Studies On Catalytic Performance And Synthesis Of Composite Oxide Magnetic Solid Acid

Solid acid catalysts have been found to be useful catalyst in a variety of organic reactions. They have many advantages, such as non-toxic, inodorous, non-volatile; non-corrosive, non-pollution, mild reaction conditions, high yields and reactivity, excellent stability and simple work-up procedure, and these are what liquid catalysts can't replace. Based on recent work about solid acids, some research was done. A series of novel magnetic nano size solid acid catalysts were prepared by enwrapping the magnetic core of Fe₃O₄ with solid acid or solid superacid. These acids have many advantages such as unique acidity, high activity, high selectivity, easy preparation and simple work-up procedure, so it may be used in reactions which can be catalyzed by acidic catalysts.In this work, three magnetic solid acid catalysts including SO₄^2-/ZrO₂/Fe₃O₄/MgO,SO₄^2-/ZrO₂/Fe₃O₄/ZnO,SO₄^2-/ZrO₂/Fe₃O₄/TiO₂ have been prepared by co-precipitation method. The structure, morphology, textural, and magnetic properties of the catalysts were systematically characterized by XRD, FT-IR, TG-DSC, TEM, SEM, NH₃-TPD, VSM and so on. Catalytic properties of the catalyst were influenced significantly by the pretreatment temperatures. The characterization of the optimum catalyst showed that the high activity and selectivity of the catalyst resulted from the high degree of dispersion of the active component. The new catalyst showed high catalytic activities in the condensation reaction of cyclohexanone, all of magnetic nano size solid acid catalysts can be separated from the reaction system by magnetism. 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 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 introduction of Fe₃O₄ magnetic substrate endowed solid superacid with superparamagnetisation, which can be easily separated and recovered in comparison with the traditional solid acid catalysts. And the optimum catalyst is SO₄^2-/ZrO₂/Fe₃O₄/ZnO, the optimum results are: the conversion of cyclohexanone is 77.36%, the selectivity of dimer is 90.87%, the recovery of the catalyst is 95.46 %. While we concluded that HC1 is the most suitable protonic acid catalyst, the conversion of cyclohexanone is 55 %.