JP2009165922A - Exhaust gas purification catalyst - Google Patents
Exhaust gas purification catalyst Download PDFInfo
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- JP2009165922A JP2009165922A JP2008004667A JP2008004667A JP2009165922A JP 2009165922 A JP2009165922 A JP 2009165922A JP 2008004667 A JP2008004667 A JP 2008004667A JP 2008004667 A JP2008004667 A JP 2008004667A JP 2009165922 A JP2009165922 A JP 2009165922A
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- 238000000746 purification Methods 0.000 title abstract description 24
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- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 14
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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
- F01N3/0814—Exhaust or silencing apparatus having means for purifying, rendering innocuous, or otherwise treating exhaust for rendering innocuous by using absorbents or adsorbents combined with catalytic converters, e.g. NOx absorption/storage reduction catalysts
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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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- B01J29/00—Catalysts comprising molecular sieves
- B01J29/04—Catalysts comprising molecular sieves having base-exchange properties, e.g. crystalline zeolites
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- B01J29/18—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of the mordenite type
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- B01J29/72—Crystalline aluminosilicate zeolites; Isomorphous compounds thereof of types characterised by their specific structure not provided for in groups B01J29/08 - B01J29/65 containing iron group metals, noble metals or copper
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- 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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- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- B01D2258/00—Sources of waste gases
- B01D2258/01—Engine exhaust gases
- B01D2258/012—Diesel engines and lean burn gasoline engines
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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
- B01D53/9459—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts
- B01D53/9477—Removing one or more of nitrogen oxides, carbon monoxide, or hydrocarbons by multiple successive catalytic functions; systems with more than one different function, e.g. zone coated catalysts with catalysts positioned on separate bricks, e.g. exhaust systems
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- B—PERFORMING OPERATIONS; TRANSPORTING
- B01—PHYSICAL OR CHEMICAL PROCESSES OR APPARATUS IN GENERAL
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- F01N2250/00—Combinations of different methods of purification
- F01N2250/12—Combinations of different methods of purification absorption or adsorption, and catalytic conversion
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- 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
- F01N3/022—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 characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous
- F01N3/0222—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 characterised by specially adapted filtering structure, e.g. honeycomb, mesh or fibrous the structure being monolithic, e.g. honeycombs
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Abstract
Description
本発明は、排ガス中に軽油など高沸点HCを添加するシステムの排気系に有用な排ガス浄化用触媒に関する。 The present invention relates to an exhaust gas purifying catalyst useful for an exhaust system of a system in which high boiling point HC such as light oil is added to exhaust gas.
近年、燃費の向上とCO2 排出量の削減の効果を有するために、リーンバーンエンジンが広く普及している。その代表的なものとして、ディーゼルエンジンがある。 In recent years, lean burn engines have become widespread in order to improve fuel efficiency and reduce CO 2 emissions. A typical example is a diesel engine.
ところがリーンバーンエンジンからの排ガスは酸素過剰のリ−ン雰囲気であるために、通常の三元触媒などを用いたのではNOx を還元浄化することが困難である。さらにディーゼルエンジンからの排ガスは、ガソリンエンジンからの排ガスと比較すると50〜 100℃も低温であり、かつパティキュレート(PM)も含むため、排ガス浄化が難しいという問題がある。 However, since the exhaust gas from the lean burn engine has a lean atmosphere with an excess of oxygen, it is difficult to reduce and purify NO x by using an ordinary three-way catalyst or the like. Further, exhaust gas from a diesel engine has a problem that it is difficult to purify exhaust gas because it is as low as 50 to 100 ° C. compared to exhaust gas from a gasoline engine and also contains particulates (PM).
そこで近年では、特開平09−173866号公報などに記載されているように、フィルタ基材のセル隔壁の表面にアルミナなどからコート層を形成し、そのコート層にPtなどを担持したフィルタ触媒が開発されている。また特開平06−159037号公報には、コート層にさらにNOx 吸蔵材を担持したフィルタ触媒が記載されている。このようにすればNOx 吸蔵材にNOx を吸蔵することができ、排ガス中に軽油などの還元剤を添加した還元雰囲気とすることで、吸蔵されたNOx を還元して浄化することが可能となる。 Therefore, in recent years, as described in JP-A-09-173866 and the like, a filter catalyst in which a coating layer is formed from alumina or the like on the surface of a cell partition wall of a filter base material and Pt or the like is supported on the coating layer is provided. Has been developed. Japanese Patent Application Laid-Open No. 06-159037 describes a filter catalyst in which a NO x storage material is further supported on a coat layer. Thus them can occlude NO x in the NO x storage material if, by a reducing atmosphere with the addition of a reducing agent such as light oil into the exhaust gas, to purify by reduction the occluded NO x It becomes possible.
ところが触媒金属とNOx 吸蔵材とを担持したコート層をもつフィルタ触媒では、圧損との兼ね合いからコート層の形成量には限界がある。そのため触媒金属を高分散で担持して高温時の粒成長を抑制するためには、触媒金属の担持量を少なくせざるを得ず、PM及びNOx の浄化性能が不足するという問題があった。また低温域の排ガスの流入が連続した場合などには、PM酸化活性が低いためにPMの堆積量が多く目詰まりによって圧損が上昇するという問題がある。 However, in the case of a filter catalyst having a coat layer carrying a catalyst metal and an NO x storage material, the amount of coat layer formed is limited in view of pressure loss. Therefore, in order to support the catalyst metal with high dispersion and suppress grain growth at high temperature, there is a problem that the amount of catalyst metal supported must be reduced, and the PM and NO x purification performance is insufficient. . In addition, when the inflow of exhaust gas in a low temperature region is continuous, there is a problem that the pressure loss increases due to clogging due to a large amount of PM accumulated due to low PM oxidation activity.
そこで特開2001−212506号公報、特開2002−153733号公報などには、ストレートフロー構造の酸化触媒又はNOx 吸蔵還元型触媒と、フィルタ触媒と、を直列に並べた排ガス浄化装置が提案されている。このようにストレートフロー構造の触媒を併用することで、圧損の増大なく浄化性能を向上させることができる。またフィルタ触媒の排ガス上流側にこのような触媒を配置すれば、その前段触媒による浄化反応によって排ガス温度が昇温されるため、フィルタ触媒におけるPM酸化性能が向上し、目詰まりによる圧損の上昇を防止するとともにフィルタ機能を再生することができる。 Therefore, JP 2001-212506 A, JP 2002-153733 A, etc. propose an exhaust gas purification apparatus in which an oxidation catalyst or NO x storage reduction catalyst having a straight flow structure and a filter catalyst are arranged in series. ing. Thus, the purification performance can be improved without increasing the pressure loss by using the straight flow structure catalyst together. In addition, if such a catalyst is arranged upstream of the exhaust gas of the filter catalyst, the exhaust gas temperature is raised by the purification reaction by the preceding catalyst, so that the PM oxidation performance of the filter catalyst is improved and the pressure loss due to clogging is increased. It is possible to prevent and regenerate the filter function.
上記したように、還元剤として軽油などの液状還元剤を排ガス中に間欠的に供給することで、NOx の還元活性を向上させるシステムが提案され、実用化されつつある。また還元剤の酸化燃焼による発熱を利用し、堆積したPMを燃焼させてフィルタを再生することも行われている。しかしこのようなシステムに、上記したストレートフロー構造の酸化触媒又はNOx 吸蔵還元型触媒とフィルタ触媒とを直列に並べた排ガス浄化装置を採用した場合には、最上流にある触媒に液状還元剤が直接流入することとなる。また近年では、さらなる低燃費化が進み、排ガス温度はさらに低温化が進行している。 As described above, the liquid reducing agent such as light oil as the reducing agent by intermittently supplied into the exhaust gas system to improve the reducing activity of the NO x have been proposed, it is being put to practical use. In addition, the heat generated by oxidation combustion of the reducing agent is used to burn the accumulated PM and regenerate the filter. However, when an exhaust gas purification device in which the above-described straight flow structure oxidation catalyst or NO x storage reduction catalyst and filter catalyst are arranged in series in such a system is used, the liquid reducing agent is added to the most upstream catalyst. Will flow directly. In recent years, fuel consumption has been further reduced, and exhaust gas temperature has been further lowered.
そのため最上流の触媒に流入した高沸点HCは、ほとんど酸化されることなく触媒コート層に吸着する。また低温であるため、触媒コート層にはHCが連続的に吸着し、温度が上がりにくいために脱離や燃焼が生じにくい。そのため、コーキングなどのHC被毒が生じて活性が低下する。またこのように活性が低下すると、高温の排ガスが流入しない限りHCの浄化が困難となる。 Therefore, the high boiling point HC that has flowed into the most upstream catalyst is adsorbed on the catalyst coat layer with almost no oxidation. In addition, because of the low temperature, HC is continuously adsorbed on the catalyst coat layer, and the temperature does not easily rise, so that desorption and combustion are unlikely to occur. Therefore, HC poisoning such as coking occurs and the activity decreases. In addition, when the activity is reduced in this way, it becomes difficult to purify HC unless hot exhaust gas flows.
ところで上流側で排ガス中に軽油などを添加するシステムに用いられるフィルタ触媒においては、低温時や軽油添加時に、酸化されなかったHCが排出される場合があり、今後の厳しい排ガス規制においては、このような場合でもHCを浄化することが求められる。そこでフィルタ触媒に、ゼオライトなどのHC吸着材をコーティングしてHC吸着浄化機能をもたせることが考えられる。 By the way, in the filter catalyst used in the system that adds light oil to the exhaust gas upstream, HC that was not oxidized may be discharged at low temperatures or when adding light oil. Even in such a case, it is required to purify HC. Therefore, it is conceivable to provide the filter catalyst with an HC adsorption purification function by coating HC adsorbent such as zeolite.
ところがHC吸着材を一様にコーティングするだけでは、セル隔壁の細孔が埋められるため圧損の上昇が大きくなる。また堆積するPM量が多くなるため、強制再生時の発熱量が多くなり熱劣化が起こりやすい。さらに近年では、より細かいPMを捕集することが求められ、フィルタ基材におけるセル隔壁の細孔分布が小径側にシフトしている。そのためコーティングによる機能付加が難しい状況となっている。
本発明は上記事情に鑑みてなされたものであり、コーキングなどのHC被毒を抑制し、かつ圧損の上昇を抑制するとともに、低温域におけるHCの浄化活性を向上させることを解決すべき課題とする。 The present invention has been made in view of the above circumstances, and it is a problem to be solved to suppress HC poisoning such as coking, to suppress an increase in pressure loss, and to improve the purification activity of HC in a low temperature range. To do.
上記課題を解決する本発明の排ガス浄化用触媒の特徴は、セル隔壁で区画された複数のセルをもつハニカム基材と、セル隔壁に形成され酸化物担体に触媒金属を担持してなる触媒担持層と、よりなる排ガス浄化用触媒であって、
酸化物担体には、排ガス中の炭化水素を吸着可能な細孔をもつ多孔体を含み、ハニカム基材の排ガス流入側端面から下流側へ所定範囲の上流部に形成された上流側触媒担持層の少なくとも表層部には多孔体を含まず、上流側触媒担持層の下流側端部から排ガス流出側端面までの下流部に形成された下流側触媒担持層に多孔体を含むことにある。
A feature of the exhaust gas purifying catalyst of the present invention that solves the above problems is a honeycomb substrate having a plurality of cells partitioned by cell partition walls, and a catalyst support formed by supporting a catalyst metal on an oxide support formed in the cell partition walls. An exhaust gas purification catalyst comprising a layer,
The oxide carrier includes a porous body having pores capable of adsorbing hydrocarbons in exhaust gas, and is formed in an upstream portion of a predetermined range from the exhaust gas inflow side end surface of the honeycomb base material to the downstream side in a predetermined range. At least the surface layer portion of the catalyst layer does not include a porous body, and the downstream side catalyst support layer formed in the downstream portion from the downstream end of the upstream side catalyst support layer to the exhaust gas outflow side end surface includes the porous body.
多孔体は、下流側触媒担持層の表層部に含まれていることが望ましい。 The porous body is preferably contained in the surface layer portion of the downstream side catalyst support layer.
また下流側触媒担持層のコート量は、上流側触媒担持層のコート量より多いことが望ましい。 Further, it is desirable that the coating amount of the downstream catalyst supporting layer is larger than the coating amount of the upstream catalyst supporting layer.
本発明の排ガス浄化用触媒では、HCを吸着可能な細孔をもつ多孔体が、上流側触媒担持層の少なくとも表層部には含まれず、下流側触媒担持層に含まれている。したがってセル通路に流入した低温域の排ガス中に含まれるHCは、上流側触媒担持層は素通りして下流側触媒担持層に含まれる多孔体に吸着するため、上流側におけるコーキングなどのHC被毒を抑制することができる。また上流側触媒担持層にHCが吸着したとしても、多孔体を含まないためHCが脱離しやすく、脱離したHCは下流側触媒担持層に存在する多孔体に吸着するため排出が抑制される。 In the exhaust gas purifying catalyst of the present invention, the porous body having pores capable of adsorbing HC is not included in at least the surface layer portion of the upstream catalyst supporting layer, but is included in the downstream catalyst supporting layer. Therefore, HC contained in the low-temperature exhaust gas flowing into the cell passage passes through the upstream catalyst support layer and is adsorbed to the porous material contained in the downstream catalyst support layer, so HC poisoning such as coking on the upstream side Can be suppressed. Even if HC is adsorbed on the upstream catalyst-carrying layer, it does not contain a porous material, so HC is easily desorbed, and the desorbed HC is adsorbed on the porous material present in the downstream-side catalyst-carrying layer, thus suppressing discharge .
さらに、ストレートフロー構造のハニカム基材を用い、下流側触媒担持層のコート量を上流側触媒担持層のコート量より多くすれば、上流側触媒担持層のコート量を少なくすることが可能となる。すると上流側の熱容量が小さくなるため、軽油などの液状還元剤が流入した時に生じる流入側端面の閉塞を抑制することができる。 Furthermore, if a honeycomb substrate having a straight flow structure is used and the coating amount of the downstream catalyst supporting layer is made larger than the coating amount of the upstream catalyst supporting layer, the coating amount of the upstream catalyst supporting layer can be reduced. . Then, since the heat capacity on the upstream side becomes small, it is possible to suppress the closing of the inflow side end face that occurs when a liquid reducing agent such as light oil flows in.
そして触媒金属が活性化する温度まで排ガス温度が上昇すると、上流側触媒担持層における酸化反応の発熱によって下流部の昇温が促進される。そのため下流側触媒担持層の多孔体に吸着したHCが脱離するとともに、触媒反応によって効率良く酸化浄化される。 When the exhaust gas temperature rises to a temperature at which the catalyst metal is activated, the temperature rise in the downstream portion is promoted by the heat generated by the oxidation reaction in the upstream catalyst support layer. Therefore, the HC adsorbed on the porous body of the downstream side catalyst support layer is desorbed and efficiently oxidized and purified by the catalytic reaction.
したがって本発明の排ガス浄化用触媒によれば、低温域から高温域までHCの排出を大きく抑制することができる。この効果は、ストレートフロー構造及びウォールフロー構造の触媒の両方で奏される。また多孔体が下流側触媒担持層の表層部に含まれていれば、この効果が増幅される。 Therefore, according to the exhaust gas purifying catalyst of the present invention, HC emission can be greatly suppressed from a low temperature range to a high temperature range. This effect is exhibited by both a straight flow structure and a wall flow structure catalyst. Further, if the porous body is included in the surface layer portion of the downstream catalyst supporting layer, this effect is amplified.
さらにフィルタ触媒に本発明を適用した場合には、多孔体は流出側セルの下流部に形成された下流側触媒担持層に存在し、流入側セルに形成されている上流側触媒担持層の少なくとも表層部には多孔体が存在しない。したがって上流側触媒担持層の形成量は従来と同等となり、セル隔壁の細孔分布も従来と同等となるため、圧損の上昇を抑制することができる。 Further, when the present invention is applied to the filter catalyst, the porous body exists in the downstream catalyst supporting layer formed in the downstream portion of the outflow side cell, and at least the upstream catalyst supporting layer formed in the inflow side cell. There is no porous material in the surface layer portion. Accordingly, the amount of the upstream catalyst support layer formed is equivalent to that of the conventional one, and the pore distribution of the cell partition walls is also equivalent to that of the conventional one.
またフィルタ触媒では、PMの燃焼後に生成するアッシュが堆積するにつれて圧損が上昇し、圧損が所定値以上になるとエンジン出力を制限するか、あるいはフィルタ触媒を交換しなければならない。しかし本発明によれば、PMが堆積しない流出側セルの下流側触媒担持層に多孔体を含有している。したがって、流入側セルの容積、すなわちアッシュが堆積する容積は減少せず、またアッシュの多くはフィルタのセル隔壁通過抵抗が上流部より大きい下流部奥から堆積していく。このため、アッシュによる圧損上昇感度はむしろ小さくなり、アッシュの堆積の影響が小さく、出力制限時期や交換時期を早めるような不具合がない。 Further, in the filter catalyst, the pressure loss increases as ash generated after PM combustion accumulates, and when the pressure loss exceeds a predetermined value, the engine output must be limited or the filter catalyst must be replaced. However, according to the present invention, the porous body is contained in the downstream catalyst support layer of the outflow side cell where PM is not deposited. Therefore, the volume of the inflow side cell, that is, the volume in which the ash is deposited does not decrease, and most of the ash is deposited from the downstream part where the cell partition wall passage resistance of the filter is larger than the upstream part. For this reason, the pressure drop increase sensitivity due to ash is rather small, the influence of ash accumulation is small, and there is no inconvenience that the output restriction time or replacement time is advanced.
さらに、下流側触媒担持層は初期の圧損には影響しないので、上流側触媒担持層のコート量より多く形成することができる。このようにすれば、フィルタ触媒の下流側部分の熱容量が大きくなる。したがってフィルタ触媒の強制再生時に最も高温となる下流側端部の昇温が抑制され、再生処理までの間隔を長くできるため燃費が向上する。 Furthermore, since the downstream catalyst support layer does not affect the initial pressure loss, it can be formed in a larger amount than the coating amount of the upstream catalyst support layer. If it does in this way, the heat capacity of the downstream part of a filter catalyst will become large. Accordingly, the temperature rise at the downstream end, which is the highest temperature during forced regeneration of the filter catalyst, is suppressed, and the interval until regeneration processing can be increased, thereby improving fuel efficiency.
本発明の排ガス浄化用触媒は、ハニカム基材と、ハニカム基材のセル隔壁に形成され酸化物担体に触媒金属を担持してなる触媒担持層と、よりなる。ハニカム基材としては、ストレートフロー構造のもの、あるいはウォールフロー構造のものが用いられる。その材質は、従来と同様にコージェライト、SiC などのセラミックス製、あるいは金属製のものを用いることができる。 The exhaust gas purifying catalyst of the present invention comprises a honeycomb base material and a catalyst support layer formed on the cell partition walls of the honeycomb base material and supporting a catalyst metal on an oxide support. As the honeycomb substrate, a straight flow structure or a wall flow structure is used. As the material, cordierite, ceramics such as SiC, or metal can be used as in the conventional case.
ウォールフロー構造のハニカム基材の場合には、セル隔壁の気孔率は、40〜70%であることが望ましく、平均細孔径が10〜40μmであることが望ましい。気孔率及び平均細孔径がこの範囲にあることで、触媒担持層を 100〜 200g/L形成しても圧損の上昇を抑制することができ、強度の低下も抑制することができる。そしてPMをさらに効率よく捕集することができる。 In the case of a honeycomb substrate having a wall flow structure, the porosity of the cell partition walls is preferably 40 to 70%, and the average pore diameter is preferably 10 to 40 μm. When the porosity and average pore diameter are in this range, an increase in pressure loss can be suppressed and a decrease in strength can be suppressed even when the catalyst support layer is formed at 100 to 200 g / L. And PM can be collected more efficiently.
触媒担持層は、上流側触媒担持層と下流側触媒担持層とに分けられる。上流側触媒担持層とは、ハニカム基材の排ガス流入側端面から下流側へ所定の範囲に形成された部位をいう。また下流側触媒担持層とは、上流側触媒担持層以外の触媒担持層をいい、上流側触媒担持層の下流側端部から排ガス流出側端面までの範囲に形成された部位をいう。またウォールフロー構造のものの場合には、下流側触媒担持層は流出側セルの下流側に形成されている。流出側セルの上流側(目詰め部に近い部位)には、上流側触媒担持層が形成される。 The catalyst support layer is divided into an upstream catalyst support layer and a downstream catalyst support layer. The upstream catalyst support layer refers to a portion formed in a predetermined range from the exhaust gas inflow side end face of the honeycomb base material to the downstream side. The downstream catalyst support layer refers to a catalyst support layer other than the upstream catalyst support layer, and refers to a portion formed in the range from the downstream end of the upstream catalyst support layer to the exhaust gas outflow side end face. In the case of the wall flow structure, the downstream side catalyst support layer is formed on the downstream side of the outflow side cell. An upstream catalyst support layer is formed on the upstream side of the outflow side cell (site close to the clogging portion).
下流側触媒担持層には、多孔体が含まれている。多孔体とは、排ガス中のHCを吸着可能な細孔をもつものであり、ゼオライトが代表的に例示される。ゼオライトとしては、例えばフェリエライト、ZSM-5、モルデナイト、Y型ゼオライト、β型ゼオライト、X型ゼオライト、L型ゼオライト、シリカライト、シリカゾルにテンプレート材を加えてゲルを形成し水熱合成した後焼成することで製造された合成ゼオライトなどの、ゼオライトを用いることができる。中でも、モルデナイト、β型ゼオライトなどが好ましい。またこれらのゼオライトを脱Al処理した改質ゼオライトを用いることもできる。脱Al処理としては、酸処理、沸騰水処理、スチーム処理などが知られている。また、Fe、Ag、Cu、Mnなどをイオン交換担持したゼオライトを用いることも可能である。 The downstream side catalyst support layer includes a porous body. The porous body has pores capable of adsorbing HC in the exhaust gas, and is typically exemplified by zeolite. Examples of zeolites include ferrierite, ZSM-5, mordenite, Y-type zeolite, β-type zeolite, X-type zeolite, L-type zeolite, silicalite, silica sol, a template material added to form a gel, hydrothermal synthesis, and firing. Thus, zeolite such as synthetic zeolite produced can be used. Of these, mordenite, β-type zeolite and the like are preferable. Further, modified zeolite obtained by removing Al from these zeolites can also be used. As de-Al treatment, acid treatment, boiling water treatment, steam treatment and the like are known. Moreover, it is also possible to use zeolite carrying ion exchange on Fe, Ag, Cu, Mn or the like.
上流側触媒担持層を構成する酸化物担体としては、アルミナ、ジルコニア、チタニア、セリア、シリカなどの単品あるいは混合物を用いることができる。これらの複数種からなる複合酸化物を用いることもできる。上流側触媒担持層には、多孔体を含んでもよいが、少なくとも表層部には多孔体を含まないことが必要である。表層部に多孔体を含むと、排ガス低温域で上流側におけるコーキングなどのHC被毒が生じるようになり好ましくない。 As the oxide carrier constituting the upstream catalyst supporting layer, a single product such as alumina, zirconia, titania, ceria, silica, or a mixture thereof can be used. A composite oxide composed of a plurality of these can also be used. The upstream catalyst support layer may contain a porous material, but at least the surface layer portion needs to contain no porous material. If the surface layer includes a porous body, HC poisoning such as coking on the upstream side occurs in the exhaust gas low temperature region, which is not preferable.
下流側触媒担持層は、多孔体と上記酸化物担体との混合物から形成してもよいし、多孔体のみから形成してもよい。また多孔体は、表層に含まれることが望ましい。したがって下流側触媒担持層は、多孔体を含まず上記した酸化物担体に触媒金属を担持した層とし、その表面に多孔体を含む層を形成した二層構造とすることも好ましい。このようにすれば、上層でHCを吸着し、下層で浄化反応を促進させることができる。この場合、下層を上流側触媒担持層と同様の触媒担持層とすれば、上流側触媒担持層の形成時に下層を同時に形成できるので都合がよい。 The downstream catalyst support layer may be formed from a mixture of a porous body and the above oxide carrier, or may be formed from only the porous body. The porous body is preferably included in the surface layer. Therefore, it is also preferable that the downstream catalyst-carrying layer has a two-layer structure in which a catalyst metal is supported on the above-described oxide support without including a porous material, and a layer containing the porous material is formed on the surface thereof. In this way, HC can be adsorbed in the upper layer and the purification reaction can be promoted in the lower layer. In this case, if the lower layer is a catalyst supporting layer similar to the upstream catalyst supporting layer, it is advantageous because the lower layer can be formed simultaneously with the formation of the upstream catalyst supporting layer.
ストレートフロー構造のハニカム基材を用いた場合には、上流側触媒担持層及び下流側触媒担持層はセル隔壁の表面に形成される。この場合、上流側触媒担持層は排ガス流入側端面から全長の2/3以下、さらには1/2以下の範囲に形成されていることが望ましい。この範囲を超えて上流側触媒担持層を形成すると、下流側触媒担持層における多孔体の含有量を大きく増量する必要があり、そうすると初期圧損が上昇するため好ましくない。なお下限は特に形成されないが、流入側端面から少なくとも30mmの範囲に形成することが望ましい。 When a honeycomb substrate having a straight flow structure is used, the upstream side catalyst supporting layer and the downstream side catalyst supporting layer are formed on the surface of the cell partition wall. In this case, it is desirable that the upstream side catalyst support layer is formed within a range of 2/3 or less of the total length from the exhaust gas inflow side end surface, and more preferably 1/2 or less. If the upstream catalyst support layer is formed beyond this range, it is necessary to greatly increase the content of the porous material in the downstream catalyst support layer, which is not preferable because the initial pressure loss increases. The lower limit is not particularly formed, but it is desirable that the lower limit be formed within a range of at least 30 mm from the inflow side end face.
ストレートフロー構造のハニカム基材を用いた場合には、初期圧損の上昇を抑制するという観点から、及び担持密度の増大による触媒金属の粒成長を抑制するという観点から、上流側触媒担持層の形成量はハニカム基材の1リットルあたり30〜 250gとすることが望ましい。下流側触媒担持層の形成量も同様としてもよいし、上流側触媒担持層の形成量より多くすることも好ましい。 In the case of using a honeycomb substrate with a straight flow structure, from the viewpoint of suppressing an increase in initial pressure loss and from the viewpoint of suppressing catalyst metal grain growth due to an increase in the loading density, formation of an upstream catalyst supporting layer The amount is desirably 30 to 250 g per liter of the honeycomb substrate. The formation amount of the downstream side catalyst support layer may be the same, or it is preferable to make it larger than the formation amount of the upstream side catalyst support layer.
ウォールフロー構造のハニカム基材を用いた場合には、上流側触媒担持層は少なくとも流入側セルのセル隔壁表面とセル隔壁の細孔内表面に形成される。また下流側触媒担持層は、流出側セルの下流側に形成される。下流側触媒担持層は、ハニカム基材の外径をDとしたとき、流出側セルの流入側端面(目詰めされた部位)からD/2の長さ以降に形成されていることが望ましい。流入側端面からD/2の長さの範囲にまで下流側触媒担持層が形成されると、初期圧損が上昇する場合があるため好ましくない。なお流出側セルの流入側端面からD/2の範囲には、上流側触媒担持層と同様の触媒担持層を形成することが望ましい。 When a honeycomb substrate having a wall flow structure is used, the upstream catalyst support layer is formed at least on the cell partition wall surface of the inflow side cell and the pore inner surface of the cell partition wall. Further, the downstream side catalyst support layer is formed on the downstream side of the outflow side cell. The downstream side catalyst support layer is preferably formed after a length of D / 2 from the inflow side end face (the clogged portion) of the outflow side cell, where D is the outer diameter of the honeycomb substrate. If the downstream side catalyst support layer is formed from the inflow side end face to the range of D / 2 in length, the initial pressure loss may increase, which is not preferable. In addition, it is desirable to form a catalyst support layer similar to the upstream catalyst support layer in a range of D / 2 from the inflow side end face of the outflow side cell.
ウォールフロー構造のハニカム基材を用いた場合には、上流側触媒担持層の形成量はハニカム基材の1Lあたり30〜 200gとすることが好ましい。30g/L未満では、触媒金属の耐久性の低下が避けられず、 200g/Lを超えると初期圧損が高くなりすぎて実用的ではない。また下流側触媒担持層の形成量は、圧損が上昇しない範囲であれば特に制限されず、多孔体を多く含むほど好ましい。したがって下流側触媒担持層のコート量は、上流側触媒担持層のコート量より多くすることが望ましい。 When a honeycomb substrate having a wall flow structure is used, the amount of the upstream catalyst support layer formed is preferably 30 to 200 g per liter of the honeycomb substrate. If it is less than 30 g / L, the durability of the catalyst metal is inevitably lowered. If it exceeds 200 g / L, the initial pressure loss becomes too high, which is not practical. Further, the amount of the downstream catalyst-carrying layer formed is not particularly limited as long as the pressure loss does not increase, and the more the porous body is contained, the more preferable. Therefore, it is desirable that the coating amount of the downstream catalyst supporting layer is larger than the coating amount of the upstream catalyst supporting layer.
上流側触媒担持層及び下流側触媒担持層に担持された触媒金属としては、Pt、Pd、Rhなどの貴金属を主として用いることができる。場合によってはFe、Co、W、Niなどの遷移金属を用いてもよい。触媒金属は、均一に担持してもよいし、上流側触媒担持層と下流側触媒担持層とで担持密度あるいは触媒金属種を異ならせることも可能である。また触媒金属として、貴金属に加えてアルカリ金属及びアルカリ土類金属などのNOx 吸蔵材を用いることもできる。 As the catalyst metal supported on the upstream side catalyst supporting layer and the downstream side catalyst supporting layer, precious metals such as Pt, Pd, and Rh can be mainly used. In some cases, transition metals such as Fe, Co, W, and Ni may be used. The catalyst metal may be supported uniformly, or the support density or the catalyst metal species may be different between the upstream catalyst support layer and the downstream catalyst support layer. In addition to noble metals, NO x storage materials such as alkali metals and alkaline earth metals can also be used as catalyst metals.
触媒金属の担持量は、ハニカム基材の1リットルあたり 0.1〜10gの範囲とすることが好ましい。担持量がこれより少ないと活性が低すぎて実用的でなく、この範囲より多く担持しても活性が飽和するとともにコストアップとなってしまう。また触媒金属を担持するには、触媒金属の硝酸塩などを溶解した溶液を用い、吸着担持法、含浸担持法などによって担持させることができる。 The amount of catalyst metal supported is preferably in the range of 0.1 to 10 g per liter of the honeycomb substrate. If the loading amount is less than this, the activity is too low to be practical, and if the loading amount exceeds this range, the activity is saturated and the cost is increased. In order to support the catalyst metal, a solution in which a catalyst metal nitrate or the like is dissolved can be used and supported by an adsorption support method, an impregnation support method, or the like.
各触媒担持層を形成するには、酸化物担体粉末あるいは多孔体粉末をアルミナゾルなどのバインダ成分及び水とともにスラリーとし、そのスラリーをセル隔壁に付着させた後に焼成するウォッシュコート法を用いる。触媒金属は、このように形成されたコート層に担持してもよいし、予め触媒金属を担持した酸化物担体粉末を用いてウォッシュコートすることもできる。 In order to form each catalyst supporting layer, a wash coat method is used in which oxide carrier powder or porous powder is made into a slurry together with a binder component such as alumina sol and water, and the slurry is attached to the cell partition and then fired. The catalytic metal may be supported on the coating layer formed as described above, or may be wash coated using an oxide carrier powder that has previously supported the catalytic metal.
ウォールフロー構造のハニカム基材を用いた場合には、上流側触媒担持層を形成する際には、流入側端面から流入側セルにスラリーを供給し、エアブローあるいは吸引によって流出側セルからスラリーを排出することで、セル隔壁の細孔に強制的にスラリーを充填することが望ましい。一方、下流側触媒担持層を形成する際には、多孔体の粒径はセル隔壁の細孔径より一般に大きく、細孔の開口を塞いで初期圧損が上昇する可能性がある。そこで、流出側端面から流出側セルに所定深さの範囲でスラリーを供給し、同じ流出側端面からスラリーを排出することが望ましい。 When a honeycomb substrate with a wall flow structure is used, when forming the upstream catalyst support layer, the slurry is supplied from the inflow side end surface to the inflow side cell and discharged from the outflow side cell by air blow or suction. By doing so, it is desirable to forcibly fill the pores of the cell partition walls with the slurry. On the other hand, when the downstream catalyst support layer is formed, the particle size of the porous body is generally larger than the pore diameter of the cell partition wall, and there is a possibility that the initial pressure loss increases by closing the pore opening. Therefore, it is desirable to supply the slurry from the outflow side end face to the outflow side cell within a predetermined depth and discharge the slurry from the same outflow side end face.
以下、実施例、比較例及び試験例により本発明を具体的に説明する。 Hereinafter, the present invention will be specifically described with reference to Examples, Comparative Examples, and Test Examples.
(実施例1)
図1に本実施例に係る排ガス浄化用触媒を用いた排ガス浄化装置を示す。この排ガス浄化装置は、ディーゼルエンジン 100と、その排気系に配置された触媒コンバータ 200と、触媒コンバータ 200の上流側で排ガス中に軽油を添加するポンプ 300とを備えている。触媒コンバータ 200には、酸化触媒 400とフィルタ触媒 500が直列に収納され、酸化触媒 400はフィルタ触媒 500の上流側に配置されている。
Example 1
FIG. 1 shows an exhaust gas purification apparatus using an exhaust gas purification catalyst according to this embodiment. This exhaust gas purification apparatus includes a
図2に、酸化触媒 400の模式的断面図を示す。この酸化触媒は、コージェライト製でストレートフロー構造のハニカム基材1と、ハニカム基材1のセル隔壁10の表面に全長に亘って形成された第1触媒層2と、ハニカム基材1の流入側端面から500mm入った位置から流出側端面までの範囲で第1触媒層2の表面に形成された第2触媒層3と、から構成されている。ハニカム基材1の流入側端面から50mm入った位置の範囲に形成された第1触媒層2が上流側触媒担持層を構成し、第2触媒層3とその下層に形成された第1触媒層2が下流側触媒担持層を構成している。以下、この酸化触媒の製造方法を説明し、構成の詳細な説明に代える。
FIG. 2 shows a schematic cross-sectional view of the
コージェライト製でストレートフロー構造のハニカム基材1(セル数: 400cell/inch2 、セル隔壁厚さ: 0.1mm、φ: 129mm、全長: 150mm)を用意し、アルミナゾル( Al2O3:40質量%)に浸漬した後に引き上げて余分なアルミナゾルを吹き払い、乾燥、焼成して第1のコート層を形成した。第1のコート層の形成量は、ハニカム基材1リットルあたり50gであり、その厚さは約2μmと薄い。 Cordierite-made honeycomb substrate 1 with straight flow structure (cell number: 400cell / inch 2 , cell partition wall thickness: 0.1mm, φ: 129mm, total length: 150mm), alumina sol (Al 2 O 3 : 40 mass) %) And then pulled up to blow off excess alumina sol, dried and fired to form a first coat layer. The amount of the first coat layer formed is 50 g per liter of honeycomb substrate, and the thickness is as thin as about 2 μm.
次に、β型ゼオライト粉末75質量部、γ−アルミナ粉末75質量部、バインダとしてのアルミナゾル( Al2O3:40質量%)30質量部及びイオン交換水からなるスラリーを調製した。第1のコート層をもつハニカム基材1の流出側端面から 100mm入った位置までの範囲をこのスラリーに浸漬し、引き上げて余分なスラリーを吹き払い、乾燥、焼成して第2のコート層を形成した。第2のコート層の形成量は、ハニカム基材1リットルあたり 150gであり、β型ゼオライト粉末が75g/L、γ−アルミナが75g/L含まれている。
Next, a slurry comprising 75 parts by mass of β-type zeolite powder, 75 parts by mass of γ-alumina powder, 30 parts by mass of alumina sol (Al 2 O 3 : 40% by mass) as a binder and ion-exchanged water was prepared. The area from the outflow side end face of the honeycomb substrate 1 having the first coat layer to the
その後、ジニトロジアンミン白金溶液を用い、第1のコート層及び第2のコート層に吸着担持させた後、 500℃で1時間焼成した。Ptは第1のコート層及び第2のコート層に均一に担持され、その担持量はハニカム基材1リットルあたり2gである。 Thereafter, the dinitrodiammine platinum solution was adsorbed and supported on the first coat layer and the second coat layer, and then baked at 500 ° C. for 1 hour. Pt is uniformly supported on the first coat layer and the second coat layer, and the supported amount is 2 g per liter of the honeycomb substrate.
(実施例2)
セル数が 600cell/inch2 、セル隔壁厚さが 0.075mmのハニカム基材を用いたこと以外は、実施例1と同様にして調製された排ガス浄化用触媒を実施例2とした。実施例2の排ガス浄化用触媒は、セル密度が実施例1より高く、各セル通路の開口面積が実施例1より小さい。
(Example 2)
Example 2 was an exhaust gas purification catalyst prepared in the same manner as Example 1 except that a honeycomb substrate having a cell number of 600 cells / inch 2 and a cell partition wall thickness of 0.075 mm was used. The exhaust gas purifying catalyst of Example 2 has a cell density higher than that of Example 1, and an opening area of each cell passage is smaller than that of Example 1.
(比較例1)
第2のコート層を第1のコート層の表面全面に形成したこと以外は、実施例1と同様にして調製された排ガス浄化用触媒を比較例1とした。第2のコート層の形成量は、ハニカム基材1リットルあたり 150gである。
(Comparative Example 1)
A catalyst for exhaust gas purification prepared in the same manner as in Example 1 except that the second coat layer was formed on the entire surface of the first coat layer was used as Comparative Example 1. The amount of the second coat layer formed is 150 g per liter of honeycomb substrate.
(比較例2)
実施例2と同様のハニカム基材を用い、第2のコート層を第1のコート層の表面全面に形成したこと以外は、実施例1と同様にして調製された排ガス浄化用触媒を比較例2とした。第2のコート層の形成量は、ハニカム基材1リットルあたり 150gである。
(Comparative Example 2)
An exhaust gas purifying catalyst prepared in the same manner as in Example 1 except that the same honeycomb substrate as in Example 2 was used and the second coat layer was formed on the entire surface of the first coat layer. 2. The amount of the second coat layer formed is 150 g per liter of honeycomb substrate.
<試験例1>
各実施例及び各比較例の排ガス浄化用触媒を、それぞれ大気中にて 700℃で20時間保持する耐熱試験を行った。耐熱試験後の各触媒を、エンジンベンチにて2Lのディーゼルエンジンの排気管にそれぞれ装着し、2000rpm でトルクを可変しながら、 150℃から 400℃まで25℃/分の速度で昇温し、その時のHC浄化率を連続的に測定した。そしてHCを50%浄化できる温度(HC50%浄化温度)を求め、結果を表1に示す。
<Test Example 1>
A heat resistance test was performed in which the exhaust gas purifying catalysts of each Example and each Comparative Example were kept in the atmosphere at 700 ° C. for 20 hours. Each catalyst after the heat resistance test is mounted on the exhaust pipe of a 2L diesel engine on the engine bench, and the temperature is increased from 150 ° C to 400 ° C at a rate of 25 ° C / min while changing the torque at 2000rpm. The HC purification rate was continuously measured. The temperature at which HC can be purified by 50% (
<試験例2>
耐熱試験後の各触媒を、エンジンベンチにて2Lディーゼルエンジンの排気管にそれぞれ装着し、1800rpm ×50Nmの条件で運転しながら、触媒の上流側の排ガス中に約 0.5cc/秒の流量にて軽油を間欠的に10時間噴霧添加した。運転開始から10分後における触媒内部の温度を、排ガス流通方向で複数の点で測定し、結果を図3に示す。図3から、上流側より下流側の方が高温であり、流入側端面から50mm未満の範囲では温度が上がりにくいことがわかる。なお、各触媒間における差異は認められなかった。
<Test Example 2>
Each catalyst after the heat resistance test is installed in the exhaust pipe of a 2L diesel engine on the engine bench and operated at 1800rpm x 50Nm, while flowing at about 0.5cc / sec in the exhaust gas upstream of the catalyst. Light oil was intermittently sprayed for 10 hours. The temperature inside the
軽油噴霧後の各触媒について、流入側端面で閉塞されているセル数を数え、端面閉塞率を算出した。また軽油噴霧後の各触媒について、試験例1と同様にしてHC50%浄化温度を測定し、結果を表1に示す。 For each catalyst after light oil spraying, the number of cells blocked at the inflow side end surface was counted, and the end surface blocking rate was calculated. Further, the HC50% purification temperature was measured in the same manner as in Test Example 1 for each catalyst after light oil spraying, and the results are shown in Table 1.
<試験例3>
排気量2Lのディーゼルエンジンを搭載したエンジンベンチの排気管に、酸化触媒を装着し、その排ガス下流側に上記耐熱試験と軽油噴霧を行った各触媒を直列に装着した。酸化触媒は、 1.3リットルのコージェライト製ストレートフロー構造のハニカム基材に、アルミナとPtとからなる触媒担持層が形成されてなる。Ptの担持量はハニカム基材の1リットルあたり2gである。
<Test Example 3>
An oxidation catalyst was attached to an exhaust pipe of an engine bench equipped with a diesel engine with a displacement of 2 L, and each catalyst subjected to the heat resistance test and light oil spraying was attached in series to the exhaust gas downstream side. The oxidation catalyst is obtained by forming a catalyst support layer made of alumina and Pt on a honeycomb substrate of 1.3 liter cordierite straight flow structure. The amount of Pt supported is 2 g per liter of the honeycomb substrate.
そして2000rpm でトルクを可変しながら、上記耐熱試験と軽油噴霧を行った各触媒の入りガス温度が 600℃となるように軽油噴霧量を調整し、その後のHC50%浄化温度を試験例1と同様に測定した。結果を表1に示す。 While changing the torque at 2000 rpm, the gas oil spray amount was adjusted so that the gas temperature of each catalyst subjected to the above heat resistance test and light oil spray was 600 ° C., and the subsequent HC50% purification temperature was the same as in Test Example 1 Measured. The results are shown in Table 1.
<評価> <Evaluation>
表1より試験例1においては、各実施例の触媒は対応する比較例の触媒に比べて若干劣るものの、試験例2及び試験例3では各実施例の触媒は高い浄化活性を示し、端面閉塞も生じていない。これは、第2触媒層3(下流側触媒担持層)を上流側に形成せず下流側のみに形成した効果であることが明らかである。 From Table 1, in Test Example 1, the catalyst of each Example is slightly inferior to the corresponding catalyst of Comparative Example, but in Test Example 2 and Test Example 3, the catalyst of each Example shows high purification activity and end face clogging. Neither has occurred. This is clearly the effect of forming the second catalyst layer 3 (downstream catalyst support layer) only on the downstream side without forming it on the upstream side.
(実施例3)
本実施例に係るフィルタ触媒の模式的断面図を図4に示す。このフィルタ触媒は、図1に示したフィルタ触媒 500に相当するものであり、コージェライト製でウォールフロー構造のDPF基材4を有している。DPF基材4は、流出側端部で目詰めされた流入側セル40と、流入側セル40に隣接し流入側端部で目詰めされた流出側セル41と、流入側セル40及び流出側セル41を区画するセル隔壁42と、からなる。流入側セル40及び流出側セル41のセル隔壁40の表面及びセル隔壁40の細孔内表面には、全長に亘って第1触媒層5が形成され、流出側セル41の下流側でセル隔壁40の表面及びセル隔壁40の細孔内表面には第2触媒層6が形成されている。DPF基材4の流入側セル40に形成された第1触媒層5と、流出側セル41の流入側端面(目詰め部位)から 100mmの深さの範囲に形成されあ第1触媒層5が上流側触媒担持層を構成し、流出側セル41の流出側端面から深さ50mmの範囲に形成された第2触媒層6とその下層に形成されている第1触媒層5が下流側触媒担持層を構成している。以下、このフィルタ触媒の製造方法を説明し、構成の詳細な説明に代える。
(Example 3)
FIG. 4 shows a schematic cross-sectional view of the filter catalyst according to this example. This filter catalyst corresponds to the
コージェライト製でウォールフロー構造のDPF基材4(セル数:46.5cell/cm2 、セル隔壁厚さ: 0.3mm、φ: 129mm、全長: 150mm、平均細孔径:12μm)を用意し、流入側セル40からアルミナゾル( Al2O3:40質量%)を供給し流出側セル41から吸引して余分なアルミナゾルを除去し、乾燥、焼成して第1のコート層を形成した。第1のコート層の形成量は、DPF基材1リットルあたり30gである。
Cordierite-made DPF base material with wall flow structure 4 (cell number: 46.5cell / cm 2 , cell partition wall thickness: 0.3mm, φ: 129mm, total length: 150mm, average pore size: 12μm), inflow side Alumina sol (Al 2 O 3 : 40% by mass) was supplied from the
次に、β型ゼオライト粉末(モル比SiO2/ Al2O3= 100)90質量部、バインダとしてのアルミナゾル( Al2O3:40質量%)30質量部及びイオン交換水からなるスラリーを調製した。第1のコート層をもつDPF基材1の流出側端面から流出側セル41内へ深さ50mmの範囲をスラリーに浸漬し、流出側端面から吸引して余分なスラリーを除去し、乾燥、焼成して第2のコート層を形成した。第2のコート層の形成量は60gであり、DPF基材1リットルあたり90gとなる。 Next, a slurry comprising 90 parts by mass of β-type zeolite powder (molar ratio SiO 2 / Al 2 O 3 = 100), 30 parts by mass of alumina sol (Al 2 O 3 : 40% by mass) as a binder and ion-exchanged water is prepared. did. A 50mm depth range is immersed in the slurry from the outflow side end face of the DPF substrate 1 having the first coat layer into the outflow side cell 41, and the excess slurry is removed by suction from the outflow side end face, followed by drying and firing. Thus, a second coat layer was formed. The amount of the second coat layer formed is 60 g, which is 90 g per liter of DPF base material.
続いてジニトロジアンミン白金溶液を流入側セル40から供給し、流出側セル41から吸引した後、 500℃で1時間焼成してPtを担持した。Ptは第1のコート層及び第2のコート層に均一に担持され、その担持量はDPF基材1リットルあたり1gである。
Subsequently, a dinitrodiammine platinum solution was supplied from the
得られたフィルタ触媒では、図4に拡大して示すように、第1触媒層5はセル隔壁42の細孔の内表面にも均一に形成されているが、第2触媒層6は細孔の内部には形成されていない。
In the obtained filter catalyst, as shown in an enlarged view in FIG. 4, the first catalyst layer 5 is uniformly formed on the inner surface of the pores of the
(実施例4)
第2のコート層の形成範囲を流出側端面から深さ75mmの範囲としたこと以外は、実施例3と同様にして調製されたフィルタ触媒を実施例4とした。第2のコート層の形成量は実施例3と同様に60gであり、DPF基材1リットルあたり60gとなる。
Example 4
A filter catalyst prepared in the same manner as in Example 3 was used in Example 4 except that the formation range of the second coat layer was set to a range of 75 mm in depth from the outflow side end face. The formation amount of the second coat layer is 60 g as in Example 3, and is 60 g per liter of DPF base material.
(比較例3)
第2のコート層を形成しなかったこと以外は、実施例3と同様にして調製されたフィルタ触媒を比較例3とした。
(Comparative Example 3)
A filter catalyst prepared in the same manner as in Example 3 except that the second coat layer was not formed was used as Comparative Example 3.
(比較例4)
第2のコート層を流出側セル41の全長に形成したこと以外は、実施例3と同様にして調製されたフィルタ触媒を比較例4とした。第2のコート層の形成量は実施例3と同様に60gであり、DPF基材1リットルあたり30gとなる。
(Comparative Example 4)
A filter catalyst prepared in the same manner as in Example 3 except that the second coat layer was formed over the entire length of the outflow side cell 41 was used as Comparative Example 4. The amount of the second coat layer formed is 60 g as in Example 3, and 30 g per liter of DPF base material.
<試験例4>
排気量2Lのディーゼルエンジンを搭載したエンジンベンチの排気管に、酸化触媒を装着し、その排ガス下流側に各実施例及び各比較例のフィルタ触媒を直列に装着した。酸化触媒は、 1.3リットルのコージェライト製ストレートフロー構造のハニカム基材に、アルミナとPtとからなる触媒担持層が形成されてなる。Ptの担持量はハニカム基材の1リットルあたり2gである。
<Test Example 4>
An oxidation catalyst was mounted on the exhaust pipe of an engine bench equipped with a diesel engine with a displacement of 2 L, and the filter catalysts of the examples and comparative examples were mounted in series on the exhaust gas downstream side. The oxidation catalyst is obtained by forming a catalyst support layer made of alumina and Pt on a honeycomb substrate of 1.3 liter cordierite straight flow structure. The amount of Pt supported is 2 g per liter of the honeycomb substrate.
先ず2000rpm × 100Nmで運転しながら、酸化触媒の上流側で排ガス中に1cc/秒の流量で軽油を間欠的に噴射し、各フィルタ触媒の床温 700℃で10分間保持するのを 100回繰り返す耐久試験を行った。
First, while operating at 2000 rpm x 100 Nm, light oil is intermittently injected into the exhaust gas at a flow rate of 1 cc / sec upstream of the oxidation catalyst, and each filter catalyst is held at a bed temperature of 700 ° C for 10
排気量2Lのディーゼルエンジンを搭載したエンジンベンチの排気管に耐久試験後の各フィルタ触媒をそれぞれ装着し、2000rpm × 100Nmで運転しながら、初期(煤堆積無し)の圧損と、DPF基材4の1リットルあたり4gの煤が堆積した堆積後の圧損を測定した。比較例3の圧損に対する比を算出し、結果を表2に示す。 Each filter catalyst after the endurance test is mounted on the exhaust pipe of an engine bench equipped with a diesel engine with a displacement of 2L, operating at 2000rpm x 100Nm, the initial pressure loss (no soot accumulation), and the DPF base 4 The pressure loss after deposition in which 4 g of soot was deposited per liter was measured. The ratio of the pressure loss of Comparative Example 3 was calculated, and the results are shown in Table 2.
<試験例5>
排気量2Lのディーゼルエンジンを搭載したエンジンベンチの排気管に耐久試験後の各フィルタ触媒をそれぞれ装着し、1800rpm ×30Nmで運転しながら、フィルタ触媒の上流側で排ガス中に軽油を 0.1cc/秒の流量で噴射し、フィルタ触媒への入りガス温度が 150℃の時の出ガス中のHC濃度をそれぞれ測定した。結果を表2に示す。
<Test Example 5>
Each filter catalyst after the endurance test is mounted on the exhaust pipe of an engine bench equipped with a diesel engine with a displacement of 2L, and while operating at 1800rpm x 30Nm, 0.1 cc / sec of light oil in the exhaust gas upstream of the filter catalyst The HC concentration in the output gas when the gas entering the filter catalyst was 150 ° C. was measured. The results are shown in Table 2.
<試験例6>
排気量2Lのディーゼルエンジンを搭載したエンジンベンチの排気管に、試験例4と同様に耐久試験後の各フィルタ触媒と酸化触媒をそれぞれ装着し、1800rpm ×50Nmで運転しながらDPF基材4の1リットルあたり4gの煤を堆積させた。
<Test Example 6>
In the exhaust pipe of an engine bench equipped with a diesel engine with a displacement of 2L, each filter catalyst and oxidation catalyst after endurance test was mounted in the same manner as in Test Example 4, and 1 of DPF base material 4 was operated while operating at 1800rpm x 50Nm. 4 g of soot was deposited per liter.
その後、2000rpm × 100Nmで運転しながら、酸化触媒の上流から排ガス中へ1cc/秒で軽油を間欠的に噴射し、 650℃まで 300℃/分の速度でフィルタ触媒の入りガス温度を昇温させ、フィルタ触媒の入りガス温度が 650℃に到達した時点でエンジンへの燃料供給を停止して、堆積した煤を強制的に燃焼させた。その際のフィルタ触媒中の最高床温を測定し、結果を表2に示す。 After that, while operating at 2000 rpm x 100 Nm, light oil is intermittently injected from the upstream of the oxidation catalyst into the exhaust gas at 1 cc / second, and the gas temperature entering the filter catalyst is raised to 650 ° C at a rate of 300 ° C / minute. When the gas temperature entering the filter catalyst reached 650 ° C, the fuel supply to the engine was stopped and the soot deposited was forcibly burned. The maximum bed temperature in the filter catalyst at that time was measured, and the results are shown in Table 2.
<評価> <Evaluation>
表2より、各実施例のフィルタ触媒は、初期及び堆積後の圧損が比較例3には及ばないものの、比較例4より小さいことがわかり、実用の範囲内である。また第2触媒層6を長く形成した実施例4では、実施例3より圧損が上昇していることもわかる。 From Table 2, it can be seen that the filter catalyst of each example has an initial and post-deposition pressure loss that does not reach that of Comparative Example 3, but is smaller than that of Comparative Example 4, and is within the practical range. It can also be seen that in Example 4 in which the second catalyst layer 6 was formed longer, the pressure loss was higher than in Example 3.
そして試験例5の結果から、各実施例のフィルタ触媒は各比較例に比べて低温域におけるHC浄化性能に優れていることがわかり、試験例6の結果から再生処理時の熱損傷が抑制されることがわかる。これは、第2触媒層6を流出側セル41の下流側にのみ形成したことによる効果であることが明らかである。 From the results of Test Example 5, it can be seen that the filter catalyst of each Example is superior in HC purification performance in a low temperature region as compared with each Comparative Example, and from the results of Test Example 6, thermal damage during the regeneration process is suppressed. I understand that This is clearly an effect obtained by forming the second catalyst layer 6 only on the downstream side of the outflow side cell 41.
<試験例7>
コージェライト製でウォールフロー構造のDPF基材4(セル数:46.5cell/cm2 、セル隔壁厚さ: 0.3mm、φ(D): 160mm、全長: 200mm、平均細孔径:12μm)を用意し、実施例1と同様にしてフィルタ触媒を調製した。第2のコート層を形成する際に、流出側セル41の流出側端面からの深さを種々変更し、第2触媒層6の形成範囲が異なる種々のフィルタ触媒を調製した。
<Test Example 7>
Cordierite-made DPF base material with wall flow structure 4 (cell number: 46.5cell / cm 2 , cell partition wall thickness: 0.3mm, φ (D): 160mm, total length: 200mm, average pore diameter: 12μm) A filter catalyst was prepared in the same manner as in Example 1. When forming the second coat layer, the depth from the outflow side end face of the outflow side cell 41 was variously changed, and various filter catalysts having different formation ranges of the second catalyst layer 6 were prepared.
得られた複数のフィルタ触媒について、試験例4と同様にして初期圧損を測定した結果を図5に示す。 FIG. 5 shows the results of measuring the initial pressure loss in the same manner as in Test Example 4 for the obtained plurality of filter catalysts.
図5より、流出側セル41において第2触媒層6の未形成部分が少なくなるほど圧損が上昇していることがわかり、未形成部分の長さはDPF基材の外径( 160mm)の半分(80mm)以上の範囲が望ましいこと、すなわち下流側触媒担持層は流入側端面からD/2の長さ以降に形成されていることが望ましいことが明らかである。 From FIG. 5, it can be seen that the pressure loss increases as the unformed portion of the second catalyst layer 6 decreases in the outflow side cell 41, and the length of the unformed portion is half the outer diameter (160 mm) of the DPF substrate ( It is apparent that a range of 80 mm) or more is desirable, that is, it is desirable that the downstream side catalyst support layer be formed after a length of D / 2 from the end surface on the inflow side.
本発明の排ガス浄化用触媒は、酸化触媒、三元触媒、NOx 吸蔵還元触媒、リーンNOx 触媒、フィルタ触媒などとして利用できる他、HC吸着材などに応用することもできる。 The exhaust gas purifying catalyst of the present invention can be used as an oxidation catalyst, a three-way catalyst, a NO x storage reduction catalyst, a lean NO x catalyst, a filter catalyst, etc., and can also be applied to HC adsorbents and the like.
1:ハニカム基材
2、5:第1触媒層(上流側触媒担持層)
3、6:第2触媒層(下流側触媒担持層)
1:
3, 6: Second catalyst layer (downstream catalyst support layer)
Claims (6)
該酸化物担体には、排ガス中の炭化水素を吸着可能な細孔をもつ多孔体を含み、
該ハニカム基材の排ガス流入側端面から下流側へ所定範囲の上流部に形成された上流側触媒担持層の少なくとも表層部には該多孔体を含まず、該上流側触媒担持層の下流側端部から排ガス流出側端面までの下流部に形成された下流側触媒担持層に該多孔体を含むことを特徴とする排ガス浄化用触媒。 A honeycomb base material having a plurality of cells partitioned by cell partition walls, a catalyst support layer formed on the cell partition walls and supporting a catalyst metal on an oxide carrier, and an exhaust gas purifying catalyst,
The oxide carrier includes a porous body having pores capable of adsorbing hydrocarbons in exhaust gas,
At least the surface layer portion of the upstream catalyst support layer formed in the upstream portion of the predetermined range from the exhaust gas inflow side end surface of the honeycomb base material to the downstream side does not include the porous body, and the downstream end of the upstream catalyst support layer An exhaust gas purifying catalyst, comprising the porous body in a downstream catalyst support layer formed in a downstream portion from the exhaust portion to the exhaust gas outflow side end surface.
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