Ionic Liquids in Catalysis
Ionic Liquids in Catalysis
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DOI：
10.1007/s10562-014-1435-x
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发表时间：
2015-01-01
影响因子：
2.8
通讯作者：
Wasserscheid, Peter
中科院分区：
文献类型：
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作者：
Steinrueck, Hans-Peter;Wasserscheid, Peter
离子液体（IL），熔点低于100 A ℃的盐，代表了一类迷人的液体材料，其典型特征是极低的蒸气压。离子液体除了作为新型溶剂或电解质用于电化学目的外，还有两个重要的概念将其用于催化：液-液两相催化和离子液体薄膜催化。液-液两相催化能够以非常有效的方式应用催化IL，例如在Friedel-Crafts反应中，或者应用离子过渡金属催化剂溶液。在这两种情况下，反应后的相分离允许反应产物的容易分离和催化剂的再利用。液-液两相催化的一个问题是传质限制。如果化学反应比液-液传质快得多，则后者限制了总反应速率。这个问题在离子液体薄膜催化中得到了克服，其中扩散途径很短，因此扩散的特征时间很短。其中，负载离子液相（SILP）和离子液体层固体催化剂（SCILL）是两个最重要的概念。在这两种情况下，高表面积的固体基底覆盖有薄IL膜，其含有用于SILP的均匀溶解的过渡金属络合物，或者其修饰用于SCILL的载体处的催化活性表面位点。在每一个概念中，界面现象都起着非常重要的作用：在液-液两相催化的情况下，这些现象可能涉及IL相与有机相的界面。对于IL薄膜催化，IL与气相和与催化纳米颗粒和/或载体材料的界面是至关重要的。它最近已被证明，这些接口，也可以使用表面科学研究，这大大有助于从根本上理解的IL和支持IL材料的催化性能的IL的大部分进行了非常详细的调查。介绍了离子液体/真空或离子液体/气体界面、溶解金属络合物的溶解度和表面富集、离子液体/载体界面以及离子液体中化学反应的原位监测等方面的典型结果，综述了离子液体催化的重要概念，包括负载离子液体相（SILP）和离子液体层固体催化剂（SCILL），沿着使用表面科学方法对相关界面的详细分析。
Ionic liquids (ILs), salts with melting points below 100 A degrees C, represent a fascinating class of liquid materials typically characterized by an extremely low vapor pressure. Besides their application as new solvents or as electrolytes for electrochemical purposes, there are two important concepts of using ILs in catalysis: Liquid-liquid biphasic catalysis and IL thin film catalysis. Liquid-liquid biphasic catalysis enables either a very efficient manner to apply catalytic ILs, e.g. in Friedel-Crafts reactions, or to apply ionic transition metal catalyst solutions. In both cases, phase separation after reaction allows an easy separation of reaction products and catalyst re-use. One problem of liquid-liquid biphasic catalysis is mass transfer limitation. If the chemical reaction is much faster than the liquid-liquid mass transfer the latter limits the overall reaction rate. This problem is overcome in IL thin film catalysis where diffusion pathways and thus the characteristic time of diffusion are short. Here, Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL) are the two most important concepts. In both, a high surface area solid substrate is covered with a thin IL film, which contains either a homogeneously dissolved transition metal complex for SILP, or which modifies catalytically active surface sites at the support for SCILL. In each concept, interface phenomena play a very important role: These may concern the interface of an IL phase with an organic phase in the case of liquid-liquid biphasic catalysis. For IL thin film catalysis, the interfaces of the IL with the gas phase and with catalytic nanoparticles and/or support materials are of critical importance. It has recently been demonstrated that these interfaces and also the bulk of ILs can be investigated in great detail using surface science studies, which greatly contributed to the fundamental understanding of the catalytic properties of ILs and supported IL materials. Exemplary results concerning the IL/vacuum or IL/gas interface, the solubility and surface enrichment of dissolved metal complexes, the IL/support interface and the in situ monitoring of chemical reactions in ILs are presented.Important concepts in catalysis with ionic liquids are reviewed, including Supported Ionic Liquid Phase (SILP) and Solid Catalyst with Ionic Liquid Layer (SCILL), along with the detailed analysis of the relevant interfaces using surface science methods.