JP4770132B2 - HC adsorption catalyst and exhaust gas purification apparatus using the same - Google Patents
HC adsorption catalyst and exhaust gas purification apparatus using the same Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims description 113
- 238000001179 sorption measurement Methods 0.000 title claims description 57
- 238000000746 purification Methods 0.000 title claims description 41
- 229910000510 noble metal Inorganic materials 0.000 claims description 41
- 239000007789 gas Substances 0.000 claims description 37
- 229910052760 oxygen Inorganic materials 0.000 claims description 27
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 26
- 239000001301 oxygen Substances 0.000 claims description 26
- 239000003463 adsorbent Substances 0.000 claims description 10
- 239000011232 storage material Substances 0.000 claims description 5
- 229910052763 palladium Inorganic materials 0.000 claims description 4
- 229910052697 platinum Inorganic materials 0.000 claims description 4
- 229910052703 rhodium Inorganic materials 0.000 claims description 4
- 238000002485 combustion reaction Methods 0.000 claims description 3
- 230000007423 decrease Effects 0.000 claims description 3
- 230000003247 decreasing effect Effects 0.000 claims description 3
- 238000011144 upstream manufacturing Methods 0.000 claims description 3
- 239000003795 chemical substances by application Substances 0.000 description 21
- 238000007254 oxidation reaction Methods 0.000 description 12
- 230000003647 oxidation Effects 0.000 description 11
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 9
- 238000003795 desorption Methods 0.000 description 5
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 description 4
- 229910021536 Zeolite Inorganic materials 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000002950 deficient Effects 0.000 description 3
- 230000006866 deterioration Effects 0.000 description 3
- 238000010586 diagram Methods 0.000 description 3
- 239000010457 zeolite Substances 0.000 description 3
- 229910002091 carbon monoxide Inorganic materials 0.000 description 2
- 229910052878 cordierite Inorganic materials 0.000 description 2
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 2
- 239000000463 material Substances 0.000 description 2
- 239000010970 precious metal Substances 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 206010021143 Hypoxia Diseases 0.000 description 1
- 230000033228 biological regulation Effects 0.000 description 1
- 239000000919 ceramic Substances 0.000 description 1
- 230000002542 deteriorative effect Effects 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- 238000010030 laminating Methods 0.000 description 1
- 238000004519 manufacturing process Methods 0.000 description 1
- 238000000034 method Methods 0.000 description 1
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- 230000000717 retained effect Effects 0.000 description 1
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Description
本発明は、ＨＣ吸着触媒及びこれを用いた排気ガス浄化装置に関する。 The present invention relates to an HC adsorption catalyst and an exhaust gas purification apparatus using the same.
エンジン等から排出される排気ガスには、ＨＣ（炭化水素）、ＮＯｘ（窒素酸化物）、ＣＯ（一酸化炭素）等の成分が含まれる。近年の排ガス規制強化に伴い、これらの成分を効果的に浄化するため、高い浄化性能を有する排気ガス浄化装置の開発が要求されている。 The exhaust gas discharged from the engine or the like includes components such as HC (hydrocarbon), NOx (nitrogen oxide), and CO (carbon monoxide). With the recent tightening of exhaust gas regulations, development of exhaust gas purification devices having high purification performance is required to effectively purify these components.
特に、排ガス中のＨＣは、エンジンの始動時等のような排ガス温度が低い場合（約３００℃未満）には、排気ガス浄化装置で浄化されにくく、ＨＣを大量に含んだままの排気ガスが放出されてしまう。そこで、排気ガス浄化装置に各種のゼオライト（ＦＥＲ型、ＭＯＲ型、ＦＡＵ型、ＭＦＩ型、β型ゼオライトなど）からなるＨＣ吸着剤を設け、低温時にはＨＣを吸着・保持する一方、高温時には吸着・保持したＨＣを放出すると同時に浄化することにより、排気ガスを確実に処理する技術も開発されている。 In particular, when the exhaust gas temperature is low (less than about 300 ° C.), such as when the engine is started, HC in the exhaust gas is not easily purified by the exhaust gas purification device, and the exhaust gas containing a large amount of HC It will be released. Therefore, an HC adsorbent made of various types of zeolite (FER type, MOR type, FAU type, MFI type, β type zeolite, etc.) is provided in the exhaust gas purification device, and adsorbs and holds HC at low temperatures, while adsorbing and holding at high temperatures. A technology has also been developed for reliably treating exhaust gas by releasing and purifying the retained HC.
実用上は、ＨＣを浄化する排気ガス浄化装置内の三元触媒等が適正に機能する温度まで昇温して、活性化した後に、ＨＣ吸着剤からＨＣが脱離し始めることが望ましいので、ＨＣ吸着剤に用いられているゼオライトに種々の条件を付加し、ＨＣ吸着剤の最適化を図った排気ガス浄化装置が開発されている（下記、特許文献１を参照。）。 In practice, it is desirable that HC starts to be desorbed from the HC adsorbent after the temperature is raised to a temperature at which the three-way catalyst or the like in the exhaust gas purification device for purifying HC functions properly and activated. An exhaust gas purifying apparatus has been developed in which various conditions are added to the zeolite used for the adsorbent to optimize the HC adsorbent (see Patent Document 1 below).
しかしながら、三元触媒等をエンジンの排気ガス用として使用するには、ＨＣの浄化（酸化）時における酸素の利用効率が低いため、浄化が十分進まないなどの問題がある。また、酸素の供給量不足を補うため、単に多量のＯＳＣ（酸素ストレージ機能）剤を担持させることも可能であるが、触媒を劣化させてしまう結果、触媒の耐熱性に問題がでる場合がある。 However, in order to use a three-way catalyst or the like for engine exhaust gas, there is a problem that the purification does not proceed sufficiently because the use efficiency of oxygen at the time of HC purification (oxidation) is low. In addition, in order to compensate for the shortage of oxygen supply, it is possible to simply carry a large amount of OSC (oxygen storage function) agent, but as a result of deteriorating the catalyst, there may be a problem in the heat resistance of the catalyst. .
また、一般に、触媒はコージェライト等のセラミックの担体と、それに担持された貴金属とから構成される。ここで、触媒の浄化性能は、触媒担体に担持された貴金属の量に依存する。しかしながら、触媒に使用する貴金属は量的に貴重な資源であると共に、これを多量に使用することは製品としての排気ガス浄化触媒のコスト増加を招く。 In general, the catalyst is composed of a ceramic carrier such as cordierite and a noble metal supported thereon. Here, the purification performance of the catalyst depends on the amount of the noble metal supported on the catalyst carrier. However, the noble metal used for the catalyst is a valuable resource in quantitative terms, and the use of a large amount of this causes an increase in the cost of the exhaust gas purification catalyst as a product.
本発明は上記状況に鑑みてなされたもので、使用するＯＳＣ剤及び貴金属触媒を最適な担持構造とすることにより、耐熱性及び排気ガス浄化性能を向上させたＨＣ吸着触媒及びこれを用いた排気ガス浄化装置、移動手段を提供することを目的とする。 The present invention has been made in view of the above situation, and an HC adsorption catalyst having improved heat resistance and exhaust gas purification performance by using an OSC agent and a noble metal catalyst to be used in an optimal support structure, and an exhaust using the same. It is an object of the present invention to provide a gas purification device and moving means.
上記課題を解決する本発明に係るＨＣ吸着触媒は、
担体と、当該担体上に担持されたＨＣ吸着剤、酸素ストレージ剤及び貴金属触媒とを有するＨＣ吸着触媒において、
前記酸素ストレージ剤は、前記ＨＣ吸着触媒の入口側から出口側に向かって、担持濃度が高くなるように漸増して担持され、
前記貴金属触媒は、前記ＨＣ吸着触媒の入口側から出口側に向かって、貴金属の担持濃度が低くなるように漸減して担持されている
ことを特徴とするＨＣ吸着触媒である。
The HC adsorption catalyst according to the present invention that solves the above problems is
In an HC adsorption catalyst having a carrier and an HC adsorbent, an oxygen storage agent and a noble metal catalyst supported on the carrier,
The oxygen storage agent is gradually supported from the inlet side to the outlet side of the HC adsorption catalyst so as to increase the supporting concentration,
The HC adsorption catalyst is characterized in that the noble metal catalyst is supported while being gradually decreased from the inlet side to the outlet side of the HC adsorption catalyst so that the concentration of the noble metal supported decreases .
酸素ストレージ剤（ＯＳＣ剤）を触媒の後段ほど多く担持させて、後段の酸素貯蔵量を確保し、ＨＣ脱離時の酸化用酸素が不足することを防止する。また、酸素不足を補うため、多量のＯＳＣ剤を担持させるのではなく、上記効率的な担持形態として、ＯＳＣ剤の使用量を抑制し、触媒の劣化を防止する。 A larger amount of oxygen storage agent (OSC agent) is supported in the subsequent stage of the catalyst to secure the subsequent oxygen storage amount and prevent the oxygen for oxidization from deficient during HC desorption. In addition, in order to compensate for the lack of oxygen, a large amount of OSC agent is not supported, but the amount of the OSC agent used is suppressed as the above efficient support form to prevent catalyst deterioration.
貴金属触媒を触媒の前段ほど多く担持させることにより、触媒の前段付近では高い貴金属担持濃度とし、早期に着火させて脱離したＨＣを浄化する。また、高価な貴金属を効率よく使用する。 By carrying a larger amount of the noble metal catalyst in the previous stage of the catalyst, a higher noble metal loading concentration is provided in the vicinity of the previous stage of the catalyst, and the HC that has been desorbed by early ignition is purified. Moreover, expensive noble metals are used efficiently.
また、上記ＨＣ吸着触媒において、
前記貴金属触媒は、Ｐｔ，Ｒｈ，Ｐｄのうち少なくとも一種類の貴金属を含有することを特徴とするＨＣ吸着触媒である。
酸化性能の高いＰｔ，Ｒｈ，Ｐｄを用いることで、浄化効率が向上する。
In the HC adsorption catalyst,
The noble metal catalyst is an HC adsorption catalyst characterized by containing at least one kind of noble metal among Pt, Rh, and Pd.
By using Pt, Rh, Pd having high oxidation performance, purification efficiency is improved.
上記課題を解決する本発明に係る排気ガス浄化装置は、
内燃機関の排気通路に設けられ、排気方向の上流側に設置される三元触媒と、排気ガスの下流側に設置される上記ＨＣ吸着触媒とを有することを特徴とする排気ガス浄化装置である。
An exhaust gas purification apparatus according to the present invention that solves the above problems is
An exhaust gas purification apparatus comprising a three-way catalyst provided in an exhaust passage of an internal combustion engine and installed upstream in an exhaust direction and the HC adsorption catalyst installed downstream of exhaust gas .
上記本発明によれば、ＨＣ吸着剤から脱離するＨＣを浄化するのに十分な酸素を確保することができ、また、高価な貴金属を効率よく使用することができる。また、酸素不足を補うと共に、ＯＳＣ剤の使用量を抑制して、触媒の劣化を防ぐことができる。 According to the present invention, oxygen sufficient to purify HC desorbed from the HC adsorbent can be secured, and expensive noble metals can be used efficiently. In addition, oxygen shortage can be compensated and the amount of OSC agent used can be suppressed to prevent catalyst deterioration.
以下、図面に基づいて本発明の実施形態を具体的に説明するが、以下の実施形態は本発明を限定するものではない。図１は、本発明の実施形態に係る排気ガス浄化装置を示す概略構成図である。 Hereinafter, embodiments of the present invention will be specifically described with reference to the drawings. However, the following embodiments do not limit the present invention. FIG. 1 is a schematic configuration diagram showing an exhaust gas purifying apparatus according to an embodiment of the present invention.
図１に示すように、実施形態に係る排気ガス浄化装置１０は、内燃機関であるエンジン１００に連結された排気通路１０１の途中に設けられている。排気ガス浄化装置１０は、ケーシング１１と、ケーシング１１内における排気ガス流通方向の上流側に設けられた三元触媒１２と、ケーシング１１内における排気ガス流通方向の下流側に設けられたＨＣ吸着触媒１３とからなる。
As shown in FIG. 1, an exhaust
三元触媒１２は、排気ガス中のＣＯ，ＮＯｘ，ＨＣ等の成分をＨ2Ｏ，ＣＯ2，Ｎ2に酸化して、処理する機能を有する触媒である。ＨＣ吸着触媒１３は、規定温度未満の低温時（例えば、約１５０℃未満）にＨＣを吸着・保持する一方、規定温度以上の高温時（例えば、約１５０℃以上）にＨＣを放出すると同時に酸化処理する機能を有する触媒である。
The three-
図２は、本発明の実施形態に係る排気ガス浄化装置内のＨＣ吸着触媒を示す概略断面構造図である。同図には、ＨＣ吸着触媒１３のセル構造の一部を断面図にて示してある。同図に示すように、ＨＣ吸着触媒１３は、セル格子を形成する担体１３ａの表面にＨＣ吸着層１３ｂ及び三元触媒層１３ｃが積層されてなる。
FIG. 2 is a schematic sectional view showing an HC adsorption catalyst in the exhaust gas purifying apparatus according to the embodiment of the present invention. In the figure, a part of the cell structure of the
担体１３ａとしては、コージライト製ハニカムを採用し、ＨＣ吸着層１３ｂとしては、異なる径を有する細孔が内部で交差するゼオライト構造を有する材料で形成した。また、三元触媒層１３ｃとしては、三元触媒１２と同様に三元浄化機能を有する貴金属触媒と、これに含有させたＯＳＣ剤とから形成した。
A cordierite honeycomb was employed as the carrier 13a, and the HC adsorption layer 13b was formed of a material having a zeolite structure in which pores having different diameters intersected inside. In addition, the three-way catalyst layer 13c was formed from a noble metal catalyst having a three-way purification function similarly to the three-
三元触媒層１３ｃに含まれる貴金属触媒は、Ｐｔ，Ｒｈ，Ｐｄの少なくとも一種類以上の貴金属を用い、主として、排気ガスの温度が規定温度以上の高温時（例えば、約１５０℃以上）にＨＣ吸着層１３ｂから放出されるＨＣを浄化する機能を有するが、さらに、三元触媒１２を補助する機能も有する。
The noble metal catalyst included in the three-way catalyst layer 13c uses at least one kind of noble metal of Pt, Rh, Pd, and mainly HC when the temperature of the exhaust gas is higher than a specified temperature (for example, about 150 ° C. or higher). Although it has a function of purifying HC released from the adsorption layer 13b, it also has a function of assisting the three-
図３は、ＨＣ吸着触媒における貴金属及びＯＳＣ剤の担持濃度を示すグラフである。同図に示すように、本実施形態では、ＨＣ吸着触媒１３における排気ガスの入口側から出口側に向かって、担持させる貴金属触媒及びＯＳＣ剤の濃度を変化させた。
FIG. 3 is a graph showing the supported concentrations of noble metal and OSC agent in the HC adsorption catalyst. As shown in the figure, in the present embodiment, the concentrations of the noble metal catalyst and the OSC agent to be supported are changed from the exhaust gas inlet side to the outlet side of the
すなわち、三元触媒である貴金属触媒については、入口側から出口側に向かって担持濃度が徐々に小さくなるようにして担持させた。例えば、入口側を５ｇ／ｌの担持濃度とし、出口側を３ｇ／ｌの担持濃度となるように変化させた。 That is, the noble metal catalyst, which is a three-way catalyst, was supported so that the supported concentration gradually decreased from the inlet side toward the outlet side. For example, the loading concentration was changed to 5 g / l on the inlet side and the loading concentration on the outlet side was 3 g / l.
また、ＯＳＣ剤については、入口側から出口側に向かって担持濃度が徐々に大きくなるようにして担持させた。例えば、入口側を２０ｇ／ｌの担持濃度とし、出口側を４０ｇ／ｌの担持濃度となるように変化させた。なお、ＨＣ吸着層１３ｂを形成するＨＣ吸着剤については、入口側から出口側に至るまで均一の構成とした。 In addition, the OSC agent was supported so that the supported concentration gradually increased from the inlet side toward the outlet side. For example, the loading concentration was changed to 20 g / l on the inlet side and the loading concentration on the outlet side was 40 g / l. The HC adsorbent that forms the HC adsorption layer 13b has a uniform configuration from the inlet side to the outlet side.
次に、本実施形態に係るＨＣ吸着触媒について、貴金属触媒及びＯＳＣ剤を上述する担持濃度とした理由について詳細に説明する。まず、比較例に係るＨＣ吸着触媒として、触媒の入口側から出口側までＨＣ吸着剤、貴金属触媒及びＯＳＣ剤、すべて均一の構成とし、貴金属の担持濃度を５ｇ／ｌ、３ｇ／ｌとした２種類のＨＣ吸着触媒を用意した。次に、比較例に係るＨＣ吸着触媒をエンジンの排気経路に設置し、エンジン運転開始から所定時間（暖機運転終了まで）、ＨＣ吸着触媒通過後の排気ガス中のＨＣ濃度を測定した。 Next, in the HC adsorption catalyst according to the present embodiment, the reason why the noble metal catalyst and the OSC agent are used in the above-described supported concentration will be described in detail. First, as the HC adsorption catalyst according to the comparative example, the HC adsorbent, the noble metal catalyst, and the OSC agent are all uniform from the inlet side to the outlet side of the catalyst, and the noble metal loading concentration is 5 g / l, 3 g / l. Various types of HC adsorption catalysts were prepared. Next, the HC adsorption catalyst according to the comparative example was installed in the exhaust path of the engine, and the HC concentration in the exhaust gas after passing through the HC adsorption catalyst was measured for a predetermined time (until the end of the warm-up operation) from the start of engine operation.
図４は、ＨＣ吸着触媒における貴金属の担持量を変化させたときの排出ＨＣ濃度を示すグラフであり、上述する比較例に係る２種類のＨＣ吸着触媒の浄化性能の結果を示している。同図において、「３ｇ／ｌ」で示す点線は、貴金属の担持濃度が３ｇ／ｌのＨＣ吸着触媒のＨＣ浄化性能を示し、「５ｇ／ｌ」で示す点線は、貴金属の担持濃度が５ｇ／ｌのＨＣ吸着触媒のＨＣ浄化性能を示している。また、横軸はエンジンの運転時間、換言すれば、排気ガス温度を示し、右になるほど長い運転時間、高い排気ガス温度となる。 FIG. 4 is a graph showing the exhaust HC concentration when the amount of noble metal supported on the HC adsorption catalyst is changed, and shows the results of the purification performance of the two types of HC adsorption catalysts according to the comparative example described above. In the figure, a dotted line indicated by “3 g / l” indicates the HC purification performance of the HC adsorption catalyst having a noble metal loading concentration of 3 g / l, and a dotted line indicated by “5 g / l” indicates a noble metal loading concentration of 5 g / l. 1 shows the HC purification performance of 1 HC adsorption catalyst. Further, the horizontal axis indicates the engine operating time, in other words, the exhaust gas temperature, and the longer the right side, the longer the operating time and the higher the exhaust gas temperature.
同図から、担持濃度が高い５ｇ／ｌのＨＣ吸着触媒では、運転開始直後はＨＣ吸着によりＨＣの排出濃度は低い。その後、ＨＣの脱離が開始される暖機運転前半にはＨＣ排出濃度が比較的低く、ＨＣ浄化（酸化）が効果的に行われていることが分かるが、更に運転時間が経過したとき（暖機運転の後半）にはＨＣ排出濃度が比較的高く、ＨＣ浄化（酸化）が効果的に行われていないことが分かる。 From the figure, in the 5 g / l HC adsorption catalyst having a high loading concentration, immediately after the start of operation, the HC emission concentration is low due to HC adsorption. Thereafter, it can be seen that the HC emission concentration is relatively low in the first half of the warm-up operation when HC desorption starts, and that HC purification (oxidation) is effectively performed, but when the operation time has passed ( It can be seen that in the latter half of the warm-up operation, the HC emission concentration is relatively high and HC purification (oxidation) is not effectively performed.
一方、担持濃度が低い３ｇ／ｌのＨＣ吸着触媒では、運転開始直後は５ｇ／ｌのときと同様、ＨＣ吸着によりＨＣの排出濃度は低い。その後、暖機運転前半にはＨＣ排出濃度が比較的高く、ＨＣ浄化（酸化）が効果的に行われていないことが分かるが、更に運転時間が経過したとき（暖機運転の後半）にはＨＣ排出濃度が比較的低く、ＨＣ浄化（酸化）が効果的に行われていることが分かる。 On the other hand, with a 3 g / l HC adsorption catalyst with a low loading concentration, the HC emission concentration is low due to HC adsorption just as at 5 g / l immediately after the start of operation. Thereafter, it can be seen that the HC emission concentration is relatively high in the first half of the warm-up operation and HC purification (oxidation) is not effectively performed, but when the operation time has passed (the second half of the warm-up operation) It can be seen that the HC emission concentration is relatively low and HC purification (oxidation) is effectively performed.
上述するように貴金属の担持濃度によって、運転開始初期に有利なＨＣ吸着触媒となるか、また、運転開始から所定期間経過後に有利なＨＣ吸着触媒となるか、分かれるが、いずれのＨＣ吸着触媒であっても、テスト期間内の全ＨＣ浄化量はほぼ同じであった（図５を参照。）。 As described above, depending on the noble metal loading concentration, it may be an advantageous HC adsorption catalyst at the beginning of operation or an advantageous HC adsorption catalyst after a predetermined period from the start of operation. Even in such a case, the total HC purification amount within the test period was almost the same (see FIG. 5).
上述する結果は、触媒中の酸素の使われ方が異なるためと考えられる。すわなち、担持濃度が高い５ｇ／ｌのＨＣ吸着触媒では、触媒の入口側でＨＣの脱離が開始される暖機運転前半に貴金属の濃度の高さから効果的にＨＣ浄化（酸化）が行われる結果、触媒の出口側で脱離が開始される暖気運転後半で入口側の酸素消費によりＯＳＣの酸素ストレージが活発なため出口側で酸素欠乏状態となり、ＨＣ浄化（酸化）が効果的に行われない結果となったと考えられる。 The above results are considered to be due to the difference in the use of oxygen in the catalyst. In other words, with a 5 g / l HC adsorption catalyst with a high loading concentration, HC purification (oxidation) is effectively performed from the high precious metal concentration in the first half of the warm-up operation when HC desorption starts on the catalyst inlet side. As a result, in the latter half of the warm-up operation where desorption starts on the catalyst outlet side, oxygen storage on the OSC is active due to oxygen consumption on the inlet side, so that the outlet side becomes oxygen-deficient and HC purification (oxidation) is effective. It is thought that the result was not performed.
一方、担持濃度が低い３ｇ／ｌのＨＣ吸着触媒では、暖機運転前半には触媒濃度の低さからＨＣ浄化（酸化）が効果的に行われない結果、５ｇ／ｌと比較して浄化率は劣るが、暖機運転後半では入口側で消費されていない残存する酸素で出口側に酸素が供給され、ＨＣ浄化（酸化）が効果的に行われる結果となったと考えられる。 On the other hand, in the HC adsorption catalyst having a low supported concentration of 3 g / l, the HC purification (oxidation) is not effectively performed due to the low catalyst concentration in the first half of the warm-up operation. As a result, the purification rate compared with 5 g / l However, in the latter half of the warm-up operation, the remaining oxygen that is not consumed on the inlet side is supplied with oxygen to the outlet side, which is considered to result in effective HC purification (oxidation).
したがって、高効率のＨＣ浄化性能を有するＨＣ吸着触媒とするためには、貴金属の担持濃度と酸素の残存量との関係が重要となる。更に、触媒の製造コストを低減させるためにも、単に貴金属触媒の担持濃度を大きくするだけではなく、貴金属触媒についてもその担持構造を最適なものとする必要がある。 Therefore, in order to obtain an HC adsorption catalyst having a highly efficient HC purification performance, the relationship between the noble metal loading concentration and the remaining amount of oxygen is important. Furthermore, in order to reduce the manufacturing cost of the catalyst, it is necessary not only to increase the support concentration of the noble metal catalyst but also to optimize the support structure of the noble metal catalyst.
そこで、本実施形態に係るＨＣ吸着触媒では、上述するＯＳＣ剤及び貴金属触媒の担持構造とした。すなわち、ＯＳＣ剤については触媒の後段ほど多く担持させ、触媒出口側の酸素欠乏を解消し、貴金属触媒については触媒の前段ほど多く担持させ、浄化効率を向上させた。 Therefore, the HC adsorption catalyst according to the present embodiment has the above-described support structure for the OSC agent and the noble metal catalyst. In other words, the OSC agent was supported in the later stage of the catalyst to eliminate oxygen deficiency on the catalyst outlet side, and the precious metal catalyst was supported in the earlier stage of the catalyst to improve the purification efficiency.
このような担持構造とすることにより、図４において、本発明の指す浄化特性カーブから分かるように、暖気運転前半から後半まで、従来のＨＣ吸着触媒よりも高い浄化性能を有するＨＣ吸着触媒とすることができた（図５を参照。）。 By adopting such a supporting structure, as can be seen from the purification characteristic curve indicated by the present invention in FIG. 4, the HC adsorption catalyst having higher purification performance than the conventional HC adsorption catalyst from the first half to the second half of the warm-up operation is obtained. (See FIG. 5).
一般的に、触媒前段のＯＳＣ剤による酸素貯蔵により、触媒の後段ほど、ＯＳＣ剤の酸素貯蔵量が減って酸素欠乏状態を招くが、ＯＳＣ剤を触媒の後段ほど多く担持させることにより、後段の酸素貯蔵量を確保することができ、ＨＣ脱離時の酸化用酸素が不足することを防ぐことができる。また、貴金属触媒を触媒の前段ほど多く担持させることにより、触媒の前段付近では高い貴金属担持濃度のため、早期に着火して脱離したＨＣを浄化することができる。 In general, the oxygen storage by the OSC agent in the first stage of the catalyst causes the oxygen storage amount of the OSC agent to decrease as the latter stage of the catalyst leads to an oxygen-deficient state. An oxygen storage amount can be ensured, and it is possible to prevent a lack of oxygen for oxidation during HC desorption. In addition, by loading a larger amount of the noble metal catalyst in the front stage of the catalyst, the HC that has been ignited early and desorbed can be purified because of the higher noble metal loading concentration in the vicinity of the front stage of the catalyst.
本実施形態に係る排気ガス浄化装置とすることにより、ＨＣ吸着剤から脱離するＨＣを浄化するのに十分な酸素を確保することができ、また、高価な貴金属を効率よく使用することができる。また、酸素不足を補うため、多量のＯＳＣ剤を担持させる方法に対して、本実施形態のように効率的な担持形態とすることにより、ＯＳＣ剤の使用量を抑制して、触媒の劣化を防ぐことができる。 By using the exhaust gas purification apparatus according to the present embodiment, sufficient oxygen can be secured to purify HC desorbed from the HC adsorbent, and expensive noble metals can be used efficiently. . In addition, in order to make up for the lack of oxygen, a method for supporting a large amount of OSC agent is used as an efficient support configuration as in this embodiment, thereby suppressing the amount of OSC agent used and reducing the catalyst deterioration. Can be prevented.
なお、本実施形態では、貴金属触媒及びＯＳＣ剤の担持構造について、図３に示すように、触媒入口側から出口側に亘って滑らかに変化する濃度勾配としたが、段階的に変化させるようにしてもよい。また、図２に示すように、担体１３ａの表面にＨＣ吸着層１３ｂと三元触媒層１３ｃを積層した構造としたが、各層を構成する材料を混合して、担体１３ａの表面に担持させてもよい。また、積層をＨＣ吸着層１３ｂと三元触媒層１３ｃを入れ換えて担持したものでもよい。 In this embodiment, the noble metal catalyst and OSC agent support structure has a concentration gradient that smoothly changes from the catalyst inlet side to the outlet side as shown in FIG. 3, but it is changed stepwise. May be. Further, as shown in FIG. 2, the HC adsorption layer 13b and the three-way catalyst layer 13c are stacked on the surface of the carrier 13a. However, the materials constituting each layer are mixed and supported on the surface of the carrier 13a. Also good. Alternatively, the stack may be supported by replacing the HC adsorption layer 13b and the three-way catalyst layer 13c.
１００ エンジン
１０１ 排気通路
１０ 排気ガス浄化装置
１１ ケーシング
１２ 三元触媒
１３ ＨＣ吸着触媒
１３ａ 担体
１３ｂ ＨＣ吸着層
１３ｃ 三元触媒層（ＯＳＣ剤を含む）
DESCRIPTION OF
Claims (3)
前記酸素ストレージ剤は、前記ＨＣ吸着触媒の入口側から出口側に向かって、担持濃度が高くなるように漸増して担持され、
前記貴金属触媒は、前記ＨＣ吸着触媒の入口側から出口側に向かって、貴金属の担持濃度が低くなるように漸減して担持されている
ことを特徴とするＨＣ吸着触媒。 In an HC adsorption catalyst having a carrier and an HC adsorbent, an oxygen storage agent and a noble metal catalyst supported on the carrier,
The oxygen storage agent is gradually supported from the inlet side to the outlet side of the HC adsorption catalyst so as to increase the supporting concentration,
The HC adsorption catalyst, wherein the noble metal catalyst is supported while being gradually decreased from the inlet side to the outlet side of the HC adsorption catalyst so that the concentration of the noble metal supported decreases .
前記貴金属触媒は、Ｐｔ，Ｒｈ，Ｐｄのうち少なくとも一種類の貴金属を含有する
ことを特徴とするＨＣ吸着触媒。 In the HC adsorption catalyst according to claim 1,
The HC adsorption catalyst, wherein the noble metal catalyst contains at least one kind of noble metal of Pt, Rh, and Pd.
排気ガスの下流側に設置される請求項１または２に記載するＨＣ吸着触媒とを有する
ことを特徴とする排気ガス浄化装置。 A three-way catalyst provided in the exhaust passage of the internal combustion engine and installed upstream in the exhaust direction;
An exhaust gas purification apparatus comprising the HC adsorption catalyst according to claim 1 or 2 installed downstream of the exhaust gas.
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