Zeolite computational study

Jackson and Catlow [12-13] studied the stabilities of various zeolites using the static lattice energy simulation technique. In addition, the energetic distribution of non-framework cations and the relative stabilities as a function of Si/Al ratio in faujasite, zeolite A and silicalite were also studied. Reliable interatomic potentials necessary for such calculations were derived empirically in collaboration with Sanders [14]. These potentials and related force fields commonly used in zeolite computational studies are discussed later in this section. The adsorption of various molecules in zeolites leading to... 

The currently available quantum chemical computational methods and computer programs have not been utilized to their potential in elucidating the electronic origin of zeolite properties. As more and more physico-chemical methods are used successfully for the description and characterization of zeolites, (e.g. (42-45)), more questions will also arise where computational quantum chemistry may have a useful contribution towards the answer, e.g. in connection with combined approaches where zeolites and metal-metal bonded systems (e.g. (46,47)) are used in combination. The spectacular recent and projected future improvements in computer technology are bound to enlarge the scope of quantum chemical studies on zeolites. Detailed studies on optimum intercavity locations for a variety of molecules, and calculations on conformation analysis and reaction mechanism in zeolite cavities are among the promises what an extrapolation of current developments in computational quantum chemistry and computer technology holds out for zeolite chemistry. 

There are a few ab initio computational studies which deal with the order of stability of acid sites in other zeolite frameworks, where precise experimental data are lacking and only indirect information is available about preferential... 

Owing to the complexity of zeolitic systems, most computational studies are still performed with the help of classical models. These methods use a set of potential functions to describe the potential energy surface (PES) in a manydimensional space of geometrical parameters of the system. Although the PES can be tested in terms of observables such as equilibrium atom positions, vibrational frequencies, heats of formation, and other experimental information, the PES itself is not an observable quantity. Because of that, there is no unique representation of the PES, and several coordinate systems and parameteriza-... 

We shall concentrate on computational studies of the interaction between the methanol molecule and the acidic proton of the bridging (A1 0-H Si) hydroxyl group in zeolites to exemplify the contribution of simulation techniques in understanding chemical reactivity of zeolites. This interaction is the initial step of the industrially important conversion of methanol to gasoline. Therefore, understanding this primary step at the microscopic level has a direct impact on our understanding (and possibly rationalization) of the process. Before considering the results of calculations, let us outline the experimental information available for these systems. 

K. S. Smirnov and D. Bougeard, Zeolites, 14, 203 (1994). Molecular Dynamics Computer Study of Window Fluctuations in Zeolite A. 

G. Vitale, C. F. Mellot, and A. K. Cheetham,/. Phys. Chem. B, 101, 9886 (1997). Localization of Adsorbed Cyclohexane in the Acid Form of Zeolite Y. A Powder Neutron Diffraction and Computational Study. 

Zeolites are microporous aluminosilicates that have interesting molecular sieve properties and contain microenvironments giving rise to a wide range of interesting chemical reactions. Because of the economic importance of these materials, scientists have been carrying out computational studies on both the... 

While these computational studies [34] were awaiting publication, a neutron diffraction study on H-SAPO-34 provided evidence for a protonated water molecule [38]. Whereas comments in the more popular press [39] stressed the apparent disagreement with previous calculations ( much of the confusion about how zeolites work stems from quantum calculations ) and used the entertaining title Quantum mechanics proved wrong , a comment to the original paper in the same issue... 

Presented text does not give a final word about what model is the best suited for applications in the zeolite science. We have attempted to show that the choice of the model depends primarily on the property under investigation. It is important to stress that other factors must be also taken into consideration, e. g., software and hardware limitations. It is always a difficult decision to find a suitable compromise among the size of the model and reliability of the method (under the constraint of available computational resources). It is equally difficult to judge the reliability of any computational study in the zeolite science. We hope that the present manuscript helps the reader to acquire some initial orientation in the computational zeolite science. 

The process of adsorption and interaction of probe molecules such as ammonia, carbon monoxide as well as the whole spectrum of organic reactant molecules with zeolite catalysts has been the subject of numerous experimental and computational studies. These interaction processes are studied using several computational methods involving force fields (Monte Carlo, molecular dynamics emd energy minimization) or quantum chemical methods. Another paper [1] discusses the application of force field methods for studying several problems in zeolite chemistry. Theoretical quantum chemical studies on cluster models of zeolites help us to understand the electronic and catalytic properties of zeolite catalysts. Here we present a brief summary of the application of quantum chemical methods to understand the structure and reactivity of zeolites. 

Anderson C-R, Coker D F, Eckert J and Bug A L R (1999), Computational study of molecular hydrogen in zeolite Na-A. I. Potential energy surfaces and thermodynamic separation factors for ortho and para hydrogen , J Chem Phys, 111, 7599. 

Nachtigall P, Garrone P, Tumes Palomino G, Rodriguez Delgado M, Nachtigallova D and Otero Arean C (2006), FTIR spectroscopic and computational studies on hydrogen adsorption on the zeolite Li-FER , Phys Chem Chem Phys, 8, 2286. 

Foerster H (1992) In Davis JE (ed) Spectroscopic and computational studies of supra-molecular systems. Infrared studies of zeolite complexes, Kluwer Academic Publishers, Dordrecht, The Netherlands, 1992, p 29... 

Liu et al. [32] have recently reported a computational study on the adsorption site and the ESR magnetic parameters of NO adsorbed in Na-LTA zeolite employing... 

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