JP4630179B2 - Method for producing exhaust gas purifying catalyst - Google Patents
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- JP4630179B2 JP4630179B2 JP2005337091A JP2005337091A JP4630179B2 JP 4630179 B2 JP4630179 B2 JP 4630179B2 JP 2005337091 A JP2005337091 A JP 2005337091A JP 2005337091 A JP2005337091 A JP 2005337091A JP 4630179 B2 JP4630179 B2 JP 4630179B2
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- 239000003054 catalyst Substances 0.000 title claims description 65
- 238000004519 manufacturing process Methods 0.000 title claims description 8
- 229910052751 metal Inorganic materials 0.000 claims description 34
- 239000002184 metal Substances 0.000 claims description 34
- 239000011148 porous material Substances 0.000 claims description 31
- 239000011232 storage material Substances 0.000 claims description 28
- 238000000746 purification Methods 0.000 claims description 21
- 239000011164 primary particle Substances 0.000 claims description 20
- 239000011163 secondary particle Substances 0.000 claims description 18
- 239000002245 particle Substances 0.000 claims description 15
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 claims description 13
- 238000007872 degassing Methods 0.000 claims description 9
- 229910021645 metal ion Inorganic materials 0.000 claims description 9
- 239000000725 suspension Substances 0.000 claims description 9
- 239000007864 aqueous solution Substances 0.000 claims description 8
- 238000000034 method Methods 0.000 claims description 6
- 229910052684 Cerium Inorganic materials 0.000 claims description 5
- 229910052726 zirconium Inorganic materials 0.000 claims description 5
- 239000007788 liquid Substances 0.000 claims 1
- 239000007789 gas Substances 0.000 description 30
- 239000001301 oxygen Substances 0.000 description 22
- 229910052760 oxygen Inorganic materials 0.000 description 22
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 20
- 239000000243 solution Substances 0.000 description 12
- 230000000052 comparative effect Effects 0.000 description 10
- 239000000843 powder Substances 0.000 description 9
- 238000010438 heat treatment Methods 0.000 description 7
- 238000011068 loading method Methods 0.000 description 7
- 239000011257 shell material Substances 0.000 description 7
- 230000003197 catalytic effect Effects 0.000 description 6
- 238000001704 evaporation Methods 0.000 description 6
- 229910000510 noble metal Inorganic materials 0.000 description 6
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 5
- 238000001035 drying Methods 0.000 description 5
- 230000008020 evaporation Effects 0.000 description 5
- 239000000463 material Substances 0.000 description 5
- 239000000203 mixture Substances 0.000 description 5
- CSNNHWWHGAXBCP-UHFFFAOYSA-L Magnesium sulfate Chemical compound [Mg+2].[O-][S+2]([O-])([O-])[O-] CSNNHWWHGAXBCP-UHFFFAOYSA-L 0.000 description 4
- 239000002002 slurry Substances 0.000 description 4
- 230000000694 effects Effects 0.000 description 3
- 239000002994 raw material Substances 0.000 description 3
- 238000005245 sintering Methods 0.000 description 3
- 238000003860 storage Methods 0.000 description 3
- 238000009849 vacuum degassing Methods 0.000 description 3
- 229910004625 Ce—Zr Inorganic materials 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- ITHZDDVSAWDQPZ-UHFFFAOYSA-L barium acetate Chemical compound [Ba+2].CC([O-])=O.CC([O-])=O ITHZDDVSAWDQPZ-UHFFFAOYSA-L 0.000 description 2
- 239000011230 binding agent Substances 0.000 description 2
- 230000015572 biosynthetic process Effects 0.000 description 2
- 238000001354 calcination Methods 0.000 description 2
- HSJPMRKMPBAUAU-UHFFFAOYSA-N cerium(3+);trinitrate Chemical compound [Ce+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O HSJPMRKMPBAUAU-UHFFFAOYSA-N 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
- 238000010304 firing Methods 0.000 description 2
- 229910052943 magnesium sulfate Inorganic materials 0.000 description 2
- 235000019341 magnesium sulphate Nutrition 0.000 description 2
- BASFCYQUMIYNBI-UHFFFAOYSA-N platinum Substances [Pt] BASFCYQUMIYNBI-UHFFFAOYSA-N 0.000 description 2
- 238000002360 preparation method Methods 0.000 description 2
- 239000010948 rhodium Substances 0.000 description 2
- VXNYVYJABGOSBX-UHFFFAOYSA-N rhodium(3+);trinitrate Chemical compound [Rh+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VXNYVYJABGOSBX-UHFFFAOYSA-N 0.000 description 2
- 239000007787 solid Substances 0.000 description 2
- RXSHXLOMRZJCLB-UHFFFAOYSA-L strontium;diacetate Chemical compound [Sr+2].CC([O-])=O.CC([O-])=O RXSHXLOMRZJCLB-UHFFFAOYSA-L 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- 238000005054 agglomeration Methods 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 230000032683 aging Effects 0.000 description 1
- 229910052783 alkali metal Inorganic materials 0.000 description 1
- 150000001340 alkali metals Chemical class 0.000 description 1
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 1
- 150000001342 alkaline earth metals Chemical class 0.000 description 1
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 239000012159 carrier gas Substances 0.000 description 1
- 239000006185 dispersion Substances 0.000 description 1
- 238000011156 evaluation Methods 0.000 description 1
- 238000007667 floating Methods 0.000 description 1
- 239000000446 fuel Substances 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 238000005470 impregnation Methods 0.000 description 1
- 239000011259 mixed solution Substances 0.000 description 1
- UJVRJBAUJYZFIX-UHFFFAOYSA-N nitric acid;oxozirconium Chemical compound [Zr]=O.O[N+]([O-])=O.O[N+]([O-])=O UJVRJBAUJYZFIX-UHFFFAOYSA-N 0.000 description 1
- UYXRCZUOJAYSQR-UHFFFAOYSA-N nitric acid;platinum Chemical compound [Pt].O[N+]([O-])=O UYXRCZUOJAYSQR-UHFFFAOYSA-N 0.000 description 1
- 150000002926 oxygen Chemical class 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- NWAHZABTSDUXMJ-UHFFFAOYSA-N platinum(2+);dinitrate Chemical compound [Pt+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O NWAHZABTSDUXMJ-UHFFFAOYSA-N 0.000 description 1
- 239000000047 product Substances 0.000 description 1
- 238000010298 pulverizing process Methods 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000012265 solid product Substances 0.000 description 1
- 238000005118 spray pyrolysis Methods 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000003764 ultrasonic spray pyrolysis Methods 0.000 description 1
Description
本発明は、排気ガス浄化用触媒の製造方法に関する。 The present invention relates to a method for producing an exhaust gas purification catalyst.
自動車用の排気ガス浄化用触媒は、基本的にはアルミナ等の多孔質担体に触媒金属を担持させて構成されている。この触媒金属の担体への担持に関し、特許文献１には、担体に触媒金属溶液を含浸させ、次いでアンモニア水によって触媒金属を水酸化物に変換して担体に不溶化させた状態で固定化し、次いで不活性雰囲気又は減圧雰囲気で加熱する活性化処理を行なうことが記載されている。この活性化処理は触媒金属を０価の金属単体にするというものである。また、特許文献２には、担体粒子に触媒金属溶液を含浸させ、乾燥及び焼成を行なうにあたり、当該含浸粒子を遊動状態で乾燥処理を行なうことにより、一つの粒子の全表面からの水分蒸発速度が均一になるようにして触媒金属の高分散化を図ること、その乾燥処理を減圧下で行なうことにより、蒸発水分を系外に排出することが記載されている。
ところで、排気ガス浄化用触媒は、触媒金属等の金属成分を高分散化させて排気ガス成分との接触機会を増やすとともに、それら金属成分のシンタリング防止を図ることが重要である。そのために、上記金属成分を担持する酸化物担体の比表面積を大きくすることが望まれ、特に酸素吸蔵材については、当該触媒が三元触媒として働くＡ／Ｆウインド（空燃比の幅）の拡大や、該酸素吸蔵材が担持する金属成分の還元（即ち、還元による活性の維持）に大きな役割を果たすので、高温の排気ガスに晒された後でも高い比表面積を有することが要望される。 By the way, it is important for the exhaust gas purification catalyst to increase the chance of contact with the exhaust gas component by highly dispersing metal components such as a catalyst metal and to prevent sintering of these metal components. For this purpose, it is desired to increase the specific surface area of the oxide carrier supporting the metal component. Especially for the oxygen storage material, the A / F window (the width of the air-fuel ratio) where the catalyst acts as a three-way catalyst is expanded. In addition, since it plays a major role in reducing the metal component carried by the oxygen storage material (that is, maintaining the activity by reduction), it is desired to have a high specific surface area even after being exposed to high-temperature exhaust gas.
上記担体は通常一次粒子が凝集してなる二次粒子で形成されている。従って、上記比表面積の増大には、一次粒子の粒径を小さくすることが有効である。しかし、一次粒子径が小さくなると、一次粒子間に形成される細孔の孔径が小さくなるため、通常の含浸法や蒸発乾固法では、触媒金属溶液が細孔内に入り難くなる。その結果、触媒金属が細孔内部には担持されずに、担体表面のみに担持された状態になり易い。すなわち、触媒金属の担体における分散度が低くなり、触媒性能の向上を図ることが難しくなる。 The carrier is usually formed of secondary particles obtained by agglomerating primary particles. Therefore, to increase the specific surface area, it is effective to reduce the particle size of the primary particles. However, when the primary particle size is reduced, the pore size of the pores formed between the primary particles is reduced, so that the catalyst metal solution is difficult to enter the pores by a normal impregnation method or evaporation to dryness method. As a result, the catalyst metal is not supported inside the pores, and tends to be supported only on the support surface. That is, the degree of dispersion of the catalyst metal carrier becomes low, and it becomes difficult to improve the catalyst performance.
そこで、本発明は、Ｃｅ−Ｚｒ系複酸化物よりなる担体の比表面積を大きくするとともに、その微細な細孔内にも触媒金属を確実に担持できるようにすることを課題とする。 Accordingly, an object of the present invention is to increase the specific surface area of a support made of a Ce—Zr-based double oxide and to ensure that the catalyst metal can be supported in the fine pores.
本発明は、そのために、微細な一次粒子が凝集してなる中空状の二次粒子担体に、減圧脱気法によって触媒金属を担持させるようにした。 Therefore, in the present invention, a catalyst metal is supported on a hollow secondary particle carrier formed by agglomerating fine primary particles by a vacuum degassing method.
すなわち、請求項１に係る発明は、ＣｅとＺｒとを含有する複酸化物よりなり且つ平均粒径１０ｎｍ未満の一次粒子が凝集して内部に細孔を有するシェルが形成されている中空状の二次粒子担体を得る工程と、
上記二次粒子担体を触媒金属イオンの水溶液に分散させてなる懸濁液を、容器内で減圧脱気しつつ加熱することにより、水分を蒸発させ、触媒金属を上記二次粒子担体の表面及び上記細孔内に担持させる工程とを備えていることを特徴とする排気ガス浄化用触媒の製造方法である。
That is, the invention according to claim 1 is a hollow-shaped structure in which a primary oxide having a mean particle size of less than 10 nm is agglomerated to form a shell having pores therein, which is made of a double oxide containing Ce and Zr. Obtaining a secondary particle carrier;
A suspension obtained by dispersing the secondary particle carrier in an aqueous solution of catalyst metal ions is heated while degassing in a container under reduced pressure to evaporate water, and the catalyst metal is removed from the surface of the secondary particle carrier and And a step of supporting the catalyst in the pores.
従って、担体は、その結晶子が凝集してなる一次粒子径が小さいことから、細孔はその孔径が微細になり、担体の比表面積が大きなものになる。しかも中空状であることによって比表面積がさらに大きくなる。そうして、減圧脱気により、上記微細細孔内の空気が除去されると同時に、その細孔内に触媒金属イオンの水溶液が入ることになる。その状態で加熱されて水分が蒸発するため、触媒金属が酸素吸蔵材の表面だけでなく、細孔内にも確実に担持されることになる。よって、触媒金属が担体の表面から微細細孔内に亘って略均一に担持された高比表面積の触媒が得られ、微細細孔に入ってきた排気ガス成分と触媒金属との接触が図れるから、排気ガス浄化性能の向上に有利になる。 Therefore, since the support has a small primary particle diameter formed by agglomeration of the crystallites, the pores have a fine pore diameter and a large specific surface area of the support. Moreover, the specific surface area is further increased due to the hollow shape. Thus, the air in the fine pores is removed by degassing under reduced pressure, and at the same time, an aqueous solution of catalytic metal ions enters the pores. Since the water is evaporated by heating in this state, the catalyst metal is reliably supported not only on the surface of the oxygen storage material but also in the pores. Therefore, a catalyst having a high specific surface area in which the catalyst metal is supported substantially uniformly from the surface of the support to the inside of the fine pores can be obtained, and contact between the exhaust gas component entering the fine pores and the catalytic metal can be achieved. This is advantageous for improving exhaust gas purification performance.
また、上記担体はＣｅとＺｒとを含有する複酸化物よりなるから、酸素吸蔵能を有し、一次粒子の粒径が微小であることによって、酸素の吸蔵放出が速やかに行なわれ、さらに、中実状（塊状）となっている場合に比べて、表面（シェルの外面及び内面を含む）に露出する一次粒子が多くなるとともに、排気ガスが当該担体のシェル壁を通り抜けやすくなり、一次粒子に担持されている触媒金属と排気ガスとが接触し易くなる。このことが、触媒活性（ライトオフ性能）の向上に有利に働く。 In addition, since the carrier is made of a double oxide containing Ce and Zr, it has an oxygen storage ability, and the primary particles have a very small particle size, so that oxygen can be stored and released quickly. Compared to a solid (lumped) shape, the primary particles exposed on the surface (including the outer and inner surfaces of the shell) increase, and the exhaust gas easily passes through the shell wall of the carrier. The supported catalyst metal and the exhaust gas are easily brought into contact with each other. This is advantageous for improving the catalyst activity (light-off performance).
しかも、一次粒子径が小さいにも拘わらず、中空状になっていることにより、触媒が高温の排気ガスに晒された後でも比較的大きな比表面積を有するようになり、触媒金属のシンタリングも抑制され、高い排気ガス浄化性能を長期間にわたって確保する上で有利になる。 Moreover, despite the small primary particle size, the hollow shape allows the catalyst to have a relatively large specific surface area even after being exposed to high-temperature exhaust gas. This is advantageous for ensuring high exhaust gas purification performance over a long period of time.
上記一次粒子の平均粒径が過度に小さくなると、上記一次粒子間に形成されている細孔径が小さくなりすぎて排気ガス成分の細孔内への拡散進入が難しくなる。従って、上記平均粒径の下限は、特に限定するわけではないが、例えば３〜４ｎｍ程度を目安にすればよい。 If the average particle size of the primary particles becomes excessively small, the pore diameter formed between the primary particles becomes too small, making it difficult for the exhaust gas component to diffuse into the pores. Therefore, the lower limit of the average particle diameter is not particularly limited, but may be about 3 to 4 nm, for example.
また、上記容器内圧力は１０ｋＰａ以上３０ｋＰａ以下程度にすることが好ましく、また、容器内温度は６５℃以上にすることが好ましい。 The internal pressure of the container is preferably about 10 kPa to 30 kPa, and the internal temperature is preferably 65 ° C. or higher.
請求項２に係る発明は、請求項１において、
上記水溶液を上記触媒金属イオンとＮＯｘ吸蔵材となる金属イオンとの混合液とし、触媒金属及びＮＯｘ吸蔵材を上記二次粒子担体の表面及び細孔内に担持させることを特徴とする。
The invention according to claim 2 is the invention according to claim 1,
The aqueous solution is a mixed solution of the catalyst metal ions and the metal ions serving as the NOx storage material, and the catalyst metal and the NOx storage material are supported on the surface and pores of the secondary particle carrier.
従って、触媒金属及びＮＯｘ吸蔵材とを担体の表面から細孔内に亘って略均一に担持させることができ、ＮＯｘ浄化性能の向上に有利になる。すなわち、エンジンのＡ／Ｆリーン時に排気ガス中のＮＯｘをＮＯｘ吸蔵材に吸蔵し、Ａ／Ｆリッチ時に該ＮＯｘ吸蔵材から放出されるＮＯｘを上記触媒金属で還元浄化することができ、ＮＯｘ浄化性能の向上に有利になる。 Therefore, the catalyst metal and the NOx occlusion material can be supported substantially uniformly from the surface of the carrier to the inside of the pores, which is advantageous in improving the NOx purification performance. That is, NOx in the exhaust gas can be stored in the NOx storage material when the engine is A / F lean, and NOx released from the NOx storage material can be reduced and purified with the catalyst metal when the A / F is rich. This is advantageous for improving performance.
上記各発明において、触媒金属としては、Ｐｔ、Ｒｈ、Ｉｒ等の貴金属が好ましく、また、ＮＯｘ吸蔵材としては、Ｂａ等のアルカリ土類金属、Ｋ等のアルカリ金属を採用することが好ましい。 In each of the above inventions, the catalyst metal is preferably a noble metal such as Pt, Rh, or Ir, and the NOx storage material is preferably an alkaline earth metal such as Ba or an alkali metal such as K.
以上のように、本発明に係る排気ガス浄化用触媒の製造方法によれば、ＣｅとＺｒとを含有する複酸化物よりなり且つ平均粒径１０ｎｍ未満の一次粒子が凝集して内部に細孔を有するシェルが形成されている中空状の二次粒子担体を得る工程と、この二次粒子担体を触媒金属イオンの水溶液に分散させてなる懸濁液を、容器内で減圧脱気しつつ加熱することにより、水分を蒸発させ、触媒金属を上記二次粒子担体の表面及び上記細孔内に担持させる工程とを備えているから、触媒金属が比表面積の大きな中空状担体の表面から微細細孔内に亘って略均一に担持された触媒が得られ、触媒活性の向上、触媒金属のシンタリング抑制に有利になる。 As described above, according to the method for producing an exhaust gas purifying catalyst according to the present invention, primary particles made of a double oxide containing Ce and Zr and having an average particle size of less than 10 nm aggregate to form pores. A step of obtaining a hollow secondary particle carrier in which a shell having a surface is formed, and a suspension obtained by dispersing the secondary particle carrier in an aqueous solution of catalytic metal ions is heated while degassing in a container under reduced pressure By evaporating moisture and supporting the catalyst metal on the surface of the secondary particle carrier and the pores, the catalyst metal is finely divided from the surface of the hollow carrier having a large specific surface area. A catalyst supported substantially uniformly over the pores is obtained, which is advantageous for improving the catalytic activity and suppressing sintering of the catalytic metal.
以下、本発明の実施形態を図面に基づいて説明する。 Hereinafter, embodiments of the present invention will be described with reference to the drawings.
本発明に係る排気ガス浄化用触媒の製造方法は、自動車エンジンの排気ガス中のＨＣ、ＣＯ及びＮＯｘを浄化する三元触媒の製造、或いは適宜Ａ／Ｆリーンで運転されるエンジンの排気ガス中のＮＯｘの浄化に適したＮＯｘ吸蔵触媒の製造に特に有用である。排気ガスの浄化にあたっては、コージェライト等の無機多孔質によって形成されたハニカム形状等の担体上に触媒をバインダによって担持させ、これを排気通路に配置する。 The method for producing an exhaust gas purifying catalyst according to the present invention includes the production of a three-way catalyst for purifying HC, CO and NOx in the exhaust gas of an automobile engine, or in the exhaust gas of an engine operated with an A / F lean as appropriate. This is particularly useful for the production of NOx storage catalysts suitable for the purification of NOx. In purifying exhaust gas, a catalyst is supported by a binder on a honeycomb-shaped carrier formed of inorganic porous material such as cordierite, and this is disposed in the exhaust passage.
当該製造方法は、ＣｅとＺｒとを含有する複酸化物よりなり且つ平均粒径１０ｎｍ未満の一次粒子が凝集して内部に細孔を有するシェルが形成されている中空状の二次粒子担体を得て、この二次粒子担体を触媒金属イオンの水溶液に分散させてなる懸濁液を、容器内で減圧脱気しつつ加熱することにより、水分を蒸発させ、触媒金属を上記二次粒子担体の表面及び上記細孔内に担持させる点に特徴がある。以下、ＮＯｘ吸蔵触媒を例に具体的に説明する。 The manufacturing method includes a hollow secondary particle carrier made of a double oxide containing Ce and Zr and having a shell having pores formed by agglomerating primary particles having an average particle size of less than 10 nm. The suspension obtained by dispersing the secondary particle carrier in an aqueous solution of the catalyst metal ions is heated while degassing in a container under reduced pressure to evaporate the water, thereby removing the catalyst metal from the secondary particle carrier. It is characterized in that it is supported on the surface of the metal and the pores. Hereinafter, the NOx occlusion catalyst will be specifically described as an example.
＜実施例及び比較例＞
−実施例−
酸素吸蔵材を噴霧熱分解法によって調製した。すなわち、オキシ硝酸ジルコニウム、硝酸セリウム及び硫酸マグネシウムの各所定量を水に溶解させることにより、原料溶液を調製した（原料溶液調製）。ここで、硫酸マグネシウムは、中空状酸素吸蔵材を製造する際の一次粒子のシンタリングを抑制する、一次粒子同士の接触点を減らしつつ中空構造に導く、という作用を有するものとして、各種添加化合物の中から選定されたものであり、その添加量、濃度等は適宜決定することができる。
<Examples and Comparative Examples>
-Example-
Oxygen storage material was prepared by spray pyrolysis method. That is, a raw material solution was prepared by dissolving predetermined amounts of zirconium oxynitrate, cerium nitrate, and magnesium sulfate in water (preparation of raw material solution). Here, magnesium sulfate has various actions such as suppressing the sintering of primary particles when producing a hollow oxygen storage material and leading to a hollow structure while reducing the contact points between primary particles. The amount added, concentration, etc. can be determined as appropriate.
次いで、上記原料溶液を、空気をキャリアガスとして噴霧することにより、液滴化させて加熱炉に供給した（超音波噴霧熱分解）。加熱炉の温度は１０００℃に設定した。加熱炉を出た粒子はバグフィルターによって捕集し、これを水洗後、乾燥させることにより、当該中空状酸素吸蔵材（Ｃｅ−Ｚｒ複酸化物）を得た。この実施例においては、ＣｅＯ2：ＺｒＯ2＝７５：２５（質量比）となるようにした。 Next, the raw material solution was sprayed using air as a carrier gas to form droplets and supplied to a heating furnace (ultrasonic spray pyrolysis). The temperature of the heating furnace was set to 1000 ° C. The particles exiting the heating furnace were collected by a bag filter, washed with water, and dried to obtain the hollow oxygen storage material (Ce—Zr double oxide). In this example, CeO 2 : ZrO 2 = 75: 25 (mass ratio).
次いで、上記中空状酸素吸蔵材、γ−アルミナ粉末、貴金属溶液（ジニトロジアミン白金硝酸溶液及び硝酸ロジウム溶液）、ＮＯｘ吸蔵材（酢酸バリウム、酢酸ストロンチウム）及び水の各所定量を容器に入れ攪拌することにより懸濁液とした（懸濁液調製）。この懸濁液を攪拌しながら容器内圧力を２０ｋＰａに減圧することにより、脱気しつつ７０〜８０℃に加熱することにより、水分を蒸発させた（減圧脱気）。 Next, the hollow oxygen storage material, γ-alumina powder, noble metal solution (dinitrodiamine platinum nitric acid solution and rhodium nitrate solution), NOx storage material (barium acetate, strontium acetate) and water are put in a container and stirred. To prepare a suspension (suspension preparation). While this suspension was stirred, the internal pressure of the container was reduced to 20 kPa, and the water was evaporated by heating to 70 to 80 ° C. while degassing (vacuum degassing).
上記減圧脱気で得られた乾固物を粉砕して粉末状にした（粉砕）。得られた粉末を５００℃の温度に２時間加熱保持する焼成を行なうことにより、上記酸素吸蔵材及びγ−アルミナ粉末をサポート材として、これに貴金属及びＮＯｘ吸蔵材が担持された触媒粉末を得た（焼成）。 The dried product obtained by degassing under reduced pressure was pulverized into a powder (pulverization). The obtained powder is fired at a temperature of 500 ° C. for 2 hours to obtain a catalyst powder in which the oxygen storage material and the γ-alumina powder are used as a support material and on which the noble metal and NOx storage material are supported. (Fired).
次に上記触媒粉末を塩基性Ｚｒバインダ及び水と混合してスラリーとした（スラリー化）。このスラリーにコージェライト製ハニカム担体（１平方インチ（約６．５４ｃｍ2）当たりのセル数４００、相隣るセルを隔てる壁厚４ミル（約０．１０ｍｍ））に浸漬して引き上げ、余分なスラリーをエアブローで吹き飛ばした（触媒コート層の形成）。次いで、コート層を乾燥させた後、５００℃の温度に２時間加熱保持する焼成を行なうことにより、排気ガス浄化用触媒を得た（焼成）。ハニカム担体１Ｌ当たりの酸素吸蔵材担持量は１５０ｇ／Ｌ、γ−アルミナ担持量は１５０ｇ／Ｌ、Ｐｔ担持量は３．５ｇ／Ｌ、Ｒｈ担持量は０．３ｇ／Ｌ、Ｂａ担持量は３５ｇ／Ｌ、Ｓｒ担持量５ｇ／Ｌである。 Next, the catalyst powder was mixed with a basic Zr binder and water to form a slurry (slurry). This slurry is dipped in a cordierite honeycomb carrier (400 cells per square inch (about 6.54 cm 2 ), wall thickness of 4 mil (about 0.10 mm) separating adjacent cells) and pulled up. The slurry was blown off by air blow (formation of catalyst coat layer). Next, after drying the coat layer, the catalyst for exhaust gas purification was obtained (calcination) by performing calcination by heating and holding at a temperature of 500 ° C. for 2 hours. Oxygen storage material loading per 1 L of honeycomb carrier is 150 g / L, γ-alumina loading is 150 g / L, Pt loading is 3.5 g / L, Rh loading is 0.3 g / L, Ba loading is 35 g. / L, Sr loading 5 g / L.
−酸素吸蔵材のＴＥＭ写真−
図１及び図２は実施例に係る酸素吸蔵材のＴＥＭ（透過型電子顕微鏡）写真である。この酸素吸蔵材は、図２に示すように、粒径が４〜１０ｎｍの一次粒子がシェル材となって凝集した中空状の二次粒子となったものであり、一次粒子間には孔径数ｎｍの細孔が形成されている。
-TEM photograph of oxygen storage material-
1 and 2 are TEM (transmission electron microscope) photographs of the oxygen storage material according to the example. As shown in FIG. 2, this oxygen storage material is a hollow secondary particle in which primary particles having a particle size of 4 to 10 nm are aggregated into shell materials, and the number of pores is between the primary particles. nm pores are formed.
−比較例１−
貴金属及びＮＯｘ吸蔵材の担持に、上記減圧脱気法に代えて常圧蒸発乾固法を採用する他は実施例と同じ方法で排気ガス浄化用触媒を得た。
-Comparative Example 1-
Exhaust gas purifying catalysts were obtained in the same manner as in Example except that the atmospheric pressure evaporation / drying method was adopted instead of the above-mentioned reduced pressure degassing method for supporting the noble metal and NOx occlusion material.
すなわち、上記中空状酸素吸蔵材、γ−アルミナ粉末、貴金属溶液（ジニトロジアミン白金硝酸溶液及び硝酸ロジウム溶液）、ＮＯｘ吸蔵材（酢酸バリウム、酢酸ストロンチウム）及び水の各所定量を容器に入れ攪拌することにより懸濁液とした。この懸濁液を攪拌しながら大気圧下で１００℃まで加熱することにより、水分を蒸発させて粉末を得た（常圧蒸発乾固）。 That is, a predetermined amount of each of the above hollow oxygen storage material, γ-alumina powder, noble metal solution (dinitrodiamine platinum nitrate solution and rhodium nitrate solution), NOx storage material (barium acetate, strontium acetate) and water is placed in a container and stirred. To make a suspension. The suspension was heated to 100 ° C. under atmospheric pressure with stirring to evaporate the water and obtain a powder (normal pressure evaporation to dryness).
そうして、得られた乾固物に対して実施例と同じく粉砕及び焼成の処理を行なうことにより、触媒粉末を得て、さらに同様のスラリー化、触媒コート層の形成、乾燥・焼成の処理を行なうことにより、比較例１に係る排気ガス浄化用触媒を得た。 Then, the obtained dried solid product is pulverized and fired in the same manner as in the examples to obtain a catalyst powder. Further, the same slurrying, formation of a catalyst coat layer, and drying / firing treatment are performed. As a result, an exhaust gas purifying catalyst according to Comparative Example 1 was obtained.
従って、比較例１の中空状酸素吸蔵材の一次粒子の粒径は実施例と同じく１０ｎｍ未満であり、触媒の組成も実施例と同じである。 Therefore, the particle size of the primary particles of the hollow oxygen storage material of Comparative Example 1 is less than 10 nm as in the example, and the composition of the catalyst is the same as in the example.
−比較例２−
酸素吸蔵材を平均粒径１０ｎｍ未満の一次粒子が凝集した中実状（塊状）の二次粒子とする他は比較例１と同じ方法（常圧蒸発乾固）で排気ガス浄化用触媒を得た。触媒の組成は実施例と同じである。
-Comparative Example 2-
Exhaust gas purification catalyst was obtained by the same method (atmospheric pressure evaporation to dryness) as in Comparative Example 1 except that the oxygen storage material was solid (lumped) secondary particles in which primary particles having an average particle size of less than 10 nm were agglomerated. . The composition of the catalyst is the same as in the examples.
−ＮＯｘ浄化性能の評価−
上記実施例及び比較例１，２の各触媒について、大気雰囲気で７５０℃の温度に２４時間保持するエージングを行なった後、モデルガス流通反応装置と排気ガス分析装置とを用いて、ＮＯｘ浄化性能を調べた。
-Evaluation of NOx purification performance-
Each catalyst of the above Examples and Comparative Examples 1 and 2 is subjected to aging that is maintained at a temperature of 750 ° C. for 24 hours in an air atmosphere, and then is subjected to NOx purification performance using a model gas flow reactor and an exhaust gas analyzer. I investigated.
すなわち、Ａ／Ｆリーンのモデル排気ガスを６０秒間流し、次にガス組成をＡ／Ｆリッチのモデル排気ガスに切り換えてこれを６０秒間流す、というサイクルを数回繰り返した後、ガス組成をＡ／ＦリッチからＡ／Ｆリーンに切り換えた時点から６０秒間のＮＯｘ浄化率（リーンＮＯｘ浄化率）と、ガス組成をＡ／ＦリーンからＡ／Ｆリッチに切り換えた時点から６０秒間のＮＯｘ浄化率（リッチＮＯｘ浄化率）とを測定した。触媒入口ガス温度は４００℃とした。結果を図３に示す。 That is, after repeating the cycle of flowing the A / F lean model exhaust gas for 60 seconds, then switching the gas composition to the A / F rich model exhaust gas and flowing it for 60 seconds, the gas composition was changed to A NOx purification rate (lean NOx purification rate) for 60 seconds from the time of switching from / F rich to A / F lean and NOx purification rate for 60 seconds from the time of switching the gas composition from A / F lean to A / F rich (Rich NOx purification rate) was measured. The catalyst inlet gas temperature was 400 ° C. The results are shown in FIG.
リーンＮＯｘ浄化率及びリッチＮＯｘ浄化率のいずれも、実施例は比較例１，２よりも高くなっている。このように実施例のＮＯｘ浄化性能が高いのは、減圧脱気法の採用により、酸素吸蔵材のシェルの微細な細孔内の空気が除去されると同時に、その細孔内に触媒貴金属及びＮＯｘ吸蔵材の水溶液が入り、それらが酸素吸蔵材の表面だけでなく、細孔内にも同様に担持されているためと認められる。比較例１のＮＯｘ浄化率が比較例２よりも高いのは酸素吸蔵材が中空状になっているためであるが、実施例はこの比較例２よりもＮＯｘ浄化率が高くなっており、減圧脱気法の効果が明瞭に現れている、ということができる。 In both the lean NOx purification rate and the rich NOx purification rate, the example is higher than the comparative examples 1 and 2. Thus, the NOx purification performance of the example is high because the air in the fine pores of the shell of the oxygen storage material is removed by adopting the vacuum degassing method, and at the same time, the catalyst noble metal and It is recognized that an aqueous solution of NOx occlusion material enters and they are supported not only on the surface of the oxygen occlusion material but also in the pores. The NOx purification rate of Comparative Example 1 is higher than that of Comparative Example 2 because the oxygen storage material is hollow, but the Example has a higher NOx purification rate than Comparative Example 2, and the pressure reduction It can be said that the effect of the degassing method is clearly shown.
なし None
Claims (2)
上記二次粒子担体を触媒金属イオンの水溶液に分散させてなる懸濁液を、容器内で減圧脱気しつつ加熱することにより、水分を蒸発させ、触媒金属を上記二次粒子担体の表面及び上記細孔内に担持させる工程とを備えていることを特徴とする排気ガス浄化用触媒の製造方法。 A step of obtaining a hollow secondary particle carrier made of a double oxide containing Ce and Zr and having primary particles with an average particle size of less than 10 nm aggregated to form a shell having pores inside;
A suspension obtained by dispersing the secondary particle carrier in an aqueous solution of catalyst metal ions is heated while degassing in a container under reduced pressure to evaporate water, and the catalyst metal is removed from the surface of the secondary particle carrier and A process for supporting the exhaust gas in the pores.
上記水溶液を上記触媒金属イオンとＮＯｘ吸蔵材になる金属イオンとの混合液とし、触媒金属及びＮＯｘ吸蔵材を上記二次粒子担体の表面及び上記細孔内に担持させることを特徴とする排気ガス浄化用触媒の製造方法。 In claim 1,
An exhaust gas characterized in that the aqueous solution is a mixed liquid of the catalyst metal ions and metal ions that become the NOx storage material, and the catalyst metal and the NOx storage material are supported on the surface of the secondary particle carrier and in the pores. A method for producing a purification catalyst.
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