Paper SS1-TuM6
The Adsorption and Reaction of Alcohols on Poorly Crystalline γ–Al₂O₃ Surfaces

Tuesday, November 10, 2009, 9:40 am, Room M

γ‑alumina, one of the metastable ‘transition’ alumina structural polymorphs, is an important catalytic material both as an active phase and as a support for other catalytically active phases, with widespread applications ranging from petroleum refining to automotive emission control. As such, the bulk and surface structure of γ‑alumina, and its formation and thermal stability have been and continue to be the subject of a considerable amount of research, including attempts to prepare model surfaces via the controlled oxidation of NiAl alloy single crystals. However, due to the low crystallinity and very fine particle size of γ‑alumina, it is very difficult to apply well-established analytical techniques for determining its surface structures. Of particular importance for understanding the catalytic properties of γ‑alumina, relating its surface structure to the origin of Lewis and Brönsted acidity has been of considerable interest and has been studied by solid state NMR and FTIR spectroscopies, and most recently by theoretical calculations. In this presentation, we describe recent studies using ultra-high resolution NMR spectroscopy as an especially useful probe of the γ‑alumina surface structure, and its relevance to catalytic behavior. In particular, we coorelate the NMR spectra with measurements of the adsorption and reaction of alcohols. In this way, we demonstrate a strong dependence of this chemistry on the presence of specific 5-coordinate Al³⁺ ions. These sites, in turn are a function of the dehydration temperature of the alumina material before use. From these correlations, we are able to explain a considerable number of prior observed phenomena.