Synthesis and characterization of various MgO and related systems

Abstract

Various magnesium oxide catalysts have been prepared by thermal treatment of two different precursors: Mg(OH)₂ and Mg₅(OH)₂(CO₃)₄. An additional system based on MgO and doped with B₂O₃ 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), ¹H 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 (viz. the precursor and calcination method used). Use of Mg(OH)₂ as the precursor and in vacua 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 vacuo, probably as the result of the presence of Mg²⁺ cations of low coordination after the calcination.