Supported Aqueous-phase Catalysts Research Articles

A supported aqueous phase catalyst coating in micro flow Mizoroki–Heck reaction

The application of a supported aqueous phase catalyst (SAPC) coating was investigated for the Mizoroki–Heck reaction in micro flow and favorably compared to the use of an SAPC in a batch system. In batch, an 83% yield was observed after 4h at 180°C with a catalyst loading of 0.4mol%, while in flow a residence time of 2.9min provided a 21% yield with only 0.01mol% catalyst loading. In batch the SAPC could be re-used twice without any significant loss in yield, but further re-use was prevented due to problematic accumulation of an ammonium salt. In the micro flow system, this problem could be overcome by adding water to the product flow prior to cooling, allowing even more effective use of the catalyst.

The hydrogenation of cinnamaldehyde by supported aqueous phase (SAP) catalyst of RhCl(TPPTS) 3: Selectivity, kinetic and mass transfer aspects

The hydrogenation of trans-cinnamaldehyde catalysed by a supported aqueous phase catalyst of RhCl(TPPTS) 3 [TPPTS: trisodium salt of tris(m-sulfophenyl)phosphine] on silica was investigated in terms of the product selectivity, reaction kinetics and mass transfer characteristics. The hydrogenation is selective at the C C bonds in cinnamaldehyde giving hydrocinnamaldehyde as the main product. To achieve high selectivity (99.9%), it is necessary to employ a low initial concentration of cinnamaldehyde (0.076 M). The selectivity also depended on the reaction operating conditions (pressure, temperature, catalyst loading) and the water content property of the SAP catalyst. Optimum water content of the SAP catalyst giving maximum activity was obtained when the pore volume of the supports was completely filled with water. The overall order of reaction was first-order and therefore the conventional three-phase slurry model was applied to the SAP system for the mass transfer analysis. The gas–liquid mass transfer and the reaction resistances were the controlling steps of comparable significance, while liquid–solid mass transfer resistance was negligible in this system. Under similar conditions, the SAP catalyst gave a lower reaction rate than the analogous biphasic catalyst.

Propene hydroformylation by supported aqueous-phase Rh-NORBOS catalysts

The gas-phase hydroformylation reaction of propene using supported aqueous-phase (SAP) Rh-NORBOS modified catalysts in a continuous flow reactor has been examined. SAP catalysts supported on six different support materials were made by wet impregnation using solutions of the precursor complex Rh(acac)(CO) 2 and NORBOS ligand. Catalytic performance of silica gel-based catalysts was examined by altering catalyst composition and reaction conditions. Results were compared to analogous TPPTS catalysts and to catalysts supported on alternative support materials, e.g. silica glass, alumina and carbon. Based on these results the aqueous and the homogeneous nature of the SAP catalysts are discussed.

Aqueous phosphine–Rh complexes supported on non-porous fumed-silica nanoparticles for higher olefin hydroformylation

Non-porous fumed-silica nanoparticles were used as supports for the first time to immobilize water-soluble complex HRh(CO)(P( m-C 6H 4SO 3Na) 3 ( 1) [P( m-C 6H 4SO 3Na) 3, i.e. trisodium salt of tri-( m-sulfophenyl)-phosphine, TPPTS] to obtain supported aqueous-phase catalysts (SAPC) (fumed-SiO 2-SAPC) for hydroformylation of 1-hexene. The experimental results proved that the structure of support and the support hydration were the determining factors contributing to the hydroformylation performance. The fumed-SiO 2-SAPC where the water-soluble rhodium complexes were well dispersed onto the external surface of the silica nanoparticles presented a higher hydroformylation performance over a relatively wider range of support hydration as compared to the SAPC with conventional porous granular-SiO 2 support (porous SiO 2-SAPC). A positive effect on the reaction performance was observed from the particle size and surface area of the fumed-silica nanoparticles. The hydroformylation performance with fumed-SiO 2-SAPC was promoted by an addition of basic alkali metal salts such as Na 2CO 3, K 2CO 3, and NaH 2PO 4, which depressed the oxidation of ligand TPPTS to OTPPTS [OTPPTS, i.e. trisodium salt of tri-( m-sulfophenyl)-phosphine oxide, OP( m-C 6H 4SO 3Na) 3] as evidenced by 31 P NMR observation.

Alternative supported aqueous-phase catalyst systems

The concept of supported aqueous-phase (SAP) catalysis has been extended to olefin hydroformylations by the use of in situ formed Rh-, PtSnCl 3- and Co-complexes containing HexDPPDS, TAPTS and TPrPTS as ligands, respectively. (HexDPPDS = hexyl-bis(sodium- m-sulfonatophenyl)phosphine; TAPTS = tris(ω-(sodium- p-sulfonatophenyl)alkyl)phosphines, where alkyl CH 2, TBeTS; C 2H 4, TEtPTS, C 3H 6, TPrPTs). Furthermore, some data are reported on the SAP asymmetric hydroformylation of styrene by the use of PtCl 2[( S,S)-BDPP-(( p-NMe 3)(BF 4)) 4] + SnCl 2 system and on the SAP asymmetric hydrogenation of dehydro-phenylalanine derivatives with Rh(COD)[( S,S)-BDPP-( p-NME 3) 4](BF 4) 5 and Rh(COD)[( S,S)-Chiraphos-( p-NMe 3) 4](BF 4) 5 complexes. (BDPP = 2,4-bis(diphenylphosphino)pentane; Chiraphos = 2,3-bis(diphenylphosphino)butane). For the sake of comparison, the two-phase catalytic results are also given with each alternative SAP catalytic applications, as well as the appropriate (organic) homogeneous values, which were obtained with the analogous complexes containing the respective non-funtionalized ligands. With the exception of the Co-system, the SAP catalytic systems show similar selectivity only to the analogous non-aqueous catalysts. The anomalous behavior of the Co-system in the presence of water is attributed to the presence of sulfonate groups on the ligand which may interact with the cobalt.

Expanded Scope of Supported Aqueous Phase Catalysis: Efficient Rhodium-Catalyzed Hydroformylation of α,β-Unsaturated Esters

The use of supported aqueous-phase (SAP) catalysts for the rhodium-based hydroformylation of methyl acrylate leads under optimal conditions to much higher activities than those observed under comparable homogeneous and biphasic conditions. The results obtained with a series of acrylic esters are found to be dependent on the water content of the solid support and on the solubility of the functionalized olefin in water. For soluble organic reactants, like methyl acrylate, optimal activities are obtained for fully filled pore volume materials. For less soluble organic reactants, like butyl acrylate, hydroformylations are best achieved with a lower degree of pore filling, strictly dependent on the nature of the functionalized olefin. It is assumed that the reaction of hydrophilic olefins occurs mainly in the homogeneous water film dispersed over the solid support, whilst that of lipophilic olefins takes place at the interface between the organic phase and the aqueous film. The effects of temperature and the nature of the solid support are reported. Experiments are described that indicate that the surface area and the chemical nature of the solid play a major role on the activity of the SAP catalyst, whilst the pore diameter has almost no influence. However, a decrease in the activity of methyl acrylate hydroformylation was observed upon recycling of the SAPC materials, which was attributed to the leaching of rhodium into the organic phase and the gradual dehydration of silica.

Asymmetric Synthesis of Naproxen by a New Heterogeneous Catalyst

A new heterogeneous, asymmetric catalyst is described. The catalyst is a modified version of the supported aqueous-phase catalyst reported previously (Wan and Davis, J. Catal. 148, 1 (1994)); ethylene glycol is used in place of water as the hydrophilic phase. Both the enantioselectivity and the activity of this new heterogeneous catalyst are comparable to the homogeneous analogue in neat methanol (or ethylene glycol); e.e.′s are 95.7% vs 96.1% and t.o.f.′s are 40.7 hr −1 vs 131.0 hr −1, respectively. Recycling of the catalyst is possible without leaching of ruthenium at a detection limit of 32 ppb.

The beneficial effect of alkali metal salt on supported aqueous-phase catalysts for olefin hydroformylation

Alkali metal salt modified SAP (supported aqueous-phase) rhodium catalysts prepared by coimpregnation method using alkali metal chloride were found to be active and selective for olefin hydroformylation. The salt addition promoted the formation of aldehydes with high selectivity, the aldehyde yield being increased more than 2.5 times at a proper salt/Rh ratio. Changes in stretching frequency of the carbonyl species were detected during ethene hydroformylation, which appeared at ca. 1625 cm−1 on the non-modified SAP catalyst sample, while at ca. 1586 cm−1 on the KCl-modified one, as shown by in situ IR spectroscopy. The results of a deuterium isotope effect experiment showed that the hydroformylation rate for aldehyde formation on SAP rhodium catalyst under atmospheric pressure of CO/D2 was about 1.3 times faster than that under CO/H2, implying that the rate-determining step involved in aldehyde formation is most probably a step related with hydrogen. The role of the alkali metal salt is discussed in relation with the reaction mechanism.

Selective hydrogenation of α,β-unsaturated aldehydes catalyzed by supported aqueous-phase catalysts and supported homogeneous catalysts

Selective hydrogenations of different α,β-unsaturated aldehydes into allylic alcohols with immobilized homogeneous catalysts are reported. Different kinds of catalysts were used: supported aqueous-phase catalysts (RuCl 2(TPPTS) 3/SiO 2 and RuH 2(TPPTS) 4/SiO 2) and supported homogeneous catalysts (especially phosphino-iridium catalysts like IrCl 3{(C 6H 5)P[(CH 2) 3SiO 3 2 ] 2·2N[(CH 2) 3SiO 3 2 ] 3·2SiO 2} 3). Some of them are good alternatives to homogeneous catalysts since they are chemoselective, sometimes stereoselective and easy to recover.

Catalysts span aqueous, organic phase gap

The search for new catalysts follows many different paths. One of the more intriguing new approaches to catalysis is the development of catalysts that bridge the gap between aqueous and organic phases that are normally active only at their interfaces. A number of catalysts are operative only in aqueous solution, but have potential applications in petrochemistry. Work aimed at reconciling the usual intractabilities has begun. Mark E. Davis, a chemical engineering professor at California Institute of Technology, has developed a new immobilization method designed to convert liquid-phase reactants. At a session of the Division of Industrial & Engineering Chemistry, he described the catalysts as supported-aqueous-phase (SAP) catalysts, consisting of thin films that reside on high-surface-area hydrophilic supports. The film is composed of watersoluble organometallic complexes and water. Reactions of liquid-phase waterinsoluble organics take place at the filmorganic interface. SAP catalysts are distinguished fro...

Supported aqueous-phase, rhodium hydroformylation catalysts I. New methods of preparation

Improved methods for the preparation of supported aqueous phase (SAP) catalysts are described. An in situ preparation of the supported rhodium complex and a more effective hydration procedure are presented. SAP catalysts are also prepared by a self-assembly experiment in which the separated components of a SAP catalyst spontaneously adopt a SAP configuration under reaction conditions.

Supported aqueous-phase catalysts

This work describes a novel family of catalysts denoted supported aqueous-phase catalysts. These catalysts consist of a water-soluble organometallic complex supported in a thin film of water residing on a high-surface-area hydrophilic solid. The catalytic reaction takes place at the water-organic interface where the organic phase contains the reactants and products. Supported aqueous-phase catalysis is demonstrated by liquid-phase hydroformylation. The solid support used here was either CPG-240 or CPG-350; both are porous glasses with narrow pore volume distributions. The catalytic species, HRh(CO)[ m-P(PhS0 3Na) 3] 3 was synthesized from Rh(CO) 2(acac) by a new synthetic route and impregnated onto CPG-240. Solution and solid-state 31P NMR data are consistent with a mobile rhodium species in the aqueous phase in hydrated forms of the catalyst. The hydroformylation of oleyl alcohol (OLOH) was accomplished at 100°C and 5.1 MPa of H 2/CO (1/1) using 0.002 g Rh/g OLOH. For example, conversions of up to 96.6% could be achieved in 5.5 h. It is postulated that no significant leaching of Rh occurs, since after filtration to remove the solid catalyst the remaining solution showed no activity for either the hydroformylation of additional OLOH or the hydrogenation of added 1-hexene. The observations that (1) OLOH and its hydroformylation products are not water soluble, (2) the double bond of OLOH is internal, and (3) the Rh does not leach into the organic phase demonstrate the concept of SAP catalysis; the immobilized homogeneous catalyst is active at the interface of two immiscible phases.

ChemInform Abstract: Hydroformylation by Supported Aqueous‐Phase Catalysis: A New Class of Heterogeneous Catalysts.

HOMOGENEOUS catalysts typically operate at relatively mild temperatures and exhibit high activities and selectivities1. However, it has long been recognized that many homogeneous reactions are not commercially viable because of problems of catalyst recovery. Thus, significant efforts have centred around the immobilization of the organometallic species responsible for catalysis2. At best, the performance of such heterogeneous catalysts only approximate those of their homogeneous counterparts. Here we describe a novel family of heterogeneous catalysts, denoted supported aqueousphase catalysts (SAPCs), designed to facilitate chemical reactions at the interface of two liquids. These catalysts consist of a watersoluble organometallic complex dissolved in a film of water which is supported on a high-surface-area hydrophilic solid. Reactions of liquid-phase organic reactants take place at the water–organic interface. Heterogeneous hydroformylation of alkenes by SAPCs containing water-soluble organometallic rhodium complexes is used to illustrate the efficacy of these new catalysts.

Hydroformylation by supported aqueous-phase catalysis: a new class of heterogeneous catalysts

HOMOGENEOUS catalysts typically operate at relatively mild temperatures and exhibit high activities and selectivities1. However, it has long been recognized that many homogeneous reactions are not commercially viable because of problems of catalyst recovery. Thus, significant efforts have centred around the immobilization of the organometallic species responsible for catalysis2. At best, the performance of such heterogeneous catalysts only approximate those of their homogeneous counterparts. Here we describe a novel family of heterogeneous catalysts, denoted supported aqueousphase catalysts (SAPCs), designed to facilitate chemical reactions at the interface of two liquids. These catalysts consist of a watersoluble organometallic complex dissolved in a film of water which is supported on a high-surface-area hydrophilic solid. Reactions of liquid-phase organic reactants take place at the water–organic interface. Heterogeneous hydroformylation of alkenes by SAPCs containing water-soluble organometallic rhodium complexes is used to illustrate the efficacy of these new catalysts.