Catalysts for exhaust gas purification

Abstract

The object of the present invention is to provide a method for purifying exhaust gas (especially NO x To achieve the purpose, the present invention provides a catalyst for purifying exhaust gas (10A), which comprises a substrate (20) and a catalyst layer (30 or 40) arranged on the substrate (20), wherein the catalyst layer (30 or 40) contains rhodium, phosphorus and a rare earth element other than cerium, the mass ratio of the phosphorus element contained in the catalyst layer (30 or 40) to the mass ratio of the rhodium element contained in the catalyst layer (30 or 40) is greater than 1 and less than 10, and the mass ratio of the oxide-converted mass of the rare earth element other than cerium contained in the catalyst layer (30 or 40) to the mass ratio of the rhodium element contained in the catalyst layer (30 or 40) is greater than 1 and less than 5.

Description

Technical Field

[0001] The present invention relates to a catalyst for purifying exhaust gas. Background Art

[0002] The exhaust gas emitted from internal combustion engines of cars and motorcycles contains hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO x ) and other harmful components. In order to purify these harmful components and make them harmless, a three-way catalyst is used. As a three-way catalyst, precious metal catalysts such as platinum (Pt), palladium (Pd), and rhodium (Rh) are used. Pt and Pd are mainly involved in the oxidation purification of HC and CO, and Rh is mainly involved in the oxidation purification of NO x Reduction purification.

[0003] The air / fuel ratio (air-fuel ratio A / F) supplied to the internal combustion engine is expected to be controlled near the theoretical air-fuel ratio (ideal ratio). However, since the actual air-fuel ratio fluctuates toward the rich (fuel-rich atmosphere) side or the lean (fuel-lean atmosphere) side around the ideal ratio due to the driving conditions of the vehicle, etc., the air-fuel ratio of the exhaust gas will also fluctuate toward the rich side or the lean side in the same way. Therefore, in order to mitigate the fluctuation of the oxygen concentration in the exhaust gas and improve the exhaust gas purification ability of the catalyst, a material (hereinafter sometimes referred to as "OSC material") that has the ability to store oxygen when the oxygen concentration in the exhaust gas is high and release oxygen when the oxygen concentration in the exhaust gas is low (i.e., oxygen storage capacity (OSC)) is used, for example, a CeO2-ZrO2 composite oxide.

[0004] It is known that exhaust gas contains not only HC, CO, NO x It contains harmful components such as particulate matter (PM), which is the cause of air pollution. For example, the direct injection engine (GDI: Gasoline Direct Injection engine) used in vehicles equipped with gasoline engines is known to have low fuel consumption and high output, but the amount of PM discharged in the exhaust gas is larger than that of the previous intake port injection engine. In order to comply with environmental regulations related to PM, vehicles equipped with gasoline engines such as GDI are also required to be equipped with filters with PM trapping function (GPF: Gasoline Particulate Filter) like vehicles equipped with diesel engines.

[0005] As the GPF, for example, a substrate having a so-called wall-flow type structure is used. In the wall-flow type substrate, when the exhaust gas flowing in from the chamber inlet flows out from the chamber outlet through the porous partition wall portion that partitions the chamber, PM in the exhaust gas is captured in the pores inside the partition wall portion.

[0006] Generally speaking, the configuration space of exhaust gas purification catalysts is limited. Therefore, research has been conducted to load precious metal catalysts such as Pt, Pd, and Rh on GPF to simultaneously capture PM and remove HC, CO, and NO. x Purification of harmful components.

[0007] For example, Patent Document 1 describes an exhaust gas purifying catalyst in which a palladium-containing layer and a rhodium-containing layer are stacked such that one of the palladium-containing layer and the rhodium-containing layer is located inside a partition and the other is located on the surface of the partition.

[0008] In addition, Patent Document 2 describes a catalyst for exhaust gas purification, which comprises a substrate with a wall flow structure, an upstream catalyst layer arranged inside a partition wall portion, and a downstream catalyst layer arranged inside the partition wall portion, wherein the substrate has an inlet chamber with an opening only at the end on the exhaust gas inlet side, an outlet chamber adjacent to the inlet chamber and with an opening only at the end on the exhaust gas outflow side, and a porous partition wall separating the inlet chamber and the outlet chamber; the upstream catalyst layer and the downstream catalyst layer respectively contain a carrier and at least one precious metal of platinum (Pt), palladium (Pd) and rhodium (Rh) loaded on the carrier, and the precious metal contained in the upstream catalyst layer is different from the precious metal contained in the downstream catalyst layer.

[0009] Prior art literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Publication No. 2009-82915

[0012] Patent Document 2: Japanese Patent Application Publication No. 2016-78016 Summary of the invention

[0013] Problem that the invention aims to solve

[0014] However, the exhaust gas purification performance (especially NO x Purification performance) is not sufficient.

[0015] Therefore, the object of the present invention is to provide an exhaust gas purification performance (especially NO x A catalyst for purifying exhaust gas having improved purification performance.

[0016] Solutions for solving problems

[0017] In order to solve the above-mentioned technical problems, the present invention provides a catalyst for exhaust gas purification, which comprises a substrate and a catalyst layer arranged on the substrate, the catalyst layer contains rhodium, phosphorus and rare earth elements other than cerium, the ratio of the mass of the phosphorus element contained in the catalyst layer to the mass of the rhodium element contained in the catalyst layer is greater than 1.0 and less than 10, and the ratio of the mass of the oxide-converted rare earth element other than cerium contained in the catalyst layer to the mass of the rhodium element contained in the catalyst layer is greater than 1.0 and less than 5.0.

[0018] Effects of the Invention

[0019] According to the present invention, exhaust gas purification performance (especially NO x A catalyst for purifying exhaust gas having improved purification performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] Figure 1 It is a partial cross-sectional view showing a state where the exhaust gas purifying catalyst according to the first embodiment of the present invention is arranged in an exhaust passage of an internal combustion engine.

[0021] Figure 2 for Figure 1 AA line section view.

[0022] Figure 3 It is a partial cross-sectional view showing a state where an exhaust gas purifying catalyst according to a second embodiment of the present invention is arranged in an exhaust passage of an internal combustion engine.

[0023] Figure 4 for Figure 3 BB line cross-sectional view. DETAILED DESCRIPTION

[0024] Hereinafter, the exhaust gas-purifying catalyst of the present invention will be described.

[0025] The exhaust gas-purifying catalyst of the present invention comprises a substrate and the catalyst layer of the present invention provided on the substrate.

[0026] The substrate can be appropriately selected from substrates generally used as substrates for exhaust gas purifying catalysts. Examples of the substrate include wall flow type substrates and flow-through type substrates.

[0027] The material constituting the substrate can be appropriately selected from materials commonly used as the substrate material of the exhaust gas purification catalyst. The material constituting the substrate is preferably a material that can stably maintain the shape of the substrate even when the substrate is exposed to high temperature (for example, above 400°C) exhaust gas. Examples of the material of the substrate include ceramics such as cordierite, silicon carbide (SiC), and aluminum titanate; alloys such as stainless steel, etc.

[0028] The amount of the catalyst layer of the present invention provided on the substrate can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost, etc.

[0029] The catalyst layer of the present invention contains rhodium (Rh) element, phosphorus (P) element and rare earth element other than cerium (Ce) element, the mass ratio of phosphorus element contained in the catalyst layer of the present invention to the mass ratio of rhodium element contained in the catalyst layer of the present invention is 1.0 or more and 10 or less, and the mass ratio of oxide-converted rare earth element other than cerium element contained in the catalyst layer of the present invention to the mass ratio of rhodium element contained in the catalyst layer of the present invention is 1.0 or more and 5.0 or less. As a result, the exhaust gas purification catalyst of the present invention can exert excellent exhaust gas purification performance (especially NO) at low to medium temperatures. x Purification performance). The exhaust gas purification performance at low to medium temperatures can be evaluated based on the ignition temperature T50. The ignition temperature T50 is the temperature at which the purification rate reaches 50%, and can be measured according to the conditions described in the embodiments of this specification. It should be noted that in this specification, "low to medium temperature" refers to a temperature above 200°C and below 400°C.

[0030] The catalyst layer of the present invention contains rhodium. Rhodium is the main element involved in NO x The rhodium element is contained in the catalyst layer of the present invention in a form that can function as a catalytically active component, such as metal rhodium, a compound containing the rhodium element (e.g., an oxide of the rhodium element), etc. From the perspective of improving the exhaust gas purification performance, the catalytically active component is preferably in a granular form.

[0031] The catalyst layer of the present invention may contain catalytically active components other than rhodium. Catalytically active components other than rhodium may be selected from precious metal elements such as platinum (Pt), palladium (Pd), ruthenium (Ru), iridium (Ir), and osmium (Os). Precious metal elements are contained in the catalyst layer of the present invention in the form of precious metals, compounds containing precious metal elements (e.g., oxides of precious metal elements) that can function as catalytically active components. From the perspective of improving exhaust gas purification performance, the catalytically active component is preferably in a granular form. However, in the case where the catalyst layer of the present invention contains rhodium and precious metal elements other than rhodium, there is an alloy formed by the rhodium and precious metal elements other than rhodium, which participates in NO x In addition, when the catalyst layer of the present invention contains rhodium and precious metal elements other than rhodium, there is a possibility that the phosphorus element contained in the catalyst layer of the present invention causes poisoning of precious metal elements other than rhodium (such as palladium, platinum, etc.). Therefore, the catalyst layer of the present invention preferably does not contain precious metal elements other than rhodium.

[0032] The amount of rhodium contained in the catalyst layer of the present invention can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost. From the perspective of the balance between exhaust gas purification performance and cost, the mass of rhodium contained in the catalyst layer of the present invention is based on the unit volume of the substrate, preferably 0.10 g / L or more and 1.2 g / L or less, more preferably 0.30 g / L or more and 1.1 g / L or less, further preferably 0.40 g / L or more and 1.1 g / L or less, further preferably 0.50 g / L or more and 1.1 g / L or less. It should be noted that in this specification, the volume of the substrate refers to the apparent volume of the substrate. For example, when the substrate is cylindrical with an outer diameter of 2r, the volume of the substrate is expressed by the formula: Volume of substrate = π×r 2 It is represented by × (length of substrate).

[0033] The catalyst layer of the present invention contains phosphorus. Phosphorus is used to improve the exhaust gas purification performance (especially NO x The phosphorus element is contained in the catalyst layer of the present invention in the form of, for example, an oxide. The phosphorus element oxide can form a composite oxide with the oxide of other elements. Examples of the oxide of other elements include CeO2 and / or ZrO2 contained in the oxygen storage component. The oxygen storage component will be described in detail later.

[0034] The amount of phosphorus contained in the catalyst layer of the present invention is not particularly limited as long as the ratio of the mass of phosphorus contained in the catalyst layer of the present invention to the mass of rhodium contained in the catalyst layer of the present invention is 1.0 or more and 10 or less. x From the perspective of purification performance, the ratio of the mass of the phosphorus element contained in the catalyst layer of the present invention to the mass of the rhodium element contained in the catalyst layer of the present invention is preferably greater than 2.0 and less than 8.0, more preferably greater than 2.5 and less than 7.5, further preferably greater than 3.0 and less than 7.0, further preferably greater than 3.0 and less than 6.0, further preferably greater than 3.0 and less than 5.0, further preferably greater than 3.0 and less than 4.5.

[0035] The ratio of the mass of the phosphorus element contained in the catalyst layer of the present invention to the mass of the rhodium element contained in the catalyst layer of the present invention can be calculated by the following method.

[0036] The catalyst for exhaust gas purification of the present invention is cut along a plane perpendicular to the axial direction (exhaust gas flow direction X) of the substrate to prepare a slice C1 that includes the catalyst layer of the present invention but does not include a catalyst layer other than the catalyst layer of the present invention. The slice C1 has a specified size. The slice C1 is, for example, cylindrical with a diameter of 25.4 mm and a length of 30 mm. The length of the catalyst layer of the present invention contained in the slice C1 is equal to the length of the slice C1 (the length of the axial direction (exhaust gas flow direction X) of the slice C1) (that is, the catalyst layer of the present invention extends from one end of the slice C1 to the other end along the axial direction (exhaust gas flow direction X) of the slice C1).

[0037] The mass of rhodium and phosphorus contained in the slice C1 is measured by conventional methods such as inductively coupled plasma atomic emission spectrometry (ICP-AES), and the mass of rhodium and phosphorus per unit volume of the slice C1 is calculated based on the following formula. It should be noted that the volume of the slice C1 refers to the apparent volume of the slice C1. For example, when the slice C1 is cylindrical with an outer diameter of 2r, the volume of the slice C1 is calculated by the formula: Volume of the slice C1 = π × r 2 ×(slice length).

[0038] The mass of rhodium element per unit volume of slice C1 = the mass of rhodium element contained in slice C1 / the volume of slice C1

[0039] The mass of phosphorus per unit volume of the slice C1 = the mass of phosphorus contained in the slice C1 / the volume of the slice C1

[0040] For the five slices C1, the mass of rhodium per unit volume of the slice C1 was calculated, and the average value V was obtained. r .

[0041] For the five slices C1, the mass of phosphorus per unit volume of the slice C1 was calculated, and the average value V was obtained. p .

[0042] Based on the following formula, the ratio of the mass of the phosphorus element contained in the catalyst layer of the present invention to the mass of the rhodium element contained in the catalyst layer of the present invention was calculated.

[0043] The ratio of the mass of the phosphorus element contained in the catalyst layer of the present invention to the mass of the rhodium element contained in the catalyst layer of the present invention = average value V p / Average value V r

[0044] The catalyst layer of the present invention contains rare earth elements other than cerium. The rare earth elements other than cerium are used to improve the exhaust gas purification performance (especially NO xThe rare earth elements other than cerium are contained in the catalyst layer of the present invention in the form of, for example, oxides. The oxides of rare earth elements other than cerium can form composite oxides with oxides of other elements. Examples of oxides of other elements include CeO2 and / or ZrO2 contained in the oxygen storage component. The oxygen storage component will be described in detail later.

[0045] Rare earth elements other than cerium can be selected from, for example, yttrium (Y), praseodymium (Pr), scandium (Sc), lanthanum (La), neodymium (Nd), samarium (Sm), europium (Eu), gadolinium (Gd), terbium (Tb), dysprosium (Dy), holmium (Ho), erbium (Er), thulium (Tm), ytterbium (Yb), and lutetium (Lu), in order to further improve the exhaust gas purification performance at low to medium temperatures (especially NO x From the perspective of purification performance, it is preferably selected from lanthanum, neodymium, yttrium, etc., and more preferably selected from neodymium, yttrium, etc. Except for praseodymium and terbium, the oxide of rare earth elements is sesquioxide (Re2O3, Re is a rare earth element). Praseodymium oxide is usually Pr6O 11 , terbium oxide is usually Tb4O7.

[0046] The catalyst layer of the present invention may contain one rare earth element other than cerium, or may contain two or more rare earth elements other than cerium. When the catalyst layer of the present invention contains two or more rare earth elements other than cerium, "the mass of the oxide-converted rare earth elements other than cerium contained in the catalyst layer of the present invention" refers to the total mass of the oxide-converted rare earth elements other than cerium.

[0047] The amount of the rare earth element other than cerium contained in the catalyst layer of the present invention is not particularly limited as long as the ratio of the mass of the oxide of the rare earth element other than cerium contained in the catalyst layer of the present invention to the mass of the rhodium element contained in the catalyst layer of the present invention is 1.0 or more and 5.0 or less. x From the perspective of purification performance, the ratio of the mass of the oxide of the rare earth element other than cerium contained in the catalyst layer of the present invention to the mass of the rhodium element contained in the catalyst layer of the present invention is preferably greater than 1.5 and less than 4.5, more preferably greater than 2.0 and less than 4.0, and even more preferably greater than 2.5 and less than 3.5.

[0048] The ratio of the mass of the oxide of the rare earth element other than the cerium element contained in the catalyst layer of the present invention to the mass of the rhodium element contained in the catalyst layer of the present invention can be calculated in the same manner as the ratio of the mass of the phosphorus element contained in the catalyst layer of the present invention to the mass of the rhodium element contained in the catalyst layer of the present invention. It should be noted that the mass of the oxide of the rare earth element other than the cerium element can be calculated from the mass of the rare earth element other than the cerium element.

[0049] To further improve the exhaust gas purification performance at low to medium temperatures (especially NO x From the perspective of purification performance, the ratio of the mass of the oxide of the rare earth element other than the cerium element contained in the catalyst layer of the present invention to the mass of the phosphorus element contained in the catalyst layer of the present invention is preferably greater than 0.50 and less than 5.0, more preferably greater than 1.0 and less than 4.5, further preferably greater than 1.0 and less than 4.0, further preferably greater than 1.0 and less than 3.5, further preferably greater than 1.0 and less than 3.0, further preferably greater than 1.0 and less than 2.5.

[0050] To further improve the exhaust gas purification performance at low to medium temperatures (especially NO x From the perspective of purification performance, the catalyst layer of the present invention preferably comprises inorganic oxide particles, and rhodium, phosphorus and rare earth elements other than cerium are supported on the inorganic oxide particles.

[0051] The inorganic oxide particles are preferably porous in order to facilitate the loading of rhodium, phosphorus, and rare earth elements other than cerium. The BET specific surface area of ​​the porous body is, for example, 50 to 150 m 2 / g. It should be noted that the BET specific surface area can be measured by "(3.5) Single Point Method" in "6.2 Flow Method" of JIS R1626:1996 "Specific Surface Area Determination Method of Fine Ceramic Powder Based on Gas Adsorption BET Method". At this time, a nitrogen-helium mixed gas containing 30% by volume of nitrogen as an adsorbed gas and 70% by volume of helium as a carrier gas was used as a gas, and "BELSORP-MR6" manufactured by Microtrac Bell was used as a measuring device.

[0052] The inorganic oxide constituting the inorganic oxide particles may or may not have the ability to store oxygen. In this specification, an inorganic oxide having the ability to store oxygen is sometimes referred to as an oxygen storage component or an OSC material. From the perspective of enabling the exhaust gas purification performance to be stably and efficiently exerted relative to fluctuations in the air-fuel ratio, the catalyst layer of the present invention preferably contains an oxygen storage component, and more preferably contains an oxygen storage component and an inorganic oxide other than the oxygen storage component.

[0053] "Rare earth elements other than rhodium, phosphorus and cerium are loaded on inorganic oxide particles" refers to the state in which rare earth elements other than rhodium, phosphorus and cerium are physically or chemically adsorbed or retained on the outer surface or inner surface of pores of inorganic oxide particles. For example, in the element distribution diagram obtained by analyzing the cross section of the catalyst layer of the present invention by EDS (energy dispersive spectrometer), when the existence area of ​​rhodium, the existence area of ​​phosphorus and the existence area of ​​rare earth elements other than cerium overlap with the existence area of ​​inorganic oxide particles, it can be judged that the rare earth elements other than rhodium, phosphorus and cerium are loaded on inorganic oxide particles. It should be noted that the existence area of ​​rhodium, the existence area of ​​phosphorus and the existence area of ​​rare earth elements other than cerium may overlap or not overlap with each other. That is, the rare earth elements other than rhodium, phosphorus and cerium can be loaded on a certain inorganic oxide particle, and the rare earth elements other than rhodium, phosphorus and cerium do not need to be loaded on the same inorganic oxide particle. Of course, two or more of the rare earth elements other than rhodium, phosphorus and cerium can be loaded on the same inorganic oxide particle.

[0054] The average particle size of another particle (e.g., a catalytically active component) supported on a certain particle (e.g., an inorganic oxide particle) is preferably 10% or less, more preferably 3% or less, and even more preferably 1% or less relative to the average particle size of the certain particle. The average particle size referred to here is the average value of the Feret diameters of more than 30 particles when observed by SEM.

[0055] The oxygen storage component is, for example, a metal oxide whose valence number of constituent elements changes under the working conditions of the exhaust gas purification catalyst. Examples of oxygen storage components include metal oxides containing cerium (Ce) elements. Examples of metal oxides containing cerium elements include composite oxides containing cerium oxide (CeO2), cerium (Ce) elements, and zirconium (Zr) elements (hereinafter referred to as "CeO2-ZrO2 composite oxides"), among which CeO2-ZrO2 composite oxides are preferred. In the CeO2-ZrO2 composite oxides, Ce2O and ZrO2 preferably form a solid solution phase. In the CeO2-ZrO2 composite oxides, Ce2O and ZrO2 can also form separate phases (Ce2O separate phase or ZrO2 separate phase) on the basis of the solid solution phase. The phenomenon that CeO2 and ZrO2 form a solid solution phase can be confirmed by using an X-ray diffraction device (XRD) to confirm the formation of a single phase derived from CeO2-ZrO2.

[0056] The phosphorus element or its oxide contained in the catalyst layer of the present invention can form a composite oxide together with Ce2O and / or ZrO2. The phosphorus element or its oxide contained in the catalyst layer of the present invention can form a solid solution phase together with Ce2O and / or ZrO2, or can form a separate phase.

[0057] The rare earth element or its oxide other than the cerium element contained in the catalyst layer of the present invention can form a composite oxide with Ce2O and / or ZrO2. The rare earth element or its oxide other than the cerium element contained in the catalyst layer of the present invention can form a solid solution phase with Ce2O and / or ZrO2, or can form a single phase. The phenomenon that the rare earth element or its oxide other than the cerium element forms a solid solution phase with Ce2O and / or ZrO2 can be confirmed by an X-ray diffraction device (XRD) in the same manner as described above.

[0058] The catalyst layer of the present invention may contain one or more other metal elements. Other metal elements are contained in the catalyst layer of the present invention in the form of, for example, oxides. Other metal elements or their oxides may form composite oxides with Ce2O and / or ZrO2. Other metal elements or their oxides may form a solid solution phase with Ce2O and / or ZrO2, or may form a single phase. The phenomenon that other metal elements or their oxides form a solid solution phase with Ce2O and / or ZrO2 can be confirmed by an X-ray diffraction device (XRD) in the same manner as described above.

[0059] The other one or more metal elements can be selected from, for example, alkaline earth metal elements and transition metal elements. Examples of alkaline earth metal elements include calcium (Ca), strontium (Sr), barium (Ba), and radium (Ra). Examples of transition metal elements include manganese (Mn), iron (Fe), cobalt (Co), nickel (Ni), and copper (Cu).

[0060] Examples of inorganic oxides other than the oxygen storage component include alumina, silica, silica-alumina, aluminosilicates, alumina-zirconia, alumina-chromia, alumina-ceria, and alumina-lanthanum oxides. Among them, alumina is preferred from the viewpoint of heat resistance.

[0061] Inorganic oxides other than oxygen storage components may be modified with oxygen storage components to load oxygen storage components. For example, the inner surface or outer surface of a pore portion such as alumina may be modified with an oxygen storage component. In addition, the inner surface or outer surface of a pore portion such as alumina may load a dispersed oxygen storage component.

[0062] The catalyst layer of the present invention is composed of a single layer. The catalyst layer of the present invention typically has a surface on the substrate side and a surface on the opposite side of the substrate. Other catalyst layers may be provided on one or both surfaces of the catalyst layer of the present invention. Other catalyst layers are catalyst layers having different compositions from the catalyst layer of the present invention. However, when other catalyst layers are provided on one or both surfaces of the catalyst layer of the present invention, there is a possibility that gas diffusivity decreases at the boundary between the catalyst layer of the present invention and the other catalyst layers. In addition, when a catalyst layer containing a palladium element is provided on one or both surfaces of the catalyst layer of the present invention, there is a possibility that the phosphorus element contained in the catalyst layer of the present invention enters the catalyst layer containing the palladium element, and the palladium element is poisoned by phosphorus. Therefore, it is preferred that no other catalyst layer is provided on any surface of the catalyst layer of the present invention.

[0063] In the exhaust gas purification catalyst of the present invention, a catalyst layer other than the catalyst layer of the present invention can be provided in a portion of the substrate where the catalyst layer of the present invention is not provided. The composition of the catalyst layer other than the catalyst layer of the present invention can be adjusted in the same manner as the composition of the known catalyst layer. The catalyst layer other than the catalyst layer of the present invention is, for example, a catalyst layer containing a palladium element. When a catalyst layer other than the catalyst layer of the present invention, for example, a catalyst layer containing a palladium element is provided in a portion of the substrate where the catalyst layer of the present invention is not provided, the catalyst layer of the present invention and the catalyst layer containing a palladium element are separated by the substrate. Therefore, it is possible to prevent the phosphorus element contained in the catalyst layer of the present invention from entering the catalyst layer containing a palladium element, which may cause the palladium element to be poisoned.

[0064] The exhaust gas purification catalyst of the present invention can be manufactured by coating the slurry for forming the catalyst layer of the present invention on a substrate, drying and calcining. The drying temperature is usually 70°C or more and 200°C or less, preferably 90°C or more and 160°C or less, and the drying time is usually 1 hour or more and 3 hours or less, preferably 1.5 hours or more and 2.5 hours or less. The calcination temperature is usually 450°C or more and 700°C or less, preferably 450°C or more and 650°C or less, and the calcination time is usually 1 hour or more and 4 hours or less, preferably 1.5 hours or more and 2.5 hours or less. Calcination can be carried out, for example, in an atmospheric atmosphere.

[0065] The composition of the slurry used to form the catalyst layer of the present invention is adjusted according to the composition of the catalyst layer of the present invention. The slurry contains, for example, a source of rhodium element, a source of phosphorus element, a source of rare earth element other than cerium element, inorganic oxide particles, a binder, a pore former, a solvent, and the like. As a source of rhodium element, for example, salts of rhodium element can be listed; as salts of rhodium element, for example, nitrates, ammine salts, chlorides, and the like can be listed. As a source of phosphorus element, for example, phosphates can be listed; as phosphates, for example, diammonium hydrogen phosphate, disodium hydrogen phosphate, calcium hydrogen phosphate, and the like can be listed. As a source of rare earth element other than cerium element, for example, salts of rare earth element other than cerium element can be listed; as salts of rare earth element other than cerium element, for example, nitrates, sulfates, chloride salts, and the like can be listed. As inorganic oxides constituting inorganic oxide particles, for example, oxygen storage components, inorganic oxides other than oxygen storage components, and the like can be listed. The description of the oxygen storage component and the inorganic oxide other than the oxygen storage component is the same as above. As the binder, for example, alumina sol, zirconia sol, titania sol, silica sol, etc. can be listed. As the pore-forming agent, for example, cross-linked poly(meth) methyl acrylate particles, cross-linked poly(meth) butyl acrylate particles, cross-linked polystyrene particles, cross-linked polyacrylate particles, etc. can be listed. As the solvent, for example, water, organic solvents, etc. can be listed. As the organic solvent, for example, alcohol, acetone, dimethyl sulfoxide, dimethylformamide, etc. can be listed. The solvent can be one solvent or a mixture of two or more solvents. As a mixture of two or more solvents, for example, a mixture of water and one or more organic solvents, a mixture of two or more organic solvents, etc. can be listed.

[0066] From the perspective of heat resistance, the median particle size D of the inorganic oxide particles is 50 The median diameter D is preferably 1 μm or more and 15 μm or less, and more preferably 3 μm or more and 10 μm or less. 50 The median diameter is the particle size at which the cumulative volume accounts for 50% in the volume-based particle size distribution measured by the laser diffraction scattering particle size distribution measurement method. 50 The measurement can be performed as follows. That is, the inorganic oxide particles are put into an aqueous solvent using an automatic sample feeder for a laser diffraction particle size distribution measuring device (Microtrac Bell "Microtorac SDC"), and irradiated with 40W ultrasonic waves for 360 seconds at a flow rate of 40%. Then, a laser diffraction scattering particle size distribution meter (Microtrac Bell "Microtrac MT3300EXII") is used to measure the median particle size D of the inorganic oxide particles. 50 The measurement conditions were adjusted to particle refractive index 1.5, particle shape true spherical, solvent refractive index 1.3, zeroing for 30 seconds, and measurement time of 30 seconds. The average of the two measurements was taken as the median particle size D50 . Pure water was used as the aqueous solvent.

[0067] A supply source of rhodium element, a supply source of phosphorus element, a supply source of rare earth element other than cerium element, inorganic oxide particles and a solvent can be mixed, dried and pulverized to prepare a powder containing inorganic oxide particles and rhodium element, phosphorus element and rare earth element other than cerium element supported on the inorganic oxide particles. The obtained powder can be mixed with a binder, a pore-forming agent, a solvent, etc. to prepare a slurry for forming the catalyst layer of the present invention.

[0068] The following is based on Figure 1 and Figure 2 , an exhaust gas purifying catalyst 10A according to a first embodiment of the present invention will be described. Figure 1 FIG. 1 is a partial cross-sectional view showing a state in which an exhaust gas purifying catalyst 10A according to a first embodiment of the present invention is arranged in an exhaust passage of an internal combustion engine. Figure 2 for Figure 1 AA line section view.

[0069] like Figure 1 As shown, the exhaust gas purification catalyst 10A involved in the first embodiment of the present invention is arranged in the exhaust passage P of the internal combustion engine, and is used to purify the exhaust gas discharged from the internal combustion engine. The exhaust gas purification catalyst 10A is arranged in the exhaust passage of, for example, a gasoline engine (for example, a GDI engine, etc.), and is used as a gasoline particulate filter (GPF). In the accompanying drawings, the exhaust gas flow direction in the exhaust passage P of the internal combustion engine is represented by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas inflow side", and the downstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas outflow side".

[0070] like Figure 2 As shown, the exhaust gas-purifying catalyst 10A includes a wall-flow type substrate 20 , a first catalyst layer 30 , and a second catalyst layer 40 .

[0071] In the exhaust gas purifying catalyst 10A, one or both of the first catalyst layer 30 and the second catalyst layer 40 are catalyst layers of the present invention. As a result, the exhaust gas purifying catalyst 10A can exhibit excellent exhaust gas purification performance (especially NO x purification performance).

[0072] In the exhaust gas purification catalyst 10A, when one of the first catalyst layer 30 and the second catalyst layer 40 is a catalyst layer other than the catalyst layer of the present invention, the composition of the catalyst layer other than the catalyst layer of the present invention can be adjusted in the same manner as the composition of the known catalyst layer. The catalyst layer other than the catalyst layer of the present invention is, for example, a catalyst layer containing a palladium element. When one of the first catalyst layer 30 and the second catalyst layer 40 is the catalyst layer of the present invention, and the other of the first catalyst layer 30 and the second catalyst layer 40 is a catalyst layer containing a palladium element, the catalyst layer of the present invention and the catalyst layer containing a palladium element are separated by a partition wall 23. Therefore, it is possible to prevent the phosphorus element contained in the catalyst layer of the present invention from entering the catalyst layer containing the palladium element, which may cause the generated palladium element to be poisoned.

[0073] like Figure 1 and Figure 2 As shown, the exhaust gas purifying catalyst 10A is arranged in the exhaust passage P of the internal combustion engine in such a manner that the axial direction of the wall flow type substrate 20 is substantially consistent with the exhaust gas flow direction X. In this specification, unless otherwise specified, "length" refers to the dimension in the axial direction of the wall flow type substrate 20; unless otherwise specified, "thickness" refers to the dimension in the direction perpendicular to the axial direction of the wall flow type substrate 20.

[0074] like Figure 2 As shown, the wall-flow type substrate 20 includes an inlet side chamber 21, an outlet side chamber 22, and a porous partition wall 23 that separates the inlet side chamber 21 and the outlet side chamber 22. In the wall-flow type substrate 20, a plurality of (for example, 4) outlet side chambers 22 are adjacently arranged around an inlet side chamber 21, and the inlet side chamber 21 and the outlet side chamber 22 adjacent to the inlet side chamber 21 are separated by the porous partition wall 23. It should be noted that the wall-flow type substrate 20 includes a cylindrical portion (not shown) that limits the outer shape of the wall-flow type substrate 20, and the partition wall 23 is formed in the cylindrical portion. The shape of the cylindrical portion is, for example, cylindrical, and may be other shapes. As other shapes, for example, an elliptical cylinder, a polygonal cylinder, etc. can be listed. The axial direction of the wall-flow type substrate 20 is consistent with the axial direction of the cylindrical portion.

[0075] like Figure 2 As shown, a recessed portion with an opening on the exhaust gas inlet side and a recessed portion with an opening on the exhaust gas outlet side are formed on the wall flow type substrate 20. An inlet side chamber 21 is formed by the space inside the recessed portion with an opening on the exhaust gas inlet side, and an outlet side chamber 22 is formed by the space inside the recessed portion with an opening on the exhaust gas outlet side.

[0076] like Figure 2 As shown, the inlet side chamber 21 extends along the exhaust gas flow direction X and has an end on the exhaust gas inlet side and an end on the exhaust gas outlet side. Figure 2As shown, the end of the exhaust gas inlet side of the inlet side chamber 21 is open, and the end of the exhaust gas outflow side of the inlet side chamber 21 is closed. Hereinafter, the end of the exhaust gas inlet side of the inlet side chamber 21 may be referred to as "the opening of the inlet side chamber 21".

[0077] like Figure 2 As shown, the wall flow type substrate 20 is provided with a first sealing portion 24 for sealing the end of the inflow side chamber 21 on the exhaust gas outflow side. The end of the inflow side chamber 21 on the exhaust gas outflow side is closed by the first sealing portion 24 .

[0078] The top view shape of the opening of the inflow side chamber 21 (the shape when looking down at the wall flow type substrate 20 from the exhaust gas flow direction X) is, for example, a square, but may be other shapes. Other shapes include rectangular shapes such as parallelograms, rectangles, and trapezoids; polygonal shapes such as triangles, hexagons, and octagons; and various geometric shapes such as circles and ellipses.

[0079] like Figure 2 As shown, the outflow side chamber 22 extends along the exhaust gas flow direction X and has an end on the exhaust gas inflow side and an end on the exhaust gas outflow side. Figure 2 As shown, the exhaust gas inlet end of the outlet chamber 22 is closed, and the exhaust gas outlet end of the outlet chamber 22 is open. Hereinafter, the exhaust gas outlet end of the outlet chamber 22 is sometimes referred to as "the opening of the outlet chamber 22".

[0080] like Figure 2 As shown, the wall flow type substrate 20 is provided with a second sealing portion 25 for sealing the end of the outflow side chamber 22 on the exhaust gas inflow side. The end of the outflow side chamber 22 on the exhaust gas inflow side is closed by the second sealing portion 25 .

[0081] The top view shape of the opening of the outflow side chamber 22 (the shape when the wall flow type substrate 20 is viewed from the direction opposite to the exhaust gas flow direction X) is, for example, a square, but may be other shapes. Other shapes include rectangular shapes such as parallelograms, rectangles, and trapezoids; polygons such as triangles, hexagons, and octagons; and various geometric shapes such as circles and ellipses.

[0082] The area of ​​the opening of the inlet-side chamber 21 in a plan view and the area of ​​the opening of the outlet-side chamber 22 in a plan view may be the same as or different from each other.

[0083] The cell density per square inch of the wall-flow type substrate 20 is, for example, 200 cells or more and 400 cells or less. It should be noted that the cell density per square inch of the wall-flow type substrate 20 is the total number of inflow side chambers 21 and outflow side chambers 22 per square inch in the cross section obtained by cutting the wall-flow type substrate 20 along a plane perpendicular to the exhaust gas flow direction X.

[0084] The partition wall 23 has a porous structure through which exhaust gas can pass. The thickness of the partition wall 23 is, for example, 150 μm or more and 500 μm or less. When the thickness of the partition wall 23 is not constant, the average value of the thicknesses measured at a plurality of locations is taken as the thickness of the partition wall 23 .

[0085] like Figure 2 As shown, on the inflow-side chamber 21 side of the partition wall 23 , the first catalyst layer 30 is formed along the exhaust gas flow direction X from the end portion of the partition wall 23 on the exhaust gas inflow side.

[0086] The amount of the first catalyst layer 30 provided on the wall flow type substrate 20 can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost.

[0087] The first catalyst layer 30 has a portion existing inside the partition wall 23. Since the partition wall 23 is porous, the portion existing inside the partition wall 23 is formed when the first catalyst layer 30 is formed. The first catalyst layer 30 has a portion existing inside the partition wall 23 and a portion formed on the surface of the partition wall 23 on the side of the inflow side chamber 21. "The surface of the partition wall 23 on the side of the inflow side chamber 21" refers to the outer surface of the inflow side chamber 21 that defines the outer shape of the partition wall 23. "The portion formed on the surface of the partition wall 23 on the side of the inflow side chamber 21" refers to a portion protruding from the outer surface of the partition wall 23 on the side of the inflow side chamber 21 toward the inflow side chamber 21. The existence area of ​​the portion formed on the surface of the partition wall 23 on the side of the inflow side chamber 21 does not overlap with the existence area of ​​the partition wall 23, and the existence area of ​​the portion existing inside the partition wall 23 overlaps with the existence area of ​​the partition wall 23. Therefore, the first catalyst layer 30 is cut, and the cross section is analyzed by composition analysis using X-ray fluorescence analysis, inductively coupled plasma emission spectrometry (ICP-AES), or the like, or cross-sectional observation using a scanning electron microscope (SEM), and based on the composition, morphology, etc., the portion formed on the surface of the inflow side chamber 21 side of the partition wall 23 and the portion existing inside the partition wall 23 can be determined. The thickness of the portion formed on the surface of the inflow side chamber 21 side of the partition wall 23 can be appropriately adjusted. The thickness of the portion formed on the surface of the inflow side chamber 21 side of the partition wall 23 is, for example, greater than 10 μm and less than 100 μm. It should be noted that when the thickness of the portion formed on the surface of the inflow side chamber 21 side of the partition wall 23 is not constant, the average value of the thicknesses measured at multiple locations is taken as the thickness of the portion formed on the surface of the inflow side chamber 21 side of the partition wall 23.

[0088] like Figure 2 As shown, on the outflow-side chamber 22 side of the partition wall 23 , a second catalyst layer 40 is formed along a direction opposite to the exhaust gas flow direction X from an end portion of the partition wall 23 on the exhaust gas outflow side.

[0089] The amount of the second catalyst layer 40 provided on the wall flow type substrate 20 can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost.

[0090] The second catalyst layer 40 has a portion existing inside the partition wall 23. Since the partition wall 23 is porous, the portion existing inside the partition wall 23 is formed when the second catalyst layer 40 is formed. The second catalyst layer 40 has a portion existing inside the partition wall 23 and a portion formed on the surface of the outflow side chamber 22 side of the partition wall 23. "The surface of the outflow side chamber 22 side of the partition wall 23" refers to the outer surface of the outflow side chamber 22 side that defines the outer shape of the partition wall 23. "The portion formed on the surface of the outflow side chamber 22 side of the partition wall 23" refers to the portion protruding from the outer surface of the outflow side chamber 22 side of the partition wall 23 toward the outflow side chamber 22 side. The existence area of ​​the portion formed on the surface of the outflow side chamber 22 side of the partition wall 23 does not overlap with the existence area of ​​the partition wall 23, and the existence area of ​​the portion existing inside the partition wall 23 overlaps with the existence area of ​​the partition wall 23. Therefore, the second catalyst layer 40 is cut and the cross section is analyzed by composition analysis using X-ray fluorescence analysis, inductively coupled plasma emission spectrometry (ICP-AES), or cross-sectional observation using a scanning electron microscope (SEM). Based on the composition, morphology, etc., the portion formed on the surface of the outflow side chamber 22 side of the partition wall 23 and the portion existing inside the partition wall 23 can be determined. The thickness of the portion formed on the surface of the outflow side chamber 22 side of the partition wall 23 can be appropriately adjusted. The thickness of the portion formed on the surface of the outflow side chamber 22 side of the partition wall 23 is, for example, greater than 10 μm and less than 100 μm. It should be noted that when the thickness of the portion formed on the surface of the outflow side chamber 22 side of the partition wall 23 is not constant, the average value of the thicknesses measured at multiple locations is taken as the thickness of the portion formed on the surface of the outflow side chamber 22 side of the partition wall 23.

[0091] The exhaust gas purifying catalyst 10A can be manufactured by applying a slurry for forming the first catalyst layer 30 and a slurry for forming the second catalyst layer 40 onto the wall flow type substrate 20 , followed by drying and calcining.

[0092] The composition of the slurry for forming the first catalyst layer 30 is adjusted according to the composition of the first catalyst layer 30. The slurry for forming the first catalyst layer 30 can be applied by, for example, immersing the end of the exhaust gas inflow side of the wall flow type substrate 20 in the slurry for forming the first catalyst layer 30 and sucking the slurry from the opposite side.

[0093] The composition of the slurry for forming the second catalyst layer 40 is adjusted according to the composition of the second catalyst layer 40. The application of the slurry for forming the second catalyst layer 40 can be performed, for example, by immersing the end of the exhaust gas outflow side of the wall flow type substrate 20 in the slurry for forming the second catalyst layer 40 and sucking the slurry from the opposite side.

[0094] The following is based on Figure 3 and Figure 4 , an exhaust gas-purifying catalyst 10B according to a second embodiment of the present invention will be described. Figure 3 This is a partial cross-sectional view showing a state in which an exhaust gas purifying catalyst 10B according to a second embodiment of the present invention is arranged in an exhaust passage of an internal combustion engine. Figure 4 for Figure 2 BB line cross-sectional view.

[0095] like Figure 3 As shown, the exhaust gas purification catalyst 10B involved in the second embodiment of the present invention is arranged in the exhaust passage P of the internal combustion engine, and is used to purify the exhaust gas discharged from the internal combustion engine. The exhaust gas purification catalyst 10B is arranged in the exhaust passage of, for example, a gasoline engine (for example, a GDI engine, etc.). In the accompanying drawings, the exhaust gas flow direction in the exhaust passage P of the internal combustion engine is represented by the symbol X. In this specification, the upstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas inflow side", and the downstream side of the exhaust gas flow direction X is sometimes referred to as the "exhaust gas outflow side".

[0096] It should be noted that the exhaust gas purifying catalyst 10B can be used in combination with the exhaust gas purifying catalyst 10A. When the exhaust gas purifying catalyst 10B is used in combination with the exhaust gas purifying catalyst 10A, the exhaust gas purifying catalyst 10B can be arranged in the exhaust passage P of the internal combustion engine together with the exhaust gas purifying catalyst 10A. For example, the exhaust gas purifying catalyst 10B is arranged on the upstream side of the exhaust passage P of the internal combustion engine, and the exhaust gas purifying catalyst 10A is arranged on the downstream side of the exhaust passage P of the internal combustion engine.

[0097] like Figure 3 As shown, the exhaust gas-purifying catalyst 10B includes a flow-through substrate 50 and a catalyst layer 60 .

[0098] In the exhaust gas purifying catalyst 10B, the catalyst layer 60 is the catalyst layer of the present invention. As a result, the exhaust gas purifying catalyst 10B can exhibit excellent exhaust gas purification performance (especially NO x Purification performance). The exhaust gas purification performance at low to medium temperatures can be evaluated based on the light-off temperature T50. The light-off temperature T50 is the temperature at which the purification rate reaches 50%, and can be measured under the conditions described in the examples of this specification.

[0099] like Figure 3As shown, the exhaust gas purifying catalyst 10B is arranged in the exhaust passage P of the internal combustion engine in such a manner that the axial direction of the flow-through type substrate 50 is substantially consistent with the exhaust gas flow direction X. In this specification, unless otherwise specified, "length" refers to the dimension in the axial direction of the flow-through type substrate 50; unless otherwise specified, "thickness" refers to the dimension in the direction perpendicular to the axial direction of the flow-through type substrate 50.

[0100] The flow-through substrate 50 is, for example, a honeycomb structure.

[0101] like Figure 4 As shown, the flow-type substrate 50 has a plurality of chambers 51 and a partition wall 52 that separates the plurality of chambers 51. In the flow-type substrate 50, there is a partition wall 52 between two adjacent chambers 51, and the two adjacent chambers 51 are separated by the partition wall 52. It should be noted that the flow-type substrate 50 has a cylindrical portion (not shown) that limits the outer shape of the flow-type substrate 50, and the partition wall 52 is formed in the cylindrical portion. The shape of the cylindrical portion is, for example, cylindrical, and may also be other shapes. As other shapes, for example, an elliptical cylinder, a polygonal cylinder, etc. can be listed. The axial direction of the flow-type substrate 50 is consistent with the axial direction of the cylindrical portion.

[0102] like Figure 4 As shown, a plurality of holes opened on both the exhaust gas inlet side and the exhaust gas outlet side are formed in the flow-through type substrate 50 , and the spaces within these holes form a chamber 51 .

[0103] like Figure 4 As shown, the plurality of chambers 51 extend along the exhaust gas flow direction X, and have an end portion on the exhaust gas inflow side in the exhaust gas flow direction X and an end portion on the exhaust gas outflow side in the exhaust gas flow direction X. Figure 4 As shown, both the end portion on the exhaust gas inlet side in the exhaust gas flow direction X and the end portion on the exhaust gas outlet side in the exhaust gas flow direction X are open. Hereinafter, the end portion on the exhaust gas inlet side of the chamber 51 is sometimes referred to as the "opening portion on the exhaust gas inlet side of the chamber 51", and the end portion on the exhaust gas outlet side of the chamber 51 is sometimes referred to as the "opening portion on the exhaust gas outlet side of the chamber 51".

[0104] The top-view shape of the opening on the exhaust gas inlet side of the chamber 51 (the shape when looking down on the flow-type substrate 50 from the exhaust gas flow direction X) includes rectangles such as squares, parallelograms, rectangles, trapezoids, etc.; polygons such as triangles, hexagons, octagons, etc.; and various geometric shapes such as circles and ellipses.

[0105] The top-view shape of the opening on the exhaust gas outflow side of the chamber 51 (the shape when looking down at the flow-through substrate 50 from the direction opposite to the exhaust gas flow direction X) can include rectangles such as squares, parallelograms, rectangles, trapezoids, etc.; polygons such as triangles, hexagons, octagons, etc.; and various geometric shapes such as circles and ellipses.

[0106] The area of ​​the opening portion of the chamber 51 on the exhaust gas inlet side in plan view may be the same as or different from the area of ​​the opening portion of the chamber 51 on the exhaust gas outlet side in plan view.

[0107] The cell density per square inch of the flow-through substrate 50 is, for example, 400 cells or more and 1200 cells or less. It should be noted that the cell density per square inch of the flow-through substrate 50 is the total number of cells 51 per square inch in a cross section obtained by cutting the flow-through substrate 50 along a plane perpendicular to the exhaust gas flow direction X.

[0108] The thickness of the partition wall 52 is, for example, 50 μm or more and 120 μm or less. When the thickness of the partition wall 52 is not constant, the thickness of the partition wall 52 is determined as an average value of thicknesses measured at a plurality of locations.

[0109] like Figure 4 As shown, the catalyst layer 60 may be formed on both sides of the partition wall 52, from the end of the partition wall 52 on the exhaust gas inlet side to the end of the partition wall 52 on the exhaust gas outlet side, along the exhaust gas flow direction X. In addition, the catalyst layer 60 may be formed on a portion of the partition wall 52 from the end of the partition wall 52 on the exhaust gas inlet side along the exhaust gas flow direction X, and another catalyst layer may be formed from the catalyst layer 60 to the end of the partition wall 52 on the exhaust gas outlet side along the exhaust gas flow direction X. In addition, the catalyst layer 60 may be formed on a portion of the partition wall 52 from the end of the partition wall 52 on the exhaust gas outlet side in the direction opposite to the exhaust gas flow direction X, and another catalyst layer may be formed from the catalyst layer 60 to the end of the partition wall 52 on the exhaust gas inlet side in the direction opposite to the exhaust gas flow direction X.

[0110] The amount of the catalyst layer 60 provided on the flow-through substrate 50 can be appropriately adjusted in consideration of the balance between exhaust gas purification performance and cost.

[0111] The catalyst layer 60 has a portion existing inside the partition wall 52. When the partition wall 52 is porous, the portion existing inside the partition wall 52 is formed when the catalyst layer 60 is formed. The catalyst layer 60 has a portion existing inside the partition wall 52 and a portion formed on the surface of the partition wall 52. "The surface of the partition wall 52" refers to the outer surface that defines the outer shape of the partition wall 52. "The portion formed on the surface of the partition wall 52" means a portion protruding from the outer surface of the partition wall 52 toward the chamber 51 side. The existence area of ​​the portion formed on the surface of the partition wall 52 does not overlap with the existence area of ​​the partition wall 52, and the existence area of ​​the portion existing inside the partition wall 52 overlaps with the existence area of ​​the partition wall 52. Therefore, by cutting the catalyst layer 60, analyzing the cross section by composition analysis using X-ray fluorescence analysis, inductively coupled plasma emission spectrometry (ICP-AES), etc., cross-sectional observation using a scanning electron microscope (SEM), etc., it is possible to determine the portion formed on the surface of the partition wall 52 and the portion existing inside the partition wall 52 based on the composition, morphology, etc. The thickness of the portion formed on the surface of the partition wall 52 can be adjusted appropriately. It should be noted that when the thickness of the portion formed on the surface of the partition wall 52 is not constant, the average value of the thicknesses measured at multiple locations is used as the thickness of the portion formed on the surface of the partition wall 52.

[0112] The exhaust gas-purifying catalyst 10B can be produced by applying a slurry for forming the catalyst layer 60 onto the flow-through type substrate 50 , followed by drying and calcining.

[0113] The composition of the slurry for forming the catalyst layer 60 is adjusted according to the composition of the catalyst layer 60. The slurry for forming the catalyst layer 60 can be applied by, for example, immersing the entire flow-through substrate 50 in the slurry for forming the catalyst layer 60, or immersing the end of the exhaust gas inlet side or the exhaust gas outlet side of the flow-through substrate 50 in the slurry for forming the catalyst layer 60 and sucking the slurry from the opposite side.

[0114] Example

[0115] Hereinafter, embodiments of the present invention will be described in detail with reference to Examples, but the present invention is not limited to these Examples.

[0116] <Examples 1 to 7 and Comparative Examples 1 to 4>

[0117] (1) Preparation of precious metal loaded powder

[0118] Rhodium nitrate and neodymium nitrate were dissolved in water to prepare a mixed aqueous solution of rhodium nitrate and neodymium nitrate. The mixed solution was heated to 50°C, and cerium-zirconium composite oxide powder (CeO2: 40 mass%, ZrO2: 60 mass%, specific surface area: 80 m2) was added to the mixed solution. 2 / g, median particle size D 50 :7.6μm) and alumina powder (specific surface area: 100m 2 / g, median particle size D 50 :6.8μm), after the cerium-zirconium composite oxide powder and the alumina powder are loaded with rhodium and neodymium, diammonium hydrogen phosphate is added to make it also load phosphorus. The solution is heated to evaporate and dry, and dried at 150°C for 2 hours using a large hot air dryer. The obtained dry powder is crushed with an agate mortar, passed through a 150-mesh sieve, and then calcined at 600°C for 2 hours in an atmospheric atmosphere to prepare a precious metal-loaded powder. It should be noted that the amount of each component in the precious metal-loaded powder is adjusted in such a way that the amount of each component in the catalyst layer after calcination is the value of Table 1. In Table 1, the amount of each component in the catalyst layer after calcination is expressed as the mass (g / L) of each component per unit volume of the wall flow type substrate.

[0119] (2) Preparation of slurry for catalyst layer formation

[0120] The noble metal-supported powder obtained in (1), spherical pore-forming agent (cross-linked poly(methyl)acrylate particles), zirconium oxide sol and water as a liquid medium were mixed to prepare a catalyst layer-forming slurry. The content ratio of each component in the catalyst layer-forming slurry was adjusted so that the noble metal-supported powder was 16.7% by mass, the pore-forming agent was 1.8% by mass, the zirconium oxide sol was 1.5% by mass, and water was 80% by mass.

[0121] (3) Formation of Catalyst Layer

[0122] As the substrate, a wall flow type substrate was used. The wall flow type substrate used was a substrate having a surface perpendicular to the axial direction at 300 rooms / inch. 2 A wall-flow type substrate with a density of 1.4 L having an axially extending chamber divided by a partition wall with a thickness of 200 to 250 μm. The upstream end of the substrate in the exhaust gas flow direction is immersed in the catalyst layer forming slurry obtained by (2), and after suction from the downstream side, it is dried at 150°C for 2 hours in an atmospheric atmosphere. Thus, a layer composed of the solid components of the slurry is provided on the surface of the inflow side chamber in the partition wall. Then, the substrate is calcined at 600°C for 2 hours in an atmospheric atmosphere. Thus, a catalyst for exhaust gas purification having a wall-flow type substrate and a catalyst layer formed on the wall-flow type substrate is obtained. The obtained catalyst layer is a single layer.

[0123] (4) Durable treatment

[0124] The exhaust gas purification catalyst obtained by (3) is subjected to the following durability treatment. Specifically, the exhaust gas purification catalyst is arranged in the exhaust gas flow path, the engine is operated under the following conditions, the catalyst temperature is maintained at the following temperature while in contact with the exhaust gas, and the durability treatment is carried out for the following time.

[0125] (Durable treatment conditions)

[0126] Durable engine: Passenger NA 2L gasoline engine

[0127] Gasoline: Commercially available regular gasoline

[0128] Durable temperature: 930℃

[0129] Durability: 80 hours

[0130] Air-fuel ratio fluctuation before the catalyst: Repeat A / F = 14.6 (20 seconds) → fuel cut control (5 seconds) → 12.5 (5 seconds)

[0131] (5) Preparation of evaluation samples

[0132] A measurement sample having a diameter of 25.4 mm and a length of 30 mm was cut out from the exhaust gas purifying catalyst after the durability treatment.

[0133] (6) Evaluation of ignition temperature

[0134] The model gas with the following composition of A / F of 14.6 was passed into the measurement sample at a rate of 25 L / min while adjusting the CO concentration and O2 concentration so that the A / F fluctuated within the range of 14.4 to 14.8. The temperature of the gas passed into the measurement sample was gradually raised from room temperature at a rate of 20°C / min, and the NO contained in the exhaust gas that had passed through the measurement sample was measured using a measurement device (device name: MOTOR EXHAUST GAS ANALYZERMEXA7100). x The amount was measured and the purification rate was calculated based on the following formula. It should be noted that in the following formula, X represents the detected amount when the catalyst is not installed, and Y represents the detected amount after the catalyst is installed.

[0135] Purification rate (%) = (XY) / X×100

[0136] (Composition of model gas (volume basis))

[0137] CO: 0.5%, C3H6: 1200ppmC, NO: 500ppm, O2: 0.50%, CO2: 14%, H2O: 10%, H2: 0.17%, N2: balance

[0138] Find NOx The inlet gas temperature of the measurement sample when the purification rate reaches 50% is taken as the ignition temperature T50. The ignition temperature T50 is measured when the temperature is increased. The results are shown in Table 1. It should be noted that the case where the ignition temperature T50 is less than 286°C is evaluated as "S", the case where the ignition temperature T50 is greater than 286°C and less than 290°C is evaluated as "A", the case where the ignition temperature T50 is greater than 290°C and less than 300°C is evaluated as "B", and the case where the ignition temperature T50 is greater than 300°C is evaluated as "C".

[0139] [Table 1]

[0140]

[0141] As shown in Table 1, the exhaust gas purification catalysts of Examples 1 to 7 satisfy (Condition 1): the ratio of the mass of the phosphorus element contained in the catalyst layer to the mass of the rhodium element contained in the catalyst layer (P / Rh) is greater than 1.0 and less than 10; and satisfy (Condition 2): the ratio of the mass of the oxide of the rare earth element other than the cerium element contained in the catalyst layer to the mass of the rhodium element contained in the catalyst layer is greater than 1.0 and less than 5.0, and the ignition temperature T50 of the exhaust gas purification catalysts of Examples 1 to 7 is less than 300°C. On the other hand, the exhaust gas purification catalysts of Comparative Examples 1 to 4 do not satisfy one or both of Conditions 1 and 2, and their ignition temperature T50 is greater than 300°C. These results show that the exhaust gas purification performance of the exhaust gas purification catalysts of Examples 1 to 7 at low to medium temperatures (especially NO x The exhaust gas purification performance of the exhaust gas purification catalysts of Comparative Examples 1 to 4 at low to medium temperatures (especially NO x The purification performance is improved compared with that of

[0142] Description of Reference Numerals

[0143] 10A, 10B Catalysts for exhaust gas purification

[0144] 20 Wall flow substrate

[0145] 21 Flow into the side chamber

[0146] 22 Outflow side chamber

[0147] 23 Divider Wall

[0148] 24 1st sealing part

[0149] 25 Second sealing part

[0150] 30 1st catalyst layer

[0151] 40 2nd catalyst layer

[0152] 50 Flow-through substrate

[0153] Room 51

[0154] 52 partition wall

[0155] 60 Catalyst layer

[0156] X Exhaust gas flow direction

Claims

1. A catalyst for purifying exhaust gas, comprising a substrate and a catalyst layer provided on the substrate, The catalyst layer contains rhodium, phosphorus and rare earth elements other than cerium. The ratio of the mass of the phosphorus element contained in the catalyst layer to the mass of the rhodium element contained in the catalyst layer is 1.0 or more and 10 or less, The mass of the rhodium element contained in the catalyst layer is 0.10 g / L or more and 1.2 g / L or less based on the unit volume of the substrate. A ratio of the mass of the oxide of the rare earth element other than the cerium element contained in the catalyst layer to the mass of the rhodium element contained in the catalyst layer is 1.0 or more and 5.0 or less.

2. The exhaust gas purification catalyst according to claim 1, wherein A ratio of the mass of the oxide of the rare earth element other than the cerium element contained in the catalyst layer to the mass of the phosphorus element contained in the catalyst layer is 0.50 or more and 5.0 or less.

3. The exhaust gas purification catalyst according to claim 1 or 2, wherein: The catalyst layer also contains inorganic oxide particles, The rhodium element, the phosphorus element, and the rare earth element other than the cerium element are supported on the inorganic oxide particles.

4. The exhaust gas purification catalyst according to claim 1 or 2, wherein: No other catalyst layer is disposed on any surface of the catalyst layer.

5. The exhaust gas purification catalyst according to claim 1 or 2, wherein: The catalyst layer does not contain a noble metal element other than the rhodium element.

6. The exhaust gas purification catalyst according to claim 1 or 2, wherein: The substrate is a wall flow substrate.

7. The exhaust gas purification catalyst according to claim 6, wherein: The wall flow substrate comprises: an inlet side chamber, the inlet side chamber extending in the exhaust gas flow direction, wherein an end portion on the exhaust gas inlet side in the exhaust gas flow direction is open, and an end portion on the exhaust gas outflow side in the exhaust gas flow direction is closed; an outflow side chamber extending in the exhaust gas flow direction, wherein an end portion on the exhaust gas inflow side in the exhaust gas flow direction is closed and an end portion on the exhaust gas outflow side in the exhaust gas flow direction is open; and a porous partition wall, the porous partition wall partitioning the inflow side chamber and the outflow side chamber, The catalyst layer is formed on the inflow-side chamber side or the outflow-side chamber side of the partition wall.

Images