Structure and Basicity of Mesoporous Materials from Mg/Al/In Layered Double Hydroxides Prepared by Separate Nucleation and Aging Steps Method

Abstract

This paper presents the synthesis of mesoporous materials from hydrotalcite-like layered double hydroxides (LDHs) with the Mg2 +/(Al3 + + In3 +) molar ratio of 3.0 on the brucite-like lattice and the interlayer carbonate anions, using a novel separate nucleation and aging steps method developed in our laboratory. The physicochemical properties of as-synthesized LDHs and resulting calcined products at 500∘C were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermogravimetric and differential thermal analysis (TG-DTA), 27Al nuclear magnetic resonance (NMR) and low-temperature nitrogen adsorption-desorption experiments. The results indicate calcination of LDHs with a well-crystallized single phase and nanoscale crystallites leads to the formation of the type MgO-like phase, and the pore size distributions of uncalcined and calcined LDHs are mostly in the range of mesopores. Furthermore, calcined materials have higher surface areas, pore volumes, pore diameters and surface basicities than corresponding precursors. When used as solid base catalysts for the Knoevenagel condensation of ethyl cyanoacetate with benzaldehyde, the material with higher density of base sites on the surface also exhibited a higher catalytic activity. Particularly, calcined MgAlIn-LDH has highest density of base sites resulting in a highest catalytic activity, as points to an important role of indium as a modifier of the surface properties of solid base catalysts.