The influence of the synthesis routes of MgAl 2O 4 on its properties and behavior as support of dehydrogenation catalysts

Abstract

In order to synthesize MgAl 2O 4, three methods were used: (a) a solid phase reaction of MgO and γ-Al 2O 3 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(NO 3) 2·6H 2O and Al(NO 3) 3·9H 2O 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 MgAl 2O 4 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 MgAl 2O 4 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 H 2PtCl 6. The metallic dispersion of Pt/MgAl 2O 4 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.