Exhaust gas purification system

Abstract

To provide an exhaust gas purification device which exhibits high exhaust gas purification performance even after use under high temperature conditions.SOLUTION: There is provided an exhaust gas purification device which comprises: a base material in which a length between an upstream end and a downstream end is Ls; a first catalyst layer containing Pd particles formed on the base material in a first region between the upstream end and a first position separated by a first distance La from the upstream end; a second catalyst layer containing Rh-supported particles formed on the base material in a second region between the downstream end and a second position separated by a second distance Lb from the downstream end; and a third catalyst layer containing Rh particles formed on the base material in a third region between the upstream end and a third position separated by a third distance Lc from the upstream end. The Rh-supported particles include a porous support, monoclinic ZrO2 particles uniformly dispersed and supported in the pores of the porous support and Rh particles supported in the pores of the porous support. In the first region, the third catalyst layer is formed on the first catalyst layer. Ls, Lb and Lb satisfy La+Lb<Ls.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] Exhaust gas discharged from internal combustion engines used in vehicles such as automobiles contains harmful components such as carbon monoxide (CO), hydrocarbons (HC), and nitrogen oxides (NOx). Regulations on the emission amounts of these harmful components have been strengthened year by year, and noble metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) are used as catalysts to remove these harmful components.

[0003] Patent Document 1 describes an exhaust gas purification device using Rh particles with an average particle size distribution of 1.0 to 2.0 nm and a standard deviation of 0.8 nm or less, and it is described that this exhaust gas purification device exhibits a high NOx purification rate even after use under high-temperature conditions.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] There is a demand to further improve the exhaust gas purification performance of an exhaust gas purification device. An object of the present disclosure is to provide an exhaust gas purification device that exhibits high exhaust gas purification performance even after use under high-temperature conditions.

Means for Solving the Problems

[0006] Examples of aspects of the present disclosure can include the following. [1] An exhaust gas purification device, A base material having an upstream end into which exhaust gas flows and a downstream end from which the exhaust gas is discharged, and the length between the upstream end and the downstream end being Ls, In a first region between the upstream end and a first position separated from the upstream end by a first distance La toward the downstream end, a first catalyst layer containing palladium particles formed on the base material, In a second region between the downstream end and a second position separated from the downstream end by a second distance Lb toward the upstream end, a second catalyst layer containing rhodium-supported particles formed on the base material, Here, the rhodium-supported particles include a porous carrier that is a composite oxide containing Al element and Zr element, monoclinic zirconium dioxide particles uniformly dispersed and supported in the pores of the porous carrier, and rhodium particles supported in the pores of the porous carrier, Here, being uniformly dispersed and supported means that when the rhodium-supported particles are measured with an electron beam microanalyzer, the ratio of the zirconium abundance ratio in the surface region from the surface of the rhodium-supported particles to a depth of 1.5 μm to the zirconium abundance ratio in the region inside the surface region of the rhodium-supported particles is 95% to 110%. The second catalyst layer, In a third region between the upstream end and a third position separated from the upstream end by a third distance Lc toward the downstream end, a third catalyst layer containing rhodium particles formed on the base material, Comprising, In the first region, the third catalyst layer is formed on the first catalyst layer, An exhaust gas purification device in which the length Ls of the base material, the first distance La, and the second distance Lb satisfy La + Lb < Ls. [2] The ratio of the rhodium particles contained in the third catalyst layer to the total weight of the rhodium particles contained in the second catalyst layer and the third catalyst layer is more than 0 wt% and less than 50 wt%. The exhaust gas purification device according to Aspect 1. [3] The exhaust gas purification device according to embodiment 1 or 2, wherein in the rhodium-supported particles contained in the second catalyst layer, the weight of the zirconium dioxide particles is in the range of 1 to 10% by weight based on the weight of the porous carrier. [4] The third catalyst layer contains the rhodium-supported particles, The exhaust gas purification device according to any one of embodiments 1 to 3, wherein the rhodium particles contained in the third catalyst layer are the rhodium particles contained in the rhodium-supported particles. [5] The exhaust gas purification device according to embodiment 4, wherein in the rhodium-supported particles contained in the third catalyst layer, the weight of the zirconium dioxide particles is within the range of 1 to 10% by weight based on the weight of the porous carrier. [Effects of the Invention]

[0007] The exhaust gas purification device described herein exhibits high exhaust gas purification performance even after use under high-temperature conditions. [Brief explanation of the drawing]

[0008] [Figure 1] This is an enlarged end view of the main part of the exhaust gas purification device according to the embodiment, cut by a plane parallel to the direction of exhaust gas flow, schematically showing the configuration near the partition wall of the base material. [Figure 2] This is a schematic perspective view showing an example of a substrate. [Figure 3] This is an enlarged end view of a key part of an exhaust gas purification device in a modified form, cut across a plane parallel to the direction of exhaust gas flow, schematically showing the structure near the partition wall of the base material. [Figure 4] This graph shows the relationship between the weight ratio of monoclinic ZrO2 and AZ composite oxide particles in the monoclinic ZrO2-supported AZ particles used in Examples 1-3 and the NOx-T50 of the exhaust gas purification system. The dashed line in the graph represents the NOx-T50 value of the exhaust gas purification system in Comparative Example 1. [Figure 5] This graph shows the NOx-T50 values ​​for the exhaust gas purification devices of Comparative Examples 1, 3, and 4, and Example 2. [Modes for carrying out the invention]

[0009] Hereinafter, embodiments will be described with reference to the drawings as appropriate. In the drawings referred to in the following description, the same members or members having the same functions are denoted by the same reference numerals, and repeated descriptions may be omitted. For convenience of explanation, the dimensional ratios and shapes of each part in the drawings may be exaggerated and may be different from the actual dimensional ratios and shapes. In this specification, a numerical range represented by the symbol "~" includes the numerical values described before and after the symbol "~" as the lower limit value and the upper limit value, respectively, unless otherwise specified. The upper limit value and the lower limit value of the numerical range described in this specification can define a preferred range alone or in any combination. In this specification, "including ~" and "containing ~" mean that additional components may be included unless otherwise specified, and include "consisting essentially of ~" and "consisting of ~". "Consisting essentially of ~" means that additional components that do not substantially have an adverse effect may be included. "Consisting of ~" means including only the described materials, but does not exclude including inevitable impurities. In this specification, "on ~" includes both "directly on ~" and "indirectly on ~" unless otherwise specified in the context.

[0010] The exhaust gas purification device 100 according to the embodiment will be described with reference to FIGS. 1 and 2. The exhaust gas purification device 100 according to the embodiment includes a base material 10, a first catalyst layer 20, a second catalyst layer 30, and a third catalyst layer 40.

[0011] (1) Base material 10 The shape of the base material 10 is not particularly limited. For example, as shown in FIG. 2, the base material 10 may be composed of a frame portion 12 and partition walls 16 that partition the space inside the frame portion 12 to define a plurality of cells 14. The partition walls 16 extend between the first end (first end face) I and the second end (second end face) J of the base material 10 and define a plurality of cells 14 that extend between the first end I and the second end J.

[0012] The substrate 10 may be formed from a ceramic material having high heat resistance such as cordierite (2MgO·2Al2O3·5SiO2), alumina, zirconia, silicon carbide, or a metal material such as a metal foil of stainless steel.

[0013] In FIGS. 1 and 2, the dashed arrows indicate the flow direction of the exhaust gas in the exhaust gas purification device 100 and the substrate 10. The exhaust gas flows into the exhaust gas purification device 100 through the first end I and is discharged from the exhaust gas purification device 100 through the second end J. Therefore, hereinafter, the first end I will also be referred to as the upstream end I and the second end J as the downstream end J as appropriate. In this specification, the length between the upstream end I and the downstream end J, that is, the total length of the substrate 10 is represented as Ls.

[0014] (2) The first catalyst layer 20 The first catalyst layer 20 is formed on the substrate 10 in a first region X between the upstream end I and a first position P spaced apart from the upstream end I by a first distance La toward the downstream end J (that is, in the flow direction of the exhaust gas). The first distance La may be 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 mainly function as a catalyst for oxidizing HC.

[0016] The Pd particles may be supported on carrier particles. The carrier particles are not particularly limited, and for example, metal oxides can be used. The Pd particles can be supported by any supporting method such as an impregnation supporting method, an adsorption supporting method, and a water absorption supporting method.

[0017] Examples of metal oxides include oxides of at least one metal selected from the group consisting of metals in groups 3, 4, and 13 of the periodic table, as well as lanthanide metals. More specifically, these include oxides of at least one metal 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), composites of these oxides (i.e., complex oxides), and mixtures of these oxides and / or complex oxides.

[0018] The carrier particles may include materials that function as OSC (Oxygen Storage Capacity) materials, absorbing oxygen from the atmosphere under an oxygen-rich atmosphere and releasing oxygen under an oxygen-deficient atmosphere. Examples of OSC materials include ceria (CeO2), composite oxides of ceria and other oxides (e.g., composite oxides of ceria and zirconia (ZrO2) (Ce-Zr composite oxides), composite oxides of alumina (Al2O3), ceria, and zirconia (Al-Ce-Zr composite oxides)), and materials to which these are added. Examples of additives include lantana (La2O3), yttria (Y2O3), neodymia (Nd2O3), or praseodymia (Pr6O 11 ) may be at least one of these materials, and these materials can improve the heat resistance of the OSC material. The additives may form a composite oxide together with the main component of the OSC material.

[0019] The first catalyst layer 20 may further contain other optional components. Examples of other optional components include OSC material, binders, and additives.

[0020] The first catalyst layer 20 can be formed, for example, by the same method as the method for forming the first catalyst layer described in Patent Document 1.

[0021] (3) Second catalyst layer 30 The second catalyst layer 30 is formed on the substrate 10 in a second region Y between a downstream end J and a second position Q spaced apart from the downstream end J by a second distance Lb toward the upstream end I (i.e., in a direction opposite to the flow direction of the exhaust gas). The second distance Lb may be 40 to 65% of the total length Ls of the substrate 10. Also, the length Ls of the substrate, the first distance La, and the second distance Lb may satisfy La + Lb < Ls. Thereby, the exhaust gas purification device 100 can have high NOx purification performance and high THC purification performance.

[0022] The second catalyst layer 30 contains rhodium (Rh)-supported particles. The Rh-supported particles include a porous carrier, monoclinic zirconium dioxide (ZrO2) particles uniformly dispersed and supported in the pores of the porous carrier, and rhodium (Rh) particles supported in the pores of the porous carrier. The porous carrier is a composite oxide containing Al element and Zr element, and more specifically may be an Al2O3-ZrO2 composite oxide. In the pores of the porous carrier, the Rh particles may be in contact with the ZrO2 particles.

[0023] Here, being uniformly dispersed and supported means that when the Rh-supported particles are measured with an electron beam microanalyzer, the ratio of the zirconium abundance ratio in the surface region from the surface of the Rh-supported particles to a depth of 1.5 μm to the zirconium abundance ratio in the region inside the surface region of the Rh-supported particles is 95% to 110%.

[0024] By using such Rh-supported particles, as shown in the examples described later, the exhaust gas purification device 100 can exhibit high exhaust gas purification performance even after use under high-temperature conditions. The inventors consider the reason as follows.

[0025] The Rh particles supported on the carrier are usually repeatedly exposed to an oxidizing atmosphere and a reducing atmosphere at high temperature during the use of the exhaust gas purification device. In a conventional exhaust gas purification device, the Rh particles dissolve in the carrier in an oxidizing atmosphere, and the dissolved Rh precipitates as fine particles at the atomic level in a reducing atmosphere, and these fine Rh particles evaporate and move to other carriers or substrates, so the Rh particles tend to be deactivated.

[0026] The monoclinic ZrO2 used in the exhaust gas purification device 100 according to this embodiment has a higher surface energy than the porous support. Furthermore, the monoclinic ZrO2 does not lattice match with rhodium oxide. Therefore, when Rh particles are supported on the porous support together with monoclinic ZrO2 particles, solid solution of Rh particles to the support can be suppressed compared to when only Rh particles are supported on the porous support. As a result, deactivation of Rh particles is suppressed, and the exhaust gas purification device 100 can exhibit high exhaust gas purification performance even after use under high-temperature conditions.

[0027] Typically, in the manufacture of exhaust gas purification devices, the amount of Rh particles supported is set high to account for the deactivation of Rh particles during use. In the exhaust gas purification device 100 according to this embodiment, the deactivation of Rh particles is suppressed, so the amount of Rh particles used can be reduced compared to conventional technology. Reducing the amount of Rh particles used is desirable from the standpoint of resource risk.

[0028] Furthermore, monoclinic ZrO2 has the advantage of being able to reduce Rh at lower temperatures compared to ZrO2 with other crystalline structures. Generally, monoclinic ZrO2 particles do not have high heat resistance and can aggregate and coarseen under high-temperature atmospheres, but in this embodiment, the ZrO2 particles are uniformly supported within the pores of the porous carrier, making them less prone to aggregation.

[0029] Rh particles primarily function as catalysts for reducing NOx. The weight of the Rh particles may be, for example, 0.5–2% by weight, 0.6–1.5% by weight, or 0.7–1.3% by weight, relative to the weight of the porous support.

[0030] The average primary particle size (D50) of Rh particles may be 1-9 nm, 2-8 nm, 3-7 nm, or 4-6 nm.

[0031] The porous carrier may be particulate, and its average primary particle size (D50) may be, for example, 1 to 1000 μm. The average primary particle size (D50) of the porous carrier may be 1 μm or more, 10 μm or more, 50 μm or more, or 100 μm or more, and may be 1000 μm or less, 500 μm or less, 200 μm or less, or 100 μm or less.

[0032] In this specification, the average primary particle diameter is the number average of the projected area equivalent diameters of 200 or more primary particles observed with a scanning electron microscope (SEM).

[0033] The pore size of the porous carrier is not particularly limited as long as it is large enough to support Rh particles and ZrO2 particles within the pores.

[0034] The weight of the monoclinic ZrO2 particles may be in the range of 1 to 10% by weight based on the weight of the porous carrier. This allows the exhaust gas purification device 100 to have high NOx purification performance, as shown in the examples described later. The weight of the monoclinic ZrO2 particles may be in the range of 1 to 5% by weight based on the weight of the porous carrier. This allows the exhaust gas purification device 100 to have high NOx purification performance and CO purification performance, as shown in the examples described later. The weight of the monoclinic ZrO2 particles may be in the range of 1 to 3% by weight based on the weight of the porous carrier. This allows the exhaust gas purification device 100 to have high NOx purification performance, CO purification performance, and THC purification performance, as shown in the examples described later.

[0035] Rh-supported particles can be prepared, for example, as follows. First, a porous carrier and monoclinic ZrO2 particles are dispersed in an acidic dispersion medium, and then dried and calcined to support the ZrO2 particles within the pores of the porous carrier. By using acidic conditions for the dispersion medium, aggregation of ZrO2 particles in the dispersion can be suppressed. This allows the ZrO2 particles to be supported within the pores of the porous carrier while adjusting the secondary particle size of the supported ZrO2 particles so that it does not become too large. This improves the uniform dispersion of zirconium dioxide particles within the pores of the porous carrier. The pH of the dispersion medium may be, for example, 1 to 5, 1.5 to 4.5, 2 to 4, or 2.5 to 3.5. Next, Rh particles are further supported on the porous carrier on which the ZrO2 particles are supported. For example, Rh particles can be supported on the porous carrier by dispersing a porous carrier on which ZrO2 particles are supported in a dispersion medium, adding a liquid containing Rh particle precursors whose particle size distribution has been controlled in advance (Rh particle precursor dispersion), stirring, and then drying and calcining. The Rh particle precursor dispersion can be prepared, for example, according to Method 1 and Method 2 of Patent Document 1. In this way, Rh-supported particles are obtained.

[0036] The second catalyst layer 30 may further contain other optional components. Examples of other optional components include the OSC material, binder, and additives mentioned above.

[0037] The second catalyst layer 30 can be formed, for example, using a slurry containing Rh-supported particles, in the same manner as the method for forming the second catalyst layer described in Patent Document 1.

[0038] (4) Third catalyst layer 40 The third catalyst layer 40 is formed on the substrate 10 in a third region Z between an upstream end I and a third position R spaced apart from the upstream end I by a third distance Lc toward a downstream end J (i.e., in the flow direction of the exhaust gas). In the first region X, the third catalyst layer 40 is formed on the first catalyst layer 20. The third distance Lc may be 40 to 70% of the total length Ls of the substrate 10. Also, the first distance La and the third distance Lc may satisfy La < Lc. That is, the first region X where the first catalyst layer 20 is formed may be included in the third region Z where the third catalyst layer 40 is formed. Further, the length Ls of the substrate, the second distance Lb, and the third distance Lc may satisfy Lb + Lc > Ls. That is, the second region Y where the second catalyst layer 30 is formed and the third region Z where the third catalyst layer 40 is formed may overlap. Thereby, the exhaust gas purification device 100 can have high exhaust gas purification performance.

[0039] The third catalyst layer 40 contains rhodium (Rh) particles. The Rh particles mainly function as a catalyst for reducing NOx.

[0040] Similar to the second catalyst layer 30, the third catalyst layer 40 may contain Rh-supported particles. In this case, the Rh particles contained in the third catalyst layer 40 are contained in the Rh-supported particles. That is, the third catalyst layer 40 may contain Rh-supported particles including a porous carrier, monoclinic ZrO2 particles uniformly dispersed and supported in the pores of the porous carrier, and Rh particles supported in the pores of the porous carrier.

[0041] Since the Rh-supported particles that may be contained in the third catalyst layer 40 are the same as the Rh-supported particles contained in the second catalyst layer 30, a detailed description of the Rh-supported particles and the method for preparing them is omitted.

[0042] When the third catalyst layer 40 contains Rh-supported particles, similar to the second catalyst layer 30, deactivation of the Rh particles is suppressed in the third catalyst layer 40, so that the exhaust gas purification device 100 can have even higher heat resistance.

[0043] The third catalyst layer 40 may further contain other optional components. Examples of other optional components include the OSC material, binder, and additives mentioned above.

[0044] The proportion of Rh particles in the third catalyst layer 40, based on the total weight of Rh particles in the second catalyst layer 30 and the third catalyst layer 40, may be greater than 0% by weight and less than 50% by weight. By including more Rh particles in the second catalyst layer 30 than in the third catalyst layer 40, the exhaust gas purification device 100 can have higher exhaust gas purification performance. Furthermore, the proportion of Rh particles in the third catalyst layer 40, based on the total weight of Rh particles in the second catalyst layer 30 and the third catalyst layer 40, may be greater than 10% by weight and less than 50% by weight, particularly 20% by weight or more and less than 50% by weight. This allows the exhaust gas purification device 100 to have even higher exhaust gas purification performance.

[0045] The more Rh particles contained in the second catalyst layer 30, the higher the density of Rh particles in the second catalyst layer 30 becomes, making deactivation of Rh particles under the high-temperature conditions described above more likely in the second catalyst layer 30. Therefore, the more Rh particles contained in the second catalyst layer 30, the more pronounced the effect of suppressing Rh particle deactivation brought about by using Rh-supported particles in the second catalyst layer 30 becomes, and the more effectively the heat resistance of the exhaust gas purification device 100 is improved.

[0046] The third catalyst layer 40 can be formed, for example, using a slurry containing Rh-supported particles, in the same manner as the method for forming the third catalyst layer described in Patent Document 1.

[0047] Note that the formation of the second catalyst layer 30 and the third catalyst layer 40 can be performed in either order. If the third catalyst layer 40 is formed after the second catalyst layer 30, the third catalyst layer 40 will be formed on the second catalyst layer 30 in the overlapping region of the second region Y and the third region Z, as shown in Figure 1. If the second catalyst layer 30 is formed after the third catalyst layer 40, the second catalyst layer 30 will be formed on the third catalyst layer 40 in the overlapping region of the second region Y and the third region Z, as shown in Figure 3.

[0048] The exhaust gas purification device 100 according to this embodiment can be applied to various vehicles equipped with an internal combustion engine.

[0049] Although embodiments of this disclosure have been described in detail above, this disclosure is not limited to the embodiments described above, and various design modifications can be made without departing from the essence of this disclosure as described in the claims. [Examples]

[0050] The present disclosure will be specifically described below with reference to examples, but the present disclosure is not limited to these examples.

[0051] (1) Materials used in the examples and comparative examples a) Substrate (honeycomb substrate) Material: Cordierite, Volume: 875cc, Total Length: 105mm, Wall Thickness: 2mil (50.8μm), Cell Density: 600 cells per square inch, Cell Cross-sectional Shape: Hexagonal

[0052] b) Material 1: La2O3 composite Al2O3 (La2O3: 1% by weight)

[0053] c) Material 2: ACZ (Al2O3-CeO2-ZrO2) composite oxide with trace amounts of Nd2O3, La2O3, and Y2O3 added, and subjected to high heat resistance treatment (Al2O3: 30 wt%, CeO2: 20 wt%, ZrO2: 44 wt%, Nd2O3: 2 wt%, La2O3: 2 wt%, Y2O3: 2 wt%)

[0054] d) Material 3: Porous AZ (Al2O3-ZrO2) composite oxide (Al2O3: 30% by weight, ZrO2: 60% by weight, La2O3: 5% by weight, Y2O3: 5% by weight)

[0055] e) Material 4: Pyrochlore-type CZ (CeO2-ZrO2) composite oxide (CeO2: 51.5% by weight, ZrO2: 45.5% by weight, Pr6O 11 :3% by weight) In pyrochlore-type CZ complex oxides, the cerium ions and zirconium ions have a pyrochlore-type ordered arrangement structure, and some of the cerium ions and zirconium ions are substituted with praseodymium.

[0056] The pyrochlore-type CZ composite oxide was prepared using the same procedure as described in the example "Synthesis of praseodymium-doped pyrochlore-type ceria-zirconia composite oxide (Pr-doped pyrochlore CZ)" in Japanese Patent Publication No. 2018-038999.

[0057] f) Material 5: Barium sulfate

[0058] g) Material 6: Rh particle precursor dispersion The Rh particle precursor dispersion was prepared in the same manner as material 7 in the example of Patent Document 1. The median diameter (D50) of the Rh particle precursor in the dispersion was 2.0 nm.

[0059] h) Material 7: Palladium nitrate aqueous solution (Pd concentration: 8.4% by weight)

[0060] i) Material 8: Monoclinic ZrO2 particle dispersion (ZSL00013, manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd., pH 3)

[0061] j) Material 9: Amorphous ZrO2 particle dispersion Amorphous ZrO2 particle dispersion was prepared as follows: Citric acid was added to water and stirred thoroughly to dissolve the citric acid. An equal amount of zirconium oxynitrate dihydrate was then added. The resulting solution was added dropwise to an aqueous solution of tetraammonium hydroxide (10% by weight) to obtain an amorphous ZrO2 particle dispersion. The secondary particle size (D50) of the ZrO2 particles was 10 nm.

[0062] k) Material 10: Tetragonal ZrO2 particle dispersion (manufactured by Daiichi Rare Elements Chemical Industry Co., Ltd., ZSL173)

[0063] (2) Evaluation of ZrO2 crystal structure Powder X-ray diffraction measurements were performed on ZrO2 particles obtained by drying dispersions of materials 8 to 10. By analyzing the obtained X-ray diffraction patterns, it was confirmed that the ZrO2 of material 8 has a monoclinic structure, the ZrO2 of material 9 has an amorphous structure, and the ZrO2 of material 10 has a tetragonal structure.

[0064] (3) Fabrication of exhaust gas purification device Comparative Example 1 Materials 2 and 7 were added while stirring distilled water. The resulting mixture was dried and calcined to obtain Pd-supported ACZ particles, which consisted of ACZ composite oxide particles and Pd particles supported on the ACZ composite oxide particles. Pd-supported ACZ particles, material 1, material 5, and an Al2O3-based binder were added to prepare a suspended slurry 1. Next, the prepared slurry 1 was poured into the substrate from one end (upstream end), and excess material was blown away with a blower. As a result, the partition wall of the substrate was coated with slurry 1 in a first region between one end of the substrate and a first position located at a distance of 30% of the total length of the substrate from one end to the other end (downstream end) of the substrate. The substrate was placed in a dryer maintained at 120°C for 2 hours to evaporate the water in slurry 1, and then calcined in an electric furnace at 500°C for 2 hours. This formed the first catalyst layer.

[0065] At this time, based on the volume of the substrate in the first region, the content of material 1 in the first catalyst layer was 25 g / L, the content of material 2 was 75 g / L, the content of material 5 was 15 g / L, and the content of Pd derived from material 7 was 7 g / L.

[0066] Next, materials 3 and 6 were added while stirring distilled water. The resulting mixture was dried and calcined to obtain first Rh-supported AZ particles, which consisted of AZ composite oxide particles and Rh particles supported on the AZ composite oxide particles. The first Rh-supported AZ particles, materials 1, 2, 4, and an Al2O3-based binder were added to prepare a suspended slurry 2. Next, the prepared slurry 2 was poured into the substrate from the other end (downstream end), and excess material was blown away with a blower. As a result, the partition wall of the substrate was coated with slurry 2 in a second region between the other end of the substrate and a second position located at a distance of 50% of the total length of the substrate from the other end toward one end (upstream end) of the substrate. The substrate was placed in a dryer maintained at 120°C for 2 hours to evaporate the water in slurry 2, and then calcined in an electric furnace at 500°C for 2 hours. This formed a second catalyst layer.

[0067] At this time, based on the volume of the substrate in the second region, the content of material 1 in the second catalyst layer was 40 g / L, the content of material 2 was 70 g / L, the content of material 3 was 40 g / L, the content of material 4 was 30 g / L, and the Rh content derived from material 6 was 0.45 g / L.

[0068] Next, materials 3 and 6 were added while stirring distilled water. The resulting mixture was dried and calcined to obtain second Rh-supported AZ particles, which consisted of AZ composite oxide particles and Rh particles supported on the AZ composite oxide particles. The second Rh-supported AZ particles, materials 1, 2, and 4, and an Al2O3-based binder were added to prepare a suspended slurry 3. Next, the prepared slurry 3 was poured into the substrate from one end (upstream end), and excess material was blown away with a blower. As a result, a layer of slurry 3 was formed in a third region between one end of the substrate and a third position located at a distance of 50% of the total length of the substrate from one end to the other end (downstream end). The substrate was placed in a dryer maintained at 120°C for 2 hours to evaporate the water in slurry 3, and then calcined in an electric furnace at 500°C for 2 hours. This formed a third catalyst layer.

[0069] At this time, based on the volume of the substrate in the third region, the content of material 1 in the third catalyst layer was 20 g / L, the content of material 2 was 15 g / L, the content of material 3 was 20 g / L, the content of material 4 was 10 g / L, and the Rh content derived from material 6 was 0.2 g / L.

[0070] In this way, the exhaust gas purification device of Comparative Example 1 was fabricated.

[0071] Comparative Example 2 An exhaust gas purification device was manufactured in the same manner as in Comparative Example 1, except that the amount of material 7 used to form the first catalyst layer, the amount of material 6 used to form the second catalyst layer, and the amount of material 6 used to form the third catalyst layer were each 0.85 times that of Comparative Example 1.

[0072] Examples 1-3 Material 3 was added to distilled water while stirring, and nitric acid was added to adjust the pH to 3. This was mixed with material 8 and stirred. The resulting mixture was dried and calcined. This yielded monoclinic ZrO2-supported AZ particles, which consisted of AZ composite oxide particles and monoclinic ZrO2 particles supported on the AZ composite oxide particles. In Examples 1 to 3, the weight of the supported monoclinic ZrO2 particles was 2% by weight, 4% by weight, and 8% by weight, respectively, based on the weight of the AZ composite oxide particles used as the support.

[0073] Exhaust gas purification devices for Examples 1 to 3 were fabricated in the same manner as in Comparative Example 2, except that monoclinic ZrO2-supported AZ particles were used instead of material 3 in the formation of the second and third catalyst layers.

[0074] Comparative Example 3 The exhaust gas purification device for Comparative Example 3 was fabricated in the same manner as in Example 2, except that material 9 was used instead of material 8.

[0075] Comparative Example 4 The exhaust gas purification device for Comparative Example 4 was fabricated in the same manner as in Example 2, except that material 10 was used instead of material 8.

[0076] Table 1 summarizes the manufacturing conditions for the exhaust gas purification devices of Comparative Examples 1-4 and Examples 1-3. In Table 1, ZrO2 / AZ represents the weight ratio of ZrO2 particles to AZ composite oxide particles in ZrO2-supported AZ particles.

[0077] [Table 1]

[0078] (4) Electron beam microanalyzer analysis The uniformity of the ZrO2 particle distribution in the monoclinic ZrO2-supported AZ particles prepared in Examples 1-3 was evaluated using an electron beam microanalyzer (EPMA) (Shimadzu EPMA-8050G, beam current conditions: 15kV, 50nA). Specifically, the EPMA detection amounts (counts) per unit area of ​​Zr and Al were accumulated in the surface region up to 1.5 μm from the surface of the monoclinic ZrO2-supported AZ particles and in the region inside the surface region, and the Zr / Al ratio was calculated. Using the Zr / Al ratio values ​​for each region, the uniformity (%) was calculated according to the following formula.

[0079] Uniformity (%) = (Zr / Al in the surface region) / (Zr / Al in the region inside the surface region) × 100

[0080] When the uniformity (%) was between 95% and 110%, the distribution of ZrO2 particles was considered uniform; otherwise, it was considered non-uniform. The uniformity of the monoclinic ZrO2-supported AZ particles used in Examples 1 to 3 was all within the range of 95% to 110%. This confirmed that the ZrO2 particles were uniformly dispersed and supported.

[0081] (5) Evaluation of exhaust gas purification performance The exhaust gas purification devices of Examples 1-3 and Comparative Examples 1-4 were connected to the exhaust system of a V8 engine, respectively. While maintaining the floor temperature of the exhaust gas purification device at 950°C, a mixture of stoichiometric (air-fuel ratio A / F = 14.6) and oxygen-rich (lean: A / F > 14.6) fuel mixtures was repeatedly introduced into the engine for 50 hours, alternating between them at a constant time ratio of 3:1. This process aged the exhaust gas purification devices.

[0082] Next, the exhaust gas purification device was connected to the exhaust system of an L-type 4-cylinder engine, and a fuel mixture with an air-fuel ratio (A / F) of 14.4 was supplied to the engine. The exhaust gas was then introduced into the exhaust gas purification device at a flow rate of 30 g / s. The temperature of the exhaust gas introduced into the exhaust gas purification device was raised to 500°C, and the temperature of the exhaust gas when the NOx purification rate reached 50% (denoted as "NOx-T50" as appropriate), the temperature of the exhaust gas when the CO purification rate reached 50% (denoted as "CO-T50" as appropriate), and the temperature of the exhaust gas when the THC purification rate reached 50% (denoted as "THC-T50" as appropriate) were measured. The results are shown in Table 2 and Figures 4 and 5. The dotted line in Figure 4 is an approximate straight line of the plots for Examples 1 to 3.

[0083] [Table 2]

[0084] The exhaust gas purification devices of Examples 1 to 3, which were fabricated by supporting Rh particles on monoclinic ZrO2-supported AZ particles, all showed higher NOx purification performance, CO purification performance, and THC purification performance than the exhaust gas purification devices of Comparative Examples 2 to 4, which were fabricated by supporting Rh particles on AZ composite oxide particles without ZrO2 particles, AZ composite oxide particles supporting amorphous ZrO2 particles, or AZ composite oxide particles supporting tetragonal ZrO2 particles. In particular, Examples 1 to 3 achieved NOx purification performance exceeding that of Comparative Example 1, even though they used only 0.85 times the amount of Rh particles compared to Comparative Example 1. As shown in Figure 4, it is considered that NOx purification performance exceeding that of Comparative Example 1 can be obtained when the weight of monoclinic ZrO2 particles in monoclinic ZrO2-supported AZ particles is within the range of 1 to 10% by weight relative to the AZ composite oxide particles. Therefore, by setting the weight of monoclinic ZrO2 particles within the range of 1 to 10% by weight, based on the weight of AZ composite oxide particles, it is considered possible to reduce the amount of Rh used by more than 15% while maintaining NOx purification performance.

[0085] Furthermore, as shown in Table 2, in Examples 1 and 2, where the weight of monoclinic ZrO2 particles in monoclinic ZrO2-supported AZ particles was 2-4% by weight relative to the weight of AZ composite oxide particles, not only the NOx purification performance but also the CO purification performance was higher than that of Comparative Example 1. Moreover, in Example 1, where the weight of monoclinic ZrO2 particles in monoclinic ZrO2-supported AZ particles was 2% by weight relative to the weight of AZ composite oxide particles, the THC purification performance was higher than that of Comparative Example 1, in addition to the NOx and CO purification performance.

Claims

1. It is an exhaust gas purification device, A substrate having an upstream end into which exhaust gas flows and a downstream end from which the exhaust gas is discharged, with the length between the upstream end and the downstream end being Ls, In a first region between the upstream end and a first position separated by a first distance La from the upstream end toward the downstream end, a first catalyst layer containing palladium particles is formed on the substrate, In a second region between the downstream end and a second position separated by a second distance Lb from the downstream end toward the upstream end, a second catalyst layer containing rhodium-supported particles is formed on the substrate, Here, the rhodium-supported particles include a porous carrier which is a composite oxide containing Al and Zr elements, monoclinic zirconium dioxide particles uniformly dispersed and supported within the pores of the porous carrier, and rhodium particles supported within the pores of the porous carrier. Here, "uniformly dispersed and supported" means that when the rhodium-supported particles are measured with an electron beam microanalyzer, the ratio of the zirconium abundance in the surface region from the surface of the rhodium-supported particles to a depth of 1.5 μm to the zirconium abundance in the region of the rhodium-supported particles inside the surface region is 95% to 110%, and the second catalyst layer, In a third region between the upstream end and a third position separated by a third distance Lc from the upstream end toward the downstream end, a third catalyst layer containing rhodium particles is formed on the substrate, Equipped with, In the first region, the third catalyst layer is formed on the first catalyst layer. An exhaust gas purification device in which the length Ls of the base material, the first distance La, and the second distance Lb satisfy La + Lb < Ls.

2. The exhaust gas purification device according to claim 1, wherein the proportion of rhodium particles contained in the third catalyst layer is greater than 0% by weight and less than 50% by weight, based on the total weight of the rhodium particles contained in the second catalyst layer and the third catalyst layer.

3. The exhaust gas purification device according to claim 1 or 2, wherein in the rhodium-supported particles contained in the second catalyst layer, the weight of the zirconium dioxide particles is in the range of 1 to 10% by weight based on the weight of the porous carrier.

4. The third catalyst layer contains the rhodium-supported particles, The exhaust gas purification device according to claim 1 or 2, wherein the rhodium particles contained in the third catalyst layer are the rhodium particles contained in the rhodium-supported particles.

5. The exhaust gas purification device according to claim 4, wherein in the rhodium-supported particles contained in the third catalyst layer, the weight of the zirconium dioxide particles is in the range of 1 to 10% by weight based on the weight of the porous carrier.

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