title: Brønsted acid sites based on penta-coordinated aluminum species.
abstract: Zeolites and amorphous silica-alumina (ASA), which both provide Brønsted acid sites (BASs), are the most extensively used solid acid catalysts in the chemical industry. It is widely believed that BASs consist only of tetra-coordinated aluminum sites (AlIV) with bridging OH groups in zeolites or nearby silanols on ASA surfaces. Here we report the direct observation in ASA of a new type of BAS based on penta-coordinated aluminum species (AlV) by27Al-{1H} dipolar-mediated correlation two-dimensional NMR experiments at high magnetic field under magic-angle spinning. Both BAS-AlIVand -AlVshow a similar acidity to protonate probe molecular ammonia. The quantitative evaluation of1H and27Al sites demonstrates that BAS-AlVco-exists with BAS-AlIVrather than replaces it, which opens new avenues for strongly enhancing the acidity of these popular solid acids.
authors.affiliation: Laboratory for Catalysis Engineering, School of Chemical and Biomolecular Engineering, Sydney University, Chemical Engineering Building J01, Sydney, New South Wales 2006, Australia.
authors.forename: Zichun
authors.initials: Z
authors.lastname: Wang
authors.affiliation: Department of Engineering, Macquarie University, Sydney, New South Wales 2109, Australia.
authors.forename: Yijiao
authors.initials: Y
authors.lastname: Jiang
authors.affiliation: Univ. Lille, CNRS, UMR 8181-UCCS, Unité de Catalyse et de Chimie du Solide, F-59000 Lille, France.
authors.forename: Olivier
authors.initials: O
authors.lastname: Lafon
authors.affiliation: Univ. Lille, CNRS, UMR 8181-UCCS, Unité de Catalyse et de Chimie du Solide, F-59000 Lille, France.
authors.forename: Julien
authors.initials: J
authors.lastname: Trébosc
authors.affiliation: Laboratory for Catalysis Engineering, School of Chemical and Biomolecular Engineering, Sydney University, Chemical Engineering Building J01, Sydney, New South Wales 2006, Australia.
authors.forename: Kyung
authors.initials: K
authors.lastname: Duk Kim
authors.affiliation: School of Physics, Sydney University, Sydney, New South Wales 2006, Australia.
authors.forename: Catherine
authors.initials: C
authors.lastname: Stampfl
authors.affiliation: Institute for Chemical and Bioengineering, Department of Chemistry and Applied Bioscience, ETH Zürich, Hönggerberg, HCI, CH-8093 Zürich, Switzerland.
authors.forename: Alfons
authors.initials: A
authors.lastname: Baiker
authors.affiliation: Univ. Lille, CNRS, UMR 8181-UCCS, Unité de Catalyse et de Chimie du Solide, F-59000 Lille, France.
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Amoureux
authors.affiliation: Laboratory for Catalysis Engineering, School of Chemical and Biomolecular Engineering, Sydney University, Chemical Engineering Building J01, Sydney, New South Wales 2006, Australia.
authors.forename: Jun
authors.initials: J
authors.lastname: Huang