JP2006051431A - Ternary catalyst for exhaust gas purification, and its production method - Google Patents
Ternary catalyst for exhaust gas purification, and its production method Download PDFInfo
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Abstract
Description
本発明は排気ガス浄化用三元触媒及びその製造方法に関し、より詳しくは、排気ガス浄化性能が高く、低温活性が高く、耐熱性に優れている排気ガス浄化用三元触媒、例えば、自動車等の内燃機関から排出される排気ガスに含まれる有害成分を浄化する排気ガス浄化用三元触媒及びその製造方法に関する。 The present invention relates to a three-way catalyst for purifying exhaust gas and a method for producing the same, and more particularly, a three-way catalyst for purifying exhaust gas having high exhaust gas purification performance, high low-temperature activity, and excellent heat resistance, such as an automobile. The present invention relates to an exhaust gas purifying three-way catalyst for purifying harmful components contained in exhaust gas discharged from an internal combustion engine and a method for producing the same.
自動車等の内燃機関から排出される排気ガス中には、炭化水素（ＨＣ）、一酸化炭素（ＣＯ）、窒素酸化物（ＮＯx）等の有害成分が含まれている。それで、従来から、これら有害成分を浄化して無害化する三元触媒が用いられている。 Exhaust gas discharged from an internal combustion engine such as an automobile contains harmful components such as hydrocarbon (HC), carbon monoxide (CO), and nitrogen oxide (NO x ). Therefore, conventionally, a three-way catalyst for purifying and detoxifying these harmful components has been used.
このような排気ガス浄化用三元触媒は、例えば、触媒主成分の貴金属と、空燃比Ａ／Ｆのウィンドを調節する助触媒（ＯＳＣ剤）のセリウム酸化物、ジルコニウム酸化物、ペロプスカイド構造の複合酸化物、Ｋ2ＮｉＦ4構造の複合酸化物、パイロクロア構造の複合酸化物等と、貴金属、助触媒を分散させて耐熱性を与えるアルミナ等の高比表面積助剤（担体）から構成されている。触媒の排気ガス浄化性能を向上させる方法として、貴金属の分散度を向上させる方法、高耐熱性担体（助剤）に担持させることにより貴金属のシンタリングを防止する方法、ＯＳＣ剤との共同作用により触媒機能を向上させる方法等を挙げることができる。 Such a three-way catalyst for exhaust gas purification is, for example, a composite of a precious metal as a main component of catalyst and a cerium oxide, zirconium oxide, and perovskite structure of an auxiliary catalyst (OSC agent) that adjusts the air / fuel ratio A / F window. It is composed of oxide, K 2 NiF 4 structure composite oxide, pyrochlore structure composite oxide, etc., and a high specific surface area assistant (support) such as alumina that disperses precious metals and promoters to give heat resistance. . As a method for improving the exhaust gas purification performance of the catalyst, a method for improving the dispersibility of the noble metal, a method for preventing sintering of the noble metal by supporting it on a high heat-resistant carrier (auxiliary), and a joint action with the OSC agent Examples thereof include a method for improving the catalyst function.
従来の自動車排気ガス浄化用三元触媒の製造においては、例えば、セラミックス又はメタル製のモノリス担体の表面に、貴金属成分以外の又は貴金属成分を含めた上記の触媒成分を含むスラリーをコーティングし、乾燥させ、焼成する工程を１〜３回繰り返して、１〜３層の触媒層を形成し、また、貴金属成分の担持方法としては、貴金属の硝酸塩、塩酸塩、テトラアンミン錯体の塩化物、水酸化物等の溶液を用いた吸着含浸、吸液担持、蒸着担持等により担持させる方法を用いている。しかし、このような担持方法では、貴金属の担持サイト（位置）、分散状態、貴金属の粒径等を制御することができない。また、貴金属成分は粒径が小さく、広く分散している程、触媒の排気ガス浄化性能がよいが、シンタリングに起因して寿命が短くなることが知られている。なお、貴金属成分の粒径が小さい排気ガス浄化用三元触媒は公知である（例えば、特許文献１参照。）。 In the production of a conventional three-way catalyst for purifying automobile exhaust gas, for example, a slurry containing the above catalyst component other than or including a noble metal component is coated on the surface of a ceramic or metal monolith support and dried. The step of firing is repeated 1 to 3 times to form 1 to 3 catalyst layers, and the noble metal component loading method includes noble metal nitrate, hydrochloride, chloride of tetraammine complex, hydroxide The method of carrying | supporting by the adsorption | suction impregnation using a solution, etc., liquid absorption carrying | support, vapor deposition carrying etc. is used. However, such a loading method cannot control the noble metal loading site (position), dispersion state, noble metal particle size, and the like. Further, it is known that the precious metal component has a smaller particle size and a wider dispersion, the better the exhaust gas purification performance of the catalyst, but the shorter the life due to sintering. In addition, the exhaust gas purification three-way catalyst having a small particle size of the noble metal component is known (for example, see Patent Document 1).
本発明は、上記のような事情に鑑み、排気ガス浄化性能が高く、低温活性が高く、耐熱安定性に優れていて貴金属のシンタリングを防止できる排気ガス浄化用三元触媒及びその製造方法を提供することを目的としている。 In view of the circumstances as described above, the present invention provides a three-way catalyst for purifying exhaust gas, which has high exhaust gas purification performance, high low-temperature activity, excellent heat resistance stability, and can prevent precious metal sintering, and a method for producing the same. It is intended to provide.
本発明者等は上記目的を達成するために鋭意検討した結果、超微細貴金属成分粒子を用い、その貴金属成分粒子を助触媒成分で被覆することにより上記目的が達成されることを見いだし、本発明を完成した。 As a result of intensive studies to achieve the above object, the present inventors have found that the above object can be achieved by using ultrafine noble metal component particles and coating the noble metal component particles with a promoter component. Was completed.
即ち、本発明の第一態様の排気ガス浄化用三元触媒は、粒径１〜２０ｎｍの貴金属成分粒子と該貴金属成分粒子を被覆している助触媒成分被膜とからなることを特徴とする。 That is, the three-way catalyst for purifying exhaust gas according to the first aspect of the present invention is characterized by comprising noble metal component particles having a particle diameter of 1 to 20 nm and a promoter component film covering the noble metal component particles.
また、本発明の第二態様の排気ガス浄化用三元触媒は、多孔質耐火性無機酸化物粉体と該粉体に担持されている上記の第一態様の排気ガス浄化用三元触媒とからなることを特徴とする。 The exhaust gas purifying three-way catalyst of the second aspect of the present invention is a porous refractory inorganic oxide powder and the exhaust gas purifying three-way catalyst of the first aspect supported on the powder. It is characterized by comprising.
本発明の第三態様の排気ガス浄化用三元触媒は、セラミックス又は金属材料からなる担体と、該担体上に担持されている上記第一態様又は第二態様の排気ガス浄化用三元触媒の層とからなり、該三元触媒の層が１層又は２層以上であることを特徴とする。 The three-way catalyst for exhaust gas purification according to the third aspect of the present invention comprises a carrier made of ceramics or a metal material, and the three-way catalyst for exhaust gas purification according to the first or second aspect supported on the carrier. The three-way catalyst layer is composed of one layer or two or more layers.
また、本発明の第四態様の排気ガス浄化用三元触媒は、セラミックス又は金属材料からなる担体と、該担体上に担持されている多孔質耐火性無機酸化物粉体及び助触媒成分からなる層と、該層上に担持されている上記第一態様又は第二態様の排気ガス浄化用三元触媒の層とからなり、該三元触媒の層が１層又は２層以上であることを特徴とする排気ガス浄化用三元触媒。 The exhaust gas purification three-way catalyst according to the fourth aspect of the present invention comprises a carrier made of a ceramic or metal material, a porous refractory inorganic oxide powder supported on the carrier, and a promoter component. And a layer of the three-way catalyst for purifying exhaust gas of the first aspect or the second aspect supported on the layer, and the layer of the three-way catalyst is one layer or two layers or more. A three-way catalyst for exhaust gas purification.
なお、本発明の排気ガス浄化用三元触媒は、上記の第三態様又は第四態様の排気ガス浄化用三元触媒において、三元触媒の層の少なくとも１層が多孔質耐火性無機酸化物粉体を追加含有していてもよい。 The exhaust gas purifying three-way catalyst of the present invention is the exhaust gas purifying three-way catalyst of the third or fourth aspect, wherein at least one of the three-way catalyst layers is a porous refractory inorganic oxide. An additional powder may be contained.
本発明の排気ガス浄化用三元触媒の製造方法は、助触媒成分のゾル溶液に貴金属成分の塩の水溶液及び貴金属錯体形成剤兼分散安定化剤として機能する界面活性剤を添加し、十分に攪拌して、分散媒中に、中心が粒径１〜２０ｎｍの貴金属錯体イオン粒子で、その周囲に助触媒成分のゾルの層が取り囲んでおり、その界面に該貴金属錯体形成剤兼分散安定化剤として機能する界面活性剤が存在している粒子が分散している安定なゾルを形成し、次いで乾燥させ、焼成することを特徴とする上記第一態様の排気ガス浄化用三元触媒の製造方法である。 The method for producing a three-way catalyst for exhaust gas purification according to the present invention comprises adding an aqueous solution of a salt of a noble metal component and a surfactant that functions as a noble metal complex forming agent and dispersion stabilizer to a sol solution of a promoter component, The mixture is stirred with a noble metal complex ion particle having a particle diameter of 1 to 20 nm in the dispersion medium, and a sol layer of a promoter component is surrounded by the noble metal complex forming agent and dispersion stabilization at the interface. Production of a three-way catalyst for exhaust gas purification according to the first aspect, wherein a stable sol in which particles having a surfactant functioning as an agent are dispersed is formed, then dried and calcined Is the method.
本発明の別の態様の排気ガス浄化用三元触媒の製造方法は、助触媒成分のゾル溶液に貴金属成分の塩の水溶液及び貴金属錯体形成剤兼分散安定化剤として機能する界面活性剤を添加し、十分に攪拌して、分散媒中に、中心が粒径１〜２０ｎｍの貴金属錯体イオン粒子で、その周囲に助触媒成分のゾルの層が取り囲んでおり、その界面に該貴金属錯体形成剤兼分散安定化剤として機能する界面活性剤が存在している粒子が分散している安定なゾルを形成し、次いで水を加えて減粘し、攪拌しながら多孔質耐火性無機酸化物粉体を加えて該粉体に吸液させ、次いで乾燥させ、焼成することを特徴とする上記第二態様の排気ガス浄化用三元触媒の製造方法である。 According to another aspect of the present invention, there is provided a method for producing a three-way catalyst for purifying exhaust gas, wherein an aqueous solution of a salt of a noble metal component and a surfactant that functions as a noble metal complex forming agent and dispersion stabilizer are added to a sol solution of a promoter component. The noble metal complex ion particles having a particle size of 1 to 20 nm in the center and surrounding the sol layer of the promoter component are surrounded by the noble metal complex forming agent at the interface. A porous refractory inorganic oxide powder is formed by forming a stable sol in which particles having a surfactant functioning as a dispersion stabilizer are dispersed, then adding water to reduce the viscosity, and stirring. Is added to the powder, followed by drying and calcination. The method for producing a three-way catalyst for purifying exhaust gas according to the second aspect.
本発明の排気ガス浄化用三元触媒は、排気ガス浄化性能が高く、低温活性が高く、耐熱安定性に優れていて貴金属のシンタリングを防止でき、自動車等の内燃機関から排出される排気ガスに含まれる有害成分を浄化するのに好適に用いることができる。 The exhaust gas purification three-way catalyst of the present invention has high exhaust gas purification performance, high low-temperature activity, excellent heat resistance stability, can prevent sintering of precious metals, and exhaust gas discharged from internal combustion engines such as automobiles It can be suitably used to purify harmful components contained in.
以下に、本発明の実施形態を具体的に説明する。
本発明の排気ガス浄化用三元触媒は、粒径１〜２０ｎｍ、好ましくは２〜１０ｎｍの貴金属成分粒子と該貴金属成分粒子を被覆している助触媒成分被膜とからなるものであっても、或いはこのような排気ガス浄化用三元触媒が多孔質耐火性無機酸化物粉体に担持されているものであってもよい。何れの場合にも、貴金属成分粒子が助触媒成分で被覆されていて貴金属成分が露出していないことが重要であり、このことにより貴金属のシンタリングが防止され、高い排気ガス浄化性能を安定に維持することができる。
Embodiments of the present invention will be specifically described below.
Even if the three-way catalyst for exhaust gas purification of the present invention comprises a noble metal component particle having a particle size of 1 to 20 nm, preferably 2 to 10 nm, and a promoter component film covering the noble metal component particle, Alternatively, such a three-way catalyst for purifying exhaust gas may be supported on a porous refractory inorganic oxide powder. In any case, it is important that the noble metal component particles are coated with the promoter component so that the noble metal component is not exposed. This prevents sintering of the noble metal and stabilizes the high exhaust gas purification performance. Can be maintained.
排気ガス浄化用三元触媒においては貴金属成分粒子は粒径が小さい程一般的には排気ガス浄化性能がよいが、反応性ガスの活性化、ガスの拡散、ＨＣの酸化、ＮＯxの還元等を考慮すると、本発明においては、貴金属成分粒子の粒径が１〜２０ｎｍであることが好ましく、２〜１０ｎｍ以下であることが一層好ましい。 In the three-way catalyst for exhaust gas purification, the smaller the particle size of the precious metal component particles, the better the exhaust gas purification performance, but reactive gas activation, gas diffusion, HC oxidation, NO x reduction, etc. In consideration of the above, in the present invention, the particle diameter of the noble metal component particles is preferably 1 to 20 nm, and more preferably 2 to 10 nm or less.
本発明の排気ガス浄化用三元触媒の貴金属成分は、従来の排気ガス浄化用三元触媒において貴金属成分として一般に用いられている如何なる貴金属成分であってもよいが、ロジウム、パラジウム、白金、ルテニウム、金、銀又はそれらの混合物であることが好ましい。また、本発明の排気ガス浄化用三元触媒の助触媒成分は、従来の排気ガス浄化用三元触媒において助触媒成分として一般に用いられている如何なる助触媒成分であってもよいが、希土類元素（例えば、ジルコニウム、セリウム、ネオジム、プラセオジム）の酸化物、酸化ジルコニウム、ペロブスカイト構造の複合酸化物、スピネル型構造の複合酸化物、Ｋ2ＮｉＦ4構造の複合酸化物、パイロクロア構造の複合酸化物又はそれらの混合物であることが好ましい。更に、本発明の排気ガス浄化用三元触媒で用いることのできる多孔質耐火性無機酸化物粉体は、従来の排気ガス浄化用三元触媒において多孔質耐火性無機酸化物粉体として一般に用いられている如何なる多孔質耐火性無機酸化物粉体であってもよいが、Ａｌ2Ｏ3、ＳｉＯ2、ＺｒＯ2、ＣｅＯ2、ＺｒＯ2−ＣｅＯ2複合酸化物、Ｌａ2Ｏ3−Ａｌ2Ｏ3複合酸化物、ＢａＯ−Ａｌ2Ｏ3複合酸化物、ＭｇＯ−Ａｌ2Ｏ3複合酸化物、Ｌａ2Ｏ3−Ｆｅ2Ｏ3複合酸化物、ＺｒＯ2−ＣｅＯ2−Ａｌ2Ｏ3複合酸化物又はそれらの混合物であることが好ましい。 The noble metal component of the exhaust gas purifying three-way catalyst of the present invention may be any noble metal component generally used as a noble metal component in the conventional exhaust gas purifying three-way catalyst, but rhodium, palladium, platinum, ruthenium. Gold, silver or a mixture thereof is preferable. The promoter component of the exhaust gas purifying three-way catalyst of the present invention may be any promoter component generally used as a promoter component in conventional exhaust gas purifying three-way catalysts. (For example, zirconium, cerium, neodymium, praseodymium) oxide, zirconium oxide, perovskite structure composite oxide, spinel structure composite oxide, K 2 NiF 4 structure composite oxide, pyrochlore structure composite oxide or A mixture thereof is preferred. Further, the porous refractory inorganic oxide powder that can be used in the exhaust gas purifying three-way catalyst of the present invention is generally used as the porous refractory inorganic oxide powder in the conventional exhaust gas purifying three-way catalyst. Any porous refractory inorganic oxide powder may be used, but Al 2 O 3 , SiO 2 , ZrO 2 , CeO 2 , ZrO 2 —CeO 2 composite oxide, La 2 O 3 —Al 2 O 3 composite oxide, BaO—Al 2 O 3 composite oxide, MgO—Al 2 O 3 composite oxide, La 2 O 3 —Fe 2 O 3 composite oxide, ZrO 2 —CeO 2 —Al 2 O 3 composite Preference is given to oxides or mixtures thereof.
実用的な本発明の排気ガス浄化用三元触媒においては、担体に担持された従来の排気ガス浄化用三元触媒と同様に、セラミックス又は金属材料からなる担体上に上記の排気ガス浄化用三元触媒の層が担持されており、該三元触媒の層が１層又は２層以上となっている。また、この担体と三元触媒の層との間に、多孔質耐火性無機酸化物粉体及び助触媒成分からなる層が存在していてもよい。更に、この三元触媒の層の少なくとも１層が多孔質耐火性無機酸化物粉体を追加含有していてもよい。 In the practical exhaust gas purifying three-way catalyst of the present invention, the exhaust gas purifying three-way catalyst is placed on a carrier made of ceramics or a metal material in the same manner as the conventional exhaust gas purifying three-way catalyst supported on a carrier. The layer of the original catalyst is supported, and the layer of the three-way catalyst is one layer or two layers or more. Further, a layer composed of porous refractory inorganic oxide powder and a promoter component may be present between the carrier and the three-way catalyst layer. Furthermore, at least one of the three-way catalyst layers may additionally contain a porous refractory inorganic oxide powder.
上記のような排気ガス浄化用三元触媒においては、セラミックス又は金属材料からなる担体の形状は、特に限定されるものではないが、一般的にはハニカム、板等のモノリス形状や、ペレットの形状であり、好ましくはハニカム形状である。また、このような担体の材質としては、例えば、アルミナ（Ａｌ2Ｏ3）、ムライト（３Ａｌ2Ｏ3−２ＳｉＯ2）、コージライト（２ＭｇＯ−２Ａｌ2Ｏ3−５ＳｉＯ2）等のセラミックスや、ステンレス等の金属材料が挙げられる。なお、コージライト材料は熱膨張係数が１.０×１０-6／℃と極めて低いので特に有効である。 In the above three-way catalyst for purifying exhaust gas, the shape of the carrier made of ceramics or a metal material is not particularly limited, but in general, the shape of a monolith such as a honeycomb or a plate, or the shape of a pellet Preferably, it has a honeycomb shape. Examples of the material of the carrier include ceramics such as alumina (Al 2 O 3 ), mullite (3Al 2 O 3 -2SiO 2 ), cordierite (2MgO-2Al 2 O 3 -5SiO 2 ), Examples thereof include metal materials such as stainless steel. Cordierite material is particularly effective because it has an extremely low coefficient of thermal expansion of 1.0 × 10 −6 / ° C.
本発明の排気ガス浄化用三元触媒の製造方法においては、例えば、解膠剤として硝酸を用いて１種又は２種以上の助触媒成分の５〜１５ｎｍ程度のコロイド粒子を含むゾルを形成し、このようなゾルを用いる。このようなゾル中に、貴金属成分の塩の水溶液、例えば貴金属成分の硝酸塩、塩化物、テトラアンミン水酸化物塩及び塩化物の少なくとも１種の貴金属塩の水溶液を添加し、貴金属錯体形成剤兼分散安定化剤として機能する界面活性剤を例えば１〜２０質量％添加し、十分に、例えば２０時間程度攪拌する。 In the method for producing an exhaust gas purification three-way catalyst of the present invention, for example, nitric acid is used as a peptizer to form a sol containing colloidal particles of about 5 to 15 nm of one or more promoter components. Such a sol is used. In such a sol, an aqueous solution of a salt of a noble metal component, for example, an aqueous solution of at least one noble metal salt of a nitrate, chloride, tetraammine hydroxide salt and chloride of a noble metal component is added and dispersed as a noble metal complex forming agent. For example, 1 to 20% by mass of a surfactant functioning as a stabilizer is added and sufficiently stirred, for example, for about 20 hours.
上記の貴金属錯体形成剤兼分散安定化剤として機能する界面活性剤として、分子量５００〜２０００の水溶性高級アルコール類、ポリエーテル類等のノニオン系界面活性剤、ポリカルボン酸アンモニウム塩類、縮合ナフタレンスルホン酸アンモニウム塩類、ポリアクリル酸アンモニウム塩類等のアニオン系界面活性剤、ジアンミン、トリアンミン系等の多価アンミン系界面活性剤等を挙げることができる。本発明においては分子量５００〜２０００の水溶性高級アルコール類、ポリエーテル類等のノニオン系界面活性剤を用いること好ましい。 Nonionic surfactants such as water-soluble higher alcohols having a molecular weight of 500 to 2000, polyethers, polycarboxylic acid ammonium salts, condensed naphthalene sulfones as surfactants that function as the above-mentioned noble metal complex forming agents and dispersion stabilizers Examples thereof include anionic surfactants such as acid ammonium salts and ammonium polyacrylates, and polyammine surfactants such as diammine and triammine. In the present invention, it is preferable to use nonionic surfactants such as water-soluble higher alcohols and polyethers having a molecular weight of 500 to 2,000.
この操作により、分散媒中に、中心が粒径１〜２０ｎｍ程度の貴金属錯体イオン粒子で、その周囲に助触媒成分のゾルの層が取り囲んでおり、その界面に該貴金属錯体形成剤兼分散安定化剤として機能する界面活性剤が存在している粒子が分散している安定なゾルが形成される。次いで、この安定なゾルを例えば７０〜１００℃程度で１０〜２０時間程度乾燥させる。この乾燥により、中心が粒径２〜２０ｎｍ程度の貴金属錯体イオン粒子で、その周囲に助触媒成分のゾルの層が取り囲んでおり、その界面に該貴金属錯体形成剤兼分散安定化剤として機能する界面活性剤が存在している粒子が形成される。次いで、この乾燥した粒子を例えば６００〜７００℃程度で３〜７時間程度焼成する。この焼成により、中心が粒径１〜２０ｎｍ程度の貴金属成分粒子で、その粒子を助触媒成分の層が取り囲んでいる粒子粉末、即ち、本発明の排気ガス浄化用三元触媒が形成される。 By this operation, the center of the dispersion medium is a noble metal complex ion particle having a particle size of about 1 to 20 nm, and a sol layer of a promoter component is surrounded by the noble metal complex ion particle. A stable sol is formed in which particles in which a surfactant that functions as an agent is present are dispersed. Next, the stable sol is dried at about 70 to 100 ° C. for about 10 to 20 hours. By this drying, the center is a noble metal complex ion particle having a particle diameter of about 2 to 20 nm, and a sol layer of a promoter component is surrounded around the noble metal complex ion particle, and functions as the noble metal complex forming agent and dispersion stabilizer at the interface. Particles in which a surfactant is present are formed. Next, the dried particles are fired at, for example, about 600 to 700 ° C. for about 3 to 7 hours. By this calcination, a particle powder whose center is a noble metal component particle having a particle diameter of about 1 to 20 nm and in which the layer of the promoter component surrounds, that is, the exhaust gas purification three-way catalyst of the present invention is formed.
本発明の別の態様の排気ガス浄化用三元触媒の製造方法においては、上記の製造方法と同様にして、分散媒中に、中心が粒径１〜２０ｎｍ程度の貴金属錯体イオン粒子で、その周囲に助触媒成分のゾルの層が取り囲んでおり、その界面に該貴金属錯体形成剤兼分散安定化剤として機能する界面活性剤が存在している粒子分散している安定なゾルを形成し、次いで水を加えて粘度を低下させ、攪拌しながら多孔質耐火性無機酸化物粉体を加えて該粉体に吸液させ、次いで上記の製造方法と同様にして、乾燥させ、焼成する。これにより、中心が粒径１〜２０ｎｍ程度の貴金属成分粒子で、その粒子を助触媒成分の層が取り囲んでいる粒子が多孔質耐火性無機酸化物粉体に担持されている本発明の排気ガス浄化用三元触媒が形成される。 In the method for producing a three-way catalyst for exhaust gas purification according to another aspect of the present invention, in the same manner as in the above production method, the dispersion medium is a noble metal complex ion particle having a particle size of about 1 to 20 nm. A co-catalyst component sol layer surrounds the surface, and a surfactant that functions as a noble metal complex forming agent and dispersion stabilizer is present at the interface to form a stable sol in which particles are dispersed, Next, water is added to lower the viscosity, and the porous refractory inorganic oxide powder is added to the powder while stirring to absorb the liquid, and then dried and fired in the same manner as in the above production method. Thus, the exhaust gas of the present invention, in which the center is a noble metal component particle having a particle diameter of about 1 to 20 nm and the particle surrounding the particle of the promoter component is supported on the porous refractory inorganic oxide powder. A three-way catalyst for purification is formed.
本発明の製造方法により得られる排気ガス浄化用三元触媒においては、貴金属粒子が１〜２０ｎｍ程度の非常に細かい微粒子として広く分散しているので、触媒の排気ガス浄化性能がよく、従来の製造方法により得られる排気ガス浄化用三元触媒よりも浄化性能が大幅に向上している。また、貴金属粒子は高耐熱性のジルコニア等の助触媒成分で被覆されているので、貴金属粒子のシンタリングに起因する粒径増大を抑制することができ、触媒の耐熱性能が大幅に向上している。 In the exhaust gas purification three-way catalyst obtained by the production method of the present invention, the precious metal particles are widely dispersed as very fine particles of about 1 to 20 nm, so the exhaust gas purification performance of the catalyst is good, and the conventional production The purification performance is significantly improved over the exhaust gas purification three-way catalyst obtained by the method. In addition, since the noble metal particles are coated with a promoter component such as zirconia having high heat resistance, it is possible to suppress the increase in particle size due to sintering of the noble metal particles, and the heat resistance performance of the catalyst is greatly improved. Yes.
セラミックス又は金属材料からなる担体上に上記の排気ガス浄化用三元触媒の層が担持されており、該三元触媒の層が１層又は２層以上となっている実用的な本発明の排気ガス浄化用三元触媒、また、この担体と排気ガス浄化用三元触媒の層との間に、多孔質耐火性無機酸化物粉体及び助触媒成分からなる層が存在している実用的な本発明の排気ガス浄化用三元触媒、更には、この三元触媒の層の少なくとも１層が多孔質耐火性無機酸化物粉体を追加含有している実用的な本発明の排気ガス浄化用三元触媒は、担体に担持された従来の排気ガス浄化用三元触媒と同様にして製造することができる。 A practical exhaust gas according to the present invention, wherein the exhaust gas purifying three-way catalyst layer is supported on a carrier made of ceramics or a metal material, and the three-way catalyst layer is one layer or more. A three-way catalyst for gas purification, and a layer comprising a porous refractory inorganic oxide powder and a promoter component exists between this carrier and the three-way catalyst layer for exhaust gas purification. The exhaust gas purifying three-way catalyst of the present invention, and further, the practical exhaust gas purifying of the present invention, in which at least one layer of the three-way catalyst additionally contains a porous refractory inorganic oxide powder The three-way catalyst can be produced in the same manner as a conventional three-way catalyst for exhaust gas purification supported on a carrier.
例えば、（イ）粒径１〜２０ｎｍの貴金属成分粒子と該貴金属成分粒子を被覆している助触媒成分被膜とから排気ガス浄化用三元触媒粉末、（ロ）多孔質耐火性無機酸化物粉体と該粉体に担持されている該（イ）の排気ガス浄化用三元触媒粉末とからなる排気ガス浄化用三元触媒粉末、（ハ）多孔質耐火性無機酸化物粉体と助触媒成分粉末とからなる混合粉末、（ニ）上記（イ）又は（ロ）の排気ガス浄化用三元触媒粉末と多孔質耐火性無機酸化物粉末とからなる混合粉末、又は（ホ）それらの混合物と、バインダーと、水とを湿式粉砕してスラリーを調製し、それらの何れかのスラリーをセラミックス又は金属材料からなる担体上にウオッシュコートし、乾燥し、焼成することによって、更には異なる組成のスラリーを用いてこれらのウオッシュコートを繰り返すことによって、１層又は２層以上の触媒層を有する排気ガス浄化用三元触媒を製造することができる。なお、貴金属のシンタリングをより十分に抑制するために、熱安定化剤兼助触媒剤としてＮｄ、Ｉｒ、Ｌａ、Ｃｅなどの希土類又はＢａ、Ｓｒ、Ｍｇなどのアルカリ土類金属を１〜５質量％添加することが好ましい。 For example, (a) a three-way catalyst powder for purifying exhaust gas from a noble metal component particle having a particle diameter of 1 to 20 nm and a promoter component film covering the noble metal component particle, (b) a porous refractory inorganic oxide powder Three-way catalyst powder for exhaust gas purification comprising the body and the three-way catalyst powder for exhaust gas purification of (i) carried on the powder, (c) porous refractory inorganic oxide powder and promoter (D) a mixed powder comprising the three-way catalyst powder for purifying exhaust gas and (b) a porous refractory inorganic oxide powder, or (e) a mixture thereof. And a binder and water are wet pulverized to prepare a slurry, and any one of these slurries is wash-coated on a carrier made of ceramics or a metal material, dried, and fired to further reduce the composition. These wows using a slurry By repeating Shukoto, it is possible to produce a three-way catalyst for purifying exhaust gases having one or more layers of the catalyst layer. In order to sufficiently suppress the sintering of the noble metal, 1 to 5 rare earths such as Nd, Ir, La, and Ce or alkaline earth metals such as Ba, Sr, and Mg are used as a thermal stabilizer and co-catalyst. It is preferable to add mass%.
以下に、実施例及び比較例に基づいて本発明を説明する。以下の実施例及び比較例において、各成分の相対量を示す質量部は分散媒、溶媒を除いた量を示している。 Below, this invention is demonstrated based on an Example and a comparative example. In the following examples and comparative examples, the parts by mass indicating the relative amounts of the components indicate the amounts excluding the dispersion medium and the solvent.
実施例１
ジルコニアヒドロゾル（ＺｒＯ2固形分換算で１０.３６質量％、解膠剤として硝酸を使用、ｐＨ＝２.８３、ＺｒＯＯＨ微粒子径≒１０ｎｍ）１０質量部（固形分量として、以下同じ）、硝酸ランタン水溶液２質量部及び硝酸ネオジム水溶液２質量部を１Ｌのフラスコに入れ、１時間攪拌して均一なゾル溶液を調製した。このゾル溶液に硝酸ロジウム水溶液１.３質量部を添加し、ポリエチレングリコール（ＰＥＧ６００）１質量部を添加し、２０時間攪拌して、分散媒中に、中心がロジウムイオン粒子で、その周囲にジルコニアヒドロゾルの層が取り囲んでおり、その界面にポリエチレングリコールが存在している粒子が分散している均一かつ半透明なＲｈ超微粒子錯体ゾル溶液を調製した。
Example 1
Zirconia hydrosol (1036 mass% in terms of ZrO 2 solid content, using nitric acid as a peptizer, pH = 2.83, ZrOOH fine particle diameter ≈10 nm) 10 parts by mass (the same applies hereinafter as the solid content), lanthanum nitrate 2 parts by mass of an aqueous solution and 2 parts by mass of an aqueous neodymium nitrate solution were placed in a 1 L flask and stirred for 1 hour to prepare a uniform sol solution. To this sol solution, 1.3 parts by mass of an aqueous rhodium nitrate solution is added, 1 part by mass of polyethylene glycol (PEG 600) is added, and the mixture is stirred for 20 hours. A uniform and translucent Rh ultrafine particle complex sol solution was prepared in which particles having polyethylene glycol present at the interface were dispersed.
このゾル溶液に水を加えて粘度を低下させ、攪拌しながらＺｒＯ2−ＣｅＯ2複合酸化物粉末８４.７質量部を添加して吸液させた。次いで、８０℃で１５時間乾燥させ、６５０℃で５時間焼成した。これにより、中心が粒径４.０ｎｍ程度のロジウム粒子で、その粒子を酸化ジルコニウムの層が取り囲んでいる粒子がＺｒＯ2−ＣｅＯ2複合酸化物粉体に担持されているＲｈ（１.３質量％）・ＺｒＯ2／ＺｒＯ2−ＣｅＯ2粉末が得られた。 Water was added to this sol solution to reduce the viscosity, and 84.7 parts by mass of ZrO 2 —CeO 2 composite oxide powder was added to absorb the liquid while stirring. Next, it was dried at 80 ° C. for 15 hours and calcined at 650 ° C. for 5 hours. As a result, rhodium particles having a particle diameter of about 4.0 nm in the center, and particles having a zirconium oxide layer surrounding the particles are supported on the ZrO 2 —CeO 2 composite oxide powder (Rh (1.3 mass)). %) · ZrO 2 / ZrO 2 —CeO 2 powder was obtained.
上記のＲｈ（１.３質量％）・ＺｒＯ2／ＺｒＯ2−ＣｅＯ2粉末の製造で用いた硝酸ロジウム水溶液の代わりに硝酸白金水溶液１.３質量部を用い、ＺｒＯ2−ＣｅＯ2複合酸化物粉末の代わりにＡｌ2Ｏ3８４.７質量部を用いて、同様な製法によって中心が粒径５.０ｎｍ程度の白金粒子で、その粒子を酸化ジルコニウムの層が取り囲んでいる粒子がＡｌ2Ｏ3粉体に担持されているＰｔ（１.３質量％）・ＺｒＯ2／Ａｌ2Ｏ3粉末を調製した。 ZrO 2 —CeO 2 composite oxide using 1.3 parts by mass of a platinum nitrate aqueous solution instead of the rhodium nitrate aqueous solution used in the production of the above Rh (1.3 mass%) · ZrO 2 / ZrO 2 —CeO 2 powder. Instead of the powder, 84.7 parts by mass of Al 2 O 3 is used, and the same manufacturing method is used to form platinum particles having a particle size of about 5.0 nm at the center, and the particles surrounded by the zirconium oxide layer are Al 2 O. 3 Pt (1.3 mass%). ZrO 2 / Al 2 O 3 powder supported on the powder was prepared.
上記のＲｈ（１.３質量％）・ＺｒＯ2／ＺｒＯ2−ＣｅＯ2粉末の製造で用いたジルコニアヒドロゾルの代わりにセリアヒドロゾル（ＣｅＯ2固形分換算で１５.０６質量％、解膠剤として硝酸を使用、ｐＨ＝２.８３、ＣｅＯＯＨ微粒子≒１５ｎｍ）１０質量部を用い、硝酸ロジウム水溶液１.３質量部の代わりに硝酸白金水溶液１.３７質量部を用い、また、ＺｒＯ2−ＣｅＯ2複合酸化物粉末の量を８４.６３質量部に変更し、同様な製法によって中心が粒径５.０ｎｍ程度の白金粒子で、その粒子を酸化セリウムの層が取り囲んでいる粒子がＺｒＯ2−ＣｅＯ2複合酸化物粉体に担持されているＰｔ（１.３７質量％）・ＣｅＯ2／ＺｒＯ2−ＣｅＯ2粉末を調製した。 Ceria hydrosol (15.06 mass% in terms of CeO 2 solid content, peptizer) instead of the zirconia hydrosol used in the production of the above Rh (1.3 mass%) · ZrO 2 / ZrO 2 —CeO 2 powder As nitric acid, pH = 2.83, CeOOH fine particles≈15 nm), 10 parts by mass of rhodium nitrate, 1.37 parts by mass of platinum nitrate in place of 1.3 parts by mass of rhodium nitrate, and ZrO 2 —CeO 2 The amount of the composite oxide powder was changed to 84.63 parts by mass, and by the same manufacturing method, platinum particles having a particle size of about 5.0 nm at the center, and the particles surrounded by the cerium oxide layer were ZrO 2 − Pt (1.37 mass%) · CeO 2 / ZrO 2 —CeO 2 powder supported on CeO 2 composite oxide powder was prepared.
上記で調製したＰｔ（１.３質量％）・ＺｒＯ2／Ａｌ2Ｏ3粉末５８質量部、Ｐｔ（１.３７質量％）・ＣｅＯ2／ＺｒＯ2−ＣｅＯ2粉末３０質量部、バインダ１２質量部及び水１４０質量部を混合し、ボールミルで粉砕してスラリー（１）を調製した。 58 parts by mass of the Pt (1.3% by mass) · ZrO 2 / Al 2 O 3 powder prepared above, 30 parts by mass of the Pt (1.37% by mass) · CeO 2 / ZrO 2 —CeO 2 powder, and 12 parts by mass of the binder. And 140 parts by weight of water were mixed and pulverized with a ball mill to prepare slurry (1).
また、上記で調製したＲｈ（１.３質量％）・ＺｒＯ2／ＺｒＯ2−ＣｅＯ2粉末３０質量部、アルミナ５８質量部、バインダ１２質量部及び水１４０質量部を混合し、ボールミルで粉砕してスラリー（２）を調製した。 Further, 30 parts by mass of Rh (1.3% by mass) · ZrO 2 / ZrO 2 —CeO 2 powder prepared above, 58 parts by mass of alumina, 12 parts by mass of binder and 140 parts by mass of water were mixed and pulverized by a ball mill. Thus, slurry (2) was prepared.
９００セル／ｉｎｃｈ2のハニカム形状のコージライト担体の面上に上記のスラリー（１）を１２０ｇ／Ｌの量でウオッシュコートし、乾燥し、焼成して下層を形成し、その後上記のスラリー（２）を１２０ｇ／Ｌの量でウオッシュコートし、乾燥し、焼成して上層を形成して本発明の自動車排気ガス浄化用三元触媒を得た。貴金属組成はＰｔ／Ｒｈ＝２／１であり、触媒担持量は１.４ｇ／Ｌであった。 The slurry (1) was washed on the surface of a honeycomb-shaped cordierite carrier of 900 cells / inch 2 in an amount of 120 g / L, dried and fired to form a lower layer, and then the slurry (2 ) Was coated in an amount of 120 g / L, dried and fired to form an upper layer to obtain a three-way catalyst for purifying automobile exhaust gas according to the present invention. The noble metal composition was Pt / Rh = 2/1, and the catalyst loading was 1.4 g / L.
実施例２
実施例１でＰｔ（１.３質量％）・ＺｒＯ2／Ａｌ2Ｏ3粉末及びＰｔ（１.３７質量％）・ＣｅＯ2／ＺｒＯ2−ＣｅＯ2粉末のそれぞれの製造で用いた硝酸白金水溶液の量をそれぞれ半分に減らし、その減らした量に相当する量の硝酸パラジウム水溶液を追加した以外は実施例１と同様に処理して、貴金属組成がＰｄ／Ｐｔ／Ｒｈ＝１／１／１であり、触媒担持量が１.４ｇ／Ｌである本発明の自動車排気ガス浄化用三元触媒触媒を調製した。
Example 2
The platinum nitrate aqueous solution used in the production of each of Pt (1.3 mass%) · ZrO 2 / Al 2 O 3 powder and Pt (1.37 mass%) · CeO 2 / ZrO 2 —CeO 2 powder in Example 1. The precious metal composition was Pd / Pt / Rh = 1/1/1 except that the amount of each of the above was reduced to half and the amount of palladium nitrate aqueous solution corresponding to the reduced amount was added. A three-way catalyst catalyst for purifying automobile exhaust gas according to the present invention having a catalyst loading of 1.4 g / L was prepared.
実施例３
９００セル／ｉｎｃｈ2のハニカム形状の多孔質アルミナ担体の面上に実施例１に記載の方法で調製したスラリー（１）を１２０ｇ／Ｌの量でウオッシュコートし、乾燥し、焼成して下層を形成し、その後、実施例１に記載の方法で調製した、分散媒中に、中心がロジウムイオン粒子で、その周囲にジルコニアヒドロゾルの層が取り囲んでおり、その界面にポリエチレングリコールが存在している粒子が分散している均一かつ半透明なＲｈ超微粒子錯体ゾル溶液をウオッシュコートし、乾燥し、焼成して上層を形成して本発明の自動車排気ガス浄化用三元触媒を得た。貴金属組成はＰｔ／Ｒｈ＝２／１であり、触媒担持量は１.４ｇ／Ｌであった。
Example 3
The slurry (1) prepared by the method described in Example 1 was washed on the surface of a 900-cell / inch 2 honeycomb-shaped porous alumina carrier in an amount of 120 g / L, dried and fired to form a lower layer. Formed in the dispersion medium prepared by the method described in Example 1, the center is rhodium ion particles, and the layer of zirconia hydrosol is surrounded by polyethylene glycol at the interface. A uniform and translucent Rh ultrafine particle complex sol solution in which dispersed particles were dispersed was washed, dried, and baked to form an upper layer to obtain a three-way catalyst for purifying automobile exhaust gas according to the present invention. The noble metal composition was Pt / Rh = 2/1, and the catalyst loading was 1.4 g / L.
実施例４
実施例３に記載の方法と同様であるが、触媒担持量が実施例３の場合の半分の量になるようにして実施例３の方法を実施した。即ち、貴金属組成はＰｔ／Ｒｈ＝２／１であり、触媒担持量は０.７ｇ／Ｌであった。
Example 4
The method of Example 3 was carried out in the same manner as described in Example 3, except that the amount of catalyst supported was half that of Example 3. That is, the noble metal composition was Pt / Rh = 2/1, and the catalyst loading was 0.7 g / L.
比較例１
アルミナ粉末６０質量部、ＺｒＯ2−ＣｅＯ2複合酸化物粉末３０質量部、バインダ成分１０質量部及び水１４０質量部を混合し、ボールミルで粉砕して、比較例用スラリーを調製した。
Comparative Example 1
60 parts by mass of alumina powder, 30 parts by mass of ZrO 2 —CeO 2 composite oxide powder, 10 parts by mass of the binder component and 140 parts by mass of water were mixed and pulverized with a ball mill to prepare a slurry for comparative example.
実施例１に記載の方法と同様にして、９００セル／ｉｎｃｈ2のハニカム形状の多孔質アルミナ担体の面上に上記の比較例用スラリーを１２０ｇ／Ｌの量でウオッシュコートし、乾燥し、焼成して下層を形成し、該下層に硝酸白金水溶液を吸着含浸させた。次いで同じく上記の比較例用スラリーを１２０ｇ／Ｌの量でウオッシュコートし、乾燥し、焼成して上層を形成し、該上層に硝酸ロジウム水溶液を吸着含浸させ、その後焼成して比較例１の触媒を調製した。貴金属組成はＰｔ／Ｒｈ＝２／１であり、触媒担持量は１.４ｇ／Ｌであった。 In the same manner as described in Example 1, the above slurry for comparative example was wash-coated in the amount of 120 g / L on the surface of a 900-cell / inch 2 honeycomb-shaped porous alumina carrier, dried, and fired. Then, a lower layer was formed, and the lower layer was impregnated with an aqueous platinum nitrate solution. Next, the above slurry for comparative example was washcoated in an amount of 120 g / L, dried and fired to form an upper layer. The upper layer was adsorbed and impregnated with an aqueous rhodium nitrate solution, and then fired to prepare the catalyst of Comparative Example 1 Was prepared. The noble metal composition was Pt / Rh = 2/1, and the catalyst loading was 1.4 g / L.
比較例２
比較例１に記載の方法と同様であるが、触媒担持量が比較例１の場合の半分の量になるようにして比較例１の方法を実施した。即ち、貴金属組成はＰｔ／Ｒｈ＝２／１であり、触媒担持量は０.７ｇ／Ｌであった。
Comparative Example 2
The method of Comparative Example 1 was carried out in the same manner as described in Comparative Example 1, except that the amount of catalyst supported was half that of Comparative Example 1. That is, the noble metal composition was Pt / Rh = 2/1, and the catalyst loading was 0.7 g / L.
実施例５
９００セル／ｉｎｃｈ2のハニカム形状の多孔質アルミナ担体の面上に比較例１に記載の方法で調製した比較例用スラリーを１００ｇ／Ｌの量でウオッシュコートし、乾燥し、焼成して第一層を形成し、その上に実施例１に記載の方法で調製した、分散媒中に、中心が白金イオン粒子で、その周囲にジルコニアヒドロゾルの層が取り囲んでおり、その界面にポリエチレングリコールが存在している粒子が分散しているＰｔ超微粒子錯体ゾル溶液を２０ｇ／Ｌの量でコートし、乾燥し、焼成して第二層を形成し、その上に比較例１に記載の方法で調製した比較例用スラリーを１００ｇ／Ｌの量でウオッシュコートし、乾燥し、焼成して第三層を形成し、その上に実施例１に記載の方法で調製した、分散媒中に、中心がロジウムイオン粒子で、その周囲にジルコニアヒドロゾルの層が取り囲んでおり、その界面にポリエチレングリコールが存在している粒子が分散している均一かつ半透明なＲｈ超微粒子錯体ゾル溶液を２０ｇ／Ｌの量でコートし、乾燥し、焼成して第四層を形成して本発明の自動車排気ガス浄化用三元触媒を得た。貴金属組成はＰｔ／Ｒｈ＝２／１であり、触媒担持量は１.４ｇ／Ｌであった。
＜触媒性能のモデルガス評価＞
上記の実施例１〜５及び比較例１〜２の排気ガス浄化用三元触媒をそれぞれφ２５.４ｍｍ×Ｌ３０ｍｍのコアサイズにカットし、実験室用の排気ガス浄化性能評価装置（株式会社堀場製作所製ＳＩＧＵ−１０００自動ガス評価装置）の反応管内部に設置して耐久触媒性能を評価した。評価用ガスとしては、Ｃ3Ｈ6、ＣＯ、ＮＯ、ＣＯ2、Ｏ2、Ｈ2Ｏ、Ｈ2、Ｎ2のガスをＡ/Ｆ＝１４.６のストイキオメトリーの排気ガス組成となるように混合したガスを用い、触媒床温度を１０℃／分の速度で４００℃まで昇温させながらＣ3Ｈ6（ＨＣ）、ＮＯ、ＣＯの各成分の濃度を分析し（株式会社堀場製作所製ＭＥＸＡ７１００ガス自動分析装置）、浄化率を計算した。触媒性能については、これらの成分が５０％浄化される温度及び４００℃の浄化率を指標とした。耐久性能の測定は、１０質量％水蒸気雰囲気ガスに８００℃、９００℃又は１０００℃で２０時間曝す条件とした。得られた結果は第１表に示す通りであった。
Example 5
The slurry for the comparative example prepared by the method described in Comparative Example 1 was washed on the surface of the 900-cell / inch 2 honeycomb-shaped porous alumina carrier in the amount of 100 g / L, dried and fired. A layer was formed on the dispersion medium prepared by the method described in Example 1, and the center was platinum ion particles, and a layer of zirconia hydrosol was surrounded by the layer, and polyethylene glycol was formed at the interface. The Pt ultrafine particle complex sol solution in which the existing particles are dispersed is coated in an amount of 20 g / L, dried and baked to form a second layer, on which the method described in Comparative Example 1 is applied. The prepared slurry for comparative example was wash-coated in an amount of 100 g / L, dried and fired to form a third layer, on which the dispersion medium prepared by the method described in Example 1 was used. Are rhodium ion particles. A uniform and translucent Rh ultrafine particle complex sol solution in which particles having polyethylene glycol present at the interface are dispersed is coated in an amount of 20 g / L and surrounded by a zirconia hydrosol layer. And the fourth layer was formed by firing to obtain a three-way catalyst for purifying automobile exhaust gas according to the present invention. The noble metal composition was Pt / Rh = 2/1, and the catalyst loading was 1.4 g / L.
<Model gas evaluation of catalyst performance>
The exhaust gas purification three-way catalysts of Examples 1 to 5 and Comparative Examples 1 and 2 were cut into a core size of φ25.4 mm × L30 mm, respectively, and a laboratory exhaust gas purification performance evaluation apparatus (Horiba, Ltd.) It was installed inside a reaction tube of a manufactured SIGU-1000 automatic gas evaluation apparatus) and the durable catalyst performance was evaluated. As an evaluation gas, a gas of C 3 H 6 , CO, NO, CO 2 , O 2 , H 2 O, H 2 , and N 2 has a stoichiometric exhaust gas composition of A / F = 14.6. The concentration of each component of C 3 H 6 (HC), NO, and CO was analyzed while raising the catalyst bed temperature to 400 ° C. at a rate of 10 ° C./min. (Horiba, Ltd.) Manufactured MEXA7100 gas automatic analyzer), purification rate was calculated. For the catalyst performance, the temperature at which these components were purified by 50% and the purification rate at 400 ° C. were used as indicators. The durability performance was measured under the condition of exposing to 10 mass% steam atmosphere gas at 800 ° C., 900 ° C. or 1000 ° C. for 20 hours. The obtained results were as shown in Table 1.
Claims (10)
Nonionic surfactants which are water-soluble higher alcohols or polyethers having a molecular weight of 500 to 2000, polycarboxylic acid ammonium salts, condensed naphthalene sulfonate ammonium, which function as noble metal complex forming agents and dispersion stabilizers The production method according to claim 8 or 9, which is an anionic surfactant which is a salt or a polyacrylic acid ammonium salt, or a polyammine surfactant which is a diamine or triammine.
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