JP5444755B2 - Exhaust gas purification catalyst - Google Patents
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- JP5444755B2 JP5444755B2 JP2009041209A JP2009041209A JP5444755B2 JP 5444755 B2 JP5444755 B2 JP 5444755B2 JP 2009041209 A JP2009041209 A JP 2009041209A JP 2009041209 A JP2009041209 A JP 2009041209A JP 5444755 B2 JP5444755 B2 JP 5444755B2
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- 239000003054 catalyst Substances 0.000 title claims description 107
- 238000000746 purification Methods 0.000 title description 48
- 239000013618 particulate matter Substances 0.000 claims description 73
- 238000002485 combustion reaction Methods 0.000 claims description 53
- 239000002131 composite material Substances 0.000 claims description 45
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- 238000000034 method Methods 0.000 description 26
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- JSKIRARMQDRGJZ-UHFFFAOYSA-N dimagnesium dioxido-bis[(1-oxido-3-oxo-2,4,6,8,9-pentaoxa-1,3-disila-5,7-dialuminabicyclo[3.3.1]nonan-7-yl)oxy]silane Chemical compound [Mg++].[Mg++].[O-][Si]([O-])(O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2)O[Al]1O[Al]2O[Si](=O)O[Si]([O-])(O1)O2 JSKIRARMQDRGJZ-UHFFFAOYSA-N 0.000 description 1
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Images
Description
本発明は排ガス浄化用触媒、特にディーゼルエンジン等の内燃機関から排出される排ガス中に含まれるスート（ｓｏｏｔ）を主成分とする粒子状物質を低温域で効率良く燃焼除去することができる排ガス浄化用触媒に関する。 INDUSTRIAL APPLICABILITY The present invention is an exhaust gas purification catalyst that can efficiently burn and remove particulate matter mainly composed of soot contained in exhaust gas discharged from an internal combustion engine such as a diesel engine in a low temperature range. Relates to a catalyst.
ディーゼルエンジンなどの内燃機関から排出される排ガス中には、炭化水素（ＨＣ）や一酸化炭素（ＣＯ）の他にスートを主成分とする粒子状物質（Ｐａｒｔｉｃｕｌａｔｅ Ｍａｔｔｅｒ、以下ＰＭという）が含まれている。
ＰＭは粒子径が１μｍ以下のため、大気中に浮遊しやすく、呼吸などで体内に取り込まれると人体へ悪影響を及ぼす懸念があるため、早急な対策が必要とされている。その対策として、ＰＭを大気中へ放出しないようにディーゼル車の排気系にはＰＭを捕集するためのフィルター（Ｄｉｅｓｅｌ Ｐａｒｔｉｃｕｒａｔｅ Ｆｉｌｔｅｒ、以下ＤＰＦという）が備え付けられている。しかしながら、ＤＰＦはＰＭ捕集量の増加に伴ってフィルターの目詰まりが進行することで圧損を生じる問題を抱えている。フィルターの目詰まりに対する対策としては、一定以上の圧損が生じると電気ヒーターやバーナーなどで捕集したＰＭを燃焼させ、フィルターを強制的に再生する方法が検討されている。しかしながら、上記方法では強制的にＰＭを燃焼除去するために燃費の悪化を招いたり、ＰＭの燃焼熱によるフィルター基材の溶損や触媒の劣化を引き起こしたりする。また装置が大型化、複雑化し、装置コストが増大するという課題もある。
In exhaust gas emitted from internal combustion engines such as diesel engines, particulate matter (hereinafter referred to as PM) containing soot as a main component is contained in addition to hydrocarbon (HC) and carbon monoxide (CO). ing.
Since PM has a particle size of 1 μm or less, it tends to float in the atmosphere, and if it is taken into the body by breathing or the like, there is a concern that it may adversely affect the human body, so immediate measures are required. As a countermeasure, a diesel vehicle exhaust filter (Diesel Particulate Filter, hereinafter referred to as DPF) is provided in the exhaust system of a diesel vehicle so as not to release the PM into the atmosphere. However, DPF has a problem of causing pressure loss due to the clogging of the filter as the amount of collected PM increases. As a countermeasure against clogging of the filter, a method of forcibly regenerating the filter by burning PM collected by an electric heater or a burner when a pressure loss of a certain level or more occurs has been studied. However, in the above method, PM is forcibly burned and removed, so that fuel consumption is deteriorated, or the filter base material is melted by the combustion heat of PM or the catalyst is deteriorated. In addition, there is a problem that the apparatus becomes larger and complicated and the apparatus cost increases.
このため近年、ＰＭの燃焼に触媒を用いて、ＰＭをより低温で燃焼させることでＤＰＦを連続的に再生させる方法が検討されている。酸素放出能を有するＣｅ系複合酸化物がＰＭの燃焼温度を低温化させる効果を有することが見出され、後述のタイトコンタクト条件下で燃焼温度を３００℃付近まで低下させた触媒も報告されている。
しかしながら、Ｃｅ系複合酸化物は高温に曝されると触媒劣化を生じるため、熱耐久性に課題がある。
Therefore, in recent years, a method for continuously regenerating DPF by using a catalyst for burning PM and burning PM at a lower temperature has been studied. It has been found that Ce-based composite oxides having oxygen releasing ability have the effect of lowering the combustion temperature of PM, and a catalyst for reducing the combustion temperature to around 300 ° C. under tight contact conditions described later has been reported. Yes.
However, since Ce-based composite oxides are subject to catalyst degradation when exposed to high temperatures, there is a problem in thermal durability.
耐久性を改善する検討として、例えば特許文献１にはＰＭ燃焼触媒としてＣｅとＢｉの複合酸化物が記載されており、ＣｅとＢｉのモル比がＣｅ：Ｂｉ＝（１−ｘ）：ｘとするとき、０ ＜ ｘ ≦ ０．９の範囲、さらに好適には０ ＜ ｘ ≦ ０．７の範囲であればタイトコンタクト条件下において高いＰＭ浄化性能が発揮され、かつ高い熱耐久性を有することが示されている。 As a study for improving durability, for example, Patent Document 1 describes a composite oxide of Ce and Bi as a PM combustion catalyst, and the molar ratio of Ce and Bi is Ce: Bi = (1-x): x. In the case of 0 <x ≦ 0.9, more preferably 0 <x ≦ 0.7, high PM purification performance is exhibited under tight contact conditions and high thermal durability It is shown.
一方、ＢｉもＰＭを低温で燃焼させる効果があることが知られており、例えば、特許文献２にはＰＭ燃焼触媒としてＢｉとその化合物からなる触媒に関する記載がある。しかし、これらの触媒は白金族金属を担持させない場合、５５０℃に至ってもＰＭの燃え残りが生じており、十分な浄化性能を発揮できていない。 On the other hand, Bi is also known to have an effect of burning PM at a low temperature. For example, Patent Document 2 describes a catalyst composed of Bi and its compound as a PM combustion catalyst. However, when these catalysts do not carry a platinum group metal, PM remains unburned even at 550 ° C., and sufficient purification performance cannot be exhibited.
さらに本発明者らが検討したところ、ＰＭと触媒との燃焼反応は固体同士の接触による反応（固−固反応）であるため、ＰＭと触媒との接触効率が低いと十分な浄化性能が発揮されないという問題があることが判明した。
一般に、ＰＭ燃焼触媒の活性評価には、ＰＭと触媒の接触状態によって「タイトコンタクト」と「ルーズコンタクト」の２種類の条件による評価方法がある。
「タイトコンタクト」とは、ＰＭと触媒を混合し、この混合物を破砕して接触効率を高めた状態での性能評価をいう。具体的には、擬似ＰＭとしてカーボンブラックを用い、使用する燃焼触媒とカーボンブラックを乳鉢あるいは自動乳鉢機を用いて１０〜２０分間ほど混合し、得られた混合粉体について熱重量測定（ＴＧ）あるいは燃焼に伴って発生するＣＯ２発生量の測定をおこない、触媒性能を評価する。すなわち、触媒の浄化性能を効果的に発揮させうる評価条件であると考えられる。
Furthermore, when the present inventors examined, since the combustion reaction of PM and a catalyst is reaction (solid-solid reaction) by contact of solids, when the contact efficiency of PM and a catalyst is low, sufficient purification performance is exhibited. It turns out that there is a problem of not being.
In general, the activity evaluation of a PM combustion catalyst includes an evaluation method based on two types of conditions, “tight contact” and “loose contact”, depending on the contact state between the PM and the catalyst.
“Tight contact” refers to performance evaluation in a state in which PM and a catalyst are mixed and the mixture is crushed to improve contact efficiency. Specifically, carbon black is used as pseudo PM, the combustion catalyst to be used and carbon black are mixed for about 10 to 20 minutes using a mortar or automatic mortar machine, and the obtained mixed powder is subjected to thermogravimetry (TG). Alternatively, the amount of CO 2 generated with combustion is measured to evaluate the catalyst performance. That is, it is considered that the evaluation conditions can effectively exhibit the purification performance of the catalyst.
一方、「ルーズコンタクト」とは、排ガス流下に近い状態でＰＭと触媒を接触させる、物理的接触の状態での性能評価をいう。具体的には、擬似ＰＭとしてカーボンブラックを用い、使用する燃焼触媒とカーボンブラックをスパチュラで軽く混合し、得られた混合粉体について熱重量測定（ＴＧ）あるいは燃焼に伴って発生するＣＯ２発生量の測定をおこない、触媒性能を評価する。すなわち排ガス浄化用触媒の実際の使用条件に近い接触状態での評価条件であると考えられる。 On the other hand, “loose contact” refers to performance evaluation in a physical contact state in which PM and a catalyst are brought into contact with each other in a state close to the flow of exhaust gas. Specifically, carbon black is used as pseudo PM, the combustion catalyst to be used and carbon black are mixed lightly with a spatula, and the resulting mixed powder is subjected to thermogravimetry (TG) or CO 2 generation generated by combustion Measure the amount and evaluate the catalyst performance. That is, it is considered that the evaluation conditions are in a contact state close to the actual use conditions of the exhaust gas purification catalyst.
したがって、実用性を考慮すると、ルーズコンタクト条件下でも十分な浄化性能を発揮することが望ましい。しかし本発明者らの検討によれば、特許文献１、特許文献２に記載のＢｉを含む触媒においても、ルーズコンタクト条件下で評価すると十分な性能を発揮できないことが確かめられた。そのためルーズコンタクト条件下においても十分な燃焼性能を有するＰＭ燃焼触媒の開発が望まれている。 Therefore, in view of practicality, it is desirable to exhibit sufficient purification performance even under loose contact conditions. However, according to the study by the present inventors, it was confirmed that even the catalysts containing Bi described in Patent Document 1 and Patent Document 2 cannot exhibit sufficient performance when evaluated under loose contact conditions. Therefore, it is desired to develop a PM combustion catalyst having sufficient combustion performance even under loose contact conditions.
ＰＭをより低い温度で燃焼させる触媒成分として、Ｂｉをベースとした触媒により、高価な白金族を担持させることなく、またルーズコンタクト条件下での評価においても高いＰＭ浄化性能を発揮できるＰＭ燃焼触媒を提供することを目的とする。 As a catalyst component for burning PM at a lower temperature, a PM-based combustion catalyst capable of exhibiting high PM purification performance even in evaluation under loose contact conditions without supporting an expensive platinum group by a catalyst based on Bi The purpose is to provide.
本発明者らは上記課題を解決すべく鋭意検討をおこなった結果、ＢｉとＣｅを主成分とする複合酸化物を含む排ガス浄化用触媒であって、複合酸化物の基本構造がＢｉ２Ｏ３の正方晶であることを特徴とする排ガス浄化用触媒が、ＰＭ燃焼に対して高い浄化性能を示し、更に加熱劣化試験をおこなっても触媒性能が低下しない熱耐久性が高い排ガス浄化用触媒であることを見出した。またルーズコンタクト条件下でも非常に低い３００℃台の燃焼開始温度を示すことを見出した。 As a result of intensive studies to solve the above problems, the inventors of the present invention are exhaust gas purifying catalysts containing a composite oxide containing Bi and Ce as main components, and the basic structure of the composite oxide is Bi 2 O 3. Exhaust gas purification catalyst, characterized by the fact that it is a tetragonal crystal, is an exhaust gas purification catalyst that exhibits high purification performance against PM combustion and has high thermal durability that does not deteriorate even when subjected to a heat deterioration test. I found out. The inventors have also found that the combustion start temperature in the 300 ° C. range is very low even under loose contact conditions.
すなわち本発明の第一の要旨は、内燃機関から排出される排ガス中の粒子状物質を浄化するための排ガス浄化用触媒であって、Ｂｉ及びＣｅを主成分とする複合酸化物を含み、その複合酸化物の基本構造がＢｉ２Ｏ３の正方晶であり、該複合酸化物が、粉末Ｘ線回折ピーク（Ｘ線源としてＣｕＫα線を使用）のパターン回折角２θにおいて、後述の８つの主要回折ピークが認められるものであることを特徴とする排ガス浄化用触媒に存する。
第二の要旨は、上記Ｂｉ及びＣｅを主成分とする複合酸化物を含む排ガス浄化用触媒において、ＢｉとＣｅのモル比が５≦Ｂｉ／Ｃｅ ≦３８の範囲であることを特徴とする排ガス浄化用触媒に存する。
That is, the first gist of the present invention is an exhaust gas purifying catalyst for purifying particulate matter in exhaust gas discharged from an internal combustion engine, comprising a composite oxide mainly composed of Bi and Ce, The basic structure of the composite oxide is a tetragonal crystal of Bi 2 O 3 , and the composite oxide has the following eight main components at the pattern diffraction angle 2θ of the powder X-ray diffraction peak (CuKα ray is used as the X-ray source). It exists in the catalyst for exhaust gas purification characterized by a diffraction peak being recognized .
The second gist is an exhaust gas purification catalyst containing a composite oxide containing Bi and Ce as main components, wherein the molar ratio of Bi and Ce is in the range of 5 ≦ Bi / Ce ≦ 38. It exists in the catalyst for purification.
第三の要旨は、上記複合酸化物中にＢｉとＣｅに加えて希土類元素（Ａ）を含む複合酸化物であって、Ｃｅと希土類元素（Ａ）のモル比が０．０１≦（Ａ）／Ｃｅ ＜ １である排ガス浄化用触媒に存する。
第四の要旨は、上記排ガス浄化用触媒において含まれる希土類元素（Ａ）がＬａである排ガス浄化用触媒に存する。
The third gist is a composite oxide containing the rare earth element (A) in addition to Bi and Ce in the complex oxide, wherein the molar ratio of Ce to the rare earth element (A) is 0.01 ≦ (A). / Ce <1 in the exhaust gas-purifying catalyst.
The fourth gist lies in an exhaust gas purification catalyst in which the rare earth element (A) contained in the exhaust gas purification catalyst is La.
第五の要旨は、上記排ガス浄化用触媒において含まれる該希土類元素（Ａ）がＬａであって、Ｂｉと（Ｃｅ＋Ｌａ）のモル比が８ ≦ Ｂｉ／（Ｃｅ＋Ｌａ）≦ ２０の範囲にある排ガス浄化用触媒に存する。
第六の要旨は、前記排ガス浄化用触媒を含む粒子状物質捕集フィルターに存する。
The fifth gist is exhaust gas purification in which the rare earth element (A) contained in the exhaust gas purification catalyst is La and the molar ratio of Bi to (Ce + La) is in the range of 8 ≦ Bi / (Ce + La) ≦ 20. Exist in the catalyst.
The sixth gist lies in a particulate matter collecting filter including the exhaust gas-purifying catalyst.
本発明によれば、ディーゼルエンジン等の内燃機関から排出される排ガス中に含まれるスートを主成分とする粒子状物質（ＰＭ）を、実際の触媒の使用条件に近いルーズコンタクト条件下でも低温で効率よく十分に燃焼させることができ、更に熱耐久性にも優れた、実用に供し得る排ガス浄化用触媒が提供される。さらに、高価な白金族を全く使用せず、かつ近年価格の高騰が懸念されている希少資源の希土類元素の使用量を低減した安価な排ガス浄化用触媒を提供しうる。 According to the present invention, particulate matter (PM) mainly composed of soot contained in exhaust gas discharged from an internal combustion engine such as a diesel engine can be obtained at a low temperature even under loose contact conditions close to the actual catalyst use conditions. Provided is a catalyst for exhaust gas purification that can be burned efficiently and sufficiently, and that is excellent in thermal durability and can be used practically. Furthermore, it is possible to provide an inexpensive exhaust gas purifying catalyst that does not use an expensive platinum group at all and that reduces the amount of rare earth elements, which are rare resources, which have been feared to increase in price in recent years.
以下、本発明の実施の形態について詳細に説明するが、本発明は以下の実施の形態に限定されるものではなく、その要旨の範囲内で種々変形して実施することができる。
＜排ガス浄化用触媒＞
本発明に係る排ガス浄化用触媒は、ディーゼル等の内燃機関から排出される排ガスに含まれているスートを主成分とする粒子状物質（ＰＭ）を酸化、燃焼することで浄化する触媒である。
Hereinafter, embodiments of the present invention will be described in detail. However, the present invention is not limited to the following embodiments, and various modifications can be made within the scope of the gist of the present invention.
<Exhaust gas purification catalyst>
The exhaust gas purifying catalyst according to the present invention is a catalyst that purifies by oxidizing and burning particulate matter (PM) mainly containing soot contained in exhaust gas discharged from an internal combustion engine such as diesel.
前記触媒は、主成分としてＢｉとＣｅの複合酸化物を含むものである。また複合酸化物は、ＢｉとＣｅに加えて希土類元素（Ａ）を含んでいてもよい。
＜複合酸化物＞
本発明における複合酸化物とは、２種以上の酸化物が組み合わさり、Ｏ２−の最密充填の隙間にそれぞれの金属イオンが平等なイオン格子を形成したものをいう。
The catalyst contains a composite oxide of Bi and Ce as a main component. The composite oxide may contain a rare earth element (A) in addition to Bi and Ce.
<Composite oxide>
The composite oxide in the present invention refers to a compound in which two or more kinds of oxides are combined and each metal ion forms an equal ion lattice in a close packed space of O 2− .
Ｂｉ及びＣｅを主成分とする複合酸化物とは、Ｂｉ２Ｏ３（酸化ビスマス）とＣｅＯ２（酸化セリウム）を含む酸化物をいい、好ましくは主たる触媒成分がＢｉ２Ｏ３とＣｅＯ２が複合化した酸化物が好ましい。またそれぞれの単独酸化物が少量混合していてもよい。
Ｂｉ及びＣｅを主成分とする複合酸化物に希土類元素（Ａ）を加える場合は、上記と同様に、好ましくは主たる触媒成分Ｂｉ２Ｏ３とＣｅＯ２と希土類元素（Ａ）の酸化物が複合化した酸化物であることが好ましく、またそれぞれの単独酸化物が少量混合していてもよい。
The composite oxide containing Bi and Ce as main components refers to an oxide containing Bi 2 O 3 (bismuth oxide) and CeO 2 (cerium oxide). Preferably, the main catalyst components are Bi 2 O 3 and CeO 2. Complex oxides are preferred. Each single oxide may be mixed in a small amount.
When the rare earth element (A) is added to the composite oxide containing Bi and Ce as the main components, the main catalyst components Bi 2 O 3 , CeO 2 and the oxide of the rare earth element (A) are preferably combined as described above. preferably that it is an oxide made into, but also may be mixed each single oxide minor amounts.
本発明のＢｉ及びＣｅを主成分とする複合酸化物は、Ｂｉ含有量がＣｅ含有量よりも多いことを特徴としており、主成分である複合酸化物の構造はＢｉ２Ｏ３構造を取る。したがって、本願発明において好ましいＢｉ２Ｏ３とＣｅＯ２が複合化した酸化物は、好ましくはＢｉ２Ｏ３の基本構造に対し、Ｃｅが固溶しているものである。そのことは当該複合酸化物の粉末Ｘ線回折パターンにおける回折ピークが、対応するＢｉ２Ｏ３のピークからシフトしていることで判別できる。 The composite oxide containing Bi and Ce as main components of the present invention is characterized in that the Bi content is higher than the Ce content, and the structure of the composite oxide as the main component takes a Bi 2 O 3 structure. Therefore, the oxide in which Bi 2 O 3 and CeO 2 are preferably combined in the present invention is preferably one in which Ce is dissolved in the basic structure of Bi 2 O 3 . This can be determined by the fact that the diffraction peak in the powder X-ray diffraction pattern of the composite oxide is shifted from the corresponding Bi 2 O 3 peak.
本発明においては、好ましい複合酸化物の基本構造はＢｉ２Ｏ３の正方晶構造を持つものである。
Ｂｉ含有量がＣｅ含有量よりも多い領域について発明者らが詳細に検討した結果、複合酸化物の基本構造がＢｉ２Ｏ３の正方晶であるものがルーズコンタクト条件下でのＰＭ浄化性能が良いことを見出した。
In the present invention, the basic structure of a preferable composite oxide has a tetragonal structure of Bi 2 O 3 .
As a result of detailed investigations by the inventors on a region where the Bi content is larger than the Ce content, the PM purification performance under the loose contact condition is obtained when the basic structure of the composite oxide is a tetragonal crystal of Bi 2 O 3. I found a good thing.
Ｂｉ２Ｏ３の結晶構造には低温安定相の単斜晶、高温安定相の立方晶、準安定相の正方晶と体心立方晶の４つの結晶系が存在する。このうちＣｅをＢｉ２Ｏ３に複合化させることで安定的に合成できる準安定相の正方晶がＢｉ及びＣｅの複合酸化物において好ましい。
複合酸化物中に含まれるＢｉとＣｅの比率が同じであっても、Ｂｉ２Ｏ３正方晶であるものがルーズコンタクト条件下で良好なＰＭ浄化性能を有する。
The crystal structure of Bi 2 O 3 includes four crystal systems: a monoclinic crystal having a low temperature stable phase, a cubic crystal having a high temperature stable phase, a tetragonal crystal having a metastable phase, and a body-centered cubic crystal. Among these, a metastable tetragonal crystal that can be stably synthesized by complexing Ce with Bi 2 O 3 is preferable in the complex oxide of Bi and Ce.
Even if the ratio of Bi and Ce contained in the composite oxide is the same, Bi 2 O 3 tetragonal crystals have good PM purification performance under loose contact conditions.
本発明におけるＢｉ及びＣｅの複合酸化物がＰＭ酸化に高い浄化性能を示すのは、基本的にはＢｉ２Ｏ３の易還元性、すなわち酸素イオンを放出しやすい性質および高い酸素イオン伝導性に起因し、Ｂｉサイトの一部をＣｅに置換することで酸素イオンが移動し易くなり、ＰＭへの酸素イオン供給が容易になる効果が得られるためであると推察される。さらに、この効果が複合酸化物のとる基本構造によって異なるものと考えられ、正方晶以外の結晶系をとる場合にはＰＭの燃え残りが生じてしまうのに対し、正方晶の場合は上述した効果が大きく、ＰＭを燃え残りなく浄化できることから特に好ましい。 The complex oxide of Bi and Ce in the present invention shows a high purification performance for PM oxidation, basically because of the easy reduction property of Bi 2 O 3 , that is, the property of easily releasing oxygen ions and the high oxygen ion conductivity. This is presumably because oxygen ions can easily move by substituting part of the Bi site with Ce, and the effect of facilitating the supply of oxygen ions to PM can be obtained. Furthermore, this effect is considered to be different depending on the basic structure taken by the complex oxide. When a crystal system other than tetragonal crystal is used, PM remains unburned, whereas in the case of tetragonal crystal, the above-described effect is obtained. Is particularly preferable because it can purify PM without burning.
本発明触媒として用いる複合酸化物が特定の結晶構造を有することを示す指標は、粉末Ｘ線回折のパターンである。該複合酸化物の粉末Ｘ線回折ピーク（Ｘ線源としてＣｕＫα線を使用）のパターンとは、特定の回折角２θにおいて以下表１に示す８つの主要回折ピークが認められることにある。 An index indicating that the composite oxide used as the catalyst of the present invention has a specific crystal structure is a powder X-ray diffraction pattern. The pattern of powder X-ray diffraction peaks (using CuKα rays as an X-ray source) of the composite oxide is that eight main diffraction peaks shown in Table 1 below are observed at a specific diffraction angle 2θ.
Ｘ線回折ピーク強度は各結晶の測定条件によってずれる場合があるが、２θ ＝ ２７．９３°のピーク強度を１００とした場合の相対強度は通常上記の範囲にある。また、一般的には２θ ＝ ２７．９３°のピーク強度が大きく現れる。しかしながら、上記８本の回折ピークを認める限り該８本のピーク以外の２θにピークを有するものがあっても、副成分として少量含んでいても本発明に好適に用いることができる。例えば、Ｂｉ２Ｏ３の正方晶が主成分の場合、正方晶以外の結晶系を含んでいてもよい。ここで、正方晶が主成分であるとは、粉末Ｘ線回折パターンにおいて、２θ ＝ ２７．９３°のピーク強度が他の結晶系の主たるピークのピーク強度よりも高いことをいい、この点をもって判別する。正方晶以外の他の結晶系を含む場合、好ましくは他の結晶系の主たるピークのピーク強度がＢｉ２Ｏ３の正方晶の２θ ＝ ２７．９３°のピーク強度の１／２以下であることが好ましく、より好ましくは１／５以下、更に好ましくは１／１０以下であることが望ましい。 Although the X-ray diffraction peak intensity may deviate depending on the measurement conditions of each crystal, the relative intensity when the peak intensity at 2θ = 27.93 ° is 100 is usually in the above range. In general, a peak intensity of 2θ = 27.93 ° appears greatly. However, as long as the above eight diffraction peaks are recognized, even those having a peak at 2θ other than the eight peaks can be suitably used in the present invention even if they are contained in small amounts as subcomponents. For example, when a tetragonal crystal of Bi 2 O 3 is the main component, a crystal system other than tetragonal crystal may be included. Here, a tetragonal crystal is the main component means that in the powder X-ray diffraction pattern, the peak intensity at 2θ = 27.93 ° is higher than the peak intensity of the main peak of other crystal systems. Determine. When other crystal systems other than the tetragonal system are included, the peak intensity of the main peak of the other crystal system is preferably ½ or less of the peak intensity of 2θ = 27.93 ° of the tetragonal crystal of Bi 2 O 3 Is preferable, more preferably 1/5 or less, and still more preferably 1/10 or less.
ＢｉとＣｅのモル比は、Ｂｉ／Ｃｅモル比が５以上が、ルーズコンタクト条件下でのＰＭ浄化性能が良い点で好ましい。これはＢｉ２Ｏ３の基本構造を維持しつつＣｅを固溶させる量には限界があることによると考えられる。すなわち、Ｂｉ／Ｃｅモル比が５より小さい値であると複合酸化物の基本構造がＢｉ２Ｏ３の正方晶をとることが困難になり、ＰＭの触媒燃焼時に十分に燃焼させることができず、燃え残りが生じる。したがって、ＢｉとＣｅのモル比は Ｂｉ／Ｃｅは５以上が好ましく、より好ましくは８以上の範囲である
ことが望ましい。
The Bi / Ce molar ratio is preferably 5 or more in terms of good PM purification performance under loose contact conditions. This is considered to be due to the fact that there is a limit to the amount of Ce dissolved while maintaining the basic structure of Bi 2 O 3 . In other words, if the Bi / Ce molar ratio is less than 5, it becomes difficult for the basic structure of the composite oxide to take a tetragonal crystal of Bi 2 O 3 , and it cannot be sufficiently burned during PM catalytic combustion. , Unburned residue occurs. Therefore, the Bi / Ce molar ratio is preferably 5 or more, and more preferably 8 or more.
ＰＭ燃焼に対する触媒活性の観点からはＢｉ／Ｃｅモル比は一定値以上あればよいが、熱耐久性の観点からは、一定量以上のＣｅを固溶させる必要がある。Ｂｉ２Ｏ３にＣｅを固溶させると結晶格子に歪みが生じて構造が安定化して熱耐久性が向上する。この構造安定化の効果が得られるのに一定以上の固溶量が必要であり、Ａｉｒ中、８００℃、５ｈの加熱劣化試験をおこなってもＢｉ／Ｃｅのモル比が ３８以下の際、Ｂｉ２Ｏ３よりも高
い熱耐久性を示すので好ましい。
From the viewpoint of catalytic activity for PM combustion, the Bi / Ce molar ratio may be a certain value or more, but from the viewpoint of thermal durability, a certain amount or more of Ce must be dissolved. When Ce is dissolved in Bi 2 O 3 , the crystal lattice is distorted, the structure is stabilized, and the thermal durability is improved. In order to obtain this effect of stabilizing the structure, a solid solution amount of a certain level or more is necessary. When a Bi / Ce molar ratio is 38 or less even when a heat deterioration test is performed in Air at 800 ° C. for 5 hours, Bi This is preferable because it exhibits higher heat durability than 2 O 3 .
したがって、ＰＭ燃焼活性および熱耐久性の両面を考慮するとＢｉとＣｅのモル比は、Ｂｉ／Ｃｅのモル比で５以上が好ましく、より好ましくは８以上であることが、ＰＭ燃焼活性を上げる点で好ましい。また、Ｂｉ／Ｃｅモル比は、Ａｉｒ中、８００℃、５ｈの加熱劣化試験をおこなってもＢｉ２Ｏ３よりも高い熱耐久性を示す点で３８以下であることが好ましく、より好ましくは３０以下であり、更に好ましくは１６以下であることが、加熱劣化試験後でも触媒性能の低下を引き起こさない点で好ましい。 Therefore, in consideration of both PM combustion activity and thermal durability, the Bi / Ce molar ratio is preferably 5 or more, more preferably 8 or more in terms of increasing PM combustion activity. Is preferable. Further, the Bi / Ce molar ratio is preferably 38 or less, more preferably 30 in terms of exhibiting higher thermal durability than Bi 2 O 3 even when a heat deterioration test is performed at 800 ° C. for 5 hours in Air. It is below, More preferably, it is 16 or less from the point which does not cause a fall of catalyst performance even after a heat deterioration test.
上記の通り、Ｂｉ及びＣｅを主成分とする複合酸化物は排ガス浄化触媒として好ましいが、この複合酸化物に希土類元素（Ａ）を加えることで触媒性能が向上する。そのため第３成分として希土類元素を含んでいてもよく、含むことがより好ましい。具体的には、ＢｉとＣｅの複合酸化物を含む触媒の場合よりも高い熱耐久性を示す点で好ましい。
複合酸化物中のＣｅと（Ａ）の合計を（Ｃｅ＋（Ａ））として表した場合、Ｂｉ／（Ｃｅ＋（Ａ））モル比が８以上の範囲が、ルーズコンタクト条件下でのＰＭ浄化性能が良い点で好ましい。Ｂｉ／（Ｃｅ＋（Ａ））モル比が８未満であると、Ｂｉ−Ｃｅ系と同様にＰＭの触媒燃焼時に十分に燃焼させることができず、燃え残りが生じる。したがって、ＰＭ燃焼活性および熱耐久性の両面を考慮すると（Ａ）を含む場合においては、Ｂｉと（Ｃｅ＋（Ａ））のモル比は Ｂｉ／（Ｃｅ＋（Ａ））が８以上であることが好ましく、より
好ましくは１０以上あることが、ＰＭ浄化性能を上げる上で好ましい。また２０以下が好ましく、より好ましくは１６以下であることが、熱耐久性を有する点で好ましい。
As described above, a composite oxide containing Bi and Ce as main components is preferable as an exhaust gas purification catalyst, but the catalyst performance is improved by adding a rare earth element (A) to the composite oxide. Therefore, rare earth elements may be included as the third component, and it is more preferable to include them. Specifically, it is preferable in that it exhibits higher thermal durability than the case of a catalyst including a composite oxide of Bi and Ce.
When the total of Ce and (A) in the composite oxide is expressed as (Ce + (A)), the range of Bi / (Ce + (A)) molar ratio of 8 or more is the PM purification performance under loose contact conditions. Is preferable in terms of good. When the Bi / (Ce + (A)) molar ratio is less than 8, it cannot be sufficiently burned during PM catalytic combustion as in the Bi-Ce system, and unburned residue occurs. Therefore, considering both PM combustion activity and thermal durability, when (A) is included, the molar ratio of Bi to (Ce + (A)) is such that Bi / (Ce + (A)) is 8 or more. More preferably, 10 or more is preferable for improving the PM purification performance. Moreover, 20 or less is preferable, More preferably, it is 16 or less from the point which has heat durability.
添加する希土類元素（Ａ）はＳｃ、Ｙ、Ｌａ、Ｐｒ、Ｎｄ、Ｐｍ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｄｙ、Ｈｏ、Ｅｒ、Ｔｍ、Ｙｂ、Ｌｕ等が挙げられるが、その中でもＹ、Ｌａ、Ｐｒ、Ｎｄ、Ｓｍ、Ｅｕ、Ｇｄ、Ｔｂ、Ｅｒ、Ｙｂが好ましく、Ｌａは熱耐久性の向上に効果が高いことから特に有効であり好ましい。
またＣｅと希土類元素（Ａ）のモル比は特に限定されるものではないが、（Ａ）とＣｅのモル比 （Ａ）／Ｃｅの範囲は、０．０１以上が好ましく、より好ましくは０．０５以上、更に好ましくは０．１以上が好ましく、また１以下が好ましく、より好ましくは０．８以下、更に好ましくは０．５以下が好ましい。
Examples of the rare earth element (A) to be added include Sc, Y, La, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. Among them, Y, La , Pr, Nd, Sm, Eu, Gd, Tb, Er, and Yb are preferable, and La is particularly effective and preferable because it is highly effective in improving thermal durability.
The molar ratio of Ce to the rare earth element (A) is not particularly limited, but the molar ratio of (A) to Ce (A) / Ce is preferably 0.01 or more, more preferably 0.8. 05 or more, more preferably 0.1 or more is preferable, 1 or less is preferable, more preferably 0.8 or less, still more preferably 0.5 or less.
〈希土類金属元素以外の添加金属元素〉
本実施形態に係る排ガス浄化用触媒は、希土類金属元素以外にもアルカリ金属元素、アルカリ土類金属元素、貴金属元素、および遷移金属元素からなる群より選ばれる少なくとも１種の金属元素を添加してもよい。たとえば具体的にはＮａ、Ｋ、Ｒｂ、Ｃｓ、Ｍｇ、Ｃａ、Ｓｒ、Ｂａ、Ｒｕ、Ｒｈ、Ｐｄ、Ｏｓ、Ｉｒ、Ｐｔ、Ｔｉ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｒ、Ｎｂ、Ｍｏ、Ｔｃ、Ａｇ、Ｈｆ、Ｔａ、Ｗ、Ｒｅ、Ａｕ等が挙げられ、その中でもＮａ、Ｋ、Ｒｂ、Ｃｓ、Ｂａ、Ｒｕ、Ｒｈ、Ｐｄ、Ｏｓ、Ｉｒ、Ｐｔ、Ｖ、Ｃｒ、Ｍｎ、Ｆｅ、Ｃｏ、Ｎｉ、Ｃｕ、Ｚｒ、Ｍｏ、Ａｇ、Ｈｆ、Ｗ、Ａｕが好ましい。
<Additive metal elements other than rare earth metal elements>
The exhaust gas purifying catalyst according to the present embodiment includes at least one metal element selected from the group consisting of alkali metal elements, alkaline earth metal elements, noble metal elements, and transition metal elements in addition to rare earth metal elements. Also good. For example, specifically, Na, K, Rb, Cs, Mg, Ca, Sr, Ba, Ru, Rh, Pd, Os, Ir, Pt, Ti, V, Cr, Mn, Fe, Co, Ni, Cu, Zr Nb, Mo, Tc, Ag, Hf, Ta, W, Re, Au, etc., among which Na, K, Rb, Cs, Ba, Ru, Rh, Pd, Os, Ir, Pt, V, Cr Mn, Fe, Co, Ni, Cu, Zr, Mo, Ag, Hf, W, and Au are preferable.
特にＡｇの添加は本発明における排ガス浄化用触媒の触媒活性を高める効果があり、ＰＭの燃焼開始温度のさらなる低温化に有効であり好ましい。Ａｇの添加量については、特に限定されるものではないが、ＡｇとＢｉのモル比Ａｇ／Ｂｉが０．０００１以上であることが好ましく、より好ましくは０．００１以上であることが好ましく、また０．１以下であることが好ましく、より好ましくは０．０１以下であることが好ましい。
Ａｇ／Ｂｉの値が０．０００１以下ではＡｇ量が少なすぎてＰＭ燃焼開始温度を低温化する効果が得られず、０．１以上では加熱劣化試験でＡｇの凝集が生じて熱耐久性が得られないため、ＡｇとＢｉのモル比は上記範囲内にすることが好適である。
In particular, addition of Ag has an effect of increasing the catalytic activity of the exhaust gas purifying catalyst in the present invention, and is effective and preferable for further lowering the combustion start temperature of PM. The addition amount of Ag is not particularly limited, but the molar ratio Ag / Bi of Ag and Bi is preferably 0.0001 or more, more preferably 0.001 or more, It is preferably 0.1 or less, more preferably 0.01 or less.
If the Ag / Bi value is 0.0001 or less, the amount of Ag is too small to obtain the effect of lowering the PM combustion start temperature, and if it is 0.1 or more, Ag agglomeration occurs in the heat deterioration test and thermal durability is reduced. Since it cannot be obtained, the molar ratio of Ag and Bi is preferably within the above range.
〈排ガス浄化用触媒の粒子径〉
本発明における排ガス浄化用触媒の１次粒子径は特に限定されないが、ＰＭと触媒との接触効率の観点からすれば１次粒子径が小さいほど接触効率が高まることから小さい方が好ましい。具体的には１ｎｍ以上が好ましく、より好ましくは５ｎｍ以上、また１μｍ以下が好ましく、より好ましくは８００ｎｍ以下、更に好ましくは５００ｎｍ以下であることが好ましい。粒子径が５００ｎｍ以下であると、ＰＭと触媒の接触効率が十分に得られ、かつ十分なガス透過性が確保できるためである。
<Particle size of exhaust gas purification catalyst>
The primary particle diameter of the exhaust gas purifying catalyst in the present invention is not particularly limited, but from the viewpoint of the contact efficiency between PM and the catalyst, the smaller the primary particle diameter, the higher the contact efficiency. Specifically, it is preferably 1 nm or more, more preferably 5 nm or more, and also preferably 1 μm or less, more preferably 800 nm or less, still more preferably 500 nm or less. This is because when the particle size is 500 nm or less, sufficient contact efficiency between PM and the catalyst can be obtained, and sufficient gas permeability can be secured.
〈排ガス浄化用触媒の調製方法〉
本発明における排ガス浄化用触媒の調製方法については限定するものではないが、無機塩分解法、有機酸錯体重合法、共沈法などの方法を好適に用いることができる。
原料である各元素の塩としては特に限定されないが、例えば硫酸塩、硝酸塩、リン酸塩、塩化物などの無機塩、酢酸塩、シュウ酸塩などの有機酸塩などが使用できる。中でも硝酸塩、酢酸塩が好適に使用できる。
<Method for preparing exhaust gas purifying catalyst>
Although the method for preparing the exhaust gas purifying catalyst in the present invention is not limited, methods such as an inorganic salt decomposition method, an organic acid complex polymerization method, and a coprecipitation method can be suitably used.
Although it does not specifically limit as a salt of each element which is a raw material, For example, organic acid salts, such as inorganic salts, such as a sulfate, nitrate, phosphate, and chloride, acetate, oxalate, etc. can be used. Of these, nitrates and acetates can be preferably used.
無機塩分解法では、上記の各元素の塩を目的の化学量論比となるように水を加え、撹拌することにより原料塩水溶液を調製することができる。あるいは各元素の塩を水に溶解せず、そのまま物理混合させてもよい。この原料塩水溶液あるいは原料塩の混合物を加熱し、蒸発乾固させることで前駆体物質を得ることができる。
有機酸錯体重合法、共沈法では、上記の各元素の塩を目的の化学量論比となるように水を加え、撹拌することにより原料塩水溶液を調製することができる。
In the inorganic salt decomposition method, a raw salt aqueous solution can be prepared by adding water and stirring the salt of each of the above elements so as to achieve the desired stoichiometric ratio. Alternatively, the salt of each element may be physically mixed as it is without dissolving it in water. The precursor material can be obtained by heating the raw salt solution or the mixture of raw salts and evaporating to dryness.
In the organic acid complex polymerization method and the coprecipitation method, a raw salt aqueous solution can be prepared by adding water and stirring the salt of each of the above-described elements so as to achieve a target stoichiometric ratio.
また、有機錯体法における有機錯体を形成する塩としては特に限定されないが、例えばクエン酸、りんご酸、エチレンジアミン４酢酸ナトリウムなどが用いることができる。共沈法における中和剤としては特に限定されないが、例えばアンモニア、水酸化ナトリウム、水酸化カリウム、炭酸ナトリウム、炭酸カリウムなどの無機塩基、トリエチルアミン、ピリジンなどの有機塩基などを使用すればよい。これらの方法の場合は、錯形成剤、沈殿剤によって生成した沈殿物が前駆体物質となる。 Moreover, it does not specifically limit as a salt which forms the organic complex in an organic complex method, For example, a citric acid, malic acid, sodium ethylenediaminetetraacetate etc. can be used. Although it does not specifically limit as a neutralizing agent in a coprecipitation method, For example, organic bases, such as inorganic bases, such as ammonia, sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, a triethylamine, a pyridine, etc. may be used. In these methods, the precipitate formed by the complexing agent and the precipitating agent becomes the precursor material.
得られた前駆体物質は、十分に乾燥して粉砕した後、焼成することで本発明の触媒を得ることができる。焼成温度は各元素の塩が分解される温度以上であれば特に限定されないが、例えば３００℃以上、好ましくは５００℃以上であり、また１０００℃以下、好ましくは８００℃以下の範囲で焼成するとよい。焼成温度が３００℃よりも低いと十分に複合化が進まないことから望ましくない。また、焼成温度が１０００℃を以上になると触媒の比表面積が小さくなり、ＰＭとの接触効率が悪くなるため、焼成温度は１０００℃以下が好ましい。 The obtained precursor material is sufficiently dried and pulverized, and then calcined to obtain the catalyst of the present invention. The firing temperature is not particularly limited as long as it is a temperature at which the salt of each element is decomposed. For example, the firing temperature is 300 ° C. or higher, preferably 500 ° C. or higher, and 1000 ° C. or lower, preferably 800 ° C. or lower. . If the firing temperature is lower than 300 ° C., it is not desirable because the compounding does not proceed sufficiently. Moreover, since the specific surface area of a catalyst will become small when a calcination temperature becomes 1000 degreeC or more, and contact efficiency with PM will worsen, 1000 degreeC or less is preferable.
〈排ガス浄化用触媒の使用形態〉
次に、本発明における排ガス浄化用触媒の具体的な使用例について説明する。本発明の排ガス浄化用触媒は、ハニカム型あるいはペレット型の形状の担体基材にコートして用いてもよいが、ＰＭの捕集効率の観点からフィルターの形状の担体が好ましい。フィルターとしては金属やセラミックスなどのフォーム、金属やセラミックス繊維からなる不織布、ウォールフロータイプのフィルターなど、十分なＰＭ捕集機能を有するものであればよいが、ＰＭ捕集効率およびＰＭと触媒との接触効率の観点からウォールフロータイプのフィルターが特に好ましい。ＤＰＦは、フィルター本体がコーディエライト、炭化珪素、チタン酸アルミニウム、ムライトなどの多孔質材料から形成されており、ハニカム構造の両端面の開口部が互い違いに栓材で閉塞された構造をしている。排気ガスは、フィルター端面の開口部より流入すると薄肉の隔壁を通って隣接する細孔に流れ、反対側の端面の開口部より流出する。ＰＭは排気ガスが隔壁を通過する際に捕捉されるので、細孔壁面に触媒コート層を形成することになる。この触媒コート層は、例えば本発明の触媒粉を、水およびバインダーを混合してスラリーを調製し、このスラリーをフィルター本体にウォッシュコートすることで形成するとよい。あるいは触媒原料塩水溶液にフィルター本体を浸漬させ、引き上げた後に乾燥、焼成工程を経ることで形成してもよい。また、触媒粉あるいは触媒原料に水、バインダーおよび造孔材等の基材を加え、所望の形状に押出し成形して用いてもよく、むしろフィルター全面に均一に触媒層が形成され、ＰＭとの接触効率が高まることで高い浄化性能を発揮できることから好ましい。また、基材に対する触媒量は特に制限されないが、対象とする内燃機関に応じてその量を適宜調整することができ、基材の体積１Ｌ当たりの触媒量が１０〜３００ｇ程度となる量が好ましい。１０ｇより少ないと十分な浄化性能が得られず、３００ｇ以上になると圧損が生じるので上記の範囲であることが好ましい。
<Usage form of exhaust gas purification catalyst>
Next, a specific use example of the exhaust gas purifying catalyst in the present invention will be described. The exhaust gas purifying catalyst of the present invention may be used by coating it on a carrier substrate in the form of a honeycomb type or a pellet type, but a carrier in the form of a filter is preferable from the viewpoint of PM collection efficiency. Any filter may be used as long as it has a sufficient PM trapping function, such as a foam such as metal or ceramics, a non-woven fabric made of metal or ceramic fibers, or a wall flow type filter. A wall flow type filter is particularly preferred from the viewpoint of contact efficiency. The DPF has a structure in which the filter body is made of a porous material such as cordierite, silicon carbide, aluminum titanate, mullite, etc., and the openings on both end faces of the honeycomb structure are alternately closed with plugging materials. Yes. When the exhaust gas flows in from the opening at the end face of the filter, it flows through the thin partition wall to the adjacent pore and flows out from the opening at the opposite end face. Since PM is trapped when the exhaust gas passes through the partition wall, a catalyst coat layer is formed on the pore wall surface. The catalyst coat layer may be formed, for example, by mixing the catalyst powder of the present invention with water and a binder to prepare a slurry and wash-coating the slurry on the filter body. Alternatively, the filter main body may be immersed in the catalyst raw material salt aqueous solution, pulled up, and then dried and baked. Further, a base material such as water, a binder and a pore former may be added to the catalyst powder or the catalyst raw material, and extruded and formed into a desired shape. Rather, a catalyst layer is uniformly formed on the entire surface of the filter. It is preferable because high purification performance can be exhibited by increasing the contact efficiency. Further, the amount of catalyst for the base material is not particularly limited, but the amount can be appropriately adjusted according to the target internal combustion engine, and the amount of the catalyst amount of about 10 to 300 g per liter of the base material is preferable. . When the amount is less than 10 g, sufficient purification performance cannot be obtained, and when the amount is 300 g or more, pressure loss occurs, so the above range is preferable.
以下、本発明を実施例および比較例により更に詳細に説明するが、本発明はこれら実施例に限定されるものではない。
（実施例１）
市販の特級試薬である硝酸ビスマス・５水和物（キシダ化学社製）、硝酸セリウム・６水和物（キシダ化学社製）をＢｉとＣｅのモル比がＢｉ／Ｃｅ＝９となるように各硝酸塩を混合し、この混合物を蒸発乾固した。得られた固体をメノウ乳鉢で粉砕し、Ａｉｒ雰囲気下で６００℃にて３時間焼成した。得られた焼成物をメノウ乳鉢で粉砕して実施例１の触媒を得た。
EXAMPLES Hereinafter, although an Example and a comparative example demonstrate this invention further in detail, this invention is not limited to these Examples.
Example 1
Bismuth nitrate pentahydrate (manufactured by Kishida Chemical Co., Ltd.) and cerium nitrate hexahydrate (manufactured by Kishida Chemical Co.), which are commercially available special grade reagents, have a Bi / Ce molar ratio of Bi / Ce = 9. Each nitrate was mixed and the mixture was evaporated to dryness. The obtained solid was pulverized in an agate mortar and baked at 600 ° C. for 3 hours in an Air atmosphere. The obtained fired product was pulverized in an agate mortar to obtain the catalyst of Example 1.
上記触媒についてＰＭ燃焼に対する活性評価をおこなうための評価用試料を以下の手順で調製した。擬似ＰＭとしてカーボンブラック（以下ＣＢ；三菱化学社製 ＣＢ＃４０）を用い、上記触媒１ｇと０．０１ｇのＣＢを１０ｍＬのサンプル瓶に入れ、１分間程度よく振とうして実施例１の評価用試料とした。
（実施例２）
ＢｉとＣｅのモル比がＢｉ／Ｃｅ＝１０とした以外は実施例１と同様の手順で実施例２の触媒および評価用試料を調製した。
An evaluation sample for evaluating the activity of the catalyst against PM combustion was prepared by the following procedure. Evaluation of Example 1 using carbon black (hereinafter referred to as CB;
(Example 2)
The catalyst of Example 2 and the sample for evaluation were prepared in the same procedure as in Example 1 except that the molar ratio of Bi to Ce was Bi / Ce = 10.
（実施例３）
ＢｉとＣｅのモル比がＢｉ／Ｃｅ＝１６とした以外は実施例１と同様の手順で実施例３の触媒および評価用試料を調製した。
（実施例４）
ＢｉとＣｅのモル比がＢｉ／Ｃｅ＝３０とした以外は実施例１と同様の手順で実施例４の触媒および評価用試料を調製した。
(Example 3)
A catalyst and an evaluation sample of Example 3 were prepared in the same procedure as in Example 1 except that the molar ratio of Bi to Ce was Bi / Ce = 16.
Example 4
The catalyst of Example 4 and the sample for evaluation were prepared in the same procedure as in Example 1 except that the molar ratio of Bi to Ce was Bi / Ce = 30.
（実施例５）
市販の特級試薬である硝酸ビスマス・５水和物（キシダ化学社製）、硝酸セリウム・６水和物（キシダ化学社製）、硝酸ランタン・６水和物（キシダ化学社製）をＢｉとＣｅとＬａのモル比がＢｉ：Ｃｅ：Ｌａ ＝ １０：０．８：０．２となるように各硝酸塩を混合し、この混合物を蒸発乾固した。得られた固体をメノウ乳鉢で粉砕し、Ａｉｒ雰囲気下で６００℃にて３時間焼成した。得られた焼成物をメノウ乳鉢で粉砕して実施例５の触媒を得た。ＰＭ燃焼に対する活性評価をおこなうための評価用試料については実施例１と同様の手順で調製した。
(Example 5)
Bismuth nitrate pentahydrate (manufactured by Kishida Chemical Co., Ltd.), cerium nitrate hexahydrate (manufactured by Kishida Chemical Co., Ltd.), lanthanum nitrate hexahydrate (manufactured by Kishida Chemical Co., Ltd.), Bi Each nitrate was mixed so that the molar ratio of Ce to La was Bi: Ce: La = 10: 0.8: 0.2, and this mixture was evaporated to dryness. The obtained solid was pulverized in an agate mortar and baked at 600 ° C. for 3 hours in an Air atmosphere. The obtained fired product was pulverized in an agate mortar to obtain the catalyst of Example 5. An evaluation sample for evaluating the activity against PM combustion was prepared in the same procedure as in Example 1.
（実施例６）
BiとＣｅとＬａのモル比がＢｉ：Ｃｅ：Ｌａ ＝ ２０：０．８：０．２とした以外は実施例４と同様の手順で実施例６の触媒および評価用試料を調製した。
（実施例７）
BiとＣｅとＬａのモル比がＢｉ：Ｃｅ：Ｌａ ＝ ３０：０．８：０．２とした以外は実施例４と同様の手順で実施例７の触媒および評価用試料を調製した。
(Example 6)
A catalyst and an evaluation sample of Example 6 were prepared in the same manner as in Example 4 except that the molar ratio of Bi, Ce, and La was Bi: Ce: La = 20: 0.8: 0.2.
(Example 7)
A catalyst and an evaluation sample of Example 7 were prepared in the same manner as in Example 4 except that the molar ratio of Bi, Ce and La was Bi: Ce: La = 30: 0.8: 0.2.
（比較例１）
市販の特級試薬であるＢｉ２Ｏ３ １ｇと０．０１ｇのＣＢを１０ｍＬのサンプル瓶に
入れ、１分間程度よく振とうして比較例１の評価用試料とした。
（比較例２）
ＢｉとＣｅのモル比がＢｉ／Ｃｅ ＝ ０．２５とした以外は実施例１と同様の手順で比較例２の触媒および評価用試料を調製した。
(Comparative Example 1)
1 g of Bi 2 O 3, which is a commercially available special grade reagent, and 0.01 g of CB were placed in a 10 mL sample bottle and shaken well for about 1 minute to obtain a sample for evaluation of Comparative Example 1.
(Comparative Example 2)
A catalyst of Comparative Example 2 and a sample for evaluation were prepared in the same procedure as in Example 1 except that the molar ratio of Bi to Ce was Bi / Ce = 0.25.
（比較例３）
特許文献１に記載されている実施例７と同様の手順で比較例３の触媒を調製した。具体的な手順を以下に示す。市販の特級試薬である硝酸ビスマス・５水和物（キシダ化学社製）、硝酸セリウム・６水和物（キシダ化学社製）をＢｉとＣｅのモル比がＢｉ／Ｃｅ＝９となるように秤量し、混合した。この混合物を、ＣｅとＢｉの液中モル濃度の合計が０．２ｍｏＬ／Ｌとなるように水に添加して原料溶液を得た。この溶液を撹拌しながら沈殿剤として炭酸アンモニウムの水溶液を添加した。その後、３０分間撹拌を継続することにより、沈殿反応を十分に進行させた。得られた沈殿をろ過、水洗し、１２５℃で１５時間乾燥した。得られた粉末を前駆体とし、この前駆体を大気雰囲気下６００℃で２時間焼成してＣｅとＢｉを主成分とする複合酸化物粉体を得た。この複合酸化物粉体を本実施例１と同様の手順で評価用試料を調製した。
(Comparative Example 3)
A catalyst of Comparative Example 3 was prepared in the same procedure as Example 7 described in Patent Document 1. The specific procedure is shown below. Bismuth nitrate pentahydrate (manufactured by Kishida Chemical Co., Ltd.) and cerium nitrate hexahydrate (manufactured by Kishida Chemical Co.), which are commercially available special grade reagents, have a Bi / Ce molar ratio of Bi / Ce = 9. Weighed and mixed. This mixture was added to water such that the total molar concentration of Ce and Bi in the liquid was 0.2 mol / L to obtain a raw material solution. While this solution was stirred, an aqueous solution of ammonium carbonate was added as a precipitant. Then, precipitation reaction was fully advanced by continuing stirring for 30 minutes. The resulting precipitate was filtered, washed with water, and dried at 125 ° C. for 15 hours. The obtained powder was used as a precursor, and this precursor was calcined at 600 ° C. for 2 hours in an air atmosphere to obtain a composite oxide powder containing Ce and Bi as main components. A sample for evaluation was prepared from this composite oxide powder in the same procedure as in Example 1.
（比較例４）
ＢｉとＣｅのモル比がＢｉ／Ｃｅ ＝ ４０とした以外は比較例３と同様の手順で比較例
の触媒および評価用試料を調製した。
〈ＰＭ燃焼活性評価〉
各実施例および比較例の試料についてＰＭ燃焼に対する活性評価を以下の方法でおこなった。評価用試料１００ｍｇをガラス反応管に充填し、Ａｉｒを５．８８ｍＬ／ｍｉｎの流量で供給しながら１０℃／ｍｉｎで７００℃まで昇温させ、触媒層を通過したガスをｍｉｃｒｏ−ＧＣ装置（ＶＡＲＩＡＮ社製 ＣＰ−４９００）で分析し、各温度におけるＣＯ２発生量を測定した。図１に例示するように、燃焼開始温度はＣＯ２発生ピークの温度曲線においてＣＯ２が発生する前の接線と、ＣＯ２発生率（傾き）が最大となる点での接線とが交わる点の温度とし、燃焼ピーク温度はＣＯ２発生ピークのピークトップの温度としている。図２に実施例２および比較例１，２のＣＯ２発生ピークの温度曲線を示す。表２に各実施例および各比較例の触媒の燃焼開始温度、主燃焼ピーク温度および５５０℃におけるＣＢ浄化率を示す。ここで、主燃焼ピークとはＣＯ２発生ピークが複数検出された場合にＣＯ２発生量が最も多いピークのことをいう。本実験では実施例１−７については１本のみのＣＯ２発生ピークが検出されたが、比較例１−４においては２本のＣＯ２発生ピークが検出されたのでＣＯ２発生量が最も多い低温側のピークの値を記載した。
(Comparative Example 4)
A catalyst of comparative example and a sample for evaluation were prepared in the same procedure as in comparative example 3 except that the molar ratio of Bi to Ce was Bi / Ce = 40.
<PM combustion activity evaluation>
The activity evaluation with respect to PM combustion was performed by the following method about the sample of each Example and the comparative example. A glass reaction tube was filled with 100 mg of the sample for evaluation, and the temperature was raised to 700 ° C. at 10 ° C./min while supplying Air at a flow rate of 5.88 mL / min, and the gas passed through the catalyst layer was micro-GC device (Varian). CP-4900), and the amount of CO 2 generated at each temperature was measured. As illustrated in FIG. 1, the combustion start temperature is a point at which the tangent line before the CO 2 is generated and the tangent line at the point where the CO 2 generation rate (slope) is maximum intersect in the temperature curve of the CO 2 generation peak. The combustion peak temperature is the temperature at the peak top of the CO 2 generation peak. FIG. 2 shows temperature curves of CO 2 generation peaks in Example 2 and Comparative Examples 1 and 2 . Table 2 shows the combustion start temperature, the main combustion peak temperature, and the CB purification rate at 550 ° C. of the catalyst of each Example and each Comparative Example. Here, the main combustion peak means a peak having the largest CO 2 generation amount when a plurality of CO 2 generation peaks are detected. Although CO 2 generated peak of only one for Example 1-7 in this experiment was detected, most often CO 2 emissions because CO 2 generation Two peaks were detected in Comparative Example 1-4 The value of the peak on the low temperature side is shown.
〈加熱劣化試験〉
各実施例および比較例１、３，４の触媒についてＡｉｒ中、８００℃、５時間の条件下、加熱劣化試験をおこなった。加熱劣化試験後の試料について、実施例１と同様に評価用試料を調製し、ｍｉｃｒｏ−ＧＣ装置にて同様に活性評価をおこなった。活性評価は加熱劣化試験前後の主燃焼ピーク温度の変化量の比較によりおこなった。加熱劣化試験前に比べ、試験後に主燃焼ピーク温度が高温側に大きくシフトするほど活性が低下していると判断した。図３に実施例２および比較例１における加熱劣化試験前後のＣＯ２発生ピークの温度曲線を示す。また、表３に加熱劣化試験前後の各触媒の主燃焼ピーク温度を示し、表４に加熱劣化試験前後の実施例１と比較例３の浄化率と主燃焼ピーク温度と、それぞれの結晶系を示す。
<Heat degradation test>
The catalyst of each Example and Comparative Examples 1, 3 and 4 was subjected to a heat deterioration test in Air at 800 ° C. for 5 hours. About the sample after a heat deterioration test, the sample for evaluation was prepared similarly to Example 1, and activity evaluation was similarly performed with the micro-GC apparatus. The activity was evaluated by comparing the amount of change in the main combustion peak temperature before and after the heat deterioration test. It was judged that the activity decreased as the main combustion peak temperature greatly shifted to the high temperature side after the test as compared to before the heat deterioration test. FIG. 3 shows temperature curves of CO 2 generation peaks before and after the heat deterioration test in Example 2 and Comparative Example 1. Table 3 shows the main combustion peak temperatures of the respective catalysts before and after the heat deterioration test, and Table 4 shows the purification rates and main combustion peak temperatures of Example 1 and Comparative Example 3 before and after the heat deterioration test, and the respective crystal systems. Show.
〈粉末Ｘ線回折測定〉
実施例７および比較例１、２、３の触媒について、粉末Ｘ線回折測定をおこなった。測定条件は以下のとおりである。
・Ｘ線回折装置名；ＰＡＮａｌｙｃａｌ ＰＷ１７００
・光学系 ；集中法光学系
・管球 ；ＣｕＫα
・管電圧 ；４０ｋＶ
・管電流 ；３０ｍＡ
・測定範囲 ；２θ ＝ ３〜６０°
・スキャンスピード；３°／ｍｉｎ
・サンプリング幅 ；０．０５°
図４に、実施例１および比較例２、３のＸ線回折パターンを例示し、表２に実施例１〜７および比較例１〜４の結晶系を示す。また、表５に実施例１の２θ＝３〜６０°における主要ピークの位置およびピーク強度を示す。さらに実施例１と比較例１の２θ ＝ ２７°〜２９°の範囲のＸ線回折パターンを図５に示す。
<Powder X-ray diffraction measurement>
Powder X-ray diffraction measurement was performed on the catalyst of Example 7 and Comparative Examples 1, 2, and 3. The measurement conditions are as follows.
-X-ray diffractometer name; PANalycal PW1700
・ Optical system: Concentrated optical system, Tube: CuKα
・ Tube voltage: 40 kV
・ Tube current: 30 mA
・ Measurement range: 2θ = 3-60 °
・ Scanning speed: 3 ° / min
・ Sampling width: 0.05 °
FIG. 4 illustrates the X-ray diffraction patterns of Example 1 and Comparative Examples 2 and 3, and Table 2 shows the crystal systems of Examples 1 to 7 and Comparative Examples 1 to 4. Table 5 shows the position and peak intensity of the main peak in Example 1 at 2θ = 3 to 60 °. Further, X-ray diffraction patterns in the range of 2θ = 27 ° to 29 ° of Example 1 and Comparative Example 1 are shown in FIG.
一般に、ＣＯ２発生ピークのピークトップの温度が低いほどＰＭ燃焼に対する触媒活性が高いと評価することができる。本実施例の触媒はルーズコンタクト条件での評価にもかかわらず、ＣＯ２発生ピークのピークトップが約４００〜４２０℃付近に観測されることから、ＰＭ燃焼に対する触媒活性が非常に高いことがわかる。また、実施例１〜７の触媒の燃焼開始温度はいずれも３００℃台であり、非常に低温からＣＢを燃焼させることができることがわかる。 In general, it can be evaluated that the lower the temperature at the peak top of the CO 2 generation peak, the higher the catalytic activity for PM combustion. In spite of the evaluation under the loose contact condition, the catalyst of this example has a very high catalytic activity for PM combustion because the peak top of the CO 2 generation peak is observed at around 400 to 420 ° C. . Further, the combustion start temperatures of the catalysts of Examples 1 to 7 are all in the range of 300 ° C., and it can be seen that CB can be burned from a very low temperature.
ＣＯ２発生ピークのピークトップの温度が低い上に、触媒燃焼でＣＢの燃焼割合（浄化率）が高いことが浄化性能として好ましい。
実施例１〜７のようにＢｉとＣｅを複合化させ、かつ基本構造がＢｉ２Ｏ３正方晶であれば、触媒燃焼でほぼ全てのＣＢを燃焼させることができ、５５０℃での浄化率も９５％以上を示すことから十分な浄化性能を発揮することがわかる。
It is preferable as the purification performance that the temperature at the peak top of the CO 2 generation peak is low and the combustion ratio (purification rate) of CB is high by catalytic combustion.
When Bi and Ce are combined as in Examples 1 to 7 and the basic structure is Bi 2 O 3 tetragonal, almost all CB can be burned by catalytic combustion, and the purification rate at 550 ° C. Also, it can be seen that sufficient purification performance is exhibited because it shows 95% or more.
しかし、例えば図２に示すように、比較例１（Ｂｉ２Ｏ３）や比較例２（ＣｅＯ２立方晶）の場合、ＣＯ２発生ピークは４００℃台（触媒燃焼）と６００℃台（ＣＢの自己燃焼）の２箇所に検出される。これらの場合、触媒燃焼のみで燃焼しきれないＣＢが残存するため５５０℃での浄化率が６０％台にとどまった。そのため十分なＰＭ浄化性能を有しておらず実用的とはいえない。 However, for example, as shown in FIG. 2, in the case of Comparative Example 1 (Bi 2 O 3 ) and Comparative Example 2 (CeO 2 cubic crystal), CO 2 generation peaks are in the 400 ° C. range (catalytic combustion) and in the 600 ° C. range (CB Are detected at two locations. In these cases, CB that cannot be burned only by catalytic combustion remains, so that the purification rate at 550 ° C. remained in the 60% range. Therefore, it does not have sufficient PM purification performance and cannot be said to be practical.
一方、Ｂｉ及びＣｅを主成分とする複合酸化物であっても、比較例３（Ｂｉ２Ｏ３単斜晶）のようにＣＯ２発生ピークが４００℃台（触媒燃焼）と５００℃台（ＣＢの自己燃焼）の２箇所で検出され、５５０℃での浄化率が８０％台にとどまる場合がある。これは同じＢｉ／Ｃｅモル比である実施例１よりも浄化性能が低い。実施例１と比較例５の粉末Ｘ線回折パターン（図４）を比較すると、実施例１のＢｉ−Ｃｅ複合酸化物の基本構造がＢｉ２Ｏ３の正方晶であるのに対し、比較例３のＢｉ−Ｃｅ複合酸化物の基本構造はＢｉ２Ｏ３の単斜晶である。このように結晶系が正方晶であるほうが、ＰＭ酸化に対する浄化性能が優れており、Ｂｉ−Ｃｅ複合酸化物の結晶系が重要であることは明らかである。 On the other hand, even in the case of a composite oxide containing Bi and Ce as main components, the CO 2 generation peak is in the 400 ° C. range (catalytic combustion) and the 500 ° C. range (compared with Bi 2 O 3 monoclinic crystal). In some cases, the purification rate at 550 ° C. remains in the 80% range. This has lower purification performance than Example 1 with the same Bi / Ce molar ratio. Comparing the powder X-ray diffraction patterns (FIG. 4) of Example 1 and Comparative Example 5, the basic structure of the Bi—Ce composite oxide of Example 1 is a tetragonal crystal of Bi 2 O 3 , whereas the comparative example The basic structure of the Bi—Ce composite oxide 3 is a Bi 2 O 3 monoclinic crystal. Thus, it is clear that the crystal system of tetragonal crystal is superior in purification performance against PM oxidation, and the crystal system of Bi—Ce composite oxide is more important.
単独酸化物である正方晶のＢｉ２Ｏ３では比較例１に示すように浄化性能が低いことから、Ｃｅとの複合化が重要である。図５に示すように、本発明の複合酸化物では、該複合酸化物のＸ線回折ピークが、正方晶のＢｉ２Ｏ３のＸ線回折ピークから低角度側にシフトしており、ＢｉとＣｅが複合化していることがわかる。
以上のことから、Ｂｉ２Ｏ３の正方晶を維持したままＣｅを固溶させることが好ましく、このような複合酸化物が得られるＢｉとＣｅのモル比の範囲は好ましくは上記に示す５≦ Ｂｉ／Ｃｅである。
Since tetragonal Bi 2 O 3 , which is a single oxide, has low purification performance as shown in Comparative Example 1, it is important to combine it with Ce. As shown in FIG. 5, in the composite oxide of the present invention, the X-ray diffraction peak of the composite oxide is shifted to the low angle side from the X-ray diffraction peak of tetragonal Bi 2 O 3 , and Bi and It can be seen that Ce is complexed.
From the above, it is preferable to dissolve Ce while maintaining the tetragonal crystal of Bi 2 O 3 , and the range of the molar ratio of Bi and Ce from which such a composite oxide can be obtained is preferably 5 ≦ Bi / Ce.
表３の比較例１に示すようにＢｉ２Ｏ３では、加熱劣化試験後に燃焼ピーク温度が高温側に約１００℃程度シフトし、浄化性能の低下がみられる。一方、実施例１〜７のようにＢｉとＣｅを複合化させ、かつ基本構造がＢｉ２Ｏ３正方晶であれば、Ｂｉ２Ｏ３よりも加熱劣化試験後の燃焼ピーク温度の高温側へのシフトの程度が小さく、熱耐久性に優れていることがわかる。特に、Ｂｉ／Ｃｅ ≦ １６であれば加熱劣化試験後も浄化性能の低下が全くみられない。単独酸化物である正方晶のＢｉ２Ｏ３は、加熱劣化試験後には相転移してしまうのに対し、実施例１〜７は加熱劣化試験前後で相転移をおこさず、正方晶を維持していることを粉末Ｘ線回折測定から確認した。さらに表４に示すように、比較例３のＢｉ２Ｏ３の単斜晶を基本構造とする複合酸化物においても、加熱劣化試験後には相転移が認められ、触媒活性も低下してしまう。以上より、熱耐久性を向上させるには正方晶の基本構造を安定化させることが重要であり、そのためには一定量のＣｅを複合化させる必要がある。具体的には上記に示すＢｉ／Ｃｅ≦３８の範囲が好ましい。 As shown in Comparative Example 1 of Table 3, in Bi 2 O 3 , the combustion peak temperature shifts to about 100 ° C. on the high temperature side after the heat deterioration test, and the purification performance is reduced. On the other hand, if Bi and Ce are combined as in Examples 1 to 7 and the basic structure is Bi 2 O 3 tetragonal, the combustion peak temperature after the heat deterioration test is higher than that of Bi 2 O 3 . It can be seen that the degree of shift is small and the thermal durability is excellent. In particular, if Bi / Ce ≦ 16, no reduction in purification performance is observed even after the heat deterioration test. While tetragonal Bi 2 O 3 that is a single oxide undergoes a phase transition after the heat deterioration test, Examples 1 to 7 do not undergo a phase transition before and after the heat deterioration test, and maintain a tetragonal crystal. It was confirmed by powder X-ray diffraction measurement. Furthermore, as shown in Table 4, even in the composite oxide having the basic structure of Bi 2 O 3 monoclinic crystal of Comparative Example 3, phase transition is observed after the heat deterioration test, and the catalytic activity is also lowered. From the above, it is important to stabilize the tetragonal basic structure in order to improve the thermal durability, and for that purpose, a certain amount of Ce needs to be combined. Specifically, the range of Bi / Ce ≦ 38 shown above is preferable.
表３に示すように、希土類元素（Ａ）としてＬａを加えると熱耐久性が更に向上し、Ｂｉ／（Ｃｅ＋Ｌａ）≦ ２０では浄化性能の低下が全くみられない。このようにＢｉとの
組合せ元素としてＣｅのみであるよりもＣｅとＬａの両元素を含む方が、熱耐久性を向上させる上で好ましい。
以上の結果より、本発明の排ガス浄化用触媒は、Ｂｉ及びＣｅを主成分とする複合酸化物を含み、その複合酸化物の基本構造がＢｉ２Ｏ３の正方晶であって、特にＢｉとＣｅのモル比が８ ≦ Ｂｉ／Ｃｅ ≦１６の範囲、さらに希土類元素（Ａ）としてＬａを加えた
場合は８ ≦ Ｂｉ／（Ｃｅ＋Ｌａ） ≦ ２０の範囲にあるときに、ルーズコンタクトでも高い浄化性能を発揮させることができ、かつ加熱劣化試験をおこなっても触媒性能が低下しないことから、実用に供し得る触媒といえる。
As shown in Table 3, when La is added as the rare earth element (A), the thermal durability is further improved, and when Bi / (Ce + La) ≦ 20, no reduction in purification performance is observed. As described above, it is preferable to include both elements Ce and La rather than only Ce as a combination element with Bi in order to improve thermal durability.
From the above results, the exhaust gas purifying catalyst of the present invention includes a composite oxide mainly composed of Bi and Ce, and the basic structure of the composite oxide is a tetragonal crystal of Bi 2 O 3 , and in particular, Bi and High purification performance even in loose contacts when the molar ratio of Ce is in the range of 8 ≦ Bi / Ce ≦ 16, and further in the range of 8 ≦ Bi / (Ce + La) ≦ 20 when La is added as the rare earth element (A). It can be said that the catalyst can be put to practical use since the catalyst performance does not decrease even when a heat deterioration test is performed.
本発明によれば、ディーゼルエンジン等の内燃機関から排出される排ガス中に含まれるスートを主成分とする粒子状物質（ＰＭ）を非常に低温で効率よく燃焼させることができるため、ＰＭの堆積による圧損の上昇を防ぐことができ、かつフィルター内での温度上昇が少なくなり、フィルターへの負荷が軽減されるので熱耐久性も向上する。以上のことより、ディーゼル車などの内燃機関その他の燃焼機関から排出される排気ガスを極めて効果的に浄化する排ガス浄化装置の実用化が促進される。 According to the present invention, particulate matter (PM) mainly composed of soot contained in exhaust gas discharged from an internal combustion engine such as a diesel engine can be burned efficiently at a very low temperature. As a result, the temperature rise in the filter is reduced and the load on the filter is reduced, so that the thermal durability is improved. From the above, practical use of an exhaust gas purifying apparatus that purifies exhaust gas discharged from an internal combustion engine such as a diesel vehicle or other combustion engine extremely effectively is promoted.
Claims (6)
＜主要回折ピーク＞
回折角２θ（°） 相対強度
（１） ２７．９３±０．２ １００
（２） ３１．２７±０．２ ５〜３０
（３） ３２．６７±０．２ １０〜５０
（４） ４６．１８±０．２ １０〜５０
（５） ４６．８８±０．２ ５〜３０
（６） ５４．２２±０．２ ５〜３０
（７） ５５．４７±０．２ １０〜５０
（８） ５７．６９±０．２ ２〜２０
An exhaust gas purifying catalyst for purifying particulate matter in exhaust gas discharged from an internal combustion engine, comprising a composite oxide mainly composed of Bi and Ce, and the basic structure of the composite oxide is Bi 2 O 3 and the complex oxide has the following eight main diffraction peaks at the pattern diffraction angle 2θ of the powder X-ray diffraction peak (using CuKα ray as the X-ray source). An exhaust gas purifying catalyst characterized by.
<Main diffraction peak>
Diffraction angle 2θ (°) Relative intensity
(1) 27.93 ± 0.2 100
(2) 31.27 ± 0.2 5-30
(3) 32.67 ± 0.2 10-50
(4) 46.18 ± 0.2 10-50
(5) 46.88 ± 0.2 5-30
(6) 54.22 ± 0.2 5-30
(7) 55.47 ± 0.2 10-50
(8) 57.69 ± 0.2 2-20
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