EP2632587A1 - Diesel oxidation catalyst - Google Patents

Diesel oxidation catalyst

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Publication number
EP2632587A1
EP2632587A1 EP11774020.9A EP11774020A EP2632587A1 EP 2632587 A1 EP2632587 A1 EP 2632587A1 EP 11774020 A EP11774020 A EP 11774020A EP 2632587 A1 EP2632587 A1 EP 2632587A1
Authority
EP
European Patent Office
Prior art keywords
catalytically active
active material
oxidation catalyst
diesel oxidation
material according
Prior art date
Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
Withdrawn
Application number
EP11774020.9A
Other languages
German (de)
French (fr)
Inventor
Frank-Walter Schuetze
Anke Woerz
Gerald Jeske
Current Assignee (The listed assignees may be inaccurate. Google has not performed a legal analysis and makes no representation or warranty as to the accuracy of the list.)
Umicore AG and Co KG
Original Assignee
Umicore AG and Co KG
Priority date (The priority date is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the date listed.)
Filing date
Publication date
Application filed by Umicore AG and Co KG filed Critical Umicore AG and Co KG
Priority to EP11774020.9A priority Critical patent/EP2632587A1/en
Publication of EP2632587A1 publication Critical patent/EP2632587A1/en
Withdrawn legal-status Critical Current

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    • 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
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • 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
    • B01D53/92—Chemical or biological purification of waste gases of engine exhaust gases
    • B01D53/94—Chemical or biological purification of waste gases of engine exhaust gases by catalytic processes
    • B01D53/944—Simultaneously removing carbon monoxide, hydrocarbons or carbon making use of oxidation 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
    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
    • B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
    • B01J23/48—Silver or gold
    • B01J23/52—Gold
    • 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
    • B01J23/66—Silver or gold
    • 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
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/08—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the faujasite type, e.g. type X or Y
    • 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
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/18—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type
    • 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
    • B01J29/00—Catalysts comprising molecular sieves
    • B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
    • B01J29/06—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof
    • B01J29/70—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65
    • B01J29/7007—Zeolite Beta
    • B01J35/393—
    • B01J35/397—
    • B01J35/398—
    • B01J35/51—
    • B01J35/56—
    • 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
    • B01J37/0009—Use of binding agents; Moulding; Pressing; Powdering; Granulating; Addition of materials ameliorating the mechanical properties of the product catalyst
    • B01J37/0027—Powdering
    • B01J37/0045—Drying a slurry, e.g. spray drying
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
    • B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/0201—Impregnation
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/10—Noble metals or compounds thereof
    • B01D2255/102—Platinum group metals
    • B01D2255/1021—Platinum
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/10—Noble metals or compounds thereof
    • B01D2255/102—Platinum group metals
    • B01D2255/1023—Palladium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/10—Noble metals or compounds thereof
    • B01D2255/106—Gold
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/206—Rare earth metals
    • B01D2255/2065—Cerium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/207—Transition metals
    • B01D2255/20715—Zirconium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/20—Metals or compounds thereof
    • B01D2255/209—Other metals
    • B01D2255/2092—Aluminium
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/40—Mixed oxides
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/50—Zeolites
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/902—Multilayered catalyst
    • B01D2255/9022—Two layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/912—HC-storage component incorporated in the catalyst
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/92—Dimensions
    • B01D2255/9202—Linear dimensions
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2258/00—Sources of waste gases
    • B01D2258/01—Engine exhaust gases
    • B01D2258/012—Diesel engines and lean burn gasoline engines
    • Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
    • Y10—TECHNICAL SUBJECTS COVERED BY FORMER USPC
    • Y10T—TECHNICAL SUBJECTS COVERED BY FORMER US CLASSIFICATION
    • Y10T29/00—Metal working
    • Y10T29/49—Method of mechanical manufacture
    • Y10T29/49345—Catalytic device making

Definitions

  • the invention relates to a catalytically active material containing platinum, palladium and gold as catalytically active components, and to a diesel oxidation catalyst containing this catalytically active material.
  • the exhaust gas from diesel engines typically contains carbon monoxide CO, hydrocarbons HC and nitrogen oxides NO x , and a relatively high oxygen content of up to 15% by volume.
  • particulate emissions are contained, which consist predominantly of solid carbon black residues and optionally organic agglomerates (so-called "Volatile Organic Fraction” VOF or "Soluble Organic Fraction” SOF) and result from a partially incomplete fuel combustion in the cylinder.
  • the harmful gases carbon monoxide and hydrocarbons can be rendered harmless by oxidation to a suitable oxidation catalyst.
  • Diesel particulate filters with and without catalytically active coating are suitable aggregates for removing particulates.
  • Nitrogen oxides are today preferably removed by selective catalytic reduction (SCR) to nitrogen with ammonia liberated from urea solution as a reducing agent ("denitrification" of the exhaust gas), wherein urea solution must be added as an excipient from a source independent of the engine to the exhaust gas.
  • SCR selective catalytic reduction
  • urea solution must be added as an excipient from a source independent of the engine to the exhaust gas.
  • Diesel oxidation catalysts for the oxidative removal of carbon monoxide (CO), gaseous hydrocarbons (HC) and optionally VOF have long been known in the art and described in various embodiments.
  • CO carbon monoxide
  • HC gaseous hydrocarbons
  • VOF optionally VOF
  • platinum and / or palladium are used as oxidation-catalytically active components in these catalysts. Whether one of the precious metals is used alone or in combination with others and in what proportion of the precious metals may be present depends not infrequently on the design of the exhaust system in which the catalyst is to be used, since the precious metals, the various, in the system catalyze possible oxidation reactions with different effectiveness.
  • platinum is suitable particularly good for the oxidation of nitrogen monoxide contained in the raw exhaust NO to nitrogen dioxide N0 2
  • palladium has the highest oxidation activity of all precious metals over short-chain hydrocarbons (HC).
  • Another oxidation-active noble metal is gold, which is known in the prior art, for example, as being excellent in catalyzing the oxidation of carbon monoxide CO to CO 2 even at very low temperatures ( ⁇ 100 ° C.).
  • Gold-containing catalysts for the oxidative aftertreatment of diesel exhaust have also been described.
  • WO 2009/074308 and EP 2 070 581 A1 disclose a diesel oxidation catalyst which has a coating on a catalytically inert carrier body (for example honeycomb body) which contains platinum, palladium and a promoter applied to a carrier oxide and zeolite.
  • a catalytically inert carrier body for example honeycomb body
  • platinum palladium
  • a promoter applied to a carrier oxide and zeolite.
  • gold can be used as the promoter.
  • EP 1 925 362, US 2008/0124514, US Pat. No. 7,517,826 and US 7,534,738 disclose diesel oxidation catalysts in which a mixture of a first and a second catalytically active material is present.
  • a first and a second catalytically active material are present.
  • palladium is supported, besides gold, on a lanthana stabilized alumina.
  • platinum is optionally applied together with palladium or bismuth onto lanthanum oxide-stabilized aluminum oxide.
  • the two catalytically active materials may be applied to an inert honeycomb body as a homogeneous powder mixture in a catalytically active layer or in the form of several different coatings (e.g., as a zone catalyst or layered catalyst).
  • zeolite-containing interlayers and / or layers comprising palladium supported on cerium oxide can furthermore be present.
  • WO 2009/106849 discloses diesel oxidation catalysts which are distinguished inter alia by high conversion rates for methane and preferably contain palladium and gold as active components in alloyed form.
  • palladium ex palladium nitrate and gold ex tetrachloroauric acid are applied by precipitation and calcination on alumina as support material. From the powder component thus obtained, a suspension for coating conventional natural monocyteßwaben redesign can be prepared as a catalyst substrate.
  • WO 2008/117941 discloses diesel oxidation catalysts characterized by improved HC oxidation activity and containing gold alloyed palladium on alumina as the first catalytically active material besides palladium alloyed platinum on alumina as the second catalytically active material.
  • alumina it is also possible to use other inorganic carrier oxides, such as, for example, silicon dioxide, aluminum silicate, silicates, titanium oxide, zirconium oxide, SiC and carbon black.
  • a diesel oxidation catalyst prepared from the mixture of the catalytically active materials may further contain oxygen-storing rare earth metal oxides.
  • US 2008 / 125308A1 describes catalytic converters which comprise a platinum-containing catalyst and a palladium-and-gold-containing catalyst and which may additionally contain zeolite as an absorbent for hydrocarbons.
  • the two catalysts are arranged in different catalytically active zones of the catalytic converter in such a way that the exhaust gas first meets the platinum-containing catalyst. This is achieved by means of conventional layer or zone arrangement of the two catalysts or by the fact that both catalysts are supported on different monoliths.
  • a catalytically active material consisting of an inner core (1) and an outer shell (2) surrounding this core, wherein the core is formed of palladium and gold, which are fixed together on a first carrier oxide, and wherein the Shell contains platinum, which is fixed on a second carrier oxide.
  • FIG. 1 shows the structure of the catalytically active material according to the invention of inner core (1) and outer shell (2).
  • the special structure of the catalytically active material ensures an intensive interaction between palladium and gold, which contributes significantly to the improvement in the CO conversion performance of the resulting catalyst.
  • This microscopic separation of the palladium-gold-containing phase from the platinum-containing phase avoids a direct interaction between platinum and gold, which, in the case of prior art catalysts having comparable compositions, not infrequently leads to irreversible deactivation phenomena after an extended period of use the platinum-containing component leads.
  • the noble metals palladium and gold present in the core of the catalytically active material according to the invention are preferably in the form of alloyed metal clusters.
  • the weight ratio of palladium to gold in the core of the catalytically active material is preferably 0.9-1: 1: 1, more preferably 1: 1.
  • the outer shell (2) of the catalytically active material according to the invention is formed in one embodiment of platinum fixed on the second carrier oxide. In preferred embodiments, however, contains the outer shell (2) as another noble metal palladium. This can be present in mixed form and / or in alloyed form with the platinum also present therein. Particularly preferably, at least part of the palladium present in the shell is present in platinum-alloyed form. If both noble metals are used in the outer shell, the weight ratio of platinum to palladium is preferably between 12: 1 and 1: 1, more preferably in the range 6: 1 to 2: 1 and most preferably 4: 1.
  • the outer shell (2) preferably envelops the inner core (1) almost completely and particularly preferably completely.
  • the weight ratio of the precious metals contained in outer shell (2) and inner core (1) is platinum: palladium: gold in the particularly preferred embodiments 1: 1: 1.
  • the outer shell (2) in addition to platinum or next to platinum and Palladium also a zeolite compound with HC-storing properties.
  • the catalytically active material according to the invention is thus equipped with a hydrocarbon storage and retention function, which requires that hydrocarbons which can not be fully reacted at operating temperatures below the ignition temperature for the hydrocarbon oxidation, not "break through” the resulting diesel oxidation catalyst, but in the inventive catalytically active material are retained until the HC conversion sufficient temperatures are reached.
  • the zeolite compounds are preferably selected from the group consisting of FAU, MOR, zeolite beta, MFI and mixtures thereof. They are in the outer shell (2) preferably at 10 to 60 wt .-%, more preferably from 20 to 50 wt .-% and most preferably from 25 to 35 wt .-% before, in each case based on the total weight of the outer Shell (2).
  • the first and / or second carrier oxide used is preferably one from the group consisting of cerium oxide, zirconium oxide, aluminum oxide, silicon oxide and mixed oxides and / or mixtures thereof. Particularly preferred are aluminum oxide, aluminum silicates and aluminum-silicon mixed oxides.
  • the particles of the catalytically active material according to the invention which, as described above, of inner core (1) and outer shell (2) are each of different composition are approximately spherical and preferably have an average diameter of 1 to 12 ⁇ , more preferably from 3 to 8 ⁇ on.
  • the volume fraction of the core on a spherical particle in the preferred embodiments of the catalytically active material according to the invention is preferably 50 to 80%, particularly preferably about 60%.
  • the catalytically active material according to the invention is prepared by processes known to those skilled in the art.
  • the optionally graded co-precipitation and / or co-impregnation of the noble metals from water-soluble precursors to carrier oxides and the systematic grinding of pulverulent precursors to form defined conglomerates can be used.
  • pH values in the strongly acidic range ie pH ⁇ 4
  • pH values in the strongly basic range ie pH> 8
  • acetic acid to lower the pH and organic bases such as tetraethylammonium hydroxide (TEAH) to raise the pH.
  • TEAH tetraethylammonium hydroxide
  • the present invention also provides a diesel oxidation catalyst comprising a catalytically inert support body and at least one catalytically active coating applied thereto, characterized in that the coating contains a catalytically active material as described above.
  • a coating suspension of the above-described catalytically active material is prepared by processes known to those skilled in the art, which can be applied to an inert support body with likewise known coating methods (immersion, suction and / or pumping).
  • the resulting catalyst then consists of a catalytically inert carrier body and at least one catalytically active coating applied thereto, which contains the catalytically active material according to the invention.
  • the catalytically inert carrier body is preferably selected from the group of ceramic and metallic fürflußwaben redesign or from the group of ceramic Wandflußfiltersubstrate. If the catalytically active material according to the invention contains no or insufficient zeolite in the outer shell (2), it is also possible to add to the coating a zeolite compound having HC-storing properties selected from the group consisting of FAU, MOR, zeolite beta, MFI and mixtures thereof. The proportion of zeolite compound in the coating is then preferably 15 to 45 wt .-%, particularly preferably 20 to 30 wt .-%, based on the total weight of this coating.
  • the entire zeolitic material is present in the outer shell (2) of the catalytically active material, in particular in a proportion of 15 to 45 wt .-%, based on the total weight of the catalytically active material.
  • the diesel oxidation catalyst according to the invention is suitable for the oxidative reduction of carbon monoxide and / or hydrocarbons in the exhaust gas of diesel engines.
  • the exhaust gas is passed over the diesel oxidation catalyst.
  • the diesel oxidation catalyst is preferably used as part of an exhaust gas purification system, which is also the subject of the present invention.
  • the diesel oxidation catalyst according to the invention is preferably arranged close to the engine.
  • a diesel particle filter is preferably connected downstream in the flow direction of the exhaust gas to be cleaned.
  • the diesel particulate filter can be followed by a denitration stage, so that the effective reduction of all legally contained pollutants contained in the diesel exhaust gas is ensured.
  • Suitable diesel particulate filters and denitration stages such as NO x storage and SCR catalysts are described in the literature and known to the person skilled in the art.
  • the diesel oxidation catalyst according to the invention is characterized in particular by very high CO conversion rates and by an extraordinarily high thermal aging stability and thus has important properties that are suitable for application in modern emission control systems for fulfilling, for example, the legal emission specifications known under "Euro 5" and "Euro 6" are inevitable. Furthermore, the catalyst of the invention shows cost advantages over the otherwise customary catalysts, which generally contain a significantly higher proportion of the most expensive noble metal platinum. Exemplary embodiment:
  • alumina is suspended in water. With stirring, tetrachloroauric acid and palladium nitrate solution are added to the suspension. After an adsorption time of about one hour, the solid contained in the suspension is separated by filtration from the liquid phase and washed with demineralized water until no significant amounts of Chloridlonen are more detectable in the wash water. To remove optionally adsorbed chloride ions, the solid is then washed once more with dilute, aqueous ammonia solution. Then the solid is dried at about 120 ° C over the course of 4 hours followed by calcination at 400 ° C for a period of 3 Hours. The powder thus obtained forms the "core material" for the catalytically active material according to the invention to be produced in the last stage.
  • Step 2 Making the "shell material”.
  • the "core material" prepared in step 1 is suspended in water and optionally ground until an average particle size of 4-8 ⁇ m is achieved with the narrowest possible particle size distribution prepared "shell material” also suspended in water and optionally milled until an average particle size of 1 - 2 ⁇ is achieved with the narrowest possible particle size distribution.
  • the suspension thus obtained is admixed with a suitable zeolite compound for storing the hydrocarbons present in the exhaust gas, which likewise has the finest possible particle size distribution and has, if appropriate, been correspondingly ground in a separate preparation step.
  • the two suspensions obtained above are combined and subjected to a controlled spray drying.
  • the finely divided particles of the "shell material” form a shell around the coarser particles of the "core material”.
  • Step 4 Preparation of the catalyst according to the invention:
  • the catalytically active material obtained in step 3 is resuspended in water and applied to a conventional ceramic or metallic fürflußwaben redesign with a known in the art, usual dipping, suction or pumping.
  • the amount of Coating suspension and the number of coating steps according to the method should be selected so that the honeycomb body after drying at 120 ° C and a calcination at 400 ° C over the period of 3 hours, a coating amount of 130 to 150 grams of solid per liter of component volume.

Abstract

The present invention relates to a catalytically active material, consisting of an inner core (1) and an outer shell (2) enveloping said core, wherein the core is formed of palladium and gold, which together are fixed on a first carrier oxide, and wherein the shell contains platinum, which is fixed on a second carrier oxide. The invention further relates to a diesel oxidation catalyst containing said catalytically active material, and to an exhaust gas cleaning system comprising said diesel oxidation catalyst.

Description

Dieseloxidationskatalysator  Diesel oxidation catalyst
Beschreibung description
Die Erfindung betrifft ein katalytisch aktives Material, das als katalytisch aktive Kom- ponenten Platin, Palladium und Gold enthält, sowie einen dieses katalytisch aktive Material enthaltenden Dieseloxidationskatalysator. The invention relates to a catalytically active material containing platinum, palladium and gold as catalytically active components, and to a diesel oxidation catalyst containing this catalytically active material.
Das Abgas von Dieselmotoren enthält typischerweise Kohlenmonoxid CO, Kohlenwasserstoffe HC und Stickoxide NOx, sowie einen relativ hohen Sauerstoffgehalt von bis zu 15 Vol.-%. Außerdem sind Partikelemissionen enthalten, die überwiegend aus festen Rußrückständen und gegebenenfalls organischen Agglomeraten (sog.„Volatile Organic Fraction" VOF oder„Soluble Organic Fraction" SOF) bestehen und aus einer partiell unvollständigen Kraftstoffverbrennung im Zylinder herrühren. Die Schadgase Kohlenmonoxid und Kohlenwasserstoffe können durch Oxidation an einem geeigneten Oxidationskatalysator unschädlich gemacht werden. Zur Entfernung der Partikelemis- sionen sind Dieselpartikelfilter mit und ohne katalytisch aktive Beschichtung geeignete Aggregate. Stickoxide werden heute bevorzugt durch selektive katalytische Reduktion (Selective Catalytic Reduction SCR) zu Stickstoff mit aus Harnstofflösung freigesetztem Ammoniak als Reduktionsmittel entfernt („Entstickung" des Abgases), wobei Harnstofflösung als Hilfsstoff aus einer vom Motor unabhängigen Quelle dem Abgas zuge- fügt werden muß. Um die künftig in Europa, USA und Japan geltenden Abgasgrenzwerte einhalten zu können, werden häufig systemische Kombinationen dieser Abgasreinigungstechnologien eingesetzt. The exhaust gas from diesel engines typically contains carbon monoxide CO, hydrocarbons HC and nitrogen oxides NO x , and a relatively high oxygen content of up to 15% by volume. In addition, particulate emissions are contained, which consist predominantly of solid carbon black residues and optionally organic agglomerates (so-called "Volatile Organic Fraction" VOF or "Soluble Organic Fraction" SOF) and result from a partially incomplete fuel combustion in the cylinder. The harmful gases carbon monoxide and hydrocarbons can be rendered harmless by oxidation to a suitable oxidation catalyst. Diesel particulate filters with and without catalytically active coating are suitable aggregates for removing particulates. Nitrogen oxides are today preferably removed by selective catalytic reduction (SCR) to nitrogen with ammonia liberated from urea solution as a reducing agent ("denitrification" of the exhaust gas), wherein urea solution must be added as an excipient from a source independent of the engine to the exhaust gas. Systemic combinations of these exhaust gas purification technologies are often used to meet future emission limits in Europe, USA and Japan.
Dieseloxidationskatalysatoren zur oxidativen Entfernung von Kohlenmonoxid (CO), gasförmigen Kohlenwasserstoffen (HC) und gegebenenfalls VOF sind im Stand der Technik seit langem bekannt und in den verschiedensten Ausführungsformen beschrieben worden. Zumeist werden in diesen Katalysatoren Platin und/oder Palladium als oxidationskatalytisch aktive Komponenten eingesetzt. Ob eines der Edelmetalle alleine oder in Kombination mit anderen zum Einsatz kommt und in welchem Mengenverhältnis die Edelmetalle gegebenenfalls zueinander vorliegen, hängt nicht selten von der Ausgestaltung des Abgassystems ab, in dem der Katalysator zum Einsatz kommen soll, da die Edelmetalle die verschiedenen, im System möglichen Oxidationsreaktionen mit unterschiedlicher Effektivität katalysieren. So eignet sich Platin beispielsweise besonders gut zur Oxidation von im Rohabgas enthaltenen Stickstoffmonoxid NO zu Stickstoffdioxid N02, während Palladium die höchste Oxidationsaktivität aller Edelmetalle gegenüber kurzkettigen Kohlenwasserstoffen (HC) aufweist. Diesel oxidation catalysts for the oxidative removal of carbon monoxide (CO), gaseous hydrocarbons (HC) and optionally VOF have long been known in the art and described in various embodiments. In most cases, platinum and / or palladium are used as oxidation-catalytically active components in these catalysts. Whether one of the precious metals is used alone or in combination with others and in what proportion of the precious metals may be present depends not infrequently on the design of the exhaust system in which the catalyst is to be used, since the precious metals, the various, in the system catalyze possible oxidation reactions with different effectiveness. For example, platinum is suitable particularly good for the oxidation of nitrogen monoxide contained in the raw exhaust NO to nitrogen dioxide N0 2 , while palladium has the highest oxidation activity of all precious metals over short-chain hydrocarbons (HC).
Ein weiteres oxidationsaktives Edelmetall ist Gold, das im Stand der Technik beispiels- weise dafür bekannt ist, daß es die Oxidation von Kohlenmonoxid CO zu C02 bereits bei sehr niedrigen Temperaturen (< 100°C) hervorragend katalysiert. Auch Gold-haltige Katalysatoren zur oxidativen Nachbehandlung von Dieselabgasen sind bereits beschrieben worden. Another oxidation-active noble metal is gold, which is known in the prior art, for example, as being excellent in catalyzing the oxidation of carbon monoxide CO to CO 2 even at very low temperatures (<100 ° C.). Gold-containing catalysts for the oxidative aftertreatment of diesel exhaust have also been described.
So offenbart die WO 2009/074308 bzw. EP 2 070 581 A1 einen Dieseloxidationskatalysator, der eine Beschichtung auf einem katalytisch inerten Tragkörper (z.B. Waben körper) aufweist, die Platin, Palladium und einen Promotor aufgebracht auf einem Trägeroxid sowie Zeolith enthält. Als Promotor kann unter anderem Gold eingesetzt werden. For example, WO 2009/074308 and EP 2 070 581 A1 disclose a diesel oxidation catalyst which has a coating on a catalytically inert carrier body (for example honeycomb body) which contains platinum, palladium and a promoter applied to a carrier oxide and zeolite. Among others, gold can be used as the promoter.
EP 1 925 362, US 2008/0124514, US 7,517,826 und US 7,534,738 offenbaren Diesel- oxidationskatalysatoren, in denen eine Mischung aus einem ersten und einem zweiten katalytisch aktiven Material vorliegt. Zur Herstellung des ersten katalytisch aktiven Materials wird Palladium neben Gold auf einem mit Lanthanoxid stabilisierten Aluminiumoxid geträgert. Als zweites katalytisch aktives Material wird Platin gegebenenfalls gemeinsam mit Palladium oder Bismuth auf mit Lanthanoxid stabilisiertes Aluminiumoxid aufgebracht. Die beiden katalytisch aktiven Materialien können als homogene Pulvermischung in einer katalytisch aktiven Schicht oder in Form von mehreren, verschiedenen Beschichtungen (z.B. als Zonenkatalysator oder Schichtkatalysator) auf einen inerten Wabenkörper aufgebracht werden. Im Falle von Mehrschichtkatalysatoren können weiterhin Zeolith-haltige Zwischenschichten und/oder Schichten enthaltend Palladium geträgert auf Ceroxid enthalten sein. EP 1 925 362, US 2008/0124514, US Pat. No. 7,517,826 and US 7,534,738 disclose diesel oxidation catalysts in which a mixture of a first and a second catalytically active material is present. To produce the first catalytically active material, palladium is supported, besides gold, on a lanthana stabilized alumina. As a second catalytically active material, platinum is optionally applied together with palladium or bismuth onto lanthanum oxide-stabilized aluminum oxide. The two catalytically active materials may be applied to an inert honeycomb body as a homogeneous powder mixture in a catalytically active layer or in the form of several different coatings (e.g., as a zone catalyst or layered catalyst). In the case of multilayer catalysts, zeolite-containing interlayers and / or layers comprising palladium supported on cerium oxide can furthermore be present.
WO 2009/106849 offenbart Dieseloxidationskatalysatoren, die sich unter anderem durch hohe Konversionsraten für Methan auszeichnen und Palladium und Gold als aktive Komponenten bevorzugt in legierter Form enthalten. Zur Herstellung der Katalysatoren werden Palladium ex Palladiumnitrat und Gold ex Tetrachlorogoldsäure durch Fällung und Kalzination auf Aluminiumoxid als Trägermaterial aufgebracht. Aus der so erhaltenen Pulverkomponente kann eine Suspension zur Beschichtung herkömmlicher Durchflußwabenkörper als Katalysatorsubstrat hergestellt werden. Auch WO 2008/117941 offenbart Dieseloxidationskatalysatoren, die sich durch eine verbesserte HC-Oxidationsaktivität auszeichnen und mit Gold legiertes Palladium auf Aluminiumoxid als erstem katalytisch aktivem Material neben mit Palladium legiertem Platin auf Aluminiumoxid als zweitem katalytisch aktivem Material enthalten. Anstelle von Aluminiumoxid können auch andere anorganische Trägeroxide wie beispielsweise Siliziumdioxid, Aluminiumsilikat, Silikate, Titanoxid, Zirkonoxid, SiC und Ruß verwendet werden. Ein aus der Mischung der katalytisch aktiven Materialien hergestellter Diesel- oxidationskatalysator kann weiterhin Sauerstoff speichernde Seltenerdmetall-Oxide enthalten. US 2008/125308A1 beschreibt Abgaskatalysatoren, die einen Platin-haltigen Katalysator und einen Palladium und Gold-haltigen Katalysator umfassen und die daneben Zeolith als Absorbens für Kohlenwasserstoffe enthalten können. Die beiden Katalysatoren sind in verschiedenen katalytisch aktiven Zonen des Abgaskatalysators dergestalt angeordnet, dass das Abgas zuerst auf den Platin-haltigen Katalysator trifft. Dies wird mittels üblicher Schichten- oder Zonenanordnung der beiden Katalysatoren erreicht oder dadurch, dass beide Katalysatoren auf verschiedenen Monolithen geträgert sind. WO 2009/106849 discloses diesel oxidation catalysts which are distinguished inter alia by high conversion rates for methane and preferably contain palladium and gold as active components in alloyed form. To prepare the catalysts, palladium ex palladium nitrate and gold ex tetrachloroauric acid are applied by precipitation and calcination on alumina as support material. From the powder component thus obtained, a suspension for coating conventional Durchflußwabenkörper can be prepared as a catalyst substrate. Also, WO 2008/117941 discloses diesel oxidation catalysts characterized by improved HC oxidation activity and containing gold alloyed palladium on alumina as the first catalytically active material besides palladium alloyed platinum on alumina as the second catalytically active material. Instead of alumina, it is also possible to use other inorganic carrier oxides, such as, for example, silicon dioxide, aluminum silicate, silicates, titanium oxide, zirconium oxide, SiC and carbon black. A diesel oxidation catalyst prepared from the mixture of the catalytically active materials may further contain oxygen-storing rare earth metal oxides. US 2008 / 125308A1 describes catalytic converters which comprise a platinum-containing catalyst and a palladium-and-gold-containing catalyst and which may additionally contain zeolite as an absorbent for hydrocarbons. The two catalysts are arranged in different catalytically active zones of the catalytic converter in such a way that the exhaust gas first meets the platinum-containing catalyst. This is achieved by means of conventional layer or zone arrangement of the two catalysts or by the fact that both catalysts are supported on different monoliths.
Aufgabe der vorliegenden Erfindung ist es, einen Dieseloxidationskatalysator mit verbesserter CO-Oxidationsaktivität zur Verfügung zu stellen, der auch bei hoher thermi- scher Belastung unter Betriebsbedingungen eine verbesserte Langzeitstabilität aufweist. It is an object of the present invention to provide a diesel oxidation catalyst with improved CO oxidation activity, which has improved long-term stability even under high thermal load under operating conditions.
Die Aufgabe wird gelöst durch ein katalytisch aktives Material bestehend aus einem inneren Kern (1) und einer diesen Kern umhüllenden äußeren Schale (2), wobei der Kern gebildet wird aus Palladium und Gold, die gemeinsam auf einem ersten Trägeroxid fixiert sind, und wobei die Schale Platin enthält, welches auf einem zweiten Trägeroxid fixiert ist. The object is achieved by a catalytically active material consisting of an inner core (1) and an outer shell (2) surrounding this core, wherein the core is formed of palladium and gold, which are fixed together on a first carrier oxide, and wherein the Shell contains platinum, which is fixed on a second carrier oxide.
Figur 1 zeigt den Aufbau des erfindungsgemäßen katalytisch aktiven Materials aus innerem Kern (1) und äußerer Schale (2). FIG. 1 shows the structure of the catalytically active material according to the invention of inner core (1) and outer shell (2).
Durch den speziellen Aufbau des katalytisch aktiven Materials wird einerseits eine intensive Wechselwirkung zwischen Palladium und Gold gewährleistet, welche wesentlich zur Verbesserung der CO-Konvertierungsleistung des resultierenden Katalysators beiträgt. Andererseits wird durch die im katalytisch aktiven Material vorliegenden mikroskopische Separation der Palladium-Gold-haltigen Phase von der Platin-haltigen Phase eine direkte Wechselwirkung zwischen Platin und Gold vermieden, die bei Katalysatoren nach dem Stand der Technik, die vergleichbare Zusammensetzungen aufweisen, nach ausgedehnter zweckrelevanter Benutzungs- dauer nicht selten zu irreversiblen Deaktivierungserscheinungen der Platin-haltigen Komponente führt. Die Erfinder glauben, daß die im erfindungsgemäßen Material gewählte Form der mikroskopische Separation der Palladium-Gold-haltigen Phase und der Platin-haltigen Phase ein synergistisches Zusammenwirken dieser beiden kata- lytisch aktiven Phasen ermöglicht, was in einem katalytisch aktiven Material mit verbes- serter CO-Oxidationsaktivität und hervorragender HC-Konvertierungsaktivität bei zugleich exzellenter thermischer Alterungsstabilität resultiert. The special structure of the catalytically active material, on the one hand, ensures an intensive interaction between palladium and gold, which contributes significantly to the improvement in the CO conversion performance of the resulting catalyst. On the other hand, by the catalytically active material This microscopic separation of the palladium-gold-containing phase from the platinum-containing phase avoids a direct interaction between platinum and gold, which, in the case of prior art catalysts having comparable compositions, not infrequently leads to irreversible deactivation phenomena after an extended period of use the platinum-containing component leads. The inventors believe that the form of microscopic separation of the palladium-gold-containing phase and the platinum-containing phase chosen in the material according to the invention enables a synergistic interaction of these two catalytically active phases, which results in a catalytically active material with improved CO Oxidation activity and excellent HC conversion activity at the same time excellent thermal aging stability results.
Die im Kern des erfindungsgemäßen katalytisch aktiven Materials vorhandenen Edelmetalle Palladium und Gold liegen bevorzugt in Form von legierten Metallclustern vor. Das Gewichtsverhältnis von Palladium zu Gold im Kern des katalytisch aktiven Mate- rials liegt bevorzugt bei 0,9 - 1 , 1 : 1 , besonders bevorzugt bei 1 : 1. The noble metals palladium and gold present in the core of the catalytically active material according to the invention are preferably in the form of alloyed metal clusters. The weight ratio of palladium to gold in the core of the catalytically active material is preferably 0.9-1: 1: 1, more preferably 1: 1.
Die äußere Schale (2) des erfindungsgemäßen katalytisch aktiven Materials wird in einer Ausführungsform von Platin fixiert auf dem zweiten Trägeroxid gebildet. In bevorzugten Ausführungsformen enthält aber die äußere Schale (2) als weiteres Edelmetall Palladium. Dieses kann mit dem darin ebenfalls vorhandenen Platin in gemischter Form und/oder in legierter Form vorliegen. Besonders bevorzugt liegt wenigstens ein Teil des in der Schale vorhandenen Palladiums in mit Platin legierter Form vor. Werden beide Edelmetalle in der äußeren Schale eingesetzt, so liegt das Gewichtsverhältnis von Platin zu Palladium bevorzugt zwischen 12 : 1 und 1 : 1 , besonders bevorzugt im Bereich 6 : 1 bis 2 : 1 und ganz besonders bevorzugt bei 4 : 1. Die äußere Schale (2) umhüllt den inneren Kern (1) bevorzugt nahezu vollständig und besonders bevorzugt vollständig. The outer shell (2) of the catalytically active material according to the invention is formed in one embodiment of platinum fixed on the second carrier oxide. In preferred embodiments, however, contains the outer shell (2) as another noble metal palladium. This can be present in mixed form and / or in alloyed form with the platinum also present therein. Particularly preferably, at least part of the palladium present in the shell is present in platinum-alloyed form. If both noble metals are used in the outer shell, the weight ratio of platinum to palladium is preferably between 12: 1 and 1: 1, more preferably in the range 6: 1 to 2: 1 and most preferably 4: 1. The outer shell (2) preferably envelops the inner core (1) almost completely and particularly preferably completely.
Betrachtet man das gesamte erfindungsgemäße katalytisch aktive Material, so beträgt das Gewichtsverhältnis der in äußerer Schale (2) und innerem Kern (1) insgesamt enthaltenen Edelmetalle Platin : Palladium : Gold in den besonders bevorzugten Ausführungsformen 1 : 1 : 1. Considering the entire catalytically active material according to the invention, the weight ratio of the precious metals contained in outer shell (2) and inner core (1) is platinum: palladium: gold in the particularly preferred embodiments 1: 1: 1.
In weiteren bevorzugten Ausführungsformen des erfindungsgemäßen katalytisch aktiven Materials enthält die äußere Schale (2) neben Platin bzw. neben Platin und Palladium weiterhin eine Zeolithverbindung mit HC-speichernden Eigenschaften. Das erfindungsgemäße katalytisch aktive Material wird somit mit einer Kohlenwasserstoffeinlagerungs- und -rückhaltefunktion ausgestattet, die bedingt, dass Kohlenwasserstoffe, die bei Betriebstemperaturen unterhalb der Zündtemperatur für die Kohlenwasserstoffoxidation noch nicht vollständig umgesetzt werden können, nicht durch den resultierenden Dieseloxidationskatalysator „durchbrechen", sondern im erfindungsgemäßen katalytisch aktiven Material zurückgehalten werden, bis zur HC- Konvertierung ausreichende Temperaturen erreicht sind. In further preferred embodiments of the catalytically active material according to the invention, the outer shell (2) in addition to platinum or next to platinum and Palladium also a zeolite compound with HC-storing properties. The catalytically active material according to the invention is thus equipped with a hydrocarbon storage and retention function, which requires that hydrocarbons which can not be fully reacted at operating temperatures below the ignition temperature for the hydrocarbon oxidation, not "break through" the resulting diesel oxidation catalyst, but in the inventive catalytically active material are retained until the HC conversion sufficient temperatures are reached.
Die Zeolithverbindungen sind bevorzugt ausgewählt aus der Gruppe bestehend aus FAU, MOR, Zeolith beta, MFI und Mischungen davon. Sie liegen in der äußeren Schale (2) bevorzugt zu 10 bis 60 Gew.-%, besonders bevorzugt zu 20 bis 50 Gew.-% und ganz besonders bevorzugt zu 25 bis 35 Gew.-% vor, jeweils bezogen auf das Gesamtgewicht der äußeren Schale (2). The zeolite compounds are preferably selected from the group consisting of FAU, MOR, zeolite beta, MFI and mixtures thereof. They are in the outer shell (2) preferably at 10 to 60 wt .-%, more preferably from 20 to 50 wt .-% and most preferably from 25 to 35 wt .-% before, in each case based on the total weight of the outer Shell (2).
Als erstes und/oder zweites Trägeroxid wird bevorzugt eines aus der Gruppe beste- hend aus Ceroxid, Zirkonoxid, Aluminiumoxid, Siliziumoxid und Mischoxiden und/oder Mischungen davon verwendet. Besonders bevorzugt sind Aluminiumoxid, Aluminiumsilikate und Aluminium-Silizium-Mischoxide. The first and / or second carrier oxide used is preferably one from the group consisting of cerium oxide, zirconium oxide, aluminum oxide, silicon oxide and mixed oxides and / or mixtures thereof. Particularly preferred are aluminum oxide, aluminum silicates and aluminum-silicon mixed oxides.
Die Partikel des erfindungsgemäßen katalytisch aktiven Materials, die, wie vorstehend beschrieben, aus innerem Kern (1) und äußerer Schale (2) jeweils unterschiedlicher Zusammensetzung aufgebaut sind, sind annähernd kugelförmig und weisen bevorzugt einen mittleren Durchmesser von 1 bis 12 μηι, besonders bevorzugt von 3 bis 8 μηι auf. Dabei beträgt der Volumenanteil des Kerns an einem kugelförmigen Partikel in den bevorzugten Ausführungsformen des erfindungsgemäßen katalytisch aktiven Materials bevorzugt 50 bis 80 %, besonders bevorzugt etwa 60 %. Das erfindungsgemäße katalytisch aktive Material wird nach dem Fachmann an sich bekannten Verfahren hergestellt. Als typische Verfahrensschritte können beispielsweise die gegebenenfalls gestufte Cofällung und/oder Coimprägnierung der Edelmetalle aus wasserlöslichen Vorstufen auf Trägeroxide sowie das systematische Vermählen pulverförmiger Vorstufen unter Bildung definierter Konglomerate zur Anwen- dung kommen. Zu beachten ist bei der Herstellung des erfindungsgemäßen katalytisch aktiven Materials jedoch, daß während des gesamten Herstellprozesses pH-Werte im stark sauren Bereich (d.h. pH < 4), ebenso wie pH-Werte im stark basischen Bereich (d.h. pH > 8) konsequent vermieden werden sollten. Bevorzugt wird während des gesamten Herstellprozesses in einem pH-Wertebereich zwischen pH = 5 und pH = 7 gearbeitet. Falls pH-Variationen während des Herstellprozesses notwendig sind, werden vorzugsweise Essigsäure zur Absenkung des pH-Wertes und organische Basen wie Tetraethylammonium-hydroxid (TEAH) zur Anhebung des pH-Wertes eingesetzt. The particles of the catalytically active material according to the invention, which, as described above, of inner core (1) and outer shell (2) are each of different composition are approximately spherical and preferably have an average diameter of 1 to 12 μηι, more preferably from 3 to 8 μηι on. In this case, the volume fraction of the core on a spherical particle in the preferred embodiments of the catalytically active material according to the invention is preferably 50 to 80%, particularly preferably about 60%. The catalytically active material according to the invention is prepared by processes known to those skilled in the art. As typical process steps, for example, the optionally graded co-precipitation and / or co-impregnation of the noble metals from water-soluble precursors to carrier oxides and the systematic grinding of pulverulent precursors to form defined conglomerates can be used. In the preparation of the catalytically active material according to the invention, however, it should be noted that pH values in the strongly acidic range (ie pH <4), as well as pH values in the strongly basic range (ie pH> 8), are consistently avoided during the entire production process should. It is preferred during the worked the entire manufacturing process in a pH range between pH = 5 and pH = 7. If pH variations are necessary during the production process, it is preferable to use acetic acid to lower the pH and organic bases such as tetraethylammonium hydroxide (TEAH) to raise the pH.
Gegenstand der vorliegenden Erfindung ist auch ein Dieseloxidationskatalysator bestehend aus einem katalytisch inerten Tragkörper und mindestens einer darauf aufgebrachten katalytisch aktiven Beschichtung, dadurch gekennzeichnet, dass die Beschichtung ein vorstehend beschriebenes katalytisch aktives Material enthält. Zur Herstellung des erfindungsgemäßen Dieseloxidationskatalysators wird nach dem Fachmann bekannten Verfahren eine Beschichtungssuspension aus dem vorstehend beschriebenen katalytisch aktiven Material angefertigt, die mit ebenfalls bekannten Beschichtungsverfahren (Tauch-, Saug- und/oder Pumpverfahren) auf einen inerten Tragkörper aufgebracht werden kann. Der resultierende Katalysator besteht dann aus einem katalytisch inerten Tragkörper und mindestens einer darauf aufgebrachten katalytisch aktiven Beschichtung, die das erfindungsgemäße katalytisch aktive Material enthält. Der katalytisch inerte Tragkörper ist bevorzugt ausgewählt aus der Gruppe der keramischen und metallischen Durchflußwabenkörper oder aus der Gruppe der keramischen Wandflußfiltersubstrate. Falls das erfindungsgemäße katalytisch aktive Material kein oder nicht ausreichend Zeolith in der äußeren Schale (2) enthält, kann auch der Beschichtung eine Zeolithverbindung mit HC-speichernden Eigenschaften zugesetzt werden, die ausgewählt ist aus der Gruppe bestehend aus FAU, MOR, Zeolith beta, MFI und Mischungen davon. Der Anteil der Zeolithverbindung in der Beschichtung beträgt dann vorzugsweise 15 bis 45 Gew.-%, besonders bevorzugt 20 bis 30 Gew.-%, bezogen auf das Gesamtgewicht dieser Beschichtung. In den besonders bevorzugten Ausführungsformen liegt jedoch das gesamte zeolithische Material in der äußeren Schale (2) des katalytisch aktiven Materials vor und zwar insbesondere mit einem Anteil von 15 bis 45 Gew.-%, bezogen auf das Gesamtgewicht des katalytisch aktiven Materials. The present invention also provides a diesel oxidation catalyst comprising a catalytically inert support body and at least one catalytically active coating applied thereto, characterized in that the coating contains a catalytically active material as described above. For the preparation of the diesel oxidation catalyst according to the invention, a coating suspension of the above-described catalytically active material is prepared by processes known to those skilled in the art, which can be applied to an inert support body with likewise known coating methods (immersion, suction and / or pumping). The resulting catalyst then consists of a catalytically inert carrier body and at least one catalytically active coating applied thereto, which contains the catalytically active material according to the invention. The catalytically inert carrier body is preferably selected from the group of ceramic and metallic Durchflußwabenkörper or from the group of ceramic Wandflußfiltersubstrate. If the catalytically active material according to the invention contains no or insufficient zeolite in the outer shell (2), it is also possible to add to the coating a zeolite compound having HC-storing properties selected from the group consisting of FAU, MOR, zeolite beta, MFI and mixtures thereof. The proportion of zeolite compound in the coating is then preferably 15 to 45 wt .-%, particularly preferably 20 to 30 wt .-%, based on the total weight of this coating. In the particularly preferred embodiments, however, the entire zeolitic material is present in the outer shell (2) of the catalytically active material, in particular in a proportion of 15 to 45 wt .-%, based on the total weight of the catalytically active material.
Der erfindungsgemäße Dieseloxidationskatalysator eignet sich zur oxidativen Verminderung von Kohlenmonoxid und/oder Kohlenwasserstoffen im Abgas von Dieselmotoren. Dazu wird das Abgas über den Dieseloxidationskatalysator geleitet. Der Dieseloxidationskatalysator wird bevorzugt als Bestandteil einer Abgasreinigungsanlage eingesetzt, die ebenfalls Gegenstand der vorliegenden Erfindung ist. The diesel oxidation catalyst according to the invention is suitable for the oxidative reduction of carbon monoxide and / or hydrocarbons in the exhaust gas of diesel engines. For this purpose, the exhaust gas is passed over the diesel oxidation catalyst. The diesel oxidation catalyst is preferably used as part of an exhaust gas purification system, which is also the subject of the present invention.
In der erfindungsgemäßen Abgasreinigungsanlage wird der erfindungsgemäße Dieseloxidationskatalysator bevorzugt motornah angeordnet. Nach dem Dieseloxidationskatalysator ist bevorzugt in Strömungsrichtung des zu reinigenden Abgases ein Dieselpartikelfilter nachgeschaltet. Gegebenenfalls kann auf das Dieselpartikelfilter noch eine Entstickungsstufe folgen, so daß die effektive Verminderung aller im Dieselabgas enthaltenen, gesetzlich limitierten Schadstoffe sichergestellt ist. Geeignete Dieselpartikelfilter und Entstickungsstufen wie NOx-Speicher und SCR- Katalysatoren sind in der Literatur beschrieben und dem Fachmann bekannt. In the exhaust gas purification system according to the invention, the diesel oxidation catalyst according to the invention is preferably arranged close to the engine. After the diesel oxidation catalyst, a diesel particle filter is preferably connected downstream in the flow direction of the exhaust gas to be cleaned. Optionally, the diesel particulate filter can be followed by a denitration stage, so that the effective reduction of all legally contained pollutants contained in the diesel exhaust gas is ensured. Suitable diesel particulate filters and denitration stages such as NO x storage and SCR catalysts are described in the literature and known to the person skilled in the art.
Der erfindungsgemäße Dieseloxidationskatalysator zeichnet sich insbesondere durch sehr hohe CO-Konvertierungsraten und durch eine außerordentlich hohe thermische Alterungsstabilität aus und weist somit wichtige Eigenschaften auf, die zur Applikation in modernen Abgasreinigungssystemen zur Erfüllung beispielsweise der unter„Euro 5" und „Euro 6" bekannten gesetzlichen Emissionsvorgaben unumgänglich sind. Weiterhin zeigt der erfindungsgemäße Katalysator Kostenvorteile gegenüber den ansonsten üblichen Katalysatoren, die in der Regel einen insgesamt deutlich höheren Anteil des teuersten Edelmetalls Platin enthalten. Ausführungsbeispiel : The diesel oxidation catalyst according to the invention is characterized in particular by very high CO conversion rates and by an extraordinarily high thermal aging stability and thus has important properties that are suitable for application in modern emission control systems for fulfilling, for example, the legal emission specifications known under "Euro 5" and "Euro 6" are inevitable. Furthermore, the catalyst of the invention shows cost advantages over the otherwise customary catalysts, which generally contain a significantly higher proportion of the most expensive noble metal platinum. Exemplary embodiment:
Schritt 1 : Herstellung des„Kernmaterials": Step 1: Production of the "core material":
Zur Herstellung den Kern des erfindungsgemäßen, katalytisch aktiven Materials bildenden Materials wird Aluminiumoxid in Wasser suspendiert. Unter Rühren werden der Suspension Tetrachlorogoldsäure und Palladiumnitratlösung hinzugefügt. Nach einer Adsorptionszeit von ca. einer Stunde wird der in der Suspension enthaltene Feststoff durch Filtration von der flüssigen Phase getrennt und mit vollentsalztem Wasser gewaschen, bis im Waschwasser keine nennenswerten Mengen an Chloridlonen mehr nachweisbar sind. Zur Entfernung von gegebenenfalls adsorbierten Chloridionen wird der Feststoff anschließend noch einmal mit verdünnter, wässriger Ammoniaklösung nachgewaschen. Dann erfolgt die Trocknung des Feststoffs bei etwa 120°C über die Dauer von 4 Stunden mit anschließender Kalzination bei 400°C für die Dauer von 3 Stunden. Das so erhaltene Pulver bildet das„Kernmaterial" für das in der letzten Stufe herzustellende, erfindungsgemäße, katalytisch aktive Material. To produce the core of the catalytically active material forming material of the invention, alumina is suspended in water. With stirring, tetrachloroauric acid and palladium nitrate solution are added to the suspension. After an adsorption time of about one hour, the solid contained in the suspension is separated by filtration from the liquid phase and washed with demineralized water until no significant amounts of Chloridlonen are more detectable in the wash water. To remove optionally adsorbed chloride ions, the solid is then washed once more with dilute, aqueous ammonia solution. Then the solid is dried at about 120 ° C over the course of 4 hours followed by calcination at 400 ° C for a period of 3 Hours. The powder thus obtained forms the "core material" for the catalytically active material according to the invention to be produced in the last stage.
Schritt 2: Herstellung des„Schalenmaterials": Step 2: Making the "shell material":
Zur Herstellung des „Schalenmaterials" wird Aluminiumoxid mit zunächst mit Palla- diumnitratlösung und anschließend mit Platinnitratlösung porenfüllend imprägniert. Die Gesamtmenge des aufzubringenden Edelmetalls beträgt 2 Massen. -%, bezogen auf die Gesamtmenge des Pd/Pt-haltigen Aluminiumoxidpulvers. Das so hergestellte, rieselfähige Pulver wird anschließend für die Dauer von 4 Stunden bei 120°C getrocknet und dann für die Dauer von 3 Stunden bei 400°C kalziniert. Schritt 3: Herstellung des erfindungsgemäßen katalytisch aktiven Materials: For the production of the "shell material" aluminum oxide is impregnated with pore-filling first with palladium nitrate solution and then with platinum nitrate solution.The total amount of noble metal to be applied is 2 mass%, based on the total amount of Pd / Pt-containing alumina powder Powder is then dried for 4 hours at 120 ° C. and then calcined for 3 hours at 400 ° C. Step 3: Preparation of the catalytically active material according to the invention:
Zur Herstellung des erfindungsgemäßen, katalytisch aktiven Materials wird das in Schritt 1 hergestellte„Kernmaterial" in Wasser suspendiert und gegebenenfalls vermählen, bis eine mittlere Partikelgröße von 4 - 8 μηι mit einer möglichst schmalen Partikelgrößenverteilung erreicht ist. In einem zweiten Behältnis wird das in Schritt 2 hergestellte„Schalenmaterial" ebenfalls in Wasser suspendiert und gegebenenfalls vermählen, bis eine mittlere Partikelgröße von 1 - 2 μηι mit einer möglichst schmalen Partikelgrößenverteilung erreicht ist. Gegebenenfalls wird der so erhaltenen Suspension eine geeignete Zeolithverbindung zur Speicherung der im Abgas vorhandenen Kohlenwasserstoffe zugesetzt, die eben- falls eine möglichst feine Partikelgrößenverteilung aufweist und gegebenenfalls in einem separaten Vorbereitungsschritt entsprechend gemahlen wurde. To produce the catalytically active material according to the invention, the "core material" prepared in step 1 is suspended in water and optionally ground until an average particle size of 4-8 μm is achieved with the narrowest possible particle size distribution prepared "shell material" also suspended in water and optionally milled until an average particle size of 1 - 2 μηι is achieved with the narrowest possible particle size distribution. If appropriate, the suspension thus obtained is admixed with a suitable zeolite compound for storing the hydrocarbons present in the exhaust gas, which likewise has the finest possible particle size distribution and has, if appropriate, been correspondingly ground in a separate preparation step.
Die beiden vorstehend erhaltenen Suspensionen werden vereinigt und einer gezielten Sprühtrocknung unterworfen. Während des Sprühtrocknungsprozesses bilden die fein- teiligen Partikel des „Schalenmaterials" eine Schale um die gröberen Partikel des „Kernmaterials" aus. The two suspensions obtained above are combined and subjected to a controlled spray drying. During the spray-drying process, the finely divided particles of the "shell material" form a shell around the coarser particles of the "core material".
Schritt 4: Herstellung des erfindungsgemäßen Katalysators: Step 4: Preparation of the catalyst according to the invention:
Zur Herstellung eines erfindungsgemäßen Katalysators wird das in Schritt 3 erhaltene katalytisch aktive Material in Wasser resuspendiert und mit einem dem Fachmann bekannten, üblichen Tauch-, Saug- oder Pumpverfahren auf einen herkömmlichen keramischen oder metallischen Durchflußwabenkörper aufgebracht. Die Menge der Beschichtungssuspension und die Anzahl der verfahrensgemäßen Beschichtungs- schritte ist so zu wählen, daß der Wabenkörper nach Trocknung bei 120°C und einer Kalzination bei 400°C über die Dauer von 3 Stunden eine Beschichtungsmenge von 130 bis 150 Gramm Feststoff pro Liter Bauteilvolumen aufweist. To produce a catalyst according to the invention, the catalytically active material obtained in step 3 is resuspended in water and applied to a conventional ceramic or metallic Durchflußwabenkörper with a known in the art, usual dipping, suction or pumping. The amount of Coating suspension and the number of coating steps according to the method should be selected so that the honeycomb body after drying at 120 ° C and a calcination at 400 ° C over the period of 3 hours, a coating amount of 130 to 150 grams of solid per liter of component volume.

Claims

Patentansprüche claims
Katalytisch aktives Material bestehend aus einem inneren Kern (1) und einer diesen Kern umhüllenden äußeren Schale (2), wobei der Kern gebildet wird aus Palladium und Gold, die gemeinsam auf einem ersten Trägeroxid fixiert sind, und wobei die Schale Platin enthält, welches auf einem zweiten Trägeroxid fixiert ist. A catalytically active material comprising an inner core (1) and an outer shell (2) surrounding said core, said core being formed from palladium and gold, which are fixed together on a first support oxide, and wherein said shell contains platinum, which a second carrier oxide is fixed.
Katalytisch aktives Material nach Anspruch 2, dadurch gekennzeichnet, dass die äußere Schale (2) als weiteres Edelmetall Palladium enthält. Catalytically active material according to claim 2, characterized in that the outer shell (2) contains as further noble metal palladium.
Katalytisch aktives Material nach Anspruch 1 und/oder 2, dadurch Catalytically active material according to claim 1 and / or 2, characterized
gekennzeichnet, dass die äußere Schale (2) eine Zeolithverbindung mit HC- speichernden Eigenschaften enthält.  characterized in that the outer shell (2) contains a zeolite compound having HC-storing properties.
Katalytisch aktives Material nach Anspruch 3, dadurch gekennzeichnet, dass die Zeolithverbindung ausgewählt ist aus der Gruppe bestehend aus FAU, MOR, Zeolith beta, MFI und Mischungen davon. Catalytically active material according to claim 3, characterized in that the zeolite compound is selected from the group consisting of FAU, MOR, zeolite beta, MFI and mixtures thereof.
Katalytisch aktives Material nach Anspruch 3 und/oder 4, dadurch Catalytically active material according to claim 3 and / or 4, characterized
gekennzeichnet, dass die Zeolithverbindung in einem Anteil von 10 bis 60 Gew.- % vorliegt, bezogen auf das Gesamtgewicht der äußeren Schale (2).  in that the zeolite compound is present in a proportion of 10 to 60% by weight, based on the total weight of the outer shell (2).
Katalytisch aktives Material nach einem oder mehreren der Ansprüche 1 bis 5, dadurch gekennzeichnet, dass das erste und/oder zweite Trägeroxid ausgewählt ist aus der Gruppe bestehend aus Ceroxid, Zirkonoxid, Aluminiumoxid, Catalytically active material according to one or more of claims 1 to 5, characterized in that the first and / or second carrier oxide is selected from the group consisting of cerium oxide, zirconium oxide, aluminum oxide,
Siliziumoxid und Mischoxiden und/oder Mischungen davon.  Silica and mixed oxides and / or mixtures thereof.
Katalytisch aktives Material nach einem oder mehreren der Ansprüche 1 bis 6, dadurch gekennzeichnet, dass die aus innerem Kern (1) und äußerer Schale (2) bestehenden Partikel annähernd kugelförmig sind und einen mittleren Catalytically active material according to one or more of Claims 1 to 6, characterized in that the particles consisting of inner core (1) and outer shell (2) are approximately spherical and have a central one
Durchmesser von 1 bis 12 μηι aufweisen.  Have diameter of 1 to 12 μηι.
Katalytisch aktives Material nach Anspruch 7, dadurch gekennzeichnet, dass der Volumenanteil des inneren Kerns (1) an einem kugelförmigen Partikel 50 bis 80 % beträgt. Catalytically active material according to claim 7, characterized in that the volume fraction of the inner core (1) on a spherical particle is 50 to 80%.
9. Dieseloxidationskatalysator bestehend aus einem katalytisch inerten Tragkörper und mindestens einer darauf aufgebrachten katalytisch aktiven Beschichtung, dadurch gekennzeichnet, dass die Beschichtung ein katalytisch aktives Material nach einem oder mehreren der Ansprüche 1 bis 8 enthält. 9. Diesel oxidation catalyst consisting of a catalytically inert support body and at least one catalytically active coating applied thereto, characterized in that the coating contains a catalytically active material according to one or more of claims 1 to 8.
10. Dieseloxidationskatalysator nach Anspruch 9, dadurch gekennzeichnet, dass die Beschichtung eine Zeolithverbindung mit HC-speichernden Eigenschaften enthält, die ausgewählt ist aus der Gruppe bestehend aus FAU, MOR, Zeolith beta, MFI und Mischungen davon. 10. A diesel oxidation catalyst according to claim 9, characterized in that the coating contains a zeolite compound having HC-storing properties, which is selected from the group consisting of FAU, MOR, zeolite beta, MFI and mixtures thereof.
1 1. Dieseloxidationskatalysator nach Anspruch 10, dadurch gekennzeichnet, dass der Anteil der Zeolithverbindung in der Beschichtung 15 bis 45 Gew.-% beträgt, bezogen auf das Gesamtgewicht der Beschichtung. 12. Dieseloxidationskatalysator nach einem oder mehreren der Ansprüche 9 bis 1 1 , dadurch gekennzeichnet, dass der katalytisch inerte Tragkörper ausgewählt ist aus der Gruppe der keramischen und metallischen Durchflußwabenkörper oder aus der Gruppe der keramischen Wandflußfiltersubstrate. 1 1. Diesel oxidation catalyst according to claim 10, characterized in that the proportion of the zeolite compound in the coating 15 to 45 wt .-%, based on the total weight of the coating. 12. Diesel oxidation catalyst according to one or more of claims 9 to 1 1, characterized in that the catalytically inert support body is selected from the group of ceramic and metallic Durchflußwabenkörper or from the group of ceramic Wandflußfiltersubstrate.
13. Verwendung eines Dieseloxidationskatalysators nach einem oder mehreren der Ansprüche 9 bis 12 zur Verminderung von Kohlenmonoxid und/oder 13. Use of a diesel oxidation catalyst according to one or more of claims 9 to 12 for the reduction of carbon monoxide and / or
Kohlenwasserstoffen im Abgas von Dieselmotoren.  Hydrocarbons in the exhaust gas of diesel engines.
14. Abgasreinigungsanlage zur Behandlung der Abgase von Dieselmotoren, dadurch gekennzeichnet, dass sie einen Dieseloxidationskatalysator nach einem oder mehreren der Ansprüche 9 bis 12 umfasst. 15. Abgasreinigungsanlage nach Anspruch 14, dadurch gekennzeichnet, dass dem Dieseloxidationskatalysator nach einem oder mehreren der Ansprüche 9 bis 12 ein Dieselpartikelfilter in Strömungsrichtung des zu reinigenden Abgases nachgeschaltet ist. 14. An exhaust gas purification system for treating the exhaust gases of diesel engines, characterized in that it comprises a diesel oxidation catalyst according to one or more of claims 9 to 12. 15. An exhaust gas purification system according to claim 14, characterized in that the diesel oxidation catalyst according to one or more of claims 9 to 12 is followed by a diesel particulate filter in the flow direction of the exhaust gas to be cleaned.
EP11774020.9A 2010-10-26 2011-10-19 Diesel oxidation catalyst Withdrawn EP2632587A1 (en)

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US20130202509A1 (en) 2013-08-08
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