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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