JP2006272064A - Oxidation catalyst - Google Patents
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- JP2006272064A JP2006272064A JP2005091891A JP2005091891A JP2006272064A JP 2006272064 A JP2006272064 A JP 2006272064A JP 2005091891 A JP2005091891 A JP 2005091891A JP 2005091891 A JP2005091891 A JP 2005091891A JP 2006272064 A JP2006272064 A JP 2006272064A
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- 239000003054 catalyst Substances 0.000 title claims abstract description 168
- 238000007254 oxidation reaction Methods 0.000 title claims abstract description 62
- 230000003647 oxidation Effects 0.000 title claims abstract description 60
- 230000002093 peripheral effect Effects 0.000 claims abstract description 52
- 239000000843 powder Substances 0.000 claims abstract description 23
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- 239000002184 metal Substances 0.000 claims abstract description 12
- 239000000203 mixture Substances 0.000 claims abstract description 8
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 claims description 9
- 239000001301 oxygen Substances 0.000 claims description 9
- 229910052760 oxygen Inorganic materials 0.000 claims description 9
- 229910021536 Zeolite Inorganic materials 0.000 claims description 6
- HNPSIPDUKPIQMN-UHFFFAOYSA-N dioxosilane;oxo(oxoalumanyloxy)alumane Chemical compound O=[Si]=O.O=[Al]O[Al]=O HNPSIPDUKPIQMN-UHFFFAOYSA-N 0.000 claims description 6
- 239000011232 storage material Substances 0.000 claims description 6
- 239000010457 zeolite Substances 0.000 claims description 6
- TWNQGVIAIRXVLR-UHFFFAOYSA-N oxo(oxoalumanyloxy)alumane Chemical compound O=[Al]O[Al]=O TWNQGVIAIRXVLR-UHFFFAOYSA-N 0.000 claims description 4
- 230000003197 catalytic effect Effects 0.000 abstract 2
- 239000007789 gas Substances 0.000 description 44
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- WCUXLLCKKVVCTQ-UHFFFAOYSA-M Potassium chloride Chemical compound [Cl-].[K+] WCUXLLCKKVVCTQ-UHFFFAOYSA-M 0.000 description 3
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- 229910000420 cerium oxide Inorganic materials 0.000 description 3
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- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- 101000708874 Homo sapiens Zinc finger protein ubi-d4 Proteins 0.000 description 2
- 239000004372 Polyvinyl alcohol Substances 0.000 description 2
- 102100032701 Zinc finger protein ubi-d4 Human genes 0.000 description 2
- 238000006243 chemical reaction Methods 0.000 description 2
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- 229910052684 Cerium Inorganic materials 0.000 description 1
- DYVVJDIYXSZELU-UHFFFAOYSA-N [N+](=O)([O-])[O-].[Pt+2].[N+](=O)([O-])N[N+](=O)[O-].[N+](=O)([O-])[O-] Chemical compound [N+](=O)([O-])[O-].[Pt+2].[N+](=O)([O-])N[N+](=O)[O-].[N+](=O)([O-])[O-] DYVVJDIYXSZELU-UHFFFAOYSA-N 0.000 description 1
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- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical compound [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- 229910052878 cordierite Inorganic materials 0.000 description 1
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- 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 1
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- 239000004570 mortar (masonry) Substances 0.000 description 1
- RVTZCBVAJQQJTK-UHFFFAOYSA-N oxygen(2-);zirconium(4+) Chemical compound [O-2].[O-2].[Zr+4] RVTZCBVAJQQJTK-UHFFFAOYSA-N 0.000 description 1
- 239000001103 potassium chloride Substances 0.000 description 1
- 235000011164 potassium chloride Nutrition 0.000 description 1
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- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 1
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Landscapes
- Exhaust Gas After Treatment (AREA)
- Processes For Solid Components From Exhaust (AREA)
- Filtering Of Dispersed Particles In Gases (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
- Catalysts (AREA)
Abstract
Description
本発明は、ディーゼルエンジンの排気通路中のパティキュレートフィルターの上流に配置される酸化触媒に関するものである。 The present invention relates to an oxidation catalyst disposed upstream of a particulate filter in an exhaust passage of a diesel engine.
ディーゼルエンジンから排出されるパティキュレート（以下、ＰＭという）は環境に与える影響が大きいため、このＰＭを捕集するディーゼルパティキュレートフィルタ（以下、ＤＰＦという）が排気通路に設けられた自動車が増加してきている。このようにＤＰＦを設ける場合、ＤＰＦに捕集されたＰＭを除去する必要があり、そのための手段としてＤＰＦの上流にバーナーを設けてその熱でＰＭを燃焼させるようにしたものがあるが、ＤＰＦを構成するフィルタ担体が過熱されて溶損するおそれがある。 Since particulates discharged from diesel engines (hereinafter referred to as PM) have a large impact on the environment, the number of automobiles provided with diesel particulate filters (hereinafter referred to as DPF) for collecting PM has increased. ing. When the DPF is provided in this way, it is necessary to remove the PM collected in the DPF, and as a means for that purpose, there is one in which a burner is provided upstream of the DPF and the PM is burned by the heat. There is a possibility that the filter carrier that constitutes is heated and melted.
このような問題を避けるため、例えば特許文献１に示されるように、排気通路のＤＰＦの上流に酸化触媒を設け、この酸化触媒で排気ガス中のＮＯを酸化させてＮＯ２とし、このＮＯ２をＤＰＦに送ることにより、ＤＰＦに捕集されたＰＭをＮＯ２で酸化除去させるようにした排気ガス浄化装置が開発されている。 In order to avoid such a problem, for example, as shown in Patent Document 1, an oxidation catalyst is provided upstream of the DPF in the exhaust passage, and NO in the exhaust gas is oxidized to NO 2 by this oxidation catalyst, and this NO 2 An exhaust gas purifying apparatus has been developed in which PM trapped in the DPF is oxidized and removed with NO 2 by sending it to the DPF.
ところで、ＤＰＦとして一般に用いられているウォールフロータイプの円筒状のフィルタでは、放射熱が大きく低温になり易い外周側通路部分と、中央側通路の下流側部分へのＰＭ堆積量が増加し易い傾向がある。これに対し、上記特許文献１に示された装置では、ＤＰＦの上流に設けた酸化触媒の外周側通路部分に強酸化触媒を、中央側通路部分に弱酸化触媒をそれぞれ担持させた構造となっている。そして、特許文献１には、このような酸化触媒の構造によると外周側通路部分の強酸化触媒は中央側通路部分の弱酸化触媒よりも酸化反応が強いため、ＮＯの酸化反応によって外周側通路部分からの排気ガス温度は中央側通路部分のそれよりも高まることとなり、結果としてＤＰＦにおける温度分布は全体的に見て均等化されるというように記載されている。
上記の特許文献１の記載によると、強酸化触媒と弱酸化触媒とは、同種の触媒であれば、担持密度や担持濃度を変えることにより形成され、つまり外周側通路部分に中央側通路部分より多くの触媒が担持される。 According to the description of Patent Document 1 above, if the strong oxidation catalyst and the weak oxidation catalyst are the same type of catalyst, they are formed by changing the carrying density and the carrying concentration. Many catalysts are supported.
しかし、このように外周側通路部分に中央側通路部分より多くの触媒を担持させると、外周側通路部分では、通路抵抗が中央側通路部分より増大することにより排気ガスの流量が少なくなり、このため強酸化触媒であっても発熱量は少なくなる。一方、中央側通路部分では、排気ガス量は多いが弱酸化触媒であるため酸化反応が起きにくく、この部分の昇温への寄与率は低くなる。 However, if more catalyst is supported on the outer peripheral side passage portion than the central side passage portion in this way, the flow rate of the exhaust gas is reduced in the outer peripheral side passage portion because the passage resistance is larger than that in the central side passage portion. Therefore, even if it is a strong oxidation catalyst, the calorific value is reduced. On the other hand, in the central passage portion, the amount of exhaust gas is large, but since it is a weak oxidation catalyst, the oxidation reaction hardly occurs, and the contribution rate to the temperature rise in this portion is low.
従って、酸化触媒全体としてＤＰＦを昇温させる効果は充分に得られ難かった。 Accordingly, it has been difficult to sufficiently obtain the effect of increasing the temperature of the DPF as the whole oxidation catalyst.
本発明は上記の事情に鑑み、ＤＰＦの上流に配置される酸化触媒においてＤＰＦへ流れる排気ガスの温度を効果的に高めることができる酸化触媒を提供するものである。 In view of the above circumstances, the present invention provides an oxidation catalyst that can effectively increase the temperature of exhaust gas flowing to the DPF in the oxidation catalyst disposed upstream of the DPF.
本発明は、ディーゼルエンジンの排気通路中のパティキュレートフィルターの上流に配置される酸化触媒であって、筒状のハニカム担体の径方向中心部に、中空状酸化物粉末の破砕殻と触媒金属とからなる触媒層が形成されているものである。 The present invention relates to an oxidation catalyst disposed upstream of a particulate filter in an exhaust passage of a diesel engine, and a crushed shell of hollow oxide powder, a catalyst metal, and a central portion in a radial direction of a cylindrical honeycomb carrier. The catalyst layer which consists of is formed.
この構成によると、ＤＰＦの上流に配置される酸化触媒において、中心部触媒層が中空状酸化物粉末の破砕殻を含んでいることにより嵩高になって層の厚みが増加し、排気ガスの流通抵抗が増えて流量、流速が低下する。そして、中空状酸化物粉末の破砕殻は中実状粒子と比べて嵩高になる分だけポーラスでガスの拡散が良好になり、ガスと触媒との接触機会が増えるため酸化性能が高まって反応熱が増大することにより、中心部触媒層を通る排気ガスの温度が上昇する。 According to this configuration, in the oxidation catalyst disposed upstream of the DPF, the central catalyst layer contains a crushed shell of hollow oxide powder, which increases the bulk of the layer and increases the thickness of the layer. Resistance increases and flow rate and flow velocity decrease. The crushed shell of the hollow oxide powder is porous and gas diffusion is better than the solid particles, and the opportunity for contact between the gas and the catalyst increases, so the oxidation performance increases and the reaction heat increases. By increasing, the temperature of the exhaust gas passing through the central catalyst layer increases.
一方、酸化触媒の外周部は放熱による温度低下が生じ易い部分であるが、中心部での流通抵抗の増加に伴い、排気ガスの流量が外周部で多くなるため、放熱以上に、排気ガス中の未燃ＨＣ等の燃焼による発熱が生じて、排気ガス温度が上昇する。 On the other hand, the outer peripheral portion of the oxidation catalyst is a portion where the temperature is likely to decrease due to heat dissipation, but the flow rate of the exhaust gas increases at the outer peripheral portion as the flow resistance increases in the central portion. Exothermic HC or the like generates heat due to combustion, and the exhaust gas temperature rises.
こうして、酸化触媒の中心部と外周部とでそれぞれ排気ガス温度が高められ、かつ、これらの部分の排気ガス温度が均等化される。 In this way, the exhaust gas temperatures are increased at the central portion and the outer peripheral portion of the oxidation catalyst, respectively, and the exhaust gas temperatures at these portions are equalized.
本発明の酸化触媒において、中空状酸化物粉末の破砕殻と触媒金属とからなる中心部触媒層は、ハニカム担体の半径の１／４〜３／４の半径の範囲に形成されていることが好ましい。このようにすると、中心部と外周部とで排気ガス温度の格差が充分に小さく抑えられる。 In the oxidation catalyst of the present invention, the central catalyst layer composed of the crushed shell of the hollow oxide powder and the catalyst metal is formed in a radius range of 1/4 to 3/4 of the radius of the honeycomb carrier. preferable. In this way, the difference in exhaust gas temperature between the central portion and the outer peripheral portion can be suppressed sufficiently small.
また、本発明の酸化触媒において、ハニカム担体の上記中心部を囲う外周部には、上記中空状酸化物粉末と同じ組成の中実状粒子と触媒金属とからなる触媒層が形成され、中心部触媒層の担体単位体積あたりの触媒量が外周部触媒層の担体単位体積あたりの触媒量の４／５〜３／２に設定されていることが好ましい。このようにすると、可及的に触媒量を少なくしつつ、効果的に排気ガス温度を高めることができる。 Further, in the oxidation catalyst of the present invention, a catalyst layer composed of solid particles having the same composition as the hollow oxide powder and a catalyst metal is formed on the outer peripheral portion surrounding the center portion of the honeycomb carrier, and the center portion catalyst is formed. The catalyst amount per carrier unit volume of the layer is preferably set to 4/5 to 3/2 of the catalyst amount per carrier unit volume of the outer peripheral catalyst layer. If it does in this way, exhaust gas temperature can be raised effectively, reducing the catalyst amount as much as possible.
また、上記酸化物は酸化アルミニウムと、酸素吸蔵材と、ゼオライトとの混合物であることが好ましい。 The oxide is preferably a mixture of aluminum oxide, an oxygen storage material, and zeolite.
このようにすると、ゼオライトは未燃ＨＣをクラッキングにより炭素数の少ないＨＣ成分、つまり燃焼し易い成分に変換し、また、酸素吸蔵材は排気ガスの空燃比がリーンのときに酸素を吸蔵して、リッチのときに酸素を放出する。従って、排気ガスの空燃比がリッチ状態にされると、排気ガス中の未燃ＨＣがゼオライトで燃焼し易い成分に変えられるとともに酸素吸蔵材から放出される酸素により効率良く燃焼され、排気ガス温度の上昇が促進される。 In this way, zeolite converts unburned HC into HC components with a small number of carbons by cracking, that is, combustible components, and the oxygen storage material stores oxygen when the air-fuel ratio of the exhaust gas is lean. Releases oxygen when rich. Therefore, when the air-fuel ratio of the exhaust gas is made rich, the unburned HC in the exhaust gas is changed to a component that is easily combusted by zeolite and is efficiently burned by the oxygen released from the oxygen storage material. Is promoted.
以上のように、本発明の酸化触媒によると、ハニカム担体の径方向中心部では中空状酸化物粉末の破砕殻により酸化性能が高められて排気ガスの温度が上昇するとともに、中心部で流量が低下してその分だけ外周部で排気ガスの流量が増加し、放熱し易い外周部でも排気ガスの温度が高められるため、酸化触媒の中心部、外周部の全体にわたり排気ガスの温度を充分に上昇させることができ、ＤＰＦに堆積するＰＭの酸化除去を効果的に行うことができる。 As described above, according to the oxidation catalyst of the present invention, the oxidation performance is enhanced by the crushed shell of the hollow oxide powder at the radial center portion of the honeycomb carrier, the exhaust gas temperature rises, and the flow rate at the central portion is increased. The flow rate of the exhaust gas increases at the outer peripheral portion and the exhaust gas temperature increases at the outer peripheral portion where heat dissipation is easy. It is possible to raise the PM, and it is possible to effectively remove the PM deposited on the DPF.
以下、図面に基づいて本発明の実施の形態を説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
図１はディーゼルエンジンの排気通路１にＤＰＦ２及び酸化触媒３を組付けた状態を示している。この図において、排気通路１を構成する排気管は、図外のディーゼルエンジン本体に排気マニフォールドを介して接続される。そして、ディーゼルエンジン本体から排出される排気ガスは、白抜き矢印で示すように、排気通路１中を図１で左側から右側へ流れる。 FIG. 1 shows a state in which a DPF 2 and an oxidation catalyst 3 are assembled in an exhaust passage 1 of a diesel engine. In this figure, an exhaust pipe constituting the exhaust passage 1 is connected to a diesel engine body (not shown) via an exhaust manifold. And the exhaust gas discharged | emitted from a diesel engine main body flows into the exhaust passage 1 from the left side to the right side in FIG. 1, as shown by the white arrow.
上記排気通路１には、排気ガス中のＰＭを捕集するＤＰＦ２が設けられるとともに、このＤＰＦ２に近接してその上流（図１で左側）に酸化触媒３が設けられている。 The exhaust passage 1 is provided with a DPF 2 for collecting PM in the exhaust gas, and an oxidation catalyst 3 is provided in the vicinity of the DPF 2 and upstream (left side in FIG. 1).
上記ＤＰＦ２は、所謂ウォールフロータイプのフィルタであって、コーディエライトやセラミックスにより、多孔質壁で区画した多数の通路（セル）を有するハニカム状に形成されるとともに、千鳥状に一部の通路の上流端側と他の通路の下流端側とが目封止されることにより、上流端側が開口した通路から流入した排気ガスが多孔質壁を通って下流端側が開口した通路へ流れ、その間にＰＭが捕集されるようになっている。このようなウォールフロータイプのＤＰＦ２は従来から知られているため、詳しい図示及び説明は省略する。 The DPF 2 is a so-called wall flow type filter, and is formed into a honeycomb shape having a large number of passages (cells) partitioned by a porous wall by cordierite or ceramics, and a part of the passages in a staggered manner. By plugging the upstream end side and the downstream end side of the other passage, the exhaust gas flowing in from the passage opened on the upstream end side flows through the porous wall to the passage opened on the downstream end side. PM is collected. Since such a wall flow type DPF 2 is conventionally known, detailed illustration and description thereof will be omitted.
上記ＤＰＦ２の外形は円筒状となっている。 The outer shape of the DPF 2 is cylindrical.
上記ＤＰＦ２の上流に設けられた酸化触媒３は、図２および図３に示すように、ＤＰＦ２に対応する円筒状に形成され、多数の通路３０を有するハニカム担体３１と、このハニカム担体３１に担持された触媒層３２ａ，３２ｂとを有しており、触媒層３２ａ，３２ｂは酸化物粉末と触媒金属とを含んでいる。特に本発明の特徴とする構造として、ハニカム担体３１の径方向中心部Ａには、中空状酸化物粉末の破砕殻と触媒金属とからなる触媒層３２ａが形成されている。また、この中心部を囲う外周部Ｂには、上記中空状酸化物粉末と同じ組成の中実状粒子と触媒金属とからなる触媒層３２ｂが形成されている。 As shown in FIGS. 2 and 3, the oxidation catalyst 3 provided upstream of the DPF 2 is formed in a cylindrical shape corresponding to the DPF 2, and has a honeycomb carrier 31 having a large number of passages 30, and is supported on the honeycomb carrier 31. Catalyst layers 32a and 32b, and the catalyst layers 32a and 32b contain an oxide powder and a catalyst metal. In particular, as a characteristic feature of the present invention, a catalyst layer 32 a made of a crushed shell of hollow oxide powder and a catalyst metal is formed at the radial center A of the honeycomb carrier 31. In addition, a catalyst layer 32b made of solid particles having the same composition as the hollow oxide powder and a catalyst metal is formed on the outer peripheral portion B surrounding the central portion.
なお、上記のように中心部Ａに触媒層３２ａを形成し、外周部Ｂに触媒層３２ｂを形成するには、先ず外周部Ｂの担体両端面にマスキング部材を配置した後、中心部Ａに触媒層３２ａ用の触媒スラリーを塗布する。エアブローにより余分なスラリーを除去し、外周部Ｂのマスキングを取り去った後、乾燥する。続いて、中心部Ａの担体両端面にマスキング部材を配置した後、外周部Ｂに触媒層３２ｂ用の触媒スラリーを塗布し、中心部と同様にスラリーの除去、乾燥を行う。最後に焼成を行う。 In order to form the catalyst layer 32a in the central portion A and the catalyst layer 32b in the outer peripheral portion B as described above, first, a masking member is disposed on both end faces of the carrier in the outer peripheral portion B, and then the central portion A is formed. A catalyst slurry for the catalyst layer 32a is applied. The excess slurry is removed by air blowing, and the masking of the outer peripheral portion B is removed, followed by drying. Subsequently, after disposing a masking member on both end faces of the carrier in the central part A, a catalyst slurry for the catalyst layer 32b is applied to the outer peripheral part B, and the slurry is removed and dried in the same manner as in the central part. Finally, firing is performed.
上記中空状酸化物粉末の破砕殻と触媒金属とからなる中心部触媒層３２ａは、好ましくはハニカム担体３１の半径の１／４〜３／４の半径の範囲に形成されている。中心部触媒層３２ａの担体単位体積あたりの触媒量は、外周部触媒層３２ｂの担体単位体積あたりの触媒量の４／５〜３／２に設定されている。また、触媒層３２ａ，３２ｂに含まれる酸化物は、好ましくは酸化アルミニウム（Ａｌ２Ｏ３）と、酸化セリウム（ＣｅＯ２）等の酸素吸蔵材と、ゼオライトとの混合物である。なお、酸素吸蔵材は、酸化セリウム（ＣｅＯ２）と酸化ジルコニウム（ＺｒＯ２）との複酸化物、あるいはさらにセリウム以外の希土類金属の酸化物を第３成分として含む複酸化物等であってもよい。 The central catalyst layer 32 a made of the crushed shell of the hollow oxide powder and the catalyst metal is preferably formed in a radius range of ¼ to ¾ of the radius of the honeycomb carrier 31. The catalyst amount per carrier unit volume of the central catalyst layer 32a is set to 4/5 to 3/2 of the catalyst amount per carrier unit volume of the outer peripheral catalyst layer 32b. The oxide contained in the catalyst layers 32a and 32b is preferably a mixture of aluminum oxide (Al 2 O 3 ), an oxygen storage material such as cerium oxide (CeO 2 ), and zeolite. The oxygen storage material may be a double oxide of cerium oxide (CeO 2 ) and zirconium oxide (ZrO 2 ), or a double oxide containing a rare earth metal oxide other than cerium as a third component. Good.
中心部触媒層３２ａに含まれる破砕殻の製法の一例を、次に説明する。 Next, an example of a method for producing a crushed shell contained in the central catalyst layer 32a will be described.
（工程１） 直径約０．１〜５μｍのポリビニルブチラール（ＰＶＢ）粒子を５％ポリビニルアルコール（ＰＶＡ）水溶液に入れて、混合溶液を作成する。 (Step 1) A polyvinyl butyral (PVB) particle having a diameter of about 0.1 to 5 μm is placed in a 5% polyvinyl alcohol (PVA) aqueous solution to prepare a mixed solution.
（工程２） 上記混合溶液６０wt％に対し、後述のように調製された触媒粉末４０wt％を添加し、混合スラリーにする。 (Step 2) To 60 wt% of the mixed solution, 40 wt% of catalyst powder prepared as described below is added to form a mixed slurry.
（工程３） ロート状滴下器具を用いて、混合スラリーを塩化カリウム（ＫＣｌ）溶液中に滴下し、ＰＶＢ粒子表面に触媒粉末がコーティングされた状態の球体として堆積させる。 (Step 3) Using a funnel-shaped dropping device, the mixed slurry is dropped into a potassium chloride (KCl) solution and deposited as spheres in which catalyst powder is coated on the surface of PVB particles.
（工程４） 堆積した球体を乾燥し、さらに乾燥させた球体を焼成する。乾燥の条件は大気中で１５０°Ｃ、２時間とし、焼成の条件は大気中で５００°Ｃ、２時間とする。このように乾燥、焼成を行うことにより、球体内部のＰＶＢ成分が熱分解して焼失し、中空材が得られる。 (Step 4) The deposited spheres are dried, and the dried spheres are fired. The drying conditions are 150 ° C. for 2 hours in the air, and the firing conditions are 500 ° C. for 2 hours in the air. By performing drying and firing in this manner, the PVB component inside the sphere is thermally decomposed and burned off, and a hollow material is obtained.
（工程５）上記中空材の粉末を数ｍｍの厚さに引き伸ばし、メカプレスを用いて比較的低圧で圧粉する。 (Step 5) The hollow material powder is stretched to a thickness of several millimeters and compacted at a relatively low pressure using a mechanical press.
こうして、中空状酸化物粉末の破砕殻が得られる。この破砕殻は、図４の顕微鏡写真に示すように、球状の殻が砕かれた破片状であって、中実の粒子と比べて空隙が多く、嵩高となる。 Thus, a crushed shell of hollow oxide powder is obtained. As shown in the photomicrograph of FIG. 4, the crushed shell is a fragmented shape in which a spherical shell is crushed, and has more voids and is bulky than solid particles.
なお、上記工程２で混合溶液に添加される触媒粉末は、次のように調整される。すなわち、酸化アルミニウム（Ａｌ２Ｏ３）、酸化セリウム（ＣｅＯ２）およびゼオライトを同じ重量比で混合し、その混合物に対し、白金（Ｐｔ）が２ｗｔ％担持されるように、ジニトロアミン白金硝酸溶液を加える。さらに、イオン交換水を混合してスラリー状とした後、蒸発乾固を行い、充分に乾燥した後、乳鉢で粉砕し、電気炉で焼成する。焼成の条件は大気中で５００°Ｃ、２時間とする。 In addition, the catalyst powder added to a mixed solution at the said process 2 is adjusted as follows. That is, aluminum oxide (Al 2 O 3 ), cerium oxide (CeO 2 ), and zeolite are mixed in the same weight ratio, and dinitroamine platinum nitrate solution is added so that 2 wt% of platinum (Pt) is supported on the mixture. Add Further, after mixing with ion-exchanged water to form a slurry, it is evaporated to dryness, sufficiently dried, pulverized in a mortar, and baked in an electric furnace. The firing conditions are 500 ° C. and 2 hours in the air.
以上のような酸化触媒３によると、ディーゼルエンジンの排気通路１のＤＰＦ２の上流に配置された状態で、エンジンがＤＰＦ２の再生のためにポスト噴射（通常の燃料噴射の後に排気ガス中のＨＣ成分等の増加のために行う燃料噴射）などの再生モード運転を行っているとき、酸化触媒３を通る排気ガス中のＨＣ、ＮＯなどが酸化され、温度が高められつつ排気ガスがＤＰＦ２に流れて、Ｏ２およびＮＯ２等により、ＤＰＦ２に堆積しているＰＭが酸化除去される。 According to the oxidation catalyst 3 as described above, in the state where the engine is disposed upstream of the DPF 2 in the exhaust passage 1 of the diesel engine, the engine performs post-injection for regeneration of the DPF 2 (the HC component in the exhaust gas after normal fuel injection). When performing a regeneration mode operation such as fuel injection performed for the purpose of increase, etc., HC, NO, etc. in the exhaust gas passing through the oxidation catalyst 3 are oxidized, and the exhaust gas flows into the DPF 2 while the temperature is raised. , O 2, NO 2, etc., oxidize and remove PM deposited on DPF 2 .
この場合に、特に中心部触媒層３２ａが中空状酸化物粉末の破砕殻を含んでいることにより嵩高になって層の厚みが増加し、排気ガスの流通抵抗が増えるため、中心部Ａでは排気ガス流量および流速が低下するが、中空状酸化物粉末の破砕殻が嵩高になる分だけガスと触媒との接触機会が増えるため酸化性能が高まって反応熱が増大する。このような作用により、中心部Ａを通る排気ガスの温度が上昇する。 In this case, in particular, since the central catalyst layer 32a includes a crushed shell of hollow oxide powder, it becomes bulky to increase the thickness of the layer and increase the flow resistance of the exhaust gas. Although the gas flow rate and the flow rate are reduced, the opportunity for contact between the gas and the catalyst increases as the crushed shell of the hollow oxide powder becomes bulky, so that the oxidation performance increases and the reaction heat increases. Due to such an action, the temperature of the exhaust gas passing through the central portion A rises.
一方、中心部Ａで排気ガス流量が低下する分だけ、酸化触媒３の外周部では排気ガスの流量が増加し、それにより、排気ガス中のＨＣ等の燃焼による発熱量が増加する。従って、放熱し易い外周部でも、排気ガス温度が上昇する。 On the other hand, the flow rate of the exhaust gas increases at the outer peripheral portion of the oxidation catalyst 3 by the amount that the exhaust gas flow rate decreases in the central portion A, thereby increasing the amount of heat generated by combustion of HC or the like in the exhaust gas. Therefore, the exhaust gas temperature rises even at the outer peripheral portion where heat dissipation is easy.
こうして、酸化触媒の中心部と外周部とでそれぞれ排気ガス温度が充分に高められ、ＤＰＦ２におけるＰＭの燃焼性能が高められる。 Thus, the exhaust gas temperature is sufficiently increased at the central portion and the outer peripheral portion of the oxidation catalyst, respectively, and the PM combustion performance in the DPF 2 is enhanced.
このような効果を確認するため、酸化触媒３による排気ガス温度の上昇およびＤＰＦ２におけるＰＭの燃焼性能についての評価のために行った実験とその結果を、次に説明する。
（サンプルおよび実験方法）
評価実験のための酸化触媒３のサンプルとして、後述の各種実施例および比較例に相当するものを作製した。これらのサンプルはいずれも、酸化触媒３のサイズが直径１４３．８ｍｍ、長さ１１８．０ｍｍ、セルの構造が６ｍｉｌ／４００ｃｐｓｉであり、触媒層が破砕殻と中実粒子のいずれについても２ｗｔ％の白金が担持されているものである。
In order to confirm such an effect, an experiment conducted for evaluating the rise of the exhaust gas temperature by the oxidation catalyst 3 and the combustion performance of PM in the DPF 2 and the result thereof will be described below.
(Sample and experimental method)
As a sample of the oxidation catalyst 3 for the evaluation experiment, samples corresponding to various examples and comparative examples described later were prepared. In all of these samples, the size of the oxidation catalyst 3 is 143.8 mm in diameter, the length is 118.0 mm, the cell structure is 6 mil / 400 cpsi, and the catalyst layer is 2 wt% for both crushed shells and solid particles. Platinum is supported.
各サンプルにつき、排気通路１のＤＰＦ２の上流に配置した状態で、酸化触媒３の排気ガス昇温性能を調べる昇温性能評価実験と、酸化触媒３の後段のＤＰＦ２におけるスート（ｓｏｏｔ：ＰＭに含まれる煤）の燃焼性能を調べる燃焼性能評価実験とを行った。 For each sample, the temperature rise performance evaluation experiment for examining the exhaust gas temperature rise performance of the oxidation catalyst 3 in the state of being arranged upstream of the DPF 2 in the exhaust passage 1 and the soot (soot: PM) included in the DPF 2 downstream of the oxidation catalyst 3 A combustion performance evaluation experiment was conducted to examine the combustion performance of
上記昇温性能評価実験としては、排気通路１中に酸化触媒３のサンプルとＤＰＦ２とを組み込んだ状態で、ディーゼルエンジンを運転するとともに上記ポスト噴射を行うことにより排気ガス中の未燃焼成分を増加させつつ、酸化触媒入口温度を３００°Ｃに保ち、酸化触媒出口温度が安定したときに、酸化触媒出口側端面における中央部と外周部から１ｃｍの部分との２点（図２中に×印を付して示す）の温度を測定した。 As the temperature rise performance evaluation experiment, the diesel engine was operated with the sample of the oxidation catalyst 3 and the DPF 2 incorporated in the exhaust passage 1, and the post-injection was performed to increase the unburned components in the exhaust gas. When the oxidation catalyst inlet temperature is kept at 300 ° C. and the oxidation catalyst outlet temperature is stabilized, two points (a cross mark in FIG. 2), a center portion on the oxidation catalyst outlet side end surface and a portion of 1 cm from the outer peripheral portion. The temperature was measured.
また、上記燃焼性能評価実験としては、排気通路１中に酸化触媒３のサンプルとＤＰＦ２とを組み込んだ状態で、ＤＰＦ２にスートが４ｇ／ｌ堆積した後、上記ポスト噴射を行うことによりＤＰＦ２の再生を開始し、その再生開始から３分で再生を停止した後、ＤＰＦ２を排気通路から取り出し、ＤＰＦ２内部に残存したスートの堆積分布を調査した。この堆積分布の調査としては、図５（ａ）に示すＤＰＦ２の中央部と図５（ｂ）に示すＤＰＦ２の周辺近傍部（外周端から５ｍｍの位置）とにおいて小径円柱状部分Ｐをカップ上コア抜きドリルなどで切り出し、さらに切り出した小径円柱状部分Ｐから図５（ｃ）のように入口部Ｐ１、長さ方向中央部Ｐ２および出口部Ｐ３を切り出し、その各部Ｐ１〜Ｐ３についてスート堆積量を測定した。堆積量の測定は、切り出し後に各部Ｐ１〜Ｐ３について重量を測定し、次に各部Ｐ１〜Ｐ３に堆積したスートを燃焼、除去してから、再度各部Ｐ１〜Ｐ３について重量を測定し、先に測定した重量とスート燃焼、除去後に測定した後の重量との差を求めるようにしたものである。
（実験結果１）
次の表１に示す実施例１〜３と比較例１，２とについて上記昇温性能評価実験を行った結果を図６に示す。
Further, as the combustion performance evaluation experiment, in the state where the sample of the oxidation catalyst 3 and the DPF 2 are incorporated in the exhaust passage 1, 4 g / l of soot is deposited on the DPF 2, and then the post-injection is performed to regenerate the DPF 2. The regeneration was stopped 3 minutes after the start of regeneration, and then DPF2 was taken out from the exhaust passage, and the accumulation distribution of soot remaining inside DPF2 was investigated. As the investigation of the deposition distribution, a small-diameter columnar portion P is placed on the cup in the central portion of the DPF 2 shown in FIG. 5A and the peripheral vicinity of the DPF 2 shown in FIG. An inlet portion P1, a lengthwise central portion P2 and an outlet portion P3 are cut out from the cut-out small-diameter cylindrical portion P as shown in FIG. 5C, and the soot deposition amount for each of the portions P1 to P3. Was measured. The amount of deposition is measured by measuring the weight for each part P1 to P3 after cutting out, then burning and removing the soot deposited on each part P1 to P3, and then measuring the weight for each part P1 to P3 again. The difference between the measured weight and the weight after measurement after soot combustion and removal is obtained.
(Experimental result 1)
FIG. 6 shows the results of the temperature rise performance evaluation experiment performed on Examples 1 to 3 and Comparative Examples 1 and 2 shown in Table 1 below.
表１中の実施例１〜３は中心部触媒層を破砕殻、外周部触媒層を中実粒子としたものであり、一方、比較例１，２は中心部、外周部のいずれの触媒層も中実粒子としたものである。 Examples 1 to 3 in Table 1 are those in which the central catalyst layer is a crushed shell and the outer peripheral catalyst layer is a solid particle, while Comparative Examples 1 and 2 are either the central or outer peripheral catalyst layer. Are solid particles.
なお、実施例１〜３および比較例１，２はいずれも、中心部Ａの半径を酸化触媒全体の半径ｒに対してｒ／２となっている。また、実施例１〜３および比較例１，２はいずれも外周部の触媒担持量が１００ｇ／ｌとされ、中心部Ａの触媒担持量が比較例１と２とで異なり、実施例１〜３でもそれぞれ異なっているが、比較例２と比べると実施例１〜３は中心部Ａの触媒担持量が少なくなっている。ここで、触媒担持量とは、担体の単位体積あたり（１リットルあたり）の触媒量である。 In all of Examples 1 to 3 and Comparative Examples 1 and 2, the radius of the central portion A is r / 2 with respect to the radius r of the entire oxidation catalyst. In Examples 1 to 3 and Comparative Examples 1 and 2, the amount of catalyst supported on the outer peripheral portion was 100 g / l, and the amount of catalyst supported on the central portion A was different between Comparative Examples 1 and 2; 3 differs from Example 3 in comparison with Comparative Example 2, but Examples 1 to 3 have a smaller amount of catalyst supported in the central portion A. Here, the catalyst loading is the amount of catalyst per unit volume of the carrier (per liter).
図６の実験結果によると、中心部触媒層が破砕殻を含んでいる実施例１〜３は、中心部触媒層も中実状粒子で構成される比較例１，２と比べ、中央部と外周部の両方で出口ガス温度が高められ、中央部と外周部の温度格差が小さくなる。とくに、比較例１と比べると外周部の温度が高くなって上記温度格差が大幅に減少し、また、比較例２と比べると、中心部の触媒担持量が少ないにもかかわらず、出口ガス温度が高められる。
（実験結果２）
次の表２および図７に示すように、中心部触媒層を破砕殻、外周部触媒層を中実粒子とした実施例相当の酸化触媒３で、中心部Ａの半径を触媒全体の半径ｒに対してｒ／８から７ｒ／８まで種々変えた５種類のサンプル（図７（ａ）〜（ｅ））を作製し、これらのサンプルと上記比較例１とにつき、上記昇温性能評価実験を行った結果を図８に示す。なお、これらのサンプルおよび比較例１は、中心部の触媒担持量を１００ｇ／ｌ、外周部の触媒担持量も１００ｇ／ｌとしている。
According to the experimental results of FIG. 6, Examples 1 to 3 in which the central catalyst layer includes a crushed shell are compared with Comparative Examples 1 and 2 in which the central catalyst layer is also composed of solid particles. The outlet gas temperature is increased in both of the parts, and the temperature difference between the central part and the outer peripheral part is reduced. In particular, the temperature at the outer peripheral portion is higher than that in Comparative Example 1 and the temperature difference is greatly reduced. In addition, the temperature of the outlet gas is lower than that in Comparative Example 2 although the amount of catalyst supported in the center is small. Is increased.
(Experimental result 2)
As shown in the following Table 2 and FIG. 7, in the oxidation catalyst 3 corresponding to the example in which the central catalyst layer is a crushed shell and the outer peripheral catalyst layer is solid particles, the radius of the central portion A is the radius r of the entire catalyst. Five types of samples (FIGS. 7A to 7E) with various changes from r / 8 to 7r / 8 were prepared, and the temperature rise performance evaluation experiment was performed for these samples and Comparative Example 1 described above. The results of performing are shown in FIG. In these samples and Comparative Example 1, the catalyst loading at the center is 100 g / l, and the catalyst loading at the outer periphery is also 100 g / l.
図８の実験結果によると、中心部触媒層３２ａを破砕殻、外周部触媒層３２ｂを中実粒子とするとともに、その中心部Ａの半径をｒ／４〜３ｒ／４とすれば、上記比較例１と比べて外周部の温度が充分に高くなり、中心部と外周部の温度格差が小さくなる。これに対し、中心部Ａの半径がｒ／８であれば、中心部触媒層での破砕殻による流通抵抗増大によって外周部で排気ガスの流量を増加させるという作用が低減し、また、中心部Ａの半径が７ｒ／８であれば、外周部のエリアが小さくなりすぎるため、外周部の温度上昇が少なくなる。 According to the experimental results shown in FIG. 8, if the central catalyst layer 32a is a crushed shell, the outer peripheral catalyst layer 32b is a solid particle, and the radius of the central portion A is r / 4 to 3r / 4, the above comparison is made. Compared with Example 1, the temperature of the outer peripheral portion is sufficiently high, and the temperature difference between the central portion and the outer peripheral portion is reduced. On the other hand, if the radius of the central portion A is r / 8, the effect of increasing the flow rate of the exhaust gas at the outer peripheral portion due to increased flow resistance due to the crushing shell in the central catalyst layer is reduced, and the central portion If the radius of A is 7r / 8, the area at the outer peripheral portion becomes too small, and the temperature rise at the outer peripheral portion is reduced.
従って、破砕殻を含む触媒層が形成される中心部の半径はｒ／４〜３ｒ／４程度が好ましい。
（実験結果３）
酸化触媒３の中心部触媒層を破砕殻、外周部触媒層を中実粒子とし、かつ、中心部の触媒担持量を８０ｇ／ｌ、外周部の触媒担持量を１００ｇ／ｌとして、中心部Ａの半径が触媒全体の半径ｒに対してｒ／４とｒ／２と３ｒ／４の３種類のサンプルを作製し、これらのサンプルと上記比較例２とにつき、上記昇温性能評価実験を行った結果を図９に示す。
Accordingly, the radius of the central portion where the catalyst layer including the crushed shell is formed is preferably about r / 4 to 3r / 4.
(Experimental result 3)
The central catalyst layer of the oxidation catalyst 3 is a crushed shell, the outer peripheral catalyst layer is solid particles, the central catalyst loading is 80 g / l, and the outer catalyst loading is 100 g / l. Three types of samples with a radius of r / 4, r / 2, and 3r / 4 with respect to the radius r of the entire catalyst were prepared, and the temperature rise performance evaluation experiment was conducted for these samples and Comparative Example 2 above. The results are shown in FIG.
また、中心部触媒層を破砕殻、外周部触媒層を中実粒子とし、かつ、中心部の触媒担持量を１５０ｇ／ｌ、外周部の触媒担持量を１００ｇ／ｌとして、中心部Ａの半径が触媒全体の半径ｒに対してｒ／４とｒ／２と３ｒ／４の３種類のサンプルを作製し、これらのサンプルと上記比較例２とにつき、上記昇温性能評価実験を行った結果を図１０に示す。 Further, the radius of the central portion A is set such that the central catalyst layer is a crushed shell, the outer peripheral catalyst layer is solid particles, the central catalyst loading is 150 g / l, and the outer peripheral catalyst loading is 100 g / l. Produced three types of samples of r / 4, r / 2, and 3r / 4 with respect to the radius r of the entire catalyst, and the results of the temperature rise performance evaluation experiment conducted on these samples and Comparative Example 2 above. Is shown in FIG.
これら図９，図１０に示した実験結果と前述の図６に示した実験結果とを考察する。中心部と外周部の各触媒層をともに中実粒子とした比較例の中では中心部の触媒担持量を外周部よりも多くした比較例２の方が外周部の温度が高められるが、この比較例２と比べても、中心部触媒層を破砕殻として中心部の触媒担持量を８０ｇ／ｌ（外周部の触媒担持量の４／５）とした場合（図９参照）では中央部及び外周部で出口側ガス温度が高まる効果が得られた。また、同じく中心部触媒層を破砕殻として中心部の触媒担持量を１５０ｇ／ｌ（外周部の触媒担持量の３／２）とした場合（図１０参照）は、より一層外周部の温度が高められて、中央部と外周部の温度格差が小さくなり、しかも、触媒担持量が比較例２と比べて少なくなる。 The experimental results shown in FIGS. 9 and 10 and the experimental results shown in FIG. 6 will be considered. Among the comparative examples in which the catalyst layers in the central portion and the outer peripheral portion are both solid particles, the temperature of the outer peripheral portion is higher in the comparative example 2 in which the amount of catalyst supported in the central portion is larger than that in the outer peripheral portion. Even in comparison with Comparative Example 2, when the central catalyst layer is a crushed shell and the catalyst loading at the center is 80 g / l (4/5 of the catalyst loading at the outer periphery) (see FIG. 9), An effect of increasing the outlet side gas temperature at the outer peripheral portion was obtained. Similarly, when the central catalyst layer is a crushed shell and the catalyst loading at the center is 150 g / l (3/2 of the catalyst loading at the outer periphery) (see FIG. 10), the temperature at the outer periphery is further increased. As a result, the temperature difference between the central portion and the outer peripheral portion is reduced, and the amount of the catalyst supported is reduced as compared with Comparative Example 2.
つまり、破砕殻を含む触媒層が形成される中心部の触媒担持量を外周部の触媒担持量の４／５〜３／２とすれば、触媒担持量を少なくしつつ、酸化触媒全体にわたり排気ガス温度を高める作用が良好に得られる。
（実験結果４）
本発明の実施例に相当するサンプルとして、破砕殻を含む触媒層を形成した中心部の触媒担持量が８０ｇ／ｌ、中実粒子を含む触媒層を形成した外周部の触媒担持量が１００ｇ／ｌであって、中心部の破砕殻部分の半径が酸化触媒全体の半径に対してｒ／４とｒ／２である２種類のサンプルを作製し、これらの実施例に相当する２種類のサンプルと前述の比較例２とを用い、上記燃焼性能評価実験を行った結果を、図１１および図１２に示す。図１１は酸化触媒の下流に配置されていたＤＰＦの中央部から切り出した小径円柱状部分Ｐ（図５（ａ）参照）の入口部Ｐ１、中央部Ｐ２、出口部Ｐ３の各部位（図５（ｃ）参照）においてスート堆積量を測定したデータである。また、図１２は、上記ＤＰＦの外周端近傍から切り出した小径円柱状部分Ｐ（図５（ｂ）参照）の入口部Ｐ１、中央部Ｐ２、出口部Ｐ３の各部位（図５（ｃ）参照）においてスート堆積量を測定したデータである。
That is, if the amount of catalyst supported in the center where the catalyst layer including the crushed shell is formed is 4/5 to 3/2 of the amount of catalyst supported in the outer peripheral portion, the entire amount of exhaust catalyst is exhausted while reducing the amount of catalyst supported. The effect of increasing the gas temperature can be obtained satisfactorily.
(Experimental result 4)
As a sample corresponding to an example of the present invention, the catalyst loading amount in the center portion where the catalyst layer including the crushed shell is formed is 80 g / l, and the catalyst loading amount in the outer periphery portion where the catalyst layer including the solid particles is formed is 100 g / l. 2 samples having a radius of the crushing shell portion at the center of r / 4 and r / 2 with respect to the radius of the entire oxidation catalyst, and two types of samples corresponding to these examples FIG. 11 and FIG. 12 show the results of the above-described combustion performance evaluation experiment using the above and Comparative Example 2 described above. FIG. 11 shows each part of the inlet portion P1, the central portion P2, and the outlet portion P3 of the small-diameter cylindrical portion P (see FIG. 5A) cut out from the central portion of the DPF arranged downstream of the oxidation catalyst (FIG. 5). It is the data which measured the amount of soot deposition in (c) reference). FIG. 12 shows each part of the inlet portion P1, the central portion P2, and the outlet portion P3 (see FIG. 5C) of the small-diameter cylindrical portion P cut out from the vicinity of the outer peripheral end of the DPF (see FIG. 5B). ) In which the amount of soot deposition was measured.
これらの実験結果によると、本発明の実施例に相当する上記２種類のサンプルは比較例２よりも中心部の触媒担持量が大幅に少なくされているにもかかわらず、上記２種類のサンプルを用いた場合、比較例２を用いた場合と比べ、ＤＰＦのスート堆積量が全体的に少なくなり、燃焼性能が改善されていることが解る。 According to these experimental results, the two types of samples corresponding to the examples of the present invention were compared with the two types of samples although the amount of catalyst supported in the central portion was significantly smaller than that of Comparative Example 2. When used, it can be seen that the amount of soot deposition of DPF is reduced as a whole and the combustion performance is improved as compared with the case of using Comparative Example 2.
また、このように、ＤＰＦの内部でのスート燃焼がより均一に近づくと、局所的に異常燃焼が起こり難いため、熱応力による破損や溶損等を回避することができる点でも有利である。 In addition, when soot combustion within the DPF becomes more uniform in this way, abnormal combustion is unlikely to occur locally, which is advantageous in that damage or melting damage due to thermal stress can be avoided.
１ 排気通路
２ ＤＰＦ
３ 酸化触媒
３０ 通路
３１ ハニカム担体
３２ａ 中心部触媒層
３２ｂ 外周部触媒層
1 Exhaust passage 2 DPF
3 Oxidation catalyst 30 Passage 31 Honeycomb carrier 32a Center part catalyst layer 32b Peripheral part catalyst layer
Claims (4)
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| JP2005091891A JP2006272064A (en) | 2005-03-28 | 2005-03-28 | Oxidation catalyst |
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|---|---|---|---|
| JP2005091891A JP2006272064A (en) | 2005-03-28 | 2005-03-28 | Oxidation catalyst |
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| EP2127729A1 (en) | 2008-05-30 | 2009-12-02 | Mazda Motor Corporation | Exhaust gas purification catalyst |
| JP2009285623A (en) * | 2008-05-30 | 2009-12-10 | Mazda Motor Corp | Catalyst for cleaning exhaust gas |
| WO2013050784A2 (en) | 2011-10-06 | 2013-04-11 | Johnson Matthey Public Limited Company | Oxidation catalyst for internal combustion engine exhaust gas treatment |
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