【作者】 王彬；

【导师】 黄昕；

【作者基本信息】 福州大学 ， 物理化学， 2010， 博士

【摘要】 过渡金属氧化物因其在催化剂、催化剂载体、传感材料、电致变色装置等方面的广泛应用引起人们极大的兴趣。例如，VB、VIB族过渡金属氧化物是一种便利且有效的催化剂，可直接（单罐）将烷烃转换为相应的羧酸、醇和酮。从微观层面上了解这些过渡金属氧化物的物理化学性质，将帮助我们剪裁出具有特殊性质的新材料。对气相簇合物的研究搭建了一条有望实现该目标的桥梁，并可作为研究块材表面及催化反应机理的分子模型。气相簇合物的组成及电荷态在实验中可以通过改变实验条件得到很好的控制。在理论模拟的帮助下，我们能够使各种气相簇合物的研究“精细化”。在本论文中,我们采用理论计算方法对一系列VB、VIB族过渡金属及其氧化物簇合物进行了研究，它们包括：三核簇合物M₃O_n^-/0（M=Nb, n=0-2; M=Ta, n=0-8）以及四核簇合物W₄O_n^-/0（n=10-13）。下面对本论文的主要工作做一简要归纳。对于三核的铌氧化物簇合物Nb₃O_n^-/0（n=0-2）来说，我们采用密度泛函理论计算的方法来研究它们的几何与电子结构、化学成键以及它们的顺序氧化过程。我们发现Nb₃O^2-具有低对称性C₁（¹A），且两个氧原子分别为一个桥氧和一个端氧。端氧Nb=O在铌氧化物催化剂中很常见，Nb₃O^2-簇合物可以作为研究催化剂活性位以及金属铌表面初步氧化的分子模型。对于VB族的另一重金属元素钽，我们对其裸金属簇Ta₃^-/0进行了理论研究。我们发现Ta^3-具有多重的d轨道芳香性，该芳香性正好与其D3h高对称性相对应。进一步的分子轨道分析被用来阐述其化学成键方面的性质。在研究Ta₃^-/0裸簇基础上，我们对一系列钽氧化物簇合物Ta3On-/0（n=1-8）的顺序氧化行为进行了研究。文中我们对Ta3On-/0（n=1-8）簇合物的几何及电子结构的演化过程也进行了详细考察。除了上述工作，我们还对一系列VIB族的四核钨氧化物簇合物W₄O_n^-/0（n=10-13）进行了理论研究。阐述了它们在几何及电子结构上的演化，发现W4O11含有一个定域的W³⁺位，可以和O₂反应形成W₄O₁₃^-簇合物。分子轨道分析被用来理解该系列簇合物的化学成键，并进一步阐释了它们的电子及几何结构的演化过程。更多还原

【Abstract】 Transition metal oxides (TMOs) have attracted considerable interest dueto their wide applications in catalysis, catalyst support, sensor materials,electrochromic devices and so forth. For example, group VB/VIB metaloxides are convenient and efficient catalysts for the direct (single-pot)conversion of alkanes to the corresponding carboxylic acids, alcohols andketones. The understanding of their chemical and physical properties at themicroscopic level will help us to design the materials with desired properties.Studies on the gas-phase clusters may build a bridge to this goal. Molecularclusters of TMOs have been considered as models for surfaces and catalyticreaction mechanism. Both experimental and theoretical approaches have beenemployed to investigate the TMO clusters. The compositions and chargestates of gas-phase clusters can be well controlled through experimentalconditions. With the aid of quantum chemical calculation, we are able tostudy these clusters more elaborately.In this dissertation, the theoretical studies on a series of group VB/VIBtransition metal and their oxide clusters are presented, i.e., the trinuclear M3On-/0(M=Nb, n=0-2; M=Ta, n=0-8) and the tetranuclear W4On-/0(n=10-13)clusters. A summary of our work is given as following:For the trinuclear niobium oxide clusters, Nb3On/0(n=0-2), DFTcalculations were used to investigate the structural and electronic properties,chemical bonding and their sequential oxidation. We found that Nb3O2possesses a low symmetry C1(1A) structure, which contains a bridging and aterminal O atom. The terminal Nb=O unit is common in niobia catalysts andthe Nb3O2cluster with a Nb=O unit may be viewed as a molecular model forthe catalytic sites or the initial oxidation of a Nb surface.As for the heavier element of group VB, i.e., tantalum, its bare metalcluster Ta3/0was investigated using density functional theory calculations.Multiple d-orbital aromaticity was found for the Ta3ground-state,commensurate with its highly symmetric D3hstructure. A detailed molecularorbital analysis was performed to elucidate the chemical bonding in Ta3-. Then, theoretical study on the sequential oxidation behaviors oftritantalum oxide clusters, Ta3On-/0(n=1-8), were performed using densityfunctional theory calculations. The evolutions of geometric and electronicstructures were elaborated for the clusters, Ta3On-/0(n=1-8).We also reported the theoretical calculations for a series of tetratungstenoxide clusters, W4On-/0(n=10-13). The evolutions of geometric andelectronic structures were presented. We showed that W4O11contains alocalized W3+site, which can readily react with O2to form the W4O13cluster.Molecular orbital analyses were performed to analyze the chemical bonding inthe tetratungsten oxide clusters and to elucidate their electronic and structuralevolution.更多还原