EP1126914A1 - Preparation de catalyseurs metalliques nanocristallins et dispersibles sur support - Google Patents

Preparation de catalyseurs metalliques nanocristallins et dispersibles sur support

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Publication number
EP1126914A1
EP1126914A1 EP99954150A EP99954150A EP1126914A1 EP 1126914 A1 EP1126914 A1 EP 1126914A1 EP 99954150 A EP99954150 A EP 99954150A EP 99954150 A EP99954150 A EP 99954150A EP 1126914 A1 EP1126914 A1 EP 1126914A1
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European Patent Office
Prior art keywords
metal
metal oxide
product
catalyst
heated
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EP99954150A
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German (de)
English (en)
Inventor
Ashok Kumar Warwick Process Techn. BHATTACHARYA
Adrian Warwick Process Techn. HARTRIDGE
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University of Warwick
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University of Warwick
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    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01F—COMPOUNDS OF THE METALS BERYLLIUM, MAGNESIUM, ALUMINIUM, CALCIUM, STRONTIUM, BARIUM, RADIUM, THORIUM, OR OF THE RARE-EARTH METALS
    • C01F17/00—Compounds of rare earth metals
    • C01F17/20—Compounds containing only rare earth metals as the metal element
    • C01F17/206—Compounds containing only rare earth metals as the metal element oxide or hydroxide being the only anion
    • C01F17/224—Oxides or hydroxides of lanthanides
    • C01F17/235—Cerium oxides or hydroxides
    • 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
    • B01D—SEPARATION
    • B01D53/00—Separation of gases or vapours; Recovering vapours of volatile solvents from gases; Chemical or biological purification of waste gases, e.g. engine exhaust gases, smoke, fumes, flue gases, aerosols
    • B01D53/34—Chemical or biological purification of waste gases
    • B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
    • B01D53/86—Catalytic processes
    • B01D53/88—Handling or mounting catalysts
    • B01D53/885—Devices in general for catalytic purification of waste gases
    • 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
    • B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/56—Platinum group metals
    • B01J23/63—Platinum group metals with rare earths or actinides
    • 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
    • B01J23/70—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper
    • B01J23/76—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
    • B01J23/83—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of the iron group metals or copper combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36 with rare earths or actinides
    • B01J35/23—
    • 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
    • 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
    • B01J37/08—Heat treatment
    • B01J37/082—Decomposition and pyrolysis
    • B01J37/088—Decomposition of a metal salt
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01B—NON-METALLIC ELEMENTS; COMPOUNDS THEREOF; METALLOIDS OR COMPOUNDS THEREOF NOT COVERED BY SUBCLASS C01C
    • C01B13/00—Oxygen; Ozone; Oxides or hydroxides in general
    • C01B13/14—Methods for preparing oxides or hydroxides in general
    • C01B13/18—Methods for preparing oxides or hydroxides in general by thermal decomposition of compounds, e.g. of salts or hydroxides
    • C01B13/185—Preparing mixtures of oxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01G—COMPOUNDS CONTAINING METALS NOT COVERED BY SUBCLASSES C01D OR C01F
    • C01G25/00—Compounds of zirconium
    • C01G25/02—Oxides
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/50—Solid solutions
    • C01P2002/52—Solid solutions containing elements as dopants
    • C01P2002/54—Solid solutions containing elements as dopants one element only
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/60—Compounds characterised by their crystallite size
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2002/00—Crystal-structural characteristics
    • C01P2002/70—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data
    • C01P2002/72—Crystal-structural characteristics defined by measured X-ray, neutron or electron diffraction data by d-values or two theta-values, e.g. as X-ray diagram
    • C—CHEMISTRY; METALLURGY
    • C01—INORGANIC CHEMISTRY
    • C01P—INDEXING SCHEME RELATING TO STRUCTURAL AND PHYSICAL ASPECTS OF SOLID INORGANIC COMPOUNDS
    • C01P2004/00—Particle morphology
    • C01P2004/60—Particles characterised by their size
    • C01P2004/64—Nanometer sized, i.e. from 1-100 nanometer

Definitions

  • the present invention relates to the field of the preparation of supported metal and metal oxide products, particularly catalysts.
  • the lower or higher valent dopant for example Ln 3+ , Y 3+ or Zr 4+ (wherein Ln represents a lanthanide metal), creates oxygen ion vacancies in the fluorite lattice, thus allowing facile oxygen ion transport within the lattice to the surface.
  • an "active" metal (or metal oxide) on the surface of an oxygen ion conductor catalyses redox reactions with atmospheric gases.
  • An example of this is in exhaust emission control (catalytic converters), where oxygen may react with CO gas, or unbumed hydrocarbons, to form C0 2 and water (oxidation), and where NO may react with CO to produce N 2 and C0 2 (reduction/oxidation) .
  • the ability of the oxide ion conductor (the "promoting" oxide ion conductor) supporting the active metal/metal oxide in such a system to release oxygen under reducing conditions (acceleration), and to take up oxygen under oxidizing conditions (deceleration), has a direct effect upon the size of the window of oxygen partial pressures over which the active metal (e.g. Pt, Rh or Pd) is effective.
  • the active metal e.g. Pt, Rh or Pd
  • catalytic efficiency relies on the high dispersion of active metal on the promoter alone.
  • this technique may be modified by including at least one reducible salt of an active metal in the initial reaction mixture in order to produce an aqueous dispersion of individual crystalline nanoparticles cont ⁇ ining both the active metal/metal oxide and the promoter as a single phase.
  • at least one reducible salt of an active metal in the initial reaction mixture in order to produce an aqueous dispersion of individual crystalline nanoparticles cont ⁇ ining both the active metal/metal oxide and the promoter as a single phase.
  • simple reduction of these nanocrystals results in the active metal/metal particles being substantially dispersed on the surface of the promoter oxide. This results in a process that may be employed in the preparation of inter alia improved catalyst products.
  • a process for the production of a product comprising nanocrystalline particles, which particles comprise at least one metal, or at least one metal oxide, substantially dispersed on the surface of at least one metal oxide, or mixed metal oxide, which process includes the steps of:
  • process steps (a), (b) and (c) are preferably carried out in the above order.
  • the process of the invention may be used to prepare particles that are substantially nanocrystalline in nature (i.e. up to 100% of the individual, unagglomerated crystallites have a particle size of less than 500 nm (e.g. less than 250 nm, preferably less than 50 nm)), as used herein, the term "nanocrystalline" particles, includes that no more than 1 % of particles produced via the process of the invention are non-crystalline, and/or that no more than 1 % of particles produced via the process of the invention exceed a particle size of 500 nm, and in which the average crystallite sizes (Z av ) are in the range 3 to 250 nm (e.g. 4 to 100 nm and preferably 10 to 30 nm).
  • substantially dispersed we include that at least 40%, preferably at least 60%, and more preferably at least 80%, of the relevant metal or metal oxide (as appropriate) is presented, e.g. as particles, on the surface of the metal oxide support, as opposed to within the matrix thereof.
  • wet hydrous metal oxides, and mixed metal oxides includes systems comprising a hydrous metal oxide and water, wherein the combined lattice water and/or free water content, is present in excess of 10% w/w, and preferably between 10 and 200% w/w, of the metal oxide system, whether coordinated to the metal ions of the metal oxide system or otherwise.
  • the term "wet gel” as used herein includes a gel system containing a metal oxide, lattice water and, optionally, depending upon the oxide system that is employed, excess free water, wherein any excess free water that is present, is present in an excess of between 0 and 95 % , preferably 0 and 70% , and especially 0 and 60% , w/w of the total weight of the gel.
  • step (b) of the process of the invention results in the production of deaggregated material.
  • the heating step (b) may preferably be carried out until the reducible metal salt is decomposed and/or the product is deaggregated.
  • the product of step (b) may preferably be dispersed onto a suitable substrate (e.g. a high surface area support) before or after carrying out the reduction step (c).
  • a suitable substrate e.g. a high surface area support
  • This dispersion may be achieved by dispersing the product of step (b) into a suitable medium (e.g. an aqueous solvent, such as distilled water), casting the resultant mixture onto the relevant substrate and drying as necessary.
  • a suitable medium e.g. an aqueous solvent, such as distilled water
  • non-dispersible product which may be formed following step (b) may be removed using conventional techniques.
  • non-dispersible product we include product, which is of a particle size which is too great to allow it to enter the colloidal state.
  • non-dispersible product may be removed by dispersing the product of step (b) as described above to form a sol. In such an instance, dispersion may take place with stirring over an appropriate period (e.g. approximately 1 hour) followed by standing over 2 hours. Any non-dispersible sediment may then be removed by an appropriate means (e.g. decanting the supernatant).
  • the resultant sol which may or may not be dialysed using techniques known to those skilled in the art in order to remove any excess anions, may comprise a single phase nanocrystalline solid solution (i.e. it does not comprise particles of a size of greater than 500 nm, preferably greater than 250 nm, once the non-dispersible product is removed).
  • the nanocrystals may then be dispersed onto an appropriate substrate (e.g. ⁇ -Al 2 0 3 ) before carrying out the reduction step (c).
  • an appropriate substrate e.g. ⁇ -Al 2 0 3
  • the reduction step (c) may be performed directly after step (b), and any non-dispersible product may then be removed by dispersing the product of step (c) into a solvent to form a sol in the above-described manner.
  • the resultant nanocrystals comprising reduced metal, or metal oxide may then be dispersed onto an appropriate substrate (e.g. ⁇ - A1 2 0 3 ).
  • reduction step (c) results in reduced metal migrating to, and being presented on, the surface of the metal oxide particles.
  • Such metals may or may not re-oxidise (or partially re-oxidise), if subjected to an oxygen-containing atmosphere (such as air), once they have migrated to the surface such that a metal oxide (and/or mixed metal/metal oxide) is presented on the surface of the metal oxide particles (though this surface re-oxidation may be prevented if the product of step (c) is kept in a reducing environment).
  • the process of the invention finds particular utility in the production of products (e.g. catalysts) in which an active metal, or active metal oxide, is supported on (i.e. dispersed, or presented, on the surface of) a metal oxide (e.g. a promoter or stabilising oxide, or a solid solution of metal oxides).
  • the process of the invention may be used to form products comprising a wide variety of metals or metal oxides, which are supported on metal oxide systems, mixed metal oxide systems, and/or metal oxide hydrate systems.
  • any "active" metal (e.g. transition metal) or “active” metal (e.g. transition metal) oxide that is capable of catalysing a chemical reaction to a experimentally determinable degree may be employed in the process of the invention.
  • Suitable active metals include palladium, platinum, rhodium, copper, iron, chromium, silver, cobalt, ruthenium and nickel and suitable active metal oxides include those of copper.
  • Suitable supporting metal oxide systems include any single or multicomponent oxide system, especially those that are capable of promoting the reaction of a given active metal, and/or metal oxide, for a specific catalytic reaction.
  • Suitable supporting metal oxides thus include lanthanide oxide systems (including, but not limited to, those of lanthanum, cerium, gadolinium, neodymium and praeseodymium), transition metal oxides (including, but not limited to, those of yttrium, zirconium, iron, palladium, nickel, titanium and chromium) and even oxides of main group metals (including, but not limited to, magnesium and aluminium).
  • the process according to the invention may be used to prepare mixed oxides and solid solutions of two or more of the abovementioned metals.
  • Particularly preferred metal oxide systems include those which are promoters (e.g. promotors of redox rections), for example those of cerium, zirconium, yttrium and mixtures of such oxide systems.
  • the process of the invention may be used to prepare, at low temperatures, supported metal/metal oxide systems in which the supporting metal oxide system possesses a high degree of accuracy in the desired compositional stoichiometry and a minimal point defect concentration.
  • the wet gel comprising the hydrous metal oxide may be formed (step (a)) by heating a mixture of wet hydrous oxide system and reducible metal salt, in the desired proportions. It is preferred that the heating is performed under atmospheric pressure (i.e. in an open atmosphere, rather than in a sealed vessel).
  • the mixture may be heated such that it is dried up to a specific, or critical, oxide:free water ratio, which ratio depends upon the hydrous metal oxide(s) that is/are employed.
  • critical ( ⁇ iinimum) amount of water that must be present in the wet gel depends upon the oxide system that is used, it can be determined non- inventively by the skilled person as the minimum amount of free water that must be present in the resultant gel that will enable deaggregation during the course of carrying out the next step in the process of the invention (step (b)).
  • the mixture may be heated until it is sufficiently dried such that it forms a gel which, depending upon the metal oxide system that is employed in the first instance, may include drying until the gel so formed is of a soft and/or crumbly consistency or drying to a constant weight (i.e. no free water).
  • a constant weight i.e. no free water.
  • systems comprising cerium oxide and aluminium oxide may be dried to a constant weight (though this is not critical).
  • Systems comprising other oxides e.g. those of zirconium and titanium
  • may be dried to form a gel with a soft and/or crumbly consistency which may comprise e.g. 60 to 70% water (lattice and combined) based on the total weight of the gel).
  • the temperature at, and length of time over, which the mixture should be heated will depend upon factors such as the composition of the mixture and the degree of hydration (i.e. "wetness") of the hydrous metal oxide.
  • suitable temperatures are in the range room temperature to 120°C, preferably 40 to 110°C and more preferably 55 to 110°C (e.g. 105°C)
  • suitable time periods are in the range 1 to 24, preferably 1 to 6, more preferably 1.5 to 5 and especially 1.75 to 4.5 hours.
  • reducible metal salts that may be employed in the process of the invention include any salt of a metal in which the oxidation state of that metal may be lowered using conventional reducing techniques.
  • suitable salts include metal nitrates, metal chlorides, metal perchlorates, metal acetates, metal carbonates and higher metal oxides.
  • the reducible metal salt is a metal nitrate or a metal chloride.
  • wet hydrous metal oxides and reducible metal salts are commercially available, are well known in the literature or are readily available using techniques which are well known to those skilled in the art, such as those described hereinafter.
  • Appropriate vessels which may be used to heat the mixtare to form the wet gel (step (a)) will be well known to those skilled in the art and include standard evaporating dishes made from an appropriate material (e.g. pyrex).
  • the product of step (a) may be heated (step (b)) in a suitable atmosphere e.g. a furnace or a controlled pressure/water atmosphere by, for example, sealing in an appropriate reaction vessel (e.g. a pressure reactor vessel (e.g. an autoclave) or a hydrothermal reactor).
  • a suitable atmosphere e.g. a furnace or a controlled pressure/water atmosphere by, for example, sealing in an appropriate reaction vessel (e.g. a pressure reactor vessel (e.g. an autoclave) or a hydrothermal reactor).
  • a reaction vessel e.g. a pressure reactor vessel (e.g. an autoclave) or a hydrothermal reactor).
  • the reaction vessel may be composed of appropriate materials, which may depend upon the constituents of the we
  • the wet gel may, for example, be heated to the decomposition temperature of the salt. This is typically in the region of 220 to 330°C, for example 305 to 320°C, for metal nitrates and metal chlorides. Suitable heating rates are in the region 10 to 500 °C per hour, for example 200 °C per hour.
  • the wet gel may be heated for between 1 and 60 minutes, preferably 10 to 30 minutes at the appropriate temperature, depending on the hydrous metal oxide system that is used and the total mass.
  • the decomposition of the reducible salt as appropriate may be monitored via an appropriate means (e.g., in the case of an autoclave, by observing the presence of an endotherm by means of a temperature gauge, and/or an increase in pressure on a pressure gauge).
  • the heating step (b) may also be carried out in a furnace (e.g. a muffle furnace), or in an open atmosphere. Suitable heating rates are in the region 10 to 500°C per hour, for example 200°C per hour, and a heating time of between 1 and 180 minutes, preferably 30 to 120 minutes, depending on the hydrous metal oxide system that is used and the total mass.
  • a furnace e.g. a muffle furnace
  • Suitable heating rates are in the region 10 to 500°C per hour, for example 200°C per hour, and a heating time of between 1 and 180 minutes, preferably 30 to 120 minutes, depending on the hydrous metal oxide system that is used and the total mass.
  • step (b) the reducible metal salt is decomposed and is substantially in the form of a reducible metal oxide that is present within the supporting metal oxide matrix. Further, the product of step (b) is preferably deaggregated, and in the form of nanocrystals.
  • the reduction step (c) may be performed using standard reduction techniques, which are known to those skilled in the art, for example reduction in a suitable reducing atmosphere (e.g. H 2 in N 2 ; such as 5% H 2 /N 2 ) at an appropriate pressure (e.g. atmospheric pressure) and temperature (e.g. 800°C to 1000°C).
  • a suitable reducing atmosphere e.g. H 2 in N 2 ; such as 5% H 2 /N 2
  • an appropriate pressure e.g. atmospheric pressure
  • temperature e.g. 800°C to 1000°C
  • Products obtainable by the process of the invention may be dispersed into an appropriate solvent to form a sol, which may then be used to coat or impregnate a variety of substrates in order to yield a coating which is nanocrystalline in nature.
  • products may be dispersed onto a catalyst support to form a catalyst.
  • Other layered materials comprising coated substrates may be readily produced in a similar fashion. It will be appreciated by the skilled person that the process of the invention offers the flexibility that the reduction step (c) may be performed before or after dispersion on a substrate.
  • Products obtainable by the process of the invention have the advantage that, following the reduction step (c), metals/metal oxides may be dispersed substantially to entirely on the surface of a metal oxide system (e.g. a promoter or stabilising oxide).
  • a metal oxide system e.g. a promoter or stabilising oxide.
  • the process of the invention has advantages over standard active metal/metal oxide deposition techniques described hereinbefore, which prior art techniques result in a lower proportion of active metal/metal oxide being dispersed on the promoting oxide system (see Figure 1).
  • the process of the invention may result in catalyst products in which less than 1 % (e.g. none) of the metal/metal oxide is presented on the catalyst support, and thus catalyst products possessing a higher surface area of active metal/metal oxide. This may greatly increase the catalyst efficiency and lifetime of the resultant catalyst.
  • the process of the invention also has the advantage that a wide variety of cheap, readily available inorganic precursors may be used.
  • Figure 1 illustrates the structural differences between a catalyst produced using the process of the invention, and according to the prior art.
  • Figure 2 shows an x-ray diffraction pattern for (a) Ce 075 Zr 0 2 Pto 05 O 2- ⁇ sol dried at 100°C, and (b) the same gel following reduction at 850 °C for 3 hours in 5% H 2 /N 2 .
  • Figure 3 shows an x-ray diffraction pattern for (a) sol dried at 100°C, and (b) the same gel following reduction at 850°C for 3 hours in 5% H 2 /N 2 .
  • Figure 4 shows an x-ray diffraction pattern for (a) s °l dried at 100°C, and (b) the same gel following reduction at 850°C for 3 hours in 5% H 2 /N 2 . Characterisation
  • Ce(N0 3 ) 3 .6H 2 0 50 g was added to 250 mL of distilled water and dissolved at room temperature. Separately, cone, ammonia solution (880 s.g.; 30 g) and hydrogen peroxide solution (27.5% wt.; 17.5 g) were dissolved in 150 mL of distilled water and were added rapidly to the cerium solution with stirring. Stirring was continued for 5 minutes to give a deep red/orange precipitate. The mixtare was diluted to 750 mL with distilled water and centrifuged at 2000 rpm for 5 minutes, removing the supernatant.
  • the resultant solid was washed with 4 x 750 mL of distilled water, with centrifuging in between to remove all anions and excess precipitating reagents. Finally, the precipitate was slurried to a 250 mL total volume, and 2M HN0 3 was added drop wise with stirring until a pH value of 6 was attained. Heating of the resultant mixture to 50 °C with stirring resulted in a banana yellow precipitate. Centrifuging at 3000 rpm for 5 rninutes, and removal of the supernatant, yielded a crystalline ceria hydrate with a primary crystallite size of 20 A.
  • a zirconium oxynitrate solution was prepared made by adding ZrO(C0 3 ) 2 .xH 2 0 powder (7.67 g) to 15 mL of distilled water and mixing to a thin slurry. Cone. HN0 3 acid (5 g) was then added and the resultant mixed until the fizzing stopped. The mixture was then heated briefly to give a clear solution. Separately, H 2 PtCl 6 .xH 2 0 (3.2 g) was added to 10 mL of distilled water containing 2 drops of cone. HN0 3 acid and dissolved. The platinum salt solution was then added drop wise with stirring to the zirconia solution to give a deep red/orange solution.
  • the sol was orange, transparent and stable, and consisted of single phase crystalline fluorite structured nano- particles (see Figure 2(a)) with an average particle size of about 10 nm and a primary crystallite size of about 5 nm.
  • This sol was used to impregnate a suitable high surface area and porous support ( ⁇ -Al 2 0 3 ), dried and fired to 600 °C for 30 minutes.
  • the catalyst was then activated by reduction at 850 °C for 2 hours in 5% H 2 /N 2 , producing platinum metal finely dispersed on the surface of Ce 08 Zr 0.2 0 2-x ⁇ nanocrystals, which in turn were dispersed on ⁇ -Al 2 0 3 .
  • Figure 2(b) which shows the X-Ray diffraction pattern of the reduced undispersed nanocrystals.
  • La(N0 3 ) 3 .5H 2 0 (8.47 g) was added to 15 mL of water and dissolved. To this, Cu(N0 3 ) 2 .3H 2 0 (1.645 g) was added and dissolved. The solution was added to 25 g of ceria hydrate (75.4% Ce0 2 ; see Example l(i) above) mixed thoroughly and dried to constant weight at 60°C. The dried mixtare was lightly crushed and placed in a pyrex beaker to a bed depth of 1.5 cm. The mixture was then heated to 310°C for 40 minutes at a heating rate of 200°C/hr. The resulting gravel was ground to a dark green powder and added, with stirring, to 800 mL of distilled water.
  • ceria hydrate 75.4% Ce0 2 ; see Example l(i) above
  • the stirring was continued for 30 minutes. Any non-dispersible solids ( ⁇ 5%) were removed by centrifuging at 4000 rpm for 10 minutes to leave an olive green transparent sol.
  • the sol consisted of single phase fluorite nanocrystals with 10 to 15 nm particle size and a primary crystallite size of 5 nm (see Figure 3(a)). This sol was then used to impregnate a suitable high surface area and porous support ( ⁇ -Al 2 0 3 ), dried and fired to 600 °C for 30 minutes.
  • the catalyst was then activated by reduction at 850 °C for 2 hours in 5% H 2 /N 2 , to produce a fine dispersion of copper metal on the surface of Ce 0.75 Lao .
  • zirconium basic carbonate Small quantities of zirconium basic carbonate (total quantity 60 g) were added to 6M HN0 3 (43 mL). A further portion of zirconium basic carbonate (40 g) was then slurried with water before adding to the acid mixture. The mixture was heated with stirring and after 10 to 15 minutes a clear sol developed. After diluting with distilled water (500 mL) and stirring for 20 minutes, the mixture was allowed to cool to room temperature. 880 ammonia (23 mL) was then added to water (880 mL) with stirring. The zirconium sol was added slowly to this mixtare over 10 minutes with stirring. The resultant was allowed to settle and the supernatant decanted off. The sol was washed 4 times with 2 L of distilled water.
  • the resultant gel was decanted to 900 mL, and 100 mL of HN0 3 was added. The mixture was centrifuged and the supernatant discarded to leave acid conditioned ZrO(OH) 2 .xH 2 0 hydrate gel.
  • the resulting slurry was dried to a soft crumbly gel at 40 °C (about 70% water by weight) and placed in a sealed reactor vessel.
  • the vessel was heated to 295 to 300°C for 15 minutes and pressure was released after this time from 1020 psi to 600 psi (72 to 43 bar) quickly to remove excess nitric acid.
  • the rector vessel was then cooled to room temperature quickly and the product added to 900 mL of distilled water and stirred for 1 hour to give a brown/beige translucent sol. Any non-dispersible product was again centrifuged off at 4000 m for 10 rninutes.
  • the resultant sol was transparent and beige in colour, and consisted of single phase cubic stabilised zirconia nanocrystals containing rhodium within the lattice (see Figure 4(a)).
  • the average particle size of the sol was about 20 nm with a primary crystallite size of about 8 to 9 nm.
  • This sol was used to impregnate a suitable support ( ⁇ -Al 2 0 3 ), and dried and fired to 600°C for 30 minutes.
  • the powder was then reduced at 900 °C for 3 hours in 5% H 2 /N 2 to produce highly dispersed rhodium metal entirely on the surface of yttria stabilized zirconia nanocrystals in turn dispersed on gamma alumina.
  • the x-ray diffraction pattern of the undispersed material is shown in Figure 4(b).

Abstract

L'invention concerne un procédé de fabrication d'un produit comprenant des particules nanocristallines qui sont constituées d'au moins un métal ou d'au moins un oxyde métallique, sensiblement dispersé sur la surface d'au moins un oxyde métallique ou oxyde métallique mélangé. Le procédé consiste à : (a) chauffer un mélange comprenant au moins un oxyde métallique hydraté humide ou un oxyde métallique mélangé hydraté humique avec au moins un sel métallique réductible, pour former un gel humide ; (b) chauffer le gel humide à la température de décomposition du sel métallique réductible ; et (c) réduire la composition résultante.
EP99954150A 1998-11-05 1999-11-04 Preparation de catalyseurs metalliques nanocristallins et dispersibles sur support Withdrawn EP1126914A1 (fr)

Applications Claiming Priority (3)

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GB9824152 1998-11-05
GBGB9824152.4A GB9824152D0 (en) 1998-11-05 1998-11-05 New product
PCT/GB1999/003657 WO2000027527A1 (fr) 1998-11-05 1999-11-04 Preparation de catalyseurs metalliques nanocristallins et dispersibles sur support

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EP1180397B1 (fr) 2000-08-19 2007-03-28 Umicore AG & Co. KG Matériau à base de cérium oxide pour le stockage de l'oxygène, procédé de préparation dudit matériau et utilisation pour le traitment des gaz d'échappement des moteurs à combustion interne
GB0120962D0 (en) * 2001-08-30 2001-10-17 Univ Dundee "Sensor"
FR2832328B1 (fr) * 2001-11-20 2004-10-29 Centre Nat Rech Scient Catalyseur heterogene compose d'un agregat de nanoparticules metallisees
JP2005097642A (ja) * 2003-09-22 2005-04-14 Tanaka Kikinzoku Kogyo Kk 貴金属−金属酸化物複合クラスター
GB0413767D0 (en) 2004-06-21 2004-07-21 Johnson Matthey Plc Metal oxide sols
GB0413771D0 (en) 2004-06-21 2004-07-21 Johnson Matthey Plc Metal oxide sols
JP4562776B2 (ja) 2005-11-01 2010-10-13 日産自動車株式会社 排気ガス浄化用触媒
JP4265626B2 (ja) 2006-07-12 2009-05-20 トヨタ自動車株式会社 触媒担体粒子及びその製造方法、並びに排ガス浄化触媒
EP1920830A1 (fr) * 2006-11-08 2008-05-14 L'AIR LIQUIDE, Société Anonyme pour l'Etude et l'Exploitation des Procédés Georges Claude Catalysateur contenant des metaux du groupe VIII, de l'oxyde de cerium et de l'oxide de zirconium pour le traitement des hydrocarbures par oxydation ou reformage catalytique
DE102011108620B4 (de) * 2011-07-22 2015-08-27 Technische Universität Dresden Verfahren zur Herstellung eines Bauelements für Hochtemperaturanwendungen, mit dem Verfahren hergestelltes Bauteil sowie seine Verwendung
FR2991713A1 (fr) * 2012-06-11 2013-12-13 Air Liquide Dispositif d'epuration des gaz d'echappement d'un moteur thermique comprenant un support ceramique fractionne a l'echelle nanometrique
WO2015143225A1 (fr) * 2014-03-21 2015-09-24 SDCmaterials, Inc. Compositions pour systèmes d'adsorption de nox passive (pna) et leurs procédés de fabrication et d'utilisation
CN117466251B (zh) * 2023-11-22 2024-04-05 山东科源生化有限公司 一种利用稀土氧化钇制备高氯酸钇的方法

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GB1522191A (en) * 1976-01-07 1978-08-23 Atomic Energy Authority Uk Supported catalysts
EP0078098B1 (fr) * 1981-08-07 1986-05-14 United Kingdom Atomic Energy Authority Traitements de composés de cérium
GB9709449D0 (en) * 1997-05-10 1997-07-02 Univ Warwick Low temperature production of metal oxides

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