Transition-metal ions in zeolites: coordination and activation of oxygen.
Transition-metal ions in zeolites: coordination and activation of oxygen.
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DOI：
10.1021/ic901814f
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发表时间：
2010-04-19
影响因子：
4.6
通讯作者：
Schoonheydt, Robert A.
中科院分区：
文献类型：
--
作者：
Smeets, Pieter J.;Woertink, Julia S.;Sels, Bert F.;Solomon, Edward I.;Schoonheydt, Robert A.
含有过渡金属离子（TMI）的沸石通常在污染消除和选择性氧化反应中作为多相催化剂表现出有前景的活性。本文讨论了沸石中 TMI Cu、Co 和 Fe 的两个方面的研究：(i) 与晶格的配位和 (ii) 活化氧物种。在低负载下，TMI优选占据六元氧环(6MR)中的交换位点，其中TMI优先与Al四面体的氧原子配位。高 TMI 负载量会导致在沸石表面形成多种 TMI 物质。在高温预处理过程中去除晶格外氧会导致自动还原。还原 TMI 位点的氧化通常会导致高活性氧的形成。在 Cu-ZSM-5 中，用 O2 煅烧会形成一种物质，该物质被发现是 NO 和 N2O 直接分解以及甲烷选择性氧化成甲醇的关键中间体。 Fe-ZSM5 中形成一种被称为 α-氧的活化氧物质，据报道它是甲烷和苯分别部分氧化成甲醇和苯酚的活性位点。然而，这种活性α-氧只能与N2O形成，而不能与O2形成。八面沸石 (FAU) 沸石中的 O2 活化 Co 中间体可以选择性氧化 α-蒎烯并环氧化苯乙烯。在Co-FAU中，CoIII超氧和过氧复合物被认为是活性核心，而在Cu和Fe-ZSM-5中，已经提出了各种单体和二聚位点，但尚未达成共识。最近，Cu-ZSM-5 中的活性位点被确定为弯曲的 [Cu-O-Cu]2+ 核心 (Proc. Natl. Acad. Sci. USA 2009, 106, 18908-18913)。总体而言，O2 活化取决于结构因素（例如沸石类型、通道和笼的尺寸）以及化学因素（例如 Si/Al 比率以及电荷平衡阳离子的性质、电荷和分布）的相互作用。多个不同 TMI 位点的存在阻碍了对活性位点光谱特征的直接研究。因此，需要能够选择性探测这些位点的光谱技术，即使它们只占 TMI 位点总量的一小部分。反应活性位点的几何和电子结构的基础知识有助于设计新型选择性氧化催化剂。
Zeolites containing transition metal ions (TMI) often show promising activity as heterogeneous catalysts in pollution abatement and selective oxidation reactions. In this paper, two aspects of research on the TMI Cu, Co and Fe in zeolites are discussed: (i) coordination to the lattice and (ii) activated oxygen species. At low loading, TMI preferably occupy exchange sites in six-membered oxygen rings (6MR) where the TMI preferentially coordinate with the oxygen atoms of Al tetrahedra. High TMI loadings result in a variety of TMI species formed at the zeolite surface. Removal of the extra-lattice oxygens during high temperature pretreatments can result in auto-reduction. Oxidation of reduced TMI sites often results in the formation of highly reactive oxygen species. In Cu-ZSM-5, calcination with O2 results in the formation of a species, which was found to be a crucial intermediate in both the direct decomposition of NO and N2O and the selective oxidation of methane into methanol. An activated oxygen species, called α-oxygen, is formed in Fe-ZSM5 and reported to be the active site in the partial oxidation of methane and benzene into methanol and phenol, respectively. However, this reactive α-oxygen can only be formed with N2O, not with O2. O2 activated Co intermediates in Faujasite (FAU) zeolites can selectively oxidize α-pinene and epoxidize styrene. In Co-FAU, CoIII superoxo and peroxo complexes are suggested to be the active cores, whereas in Cu and Fe-ZSM-5 various monomeric and dimeric sites have been proposed, but no consensus has been obtained. Very recently, the active site in Cu-ZSM-5 was identified as a bent [Cu-O-Cu]2+ core (Proc. Natl. Acad. Sci. USA 2009, 106, 18908-18913). Overall, O2 activation depends on the interplay of structural factors such as type of zeolite, size of the channels and cages and chemical factors such as Si/Al ratio and the nature, charge and distribution of the charge balancing cations. The presence of several different TMI sites hinders the direct study of the spectroscopic features of the active site. Spectroscopic techniques capable of selectively probing these sites, even if they only constitute a minor fraction of the total amount of TMI sites, are thus required. Fundamental knowledge of the geometric and electronic structure of the reactive active site can help in the design of novel selective oxidation catalysts.
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影响因子：
3.3
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