Beyond γ-Al2O3 crystallite surfaces: The hidden features of edges revealed by solid-state 1H NMR and DFT calculations

Elucidating the nature of high surface area gamma alumina sites is of great interest for numerous catalytic applications. In this work, the structural and spectroscopic features of edge sites are unravelled thanks to density functional theory (DFT) calculations combined with high field H-1 MAS NMR of two high surface area alumina samples exhibiting distinct morphologies. DFT chemical shift calculations were carried out for relevant surface models with different hydration degrees. However, the best assignment is achieved by considering the first DFT model representing the hydroxylated edges located at the intersection of (1 1 0) and (1 0 0) alumina facets. The sharp H-1 NMR peak at 0 ppm corresponds to mu(1)-OH groups which are located on this edge and are free from hydrogen bonding. Moreover, we show that these edge sites are the most reactive with respect to chlorine exchange. (C) 2019 Elsevier Inc. All rights reserved.