Strong Lewis acidity of a phase-pure γ-Ga 2 O 3 was studied by the adsorption of CO at ambient temperature, with the combined use of adsorption microcalorimetry and in situ Fourier transform infrared spectroscopy. The concentration of strong Lewis acid sites turned out to be quite low, but it grew fast with increasing surface dehydration upon thermal treatments in the 573−773 K range. Two main families of Lewis acid sites were observed, characterized by rather different molar adsorption heats and CO stretching frequencies. These acid sites have been ascribed to coordinatively unsaturated Ga 3+ ions located in defective (higher ν CO ) and regular (lower ν CO ) crystallographic sites, respectively. The possibility of extracting, for the CO/γ-Ga 2 O 3 system, quantitative information from the IR spectroscopic data is discussed in some detail.
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Morterra et al. (2002) studied this question.
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