EXHAUST PURIFICATION DEVICE

Abstract

Exhaust gas purification device (100), comprising: a substrate (10) comprising an upstream end (I) through which an exhaust gas is introduced into the device and a downstream end (J) through which the exhaust gas is discharged from the device, wherein the substrate (10) has a length Ls between the upstream end (I) and the downstream end (J); a first catalyst layer (20) containing palladium particles, which extends over a first region (X) and is in contact with the substrate (10), wherein the first region (X) extends between the upstream end (I) and a first position (P), wherein the first position (P) is located at a first distance La from the upstream end (I) in the direction of the downstream end (J); a second catalyst layer (30) containing rhodium particles, which extends over a second region (Y) and is in contact with the substrate (10), wherein the second region (Y) extends between the downstream end (J) and a second position (Q), the second position (Q) being located at a second distance Lb from the downstream end (J) in the direction of the upstream end (I); and a third catalyst layer (40) containing rhodium particles, which extends over a third region (Z) and is in contact with at least the first catalyst layer (20), wherein the third region (Z) extends between the upstream end (I) and a third position (R), wherein the third position (R) is located at a third distance Lc from the upstream end (I) in the direction of the downstream end (J), wherein a mean particle size distribution of the rhodium particles contained in the second catalyst layer (30) and the third catalyst layer (40) is from 1.0 nm to 2.0 nm, and a standard deviation of the particle size distribution of the rhodium particles contained in the second catalyst layer (30) and the third catalyst layer (40) is 0.8 nm or less.

Description

BACKGROUND Technical area

[0001] The present invention relates to an exhaust gas purification device. State of the art

[0002] Exhaust gas emitted by an internal combustion engine used in a vehicle, such as a car, contains harmful substances such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). x Regulations regarding emission levels of these harmful substances have been tightened year after year. To remove these harmful substances, a precious metal such as platinum (Pt), palladium (Pd), and rhodium (Rh) is used as a catalyst.

[0003] Meanwhile, with regard to resource conservation and resource scarcity, a reduction in the use of precious metal catalysts is required. One known method for reducing the use of precious metals in exhaust gas purification devices involves a process in which a precious metal is supported on a substrate in the form of fine particles. For example, JP 2016-147256 A discloses a manufacturing process for a catalyst, comprising a step of supporting precious metal particles on an oxide substrate to produce a precious metal-bearing catalyst, and a step of performing a heat treatment process on the precious metal-supported catalyst under reduced pressure to control the size of the precious metal particles within a predetermined range.The example of JP 2016-147256 A reveals that it was possible to control the particle sizes of the precious metal particles on the oxide support in a range of 2.8 nm or more and 3.8 nm or less.

[0004] Furthermore, the published patent specification US 10 150 082 B2 discloses a catalyst for the exhaust gas purification of internal combustion engines and a system thereof from the prior art. SUMMARY

[0005] Among the precious metals, Rh exhibits a NO x -Reduction activity. However, Rh particles whose particle sizes were controlled by the method described in JP 2016-147256 A were insufficient with regard to high temperature stability, which can cause sintering of the Rh particles under high temperature conditions, leading in some cases to a deterioration of the catalytic activity.

[0006] The present invention provides an exhaust gas purification device which achieves a high NOₓ level. x -Turnover rate shows, even after use under high temperature conditions.

[0007] According to the present invention, an exhaust gas purification device is provided, which comprises: a substrate comprising an upstream end through which an exhaust gas is introduced into the device and a downstream end through which the exhaust gas is expelled from the device, wherein the substrate has a length Ls between the upstream end and the downstream end; a first catalyst layer containing palladium particles, which extends over a first region and is in contact with the substrate, wherein the first region extends between the upstream end and a first position, the first position being located at a first distance La from the upstream end in the direction of the downstream end; a second catalyst layer containing rhodium particles, which extends over a second region and is in contact with the substrate, wherein the second region extends between the downstream end and a second position, the second position being located at a second distance Lb from the downstream end towards the upstream end; and a third catalyst layer containing rhodium particles, which extends over a third region and is in contact with at least the first catalyst layer, wherein the third region extends between the upstream end and a third position, the third position being located at a third distance Lc from the upstream end in the direction of the downstream end, wherein a mean particle size distribution of the rhodium particles contained in the second catalyst layer and the third catalyst layer is from 1.0 nm to 2.0 nm, and a standard deviation of the particle size distribution of the rhodium particles contained in the second catalyst layer and the third catalyst layer is 0.8 nm or less.

[0008] The exhaust gas purification device of the present invention exhibits a high NO x-Turnover rate, even after use under high temperature conditions. BRIEF DESCRIPTION OF THE DRAWING Fig. Figure 1 is an enlarged end view of a main part of an exhaust gas purification device according to an embodiment, which is taken along a surface parallel to a flow direction of an exhaust gas and schematically represents a configuration near a partition wall of a substrate; Fig. Figure 2 is a perspective view that schematically represents an example of the substrate; Fig. Figure 3 is an enlarged end view of a main part of an exhaust gas purification device according to a modified embodiment, which is taken along a surface parallel to a flow direction of an exhaust gas and schematically represents a configuration near a partition wall of a substrate; and Fig. 4 is a graph which NO x-Turnover rates and total hydrocarbon (THC) turnover rates of exhaust gas purification devices from examples and comparative examples. DETAILED DESCRIPTION

[0009] The following describes embodiments of the present invention with reference to the drawing. In the drawing to which the following description refers, the same reference numerals are used for the same elements, or elements having similar functions, and their repeated description may be omitted in some cases. For the sake of clarity, a dimensional ratio or size ratio in the drawing may differ from the actual ratio, and part of an element may be omitted from the drawing in some cases. In this application, a numerical range expressed using the word "to" includes the values ​​above and those described after the word "to" as the lower limit and the upper limit, respectively.

[0010] An exhaust gas purification device 100 according to one embodiment is described with reference to the Fig. 1 and Fig.2 described. The exhaust gas purification device 100 according to the embodiment comprises a substrate 10, a first catalyst layer 20, a second catalyst layer 30, and a third catalyst layer 40. (1) Substrate 10

[0011] The shape of substrate 10 is not specifically restricted. For example, however, as in Fig.As shown in Figure 2, the substrate 10 comprises a frame section 12 and partitions 16 that divide a space within the frame section 12 to define a plurality of cells 14. The frame section 12 and the partitions 16 can be formed entirely or completely. The frame section 12 can have any shape, such as a cylindrical shape, an elliptical-cylindrical shape, or a polygonal-cylindrical shape. The partitions 16 extend between a first end (a first end surface) I and a second end (a second end surface) J of the substrate 10 to define the plurality of cells 14 that extend between the first end I and the second end J. Each cell 14 can have any cross-sectional shape, including a quadrilateral orFour-sided shape, such as a square shape, a parallelogram, a rectangular shape, and a trapezoidal shape; a triangular shape; any polygonal shape (for example, a hexagonal or six-sided shape and an octagonal or eight-sided shape); and a circular shape.

[0012] For example, the substrate 10 can be made of a ceramic material with high heat resistance, such as cordierite (2MgO·2Al2O3·5SiO2), aluminum oxide, zirconium dioxide, and silicon carbide, or of a metal material formed from a metal foil, such as stainless steel foil. With regard to cost, the substrate 10 can be made of cordierite in some embodiments.

[0013] In the Fig. 1 and Fig.2. The dashed arrows indicate the direction of flow of exhaust gas in the exhaust gas cleaning device 100 and the substrate 10. The exhaust gas is introduced into the exhaust gas cleaning device 100 through the first end I and expelled from the exhaust gas cleaning device 100 through the second end J. Therefore, the first end I is also referred to below, where necessary, as an upstream end I and the second end J is also referred to as a downstream end J. In this description, the length between the upstream end I and the downstream end J, that is, the total length of the substrate 10, is referred to as Ls. (2) First catalyst layer 20

[0014] The first catalyst layer 20 is in contact with the substrate 10 and extends over a first region X, which lies between the upstream end I and a first position P located at a first distance La from the upstream end I in the direction of the downstream end J (i.e., in the direction of exhaust gas flow). The first distance La can be from 15% to 35% of the total length Ls of the substrate 10.

[0015] The first catalyst layer 20 contains palladium (Pd) particles. The Pd particles can function as a catalyst to oxidize hydrocarbons (HC). The amount of Pd particles contained in the first catalyst layer 20 can, for example, range from 0.1 g / L to 10 g / L, based on a substrate capacity in the first region X; in some embodiments, it can range from 1 g / L to 9 g / L, based on a substrate capacity in the first region X; and in some embodiments, it can range from 3 g / L to 7 g / L, based on a substrate capacity in the first region X. This enables the exhaust gas purification device 100 to exhibit a sufficiently high exhaust gas purification performance.

[0016] The Pd particles can be carried on carrier particles. The carrier particles are not specifically limited. For example, oxide carrier particles can be used. The Pd particles can be carried by any carrier method, such as an impregnation carrier method, an adsorption carrier method, and a water absorption carrier method.

[0017] Examples of oxide carrier particles include metal oxide particles, for example, particles of the oxide of one or more metals selected from the group consisting of the elements of Groups 3, 4, and 13 of the periodic table, and lanthanide-based metals. If the oxide carrier particles are particles of the oxide of two or more metals, the oxide carrier particles can be a mixture of two or more metal oxides, a composite oxide containing two or more metals, or a mixture of one or more metal oxides and one or more composite oxides.

[0018] For example, the metal oxide can be an oxide of one or more metals selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), lutetium (Lu), titanium (Ti), zirconium (Zr), and aluminum (Al). In some embodiments, the metal oxide can be an oxide of one or more metals selected from the group consisting of Y, La, Ce, Ti, Zr, and Al. In particular, the metal oxide can be aluminum oxide (Al₂O₃) or a composite oxide of Al₂O₃ and lanthanum oxide (La₂O₃).

[0019] The quantity of carrier particles contained in the first catalyst layer 20 can, for example, range from 1 g / L to 100 g / L, based on the substrate capacity in the first region X; in some embodiments, it can range from 10 g / L to 90 g / L, based on the substrate capacity in the first region X; and in some embodiments, it can range from 30 g / L to 70 g / L, based on the substrate capacity in the first region X. This enables the exhaust gas purification device 100 to exhibit a sufficiently high exhaust gas purification performance. The particle sizes of the carrier particles are not specifically limited and can be appropriately adjusted.

[0020] Using the Pd particles which are carried on the carrier particles, the amount of carried Pd particles can be, for example, 40 wt% or less, 30 wt% or less, 20 wt% or less, 15 wt% or less, 13 wt% or less, or 11 wt% or less, based on the weight of the carrier particles, and the amount of carried Pd particles can be, for example, 0.1 wt% or more, 0.5 wt% or more, 1 wt% or more, 5 wt% or more, 7 wt% or more, or 9 wt% or more, based on the weight of the carrier particles.

[0021] The first catalyst layer 20 may also contain other optional components or ingredients. Examples of other optional components include an oxygen storage capacity ( „Oxygen Storage Capacity (OSC) material that traps or occludes oxygen in the atmosphere under an oxygen-excess atmosphere and releases or emits oxygen under an oxygen-deficient atmosphere.

[0022] The OSC material is not specifically limited, and examples include cerium oxide (cerium dioxide: CeO2), a composite oxide comprising cerium oxide (for example, cerium oxide-zirconium dioxide (ZrO2) composite oxide (CZ or ZC composite oxide), and aluminum oxide (Al2O3)-cerium oxide-zirconium dioxide composite oxide (ACZ composite oxide)). In particular, CZ composite oxide can be used in some embodiments due to its high oxygen storage capacity and relatively low cost. A composite oxide produced by further combining CZ composite oxide with lanthanum oxide (La2O3), yttrium oxide (Y2O3), or similar materials can also be used as an OSC material. The weight ratio of cerium oxide to zirconium dioxide in the cerium oxide-zirconium dioxide composite oxide (CeO2 / ZrO2) can be 0.1 to 1.0.

[0023] The amount of OSC material contained in the first catalyst layer 20 can, for example, range from 1 g / L to 100 g / L, based on the substrate capacity in the first region X; in some embodiments, it can range from 10 g / L to 90 g / L, based on the substrate capacity in the first region X; and in some embodiments, it can range from 30 g / L to 70 g / L, based on the substrate capacity in the first region X. This enables the exhaust gas purification device 100 to exhibit a sufficiently high exhaust gas purification performance.

[0024] The first catalyst layer 20 can be formed, for example, as follows. First, a slurry containing Pd particle precursors and support powder is prepared. Alternatively, a slurry containing support powder on which Pd particles are temporarily supported can be prepared. The slurry can also contain an OSC material, a binder, an additive, or similar. Properties of the slurry, such as viscosity and the particle diameter of a solid component, can be adjusted accordingly. The prepared slurry is applied to the substrate 10 in the first area X.For example, substrate 10 is immersed in the slurry from the upstream end I to a depth corresponding to the first distance La, and after a predetermined time has elapsed, substrate 10 is withdrawn from the slurry, allowing the substrate 10 to be covered or coated with the slurry in the first region X. Alternatively, the slurry can be poured into cells 14 through the upstream end I of substrate 10, and a blower can blow the slurry from the upstream end I to distribute it towards the downstream end J, allowing the substrate 10 to be covered or coated with the slurry. Next, the slurry is dried and sintered at a predetermined temperature for a predetermined time. This forms the first catalyst layer 20, which is in contact with substrate 10, in the first region X.

[0025] A suitable Pd salt of an inorganic salt, for example hydrochloride, nitrate, phosphate, sulfate, borate, and hydrofluoride, can be used as the Pd particle precursor or precursor. (3) Second catalyst layer 30

[0026] The second catalyst layer 30 is in contact with the substrate 10 and extends over a second region Y, which lies between the downstream end J and a second position Q located at a second distance Lb from the downstream end J towards the upstream end I (i.e., in a direction opposite to the exhaust gas flow direction). The second distance Lb can be from 40% to 65% of the total length Ls of the substrate 10. The length Ls, the first distance La, and the second distance Lb of the substrate can satisfy La + Lb < Ls. This enables the exhaust gas purification device 100 to achieve a high NOₓ reduction. x-Sales rate and a high THC sales rate, as shown in the examples described below.

[0027] The second catalyst layer 30 contains rhodium (Rh) particles. The Rh particles primarily function as a catalyst to convert NO. x to reduce the amount of Rh particles contained in the second catalyst layer 30, for example, can be from 0.05 g / L to 5 g / L, from 0.1 g / L to 0.8 g / L, or from 0.4 g / L to 0.6 g / L, based on the substrate capacity in the second region Y. This enables the exhaust gas purification device 100 to exhibit a sufficiently high exhaust gas purification performance.

[0028] The mean particle size distribution of the Rh particles contained in the second catalyst layer 30 ranges from 1.0 nm to 2.0 nm. Rh particles with a mean particle size of 1.0 nm or more comprise a small number of fine Rh particles with a particle size of less than 1.0 nm, which are assumed to aggregate and coarsen during the catalytic reaction. This helps to prevent or reduce the deterioration of the catalytic ability of the Rh particles, thereby improving the durability of the exhaust gas purification device 100. Furthermore, Rh particles with a mean particle size of 2.0 nm or less can exhibit a large specific surface area, enabling them to display high catalytic activity.

[0029] The mean particle size distribution of the Rh particles can be 1.1 nm or more, and in some embodiments can be 1.2 nm or more. The mean particle size distribution of the Rh particles can be 1.9 nm or less, and in some embodiments can be 1.8 nm or less, and in some embodiments can be 1.6 nm or less. The mean particle size distribution of the Rh particles can be from 1.1 nm to 1.9 nm, and in some embodiments can be from 1.2 nm to 1.8 nm.

[0030] A standard deviation σ of the particle size distribution of the Rh particles contained in the second catalyst layer 30 is 0.8 nm or less. In this case, the particle size distribution of the Rh particles is sharp, meaning that the Rh particles comprise a small number of fine and coarse Rh particles. The small number of fine Rh particles prevents or reduces aggregation of the Rh particles during the catalytic reaction, thereby preventing or reducing a deterioration of the catalytic ability of the Rh particles and improving the durability of the exhaust gas purification device 100. The small number of coarse Rh particles results in a large specific surface area of ​​the Rh particles, which improves the catalytic activity.

[0031] The standard deviation σ of the particle size distribution of the Rh particles can be 0.7 nm or less, 0.6 nm or less in some embodiments, and 0.5 nm or less in some embodiments. While the Rh particles can be monodispersed, they exhibit a particle size distribution with a standard deviation σ of 0.2 nm or more, 0.3 nm or more, or 0.4 nm or more, which allows for improved stability of the exhaust gas purification device 100.

[0032] The Rh particles, which exhibit the particle size distribution described above, include in particular a small number of fine particles with a particle size of less than 1.0 nm. This makes it possible to prevent or reduce the aggregation of the Rh particles during the catalytic reaction, thereby preventing or reducing the deterioration of the catalytic ability of Rh and improving the durability of the exhaust gas purification device 100. The amount of Rh particles with a particle size of less than 1.0 nm can be 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.3 wt% or less, or 0.1 wt% or less, based on the total weight of the Rh particles in the second catalyst layer 30. Alternatively, the second catalyst layer 30 may contain no Rh particles with a particle size of less than 1.0 nm.

[0033] In this application, the particle size distribution of the Rh particles is based on numbers and is obtained by measuring a projected circular area equivalent diameter, based on an image taken during observation with a transmission electron microscope (TEM), and particle groups comprising 100 or more particles are analyzed or investigated.

[0034] The Rh particles can be carried on the carrier particles. The carrier particles are not specifically limited. For example, oxide carrier particles can be used as carrier particles.

[0035] Examples of oxide-supporting particles include metal oxide particles, for example, particles of the oxide of one or more metals selected from the group consisting of elements in Groups 3, 4, and 13 of the periodic table, and lanthanide-based metals. If the oxide-supporting particles are oxide particles of two or more metals, they may be a mixture of two or more metal oxides, a composite oxide containing two or more elements, or a mixture of one or more metal oxides and one or more composite oxides.

[0036] For example, the metal oxide can be an oxide of one or more metals selected from the group consisting of scandium (Sc), yttrium (Y), lanthanum (La), cerium (Ce), neodymium (Nd), samarium (Sm), europium (Eu), lutetium (Lu), titanium (Ti), zirconium (Zr), and aluminum (Al). In some embodiments, the metal oxide can be an oxide of one or more metals selected from the group consisting of Y, La, Ce, Ti, Zr, and Al. In particular, the metal oxide can be a composite oxide of aluminum oxide, cerium oxide, and zirconium dioxide. A trace amount of yttrium oxide, lanthanum oxide, and neodymium oxide (Nd₂O₃) can be added to the composite oxide of aluminum oxide, cerium oxide, and zirconium dioxide to improve heat resistance.

[0037] The amount of carrier particles contained in the second catalyst layer 30 can, for example, range from 1 g / L to 100 g / L, based on the substrate capacity in the second region Y; in some embodiments, it can range from 10 g / L to 90 g / L, based on the substrate capacity in the second region Y; and in some embodiments, it can range from 30 g / L to 70 g / L, based on the substrate capacity in the second region Y. This enables the exhaust gas purification device 100 to exhibit a sufficiently high exhaust gas purification performance. The particle sizes of the carrier particles are not specifically limited and can be adjusted accordingly.

[0038] Using the Rh particles which are carried on the carrier particles, the amount of carried Rh particles can be, for example, 7 wt% or less, 5 wt% or less, 3 wt% or less, 2 wt% or less, 1.5 wt% or less, or 1.2 wt% or less, based on the weight of the carrier particles, and the amount of carried Rh particles can be, for example, 0.01 wt% or more, 0.02 wt% or more, 0.05 wt% or more, 0.07 wt% or more, 0.1 wt% or more, 0.2 wt% or more, 0.5 wt% or more, or 0.9 wt% or more, based on the weight of the carrier particles.

[0039] Rh particles can be carried on the carrier particles by contacting the carrier particles with an Rh particle precursor dispersion fluid containing the Rh particle precursors, which have been previously controlled to exhibit a predetermined particle size distribution, and by subsequent sintering of the result.

[0040] The Rh particle precursor dispersion fluid contains a dispersion medium in a liquid form and the Rh particle precursors, which are dispersed in the dispersion medium.

[0041] The dispersion medium can be aqueous, and can be water or a mixture of water and an aqueous organic solvent. Typically, the dispersion medium is water.

[0042] The Rh particle precursors can be rhodium hydroxide. Here, the rhodium hydroxide is typically a compound in which Rh ions are bonded to the same number of hydroxyl groups as the valence of Rh ions, but may partially contain an Rh-Rh bond, a partial Rh-oxygen-Rh bond, or a partial Rh-organic group bond.

[0043] The Rh precursors are pre-controlled to exhibit a predetermined particle size distribution and can have a mean diameter (D50) of 1.4 nm or more, 1.6 nm or more, 1.8 nm or more, or 2.0 nm or more, or can have a mean diameter (D50) of 2.9 nm or less, 2.8 nm or less, 2.7 nm or less, 2.6 nm or less, 2.5 nm or less, or 2.4 nm or less. In this application, the particle size distribution and mean diameter of the Rh particle precursors in the Rh particle precursor dispersion liquid are measured using a dynamic light scattering method (DLS).

[0044] The Rh particle precursor dispersion fluid, which was controlled to exhibit the predetermined particle size distribution, can be produced, for example, by any of the following methods: a) a process in which an acidic solution of an Rh compound reacts with a basic solution in a reactor whose reaction field exhibits a clearance in a predetermined range (Process 1); or b) a process in which an acidic solution of a Rh compound and a basic solution are mixed together and react together, and the result is then stirred in a high-speed mixer (Process 2).

[0045] In method 1, the reactor can include a suitable clearance adjustment element and similar device by which the clearance of the reaction field can be set to a predetermined value.

[0046] The introduction of the acidic Rh compound solution and the basic solution into the reaction chamber leads to a reaction of the acidic Rh compound solution with the basic solution at or within the reaction chamber, and the resulting product is expelled from the reaction chamber. Since the distance of the reaction chamber is set to a predetermined value, the particle size of any insoluble component generated by the reaction between the acidic Rh compound solution and the basic solution is limited by this distance, thus suppressing an excessive increase in the particle size of the insoluble component. Therefore, the particle size distribution of the produced Rh particle precursors in the Rh particle precursor dispersion liquid can be controlled.

[0047] The spacing adjustment element in the reactor can be two flat plates, a combination of a flat plate and a corrugated plate, a narrow tube, and the like.

[0048] If the spacing adjustment elements are two flat plates, the two flat plates are arranged at a predetermined distance or interval. A gap between the two flat plates becomes the reaction field, and a distance between the two flat plates becomes the distance of the reaction field. At least one of the two flat plates can have a slot. The two flat plates can be rotated relative to each other or moved parallel to each other during the reaction. The planar or flat shape of the plate can be any shape, for example, rectangular, circular (disc-shaped), or polygonal.

[0049] If the spacing adjustment elements are the combination of the flat plate and the corrugated plate, they are arranged to be in contact with each other. A gap in a recessed section of the flat plate and the corrugated plate becomes the reaction field, and the depth of the recessed section becomes the distance of the reaction field. The flat plate and the corrugated plate can be rotated relative to each other or moved parallel to each other during the reaction. The planar or flat shapes of the flat plate and the corrugated plate can be any shape, for example, a rectangle, a circular shape (a disc shape), and a polygonal shape.

[0050] If the distance-adjusting element is the thin tube, the inside of the tube becomes the reaction field, and the inner diameter of the thin tube becomes the distance of the reaction field.

[0051] The reaction field spacing can be adjusted to suit the desired particle size distribution of the Rh particle precursor. For example, the reaction field spacing can be 1 µm or more, 2 µm or more, 4 µm or more, 6 µm or more, 8 µm or more, 10 µm or more, 15 µm or more, 20 µm or more, 25 µm or more, or 30 µm or more. Alternatively, the reaction field spacing can be 50 µm or less, 45 µm or less, 40 µm or less, 35 µm or less, 30 µm or less, 25 µm or less, or 20 µm or less.

[0052] Examples of reactors in which the distance of the reaction field is set within a predetermined range include a microreactor with a suitable distance-adjusting element. It is possible and permissible to use a commercially available reactor.

[0053] In process 2, the acidic solution of the Rh compound and the basic solution are mixed and react to generate Rh particle precursors, which have large particle sizes. Next, a reaction solution is introduced into a stirred tank reactor of the high-speed mixer and stirred at high speed. The Rh particle precursors in the reaction solution are pressed against the inner wall of the stirred tank by centrifugal force, suppressing any movement of the Rh particle precursors relative to the inner wall. Meanwhile, the dispersion medium continues to flow into the reaction solution while the stirred tank reactor is being stirred. The rotational flow of the dispersion medium into the stirred tank exerts a strong shear stress on the Rh particle precursors, pressing them against the inner wall of the stirred tank.Shear stress reduces the size of the coarse Rh particle precursors. This allows the particle size distribution of the Rh particle precursors in the produced Rh particle precursor dispersion fluid to be controlled.

[0054] A high-speed mixer, for example, could be one with a peripheral speed of 6 m / s or more, or something similar. It is possible to use a commercially available high-speed mixer.

[0055] The acidic solution of the Rh compound used in process 1 and process 2 can be a solution prepared by dissolving the Rh compound in a suitable solvent.

[0056] The Rh compound can be a suitable Rh salt of an inorganic acid, and can be, for example, hydrochloride, nitrate, phosphate, sulfate, borate, or hydrofluoride.

[0057] The solvent for the acidic solution of the Rh compound can be an aqueous medium, and can be water or a mixture of water and an aqueous organic solvent. Typically, the solvent is water.

[0058] The pH of the acidic solution of the Rh compound is less than 7.0, and may be, for example, 6.0 or less, 5.0 or less, 4.0 or less, 3.0 or less, 2.0 or less, or 1.0 or less, and / or may be 0.1 or more, 0.3 or more, 0.5 or more, 0.7 or more, or 1.0 or more.

[0059] The basic solution used in process 1 and process 2 can be a solution prepared by dissolving a base, in particular an organic base, in a suitable solvent.

[0060] The organic base can be a nitrogen-containing organic compound and can be selected from an amine compound, a heterocyclic compound containing a nitrogen atom as a ring element, or similar. Examples of amine compounds include trimethylamine, triethylamine, tetramethylammonium hydroxide, tetraethylammonium hydroxide, and dimethylaminonaphthalene. Examples of heterocyclic compounds containing the nitrogen atom in a ring include pyridine and diazabicycloundecene.

[0061] The solvent in the basic solution can be an aqueous medium, and can be water or a mixture of water and an aqueous organic solvent. Typically, the solvent is water.

[0062] The pH value of the basic solution is greater than 7.0, and may be, for example, 8.0 or more, 9.0 or more, 10.0 or more, 11.0 or more, 12.0 or more, or 13.0 or more, and / or may be 14.0 or less, 13.5 or less, 13.0 or less, 12.5 or less, or 12.0 or less.

[0063] In both Process 1 and Process 2, the Rh particle precursor dispersion obtained by reacting the acidic Rh compound solution with the basic solution can be basic (alkaline) or acidic. To produce a basic Rh particle precursor dispersion, the molar ratio of base to Rh compound (base / Rh compound) can be, for example, 2 or more, 5 or more, 10 or more, 15 or more, or 20 or more, and / or 100 or less, 75 or less, 50 or less, 40 or less, 30 or less, or 20 or less. To produce an acidic Rh particle precursor dispersion, the molar ratio of base to Rh compound (base / Rh compound) can be 1 or less.

[0064] In both Process 1 and Process 2, a suitable reaction temperature can be set within the range of -10 °C to 100 °C, and can, for example, be room temperature. The reaction time can be adjusted depending on the reactor type, for example, within the range of 0.1 seconds to one hour.

[0065] The second catalyst layer 30 may further contain another optional ingredient or component. Examples of another optional component include an OSC material.

[0066] The OSC material is not specifically limited, and examples include cerium oxide and a composite oxide containing cerium oxide (for example, CZ composite oxide and ACZ composite oxide). In particular, a CZ composite oxide can be used in some embodiments due to its high oxygen storage capacity and relatively low cost. A composite oxide produced by further combining the CZ composite oxide with lanthanum oxide (La₂O₃), yttrium oxide (Y₂O₃), or similar materials can also be used as an OSC material. The weight ratio of cerium oxide to zirconium dioxide in the cerium oxide-zirconium dioxide composite oxide (CeO₂ / ZrO₂) can be 0.1 to 1.0.

[0067] The amount of OSC material contained in the second catalyst layer 30 can, for example, range from 10 g / L to 200 g / L, based on the substrate capacity in the second region Y; in some embodiments, it can range from 50 g / L to 100 g / L, based on the substrate capacity in the second region Y; and in some embodiments, it can range from 80 g / L to 120 g / L, based on the substrate capacity in the second region Y. This enables the exhaust gas purification device 100 to exhibit a sufficiently high exhaust gas purification performance.

[0068] The second catalyst layer 30 can be formed, for example, as follows. First, a slurry containing an Rh particle precursor and support powder is prepared. Alternatively, a slurry containing support powder on which Rh particles are temporarily supported can be prepared. The slurry can further comprise an OSC material, a binder, an additive, or similar components. Properties of the slurry, such as viscosity and particle diameter of a solid component, can be adjusted accordingly. The prepared slurry is applied to the substrate 10 in the second region Y.For example, substrate 10 is immersed in the slurry from the downstream end J to a depth corresponding to the second distance Lb, and after a predetermined time has elapsed, substrate 10 is withdrawn from the slurry, allowing the substrate 10 to be covered or coated with the slurry in the second region Y. Alternatively, the slurry can be poured into cells 14 through the downstream end J of substrate 10, and a blower can blow the slurry out of the downstream end J to distribute it towards the upstream end I, allowing the substrate 10 to be covered or coated with the slurry. Next, the slurry is dried and sintered at a predetermined temperature for a predetermined time. Therefore, the second catalyst layer 30 is formed in contact with substrate 10 in the second region Y. (4) Third catalyst layer 40

[0069] The third catalyst layer 40 is in contact with at least the first catalyst layer 20 and extends over a third region Z, which lies between the upstream end I and a third position R located at a third distance Lc from the upstream end I towards the downstream end J (i.e., in the direction of exhaust gas flow). The third distance Lc can be from 40% to 70% of the total length Ls of the substrate 10. The first distance La and the third distance Lc can satisfy La < Lc. That is, the first region X, over which the first catalyst layer 20 extends, can be contained within the third region Z, over which the third catalyst layer 40 extends. Furthermore, the length Ls of the substrate, the second distance Lb, and the third distance Lc can satisfy Lb + Lc > Ls.This means that the second area Y, over which the second catalyst layer 30 extends, can overlap with the third area Z, over which the third catalyst layer 40 extends. This enables the exhaust gas purification device 100 to exhibit high exhaust gas purification performance.

[0070] The third catalyst layer 40 contains rhodium (Rh) particles. The Rh particles primarily act as a catalyst to convert NO. x to reduce the amount of Rh particles contained in the third catalyst layer 40, for example, can be from 0.02 g / L to 2 g / L, from 0.05 g / L to 0.7 g / L, or from 0.2 g / L to 0.4 g / L, based on the substrate capacity in the third region Z. This enables the exhaust gas purification device 100 to exhibit a sufficiently high exhaust gas purification performance.

[0071] The mean particle size distribution of the Rh particles contained in the third catalyst layer 40 ranges from 1.0 nm to 2.0 nm. Rh particles with a mean particle size of 1.0 nm or more comprise a small number of fine Rh particles with a particle size of less than 1.0 nm, which are assumed to aggregate and coarsen during a catalytic reaction. This helps to prevent or reduce a deterioration in the catalytic ability of the Rh particles, thereby improving the durability of the exhaust gas purification device 100. Additionally, Rh particles with a mean particle size of 2.0 nm or less can exhibit a high specific surface area, enabling them to display high catalytic activity.

[0072] The mean particle size distribution of the Rh particles can be 1.1 nm or more, and in some embodiments can be 1.2 nm or more. The mean particle size distribution of the Rh particles can be 1.9 nm or less, and in some embodiments can be 1.8 nm or less, and in some embodiments can be 1.6 nm or less. The mean particle size distribution of the Rh particles can be from 1.1 nm to 1.9 nm, and in some embodiments can be from 1.2 nm to 1.8 nm.

[0073] The standard deviation σ of the particle size distribution of the Rh particles contained in the third catalyst layer 40 is 0.8 nm or less. In this case, the particle size distribution of the Rh particles is sharp, meaning that the Rh particles comprise a small number of fine and coarse Rh particles. The small number of fine Rh particles prevents or reduces aggregation of the Rh particles during the catalytic reaction, thereby preventing or reducing the deterioration of the catalytic ability of the Rh particles and improving the durability of the exhaust gas purification device 100. The small number of coarse Rh particles results in a high specific surface area of ​​the Rh particles, which improves the catalytic activity.

[0074] The standard deviation σ of the particle size distribution of the Rh particles can be 0.7 nm or less, can be 0.6 nm or less in some embodiments, and can be 0.5 nm or less in some embodiments. While the Rh particles can be monodispersed, those Rh particles exhibiting a particle size distribution with a standard deviation σ of 0.2 nm or more, 0.3 nm or more, or 0.4 nm or more enable the stability of the exhaust gas purification device 100 to be improved.

[0075] The Rh particles, which have the particle size distribution described above, include in particular a small number of fine particles with a particle size of less than 1.0 nm. This makes it possible to prevent or reduce the aggregation of the Rh particles during the catalytic reaction, thereby preventing or reducing a deterioration of the catalytic ability of the Rh particles and improving the durability of the exhaust gas purification device 100. The amount of Rh particles with a particle size of less than 1.0 nm can be 5 wt% or less, 4 wt% or less, 3 wt% or less, 2 wt% or less, 1 wt% or less, 0.5 wt% or less, 0.3 wt% or less, or 0.1 wt% or less, based on the total weight of the Rh particles in the third catalyst layer 40. Alternatively, the third catalyst layer 40 can contain no Rh particles with a particle size of less than 1.0 nm.

[0076] The Rh particles can be carried on the support particles. The support particles are not specifically limited. For example, oxide support particles can be used as the support particles.

[0077] The oxide support particles can be made of a material similar to that which can be used for the second catalyst layer 30.

[0078] The amount of carrier particles contained in the third catalyst layer 40 can, for example, range from 1 g / L to 100 g / L, based on the substrate capacity in the third region Z; in some embodiments, it can range from 10 g / L to 50 g / L, based on the substrate capacity in the third region Z; and in some embodiments, it can range from 30 g / L to 40 g / L, based on the substrate capacity in the third region Z. This enables the exhaust gas purification device 100 to exhibit a sufficiently high exhaust gas purification performance. The particle sizes of the carrier particles are not specifically limited and can be adjusted as appropriate.

[0079] Using the Rh particles which are carried on the carrier particles, the amount of carried Rh particles can be, for example, 7 wt% or less, 5 wt% or less, 3 wt% or less, 2 wt% or less, or 1 wt% or less, based on the weight of the carrier particles, and the amount of carried Rh particles can be, for example, 0.01 wt% or more, 0.02 wt% or more, 0.05 wt% or more, 0.07 wt% or more, 0.1 wt% or more, 0.2 wt% or more, 0.4 wt% or more, 0.6 wt% or more, or 0.7 wt% or more, based on the weight of the carrier particles.

[0080] Rh particles can be or become supported on the carrier particles by contacting the carrier particles with an Rh particle precursor dispersion fluid containing the Rh particle precursors, which have been previously controlled to exhibit a predetermined particle size distribution, and subsequent sintering of the result.

[0081] The Rh particle precursor dispersion fluid, which was controlled to exhibit a predetermined particle size distribution, can be produced by either Method 1 or Method 2, as described in section “(3) Second catalyst layer 30”.

[0082] The third catalyst layer 40 may further comprise another optional ingredient or component. Examples of another optional component include an OSC material.

[0083] The OSC material can be the OSC material described in section “(3) Second catalyst layer 30”.

[0084] The amount of OSC material contained in the third catalyst layer 40 can, for example, range from 10 g / L to 120 g / L, based on the substrate capacity in the third region Z; in some embodiments, it can range from 40 g / L to 90 g / L, based on the substrate capacity in the third region Z; and in some embodiments, it can range from 60 g / L to 70 g / L, based on the substrate capacity in the third region Z. This enables the exhaust gas purification device 100 to exhibit a sufficiently high exhaust gas purification performance.

[0085] The amount of rhr particles contained in the third catalyst layer 40 can be more than 0% and less than 50%, based on the total weight of the rhr particles contained in the second catalyst layer 30 and the third catalyst layer 40. This allows the exhaust gas purification device 100 to exhibit an improved THC conversion rate, as described in the examples below. Furthermore, the amount of rhr particles contained in the third catalyst layer 40 can be more than 10% and less than 50%, in particular 20% or more and less than 50%, based on the total weight of the rhr particles contained in the second catalyst layer 30 and the third catalyst layer 40. This allows for an improvement in both NOₓ and NOₓ reduction. x -turnover rate as well as the THC turnover rate in the exhaust gas purification device 100 to be achieved, as described in the examples below.

[0086] The third catalyst layer 40 can be formed, for example, as follows. First, a slurry containing an Rh particle precursor and support powder is prepared. Alternatively, a slurry containing support powder on which Rh particles are temporarily supported can be prepared. The slurry can further comprise an OSC material, a binder, an additive, or similar components. Properties of the slurry, such as viscosity and particle diameter of a solid component, can be adjusted as appropriate. The prepared slurry is applied to the third area Z of the substrate 10, on which at least the first catalyst layer 20 has been formed.For example, the substrate 10 is immersed in the slurry from the upstream end I to a depth corresponding to the third distance Lc, and after a predetermined time has elapsed, the substrate 10 is withdrawn from the slurry, allowing the slurry to be applied to at least the first catalyst layer 20 in the third region Z. Alternatively, the slurry can be poured into the cells 14 through the upstream end I of the substrate 10, and a blower can blow the upstream end I to distribute the slurry towards the downstream end J, allowing the slurry to be applied to at least the first catalyst layer 20. Next, the slurry is dried and sintered at a predetermined temperature for a predetermined time. Thus, the third catalyst layer 40 is formed in contact with at least the first catalyst layer 20 in the third region Z.

[0087] Note that the formation of the third catalyst layer 40 can be carried out either before or after the formation of the second catalyst layer 30. If the second catalyst layer 30 is formed and the third catalyst layer 40 is formed subsequently, the third catalyst layer 40 lies in an overlapping region of the second region Y with the third region Z on the second catalyst layer 30, as shown in Fig. Figure 1 shows that when the third catalyst layer 40 is formed and the second catalyst layer 30 is subsequently formed, the second catalyst layer 30 lies in an overlapping region of the second region Y with the third region Z on the third catalyst layer 40, as shown in Figure 1. Fig. 3 shown.

[0088] The exhaust gas purification device 100 according to the embodiment can be applied to various vehicles which include an internal combustion engine. EXAMPLES

[0089] The following describes the present invention specifically with examples, but the present invention is not limited to these examples. (1) Materials used in the examples and comparative examples a) Substrate (honeycomb substrate) Material: Cordierite Capacity: 875 cm³ 3 Partition thickness: 2 mil (50.8 µm) Cell density: 600 cells per square inch Cross-sectional shape of the cell: hexagonal shape b) Material 1 Composite of Al2O3 and La2O3 (La2O3: 1 wt.% to 10 wt.%) c) Material 2 A material produced by adding trace amounts of Nd2O3, La2O3, and Y2O3 to the ACZ (Al2O3-CeO2-ZrO2) composite oxide (CeO2: 15 wt.% to 30 wt.%) and treating the result to increase its heat resistance. d) Material 3 CZ (CeO2-ZrO2) composite oxide (CeO2: 40 wt.%, ZrO2: 50 wt.%, La2O3: 5 wt.%, Y2O3: 5 wt.%) e) Material 4 CZ (CeO2-ZrO2) composite oxide (CeO2: 20 wt.%, ZrO2: 70 wt.%, La2O3: 5 wt.%, Y2O3: 5 wt.%) f) Material 5 Palladium nitrate g) Material 6 Rhodium nitrate h) Material 7 Rh particle precursor dispersion fluid, prepared as follows: 0.2 g of rhodium nitrate(III) were dissolved in 50 mL of ion-exchanged water to prepare an aqueous solution of rhodium nitrate (RN) (pH 1.0). An aqueous solution of tetraethylammonium hydroxide (TEAH) (pH 14) was also prepared at a concentration of 175 g / L. In a reactor (a microreactor) comprising two flat plates as spacer elements, the aqueous RN solution reacted with the aqueous TEAH solution. Specifically, the aqueous RN and TEAH solutions were introduced into a reaction chamber at a distance of 10 µm and a molar ratio of TEAH:RN = 18:1, and reacted to produce the rhodium particle precursor dispersion. The resulting dispersion had a pH of 14.The Rh particle precursors in the dispersion liquid had a mean diameter (D50) of 2.0 nm, which was determined using the dynamic light scattering method (DLS). i) Material 8 Barium sulfate (2) Evaluation for Rh particles produced from material 6

[0090] 0.2 g of material 6 were dissolved in 50 mL of ion-exchanged water to prepare an aqueous solution of rhodium nitrate (pH 1.0). After bringing the aqueous rhodium nitrate solution into contact with aluminum oxide, such that the mass of Rh was 0.5% of the mass of the aluminum oxide, the resulting mixture was sintered. Therefore, the Rh particles were supported on the aluminum oxide.

[0091] The particle size distribution of Rh particles supported on aluminum oxide was investigated using a scanning transmission electron microscope (STEM). The mean particle size distribution of Rh particles was 0.7 nm, and the standard deviation of the particle size distribution was 0.48 nm. (3) Evaluation of the Rh particles produced from material 7

[0092] After material 7 was brought into contact with aluminum oxide such that the mass of Rh was 0.5%, based on the mass of the aluminum oxide, the resulting mixture was sintered. This process carried the Rh particles on the aluminum oxide.

[0093] The particle size distribution of rhrhodium particles supported on aluminum oxide was investigated using a scanning transmission electron microscope (STEM). The mean particle size distribution of the rhrhodium particles was 1.4 nm, and the standard deviation of the particle size distribution was 0.48 nm. (4) Manufacture of the exhaust gas purification device Examples 1 to 5

[0094] While distilled water was being stirred, material 1, material 3, material 5, material 8, and an Al2O3-based binder were added to the distilled water to produce a suspended slurry 1. The prepared slurry 1 was poured into the cells through one end (an upstream end) of a substrate, and excess slurry was blown off with a blower.

[0095] Consequently, the substrate's partition walls were coated with slurry 1 in the first region, which extends between one end of the substrate and the first position located 35% of the substrate's total length from one end towards the other (downstream) end. The substrate was placed in a drying machine, the interior of which was maintained at 120 °C to evaporate any water contained in slurry 1 for two hours. Next, the substrate was baked in an electric oven at 500 °C for two hours. This formed an initial catalyst layer.

[0096] At this time, the amount of material 1 contained in the first catalyst layer was 50 g / L, the amount of material 3 contained in the first catalyst layer was 50 g / L, the amount of Pd originating from material 5 and contained in the first catalyst layer was 5 g / L, and the amount of material 8 contained in the first catalyst layer was 5 g / L, each based on the capacity of the substrate in the first region.

[0097] Next, while distilled water was stirred, material 1, material 2, material 4, material 7, and an Al₂O₃-based binder were added to the distilled water to produce a suspended slurry 2. The prepared slurry 2 was poured into the cells through the other end (the downstream end) of the substrate, and excess slurry was blown off. Subsequently, the substrate partitions were coated with slurry 2 in the second region, which extends between the other end of the substrate and the second position located 55% of the total length of the substrate from the other end towards the one end (the upstream end). The substrate was placed in the drying machine, the interior of which was maintained at 120 °C to evaporate any water contained in slurry 2 for two hours.Next, the substrate was baked in an electric oven at 500 °C for two hours. This formed a second catalyst layer.

[0098] At this time, the amount of material 1 contained in the second catalyst layer was 50 g / L, the amount of material 2 contained in the second catalyst layer was 50 g / L, the amount of material 4 contained in the second catalyst layer was 50 g / L, and the amount of Rh derived from material 7 and contained in the second catalyst layer was as described in Table 1, each based on the capacity of the substrate in the second region.

[0099] Next, while distilled water was stirred, material 1, material 2, material 4, material 7, and an Al₂O₃-based binder were added to the distilled water to produce a suspended slurry 3. The prepared slurry 3 was poured into the cells through one end (the upstream end) of the substrate, and excess slurry was blown off. Consequently, a layer of slurry 3 was formed in the third region, which extends between one end of the substrate and the third position located 50% of the total length of the substrate from one end towards the other end (the downstream end). The substrate was placed in the drying machine, the interior of which was maintained at 120 °C to evaporate any water contained in the slurry 3 for two hours.Next, the substrate was baked in an electric oven at 500 °C for two hours. This formed a third catalyst layer.

[0100] At this time, the amount of material 1 contained in the third catalyst layer was 33 g / L, the amount of material 2 contained in the third catalyst layer was 33 g / L, the amount of material 4 contained in the third catalyst layer was 33 g / L, and the amount of Rh derived from material 7 and contained in the third catalyst layer was, as described in Table 1, based on the capacity of the substrate in the third region.

[0101] This resulted in the production of the exhaust gas purification devices of Examples 1 to 5. The amounts of Rh contained in the third catalyst layers, based on the total weights of Rh contained in the second and third catalyst layers, were as described in Table 1. Example 6

[0102] An exhaust gas purification device was manufactured similarly to Example 3, except that the second position is located at a distance of 80% of the total length of the substrate from the other end (the downstream end) of the substrate towards one end (the upstream end) of the substrate. Comparative examples 1 to 3

[0103] An exhaust gas purification device was manufactured similarly to Example 1, except that in the formation of the second catalyst layer and the third catalyst layer, material 6 was used instead of material 7, and the amount of Rh which originates from material 6 and is contained in the second catalyst layer and the third catalyst layer, respectively, was as described in Table 1. (5) Evaluation of exhaust gas purification performance

[0104] The exhaust gas purification devices of Examples 1 to 6 and Comparative Examples 1 to 3 were each coupled to the exhaust system of a V-8 engine. While a stoichiometric air-fuel mixture (an air-fuel ratio A / F = 14.6) and a mixture containing excess oxygen (lean: A / F > 14.6) were alternately introduced into the engine at a time ratio of 3:1 in a fixed cycle, the bed temperature of each exhaust gas purification device was maintained at 950 °C for 50 hours. This aged each of the exhaust gas purification devices.

[0105] Next, the exhaust gas purification devices were each coupled to an exhaust system of an R-4 engine. An air-fuel mixture with an air-fuel ratio (A / F) of 14.4 was supplied to the engine, and an engine operating condition was controlled such that the temperature of the exhaust gas introduced into each of the exhaust gas purification devices was 550 °C.

[0106] The NO x -Content in the gas introduced into each of the exhaust gas purification devices, and the NO x The NO content in the gas emitted by each of the exhaust gas purification devices was measured to determine (the NO). x -Content in the gas emitted by the exhaust gas cleaning device) / (the NO x -Content in the gas introduced into the exhaust gas cleaning device) as an NO x-turnover rate. Furthermore, the total hydrocarbon (THC) content in the gas introduced into each of the exhaust gas purification devices and the total carbon (THC) content in the gas expelled from each of the exhaust gas purification devices were measured to obtain (THC content in the gas expelled from the exhaust gas purification device) / (THC content in the gas introduced into the exhaust gas purification device) as a THC turnover rate. Table 1 and Fig. Figure 4 shows the results.

[0107] All exhaust gas purification devices of examples 1 to 6 showed higher NOₓ levels. x-Turnover rates than those of the exhaust gas purification devices of comparative examples 1 to 3. It is assumed that in examples 1 to 6, the use of material 7 for the formation of the second and third catalyst layers introduced Rh particles into each of the second and third catalyst layers to exhibit a mean particle size distribution of 1.0 nm to 2.0 nm and a standard deviation of the particle size distribution of 0.8 nm or less, thus preventing or reducing the sintering of the Rh particles, resulting in high NO x -Sales rates result.

[0108] Furthermore, the exhaust gas purification device of Example 3, in which the length Ls of the substrate, the first distance La, and the second distance Lb satisfied La + Lb < Ls, showed a higher NO x-transaction rate and a higher THC conversion rate than that of the exhaust gas purification device of Example 6. It is assumed that in Example 3, which satisfies the inequality La + Lb < Ls, the Rh particles in the second catalyst layer are prevented from coming into contact with the Pd particles in the first catalyst layer, thereby preventing decomposition or degradation of the Rh particles and the Pd particles, which could otherwise be caused by the formation of an alloy of Rh particles and the Pd particles.

[0109] In particular, the exhaust gas purification devices of Examples 2 to 5, in which the amounts of Rh particles contained in the third catalyst layers were more than 10%, based on the total weights of the Rh particles, showed higher NO x-Transaction rates than those of the exhaust gas purification device of Example 1, in which the amount of Rh particles contained in the third catalyst layer was 10%, based on the total weight of the Rh particles. Furthermore, the exhaust gas purification devices of Examples 1 to 3, in which the amounts of Rh particles contained in the third catalyst layers were more than 0% and less than 50%, based on the total weight of the Rh particles, showed higher THC conversion rates than those of the exhaust gas purification devices of Examples 4 and 5, in which the amounts of Rh particles contained in the third catalyst layers were 50% or more, based on the total weight of the Rh particles.Consequently, the exhaust gas purification devices of Examples 2 and 3, in which the amounts of Rh particles contained in the third catalyst layer were more than 10% and less than 50% based on the total weight of the Rh particles, in particular 20% or more and less than 50% based on the total weight of the Rh particles, were capable of producing both a higher NO. x -to achieve both a higher sales rate and a higher THC sales rate. [Table 1] Rh precursor Second catalyst layer Third catalyst layer Rh content in the third catalyst layer based on the total Rh weight [wt.%] THC conversion rate [%] NOx turnover rate [%] Rh content [g / L] Coating length based on the total length of the substrate [%] Rh content [g / L] Example 1 Material 7 0,72 55 0,08 10 94,8 96,5 Example 2 Material 7 0,56 55 0,24 30 92,1 97,6 Example 3 Material 7 0,48 55 0,32 40 91,5 97,3 Example 4 Material 7 0,40 55 0,40 50 89,1 97,5 Example 5 Material 7 0,16 55 0,64 80 88 97,6 Example 6 Material 7 0,48 80 0,32 40 90,1 95,4 Comparative example 1 Material 6 0,56 55 0,24 30 91 92,1 Comparative example 2 Material 6 0,48 55 0,32 40 90,8 93,2 Comparative example 3 Material 6 0,40 55 0,40 50 90,4 94,7 DESCRIPTION OF REFERENCE MARKS 10 substrate 12 Framework section 14 cells 16 Partition wall 20 First catalyst layer 30 Second catalyst layer 40 Third catalyst layer 100 Exhaust gas purification device I Upstream end (first end) J Downstream end (second end) P First position Q Second position Third position X First area Y Second Area Third area

Claims

[1] Exhaust gas purification device (100), comprising: a substrate (10) comprising an upstream end (I) through which an exhaust gas is introduced into the device and a downstream end (J) through which the exhaust gas is discharged from the device, wherein the substrate (10) has a length Ls between the upstream end (I) and the downstream end (J); a first catalyst layer (20) containing palladium particles, which extends over a first region (X) and is in contact with the substrate (10), wherein the first region (X) extends between the upstream end (I) and a first position (P), wherein the first position (P) is located at a first distance La from the upstream end (I) in the direction of the downstream end (J); a second catalyst layer (30) containing rhodium particles, which extends over a second region (Y) and is in contact with the substrate (10), wherein the second region (Y) extends between the downstream end (J) and a second position (Q), the second position (Q) being located at a second distance Lb from the downstream end (J) in the direction of the upstream end (I); and a third catalyst layer (40) containing rhodium particles, which extends over a third region (Z) and is in contact with at least the first catalyst layer (20), wherein the third region (Z) extends between the upstream end (I) and a third position (R), wherein the third position (R) is located at a third distance Lc from the upstream end (I) in the direction of the downstream end (J), wherein a mean particle size distribution of the rhodium particles contained in the second catalyst layer (30) and the third catalyst layer (40) is from 1.0 nm to 2.0 nm, and a standard deviation of the particle size distribution of the rhodium particles contained in the second catalyst layer (30) and the third catalyst layer (40) is 0.8 nm or less. [2] Exhaust gas purification device (100) according to claim 1, wherein the length Ls of the substrate (10), the first distance La, and the second distance Lb satisfy La + Lb < Ls. [3] Exhaust gas purification device (100) according to claim 1 or 2, wherein the amount of rhodium particles contained in the third catalyst layer (40) is more than 0% and less than 50%, based on a total weight of the rhodium particles contained in the second catalyst layer and the third catalyst layer (40). [4] Exhaust gas purification device (100) according to claim 3, wherein the amount of rhodium particles contained in the third catalyst layer (40) is more than 10%, based on the total weight of the rhodium particles contained in the second catalyst layer (30) and the third catalyst layer (40). [5] Exhaust gas purification device (100) according to claim 3, wherein the amount of rhodium particles contained in the third catalyst layer (40) is 20% or more, based on the total weight of the rhodium particles contained in the second catalyst layer (30) and the third catalyst layer (40).

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