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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Journal: Applied Catalysis A: General - Volume 483, 5 August 2014, Pages 41–51