JP2012187519A - Catalyst for exhaust gas purification - Google Patents

Abstract

An exhaust gas purification catalyst capable of maintaining purification performance even when exposed to high temperature (for example, 600 ° C. to 1100 ° C.) exhaust gas is provided.
An exhaust gas purification catalyst 1 disclosed herein is an exhaust gas purification catalyst comprising a porous carrier 20 and palladium 30 supported on the porous carrier 20, wherein the porous carrier 20 comprises: It includes a CZ support 10 made of a ceria-zirconia composite oxide and a silica-alumina support 12 made of alumina to which silica is added, and the palladium 30 is selectively supported on the CZ support. And In such an exhaust gas purifying catalyst, the catalytic activity at a high temperature (for example, 600 ° C. to 1100 ° C.) is improved by the interaction between the silica component in the silica-alumina carrier 12 and palladium 30.
[Selection] Figure 1

Description

  The present invention relates to an exhaust gas purification catalyst. Specifically, the present invention relates to an exhaust gas purification catalyst using palladium as a metal catalyst.

So-called three-way catalysts are widely used to purify hydrocarbons (HC), carbon monoxide (CO), and nitrogen oxides (NOx) contained in exhaust gas discharged from automobile internal combustion engines. In general, in a three-way catalyst, only when the air-fuel ratio is in the vicinity of the stoichiometric air-fuel ratio (stoichiometric), the three components in the exhaust gas can be efficiently purified by oxidation / reduction, and the air-fuel ratio is in the range in the vicinity of the stoichiometric. If it is out of the range, the catalytic activity is extremely reduced. Therefore, it is widely practiced to expand the air-fuel ratio range in which the catalyst can exhibit activity by using an oxygen storage material typified by ceria (CeO ₂ ) as a promoter. Also, instead of ceria with low heat resistance, a ceria-zirconia composite oxide (or solid solution) made of ceria and zirconia (ZrO ₂ ) as a composite oxide (or solid solution) is used as a co-catalyst to improve the heat resistance characteristics of the catalyst. It is also widely done.

  Examples of noble metal catalysts used for the three-way catalyst include palladium, platinum, and rhodium. Usually, for use as an exhaust gas purifying catalyst, one or more kinds of noble metal catalysts selected from the above noble metal catalysts are supported on a porous carrier. In some cases, multiple types of noble metal catalysts are supported on a single carrier, and in order to prevent a decrease in catalytic activity due to alloying and sintering of noble metal catalysts during high temperature use, separate each noble metal catalyst type and separate it. The catalyst structure may be supported on a carrier. In the latter case, in order to develop the best catalytic activity for the noble metal catalysts having different characteristics, it is necessary to search for an optimal porous support for each noble metal catalyst. For example, Patent Document 1 discloses a first catalyst in which rhodium is supported on a porous carrier mainly composed of θ-alumina, at least one of platinum and palladium, a porous carrier such as γ-alumina, and a ceria-zirconia composite oxidation. An exhaust gas purifying catalyst comprising a second catalyst supported on a mixture with a product is disclosed. Patent Document 2 discloses an exhaust gas purification catalyst characterized in that palladium is supported on activated alumina powder and platinum is supported on cerium oxide powder.

  Conventionally, a porous support for supporting palladium, which is one of the noble metal catalysts, is composed of a mixture of alumina and ceria-zirconia composite oxide (hereinafter also referred to as “CZ composite oxide”). It is a carrier (for example, Patent Document 1 and Patent Document 3). The carrier has the characteristics of the large specific surface area and high durability (particularly heat resistance) of alumina and the oxygen storage / release ability (hereinafter also referred to as “OSC”) of the ceria-zirconia composite oxide. It is useful because it can.

Japanese Patent Laid-Open No. 10-277389 Japanese Patent Laid-Open No. 7-255103 JP 2009-648 A

However, the conventional exhaust gas purification catalyst in which palladium is supported on a porous carrier made of a mixture of alumina and CZ composite oxide has a good exhaust gas purification rate when the catalyst bed temperature is low (for example, 300 ° C. to 600 ° C.). However, when used in a high temperature range of 600 ° C. or higher, there is a problem that the activity is lowered. For this reason, it has been unavoidable that the catalyst activity after the endurance use of the conventional exhaust gas purifying catalyst is greatly reduced as compared with that before use.
Regarding such a decrease in catalytic activity, the present inventors have found that palladium tends to be oxidized in a high temperature atmosphere of 600 ° C. or higher, and that the valence of palladium tends to increase, that is, palladium It was thought that the cause was that the metal state became closer to the oxide.
The present invention has been made in view of the circumstances of such an exhaust gas purification catalyst, and is an exhaust gas purification catalyst capable of maintaining exhaust gas purification performance even when exposed to high temperature (for example, 600 ° C. to 1100 ° C.) exhaust gas. For the purpose of provision.

The present inventors have studied from various angles and have come to create the present invention capable of realizing the above object. That is, the exhaust gas-purifying catalyst disclosed herein comprises a porous carrier and palladium supported on the porous carrier, and the porous carrier comprises a CZ carrier made of ceria-zirconia composite oxide, and silica. And a silica-alumina support composed of added alumina. The exhaust gas purifying catalyst disclosed herein is characterized in that the palladium is selectively supported on the CZ support.
In the exhaust gas purifying catalyst having such a configuration, a silica-alumina carrier is present in the vicinity of the CZ carrier on which palladium is supported. By setting it as said structure, the catalyst activity fall of palladium at high temperature (for example, 600 to 1100 degreeC) is suppressed, and a catalyst shows high purification performance even after the endurance test at high temperature. This is considered to be caused by the fact that the silica component in the silica-alumina carrier and palladium as the noble metal catalyst interact with each other, so that the valence of palladium at a high temperature is kept low.
Further, in the exhaust gas purifying catalyst having such a configuration, palladium is hardly supported directly on the silica-alumina carrier. This is because the silica-alumina support is likely to cause crystal growth at high temperatures. If palladium is directly supported on the silica-alumina support, palladium crystal growth (sintering) is likely to occur during high-temperature use, and the activity of the catalyst is reduced. It is. That is, by using the above configuration, it is possible to suppress a decrease in the catalytic activity of palladium after durable use at high temperatures.
In the exhaust gas purifying catalyst having such a configuration, palladium is directly supported on the CZ carrier. Therefore, in the near field of palladium, the oxygen partial pressure is appropriately adjusted by the oxygen storage / release capability (OSC) of the CZ carrier. Therefore, in the exhaust gas purifying catalyst having such a configuration, the change in the air-fuel ratio in the vicinity of palladium is moderate with respect to fluctuations in the exhaust gas components, and the exhaust gas purifying catalyst stably exhibits high catalytic activity.

In a preferred embodiment of the exhaust gas purifying catalyst disclosed herein, when the entire CZ support is 100% by mass, the palladium loading rate is 0.1% by mass or more and 3% by mass or less (preferably 0.8%). 1% by mass or more and 1.5% by mass or less).
When the palladium loading is within the above range, it is desirable that a sufficient catalytic effect is obtained by palladium and that there is no excessive burden in terms of cost.

In another preferred embodiment of the exhaust gas purifying catalyst disclosed herein, the mass mixing ratio of the palladium-supported CZ support and the silica-alumina support (CZ support: silica-alumina support) is 1: 1. It is characterized by being in the range of ˜4: 1.
Regarding the mass mixing ratio of the CZ support and the silica-alumina support, if the mixing ratio of the CZ support is too small than the above range, the absolute value of the OSC of the entire porous support is insufficient, which is not preferable because the catalytic activity decreases. In addition, when the mixing ratio of the silica-alumina carrier is too smaller than the above range, the effect of improving the palladium activity at high temperature due to the addition of silica does not appear, and in addition, the content of the alumina component decreases, The specific surface area decreases, which is not preferable.

In a preferred embodiment of the exhaust gas purifying catalyst disclosed herein, the mass content of the silica component in the silica-alumina carrier is 1% by mass or more and 10% by mass or less (preferably, when the total catalyst is 100% by mass). 1.25 mass% to 7 mass%, more preferably 2 mass% to 5 mass%).
When the content of the silica component is less than 1% by mass, the effect of improving the palladium activity at high temperature due to the addition of silica is not observed. Moreover, when the content rate of the said silica component is more than 10 mass%, purification performance falls by the heat resistance of the exhaust gas purification catalyst falling.

In another preferred embodiment of the exhaust gas purifying catalyst disclosed herein, the mass content of the alumina component in the silica-alumina support is 15% by mass or more and 25% by mass when the total catalyst is 100% by mass. Or less (preferably 20% by mass or more and 24% by mass or less).
By making the content rate of an alumina component into the said range, high durability (especially heat resistance) and a large specific surface area as a whole porous support | carrier can be implement | achieved.

It is a schematic structure explanatory view of an exhaust gas purifying catalyst according to an embodiment. It is a graph which shows the NOx purification rate (vertical axis:%) concerning a plurality of examples and comparative examples. It is a graph which shows the specific surface area (vertical axis: m < ² > / g) after the durability test which concerns on a several Example.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of the invention will be described with reference to the drawings. It should be noted that matters other than the matters specifically mentioned in the present specification (for example, the composition of the porous carrier) and matters necessary for the implementation of the present invention (for example, the general arrangement relating to the arrangement of the exhaust gas purifying catalyst in an automobile). Matter) can be understood as a design matter of those skilled in the art based on the prior art in the field. The present invention can be carried out based on the contents disclosed in this specification and common technical knowledge in the field.
FIG. 1 shows a rough configuration of an exhaust gas purifying catalyst 1 according to an embodiment of the present invention. The exhaust gas-purifying catalyst 1 disclosed here comprises a porous carrier 20 and palladium 30 typically carried in the form of fine particles of a noble metal on the porous carrier 20, and the porous carrier 20 is a CZ carrier. 10 and a silica-alumina support 12. The palladium 30 is selectively supported on the CZ support 10.

The porous carrier 20 constituting the exhaust gas-purifying catalyst 1 disclosed here contains the CZ carrier 10.
The production method of the CZ composite oxide constituting the CZ support 10 is not particularly limited, and is produced by, for example, a coprecipitation method, a sol-gel method, a hydrothermal synthesis method, or the like. The preparation method of CZ complex oxide by a typical coprecipitation method is as follows. That is, a surfactant is mixed with a mixed aqueous solution composed of a water-soluble salt of cerium and zirconium (for example, nitrate) as needed, and then the pH is gradually increased by adding ammonia water, which is an alkaline substance. The composite oxide can be obtained by generating a coprecipitate and heat-treating the coprecipitate.
The CZ carrier 10 is preferably in the form of powder (particulate) from the viewpoint that a larger specific surface area can be secured. There is no particular restriction on the specific surface area of the CZ carrier 10, it is preferable that the specific surface area (specific surface area as measured by BET method. Hereinafter the same.) Is 50 to 300 m ² / g, with 100 to 200 m ² / g More preferably. When the specific surface area of the CZ support 10 is too smaller than 50 m ² / g, the OSC of the CZ support 10 tends to decrease. On the other hand, when the specific surface area is more than 300 m ² / g, the heat resistance of the CZ support 10 This is not preferable because the properties are lowered.

The palladium 30 used in the exhaust gas-purifying catalyst 1 disclosed herein is selectively supported on the CZ carrier 10. With such a catalyst structure, the exhaust gas purification catalyst 1 can exhibit a stable purification performance against fluctuations in exhaust gas components due to the OSC of the CZ carrier 10 existing in the near field of the palladium 30.
The amount of palladium 30 supported on the CZ carrier 10 is preferably 0.1% by mass or more and 3% by mass or less, and 0.1% by mass or more and 1.5% by mass or less when the entire CZ support 10 is 100% by mass. More preferably, it is at most mass%. If the supported amount of palladium 30 is less than 0.1% by mass, the catalytic activity obtained by palladium 30 becomes insufficient. On the other hand, if it is more than 3% by mass, palladium 30 is liable to cause grain growth and cost. But it is disadvantageous.
The method for supporting the palladium 30 on the CZ support 10 is not particularly limited. For example, after impregnating the CZ support 10 in an aqueous solution containing a palladium salt (for example, nitrate) or a palladium complex (for example, a tetraammine complex). It can be prepared by drying and baking.

  The porous carrier 20 constituting the exhaust gas purification catalyst 1 disclosed herein contains the silica-alumina carrier 12. The silica-alumina carrier 12 is made of alumina to which silica is added, and is produced, for example, by a sol-gel method, a coprecipitation method, a hydrothermal synthesis method, or the like. A method for preparing the silica-alumina carrier 12 by a typical sol-gel method is as follows. That is, a wet gel is obtained by using a silicon alkoxide and an aluminum salt as raw materials and mixing with an appropriate solvent while adjusting temperature and pH. The silica-alumina carrier 12 can be obtained by dehydrating and drying the wet gel by heat treatment and baking.

The silica-alumina carrier 12 used in the exhaust gas-purifying catalyst 1 disclosed herein can be used regardless of whether it is in the form of powder or liquid, but from the viewpoint of ensuring a larger specific surface area, The shape (particulate) is preferably used. The average particle size of the silica-alumina carrier 12 (average particle size measured by laser diffraction / scattering method; the same applies hereinafter) is preferably 5 to 500 μm, more preferably 10 to 70 μm. Further, the silica - is preferable that the specific surface area of the alumina support 12 is 50~700m ² / g, more preferably 200 to 500 m ² / g. When the average particle diameter of the silica-alumina support 12 is too larger than 500 μm, or the specific surface area is too small than 50 m ² / g, the interaction between the silica component in the silica-alumina support 12 and palladium 30 is weakened. Since the effect of silica addition is difficult to appear, it is not preferable. Further, when the average particle diameter of the silica-alumina support 12 is too smaller than 5 μm or the specific surface area is too larger than 700 m ² / g, the silica-alumina support 12 is thermally unstable, so that the high temperature of the catalyst. Use tends to cause palladium 30 sintering, which is not preferable.
The silica-alumina carrier 12 used in the exhaust gas purification catalyst 1 disclosed herein is amorphous regardless of whether it contains a compound having high crystallinity (for example, zeolite). Can be used.

The porous carrier 20 used in the exhaust gas purifying catalyst 1 disclosed here is obtained by simply mixing the CZ carrier 10 on which the palladium 30 is supported and the silica-alumina carrier 12. Here, the CZ support 10 and the silica-alumina support 12 are preferably mixed within a mass mixing ratio (CZ support: silica-alumina support) in the range of 1: 1 to 4: 1.
Regarding the mass mixing ratio of the CZ support 10 and the silica-alumina support 12, if the mixing ratio of the CZ support 10 is too smaller than the above range, the OSC of the porous support 20 as a whole is lowered, which is not preferable. In addition, when the mixing ratio of the silica-alumina carrier 12 is too smaller than the above range, the effect of improving the palladium activity at a high temperature due to the addition of silica does not appear, and in addition, the content of the alumina component is lowered. Since the whole specific surface area decreases and the dispersibility of palladium 30 falls, it is not preferable.

The mass content of the silica component in the silica-alumina support 12 when the entire exhaust gas-purifying catalyst 1 disclosed herein is 100 mass% is 1 mass% or more and 10 mass% or less (preferably 1.25 mass%). It is desirable that the content is 7% by mass or less, more preferably 2% by mass or more and 5% by mass or less.
By making the content rate of a silica component into the said range, the improvement of the catalytic activity of the palladium 30 by the silica component addition at high temperature and the high heat resistance of the exhaust gas purification catalyst 1 can be made compatible.
Moreover, when the exhaust gas purification catalyst 1 disclosed herein is 100% by mass, the mass content of the alumina component in the silica-alumina carrier 12 is 15% by mass to 25% by mass (preferably 20% by mass). It is desirable that it is 24 mass% or less.
By making the content rate of an alumina component into the said range, high heat resistance and the large specific surface area as the whole porous support | carrier 20 are realizable.

  Further, as long as the total mass of the mixture of the CZ support 10 and the silica-alumina support 12 is 50% by mass or more with respect to the entire porous support 20, the porous support 20 includes the CZ support 10 and the silica-alumina support 12. Other ingredients besides can be added. For example, an alkaline earth metal element (or alkaline earth metal oxide) for the purpose of increasing mechanical strength, improving durability (thermal stability), suppressing sintering of the catalyst, or preventing poisoning of the catalyst, One or more elements or oxides selected from rare earth elements (or rare earth oxides), silica, titania, ceria, zirconia, and the like can be added to the porous carrier 20.

  The exhaust gas-purifying catalyst 1 disclosed herein can be molded into a shape similar to that conventionally used for this type of catalyst, such as a pellet shape, a foam shape, a honeycomb shape, or a filter shape. For example, when forming into a honeycomb shape, the palladium 30 is supported on the surface of a honeycomb substrate having a honeycomb structure formed of ceramic or alloy (stainless steel or the like) having high thermal shock resistance such as cordierite or silicon carbide (SiC). It is produced by coating the porous carrier 20 made. Moreover, when shape | molding in a pellet shape, it manufactures by shape | molding the porous support | carrier 20 with which the said palladium 30 was carry | supported by the conventional method using a press machine.

Several examples relating to the present invention will be described below, but the present invention is not intended to be limited to those shown in the specific examples.

Example 1
A predetermined amount of a commercially available ceria-zirconia composite oxide powder (CZ powder) is impregnated with a predetermined amount of an aqueous palladium nitrate solution having a Pd content of 8.2% by mass, dried at 120 ° C. for 12 hours, and then an electric furnace. Was calcined at 500 ° C. for 2 hours to prepare Pd / CZ powder carrying palladium. At this time, the supported amount of Pd was 0.42% by mass with respect to the CZ powder. To 12 g of the obtained Pd / CZ powder, silica-alumina powder (manufactured by Sasol; silica component content is 5% by mass when the total silica-alumina is 100% by mass, alumina component content is 95% by mass) 4 g Were mixed. A load of about 1 ton was applied to this mixed powder by a cold isostatic press, and a pellet having a volume of about 1 mm ³ was formed to obtain a sample of Example 1.
About Example 1, the mass content rate of a silica component when the whole catalyst is 100 mass% is 1.25 mass%. Moreover, the mass content rate of an alumina component when the whole catalyst is 100 mass% is 23.75 mass%. The average particle size of the silica-alumina used was 50 μm, and the BET specific surface area was 370 m ² / g.

(Example 2)
Pd / CZ powder was prepared by the same composition ratio and manufacturing process as in Example 1, and 12 g of the obtained Pd / CZ powder was mixed with silica-alumina powder (manufactured by Sasol; 100% by mass of the entire silica-alumina). The silica component content was 10% by mass and the alumina component content was 90% by mass). This mixed powder was formed into pellets in the same manner as in the manufacturing process according to Example 1 to obtain a sample of Example 2.
About Example 2, the mass content rate of a silica component when the whole catalyst is 100 mass% is 2.5 mass%. Moreover, the mass content rate of an alumina component when the whole catalyst is 100 mass% is 22.5 mass%. The silica-alumina used had an average particle size of 50 μm and a BET specific surface area of 400 m ² / g.

(Example 3)
Pd / CZ powder was prepared by the same composition ratio and manufacturing process as in Example 1, and 12 g of the obtained Pd / CZ powder was mixed with silica-alumina powder (manufactured by Sasol; 100% by mass of the entire silica-alumina). The silica component content was 40 mass% and the alumina component content was 60 mass%). This mixed powder was formed into pellets in the same manner as in the manufacturing process according to Example 1 to obtain a sample of Example 3.
About Example 3, the mass content rate of a silica component when the whole catalyst is 100 mass% is 10 mass%. Moreover, the mass content rate of an alumina component when the whole catalyst is 100 mass% is 15 mass%. The silica-alumina used had an average particle size of 50 μm and a BET specific surface area of 500 m ² / g.

(Comparative Example 1)
In the production processes according to Examples 1 to 3, a porous carrier was produced using alumina instead of silica-alumina. That is, Pd / CZ powder was prepared by the same composition ratio and manufacturing process as in Example 1, and 4 g of alumina powder was mixed with 12 g of the obtained Pd / CZ powder. This mixed powder was formed into pellets in the same manner as in the manufacturing process according to Example 1, and a sample of Comparative Example 1 was obtained. About the comparative example 1, the mass content rate of an alumina when the whole catalyst is 100 mass% is 25 mass%.

(Comparative Example 2)
In the production processes according to Examples 1 to 3, a porous carrier was produced using silica instead of silica-alumina. That is, Pd / CZ powder was prepared by the same composition ratio and manufacturing process as in Example 1, and 4 g of silica powder was mixed with 12 g of the obtained Pd / CZ powder. This mixed powder was formed into pellets in the same manner as in the manufacturing process according to Example 1, and used as a sample of Comparative Example 2. About the comparative example 2, the mass content rate of a silica when the whole catalyst is 100 mass% is 25 mass%.
For the exhaust gas purifying catalysts according to Examples 1 to 3 and Comparative Examples 1 and 2, the composition ratio (% by mass) of the porous carrier with respect to the whole catalyst is summarized in Table 1.

<Durability test>
A durability test was carried out on a total of five types of exhaust gas purifying catalysts according to Examples 1 to 3 and Comparative Examples 1 and 2 using an annular reactor. In the durability test, the above exhaust gas purifying catalyst was held at 1100 ° C., 1% by volume of carbon monoxide (CO) gas (balance gas was nitrogen) and 5% by volume of oxygen (O ₂ ) gas (balance gas was nitrogen) Was carried out by alternately repeating the flow for 5 hours in a 5-minute cycle.

<Catalyst performance evaluation test>
About the exhaust gas purifying catalysts according to Examples 1 to 3 and Comparative Examples 1 and 2 after the durability test, 1.0 g was weighed and placed in the evaluation device. Thereafter, a gas having the composition shown in Table 2 was circulated at 700 ° C. under a gas flow rate of 20 L / min, and the NOx purification rate was calculated by measuring the NOx concentration at the inlet and outlet of the exhaust gas purification catalyst. The gas shown in Table 2 has a gas composition with a rich air-fuel ratio (that is, an oxygen-deficient side). The results are shown in FIG.
As is clear from the results shown in FIG. 2, it can be seen that the exhaust gas purification catalysts according to Examples 1 to 3 have an improved NOx purification rate as compared with the exhaust gas purification catalyst according to Comparative Example 1. That is, it can be seen that the exhaust gas purification catalyst in which the silica-alumina carrier is added to the porous carrier shows a higher NOx purification rate than the exhaust gas purification catalyst in which alumina is added instead of the silica-alumina carrier. This is because the introduction of the silica component into the porous carrier suppressed the decrease in the activity of palladium due to the interaction between the silica component and palladium.
Further, it was found that the exhaust gas purification catalyst according to Comparative Example 2 has a greatly reduced NOx purification rate as compared with the exhaust gas purification catalysts according to Examples 1 to 3. That is, the exhaust gas purification catalyst in which the silica-alumina carrier was added to the porous carrier showed a higher NOx purification rate than the exhaust gas purification catalyst in which silica was added instead of the silica-alumina carrier.
It can be seen that the preferred range for the exhaust gas-purifying catalyst exhibiting higher catalytic activity is a case where the silica component content relative to the whole catalyst is 1% by mass or more and 10% by mass or less.

<Specific surface area evaluation>
With respect to a total of three types of exhaust gas purifying catalysts according to Examples 1 to 3 after the durability test, the specific surface area was measured from the nitrogen adsorption amount by the BET method. The results are shown in FIG.
As is clear from the results shown in FIG. 3, the exhaust gas purifying catalysts according to the respective examples can maintain a relatively high specific surface area even after the endurance test. In particular, it is possible to maintain a high specific surface area in a range where the silica component content is 1.25% by mass (Example 1) to 2.5% by mass (Example 2) when the total catalyst is 100% by mass. Admitted. Further, according to this evaluation test, when the content of the silica component in the catalyst was more than 10% by mass, the heat resistance of the porous carrier was lowered and a tendency to cause crystal growth was observed. Therefore, this evaluation test indicates that the preferable silica component content when the total catalyst is 100% by mass is about 1.25% by mass to 7% by mass (more preferably 2% by mass to 5% by mass). Was also supported by. This also confirms that in the catalyst performance evaluation test, the results of which are shown in FIG. 2, the cause of the reduction in purification performance due to the excessive silica component in the silica-alumina support is due to the decrease in heat resistance of the porous support. But there is.

1 Exhaust gas purification catalyst 10 CZ support 12 Silica-alumina support 20 Porous support 30 Palladium (Pd fine particles)

Claims (5)

An exhaust gas purifying catalyst comprising a porous carrier and palladium supported on the porous carrier,
The porous carrier includes a CZ carrier made of ceria-zirconia composite oxide and a silica-alumina carrier made of alumina to which silica is added,
The exhaust gas-purifying catalyst, wherein the palladium is selectively supported on the CZ support.   The exhaust gas-purifying catalyst according to claim 1, wherein the palladium loading rate when the entire CZ carrier is 100 mass% is 0.1 mass% or more and 3 mass% or less.   The mass mixing ratio (CZ support: silica-alumina support) of the CZ support on which the palladium is supported and the silica-alumina support is in the range of 1: 1 to 4: 1. Exhaust gas purification catalyst.   The exhaust gas-purifying catalyst according to any one of claims 1 to 3, wherein a mass content of the silica component in the silica-alumina support is 1% by mass or more and 10% by mass or less when the total catalyst is 100% by mass. .   5. The mass content of the alumina component in the silica-alumina carrier is 15% by mass or more and 25% by mass or less when the total catalyst is 100% by mass. Exhaust gas purification catalyst.

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