JP4779271B2 - catalyst - Google Patents

Description

【００５１】
【表２】

【００５２】
【表３】

【図面の簡単な説明】
【図１】耐久処理条件と触媒浄化性能の関係を示すグラフである。
【図２】触媒成分の粒子構造を示す透過型電子顕微鏡写真である。
【図３】触媒成分の粒子構造を示す透過型電子顕微鏡写真である。
【図４】触媒成分の粒子構造を示す透過型電子顕微鏡写真である。
【図５】触媒浄化性能を比較したグラフである。
【図６】触媒浄化性能を比較したグラフである。[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a catalyst having a high durability performance in which sintering of a catalyst component under a high temperature atmosphere is remarkably suppressed.
[0002]
[Prior art]
Exhaust gas discharged from internal combustion engines such as automobile engines includes carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NO _x ), etc. These harmful substances are generally platinum. It is purified by an exhaust gas purifying catalyst using a noble metal such as (Pt), gold (Au), palladium (Pd), ruthenium (Ru), rhodium (Rh) as a catalyst component.
[0003]
This exhaust gas purifying catalyst is usually configured by supporting the above catalyst component on a metal oxide support. However, in order to efficiently promote the purification reaction of these harmful substances, the catalyst component is exhausted. It is necessary that the catalyst component be supported in a highly dispersed manner on the support so as to exhibit a high contact area with the gas. This highly dispersed support state needs to be maintained over time in an exhaust gas atmosphere.
[0004]
For example, in the case of an exhaust gas purifying catalyst for an automobile engine, a reducing atmosphere in which the temperature repeatedly fluctuates between room temperature and about 1000 ° C., the HC and CO concentrations are relatively high, and the O ₂ concentration is low, This highly dispersed support state needs to be maintained under conditions in which an oxidizing atmosphere having relatively low HC and CO concentrations and high O ₂ concentration is repeated.
[0005]
However, the above-mentioned precious metal catalyst component has the property of causing so-called sintering, when the catalyst component is exposed to such an atmosphere for a long period of time, forming particles that are enlarged by moving on the support. Is easily promoted particularly in a high-temperature oxidizing atmosphere.
For this reason, the catalyst component cannot maintain a high contact area with the exhaust gas, and there is a problem that the exhaust gas purification performance decreases with time.
[0006]
By the way, the present applicant has previously proposed an alloy catalyst containing a noble metal in Japanese Patent Application Laid-Open No. 11-156193, based on the idea of increasing the catalytic activity by alloying the metal of the catalyst component. However, this publication does not disclose any particulars regarding suppression of sintering of the alloy catalyst.
[0007]
[Problems to be solved by the invention]
Accordingly, an object of the present invention is to provide a catalyst in which such sintering is suppressed and which stably exhibits high catalyst performance over time.
[0008]
[Means for Solving the Problems]
The above object includes a first catalyst in which Pt is supported on a support and a second catalyst in which Rh is supported on a support, and Au is further supported on at least one of the first catalyst and the second catalyst. This is achieved by a catalyst characterized in that.
That is, the catalyst according to the present invention is a catalyst in which Pt, Rh, and Au are supported on a carrier in the first embodiment, and each of Pt and Rh is supported on separate carriers. It is.
[0009]
Further, the above object is achieved by a catalyst characterized in that alloy particles in which Pt, Rh, and Au coexist are supported on a support.
That is, in the second aspect, the catalyst of the present invention is a catalyst in which Pt, Rh, and Au form one alloy particle on the support.
[0010]
In such a catalyst of the present invention, the mechanism by which sintering is suppressed and high exhaust gas purification performance can be continuously exhibited is considered as follows.
The catalyst of the first aspect is prepared by supporting Pt, Rh, and Au catalyst components on a support using, for example, a solution of a soluble noble metal compound. Furthermore, it can be supported in a very fine and highly dispersed state.
[0011]
The catalyst prepared in this way can exhibit high initial activity catalyst performance due to the highly dispersed supported catalyst component for a certain period after the start of use in which sintering has not progressed significantly. .
Subsequently, sintering of the catalyst component occurs due to long-term exposure to high-temperature exhaust gas. Here, the catalyst of the first aspect is transferred to the catalyst of the second aspect by sintering. In the catalyst of the second aspect, sintering substantially stops.
[0012]
That is, Pt, Rh, and Au are supported on a carrier, and Pt and Rh, each of which is supported in a highly dispersed state on separate carriers, are exposed to a high-temperature exhaust gas. By moving up or forming volatile oxides, mass transfer occurs through the gas phase, and Pt, Rh, and Au form alloy particles on the support. Even if the alloy particles are further exposed to high-temperature exhaust gas, no further enlargement of the particle size occurs, the highly dispersed support state of the catalyst components is maintained, and high catalyst performance is maintained. It can be demonstrated.
In addition, the transition to the catalyst of the second aspect is delayed by loading Pt and Rh on separate carriers, thereby allowing a longer period of initial activity.
[0013]
The transition from the catalyst of the first aspect to the catalyst of the second aspect, and the sintering substantially stops in the catalyst of the second aspect, as described in Examples below. This is demonstrated by morphological observation with a microscope (TEM).
As described above, the present invention is based on a unique phenomenon in which Pt, Rh, and Au form alloy particles by sintering, thereby substantially stopping the subsequent sintering.
[0014]
The reason why such a phenomenon occurs is not necessarily clear, but Au and Pt, Au and Rh each form an alloy, and these alloys move on the carrier, but this movement causes Pt, Rh, and Au to coalesce. Then, since a high melting point Pt—Rh—Au alloy is formed, it is presumed that subsequent movement is suppressed.
[0015]
DETAILED DESCRIPTION OF THE INVENTION
The first aspect of the present invention includes a first catalyst in which Pt is supported on a support, and a second catalyst in which Rh is supported on a support, and Au is provided on at least one of the first catalyst and the second catalyst. Is a catalyst further supported.
The first catalyst is formed by supporting Pt on a support, and this support includes oxides such as alumina, silica and zirconia, silica-alumina, zirconia-ceria, alumina-ceria-zirconia, and ceria-zirconia. A composite oxide such as yttria and zirconia-calcia can be preferably used.
[0016]
Pt is supported on such a carrier, for example, by using a platinum compound such as platinum dinitrodiammine Pt (NH ₃ ) ₂ (NO ₂ ) ₂ or chloroplatinic acid H ₂ PtCl ₆ .6H ₂ O, and evaporating to dryness. It can be carried out by the method, precipitation method, ion exchange method, adsorption method, reduction precipitation method and the like. Next, it is preferable that the support of Pt be further strengthened by heating to a temperature of 300 to 700 ° C. for several hours in the atmosphere.
[0017]
The second catalyst is configured such that Rh is supported on a support. Similarly, a rhodium compound such as rhodium nitrate Rh (NO ₃ ) ₃ or rhodium chloride RhCl ₃ is formed on the above oxide or composite oxide support. And can be obtained by carrying Rh by evaporation to dryness, precipitation, ion exchange, adsorption, reduction precipitation or the like.
Note that the carrier for the first catalyst and the carrier for the second catalyst can be of the same type as long as the first catalyst and the second catalyst are prepared separately.
[0018]
Au is supported on at least one of the first catalyst and the second catalyst. Before or after the above-described support of Pt or Rh, Au is applied to one of the first catalyst and the second catalyst, or both the first catalyst and the second catalyst. It can be supported by the evaporation to dryness method, precipitation method, ion exchange method, adsorption method, reduction precipitation method and the like.
Preferably, the loading of Au is performed by adding a reducing agent to an aqueous solution of a gold compound that generates Au ions in an aqueous solution, reducing the Au ions to insolubilize, and precipitating Au particles.
[0019]
Specifically, a gold compound such as chloroauric acid HAuCl ₄ .4H ₂ O and gold chloride AuCl _{3 is} dissolved in the first catalyst, the second catalyst, or an aqueous slurry in which the first catalyst and the second catalyst are dispersed. In this slurry, sodium thiosulfate Na ₂ S ₂ O ₃ , potassium thiosulfate K ₂ S ₂ O ₃ , ammonium thiosulfate (NH ₄ ) ₂ S ₂ O ₃ , sodium sulfite Na ₂ SO ₃ , sodium metabisulfite Na ₂ S ₂ O ₅ , potassium metabisulfite K ₂ S ₂ O ₅ , ammonium metabisulfite (NH ₄ ) ₂ S ₂ O ₅ , hydrazine N ₂ H ₄ , sodium tetrahydroborate NaBH ₄ , borohydride, hypophosphorous acid A reducing agent such as acid salt and citrate and a buffer such as sodium L-ascorbate C ₆ H ₇ O ₆ Na and ethylenediaminetetraacetate are added to reduce Au ions, and Au fine particles are converted into the first catalyst, Second catalyst Or deposited on the first catalyst and the second catalyst.
[0020]
According to such reduction deposition, it is relatively easy to deposit substantially all Au fine particles having a diameter of about 1 nm (nanometer) on Pt or Rh.
For the catalyst of the first mode in which Au is supported only on the first catalyst, the first catalyst supporting Au is prepared in this way, and then mixed with the second catalyst by, for example, a ball mill, a Henschel mixer, or the like. Similarly, the catalyst of the first aspect in which Au is supported only on the second catalyst can be obtained by mixing the second catalyst supporting Au and the first catalyst.
In addition, the catalyst of the first aspect in which Au is supported on both the first catalyst and the second catalyst, the Au catalyst is supported after the first catalyst and the second catalyst are mixed by, for example, a ball mill, a Henschel mixer or the like. Obtainable.
[0021]
The catalyst of the first aspect thus obtained preferably has a Pt / Au molar ratio of 200/1 to 1/1 and a Rh / Au molar ratio of 200/1 to 1/1. More preferably, the raw material ratio is adjusted so that the molar ratio of Pt / Au is 200/1 to 4/1 and the molar ratio of Rh / Au is 200/1 to 7/3.
In addition, even if a metal component other than Pt, Rh, and Au is contained in an amount of several mass% or less based on the total mass of Pt, Rh, and Au, it can be allowed for the purpose of the present invention. .
[0022]
The catalyst of the second aspect is expressed by exposing the catalyst of the first aspect to a high temperature atmosphere for a long period of time, that is, the catalyst components Pt, Rh, and Au contained in the catalyst of the first aspect move. Thus, the alloy particles coexisting in one particle are formed, and the catalyst of the second mode is formed in a state where the alloy particles are supported on both carriers of the first catalyst and the second catalyst.
In this second aspect of the catalyst, the catalyst components Pt, Rh, and Au are at least 50% by weight, more preferably at least 75% by weight, based on their total weight, with a particle size of about 5-40 nm in diameter. The Pt / Au molar ratio and the Rh / Au molar ratio are equivalent to those of the catalyst of the first aspect.
[0023]
Although the catalyst of the second aspect shows a slight decrease in the catalyst performance as compared with the initial activity of the catalyst of the first aspect, it remains constant even after exposure to a high-temperature oxidizing atmosphere in which sintering is usually promoted. Thus, the exhaust gas purification performance can be maintained.
[0024]
A normal honeycomb type exhaust gas purification catalyst to which the catalyst of the present invention is applied can be prepared by carrying the catalyst of the first aspect on a monolith support by a wash coat or the like, and is used as an exhaust gas purification catalyst. In this process, or in some cases, in the calcination step during the preparation, the catalyst of the second aspect is developed.
Hereinafter, the present invention will be described more specifically with reference to examples.
[0025]
【Example】
Example 1
Al ₂ O ₃ —CeO ₂ —ZrO ₂ composite oxide powder prepared by coprecipitation / firing using aluminum nitrate, cerium nitrate and zirconium nitrate as raw materials (specific surface area of about 100 m ² / g, Al ₂ O ₃ / CeO ₂ / ZrO ₂ molar ratio = 2/1/1, indicated as “ACZ” in Table 2), this composite oxide powder was dispersed in ion-exchanged water, and dinitrodiammine platinum was dissolved in the resulting slurry. Next, evaporation to dryness and heat treatment at 500 ° C. for 2 hours in the atmosphere were performed, and a first mass in which 5.0 mass% of Pt was supported on the Al ₂ O ₃ —CeO ₂ —ZrO ₂ composite oxide powder. A catalyst was obtained.
[0026]
Separately, ZrO ₂ powder (specific surface area of about 70 m ² / g) was used as a carrier, this ZrO ₂ powder was dispersed in ion-exchanged water, rhodium nitrate was dissolved in the resulting slurry, and then evaporated to dryness. Further, 1.0% by mass of Rh was supported on the ZrO ₂ powder.
[0027]
Reagents were sequentially added in an amount of the following concentration to a slurry in which 100 g of this Rh-supported ZrO ₂ powder was dispersed in 500 cc of ion-exchanged water at 60 ° C., and placed under gentle stirring for 24 hours. Au was reduced and precipitated from the acid.
HAuCl ₄ · 4H ₂ O 2.00 × 10 ^-2 mass%
Na ₂ S ₂ O ₃ .5H ₂ O 1.00 × 10 ⁻¹ mass%
Na ₂ SO ₃ 3.00 × 10 ⁻¹ mass%
C ₆ H ₇ O ₆ Na 1.00% by mass
[0028]
After this reduction precipitation, the slurry was filtered and washed, dried in air at 120 ° C. for 2 hours, and then heat-treated in air at 500 ° C. for 2 hours. As a result, a second catalyst in which 0.99% by mass of Rh and 0.01% by mass of Au were supported in a highly dispersed manner on the ZrO ₂ powder was obtained.
Said 1st catalyst and 2nd catalyst were mixed with an equal mass using a mortar, and it compressed and crushed, and obtained the catalyst A of this invention of the pellet form of a diameter of about 1-3 mm.
[0029]
Comparative Example 1
The Al ₂ O ₃ —CeO ₂ —ZrO ₂ composite oxide powder supporting 5.0% by mass of Pt and the ZrO ₂ powder supporting 1.0% by mass of Rh prepared in Example 1 were used in Example 1. In the same manner as above, they were mixed at an equal mass, and compressed and crushed to obtain pellets of comparative catalyst a having a diameter of about 1 to 3 mm containing Pt and Rh.
[0030]
-Catalyst performance evaluation (1)-
2.0 g of each of the catalyst A of the above example and the catalyst a of the comparative example was installed inside the reaction tube of the laboratory exhaust gas purification performance evaluation apparatus. Next, a model atmosphere gas of A / F = 14.4, 14.7, or 20.0 having the composition shown in Table 1 was circulated, and the catalyst bed temperature was raised at a rate of 20 ° C./min. , 800 ° C. or 900 ° C., and subjected to an endurance treatment by exposing to those temperatures for 3 hours.
Next, a 50% purification temperature (T50) of C ₃ H ₆ was measured while flowing a model atmosphere gas of A / F = 14.6 (Stoichi) and lowering the catalyst bed temperature at a rate of 10 ° C./min. . The Stiki model atmosphere gas flow rate was 6.0 liters / minute / 0.03 g noble metal.
[0031]
FIG. 1 shows the relationship between the endurance treatment temperature and T50 for the model atmosphere gas. From the results shown in FIG. 1, in the catalyst a of the comparative example, T50 is remarkable by the endurance treatment at 800 ° C., particularly in the atmosphere of light lean with A / F = 14.7 and lean with A / F = 20.0. It can be clearly seen that the exhaust gas purification performance is greatly reduced and the catalyst A of the embodiment is significantly reduced.
[0032]
-Morphological observation of alloy catalyst-
For the catalyst A of the above example and the catalyst a of the comparative example, morphological observation by transmission electron microscope (TEM) and elemental analysis in the spot region of the electron microscope image by energy dispersive X-ray spectroscopy (EDX) were performed. . The results are shown in FIGS.
2A is a TEM image before the endurance treatment of the catalyst A, and FIG. 2B is a TEM image before the endurance treatment of the catalyst a. The metal particles are not observed from these TEM images, and are judged to be supported on the carrier in a very fine state.
[0033]
FIG. 3 (a) is a TEM image after subjecting the catalyst A to an endurance treatment at 800 ° C. for 3 hours under the condition of A / F = 14.7, and metal particles having a diameter of about 20 nm grown by sintering. Observed. When this metal particle was subjected to elemental analysis by EDX, three components of Pt, Rh, and Au were analyzed, and it was confirmed that these three components coexist in one particle.
FIG. 3B is a TEM image after subjecting the catalyst a of Comparative Example 1 to an endurance treatment at 800 ° C. for 3 hours under the condition of A / F = 14.7. Similarly, the catalyst a grew by sintering. Metal particles with a diameter of about 100 nm are observed. When this metal particle was elementally analyzed by EDX, only Pt was analyzed.
[0034]
FIG. 4 (a) is a TEM image after subjecting the catalyst A to an endurance treatment at 800 ° C. for 3 hours under a more severe condition of A / F = 20.0, and a metal particle having a diameter of about 20 nm grown by sintering. However, it can be seen that the particle diameter is the same as that after the durability treatment at A / F = 14.7. Elemental analysis of the metal particles by EDX confirmed that three components of Pt, Rh, and Au coexist in one particle.
[0035]
FIG. 4 (b) is a TEM image after subjecting the catalyst a to endurance treatment at 800 ° C. for 3 hours under more severe A / F = 20.0 conditions. Metal particles are observed. When this particle was subjected to elemental analysis by EDX, only Pt was analyzed.
[0036]
From these TEM images and EDX analysis, both catalyst A and catalyst a exist in a fine state where the catalyst component is not observed by the TEM image before the durability treatment, but the catalyst component is sintered by the durability treatment, From the TEM image, it can be seen that the particles grow to the diameters observed. However, in Catalyst A, particles having a diameter of more than about 20 nm are not observed, and sintering stops when the particle diameter becomes constant, whereas in Catalyst a, large particles having a diameter of about 400 nm are observed and sintering continues. I understand that
[0037]
In addition, from the catalyst of the first aspect prepared by supporting Pt and Rh on different carriers, the catalyst of the second aspect in which three components of Pt, Rh, and Au coexist in one particle is expressed. I understand that The coexistence state of these three components is presumed to have a sintering suppressing effect, and it is considered that the exhaust gas purification performance is not significantly reduced by the durability treatment as shown in FIG.
[0038]
Examples 2-5
In the same manner as in Example 1, Catalysts B to E of the first embodiment of Examples 2 to 5 which are summarized in Table 2 were prepared.
As the preparation of the first catalyst, Examples 2 to 5 were all carried out by supporting Pt on the Al ₂ O ₃ —CeO ₂ —ZrO ₂ composite oxide powder by evaporation to dryness of dinitrodiammine platinum. In Examples 2, 3, and 5, the first catalyst was prepared by reducing and precipitating Au from HAuCl ₄ · 4H ₂ O in the same manner as in Example 1. In Example 4, the first catalyst was used as it was without performing this reduction and precipitation. One catalyst was used.
[0039]
As the preparation of the second catalyst, in Examples 2 to 3, Al ₂ O ₃ powder (specific surface area of about 180 m ² / g) was used as the carrier, and in Examples 4 to 5, the same ZrO as that used in Example 1 was used. Using these _two powders, Rh was supported on these carriers by evaporation to dryness of rhodium nitrate in the same manner as in Example 1. Subsequently, Au was reduced and precipitated from HAuCl ₄ .4H ₂ O in the same manner as in Example 1 to prepare second catalysts of Examples 2, 4, and 5. In Example 3, a material in which Rh was supported on Al ₂ O ₃ powder was used as the second catalyst as it was.
[0040]
The obtained first catalyst and second catalyst were mixed in equal masses to obtain first to fifth catalysts B to E containing three components of Pt, Rh and Au.
In the summary shown in Table 2, “supported amount” is the mass% of the noble metal based on the total mass of the support and the noble metal, and “ratio” indicates the mass ratio of Pt or Rh / Au.
[0041]
Comparative Example 2
Except not performing Au reduction precipitation in Example 5, it carried out similarly to Example 4, and obtained the catalyst b of the comparative example containing 2 components of Pt and Rh which are summary in Table 2.
[0042]
Examples 6-9
In the same manner as in Example 1, Catalysts F to I of the first embodiment of Examples 6 to 9 which are summarized in Table 3 were prepared.
As for the preparation of the first catalyst, CeO ₂ —ZrO ₂ —Y ₂ O ₃ composite oxide powder (specific surface area of about 70 m) prepared by coprecipitation and calcination using cerium nitrate, zirconium nitrate, and yttrium nitrate as raw materials. ² / g, CeO ₂ / ZrO ₂ / Y ₂ O ₃ molar ratio = 50/47/3, indicated as “CZY” in Table 3.), both of which were obtained by evaporating to dryness of dinitrodiammine platinum. Pt was supported on the powder.
Next, in Examples 6, 7, and 9, the first catalyst was prepared by reducing and precipitating Au from HAuCl ₄ · 4H ₂ O in the same manner as in Example 1. In Example 8, this reduction and precipitation was not performed. The first catalyst was used as it was.
[0043]
As the preparation of the second catalyst, in Examples 6 to 8, ZrO ₂ —CaO composite oxide powder (specific surface area of about 80 m ² / g, prepared by coprecipitation / calcination using zirconium nitrate as a carrier and calcium nitrate as raw materials) ZrO ₂ / CaO molar ratio = 24/1, indicated as “ZCO” in Table 3.) In Example 9, the same ZrO ₂ powder as used in Example 1 was used, and these carriers were used. In the same manner as in Example 1, Rh was supported by evaporation to dryness of rhodium nitrate.
[0044]
Subsequently, Au was reduced and precipitated from HAuCl ₄ .4H ₂ O in the same manner as in Example 1 to prepare second catalysts of Examples 6, 8, and 9. In Example 7, Rh supported on ZrO ₂ —CaO composite oxide powder was used as the second catalyst as it was.
The obtained first catalyst and second catalyst were mixed in equal masses to obtain catalysts F to I containing three components of Pt, Rh, and Au.
Comparative Example 3
Except not performing Au reduction precipitation in Example 9, it carried out similarly to Example 9, and obtained the catalyst c of the comparative example containing 2 components of Pt and Rh which are shown in Table 2.
[0045]
-Catalyst performance evaluation (2)-
30 g of 40 mass% aluminum nitrate aqueous solution, 1.5 g of boehmite, and 60 cc of ion-exchanged water were added to 100 g of each of the alloy catalysts of Examples 2 to 9 and Comparative Examples 2 to 3 to prepare slurry.
[0046]
This slurry was wash-coated on a monolith carrier (diameter 30 mm × length 50 mm) (wall thickness 75 μm, cell density 93 cells / cm ² , hexagonal cell), pre-dried at 100 ° C. × 2 hours and 250 ° C. × 3 in air. After drying for a period of time, it was calcined at 550 ° C. for 2 hours to obtain an exhaust gas purifying catalyst in which the above-mentioned catalyst was coated on a monolith support.
Each of these exhaust gas purifying catalysts is placed in a normal pressure flow type endurance treatment apparatus, and is 900 ° C. × 5 hours in a model exhaust gas atmosphere having an air / fuel (A / F) ratio of 14.6 / 1. This was subjected to an endurance treatment for heating.
[0047]
Each exhaust gas purifying catalyst after the durability treatment was placed in a fixed bed flow reactor, was circulated model exhaust gas lean atmosphere and the rich atmosphere of the following is changed every one second, C ₃ H ₆ while increasing the catalyst temperature The purification rate was measured.
Rich atmosphere gas composition:
0.15% C ₃ H ₆ + 1.05% CO + 0.33% O ₂ + 0.3% NO
+ 0.35% H ₂ + 14.19% CO ₂ + 10% H ₂ O (residual N ₂ )
Lean atmosphere gas composition:
0.05% C ₃ H ₆ + 0.14% CO + 0.94% O ₂ + 0.34% NO
+ 14.27% CO ₂ + 10% H ₂ O (residual N ₂ )
In this exhaust gas purification performance test, the flow rate of the model exhaust gas was 30 liters / minute, and the temperature increase rate was 25 ° C./minute.
[0048]
The 50% purification rate (T50) of C ₃ H ₆ of each catalyst is summarized in FIGS. From this result, it can be seen that the catalyst of the present invention containing three components of Pt, Rh and Au has significantly higher exhaust gas purification performance than the catalyst of the comparative example containing two components of Pt and Rh. This is considered to be because the sintering of the catalyst component was suppressed as in the catalyst A of Example 1. It can also be seen that this sintering suppression effect is obtained when Au is supported on one or both of the first catalyst and the second catalyst.
[0049]
【The invention's effect】
It is possible to provide a catalyst in which sintering of the catalyst component is suppressed and the catalyst performance is stably exhibited over time.
[0050]
[Table 1]

[0051]
[Table 2]

[0052]
[Table 3]

[Brief description of the drawings]
FIG. 1 is a graph showing the relationship between durability treatment conditions and catalyst purification performance.
FIG. 2 is a transmission electron micrograph showing the particle structure of a catalyst component.
FIG. 3 is a transmission electron micrograph showing the particle structure of a catalyst component.
FIG. 4 is a transmission electron micrograph showing the particle structure of a catalyst component.
FIG. 5 is a graph comparing catalyst purification performance.
FIG. 6 is a graph comparing catalyst purification performance.

Claims (2)

A first catalyst having Pt supported on a carrier and a second catalyst having Rh supported on the carrier, and Au is further supported on at least one of the first catalyst and the second catalyst. Exhaust gas purification catalyst. The exhaust gas purifying catalyst according to claim 1, wherein the molar ratio of Pt / Au is 200/1 to 1/1, and the molar ratio of Rh / Au is 200/1 to 1/1.

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