Degradation of methyl paraoxon in the presence of Mg²⁺-Al ³⁺ mixed oxides

Al³⁺-Mg²⁺ mixed oxides were prepared by coprecipitation and characterized with scanning electron microscopy (SEM), energy dispersive X-ray fluorescence (EDXRF), temperature programmed desorption of CO₂ (CO₂-TPD), and N₂ adsorption/desorption isotherms (BET and BJH methods). By increasing the MgO concentration up to 31.8% (w/w), X-ray diffraction (XRD) measurements suggested an incipient magnesium aluminate spinel (MgAl₂O₄) phase. However, the spinel crystalline structure was obtained only after calcination at 950 C. These materials were tested as catalysts in the propanolysis reaction of methyl paraoxon. This reaction in the presence of the more efficient incipient MgAl₂O₄ spinel is of the order of 2.5 × 10 ⁵-fold faster than the spontaneous propanolysis reaction and results in the formation of a product that is structurally related to a family of flame retardants. The different products of propanolysis and hydrolysis were identified by electrospray ionization mass spectrometry (ESI(+)-MS), ESI(+)-MS/MS) and liquid chromatography mass spectrometry (LC-MS/MS).