Study of the surface acidity of an hematite powder

In this work, the interaction between alpha-Fe2O3 (hematite) powder samples and pyridine, 2,6-dimethyl pyridine, carbon monoxide and carbon dioxide was studied, at atmospheric pressure as well as under high vacuum (HV) conditions. The powder was characterised by means of diffuse reflectance infrared Fourier transform (DRIFT) and X-ray photoelectron spectroscopics (XPS), X-ray diffraction (XRD) and thermal analysis (TGA-DSC). Chemisorption experiments at atmospheric pressure were studied by means of DRIFT spectroscopy while those carried out under HV conditions were followed by means of quadrupolar mass spectrometry (QMS) and XPS. The study of the interaction of pyridine with alpha-Fe2O3 allowed us to appreciate the presence of both Bronsted and Lewis acid sites on the powder surfaces. Moreover, the use of CO as probe molecule indicated the existence of non equivalent Lewis acid sites. Finally, CO2 may interact with the powder sample either reacting with surface OH groups giving rise to bicarbonate species, or with surface cations and neighbouring oxide ions to originate bidentate carbonate species. (C) 2002 Elsevier Science B.V. All rights reserved.