Structure and Catalytic Property of Li–Al Metal Oxides from Layered Double Hydroxide Precursors Prepared via a Facile Solution Route

This paper presents the synthesis of Li–Al mixed metal oxides from Li–Al layered double hydroxides (LiAl-LDHs) by using a novel separate nucleation and solvothermal aging steps method. The physicochemical properties of as-synthesized LiAl-LDHs and resulting calcined products at 600 °C were investigated by powder X-ray diffraction (XRD), Fourier transform infrared spectroscopy (FT-IR), simultaneous thermogravimetric and differential thermal analysis (TG-DTA), scanning electron microscope (SEM), and low-temperature nitrogen adsorption–desorption experiments. The results indicated that uniform LiAl-LDH particles with smaller sizes were obtained by using ethanol as solvent in the aging step, in contrast with those by using water and water/ethanol mixture. Especially, after calcination, the resulting mixed metal oxides showed variable surface basicities, which were strongly dependent on their crystallite sizes and surface areas. When used as solid base catalysts for the Knoevenagel condensation of benzaldehyde with ethyl cyanoacetate, the mixed metal oxides with more strong basic sites exhibited a higher catalytic activity.