MOF/Al2O3 Composites Obtained by Immobilization of MIL-53(Cr) or MIL-101(Cr) on Γ-Alumina: Preparation and Characterization

The synthesis of hierarchical MOFs/gamma-Al2O3 composites under hydrothermal conditions by deposition of either MIL-53(Cr), or MIL-101(Cr) on the surface of porous alumina supports has been studied. The influence of different parameters (reaction temperature, synthesis duration, reactants/alumina ratio, volume of water, the type of alumina support) on the nature and the quality of the composites were systematically investigated by X-ray powder diffraction (XRD), thermogravimetric analysis (TGA), optical microscopy, scanning electron mi-croscopy (SEM), and N2 adsorption-desorption. The research results showed that the best synthesis conditions for the formation of MIL-53(Cr)/gamma-Al2O3 composites were 150 degrees C, 12 h for the optimum molar ratio (1)CrCl3 center dot 6H2O/ (1)H2BDC/(0.7)gamma-Al2O3/(64)H2O. In contrast, in all the cases, the deposition of MIL-101(Cr) on the gamma-Al2O3 support was not surface-selective at all. Thus, to increase the quality of the deposited MOF on the selected alumina support, successive depositions of MIL-53 or MIL-101 under solvothermal conditions have been explored on two types of porous gamma-Al2O3, (S, particles size <2.0 mm, SBET = 110 m2/g) and (S1, 0.5-2.0 mm particle size, SBET = 247 m2/g). The experimental results show that MIL-101(Cr) formation on alumina S1 is initiated after the second deposition under the synthesis conditions used in this study.