US20010004832A1 - Exhaust gas purifying system and catalyst - Google Patents

Exhaust gas purifying system and catalyst Download PDF

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US20010004832A1
US20010004832A1 US09/736,369 US73636900A US2001004832A1 US 20010004832 A1 US20010004832 A1 US 20010004832A1 US 73636900 A US73636900 A US 73636900A US 2001004832 A1 US2001004832 A1 US 2001004832A1
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exhaust gas
oxygen
hydrogen
nox
reducing catalyst
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Yasunari Hanaki
Katsuo Suga
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Nissan Motor Co Ltd
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Assigned to NISSAN MOTOR CO., LTD. reassignment NISSAN MOTOR CO., LTD. ASSIGNMENT OF ASSIGNORS INTEREST (SEE DOCUMENT FOR DETAILS). Assignors: HANAKI, YASUNARI, SUGA, KATSUO
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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]
    • 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
    • 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
    • B01D53/9495—Controlling the catalytic process
    • 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
    • F01N13/009—Exhaust or silencing apparatus characterised by constructional features 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
    • 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
    • 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
    • B01D2251/10—Oxidants
    • B01D2251/104—Ozone
    • B—PERFORMING OPERATIONS; TRANSPORTING
    • B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
    • B01D—SEPARATION
    • B01D2259/00—Type of treatment
    • B01D2259/80—Employing electric, magnetic, electromagnetic or wave energy, or particle radiation
    • B01D2259/804—UV light
    • 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
    • F01N2240/30—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 a fuel reformer
    • 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
    • F01N2570/14—Nitrogen oxides
    • 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
    • F01N2610/00—Adding substances to exhaust gases
    • F01N2610/04—Adding substances to exhaust gases the substance being hydrogen
    • 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
    • Y02C—CAPTURE, STORAGE, SEQUESTRATION OR DISPOSAL OF GREENHOUSE GASES [GHG]
    • Y02C20/00—Capture or disposal of greenhouse gases
    • Y02C20/10—Capture or disposal of greenhouse gases of nitrous oxide (N2O)
    • 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

  • This invention relates to improvements in an exhaust gas purifying system for purifying exhaust gas discharged from an internal combustion engine, a furnace, a burner or the like, and more particularly to the exhaust gas purifying system for effectively reducing nitrogen oxides (NOx) in oxygen-excessive exhaust gas discharged from the engine under lean-burn operation.
  • NOx nitrogen oxides
  • NOx is trapped when exhaust gas takes an oxygen-excessive or lean atmosphere (having the air-fuel ratio leaner than the stoichiometric value), and then the trapped NOx is released and reduced by temporarily lowering an oxygen concentration of exhaust gas so that exhaust gas takes a rich atmosphere (having the air-fuel ratio richer than the stoichiometric value).
  • the catalyst contains a large amount of alkali metal and alkaline earth metal for the purpose of trapping NOx in the oxygen-excessive atmosphere of exhaust gas, and therefore a catalytic activity (for oxidation) of platinum and rhodium cannot be sufficiently exhibited when exhaust gas is low in temperature. Furthermore, in order to sufficiently oxidize or remove HO and CO components which have not been consumed under NOx reduction reaction, it is required to oxidize or remove the components by making oxidation reaction on the NOx reducing catalyst, or otherwise by a three-way catalyst disposed downstream of the NOx reducing catalyst for reducing NOx.
  • a catalyst includes a catalytic metal such as copper or the like carried on a carrier formed of a metal oxide such as alumina or the like.
  • HC hydrocarbons
  • nitrogen oxides in exhaust gas can be reduced to be removed under the oxygen-excessive atmosphere.
  • hydrocarbons are used as the reducing agent, and therefore chemical reaction rate for reduction of nitrogen oxides is low. This requires a large volume of the catalyst. It will be understood that mounting the large volume catalyst on a movable body such as an automotive vehicle is not practical.
  • Japanese Patent Provisional Publication No. 5-168856 discloses such a technique that exhaust gas containing nitrogen oxides and oxygen gas is supplied with hydrogen produced by electrolysis of water vapor by using a solid electrolyte and brought into contact with a catalyst containing platinum carried on a carrier formed of alumina, silica, zeolite or the like.
  • the temperature range where nitrogen oxides can be effectively reduced is so low as to be from 60 to 130° C.
  • Japanese Patent Provisional Publication No. 8-10574 discloses the following technique for removing nitrogen oxides: Exhaust gas is oxygen-excessive and therefore has an oxygen concentration higher than a stoichiometric value to oxidize oxidizable components in exhaust gas.
  • the oxygen-excessive exhaust gas containing hydrogen is brought into contact with a reducing catalyst (for nitrogen oxides) containing noble metal element and molybdenum carried on a porous carrier.
  • the temperature range where nitrogen oxides can effectively reduced At are from 90 to 250° C. Therefore, nitrogen oxides cannot be effectively reduced in a temperature range higher than the above temperature range.
  • an object of the present invention is to provide an improved exhaust gas purifying catalyst which can effectively overcome drawbacks encountered in conventional techniques for reducing NOx in exhaust gas.
  • Another object of the present invention is to provide an improved exhaust gas purifying system which can effectively remove NOx, HC and CO in the oxygen-excessive exhaust gas under a high temperature condition higher than 250° C. while obtaining a high fuel economy improvement effect.
  • An aspect of the present invention resides in an exhaust gas purifying system comprising a NOx reducing catalyst for reducing NOx in the presence of at least hydrogen serving as reducing agent.
  • the NOx reducing catalyst is disposed in an exhaust gas passageway of a combustion device.
  • the NOx reducing catalyst includes a porous substrate, and platinum and cesium carried on the porous substrate.
  • a device is provided to enrich oxygen-excessive exhaust gas with hydrogen before the oxygen-excessive exhaust gas reaches the NOx reducing catalyst, the oxygen-excessive exhaust gas enriched with hydrogen being introduced through the exhaust gas passageway to the NOx reducing catalyst.
  • the oxygen-excessive exhaust gas enriched with hydrogen is brought into contact with the NOx reducing catalyst under a condition in which temperature of at least one of the NOx reducing catalyst and the oxygen-excessive exhaust gas enriched with hydrogen is within a range of from 250 to 600° C.
  • a exhaust gas purifying system for an internal combustion engine comprising a NOx reducing catalyst for reducing NOx in the presence of at least hydrogen serving as reducing agent.
  • the NOx reducing catalyst is disposed in an exhaust gas passageway of the engine.
  • the NOx reducing catalyst includes a porous substrate, and platinum and cesium carried on the porous substrate.
  • At least one of a control unit for controlling engine operating parameters of the engine and a catalyst disposed in the exhaust gas passageway upstream of the NOx reducing catalyst are provided.
  • the control unit and catalyst are arranged to enrich oxygen-excessive exhaust gas with hydrogen before the oxygen-excessive exhaust gas reaches the NOx reducing catalyst, the oxygen-excessive exhaust gas enriched with hydrogen being introduced through the exhaust gas passageway to the NOx reducing catalyst.
  • the oxygen-excessive exhaust gas enriched with hydrogen is brought into contact with the NOx reducing catalyst under a condition in which temperature of at least one of the NOx reducing catalyst and the oxygen-excessive exhaust gas enriched with hydrogen is within a range of from 250 to 600° C.
  • a further aspect of the present invention resides in a catalyst for reducing NOx in an exhaust gas purifying system including a device for enriching oxygen-excessive exhaust gas with hydrogen, the oxygen-excessive exhaust gas flowing through an exhaust gas passageway of a combustion device.
  • the NOx reducing catalyst functions in the presence of at least hydrogen, serving as reducing agent, which is in the oxygen-excessive exhaust gas enriched with hydrogen.
  • the NOx reducing catalyst is disposed in the exhaust gas passageway and includes a porous substrate, and platinum and cesium carried on the porous substrate in a mol ratio of cesium/platinum ⁇ 0.5/I.
  • the oxygen-excessive exhaust gas enriched with hydrogen is brought into contact with the NOx reducing catalyst under a condition in which temperature of at least one of the NOx reducing catalyst and the oxygen-excessive exhaust gas enriched with hydrogen is within a range of from 250 to 600° C.
  • a still further aspect of the present invention resides in a process of purifying exhaust gas, comprising (a) providing a NOx reducing catalyst for reducing NOx in the presence of at least hydrogen serving as reducing agent, the NOx reducing catalyst being disposed in an exhaust gas passageway of a combustion device, the NOx reducing catalyst including a porous substrate, and platinum and cesium carried on the porous substrate; (b)enriching oxygen-excessive exhaust gas with hydrogen before the oxygen-excessive exhaust gas reaches the NOx reducing catalyst, the oxygen-excessive exhaust gas enriched with hydrogen being introduced through the exhaust gas passageway to the NOx reducing catalyst; and (c) causing the oxygen-excessive exhaust gas enriched with hydrogen to be brought into contact with the NOx reducing catalyst under a condition in which temperature of at least one of the NOx reducing catalyst and the oxygen-excessive exhaust gas enriched with hydrogen is within a range of from 250 to 600° C.
  • FIG. 1 is a schematic illustration of an engine system to which an exhaust gas purifying system according to the present invention is incorporated, usable for evaluation of performance of the exhaust gas purifying system.
  • Au exhaust gas purifying system comprises a NOx (nitrogen oxides) reducing catalyst for reducing NOx in the presence of at least H 2 (hydrogen) serving as reducing agent.
  • the NOx reducing catalyst is disposed in an exhaust gas passageway of a combustion device.
  • the NOx reducing catalyst includes a porous substrate, and platinum and cesium carried on the porous substrate.
  • the exhaust gas purifying system further comprises a device or means for enriching oxygen-excessive exhaust gas with hydrogen before the oxygen-excessive exhaust gas reaches the NOx reducing catalyst, the oxygen-excessive exhaust gas enriched with hydrogen being introduced through the exhaust gas passageway to the NOx reducing catalyst.
  • the oxygen-excessive exhaust gas enriched with hydrogen is brought into contact with the NOx reducing catalyst under a condition in which temperature of at least one of the NOx reducing catalyst and the oxygen-excessive exhaust gas enriched with hydrogen is within a range of from 250 to 600° C.
  • the combustion device is an internal combustion engine for an automotive vehicle, or a burning device such as a furnace or a burner.
  • the combustion device has the exhaust gas passageway through which exhaust gas from the combustion device flows.
  • the NOx reducing catalyst is disposed in the exhaust gas passageway.
  • the oxygen-excessive exhaust gas means exhaust gas having an air-fuel ratio (or oxygen-combustibles ratio) leaner than stoichiometric value, and therefore referred also as to “lean-burn exhaust gas (exhaust gasp produced as a result of lean-burn operation of the engine)”. It will be understood that air-fuel mixture having air-fuel ratio leaner than the stoichiometric value is supplied to combustion chambers or cylinders of the engine under the lean-burn operation.
  • NOx trap catalyst or agent has been developed in order to reduce NOx in the oxygen-excessive exhaust gas as disclosed in Japanese Patent No. 2600492, in which the NOx trap catalyst can trap NOx in oxygen-excessive exhaust gas.
  • NOx trapped to the NOx trap catalyst it is required that the oxygen concentration in exhaust gas is temporarily lowered under the rich spike process, thereby causing NOx trapped to the catalyst to release and allowing the released NOx to react with HC (hydrocarbons), CO (carbon monoxide) and/or the like.
  • the oxygen-excessive exhaust gas enriched with hydrogen is supplied to the NOx reducing catalyst, thereby improving a NOx reducing efficiency.
  • the oxygen-excessive exhaust gas enriched with hydrogen can be prepared by adding hydrogen to the oxygen-excessive exhaust gas or by raising the concentration of hydrogen in the oxygen-excessive exhaust gas.
  • a catalyst for producing hydrogen (H 2 ) by reforming HC and CO or a device for generating hydrogen (H 2 ) is preferably provided.
  • Hydrogen (H 2 ) from the hydrogen producing catalyst or the hydrogen generating device is supplied into the exhaust gas passageway upstream of the NOx reducing catalyst.
  • Such hydrogen from the hydrogen producing catalyst or the hydrogen generating device is used as reducing agents in the NOx reducing catalyst (may accompany with a small amount of HC and CO in exhaust gas), thereby effectively removing NOx, HC and CO.
  • the NOx reducing catalyst which uses at least hydrogen as reducing agent is constituted of the porous substrate which carries noble metal(s), alkali metal(s) and/or the like. It is preferable that the porous substrate carries at least platinum (Pt) for improving adsorption and activation of hydrogen and NOx in the NOx reducing catalyst. Such adsorption and activation improvement is assumed to result from the fact that platinum largely contributes to proceed selective reducing reaction for NOx by hydrogen.
  • the porous substrate carries cesium (Cs).
  • Cs cesium
  • activation of oxygen on platinum can be suppressed thereby making it possible to reduce NOx by hydrogen.
  • the character of Pt for adsorbing HC can be suppressed thereby improving the selective reactivity between hydrogen and NOx.
  • the porous substrate may carry other noble metals (such as Pd, Rh and/or the like) than Pt, and may carry other alkali metal(s) other than Cs and/or alkaline earth metal(s). Such alkali metal(s) and/or alkaline earth metal(s) may be carried together with Cs on the porous substrate.
  • noble metals such as Pd, Rh and/or the like
  • alkali metal(s) and/or alkaline earth metal(s) may be carried together with Cs on the porous substrate.
  • NOx has been able to be effectively reduced when the temperature of a NOx reducing catalyst and/or the oxygen-excessive exhaust gas enriched with hydrogen is lower than 150° C. because activation of oxygen can be suppressed at such a temperature lower than 150° C.
  • the temperature exceeds 150° C. activation rate of oxygen is raised, and therefore reaction between H 2 and oxygen tends to readily occur as compared with reaction between H 2 and NO, so that occurrence of reduction reaction of NOx becomes difficult.
  • the NOx reducing catalyst in the exhaust gas purifying system of the present invention even when the temperature of the NOx reducing catalyst and/or the oxygen-excessive exhaust gas enriched with hydrogen exceeds 150° C., activation of oxygen on Pt and adsorption of HC to Pt can be suppressed under the mutual effects between Pt and Cs, so that it is made possible to reduce NOx by hydrogen. It is to be noted that the NOx reducing catalyst of the present invention is arranged to purify exhaust gas in a further high temperature range of from 250 to 600° C.
  • the temperature of the NOx reducing catalyst and/or the oxygen-excessive exhaust gas is lower than 250° C., HO and CO in exhaust gas cannot be sufficiently oxidized since activity of oxygen on Pt is suppressed while NOx can be reduced as discussed above. If the temperature exceeds 600° C., hydrogen and oxygen unavoidably directly react with each other so that NOx cannot be reduced.
  • the exhaust gas purifying system of the present invention can purify exhaust gas even within a low temperature range lower than 150° C. as discussed above. However, at a further low temperature range lower than 90° C., water produced under reduction reaction of NOx will condense to be accumulated on the catalyst thereby lowering NOx reducing efficiency.
  • the oxygen-excessive exhaust gas is enriched with hydrogen.
  • This enrichment is preferably accomplished by reforming HC and CO under action of a HC reforming device or means and a CO reforming device or means.
  • the HC reforming device includes a HC partial oxide producing device or means for producing partial oxide of HC by causing HC in the oxygen-excessive exhaust gas to react with oxygen at high temperatures, typically according to the following reaction formula (1):
  • HC(O) represents partial oxide of HC, produced by partially oxidizing HC.
  • the CO reforming device is for producing hydrogen by causing CO in the oxygen-excessive exhaust gas to react with water, typically according to the following reaction formula (2):
  • hydrogen gas serving as the reducing agent for NOx can be produced thereby increasing the concentration of hydrogen in the oxygen-excessive exhaust gas. It is sufficient that the above HC reforming device and CO reforming device produce partial oxide of HC and makes CO reforming in combustion gas and/or exhaust gas.
  • the combustion gas is burning gas within each cylinder of the engine.
  • the HC reforming device and CO reforming device include ones of the combustion system and of the catalytic system.
  • the HC reforming device and the CO reforming device of the combustion system are arranged to control production of hydrogen gas and therefore preferably includes a device or means for controlling temperature and pressure of the oxygen-excessive exhaust gas and concentrations of oxygen, water, HC and CO in the oxygen-excessive exhaust gas.
  • a controlling device include a device for controlling at least one of engine operating parameters such as fuel injection amount (amount of fuel injected from a fuel injector), fuel injection timing (timing at which fuel is injected from the fuel injector), spark timing (timing at which a spark plug generates spark), opening and/or closing timings of intake and/or exhaust valves of the engine.
  • Such a controlling device is, for example, an electronic control unit (shown in FIG. 1) for electronically controlling the engine operating parameters in accordance with engine operating conditions including the conditions of exhaust gas flowing through the exhaust gas passageway.
  • the HC reforming device and the CO reforming device of the catalytic system preferably include a HC reforming catalyst section for causing the reaction represented by the reaction formula (1), and a CO reforming catalyst section for causing the reaction represented by the reaction formula (2).
  • catalyst components used in the HO reforming catalyst section and the CO reforming catalyst section can cause the reactions represented by the above reaction formulae (1) and (2)
  • examples of the catalyst components are Pt, Pd, Rh, Ce and Zr.
  • the catalyst components used in the HC reforming catalyst section contains cerium (Ce) oxide carrying Pd
  • the catalyst components used in the CO reforming catalyst section contains zirconium (Zr) oxide carrying Rh.
  • the porous substrate carries Pd in an amount ranging 3 to 20 g, Rh in an amount ranging from 0.1 to 10 g, and Pt in an amount ranging from 0.1 to 2 g per one liter of the porous substrate (preferably a monolithic porous substrate).
  • an oxidizing catalyst or a three-way catalyst may be typically used as the HC and CO reforming device.
  • the HC and CO reforming devices of the combustion system and of the catalytic system may be used in combination.
  • a hydrogen gas generating device disposed outside of the exhaust gas passageway may be used in place of the HC and CO reforming devices in order to supply hydrogen gas into the oxygen-excessive exhaust gas.
  • the hydrogen gas generating device is a hydrogen gas bomb (container) disposed to supply hydrogen gas into the exhaust gas passageway upstream of the NOx reducing catalyst.
  • the composition of the oxygen-excessive exhaust gas enriched with hydrogen, to be brought into contact with the NOx reducing catalyst can meet the relation represented by the above formula (3) by supplying hydrogen gas into the exhaust gas.
  • the oxygen-excessive exhaust gas to be introduced to the NOx reducing catalyst may contain water vapor, carbon dioxide gas and the like if the composition of the oxygen-excessive exhaust gas to be introduced to the NOx reducing catalyst can meet the relation represented by the above formula (3).
  • the NOx reducing catalyst is disposed in the exhaust gas passageway so as to be supplied with the oxygen-excessive exhaust gas enriched with hydrogen.
  • the NOx reducing catalyst it is preferable that Cs and Pt are carried on the porous substrate in a mol ratio of Cs/Pt ⁇ 0.5/1. With the mol ratio of Cs/Pt ⁇ 0.5/1, a large amount of mutually effected sites of the noble metal element-Cs system exist on the surface of the NOx reducing catalyst, and therefore the catalyst can exhibit further excellent NOx reducing activity.
  • the ratio is Cs/Pt ⁇ 0.5/1, the mutual effects between the noble metal and Cs are weak so that NOx reducing action is degraded at a high temperature region of not lower than 250° C. If the mol ratio is Cs/Pt ⁇ 20, NOx reducing activity can be exhibited while no improvement in reducing activity can be hardly found.
  • the porous substrate of the NOx reducing catalyst may carry Rh, Pd and/or the like as the noble metal in addition to Pt.
  • the amount of the noble metal(s) is not limited to a particular range, in which it is practically preferable that the noble metal(s) is carried in an amount ranging from 0.1 to 20% by weight relative to the porous substrate.
  • the porous substrate is preferably a monolithic substrate formed of heat resistant material.
  • the monolithic substrate is preferably of a honeycomb-type.
  • the heat resistant material is preferably ceramic material such as cordierite ceramic, or metal such as ferrite stainless steel. However, the heat resistant material is not limited to the above ones.
  • the honeycomb-type monolithic substrate is formed with a plurality of cells which axially extend. Each cell is defined by thin walls which axially extend.
  • the noble metal element(s) are carried on porous carrier (powder) which is formed as a layer on the surface of the porous substrate (monolithic substrate) in order to improve dispersibility of the noble metal element(s) and to increase a reactive surface area.
  • porous carrier porous carrier
  • examples of such porous carrier (powder) are alumina including activated alumina), silica-alumina and zeolite, and any mixtures thereof. Of these, the activated alumina is the most preferable.
  • rare earth element(s), zirconium and/or the like may be added to the porous carrier in order to increase the heat resistance of the porous carrier so as to keep a high specific surface area of the porous carrier.
  • the amount of the porous carrier to be used in the NOx reducing catalyst is preferably within a range of from 50 to 300 g per one liter of the monolithic substrate.
  • the NOx reducing catalyst and/or the oxygen-excessive exhaust gas are at a temperature within a range of from 250 to 600° C., in which the NOx reducing catalyst is preferably at the temperature within a range of from 250 to 500° C. at which range the efficiency of reducing NOx can be largely improved.
  • Pt, Pd and Rh (noble metals) and Ce and Zr (added components) were carried on activated alumina powder thereby to prepare catalytic powder.
  • the catalytic powder was formed into slurry.
  • This slurry was coated on a ceramic honeycomb-type monolithic substrate having a volume of 1.3 liters and formed with a plurality of axially extending cells each of which is defined by axially extending thin walls, so that the walls of the cells were coated with the slurry. Thereafter, the coated monolithic substrate was blown with air stream to remove excessive slurry in the cells, and dried at 130° C. and then fired at 400° C. for 1 hour.
  • a closed coupled three-way catalyst was obtained carrying the noble metals in a total amount of 500 g per one cubic feet of the monolithic substrate, in which a weight ratio of Pt/Pd/Rh was 1/1/100/1/4.
  • the closed coupled three-way catalyst was designed to be disposed closed and coupled to an exhaust manifold of the engine and therefore located upstream of the NOx reducing catalyst.
  • Activated alumina powder was impregnated with an aqueous solution of Pd nitrate, and dried and then fired in air at 400° C. for 1 hour thereby to form Pd-carried alumina powder (Powder 1) whose concentration of Pd carried was 4% by weight.
  • Activated alumina powder was impregnated with an aqueous solution of dinitrodiammine platinum, and dried and then fired in air at 400° C. for 1 hour thereby to form Pt-carried alumina powder (Powder 2) whose concentration of Pt carried was 6% by weight.
  • activated alumina powder was impregnated with an aqueous solution of Rh nitrate, and dried and then fired in air at 400° C. for 1 hour thereby to form Rh-carried alumina powder (Powder 3) whose concentration of Rh carried was 4% by weight.
  • a porcelain ball mill was charged with 64 g of Powder 1, 107 g of Powder 2, 16 g of Powder 3, 13 g of alumina and 200 g of water, followed by mixing and pulverizing, thereby obtaining slurry containing powder materials whose average particle size was 3.2 ⁇ m.
  • This slurry was coated on a cordierite ceramic honeycomb-type monolithic substrate having a volume of 1.3 liters and 400 (axially extending) cells per square inch, so that thin 4 walls of cells were coated with the slurry.
  • the coated monolithic substrate was blown with air stream to remove excessive slurry in the cells, and dried at 130° C. and then fired at 400° C. for 1 hour.
  • a catalyst A was prepared in which a catalytic coat layer was formed on the wall of the cells of the monolithic substrate.
  • the weight of the catalytic coat layer was 110 g per one liter of the monolithic carrier.
  • a porcelain ball mill was charged with 64 g of Powder 1, 54 g of Powder 2, 82 g of alumina and 200 g of water, followed by mixing and pulverizing, thereby obtaining slurry containing powder materials whose average particle size was 3.2 ⁇ m.
  • This slurry was coated on the catalyst A, so that the walls of the cells were coated with the slurry.
  • the coated monolithic carrier was blown with air stream to remove excessive slurry in the cells, and dried at 130° C. and then fired at 400° C. a for 1 hour.
  • a catalyst B was prepared in which a catalytic coat layer was formed on the catalytic layer of the catalyst A.
  • the weight of total catalytic coat layers was 330 g per one liter of the monolithic crier.
  • the catalyst B was impregnated with an aqueous 5 solution of cesium carbonate. Then, the coated monolithic substrate was dried at 130° C., and then fired at 400° C. for 1 hour. As a result, a catalyst C (NOx reducing catalyst) was prepared carrying 80 g of Cs (calculated as oxide) per one liter of the monolithic substrate.
  • the closed coupled three-way catalyst was disposed in an exhaust gas passageway leading from a cylinder direct injection internal combustion engine (identified as “ENGINE”).
  • ENGINE direct injection internal combustion engine
  • the closed coupled three-way catalyst was located close to and coupled to an exhaust manifold of the engine.
  • the NOx reducing catalyst was disposed in the exhaust gas passageway and located downstream of the closed coupled three-way catalyst.
  • a closed coupled catalyst was prepared in the same manner as that in Example 1.
  • a NOx reducing catalyst was prepared by repeating the procedure for preparation of that in Example 1 with the exception that 15 g of Cs was carried per one liter of the monolithic substrate.
  • Example 2 An exhaust gas purifying system of Example 2 was constructed similarly to that in Example 1.
  • a closed coupled catalyst was prepared in the same manner as that in Example 1.
  • a NOx reducing catalyst was prepared by repeating the procedure for preparation of that in Example 1 with the exception that the catalyst C was further impregnated with barium acetate and magnesium acetate so that 10 g of Ba (calculated as oxide) and 5 g of Mg (calculated as oxide) were carried per one liter of the monolithic substrate.
  • Example 3 An exhaust gas purifying system of Example 3 was constructed similarly to that in Example 1.
  • a closed coupled catalyst was prepared in the same manner as that in Example 1.
  • Activated alumina powder was impregnated with an aqueous solution of Pd nitrate, and dried and then fired in air at 400° C. for 1 hour thereby to form Pd-carried alumina powder (Powder 1) whose concentration of Pd carried was 2% by weight.
  • Activated alumina powder was impregnated with an aqueous solution of dinitrodiammine platinum, and dried and then fired in air at 400° C. for 1 hour thereby to form Pt-carried alumina powder (Powder 2) whose concentration of Pt carried was 3% by weight.
  • activated alumina powder was impregnated with an aqueous solution of Rh nitrate, and dried and then fired in air at 400° C. for 1 hour thereby to form Rh-carried alumina powder (Powder 3) whose concentration of Rh carried was 2% by weight.
  • a porcelain ball mill was charged with 64 g of Powder 1, 107 g of Powder 2, 16 g of Powder 3, 13 g of alumina and 200 g of water, followed by mixing and pulverizing, thereby obtaining slurry containing powder materials whose average particle size was 3.2 ⁇ m.
  • This slurry was coated on a cordierite ceramic honeycomb-type monolithic substrate having a volume of 1.3 liters and 400 (axially extending) cells per square inch, so that thin walls of cells were coated with the slurry.
  • the coated monolithic substrate was blown with air stream to remove excessive slurry in the cells, and dried at 130° C. and then fired at 400° C. for 1 hour.
  • a catalyst A was prepared in which a catalytic coat layer was formed on the wall of the cells of the monolithic substrate The weight of the catalytic coat layer was 110 g per one liter of the monolithic carrier.
  • a porcelain ball mill was charged with 64 g of Powder 1, 54 g of Powder 2, 82 g of alumina and 200 g of water, followed by mixing and pulverizing, thereby obtaining slurry containing powder materials whose average particle size was 3.2 ⁇ m.
  • This slurry was coated on the catalyst A, so that the walls of the cells were coated with the slurry.
  • the coated monolithic carrier was blown with air stream to remove excessive slurry in the cells, and dried at 130° C. and then fired at 400° C. for 1 hour.
  • a catalyst B was prepared in which a catalytic coat layer was formed on the catalytic layer of the catalyst A.
  • the weight of total catalytic coat layers was 330 g per one liter of the monolithic carrier.
  • the catalyst B was impregnated with an aqueous solution of cesium carbonate. Then, the coated monolithic substrate was dried at 130° C., and then fired at 400° C. for 1 hour. As a result, a catalyst C (NOx reducing catalyst) was prepared carrying 30 g of Cs (calculated as oxide) per one liter of the monolithic substrate.
  • Example 4 An exhaust gas purifying system of Example 4 was constructed similarly to that in Example 1.
  • a closed coupled catalyst was prepared in the same manner as that in Example 1.
  • a NOx reducing catalyst was prepared by repeating the procedure for preparation of that in Example 4 with the exception that the catalyst C was further impregnated with barium acetate and magnesium acetate so that 10 g of Ba (calculated as oxide) and 5 g of Mg (calculated as oxide) were carried per one liter of the monolithic substrate.
  • Example 5 An exhaust gas purifying system of Example 5 was constructed similarly to that in Example 1.
  • a closed coupled catalyst was prepared in the same manner as that in Example 1.
  • a NOx reducing catalyst was prepared by repeating the procedure for preparation of that in Example 1 with the exception that 5 g of Cs was carried per one liter of the monolithic substrate.
  • a closed coupled catalyst was prepared in the same manner as that in Example 1.
  • a NOx reducing catalyst was prepared by repeating the procedure for preparation of that in Example 1 with the exception that no Cs was carried.
  • a closed coupled catalyst was prepared in the same manner as that in Example 1.
  • a NOx reducing catalyst was prepared in the same manner as that in Example 1.
  • An exhaust gas purifying system of Comparative Example 1 was constructed similarly to that in Example 1.
  • the exhaust gas purifying system of Comparative Example 3 will be subjected to an emission performance evaluation test (discussed hereinafter) at a temperature range different from that for Example 1.
  • Evaluation test for emission performance was conducted on the exhaust gas purifying systems of Examples and Comparative Examples, using an evaluation engine system as shown in FIG. 1.
  • each exhaust gas purifying system was incorporated in the evaluation engine system including the engine which was a cylinder direct injection internal combustion engine having a displacement of 1.8 liters and produced by Nissan Motor Co., Ltd.
  • the cylinder direct injection internal combustion engine fuel was directly injected into each cylinder of the engine.
  • the closed coupled three-way catalyst and the NOx reducing catalyst of Examples and Comparative Example underwent a durability test in which the both catalysts were disposed in an exhaust gas passageway connected to an internal combustion engine produced by Nissan Motor Co., Ltd, in such a manner as to be shown in FIG. 1.
  • the engine was operated under the following test conditions:
  • Fuel “Nisseki Dasshu Gasoline” produced by Nippon Oil Co., Ltd. and having a Pb content of 0 mg/usg (US gallon) and a S content of not more than 30 ppm;
  • Time of operation of the engine 50 hours.
  • the catalyst 1 undergone the durability test was subjected to the emission performance evaluation test conducted under a test mode “FTP-75 (LA4) mode” employed in the Unites States of America.
  • the exhaust gas purifying system was incorporated in the evaluation engine system of FIG. 1.
  • each of the dosed coupled three-way catalyst and the NOx reducing catalyst had the volume of 1.3 liters.
  • a concentration A of gas components (HO, CO and NOx) in exhaust gas from the engine in a state where no exhaust gas purifying system was provided was measured, and a concentration B in exhaust gas emitted from the NOx reducing catalyst in FIG.
  • the remaining rate (%) was calculated by [(the concentration B of the gas component I the concentration A of the gas component) ⁇ 100], in which the concentrations were measured as “ppm”.
  • Table 2 shows catalytic compositions of the NOx reducing catalysts of Examples and Comparative Examples, in which “Carried noble metals (g/l.)” indicates the amount (g) of noble metals carried per one liter of the monolithic substrate of each NOx reducing catalyst; “Cs (mol/I)” indicates the amount (mol) of Cs carried per one liter of the monolithic substrate of each NOx reducing catalyst; and “Cs mol ratio” indicates the mol ratio of Cs (in the NOx reducing catalyst) relative to the total noble metals (in the NOx reducing catalyst).
  • Table 2 further shows temperature ranges (“Exhaust gas temperature (° C)”) of exhaust gas in the exhaust gas passageway immediately upstream of the NOx reducing catalysts in the emission performance evaluation test.
  • the catalyst for accomplishing HC and CO reforming reactions is disposed in the exhaust gas passageway leading from the combustion device so as to produce hydrogen
  • the specified NOx reducing catalyst is disposed in the exhaust gas passageway downstream of the catalyst, in which the oxygen-excessive exhaust gas discharged under lean-burn operation of the combustion device and enriched with hydrogen is supplied into the exhaust gas passageway upstream of the NOx reducing catalyst.

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  • Engineering & Computer Science (AREA)
  • Chemical & Material Sciences (AREA)
  • Combustion & Propulsion (AREA)
  • Chemical Kinetics & Catalysis (AREA)
  • Health & Medical Sciences (AREA)
  • Oil, Petroleum & Natural Gas (AREA)
  • Analytical Chemistry (AREA)
  • General Chemical & Material Sciences (AREA)
  • Environmental & Geological Engineering (AREA)
  • Biomedical Technology (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Toxicology (AREA)
  • Exhaust Gas After Treatment (AREA)
  • Exhaust Gas Treatment By Means Of Catalyst (AREA)
  • Catalysts (AREA)
US09/736,369 1999-12-15 2000-12-15 Exhaust gas purifying system and catalyst Abandoned US20010004832A1 (en)

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JP35660299A JP2001170454A (ja) 1999-12-15 1999-12-15 排気ガス浄化システム及び排気ガス浄化用触媒
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US20030167752A1 (en) * 2002-02-19 2003-09-11 Nissan Motor Co., Ltd. Exhaust gas purifying catalyst
US6758036B1 (en) 2000-10-27 2004-07-06 Delphi Technologies, Inc. Method for sulfur protection of NOx adsorber
US20040216451A1 (en) * 2002-11-21 2004-11-04 Labarge William J. Exhaust system and method of thermal management
US20050022450A1 (en) * 2003-02-12 2005-02-03 Cher-Dip Tan Reformer system, a method of producing hydrogen in the reformer system, and a method of using the reformer system
US20050215429A1 (en) * 2004-03-23 2005-09-29 Nissan Motor Co., Ltd Catalyst powder, exhaust gas purifying catalyst, and method of producing the catalyst powder
US20050221978A1 (en) * 2004-03-31 2005-10-06 Nissan Motor Co., Ltd. Catalyst powder, method of producing the catalyst powder, and exhaust gas purifying catalyst
US20050232826A1 (en) * 2004-04-20 2005-10-20 Labarge William J Treatment devices, exhaust emission control systems, and methods of using the same
US20070003455A1 (en) * 2004-04-19 2007-01-04 Honda Motor Co., Ltd. Exhaust purifying device for internal combustion engine
US20070033872A1 (en) * 2005-08-11 2007-02-15 Haskell Simpkins System and method of heating an exhaust treatment device
US20070084116A1 (en) * 2005-10-13 2007-04-19 Bayerische Motoren Werke Aktiengesellschaft Reformer system having electrical heating devices
US20070153390A1 (en) * 2003-12-25 2007-07-05 Masanori Nakamura Powdery catalyst, exhaust-gas purifying catalyzer, and powdery catalyst production method
US20070155626A1 (en) * 2004-02-17 2007-07-05 Nissan Motor Co., Ltd Catalyst powder, exhaust gas purifying catalyst, and method of producing the catalyst powder
US20070203021A1 (en) * 2004-02-24 2007-08-30 Nissan Motor Co., Ltd. Catalyst Powder, Exhaust Gas Purifying Catalyst, And Method Of Producing The Catalyst Powder
US20090280978A1 (en) * 2004-12-22 2009-11-12 Nissan Motor Co., Ltd. Exhaust gas purifying catalyst and method of producing exhaust gas purifying catalyst
US20090298673A1 (en) * 2008-05-30 2009-12-03 Mazda Motor Corporation Exhaust gas purification catalyst
US20100203238A1 (en) * 2009-02-12 2010-08-12 Eaton Corporation Preparation method for a partially coated monolith

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FR2846893B1 (fr) * 2002-11-07 2006-06-23 Renault Sa Dispositif de depollution catalytique pour un moteur de vehicule automobile et procede de production d'hydrogene associe

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US6758036B1 (en) 2000-10-27 2004-07-06 Delphi Technologies, Inc. Method for sulfur protection of NOx adsorber
US7134272B2 (en) * 2002-02-19 2006-11-14 Nissan Motor Co., Ltd. Exhaust gas purifying catalyst
US20030167752A1 (en) * 2002-02-19 2003-09-11 Nissan Motor Co., Ltd. Exhaust gas purifying catalyst
US7093428B2 (en) 2002-11-21 2006-08-22 Delphi Technologies, Inc. Exhaust system and method of thermal management
US6832473B2 (en) 2002-11-21 2004-12-21 Delphi Technologies, Inc. Method and system for regenerating NOx adsorbers and/or particulate filters
US20040216451A1 (en) * 2002-11-21 2004-11-04 Labarge William J. Exhaust system and method of thermal management
US20050022450A1 (en) * 2003-02-12 2005-02-03 Cher-Dip Tan Reformer system, a method of producing hydrogen in the reformer system, and a method of using the reformer system
US7601669B2 (en) 2003-12-25 2009-10-13 Nissan Motor Co., Ltd. Powdery catalyst, exhaust-gas purifying catalyzer, and powdery catalyst production method
US20070153390A1 (en) * 2003-12-25 2007-07-05 Masanori Nakamura Powdery catalyst, exhaust-gas purifying catalyzer, and powdery catalyst production method
US7601670B2 (en) 2004-02-17 2009-10-13 Nissan Motor Co., Ltd. Catalyst powder, exhaust gas purifying catalyst, and method of producing the catalyst powder
US20070155626A1 (en) * 2004-02-17 2007-07-05 Nissan Motor Co., Ltd Catalyst powder, exhaust gas purifying catalyst, and method of producing the catalyst powder
US20070203021A1 (en) * 2004-02-24 2007-08-30 Nissan Motor Co., Ltd. Catalyst Powder, Exhaust Gas Purifying Catalyst, And Method Of Producing The Catalyst Powder
US7585811B2 (en) 2004-02-24 2009-09-08 Nissan Motor Co., Ltd. Catalyst powder, exhaust gas purifying catalyst, and method of producing the catalyst powder
US7713911B2 (en) 2004-03-23 2010-05-11 Nissan Motor Co., Ltd. Catalyst powder, exhaust gas purifying catalyst, and method of producing the catalyst powder
US20050215429A1 (en) * 2004-03-23 2005-09-29 Nissan Motor Co., Ltd Catalyst powder, exhaust gas purifying catalyst, and method of producing the catalyst powder
US20050221978A1 (en) * 2004-03-31 2005-10-06 Nissan Motor Co., Ltd. Catalyst powder, method of producing the catalyst powder, and exhaust gas purifying catalyst
US7674744B2 (en) 2004-03-31 2010-03-09 Nissan Motor Co., Ltd. Catalyst powder, method of producing the catalyst powder, and exhaust gas purifying catalyst
US20070003455A1 (en) * 2004-04-19 2007-01-04 Honda Motor Co., Ltd. Exhaust purifying device for internal combustion engine
US20050232826A1 (en) * 2004-04-20 2005-10-20 Labarge William J Treatment devices, exhaust emission control systems, and methods of using the same
US7767163B2 (en) 2004-04-20 2010-08-03 Umicore Ag & Co. Kg Exhaust treatment devices
US20090280978A1 (en) * 2004-12-22 2009-11-12 Nissan Motor Co., Ltd. Exhaust gas purifying catalyst and method of producing exhaust gas purifying catalyst
US7435275B2 (en) 2005-08-11 2008-10-14 Delphi Technologies, Inc. System and method of heating an exhaust treatment device
US20070033872A1 (en) * 2005-08-11 2007-02-15 Haskell Simpkins System and method of heating an exhaust treatment device
US20070084116A1 (en) * 2005-10-13 2007-04-19 Bayerische Motoren Werke Aktiengesellschaft Reformer system having electrical heating devices
US20090298673A1 (en) * 2008-05-30 2009-12-03 Mazda Motor Corporation Exhaust gas purification catalyst
US20100203238A1 (en) * 2009-02-12 2010-08-12 Eaton Corporation Preparation method for a partially coated monolith
US8357427B2 (en) * 2009-02-12 2013-01-22 International Engine Intellectual Property Company, Llc Preparation method for a partially coated monolith

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EP1108863A3 (de) 2003-06-04
EP1108863A2 (de) 2001-06-20

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