Synthesis of tris(2,2′-bipyridine)iron(II) complexes in zeolite Y cages:: Influence of exchanged alkali metal cations on physicochemical properties and catalytic activity
Synthesis of tris(2,2′-bipyridine)iron(II) complexes in zeolite Y cages:: Influence of exchanged alkali metal cations on physicochemical properties and catalytic activity
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DOI：
10.1021/jp709571v
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发表时间：
2008-02-21
影响因子：
3.7
通讯作者：
Yamashita, Hiromi
中科院分区：
文献类型：
--
作者：
Mori, Kohsuke;Kagohara, Kento;Yamashita, Hiromi
采用“瓶中船”法合成了一系列含Fe（bpy）（3）（2+）的Y型分子筛笼型催化剂，笼型分子筛笼中含有各种碱金属阳离子（Li+，Na+，K+，Rb+，Cs+）.在本研究中，碱金属阳离子对催化剂的物理化学性质的影响，以及它们的催化性能进行了研究。通过XRD、漫反射紫外-可见光谱和Fe K边XAFS测定确定了Fe（bpy）（3）（2+）配合物的形成。通过增加碱金属阳离子的尺寸引起的空间约束导致Fe含量和BET表面积两者的降低。在重碱金属离子存在下，Fe（bpY）（3）（2+）配合物的MLCT吸收带强度增加，而Fe原子的电子密度随碱金属离子半径的增大而减小。将Fe（bpy）（3）（2+）包封在Y型沸石笼中导致了一种新的光催化体系的产生，该体系能够在分子氧存在下在可见光照射（λ> 430 nm）下有效地将苯乙烯氧化成苯甲醛和氧化苯乙烯。发现TON与MLCT带的强度增加和Fe原子的电子密度降低相关。此外，包封在沸石笼中的Fe（bpy）（3）（2+）络合物已被证明用作使用过氧化氢作为氧化剂将苯氧化成苯酚的非均相催化剂。与苯乙烯的光氧化反应相反，在较轻的碱金属阳离子存在下，催化活性得到增强。有人建议，铁原子的电子密度主要决定的氧化速率，这可能是合理的机械方面的考虑。
A series of catalysts containing tris(2,2'-bipyridine)iron(II) (Fe(bpy)(3)(2+)) complexes inside zeolite Y cages with various extraframework alkali metal cations (Li+, Na+, K+, Rb+, and Cs+) have been synthesized via a "ship-in-a-bottle" method. In this study, the influences of the alkali metal cations on the physicochemical properties of the catalysts as well as their catalytic performances were investigated. Formation of the Fe(bpy)(3)(2+) complexes was ascertained by XRD, diffuse-reflectance UV-vis spectroscopy, and Fe K-edge XAFS measurement. The steric constraint induced by increasing the size of the alkali metal cations resulted in a decrease in both Fe content and BET surface area. The intensity of the MLCT absorption band of Fe(bpY)(3)(2+) complexes associated with zeolites increased in the presence of heavier alkali metal cations, while the electron density of the Fe atoms decreased as the ionic radius of the alkali metal cations increased. The encapsulation of Fe(bpy)(3)(2+) within zeolite Y cages resulted in the creation of a new photocatalytic system, enabling efficient oxidation of styrene to benzaldehyde and styrene oxide under visible-light irradiation (lambda > 430 nm) in the presence of molecular oxygen. The TON was found to correlate with the increased intensity of the MLCT band and the decreased electron density of the Fe atoms. Additionally, Fe(bpy)(3)(2+) complexes encapsulated within zeolite cages have been shown to act as heterogeneous catalysts for the oxidation of benzene to phenol using hydrogen peroxide as an oxidant. In contrast to the photooxidation of styrene, catalytic activity was enhanced in the presence of lighter alkali metal cations. It is suggested that the electron density of the Fe atom predominantly determines the oxidation rate; this may be rationalized in terms of mechanistic considerations.