Various magnesium oxide catalysts have been prepared by thermal treatment of two different precursors: Mg(OH), and Mg5(OH),(C03),. An additional system based on MgO and doped with B203 was also prepared. The textural and acid-base properties of the catalysts were investigated. The synthesized solids were characterized from adsorption isotherms, X-ray diffraction (XRD), 'H MAS NMR, diffuse reflectance IR Fourier transform spectroscopy (DRIFT) and temperature-programmed desorption-mass spectrometry (TPD-MS) of adsorbed probe molecules (pyridine, 2,6-dimethylpyridine and carbon dioxide). The surface properties of the solids were found to be strongly influenced by the magnesium oxide preparation conditions (uiz. the precursor and calcination method used). Use of Mg(OH), as the precursor and in uucuo calcination provided highly basic solids (those with the highest proportions of strong basic sites). Various types of Lewis-acid sites were observed in the catalysts prepared in uacuo, probably as the result of the presence of Mg2+ cations of low coordination after the calcination.

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We studied changes in magnesium oxide upon rehydration under operating conditions similar to those used in the subsequent impregnation of a metal salt on its surface. The ensuing transformations were monitored by using the XRD, TPR, and 1H MAS NMR techniques. On the basis of the results, magnesium oxide (periclase phase) is rehydrated to magnesium hydroxide (brucite phase) and dehydrated back to periclase when the calcination temperature is raised to 600 °C. At this point, the transformation occurs simultaneously with changes in the textural and basic properties of the solid. Pt/MgO catalysts prepared by impregnation of magnesium oxide exhibit variable metallic and surface properties depending on whether Pt(NH3)4(NO3)2 or H2PtCl6 is used as the impregnating salt.

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