WO2003094195A1 - Method for the production of catalysts - Google Patents

Method for the production of catalysts Download PDF

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Publication number
WO2003094195A1
WO2003094195A1 PCT/EP2003/004553 EP0304553W WO03094195A1 WO 2003094195 A1 WO2003094195 A1 WO 2003094195A1 EP 0304553 W EP0304553 W EP 0304553W WO 03094195 A1 WO03094195 A1 WO 03094195A1
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WO
WIPO (PCT)
Prior art keywords
catalysts
support structure
catalytically active
substrate
porous support
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PCT/EP2003/004553
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German (de)
French (fr)
Inventor
Mario Birkholz
Thomas Jung
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Fraunhofer-Gesellschaft zur Förderung der angewandten Forschung e.V.
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Publication of WO2003094195A1 publication Critical patent/WO2003094195A1/en

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Classifications

    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/228—Gas flow assisted PVD deposition
    • 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
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/56—Foraminous structures having flow-through passages or channels, e.g. grids or three-dimensional monoliths
    • 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
    • B01J35/50—Catalysts, in general, characterised by their form or physical properties characterised by their shape or configuration
    • B01J35/58—Fabrics or filaments
    • 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
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/341—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of electric or magnetic fields, wave energy or particle radiation
    • B01J37/347—Ionic or cathodic spraying; Electric discharge
    • 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
    • B01J37/34—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation
    • B01J37/349—Irradiation by, or application of, electric, magnetic or wave energy, e.g. ultrasonic waves ; Ionic sputtering; Flame or plasma spraying; Particle radiation making use of flames, plasmas or lasers
    • C—CHEMISTRY; METALLURGY
    • C23—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; CHEMICAL SURFACE TREATMENT; DIFFUSION TREATMENT OF METALLIC MATERIAL; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL; INHIBITING CORROSION OF METALLIC MATERIAL OR INCRUSTATION IN GENERAL
    • C23C—COATING METALLIC MATERIAL; COATING MATERIAL WITH METALLIC MATERIAL; SURFACE TREATMENT OF METALLIC MATERIAL BY DIFFUSION INTO THE SURFACE, BY CHEMICAL CONVERSION OR SUBSTITUTION; COATING BY VACUUM EVAPORATION, BY SPUTTERING, BY ION IMPLANTATION OR BY CHEMICAL VAPOUR DEPOSITION, IN GENERAL
    • C23C14/00—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material
    • C23C14/22—Coating by vacuum evaporation, by sputtering or by ion implantation of the coating forming material characterised by the process of coating
    • C23C14/34—Sputtering
    • C23C14/3407—Cathode assembly for sputtering apparatus, e.g. Target

Definitions

  • the invention relates to a method for producing catalysts, in which a porous support structure and / or at least one catalytically active substance is deposited on a substrate.
  • the invention also relates to catalysts produced in this way. These catalysts are used inter alia. in the area of reducing exhaust emissions from internal combustion engines, fuel cells and in organic synthesis.
  • Catalysis is to be understood as the support of a chemical process by adding a material in which the reactants are reacted more quickly, with increased product concentration or selectivity, more energy- or raw material-friendly than without addition, and the catalyst material only participates in the reaction without being consumed or is used only to a very small extent.
  • the term marriage Mixing process also includes electrochemical, photochemical or photoelectrochemical processes.
  • catalysts in technology are: Reduction of N0 2 and CO emissions or degradation of soot particles in the exhaust gas of internal combustion engines, cathode-side oxygen reduction in the polymer fuel cell (PEM-BZ), methanol reforming.
  • PEM-BZ polymer fuel cell
  • methanol reforming for hydrogen production, organic syntheses such as tetrahydrofuran (THF) from n-butane, petrochemical refining processes and many other processes used in energy and drive technology as well as in the chemical and pharmaceutical industries.
  • THF tetrahydrofuran
  • a catalytic converter is characterized by a large inner surface and a structure in the form of a composite, ie a heterogeneously structured material system.
  • the catalytically active substances are often highly dispersed, ie extremely finely divided metal particles that are applied to a ceramic support structure.
  • Car exhaust catalysts are characterized, for example, by a porous ceramic structure, usually consisting of aluminum oxide or cordierite, on which noble metal or general transition metal particles are upset.
  • the catalytically active species can also be metal compounds, such as vanadium phosphorus oxides In the case of THF synthesis or transition metal chalcogenides such as MoS 2 , NiS or CoS in the reduction of the sulfur content in petroleum and its derivatives.
  • Typical process steps in the manufacture of catalysts are impregnation, followed by a drying and calcining step.
  • the catalytically active metals in the form of their compounds such as carbonates, nitrates or other, are applied wet-chemically to the ceramic support structures and subsequently converted into the metals. While only the water introduced is evaporated at 100-200 ° C in the drying step, process temperatures of several hundred to over a thousand degrees Celsius are used in the calcination in order to decompose the carbonate or nitrate to the metal.
  • Particle dispersions consisting of metal oxide or hydroxide (washcoats) are often used as carrier structures and were applied to a base carrier structure by wet-chemical preparation steps.
  • the latter is mostly used only for the shape and structural stability of the catalyst, but has an inner surface that is too small to act as a carrier for the catalytically active centers. Drying and calcining are often followed by a so-called reduction step, in which the metal in oxidized form is reduced by the influence of hydrogen or another reducing agent.
  • catalytic converters as powder, pellets, etc. in a so-called fixed bed, as dispersions in clay minerals and pumice stone, in fibrous structures through which gases flow, etc. etc.
  • the reactants and catalyst consist in the use of so-called monoliths.
  • the catalytically active substances are applied to surfaces through which a liquid or gaseous phase flows.
  • the supporting structures of the monolith can consist of metal, ceramic or other shaping materials.
  • the catalyst it makes sense to think of the catalyst as being made up of three different materials or structures, namely the base support, such as a metallic monolith, the support , for example a washcoat and the active species, which can be formed, for example, by precious metal particles.
  • the metals introduced with the impregnation are in the preliminary stage of nitrates or carbonates, and are only converted into the actually catalytically active metal particles by energy-consuming calcination.
  • Hollow cathode discharge is used in the field of plasma-assisted surface treatment. It is based on the hollow cathode effect, i.e. a glow discharge which takes place in a dilute gas and has high densities of electrical charge carriers, i.e. ionized gas atoms and free electrons.
  • the cathode is designed as a hollow body, in the interior of which the negative glow lights are superimposed.
  • a hollow cathode is characterized in that the ratio of cathode area to opening area is greater than 1.
  • the condition applies that the product from one of the cathode dimensions D times the working pressure p must lie within the range from 0.1 mbar-cm to 10 mbar-cm, 0, KDp ⁇ 10 mbar-cm (G. Schaefer & KH Schoenbach: "Basic mechanis s contributing to the hollow cathode effect", in: NATO Asi series - Advanced science institutes series H. 219 (1990), 55 ff.).
  • Coating processes based on the hollow cathode principle are characterized by a plasma discharge, in which the material to be deposited is either removed from a source by sputtering or by decomposition of chemical substances in the
  • Gas plasma phase is formed.
  • hollow cathode-based processes operate at comparatively high pressures of around 1 mbar, so that only a small amount of vacuum is required to evacuate the process chamber.
  • high deposition rates occur in this pressure regime, so that Fast coating processes can be carried out, as they are required in the industry.
  • the hollow cathode gas flow sputtering a hollow cathode is flushed from one side with a working gas such as argon. Atoms detached by sputtering are subsequently carried out on the other side, with which a coating process can be carried out.
  • coatings can be produced from practically all solid substances, ie only a few substances such as pure metals, alloys, metal compounds such as oxides, hydroxides, nitrides, sulfides, etc.
  • Amorphous or crystalline structure and porous or compact morphology of the substances to be deposited can be set by process control.
  • a method for producing catalysts in which a porous support structure and / or at least one catalytically active substance is deposited on a substrate becomes.
  • the coating is carried out by means of a plasma treatment using the hollow cathode effect.
  • Transition metals and / or their compounds are preferably used as catalytically active substances, the nanogranular particles being preferred have a diameter between 1 and 100 nm.
  • Platinum and rhodium, but also vanadium phosphorus oxides, molybdenum sulfides, nickel sulfides or cobalt sulfides may be mentioned here only as examples.
  • Metal compounds e.g. Metal oxides or metal hydroxides used.
  • a monolith is preferably used as the substrate, on the inner and outer surfaces of which the support structure can be deposited.
  • porous formers such as Nets, wire mesh, steel wool, metal gauze, glass fabric, powder, activated carbon, carbon nanorolls or spheres with diameters between 100 nm and 1 cm can be used.
  • the substrate is preferably made of a metal or a ceramic metal, e.g. made of aluminum oxide or cordierite.
  • the porous support structure is preferably constructed from metal compounds, in particular metal oxides or metal hydroxides.
  • the porous support structure can be applied in a first step and the at least one catalytically active substance can be deposited in a subsequent step.
  • the catalytically active substance is preferred in
  • the nanogranular particles preferably have a diameter between 1 and 100 nm.
  • the substrate is preferably provided by plasma treatment with the support structure made up of metal compounds.
  • the support structure made up of metal compounds.
  • the hollow cathode effect is used.
  • the substrate can be provided with the porous support structure by oblique vapor deposition or deposition without applying an electrical bias.
  • a planar substrates generally result in a columnar growth morphology of the layer, the pore size distribution function of which can be set in a targeted manner by process parameters such as total pressure, geometry of the source-substrate configuration and rate.
  • the porous structure by depositing a dispersion of two phases on the substrate, one of the two phases then being removed to form the cavities.
  • This method is based on the fact that two different chemical phases are dispersed either by separate growth of the particles in the gas-plasma phase or by precipitation due to the thermodynamic properties of the two-phase system.
  • One of the two phases should be chosen so that it can be more easily removed from the layer by a subsequent process step than the other phase.
  • steps such as chemical etching or plasma etching are used.
  • the coating can be produced in such a way that a one-component film with adjustable porosity is subsequently obtained.
  • the technical implementation of the plasma treatment can be carried out according to three basic alternatives.
  • the first is based on plasma treatment by sputtering the coating material as physical vapor deposition, also called PVD.
  • the coating material is converted by sputtering and its chemical reaction with a reactive gas component and then deposited. This is also known as the reactive PVD process.
  • the coating material is formed from a chemical reaction of the gases supplied and then deposited. This procedure is known as chemical vapor deposition (CVD).
  • the plasma treatment is preferably carried out at a working pressure between 0.01 mbar and 1 bar, preferably between 0.1 mbar and 1 mbar.
  • the hollow cathode can be designed both as a tube and as an arrangement of two or more parallel or inclined plates. It is also possible for the hollow cathode to be a metal mesh, the gas introduced flowing through the mesh one or more times.
  • the hollow cathode discharge can be controlled so that the material deposition takes place inside the hollow cathode (so-called Inside Hollow Cathode, IHC).
  • IHC Inside Hollow Cathode
  • Another Re variant of the method provides that the hollow cathode discharge takes place on a rolling sheet metal strip, the hollow cathode discharge being operated in a loop between the two regions of the sheet metal.
  • the excitation voltages for the hollow cathode discharge are between 1 V and 2000 V.
  • the plasma can be maintained by direct or alternating voltage.
  • the low, medium and high frequency range can be used as the frequency range.
  • a plasma fed with microwaves can be used in the same way.
  • a catalyst produced by the process according to the invention is provided.
  • the porous support structure and the at least one catalytically active substance are deposited on the substrate as a heterogeneously distributed dispersion of nanogranular particles.
  • the deposited nanogranular particles have a diameter of between 1 and 100 nm.
  • Such catalysts are notable for their high activity, at the same time the proportion of the catalytically active metals used is very low.
  • the method according to the invention is used in the production of catalysts for reducing the NO x and CO emissions or the breakdown of soot particles in the exhaust of internal combustion engines.
  • catalysts produced in this way can be used for the cathode-side oxygen reduction in fuel cells, in particular polymer fuel cells (PEM).
  • PEM polymer fuel cells
  • Another field of application concerns methanol reforming in hydrogen synthesis.
  • the catalysts are also used in organic synthesis.
  • all synthetic processes in energy and drive technology as well as in the chemical and pharmaceutical industries are suitable as fields of application.
  • FIG. 1 schematically shows two variants of the coating method according to the invention.
  • FIG. 2 shows a further variant of the method according to the invention using two hollow cathodes.
  • Fig. 3 shows schematically a further variant in which the coating on a rolling
  • the method for coating a monolith sheet 4 is shown in FIG. Gas is passed through the hollow cathode 2 via the gas supply 1, causing a plasma discharge 3. The atomic coating material formed in the process is then deposited on the monolith sheet 4. ⁇ £ -
  • a hollow cathode 2 is shown from two opposite parallel plates.
  • the gas is passed between the plates via the gas supply 1, whereby a hollow cathode discharge takes place in the region 3.
  • a monolith which consists of several honeycomb segments, is shown here as the substrate. In this way, a loading Layering of the inner and outer surfaces of these segments are done.
  • Fig. 2 shows a variant in which two hollow cathodes 2, 6 are used.
  • the hollow cathode 2 serves the deposition of the support structure, while the hollow cathode 6 serves the deposition of the catalytically active substance.
  • this variant of the method it is possible to produce heterogeneously distributed particle dispersions of the catalytically active substance and the support structure on the substrate 4.
  • a tape 2 e.g. made of metallic material, transported.
  • the gas supply 1 is arranged so that the hollow cathode discharge takes place in the intermediate space 3 between the opposite band cuts 2.
  • the starting material are metal sheets coated with an aluminum oxide washcoat, which are designed in such a way that they can be plugged into one another and thus form parallel, flowable channels.
  • the task of the process is to activate the washcoat layer by applying a nanogranular noble metal layer (platinum / rhodium).
  • the starting sheets are coated with a gas flow sputter source, the cathode of which consists of the noble metal to be deposited.
  • a gas flow sputtering source of the tube type is used in a vacuum recipe.
  • the tube consisting of platinum and rhodium is placed at a negative electrical potential and flushed with argon from one side.
  • the tube source is flushed with an argon volume flow of one standard liter per minute and, depending on the suction power of the pumping station and the size of the recipient, a total pressure of 0.5 mbar is established.
  • the hollow cathode has an inner diameter of 30 mm and is supplied with an electrical power of 2 kW, which is used to maintain the plasma discharge.
  • Cathode sputtering knocks out individual atoms from the hollow tube cathode and carries them out with the gas flow in the gas-plasma phase by collisions of the metal atoms to form nanometer-sized particles whose
  • Size distribution function through the Ar flow, the power applied to the pipe source, the distance between the source and the plate and other process parameters can be set in a targeted manner.
  • the particle-containing argon stream hits the monolith sheets, where the precious metal particles are deposited on the aluminum oxide washcoat. The density of the particles is adjusted over the period of time that the process is allowed to act on the monolith sheet.
  • the execution of the method can also be such that the gas flow behind the gas flow sputter source directly onto the openings of the monolith or one Segment of the monolith is directed and the activation of the washcoat layer is carried out by an inner coating with precious metal or precious metal particles.

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Abstract

The invention relates to a method for the production of catalysts, wherein a porous carrier structure and/or at least one catalytically active substance is deposited onto a substrate. The invention also relates to catalysts produced according to said method. The catalysts are used, inter alia, in the reduction of exhaust gas emissions of internal combustion engines, fuel cells and in organic synthesis.

Description

Verfahren zur Herstellung von Katalysatoren Process for the production of catalysts
Die Erfindung betrifft ein Verfahren zur Herstellung von Katalysatoren, bei dem auf einem Substrat eine poröse Trägerstruktur und/oder mindestens eine kata- lytisch aktive Substanz abgeschieden wird. Ebenso betrifft die Erfindung derart hergestellte Katalysatoren. Verwendung finden diese Katalysatoren u.a. im Bereich der Reduzierung der Abgasemission von Ver- brennungsmotoren, den Brennstoffzellen sowie in der organischen Synthese.The invention relates to a method for producing catalysts, in which a porous support structure and / or at least one catalytically active substance is deposited on a substrate. The invention also relates to catalysts produced in this way. These catalysts are used inter alia. in the area of reducing exhaust emissions from internal combustion engines, fuel cells and in organic synthesis.
Unter Katalyse ist die Unterstützung eines chemischen Prozesses durch Zusatz eines Materials zu verstehen, bei dem die Reaktionspartner schneller, mit erhöhter Produktkonzentration oder Selektivität, energie- oder rohstoffschonender umgesetzt werden als ohne Zusatz, und wobei das Katalysatormaterial nur an der Reaktion teilnimmt ohne verbraucht zu werden oder nur in sehr geringem Umfang verbraucht wird. Die Bezeichnung ehe- mischer Prozeß umfaßt gleichermaßen elektrochemische, photochemische oder photoelektrochemische Prozesse.Catalysis is to be understood as the support of a chemical process by adding a material in which the reactants are reacted more quickly, with increased product concentration or selectivity, more energy- or raw material-friendly than without addition, and the catalyst material only participates in the reaction without being consumed or is used only to a very small extent. The term marriage Mixing process also includes electrochemical, photochemical or photoelectrochemical processes.
J. E. Otterstedt und D. A. Branreth geben in Kapitel 7 "Catalyst Supports and Small Particles Catalysts" ihrer Monographie "Small Particles Technology" (Plenum Press, 1998) einen Überblick über moderne Katalysatoren und die Bedeutung kleiner Teilchen, d.h. solcher mit Abmessungen im Bereich von Nanometern, für die Katalyse.J.E. Otterstedt and D.A. Branreth give an overview of modern catalysts and the importance of small particles in Chapter 7 "Catalyst Supports and Small Particles Catalysts" of their monograph "Small Particles Technology" (Plenum Press, 1998). those with dimensions in the range of nanometers, for catalysis.
Beispiele für die Verwendung von Katalysatoren in der Technik sind: Verminderung der N02- und CO-Emissionen oder Abbau von Rußpartikeln im Abgas von Verbren- nungsmotoren, kathodenseitige Sauerstoffreduktion in der Polymerbrennstoffzelle (PEM-BZ) , Methanolrefor- mierung. zur Wasserstofferzeugung, organische Synthesen wie z.B. von Tetrahydrofuran (THF) aus n-Butan, petrochemische Raffinierungsprozesse und viele ande- re, in der Energie- und Antriebstechnik sowie der chemischen und pharmazeutischen Industrie eingesetzte Prozesse.Examples of the use of catalysts in technology are: Reduction of N0 2 and CO emissions or degradation of soot particles in the exhaust gas of internal combustion engines, cathode-side oxygen reduction in the polymer fuel cell (PEM-BZ), methanol reforming. for hydrogen production, organic syntheses such as tetrahydrofuran (THF) from n-butane, petrochemical refining processes and many other processes used in energy and drive technology as well as in the chemical and pharmaceutical industries.
Charakteristisch für einen Katalysator ist eine große innere Oberfläche und ein Aufbau in Form eines Kompo- sits, d.h. eines heterogen strukturierten Materialsystems. Die katalytisch aktiven Substanzen sind oft hoch dispergierte, d.h. extrem fein verteilte Metallpartikel, die auf eine keramische Trägerstruktur auf- gebracht sind, Autoabgaskatalysatoren sind z.B. gekennzeichnet durch eine poröse Keramik-Struktur, meist aus Aluminiumoxid oder Cordierit bestehend, auf denen Edelmetall- oder allgemeiner Übergangsmetallpartikel aufgebracht sind. Bei den katalytisch akti- ven Spezies kann es sich aber auch um Metallverbindungen handeln, wie z.B. Vanadiumphosphoroxiden im Falle der THF-Synthese oder Übergangsmetallchalkoge- nide wie MoS2, NiS oder CoS bei der Reduzierung des Schwefelgehalts in Erdöl und seinen Derivaten.A catalytic converter is characterized by a large inner surface and a structure in the form of a composite, ie a heterogeneously structured material system. The catalytically active substances are often highly dispersed, ie extremely finely divided metal particles that are applied to a ceramic support structure. Car exhaust catalysts are characterized, for example, by a porous ceramic structure, usually consisting of aluminum oxide or cordierite, on which noble metal or general transition metal particles are upset. The catalytically active species can also be metal compounds, such as vanadium phosphorus oxides In the case of THF synthesis or transition metal chalcogenides such as MoS 2 , NiS or CoS in the reduction of the sulfur content in petroleum and its derivatives.
Typische Prozeßschritte bei der Herstellung von Katalysatoren sind die Imprägnierung, auf die ein Trocknungs- und Kalzinierungsschritt folgt. Bei der Imprägnierung werden die katalytisch aktiven Metalle in Form ihrer Verbindungen wie Carbonaten, Nitraten oder anderen naßchemisch auf die keramischen Trägerstrukturen aufgebracht und nachfolgend in die Metalle überführt. Während beim Trocknungsschritt lediglich das eingebrachte Wasser bei 100-200°C verdampft wird, werden bei der Kalzinierung Prozeßtemperaturen von mehreren hundert bis zu über eintausend Grad Celsius eingesetzt, um das Carbonat oder Nitrat zum Metall zu zersetzen. Als Trägerstrukturen werden häufig aus Metalloxid oder -hydroxid bestehende Partikeldispersionen eingesetzt (washcoats) , die durch naßchemische Präparationsschritte auf eine Grundträgerstruktur auftragen wurden. Die letztere dient meist nur der Formgebung und strukturellen Stabilität das Katalysators, weist aber eine zu kleine innere Oberfläche - auf, um als Träger der katalytisch aktiven Zentren zu fungieren. Oft wird der Trocknung und Kalzinierung auch noch ein sog. Reduktionsschritt angeschlossen, bei dem das in oxidierter Form vorliegende Metall durch den Einfluß von Wasserstoff oder eines andere» Reduktionsmittels reduziert wird.Typical process steps in the manufacture of catalysts are impregnation, followed by a drying and calcining step. During the impregnation, the catalytically active metals in the form of their compounds, such as carbonates, nitrates or other, are applied wet-chemically to the ceramic support structures and subsequently converted into the metals. While only the water introduced is evaporated at 100-200 ° C in the drying step, process temperatures of several hundred to over a thousand degrees Celsius are used in the calcination in order to decompose the carbonate or nitrate to the metal. Particle dispersions consisting of metal oxide or hydroxide (washcoats) are often used as carrier structures and were applied to a base carrier structure by wet-chemical preparation steps. The latter is mostly used only for the shape and structural stability of the catalyst, but has an inner surface that is too small to act as a carrier for the catalytically active centers. Drying and calcining are often followed by a so-called reduction step, in which the metal in oxidized form is reduced by the influence of hydrogen or another reducing agent.
Katalysatoren werden in verschiedenen Bauformen eingesetzt: als Pulver, Preßlinge usw. im sog. Festbett, als in Tonmineralien und Bimsstein eingebrachte Dispersionen, in von Gasen durchströmten fibrösen Struk- turen usw. usf.. Eine weit verbreitete Methode zurVarious types of catalytic converters are used: as powder, pellets, etc. in a so-called fixed bed, as dispersions in clay minerals and pumice stone, in fibrous structures through which gases flow, etc. etc. A widely used method for
Herstellung eines engen räumlichen Kontakts zwischen Reaktanden und Katalysator besteht in der Verwendung von sog. Monolithen. Bei diesen sind die katalytisch aktiven Substanzen auf Oberflächen aufgebracht, die von einer flüssigen oder gasförmigen Phase durch- strömt werden. Durch eine parallele Anordnung dieser Einheiten wie z.B. in einer Honigwabenstruktur finden viele der zu fördernden chemischen Reaktion parallel statt. Die tragenden Strukturen des Monolithen können aus Metall, Keramik oder anderen, formgebenden Mate- rialien bestehen, in manchen Fällen ist es sinnvoll, sich den Katalysator aus drei verschiedenen Materialien bzw. Strukturen aufgebaut vorzustellen, nämlich dem Grundträger, etwa einem metallischen Monolithen, dem Träger, z.B. einer Washcoat und den aktiven Spe- zies, die z.B. durch Edelmetallpartikel gebildet werden können.Establishing close spatial contact between The reactants and catalyst consist in the use of so-called monoliths. In these, the catalytically active substances are applied to surfaces through which a liquid or gaseous phase flows. By arranging these units in parallel, for example in a honeycomb structure, many of the chemical reactions to be promoted take place in parallel. The supporting structures of the monolith can consist of metal, ceramic or other shaping materials. In some cases it makes sense to think of the catalyst as being made up of three different materials or structures, namely the base support, such as a metallic monolith, the support , for example a washcoat and the active species, which can be formed, for example, by precious metal particles.
Die Nachteile der bekannten Verfahren zur Herstellung von Katalysatoren sind:The disadvantages of the known processes for the production of catalysts are:
• Durch die Imprägnierung wird Wasser in das Materialsystem eingebracht das durch einen weiteren, e- nergieverbrauchenden Prozeßschritt ausgetrieben werden mu .• The impregnation introduces water into the material system, which must be expelled through a further, energy-consuming process step.
• Die mit der Imprägnierung eingebrachten Metalle liegen in der Vorstufe von Nitraten oder Carbona- ten vor, und werden erst durch energieverbrauchende Kalzinierung in die eigentlich katalytisch ak- tiven Metallpartikel überführt.• The metals introduced with the impregnation are in the preliminary stage of nitrates or carbonates, and are only converted into the actually catalytically active metal particles by energy-consuming calcination.
• Die Prozesse sind häufig sehr zeitbeanspruchend und aufwendig.• The processes are often very time-consuming and time-consuming.
• - Die naßchemische Prozeßführung und die nachfolgenden Temperaturbehandlungen gestatten nur eine man- gelhafte Kontrolle der Partikelgrößenverteilungsfunktion der katalytisch aktiven Metallpartikel, wodurch die Selektivität des Prozesses unnötig eingeschränkt sein kann.• - The wet chemical process control and the subsequent temperature treatments only allow one Geligen control of the particle size distribution function of the catalytically active metal particles, which can unnecessarily limit the selectivity of the process.
Die Hohlkathodenentladung findet im Bereich der Verfahren zur plasmagestützten Oberflächenvergütung Anwendung. Sie basiert auf dem Hohlkathodeneffekt, also einer in einem verdünnten Gas ablaufenden Glimmentla- düng mit hohen Dichten elektrischer Ladungsträger, d.h. ionisierten Gasatomen und freien Elektronen. Dabei ist die Kathode als Hohlkörper ausgeführt, in dessen Innenraum es zur Überlagerung der negativen Glimmlichter kommt. Geometrisch ist eine Hohlkathode dadurch gekennzeichnet, daß das Verhältnis von Kathodenfläche zu Öffnungsfläche größer als 1 ist. Für das Auftreten des Hohlkathodeneffekts gilt die Bedingung, daß das Produkt aus einer der Kathodenabmessungen D mal Arbeitsdruck p innerhalb des Bereichs von 0.1 mbar-cm bis 10 mbar-cm liegen muß, 0,KDp<10 mbar-cm (G. Schaefer & K. H. Schoenbach: "Basic mechanis s contributing to the hollow cathode effect", in: NATO Asi series - Advanced science institutes series H. 219 (1990) , 55 ff.) .Hollow cathode discharge is used in the field of plasma-assisted surface treatment. It is based on the hollow cathode effect, i.e. a glow discharge which takes place in a dilute gas and has high densities of electrical charge carriers, i.e. ionized gas atoms and free electrons. The cathode is designed as a hollow body, in the interior of which the negative glow lights are superimposed. Geometrically, a hollow cathode is characterized in that the ratio of cathode area to opening area is greater than 1. For the occurrence of the hollow cathode effect, the condition applies that the product from one of the cathode dimensions D times the working pressure p must lie within the range from 0.1 mbar-cm to 10 mbar-cm, 0, KDp <10 mbar-cm (G. Schaefer & KH Schoenbach: "Basic mechanis s contributing to the hollow cathode effect", in: NATO Asi series - Advanced science institutes series H. 219 (1990), 55 ff.).
Auf dem Hohlkathodenprinzip basierende Beschichtungs- prozesse sind durch eine Plasmaentladung gekennzeichnet, ixe der das zu deponierende Material entweder durch Kathodenzerstäubung von einer Quelle abgetragen oder durch Zersetzung chemischer Substanzen in derCoating processes based on the hollow cathode principle are characterized by a plasma discharge, in which the material to be deposited is either removed from a source by sputtering or by decomposition of chemical substances in the
Gas-Plasma-Phase gebildet wird. In vielen Fällen arbeiten hohlkathodenbasierte Prozesse bei vergleichsweise hohen Drücken um 1 mbar, so daß nur ein geringer vakuumtechnischer Aufwand für die Evakuierung der Prozeßkammer zu betreiben ist. Zum anderen treten in diesem Druckregime hohe Abscheideraten auf, so daß schnelle Beschichtungsprozesse durchgeführt werden können, wie sie in der Industrie benötigt werden. In einer wichtigen Verfahrensvariante, dem Hohlkathoden- Gasflußsputtern, wird eine Hohlkathode von einer Sei- te mit einem Arbeitsgas wie Argon durchspült. Durch Kathodenzerstäubung abgelöste Atome werden nachfolgend auf der anderen Seite herausgetragen, mit denen ein Beschichtungsprozeß durchgeführt werden kann. Mit hohlkathodenbasierten Prozessen können Beschichtungen aus praktisch allen festen Stoffen, d.h. einele enti- ge Substanzen wie reine Metalle, Legierungen, Metallverbindungen wie Oxiden, Hydroxiden, Nitriden, Sulfiden usw. erzeugt werden. Amorphe oder kristalline Struktur und poröse oder kompakte Morphologie der ab- zuscheidenden Substanzen ist durch Prozeßführung einstellbar.Gas plasma phase is formed. In many cases, hollow cathode-based processes operate at comparatively high pressures of around 1 mbar, so that only a small amount of vacuum is required to evacuate the process chamber. On the other hand, high deposition rates occur in this pressure regime, so that Fast coating processes can be carried out, as they are required in the industry. In an important process variant, the hollow cathode gas flow sputtering, a hollow cathode is flushed from one side with a working gas such as argon. Atoms detached by sputtering are subsequently carried out on the other side, with which a coating process can be carried out. With hollow cathode-based processes, coatings can be produced from practically all solid substances, ie only a few substances such as pure metals, alloys, metal compounds such as oxides, hydroxides, nitrides, sulfides, etc. Amorphous or crystalline structure and porous or compact morphology of the substances to be deposited can be set by process control.
Ausgehend hiervon war es Aufgabe der vorliegenden Erfindung die aus dem Stand der Technik bekannten Nachteile zu beseitigen und ein einfach zu handhabendes und damit mit geringem Zeitaufwand durchführbares Verfahren zur Herstellung von Katalysatoren unter dem Gesichtspunkt der Kostenreduktion bereitzustellen.Proceeding from this, it was an object of the present invention to eliminate the disadvantages known from the prior art and to provide an easy-to-use and therefore inexpensive method for producing catalysts from the point of view of reducing costs.
Diese Aufgabe wird durch das gattungsgemäße Verfahren mit den kennzeichnenden Merkmalen des Anspruchs 1 sowie die hierüber hergestellten Katalysatoren gemäß Anspruch 20 gelöst. Die weiteren-abhängigen Ansprüche zeigen vorteilhafte Weiterbildungen auf. Die Verwen- düng der derart hergestellten Katalysatoren wird in den Ansprüche 23 bis 26 dargestellt.This object is achieved by the generic method with the characterizing features of claim 1 and the catalysts produced therefrom according to claim 20. The further dependent claims show advantageous developments. The use of the catalysts produced in this way is presented in claims 23 to 26.
Erfindungsgemäß wird ein Verfahren zur Herstellung von Katalysatoren bereitgestellt, bei dem auf einem Substrat eine poröse Trägerstruktur und/oder mindestens eine katalytisch aktive Substanz abgeschieden wird. Dabei erfolgt die Beschichtung mittels einer Plasmabehandlung unter Ausnutzung des Hohlkathodenef- fektes.According to the invention, a method for producing catalysts is provided in which a porous support structure and / or at least one catalytically active substance is deposited on a substrate becomes. The coating is carried out by means of a plasma treatment using the hollow cathode effect.
Durch die gegenüber dem Stand der Technik entfallenen Prozeßschritte der Trocknung, Kalzinierung und Reduktion machen plasmagestützte Hohlkathodenprozesse eine schnellere Herstellung von Katalysatoren möglich. Zudem wird das Zusammensintern der katalytisch aktiven Metallpartikel vermieden, weil nach der Herstellung keine Temperaturbehandlungen durchzuführen sind. Durch das in-situ-Wachstum der Partikel in der Gasphase wird die Agglomeration katalytisch aktiver Na- nopartikel vermieden, so daß nachfolgende, aufwendige Maßnahmen zur Deagglomeration entfallen können.Due to the process steps of drying, calcining and reduction which are omitted from the prior art, plasma-supported hollow cathode processes make it possible to produce catalysts more quickly. In addition, the sintering together of the catalytically active metal particles is avoided because no temperature treatments have to be carried out after the production. The in-situ growth of the particles in the gas phase avoids the agglomeration of catalytically active nanoparticles, so that subsequent, complex measures for deagglomeration can be omitted.
Im Ergebnis bewirken diese Punkte, daß die Korngrößenverteilungsfunktion der katalytisch aktiven Zentren definierter eingestellt werden kann als bei dem aus dem Stand der Technik bekannten Verfahren. Dadurch werden Einsparungen beim Ersatz der katalytisch aktiven Metalle, bei denen es sich häufig um teure Edelmetalle handelt, und eine verbesserte katalyti- sche Aktivität ermöglicht.As a result, these points have the effect that the particle size distribution function of the catalytically active centers can be set in a more defined manner than in the method known from the prior art. This enables savings in the replacement of the catalytically active metals, which are often expensive precious metals, and improved catalytic activity.
Überraschenderweise konnte gezeigt werden, daß der Hohlkathoden-Beschichtungsprozeß im Druckbereich um 1 mbar zu-1 Ausbildung von nanometergroßen Partikeln in der Gasphase führt. Durch die Abscheidung solch nanogranularer Partikel auf Trägerstrukturen oder auf Substraten können somit besonders einfach aktive Zentren für Katalysatoren präpariert werden.Surprisingly, it was shown that the hollow cathode coating process in the pressure range of 1 mbar to-1 formation of nanometer-sized particles results in the gas phase. The deposition of such nanogranular particles on support structures or on substrates makes it particularly easy to prepare active centers for catalysts.
Als katalytisch aktive Substanzen werden vorzugsweise Übergangsmetalle und/oder deren Verbindung eingesetzt, wobei die nanogranulären Partikel bevorzugt einen Durchmesser zwischen 1 und 100 nm aufweisen. Nur beispielhaft seien hier Platin und Rhodium, aber auch Vanadiumphosphoroxide, Molybdensulfide, Nickelsulfide oder Kobaltsulfide genannt.Transition metals and / or their compounds are preferably used as catalytically active substances, the nanogranular particles being preferred have a diameter between 1 and 100 nm. Platinum and rhodium, but also vanadium phosphorus oxides, molybdenum sulfides, nickel sulfides or cobalt sulfides may be mentioned here only as examples.
Vorzugsweise werden zur Herstellung der porösen Trägerstruktur Metallverbindungen, z.B. Metalloxide oder Metallhydroxide, verwendet.Metal compounds, e.g. Metal oxides or metal hydroxides used.
Als Substrat wird bevorzugt ein Monolith verwendet, auf dessen inneren wie äußeren Oberflächen die Trägerstruktur abgeschieden werden kann. Alternativ können aber auch poröse Formgeber wie z.B. Netze, Drahtgeflechte, Stahlwolle, Metallgaze, Glasgewebe, Pul- ver, Aktivkohle, Kohlenstoff-Nanoröllchen oder Kugeln mit Durchmessern zwischen 100 nm und 1 cm verwendet werden.A monolith is preferably used as the substrate, on the inner and outer surfaces of which the support structure can be deposited. Alternatively, porous formers such as Nets, wire mesh, steel wool, metal gauze, glass fabric, powder, activated carbon, carbon nanorolls or spheres with diameters between 100 nm and 1 cm can be used.
Das Substrat besteht vorzugsweise aus einem Metall oder einem keramischen Metall, z.B. aus Aluminiumoxid oder Cordierit. Die poröse Trägerstruktur wird vorzugsweise aus Metallverbindungen, insbesondere Metalloxiden oder Metallhydroxiden aufgebaut.The substrate is preferably made of a metal or a ceramic metal, e.g. made of aluminum oxide or cordierite. The porous support structure is preferably constructed from metal compounds, in particular metal oxides or metal hydroxides.
In einer weiteren Variante kann die poröse Trägerstruktur in einem ersten Schritt aufgetragen und in einem darauf folgenden Schritt die mindestens eine katalytisch aktive Substanz abgeschieden werden.In a further variant, the porous support structure can be applied in a first step and the at least one catalytically active substance can be deposited in a subsequent step.
Bevorzugt Wird die katalytisch aktive Substanz inThe catalytically active substance is preferred in
Form leicht flüchtiger Precursor in die Hohlräume der .porösen Trägerstruktur eingebracht. Aufgrund des hohlkathodengestützten Beschichtungsverfahrens kommt es zur Ausbildung einer Plasmaentladung in den Hohl- räumen, die zur Zersetzung des Precursors in die zu deponierenden Atome führt. Diese in der Gasphase vor- liegenden Atome können anschließend auf den inneren Oberflächen der Hohlräume abgeschieden werden. Bei einer derartigen Vorgehensweise weisen die nanogranu- laren Partikel vorzugsweise einen Durchmesser zwischen 1 und 100 nm auf.Form volatile precursor introduced into the cavities of the .porous support structure. The hollow cathode-supported coating process leads to the formation of a plasma discharge in the cavities, which leads to the decomposition of the precursor into the atoms to be deposited. This in the gas phase lying atoms can then be deposited on the inner surfaces of the cavities. In such a procedure, the nanogranular particles preferably have a diameter between 1 and 100 nm.
In analoger Verfahrensweise wird bevorzugt das Substrat durch Plasmabehaήdlung mit der aus Metallver- bindungen aufgebauten TrägerStruktur versehen. Auch hier wird dazu der Hohlkathodeneffekt ausgenutzt.In an analogous procedure, the substrate is preferably provided by plasma treatment with the support structure made up of metal compounds. Here too, the hollow cathode effect is used.
Hierzu stehen verschiedene Varianten zur Verfügung. So kann das Substrat durch Schrägbedampfung oder Ab- Scheidung ohne Anlegen einer elektrischen Vorspannung mit der porösen Trägerstruktur versehen werden. Auf planaren Substraten ergibt sich dann im Allgemeinen eine säulenförmige Wachstumsmorphologie der Schicht, deren Porengrößenverteilungsfunktion durch Prozeßpa- rameter wie Gesamtdruck, Geometrie der Quelle- Substrat-Konfiguration und Rate gezielt eingestellt werden kann.Different variants are available for this. For example, the substrate can be provided with the porous support structure by oblique vapor deposition or deposition without applying an electrical bias. A planar substrates generally result in a columnar growth morphology of the layer, the pore size distribution function of which can be set in a targeted manner by process parameters such as total pressure, geometry of the source-substrate configuration and rate.
Alternativ ist es auch möglich, die poröse Struktur durch Abscheidung einer Dispersion zweier Phasen auf dem Substrat zu erzeugen, wobei im Anschluß eine der beiden Phasen unter Ausbildung der Hohlräume entfernt wird. Diese Methode basiert darauf, daß zwei unterschiedliche chemische Phasen entweder durch getrenn- tes Wachstum der Partikel in der Gas-Plasma-Phase o- der durch Ausscheidung aufgrund der thermodynamischen Eigenschaften des Zweiphasensystems dispergiert werden. Eine der beiden Phasen ist dabei so zu wählen, daß sie durch einen nachfolgenden Prozeßschritt leichter aus der Schicht herausgelöst werden kann als die andere Phase. Vorzugsweise werden hierfür Pro- zeßschritte wie chemisches Ätzen oder Plasma-Ätzen verwendet. Je nach relativem Volumenanteil der beiden Phasen und jeweiliger nanogranularer Struktur kann die Beschichtung so hergestellt werden, daß sich an- schließend ein einko ponentiger Film mit einstellbarer Porosität ergibt.Alternatively, it is also possible to produce the porous structure by depositing a dispersion of two phases on the substrate, one of the two phases then being removed to form the cavities. This method is based on the fact that two different chemical phases are dispersed either by separate growth of the particles in the gas-plasma phase or by precipitation due to the thermodynamic properties of the two-phase system. One of the two phases should be chosen so that it can be more easily removed from the layer by a subsequent process step than the other phase. For this, preferably steps such as chemical etching or plasma etching are used. Depending on the relative volume fraction of the two phases and the respective nanogranular structure, the coating can be produced in such a way that a one-component film with adjustable porosity is subsequently obtained.
Die technische Durchführung der Plasmabehandlung kann nach drei grundsätzlichen Alternativen erfolgen. Die erste beruht auf einer Plasmabehandlung durch Kathodenzerstäubung des Beschichtungsmaterials als physikalische Gasphasenabscheidung, auch PVD genannt. Bei der zweiten Variante wird das Beschichtungsmaterial durch Kathodenzerstäubung und dessen chemische Reak- tion mit einer reaktiven Gaskomponente umgesetzt und anschließend abgeschieden. Hierbei spricht man auch vom reaktiven PVD-Verfahren. In der dritten Variante wird das Beschichtungsmaterial aus einer chemischen Reaktion der zugeführten Gase gebildet und anschlie- ßend abgeschieden. Diese Verfahrensweise wird als chemische Gasphasenabscheidung (CVD) bezeichnet.The technical implementation of the plasma treatment can be carried out according to three basic alternatives. The first is based on plasma treatment by sputtering the coating material as physical vapor deposition, also called PVD. In the second variant, the coating material is converted by sputtering and its chemical reaction with a reactive gas component and then deposited. This is also known as the reactive PVD process. In the third variant, the coating material is formed from a chemical reaction of the gases supplied and then deposited. This procedure is known as chemical vapor deposition (CVD).
Vorzugsweise wird die Plasmabehandlung bei einem Arbeitsdruck zwischen 0,01 mbar und 1 bar, bevorzugt zwischen 0,1 mbar und 1 mbar durchgeführt.The plasma treatment is preferably carried out at a working pressure between 0.01 mbar and 1 bar, preferably between 0.1 mbar and 1 mbar.
Hinsichtlich der Ausbildung der Hohlkathodenentladung stehen verschiedene apparative Varianten zur Verfügung. So kann die Hohlkathode sowohl als, Rohr als auch als Anordnung aus zwei oder mehreren parallelen oder zueinander geneigten Platten ausgebildet sein. Ebenso ist es möglich, daß die Hohlkathode ein Metallnetz darstellt, wobei das eingeführte Gas das Netz ein- oder mehrmals durchströmt. Die Hohlkathodenentladung kann dabei so gesteuert werden, daß die Materialdeposition im Inneren der Hohlkathode stattfindet (sog. Inside Hollow Cathode, IHC) . Eine weite- re Verfahrensvariante sieht vor, daß die Hohlkathodenentladung an einem abrollenden Blechband erfolgt, wobei die Hohlkathodenentladung zwischen den zwei Bereichen des Blechs in einer Schlaufe betrieben wird. Die AnregungsSpannungen für die Hohlkathodenentladung liegen zwischen 1 V und 2000 V. Das Plasma kann dabei durch Gleich- oder Wechselspannung unterhalten werden. Als Frequenzbereich kommen der Nieder-, Mittel- und Hochfrequenzbereich in Frage. In gleicher Weise kann ein mit Mikrowellen gespeistes Plasma eingesetzt werden.Various apparatus variants are available with regard to the formation of the hollow cathode discharge. Thus, the hollow cathode can be designed both as a tube and as an arrangement of two or more parallel or inclined plates. It is also possible for the hollow cathode to be a metal mesh, the gas introduced flowing through the mesh one or more times. The hollow cathode discharge can be controlled so that the material deposition takes place inside the hollow cathode (so-called Inside Hollow Cathode, IHC). Another Re variant of the method provides that the hollow cathode discharge takes place on a rolling sheet metal strip, the hollow cathode discharge being operated in a loop between the two regions of the sheet metal. The excitation voltages for the hollow cathode discharge are between 1 V and 2000 V. The plasma can be maintained by direct or alternating voltage. The low, medium and high frequency range can be used as the frequency range. A plasma fed with microwaves can be used in the same way.
In gleicher Weise wird ein nach dem erfindungsgemäßen Verfahren hergestellter Katalysator bereitgestellt. Die poröse Trägerstruktur und die mindestens eine katalytisch aktive Substanz sind dabei als heterogen verteilte Dispersion nanogranularer Partikel auf dem Substrat abgeschieden. Die abgeschiedenen nanogranu- laren Partikel haben dabei einen Durchmesser zwischen 1 und 100 nm. Derartige Katalysatoren zeichnen sich durch ihre hohe Aktivität aus, wobei gleichzeitig der Anteil der verwendeten katalytischen aktiven Metalle sehr gering ist.In the same way, a catalyst produced by the process according to the invention is provided. The porous support structure and the at least one catalytically active substance are deposited on the substrate as a heterogeneously distributed dispersion of nanogranular particles. The deposited nanogranular particles have a diameter of between 1 and 100 nm. Such catalysts are notable for their high activity, at the same time the proportion of the catalytically active metals used is very low.
Verwendung findet das erfindungsgemäße Verfahren bei der Herstellung von Katalysatoren für die Verminderung der NOx- und CO-Emission bzw. dem Abbau von Rußpartikeln im Abga--.. von Verbrennungsmotoren. Ebenso können derart hergestellte Katalysatoren für die ka- thodenseitige Sauerstoffreduktion in Brennstoffzellen, insbesondere Polymerbrennstoffzellen (PEM) eingesetzt werde. Ein weiteres Anwendungsfeld betrifft die Methanolreformierung bei der Wasserstoffsynthese. Letztlich finden die Katalysatoren auch Anwendung bei der organischen Synthese. Nur beispielhaft soll hier die Synthese von Tetrahydrofuran aus n-Butan und die petrochemische Raffinierung genannt werden. Gleichzeitig sind aber auch sämtliche Syntheseverfahren in der Energie- und Antriebstechnik sowie der chemischen und pharmazeutischen Industrie als Anwendungsfelder geeignet.The method according to the invention is used in the production of catalysts for reducing the NO x and CO emissions or the breakdown of soot particles in the exhaust of internal combustion engines. Similarly, catalysts produced in this way can be used for the cathode-side oxygen reduction in fuel cells, in particular polymer fuel cells (PEM). Another field of application concerns methanol reforming in hydrogen synthesis. Ultimately, the catalysts are also used in organic synthesis. The synthesis of tetrahydrofuran from n-butane and the be called petrochemical refining. At the same time, however, all synthetic processes in energy and drive technology as well as in the chemical and pharmaceutical industries are suitable as fields of application.
Anhand der folgenden Figuren und des folgenden Beispiels soll der anmeldungsgemäße Gegenstand näher erläutert werden, ohne diesen auf diese speziellen Aus- führungsformen zu beschränken.The subject according to the application is intended to be explained in more detail with reference to the following figures and the following example, without restricting it to these special embodiments.
Fig. 1 zeigt schematisch zwei Varianten des erfindungsgemäßen Beschichtungsverfahrens .1 schematically shows two variants of the coating method according to the invention.
Fig. 2 zeigt eine weitere Variante des erfindungsgemäßen Verfahrens unter Verwendung zweier Hohlkathoden.2 shows a further variant of the method according to the invention using two hollow cathodes.
Fig. 3 zeigt schematisch eine weitere Variante, bei der die Beschichtung an einem abrollendenFig. 3 shows schematically a further variant in which the coating on a rolling
Band erfolgt.Tape is done.
In Fig. la) wird das Verfahren zur Beschichtung eines Monolithbleches 4 dargestellt. Über die Gaszufuhr 1 wird Gas durch die Hohlkathode 2 geleitet, wobei es zur Plasmaentladung 3 kommt. Das hierbei gebildete atomare Beschichtungsmaterial wird im Anschluß auf '"•-. dem Monolithblech 4 abgeschieden. ■£-The method for coating a monolith sheet 4 is shown in FIG. Gas is passed through the hollow cathode 2 via the gas supply 1, causing a plasma discharge 3. The atomic coating material formed in the process is then deposited on the monolith sheet 4. ■ £ -
In Fig. lb) wird eine Hohlkathode 2 aus zwei gegenüber liegenden parallelen Platten dargestellt. Über die Gaszuführung 1 wird das Gas zwischen den Platten hindurchgeleitet, wodurch eine Hohlkathodenentladung im Bereich 3 erfolgt. Als Substrat ist hier ein Mono- lith dargestellt, der aus mehreren wabenförmigen Segmenten besteht. Auf diese Weise kann nun eine Be- Schichtung der inneren und der äußeren Oberflächen dieser Segmente erfolgen.In Fig. Lb), a hollow cathode 2 is shown from two opposite parallel plates. The gas is passed between the plates via the gas supply 1, whereby a hollow cathode discharge takes place in the region 3. A monolith, which consists of several honeycomb segments, is shown here as the substrate. In this way, a loading Layering of the inner and outer surfaces of these segments are done.
Fig. 2 zeigt eine Variante, bei der zwei Hohlkathoden 2, 6 verwendet werden. Die Hohlkathode 2 dient dabei der Deposition der Trägerstruktur, während die Hohlkathode 6 der Deposition der katalytisch aktiven Substanz dient. Bei dieser Verfahrensvariante ist es möglich, heterogen verteilte Partikeldispersionen der katalytisch aktiven Substanz und der Trägerstruktur auf dem Substrat 4 zu erzeugen.Fig. 2 shows a variant in which two hollow cathodes 2, 6 are used. The hollow cathode 2 serves the deposition of the support structure, while the hollow cathode 6 serves the deposition of the catalytically active substance. In this variant of the method it is possible to produce heterogeneously distributed particle dispersions of the catalytically active substance and the support structure on the substrate 4.
In Fig. 3 ist eine Variante zur kontinuierlichen Durchführung des Beschichtungsvorganges dargestellt. Über Ablaufrollen 7 wird ein Band 2, z.B. aus metallischem Material, transportiert. Die Gaszufuhr 1 ist dabei so angeordnet, daß die Hohlkathodenentladung im Zwischenraum 3 zwischen den gegenüber liegenden Bandschnitten 2 erfolgt.3 shows a variant for the continuous implementation of the coating process. A tape 2, e.g. made of metallic material, transported. The gas supply 1 is arranged so that the hollow cathode discharge takes place in the intermediate space 3 between the opposite band cuts 2.
Beispielexample
Aktivierung von Monolith-BlechenActivation of monolith sheets
Ausgangsmaterial sind mit einer Washcoat aus Aluminiumoxid beschichtete Metallbleche, die derart gestaltet sind, daß sie Ineinander gesteckt werden können und so parallele, durchströmbare Kanäle bilden. Die Aufgabe des Verfahrens besteht darin, die Washcoat- Schicht durch Aufbringung einer nanogranularen Edelmetallschicht (Platin/Rhodium) zu aktivieren, Zu diesem Zweck werden die Ausgangsbleche mit einer Gas- flußsputterquelle beschichtet, deren Kathode aus dem zu deponierenden Edelmetall besteht. Für die Erzeugung der Metall-Partikel werde eine Gasflußsputterquelle vom Rohrtyp in einen Vakuumrezi- pienten eingesetzt. Dabei wird das aus Platin und Rhodium bestehende Rohr auf ein negatives elektri- sches Potential gelegt und von einer Seite mit Argon durchspült, Abmessungen der Rohrquelle, Argon-Durchfluß und Kammergesamtdruck werden dabei so aufeinander abgestellt, daß es in der Quelle zur Zündung einer selbsterhaltenden Plasmaentladung kommt. In einer typischen Anordnung wird die Rohrquelle mit einem Argonvolumenstrom von einem Standardliter pro Minute durchspült und es stellt sich - je nach Saugleistung des Pumpstand und Größe das Rezipienten - ein Gesamtdruck von 0,5 mbar ein. Die Hohlkathode habe einen Innendurchmesser von 30 mm und werden mit einer e- lektrischen Leistung von 2 kW beaufschlagt, die der Aufrechterhaltung der Plasmaentladung dient, Durch Kathodenzerstäubung werden einzelne Atome aus der Rohr-Hohlkathode herausgeschlagen und mit dem Gas- ström herausgetragen, Dabei kommt es in der Gas- Plasma-Phase durch Stöße der Metall-Atome zur Bildung von nanometergroßen Partikeln, derenThe starting material are metal sheets coated with an aluminum oxide washcoat, which are designed in such a way that they can be plugged into one another and thus form parallel, flowable channels. The task of the process is to activate the washcoat layer by applying a nanogranular noble metal layer (platinum / rhodium). For this purpose, the starting sheets are coated with a gas flow sputter source, the cathode of which consists of the noble metal to be deposited. For the generation of the metal particles, a gas flow sputtering source of the tube type is used in a vacuum recipe. The tube consisting of platinum and rhodium is placed at a negative electrical potential and flushed with argon from one side. Dimensions of the tube source, argon flow and total chamber pressure are adjusted so that they are in the source to ignite a self-sustaining plasma discharge comes. In a typical arrangement, the tube source is flushed with an argon volume flow of one standard liter per minute and, depending on the suction power of the pumping station and the size of the recipient, a total pressure of 0.5 mbar is established. The hollow cathode has an inner diameter of 30 mm and is supplied with an electrical power of 2 kW, which is used to maintain the plasma discharge. Cathode sputtering knocks out individual atoms from the hollow tube cathode and carries them out with the gas flow in the gas-plasma phase by collisions of the metal atoms to form nanometer-sized particles whose
Größenverteilungsfunktion durch den Ar-Durchfluß, die an der Rohrquelle anliegende Leistung, die Entfernung zwischen Quelle und Blech und andere Prozeßparameter gezielt eingestellt werden kann. In einer Entfernung von einigen Zentimetern trifft der partikelhaltige Argon-Strom auf die Monolithbleche, wo die Edelϊϊe- tallpartikel auf der Aluminiumoxid-Washcoat abge- schieden werden. Die Dichte der Partikel wird über die Zeitdauer eingestellt, den man den Prozeß auf das Monolithblech einwirken läßt.Size distribution function through the Ar flow, the power applied to the pipe source, the distance between the source and the plate and other process parameters can be set in a targeted manner. At a distance of a few centimeters, the particle-containing argon stream hits the monolith sheets, where the precious metal particles are deposited on the aluminum oxide washcoat. The density of the particles is adjusted over the period of time that the process is allowed to act on the monolith sheet.
Die Ausführung des Verfahrens kann auch dergestalt sein, daß der Gasstrom hinter der Gasflußsputterquelle direkt auf die Öffnungen des Monolithen oder eines Segmentes des Monolithen gerichtet wird und die Aktivierung der Washcoat-Schicht durch eine Innenbe- schichtung mit Edelmetall oder Edelmetallpartikeln erfolgt. The execution of the method can also be such that the gas flow behind the gas flow sputter source directly onto the openings of the monolith or one Segment of the monolith is directed and the activation of the washcoat layer is carried out by an inner coating with precious metal or precious metal particles.

Claims

Patentansprücheclaims
1. Verfahren zur Herstellung von Katalysatoren, bei dem auf einem Substrat eine poröse Trägerstruk- tur und/oder mindestens eine katalytisch aktive1. A process for the preparation of catalysts, in which a porous support structure and / or at least one catalytically active one on a substrate
Substanz abgeschieden wird,Substance is deposited,
d a d u r c h g e k e n n z e i c h n e t ,characterized ,
dass die Abscheidung mittels einer Plasmabehandlung unter Ausnutzung des Hohlkathodeneffekts erfolgt.that the deposition takes place by means of a plasma treatment using the hollow cathode effect.
Verfahren nach Anspruch 1,Method according to claim 1,
dadurch gekennzeichnet, dass die poröse Trägerstruktur und/oder die mindestens eine katalytisch aktive Substanz in Form von nanogranularen Partikeln abgeschieden wird.characterized in that the porous support structure and / or the at least one catalytically active substance is deposited in the form of nanogranular particles.
Verfahren nach Anspruch 2,Method according to claim 2,
dadurch gekennzeichnet, dass die nanogranularen Partikel einen Durchmesser zwischen 1 und 100 nm aufweisen.characterized in that the nanogranular particles have a diameter between 1 and 100 nm.
. Verfahren nach mindestens einem der Ansprüche 1 bis 3,, Method according to at least one of claims 1 to 3,
dadurch gekennzeichnet, dass als katalytische aktive Substanzen Übergangsmetalle und/oder deren Verbindungen eingesetzt werden. Verfahren nach mindestens einem der Ansprüche 1 bis 4,characterized in that transition metals and / or their compounds are used as catalytically active substances. Method according to at least one of claims 1 to 4,
dadurch gekennzeichnet, dass zur Herstellung der porösen Trägerstruktur Metallverbindungen, z.B. Metalloxide oder Metallhydroxide, verwendet werden.characterized in that for the production of the porous support structure metal compounds, e.g. Metal oxides or metal hydroxides can be used.
6. Verfahren nach mindestens einem der Ansprüche 1 bis 5,6. The method according to at least one of claims 1 to 5,
dadurch gekennzeichnet, dass als Substrat ein Monolith eingesetzt wird.characterized in that a monolith is used as the substrate.
7. Verfahren nach mindestens einem der Ansprüche 1 bis 57. The method according to at least one of claims 1 to 5
dadurch gekennzeichnet, dass als Substrat Netze, Drahtgeflechte, Stahlwolle, Metallgaze, Glasge- webe, Pulver, Aktivkohle, Kohlenstoff-characterized in that as substrate nets, wire mesh, steel wool, metal gauze, glass fabric, powder, activated carbon, carbon
Nanoröhrchen oder Kugeln mit Durchmessern zwischen 100 nm und 1 cm verwendet werden.Nanotubes or spheres with diameters between 100 nm and 1 cm can be used.
8. Verfahren nach mindestens einem der Ansprüche 1 bis 7,8. The method according to at least one of claims 1 to 7,
dadurch gekennzeichnet, dass ein metallisches oder ein keramisches Substrat, z.B. aus Aluminiumoxid oder Cordierit, verwendet wird. characterized in that a metallic or a ceramic substrate, for example made of aluminum oxide or cordierite, is used.
9. Verfahren nach mindestens einem der Ansprüche 1 bis 8,9. The method according to at least one of claims 1 to 8,
dadurch gekennzeichnet, dass zunächst die poröse Trägerstruktur und im Anschluß die mindestens eine katalytisch aktive Substanz abgeschieden wird.characterized in that first the porous support structure and then the at least one catalytically active substance is deposited.
10. Verfahren nach mindestens einem der Ansprüche 9 oder 10,10. The method according to at least one of claims 9 or 10,
dadurch gekennzeichnet, dass das Substrat durch Schrägbedampfung oder Abscheidung ohne elektrische Vorspannung mit einer porösen Trägerstruk- tur versehen wird.characterized in that the substrate is provided with a porous support structure by oblique vapor deposition or deposition without electrical bias.
11. Verfahren nach Anspruch 9,11. The method according to claim 9,
dadurch gekennzeichnet, dass die mindestens eine katalytisch aktive Substanz in Form leichtflüchtiger Precursor in Hohlräume der porösen Trägerstruktur eingebracht, in dem dort betriebenen Plasma zersetzt und auf der inneren Oberfläche der Hohlräume abgeschieden wird.characterized in that the at least one catalytically active substance in the form of volatile precursors is introduced into cavities of the porous support structure, is decomposed in the plasma operated there and is deposited on the inner surface of the cavities.
12. Verfahren nach mindestens einem der Ansprüche 1 bis 8,12. The method according to at least one of claims 1 to 8,
dadurch gekennzeichnet, dass die Abscheidung der porösen Trägerstruktur und der mindestens einen katalytisch aktiven Substanz simultan unter Ausbildung einer Partikeldispersion erfolgt. characterized in that the deposition of the porous support structure and the at least one catalytically active substance takes place simultaneously with the formation of a particle dispersion.
13. Verfahren nach mindestens einem der Ansprüche 1 bis 12,13. The method according to at least one of claims 1 to 12,
dadurch gekennzeichnet, dass die poröse Struktur durch Abscheidung einer Dispersion zweier Phasen auf dem Substrat erfolgt, wobei im Anschluß eine der beiden Phasen unter Ausbildung der Hohlräume entfernt wird.characterized in that the porous structure takes place by depositing a dispersion of two phases on the substrate, one of the two phases subsequently being removed to form the cavities.
14. Verfahren nach Anspruch 13,14. The method according to claim 13,
dadurch gekennzeichnet, dass die eine Phase durch chemisches Ätzen oder Plasma-Ätzen entfernt wird.characterized in that the one phase is removed by chemical etching or plasma etching.
15. Verfahren nach mindestens einem der Ansprüche 13 oder 14,15. The method according to at least one of claims 13 or 14,
dadurch gekennzeichnet, dass die Porosität über das Volumenverhältnis der beiden Phasen einstellbar ist.characterized in that the porosity is adjustable via the volume ratio of the two phases.
16. Verfahren nach mindestens einem der Ansprüche 1 bis 15,16. The method according to at least one of claims 1 to 15,
dadurch gekennzeichnet, dass die Plasmabehandlung durch Kathodenzerstäubung des Beschich- tungsmaterials als physikalische Gasphasenabscheidung (PVD) erfolgt. characterized in that the plasma treatment is carried out by sputtering the coating material as physical vapor deposition (PVD).
17. Verfahren nach Anspruch 16,17. The method according to claim 16,
dadurch gekennzeichnet, dass die Plasmabehandlung durch Kathodenzerstäubung des Beschich- tungsmaterials und chemische Reaktion mit einer reaktiven Gaskomponente als reaktive PVD erfolgt.characterized in that the plasma treatment is carried out by sputtering the coating material and chemical reaction with a reactive gas component as reactive PVD.
18. Verfahren nach mindestens einem der Ansprüche 1 bis 15,18. The method according to at least one of claims 1 to 15,
dadurch gekennzeichnet, dass die Plasmabehandlung durch chemische Reaktion des zugeführten Gases als chemische Gasphasenabscheidung (CVD) erfolgt.characterized in that the plasma treatment is carried out by chemical reaction of the supplied gas as chemical vapor deposition (CVD).
19. Verfahren nach mindestens einem der Ansprüche 1 bis 18,19. The method according to at least one of claims 1 to 18,
dadurch gekennzeichnet, dass die Plasmabehandlung bei einem Arbeitsdruck zwischen 0,01 mbar und 1 bar mbar, bevorzugt zwischen 0,1 mbar und 1 mbar erfolgt.characterized in that the plasma treatment is carried out at a working pressure between 0.01 mbar and 1 bar mbar, preferably between 0.1 mbar and 1 mbar.
20. Katalysator hergestellt durch das Verfahren nach mindestens einem der Ansprüche 1 bis 19.20. A catalyst produced by the process according to at least one of claims 1 to 19.
21. Katalysator nach Anspruch 18,21. A catalyst according to claim 18,
dadurch gekennzeichnet, dass die poröse Trägerstruktur und die mindestens eine katalytisch ak¬ tive Substanz als heterogen verteilte Dispersion nanogranularer Partikel auf dem Substrat abge- schieden ist .characterized in that the porous support structure and the at least one catalytically ak ¬ tive substance off as a heterogeneous distributed dispersion nanogranularer particles on the substrate is divorced.
22. Katalysator nach mindestens einem der Ansprüche 20 oder 21,22. A catalyst according to at least one of claims 20 or 21,
dadurch gekennzeichnet, dass die nanogranularen Partikel einen Durchmesser zwischen 1 und 100 nm aufweisen.characterized in that the nanogranular particles have a diameter between 1 and 100 nm.
23. Verwendung des Verfahrens nach mindestens einem der Ansprüche 1 bis 19 zur Herstellung von Katalysatoren für die Verminderung der NOx- und CO- Emission bzw. dem Abbau von Rußpartikeln im Abgas von Verbrennungsmotoren.23. Use of the method according to at least one of claims 1 to 19 for the production of catalysts for reducing the NO x and CO emissions or the degradation of soot particles in the exhaust gas of internal combustion engines.
24. Verwendung des Verfahrens nach mindestens einem der Ansprüche 1 bis 19 zur Herstellung von Katalysatoren für die kathodenseitige Sauerstoffreduktion in Brennstoffzellen.24. Use of the method according to at least one of claims 1 to 19 for the production of catalysts for the cathode-side oxygen reduction in fuel cells.
25. Verwendung des Verfahrens nach mindestens einem der Ansprüche 1 bis 19 zur Herstellung von Katalysatoren für die Methanolreformierung zur WasserstoffSynthese .25. Use of the method according to at least one of claims 1 to 19 for the production of catalysts for methanol reforming for hydrogen synthesis.
26. Verwendung des Verfahrens nach mindestens einem der Ansprüche 1 bis 19 zur Herstellung von Katalysatoren für die organische Synthese. 26. Use of the method according to at least one of claims 1 to 19 for the preparation of catalysts for organic synthesis.
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