Anharmonicity and Confinement in Zeolites

Structure, Spectroscopy, and Adsorption Free Energy of Ethanol in H-ZSM-5

Konstantinos Alexopoulos, Mal Soon Lee, Yue Liu, Yuchun Zhi, Yuanshuai Liu, Marie Françoise Reyniers, Guy B. Marin, Vassiliki Alexandra Glezakou, Roger Rousseau, Johannes A. Lercher

Research output: Contribution to journalArticle

29 Citations (Scopus)

Abstract

To account for thermal and entropic effects caused by the dynamics of the motion of the reaction intermediates, ethanol adsorption on the Brønsted acid site of the H-ZSM-5 catalyst has been studied at different temperatures and ethanol loadings using ab initio molecular dynamics (AIMD) simulations, infrared (IR) spectroscopy, and calorimetric measurements. At low temperatures (T ≤ 400 K) and ethanol loading, a single ethanol molecule adsorbed in H-ZSM-5 forms a Zundel-like structure where the proton is equally shared between the oxygen of the zeolite and the oxygen of the alcohol. At higher ethanol loading, a second ethanol molecule helps to stabilize the protonated ethanol at all temperatures by acting as a solvating agent. The vibrational density of states (VDOS), as calculated from the AIMD simulations, are in excellent agreement with measured IR spectra for C2H5OH, C2H5OD, and C2D5OH isotopomers and support the existence of both monomers and dimers. A quasi-harmonic approximation (QHA), applied to the VDOS obtained from the AIMD simulations, provides estimates of adsorption free energy within ∼10 kJ/mol of the experimentally determined quantities, whereas the traditional approach, employing harmonic frequencies from a single ground state minimum, strongly overestimates the adsorption free energy by at least 20∼50 kJ/mol. This discrepancy is traced back to the inability of the harmonic approximation to represent the contributions to the vibrational motions of the ethanol molecule upon confinement in the zeolite.

Original languageEnglish
Pages (from-to)7172-7182
Number of pages11
JournalJournal of Physical Chemistry C
Volume120
Issue number13
DOIs
Publication statusPublished - Apr 21 2016

Fingerprint

Zeolites
zeolites
Free energy
Ethanol
ethyl alcohol
free energy
Spectroscopy
Adsorption
adsorption
spectroscopy
Molecular dynamics
molecular dynamics
harmonics
Molecules
Computer simulation
Oxygen
molecules
Reaction intermediates
reaction intermediates
simulation

ASJC Scopus subject areas

  • Physical and Theoretical Chemistry
  • Electronic, Optical and Magnetic Materials
  • Surfaces, Coatings and Films
  • Energy(all)

Cite this

Anharmonicity and Confinement in Zeolites : Structure, Spectroscopy, and Adsorption Free Energy of Ethanol in H-ZSM-5. / Alexopoulos, Konstantinos; Lee, Mal Soon; Liu, Yue; Zhi, Yuchun; Liu, Yuanshuai; Reyniers, Marie Françoise; Marin, Guy B.; Glezakou, Vassiliki Alexandra; Rousseau, Roger; Lercher, Johannes A.

In: Journal of Physical Chemistry C, Vol. 120, No. 13, 21.04.2016, p. 7172-7182.

Research output: Contribution to journalArticle

Alexopoulos, K, Lee, MS, Liu, Y, Zhi, Y, Liu, Y, Reyniers, MF, Marin, GB, Glezakou, VA, Rousseau, R & Lercher, JA 2016, 'Anharmonicity and Confinement in Zeolites: Structure, Spectroscopy, and Adsorption Free Energy of Ethanol in H-ZSM-5', Journal of Physical Chemistry C, vol. 120, no. 13, pp. 7172-7182. https://doi.org/10.1021/acs.jpcc.6b00923
Alexopoulos, Konstantinos ; Lee, Mal Soon ; Liu, Yue ; Zhi, Yuchun ; Liu, Yuanshuai ; Reyniers, Marie Françoise ; Marin, Guy B. ; Glezakou, Vassiliki Alexandra ; Rousseau, Roger ; Lercher, Johannes A. / Anharmonicity and Confinement in Zeolites : Structure, Spectroscopy, and Adsorption Free Energy of Ethanol in H-ZSM-5. In: Journal of Physical Chemistry C. 2016 ; Vol. 120, No. 13. pp. 7172-7182.
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