Investigation of ethylene dimerization over faujasite zeolite by the ONIOM method. |
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Authors: | Supawadee Namuangruk Piboon Pantu Jumras Limtrakul |
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Institution: | Laboratory for Computational and Applied Chemistry, Physical Chemistry Division, Chemistry Department, Kasetsart University, Bangkok 10900, Thailand. |
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Abstract: | Ethylene dimerization was investigated by using an 84T cluster of faujasite zeolite modeled by the ONIOM3(MP2/6-311++G(d,p):HF/6-31G(d):UFF) method. Concerted and stepwise mechanisms were evaluated. In the stepwise mechanism, the reaction proceeds by protonation of ethylene to form the surface ethoxide and then C--C bond formation between the ethoxide and the second ethylene molecule to give the butoxide product. The first step is rate-determining and has an activation barrier of 30.06 kcal mol(-1). The ethoxide intermediate is rather reactive and readily reacts with another ethylene molecule with a smaller activation energy of 28.87 kcal mol(-1). In the concerted mechanism, the reaction occurs in one step of simultaneous protonation and C--C bond formation. The activation barrier is calculated to be 38.08 kcal mol(-1). Therefore, the stepwise mechanism should dominate in ethylene dimerization. |
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Keywords: | ab initio calculations dimerization reaction mechanisms transitions states zeolites |
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