Catalyst noble metal particles

Abstract

The catalyst noble metal particles for exhaust gas purification are composed of an alloy containing Pt and Pd, and the standard deviation [sigma] COM of the composition represented by the ratio of the mass of Pt to the total mass of Pt and Pd (Pt / (Pt + Pd)) in the catalyst noble metal particles is 3.0 mass% or less.

Description

Technical Field

[0001] The present invention relates to catalyst noble metal particles. Background Art

[0002] The exhaust gas (waste gas) discharged from an internal combustion engine such as an automobile engine contains hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NOx). These are purified by an exhaust gas purification catalyst device provided in the exhaust system and then released into the atmosphere. The exhaust gas purification catalyst device has, for example, a structure in which a catalyst coating is arranged on the partition wall of a honeycomb substrate.

[0003] The catalyst coating of the exhaust gas purification catalyst device contains a catalyst precious metal as an active component for exhaust gas purification. The catalyst precious metal contains, for example, one or more selected from Pt, Pd and Rh. It is believed that Pt and Pd show catalytic activity in oxidation purification of HC and CO, and Rh shows catalytic activity in reduction purification of NOx.

[0004] HC includes saturated hydrocarbons and unsaturated hydrocarbons, among which saturated hydrocarbons are considered to be more difficult to oxidatively purify.

[0005] Regarding the oxidation purification of HC, Non-Patent Document 1 reports that, between Pt and Pd, Pt is superior in oxidation purification capability for saturated hydrocarbons, while Pd is superior in oxidation purification capability for unsaturated hydrocarbons.

[0006] Since HC in the exhaust gas of an actual vehicle includes both saturated hydrocarbons and unsaturated hydrocarbons, it is desirable that the catalyst coating of the exhaust gas purification catalyst device include both Pt having excellent oxidation purification ability for saturated hydrocarbons and Pd having excellent oxidation purification ability for unsaturated hydrocarbons.

[0007] Patent Document 1 describes that, regarding catalytic noble metal powder containing Pt, Pd, and Rd, the heat resistance and durability of the catalytic noble metal powder can be improved by adjusting the standard deviation of the content of each element to 20 mass % or less.

[0008] Patent Document 2 describes a catalyst containing both Pt and Pd useful for treating exhaust gas from a vehicle, wherein the weight ratio of Pt to Pd is 20:1 to 1:20.

[0009] Prior Art Literature

[0010] Patent Literature

[0011] Patent Document 1: Japanese Patent Application Publication No. 2011-123004

[0012] Patent Document 2: Japanese Patent Application Publication No. 2017-039121

[0013] Non-patent literature

[0014] Non-patent document 1: Applied Catalysis B. Environmental 251 (2019), pp283-294 Summary of the invention

[0015] Non-Patent Document 1 describes that the oxidation purification capability of Pt for saturated hydrocarbons is impaired by its alloy with Pd.

[0016] Furthermore, the catalysts of Patent Documents 1 and 2 have insufficient heat resistance and durability in a severe environment such as an exhaust gas path of a vehicle, where the catalysts are alternately exposed to an oxidizing lean atmosphere and a reducing rich atmosphere at a high temperature of 1000° C. or higher, and their HC oxidation purification activity is impaired over time.

[0017] The present invention has been accomplished in view of the above circumstances.

[0018] An object of the present invention is to provide catalytic noble metal particles which exhibit sufficiently high heat resistance and durability even in a severe environment of alternate exposure to a dilute atmosphere and a rich atmosphere, and which exhibit high oxidation purification activity for both saturated hydrocarbons and unsaturated hydrocarbons, particularly saturated hydrocarbons which are generally considered difficult to purify.

[0019] The present invention is as follows.

[0020] <Scheme 1> A catalytic noble metal particle for purifying exhaust gas, the catalytic noble metal particle being composed of an alloy containing Pt and Pd,

[0021] The standard deviation σ of the composition represented by the ratio of the mass of Pt to the total mass of Pt and Pd (Pt / (Pt+Pd)) in the catalytic noble metal particles is COM It is 3.0 mass % or less.

[0022] <Scheme 2> According to the catalyst noble metal particle of Scheme 1, the standard deviation σ of the composition COM It is 2.5 mass % or less.

[0023] <Scheme 3> The catalytic noble metal particle according to Scheme 1 or 2, wherein the composition (Pt / (Pt+Pd)) is 1.0 mass % or more and 70 mass % or less.

[0024] <Scheme 4> The catalytic noble metal particles according to Scheme 3, wherein the composition (Pt / (Pt+Pd)) is 3.0 mass % or more and 40 mass % or less.

[0025] <Structure 5> The catalytic noble metal particle according to any one of Structures 1 to 4, wherein the average particle diameter of the catalytic noble metal particle is 2.0 nm or more and 5.0 nm or less.

[0026] <Structure 6> The catalytic noble metal particle according to any one of Structures 1 to 5, wherein the standard deviation σ of the particle diameter of the catalytic noble metal particle is rad It is less than 2.0nm.

[0027] <Scheme 7> The catalyst noble metal particles according to Scheme 6, wherein the standard deviation σ of the particle diameter of the catalyst noble metal particles is rad It is less than 1.5nm.

[0028] <Structure 8> The catalytic noble metal particle according to any one of Structures 1 to 7, wherein the coefficient of variation of the composition of the catalytic metal particle is 0.45 or less.

[0029] <Scheme 9> A method for producing catalytic noble metal particles is a method for producing catalytic noble metal particles described in any one of Schemes 1 to 8, comprising: reacting a solution containing a Pt precursor and a Pd precursor and a solution containing an organic base in a microreactor (microreactor: micro reactor).

[0030] <Scheme 10> According to the production method described in Scheme 9, the organic base is selected from amines and quaternary ammonium salts.

[0031] <Scheme 11> In the production method according to Scheme 9 or 10, the amount of the organic base is 0.5 times or more and 10 times or less the total molar amount of Pt and Pd contained in the solution containing the Pt precursor and the Pd precursor.

[0032] <Structure 12> A supported catalyst for purifying exhaust gas, comprising inorganic oxide support particles and the catalytic noble metal particles according to any one of Structures 1 to 8 supported on the inorganic oxide support particles.

[0033] According to the present invention, it is possible to provide catalytic noble metal particles which exhibit sufficiently high heat resistance and durability even in a severe environment of alternate exposure to a dilute atmosphere and a rich atmosphere and which exhibit high oxidation purification activity against both saturated hydrocarbons and unsaturated hydrocarbons. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 is the standard deviation σ of the composition of the catalytic noble metal particles in Examples 1 to 5 and Comparative Examples 1 to 3. COM Propane 50% purge temperature (T50(C 3 H 8 ))’s relationship curve.

[0035] Figure 2 The composition of the catalyst noble metal particles (Pt / (Pt+Pd) ratio) and the propane 50% purification temperature (T50 (°C)) in Examples 7 to 12 and Comparative Examples 5 to 11 are shown. 3 H 8 ))’s relationship curve. DETAILED DESCRIPTION

[0036] 〈Catalyst precious metal particles〉

[0037] The catalyst noble metal particle of the present invention is a catalyst noble metal particle for exhaust gas purification composed of an alloy containing Pt and Pd, and the standard deviation σ of the composition represented by the ratio of the mass of Pt to the total mass of Pt and Pd (Pt / (Pt+Pd)) in the catalyst noble metal particle is COM It is 3.0 mass % or less.

[0038] The present inventors have investigated the reason why the catalytic activity, in particular the oxidation purification activity for saturated hydrocarbons, deteriorates when conventionally known catalytic noble metal particles containing Pt and Pd are alternately exposed to a lean atmosphere and a rich atmosphere at high temperatures.

[0039] As a result, it was found that the durability of Pt in a dilute atmosphere is low, and Pt in a Pt-rich portion of the catalytic noble metal particle is preferentially and rapidly oxidized and degraded, thereby significantly impairing the catalytic activity of the entire catalytic noble metal particle.

[0040] Therefore, in the present invention, the degree of composite formation of Pt and Pd in ​​the catalyst noble metal particles is made uniform, and the proportion of the Pt-rich part that is preferentially oxidatively degraded in a dilute state is reduced as much as possible. As a result, the oxidative degradation of Pt in a dilute atmosphere is suppressed, and the oxidation purification activity for saturated hydrocarbons is maintained for a long time. In addition, according to the configuration of the present invention, the oxidation purification activity for unsaturated hydrocarbons is not impaired.

[0041] For the reasons described above, the catalytic noble metal particles of the present invention exhibit sufficiently high heat resistance and durability even under severe environments, and can exhibit high oxidation purification activity against both saturated hydrocarbons and unsaturated hydrocarbons.

[0042] The standard deviation of the composition is COM Small catalytic noble metal particles can be produced, for example, by a method comprising reacting a solution containing a Pt precursor and a Pd precursor with a solution containing an organic base in a microreactor.

[0043] 〈Composition of Catalyst Noble Metal Particles〉

[0044] The catalyst noble metal particles of the present invention are composed of an alloy containing Pt and Pd. In addition to Pt and Pd, the alloy may also contain other noble metals (such as Rh, etc.). However, the catalyst noble metal particles may not substantially contain metals other than Pt and Pd.

[0045] The so-called catalyst precious metal particles of the present invention substantially do not contain metals other than Pt and Pd means that the ratio of the mass of metals other than Pt and Pd in ​​the catalyst precious metal particles to the total mass of the catalyst precious metal particles is 5 mass% or less, 3 mass% or less, 1 mass% or less, 0.5 mass% or less, or 0.1 mass% or less, and also includes the case of 0 mass%.

[0046] In this specification, the composition of the catalytic noble metal particles is referred to by the ratio of the mass of Pt to the total mass of Pt and Pd (Pt / (Pt+Pd)) and is expressed as a percentage.

[0047] The catalyst noble metal particles of the present invention have high HC oxidation purification capability in a relatively wide composition range, especially high oxidation purification capability for saturated hydrocarbons. In this regard, the composition range in which the catalyst metal particles of the prior art exhibit the desired HC oxidation purification capability is limited to a specific narrow range. However, the catalyst noble metal particles of the present invention exhibit high HC purification capability in a wide composition range, and therefore have the advantage of high degree of freedom in catalyst design.

[0048] From the viewpoint of ensuring high oxidation purification activity for saturated hydrocarbons, the composition (mass %) of the catalyst precious metal particles expressed by the Pt / (Pt+Pd) ratio can be 1.5 mass % or more, 2.0 mass % or more, 3.0 mass % or more, 5.0 mass % or more, 10 mass % or more, 12 mass % or more, 15 mass % or more, 17 mass % or more, or 20 mass % or more.

[0049] On the other hand, from the viewpoint of ensuring high oxidation purification activity for unsaturated hydrocarbons, the composition (mass %) of the catalyst precious metal particles can be 70 mass % or less, 65 mass % or less, 60 mass % or less, 55 mass % or less, 50 mass % or less, 45 mass % or less, 40 mass % or less, 35 mass % or less, or 30 mass % or less.

[0050] The composition (mass %) of the catalytic noble metal particles may typically be 1.0 mass % or more and 70 mass % or less, or 3.0 mass % or more and 40 mass % or less.

[0051] The composition of the catalytic noble metal particles can be known by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX).

[0052] Specifically, 50 catalytic noble metal particles are randomly selected, and elemental analysis is performed on these 50 catalytic noble metal particles using EDX to determine the composition of each catalytic noble metal particle, and the composition of the catalytic noble metal particles is calculated as the number average thereof.

[0053] The catalyst noble metal particles can be subjected to STEM-EDX analysis, and when the catalyst noble metal particles are in the form of supported catalysts supported on a carrier, the supported catalysts can also be subjected to STEM-EDX analysis. When the supported catalyst is subjected to STEM-EDX analysis, it is sufficient to use the EDX information on the portion corresponding to the catalyst noble metal particles in the STEM image.

[0054] <Standard Deviation of Composition of Catalytic Noble Metal Particles>

[0055] The standard deviation σ of the composition of the catalyst noble metal particles of the present invention COM It is 3.0 mass % or less.

[0056] The catalyst noble metal particles of the present invention have a standard deviation σ of the composition. COM The content of Pt and Pd in ​​the catalyst noble metal particles is 3.0% by mass or less, which ensures uniformity of the degree of complexation of Pt and Pd in ​​the catalyst noble metal particles. In addition, the proportion of the Pt-rich part that is preferentially oxidatively degraded in a dilute state becomes extremely small, so that the oxidative degradation of Pt in a dilute atmosphere is suppressed, showing high stability and durability.

[0057] Standard deviation of the composition of the catalyst noble metal particles σ COM It may be 2.9 mass % or less, 2.7 mass % or less, 2.5 mass % or less, 2.2 mass % or less, or 2.0 mass % or less. The standard deviation of the composition σ COM The lower the value, the better. However, even if this value is extremely low, the exhaust purification ability of the catalyst noble metal particles cannot be infinitely improved. In order to demonstrate the effect of the present invention, the standard deviation σ of the composition of the catalyst noble metal particles is COM The content may be 0.1% by mass or more, 0.5% by mass or more, 1.0% by mass or more, 1.2% by mass or more, 1.5% by mass or more, or 2.0% by mass or more.

[0058] Standard deviation of the composition of the catalyst noble metal particles σ COM The composition can be calculated from the composition of each catalytic noble metal particle obtained as described above by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX).

[0059] The standard deviation σ of the composition of the above-mentioned catalyst noble metal particles is COMThe recommended range of is related to the initial value measured immediately after the catalyst noble metal particles of the present invention are prepared. The catalyst noble metal particles of the present invention can be seen to have a composition standard deviation σ as the degree of durability progresses during use. COM However, this does not impair the effect of the present invention.

[0060] <Coefficient of variation of composition of catalyst noble metal particles>

[0061] The catalyst metal particles of the present invention are prepared by using the standard deviation σ of the composition obtained as described above. COM The coefficient of variation of the composition, which is defined by dividing the value obtained by dividing the average value of the composition, may be 0.45 or less. COM In addition to being 3.0 mass % or less, the coefficient of variation of the composition is 0.45 or less, and the degree of composite formation of Pt and Pd in ​​the catalytic noble metal particles can be ensured to be uniform at a high level.

[0062] The coefficient of variation of the composition of the catalyst metal particles of the present invention may be 0.40 or less, 0.30 or less, or 0.20 or less. In order to achieve the effect of the present invention, the coefficient of variation of the composition of the catalyst noble metal particles may be 0.02 or more, 0.04 or more, 0.06 or more, or 0.10 or more.

[0063] 〈Particle size of catalyst noble metal particles〉

[0064] From the viewpoint of maintaining the stability of the composition of the alloy containing Pt and Pd, the particle size of the catalyst metal particles of the present invention may be larger to a certain extent. From this viewpoint, the average particle size of the catalyst noble metal particles may be 1.5 nm or more, 2.0 nm or more, 2.5 nm or more, 3.0 nm or more, or 3.5 nm or more.

[0065] On the other hand, from the viewpoint of increasing the specific surface area of ​​the catalyst metal particles and increasing the number of exhaust purification active sites exposed on the surface, the smaller the particle size, the better. From this viewpoint, the average particle size of the catalyst noble metal particles can be 10.0 nm or less, 8.0 nm or less, 6.0 nm or less, or 4.0 nm or less.

[0066] The average particle size of the catalytic noble metal particles of the present invention may typically be 2.0 nm or more and 6.0 nm or less.

[0067] The average particle size of the catalytic noble metal particles of the present invention can be calculated from, for example, a STEM image.

[0068] The recommended range of the average particle size of the catalyst noble metal particles mentioned above is related to the initial value measured immediately after the catalyst noble metal particles of the present invention are prepared. The catalyst noble metal particles of the present invention have a tendency to have an average particle size that increases as the degree of durability increases during use. However, this does not impair the effects of the present invention.

[0069] <Standard Deviation of Particle Diameter of Catalytic Noble Metal Particles>

[0070] From the viewpoint of achieving both high catalytic activity and heat resistance and durability, the catalyst noble metal particles of the present invention may not contain fine particles and coarse particles. From this viewpoint, the standard deviation σ of the particle size of the catalyst noble metal particles is rad It can be 1.2 nm or less, 1.0 nm or less, 0.8 nm or less, or 0.6 nm or less. In addition, in order to demonstrate the effect of the present invention, the standard deviation σ of the particle size of the catalyst noble metal particles is rad It may be 0.1 nm or more, 0.2 nm or more, 0.3 nm or more, or 0.4 nm or more.

[0071] The standard deviation σ of the particle size of the catalyst noble metal particles is rad The recommended range of is related to the initial value measured immediately after the catalyst noble metal particles of the present invention are prepared. The catalyst noble metal particles of the present invention can be seen to have a standard deviation of particle size σ as the durability progresses during use. rad However, this does not impair the effect of the present invention.

[0072] 〈Supported catalyst for exhaust gas purification〉

[0073] According to another aspect of the present invention, there is provided an exhaust gas purification supported catalyst comprising inorganic oxide support particles and the catalytic noble metal particles of the present invention supported on the inorganic oxide support particles.

[0074] The inorganic oxide carrier particles may be particles composed of oxides containing one or more metal elements selected from Al, Ti, Si, Zr, Ce, rare earth elements other than Ce, etc. When the inorganic oxide carrier particles are composed of oxides of two or more metal elements, they may be a mixture of metal oxides, a composite oxide, or a mixture thereof.

[0075] The inorganic oxide support particles may contain oxides of one or more metal elements selected from alkali metals and alkaline earth metals in addition to the above-mentioned oxides of the metal elements.

[0076] The particle size of the inorganic oxide carrier particles can be appropriately set according to the purpose of the exhaust gas purification supported catalyst. The particle size of the inorganic oxide carrier particles can be, for example, 0.1 μm or more, 0.5 μm or more, or 1.0 μm or less, or 20.0 μm or less, 15.0 μm or less, or 10.0 μm or less.

[0077] The loading rate of the catalyst precious metal particles in the exhaust gas purification supported catalyst of the present invention, as the mass ratio of the catalyst precious metal particles to the total mass of the exhaust gas purification supported catalyst, can be 0.1 mass % or more, 0.3 mass % or more, or 0.5 mass % or less, and can be 5.0 mass % or less, 3.0 mass % or less, or 2.0 mass % or less.

[0078] 〈Exhaust purification catalyst device〉

[0079] According to another aspect of the present invention, there is provided an exhaust gas purification catalyst device comprising a substrate and a catalyst coating layer on the substrate, wherein the catalyst coating layer contains the catalytic noble metal particles of the present invention.

[0080] 〈Base Material〉

[0081] The substrate suitable for the exhaust gas purification catalyst device of the present invention may be a substrate having a plurality of cell flow paths divided by partition walls, and may be a honeycomb substrate used in the exhaust gas purification catalyst device of the prior art. The partition walls of the substrate may have pores that fluidically connect adjacent exhaust flow paths, or may not have such pores.

[0082] The constituent material of the substrate may be, for example, a refractory inorganic oxide such as cordierite, or may be a metal. The substrate may be a direct-flow type or a wall-flow type.

[0083] The substrate in the method for manufacturing the exhaust gas purification catalyst device of the present invention may be typically a cordierite straight-flow type monolithic honeycomb substrate, a cordierite wall-flow type monolithic honeycomb substrate, a metal honeycomb substrate, or the like.

[0084] 〈Catalyst coating〉

[0085] The catalyst coating layer in the exhaust gas purification catalyst device of the present invention contains the catalytic noble metal particles of the present invention.

[0086] The catalytic noble metal particles in the catalyst coating layer may be in the form of a supported catalyst for exhaust gas purification in which the catalytic noble metal particles are supported on inorganic oxide support particles, for example.

[0087] The catalyst coating in the exhaust gas purification catalyst device of the present invention may contain any component in addition to the catalytic noble metal particles or the supported catalyst for exhaust gas purification. Such an optional component may be, for example, inorganic oxide particles other than the inorganic oxide support particles, a binder, and the like.

[0088] The exhaust gas purification catalyst device of the present invention can be manufactured by any method. A typical manufacturing method is to apply a catalyst coating forming slurry on a substrate and then calcine it, wherein the catalyst coating forming slurry contains: catalyst noble metal particles or exhaust gas purification supported catalyst; and any components contained as needed.

[0089] The catalyst coating layer forming slurry may have a known composition except for the catalytic noble metal particles or the exhaust gas purification supported catalyst of the present invention. The catalyst coating layer forming slurry may be applied to the substrate and calcined by a known method or a method in accordance with a known method.

[0090] <Method for producing catalytic noble metal particles>

[0091] The catalytic noble metal particles of the present invention can be produced, for example, by a method comprising reacting a solution containing a Pt precursor and a Pd precursor with a solution containing an organic base in a microreactor.

[0092] By reacting a solution containing a Pt precursor and a Pd precursor with a solution containing an organic base, a coprecipitate containing a Pt precursor and a Pd precursor can be obtained. By calcining the coprecipitate in the presence or absence of appropriate inorganic oxide carrier particles, catalyst noble metal particles can be obtained. Here, if the coprecipitate is calcined in the presence of inorganic oxide carrier particles, a supported catalyst for exhaust gas purification in which catalyst noble metal particles are supported on inorganic oxide carrier particles can be obtained. If the coprecipitate is calcined in the absence of inorganic oxide carrier particles, catalyst noble metal particles can be obtained.

[0093] <Solution containing Pt precursor and Pd precursor>

[0094] The Pt precursor may be a salt soluble in a solvent, specifically, for example, a nitrate, sulfate, or complex salt of Pt. The Pd precursor may be a salt soluble in a solvent, specifically, for example, a nitrate, sulfate, or halide of Pd.

[0095] The ratio of Pt to Pd in ​​the solution can be appropriately set according to the desired ratio of Pt to Pd in ​​the catalytic noble metal particles.

[0096] The solvent of the solution containing the Pt precursor and the Pd precursor is not particularly limited as long as it can dissolve the Pt precursor and the Pd precursor. The solvent may be, for example, one or more selected from water and a water-soluble organic solvent, and typically water.

[0097] The concentrations of Pt and Pd in ​​the solution can be appropriately set within the range in which the Pt precursor and the Pd precursor are soluble. The total concentration of the Pt precursor and the Pd precursor may be, for example, 1% by mass or more or 5% by mass or less and 25% by mass or less than 20% by mass.

[0098] <Solution containing organic base>

[0099] The organic base may be an amine, a quaternary ammonium salt, a nitrogen atom-containing heterocyclic compound, a basic amino acid or the like.

[0100] The amine may be, for example, pyridine, triethylamine, etc.;

[0101] The quaternary ammonium salt may be, for example, tetramethylammonium hydroxide, tetraethylammonium hydroxide, etc.

[0102] The heterocyclic compound containing a nitrogen atom may be, for example, diazabicycloundecene, 1,8-bis(dimethylamino)naphthalene, 1,8-bis(diethylamino)naphthalene, etc.;

[0103] Examples of the basic amino acid include lysine, arginine, histidine, and tryptophan.

[0104] The organic base may be one or more selected from amines and quaternary ammonium salts.

[0105] The solvent of the solution containing the organic base is not particularly limited as long as it can dissolve the organic base. The solvent may be, for example, one or more selected from water and a water-soluble organic solvent, and typically water.

[0106] The concentration of the organic base in the solution can be appropriately set within the range in which the organic base is soluble. The total concentration of the organic base is, for example, 5 mass % or more or 10 mass % or more and 30 mass % or less or 25 mass % or less.

[0107] <Usage ratio of the solution containing the Pt precursor and the Pd precursor and the solvent containing the organic base>

[0108] The ratio of the solvent used in the solution containing the Pt precursor and the Pd precursor and the solution containing the organic base can be set within a range in which the coprecipitation reaction of the Pt precursor and the Pd precursor proceeds rapidly and uniformly.

[0109] Regarding the usage ratio of the solvent of the solution containing a Pt precursor and a Pd precursor and the solution containing an organic base, the ratio of the molar amount of the organic base contained in the solution containing the organic base to the total molar amount of Pt and Pd contained in the solution containing the Pt precursor and the Pd precursor can be 0.5 times the molar amount or more, 1 times the molar amount or more, 2 times the molar amount or more, 3 times the molar amount or more, 4 times the molar amount or more, or 5 times the molar amount or less, and can be 12 times the molar amount or less, 10 times the molar amount or less, 8 times the molar amount or less, 6 times the molar amount or less, or 5 times the molar amount or less.

[0110] The ratio of the molar amount of the organic base to the total molar amount of Pt and Pd can be typically 0.5 times or more and 10 times or less.

[0111] 〈Microreactor〉

[0112] The method for producing catalytic noble metal particles of the present invention is characterized in that a solution containing a Pt precursor and a Pd precursor and a solution containing an organic base are reacted in a microreactor.

[0113] The microreactor in this specification refers to a flow-through reactor in which the volume (reaction volume) of the reaction field (mixer part) where the first reaction stock solution (a solution containing a Pt precursor and a Pd precursor) and the second reaction stock solution (a solution containing an organic base) come into contact is less than 1.0 mL, less than 0.5 mL, less than 0.3 mL, less than 0.2 mL, or less than 0.1 mL.

[0114] The reaction volume of the microreactor may be 0.01 mL or more, 0.03 mL or more, 0.05 mL or more, or 0.07 mL or more.

[0115] The type of reaction field is arbitrary, for example, it can be a T-shaped, J-shaped, V-shaped, interdigital triangle type, interdigital rectangle type, superfocus type, cyclone type, pillar type, disc type, collision type, capillary type, slit type or other appropriate form.

[0116] The heat transfer coefficient of the reaction field of the microreactor can be relatively high, for example, 1 MW / (m 3 ·K) and above and 500MW / (m 3 By setting the heat transfer coefficient of the reaction field of the microreactor within this range, the reaction heat generated when the first reaction stock solution contacts the second reaction stock solution can be efficiently dissipated. This can avoid local temperature rise and ensure the uniformity of the reaction.

[0117] Regarding the supply amount of the reaction stock solution to the microreactor, the total supply amount of the first reaction stock solution and the second reaction stock solution can be 50 mL / minute or more, 75 mL / minute or more, 100 mL / minute or more, 125 mL / minute or more, or 150 mL / minute or less, 450 mL / minute or less, 400 mL / minute or less, 350 mL / minute or less, 300 mL / minute or less, or 250 mL / minute or less.

[0118] The reaction temperature may be a temperature at which the first reaction stock solution and the second reaction stock solution are in a liquid state, for example, may be above 0°C, above 10°C, above 20°C, above 30°C, above 40°C, above 50°C, or above 60°C, and may be below 100°C, below 90°C, below 80°C, below 70°C, below 60°C, below 50°C, or below 40°C.

[0119] The first reaction stock solution and the second reaction stock solution stay in the reaction field of the microreactor for a very short time. Therefore, the reaction temperature can be controlled by adjusting the temperature of the first reaction stock solution and the second reaction stock solution to a predetermined temperature before introducing them into the microreactor.

[0120] The catalytic noble metal particles or the supported catalyst for exhaust gas purification of the present invention are obtained as described above. The obtained catalytic noble metal particles or the supported catalyst for exhaust gas purification can be classified as necessary and used.

[0121] Example

[0122] <Example 1>

[0123] (1) Preparation of precious metal particles for exhaust gas purification catalysts

[0124] (i) Preparation of coprecipitate slurry

[0125] An aqueous platinum nitrate solution containing 0.0909 g (0.466 mmol) of platinum nitrate in terms of Pt metal and an aqueous palladium nitrate solution containing 0.909 g (8.54 mmol) of palladium nitrate in terms of Pd metal were mixed to obtain a reaction stock solution A. The total amount of Pt and Pd in ​​terms of metal in the reaction stock solution A was 1.0 g (9.01 mmol), and the composition ratio of Pt / (Pt+Pd) was 9.10 mass %.

[0126] On the other hand, a tetraethylammonium hydroxide (TEAH) aqueous solution containing 10.61 g (72.07 mmol) of TEAH was prepared and used as a reaction stock solution B.

[0127] The contact between the reaction stock solution A and the reaction stock solution B is carried out using a disk-type microreactor in which the gap between the fixed disk and the rotating disk is used as a reaction field (mixer). The above-mentioned reaction stock solution A and reaction stock solution B are supplied to the microreactor, and are contacted and reacted in the reaction field of the microreactor to obtain a slurry containing a coprecipitate (coprecipitate slurry). The conditions of the microreactor at this time are as follows.

[0128] Reaction volume: 85mm 3 (0.085mL)

[0129] Disc diameter: 100mm

[0130] Rotation speed of rotating disk: 1000rpm

[0131] The temperature of reaction stock solution A and B: 50℃ respectively

[0132] Flow rate of reaction stock solution A and B: 200 mL / min in total

[0133] In Example 1, the reaction was performed by adjusting the supply rates of the reaction stock solutions A and B so that the molar ratio of TEAH / (Pt+Pd) became 8.0.

[0134] (ii) Supporting of Catalytic Noble Metal Particles on Oxide Supports

[0135] The coprecipitate slurry obtained above was added to the slurry obtained by mixing alumina powder and ion exchange water, and stirred for 30 minutes. Then, the solid matter was filtered out, dried at 120°C for 8 hours, and calcined at 500°C in an electric furnace for 1 hour, thereby supporting the catalyst precious metal particles composed of Pt-Pd alloy on the alumina, thereby obtaining a supported catalyst for exhaust gas purification. At this time, the amount of ion exchange water used was adjusted so that the solid content concentration in the reaction mixture became 30% by mass. In addition, the coprecipitate slurry used contained: 0.0909g (0.466mmol) of Pt precursor calculated as Pt metal and 0.909g (8.54mmol) of Pd precursor calculated as Pd metal relative to 99.0g of alumina powder.

[0136] (2) Evaluation of the particle size of the catalyst noble metal particles, the standard deviation of the particle size, and the standard deviation of the composition (initial value)

[0137] The particle size and standard deviation of the particle size and the standard deviation of the composition of the catalytic noble metal particles in the obtained exhaust gas purification supported catalyst were investigated by scanning transmission electron microscopy-energy dispersive X-ray spectroscopy (STEM-EDX).

[0138] Specifically, the obtained exhaust gas purification supported catalyst was observed by STEM, and the particle diameters of 50 randomly selected catalyst noble metal particles were measured, and the average particle diameter was obtained as the number mean, and the standard deviation σ of the particle diameter was calculated. rad In addition, elemental analysis based on EDX was performed on the same 50 catalyst noble metal particles to obtain the composition of each catalyst noble metal particle and calculate the standard deviation σ of Pt / (Pt+Pd). com .

[0139] The average particle size of the catalytic noble metal particles of the exhaust gas purification supported catalyst in Example 1 immediately after preparation was 3.44 nm, and the standard deviation σ of the particle size was rad The standard deviation of Pt / (Pt+Pd) is 0.62nm. com It is 2.22 mass %.

[0140] (3) Evaluation of supported catalysts for exhaust gas purification

[0141] (i) Heat durability treatment

[0142] 10 g of the obtained exhaust gas-purifying supported catalyst powder was placed in a tubular endurance furnace having a diameter of 65 mm and a length of 900 mm (capacity of 3000 mL), and subjected to a heat endurance treatment under the following conditions.

[0143] First, while making N 2 The gas was circulated at a flow rate of 10 L / min, and the catalyst temperature was raised from 20°C to 1050°C over 5 hours at a heating rate of about 3.43°C / min. Then, the catalyst temperature was maintained at 1050°C, and the model gas was switched between a rich atmosphere and a lean atmosphere every 5 minutes while being circulated at a flow rate of 10 L / min to perform a 5-hour heat durability treatment. 2 The gas was flowed at a flow rate of 10 L / min, and the catalyst temperature was lowered from 1050° C. to 20° C. over 5 hours at a temperature lowering rate of about 3.43° C. / min.

[0144] The compositions of the model gases of the rich atmosphere and the dilute atmosphere used for the above-mentioned heat durability treatment are respectively as follows.

[0145] 〈Model gas of rich atmosphere〉

[0146] CO: 2% by volume

[0147] H 2 O: 10% by volume

[0148] N 2 :margin

[0149] <Model gas for dilute atmosphere>

[0150] O2 : 5 volume%

[0151] H 2 O: 10% by volume

[0152] N 2 :margin

[0153] (ii) Exhaust purification test

[0154] After the above-mentioned heat-resistant treated exhaust gas purification supported catalyst is compression molded, crushed and classified to form irregular shaped particles of 1.0 to 2.0 mm in size. 1.0 g of the obtained particles are loaded into a tubular reactor with a diameter of 10.0 mm and a length of 55 mm (capacity of 4.3 mL). Here, while the exhaust model gas is circulated at a flow rate of 8 L / min, after pre-treatment at a catalyst temperature of 700°C for 5 minutes, the exhaust model gas is maintained to circulate while cooling to 80°C.

[0155] Next, while maintaining the flow of the exhaust gas model, the catalyst temperature was raised at a heating rate of 35°C / min, and the temperature at which the purification rates of propane and propylene in the model gas reached 50% was taken as the propane 50% purification temperature (T50 (°C) 3 H 8 )) and propylene 50% purification temperature (T50(C 3 H 6 )).

[0156] The composition of the exhaust gas model gas used in the exhaust gas purification test is as follows.

[0157] 〈Exhaust model gas〉

[0158] Propane (C 3 H 8 )): 600ppm

[0159] Propylene (C 3 H 6 ): 2400ppm

[0160] CO: 11.1% by volume

[0161] O 2 : 0.77 volume %

[0162] NO: 2111ppm

[0163] CO: 5600ppm

[0164] H 2 : 2000ppm

[0165] H 2 O: 10% by volume

[0166] N 2 :margin

[0167] The unit “ppm” of the component concentration in the above-mentioned exhaust model gas is a value based on volume.

[0168] The propane 50% purification temperature (T50 (°C) of the supported catalyst for exhaust gas purification of Example 1 3 H 8 )) is 325.0℃, propylene 50% purification temperature (T50(C 3 H 6 )) is 262.9℃.

[0169] (iii) Evaluation of the particle size and standard deviation of the particle size and the standard deviation of the composition of the catalyst noble metal particles (after durability)

[0170] The particle size, standard deviation of the particle size, and standard deviation of the composition of the catalyst noble metal particles after the thermal durability treatment were investigated using the same method as in the above-mentioned "(2) Evaluation of the particle size of the catalyst noble metal particles, the standard deviation of the particle size, and the standard deviation of the composition (initial value)". The average particle size of the catalyst noble metal particles of the exhaust gas purification supported catalyst after durability in Example 1 was 31.0 nm, and the standard deviation of the particle size σ rad The standard deviation of Pt / (Pt+Pd) is 11.3nm. com It is 0.58 mass %.

[0171] <Examples 2 to 5>

[0172] In "(i) Preparation of coprecipitate slurry", except that the amount of TEAH contained in the reaction stock solution B was changed as described in Table 1, and the molar ratio of TEAH / (Pt+Pd) was adjusted as described in Table 1, exhaust gas purification supported catalysts were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2.

[0173] In “(ii) Supporting of Catalytic Noble Metal Particles on Oxide Support”, the amount of ion-exchanged water used was adjusted so that the solid content concentration in the reaction mixture would be 30% by mass.

[0174] <Comparative Examples 1 to 3>

[0175] In "(i) Preparation of coprecipitate slurry", except that a flask was used instead of a microreactor, the amounts of reaction stock solution A and reaction stock solution B were changed, and the molar ratio of TEAH / (Pt+Pd) was adjusted as described in Table 1, exhaust gas purification supported catalysts were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 2.

[0176] In “(ii) Supporting of Catalytic Noble Metal Particles on Oxide Support”, the amount of ion-exchanged water used was adjusted so that the solid content concentration in the reaction mixture would be 30% by mass.

[0177] In Comparative Example 3, the reaction stock solution B was not used, and the reaction stock solution A was directly provided to the "(ii) Supporting of Catalytic Noble Metal Particles on the Oxide Support" to prepare an exhaust gas purification catalyst.

[0178] <Example 6>

[0179] A supported catalyst for exhaust gas purification was prepared in the same manner as in Example 3, except that a TMAH aqueous solution containing 3.29 g (36.04 mmol) of tetramethylammonium hydroxide (TMAH) was used as the reaction stock solution B, and various evaluations were performed.

[0180] <Comparative Example 4>

[0181] A supported catalyst for exhaust gas purification was prepared in the same manner as in Comparative Example 2, except that a TMAH aqueous solution containing 3.29 g (36.04 mmol) of tetramethylammonium hydroxide (TMAH) was used as the reaction stock solution B, and various evaluations were performed.

[0182] <Reference Example 1 and Examples 7 to 12>

[0183] In "(i) Preparation of coprecipitate slurry", the amounts of platinum nitrate and palladium nitrate contained in the reaction stock solution A were changed as shown in Table 5 to maintain the total amount of Pt and Pd in ​​terms of metal conversion at 1.0 g, and the mass ratio of Pt / (Pt+Pd) was set as shown in Table 5, and the amount of TEAH contained in the reaction stock solution B was changed as shown in Table 5 to adjust the molar ratio of TEAH / (Pt+Pd) to 4.0. Other than this, exhaust gas purification supported catalysts were prepared in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 6.

[0184] In “(ii) Supporting of Catalytic Noble Metal Particles on Oxide Support”, the amount of ion-exchanged water used was adjusted so that the solid content concentration in the reaction mixture would be 30% by mass.

[0185] <Comparative Examples 5 to 11>

[0186] Except for using a flask instead of a microreactor in "(i) Preparation of coprecipitate slurry", exhaust gas purification supported catalysts were prepared in the same manner as in Reference Example 1 and Examples 7 to 12, and various evaluations were performed. The results are shown in Table 6.

[0187] in addition, Figure 1 The standard deviation σ of the composition of the catalyst noble metal particles in Examples 1 to 5 and Comparative Examples 1 to 3 is shown. COM Propane 50% purge temperature (T50(C 3 H 8 ))’s relationship curve.

[0188] also, Figure 2 The composition of the catalyst noble metal particles (Pt / (Pt+Pd) ratio) and the propane 50% purification temperature (T50 (°C)) in Examples 7 to 12 and Comparative Examples 5 to 11 are shown. 3 H 8 ))’s relationship curve.

[0189]

[0190]

[0191]

[0192]

[0193]

[0194]

[0195] From Tables 1 to 6 and Figure 1 and Figure 2 The results show the following.

[0196] Contains the standard deviation of the composition σ con The exhaust gas purification supported catalysts of Comparative Examples 1 to 4 and Comparative Examples 7 to 11, which contained more than 3.0 mass% of the catalyst noble metal particles (initial value), contained Pt. However, these exhaust gas purification supported catalysts had a lower propane 50% purification temperature (T50 (°C) than the exhaust gas purification supported catalyst of Comparative Example 5 which did not contain Pt. 3 H 8 )) is almost not reduced, therefore, for saturated hydrocarbons (C 3 H 8 )'s purification capacity has hardly improved.

[0197] In contrast, the standard deviation σ of the compositioncon The exhaust gas purification supported catalysts of the present invention shown in Examples 1 to 5 and Examples 7 to 12, in which the catalyst noble metal particles (initial value) are 3.0 mass % or less, do not impair the resistance to unsaturated hydrocarbons (C 3 H 6 ) and improves the purification capacity for saturated hydrocarbons (C 3 H 8 ) purification capacity. The exhaust gas purification supported catalyst of the present invention has a purification capacity for saturated hydrocarbons (C 3 H 8 ) purification capacity improvement (propane 50% purification temperature (T50 (C 3 H 8 )) of the decrease Figure 1 It is also prominently shown in.

[0198] It has been verified that such effects of the present invention are exhibited in a wide range of the Pt / (Pt+Pd) ratio in the catalytic noble metal particles and the TEHA / (Pt+Pd) ratio when producing the catalytic noble metal particles.

[0199] Especially if Figure 2 As can be seen in FIG. 1 , when the Pt / (Pt+Pd) ratio is the same, the exhaust gas purification supported catalyst of the embodiment including the catalytic noble metal particles of the present invention has a propane 50% purification temperature (T50 (° C.)) higher than that of the exhaust gas purification supported catalyst of the comparative example. 3 H 8 )) is reduced, so it is verified that for saturated hydrocarbons (C 3 H 8 )’s purification capacity is improved.

[0200] In addition, in the exhaust gas purification supported catalyst of the comparative example including the catalytic noble metal particles produced by the method in the prior art, the optimum range of the Pt / (Pt+Pd) ratio is relatively narrow. In contrast, in the exhaust gas purification supported catalyst of the embodiment including the catalytic noble metal particles produced by the method using a microreactor of the present invention, it was verified that a high saturated hydrocarbon purification capability is exhibited in a wide range of the Pt / (Pt+Pd) ratio.

[0201] Furthermore, by comparing Example 6 with Comparative Example 4, it was confirmed that the effects of the present invention were also achieved when TMAH was used instead of TEAH.

Claims

1. A catalyst noble metal particle for exhaust gas purification, which is composed of an alloy containing Pt and Pd, The standard deviation σ of the composition expressed by the ratio of the mass of Pt to the total mass of Pt and Pd in ​​the catalytic noble metal particles, that is, Pt / (Pt+Pd) COM It is 3.0 mass % or less.

2. The catalyst noble metal particle according to claim 1, wherein the standard deviation of the composition is COM It is 2.5 mass % or less. 3 . The catalytic noble metal particle according to claim 1 , wherein the composition (Pt / (Pt+Pd)) is 1.0 mass % or more and 70 mass % or less. 4 . The catalytic noble metal particle according to claim 3 , wherein the composition (Pt / (Pt+Pd)) is 3.0 mass % or more and 40 mass % or less. 5 . The catalytic noble metal particle according to claim 1 , wherein the average particle diameter of the catalytic noble metal particle is 2.0 nm or more and 5.0 nm or less.

6. The catalyst noble metal particle according to claim 5, wherein the standard deviation σ of the particle diameter of the catalyst noble metal particle is rad It is less than 2.0nm.

7. The catalyst noble metal particle according to claim 6, wherein the standard deviation σ of the particle diameter of the catalyst noble metal particle is rad It is less than 1.5nm. 8 . The catalytic noble metal particle according to claim 1 , wherein a coefficient of variation of the composition of the catalytic noble metal particle is 0.45 or less. 9 . A method for producing catalytic noble metal particles, the method for producing the catalytic noble metal particles according to any one of claims 1 to 7, comprising: reacting a solution containing a Pt precursor and a Pd precursor with a solution containing an organic base in a microreactor.

10. The production method according to claim 9, wherein the organic base is selected from amines and quaternary ammonium salts. 11 . The production method according to claim 9 , wherein the amount of the organic base is 0.5 times or more and 10 times or less the total molar amount of Pt and Pd contained in the solution containing the Pt precursor and the Pd precursor. 12 . A supported catalyst for purifying exhaust gas, comprising inorganic oxide support particles and the catalytic noble metal particles according to claim 1 supported on the inorganic oxide support particles.

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