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Title: Tracking the Chemical Transformations at the Brønsted Acid Site upon Water-Induced Deprotonation in a Zeolite Pore

Abstract

We report the structural changes induced by Brønsted acidic site deprotonation in a zeolite with MFI structure as a function of temperature up to 430°C using in situ Al K-edge X-ray absorption fine structure spectroscopy (XAFS). At ambient conditions, the protons are present as hydrated hydronium ions (H3O+(H2O)n) that are ion-paired to the anionic, Al tetrahedral (T) site. At elevated temperatures, loss of water molecules hydrating the hydronium ions leads to an unstable free hydronium ion that disso-ciates to form the hydroxylated T-site. The formation of this (-O3)-Al-(OH-) species leads to the elongation of one of the four Al-O bonds and causes significant distortion of the tetrahedral symmetry about the Al atom. This distortion leads to the appearance of new pre-edge features in the Al K-edge X-ray absorption near edge structure (XANES) spectra. The pre-edge peak assignment is confirmed by time-dependent density functional theory calculation of the XANES spectrum. The XANES spectra are also sensitive to solutes or solvent that are in proximity to the T-site. A second structural transition occurs at about the same temperature, namely the conversion of a minor fraction of extra-framework octahedral Al present in the sample at ambient conditions to a tetrahedral species through themore » de-coordination of H2O-ligands. Both IR spectroscopy and thermogravimetric analysis (TGA) are further used to confirm the overall chemical transformation of the T-site.« less

Authors:
 [1]; ORCiD logo [1];  [2];  [3]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [1]; ORCiD logo [4]
  1. Institute for Integrated Catalysis and Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
  2. Environmental Molecular Sciences Laboratory, Pacific Northwest National Laboratory, Richland, Washington 99354, United States
  3. Swiss Light Source, Paul Scherrer Institut (PSI), 5232 Villigen, Switzerland
  4. Institute for Integrated Catalysis and Physical Sciences Division, Pacific Northwest National Laboratory, Richland, Washington 99354, United States; Department of Chemistry and Catalysis Research Institute, TU München, Lichtenbergstrasse 4, 85748 Garching, Germany
Publication Date:
Research Org.:
Pacific Northwest National Laboratory (PNNL), Richland, WA (US), Environmental Molecular Sciences Laboratory (EMSL)
Sponsoring Org.:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
OSTI Identifier:
1411916
Report Number(s):
PNNL-SA-126468
Journal ID: ISSN 0897-4756; 48810; KC0302010
DOE Contract Number:  
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Chemistry of Materials; Journal Volume: 29; Journal Issue: 21
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; zeolite MFI; Bronsted acid sites; hydronium ion; pore dehydration; Environmental Molecular Sciences Laboratory

Citation Formats

Vjunov, Aleksei, Wang, Meng, Govind, Niranjan, Huthwelker, Thomas, Shi, Hui, Mei, Donghai, Fulton, John L., and Lercher, Johannes A. Tracking the Chemical Transformations at the Brønsted Acid Site upon Water-Induced Deprotonation in a Zeolite Pore. United States: N. p., 2017. Web. doi:10.1021/acs.chemmater.7b02133.
Vjunov, Aleksei, Wang, Meng, Govind, Niranjan, Huthwelker, Thomas, Shi, Hui, Mei, Donghai, Fulton, John L., & Lercher, Johannes A. Tracking the Chemical Transformations at the Brønsted Acid Site upon Water-Induced Deprotonation in a Zeolite Pore. United States. doi:10.1021/acs.chemmater.7b02133.
Vjunov, Aleksei, Wang, Meng, Govind, Niranjan, Huthwelker, Thomas, Shi, Hui, Mei, Donghai, Fulton, John L., and Lercher, Johannes A. Mon . "Tracking the Chemical Transformations at the Brønsted Acid Site upon Water-Induced Deprotonation in a Zeolite Pore". United States. doi:10.1021/acs.chemmater.7b02133.
@article{osti_1411916,
title = {Tracking the Chemical Transformations at the Brønsted Acid Site upon Water-Induced Deprotonation in a Zeolite Pore},
author = {Vjunov, Aleksei and Wang, Meng and Govind, Niranjan and Huthwelker, Thomas and Shi, Hui and Mei, Donghai and Fulton, John L. and Lercher, Johannes A.},
abstractNote = {We report the structural changes induced by Brønsted acidic site deprotonation in a zeolite with MFI structure as a function of temperature up to 430°C using in situ Al K-edge X-ray absorption fine structure spectroscopy (XAFS). At ambient conditions, the protons are present as hydrated hydronium ions (H3O+(H2O)n) that are ion-paired to the anionic, Al tetrahedral (T) site. At elevated temperatures, loss of water molecules hydrating the hydronium ions leads to an unstable free hydronium ion that disso-ciates to form the hydroxylated T-site. The formation of this (-O3)-Al-(OH-) species leads to the elongation of one of the four Al-O bonds and causes significant distortion of the tetrahedral symmetry about the Al atom. This distortion leads to the appearance of new pre-edge features in the Al K-edge X-ray absorption near edge structure (XANES) spectra. The pre-edge peak assignment is confirmed by time-dependent density functional theory calculation of the XANES spectrum. The XANES spectra are also sensitive to solutes or solvent that are in proximity to the T-site. A second structural transition occurs at about the same temperature, namely the conversion of a minor fraction of extra-framework octahedral Al present in the sample at ambient conditions to a tetrahedral species through the de-coordination of H2O-ligands. Both IR spectroscopy and thermogravimetric analysis (TGA) are further used to confirm the overall chemical transformation of the T-site.},
doi = {10.1021/acs.chemmater.7b02133},
journal = {Chemistry of Materials},
number = 21,
volume = 29,
place = {United States},
year = {Mon Oct 23 00:00:00 EDT 2017},
month = {Mon Oct 23 00:00:00 EDT 2017}
}