JP6398918B2 - Exhaust gas purification catalyst material manufacturing method, exhaust gas purification catalyst material, and exhaust gas purification catalyst including the exhaust gas purification catalyst material - Google Patents

Description

  The present invention relates to a method for producing a catalyst material for purifying hydrocarbons (HC) contained in engine exhaust gas, a catalyst material, and an exhaust gas purifying catalyst containing the catalyst material.

  Conventionally, as a method for supporting a catalyst metal on a support material made of an inorganic oxide, an evaporating and drying method and an impregnation supporting method are known and commonly used.

  As the support material, a material having a high specific surface area having pores on the surface is generally used. This is because by disposing the catalyst metal in the pores, the catalyst metal is prevented from moving and aggregating on the surface of the support material.

  On the other hand, from the viewpoint of enhancing the contact property of the catalyst metal with the exhaust gas, it is desirable to dispose the catalyst metal in a highly dispersed state not only in the pores but also on the entire support material surface. However, it is difficult to dispose a large amount of catalyst metal on the surface of the support material other than in the pores by the evaporation to dryness method or the impregnation support method.

  Therefore, a method is known in which noble metal particles are dispersed and supported on a support made of a Ce-containing composite oxide as a support material (see, for example, Patent Document 1).

  According to the method of Patent Document 1, after supporting noble metal particles on a Ce-containing composite oxide, it is protected with organic molecules, and this is subjected to heat treatment in an inert gas atmosphere, followed by air or oxygen atmosphere, Remove carbides. According to this method, it is possible to suppress the catalyst metal from being thermally transferred and aggregated during the heat treatment.

JP 2009-247955 A

  However, in the method of Patent Document 1, when the noble metal particles are first supported on the carrier, the noble metal complex ions are electrostatically adsorbed on the carrier surface and chemically reduced with a reducing agent. In this method, it is unclear whether a large amount of the catalytic metal can be supported not only in the pores but also on the surface other than the pores.

  Therefore, in the present invention, the catalyst metal is supported in a highly dispersed state not only in the pores of the support material but also in the entire surface, thereby improving the contact property of the catalyst metal with the exhaust gas and improving the catalyst performance of the catalyst material. This is the issue.

  In order to solve the above problems, in the present invention, the catalyst metal is supported on the carbon particles, and then supported on the support material, and then fired in a non-oxidizing atmosphere.

That is, a method of producing an exhaust gas purifying catalyst material according to the present invention, a catalyst metal, the catalyst metal is a manufacturing method of an exhaust gas purifying catalyst material containing an inorganic oxide particles supported, the catalyst A mixing step of mixing a solution containing a metal salt and a dispersion of carbon particles having a porosity of 50% or more to obtain a mixed solution, a stirring step of stirring the mixed solution, and the stirred mixed solution A step of contacting the inorganic oxide particles with the inorganic oxide particles to obtain an inorganic oxide particle-containing mixed solution, and a baking step of drying the inorganic oxide particle-containing mixed solution and firing at a temperature of 600 ° C. or less in a non-oxidizing atmosphere. It is characterized by comprising.

  According to the present invention, the catalyst metal is supported on the surface or inside of the carbon particles, then supported on the surface of the inorganic oxide particles, and fired in a non-oxidizing atmosphere. A carbon layer derived from is formed, and the catalytic metal is supported on the carbon layer. As a result, the catalyst metal hardly enters the pores on the surface of the inorganic oxide particles, and the catalyst metal can be supported in a highly dispersed state not only in the pores but also on the entire surface. In the present invention, the “porosity” of the carbon particles refers to the pore volume (%) per unit volume of the carbon particles.

  The catalyst metal is at least one selected from the group of Pt, Pd, and Rh. These may be used alone or in combination of two or more.

  In a preferred embodiment, the average primary particle diameter of the carbon particles is in the range of 30 nm to 50 nm. And it is preferable that the average secondary particle diameter of a carbon particle is larger than the average pore diameter of an inorganic oxide particle. This makes it difficult for the carbon particles carrying the catalyst metal to enter the pores of the inorganic oxide particles, so that the catalyst metal is less likely to be taken into the pores on the surface of the inorganic oxide particles, and only within the pores. In addition, the catalyst metal can be supported on the entire surface in a highly dispersed state.

  The inorganic oxide particles are preferably activated alumina particles, Ce-containing Zr-based composite oxide particles, Ce-free Zr-based composite oxide particles, and the like.

  In a preferred embodiment, the ratio of the mass of the catalyst metal to the mass of the carbon particles (catalyst metal / carbon particles) mixed in the mixing step is in the range of 1/10 to 1/2. Thereby, the catalyst metal can be supported on the carbon particles in a highly dispersed state.

Exhaust gas purification catalyst member of the present invention is a catalyst material for exhaust gas purification produced by the above production method, the inorganic oxide particle surface, the carbon layer in which the catalytic metal is supported is formed It is characterized by being. The carbon layer is formed by firing in a state where carbon particles are aggregated. Since the carbon particles are porous, the dispersibility of the catalyst metal is high, the contact property with the exhaust gas is increased, and the catalyst performance is improved.

The exhaust gas purifying catalyst material according to the present invention is manufactured by the above manufacturing method, wherein the catalytic metal is Pt, and after calcination at 600 ° C. for 2 hours in a non-oxidizing atmosphere, The crystallite diameter of Pt is in the range of 30 nm to 50 nm. Thereby, contact property with exhaust gas increases and catalyst performance improves.

The exhaust gas purifying catalyst material according to the present invention is manufactured by the above manufacturing method, wherein the catalytic metal is Pd, and after calcination at 600 ° C. for 2 hours in a non-oxidizing atmosphere, The crystallite diameter of the Pd is in the range of 40 nm to 50 nm. Thereby, contact property with exhaust gas increases and catalyst performance improves.

The exhaust gas purifying catalyst material according to the present invention is manufactured by the above manufacturing method, wherein the catalytic metal is Rh, and after calcination at 600 ° C. for 2 hours in a non-oxidizing atmosphere, The Rh crystallite diameter is in the range of 5 nm to 20 nm. Thereby, contact property with exhaust gas increases and catalyst performance improves.

An exhaust gas purifying catalyst according to the present invention includes a base material and a catalyst layer provided on an exhaust gas passage wall of the base material, and the catalyst layer is any one of the exhaust gases described above. A catalyst material for purification is included. Thereby, HC contained in the exhaust gas can be effectively purified.

  In a preferred embodiment, the exhaust gas purifying catalyst according to the present invention is suitably used for purifying exhaust gas components of engines that perform premixed compression auto-ignition (HCCI) combustion. In a particularly preferred aspect, the present invention is suitably used for purifying exhaust gas components of an engine that performs HCCI combustion over the entire region from the low load side to the high load side of the engine. In an engine that performs HCCI combustion, the exhaust gas temperature is low, and the exhaust gas contains a large amount of saturated hydrocarbons (n-pentane, i-pentane) having 5 carbon atoms and CO. In the exhaust gas purifying catalyst according to the present invention, the catalytic metal is supported on the carbon particles. The carbon particles have a high specific surface area, and the catalyst metal exists in a highly dispersed state. Further, the carbon particles are not easily burned out and maintain the dispersibility of the catalyst metal. Thereby, even if exhaust gas is low temperature, a catalyst metal is easy to activate and the purification | cleaning performance excellent about the said saturated hydrocarbon is shown.

  According to the present invention, the catalyst metal is supported on the surface or inside of the carbon particles, then supported on the surface of the inorganic oxide particles, and fired in a non-oxidizing atmosphere. A carbon layer derived from is formed, and the catalytic metal is supported on the carbon layer. As a result, the catalyst metal hardly enters the pores on the surface of the inorganic oxide particles, and the catalyst metal can be supported in a highly dispersed state not only in the pores but also on the entire surface.

FIG. 1 is a schematic cross-sectional view showing an exhaust gas purifying catalyst according to an embodiment of the present invention. FIG. 2 is a schematic enlarged cross-sectional view of the catalyst material shown in FIG. FIG. 3 is a flowchart showing the method for manufacturing the catalyst material according to the present embodiment. FIG. 4 is a transmission electron microscope image of the catalyst material surface when the catalyst material according to Example 1 is aged at 800 ° C. for 2 hours in the atmosphere. FIG. 5 is a transmission electron microscope image of the catalyst material surface when the catalyst material according to Comparative Example 1 is aged at 800 ° C. for 2 hours in the atmosphere.

  Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. The following description of the preferred embodiments is merely exemplary in nature and is not intended to limit the invention, its application, or its use.

  FIG. 1 shows a basic configuration of a catalyst layer of an exhaust gas purifying catalyst D suitable for purifying exhaust gas of an engine according to this embodiment.

  In the figure, a catalyst layer 2 is formed on a cell wall (exhaust gas passage wall) 1 of a carrier (base material) S.

<Catalyst layer>
As shown in FIG. 1, the catalyst layer 2 contains a catalyst material 11. The catalyst material 11 contains inorganic oxide particles 3. A carbon layer 4 derived from carbon particles 4 ′ is formed on the surface of the inorganic oxide particles 3, and a catalyst metal 5 is supported on the carbon layer 4. The binder material 6 is interposed between the particles of the catalyst material 11.

  The inorganic oxide particles 3 have a role as a support material for supporting the catalyst metal 5, and specifically include, for example, activated alumina particles, Ce-containing Zr-based composite oxides, Ce-free Zr-based composite oxides, and the like. Can be used.

The activated alumina particles are excellent in heat resistance and durability, and have a large specific surface area and high dispersibility of the catalyst metal. By supporting the catalyst metal 5 on the activated alumina particles, the dispersibility of the catalyst metal 5 is improved, the contact area with the exhaust gas is increased, and the catalyst performance is improved. The alumina can be used as the Zr-La-containing alumina is La-containing alumina carrying a Zr-based composite oxide containing La-containing alumina containing _La 2 _{O 3} 4% by weight, the Zr. In addition, the average pore diameter of the activated alumina particles is about 10 nm to 60 nm.

  The Ce-containing Zr-based composite oxide is an oxygen storage / release material, and has an excellent oxygen storage / release capability based on a reversible reaction accompanied by a change in the valence of Ce. Even if fluctuates, the Ce-containing Zr-based composite oxide absorbs fluctuations in air fuel consumption by occluding and releasing oxygen. By supporting the catalyst metal 5 on such a Ce-containing Zr-based composite oxide, the air-fuel consumption window in which the catalyst metal 5 effectively works for purification of HC or the like is expanded. The Ce-containing Zr-based composite oxide may further contain a rare earth metal other than Ce in addition to Ce. The rare earth metal other than Ce is, for example, Nd, Y, La, Sc, etc., and particularly preferably Nd. Note that the average pore diameter of the Ce-containing Zr-based composite oxide is about 10 nm to 100 nm.

  The Ce-free Zr-based composite oxide can undergo an oxygen ion exchange reaction and releases active oxygen without changing the valence of metal ions. By supporting the catalyst metal 5 on such a Ce-free Zr-based composite oxide, the catalyst performance of the catalyst metal 5 is improved. The Ce-free Zr-based composite oxide may further contain a rare earth metal other than Ce in addition to Ce. The rare earth metal other than Ce is, for example, Nd, Y, La, Sc, etc., and particularly preferably La, Y. The average pore diameter of the Ce-free Zr-based composite oxide is about 20 nm to 80 nm.

  The catalyst metal 5 is at least one selected from the group of Pt, Pd, and Rh. Thereby, HC in the exhaust gas can be effectively purified.

  As the binder material 6, for example, Ce-containing Zr-based composite oxide having oxygen storage / release ability, Ce-free Zr-based composite oxide fine particles having oxygen ion conductivity, or the like can be used. Thereby, even when the exhaust gas atmosphere is inclined to either lean or rich, the binder material 6 releases active oxygen, or the binder material 6 takes in oxygen from the surroundings and releases active oxygen. As a result, exhaust gas purification can be promoted. In addition, a catalyst metal supported on and dissolved in these fine particles may be used. Thereby, since binder material also has catalyst performance, the contact property of exhaust gas and a catalyst metal improves, and catalyst performance improves effectively.

  In the catalyst material 11 according to the present embodiment, as shown in FIG. 2, the carbon layer 4 derived from the carbon particles 4 ′ is formed on the surface of the inorganic oxide particles 3. A catalytic metal 5 is supported on the carbon layer 4. The carbon layer 4 may be formed entirely on the surface of the inorganic oxide particles 3 or may be partially formed.

  As the carbon particles 4 ′, those having a porosity of preferably 50% or more, more preferably 60% or more, and particularly preferably 70% or more are used from the viewpoint of maintaining the catalyst metal 5 in a highly dispersed state. desirable. The carbon particles 4 ′ are preferably hollow particles from the viewpoint of improving the dispersibility of the catalyst metal 5. Specifically, for example, carbon black, graphite, acetylene black (AB), ketjen black (KB), or the like can be used as the carbon particle 4 ′, and ketjen black (KB) can be used particularly preferably. .

  The carbon particles 4 'are preferably substantially spherical from the viewpoint of improving the contact property with the exhaust gas. The average primary particle diameter of the carbon particles 4 ′ is preferably in the range of 20 nm to 100 nm, more preferably 25 nm to 80 nm, and particularly preferably 30 nm to 50 nm. The carbon particles 4 ′ are usually present as secondary particles by aggregating a plurality of particles, and the average secondary particle size of the carbon particles 4 ′ is larger than the average pore size of the inorganic oxide particles 3. Is preferred. As a result, the carbon particles 4 ′ are not easily taken into the pores of the inorganic oxide particles 3, and as a result, the catalyst metal 5 supported on the carbon particles 4 ′ is hardly taken into the pores of the inorganic oxide particles 3.

<Method for producing catalyst material>
Next, a method for manufacturing the catalyst material 11 according to this embodiment will be described.

-Preparation of catalyst metal salt solution-
First, a catalyst metal salt solution is prepared. Specific examples of the salt of the catalytic metal 5 include a nitric acid solution of an amine-based complex such as a dinitrodiamine complex of the catalytic metal 5.

-Preparation of carbon particle dispersion-
The carbon particle dispersion can be prepared by adding an aqueous nitric acid solution and a solvent to the carbon particles and stirring them.

-Preparation of inorganic oxide particles-
Commercially available alumina particles can be used.

  Ce-containing Zr-based composite oxide particles and Ce-free Zr-based composite oxide particles can be prepared using a coprecipitation method. In the coprecipitation method, a basic solution is added to an acidic solution of a metal salt, preferably nitrate, contained in a composite oxide to obtain a hydroxide coprecipitate, and then the hydroxide is dried and pulverized. In this method, desired composite oxide particles are prepared by firing.

-Preparation of catalyst material-
The catalyst material 11 according to this embodiment can be prepared by the steps shown in FIG.

  First, as shown in FIG. 3, the catalyst metal salt solution and the carbon particle dispersion are mixed (S1).

  Thereafter, these mixed liquids are heated and stirred at a predetermined temperature for a predetermined time (S2). Thereby, a carbon mixed catalyst metal solution is obtained.

  In the mixing step S1, the ratio of the mass of the catalyst metal 5 to the mass of the carbon particles 4 ′ (catalyst metal / carbon particles) is preferably 1/10 or more and 1/2 or less, more preferably 1/10 or more and 2/5 or less. Especially preferably, it is the range of 1/10 or more and 3/10 or less. Thereby, the catalyst metal 5 can be supported on the carbon particles 4 ′ in a highly dispersed state.

  In the heating / stirring step S2, the heating temperature is preferably 65 ° C to 95 ° C, more preferably 70 ° C to 90 ° C, and particularly preferably 75 ° C to 85 ° C. The stirring time is preferably 30 minutes to 3 hours, more preferably 45 minutes to 2 hours, and particularly preferably 1 hour to 1.5 hours. Thereby, the catalyst metal salt can be supported on the carbon particles 4 ′ in a highly dispersed state.

  Then, the carbon mixed catalyst metal solution is brought into contact with the inorganic oxide particles 3 (S3). Specifically, for example, inorganic oxide particles are added to the carbon mixed catalyst metal solution, and mixed and stirred (S3). In addition, as this process S3, the evaporative drying method and the impregnation supporting method can be used.

  In this step S3, the mixing ratio of the inorganic oxide particles 3 is the ratio of the mass of the carbon particles 4 ′ to the mass of the inorganic oxide particles 3 (carbon particles 4 ′ / inorganic oxide particles 3), preferably 1/50. The range is 3/10 or less, more preferably 1/50 or more and 2.5 / 10 or less, and particularly preferably 1/50 or more and 1/10 or less. Thereby, the carbon particles 4 ′ on which the catalyst metal 5 is supported are supported in a highly dispersed state on the surface of the inorganic oxide particles 3, and a layer of the carbon particles 4 ′ is formed.

  The stirring time is preferably 5 minutes to 30 minutes, more preferably 10 minutes to 25 minutes, and particularly preferably 10 minutes to 20 minutes. Thereby, the carbon particles 4 ′ on which the catalyst metal 5 is supported are supported in a highly dispersed state on the surface of the inorganic oxide particles 3, and a layer of the carbon particles 4 ′ is formed.

  The mixture is dried and then calcined for a predetermined time at a predetermined temperature in a non-oxidizing atmosphere (S4), whereby catalyst metal-supported inorganic oxide particles that are the catalyst material 11 according to the present embodiment can be obtained.

The non-oxidizing atmosphere is, for example, in Ar, N ₂ or the like. Thereby, it can suppress that carbon particle burns down by an oxidation reaction.

  The firing temperature is preferably 600 ° C. or less, more preferably 550 ° C. or less, from the viewpoint of effectively suppressing aggregation of the catalyst metal during the firing process while holding the carbon particle 4 ′ layer and forming the carbon layer 4. Particularly preferably, it is 500 ° C. or lower.

  In addition, the rate of temperature rise (° C./hour) until the calcination temperature is preferably 150 ° C./hour or less, more preferably 120 ° C./hour or less, particularly preferably 100 from the viewpoint of suppressing aggregation of the catalyst metal. It is below ℃ / hour.

  The calcination time at the calcination temperature is preferably 1 hour or more and 4 hours or less from the viewpoint of effectively suppressing aggregation of the catalyst metal during the calcination step while holding the carbon particle 4 ′ layer and forming the carbon layer 4. More preferably, it is 1.5 hours or more and 3 hours or less, Most preferably, it is 1.5 hours or more and 2.5 hours or less.

  Although it is difficult to specify the thickness of the carbon layer 4 after the firing step S4 and the surface coverage on the inorganic oxide particles 3 by the carbon layer 4 at this time, the catalyst metal 5 supported on the carbon particles 4 ' From the viewpoint of improving the contact property with the exhaust gas, the thickness of the carbon layer 4 is preferably 1 μm or less, more preferably 500 nm or less, and particularly preferably 200 nm or less.

  As described above, the method for producing the catalyst material 11 according to the present embodiment is such that the catalyst particles 5 supported on the carbon particles 4 ′ are supported on the inorganic oxide particles 3 as the support material, and then non-oxidizing. The carbon layer 4 derived from the carbon particles 4 ′ carrying the catalyst metal 5 is formed on the surface of the inorganic oxide particles 3 by drying and firing under predetermined conditions in an atmosphere. .

  Thereby, the catalyst metal 5 is supported on the surface of the inorganic oxide particle 3 in a state of being supported on the surface of the carbon particle 4 ′ and in the pores. At this time, since the average secondary particle diameter of the carbon particles 4 ′ is larger than the average pore diameter of the surface of the inorganic oxide particles 3, most of the carbon particles 4 ′ are taken into the pores of the inorganic oxide particles 3. A layer of carbon particles 4 ′ is hardly formed on the surface of the inorganic oxide particles 3. Therefore, the catalyst metal 5 supported on the carbon particles 4 ′ is not easily taken into the pores on the surface of the inorganic oxide particles 3, and is supported on the layer of the carbon particles 4 ′ formed on the surface of the inorganic oxide particles 3. It is held in the state. And the catalyst material 11 by which the catalyst metal was carry | supported in the highly dispersed state by the carbon layer 4 formed in the inorganic oxide particle surface by performing the said baking can be obtained.

  Therefore, according to this configuration, as much catalyst metal 5 as possible is supported not only in the pores of the inorganic oxide particles 3 as the support material but also on the entire surface, thereby improving the contact property with the exhaust gas component. The purification performance of the catalyst material 11 is improved.

<Method for producing exhaust gas purification catalyst>
-Preparation of binder material-
The binder material 6 can be obtained, for example, by wet-grinding a Zr-based composite oxide.

-Loading of catalyst material 11 on a carrier-
The catalyst material 2 and the binder material 6 contained in the catalyst layer 2 are suspended in a solvent to prepare a slurry. After the carrier S is immersed in the slurry, the carrier S is dried, whereby the catalyst layer 2 is obtained. Can be formed on the cell wall 1 of the carrier S.

  The exhaust gas purification catalyst D according to the present embodiment can be suitably used for purification of exhaust gas components of an engine that performs HCCI combustion, and in particular, performs HCCI combustion in the entire region from the low load side to the high load side of the engine. It can be suitably used for purifying engine exhaust gas components.

  HCCI combustion is a combustion method in which gasoline in a combustion chamber is combusted by compression self-ignition in a lean atmosphere in accordance with the operating state of the engine. In the HCCI combustion, fuel gasoline is burned at a low temperature, and the exhaust gas contains a large amount of saturated hydrocarbons (n-pentane, i-pentane) and CO having 5 carbon atoms. In particular, in an engine that performs HCCI combustion in the entire region from the low load side to the high load side of the engine, the exhaust gas temperature decreases to about 100 ° C to 200 ° C. In such a low temperature state, in the conventional exhaust gas purifying catalyst, the agglomerated catalytic metal is not yet activated, and the saturated hydrocarbon and the like are discharged without being sufficiently oxidized and purified.

  In this regard, in the catalyst material 11 included in the exhaust gas purification catalyst D according to this embodiment, the catalyst metal 5 is supported on the carbon particles 4 ′. The carbon particles 4 ′ have a high specific surface area, and the catalyst metal 5 is held in a highly dispersed state. Further, in an engine that performs HCCI combustion, since the exhaust gas temperature is low, the carbon particles 4 ′ are not easily burned off and maintain the dispersibility of the catalytic metal 5, and thus the exhaust gas is at a low temperature. The catalyst metal 5 is easily activated and exhibits excellent catalytic performance.

  The loading amount of the catalyst material 11 on the carrier S (the loading amount per liter of the carrier. The same applies hereinafter) is preferably 50 g / L or more and 300 g / L or less, more preferably 70 g / L or more and 250 g / L or less, particularly Preferably they are 100 g / L or more and 200 g / L or less. The amount of the catalyst metal 5 supported on the carrier S is preferably 1 g / L or more and 15 g / L or less, more preferably 2 g / L or more and 10 g / L or less, and particularly preferably 4 g / L or more and 7 g / L or less. Thereby, exhaust gas HC can be effectively purified.

  Next, specific examples will be described.

  In Table 1, the structure of the catalyst material used for Examples 1-3 and Comparative Examples 1-3 is shown.

  As shown in Table 1, in Example 1 and Comparative Example 1, Pt was used as the catalyst metal 5 and activated alumina particles were used as the inorganic oxide particles. In Example 2 and Comparative Example 2, Pd was used as the catalyst metal 5, and activated alumina particles were used as the inorganic oxide particles. In Example 3 and Comparative Example 3, CeZrNdOx, which is a Ce-containing Zr-based composite oxide containing Rh as the catalyst metal 5 and Nd as the inorganic oxide particles, was used. In Examples 1 to 3, the carbon layer 4 is present, whereas in Comparative Examples 1 to 3, the carbon layer 4 is not present.

-Preparation of catalyst material-
[Example 1]
A 5 mass% dinitrodiamine Pt nitric acid solution was used as the catalyst metal salt solution.

  As a carbon particle dispersion, a mixture obtained by adding 25 mL of 0.1N nitric acid aqueous solution and 25 mL of ethanol to 2.5 g of Ketjen Black (KB) and stirring was used.

  4.70 g of the dinitrodiamine Pt nitric acid solution was added to the carbon particle dispersion and stirred for 3 hours while heating at 70 to 90 ° C. to obtain a carbon mixed Pt solution.

  After adding 10.0 g of La-containing alumina powder as inorganic oxide particles to the carbon-mixed Pt solution and mixing and stirring, the resulting mixture was dried, heated at 100 ° C./hour in an Ar atmosphere, and then 600 ° C. Was calcined for 2 hours to obtain Pt / carbon-supported alumina as a catalyst material.

[Comparative Example 1]
Pt was supported by evaporation to dryness using a 5% by mass dinitrodiamine Pt nitric acid solution with respect to the alumina powder, dried and then fired at 800 ° C. for 2 hours in the air to obtain Pt-supported alumina.

[Example 2]
Pd / carbon-supported alumina as a catalyst material was prepared in the same manner as in Example 1 except that a 5% by mass dinitrodiamine Pd nitric acid solution was used as the catalyst metal salt solution.

[Comparative Example 2]
Pd was supported on the alumina powder by evaporation to dryness using a 5% by mass dinitrodiamine Pd nitric acid solution, dried, and then fired in air at 800 ° C. for 2 hours to obtain Pd-supported alumina.

[Example 3]
As a catalyst metal salt solution, a 5% by mass dinitrodiamine Rh nitric acid solution was used.

  CeZrNdOx, which is a Ce-containing Zr-based composite oxide, was used as the inorganic oxide particles. CeZrNdOx was prepared as follows. That is, by dissolving cerium nitrate hexahydrate, zirconium oxynitrate, and neodymium nitrate hexahydrate in ion-exchanged water, and neutralizing the nitrate solution by mixing an 8-fold diluted solution of 28% by mass ammonia water. And obtained coprecipitate. The coprecipitate was washed with water by a centrifugal separation method, dried in air at a temperature of 150 ° C. overnight, pulverized, and then fired in air at a temperature of 500 ° C. for 2 hours to obtain a CeZrNdOx powder.

  After obtaining a carbon mixed Rh solution by the same method as in Example 1, the CeZrNdOx powder was added to and mixed with this solution. And it dried and baked on the conditions similar to Example 1, and prepared Rh / carbon carrying | support CeZrNdOx as a catalyst material.

[Comparative Example 3]
Rh was supported on the CeZrNdOx powder prepared in Example 3 by evaporating to dryness using a 5% by mass dinitrodiamine Rh nitric acid solution, dried, and then calcined in the atmosphere at 800 ° C. for 2 hours to obtain Rh-supported CeZrNdOx. It was.

-Dispersibility of catalytic metals in catalyst materials-
[Catalyst metal crystallite size]
The measurement results of the crystallite diameter of the catalyst metal after calcination at 600 ° C. for 2 hours in an Ar atmosphere in each of the catalyst materials of Examples 1 to 3 above and 800 ° C. in the atmosphere for each of the catalyst materials of Comparative Examples 1 to 2 hours Table 1 shows the measurement results of the crystallite diameter of the catalyst metal after calcination. The “crystallite diameter” is an X-ray diffractometer, and Scherrer's formula (crystallite diameter (hkl) = 0.9λ / (β1 / ₂ · cosθ), where hkl is the Miller index and λ is the characteristic. X-ray wavelength (angstrom), β _1/2 is the half width (radian) of the (hkl) plane, and θ is the X-ray reflection angle.

  As shown in Table 1, in the catalyst materials of Examples 1 to 3 in which the catalyst metal is supported using carbon particles, compared to the catalyst materials of Comparative Examples 1 to 3 in which the catalyst metal is supported by the conventional evaporation to dryness method. It can be seen that the crystallite diameter (nm) of the catalytic metal is a small value. Therefore, from these results, the catalyst materials of Examples 1 to 3 supported using carbon particles are more suitable for the evaporation to dryness method even when any of the catalyst metals Pt, Pd, and Rh is supported. It can be seen that the catalyst metal is supported on the carbon layer on the surface of the support material particles in a highly dispersed state as compared with the supported catalyst materials of Comparative Examples 1 to 3.

[Transmission electron microscope observation]
In order to evaluate the supported state of the catalyst metal 5, the catalyst materials of Example 1 and Comparative Example 1 in which Pt was supported as the catalyst metal 5 were subjected to 2 at 800 ° C. in an air atmosphere instead of firing in a non-oxidizing atmosphere. A transmission electron microscope (TEM) observation was performed on the surface of the inorganic oxide particles 3 after the carbon particles 4 ′ were burned out by firing for a period of time. In the TEM observation, the catalyst material was dispersed in methanol and dropped on a TEM grid to prepare a sample and measured. The observation results are shown in FIGS. 4 and 5, respectively. In FIGS. 4 and 5, black portions indicate Pt particles.

  First, as shown in FIG. 5, in the catalyst material of Comparative Example 1 carrying Pt by the conventional evaporation to dryness method, the Pt particles are scattered on the surface of the alumina particles, but the size of each Pt particle was measured. It can be seen that it is larger than that of Example 1. This is probably because the dinitrodiamine Pt nitric acid solution pools in the pores of alumina by the evaporation to dryness method, and as a result, Pt aggregates and precipitates in the pores, and the Pt particles are enlarged.

  On the other hand, as shown in FIG. 4, it can be seen that in the catalyst material of Example 1 in which Pt is supported using carbon particles, a plurality of Pt particles are scattered and gathered on the surface of the alumina particles. Carbon particles usually exist as secondary particles by agglomerating a plurality of particles, but since these secondary particles are larger than the pores of alumina, the Pt salt supported on the carbon particles is in the pores of alumina. It is thought that it is hard to be taken in. Therefore, the Pt salt supported on the carbon particles is dispersed and supported on the entire surface of the alumina while being held in the pores of the carbon particles. It is thought that it is maintained and deposited on the entire surface of the alumina.

  Therefore, these results suggest that the catalyst material of Example 1 is supported on the surface of the carbon particles in a higher dispersion state than the catalyst material of Comparative Example 1.

  In addition, at present, the ratio of the catalyst metal such as Pt particles supported on the pores on the surface of the inorganic oxide particles, the surface other than the pores, or the carbon particles is specified for the catalyst material after the firing step. It is difficult.

-Catalyst performance of catalyst material-
[Preparation of honeycomb catalyst]
As the carrier S forming the catalyst layer, a ceramic honeycomb carrier having a cell wall thickness of 3.5 mil (8.89 × 10 ⁻² mm) and 600 cells per square inch (645.16 mm ² ) (capacity 25 mL) Was used.

  To the catalyst materials of Examples 1 to 3 and Comparative Examples 1 to 3, ion exchange water and ZrYO as a binder material were added, and the resulting slurry was coated on the honeycomb carrier, and then dried at 150 ° C. and 500 ° C. The catalyst layer was provided on the support by calcining for 2 hours. The carrier was provided with a catalyst layer so that the carrying amount per liter of the carrier contained 150 g / L of catalyst material (10 g / L of catalyst metal).

[Saturated hydrocarbon combustion performance of honeycomb catalyst]
In order to measure the combustion performance of i-pentane (i-C ₅ H ₁₂ ) of the honeycomb catalyst, the following test was performed.

First, each manufactured honeycomb catalyst was attached to a model gas flow reactor, and a model gas containing i-C ₅ H ₁₂ was introduced. The composition of the model _{gas, i-C 5 H 12} is 3000PpmC, CO is 1700 ppm, _{O 2} is 10.5% CO ₂ is 13.9% _{H 2} O 10%, the remainder being _{N 2.} The gas flow rate was 26.1 L / min, and the space velocity was SV = 60000 h ⁻¹ . The temperature of the model exhaust gas flowing into the catalyst is gradually increased from the normal temperature, a change in the concentration of i-C ₅ H _{12 in} the gas flowing out from the catalyst is detected, and based on the amount of i-C ₅ H ₁₂ flowing out. It was measured _{i-C 5 H 12} purification ratio of each of the honeycomb catalyst. Table 1 shows the i-C ₅ H ₁₂ purification rate at an exhaust gas temperature of 350 ° C. among the measurement results.

As shown in Table 1, in all the honeycomb catalysts of Examples 1 to 3, i-C ₅ H ₁₂ purification rates were higher than those of the honeycomb catalysts of Comparative Examples 1 to 3, respectively. From this result, it is found that by supporting the catalytic metal using the manufacturing method according to the present embodiment, the catalytic performance of the catalyst material is effectively improved and the purification performance of saturated hydrocarbons such as pentane is improved. It was.

  The present invention is extremely useful because the catalyst metal can be supported in a highly dispersed state on the entire surface of the inorganic oxide particles.

1 Cell wall (exhaust gas passage wall)
2 catalyst layer 3 inorganic oxide particle 4 carbon layer 4 ′ carbon particle 5 catalyst metal 11 catalyst material, catalyst metal / carbon-supported inorganic oxide particle 21 catalyst metal salt solution (solution containing salt of catalyst metal)
22 Carbon particle dispersion (carbon particle dispersion)
23 Carbon mixed catalyst metal solution (mixed solution)
D Exhaust gas purification catalyst S Carrier (base material)

Claims (8)

A method for producing a catalyst material for exhaust gas purification comprising a catalyst metal and inorganic oxide particles carrying the catalyst metal,
A mixing step of mixing a solution containing the catalyst metal salt with a dispersion of carbon particles having a porosity of 50% or more to obtain a mixed solution;
A stirring step of stirring the mixed solution;
A contact step of bringing the stirred mixed liquid into contact with the inorganic oxide particles to obtain a mixed liquid containing inorganic oxide particles;
A method for producing an exhaust gas purifying catalyst material, comprising: a drying step of drying the inorganic oxide particle-containing mixed solution, followed by firing in a non-oxidizing atmosphere at a temperature of 600 ° C. or lower. In claim 1,
Are mixed in the mixing step, the mass of the catalyst metal mass ratio (catalyst metal / carbon particles) of relative of the carbon particles, an exhaust gas purification, characterized in that in the range of 1/10 to 1/2 For producing a catalyst material for use . In claim 1 or claim 2,
The method for producing an exhaust gas purifying catalyst material, wherein the carbon particles have an average primary particle diameter in a range of 30 nm to 50 nm. An exhaust gas purifying catalyst material manufactured by the manufacturing method according to any one of claims 1 to 3,
An exhaust gas purifying catalyst material, wherein a carbon layer carrying the catalyst metal is formed on the surface of the inorganic oxide particles. An exhaust gas purifying catalyst material manufactured by the manufacturing method according to any one of claims 1 to 3,
The catalytic metal is Pt;
A catalyst material for purifying exhaust gas , wherein the Pt crystallite diameter after firing for 2 hours at 600 ° C in a non-oxidizing atmosphere is in the range of 30 nm to 50 nm. An exhaust gas purifying catalyst material manufactured by the manufacturing method according to any one of claims 1 to 3,
The catalytic metal is Pd;
An exhaust gas purifying catalyst material, wherein the Pd crystallite diameter after firing at 600 ° C. for 2 hours in a non-oxidizing atmosphere is in the range of 40 nm to 50 nm. An exhaust gas purifying catalyst material manufactured by the manufacturing method according to any one of claims 1 to 3,
The catalytic metal is Rh;
An exhaust gas purifying catalyst material, wherein the Rh crystallite diameter is 2 nm or more and 20 nm or less after firing at 600 ° C. for 2 hours in a non-oxidizing atmosphere. An exhaust gas purifying catalyst comprising a base material and a catalyst layer provided on an exhaust gas passage wall of the base material,
An exhaust gas purification catalyst, wherein the catalyst layer includes the exhaust gas purification catalyst material according to any one of claims 4 to 7.