JP5760623B2 - Exhaust gas purification catalyst and method for producing the same - Google Patents
Exhaust gas purification catalyst and method for producing the same Download PDFInfo
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- 239000003054 catalyst Substances 0.000 title claims description 101
- 238000004519 manufacturing process Methods 0.000 title claims description 6
- 238000000746 purification Methods 0.000 title description 57
- XEEYBQQBJWHFJM-UHFFFAOYSA-N Iron Chemical compound [Fe] XEEYBQQBJWHFJM-UHFFFAOYSA-N 0.000 claims description 52
- 229910052712 strontium Inorganic materials 0.000 claims description 46
- 229910052742 iron Inorganic materials 0.000 claims description 33
- PNEYBMLMFCGWSK-UHFFFAOYSA-N aluminium oxide Inorganic materials [O-2].[O-2].[O-2].[Al+3].[Al+3] PNEYBMLMFCGWSK-UHFFFAOYSA-N 0.000 claims description 32
- KRKNYBCHXYNGOX-UHFFFAOYSA-N citric acid Chemical compound OC(=O)CC(O)(C(O)=O)CC(O)=O KRKNYBCHXYNGOX-UHFFFAOYSA-N 0.000 claims description 30
- 239000011246 composite particle Substances 0.000 claims description 30
- CIOAGBVUUVVLOB-UHFFFAOYSA-N strontium atom Chemical compound [Sr] CIOAGBVUUVVLOB-UHFFFAOYSA-N 0.000 claims description 22
- 229910052751 metal Inorganic materials 0.000 claims description 19
- 239000002184 metal Substances 0.000 claims description 19
- 229910052726 zirconium Inorganic materials 0.000 claims description 18
- QCWXUUIWCKQGHC-UHFFFAOYSA-N Zirconium Chemical compound [Zr] QCWXUUIWCKQGHC-UHFFFAOYSA-N 0.000 claims description 17
- 150000001875 compounds Chemical class 0.000 claims description 14
- 239000002245 particle Substances 0.000 claims description 13
- 239000002131 composite material Substances 0.000 claims description 12
- 150000002506 iron compounds Chemical class 0.000 claims description 12
- 239000000203 mixture Substances 0.000 claims description 8
- 229910052746 lanthanum Inorganic materials 0.000 claims description 5
- 239000000463 material Substances 0.000 claims description 4
- 230000003197 catalytic effect Effects 0.000 claims description 3
- FZLIPJUXYLNCLC-UHFFFAOYSA-N lanthanum atom Chemical compound [La] FZLIPJUXYLNCLC-UHFFFAOYSA-N 0.000 claims description 3
- 238000002156 mixing Methods 0.000 claims description 2
- MWUXSHHQAYIFBG-UHFFFAOYSA-N Nitric oxide Chemical compound O=[N] MWUXSHHQAYIFBG-UHFFFAOYSA-N 0.000 description 189
- 239000007789 gas Substances 0.000 description 46
- 239000000446 fuel Substances 0.000 description 39
- 239000000843 powder Substances 0.000 description 23
- 229910018072 Al 2 O 3 Inorganic materials 0.000 description 21
- 229910052760 oxygen Inorganic materials 0.000 description 21
- 239000001301 oxygen Substances 0.000 description 20
- QVGXLLKOCUKJST-UHFFFAOYSA-N atomic oxygen Chemical compound [O] QVGXLLKOCUKJST-UHFFFAOYSA-N 0.000 description 19
- 230000000052 comparative effect Effects 0.000 description 15
- 238000011156 evaluation Methods 0.000 description 12
- 238000000034 method Methods 0.000 description 10
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- 238000002441 X-ray diffraction Methods 0.000 description 6
- 239000000243 solution Substances 0.000 description 6
- 238000003860 storage Methods 0.000 description 6
- 229910021193 La 2 O 3 Inorganic materials 0.000 description 5
- 239000011521 glass Substances 0.000 description 5
- 238000009434 installation Methods 0.000 description 5
- 238000001704 evaporation Methods 0.000 description 4
- 230000008020 evaporation Effects 0.000 description 4
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- 229910002651 NO3 Inorganic materials 0.000 description 2
- NHNBFGGVMKEFGY-UHFFFAOYSA-N Nitrate Chemical compound [O-][N+]([O-])=O NHNBFGGVMKEFGY-UHFFFAOYSA-N 0.000 description 2
- -1 Sr oxide Chemical class 0.000 description 2
- 230000002950 deficient Effects 0.000 description 2
- 238000001514 detection method Methods 0.000 description 2
- 238000010304 firing Methods 0.000 description 2
- 229910021645 metal ion Inorganic materials 0.000 description 2
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- 239000002244 precipitate Substances 0.000 description 2
- 239000000047 product Substances 0.000 description 2
- 229910052761 rare earth metal Inorganic materials 0.000 description 2
- 150000002910 rare earth metals Chemical class 0.000 description 2
- 239000002002 slurry Substances 0.000 description 2
- 239000011232 storage material Substances 0.000 description 2
- 230000036962 time dependent Effects 0.000 description 2
- XLYOFNOQVPJJNP-UHFFFAOYSA-N water Substances O XLYOFNOQVPJJNP-UHFFFAOYSA-N 0.000 description 2
- OERNJTNJEZOPIA-UHFFFAOYSA-N zirconium nitrate Chemical compound [Zr+4].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O OERNJTNJEZOPIA-UHFFFAOYSA-N 0.000 description 2
- VHUUQVKOLVNVRT-UHFFFAOYSA-N Ammonium hydroxide Chemical compound [NH4+].[OH-] VHUUQVKOLVNVRT-UHFFFAOYSA-N 0.000 description 1
- 239000004215 Carbon black (E152) Substances 0.000 description 1
- UGFAIRIUMAVXCW-UHFFFAOYSA-N Carbon monoxide Chemical compound [O+]#[C-] UGFAIRIUMAVXCW-UHFFFAOYSA-N 0.000 description 1
- 229910052684 Cerium Inorganic materials 0.000 description 1
- 229910017493 Nd 2 O 3 Inorganic materials 0.000 description 1
- 229910052779 Neodymium Inorganic materials 0.000 description 1
- GRYLNZFGIOXLOG-UHFFFAOYSA-N Nitric acid Chemical compound O[N+]([O-])=O GRYLNZFGIOXLOG-UHFFFAOYSA-N 0.000 description 1
- 229910052777 Praseodymium Inorganic materials 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
- 235000011114 ammonium hydroxide Nutrition 0.000 description 1
- 239000007864 aqueous solution Substances 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000001354 calcination Methods 0.000 description 1
- 229910052791 calcium Inorganic materials 0.000 description 1
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- 229910052878 cordierite Inorganic materials 0.000 description 1
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- 238000002447 crystallographic data Methods 0.000 description 1
- 238000010586 diagram Methods 0.000 description 1
- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 1
- 238000001035 drying Methods 0.000 description 1
- 229930195733 hydrocarbon Natural products 0.000 description 1
- 150000002430 hydrocarbons Chemical class 0.000 description 1
- XLYOFNOQVPJJNP-UHFFFAOYSA-M hydroxide Chemical compound [OH-] XLYOFNOQVPJJNP-UHFFFAOYSA-M 0.000 description 1
- 238000002347 injection Methods 0.000 description 1
- 239000007924 injection Substances 0.000 description 1
- FYDKNKUEBJQCCN-UHFFFAOYSA-N lanthanum(3+);trinitrate Chemical compound [La+3].[O-][N+]([O-])=O.[O-][N+]([O-])=O.[O-][N+]([O-])=O FYDKNKUEBJQCCN-UHFFFAOYSA-N 0.000 description 1
- 229910052749 magnesium Inorganic materials 0.000 description 1
- 150000002823 nitrates Chemical class 0.000 description 1
- 229910017604 nitric acid Inorganic materials 0.000 description 1
- 230000003647 oxidation Effects 0.000 description 1
- 238000007254 oxidation reaction Methods 0.000 description 1
- 230000001590 oxidative effect Effects 0.000 description 1
- 150000002926 oxygen Chemical class 0.000 description 1
- 229910052763 palladium Inorganic materials 0.000 description 1
- 229910052697 platinum Inorganic materials 0.000 description 1
- 238000003756 stirring Methods 0.000 description 1
- 238000000547 structure data Methods 0.000 description 1
- 230000007704 transition Effects 0.000 description 1
- 229910052727 yttrium Inorganic materials 0.000 description 1
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- Catalysts (AREA)
- Exhaust Gas After Treatment (AREA)
- Exhaust Gas Treatment By Means Of Catalyst (AREA)
Description
本発明は、排気ガス浄化用触媒及びその製造方法に関する。 The present invention relates to an exhaust gas purification catalyst and a method for producing the same.
排気ガス浄化用触媒には種々の触媒金属が採用されている。例えば三元触媒では、ＨＣ（炭化水素）、ＣＯ（一酸化炭素）及びＮＯｘ（窒素酸化物）を同時に浄化させる必要から、ＨＣ及びＣＯの酸化能に優れるＰｔ及びＰｄと、ＮＯｘ還元能に優れるＲｈとが採用されることが多い。それら触媒金属のサポート材としては、一般に比表面積の大きな酸化物が用いられている。そのなかでも、特に活性アルミナは上記触媒金属を高分散状態に担持できることから有用である。 Various catalyst metals are employed for the exhaust gas purifying catalyst. For example, in a three-way catalyst, HC (hydrocarbon), CO (carbon monoxide), and NOx (nitrogen oxide) need to be purified simultaneously, so that Pt and Pd, which are excellent in oxidizing ability of HC and CO, and NOx reducing ability are excellent Rh is often adopted. In general, an oxide having a large specific surface area is used as a support material for these catalytic metals. Among these, activated alumina is particularly useful because it can support the catalyst metal in a highly dispersed state.
上記排気ガス浄化用触媒のＮＯｘ還元能を向上させる技術の一例が特許文献１に記載されている。それは、活性アルミナ粒子の少なくとも一部を被覆しているＺｒＬａ複酸化物にＲｈが担持されてなる触媒成分と、酸素吸蔵材にＲｈが担持されてなる触媒成分とを、担体上の触媒層に共存させるというものである。上記ＺｒＬａ複酸化物に担持されているＲｈは、排気ガスの雰囲気（Ａ／Ｆ）がリーンからリッチに変化したときでも酸化状態を保持し易い。このため、雰囲気がリーンであるかリッチであるかに拘わらず、酸素吸蔵材上の還元されたＲｈと、ＺｒＬａ複酸化物上の酸化されたＲｈとが共存した状態が得られ、排気ガス浄化性能が高くなる。 An example of a technique for improving the NOx reduction ability of the exhaust gas purification catalyst is described in Patent Document 1. It consists of a catalyst component in which Rh is supported on a ZrLa complex oxide covering at least a part of activated alumina particles, and a catalyst component in which Rh is supported on an oxygen storage material on a catalyst layer on the carrier. It is to coexist. Rh supported on the ZrLa composite oxide is easily maintained in an oxidized state even when the exhaust gas atmosphere (A / F) changes from lean to rich. Therefore, regardless of whether the atmosphere is lean or rich, a state in which the reduced Rh on the oxygen storage material and the oxidized Rh on the ZrLa double oxide coexist is obtained, and exhaust gas purification is achieved. Increases performance.
ところで、ハイブリッド自動車に関しては、エンジンを専ら発電機として使用し、その電力をモータによる自動車の駆動に利用するシリーズ方式、モータによる駆動とエンジンによる駆動とを組み合わせるパラレル方式等が知られている。いずれにしても、始動と停止とが頻繁に繰り返されるのがハイブリッド自動車におけるエンジンの特徴である。そして、エンジン停止時においては、燃料噴射を停止させてからエンジンの回転が停止するまでの間に、空気のみがいずれかの気筒を通過して排気系に流入し、その空気に排気ガス浄化用触媒が晒される。その結果、その触媒は、空燃比リーンの雰囲気（例えば、Ａ／Ｆ≧２０）に包まれ且つ低温状態で次のエンジン始動を迎え、急に空燃比リッチの排気ガスに晒されることになる。そのため、触媒によるＮＯｘ（窒素酸化物）浄化が進みにくくなり、エンジン再始動時の大気中へ排出されるＮＯｘが増加するという問題がある。 By the way, as for hybrid vehicles, there are known a series method in which an engine is exclusively used as a generator and the electric power is used for driving a vehicle by a motor, a parallel method in which driving by a motor and driving by an engine are combined. In any case, it is a feature of the engine in a hybrid vehicle that start and stop are frequently repeated. When the engine is stopped, only air passes through one of the cylinders and flows into the exhaust system after the fuel injection is stopped until the engine stops. The catalyst is exposed. As a result, the catalyst is enveloped in an air-fuel ratio lean atmosphere (for example, A / F ≧ 20), reaches the next engine start in a low temperature state, and is suddenly exposed to the air-fuel ratio rich exhaust gas. Therefore, NOx (nitrogen oxide) purification by the catalyst is difficult to proceed, and there is a problem that NOx discharged into the atmosphere at the time of engine restart increases.
同様の問題は、エンジンだけを駆動源とする自動車においてもみられ、さらに、減速運転時に燃料カットを実施する場合、燃料カット中は、空気のみがエンジン排気系に送られる状態となるから、排気ガス浄化用触媒はその蓄積酸素量が増加し且つ低温状態になる。また、低燃費化のために空燃比リーンでエンジンを始動するケース（リーンスタート）においても、排気ガス浄化用触媒は、低温且つリーン雰囲気に包まれた状態になるから、同様の問題がある。 The same problem is observed in automobiles that use only the engine as the drive source. Further, when fuel cut is performed during deceleration operation, only air is sent to the engine exhaust system during fuel cut. The purifying catalyst increases in the amount of accumulated oxygen and enters a low temperature state. Further, even in the case of starting the engine with an air-fuel ratio lean for low fuel consumption (lean start), the exhaust gas purifying catalyst is in a state of being wrapped in a low temperature and lean atmosphere, and thus has the same problem.
これに対して、上記特許文献１に記載された排気ガス浄化用触媒の場合、空燃比が理論空燃比近傍においてリーンとリッチとに小さい振幅で変動する場合には、比較的高い排気ガス浄化性能が得られる。しかし、上述の如く空燃比変動が大きい場合、特に低温時には、排気ガスの浄化力が低くなる。 On the other hand, in the case of the exhaust gas purification catalyst described in Patent Document 1, when the air-fuel ratio fluctuates with a small amplitude between lean and rich in the vicinity of the theoretical air-fuel ratio, a relatively high exhaust gas purification performance. Is obtained. However, when the air-fuel ratio fluctuation is large as described above, the purification power of the exhaust gas is low particularly at low temperatures.
そこで、本発明は、排気ガス浄化用触媒が低温で且つ空燃比リーン雰囲気に包まれている状態であっても、空燃比リッチの排気ガスが触媒に流入してきた過渡期にＮＯｘを効率良く浄化できるようにして、例えば、エンジン始動時に大気中にＮＯｘが未浄化のまま排出される量を低減する。 Therefore, the present invention efficiently purifies NOx during a transition period when exhaust gas rich in air-fuel ratio flows into the catalyst even when the exhaust gas-purifying catalyst is in a low temperature and air-fuel ratio lean atmosphere. In this way, for example, the amount of NOx that is exhausted without being purified into the atmosphere when the engine is started is reduced.
本発明は、上記課題を解決するために、活性アルミナ粒子の少なくとも一部がランタンを含有するジルコニウム系複酸化物によって被覆されてなる複合粒子に、ストロンチウム及び鉄を含有する複酸化物を担持させるようにした。 In order to solve the above problems, the present invention supports a composite oxide containing strontium and iron on a composite particle in which at least a part of activated alumina particles is coated with a zirconium-based composite oxide containing lanthanum. I did it.
すなわち、ここに提示する排気ガス浄化用触媒では、触媒金属としてのＲｈと、ジルコニウム系複酸化物（以下、各種の元素名には元素記号を用いて、例えば「Ｚｒ系複酸化物」とする。）と、活性アルミナと、Ｓｒ及びＦｅの化合物とが、担体上の触媒層に含まれている。上記Ｚｒ系複酸化物は、Ｚｒを主成分とし且つＬａを含有する複酸化物である。上記Ｓｒ及びＦｅの化合物の少なくとも一部は、ＳｒとＦｅとを含有する複酸化物である。上記活性アルミナの少なくとも一部と上記Ｚｒ系複酸化物の少なくとも一部とは、活性アルミナの粒子表面の少なくとも一部がＺｒ系複酸化物で被覆されてなる複合粒子を形成している。この複合粒子に、上記ストロンチウムと鉄とを含有する複酸化物の少なくとも一部が担持され、且つ上記触媒金属としてのＲｈの少なくとも一部が、当該複合粒子と当該ストロンチウム及び鉄を含有する複酸化物とに担持されている。 That is, in the exhaust gas purifying catalyst presented here, Rh as a catalyst metal and zirconium-based double oxide (hereinafter referred to as “Zr-based double oxide” using element symbols for various element names, for example) ), Activated alumina, and a compound of Sr and Fe are contained in the catalyst layer on the support. The Zr-based double oxide is a double oxide containing Zr as a main component and containing La. At least a part of the compound of Sr and Fe is a double oxide containing Sr and Fe. At least a part of the activated alumina and at least a part of the Zr-based double oxide form composite particles in which at least a part of the active alumina particle surface is coated with the Zr-based double oxide. At least a part of the composite oxide containing strontium and iron is supported on the composite particles, and at least a part of Rh as the catalyst metal is composite oxide containing the composite particles, the strontium and iron. It is carried on the object .
そうして、上記ジルコニウム系複酸化物と、上記活性アルミナと、上記ストロンチウム及び鉄の化合物とは、上記ジルコニウム系複酸化物と上記活性アルミナとの合計量に対する上記ストロンチウム及び鉄の化合物の比率が２質量％以上１０質量％以下となるように、上記触媒層に含まれている。 Thus, the zirconium double oxide, the activated alumina, and the strontium and iron compound have a ratio of the strontium and iron compound to the total amount of the zirconium double oxide and the activated alumina. It is contained in the catalyst layer so as to be 2% by mass or more and 10% by mass or less.
上記排気ガス浄化用触媒の場合、低温雰囲気において空燃比がリーンからリッチに大きく変化したときにＮＯｘが比較的高い効率で浄化される（この点は後述の実施形態において明らかにする。）。これは、空燃比がリッチになった際に上記Ｓｒ及びＦｅを含有する複酸化物から活性酸素が速やかに放出され、この活性酸素によって触媒金属まわりに還元性が高い部分酸化ＨＣが生成され、当該触媒金属によるＮＯｘの還元浄化が効率良く進むことが一因になっていると推測される。 In the case of the exhaust gas purifying catalyst, NOx is purified with relatively high efficiency when the air-fuel ratio changes greatly from lean to rich in a low temperature atmosphere (this point will be clarified in an embodiment described later). This is because when the air-fuel ratio becomes rich, active oxygen is rapidly released from the double oxide containing Sr and Fe, and this active oxygen generates highly oxidized partially oxidized HC around the catalyst metal, It is speculated that this is due to the efficient reduction and reduction of NOx by the catalyst metal.
上記触媒金属としてＲｈを採用したから、ＮＯｘの還元に良好な触媒活性を示し、且つＨＣ及びＣＯの酸化にも有効となる。 Since Rh is employed as the catalyst metal, it exhibits good catalytic activity for NOx reduction and is also effective for the oxidation of HC and CO .
上記Ｚｒ系複酸化物としては、金属イオンとして主成分であるＺｒと少量のＬａとの二種類のみを含有する複酸化物を採用することができるが、さらにＬａ及びＣｅ以外の希土類金属やアルカリ土類金属を含有するものであってもよい。希土類金属としては、例えば、Ｎｄ、Ｙ及びＰｒから選ばれる少なくとも一種を採用することが好ましい。アルカリ土類金属としては、例えば、Ｍｇ、Ｃａ及びＳｒから選ばれる少なくとも一種を採用することが好ましい。 As the Zr-based double oxide, a double oxide containing only two types of metal ions, Zr, which is a main component, and a small amount of La, can be adopted. Further, rare earth metals other than La and Ce and alkalis can be used. It may contain an earth metal. As the rare earth metal, for example, it is preferable to employ at least one selected from Nd, Y, and Pr. As the alkaline earth metal, for example, it is preferable to employ at least one selected from Mg, Ca and Sr.
上記Ｓｒ及びＦｅを含有する複酸化物としては、酸素吸蔵放出能に優れた酸素欠損型ペロブスカイト構造のものが好ましい。 As the double oxide containing Sr and Fe, those having an oxygen deficient perovskite structure excellent in oxygen storage / release ability are preferable.
上記Ｚｒ系複酸化物と、上記活性アルミナと、上記Ｓｒ及びＦｅの化合物とは、上記Ｚｒ系複酸化物と上記活性アルミナとの合計量に対する上記Ｓｒ及びＦｅの化合物の比率が２質量％以上１０質量％以下となるように、上記触媒層に含まれているから、排気ガス浄化用触媒のライトオフ性能の向上に有利になる。 The Zr-based double oxide, the active alumina, and the Sr and Fe compound are such that the ratio of the Sr and Fe compound to the total amount of the Zr-based double oxide and the active alumina is 2% by mass or more. Since it is contained in the catalyst layer so as to be 10 % by mass or less, it is advantageous for improving the light-off performance of the exhaust gas purifying catalyst.
上記排気ガス浄化用触媒の触媒層に設ける触媒材は次の方法によって製造することができる。すなわち、その方法は、活性アルミナの粒子表面の少なくとも一部が、Ｚｒを主成分とし且つＬａを含有するＺｒ系複酸化物で被覆されてなる複合粒子を準備する工程と、上記複合粒子と、Ｓｒ及びＦｅを含有する溶液とを混合する工程と、得られた混合物を乾燥し焼成することにより、上記ストロンチウム及び鉄の化合物を含有し、且つ該化合物の少なくとも一部は上記ストロンチウム及び鉄を含有する複酸化物となっており、該複酸化物の少なくとも一部が上記複合粒子に担持されてなる焼成物を得る工程と、得られた焼成物に触媒金属としてのＲｈを担持する工程とを備え、
上記ジルコニウム系複酸化物と、上記活性アルミナと、上記ストロンチウム及び鉄の化合物とは、上記ジルコニウム系複酸化物と上記活性アルミナとの合計量に対する上記ストロンチウム及び鉄の化合物の比率が２質量％以上１０質量％以下となるようにする。
The catalyst material provided in the catalyst layer of the exhaust gas purification catalyst can be manufactured by the following method. That is, the method comprises preparing a composite particle in which at least a part of the particle surface of activated alumina is coated with a Zr-based double oxide containing Zr as a main component and containing La, and the composite particle, A step of mixing a solution containing Sr and Fe, and drying and calcining the obtained mixture , thereby containing the strontium and iron compound, and at least a part of the compound contains the strontium and iron. A step of obtaining a fired product in which at least a part of the double oxide is supported on the composite particles, and a step of supporting Rh as a catalyst metal on the obtained fired product. Prepared ,
The zirconium-based double oxide, the active alumina, and the strontium and iron compound are such that the ratio of the strontium and iron compound to the total amount of the zirconium-based double oxide and the active alumina is 2% by mass or more. It shall be 10 mass% or less .
好ましいのは、上記Ｓｒ及びＦｅを含有する溶液としてクエン酸錯体溶液を用い、上記混合物の焼成温度を６００℃以上１０００℃以下とすることである。これにより、酸素吸蔵放出能に優れた酸素欠損型ペロブスカイト構造のＳｒＦｅ複酸化物の生成に有利になる。 Preferably, a citric acid complex solution is used as the solution containing Sr and Fe, and the firing temperature of the mixture is 600 ° C. or higher and 1000 ° C. or lower. This is advantageous for the generation of SrFe double oxide having an oxygen-deficient perovskite structure excellent in oxygen storage / release capability.
本発明に係る排気ガス浄化用触媒によれば、活性アルミナの粒子表面の少なくとも一部がＺｒ系複酸化物で被覆されてなる複合粒子に、Ｓｒ及びＦｅを含有する複酸化物が担持され、触媒金属としてのＲｈの少なくとも一部が当該複合粒子と当該Ｓｒ及びＦｅを含有する複酸化物とに担持され、上記Ｚｒ系複酸化物と、上記活性アルミナと、上記Ｓｒ及びＦｅの化合物とは、上記Ｚｒ系複酸化物と上記活性アルミナとの合計量に対する上記Ｓｒ及びＦｅの化合物の比率が２質量％以上１０質量％以下となるように、触媒層に含まれているから、当該排気ガス浄化用触媒が空燃比リーンの雰囲気に包まれ且つ温度が低い状態にあっても、空燃比リッチの排気ガスが当該触媒に流入したときのＮＯｘ浄化性に優れ、例えば、エンジン始動時に大気中にＮＯｘが未浄化のまま排出される量を低減する上で有利になる。 According to the exhaust gas purifying catalyst of the present invention, a composite oxide containing Sr and Fe is supported on a composite particle in which at least a part of the particle surface of activated alumina is coated with a Zr-based composite oxide , At least a part of Rh as a catalyst metal is supported on the composite particles and the composite oxide containing Sr and Fe, and the Zr-based composite oxide, the activated alumina, and the compound of Sr and Fe are: The exhaust gas is contained in the catalyst layer so that the ratio of the Sr and Fe compounds to the total amount of the Zr-based double oxide and the activated alumina is 2% by mass or more and 10% by mass or less. Even if the purification catalyst is enclosed in an air-fuel ratio lean atmosphere and the temperature is low, the NOx purification performance when the exhaust gas rich in the air-fuel ratio flows into the catalyst is excellent. NOx is effective in reducing the amount of discharged remains unpurified to.
以下、本発明を実施するための形態を図面に基づいて説明する。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 for carrying out the present invention will be described with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use.
図１は排気ガス浄化用触媒（三元触媒）１を示す。コージェライト製のハニカム担体１ａの排気ガス通路壁に触媒層１ｂが形成されている。触媒層１ｂには、触媒金属と、Ｚｒ系複酸化物と、活性アルミナと、Ｓｒ及びＦｅを含有するＳｒＦｅ複酸化物とが含まれている。なお、本発明は、上記触媒層１ｂに他の触媒成分を含ませることを制限するものではない。また、上記触媒層１ｂと、触媒成分が異なる別の触媒層とを層状に重ねた複数層構造を採用してもよい。 FIG. 1 shows an exhaust gas purification catalyst (three-way catalyst) 1. A catalyst layer 1b is formed on the exhaust gas passage wall of the cordierite honeycomb carrier 1a. The catalyst layer 1b contains a catalyst metal, a Zr-based double oxide, activated alumina, and a SrFe double oxide containing Sr and Fe. Note that the present invention does not limit the inclusion of other catalyst components in the catalyst layer 1b. Moreover, you may employ | adopt the multi-layered structure which laminated | stacked the said catalyst layer 1b and another catalyst layer from which a catalyst component differs in layered form.
＜触媒層の触媒成分＞
以下、上記触媒層１ｂの触媒成分について具体的に説明する。Ｚｒ系複酸化物は、Ｚｒを主成分とし且つＬａを含有するＺｒＬａ複酸化物である。本実施形態では触媒金属としてＲｈを採用している。活性アルミナの少なくとも一部とＺｒＬａ複酸化物の少なくとも一部とは、活性アルミナの粒子表面の少なくとも一部がＺｒＬａ複酸化物で被覆されてなる複合粒子を形成している。便宜的に、活性アルミナを「Ａｌ２Ｏ３」で表し、ＺｒＬａ複酸化物を「ＺｒＬａＯ」で表すと、当該複合粒子は「ＺｒＬａＯ／Ａｌ２Ｏ３」と表すことができる。この複合粒子に、ＳｒＦｅ複酸化物の少なくとも一部とＲｈの少なくとも一部とが担持されている。
<Catalyst component of catalyst layer>
Hereinafter, the catalyst component of the catalyst layer 1b will be specifically described. The Zr-based double oxide is a ZrLa double oxide containing Zr as a main component and containing La. In this embodiment, Rh is adopted as the catalyst metal. At least a part of the activated alumina and at least a part of the ZrLa double oxide form composite particles in which at least a part of the particle surface of the activated alumina is coated with the ZrLa double oxide. For convenience, when the activated alumina is represented by “Al 2 O 3 ” and the ZrLa double oxide is represented by “ZrLaO”, the composite particle can be represented by “ZrLaO / Al 2 O 3 ”. At least part of the SrFe double oxide and at least part of Rh are supported on the composite particles.
本実施形態では、複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３にＳｒＦｅ複酸化物を担持した上で、これに触媒金属としてのＲｈを担持している。便宜的に、ＳｒＦｅ複酸化物を「ＳｒＦｅＯ」で表すと、本発明の特徴ある触媒成分は「Ｒｈ／ＳｒＦｅＯ／ＺｒＬａＯ／Ａｌ２Ｏ３」と表すことができる。 In this embodiment, the composite particles ZrLaO / Al 2 O 3 carry SrFe double oxide, and then carry Rh as a catalyst metal. For convenience, when the SrFe double oxide is represented by “SrFeO”, the characteristic catalyst component of the present invention can be represented by “Rh / SrFeO / ZrLaO / Al 2 O 3 ”.
上記触媒成分の製法を説明する。まず、共沈法を利用して複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３を生成する。すなわち、硝酸ジルコニウム及び硝酸ランタンの混合溶液に活性アルミナ粉末を分散させ、これにアンモニア水を加えて上記混合溶液中の各金属成分を含む水酸化物の沈殿を生成する。得られた沈殿物を濾過、洗浄し、２００℃に２時間保持する乾燥、並びに５００℃に２時間保持する焼成を行なう。これにより、複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３を含む粉末を得ることができる。なお、この粉末には、当該複合粒子の他に、活性アルミナ粒子に担持されていないＺｒＬａ複酸化物単独の粒子も一部含まれている。 The manufacturing method of the said catalyst component is demonstrated. First, composite particles ZrLaO / Al 2 O 3 are generated using a coprecipitation method. That is, activated alumina powder is dispersed in a mixed solution of zirconium nitrate and lanthanum nitrate, and ammonia water is added thereto to form a hydroxide precipitate containing each metal component in the mixed solution. The obtained precipitate is filtered, washed, dried at 200 ° C. for 2 hours, and baked at 500 ° C. for 2 hours. Thereby, the powder containing the composite particles ZrLaO / Al 2 O 3 can be obtained. In addition to the composite particles, the powder includes a part of ZrLa complex oxide particles that are not supported on the activated alumina particles.
次に、クエン酸錯体法を利用して上記複合粒子にＳｒＦｅ複酸化物が担持されたＳｒＦｅＯ／ＺｒＬａＯ／Ａｌ２Ｏ３を得る。すなわち、Ｓｒ及びＦｅの硝酸塩と水とを混合し、加熱しながら攪拌する。硝酸塩が溶解したら、クエン酸を加え、更に加熱しながら攪拌する。クエン酸はモル比で全金属イオンの１．５倍等量加える。この時点でクエン酸錯体が生成する。温度は６０℃にキープする。Ｓｒ及びＦｅを含むクエン酸錯体溶液に粘性が出てきたら、加熱を止め、金属容器に移す。次いで、そのクエン酸錯体溶液と上記複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３を含む粉末とを混合してスラリーにする。このスラリーを４００℃に２時間保持する仮焼成を行ない（水分と硝酸塩の除去）、次いで８００℃に２時間保持する本焼成を行なう。 Next, SrFeO / ZrLaO / Al 2 O 3 in which SrFe double oxide is supported on the composite particles is obtained using a citric acid complex method. That is, Sr and Fe nitrates and water are mixed and stirred while heating. When the nitrate is dissolved, add citric acid and stir while heating. Citric acid is added in a molar ratio equal to 1.5 times the total metal ions. At this point, a citric acid complex is formed. Keep temperature at 60 ° C. When the viscosity of the citric acid complex solution containing Sr and Fe becomes viscous, the heating is stopped and transferred to a metal container. Next, the citric acid complex solution and the powder containing the composite particles ZrLaO / Al 2 O 3 are mixed to form a slurry. The slurry is pre-baked at 400 ° C. for 2 hours (removal of water and nitrate), and then main baking is held at 800 ° C. for 2 hours.
そうして、本焼成で得られた粉末にＲｈを蒸発乾固法にて担持させる。この蒸発乾固にはＲｈ溶液として硝酸Ｒｈ水溶液を採用することができる。以上により、上述のＲｈ／ＳｒＦｅＯ／ＺｒＬａＯ／Ａｌ２Ｏ３成分を含む触媒粉末が得ることができる。 Then, Rh is supported on the powder obtained by the main firing by the evaporation to dryness method. For this evaporation to dryness, an Rh nitric acid aqueous solution can be employed as the Rh solution. By the above, the catalyst powder containing the above-mentioned Rh / SrFeO / ZrLaO / Al 2 O 3 component can be obtained.
上記触媒粉末には、上記Ｒｈ／ＳｒＦｅＯ／ＺｒＬａＯ／Ａｌ２Ｏ３成分の粒子の他に、上記ＺｒＬａ複酸化物単独粒子にＳｒＦｅ複酸化物及びＲｈが担持された触媒成分が含まれ、その他にも様々な触媒成分が含まれる。すなわち、上記クエン酸錯体法では、ＳｒＦｅ複酸化物として、ペロブスカイト構造の複酸化物だけでなく、それ以外の複酸化物、Ｓｒ酸化物及びＦｅ酸化物も生成する。従って、上記触媒粉末には、それら各種の酸化物が、単独状態で、或いはＲｈが担持された状態で、或いはＲｈと共に上記複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３やＺｒＬａ複酸化物単独粒子に担持された状態など、様々な形態で含まれることになる。 In addition to the particles of the Rh / SrFeO / ZrLaO / Al 2 O 3 component, the catalyst powder includes a catalyst component in which SrFe double oxide and Rh are supported on the ZrLa double oxide single particle. Also contain various catalyst components. That is, in the citric acid complex method, not only a double oxide having a perovskite structure but also other double oxides, Sr oxides and Fe oxides are generated as SrFe double oxides. Therefore, in the catalyst powder, these various oxides are supported on the composite particles ZrLaO / Al 2 O 3 or ZrLa composite oxide alone particles in a single state, in a state where Rh is supported, or together with Rh. It will be included in various forms such as a state.
＜実施例及び比較例＞
−実施例１〜３，参考例１，２−
上記製法により、各種酸化物の質量比が異なる実施例１〜３，参考例１，２の各触媒粉末を調製し、それぞれハニカム担体に担持させた。各触媒粉末の質量比は、Ｓｒ、Ｆｅ、Ｚｒ、Ｌａ及びＡｌを酸化物ＳｒＯ、Ｆｅ２Ｏ３、ＺｒＯ２、Ｌａ２Ｏ３及びＡｌ２Ｏ３に換算したときの値であり、表１に示すとおりである。ＺｒＬａ複酸化物と活性アルミナとの合計量（ＺｒＯ２＋Ｌａ２Ｏ３＋Ａｌ２Ｏ３）に対するＳｒ及びＦｅの化合物（ＳｒＯ＋Ｆｅ２Ｏ３）の比率も併せて表１に示している。担体１Ｌ当たりの触媒粉末担持量はいずれも３０ｇとし、また、担体１Ｌ当たりのＲｈ担持量はいずれも０．１ｇとした。
<Examples and Comparative Examples>
-Examples 1 to 3, Reference Examples 1 and 2-
The catalyst powders of Examples 1 to 3, Reference Examples 1 and 2 having different mass ratios of various oxides were prepared by the above production method, and each catalyst powder was supported on a honeycomb carrier. The mass ratio of each catalyst powder is a value when Sr, Fe, Zr, La, and Al are converted into oxides SrO, Fe 2 O 3 , ZrO 2 , La 2 O 3, and Al 2 O 3 , and Table 1 As shown in Table 1 also shows the ratio of Sr and Fe compounds (SrO + Fe 2 O 3 ) to the total amount of ZrLa double oxide and activated alumina (ZrO 2 + La 2 O 3 + Al 2 O 3 ). The amount of catalyst powder supported per liter of carrier was 30 g, and the amount of Rh supported per liter of carrier was 0.1 g.
−比較例１−
上記複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３を含む粉末にＲｈを蒸発乾固法で担持させてなる触媒粉末を調製し、ハニカム担体に担持させた。この触媒粉末の酸化物換算質量比は表１に示すとおりである。この比較例１の場合、上記（ＳｒＯ＋Ｆｅ２Ｏ３）／（ＺｒＯ２＋Ｌａ２Ｏ３＋Ａｌ２Ｏ３）比率は零である。また、実施例１〜３，参考例１，２と同じく、担体１Ｌ当たりの触媒粉末担持量は３０ｇ、担体１Ｌ当たりのＲｈ担持量は０．１ｇとした。
-Comparative Example 1-
A catalyst powder was prepared by supporting Rh on the powder containing the composite particles ZrLaO / Al 2 O 3 by evaporation to dryness, and supported on a honeycomb carrier. The oxide-converted mass ratio of this catalyst powder is as shown in Table 1. In the case of this comparative example 1, the (SrO + Fe 2 O 3 ) / (ZrO 2 + La 2 O 3 + Al 2 O 3 ) ratio is zero. Further, as in Examples 1 to 3 and Reference Examples 1 and 2 , the amount of catalyst powder supported per liter of carrier was 30 g, and the amount of Rh supported per liter of carrier was 0.1 g.
−比較例２，３−
上記複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３とは別に、クエン酸錯体法によって、Ｓｒ及びＦｅの化合物（Ｓｒ酸化物、Ｆｅ酸化物及びＺｒＦｅ複酸化物が含まれる）を調製した。そして、このＳｒ及びＦｅの化合物と複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３とを機械的に混合し、これにＲｈを蒸発乾固法で担持させてなる触媒粉末を調製し、ハニカム担体に担持させた。比較例２と比較例３とは、上記（ＳｒＯ＋Ｆｅ２Ｏ３）／（ＺｒＯ２＋Ｌａ２Ｏ３＋Ａｌ２Ｏ３）比率が相違するだけで、他の構成は同じである。また、いずれも担体１Ｌ当たりの触媒粉末担持量は３０ｇ、担体１Ｌ当たりのＲｈ担持量は０．１ｇである。
-Comparative Examples 2, 3-
Apart from the composite particles ZrLaO / Al 2 O 3 , Sr and Fe compounds (including Sr oxide, Fe oxide and ZrFe double oxide) were prepared by the citric acid complex method. Then, this Sr and Fe compound and composite particles ZrLaO / Al 2 O 3 were mechanically mixed, and a catalyst powder was prepared by supporting Rh by evaporation to dryness, and supported on the honeycomb carrier. . Comparative Example 2 and Comparative Example 3 are the same except for the above-mentioned (SrO + Fe 2 O 3 ) / (ZrO 2 + La 2 O 3 + Al 2 O 3 ) ratio. In both cases, the amount of catalyst powder supported per liter of carrier is 30 g, and the amount of Rh supported per liter of carrier is 0.1 g.
＜Ｘ線回折分析＞
実施例３、参考例１，２及び比較例１各々の触媒粉末中のＳｒ及びＦｅの化合物の結晶構造をＸ線回折にて調べた。結果を図２に示す。図２には、ペロブスカイト構造のＳｒＦｅＯのＸ線回折チャート、並びに該ＳｒＦｅＯ２．９７（ペロブスカイト構造）、Ｓｒ３Ｆｅ２Ｏ６．７５、ＳｒＦｅ１２Ｏ１９、及びＳｒＣＯ３の回折データを併せて図２に示す。同図によれば、実施例３及び参考例１，２の触媒粉末には、Ｓｒ酸化物、Ｆｅ酸化物、各種のＳｒＦｅ複酸化物など様々のＳｒ及びＦｅの化合物が含まれていることがわかる。
<X-ray diffraction analysis>
The crystal structures of the Sr and Fe compounds in the catalyst powders of Example 3 , Reference Examples 1 and 2 and Comparative Example 1 were examined by X-ray diffraction. The results are shown in FIG. FIG. 2 also shows an X-ray diffraction chart of SrFeO having a perovskite structure and diffraction data of SrFeO 2.97 (perovskite structure), Sr 3 Fe 2 O 6.75 , SrFe 12 O 19 , and SrCO 3 . It is shown in 2. According to the figure, the catalyst powders of Example 3 and Reference Examples 1 and 2 contain various Sr and Fe compounds such as Sr oxide, Fe oxide, and various SrFe double oxides. Recognize.
図２では、実施例３及び参考例１，２の触媒粉末にペロブスカイト構造のＳｒＦｅ複酸化物が含まれているか否か明確でないが、図３によれば、ペロブスカイト構造のＳｒＦｅ複酸化物に由来する回折が認められる。図３は図２のＸ線回折チャートの一部を対数目盛りにして拡大したチャートである。同図の３３deg付近の回折ピークはペロブスカイト構造のＳｒＦｅ複酸化物に特有のピークである。ペロブスカイト構造のＳｒＦｅ複酸化物の絶対量が少ないために、図２では同複酸化物に特有の回折ピークが明確に現れていないということである。また、上記触媒粉末にＳｒＦｅ複酸化物が含まれていることはＴＥＭ（透過型電子顕微鏡）観察で確認することができる。 In FIG. 2, it is not clear whether or not the catalyst powders of Example 3 and Reference Examples 1 and 2 contain a SrFe double oxide having a perovskite structure, but according to FIG. 3, it is derived from the SrFe double oxide having a perovskite structure. Diffraction is observed. FIG. 3 is an enlarged chart of a part of the X-ray diffraction chart of FIG. 2 on a logarithmic scale. The diffraction peak near 33 deg in the figure is a peak peculiar to SrFe double oxide having a perovskite structure. This is because the diffraction peak peculiar to the double oxide does not appear clearly in FIG. 2 because the absolute amount of the SrFe double oxide having the perovskite structure is small. Moreover, it can be confirmed by TEM (transmission electron microscope) observation that the catalyst powder contains SrFe double oxide.
＜ライトオフ性能＞
実施例１〜３，参考例１，２及び比較例１〜３の各触媒を２％Ｏ２及び１０％Ｈ２Ｏの雰囲気中で、１０００℃×２４時間の条件で、エージングした後、固定床流通式反応評価装置に取り付け、模擬排気ガスにより、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、触媒に流入する模擬排気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。模擬排気ガスは、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。モデル排気ガスのＡ／Ｆ＝１４．７、Ａ／Ｆ＝１３．８及びＡ／Ｆ＝１５．６のときのガス組成を表２に示す。
<Light-off performance>
Each of the catalysts of Examples 1 to 3, Reference Examples 1 and 2 and Comparative Examples 1 to 3 was aged in an atmosphere of 2% O 2 and 10% H 2 O under conditions of 1000 ° C. × 24 hours and then fixed. The light-off temperature T50 relating to the purification of HC, CO and NOx was measured with a simulated exhaust gas attached to a bed flow reaction evaluation apparatus. T50 is the gas temperature (° C.) at the catalyst inlet when the temperature of the simulated exhaust gas flowing into the catalyst is gradually increased from room temperature and the purification rate reaches 50%. The simulated exhaust 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. Table 2 shows the gas composition of the model exhaust gas when A / F = 14.7, A / F = 13.8 and A / F = 15.6.
結果を図４に示す。同図によれば、実施例１〜３は、比較例１〜３よりもライトオフ温度Ｔ５０が低く、排気ガス浄化性能が優れていることがわかる。また、同図から、ＺｒＬａ複酸化物と活性アルミナとの合計量に対するＳｒ及びＦｅの化合物の比率（ＳｒＯ＋Ｆｅ２Ｏ３）／（ＺｒＯ２＋Ｌａ２Ｏ３＋Ａｌ２Ｏ３）は、２質量％以上１５質量％以下にすることが好ましく、特に２質量％以上１０質量％以下にすることが好ましいということができる。 The results are shown in FIG. According to the figure, it can be seen that Examples 1 to 3 have a lower light-off temperature T50 than Comparative Examples 1 to 3, and are superior in exhaust gas purification performance. Moreover, from the same figure, the ratio (SrO + Fe 2 O 3 ) / (ZrO 2 + La 2 O 3 + Al 2 O 3 ) of the compound of Sr and Fe with respect to the total amount of ZrLa double oxide and activated alumina is 2% by mass or more. It is preferably 15% by mass or less, and particularly preferably 2% by mass or more and 10% by mass or less.
＜ＮＯｘ浄化速度及びＮＯｘ浄化量＞
空燃比がリーンからリッチに大きく変化するときの触媒のＮＯｘ浄化性能を以下に説明するＮＯｘ浄化速度及びＮＯｘ浄化量の測定によって評価した。
<NOx purification rate and NOx purification amount>
The NOx purification performance of the catalyst when the air-fuel ratio changes greatly from lean to rich was evaluated by measuring the NOx purification rate and the NOx purification amount described below.
[評価方法]
図５にＮＯｘ浄化性能評価装置の要部構成を示す。この評価装置は、評価すべきサンプル触媒１１の設置部を有するガス流通管１２を備え、設置したサンプル触媒１１に模擬排気ガスを流通させるようになっている。サンプル設置部の入口及び出口にそれぞれＮＯｘ濃度検出手段１３が設けられている。
[Evaluation method]
FIG. 5 shows a main configuration of the NOx purification performance evaluation apparatus. This evaluation apparatus includes a gas circulation pipe 12 having an installation portion for a sample catalyst 11 to be evaluated, and allows simulated exhaust gas to flow through the installed sample catalyst 11. NOx concentration detection means 13 is provided at the inlet and the outlet of the sample installation section, respectively.
図６に上記評価装置を用いたＮＯｘ浄化性能の評価フローを示す。サンプル触媒１１をガス流通管１２のサンプル設置部に設置する（ステップＳ１）。サンプル設置部のサンプル触媒１１に空燃比（Ａ／Ｆ）がリッチ（例えば、ストイキ）である模擬排気ガスを流しつつ、設置部内温度を室温から評価温度（例えば、２５０℃）まで上昇させる（ステップＳ２）。 FIG. 6 shows an evaluation flow of NOx purification performance using the above evaluation apparatus. The sample catalyst 11 is installed in the sample installation part of the gas flow pipe 12 (step S1). While flowing the simulated exhaust gas having a rich air-fuel ratio (A / F) (for example, stoichiometric) to the sample catalyst 11 of the sample installation section, the temperature in the installation section is raised from room temperature to an evaluation temperature (for example, 250 ° C.) (step) S2).
次に、模擬排気ガスの空燃比をリーン（例えば、Ａ／Ｆ＝２０）に切り替え、サンプル触媒１１の上流側と下流側のＮＯｘ濃度の検出を開始する（ステップＳ３）。空燃比をリーンに切り替えてから所定時間（例えば３０秒）が経過したときに、空燃比をリッチに切り替える（ステップＳ４）。次いで、リッチに切り替えてから所定時間（例えば３０秒）が経過したときに、空燃比をリーンに切り替える（ステップＳ５）。ステップＳ４とＳ５とを必要に応じて適宜回数繰り返す。 Next, the air-fuel ratio of the simulated exhaust gas is switched to lean (for example, A / F = 20), and detection of NOx concentrations on the upstream side and downstream side of the sample catalyst 11 is started (step S3). When a predetermined time (for example, 30 seconds) has elapsed since the air-fuel ratio was switched to lean, the air-fuel ratio is switched to rich (step S4). Next, when a predetermined time (for example, 30 seconds) elapses after switching to rich, the air-fuel ratio is switched to lean (step S5). Steps S4 and S5 are repeated as many times as necessary.
そうして、空燃比リッチ期間におけるＮＯｘ浄化速度とＮＯｘ浄化量とを求める（ステップＳ６）。この場合のＮＯｘ浄化速度は、所定時間での下流側ＮＯｘ濃度の減少変化量であり、例えば、空燃比リッチ期間全体での最大ＮＯｘ浄化速度又は平均ＮＯｘ浄化速度、或いは該リッチ期間中の所定期間（例えば、前半期間、後半期間又は中間期間等）での最大ＮＯｘ浄化速度又は平均ＮＯｘ浄化速度を求める。この場合のＮＯｘ浄化量は、空燃比リッチ期間全体又は上記所定期間に浄化されたＮＯｘの積算量である。上記ステップＳ４とＳ５とを繰り返して実行するときは、各空燃比リッチ期間における上記ＮＯｘ浄化速度及びＮＯｘ浄化量を求めて、それらの平均値をとる。 Then, the NOx purification rate and the NOx purification amount in the air-fuel ratio rich period are obtained (step S6). The NOx purification rate in this case is the amount of decrease in the downstream NOx concentration during a predetermined time. For example, the maximum NOx purification rate or the average NOx purification rate in the entire air-fuel ratio rich period, or a predetermined period during the rich period The maximum NOx purification rate or the average NOx purification rate in the first half period, the second half period, or the intermediate period is obtained. The NOx purification amount in this case is the integrated amount of NOx purified during the entire air-fuel ratio rich period or the predetermined period. When the steps S4 and S5 are repeatedly executed, the NOx purification rate and the NOx purification amount in each air-fuel ratio rich period are obtained and their average values are taken.
上記ステップＳ１〜Ｓ６を評価すべき各温度（例えば、２５０℃〜４００℃の５０℃刻み）に関して実行する（ステップＳ７）。各評価温度でのＮＯｘ浄化速度及びＮＯｘ浄化量に基いて当該触媒の性能を評価する（ステップＳ８）。 The above steps S1 to S6 are executed for each temperature to be evaluated (for example, in increments of 50 ° C from 250 ° C to 400 ° C) (step S7). The performance of the catalyst is evaluated based on the NOx purification rate and the NOx purification amount at each evaluation temperature (step S8).
図７の（ａ）には空燃比（Ａ／Ｆ）の変化と下流側ＮＯｘ濃度の変化の一例が示されている。サンプル触媒１１では、空燃比がリーンであるときのＮＯｘの浄化性が低いが、空燃比がリッチになると、ＮＯｘの浄化が急に進むようになる。そのため、空燃比がリーンからリッチに変化すると、下流側ＮＯｘ濃度が減少していき、リッチからリーンに変化すると、下流側ＮＯｘ濃度が急に高くなる。図７の（ｂ）に示すように、ＮＯｘ浄化速度は、空燃比がリーンからリッチに切り替えられるたびに急激に高くなり、時間の経過とともに、低下していく。 FIG. 7A shows an example of changes in the air-fuel ratio (A / F) and changes in the downstream NOx concentration. In the sample catalyst 11, the NOx purification performance when the air-fuel ratio is lean is low, but when the air-fuel ratio becomes rich, the purification of NOx proceeds rapidly. Therefore, when the air-fuel ratio changes from lean to rich, the downstream NOx concentration decreases, and when it changes from rich to lean, the downstream NOx concentration suddenly increases. As shown in FIG. 7 (b), the NOx purification rate rapidly increases every time the air-fuel ratio is switched from lean to rich, and decreases with time.
[ＮＯｘ浄化速度及びＮＯｘ浄化量の測定結果]
図８及び図９に上記評価装置を用いた実施例３及び比較例１各々のＮＯｘ浄化速度及びＮＯｘ浄化量の測定結果を示す。ＮＯｘ浄化速度は、上記空燃比リッチ期間における最大値（測定３回の平均値）である。ＮＯｘ浄化量は、上記空燃比リッチ期間に浄化されたＮＯｘの積算量（測定３回の平均値）である。空燃比リーン及びリッチの各模擬排気ガスの組成は表３のとおりである。模擬排気ガスは、空燃比リッチ時にはストイキの組成となるようにし、このストイキの模擬排気ガスにＯ２を０．３％分追加することにより、空燃比がリーン（Ａ／Ｆ＝２０）になるようにした。模擬排気ガス流量はＳＶ値が６００００ｈ−１になるようにした。
[Measurement results of NOx purification rate and NOx purification amount]
FIG. 8 and FIG. 9 show the measurement results of the NOx purification rate and NOx purification amount of Example 3 and Comparative Example 1 using the evaluation apparatus. The NOx purification rate is the maximum value (average value of three measurements) in the air-fuel ratio rich period. The NOx purification amount is an integrated amount (average value of three measurements) of NOx purified in the air-fuel ratio rich period. Table 3 shows the compositions of the air-fuel ratio lean and rich simulated exhaust gases. The simulated exhaust gas has a stoichiometric composition when the air-fuel ratio is rich, and the air-fuel ratio becomes lean (A / F = 20) by adding 0.3% of O 2 to the stoichiometric simulated exhaust gas. I did it. The simulated exhaust gas flow rate was set such that the SV value was 60000h- 1 .
図８によれば、実施例３は比較例１よりもＮＯｘ浄化速度が大きい。図９によれば、ＮＯｘ浄化量は、３００℃以上では実施例３と比較例１とに差は殆どないが、２５０℃では実施例３は比較例１よりもＮＯｘ浄化量が格段に大きい。この結果から、実施例に係る触媒は、低温雰囲気において空燃比がリーンからリッチに大きく変動したときのＮＯｘ浄化性能が良いことがわかる。 According to FIG. 8, Example 3 has a higher NOx purification rate than Comparative Example 1. According to FIG. 9, when the NOx purification amount is 300 ° C. or higher, there is almost no difference between Example 3 and Comparative Example 1, but at 250 ° C., Example 3 has a significantly larger NOx purification amount than Comparative Example 1. From this result, it can be seen that the catalyst according to the example has good NOx purification performance when the air-fuel ratio fluctuates greatly from lean to rich in a low temperature atmosphere.
＜ＳｒＦｅ複酸化物の酸素放出性能＞
実施例に係る触媒の排気ガス浄化性能が上述の如く優れているのは、複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３にペロブスカイト構造のＳｒＦｅ複酸化物とＲｈとが共存しているためと認められる。そこで、ＳｒＦｅ複酸化物及び酸素吸蔵放出材ＺｒＣｅＮｄ複酸化物各々の酸素放出速度を調べた。
<Oxygen release performance of SrFe double oxide>
It is recognized that the exhaust gas purification performance of the catalyst according to the example is excellent as described above because the SrFe double oxide having a perovskite structure and Rh coexist in the composite particles ZrLaO / Al 2 O 3 . Therefore, the oxygen release rates of the SrFe double oxide and the oxygen storage / release material ZrCeNd double oxide were examined.
すなわち、図１０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３１はサンプル３２を保持するガラス管であり、サンプル３２はヒータ３３によって所定温度に加熱保持される。ガラス管３１のサンプル３２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３４が接続され、ガラス管３１のサンプル３２よりも下流側には排気部３８が設けられている。ガラス管３１のサンプル３２よりも上流側及び下流側にはＡ／Ｆセンサ（酸素センサ）３５，３６が設けられている。ガラス管３１のサンプル保持部には温度制御用の熱電対３９が取付けられている。 That is, FIG. 10 shows the configuration of a test apparatus for measuring the oxygen storage / release amount. In the figure, reference numeral 31 denotes a glass tube that holds a sample 32, and the sample 32 is heated and held at a predetermined temperature by a heater 33. Connected to the upstream side of the sample 32 of the glass tube 31 is a pulse gas generator 34 capable of supplying O 2 and CO gases in a pulsed manner while supplying the base gas N 2. In addition, an exhaust part 38 is provided on the downstream side. A / F sensors (oxygen sensors) 35 and 36 are provided upstream and downstream of the sample 32 of the glass tube 31. A temperature control thermocouple 39 is attached to the sample holder of the glass tube 31.
測定にあたっては、ガラス管３１内の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３８から排気しながら、図８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。リーンからストイキに切り換えた直後の、図１１に示す、サンプル前後のＡ／Ｆセンサ３５，３６によって得られるＡ／Ｆ値出力差（前側Ａ／Ｆ値−後側Ａ／Ｆ値）の変化率（単位時間当たりの変化量）に基いて酸素放出速度を算出した。この酸素放出速度を４５０℃から６００℃までの５０℃刻みの各温度で測定した。 In the measurement, the sample temperature in the glass tube 31 is kept at a predetermined value, and the base gas N 2 is supplied and exhausted from the exhaust part 38, while the O 2 pulse (20 seconds) and the CO pulse ( 20 seconds) alternately and at intervals (20 seconds) to repeat the cycle of lean → stoichi → rich → stoichi. The change rate of the A / F value output difference (front A / F value−rear A / F value) obtained by the A / F sensors 35 and 36 before and after the sample shown in FIG. 11 immediately after switching from lean to stoichiometry. The oxygen release rate was calculated based on (change amount per unit time). This oxygen release rate was measured at each temperature in increments of 50 ° C. from 450 ° C. to 600 ° C.
上記ＳｒＦｅ複酸化物及びＺｒＣｅＮｄ複酸化物のいずれも、上記複合粒子ＺｒＬａＯ／Ａｌ２Ｏ３の粉末と混合してサンプルとした。そのＳｒＦｅ複酸化物は、組成式ＳｒＦｅＯ２．５のペロブスカイト構造の複酸化物であり、ＺｒＣｅＮｄ複酸化物はＺｒＯ２：ＣｅＯ２：Ｎｄ２Ｏ３＝７４：１３：１３（質量比）である。 Both the SrFe double oxide and the ZrCeNd double oxide were mixed with the composite particle ZrLaO / Al 2 O 3 powder to prepare a sample. The SrFe double oxide is a double oxide having a perovskite structure of the composition formula SrFeO 2.5 , and the ZrCeNd double oxide is ZrO 2 : CeO 2 : Nd 2 O 3 = 74: 13: 13 (mass ratio). .
結果を図１２に示す。同図から、ペロブスカイト構造のＳｒＦｅ複酸化物は、空燃比がリーンからリッチに切り換わった直後の酸素放出速度が極めて大きいことがわかる。このことが、実施例に係る触媒が上述の優れたライトオフ性能及びＮＯｘ浄化性能を示す要因であると考えられる。 The results are shown in FIG. From the figure, it can be seen that the SrFe double oxide having a perovskite structure has an extremely high oxygen release rate immediately after the air-fuel ratio is switched from lean to rich. This is considered to be a factor in which the catalyst according to the example exhibits the above-described excellent light-off performance and NOx purification performance.
１ 排気ガス浄化用触媒
１ａ 担体
１ｂ 触媒層
1 Exhaust gas purification catalyst 1a Support 1b Catalyst layer
Claims (3)
上記ジルコニウム系複酸化物は、ジルコニウムを主成分とし且つランタンを含有する複酸化物であり、
上記ストロンチウム及び鉄の化合物の少なくとも一部は、ストロンチウムと鉄とを含有する複酸化物であり、
上記活性アルミナの少なくとも一部と上記ジルコニウム系複酸化物の少なくとも一部とは、活性アルミナの粒子表面の少なくとも一部がジルコニウム系複酸化物で被覆されてなる複合粒子を形成し、
上記複合粒子に、上記ストロンチウムと鉄とを含有する複酸化物の少なくとも一部が担持され、且つ上記触媒金属としてのＲｈの少なくとも一部が、当該複合粒子と当該ストロンチウム及び鉄を含有する複酸化物とに担持され、
上記ジルコニウム系複酸化物と、上記活性アルミナと、上記ストロンチウム及び鉄の化合物とは、上記ジルコニウム系複酸化物と上記活性アルミナとの合計量に対する上記ストロンチウム及び鉄の化合物の比率が２質量％以上１０質量％以下となるように、上記触媒層に含まれていることを特徴とする排気ガス浄化用触媒。 An exhaust gas purifying catalyst containing Rh as a catalytic metal, zirconium-based double oxide, activated alumina, strontium and iron compound in a catalyst layer on a carrier,
The zirconium-based double oxide is a double oxide containing zirconium as a main component and containing lanthanum,
At least a part of the strontium and iron compound is a double oxide containing strontium and iron,
At least a part of the active alumina and at least a part of the zirconium-based double oxide form composite particles in which at least a part of the particle surface of the active alumina is coated with the zirconium-based double oxide,
At least a part of the composite oxide containing strontium and iron is supported on the composite particle, and at least a part of Rh as the catalyst metal is a composite oxide containing the composite particle, strontium and iron. Carried on the object ,
The zirconium-based double oxide, the active alumina, and the strontium and iron compound are such that the ratio of the strontium and iron compound to the total amount of the zirconium-based double oxide and the active alumina is 2% by mass or more. An exhaust gas purifying catalyst, which is contained in the catalyst layer so as to be 10% by mass or less .
上記複合粒子と、ストロンチウム及び鉄を含有する溶液とを混合する工程と、
得られた混合物を乾燥し焼成することにより、上記ストロンチウム及び鉄の化合物を含有し、且つ該化合物の少なくとも一部は上記ストロンチウム及び鉄を含有する複酸化物となっており、該複酸化物の少なくとも一部が上記複合粒子に担持されてなる焼成物を得る工程と、
得られた焼成物に触媒金属としてのＲｈを担持する工程とを備え、
上記ジルコニウム系複酸化物と、上記活性アルミナと、上記ストロンチウム及び鉄の化合物とは、上記ジルコニウム系複酸化物と上記活性アルミナとの合計量に対する上記ストロンチウム及び鉄の化合物の比率が２質量％以上１０質量％以下となるようにすることを特徴とする排気ガス浄化用触媒材の製造方法。 Preparing a composite particle in which at least a part of the particle surface of the activated alumina is coated with a zirconium-based double oxide containing zirconium as a main component and containing lanthanum;
Mixing the composite particles with a solution containing strontium and iron;
The obtained mixture is dried and calcined to contain the strontium and iron compound, and at least a part of the compound is a double oxide containing the strontium and iron. A step of obtaining a fired product at least partially supported on the composite particles ;
A step of supporting Rh as a catalyst metal on the obtained fired product ,
The zirconium-based double oxide, the active alumina, and the strontium and iron compound are such that the ratio of the strontium and iron compound to the total amount of the zirconium-based double oxide and the active alumina is 2% by mass or more. A method for producing an exhaust gas purifying catalyst material, characterized in that the content is 10% by mass or less .
上記ストロンチウム及び鉄を含有する溶液としてクエン酸錯体溶液を用い、上記混合物の焼成を６００℃以上の温度で行なうことを特徴とする排気ガス浄化用触媒の製造方法。 In claim 2 ,
A method for producing an exhaust gas purifying catalyst, wherein a citric acid complex solution is used as a solution containing strontium and iron, and the mixture is calcined at a temperature of 600 ° C or higher.
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