requirement. Moreover, an integrated approach requires the consideration of a catalyst as a hierarchical system taking into account mass transport and thermal conduction properties, as well as mechanical stability in the early stages of the development of synthetic concepts closing the cycle of rational catalyst design. 

Hartwig, J. F. Palladium-catalyzed amination of aryl halides. Mechanism and rational catalyst design. Synlett 1997, 329-340. 

Motivated by the idea of rational catalyst design, we take advantage of the computational efficiency of DFT methods to examine a variety of Ag-containing bimetallic catalysts. We focus initially on the branching reactions of the OME since these have been shown to control selectivity [9]. Initial screening based solely on OME reactions suggests several promising bimetallic combinations. However, if one considers a more complete microkinetic model, copper stands out for its ability to enhance the selectivity of silver-based bimetallic catalysts. 

Since the periodic DFT calculations, especially the NEB calculations, are extremely time consuming, we use a hybrid approach for rational catalyst design. The OME was taken as the reactant, whereas adsorbed EO and acetaldehyde were considered as the products of different competitive reactions. ADE was used to provide initial guesses for species geometries to enhance efficiency. As a first step, structures of the reactants and products were optimized on the periodic Ag slab. Two NEB calculations were performed for the formation of adsorbed EO and acetaldehyde starting from the common OME intermediate. The difference between these two activation energies is the main factor responsible for the selectivity to the... 

Several designed polypeptide catalysts have been reported to date, together with reasonably complete reaction mechanistic analyses. These may serve as good introductions to rational catalyst design and are listed here for reference purposes. 

This paper reviews our recent work dealing with designed active structures at oxide surfaces and their spectroscopic characterizations in an atomic or molecular scale. The paper also provides the information on the key issues in catalytic research such as behavior of adsorbed active species during catalysis which are well characterized by recent in-situ spectroscopy and also by traditional spectroscopy. The paper also presents a concept of surface design relevant to supported oxide catalysis, which world allow us to move toward the ulitmate goals of more rational catalyst design. 

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