(714c) Structure-Dependent Organization of Alkanols inside Zeolites Influences the Enthalpic and Entropic Contributions Towards Dehydration Kinetics
Molecular-sized zeolite confinements enhance reaction rates for a wide range of organic transformations. These rate enhancements for active sites within these environments are accompanied by an increased complexity that limits understanding on a fundamental level. The dehydration of alcohols by Brønsted acid sites (BAS) is used in various organic transformations, including the deoxygenation of biomass-derived oxygenates. BAS form hydrated hydronium ions in the presence of a large concentration of water, and provide a confined environment that leads to about two orders of magnitude higher reactivity for condensed-aqueous phase cyclohexanol dehydration in BEA and MFI zeolites than in acidic solutions. Due to the structural complexity of biomass, alcohols with a diversity of molecular structure will need upgrading. The question arises, therefore, how zeolites can be tailored for conversion of more complex feedstocks and it is imperative to understand the influence of organic structure on the condensed phase dehydration of alcohols Herein, thermochemical and kinetic measurements along with isotope labeling were used to quantitatively investigate the reaction pathway and kinetics of the dehydration of C6-C8 alkanols to study the influence of alcohol branching and functionality on the organization of the substrates in the pore and the stabilization of the elimination transition state (TS) inside zeolites.