Particles for exhaust gas purification catalyst

Abstract

An exhaust gas purification catalyst particle is an exhaust gas purification catalyst particle comprising inorganic oxide particles and an inorganic coating layer coating the inorganic oxide particles, wherein the cumulative fine pore volume in the range of 0.1 to 20 μm in pore diameter is reduced as compared to the cumulative fine pore volume in the range of 0.1 to 20 μm in pore diameter of the inorganic oxide particles before being coated with the inorganic coating layer, and the thermal conductivity is higher than that of the inorganic oxide particles before being coated with the inorganic coating layer.

Description

Technical Field

[0001] This invention relates to particles for exhaust gas purification catalysts. Background Technology

[0002] Exhaust gases from internal combustion engines such as automobile engines contain nitrogen oxides (NOx). x The exhaust gas contains carbon monoxide (CO), hydrocarbons (HC), etc. After being purified by an exhaust gas purification catalyst by oxidizing CO and HC and reducing NOx, it is released into the atmosphere.

[0003] Exhaust gas purification catalysts are mostly used in the form of exhaust gas purification catalyst devices having, for example, a honeycomb-shaped substrate and a catalyst coating formed on the substrate. The catalyst coating of the exhaust gas purification catalyst device generally contains catalyst noble metal particles and inorganic oxide particles, as well as optional other components, wherein at least a portion of the catalyst noble metal particles are supported within the inorganic oxide particles.

[0004] Exhaust gas purification catalysts generally exhibit high exhaust gas purification activity at high temperatures but low activity at low temperatures. Therefore, for example, in a situation known as a "cold start," where the engine is started from a stopped position, NO in the exhaust gas... x The emissions of CO and HC have become a problem.

[0005] In recent years, the method for measuring the fuel economy of automobiles has been changed to an international benchmark known as WLTC (Worldwide Harmonized Light Duty Driving Test Cycle).

[0006] In this regard, Japan has previously used the JC08 model, which measures fuel efficiency using a 25% cold start and 75% hot start ratio, as a fuel efficiency testing method. However, in recent years, the WLTC model has used a 100% cold start ratio for fuel efficiency testing.

[0007] As a result, the importance of the cold start zone has increased in recent years, and with it, the importance of exhaust gas purification in the cold start zone is also increasing.

[0008] Therefore, various studies are being conducted in this industry to improve the exhaust purification performance in the cold start zone.

[0009] For example, Patent Document 1 discloses a catalyst for exhaust gas purification, in which a wash coat layer is divided into a front portion on the exhaust gas inlet side and a rear portion on the exhaust gas outlet side. The amount of coating on the front portion is reduced to decrease its heat capacity, and palladium is loaded at a high concentration thereon. Patent Document 1 explains that, according to this configuration, the wash coat layer on the front portion is easily heated by the heat of the exhaust gas, thus rapidly raising the palladium to its catalytically active temperature, thereby increasing the activity in the low-temperature region.

[0010] Furthermore, Patent Document 2 discloses an exhaust gas purification device for vehicles, which includes an exhaust gas purification catalyst and a microwave generator. The exhaust gas purification catalyst has a substrate and a coating applied to the substrate. The coating includes a catalyst carrying a precious metal and a microwave absorber. This exhaust gas purification device is designed to forcibly raise the temperature of the coating by irradiating it with microwaves immediately after a cold start, in order to obtain the desired activity of the exhaust gas purification catalyst.

[0011] Prior art literature

[0012] Patent documents

[0013] Patent Document 1: Japanese Patent Application Publication No. 2001-162166

[0014] Patent Document 2: Japanese Patent Application Publication No. 2019-048268 Summary of the Invention

[0015] The purpose of this invention is to provide an exhaust gas purification catalyst material that can improve the exhaust gas purification performance in the cold start zone.

[0016] The present invention is as follows.

[0017] [Solution 1] An exhaust gas purification catalyst particle, comprising inorganic oxide particles and an inorganic coating layer covering the inorganic oxide particles.

[0018] The particles used in the exhaust gas purification catalyst

[0019] The cumulative pore volume in the range of 0.1 to 20 μm is reduced compared to the cumulative pore volume in the range of 0.1 to 20 μm of inorganic oxide particles before being coated with the inorganic coating layer, thereby resulting in a higher thermal conductivity than that of inorganic oxide particles before being coated with the inorganic coating layer.

[0020] [Scheme 2] The exhaust gas purification catalyst particles according to Scheme 1 have a thermal conductivity of more than 1.10 times that of the inorganic oxide particles.

[0021] [Solution 3] The particles for exhaust gas purification catalyst according to Solution 1 or 2, wherein the inorganic coating layer is a layer of metal oxide.

[0022] [Scheme 4] According to the exhaust gas purification catalyst particles described in Scheme 3, the correlation coefficient between the inorganic elements in the inorganic oxide particles and the metal elements in the metal oxides in the inorganic coating layer, as measured by FE-EPMA, is greater than 0.70.

[0023] [Scheme 5] The particles for exhaust gas purification catalyst according to Scheme 3 or 4, wherein the metal element in the metal oxide includes cerium.

[0024] [Solution 6] According to the exhaust gas purification catalyst particles of Solution 5, the metal element in the metal oxide further includes praseodymium.

[0025] [Scheme 7] The particles for exhaust gas purification catalysts according to any one of Schemes 3 to 6, wherein the microcrystal diameter of the metal oxide constituting the inorganic coating layer is 5 nm or more and 30 nm or less.

[0026] [Solution 8] The exhaust gas purification catalyst particles according to any one of Solutions 1 to 7, wherein the bulk density of the exhaust gas purification catalyst particles is 0.59 g / cm³. 3 above.

[0027] [Scheme 9] The exhaust gas purification catalyst particles according to any one of Schemes 1 to 8,

[0028] The inorganic oxide particles are aluminum oxide particles.

[0029] The inorganic coating is a layer containing cerium dioxide in a mass fraction of more than 50% by mass relative to the inorganic coating.

[0030] [Solution 10] An exhaust gas purification catalyst, comprising:

[0031] The particles for exhaust gas purification catalysts as described in any one of schemes 1 to 9; and

[0032] Catalysts, precious metals,

[0033] The catalyst, a precious metal, is supported on particles used in the exhaust gas purification catalyst.

[0034] [Solution 11] An exhaust gas purification catalyst, comprising:

[0035] The particles for exhaust gas purification catalysts described in any one of Schemes 1 to 9;

[0036] The supporting particles are composed of inorganic oxide particles, but differ from the particles used in the exhaust gas purification catalyst; and

[0037] Catalysts, precious metals,

[0038] The catalyst precious metal is supported on at least one of the exhaust gas purification catalyst particles and the supported particles.

[0039] [Solution 12] An exhaust gas purification catalyst device, comprising a substrate and a coating on the substrate, is an exhaust gas purification catalyst device.

[0040] The coating comprises particles for exhaust gas purification catalysts as described in any one of Schemes 1 to 8.

[0041] [Solution 13] An exhaust gas purification catalyst device having a substrate and a coating on the substrate, the coating comprising the exhaust gas purification catalyst described in Solution 10 or 11.

[0042] According to the present invention, an exhaust gas purification catalyst material capable of improving exhaust gas purification performance in the cold start zone can be provided. Detailed Implementation

[0043] [Exhaust gas purification catalyst particles]

[0044] The exhaust gas purification catalyst particles of the present invention are exhaust gas purification catalyst particles comprising inorganic oxide particles and an inorganic coating layer covering the inorganic oxide particles.

[0045] The particles used in the exhaust gas purification catalyst have a reduced cumulative pore volume in the range of 0.1 to 20 μm compared to the cumulative pore volume in the range of 0.1 to 20 μm of the inorganic oxide particles before being coated with the inorganic coating layer. As a result, the thermal conductivity is higher than that of the inorganic oxide particles before being coated with the inorganic coating layer.

[0046] In the past, there have been improvement technologies aimed at enhancing exhaust purification performance in the cold start zone. Examples of such technologies include: technologies that focus on the formulation of precious metals in the catalyst; technologies that focus on the composition of the carrier particles used to support the precious metals in the catalyst; technologies that utilize adsorption materials to adsorb and desorb exhaust components; and technologies that use heating wires or the like to forcibly heat the exhaust purification device.

[0047] In contrast to these technologies, the present invention is based on the concept of accelerating the heating rate of the coating by incorporating a component that improves thermal conductivity (particles for exhaust gas purification catalyst) into the coating, thereby improving the exhaust gas purification performance in the cold start zone.

[0048] In the particles for the exhaust gas purification catalyst of the present invention, by coating the surface of porous inorganic oxide particles, preferably including the interior of the pores, with an inorganic coating layer, the pore volume in the range of 0.1 to 20 μm is reduced, the particle density is improved, and thus the thermal conductivity is improved.

[0049] The particles for the exhaust gas purification catalyst of the present invention can be used as a carrier for supporting precious metal catalysts, or as a component that does not support precious metal catalysts.

[0050] <Inorganic oxide particles>

[0051] The inorganic oxide particles in the exhaust gas purification catalyst particles of the present invention can be appropriately selected from inorganic oxide particles commonly used in the catalyst coating of exhaust gas purification catalyst devices. For example, they can be oxides of one or more elements selected from Al, Si, Ti, Zr, Ce, etc. When the inorganic oxide is an oxide of two or more elements, it can be a mixture of multiple inorganic oxides, a composite oxide containing multiple elements, or an inorganic oxide containing both of these elements.

[0052] Specifically, the inorganic oxide particles in this invention may be, for example, alumina, silicon dioxide, titanium dioxide, silicon dioxide-alumina composite oxide, cerium dioxide, zirconium oxide, cerium dioxide-zirconia composite oxide (CZ), etc. Furthermore, particles obtained by combining these with alkali metal elements, alkaline earth metal elements, rare earth elements other than Ce are also included in the inorganic oxide particles of this invention.

[0053] The inorganic oxide particles in this invention can typically be aluminum oxide.

[0054] The inorganic oxide particles in this invention can be porous particles.

[0055] The cumulative micropore volume of the inorganic oxide particles, with a pore size ranging from 0.1 to 20 μm, can be, for example, 0.3 mL / g or more, 0.4 mL / g or more, 0.5 mL / g or more, 0.6 mL / g or more, 0.7 mL / g or more, or 0.8 mL / g or more, or, for example, less than 1.5 mL / g, less than 1.2 mL / g, less than 1.1 mL / g, less than 1.0 mL / g, less than 0.9 mL / g, less than 0.8 mL / g, less than 0.7 mL / g, less than 0.6 mL / g, or less than 0.5 mL / g.

[0056] The cumulative pore volume, which is in the range of 0.1 to 20 μm, is a value determined by mercury indentation method using a mercury porosimeter for inorganic oxide particles.

[0057] The volume density of the inorganic oxide particles in this invention can be, for example, 0.30 g / mL or more, 0.35 g / mL or more, 0.40 g / mL or more, 0.45 g / mL or more, 0.50 g / mL or more, 0.55 g / mL or more, or 0.60 g / mL or more, or for example, 1.20 g / mL or less, 1.10 g / mL or less, 1.00 g / mL or less, 0.95 g / mL or less, 0.90 g / mL or less, 0.85 g / mL or less, or 0.80 g / mL or less.

[0058] This bulk density is the value obtained by dividing the mass of the inorganic oxide particles by the apparent volume (including the volume of the pores).

[0059] The exhaust gas purification catalyst particles of the present invention are particles that have a higher thermal conductivity than the original inorganic oxide particles by coating inorganic oxide particles with an inorganic coating layer. Therefore, the thermal conductivity of the inorganic oxide particles can be any value. The thermal conductivity of the inorganic oxide particles, as a value at room temperature (24±2℃), can be, for example, 0.075 W / (m·K) or higher and 0.125 W / (m·K) or lower.

[0060] The thermal conductivity values ​​in this specification are values ​​determined using the hot plate method. Specifically, the thermal conductivity can be determined using the methods described in the examples below.

[0061] <Inorganic Coating>

[0062] The inorganic coating layer in the particles of the exhaust gas purification catalyst of the present invention has the following function: by coating the surface of the above-mentioned inorganic oxide particles, preferably including the pores, with the inorganic coating layer, the pore volume in the range of 0.1 to 20 μm is reduced, the particle density is improved, and thus the thermal conductivity is improved.

[0063] The inorganic coating layer can be a layer of metal oxide. From the viewpoint of increasing the thermal conductivity of the resulting exhaust gas purification catalyst particles, the metal element in the metal oxide can include rare earth metals. That is, rare earth elements have a large atomic mass number, and consequently, a large number of free electrons. Therefore, it is believed that if the inorganic coating layer includes rare earth metal oxides, the heat transfer achieved by the free movement of electrons increases, and the overall thermal conductivity of the exhaust gas purification catalyst particles improves. However, this invention is not bound by a specific theory.

[0064] The inorganic coating layer in the particles of the exhaust gas purification catalyst of the present invention may be a layer of oxides of rare earth metal elements, or a layer of composite oxides of rare earth metal elements and one or more elements selected from Al, Si, Ti, Zr, etc.

[0065] From the viewpoint of atomic mass number and free electrons, the metal element in the metal oxide constituting the inorganic coating layer can include cerium. That is, the inorganic coating layer in the exhaust gas purification catalyst particles of the present invention can be a layer containing cerium dioxide. Since cerium can increase or decrease the number of free electrons through changes in its valence, it is considered particularly advantageous from the viewpoint of heat transfer achieved by the free movement of electrons.

[0066] The cerium dioxide content in the inorganic coating layer can be more than 50% by mass, 60% by mass or more, 70% by mass or more, 75% by mass or more, 80% by mass or more, 85% by mass or more, 90% by mass or more, or 95% by mass, or even 100% by mass, relative to the mass of the inorganic coating layer. However, from the viewpoint of enjoying the advantages of the inorganic oxide layer containing oxides of metal elements other than cerium dioxide, especially praseodymium oxide as described later, the cerium dioxide content in the inorganic coating layer can be less than 99% by mass, less than 98% by mass, less than 96% by mass, less than 94% by mass, less than 92% by mass, or less than 90% by mass, relative to the mass of the inorganic coating layer.

[0067] Similarly, from the viewpoint of atomic mass number and free electrons, the metal element in the metal oxide constituting the inorganic coating layer can contain praseodymium while also containing cerium. That is, the inorganic coating layer in the exhaust gas purification catalyst particles of the present invention can be a layer containing praseodymium oxide while containing cerium dioxide. The content of praseodymium oxide in the inorganic coating layer, relative to the mass of the inorganic coating layer, can be 1% or more by mass, 3% or more by mass, 5% or more by mass, 10% or more by mass, 15% or more by mass, 20% or more by mass, or 30% or more by mass, and can be less than 80% by mass, less than 60% by mass, less than 50% by mass, less than 40% by mass, less than 30% by mass, less than 20% by mass, less than 18% by mass, less than 15% by mass, less than 12% by mass, or less than 10% by mass.

[0068] The particles used in the exhaust gas purification catalyst of the present invention are, typically, alumina particles as inorganic oxide particles and an inorganic coating layer comprising a layer of cerium dioxide comprising more than 50% by mass relative to the inorganic coating layer, especially a layer composed of cerium dioxide as the inorganic coating layer.

[0069] Regarding the inorganic coating layer in the particles for the exhaust gas purification catalyst of the present invention, the inorganic coating layer preferably covers the surface of the aforementioned inorganic oxide particles, including the pores. Therefore, the inorganic coating layer can be composed of small microcrystals capable of penetrating into the pores of the inorganic oxide particles.

[0070] In this case, the crystallite diameter of the metal oxide constituting the inorganic coating layer can be, for example, 5.0 nm or more, 5.5 nm or more, 6.0 nm or more, or 6.5 nm or more, or, for example, 30 nm or less, 25 nm or less, 20 nm or less, 15 nm or less, 12 nm or less, 10 nm or less, 9 nm or less, or 8 nm or less.

[0071] The crystallite diameter of the metal oxide is determined by XRD, specifically by the method described in the examples below.

[0072] From the viewpoint of effectively coating the surface of inorganic oxide particles, including the pores, to improve the thermal conductivity of the resulting exhaust gas purification catalyst particles, the proportion of the inorganic coating layer in the exhaust gas purification catalyst particles of the present invention can be high. On the other hand, from the viewpoint of maintaining a high specific surface area without clogging the pores of inorganic oxide particles, the proportion of the inorganic coating layer in the exhaust gas purification catalyst particles of the present invention can be low.

[0073] If these viewpoints are considered together, the proportion of the inorganic coating in the particles of the exhaust gas purification catalyst of the present invention, as the proportion of the mass of the inorganic coating in the total mass of the particles of the exhaust gas purification catalyst, can be, for example, 1% or more by mass, 3% or more by mass, 5% or more by mass, 8% or more by mass, or 10% or more by mass, or can be, for example, less than 50% by mass, less than 40% by mass, less than 30% by mass, less than 25% by mass, less than 20% by mass, less than 15% by mass, or less than 10% by mass.

[0074] <Particles for Exhaust Gas Purification Catalysts>

[0075] In the exhaust gas purification catalyst particles of the present invention, the cumulative pore volume in the range of 0.1 to 20 μm is reduced compared to the cumulative pore volume in the range of 0.1 to 20 μm of the inorganic oxide particles before being coated with the inorganic coating layer. Furthermore, the bulk density and thermal conductivity of the exhaust gas purification catalyst particles are increased compared to the bulk density and thermal conductivity of the inorganic oxide particles before being coated with the inorganic coating layer.

[0076] The cumulative pore volume of the exhaust gas purification catalyst particles of the present invention, having a pore size in the range of 0.1 to 20 μm, can be, for example, 99% or less, 98% or less, 95% or less, 93% or less, 90% or less, or 85% or less of the cumulative pore volume of the inorganic oxide particles having a pore size in the range of 0.1 to 20 μm before being coated with the inorganic coating layer. However, from the viewpoint of maintaining a high specific surface area of ​​the obtained exhaust gas purification catalyst particles, the cumulative pore volume of the exhaust gas purification catalyst particles, having a pore size in the range of 0.1 to 20 μm, can be, for example, 65% or more, 70% or more, 75% or more, 80% or more, 85% or more, or 90% or more of the cumulative pore volume of the inorganic oxide particles having a pore size in the range of 0.1 to 20 μm before being coated with the inorganic coating layer.

[0077] The cumulative pore volume of the particles used in the exhaust gas purification catalyst of the present invention, with a pore size ranging from 0.1 to 20 μm, can typically be, for example, 0.2 mL / g or more, 0.3 mL / g or more, 0.4 mL / g or more, 0.5 mL / g or more, 0.6 mL / g or more, or 0.7 mL / g or more, or for example, 1.2 mL / g or less, 1.1 mL / g or less, 1.0 mL / g or less, 0.9 mL / g or less, 0.8 mL / g or less, 0.7 mL / g or less, 0.6 mL / g or less, 0.5 mL / g or less, or 0.45 mL / g or less.

[0078] The cumulative pore volume in the range of 0.1 to 20 μm is a value determined by mercury indentation method using a mercury porosimeter for exhaust gas purification catalyst particles.

[0079] The bulk density of the particles used in the exhaust gas purification catalyst of the present invention can be, for example, more than 101%, more than 105%, more than 110%, more than 115%, or more than 120% of the bulk density of the inorganic oxide particles before being coated with the inorganic coating layer, or, for example, less than 150%, less than 140%, less than 130%, less than 125%, less than 120%, less than 115%, or less than 110%.

[0080] The bulk density of the particles used in the exhaust gas purification catalyst can be, for example, 0.35 g / mL or more, 0.40 g / mL or more, 0.45 g / mL or more, 0.50 g / mL or more, 0.55 g / mL or more, 0.59 g / L or more, 0.60 g / mL or more, or 0.70 g / mL or more, and can be, for example, less than 1.25 g / L, less than 1.20 g / mL, less than 1.10 g / mL, less than 1.00 g / mL, less than 0.95 g / mL, less than 0.90 g / mL, or less than 0.85 g / mL.

[0081] This bulk density is the value obtained by dividing the mass of the particles used in the exhaust gas purification catalyst by the apparent volume (including the volume of the pores).

[0082] The thermal conductivity of the particles used in the exhaust gas purification catalyst of the present invention can be, for example, more than 1.05 times, more than 1.10 times, more than 1.15 times, more than 1.20 times, more than 1.25 times, or more than 1.30 times the thermal conductivity of the inorganic oxide particles before being coated with the inorganic coating layer.

[0083] On the other hand, the thermal conductivity of the particles used in exhaust gas purification catalysts does not increase indefinitely with the increase of the proportion of inorganic coatings; there is a finite upper limit. The thermal conductivity of the particles used in exhaust gas purification catalysts can be, for example, less than 1.80 times, less than 1.50 times, less than 1.40 times, less than 1.30 times, or less than 1.20 times the thermal conductivity of the inorganic oxide particles before being coated with the inorganic coating layer.

[0084] The exhaust gas purification catalyst particles of the present invention have a higher thermal conductivity than the original inorganic oxide particles by coating the inorganic oxide particles with an inorganic coating layer. Therefore, the thermal conductivity of the exhaust gas purification catalyst particles depends on and is greater than the thermal conductivity of the inorganic oxide particles contained in the exhaust gas purification catalyst particles. The thermal conductivity of the particles used in the exhaust gas purification catalyst, as a value at room temperature (24±2℃), can be, for example, 0.090 W / (m·K) or higher, 0.095 W / (m·K) or higher, 1.000 W / (m·K) or higher, 1.100 W / (m·K) or higher, or 1.200 W / (m·K) or higher, and can be, for example, 0.180 W / (m·K) or lower, 0.160 W / (m·K) or lower, 0.140 W / (m·K) or lower, 0.130 W / (m·K) or lower, 0.125 W / (m·K) or lower, or 0.120 W / (m·K) or lower.

[0085] As stated above, the thermal conductivity in this specification is a value determined using the hot plate method. Specifically, the thermal conductivity can be determined using the methods described in the examples described later.

[0086] In the particles for the exhaust gas purification catalyst of the present invention, the inorganic oxide particles have a higher thermal conductivity than the original inorganic oxide particles due to being coated with an inorganic coating layer. This can be attributed to the fact that the inorganic coating layer reduces the cumulative pore volume of the inorganic oxide particles in the pore size range of 0.1 to 20 μm, thereby increasing the particle density. Therefore, the inorganic coating layer can cover the surface of the inorganic oxide particles, including the pores.

[0087] The surface of the inorganic coating layer within the pores of the inorganic oxide particles can be identified by a high correlation coefficient between the positions of inorganic elements in the inorganic oxide particles and the positions of metal elements in the metal oxides within the inorganic coating layer. If the inorganic coating layer only covers the outer surface of the inorganic oxide particles, then this correlation coefficient becomes a low value.

[0088] Based on the above viewpoints, regarding the particles used in the exhaust gas purification catalyst of the present invention, the correlation coefficient between the inorganic elements in the inorganic oxide particles and the metal elements in the metal oxides of the inorganic coating layer, as measured by FE-EPMA, can be 0.70 or higher, 0.75 or higher, 0.80 or higher, 0.85 or higher, or 0.90 or higher. However, in order to achieve the desired effect of the present invention, this correlation coefficient can be 0.99 or lower, 0.98 or lower, 0.97 or lower, 0.95 or lower, 0.92 or lower, or 0.90 or lower.

[0089] The correlation coefficients between inorganic elements in inorganic oxide particles and metal elements in metal oxides in inorganic coatings, measured by FE-EPMA, can be specifically obtained using the methods described in the examples below.

[0090] [Manufacturing method for particles used in exhaust gas purification catalysts]

[0091] The particles used in the exhaust gas purification catalyst of the present invention described above can be manufactured using any method.

[0092] However, the particles for the exhaust gas purification catalyst of the present invention can, for example, be manufactured by spraying a solution containing a desired metal oxide precursor constituting an inorganic coating onto the desired inorganic oxide particles and then calcining them.

[0093] Metal oxide precursors can be strong acid salts of metals, such as metal hydrochlorides, hydrobromates, nitrates, sulfates, etc.

[0094] The solvent for a solution containing a metal oxide precursor can be a liquid compound capable of dissolving the metal oxide precursor, typically water.

[0095] Drying can also be performed as needed after spraying the metal oxide precursor solution and before calcination. This drying can be carried out at a temperature of, for example, above 80°C and below 300°C for a time of, for example, more than 0.5 hours and less than 48 hours.

[0096] Firing can be carried out at a temperature, for example, above 400°C and below 1000°C, for example, for a time, for example, more than 0.5 hours and less than 48 hours. Firing can be carried out in an oxidizing atmosphere, typically in air.

[0097] Subsequently, exhaust gas purification catalyst particles of the desired particle size are obtained by crushing and classifying them as needed.

[0098] [Exhaust gas purification catalyst]

[0099] According to another aspect of the present invention, an exhaust gas purification catalyst (first exhaust gas purification catalyst) is provided, comprising:

[0100] The exhaust gas purification catalyst particles of the present invention described above; and

[0101] Catalysts, precious metals,

[0102] Precious metal catalysts are loaded into particles used in exhaust gas purification catalysts.

[0103] The catalyst noble metal in the first exhaust purification catalyst mentioned above can be one or more noble metals selected from the platinum group elements, such as one, two or three selected from Pt, Pd and Rh.

[0104] The first exhaust purification catalyst can be manufactured, for example, by impregnating the exhaust purification catalyst particles of the present invention in a solution containing a noble metal precursor and then calcining them.

[0105] The precursor of a noble metal can be a strong acid salt or coordination compound of the desired noble metal, such as a hydrochloride, hydrobromide, nitrate, sulfate, or amine complex.

[0106] The solvent for the solution containing the noble metal precursor can be a liquid compound capable of dissolving the aforementioned noble metal precursor, typically water.

[0107] After impregnating the exhaust purification catalyst particles in a precious metal precursor solution and before calcination, drying can also be performed as needed.

[0108] The drying and calcination processes in the manufacture of the first exhaust gas purification catalyst can be carried out using known methods or methods obtained by applying appropriate modifications by those skilled in the art to known methods.

[0109] According to another aspect of the present invention, an exhaust gas purification catalyst (second exhaust gas purification catalyst) is provided, comprising:

[0110] The exhaust gas purification catalyst particles of the present invention described above;

[0111] The supporting particles are composed of inorganic oxide particles, but differ from the particles used in the exhaust gas purification catalyst of the present invention; and

[0112] Catalysts, precious metals,

[0113] The catalyst precious metal is supported on at least one of the particles for exhaust gas purification catalyst and the supported particles.

[0114] The supporting particles in the second exhaust gas purification catalyst are composed of inorganic oxide particles other than those used in the exhaust gas purification catalyst of the present invention. These particles can be oxides of one or more elements selected from, for example, Al, Si, Ti, Zr, Ce, etc., and can be alumina, silicon dioxide, titanium dioxide, silicon dioxide-alumina composite oxide, cerium dioxide, zirconium oxide, cerium dioxide-zirconium oxide composite oxide (CZ), etc. Furthermore, particles obtained by combining these with alkali metal elements, alkaline earth metal elements, rare earth elements other than Ce are also included in this category of supporting particles.

[0115] The catalyst precious metal in the second exhaust purification catalyst can be selected from the precious metals described above, which were used as the catalyst precious metal in the first exhaust purification catalyst.

[0116] The second exhaust gas purification catalyst can be manufactured, for example, by impregnating the exhaust gas purification catalyst particles and supporting particles of the present invention in a solution containing a noble metal precursor, followed by calcination. After impregnating these particles in the noble metal precursor solution and before calcination, drying may be performed as needed.

[0117] The instructions for the preparation, drying, and calcination of the solution containing the precious metal precursor can be used as is for the manufacture of the first exhaust gas purification catalyst.

[0118] [Exhaust gas purification catalyst device]

[0119] According to another aspect of the present invention, an exhaust gas purification catalyst device (first exhaust gas purification catalyst device) is provided, which is an exhaust gas purification catalyst device having a substrate and a coating on the substrate, the coating comprising the exhaust gas purification catalyst particles of the present invention described above.

[0120] The substrate in the first exhaust gas purification catalyst device can be appropriately selected from substrates known as substrates in known exhaust gas purification catalyst devices. It can be a honeycomb substrate made of a suitable material such as cordierite or metal. This honeycomb substrate can be either a direct-flow type or a wall-flow type.

[0121] The coating can be formed on the substrate.

[0122] The coating contains the particles for the exhaust gas purification catalyst of the present invention. The exhaust gas purification catalyst particles in the first exhaust gas purification catalyst device do not include those loaded with precious metal catalysts.

[0123] The coating may also contain other components besides the particles for the exhaust gas purification catalyst of the present invention. Other components may be selected from, for example, catalyst noble metals, inorganic oxide particles other than the particles for the exhaust gas purification catalyst of the present invention, binders, etc.

[0124] The catalyst precious metal in the first exhaust purification catalyst device can be one or more precious metals selected from the platinum group elements, such as one, two, or three selected from Pt, Pd, and Rh.

[0125] In the first exhaust gas purification catalyst device, the inorganic oxide particles other than the particles used in the exhaust gas purification catalyst of the present invention can be oxides of one or more elements selected from, for example, Al, Si, Ti, Zr, Ce, etc.

[0126] When the coating of the first exhaust purification catalyst device contains a catalyst noble metal, the coating also contains inorganic oxide particles other than the exhaust purification catalyst particles of the present invention, and the catalyst noble metal can be supported on the inorganic oxide particles other than the exhaust purification catalyst particles of the present invention.

[0127] The first exhaust gas purification catalyst device may have only one layer of coating containing the exhaust gas purification catalyst particles of the present invention, or it may have two or more layers of such coating. Furthermore, the first exhaust gas purification catalyst device may also have coatings other than the coating containing the exhaust gas purification catalyst particles of the present invention. These coatings other than the coating containing the exhaust gas purification catalyst particles of the present invention can be any coating in known exhaust gas purification catalyst devices.

[0128] The first exhaust gas purification catalyst device can be manufactured using any method.

[0129] However, the first exhaust gas purification catalyst device can be manufactured, for example, by coating a substrate with a coating liquid containing the exhaust gas purification catalyst particles of the present invention and then firing it. The coating liquid may also contain any component or its precursor in addition to the exhaust gas purification catalyst particles of the present invention. Drying may be performed as needed after coating and before firing.

[0130] The coating, drying, and firing of the coating liquid can be carried out using known methods or methods obtained by applying appropriate modifications to known methods by those skilled in the art.

[0131] According to another aspect of the present invention, an exhaust gas purification catalyst device (second exhaust gas purification catalyst device) is provided, which is an exhaust gas purification catalyst device having a substrate and a coating on the substrate, the coating comprising the exhaust gas purification catalyst of the present invention described above.

[0132] The substrate in the second exhaust gas purification catalyst unit can be the same as the substrate in the first exhaust gas purification catalyst unit.

[0133] The coating of the second exhaust purification catalyst device can be formed on the aforementioned substrate.

[0134] The coating contains the exhaust gas purification catalyst of the present invention. The exhaust gas purification catalyst may be one or both selected from the first exhaust gas purification catalyst and the second exhaust gas purification catalyst.

[0135] The coating may also contain other components besides the exhaust gas purification catalyst of the present invention. Other components may be selected from, for example, the particles for the exhaust gas purification catalyst of the present invention (particles without catalyst precious metals), catalyst precious metals, inorganic oxide particles other than the particles for the exhaust gas purification catalyst of the present invention, binders, etc.

[0136] The catalyst precious metal in the second exhaust purification catalyst device, and the inorganic oxide particles other than the particles used in the exhaust purification catalyst of the present invention, can be the same as those in the first exhaust purification catalyst device.

[0137] The second exhaust gas purification catalyst device may have only one layer of coating containing the exhaust gas purification catalyst of the present invention, or it may have two or more layers of such coating. Additionally, the second exhaust gas purification catalyst device may also have coatings other than the coating containing the exhaust gas purification catalyst of the present invention. These coatings other than the coating containing the exhaust gas purification catalyst of the present invention may be one or two or more layers selected from, for example, coatings containing particles of the exhaust gas purification catalyst of the present invention and coatings in known exhaust gas purification catalyst devices.

[0138] The second exhaust purification catalyst device can be manufactured using any method.

[0139] However, the second exhaust gas purification catalyst device can be manufactured, for example, by coating a substrate with a coating liquid containing the exhaust gas purification catalyst of the present invention and then firing it. This coating liquid may also contain any component or its precursor in addition to the exhaust gas purification catalyst of the present invention. Drying may also be performed as needed after coating and before firing.

[0140] The coating, drying, and firing of the coating liquid can be carried out using known methods or methods obtained by applying appropriate modifications to known methods by those skilled in the art.

[0141] Example

[0142] [Methods for analyzing particles]

[0143] 1. Bulk density

[0144] Approximately 20 g of the powder sample obtained in each experimental example was accurately weighed and placed into a graduated cylinder to determine its volume. The bulk density was calculated by substituting the obtained sample weight (g) and volume (mL) into the following formula.

[0145] Bulk density (g / mL) = Sample weight (g) / Sample volume (mL)

[0146] 2. Pore volume

[0147] Regarding the pore volume of the powder samples obtained in each experimental example, a mercury porosimeter was used to investigate the relationship between the mercury injection pressure and the mercury injection volume in the mercury injection method. The mercury injection pressure (P) was converted into the pore diameter using the Washburn formula expressed by the following mathematical formula, and the cumulative pore volume of 0.1 to 20 μm was calculated.

[0148] PD = -4σcosθ

[0149] Furthermore, in the above formula, P is the mercury injection pressure, D is the orifice diameter, σ is the surface tension of mercury, and θ is the contact angle between mercury and the sample. In this embodiment, σ is set to 485 mN / m and θ = 130° for calculation.

[0150] 3. Correlation coefficients between Al and metallic elements in inorganic coatings

[0151] Regarding the inorganic coating-alumina composite particles obtained in each experimental example, the correlation coefficient (ρ) between Al and the metal elements in the inorganic coating was investigated. Al，Me The correlation coefficient (ρ) between Al and metallic elements in inorganic coatings. Al，Me The characteristic X-ray intensities of each element were determined using a field emission electron probe microanalyzer (FE-EPMA). Specifically, firstly, the 275 μm × 275 μm field of view observed at 300x magnification was divided into 65,536 regions of 256 x 256 pixels. The characteristic X-ray intensities of Al and the characteristic X-ray intensities of the metallic elements in the inorganic coating were calculated in each region. Then, using these values, the covariance (Ci) of the characteristic X-ray intensities of Al and the characteristic X-ray intensities of the metallic elements in the inorganic coating was calculated using the following mathematical formula. Al，Me The standard deviation (σ) of the X-ray intensity of Al Al ) and the standard deviation (σ) of the characteristic X-ray intensity of Ce. Me ), through covariance (C Al，Me Divide by the product of standard deviations (σ) Al ·σ Me And calculate the correlation coefficient (ρ) Al，Me ).

[0152]

[0153]

[0154]

[0155]

[0156] In the above mathematical formula, I Me,i I is the characteristic X-ray intensity of the metallic element in the inorganic coating layer within the i-th segmented region. Me,av It is the average value of the characteristic X-ray intensity of the metallic elements in the inorganic coating, I Al,i I is the characteristic X-ray intensity of Al in the i-th segmented region. Al,av is the average value of the characteristic X-ray intensity of Al, and n is the number of segmented regions (65536).

[0157] 4. XRD determination

[0158] XRD analysis was performed on the inorganic coating-alumina composite particles obtained in each experimental example. The metal elements in the inorganic coating were confirmed to exist in the form of oxides, and the crystallite diameter of these oxides was investigated. The XRD measurements were performed under the following conditions.

[0159] Detector: RINT-TTR III, manufactured by Rigaku Corporation, a horizontal-type high-power X-ray diffractometer.

[0160] Tube pie: CuK α

[0161] Output: 40kV-250mA

[0162] Measurement angle range (2θ): 5~85°

[0163] Sampling interval: 0.02°

[0164] 5. Thermal conductivity

[0165] The thermal conductivity of each powder sample obtained in each experimental example was measured at room temperature (24±2℃) using a hot plate thermophysical property measuring device (model name "TPS 500S") manufactured by Hot Disk AB (aktiebolag) of Sweden, with a mold size of 2.4 cmΦ, a sample filling height of 1.0 cm, and a measuring pressure of 20 cmN.

[0166] [Comparative Example 1]

[0167] Regarding the bulk density of 0.44 g / cm³ 3The cumulative pore size volume of 0.1–20 μm is 0.91 cm³. 3 / g of alumina particles (alumina(1)) were evaluated.

[0168] [Comparative Example 2]

[0169] The mixed particles obtained by dry mixing 450g of alumina (1) of the same type as the alumina (1) used in Comparative Example 1 and 50g of cerium dioxide particles were evaluated.

[0170] [Example 1]

[0171] 299.4 g of an aqueous solution of cerium nitrate with a Ce concentration of 16.7% by mass (equivalent to 50 g of Ce) was sprayed onto 450 g of alumina (1), the same type as the alumina (1) used in Comparative Example 1. The mixture was dried in the atmosphere at 250°C for 8 hours, and then calcined in the atmosphere at 500°C for 2 hours, thereby obtaining the cerium dioxide-alumina composite particles (particles for exhaust gas purification catalyst) of Example 1. The cerium dioxide-alumina composite particles were evaluated.

[0172] The evaluation results for the particles of Comparative Examples 1, 2 and Example 1 are shown in Table 1.

[0173]

[0174] [Comparative Example 3]

[0175] Regarding the bulk density of 0.67 g / cm³ 3 The cumulative pore size volume of 0.1–20 μm is 0.48 cm³. 3 / g of alumina particles (alumina(2)) were evaluated.

[0176] [Comparative Example 4]

[0177] The mixed particles obtained by dry mixing 450g of alumina (2) of the same type as the alumina (2) used in Comparative Example 3 and 50g of cerium dioxide particles were evaluated.

[0178] [Comparative Example 5]

[0179] 450g of alumina (2), the same type as that used in Comparative Example 3, was impregnated in 1111g of an aqueous solution of cerium nitrate with a Ce concentration of 4.5% by mass (calculated as CeO2, equivalent to 50g of Ce). After stirring at room temperature for 1 hour, the mixture was dried at 250°C in the atmosphere for 8 hours, and then calcined at 500°C in the atmosphere for 2 hours, thereby obtaining the cerium dioxide-alumina composite particles of Comparative Example 5. The cerium dioxide-alumina composite particles were evaluated.

[0180] [Example 2]

[0181] 304.9 g of an aqueous solution of cerium nitrate with a Ce concentration of 16.4% by mass (equivalent to CeO2) (50 g of Ce) was sprayed onto 450 g of alumina (2), the same type as the alumina (2) used in Comparative Example 3. After drying in the atmosphere at 250°C for 8 hours, the alumina was calcined in the atmosphere at 500°C for 2 hours, thereby obtaining the cerium dioxide-alumina composite particles (particles for exhaust gas purification catalyst) of Example 2. The thermal conductivity of the cerium dioxide-alumina composite particles was evaluated.

[0182] [Example 3]

[0183] The amount of alumina (2) was set to 400g, and 380.23g of a cerium nitrate aqueous solution with a Ce concentration of 26.3% by mass (calculated as CeO2) (calculated as CeO2, equivalent to 100g of Ce) was used as the cerium nitrate aqueous solution. Otherwise, the same procedure as in Example 2 was performed to obtain the cerium dioxide-alumina composite particles (particles for exhaust gas purification catalyst) of Example 3. The cerium dioxide-alumina composite particles were evaluated.

[0184] The evaluation results for the particles of Comparative Examples 3-5 and Examples 2 and 3 are shown in Table 2.

[0185]

[0186] The following can be understood from the results in Tables 1 and 2.

[0187] The composite of alumina particles and cerium dioxide resulted in a reduction in the cumulative pore volume in Comparative Examples 2, 4, and 5, and Examples 1-3, where the cerium dioxide-alumina composite particles had a pore size range of 0.1–20 μm, and exhibited improved thermal conductivity compared to the original alumina particles. However, in Comparative Examples 2, 4, and 5, where the correlation coefficient between Al and rare earth metal elements was low, the improvement in thermal conductivity was minimal.

[0188] In contrast, the cerium dioxide-alumina composite particles from Examples 1-3, which combine alumina particles with cerium dioxide, exhibit significantly improved thermal conductivity compared to the original alumina particles. The cumulative pore volume in the pore size range of 0.1–20 μm is reduced compared to the original alumina particles, and the correlation coefficient between Al and Ce is high. Based on XRD and the correlation coefficients between Al and Ce, it is inferred that in these cerium dioxide-alumina composite particles, primary cerium dioxide particles are supported on the secondary surface of the alumina particles.

[0189] [Evaluation Methods for the Exhaust Gas Purification Performance of Exhaust Gas Purification Catalyst Devices]

[0190] The exhaust gas purification catalyst device was installed in an atmospheric pressure fixed-bed flow-through reactor. While an exhaust gas model gas (composition below) with a stoichiometric ratio (theoretical ratio) was circulated, the gas temperature was increased from 100°C to 600°C at a rate of 20°C / min. The concentrations of HC, CO, and NOx in the exhaust gas from the exhaust gas purification catalyst device were continuously monitored. At this point, the gas temperature at which the purification rates of HC, CO, and NOx reached 50% (50% purification temperature) was investigated.

[0191] The composition of the exhaust gas in the model is as follows. All concentrations listed below are mass ratios under standard conditions.

[0192] HC: 1500ppm

[0193] CO: 2600ppm

[0194] NO: 1650ppm

[0195] O2: 0.27%

[0196] CO2: 7.0%

[0197] H2O: 1.5%

[0198] N2: Balance

[0199] [Example 4]

[0200] 450g of cerium dioxide-alumina composite particles (particles for exhaust gas purification catalyst) obtained in Example 2 above were dispersed in 1000mL of ion-exchange water. 26.7g of an aqueous palladium nitrate solution with a Pd content of 8.44% by mass (equivalent to 2.25g of Pd) was added, and the mixture was stirred at room temperature for 1 hour. The solids were recovered from the stirred mixture using a suction filter. After drying in air at 110°C for 2 hours, the mixture was calcined in air at 500°C for 2 hours to obtain the exhaust gas purification catalyst.

[0201] On the other hand, the filtrate during the filtration process was analyzed by ICP luminescence analysis, and no Pd was detected in the filtrate. Therefore, the Pd loading efficiency in the exhaust gas purification catalyst obtained above is 100%. This Pd loading rate is 0.5% by setting the mass of the cerium dioxide-alumina composite particles to 100% by mass.

[0202] 300g of the exhaust gas purification catalyst obtained above was mixed with 450mL of ion-exchange water and wet-milled using a ball mill to obtain an exhaust gas purification catalyst slurry with an average particle size adjusted to 5μm.

[0203] As a substrate, a cordierite monolithic honeycomb carrier with a diameter of 30 mm and a length of 50 mm (volume 0.035 L) was used. The above-mentioned slurry was coated onto the carrier at a rate of 3.5 g (100 g / L) after drying. Then, after drying in the atmosphere at 250°C for 2 hours, it was calcined in the atmosphere at 500°C for 2 hours, thereby obtaining the exhaust gas purification catalyst device of Example 4.

[0204] The obtained exhaust gas purification catalyst device was used to evaluate the catalyst performance using the method described above.

[0205] [Comparative Example 6]

[0206] Instead of cerium dioxide-alumina composite particles, 456g of the same type of alumina (2) used in Comparative Example 3 was used. Otherwise, the same procedure as in Example 4 was followed to manufacture the exhaust gas purification catalyst device of Comparative Example 6, and its exhaust gas purification performance was evaluated.

[0207] The exhaust purification performance of the exhaust purification catalyst devices obtained in Example 4 and Comparative Example 6 is shown in Table 3.

[0208]

[0209] Based on the results in Table 3, it was verified that the exhaust gas purification catalyst device of Example 4, which used the particles of the present invention as the carrier for the noble metal catalyst, exhibited a lower 50% purification temperature for all HC, CO, and NOx compared to the exhaust gas purification catalyst device of Comparative Example 6, which used alumina particles as the carrier. This is believed to be because the cerium dioxide-alumina composite particles constituting the exhaust gas purification catalyst device have high thermal conductivity, allowing for rapid heat transfer from the exhaust gas to the catalyst coating, resulting in a rapid temperature rise in the catalyst coating and consequently, higher exhaust gas purification performance at an earlier stage.

[0210] [Example 5]

[0211] 274.4 g of a cerium nitrate aqueous solution with a Ce concentration of 16.4% by mass (calculated as CeO2, equivalent to 45 g of Ce) and Pr6O 11 The converted Pr concentration is 18.0 g of praseodymium nitrate aqueous solution with a mass of 27.9% (based on Pr6O). 11 A mixed aqueous solution for spraying was prepared by mixing 5g of the converted Pr amount.

[0212] The above-mentioned spray-dried mixed aqueous solution was sprayed onto 450g of alumina (2), which was the same type of alumina (2) used in Comparative Example 3. After drying in the atmosphere at 250°C for 8 hours, it was calcined in the atmosphere at 500°C for 2 hours, thereby obtaining the cerium dioxide-alumina composite particles (particles for exhaust gas purification catalyst) of Example 5. The thermal conductivity of the cerium dioxide / praseodymium-alumina composite particles was evaluated.

[0213] [Examples 6-8]

[0214] The mixing amounts of cerium nitrate aqueous solution and praseodymium nitrate aqueous solution were changed during the preparation of the spray-applied mixed aqueous solution to adjust the Ce content calculated based on CeO2 and the Pr6O content. 11 The total amount of Pr converted was 50g, and the ratio of the two was the value recorded in Table 4. Otherwise, the same procedure as in Example 5 was followed to prepare cerium dioxide-alumina composite particles (particles for exhaust gas purification catalysts), and the thermal conductivity was evaluated.

[0215] The evaluation results of Examples 5-8 are shown together with the results of Comparative Examples 3 and 2 in Table 4.

[0216]

[0217] Based on the results in Table 4, it was verified that the composite particles of Examples 5 to 8, which combined alumina particles with cerium-praseodymium composite oxide, also showed a significant increase in thermal conductivity compared to the original alumina particles (Comparative Example 3), similar to the composite particles of Example 2, which combined alumina particles with cerium dioxide.

Claims

1. A particle for exhaust gas purification catalyst, comprising inorganic oxide particles and an inorganic coating layer covering the inorganic oxide particles. The inorganic oxide particles are particles of aluminum oxide, silicon dioxide-alumina composite oxides, or inorganic oxides obtained by combining them with one or more rare earth elements selected from alkali metals, alkaline earth metals, and Ce. The inorganic coating is a layer comprising a metal oxide of cerium dioxide in an amount exceeding 50% by mass relative to the inorganic coating. The particles used in the exhaust gas purification catalyst have a reduced cumulative pore volume in the range of 0.1 to 20 μm compared to the cumulative pore volume in the range of 0.1 to 20 μm of the inorganic oxide particles before being coated with the inorganic coating layer, thereby resulting in a higher thermal conductivity than the inorganic oxide particles before being coated with the inorganic coating layer.

2. The particles for exhaust gas purification catalyst according to claim 1, The thermal conductivity of the particles used in the exhaust gas purification catalyst is more than 1.10 times that of the inorganic oxide particles.

3. The particles for exhaust gas purification catalyst according to claim 1 or 2, The inorganic coating layer is a layer of cerium dioxide, or a layer of cerium dioxide and praseodymium oxide.

4. The particles for exhaust gas purification catalyst according to claim 1 or 2, Regarding the particles used in the exhaust gas purification catalyst, the correlation coefficient between the aluminum element in the inorganic oxide particles and the cerium element in the metal oxide in the inorganic coating layer, as measured by FE-EPMA, is greater than 0.

70.

5. The particles for exhaust gas purification catalyst according to claim 1 or 2, wherein the mass of the inorganic coating layer accounts for more than 5% by mass and less than 50% by mass of the total mass of the particles for exhaust gas purification catalyst.

6. The particles for exhaust gas purification catalyst according to claim 1 or 2, The crystallite diameter of the metal oxide constituting the inorganic coating layer is 5 nm or more and 30 nm or less.

7. The particles for exhaust gas purification catalyst according to claim 1 or 2, The bulk density of the particles used in the exhaust gas purification catalyst is 0.59 g / cm³. 3 above.

8. The particles for exhaust gas purification catalyst according to claim 1 or 2, The thermal conductivity of the particles used in the exhaust gas purification catalyst is above 0.095 W / (m·K) and below 0.160 W / (m·K) at room temperature (24±2℃).

9. An exhaust gas purification catalyst, comprising: The particles for exhaust gas purification catalysts according to any one of claims 1 to 8; and Catalysts, precious metals, The catalyst, a precious metal, is supported on particles used in the exhaust gas purification catalyst.

10. An exhaust gas purification catalyst, comprising: The particles for exhaust gas purification catalyst according to any one of claims 1 to 8; The supporting particles are composed of inorganic oxide particles, but differ from the particles used in the exhaust gas purification catalyst; and Catalysts, precious metals, The catalyst precious metal is supported on at least one of the exhaust gas purification catalyst particles and the supported particles.

11. An exhaust gas purification catalyst device, comprising an exhaust gas purification catalyst device having a substrate and a coating on the substrate, The coating comprises particles for exhaust gas purification catalysts as described in any one of claims 1 to 8.

12. An exhaust gas purification catalyst device, comprising an exhaust gas purification catalyst device having a substrate and a coating on the substrate, The coating comprises the exhaust gas purification catalyst as described in claim 9 or 10.

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