Introduction
	Heterogeneous catalysis is an utmost important area of research that has direct impact on the chemical industries. Currently, the environmental impacts of industrial processes are becoming important issues, meaning that moving toward replacing liquid acid/base catalysts with novel solid catalysts is receiving great attention. Unlike liquid acid/base catalysts, solid acid/base catalysts do not produce significant amounts of waste byproducts, making them more environmentally sound. One of the most recognized heterogeneous catalysts are zeolite-type catalysts which are ideal catalytic materials for many processes because of their well-defined nanostructure with pore sizes in the molecular scale, thus enabling unprecedented shape selected chemistries. Zeolites are now widely used in petroleum refineries and petrochemical industries and fine chemical productions. It has been estimated that the employment of zeolites in petroleum refining alone resulted in an added value of several billion US dollars per year. Although experimental techniques provide us many informative data, using these techniques to study heterogeneous catalysts and their reactions is quite limited. With the advance in computer technology, scientific equipment and theoretical methodology, it has become apparent that molecular modeling provides a cost effective route to enhance the competitiveness of these industries. Understanding reactivity of zeolites has been a scientific challenge from both experimental and theoretical points of view. Our focus is to study mechanisms, kinetics and dynamics of reactions in zeolites using experimental and theoretical methodologies in parallel. The development of innovative crystalline materials is of our interest as well. Chemical Physics Letters 2001 350 (1,2) 128-134; J. Phys. Chem. B. 2001 105 (12) 2421-2428; J. Catal. 2000 153 (1-2) 155-163; Chem. Phys. 1997 215 (1) 77-87.

The topics on which we are currently focusing are:
The protonation reaction of unsaturated hydrocarbons within zeolites:
	Of the most interest in this active research is the protonation reaction of ethylene with Brønsted zeolites that is the foundation step of several industrially important reactions, namely the polymerization and hydrocarbon cracking processes. It was found that the electrostatic contribution is a major part of long-range interactions. This raises the need for a better understanding on the effects of the Madelung potential in the potential energies of reaction intermediates.In this study, the embedded cluster approach is used to study complete protonation reaction of ethylene within both H-FAU and H-ZSM-5 zeolites.   Cluster model calculations of the reactants and intermediate	Transition state of ethylene protonation on H-ZSM-5
	complexes have been compared with results obtained at the same level of theory using embedded cluster approach. The apparent activation energy is evaluated to be 14.6 and 17.9 kcal/mol for the ZSM-5 and FAU, respectively and can be compared well with the experimental apparent activation energy of 16 kcal/mol determined for deuterium exchange of ethylene on a Y zeolite. Chemical Physics Letters, (2001) 349 (1,2) 161-166; Stud. Surf. Sci. Catal., (2001) 135, 2469-2476.

 

Synthesis, Characterization and Modelling of Ga-MFI-type Zeolites:
Scanning electron micrographs of Na/Ga-MFI-type zeolite: Si/Ga=100		A combined study employing both theoretical and experimental methods has been carried out for the first time to investigate the structures and bonding of gallosilicate MFI-type (ZSM-5) zeolites. The hydrogel compositions with varying Si/Ga ratios of 25, 50, 75 and 100 were 62Na2O : xGa2O3 : 60SiO2 : 4TPABr : 3134H2O : 60NaCl (x=1.2, 0.6, 0.4 and 0.3). The four Ga-MFI-type zeolites were synthesized by a rapid crystallization method in 1 hour. The obtained solids were characterized by XRPD, SEM and FT-IR. The results reveal that the profile corresponded to of MFI structure and that no crystalline impurity was present in the products. The Brønsted acid strength of various cluster models representing H/Ga-MFI-type zeolite has been carried out at density functional theory (DFT) and
	Hartree-Fock (HF) levels of theory. We have investigated the influence of its composition on the structure and acid strength by varying Si/Ga ratios of 13 (cluster A), 15 (cluster B) and 17 (cluster C). Changes in Si/Ga ratio have a great effect on the proton affinity of hydroxyl proton due to the long-range electrostatic interaction. Our calculated results estimate that the acid strength increases in the order: cluster A < cluster B < cluster C, which exhibit an exceptional agreement with both previously experimental and theoretical studies.  2002 Patented.; J. Mol. Struct.1999 510 (1-3) 131-147.

 

Ethylene Epoxidation over Ti-substituted Silicalite (TS-1):
	Mechanism of the ethylene epoxidation with hydrogen peroxide over Ti-substituted silicalite (TS-1) catalyst was investigated by using both the quantum cluster and embedded quantum cluster approaches. The predicted structure of TS-1 is in a good agreement with the experimental results. The epoxidation of ethylene consists of two steps.  First, the chemisorption of H2O2 at the Ti active site forms the oxygen donating Ti-OOH species and then the transfer of an oxygen atom from the Ti-OOH species to the adsorbed ethylene.  The later step was found to be the rate limiting step with the barrier of 17.0 kcal/mol,  which  is in good agreement  with the experimental estimate	Schematic energy profile for the epoxidation of ethylene by TS-1.
	of about 16.7 kcal/mol.  This result also shows that inclusion of the effects of the zeolite crystal framework is crucial for obtaining quantitative energetic information.  For instance, the Madelung potential increases the barrier of the oxygen atom transfer step by 4.6 kcal/mol. Journal of Physical Chemsitry B 2002, in press.

 

Beckmann rearrangement:
	Beckmann rearrangement is an industrially important reaction for producing e-caprolactam, which is a raw material for the production of Nylon-6 with the market of 3.6 million tons in 1998. Caprolactam is produced by Beckmann rearrangement of cyclohexanone oxime with oleum or concentrated sulfuric acid as a reaction medium. Although this procedure is convenient from the chemical standpoint, corrosion difficulty of the manufacturing equipment and elimination a large amount of ammonium sulfate formed during the neutralization process make the process environmentally unacceptable.	1,2 H-shift transition state
	Then using heterogeneous catalyst in this reaction, usually called the vapor phase Beckmann rearrangement, can solve these problems. Zeolite proves to be an excellent candidate for taking over the catalytic function, since the use of a zeolitic catalyst is benefit not only from an economical point of view but also from an ecological viewpoint. Journal of Physical Chemsitry B 2002, in press.