Transition-metal complexes in supported liquid phase and supercritical fluids: A beneficial combination for selective continuous-flow catalysis with integrated product separation
Transition-metal complexes in supported liquid phase and supercritical fluids: A beneficial combination for selective continuous-flow catalysis with integrated product separation
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DOI：
10.1002/9783527645824.ch12
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发表时间：
2012-04
期刊：
影响因子：
--
通讯作者：
Ulrich Hintermair;T. Chinnusamy;W. Leitner
中科院分区：
文献类型：
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作者：
Ulrich Hintermair;T. Chinnusamy;W. Leitner
人们一直对开发从反应混合物中分离均相催化剂的方法感兴趣[1]。回收和再利用有机金属催化剂的动机不仅来自催化剂效率的经济论证，而且来自关于产品纯度的法规[2]。用于区分反应器内的催化剂和产物的永久性分离屏障的集成允许直接连续操作，出于工艺控制和效率的原因，这是非常理想的操作模式[3]。为此，由在产物可分离的流体相中或在固体载体表面上的分子催化剂组成的多相系统已被证明是有机金属催化的可行方法[4]。相边界是方便的分离策略，其可以通过例如无机氧化物材料、有机聚合物、水和特定溶剂如氟相或离子液体（IL）引入[1]。然而，大多数寻求弥合均相和多相催化之间的差距的多相体系[5]同时也联合收割机结合了它们各自的一些缺点。当在多相体系中使用分子催化剂时，曾经均相催化剂的可接近性、表征性和可调谐性在不同程度上降低，以使催化剂在连续操作中有效保留[3]。一种折衷固定化分子催化剂的可及性和可变性并具有有效保留的有前景的方法是将其用于负载液相（SLP）中;将浓缩的催化剂溶液分散在多孔载体的表面上结合了液相和固相固定的各自优势（图12.1和表12.1）[6]。在分子水平上，SLP代表了一种“温和”的固定化技术，因为它固定了溶剂，而不是催化剂。这也有利于宏观规模的工艺方案，因为催化剂材料的整体性质由固体载体主导，因此溶剂完全保持在中尺度上，其中它允许均匀的催化转换[3]。
There is sustained interest in developing methods to separate homogeneous catalysts from a reaction mixture [1]. Motivation to recover and reuse organometallic catalysts stems not only from economic arguments on catalyst efficiency but also from regulations regarding product purity [2]. The integration of a permanent separation barrier for the discrimination of catalyst and products inside a reactor allows for straightforward continuous operation, which is a highly desirable mode of operation for reasons of process control and efficiency [3]. To this end, multiphasic systems consisting of a molecular catalyst in a product-separable fluid phase or on the surface of a solid support have proven to be viable approaches for organometallic catalysis [4]. Phase boundaries are convenient separation strategies that may be introduced by, for example, inorganic oxide materials, organic polymers, water, and specific solvents such as fluorous phases or ionic liquids (ILs)[1]. However, most multiphasic systems seeking to bridge the gap between homogeneous and heterogeneous catalysis [5] also combine some of their respective disadvantages at the same time. When using molecular catalysts in multiphasic systems, accessibility, characterizability, and tunability of the once homogeneous catalysts are reduced by various degrees to enable effective catalyst retention in continuous operation [3]. One promising approach to compromise accessibility and variability of immobilized molecular catalysts with effective retention is to use them in supported liquid phases (SLPs); dispersion of a concentrated catalyst solution on the surface of a porous support combines the respective advantages of liquid-and solid-phase immobilization (Figure 12.1 and Table 12.1)[6]. On the molecular level, SLPs represent a ‘‘gentle’’immobilization technique because it immobilizes the solvent, and not the catalyst. It is also beneficial to the macroscale process scheme because the bulk properties of the catalyst material are dominated by the solid support, and thus the solvent is kept entirely on the meso-scale where it permits homogeneous catalytic turnover [3].