Surface and catalytic properties of some γ-Al2O3 powders

• Surface and catalytic properties of γ-Al2O3 depend on morphology and purity.
• 300 ppm of alkali kill part of alumina strongest Lewis sites, 1500 ppm kill all.
• Lamellar sample has more strongest Lewis sites than bulky sample.
• Lewis sites, OH's and Na located on edges, corners and defects of the crystals.

The physicochemical and catalytic properties of some γ-Al2O3 samples have been investigated by XRD, SBET, porosity measurements, TEM, chemical analysis (ICP-MS) and IR spectroscopy of the surface OH groups and of adsorbed CO and pyridine. Catalytic activities in the ethanol dehydration reaction were also studied in gas phase in a tubular flow reactor from 423 K to 723 K at atmospheric pressure with 1.44 h−1 WHSV in nitrogen as well as by ethanol temperature programmed reaction (Ethanol-TPR) in a TG/DTA/MS thermal analyzer. Even small amounts of alkali (300 ppm) modify significantly the spectra in the OH stretching region and kill part of the alumina strongest Lewis acid sites with a clear decrease of catalytic activity, while 1% Na completely modifies the surface behaviour. Differences are also observed for clean samples showing slightly different morphology (lamellar versus bulky). The data showed that the catalytic activity of γ-Al2O3 is determined by a small number of sites, which are likely located on edges, corners and defects of the crystals more than on plain surfaces.

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