Exhaust gas purifying catalyst device

Abstract

To provide an exhaust gas purifying catalyst device where an adsorption amount of NOx in a cold region is large and NOx emission in the cold region is reduced.SOLUTION: In an exhaust gas purifying catalyst device having a first catalyst coat layer 200 and a second catalyst coat layer 300 on a base material 100: the first catalyst coat layer 200 contains first inorganic oxide particles 10 and first catalyst noble metal particles 40; the second catalyst coat layer 300 contains second inorganic oxide particles 60 and second catalyst noble metal particles 70; the first inorganic oxide particles 10 contain a composite oxide carrier 30 containing an OSC material 11 and an alkaline earth metal oxide 20; the first catalyst noble metal particles 40 contain one or two kinds selected from Pt and Pd; the second inorganic oxide particles 60 contain the OSC material 11; the second catalyst noble metal particles 70 contain Rh; the first catalyst coat layer 200 does not substantially contain Rh; and the second catalyst coat layer 300 does not substantially contain Pt, Pd and the alkaline earth metal oxide.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas purification catalyst device. [Background technology]

[0002] Nitrogen oxides (NO x These exhaust gases contain NOx, carbon monoxide (CO), hydrocarbons (HC), etc. These exhaust gases are purified by an exhaust gas purification catalyst that oxidizes CO and HC and reduces NOx before being released into the atmosphere.

[0003] With a view to mitigating air pollution, each country regulates the weight of CO, HC, and NOx contained in exhaust gas per unit distance traveled by an automobile.

[0004] Exhaust gas regulations are becoming stricter every year. Currently, LEV III regulations are in effect in the United States, and Euro 6 regulations are in effect in Europe. Europe is expected to transition to Euro 7 regulations in the near future.

[0005] The Euro 7 regulations require a reduction in NOx emissions in the cold region, for example, during engine start-up. The exhaust gas atmosphere during engine start-up is in the rich to stoichiometric region. Therefore, it is difficult to reduce NOx emissions in the cold region using conventional NOx purification technologies that are based on lean-burn engines.

[0006] As a conventional NOx emission reduction technology, for example, Patent Document 1 discloses: a lower catalyst layer containing a first composite oxide containing Ce and Zr and Pd supported on the first composite oxide; and an upper catalyst layer containing a second composite oxide containing Ce and Zr and Rh supported on the second composite oxide; and an alkaline earth metal selected from Ca, Sr, and Mg is dissolved in at least one of the first composite oxide and the second composite oxide.

[0007] Patent Document 1 explains that the NOx adsorption properties of a composite oxide are improved by dissolving an alkaline earth metal in the composite oxide.

[0008] Furthermore, Patent Document 2 describes an oxidation-reduction catalyst in which palladium and an alkaline earth metal are supported on an oxide having oxygen storage and release capacity.

[0009] Patent Document 2 explains that by configuring the catalyst as described above, the alkaline earth metal is preferably involved in the adsorption or reaction of NOx. [Prior art documents] [Patent documents]

[0010] [Patent Document 1] Japanese Patent Application Laid-Open No. 2010-119994 [Patent Document 2] Japanese Patent Application Laid-Open No. 2001-198461 Summary of the Invention [Problem to be solved by the invention]

[0011] The above-mentioned Patent Documents 1 and 2 are both related to prior art exhaust gas purification catalysts, and the amount of NOx adsorption in the cold region, such as at engine start, is insufficient.

[0012] The present invention has been made in view of the above circumstances, and has an object to provide an exhaust gas purification catalyst device that has a large amount of NOx adsorption in the cold region and reduces NOx emissions in the cold region. [Means for solving the problem]

[0013] The present invention is as follows.

[0014] Aspect 1: A catalyst having a substrate, a first catalyst coating layer on the substrate, and a second catalyst coating layer on the first catalyst coating layer, the first catalytic coating layer includes first inorganic oxide particles and first catalytic noble metal particles, the second catalytic coating layer includes second inorganic oxide particles and second catalytic noble metal particles, the first inorganic oxide particles include an OSC material and an alkaline earth metal oxide; the first catalytic noble metal particles contain one or two selected from Pt and Pd, the second inorganic oxide particles include an OSC material; the second catalytic noble metal particles contain Rh; the first catalyst coating layer has a metal-equivalent Rh content of 0.05 g / L or less per 1 L of the substrate volume; In the second catalyst coating layer, the total amount of Pt and Pd in ​​terms of metal per 1 L of the volume of the substrate is 0.05 g / L or less, and the amount of alkaline earth metal oxide per 1 L of the volume of the substrate is 0.5 g / L or less. Exhaust gas purification catalytic device. <<Aspect 2>> The first inorganic oxide particles are: a composite oxide support including an OSC material and a first alkaline earth metal oxide; a second alkaline earth metal oxide supported on the composite oxide support; Including, 2. The catalytic converter for exhaust gas purification according to claim 1. Aspect 3: The exhaust gas purification catalyst device according to Aspect 2, wherein at least a portion of the first catalytic noble metal particles, together with the second alkaline earth metal oxide, are supported on the composite oxide support. Aspect 4: The exhaust gas purification catalyst device according to Aspect 2 or 3, wherein the first alkaline earth metal oxide is magnesium oxide. Aspect 5: The exhaust gas purification catalyst device according to any one of Aspects 2 to 4, wherein the second alkaline earth metal oxide is one or more selected from the group consisting of magnesium oxide, barium oxide, and strontium oxide. Aspect 6: The exhaust gas purification catalyst device according to any one of Aspects 2 to 5, wherein the amount of the first alkaline earth metal oxide is 0.1 mass % or more and 20 mass % or less, when the total mass of the composite oxide support is 100 mass %. Aspect 7: The exhaust gas purification catalyst device according to any one of Aspects 2 to 6, wherein the amount of the second alkaline earth metal oxide supported is 0.5% by mass or more and 25% by mass or less, when the total mass of the composite oxide support is taken as 100% by mass. Aspect 8: The exhaust gas purification catalyst device according to any one of Aspects 2 to 7, wherein the amount of the first catalytic noble metal particles per 1 L of the volume of the substrate is 0.5 g / L or more and 10.0 g / L or less. Aspect 9: The catalytic device for purifying exhaust gas according to any one of Aspects 2 to 8, wherein the first inorganic oxide particles further contain alumina. Aspect 10: The exhaust gas purification catalyst device according to any one of Aspects 1 to 9, wherein the amount of the second catalytic precious metal particles per 1 L of the volume of the substrate is 0.05 g / L or more and 2.0 g / L or less. Aspect 11: The catalytic device for purifying exhaust gas according to any one of Aspects 1 to 10, wherein the second inorganic oxide particles further contain alumina. Aspect 12: The catalytic device for purifying exhaust gas according to any one of Aspects 1 to 11, wherein the OSC material contains ceria in a cerium-zirconium composite oxide. Aspect 13: The catalytic device for purifying exhaust gas according to any one of Aspects 1 to 12, wherein the first catalytic noble metal particles contain both Pt and Pd. Aspect 14: The catalytic device for purifying exhaust gas according to any one of Aspects 1 to 13, wherein the coating length of the first catalyst coating layer is 35% or more of the entire length of the substrate. Aspect 15: The catalytic device for purifying exhaust gas according to any one of Aspects 1 to 14, wherein the coating length of the second catalyst coating layer is 70% or more of the entire length of the substrate. Aspect 16: A method for purifying exhaust gas, comprising contacting exhaust gas with the catalytic device for exhaust gas purification according to any one of aspects 1 to 15. [Effects of the Invention]

[0015] The catalytic device for purifying exhaust gas of the present invention has a large amount of NOx adsorption in the cold region, and NOx emissions in the cold region are reduced. [Brief explanation of the drawings]

[0016] [Figure 1] FIG. 1 is a conceptual diagram for explaining an example of the configuration of an exhaust gas purification catalyst device of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0017] <<Exhaust gas purification catalytic device>> The exhaust gas purification catalyst device of the present invention comprises: a substrate, a first catalyst coating layer on the substrate, and a second catalyst coating layer on the first catalyst coating layer; the first catalytic coating layer includes first inorganic oxide particles and first catalytic noble metal particles, the second catalytic coating layer includes second inorganic oxide particles and second catalytic noble metal particles, the first inorganic oxide particles include an OSC material and an alkaline earth metal oxide; the first catalytic noble metal particles contain one or two selected from Pt and Pd, the second inorganic oxide particles include an OSC material; the second catalytic noble metal particles contain Rh; the first catalyst coating layer has a metal-equivalent Rh content of 0.05 g / L or less per 1 L of the substrate volume; In the second catalyst coating layer, the total amount of Pt and Pd in ​​terms of metal per 1 L of substrate volume is 0.05 g / L or less, and the amount of alkaline earth metal oxide per 1 L of substrate volume is 0.5 g / L or less.

[0018] The catalytic device for purifying exhaust gas of the present invention has a first catalyst coating layer as a lower layer and a second catalyst coating layer as an upper layer on a substrate.

[0019] The first catalytic coating layer contains an OSC material, an alkaline earth metal oxide, and first catalytic noble metal particles selected from Pt and Pd.

[0020] The exhaust gas atmosphere at engine start (cold operation) is in the rich to stoichiometric region. Therefore, it is thought that OSC materials such as ceria are in a reduced state and have oxygen deficiencies at engine start. The first catalyst coating layer in the exhaust gas purification catalytic device of the present invention contains an OSC material that has oxygen deficiencies at engine start, thereby increasing the number of NOx adsorption sites at cold operation.

[0021] The first catalyst coating layer also contains an alkaline earth metal oxide, which increases the number of base points in the first catalyst coating layer and increases the number of NOx adsorption points.

[0022] Furthermore, the first catalytic coating layer contains first catalytic noble metal particles selected from Pt and Pd. The first catalytic noble metal particles have an oxidation catalytic function, and therefore can convert NOx into, for example, NO3 - It converts to ions, facilitating NOx adsorption on basic sites.

[0023] Furthermore, the first catalyst coating layer is substantially free of Rh, which allows the first catalyst precious metal particles (Pd, Pt) in the first catalyst coating layer to exhibit a high level of NOx adsorption ability without impairing their catalytic activity.

[0024] The first catalyst coat is disposed in the lower layer of the exhaust gas purification catalytic device of the present invention. Therefore, the first catalyst coat is less likely to warm up when the engine is started, and can extremely effectively exhibit the above-mentioned NOx adsorption ability.

[0025] The NOx adsorbed on the first catalyst coat is gradually released as the engine warms up after starting.

[0026] Here, the second catalytic coating layer contains an OSC material and second catalytic noble metal particles, which are Rh.

[0027] The second catalytic precious metal particles contained in the second catalytic coating layer have a reduction catalytic function. Therefore, NOx released from the first catalytic coating is reduced and purified by the second catalytic precious metal particles in the second catalytic coating layer. The second catalytic coating layer also contains an OSC material. Therefore, even if the exhaust gas atmosphere fluctuates, the OSC material alleviates the exhaust gas atmosphere, allowing the second catalytic precious metal particles to maintain their reduction catalytic activity.

[0028] The second catalyst coating layer is substantially free of Pt, Pd, and alkaline earth metal oxides, which allows the NOx reduction and purification activity of the second catalytic precious metal particles (Rh) in the second catalyst coating layer to be maintained and high NOx purification performance to be exhibited.

[0029] The second catalyst coat is disposed on the upper layer of the exhaust gas purification catalyst device of the present invention, and therefore the second catalyst coat is quickly warmed up after the engine starts, and can extremely effectively demonstrate the above-mentioned NOx reduction and purification ability.

[0030] The catalytic converter for purifying exhaust gas of the present invention exhibits excellent NOx removal performance due to the above-mentioned mechanism of action, however, the present invention is not limited to any particular theory.

[0031] The components of the exhaust gas purification catalyst device of the present invention will be described below in order.

[0032] 《Base material》 The substrate in the exhaust gas purification catalyst device of the present invention may be the same as a substrate used in an exhaust gas purification catalyst device. The substrate may be, for example, a honeycomb substrate having a plurality of exhaust gas flow passages separated by partition walls. The partition walls of the substrate may have pores that fluidly communicate adjacent exhaust gas flow passages.

[0033] The constituent material of the substrate may be, for example, a refractory inorganic oxide such as cordierite, etc. The substrate may be of a straight flow type or a wall flow type.

[0034] The substrate in the catalytic device for purifying exhaust gas of the present invention may typically be, for example, a monolith honeycomb substrate of a straight-flow type or a wall-flow type made of cordierite.

[0035] <<First catalyst coating layer>> The first catalyst coating layer in the exhaust gas purification catalytic device of the present invention is disposed on a substrate. A second catalyst coating layer may be disposed on at least a part, preferably the entirety, of the first catalyst coating layer. Therefore, the first catalyst coating layer may be the lower layer of a two-layer catalyst coating layer.

[0036] The first catalytic coating layer includes first inorganic oxide particles and first catalytic noble metal particles.

[0037] <First inorganic oxide particles> The first inorganic oxide particles contained in the first catalyst coating layer include an OSC material and an alkaline earth metal oxide. "OSC" stands for "Oxygen Storage Capacity" or "Oxygen Storage / release Capacity" and means "oxygen storage / release capacity." "OSC material" means "a material with oxygen storage / release capacity."

[0038] The OSC material contained in the first inorganic oxide particles is, for example, ceria (CeO2). The concept of ceria as an OSC material includes not only the case where it exists as a single type of ceria in the first inorganic oxide particles, but also the case where it forms a composite oxide of cerium and another metal.

[0039] When the OSC material is ceria and forms a composite oxide of cerium and another metal, the composite oxide may be, for example, a cerium-zirconium composite oxide. When ceria exists as ceria in the cerium-zirconium composite oxide, the amount of oxygen vacancies in the ceria increases in the rich to stoichiometric range, thereby further increasing the number of NOx adsorption sites of the first inorganic oxide particles during cold operation.

[0040] The ceria content in the cerium-zirconium composite oxide may be 5 mass% or more, 10 mass% or more, 15 mass% or more, or 20 mass% or more, or 50 mass% or less, 45 mass% or less, 40 mass% or less, 35 mass% or less, 30 mass% or less, or 25 mass% or less, where the mass of the cerium atomic weight in the composite oxide, expressed in terms of ceria (Ce2O3), accounts for a proportion of the total mass of the composite oxide.

[0041] The alkaline earth metal oxide contained in the first inorganic oxide particles may be one or more selected from beryllium oxide, magnesium oxide, calcium oxide, strontium oxide, barium oxide, and radium oxide, and in particular, may be one or more selected from magnesium oxide, calcium oxide, strontium oxide, and barium oxide.

[0042] The first inorganic oxide particles may contain other components in addition to the OSC material and alkaline earth metal oxide, such as alumina, silica, titania, or one or more rare earth oxides selected from oxides of rare earth elements other than ceria.

[0043] The amount of the OSC material (typically ceria) contained in the first inorganic oxide particles may be 5% by mass or more, 7.5% by mass or more, or 15% by mass or more, relative to the total mass of the first inorganic oxide particles (100% by mass), in order to ensure a sufficient number of NOx adsorption sites in the cold state. On the other hand, the amount of the OSC material contained in the first inorganic oxide particles may be 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, 25% by mass or less, or 20% by mass or less, relative to the total mass of the first inorganic oxide particles (100% by mass), in order to enjoy the benefits of the first inorganic oxide particles containing other components.

[0044] The amount of the OSC material (typically ceria) in the first catalyst coating layer, expressed as the mass of the OSC material per 1 L of the volume of the substrate, may be 3.0 g / L or more, 4.0 g / L or more, 5.0 g / L or more, or 6.0 g / L or more, and may be 20.0 g / L or less, 15.0 g / L or less, 12.0 g / L or less, 11.0 g / L or less, or 10.0 g / L or less.

[0045] When ceria is used as an OSC material, if the ceria forms a complex oxide with another metal, the amount of ceria is the amount of cerium atoms in the complex oxide expressed in terms of ceria (CeO2).

[0046] The amount of alkaline earth metal oxide in the first inorganic oxide particles may be 1% by mass or more, 3% by mass or more, 5% by mass or more, 8% by mass or more, 10% by mass or more, 12% by mass or more, 15% by mass or more, or 20% by mass or more, and may be 50% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, or 25% by mass or less, when the mass of the first inorganic oxide particles is 100% by mass.

[0047] The amount of alkaline earth metal oxide in the first catalyst coating layer may be, in terms of the mass of alkaline earth metal oxide per 1 L of base material volume, 3.0 g / L or more, 3.5 g / L or more, 4.0 g / L or more, 4.5 g / L or more, 5.0 g / L or more, or 5.5 g / L or more, and may be 15.0 g / L or less, 12.0 g / L or less, 10.0 g / L or less, 9.0 g / L or less, 8.0 g / L or less, or 7.5 g / L or less.

[0048] The first inorganic oxide particles in the exhaust gas purification catalyst device of the present invention are a composite oxide support including an OSC material and a first alkaline earth metal oxide; a second alkaline earth metal oxide supported on the composite oxide support; and may include:

[0049] The composite oxide support includes an OSC material and a first alkaline earth metal oxide.

[0050] The OSC material contained in the composite oxide support may be the same as that contained in the first inorganic oxide particles. The content of the OSC material in the composite oxide support may be 5 mass% or more, 7.5 mass% or more, 15 mass% or more, or 20 mass% or more, or 50 mass% or less, 45 mass% or less, 40 mass% or less, 35 mass% or less, 30 mass% or less, or 25 mass% or less, when the total mass of the composite oxide support is 100 mass%.

[0051] The first alkaline earth metal oxide contained in the composite oxide support may be, for example, one or more oxides selected from magnesium oxide, calcium oxide, and strontium oxide, and may particularly be magnesium oxide.

[0052] The first alkaline earth metal oxide may be present in the composite oxide support as a single type of alkaline earth metal oxide, or may form a solid solution with the OSC material or a composite oxide containing an OSC material (e.g., cerium-zirconium composite oxide).

[0053] The amount of the first alkaline earth metal oxide contained in the composite oxide support may be 0.1 mass% or more, 0.5 mass% or more, 1.0 mass% or more, 2.0 mass% or more, 3.0 mass% or more, or 4.0 mass% or more, when the total mass of the composite oxide support is taken as 100 mass%, from the viewpoint of sufficiently increasing the number of NOx adsorption sites of the composite oxide support. On the other hand, in order to enjoy the benefits of the composite oxide containing other components, the amount of the first alkaline earth metal oxide may be 20 mass% or less, 15 mass% or less, 12 mass% or less, 10 mass% or less, or 8 mass% or less, when the total mass of the composite oxide support is taken as 100 mass%.

[0054] The amount of the first alkaline earth metal oxide in the first catalyst coating layer may be, in terms of the mass of the first alkaline earth metal oxide per 1 L of the base material volume, 0.1 g / L or more, 0.2 g / L or more, 0.3 g / L or more, 0.5 g / L or more, 0.7 g / L or more, 1.0 g / L or more, 1.5 g / L or more, or 2.0 g / L or more, and may be 10.0 g / L or less, 8.0 g / L or less, 6.0 g / L or less, 5.0 g / L or less, 4.0 g / L or less, 3.0 g / L or less, or 2.0 g / L or less.

[0055] When the first alkaline earth metal oxide forms a solid solution with an OSC material or a composite oxide containing an OSC material, the amount of the first alkaline earth metal oxide is the amount of the first alkaline earth metal in the solid solution expressed in terms of oxide.

[0056] The composite oxide support may further contain components other than the OSC material and the first alkaline earth metal oxide.

[0057] As described above, the OSC material in the composite oxide support may be present as ceria in a cerium-zirconium composite oxide, for example, and therefore the composite oxide support may contain zirconia. The amount of zirconia in the composite oxide support may be 20 mass% or more, 30 mass% or more, 40 mass% or more, 50 mass% or more, 60 mass% or more, or 65 mass% or more, based on the total mass of the composite oxide support being 100 mass%. On the other hand, to enjoy the benefits of the composite oxide support containing other components, the amount of the first alkaline earth metal oxide may be 90 mass% or less, 85 mass% or less, 80 mass% or less, 75 mass% or less, or 70 mass% or less, based on the total mass of the composite oxide support being 100 mass%.

[0058] The amount of zirconia in the first catalyst coating layer may be, in terms of the mass of zirconia per 1 L of substrate volume, 10.0 g / L or more, 12.0 g / L or more, 15.0 g / L or more, 17.0 g / L or more, or 20.0 g / L or more, and may be 70.0 g / L or less, 60.0 g / L or less, 50.0 g / L or less, 40.0 g / L or less, or 30.0 g / L or less.

[0059] When zirconium forms a composite oxide with another metal, the amount of zirconia is the amount of zirconium atoms in the composite oxide expressed in terms of zirconia (ZrO2).

[0060] The composite oxide support may contain one or more oxides selected from alumina, silica, titania, etc., and oxides of rare earth elements other than ceria. When the composite oxide support contains two or more of these oxides, these two or more oxides may exist as a single oxide or as a composite oxide containing two or more metal atoms.

[0061] The second alkaline earth metal oxide is supported on the above-mentioned composite oxide support.

[0062] The second alkaline earth metal oxide may be one or more selected from the group consisting of magnesium oxide, barium oxide, and strontium oxide, and in particular may be barium oxide or strontium oxide.

[0063] The second alkaline earth metal oxide may be in the form of particles. The particle size of the second alkaline earth metal oxide particles may be 5 nm or more, 10 nm or more, 15 nm or more, 20 nm or more, or 25 nm or more, as a number average primary particle size calculated from XRD, and may be 50 nm or less, 45 nm or less, 40 nm or less, or 35 nm or less.

[0064] From the viewpoint of ensuring a sufficient amount of NOx adsorption, the amount of the second alkaline earth metal oxide supported may be 0.5 mass% or more, 1.0 mass% or more, 2.0 mass% or more, 3.0 mass% or more, 4.0 mass% or more, 5.0 mass% or more, or 6.0 mass% or more, when the mass of the composite oxide support is taken as 100 mass%.

[0065] However, even if the amount of the second alkaline earth metal oxide supported is increased, the amount of NOx adsorption does not increase without limit. From this perspective, the amount of the second alkaline earth metal oxide supported may be 25 mass% or less, 20 mass% or less, 15 mass% or less, 12 mass% or less, 10 mass% or less, or 8 mass% or less, when the mass of the composite oxide support is 100 mass%.

[0066] The amount of the first inorganic oxide particles in the first catalyst coating layer may be, in terms of the mass of the first inorganic oxide particles per 1 L of substrate volume, 5.0 g / L or more, 10.0 g / L or more, 20.0 g / L or more, 30.0 g / L or more, 50.0 g / L or more, or 60.0 g / L or more, and may be 200.0 g / L or less, 150.0 g / L or less, 120.0 g / L or less, 100.0 g / L or less, or 80.0 g / L or less.

[0067] <Other ingredients> The first catalyst coating layer may contain other components in addition to the first inorganic oxide particles described above. The other components may be, for example, inorganic oxide particles other than the first inorganic oxide particles, a binder, etc.

[0068] The inorganic oxide particles other than the first inorganic oxide particles may be, for example, one type of inorganic oxide selected from alumina, silica, titania, zirconia, etc., or a composite oxide composed of two or more of these, or a composite oxide of these inorganic oxides or composite oxides and one or more types selected from oxides of rare earth elements other than ceria.

[0069] The first inorganic oxide particles preferably contain alumina in terms of the heat resistance of the exhaust gas purification catalytic device. The content of alumina in the first inorganic oxide particles may be 10 mass% or more, 20 mass% or more, 30 mass% or more, 40 mass% or more, or 50 mass% or more, and may be 90 mass% or less, 80 mass% or less, 70 mass% or less, 60 mass% or less, or 50 mass% or less, when the total mass of the first inorganic oxide particles is 100 mass%.

[0070] The amount of alumina in the first catalyst coating layer may be, in terms of the mass of alumina per 1 L of substrate volume, 5.0 g / L or more, 10.0 g / L or more, 20.0 g / L or more, 30.0 g / L or more, 50.0 g / L or more, or 60.0 g / L or more, and may be 200.0 g / L or less, 150.0 g / L or less, 120.0 g / L or less, 100.0 g / L or less, or 80.0 g / L or less.

[0071] <First catalytic precious metal particles> The first catalytic coating layer includes first catalytic precious metal particles together with first inorganic oxide particles. The first catalytic precious metal particles include one or two selected from Pt and Pd, and may particularly include both Pt and Pd.

[0072] The amount of the first catalytic precious metal particles in the first catalytic coating layer may be, in terms of the mass of the first catalytic precious metal particles per 1 L of substrate volume (total mass if multiple types of precious metals are included), 0.5 g / L or more, 0.7 g / L or more, 1.0 g / L or more, 2.0 g / L or more, 3.0 g / L or more, or 4.0 g / L or more, and may be 10.0 g / L or less, 8.0 g / L or less, 7.0 g / L or less, 6.0 g / L or less, or 5.0 g / L or less.

[0073] In the first catalyst coating layer, the amount of Rh in terms of metal per 1 L of substrate volume is 0.05 g / L or less. The amount of Rh in the first catalyst coating layer being 0.05 g / L or less means that the first catalyst coating layer is substantially free of Rh. By making the first catalyst coating layer substantially free of Rh, it is possible to suppress a decrease in activity due to alloying of the first catalytic precious metal particles with Rh.

[0074] The amount of Rh in the first catalyst coating layer in terms of metal per 1 L of substrate volume may be 0.03 g / L or less, 0.01 g / L or less, 0.005 g / L or less, 0.003 g / L or less, or 0.001 g / L or less, or the first catalyst coating layer may not contain any Rh at all.

[0075] The first catalytic noble metal particles in the first catalytic coating layer may be supported on first inorganic oxide particles.

[0076] The first catalytic noble metal particles in the first catalytic coating layer may be supported on first inorganic oxide particles.

[0077] When the first catalyst coating layer contains, together with the first inorganic oxide particles, inorganic oxide particles other than the first inorganic oxide particles, the first catalytic precious metal particles may be supported on either the first inorganic oxide particles or the inorganic oxide particles other than the first inorganic oxide particles, or may be supported on both of them.

[0078] When the first catalytic noble metal particles are supported on the first inorganic oxide particles, at least a portion of the first catalytic noble metal particles is supported on the composite oxide support together with the second alkaline earth metal oxide.

[0079] <Coating length of first catalyst coating layer> From the viewpoint of ensuring a sufficient amount of NOx adsorption, the coating length of the first catalyst coating layer may be 35% or more, 50% or more, 60% or more, 70% or more, 80% or more, 90% or more, or 95% or more of the total length of the substrate, or the first catalyst coating layer may be disposed over the entire length of the substrate.

[0080] When the coating length of the first catalyst coating layer is shorter than the overall length of the substrate, from the viewpoint of bringing the first catalyst coating layer into contact with the exhaust gas as quickly as possible and enabling it to contribute to the adsorption of NOx, it is desirable to position the first catalyst coating layer as far upstream in the exhaust gas flow as possible on the substrate, and it is preferable to position the first catalyst coating layer so that its upstream end coincides with the upstream end of the substrate.

[0081] <<Second catalyst coating layer>> The second catalyst coating layer in the exhaust gas purification catalytic device of the present invention is disposed on the first catalyst coating layer. The first catalyst coating layer may be disposed at least partially, preferably entirely, below the second catalyst coating layer. Therefore, the second catalyst coating layer may be the upper layer of a two-layer catalyst coating layer. When the first catalyst coating layer is not disposed below the second catalyst coating layer, that portion of the second catalyst coating layer may be disposed directly on the substrate.

[0082] The second catalytic coating layer contains second inorganic oxide particles and second catalytic noble metal particles.

[0083] <Second inorganic oxide particles> The second inorganic oxide particles include an OSC material.

[0084] The OSC material contained in the second inorganic oxide particles is, for example, ceria (CeO2). The concept of ceria as an OSC material includes not only the case where it exists as a single type of ceria in the second inorganic oxide particles, but also the case where it forms a composite oxide of cerium and another metal.

[0085] When the OSC material is ceria and forms a composite oxide of cerium and another metal, the composite oxide may be, for example, a cerium-zirconium composite oxide. When ceria exists as ceria in a cerium-zirconium composite oxide, it can exist metastable even if the amount of oxygen vacancies in the ceria increases, thereby increasing the atmospheric relaxation ability of the ceria.

[0086] The content of the OSC material in the second inorganic oxide particles may be 5% by mass or more, 7.5% by mass or more, 15% by mass or more, or 20% by mass or more, and may be 50% by mass or less, 45% by mass or less, 40% by mass or less, 35% by mass or less, 30% by mass or less, or 25% by mass or less, when the total mass of the second inorganic oxide particles is 100% by mass.

[0087] Furthermore, the amount of the OSC material (typically ceria) in the second catalyst coating layer, in terms of the mass of the OSC material per 1 L of the volume of the substrate, may be 3.0 g / L or more, 4.0 g / L or more, 5.0 g / L or more, 6.0 g / L or more, or 8.0 g / L or more, and may be 20.0 g / L or less, 15.0 g / L or less, 12.0 g / L or less, 11.0 g / L or less, or 10.0 g / L or less.

[0088] <Other ingredients> The second inorganic oxide particles contained in the second catalyst coating layer may contain other components in addition to the second inorganic oxide particles described above. The other components may be, for example, inorganic oxide particles other than the second inorganic oxide particles, a binder, etc.

[0089] The inorganic oxide particles other than the second inorganic oxide particles may be, for example, one type of inorganic oxide selected from alumina, silica, titania, zirconia, etc., or a composite oxide composed of two or more of these, or a composite oxide of these inorganic oxides or composite oxides and one or more types selected from oxides of rare earth elements other than ceria.

[0090] The second inorganic oxide particles preferably contain alumina in terms of the heat resistance of the exhaust gas purification catalytic device. The content of alumina in the second inorganic oxide particles may be 20% by mass or more, 30% by mass or more, 40% by mass or more, 50% by mass or more, or 60% by mass or more, and may be 90% by mass or less, 80% by mass or less, 70% by mass or less, or 60% by mass or less, when the total mass of the second inorganic oxide particles is 100% by mass.

[0091] The amount of alumina in the second catalyst coating layer may be, in terms of the mass of alumina per 1 L of substrate volume, 10.0 g / L or more, 20.0 g / L or more, 30.0 g / L or more, 50.0 g / L or more, 60.0 g / L or more, or 70.0 g / L or more, and may be 200.0 g / L or less, 150.0 g / L or less, 120.0 g / L or less, 100.0 g / L or less, or 80.0 g / L or less.

[0092] <Second catalytic precious metal particles> The second catalytic coating layer contains second catalytic noble metal particles together with second inorganic oxide particles, and the second catalytic noble metal particles contain Rh.

[0093] The amount of the second catalytic precious metal particles in the second catalytic coating layer may be, in terms of the mass of the first catalytic precious metal particles per 1 L of substrate volume (total mass when multiple types of precious metals are included), 0.03 g / L or more, 0.05 g / L or more, 0.06 g / L or more, 0.08 g / L or more, 0.10 g / L or more, or 0.12 g / L or more, and may be 2.0 g / L or less, 1.5 g / L or less, 1.00 g / L or less, 0.50 g / L or less, 0.30 g / L or less, 0.20 g / L or less, 0.18 g / L or less, or 0.15 g / L or less.

[0094] In the second catalyst coating layer, the total amount of Pt and Pd in ​​terms of metal per 1 L of substrate volume is 0.05 g / L or less. The total amount of Pt and Pd in ​​the second catalyst coating layer being 0.05 g / L or less means that the second catalyst coating layer is substantially free of Pt and Pd. The second catalyst coating layer being substantially free of Pt and Pd improves the NOx reduction and purification ability.

[0095] The total amount of Pt and Pd in ​​terms of metal per 1 L of substrate volume in the first catalyst coating layer may be 0.03 g / L or less, 0.01 g / L or less, 0.005 g / L or less, 0.003 g / L or less, or 0.001 g / L or less, or the second catalyst coating layer may be completely free of Pt and Pd.

[0096] The second catalytic noble metal particles in the second catalytic coating layer may be supported on second inorganic oxide particles.

[0097] The second catalytic noble metal particles in the second catalytic coating layer may be supported on second inorganic oxide particles.

[0098] When the second catalyst coating layer contains, together with the second inorganic oxide particles, inorganic oxide particles other than the second inorganic oxide particles, the second catalytic precious metal particles may be supported on either the second inorganic oxide particles or the inorganic oxide particles other than the second inorganic oxide particles, or may be supported on both of them.

[0099] <Amount of alkaline earth metal oxide in second catalyst coating layer> The amount of alkaline earth metal oxide in the second catalyst coating layer per 1 L of substrate volume is 0.5 g / L or less. The alkaline earth metal oxide content of the second catalyst coating layer being 0.5 g / L or less means that the second catalyst coating layer is substantially free of alkaline earth metal oxide. By making the second catalyst coating layer substantially free of alkaline earth metal oxide, it is possible to suppress a decrease in the NOx reduction and purification activity of Rh due to an interaction between Rh and alkaline earth metal oxide.

[0100] The amount of alkaline earth metal oxide in the second catalyst coating layer per liter of substrate volume may be 0.3 g / L or less, 0.01 g / L or less, 0.05 g / L or less, 0.03 g / L or less, or 0.01 g / L or less, or the second catalyst coating layer may contain no alkaline earth metal oxide at all.

[0101] <Coating length of second catalyst coating layer> From the viewpoint of ensuring sufficient NOx reduction and purification performance, the coating length of the second catalyst coating layer may be 70% or more, 75% or more, 80% or more, 85% or more, 90% or more, or 95% or more of the total length of the substrate, or the second catalyst coating layer may be disposed over the entire length of the substrate.

[0102] When the coating length of the second catalyst coating layer is shorter than the overall length of the substrate, in order to ensure contact with the NOx released from the first catalyst coating layer, it is desirable to position the second catalyst coating layer as far downstream in the exhaust gas flow as possible on the substrate, and it is preferable to position the second catalyst coating layer so that its downstream end coincides with the downstream end of the substrate.

[0103] <<Specific example of the configuration of an exhaust gas purification catalyst device>> FIG. 1 shows an example of the configuration of an exhaust gas purification catalyst device of the present invention.

[0104] The catalytic device for purifying exhaust gas in FIG. 1 comprises a substrate (100), a first catalyst coating layer (200) on the substrate (100), and a second catalyst coating layer (300) on the first catalyst coating layer (200).

[0105] The first catalyst coating layer (200) contains first inorganic oxide particles (10) and first catalytic precious metal particles (40), and may further contain inorganic oxide particles (50) other than the first inorganic oxide particles (10).

[0106] The first inorganic oxide particles (10) contain an OSC material (11) and an alkaline earth metal oxide (20). The first inorganic oxide particles (10) contain a composite oxide support (30) and a second alkaline earth metal oxide (22) supported on the composite oxide support (30). The composite oxide support (30) contains the OSC material (11) and the first alkaline earth metal oxide (21), and may optionally contain other components (12).

[0107] The first catalytic precious metal particles (40) in the first catalytic coating layer (200) contain one or two kinds of metals selected from Pt and Pd. The first catalytic precious metal particles (40) are supported on the first inorganic oxide particles (10) and may also be supported on other inorganic oxide particles (50).

[0108] In other words, in one embodiment, the first catalyst coating layer (200) is a composite oxide support (30) including an OSC material (11) and a first alkaline earth metal oxide (21); Other inorganic oxide particles (50) Including, The composite oxide support (30) supports first catalytic noble metal particles (40) and a second alkaline earth metal oxide (22), The other inorganic oxide particles (50) carry first catalytic noble metal particles (40).

[0109] The first catalyst coating layer (200) does not substantially contain Rh.

[0110] The second catalyst coating layer (300) contains second inorganic oxide particles (60) and second catalytic precious metal particles (70), and may further contain inorganic oxide particles (80) other than the second inorganic oxide particles (60).

[0111] The second inorganic oxide particles (60) contain an OSC material (11). The second inorganic oxide particles (60) contain the OSC material (11) and may optionally contain other components (13).

[0112] The second catalytic noble metal particles (70) in the second catalytic coating layer (300) contain Rh. The second catalytic noble metal particles (70) are supported on the second inorganic oxide particles (60) and may also be supported on other inorganic oxide particles (80).

[0113] In other words, the second catalyst coating layer (300) in one embodiment is Second inorganic oxide particles (60) containing an OSC material (11); Other inorganic oxide particles (80) Including, The second inorganic oxide particles (60) and the other inorganic oxide particles (80) carry second catalytic noble metal particles (70).

[0114] The second catalytic coating layer (300) is substantially free of Pd, Pt, and alkaline earth metal oxides.

[0115] <<Method for manufacturing an exhaust gas purification catalyst device>> The exhaust gas purification catalyst device of the present invention may be produced by any method as long as it has the above-mentioned configuration.

[0116] The exhaust gas purification catalyst device of the present invention includes, for example, Forming a first catalyst coating layer containing first inorganic oxide particles and first catalytic noble metal particles on a substrate (first catalyst coating layer forming step); forming a second catalyst coating layer on the substrate on which the first catalyst coating layer has been formed (second catalyst coating layer forming step); It may be produced by a method comprising:

[0117] Hereinafter, as a typical example of the catalytic device for purifying exhaust gas according to the present invention, the case of manufacturing the catalytic device for purifying exhaust gas shown in FIG. 1 will be described as an example.

[0118] <First catalyst coating layer forming step> The first catalyst coating layer forming step may be carried out, for example, by coating a substrate with a first catalyst coating layer forming coating liquid and then baking the coating liquid. After coating, the coating layer may be dried, if necessary, before baking.

[0119] The substrate may be appropriately selected depending on the desired configuration of the exhaust gas purification catalytic device, and may be, for example, a monolith honeycomb substrate of a straight-flow type or a wall-flow type made of cordierite.

[0120] In one embodiment, the first catalyst coating layer (200) in the exhaust gas purification catalytic device shown in FIG. 1 is a composite oxide support (30) including an OSC material (11) and a first alkaline earth metal oxide (21); Other inorganic oxide particles (50) Including, The composite oxide support (30) supports first catalytic noble metal particles (40) and a second alkaline earth metal oxide (22), The other inorganic oxide particles (50) carry first catalytic noble metal particles (40).

[0121] The first catalyst coating layer forming coating liquid for forming such a first catalyst coating layer (200) may be a liquid composition containing the composite oxide support (30), other inorganic oxide particles (50), a precursor of the first catalytic precious metal particles (40), and a precursor of the second alkaline earth metal oxide (22), and, if necessary, other components are dissolved or suspended in a suitable solvent.

[0122] The composite oxide support 30 may be produced, for example, by a coprecipitation method. Specifically, the composite oxide support 30 may be produced by adding an appropriate precipitant to a liquid mixture (preferably an aqueous solution) containing a precursor of the OSC material 11, a precursor of the first alkaline earth metal oxide 21, and precursors of optional components as needed, drying and calcining the resulting precipitate, followed by pulverization and classification.

[0123] The precursor of the OSC material (11), the precursor of the first alkaline earth metal oxide (21), and the precursor of the optional components may be a nitrate, sulfate, hydrochloride, acetate, etc. of the desired metal. The precipitant may be an alkali, such as sodium hydroxide, potassium hydroxide, ammonium hydroxide, etc., and may be used as a solution thereof, preferably an aqueous solution.

[0124] The drying and calcination of the precipitate, and the pulverization and classification of the calcined product may be carried out by known methods or by methods modified as appropriate by those skilled in the art.

[0125] The precursor of the first catalytic noble metal particles (40) and the precursor of the second alkaline earth metal oxide (22) may be a nitrate, sulfate, hydrochloride, acetate, or the like of the desired metal, respectively. The other components may be, for example, a binder, etc. The solvent may be, for example, water, a mixture of water and a water-soluble organic solvent, etc., and is typically water.

[0126] Coating of the first catalyst coating layer-forming coating liquid onto the substrate, and drying and baking after coating may each be carried out in accordance with a known method.

[0127] <Second catalyst coating layer forming step> In the second catalyst coating layer forming step, for example, a second catalyst coating layer is formed on the substrate on which the first catalyst coating layer has been formed as described above.

[0128] In one embodiment, the second catalyst coating layer (300) in the exhaust gas purification catalytic device shown in FIG. 1 is Second inorganic oxide particles (60) containing an OSC material (11); Other inorganic oxide particles (80) Including, The second inorganic oxide particles (60) and the other inorganic oxide particles (80) carry second catalytic noble metal particles (70).

[0129] The second catalyst coating layer forming coating liquid for forming such a second catalyst coating layer (300) may be a liquid composition containing the second inorganic oxide particles (60), the other inorganic oxide particles (80), and a precursor of the second catalytic precious metal particles (70), and, if necessary, other components are dissolved or suspended in a suitable solvent.

[0130] The precursor of the second catalytic noble metal particles (70) may be a nitrate, sulfate, hydrochloride, acetate, etc. of the desired metal. Other components may be, for example, a binder, etc. The solvent may be, for example, water, a mixture of water and a water-soluble organic solvent, etc., and is typically water.

[0131] The coating of the second catalyst coat layer forming coating liquid, and the drying and baking after coating may each be carried out in accordance with a known method.

[0132] <<Exhaust gas purification method>> The catalytic converter for exhaust gas purification of the present invention is suitable as a catalytic converter for purifying exhaust gas emitted from the engine of an automobile, etc. When the catalytic converter for exhaust gas purification of the present invention is used, NOx emissions are effectively reduced even in a cold state, such as immediately after starting the engine, when the exhaust gas contains NOx.

[0133] Therefore, in another aspect, the present invention provides a method for purifying exhaust gases, which comprises contacting exhaust gases with the catalytic device for purifying exhaust gases of the present invention.

[0134] The contact of exhaust gas with the catalytic device for purifying exhaust gas of the present invention may be achieved by a known method, for example, by placing the catalytic device for purifying exhaust gas of the present invention in the exhaust system of an engine. [Example]

[0135] <Synthesis of composite oxide support 1> Zirconium oxynitrate, cerium nitrate, aluminum nitrate, neodymium nitrate, lanthanum nitrate, and magnesium acetate (precursors of the first alkali metal oxide (MgO)) were dissolved in pure water so that the mass ratios calculated on oxide basis were as follows, to obtain an acidic mixed solution. A sodium hydroxide aqueous solution was added to this mixed solution until the pH reached 7, and a coprecipitation operation was performed to obtain a precipitate. The precipitate was collected by filtration, thoroughly washed with pure water, dried in air at 250°C for 8 hours, and then calcined in air at 500°C for 2 hours to obtain a calcined product. The calcined product obtained was pulverized in an agate mortar and classified to obtain a powdery composite oxide support 1 having a particle size range of 2 to 10 μm.

[0136] The mass proportions of the respective components in the composite oxide support 1, calculated as oxides, are as follows: ZrO2: 69.0% by mass CeO2:21.0% by mass Nd2O3: 5.3% by mass La2O3: 1.7% by mass MgO: 3.0% by mass

[0137] Other Oxide Carriers As other oxide supports, the following were used. Composite oxide support 2: A composite oxide support in which the mass ratio of each component, calculated as oxide, is as follows: ZrO2:66.0% by mass CeO2:21.0% by mass Nd2O3: 5.3% by mass La2O3: 1.7% by mass MgO: 6.0% by mass

[0138] Composite oxide support 3: A composite oxide support in which the mass ratio of each component, calculated as oxide, is as follows: ZrO2:72.0% by mass CeO2:21.0% by mass Nd2O3: 5.3% by mass La2O3: 1.7% by mass MgO: 0% by mass

[0139] Composite oxide support 4: A composite oxide support (spinel) having the following mass ratios of the respective components converted into oxides: Al2O3:65.0% by mass CeO2: 17.0% by mass La2O3: 2.0% by mass MgO: 16.0% by mass

[0140] Other inorganic oxide particles 1: Cerium-zirconium composite oxide particles containing 40 mass% CeO2, with trace amounts of Pr2O3 and La2O3 added, and calcined at 800°C for 5 hours. Other inorganic oxide particles 2: La2O3 composite alumina, La2O3 content 4.0 mass% Other inorganic oxide particles 3: Cerium-zirconium composite oxide particles containing 20 mass% CeO2, with trace amounts of Nd2O3, La2O3, and Y2O3 added, and calcined at 800°C for 5 hours.

[0141] 《Base material》 The substrate used was a cordierite honeycomb substrate with a rectangular prism shape, 600 cells, a total length of 115 mm, a wall thickness of 2 mil (0.0508 mm), and a capacity of 1,259 mL.

[0142] Example 1 (1) Preparation of coating solution for forming Pt-Pd layer Palladium nitrate, platinum nitrate, barium sulfate (precursor of the second alkaline earth metal oxide), the powdered composite oxide support 1 obtained in the above "Synthesis of composite oxide support 1", other inorganic oxide particles 1, other inorganic oxide particles 2, and an alumina-based binder were added to pure water and stirred thoroughly to obtain a coating liquid for forming a Pt-Pd layer in the form of a suspension.

[0143] The content of each component in the obtained Pt—Pd layer-forming coating liquid was determined as follows, expressed as a mass per 1 L of the substrate volume. Barium sulfate: 5.0g / L as barium oxide equivalent Palladium nitrate: 3.0g / L as palladium metal equivalent Platinum nitrate: 1.39g / L as platinum metal equivalent Composite oxide carrier 1: 40g / L Other inorganic oxide particles 1: 40g / L Other inorganic oxide particles 2: 40g / L

[0144] (2) Preparation of coating solution for Rh layer formation Rhodium nitrate, other inorganic oxide particles 2, and other inorganic oxide particles 3 were added to pure water and stirred thoroughly to obtain a coating liquid for forming an Rh layer in the form of a suspension.

[0145] The content of each component in the obtained Rh layer-forming coating liquid was determined as follows, expressed as the mass per 1 L of the substrate volume. Rhodium nitrate: 0.13g / L as rhodium metal equivalent Other inorganic oxide particles 2: 70g / L Other inorganic oxide particles 3: 50g / L

[0146] (3) Manufacturing of exhaust gas purification catalyst devices After pouring the Pt-Pd layer coating solution onto the substrate, the excess was blown off with a blower, and the entire length of the substrate was coated with the Pt-Pd layer coating solution. The coated substrate was then left to dry in a dryer adjusted to 120°C for 2 hours, and then fired in an electric furnace at 500°C for 2 hours to form a Pt-Pd layer on the substrate.

[0147] The Rh layer-forming coating liquid was poured onto the substrate with the Pt-Pd layer formed, and then the unnecessary portions were blown off with a blower to coat the entire length of the substrate with the Rh layer-forming coating liquid. The coated substrate was left to dry for 2 hours in a dryer adjusted to 120°C, and then baked in an electric furnace at 500°C for 2 hours to form an Rh layer, thereby obtaining an exhaust gas purification catalyst device having a Pt-Pd layer and a Rh layer, in that order, on the substrate.

[0148] (4) Evaluation The resulting exhaust gas purification catalyst device was installed in the exhaust system of a 4,608cc V8 engine, and the durability of the catalyst device was tested by repeatedly passing exhaust gas in a stoichiometric atmosphere and a lean atmosphere at specified intervals for 50 hours at a catalyst bed temperature of 1,000°C.

[0149] Using the exhaust gas purification catalyst device after durability testing, NOx emissions in the cold region were measured in the WLTC driving mode, and the reduction rate, assuming the amount of NOx in the exhaust gas in the cold region to be 100%, was calculated using the following formula. The results are shown in Table 1. NOx reduction rate (%) = (NOx amount in exhaust gas - NOx emissions) / NOx amount in exhaust gas x 100

[0150] Examples 2 to 7 and Comparative Examples 1 and 2 Except for changing the compositions of the Pt-Pd layer-forming coating liquid and the Rh layer-forming coating liquid as shown in Table 1 or Table 2, exhaust gas purification catalyst devices were manufactured and evaluated in the same manner as in Example 1. The results are shown in Table 1 or Table 2.

[0151] Comparative Example 3 Except for the fact that the order of forming the Pt-Pd layer and the Rh layer was reversed, an exhaust gas purification catalyst device having an Rh layer and a Pt-Pd layer formed in this order on a substrate was produced in the same manner as in Comparative Example 2. The obtained exhaust gas purification catalyst device was evaluated in the same manner as in Example 1. The results are shown in Table 2.

[0152] Comparative Example 4 Except for changing the compositions of the Pt—Pd layer-forming coating liquid and the Rh layer-forming coating liquid as shown in Table 2, exhaust gas purification catalyst devices were manufactured and evaluated in the same manner as in Comparative Example 3. The results are shown in Table 2.

[0153] [Table 1]

[0154] [Table 2]

[0155] As can be seen from Table 1 above, on the substrate, a first catalyst coating layer including a composite oxide support containing an OSC material and one or two first catalytic precious metal particles selected from Pt and Pd; a second catalytic coating layer containing second inorganic oxide particles and second catalytic precious metal particles containing Rh; In an exhaust gas purification catalyst device having When the first catalyst coating layer is the lower layer and the second catalyst coating layer is the upper layer, An exhaust gas purification catalyst device of Comparative Example 1 in which neither the first catalyst coating layer nor the second catalyst coating layer contains alkaline earth metal oxides; and The exhaust gas purification catalyst device of Comparative Example 2, in which both the first catalyst coating layer and the second catalyst coating layer contain alkaline earth metal oxides. In both cases, the reduction rate of NOx in exhaust gas in the cold region was insufficient.

[0156] In contrast, The first catalyst coating layer is a lower layer, and the second catalyst coating layer is an upper layer, The first catalytic coating layer contains an alkaline earth metal oxide, and the second catalytic coating layer does not contain a significant amount of alkaline earth metal oxides; In Examples 1 to 7, it was verified that the reduction rate of NOx in exhaust gas in the cold region was large.

[0157] however, Even if the first catalyst coating layer contains an alkaline earth metal oxide and the second catalyst coating layer does not contain an alkaline earth metal oxide, The second catalyst coating layer is a lower layer and the first catalyst coating layer is an upper layer. In Comparative Examples 3 and 4, it was confirmed that the reduction rate of NOx in the exhaust gas in the cold region was insufficient.

[0158] From the above, it was verified that the catalytic device for purifying exhaust gas of the present invention exhibits particularly excellent NOx purification performance in the cold region. [Explanation of symbols]

[0159] 10. First inorganic oxide particles 11 OSC material 12, 13 Other ingredients 20 Alkaline earth metal oxides 21 First alkaline earth metal oxide 22 Second alkaline earth metal oxide 30 Composite oxide support 40 First catalytic precious metal particles 50, 80 Other inorganic oxide particles 60 Second inorganic oxide particles 70 Second catalytic precious metal particles 100 Base material 200 First catalyst coating layer 300 Second catalyst coating layer

Claims

1. A catalyst system comprising: a substrate; a first catalyst coating layer on the substrate; and a second catalyst coating layer on the first catalyst coating layer; The first catalytic coating layer includes first inorganic oxide particles and first catalytic precious metal particles, the second catalytic coating layer includes second inorganic oxide particles and second catalytic precious metal particles; The first inorganic oxide particles include an OSC material and an alkaline earth metal oxide; The first catalytic precious metal particles contain one or two types selected from Pt and Pd, The first inorganic oxide particles are A composite oxide support comprising an OSC material and a first alkaline earth metal oxide; A second alkaline earth metal oxide supported on the composite oxide support; Including, the amount of the first alkaline earth metal oxide is 0.1 mass% or more and 15 mass% or less when the total mass of the composite oxide support is 100 mass%, The second inorganic oxide particles include an OSC material; the second catalytic precious metal particles contain Rh; In the first catalyst coating layer, the amount of Rh in terms of metal per 1 L of the base material is 0.05 g / L or less, In the second catalyst coating layer, the total amount of Pt and Pd in ​​terms of metal per 1 L of the substrate volume is 0.05 g / L or less, and the amount of alkaline earth metal oxide per 1 L of the substrate volume is 0.5 g / L or less. Exhaust gas purification catalytic converter.

2. The composite oxide support, An OSC material; a first alkaline earth metal oxide; One or more oxides selected from oxides of rare earth elements other than ceria, zirconia, silica, and tungsten oxide; Consists of: The exhaust gas purification catalyst device according to claim 1.

3. 3. The exhaust gas purification catalyst device according to claim 1, wherein at least a part of the first catalytic precious metal particles is supported on the composite oxide support together with the second alkaline earth metal oxide.

4. 4. The exhaust gas purification catalyst device according to claim 1, wherein the first alkaline earth metal oxide is magnesium oxide.

5. 5. The exhaust gas purification catalyst device according to claim 1, wherein the second alkaline earth metal oxide is one or more selected from the group consisting of magnesium oxide, barium oxide, and strontium oxide.

6. The amount of the second alkaline earth metal oxide supported is 0.5 mass% or more and 25 mass% or less when the total mass of the composite oxide support is 100 mass%. The exhaust gas purification catalyst device according to any one of claims 1 to 5.

7. 7. The exhaust gas purification catalyst device according to claim 1, wherein the amount of the first catalytic precious metal particles per 1 L of the capacity of the substrate is 0.5 g / L or more and 10.0 g / L or less.

8. The exhaust gas purification catalyst device according to any one of claims 1 to 7, wherein the first inorganic oxide particles further contain alumina.

9. 9. The exhaust gas purification catalyst device according to claim 1, wherein the amount of the second catalytic precious metal particles per 1 L of the volume of the substrate is 0.05 g / L or more and 2.0 g / L or less.

10. The exhaust gas purification catalyst device according to any one of claims 1 to 9, wherein the second inorganic oxide particles further contain alumina.

11. The exhaust gas purification catalyst device according to any one of claims 1 to 10, wherein the OSC material contains ceria in a cerium-zirconium composite oxide.

12. The exhaust gas purification catalyst device according to any one of claims 1 to 11, wherein the first catalytic precious metal particles contain both Pt and Pd.

13. 13. The exhaust gas purification catalyst device according to claim 1, wherein a coating length of the first catalyst coating layer is 35% or more of a total length of the substrate.

14. 14. The exhaust gas purification catalyst device according to claim 1, wherein the coating length of the second catalyst coating layer is 70% or more of the entire length of the substrate.

15. A method for purifying exhaust gas, comprising contacting exhaust gas with the exhaust gas purification catalyst device according to any one of claims 1 to 14.

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