Shedding light on the atomic-scale structure of amorphous silica-alumina and its Brønsted acid sites

Frédéric A. Perras; Zichun Wang; Takeshi Kobayashi; Alfons Baiker; Jun Huang; Marek Pruski

doi:10.1039/c9cp04099d

Shedding light on the atomic-scale structure of amorphous silica-alumina and its Brønsted acid sites

Frédéric A. Perras, Zichun Wang, Takeshi Kobayashi, Alfons Baiker, Jun Huang, Marek Pruski

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Abstract

In spite of the widespread applications of amorphous silica–aluminas (ASAs) in many important industrial chemical processes, their high-resolution structures have remained largely elusive. Specifically, the lack of long-range ordering in ASA precludes the use of diffraction methods while NMR spectroscopy has been limited by low sensitivity. Here, we use conventional as well as DNP-enhanced ²⁹Si–²⁹Si, ²⁷Al–²⁷Al, and ²⁹Si–²⁷Al solid-state NMR experiments to shed light on the ordering of atoms in ASAs prepared by flame-spray-pyrolysis. These experiments, in conjunction with a novel Monte Carlo-based approach to simulating RESPDOR dephasing curves, revealed that ASA materials obey Loewenstein's rule of aluminum avoidance. 3D ¹⁷O{¹H} and 2D ¹⁷O{¹H,²⁷Al} experiments were developed to measure site-specific O–H and HO–Al distances, and show that the Brønsted acid sites originate predominantly from the pseudo-bridging silanol groups.

Original language	English
Pages (from-to)	19529-19537
Number of pages	9
Journal	Physical Chemistry Chemical Physics
Volume	21
Issue number	35
DOIs	https://doi.org/10.1039/c9cp04099d
Publication status	Published - 21 Sept 2019
Externally published	Yes

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Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

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title = "Shedding light on the atomic-scale structure of amorphous silica-alumina and its Br{\o}nsted acid sites",

abstract = "In spite of the widespread applications of amorphous silica–aluminas (ASAs) in many important industrial chemical processes, their high-resolution structures have remained largely elusive. Specifically, the lack of long-range ordering in ASA precludes the use of diffraction methods while NMR spectroscopy has been limited by low sensitivity. Here, we use conventional as well as DNP-enhanced 29Si–29Si, 27Al–27Al, and 29Si–27Al solid-state NMR experiments to shed light on the ordering of atoms in ASAs prepared by flame-spray-pyrolysis. These experiments, in conjunction with a novel Monte Carlo-based approach to simulating RESPDOR dephasing curves, revealed that ASA materials obey Loewenstein's rule of aluminum avoidance. 3D 17O\{1H\} and 2D 17O\{1H,27Al\} experiments were developed to measure site-specific O–H and HO–Al distances, and show that the Br{\o}nsted acid sites originate predominantly from the pseudo-bridging silanol groups.",

author = "Perras, \{Fr{\'e}d{\'e}ric A.\} and Zichun Wang and Takeshi Kobayashi and Alfons Baiker and Jun Huang and Marek Pruski",

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doi = "10.1039/c9cp04099d",

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T1 - Shedding light on the atomic-scale structure of amorphous silica-alumina and its Brønsted acid sites

AU - Perras, Frédéric A.

AU - Wang, Zichun

AU - Kobayashi, Takeshi

AU - Baiker, Alfons

AU - Huang, Jun

AU - Pruski, Marek

N1 - Version archived for private and non-commercial use with the permission of the author/s and according to publisher conditions. For further rights please contact the publisher.

PY - 2019/9/21

Y1 - 2019/9/21

N2 - In spite of the widespread applications of amorphous silica–aluminas (ASAs) in many important industrial chemical processes, their high-resolution structures have remained largely elusive. Specifically, the lack of long-range ordering in ASA precludes the use of diffraction methods while NMR spectroscopy has been limited by low sensitivity. Here, we use conventional as well as DNP-enhanced 29Si–29Si, 27Al–27Al, and 29Si–27Al solid-state NMR experiments to shed light on the ordering of atoms in ASAs prepared by flame-spray-pyrolysis. These experiments, in conjunction with a novel Monte Carlo-based approach to simulating RESPDOR dephasing curves, revealed that ASA materials obey Loewenstein's rule of aluminum avoidance. 3D 17O{1H} and 2D 17O{1H,27Al} experiments were developed to measure site-specific O–H and HO–Al distances, and show that the Brønsted acid sites originate predominantly from the pseudo-bridging silanol groups.

AB - In spite of the widespread applications of amorphous silica–aluminas (ASAs) in many important industrial chemical processes, their high-resolution structures have remained largely elusive. Specifically, the lack of long-range ordering in ASA precludes the use of diffraction methods while NMR spectroscopy has been limited by low sensitivity. Here, we use conventional as well as DNP-enhanced 29Si–29Si, 27Al–27Al, and 29Si–27Al solid-state NMR experiments to shed light on the ordering of atoms in ASAs prepared by flame-spray-pyrolysis. These experiments, in conjunction with a novel Monte Carlo-based approach to simulating RESPDOR dephasing curves, revealed that ASA materials obey Loewenstein's rule of aluminum avoidance. 3D 17O{1H} and 2D 17O{1H,27Al} experiments were developed to measure site-specific O–H and HO–Al distances, and show that the Brønsted acid sites originate predominantly from the pseudo-bridging silanol groups.

UR - https://www.scopus.com/pages/publications/85072058092

UR - http://purl.org/au-research/grants/arc/DP150103842

UR - http://purl.org/au-research/grants/arc/DP180104010

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DO - 10.1039/c9cp04099d

M3 - Article

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AN - SCOPUS:85072058092

SN - 1463-9076

VL - 21

SP - 19529

EP - 19537

JO - Physical Chemistry Chemical Physics

JF - Physical Chemistry Chemical Physics

IS - 35

ER -

Shedding light on the atomic-scale structure of amorphous silica-alumina and its Brønsted acid sites

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