EP2175988A1 - Procédés pour produire des matériaux à couche superficielle profonde, constitués de fines particules, revêtus de nanoparticules inorganiques et utilisation desdits matériaux - Google Patents

Procédés pour produire des matériaux à couche superficielle profonde, constitués de fines particules, revêtus de nanoparticules inorganiques et utilisation desdits matériaux

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Publication number
EP2175988A1
EP2175988A1 EP08786726A EP08786726A EP2175988A1 EP 2175988 A1 EP2175988 A1 EP 2175988A1 EP 08786726 A EP08786726 A EP 08786726A EP 08786726 A EP08786726 A EP 08786726A EP 2175988 A1 EP2175988 A1 EP 2175988A1
Authority
EP
European Patent Office
Prior art keywords
nanoparticles
finely divided
biopolymers
surface area
high surface
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP08786726A
Other languages
German (de)
English (en)
Inventor
Jürgen HOFINGER
Daniela Keck
Steffen Roos
Kevin Zirpel
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Namos GmbH
Original Assignee
Namos GmbH
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Namos GmbH filed Critical Namos GmbH
Publication of EP2175988A1 publication Critical patent/EP2175988A1/fr
Withdrawn legal-status Critical Current

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Classifications

    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/42—Platinum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
    • B01J23/44—Palladium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/48—Silver or gold
    • B01J23/50—Silver
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J33/00—Protection of catalysts, e.g. by coating
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/20—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state
    • B01J35/23—Catalysts, in general, characterised by their form or physical properties characterised by their non-solid state in a colloidal state
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • B01J37/0211—Impregnation using a colloidal suspension
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0215—Coating
    • B01J37/0221—Coating of particles
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B82—NANOTECHNOLOGY
    • B82Y—SPECIFIC USES OR APPLICATIONS OF NANOSTRUCTURES; MEASUREMENT OR ANALYSIS OF NANOSTRUCTURES; MANUFACTURE OR TREATMENT OF NANOSTRUCTURES
    • B82Y30/00—Nanotechnology for materials or surface science, e.g. nanocomposites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J21/00—Catalysts comprising the elements, oxides, or hydroxides of magnesium, boron, aluminium, carbon, silicon, titanium, zirconium, or hafnium
    • B01J21/02—Boron or aluminium; Oxides or hydroxides thereof
    • B01J21/04—Alumina

Definitions

  • the invention relates to a process for the preparation of finely divided, highly surface-area materials coated with inorganic nanoparticles, and to the materials produced thereby, in particular catalysts for heterogeneous catalysis.
  • particles are synthesized homogeneously in solutions with a very low concentration of the components to be precipitated. Due to the large distances of the particles formed, these are relatively stable in the solution. This is achieved by a precipitation reaction without nucleating agent. Under suitable reaction conditions, the particle size is limited downwards by the increased solution pressure of small particles, which dissolve in favor of larger particles, and upwards by falling below the critical concentration in the solution necessary for further growth.
  • partial particle suspensions with a very narrow size distribution can be produced.
  • the methods are generally very simple and inexpensive.
  • the preparation is generally carried out in low concentrations in order to prevent coagulation of the particles.
  • a particular embodiment of this method is described in DE 10 2005 048 201 A1.
  • the spatio-temporal course of the Particle formation influenced. Thereby, the growth of larger particles can be prevented by a corresponding control of the concentration of the reactants.
  • Already formed metal particles serve as germinal centers for further deposits and cause their further growth. The higher the concentration of possible germinal centers, the smaller and more numerous the resulting particles. This leads to an improvement in the size distribution of the nanoparticles.
  • growth inhibitors such as, for example, water-soluble polymers (polyvinyl alcohol, polyvinylpyrrolidone, Gelatin) or surfactants
  • the particle growth is stopped at an early stage.
  • growth inhibitors such as, for example, water-soluble polymers (polyvinyl alcohol, polyvinylpyrrolidone, Gelatin) or surfactants
  • capping agents also prevent the agglomeration of the particles as a protective colloid.
  • the task of the capping agent is even reduced to that of the protective colloid.
  • the solution is completely consumed in favor of the resulting particles.
  • this is technically difficult especially at higher concentrations of the particles in solution.
  • heterogeneous nucleation is silver staining in protein analysis on an electrophoresis gel (eg Blum et al., Electrophoresis 8, 93-99, 1987). Proteins are separated in a gel and silver ions are bound to various side groups of the proteins. After addition of a reducing agent, nanoclusters are formed which mark the protein bands as a brown discoloration.
  • WO2004033488A2 describes the synthesis of nanoparticles via a specific binding of specific biotemplates (phage peptides) with a genetically modified metal-binding region (MBR).
  • biotemplates phage peptides
  • MLR genetically modified metal-binding region
  • special biotemplates must be selected by biopanning and then allow a highly specific synthesis of the nanoparticles.
  • the preparation of the template is very complicated, since they must first be bound in a number of steps to conventionally produced nanoparticles and must be prepared by genetic amplification in sufficient quantity biotechnologically.
  • the selected peptides do not like growth inhibitors occupy the entire surface of the particles and have a length of 7 or 12 amino acid residues. For this reason, agglomeration of the nanoparticles can not be prevented thereby.
  • DE19624332A1 discloses a metallic nanostructure based on self-assembling proteins.
  • the biomolecules used represent templates which are either coated with individual metallic particles or coated with closed metallic layers. The shape of the particles, but also largely their size, are thus determined by the template.
  • tubular microtubules and sheet-like S-layers are cited.
  • a special variant of nanoparticle synthesis based on biological templates is the use of DNA molecules.
  • appropriately prepared nucleic acids are adsorbed in solution or even on surfaces and subjected to a chemical metal coating.
  • the nucleic acids thus represent the template for the nucleation and the growth of metallic particles and layers.
  • the template form and essentially size-determining and allow the production of filamentous nanoparticles with a very high aspect ratio.
  • either a plurality of particles are deposited on one of these templates (eg EP 1 283 526 A1 or Pompe et al., Z. Metallkd.
  • EP 1 666 177 A1 describes a noble metal colloid which is prepared by reduction of a metal oxide solution on a biomolecule in basic solution. The formation of metallic particles takes place directly on the biomolecule, which simultaneously prevents agglomeration of the particles. Since the biocomponent is used as a reducing agent in a basic environment, however, only metallic particles are generated. Further use of the biocomponent in connection with the formation of nanostructures or deposition on surfaces is not disclosed.
  • WO2006053225 the production of silver nanoparticles in suspensions by functionalization of RSA (bovine serum albumin) molecules is disclosed.
  • the method involves the chemical reduction of an ionic metal precursor at room temperature in an aqueous solution. At appropriate pH levels, disulfide bonds are formed between the protein and the precious metals.
  • the protein is thus a nucleating agent and simultaneously stabilizes the metallic nanoparticles against agglomeration. It is particularly advantageous in this method that the nanoparticles thus formed are not completely coated by the stabilizing components and are therefore relatively freely accessible for reactions. Again, however, a formation of nanostructures on surfaces is not described.
  • Metallic and metal salts nanostructures on the surface of support materials are still needed for a variety of applications, such.
  • coating honeycomb bodies for catalytic converters (washcoats), anode and cathode catalysts in fuel cells, particulate filters such as particulate filters, and catalyst-coated membranes in PEM (proton exchange membrane) electrolyzers are still needed for a variety of applications, such.
  • particulate filters such as particulate filters
  • PEM proto exchange membrane
  • Supported catalysts usually consist of metallic or ceramic honeycomb bodies, which are coated by dip-coating processes with finely divided, high-surface-area support materials, such as, for example, ceramic powders (washcoat). These support materials are loaded either before or after the coating with the catalytically active metals, which should be distributed as homogeneously as possible and in the form of nanoparticles on the surface of the powder particles.
  • support materials such as, for example, ceramic powders (washcoat).
  • nanoparticle suspensions prepared according to the prior art are only stable with low particle concentrations (0.016 g / l-0.2 g / l), since the attractive interaction of the particles dominates and leads to agglomeration and, as a consequence, precipitation in the solution leads.
  • hitherto known chemical synthesis methods for the production of nanoparticles in solution compared to a simple deposition of the particles on surfaces of support materials, especially industrially relatively expensive and complex.
  • a method which is as simple and cost-effective as possible for producing metallic and / or metal salts To provide nanostructures on surfaces of finely divided high surface area materials, in which first a suspension of inorganic nanoparticles is produced in high concentration without forming agglomerates, and as a result of which the nanoparticles are distributed as evenly as possible on surfaces of the finely divided high surface area materials.
  • the object is achieved by a process for the production of finely divided, high surface area materials coated with inorganic nanoparticles.
  • finely divided high surface area material is contacted with a suspension of inorganic nanoparticles in a liquid medium in which the nanoparticles are bound to biopolymers.
  • the thus coated finely divided high surface area material is subsequently dried.
  • the suspensions used in the process according to the invention comprise biopolymers-bound inorganic nanoparticles, which are also referred to below as biopolymer nanoparticle conjugates or conjugates.
  • biopolymer-nanoparticle conjugates are produced by incubating the biopolymers in a metal salt solution and initially producing nanoparticles of metal salt on the biopolymers.
  • a metal salt solution is selected from an aqueous AgNO 3 , (CH 3 COO) 2 Pd, Pt (NO 3 ) 2 , H 2 (Pt (OH) 6 - K 2 PtCl 4 solution or mixtures thereof
  • a reduction step must be carried out while retaining the binding of the inorganic nanoparticle to the biopolymer.
  • a solution of an inorganic salt having a concentration of at least 1 mmol / l is incubated with 0.25% to 100% equivalents of a solution of a biopolymer with intensive mixing.
  • these nano-particles bound to biopolymers form metal nanoparticles from metal salts, which, however, remain bound to the biopolymers.
  • free metal ions present in the solution can be attached to them emerging germ are bound and thus lead to further growth of the metallic nanoparticles.
  • metallic nanoparticles and / or nanoparticles consisting of metal salts are preferably used in the process according to the invention.
  • the metal salts according to the invention also include the metal oxides.
  • the nanoparticles preferably consist of an element or of an element compound of groups 3 to 12 of the Periodic Table of the Elements or of mixtures or alloys of elements or element compounds of groups 3 to 12 of the Periodic Table of the Elements.
  • elements or element compounds of the platinum group such as Os, Ir, Pt, Ru, Rh and Pd or mixtures or alloys thereof.
  • the elements of the so-called precious metals such as Ru, Rh, Pd, Ag, Re, Os, Ir, Pt, Au, Hg, Tc, Ni, Cu, As, Sn, Sb, Bi and their salts such as Ru 3 (O) 2 (NH 3 ) I 4 ] CI 6 .4H 2 O, (NH 4 ) 3 [RhCl 6 ], [Pd (NO 3 ) J, AgNO 3 , NH 4 ReO 4 , OsO 2 (NH 3 ) 4 Cl 2 , IrCl 3 , H 2 Pt (OH) 6 , AuCl 3 , Hg (NO 3 ) 2 , Tc 2 O 7 , NiCl 2 , CuSO 4 , As 2 O 3 , Sn (SO 4 ) 2 , Sb 2 O 3 , Bi 2 S 3 .
  • the elements of the so-called platinum metals and their salts are of great importance, for example:
  • the individual nanoparticles have a size less than 500 nm.
  • the nanoparticles preferably have a particle size of 1 nm to 100 nm.
  • biopolymers used according to the invention advantageously initiate the nucleation of the nanoparticles without an accumulation of competing nuclei occurring. At the same time, the biopolymers stabilize the suspension according to the invention and prevent the agglomeration of the particles.
  • the suspension according to the invention With the suspension according to the invention, a very high concentration of the nanoparticles is advantageously made possible.
  • the nanoparticles are present in the suspension in a concentration of at least 0.25 g / l.
  • the suspension according to the invention is virtually free of agglomerates.
  • Agglomerates are understood as meaning particles having a diameter of more than 100 nm. After the synthesis according to the invention, at most 3% by weight of the nanoparticles are present in such agglomerates.
  • the suspension is stable for several months. Settling of particles is not observed.
  • a reducing agent is preferably used.
  • NaBH 4 solution is preferred, but other reducing agents such as DMAB (dimethylaminoborane) or hydrazinium hydrochloride (N 2 H 5 CI) can be used.
  • DMAB dimethylaminoborane
  • N 2 H 5 CI hydrazinium hydrochloride
  • the nanoparticles are bound in the thus prepared suspension according to the invention by non-specific bonds to the biopolymers.
  • the biopolymers induce the formation of nanoparticles and act as stabilizers of the suspension. The latter happens by inhibiting the agglomeration or preventing the formation of large crystals, ie, the biopolymers initiate the nucleation of the nanoparticles on the one hand and, on the other hand, simultaneously prevent the binding of the nanoparticles to one another. Since the binding of the nanoparticles to the biopolymer takes place independently of the type of nanoparticles, the process according to the invention can advantageously be used universally for the production of highly concentrated suspensions of very different inorganic nanoparticles.
  • the formation of nanoparticles spatially and temporally separated from the application is carried out on the finely divided high surface area materials
  • the individual processes can be better optimized.
  • the optimal conditions for the formation of nanoparticles eg by precipitation on the substrate
  • the nanoparticles are already preformed on the biopolymer, advantageously optimize the binding of the conjugates to the finely divided high surface area materials.
  • binding of defined particles is possible since the size of the nanoparticles is defined by the biopolymers when they are generated from a salt solution and no further growth can take place during deposition and subsequent reduction of the nanoparticles.
  • the suspension of biopolymer nanoparticle conjugates can advantageously be further concentrated.
  • the suspension is concentrated by ultrafiltration.
  • a concentrated suspension of biopolymer-nanoparticle conjugates for the process of the invention, it may be subjected to lyophilization or a drying process (eg spray-drying) to obtain a dry powder.
  • a drying process eg spray-drying
  • the conjugate powder is reconverted by dissolving in a suitable solvent.
  • the suspensions of biopolymer nanoparticle conjugates are contacted with the finely divided high surface area materials by the method according to the invention so that the biopolymer nanoparticle conjugates bind to the finely divided high surface area material.
  • This can be done by spraying on a dry or moistened and still flowable powder. A soaking of a powder in the suspension is possible.
  • a preferred form of contacting consists in intensive mixing of the powder and slow addition of high concentrations of the suspension, so that the distribution of the noble metals on the powder is as uniform as possible.
  • biopolymer-nanoparticle conjugates to the finely divided high-surface-area materials results in a coating with biopolymer-nanoparticle conjugates, which is not a closed layer, but a nanoscale structure on the surface of the finely divided high surface area material uniform distribution of the individual nanoparticles or conjugates is achieved.
  • the finely divided high surface area carrier materials consist of metallic, ceramic or polymeric materials or materials of carbon (eg activated carbon). Particularly preferred are support materials of aluminum oxides, aluminum silicates, zeolite, silica, titanium oxide, zirconium oxide or cerium oxide or mixtures or mixed oxides.
  • the support materials used are preferably finely divided, ie they have an open meso or microporosity with a pore size of 1 to 50 nm and / or have a surface roughness in which either the wavelength or the depth of the surface structure is in the range of 1 to 100 nm ,
  • the surface of the finely divided high surface area material can also be characterized by the BET values for nitrogen.
  • a suitable alumina powder has a specific surface area of greater than 150, preferably greater than 250 m 2 / g.
  • the thus high surface area support materials can be present as particles, as bulk material or as a coating.
  • the surfaces of the finely divided high surface area materials are conditioned by a pretreatment in order to increase the binding of the subsequently deposited conjugates to the surfaces.
  • the combination of the nanoparticles with the biopolymers allows the electrostatic or covalent coupling of the conjugates to the surfaces of the finely divided high surface area materials.
  • standard methods for crosslinking of proteins can be used. This can be done by suitable pretreatment of either the finely divided surfaces or the conjugates.
  • electrostatic coupling is the silanization or silicatization or the use of polyelectrolytes.
  • Covalent couplings can be achieved, for example, by the use of crosslinkers, e.g. EDC / NHS (1-ethyl-3- (3-dimethylaminopropyl)) carbodiimide, N-hydroxysuccinimide), HDI (hexamethyl diisocyanate) or glutaraldehyde.
  • crosslinkers e.g. EDC / NHS (1-ethyl-3- (3-dimethylaminopropyl)) carbodiimide, N-hydroxysuccinimide), HDI (hexamethyl diisocyanate) or glutaraldehyde.
  • a particular embodiment is the combination of electrostatic and covalent coupling in which e.g. an electrostatic silanization allows coupling via covalently binding groups.
  • an electrostatic silanization allows coupling via covalently binding groups.
  • a polysiloxane network is deposited on the surface, which is suitable for the covalent coupling of the nanoparticle conjugates to the carrier.
  • the material is incubated with 10% APTES (3-aminopropyltriethoxysilane in acetone).
  • a further preferred embodiment relates to the coating of the nanoparticles present in the suspension with porous materials, for example with a thin silicon layer, which can likewise increase the bond to the substrate surface.
  • the coating after deposition at higher temperatures, such as may arise when used in catalytic converters, a sintering barrier. At higher temperatures, there is often an increase in the deposited particles (sintering), which is inhibited by the coating.
  • the nanoparticles conjugated to the biopolymers are reduced in metallic nanoparticles, for example by adding a reducing agent such as NaBH 4 . Suspensions of metallic nanoparticles bound to biopolymers are then used for the process according to the invention.
  • the reduction takes place only after the metal salt nanoparticle biopolymer conjugates have been deposited directly on the surfaces of the finely divided high surface area materials.
  • the finely divided high-surface-area material is dried after the coating, and subsequently the metal salt-bound nanoparticles bound thereto are reduced by dry reduction with hydrogen gas to give metallic nanoparticles.
  • the reduction can also be carried out during the conditioning of the catalyst.
  • the metallic nanoparticles thus produced are prepared by a dry reduction with hydrogen at temperatures greater than 100 ° C.
  • the nanoparticles are produced on biopolymers.
  • Biopolymers are high molecular weight polymers produced by living organisms and composed of monomers such as monosaccharides, nucleotides or amino acids. Such biopolymers are, for example, proteins or nucleic acids.
  • a globular protein or a globular folded peptide is used as the biopolymer.
  • the protein is selected from the family of albumins, such as human serum albumin (HSA), Prealbumin lactalbumin, conalbumin, ovalbumin, or parvalbumin, or from the family of globulins, such as. B. transferrin.
  • the protein is a bovine serum albumin (RSA).
  • RSA bovine serum albumin
  • Proteins in the context of this invention are also to be understood as meaning proteins and peptides which are naturally or artificially modified by non-protein components and / or whose backbone has been modified or artificial proteins, peptides or polymers analogous thereto, such as, for example, ⁇ -peptides.
  • non-recrystallizable S-layer proteins are used. These are S-layer proteins that have been altered so that they no longer self-assemble, but still retain their metal-binding properties.
  • the increased affinity for metal advantageously increases the efficiency of the production of nanoparticles and it is possible to use less concentrated metal salt solutions for the production of the nanoparticles.
  • proteins When using proteins as biopolymers, these have more than 20, preferably more than 100, particularly preferably 375 to 1250 amino acid residues.
  • the mass of the biopolymers used according to the invention is 15 to 200 kD, preferably 15 to 150 kD and particularly preferably 45 to 150 kD.
  • the biopolymers used according to the invention are present in the suspension in a concentration of 0.017 g / l to 80 g / l, more preferably in a concentration of 0.017 g / l to 40 g / l.
  • the isoelectric point of the biopolymer is 3 to 6, more preferably 4 to 5.
  • the biopolymers used according to the invention have on their surface functional groups which can be used for binding of inorganic molecules.
  • the metal salts are bound to the biopolymers, resulting in the production of an inorganic nanoparticle bound to the biopolymer.
  • the binding of the inorganic molecules to the biopolymer is preferably unspecific.
  • the number and density of the bound inorganic molecules is such that a particle is displayed with one biopolymer each.
  • larger particles can be formed from several biopolymers beyond.
  • the object of the biopolymers according to the invention is therefore, on the one hand, by localized binding centers to a concentration inorganic molecules that represent on the subsequently coated surfaces as individual particles, without the need for a separate precipitation step for precipitation of the particles from the metal salt solution, for example by changing the pH value would be necessary.
  • the metallic nanoparticles uniformly distributed on the surface of the metallic, ceramic or polymeric materials are prepared from metal salts which have been produced in a suspension of biopolymers and deposited on the carrier materials and which are subsequently incompatible with the biopolymers Environmental conditions were reduced to metallic nanoparticles.
  • the biopolymers necessary for generating the uniform distribution of the nanoparticles on the surface are denatured.
  • the particles produced according to the invention consist of more than one metal or more than one metal salt, wherein the various metals may be present in the particle as an alloy or as a mixed crystal, or as a mixture of different particles of different material.
  • the suspension used for the process according to the invention can be used particularly advantageously for the preparation of such polymetallic nanoparticles.
  • nanoparticles which consist of a mixture of the metal salts from the solution are formed on the biopolymers.
  • the production of nanoparticles from metal salts with defined ratios of the individual components is not possible with standard methods since the metal salts involved can generally only be precipitated at different pH values and thus not at the same time.
  • by binding a large number of metal salt molecules to a biopolymer it is also possible, without precipitation, to form particles from a mixture of metal salts which are retained even after coating and after reduction to surfaces.
  • a low specificity of the binding mechanism on the biopolymer favors the setting of arbitrary ratios of different metal salts. Since each individual biopolymer leads to the formation of a particle or polymers of biopolymers lead to correspondingly larger particles, the ratio of the metal salts set in the solution, as opposed to precipitation reactions of molecules among one another, also remains after particle formation.
  • nanoparticles of a plurality of metal salts are initially produced on the biopolymers present in the suspension.
  • these nanoparticles produce metallic nanoparticles that consist of several metals.
  • Such nanoparticles may have preferred properties, e.g. Bimetallic nanoparticles of Pd and Pt are more stable to sintering and, for example, lead to a longer service life of the catalyst when used in catalytic converters.
  • the invention therefore also encompasses the use of suspensions of inorganic nanoparticles in a liquid medium, in which the nanoparticles are bound to biopolymers, for the production of finely divided high surface area materials coated with inorganic nanoparticles.
  • the invention also encompasses the use of a suspension of inorganic nanoparticles in a liquid medium, in which the nanoparticles are bound to biopolymers, for coating pretreated surfaces of materials.
  • the pretreatment increases the binding of the subsequently deposited conjugates to the surfaces.
  • Also part of the invention is the use of a suspension of metal salt nanoparticles or metallic nanoparticles, each particle containing a defined ratio of a plurality of metallic or metal salt components and the nanoparticles bound to biopolymers.
  • a multiphase suspension produced in this way in which the individual nanoparticles in the solution from a defined ratio of different Inorganic components with the same mixing ratio are used to produce a regular distribution of inorganic nanoparticles on surfaces of finely divided high surface area materials.
  • Nanoparticle suspensions may be concentrated by ultrafiltration to increase the concentration. Due to the higher initial concentration of the inventively prepared compared to the prior art
  • Nanoparticle suspension the ultrafiltration can be performed significantly faster and due to the lower filter surface at a lower cost.
  • the use of the suspensions of conjugates of nanoparticles and biopolymers advantageously prevents penetration of the nanoparticles into the porous interior of the catalyst support, since their overall diameter, depending on the biopolymer used, exceeds that of the pores.
  • the conjugates thus cause an almost complete deposition of the catalytically active nanoparticles on the surface of the catalyst support, where they have maximum effect when using the catalyst.
  • the process according to the invention advantageously leads to an extremely uniform dispersion of the metallic or metal salt nanoparticles bound to biopolymers on metallic, ceramic or polymeric materials. If metallic or metal salt nanoparticles are deposited from a suspension on the surface of the materials, during the Drying process along the drying fronts considerable forces, which usually lead to local concentrations of the deposited nanoparticles (drying pattern) and significantly reduce the uniformity of the distribution of the particles on the surface.
  • the nanoparticles prepared according to the invention are present as conjugates with a biopolymer. If the solution of conjugates of nanoparticles and biopolymer is incubated with the carrier material, adsorption of the conjugates to the carrier occurs. Without biopolymers, the agglomeration of the particles on the surface is unavoidable by conventional methods known in the art. Due to the conjugation with a biopolymer, the distribution after the drying process surprisingly remains even for nanoparticles with an average diameter of less than 50 nm.
  • the invention therefore also encompasses the nanoparticle-coated finely divided high surface area materials obtainable by the process according to the invention.
  • the carrier material coated with the nanoparticles is used to produce a solid catalyst for heterogeneous catalysis.
  • the catalytically active constituents are often applied to a support with a high surface area in order to increase the catalytically active surface and to save valuable catalytically active substances.
  • metal or metal oxide nanoparticles or nanoparticles consisting of one or more metal salts are used in the catalysts according to the invention, preferably nanoparticles of one element or element compound of the platinum metal group or of mixtures or alloys of several elements or element compounds of the platinum metal group, more preferably platinum and / or palladium or their salts.
  • the process according to the invention can therefore be used for the preparation of such catalysts.
  • the suspensions used initially formed on biopolymers conjugated metal salt nanoparticles formed In the suspensions used initially formed on biopolymers conjugated metal salt nanoparticles formed.
  • a reduction step must take place, which is carried out either before or after the deposition on the fine-particle high-surface-area support material used as the catalyst support.
  • the reduction step is carried out after the coating.
  • the catalyst according to the invention is particularly preferably prepared in which the support material is first coated from a suspension of biopolymer conjugates with metal salt nanoparticles. After the coating is then dried first and then carried out a dry reduction with hydrogen gas, in which the existing of metal salt nanoparticles are reduced to metallic nanoparticles and denatured simultaneously the biopolymers. The removal of the biopolymers can alternatively be carried out when starting the catalyst (conditioning).
  • Shaped catalysts are primarily used in fixed bed reactors and consist of ceramic particles which are coated with the catalytically active component.
  • Powder catalysts are used in stirred tank and fluidized bed reactors. In them, a powdery carrier is coated with the catalytically active material.
  • a so-called honeycomb body is coated with a coating suspension (washcoat), which consists of a powdery carrier layer which itself is coated with the catalytically active material.
  • washcoat consists of a powdery carrier layer which itself is coated with the catalytically active material.
  • this is soaked after application of a washcoat without catalytically active metals in a metal salt solution.
  • the process according to the invention is suitable for the preparation of all these catalysts, but it is particularly advantageously suitable for the preparation of coating suspensions for monolith catalysts.
  • This will be appropriate Support materials coated with the conjugates of nanoparticles and biopolymers by contacting with the suspension of the invention and then coated the honeycomb body with the catalytically coated support materials.
  • the biopolymers may be removed after the coating, for example by heat treatment or by enzymes.
  • the biopolymers can also be denatured as described above due to reduction.
  • the loading of the catalyst support with the nanoparticles according to the invention is usually realized according to the prior art by mixing the carrier powder with a noble metal solution and precipitation of the metal salts on the support (pore filling method).
  • pore filling method pore filling method
  • the conjugates used in the process according to the invention cause an almost complete deposition of the catalytically active nanoparticles on the accessible surface of the catalyst support, since their total diameter depending on the used biopolymer exceeds that of the pores and thus advantageously prevents penetration of the nanoparticles into the porous interior of the catalyst support.
  • the nanoparticle suspensions prepared according to the invention do not have complete surface functionalization, that is, the surface of the nanoparticles remains accessible, since the nanoparticles are only bound nonspecifically to the biopolymer at certain points.
  • the spatial constellation of the proteins still prevents agglomeration of the particles.
  • the proteins used according to the invention do not interfere with the catalytic activity, but if nevertheless necessary, for example, be removed thermally or with the aid of enzymes after deposition of the particles.
  • the catalysts prepared according to the invention have a high activity with small amounts of metals used.
  • the tailor-made production of nanoparticles of defined size and surface properties, but in particular combinations of different nanoparticles, allow increased catalytic activity on surfaces and a high resistance to aging, especially at high temperatures, since sintering-induced coarsening of the particles can be reduced.
  • Such catalysts can be used both in the gas and in the liquid phase.
  • the use is possible even at high temperatures, since the stabilizing biopolymer is required only in the preparation of the catalyst and can be removed after deposition on the support.
  • a synthesis of the nanoparticles in advance in solution offers further advantages, since good carrier properties for the catalysis are not necessarily associated with good template properties for the particle separation.
  • the dispersion of the nanoparticles on the support material can be controlled only poorly and leads to a high heterogeneity of the distribution. Drying of the carrier layer results in dewetting of the bound nanoparticles and formation of drying patterns by the nanoparticles bound to the carrier materials.
  • the invention therefore also includes inorganic nanoparticles from a solution, preferably an aqueous solution, coated finely divided high surface area Material in which the nanoparticles on the surface of the finely divided high surface area material do not form any island-like structures and no drying patterns.
  • the invention also encompasses nanoparticle-coated materials in which the nanoparticles do not form any island-like structures or drying patterns on the surface of the coated material. These materials are available by depositing biopolymer-bound nanoparticles from solution.
  • Fig. 1 is a SEM micrograph of a nanoparticle suspension, which were formed with protein oligomers.
  • FIG. 3 TEM image of a cross-section of an Al 2 O 3 carrier particle (70 nm thickness).
  • FIG. Prevention of the penetration of precious metals into the particle volume.
  • Bovine serum albumin Bovine serum albumin
  • An aqueous solution is prepared with 3 mmol / l Pt (NOs) 2 .
  • Embodiment 2 30 ⁇ l of the 20 g / l aqueous RSA solution (stock solution) are incubated with 3 ml of the platinum solution for 30 min. It is important to ensure an intensive mixing of the components. The complete and homogeneous mixing of the component is carried out by vortexing.
  • Embodiment 2 30 ⁇ l of the 20 g / l aqueous RSA solution (stock solution) are incubated with 3 ml of the platinum solution for 30 min. It is important to ensure an intensive mixing of the components. The complete and homogeneous mixing of the component is carried out by vortexing.
  • Embodiment 2 30 ⁇ l of the 20 g / l aqueous RSA solution (stock solution) are incubated with 3 ml of the platinum solution for 30 min. It is important to ensure an intensive mixing of the components. The complete and homogeneous mixing of the component is carried out by vortexing.
  • Embodiment 2 30 ⁇ l of the 20 g /
  • Solution is here 3 mmol / l, the dilution of the solution by means of distilled
  • Example 1 In contrast to the RSA stock solution used in Example 1 is the
  • Embodiment 5 is a diagrammatic representation of Embodiment 5:
  • the immediate addition of the reducing agent ie, 1, 5 ml of a freshly prepared aqueous 0.1 mol / l NaBH 4 solution.
  • the reducing agent is left in the solution for 2 hours. Subsequently, interfering substances are removed from the product by means of dialysis.
  • This purification step is carried out using dialysis chambers or dialysis tubing with exclusion limits of 10 kDa and a dialysis time of 4 h.
  • the suspension is then sterile filtered directly into the storage vessels.
  • a microfilter with a pore size of 0.2 microns is used.
  • the suspension prepared in this way was stable for more than 2 months without sedimentation phenomena.
  • Exemplary Embodiment 6 Preparation of a Stable Platinum Sol as Described in Exemplary Embodiment 5, but Using H 2 Pt (OH) 6 Dissolved in Ethanolamine (14.44%).
  • a stable H 2 Pt (OH) 6 solution according to Embodiment 2 is prepared. After the end of the incubation time, using 1.5 ml of the reducing agent NaBH 4 (0.1 mol / l) and a reaction time of 2 h, platinum particles are generated which are available for further processing after dialysis and sterile filtration
  • the concentration of the particles results from the amounts used to 0.39 g / l.
  • the measurement of the particle size by means of dynamic light scattering gives a value of 18 nm.
  • the suspension thus prepared was stable for more than 2 months without sedation.
  • Embodiment 7 Preparation of Stable Silver Sol Using Bovine Serum Albumin (RSA) as Stabilizing Reagent and Ag (NOs) 2 .
  • RSA Bovine Serum Albumin
  • Reducing agent NaBH 4 (0.1 mol / l) and a reaction time of 2 h reduced.
  • the size of the Ag nanoparticles is in the range of less than 100 nm.
  • the concentration of the Ag particles results from the amounts used to 0.14 mg / ml.
  • a nanoparticle suspension according to embodiments 1 to 2 is applied to suitable alumina powder, which serves as a substrate.
  • Exemplary Embodiment 9 Production of a Finely Divided, High Surface Fiber-like Support Material Coated with Metallic Nanoparticles by the Use of a Nanoparticle Suspension of Metal Salts and Subsequent Reduction.
  • Exemplary Embodiment 10 Production of a Finely Divided, High Surface Powdery Support Material Coated with Metallic Nanoparticles by the Use of a Metallic Nanoparticle Suspension.
  • the preparation of the Al 2 O 3 powder is carried out according to Embodiment 8.
  • a nanoparticle suspension according to Embodiment 5 to 6 is applied to a suitable alumina powder, which serves as a substrate.
  • a suitable alumina powder which serves as a substrate.
  • platinum particles to the substrate gamma Al 2 ⁇ 3 powder, average particle size 1 1 microns, average BET surface area 169 m 2 / g
  • 640 ml of a finished solution according to Embodiment 5 to 6 is added to 25 g of substrate and Agitate for 24 h at room temperature with agitation.
  • Exemplary Embodiment 11 Production of a Nanoparticle-Coated, Fine-particle, High-Surface Support Material, wherein the nanoparticles consist of a mixture of two metal salts.
  • the preparation of the nanoparticle suspension from two metal salts takes place according to exemplary embodiment 4.
  • the deposition of the nanoparticles onto an aluminum oxide surface takes place according to example 8.
  • the nanoscale structures have a high sintering stability under thermal stress.
  • Exemplary Embodiment 12 Production of a Finely-Divided, High-Surface Support Material Coated with Bimetallic Nanoparticles.
  • the evenly distributed bimetallic particles have a constant ratio of platinum and palladium in the ratio 1: 1.
  • Embodiment 13 Coating of the Nanoparticles with a Silicon Layer
  • a silicon shell forms, which increases the sintering stability of the noble metal particles produced after coating on a substrate and improves the binding of the particles to various substrates.
  • the solution is allowed to stand for 24 h.
  • the stopping of the silicate separation is subsequently carried out by dialysis for 24 hours (dialysis membrane 14 kDa) against 1000 times the amount of distilled water.
  • Embodiment 14 Preparation of a stable platinum sol using unrecrystallized S-layers as a stabilizing reagent and Pt (NO 3 ) 2 .
  • a freshly harvested culture of Bacillus sphaericus NCTC9602 is concentrated to a dry biomass content of 30 g / l. 10 ml of this biomass concentrate are incubated with 20 ml of an aqueous 3-molar MgCl 2 solution for 10 min at room temperature with gentle agitation. Thereafter, the solution is centrifuged at 20,000 g for 20 min and 4 0 C. The centrifugation supernatant is dialysed for 24 h against 10 liters of distilled water at 4 0 C, wherein the exclusion limit of the dialysis membrane should be 14 kDa. The dialysate is again centrifuged at 20,000 g for 20 min and 4 0 C and the pellet discarded.
  • 1 ml of the supernatant is mixed with 15 ml of an aqueous 3 mmol / l Pt (NOs) 2 solution and incubated for 30 min. It is important to ensure an intensive mixing of the components.
  • the complete and homogeneous mixing of the component is carried out by vortexing. This mixture is mixed with 8 ml of a freshly prepared aqueous NaBH4 solution (0.1 mol / l) and briefly mixed by means of vortexer. This is followed by an incubation period of 2 h, in which the reduction to metallic particles takes place.

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Abstract

L'invention concerne des procédés pour produire des matériaux à couche superficielle profonde, constitués de fines particules, revêtus de nanoparticules inorganiques, et les matériaux ainsi produits, notamment des catalyseurs servant à réaliser une catalyse hétérogène. Le procédé selon l'invention est caractérisé en ce que le matériau à couche superficielle profonde, constitué de fines particules est mis en contact avec une suspension constituée de nanoparticules inorganiques dans un milieu liquide et en ce que, éventuellement, le matériau à couche superficielle profonde, constitué de fines particules, revêtu par voie catalytique, est soumis à un séchage.
EP08786726A 2007-07-31 2008-07-31 Procédés pour produire des matériaux à couche superficielle profonde, constitués de fines particules, revêtus de nanoparticules inorganiques et utilisation desdits matériaux Withdrawn EP2175988A1 (fr)

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WO2011073120A1 (fr) * 2009-12-17 2011-06-23 Basf Se Matériau de support d'oxyde de métal contenant des particules métalliques du groupe fer-platine à l'échelle nanométrique
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