Fifty Years of My Romance with Vanadium Oxide Catalysts
Fifty Years of My Romance with Vanadium Oxide Catalysts
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DOI：
10.1002/chin.200928208
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发表时间：
2009-04
期刊：
影响因子：
--
通讯作者：
J. Haber
中科院分区：
文献类型：
--
作者：
J. Haber
世纪的50年代是固体物理和化学在实验和理论上都取得巨大成就的时代--晶体管的发现和固体电子结构理论的迅速发展。人们相信，这一理论将允许理解在金属和氧化物表面的化学反应的机制和催化的电子理论的发展。钒氧化物是一个很好的研究例子，因为钒氧化物和钒氧化物基催化剂的极其丰富的化学性质是由许多不同的相互关联的电子和结构因素造成的。这些化合物具有部分填充的d-轨道，这是负责各种各样的电子，磁性和催化性能。相图显示钒原子以不同的形式氧化态存在，从2到5不等。不同化学计量的氧化物之间的容易转化和氧空位的形成使得氧化物能够在选择性氧化中起催化剂的作用。暴露于氧化还原电位足够的气相中，表面可能发生还原和重构成V6 O 13相。由于微晶的各向异性，不同的晶面具有不同的吸附性质，存在不同的催化活性位点。还原度取决于分散程度。当沉积在其他氧化物载体上时，观察到它们的润湿，并且根据表面自由能比，可以发生从一个载体到另一个载体的表面迁移。在暴露于水蒸气时，钒单层转化为聚阴离子。根据载体的类型，氧化钒显示出各种催化性能。量子化学计算表明，钒离子的非键d轨道具有LUMO特征，表现为刘易斯酸位，而桥氧离子的孤电子对具有HOMO特征，表现为刘易斯碱位。沿（1 0 0）面的沿着裂解留下配位不饱和的钒离子和氧离子，它们与反应分子形成布朗斯台德酸碱相互作用并引起它们的异相化学吸附。根据近50年来收集的结果，可以编写一本关于钒-氧体系物理化学的书。
Abstract The fifties of XXth century were times when solid state physics and chemistry scored great successes both experimental and theoretical – transistors were discovered and the theory of electronic structure of solids made rapid progress. It was believed that this theory will permit the understanding of the mechanism of chemical reactions at metal and oxide surfaces and electronic theory of catalysis was developed. Vanadium oxides were a good example to be studied, because extremely rich chemistry of vanadium oxides and vanadium oxide based catalysts results from a number of different interrelated electronic and structural factors. These compounds have partially filled d-orbitals which are responsible for a wide variety of electronic, magnetic and catalytic properties. The phase diagram shows that vanadium atoms exist in different formal oxidation states, which vary from two to five. The easy conversion between oxides of different stoichiometry and formation of oxygen vacancies enables the oxide to function as catalyst in selective oxidation. Exposed to gas phase of sufficient redox potential reduction and reconstruction of the surface into V 6 O 13 phase may take place. Due to the anisotropy of crystallites different crystal planes have different adsorption properties and different catalytic active sites are present. Reducibility depends on the degree of dispersion. When deposited on other oxide supports their wetting is observed and surface migration from one support onto another one may take place depending on the surface free energy ratio. On exposure to water vapour, the vanadium monolayer transforms into polyanions. Depending on the type of support vanadium oxide shows various catalytic properties. The quantum-chemical calculations show that nonbonding d-orbitals of vanadium ions have the LUMO character and act as Lewis acid sites, whereas the lone electron pairs of bridging oxygen ions have the HOMO character and behave as Lewis basic sites. Cleavage along (1 0 0) planes leaves coordinatively unsaturated vanadium and oxygen ions which develop Bronsted acid–base interactions with reacting molecules and cause their heterolytic chemisorption. On the basis of the results collected in the last 50 years a book on physical chemistry of vanadium–oxygen system could be written.