The surface basicity of magnesium and zinc aluminates has been investigated by adsorption microcalorimetry, using hexafluoro-2-propanol as an acidic probe molecule. The data have been compared to those of the component oxides Al2O3, MgO, and ZnO as well as with two aluminate samples having an excess of bivalent ions with respect to the spinel stoichiometry. The surface properties of these materials have also been investigated by Fourier transform infrared spectroscopy of surface hydroxy groups and of adsorbed pyridine. Evidence is provided for a strong parallelism of the characteristics of the two stoichiometric spinels MgAl2O4 and ZnAl2O4. The strength and distribution of surface basic sites on these materials closely reproduce those of alumina. For stoichiometric materials the basicity scale is MgO > ZnO > MgAl2O4 congruent-to ZnAl2O4 congruent-to Al2O3. Nonstoichiometric aluminates having an excess of bivalent ion show an increased basicity, still lower than that of the corresponding bivalent cations oxides.
Surface Basicity of Mixed Oxides - Magnesium and Zinc Aluminates
BUSCA, GUIDO;
1991-01-01
Abstract
The surface basicity of magnesium and zinc aluminates has been investigated by adsorption microcalorimetry, using hexafluoro-2-propanol as an acidic probe molecule. The data have been compared to those of the component oxides Al2O3, MgO, and ZnO as well as with two aluminate samples having an excess of bivalent ions with respect to the spinel stoichiometry. The surface properties of these materials have also been investigated by Fourier transform infrared spectroscopy of surface hydroxy groups and of adsorbed pyridine. Evidence is provided for a strong parallelism of the characteristics of the two stoichiometric spinels MgAl2O4 and ZnAl2O4. The strength and distribution of surface basic sites on these materials closely reproduce those of alumina. For stoichiometric materials the basicity scale is MgO > ZnO > MgAl2O4 congruent-to ZnAl2O4 congruent-to Al2O3. Nonstoichiometric aluminates having an excess of bivalent ion show an increased basicity, still lower than that of the corresponding bivalent cations oxides.
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