The influence of the synthesis routes of MgAl2O4 on its properties and behavior as support of dehydrogenation catalysts

In order to synthesize MgAl2O4, three methods were used: (a) a solid phase reaction of MgO and γ-Al2O3 oxides at 900 °C for 24 h (ceramic method), (b) wet milling during 24 h of the mixture of oxides followed by the reaction at 900 °C for 12 h (mechanochemical synthesis), and (c) coprecipitation of Mg(NO3)2·6H2O and Al(NO3)3·9H2O with ammonia solution followed by a calcination in a flow of air at 800 °C during 4 h (coprecipitation method). The synthesized materials were characterized by XRD, BET isotherm, isopropanol dehydration reaction, TGA/DTA and SEM. The results indicate that in all the cases the MgAl2O4 spinel was formed. Besides, a residue of MgO in the samples obtained by the ceramic method and mechanochemical synthesis was found, which was eliminated by purification. The surface area of MgAl2O4 obtained by mechanochemical synthesis and coprecipitation method are much higher than that of the spinel synthesized by the ceramic method. Pt (0.3%) catalysts were prepared by impregnating the three supports with H2PtCl6. The metallic dispersion of Pt/MgAl2O4 obtained by mechanochemical synthesis was higher than that of Pt catalysts supported on the other spinels, in agreement with the catalytic behavior observed in n-butane dehydrogenation reaction and test reactions of the metallic phase.