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Phenol Tautomerization Catalyzed by Acid‐Base Pairs in Lewis Acidic Beta Zeolites: A Computational Study
Author(s) -
Deepankeaw Nutsara,
Maihom Thana,
Probst Michael,
Prasertsab Anittha,
Homlamai Kan,
Sittiwong Jarinya,
Limtrakul Jumras
Publication year - 2019
Publication title -
chemphyschem
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.016
H-Index - 140
eISSN - 1439-7641
pISSN - 1439-4235
DOI - 10.1002/cphc.201900377
Subject(s) - chemistry , lewis acids and bases , tautomer , catalysis , phenol , density functional theory , protonation , inorganic chemistry , medicinal chemistry , photochemistry , computational chemistry , organic chemistry , ion
We investigate the tautomerization of phenol catalyzed by acid‐base active pair sites in Lewis acidic Beta zeolites by means of density functional calculations using the M06‐L functional. An analysis of the catalytic mechanism shows that hafnium on the Beta zeolite causes the strongest absorption of phenol compared to zirconium, tin, and germanium. This can be rationalized by the highest delocalization of electron density between the Lewis site and the oxygen of phenol which can in turn be quantified by the perturbative E (2) stabilization energy. The reaction is assumed to proceed in two steps, the phenol O−H bond dissociation and the protonation of the intermediate to form the cyclohexa‐2,4‐dien‐1‐one product. The rate determining step is the first one with a free activation energy of 26.3, 25.0, 22.1 and 22.7 kcal mol −1 for Ge‐Beta, Sn‐Beta, Zr‐Beta, and Hf‐Beta zeolites, respectively. The turnover frequencies follow these reaction barriers. Hence, the intrinsic catalytic activity of the Lewis acidic Beta zeolites studied here is in the order of Hf‐Beta≈Zr‐Beta>Sn‐Beta> Ge‐Beta for the tautomerization of phenol.