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Investigation of Ethylene Dimerization over Faujasite Zeolite by the ONIOM Method

Authors

  • Supawadee Namuangruk,

    1. Laboratory for Computational and Applied Chemistry, Physical Chemistry Division, Chemistry Department, Kasetsart University, Bangkok 10900, Thailand, Fax: (+66) 294-28900 ext. 324
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  • Piboon Pantu Dr.,

    1. Laboratory for Computational and Applied Chemistry, Physical Chemistry Division, Chemistry Department, Kasetsart University, Bangkok 10900, Thailand, Fax: (+66) 294-28900 ext. 324
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  • Jumras Limtrakul Prof. Dr.

    1. Laboratory for Computational and Applied Chemistry, Physical Chemistry Division, Chemistry Department, Kasetsart University, Bangkok 10900, Thailand, Fax: (+66) 294-28900 ext. 324
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  • ONIOM=our own n-layered integrated molecular orbital and molecular mechanics.

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[BOND]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[BOND]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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