HONG, Han (Institute of Chemical and Engineering Sciences, 1 Pesek Road,Jurong Island, Singapore 3, 62783, SG)
CHAI, Christina L.L. (Institute of Chemical and Engineering Sciences, 1 Pesek Road,Jurong Island, Singapore 3, 62783, SG)
WANG, Mian (Institute of Chemical and Engineering Sciences, 1 Pesek Road,Jurong Island, Singapore 3, 62783, SG)
NG, Yeap Hung (Institute of Chemical and Engineering Sciences, 1 Pesek Road,Jurong Island, Singapore 3, 62783, SG)
HONG, Han (Institute of Chemical and Engineering Sciences, 1 Pesek Road,Jurong Island, Singapore 3, 62783, SG)
CHAI, Christina L.L. (Institute of Chemical and Engineering Sciences, 1 Pesek Road,Jurong Island, Singapore 3, 62783, SG)
WANG, Mian (Institute of Chemical and Engineering Sciences, 1 Pesek Road,Jurong Island, Singapore 3, 62783, SG)
| WHAT IS CLAIMED IS: 1. A composite comprising a supported catalyst, said catalyst selected to catalyze a catalytic reaction, said composite comprising: a polymeric skeleton defining pores, said skeleton selected to be resistant to reagents of said catalytic reaction; a gel retained in said pores, said gel selected to capture said catalyst; said catalyst captured by said gel; and substructures formed on an internal surface of said pores to physically retain said gel in said pores during said reaction, said substructures capable of physically retaining said gel without chemically bonding said gel to said internal surface of said pores. 2. The composite of claim 1 , wherein said substructures comprise a microstructure sized and shaped to engage said gel by catching, snagging, hooking, gripping, clinching, clenching, or looping around said gel. 3. The composite of claim 1 or claim 2, wherein said substructures comprise a projection, protuberance, crossing, bridge, hook, loop, spike, wire, rod, beam, snag, clinch, or clench. 4. The composite of any one of claims 1 to 3, wherein said polymeric skeleton comprises polystyrene (PSt), poly(methyl methacrylate) (PMMA), or poly(vinylidene difluoride) (PVDF). 5. The composite of any one of claims 1 to 4, wherein said gel comprises polyhydroxypropyl acrylate (PHPA), polyacrylic acid (PAA), or polydimethylacrylamide (PDMAA). 6. The composite of any one of claims 1 to 5, wherein said catalyst is bonded to, or encapsulated in, said gel. 7. The composite of any one of claims 1 to 6, wherein said catalyst comprises a metal catalyst. 8. The composite of claim 7, wherein said metal catalyst comprises Pd, Pt, La, Ti, Hf, Fe, Co, Ni, Cu, Mn, or Cr. 9. The composite of any one of claims 1 to 6, wherein said catalyst comprises an enzyme. 10. The composite of any one of claims 1 to 9, comprising nanoparticles captured by said gel, said nanoparticles comprising said catalyst. 11.The composite of any one of claims 1 to 10, wherein said skeleton is substantially spherical. 12. The composite of any one of claims 1 to 10, wherein said skeleton is a film. 13. A method of forming a composite for supporting a catalyst selected to catalyze a catalytic reaction, comprising: providing a polymeric skeleton defining pores and comprising substructures formed on an internal surface of said pores, said skeleton selected to be resistant to reagents of said catalytic reaction; introducing a mixture into said pores, said mixture selected for forming a gel capable of capturing said catalyst; and forming said gel from said mixture in said pores so that said gel physically engages said substructures when said gel is formed, thus forming said composite, wherein said substructures are sized and shaped to physically retain said gel in said pores during said reaction, and are capable of physically retaining said gel without chemically bonding said gel to said internal surface of said pores. 14. The method of claim 13, wherein said substructures comprise a projection, protuberance, crossing, bridge, hook, loop, spike, wire, rod, beam, snag, clinch, or clench. 15. The method of claim 13 or claim 14, wherein said substructure comprise a microstructure sized and shaped to engage said gel by catching, snagging, hooking, gripping, clinching, clenching, or looping around said gel. 16. The method of any one of claims 13 to 15, wherein said polymeric skeleton comprises polystyrene (PSt), poly(methyl methacrylate) (PMMA), or poly(vinylidene difluoride) (PVDF). 17. The method of any one of claims 13 to 16, wherein said providing said skeleton comprises forming said skeleton by polymerization. 18. The method of any one of claims 13 to 17, wherein said mixture comprises a hydroxypropyl acrylate (HPA), acrylic acid (AA), or dimethylacrylamide (DMAA) monomer, and said forming said gel comprises polymerizing said monomer to form poly(HPA), poly(AA), or poly(DMAA). 19. The method of any one of claims 13 to 18, wherein said polymerizing said monomer comprises crosslinking said monomer. 20. The method of any one of claims 13 to 19, wherein said skeleton is substantially spherical. 21. The method of any one of claims 13 to 20, wherein said skeleton is a film. 22. The method of any one of claims 13 to 21 , comprising bonding said catalyst to said gel. 23. The method of any one of claims 13 to 22, comprising encapsulating said catalyst in said gel. 24. The method of any one of claims 13 to 23, wherein said catalyst comprises an enzyme. 25. The method of any one of claims 13 to 23, wherein said catalyst comprises a metal catalyst. 26. The method of claim 25, wherein said metal catalyst comprises Pd, Pt, La, Ti, Hf, Fe, Co, Ni, Cu, Mn, or Cr. 27. The method of any one of claims 13 to 26, comprising contacting said composite with a solution comprising a precursor for said catalyst to allow said gel to absorb said solution and said precursor, and converting said precursor to said catalyst in said gel. 28. A method comprising reacting reagents of a catalytic reaction in the presence of the composite of any one of claims 1 to 12. 29. The method of claim 28, wherein said reaction is a Heck reaction, Suzuki reaction, hydrogenation reaction, or oxidation reaction. |
CROSS-REFERENCE TO RELATED APPLICATION
[0001] This application claims the benefit of U.S. provisional application No.
61/136,919, filed October 14, 2008, the entire contents of which are incorporated herein by reference.
FIELD OF THE INVENTION
[0002] The present invention relates to composites and methods for supporting catalysts, such as metal catalyst and enzymes.
BACKGROUND OF THE INVENTION
[0003] A supported metal catalyst includes a catalytic metal supported on a supporting material. Supported metal catalysts are useful for catalyzing various reactions, such as coupling reactions, hydrogenation reactions, oxidation reactions, or the like. While it is desirable to be able to recycle and re 7 use catalysts, it has been a challenge to provide recyclable supported metal catalysts. One problem is that a catalytic metal species can be lost during use if it is not securely retained by the supporting material under reaction conditions. To prevent such loss, the catalytic metal may be encapsulated in the supporting material, but encapsulation can negatively affect catalytic activity and can make it difficult to re-activate the catalyst after use, when the encapsulation material is selected to be resistant to the reagents of the catalytic reaction. It is possible to chemically bond the catalytic metal to the supporting material, either directly or through an intermediate that is chemically bonded to the supporting material. A problem with such chemically bonded supported catalysts is that they are prune to damage or tend to bond with other foreign substances, both of which can negatively affect the performance of the supported catalysts. SUMMARY OF THE INVENTION
[0004] It has been discovered that a catalyst can be retained in a composite formed from a skeleton and a gel, where the skeleton defines pores and has substructures formed on an internal surface of the pores which are sized and shaped to physically engage and retain the gel in the pores, and are capable of physically retaining the gel in the pores without chemically bonding the gel to the internal surface of the pores. The gel may be swellable and is selected to capture the metal catalyst to be supported, such as by bonding or encapsulation.
[0005] The metal catalyst can be captured and securely held by the gel during use. As the gel is retained in the skeleton, loss of the metal catalyst during use can be prevented. As the gel is physically retained, it is not necessary to chemically bond the gel to the surface of the skeleton, and it is not necessary to chemically modify the skeleton surface to allow chemical bonding between the gel and the skeleton. The supported catalyst may be repeatedly re-used or recycled with stable catalytic performance.
[0006] Other catalysts may also be similarly supported. For example, an enzyme may be loaded into the gel by physical adsorption. The gel can also hold enzymes via van der Waals interaction or hydrogen bond between the gel molecules and the enzyme protein.
[0007] As the gel is retained in the skeleton, loss of the metal catalyst during use can be prevented. As the hard skeleton has good mechanical property and good ability for resisting deformation, it facilitates separation of enzymes from the reaction system and the reusability of the enzymes. As the gel is physically restrained in the skeleton, the swellable gel can provide a suitable environment for enzyme to remain catalytically active.
[0008] Accordingly, in an aspect of the present invention, there is provided a composite comprising a supported catalyst. The catalyst is selected to catalyze a catalytic reaction. The composite comprises a polymeric skeleton defining pores and a gel retained in the pores. The skeleton is selected to be resistant to reagents of the catalytic reaction. The gel is selected to capture the catalyst. The catalyst is captured by the gel in the composite. Substructures are formed on an internal surface of the pores to physically retain the gel in the pores during the reaction. The substructures are capable of physically retaining the gel without chemically bonding the gel to the internal surface of the pores.
[0009] In accordance with another aspect of the present invention, there is provided a method of forming a composite for supporting a catalyst selected to catalyze a catalytic reaction. The method comprises providing a polymeric skeleton defining pores and comprising substructures formed on an internal surface of the pores, the skeleton selected to be resistant to reagents of the catalytic reaction; introducing a mixture into the pores, the mixture selected for forming a gel capable of capturing the catalyst; and forming the gel from the mixture in the pores so that the gel physically engages the substructures when the gel is formed, thus forming the composite, wherein the substructures are sized and shaped to physically retain the gel in the pores during the reaction, and are capable of physically retaining the gel without chemically bonding the gel to the internal surface of the pores. The method may comprise bonding the catalyst to the gel. The method may comprise encapsulating the catalyst in the gel. The method may comprise contacting the composite with a solution comprising a precursor for the catalyst to allow the gel to absorb the solution and the precursor, and converting the precursor to the catalyst in the gel. The skeleton may be formed by polymerization. The mixture may comprise a hydroxypropyl acrylate (HPA), acrylic acid (AA), or dimethylacrylamide (DMAA) monomer, and the forming the gel may comprise polymerizing the monomer to form a poly(HPA) (PHPA), poly(AA) (PAA), or poly(DMAA) (PDMAA). Polymerization of the monomer may comprise crosslinking the monomer.
[0010] In the composite and method described in the two preceding paragraphs, the substructures may comprise a microstructure sized and shaped to engage the gel by catching, snagging, hooking, gripping, clinching, clenching, or looping around the gel. The substructures may comprise a projection, protuberance, crossing, bridge, hook, loop, spike, wire, rod, beam, snag, clinch, or clench. The polymeric skeleton may comprise polystyrene (PSt), poly(methyl methacrylate) (PMMA), or poly(vinylidene difluoride) (PVDF). The gel may comprise PHPA, PAA, or PDMAA. The catalyst may be bonded to, or encapsulated in, the gel. The catalyst may comprise a metal catalyst or an enzyme. The metal catalyst may comprise Pd, Pt, La, Ti, Hf, Fe, Co, Ni, Cu, Mn, or Cr. The composite may comprise nanoparticles captured by the gel, where the nanoparticles comprise the catalyst. The skeleton may be substantially spherical or be a film. The method may comprise bonding the catalyst to the gel.
[0011] In accordance with a further aspect of the invention, there is provided a method in which reagents of a catalytic reaction are reacted in the presence of the composite described herein. The reaction may be a Heck reaction, Suzuki reaction, hydrogenation reaction, or oxidation reaction.
[0012] Other aspects and features of the present invention will become apparent to those of ordinary skill in the art upon review of the following description of specific embodiments of the invention in conjunction with the accompanying figures.
BRIEF DESCRIPTION OF THE DRAWINGS
[0013] In the figures, which illustrate, by way of example only, embodiments of the present invention,
[0014] FIG. 1 is a scanning electron microscopic (SEM) image of a spherical bead formed of polystyrene, at a magnification factor of 150;
[0015] FIG. 2 is an SEM image of an internal portion of a bead as shown in
FIG. 1, at a magnification factor of 50,000;
[0016] FIG. 3 is an SEM image of an internal portion of a composite bead formed from a gel and a bead as shown in FIGS. 1 and 2, at a magnification factor of 2,000;
[0017] FIG. 4 is a transmission electron microscopic (TEM) image showing the entanglement between the gel and an internal projection in the composite of FIG. 3; [0018] FIG. 5 is a TEM image of a portion of a composite bead as shown in
FIG. 4 by the dashed-line box, but loaded with Pd(O) nanoparticles;
[0019] FIG. 6 is an SEM image of composite beads loaded with Pd, at a magnification factor of 250;
[0020] FIG. 7 is an SEM image of a cross-sectional view of a skeleton film, at a magnification factor of 500;
[0021] FIG. 8 is an SEM image of the internal structures of the skeleton film of FIG. 7, at a magnification factor of 5,000;
[0022] FIG. 9 is an SEM image, at a magnification factor of 650, of a cross- section of a composite formed from the skeleton film of FIG. 7 and a gel;
[0023] FIGS. 10 to 14 are schematic diagrams showing different chemical reactions in which a composite supported metal catalyst can be used and the reaction conditions of such reaction.
DETAILED DESCRIPTION
[0024] In an exemplary embodiment of the present invention, a composite for supporting a catalyst, such as a catalytic metal or an enzyme, is formed of a porous bead and a gel.
[0025] The bead may be substantially spherical, as illustrated in FIG. 1, which shows an image of example spherical beads 10 formed from polystyrene (PSt).
[0026] The bead provides a rigid or hard frame that forms a skeleton. The internal pores (cavities) in the bead are defined by the skeleton.
[0027] The bead may be formed of a suitable polymer. For example, the polymer may include a copolymer and may be made from a monomer or a mixture of monomers. The monomers may include styrene or it derivatives, acrylates, methacrylates, or vinylidene fluoride. The polymer may be made via condensation polymerization, and may include polysufone, polyimide, polyesters, polycarbonates or polyketones.
[0028] The skeleton material should be suitable for use in the chemical process in which the supported catalyst is to be used. The skeleton should be resistant to the reagents of the catalytic reaction in which the selected catalyst is to be used. It is not necessary that the surface of the bead is able to chemically bond to any particular material. In some embodiments, it may be advantageous that the external surface of the bead is inert and does not chemically react with other substances present in the proximity of the catalyst during use. In some embodiments, it may be advantageous to use materials that remain both physically and chemically stable under the conditions of the relevant catalytic reaction process, such as materials that remain rigid and can provide stable support under such conditions.
[0029] In one embodiment, the skeleton may be formed of PSt. In other embodiments, the skeleton may be formed of, for example, poly(methyl methacrylate) (PMMA) or poly(vinylidene difluoride) (PVDF).
[0030] In some embodiments, the pores in the skeleton may have a porosity of from about 5% to about 70%. The swelling ratio of the composite may be less than about 10%. The skeleton should be sufficiently rigid and strong to maintain the overall shape of the composite during use, such as when the composite is subjected to fast shearing and the composite beads are tightly packed.
[0031] In some embodiments, the skeleton materials may be resistant to air, selected organic solvents or reagents to be used with the catalyst, and should remain stable when exposed to air or these chemicals. The skeleton surface may be non-sticky to prevent flocculation or pile up of the composite during preparation, use, or storage. The skeleton surface should also be free of reactive groups that will chemically react with the catalytic material to be loaded.
[0032] The pores defined by the skeleton may have various sizes or shapes. For example, the pores may include micropores or macro-pores. The pores may include percolated holes, which may be micro-sized or macro-sized. Micropores refer to pores that have dimensions less than 50 microns, and macropores refer to pores that have dimensions larger than 50 microns. Typically, the pores may have random shapes, due to irregularity and fluctuation in the formation process.
[0033] In exemplary embodiments, the pores may have pore sizes ranging from about 0.1 to about 100 microns, such as from about 0.5 to about 50 microns.
[0034] Substructures, such as sharp microstructures, are formed on the internal surfaces of the pores. A substructure is substantially smaller in size than the average pore size. A substructure may have a dimension, which is comparable with the size of the particular gel molecules. The gel portion is formed from many gel molecules, which may be bonded with one another via cross-linking. A substructure is shaped so that individual gel molecules, or a number of entangled gel molecules, can be retained by engagement or entanglement with the substructure. For example, a gel molecule or a few entangled gel molecules may entwine, loop or wrap around a substructure, or pass through a hole or gap in the substructure. Microstructures may have characteristic dimensions in the range of from about 0.05 to about 50 microns. A sharp structure is a structure that has an abruptly projected or bended portion, which facilitates the physical engagement or entanglement between the structure and the gel molecules. The substructures are shaped and sized to provide sufficient physical engagement with the gel so that the gel can be physically retained in the pores by physical engagement with the substructures, without chemically bonding the gel to the internal surface of the pores.
[0035] As can be understood, a smooth or gradually varying pore surface does not provide sufficient physical engagement with the gel to securely retain it in position. Structures that have dimensions that are not comparable with the gel molecules, either substantially larger or substantially smaller, are also less effective as the individual gel molecules would be unable to effectively engage or entangle with, such as wrap or loop around, such a larger or smaller structure.
[0036] The substructures formed on the internal pore surfaces are thus movement-restricting structures, which may include projections, protuberances, crossings, bridges, hooks, loops, rings, spikes, wires, rods, beams, snags, clinches, clenches, or the like.
[0037] The substructures may be randomly shaped and arranged. The substructures include sharp portions that can pierce through a gel as will be further described below.
[0038] Thus, the movement of the gel inside the pores is physically restricted by its physical engagement with the substructures. For example, the gaps or space between different substructures or within a single substructure can be used to hold the feed solution during gel formation, thus allowing entanglement of the gel molecules with these substructures. The substructures may engage the gel molecules by catching, snagging, hooking, gripping, clinching, clenching, or looping around individual molecules of the gel.
[0039] A representative image of an internal portion of a bead as shown in
FIG. 1 is shown in FIG. 2. As shown, the skeleton 12 defines pores 14. As shown, irregularly shaped sharp microstructures 16 include protrusions and bridge-like structures that project into pores 14. In this example, the microstructures 16 are of sufficiently small dimensions, which are comparable with the dimensions of the gel molecules. A gel molecule may have a size in the range from about 0.01 to about 100 microns.
[0040] A gel is placed and retained in the pores of the bead. The gel may be formed of a polymer selected to capture and support a given catalyst such as a catalytic metal. At least a part of the gel molecules may be sufficiently entangled with the internal microstructures of the bead such that the physical entanglement between the gel molecules and the structures restricts egress of the gel from the pores of the bead.
[0041] The gel may be formed from a suitable gel material for supporting the particular metal catalyst to be supported. For example, the gel may be formed from polyacrylic acid (PAA), poly(2-hydroxypropyl acrylate) (PHPA), poly(dimethylacrylamide) (PDMAA), or the like. [0042] The gel may include functional groups for bonding with a desired catalytic metal. The functional groups may include one or more moieties that contain O, N, P, or S, or a combination thereof. The moieties may have a cyclic or acyclic structure. A moiety may contain no carbon or up to 40 carbon atoms.
[0043] A representative scanning electron microscopic (SEM) image of an internal portion of an example composite is shown in FIG. 3. The gel, made of poly(acrylic acid) (PAA), and the pores in the bead are visible in FIG. 3, but the skeleton and its internal structures are not visible. The entanglement and the engagement between the gel molecules and the skeleton structures is better illustrated in FIG. 4, which shows an image in which gel molecules 18 engages a skeleton projection structure 20. As can be seen, in this case entangled gel molecules (represented by the lighter regions) surround the projection structure 20 (represented by the darker regions).
[0044] In some embodiments, the gel may contain a flexible polymer chain and polar groups. The crosslinking density in the gel may be from about 0.5% to about 15%, such as about 1% to about 10%. The gel may be formed from a mixture of monomers with polar groups, such as -OH, -COOH, -NH 2 , -NHR, -NR 2 , - CONH 2 , -CONHR, -CONR 2 , -SH, -SR, or the like, and a crosslinking agent, wherein R is an alkyl group with 1 to 20 carbon atoms. R can have a linear, branched, or cyclic structure. The mixture may also contain an initiator or a catalyst for inducing or accelerating crosslinking reactions.
[0045] The gel in the composite may form a continuous mass or may form separate gel portions. A gel portion may form a separate soft network. A separate gel portion may be considered as a separate gel molecule. In some embodiments, the pores of the beads are not completely filled by the gel. For example, about 5% to about 95% of the pore volume may be filled with the gel. As will become clear below, it may be advantageous to leave some room in the composite for the gel to swell. However, to be stably retained and held by the skeleton in the composite, a gel portion should be sufficiently large so that it can entangle with, or otherwise engage, the movement-restricting substructures in the skeleton. As a result, the gel will be physically retained in the pores of the skeleton during the catalytic reaction for which the composite catalyst is to be used.
[0046] The composite may be formed in a process as described herein (see below).
[0047] During use, a catalyst such as a metal catalyst or an enzyme may be loaded into the composite, such as by absorption into the gel. The catalytic metal may be any suitable metal and may be incorporated in any suitable form. For example, the catalytic metal may be provided in a pure compound or a mixture containing the catalytic metal. The catalyst may be provided in the form of particles such as nanoparticles, colloids or complexes, and may be loaded into the composite in the form of a solution or liquid. Nanoparticles have particle sizes from about 1 to about 100 nm. For example, the catalytic metal may include Pd, Pt, La, Ti, Hf, Fe, Co, Ni, Cu, Mn, or Cr. When a list of items is provided with an "or" before the last item herein, any one of the items may be used; and a combination of any two or more of the items may also be used, as long as the combination is possible and the combined items are not inherently incompatible or exclusive. The metal may be in the form of a metal colloid, or a metal complex. The metal complex may be immobilized and the metal colloid may be incarcerated by the composite when the catalytic metal is captured by the gels. The gels may capture the catalytic metal by coordination or encapsulation. For example, the metal may form a coordination complex in the gel.
[0048] A supported enzyme may be catalase, penicillin G acylase (PGA),
Candida antarctica lipase B (CaI-B); oxygenases such as cytochrome P450 enzymes, integral membrane di-iron alkane hydroxylases (e.g. AIkB), soluble di-iron methane monooxygenases (sMMO), membrane-bound copper-containing (and possibly iron-containing) methane monooxygenases (pMMO), d-aminoacylase, penicillin G acylase, or aminopetidase.
[0049] In some embodiments, the catalyst may be loaded into the composite by contacting the composite with a solution that contains a precursor for the catalyst. The solution and the precursor are thus allowed to be absorbed by the gel. The precursor is subsequently converted to the catalyst. For example, a catalyst metal may be converted from a precursor by a reduction reaction. The conversion reaction may be induced in any suitable manner depending on the particular precursor used.
[0050] A representative transmission electron microscopic (TEM) image of a portion of the composite of FIG. 4 (indicated by the dashed-line box in FIG. 4) loaded with Pd(O) nanoparticles is shown in FIG. 5. The black dots shown in FIG. 5 represent the Pd(O) nanoparticles. The Pd(O) nanoparticles are captured (e.g. absorbed) and supported by gel 18. FIG. 6 shows an SEM image of the outer appearance of the representative composite beads loaded with Pd.
[0051] Advantageously, the gel can conveniently provide the flexibility of supporting different metal catalysts. For example, different functional groups may be provided in the gels for capturing and holding different catalysts. Since it is not necessary to attach these functional groups to the surfaces of the skeleton, the skeleton surface, particularly its external surface, may be substantially free of these functional groups.
[0052] Further, the skeleton can provide a hard, protective framework that protects and restricts the movement of the gel, and can in turn protect the metal catalyst captured and supported by the gel. As a result, the composite may have good mechanical and chemical properties and may be able to withstand various conditions and mechanical treatment such as shears, and can thus be used in a wide range of applications.
[0053] As the gel is physically confined within the pores by entanglement or other physical engagement with the internal substructures of the skeleton, it is not necessary to chemically bond the gel to the skeleton or to another substrate. Thus, the composite may be formed in a relatively simple and inexpensive process. Further, when the gel is not chemically bonded to the skeleton, the gel can swell more in three-dimensions, and can provide a reaction environment for improved mass diffusion and heat transfer, thus enhancing the reactor efficiency.
[0054] As now can be appreciated, in different embodiments, the skeleton may be made of different materials and may form a hard/rigid structure in various forms. For example, the skeleton may be provided in the form of resins, beads, particles, fibers, rods, plates, pipes, films, membranes, or the like.
[0055] For example, the cross-section image (SEM) of an exemplary film skeleton is shown in FIG. 7. FIG. 8 shows the pores and cavities formed in the film skeleton and the movement-restricting substructures. FIG. 9 shows an image of a composite formed form the film skeleton and a soft gel. In the composite of FIG. 9, the skeleton is formed of PVDF and the gel is formed of HPA-GDMA.
[0056] In an exemplary embodiment, a composite of a skeleton and a gel may be formed as follows.
[0057] The skeleton, either in the form of beads, films or another form, may be obtained from a commercial source or may be specifically designed and formed. For example, the skeleton may be formed from polymer solids, which can be prepared by phase separation from a polymer solution, followed by curing, polymerization or crosslinking. The skeleton may also be formed from a polymer synthesized by radical chain polymerization, condensation polymerization, ring- open polymerization, in either single- or multi-phase systems.
[0058] The material of the skeleton is selected so that the skeleton can withstand the conditions and treatment of the particular application and remain stable. That is, under the catalytic reaction conditions the skeleton, including its external surfaces, pore structures, and the substructures, maintains its size and structural shape, and can thus provide consistent and stable protection of the gels and the catalyst supported therein.
[0059] The gel may be formed in the pores of the skeleton using any suitable technique. The gel may be advantageously formed by in-situ polymerization, as sufficient physical entanglement between the gel polymer molecules and the movement-restricting structures of the skeleton can conveniently occur during polymerization. For example, the gel may be formed using a gel- forming mixture. The mixture may include various components for forming gels, such as monomers, cross-linking reagents, functional co-monomers, diluents, initiators, catalysts, surfactants, or the like. The particular combination of these ingredients can be selected by those skilled in the art for a particular application. To prevent the coagulation or sticking of the composite, the formation of the gel in the pores of the skeleton may be carried out while keeping the skeletons separated from each other with the help of a medium, which can be a gas, a liquid, or a solid such as powder, or a combination thereof. The monomers in the mixture may include a hydroxypropyl acrylate (HPA), acrylic acid (AA), or dimethylacrylamide (DMAA) monomer.
[0060] A metal catalyst may be directly loaded on to the gel. For example, the metal catalyst may be loaded into the gel using a carrier liquid.
[0061] In one embodiment, the metal catalyst may be dissolved in a solvent and the resulting solution is fed to and absorbed by the gel in the composite. For instance, the composite may be immersed in the solution. A suitable precursor for the metal catalyst may be added to the solvent to obtain the dissolved metal catalyst. The precursor and the catalyst may include a pure compound or a mixture of metal compounds. More than one catalyst may be dissolved in the solution and loaded into the composite.
[0062] In another embodiment, the metal catalyst may be loaded in the form of metal colloids suspended in the carrier liquid. The metal colloids may be prepared by various techniques, such as by reducing a metal complex using a suitable reducing agent. Suitable reducing agents may include hydrogen (gas), borohydride reagents, alcohols, azines, ascorbic acid or the like.
[0063] The composite loaded with the metal catalyst may be used in catalytic reactions to catalyze the reaction. For example, reagents may be reacted in the presence of the catalytic metal supported by the composite. The catalytic reaction may be hydrogenation, hydrogenolysis, carbon-carbon coupling reaction, carbon-nitrogen coupling reaction, selective oxidation reaction, hydrodehalogenation, or the like.
[0064] As can be appreciated, the supporting composite can be conveniently recycled by filtration. To prevent loss of metal catalyst during use, the swelling ability of the gel may be adjusted to be within the range described above. Different catalysts may be conveniently loaded at the same time or at different times. The composite may be used repeatedly. As the gel is protected by the skeleton, the composite can have stable performance after repeated use. Because the catalyst is captured (absorbed) in the gel, it is unlikely to "leach" out during use. In turn, the gel is prevented from separating from the skeleton due to the physical entanglement with the movement-restricting structures in the skeleton.
[0065] The composite can also be easy to use, and may be produced at relatively low costs.
[0066] Because the gels can swell to different degrees, the amount of loaded catalyst may be controlled and can be relatively high. Thus, good catalytic activity may be obtained.
[0067] As gels are formed in the skeletons and are entangled or otherwise engaged with the substructures in the pores of the skeleton to prevent the gels from moving out of the pores, their confinement in the skeleton does not depend on chemical bonding between the gel and the skeleton. Indeed, it is not necessary to modify the skeleton surface to allow such chemical bonding. In one embodiment, the skeleton surface is not treated or modified to allow such bonding. This embodiment is advantageous as it simplifies the preparation process. Further, as the gel is not bonded to a surface it can swell in three-dimensions, thus providing a good environment for catalyst preparation and catalytic reaction. When the skeleton has an un-modified external surface, it can retain its beneficial surface properties, such as properties that help to prevent undesirable deformation of the final catalyst product, and to prevent sticking of a foreign substance to the catalyst product, by sticking to the external surface of the skeleton. Due to its hard external surface, the supported catalyst product is less likely to be damaged due to shearing, which can occur in some catalytic reaction processes such as fixed bed and fluidized bed processes.
[0068] Due to the above mentioned features, a composite according exemplary embodiments of the present invention can provide both chemical and economical efficiency in various catalytic reaction processes, which may be batch, semi-batch or continuous processes. [0069] In one embodiment, the composite may be used in a batch process to support a Pd catalyst. The skeleton and the composite may be shaped into substantially spherical beads with a diameter of about 0.1 to about 0.5 mm.
[0070] Supported catalyst composites according to embodiments of the present invention may be used in a variety of applications. For instance, the composites may be used in various liquid phase organic reactions, which are often found in pharmaceutical or chemical industrial applications. They may also be useful in water treatment processes, which are relevant to water supply and waste treatment industries. For example, the composites may be used in hydrodechlorination of organic contaminants in water.
[0071] The composites may be used in various chemical reactions including
Heck reactions, Suzuki reactions, hydrogenation reactions, oxidation reactions and the like.
[0072] Advantageously, the composites may be relatively easy to use, and have high activity, stability and recyclability. A wide range of different catalytic metals may be supported according to an embodiment of the present invention. The composites may be prepared at low cost. It is relatively easy to control the morphology of the composite and the amount of the catalytic metal loaded in the composite.
[0073] The variation and modification discussed above is for illustration purposes and are not exhaustive. Other variations and modifications to both the composites and their preparation processes are also possible.
[0074] EXAMPLES
[0075] Example I
[0076] Sample supported-Pd composite catalysts were prepared as follows.
[0077] In a representative procedure, skeleton beads were formed from a polymer. The polymers used for forming different samples were polystyrene (PSt), polymethylmethacrylate (PMMA), and polyvinylienefluoride (PVDF), respectively. The skeleton beads had internal pores and substructures that extended into the pores. A representative image of sample PSt beads is shown in FIG. 1. A representative image showing the pores and the substructures in a sample PSt bead is shown in FIG. 2.
[0078] In a representative procedure, hard beads with meso-porous structures were prepared. Porous copolymer microspheres of styrene (ST) and divinylbenzene (DVB) (ST: DVB = 4:1 mol-mol basis) were synthesized by suspension polymerization, using benzoyl peroxide (BPO, 0.5 mol%) as the initiator and 0.5 wt % water solution of polyvinyl alcohol (PVA) as dispersant. The porogen or diluent, a mixture of toluene and decane (1 :1 , 1 :3 or 1 :5 vol/vol) were added in each preparation, with the dilution ratio being about 0.5. The preparation procedure was carried out in a three-necked round bottom flask equipped with a mechanical stirrer, a reflux condenser and a thermocouple. The mixture was stirred at a fixed agitation rate of 500 rpm, to give a suspension of oil droplets dispersed in aqueous phase, under argon gas purging. A three-ramp temperature profile (75°C/2h, 85°C/4h, 90°C/4h) was implemented to conduct the polymerization. After polymerization, the resultant poly(styrene-co-divinylbenzene) [P(ST-DVB)] powders were extracted with hot hexane in Soxhlet extractor for 12 hr. The powders were then washed with warm water for three times, followed by vacuum drying at 60 0 C for 24 hours.
[0079] Different polymer gels were formed in the sample beads, by in-situ polymerization. HPA, DMAA or AA monomers were used to form different gels in the sample composite beads.
[0080] Poly(2-hydroxypropyl acrylate-co-glycerol dimethacrylate) gel
[P(HPA-GDMA), 5% crosslinked] was embedded directly into the matrix of P(St- DVB) beads. The incorporation of the gel phase into the matrix of hard beads was done in two steps: monomer loading and in-situ polymerization.
[0081] 0.5 g P(St-DVB) were dispersed and swollen in a solution of toluene, monomers (2-HPA 2mL, GDMA 0.1846g) and initiator (ABCN 19.8mg). The mass fraction of monomers is 25 %, and the concentration of initiator was kept at 0.5 mol% of monomers. After 24-hour stirring under argon protection, the swollen beads were separated by filtration and immediately re-dispersed in 20-mL saturated sodium chloride solution. The suspension was heated to 8O 0 C for in-situ polymerization of adsorbed 2-HPA and GDMA. After polymerization for 24 hours, the resultant composite powders were washed with copious amount of water to remove NaCI, repeatedly rinsed with acetone and hexane under sonication in order to remove the unreacted monomers. The powders were then vacuum-dried at room temperature for 48 hours.
[0082] Similarly, for the synthesis of PSt-PDMAA composite, 2mL N 1 N- dimethylacrylamide, 0.2332g GDMA and 25mg ABCN were used.
[0083] The gels in the resulting composite beads were physically entangled with the skeleton structure. A representative image of a sample PDMAA-GDMA composite is shown in FIG. 4.
[0084] To load the Pd metal catalyst, 100mg of the sample composite beads were placed in a 10-mL 2-necked round bottom flask sealed by rubber septa. The flask was evacuated for 20 minutes and backfilled with Argon for 3 cycles. Dark orange solution of 5mg palladium acetate [Pd(OAc) 2 , 5mg] in 2ml_ of dry Ar-purged acetone was added. After 24-hour stirring, the supernatant liquid was removed by syringe. The solid was washed with acetone for 5 times, and dried under vacuum for one day. The resultant composite beads containing Pd(II) were light yellow in color.
[0085] The sample supported-Pd(ll) composites were reduced under an atmosphere of H 2 maintained by an inflated balloon. After 20 hours, the beads were dried under vacuum in order to remove the adsorbed acetic acid during the reduction of Pd(OAc) 2 . The reduction was then continued for 20 hours, and dried under vacuum for one day. The resultant supported-Pd(O) composite catalysts were grey in color.
[0086] Pd nano-particles were thus loaded into the sample composite beads. Pd loading in the samples was quantified using Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-OES), which indicated that the Pd loading was in the range of 0.01 to 3 wt%. [0087] The sample supported-Pd(O) composite catalysts were shaped as microspheres. The catalytic metal Pd was incarcerated in the composite.
[0088] FIG. 6 shows a representative SEM image of sample supported-Pd composite beads.
[0089] Example Il
[0090] A polymer skeleton was provided in the form of a film. A cross- section image of the sample film is shown in FIG. 7. FIG. 8 shows the internal structure of the sample.
[0091] The film skeleton was prepared from a DMF solution of PVDF. The preparation process included two steps: (i) the solution of PVDF in DMF (15%wt) was casted on the flat surface of a stainless steel panel to form a thin layer (film) with a thickness about 100 microns; (2) the liquid film was immersed into a water bath with the stainless steel substrate. The film was kept in water for 30 min. The film was then soaked in ethanol for one hour and then dried in air.
[0092] Entangled gels were formed by polymerizing HPA-GDMA in the pores of the film skeleton. The film skeleton was immersed in a mixture of 10 parts of 2-hydroxylpropyl acrylate, 10 parts of ethanol, 1 part of glycoldimethacrylate and 0.05 part of 1 ,1'-Azobis(cyclohexanecarbonitrile) (ABCN). The preparation was subjected to three cycles of freeze-pump-thaw and the liquid component was removed. The film was kept at 50 0 C for 8 hours under nitrogen atmosphere. The film composite was then washed with ethanol three times and dried at 60 °C in air.
[0093] An image of the resulting internal cross-section of the sample composite is shown in FIG. 9.
[0094] Sample PVDF-PAA-Pd composite catalyst was also prepared similarly as described in Example I. The Pd loading in the sample was 0.02 to 0.5 mol%. [0095] Example III
[0096] Sample PSt-HPA-Pd(O) (referred to as Sample A) and PMMA-HPA-
Pd(O) (referred to as Sample B) composite catalysts were prepared as described in Example I. Homogeneous catalytic metal Pd was embedded in the composite catalyst. The Pd loading in the samples was 0.06 to 0.65 mol%.
[0097] The composite catalysts were used to catalyze Heck reactions. A representative Heck reaction carried out is represented by the reaction scheme shown in FIG. 10.
[0098] For example, for Sample A composite, a two-neck round flask was charged with Sample A catalyst (100mg, 0.0065 mmol) and then evacuated-refilled with argon for three cycles. To the flask was added subsequently NMP (1.5ml_), iodobenzene (1 mmol, 204mg) Et 3 N(1.25 mmol, 126.5mg) via argon-purged syringes. The mixture was stirred and heated up to 75°C. /7-Butyl acrylate (1.5mmol, 151.7mg) purified by passing though an alumina oxide column was introduced (t=0) by argon-purged syringe and the reaction mixture was further heated to 90 0 C. At selected time intervals, aliquots were taken from the brown reaction solutions and analyzed by 1 HNMR.
[0099] After the first run, the liquid of reaction mixture was taken out via syringe and the catalyst remained in the flask and was washed with NMP (2 χ 1.5mL) under argon atmosphere. Then the same amounts of NMP, Et 3 N and substrates were introduced into the flask for the next run.
[00100] The reaction time for each run was about 2 hours. The catalyst composite was re-used after each run.
[00101] A similar procedure was performed for Type B composite.
[00102] The yields of butyl cinnamate after each use (run) of the catalyst composite are shown in Table I. The reaction time for each run was about 2 hours. The yields were determined by 1 HNMR. The reaction solution was collected and was diluted with CDCI 3 for obtaining the 1 H-NMR spectrum. In the 1 H-NMR spectrum, total peak area of aromatic protons was set as 1 and the portion from the cinnamate was taken as the yield.
[00103] It was observed that the catalytic activity showed substantial improvement over conventional composite catalysts and the yields were very high even after repeated use. The catalyst composites were reused for more than 10 times without deactivation or Pd leaching.
Table I Yields for Heck Reaction
[00104] The sample catalyst composites were used, in the form of substantially spherical beads, in various Heck reactions involving aryl iodides with acrylates in N-methylpyrrolidone (NMP), as shown in FIG. 11. The sample composite catalyst beads were found to perform well with a wide variety of substrates for Heck reactions. Table Il lists representative test results for the Heck reactions shown in FIG. 11.
Table Il Yields in Heck reaction (2)
[00105] Example IV
[00106] Sample composite supported catalysts were used to catalyze Suzuki reactions. Samples A and B were used in the form of spherical beads. Sample C was formed of a PSt skeleton and a PDMAA gel, in the form of spherical beads. Sample D was formed of a polyvinylidene difluoride (PVDF) skeleton and a PAA gel, in the form of a film. Pd was loaded into each sample composite at various loading concentrations.
[00107] Samples A, B, C and D were used in a Suzuki reaction process, involving Suzuki cross-coupling reaction of phenyl boronic acid with 4- bromobenzaldehyde, as shown in FIG. 12.
[00108] Typically, a two-neck round flask was charged with appropriate phenyl boronic acid (0.5mmol), 4-bromoaldehyde (0.55mmol), Na 2 CO 3 (1.9mmol), Pd catalyst (0.01-0.1 mol%), then evacuated and refilled with argon for three cycles. 1 ml_ of dearated EtOH and 1 ml_ of dearated H 2 O were introduced into the flask by argon-purged syringes. The reaction mixture was stirred vigorously under argon for a selected reaction time (see Table III). [00109] The reaction mixture (slurry) was then diluted with H 2 O (10 ml_) and dichloromethane (1OmL) and filtered. The organic phase was separated and the aqueous layer was extracted twice with DCM (10 ml_). The combined organic layers were washed with water (10 ml_), and the solvent was removed under reduced pressure. The product was dissolved in CDCI 3 for determination of the yield of the product via 1 H-NMR.
[00110] Even at relatively low amounts of catalyst loading, e.g. down to about
0.01 mol% with respective to the substrate, the catalytic activity of the sample catalytic composites was still much higher than the comparison supported catalysts that were also tested under the same reaction conditions.
[00111] Table III lists the comparison test results, where the listed values of yield were determined by 1 H NMR.
TABLE III
[00112] The sample catalysts showed extremely high catalytic activity. While
Suzuki-Miyaura reactions typically require a large amount of homogeneous Pd catalyst, satisfactory catalytic activity was obtained with the sample catalysts even when the amount of the sample catalyst used was as low as 0.01 mol% with respect to the substrate.
[00113] Example V
[00114] Sample A and Sample C composite catalysts were used in a hydrogenation reaction process, for hydrogenation of 2-cyclohexen-1-one, as shown in FIG. 13.
[00115] In a representative procedure, 100 mg (with 0.075mmol/g of Pd loading) of Sample A were prepared and stored in a round bottom flask under hydrogen protection. To start hydrogenation, 1 mL of substrate (0.75mmol 2- cyclohexen-1-one in toluene) was injected into the flask by H 2 -purged needle. After 15 hours, the reaction mixture was sampled for 1 H-NMR and gas chromatography (GC) analyses.
[00116] To recycle the catalyst, the product was removed by Ar-purged needle. Under Ar protection, 4ml_ of toluene was added to wash the catalyst. The solvent was then removed by needle and the catalyst was dried under high vacuum for 5 hours. The recycling reaction was carried out for 5 rounds, using the same procedures outlined above.
[00117] Sample C composite catalyst was similarly tested.
[00118] Six runs were performed with the sample composites re-used after each run. Each run of the test lasted about 15 hours. The conversion percentage remained at about 100% for each run.
[00119] Example Vl
[00120] Ru catalyst was supported in PSt-p(DMAA-EGDMA) sample composite using a procedure similar to the procedure for the preparation of supported Pd composite catalysts described in Example I. The supported-Ru Catalyst was used in an oxidation reaction of alcohol as shown in FIG. 14.
[00121] In a representative procedure for oxidation of benzyl alcohol, benzyl alcohol (O.i mmol) and 4-methylmorpholine (NMO, 0.2mmol) were mixed in acetone (1.5mL) and degassed by Argon. 50mg PSt-P(DMAA-EGDMAM(C 6 Hs) 3 P]RuCI 2 was added in a 5mL round bottomed flask under Argon protection. The liquid reactants were then added and the mixture was stirred for 8 hours at room temperature. 0.02mL liquid was sampled, diluted by O.δmL CDCI 3 and the conversion was determined by 1 H-NMR.
[00122] The Ru supported catalyst showed very good yield in the oxidation of benzyl alcohol to benzyl aldehyde with 4-methylmorpholine (NMO). The conversion was about 81.7% within 8 hours.
[00123] Example VII Procedure for immobilization of enzyme
[00124] Catalase from bovine liver (BLC) were dissolved in sodium phosphate buffer (pH=7.4) which was then centrifuged to remove the residue. The supernatant was collected and mixed with composite beads (PMMA as skeleton and PHPA as gel) and kept at 4°C overnight and then incubated in a rotary shaker at 150 rpm at 37 0 C. After 2h the solution was removed and the resulting immobilized enzyme was washed with buffer solutions several times till no protein was detected in the washing solution. The Bradford assay was conducted to determine the enzyme loading on the polymer composite.
[00125] Example VIII Determination of enzyme activity
[00126] Catalase activity in the decomposition of 0.0034% (w/w) hydrogen peroxide in sodium phosphate buffer (pH=7.4) was determined spectrophotometrically at 240 nm. The reaction and spectrophotometrical measurements were carried out at room temperature. The result showed that the absorbance of hydrogen peroxide at 240 nm decreased with time in the presence of supported catalase, indicating that the decomposition of hydrogen peroxide occurred. The activity was 2.16*10 ~7 mol/min per mg of protein.
[00127] Other features, benefits and advantages of the embodiments described herein not expressly mentioned above can be understood from this description and the drawings by those skilled in the art. [00128] Of course, the above-described embodiments are intended to be illustrative only and in no way limiting. The described embodiments are susceptible to many modifications of form, arrangement of parts, details and order of operation. The invention, rather, is intended to encompass all such modification within its scope, as defined by the claims.
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