Hexatriene cyclization in acid zeolites investigated using density functional theory methods
Date
2019
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
University of Delaware
Abstract
Aromatic compounds are an important segment of the chemical industry that
impacts many aspects of everyday life. Although the majority of aromatic compounds
are made from petroleum, there is renewed interest in converting shale-gas derived
light alkanes into aromatics over acid zeolite catalysts. It is known that these catalysts
are good at converting light hydrocarbons into higher olefins, which can then form
aromatic compounds. However, there is very little mechanistic understanding about
the elementary steps and intermediates between linear olefins and cyclic precursors to
aromatics.
Hexatriene was used as a model olefin to gain new insights into the cyclization
mechanisms that happen in acid zeolites. With the aid of electronic structure
calculations, mechanisms involving Diels-Alder cycloaddition, pericyclic
electrocyclization, and carbocation mediated cyclization were investigated in the gas
phase. In the process, new and more complete mechanisms were developed to connect
hexatriene to cyclic products via carbocation intermediates. The effect of zeolite acid
sites on these reaction pathways was then investigated. This work paves a new path
towards understanding aromatization in acid zeolites by shedding light on the
underlying fundamental chemistry.