JP4204521B2 - Exhaust gas purification catalyst - Google Patents
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Description
本発明は、排ガス浄化触媒に係り、特に、自動車等の内燃機関から排出される排ガス中の窒素酸化物（ＮＯｘ）、炭化水素（ＨＣ）及び一酸化炭素（ＣＯ）を同時に効率よく浄化、低減させることのできる排ガス浄化触媒に関する。なお、本発明は、とりわけ、排ガス浄化触媒の耐久処理後の低温運転時における浄化性能を向上させたものである。 The present invention relates to an exhaust gas purification catalyst, and in particular, efficiently and efficiently purifies and reduces nitrogen oxides (NOx), hydrocarbons (HC) and carbon monoxide (CO) in exhaust gas discharged from an internal combustion engine such as an automobile. The present invention relates to an exhaust gas purifying catalyst that can be used. The present invention particularly improves the purification performance during low temperature operation after the endurance treatment of the exhaust gas purification catalyst.
排ガス（例えばＣＯ、ＨＣ、ＮＯ、ＮＯ２等）の浄化には、貴金属元素（Ｐｔ、Ｒｈ、Ｐｄ、Ｉｒ）が高性能を示すことが知られている。このため、排ガス浄化触媒には、上記貴金属元素を用いることが好適である。通常、これらの貴金属は、Ｌａ、Ｃｅ、Ｎｄ等の添加剤とともに、高比表面積担体のＡｌ２Ｏ３に混合又は担持されて用いられる。一方、貴金属は、ペロブスカイト等の複合酸化物の構成元素とすることにより、様々な元素と組み合わせることができ、これにより貴金属のみの場合よりも多様な性質が得られ、浄化性能を向上させることができる。さらに、このような複合酸化物に貴金属を担持すると、複合酸化物の様々な性質による影響により、貴金属の性質が大きく変化することが知られている。 It is known that noble metal elements (Pt, Rh, Pd, Ir) exhibit high performance for purification of exhaust gas (for example, CO, HC, NO, NO 2, etc.). For this reason, it is suitable to use the said noble metal element for an exhaust gas purification catalyst. Usually, these noble metals are used by being mixed or supported on Al 2 O 3 which is a high specific surface area support together with additives such as La, Ce and Nd. On the other hand, noble metals can be combined with various elements by using them as constituent elements of complex oxides such as perovskites. This makes it possible to obtain various properties and improve purification performance compared to the case of noble metals alone. it can. Furthermore, it is known that when a noble metal is supported on such a composite oxide, the properties of the noble metal change greatly due to the influence of various properties of the composite oxide.
このような排ガス浄化触媒には、貴金属の劣化の主原因は凝集による活性点の減少であることに鑑み、ペロブスカイト型複合酸化物を担体とすることにより、貴金属の凝集速度を低下させる技術が開示されている（特許文献１参照）。また、貴金属がＰｄの場合はＮＯ還元反応の活性種であるＰｄＯが低活性のＰｄに還元されることに鑑み、Ａサイト欠陥型のペロブスカイト型複合酸化物を用いることで、ＰｄＯの還元を抑制する技術が開示されている（特許文献２参照）。 In view of the fact that the main cause of deterioration of noble metals is a decrease in active sites due to aggregation, such an exhaust gas purification catalyst discloses a technique for reducing the aggregation rate of noble metals by using a perovskite complex oxide as a support. (See Patent Document 1). In addition, when the noble metal is Pd, in view of the fact that PdO, which is the active species of the NO reduction reaction, is reduced to low-activity Pd, the reduction of PdO is suppressed by using an A-site defect type perovskite complex oxide. The technique to do is disclosed (refer patent document 2).
一方、貴金属は、通常、Ａ１２Ｏ３等の担体上に、単独又は複数種類の組み合わせで用いられる。しかしながら、自動車走行時等の過酷な使用条件下では、貴金属の凝集による活性点の減少により、活性が大きく低下する。この問題を解決する手段として、貴金属元素とそれ以外の元素を含む複合酸化物を形成する方法が種々提案されている。なお、貴金属の中でもＰｄを含むものに関する技術としては、希土類元素とＰｄとを組み合わせた複合酸化物が開示されている（特許文献３〜８参照）。 On the other hand, noble metals are usually used alone or in combination of a plurality of types on a carrier such as A1 2 O 3 . However, under severe usage conditions such as when driving a car, the activity is greatly reduced due to the reduction of active sites due to aggregation of noble metals. As means for solving this problem, various methods for forming complex oxides containing noble metal elements and other elements have been proposed. In addition, as a technique regarding a noble metal containing Pd, a composite oxide in which a rare earth element and Pd are combined is disclosed (see Patent Documents 3 to 8).
さらに、本発明者等は、以前に、示性式がＬａｘＰｄＯｙ（Ｘ＝２，４，ｙ＝４，７）／ＬｎＡｌＯ３なる排ガス浄化触媒を提案した。上記触媒中、被担持体であるＬａｘＰｄＯｙについては、Ｐｄ−Ｐｄ間にＬａが存在するため、Ｐｄ同士の凝集を防止することができ、また、担体であるＬａＡｌＯ３についてはアンカー効果を奏し、Ｐｄ粒子をＬａＡｌＯ３上に固定する作用がある。このため、この排ガス浄化触媒においては、Ｐｄを高分散状態に維持することができる（特許文献９参照）。 Furthermore, the present inventors have previously proposed an exhaust gas purification catalyst having a characteristic formula of LaxPdOy (X = 2, 4, y = 4, 7) / LnAlO 3 . In the above catalyst, for LaxPdOy is the carrier, because of the presence of La between Pd-Pd, it is possible to prevent aggregation of Pd each other also exhibit the anchor effect for the LaAlO 3 is a carrier, Pd There is an effect of fixing the particles on LaAlO 3 . For this reason, in this exhaust gas purification catalyst, Pd can be maintained in a highly dispersed state (see Patent Document 9).
上記した従来の排ガス浄化触媒は、浄化性能に加えて耐食性能を考慮しても、比較的高温（４００℃以上）である自動車走行時等においては、排ガス中のＣＯ、ＨＣ、及びＮＯｘを浄化するに十分な性能を発揮するものである。しかしながら、これらの排ガス浄化触媒は、比較的低温（４００℃未満）である自動車の始動時又はアイドリング時においては、十分な耐久性能を発揮し得ないのが現状である。この理由は、以下のとおりである。 The above-described conventional exhaust gas purification catalyst purifies CO, HC, and NOx in the exhaust gas when the automobile is running at a relatively high temperature (400 ° C. or higher), considering the corrosion resistance in addition to the purification performance. It exhibits sufficient performance. However, at present, these exhaust gas purification catalysts cannot exhibit sufficient durability performance at the time of start-up or idling of an automobile at a relatively low temperature (less than 400 ° C.). The reason for this is as follows.
即ち、Ｐｔ、Ｒｈ、及びＰｄ等の貴金属は、通常、高比表面積のＡ１２Ｏ３上に担持された状態で使用される。このため、これらの貴金属は、Ａ１２Ｏ３上に高分散状態に担持することができる。しかしながら、Ａ１２Ｏ３は安定化合物であるため、担持された貴金属に対して相互作用を及ぼさない。よって、単位貴金属量あたりの活性が低く、このため、触媒を高温雰囲気に長時間曝露した後には、優れた浄化性能を維持することができない。従って、近年においては、高温雰囲気に長時間曝露した後においても優れた浄化性能を維持することのできる排ガス浄化触媒の開発が要請されていた。 That is, noble metals such as Pt, Rh, and Pd are usually used in a state where they are supported on A1 2 O 3 having a high specific surface area. Therefore, these noble metals can be supported on A1 2 O 3 in a highly dispersed state. However, since A1 2 O 3 is a stable compound, it does not interact with the supported noble metal. Therefore, the activity per unit noble metal amount is low, and therefore excellent purification performance cannot be maintained after the catalyst is exposed to a high temperature atmosphere for a long time. Therefore, in recent years, there has been a demand for the development of an exhaust gas purification catalyst capable of maintaining excellent purification performance even after being exposed to a high temperature atmosphere for a long time.
また、Ｐｄの酸化状態にはＰｄ２＋とＰｄ０（金属状態）とがあるが、排ガス浄化に好ましい状態は、Ｐｄ２＋であるため、自動車走行時においては、ＰｄがＰｄＯの状態で存在することが望ましい。しかしながら、Ａ１２Ｏ３上に担持されたＰｄは、初期はＰｄＯの状態で存在していても、高温（９００℃以上）雰囲気に長時間曝露された後には、金属状態のＰｄに還元され、活性が大きく低下してしまう。また、Ａ１２Ｏ３上に担持されたＰｄを高温（９００℃以上）雰囲気に長時間曝露した後には、Ｐｄ同士が凝集することにより、活性点が減少し、活性が低下するという問題もある。 In addition, Pd 2+ and Pd 0 (metal state) exist in the oxidation state of Pd, but the preferred state for exhaust gas purification is Pd 2+ , so that Pd exists in the PdO state when the vehicle is running. Is desirable. However, Pd supported on A1 2 O 3 is reduced to Pd in a metallic state after being exposed to a high temperature (900 ° C. or higher) atmosphere for a long time, even if it initially exists in the state of PdO. The activity is greatly reduced. In addition, after Pd supported on A1 2 O 3 is exposed to a high-temperature (900 ° C. or higher) atmosphere for a long time, Pd aggregates to reduce the active sites and lower the activity. .
さらに、従来の排ガス浄化触媒の中には、上述したように、貴金属元素とそれ以外の元素とを組み合わせて複合酸化物を形成する技術も提案されている。しかしながら、このような排ガス浄化触媒には、１０００℃程度という条件下では貴金属を含む複合酸化物自体が凝集してしまい、活性点が減少して浄化性能が低下するという問題がある。また、本発明者等の以前の提案である、示性式がＬａｘＰｄＯｙ（Ｘ＝２，４、ｙ＝４，７）／ＬｎＡｌＯ３の排ガス浄化触媒についても、１０００℃程度という高温下ではＬａｘＰｄＯｙの凝集により活性点が減少し、活性が低下するという問題がある。 Further, as described above, a technique for forming a composite oxide by combining a noble metal element and other elements has been proposed among conventional exhaust gas purification catalysts. However, such an exhaust gas purification catalyst has a problem in that the complex oxide itself containing the noble metal aggregates under the condition of about 1000 ° C., and the active point is reduced to reduce the purification performance. In addition, the exhaust gas purification catalyst having the characteristic formula LaxPdOy (X = 2, 4, y = 4, 7) / LnAlO 3 , which is a previous proposal by the present inventors, is also the same as that of LaxPdOy at a high temperature of about 1000 ° C. There is a problem that the active sites are reduced by aggregation and the activity is lowered.
本発明は、上記種々の事情に鑑みてなされたものであり、特に、高温（９８０℃以上）雰囲気に長時間曝露した後にも、被担持体に含まれるＰｄのＰｄ２＋状態からの還元を抑制し、浄化性能の劣化を防止した排ガス浄化触媒を提供することを目的としている。 The present invention has been made in view of the various circumstances described above, and in particular, suppresses the reduction of Pd contained in the supported body from the Pd 2+ state even after being exposed to a high temperature (980 ° C. or higher) atmosphere for a long time. It is an object of the present invention to provide an exhaust gas purification catalyst that prevents deterioration in purification performance.
本発明者等は、上記目的に沿って優れた浄化特性を発揮することのできる排ガス浄化触媒について、鋭意、研究を重ねた。その結果、担体を、前駆体塩のカルボン酸錯体重合物を焼成することにより作製したものとするとともに、被担持体を、希土類元素から選ばれた少なくとも１種と、原子番号がＭｎよりも大きな第一遷移元素（３ｄ遷移元素）から選ばれた少なくとも１種（Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｎ）とを複合化させて作製したＰｄ系複合酸化物とすることにより、高温（９８０℃以上）雰囲気に長時間曝露された後にも、被担持体中のＰｄについて、Ｐｄ２＋状態からの還元を抑制することができ、その結果、浄化性能の劣化を防止することができるとの知見を得た。このような知見の具体的根拠は、以下のとおりである。 The inventors of the present invention have earnestly researched an exhaust gas purification catalyst that can exhibit excellent purification characteristics in accordance with the above-mentioned purpose. As a result, the carrier is prepared by firing a carboxylic acid complex polymer of a precursor salt, and the supported body is at least one selected from rare earth elements, and the atomic number is larger than Mn. By using a Pd-based composite oxide prepared by combining at least one selected from the first transition element (3d transition element) (Fe, Co, Ni, Cu, Zn), a high temperature (980 ° C. or higher) ) After being exposed to the atmosphere for a long time, the knowledge that Pd in the supported body can be reduced from the Pd 2+ state and as a result, the purification performance can be prevented from deteriorating. It was. The specific grounds for such findings are as follows.
排ガス浄化触媒の担体を作製する際に、カルボン酸を含む硝酸塩水溶液を蒸発乾固させて、中間生成物としてカルボン酸錯体重合物を得る製造工程を採用した場合には、担体（例えば、ＬａＡｌＯ３）が単相で生成する。また、上記中間生成物を経た製造工程を採用することにより、担体（例えば、ＬａＡｌＯ３）にＰｄ系複合酸化物を担持した場合には、担体の表面状態が、Ｐｄ系複合酸化物と相互作用し易い形態となる。以上の理由により、前駆体塩のカルボン酸錯体重合物を焼成して得た担体にＰｄ系複合酸化物を担持した触媒においては、優れた低温活性が得られる。 When the production process of obtaining a carboxylic acid complex polymer as an intermediate product by evaporating and drying an aqueous solution of nitrate containing carboxylic acid when producing a carrier for an exhaust gas purification catalyst, a carrier (for example, LaAlO 3 ) Is produced in a single phase. In addition, by adopting the production process through the intermediate product, when a Pd-based composite oxide is supported on a support (for example, LaAlO 3 ), the surface state of the support interacts with the Pd-based composite oxide. It becomes a form easy to do. For these reasons, excellent low-temperature activity is obtained in a catalyst in which a Pd-based composite oxide is supported on a carrier obtained by firing a carboxylic acid complex polymer of a precursor salt.
また、上記のように得られた担体（例えば、ＬａＡｌＯ３）上にＰｄ系複合酸化物を担持するにあたり、Ｐｄ系複合酸化物に、原子番号がＭｎより大きな第一遷移元素（Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｎ）を含有させた場合には、得られた排ガス浄化触媒を高温（９８０℃以上）雰囲気に長時間曝露しても、Ｐｄ系複合酸化物中のＰｄがＰｄ２＋状態からＰｄ０状態への還元され難い。このため、被担持体に上記第一遷移元素を含む排ガス浄化触媒は、長時間の高温雰囲気曝露後にも高活性を維持することができる。 Further, when supporting the Pd-based composite oxide on the support obtained as described above (for example, LaAlO 3 ), the Pd-based composite oxide has a first transition element (Fe, Co, In the case where Ni, Cu, Zn) is contained, even if the obtained exhaust gas purification catalyst is exposed to a high temperature (980 ° C. or higher) atmosphere for a long time, Pd in the Pd-based composite oxide changes from the Pd 2+ state to Pd. It is difficult to reduce to the zero state. For this reason, the exhaust gas purifying catalyst containing the first transition element in the support can maintain high activity even after being exposed to a high-temperature atmosphere for a long time.
さらに、上記Ｐｄ系複合酸化物は、高温において酸化物が不安定なＰｄと、酸化物が非常に安定な希土類元素と、酸化物が安定である、原子番号がＭｎより大きな第一遷移元素（３ｄ遷移元素）とが酸素とともに複合化された化合物である。このため、このＰｄ系複合酸化物では、Ｐｄの酸化状態が安定化され、化合物表面でのＰｄの酸化状態は大部分でＰｄ２＋となり、排ガス浄化に好ましい状態になる。従って、これらの各種元素を組み合わせて得られた被担持体を備える排ガス浄化触媒は、優れた浄化性能を発揮することができる。本発明は、以上に示した具体的根拠に基づいてなされたものである。 Furthermore, the Pd-based composite oxide includes Pd, which has an unstable oxide at a high temperature, a rare earth element in which the oxide is very stable, and a first transition element having an atomic number larger than Mn, in which the oxide is stable. 3d transition element) and oxygen. Therefore, in this Pd-based composite oxide, the oxidation state of Pd is stabilized, and the oxidation state of Pd on the compound surface is mostly Pd 2+ , which is a favorable state for exhaust gas purification. Therefore, an exhaust gas purification catalyst including a supported body obtained by combining these various elements can exhibit excellent purification performance. The present invention has been made based on the specific grounds described above.
また、発明者等は、被担持体として、示性式がＬｎ２Ｐｄ（１−Ｘ）ＭｘＯ４（Ｌｎ：希土類元素、Ｍ：Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｎ）である酸化物や、示性式がＬｎ４Ｐｄ（１−Ｘ）ＭｘＯ７（Ｌｎ：希土類元素、Ｍ：Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｎ）である酸化物を用いることにより、高温（９００℃以上）雰囲気に長時間曝露された後にも、酸化物中のＰｄがＰｄ２＋状態からＰｄ０状態への還元され難く、その結果浄化性能の劣化を特に高いレベルで防止することができるとの知見も得た。 Further, inventors have as an object carrier, rational formula is Ln 2 Pd (1-X) MxO 4 (Ln: rare earth element, M: Fe, Co, Ni , Cu, Zn) in which oxide or, By using an oxide having a formula of Ln 4 Pd (1-X) MxO 7 (Ln: rare earth element, M: Fe, Co, Ni, Cu, Zn), it can be used in a high temperature (900 ° C. or higher) atmosphere. It was also found that Pd in the oxide is difficult to be reduced from the Pd 2+ state to the Pd 0 state even after being exposed to time, and as a result, the deterioration of the purification performance can be prevented at a particularly high level.
本発明の排ガス浄化触媒は、前駆体塩のカルボン酸錯体重合物を焼成することにより得たＬｎＡｌＯ ３ （Ｌｎ：希土類元素）からなる担体上に、希土類元素から選ばれた少なくとも１種と、原子番号がＭｎよりも大きな第一遷移元素から選ばれた少なくとも１種とを複合化させてなるＰｄ系複合酸化物を担持してなり、前記Ｐｄ系複合酸化物が、示性式がＬｎ ２ Ｐｄ （１−Ｘ） ＭｘＯ ４ （Ｌｎ：希土類元素、Ｍ：Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｎ）である酸化物及び示性式がＬｎ ４ Ｐｄ （１−Ｘ） ＭｘＯ ７ （Ｌｎ：希土類元素、Ｍ：Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｎ）である酸化物のうちの少なくとも１種を含有し、前記Ｌｎ ２ Ｐｄ （１−Ｘ） ＭｘＯ ４ 及び前記Ｌｎ ４ Ｐｄ （１−Ｘ） ＭｘＯ ７ において、Ｘの範囲が、０＜Ｘ＜０．１であることを特徴としている。
The exhaust gas purifying catalyst of the present invention comprises at least one selected from rare earth elements on a support made of LnAlO 3 (Ln: rare earth element) obtained by firing a carboxylic acid complex polymer of a precursor salt, and atoms. A Pd-based composite oxide obtained by compounding at least one selected from first transition elements having a number greater than Mn is supported, and the Pd-based composite oxide has a formula of Ln 2 Pd (1-X) MxO 4 (Ln: rare earth element, M: Fe, Co, Ni, Cu, Zn) and an oxide of Ln 4 Pd (1-X) MxO 7 (Ln: rare earth element, M: Fe, Co, Ni, Cu, and containing at least one of oxide is Zn), in the Ln 2 Pd (1-X) MxO 4 and the Ln 4 Pd (1-X) MxO 7 , X range is 0 <X <0 It is characterized in that it is 1.
さらに、発明者等は、担体がＡｌ酸化物である場合（例えば、示性式がＬｎＡｌＯ３（Ｌｎ：希土類元素））や、担体の結晶系が三方晶又は菱面体晶である場合には、担体の電気的不安定さが大きく、例えば、ＬａＡｌＯ３に隣接しているＰｄ系複合酸化物は、単独で存在するＰｄ系複合酸化物に比べ電気的な揺らぎが大きくなっていることに着目した。この結果、担持されているＰｄ系複合酸化物の表面においては、Ｐｄの酸化状態は大部分でＰｄ２＋となり、つまり排ガスの浄化に好ましい状態となって、高い低温活性が得られる。なお、このような担体を備える排ガス浄化触媒は、１０００℃程度の比較的高温な雰囲気に曝露された後でも、同様の浄化性能を維持することができる。以下の発明はこのような知見に鑑みてなされたものである。 Further, the inventors have described that when the support is an Al oxide (for example, the formula is LnAlO 3 (Ln: rare earth element)) or when the support crystal system is a trigonal or rhombohedral crystal, The electric instability of the carrier is large. For example, attention was paid to the fact that the Pd-based composite oxide adjacent to LaAlO 3 has a larger electrical fluctuation than the Pd-based composite oxide existing alone. . As a result, on the surface of the supported Pd-based composite oxide, the oxidation state of Pd is mostly Pd 2+ , that is, a favorable state for purification of exhaust gas, and high low-temperature activity is obtained. The exhaust gas purification catalyst provided with such a carrier can maintain the same purification performance even after being exposed to a relatively high temperature atmosphere of about 1000 ° C. The following invention has been made in view of such knowledge.
即ち、上述した排ガス浄化触媒においては、ＬｎＡｌＯ ３ が三方晶又は菱面体晶であることが極めて望ましい。
That is, in the exhaust gas purification catalyst described above, it is highly desirable that LnAlO 3 is a trigonal or rhombohedral crystal.
本発明の排ガス浄化触媒の最大の特徴は、高温において酸化物が不安定なＰｄと、酸化物が非常に安定な希土類元素と、酸化物が安定な、原子番号がＭｎより大きな第一遷移元素（３ｄ遷移元素）とを酸素とともに複合化して得たＰｄ系複合酸化物を、被担持体としている点である。このため、本発明の排ガス浄化触媒は、高温（９８０℃以上）雰囲気に長時間曝露された後にも、ＰｄＯの還元を抑制し、浄化性能の劣化を防止することができる。以下に、このような効果を含めた本発明の効果を、さらに詳細に説明する。 The most important features of the exhaust gas purification catalyst of the present invention are Pd, whose oxide is unstable at high temperature, a rare earth element whose oxide is very stable, and a first transition element whose atomic number is larger than Mn, where the oxide is stable. A Pd-based composite oxide obtained by combining (3d transition element) with oxygen is used as a supported body. For this reason, the exhaust gas purification catalyst of the present invention can suppress the reduction of PdO and prevent the deterioration of the purification performance even after being exposed to a high temperature (980 ° C. or higher) atmosphere for a long time. Below, the effect of this invention including such an effect is demonstrated in detail.
本発明の排ガス浄化触媒の担体としては、例えば、ＬｎＡｌＯ３（Ｌｎ：希土類元素）が挙げられるが、このＬｎＡｌＯ３は、結晶系が三方晶又は菱面体晶であること、及びペロブスカイト構造の複合酸化物のＢサイトがＡｌであることを特徴とするものである。ここで、三方晶とは、図１に示すように、理想的な単位格子からｃ軸方向に格子が変化し、さらにａ軸とｂ軸との間の角度が１２０°である結晶系である。つまり、この結晶系は、理想的な立方晶のペロブスカイト構造から大きく歪みを生じたものであり、構成原子間の電子の存在状態が極めて不安定なものである。また、菱面体晶とは、図２に示すように、三方晶を異なる基本軸で表現した結晶系であり、三方晶と構造自体は同じである。従って、菱面体晶においても、構成原子間の電子の存在状態は極めて不安定となっている。さらに、担体であるＬｎＡｌＯ３中のＡｌ−Ｏ間の結合は共有結合性が強いため、通常イオン結合性が強いペロブスカイト構造の複合酸化物の結晶中に、なんらかの電気的偏りが生じている。これらの効果により、示性式がＬｎＡｌＯ３であるペロブスカイト構造の複合酸化物は、排ガス浄化用触媒として周知のＬａＦｅＯ３等に比べ、電気的不安定さに富む。ＬｎＡｌＯ３のこのような性質により、ＬｎＡｌＯ３に隣接しているＰｄ系複合酸化物は、単独で存在するＰｄ系複合酸化物に比べ電気的な揺らぎが大きくなっている。この結果、担持されているＰｄ系複合酸化物の表面におけるＰｄの酸化状態は大部分でＰｄ２＋となる。Ｐｄ系複合酸化物の表面において、Ｐｄは、Ｐｄ２＋とＰｄ０（金属状態）との２種類の酸化状態をとるが、Ｐｄ２＋の方が排ガス浄化には高活性である。つまり、Ｐｄ系複合酸化物をＬｎＡｌＯ３に担持した本発明の触媒においては、Ｐｄ系複合酸化物の表面でのＰｄの酸化状態が大部分でＰｄ２＋となっており、高活性である。また、本発明の触媒は、このような理由から、１０００℃程度の高温雰囲気に長時間曝露された後でも、曝露前と同様に高い浄化性能を維持することができる。 Examples of the carrier for the exhaust gas purifying catalyst of the present invention include LnAlO 3 (Ln: rare earth element). The LnAlO 3 has a trigonal or rhombohedral crystal system and a complex oxidation of a perovskite structure. The B site of the product is Al. Here, the trigonal crystal is a crystal system in which the lattice changes from an ideal unit lattice in the c-axis direction and the angle between the a-axis and the b-axis is 120 °, as shown in FIG. . In other words, this crystal system is greatly distorted from an ideal cubic perovskite structure, and the existence state of electrons between constituent atoms is extremely unstable. Further, the rhombohedral crystal is a crystal system in which a trigonal crystal is expressed by different basic axes as shown in FIG. 2, and the structure itself is the same as that of the trigonal crystal. Therefore, even in rhombohedral crystals, the existence state of electrons between constituent atoms is extremely unstable. Furthermore, since the bond between Al—O in the carrier LnAlO 3 has a strong covalent bond, some electric bias is generated in the crystal of a complex oxide having a perovskite structure having a strong ionic bond. Due to these effects, a composite oxide having a perovskite structure whose formula is LnAlO 3 is rich in electrical instability compared to LaFeO 3 or the like well known as an exhaust gas purifying catalyst. Such properties of LnAlO 3, Pd-based composite oxide adjacent to LnAlO 3, the electrical fluctuation compared with the Pd-based composite oxide present alone is increased. As a result, the oxidation state of Pd on the surface of the supported Pd-based composite oxide is mostly Pd 2+ . On the surface of the Pd-based composite oxide, Pd takes two types of oxidation states, Pd 2+ and Pd 0 (metal state), and Pd 2+ is more active for exhaust gas purification. That is, in the catalyst of the present invention in which the Pd-based composite oxide is supported on LnAlO 3 , the oxidation state of Pd on the surface of the Pd-based composite oxide is mostly Pd 2+ and is highly active. Moreover, the catalyst of this invention can maintain the high purification | cleaning performance similarly to before exposure, even after being exposed to a 1000 degreeC high temperature atmosphere for a long time for such a reason.
次に、ＬｎＡｌＯ３上にＰｄ系複合酸化物を担持した本発明の触媒においては、被担持体に、原子番号がＭｎより大きな第一遷移元素（３ｄ遷移元素）を含有させることにより、高温雰囲気に長時間曝露した後でも、Ｐｄ系複合酸化物中のＰｄＯのＰｄ金属への還元を抑制することができる。この理由は以下のとおりである。即ち、Ｌａ等の希土類元素は酸化物の状態でその形状を様々に変化させることができる。例えば、Ｌａ２Ｏ３にＰｄを担持した触媒を高温雰囲気に曝露すると、ＰｄとＬａ２Ｏ３との接触部からＬａ２Ｏ３がＰｄ粒子上に移動し、Ｐｄ粒子がＬａ２Ｏ３に埋没した形状となり、さらには、Ｐｄ表面に微小なＬａ２Ｏ３が移動する現象がみられる（Zhang et al., J. Phys. Chem., Vol. 100, No. 2, P. 744-754, 1996 参照）。このような現象を考慮すると、本発明の排ガス浄化触媒中、被担持体であるＰｄ系複合酸化物においては、Ｌｎ４Ｐｄ（１−Ｘ）ＭｘＯ７（Ｌｎ：希土類元素、Ｍ：Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｎ）の表面に存在する希土類元素（例えばＬａ）が、上記文献のＬａと類似した効果を発揮することにより、Ｌａと、Ｐｄと、原子番号がＭｎより大きな第一遷移元素とが酸素とともに複合化され、Ｐｄ系複合酸化物のＰｄ金属への還元を抑制するものと推定される。このような効果により、本発明の排ガス浄化触媒においては、長時間の高温雰囲気への曝露後も高活性を維持することができる。
Next, in the catalyst of the present invention in which a Pd-based composite oxide is supported on LnAlO 3 , a high temperature atmosphere is obtained by allowing the supported material to contain a first transition element (3d transition element) having an atomic number larger than Mn. Even after being exposed to a long time, reduction of PdO in the Pd-based composite oxide to Pd metal can be suppressed. The reason for this is as follows. That is, the shape of a rare earth element such as La can be variously changed in an oxide state. For example, a catalyst supporting Pd on La 2 O 3 when exposed to high temperature atmosphere, La 2 O 3 from the contact portion between Pd and La 2 O 3 is moved on the Pd particles, the
また、本発明の排ガス浄化触媒の担体（例えば、ＬｎＡｌＯ３）を作製する際には、カルボン酸を含む硝酸塩水溶液を蒸発乾固させ作製した、カルボン酸錯体重合物を例えば８００℃で焼成することにより、ＬｎＡｌＯ３が単相の状態で生成する。ＬｎＡｌＯ３を通常の方法、例えば固相反応法等で作製した場合には、１７００℃で焼成しても単相のＬｎＡｌＯ３は得られない（希土類の科学、足立吟也著、化学同人、p.564）。即ち、カルボン酸を用いることで、低温で単相のＬｎＡｌＯ３を合成することが可能となり、担体の十分な比表面積が得られるとともに、担体表面を活性な状態で触媒として用いることができる。従って、本発明の態様により作製したＬｎＡｌＯ３にＰｄ系複合酸化物を担持した触媒は、十分な比表面積を有するとともに、ＬｎＡｌＯ３とＰｄ系複合酸化物との間に強力な相互作用が得られるため、低温において高活性が実現される。 Further, when preparing the exhaust gas purifying catalyst carrier of the present invention (for example, LnAlO 3 ), the carboxylic acid complex polymer prepared by evaporating and drying a nitrate aqueous solution containing carboxylic acid is calcined at 800 ° C., for example. Thus, LnAlO 3 is produced in a single phase state. When LnAlO 3 is produced by a normal method such as a solid phase reaction method, a single-phase LnAlO 3 cannot be obtained even by firing at 1700 ° C. (Science of rare earths, written by Adachi Ginya, Chemical Dojin, p. .564). That is, by using a carboxylic acid, it is possible to synthesize single-phase LnAlO 3 at a low temperature, a sufficient specific surface area of the support can be obtained, and the support surface can be used as a catalyst in an active state. Therefore, the catalyst in which the Pd-based composite oxide is supported on the LnAlO 3 produced according to the embodiment of the present invention has a sufficient specific surface area and can provide a strong interaction between the LnAlO 3 and the Pd-based composite oxide. Therefore, high activity is realized at low temperatures.
さらに、本発明の触媒において被担持体として用いられるＰｄ系複合酸化物は、酸化物が不安定なＰｄと、酸化物が非常に安定である希土類元素と、酸化物が安定な原子番号がＭｎより大きな第一遷移元素（３ｄ元素）とが酸素とともに複合化された化合物である。Ｐｄの代表的な酸化物であるＰｄＯの表面においては、ＰｄはＰｄ０とＰｄ２＋との２種類の酸化状態をとり得る。しかしながら、Ｐｄ系複合酸化物では、希土穎元素により酸化状態が安定化された結果、化合物の表面でのＰｄの酸化状態はＰｄ２＋の割合が多くなる。Ｐｄ０とＰｄ２＋とでは、Ｐｄ２＋の方が高活性であるため、Ｐｄ系複合酸化物では、優れた浄化性能が実現される。 Furthermore, the Pd-based composite oxide used as the support in the catalyst of the present invention includes Pd where the oxide is unstable, a rare earth element where the oxide is very stable, and an atomic number where the oxide is stable is Mn. A compound in which a larger first transition element (3d element) is combined with oxygen. On the surface of PdO which is a typical oxide of Pd, Pd can take two kinds of oxidation states of Pd 0 and Pd 2+ . However, in the Pd-based composite oxide, the oxidation state is stabilized by the rare earth element, and as a result, the oxidation state of Pd on the surface of the compound increases the ratio of Pd 2+ . In Pd 0 and Pd 2+ , Pd 2+ is more active, and therefore, an excellent purification performance is realized with the Pd-based composite oxide.
図３（ａ）〜（ｃ）は、担体上に担持された各種酸化物の還元状況を示す概念図である。即ち、図３（ａ）に示すように、被担持体としてＰｄＯを使用した場合には、ＰｄＯの分解温度が８００℃程度であるため、１０００℃程度の条件下では、ＰｄＯはＰｄに還元されてしまい、排ガス浄化触媒として優れた性能を発揮することができない。これに対し、図３（ｂ）に示すように、被担持体としてＬａ２ＰｄＯ４を使用した場合には、Ｌａ２ＰｄＯ４は１１００℃においても酸化物の状態で安定して存在することができるため、１０００℃程度の条件下では、Ｐｄの還元は生じず、排ガス浄化触媒として優れた性能を発揮することができる。さらに、図３（ｃ）に示すように、酸化物の構成元素として、Ｐｄの他に、原子番号がＭｎよりも大きな第一遷移元素（Ｆｅ，Ｃｏ，Ｎｉ，Ｃｕ，Ｚｎ）をＰｄ系複合酸化物を用いた場合（図３（ｃ）ではＬａ２Ｐｄ０．９５Ｆｅ０．０５Ｏ４）には、第一遷移元素と酸素との結合が強力なため、Ｐｄ系複合酸化物の構造破壊やＰｄのモビリティーが低下し、Ｐｄ系複合酸化物粒子同士の凝集が抑制される。このため、高温雰囲気に長時間曝露された後でも、各元素が所定の位置に留まることができ、耐久性のみならず、耐熱性をも向上させることができる。この耐熱性の向上は、高温において酸化物の形態が安定でないＰｄが酸化物が安定である希土類元素又は上記第一遷移元素（３ｄ遷移元素）と複合化することに伴い、バルク内の結合が強化しために生ずるものである。 FIGS. 3A to 3C are conceptual diagrams showing the reduction status of various oxides supported on the support. That is, as shown in FIG. 3 (a), when PdO is used as the support, the decomposition temperature of PdO is about 800 ° C., so that PdO is reduced to Pd under conditions of about 1000 ° C. As a result, excellent performance as an exhaust gas purification catalyst cannot be exhibited. In contrast, as shown in FIG. 3B, when La 2 PdO 4 is used as the support, La 2 PdO 4 may exist stably in an oxide state even at 1100 ° C. Therefore, under the condition of about 1000 ° C., reduction of Pd does not occur, and excellent performance as an exhaust gas purification catalyst can be exhibited. Further, as shown in FIG. 3C, as a constituent element of the oxide, in addition to Pd, a first transition element (Fe, Co, Ni, Cu, Zn) having an atomic number larger than Mn is used as a Pd-based composite. When an oxide is used (La 2 Pd 0.95 Fe 0.05 O 4 in FIG. 3C), the bond between the first transition element and oxygen is strong, so the structure of the Pd-based composite oxide Destruction and mobility of Pd are reduced, and aggregation of Pd-based composite oxide particles is suppressed. For this reason, even after being exposed to a high temperature atmosphere for a long time, each element can remain in a predetermined position, and not only durability but also heat resistance can be improved. This improvement in heat resistance is due to the fact that Pd, whose oxide form is not stable at a high temperature, is combined with the rare earth element or the first transition element (3d transition element) in which the oxide is stable, and bonds in the bulk are reduced. It is for strengthening.
以下、本発明を実施例により、さらに詳細に説明する。
（発明例１）
＜担体用複合酸化物の作製＞
所定量の硝酸ランタン六水和物、及び硝酸アルミニウム九水和物をイオン交換水に溶解させ、混合水溶液を作製した。また、所定量のリンゴ酸をイオン交換水に溶解させ、リンゴ酸水溶液を作製した。次いで、これら２種類の水溶液を混合し、ホットプレートスターラに載せ、２５０℃で撹拝子を用いて撹拝しながら加熱し、水分を蒸発した後、分解乾固させ、乾固物を乳鉢で粉砕した。
Hereinafter, the present invention will be described in more detail with reference to examples.
(Invention Example 1)
<Preparation of complex oxide for carrier>
A predetermined amount of lanthanum nitrate hexahydrate and aluminum nitrate nonahydrate were dissolved in ion-exchanged water to prepare a mixed aqueous solution. A predetermined amount of malic acid was dissolved in ion-exchanged water to prepare an aqueous malic acid solution. Next, these two kinds of aqueous solutions are mixed, placed on a hot plate stirrer, heated while being stirred with a stirring element at 250 ° C., and after evaporating the water, it is decomposed and dried, and the dried product is dried in a mortar. Crushed.
さらに、粉砕物をアルミナ坩堝に移し、マッフル炉にて、２．５℃／ｍｉｎで３５０℃まで昇温し、３５０℃で３時間の熱処理を施した。これにより、リンゴ酸塩、硝酸根を除去した仮焼成体を作製した。この仮焼成体を乳鉢で１５分間粉砕混合した後、再びアルミナ坩堝に入れ、マッフル炉にて、５℃／ｍｉｎで８００℃まで昇温し、８００℃で１０時間の熱処理を施した。これにより、示性式がＬａＡｌＯ３の複合酸化物の粉末を得た。 Furthermore, the pulverized product was transferred to an alumina crucible, heated to 350 ° C. at 2.5 ° C./min in a muffle furnace, and subjected to heat treatment at 350 ° C. for 3 hours. Thereby, the temporary calcination body which removed malate and a nitrate radical was produced. The calcined body was pulverized and mixed for 15 minutes in a mortar, then placed in an alumina crucible again, heated to 800 ° C. at 5 ° C./min in a muffle furnace, and subjected to heat treatment at 800 ° C. for 10 hours. As a result, a composite oxide powder having the characteristic formula of LaAlO 3 was obtained.
＜Ｐｄ系複合酸化物の担持＞
所定量の硝酸パラジウム二水和物、硝酸ランタン六水和物及び硝酸鉄九水和物をイオン交換水に溶解させ、金属塩混合水溶液を作製した。また、所定量のリンゴ酸をイオン交換水に溶解させ、リンゴ酸水溶液を作製した。次いで、これら２種類の水溶液を混合したものと、上記したように得た所定量のＬａＡｌＯ３粉末とをナス型フラスコに入れ、ナス型フラスコをロータリーエバポレータで減圧しながら、６０℃の湯浴中で蒸発乾固させ、マッフル炉にて、２．５℃／ｍｉｎで２５０℃まで昇温し、さらに５℃／ｍｉｎで７５０℃まで昇温し、７５０℃で３時間保持した。これにより、Ｌａ２Ｐｄ０．９５Ｆｅ０．０５Ｏ３をＬａＡｌＯ３に含浸担持した、Ｌａ２Ｐｄ０．９５Ｆｅ０．０５Ｏ４／ＬａＡｌＯ３なる触媒粉末（発明例１）を得た。
<Supporting Pd-based composite oxide>
Predetermined amounts of palladium nitrate dihydrate, lanthanum nitrate hexahydrate, and iron nitrate nonahydrate were dissolved in ion-exchanged water to prepare a mixed metal salt aqueous solution. A predetermined amount of malic acid was dissolved in ion-exchanged water to prepare an aqueous malic acid solution. Next, a mixture of these two types of aqueous solutions and a predetermined amount of LaAlO 3 powder obtained as described above are placed in an eggplant-shaped flask, and the eggplant-shaped flask is decompressed with a rotary evaporator in a 60 ° C. hot water bath. The mixture was evaporated to dryness in a muffle furnace, heated to 250 ° C. at 2.5 ° C./min, further raised to 750 ° C. at 5 ° C./min, and held at 750 ° C. for 3 hours. Thus, to impregnation the La 2 Pd 0.95 Fe 0.05 O 3 in LaAlO 3, to obtain a La 2 Pd 0.95 Fe 0.05 O 4 / LaAlO 3 comprising catalyst powder (Invention Example 1).
（発明例２）
発明例１と同様の方法により、Ｌａ２Ｐｄ０．９５Ｃｏ０．０５Ｏ４／ＬａＡｌＯ３なる触媒粉末（発明例２）を得た。なお、本例では、発明例１で使用した硝酸鉄九水和物に替えて、硝酸コバルト九水和物を使用した。
(Invention Example 2)
A catalyst powder (Invention Example 2) of La 2 Pd 0.95 Co 0.05 O 4 / LaAlO 3 was obtained in the same manner as in Invention Example 1. In this example, cobalt nitrate nonahydrate was used in place of the iron nitrate nonahydrate used in Invention Example 1.
（発明例３）
発明例１と同様の方法により、Ｌａ２Ｐｄ０．９５Ｎｉ０．０５Ｏ４／ＬａＡｌＯ３なる触媒粉末（発明例３）を得た。なお、本例では、発明例１で使用した硝酸鉄九水和物に替えて、硝酸ニッケル九水和物を使用した。
(Invention Example 3)
In the same manner as in Invention Example 1, a catalyst powder (Invention Example 3) of La 2 Pd 0.95 Ni 0.05 O 4 / LaAlO 3 was obtained. In this example, nickel nitrate nonahydrate was used in place of the iron nitrate nonahydrate used in Invention Example 1.
（比較例１）
発明例１と同様の方法により、Ｐｄ／Ａｌ２Ｏ３なる触媒粉末（比較例１）を得た。
(Comparative Example 1)
A catalyst powder (Comparative Example 1) of Pd / Al 2 O 3 was obtained in the same manner as in Invention Example 1.
（比較例２）
発明例１と同様の方法により、Ｐｄ／ＬａＡｌＯ３なる触媒粉末（比較例２）を得た。
(Comparative Example 2)
A catalyst powder (Comparative Example 2) of Pd / LaAlO 3 was obtained in the same manner as in Invention Example 1.
（比較例３）
発明例１の被担持体であるＬａ２Ｐｄ０．９５Ｆｅ０．０５Ｏ４の製造方法と同様にして、Ｌａ４ＰｄＯ７なる触媒粉末（比較例３）を得た。
(Comparative Example 3)
A catalyst powder (Comparative Example 3) of La 4 PdO 7 was obtained in the same manner as in the production method of La 2 Pd 0.95 Fe 0.05 O 4 which is the support of Invention Example 1.
＜活性評価１：被担持体に第一遷移元素を含有させたことによる浄化性能＞
上記のように得られた各排ガス浄化触媒（発明例１〜３及び比較例１〜３）に対して、初期及び耐久処理後の活性評価を実施した。初期の活性評価は、空燃比が１４．６相当のモデル排ガスを０．５秒周期で繰り返し（周期１Ｈｚ）各触媒に流通させ、単位時間及び単位体積あたりの流量を５００００ｈ−１相当として反応温度３０〜４００℃の間で行った。耐久処理は、９８０℃×２０時間の時効処理とした。このような条件の下で、耐久処理後の評価を行った。表１に昇温試験条件を示すとともに、各活性評価の結果を表２，３に示す。即ち、表２には、初期触媒の昇温試験における、ＣＯ、ＨＣ、ＮＯの５０％浄化温度を示す。また、表３には、耐久処理後の触媒の昇温試験における、ＣＯ、ＨＣ、ＮＯの５０％浄化温度を示す。
<Activity evaluation 1: Purification performance by containing the first transition element in the support>
For each exhaust gas purification catalyst (Invention Examples 1 to 3 and Comparative Examples 1 to 3) obtained as described above, the activity evaluation after the initial treatment and the durability treatment was performed. In the initial activity evaluation, model exhaust gas having an air-fuel ratio of 14.6 is repeatedly passed through each catalyst in a cycle of 0.5 seconds (cycle: 1 Hz), and the reaction temperature is set such that the flow rate per unit time and unit volume is equivalent to 50000h- 1. It carried out between 30-400 degreeC. The durability treatment was an aging treatment at 980 ° C. × 20 hours. Under such conditions, the evaluation after the durability treatment was performed. Table 1 shows the temperature rise test conditions, and Tables 2 and 3 show the results of each activity evaluation. That is, Table 2 shows 50% purification temperatures of CO, HC, and NO in the initial catalyst temperature increase test. Table 3 shows the 50% purification temperature of CO, HC, NO in the temperature rise test of the catalyst after the endurance treatment.
表２，３によれば、本発明の範囲内にある発明例１〜３は、初期及び耐久処理後のいずれにおいても、ＣＯ、ＨＣ、ＮＯの５０％浄化温度が比較的低いことが判る。これに対し、本発明の範囲外にある比較例１〜３は、初期及び耐久処理後のいずれにおいても、ＣＯ、ＨＣ、ＮＯの５０％浄化温度が比較的高いことが判る。 According to Tables 2 and 3, it can be seen that Invention Examples 1 to 3 within the scope of the present invention have relatively low CO, HC and NO 50% purification temperatures both in the initial stage and after the endurance treatment. On the other hand, it can be seen that Comparative Examples 1 to 3 outside the scope of the present invention have a relatively high 50% purification temperature for CO, HC and NO both in the initial stage and after the endurance treatment.
このように、各発明例は、各比較例に比して、優れたＣＯ、ＨＣ、ＮＯの５０％浄化温度を示すが、この結果を裏付けるため、Ｐｄ系複合酸化物のＢサイトの組成が発明例１〜３の各被担持体と同じ複合酸化物（ＬａｘＰｄ０．９５Ｆｅ０．０５Ｏｙ、ＬａｘＰｄ０．９５Ｃｏ０．０５Ｏｙ、及びＬａｘＰｄ０．９５Ｎｉ０．０５Ｏｙ）が単相で生成していることを以下に確認し、これにより、被担持体に十分な比表面積が得られているとともに、その表面を活性な状態で触媒として用いることができることを実証する。即ち、図４は、Ｐｄ系複合酸化物のＢサイトの組成が発明例１〜３の各被担持体と同じ複合酸化物（ＬａｘＰｄ０．９５Ｆｅ０．０５Ｏｙ、ＬａｘＰｄ０．９５Ｃｏ０．０５Ｏｙ、及びＬａｘＰｄ０．９５Ｎｉ０．０５Ｏｙ）と、Ｂサイトに第一遷移元素を含まない複合酸化物（ＬａｘＰｄＯｙ）とについて、ＸＲＤスペクトルを測定した結果を示すグラフである。図４によれば、Ｂサイトに第一遷移元素を含まない複合酸化物（ＬａｘＰｄＯｙ）のＸＲＤスペクトルと同様に、各複合酸化物（ＬａｘＰｄ０．９５Ｆｅ０．０５Ｏｙ、ＬａｘＰｄ０．９５Ｃｏ０．０５Ｏｙ、及びＬａｘＰｄ０．９５Ｎｉ０．０５Ｏｙ）のＸＲＤスペクトルには、原料を硝酸鉄九水和物、硝酸コバルト九水和物、又は硝酸ニッケル九水和物とした場合に通常の焼成過程で生成する、Ｆｅ２Ｏ３、Ｃｏ２Ｏ３、ＮｉＯのピークがそれぞれみられない。このため、各複合酸化物中においては、Ｆｅ、Ｃｏ、Ｎｉがそれぞれ完全にＬａｘＰｄＯｙ内に固溶しているものと判断できる。従って、各複合酸化物（ＬａｘＰｄ０．９５Ｆｅ０．０５Ｏｙ、ＬａｘＰｄ０．９５Ｃｏ０．０５Ｏｙ、及びＬａｘＰｄ０．９５Ｎｉ０．０５Ｏｙ）は、全て単相の状態で生成されており、このため、被担持体に十分な比表面積が得られるとともに、その表面を活性な状態で触媒として用いることができる。従って、以上のような裏付けにより、上記各発明例１〜３の排ガス浄化触媒は、優れた浄化性能を示すものであるといえる。
As described above, each of the inventive examples shows an excellent 50% purification temperature for CO, HC and NO as compared with each comparative example. In order to support this result, the composition of the B site of the Pd-based composite oxide is The same composite oxide (LaxPd 0.95 Fe 0.05 Oy, LaxPd 0.95 Co 0.05 Oy, and LaxPd 0.95 Ni 0.05 Oy) as each supported body of Invention Examples 1 to 3 is a single phase. In the following, it is confirmed that a sufficient specific surface area is obtained in the supported body, and that the surface can be used as a catalyst in an active state. That is, FIG. 4, Pd-based same composite oxide with each of the carrier composition of the B site of the complex oxide is invention examples 1~3 (LaxPd 0.95 Fe 0.05 Oy, LaxPd 0.95 Co 0. 05 Oy, and the LaxPd 0.95 Ni 0.05 Oy), B site of the complex oxide without the first transition element for the (LaxPdOy), is a graph showing the result of measuring the XRD spectrum. According to FIG. 4, each composite oxide (LaxPd 0.95 Fe 0.05 Oy, LaxPd 0.95 Co 0 ) is similar to the XRD spectrum of the composite oxide (LaxPdOy) not containing the first transition element at the B site. .05 Oy, and LaxPd 0.95 Ni 0.05 Oy), the XRD spectrum shows that when the raw material is iron nitrate nonahydrate, cobalt nitrate nonahydrate, or nickel nitrate nonahydrate The peaks of Fe 2 O 3 , Co 2 O 3 , and NiO generated in the firing process are not observed. For this reason, it can be determined that Fe, Co, and Ni are completely dissolved in LaxPdOy in each composite oxide. Accordingly, each of the composite oxides (LaxPd 0.95 Fe 0.05 Oy, LaxPd 0.95 Co 0.05 Oy, and LaxPd 0.95 Ni 0.05 Oy) are all produced in a single phase state. For this reason, a sufficient specific surface area can be obtained for the support, and the surface can be used as a catalyst in an active state. Therefore, it can be said that the exhaust gas purifying catalysts of the above invention examples 1 to 3 show excellent purifying performance due to the above support.
＜活性評価２：被担持体中の第一遷移元素の含有量の違いによる浄化性能＞
次に、本発明の排ガス浄化触媒の構成要素である被担持体に含有される、原子番号がＭｎよりも大きな第一遷移元素の含有量好適範囲について調査した。担体をＬａＡｌＯ３とするとともに、被担持体をＬａとＰｄ複合酸化物と上記第一遷移元素（Ｎｉ）とを組み合わせたＬａ４Ｐｄ０．９５Ｎｉ０．０５Ｏ７及びＬａ４Ｐｄ０．８０Ｎｉ０．２０Ｏ７として、上記発明例１と同様の方法で、排ガス浄化触媒Ｌａ４Ｐｄ０．９５Ｎｉ０．０５Ｏ７／ＬａＡｌＯ３及びＬａ４Ｐｄ０．８０Ｎｉ０．２０Ｏ７／ＬａＡｌＯ３をそれぞれ得た。図５に、これらの浄化触媒についての、ＮＯｘの５０％浄化温度と測定回数との関係を示す。なお、本例では、各測定の間にテストピースを常温まで冷まし、次の測定を行った。
<Activity evaluation 2: Purification performance by the difference in the content of the first transition element in the support>
Next, the preferred range of the content of the first transition element having an atomic number larger than Mn contained in the supported body that is a constituent element of the exhaust gas purification catalyst of the present invention was investigated. La 4 Pd 0.95 Ni 0.05 O 7 and La 4 Pd 0.80 in which the carrier is LaAlO 3 and the supported body is a combination of La, Pd composite oxide and the first transition element (Ni). As Ni 0.20 O 7 , exhaust gas purification catalysts La 4 Pd 0.95 Ni 0.05 O 7 / LaAlO 3 and La 4 Pd 0.80 Ni 0.20 O 7 / LaAlO 3 was obtained respectively. FIG. 5 shows the relationship between the NOx 50% purification temperature and the number of measurements for these purification catalysts. In this example, the test piece was cooled to room temperature during each measurement, and the following measurement was performed.
図５によれば、被担持体Ｌａ４Ｐｄ（１−Ｘ）ＮｉｘＯ７において、Ｘ≧０．１の場合には、測定回数の増加に伴い、浄化性能が低下するが、Ｘ＜０．１の場合には、測定回数のいかんに関わらず、優れた浄化性能を示すことが判る。従って、本発明の排ガス浄化触媒の被担持体に、示性式Ｌａ４Ｐｄ（１−Ｘ）ＮｉｘＯ７なる酸化物を使用する場合には、上記Ｘの範囲は０＜Ｘ＜０．１であることがより好適であることが実証された。なお、浄化性能に悪影響を及ぼすと考えられるＬａＮｉＯ３がＸＲＤ測定において完全に確認できないという理由により、極めて好ましいＸの範囲は、０＜Ｘ＜０．０８３である。 According to FIG. 5, in the support La 4 Pd (1-X) NixO 7 , when X ≧ 0.1, the purification performance decreases as the number of measurements increases, but X <0.1. In this case, it can be seen that excellent purification performance is exhibited regardless of the number of measurements. Therefore, when an oxide of the formula La 4 Pd (1-X) Ni x O 7 is used for the support of the exhaust gas purification catalyst of the present invention, the range of X is 0 <X <0.1. It proved to be more suitable. In addition, because LaNiO 3 which is considered to have an adverse effect on the purification performance cannot be completely confirmed in the XRD measurement, the extremely preferable range of X is 0 <X <0.083.
本発明の排ガス浄化触媒は、近年、排ガス中の窒素酸化物（ＮＯｘ）、炭化水素（ＨＣ）及び一酸化炭素（ＣＯ）を同時に効率よく浄化、低減させることが要求される、自動車等の内燃機関に適用することができる。 The exhaust gas purifying catalyst of the present invention is an internal combustion engine such as an automobile that is required to efficiently purify and reduce nitrogen oxide (NOx), hydrocarbon (HC) and carbon monoxide (CO) in exhaust gas at the same time in recent years. Applicable to institutions.
Claims (2)
前記Ｌｎ ２ Ｐｄ （１−Ｘ） ＭｘＯ ４ 及び前記Ｌｎ ４ Ｐｄ （１−Ｘ） ＭｘＯ ７ において、Ｘの範囲が、０＜Ｘ＜０．１であることを特徴とする排ガス浄化触媒。 On the support made of LnAlO 3 (Ln: rare earth element) obtained by firing the carboxylic acid complex polymer of the precursor salt, at least one selected from rare earth elements and the first having an atomic number larger than Mn and at least one selected from the transition elements consisting by composite Pd-based composite oxide Ri name carries, the Pd-based composite oxide, rational formula is Ln 2 Pd (1-X) MxO 4 (Ln: rare earth element, M: Fe, Co, Ni, Cu, Zn) and an oxide of Ln 4 Pd (1-X) MxO 7 (Ln: rare earth element, M: Fe, Co, Ni) , Cu, Zn) containing at least one of oxides that are
The exhaust gas purifying catalyst, wherein in the Ln 2 Pd (1-X) MxO 4 and the Ln 4 Pd (1-X) MxO 7 , the range of X is 0 <X <0.1 .
The exhaust gas purifying catalyst according to claim 1 , wherein the LnAlO 3 (Ln: rare earth element) is a trigonal or rhombohedral crystal.
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