An atomistic MD simulation and pair-distribution-function study of disorder and reactivity of α-AlF3 nanoparticles

Santanu Chaudhuri; Peter Chupas; Benjamin J. Morgan; Paul A. Madden; Clare P. Grey

doi:10.1039/B604750E

An atomistic MD simulation and pair-distribution-function study of disorder and reactivity of α-AlF₃ nanoparticles†

Santanu Chaudhuri,‡*^a Peter Chupas,§^a Benjamin J. Morgan,^b Paul A. Madden^c and Clare P. Grey*^d

Author affiliations

* Corresponding authors

^a Department of Chemistry, SUNY Stony Brook

^b School of Chemistry, Trinity College, University of Dublin, Dublin 2, Ireland
E-mail: morganb@tcd.ie

^c School of Chemistry, University of Edinburgh, West Mains Road, Edinburgh, UK
E-mail: paul.madden@ed.ac.uk

^d Department of Chemistry, SUNY Stony Brook, USA
E-mail: cgrey@notes.cc.sunysb.edu

Abstract

Cubic nanoparticles of α-AlF₃ containing 864 and 2048 atoms were investigated by using molecular dynamics simulations. Significant structural rearrangements of these particles occurred, primarily at the edges and corners of the particles, and 3 and 5 membered (Al–F–)_n ring structures were observed in addition to the 4-membered rings seen in bulk α-AlF₃. These 3 and 5 membered ring structures are, however, present in other metastable forms of AlF₃, which are formed at low temperatures from high surface area precursors. The surfaces of the nanoparticles were very dynamic on the timescale of the MD run, Al–F bonds being continually broken and formed, resulting in the movement of the low coordinate Lewis acid Al sites on the surfaces of the particles. The Lewis acid sites, which represent the catalytically active sites for F/Cl exchange reactions, are largely present at the corners and edges of the particles. The particles show larger rhombohedral distortions than present in the bulk phase and do not undergo a rhombohedral to cubic phase transition at elevated temperatures. The results are compared with pair distribution function (PDF) analysis results from fluorinated γ-Al₂O₃, nanoparticles of AlF₃ prepared by plasma routes and α- and β-AlF₃. Broad peaks between 3.3 and 4.5 Å in the PDF plots of the fluorinated Al₂O₃ and the nanoparticles indicate a distribution of Al–F distances arising from Al and F atoms in connected AlF₆ octahedra; this is consistent with the presence of ring structures other than those found in α-AlF₃.

Article information

https://doi.org/10.1039/B604750E

Article type

Paper

Submitted

03 Apr 2006

Accepted

20 Jun 2006

First published

11 Jul 2006

Download Citation

Phys. Chem. Chem. Phys., 2006,8, 5045-5055

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An atomistic MD simulation and pair-distribution-function study of disorder and reactivity of α-AlF₃ nanoparticles

S. Chaudhuri, P. Chupas, B. J. Morgan, P. A. Madden and C. P. Grey, Phys. Chem. Chem. Phys., 2006, 8, 5045 DOI: 10.1039/B604750E

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