The mechanisms of skeletal isomerization of 1-butene to isobutene catalyzed by three types of 10-membered ring zeolites, Ferrierite (FER), ZSM-23 (MTT) and ZSM-48 (MRE), have been studied and compared by means of ONIOM(B3LYP/6-31G (d, p):UFF) method. Ferrierite, ZSM-23 and ZSM-48 are simulated by 57T, 80T and 96T cluster models respectively. The study includes geometry optimization, characterization of reactants, products, reaction intermediates and transition states. The calculation of the activation energies for the different processes is also involved. The monomolecular mechanisms of skeletal isomerization of linear butenes over the three types of zeolites (FER, ZSM-23 and ZSM-48) consist of three elementary steps: 1) protonation of adsorbed 1-butene to a secondary alkoxy intermediate, 2) conversion of the secondary alkoxy intermediate into a branched primary one through a cyclic transition state, and 3) decomposition of the primary alkoxy intermediate to adsorbed isobutene. The calculation results for reaction steps of FER are according well with the experimental results. The activation barriers in skeletal isomerization of 1-butene on FER, ZSM-23 and ZSM-48 zeolites are 36 kcal/mol, 37.6 kcal/mol and 33.8 kcal/mol, respectively. Therefore, FER demonstrated higher activity in skeletal isomerization of 1-butene transformation than ZSM-23, this is also in good agreement with the experimental results. ZSM-48 zeolites with slightly larger channels were supposed to have high activity for isomerization of long-chain olefins.

Skeletal isomerization of 1-butene catalyzed by HFER, HMTT, and HMRE zeolites: A theoretical study

251st National Meeting (2016)

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