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Title: Direct spectroscopic evidence for isolated silanols in SiO x/Al 2O 3 and their formation mechanism

Here, the preparation and unambiguous characterization of isolated Brønsted-acidic silanol species on silica–alumina catalysts presents a key challenge in the rational design of solid acid catalysts. In this report, atomic layer deposition (ALD) and liquid-phase preparation (chemical liquid deposition, CLD) are used to install the SiO x sites on Al 2O 3 catalysts using the same Si source (tetraethylorthosilicate, TEOS). The ALD-derived and CLD-derived SiO x sites are probed with dynamic nuclear polarization (DNP)-enhanced 29Si– 29Si double-quantum/single-quantum (DQ/SQ) correlation NMR spectroscopy. The investigation reveals conclusively that the SiO x/Al 2O 3 material prepared by ALD and CLD, followed by calcination under an O 2 stream, contains fully spatially isolated Si species, in contrast with those resulting from the calcination under static air, which is widely accepted as a postgrafting treatment for CLD. Insight into the formation mechanism of these sites is obtained via in situ monitoring of the TEOS + γ-Al 2O 3 reaction in an environmental diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) cell. Upon calcination, the DRIFTS spectra of SiO x/Al 2O 3 reveal a signature unambiguously assignable to isolated Brønsted-acidic silanol species. Surprisingly, the results of this study indicate that the method of preparing SiO x/Al 2Omore » 3 catalysts is less important to the final structure of the silanol sites than the post-treatment conditions. This finding should greatly simplify the methods for synthesizing site-isolated, Brønsted-acidic SiO x/Al 2O 3 catalysts.« less
Authors:
 [1] ;  [2] ;  [3] ;  [1] ;  [1]
  1. Northwestern Univ., Evanston, IL (United States)
  2. Ames Lab., Ames, IA (United States)
  3. Ames Lab. and Iowa State Univ., Ames, IA (United States)
Publication Date:
Report Number(s):
IS-J-9316
Journal ID: ISSN 1932-7447
Grant/Contract Number:
FG02-03ER154757; AC02-07CH11358
Type:
Accepted Manuscript
Journal Name:
Journal of Physical Chemistry. C
Additional Journal Information:
Journal Volume: 121; Journal Issue: 11; Journal ID: ISSN 1932-7447
Publisher:
American Chemical Society
Research Org:
Ames Laboratory (AMES), Ames, IA (United States)
Sponsoring Org:
USDOE Office of Science (SC), Basic Energy Sciences (BES) (SC-22)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; atomic layer deposition; chemical liquid deposition; silica-alumina catalyst; DRIFTS; DNP-SENS
OSTI Identifier:
1355896

Mouat, Aidan R., Kobayashi, Takeshi, Pruski, Marek, Marks, Tobin J., and Stair, Peter C.. Direct spectroscopic evidence for isolated silanols in SiOx/Al2O3 and their formation mechanism. United States: N. p., Web. doi:10.1021/acs.jpcc.6b11196.
Mouat, Aidan R., Kobayashi, Takeshi, Pruski, Marek, Marks, Tobin J., & Stair, Peter C.. Direct spectroscopic evidence for isolated silanols in SiOx/Al2O3 and their formation mechanism. United States. doi:10.1021/acs.jpcc.6b11196.
Mouat, Aidan R., Kobayashi, Takeshi, Pruski, Marek, Marks, Tobin J., and Stair, Peter C.. 2017. "Direct spectroscopic evidence for isolated silanols in SiOx/Al2O3 and their formation mechanism". United States. doi:10.1021/acs.jpcc.6b11196. https://www.osti.gov/servlets/purl/1355896.
@article{osti_1355896,
title = {Direct spectroscopic evidence for isolated silanols in SiOx/Al2O3 and their formation mechanism},
author = {Mouat, Aidan R. and Kobayashi, Takeshi and Pruski, Marek and Marks, Tobin J. and Stair, Peter C.},
abstractNote = {Here, the preparation and unambiguous characterization of isolated Brønsted-acidic silanol species on silica–alumina catalysts presents a key challenge in the rational design of solid acid catalysts. In this report, atomic layer deposition (ALD) and liquid-phase preparation (chemical liquid deposition, CLD) are used to install the SiOx sites on Al2O3 catalysts using the same Si source (tetraethylorthosilicate, TEOS). The ALD-derived and CLD-derived SiOx sites are probed with dynamic nuclear polarization (DNP)-enhanced 29Si–29Si double-quantum/single-quantum (DQ/SQ) correlation NMR spectroscopy. The investigation reveals conclusively that the SiOx/Al2O3 material prepared by ALD and CLD, followed by calcination under an O2 stream, contains fully spatially isolated Si species, in contrast with those resulting from the calcination under static air, which is widely accepted as a postgrafting treatment for CLD. Insight into the formation mechanism of these sites is obtained via in situ monitoring of the TEOS + γ-Al2O3 reaction in an environmental diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS) cell. Upon calcination, the DRIFTS spectra of SiOx/Al2O3 reveal a signature unambiguously assignable to isolated Brønsted-acidic silanol species. Surprisingly, the results of this study indicate that the method of preparing SiOx/Al2O3 catalysts is less important to the final structure of the silanol sites than the post-treatment conditions. This finding should greatly simplify the methods for synthesizing site-isolated, Brønsted-acidic SiOx/Al2O3 catalysts.},
doi = {10.1021/acs.jpcc.6b11196},
journal = {Journal of Physical Chemistry. C},
number = 11,
volume = 121,
place = {United States},
year = {2017},
month = {2}
}