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Title: Direct spectroscopic evidence for isolated silanols in SiOx/Al2O3 and their formation mechanism

Journal Article · · Journal of Physical Chemistry. C
 [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)
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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.

Research Organization:
Ames Laboratory (AMES), Ames, IA (United States); Northwestern Univ., Evanston, IL (United States)
Sponsoring Organization:
USDOE Office of Science (SC), Basic Energy Sciences (BES)
Grant/Contract Number:
FG02-03ER154757; AC02-07CH11358; FG02-03ER15457
OSTI ID:
1355896
Alternate ID(s):
OSTI ID: 1871001
Report Number(s):
IS-J-9316
Journal Information:
Journal of Physical Chemistry. C, Vol. 121, Issue 11; ISSN 1932-7447
Publisher:
American Chemical SocietyCopyright Statement
Country of Publication:
United States
Language:
English
Citation Metrics:
Cited by: 11 works
Citation information provided by
Web of Science

References (27)

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Cited By (5)

Acidity enhancement through synergy of penta- and tetra-coordinated aluminum species in amorphous silica networks text January 2020
Shedding light on the atomic-scale structure of amorphous silica-alumina and its Brønsted acid sites text January 2019
Shedding light on the atomic-scale structure of amorphous silica–alumina and its Brønsted acid sites journal January 2019
Acidity enhancement through synergy of penta- and tetra-coordinated aluminum species in amorphous silica networks journal January 2020
Determining the Surface Structure of Silicated Alumina Catalysts via Isotopic Enrichment and Dynamic Nuclear Polarization Surface-Enhanced NMR Spectroscopy journal October 2017

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Related Subjects

37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY
atomic layer deposition
chemical liquid deposition
silica-alumina catalyst
DRIFTS
DNP-SENS