JP2007296518A - Catalyst and device for cleaning exhaust gas - Google Patents

Catalyst and device for cleaning exhaust gas Download PDF

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JP2007296518A
JP2007296518A JP2007096317A JP2007096317A JP2007296518A JP 2007296518 A JP2007296518 A JP 2007296518A JP 2007096317 A JP2007096317 A JP 2007096317A JP 2007096317 A JP2007096317 A JP 2007096317A JP 2007296518 A JP2007296518 A JP 2007296518A
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exhaust gas
catalyst
gas purification
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JP5085176B2 (en
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Takeshi Mori
武史 森
Norihiko Suzuki
紀彦 鈴木
Yuichi Matsuo
雄一 松尾
Atsushi Furukawa
敦史 古川
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Honda Motor Co Ltd
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Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for cleaning exhaust gas which can burn PM in a lower temperature range and has excellent heat resistance. <P>SOLUTION: The catalyst for cleaning exhaust gas, which is used for burning the carbon-based particulate matter contained in the exhaust gas discharged from an internal-combustion engine, is obtained by depositing Ag on a compound oxide having oxygen releasability. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

本発明は、排ガス浄化触媒および排ガス浄化装置に係り、特に、ディーゼルエンジンの排ガスに含まれる粒子状物質(PM)を効率良く浄化、低減させる排ガス浄化触媒に関する。   The present invention relates to an exhaust gas purification catalyst and an exhaust gas purification device, and more particularly to an exhaust gas purification catalyst that efficiently purifies and reduces particulate matter (PM) contained in exhaust gas of a diesel engine.

従来、ディーゼルエンジンの排ガス中に含まれる粒子状物質を除去するために、ディーゼル微粒子除去装置(DPF)を用いている。この粒子状物質は、主として燃料に由来して生成されるものであり、易燃性成分である有機成分(SOF)と、難燃性成分であるすす(soot)等から構成されている。このような粒子状成分の燃焼温度は、有機成分で200〜550℃、およびsootで550〜700℃と非常に高い温度を必要としている。有機成分はキャタライズドスートフィルタ(CSF)のように、DPFに貴金属系触媒を担持することで早期浄化を行っているが、sootに対する浄化性能は低い。このため、特許文献1および2に記載されているように、DPFの再生中のsootをセリアを有する触媒で酸化促進する技術が提案されている。   Conventionally, a diesel particulate removal device (DPF) is used to remove particulate matter contained in exhaust gas of a diesel engine. This particulate matter is mainly produced from fuel, and is composed of an organic component (SOF) that is a flammable component and soot that is a flame retardant component. The combustion temperature of such a particulate component requires very high temperatures of 200 to 550 ° C. for organic components and 550 to 700 ° C. for soot. The organic component is purified early by loading a noble metal catalyst on the DPF, like a catalyzed soot filter (CSF), but the purification performance against soot is low. For this reason, as described in Patent Documents 1 and 2, a technique has been proposed in which oxidation during regeneration of DPF is promoted by a catalyst having ceria.

しかしながら、DPFによりPMを捕集する技術では、排気ガスの圧損となるとともに、強制的にDPFのを行うために燃費のロスやPMの燃焼熱によるDPFの溶損や触媒の劣化を引き起こす。このため、sootを含めたPMをより低温で燃焼させることで自動車の排気系への負担を軽減する技術が望まれている。   However, the technique of collecting PM by DPF causes pressure loss of exhaust gas and forcibly performs DPF, which causes fuel consumption loss, DPF dissolution by PM combustion heat, and catalyst deterioration. For this reason, the technique which reduces the burden on the exhaust system of a motor vehicle by burning PM including soot at lower temperature is desired.

自動車の排気系への負担を軽減する方法として、再生頻度を低減することやsootの燃焼効率を向上させること、さらには、DPFを使用せずに触媒コンバータの触媒のみでPMを連続的に燃焼させることが考えられる。最近では、特許文献3および4に開示されているように、PMの低温燃焼触媒として貴金属や複合酸化物を用いることが提案されている。しかしながら、それら文献に開示された触媒では、sootの燃焼には効果はあるが、燃焼温度は450〜600℃と高温である。   As a method to reduce the burden on the exhaust system of automobiles, the regeneration frequency is reduced, the soot combustion efficiency is improved, and PM is continuously burned only with the catalyst of the catalytic converter without using the DPF. It is possible to make it. Recently, as disclosed in Patent Documents 3 and 4, it has been proposed to use a noble metal or a composite oxide as a low temperature combustion catalyst for PM. However, the catalysts disclosed in these documents are effective in soot combustion, but the combustion temperature is as high as 450 to 600 ° C.

また、従来よりPMの燃焼には二酸化窒素(NO)が高活性であることが知られている。特許文献5には、DPFの上流側にNO生成触媒を配置することが提案され、特許文献6には、DPFにNO生成触媒を塗布することが提案されるなど、通常ではPMが自己燃焼しない温度域でNOを利用して燃焼除去する方法が提案されている。しかしながら、そのような方法にあっては、NOが少ない条件においては、PMの燃焼を促進する効果が少なく、また、温度が高くなるとNOとNOの濃度平衡がNO側へ偏るため、NOによるPM燃焼促進効果は極めて小さくなる。 Conventionally, it is known that nitrogen dioxide (NO 2 ) is highly active for PM combustion. Patent Document 5 proposes to arrange a NO 2 production catalyst upstream of the DPF, and Patent Document 6 proposes to apply a NO 2 production catalyst to the DPF. A method of burning and removing using NO 2 in a temperature range where combustion does not occur has been proposed. However, in such a method, under the condition where NO x is low, the effect of promoting PM combustion is small, and as the temperature increases, the concentration equilibrium between NO and NO 2 is biased toward the NO side. The PM combustion promotion effect by 2 is extremely small.

特許文献7では、NOによるPM燃焼効率をさらに高めるために、NO生成触媒とPM燃焼触媒とを組み合わせることが提案されている。この技術は、NO生成用の第1触媒と、転化されたNOをPMと反応させる第2触媒とを、2層もしくは混合層の状態でコートすることにより、第1触媒で生成したNOとPMとを第2触媒で反応させることにより、PMを効率的に除去するというものである。しかしながら、この技術では、第2触媒が第1触媒に被覆されているか混合されている状態でコートされているため、実際にはPMと第2触媒との接触確率が非常に低い状態になっている可能性があり、効果が低くなっているおそれがある。 In Patent Document 7, in order to further improve the PM combustion efficiency by NO 2, to combine the NO 2 generation catalyst and PM combustion catalyst it has been proposed. NO This technique comprises a first catalyst for NO 2 generation, the conversion has been NO 2 and a second catalytic reaction with PM, by coating in the form of two-layer or mixed layer, which is produced in the first catalytic PM is efficiently removed by reacting 2 and PM with a second catalyst. However, in this technique, since the second catalyst is coated while being coated or mixed with the first catalyst, the contact probability between PM and the second catalyst is actually very low. May be less effective.

特許文献8では、遷移金属を含む遷移金属触媒層を下層として塗布し、この下層の表面に、貴金属を無機酸化物に担持させた貴金属触媒層を上層として塗布した3次元構造体が提案されている。しかしながら、この技術では、PMは固体−固体反応であるため上層とPMは接触できるが、下層触媒とPMとは接触できないため、下層触媒の性能を充分に発揮することができない。   Patent Document 8 proposes a three-dimensional structure in which a transition metal catalyst layer containing a transition metal is applied as a lower layer, and a noble metal catalyst layer in which a noble metal is supported on an inorganic oxide is applied as an upper layer on the lower surface. Yes. However, in this technique, since PM is a solid-solid reaction, the upper layer and the PM can contact each other, but the lower layer catalyst and the PM cannot contact each other, so that the performance of the lower layer catalyst cannot be fully exhibited.

特開2004−42021号公報(要約)JP 2004-42021 A (summary) 特開2001−73748号公報(要約)JP 2001-73748 A (summary) 特表2000−502598号公報(特許請求の範囲1)JP 2000-502598 A (Claim 1) 特開平8−173770号公報(要約)JP-A-8-173770 (summary) 特開平1−318715号公報(要約)JP-A-1-318715 (Summary) 特開2003−293730号公報(要約)JP 2003-293730 A (summary) 特開2001−263051号公報(要約)JP 2001-263051 A (summary) 特開2001−157845号公報(要約)JP 2001-157845 A (summary)

ところで、ディーゼルエンジンから排出される排気ガス温度は200〜450℃と低いことことから、sootの燃焼は再生処理等を行わずに排気ガス温度域で連続燃焼させることは難しい。したがって、より低い温度域でsootを燃焼させる技術が強く要望されている。また、ディーゼルエンジンの排ガス浄化のための触媒については、今後の大排気量化および高出力化を想定すると、さらなる耐熱性が要求される。ディーゼル排ガスではガソリン排ガス雰囲気よりは触媒の耐熱性に対する要求は緩和されているものの、エンジン直下において高温の排気ガスをも浄化可能な性能まで求めると、従来の貴金属系触媒ではガソリン排気ガスの場合と同様に貴金属の凝集は生じる上、担体として用いられる酸化物等は構造破壊により性能が低下するため、触媒の耐熱性は充分と言うことはできない。一方、複合酸化物は、それ自体が高温焼成により構造を形成するために耐熱性能の問題はないが、いずれにしてもsootに対する低温燃焼の性能が必要である。したがって、本発明は、より低い温度域でPMを燃焼することができ、かつ耐熱性に優れた排ガス浄化触媒および排ガス浄化装置を提供することを目的としている。   By the way, since the exhaust gas temperature discharged from the diesel engine is as low as 200 to 450 ° C., it is difficult for the combustion of the soot to be continuously burned in the exhaust gas temperature range without performing a regeneration process or the like. Therefore, there is a strong demand for a technique for burning soot in a lower temperature range. Further, regarding a catalyst for exhaust gas purification of a diesel engine, further heat resistance is required when a future large displacement and high output are assumed. Diesel exhaust gas has a relaxed requirement for heat resistance of the catalyst than gasoline exhaust gas atmosphere. Similarly, agglomeration of precious metals occurs, and the performance of the oxide used as a support is lowered due to structural destruction. Therefore, it cannot be said that the heat resistance of the catalyst is sufficient. On the other hand, the composite oxide itself does not have a problem of heat resistance because it forms a structure by high-temperature firing, but in any case, a low-temperature combustion performance against soot is necessary. Therefore, an object of the present invention is to provide an exhaust gas purification catalyst and an exhaust gas purification device that can combust PM in a lower temperature range and have excellent heat resistance.

また、運転条件によっては、sootが全く燃焼しない条件もある。このようなときに蓄積したPMはDPFの目詰まりを引き起こし、PMの蓄積量の増加に伴いDPFによる圧力損失が増加するため、定期的に除去する必要がある。このため、外部エネルギーによりDPFの温度を600℃付近まで上昇させて燃焼除去することにより、DPFの再生を行っている。この再生処理により、燃費悪化やエミッション悪化、システムの複雑化など多くのデメリットが生じているのが現状である。このデメリットを低減するためには、再生時の温度を低下させること、あるいは、再生の時間を短くすることが必要である。したがって、本発明は、より低温でPMを燃焼させるとともに、高温でのPM燃焼速度が大きい排ガス浄化触媒および排ガス浄化装置を提供することを目的としている。   Further, depending on the operating conditions, there are also conditions where the soot does not burn at all. The PM accumulated at this time causes clogging of the DPF, and the pressure loss due to the DPF increases as the amount of accumulated PM increases. Therefore, it is necessary to periodically remove the PM. For this reason, the DPF is regenerated by raising the temperature of the DPF to around 600 ° C. by external energy and removing it by combustion. At present, this regeneration process has caused many disadvantages such as deterioration of fuel consumption, emission, and system complexity. In order to reduce this disadvantage, it is necessary to lower the temperature during reproduction or shorten the reproduction time. Accordingly, an object of the present invention is to provide an exhaust gas purification catalyst and an exhaust gas purification device that burn PM at a lower temperature and have a higher PM combustion rate at a higher temperature.

本発明の排ガス浄化触媒は、内燃機関から排出される排出ガスに含まれるカーボンを主成分とする粒子状物質を浄化するための排ガス浄化触媒であって、酸素放出能を有する複合酸化物にAgを担持したことを特徴としている。   The exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst for purifying particulate matter containing carbon as a main component contained in exhaust gas discharged from an internal combustion engine. It is characterized by having carried.

また、本発明の排ガス浄化装置は、内燃機関から排出される排出ガスに含まれるカーボンを主成分とする粒子状物質を捕集可能なフィルタの内部に、上記排ガス浄化触媒と、排ガス中に含まれるNOをNOに変換するNO生成触媒が同時に担持されていることを特徴としている。 Further, the exhaust gas purification apparatus of the present invention includes the exhaust gas purification catalyst and the exhaust gas inside the filter capable of collecting particulate matter mainly composed of carbon contained in the exhaust gas discharged from the internal combustion engine. The catalyst is characterized in that a NO 2 production catalyst for converting NO to NO 2 is supported at the same time.

本発明では、酸素放出能を有する複合酸化物にPMに対して活性の高いAgを担持することにより、複合酸化物の酸素放出能をより低温で引き出すことができるため、PMの燃焼をより低温下することができる。また、複合酸化物にAgを担持しているため、活性種であるAgをPMとの接触界面に配置することができ、PMとの反応性がより向上する。さらに、複合酸化物は耐熱性が高く、Agを複合酸化物に担持したことの相互作用効果により、Agの凝集および揮発を抑制することができるから、本発明の触媒は耐熱性の優れたものとなる。このように、本発明の排ガス浄化触媒は、より低い温度域でPMを燃焼することができ、かつ耐熱性に優れるから、今後さらなる大排気量、高出力エンジンを想定した高耐熱条件においても、排気レイアウトに左右されることなく床下は勿論のことエンジン直下においても使用可能である。また、PMを低温で燃焼することができるので、強制再生による燃費ロス、触媒劣化を抑制することができ、自動車の排気系への負担を軽減できるとともに、PMの捕集再生を行わない場合では、触媒によるPMの連続燃焼を行うことも可能となる。   In the present invention, by supporting Ag having a high activity against PM on the complex oxide having oxygen releasing ability, the oxygen releasing ability of the complex oxide can be extracted at a lower temperature, so that the combustion of PM is performed at a lower temperature. Can be taken down. In addition, since Ag is supported on the composite oxide, Ag which is an active species can be disposed at the contact interface with PM, and the reactivity with PM is further improved. Furthermore, the composite oxide has high heat resistance, and the catalyst of the present invention is excellent in heat resistance because it can suppress aggregation and volatilization of Ag due to the interaction effect of supporting Ag on the composite oxide. It becomes. Thus, since the exhaust gas purification catalyst of the present invention can burn PM at a lower temperature range and is excellent in heat resistance, even in high heat conditions assuming further large displacement and high output engines in the future, It can be used not only under the floor but also directly under the engine regardless of the exhaust layout. In addition, since PM can be burned at a low temperature, fuel consumption loss and catalyst deterioration due to forced regeneration can be suppressed, the burden on the exhaust system of the vehicle can be reduced, and when PM collection and regeneration are not performed. Further, it becomes possible to perform continuous combustion of PM using a catalyst.

また、酸素放出能を有する複合酸化物はNO吸収能も高いことが分かっており、NO生成触媒と共存させることにより、生成したNOが酸素放出能を有する複合酸化物表面に吸着されることにより、表面のNO濃度が高く保たれるため、AgによるNOとPMとの反応がより促進され、PM燃焼速度が向上する。また、Ag担持複合酸化物触媒とNO生成触媒との2層コートとし、NO生成触媒層内の気孔の大きさを平均1μm以上にすることにより、Agが担持された複合酸化物触媒へPMが接触することが容易となり、燃焼速度がさらに向上する。 In addition, it is known that the complex oxide having oxygen releasing ability has high NO 2 absorption ability. By coexisting with the NO 2 production catalyst, the produced NO 2 is adsorbed on the surface of the complex oxide having oxygen releasing ability. By this, since the surface NO 2 concentration is kept high, the reaction between NO 2 and PM by Ag is further promoted, and the PM combustion rate is improved. Further, by forming a two-layer coat of an Ag-supported composite oxide catalyst and a NO 2 generation catalyst, and setting the average pore size in the NO 2 generation catalyst layer to 1 μm or more, a composite oxide catalyst supporting Ag is obtained. It becomes easy for PM to contact, and a combustion rate improves further.

複合酸化物は、ペロブスカイト型、スピネル型、ルチル型、デラフォサイト型、マグネトプランバイト型、イルメナイト型、およびフルオライト型から選択することができる。中でも耐熱性の観点からペロブスカイト型、フルオライト型が好ましい。また、複合酸化物は、アルカリ金属、アルカリ土類金属、希土類金属、遷移金属、貴金属の中から選択される2以上の元素の組み合わせからなり、原子の価数を変化させて酸素の吸収及び放出を行うものである。複合酸化物が酸素放出能を有するためには、多原子価を持つ元素が1種類は含まれている方が好ましい。遷移金属ではV,Cr,Mn,Fe,Co,Cu,Nb,Ta,Mo,W、希土類金属ではCe,Pr,Sm,Eu,Tb,Ybである。酸素放出は、構成原子の価数の変化に応じて電荷のバランスを保つために、複合酸化物の格子中の酸素が離脱する現象である。また、アルカリ金属であるNa,K,Cs、貴金属であるPt,Pd,Rh,Ir,Ruは酸化物dとして不安定なため、メタル化することにより酸素放出する特性を付与することができる。さらに、構造安定性の観点から価数変化がなくイオン半径の比較的大きなLa,Nd,Sc,Hf,Ca,Sr,Baが含まれることが好ましい。なお、耐熱性の優れた複合酸化物とは、ある程度高温の耐熱条件に対してPM燃焼特性が変化しないか変化が少ない複合酸化物であり、PM燃焼特性の変化は、実用排ガス温度域で充分にPMを燃焼可能な領域内での変化を言う。   The composite oxide can be selected from perovskite type, spinel type, rutile type, delafossite type, magnetoplumbite type, ilmenite type, and fluorite type. Of these, a perovskite type and a fluorite type are preferable from the viewpoint of heat resistance. The composite oxide is a combination of two or more elements selected from alkali metals, alkaline earth metals, rare earth metals, transition metals, and noble metals, and absorbs and releases oxygen by changing the valence of atoms. Is to do. In order for the composite oxide to have an oxygen releasing ability, it is preferable that one kind of element having a polyvalence is included. Transition metals include V, Cr, Mn, Fe, Co, Cu, Nb, Ta, Mo, W, and rare earth metals include Ce, Pr, Sm, Eu, Tb, and Yb. Oxygen release is a phenomenon in which oxygen in the lattice of the composite oxide is desorbed in order to maintain a charge balance according to changes in the valence of constituent atoms. In addition, since Na, K, Cs, which are alkali metals, and Pt, Pd, Rh, Ir, Ru, which are noble metals, are unstable as oxides d, the characteristics of releasing oxygen can be imparted by metallization. Furthermore, La, Nd, Sc, Hf, Ca, Sr, and Ba having a relatively large ionic radius with no valence change are preferably included from the viewpoint of structural stability. A composite oxide with excellent heat resistance is a composite oxide that does not change or has little change in PM combustion characteristics under high-temperature heat resistance conditions to some extent, and changes in PM combustion characteristics are sufficient in the practical exhaust gas temperature range. The change in the region where PM can be combusted.

複合酸化物の調製方法については限定するものではないが、硝酸塩分解法、有機酸錯体重合法などを好適に用いることができる。また、複合酸化物にAgを担持させる方法は限定するものではないが、含浸法や析出沈殿法などを好適に用いることができる。   The method for preparing the composite oxide is not limited, but a nitrate decomposition method, an organic acid complex polymerization method, or the like can be suitably used. Further, the method of supporting Ag on the composite oxide is not limited, but an impregnation method, a precipitation method, or the like can be suitably used.

次に、本発明の具体的な使用例について、例えば、ディーゼルエンジンの排気通路に排ガス中のPMを捕集するフィルタを設置した場合について説明する。フィルタは三次元網目構造を有し、充分なPM捕集機能を有する発泡金属や発泡セラミックス、金属やセラミックス繊維を重ね合わせた不織布、ウォールフロータイプのフィルタなど、どのような形態でも充分な効果を発揮するが、ウォールフロータイプのフィルタが捕集効率と、PMと触媒との接触性の観点から好ましい。図10及び図11にディーゼルパティキュレートフィルタ(以下、DPFと略す。)を模式的に示す。このDPFは、ハニカム構造をなしており、互いに平行に延在する多数の排気ガス流路2,3を備えている。DPFの下流端が栓4により閉塞された排気ガス流入路2と、上流端が栓4により閉塞された排気ガス流出路3とが前後左右に交互に設けられ、排気ガス流入路2と排気ガス流出路3とは薄肉の隔壁5を介して隔てられている。なお、図10においてハッチングを付した部分は下流端の栓4を示している。DPFは、そのフィルタ本体が炭化珪素やコージライトなどのような多孔質材料から形成されており、排気ガス流入路2内に流入した排気ガスは図11において矢印で示したように周囲の隔壁5を通って隣接する排気ガス流出路3内に流出する。すなわち、図12に示すように、隔壁5は排気ガス流入路2と排気ガス流出路3とを連通する微細な細孔6を有し、この細孔6を排気ガスが通る。上記DPFのフィルタ本体の排気ガス流路(排気ガス流入路2、排気ガス流出路3及ぴ細孔)の壁面には触媒コート層7が形成されている。このコート層7は、例えぱ実施例の触媒粉を、水及びバインダと混合してスラリーとし、このスラリーをフィルタ本体にウォッシュコートし、焼成することによって形成されている。   Next, a specific use example of the present invention will be described, for example, when a filter for collecting PM in exhaust gas is installed in an exhaust passage of a diesel engine. The filter has a three-dimensional network structure and is effective in any form, such as foam metal and foam ceramic with sufficient PM collection function, non-woven fabric with metal and ceramic fibers superimposed, and wall flow type filter. However, a wall flow type filter is preferable from the viewpoint of collection efficiency and contact between PM and catalyst. 10 and 11 schematically show a diesel particulate filter (hereinafter abbreviated as DPF). This DPF has a honeycomb structure and includes a number of exhaust gas passages 2 and 3 extending in parallel to each other. An exhaust gas inflow passage 2 in which the downstream end of the DPF is closed by the plug 4 and an exhaust gas outflow passage 3 in which the upstream end is closed by the plug 4 are alternately provided in the front, rear, left and right, and the exhaust gas inflow passage 2 and the exhaust gas are provided. It is separated from the outflow channel 3 through a thin partition wall 5. In FIG. 10, the hatched portion indicates the plug 4 at the downstream end. The filter body of the DPF is made of a porous material such as silicon carbide or cordierite, and the exhaust gas flowing into the exhaust gas inflow passage 2 is surrounded by the surrounding partition walls 5 as indicated by arrows in FIG. It flows out into the adjacent exhaust gas outflow passage 3 through the air. That is, as shown in FIG. 12, the partition wall 5 has fine pores 6 that connect the exhaust gas inflow passage 2 and the exhaust gas outflow passage 3, and the exhaust gas passes through the pores 6. A catalyst coat layer 7 is formed on the wall surface of the exhaust gas flow path (exhaust gas inflow path 2, exhaust gas outflow path 3 and pores) of the DPF filter body. For example, the coating layer 7 is formed by mixing the catalyst powder of the embodiment with water and a binder to form a slurry, wash-coating the slurry on the filter body, and baking it.

次に、本発明の排ガス浄化装置の実施形態について説明する。図14は実施形態のDPFのフィルタ10の断面構造を示すものである。図14に示すように、フィルタ10は、フィルタ基材11の表面に前述のAg担持複合酸化物層12をコートし、その上にNO生成触媒層13をコートしたものである。Ag担持複合酸化物層12は、高比表面積のアルミナ、シリカ、ジルコニア、マグネシア、チタニア、セリアなどにPt,Pd,Rh等の貴金属を担持させた触媒により構成されている。排ガス中の窒素酸化物の殆どがNOで排出されるため、フィルタ基材11の表面にAgを担持した酸素放出能を有する複合酸化物を塗布し、その上層にNO生成触媒層13を重ねて塗布することにより、下層のAg担持複合酸化物層12にNOを供給することができる。 Next, an embodiment of the exhaust gas purifying apparatus of the present invention will be described. FIG. 14 shows a cross-sectional structure of the DPF filter 10 of the embodiment. As shown in FIG. 14, the filter 10 is obtained by coating the above-mentioned Ag-supporting composite oxide layer 12 on the surface of the filter base 11 and coating the NO 2 generation catalyst layer 13 thereon. The Ag-supported composite oxide layer 12 is composed of a catalyst having a high specific surface area alumina, silica, zirconia, magnesia, titania, ceria, etc. supported on a noble metal such as Pt, Pd, Rh. Since most of the nitrogen oxides in the exhaust gas are exhausted as NO, a composite oxide having an oxygen releasing capacity supporting Ag is applied to the surface of the filter base material 11, and the NO 2 generation catalyst layer 13 is overlaid thereon. To apply NO 2 to the lower Ag-supporting composite oxide layer 12.

ただし、Ag担持複合酸化物層12の上層にNO生成触媒層13を均一に塗布すると、PMがAg担持複合酸化物層12に接触することができなくなるので、NO生成触媒層13内に1μm以上の大きさの気孔を設ける。これにより、PMをAg担持複合酸化物層12に接触させることができ、PMを効率よく燃焼させることができる。図15は、各種条件における排ガス中のPMの粒子径分布を示すものである。この図に示すように、PMの大半が1μm以下に分布していることから、気孔の平均の大きさは1μm以上であることが望ましい。空隙を生成する方法としては以下の方法がある。一つは、NO生成触媒の平均粒子径を10μm以上にすることである。平均粒子径が10μm以上であれば、粒子間に生成される空隙の平均粒径は1μm以上となる。また、NO生成触媒をコートする際、スラリー中に炭素を主成分とする造孔剤を添加し、コートした後、高温熱処理することにより焼き飛ばし、気孔を生成する方法も有効である。造孔剤としてはでんぷん、カーボンブラック、樹脂などを使用することができる。 However, when uniform application of NO 2 generation catalyst layer 13 on the upper layer of Ag-supporting composite oxide layer 12, since the PM is unable to contact the Ag-supporting composite oxide layer 12, into NO 2 synthesizing catalyst layer 13 A pore having a size of 1 μm or more is provided. Thereby, PM can be contacted with Ag carrying | support composite oxide layer 12, and PM can be burned efficiently. FIG. 15 shows the particle size distribution of PM in the exhaust gas under various conditions. As shown in this figure, since most of PM is distributed to 1 μm or less, it is desirable that the average size of the pores is 1 μm or more. There are the following methods for generating the voids. One is to make the average particle size of the NO 2 production catalyst 10 μm or more. When the average particle diameter is 10 μm or more, the average particle diameter of voids generated between the particles is 1 μm or more. In addition, when coating the NO 2 production catalyst, it is also effective to add a pore-forming agent mainly composed of carbon to the slurry, coat it, and then burn it away by high-temperature heat treatment to produce pores. As the pore-forming agent, starch, carbon black, resin or the like can be used.

また、本発明者等の検討によれば、高い温度(600℃付近)になる程2層化の効果が大きくなることが判明している。すなわち、特許文献6のようなNO生成触媒のみの構成であると、600℃付近の温度になると平衡の関係でNO濃度が極端に低くなるため、NOとPMの反応は進行し難くなるが、NO生成触媒とPM燃焼触媒の2層構造を採用することにより、生成したNOがNOに戻る前にPM燃焼触媒の酸素放出能を有する複合酸化物に吸着されることにより、触媒近傍にNOが多く存在する状態となってPM燃焼が進行し易くなる。 Further, according to the study by the present inventors, it has been found that the higher the temperature (around 600 ° C.), the greater the effect of the two layers. That is, in the configuration of only the NO 2 generation catalyst as in Patent Document 6, the NO 2 concentration becomes extremely low at a temperature near 600 ° C. due to the equilibrium, and therefore the reaction between NO 2 and PM hardly proceeds. However, by adopting a two-layer structure of the NO 2 production catalyst and the PM combustion catalyst, the produced NO 2 is adsorbed by the complex oxide having the oxygen releasing ability of the PM combustion catalyst before returning to NO, PM combustion tends to proceed with a large amount of NO 2 in the vicinity of the catalyst.

触媒の塗布量は、下層のAg担持複合酸化物層12ではフィルタ1L当たり20〜60gがよい。20g以下であると、フィルタの気孔内部の表面を充分に覆うことができず、PMとの接触性が悪くなる。また、塗布量が60gを超えると、気孔の目詰まりによる圧力損失が大きくなる。また、上層のNO生成触媒層13では、フィルタ1L当たり10〜30gがよい。塗布量が10g以下であると、NO生成能力が不充分となり、塗布量が30gを超えると、NO生成触媒層13の厚さが厚くなってPMがPM燃焼触媒に接触し難くなる。 The applied amount of the catalyst is preferably 20 to 60 g per 1 L of the filter in the lower Ag-supporting composite oxide layer 12. If it is 20 g or less, the surface inside the pores of the filter cannot be sufficiently covered, and the contact property with PM becomes worse. On the other hand, when the coating amount exceeds 60 g, pressure loss due to pore clogging increases. Further, in the upper NO 2 generation catalyst layer 13, 10 to 30 g per 1 L of the filter is good. When the coating amount is 10 g or less, the NO 2 generation capability becomes insufficient, and when the coating amount exceeds 30 g, the thickness of the NO 2 generation catalyst layer 13 becomes thick and it becomes difficult for PM to contact the PM combustion catalyst.

以下、実施例により本発明の作用および効果さらに具体的に説明する。
[試料の作製]
以下の容量で実施例17および比較例1〜19の触媒試料を作製した。
<実施例1>
市販の特級試薬である硝酸ランタン、硝酸マンガンを0.01molずつと蒸留水を適量秤量し混合溶液Aとした。次に、炭酸ナトリウムを3.6g、蒸留水を適量秤量し混合溶液Bとした。混合溶液Bを60℃、300rpmで回転させながら混合し、そこに混合溶液Aを7ml/minで滴下した(逆共沈法)。沈殿物をpHが中性になるまで蒸留水で濾過洗浄し、200℃で2時間乾燥し、その後に350℃で3時間乾燥固化し。これを整粒し、2μm以下とした後、800℃で10時間焼成を行ったものを触媒Aとした。触媒Aを9g、硝酸銀を1.57gおよび蒸留水を適量秤量して混合溶液Cとした。混合溶液Cをエバポレータで蒸発乾固したものを200℃で2時間乾燥した後、600℃で2時間焼成した(含浸法)。これを整粒し、2μm以下としたものを触媒Bとした。この触媒B9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを実施例1とした。
Hereinafter, the operation and effects of the present invention will be described more specifically with reference to examples.
[Preparation of sample]
Catalyst samples of Example 17 and Comparative Examples 1-19 were prepared with the following volumes.
<Example 1>
0.01 mol each of lanthanum nitrate and manganese nitrate, which are commercially available special grade reagents, and an appropriate amount of distilled water were weighed to prepare a mixed solution A. Next, 3.6 g of sodium carbonate and an appropriate amount of distilled water were weighed to prepare a mixed solution B. The mixed solution B was mixed while rotating at 60 ° C. and 300 rpm, and the mixed solution A was added dropwise thereto at 7 ml / min (reverse coprecipitation method). The precipitate was filtered and washed with distilled water until the pH became neutral, dried at 200 ° C. for 2 hours, and then dried and solidified at 350 ° C. for 3 hours. This was sized to 2 μm or less, and then fired at 800 ° C. for 10 hours was designated as Catalyst A. 9 g of catalyst A, 1.57 g of silver nitrate and appropriate amounts of distilled water were weighed to prepare a mixed solution C. A solution obtained by evaporating and drying the mixed solution C with an evaporator was dried at 200 ° C. for 2 hours and then calcined at 600 ° C. for 2 hours (impregnation method). This was sized to make the catalyst B 2 μm or less. Example 1 was obtained by pulverizing and mixing 9.5 mg of this catalyst B with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and making a tight contact.

<実施例2>
市販の特級試薬である硝酸コバルトを0.01molおよび蒸留水を適量秤量し混合溶液Dとした。次に、酸化タンタル0.01mol、炭酸ナトリウムを1.3gおよび蒸留水を適量秤量し混合溶液Eとした。混合溶液Dおよび混合溶液Eを上記と同様に逆共沈法にて調製し、触媒Cとした。触媒Cを9.9g、硝酸銀を0.16gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒Dとした。この触媒D9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを実施例2とした。
<Example 2>
0.01 mol of cobalt nitrate which is a commercially available special grade reagent and an appropriate amount of distilled water were weighed to prepare a mixed solution D. Next, 0.01 mol of tantalum oxide, 1.3 g of sodium carbonate, and appropriate amounts of distilled water were weighed to obtain a mixed solution E. A mixed solution D and a mixed solution E were prepared by the reverse coprecipitation method in the same manner as described above, and designated as catalyst C. An appropriate amount of 9.9 g of catalyst C, 0.16 g of silver nitrate, and distilled water was weighed out and prepared by impregnation as described above to obtain catalyst D. Example 2 was obtained by pulverizing and mixing 9.5 mg of the catalyst D with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and forming a tight contact.

<実施例3>
市販の特級試薬である硝酸コバルトを0.01mol、ジニトロニアンミン硝酸白金を0.01molおよび蒸留水を適量秤量し混合溶液Fとする。次に、炭酸ナトリウムを2.5gおよび蒸留水を適量秤量し混合溶液Gとした。混合溶液Fおよび混合溶液Gを上記と同様に逆共沈法にて沈殿物を調製し、触媒Eとした。触媒Eを9.9g、硝酸銀を0.16gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒Fとした。この触媒F9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを実施例3とした。
<Example 3>
0.01 mol of cobalt nitrate, which is a commercially available special grade reagent, 0.01 mol of dinitronimine platinum nitrate, and appropriate amounts of distilled water are weighed to obtain a mixed solution F. Next, 2.5 g of sodium carbonate and an appropriate amount of distilled water were weighed to obtain a mixed solution G. A precipitate was prepared from the mixed solution F and the mixed solution G by the reverse coprecipitation method in the same manner as described above, and used as catalyst E. An appropriate amount of 9.9 g of catalyst E, 0.16 g of silver nitrate and distilled water was weighed and prepared by impregnation in the same manner as described above to obtain catalyst F. Example 3 was obtained by grinding and mixing 9.5 mg of this catalyst F with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and making a tight contact.

<実施例4>
市販の特級試薬である硝酸コバルトを0.02mol、硝酸亜鉛を0.01molおよび蒸留水を適量秤量し混合溶液Hとした。次に、炭酸ナトリウムを3.8gおよび蒸留水を適量秤量し混合溶液Iとした。混合溶液Hおよび混合溶液Iを上記と同様に逆共沈法にて調製し、触媒Gとした。触媒Gを9.9g、硝酸銀を0.16gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒Hとした。
この触媒H9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを実施例4とした。
<Example 4>
0.02 mol of cobalt nitrate, which is a commercially available special grade reagent, 0.01 mol of zinc nitrate and appropriate amounts of distilled water were weighed to prepare a mixed solution H. Next, 3.8 g of sodium carbonate and an appropriate amount of distilled water were weighed to prepare a mixed solution I. The mixed solution H and the mixed solution I were prepared by the reverse coprecipitation method in the same manner as described above, and designated as catalyst G. An appropriate amount of 9.9 g of catalyst G, 0.16 g of silver nitrate and distilled water was weighed and prepared by the impregnation method in the same manner as described above to obtain catalyst H.
Example 4 was prepared by grinding and mixing 9.5 mg of this catalyst H with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and making a tight contact.

<実施例5>
市販の特級試薬であるタングステン酸アンモニウム、硝酸カルシウム、硝酸マンガンをそれぞれ0.0067molずつおよび蒸留水を適量秤量し、混合溶液Jとした。次に、炭酸ナトリウムを3.8g、蒸留水を適量秤量し混合溶液Kとした。混合溶液Jおよび混合溶液Kを上記と同様に逆共沈法にて調製し、触媒Iとした。触蝶Iを9.9g、硝酸銀を0.16gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触蝶Jとした。この触媒J9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを実施例5とした。
<Example 5>
0.0067 mol each of ammonium tungstate, calcium nitrate, and manganese nitrate, which are commercially available special grade reagents, and appropriate amounts of distilled water were weighed to prepare a mixed solution J. Next, 3.8 g of sodium carbonate and an appropriate amount of distilled water were weighed to prepare a mixed solution K. Mixed solution J and mixed solution K were prepared by the reverse coprecipitation method in the same manner as described above, and designated as catalyst I. Appropriate amounts of 9.9 g of butterfly I, 0.16 g of silver nitrate and distilled water were weighed out and prepared by impregnation in the same manner as described above. Example 5 was prepared by grinding and mixing 9.5 mg of this catalyst J with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and making tight contact.

<実施例5>
上記触媒Bを800℃×6Hrで大気中でエージングをしたものを触媒Kとした。この触媒K9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを実施例5とした。
<Example 5>
A catalyst K was obtained by aging the catalyst B in the atmosphere at 800 ° C. × 6 Hr. Example 5 was obtained by pulverizing and mixing 9.5 mg of this catalyst K with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and making a tight contact.

<実施例6>
上記触媒Bを850℃×6Hrで大気中でエージングをしたものを触媒Lとした。この触媒L9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを実施例6とした。
<Example 6>
The catalyst B was aged at 850 ° C. × 6 Hr in the atmosphere as catalyst L. Example 6 was obtained by pulverizing and mixing 9.5 mg of this catalyst L with 0.5 mg of PM, a mortar and pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例1>
ディーゼル発電機より収集したPM粉末を比較例1の試料とした。
<Comparative Example 1>
The PM powder collected from the diesel generator was used as a sample for Comparative Example 1.

<比較例2>
市販の特級試薬であるジニトロジアミン白金硝酸溶液を1.51g、Alを9.92gおよび蒸留水を適量秤量し混合溶液Lとした。これらをエバポレータにて蒸発乾固させ、Alに銀を担持した。200℃で乾燥後、600℃で2時間焼成し、これを触媒Mとした。この触媒M9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例2とした。
<Comparative example 2>
A commercially available special grade reagent, dinitrodiamine platinum nitric acid solution (1.51 g), Al 2 O 3 (9.92 g), and distilled water were weighed in an appropriate amount to prepare a mixed solution L. These were evaporated to dryness with an evaporator, and silver was supported on Al 2 O 3 . This was dried at 200 ° C. and then calcined at 600 ° C. for 2 hours. Comparative Example 2 was prepared by grinding and mixing 9.5 mg of this catalyst M with 0.5 mg of PM, a mortar and pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例3>
上記触媒A9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例3とした。
<Comparative Example 3>
Comparative Example 3 was prepared by grinding and mixing 9.5 mg of the catalyst A with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例4>
市販の特級試薬の酸化銀(触媒N)9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例4とした。
<Comparative example 4>
A commercially available special grade silver oxide (catalyst N) (9.5 mg) was pulverized and mixed to a particle size of 2 μm or less with 0.5 mg of PM, a mortar and a pestle to make a comparative contact.

<比較例5>
市販の特級試薬である硝酸ランタンを0.01mol、硝酸アルミニウムを0.01molおよび蒸留水を適量秤量し混合溶液Mとした。次に、炭酸ナトリウムを3.4gおよび蒸留水を適量秤量し混合溶液Nとした。混合溶液Mおよび混合溶液Nを上記と同様に逆共沈法にて調製し、触媒Oとした。触媒Oを9g、硝酸銀を1.57gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒Pとした。この触媒P9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例5とした。
<Comparative Example 5>
A commercially available special grade reagent, lanthanum nitrate, 0.01 mol, aluminum nitrate, 0.01 mol, and distilled water were weighed in an appropriate amount to obtain a mixed solution M. Next, 3.4 g of sodium carbonate and an appropriate amount of distilled water were weighed to prepare a mixed solution N. A mixed solution M and a mixed solution N were prepared by the reverse coprecipitation method in the same manner as described above, and designated as catalyst O. 9 g of catalyst O, 1.57 g of silver nitrate and appropriate amounts of distilled water were weighed out and prepared by impregnation in the same manner as described above to obtain catalyst P. Comparative Example 5 was prepared by pulverizing and mixing 9.5 mg of this catalyst P with 0.5 mg of PM, a mortar and pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例6>
市販の特級試薬である硝酸ランタンを0.02molおよび蒸留水を適量秤量し混合溶液Oとした。次に、炭酸ナトリウムを2.1gおよび蒸留水を適量秤量し混合溶液Pとした。混合溶液Oおよび混合溶液Pを上記と同様に逆共沈法にて調製し、触媒Qとした。触媒Qを9g、硝酸銀を1.57gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒Rとした。この触媒R9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例6とした。
<Comparative Example 6>
An appropriate amount of 0.02 mol of lanthanum nitrate, which is a commercially available special grade reagent, and distilled water were weighed to prepare a mixed solution O. Next, 2.1 g of sodium carbonate and an appropriate amount of distilled water were weighed to obtain a mixed solution P. The mixed solution O and the mixed solution P were prepared by the reverse coprecipitation method in the same manner as described above, and designated as catalyst Q. 9 g of catalyst Q, 1.57 g of silver nitrate and appropriate amounts of distilled water were weighed out and prepared by the impregnation method in the same manner as above to obtain catalyst R. Comparative Example 6 was prepared by grinding and mixing 9.5 mg of this catalyst R with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例7>
市販の特級試薬である硝酸マンガンを0.02molおよび蒸留水を適量秤量し混合溶液Qとした。次に、炭酸ナトリウムを2.1gおよび蒸留水を適量秤量し混合溶液Rとした。混合溶液Qおよび混合溶液Rを上記と同様に逆共沈法にて調製し、触媒Sとした。触媒Sを9g、硝酸銀を1.57gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒Tとした。この触媒T9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例7とした。
<Comparative Example 7>
A mixed solution Q was prepared by weighing 0.02 mol of manganese nitrate, which is a commercially available special grade reagent, and distilled water in an appropriate amount. Next, 2.1 g of sodium carbonate and an appropriate amount of distilled water were weighed to prepare a mixed solution R. The mixed solution Q and the mixed solution R were prepared by the reverse coprecipitation method in the same manner as described above and used as the catalyst S. 9 g of catalyst S, 1.57 g of silver nitrate and appropriate amounts of distilled water were weighed out and prepared by the impregnation method in the same manner as described above to obtain catalyst T. Comparative Example 7 was obtained by grinding and mixing 9.5 mg of this catalyst T with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例8>
上記触媒Qを1gおよび触媒Sを1gを乳鉢乳棒にて粉砕混合し、800℃、10Hrで焼成し触媒Uとした。触媒Uを9g、硝酸銀を1.57gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒Vとした。この触媒V9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例8とした。
<Comparative Example 8>
1 g of the catalyst Q and 1 g of the catalyst S were pulverized and mixed with a mortar pestle and calcined at 800 ° C. for 10 hours to obtain a catalyst U. 9 g of catalyst U, 1.57 g of silver nitrate and appropriate amounts of distilled water were weighed out and prepared by the impregnation method in the same manner as above to obtain catalyst V. Comparative Example 8 was obtained by grinding and mixing 9.5 mg of this catalyst V with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例9>
上記触媒Aを9g、ジニトロジアンミン白金硝酸溶液を19.9gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒Wとした。この触媒W9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例9とした。
<Comparative Example 9>
9 g of the above catalyst A, 19.9 g of dinitrodiammine platinum nitric acid solution and appropriate amounts of distilled water were weighed out and prepared by the impregnation method in the same manner as above to obtain catalyst W. Comparative Example 9 was prepared by grinding and mixing 9.5 mg of this catalyst W with 0.5 mg of PM, a mortar and pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例10>
上記触媒Aを9g、硝酸パラジウムを2.5gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒Xとした。この触媒X9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例10とした。
<Comparative Example 10>
An appropriate amount of 9 g of the catalyst A, 2.5 g of palladium nitrate and distilled water was weighed out and prepared by the impregnation method in the same manner as described above to obtain a catalyst X. Comparative Example 10 was prepared by grinding and mixing 9.5 mg of this catalyst X with 0.5 mg of PM, a mortar and pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例11>
市販の特級試薬である硝酸銀、硝酸ランタン、硝酸マンガンをそれぞれ0.04mol、0.01mol、0.05molおよび蒸留水を適量秤量し混合溶液Sとした。混合溶液Sを250℃,300回転で混合しながら蒸発乾固し、その後200℃で2時間乾燥した後、350℃で3時間仮焼し、その後、粒径が2μm以下となるように整粒し、800℃で1O時間焼成を行ったものを触媒Yとした。この触媒Y9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例11とした。
<Comparative Example 11>
Appropriate amounts of 0.04 mol, 0.01 mol, 0.05 mol, and distilled water of commercially available special grade silver nitrate, lanthanum nitrate, and manganese nitrate were weighed to obtain a mixed solution S. The mixed solution S was evaporated to dryness while mixing at 250 ° C. and 300 rpm, then dried at 200 ° C. for 2 hours, calcined at 350 ° C. for 3 hours, and then sized so that the particle size was 2 μm or less. The catalyst Y was calcined at 800 ° C. for 10 hours. Comparative Example 11 was obtained by grinding and mixing 9.5 mg of this catalyst Y with 0.5 mg of PM, a mortar and pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例12>
上記触媒Aを9g、上記触媒Nを1g秤量し、乳鉢乳棒にて物理混合した。これを800℃で10時間焼成し固相反応させたものを触媒Zとした。この触媒Z9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例12とした。
<Comparative Example 12>
9 g of the catalyst A and 1 g of the catalyst N were weighed and physically mixed with a mortar pestle. This was calcined at 800 ° C. for 10 hours and subjected to a solid phase reaction to obtain catalyst Z. Comparative Example 12 was prepared by grinding and mixing 9.5 mg of this catalyst Z with 0.5 mg of PM, a mortar and pestle to a particle size of 2 μm or less, and making a tight contact.

<比較例13>
上記触媒C9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例13とした。
<Comparative Example 13>
Comparative Example 13 was prepared by grinding and mixing 9.5 mg of the above catalyst C with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and forming a tight contact.

<比較例14>
上記触媒E9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例14とした。
<Comparative example 14>
Comparative Example 14 was prepared by grinding and mixing 9.5 mg of the above catalyst E with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and forming a tight contact.

<比較例15>
上記触媒G9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例15とした。
<Comparative Example 15>
Comparative Example 15 was prepared by grinding and mixing 9.5 mg of the above catalyst G with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and forming a tight contact.

<比較例16>
上記触媒I9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例16とした。
<Comparative Example 16>
Comparative Example 16 was prepared by grinding and mixing 9.5 mg of the above catalyst I with 0.5 mg of PM, a mortar and a pestle to a particle size of 2 μm or less, and forming a tight contact.

<比較例17>
市販の特級試薬である硝酸セリウムを0.02molおよび蒸留水を適量秤量し混合溶液Tとした。次に、炭酸ナトリウム3.2gおよび蒸留水を適量秤量し混合溶液Uとする。混合溶液Tおよび溶液Uを上記と同様に逆共沈法にて調製し、触媒AAとした。触媒AAを9.0g、硝酸銀を1.57gおよび蒸留水を適量秤量し、上記と同様に含浸法にて調製し、触媒ABとした。この触媒AB9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例17とした。
<Comparative Example 17>
A mixed solution T was prepared by weighing 0.02 mol of cerium nitrate, which is a commercially available special grade reagent, and distilled water in an appropriate amount. Next, 3.2 g of sodium carbonate and distilled water are weighed in an appropriate amount to obtain a mixed solution U. A mixed solution T and a solution U were prepared by the reverse coprecipitation method in the same manner as described above, and used as catalyst AA. An appropriate amount of 9.0 g of catalyst AA, 1.57 g of silver nitrate and distilled water was weighed out and prepared by impregnation in the same manner as described above to obtain catalyst AB. Comparative Example 17 was obtained by grinding and mixing 9.5 mg of this catalyst AB with 0.5 mg of PM, a mortar and pestle to a particle size of 2 μm or less, and forming a tight contact.

<比較例18>
上記触媒ABを800℃で6時間大気中でエージングをしたものを触媒ACとした。この触媒AC9.5mgを0.5mgのPMと混合乳鉢および乳棒にて粒径2μm以下に粉砕し、タイトコンタクト化したものを比較例18とした。
<Comparative Example 18>
A catalyst AC was obtained by aging the catalyst AB at 800 ° C. for 6 hours in the air. 9.5 mg of this catalyst AC was pulverized to a particle size of 2 μm or less with 0.5 mg of PM and a mixed mortar and pestle to make a tight contact, and Comparative Example 18 was used.

<比較例19>
上記触媒ABを850℃×6Hrで大気中でエージングをしたものを触媒ADとした。この触媒AD9.5mgを0.5mgのPMと乳鉢および乳棒にて粒径2μm以下に粉砕混合し、タイトコンタクト化したものを比較例19とした。
<Comparative Example 19>
The catalyst AB was aged at 850 ° C. × 6 Hr in the atmosphere as catalyst AD. Comparative Example 19 was prepared by grinding and mixing 9.5 mg of this catalyst AD with 0.5 mg of PM with a mortar and pestle to a particle size of 2 μm or less and forming a tight contact.

以上の実施例1〜7および比較例1〜19の試料の成分、担体の種類、担体に担持されている金属の種類、および担体の結晶構造を表1に示す。また、以上の試料に対してPMの燃焼試験を実施し、PMの発熱特性(DTA)を調査した。燃焼試験では、セイコーインスツルメンツ社製、EXSTER6000TG/DTAを使用し、10mgの試料を試験装置に装填し、乾燥空気を空間速度(SV)が60000h−1となる流量で供給し、かつ乾燥空気の温度を20℃/minで昇温させた。各試料の発熱特性を図1〜図8に示すとともに、PMの燃焼における発熱量がピークになる際の温度を表1に併記する。 Table 1 shows the components of the samples of Examples 1 to 7 and Comparative Examples 1 to 19, types of carriers, types of metals supported on the carriers, and crystal structures of the carriers. In addition, a PM combustion test was performed on the above samples, and the heat generation characteristics (DTA) of PM were investigated. In the combustion test, an EXSTER 6000TG / DTA manufactured by Seiko Instruments Inc. is used, a 10 mg sample is loaded into the test apparatus, dry air is supplied at a flow rate at which the space velocity (SV) is 60000 h −1 , and the temperature of the dry air The temperature was raised at 20 ° C./min. 1 to 8 show the heat generation characteristics of each sample, and Table 1 also shows the temperature at which the amount of heat generated during PM combustion peaks.

Figure 2007296518
Figure 2007296518

図1にPMのみからなる試料(比較例1)、0.76wt%Pt/Al+PM(5wt%)からなる試料(比較例2)、およびペロブスカイト型複合酸化物のLaMnO+PM(5wt%)(比較例3)の燃焼特性を示す。PMのみからなる試料の燃焼ピーク温度は668℃である。これに対し、0.76wt%Pt/Al+PM(5wt%)(比較例2)のような貴金属系材料では、最初のピークは247℃、2回目のピークは561℃とピークが二つに分かれる。それぞれの燃焼ピークは発生ガス分析から最初のピークが有機成分、2回目のピークがsootに由来することが判っている。このことから、貴金属系材料は、有機成分の燃焼には効果があるが、sootに関してはそれほど低温で燃焼できないことが判る。これらのメカニズムに関しては、HCガスと同様に活性種表面での酸化反応であるためsootより熱的に不安定な有機成分は早期に活性種への解離吸着が起こりやすいことが推定される。また、これらPtやPd等の貴金属系触媒の場合、性能は貴金属量の影響をほとんど受けない。 FIG. 1 shows a sample made of only PM (Comparative Example 1), a sample made of 0.76 wt% Pt / Al 2 O 3 + PM (5 wt%) (Comparative Example 2), and a perovskite complex oxide LaMnO 3 + PM (5 wt). %) (Comparative example 3) shows the combustion characteristics. The combustion peak temperature of the sample consisting only of PM is 668 ° C. On the other hand, in a noble metal material such as 0.76 wt% Pt / Al 2 O 3 + PM (5 wt%) (Comparative Example 2), the first peak is 247 ° C., the second peak is 561 ° C., and the peak is two. Divided into two. As for each combustion peak, it is known from the generated gas analysis that the first peak is derived from the organic component and the second peak is derived from soot. From this, it can be seen that the noble metal-based material is effective in burning organic components, but the soot cannot be burned at such a low temperature. Regarding these mechanisms, since it is an oxidation reaction on the surface of the active species as in the case of HC gas, it is presumed that organic components that are thermally unstable than soot are likely to be dissociatively adsorbed to the active species at an early stage. In the case of these noble metal catalysts such as Pt and Pd, the performance is hardly affected by the amount of noble metal.

一方、LaMnO+PM(5wt%)(比較例3)のような遷移金属系複合酸化物では、貴金属系材料のように燃焼ピークの分離をほとんど起こさない。このような複合酸化物においては有機成分は早期燃焼せず、sootとともに燃焼する。また、複合酸化物の場合は貴金属系材料とは異なり、sootの燃焼は比較的低温で可能である。このため遷移金属系複合酸化物はsoot燃焼に対して効果的といえる。これらのメカニズムに関しては、複合酸化物の価数変化に伴う酸素放出能に依存していると考えられるため、酸素放出しない低温側での有機成分の燃焼はなく、燃焼がsootと同時に起こる。つまり酸素放出能が高いほど低温でPMを燃焼することが可能となる。 On the other hand, transition metal based complex oxides such as LaMnO 3 + PM (5 wt%) (Comparative Example 3) hardly cause separation of combustion peaks unlike noble metal based materials. In such a complex oxide, the organic component does not burn early but burns with soot. In the case of a composite oxide, unlike a noble metal material, soot can be burned at a relatively low temperature. Therefore, it can be said that the transition metal-based composite oxide is effective against soot combustion. These mechanisms are considered to depend on the oxygen releasing ability accompanying the valence change of the composite oxide, and therefore, there is no combustion of the organic component on the low temperature side where oxygen is not released, and combustion occurs simultaneously with soot. That is, it is possible to burn PM at a lower temperature as the oxygen releasing ability is higher.

ところで、現状の内燃機関から排出される排気ガス温度は200℃〜450℃と低いことから、有機成分は貴金属系材料を用いることで排ガス温度域内での燃焼は十分に可能であるが、sootの燃焼は上記触媒材料などによりいくらか低温で燃焼可能であり、効率を多少高めることはできるが、やはり再生処理等を行わずして排ガス温度域で連続燃焼することは難しい。   By the way, since the exhaust gas temperature discharged from the current internal combustion engine is as low as 200 ° C. to 450 ° C., the organic component can sufficiently burn within the exhaust gas temperature range by using a noble metal-based material. Combustion can be performed at a somewhat low temperature by the above catalyst material and the efficiency can be slightly increased, but it is difficult to perform continuous combustion in the exhaust gas temperature range without performing regeneration treatment or the like.

この点、本発明は、酸素放出能を有する複合酸化物にAgを担持することにより、複合酸化物の酸素放出能を向上させることができ、PM燃焼特性を向上させることに成功したものである。図2に10wt%Ag/LaMnO+PM(5wt%)(実施例1)の燃焼特性を示す。図2から判るように、実施例1では、比較例3と比べPM燃焼特性が低温化していることがわかる。表1に示すように、PM燃焼ピーク温度は、454℃から417℃へと大幅に低温化している。これは、酸素放出能を持つ複合酸化物にAgを担持したことによる効果と考えられる。 In this respect, the present invention succeeds in improving the PM combustion characteristics by improving the oxygen releasing ability of the composite oxide by supporting Ag on the composite oxide having the oxygen releasing ability. . FIG. 2 shows the combustion characteristics of 10 wt% Ag / LaMnO 3 + PM (5 wt%) (Example 1). As can be seen from FIG. 2, in Example 1, the PM combustion characteristics are lower in temperature than in Comparative Example 3. As shown in Table 1, the PM combustion peak temperature is greatly lowered from 454 ° C. to 417 ° C. This is considered to be due to the fact that Ag is supported on the complex oxide having oxygen releasing ability.

表1に示す比較例4のPM燃焼ピーク値から判るように、AgOは、PMに対して非常に高活性である。AgOは還元剤としてのPMと接触することで酸化反応を起こすと考えられる。しかしながら、AgOは揮発する特性を有しているため耐熱性の観点では単独で用いることができない。 As can be seen from the PM combustion peak value of Comparative Example 4 shown in Table 1, Ag 2 O is very active against PM. Ag 2 O is considered to cause an oxidation reaction by contacting with PM as a reducing agent. However, Ag 2 O has a property of volatilizing and cannot be used alone from the viewpoint of heat resistance.

本発明のように複合酸化物にAgを担持することにより、AgはAgもしくはAgOとして存在すると考えられる。反応により還元されたAgは複合酸化物に担持されていることにより効果的に作用する。つまり、還元されたAgの揮発を抑制しつつ、Agは再び活性化するために複合酸化物の価数を変化させ、強制的に酸素を取り込もうとする。これらを繰り返すことにより、触媒全休の酸素放出能を高め、その結果、PM燃焼温度を低温化することができると推察される。言い換えれば、酸素放出能を有する複合酸化物に、PMに対して活性の高いAgを担持することにより、複合酸化物の酸素放出能をより低温で引き出すことが可能となったといえる。 By supporting Ag on the composite oxide as in the present invention, Ag is considered to be present as Ag or Ag 2 O. Ag reduced by the reaction acts effectively by being supported on the composite oxide. That is, while suppressing the volatilization of the reduced Ag, Ag is forced to take in oxygen by changing the valence of the composite oxide in order to activate again. By repeating these steps, it is presumed that the oxygen release ability of the catalyst can be increased, and as a result, the PM combustion temperature can be lowered. In other words, it can be said that the oxygen releasing ability of the composite oxide can be brought out at a lower temperature by supporting Ag having high activity with respect to PM in the composite oxide having oxygen releasing ability.

Ag担持複合酸化物のメカニズムによれば、酸素過剰雰囲気(リッチ状態)においては酸素を吸収保持し、酸素濃度が低下すると(リーン状態)、酸素を放出する性質をもつ。排気ガス中に過剰酸素が含まれているときには排気ガス中の含炭素浮遊微粒子を捕集し、排気ガス中の酸素濃度が低下、あるいは触媒上に含炭素浮遊微粒子が堆積して周囲の酸素濃度が低下すると、活性酸素を放出して触媒上の含炭素浮遊微粒子を燃焼させることが可能である。   According to the mechanism of the Ag-supporting complex oxide, oxygen is absorbed and held in an oxygen-excess atmosphere (rich state), and oxygen is released when the oxygen concentration is lowered (lean state). When excess oxygen is contained in the exhaust gas, the carbon-containing suspended particulates in the exhaust gas are collected and the oxygen concentration in the exhaust gas decreases, or the carbon-containing suspended particulates accumulate on the catalyst and the surrounding oxygen concentration When the value decreases, it is possible to release active oxygen and burn the carbon-containing suspended fine particles on the catalyst.

ここで、酸素放出能がない複合酸化物(比較例5)、酸素放出能を有する単独酸化物およびその物理混合酸化物(比較例6〜8)についてそれぞれAgを担持した場合の性能を図3により比較する。比較例5はPM燃焼ピーク値が521℃と性能は悪く、この性能はAgのみによると考えられる。比較例6,7もそれぞれPM燃焼ピーク値が468℃、435℃と実施例1と比べて性能が劣るが、これは担体である単独酸化物の酸素放出能が低いためと考えられ、さらにこれらを物理混合した比較例8はPM燃焼ピーク値が445℃であり、それほど燃焼温度を低温化することができていない。   Here, the performance in the case of carrying Ag for each of the composite oxide having no oxygen releasing ability (Comparative Example 5), the single oxide having oxygen releasing ability and the physical mixed oxide thereof (Comparative Examples 6 to 8) is shown in FIG. Compare with In Comparative Example 5, the PM combustion peak value is 521 ° C. and the performance is poor, and this performance is considered to be due to Ag alone. In Comparative Examples 6 and 7, the PM combustion peak values are 468 ° C. and 435 ° C., respectively, and the performance is inferior to that of Example 1. This is considered due to the low oxygen releasing ability of the single oxide as the carrier. In Comparative Example 8 in which the PM is physically mixed, the PM combustion peak value is 445 ° C., and the combustion temperature cannot be lowered so much.

ディーゼル排気ガス温度域でのsootの燃焼を考えた場合、酸素放出能を持たない複合酸化物、酸素放出能の低い単独酸化物および単独酸化物の物理的な組み合わせでは期待する性能を得ることができない。よって酸素放出能を有する複合酸化物を用いることが重要と考えられる。   When considering soot combustion in the diesel exhaust gas temperature range, it is possible to obtain the expected performance with a physical combination of a complex oxide without oxygen releasing ability, a single oxide with low oxygen releasing ability and a single oxide. Can not. Therefore, it is considered important to use a complex oxide having oxygen releasing ability.

ここで、酸素放出能を有する酸化物の定義について具体的に説明する。まず、He雰囲気での酸素の昇温脱離試験(TPD)と水素による酸素の昇温還元試験(TPR)において、脱離開始温度あるいは脱離がピークに達する温度を脱離し易さとし、ピーク面積を放出量とする。これら脱離し易さおよび放出量を放出能とし、特に、複合酸化物などのような酸化物が雰囲気の変化によって価数変化を引き起こし、酸化物中の酸素が吸放出されるものを酸素放出能を有する酸素放出能を有する複合酸化物と定義する。   Here, the definition of the oxide having oxygen releasing ability will be specifically described. First, in the temperature-programmed desorption test (TPD) of oxygen in a He atmosphere and the temperature-programmed reduction test (TPR) of oxygen with hydrogen, the desorption start temperature or the temperature at which desorption reaches a peak is defined as the peak area. Is the amount released. The ease of desorption and the amount of release are defined as the release ability. In particular, oxides such as composite oxides cause valence changes due to changes in the atmosphere, and oxygen release ability is defined as oxygen in the oxide being absorbed and released. It is defined as a complex oxide having oxygen releasing ability.

図13に、La、MnO、LaMnO、およびLaAlOの酸素放出能をO−TPDで測定した結果を示す。図13において横軸は温度、縦軸は酸素離脱量であり、He雰囲気中での熱的な酸素の離脱し易さを示している。Laは360℃付近で酸素を放出するが、ピーク面積は小さく、酸素放出量は少ない。一方、MnOは400℃付近から酸素放出を開始し、そのまま高温になるに従って放出量が多くなる。また、これらの複合酸化物であるペロブスカイト構造のLaMnOでは、酸素放出開始温度がさらに低下し、250℃付近からとなる。これらに対してLaAlOでは、全温度域において酸素放出能を持たないことが判る。 Figure 13 shows the results La 2 O 3, MnO 2, LaMnO 3, and the oxygen release capacity of LaAlO 3 was measured by O 2 -TPD. In FIG. 13, the horizontal axis represents temperature and the vertical axis represents the amount of oxygen desorption, which indicates the ease of thermal oxygen desorption in a He atmosphere. La 2 O 3 releases oxygen at around 360 ° C., but the peak area is small and the amount of released oxygen is small. On the other hand, MnO 2 starts releasing oxygen from around 400 ° C., and the released amount increases as the temperature rises as it is. Further, in LaMnO 3 having a perovskite structure, which is a composite oxide of these, the oxygen release start temperature is further lowered, starting from around 250 ° C. On the other hand, it can be seen that LaAlO 3 does not have oxygen releasing ability in the entire temperature range.

このように、各酸化物、複合酸化物は酸素放出能を持つものと持たないものがあり、また、それぞれの酸素放出能は異なる。ここで、MnOは600℃付近から酸素放出能が大幅に向上しているのに対して、Laは600℃以上で酸素放出能を持たない。これから比較例6,7の結果を考慮すると、PM燃焼特性に600℃以上の酸素放出能が寄与していないことが推測される。これは、触媒における酸素の放出量よりは、低温での酸素の離脱し易さ、つまり、酸素脱離エネルギーがPM燃焼において重要なファクターとなっているからと推測される。以上から、He雰囲気での昇温脱離試験(TPD)において、600℃以下で酸素脱離開始するものを酸素放出能を有する、と定義することができる。 As described above, each oxide and composite oxide may or may not have oxygen releasing ability, and each oxygen releasing ability is different. Here, MnO 2 has greatly improved oxygen releasing ability from around 600 ° C., whereas La 2 O 3 does not have oxygen releasing ability at 600 ° C. or higher. From this, when the results of Comparative Examples 6 and 7 are considered, it is presumed that the oxygen releasing ability of 600 ° C. or higher does not contribute to the PM combustion characteristics. This is presumably because the ease of oxygen release at a low temperature, that is, the oxygen desorption energy is an important factor in PM combustion, rather than the amount of oxygen released from the catalyst. From the above, in a temperature-programmed desorption test (TPD) in a He atmosphere, a substance that starts deoxygenating at 600 ° C. or less can be defined as having oxygen releasing ability.

次に、酸素放出能を有する複合酸化物にAg以外の貴金属を担持した場合(特許文献4)について検討する。図4はLaMnOにPtおよびPdを担持した場合(比較例9,10)の燃焼特性を示すものである。図4から、特許文献4に記載のものでは、実施例1と比べ性能が劣ることが判る。 Next, a case where a noble metal other than Ag is supported on a complex oxide having oxygen releasing ability (Patent Document 4) will be examined. FIG. 4 shows combustion characteristics when Pt and Pd are supported on LaMnO 3 (Comparative Examples 9 and 10). 4 that the performance described in Patent Document 4 is inferior to that of Example 1.

PM活性において、貴金属元素ではAgは特異的に性能が高いと言える。複合酸化物との相互作用を考えた場合、比較例3からの性能向上効果という観点では、より複合酸化物の価数変化を引き出すことが可能なのはAgであると考えられるが、メカニズムに関しての詳細は不明である。   In PM activity, it can be said that Ag is specifically high in the performance of noble metal elements. Considering the interaction with the composite oxide, it is considered that Ag can extract the valence change of the composite oxide more from the viewpoint of the performance improvement effect from the comparative example 3. Is unknown.

次に、複合酸化物へのAgの添加方法を変えた場合について述べる。比較例11は複合酸化物にAgを固溶した場合(特許文献1)であり、比較例12は複合酸化物にAgを固相反応させた場合(特許文献3)である。その結果を図5に示す。図5から、比較例11および12は、実施例1と比べて性能が悪いことがわかる。まず、比較例11に関しては、同じAg量(10wt%)であっても、LaMnOの結晶構造にAgが固溶しているために活性種が埋没し、還元剤となるPMと接触することができずに上記したようなAgの価数変化を引き出すことができない。このため、実施例1のようにAgを担持した場合と比べ性能が劣ると考えられる。比較例12に関しては、耐熱性がないため活性種が揮発してしまい、LaMnOのみの性能となっていると考えられる。よって実施例1のように、LaMnOの最表面に活性種を露出しつつ、複合酸化物との相互作用により酸素放出能を低温化する必要があり、さらにAgの擬集および揮発を抑制するため、複合酸化物へのAgの添加は、担持でなくてはならないと考えられる。 Next, the case where the addition method of Ag to the composite oxide is changed will be described. Comparative Example 11 is a case where Ag is dissolved in the composite oxide (Patent Document 1), and Comparative Example 12 is a case where Ag is solid-phase reacted with the composite oxide (Patent Document 3). The result is shown in FIG. From FIG. 5, it can be seen that Comparative Examples 11 and 12 have poorer performance than Example 1. First, with respect to Comparative Example 11, even if the Ag amount is the same (10 wt%), active species are buried because Ag is dissolved in the crystal structure of LaMnO 3 , and contact is made with PM as a reducing agent. As a result, the above-described change in Ag valence cannot be derived. For this reason, it is thought that performance is inferior compared with the case where Ag is carried like Example 1. Regarding Comparative Example 12, since there is no heat resistance, active species are volatilized, and it is considered that only the performance of LaMnO 3 is obtained. Therefore, as in Example 1, it is necessary to lower the oxygen releasing ability by interacting with the composite oxide while exposing the active species on the outermost surface of LaMnO 3 , and further suppress the pseudo collection and volatilization of Ag. Therefore, it is considered that the addition of Ag to the composite oxide must be supported.

次に、ペロブスカイト構造のほかにも酸素放出能を持つ複合酸化物でのAg担持効果を確認した。比較例13はルチル型複合酸化物、比較例14はデラフォサイト型複合酸化物、比較例15はスピネル型複合酸化物、比較例16は単純な元素を混合しただけの複合酸化物である。これらにAgを1wt%担持したものが実施例2〜5となるが、その結果を図6および表1に示す。図6及び表1から、どの複合酸化物でもAgを担持したことによりPM燃焼ピーク温度が低温化していることが判る。よって、酸素放出能をもつあらゆる結晶構造、あらゆる元素で構成された複合酸化物にAgを担持することによりPM燃焼特性を向上させることができると言える。   Next, in addition to the perovskite structure, the Ag supporting effect was confirmed in the complex oxide having oxygen releasing ability. Comparative Example 13 is a rutile complex oxide, Comparative Example 14 is a delafossite complex oxide, Comparative Example 15 is a spinel complex oxide, and Comparative Example 16 is a complex oxide in which simple elements are mixed. Examples in which 1 wt% of Ag is carried on these are Examples 2 to 5, and the results are shown in FIG. From FIG. 6 and Table 1, it can be seen that the PM combustion peak temperature is lowered by supporting Ag in any composite oxide. Therefore, it can be said that PM combustion characteristics can be improved by supporting Ag on a complex oxide composed of any crystal structure and any element having oxygen releasing ability.

次に、Ag担持複合酸化物における耐熱性の観点でエージング処理(大気中)を行った結果について図7および図8を参照して説明する。図7において、比較例17および19は、CeOにAgを担持した場合のエージング処理前(特許文献2)と850℃のエージング処理後の結果を示すものである。CeOは酸素放出能では非常に優れた酸化物であることが広く知られているため、酸素放出能の高いCeOへのAg担持も効果があると考えられる。比較例17では、エージング前はPM燃焼ピーク温度が388℃と良好な性能を示している。しかし、比較例17にエージングを施した比較例19では、PM燃焼ピーク温度が445℃と大幅に劣化している。これはベース酸化物であるCeOの熱的構造破壊およびAg凝集および揮発によるものと推測される。これに対し、図8に実施例1と実施例7を対比して示すように、10wt%Ag/LaMnOのエージング前後でのPM燃焼特性は変化しないことがわかる。これは複合酸化物の構造形成温度が600℃〜1000℃の高温であるためにエージング温度域で構造破壊が起きない上、複合酸化物とAgの相互作用によりAgの凝集および揮発が起こりにくいためと推察される。 Next, the results of aging treatment (in the atmosphere) from the viewpoint of heat resistance of the Ag-supported composite oxide will be described with reference to FIGS. In FIG. 7, Comparative Examples 17 and 19 show the results before the aging treatment (Patent Document 2) and after the aging treatment at 850 ° C. when Ag is supported on CeO 2 . Since CeO 2 is known to widely be in oxygen releasing capacity is excellent oxide, Ag supported on high CeO 2 oxygen release capacity is also considered to be effective. In Comparative Example 17, the PM combustion peak temperature is 388 ° C. and good performance before aging. However, in Comparative Example 19 in which aging is applied to Comparative Example 17, the PM combustion peak temperature is greatly degraded to 445 ° C. This is presumed to be due to thermal structural destruction of the base oxide CeO 2 and Ag aggregation and volatilization. In contrast, as shown in FIG. 8 in comparison with Example 1 and Example 7, it can be seen that the PM combustion characteristics before and after aging of 10 wt% Ag / LaMnO 3 do not change. This is because the structure formation temperature of the composite oxide is 600 ° C. to 1000 ° C., so that structural destruction does not occur in the aging temperature range, and Ag aggregation and volatilization is unlikely to occur due to the interaction between the composite oxide and Ag. It is guessed.

図9は、Ag/CeOおよびAg/LaMnOのエージング前、800℃および850℃のエージング処理後の燃焼特性(実施例1,6,7、比較例17,18,19)の比較を示す。図9において横軸は大気中でのエージング処理温度であり、各例のエージング前における処理温度は、試料を調整した際の焼成温度を用いた。図9から、エージング条件によってはAg/Ce0は性能が劣化して実用排ガス温度域で十分にPMを燃焼できなくなることが判る。よって、耐熱性を有する複合酸化物へのAg担持でなければ期待する性能を発揮することができない。 Figure 9 is a front aging Ag / CeO 2 and Ag / LaMnO 3, shows a comparison of combustion properties after aging treatment of 800 ° C. and 850 ° C. (Example 1, 6 and 7, Comparative Example 17, 18, 19) . In FIG. 9, the horizontal axis represents the aging treatment temperature in the atmosphere, and the firing temperature when the sample was prepared was used as the treatment temperature before aging in each example. 9, depending aging conditions Ag / CeO 2 it can be seen that not be burned sufficiently PM in a practical exhaust gas temperature region deteriorated performance. Therefore, the expected performance cannot be exhibited unless Ag is supported on the composite oxide having heat resistance.

このように、本発明は、今後さらなる大排気量/高出力ENGを想定した場合の高耐熱条件においても、排気レイアウトに左右されることなく、自動車の床下はもちろんエンジン直下での使用にも耐えうるものである。   In this way, the present invention can withstand use under the engine floor as well as directly under the engine, regardless of the exhaust layout, even under high heat resistance conditions assuming further large displacement / high output ENG. It can be.

<実施例8>
(触媒粉末の調整)
実施例1で用いた触媒Bの粉末を調整し、酸素放出能を有する複合酸化物にAgを担持した触媒を必要量調整した。この場合の最終焼成温度は700℃とした。
<Example 8>
(Catalyst powder adjustment)
The powder of the catalyst B used in Example 1 was adjusted, and the required amount of the catalyst in which Ag was supported on the composite oxide having oxygen releasing ability was adjusted. The final firing temperature in this case was 700 ° C.

所定量の硝酸パラジウムと硝酸白金を含有する水溶液を調整した。この水溶液とγアルミナとをナスフラスコに入れ、ロータリーエバポレータにて含浸担持を行った。得られた生成物を200℃で1時間乾燥した後、700℃で2時間の焼成を行い、NO生成触媒粉末としてのPt/Alを調整した。 An aqueous solution containing a predetermined amount of palladium nitrate and platinum nitrate was prepared. This aqueous solution and γ-alumina were placed in an eggplant flask and impregnated with a rotary evaporator. The obtained product was dried at 200 ° C. for 1 hour and then calcined at 700 ° C. for 2 hours to prepare Pt / Al 2 O 3 as NO 2 production catalyst powder.

(DPFへの担持)
上記Ag担持複合酸化物粉末、水、SiOゾル、アルミナボールを容器に入れ、ボールミルにて湿式粉砕を一晩行い、触媒スラリーとした。この触媒スラリーにDPFを浸漬した後に引き上げ、エアーブローで余剰スラリーを除去した。次いで、DPFを200℃で2時間乾燥し、DPFの重量を測定を行った。触媒がDPFに所定量担持されるまでこの操作を繰り返した後、700℃で2時間の焼成を行った。こうして、DPFの表面の下層にAg担持複合酸化物層を形成した。
(Supported on DPF)
Put the Ag-supporting composite oxide powder, water, SiO 2 sol, alumina balls in a container, carried out overnight wet pulverized in a ball mill to obtain a catalyst slurry. After dipping DPF in this catalyst slurry, it was pulled up and excess slurry was removed by air blow. Next, the DPF was dried at 200 ° C. for 2 hours, and the weight of the DPF was measured. This operation was repeated until a predetermined amount of the catalyst was supported on the DPF, and then calcined at 700 ° C. for 2 hours. Thus, an Ag-supporting composite oxide layer was formed in the lower layer on the surface of the DPF.

上記NO生成触媒粉末、水、SiOゾル、アルミナボール、および造孔剤として粒子径が1μmのでんぷんを容器に入れ、ボールミルにて湿式粉砕を一晩行い、触媒スラリーとした。この触媒スラリーにDPFを浸漬した後に引き上げ、エアーブローで余剰スラリーを除去した。次いで、DPFを200℃で2時間乾燥し、DPFの重量を測定を行った。触媒がDPFに所定量担持されるまでこの操作を繰り返した後、700℃で2時間の焼成を行った。こうして、DPFの表面の上層にNO生成触媒層を形成した。 The NO 2 production catalyst powder, water, SiO 2 sol, alumina balls, and starch having a particle size of 1 μm as a pore-forming agent were placed in a container, and wet pulverization was performed overnight in a ball mill to obtain a catalyst slurry. After dipping DPF in this catalyst slurry, it was pulled up and excess slurry was removed by air blow. Next, the DPF was dried at 200 ° C. for 2 hours, and the weight of the DPF was measured. This operation was repeated until a predetermined amount of the catalyst was supported on the DPF, and then calcined at 700 ° C. for 2 hours. Thus, a NO 2 generation catalyst layer was formed on the upper surface of the DPF.

(酸化触媒のハニカム担持)
表2に示す酸化物触媒粉末、水、SiOゾル、アルミナボールを容器に入れ、ボールミルにて湿式粉砕を一晩行い、触媒スラリーとした。この触媒スラリーにコージェライトハニカムを浸漬した後に引き上げ、エアーブローで余剰スラリーを除去した。次いで、コージェライトハニカムを200℃で2時間乾燥し、コージェライトハニカムの重量を測定を行った。触媒がコージェライトハニカムに所定量担持されるまでこの操作を繰り返した後、700℃で2時間の焼成を行った。
(Supporting honeycomb of oxidation catalyst)
The oxide catalyst powder, water, SiO 2 sol, and alumina balls shown in Table 2 were placed in a container, and wet pulverization was performed overnight with a ball mill to obtain a catalyst slurry. The cordierite honeycomb was dipped in this catalyst slurry and then pulled up, and excess slurry was removed by air blow. Next, the cordierite honeycomb was dried at 200 ° C. for 2 hours, and the weight of the cordierite honeycomb was measured. This operation was repeated until a predetermined amount of the catalyst was supported on the cordierite honeycomb, followed by firing at 700 ° C. for 2 hours.

Figure 2007296518
Figure 2007296518

(コンバータ作製)
図16に本実施例で作製したコンバータ20を示す。このコンバータ20には、排ガスの流れの上流側から、上記のようにして酸化触媒を担持したコージェライトハニカム21と、上記のようにして下層にAg担持複合酸化物層、上層にNO生成触媒層を形成したDPF22が設けられている。この実施例では、コージェライトハニカム21の容量は1L、DPF22の容量は2Lとした。
(Converter production)
FIG. 16 shows a converter 20 manufactured in this example. The converter 20 includes a cordierite honeycomb 21 carrying an oxidation catalyst as described above from the upstream side of the exhaust gas flow, an Ag-supported composite oxide layer as a lower layer, and a NO 2 production catalyst as an upper layer as described above. A DPF 22 in which a layer is formed is provided. In this embodiment, the capacity of the cordierite honeycomb 21 is 1 L, and the capacity of the DPF 22 is 2 L.

<比較例20>
DPFにNO生成触媒層を形成しなかった以外は実施例8と同じ条件で図16に示すコンバータ20を作製した。
<Comparative Example 20>
A converter 20 shown in FIG. 16 was manufactured under the same conditions as in Example 8 except that the NO 2 generation catalyst layer was not formed on the DPF.

<比較例21>
DPFにAg担持複合酸化物層を形成せずにDPFに直接NO生成触媒層を形成した以外は実施例8と同じ条件で図16に示すコンバータ20を作製した。
<Comparative Example 21>
A converter 20 shown in FIG. 16 was manufactured under the same conditions as in Example 8 except that the NO 2 generation catalyst layer was directly formed on the DPF without forming the Ag-supporting complex oxide layer on the DPF.

<比較例22>
DPFにNO生成触媒層を形成する際に造孔剤を用いなかった以外は実施例8と同じ条件で図16に示すコンバータ20を作製した。
<Comparative Example 22>
A converter 20 shown in FIG. 16 was produced under the same conditions as in Example 8 except that no pore forming agent was used when the NO 2 production catalyst layer was formed on the DPF.

<比較例23>
DPFに触媒を担持させなかった以外は実施例8と同じ条件で図16に示すコンバータ20を作製した。
<Comparative Example 23>
A converter 20 shown in FIG. 16 was produced under the same conditions as in Example 8 except that the catalyst was not supported on the DPF.

(評価方法)
上記のようにして作製したコンバータ20を用い、実用条件に近い評価が可能なエンジンベンチテストを実施した。図17は、テストレイアウトを示すもので、2.2Lのディーゼルエンジン30の直下の位置にコンバータ20を配置し、運転試験を行った。
(Evaluation methods)
Using the converter 20 produced as described above, an engine bench test that can be evaluated close to practical conditions was performed. FIG. 17 shows a test layout, in which the converter 20 is disposed immediately below the 2.2 L diesel engine 30 and an operation test was performed.

(低温連続燃焼性能)
コージェライトハニカム21の直前の排ガス温度が350℃程度となる条件で8時間ディーゼルエンジン30の運転を続けた。運転終了後のコンバータ20の重量増加量をPM堆積量とした。その結果を図18に示す。図18に示すとおり、実施例8ではPM堆積量が最も少なかったことから、運転中に排出されるPMを最も良く燃焼除去したことが分かる。
(Low temperature continuous combustion performance)
The operation of the diesel engine 30 was continued for 8 hours under the condition that the exhaust gas temperature immediately before the cordierite honeycomb 21 was about 350 ° C. The amount of increase in the weight of the converter 20 after the end of operation was taken as the PM deposition amount. The result is shown in FIG. As shown in FIG. 18, in Example 8, the amount of accumulated PM was the smallest, so it can be seen that PM discharged during operation was best removed by combustion.

(強制再生性能)
DPF22の直前の排ガス温度が150℃程度となる条件でディーゼルエンジン30の運転を続けてPMを堆積させた。次いで、DPF22の直前の排ガス温度が600℃程度となる条件でディーゼルエンジン30の運転を行い、コンバータ20の強制再生を行った。強制再生では、ポストインジェクションにより燃料添加を行い、酸化触媒を担持したコージェライトハニカム21での燃焼反応熱でDPF22を目的温度まで上昇させ、所定時間毎に停止して重量測定を行った。そして、PMの燃焼が終了するまでの時間を測定し、その結果を図19に示した。図19に示すとおり、600℃における強制再生では、再生終了までに要する時間が実施例8で格段に短く、再生時の燃焼速度が最も速いことが確認された。
(Forced regeneration performance)
The operation of the diesel engine 30 was continued under the condition that the exhaust gas temperature just before the DPF 22 was about 150 ° C., and PM was deposited. Next, the diesel engine 30 was operated under the condition that the exhaust gas temperature immediately before the DPF 22 was about 600 ° C., and the converter 20 was forcibly regenerated. In forced regeneration, fuel was added by post-injection, the DPF 22 was raised to the target temperature by the combustion reaction heat in the cordierite honeycomb 21 carrying the oxidation catalyst, and stopped at predetermined time intervals to measure the weight. Then, the time until PM combustion was completed was measured, and the result is shown in FIG. As shown in FIG. 19, in forced regeneration at 600 ° C., it was confirmed that the time required for completion of regeneration was much shorter in Example 8 and the combustion speed during regeneration was the fastest.

本発明の排ガス浄化触媒および排ガス浄化装置は、排ガスに含まれるPMを低温で浄化することが可能であるとともにPMの燃焼速度が速く、今後さらなる大排気量/高出力ENGを想定したディーゼルエンジンにも適用可能である。   The exhaust gas purifying catalyst and the exhaust gas purifying apparatus of the present invention are capable of purifying PM contained in exhaust gas at a low temperature and have a fast PM combustion speed. Is also applicable.

本発明の実施例における供給空気温度とPMの発熱量との関係を示すグラフである。It is a graph which shows the relationship between the supply air temperature in the Example of this invention, and the emitted-heat amount of PM. 本発明の実施例における供給空気温度とPMの発熱量との他の関係を示すグラフである。It is a graph which shows the other relationship between the supply air temperature in the Example of this invention, and the emitted-heat amount of PM. 本発明の実施例における供給空気温度とPMの発熱量との他の関係を示すグラフである。It is a graph which shows the other relationship between the supply air temperature in the Example of this invention, and the emitted-heat amount of PM. 本発明の実施例における供給空気温度とPMの発熱量との他の関係を示すグラフである。It is a graph which shows the other relationship between the supply air temperature in the Example of this invention, and the emitted-heat amount of PM. 本発明の実施例における供給空気温度とPMの発熱量との他の関係を示すグラフである。It is a graph which shows the other relationship between the supply air temperature in the Example of this invention, and the emitted-heat amount of PM. 本発明の実施例における供給空気温度とPMの発熱量との他の関係を示すグラフである。It is a graph which shows the other relationship between the supply air temperature in the Example of this invention, and the emitted-heat amount of PM. 本発明の実施例における供給空気温度とPMの発熱量との他の関係を示すグラフである。It is a graph which shows the other relationship between the supply air temperature in the Example of this invention, and the emitted-heat amount of PM. 本発明の実施例における供給空気温度とPMの発熱量との他の関係を示すグラフである。It is a graph which shows the other relationship between the supply air temperature in the Example of this invention, and the emitted-heat amount of PM. 本発明の実施例における加熱温度(耐熱温度)とPM燃焼ピーク時の温度との関係を示すグラフである。It is a graph which shows the relationship between the heating temperature (heat-resistant temperature) in the Example of this invention, and the temperature at the time of PM combustion peak. 本発明の実施形態における触媒コンバータを示す正面図である。It is a front view which shows the catalytic converter in embodiment of this invention. 本発明の実施形態における触媒コンバータを示す側断面図である。It is a sectional side view which shows the catalytic converter in embodiment of this invention. 本発明の実施形態における触媒コンバータを示す一部拡大側断面図である。It is a partially expanded side sectional view which shows the catalytic converter in embodiment of this invention. 本発明における酸素放出能を説明するためのグラフである。It is a graph for demonstrating the oxygen releasing ability in this invention. 本発明の実施例におけるDPFの一部を示す断面図である。It is sectional drawing which shows a part of DPF in the Example of this invention. 排ガス中のPMの粒度分布を示すグラフである。It is a graph which shows the particle size distribution of PM in exhaust gas. 実施例で作製したコンバータを示す側面図である。It is a side view which shows the converter produced in the Example. 実施例におけるテストレイアウトを示す側面図である。It is a side view which shows the test layout in an Example. 実施例における低温燃焼でのPMの堆積量を示すグラフである。It is a graph which shows the deposition amount of PM in the low temperature combustion in an Example. 実施例における強制再生での再生時間を示すグラフである。It is a graph which shows the reproduction time in forced reproduction in an example.

Claims (11)

内燃機関から排出される排出ガスに含まれるカーボンを主成分とする粒子状物質を浄化するための排ガス浄化触媒であって、酸素放出能を有する複合酸化物にAgを担持したことを特徴とする排ガス浄化触媒。   An exhaust gas purification catalyst for purifying particulate matter containing carbon as a main component contained in exhaust gas discharged from an internal combustion engine, characterized in that Ag is supported on a complex oxide having oxygen releasing ability. Exhaust gas purification catalyst. 前記複合酸化物は、ペロブスカイト型、スピネル型、ルチル型、デラフォサイト型、マグネトプランバイト型、フルオライト型、およびイルメナイト型から選択された1種または2種以上であることを特徴とする請求項1に記載の排ガス浄化触媒。   The composite oxide is one or more selected from perovskite type, spinel type, rutile type, delafossite type, magnetoplumbite type, fluorite type, and ilmenite type. Item 2. The exhaust gas purifying catalyst according to Item 1. 前記複合酸化物は、アルカリ金属、アルカリ土類金属、希土類金属、遷移金属、貴金属の中から選択される2以上の元素の組み合わせからなり、原子の価数を変化させて酸素の吸収及び放出を行うことを特徴とする請求項1または2に記載の排ガス浄化触媒。   The composite oxide is a combination of two or more elements selected from alkali metals, alkaline earth metals, rare earth metals, transition metals, and noble metals, and absorbs and releases oxygen by changing the valence of atoms. The exhaust gas purification catalyst according to claim 1, wherein the exhaust gas purification catalyst is performed. 内燃機関から排出される排出ガスに含まれるカーボンを主成分とする粒子状物質を捕集可能なフィルタの内部に、請求項1〜3のいずれかに記載の排ガス浄化触媒が塗布されていることを特徴とする排ガス浄化装置。   The exhaust gas purification catalyst according to any one of claims 1 to 3 is applied to the inside of a filter capable of collecting particulate matter mainly composed of carbon contained in exhaust gas discharged from an internal combustion engine. An exhaust gas purification device characterized by the above. 内燃機関から排出される排出ガスに含まれるカーボンを主成分とする粒子状物質を捕集可能なフィルタの内部に、請求項1〜3のいずれかに記載の排ガス浄化触媒と、排ガス中に含まれるNOをNOに変換するNO生成触媒が同時に担持されていることを特徴とする排ガス浄化装置。 The exhaust gas purifying catalyst according to any one of claims 1 to 3 and an exhaust gas contained in a filter capable of collecting particulate matter mainly composed of carbon contained in exhaust gas discharged from an internal combustion engine. An exhaust gas purifying apparatus, wherein a NO 2 generating catalyst for converting NO into NO 2 is simultaneously supported. 前記排ガス浄化触媒と前記NO生成触媒が、前記フィルタの内部の基材上において下層に前記排ガス浄化触媒、上層に前記NO生成触媒の構成で塗布されていることを特徴とする請求項5に記載の排ガス浄化装置。 6. The exhaust gas purification catalyst and the NO 2 production catalyst are coated on the base material inside the filter in a configuration of the exhaust gas purification catalyst in a lower layer and the NO 2 production catalyst in an upper layer. The exhaust gas purification apparatus according to 1. 前記NO生成触媒は、Pt,Pd,Rhから選ばれる1種または2種以上の元素が高比表面積担持体上に担持されてなることを特徴とする請求項5または6に記載の排ガス浄化装置。 The exhaust gas purification according to claim 5 or 6, wherein the NO 2 generation catalyst is formed by supporting one or more elements selected from Pt, Pd, and Rh on a high specific surface area support. apparatus. 前記高比表面積担持体は、アルミナ、シリカ、チタニア、セリア、ジルコニア、マグネシアから選ばれる1種または2種以上からなることを特徴とする請求項7に記載の排ガス浄化装置。   The exhaust gas purifying apparatus according to claim 7, wherein the high specific surface area carrier comprises one or more selected from alumina, silica, titania, ceria, zirconia, and magnesia. 前記NO生成触媒の層中に、気孔を有することを特徴とする請求項6〜8のいずれかに記載の排ガス浄化装置。 The exhaust gas purifying apparatus according to any one of claims 6 to 8, wherein pores are provided in the NO 2 production catalyst layer. 前記気孔の大きさが平均で1μm以上であることを特徴とする請求項9に記載の排ガス浄化装置。   The exhaust gas purification apparatus according to claim 9, wherein the pores have an average size of 1 µm or more. 前記フィルタは、多孔質の耐火性セラミックスからなるウォールフロータイプのフィルタであることを特徴とする請求項4〜10のいずれかに記載の排ガス浄化装置。   The exhaust gas purifying apparatus according to any one of claims 4 to 10, wherein the filter is a wall flow type filter made of porous refractory ceramics.
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