Synthesis And Properties Of ZrO₂-based Complex Oxides Magnetic Solid Acid

In present, catalytic cracking of hydrocarbon, isomerization of olefins, alkylation of aromatic hydrocarbon and olefins, polymerization of olefins and diolefine, esterification and hydrolysis have attracted much attention in the field of catalysis. In the past decades, great effort have been made in developing novel solid superacid instead of liquid acid which has been mostly used in industrial applications. Recently, nano-scale solid superacid has been synthesized by rapid developing nanotechnology. These nano-scale particles with high specific surface area and large free energy can greatly improve the catalytic activity of solid superacid. However, the difficulties of separating and reclaiming in the liquid phase reaction and the large mass transfer resistance in the gas phase reaction of these catalysts have greatly limited their application. Therefore, it is essential to design a novel nano-scale solid acid catalyst with the advantages of high catalytic activity and ease of separation and recovery.In this dissertation, classification and formation mechanics of solid acid has been reviewed. Magnetic substrates with high magnetism and suspension stability were prepared by chemical co-precipitation process. In addition, a novel zirconium based ternary-oxide solid acid catalyst with high magnetism and acidity was prepared by assembling of as-made magnetic substrates and solid acid for the first time. The drawbacks of low thermal stability and low specific surface area for zirconia have been improved by doping other oxide. Multi-component heterogeneous metal oxide catalyst migrated during different phases under high heat treatment, which lead to the coordination of multi-component oxide in the phase. As a result, the crystallization temperature of zirconia has been delayed greatly, which markedly inhibited the growth of crystal particle and phase transformation from tetragonal zircoina to monoclinic zirconia. Furthermore, the thermal stability, acid amount and intensity, the number of active centers have been also increased as well. The introduction of Fe₃O₄ magnetic substrate endowed solid superacid with supermagnetism, which can be easily separated and recovered in comparison with the traditional solid acid catalysts.In this work, four magnetic solid acid catalysts includingSO₄^2-/ZrO₂/Fe₃O₄/Al₂O₃, SO₄^2-/ZrO₂/Fe₃O₄/TiO₂, SO₄^2-/ZrO₂/Fe₃O₄/B₂O₃,SO₄^2-/ZrO₂/Fe₃O₄/WO₃ have been prepared. The structure, morphology, textural, and magnetic properties of the catalysts were systematically characterized by XRD, FT-IR, TG-DSC, TEM, SEM, NH₃-TPD, Mossbauer spectra, VSM and N₂ adsorption/desorption techniques. Influence of magnetic substrate, doped amount of oxide and calcination temperature on crystalline temperature and crystal transformation temperature have been investigated. The results indicated that the introduction of magnetic substrate and oxides such as B₂O₃, WO₃, Al₂O₃ and TiO₂ markedly improved the thermal stability of tetragonal zirconia resulting from the uniform distribution of the doped oxide throughout the matrix of the zirconia. Because of the existence of Fe₃O₄ particles, magnetic solid acid catalyst shows the characteristics of superparamagnetism, and the easy-axis of samples are perpendicular to magnetic field. In addition, the HRTEM showed that the tropism of the crystal plane is (101) of tetragonal zirconia, and the interplanar spacing is d(101) = 0.29 nm.The effect of magnetic field on the mechanism of esterification was investigated by esterification which was used as probe reaction for magnetic solid acid catalysts. And some important experiment results and creative achievements have been obtained, which can provide the reference for further study of magnetism chemistry mechanics and for developing novel environmental friendly catalytic materials with double functions.