Formation of metal oxide cluster lattice and catalytic oxidation properties

金属氧化物催化剂分为两大类别的大部分结构。一种是氧化物，其中的金属-氧键简单地在三维中依次形成，就像在普通金属氧化物中观察到的那样。另一种是所谓的多金属酸氧化合物，就像三元化合物一样，它是由金属多面体组成的离散簇形成的。然而，由于最近发现了具有团簇单元的三维氧化固体，因此揭示了介于第一类和第二类之间的第三类。对于烷烃选择性氧化反应中需要控制每个元素反应步骤的催化剂来说，第三种催化剂是非常重要的。换句话说，高功能化的金属氧化物表面可以用孤立的簇晶格形成，对于实现烷烃选择性氧化这一公认的高难度反应是必不可少的。本课题采用自组织工艺设计并制备了具有催化活性的金属氧化物表面，其结构构建单元适合于簇晶格的形成。我们使用离散的Mo 132（即所谓的大球）合成了MoVSbOx催化剂，选择Mo 132是因为它的离散结构中含有金属八面体的5元环单元。我们成功地合成了具有正交结构的高结晶MoVSbOx。这一结果有力地支持了单元合成在复杂金属氧化物中形成团簇晶格的有效性。该技术也被应用于Mo-V-Ox体系，我们成功地获得了与MoVSbOx具有相同正交结构的结晶材料。用里特费尔德分析法对这些材料的结构进行了分析和细化。通过这些固体氧化物对丙烷选择性氧化制丙烯酸的催化实验，阐明了团簇晶格在反应步骤中的作用以及各组分的作用。

Metal oxide catalysts were classified into two large categories in terms of their bulk structure. One is the oxides in which metal-oxygen bonds are simply formed sequentially in three-dimension as observed in normal metal oxides. The other one is so-called polyoxometalate, like hetempolycompounds, which was formed by the construction of discrete clusters with metal polyhedra. However, third category which is as an intermediate between the first and the second are revealed, because three-dimensional oxide solid with cluster units has been found recently. The third one is found to be very important for catalysts which have to control every elemental reaction step in the alkane selective oxidation In other words, highly functionalized metal oxide surface which can be created with isolated cluster lattice seems to be indispensable for achieving catalytic selective oxidation of alkanes which is recognized as a highly difficult reaction. In this research project, catalytically active metal oxide surface has been designed and produced by self-organization process with structure building units which are suitable for the formation of cluster lattice. We synthesized MoVSbOx catalysts by using discrete Mo 132 so-called big-ball, which was selected because it has 5-member ring unit of metal octahedra in its discrete structure. We succeeded to synthesize highly crystallized MoVSbOx with orthorhombic structure. This result strongly supports the effective ness of unit synthesis to create cluster lattice in complex metal oxides. This technique was also applied to Mo-V-Ox system and we obtained successfully crystalline materials with the same orthorhombic structure that MoVSbOx had. The structure of these materials was analyzed and refined by Rietveld analysis. By the catalytic test of these solid oxides for propane selective oxidation to acrylic acid, the effect of cluster lattice in the reaction steps and the role of constituents were clarified.