Title
Shedding light on the atomic-scale structure of amorphous silica–alumina and its Brønsted acid sites
Publication Date
2019
Department
Ames Laboratory; Chemistry
Campus Units
Ames Laboratory, Chemistry
OSTI ID+
1559344
Report Number
IS-J 10031
DOI
10.1039/C9CP04099D
Journal Title
Physical Chemistry Chemical Physics
Volume Number
21
Issue Number
35
First Page
19529
Last Page
19537
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.
DOE Contract Number(s)
AC02-07CH11358; DP150103842; DP180104010
Language
en
Publisher
Iowa State University Digital Repository, Ames IA (United States)
