JP4577408B2 - Exhaust gas purification catalyst - Google Patents
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- JP4577408B2 JP4577408B2 JP2008143525A JP2008143525A JP4577408B2 JP 4577408 B2 JP4577408 B2 JP 4577408B2 JP 2008143525 A JP2008143525 A JP 2008143525A JP 2008143525 A JP2008143525 A JP 2008143525A JP 4577408 B2 JP4577408 B2 JP 4577408B2
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- 239000003054 catalyst Substances 0.000 title claims description 185
- 238000000746 purification Methods 0.000 title claims description 22
- UQSXHKLRYXJYBZ-UHFFFAOYSA-N Iron oxide Chemical compound [Fe]=O UQSXHKLRYXJYBZ-UHFFFAOYSA-N 0.000 claims description 250
- 239000002245 particle Substances 0.000 claims description 211
- 239000002131 composite material Substances 0.000 claims description 72
- 229910000510 noble metal Inorganic materials 0.000 claims description 36
- 239000011230 binding agent Substances 0.000 claims description 29
- 230000003197 catalytic effect Effects 0.000 claims description 10
- 229910052595 hematite Inorganic materials 0.000 claims description 6
- 239000011019 hematite Substances 0.000 claims description 6
- LIKBJVNGSGBSGK-UHFFFAOYSA-N iron(3+);oxygen(2-) Chemical compound [O-2].[O-2].[O-2].[Fe+3].[Fe+3] LIKBJVNGSGBSGK-UHFFFAOYSA-N 0.000 claims description 6
- 229910052598 goethite Inorganic materials 0.000 claims description 4
- AEIXRCIKZIZYPM-UHFFFAOYSA-M hydroxy(oxo)iron Chemical compound [O][Fe]O AEIXRCIKZIZYPM-UHFFFAOYSA-M 0.000 claims description 4
- JEIPFZHSYJVQDO-UHFFFAOYSA-N iron(III) oxide Inorganic materials O=[Fe]O[Fe]=O JEIPFZHSYJVQDO-UHFFFAOYSA-N 0.000 claims description 4
- 239000002994 raw material Substances 0.000 claims 1
- VCJMYUPGQJHHFU-UHFFFAOYSA-N iron(3+);trinitrate Chemical compound [Fe+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O VCJMYUPGQJHHFU-UHFFFAOYSA-N 0.000 description 50
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 43
- 239000007789 gas Substances 0.000 description 43
- 239000001301 oxygen Substances 0.000 description 43
- 229910052760 oxygen Inorganic materials 0.000 description 43
- 239000000463 material Substances 0.000 description 35
- 239000010948 rhodium Substances 0.000 description 34
- 230000032683 aging Effects 0.000 description 23
- 239000010410 layer Substances 0.000 description 23
- XEEYBQQBJWHFJM-UHFFFAOYSA-N iron Substances [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 description 22
- 229910052751 metal Inorganic materials 0.000 description 22
- 239000002184 metal Substances 0.000 description 22
- 238000003860 storage Methods 0.000 description 22
- 238000009826 distribution Methods 0.000 description 16
- 239000000843 powder Substances 0.000 description 16
- 238000013507 mapping Methods 0.000 description 15
- 239000002002 slurry Substances 0.000 description 15
- 238000010304 firing Methods 0.000 description 13
- 239000013078 crystal Substances 0.000 description 12
- 229910052742 iron Inorganic materials 0.000 description 11
- 239000000243 solution Substances 0.000 description 11
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 11
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 description 10
- 238000001035 drying Methods 0.000 description 10
- 210000002421 cell wall Anatomy 0.000 description 7
- 229910044991 metal oxide Inorganic materials 0.000 description 7
- 150000004706 metal oxides Chemical class 0.000 description 7
- 238000002156 mixing Methods 0.000 description 7
- 239000000047 product Substances 0.000 description 7
- 238000000851 scanning transmission electron micrograph Methods 0.000 description 7
- 238000012360 testing method Methods 0.000 description 7
- 229910052684 Cerium Inorganic materials 0.000 description 5
- 239000011521 glass Substances 0.000 description 5
- 238000005259 measurement Methods 0.000 description 5
- 229910052759 nickel Inorganic materials 0.000 description 5
- 238000002360 preparation method Methods 0.000 description 5
- 229910052726 zirconium Inorganic materials 0.000 description 5
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 4
- 235000011114 ammonium hydroxide Nutrition 0.000 description 4
- 239000007864 aqueous solution Substances 0.000 description 4
- 230000008859 change Effects 0.000 description 4
- 230000000694 effects Effects 0.000 description 4
- 238000011068 loading method Methods 0.000 description 4
- 239000011148 porous material Substances 0.000 description 4
- 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 4
- 229910052723 transition metal Inorganic materials 0.000 description 4
- 150000003624 transition metals Chemical class 0.000 description 4
- 229910002651 NO3 Inorganic materials 0.000 description 3
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 3
- 238000002441 X-ray diffraction Methods 0.000 description 3
- QGZKDVFQNNGYKY-UHFFFAOYSA-N ammonia Natural products N QGZKDVFQNNGYKY-UHFFFAOYSA-N 0.000 description 3
- 238000001354 calcination Methods 0.000 description 3
- 230000000052 comparative effect Effects 0.000 description 3
- 230000007423 decrease Effects 0.000 description 3
- 230000006872 improvement Effects 0.000 description 3
- MVFCKEFYUDZOCX-UHFFFAOYSA-N iron(2+);dinitrate Chemical compound [Fe+2].[O-][N+]([O-])=O.[O-][N+]([O-])=O MVFCKEFYUDZOCX-UHFFFAOYSA-N 0.000 description 3
- 150000002739 metals Chemical class 0.000 description 3
- 239000011259 mixed solution Substances 0.000 description 3
- 238000007254 oxidation reaction Methods 0.000 description 3
- 239000010970 precious metal Substances 0.000 description 3
- 238000005245 sintering Methods 0.000 description 3
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 2
- IJGRMHOSHXDMSA-UHFFFAOYSA-N Atomic nitrogen Chemical compound N#N IJGRMHOSHXDMSA-UHFFFAOYSA-N 0.000 description 2
- LFQSCWFLJHTTHZ-UHFFFAOYSA-N Ethanol Chemical compound CCO LFQSCWFLJHTTHZ-UHFFFAOYSA-N 0.000 description 2
- 229910017493 Nd 2 O 3 Inorganic materials 0.000 description 2
- MCMNRKCIXSYSNV-UHFFFAOYSA-N Zirconium dioxide Chemical compound O=[Zr]=O MCMNRKCIXSYSNV-UHFFFAOYSA-N 0.000 description 2
- 230000004913 activation Effects 0.000 description 2
- 239000003463 adsorbent Substances 0.000 description 2
- 230000005540 biological transmission Effects 0.000 description 2
- 238000006555 catalytic reaction Methods 0.000 description 2
- 210000004027 cell Anatomy 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
- 239000011247 coating layer Substances 0.000 description 2
- 229910052878 cordierite Inorganic materials 0.000 description 2
- 230000002950 deficient Effects 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
- 229910001873 dinitrogen Inorganic materials 0.000 description 2
- 238000011156 evaluation Methods 0.000 description 2
- 238000001704 evaporation Methods 0.000 description 2
- 238000010438 heat treatment Methods 0.000 description 2
- 238000000034 method Methods 0.000 description 2
- 230000003647 oxidation Effects 0.000 description 2
- 229910052763 palladium Inorganic materials 0.000 description 2
- 229910052697 platinum Inorganic materials 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 150000002910 rare earth metals Chemical class 0.000 description 2
- 239000011232 storage material Substances 0.000 description 2
- 230000036962 time dependent Effects 0.000 description 2
- 238000011144 upstream manufacturing Methods 0.000 description 2
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- VYPSYNLAJGMNEJ-UHFFFAOYSA-N Silicium dioxide Chemical compound O=[Si]=O VYPSYNLAJGMNEJ-UHFFFAOYSA-N 0.000 description 1
- 230000002776 aggregation Effects 0.000 description 1
- 238000004220 aggregation Methods 0.000 description 1
- 229910052784 alkaline earth metal Inorganic materials 0.000 description 1
- 150000001342 alkaline earth metals Chemical class 0.000 description 1
- 229910052782 aluminium Inorganic materials 0.000 description 1
- -1 at least one of Co Inorganic materials 0.000 description 1
- 229910001566 austenite Inorganic materials 0.000 description 1
- CETPSERCERDGAM-UHFFFAOYSA-N ceric oxide Chemical compound O=[Ce]=O CETPSERCERDGAM-UHFFFAOYSA-N 0.000 description 1
- GWXLDORMOJMVQZ-UHFFFAOYSA-N cerium Chemical group [Ce] GWXLDORMOJMVQZ-UHFFFAOYSA-N 0.000 description 1
- 229910000420 cerium oxide Inorganic materials 0.000 description 1
- 229910000422 cerium(IV) oxide Inorganic materials 0.000 description 1
- 239000008119 colloidal silica Substances 0.000 description 1
- 150000001875 compounds Chemical class 0.000 description 1
- 230000000593 degrading effect Effects 0.000 description 1
- 230000006866 deterioration Effects 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- 230000008034 disappearance Effects 0.000 description 1
- 230000008020 evaporation Effects 0.000 description 1
- 238000001914 filtration Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- JEGUKCSWCFPDGT-UHFFFAOYSA-M hydroxide;hydrate Chemical compound O.[OH-] JEGUKCSWCFPDGT-UHFFFAOYSA-M 0.000 description 1
- 229910052809 inorganic oxide Inorganic materials 0.000 description 1
- 238000005342 ion exchange Methods 0.000 description 1
- 150000002500 ions Chemical class 0.000 description 1
- 239000007788 liquid Substances 0.000 description 1
- 238000012423 maintenance Methods 0.000 description 1
- 238000004643 material aging Methods 0.000 description 1
- 150000002736 metal compounds Chemical class 0.000 description 1
- 239000000203 mixture Substances 0.000 description 1
- CFYGEIAZMVFFDE-UHFFFAOYSA-N neodymium(3+);trinitrate Chemical compound [Nd+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O CFYGEIAZMVFFDE-UHFFFAOYSA-N 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
- BMMGVYCKOGBVEV-UHFFFAOYSA-N oxo(oxoceriooxy)cerium Chemical compound [Ce]=O.O=[Ce]=O BMMGVYCKOGBVEV-UHFFFAOYSA-N 0.000 description 1
- 239000002244 precipitate Substances 0.000 description 1
- 230000001376 precipitating effect Effects 0.000 description 1
- 239000002243 precursor Substances 0.000 description 1
- 238000010992 reflux Methods 0.000 description 1
- 238000012827 research and development Methods 0.000 description 1
- 229910052703 rhodium Inorganic materials 0.000 description 1
- 239000011163 secondary particle Substances 0.000 description 1
- 238000010008 shearing Methods 0.000 description 1
- 239000006104 solid solution Substances 0.000 description 1
- 239000002904 solvent Substances 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 239000000758 substrate Substances 0.000 description 1
- 238000005406 washing Methods 0.000 description 1
- 229910000859 α-Fe Inorganic materials 0.000 description 1
Classifications
-
- Y—GENERAL TAGGING OF NEW TECHNOLOGICAL DEVELOPMENTS; GENERAL TAGGING OF CROSS-SECTIONAL TECHNOLOGIES SPANNING OVER SEVERAL SECTIONS OF THE IPC; TECHNICAL SUBJECTS COVERED BY FORMER USPC CROSS-REFERENCE ART COLLECTIONS [XRACs] AND DIGESTS
- Y02—TECHNOLOGIES OR APPLICATIONS FOR MITIGATION OR ADAPTATION AGAINST CLIMATE CHANGE
- Y02A—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE
- Y02A50/00—TECHNOLOGIES FOR ADAPTATION TO CLIMATE CHANGE in human health protection, e.g. against extreme weather
- Y02A50/20—Air quality improvement or preservation, e.g. vehicle emission control or emission reduction by using catalytic converters
Description
本発明は、排気ガス浄化用触媒に関する。 The present invention relates to an exhaust gas purification catalyst.
車両用エンジンの排気通路には、Ｐｔ、Ｐｄ、Ｒｈ等の触媒金属を有する排気ガス浄化用触媒が設けられている。この触媒には、エンジン始動時のような排気ガス温度が低いときから排気ガスを浄化できるように早期に活性化することが求められ、また、高速走行等によって排気ガス温度が高い状態が続いた後でも、排気ガスの浄化率が大きく低下しないことが求められる。このような要求を満たすべく、触媒には比較的多量の触媒金属が使用され、例えば三元触媒にあっては、触媒金属の使用量は触媒担体１Ｌ当たり１〜２ｇとされることが多い。 An exhaust gas purification catalyst having a catalytic metal such as Pt, Pd, or Rh is provided in the exhaust passage of the vehicle engine. This catalyst is required to be activated early so that the exhaust gas can be purified from when the exhaust gas temperature is low, such as when the engine is started, and the exhaust gas temperature has continued to be high due to high speed running etc. Even later, it is required that the purification rate of the exhaust gas does not decrease greatly. In order to satisfy such requirements, a relatively large amount of catalyst metal is used for the catalyst. For example, in the case of a three-way catalyst, the amount of catalyst metal used is often 1 to 2 g per liter of catalyst carrier.
しかし、上記触媒金属の多くは希少金属であることから、資源保護等の観点より、触媒の性能を落とすことなく、触媒金属の使用量を少なくする研究開発が進められている。その手法としては大別して２つあり、その一つは、触媒貴金属をサポート材に固定化することであり、他の一つは、触媒貴金属のシンタリングを抑制するために、立体障害となる酸化物を触媒貴金属と共にサポート材に担持することである。 However, since many of the above catalyst metals are rare metals, research and development are being carried out to reduce the amount of catalyst metal used without degrading the performance of the catalyst from the viewpoint of resource protection and the like. There are roughly two methods, one of which is to immobilize the catalytic noble metal on the support material, and the other is to oxidize as a steric hindrance to suppress sintering of the catalytic noble metal. This is to support the object together with the catalyst precious metal on the support material.
前者の一例は特許文献１に記載されている。その例では、酸素吸蔵放出能を有しサポート材となるＣｅ含有酸化物粒子の結晶格子又は結晶格子間に触媒貴金属であるＲｈが配置され、さらにサポート材表面にＲｈが後担持されている。これによれば、ＲｈはＣｅ含有酸化物粒子の内部及び表面に固定化され、Ｒｈを有しないＣｅ含有酸化物粒子に比べて、酸素吸蔵放出能（酸素吸蔵放出量及び吸蔵吸蔵放出速度）が飛躍的に高まり、排気ガス浄化性能の向上に大きく寄与することができる。 An example of the former is described in Patent Document 1. In this example, the catalyst noble metal Rh is disposed between the crystal lattices of the Ce-containing oxide particles that have the ability to store and release oxygen and serve as the support material, and Rh is post-supported on the surface of the support material. According to this, Rh is immobilized inside and on the surface of the Ce-containing oxide particles, and has an oxygen storage / release capacity (oxygen storage / release amount and storage / release speed) as compared with Ce-containing oxide particles not containing Rh. It can dramatically increase and contribute greatly to the improvement of exhaust gas purification performance.
また、後者の例が特許文献２に記載されている。すなわち、この文献２には、ＣｅＯ２−ＺｒＯ２複合酸化物よりなる担体と、該担体に担持されたＡｌ、Ｎｉ及びＦｅから選ばれる少なくとも一種の金属酸化物粒子と、該担体に担持された貴金属とからなる排気ガス浄化用触媒が開示されている。担体上での貴金属の移動を金属酸化物粒子によって規制することにより、貴金属のシンタリングを抑制するというものである。但し、実施例として開示されている金属酸化物粒子はＡｌ２Ｏ３のみであり、ＣｅＯ２−ＺｒＯ２複合酸化物と硝酸Ａｌ水溶液とを混合し、これにアンモニア水を滴下・中和して沈殿を析出させ、濾過・洗浄・乾燥・焼成を行ない、得られた粉末にＰｔ溶液を含浸させ、蒸発乾固、乾燥及び焼成を行なうことにより触媒粉末を得るとされている。Ｎｉ及びＦｅについての実施例はない。 The latter example is described in Patent Document 2. That is, in this document 2, a support made of a CeO 2 —ZrO 2 composite oxide, at least one metal oxide particle selected from Al, Ni and Fe supported on the support, and supported on the support An exhaust gas purifying catalyst comprising a noble metal is disclosed. By restricting the movement of the noble metal on the support by the metal oxide particles, sintering of the noble metal is suppressed. However, the metal oxide particles disclosed as examples are only Al 2 O 3 , CeO 2 —ZrO 2 composite oxide and Al nitrate aqueous solution are mixed, and ammonia water is dropped and neutralized thereto. It is said that a catalyst powder is obtained by precipitating a precipitate, filtering, washing, drying and calcining, impregnating the obtained powder with a Pt solution, and evaporating to dryness, drying and calcining. There are no examples for Ni and Fe.
また、触媒金属量を増大させることなく、酸素吸蔵材の酸素吸蔵放出能を向上させるようにした触媒の一例が特許文献３に記載されている。それは、セリウム酸化物を含む担体と、この担体に担持された遷移金属及び貴金属からなる触媒金属とよりなり、セリウム原子及び貴金属各々に対する遷移金属の原子比を所定の範囲にするというものである。遷移金属としては、Ｃｏ、Ｎｉ及びＦｅの少なくとも一種が好ましいとされている。但し、実施例として開示されているのはＣｏ及びＮｉだけであり、Ｆｅについての実施例はない。 Patent Document 3 describes an example of a catalyst that improves the oxygen storage / release ability of the oxygen storage material without increasing the amount of catalyst metal. It consists of a support containing cerium oxide and a catalyst metal comprising a transition metal and a noble metal supported on the support, and the atomic ratio of the transition metal to each of the cerium atom and the noble metal is within a predetermined range. As the transition metal, at least one of Co, Ni and Fe is considered preferable. However, only Co and Ni are disclosed as examples, and there is no example about Fe.
また、特許文献３では、セリアジルコニア固溶体粉末に硝酸Ｎｉ（又は硝酸Ｃｏ）を含浸させ、蒸発乾固、乾燥及び焼成を行ない、得られた粉末にＰｔ溶液を含浸させ、蒸発乾固、乾燥及び焼成を行なうことにより触媒粉末を得るとされている。そして、この触媒粉末とＲｈ／ＺｒＯ２粉末とＡｌ２Ｏ３粉末とアルミナゾルとイオン交換水とを混合してスラリーを調製し、このスラリーをハニカム担体にウォッシュコートして触媒層を形成するとされている。
上記特許文献２，３から明らかなように、排ガス浄化用触媒にＦｅ成分を含ませること自体は知られているということができる。そこで、本願発明者は、特許文献３に記載されているＮｉやＣｏの担持方法に倣って、特許文献１に記載されているＲｈを粒子内及び粒子表面に固定してなるＣｅ含有酸化物粒子に、硝酸鉄を含浸・乾燥・焼成する手法によって、酸化鉄を担持させた。しかし、得られた触媒は、硝酸鉄による酸化鉄の担持を行わない触媒に比べて、酸素吸蔵放出能及び排気ガス浄化性能が悪い、という結果になった。その原因は、Ｃｅ含有酸化物粒子表面に付着した硝酸鉄が、焼成に伴って酸化鉄に変化しながら凝集し、粒径の大きな酸化鉄粒子に成長してしまうこと（本願発明者はその粒径が５００ｎｍ以上になることを確認している。）、並びにその凝集・粒成長の過程でＣｅ含有酸化物粒子表面のＲｈが当該酸化鉄粒子に埋没することにあると考えられる。 As is apparent from Patent Documents 2 and 3, it can be said that the exhaust gas purifying catalyst itself contains an Fe component. Therefore, the present inventor follows the Ni and Co loading method described in Patent Document 3, and Ce-containing oxide particles obtained by fixing Rh described in Patent Document 1 in the particle and on the particle surface. In addition, iron oxide was supported by a method of impregnating, drying and firing iron nitrate. However, the obtained catalyst resulted in poor oxygen storage / release capability and exhaust gas purification performance compared to a catalyst that did not support iron oxide with iron nitrate. The cause is that iron nitrate adhering to the Ce-containing oxide particle surface aggregates while changing to iron oxide during firing, and grows into iron oxide particles having a large particle size (the inventor of the present application It has been confirmed that the diameter becomes 500 nm or more.), And Rh on the surface of the Ce-containing oxide particles is buried in the iron oxide particles in the course of the aggregation and grain growth.
かかる点に鑑み、本発明は、特許文献１に記載されているような排気ガス浄化用触媒に関し、酸化鉄を有効に利用して排気ガス浄化性能を高めることを課題とする。 In view of this point, the present invention relates to an exhaust gas purification catalyst as described in Patent Document 1, and an object thereof is to improve the exhaust gas purification performance by effectively using iron oxide.
また、別の本発明の課題は、酸化鉄を、上記排気ガスの浄化に利用するだけでなく、担体に触媒層を形成するためのバインダとしても利用することにある。 Another object of the present invention is to use iron oxide not only for purifying the exhaust gas but also as a binder for forming a catalyst layer on the carrier.
本発明は、このような課題を解決するために、粒径の小さな微細酸化鉄粒子を上述の如きＣｅ含有酸化物粒子に組み合わせるようにした。 In the present invention, in order to solve such problems, fine iron oxide particles having a small particle diameter are combined with the Ce-containing oxide particles as described above.
すなわち、本発明は、ハニカム担体上に設けられた触媒層内に、触媒貴金属がドープされ、且つその表面に触媒貴金属が担持されてなるＣｅＺｒ系複合酸化物粒子を含有する排気ガス浄化用触媒であって、
上記ＣｅＺｒ系複合酸化物粒子に粒径３００ｎｍ以下の微細酸化鉄粒子が接しており、
上記微細酸化鉄粒子とＣｅＺｒ系複合酸化物粒子との合計量に対する上記微細酸化鉄粒子の質量比率が２質量％以上４５質量％以下であり、
上記ドープされた触媒貴金属と表面に担持された触媒貴金属との総量に対する表面に担持された触媒貴金属の質量比率が２質量％超９８質量％以下であることを特徴とする。
That is, the present invention is an exhaust gas purifying catalyst comprising CeZr-based composite oxide particles doped with a catalyst noble metal and supported on the surface thereof in a catalyst layer provided on a honeycomb carrier. There,
Fine iron oxide particles having a particle size of 300 nm or less are in contact with the CeZr-based composite oxide particles,
The mass ratio of the fine iron oxide particles to the total amount of the fine iron oxide particles and CeZr-based composite oxide particles is 2% by mass or more and 45% by mass or less,
The mass ratio of the catalyst noble metal supported on the surface to the total amount of the doped catalyst noble metal and the catalyst noble metal supported on the surface is more than 2 mass% and 98 mass% or less.
ここに、上記ＣｅＺｒ系複合酸化物粒子はその二次粒子径が数μｍの粒子であるのが通常であるから、このＣｅＺｒ系複合酸化物粒子に接触している上記粒径３００ｎｍ以下の微細酸化鉄粒子は、ＣｅＺｒ系複合酸化物粒子表面に担持されている触媒貴金属が凝集しようとするときの立体障害となり、該触媒貴金属のシンタリングが抑制される（触媒の耐熱性向上）。 Here, since the CeZr-based composite oxide particles are usually particles having a secondary particle diameter of several μm, the fine oxidation of the particle size of 300 nm or less that is in contact with the CeZr-based composite oxide particles. The iron particles become a steric hindrance when the catalyst noble metal supported on the surface of the CeZr-based composite oxide particles is about to aggregate, and sintering of the catalyst noble metal is suppressed (improvement of heat resistance of the catalyst).
また、上記微細酸化鉄粒子の粒径が小さいことにより、該微細酸化鉄粒子とＣｅＺｒ系複合酸化物粒子との相互作用を生じ易く、この両者が相俟って、触媒の酸素吸蔵放出能が高まる。すなわち、微細酸化鉄粒子とＣｅＺｒ系複合酸化物粒子との接触点では各々の粒子内酸素が不安定な状態になるため、各々の酸素吸蔵放出能が高くなると考えられる。その結果、触媒貴金属量が少ない場合でも、優れた酸素吸蔵放出能が得られ、当該触媒による排気ガスのＨＣ（炭化水素）やＣＯの酸化反応が効率良く進む（触媒の早期活性化，排気ガス浄化性能の向上）。また、触媒の使用期間が多少長くなっても（触媒が高温の排気ガスに度々晒されても）、上記酸素吸蔵放出能が低いレベルにまで低下することが避けられる（耐熱性の向上）。 In addition, since the fine iron oxide particles have a small particle size, the fine iron oxide particles and CeZr-based composite oxide particles are likely to interact with each other. Rise. That is, it is considered that the oxygen storage / release capacity of each particle is increased because the oxygen in each particle becomes unstable at the contact point between the fine iron oxide particles and the CeZr-based composite oxide particles. As a result, even when the amount of precious metal in the catalyst is small, excellent oxygen storage / release capability is obtained, and the oxidation reaction of HC (hydrocarbon) and CO in the exhaust gas by the catalyst proceeds efficiently (early catalyst activation, exhaust gas) Improved purification performance). Further, even if the catalyst usage period is somewhat longer (even if the catalyst is frequently exposed to high-temperature exhaust gas), it is possible to avoid the oxygen storage / release capability from being lowered to a low level (improvement in heat resistance).
また、上記微細酸化鉄粒子とＣｅＺｒ系複合酸化物粒子との合計量に対する上記微細酸化鉄粒子の質量比率については、後に実験データで明らかにするが、２質量％未満になると、或いは４５質量％を越えると、排気ガス浄化性能が悪化する。２質量％未満では、上述の効果を発現するには微細酸化鉄粒子が不足し、また、４５質量％を越えると、酸化鉄の比熱はＣｅＺｒ系複合酸化物の数倍であるから、触媒の昇温が遅くなるためと考えられる。 Further, the mass ratio of the fine iron oxide particles to the total amount of the fine iron oxide particles and the CeZr-based composite oxide particles will be clarified later in experimental data, but when it is less than 2% by mass, or 45% by mass Exceeding this will deteriorate exhaust gas purification performance. If the amount is less than 2% by mass, the amount of fine iron oxide particles is insufficient to exhibit the above-described effects. If the amount exceeds 45% by mass, the specific heat of iron oxide is several times that of the CeZr-based composite oxide. Is thought to be slow.
上記ドープされた触媒貴金属と表面に担持された触媒貴金属との総量に対する表面に担持された触媒貴金属の質量比率については、後に実験データで明らかにするが、２質量％以下になると、或いは９８質量％を越えると、排気ガス浄化性能が悪化する。触媒反応には表面担持触媒貴金属の存在が必要であるところ、２質量％以下では所期の触媒反応を得るのに不足し、９８質量％を越えると、ＣｅＺｒ系複合酸化物の酸素吸蔵放出能が低下するためと考えられる。すなわち、当該比率が９８質量％を越えるということは、ＣｅＺｒ系複合酸化物の酸素吸蔵放出能を高めるためのドープ触媒貴金属量が少なくないことを意味する。 The mass ratio of the catalyst noble metal supported on the surface to the total amount of the doped catalyst noble metal and the catalyst noble metal supported on the surface will be clarified later in experimental data, but when it becomes 2% by mass or less, or 98 mass Exceeding% results in deterioration of exhaust gas purification performance. The presence of a surface-supported catalytic noble metal is necessary for the catalytic reaction. When the amount is 2% by mass or less, the desired catalytic reaction is insufficient. When the amount exceeds 98% by mass, the oxygen storage / release capacity of the CeZr-based composite oxide is insufficient. This is thought to be due to a decline. That is, that the ratio exceeds 98% by mass means that the amount of the precious metal for the dope catalyst for increasing the oxygen storage / release capability of the CeZr-based composite oxide is not small.
上記微細酸化鉄粒子は、上記触媒層において上記ＣｅＺｒ系複合酸化物粒子等を上記担体に保持するバインダの少なくとも一部を構成するものとすることができる。すなわち、触媒一般におけるバインダについては次のように定義することができる。
Ａ．バインダは、担体にウォッシュコートするスラリーに粘性を与えることにより、触媒金属を担持する酸素吸蔵材、その他の助触媒粒子をスラリー中に均一に分散させるとともに、乾燥・焼成前のウォッシュコート層を担体に安定した状態に保持する。
The fine iron oxide particles may constitute at least a part of a binder that holds the CeZr-based composite oxide particles and the like on the carrier in the catalyst layer. That is, the binder in general catalysts can be defined as follows.
A. The binder uniformly disperses the oxygen storage material and other promoter particles supporting the catalyst metal in the slurry by imparting viscosity to the slurry to be coated on the carrier, and the washcoat layer before drying and firing is supported on the carrier. To keep it stable.
そのため、粒径が１ｎｍ〜５０ｎｍ程度のコロイド粒子（水酸化物、含水物、酸化物等）が分散したコロイド溶液（市販のアルミナゾルやコロイダルシリカではコロイド粒子の粒径は１０ｎｍ〜３０ｎｍ程度）がバインダとして一般に使用される。
Ｂ．バインダは、上記乾燥・焼成後は微粒子となって触媒層に略均一に分散し、上記助触媒粒子間に介在して該助触媒粒子同士を結合するとともに、担体表面の多数の微小凹部ないし細孔に入り、触媒層が担体から剥離しないようにする（アンカー効果）。
Therefore, a colloidal solution in which colloidal particles (hydroxide, hydrate, oxide, etc.) having a particle size of about 1 nm to 50 nm are dispersed (in the case of commercially available alumina sol or colloidal silica, the particle size of the colloidal particles is about 10 nm to 30 nm) is a binder. As commonly used.
B. The binder is finely dispersed in the catalyst layer after drying and firing, and is substantially uniformly dispersed in the catalyst layer. The binder is interposed between the promoter particles and bonds the promoter particles to each other. Enter the hole so that the catalyst layer does not peel from the carrier (anchor effect).
そのため、乾燥・焼成後において、助触媒粒子よりも粒径が小さな酸化物粒子となって助触媒粒子や担体に固着するものがバインダとして一般に使用される。
Ｃ．触媒層に、触媒金属やＮＯｘ吸蔵材、ＨＣ吸着材等が後から含浸担持されるケースでは、バインダはそれら触媒成分を担持するサポート材となる。
Ｄ．バインダ粒子間、バインダ粒子と助触媒粒子との間には排気ガスが通る微細孔が形成される。
Ｅ．触媒層におけるバインダ量は、一般には触媒層全体の５質量％〜２０質量％とされる。
Therefore, what is fixed to the promoter particles or the carrier in the form of oxide particles having a particle diameter smaller than that of the promoter particles after drying and firing is generally used as the binder.
C. In the case where the catalyst layer is impregnated and supported with catalyst metal, NOx occlusion material, HC adsorbent, etc. later, the binder serves as a support material for supporting these catalyst components.
D. Micropores through which exhaust gas passes are formed between the binder particles and between the binder particles and the promoter particles.
E. The amount of binder in the catalyst layer is generally 5% by mass to 20% by mass of the entire catalyst layer.
本発明の場合、上記粒径３００ｎｍ以下の微細酸化鉄粒子は、上記ＣｅＺｒ系複合酸化物粒子の平均粒径（数μｍ程度）よりも小さく、上記触媒層に略均一に分散し、上記ＣｅＺｒ系複合酸化物粒子間に介在して該ＣｅＺｒ系複合酸化物粒子同士を結合するとともに、担体表面の多数の微小凹部ないし細孔に入り、触媒層が担体から剥離しないようにする。このため、当該酸化鉄粒子は上記触媒層においてバインダとしての機能も発揮するものである。 In the case of the present invention, the fine iron oxide particles having a particle size of 300 nm or less are smaller than the average particle size (about several μm) of the CeZr composite oxide particles, and are dispersed substantially uniformly in the catalyst layer. The CeZr-based composite oxide particles are bonded to each other by interposing between the composite oxide particles, and enter a large number of minute recesses or pores on the surface of the support so that the catalyst layer does not peel from the support. For this reason, the iron oxide particles also exhibit a function as a binder in the catalyst layer.
上記触媒層のバインダは、上記微細酸化鉄粒子のみで構成するようにしてよいが、安定な触媒層を得るために、この微細酸化鉄粒子の他に、遷移金属及び希土類金属から選ばれる少なくとも一種の金属の酸化物粒子（例えば、アルミナ粒子、ＺｒＯ２粒子、ＣｅＯ２粒子等）をバインダとして含ませるようにすることができる。このようなバインダ粒子（上記微細酸化鉄粒子及び上記金属酸化物粒子）は、担体にウォッシュコートするスラリーに粘性を与えることにより、触媒成分をスラリー中に均一に分散させるとともに、乾燥・焼成前のウォッシュコート層を担体に安定した状態で保持することができるように、前駆体である金属化合物がそれぞれコロイド粒子として分散したゾルを原料とすることが好ましい。 The binder of the catalyst layer may be composed only of the fine iron oxide particles, but in order to obtain a stable catalyst layer, in addition to the fine iron oxide particles, at least one selected from transition metals and rare earth metals These metal oxide particles (for example, alumina particles, ZrO 2 particles, CeO 2 particles, etc.) can be included as a binder. Such binder particles (the fine iron oxide particles and the metal oxide particles) impart viscosity to the slurry to be coated on the carrier to uniformly disperse the catalyst component in the slurry, and before drying / calcination. It is preferable to use a sol in which the precursor metal compound is dispersed as colloidal particles, so that the washcoat layer can be stably held on the carrier.
上記微細酸化鉄粒子の少なくとも一部はヘマタイトであることが好ましく、また、上記酸化鉄粒子は、マグヘマイト、ゲータイト及びウスタイトがコロイド粒子として分散したゾルを原料とすることが好ましい。 At least a part of the fine iron oxide particles is preferably hematite, and the iron oxide particles are preferably made from a sol in which maghemite, goethite and wustite are dispersed as colloidal particles.
上記触媒貴金属としては、Ｐｔ、Ｐｄ及びＲｈから選ばれる少なくとも１種を採用することが好ましい。 As the catalyst noble metal, it is preferable to employ at least one selected from Pt, Pd and Rh.
以上のように本発明によれば、触媒貴金属がドープされ、且つその表面に触媒貴金属が担持されてなるＣｅＺｒ系複合酸化物粒子に、粒径３００ｎｍ以下の微細酸化鉄粒子が接しており、この微細酸化鉄粒子とＣｅＺｒ系複合酸化物粒子との合計量に対する微細酸化鉄粒子の質量比率が２質量％以上４５質量％以下であり、上記ドープされた触媒貴金属と表面に担持された触媒貴金属との総量に対する表面に担持された触媒貴金属の質量比率が２質量％超９８質量％以下であるから、触媒貴金属量が少ない場合でも、優れた酸素吸蔵放出能が得られ、触媒の早期活性化、排気ガス浄化性能の向上、並びに触媒の耐熱性の向上に有利になる。 As described above, according to the present invention, fine iron oxide particles having a particle size of 300 nm or less are in contact with CeZr-based composite oxide particles doped with a catalyst noble metal and supported on the surface thereof. The mass ratio of the fine iron oxide particles to the total amount of the fine iron oxide particles and the CeZr-based composite oxide particles is 2% by mass or more and 45% by mass or less, and the doped catalyst noble metal and the catalyst noble metal supported on the surface, Since the mass ratio of the catalyst noble metal supported on the surface with respect to the total amount of the catalyst is more than 2% by mass and 98% by mass or less, even when the amount of the catalyst noble metal is small, an excellent oxygen storage / release capability can be obtained, and the early activation of the catalyst, This is advantageous for improving the exhaust gas purification performance and improving the heat resistance of the catalyst.
以下、本発明の実施形態を図面に基づいて説明する。尚、以下の好ましい実施形態の説明は、本質的に例示に過ぎず、本発明、その適用物或いはその用途を制限することを意図するものではない。 Hereinafter, embodiments of the present invention will be described with reference to the drawings. It should be noted that the following description of the preferred embodiment is merely illustrative in nature, and is not intended to limit the present invention, its application, or its use.
図１に、本発明に係る排気ガス浄化用触媒の一例として、自動車の排気ガスの浄化に適した三元触媒を模式的に示す。同図において、１は無機酸化物によるハニカム担体のセル壁、２はセル壁１に形成された触媒層である。触媒層２は、酸素吸蔵放出能を持つＣｅＺｒ系複合酸化物粒子３と、バインダ粒子４と、Ｆｅ以外の触媒金属５とを有し、図例では、ＣｅＺｒ系複合酸化物粒子３以外の助触媒粒子として、さらにアルミナ粒子６を有する。なお、触媒層２には、ＣｅＺｒ系複合酸化物粒子３及びアルミナ粒子６以外に、ＨＣ吸着材、ＮＯｘ吸蔵材など他の助触媒粒子を含ませることができる。バインダ粒子４は、ＣｅＺｒ系複合酸化物粒子３及びアルミナ粒子６各々の平均粒径よりも小さな金属酸化物粒子よりなり、少なくとも一部のバインダ粒子４は粒径３００ｎｍ以下の微細酸化鉄粒子で構成されている。すなわち、当該微細酸化鉄粒子と他の金属酸化物粒子とを組み合わせてバインダとすることもできる。 FIG. 1 schematically shows a three-way catalyst suitable for purification of automobile exhaust gas as an example of an exhaust gas purification catalyst according to the present invention. In the figure, 1 is a cell wall of a honeycomb carrier made of an inorganic oxide, and 2 is a catalyst layer formed on the cell wall 1. The catalyst layer 2 includes CeZr-based composite oxide particles 3 having an oxygen storage / release capability, binder particles 4 and catalytic metals 5 other than Fe. In the example shown in FIG. As catalyst particles, alumina particles 6 are further included. In addition to the CeZr-based composite oxide particles 3 and the alumina particles 6, the catalyst layer 2 can contain other promoter particles such as an HC adsorbent and a NOx occlusion material. The binder particles 4 are made of metal oxide particles smaller than the average particle size of each of the CeZr-based composite oxide particles 3 and the alumina particles 6, and at least some of the binder particles 4 are composed of fine iron oxide particles having a particle size of 300 nm or less. Has been. That is, the fine iron oxide particles and other metal oxide particles can be combined to form a binder.
上記微細酸化鉄粒子を含むバインダ粒子４は、触媒層２の全体にわたって略均一に分散していて、助触媒粒子（ＣｅＺｒ系複合酸化物粒子３、アルミナ粒子６等）間に介在し該助触媒粒子同士を結合している。従って、少なくとも一部の微細酸化鉄粒子はＣｅＺｒ系複合酸化物粒子３に接触している。また、上記バインダ粒子４は、担体セル壁１の表面ポア（微小凹部ないし細孔）７に充填され、アンカー効果によって触媒層２をセル壁１に保持している。触媒金属５は助触媒粒子（ＣｅＺｒ系複合酸化物粒子３、アルミナ粒子６等）に担持されている。 The binder particles 4 containing the fine iron oxide particles are substantially uniformly dispersed throughout the catalyst layer 2 and are interposed between the promoter particles (CeZr-based composite oxide particles 3, alumina particles 6 and the like). The particles are bound together. Therefore, at least some of the fine iron oxide particles are in contact with the CeZr-based composite oxide particles 3. The binder particles 4 are filled in the surface pores (microscopic recesses or pores) 7 of the carrier cell wall 1 and hold the catalyst layer 2 on the cell wall 1 by an anchor effect. The catalyst metal 5 is supported on promoter particles (CeZr-based composite oxide particles 3, alumina particles 6 and the like).
図２は上記ＣｅＺｒ系複合酸化物粒子と微細酸化鉄粒子との関係を示す。このＣｅＺｒ系複合酸化物粒子は、触媒貴金属がドープされているとともに、その粒子表面にも触媒貴金属が担持されている。そして、このＣｅＺｒ系複合酸化物粒子に上記粒径３００ｎｍ以下の微細酸化鉄粒子が接している。ここに、「ドープ」とは、触媒貴金属がＣｅＺｒ系複合酸化物粒子の結晶格子、結晶格子間、或いは酸素欠損部に配置されていることを意味する。 FIG. 2 shows the relationship between the CeZr-based composite oxide particles and fine iron oxide particles. The CeZr-based composite oxide particles are doped with a catalytic noble metal, and the catalyst noble metal is supported on the particle surface. The fine iron oxide particles having a particle size of 300 nm or less are in contact with the CeZr-based composite oxide particles. Here, “dope” means that the catalyst noble metal is disposed in the crystal lattice, between the crystal lattices, or in the oxygen deficient portion of the CeZr-based composite oxide particles.
＜触媒の調製＞
エタノール１００ｍＬ当たり硝酸第二鉄４０．４ｇを溶かし、９０℃から１００℃の温度で２時間から３時間の還流を行なうことによって、スラリー状の液体、すなわち、酸化鉄ゾル（バインダ）を得る。ＣｅＺｒ系複合酸化物粉末に酸化鉄ゾル及びイオン交換水を適量混合したスラリーを調製する。必要に応じて、他のバインダを添加する。上記スラリーを担体にコーティングし、乾燥及び焼成を施す。担体上のコーティング層に触媒金属溶液を含浸させ、乾燥及び焼成を行なう。以上により排気ガス浄化用触媒が得られる。
<Preparation of catalyst>
By dissolving 40.4 g of ferric nitrate per 100 mL of ethanol and refluxing at a temperature of 90 ° C. to 100 ° C. for 2 to 3 hours, a slurry-like liquid, that is, an iron oxide sol (binder) is obtained. A slurry is prepared by mixing an appropriate amount of iron oxide sol and ion-exchanged water with CeZr-based composite oxide powder. If necessary, other binder is added. The slurry is coated on a carrier, dried and fired. The coating layer on the support is impregnated with the catalytic metal solution, and dried and calcined. Thus, an exhaust gas purification catalyst can be obtained.
上記スラリーにはアルミナ粉末など他の助触媒材料を加えてもよい。また、触媒金属溶液と共に、ＮＯｘ吸蔵材となるアルカリ土類金属、希土類金属等の溶液を上記コーティング層に含浸させて当該ＮＯｘ吸蔵材を担持させるようにしてもよい。また、触媒金属は予めＣｅＺｒ系複合酸化物粒子等のサポート材に担持させておいてもよい。 You may add other promoter materials, such as an alumina powder, to the said slurry. Further, the NOx occlusion material may be supported by impregnating the coating layer with a solution of an alkaline earth metal, a rare earth metal or the like that becomes the NOx occlusion material together with the catalyst metal solution. Further, the catalyst metal may be previously supported on a support material such as CeZr-based composite oxide particles.
＜酸化鉄粒子の粒径等＞
上記酸化鉄ゾルによって得られる微細酸化鉄粒子の粒径を調べるために、上述の触媒貴金属のドープ及び表面担持がなされていないＣｅＺｒＮｄ複合酸化物（ＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝２３：６７：１０（質量比））を準備した。
<Iron oxide particle size>
In order to investigate the particle size of the fine iron oxide particles obtained by the iron oxide sol, the above-mentioned catalyst noble metal is doped and the CeZrNd composite oxide is not supported (CeO 2 : ZrO 2 : Nd 2 O 3 = 23: 67:10 (mass ratio)) was prepared.
上記酸化鉄ゾルとＣｅＺｒＮｄ複合酸化物とイオン交換水とを混合することによりスラリーを調製し、このスラリーを基材にコーティングし、乾燥（１５０℃）及び焼成（大気中において５００℃の温度に２時間保持）を行なうことにより、触媒材を得た。酸化鉄ゾルとＣｅＺｒＮｄ複合酸化物粉末とは、上記焼成後における質量比で、酸化鉄とＣｅＺｒＮｄ複合酸化物とが２：８となるように混合した。 A slurry is prepared by mixing the iron oxide sol, CeZrNd composite oxide, and ion-exchanged water. The slurry is coated on a substrate, dried (150 ° C.), and baked (at a temperature of 500 ° C. in the atmosphere at 2 The catalyst material was obtained by performing time holding | maintenance. The iron oxide sol and the CeZrNd composite oxide powder were mixed so that the iron oxide and the CeZrNd composite oxide were in a mass ratio of 2: 8 after firing.
図３は得られた触媒材の透過電子顕微鏡を用いたＳＴＥＭ（走査透過）像、図４乃至図６はＦｅ、Ｚｒ及びＣｅ各原子の相対濃度分布をマッピングしたものである。図３乃至図６から、ＣｅＺｒＮｄ複合酸化物粒子の粒径は１μｍ程度であること、酸化鉄粒子は粒径が３００ｎｍ以下であり、５０ｎｍ以上３００ｎｍ以下の大きさの複数個の酸化鉄粒子がＣｅＺｒＮｄ複合酸化物粒子に接触（粒子上に分布）していることがわかる。この場合、当該顕微鏡観察において、粒径３００ｎｍ以下の微細酸化鉄粒子の酸化鉄粒子総面積に占める面積比率は１００％である（つまり、全ての酸化鉄粒子が粒径３００ｎｍ以下である）ということができる。 FIG. 3 is an STEM (scanning transmission) image of the obtained catalyst material using a transmission electron microscope, and FIGS. 4 to 6 are maps of the relative concentration distribution of each atom of Fe, Zr, and Ce. From FIG. 3 to FIG. 6, the particle size of the CeZrNd composite oxide particles is about 1 μm, the iron oxide particles have a particle size of 300 nm or less, and a plurality of iron oxide particles having a size of 50 nm or more and 300 nm or less are CeZrNd. It can be seen that the composite oxide particles are in contact (distributed on the particles). In this case, in the microscopic observation, the area ratio of fine iron oxide particles having a particle diameter of 300 nm or less to the total area of iron oxide particles is 100% (that is, all iron oxide particles have a particle diameter of 300 nm or less). Can do.
図７乃至図１０は上記触媒材のエージング（酸素を２％、水蒸気を１０％含む窒素ガス中で９００℃の温度に２４時間保持）後でのＳＴＥＭ像及び各原子の相対濃度分布のマッピングである。ＣｅＺｒＮｄ複合酸化物粒子の粒径は１μｍ程度であり、酸化鉄粒子の粒径は３００ｎｍ以下であり、５０ｎｍ以上３００ｎｍ以下の大きさの酸化鉄粒子がＣｅＺｒＮｄ複合酸化物粒子に複数個接触（粒子上に分布）している。エージング後においても、当該電子顕微鏡観察によれば、全ての酸化鉄粒子の粒径が３００ｎｍ以下になっている。 FIGS. 7 to 10 are mappings of STEM images and relative concentration distributions of each atom after aging of the above catalyst material (maintained at a temperature of 900 ° C. for 24 hours in nitrogen gas containing 2% oxygen and 10% water vapor). is there. The particle size of the CeZrNd composite oxide particles is about 1 μm, the particle size of the iron oxide particles is 300 nm or less, and a plurality of iron oxide particles having a size of 50 nm to 300 nm are in contact with the CeZrNd composite oxide particles (on the particle Distributed). Even after aging, according to the observation with the electron microscope, the particle diameter of all iron oxide particles is 300 nm or less.
図１１は酸化鉄ゾルを１５０℃で乾燥したもの（乾燥品）、上記エージング前の触媒材（焼成品）、並びに上記エージング後の触媒材（焼成・エージング品）各々のＸ線回折チャートである。なお、同図の「ＯＳＣ」は上記ＣｅＺｒＮｄ複合酸化物のことを意味する（この点は他の図面でも同様である。）。酸化鉄ゾルは、マグヘマイト（γ-Ｆｅ２Ｏ３）、ゲータイト（Ｆｅ３＋Ｏ(ＯＨ)）及びウスタイト（ＦｅＯ）がコロイド粒子として分散したものであることがわかる。そして、酸化鉄ゾルのコロイド粒子は焼成によってヘマタイト（α-Ｆｅ２Ｏ３）になっている。 FIG. 11 is an X-ray diffraction chart of the iron oxide sol dried at 150 ° C. (dried product), the catalyst material before aging (calcined product), and the catalyst material after aging (calcined / aged product). . In addition, “OSC” in the figure means the CeZrNd composite oxide (this is the same in other drawings). It can be seen that the iron oxide sol is one in which maghemite (γ-Fe 2 O 3 ), goethite (Fe 3+ O (OH)) and wustite (FeO) are dispersed as colloidal particles. The colloidal particles of the iron oxide sol are converted into hematite (α-Fe 2 O 3 ) by firing.
上記エージング前の焼成品におけるヘマタイトの、結晶面（１０４）のピーク強度を１００とする各結晶面の相対ピーク強度は表１に示す通りである。また、上記エージング後のヘマタイトの、結晶面（１０４）のピーク強度を１００とする各結晶面の相対ピーク強度は表２に示す通りである。なお、表中「−」はピーク重複や、ピーク小のために、正確な数値が得られなかったものである。 Table 1 shows the relative peak intensities of the crystal faces of hematite in the fired product before aging, with the peak intensity of the crystal face (104) being 100. Further, the relative peak intensity of each crystal plane with the peak intensity of the crystal plane (104) of the hematite after aging as 100 is shown in Table 2. Note that “−” in the table indicates that an exact numerical value could not be obtained due to peak overlap or small peak.
エージング後において、Ｘ線回折測定によって得られるヘマタイトの各結晶面のピーク強度は、結晶面（１０４）、結晶面（１１０）、結晶面（１１６）の順で小さくなっている。 After aging, the peak intensity of each crystal plane of hematite obtained by X-ray diffraction measurement decreases in the order of crystal plane (104), crystal plane (110), and crystal plane (116).
一方、比較のために、上記酸化鉄ゾルに代えて、硝酸第二鉄水溶液を上記ＣｅＺｒＮｄ複合酸化物粉末に含浸させ、同様の乾燥及び焼成を行なった。硝酸第二鉄とＣｅＺｒＮｄ複合酸化物粉末とは、上記焼成後における質量比で、酸化鉄とＣｅＺｒＮｄ複合酸化物とが２：８となるように混合した。 On the other hand, for comparison, the CeZrNd composite oxide powder was impregnated with the ferric nitrate aqueous solution instead of the iron oxide sol, and the same drying and firing were performed. The ferric nitrate and the CeZrNd composite oxide powder were mixed so that the iron oxide and the CeZrNd composite oxide were in a mass ratio of 2: 8 after firing.
図１２乃至図１５は得られた上記硝酸第二鉄による触媒材のＳＴＥＭ像及び各原子の相対濃度分布のマッピングである。ＣｅＺｒＮｄ複合酸化物粒子の粒径は１μｍ程度であるが、酸化鉄粒子の粒径は６００〜７００ｎｍ程度になっている。 12 to 15 are mapping of the obtained STEM image of the catalyst material by ferric nitrate and the relative concentration distribution of each atom. The particle size of CeZrNd composite oxide particles is about 1 μm, while the particle size of iron oxide particles is about 600 to 700 nm.
図１６乃至図１９は上記硝酸第二鉄による触媒材のエージング（酸化鉄ゾルの場合と同じ条件）後でのＳＴＥＭ像及び各原子の相対濃度分布のマッピングである。ＣｅＺｒＮｄ複合酸化物粒子の粒径は１．５〜２μｍ程度であるが、酸化鉄粒子としては、粒径が６００〜７００ｎｍ程度の粒子が１個と、１００ｎｍ程度の粒子が３個見られる。当該電子顕微鏡観察において、粒径３００ｎｍ以下の酸化鉄粒子の酸化鉄粒子総面積に占める面積比率は１０％未満である。 16 to 19 are mappings of the STEM image and the relative concentration distribution of each atom after aging of the catalyst material with ferric nitrate (the same conditions as in the case of iron oxide sol). The particle size of the CeZrNd composite oxide particles is about 1.5 to 2 μm. As the iron oxide particles, one particle having a particle size of about 600 to 700 nm and three particles of about 100 nm are seen. In the electron microscope observation, the area ratio of the iron oxide particles having a particle diameter of 300 nm or less to the total area of the iron oxide particles is less than 10%.
上記酸化鉄ゾルの場合、焼成によって酸化鉄粒子となるコロイド粒子（マグヘマイト、ゲータイト及びウスタイト）が比較的安定なＦｅ化合物であり、そのために、酸化鉄粒子の粒成長を生じ難い。これに対して、上記硝酸第二鉄の場合は、反応性が高いＦｅイオンから酸化鉄粒子を生ずるから、粒成長し易い。このことが、上記酸化鉄ゾルから得られる酸化鉄粒子と上記硝酸第二鉄から得られる酸化鉄粒子の粒径の差違となっていると考えられる。 In the case of the iron oxide sol, colloidal particles (maghemite, goethite, and wustite) that become iron oxide particles upon firing are relatively stable Fe compounds, and therefore, iron oxide particle growth hardly occurs. On the other hand, in the case of ferric nitrate, iron oxide particles are generated from highly reactive Fe ions, so that the grains are easily grown. This is considered to be the difference in particle diameter between the iron oxide particles obtained from the iron oxide sol and the iron oxide particles obtained from the ferric nitrate.
＜酸素吸蔵放出能＞
上記酸化鉄ゾルを用いて調製した触媒サンプルＡと、上記硝酸第二鉄を用いて調製した触媒サンプルＢと、鉄成分を含まない触媒サンプルＣとについて、各々の酸素吸蔵放出能を調べた。但し、いずれのサンプルも触媒金属量は零とした。
<Oxygen storage and release ability>
Each of the catalyst samples A prepared using the iron oxide sol, the catalyst sample B prepared using the ferric nitrate, and the catalyst sample C containing no iron component were examined for oxygen storage / release capacity. However, the amount of catalyst metal in all samples was zero.
−触媒サンプルＡの調製−
上記ＣｅＺｒＮｄ複合酸化物と上記酸化鉄ゾルとＺｒＯ２バインダとイオン交換水とを混合することによりスラリーを調製し、このスラリーを担体にコーティングし、乾燥（１５０℃）及び焼成（大気中において５００℃の温度に２時間保持）を行なった。上記スラリーは、上記ＣｅＺｒＮｄ複合酸化物の担持量が８０ｇ／Ｌ、上記酸化鉄ゾルによる酸化鉄の担持量が２０ｇ／Ｌ、上記ＺｒＯ２バインダによるＺｒＯ２の担持量が１０ｇ／Ｌとなるように調製した。なお、各担持量は上記焼成後における上記担体１Ｌ当たりの各成分の量である。担体としては、セル壁厚さ３．５mil（８．８９×１０−２ｍｍ）、１平方インチ（６４５．１６ｍｍ２）当たりのセル数６００のコージェライト製ハニカム担体（容量２５ｍＬ）を採用した。
-Preparation of catalyst sample A-
A slurry is prepared by mixing the CeZrNd composite oxide, the iron oxide sol, the ZrO 2 binder, and ion-exchanged water. The slurry is coated on a support, dried (150 ° C.) and fired (500 ° C. in the air). For 2 hours). The slurry is such that the supported amount is 80 g / L of the CeZrNd mixed oxide, the supported amount of iron oxide by the iron oxide sol 20 g / L, the amount of supported ZrO 2 by the ZrO 2 binder is 10 g / L Prepared. Each supported amount is the amount of each component per 1 L of the carrier after the firing. As the carrier, a cordierite honeycomb carrier (capacity: 25 mL) having a cell wall thickness of 3.5 mil (8.89 × 10 −2 mm) and 600 cells per square inch (645.16 mm 2 ) was employed.
−触媒サンプルＢの調製−
上記酸化鉄ゾルに代えて硝酸第二鉄水溶液を採用し、他は触媒サンプルＡと同じ条件で第２触媒サンプル２を調製した。硝酸第二鉄水溶液による酸化鉄担持量は触媒サンプルＡの上記酸化鉄ゾルによる酸化鉄担持量と同じく、２０ｇ／Ｌである。
-Preparation of catalyst sample B-
Instead of the iron oxide sol, a ferric nitrate aqueous solution was employed, and a second catalyst sample 2 was prepared under the same conditions as in catalyst sample A. The amount of iron oxide supported by the ferric nitrate aqueous solution is 20 g / L, the same as the amount of iron oxide supported by the iron oxide sol of catalyst sample A.
−触媒サンプルＣの調製−
上記酸化鉄ゾルを用いず（酸化鉄担持量＝０ｇ／Ｌ）、上記ＣｅＺｒＮｄ複合酸化物担持量が１００ｇ／Ｌ、上記ＺｒＯ２バインダによるＺｒＯ２の担持量が１０ｇ／Ｌとなるようにする他は、触媒サンプルＡと同じ条件で触媒サンプルＣを調製した。
-Preparation of catalyst sample C-
Other to make without using the iron oxide sol (iron oxide supported amount = 0g / L), the CeZrNd mixed oxide support amount was 100 g / L, the amount of supported ZrO 2 by the ZrO 2 binder is 10 g / L Prepared catalyst sample C under the same conditions as catalyst sample A.
−酸素吸蔵放出能の評価−
図２０は、酸素吸蔵放出量を測定するための試験装置の構成を示す。同図において、符号１１は触媒サンプル１２を保持するガラス管であり、触媒サンプル１２はヒータ１３によって所定温度に加熱保持される。ガラス管１１の触媒サンプル１２よりも上流側には、ベースガスＮ２を供給しながらＯ２及びＣＯの各ガスをパルス状に供給可能なパルスガス発生装置１４が接続され、ガラス管１１の触媒サンプル１２よりも下流側には排気部１８が設けられている。ガラス管１１の触媒サンプル１２よりも上流側及び下流側にはＡ／Ｆセンサ（酸素センサ）１５，１６が設けられている。ガラス管１１のサンプル保持部には温度制御用の熱電対１９が取付けられている。
-Evaluation of oxygen storage capacity-
FIG. 20 shows the configuration of a test apparatus for measuring the oxygen storage / release amount. In the figure, reference numeral 11 denotes a glass tube that holds a catalyst sample 12, and the catalyst sample 12 is heated and held at a predetermined temperature by a heater 13. Connected to the upstream side of the catalyst sample 12 of the glass tube 11 is a pulse gas generator 14 capable of supplying O 2 and CO gases in pulses while supplying the base gas N 2. An exhaust unit 18 is provided on the downstream side of 12. A / F sensors (oxygen sensors) 15 and 16 are provided upstream and downstream of the catalyst sample 12 of the glass tube 11. A temperature control thermocouple 19 is attached to the sample holder of the glass tube 11.
測定にあたっては、ガラス管１１内の触媒サンプル温度を所定値に保ち、ベースガスＮ２を供給して排気部１８から排気しながら、図２１に示すようにＯ２パルス（２０秒）とＣＯパルス（２０秒）とを交互に且つ間隔（２０秒）をおいて発生させることにより、リーン→ストイキ→リッチ→ストイキのサイクルを繰り返すようにした。ストイキからリッチに切り換えた直後から、図２２に示すように、触媒サンプル前後のＡ／Ｆセンサ１５，１６によって得られるＡ／Ｆ値出力差（前側Ａ／Ｆ値−後側Ａ／Ｆ値）がなくなるまでの時間における、当該出力差をＯ２量に換算し、これを触媒サンプルのＯ２放出量（酸素吸蔵放出量）とした。このＯ２放出量を２００℃から６００℃までの５０℃刻みの各温度で測定した。 In measurement, the catalyst sample temperature in the glass tube 11 is kept at a predetermined value, and the base gas N 2 is supplied and exhausted from the exhaust unit 18, while the O 2 pulse (20 seconds) and the CO pulse are shown in FIG. By alternately generating (20 seconds) and intervals (20 seconds), the cycle of lean → stoichi → rich → stoichi was repeated. Immediately after switching from stoichiometric to rich, as shown in FIG. 22, the A / F value output difference (front A / F value−rear A / F value) obtained by the A / F sensors 15 and 16 before and after the catalyst sample. The output difference in the time until disappearance is converted into an O 2 amount, and this is defined as an O 2 release amount (oxygen occlusion release amount) of the catalyst sample. The amount of released O 2 was measured at each temperature in increments of 50 ° C. from 200 ° C. to 600 ° C.
結果を図２３に示す。触媒サンプルＡ（酸化鉄ゾル＋ＯＳＣ）及び触媒サンプルＢ（硝酸第二鉄＋ＯＳＣ）のいずれも、酸化鉄を含まない触媒サンプルＣ（ＯＳＣのみ）よりも酸素放出量が多くなっている。（酸化鉄ゾル＋ＯＳＣ）と（硝酸第二鉄＋ＯＳＣ）とを比較すると、２５０℃〜６００℃において、酸化鉄ゾルの方が硝酸第二鉄よりも酸素放出量が多くなっている。 The results are shown in FIG. Both the catalyst sample A (iron oxide sol + OSC) and the catalyst sample B (ferric nitrate + OSC) have a larger oxygen release amount than the catalyst sample C not containing iron oxide (OSC only). When comparing (iron oxide sol + OSC) and (ferric nitrate + OSC), the amount of oxygen released from iron oxide sol is larger than that from ferric nitrate at 250 ° C. to 600 ° C.
図２４は（酸化鉄ゾル＋ＯＳＣ）及び（硝酸第二鉄＋ＯＳＣ）の各触媒サンプルのエージング（酸素を２％、水蒸気を１０％含む窒素ガス中で９００℃の温度に２４時間保持）後の酸素放出量を測定した結果を示す。いずれもエージング後は酸素放出量が少なくなっているが、それでも、酸化鉄ゾルの方が硝酸第二鉄よりも酸素放出量が多い。 FIG. 24 shows the oxygen after aging of each catalyst sample of (iron oxide sol + OSC) and (ferric nitrate + OSC) (maintained at a temperature of 900 ° C. for 24 hours in nitrogen gas containing 2% oxygen and 10% water vapor). The result of measuring the release amount is shown. In both cases, the amount of oxygen released after aging is reduced, but the iron oxide sol still has a higher amount of released oxygen than ferric nitrate.
触媒サンプルＡの場合は、酸化鉄ゾルによる複数の粒径３００ｎｍ以下の酸化鉄粒子がＣｅＺｒＮｄ複合酸化物（ＯＳＣ）粒子に分散して接触しており（図３乃至図６参照）、そのため、それら酸化鉄粒子がＣｅＺｒＮｄ複合酸化物粒子と相俟って触媒の酸素吸蔵放出能の向上に有効に働いているものと認められる。これに対して、触媒サンプルＢの場合は、硝酸第二鉄による酸化鉄粒子の粒径が大きく（図１２乃至図１５参照）、そのため、酸化鉄粒子による酸素吸蔵放出能の向上が酸化鉄ゾルによるものに比べて低いものと認められる。 In the case of the catalyst sample A, a plurality of iron oxide particles having a particle size of 300 nm or less formed by iron oxide sol are dispersed and in contact with CeZrNd composite oxide (OSC) particles (see FIGS. 3 to 6). It is recognized that the iron oxide particles work together with the CeZrNd composite oxide particles to effectively improve the oxygen storage / release capability of the catalyst. On the other hand, in the case of the catalyst sample B, the particle size of the iron oxide particles by ferric nitrate is large (see FIGS. 12 to 15), so that the oxygen storage / release capability by the iron oxide particles is improved. It is recognized that it is lower than that by
図２５は上記エージング後の触媒サンプルＡ（酸化鉄ゾル＋ＯＳＣ）及び触媒サンプルＢ（硝酸第二鉄＋ＯＳＣ）の酸素放出量（測定温度５００℃）を、従来触媒及び実施例触媒各々の当該エージング後の酸素放出量（測定温度５００℃）と共に示すグラフである。従来触媒は、上記触媒サンプルＣ（ＯＳＣのみ）においてそのＣｅＺｒＮｄ複合酸化物粒子に触媒金属としてＰｔを１ｇ／Ｌ担持させたものである。実施例触媒は、上記触媒サンプルＡ（酸化鉄ゾル＋ＯＳＣ）においてそのＣｅＺｒＮｄ複合酸化物粒子に触媒金属としてＰｔを１ｇ／Ｌ担持させたものである。 FIG. 25 shows the oxygen release amounts (measurement temperature 500 ° C.) of the catalyst sample A (iron oxide sol + OSC) and the catalyst sample B (ferric nitrate + OSC) after the aging after the aging of the conventional catalyst and the example catalyst, respectively. It is a graph shown with the amount of oxygen release (measurement temperature 500 degreeC). The conventional catalyst is obtained by supporting 1 g / L of Pt as a catalyst metal on the CeZrNd composite oxide particles in the catalyst sample C (OSC only). In the catalyst sample A (iron oxide sol + OSC), the catalyst of the example was obtained by supporting 1 g / L of Pt as a catalyst metal on the CeZrNd composite oxide particles.
触媒サンプルＡ（酸化鉄ゾル＋ＯＳＣ）は、触媒金属ＰｔをＣｅＺｒＮｄ複合酸化物粒子に担持させていないにも拘わらず、ＣｅＺｒＮｄ複合酸化物粒子に触媒金属Ｐｔを担持させた従来触媒と同程度の酸素放出量になっている。また、触媒サンプルＡにおいてＣｅＺｒＮｄ複合酸化物粒子に触媒金属Ｐｔを担持させた実施例触媒は、従来触媒に比べて酸素放出量が格段に多くなっている。これらから、酸化鉄ゾルによる粒径の小さな酸化鉄粒子が酸素吸蔵放出能の向上に大きな効果を示すことがわかる。 The catalyst sample A (iron oxide sol + OSC) has oxygen equivalent to that of the conventional catalyst in which the catalyst metal Pt is supported on the CeZrNd composite oxide particles even though the catalyst metal Pt is not supported on the CeZrNd composite oxide particles. The amount is released. Further, in the catalyst sample A, the example catalyst in which the catalyst metal Pt is supported on the CeZrNd composite oxide particles has a much larger oxygen release amount than the conventional catalyst. From these, it can be seen that the iron oxide particles having a small particle diameter by the iron oxide sol have a great effect in improving the oxygen storage / release ability.
＜排気ガス浄化性能＞
触媒貴金属としてのＲｈドープ量及びＲｈ表面担持量が異なる複数種類のＣｅＺｒＮｄ複合酸化物粉末を調製し、このＣｅＺｒＮｄ複合酸化物粒子量と酸化鉄ゾルによる微細酸化鉄粒子量との配合比が異なる各種触媒を調製し、排気ガス浄化性能を調べた。
<Exhaust gas purification performance>
Various types of CeZrNd composite oxide powders with different amounts of Rh doping and Rh surface loading as catalyst noble metals were prepared, and various blending ratios between the amount of CeZrNd composite oxide particles and the amount of fine iron oxide particles by iron oxide sol were different. A catalyst was prepared and the exhaust gas purification performance was examined.
−供試触媒の調製方法−
オキシ硝酸ジルコニウム、硝酸第一セリウム、硝酸ネオジム(III)含水、及び硝酸ロジウム溶液各々の所定量と水とを混合して合計３００ｍＬとし、この混合溶液を室温で約１時間撹拌した。この混合溶液を８０℃まで加熱昇温させた後、これと２８％アンモニア水５０ｍＬとを混合した。この混合は、上記混合溶液及びアンモニア水をそれぞれチューブから高速ディスパーザのカップ内に落とし、回転力及びせん断力によって混合攪拌することにより、１秒以内に完了させた。アンモニア水の混合により白濁した溶液を一昼夜放置し、生成したケーキを遠心分離器にかけ、十分に水洗した。この水洗したケーキを約１５０℃の温度で乾燥させた後、４００℃の温度に５時間保持し、次いで５００℃の温度に２時間保持するという条件で焼成した。
-Preparation of test catalyst-
A predetermined amount of each of zirconium oxynitrate, cerium nitrate, neodymium (III) nitrate, and rhodium nitrate solution was mixed with water to make a total of 300 mL, and this mixed solution was stirred at room temperature for about 1 hour. This mixed solution was heated to 80 ° C., and then mixed with 28 mL of 28% aqueous ammonia. This mixing was completed within 1 second by dropping the mixed solution and aqueous ammonia from the tubes into a cup of a high-speed disperser, respectively, and mixing and stirring with rotational force and shearing force. The solution clouded by mixing with aqueous ammonia was allowed to stand overnight, and the resulting cake was centrifuged and washed thoroughly with water. The cake washed with water was dried at a temperature of about 150 ° C. and then calcined under the condition that it was kept at a temperature of 400 ° C. for 5 hours and then kept at a temperature of 500 ° C. for 2 hours.
以上により得られた複合酸化物は、Ｒｈを添加して生成され、このＲｈが複合酸化物の結晶格子、原子間又は酸素欠損部に配置された構造となるので、以下ではＲｈドープ複合酸化物という。このＲｈドープ複合酸化物のＲｈを除く組成は、ＣｅＯ２：ＺｒＯ２：Ｎｄ２Ｏ３＝２３：６７：１０（質量比）となるようにした。 The composite oxide obtained as described above is formed by adding Rh and has a structure in which this Rh is arranged in the crystal lattice, interatomic or oxygen deficient portion of the composite oxide. That's it. The composition excluding Rh of this Rh-doped composite oxide was set to be CeO 2 : ZrO 2 : Nd 2 O 3 = 23: 67: 10 (mass ratio).
上記Ｒｈドープ複合酸化物の所定量にイオン交換水及び硝酸ロジウム溶液の所定量を加え、加熱して溶媒を飛ばした（蒸発乾固）。そうして、乾燥後、５００℃で２時間の焼成を行なうことによって、Ｒｈドープ複合酸化物の表面にＲｈを担持させた。そうして、上記Ｒｈドープ複合酸化物を調製するときの硝酸ロジウム溶液の添加量及びＲｈを表面担持するときの硝酸ロジウム溶液の添加量を適宜調節することにより、Ｒｈドープ量及びＲｈ表面担持量が異なる各種のＣｅＺｒＮｄ複合酸化物粉末を得た。 A predetermined amount of ion-exchanged water and a rhodium nitrate solution was added to a predetermined amount of the Rh-doped composite oxide, and the solvent was removed by heating (evaporation to dryness). Then, after drying, baking was performed at 500 ° C. for 2 hours, thereby supporting Rh on the surface of the Rh-doped composite oxide. Then, by appropriately adjusting the amount of rhodium nitrate solution added when preparing the Rh-doped composite oxide and the amount of rhodium nitrate solution added when the surface of Rh is supported, the amount of Rh doped and the amount of Rh surface supported Various CeZrNd composite oxide powders having different values were obtained.
得られたＣｅＺｒＮｄ複合酸化物粉末に酸化鉄ゾル及びイオン交換水を混合したスラリーを調製し、これをハニカム担体にコーティングし、乾燥及び焼成を施すことにより、ＣｅＺｒＮｄ複合酸化物粒子の担持量と酸化鉄ゾルによる微細酸化鉄粒子の担持量が異なる各種の供試触媒を得た。 A slurry in which iron oxide sol and ion-exchanged water are mixed with the obtained CeZrNd composite oxide powder is prepared, and this is coated on a honeycomb carrier, followed by drying and firing, whereby the supported amount and oxidation of CeZrNd composite oxide particles are performed. Various test catalysts with different loadings of fine iron oxide particles by iron sol were obtained.
いずれの供試触媒も、Ｒｈドープ量とＲｈ表面担持量との合計量は担体１Ｌ当たりが０．１５ｇ／Ｌとなるようにした。また、ハニカム担体としては、セル壁厚さ３．５mil（８．８９×１０−２ｍｍ）、１平方インチ（６４５．１６ｍｍ２）当たりのセル数６００のコージェライト製ハニカム担体（容量１Ｌ）を採用した。 In any of the test catalysts, the total amount of the Rh doping amount and the Rh surface loading amount was set to 0.15 g / L per liter of support. As the honeycomb carrier, a cordierite honeycomb carrier (capacity 1 L) having a cell wall thickness of 3.5 mil (8.89 × 10 −2 mm) and 600 cells per square inch (645.16 mm 2 ) is used. Adopted.
−排気ガス浄化性能の評価−
各供試触媒にベンチエージング処理を施した。これは、各供試触媒をエンジン排気系に取り付け、(1)Ａ／Ｆ＝１４の排気ガスを１５秒間流す→(2)Ａ／Ｆ＝１７の排気ガスを５秒間流す→(3)Ａ／Ｆ＝１４．７の排気ガスを４０秒間流す、というサイクルが合計１２０時間繰り返されるように、且つ触媒入口ガス温度が９００℃となるように、エンジンを運転するというものである。
−Evaluation of exhaust gas purification performance−
Each test catalyst was subjected to bench aging treatment. This is because each test catalyst is attached to the engine exhaust system, (1) A / F = 14 exhaust gas flows for 15 seconds → (2) A / F = 17 exhaust gas flows for 5 seconds → (3) A The engine is operated so that the cycle of flowing exhaust gas of /F=14.7 for 40 seconds is repeated for a total of 120 hours and the catalyst inlet gas temperature is 900 ° C.
しかる後、各供試触媒から担体容量２５ｍＬのコアサンプルを切り出し、これをモデルガス流通反応装置に取り付け、ＨＣ、ＣＯ及びＮＯｘの浄化に関するライトオフ温度Ｔ５０（℃）を測定した。Ｔ５０（℃）は、触媒に流入するモデルガス温度を常温から漸次上昇させていき、浄化率が５０％に達したときの触媒入口のガス温度である。モデルガスは、Ａ／Ｆ＝１４．７±０．９とした。すなわち、Ａ／Ｆ＝１４．７のメインストリームガスを定常的に流しつつ、所定量の変動用ガスを１Ｈｚでパルス状に添加することにより、Ａ／Ｆを±０．９の振幅で強制的に振動させた。空間速度ＳＶは６００００ｈ−１、昇温速度は３０℃／分である。 Thereafter, a core sample having a carrier volume of 25 mL was cut out from each test catalyst, and this was attached to a model gas flow reactor, and a light-off temperature T50 (° C.) relating to purification of HC, CO, and NOx was measured. T50 (° C.) is the gas temperature at the catalyst inlet when the model gas temperature flowing into the catalyst is gradually increased from room temperature and the purification rate reaches 50%. The model gas was A / F = 14.7 ± 0.9. That is, the A / F is forced at an amplitude of ± 0.9 by adding a predetermined amount of fluctuation gas in a pulse form at 1 Hz while constantly flowing the main stream gas of A / F = 14.7. Vibrated. The space velocity SV is 60000 h −1 , and the heating rate is 30 ° C./min.
結果を表３に示す。この表において、「乾固Ｒｈ」は複合酸化物表面に担持されたＲｈを、「Ｆｅ２Ｏ３」は酸化鉄ゾルによる微細酸化鉄粒子を、「ＣＺＯ」は複合酸化物を、それぞれ意味する。「乾固Ｒｈ／総Ｒｈ比率」はドープＲｈと表面担持Ｒｈとの総量に対する表面担持Ｒｈの比率を意味する。 The results are shown in Table 3. In this table, “dry Rh” means Rh supported on the surface of the composite oxide, “Fe 2 O 3 ” means fine iron oxide particles formed from an iron oxide sol, and “CZO” means a composite oxide. . “Dried Rh / total Rh ratio” means the ratio of the surface-supported Rh to the total amount of the dope Rh and the surface-supported Rh.
比較例１〜３及び実施例１〜９は、乾固Ｒｈ／総Ｒｈ比率が同じく３３．３３質量％で、微細酸化鉄粒子とＣｅＺｒ系複合酸化物粒子との合計量に対する上記微細酸化鉄粒子の比率を変化させたケースである（表の「Ｆｅ２Ｏ３」と「ＣＺＯ」との比率欄参照）。微細酸化鉄粒子の比率が２質量％以上４５質量％以下であれば、Ｔ５０が２８０℃以下になって、ライトオフ性能が良いことがわかる。 In Comparative Examples 1 to 3 and Examples 1 to 9, the dry Rh / total Rh ratio is also 33.33% by mass, and the fine iron oxide particles are based on the total amount of fine iron oxide particles and CeZr-based composite oxide particles. (Refer to the ratio column of “Fe 2 O 3 ” and “CZO” in the table). If the ratio of the fine iron oxide particles is 2% by mass or more and 45% by mass or less, it can be seen that T50 is 280 ° C. or less and the light-off performance is good.
比較例４，５及び実施例１０〜１３は、上記微細酸化鉄粒子の比率を４４．４４質量％に固定して、乾固Ｒｈ／総Ｒｈ比率を変化させたケースである。該比率が２質量％超９８質量％以下であれば、Ｔ５０が２８０℃以下になって、ライトオフ性能が良いことがわかる。比較例６，７及び実施例１４〜１７は、上記微細酸化鉄粒子の比率を１４．２９質量％に固定して、乾固Ｒｈ／総Ｒｈ比率を変化させたケースである。この場合も、該比率が２質量％超９８質量％以下であれば、Ｔ５０が２８０℃以下になっている。 In Comparative Examples 4 and 5 and Examples 10 to 13, the ratio of the fine iron oxide particles was fixed to 44.44% by mass, and the ratio of dry Rh / total Rh was changed. If the ratio is more than 2% by mass and 98% by mass or less, T50 becomes 280 ° C. or less, and it is understood that the light-off performance is good. Comparative Examples 6 and 7 and Examples 14 to 17 are cases in which the ratio of the fine iron oxide particles was fixed to 14.29% by mass, and the dry Rh / total Rh ratio was changed. Also in this case, if the ratio is more than 2% by mass and 98% by mass or less, T50 is 280 ° C. or less.
また、上記実施例１〜１７はトータルＲｈ量が０．１５ｇ／Ｌであり、本発明によれば、少ない触媒貴金属量で優れた排気ガス浄化性能が得られるということができる。このトータルの触媒貴金属量は０．１ｇ／Ｌ以上３ｇ／Ｌ以下とすることが好ましい。 In Examples 1 to 17, the total Rh amount is 0.15 g / L, and according to the present invention, it can be said that excellent exhaust gas purification performance can be obtained with a small amount of catalytic noble metal. The total amount of the catalyst noble metal is preferably 0.1 g / L or more and 3 g / L or less.
１ ハニカム担体のセル壁
２ 触媒層
３ ＣｅＺｒ系複合酸化物粒子
４ バインダ粒子（酸化鉄粒子）
５ 触媒金属
６ アルミナ粒子
７ ポア
1 Cell wall of honeycomb carrier 2 Catalyst layer 3 CeZr-based composite oxide particle 4 Binder particle (iron oxide particle)
5 Catalytic metal 6 Alumina particles 7 Pore
Claims (4)
上記ＣｅＺｒ系複合酸化物粒子に粒径３００ｎｍ以下の微細酸化鉄粒子が接しており、
上記微細酸化鉄粒子とＣｅＺｒ系複合酸化物粒子との合計量に対する上記微細酸化鉄粒子の質量比率が２質量％以上４５質量％以下であり、
上記ドープされた触媒貴金属と表面に担持された触媒貴金属との総量に対する表面に担持された触媒貴金属の質量比率が２質量％超９８質量％以下であることを特徴とする排気ガス浄化用触媒。 An exhaust gas purifying catalyst containing CeZr-based composite oxide particles doped with a catalytic noble metal in a catalyst layer provided on a honeycomb carrier and supported on the surface of the catalyst noble metal,
Fine iron oxide particles having a particle size of 300 nm or less are in contact with the CeZr-based composite oxide particles,
The mass ratio of the fine iron oxide particles to the total amount of the fine iron oxide particles and CeZr-based composite oxide particles is 2% by mass or more and 45% by mass or less,
A catalyst for exhaust gas purification, wherein a mass ratio of the catalyst noble metal supported on the surface to a total amount of the doped catalyst noble metal and the catalyst noble metal supported on the surface is more than 2 mass% and 98 mass% or less.
上記微細酸化鉄粒子は、上記触媒層においてバインダの少なくとも一部を構成していることを特徴とする排気ガス浄化用触媒。 In claim 1,
The exhaust gas purifying catalyst, wherein the fine iron oxide particles constitute at least a part of a binder in the catalyst layer.
上記微細酸化鉄粒子の少なくとも一部はヘマタイトであることを特徴とする排気ガス浄化用触媒。 In claim 1 or claim 2,
An exhaust gas purifying catalyst, wherein at least a part of the fine iron oxide particles is hematite.
上記微細酸化鉄粒子は、マグヘマイト、ゲータイト及びウスタイトがコロイド粒子として分散したゾルを原料とすることを特徴とする排気ガス浄化用触媒。 In any one of Claim 1 thru | or 3,
The fine iron oxide particles are made from a sol in which maghemite, goethite, and wustite are dispersed as colloidal particles as a raw material.
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| JP2007534467A (en) * | 2004-02-06 | 2007-11-29 | ハーテーエー・アクチェンゲゼルシャフト・ザ・ハイ・スループット・イクスペリメンテイション・カンパニー | Noble metal catalyst stabilized with iron oxide for removing pollutants from exhaust gas from lean burn engine |
| JP2005246177A (en) * | 2004-03-02 | 2005-09-15 | Toyota Central Res & Dev Lab Inc | Catalyst and its manufacturing method |
| JP2007029863A (en) * | 2005-07-27 | 2007-02-08 | Nissan Motor Co Ltd | Catalyst for cleaning exhaust gas |
| JP2007229654A (en) * | 2006-03-02 | 2007-09-13 | Nissan Motor Co Ltd | Catalyst for cleaning exhaust gas and its manufacturing method |
| JP2007307485A (en) * | 2006-05-18 | 2007-11-29 | Toyota Central Res & Dev Lab Inc | Nox storage reduction type catalyst |
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