JP2017044201A - Exhaust emission control system for internal combustion engine and exhaust emission control catalyst - Google Patents

Exhaust emission control system for internal combustion engine and exhaust emission control catalyst Download PDF

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JP2017044201A
JP2017044201A JP2015169836A JP2015169836A JP2017044201A JP 2017044201 A JP2017044201 A JP 2017044201A JP 2015169836 A JP2015169836 A JP 2015169836A JP 2015169836 A JP2015169836 A JP 2015169836A JP 2017044201 A JP2017044201 A JP 2017044201A
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exhaust gas
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JP6699113B2 (en
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岩知道　均一
Kinichi Iwachido
均一 岩知道
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Mitsubishi Motors Corp
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Abstract

PROBLEM TO BE SOLVED: To improve efficiency of an internal combustion engine by reducing pressure loss of exhaust gas and reduce catalyst cost while responding to multi-functionality of exhaust emission control performance.SOLUTION: In an exhaust emission control system for an internal combustion engine, an exhaust emission control catalyst that comprises a support base material, a catalyst support layer formed on the surface of the support base material and catalyst active components supported by the catalyst support layer is provided in an exhaust passage. A first exhaust emission control catalyst is provided in the exhaust passage. The catalyst support layer of the first exhaust emission control catalyst comprises: a lower layer located near the surface of the support base material; and an upper layer located relatively distant compared to the lower layer. The catalyst active component of the upper layer includes a material for selectively reducing NOx in exhaust gas by using NH3 included in exhaust gas. The catalyst active component of the lower layer includes a material that can adsorb HC and NOx.SELECTED DRAWING: Figure 2

Description

本開示は、簡易な構成で排ガスの浄化を可能にした内燃機関の排ガス浄化システム及び排ガス浄化触媒に関する。   The present disclosure relates to an exhaust gas purification system and an exhaust gas purification catalyst for an internal combustion engine that enable purification of exhaust gas with a simple configuration.

大気のクリーン化が求められる中、ガソリンエンジンでは、触媒を用いた排ガス浄化性能のさらなる向上が求められ、特に、エンジン冷態時の排ガス浄化が重要な課題となっている。エンジン冷態時の排ガス浄化策として、排ガス通路に設けられた触媒が昇温するまでの間に排出されるＨＣの低減を狙って、ＨＣトラップ触媒など、排ガス通路に多種の触媒を直列に配置した浄化システムが検討されている。
しかし、このような浄化システムでは、排ガスの圧力損失が大きくなり、排気圧力の上昇によって、エンジン性能が低下するだけでなく、触媒コストが極めて高価になるという問題がある。特に、触媒担持層を担持する担持基材がハニカム構造体であるとき、排ガスの圧力損失がエンジン性能に及ぼす影響を無視できない。 Amidst demands for clean air, gasoline engines are required to further improve exhaust gas purification performance using a catalyst, and in particular, exhaust gas purification when the engine is cold is an important issue. As an exhaust gas purification measure when the engine is cold, various catalysts are arranged in series in the exhaust gas passage, such as an HC trap catalyst, aiming to reduce the HC discharged until the temperature of the catalyst provided in the exhaust gas passage rises. Purified systems are being considered.
However, in such a purification system, there is a problem that the pressure loss of the exhaust gas becomes large, and not only the engine performance is reduced due to the increase of the exhaust pressure, but the catalyst cost becomes extremely expensive. In particular, when the support base material supporting the catalyst support layer is a honeycomb structure, the influence of exhaust gas pressure loss on engine performance cannot be ignored.

例えば、特許文献１には、排ガス通路に排ガス上流側から第１の触媒コンバータと第２の触媒コンバータとが直列に設けられ、第１の触媒コンバータには、酸化性能を有する高温用ＮＯｘ吸着触媒と触媒温度が低いときＮＯｘを吸着する低温用ＮＯｘ吸着触媒とが内蔵され、第２の触媒コンバータには、第１の触媒コンバータから放出されたＮＯｘを還元浄化するためのＮＯｘ還元触媒と、捕集したＰＭを燃焼し浄化するＰＭ燃焼触媒とが内蔵されている。   For example, in Patent Document 1, a first catalytic converter and a second catalytic converter are provided in series in the exhaust gas passage from the exhaust gas upstream side, and the first catalytic converter includes a high-temperature NOx adsorption catalyst having oxidation performance. And a low-temperature NOx adsorption catalyst that adsorbs NOx when the catalyst temperature is low, and the second catalytic converter includes a NOx reduction catalyst for reducing and purifying NOx released from the first catalytic converter, and a trap. A PM combustion catalyst for burning and purifying the collected PM is incorporated.

特開２０１５−０２５４３３号公報Japanese Patent Laying-Open No. 2015-025433

排ガス通路に複数種の触媒を直列に配置すると、排ガスの圧力損失が増加する。特許文献１に開示された排ガス浄化システムは、排気圧力の増加を抑え、エンジン性能の低下を抑えることを目的としている。しかしながら、今後、さらなる排ガス浄化性能の向上を狙って触媒の多機能化が求められる状況下では、排気圧力の抑制と触媒コストの削減が必要である。   When a plurality of types of catalysts are arranged in series in the exhaust gas passage, the pressure loss of the exhaust gas increases. The exhaust gas purification system disclosed in Patent Document 1 aims to suppress an increase in exhaust pressure and suppress a decrease in engine performance. However, in the future, it is necessary to suppress the exhaust pressure and reduce the catalyst cost under the situation where the multi-functionalization of the catalyst is demanded with the aim of further improving the exhaust gas purification performance.

そこで、これら技術的課題に鑑み、本発明の少なくとも一つの実施形態は、排ガス浄化性能の多機能化に対応しつつ、排ガスの圧力損失をさらに低減して内燃機関の効率向上を図ると共に、触媒コストの削減を図ることを目的とする。   Accordingly, in view of these technical problems, at least one embodiment of the present invention aims to improve the efficiency of the internal combustion engine by further reducing the pressure loss of the exhaust gas while supporting the multi-functionality of the exhaust gas purification performance. The purpose is to reduce costs.

（１）本発明の少なくとも一実施形態に係る内燃機関の排ガス浄化システムは、排ガス通路に、担持基材と、該担持基材の表面に形成された触媒担持層と、該触媒担持層に担持された触媒活性成分とで構成された排ガス浄化触媒を備えた内燃機関の排ガス浄化システムにおいて、前記排ガス通路に第１の排ガス浄化触媒を備え、前記第１の排ガス浄化触媒の前記触媒担持層は、前記担持基材の表面に近い下層と該下層より相対的に遠い上層とで構成され、前記上層の前記触媒活性成分は、排ガス中に含まれるＮＨ３で排ガス中のＮＯｘを選択還元する材料を含み、前記下層の前記触媒活性成分は、ＨＣ及びＮＯｘを吸着可能な材料を含む。 (1) An exhaust gas purification system for an internal combustion engine according to at least one embodiment of the present invention includes a support base material, a catalyst support layer formed on a surface of the support base material, and a catalyst support layer. In the exhaust gas purification system of an internal combustion engine comprising an exhaust gas purification catalyst composed of the catalyst active component thus formed, the exhaust gas passage comprises a first exhaust gas purification catalyst, and the catalyst support layer of the first exhaust gas purification catalyst comprises: A lower layer close to the surface of the support substrate and an upper layer relatively far from the lower layer, and the catalytically active component of the upper layer is a material that selectively reduces NOx in the exhaust gas with NH 3 contained in the exhaust gas The catalytic active component in the lower layer includes a material capable of adsorbing HC and NOx.

排ガス中にＣＯ、ＨＣが存在すると、反応式（１）の水性ガス反応と、反応式（２）の水蒸気改質反応が進行してＨ２が生成され、反応式（３）、反応式（４）や反応式（５）の反応によりＮＨ３が生成する。これらの反応は、とくに貴金属を担持した触媒上で進行する。
ＣＯ＋Ｈ２Ｏ → ＣＯ２＋Ｈ２ （１）
ＣＨｎ＋２Ｈ２Ｏ → ＣＯ２＋（２＋ｎ/２）Ｈ２ （２）
５/２Ｈ２＋ＮＯ → ＮＨ３＋Ｈ２Ｏ （３）
３/２Ｈ２＋ＮＯ＋ＣＯ → ＮＨ３＋ＣＯ２ （４）
ＮＯ＋ＨＣ＋Ｈ２Ｏ → ＣＯ２＋ＮＨ３ （５）
上記第１の排ガス浄化触媒では、上層の触媒活性成分により排ガス中に存在するＮＨ３とＮＯｘとを反応させ、反応式（６）〜（８）の反応によりＮＯｘを選択還元する。
ＮＯ＋ＮＯ２＋２ＮＨ３ → ２Ｎ２＋３Ｈ２Ｏ （６）
４ＮＯ＋４ＮＨ３＋Ｏ２ → ４Ｎ２＋６Ｈ２Ｏ （７）
６ＮＯ２＋８ＮＨ３ → ７Ｎ２＋１２Ｈ２Ｏ （８）
また、下層の触媒活性成分で吸着したＨＣ及びＮＯｘから、上記反応式（１）〜（５）によりＮＨ３を生成し、生成したＮＨ３をＮＯｘの選択還元に用いることができる。
また、下層の触媒活性成分で吸着したＮＯｘが上層の触媒活性成分を通過する機会が与えられるため、ＮＯｘの還元率を向上できる。
このように、排ガスに曝される上層側に排ガス中に存在するＮＨ３とＮＯｘを反応させる成分を含み、下層側にＨＣ及びＮＯｘ吸着能成分を含むため、ＮＯｘを効率良く低減できる。
また、上下積層構造の触媒担持層を備えることで、排ガス通路に直列に配置される触媒担体の数を低減できるため、触媒コストを削減できると共に、排ガスの圧力損失を低減できるため、内燃機関の性能低下を抑制できる。 When CO and HC are present in the exhaust gas, the water gas reaction of the reaction formula (1) and the steam reforming reaction of the reaction formula (2) proceed to generate H 2 , and the reaction formula (3), the reaction formula ( NH 3 is produced by the reaction of 4) or reaction formula (5). These reactions proceed particularly on a catalyst supporting a noble metal.
CO + H 2 O → CO 2 + H 2 (1)
CH n + 2H 2 O → CO 2 + (2 + n / 2) H 2 (2)
5 / 2H 2 + NO → NH 3 + H 2 O (3)
3 / 2H 2 + NO + CO → NH 3 + CO 2 (4)
NO + HC + H 2 O → CO 2 + NH 3 (5)
In the first exhaust gas purification catalyst, NH 3 and NOx present in the exhaust gas are reacted with the catalytic active component in the upper layer, and NOx is selectively reduced by the reactions of the reaction formulas (6) to (8).
NO + NO 2 + 2NH 3 → 2N 2 + 3H 2 O (6)
4NO + 4NH 3 + O 2 → 4N 2 + 6H 2 O (7)
6NO 2 + 8NH 3 → 7N 2 + 12H 2 O (8)
In addition, NH 3 can be generated from the HC and NOx adsorbed by the catalytic active component in the lower layer by the above reaction formulas (1) to (5), and the generated NH 3 can be used for selective reduction of NOx.
In addition, since the NOx adsorbed by the lower catalytic active component is given an opportunity to pass through the upper catalytic active component, the NOx reduction rate can be improved.
As described above, since the upper layer side exposed to the exhaust gas includes a component that causes NH 3 and NOx present in the exhaust gas to react and the lower layer side includes HC and a NOx adsorbing component, NOx can be efficiently reduced.
In addition, since the number of catalyst carriers arranged in a stack in the exhaust gas passage can be reduced by providing the upper and lower stacked catalyst support layers, the catalyst cost can be reduced and the pressure loss of the exhaust gas can be reduced. Performance degradation can be suppressed.

（２）幾つかの実施形態では、前記構成（１）において、前記第１の排ガス浄化触媒より上流側の前記排ガス通路に、担持基材と、該担持基材の表面に形成された触媒担持層と、該触媒担持層に担持された触媒活性成分とで構成された第２の排ガス浄化触媒を備え、前記第２の排ガス浄化触媒の前記触媒活性成分は、排ガス中のＨＣ及びＣＯを酸化すると共にＮＯｘを還元することで、これらを低減する材料を含む。
上記構成（２）によれば、上記第２の排ガス浄化触媒はいわゆる三元触媒としての浄化機能を有し、排ガス中のＨＣ及びＣＯを酸化し、かつＮＯｘを還元してＮ２、ＣＯ２及びＨ２Ｏに変換し低減できる。
こうして、第１の排ガス浄化触媒及び第２の排ガス浄化触媒との組合せで排ガス浄化性能の多機能化が可能になる。 (2) In some embodiments, in the configuration (1), a support substrate and a catalyst support formed on the surface of the support substrate in the exhaust gas passage upstream of the first exhaust gas purification catalyst. A second exhaust gas purification catalyst comprising a catalyst layer and a catalytic active component supported on the catalyst support layer, wherein the catalytic active component of the second exhaust gas purification catalyst oxidizes HC and CO in the exhaust gas In addition, a material that reduces NOx by reducing NOx is included.
According to the configuration (2), the second exhaust gas purification catalyst has a purification function as a so-called three-way catalyst, oxidizes HC and CO in the exhaust gas, and reduces NOx to reduce N 2 and CO 2. And can be reduced to H 2 O.
Thus, the exhaust gas purification performance can be multi-functionalized by combining the first exhaust gas purification catalyst and the second exhaust gas purification catalyst.

（３）幾つかの実施形態では、前記構成（２）において、前記第２の排ガス浄化触媒の前記触媒担持層は、前記担持基材の表面に近い下層と該下層より相対的に遠い上層とで構成され、前記上層の前記触媒活性成分はＲｈを含み、前記下層の前記触媒活性成分はＰｄ及び触媒用酸素吸蔵材料を含む。
上記構成（３）によれば、上層に含まれるＲｈの優れた排ガス浄化性能で高い排ガス浄化効果を得ることができると共に、触媒活性成分として比較的安価なＰｄを含む下層の存在によって、高い浄化性能を維持しつつ触媒コストを低減できる。
また、下層に酸素吸蔵及び放出能を有する触媒用酸素吸蔵材料を含むことで、空燃比が変動した場合でも高い排ガス浄化効果を維持できる。
さらに、排ガス浄化効果の向上に伴って、第１の排ガス浄化触媒及び第２の排ガス浄化触媒の触媒担持層の膜厚を薄くでき、これによって、特に、担持基材がハニカム構造体である場合などで、排ガスの圧力損失の増加を抑えることができる。
さらに、ＲｈやＰｄ等の貴金属を担持した触媒担持層を積層させることで、上記反応式（１）〜（５）によりＮＨ３が多く生成され、ここで生成されたＮＨ３がＮＯｘの還元浄化に寄与する。 (3) In some embodiments, in the configuration (2), the catalyst support layer of the second exhaust gas purification catalyst includes a lower layer close to the surface of the support base and an upper layer relatively far from the lower layer. The catalytic active component in the upper layer contains Rh, and the catalytic active component in the lower layer contains Pd and an oxygen storage material for catalyst.
According to the configuration (3), it is possible to obtain a high exhaust gas purification effect with an excellent exhaust gas purification performance of Rh contained in the upper layer, and high purification by the presence of a lower layer containing Pd that is relatively inexpensive as a catalytically active component. The catalyst cost can be reduced while maintaining the performance.
Moreover, even if the air-fuel ratio fluctuates, a high exhaust gas purification effect can be maintained by including a catalyst oxygen storage material having oxygen storage and release capability in the lower layer.
Furthermore, as the exhaust gas purification effect is improved, the film thicknesses of the catalyst support layers of the first exhaust gas purification catalyst and the second exhaust gas purification catalyst can be reduced, and particularly when the support substrate is a honeycomb structure. Thus, an increase in the pressure loss of the exhaust gas can be suppressed.
Further, by laminating a catalyst support layer supporting a noble metal such as Rh or Pd, a large amount of NH 3 is generated by the above reaction formulas (1) to (5), and the generated NH 3 is reduced and purified by NOx. Contribute to.

（４）幾つかの実施形態では、前記構成（３）において、前記第２の排ガス浄化触媒の前記下層は、排ガス流れ上流側領域のみに設けられている。
上記構成（４）によれば、排ガス温度が高く排ガス浄化効果が大きい排ガス上流側領域では、上記下層の存在により排ガス浄化効果を高めることができる。他方、排ガス温度が低く上流側領域ほど排ガス浄化効果が見込めない排ガス下流側領域では、下層を形成しないことで、排ガス浄化効果を大きく低下させることなく触媒コストを低減できる。 (4) In some embodiments, in the configuration (3), the lower layer of the second exhaust gas purification catalyst is provided only in the exhaust gas flow upstream region.
According to the configuration (4), in the exhaust gas upstream region where the exhaust gas temperature is high and the exhaust gas purification effect is large, the exhaust gas purification effect can be enhanced by the presence of the lower layer. On the other hand, in the exhaust gas downstream region where the exhaust gas temperature is lower and the exhaust gas purification effect cannot be expected in the upstream region, the catalyst cost can be reduced without significantly reducing the exhaust gas purification effect by forming no lower layer.

幾つかの実施形態では、前記構成（３）又は（４）において、前記第２の排ガス浄化触媒の前記上層は、前記触媒活性成分として担持基材の容積１リットル当たり０．１乃至２．０ｇのＲｈを含み、前記第２の排ガス浄化触媒の前記下層は、前記触媒活性成分として担持基材の容積１リットル当たり１乃至１５ｇのＰｄと、助触媒としてＣｅＯ２を主成分とする１乃至８０ｇの前記触媒用酸素吸蔵材料とを含む。
上記構成によれば、触媒担持層に、触媒活性成分としてのＲｈ及びＰｄ及び助触媒としての触媒用酸素吸蔵材料が上記範囲の量を担持されることで、高い排ガス浄化効果を得ることができる。また、浄化効果が高いために上層及び下層とも膜厚を抑えることができるので、触媒担持層のコーティングが容易になる。 In some embodiments, in the configuration (3) or (4), the upper layer of the second exhaust gas purification catalyst is 0.1 to 2.0 g per liter of the support substrate as the catalytic active component. The lower layer of the second exhaust gas purifying catalyst contains 1 to 15 g of Pd as a main component of 1 to 15 g of Pd per liter of the supporting substrate as the catalytic active component and CeO 2 as a co-catalyst. The oxygen storage material for catalyst.
According to the above configuration, a high exhaust gas purification effect can be obtained by loading the catalyst supporting layer with Rh and Pd as the catalyst active components and the oxygen storage material for catalyst as the promoter in the above ranges. . Further, since the purification effect is high, the film thickness of both the upper layer and the lower layer can be suppressed, so that the coating of the catalyst support layer becomes easy.

（５）幾つかの実施形態では、前記構成（３）又は（４）において、前記第２の排ガス浄化触媒の前記上層は、前記触媒活性成分の担持量が排ガス流れ上流側領域で排ガス流れ下流側領域より多い。
上記構成（５）によれば、排ガス温度が高く排ガス浄化効果が大きい排ガス流れ上流側領域で触媒活性成分の担持量を多くすることで、排ガス浄化効果を向上できると共に、排ガス流れ下流側領域では触媒活性成分の担持量を少なくすることで、触媒コストを削減できる。 (5) In some embodiments, in the configuration (3) or (4), the upper layer of the second exhaust gas purification catalyst has an amount of the catalyst active component supported in the exhaust gas flow upstream region and the exhaust gas flow downstream. More than side area.
According to the configuration (5), the exhaust gas purification effect can be improved by increasing the supported amount of the catalytic active component in the exhaust gas flow upstream region where the exhaust gas temperature is high and the exhaust gas purification effect is large. The catalyst cost can be reduced by reducing the amount of the catalytically active component supported.

（６）幾つかの実施形態では、前記構成（１）〜（５）の何れかにおいて、前記第１の排ガス浄化触媒において、前記下層に含まれる前記触媒活性成分が吸着したＨＣ及びＮＯｘを脱離させる工程で、内燃機関をリッチ燃焼に制御するための制御装置をさらに備える。
上記構成（６）によれば、下層に含まれる触媒活性成分が吸着したＨＣ及びＮＯｘを脱離させる工程で、内燃機関をリッチ燃焼に制御することで、排ガス中のＣＯ量やＨＣ量を増やし、これによって、上記反応式（１）〜（５）から、排ガス中に含まれるＮＨ３量を増やすことができる。
そして、増加したＮＨ３によって下層の触媒活性成分から脱離したＮＯｘを高効率で低減できる。また、下層の触媒活性成分から脱離したＨＣは上層触媒や下流触媒の浄化作用によって低減できる。 (6) In some embodiments, in any one of the configurations (1) to (5), in the first exhaust gas purification catalyst, HC and NOx adsorbed by the catalytic active component contained in the lower layer are removed. A control device is further provided for controlling the internal combustion engine to rich combustion in the separating step.
According to the configuration (6), the amount of CO and HC in the exhaust gas is increased by controlling the internal combustion engine to rich combustion in the step of desorbing HC and NOx adsorbed by the catalytically active components contained in the lower layer. Thus, the amount of NH 3 contained in the exhaust gas can be increased from the reaction formulas (1) to (5).
Further, NOx desorbed from the lower catalytic active component by the increased NH 3 can be reduced with high efficiency. Further, HC desorbed from the lower layer catalytic active component can be reduced by the purification action of the upper layer catalyst and the downstream catalyst.

（７）幾つかの実施形態では、前記構成（６）において、前記第１の排ガス浄化触媒を通る排ガスの温度を検出するための温度センサをさらに備え、前記制御装置は、前記温度センサの検出値が閾値を超えた時、ＨＣ及びＮＯｘの脱離工程であると判定し、前記内燃機関をリッチ燃焼に制御するものである。
上記構成（７）によれば、第１の排ガス浄化触媒を通る排ガスの温度を検出し、この検出値に基づいてＨＣ及びＮＯｘの脱離工程が開始されたか否かを正確に判定できる。 (7) In some embodiments, the configuration (6) further includes a temperature sensor for detecting a temperature of the exhaust gas that passes through the first exhaust gas purification catalyst, and the control device detects the temperature sensor. When the value exceeds the threshold value, it is determined that the process is a desorption process of HC and NOx, and the internal combustion engine is controlled to rich combustion.
According to the configuration (7), it is possible to detect the temperature of the exhaust gas passing through the first exhaust gas purification catalyst and accurately determine whether or not the HC and NOx desorption process has been started based on the detected value.

（８）本発明の少なくとも一実施形態に係る排ガス浄化触媒は、担持基材と、該担持基材の表面に形成された触媒担持層と、該触媒担持層に担持された触媒活性成分とで構成された排ガス浄化触媒において、前記触媒担持層は、前記担持基材の表面に近い下層と該下層より相対的に遠い上層とで構成され、前記上層の前記触媒活性成分は、排ガス中に含まれるＮＨ３で排ガス中のＮＯｘを選択還元する材料を含み、前記下層の前記触媒活性成分は、ＨＣ及びＮＯｘを吸着可能な材料を含む。
上記構成（８）によれば、上記排ガス浄化触媒では、上層の触媒活性成分により排ガス中に存在するＮＨ３とＮＯｘとを反応させ、ＮＯｘを選択還元する。また、下層の触媒活性成分で吸着したＨＣ及びＮＯｘから、上記反応式（１）〜（５）によりＮＨ３を生成し、生成したＮＨ３を上記反応式（６）〜（８）によりＮＯｘの選択還元に寄与させることができる。
また、下層の触媒活性成分で吸着したＨＣ、ＮＯｘが上層の触媒活性成分を通る間に、ＮＯｘの還元率を向上できる。さらに、下層の触媒活性成分で吸着したＨＣが上層の触媒活性成分を通る間に、ＨＣの酸化率を向上できる。
このように、上下積層構造の触媒担持層を備えることで、排ガス通路に直列に配置される触媒担体の数を低減できるため、触媒コストを削減できる。また、排ガスの圧力損失を低減できるため、内燃機関の性能低下を抑制できる。 (8) An exhaust gas purifying catalyst according to at least one embodiment of the present invention comprises a supporting substrate, a catalyst supporting layer formed on the surface of the supporting substrate, and a catalytically active component supported on the catalyst supporting layer. In the exhaust gas purification catalyst configured, the catalyst support layer is composed of a lower layer close to the surface of the support base and an upper layer relatively far from the lower layer, and the catalytic active component of the upper layer is included in the exhaust gas The material that selectively reduces NOx in the exhaust gas with NH 3 , and the catalytically active component in the lower layer includes a material that can adsorb HC and NOx.
According to the configuration (8), in the exhaust gas purification catalyst, NH 3 and NOx existing in the exhaust gas are reacted by the catalytic active component in the upper layer, and NOx is selectively reduced. Further, NH 3 is generated from the HC and NOx adsorbed by the lower layer catalytic active component by the above reaction formulas (1) to (5), and the generated NH 3 is converted to NOx by the above reaction formulas (6) to (8). This can contribute to selective reduction.
In addition, the reduction rate of NOx can be improved while HC and NOx adsorbed by the lower catalytic active component pass through the upper catalytic active component. Furthermore, the HC oxidation rate can be improved while HC adsorbed by the lower catalytic active component passes through the upper catalytic active component.
Thus, by providing the catalyst support layer of the upper and lower laminated structure, the number of catalyst carriers arranged in series in the exhaust gas passage can be reduced, so that the catalyst cost can be reduced. Moreover, since the pressure loss of exhaust gas can be reduced, the performance fall of an internal combustion engine can be suppressed.

（９）幾つかの実施形態では、前記構成（８）において、前記下層は排ガス上流側領域のみに設けられている。
上記構成（９）によれば、排ガス温度が高く排ガス浄化効果が大きい排ガス上流側領域では、下層の存在により排ガス浄化効果を高めることができる。他方、排ガス温度が低下し上流側領域ほど排ガス浄化効果が見込めない排ガス下流側領域では、下層を形成しないことで、排ガス浄化効果をそれほど低下させることなく触媒コストを低減できる。 (9) In some embodiments, in the configuration (8), the lower layer is provided only in the exhaust gas upstream region.
According to the above configuration (9), in the exhaust gas upstream region where the exhaust gas temperature is high and the exhaust gas purification effect is large, the exhaust gas purification effect can be enhanced by the presence of the lower layer. On the other hand, in the exhaust gas downstream side region where the exhaust gas temperature is lowered and the exhaust gas purification effect cannot be expected in the upstream region, the catalyst cost can be reduced without reducing the exhaust gas purification effect so much by not forming the lower layer.

幾つかの実施形態では、前記構成（８）又は（９）において、前記上層及び前記下層は、夫々前記担持基材の容積１リットル当たり２０乃至３００ｇの前記触媒活性成分を含む。
上記構成によれば、上層及び下層において、上記含有量の触媒活性成分を含むため、ＮＯｘの浄化効果を向上できる。また、上層及び下層の膜厚を抑えることができるので、排ガスの圧力損失を抑制できると共に、触媒担持層のコーティングが容易になる。 In some embodiments, in the configuration (8) or (9), the upper layer and the lower layer each include 20 to 300 g of the catalytically active component per liter of the support substrate.
According to the above configuration, the NOx purification effect can be improved because the upper layer and the lower layer contain the catalytic active component with the above content. Moreover, since the film thickness of an upper layer and a lower layer can be suppressed, the pressure loss of exhaust gas can be suppressed and coating of the catalyst support layer is facilitated.

本発明の少なくとも一実施形態によれば、排ガス浄化性能の多機能化に対応しつつ、内燃機関の排ガス通路を流れる排ガスの圧力損失を低減して内燃機関の効率を向上できると共に、排ガス通路に設けられる排ガス浄化触媒のコストを削減できる。   According to at least one embodiment of the present invention, the efficiency of the internal combustion engine can be improved by reducing the pressure loss of the exhaust gas flowing through the exhaust gas passage of the internal combustion engine while supporting the multi-function of the exhaust gas purification performance. The cost of the exhaust gas purification catalyst provided can be reduced.

一実施形態に係る内燃機関の排ガス浄化システムを示す概略構成図である。It is a schematic block diagram which shows the exhaust gas purification system of the internal combustion engine which concerns on one Embodiment. 一実施形態に係る触媒コンバータの概略構成図である。It is a schematic block diagram of the catalytic converter which concerns on one Embodiment. （Ａ）は図２中のＡ―Ａ線に沿う断面図であり、（Ｂ）は同じくＢ―Ｂ線に沿う断面図であり、（Ｃ）は同じくＣ―Ｃ線に沿う断面図であり、（Ｄ）は同じくＤ―Ｄ線に沿う断面図である。(A) is a cross-sectional view taken along the line AA in FIG. 2, (B) is a cross-sectional view taken along the line BB, and (C) is a cross-sectional view taken along the line CC. , (D) is a cross-sectional view along the line DD. 一実施形態に係る触媒の断面図である。It is sectional drawing of the catalyst which concerns on one Embodiment. （Ａ）は図４中のＥ―Ｅ線に沿う断面図であり、（Ｂ）は同じくＦ―Ｆ線に沿う断面図である。(A) is sectional drawing which follows the EE line in FIG. 4, (B) is sectional drawing which follows the FF line similarly. 排ガス浄化プロセスを時系列で示す線図である。It is a diagram which shows an exhaust gas purification process in time series. 触媒内部の排ガス温度分布を示す線図である。It is a diagram which shows the exhaust gas temperature distribution inside a catalyst. 貴金属担持量と総ＨＣの浄化効率との関係を示す線図である。It is a diagram which shows the relationship between the noble metal carrying amount and the purification efficiency of total HC.

以下、添付図面を参照して、本発明の幾つかの実施形態について説明する。ただし、これらの実施形態に記載されている又は図面に示されている構成部品の寸法、材質、形状及びその相対的配置等は、本発明の範囲をこれに限定する趣旨ではなく、単なる説明例にすぎない。
例えば、「ある方向に」、「ある方向に沿って」、「平行」、「直交」、「中心」、「同心」或いは「同軸」等の相対的或いは絶対的な配置を表す表現は、厳密にそのような配置を表すのみならず、公差、若しくは、同じ機能が得られる程度の角度や距離をもって相対的に変位している状態も表すものとする。
例えば、「同一」、「等しい」及び「均質」等の物事が等しい状態であることを表す表現は、厳密に等しい状態を表すのみならず、公差、若しくは、同じ機能が得られる程度の差が存在している状態も表すものとする。
例えば、四角形状や円筒形状等の形状を表す表現は、幾何学的に厳密な意味での四角形状や円筒形状等の形状を表すのみならず、同じ効果が得られる範囲で、凹凸部や面取り部等を含む形状も表すものとする。
一方、一つの構成要素を「備える」、「具える」、「具備する」、「含む」、又は「有する」という表現は、他の構成要素の存在を除外する排他的な表現ではない。 Several embodiments of the present invention will be described below with reference to the accompanying drawings. However, the dimensions, materials, shapes, and relative arrangements of the components described in these embodiments or shown in the drawings are not intended to limit the scope of the present invention, but are merely illustrative examples. Only.
For example, expressions expressing relative or absolute arrangements such as “in a certain direction”, “along a certain direction”, “parallel”, “orthogonal”, “center”, “concentric” or “coaxial” are strictly In addition to such an arrangement, it is also possible to represent a state of relative displacement with an angle or a distance such that tolerance or the same function can be obtained.
For example, an expression indicating that things such as “identical”, “equal”, and “homogeneous” are in an equal state not only represents an exactly equal state, but also has a tolerance or a difference that can provide the same function. It also represents the existing state.
For example, expressions representing shapes such as quadrangular shapes and cylindrical shapes represent not only geometrically strict shapes such as quadrangular shapes and cylindrical shapes, but also irregularities and chamfers as long as the same effects can be obtained. A shape including a part or the like is also expressed.
On the other hand, the expressions “comprising”, “comprising”, “comprising”, “including”, or “having” one constituent element are not exclusive expressions for excluding the existence of other constituent elements.

本発明の幾つかの実施形態に係る排ガス浄化システム１０は、図１に示すように、内燃機関（例えばガソリンエンジン）１１の燃焼室（不図示）と連通する排気ポート１２が気筒毎に形成されている。そして、内燃機関１１には夫々の排気ポート１２と連通するように排気マニフォールド１４が接続されている。
排気マニフォールド１４の排ガス流れ方向下流には、排気過給機１６が設けられている。排気過給機１６ではタービンハウジング１６ａと排気管（排ガス通路）１８とが連通し、内燃機関１１から排出される排ガスｅのエネルギを利用して吸入された新気を圧縮し、内燃機関１０の燃焼室に供給する。
排気管１８には、第１の排ガス浄化触媒２０を内蔵した触媒コンバータ２２が設けられている。 As shown in FIG. 1, an exhaust gas purification system 10 according to some embodiments of the present invention has an exhaust port 12 communicating with a combustion chamber (not shown) of an internal combustion engine (for example, a gasoline engine) 11 for each cylinder. ing. An exhaust manifold 14 is connected to the internal combustion engine 11 so as to communicate with the respective exhaust ports 12.
An exhaust supercharger 16 is provided downstream of the exhaust manifold 14 in the exhaust gas flow direction. In the exhaust supercharger 16, a turbine housing 16 a and an exhaust pipe (exhaust gas passage) 18 communicate with each other, compressing fresh air sucked using the energy of the exhaust gas e discharged from the internal combustion engine 11, and Supply to the combustion chamber.
The exhaust pipe 18 is provided with a catalytic converter 22 incorporating a first exhaust gas purification catalyst 20.

図２に示すように、第１の排ガス浄化触媒２０は、担持基材２４と、担持基材２４の表面に形成された触媒担持層２６と、触媒担持層２６に担持される触媒活性成分（不図示）で構成されている。
図示した実施形態では、担持基材２４は例えばコーディエライト製や金属箔製のハニカム構造体で構成される。
触媒担持層２６は、担持基材２４の表面に近い下層２８と、下層２８より相対的に遠い上層３０とで構成される。上層３０は、触媒活性成分として排ガスｅに含まれるＮＨ３とＮＯｘを選択還元する材料（以下「ＳＣＲ材」とも言う。）、例えば、ゼオライト（結晶性アルミノケイ酸塩）やＶ（バナジウム）を触媒活性の主成分として担持する。ゼオライトとしては、様々な結晶構造を有する材料があるが、ここでは、ＮＨ３によるＮＯｘの選択還元作用を有する材料であればよい。また、Ｆｅ−ゼオライト、Ｃｕ−ゼオライトのように少なくとも１種類の遷移金属元素を含んでもよい。
また、下層２８は、触媒活性成分として、ＨＣ及びＮＯｘを吸着可能な材料（以下「ＨＣ・ＮＯｘ吸着材」とも言う。）担持する。例えば、ＡｇやＦｅなどの遷移金属やβ―ゼオライトやＹ−ゼオライトのように１５０℃以下の温度でＨＣやＮＯｘの吸着作用を有する材料である。 As shown in FIG. 2, the first exhaust gas purification catalyst 20 includes a supporting base 24, a catalyst supporting layer 26 formed on the surface of the supporting base 24, and a catalytically active component ( (Not shown).
In the illustrated embodiment, the support base 24 is formed of a honeycomb structure made of, for example, cordierite or metal foil.
The catalyst support layer 26 includes a lower layer 28 that is close to the surface of the support substrate 24 and an upper layer 30 that is relatively far from the lower layer 28. The upper layer 30 catalyzes a material (hereinafter also referred to as “SCR material”) that selectively reduces NH 3 and NOx contained in the exhaust gas e as a catalytic active component, for example, zeolite (crystalline aluminosilicate) or V (vanadium). It is supported as the main component of activity. There are materials having various crystal structures as zeolite, but here, any material may be used as long as it has a selective reduction action of NOx by NH 3 . Moreover, you may contain at least 1 type of transition metal element like Fe-zeolite and Cu-zeolite.
The lower layer 28 carries a material capable of adsorbing HC and NOx (hereinafter also referred to as “HC / NOx adsorbent”) as a catalytic active component. For example, it is a material having an action of adsorbing HC and NOx at a temperature of 150 ° C. or lower, such as transition metals such as Ag and Fe, β-zeolite and Y-zeolite.

排ガス中にＣＯ、ＨＣ、ＮＯｘが存在すると、前記反応式（１）から（５）に示す反応によって、第１の排ガス浄化触媒２０の上流部にはＮＨ３が存在する。
第１の排ガス浄化触媒２０では、排ガス中に存在するＮＨ３とＮＯｘとを上層３０に含まれるＳＣＲ材で反応させ、ＮＯｘを選択還元する。また、下層２８に担持されるＨＣ・ＮＯｘ吸着材に吸着されたＨＣ及びＮＯｘは、排ガス温度の上昇と共に脱離しＮＨ３の生成を促進する。生成されたＮＨ３がＮＯｘを選択還元する。
また、下層２８の触媒活性成分で吸着したＮＯｘが下層２８から上層３０に向かい、上層３０を通る間にＳＣＲ材でＮＯｘを選択還元する。
さらに、下層２８の触媒活性成分で吸着したＨＣが下層２８から上層３０に向かい、上層３０を通る間に減少する。 When CO, HC, and NOx exist in the exhaust gas, NH 3 exists in the upstream portion of the first exhaust gas purification catalyst 20 by the reactions shown in the reaction formulas (1) to (5).
In the first exhaust gas purification catalyst 20, NH 3 and NOx present in the exhaust gas are reacted with the SCR material contained in the upper layer 30 to selectively reduce NOx. Further, HC and NOx adsorbed on the HC / NOx adsorbent carried on the lower layer 28 are desorbed as the exhaust gas temperature rises to promote the production of NH 3 . The produced NH 3 selectively reduces NOx.
Further, NOx adsorbed by the catalytically active component of the lower layer 28 is directed from the lower layer 28 to the upper layer 30 and is selectively reduced by the SCR material while passing through the upper layer 30.
Further, HC adsorbed by the catalytic active component of the lower layer 28 decreases from the lower layer 28 toward the upper layer 30 and passes through the upper layer 30.

例示的な実施形態では、図２に示すように、下層２８は排ガス上流側領域のみ（例えば、上流側略半分の領域）に設けられている。
例示的な実施形態では、下層２８及び上層３０は、夫々担持基材２４の容積１リットル当たり２０〜３００ｇの触媒活性成分を含む。 In the exemplary embodiment, as shown in FIG. 2, the lower layer 28 is provided only in the exhaust gas upstream side region (for example, the upstream substantially half region).
In the exemplary embodiment, lower layer 28 and upper layer 30 each comprise 20-300 g of catalytically active component per liter volume of support substrate 24.

例示的な実施形態では、図１に示すように、第１の排ガス浄化触媒２０の排ガス流れ方向上流側の排気管１８に、第２の排ガス浄化触媒３２を内蔵した触媒コンバータ３４が設けられる。
図２及び図３に示すように、第２の排ガス浄化触媒３２は、担持基材３６と、担持基材３６の表面に形成された触媒担持層３８と、触媒担持層３８に担持された触媒活性成分（不図示）で構成されている。
図示した実施形態では、担持基材３６はコーディエライト製や金属箔製のハニカム構造体で構成される。触媒担持層３８は、例えばＡｌ２Ｏ３、ＺｒＯ２、ＴｉＯ２、ＣｅＯ２のうち少なくとも１つを含む触媒活性主のサポート材料で構成される。
触媒担持層３８に担持される触媒活性成分は、排ガスに含まれるＨＣ及びＣＯを酸化すると共に、ＮＯｘを還元して低減する材料であり、いわゆる三元触媒を構成する触媒活性成分を含む。
内燃機関１１が車両に搭載される場合、第１の排ガス浄化触媒２０は例えば床下に配置され、第２の排ガス浄化触媒３２は例えば内燃機関１１の近傍に配置される。ただし、第１の排ガス浄化触媒２０と第２の排ガス浄化触媒３２の車両への搭載位置は、車両サイズにも依存するので種々考えられ、第１の排ガス浄化触媒２０が第２の排ガス浄化触媒３２の下流にあればよい。 In the exemplary embodiment, as shown in FIG. 1, a catalytic converter 34 incorporating a second exhaust gas purification catalyst 32 is provided in the exhaust pipe 18 upstream of the first exhaust gas purification catalyst 20 in the exhaust gas flow direction.
As shown in FIGS. 2 and 3, the second exhaust gas purification catalyst 32 includes a supporting substrate 36, a catalyst supporting layer 38 formed on the surface of the supporting substrate 36, and a catalyst supported on the catalyst supporting layer 38. It consists of active ingredients (not shown).
In the illustrated embodiment, the support substrate 36 is formed of a honeycomb structure made of cordierite or metal foil. The catalyst support layer 38 is made of, for example, a support material mainly having catalytic activity including at least one of Al 2 O 3 , ZrO 2 , TiO 2 , and CeO 2 .
The catalytically active component supported on the catalyst supporting layer 38 is a material that oxidizes HC and CO contained in the exhaust gas and reduces NOx to reduce it, and includes a catalytically active component that constitutes a so-called three-way catalyst.
When the internal combustion engine 11 is mounted on a vehicle, the first exhaust gas purification catalyst 20 is disposed, for example, under the floor, and the second exhaust gas purification catalyst 32 is disposed, for example, in the vicinity of the internal combustion engine 11. However, various mounting positions of the first exhaust gas purification catalyst 20 and the second exhaust gas purification catalyst 32 on the vehicle depend on the vehicle size, so that the first exhaust gas purification catalyst 20 is considered to be the second exhaust gas purification catalyst. 32 may be downstream.

例示的な実施形態では、図２及び図３に示すように、第２の排ガス浄化触媒３２の触媒担持層３８は、担持基材３６の表面に近い下層４０と、下層４０より相対的に遠い上層４２とで構成される。上層４２は触媒活性成分としてＲｈ（ロジウム）を含み、下層４０は触媒活性成分としてのＰｄ（パラジウム）と、助触媒として酸素の吸蔵及び放出能を有する触媒用酸素吸蔵材料（以下「ＯＳＣ材」とも言う。）を含む。ＯＳＣ材は例えばＣｅＯ２やＣｅＯ２−ＺｒＯ２を主成分とする複合酸化物を含む。
第２の排ガス浄化触媒３２では、上層４２に含まれるＲｈ及び下層４０に含まれるＰｄによって、排ガスｅに含まれるＨＣ及びＣＯを酸化し、ＮＯｘを還元してこれらを無害なＨ２Ｏ、ＣＯ２及びＮ２に変える。また、下層４０にＯＳＣ材を含むことで、空燃比が変動しても高い排ガス浄化効果を維持できる。なお、上層４２にはＰｔ、Ｐｄ、ＯＳＣ材を添加してもよく、下層４０にはＲｈ、Ｐｔを添加してもよい。 In the exemplary embodiment, as shown in FIGS. 2 and 3, the catalyst support layer 38 of the second exhaust gas purification catalyst 32 is a lower layer 40 close to the surface of the support substrate 36 and relatively far from the lower layer 40. The upper layer 42 is configured. The upper layer 42 includes Rh (rhodium) as a catalytic active component, and the lower layer 40 includes Pd (palladium) as a catalytic active component and a catalyst oxygen storage material (hereinafter referred to as “OSC material”) having oxygen storage and release capability as a promoter. Also called). The OSC material includes, for example, a composite oxide mainly composed of CeO 2 or CeO 2 —ZrO 2 .
In the second exhaust gas purification catalyst 32, Rh contained in the upper layer 42 and Pd contained in the lower layer 40 oxidize HC and CO contained in the exhaust gas e, reduce NOx, and remove these harmless H 2 O, CO change to 2 and N 2. Further, by including the OSC material in the lower layer 40, a high exhaust gas purification effect can be maintained even if the air-fuel ratio varies. Note that Pt, Pd, and OSC materials may be added to the upper layer 42, and Rh and Pt may be added to the lower layer 40.

例示的な実施形態では、図２及び図３に示すように、第２の排ガス浄化触媒３２の下層４０は、排ガス流れ上流側領域のみ（上流側略半分の領域）に設けられている。
例示的な実施形態では、第２の排ガス浄化触媒３２の上層４２は、担持基材３６も容積１リットル当たり０．１〜２．０ｇのＲｈを含み、下層４０は担持基材３６の容積１リットル当たり１〜１５ｇのＰｄと、ＣｅＯ２を主成分とする１〜８０ｇのＯＳＣ材とを含む。
例示的な実施形態では、図４及び図５に示すように、第２の排ガス浄化触媒３２の上層４２は、触媒活性成分の担持量が排ガス流れ上流側領域４２ａで排ガス流れ下流側領域４２ｂより多い。 In the exemplary embodiment, as shown in FIGS. 2 and 3, the lower layer 40 of the second exhaust gas purification catalyst 32 is provided only in the exhaust gas flow upstream side region (upstream substantially half region).
In the exemplary embodiment, the upper layer 42 of the second exhaust gas purification catalyst 32 also includes 0.1 to 2.0 g of Rh per liter of the supporting substrate 36, and the lower layer 40 has a volume 1 of the supporting substrate 36. 1 to 15 g of Pd per liter and 1 to 80 g of OSC material mainly composed of CeO 2 are included.
In the exemplary embodiment, as shown in FIGS. 4 and 5, the upper layer 42 of the second exhaust gas purification catalyst 32 has an amount of catalyst active component supported in the exhaust gas flow upstream region 42a than in the exhaust gas flow downstream region 42b. Many.

例示的な実施形態では、図１に示すように、第１の排ガス浄化触媒２０において、下層２８に含まれるＨＣ・ＮＯｘ吸着材が吸着したＨＣ及びＮＯｘを脱離させる工程（以下「脱離工程」とも言う。）で、内燃機関１１をリッチ燃焼に制御するための制御装置４４をさらに備える。
制御装置４４によって脱離工程で内燃機関１１をリッチ燃焼とすることで、排ガス中のＣＯやＨＣの量を増やすことができる。これによって、上記反応式（１）〜（５）から、第２の触媒下流の排ガス中に含まれるＮＨ３量が増え、増えたＮＨ３で下層２８から脱離したＮＯｘを低減できる。 In the exemplary embodiment, as shown in FIG. 1, the first exhaust gas purification catalyst 20 desorbs HC and NOx adsorbed by the HC / NOx adsorbent contained in the lower layer 28 (hereinafter referred to as “desorption step”). And a control device 44 for controlling the internal combustion engine 11 to rich combustion.
By making the internal combustion engine 11 rich combustion in the desorption process by the controller 44, the amount of CO and HC in the exhaust gas can be increased. Thereby, from the above reaction formulas (1) to (5), the amount of NH 3 contained in the exhaust gas downstream of the second catalyst is increased, and NOx desorbed from the lower layer 28 by the increased NH 3 can be reduced.

例示的な実施形態では、図１に示すように、第１の排ガス浄化触媒２０の入口に、第１の排ガス浄化触媒２０を通る排ガスの温度を検出するための温度センサ４６をさらに備える。制御装置４４は、温度センサ４６の検出値が閾値Ｔ１（図６参照）を超えた時、脱離工程が開始されたと判定し、内燃機関１１をリッチ燃焼に制御する。 In the exemplary embodiment, as shown in FIG. 1, a temperature sensor 46 for detecting the temperature of the exhaust gas passing through the first exhaust gas purification catalyst 20 is further provided at the inlet of the first exhaust gas purification catalyst 20. When the detected value of the temperature sensor 46 exceeds the threshold value T 1 (see FIG. 6), the control device 44 determines that the desorption process has started and controls the internal combustion engine 11 to rich combustion.

図６は内燃機関１１の稼動開始からの排ガス浄化プロセスを示している。横軸は稼動開始からの時間を示している。図において、内燃機関１１の稼動開始と共に第１の排ガス浄化触媒２０の下層２８でＨＣ及びＮＯｘの吸着工程が始まり、その後、第１の排ガス浄化触媒２０が閾値温度Ｔ１（例えば１５０℃）を超えると脱離工程が始まる。この脱離行程中のＨＣ、ＮＯｘが最も多く排出されるタイミングに空燃比をリッチ化することで，上流触媒３２でより多くのＮＨ３が生成されるので，触媒２０から脱離したＮＯｘの浄化効率が高まる。
図７は、内燃機関１１の稼動開始から２０秒後の触媒内部の温度を示している。図７から、稼動初期には、触媒担体の熱容量の影響で、触媒担体の入口領域と出口領域との間に大きな温度勾配を生じる。したがって、ＨＣ、ＣＯ、ＮＯｘが極めて多く排出される触媒の昇温過程においては、触媒担体の入口領域に触媒活性成分を高密度に担持することが排ガス低減に有効であることがわかる。
図８は、貴金属（ＰＧＭ）の触媒入口温度及び貴金属担持量に対する総ＨＣ量の浄化効率を示し、数値は貴金属担持量を示している。図８から、貴金属担持量が多く、かつ触媒温度が高いほど、触媒活性が優れる。したがって、ＨＣ、ＣＯ、ＮＯｘが極めて多く排出される触媒の昇温過程においては、排ガス浄化効率を高めるには、触媒活性主である貴金属の担持量を増大することが排ガス低減に有効であることがわかる。 FIG. 6 shows an exhaust gas purification process from the start of operation of the internal combustion engine 11. The horizontal axis indicates the time from the start of operation. In the figure, the HC and NOx adsorption process starts in the lower layer 28 of the first exhaust gas purification catalyst 20 with the start of operation of the internal combustion engine 11, and then the first exhaust gas purification catalyst 20 has a threshold temperature T 1 (for example, 150 ° C.). If exceeded, the desorption process begins. By enriching the air-fuel ratio at the timing when the largest amount of HC and NOx is discharged during this desorption process, more NH 3 is generated in the upstream catalyst 32, so the NOx desorbed from the catalyst 20 is purified. Increases efficiency.
FIG. 7 shows the temperature inside the catalyst 20 seconds after the start of operation of the internal combustion engine 11. From FIG. 7, at the initial stage of operation, a large temperature gradient is generated between the inlet region and the outlet region of the catalyst carrier due to the influence of the heat capacity of the catalyst carrier. Therefore, it can be seen that, in the process of raising the temperature of the catalyst from which a large amount of HC, CO, and NOx is discharged, it is effective in reducing exhaust gas to carry the catalyst active component at a high density in the inlet region of the catalyst carrier.
FIG. 8 shows the purification efficiency of the total HC amount with respect to the catalyst inlet temperature and the noble metal loading amount of noble metal (PGM), and the numerical value shows the noble metal loading amount. From FIG. 8, the catalytic activity is excellent as the amount of noble metal supported is large and the catalyst temperature is high. Therefore, in the process of raising the temperature of a catalyst that discharges a very large amount of HC, CO, and NOx, increasing the amount of noble metal supported, which is the main catalyst activity, is effective in reducing exhaust gas in order to increase the exhaust gas purification efficiency. I understand.

幾つかの実施形態によれば、図２及び図３に示すように、第１の排ガス浄化触媒２０では、排ガス中に存在するＮＯやＨＣ及び下層２８で吸着したＨＣからＮＨ３が生成され、生成したＮＨ３と排ガス中のＮＯｘとを反応させ、ＮＯｘを選択還元するので、ＮＯｘの浄化効率を向上できる。また、下層２８に吸着したＮＯｘが脱離して上層３０を通る間にＮＯｘの還元率を向上できる。さらに、下層２８に吸着したＨＣが脱離して上層３０を通る間にＨＣの酸化率を向上できる。
このように、ＮＯｘ、ＨＣ浄化効果を高め、且つ上下積層構造の触媒担持層を備えることで、排気管１８に直列に配置される触媒担体の数を低減できるため、触媒コストを削減できる。また、排ガス浄化効果を高めたことで、触媒担持層２６の膜厚を低減できるため、排ガスｅの圧力損失を抑制でき、これによって、内燃機関１１の性能低下を抑制できる。 According to some embodiments, as shown in FIGS. 2 and 3, the first exhaust gas purification catalyst 20 generates NH 3 from NO and HC present in the exhaust gas and HC adsorbed by the lower layer 28, Since the produced NH 3 reacts with NOx in the exhaust gas to selectively reduce NOx, the purification efficiency of NOx can be improved. Further, the NOx reduction rate can be improved while NOx adsorbed on the lower layer 28 is desorbed and passes through the upper layer 30. Furthermore, the HC oxidation rate can be improved while HC adsorbed on the lower layer 28 is desorbed and passes through the upper layer 30.
As described above, the NOx and HC purification effect is enhanced, and the number of catalyst carriers arranged in series in the exhaust pipe 18 can be reduced by providing the catalyst support layer having an upper and lower laminated structure, so that the catalyst cost can be reduced. Moreover, since the film thickness of the catalyst support layer 26 can be reduced by increasing the exhaust gas purification effect, the pressure loss of the exhaust gas e can be suppressed, and thereby the performance degradation of the internal combustion engine 11 can be suppressed.

例示的な実施形態によれば、図２及び図３に示すように、第１の排ガス浄化触媒２０の上流側に、いわゆる三元触媒と称される機能を有する第２の排ガス浄化触媒３２を設けることで、排ガス中のＨＣ、ＣＯ及びＮＯｘを同時に低減できる。こうして、第１の排ガス浄化触媒２０と第２の排ガス浄化触媒３２とを組み合わせることで、排ガス浄化性能の多機能化が可能になる。
例示的な実施形態によれば、第２の排ガス浄化触媒３２は、触媒活性成分として貴金属のなかで担持量当たりの触媒活性が最も優れるＲｈを含む上層４２と、触媒活性成分として比較的安価なＰｄを含む下層４０とで構成されるので、高い排ガス浄化性能を持ちつつ、触媒コストを抑えることができる。
また、第２の排ガス浄化触媒３２ではＲｈやＰｄ等の貴金属を担持した触媒担持層を積層させることで、反応式（１）〜（５）で示すＮＨ３生成反応も触媒コストを抑えた上で効率良く進行する。従って、第１の排ガス浄化触媒２０でＮＨ３が多く生成され、ここで生成されたＮＨ３が第１の排ガス浄化触媒２０でのＮＯｘの還元浄化に寄与する。
さらに、下層２８はＯＳＣ材を含むので、空燃比が変動しても高い排ガス浄化性能を維持できる。
これにより、排ガス浄化効果が向上するに伴って、第１の排ガス浄化触媒２０及び第２の排ガス浄化触媒３２の触媒担持層の膜厚を薄くできるため、特に、担持基材がハニカム構造体である場合などで、排ガスの圧力損失の増加を抑えることができる。 According to the exemplary embodiment, as shown in FIGS. 2 and 3, the second exhaust gas purification catalyst 32 having a function called a so-called three-way catalyst is provided upstream of the first exhaust gas purification catalyst 20. By providing, HC, CO, and NOx in exhaust gas can be reduced simultaneously. In this way, by combining the first exhaust gas purification catalyst 20 and the second exhaust gas purification catalyst 32, it is possible to make the exhaust gas purification performance multifunctional.
According to the exemplary embodiment, the second exhaust gas purification catalyst 32 includes an upper layer 42 containing Rh that has the highest catalytic activity per supported amount among noble metals as a catalytic active component, and a relatively inexpensive catalytic active component. Since it is comprised with the lower layer 40 containing Pd, the catalyst cost can be suppressed while having high exhaust gas purification performance.
Further, in the second exhaust gas purification catalyst 32, the catalyst supporting layer supporting a noble metal such as Rh or Pd is laminated, so that the NH 3 generation reaction represented by the reaction formulas (1) to (5) is also suppressed in the catalyst cost. And proceed efficiently. Accordingly, the NH 3 number generated by the first exhaust gas purifying catalyst 20, is NH 3 generated here contributes to reduction purification of NOx in the first exhaust gas purifying catalyst 20.
Furthermore, since the lower layer 28 contains the OSC material, high exhaust gas purification performance can be maintained even if the air-fuel ratio varies.
Thereby, as the exhaust gas purification effect is improved, the film thicknesses of the catalyst support layers of the first exhaust gas purification catalyst 20 and the second exhaust gas purification catalyst 32 can be reduced. In some cases, an increase in exhaust gas pressure loss can be suppressed.

例示的な実施形態によれば、第１の排ガス浄化触媒２０及び第２の排ガス浄化触媒３２において、下層２８及び４０は排ガス温度が高く排ガス浄化効果が大きい排ガス上流側領域のみに設けられるので、排ガス上流側領域では下層２８及び４０の存在により排ガス浄化効果を高めることができると共に、排ガス上流側領域ほど排ガス浄化効果が見込めない排ガス流れ下流側領域では、下層２８及び４０をなくすことで、触媒システムのコストをより効果的に低減できる。
例示的な実施形態によれば、第１の排ガス浄化触媒２０の上層３０及び下層２８では、夫々触媒活性成分の担持量を担持基材２４の容積１リットル当たり２０〜３００ｇとしたことで、ＮＯｘの浄化効果を維持しつつ、触媒担持層２６の膜厚を抑制できるので、排ガスｅの圧力損失を抑制できる。
第２の排ガス浄化触媒３２においても、上層４２の触媒活性成分であるＲｈの担持量を担持基材３８の容積１リットル当たり０．１〜２．０ｇとし、下層２８の触媒活性成分であるＰｄの担持量を同じく１〜１５ｇとし、ＯＳＣ材の担持量を同じく１〜８０ｇとしたことで、排ガス浄化効果を維持しつつ、触媒担持層３８の膜厚を抑制できるので、排ガスｅの圧力損失を抑制できる。 According to the exemplary embodiment, in the first exhaust gas purification catalyst 20 and the second exhaust gas purification catalyst 32, the lower layers 28 and 40 are provided only in the exhaust gas upstream region where the exhaust gas temperature is high and the exhaust gas purification effect is large. In the exhaust gas upstream region, the exhaust gas purification effect can be enhanced by the presence of the lower layers 28 and 40, and in the exhaust gas flow downstream region where the exhaust gas purification effect cannot be expected as much as in the exhaust gas upstream region, the lower layers 28 and 40 are eliminated. The cost of the system can be reduced more effectively.
According to the exemplary embodiment, in the upper layer 30 and the lower layer 28 of the first exhaust gas purification catalyst 20, the loading amount of the catalytically active component is 20 to 300 g per liter of the loading substrate 24, respectively. Since the film thickness of the catalyst support layer 26 can be suppressed while maintaining the purification effect, the pressure loss of the exhaust gas e can be suppressed.
Also in the second exhaust gas purification catalyst 32, the loading amount of Rh, which is the catalytic active component of the upper layer 42, is 0.1-2.0 g per liter of the volume of the supporting substrate 38, and Pd, which is the catalytic active component of the lower layer 28. Since the loading amount of the catalyst is set to 1 to 15 g and the loading amount of the OSC material is also set to 1 to 80 g, the film thickness of the catalyst supporting layer 38 can be suppressed while maintaining the exhaust gas purification effect. Can be suppressed.

例示的な実施形態によれば、図４及び図５に示すように、第２の排ガス浄化触媒３２の上層４２は、触媒活性成分の担持量を排ガス流れ上流側領域４２ａで排ガス流れ下流側領域４２ｂより多くしたので、排ガス浄化効果を維持しつつ触媒コストを低減できる。また，触媒担持層当たりのＮＨ３の生成能も高くすることができる。
例示的な実施形態によれば、第１の排ガス浄化触媒２０の下層２８で吸着したＨＣ及びＮＯｘの脱離工程で、制御装置４４により内燃機関１１をリッチ燃焼に制御することで、排ガス中に含まれるＮＨ３の量を増やし、ＮＨ３でＮＯｘを高効率で低減できる。
また、第１の排ガス浄化触媒２０の入口における排ガス温度を検出することで、ＨＣ及びＮＯｘの脱離工程の開始時期を正確に判定できる。 According to the exemplary embodiment, as shown in FIGS. 4 and 5, the upper layer 42 of the second exhaust gas purification catalyst 32 is configured so that the supported amount of the catalytic active component is in the exhaust gas flow upstream region 42 a and the exhaust gas flow downstream region. Since the amount is larger than 42b, the catalyst cost can be reduced while maintaining the exhaust gas purification effect. In addition, the ability to generate NH 3 per catalyst support layer can be increased.
According to the exemplary embodiment, in the process of desorbing HC and NOx adsorbed on the lower layer 28 of the first exhaust gas purification catalyst 20, the control device 44 controls the internal combustion engine 11 to rich combustion, thereby The amount of NH 3 contained can be increased, and NO 3 can be reduced with NH 3 with high efficiency.
Further, by detecting the exhaust gas temperature at the inlet of the first exhaust gas purification catalyst 20, the start timing of the HC and NOx desorption process can be accurately determined.

上記実施形態では、排ガス中の含まれるＮＨ３、特に第２の排ガス浄化触媒３２で生成するＮＨ３を用いて、第１の排ガス浄化触媒２０に流入するＮＯｘを選択還元浄化しているが、排ガス通路の外部からＮＨ３を供給するようにしてもよい。例えば、第１の排ガス浄化触媒２０と第２の排ガス浄化触媒３２との間の排ガス通路に外部から尿素水溶液を供給するようにしてもよい。 In the above embodiment, NH 3 contained in exhaust gas, in particular with a NH 3 produced in the second exhaust gas purifying catalyst 32, although selective reduction purification of NOx flowing into the first exhaust gas purifying catalyst 20, NH 3 may be supplied from the outside of the exhaust gas passage. For example, an aqueous urea solution may be supplied from the outside to the exhaust gas passage between the first exhaust gas purification catalyst 20 and the second exhaust gas purification catalyst 32.

本発明の少なくとも一実施形態によれば、内燃機関の排ガス通路を流れる排ガスの圧力損失を低減して内燃機関の効率を向上できると共に、触媒コストを削減できる。   According to at least one embodiment of the present invention, the pressure loss of the exhaust gas flowing through the exhaust gas passage of the internal combustion engine can be reduced to improve the efficiency of the internal combustion engine, and the catalyst cost can be reduced.

１０ 排ガス浄化システム
１１ 内燃機関
１２ 排気ポート
１４ 排気マニフォールド
１６ 排気過給機
１６ａ タービンハウジング
１８ 排気管
２０ 第１の排ガス浄化触媒
２２、３４ 触媒コンバータ
２４、３６ 担持基材
２６、３８ 触媒担持層
２８、４０ 下層
３０、４２ 上層
４２ａ 排ガス流れ上流側領域
４２ｂ 排ガス流れ下流側領域
３２ 第２の排ガス浄化触媒
４４ 制御装置
４６ 温度センサ
ｅ 排ガス DESCRIPTION OF SYMBOLS 10 Exhaust gas purification system 11 Internal combustion engine 12 Exhaust port 14 Exhaust manifold 16 Exhaust supercharger 16a Turbine housing 18 Exhaust pipe 20 1st exhaust gas purification catalyst 22, 34 Catalytic converter 24, 36 Support base material 26, 38 Catalyst support layer 28, 40 Lower layer 30, 42 Upper layer 42a Exhaust gas flow upstream region 42b Exhaust gas flow downstream region 32 Second exhaust gas purification catalyst 44 Controller 46 Temperature sensor e Exhaust gas

Claims (9)

排ガス通路に、担持基材と、該担持基材の表面に形成された触媒担持層と、該触媒担持層に担持された触媒活性成分とで構成された排ガス浄化触媒を備えた内燃機関の排ガス浄化システムにおいて、
前記排ガス通路に第１の排ガス浄化触媒を備え、
前記第１の排ガス浄化触媒の前記触媒担持層は、前記担持基材の表面に近い下層と該下層より相対的に遠い上層とで構成され、
前記上層の前記触媒活性成分は、排ガス中に含まれるＮＨ３で排ガス中のＮＯｘを選択還元する材料を含み、
前記下層の前記触媒活性成分は、ＨＣ及びＮＯｘを吸着可能な材料を含むことを特徴とする内燃機関の排ガス浄化システム。 Exhaust gas of an internal combustion engine provided with an exhaust gas purification catalyst comprising a support base, a catalyst support layer formed on the surface of the support base, and a catalytically active component supported on the catalyst support layer in an exhaust gas passage In the purification system,
The exhaust gas passage includes a first exhaust gas purification catalyst,
The catalyst support layer of the first exhaust gas purification catalyst is composed of a lower layer close to the surface of the support substrate and an upper layer relatively far from the lower layer,
The catalytic active component of the upper layer includes a material that selectively reduces NOx in the exhaust gas with NH 3 contained in the exhaust gas,
The exhaust gas purification system for an internal combustion engine, wherein the catalytically active component in the lower layer contains a material capable of adsorbing HC and NOx. 前記第１の排ガス浄化触媒より上流側の前記排ガス通路に、担持基材と、該担持基材の表面に形成された触媒担持層と、該触媒担持層に担持された触媒活性成分とで構成された第２の排ガス浄化触媒を備え、
前記第２の排ガス浄化触媒の前記触媒活性成分は、排ガス中のＨＣ及びＣＯを酸化すると共に、ＮＯｘを還元して低減する材料を含むことを特徴とする請求項１に記載の内燃機関の排ガス浄化システム。 The exhaust gas passage on the upstream side of the first exhaust gas purification catalyst includes a supporting base material, a catalyst supporting layer formed on the surface of the supporting base material, and a catalytically active component supported on the catalyst supporting layer. A second exhaust gas purification catalyst,
2. The exhaust gas of an internal combustion engine according to claim 1, wherein the catalytically active component of the second exhaust gas purification catalyst contains a material that oxidizes HC and CO in the exhaust gas and reduces NOx to reduce it. Purification system. 前記第２の排ガス浄化触媒の前記触媒担持層は、前記担持基材の表面に近い下層と該下層より相対的に遠い上層とで構成され、
前記上層の前記触媒活性成分はＲｈを含み、
前記下層の前記触媒活性成分はＰｄ及び触媒用酸素吸蔵材料を含むことを特徴とする請求項２に記載の内燃機関の排ガス浄化システム。 The catalyst supporting layer of the second exhaust gas purification catalyst is composed of a lower layer close to the surface of the supporting substrate and an upper layer relatively far from the lower layer,
The catalytically active component of the upper layer comprises Rh;
The exhaust gas purification system for an internal combustion engine according to claim 2, wherein the catalytically active component in the lower layer contains Pd and an oxygen storage material for catalyst. 前記第２の排ガス浄化触媒の前記下層は、排ガス流れ上流側領域のみに設けられていることを特徴とする請求項３に記載の内燃機関の排ガス浄化システム。   The exhaust gas purification system for an internal combustion engine according to claim 3, wherein the lower layer of the second exhaust gas purification catalyst is provided only in an upstream region of the exhaust gas flow. 前記第２の排ガス浄化触媒の前記上層は、前記触媒活性成分の担持量が排ガス流れ上流側領域で排ガス流れ下流側領域より多いことを特徴とする請求項３又は４に記載の内燃機関の排ガス浄化システム。   The exhaust gas of the internal combustion engine according to claim 3 or 4, wherein the upper layer of the second exhaust gas purification catalyst has a larger amount of the catalytic active component supported in the exhaust gas flow upstream region than in the exhaust gas flow downstream region. Purification system. 前記第１の排ガス浄化触媒において、前記下層に含まれる前記触媒活性成分が吸着したＨＣ及びＮＯｘを脱離させる工程で、内燃機関をリッチ燃焼に制御するための制御装置をさらに備えることを特徴とする請求項１乃至５の何れか１項に記載の内燃機関の排ガス浄化システム。   The first exhaust gas purification catalyst further comprises a control device for controlling the internal combustion engine to rich combustion in the step of desorbing HC and NOx adsorbed by the catalytically active component contained in the lower layer. The exhaust gas purification system for an internal combustion engine according to any one of claims 1 to 5. 前記第１の排ガス浄化触媒を通る排ガスの温度を検出するための温度センサをさらに備え、
前記制御装置は、前記温度センサの検出値が閾値を超えた時、ＨＣ及びＮＯｘの脱離工程であると判定し、前記内燃機関をリッチ燃焼に制御することを特徴とする請求項６に記載の内燃機関の排ガス浄化システム。 A temperature sensor for detecting the temperature of the exhaust gas passing through the first exhaust gas purification catalyst;
7. The control device according to claim 6, wherein when the detected value of the temperature sensor exceeds a threshold value, the control device determines that it is a HC and NOx desorption process and controls the internal combustion engine to rich combustion. Exhaust gas purification system for internal combustion engines. 担持基材と、該担持基材の表面に形成された触媒担持層と、該触媒担持層に担持された触媒活性成分とで構成された排ガス浄化触媒において、
前記触媒担持層は、前記担持基材の表面に近い下層と該下層より相対的に遠い上層とで構成され、
前記上層の前記触媒活性成分は、排ガス中に含まれるＮＨ３で排ガス中のＮＯｘを選択還元する材料を含み、
前記下層の前記触媒活性成分は、ＨＣ及びＮＯｘを吸着可能な材料を含むことを特徴とする排ガス浄化触媒。 In an exhaust gas purification catalyst comprising a supporting substrate, a catalyst supporting layer formed on the surface of the supporting substrate, and a catalytically active component supported on the catalyst supporting layer,
The catalyst support layer is composed of a lower layer close to the surface of the support substrate and an upper layer relatively far from the lower layer,
The catalytic active component of the upper layer includes a material that selectively reduces NOx in the exhaust gas with NH 3 contained in the exhaust gas,
The exhaust gas purifying catalyst, wherein the catalytically active component in the lower layer contains a material capable of adsorbing HC and NOx. 前記下層は排ガス流れ上流側領域のみに設けられていることを特徴とする請求項８に記載の排ガス浄化触媒。
The exhaust gas purifying catalyst according to claim 8, wherein the lower layer is provided only in a region upstream of the exhaust gas flow.
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