US20090255238A1 - Exhaust Gas Purifying Apparatus and Exhaust Gas Purifying Method - Google Patents
Exhaust Gas Purifying Apparatus and Exhaust Gas Purifying Method Download PDFInfo
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- US20090255238A1 US20090255238A1 US12/084,822 US8482206A US2009255238A1 US 20090255238 A1 US20090255238 A1 US 20090255238A1 US 8482206 A US8482206 A US 8482206A US 2009255238 A1 US2009255238 A1 US 2009255238A1
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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
- B01D53/74—General processes for purification of waste gases; Apparatus or devices specially adapted therefor
- B01D53/86—Catalytic processes
- B01D53/8621—Removing nitrogen compounds
- B01D53/8625—Nitrogen oxides
- B01D53/8628—Processes characterised by a specific catalyst
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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
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/40—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals of the platinum group metals
- B01J23/44—Palladium
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/56—Platinum group metals
- B01J23/58—Platinum group metals with alkali- or alkaline earth metals
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J23/00—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00
- B01J23/38—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals
- B01J23/54—Catalysts comprising metals or metal oxides or hydroxides, not provided for in group B01J21/00 of noble metals combined with metals, oxides or hydroxides provided for in groups B01J23/02 - B01J23/36
- B01J23/56—Platinum group metals
- B01J23/63—Platinum group metals with rare earths or actinides
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01J—CHEMICAL OR PHYSICAL PROCESSES, e.g. CATALYSIS OR COLLOID CHEMISTRY; THEIR RELEVANT APPARATUS
- B01J37/00—Processes, in general, for preparing catalysts; Processes, in general, for activation of catalysts
- B01J37/02—Impregnation, coating or precipitation
- B01J37/024—Multiple impregnation or coating
- B01J37/0242—Coating followed by impregnation
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- 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
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- 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
- F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
- F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
- F01N3/023—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles
- F01N3/025—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles using fuel burner or by adding fuel to exhaust
- F01N3/0253—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters using means for regenerating the filters, e.g. by burning trapped particles using fuel burner or by adding fuel to exhaust adding fuel to exhaust gases
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- 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
- F01N3/02—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust
- F01N3/021—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters
- F01N3/033—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices
- F01N3/035—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for cooling, or for removing solid constituents of, exhaust by means of filters in combination with other devices with catalytic reactors, e.g. catalysed diesel particulate filters
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- 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
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- 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
- F01N3/0821—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with particulate filters
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- 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
- F01N3/0871—Regulation of absorbents or adsorbents, e.g. purging
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
- B01D—SEPARATION
- B01D2255/00—Catalysts
- B01D2255/10—Noble metals or compounds thereof
- B01D2255/102—Platinum group metals
- B01D2255/1023—Palladium
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- 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
- F01N2370/00—Selection of materials for exhaust purification
- F01N2370/02—Selection of materials for exhaust purification used in catalytic reactors
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B29/00—Engines characterised by provision for charging or scavenging not provided for in groups F02B25/00, F02B27/00 or F02B33/00 - F02B39/00; Details thereof
- F02B29/04—Cooling of air intake supply
- F02B29/0406—Layout of the intake air cooling or coolant circuit
- F02B29/0437—Liquid cooled heat exchangers
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02B—INTERNAL-COMBUSTION PISTON ENGINES; COMBUSTION ENGINES IN GENERAL
- F02B37/00—Engines characterised by provision of pumps driven at least for part of the time by exhaust
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
- F02M26/02—EGR systems specially adapted for supercharged engines
- F02M26/04—EGR systems specially adapted for supercharged engines with a single turbocharger
- F02M26/05—High pressure loops, i.e. wherein recirculated exhaust gas is taken out from the exhaust system upstream of the turbine and reintroduced into the intake system downstream of the compressor
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
- F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
- F02M26/14—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories in relation to the exhaust system
- F02M26/15—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories in relation to the exhaust system in relation to engine exhaust purifying apparatus
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- F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
- F02—COMBUSTION ENGINES; HOT-GAS OR COMBUSTION-PRODUCT ENGINE PLANTS
- F02M—SUPPLYING COMBUSTION ENGINES IN GENERAL WITH COMBUSTIBLE MIXTURES OR CONSTITUENTS THEREOF
- F02M26/00—Engine-pertinent apparatus for adding exhaust gases to combustion-air, main fuel or fuel-air mixture, e.g. by exhaust gas recirculation [EGR] systems
- F02M26/13—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories
- F02M26/22—Arrangement or layout of EGR passages, e.g. in relation to specific engine parts or for incorporation of accessories with coolers in the recirculation passage
- F02M26/23—Layout, e.g. schematics
- F02M26/28—Layout, e.g. schematics with liquid-cooled heat exchangers
Definitions
- the present invention relates to an exhaust gas purifying apparatus used for a lean burn engine operated at an oxygen-excess air to fuel ratio, and an exhaust gas purifying method for purifying NO x by using this exhaust gas purifying apparatus.
- a NO x storage and reduction type catalyst (hereinafter referred to as an NSR) is known as an exhaust gas purifying catalyst for a lean burn engine operated at an oxygen-excess air to fuel ratio.
- This NSR is formed by loading a noble metal such as Pt and a NO x storage material selected from alkali metals and alkaline earth metals on a porous oxide such as alumina. NO in exhaust gas in a lean atmosphere is oxidized into NO x by the noble metal, and the NO x react with the NO x storage material and are stored in the catalyst as nitrates.
- the nitrates are decomposed to release NO x and the NO x storage material recovers its NO x storage ability and at the same time the NO x react with reducing components such as HC and CO, which are abundant in the atmosphere, and are reduced and purified into N 2 .
- Japanese Unexamined Patent Publication No. H09-085093 describes an NSR loaded with a NO x storage material comprising three components of K, Na and Li.
- the NO x storage material comprising the three components of K, Na and Li reacts with carbon dioxide in the air and exists as a composite carbonate.
- This composite carbonate has such a remarkably low melting point of 400° C. or less that it becomes unstable in a typical operating temperature range (300° C. to 400° C.) of the catalyst and thus it improves in NO x storing and releasing characteristics.
- the NO x storage material selected from alkali metals and alkaline earth metals has a problem of lowering oxidation activity of Pt or the like. To deal with this problem, the amount of noble metal loaded is increased but activity appropriate for the amount loaded cannot be obtained due to enhancement of noble metal grain growth or the like.
- the NO x storage material selected from alkali metals and alkaline earth metals has not only an inconvenience of lowing activity as a result of a reaction with a substrate such as cordierite, but also a problem of being susceptible to sulfur poisoning of reacting with SO x to lose its NO x storage ability. Therefore, as described in the above publication, it has been carried out to generate an easily decomposable composite sulfate by using a NO x storage material comprising three components or obstruct SO x access by using an acidic porous oxide. However, since an alkaline NO x storage material is used, it is unavoidable that NO x storage ability is decreased due to reactions with SO x .
- the present invention has been conceived in view of these circumstances, and it is a main object of the present invention to enable NO x to be reduced and purified in a low temperature range from 200° C. to 300° C. without using a NO x storage material comprising an alkaline component.
- An exhaust gas purifying apparatus recited in claim 1 which dissolves the above problems, is characterized in that the apparatus comprises a lean burn engine operated at an oxygen-excess air to fuel ratio, a Pd catalyst placed in exhaust gas from the lean burn engine and formed by loading a high concentration of Pd in the range of 3% by weight or more on a porous oxide, and enriching means for temporally making an exhaust gas atmosphere around the Pd catalyst a rich atmosphere.
- an exhaust gas purifying method of the present invention is characterized in purifying NO x in exhaust gas by placing the exhaust gas purifying apparatus of the present invention in an exhaust system of the lean burn engine operated at an oxygen-excess air to fuel ratio, temporally making an exhaust gas atmosphere around the Pd catalyst a rich atmosphere by the enriching means, and repeating a lean atmosphere and the rich atmosphere thereafter.
- FIG. 1 is an explanatory drawing illustrating a reaction mechanism of an exhaust gas purifying apparatus of the present invention.
- FIG. 2 is a graph showing the relationship between inlet-gas temperature and NO x conversion efficiency.
- FIG. 3 is a graph showing NO x concentration in exhaust gas from a Pd catalyst according to the present invention.
- FIG. 4 is a graph showing the relationship between the weight ratio of Pt/Pd and NO x conversion efficiency.
- FIG. 5 is an explanatory drawing showing an exhaust gas purifying apparatus according to Example 6 of the present invention.
- FIG. 6 is a graph showing the relationship between inlet-gas temperature and NO x conversion efficiency in Example 6 of the present invention.
- the exhaust gas purifying apparatus recited in claim 1 uses a Pd catalyst formed by loading a high concentration of Pd in the range of 3% by weight or more on a porous oxide.
- a porous oxide it is possible to use at least one of oxides such as Al 2 O 3 , ZrO 2 , TiO 2 , CeO 2 and SiO 2 , or a composite oxide comprising a plurality of these oxides.
- This Pd catalyst can be a pellet catalyst formed of catalyst powder produced by loading Pd on the porous oxide.
- This Pd catalyst can also be a foam catalyst produced by coating that catalyst powder on a metal foam substrate, or a honeycomb catalyst produced by forming, from that catalyst powder, a catalyst coating layer on cell partition wall surfaces of a honeycomb substrate formed of cordierite or metal.
- the amount of the catalyst coating layer formed is preferably 120 g or more per liter of the volume of the catalyst, and it is more preferable to form a coating layer of 150 g or more per liter of the volume of the catalyst. If the amount of the catalyst coating layer formed is small, the density of Pd loaded is increased and accordingly sometimes grain growth is caused and activity is lowered when subjected to high temperatures.
- the amount of Pd loaded in the Pd catalyst is 3% by weight or more, which is larger than those loaded in ordinary exhaust gas purifying catalysts.
- Japanese Unexamined Patent Publication No. H08-332350 describes a three-way catalyst in which a high concentration of Pd is loaded on the upstream side.
- This Japanese Patent Publication No. H08-332350 relates to a three-way catalyst and is not used for a lean burn engine operated at an oxygen-excess air to fuel ratio, but the amount of Pd loaded can be as much as those described there.
- the amount of Pd loaded is less than 3% by weight, the catalyst cannot store NO x due to a sharp decrease in NO 2 adsorbing ability.
- the amount of Pd loaded is desirably in the range of 5 to 10 g and especially desirably in the range of 8 to 10 g per liter of the volume of the Pd catalyst.
- an exhaust gas atmosphere around the Pd catalyst is temporally made into a rich atmosphere by enriching means. It is believed that owing to this, oxygen adsorbed on Pd is consumed and the surface of Pd is put in a reset state. Then in an oxygen-excess lean atmosphere the reaction shown in FIG. 1 is assumed to occur.
- NO in exhaust gas reacts with oxygen in the atmosphere by Pd catalysis and is oxidized into NO 2 .
- NO 2 also exists originally in the exhaust gas. These kinds of NO 2 are adsorbed on Pd, which means that NO x are stored.
- Examples of the enriching means include means for adding a reducing agent in exhaust gas and means for adjusting the air to fuel ratio of an engine.
- a reducing agent in exhaust gas it is necessary to temporally make surroundings of the Pd catalyst a rich atmosphere, while taking, into consideration, the amount to be consumed by the Pd catalyst as mentioned above. Therefore, it is desirable to add a high-boiling HC in exhaust gas.
- a low-boiling HC such as propylene does not improve NO x conversion efficiency greatly
- the use of a high-boiling HC enables surroundings of the Pd catalyst to be rapidly and temporally made into a rich atmosphere, and NO x to be reduced and purified efficiently.
- the high-boiling HC is preferably saturated aliphatic HC having 6 or more carbon atoms and being in a liquid state at room temperature and, when used for a diesel engine, especially preferably light oil.
- a small amount of Pt is additionally loaded on the Pd catalyst. Since Pt has a higher NO oxidation activity in a lean atmosphere than Pd, a larger amount of NO 2 is generated and the Pd catalyst improves in NO x storage ability.
- the weight ratio of Pt/Pd is desirably in the range of 0.02 to 0.18. When Pt is loaded above this range, since Pd activity is damaged, NO x conversion efficiency is lowered.
- a lean atmosphere and a rich atmosphere are repeated.
- Time allocated for a lean atmosphere is not more than time in which the amount of NO 2 adsorbed on the Pd catalyst is saturated, and time allocated for a rich atmosphere is not more than time in which oxygen adsorbed on the Pd catalyst is consumed and NO x released from the Pd catalyst are reduced. Accordingly, the time allocated for the lean and the time allocated for the rich largely depend on the Pd amount of the Pd catalyst.
- the exhaust gas purifying apparatus of the present invention can efficiently purify NO x in a low temperature range from about 200° C. to about 300° C. but has a low NO x conversion efficiency at temperatures above 300° C. Therefore, it is desirable to place an NSR loaded with a noble metal and a NO x storage material on the exhaust gas downstream side of the Pd catalyst. Since the NSR exhibits a high NO x storage ability at about 300° C. or more, a high NO x purifying performance is exhibited in a wide temperature range from a low temperature range around about 200° C. to a high temperature range above 450° C.
- the NSR When the NSR is placed on the downstream side of the Pd catalyst, an additional effect is exhibited. Namely, since the Pd catalyst starts a reaction from a low temperature, the reaction heat can warm up the NSR. Therefore, when the NSR alone is used, a change into a rich atmosphere is executed from about 250° C., but in the present invention, a change into a rich atmosphere is desirably executed from the vicinity of about 200° C. Moreover, in a region of 350° C. to 450° C. in which the NSR easily exhibits its power, the Pd catalyst consumes oxygen for oxidation of HC even in a rich atmosphere. The NSR reduces NO x more easily as the oxygen concentration is lower in a rich atmosphere, and therefore upon placing the Pd catalyst on the upstream side, the NO x conversion efficiency of the NSR further improves in a high temperature range.
- NO x can be reduced and purified in a low temperature range from about 200° C. to about 300° C.
- an alkaline component is not used, oxidation activity of noble metal is not damaged or activity is not lowered by a reaction with the substrate or sulfur poisoning. Therefore, the apparatus is excellent in durability and can maintain high NO x purifying performance in a low temperature range for a long time.
- an NSR loaded with a noble metal and a NO x storage material is placed on the exhaust gas downstream side of the Pd catalyst, since the NSR exhibits a high NO x storage ability at about 300° C. or more, a high NO x purifying performance is exhibited in a wide temperature range from a low temperature range around about 200° C. to a high temperature range above 450° C.
- the exhaust gas purifying apparatus and the exhaust gas purifying method of the present invention can be carried out by using the Pd catalyst alone or by using the Pd catalyst in combination with an oxidation catalyst, a NO x storage and reduction catalyst, a filter catalyst or the like.
- a 35 cc honeycomb substrate formed of cordierite (6 mil, 400 cells) was wash-coated with slurry mainly comprising alumina powder, dried and then burned at 500° C. for one hour, thereby forming a coating layer.
- the coating layer was impregnated with a predetermined amount of an aqueous palladium nitrate solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pd.
- the obtained Pd catalyst had 120 g of a catalytic coating layer per liter of the honeycomb substrate and the catalytic coating layer was loaded with 10 g of Pd per liter of the honeycomb substrate.
- a coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt.
- 10 g of Pd were loaded per liter of the honeycomb substrate in an entirely similar way to Example 1.
- the catalytic coating layer was loaded with 1 g of Pt per liter of the honeycomb substrate in addition to 10 g/L of Pd.
- a coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt.
- 10 g of Pd were loaded per liter of the honeycomb substrate in an entirely similar way to Example 1.
- the catalytic coating layer was loaded with 2.2 g of Pt per liter of the honeycomb substrate in addition to 10 g/L of Pd.
- a coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt.
- 10 g of Pd were loaded per liter of the honeycomb substrate in an entirely similar way to Example 1.
- the catalytic coating layer was loaded with 3 g of Pt per liter of the honeycomb substrate in addition to 10 g/L of Pd.
- a coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt.
- 0.8 g of Pd was loaded per liter of the honeycomb substrate in a similar way to Example 1.
- the catalytic coating layer was loaded with 2.2 g of Pt per liter of the honeycomb substrate in addition to 0.8 g/L of Pd.
- a coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt.
- 1.1 g of Pd were loaded per liter of the honeycomb substrate in a similar way to Example 1.
- the catalytic coating layer was loaded with 3 g of Pt per liter of the honeycomb substrate in addition to 1.1 g/L of Pd.
- a coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt.
- 1.3 g of Pd were loaded per liter of the honeycomb substrate in a similar way to Example 1.
- the catalytic coating layer was loaded with 5 g of Pt per liter of the honeycomb substrate in addition to 1.3 g/L of Pd.
- a coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt.
- 2.5 g of Pd were loaded per liter of the honeycomb substrate in a similar way to Example 1.
- the catalytic coating layer was loaded with 7 g of Pt per liter of the honeycomb substrate in addition to 2.5 g/L of Pd.
- a coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt.
- 0.8 g of Pd was loaded per liter of the honeycomb substrate in a similar way to Example 1.
- the catalytic coating layer was loaded with 10 g of Pt per liter of the honeycomb substrate in addition to 0.8 g/L of Pd.
- a 35 cc honeycomb substrate formed of cordierite (3 mil, 400 cells) was wash-coated with slurry mainly comprising alumina powder, dried and then burned at 500° C. for one hour, thereby forming a coating layer.
- the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt.
- the coating layer was impregnated with a predetermined amount of an aqueous rhodium nitrate solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Rh.
- the obtained NSR had 120 g of a catalytic coating layer per liter of the honeycomb substrate and the catalytic coating layer was loaded with 3 g of Pt, 0.5 g of Rh, 0.1 mol of Ba, 0.1 mol of K and 0.1 mol of Li per liter of the honeycomb substrate.
- the respective catalysts prepared above were subjected to an endurance test in which the catalysts were respectively heated at 700° C. for 50 hours in the air.
- the respective catalysts after the endurance test were installed on a constant-pressure fixed-bed flow-type reactor and, while the model gases shown in Table 1 were alternately introduced in a ratio of 20 seconds of the rich gas and 55 seconds of the lean gas, NO x conversion efficiency of the catalysts were respectively measured at each temperature.
- An atmosphere around the Pd catalyst in introducing the rich gas was a reducing atmosphere which was more reducing than required for consuming oxygen adsorbed on the Pd catalyst.
- Measurement results of NO x conversion efficiency are shown in FIG. 2 . It should be noted that the gas flow rate was 30000 cm 3 /min and space velocity at that time was about 51,000 h ⁇ 1 .
- NO x conversion behavior of the catalyst of Example 3 was measured under similar conditions while keeping inlet gas temperature at 250° C. and its profile is shown in FIG. 3 .
- the catalysts of the respective examples exhibited higher NO x conversion efficiency in the range from 200° C. to 350° C. than that of the NSR of Comparative Example 6 and were superior in NO x purifying performance in a low temperature range to the NSR.
- the catalysts of the respective examples had higher NO x conversion efficiency especially in a low temperature range than those of the catalysts of Comparative Examples 1 to 5, and this is apparently an effect of loading Pd at a high concentration of 10 g/L.
- the NO x conversion behavior of the catalyst of Example 3 showed a similar behavior to that of the NSR, in which NO x concentration in exhaust gas instantaneously increased immediately after a change into a rich atmosphere but the NO x concentration sharply decreased thereafter and when the atmosphere was made into a lean atmosphere, the NO x concentration gradually increased. Therefore, NO x emissions can be greatly suppressed by making an atmosphere into a rich atmosphere before NO x concentration reaches NO x concentration in an inlet gas in a lean atmosphere.
- the data of the catalysts of the respective examples were sorted out by NO x conversion efficiency at 200° C. and are shown in FIG. 4 .
- FIG. 5 shows an exhaust gas purifying apparatus of this example.
- This exhaust gas purifying apparatus is formed by placing the Pd catalyst 1 of the abovementioned Example 3 and a filter catalyst 2 adjacently in this order from the exhaust gas upstream side to the downstream side within a catalytic converter 3 .
- the catalytic converter 3 is connected to an exhaust manifold 31 of a diesel engine 30 .
- An injection nozzle 32 is placed in the exhaust manifold 31 and constructed to inject light oil intermittently in exhaust gas. It should be noted that part of exhaust gas from the exhaust gas manifold 31 is returned to an intake manifold 35 of the diesel engine 30 by way of a turbo charger 33 and an intercooler 34 .
- honeycomb structural body formed of cordierite and having a wall flow structure was prepared.
- This honeycomb structural body had a volume of about 2 liters and cell partition walls of 300 cells/inch 2 (46.5 cells/cm 2 ) in cell density and 0.3 mm in thickness.
- the porosity of the cell partition walls was 65% and the average pore diameter was 25 ⁇ m.
- outflow cells having upstream end faces closed and downstream end faces open and inflow cells having upstream end faces open and downstream end faces closed were alternately arranged.
- the outflow cells and the inflow cells were partitioned by the cell partition walls.
- a mixed slurry in which respective powders of alumina, titania, zirconia and ceria were dispersed in water was prepared and a coating layer of 150 g/L was formed on cell partition wall surfaces and pore surfaces inside cell partition walls of the abovementioned honeycomb structural body by wash coating.
- 2 g/L of Pt were loaded by a loading-by-water-absorption method and burned, and 0.3 mol/L of Li, 0.05 mol/L of Ba and 0.025 mol/L of K were respectively loaded by the loading-by-water-absorption method, and then burned at 500° C., thereby preparing a NO x storage and reduction type filter catalyst 2 .
- the catalytic converter was installed on an exhaust system of the diesel engine 30 of 2 liter displacement, and subjected to an endurance treatment at 700° C. for 50 hours, and then the diesel engine 30 was driven at 2900 rpm. While light oil was added for 20 seconds after every 55 seconds from the injection nozzle 32 , NO x conversion efficiency was measured at each inlet gas temperature. The A/F ratio in adding the light oil was controlled to be 15 to 16 based on the whole gas and an atmosphere around the Pd catalyst 1 at that time was a reducing atmosphere which was more reducing than required for consumption of oxygen adsorbed on the Pd catalyst 1 . Measurement results of NO x conversion efficiency are shown in FIG. 6 .
- Exhaust gas purifying apparatus were constructed in a similar way to Example 5, except that the catalysts of Comparative Example 1 and Comparative Example 5 were respectively used in place of the Pd catalyst of Example 3, and NO x conversion efficiency of the apparatus was measured in a similar way to Example 5. The results are shown in FIG. 6 .
- the example number and comparative example numbers indicate those corresponding to the upstream catalysts used in Example 5 and Comparative Example 7.
- the apparatus in which the Pd catalyst 1 of Example 3 was placed on the upstream side of the filter catalyst 2 improved in NO x conversion efficiency in a low temperature range from 200° C. to 300° C. than those in which the catalyst of Comparative Example 1 or that of Comparative Example 5 was placed on the upstream side of the filter catalyst 2 .
- high NO x purifying performance was exhibited in a wide temperature range from a low temperature range around about 200° C. to a high temperature range above 450° C. This is apparently an effect of placing the Pd catalyst 1 loaded with a high concentration of Pd on the upstream side of the NO x storage and reduction type filter catalyst 2 .
Abstract
The apparatus comprises a lean burn engine, a Pd catalyst 1 placed in exhaust gas from the lean burn engine and formed by loading a high concentration of Pd in the range of 3% by weight or more on a porous oxide, and enriching means 32 for temporally making an exhaust gas atmosphere around the Pd catalyst a rich atmosphere.
It is believed that NO is oxidized into NO2 on the Pd catalyst 1 in the exhaust gas in a lean atmosphere and that NO2 originally existing in the exhaust gas and NO2 generated are adsorbed on Pd. This reaction occurs at low temperatures of about 200° C. to about 300° C., and thereby NOx are stored on the Pd catalyst 1. Therefore, NOx can be reduced and purified in a low temperature range from 200° C. to 300° C. without using a NOx storage material comprising an alkaline component.
Description
- The present invention relates to an exhaust gas purifying apparatus used for a lean burn engine operated at an oxygen-excess air to fuel ratio, and an exhaust gas purifying method for purifying NOx by using this exhaust gas purifying apparatus.
- A NOx storage and reduction type catalyst (hereinafter referred to as an NSR) is known as an exhaust gas purifying catalyst for a lean burn engine operated at an oxygen-excess air to fuel ratio. This NSR is formed by loading a noble metal such as Pt and a NOx storage material selected from alkali metals and alkaline earth metals on a porous oxide such as alumina. NO in exhaust gas in a lean atmosphere is oxidized into NOx by the noble metal, and the NOx react with the NOx storage material and are stored in the catalyst as nitrates. Upon temporally making the exhaust gas a rich atmosphere, the nitrates are decomposed to release NOx and the NOx storage material recovers its NOx storage ability and at the same time the NOx react with reducing components such as HC and CO, which are abundant in the atmosphere, and are reduced and purified into N2.
- For example, Japanese Unexamined Patent Publication No. H09-085093 describes an NSR loaded with a NOx storage material comprising three components of K, Na and Li. The NOx storage material comprising the three components of K, Na and Li reacts with carbon dioxide in the air and exists as a composite carbonate. This composite carbonate has such a remarkably low melting point of 400° C. or less that it becomes unstable in a typical operating temperature range (300° C. to 400° C.) of the catalyst and thus it improves in NOx storing and releasing characteristics.
- However, since the NSR described in the above publication sharply deteriorates in NOx storing and releasing characteristics at exhaust gas temperatures of 300° C. or less, it is difficult for the NSR to purify NOx efficiently at a constant atmosphere temperature around 250° C., such as that of exhaust gas from a diesel engine.
- Besides, the NOx storage material selected from alkali metals and alkaline earth metals has a problem of lowering oxidation activity of Pt or the like. To deal with this problem, the amount of noble metal loaded is increased but activity appropriate for the amount loaded cannot be obtained due to enhancement of noble metal grain growth or the like.
- Moreover, the NOx storage material selected from alkali metals and alkaline earth metals has not only an inconvenience of lowing activity as a result of a reaction with a substrate such as cordierite, but also a problem of being susceptible to sulfur poisoning of reacting with SOx to lose its NOx storage ability. Therefore, as described in the above publication, it has been carried out to generate an easily decomposable composite sulfate by using a NOx storage material comprising three components or obstruct SOx access by using an acidic porous oxide. However, since an alkaline NOx storage material is used, it is unavoidable that NOx storage ability is decreased due to reactions with SOx.
- The present invention has been conceived in view of these circumstances, and it is a main object of the present invention to enable NOx to be reduced and purified in a low temperature range from 200° C. to 300° C. without using a NOx storage material comprising an alkaline component.
- An exhaust gas purifying apparatus recited in
claim 1, which dissolves the above problems, is characterized in that the apparatus comprises a lean burn engine operated at an oxygen-excess air to fuel ratio, a Pd catalyst placed in exhaust gas from the lean burn engine and formed by loading a high concentration of Pd in the range of 3% by weight or more on a porous oxide, and enriching means for temporally making an exhaust gas atmosphere around the Pd catalyst a rich atmosphere. - Moreover, an exhaust gas purifying method of the present invention is characterized in purifying NOx in exhaust gas by placing the exhaust gas purifying apparatus of the present invention in an exhaust system of the lean burn engine operated at an oxygen-excess air to fuel ratio, temporally making an exhaust gas atmosphere around the Pd catalyst a rich atmosphere by the enriching means, and repeating a lean atmosphere and the rich atmosphere thereafter.
-
FIG. 1 is an explanatory drawing illustrating a reaction mechanism of an exhaust gas purifying apparatus of the present invention. -
FIG. 2 is a graph showing the relationship between inlet-gas temperature and NOx conversion efficiency. -
FIG. 3 is a graph showing NOx concentration in exhaust gas from a Pd catalyst according to the present invention. -
FIG. 4 is a graph showing the relationship between the weight ratio of Pt/Pd and NOx conversion efficiency. -
FIG. 5 is an explanatory drawing showing an exhaust gas purifying apparatus according to Example 6 of the present invention. -
FIG. 6 is a graph showing the relationship between inlet-gas temperature and NOx conversion efficiency in Example 6 of the present invention. - The exhaust gas purifying apparatus recited in
claim 1 uses a Pd catalyst formed by loading a high concentration of Pd in the range of 3% by weight or more on a porous oxide. As the porous oxide it is possible to use at least one of oxides such as Al2O3, ZrO2, TiO2, CeO2 and SiO2, or a composite oxide comprising a plurality of these oxides. - This Pd catalyst can be a pellet catalyst formed of catalyst powder produced by loading Pd on the porous oxide. This Pd catalyst can also be a foam catalyst produced by coating that catalyst powder on a metal foam substrate, or a honeycomb catalyst produced by forming, from that catalyst powder, a catalyst coating layer on cell partition wall surfaces of a honeycomb substrate formed of cordierite or metal.
- In the case of the Pd catalyst produced by forming a catalyst coating layer on cell partition wall surfaces of a honeycomb substrate, the amount of the catalyst coating layer formed is preferably 120 g or more per liter of the volume of the catalyst, and it is more preferable to form a coating layer of 150 g or more per liter of the volume of the catalyst. If the amount of the catalyst coating layer formed is small, the density of Pd loaded is increased and accordingly sometimes grain growth is caused and activity is lowered when subjected to high temperatures.
- The amount of Pd loaded in the Pd catalyst is 3% by weight or more, which is larger than those loaded in ordinary exhaust gas purifying catalysts. For example, Japanese Unexamined Patent Publication No. H08-332350 describes a three-way catalyst in which a high concentration of Pd is loaded on the upstream side. This Japanese Patent Publication No. H08-332350 relates to a three-way catalyst and is not used for a lean burn engine operated at an oxygen-excess air to fuel ratio, but the amount of Pd loaded can be as much as those described there. When the amount of Pd loaded is less than 3% by weight, the catalyst cannot store NOx due to a sharp decrease in NO2 adsorbing ability. On the other hand, when the amount of Pd loaded is too much, the amount of NOx adsorbed is saturated and the excess amount of Pd is wasteful. The amount of Pd loaded is desirably in the range of 5 to 10 g and especially desirably in the range of 8 to 10 g per liter of the volume of the Pd catalyst.
- In an exhaust gas purifying method of the present invention, first an exhaust gas atmosphere around the Pd catalyst is temporally made into a rich atmosphere by enriching means. It is believed that owing to this, oxygen adsorbed on Pd is consumed and the surface of Pd is put in a reset state. Then in an oxygen-excess lean atmosphere the reaction shown in
FIG. 1 is assumed to occur. - Namely, NO in exhaust gas reacts with oxygen in the atmosphere by Pd catalysis and is oxidized into NO2. In addition, NO2 also exists originally in the exhaust gas. These kinds of NO2 are adsorbed on Pd, which means that NOx are stored.
- Next, when surroundings of the Pd catalyst are temporally made into a rich atmosphere by the enriching means, since Pd has a high oxidation activity even in a rich atmosphere, Pd oxidizes HC and CO and as shown in
FIG. 1 , a reaction between the NO2 adsorbed and HC or CO occurs on Pd and thus NOx are reduced and purified. At the same time with this, Pd restores its NO2 adsorbing ability. - However, if oxygen is adsorbed on Pd in a lean atmosphere, it becomes difficult for NO2 to be adsorbed on Pd. Therefore, at the foregoing time of a rich atmosphere, at least an atmosphere around the Pd catalyst is temporally made into a rich atmosphere and this is carried out, taking, into consideration, the amount to be consumed by adsorbed oxygen. The fact that the atmosphere around the Pd catalyst becomes a rich atmosphere means that oxygen is not adsorbed on Pd and in the following lean atmosphere NO2 is efficiently adsorbed on Pd.
- Examples of the enriching means include means for adding a reducing agent in exhaust gas and means for adjusting the air to fuel ratio of an engine. However, it is necessary to temporally make surroundings of the Pd catalyst a rich atmosphere, while taking, into consideration, the amount to be consumed by the Pd catalyst as mentioned above. Therefore, it is desirable to add a high-boiling HC in exhaust gas. Although it is known that addition of a low-boiling HC such as propylene does not improve NOx conversion efficiency greatly, the use of a high-boiling HC enables surroundings of the Pd catalyst to be rapidly and temporally made into a rich atmosphere, and NOx to be reduced and purified efficiently.
- The reason above is not clear but believed to be that time for a reducing agent to exist on a surface of Pd can be increased and that oxygen existing in exhaust gas and oxygen adsorbed on Pd can be consumed for a reaction of cracking into low-boiling HCs and a reaction of oxidizing low-boiling HCs into water and carbon dioxide. It should be noted that the high-boiling HC is preferably saturated aliphatic HC having 6 or more carbon atoms and being in a liquid state at room temperature and, when used for a diesel engine, especially preferably light oil.
- Desirably a small amount of Pt is additionally loaded on the Pd catalyst. Since Pt has a higher NO oxidation activity in a lean atmosphere than Pd, a larger amount of NO2 is generated and the Pd catalyst improves in NOx storage ability. As for the amount of Pt loaded in the Pd catalyst, the weight ratio of Pt/Pd is desirably in the range of 0.02 to 0.18. When Pt is loaded above this range, since Pd activity is damaged, NOx conversion efficiency is lowered.
- In the exhaust gas purifying method of the present invention, a lean atmosphere and a rich atmosphere are repeated. Time allocated for a lean atmosphere is not more than time in which the amount of NO2 adsorbed on the Pd catalyst is saturated, and time allocated for a rich atmosphere is not more than time in which oxygen adsorbed on the Pd catalyst is consumed and NOx released from the Pd catalyst are reduced. Accordingly, the time allocated for the lean and the time allocated for the rich largely depend on the Pd amount of the Pd catalyst.
- Besides, the exhaust gas purifying apparatus of the present invention can efficiently purify NOx in a low temperature range from about 200° C. to about 300° C. but has a low NOx conversion efficiency at temperatures above 300° C. Therefore, it is desirable to place an NSR loaded with a noble metal and a NOx storage material on the exhaust gas downstream side of the Pd catalyst. Since the NSR exhibits a high NOx storage ability at about 300° C. or more, a high NOx purifying performance is exhibited in a wide temperature range from a low temperature range around about 200° C. to a high temperature range above 450° C.
- When the NSR is placed on the downstream side of the Pd catalyst, an additional effect is exhibited. Namely, since the Pd catalyst starts a reaction from a low temperature, the reaction heat can warm up the NSR. Therefore, when the NSR alone is used, a change into a rich atmosphere is executed from about 250° C., but in the present invention, a change into a rich atmosphere is desirably executed from the vicinity of about 200° C. Moreover, in a region of 350° C. to 450° C. in which the NSR easily exhibits its power, the Pd catalyst consumes oxygen for oxidation of HC even in a rich atmosphere. The NSR reduces NOx more easily as the oxygen concentration is lower in a rich atmosphere, and therefore upon placing the Pd catalyst on the upstream side, the NOx conversion efficiency of the NSR further improves in a high temperature range.
- In the exhaust gas purifying apparatus and the exhaust gas purifying method of the present invention, it is believed that in exhaust gas in a lean atmosphere NO is oxidized into NO2 on the Pd catalyst and NO2 originally existing in the exhaust gas and NO2 generated are adsorbed on Pd. This reaction occurs at low temperatures of about 200° C. to about 300° C. and thereby NOx are stored on the Pd catalyst.
- Then, when an atmosphere around the Pd catalyst is temporally made into a rich atmosphere by the enriching means, the NO2 adsorbed is released from Pd and NOx are reduced and purified by HC and CO, which are abundant in the atmosphere. Furthermore, excessive HC and CO are oxidized by Pd, which exhibits a high oxidation activity even in a reducing atmosphere. Then Pd restores its NO2 adsorbing ability again and, when the atmosphere is made into a lean atmosphere next, Pd adsorbs NO2.
- Namely, according to the exhaust gas purifying apparatus of the present invention, NOx can be reduced and purified in a low temperature range from about 200° C. to about 300° C. In addition, because an alkaline component is not used, oxidation activity of noble metal is not damaged or activity is not lowered by a reaction with the substrate or sulfur poisoning. Therefore, the apparatus is excellent in durability and can maintain high NOx purifying performance in a low temperature range for a long time.
- Moreover, if a small amount of Pt is loaded in addition to Pd, since reaction activity to convert NO into NO2 improves largely and the amount of NOx adsorbed on Pd increases, NOx conversion efficiency improves.
- Furthermore, if an NSR loaded with a noble metal and a NOx storage material is placed on the exhaust gas downstream side of the Pd catalyst, since the NSR exhibits a high NOx storage ability at about 300° C. or more, a high NOx purifying performance is exhibited in a wide temperature range from a low temperature range around about 200° C. to a high temperature range above 450° C.
- The exhaust gas purifying apparatus and the exhaust gas purifying method of the present invention can be carried out by using the Pd catalyst alone or by using the Pd catalyst in combination with an oxidation catalyst, a NOx storage and reduction catalyst, a filter catalyst or the like.
- Hereinafter, the present invention will be described concretely by way of examples and comparative examples.
- A 35 cc honeycomb substrate formed of cordierite (6 mil, 400 cells) was wash-coated with slurry mainly comprising alumina powder, dried and then burned at 500° C. for one hour, thereby forming a coating layer. Next, the coating layer was impregnated with a predetermined amount of an aqueous palladium nitrate solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pd. The obtained Pd catalyst had 120 g of a catalytic coating layer per liter of the honeycomb substrate and the catalytic coating layer was loaded with 10 g of Pd per liter of the honeycomb substrate.
- A coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt. Next, 10 g of Pd were loaded per liter of the honeycomb substrate in an entirely similar way to Example 1. The catalytic coating layer was loaded with 1 g of Pt per liter of the honeycomb substrate in addition to 10 g/L of Pd.
- A coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt. Next, 10 g of Pd were loaded per liter of the honeycomb substrate in an entirely similar way to Example 1. The catalytic coating layer was loaded with 2.2 g of Pt per liter of the honeycomb substrate in addition to 10 g/L of Pd.
- A coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt. Next, 10 g of Pd were loaded per liter of the honeycomb substrate in an entirely similar way to Example 1. The catalytic coating layer was loaded with 3 g of Pt per liter of the honeycomb substrate in addition to 10 g/L of Pd.
- A coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt. Next, 0.8 g of Pd was loaded per liter of the honeycomb substrate in a similar way to Example 1. The catalytic coating layer was loaded with 2.2 g of Pt per liter of the honeycomb substrate in addition to 0.8 g/L of Pd.
- A coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt. Next, 1.1 g of Pd were loaded per liter of the honeycomb substrate in a similar way to Example 1. The catalytic coating layer was loaded with 3 g of Pt per liter of the honeycomb substrate in addition to 1.1 g/L of Pd.
- A coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt. Next, 1.3 g of Pd were loaded per liter of the honeycomb substrate in a similar way to Example 1. The catalytic coating layer was loaded with 5 g of Pt per liter of the honeycomb substrate in addition to 1.3 g/L of Pd.
- A coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt. Next, 2.5 g of Pd were loaded per liter of the honeycomb substrate in a similar way to Example 1. The catalytic coating layer was loaded with 7 g of Pt per liter of the honeycomb substrate in addition to 2.5 g/L of Pd.
- A coating layer was formed in a similar way to Example 1, and the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt. Next, 0.8 g of Pd was loaded per liter of the honeycomb substrate in a similar way to Example 1. The catalytic coating layer was loaded with 10 g of Pt per liter of the honeycomb substrate in addition to 0.8 g/L of Pd.
- A 35 cc honeycomb substrate formed of cordierite (3 mil, 400 cells) was wash-coated with slurry mainly comprising alumina powder, dried and then burned at 500° C. for one hour, thereby forming a coating layer. Next, the coating layer was impregnated with a predetermined amount of an aqueous dinitrodiammine platinum solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Pt. Additionally, the coating layer was impregnated with a predetermined amount of an aqueous rhodium nitrate solution of a predetermined concentration, dried and then burned at 500° C. for one hour, thereby loading Rh. Consequently, Ba, K and Li were respectively and similarly loaded by using an aqueous potassium nitrate solution of a predetermined concentration, an aqueous barium nitrate solution of a predetermined concentration and an aqueous lithium nitrate solution of a predetermined concentration, respectively. The obtained NSR had 120 g of a catalytic coating layer per liter of the honeycomb substrate and the catalytic coating layer was loaded with 3 g of Pt, 0.5 g of Rh, 0.1 mol of Ba, 0.1 mol of K and 0.1 mol of Li per liter of the honeycomb substrate.
- The respective catalysts prepared above were subjected to an endurance test in which the catalysts were respectively heated at 700° C. for 50 hours in the air. The respective catalysts after the endurance test were installed on a constant-pressure fixed-bed flow-type reactor and, while the model gases shown in Table 1 were alternately introduced in a ratio of 20 seconds of the rich gas and 55 seconds of the lean gas, NOx conversion efficiency of the catalysts were respectively measured at each temperature. An atmosphere around the Pd catalyst in introducing the rich gas was a reducing atmosphere which was more reducing than required for consuming oxygen adsorbed on the Pd catalyst. Measurement results of NOx conversion efficiency are shown in
FIG. 2 . It should be noted that the gas flow rate was 30000 cm3/min and space velocity at that time was about 51,000 h−1. - Moreover, NOx conversion behavior of the catalyst of Example 3 was measured under similar conditions while keeping inlet gas temperature at 250° C. and its profile is shown in
FIG. 3 . -
TABLE 1 CO H2 C10H22 NO O2 CO2 H2O (%) (%) (ppmC) (ppm) (%) (%) (%) N2 LEAN 0.0 0.0 33 250 10 10.4 10.0 re- GAS mainder RICH 6.0 2.0 5500 250 0.2 10.4 10.0 re- GAS mainder - As apparent from
FIG. 2 , the catalysts of the respective examples exhibited higher NOx conversion efficiency in the range from 200° C. to 350° C. than that of the NSR of Comparative Example 6 and were superior in NOx purifying performance in a low temperature range to the NSR. Besides, the catalysts of the respective examples had higher NOx conversion efficiency especially in a low temperature range than those of the catalysts of Comparative Examples 1 to 5, and this is apparently an effect of loading Pd at a high concentration of 10 g/L. - As shown in
FIG. 3 , the NOx conversion behavior of the catalyst of Example 3 showed a similar behavior to that of the NSR, in which NOx concentration in exhaust gas instantaneously increased immediately after a change into a rich atmosphere but the NOx concentration sharply decreased thereafter and when the atmosphere was made into a lean atmosphere, the NOx concentration gradually increased. Therefore, NOx emissions can be greatly suppressed by making an atmosphere into a rich atmosphere before NOx concentration reaches NOx concentration in an inlet gas in a lean atmosphere. - The data of the catalysts of the respective examples were sorted out by NOx conversion efficiency at 200° C. and are shown in
FIG. 4 . The catalyst of Example 2 in which the weight ratio of Pt to Pd was Pt:Pd=1:10 showed a remarkably high NOx conversion efficiency and a catalyst with a higher or lower Pt content deteriorated in NOx conversion efficiency. It is understood that NOx conversion efficiency of 50% or more is exhibited when the weight ratio of Pt/Pd is in the range from 0.02 to 0.18 and that it is preferable that the amount of Pt loaded is in this range. -
FIG. 5 shows an exhaust gas purifying apparatus of this example. This exhaust gas purifying apparatus is formed by placing thePd catalyst 1 of the abovementioned Example 3 and afilter catalyst 2 adjacently in this order from the exhaust gas upstream side to the downstream side within acatalytic converter 3. Thecatalytic converter 3 is connected to anexhaust manifold 31 of adiesel engine 30. Aninjection nozzle 32 is placed in theexhaust manifold 31 and constructed to inject light oil intermittently in exhaust gas. It should be noted that part of exhaust gas from theexhaust gas manifold 31 is returned to anintake manifold 35 of thediesel engine 30 by way of aturbo charger 33 and anintercooler 34. - Hereinafter, a production process of the
filter catalyst 2 will be described instead of giving a detailed description of the construction. First a honeycomb structural body formed of cordierite and having a wall flow structure was prepared. This honeycomb structural body had a volume of about 2 liters and cell partition walls of 300 cells/inch2 (46.5 cells/cm2) in cell density and 0.3 mm in thickness. The porosity of the cell partition walls was 65% and the average pore diameter was 25 μm. In this honeycomb structural body, outflow cells having upstream end faces closed and downstream end faces open and inflow cells having upstream end faces open and downstream end faces closed were alternately arranged. The outflow cells and the inflow cells were partitioned by the cell partition walls. - Next a mixed slurry in which respective powders of alumina, titania, zirconia and ceria were dispersed in water was prepared and a coating layer of 150 g/L was formed on cell partition wall surfaces and pore surfaces inside cell partition walls of the abovementioned honeycomb structural body by wash coating. Thereafter, 2 g/L of Pt were loaded by a loading-by-water-absorption method and burned, and 0.3 mol/L of Li, 0.05 mol/L of Ba and 0.025 mol/L of K were respectively loaded by the loading-by-water-absorption method, and then burned at 500° C., thereby preparing a NOx storage and reduction
type filter catalyst 2. - The catalytic converter was installed on an exhaust system of the
diesel engine 30 of 2 liter displacement, and subjected to an endurance treatment at 700° C. for 50 hours, and then thediesel engine 30 was driven at 2900 rpm. While light oil was added for 20 seconds after every 55 seconds from theinjection nozzle 32, NOx conversion efficiency was measured at each inlet gas temperature. The A/F ratio in adding the light oil was controlled to be 15 to 16 based on the whole gas and an atmosphere around thePd catalyst 1 at that time was a reducing atmosphere which was more reducing than required for consumption of oxygen adsorbed on thePd catalyst 1. Measurement results of NOx conversion efficiency are shown inFIG. 6 . - Exhaust gas purifying apparatus were constructed in a similar way to Example 5, except that the catalysts of Comparative Example 1 and Comparative Example 5 were respectively used in place of the Pd catalyst of Example 3, and NOx conversion efficiency of the apparatus was measured in a similar way to Example 5. The results are shown in
FIG. 6 . - In
FIG. 6 , the example number and comparative example numbers indicate those corresponding to the upstream catalysts used in Example 5 and Comparative Example 7. As apparent fromFIG. 6 , the apparatus in which thePd catalyst 1 of Example 3 was placed on the upstream side of thefilter catalyst 2 improved in NOx conversion efficiency in a low temperature range from 200° C. to 300° C. than those in which the catalyst of Comparative Example 1 or that of Comparative Example 5 was placed on the upstream side of thefilter catalyst 2. Namely, upon placing thePd catalyst 1 on the upstream side of thefilter catalyst 2, high NOx purifying performance was exhibited in a wide temperature range from a low temperature range around about 200° C. to a high temperature range above 450° C. This is apparently an effect of placing thePd catalyst 1 loaded with a high concentration of Pd on the upstream side of the NOx storage and reductiontype filter catalyst 2.
Claims (6)
1-7. (canceled)
8. An exhaust gas purifying apparatus, comprising:
a lean burn engine operated at an oxygen-excess air to fuel ratio;
a Pd catalyst placed in exhaust gas from the lean burn engine, formed by loading a high concentration of Pd in the range of 3% by weight or more on a porous oxide and being free of an NOx adsorbing material selected from alkali metals and alkaline earth metals; and
enriching means for temporally making an exhaust gas atmosphere around the Pd catalyst a rich atmosphere by supplying a high-boiling HC to the exhaust gas, wherein
the Pd catalyst is used in an atmosphere in which a lean atmosphere and the rich atmosphere are alternately repeated and reduces and purifies NOx in the exhaust gas in a low temperature range from 200° C. to 300° C.
9. The exhaust gas purifying apparatus recited in claim 8 , wherein the amount of Pd loaded on the Pd catalyst is 5 to 10 g per liter of the volume of the Pd catalyst.
10. the exhaust gas purifying apparatus recited in claim 8 or claim 9 , wherein the Pd catalyst further contains Pt and the weight ratio of Pt/Pd is 0.02 to 0.18.
11. The exhaust gas purifying apparatus recited in claim 8 , wherein an NOx storage and reduction type catalyst loaded with a noble metal and an NOx storage material is placed on the exhaust gas downstream side of the Pd catalyst.
12. An exhaust gas purifying method for purifying NOx in exhaust gas by placing the exhaust gas purifying apparatus recited in claim 8 in an exhaust system of the lean burn engine operated at an oxygen-excessive air to fuel ratio, temporally making an exhaust gas atmosphere around the Pd catalyst a rich atmosphere by the enriching means, and repeating a lean atmosphere and the rich atmosphere thereafter.
Applications Claiming Priority (3)
Application Number | Priority Date | Filing Date | Title |
---|---|---|---|
JP2005326388A JP2007130580A (en) | 2005-11-10 | 2005-11-10 | Apparatus and method of purifying exhaust gas |
JP2005-326388 | 2005-11-10 | ||
PCT/JP2006/322219 WO2007055216A1 (en) | 2005-11-10 | 2006-10-31 | Exhaust gas clean-up system and exhaust gas clean-up method |
Publications (1)
Publication Number | Publication Date |
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US20090255238A1 true US20090255238A1 (en) | 2009-10-15 |
Family
ID=38023219
Family Applications (1)
Application Number | Title | Priority Date | Filing Date |
---|---|---|---|
US12/084,822 Abandoned US20090255238A1 (en) | 2005-11-10 | 2006-10-31 | Exhaust Gas Purifying Apparatus and Exhaust Gas Purifying Method |
Country Status (9)
Country | Link |
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US (1) | US20090255238A1 (en) |
EP (1) | EP1949953A4 (en) |
JP (1) | JP2007130580A (en) |
KR (1) | KR20080066944A (en) |
CN (1) | CN101304801A (en) |
BR (1) | BRPI0619681A2 (en) |
CA (1) | CA2628979A1 (en) |
RU (1) | RU2385760C2 (en) |
WO (1) | WO2007055216A1 (en) |
Cited By (2)
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US20130232953A1 (en) * | 2012-03-09 | 2013-09-12 | Ford Global Technologies, Llc | Exhaust-gas aftertreatment system and method for exhaust-gas aftertreatment |
US9657626B2 (en) * | 2015-05-18 | 2017-05-23 | Ford Global Technologies, Llc | Emissions reduction system |
Families Citing this family (4)
Publication number | Priority date | Publication date | Assignee | Title |
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US6921634B2 (en) | 1999-12-23 | 2005-07-26 | Board Of Regents, The University Of Texas System | Replication competent hepatitus C virus and methods of use |
JP5272455B2 (en) * | 2008-03-11 | 2013-08-28 | いすゞ自動車株式会社 | NOx purification system control method and NOx purification system |
JP5065180B2 (en) * | 2008-06-30 | 2012-10-31 | トヨタ自動車株式会社 | Exhaust gas purification catalyst |
DE102009023550A1 (en) * | 2009-05-30 | 2010-12-09 | Deutz Ag | aftertreatment system |
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- 2006-10-31 CN CNA2006800417668A patent/CN101304801A/en active Pending
- 2006-10-31 KR KR1020087011033A patent/KR20080066944A/en active IP Right Grant
- 2006-10-31 EP EP06823123A patent/EP1949953A4/en not_active Withdrawn
- 2006-10-31 CA CA002628979A patent/CA2628979A1/en not_active Abandoned
- 2006-10-31 BR BRPI0619681-0A patent/BRPI0619681A2/en not_active IP Right Cessation
- 2006-10-31 RU RU2008123510/15A patent/RU2385760C2/en not_active IP Right Cessation
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Also Published As
Publication number | Publication date |
---|---|
CA2628979A1 (en) | 2007-05-18 |
KR20080066944A (en) | 2008-07-17 |
JP2007130580A (en) | 2007-05-31 |
WO2007055216A1 (en) | 2007-05-18 |
EP1949953A4 (en) | 2009-09-30 |
BRPI0619681A2 (en) | 2011-10-11 |
RU2385760C2 (en) | 2010-04-10 |
EP1949953A1 (en) | 2008-07-30 |
RU2008123510A (en) | 2009-12-20 |
CN101304801A (en) | 2008-11-12 |
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