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

Date
2019-01-01
Authors
Perras, Frédéric
Wang, Zichun
Kobayashi, Takeshi
Baiker, Alfons
Huang, Jun
Pruski, Marek
Journal Title
Journal ISSN
Volume Title
Publisher
Altmetrics
Authors
Research Projects
Organizational Units
Journal Issue
Series
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.

Description
Keywords
Citation
DOI
Collections