JP2007130590A - Exhaust gas cleaning catalyst and manufacturing method of exhaust gas cleaning catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas cleaning catalyst preventing lowering of promotor action caused by multiplexing of a transition metal compound in the exhaust gas cleaning catalyst having multiplexed particles formed by bringing transition metal compound particles having a promotor action into contact with noble metal particles, with a heat resisting inorganic oxide of a carrier. <P>SOLUTION: This exhaust gas cleaning catalyst has the noble metal particles 1, the transition metal compound particles 2 forming composite particles by contact with the noble metal particles 1, and the heat resisting inorganic oxide 4 formed by covering composite particles 3 of the noble metal particles 1 and transition metal compound particles 2. An average particle size of the transition metal compound particles 2 is larger than that of the noble metal particles 1, and the composite particles 3 are dispersed in the heat resisting inorganic oxide 4. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to an exhaust gas purification catalyst and an exhaust gas purification catalyst manufacturing method for purifying exhaust gas discharged from an automobile engine.

  With increasing awareness of environmental conservation, regulations on exhaust emissions from automobiles and the like have been strengthened. For this reason, various studies have been conducted to improve the performance of exhaust gas purification catalysts that purify exhaust gas discharged from automobile engines.

Exhaust gas purification catalysts are usually composed of a particulate metal oxide carrier made of alumina (Al ₂ O ₃ ) or the like and supported with noble metal fine particles such as platinum (Pt), palladium (Pd), or rhodium (Rh). Due to the catalytic activity of these noble metal particles, harmful gases such as unburned hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) contained in the exhaust gas, It is converted into harmless water and gas.

  The above-mentioned noble metals having catalytic activity are expensive and there is a concern about resource depletion. Thus, various attempts have been made to reduce the amount of noble metal used in the exhaust gas purification catalyst. For example, the precious metal particles are atomized to increase the surface area, the contact area between the exhaust gas and the precious metal particles is increased to improve the purification efficiency, or particles of a metal other than the precious metal or a compound thereof are included as a promoter component. There is an attempt to do.

  Examples of the promoter component include transition metal compounds. The transition metal compound used for the cocatalyst component has an oxygen supply ability, and when the transition metal compound is combined with a noble metal, the noble metal and the transition metal come into contact with each other, and the oxygen supply ability of the transition metal compound makes the noble metal oxidation activity. Will improve. Therefore, the transition metal compound effectively contributes to the improvement of the catalytic activity when the amount of noble metal used is reduced.

  The composite noble metal and transition metal compound are generally supported on a carrier made of a heat-resistant inorganic oxide. However, among various heat-resistant inorganic oxides applied to exhaust gas purification catalysts, alumina having high heat resistance and mainly used reacts with the above-described transition metal compound as a promoter component to form a composite. It is likely to occur. For this reason, the transition metal compound supported on the alumina carrier is complexed with the alumina, and the amount contributing to the catalytic activity of the noble metal is reduced, so that the effect of including the transition metal compound in the catalyst is sufficiently obtained. I couldn't.

  In this regard, when a heat-resistant inorganic oxide that does not react with the transition metal compound instead of alumina, such as zirconia, is used as the support, the transition metal compound does not form a solid solution or complex with the zirconia. . However, in this case, since the transition metal compound aggregates on a support such as zirconia, the effect of including the transition metal compound in the catalyst was not sufficiently obtained.

Moreover, there exists a reverse micelle method in the manufacturing method of a catalyst (for example, refer patent document 1). When a catalyst is produced by the reverse micelle method, a catalyst in which a composite particle of a noble metal and a transition metal is partially embedded in a support is obtained. Therefore, the particles of the transition metal or its compound do not aggregate.
Japanese Patent Laid-Open No. 10-216527

  Although the catalyst obtained by the reverse micelle method does not aggregate the transition metal, it uses an organic solvent to form the reverse micelle of the noble metal salt and the transition metal salt. It will be expensive. In addition, in the catalyst manufactured by the reverse micelle method, the transition metal particles have the same particle size as that of the noble metal particles. Therefore, when alumina is used as the carrier, the transition metal particles are added to the alumina. In some cases, the effect of containing the transition metal compound in the catalyst was not sufficiently obtained.

  The exhaust gas purification catalyst of the present invention covers noble metal particles, transition metal compound particles that come into contact with the noble metal particles to form composite particles, and composite particles of the noble metal particles and the transition metal compound particles. The transition metal compound particles are larger in average particle diameter than the noble metal particles, and the composite particles are the heat-resistant inorganic oxide. The main point is that it is dispersed within the network.

  The exhaust gas purifying catalyst of the present invention covers noble metal particles, particles of a transition metal compound that contacts the noble metal to form a composite particle, and composite particles of the noble metal particle and the transition metal compound particle. And the average particle size of the transition metal compound particles is 30 nm or more.

  The method for producing an exhaust gas purifying catalyst of the present invention is a step of producing composite particles having noble metal particles and transition metal compound particles having an average particle size larger than the average particle size of the noble metal particles. And a step of coating the periphery of the composite grain with a hydroxide which is a precursor of a heat-resistant inorganic oxide to form a catalyst precursor, and a step of firing the catalyst precursor in an oxidizing atmosphere. It is summarized as having.

  According to the exhaust gas purification catalyst of the present invention, it is possible to suppress the aggregation of the transition metal compound particles and the combination with a carrier such as alumina, and to obtain a catalyst having excellent purification performance.

  According to the method for producing an exhaust gas purification catalyst of the present invention, the exhaust gas purification catalyst of the present invention can be reliably and easily produced.

  FIG. 1 is a cross-sectional view schematically showing a main part of an example of an exhaust gas purification catalyst of the present invention. In the drawing, noble metal particles 1 are in contact with the transition metal compound particles 2 on the surface of the transition metal compound particles 2 to form composite particles 3. The composite grain 3 is dispersed in a heat-resistant inorganic oxide 4 formed so as to cover the composite grain 3. The heat-resistant inorganic oxide has a large number of pores (not shown) so that the noble metal particles 1 and the transition metal compound particles 2 can come into contact with the exhaust gas through the pores to sufficiently exhibit catalytic activity. It has become. The particle diameter D2 of the transition metal compound particle 2 is larger than the particle diameter D1 of the noble metal particle 1.

  As easily understood from the embodiment shown in FIG. 1, the catalyst of the present invention is characterized in that the average particle diameter of the transition metal compound particles is larger than the average particle diameter of the noble metal particles. . In a conventional exhaust gas purification catalyst, as one of the factors that deteriorate the transition metal compound, the transition metal compound is dissolved in the heat-resistant inorganic oxide that is the material of the carrier on which the transition metal compound is supported. Can be mentioned. This solid solution phenomenon proceeds as the interface between the transition metal compound and the heat-resistant inorganic oxide of the support is larger. This is because the reaction between solids, so-called solid phase reaction, proceeds as the number of interfaces increases. When the average particle size of the transition metal compound is as small as that of the precious metal particles as in the conventional exhaust gas purification catalyst, the above-mentioned interface is relatively large, so that the transition metal compound solid solution phenomenon proceeds. To do.

  In contrast, the exhaust gas purification catalyst of the present invention uses a transition metal compound having a larger average particle size than the noble metal, so that the content in the catalyst is the same as the conventional catalyst, The interface between the above-described transition metal compound and the heat-resistant inorganic oxide of the support can be reduced. Therefore, the solid solution of the transition metal compound can be suppressed, and the noble metal particles may be in contact with the transition metal compound particles. Even after the exhaust gas purification catalyst has been used for a long time, the noble metal particles It is possible to exhibit a co-catalytic action on the catalyst, and to sufficiently obtain the effect of including the transition metal compound in the catalyst.

  In the exhaust gas purification catalyst according to the embodiment of the present invention, the average particle diameter of the transition metal compound particles is preferably 30 nm or more. If the average particle diameter of the transition metal compound particles is 30 nm or more, the effect of suppressing the solid solution of the transition metal compound can be obtained even if the exhaust gas purification catalyst is used at a high temperature for a long time. It is also possible to expect an inclusion effect to reduce the aggregation degradation of particles. More desirably, the average particle diameter of the transition metal compound particles is 50 nm or more, and the effects described above are sufficiently obtained when the average particle diameter is 50 nm or more. The upper limit of the average particle diameter of the transition metal compound particles is not particularly limited from the viewpoint of the above-described effect. For example, even if the particle diameter is on the order of 100 nm, the expected effect can be obtained. According to the present invention, the above-mentioned form can be formed within the range of the preferable catalyst powder particle diameter in the catalyst powder particle having a form in which the composite grain is formed with noble metal particles and the composite grain is clad with a heat-resistant inorganic oxide. The particle size of the transition metal compound can be determined. If the transition metal compound has a too large particle size, the dispersibility in the heat-resistant inorganic oxide is lowered, and a sufficient inclusion effect cannot be obtained.

  In the exhaust gas purification catalyst according to the embodiment of the present invention, the average particle diameter Da of the noble metal particles is 1.5 nm or more, and the average particle diameter of the transition metal compound particles with respect to the average particle diameter Da of the noble metal particles The Db ratio Db / Da is preferably 20 or more. If the average particle diameter of the noble metal particles is 1.5 nm or more, the inclusion effect by the heat-resistant inorganic oxide can be expected. On the other hand, in a catalyst produced by simply impregnating a carrier with a noble metal salt solution, such as a conventional exhaust gas purification catalyst, the particle diameter of the noble metal particles is on the order of Å, its melting point is lowered, and the noble metal Its own movement aggregation is promoted. The upper limit of the average particle diameter of the noble metal particles is not particularly limited, but is preferably a particle diameter that satisfies Db / Da of 20 or more in relation to the average particle diameter of the transition metal compound particles. .

  Further, if the ratio Db / Da of the average particle diameter Db of the transition metal compound particles to the average particle diameter Da of the noble metal particles is 20 or more, the above-described durability improvement effect can be further expected.

  As the noble metal, at least one selected from Pt and Pd is effective. Among them, the exhaust gas purification catalyst of the present invention in which a noble metal and a transition metal compound are brought into contact is more effective when the noble metal is Pd. Although the details are unknown, the transition metal compound has an excellent oxygen supply capability, so it promotes the production of PdO, which is an active species of Pd, and thus, for example, a stoichiometric air / fuel ratio A / F of about 14.6. This is particularly effective for the oxidizing activity of reducing exhaust gases such as HC and CO when the exhaust gas atmosphere is shifted to a slightly reducing atmosphere from around the ratio. In addition, composite particles obtained by bringing mixed particles of Pt particles and Pd particles into contact with particles of a transition metal compound can be applied to the exhaust gas purification catalyst of the present embodiment.

  An oxide containing at least one selected from Co, Ni, and Mn is desirable for the transition metal compound that forms a composite grain upon contact with a noble metal. When the noble metal is in contact with the transition metal compound, the catalyst performance is improved. This is presumably because the oxidation activity of the noble metal is improved by the active oxygen supply ability of the transition metal compound. As the transition metal compound having such an effect, each of oxides of Co, Ni or Mn, or a composite oxide thereof is desirable. Further, the present invention is not limited to the case of containing only each of these oxides and complex oxides, and for example, the above-described effects can also be exhibited by grains of complex oxides of Mn and Ce.

The heat-resistant inorganic oxide is preferably an oxide containing at least one selected from Al, Ce, Zr and La. By forming these oxides around the active points of the composite grains of the noble metal and the transition metal, the effect of improving the dispersibility and the effect of preventing the sintering (aggregation) of the noble metal and the transition metal compound can be expected. Of these oxides, Al ₂ O ₃ (alumina) is advantageous because of its high heat resistance. When Al ₂ O ₃ is the main component, CeO ₂ can be added as an additive, and the composite of noble metal and transition metal compound while exhibiting the pore maintaining effect (improving heat resistance) of alumina itself The effect of strengthening the inclusion effect of the grains is exhibited. Furthermore, even when an oxide such as ZrO ₂ where the transition metal compound is not dissolved in the first place is applied to the heat-resistant inorganic oxide, an effect of suppressing the aggregation of the transition metal compound itself can be expected. We think that durability improves.

As a mode of combination of the above-mentioned noble metal and transition metal compound, it is a more preferable mode that the noble metal is Pd and the transition metal compound is manganese oxide (Mn ₂ O ₃ ). In the case of this combination, the production of PdO, which is an active species of Pd, is further promoted, whereby the oxidation activity of Pd is improved and particularly effective.

  Next, the manufacturing method of the exhaust gas purification catalyst of the present invention will be described.

  The method for producing an exhaust gas purification catalyst of the present invention includes a step of creating composite particles having noble metal particles and transition metal compound particles having an average particle size larger than the average particle size of the noble metal particles; The composite grain has a step of coating a hydroxide, which is a precursor of a heat-resistant inorganic oxide, to form a catalyst precursor, and a step of firing the catalyst precursor in an oxidizing atmosphere.

  As described above, the exhaust gas purifying catalyst of the present invention is in a form in which a composite particle of noble metal particles and transition metal compound particles is covered and a heat-resistant inorganic oxide is included. In order to obtain exhaust gas purification having such a form, a catalyst precursor is formed by coating a hydroxide, which is a precursor of a heat-resistant inorganic oxide, around a composite grain prepared in advance, and then the catalyst. It is preferable to use an inclusion method in which the precursor is calcined in an oxidizing atmosphere to obtain an exhaust gas purification catalyst.

  FIG. 2 is an explanatory view of an inclusion method in the manufacturing process of the exhaust gas purification catalyst according to the embodiment of the present invention. As shown in FIG. 2 (a), in the manufacturing method of the present embodiment, composite colloidal particles 3A of noble metal particles 1 and transition metal compound particles 2 are formed. Next, as shown in FIG. 2B, a hydroxide 4A which is a precursor of a heat-resistant inorganic oxide is formed around the composite colloidal particles 3A. Thereafter, the hydroxide 4 is converted into an oxide by firing in an oxidizing atmosphere.

  As described above, in the method for producing an exhaust gas purification catalyst of the present invention, it is possible to disperse and carry the composite particles inside the carrier by producing the exhaust gas purification catalyst using the inclusion method. Furthermore, since a hydroxide which is a precursor of a heat-resistant inorganic oxide is formed around the composite grain, a catalyst having a form in which a part of the composite grain is embedded in a carrier is obtained. For this reason, it becomes possible to fix the composite grains, and the obtained catalyst has high heat resistance because aggregation of the composite grains is suppressed.

  Further, when the catalyst precursor is calcined in an oxidizing atmosphere, water is evaporated from the hydroxide which is a precursor of the heat-resistant inorganic oxide, so that the heat-resistant inorganic oxide obtained after the firing has pores. A large number of catalyst supports having a high specific surface area are formed. In this catalyst carrier, the composite particles are uniformly dispersed and supported on the carrier surface including the inner surface.

  The precursor of the heat-resistant inorganic oxide is preferably an oxide precursor containing at least one selected from the group consisting of Al, Ce, Zr, and La. These precursors, for example, in the form of water-soluble inorganic salts such as nitrates and acetates, are first introduced into an aqueous solution containing composite colloidal particles of a noble metal and a transition metal compound, and then ammonia water or tetramethylammonium (TMAH ) It can be obtained by adding a basic precipitant such as an aqueous solution to form a hydroxide. It can also be obtained by introducing an alkoxide into the aqueous composite colloid solution to form a hydroxide around the composite colloidal particles. Furthermore, if the polymer chain of the organic molecules that make up the composite colloid has, for example, an imino (NH) group and the liquidity of the colloid solution is basic, the precipitant and the composite colloid are added to the aqueous solution containing the precursor. By introducing the mixed aqueous solution, it becomes possible to stably support the composite colloidal particles on the carrier.

  As an example of the precursor of the heat-resistant inorganic oxide, a case where an alumina precursor is formed will be described. In one method, a composite colloidal particle of a noble metal and a transition metal compound is preliminarily prepared with aluminum isopropoxide (hereinafter referred to as “aluminum isopropoxide”). A method of forming Al hydroxide around a composite colloidal particle of a noble metal and a transition metal compound by dropping it into hexylene glycol (hereinafter also referred to as "HEG") in which "AIP" is dissolved. There is. Another method is to drop a complex colloidal solution of a noble metal and a transition metal compound into an aqueous solution in which boehmite is dispersed, add nitric acid, etc. There is a way to do. In the former method, since a highly heat-resistant carrier can be formed, the inclusion effect can be further exhibited. On the other hand, the latter method can reduce the manufacturing cost.

  The composite particles for coating the hydroxide, which is the precursor of the heat-resistant inorganic oxide, described above, that is, the noble metal particles and the transition metal compound having an average particle size larger than the average particle size of the noble metal particles. A plurality of methods can be considered for the step of producing composite particles having particles, and the method for producing an exhaust gas purification catalyst of the present invention is not particularly limited, but a polymer layer around the particles of the transition metal compound It is preferable that the step of forming a colloid to form a noble metal on the surface of the colloid. According to this process, it is possible to use commercially available transition metal compound particles as raw materials, and it is possible to form composite particles of a noble metal and a transition metal compound at a lower cost. However, since the commercially available transition metal compound is in a powder state, simply adding the powder to a system such as an aqueous solution causes aggregation of each particle and only precipitates in the system. It is difficult to obtain composite grains.

  Therefore, in the manufacturing method according to the embodiment of the present invention, after the powder of the transition metal compound such as an oxide is dispersed in the aqueous solution, a polymer layer is formed around the particles of the transition metal compound by adding a dispersant. Form and colloid. By this colloidalization treatment, each particle is dispersed in the system and no sedimentation occurs. By passing through the state in which the particles of each transition metal compound are dispersed, the amount of the noble metal salt once adsorbed on each transition metal compound particle can be controlled at the time of subsequent precipitation of the noble metal particles. Unnecessary aggregation can be controlled.

  As an organic molecule for producing a colloid of metal particles, a highly stable compound such as polyvinyl pyrrolidone, polyvinyl alcohol, polyethylene imide, polyacrylic acid, oxalic acid, citric acid, maleic acid or a mixture thereof may be used. preferable. As the dispersion medium, water, alcohols such as methanol and ethanol, esters such as acetic acid methyl ester and ethyl acetate, ethers such as diethyl ether, or a mixture thereof can be used. By using these organic molecules and the dispersion medium, the metal particles can be uniformly dispersed in the dispersion medium. Furthermore, the stability of the colloidal solution, that is, the sedimentation separation can be suppressed. For this reason, the catalyst precursor is formed in a state where the composite particles are uniformly incorporated into the precursor of the heat-resistant inorganic oxide.

Precipitation of the noble metal particles can be performed by adding a noble metal salt and further adding a reducing agent to the system containing the colloidal transition metal compound particles. As this noble metal salt, a noble metal complex such as a dinitrodiamine salt, a triammine salt, a tetraammine salt or a hexaammine salt, or an inorganic salt such as a nitrate, chloride or sulfate can be used. Further, for example, ethanol can be used as the reducing agent. In order to obtain the exhaust gas purification catalyst according to the embodiment of the present invention, the ratio Db / Da of the average particle diameter Db of the transition metal compound particles to the average particle diameter Da of the noble metal particles is 20 or more. Although it is preferable to control the particle size of the particles, a means for controlling the particle size of the noble metal particles includes changing the above-described reduction conditions. For example, when ethanol is used as the reducing agent, the particle size of the noble metal can be controlled by changing the ethanol / water ratio and changing its boiling point. Details are unknown, but this is presumed to be due to the fact that the reducing power of ethanol vapor increases as the boiling point increases. Examples of the reducing agent include NaBH ₄ , N ₂ H ₄ , and ascorbic acid in addition to ethanol, and the same effect can be obtained by using any of them.

  The exhaust gas purifying catalyst of the present invention is an exhaust gas purifying method by applying a slurry containing the catalyst powder obtained by the above production method to a wall surface of a ceramic or heat-resistant metal substrate, drying and firing. The catalyst layer containing the catalyst is coated on the wall surface of the base material and used in an actual machine.

  FIG. 3 is a graph showing the result of examining the Pt particle diameter of the noble metal after the durability test under the same conditions as the actual machine by TEM. In the figure, the conventional product is an example in which fine noble metal particles are supported on the surface of the carrier particles by the impregnation method, and the reference product is a composite particle dispersed in the carrier by the inclusion method, and the noble metal of the composite particles An example in which the particle size of the particle and the particle size of the transition metal compound particle are the same level, and the product of the present invention is an example in which the particle size of the transition metal compound particle is larger than the particle size of the noble metal particle according to the present invention. . As shown in the figure, in the conventional example by the impregnation method, the particle size of Pt after the durability test is increased by sintering, and the particle size is remarkably increased particularly after the durability test at a high temperature. On the other hand, since the reference product and the product of the present invention manufactured by the clathrate method suppressed sintering, the increase in the Pt particle size after the durability test was smaller than that of the conventional product.

  FIG. 4A is a diagram depicting an image obtained by observing the noble metal particles and the transition metal compound particles in the colloid solution with an electron microscope. The transition metal compound particles 2 manufactured by the atomizing method or the like are commercially available and have an indefinite shape as shown in the figure. Noble metal particles 1 are deposited on the colloid of transition metal compound particles 2.

  FIG. 4B is a diagram depicting an image obtained by observing the exhaust gas purification catalyst before the durability test with an electron microscope. For convenience of understanding, the composite grain 3 and the heat-resistant inorganic oxide 4 are hatched. Composite particles 3 of a noble metal and a transition metal compound are dispersed in a heat-resistant inorganic oxide 4.

  FIG. 3C is a diagram depicting an image obtained by observing the exhaust gas purification catalyst after the durability test with an electron microscope. For convenience of understanding, the composite grain 3 and the heat-resistant inorganic oxide 4 are hatched. Further, the position where the catalyst is observed is different from the position shown in FIG. As shown in FIG. 4C, even after the durability test, the composite particles 3 of the noble metal and the transition metal compound remain, that is, the transition metal compound is combined with the heat-resistant inorganic oxide 4 and disappears. I didn't.

Example 1
1. Colloid solution preparation:
A predetermined amount of Mn ₂ O ₃ nanoparticle (average particle size 51 nm) powder is seeded, dropped into an aqueous solution, and in an ultrasonically dispersed state, the molar ratio of the monomer is 20 times the amount of this Mn ₂ O ₃ Polyvinylpyrrolidone (K30) was added to prepare a Mn ₂ O ₃ colloid solution. A predetermined amount of dinitrodiamine Pt solution was dropped into this Mn ₂ O ₃ colloidal solution and stirred and mixed for 1 hour, and then ethanol and ion-exchanged water were added so that the weight ratio of ethanol / water was 1.0. After stirring at ° C., Pt (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%)-PVP colloidal solution was obtained.

2. Preparation of catalyst powder:
A predetermined amount of aluminum isopropoxide (AIP) was added to hexylene glycol (solvent), stirred at 120 ° C for 1 hour, a predetermined amount of acetylacetonatocerium powder was added, and the temperature was lowered to 80 ° C. A predetermined amount of the Pt (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%)-PVP colloid solution was added dropwise to obtain a catalyst precursor gel. This gel was transferred to a rotary evaporator, vacuum dried at 150 ° C., and then calcined at 400 ° C. for 1 hour in an air stream. The catalyst powder of Example 1 (Pt (0.3 wt%) + Mn ₂ O ₃ (0.9 wt%)) / CeO ₂ (10 wt%) / Al ₂ O ₃ ). The obtained catalyst powder was confirmed by TEM to have a Pt particle size of 1.5 nm.

3. Coating on honeycomb substrate:
40 g of the obtained catalyst powder, 4 g of boehmite, and 125.6 g of a 10% nitric acid-containing aqueous solution were placed in an alumina magnetic pot, and shaken and pulverized with alumina balls to obtain a catalyst slurry. Furthermore, this catalyst slurry was put into a cordierite-made 0.0595L honeycomb substrate (400 cells / 6 mil), excess slurry was removed by air flow, dried at 120 ° C, and then at a temperature of 400 ° C. Firing in an air stream yielded a catalyst-supporting honeycomb substrate of Example 1. The amount of catalyst coated on the obtained catalyst-supporting honeycomb substrate was 110 g per liter of catalyst, and the weight of the catalyst noble metal per liter of catalyst was 0.3 g.

(Example 2)
Example 2 is an example in which the ratio Db / Da of the average particle diameter Db of the transition metal compound particles to the average particle diameter Da of the noble metal particles is made different from that of Example 1 by increasing the particle diameter of the noble metal. It is.

1. Colloid solution preparation:
A predetermined amount of Mn ₂ O ₃ nanoparticle (average particle size 51 nm) powder is seeded, dropped into an aqueous solution, and in an ultrasonically dispersed state, the molar ratio of the monomer is 20 times the amount of this Mn ₂ O ₃ Polyvinylpyrrolidone (K30) was added to prepare a Mn ₂ O ₃ colloid solution. A predetermined amount of dinitrodiamine Pt solution was dropped into this Mn ₂ O ₃ colloid solution, and after stirring and mixing for 1 hour, ethanol and ion-exchanged water were added so that the weight ratio of ethanol / water was 0.1. After stirring at ° C., Pt (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%)-PVP colloidal solution was obtained.

2. Preparation of catalyst powder:
A predetermined amount of aluminum isopropoxide (AIP) was added to hexylene glycol (solvent), stirred at 120 ° C for 1 hour, a predetermined amount of acetylacetonatocerium powder was added, and the temperature was lowered to 80 ° C. A predetermined amount of the Pt (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%)-PVP colloid solution was added dropwise to obtain a catalyst precursor gel. This gel was transferred to a rotary evaporator, vacuum-dried at 150 ° C., and then calcined at 400 ° C. for 1 hour in an air stream. The catalyst powder of Example 2 (Pt (0.3 wt%) + Mn ₂ O ₃ (0.9 wt%)) / CeO ₂ (10 wt%) / Al ₂ O ₃ ). The obtained catalyst powder was confirmed by TEM to have a Pt particle size of 2.5 nm.

3. Coating on honeycomb substrate:
40 g of the obtained catalyst powder, 4 g of boehmite, and 125.6 g of a 10% nitric acid-containing aqueous solution were put into an alumina magnetic pot, and shaken and pulverized with alumina balls to obtain a catalyst slurry. Furthermore, this catalyst slurry was put into a cordierite 0.0595 L honeycomb substrate (400 cells / 6 mil), excess slurry was removed by air flow, dried at 120 ° C., and air at 400 ° C. The catalyst-supported honeycomb substrate of Example 2 was obtained by firing in an air stream. The amount of catalyst coated on the obtained catalyst-supporting honeycomb substrate was 110 g per liter of catalyst, and the weight of the catalyst noble metal per liter of catalyst was 0.3 g.

(Example 3)
Example 3 is an example in which the noble metal having catalytic activity is Pd.

1. Colloid solution preparation:
A predetermined amount of Mn ₂ O ₃ nanoparticle (33 nm) powder was seeded, dropped into an aqueous solution, and in an ultrasonically dispersed state, a 20-fold amount of polyvinylpyrrolidone (molar ratio of monomer to this Mn ₂ O ₃₎ ( K30) was added to prepare a Mn ₂ O ₃ colloidal solution. To this Mn ₂ O ₃ colloidal solution, a predetermined amount of dinitrodiamine Pd solution was dropped and mixed with stirring for 1 hour, and then ethanol and ion-exchanged water were added so that the weight ratio of ethanol / water was 1.0. After stirring at ° C., Pd (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%)-PVP colloidal solution was obtained.

2. Preparation of catalyst powder:
A predetermined amount of aluminum isopropoxide (AIP) was added to hexylene glycol (solvent) and stirred at 120 ° C. for 1 hour. Then, a predetermined amount of acetylacetonatocerium powder was added and the temperature was lowered to 80 ° C. A predetermined amount of Pd (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%)-PVP colloid solution was added dropwise to obtain a catalyst precursor gel. This gel was transferred to a rotary evaporator, vacuum-dried at 150 ° C., and then calcined at 400 ° C. for 1 hour in an air stream. The catalyst powder of Example 3 (Pd (0.7 wt%) + Mn ₂ O ₃ (2.1 wt%)) / CeO ₂ (10 wt%) / Al ₂ O ₃ ). The obtained catalyst powder was confirmed by TEM and the particle size of Pd was 1.7 nm.

3. Coating on honeycomb:
40 g of the obtained catalyst powder, 4 g of boehmite, and 125.6 g of a 10% nitric acid-containing aqueous solution were placed in an alumina magnetic pot, and shaken and pulverized with alumina balls to obtain a catalyst slurry. Furthermore, this catalyst slurry was put into a cordierite-made 0.0595 L honeycomb substrate (400 cells / 6 mils), excess slurry was removed by air flow, dried at 120 ° C, and then heated to 400 ° C. Was fired in an air stream to obtain a catalyst-supporting honeycomb substrate of Example 3. The amount of catalyst coated on the obtained catalyst-supporting honeycomb substrate was 110 g per liter of catalyst, and the weight of catalyst noble metal per liter of catalyst was 0.7 g.

Example 4
Example 4 is an example in which the ratio Db / Da of the average particle diameter Db of the transition metal compound particles to the average particle diameter Da of the noble metal particles is made different from that of Example 3 by increasing the particle diameter of the noble metal. It is.

1. Colloid solution preparation:
A predetermined amount of Mn ₂ O ₃ nanoparticle (33 nm) powder was seeded, dropped into an aqueous solution, and in an ultrasonically dispersed state, a 20-fold amount of polyvinylpyrrolidone (molar ratio of monomer to this Mn ₂ O ₃₎ ( K30) was added to prepare a Mn ₂ O ₃ colloidal solution. To this Mn ₂ O ₃ colloidal solution, a predetermined amount of dinitrodiamine Pd solution was dropped and mixed with stirring for 1 hour, and then ethanol and ion-exchanged water were added so that the weight ratio of ethanol / water was 1.3. After stirring at ° C., Pd (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%)-PVP colloidal solution was obtained.

2. Preparation of catalyst powder:
A predetermined amount of aluminum isopropoxide (AIP) was added to hexylene glycol (solvent) and stirred at 120 ° C. for 1 hour. Then, a predetermined amount of acetylacetonatocerium powder was added and the temperature was lowered to 80 ° C. A predetermined amount of Pd (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%)-PVP colloid solution was added dropwise to obtain a catalyst precursor gel. This gel was transferred to a rotary evaporator, vacuum-dried at 150 ° C., and then calcined in an air stream at 400 ° C. for 1 hour. The catalyst powder of Example 4 (Pd (0.7 wt%) + Mn ₂ O ₃ (2.1 wt%)) / CeO ₂ (10%) / Al ₂ O ₃ ). The obtained catalyst powder was confirmed by TEM to have a Pd particle size of 1.9 nm.

3. Coating on honeycomb:
40 g of the obtained catalyst powder, 4 g of boehmite, and 125.6 g of a 10% nitric acid-containing aqueous solution were placed in an alumina magnetic pot, and shaken and pulverized with alumina balls to obtain a catalyst slurry. Furthermore, this catalyst slurry was put into a cordierite-made 0.0595L honeycomb substrate (400 cells / 6 mil), excess slurry was removed by air flow, dried at 120 ° C, and then at a temperature of 400 ° C. Firing was performed in an air stream to obtain a catalyst-supporting honeycomb substrate of Example 4. The amount of catalyst coated on the obtained catalyst-supporting honeycomb substrate was 110 g per liter of catalyst, and the weight of the catalyst noble metal per liter of catalyst was 0.7 g.

(Example 5)
In Example 5, the ratio Db / Da of the average particle diameter Db of the transition metal compound particles to the average particle diameter Da of the noble metal particles is increased by increasing the particle diameter of the noble metal compared to Example 1 and Example 2. This is a different example.

1. Colloid solution preparation:
A predetermined amount of Mn ₂ O ₃ nanoparticle (51 nm) powder is seeded, dropped into an aqueous solution, and in an ultrasonically dispersed state, a 20-fold amount of polyvinylpyrrolidone (molar ratio of monomer to this Mn ₂ O ₃₎ ( K30) was added to prepare a Mn ₂ O ₃ colloidal solution. To this Mn ₂ O ₃ colloidal solution, a predetermined amount of dinitrodiamine Pt solution was dropped, and after stirring for 1 hour, 0.1 wt% hydrazine aqueous solution was added, and Pt (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%) ) -PVP colloidal solution was obtained.

2. Preparation of catalyst powder:
A predetermined amount of aluminum isopropoxide (AIP) was added to hexylene glycol (solvent) and stirred at 120 ° C. for 1 hour. Then, a predetermined amount of acetylacetonatocerium powder was added and the temperature was lowered to 80 ° C. A predetermined amount of Pt (0.2 wt%) + Mn ₂ O ₃ (0.6 wt%)-PVP colloid solution was added dropwise to obtain a catalyst precursor gel. This gel was transferred to a rotary evaporator, vacuum-dried at 150 ° C., and then calcined at 400 ° C. for 1 hour in an air stream. The catalyst powder of Example 5 (Pt (0.3 wt%) + Mn ₂ O ₃ (0.9 wt%)) / CeO ₂ (10 wt%) / Al ₂ O ₃ ). The obtained catalyst powder was confirmed by TEM to have a Pt particle size of 3.0 nm.

3. Coating on honeycomb:
40 g of the obtained catalyst powder, 4 g of boehmite, and 125.6 g of a 10% nitric acid-containing aqueous solution were put into an alumina magnetic pot and shaken and pulverized with alumina balls to obtain a catalyst slurry.

Furthermore, this catalyst slurry was put into a cordierite-made 0.0595L honeycomb substrate (400 cells / 6 mil), excess slurry was removed with an air stream, dried at 120 ° C, and 400 ° C in an air stream To obtain a catalyst-supporting honeycomb substrate of Example 1. The amount of catalyst coated on the obtained catalyst-supporting honeycomb substrate was 110 g per liter of catalyst, and the weight of the catalyst noble metal per liter of catalyst was 0.3 g.

(Example 6)
In the same manner as in Example 6 except that manganese oxide of Example 5 was changed to nickel oxide (particle diameter: 65 nm), and in the catalyst powder preparation step, zirconyl nitrate and an aqueous solution of La nitrate were added dropwise after forming the catalyst precursor gel. The catalyst was obtained.

The obtained catalyst powder has a component composition of Pt (0.3 wt%) + NiO (0.9 wt%) / CeO ₂ (10 wt%) + La ₂ O ₃ (3 wt%) + ZrO ₂ (5 wt%) / Al ₂ O ₃ ). The noble metal particle diameter was 3.0 nm.

(Example 7)
In the same manner as in Example 7 except that the manganese oxide of Example 5 was changed to cobalt oxide (particle diameter: 73 nm), and in the catalyst powder preparation step, zirconyl nitrate and an aqueous solution of La nitrate were added dropwise after forming the catalyst precursor gel. The catalyst was obtained.
The resulting catalyst powder _{Pt (0.3wt%) + Co 3} O 4 (0.9wt%) / CeO 2 (10wt%) + La2O 3 (3wt%) + ZrO2 (5wt%) / Al 2 O 3) be a composition of The noble metal particle diameter was 2.9 nm.

(Comparative Example 1)
Comparative Example 1 is an example in which noble metal particles and transition metal particles are formed on a heat-resistant inorganic oxide by an impregnation method.

After impregnating and supporting 10% by weight of cerium nitrate aqueous solution as CeO _{2 on} γ-alumina, it was dried at 120 ° C. overnight and then calcined at 400 ° C. for 1 hour in an air stream. Further, the powder obtained by firing was impregnated with manganese acetate aqueous solution so as to become 0.9 wt% as Mn ₂ O ₃ , dried at 120 ° C. overnight, and then in an air stream at 400 ° C. for 1 hour. Baked. Subsequently, a predetermined amount of a dinitrodiamine Pt aqueous solution was impregnated and supported, dried at 120 ° C. overnight, and calcined at 400 ° C. for 1 hour in an air stream to obtain the powder of Comparative Example 1 (Pt (0.3 wt%) / Mn ₂ O ₃ (0.9 wt%) / CeO ₂ (10 wt%) / alumina) was obtained. Next, the obtained powder was coated on a honeycomb substrate in the same manner as in Example 1 to obtain a catalyst-supporting honeycomb substrate of Comparative Example 1.

(Comparative Example 2)
Comparative Example 2 is an example in which noble metal having catalytic activity is Pd, and noble metal particles and transition metal particles are formed on a heat-resistant inorganic oxide by an impregnation method.

After impregnating and supporting 10% by weight of cerium nitrate aqueous solution as CeO _{2 on} γ-alumina, it was dried at 120 ° C. overnight and then calcined at 400 ° C. for 1 hour in an air stream. Furthermore, the powder obtained by firing was impregnated with manganese acetate aqueous solution so as to be 2.1 wt% as Mn ₂ O ₃ , dried at 120 ° C. overnight, and then in an air stream at 400 ° C. for 1 hour. Baked. Next, a predetermined amount of a dinitrodiamine Pd aqueous solution was impregnated and supported, dried at 120 ° C. overnight, and calcined at 400 ° C. for 1 hour in an air stream. The powder of Comparative Example 2 (Pd (0.7 wt%) / Mn ₂ O ₃ (2.1 wt%) / CeO ₂ (10 wt%) / alumina) was obtained. Next, the obtained powder was coated on a honeycomb substrate in the same manner as in Example 1 to obtain a catalyst-supporting honeycomb substrate of Comparative Example 2.

  A catalyst durability test was performed on the exhaust gas purification catalysts of Examples 1 to 7 and Comparative Examples 1 and 2 described above. In this catalyst endurance test, an unrelated gasoline was used as fuel, using an engine of Nissan Motor Co., Ltd., V type 6 cylinder, displacement 3.5L (liter, the same applies hereinafter). The catalyst inlet temperature was set to 700 ° C. and the engine was operated for 30 hours.

The catalyst after the durability test was cut to evaluate the catalyst activity with a catalyst capacity of 40 cc. This catalytic activity was evaluated using a model gas with a stoichiometric composition in which the amount of oxygen and the amount of reducing agent were equal, and when the concentration at the catalyst inlet and the HC concentration at the catalyst outlet were stabilized, the HC purification rate (ηHC) at 500 ° C Was calculated according to the HC purification rate. The composition of the model gas is shown in Table 1, and the equation for obtaining the HC purification rate is shown in the following equation. In addition, Table 2 shows the HC purification rates of Examples 1 to 3 and Comparative Examples 1 and 2.

  Further, FIG. 5 compares the HC purification rates shown in Table 2 for Example 1 and Comparative Example 1 in which Pt is used as the noble metal and the amount of Pt supported is the same. 6 shows a comparison of the HC purification rates shown in Table 2 for Example 3 and Comparative Example 2 in which Pd is used as the noble metal and the amount of Pd supported is the same.

  From Table 2, FIG. 5, and FIG. 6, Examples 1-7 according to this invention are all excellent in HC purification rate compared with a comparative example. Further, when the ratio Db / Da of the average particle diameter Db of the transition metal compound to the average particle diameter Da of the noble metal is 20 or more by comparing Example 1, Example 2 and Example 5, particularly excellent purification performance. showed that.

On the other hand, Comparative Example 1 and Comparative Example 2 were produced by the impregnation method, and the transition metal compound (Mn ₂ O ₃ ) supported on the support was combined with this support (Al ₂ O ₃ ) to form MnAl ₂ Since O ₄ was formed, the form of the transition metal compound particles did not remain, and the HC purification rate was inferior to that of the example.

The schematic diagram of the principal part of an example of the exhaust-gas purification catalyst of this invention. Explanatory drawing of the inclusion method in the manufacture process of the exhaust-gas purification catalyst which concerns on embodiment of this invention. The graph which shows the relationship between durability experiment temperature and the Pt particle diameter of a noble metal. The figure which depicted the image observed with the electron microscope. The graph which shows the HC purification rate about an Example and a comparative example. The graph which shows the HC purification rate about an Example and a comparative example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Noble metal particle 2 Transition metal compound particle 3 Composite particle 4 Heat resistant inorganic oxide

Claims (8)

Noble metal particles,
Transition metal compound particles that come into contact with the noble metal particles to form composite grains;
A heat-resistant inorganic oxide formed over a composite grain of the noble metal particles and the transition metal compound particles, and
An exhaust gas purification catalyst, wherein the average particle size of the transition metal compound particles is larger than the average particle size of the noble metal particles, and the composite particles are dispersed in the heat-resistant inorganic oxide. Precious metal particles,
Transition metal compound particles that form composite grains in contact with the noble metal;
A heat-resistant inorganic oxide formed over a composite grain of the noble metal particles and the transition metal compound particles, and
An exhaust gas purification catalyst, wherein the average particle diameter of the transition metal compound particles is 30 nm or more. The average particle diameter Da of the noble metal particles is 1.5 nm or more, and the ratio Db / Da of the average particle diameter Db of the transition metal compound particles to the average particle diameter Da of the noble metal particles is 20 or more. The exhaust gas purifying catalyst according to claim 1 or 2, characterized in that: The noble metal is at least one selected from Pt and Pd, the transition metal compound is a compound containing at least one transition metal selected from Co, Mn, and Ni, and the heat-resistant inorganic oxide is Al, The exhaust gas purification catalyst according to any one of claims 1 to 3, wherein the exhaust gas purification catalyst is an oxide containing at least one selected from Ce, Zr and La. The exhaust gas purification catalyst according to claim 4, wherein the noble metal is Pd and the transition metal compound is manganese oxide. An exhaust gas purification catalyst, wherein a catalyst layer containing the exhaust gas purification catalyst according to any one of claims 1 to 5 is coated on a wall surface of a base material. Creating a composite particle having noble metal particles and transition metal compound particles having an average particle size larger than the average particle size of the noble metal particles;
A step of forming a catalyst precursor by coating a hydroxide that is a precursor of a heat-resistant inorganic oxide around the composite grains;
And a step of calcining the catalyst precursor in an oxidizing atmosphere. 8. The step of creating the composite grain includes a step of forming a polymer layer around the transition metal compound particles to form a colloid and then reducing and precipitating a noble metal on the colloid surface. The manufacturing method of the exhaust-gas purification catalyst as described.

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