On the product and transition-state shape selectivities in 2-heptene isomerization

Abstract

Isomerization of n-alkanes is industrially applied to improve the octane number of gasoline. The origin of shape selectivity and influence of micropore confinement in this reaction have not been fully understood. In this work, periodic DFT calculations have been performed to examine the mechanism for n-heptene isomerization in H-BEA and H-MFI. Three reaction pathways, including the protonated cyclopropane, edged-protonated cyclopropane, and alkyl shift mechanisms, have been examined. It is found the formation of smaller di-branched isomers is determined by product shape selectivity, but that of relatively bulky isomers is kinetically relevant and can be accounted for by transition-state shape selectivity.