Exhaust gas purification catalyst and exhaust gas purification system using the same

Abstract

Provided are an exhaust gas purification catalyst capable of exerting higher exhaust gas purification performance without impairing the catalytic activity of Pd, and an exhaust gas purification system using the exhaust gas purification catalyst. An exhaust gas purification catalyst comprising a substrate and a catalyst layer disposed on the substrate, the catalyst layer having a first partition located on the upstream side and a second partition located on the downstream side relative to the first partition along the flow direction of the exhaust gas, the catalyst layer of the first partition comprising a first catalyst layer containing palladium and a second catalyst layer containing rhodium covering the first catalyst layer, the ratio of the pore volume of the substrate and the catalyst layer to the volume of the first partition being 12% or more and less than 18%, and the amount of the carrier coating layer of the catalyst layer of the first partition being 100 g / L or more and 190 g / L or less relative to the volume of the substrate present in the first partition.

Description

Technical Field

[0001] The present invention relates to an exhaust gas purification catalyst provided in an exhaust system of an internal combustion engine and an exhaust gas purification system using the exhaust gas purification catalyst. Background Art

[0002] The tail gas (also called exhaust gas) discharged from the internal combustion engines of automobiles, motorcycles, etc. contains harmful components such as HC (hydrocarbons), CO (carbon monoxide) and NOx (nitrogen oxides). In the past, three-way catalysts were used for the purpose of purifying these harmful components and rendering them harmless. As three-way catalysts, catalysts obtained using precious metals such as Pt (platinum), Pd (palladium), and Rh (rhodium) are known. Pt and Pd mainly act on the oxidation purification of HC and CO, and Rh mainly acts on the reduction purification of NOx. In recent years, with the strengthening of exhaust gas control and the improvement of environmental awareness, attempts have been made to improve the exhaust gas purification performance of precious metal catalysts such as those mentioned above.

[0003] For example, Patent Document 1 proposes a catalyst for exhaust gas purification, which is partitioned by catalyst layers with different catalyst compositions on the upstream and downstream sides in the exhaust gas flow direction, and Pd with excellent low-temperature catalytic activity is configured in the partition on the upstream side where the temperature rises quickly, and the catalyst loading amount (i.e., the amount of carrier coating of the Pd catalyst in the catalyst layer) is reduced to reduce the heat capacity, thereby being able to exert high exhaust gas purification performance even when the internal combustion engine is preheated.

[0004] In addition, Patent Document 2 proposes a catalyst for exhaust gas purification, wherein, for the catalyst layer on the upstream side of the exhaust gas flow direction, the Pd concentration is made different in the cross-sectional thickness direction of the catalyst layer, and the Pd concentration is increased closer to the surface side of the catalyst layer that the exhaust gas initially contacts, thereby being able to exert high exhaust gas purification performance even during preheating.

[0005] Prior art literature

[0006] Patent Literature

[0007] Patent Document 1: Japanese Patent Application Publication No. 2010-5592

[0008] Patent Document 2: International Publication No. 2016 / 039302 Summary of the invention

[0009] Problem that the invention aims to solve

[0010] However, it is known that the catalytic activity of the Pd catalyst used for the oxidation purification of HC and CO is lost due to phosphorus from engine oil and the like (phosphorus poisoning). Therefore, it can be considered that in the exhaust gas purification catalysts proposed in Patent Documents 1 and 2, the Pd catalyst layer arranged on the upstream side of the catalyst layer will also be subject to phosphorus poisoning. It can be considered that in order to suppress the phosphorus poisoning of the Pd catalyst layer, by making the catalyst layer on the upstream side into multiple layers and providing other catalyst layers containing Rh and the like on the surface of the Pd catalyst layer, it is possible to produce an exhaust gas purification catalyst having excellent exhaust gas purification performance during preheating and high-speed operation without reducing the catalytic activity of Pd.

[0011] However, it can be considered that: for the exhaust gas purification catalyst proposed in Patent Document 1, if an Rh catalyst layer is provided on the surface of the Pd catalyst layer on the upstream side, the exhaust gas will contact the Pd catalyst layer after passing through the Rh catalyst layer. Therefore, not only the characteristics of Pd cannot be manifested, but also the amount of carrier coating is increased due to the formation of multiple layers of the catalyst layer on the upstream side. Therefore, the heat capacity increases and the temperature rise performance is impaired.

[0012] Furthermore, it can be considered that, in the exhaust gas purification catalyst of Patent Document 2, similarly to the above, the Pd catalyst layer is hindered from contacting the exhaust gas due to the Rh catalyst layer disposed on its surface, and if the surface of the Pd catalyst layer in which the Pd concentration is increased is covered with the Rh catalyst layer, the characteristic of the Pd catalyst of excellent low-temperature activity cannot be fully exerted, and the significance of increasing the Pd concentration on the surface of the Pd catalyst layer is impaired.

[0013] Therefore, an object of the present invention is to provide an exhaust gas purification catalyst capable of exhibiting higher exhaust gas purification performance without impairing the catalytic activity of Pd, and an exhaust gas purification system using the exhaust gas purification catalyst.

[0014] Solutions for solving problems

[0015] The present inventors have obtained the following findings: for the upstream catalyst layer, when a Rh catalyst layer is provided on the surface of a Pd catalyst layer, if the amount of the carrier coating layer when forming the upstream catalyst layer is set to a specific amount and certain pores are provided in the formed catalyst layer, it is possible to provide an exhaust gas purification catalyst that suppresses the reduction in catalytic activity caused by phosphorus poisoning of the Pd catalyst layer and has excellent exhaust gas purification performance during preheating and high-speed operation. The present invention is based on the above findings.

[0016] That is, the gist of the present invention is as follows.

[0017] [1] An exhaust gas purification catalyst comprising a substrate and a catalyst layer provided on the substrate,

[0018] The exhaust gas purifying catalyst has a first partition located on the upstream side and a second partition located on the downstream side of the first partition along the flow direction of the exhaust gas.

[0019] The catalyst layer of the first partition includes a first catalyst layer containing palladium and a second catalyst layer containing rhodium covering the first catalyst layer.

[0020] The ratio of the total volume of pores in the substrate and the catalyst layer of the first partition and having a pore diameter of 0.06 μm or more and 30.0 μm or less measured by mercury intrusion porosimetry to the volume of the entire first partition, i.e., the pore volume ratio, is 12% or more and less than 18%,

[0021] The mass per unit volume of the catalyst layer in the first section relative to the volume of the substrate present in the first section, that is, the washcoat amount, is 100 g / L or more and 190 g / L or less.

[0022] [2] The exhaust gas purification catalyst according to [1], wherein the first catalyst layer is divided into two equal parts along the thickness direction, the mass of palladium existing on the surface side of the first catalyst layer is denoted as a1, and the mass of palladium existing on the opposite side relative to the surface side of the first catalyst layer is denoted as a2, and the value of a1 / a2 is greater than 1.2.

[0023] [3] A catalyst for purifying exhaust gas according to [1] or [2], wherein the ratio of the total volume of pores having a pore diameter of 0.06 μm or more and 30.0 μm or less, as measured by mercury intrusion porosimetry, present in the substrate and catalyst layer of the second partition to the volume of the entire second partition, i.e., the pore volume ratio, is 18% or more and 25% or less.

[0024] [4] The exhaust gas purification catalyst according to any one of [1] to [3], wherein the catalyst layer of the second section includes a third catalyst layer containing palladium and a fourth catalyst layer containing rhodium covering the third catalyst layer.

[0025] [5] The exhaust gas purification catalyst according to any one of [1] to [4], wherein the pore volume ratio of the substrate and the catalyst layer in the first partition is 90% or less of the pore volume ratio of the substrate and the catalyst layer in the second partition.

[0026] [6] The exhaust gas purification catalyst according to any one of [1] to [5], wherein the mass per unit volume of the catalyst layer of the second partition relative to the volume of the substrate present in the second partition, i.e., the carrier coating amount, is greater than 180 g / L and less than 300 g / L.

[0027] [7] The exhaust gas purification catalyst according to any one of [1] to [6], wherein the second catalyst layer has through holes with a width of 10 μm or more that allow air to pass from the surface to the first catalyst layer.

[0028] [8] The exhaust gas purification catalyst according to any one of [1] to [7], wherein the length of the first partition in the exhaust gas flow direction is 20% or more and 70% or less relative to the length of the substrate in the exhaust gas flow direction.

[0029] [9] An exhaust gas purification system, wherein, in an exhaust passage connected to the internal combustion engine, exhaust gas from the internal combustion engine is introduced into the exhaust gas purification catalyst according to any one of [1] to [8] without passing through another exhaust gas purification catalyst.

[0030] Effects of the Invention

[0031] According to the present invention, for a catalyst for exhaust gas purification in which a catalyst layer is divided into a first partition on an upstream side and a second partition on a downstream side, by making the catalyst layer of the first partition have a first catalyst layer containing palladium and a second catalyst layer containing rhodium covering the first catalyst layer, and by making the first partition into a catalyst layer with a carrier coating amount of not less than 100 g / L and not more than 190 g / L so as to have a pore volume ratio of not less than 12% and not more than 18%, it is possible to provide a catalyst for exhaust gas purification that suppresses the reduction in catalytic activity of the Pd catalyst layer caused by phosphorus poisoning and has excellent exhaust gas purification performance during preheating and high-speed operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Figure 1 This is a schematic diagram showing a state in which an exhaust gas-purifying catalyst according to one embodiment of the present invention is accommodated in a casing through which exhaust gas flows.

[0033] Figure 2 yes Figure 1 A partially enlarged schematic diagram of the II' line cross section of the exhaust gas purification catalyst. DETAILED DESCRIPTION

[0034] An exhaust gas-purifying catalyst according to an embodiment of the present invention will be described with reference to the drawings. Figure 1 Schematic diagram showing a state in which an exhaust gas purifying catalyst is accommodated in a casing through which exhaust gas flows. Figure 2 yes Figure 1 A partially enlarged schematic diagram of the II' line cross section of the exhaust gas purification catalyst. Figure 1 As shown, it is arranged in the casing 20 and provided in the flow path of the exhaust gas.

[0035] The exhaust gas purifying catalyst 10 includes a substrate 11 and a catalyst layer 12 formed on the substrate 11. The exhaust gas purifying catalyst 10 includes a first partition V1 located on the upstream side and a second partition V2 located on the downstream side of the first partition along the flow direction X of the exhaust gas. The catalyst layer of the first partition V1 located on the upstream side of the exhaust gas flow direction has a multilayer structure in which a first catalyst layer 13 and a second catalyst layer 14 are stacked in sequence from the substrate 111 side, and the first catalyst layer 13 is covered by the second catalyst layer 14. Figure 2 In the illustrated embodiment, the catalyst layer of the first partition V1 has a two-layer stacked structure, but another catalyst layer (not shown) may be further provided on the surface of the second catalyst layer 14. In addition, another catalyst layer (not shown) may be provided between the first catalyst layer 13 and the second catalyst layer 14. Furthermore, another catalyst layer (not shown) may be provided between the substrate 111 and the first catalyst layer 13.

[0036] The catalyst layer of the second partition V2 has a multilayer structure in which the third catalyst layer 15 and the fourth catalyst layer 16 are stacked in order from the substrate 112 side, and the third catalyst layer 15 is covered by the fourth catalyst layer 16. Figure 2 In the illustrated embodiment, the catalyst layer of the second partition V2 has a two-layer stacked structure, but the catalyst layer of the second partition V2 may be a single-layer structure, in which case the fourth catalyst layer 16 may be omitted. In addition, another catalyst layer (not shown) may be further provided on the surface of the third catalyst layer 15 or the fourth catalyst layer 16, or another catalyst layer (not shown) may be provided between the third catalyst layer 15 and the fourth catalyst layer 16. Furthermore, another catalyst layer (not shown) may be provided between the substrate 112 and the third catalyst layer 15.

[0037] From the viewpoint of easily utilizing heat generated by exothermic reactions such as HC oxidation and CO oxidation promoted by the catalytically active components in the first section V1 to efficiently raise the temperature of the second section V2 , it is preferred that the first section V1 and the second section V2 are in contact with each other in the exhaust gas flow direction X without a gap.

[0038] <Base Material>

[0039] The substrate 11 may be a substrate used in a conventionally known exhaust gas purification catalyst. For example, a substrate having a partition wall formed of a porous material and an exhaust gas flow path (space between the partition walls) divided by the partition wall may be appropriately used. As the shape of the substrate 11, a known substrate such as a honeycomb, a DPF, or a GPF may be appropriately used. In addition, as the material of the partition wall of the substrate 11, for example, aluminum oxide (Al 2 O 3 ), mullite (3Al 2O 3 -2SiO 2 )、Cordierite (2MgO-2Al 2 O 3 -5SiO 2 ), aluminum titanate (Al 2 TiO 5 ), ceramics such as silicon carbide (SiC); metal materials such as stainless steel.

[0040] The exhaust gas purifying catalyst 10 including the substrate 11 and the catalyst layer 12 formed on the substrate 11 (that is, the catalyst layer formed on the surface of the partition wall of the substrate) is also referred to as a catalytic converter. Figure 1 In the example shown, the substrate 11 has a shape that is long in one direction and is arranged in such a way that the exhaust gas flow direction X is consistent with the length direction. Figure 1 In , R represents the boundary portion that distinguishes the first partition V1 from the second partition V2. Figure 2 In the present invention, the substrate 11 existing in the first partition V1 is recorded as substrate 111, and the substrate existing in the second partition V2 is recorded as substrate 112. For the convenience of explaining the invention, the substrate 11 is divided into substrate 111 and substrate 112, but in essence, substrate 111 and substrate 112 are formed of the same material.

[0041] <Catalyst Layer of the First Section>

[0042] The first catalyst layer 13 constituting the catalyst layer of the first partition V1 contains palladium (Pd) as a catalytically active component, and may also contain other catalytically active components such as platinum (Pt) and rhodium (Rh). In particular, from the viewpoint of high purification performance of carbon monoxide (CO) and hydrocarbons (HC) and the ability to obtain a warming function, it is preferred that Pd and Pt are contained as catalytically active components.

[0043] From the viewpoint of efficiently exerting the exhaust gas purification performance achieved by the catalytically active component, it is preferred that the first catalyst layer 13 further contains a carrier component that supports the above-mentioned catalytically active component. As the carrier component mentioned here, there can be listed an oxygen storage component (hereinafter also referred to as an OSC material) and an inorganic oxide other than the oxygen storage component. When the exhaust gas purification catalyst is used for a gasoline engine that controls the theoretical air-fuel ratio, it is preferred that the first catalyst layer 13 contains an oxygen storage component as a carrier component because it can stably exert a high purification rate relative to changes in the air-fuel ratio. When containing an oxygen storage component, it is preferred that the oxygen storage component and the inorganic oxide other than the oxygen storage component exist in a mixed state.

[0044] It should be noted that the catalytically active component is physically or chemically adsorbed or retained on the outer surface or the inner surface of the pores. Specifically, regarding the catalytically active component being loaded on the carrier component, for example, based on the element image obtained by analyzing the cross section of the exhaust gas purification catalyst 10 using EDS (energy dispersive spectrometer), it is confirmed that the carrier component and the catalytically active component exist in the same area, thereby determining that the carrier component is "loaded" with the catalytically active component.

[0045] As the oxygen storage component, any metal oxide that undergoes a change in the valence of the constituent elements due to the operating conditions of the exhaust gas purification catalyst and has the ability to store oxygen can be used without particular limitation, for example, CeO 2 、CeO 2 -ZrO 2 (Cerium oxide-zirconia composite oxide containing Ce and Zr, CeO 2 and ZrO 2 The solid solution of CeO is preferred because the OSC of the exhaust gas purification catalyst is high. The X-ray diffraction device (XRD) can be used to determine whether CeO is formed. 2 -ZrO 2 The single phase of CeO 2 and ZrO 2 A solid solution is formed. As an oxygen storage component, a porous material is preferred because it is easy to load the catalytic active component. Examples of porous materials include those with a BET specific surface area of ​​30 m 2 / g~210m 2 / g porous body.

[0046] The oxygen storage component may contain rare earth elements other than cerium (Ce); alkaline earth metal elements such as barium (Ba), strontium (Sr), and calcium (Ca). Rare earth elements other than cerium include scandium (Sc), yttrium (Y), lanthanum (La), praseodymium (Pr), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu). These rare earth elements are added to the oxygen storage component in the form of oxides, for example. The oxides of rare earth elements, except for praseodymium (Pr) and terbium (Tb), are sesquioxides (Re 2 O 3 , Re is a rare earth element). They can be two or more composite oxides. Praseodymium oxide is usually Pr 6 O 11 , terbium oxide is usually Tb 4 O 7 The oxides of these rare earth elements except cerium can be combined with CeO 2 -ZrO 2Can the oxides of rare earth elements other than cerium be combined with CeO? 2 -ZrO 2 The formation of a solid solution can be confirmed by using an X-ray diffraction apparatus (XRD) in the same manner as described above.

[0047] In addition, as oxygen storage components, in addition to the above components, oxides of elements such as manganese (Mn), iron (Fe), copper (Cu), etc. that easily undergo changes in valence state under the use conditions of the catalyst; and composite oxides containing these elements, etc. can also be listed.

[0048] As for the inorganic oxide other than the oxygen storage component as the carrier component for supporting the catalytic active component, metal oxides other than the above oxygen storage components such as Al 2 O 3 、ZrO 2 、SiO 2 、TiO 2 ,La 2 O 3 Rare earth oxides (Re 2 O 3 ), zeolite (aluminosilicate), MgO, ZnO, SnO 2 Oxide materials with the like as the matrix; oxide materials obtained by compounding these materials with each other. In addition, phosphates and borates of aluminum (Al), zirconium (Zr), silicon (Si), titanium (Ti), rare earth elements, magnesium (Mg), zinc (Zn), etc.; sparingly soluble sulfates formed with alkaline earth metals such as Ba and Sr, etc. can be listed. Inorganic oxides other than oxygen storage components are preferably porous bodies. As porous bodies, BET specific surface area of ​​30m 2 / g~600m 2 / g porous body.

[0049] It should be noted that the above-mentioned inorganic oxides include those obtained by modifying and / or supporting oxygen storage components. For example, the inner surface and outer surface of the pores of alumina or the like can be modified by CeO 2 Modification mentioned here refers to a concept including a supported state, and examples thereof include a state in which fine particles of oxygen storage components are dispersed on the inner surface and outer surface of the pores of alumina. It should be noted that alumina can be modified by lanthanum oxide, ZrO 2 Modified by etc.

[0050] Furthermore, from the viewpoint of suppressing the decrease in catalytic activity and heat resistance caused by phosphorus poisoning, the first catalyst layer 13 may contain an alkaline earth metal compound. Preferred alkaline earth metals include Sr and Ba. The alkaline earth metal compound may be an oxide in addition to nitrates and carbonates.

[0051] In order to form the first catalyst layer 13 on the substrate 11 (i.e., the partition wall of the substrate), a slurry is prepared by kneading the salt of the above-mentioned catalytic active component (e.g., palladium nitrate, rhodium nitrate, platinum nitrate, etc.), a carrier component, and a liquid medium such as water using a ball mill, and the slurry is applied to the surface of the substrate by a carrier coating method, followed by drying and calcining. By adjusting the amount of the carrier coating, the first catalyst layer 13 of the desired thickness can be formed. The amount of the carrier coating of the slurry is described below.

[0052] From the viewpoint of the catalytic activity of the exhaust gas purification catalyst, the temperature for calcining the substrate coated with the slurry is preferably 400°C to 800°C, and more preferably 450°C to 600°C. The calcination time is preferably 0.5 hours to 6 hours, and more preferably 1 hour to 4 hours. In addition, the slurry applied to the substrate is preferably dried before calcination, and the temperature is preferably 40°C to 200°C, and more preferably 70°C to 150°C. The drying time is preferably 5 minutes to 6 hours, and more preferably 10 minutes to 2 hours.

[0053] The second catalyst layer 14 covering the first catalyst layer 13 contains rhodium (Rh) as a catalytically active component. As described above, if the first catalyst layer 13 containing Pd as a catalytically active component is exposed, the exhaust gas first contacts the first catalyst layer 13. Therefore, if phosphorus is contained in the exhaust gas, the catalytic activity of Pd is reduced. In the present invention, the first catalyst layer 13 is covered with the second catalyst layer 14 in order to reduce phosphorus poisoning of Pd.

[0054] The second catalyst layer 14 may contain a catalytically active component other than Rh as a catalytically active component, for example, Pt or Pd.

[0055] In order to efficiently exert the exhaust gas purification performance of the catalytically active component, the second catalyst layer 14 preferably further contains a support component that supports the catalytically active component. As the support component mentioned here, the same oxygen storage component and inorganic oxide as used in the first catalyst layer 13 can be used.

[0056] In order to form the second catalyst layer 14 on the first catalyst layer 13, the salt of the above-mentioned catalytically active component (such as palladium nitrate, rhodium nitrate and platinum nitrate, etc.), the carrier component and the liquid medium such as water are kneaded by a ball mill or the like in the same manner as the formation method of the first catalyst layer 13 to prepare a slurry, and the slurry is applied to the surface of the first catalyst layer 13 by a carrier coating method, and then dried and calcined. By adjusting the amount of carrier coating, a second catalyst layer 14 of a desired thickness can be formed. The amount of carrier coating for the slurry is described later. It should be noted that the calcination temperature and the drying temperature can be set to the same conditions as those for the formation of the first catalyst layer.

[0057] The mass per unit volume of the catalyst layer (the first catalyst layer 13 and the second catalyst layer 14) of the first partition V1 relative to the volume of the substrate present in the first partition V1 (hereinafter referred to as the "carrier coating amount") is 100 g / L or more and 190 g / L or less. The carrier coating amount here refers to the amount of slurry attached to each 1L of the substrate 111 present in the first partition V1 (solid content mass). It should be noted that the solid content mass refers to the mass obtained by subtracting the mass of the components (such as solvents, pore-forming agents, etc.) that disappear due to drying and calcining of the slurry.

[0058] If the amount of carrier coating is increased, there is an advantage that the support material and OSC material that can improve the dispersibility of the catalytically active components in the formed catalyst layer can be increased. On the other hand, the amount of catalyst is also increased. As a result, the heat capacity of the catalyst layer becomes larger, and time is required to increase the temperature of the catalyst layer. Therefore, there is a tendency for the exhaust gas purification performance during preheating to decrease. In the present invention, by setting the amount of carrier coating to 190g / L or less, the heat capacity will not be too large, and high exhaust gas purification performance can be exerted during preheating. On the other hand, if the amount of carrier coating of the catalyst layer of the first partition exceeds 190g / L, sometimes the heat capacity of the catalyst layer of the first partition becomes larger, and the exhaust gas purification performance of the internal combustion engine during preheating is insufficient. In addition, if the amount of carrier coating of the catalyst layer of the first partition is less than 100g / L, sometimes the amount of catalytically active components is insufficient, and the oxidation purification of HC and CO and the reduction purification of NOx are insufficient. The preferred carrier coating amount of the catalyst layer of the first partition is 140g / L or more and 170g / L or less.

[0059] Hereinafter, an example of a method for calculating the washcoat amount of the catalyst layer (the first catalyst layer 13 and the second catalyst layer 14 ) in the first section V1 will be described.

[0060] First, a portion of the exhaust gas purifying catalyst 10 along the exhaust gas flow direction ( Figure 2The sample is a sample extending in the X direction (in the X direction) and having the same length as the length L1 of the substrate 111. The sample is, for example, a cylindrical shape with a diameter of 25.4 mm. Next, the cut sample is cut with a plane perpendicular to the exhaust gas flow direction of the substrate 11 to prepare a slice S1 of the exhaust gas purifying catalyst 10 containing the catalyst layer (the first catalyst layer 13 and the second catalyst layer 14) of the first partition V1. The slice S1 is, for example, a cylindrical shape with a diameter of 25.4 mm and a length of 10 mm. It should be noted that the diameter value of the slice S1 can be changed as needed. From the viewpoint of suppressing the deviation of the carrier coating amount caused by the cutting position of the sample, the exhaust gas purifying catalyst 10 can be directly cut with a plane perpendicular to the exhaust gas flow direction so that it has the same diameter as the exhaust gas purifying catalyst 10. In addition, the length value of the slice S1 can be changed as needed. The length of the catalyst layer of the first partition V1 contained in the slice S1 is equal to the length of the slice S1.

[0061] Next, a slice of the substrate 11 having the same size as the slice S1 is prepared. The slice of the substrate 11 is prepared without the catalyst layer of the first sub-area V1 and the catalyst layer of the second sub-area V2.

[0062] The mass of the slice S1 and the mass of the slice of the substrate 11 are measured, and the mass of the catalyst layer of the first section V1 per unit volume of the slice S1 is calculated according to the following formula.

[0063] The mass of the catalyst layer of the first subarea V1 per unit volume of the slice S1 = ((mass of the slice S1) - (mass of the slice of the substrate 11)) / (volume of the slice S1)

[0064] It should be noted that the volume of the slice S1 is the apparent volume of the slice S1. For example, if the slice S1 is cylindrical with a diameter of 25.4 mm and a length of 10 mm, the volume of the slice S1 is π×(12.7 mm). 2 × 10 mm. The volumes of other slices (slice S2 described later) are also the same.

[0065] Regarding the three slices S1 made from any parts of the exhaust gas purification catalyst 10, the mass of the catalyst layer of the first partition V1 per unit volume of the slice S1 is calculated, and their average value is taken as the carrier coating amount of the catalyst layer (the first catalyst layer 13 and the second catalyst layer 14) of the first partition V1 relative to the volume of the substrate 111 existing in the first partition V1.

[0066] It should be noted that when calculating the washcoat amount of the catalyst layer in the first section V1, the mass of the catalyst layer in the first section V1 per unit volume of the slice S1 may be calculated instead of using the slice of the substrate 11. An example of such a calculation method is shown below.

[0067] First, measure the mass and volume of the slice S1 produced in the same manner as described above. The composition of the substrate 11 contained in the slice S1 is determined using the elemental image of the cut surface of the slice S1. The elemental image can be performed using a scanning electron microscope (SEM), an electron beam microanalyzer (EPMA), or the like. In addition, the composition of the slice S1 is determined by analyzing using an inductively coupled plasma atomic emission spectrometer (ICP-AES). Next, based on the determined composition of the substrate 11 and the slice S1, calculate the proportion of the mass of the catalyst layer in the mass of the slice S1, and calculate the mass of the catalyst layer of the first partition V1 per unit volume of the slice S1 according to the following formula.

[0068] The mass of the catalyst layer of the first partition V1 per unit volume of the slice S1 = (mass of the slice S1) × (ratio of the mass of the catalyst layer of the first partition V1 to the mass of the slice S1) / (volume of the slice S1)

[0069] Next, an example of a method for calculating the amount of carrier coating of each of the first catalyst layer 13 and the second catalyst layer 14 constituting the catalyst layer of the first partition V1 is described. Regarding the amount of carrier coating of the first catalyst layer 13, the composition of the substrate 11 and the first catalyst layer 13 contained in the slice S1 is determined using the elemental image of the cut surface of the slice S1. In addition, the composition of the slice S1 is determined by analyzing using ICP-AES or the like. Based on the determined composition of the substrate 11, the first catalyst layer 13, and the slice S1, the proportion of the mass of the first catalyst layer 13 in the mass of the slice S1 is calculated. The mass of the first catalyst layer 13 per unit volume of the slice S1 is calculated according to the following formula.

[0070] The mass of the first catalyst layer 13 per unit volume of the slice S1 = (the mass of the slice S1) x (the ratio of the mass of the first catalyst layer 13 to the mass of the slice S1) / (the volume of the slice S1)

[0071] Similarly, regarding the amount of carrier coating of the second catalyst layer 14, the composition of the substrate 11 and the second catalyst layer 14 contained in the slice S1 is determined by using the elemental image of the cut surface of the slice S1. In addition, the composition of the slice S1 is determined by analyzing using ICP-AES or the like. Based on the determined composition of the substrate 11, the second catalyst layer 14, and the slice S1, the proportion of the mass of the second catalyst layer 14 in the mass of the slice S1 is calculated. The mass of the second catalyst layer 14 per unit volume of the slice S1 is calculated according to the following formula.

[0072] The mass of the second catalyst layer 14 per unit volume of the slice S1 = (the mass of the slice S1) x (the ratio of the mass of the second catalyst layer 14 to the mass of the slice S1) / (the volume of the slice S1)

[0073] Among the catalyst layers of the first partition V1, from the viewpoint of improving the exhaust gas purification performance during preheating and high-speed operation, the carrier coating amount of the first catalyst layer 13 is preferably 50 g / L or more and 140 g / L or less, and more preferably 80 g / L or more and 130 g / L or less.

[0074] Among the catalyst layers of the first partition V1, from the viewpoint of inhibiting Pd poisoning and improving the exhaust gas purification performance during preheating and high-speed operation, the carrier coating amount of the second catalyst layer 14 is preferably greater than 30 g / L and less than 65 g / L, and more preferably greater than 35 g / L and less than 60 g / L.

[0075] In addition, the pore volume ratio of the substrate 111 and the catalyst layer (the first catalyst layer 13 and the second catalyst layer 14) relative to the volume of the first partition V1 is 12% or more and less than 18%. It should be noted that in the present invention, the "pore volume ratio" refers to a value calculated by the following operation. First, from the first partition (i.e., Figure 1 and Figure 2 A 10 mm square cubic sample is taken from any part of the sample (the portion of V1 shown), and the mass, volume and pore diameter distribution based on the mercury intrusion method are measured. The pore diameter distribution can be calculated by a known method based on the mercury intrusion method. The measured sample mass is recorded as W (g), and the geometric volume of the cube is recorded as V (mL). In the pore distribution measurement results, the volume of mercury pressed in with an applied pressure of 0.049 to 255 MPa (corresponding to a pore diameter of 0.06 μm or more and 30.0 μm or less: Hg contact angle of 140°) is recorded as the pore volume P (mL / g). The pore volume ratio of the substrate and the catalyst layer relative to the volume of the first partition can be calculated by the following formula: Pore volume ratio (%) = W×P / V×100. In addition, for the substrate and catalyst layer relative to the volume of the second partition described later, the pore volume ratio of the substrate and the catalyst layer relative to the volume of the first partition can be measured in the same manner as the pore volume ratio of the substrate and the catalyst layer relative to the volume of the first partition.

[0076] Regarding the pore volume ratio of the substrate and the catalyst layer relative to the volume of the first partition, relative to the volume of the first partition (that is, it means: not only the volume of the partition wall of the substrate and the catalyst layer, but also the apparent volume of the first partition as a whole, including the space between the partition walls in the substrate), it is 12% or more and less than 18%. It should be noted that the catalyst layer of the exhaust gas purification catalyst is composed of a porous material with an oxide support material as the skeleton and containing micropores, so it can be said that more than half of the volume occupied by the catalyst layer is voids. Therefore, it can be said that the pore volume measured using the above conditions reflects the thickness of the catalyst layer. The thickness of the catalyst layer indicates the volume per unit area of ​​the purified gas that can contact the active component. If the catalyst layer does not have sufficient thickness, the probability of contact between the purified gas and the active component is reduced, and high purification performance cannot be obtained. On the other hand, if the catalyst layer is excessively thickened, the pressure loss in the catalyst layer increases when the exhaust gas flows through the catalyst. That is, as mentioned above, in order to improve the exhaust gas purification performance during preheating and reduce the amount of carrier coating, the support material for dispersing the catalytic active component also becomes less, so the thickness of the catalyst layer has to be thinned in the previous method. The present invention focuses on the above aspects and finds that by setting the pore volume ratio of the substrate and the catalyst layer to the volume of the first partition to 12% or more, the exhaust gas purification performance during high-speed operation can also be improved. In addition, if the pore volume ratio is less than 18%, it can be said that a significant pressure loss will also occur. That is, if the pore volume ratio is 12% or more and less than 18%, by forming a catalyst layer with sufficient thickness, the contact between the exhaust gas and the catalytically active component becomes active, and high exhaust gas purification performance can be achieved without significant pressure loss. In addition, even if the carrier coating amount is less than 190g / L, by designing the catalyst layer in a manner that the pore volume ratio is 12% or more and less than 18%, the density of the catalyst layer in the first partition is appropriately reduced, and even if the first catalyst layer is covered by the second catalyst layer, the exhaust gas is easy to pass through the second catalyst layer and contact the first catalyst layer, so the reaction heat becomes more, and as a result, the temperature rise of the first catalyst layer can be accelerated. In addition, the high-temperature exhaust gas is easy to pass through the catalyst layer in the first partition, which can complement the thickness (carrier coating amount) of the catalyst layer in the first partition to accelerate the temperature rise of the catalyst layer. As a result, it is possible to improve the exhaust gas purification performance during warm-up and high-speed operation while suppressing a decrease in the catalytic activity of the Pd catalyst layer due to phosphorus poisoning.

[0077] As described above, the value of the pore volume ratio reflects the thickness of the catalyst layer, and there is a tendency that the lower the density of the catalyst layer (the more fluffy the catalyst layer) or the more the amount of carrier coating of the catalyst layer, the greater the value of the pore volume ratio. That is, by adjusting the density of the catalyst layer and the amount of carrier coating of the catalyst layer, the value of the pore volume ratio can be controlled. For example, as shown in the evaluation results of Example 1, Example 4 and Comparative Example 1 described later, for example, when the same slurry is used to form the first catalyst layer 13 and the density of the first partition is the same, as the amount of carrier coating increases, there is a tendency for the value of the pore volume ratio of the first partition to become larger. On the other hand, as shown in the evaluation results of Comparative Example 5 described later, for example, when the particles in the slurry used to form the first catalyst layer 13 use particles with a small particle size, when the density of the first partition is increased, there is a tendency that the value of the pore volume ratio is smaller even if the amount of carrier coating is increased. According to the exhaust gas purification catalyst of this embodiment, for the first partition, by controlling such pore volume ratio and carrier coating amount respectively, it is possible to suppress the reduction of catalytic activity caused by phosphorus poisoning of the Pd catalyst layer and improve the exhaust gas purification performance during preheating and high-speed operation.

[0078] On the other hand, if the pore volume ratio of the catalyst layer of the first partition is less than 12%, the exhaust gas has difficulty passing through the catalyst layer of the first partition, and thus the exhaust gas purification performance may be impaired. The pore volume ratio of the catalyst layer of the first partition is preferably 13% or more and less than 17%.

[0079] As a method for setting the amount of the carrier coating layer of the catalyst layer of the first partition to the above range and controlling the pore volume ratio of the catalyst of the first partition to the above range, for example, a method of controlling the particle size of the constituent materials of the slurry used to form the first catalyst layer 13 and the second catalyst layer 14, respectively, can be cited. As the particle size of the slurry constituent material used to form the first catalyst layer 13, when the volume-converted particle size distribution is observed at regular intervals using a particle size distribution meter using a light scattering method, the cumulative distribution obtained by sieving for the spherical equivalent diameter is as follows: the particle size (D50) that reaches 50% cumulatively is preferably greater than 10μm and less than 20μm, more preferably greater than 11μm and less than 15μm. In addition, the particle size (D90) that reaches 90% cumulatively is preferably greater than 20μm and less than 45μm, more preferably greater than 20μm and less than 40μm. In addition, as the particle size of the slurry constituent material used to form the second catalyst layer 14, the D50 particle size is preferably greater than 10μm and less than 25μm, more preferably greater than 11μm and less than 20μm. Furthermore, the D90 particle size is preferably greater than 20 μm and less than 50 μm, and more preferably greater than 21 μm and less than 45 μm.

[0080] The second catalyst layer 14 covering the first catalyst layer 13 preferably has through holes with a width of 10 μm or more that can allow air to flow from the surface to the first catalyst layer. By having such interconnected pores, high-temperature exhaust gas can easily pass through the second catalyst layer and contact the first catalyst layer, thereby further improving the exhaust gas purification performance during preheating and high-speed operation.

[0081] From the viewpoint of improving the exhaust gas purification performance during preheating and high-speed operation, it is preferred that: the closer to the surface layer (that is, the closer to the side in contact with the second catalyst layer), the higher the concentration of palladium in the first catalyst layer. In particular, in the first catalyst layer, when the layer is divided into two equal parts along the thickness direction, the mass of palladium existing on the surface side of the first catalyst layer is denoted as a1, and the mass of palladium existing on the opposite side relative to the surface side of the first catalyst layer is denoted as a2, the value of a1 / a2 (hereinafter also referred to as concentration gradient) is more preferably 1.2 or more. In the first catalyst layer, by configuring more palladium on the surface side compared to the substrate side, the catalytic function achieved by the specific elements of the catalyst layer can be efficiently exerted at a high spatial velocity. As a result, compared with the case where the concentration of palladium is uniform in the layer thickness direction, CO oxidation and HC oxidation, which are exothermic reactions, are further promoted, and the temperature rise property of the catalyst can be improved. In addition, by improving the temperature rise property of the catalyst, NO in the second catalyst layer x The reducing property is also improved. From the viewpoint of enhancing the exhaust gas purification effect during warm-up and high-speed operation, especially the effect during high-speed operation, the concentration gradient is more preferably 1.3 or more and 3.0 or less.

[0082] Specifically, the concentration gradient of palladium in the first catalyst layer can be obtained by the following method. That is, in the swing curve of palladium obtained by digitizing the distribution of palladium by line analysis of energy dispersive X-ray analysis (EDX) (unit: cps), the ratio of the integral value of the count value closer to the surface side than the half position in the thickness direction in the first catalyst layer to the integral value of the count value closer to the substrate side than the half position is obtained, and the ratio is converted into a mass ratio as the concentration gradient of palladium in the thickness direction.

[0083] <Catalyst Layer of Second Section>

[0084] The third catalyst layer 15 constituting the catalyst layer of the second partition V2 contains palladium (Pd) as a catalytically active component, and may also contain other catalytically active components such as platinum (Pt) and rhodium (Rh). In particular, from the viewpoint of high purification performance of carbon monoxide (CO) and hydrocarbons (HC) and the ability to obtain a warming function, it is preferred to contain Pd and Pt as catalytically active components. As a preferred embodiment, it is set to be the same catalytically active component as the above-mentioned first catalyst layer.

[0085] From the viewpoint of efficiently exerting the exhaust gas purification performance by the catalytically active component, the third catalyst layer 15 preferably further includes a support component that supports the catalytically active component. As the support component, the same component as that of the first catalyst layer 13 of the first section V1 can be used.

[0086] In addition, in order to form the third catalyst layer 15 on the substrate 11, a slurry is prepared in the same manner as the first catalyst layer 13, and the slurry is applied to the substrate surface by a carrier coating method, followed by drying and calcining. In particular, from the viewpoint of improving the exhaust gas purification performance during high-speed operation, the amount of the carrier coating of the third catalyst layer 15 is preferably greater than the amount of the carrier coating of the first catalyst layer 13.

[0087] In addition, the fourth catalyst layer 16 covering the third catalyst layer 15 preferably contains rhodium (Rh) as a catalytically active component. As with the catalyst layer of the first partition, when the third catalyst layer 15 containing Pd as a catalytically active component is exposed, the exhaust gas first contacts the third catalyst layer 15. Therefore, if phosphorus is contained in the exhaust gas, the catalytic activity of Pd decreases. In order to reduce phosphorus poisoning of Pd, it is preferred that the third catalyst layer 15 is covered with the fourth catalyst layer 16.

[0088] As a preferred embodiment, the fourth catalyst layer 16 of the second section V2 is formed of the same catalytically active component as that of the second catalyst layer.

[0089] In order to efficiently exert the exhaust gas purification performance of the catalytically active component, the fourth catalyst layer 16 preferably further includes a support component that supports the catalytically active component. As the support component, the same component as that of the second catalyst layer 14 of the first section V1 can be used.

[0090] In addition, the fourth catalyst layer 16 can be formed by applying the slurry to the surface of the third catalyst layer 15 by a carrier coating method, followed by drying and calcining, in the same manner as the second catalyst layer 14 of the first partition V1. The fourth catalyst layer 16 of a desired thickness can be formed by adjusting the amount of carrier coating, and in a preferred embodiment, the same amount of carrier coating as that of the second catalyst layer 14 is used.

[0091] The amount of the carrier coating of the catalyst layer of the second partition V2 composed of the third catalyst layer 15 and the fourth catalyst layer 16 is preferably 180 g / L or more and 300 g / L or less per 1 L of the substrate 112 present in the first partition V2. By increasing the amount of the carrier coating of the catalyst layer (i.e., increasing the thickness) more than that of the first partition, the exhaust gas purification effect during high-speed operation can be further improved. A more preferred amount of the carrier coating is 190 g / L or more and 210 g / L or less.

[0092] The mass per unit volume of the catalyst layer of the second section V2 relative to the volume of the substrate present in the second section V2 (hereinafter referred to as the washcoat amount) can be determined in the same manner as the above-mentioned method for determining the washcoat amount of the catalyst layer of the first section V1. That is, first, a portion of the exhaust gas-purifying catalyst 10 along the exhaust gas flow direction ( Figure 2 A sample extending in the X direction (in the X direction) and having the same length as the length L2 of the substrate 112. The sample is, for example, a cylindrical shape with a diameter of 25.4 mm. Next, the cut sample is cut with a plane perpendicular to the exhaust gas flow direction of the substrate 11 to prepare a slice S2 of the exhaust gas purifying catalyst 10 containing the second partition V2. The slice S1 is, for example, a cylindrical shape with a diameter of 25.4 mm and a length of 10 mm. It should be noted that the diameter value of the slice S2 can be changed as needed. From the viewpoint of suppressing the deviation in the amount of carrier coating caused by the cutting position of the sample, the exhaust gas purifying catalyst 10 can be directly cut with a plane perpendicular to the exhaust gas flow direction so that it has the same diameter as the exhaust gas purifying catalyst 10. In addition, the length value of the slice S2 can be changed as needed. The length of the catalyst layer of the second partition V2 contained in the slice S2 is equal to the length of the slice S2.

[0093] The carrier coating amount of the catalyst layer of the second subarea V2 (and the carrier coating amounts of the third catalyst layer 15 and the fourth catalyst layer 16) can be determined from the slice S2 thus produced in the same manner as the method for determining the carrier coating amount of the catalyst layer of the first subarea V1. In addition, when calculating the carrier coating amount of the catalyst layer of the second subarea V2, the mass of the catalyst layer of the second subarea V2 per unit volume of the slice S2 can be calculated without using the slice of the substrate 11. The calculation method is the same as the method for calculating the carrier coating amount of the catalyst layer of the first subarea V1.

[0094] From the viewpoint of further improving the exhaust gas purification performance during warm-up and high-speed operation, the washcoat amount of the catalyst layer in the first section V1 is preferably 90% or less, more preferably 80% or less of the washcoat amount of the catalyst layer in the second section V2.

[0095] In addition, the pore volume ratio of the substrate and the catalyst layer relative to the volume of the second partition V2 is preferably greater than 18% and less than 25%. By making the catalyst layer thicker than the first partition V1, the exhaust gas purification effect during high-speed operation can be improved. In particular, by arranging each catalyst layer in such a manner that the pore volume ratio of the substrate and the catalyst layer relative to the volume of the first partition is less than 90% of the pore volume ratio of the substrate and the catalyst layer relative to the volume of the second partition, the exhaust gas purification effect during high-speed operation can be further improved. It should be noted that the pore volume ratio of the substrate and the catalyst layer relative to the volume of the second partition V2 can be measured in the same manner as the pore volume ratio of the substrate and the catalyst layer relative to the volume of the second partition V1.

[0096] There is no particular limitation on the length ratio of the exhaust gas flow direction X between the first partition V1 and the second partition V2. From the perspective of further improving the exhaust gas purification performance during startup and high-speed operation and the ease of manufacturing, the length of the exhaust gas flow direction X of the first partition V1 relative to the length of the exhaust gas flow direction of the substrate 11 is preferably greater than 20% and less than 70%.

[0097] Compared with conventional exhaust gas purification catalysts, the exhaust gas purification catalyst of the present invention can be made into an exhaust gas purification catalyst having excellent exhaust gas purification performance during preheating and high-speed operation without reducing the catalytic activity of Pd, although the amount of catalytically active components is limited. Therefore, the exhaust gas purification catalyst of the present invention can be used as an exhaust gas purification catalyst for internal combustion engines such as gasoline engines and diesel engines that use fossil fuels as power sources, and can efficiently remove NO x , HC, and CO. Therefore, it is possible to provide an exhaust gas purification system that guides exhaust gas from an internal combustion engine to an exhaust gas purification catalyst in an exhaust passage connected to the internal combustion engine without passing through other exhaust gas purification catalysts.

[0098] Example

[0099] Next, the embodiments of the present invention will be described in detail with reference to the following examples, but the present invention is not limited to these examples.

[0100] <Example 1>

[0101] (1) Preparation of base slurry for forming lower catalyst layer (first catalyst layer 13 and third catalyst layer 15)

[0102] An OSC material having the following composition and specific surface area was prepared.

[0103] CeO 2 : 30 mass%, ZrO 2 : 58 mass%, La 2 O 3 : 8 mass%, Nd 2 O 3 : 4 mass%, specific surface area: 50m 2 / g

[0104] It should be noted that in OSC materials, CeO 2 ,La 2 O 3 、Nd 2 O 3 and ZrO 2 A solid solution is formed.

[0105] In a ball mill, OSC materials, lanthanum oxide modified alumina (La2 O 3 Modification amount: 3 mass%, specific surface area: 100m 2 / g), water is added to barium acetate and alumina sol, mixed and crushed by a ball mill to obtain a base slurry for the lower catalyst layer. When the ball mill is running, the particle size distribution converted by volume is observed at regular intervals using a particle size distribution meter using a light scattering method. The mixing / crushing based on the ball mill is carried out to the following extent: with respect to the ball equivalent diameter of the slurry constituent materials, the cumulative distribution obtained by sieving falls into the range where the cumulative particle size reaching 50% is 12μm or less and the cumulative particle size reaching 90% is 20μm or more and 35μm or less. The amount ratio of each component in the slurry is set to the following amount: OSC material reaches 50% by mass, lanthanum oxide modified alumina reaches 30% by mass, barium carbonate reaches 10% by mass, and alumina reaches 10% by mass.

[0106] (2) Formation of the first catalyst layer 13 before surface enrichment treatment

[0107] The base slurry was prepared from a cordierite honeycomb porous substrate 11 (manufactured by Nippon Insulator Co., Ltd., with an axial length of 100 mm, an outer diameter of 93 mm, and a cell number of 600 cells / inch). 2 ) was dip-coated to the middle position of the substrate 11 in the same direction. Thereafter, the substrate 11 was dried at 150°C for 2.5 hours and then calcined at 450°C for 2.5 hours to form the first catalyst layer 13 of the first partition V1. The mass per unit volume (carrier coating amount) of the first catalyst layer 13 relative to the volume of the substrate 111 present in the first partition V1 was 95 g / L.

[0108] (3) Formation of the Third Catalytic Layer 15

[0109] The above-mentioned base slurry is mixed with an aqueous palladium nitrate solution to obtain a slurry for the third catalyst layer 15. The amount of palladium nitrate in the slurry for the third catalyst layer 15 is set to an amount in which Pd occupies 0.667% by mass in the third catalyst layer 15 after calcination. The portion of the substrate 11 from the downstream end in the exhaust gas flow direction X to the middle position in the same direction of the substrate 11 is dip-coated with the slurry for the third catalyst layer 15. Thereafter, the substrate 11 is dried at 150°C for 2.5 hours and then calcined at 450°C for 2.5 hours to form the third catalyst layer 15 of the second partition V2. The mass per unit volume of the third catalyst layer 15 relative to the volume of the substrate 112 present in the second partition V2 (the amount of carrier coating) is 150 g / L. The Pd content in the third catalyst layer 15 is 1.00 g / L relative to the volume of the third catalyst layer 15.

[0110] The first catalyst layer 13 and the third catalyst layer 15 are continuous without gaps on the substrate 11 in the exhaust gas flow direction X. The length ratio of the first catalyst layer 13 and the third catalyst layer 15 in the exhaust gas flow direction X is 1:1, and the length of the lower catalyst layer composed of the first catalyst layer 13 and the third catalyst layer 15 in the exhaust gas flow direction X is the same as the length of the substrate 11 in the exhaust gas flow direction X.

[0111] (4) Pd surface enrichment loading

[0112] Only the portion of the substrate 11 where the first catalyst layer 13 was formed (i.e., the portion of the substrate 111) was immersed in a palladium nitrate aqueous solution (Pd conversion concentration: 5.00 g / L, liquid volume: 340 ml) at 25° C. for 48 hours. After the immersion, the water was controlled, and the substrate 11 was dried at 150° C. for 2.5 hours and calcined at 450° C. for 2.5 hours. The amount of Pd in ​​the first catalyst layer 13 was 5.00 g / L relative to the volume of the first catalyst layer 13.

[0113] (5) Formation of upper catalyst layer (second catalyst layer 14 and fourth catalyst layer 16)

[0114] An OSC material having the following composition and specific surface area was prepared.

[0115] CeO 2 : 15 mass%, ZrO 2 : 73 mass%, La 2 O 3 : 8 mass%, Nd 2 O 3 : 4 mass%, BET specific surface area: 50m 2 / g

[0116] It should be noted that in OSC materials, CeO 2 、ZrO 2 ,La 2 O 3 and Nd 2 O 3 A solid solution is formed.

[0117] In the ball mill pot, add ZrO 2 System materials, lanthanum modified alumina (La 2 O 3 Modification amount: 3 mass%, BET specific surface area: 100 m 2 / g), alumina sol, and water, are mixed and crushed in a ball mill to obtain a basic slurry for the upper catalyst layer. When the ball mill is running, the particle size distribution converted by volume is observed at regular intervals using a particle size distribution meter using a light scattering method. The ball mill is run to the following extent: With respect to the ball equivalent diameter of the slurry constituent materials, the cumulative distribution obtained by screening falls into the range where 50% of the particle sizes are 15μm or less and 90% of the particle sizes are 25μm or more and 40μm or less. The slurry is mixed with an aqueous solution of rhodium nitrate to obtain a slurry for the upper catalyst layer. The quantitative ratio of each component in the slurry for the upper catalyst layer is set to the following amounts: After calcination, the ratio of the components other than rhodium in the upper catalyst layer is ZrO 2 The amount of the system material is 60 mass %, the amount of lanthanum-modified alumina is 30 mass %, the amount of alumina is 10 mass %, and the amount of rhodium in the upper catalyst layer is 0.5 mass %.

[0118] The substrate 11 formed with the lower catalyst layer (the first catalyst layer 13 and the third catalyst layer 15) is immersed in the obtained slurry for the upper catalyst layer. Thereafter, the substrate 11 is dried at 150°C for 2.5 hours and then calcined at 450°C for 2.5 hours to form the upper catalyst layer on the entire surface of the lower catalyst layer, thereby obtaining the exhaust gas purification catalyst of Example 1.

[0119] The mass per unit volume of the upper catalyst layer (the amount of washcoat layer) relative to the volume of the substrate 11 (111 and 112) present in the first and second subareas V1 and V2 was 45 g / L. The rhodium content in the upper catalyst layer relative to the volume of the substrate 11 was 0.225 g / L.

[0120] (6) Determination of pore volume ratio

[0121] A cubic catalyst sheet sample of approximately 10 mm square is cut out from the central part of the axial direction (exhaust gas flow direction) of the first partition (first catalyst layer 13 and second catalyst layer 14) and the second partition (third catalyst layer 15 and fourth catalyst layer 16) and the portion after removing 5 mm from the outer periphery of the side surface. For the cut catalyst sheet, the dimensions of each side are measured, and the volume V (mL) of the cubic catalyst sheet is calculated. In addition, attention is paid to the absorption of moisture, etc., and the weight W (g) of the catalyst sheet is measured in a fully dried state. For the above-mentioned catalyst sheet, the pore distribution is measured using the mercury injection method (atmospheric pressure ~ 255Mpa).

[0122] In the pore distribution measurement results, the volume of mercury pressed in at an applied pressure of 0.049 to 255 MPa (corresponding to a pore diameter of 0.06 μm or more and 30.0 μm or less: Hg contact angle of 140°) was taken as the pore volume P (mL / g), and the pore volume ratio was calculated by the following formula.

[0123] Pore ​​volume ratio (%) = W × P / V × 100

[0124] (7) Determination of Pd concentration gradient

[0125] For the exhaust gas purification catalyst, the above-mentioned concentration inclination a1 / a2 was measured. Specifically, the central part of the axial direction (exhaust gas flow direction) of the first partition (the first catalyst layer 13 and the second catalyst layer 14) and the part after removing 5 mm from the outer periphery (skin) of the side surface were used as the observation surface, and the concentration change of Pd was measured from the surface of the upper catalyst layer toward the substrate 11 using EDX (manufactured by JEOL Ltd., model: XM-8101). Based on the measurement results, when the first catalyst layer 13 is divided into two equal parts along the thickness direction into the surface side and the substrate 11 side, the ratio (a1 / a2) of the concentration a1 of Pd on the surface side to the concentration a2 of Pd on the opposite side (substrate 11 side) was obtained.

[0126] <Example 2>

[0127] In the formation of the third catalyst layer 15 (3), the Pd content in the third catalyst layer 15 is changed to 2.00 g / L. In the Pd surface enrichment loading (4), the Pd concentration of the palladium nitrate aqueous solution is adjusted, and the Pd amount in the first catalyst layer 13 is changed to 4.00 g / L. Other than this, the same operations are performed as in Example 1 to prepare the exhaust gas purification catalyst of Example 2.

[0128] <Example 3>

[0129] The length of the first partition V1 is changed to 25 mm, and the length of the second partition V2 is changed to 75 mm. The Pd concentration of the palladium nitrate aqueous solution is adjusted by utilizing the Pd surface enrichment load of (4), and the Pd amount in the first partition V1 is changed to 9.00 g / L. Other than that, the same operations are performed as in Example 1 to prepare the exhaust gas purification catalyst of Example 3.

[0130] <Example 4>

[0131] The exhaust gas purification catalyst of Example 4 was prepared in the same manner as in Example 1 except that the amount of the carrier coating layer of the upper catalyst layer was changed to 60 g / L. It should be noted that the mixing ratio of the base slurry and rhodium nitrate was adjusted so that the Rh content of the upper catalyst layer reached 0.225 g / L to form the upper catalyst layer.

[0132] <Comparative Example 1>

[0133] The exhaust gas purification catalyst of Comparative Example 1 was prepared in the same manner as in Example 1 except that the carrier coating amount of the upper catalyst layer was changed to 70 g / L. The upper catalyst layer was formed by adjusting the mixing ratio of the base slurry and rhodium nitrate so that the Rh content of the upper catalyst layer reached 0.225 g / L.

[0134] <Comparative Examples 2 to 4>

[0135] Exhaust gas purifying catalysts of Comparative Examples 2 to 4 were prepared in the same manner as in Example 1 except that the coating amounts of the first segment, the second segment and the upper catalyst layer were changed as shown in Table 1.

[0136] <Comparative Example 5>

[0137] In (1) the preparation of the base slurry for forming the lower catalyst layer, the ball mill is operated for a longer time than in Example 1 until the cumulative distribution of the ball equivalent diameters of the slurry constituent materials obtained by screening falls within the range in which 50% of the particle sizes (D50) are less than 10 μm and 90% of the particle sizes (D90) are less than 20 μm.

[0138] In addition, in the formation of the (5) upper catalyst layer, the ball mill is also operated for a longer time than in Example 1, until the cumulative distribution obtained by screening the ball equivalent diameter of the slurry constituent material falls within the range of D50 particle size below 10 μm and D90 particle size below 20 μm.

[0139] Furthermore, the exhaust gas purifying catalyst of Comparative Example 5 was prepared in the same manner as in Example 1 except that the washcoat amounts of the first catalyst layer 13 and the upper catalyst layers (the second catalyst layer 14 and the fourth catalyst layer 16) in the first section V1 were changed as shown in Table 1.

[0140] [Table 1]

[0141]

[0142] <Evaluation of exhaust gas purification performance>

[0143] The exhaust gas purifying catalyst was subjected to the following durability conditions as a degradation treatment assuming 50,000 to 100,000 km of driving. Specifically, the exhaust gas purifying catalyst was brought into contact with exhaust gas discharged from an engine operated under the following conditions, and the catalyst temperature was maintained at the following temperature for the following time.

[0144] (Durability conditions)

[0145] Durable engine: Passenger NA 2L gasoline engine

[0146] Gasoline used: Commercially available regular gasoline

[0147] Durable temperature / time: 900℃-100 hours

[0148] Change in air-fuel ratio before the catalyst: A / F = 13.5 (10 seconds) → 15.5 (20 seconds) → 13.5 (10 seconds) repeatedly

[0149] After the durability test was carried out under the above conditions, the exhaust gas purification catalyst after durability was set in the following vehicle. As a vehicle test, the vehicle was operated according to the operating conditions of the New European Driving Cycle (NEDC). The emissions of non-methane hydrocarbons (NMHC) and nitrogen oxides (NOx) in the exhaust gas of the urban driving mode (ECE) from 780 seconds from the start of operation to 1180 seconds from the start of operation were measured (emission value: g / test). For the emission values ​​of the obtained urban driving mode (ECE) and the emission values ​​of the high-speed driving mode (EUDC), the values ​​when the values ​​of Example 1 that will serve as the benchmark are set to 1 are shown in Table 2. In addition, for NMHC and NOx, the total amount of emissions in ECE and EUDC, that is, the NEDC emissions (Total emissions) are also shown in Table 2.

[0150] (Purification rate measurement conditions)

[0151] ·Evaluation vehicle: Small passenger car

[0152] Use gasoline: fuel for certification test

[0153] [Table 2]

[0154]

[0155] The evaluation results shown in Table 2 also clearly show that the Total NMHC emissions of the exhaust gas purifying catalysts of Examples 1 to 3 are also reduced compared to the exhaust gas purifying catalysts of Comparative Examples 1 to 5, thereby confirming that the exhaust gas purifying catalysts constructed using the present invention can exhibit high exhaust gas purification performance without impairing the Pd catalytic activity.

[0156] Industrial Applicability

[0157] 10 Catalysts for exhaust gas purification

[0158] 11. Substrate

[0159] 111 Substrate present in the first partition

[0160] 112 Base materials present in the second partition

[0161] 12 Catalyst layer

[0162] 13. First catalyst layer

[0163] 14. Second catalyst layer

[0164] 15 Third catalyst layer

[0165] 16 Fourth catalyst layer

[0166] 20 Shell

[0167] V1 First Partition

[0168] V2 Second Partition

Claims

1. A catalyst for purifying exhaust gas, comprising a substrate and a catalyst layer provided on the substrate, The exhaust gas purifying catalyst has a first partition located on the upstream side and a second partition located on the downstream side of the first partition along the flow direction of the exhaust gas. The catalyst layer of the first partition comprises a first catalyst layer containing palladium and a second catalyst layer containing rhodium covering the first catalyst layer. The ratio of the total volume of pores in the substrate and the catalyst layer of the first partition and having a pore diameter of 0.06 μm or more and 30.0 μm or less measured by mercury intrusion porosimetry to the volume of the entire first partition, i.e., the pore volume ratio, is 12% or more and less than 18%, The mass per unit volume of the catalyst layer in the first partition relative to the volume of the substrate present in the first partition, that is, the amount of the washcoat layer, is 100 g / L or more and 190 g / L or less, The mass per unit volume of the catalyst layer in the second section relative to the volume of the substrate present in the second section, that is, the amount of the washcoat layer, is 180 g / L or more and 300 g / L or less, The amount of the carrier coating of the catalyst layer in the first partition is less than 90% of the amount of the carrier coating of the catalyst layer in the second partition, The catalyst layer of the second partition includes a third catalyst layer containing palladium and a fourth catalyst layer containing rhodium covering the third catalyst layer. When the first catalyst layer and the third catalyst layer are used as the lower catalyst layer and the second catalyst layer and the fourth catalyst layer are used as the upper catalyst layer, the upper catalyst layer is formed on the entire surface of the lower catalyst layer.

2. The exhaust gas purification catalyst according to claim 1, in, In the first catalyst layer, when the first catalyst layer is divided into two equal parts along the thickness direction, and the mass of palladium on the surface side of the first catalyst layer is set to a1, and the mass of palladium on the opposite side relative to the surface side of the first catalyst layer is set to a2, the value of a1 / a2 is greater than 1.

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3. The exhaust gas purification catalyst according to claim 1 or 2, in, The ratio of the total volume of pores having a pore diameter of 0.06 μm to 30.0 μm as measured by mercury porosimetry and present in the substrate and catalyst layer of the second partition to the volume of the entire second partition, i.e., the pore volume ratio, is 18% to 25%.

4. The exhaust gas purification catalyst according to claim 1 or 2, in, The pore volume ratio of the substrate and the catalyst layer in the first partition is 90% or less of the pore volume ratio of the substrate and the catalyst layer in the second partition.

5. The exhaust gas purification catalyst according to claim 1 or 2, in, The second catalyst layer has through holes having a width of 10 μm or more that allow air to pass from the surface to the first catalyst layer.

6. The exhaust gas purification catalyst according to claim 1 or 2, in, The length of the first partition in the exhaust gas flow direction is 20% or more and 70% or less of the length of the substrate in the exhaust gas flow direction.

7. An exhaust gas purification system, in, In an exhaust passage connected to an internal combustion engine, exhaust gas from the internal combustion engine is introduced into the exhaust gas purifying catalyst according to claim 1 or 2 without passing through other exhaust gas purifying catalysts.

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