Structured fiber supports for ionic liquid-phase catalysis used in gas-phase continuous hydrogenation

Abstract

Structured supported ionic liquid-phase (SSILP) catalysis is a new concept with the advantages of ionic liquids (ILs) used as solvents for homogeneous catalyst and the further benefits of structured heterogeneous catalysts. This is achieved by confining the IL with the transition metal complex to the surface of a structured support consisting of sintered metal fibers (SMFs). In an attempt to improve the homogeneity of the IL film, the SMFs were coated by a layer of carbon nanofibers (CNFs). The IL thin film immobilized on CNF/SMF supports presents a high interface area, ensuring efficient use of the transition metal catalyst. The regular structure of the support with high porosity (>0.8) allows a low pressure drop and even gas-flow distribution in a fixed-bed reactor. The high thermoconductivity of the CNF/SMF support suppresses the formation of hot spots during exothermic hydrogenation reactions. The selective gas-phase hydrogenation of 1,3-cyclohexadiene to cyclohexene over a homogeneous Rh catalyst immobilized in IL supported on CNF/SMF was used as a test reaction to demonstrate the feasibility of the SSILP concept. The catalyst [Rh(H) 2 Cl(PPh 3 ) 3 /IL/CNF/SMF] showed a turnover frequency of 150-250 h −1 and a selectivity of >96%. High-pressure 1 H NMR and 1 H{ 31 P} NMR spectroscopy was used to provide insights into the nature of the active catalytic species.

Insight into the immobilization of ionic liquids on porous carbons

“…This allows, thus, a broad variety of arrangements and interactions of the IL within the support surface. There are some works dealing with SILP systems based on carbon materials using for example a carbon cloth [17,18], carbon nanofibres that cover sintered metal fibres [19], commercially available mesoporous and microporous carbon beads [20], commercial activated carbons [21] and carbon nanotubes [22][23][24][25].…”

Hydrogenation in Ionic Liquids

“…Ruta et al [30] when carried out gas phase hydrogenation of 1, [24] in which the hydrogenation of 1,4-cyclooctadiene was performed using a [bmim][n-C 8 H 17 OSO 3 ] coated Ni catalyst in n-dodecane. This IL/ n -dodecane biphasic system allows effective partitioning of the intermediate (in this case cyclooctene) into the hydrocarbon layer, preventing over-reduction to cyclooctane.…”

“…The application of their novel material soaked with a palladium catalyst was used for the hydrogenation of styrene (Figure 53), where, under mild and solvent-free conditions, a good TON (5,000) and TOF (250 h -1 ) were obtained. [30] demonstrated the catalytic activity of their rhodium-based structured supported ionic liquid-phase (SSILP) catalyst with the hydrogenation of 1,3-cyclohexadiene. The IL containing the metal catalyst was confined to a structured support surface consisting of sintered metal fibres.…”

Pd Nanoparticles in a Supported Ionic Liquid Phase: Highly Stable Catalysts for Selective Acetylene Hydrogenation under Continuous-Flow Conditions

“…Thus, the configuration of Figure 1-C (9 wt % IL phase on CNF/ SMF Inconel ) is preferred because it provides higher quantities of the active phase on the support while maintaining the homogeneity of the IL layer. 27 For fast kinetics, as for acetylene hydrogenation, the morphology of Figure 1-A/B is better because it provides a higher surface area in contact with the gas phase and a thinner layer of IL in which the active Pd nanoparticles are embedded. Figure 2 shows HR-TEM images of Pd nanoparticles (confirmed by in situ EDX) with a narrow size distribution.…”