Isolated Vanadium Surface Complexes on Aluminum Fluoride ‐ A Model for the Relevance of Oxygen Atoms of Aluminum Oxide Supports in Catalytic Oxidation Reactions
Isolated Vanadium Surface Complexes on Aluminum Fluoride ‐ A Model for the Relevance of Oxygen Atoms of Aluminum Oxide Supports in Catalytic Oxidation Reactions
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DOI：
10.1002/cctc.201300334
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发表时间：
2013-11
期刊：
影响因子：
4.5
通讯作者：
Carmen Haessner;B. Müller;Oksana Storcheva;K. Köhler
中科院分区：
文献类型：
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作者：
Carmen Haessner;B. Müller;Oksana Storcheva;K. Köhler
比较了以氟化铝AlF3和氧化铝Al_2O_3为载体的单核氧钒络合物的氧化还原性能和反应活性。AlF3是一个有趣的非氧化物载体模型，用于研究不可还原氧化物载体上的氧原子在负载型钒氧化物催化剂催化氧化过程中的作用。固体核磁共振氢谱表明，AlF3表面存在反应性的FH和OH基团，而Al_2O_3表面存在反应性的OH基团。将氧钒(V)三异丙氧基VO(OIPR)3接枝到两种载体的表面。固载化导致了+V(主要)和+IV(次要)氧化态的单核钒配合物的形成。与氧化铝相反，钒的表面物种在AlF3上既不能还原，也不能氧化。用钒(IV)的电子顺磁共振研究了氧化还原循环。原位红外光谱研究表明，两种催化剂对丙烷具有较高的初始化学计量比反应活性。由于载体表面氧的缺乏，在AlF3上的反应在很短的初始时间后停止。结果表明，氧化铝载体的表面氧与氧化反应有关。与氧化铝上的钒不同，VOx/AlF3在丙烷氧化脱氢反应中没有催化活性。只有在500℃以上将AlF3部分氧化为Al_2O_3后，才能观察到催化活性。这些调查支持了最近的一份报告，该报告与常见的氧交换模型相矛盾，该模型假设只涉及表面的氧化钒层，因此似乎正在运行一个更复杂的过程。
The redox properties and reactivity of oxidation catalysts of isolated mononuclear oxovanadium complexes supported on aluminum fluoride, AlF3, and on aluminum oxide, Al2O3, were compared. AlF3 is an interesting model for a non‐oxide support to study the role of oxygen atoms of nonreducible oxide supports during catalytic oxidation with supported vanadium oxide catalysts. Solid‐state 1H NMR indicate the presence of reactive FH and OH groups on the surface of AlF3 and the presence of reactive OH groups on the surface of Al2O3. Oxovanadium(V) triisopropoxide, VO(OiPr)3, was grafted onto the surfaces of both supports. Immobilization led to mononuclear vanadium complexes with oxidation states of +V (major) and +IV (minor). In contrast to alumina, the vanadium surface species were neither reducible nor oxidizable on AlF3. Redox cycles were studied by electron paramagnetic resonance of vanadium(IV). In situ IR spectroscopic investigations showed high and comparable initial stoichiometric reactivity to propane for both catalysts. Reactions on AlF3 stopped after a short initial period as a result of the absence of surface oxygen of the support. The results indicate the relevance of surface oxygen of the alumina support in oxidation reactions. In contrast to vanadium on alumina, VOx/AlF3 is catalytically inactive in the oxidative dehydrogenation of propane. Only after partial oxidation of AlF3 to Al2O3 above 500 °C was catalytic activity observed. The investigations support a recent report contradicting common oxygen‐exchange models, which assume the involvement of only surface vanadium oxide layers, and thus it appears as though a more complex process is in operation.