JP2007090223A - Exhaust gas purifying catalyst - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an exhaust gas purifying catalyst which can maintain a high catalyst activity even under an oxidative atmosphere. <P>SOLUTION: In the exhaust gas purifying catalyst formed by depositing noble metal particles containing rhodium particles 3 on oxide carriers 2, electron donors 4 having electron donation capability for providing electrons to the rhodium particles 3 are deposited on the oxide carriers 2. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

The present invention relates to an exhaust gas purification catalyst.

  In recent years, exhaust gas regulations for automobiles have become more and more stringent, and exhaust gas purification catalysts include purification of harmful components contained in exhaust gas, such as unburned hydrocarbons (HC) and carbon monoxide (CO). Is required to be performed more efficiently. An exhaust gas purification catalyst is a catalyst in which noble metal particles are supported on the surface of a carrier such as alumina, and harmful components contained in the exhaust gas, such as unburned hydrocarbons (HC) and carbon monoxide (CO), are oxidized with noble metal particles. It is then converted into water and gas, which are harmless components.

  On the other hand, in the exhaust gas regulations that have become stricter in recent years, the amount of precious metals used and the number of catalysts are constantly increasing, and there is a problem of depletion of resources and an increase in manufacturing cost, so it is necessary to reduce the amount of precious metals in the catalyst.

  Since the activity of the noble metal particles is substantially proportional to the surface area of the noble metal particles, it is necessary to maintain the surface area of the noble metal as large as possible, that is, with fine particles, in order to maintain the maximum catalytic activity with a small amount of noble metal. In particular, rhodium (Rh) is an element indispensable for an exhaust gas purification catalyst, and is known to exhibit high activity in a small amount (see, for example, Patent Document 1).

  Here, since the noble metal particles have a small particle diameter and a large surface energy, they have a characteristic that they tend to aggregate and enlarge.

JP 2003-117393 A

However, in the conventional exhaust gas purifying catalyst, as a factor of performance degradation due to thermal degradation of Rh, (1) Rh approaches each other mainly due to the large surface energy possessed by Rh, in addition to surface area degradation due to phase transition of the carrier. As a result of agglomeration, there are two points of reduction in catalytic activity due to reduction in the surface area of Rh, and (2) deactivation due to solid solution of Rh ₂ O ₃ produced by oxidation into the oxide support.

Here, the deactivation due to the solid solution of Rh ₂ O _{3 in} the oxide carrier of (2) is caused by the solid solution by using an element having a relatively low reaction activity with respect to Rh as the oxide carrier. Although it is possible to suppress the decrease in activity to some extent, it is difficult to prevent the decrease in activity due to oxidation from Rh metal to Rh ₂ O ₃ easily in an oxidizing atmosphere.

  Accordingly, an object of the present invention is to provide an exhaust gas purifying catalyst capable of maintaining high catalytic activity even in an oxidizing atmosphere.

  In order to achieve the above-mentioned object, the present invention provides an electron-donating agent having an electron-donating ability for donating electrons to the rhodium particles in an exhaust gas purification catalyst in which noble metal particles containing rhodium particles are supported on an oxide carrier. The body is supported on the oxide carrier.

  According to the present invention, rhodium particles and an electron donor are supported on the oxide carrier, and electrons are donated from the electron donor to the rhodium particles, so that the exhaust gas purification catalyst is exposed to an oxidizing atmosphere. However, the oxidation of the rhodium particles is suppressed, and high catalytic activity can be maintained.

  Hereinafter, an exhaust gas purifying catalyst according to an embodiment of the present invention will be described in detail.

[Composition of catalyst]
As shown in FIG. 1, an exhaust gas purifying catalyst 1 according to an embodiment of the present invention includes a porous oxide carrier 2, a noble metal particle including rhodium particles 3 supported on the surface of the oxide carrier 2, and And an electron donor 4 supported on the surface of the oxide carrier 2, and the electron donor 4 has an electron donating ability to donate electrons to the rhodium particles 3.

[Precious metal particles]
The noble metal particles as the catalyst particles include rhodium (Rh) particles 3 which are elements that have high conversion performance from a low temperature range in the exhaust gas purification catalyst 1 and have a wide ternary window width and are very effective against atmospheric fluctuations. Is included at least.

  The supported amount of Rh particles 3 contained in the catalyst is preferably 0.3 g / L or less. This is because the electron donating effect of the electron donor 4 is most effectively exhibited when the amount of Rh used in the catalyst is 0.3 g / L or less. Thereby, it is possible to provide an inexpensive exhaust gas purification catalyst by improving the catalyst performance according to the present invention and reducing the amount of expensive Rh used.

  The catalyst can also contain other noble metal elements such as Pt and Pd, which can further improve the catalyst performance.

[Oxide support]
The oxide carrier 2 according to the present invention preferably includes at least one selected from the group consisting of ZrO ₂ , TiO ₂ , and SiO ₂ .

  The electron donor 4 having an electron donating ability needs to be supported on the oxide surface even after high temperature durability. When the electron donor 4 and the oxide carrier 2 form a complex oxide, for example, or when the electron donor 4 is dissolved between the oxide carrier lattices, the surface concentration of the electron donor 4 decreases. This is because, as a result, the interface between Rh and the electron donor 4 decreases, so that the electron donating ability for Rh is reduced or deactivated.

For this reason, it is preferable that ZrO ₂ , TiO ₂ , and SiO ₂ are included as the oxide carrier 2 that is relatively difficult to take the form of the electron donor 4 and the composite oxide and in which Rh can be dispersed. Further, for water vapor present in a large amount in automobile exhaust gas, it is particularly preferable to contain ZrO ₂ having relatively high durability.

The form of the oxide support 2 may be a mixture of a plurality of oxide supports or a form of a composite oxide. For example, in order to improve heat resistance, ZrO ₂ -La prepared by a coprecipitation method is used. ₂ O ₃ —CeO ₂ mixed oxide and the like can be mentioned.

  By using these oxide carriers 2, the electron donor 4 having an electron donating ability can be used in the oxide carrier 2 even in an oxidizing atmosphere at a high temperature of 700 ° C. or higher, or in a state where an oxidizing atmosphere and a reducing atmosphere are repeated. The state of being reliably supported on the surface can be maintained.

[High oxidation of Rh]
Note that when Al ₂ O ₃ is used as the oxide support 2, the bond energy of the Rh3d5 orbit is preferably 308.8 eV or less.

  This is because when the 3d orbital binding energy of Rh is shifted to a higher energy side, Rh becomes in a highly oxidized state, which causes a decrease in catalyst activity, resulting in a decrease in catalyst performance at 308.8 eV or more.

High oxidation of Rh can be measured by Rh binding energy analysis by XPS. In general, it is known that the Rh3d5 orbital binding energy is 307.2 eV in the Rh in the metal state, and the Rh in the high oxidation state is around 310.2 eV. As described above, when Al ₂ O ₃ is used as the oxide support 2, the catalyst performance deteriorates at 308.8 eV or more. Therefore, the Rh3d5 orbital binding energy is desirably 308.8 eV or less. It is common to perform charge correction using a certain element at the time of measurement, and the bond energy of an element with a large content is corrected with respect to a literature value.

[Electron donor]
The electron donor 4 preferably contains at least one selected from the group of barium (Ba), cesium (Cs), and potassium (K).

In the oxidizing atmosphere, the Rh particles 3 are oxidized to become a higher oxidation state Rh, and the original catalytic performance is lowered. For example, when Al ₂ O ₃ is used as the oxide carrier 2, the Rh particles 3 are dispersed as highly oxidized Rh on the Al ₂ O ₃ , and a part thereof is in a solid solution state on the surface and inside of the Al ₂ O ₃ , The catalyst performance of Rh becomes a factor that deactivates. This phenomenon is conspicuous in a high-temperature oxidizing atmosphere, and is one of the main factors that decrease the catalytic performance of Rh after durability when used as a catalyst for purifying automobile exhaust gas.

  In the present invention, as a result of intensive studies in view of such degradation factors peculiar to Rh, the inventors have arrived at the above-described invention.

  The method for suppressing the high oxidation of Rh according to the present invention is to maintain the Rh particles 3 in a more reduced state by donating electrons to the Rh particles 3, so that even when exposed to a high temperature oxidizing atmosphere, the catalyst is high. The performance is maintained. As an electron donating method to the Rh particles 3, there can be considered a method of donating electrons from the oxide carrier 2 and an electron donation by other additive elements, but an electron donor 4 which is an element having an electron donating property is appropriately added. As a result, it was found that the Rh particles 3 can be maintained in a reduced state and high oxidation can be suppressed. As a result, an exhaust gas purification catalyst 1 in which noble metal particles including at least Rh particles 3 and an electron donor 4 having an electron donating property are supported on an oxide carrier 2 has been conceived.

  Further, the electron donor 4 needs to select an element having as low an electronegativity as possible with respect to Rh. This is in order to more efficiently donate electrons to Rh. As a result of intensive studies, the electronegativity of Pauling is very low below 0.90, in other words, the electron donating ability is extremely low. Most desirable is a high element. Ba, Cs, and K satisfy this condition, and all have high electron donating ability. Of these, Ba is particularly preferable. This is because, in an automobile exhaust gas containing a large amount of water vapor, an element having a high solubility in water diffuses into the catalyst and the inorganic base material, and the possibility that the supported amount in the catalyst decreases is the lowest.

[Exhaust gas purification catalyst with multiple catalyst layers]
It is also possible to form a plurality of catalyst layers on a honeycomb cordierite base material or a stainless steel foil base material.

  FIG. 2 is an enlarged cross-sectional view showing an exhaust gas purifying catalyst in which a plurality of catalyst layers are formed on a cordierite base material.

  In the exhaust gas purification catalyst 5, a second catalyst layer 7 is formed on a cordierite base material 8 with a first catalyst layer 6 interposed therebetween. In the first catalyst layer 6, platinum (Pt) or palladium (Pd) particles are contained on the oxide support as noble metal particles, and in the second catalyst layer 7, the oxide support 2 is formed on the oxide support 2. The Rh particles 3 and the electron donor 4 are contained in a state of being arranged close to each other. According to this, electron donation by the electron donor 4 can be performed efficiently and in a short time.

  Here, it is desirable that the second catalyst layer 7 is disposed on the surface layer side of the exhaust gas purification catalyst 5 with respect to the first catalyst layer 6. This is because Rh is expensive compared to other noble metals such as Pt and Pd, so it is necessary to reduce the amount of use as much as possible. For this purpose, Rh should be arranged on the surface layer side that is more easily contacted with exhaust gas. This is because the catalyst design is efficient.

[Content of electron donor]
The amount of the electron donor 4 supported on the Rh particles 3 is desirably 0.5 to 3 in terms of the molar ratio of the Rh particles 3 and the electron donor 4. When the molar ratio is 0.5 or less, the amount of the electron donor 4 supported is too small to provide a sufficient electron donating effect. On the other hand, when the molar ratio is 3 or more, the unburned HC contained in the exhaust gas of the automobile is adsorbed on the electron donor 4 and the electron donating ability of the electron donor 4 is reduced, so that the purification reaction is easily inhibited. It is.

[Positional relationship between Rh particles and electron donor]
The electron donor 4 is preferably arranged in the vicinity of the Rh particles 3 on the same oxide carrier 2. Thereby, electron donation can be performed more efficiently and in a short time.

  As a method for confirming that the electron donor 4 and the Rh particles 3 are arranged close to each other, the top of the oxide carrier 2 is observed by TEM, and X-rays with a beam width reduced to about several nm are selectively irradiated. In this case, Rh and an element having an electron donating ability are detected from the same location. In the present embodiment, the Rh and the electron donor 4 peak are detected at the same location by EDX measurement with a beam width of 5 nm or less, so that the electron donor 4 and the Rh particle 3 are arranged close to each other. Can be confirmed.

  Further, as a specific adjustment method, a supporting method by adsorption impregnation and the like can be mentioned. In this adsorption impregnation, the oxide carrier powder is dispersed and adsorbed in an aqueous solution in which the Rh complex salt and the electron donor precursor salt are dissolved, dried and rectified, and then baked to obtain Rh and the electron donor 4. This is a method for obtaining a catalyst in which is supported on an oxide support. If the salts are all soluble in an organic solvent, it can be carried out in an organic solvent.

  As an adjustment method other than the adsorption impregnation, an adjustment method by spray impregnation or a reverse micelle method is used, and after depositing Rh particles 3 from a Rh complex salt with a reducing material in a micelle, the electron donor precursor salt is micelle. There is a method of obtaining a catalyst precursor by introducing the oxide carrier precursor salt into the micelle and insolubilizing it in the micelle through a step of introducing into the micelle and insolubilizing in the micelle.

  In addition, in order to further increase the interface between Rh and electron donor 4, Rh precursor salt and electron donor precursor salt and polymers such as polyamide, polyacrylamine and polyvinylpyrrolidone are mixed in an aqueous solution. Then, there is a method of forming a composite colloid of Rh and the electron donor 4 with an insolubilizing material or a reducing agent.

  Next, the behavior of the noble metal particles when the exhaust gas purifying catalyst according to the present embodiment and the exhaust gas purifying catalyst according to the comparative example are each exposed to a high-temperature oxidizing atmosphere with reference to FIGS. 1 and 3. explain.

  First, as shown in FIG. 1, in the exhaust gas purifying catalyst 1 according to the present invention, Rh particles 3 and an electron donor 4 are arranged close to each other on an oxide carrier 2, and this electron donor. 4 donates electrons to the Rh particles 3. Therefore, even when the catalyst is exposed to an oxidizing atmosphere, high catalytic activity can be maintained without the Rh particles 3 being oxidized.

On the other hand, as shown in FIG. 3, in the exhaust gas purifying catalyst 8 according to Comparative Examples 1 and 2, since the electron donor 4 is not supported on the oxide carrier 2, the catalyst 8 is exposed to an oxidizing atmosphere. In this case, the Rh particles 3 are oxidized to Rh ₂ O ₃ , and high oxidation proceeds, so that the catalytic activity decreases.

  Next, the present invention will be described in more detail through examples.

[Example 1]
First, commercially available ZrO ₂ having a specific surface area of 95 m ² / g was dispersed in ion-exchanged water, and an aqueous rhodium nitrate solution (made by Tanaka Kikinzoku Co., Ltd., 8.83 wt%), barium acetate, and aluminum nitrate nonahydrate were respectively added to Rh. Is simultaneously adsorbed and supported so as to be 0.3 wt% with respect to ZrO ₂ and Ba: Al: Rh = 0.5: 1.0: 1.0 in terms of molar ratio of Ba, Al and Rh. It was.

  Next, this was filtered, evaporated to dryness, and calcined in a 400 ° C. air stream for 1 hour to obtain the catalyst powder of Example 1.

As shown in Table 1 below, as the electron donor 4, a composite of Ba added with Al was used.

[Example 2]
(1) First, a zirconium butoxide / butanol solution (85 wt%) was mixed with 2,2,4-pentanediol and stirred for about 2 hours at 120 ° C. under reflux. A Rh colloid solution obtained by mixing Rh—PVP colloid (made by Tanaka Kikinzoku) containing 2.0 wt% Rh and pure water was added dropwise to this solution to perform hydrolysis.

(2) Next, the gel-like mixture was aged with stirring at 80 ° C. for about 2 hours, and then heated to 160 ° C. under reduced pressure to remove the solvent.

(3) Further, the powder obtained in (2) was dried at 85 ° C. for 12 hours, further dried at 150 ° C. for 12 hours, and sized and calcined for 1 hour in a 400 ° C. air stream.

(4) Then, the powder obtained in (3) is dispersed and adsorbed and supported in an aqueous barium acetate solution, filtered, evaporated to dryness, sized and calcined at 400 ° C. for 1 hour in an air stream. Thus, catalyst powder of Example 2 in which 0.3 wt% of Rh was supported on zirconium oxide and Ba was supported so that the molar ratio of Rh to Ba was 3.0 was obtained.

[Example 3]
(1) Catalyst adjustment using the reverse micelle method was performed. As a surfactant, polyethylene glycol (5) mono-4-nonylphenyl ether and 1000 ml of cyclohexane were mixed to prepare a solution containing 0.15 mol% / L of a surfactant, which was stirred. To this solution, an aqueous rhodium nitrate solution (Tanaka Kikinzoku, 13.812 wt%) and 16.14 ml of pure water were added, mixed and stirred, and the mixture was stirred for about 2 hours to prepare a reverse micelle solution containing Rh ions. did.

(2) Next, sodium borohydride was added to the Rh reverse micelle solution as a reducing agent for Rh, and the mixture was further stirred for 2 hours to obtain a dispersion containing metalated Rh.

(3) An aqueous solution in which zirconium oxynitrate and lanthanum nitrate were dissolved in pure water was dropped into the dispersion obtained in (2) and stirred for 2 hours.

(4) After that, an excessive amount of 25% ammonia is dropped into the reverse micelle solution to insolubilize the zirconia and lanthanum in the micelle, and the mixture is further stirred for 2 hours, and the Rh in the micelle is wrapped with hydroxide of zirconia and lanthanum. Contacted micelles were obtained.

(5) 100 ml of methanol was added to the mixed solution prepared in (4) to disrupt the micelles, stirred for about 2 hours, filtered, and separated from the solvent. The resulting precipitate was washed with alcohol to remove excess surfactant. This precipitate was dried at 100 ° C. for 12 hours and then calcined in an air stream at 400 ° C. By repeating this operation, a catalyst powder of Example 3 in which 0.3 wt% Rh was supported on 1 g of mixed oxide in which ZrO ₂ and La ₂ O ₃ were present at a molar ratio of 8: 2 was obtained. .

[Example 4]
Commercially available ZrO ₂ having a specific surface area of 95 m ² / g is dispersed in ion-exchanged water, and an aqueous rhodium nitrate solution (made by Takanaka Tanaka, 8.83 wt%) and barium acetate are used, and Rh is 0.3 wt% with respect to ZrO _2. , Ba was simultaneously adsorbed and supported so that the molar ratio of Ba to Rh was 1: 1.

  Next, this was filtered, evaporated to dryness, and fired in an air stream at 400 ° C. for 1 hour to obtain the powder of Example 4.

[Example 5]
Commercially available TiO ₂ (specific surface area: ^10m 2 / g) was dispersed in ion-exchanged water, 0.3 wt rhodium nitrate aqueous solution (Tanaka Kikinzoku, 8.83wt%) and each of cesium nitrate及, Rh Whereas ZrO ₂ % And Cs were simultaneously adsorbed and supported so that the molar ratio with respect to Rh was 1.5.

  Next, this was filtered, evaporated to dryness, and calcined in a 400 ° C. air stream for 1 hour to obtain the powder of Example 5.

[Example 6]
A commercially available TiO ₂ having a specific surface area of 10 m ² / g is dispersed in ion-exchanged water, and an aqueous rhodium nitrate solution (manufactured by Takanaka Tanaka, 8.83 wt%), potassium nitrate, and Rh are each 0.3 wt% based on ZrO _2. , And K were simultaneously adsorbed and supported so that the molar ratio with respect to Rh was 1.

  Next, this was filtered, evaporated to dryness, and calcined in a 400 ° C. air stream for 1 hour to obtain the powder of Example 6.

[Comparative Example 1]
Commercially available ZrO ₂ having a specific surface area of 95 m ² / g was dispersed in ion-exchanged water, and an aqueous rhodium nitrate solution (manufactured by Tanaka Kikinzoku Co., Ltd., 8.83 wt%) was dropped and supported by adsorption.

  Next, this was filtered, evaporated to dryness, and fired in a 400 ° C. air stream for 1 hour to obtain a powder of Comparative Example 1.

  In addition, as shown in the said Table 1, in the comparative example 1, the electron donor 4 is not added.

[Comparative Example 2]
A commercially available activated alumina having a specific surface area of 150 m ² / g was dispersed in ion-exchanged water, and an aqueous rhodium nitrate solution (manufactured by Tanaka Kikinzoku, 8.83 wt%) was dropped and supported.

  Next, this was filtered, evaporated to dryness, and fired in a 400 ° C. air stream for 1 hour to obtain a powder of Comparative Example 2.

  As shown in Table 1, in Comparative Example 2, the carrier main component is alumina, and the solid solution of Rh proceeds immediately after the adjustment, so that the binding energy becomes very high. Moreover, Rh is dissolved in alumina and the catalytic activity is lowered.

[Comparative Example 3]
A commercially available ZrO ₂ having a specific surface area of 95 m ² / g is dispersed in ion-exchanged water, and an aqueous rhodium nitrate solution (made by Takanaka Tanaka, 8.83 wt%) and barium acetate are respectively Rh 0.3 wt% and Ba Rh. At the same time, it was adsorbed and supported so that the molar ratio was 10.

  Next, this was filtered, evaporated to dryness, and fired in an air stream at 400 ° C. for 1 hour to obtain a powder of Comparative Example 3.

  As shown in Table 1, in Comparative Example 3, the molar ratio of Ba, which is the electron donor 4, exceeds 3, and the binding energy becomes a low value. Will decline.

[Coating]
Thereafter, 500 g of the obtained catalyst powder, 50 g of boehmite, and 1570 g of a 10% nitric acid-containing aqueous solution were put into an alumina magnetic pot and shaken and ground with aluminum balls to obtain a catalyst slurry.

  Furthermore, this catalyst slurry is put into a cordierite honeycomb carrier (900 cells / 2.5 mil), excess slurry is removed by an air stream, dried at a temperature of 120 ° C., and fired in an air stream at 400 ° C. Thus, the exhaust gas purifying catalyst of Example 1 was obtained.

  The coating amount of the exhaust gas purifying catalyst was adjusted so that the coating amount was 100 g / L in each Example and Comparative Example.

[Catalyst performance evaluation]
Part of the exhaust gas purification catalyst obtained by the above-described treatment was cut out to 40 cc, and after 30 hours of durability treatment at 700 ° C., the catalyst performance was evaluated using model gas. The reaction gas conditions used in the model gas evaluation are shown in Table 2 below. Table 3 shows the measurement conditions when the Rh3d5 orbital binding energy of the catalyst was measured. Table 1 shows the model gas evaluation (NOx-T50) of the catalyst after the durability treatment and the value of the Rh3d5 orbital binding energy of the catalyst immediately after the adjustment before the durability treatment. Further, for Example 4 and Comparative Example 1, the graph of FIG. 4 shows the correlation between the Rh3d5 orbital binding energy immediately after catalyst adjustment and the relative strength. In the figure, the solid line indicates Example 4 and the broken line indicates Comparative Example 1. The charge correction was performed with the Zr3d5 peak top binding energy value set to 182.2 eV.

  From the results of Table 1 above, it was found that Examples 1 to 6 were superior to Comparative Examples 1 to 3 in the value of NOx-T50. As a result, it was found that high catalytic activity was maintained by supporting an appropriate amount (0.5 to 3 in molar ratio) of the electron donor 4 on the oxide carrier 2.

  Further, as shown in Table 1 and FIG. 4, the measurement results of the Rh3d5 orbital binding energy of the catalyst immediately after the adjustment were 308.3 to 308.8 eV in Examples 1 to 6, that is, the Rh was lower. In comparison examples 1 and 2, it is considered to be Rh in a highly oxidized state with low activity, whereas Rh is more active immediately after adjustment. Since it was in the state, it turned out that Examples 1-6 are more excellent than Comparative Examples 1-2 also about the catalyst performance after an endurance process.

  In Comparative Example 3, although the Rh3d5 orbital binding energy of the catalyst is 308.8 eV, the catalyst performance is inferior to that of Examples 1 to 6 because Ba exceeding the appropriate amount relative to Rh is added. This is because when an electron donor exceeding 3 by molar ratio is added, reaction inhibition by Ba is relatively likely to occur, and the catalyst performance is lowered.

It is the schematic which expands and shows the state of the surface of the catalyst for exhaust gas purification by embodiment of this invention. It is an expanded sectional view showing an exhaust gas purifying catalyst in which a plurality of catalyst layers are formed on a cordierite substrate. It is the schematic which expands and shows the state of the surface of the exhaust gas purification catalyst after the endurance process by the comparative example. It is a graph which shows the correlation of binding energy and relative intensity about Example 4 and Comparative Example 1.

Explanation of symbols

1,5,9 Exhaust gas purification catalyst 2 Oxide support 3 Rhodium particles 4 Electron donor 6 First catalyst layer (layer containing Pt, Pd, etc.)
7 Second catalyst layer (layer containing Rh)
8 Cordierite base material (structure)
10 Highly oxidized rhodium dissolved in an oxide carrier

Claims (6)

In an exhaust gas purification catalyst in which noble metal particles including rhodium particles are supported on an oxide carrier,
An exhaust gas purifying catalyst, wherein an electron donor having an electron donating ability for donating electrons to the rhodium particles is supported on the oxide carrier.   2. The exhaust gas purifying catalyst according to claim 1, wherein the electron donor is made of particles containing at least one selected from the group of barium, cesium, and potassium.   A plurality of catalyst layers containing the noble metal particles are formed on an oxide support, and the electron donor is arranged in the vicinity of the rhodium particles in a catalyst layer containing rhodium particles among these catalyst layers. The exhaust gas purifying catalyst according to claim 1 or 2. The oxide _support, ZrO 2, TiO _2, and the exhaust gas purifying catalyst according to claim 1, characterized in that it comprises at least one selected from the group of SiO _2.   The exhaust gas purifying catalyst according to any one of claims 1 to 4, wherein a molar ratio of the electron donor to rhodium particles is 0.5 to 3. The exhaust gas purifying catalyst according to any one of claims 1 to 5, wherein a binding energy of an Rh3d5 orbit when Al ₂ O ₃ is contained in the oxide support is 308.8 eV or less.

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