WO2005064130A1 - Device and process for removing nitrogen oxides from the exhaust gas of internal combustion engines with the aid of catalytically generated ammonia - Google Patents

Device and process for removing nitrogen oxides from the exhaust gas of internal combustion engines with the aid of catalytically generated ammonia Download PDF

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Publication number
WO2005064130A1
WO2005064130A1 PCT/EP2004/010261 EP2004010261W WO2005064130A1 WO 2005064130 A1 WO2005064130 A1 WO 2005064130A1 EP 2004010261 W EP2004010261 W EP 2004010261W WO 2005064130 A1 WO2005064130 A1 WO 2005064130A1
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catalyst
exhaust
gas
purification system
gas purification
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PCT/EP2004/010261
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English (en)
French (fr)
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Marcus Pfeifer
Nicola SÖGER
Paul Spurk
Roger Staab
Christian Kühn
Jürgen GIESHOFF
Egbert Lox
Thomas Kreuzer
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Umicore Ag & Co. Kg
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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
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • 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
    • B01D53/9445—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC]
    • B01D53/9454—Simultaneously removing carbon monoxide, hydrocarbons or nitrogen oxides making use of three-way catalysts [TWC] or four-way-catalysts [FWC] characterised by a specific device
    • 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
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • 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
    • F01N13/00—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series
    • F01N13/0097—Exhaust or silencing apparatus characterised by constructional features ; Exhaust or silencing apparatus, or parts thereof, having pertinent characteristics not provided for in, or of interest apart from, groups F01N1/00 - F01N5/00, F01N9/00, F01N11/00 having two or more separate purifying devices arranged in series the purifying devices are arranged in a single housing
    • 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
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction 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
    • 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
    • F01N3/0807—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents
    • F01N3/0828—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents characterised by the absorbed or adsorbed substances
    • 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
    • F01N3/206—Adding periodically or continuously substances to exhaust gases for promoting purification, e.g. catalytic material in liquid form, NOx reducing agents
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2251/00—Reactants
    • B01D2251/20—Reductants
    • B01D2251/206—Ammonium compounds
    • B01D2251/2062—Ammonia
    • 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
    • F01N2240/00—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being
    • F01N2240/25—Combination or association of two or more different exhaust treating devices, or of at least one such device with an auxiliary device, not covered by indexing codes F01N2230/00 or F01N2250/00, one of the devices being an ammonia generator
    • 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
    • F01N2430/00—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics
    • F01N2430/06—Influencing exhaust purification, e.g. starting of catalytic reaction, filter regeneration, or the like, by controlling engine operating characteristics by varying fuel-air ratio, e.g. by enriching fuel-air mixture
    • 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
    • F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • 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
    • F01N2570/00—Exhaust treating apparatus eliminating, absorbing or adsorbing specific elements or compounds
    • F01N2570/18—Ammonia
    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
    • F02D—CONTROLLING COMBUSTION ENGINES
    • F02D41/00—Electrical control of supply of combustible mixture or its constituents
    • F02D41/02—Circuit arrangements for generating control signals
    • F02D41/021—Introducing corrections for particular conditions exterior to the engine
    • F02D41/0235—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus
    • F02D41/027—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus
    • F02D41/0275—Introducing corrections for particular conditions exterior to the engine in relation with the state of the exhaust gas treating apparatus to purge or regenerate the exhaust gas treating apparatus the exhaust gas treating apparatus being a NOx trap or adsorbent
    • 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
    • Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
    • Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
    • Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
    • 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 an exhaust-gas purification system for removing nitrogen oxides from the exhaust gas of internal combustion engines with the aid of catalytically generated ammonia, and to a process for purifying the exhaust gases from lean-burn internal combustion engines, in particular from diesel engines.
  • lean-burn engines Internal combustion engines which are operated in lean-burn mode are also referred to below as lean-burn engines. They are operated with a lean air/fuel mixture. Therefore, in addition to the usual pollutants, namely carbon monoxide (CO), nitrogen oxides (NOx) and unburnt hydrocarbons (HC) and particulates (PM), their exhaust gas also contains a high proportion, amounting to up to 15% by volume, of oxygen, and consequently the exhaust gas has a net oxidizing action. Therefore, the exhaust-gas purification processes by means of three-way catalysts which are customary for stoichiometrically operated internal combustion engines cannot be employed. In particular, conversion of the nitrogen oxides into nitrogen presents considerable difficulties in the oxidizing exhaust-gas atmosphere.
  • CO carbon monoxide
  • NOx nitrogen oxides
  • HC unburnt hydrocarbons
  • PM particulates
  • the main components of the nitrogen oxides in the exhaust gas from lean-burn engines are nitrogen monoxide (NO) and nitrogen dioxide (NO 2 ), with nitrogen monoxide forming the majority.
  • NO nitrogen monoxide
  • NO 2 nitrogen dioxide
  • the nitrogen monoxide makes up from 60 to 95% by volume of the nitrogen oxides as a whole.
  • SCR selective catalytic reduction
  • ammonia is added to the exhaust gas as reducing agent, and this gas mixture is then passed over a catalyst for selective catalytic reduction (SCR catalyst).
  • SCR catalyst the nitrogen oxides are selectively reacted with the ammonia to form nitrogen and water.
  • This process is nowadays employed on a large industrial scale for the purification of power plant exhaust gases.
  • Typical SCR catalysts contain, as catalytically active components, by way of example solid-state acids selected from the TiO 2 /WO 3 /MoO 3 /N 2 O5/SiO 2 /SO 3 system.
  • SCR catalysts are based on acid-resistant zeolites which have been exchanged with transition metals, such as for example dealuminized Y-zeolite, mordenite, silicalite or ZSM-5. Furthermore, the catalysts may contain further components, such as for example copper, iron, cerium and manganese.
  • SCR catalysts based on solid-state acid systems or based on zeolites are referred to below as standard SCR catalysts. They also always have a certain ability to store ammonia. Their operating temperature is approximately between 300 and 500°C.
  • the SCR process is highly complex for use in mobile applications. Therefore, the NOx storage technology has been developed as an alternative to the SCR process.
  • the nitrogen oxides contained in the lean exhaust gas are temporarily stored in the form of nitrates on a nitrogen oxide storage catalyst. Once the storage capacity of the storage catalyst is exhausted, the catalyst has to be regenerated.
  • the internal combustion engine is briefly operated with a rich air/fuel mixture, i.e. more fuel is fed to the air/fuel mixture than can be completely burnt by the combustion air — the exhaust gas is rich. It therefore still contains unburnt hydrocarbons.
  • the stored nitrates are decomposed to form nitrogen oxides and are reacted with the unburnt hydrocarbons contained in the rich exhaust gas as reducing agents to form nitrogen and water.
  • nitrogen oxide storage catalysts contain basic components, such as the metal oxides of the alkali metals and of the alkaline-earth metals, or also rare earths, such as cerium oxide and lanthanum oxide. It is preferable to use barium oxide and strontium oxide.
  • the nitrogen oxide storage catalysts also contain catalytically active precious metals, generally platinum. The role of these precious metals is to oxidize the nitrogen monoxide, which is the dominant nitrogen oxide in the exhaust gas, to form nitrogen dioxide. Only nitrogen dioxide is able to react with the storage components to form nitrates with the aid of the steam which is present in the exhaust gas. During the regeneration of the storage catalyst, the desorbed nitrogen oxides are reduced at the catalytically active precious metals to form nitro J gae"n and water.
  • the lean-burn mode is in this case the normal running mode of the lean-burn engine.
  • the nitrogen oxides in the exhaust gas are stored by the storage catalyst (storage phase).
  • the nitrogen oxides are desorbed again and converted (desorption phase).
  • the storage phase usually lasts from 1 to 2 minutes, whereas the desorption phase requires only a short time, of from 1 to 20 seconds.
  • Drawbacks of the nitrogen oxide storage technology include the fact that the storage components can easily become poisoned by sulfur, and the relatively low conversion rates of at most 60 to 70%.
  • the SCR technology is superior to the nitrogen oxide storage technology in terms of its conversion rates, its temperature activity range and its durability, but requires the use of a second operating medium - ammonia or a precursor compound which can be decomposed to form ammonia, for example urea or ammonium carbamate.
  • EP 1 226 861 Al proposes, as a further possible improvement, the integration of an oxidation catalyst in the exhaust system upstream of the SCR catalyst. With the aid of this oxidation catalyst, a proportion of the nitrogen oxides, which are predominantly present as NO in the exhaust gas, is oxidized to form NO 2 under lean operating conditions. It is known from prior art that at temperatures below approximately 300°C an NO/NO 2 mixture is more reactive in the SCR reaction than pure NO, and conse- quently the SCR catalyst achieves significantly higher conversion rates even at lower temperatures.
  • an exhaust-gas purification system for an internal combustion engine which includes, in the direction of flow of the exhaust gas, at least a first catalyst and a downstream second catalyst, the first catalyst generating ammonia from corresponding exhaust-gas constituents when the exhaust-gas composition is rich, and the second catalyst temporarily storing the ammonia generated by the first catalyst when the exhaust-gas composition is rich and subjecting the nitrogen oxides (NOx) contained in the exhaust gas to a reduction reaction using the temporarily stored ammonia as reducing agent when the exhaust-gas composition is lean.
  • NOx nitrogen oxides
  • This exhaust-gas purification system is characterized in that the exhaust-gas purification system has, downstream of the second catalyst, a third, precious-metal-containing catalyst, which contains at least one of the platinum group metals platinum, palladium and rhodium on support materials which are able to store ammonia when the exhaust-gas composition is rich and to release ammonia when the exhaust-gas composition is lean.
  • a third, precious-metal-containing catalyst which contains at least one of the platinum group metals platinum, palladium and rhodium on support materials which are able to store ammonia when the exhaust-gas composition is rich and to release ammonia when the exhaust-gas composition is lean.
  • Catalysts containing platinum group metals are highly reactive with regard to the SCR reaction in the temperature range between 150 and 250°C.
  • these catalysts cannot be used effectively at higher temperatures, since at these temperatures they preferentially convert the ammonia into nitrogen or nitrogen oxides.
  • two different SCR catalysts are combined with one another: a standard SCR catalyst with a precious-metal-containing catalyst. This makes it possible to boost the temperature activity ranges of both SCR catalysts; the precious-metal-containing SCR catalyst covers the temperature range between 150 and 250°C, and the standard SCR catalyst covers the temperature range above 250°C.
  • the standard SCR catalyst be arranged upstream of the precious-metal-containing catalyst, since otherwise the ammonia formed in the rich phases would at higher temperatures already be undesirably oxidized to form nitrogen or nitrogen oxides by the precious- metal-containing SCR catalyst and would therefore no longer be available to the standard SCR catalyst as reducing agent.
  • the ammonia formed is stored in the standard SCR catalyst.
  • the stored ammonia is reacted with the nitrogen oxides in the exhaust gas directly on the standard SCR catalyst.
  • temperatures from approximately 200 to 300°C, i.e. below the activity range of the standard SCR catalyst the ammonia which has been stored during the rich phases is reacted with the nitrogen oxides in the exhaust gas by the precious-metal- containing third catalyst.
  • the proposed exhaust-gas purification system enables the nitrogen oxide conversion levels to be increased considerably in particular at low temperatures.
  • the exhaust-gas purification system according to the invention is preferably used to purify the exhaust gases from diesel engines.
  • Catalysts of this type contain, for example, platinum on an active aluminum oxide as support material.
  • the SCR catalyst has to have a correspondingly high ammonia storage capacity, enabling it to store ammonia formed in the rich phases and to react the stored ammonia with the nitrogen oxides in the exhaust gas in the lean phases.
  • standard SCR catalysts have an ammonia storage capacity of this nature, such a capacity is not present in typical, precious-metal-containing catalysts, such as for example diesel oxidation catalysts, since the support materials used for the precious metals in these catalysts have only a low ability to store ammonia.
  • the platinum group metals of the third catalyst are applied to support materials with a correspondingly high ammonia storage capacity.
  • Suitable support materials with a capacity to store ammonia include, for example, the oxidic materials selected from the group consisting of titanium oxide, titanium oxide/aluminum oxide, titanium oxide/silicon dioxide, vanadium, vanadium/tungsten oxide, vanadium/molybdenum oxide or zeolites or mixtures thereof used for standard SCR catalysts.
  • the third catalyst is preferably applied to a downstream-side zone of the second catalyst, this zone amounting to 5 to 50% of the overall length L of the second catalyst.
  • the third catalyst is formed by platinum group metals which have previously been deposited on support materials with a capacity to store ammonia and is in the form of a coating on the downstream-side zone of the second catalyst.
  • the third catalyst is formed by platinum group metals which have previously been deposited on support materials without or with only a slight capacity to store ammo- nia.
  • the third catalyst can be applied in the form of a coating to the downstream-side zone of the second catalyst.
  • the required ammonia storage capacity is in this case provided by the second catalyst beneath it.
  • the third catalyst is particularly preferable for the third catalyst to be produced by impregnating the downstream-side zone of the second catalyst with compounds containing platinum, palladium or rhodium.
  • the materials of the second catalysts form the support materials for the platinum group metals of the , third catalyst and at the same time provide the required ammonia storage capacity.
  • the second catalyst is a standard SCR catalyst which includes at least one zeolite which has been exchanged with a transition metal or contains a solid-state acid system selected from the group consisting of titanium oxide or titanium oxide/aluminum oxide or titanium oxide/silicon dioxide in combination with vanadium, vanadium/tungsten oxide or vanadium/molybdenum oxide or zeolites or mixtures thereof.
  • the catalytically active components of the SCR catalyst may on the one hand be applied in the form of a coating to the flow passages of an inert honeycomb carrier made from cordierite or metal, in which case the SCR catalyst takes the form of what is known as a coated catalyst.
  • the catalytically active components may also be processed to form an extrudable compound and extruded to form a honeycomb carrier with flow passages for the exhaust gas. This may be called an extruded catalyst.
  • the first catalyst of the exhaust-gas purification system serves the purpose of forming ammonia from the components of the exhaust gas when the exhaust-gas composition is rich; this ammonia is then stored on the downstream catalysts and consumed for reduction of the nitrogen oxides during the lean phases.
  • Conventional three-way catalysts are eminently suitable for this purpose, but it is also possible to use other catalysts which perform this function.
  • Figures 1 to 5 show block diagrams illustrating various embodiments of the exhaust- gas purification system according to the invention
  • Figure 6 shows the NOx conversion curve in the synthesized exhaust gas for an exhaust-gas purification system a) having ah NOx storage catalyst (aged) and b) having an NOx storage catalyst (aged) and a downstream standard SCR catalyst based on zeolites exchanged with metal ions
  • Figure 7 shows the NOx conversion curve in the synthesized exhaust gas for an exhaust-gas purification system a) having an NOx storage catalyst (aged), b) having an NOx storage catalyst (aged) + standard SCR catalyst + downstream diesel oxidation catalyst c) having an NOx storage catalyst, (aged) + standard SCR catalyst with Pt-containing zone coating.
  • Figure 1 shows a block diagram of an embodiment of the exhaust-gas purification system according to the invention. It includes, arranged one behind the other in the direction of flow of the exhaust gas, a three-way catalyst (1), a standard SCR catalyst (2) and a catalyst (3) containing platinum group metals, the catalysts (2) and (3) each being able to store the ammonia formed by catalyst (1) during the rich phases.
  • FIG 2 shows a preferred variant of the exhaust-gas purification system shown in Figure 1.
  • catalyst (3) is applied to a downstream-side zone of the catalyst (2).
  • the width of this zone amounts to 5 to 50% of the length L of the catalyst (2).
  • FIG. 3 shows a further embodiment of the exhaust-gas purification system according to the invention.
  • a fourth catalyst (4) which is a nitrogen oxide storage catalyst, i.e. this catalyst stores the nitrogen oxides contained in the exhaust gas when the exhaust- gas composition is lean and releases them again when the exhaust-gas composition is rich, so that they can then be at least partially reduced with the aid of the reducing agents which are present in the rich exhaust gas, such as hydrocarbons, hydrogen or carbon monoxide, is arranged between the first and second catalysts.
  • the nitrogen oxide storage catalyst which is a nitrogen oxide storage catalyst, i.e. this catalyst stores the nitrogen oxides contained in the exhaust gas when the exhaust- gas composition is lean and releases them again when the exhaust-gas composition is rich, so that they can then be at least partially reduced with the aid of the reducing agents which are present in the rich exhaust gas, such as hydrocarbons, hydrogen or carbon monoxide, is arranged between the first and second catalysts.
  • the nitrogen oxide storage catalyst (4) also performs the function of the three-way catalyst (1), and consequently there is no need for the latter. This arrangement is particularly advantageous for purifying the exhaust gas from diesel engines.
  • Figure 5 shows a further variant of the embodiment from Figure 3.
  • the nitrogen oxide storage catalyst (4) is replaced by an oxidation catalyst (5), which partially oxidizes the nitrogen oxides contained in the exhaust gas to form nitrogen dioxide when the exhaust-gas composition is lean and thereby improves the conversion of the nitrogen oxides at the downstream SCR catalyst.
  • the catalysts were aged hydrothermally for 10 hours at a temperature of 800°C in a furnace, and their ability to remove the nitrogen oxides from an oxygen-rich exhaust gas was then tested in various combinations.
  • the catalytic activity was checked with the aid of a model exhaust gas having the following compositions: Table: Measurement conditions for determining the catalytic activity at a model gas system:
  • Figure 6 shows that the NOx conversion for the nitrogen oxide storage catalyst (curve a)) in lean/rich operation can be considerably increased by a downstream standard SCR catalyst (curve b)) based on zeolites exchanged with iron, in particular in the temperature range over 230°C. Below this temperature limit, the NOx conversions achieved by the NOx storage catalyst alone and in combination with the SCR catalyst are practically identical. At these low temperatures, in the present NO 2 -free model exhaust gas, therefore, the standard SCR catalyst has scarcely any activity.
  • Figure 7 compares the NOx conversion of the same NOx storage catalyst in lean/rich mode (curve a)) with a combination of the NOx storage catalyst together with the downstream standard SCR catalyst and a diesel oxidation catalyst arranged further downstream (curve c)).
  • the figure also shows the NOx conversion curve for the same NOx storage catalyst in lean/rich mode with the downstream standard SCR catalyst, the standard SCR catalyst additionally having been provided over 25% of its length, on the downstream side in accordance with the invention, with a Pt-containing coating (curve d)).
  • the precious metal catalyst can make use of the ammonia store provided by the standard SCR catalyst in contact with it; therefore, unlike in the system comprising the pure diesel oxidation catalyst, sufficient ammonia is available to it to reduce the nitrogen oxides. On account of its high activity even at low temperatures, therefore, it is particularly recommended to use this system for purifying the exhaust gases from diesel engines.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • General Engineering & Computer Science (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Mechanical Engineering (AREA)
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  • Catalysts (AREA)
  • Exhaust Gas After Treatment (AREA)
PCT/EP2004/010261 2003-12-23 2004-09-14 Device and process for removing nitrogen oxides from the exhaust gas of internal combustion engines with the aid of catalytically generated ammonia WO2005064130A1 (en)

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DE10360955.5 2003-12-23
DE10360955A DE10360955A1 (de) 2003-12-23 2003-12-23 Abgasreinigungsanlage und Verfahren zur Entfernung von Stickoxiden aus dem Abgas von Verbrennungsmotoren mit Hilfe von katalytisch erzeugtem Ammoniak

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EP1961933A1 (de) * 2007-02-23 2008-08-27 Umicore AG & Co. KG Katalytisch aktiviertes Dieselpartikelfilter mit Ammoniak-Sperrwirkung
WO2009056958A1 (en) * 2007-11-02 2009-05-07 Toyota Jidosha Kabushiki Kaisha Exhaust gas purification device for internal combustion engine
WO2010096641A1 (en) * 2009-02-23 2010-08-26 Corning Incorporated Exhaust gas after-treatment system
US8207084B2 (en) 2009-06-23 2012-06-26 Ford Global Technologies, Llc Urea-resistant catalytic units and methods of using the same
CN102844534A (zh) * 2010-04-01 2012-12-26 排放技术有限公司 用于运行排气处理设备的方法
US8389432B2 (en) 2006-09-25 2013-03-05 Umicore Ag & Co. Kg Structured automotive catalyst with improved thermal ageing stability
US8398943B2 (en) 2006-07-08 2013-03-19 Man Truck & Bus Ag Arrangement for reducing nitrogen oxides in exhaust gases
DE202007019652U1 (de) 2006-05-31 2014-12-19 Umicore Ag & Co. Kg Katalysator zur Verminderung Stickstoff-haltiger Schadgase aus dem Abgas von Dieselmotor
EP2567081A4 (de) * 2010-05-05 2015-05-27 Basf Corp Integrierte scr- und amox-katalysatorsysteme
EP2732141B1 (de) 2011-07-13 2017-03-08 Umicore AG & Co. KG Verfahren und vorrichtung zur reaktivierung von abgasreinigungssystemen von dieselmotoren mit niederdruck-agr

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Publication number Priority date Publication date Assignee Title
DE102006031724B3 (de) * 2006-07-08 2008-04-30 Umicore Ag & Co. Kg Strukturierter SCR-Katalysator zur Reduktion von Stickoxiden im Abgas von Magermotoren unter Verwendung von Ammoniak als Reduktionsmittel
KR101362685B1 (ko) 2006-07-08 2014-02-13 우미코레 아게 운트 코 카게 환원제로서 암모니아를 사용하여 희박 혼합 기관의 배기 가스로부터의 질소 산화물을 환원시키기 위한 구조화된 ｓｃｒ 촉매
DE102006031660A1 (de) * 2006-07-08 2008-01-17 Man Nutzfahrzeuge Ag Anordnung zur Verminderung von Stickoxiden in Abgasen

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US5409681A (en) * 1991-11-27 1995-04-25 Babcock-Hitachi Kabushiki Kaisha Catalyst for purifying exhaust gas
EP0773354A1 (de) * 1995-11-10 1997-05-14 Toyota Jidosha Kabushiki Kaisha Vorrichtung zum Reinigen des Abgases einer Brennkraftmaschine
EP0773057A1 (de) * 1995-11-09 1997-05-14 Toyota Jidosha Kabushiki Kaisha Abgasreinigungskatalysator
US5974793A (en) * 1996-04-19 1999-11-02 Toyota Jidosha Kabushiki Kaisha Exhaust gas purification device for an internal combustion engine
DE10113947A1 (de) * 2001-03-22 2002-09-26 Daimler Chrysler Ag Verfahren zur Verringerung des Stickoxidgehalts im Abgas einer im Mager-Fett-Wechsel betreibbaren Brennkraftmaschine

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US5409681A (en) * 1991-11-27 1995-04-25 Babcock-Hitachi Kabushiki Kaisha Catalyst for purifying exhaust gas
EP0773057A1 (de) * 1995-11-09 1997-05-14 Toyota Jidosha Kabushiki Kaisha Abgasreinigungskatalysator
EP0773354A1 (de) * 1995-11-10 1997-05-14 Toyota Jidosha Kabushiki Kaisha Vorrichtung zum Reinigen des Abgases einer Brennkraftmaschine
US5974793A (en) * 1996-04-19 1999-11-02 Toyota Jidosha Kabushiki Kaisha Exhaust gas purification device for an internal combustion engine
DE10113947A1 (de) * 2001-03-22 2002-09-26 Daimler Chrysler Ag Verfahren zur Verringerung des Stickoxidgehalts im Abgas einer im Mager-Fett-Wechsel betreibbaren Brennkraftmaschine

Cited By (18)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
DE202007019652U1 (de) 2006-05-31 2014-12-19 Umicore Ag & Co. Kg Katalysator zur Verminderung Stickstoff-haltiger Schadgase aus dem Abgas von Dieselmotor
US8398943B2 (en) 2006-07-08 2013-03-19 Man Truck & Bus Ag Arrangement for reducing nitrogen oxides in exhaust gases
US8389432B2 (en) 2006-09-25 2013-03-05 Umicore Ag & Co. Kg Structured automotive catalyst with improved thermal ageing stability
WO2008101585A1 (de) * 2007-02-23 2008-08-28 Umicore Ag & Co. Kg Katalytisch aktiviertes dieselpartikelfilter mit ammoniak-sperrwirkung
US8226896B2 (en) 2007-02-23 2012-07-24 Umicore Ag & Co. Kg Catalytic activated diesel particle filter with ammonia trap effect
EP1961933A1 (de) * 2007-02-23 2008-08-27 Umicore AG & Co. KG Katalytisch aktiviertes Dieselpartikelfilter mit Ammoniak-Sperrwirkung
RU2449135C2 (ru) * 2007-02-23 2012-04-27 Умикоре Аг Унд Ко. Кг Каталитически активированный фильтр для отфильтровывания твердых частиц из отработавших газов дизельного двигателя, обладающий задерживающим аммиак действием
WO2009056958A1 (en) * 2007-11-02 2009-05-07 Toyota Jidosha Kabushiki Kaisha Exhaust gas purification device for internal combustion engine
WO2010096641A1 (en) * 2009-02-23 2010-08-26 Corning Incorporated Exhaust gas after-treatment system
US8207084B2 (en) 2009-06-23 2012-06-26 Ford Global Technologies, Llc Urea-resistant catalytic units and methods of using the same
US8404202B2 (en) 2009-06-23 2013-03-26 Ford Global Technologies, Llc Urea-resistant catalytic units and methods of using the same
US20130255235A1 (en) * 2010-04-01 2013-10-03 Emitec Gesellschaft Fuer Emissionstechnologie Mbh Method for operating an exhaust-gas treatment device and motor vehicle having the device
CN102844534A (zh) * 2010-04-01 2012-12-26 排放技术有限公司 用于运行排气处理设备的方法
US9151199B2 (en) 2010-04-01 2015-10-06 Emitec Gesellschaft Fuer Emissionstechnologie Mbh Method for operating an exhaust-gas treatment device and motor vehicle having the device
EP2567081A4 (de) * 2010-05-05 2015-05-27 Basf Corp Integrierte scr- und amox-katalysatorsysteme
JP2016193429A (ja) * 2010-05-05 2016-11-17 ビーエーエスエフ コーポレーション 一体型ｓｃｒおよびａｍｏｘ触媒システム
EP3674524A1 (de) * 2010-05-05 2020-07-01 BASF Corporation Integrierte scr- und amox-katalysatorsysteme
EP2732141B1 (de) 2011-07-13 2017-03-08 Umicore AG & Co. KG Verfahren und vorrichtung zur reaktivierung von abgasreinigungssystemen von dieselmotoren mit niederdruck-agr

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