Preparation Of Large-size Tetragonal ZrO₂ From Zr-MOF And Catalytic Performance Of SO₄^2-/ZrO₂ Towards Biodiesel

The zirconium oxide modified with sulfate ions can form superacidic catalyst that has ever found. People pay a lot of attention to it as this catalyst can be made easily and ha s little corrosion to the equipment. The crystal of Zr O2 has an important influence on its catalytic performance. Compared to monoclinic phase, the catalytic activity of tetragonal is higher in various industrial applications. Tetragonal zirconia is thermodynamically metastable at room temperatures and would tend to transform to m-Zr O2 upon thermal treatment or contact with water. The tetragonal zirconia can also be stablized at room temperature by two means, one is to calcinate the relatively expensive Zr alkoxide precursors to get Zr O2 whose size is smaller than the critical size(6nm),while this way is limited because of the expensive material, Another way is introducing transition metal ions to be stabilizer. However, the doped metal ions are costly, and sometimes have some uncertainable influences on the catalytic reaction more or less. Meanwhile the stabilizer may get lost during the reaction.It is certified both from the theory and the experimental techniques that a small amount of carbon can stabilize t-Zr O2. Although the carbon is stable in acid、alkali、water、solvent and reagent, but the preparation of t-Zr O2 stabilized by a small amount of carbon is relatively difficult because of using expensive organic zirconium reagent. Zr-MOF is a kind of porous material that constitutes of tetrahedral and octahedral cage and also connected by Zr6(OH)4O4(CO2)12 cluster and organic ligands. Taking into account that the Zr6(OH)4O4(CO2)12 clusters contain Oh molecular symmetry and carbon organic ligands, we use Zr-MOF as precursor to prepare t-Zr O2 by simple calcination in this experiment. XPS showed that the t-Zr O2 from UIO-66 contains both dissociation carbon and C-,which indicates that carbon plays a key role in the formation of t-Zr O2.We can get tetragonal Zr O2 nanoparticle of ~200nm integrated by~20nm nanoparticle by calcinating at the temperature of 500℃.In order to explore the formation of large-size tetragonal Zr O2, cluster Zr6(OH)4O4(OMc)12(OMc=methacrylate), short-chain UIO-FA and long-chain UIO-67 has successively been investigated. The results showed that the crystal phase of Zr O2 is related to the thermal stability of the precursor.What’s more,the particle size of Zr O2 and the existence of carbon stabilizer are different among the different precursors.In order to explore the performance of carbon stabled t-Zr O2, we prepared SO42-/Zr O2 catalyst and characterized the structure. TG and ICP-AES results show that the S of SO42-/Zr O2 is about 15% and the SO42-corresponding to TG is about 30%. We conclude that large-size tetragonal Zr O2 give rise to high sulfur content and strong acidic site owing the formation of polysulfuric acid. The absorb of PY and DMPY together with TG show that SO42-/Zr O2 display strong acidic site. The catalytic reaction towards biodiesel exhibits high efficiency. The SO42-/Zr O2 catalyst can be regenerated by impregnation and calcinations. Although a small amount of monoclinic phase is formed after regenerated but the efficiency of the catalytic reaction changes little which show that the monoclinic phase is arised from the transformation of amorphous Zr O2.