Catalyst supported ionic liquid phase SILP

The term Supported Ionic Liquid Phase (SILP) catalysis has recently been introduced into the literature to describe the heterogenisation of a homogeneous catalyst system by confining an ionic liquid solution of catalytically active complexes on a solid support [68], In comparison to the conventional liquid-liquid biphasic catalysis in organic-ionic liquid mixtures, the concept of SILP-catalysis offers very efficient use of the ionic liquid. Figure 7.10 exemplifies the concept for the Rh-catalysed hydroformylation. 

A rather new concept for biphasic reactions with ionic liquids is the supported ionic liquid phase (SILP) concept [115]. The SILP catalyst consists of a dissolved homogeneous catalyst in ionic liquid, which covers a highly porous support material (Fig. 41.13). Based on the surface area of the solid support and the amount of the ionic liquid medium, an average ionic liquid layer thickness of between 2 and 10 A can be estimated. This means that the mass transfer limitations in the fluid/ionic liquid system are greatly reduced. Furthermore, the amount of ionic liquid required in these systems is very small, and the reaction can be carried in classical fixed-bed reactors. 

Fig. 41.13 Supported ionic liquid phase (SILP) catalyst. The ionic liquid phase containing a rhodium complex is immobilized on the surface of a silica gel support material.

Fig.1 Schematic presentation of supported ionic Liquid Phase (SILP) catalyst...

The catalyst/substrate ratio is 1.5 mol% for the supported ionic liquid phase (SILP) catalyst, 3 mol% for the impregnated catalyst and 2 mol% for the homogeneous reaction aRuns 1 -4 are consecutive experiments with the same catalyst in a stirred batch reactor. bDimeric Cr (salen) catalyst impregnated on silica cHomogeneous reaction at 0-2 OC optimized for product selectivity dHomogeneous reaction at room temperature optimized for product selectivity... 

Joni J, Haumann M, Wasserscheid P (2010) Continuous gas-phase isopropylation of toluene and cumene using highly acidic supported ionic liquid phase (SILP) catalysts. Appl Catal A Gen 372 8-15... 

If the transport limitation is significant, the catalysis occurs predominantly near the surface of the ionic liquid, and the [Rh(CO)2l2] dissolved in the bulk is not fully utilized. One attempt to address these issues was to use a supported ionic liquid phase (SILP) catalyst, as reported by Riisager et al. [Ill], In this system, the ionic liquid (l-butyl-3-methylimidazolium iodide) was supported as a thin film on solid silica (the thin film offers little mass-transport resistance) and used in a fixed-bed continuous reactor with gas-phase methanol. Rates were achieved that were comparable to those in Eastman s bubble column carbonylation reactor with gas-phase reactants [109], but using a much smaller amount of ionic liquid. 

Some potential applications for TSILs have been briefly highlighted in Figs. 2.3-3 and 2.3-4. Many more examples can be found throughout this book. The reader interested in catalytic applications of TSILs is referred to Chapter 5, Section 5.3 for more details. Section 5.5 describes explicitly the role of task-specific ionic liquids as new liquid supports in combinatorial syntheses. This section also provides more details on the synthetic procedures leading to the specific functionalized ionic liquids that have turned out to be particularly suitable for this purpose. While Section 5.6 expands on the role of alkoxysilyl functionalized ionic liquids for surface modification in the preparation of supported ionic liquid phase (SILP) catalysts, Section 6.3 is devoted to the synthesis of nanoparticles and nanostructures in which TSILs often play a decisive role as templates or particle stabilizing agents. 

Fig. 5.3-2 Schematic representation of a supported ionic liquid phase (SILP) catalyst exemplified for a typical rhodium hydroformylation catalyst.

In Section 5.3 it was demonstrated with many examples that ionic hquids are indeed a very attractive class of solvents for catalysis in liquid-liquid biphasic operation (for some selected reviews see Refs. [16-20]). In this section, we wfll focus on a different way to apply ionic liquids in catalysis, namely the use of an ionic liquid catalyst phase supported on a solid carrier, a technology that has become known as supported ionic liquid phase (SILP) catalysis. In comparison to the conventional liquid-liquid biphasic catalysis in ionic liquid-organic liquid mixtures, the concept of SILP-catalysis combines well-defined catalyst complexes, nonvolatile ionic liquids, and porous solid supports in a manner that offers a very efficient use of the ionic liquid catalyst phase, since it is dispersed as a thin film on the surface of the high-area support. Recently, the initial applications using such supported ionic liquid catalysts have been briefly summarized [21]. In contrast to this report, where the applications were distinguished by the choice of support material, the compilation here will divide the applications using the supported ionic liquid catalysts into sections according to the nature of the interaction between the ionic liquid catalyst phase and the support. 

In the literature terms such as supported molten salt (SMS) catalysts, supported ionic liquid catalysts (SILC) and supported ionic liquid-phase (SILP) catalysts, have been used somewhat indiscriminately to describe catalyst systems containing a catalytic ionic phase. In this section vye will use the terms molten salt or ionic liquid to indicate the melting point of the fluid phase in the systems. Furthermore, we will distinguish between the terms SILC and SILP. SILP is used when the ionic liquid is performing mainly as an immobihzing solvent for the catalytic components. SILC is used in cases where the ionic hquid itself, ionic hquid ions or ionic liquid-like fragments are behaving as the catalytic species. 

I Ls can also be immobilized by impregnation of an inorganic support. This is a direct transposition of the Supported Aqueous-Phase Catalysis (SAPC) concept to ionic liquids (see Section 2.6). Supported Ionic Liquid Phase (SILP) catalysts containing Rh-biphosphine ligands were applied to perform continuous-flow gas-phase hydroformylation of propene in [BMIMJIPFg] or [BMIMJIRSOJ (R=octyl). 

Wasserscheid, P, and Fehrmann, R. (2003) Propene and 1-octene hydro-formylation with silica-supported, ionic liquid-phase (SILP) Rh-phosphine catalysts in continuous fixed-bed mode. CataL Lett., 90 (3-4), 149-153. 

Riisager, A., Wasserscheid, P, Van Hal, R., and Fehrmaim, R. (2003) Continuous fixed-bed gas-phase hydroformylation using supported ionic liquid-phase (SILP) Rh catalysts. /. Catal., 219 (2), 452-455. 

Figure 4.1 Major types of supported ionic liquids multilayer ionic liquid film (supported ionic liquid phase SILP) type A, coated heterogeneous catalyst (solid catalyst with ionic liquid layer SCILL) type B, covalently bound monolayer (supported ionic liquid SIL) type C.

Regelein, D. (2005) Hydroformylation of 1 Octene using Supported Ionic Liquid Phase (SILP) Catalysts Diploma Thesis. FAU Erlangen-Nuremherg. 

If supported ILs are used for catalysis (supported ionic liquid phase, SILP solid catalyst with ionic liquid layer, SCILL), the layer thickness (Sj ) is small, mostly only a few layers or even only a monolayer, that is, 1 run. For a conservative estimation of the characteristic time of diffusion, we assume a value of 10 run, which is in the order of magnitude of the diameter of a mesopore. The characteristic... 

P. (2011) Challenging the scope of continuous, gas-phase reactions with supported ionic liquid phase (SILP) catalysts-Asymmetric hydrogenation of methyl acetoacetate. Appl. Catal, A Gen., 399, 35-41. 

Promising approaches to tackle those challenges include use of noble metals [17-19] and the efficient immobilization of homogeneous catalysts in supported ionic liquid phase (SILP) materials [52]. 

Supported ionic liquid phase (SILP) methodology combines the advantage of ionic liquids and those of heterogeneous supports [77], Recently, various SILP-Pd catalysts XXVI, based on imidazolium ionic liquids coordinated to Pd and supported on silica gel, have been prepared. These species were active in the double carbonylation of iodobenzene in the presence of secondary amines, yielding a-ketoamides 78 (Scheme 5.56). In general, the SILP-Pd catalysts XXVI showed selectivity toward double carbonylation, except for the case of using bulky amines, where amides 79 were obtained as the main products. Moreover, under the optimal conditions, these catalysts could be recycled up to six times [78]. 

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