Synthesis And Characterization Of Magnetic Hydrotalcite

Hydrotalcite-like compounds have been widely used in hydrogenation, polymerization, condensation, alkylation and reforming reaction which can substitute for traditional homogeneous base catalysts such as NaOH. In recent years, nano-scale hydrotalcite has been synthesized by rapid developing nanotechnology. Nano-scale particles with high specific surface area and free energy can greatly improve the catalytic activity of solid base. But the disadvantages of these catalysts such as difficulties of separating and reclaiming in the liquid phase greatly limited their applications. Therefore, it is essential to design and prepare a novel nano-scale solid base catalyst with high catalytic activity, which makes it possible to be easily separated and recovered.In this dissertation, magnetic nano-scale hydrotalcite-like compounds have been prepared by assembling of magnetic substrates and layered hydrotalcite-like compounds which was used as precursor, aiming to achieve one kind of novel environmental friendly catalytic material.In the paper, magnetic Ni-based and Zn-based hydrotalcite-like compounds have been prepared by chemical co-precipitation method. On the basis of binary magnetic hydrotalcite-like compounds, magnetic ternary CuNiAl and ZnMgAl hydrotalcite-like compounds have also been prepared. The influence of the molar ratio of the composition components, the calcination temperatures on the structure, purity, crystallinity, and magnetic properties of the materials has been systematically investigated. The results revealed that the crystallinity of the samples decreases after the incorporation magnetic substrate into the hydrotalcite material. While the typical layered structure of hydrotalcite has been not affected by introducing a certain range of magnetic substrates during the preparation process. Characteristic diffractions of magnetic CuNiAl hydrotalcite-like compound are observed in the XRD patterns. HTLc with integrated crystal structure and good crystallinity can be obtained by controlling the binary ion molar ratio in the certain amount of magnetic substrates. Furthermore, introducing of Cu²⁺ leaded to obvious Jahn-Teller effect, and the effect was remarkable with the increasing amount of Cu²⁺. The magnetic hydrotalcite saturation magnetization was determined by the amount of magnetic substrates.High crystalline magnetic Ni-Al hydrotalcite-like compounds were prepared through hydrothermal method. The results indicated the successful assembling of magnetic substrates and the mother hydrotalcites.The POM-HTLc (polyoxometalate pillared layered hydroxides) were synthesized through introducing the intercalation of POM with Keggin-type into the layers of Ni-Al HTLc using ion exchange reaction method. The results demonstrated that the introduction of magnetic substrates into the POM-HTLc did not affect the typical layered structure of hydrotalcites. Macroporous magnetic HTLc material with 1.04 nm of inter space was obtained. The structure and thermal properties of as-mde samples were characterized by FT-IR, XRD, TG-DSC techniques. Thermal stability of HTLc was higher than precursor accordingly. Thermal decomposition and layer destruction of POM anion in HTLc occurred at the same time and the temperature was lower than decomposition temperature of POM.