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Kinetic, Spectroscopic, and Theoretical Assessment of Associative and Dissociative Methanol Dehydration Routes in Zeolites
Author(s) -
Jones Andrew J.,
Iglesia Enrique
Publication year - 2014
Publication title -
angewandte chemie
Language(s) - English
Resource type - Journals
eISSN - 1521-3757
pISSN - 0044-8249
DOI - 10.1002/ange.201406823
Subject(s) - dimethyl ether , methanol , chemistry , enthalpy , transition state , catalysis , dehydration , van der waals force , hydrocarbon , dehydration reaction , thermodynamics , entropy (arrow of time) , computational chemistry , organic chemistry , molecule , biochemistry , physics
Mechanistic interpretations of rates and in situ IR spectra combined with density functionals that account for van der Waals interactions of intermediates and transition states within confining voids show that associative routes mediate the formation of dimethyl ether from methanol on zeolitic acids at the temperatures and pressures of practical dehydration catalysis. Methoxy‐mediated dissociative routes become prevalent at higher temperatures and lower pressures, because they involve smaller transition states with higher enthalpy, but also higher entropy, than those in associative routes. These enthalpy–entropy trade‐offs merely reflect the intervening role of temperature in activation free energies and the prevalence of more complex transition states at low temperatures and high pressures. This work provides a foundation for further inquiry into the contributions of H‐bonded methanol and methoxy species in homologation and hydrocarbon synthesis reactions from methanol.