EP2640513A1 - Catalyseur destiné à supprimer les oxydes d'azote contenus dans les gaz d'échappement de moteurs diesel - Google Patents

Catalyseur destiné à supprimer les oxydes d'azote contenus dans les gaz d'échappement de moteurs diesel

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Publication number
EP2640513A1
EP2640513A1 EP11785641.9A EP11785641A EP2640513A1 EP 2640513 A1 EP2640513 A1 EP 2640513A1 EP 11785641 A EP11785641 A EP 11785641A EP 2640513 A1 EP2640513 A1 EP 2640513A1
Authority
EP
European Patent Office
Prior art keywords
oxide
catalyst
exhaust gas
alkali metal
catalytically active
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Withdrawn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
EP11785641.9A
Other languages
German (de)
English (en)
Inventor
Paul Spurk
Nicola Soeger
Elena Mueller
Stephan Malmberg
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 EP11785641.9A priority Critical patent/EP2640513A1/fr
Publication of EP2640513A1 publication Critical patent/EP2640513A1/fr
Withdrawn legal-status Critical Current

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    • 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
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9418—Processes characterised by a specific catalyst for removing nitrogen oxides by selective catalytic reduction [SCR] using a reducing agent in a lean exhaust gas
    • 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
    • B01D53/9404—Removing only nitrogen compounds
    • B01D53/9409—Nitrogen oxides
    • B01D53/9413—Processes characterised by a specific catalyst
    • B01D53/9422—Processes characterised by a specific catalyst for removing nitrogen oxides by NOx storage or reduction by cyclic switching between lean and rich exhaust gases (LNT, NSC, NSR)
    • 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
    • B01J23/002—Mixed oxides other than spinels, e.g. perovskite
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    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/20—Vanadium, niobium or tantalum
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    • B01J23/16—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
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    • B01J23/66—Silver or gold
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    • B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
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    • B01J23/68—Silver or gold with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium
    • B01J23/683—Silver or gold with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium with chromium, molybdenum or tungsten
    • B01J23/687—Silver or gold with arsenic, antimony, bismuth, vanadium, niobium, tantalum, polonium, chromium, molybdenum, tungsten, manganese, technetium or rhenium with chromium, molybdenum or tungsten with tungsten
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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    • B01J35/00—Catalysts, in general, characterised by their form or physical properties
    • B01J35/19—Catalysts containing parts with different compositions
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • 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
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    • B01J37/02—Impregnation, coating or precipitation
    • B01J37/024—Multiple impregnation or coating
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    • B01D2255/407—Zr-Ce mixed oxides
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    • B01D—SEPARATION
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    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/902—Multilayered catalyst
    • B01D2255/9022—Two layers
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01D2255/9032—Two zones
    • B—PERFORMING OPERATIONS; TRANSPORTING
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    • B01D—SEPARATION
    • B01D2255/00—Catalysts
    • B01D2255/90—Physical characteristics of catalysts
    • B01D2255/91—NOx-storage component incorporated in the catalyst
    • 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
    • B01J2523/00—Constitutive chemical elements of heterogeneous catalysts
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N2510/00—Surface coverings
    • F01N2510/06—Surface coverings for exhaust purification, e.g. catalytic reaction
    • F01N2510/068—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings
    • F01N2510/0684—Surface coverings for exhaust purification, e.g. catalytic reaction characterised by the distribution of the catalytic coatings having more than one coating layer, e.g. multi-layered coatings
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F01—MACHINES OR ENGINES IN GENERAL; ENGINE PLANTS IN GENERAL; STEAM ENGINES
    • F01N—GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR MACHINES OR ENGINES IN GENERAL; GAS-FLOW SILENCERS OR EXHAUST APPARATUS FOR INTERNAL COMBUSTION ENGINES
    • F01N3/00—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust
    • F01N3/08—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous
    • F01N3/10—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust
    • F01N3/18—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control
    • F01N3/20—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by thermal or catalytic conversion of noxious components of exhaust characterised by methods of operation; Control specially adapted for catalytic conversion ; Methods of operation or control of catalytic converters
    • F01N3/2066—Selective catalytic reduction [SCR]
    • 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
    • Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
    • Y02T—CLIMATE CHANGE MITIGATION TECHNOLOGIES RELATED TO TRANSPORTATION
    • Y02T10/00—Road transport of goods or passengers
    • Y02T10/10—Internal combustion engine [ICE] based vehicles
    • Y02T10/12—Improving ICE efficiencies

Definitions

  • the invention relates to a catalyst for the removal of nitrogen oxides from the exhaust gas of diesel engines, and a method for reducing nitrogen oxides in the exhaust gas of diesel engines.
  • the exhaust gas from diesel engines contains in addition to the resulting from incomplete combustion of the fuel harmful gases carbon monoxide (CO) and hydrocarbons (HC) soot particles (PM) and nitrogen oxides (NO x ).
  • the exhaust gas from diesel engines contains up to 15% by volume of oxygen. It is known that the oxidizable noxious gases CO and HC can be converted by passing over a suitable oxidation catalyst into harmless carbon dioxide (C0 2 ), and particles can be removed by passing the exhaust gas through a suitable soot particle filter.
  • SCR Selective Catalytic Reduction
  • a source for providing the reducing agent, an injection device for the demand-based metering of the reducing agent into the exhaust gas and an SCR catalyst arranged in the flow path of the exhaust gas are necessary.
  • the entirety of the reducing agent source, the SCR catalyst and the injector arranged upstream of the SCR catalytic converter is also referred to as the SCR system.
  • nitrogen oxide storage catalysts can be used for denitrification of diesel exhaust gases. Their operation is described in detail in SAE SAE 950809.
  • the cleaning effect of the nitrogen oxide storage catalysts is based on the fact that in a lean operating phase of the engine, the nitrogen oxides from the feed chermaterial of the storage catalyst are stored mainly in the form of nitrates. In a subsequent rich operating phase of the engine, the previously formed nitrates are decomposed and the released nitrogen oxides are reacted with the reducing exhaust gas components on the storage catalyst to nitrogen, carbon dioxide and water.
  • EP 1 203 61 1 discloses an exhaust gas purification device for the selective catalytic reduction of nitrogen oxides under lean exhaust conditions, comprising at least one catalyst with a catalytically active component for the selective catalytic reduction (SCR component) and additionally at least one nitrogen oxide storage component ( ⁇ component) ,
  • SCR component selective catalytically active component for the selective catalytic reduction
  • ⁇ component nitrogen oxide storage component
  • the catalyst is operated by the urea-SCR process, ie ammonia is used as the reducing agent for nitrogen oxides, which is generated from the lean exhaust gas added urea.
  • DE 198 06 062 also discloses a reduction catalytic converter for reducing pollutants in diesel engine exhaust gases, which in its active composition contains, in addition to an SCR catalyst material based on the catalytically active oxides TiO 2 , WO 3 , MoO 3 and V 2 O 5, a ⁇ storage material.
  • the NO x storage material contains as active component at least one high-surface-area inorganic oxide, which is preferably selected from the group Al 2 O 3 , Si0 2 , Zr0 2 , zeolites and phyllosilicates.
  • EP 0 666 099 describes a process for removing nitrogen oxides from oxidizing exhaust gases, which are passed through a special catalyst which stores the nitrogen oxides, wherein subsequently a reducing agent is added to the exhaust gas, whereby the nitrogen oxides adsorbed in the catalyst are reduced to nitrogen ,
  • the catalyst contains inorganic oxides and catalytically active components.
  • the catalytically active components comprise on the one hand noble metals selected from platinum, palladium, rhodium and ruthenium, and on the other hand at least one alkali and / or alkaline earth metal.
  • the catalyst may contain heavy metals selected from manganese, copper, cobalt, molybdenum, tungsten and vanadium or compounds thereof.
  • the SCR process for denitrification of diesel exhaust gases for passenger car applications and commercial vehicle application is considered to be the most promising method of purifying nitrogen oxides.
  • the temperatures of the exhaust gas to be cleaned which occur in the New European Driving Cycle (NEDC) are shifting more and more into the colder range, since dosing of urea as the source of the reducing agent ammonia only takes place at temperatures 180 ° C is controlled, without accepting unwanted deposits of urea and secondary products in the exhaust systems, this development of exhaust temperatures to the fact that the SCR process in the so-called “inner city part” (ECE) of the NEDC no longer effective can be used.
  • ECE ner city part
  • the object of the present invention is to provide a catalyst and an exhaust gas purification process which, compared with the prior art systems, has an improved NO x conversion performance throughout the NEDC-relevant Temperature range, but especially at lower temperatures, for example between 100 and 230 ° C, especially between 100 and 200 ° C, shows.
  • a catalyst for removing nitrogen oxides from the exhaust gas of diesel engines comprising a support body of length L and a catalytically active coating comprising one or more material zones
  • a catalytically active mixed oxide consisting of cerium oxide, zirconium oxide,
  • the particular composition of the catalyst according to the invention has the effect that the nitrogen oxides present in the exhaust gas to be purified can be stored in the catalyst in the form of nitrates at temperatures which are less than or equal to 200.degree.
  • nitrogen oxide breakthroughs in the catalyst in temperature ranges in which a urea dosage is not meaningfully possible largely avoided.
  • Exceed the exhaust gas temperatures 200 ° C so that the need adapted metering of the reducing agent urea controlled, the stored at colder temperatures in the catalyst nitrogen oxides are released again and selectively reduced with ammonia to nitrogen.
  • the NO conversion in the entire NEDC-relevant temperature range but in particular at lower temperatures, e.g. between 100 and 230 ° C, especially between 100 and 200 ° C, compared to systems according to the prior art significantly increased.
  • the catalytically active mixed oxide contained in the catalyst according to the invention consists of 15 to 50 wt .-% Ce0 2 , 3 to 25 wt .-% Nb 2 0 5 , 3 to 10 wt .-% rare earth sesquioxide SE 2 0 3 and zirconium oxide Zr0 2 , based on the total amount of this catalytically active mixed oxide.
  • the catalytically active mixed oxide contains tungsten oxide, it is preferably composed of 15 to 50 wt .-% Ce0 2 , 3 to 25 wt .-% Nb 2 0 5 , 3 to 10 wt .-% rare earth sesquioxide SE 2 0 3 , 3 bis 20 wt .-% W0 3 and zirconium oxide Zr0 2 , based on the total amount of this catalytically active mixed oxide.
  • Seltenerdsesquioxide SE 2 0 3 in particular lanthanum oxide La 2 0 3, yttrium oxide Y 2 0 3, and neodymium oxide Nd 2 0 2 are used.
  • Such a material is characterized by an excellent catalytic activity in the SCR reaction.
  • this material In contrast to the usual SCR catalysts based on zeolite, this material has only a low ammonia storage capacity, which is very stable on the typical operating and aging conditions occurring in the exhaust system. This requires that the catalyst reacts very flexibly to the different reducing agent supply at a frequently required in automotive application highly dynamic dosing of urea and converts the offered reducing agent very quickly with the nitrogen oxides.
  • This improvement in the light-off and turnover behavior in the catalyst according to the invention is synergistically supported by the presence of a nitrogen oxide storage material selected from the group consisting of barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate, praseodymium oxide, lanthanum oxide, magnesium oxide, magnesium / aluminum mixed oxide, Alkali metal oxide, alkali metal hydroxide, alkali metal carbonate and mixtures thereof.
  • a nitrogen oxide storage material selected from the group consisting of barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate, praseodymium oxide, lanthanum oxide, magnesium oxide, magnesium / aluminum mixed oxide, Alkali metal oxide, alkali metal hydroxide, alkali metal carbonate and mixtures thereof.
  • the catalyst according to the invention preferably contains 0.1 to 25% by weight of a compound selected from the group consisting of barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate, praseodymium oxide, lanthanum oxide, alkali metal oxide, alkali metal hydroxide, alkali metal carbonate and mixtures thereof on the total amount of the catalyst.
  • the catalyst according to the invention particularly preferably contains from 0.2 to 10% by weight of a compound selected from the group consisting of barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate, praseodymium oxide, lanthanum oxide, alkali metal oxide, alkali metal hydroxide, alkali metal carbonate and mixtures thereof. based on the total amount of the catalyst. Most preferably, the catalyst of the invention contains 1 to 5 wt .-% barium oxide, based on the total amount of the catalyst.
  • the catalyst preferably contains 0.1 to 50% by weight of a magnesium oxide or a magnesium / aluminum mixed oxide in addition to the compound selected from the group consisting of barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate , Praseodymium oxide, lanthanum oxide, alkali metal oxide, alkali metal hydroxide and alkali metal carbonate and based on the total amount of the catalyst.
  • a magnesium oxide or a magnesium / aluminum mixed oxide in addition to the compound selected from the group consisting of barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate , Praseodymium oxide, lanthanum oxide, alkali metal oxide, alkali metal hydroxide and alkali metal carbonate and based on the total amount of the catalyst.
  • the catalyst of this embodiment of the invention contains 10 to 40 wt .-%, most preferably 15% to 25 wt .-% magnesium oxide or magnesium / aluminum mixed oxide in addition to the compound selected from the group consisting of barium oxide, barium hydroxide, barium carbonate , Strontium oxide, strontium hydroxide, strontium carbonate, praseodymium oxide, lanthanum oxide, alkali metal oxide, alkali metal hydroxide and alkali metal carbonate and based on the total amount of the catalyst.
  • the nitrogen oxides are incorporated with the formation of nitrates in the nitrogen oxide storage material. If the exhaust gas temperature upstream of the catalyst according to the invention exceeds a predetermined value, the metered addition of urea can take place such that the nitrogen oxides stored in the nitrogen oxide storage material are reduced in a very short time with ammonia from urea to nitrogen.
  • the availability of the low but fast-working ammonia storage in the mixed oxide according to the invention makes it possible to guide this process in a particularly advantageous manner.
  • the catalytically active coating contains in preferred embodiments of the catalyst according to the invention, in addition to the catalytically active mixed oxide, a further oxide or further oxides, in particular a further cerium oxide and / or cerium / zirconium mixed oxide.
  • Cerium oxides or cerium / zirconium mixed oxides - especially if they are cerium-rich, ie cerium oxide contents greater than 40 wt .-%, particularly preferably greater 60 wt .-%, each based on the total weight of the cerium / zirconium mixed oxide, have - promote the nitrogen oxide storage capacity in the low temperature range up to 200 ° C.
  • this additional cerium oxide and / or cerium / zirconium mixed oxide is used as carrier oxide for the compound selected from the group consisting of barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, Strontium carbonate, praseodymium oxide, lanthanum oxide, magnesium oxide, magnesium / aluminum mixed oxide, alkali metal oxide, alkali metal hydroxide, alkali metal carbonate and mixtures.
  • the oxides mentioned are preferably doped or stabilized with other metals.
  • Examples of the oxides mentioned are in particular lanthanum-doped aluminum / cerium mixed oxides, cerium / zirconium / praseodymium mixed oxides, cerium / zirconium / lanthanum mixed oxides, cerium oxide and cerium / zirconium mixed oxide.
  • Both the speed of the SCR reaction and the effectiveness of the storage of nitrogen oxides in the form of nitrates depend on the NO / N0 2 ratio in the exhaust gas to be cleaned.
  • the SCR reaction is fastest when the NO / N0 2 ratio is 1.
  • the storage of nitrogen oxides in the form of nitrates proceeds most rapidly in the case of some storage materials such as, for example, barium oxide, if as much of the NO present in the exhaust gas has been previously oxidized to N0 2 .
  • the adjustment of the NO / N0 2 ratio in situ on the catalyst surface can take place in a step upstream of the actual target reaction.
  • preferred embodiments of the catalyst according to the invention in the catalytically active coating contain one or more noble metals which are selected from the group consisting of platinum, palladium, rhodium, iridium, ruthenium, gold, silver and mixtures and / or alloys thereof. Particularly preferred are the platinum group metals platinum, palladium, rhodium, ruthenium and mixtures and / or alloys thereof.
  • the type and amount of precious metals to be used in the catalytic coating should be selected such that the resulting catalyst does not have any significant ammonia oxidation capability in the application-relevant temperature range. The preferable Selection of precious metals and their concentration is also determined by the overall composition of the catalyst and opens to the expert from the customary optimization experiments.
  • the components contained in the catalyst can be present in a homogeneous coating on the support body.
  • good de-icing success can be achieved with such embodiments.
  • the catalytically active coating consists of two material zones
  • the first material zone comprises the catalytically active mixed oxide consisting of cerium oxide, zirconium oxide, rare earth sesquioxide and niobium oxide and optionally tungsten oxide
  • the compound is selected from the group consisting of barium oxide , Barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate, praseodymium oxide, lanthanum oxide, magnesium oxide, magnesium / aluminum mixed oxide, alkali metal oxide, alkali metal hydroxide, alkali metal carbonate and mixtures thereof in the second material zone.
  • the first material zone comprises the catalytically active mixed oxide consisting of cerium oxide, zirconium oxide, rare earth sesquioxide and niobium oxide and optionally tungsten oxide, while the noble metal selected from the group consisting of platinum, palladium, rhodium, iridium , Ruthenium, gold, silver and mixtures and / or alloys thereof, contained in the second material zone.
  • the spatial separation of the noble metal and the SCR reaction catalyzing mixed oxide of cerium oxide, zirconium oxide, rare earth sesquioxide and niobium oxide and optionally tungsten oxide ensures that the catalyst according to the invention has an excellent selectivity to nitrogen even at higher exhaust gas temperatures in the SCR reaction. As a result, under appropriate operating conditions, little NO x is formed from the overoxidation of excess ammonia.
  • Embodiments of the catalyst according to the invention in which two different material zones are present can in principle be configured as layered catalysts or as zone catalysts. To prepare such catalysts, two differently composed coating suspensions are used to provide a preferably used as a support body fürflußwaben redesign of ceramic or metal with the corresponding catalytically active part coatings that form the material zones.
  • a catalytically active layer with a correspondingly composed coating suspension is applied over the entire length of the support body according to one of the conventional dipping, suction and / or pumping methods. After drying and optionally calcination of this first layer, the process is repeated with a second, differently composed coating suspension, so that a second catalytically active partial coating (material zone) is formed on the first catalytically active partial coating.
  • a material zone is thus applied directly to the support body and covers its entire length L. The other material zone is applied over it and completely covers that material zone on the exhaust side.
  • FIG. 1 schematically shows the structure of such a layered catalyst
  • FIG. 1 b shows schematically a single flow channel (2) as a section of the layered catalyst.
  • the two superposed material zones (3a and 3b) are arranged on the flow channel limiting, gas-tight walls (4), from which the catalytically active coating of preferred embodiments of the catalyst according to the invention is composed.
  • the arrows indicate the flow direction of the exhaust gas to be cleaned.
  • a coating suspension of suitable composition is introduced by means of one of the conventional dipping, suction and / or pumping methods, for example from the later upstream side of the catalyst into the throughflow honeycomb body of ceramic or metal which is preferably used as support body.
  • the application ends after a defined distance in the support body, which is smaller than the length of the support body L.
  • FIGS. 2b to 2d schematically show a single flow channel (2) as a section of the zone catalyst and the partial coatings (material zones) arranged therein on the gas-tight walls (4) delimiting the flow channel.
  • the length of the zones can be selected during the coating so that the material zones touch each other at a selected point on a partial length piece of the support body ("zones on impact", Figure 2b) 2d)
  • the zone lengths are selected such that a gap remains between the two material zones ( Figure 2c) .
  • the gap is preferably between 2 and 10 millimeters, more preferably between 3 and 6 millimeters long.
  • This embodiment has particular advantages in noble metal-containing variants of the catalyst according to the invention, since herein the intimate contact between the precious metal contained in one material zones and the SCR catalytically active mixed oxide contained in the other material zone consisting of cerium oxide, zirconium oxide, rare earth sesquioxide and niobium oxide and optionally Tungsten oxide is completely suppressed d prevents the thermally diffusive transfer of the noble metal into the mixed oxide, resulting in a higher selectivity to nitrogen of the resulting catalyst as a result.
  • the second material zone is the compound selected from the group consisting of barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate, praseodymium oxide, lanthana, magnesia, magnesium / aluminum mixed oxide, alkali metal oxide, alkali metal hydroxide, alkali metal carbonate and mixtures thereof and / or precious metal, directly applied to the support body and covers it over its entire length L.
  • the first material zone containing the catalytically active mixed oxide consisting of cerium oxide, zirconium oxide, rare earth sesquioxide and niobium oxide and optionally tungsten oxide is on the second material zone applied and covered over the entire length L completely. This arrangement of the material zones requires that nitrogen oxides from the second Material zone can be desorbed in the overlying SCR active material zone with ammonia to nitrogen.
  • the second material zone covers 10 to 70% of the length L of the support body, calculated from the first end, while the first material zone 30 to 90% The length L of the support body covered, calculated from the second end.
  • the zone catalysts according to the invention are generally used so that the first end on the inflow side and the second end is downstream.
  • This arrangement also has the advantage that nitrogen oxides which are desorbed from the second material zone storing the nitrogen oxides can be converted with ammonia to nitrogen at the downstream first material zone.
  • a maximum possible temperature level is ensured in the catalyst by the upstream arrangement of the second material zone, which in total to optimal, i. compared to the inverse arrangement improved NOx storage rates of the second material zone leads.
  • the zones in reverse so that the first material zone containing the SCR catalytically active mixed oxide of cerium oxide, zirconium oxide, rare earth sesquioxide and niobium oxide and optionally tungsten oxide, at the first end, that is arranged upstream, while the second material zone at the second end, that is arranged downstream.
  • the catalyst according to the invention is preferably followed by an additional SCR catalyst in the exhaust gas purification system. This results in a device which, in addition to a catalyst according to the invention comprises an SCR catalyst, which is arranged downstream of the catalyst according to the invention.
  • Such a device is particularly preferably supplemented by an additional metering device for reducing agent, which is arranged between the catalyst according to the invention and the downstream SCR catalytic converter.
  • an additional metering device for reducing agent which is arranged between the catalyst according to the invention and the downstream SCR catalytic converter.
  • both nitrogen oxides which are desorbed at higher exhaust gas temperatures from the second material zone of the upstream catalyst according to the invention, as well as nitrogen oxides which at higher temperatures optionally by overoxidation of ammonia over the arise second material zone, effectively be implemented over the downstream SCR catalyst to nitrogen.
  • the catalyst according to the invention is suitable for removing nitrogen oxides from the exhaust gas of diesel engines. Although the catalyst has the ability to store nitrogen oxides, it is not operated cyclically in alternately rich and lean exhaust gas.
  • the exhaust gas to be cleaned has an air ratio ⁇ , which is greater than 1, and is passed to the denitration over the catalyst of the invention.
  • Preference is given to the exhaust gas to be purified before it enters the catalyst ammonia or a compound decomposable to ammonia as a reducing agent from a source independent of the engine supplied.
  • Particularly preferred is the use of urea as decomposable to ammonia compound, which is supplied to the exhaust gas to be cleaned only when the temperatures are higher than or equal to 180 ° C.
  • the catalyst according to the invention via which the exhaust gas to be purified is passed, stores nitrogen oxides in the form of nitrates. At temperatures higher than 200 ° C, these nitrogen oxides are released again. Still on the catalyst according to the invention their selective catalytic reduction takes place with ammonia to nitrogen.
  • the exhaust gas may be purified via a catalyst which predominantly accelerates the selective catalytic reduction of nitrogen oxides with ammonia.
  • the supplementary aftertreatment over an SCR catalyst is useful, for example, if there is a risk that nitrogen oxides break through the catalyst according to the invention in specific operating points or are released from the nitrogen oxide storage in the catalyst according to the invention, without sufficient catalyst being present on the catalyst according to the invention Reduction of nitrogen oxides to nitrogen can take place.
  • the SCR catalytically active mixed oxide consisting of cerium oxide, zirconium oxide, rare earth sesquioxide and niobium oxide and optionally tungsten oxide is present in a zone which is dimensioned comparatively short.
  • the integration of the catalyst according to the invention in an exhaust system is required, which may - in addition to other emission control units such as diesel oxidation catalyst and / or diesel particulate filter - also contain other Entstickungskatalysatoren, preferably SCR catalysts.
  • Figure 1 Schematic representation of a layered catalyst according to the invention comprising a naturalflußwaben redesign (1) and the catalytically active coating (3), which is composed of two superimposed material zones (3a and 3b).
  • Material zone (3a) contains a catalytically active ischoxide consisting of cerium oxide, zirconium oxide, rare earth sesquioxide and niobium oxide and optionally tungsten oxide.
  • Material zone (3b) contains at least one compound selected from among barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate, praseodymium oxide, lanthanum oxide, magnesium oxide, magnesium / aluminum mixed oxide, alkali metal oxide, alkali metal hydroxide, alkali metal carbonate and
  • Figure 1 b shows a section of the coated fürflußwaben endeavor comprise a single flow channel (2), on the gas-tight walls (4), the coating is applied.
  • FIG. 2 Schematic representation of a zone catalyst according to the invention comprising a convexylation factor (1) and the catalytically active
  • Coating (3) which is composed of two superposed material zones (3a and 3b).
  • Material zone (3a) contains a catalytically active mixed oxide consisting of cerium oxide, zirconium oxide, rare earth sesquioxide and niobium oxide and optionally tungsten oxide.
  • Material zone (3b) contains at least one compound selected from among barium oxide, barium hydroxide, barium carbonate, strontium oxide, strontium hydroxide, strontium carbonate, praseodymium oxide, lanthanum oxide, magnesium oxide, magnesium / aluminum mixed oxide, alkali metal oxide, alkali metal hydroxide, alkali metal carbonate and
  • FIGS. 2 b) to 2 d) show a single flow channel (2) as a section of the zone catalyst and the material zones arranged therein on the gas-tight walls (4) delimiting the flow channel.
  • FIGS. 2 b) to 2 d) show a single flow channel (2) as a section of the zone catalyst and the material zones arranged therein on the gas-tight walls (4) delimiting the flow channel.
  • the flow-through honeycomb bodies used are, unless stated otherwise, those made of cordierite, which at a diameter of 38.1 mm have a length of 76.2 mm, a cell density of 62 cells / cm 2 and a wall thickness of 0.165 millimeters.
  • a layered catalyst according to the invention according to FIG. 1 was produced as follows: a) To produce the second material zone (3b) to be applied directly to the throughflow honeycomb body, a coating suspension of the following composition was prepared:
  • a flow honeycomb body was in a known manner with 320g / L of a mixture of the composition described in Example 2a) (68.75%) with a mixed oxide composition Zr 0.6 4Ce 0, 2Yo , o75Nb 0, o7502 (corresponding to the teaching of US 6,468,941 ) (31, 25%) coated. Drying and calcining in a known manner resulted in a catalyst according to the invention.
  • a layered catalyst according to the invention according to FIG. 1 was produced as follows: a) To produce the second material zone (3b) to be applied directly to the throughflow honeycomb body, a coating suspension of the following composition was prepared:
  • No. 6,468,941 produced a coating suspension and thus once more coated the simply coated flow-through honeycomb body obtained according to a).
  • the applied amount was 100 g / L. Drying and calcination in a known manner resulted in a layered catalyst according to the invention.
  • a zone catalyst according to the invention according to FIG. (2b) was produced as follows: a) For the production of the front, upstream material zone (3b), a flow honeycomb body with a length of 76.2 mm over a length of 50.8 mm from a first end with the coated in Example 4a) coating. The applied amount was 320 g / L. It was then dried and calcined. b) For the production of the rear, outflow-side material zone (3a), the flow-through honeycomb body obtained according to a) was coated starting from the second end over a length of 25.4 mm with a coating suspension comprising a mixed oxide of composition Zr 0 , 49Ce 0 , 3iYo , o4 3 Nb 0 , i502. The applied amount was 200 g / L. It was then dried and calcined.
  • the resulting catalyst is hereinafter referred to as K5.
  • a zone catalyst according to the invention in the use of which the material zone (3a) is arranged on the inflow side and the material zone (3b) downstream, was produced as follows: a) For the production of the rear, downstream material zone, a flow honeycomb body with a length of 76.2 mm was placed on a Length of 50.8 mm coated from a first end with a coating suspension containing the following ingredients:
  • the applied amount was 320 g / L. It was then dried and calcined.
  • upstream material zone of the flow honeycomb body obtained according to a) was coated starting from the second end over a length of 25.4 mm with the coating suspension described in Example 5b).
  • the applied amount was 200 g / L. It was then dried and calcined.
  • a separate SCR catalytic converter is connected downstream of the flow honeycomb body thus obtained. This was obtained by coating a flow honeycomb body of length 76.22 mm with the coating suspension described in Example 5b).
  • the applied amount was 200 g / L. It was then dried and calcined.
  • a layered catalyst according to the invention according to FIG. 1 was produced as follows:
  • Example 8 The single-coated flow honeycomb body produced in accordance with Example 2a) was used to prepare the first material zone (3a) with a mixed oxide having the composition Zr 0 .5 9 Ce 0. 2 iYo , i Nb 0 , i0 2 (corresponding to the teaching of US Pat. No. 6,468,941). coated coating suspension coated once more. The applied amount was 100 g / L. Drying and calcination in a known manner resulted in a layered catalyst according to the invention, which is referred to below as K7.
  • Example 8 Example 8
  • a layered catalyst according to the invention according to FIG. 1 was produced as follows:
  • the single-coated flow honeycomb body produced according to Example 4a) was used to prepare the first material zone (3a) with a mixed oxide having the composition Zr 0, 5 9 Ce 0 , 2 iYo , i Nb 0 , i0 2 (corresponding to the teaching of US Pat. No. 6,468,941). coated coating suspension coated once more. The applied amount was 100 g / L. Drying and calcination in a known manner resulted in a layered catalyst according to the invention, which is referred to below as K8.
  • a layered catalyst according to the invention according to FIG. 1 was produced as follows: a) A coating suspension of the following was used to produce the second material zone (3b) to be applied directly to the throughflow honeycomb body
  • composition made:
  • a flow honeycomb body was coated in a known manner with 400 g / L of a mixture of 20 wt .-% cerium oxide, 10 wt .-% of a lanthanum-doped aluminum / cerium mixed oxide and 20 wt .-% of a lanthanum-doped cerium / zirconium / praseodymium mixed oxide and 50 wt .-% of a mixed oxide of the composition Zr 0, 5Ce 0, 2Yo, o6Nbo, o6Wo , i502 (according to the teaching of US 6,468,941) (200 g / L) coated. Drying and calcination in a known manner resulted in a catalyst according to the invention, which is referred to below as K11.
  • a zone catalyst according to the invention in the use of which the material zone (3a) is arranged on the inflow side and the material zone (3b) downstream, was produced as follows: a) For the production of the rear, downstream material zone, a flow honeycomb body with a length of 76.2 mm was placed on a Length of 50.8 mm coated from a first end with a coating suspension containing the following ingredients:
  • the applied amount was 320 g / L. It was then dried and calcined.
  • a coating suspension having the following composition was prepared (the amounts refer to the volume L of the resulting catalyst): 45 g / L of a lanthanum-doped aluminum / cerium mixed oxide;
  • Barium oxide coated cerium / zirconium mixed oxide is a self-produced powder component.
  • a commercially available cerium / zirconium mixed oxide was slurried in an aqueous barium acetate solution.
  • the suspension thus obtained was dried at 120 ° C over the period of 10 h and then calcined at 500 ° C for 2 hours.
  • the powder thus obtained was ground and used to prepare the coating suspension.
  • a naturalflußwaben endeavor was coated with 62 cells per square centimeter, a cell wall thickness of 0, 165 millimeters and a length of 76.2 mm in a conventional and known in the art dip coating process.
  • the component was dried and calcined at 500 ° C for 2 hours.
  • the first material zone (3a) was a commercially available cerium-zirconium mixed oxide having a weight ratio of Ce0 2 : Zr0 2 of 1: 1, 1 and a Nd 2 0 3 content of 5.3 wt .-% with an aqueous solution of ammonium niobium oxalate and calcined at 500 ° C for a period of 2 hours.
  • the composite oxide composition according to the invention thus obtained consisted of 38% by weight of CeO 2 , 14.5% by weight of Nb 2 O 5 , 4.5% by weight of Nd 2 O 3 and 43% by weight of ZrO 2 . From the mixed oxide, a coating suspension was prepared, with which the naturalflußwaben redesign already simply coated as described above was coated again. The resulting component was calcined after drying at 500 ° C for a period of 2 hours.
  • the catalyst according to the invention exhibits significantly improved nitrogen oxide conversions in the NEDC-relevant temperature range and in particular in the low-temperature range up to 230 ° C., above all up to 200 ° C., compared with prior art catalysts and thus has reduced NO in the NEDC compared to conventional emissions x emissions.
  • a flow honeycomb body with a length of 76.2 mm was coated in a known manner with a coating suspension containing a mixed oxide composition Zr 0.59 Ce 0.2 iYo , iNb 0, i0 2 (according to the teaching of US 6,468,941).
  • the amounts applied were:
  • VK1, VK2 and VK3 are hereinafter referred to as VK1, VK2 and VK3, respectively.
  • a flow honeycomb body with a length of 76.2 mm was coated in a known manner with a coating suspension containing a mixed oxide of composition Zr 0.49 Ce 0 , 3iYo, o43Nb 0, i 5 0 2 .
  • the applied amount was 200 g / L.
  • After the coating was dried and calcined in a known manner.
  • the resulting catalyst is hereinafter referred to as VK4. Comparative Example 5
  • a flow honeycomb body with a length of 76.2 mm was coated in a known manner with a coating suspension containing a mixed oxide composition Zr 0.5 Ce 0 , 2Yo, o6Nbo, o6Wo, i702.
  • the applied amount was 200 g / L.
  • After the coating was dried and calcined in a known manner.
  • the obtained catalyst is hereinafter referred to as VK5.
  • the ⁇ -conversion of the inventive catalysts K7, K8 and K10 were compared with the catalysts VK1, VK2 and VK3 in a test gas plant.
  • the NO x conversion of the inventive catalysts K5 and K12 were compared with VK4 and the NO x conversion of the inventive catalyst K1 1 with VK5.
  • the catalysts according to the invention and comparison catalysts each compared contain in each case the identical mixed oxide consisting of cerium oxide, zirconium oxide, rare earth sesquioxide, niobium oxide and optionally tungsten oxide.
  • conditioning takes place at 550 ° C, so that the
  • Catalyst sample at the beginning of the test phase is free of adhering NO x and NH 3 .
  • the mean nitrogen oxide conversion in the test phase was determined over the entire period of 5 minutes.

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Abstract

L'invention concerne un catalyseur destiné à supprimer les oxydes d'azote contenus dans les gaz d'échappement de moteurs diesel ainsi qu'un procédé destiné à diminuer les oxydes d'azote dans les gaz d'échappement de moteurs diesel. Ledit catalyseur est constitué d'un corps de support d'une longueur L et d'un revêtement à action catalytique, ce dernier pouvant être composé d'une ou de plusieurs zones de matériaux. Lesdites zones de matériaux contiennent de l'oxyde mixte à action catalytique SCR, constitué d'oxyde de cérium, d'oxyde de zirconium, de sesquioxyde de terres rares et d'oxyde de niobium et, optionnellement, d'oxyde de tungstène. En outre, lesdites zones de matériaux contiennent au moins un composé choisi dans le groupe constitué d'oxyde de baryum, d'hydroxyde de baryum, de carbonate de baryum, d'oxyde de strontium, d'hydroxyde de strontium, de carbonate de strontium, d'oxyde de praséodyme, d'oxyde de lanthane, d'oxyde de magnésium, d'oxyde mixte de magnésium/aluminium, d'oxyde de métaux alcalins, d'hydroxyde de métaux alcalins, de carbonate de métaux alcalins et de leurs mélanges. Le cas échéant, ledit catalyseur peut également contenir du métal noble.
EP11785641.9A 2010-11-16 2011-11-14 Catalyseur destiné à supprimer les oxydes d'azote contenus dans les gaz d'échappement de moteurs diesel Withdrawn EP2640513A1 (fr)

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EP10014644 2010-11-16
EP11785641.9A EP2640513A1 (fr) 2010-11-16 2011-11-14 Catalyseur destiné à supprimer les oxydes d'azote contenus dans les gaz d'échappement de moteurs diesel
PCT/EP2011/070005 WO2012065933A1 (fr) 2010-11-16 2011-11-14 Catalyseur destiné à supprimer les oxydes d'azote contenus dans les gaz d'échappement de moteurs diesel

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FR2972366B1 (fr) * 2011-03-08 2016-01-15 Rhodia Operations Procede de traitement d'un gaz contenant des oxydes d'azote (nox) utilisant comme catalyseur une composition a base de zirconium, de cerium et de niobium
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US9095816B2 (en) 2015-08-04
US20130189172A1 (en) 2013-07-25
CN103180046A (zh) 2013-06-26
WO2012065933A1 (fr) 2012-05-24
CN103180046B (zh) 2016-11-16

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