JP4997176B2 - Exhaust gas purification catalyst composition - Google Patents

Description

The present invention is related to an exhaust gas purification catalyst composition.

Exhaust gas discharged from an internal combustion engine such as an automobile includes hydrocarbon (HC), nitrogen oxide (NO _x ), carbon monoxide (CO), and the like. As a catalyst for purifying them, an exhaust gas in which a noble metal element as an active component is dissolved and / or supported on a heat-resistant oxide such as a cerium composite oxide, a zirconium composite oxide, or a perovskite composite oxide Various purification catalysts have been proposed.

For example, it is prepared by supporting platinum on particles (powder) made of an oxide represented by the chemical formula: (Ce, Zr) O _{2 so} that the supported amount becomes 1 wt% in the exhaust gas purifying catalyst as the final product. An exhaust gas purifying catalyst has been proposed (see Patent Document 1).
JP 2006-346587 A

However, in the exhaust gas purifying catalyst described in Patent Document 1, when high temperatures, oxidation-reduction fluctuations, long-term use, etc., platinum coalesces, grain growth occurs, and the effective surface area of platinum decreases. There is a problem that the activity decreases.
Moreover, since noble metals, such as platinum, are generally expensive, improvement in cost performance is desired.

An object of the present invention is to provide a catalyst composition for exhaust gas purification that can exhibit excellent catalytic activity over a long period of time under high temperature or oxidation-reduction fluctuations, and further has excellent cost performance.

In order to achieve the above object, the exhaust gas purifying catalyst composition of the present invention has Pd dissolved and / or supported only on a heat-resistant oxide containing cerium, zirconium and / or rare earth elements (excluding cerium). Furthermore, an alkaline earth metal is supported, and the Pd content is 0.3 to 0.8% by weight .

According to the exhaust gas-purifying catalyst composition of the present invention (hereinafter referred to as catalyst composition) , the content of Pd that is solid-solved and / or supported by the heat-resistant oxide, that is, contained in the catalyst composition. Since the content of Pd is 0.3 to 0.8% by weight, it is possible to maintain high catalytic activity by preventing cost reduction due to Pd grain growth over a long period of time with excellent cost performance.

  As a result, when the catalyst composition of the present invention is used, excellent catalytic activity can be exhibited over a long period of time at high temperatures or under redox fluctuation.

The catalyst composition of the present invention contains a heat-resistant oxide containing cerium, zirconium and / or rare earth elements (excluding cerium). For example, an aggregate of particles containing particles made of the above-mentioned heat-resistant oxide It is formed as.
In the catalyst composition of the present invention, the refractory oxide contains cerium and at least one of zirconium and rare earth elements (excluding cerium) as essential components, preferably cerium, zirconium and rare earth elements ( Excluding CE.)

  In the heat-resistant oxide, examples of rare earth elements (excluding cerium) include Sc (scandium), Y (yttrium), La (lanthanum), Pr (praseodymium), Nd (neodymium), Pm (promethium), Sm (samarium), Eu (europium), Gd (gadolinium), Tb (terbium), Dy (dysprosium), Ho (holmium), Er (erbium), Tm (thulium), Yb (ytterbium), Lu (lutetium), etc. Is mentioned. Preferred rare earth elements include Y, La, Pr, and Nd. These rare earth elements may be used alone or in combination of two or more.

In the above heat-resistant oxide, the atomic ratio of cerium is, for example, 10 to 80, preferably 20 to 70, when the total of cerium, zirconium and rare earth elements is 100.
In the above heat-resistant oxide, the atomic ratio of zirconium is, for example, 10 to 90, preferably 30 to 80, when the sum of cerium, zirconium and rare earth elements is 100.

In the above heat-resistant oxide, the atomic ratio of the rare earth element is, for example, 0 to 20, preferably 0 to 10, when the sum of cerium, zirconium and the rare earth element is 100.
The specific surface area (BET specific surface area) of the heat-resistant oxide varies depending on the solid solution and / or the amount of supported Pd (Pd content), but is preferably 120 to ²⁰ m ² / g, for example. Is 100 to ²⁰ m ² / g.

In the catalyst composition of the present invention, an alkaline earth metal is further supported on the heat-resistant oxide.
Examples of the alkaline earth metal include Be (beryllium), Mg (magnesium), Ca (calcium), Sr (strontium), Ba (barium), Ra (radium), and the like. As the alkaline earth metal, Mg, Ca, Sr, and Ba are preferable, and Ba is more preferable. These alkaline earth metals may be used alone or in combination of two or more.

  In the above heat-resistant oxide, the alkaline earth metal is, for example, an amount in which the atomic ratio of the alkaline earth metal is 1 to 30 with respect to the total atomic ratio 100 of cerium, zirconium and / or rare earth elements. Preferably, it is carried in an amount of 2 to 15. If the alkaline earth metal is supported in the above range, the Pd grain growth can be effectively suppressed.

The alkaline earth metal may be supported on the heat-resistant oxide as an alkaline-earth metal salt, and the constituent elements of the heat-resistant oxide, that is, cerium, zirconium and / or rare earth elements, A composite oxide may be formed with Pd described later, and the composite oxide may be supported on a heat-resistant oxide.
The above heat-resistant oxide contains Pd as a solid solution and / or supported, that is, contained. The fact that Pd is dissolved in the heat-resistant oxide means that Pd is coordinated in the crystal lattice of the heat-resistant oxide so that the heat-resistant oxide and Pd form a solid solution. It is.

  On the other hand, Pd is supported on the heat-resistant oxide means that Pd is held on the surface of the heat-resistant oxide without being dissolved in the heat-resistant oxide. It is adsorbed and / or physically supported. In addition, adsorption | suction carrying | support is that a precursor oxide hold | maintains Pd spontaneously when a precursor oxide is disperse | distributed to palladium salt aqueous solution in the manufacturing method of the heat resistant oxide mentioned later. In addition, physical support means that after the precursor oxide is dispersed in an aqueous palladium salt solution, the dispersion is heated (for example, evaporation to dryness or secondary firing described later) to force the precursor oxide. In other words, Pd is retained.

For example, when the above heat-resistant oxide carries a composite oxide containing the above-mentioned alkaline earth metal, when Pd is dissolved and / or supported, the composite oxide containing the alkaline-earth metal is General formula: Ba (Ce, Pd) O ₃ , Ba (Ce, Zr, Pd) O ₃ , Ba (Zr, Y, Pd) O ₃ , Ba (Ce, Zr, Y, Pd) O ₃ , PdO / BaCeO ₃ , PdO / Ba (Ce, Zr) O ₃ , PdO / Ba (Zr, Y) O ₃ , PdO / Ba (Ce, Zr, Y) O _{3 and the} like.

When Pd is dissolved in the heat-resistant oxide, the solid solution ratio of Pd with respect to the composite oxide containing the heat-resistant oxide and the alkaline earth metal is, for example, 5 to 95%, preferably 30-95.
In addition, the solid solution rate (unit:%) of Pd can be measured by, for example, ICP emission spectroscopy (high frequency inductively coupled plasma emission spectroscopy). Specifically, for example, the particles made of the heat-resistant oxide are immersed in a solution in which PdO is insoluble and the heat-resistant oxide is soluble, the solution is filtered, and the filtrate is analyzed by ICP emission spectrometry. Measure by the method. Thereby, the content of Pd contained in the filtrate is calculated, and the solid solution rate of Pd is calculated from the obtained calculated value.

  On the other hand, when Pd is supported on the heat-resistant oxide, the amount of Pd supported on the heat-resistant oxide is, for example, the entire amount of Pd contained in the heat-resistant oxide is supported on the heat-resistant oxide. In this case, it is the content of Pd described later. For example, when a part of Pd contained in the heat-resistant oxide is dissolved and the rest is supported, the content of Pd described later is described above. It is the difference from the solid solution amount of Pd calculated from the solid solution rate of Pd.

  And the content of Pd solid-solved and / or supported on the heat-resistant oxide, that is, the content of Pd contained in the catalyst composition of the present invention is 0.3 to 0.8% by weight. . When the content of Pd is less than 0.3% by weight, there is a problem that exhaust gas or the like cannot be sufficiently purified. When the Pd content exceeds 0.8% by weight, the particle size of Pd increases due to coalescence of Pd at high temperatures, under oxidation-reduction fluctuations, or during long-term use, and the effective surface area of Pd increases. There is a problem in that the catalytic activity decreases due to the decrease. Further, since the amount of Pd used increases, there is a problem that the cost performance is lowered.

The above heat-resistant oxide is not particularly limited, and can be produced by an appropriate method for preparing the oxide, for example, a coprecipitation method, a citric acid complex method, an alkoxide method, or the like.
In the coprecipitation method, for example, a mixed salt aqueous solution containing the above-described salt of each element (excluding palladium salt and alkaline earth metal salt) in the above stoichiometric ratio is prepared, and a neutralizing agent is added to the mixed salt aqueous solution. In addition, after coprecipitation, the obtained coprecipitate is dried and then heat-treated.

Examples of the salt of each element include inorganic salts such as sulfate, nitrate, chloride, and phosphate, and organic acid salts such as acetate and oxalate. Further, the mixed salt aqueous solution can be prepared, for example, by adding the salt of each element to water at a ratio such as the above stoichiometric ratio and stirring and mixing.
Thereafter, a neutralizing agent is added to the mixed salt aqueous solution to coprecipitate. Examples of the neutralizing agent include ammonia, for example, organic bases such as amines such as triethylamine and pyridine, and inorganic bases such as sodium hydroxide, potassium hydroxide, sodium carbonate, potassium carbonate, ammonium carbonate, and ammonium hydroxide. Is mentioned. As a neutralizing agent, Preferably, ammonium hydroxide salt is mentioned, More preferably, ammonium hydroxide aqueous solution is mentioned. In addition, a neutralizing agent is added so that the pH of the solution after adding the neutralizing agent may become about 6-10.

Then, the obtained coprecipitate is washed with water if necessary, and is dried by, for example, vacuum drying or ventilation drying, followed by heat treatment (primary firing) to thereby obtain a precursor containing cerium, zirconium and / or rare earth elements. A body oxide is obtained.
The firing temperature and firing time during the primary firing vary depending on the BET specific surface area of the precursor oxide. For example, in order to obtain a precursor oxide having a BET specific surface area of 100 m ² / g, the firing temperature and the firing time are set to 0.00 at 400 to 600 ° C. 5 to 5 hours. For example, in order to obtain a precursor oxide having a BET specific surface area of 70 m ² / g, it is 0.5 to 5 hours at 500 to 900 ° C. Furthermore, for example, in order to obtain a precursor oxide having a BET specific surface area of 30 m ² / g, it is 0.5 to 5 hours at 800 to 1200 ° C.

Next, the obtained precursor oxide is dispersed in an aqueous palladium salt solution in an amount of 0.3 to 0.8% by weight of Pd in a heat-resistant oxide particle to be described later. To dryness.
Thereafter, the precursor oxide is supported on the total amount of Pd contained in the palladium salt aqueous solution by, for example, heat treatment (secondary firing) at 300 to 800 ° C., preferably 400 to 600 ° C.

Examples of the palladium salt include the same salts as described above, and can be prepared in the same manner as described above. Practically, nitrate aqueous solution, dinitrodiammine nitric acid aqueous solution, chloride aqueous solution and the like can be mentioned. Specific examples include an aqueous palladium nitrate solution, an aqueous dinitrodiammine palladium nitric acid solution, and an aqueous tetravalent palladium ammine nitric acid solution.
Next, an alkaline earth metal is supported on the precursor oxide supporting Pd.

The alkaline earth metal is not particularly limited, and the precursor oxidation is performed by an appropriate method for supporting the alkaline earth metal on the oxide, such as an adsorption supporting method, an impregnation method, a coprecipitation method, and an alkoxide method. It can be carried on an object.
In the adsorption carrying method, for example, a Pd carrying precursor oxide is added to an alkaline earth metal salt aqueous solution to prepare a slurry, and this slurry is filtered.

Alkaline earth metal salts include the same salts as described above, and can be prepared in the same manner as described above. Practically, an aqueous acetate solution, an aqueous nitrate solution, and the like can be given. Specifically, examples of the barium salt aqueous solution include a barium acetate aqueous solution and a barium nitrate aqueous solution.
The obtained filter cake is dried by, for example, vacuum drying or ventilation drying, and then heat treated (final firing) at 400 ° C. to 1200 ° C., preferably 600 ° C. to 1100 ° C. An alkaline earth metal is supported on the precursor oxide on which is supported. Thus, particles made of a heat-resistant oxide in which Pd is dissolved and / or supported and an alkaline earth metal is supported are obtained.

In the above method, an aqueous solution of all the constituent elements (including palladium and alkaline earth metal) is prepared, and a co-precipitate is obtained by adding a neutralizing agent thereto and coprecipitating. After drying, heat treatment (final firing) can also be performed.
Further, in the citric acid complex method, for example, citric acid and salts of each of the above elements (excluding palladium salts and alkaline earth metal salts) are used, and each of the above elements (excluding palladium salts and alkaline earth metal salts) are used. A citric acid mixed salt aqueous solution is prepared by adding a slightly excess citric acid aqueous solution to the stoichiometric ratio, and the citric acid mixed salt aqueous solution is dried to solidify each element (palladium salt and alkaline earth metal salt). And the obtained citric acid complex is pre-baked and then heat-treated.

Examples of the salt of each element include the same salts as described above. For the citric acid mixed salt aqueous solution, for example, a mixed salt aqueous solution is prepared in the same manner as described above, and an aqueous citric acid solution is added to the mixed salt aqueous solution. It can be prepared by adding.
Thereafter, the citric acid mixed salt aqueous solution is dried to form a citric acid complex of each element described above. Drying removes moisture at a temperature at which the formed citric acid complex does not decompose, for example, from room temperature to 150 ° C. Thereby, a citric acid complex of each element described above (excluding palladium salts and alkaline earth metal salts) can be formed. Thereafter, the formed citric acid complex is temporarily calcined. In the preliminary firing, for example, heating is performed at 250 to 350 ° C. in a vacuum or an inert atmosphere.

And a precursor oxide is obtained by heat-processing (primary baking) at 400-1000 degreeC, for example.
Next, the obtained precursor oxide is dispersed in an aqueous palladium salt solution in the same manner as in the coprecipitation method, and this dispersion is evaporated to dryness. Then, for example, the precursor oxide supports the entire amount of Pd contained in the palladium salt aqueous solution by heat treatment (secondary firing) at 300 to 800 ° C., preferably 400 to 600 ° C.

Then, an alkaline earth metal is supported on the precursor oxide on which Pd is supported in the same manner as in the coprecipitation method, and then, for example, heat treatment is performed at 400 ° C. to 1200 ° C., preferably 600 ° C. to 1100 ° C. By firing), particles made of the above heat-resistant oxide in which Pd is dissolved and / or supported and an alkaline earth metal is supported are obtained.
In the alkoxide method, for example, a mixed alkoxide solution containing the alkoxide of each of the above elements (excluding palladium salts and alkaline earth metal salts) in the above stoichiometric ratio is prepared, and water is added to the mixed alkoxide solution. To obtain a precipitate.

Examples of the alkoxide of each element include (mono, di, tri) alcoholate formed from each element and alkoxy such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, and the following general formula (1). Examples include (mono, di, tri) alkoxy alcoholates of each element.
_{E [OCH (R 1) -} (CH 2) i -OR 2] j (1)
(In the formula, E represents each element, R ₁ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms, R ₂ represents an alkyl group having 1 to 4 carbon atoms, and i represents 1 to 1) (An integer of 3 and j represents an integer of 2 to 4.)
More specifically, examples of the alkoxy alcoholate include methoxyethylate, methoxypropylate, methoxybutyrate, ethoxyethylate, ethoxypropylate, propoxyethylate, butoxyethylate, and the like.

And a mixed alkoxide solution can be prepared by, for example, adding the alkoxide of each element to an organic solvent so that it may become said stoichiometric ratio, and stirring and mixing.
The organic solvent is not particularly limited as long as the alkoxide of each element can be dissolved, and examples thereof include aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, ketones, and esters. Preferably, aromatic hydrocarbons such as benzene, toluene and xylene are used.

Then, the obtained precipitate is evaporated to dryness, and then dried by, for example, vacuum drying or ventilation drying, followed by heat treatment (primary firing) at, for example, 400 to 1000 ° C., thereby oxidizing the precursor. Get things.
Next, the obtained precursor oxide is dispersed in an aqueous palladium salt solution in the same manner as in the coprecipitation method, and this dispersion is evaporated to dryness. Then, for example, the precursor oxide supports the entire amount of Pd contained in the palladium salt aqueous solution by heat treatment (secondary firing) at 300 to 800 ° C., preferably 400 to 600 ° C.

Then, an alkaline earth metal is supported on the precursor oxide on which Pd is supported in the same manner as in the coprecipitation method, and then, for example, heat treatment is performed at 400 ° C. to 1200 ° C., preferably 600 ° C. to 1100 ° C. By firing), particles made of the above heat-resistant oxide in which Pd is dissolved and / or supported and an alkaline earth metal is supported are obtained.
In the alkoxide method, for example, after preparing a homogeneous mixed solution containing a mixed alkoxide solution and an organometallic salt of palladium so as to have the above stoichiometric ratio, and adding water thereto to precipitate it, The obtained precipitate can be dried and subjected to a heat treatment (for example, 400 to 800 ° C.) to obtain a precursor oxide carrying Pd.

  Examples of the organometallic salt of palladium include, for example, palladium carboxylate formed from acetate, propionate, and the like, for example, β-diketone compound or β-ketoester compound represented by the following general formula (2), and / or Or the metal chelate complex etc. of palladium formed from the (beta) -dicarboxylic acid ester compound shown by following General formula (3) are mentioned.

R ₃ COCHR ₅ COR ₄ (2)
(In the formula, R ₃ represents an alkyl group having 1 to 6 carbon atoms, a fluoroalkyl group having 1 to 6 carbon atoms, or an aryl group, and R ₄ represents an alkyl group having 1 to 6 carbon atoms, or 1 to 6 carbon atoms. A fluoroalkyl group, an aryl group or an alkoxy group having 1 to 4 carbon atoms, and R ₅ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.)
R ₇ CH (COR ₆ ) ₂ (3)
(In the formula, R ₆ represents an alkyl group having 1 to 6 carbon atoms, and R ₇ represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.)
In the general formula (2) and the general formula (3), examples of the alkyl group having 1 to ₆ carbon atoms of R ₃ , R ₄ and R ₆ include methyl, ethyl, propyl, isopropyl, n-butyl, s -Butyl, t-butyl, t-amyl, t-hexyl and the like. The alkyl group having 1 to 4 carbon atoms of R ₅ and R _7, for example, methyl, ethyl, propyl, isopropyl, n- butyl, s- butyl, t- butyl.

In the general formula (2), examples of the fluoroalkyl group having 1 to 6 carbon atoms of R ₃ and R ₄ include trifluoromethyl. The aryl group of R ₃ and R _4, for example, phenyl. Examples of the alkoxy group having 1 to 4 carbon atoms of R ₃ include methoxy, ethoxy, propoxy, isopropoxy, n-butoxy, s-butoxy, t-butoxy and the like.

  More specifically, β-diketone compounds are, for example, 2,4-pentanedione, 2,4-hexanedione, 2,2-dimethyl-3,5-hexanedione, 1-phenyl-1,3-butanedione. 1-trifluoromethyl-1,3-butanedione, hexafluoroacetylacetone, 1,3-diphenyl-1,3-propanedione, dipivaloylmethane and the like.

More specific examples of the β-keto ester compound include methyl acetoacetate, ethyl acetoacetate, t-butyl acetoacetate, and the like.
Specific examples of the β-dicarboxylic acid ester compound include dimethyl malonate and diethyl malonate.
The particles composed of the heat-resistant oxide obtained as described above have a BET specific surface area of, for example, 20 to 120 m ² / g, and preferably 30 to 100 m ² / g.

The particles comprising the heat-resistant oxide can be used as they are as a catalyst composition, but are usually prepared as a catalyst composition by a known method such as loading on a catalyst carrier.
Examples of the catalyst carrier include known catalyst carriers such as a honeycomb monolith carrier made of cordierite. In order to carry on the catalyst carrier, for example, first, water is added to the heat-resistant oxide particles (powder) obtained above to form a slurry, which is then coated on the catalyst carrier and dried. Thereafter, heat treatment is performed at 300 to 800 ° C., preferably 300 to 600 ° C.

  In the catalyst composition of the present invention thus obtained, the content of Pd solid-solved and / or supported on the heat-resistant oxide, that is, the content of Pd contained in the catalyst composition is 0. Since it is 0.3 to 0.8% by weight, Pd grain growth is effectively suppressed even in long-term use with excellent cost performance, and the dispersion state of Pd in the composite oxide is well maintained.

As a result, when the catalyst composition of the present invention is used, excellent exhaust gas purification performance can be exhibited over a long period of time at high temperatures or under oxidation-reduction fluctuations.
Since the catalyst composition of the present invention can achieve excellent exhaust gas purification performance over a long period of time, for example, exhaust gas for purifying exhaust gas discharged from internal combustion engines such as gasoline engines and diesel engines, boilers, etc. It can be used effectively as a purification catalyst.

Next, although this invention is demonstrated based on an Example and a comparative example, this invention is not limited by the following Example.
Example 1 (Particle A Pd content: 0.3% by weight BET specific surface area 100 m ² / g)
Cerium nitrate 0.050 mol in terms of Ce Zirconium oxynitrate 0.045 mol in terms of Zr Yttrium nitrate 0.005 mol in terms of Y A mixed salt aqueous solution was prepared. Next, a 10% by weight ammonium hydroxide aqueous solution was gradually added dropwise to the mixed salt aqueous solution at room temperature to form a coprecipitate in the mixed salt aqueous solution. Subsequently, the mixed salt aqueous solution in which the coprecipitate was generated was stirred for 60 minutes, and then this aqueous solution was filtered to obtain a coprecipitate.

Subsequently, the coprecipitate is sufficiently washed with deionized water and vacuum dried at 110 ° C., and the coprecipitate is pulverized into particles. The particles are fired at 600 ° C. for 1 hour in the atmosphere (primary firing). ) To obtain particles of a composite oxide (precursor oxide) made of cerium, zirconium and yttrium. The precursor oxide had a BET specific surface area of 100 m ² / g.
Next, 50 g of the particles were added to a round bottom flask, and 500 mL of deionized water was added and stirred for 10 minutes to prepare a slurry by dispersing in deionized water.

Next, this slurry was added to an aqueous solution of palladium nitrate in an amount such that the content of Pd was 0.3% by weight in particles A described later.
After that, the solution to which the slurry (precursor oxide) is added is evaporated to dryness, and is fired at 500 ° C. for 1 hour in the atmosphere (secondary firing), thereby supporting the entire amount of Pd contained in the palladium nitrate aqueous solution. Precursor oxide particles were obtained. In addition, the ratio (Pd loading efficiency) that was adsorbed and supported on the precursor oxide out of the total amount of Pd contained in the palladium nitrate aqueous solution was 100%.

  Barium acetate was then added to the round bottom flask and 100 mL of deionized water was added and dissolved. Next, 50 g of precursor oxide particles carrying Pd was added to an aqueous barium acetate solution to prepare a slurry. The concentration of the barium acetate aqueous solution was adjusted so that the atomic ratio of barium was 5 with respect to the sum 100 of atomic ratios of cerium, zirconium and yttrium in the particle A described later.

Next, this slurry was vacuum-dried to remove moisture, thereby further supporting barium on the precursor oxide supporting Pd.
Then, by firing (final firing) at 1000 ° C. for 3 hours in an air atmosphere, Pd is dissolved and / or supported, and Ba is supported. Thus, composite oxide particles A containing Ce, Zr, and Y are obtained. (Pd content: 0.3% by weight BET specific surface area 100 m ² / g).

In addition, when the particle A was subjected to X-ray diffraction analysis, the particle A contains a complex oxide represented by the general formula: (Ce, Zr, Y, Pd) O ₂ as a main component, and is generally used as a subcomponent. It was confirmed that a composite oxide represented by the formula: Ba (Ce, Pd) O ₃ was included. As a result, in the particle A, it was confirmed that Ba (Ce, Pd) O ₃ was supported on (Ce, Zr, Y, Pd) O ₂ .

The particles A were immersed in an aqueous hydrogen fluoride solution (HF / H ₂ O = 1/10) maintained at room temperature for 12 hours, this liquid was filtered, and the filtrate was measured by ICP emission spectroscopic analysis. As a result, it was confirmed that the solid solution rate of palladium was 70%.
Example 2 (Particle B Pd content: 0.6% by weight BET specific surface area 100 m ² / g)
A slurry of complex oxide particles (precursor oxide) composed of cerium, zirconium and yttrium is added to an aqueous solution of palladium nitrate in an amount such that the Pd content is 0.6% by weight in the particle B described later. Produced particles B by the same method as in Example 1 (Pd content: 0.6 wt%, BET specific surface area 100 m ² / g). In Example 2, the loading efficiency of Pd with respect to the precursor oxide was 100%.

Example 3 (Particle C Pd content: 0.8 wt% BET specific surface area 100 m ² / g)
A slurry of composite oxide particles (precursor oxide) composed of cerium, zirconium and yttrium is added to an aqueous solution of palladium nitrate in an amount such that the Pd content is 0.8 wt% in the particles C described later. Produced particles C in the same manner as in Example 1 (Pd content: 0.8 wt%, BET specific surface area: 100 m ² / g). In Example 3, the supporting efficiency of Pd with respect to the precursor oxide was 99%.

Example 4 (Particle D Pd content: 0.3 wt% BET specific surface area 70 m ² / g)
The same components as in Example 1 were added to a round bottom flask, and 500 mL of deionized water was added and dissolved by stirring to prepare a mixed salt aqueous solution. Next, a 10% by weight ammonium hydroxide aqueous solution was gradually added dropwise to the mixed salt aqueous solution at room temperature to form a coprecipitate in the mixed salt aqueous solution. Subsequently, the mixed salt aqueous solution in which the coprecipitate was generated was stirred for 60 minutes, and then this aqueous solution was filtered to obtain a coprecipitate.

Subsequently, the coprecipitate is thoroughly washed with deionized water, vacuum dried at 110 ° C., and the coprecipitate is pulverized into particles. The particles are fired at 1000 ° C. for 1 hour in the atmosphere (primary firing). ) To obtain particles of a composite oxide (precursor oxide) made of cerium, zirconium and yttrium. The precursor oxide had a BET specific surface area of 70 m ² / g.
Next, 50 g of the particles were added to a round bottom flask, and 500 mL of deionized water was added and stirred for 10 minutes to prepare a slurry by dispersing in deionized water.

Next, this slurry was added to an aqueous solution of palladium nitrate in an amount such that the content of Pd was 0.3 wt% in particles D described later.
After that, the solution to which the slurry (precursor oxide) is added is evaporated to dryness, and is fired at 500 ° C. for 1 hour in the atmosphere (secondary firing), thereby supporting the entire amount of Pd contained in the palladium nitrate aqueous solution. Precursor oxide particles were obtained. In addition, the ratio (Pd loading efficiency) that was adsorbed and supported on the precursor oxide out of the total amount of Pd contained in the palladium nitrate aqueous solution was 100%.

  Barium acetate was then added to the round bottom flask and 100 mL of deionized water was added and dissolved. Next, 50 g of precursor oxide particles carrying Pd was added to an aqueous barium acetate solution to prepare a slurry. The concentration of the barium acetate aqueous solution was adjusted so that the atomic ratio of barium was 10 with respect to the sum 100 of atomic ratios of cerium, zirconium and yttrium in the particle A described later.

Next, this slurry was vacuum-dried to remove moisture, thereby further supporting barium on the precursor oxide supporting Pd.
Then, by firing (final firing) at 1000 ° C. for 3 hours in the air atmosphere, the composite oxide particles D containing Ce, Zr and Y in which Pd is dissolved and / or supported and Ba is supported are obtained. (Pd content: 0.3% by weight BET specific surface area 70 m ² / g).

Note that when the particle D was subjected to X-ray diffraction analysis, the particle D contains a composite oxide represented by the general formula: (Ce, Zr, Y, Pd) O ₂ as a main component, It was confirmed that a composite oxide represented by the formula: Ba (Ce, Pd) O ₃ was included. As a result, in the particle D, it was confirmed that Ba (Ce, Pd) O ₃ was supported on (Ce, Zr, Y, Pd) O ₂ .

Further, the particles D were immersed in an aqueous hydrogen fluoride solution (HF / H ₂ O = 1/10) maintained at room temperature for 12 hours, this liquid was filtered, and the filtrate was measured by ICP emission spectroscopic analysis. As a result, it was confirmed that the solid solution rate of palladium was 80%.
Example 5 (Particle E Pd content: 0.6% by weight BET specific surface area 70 m ² / g)
A slurry of composite oxide particles (precursor oxide) composed of cerium, zirconium and yttrium is added to an aqueous solution of palladium nitrate in an amount such that the content of Pd is 0.6% by weight in particles E described later. Produced particles E by the same method as in Example 4 (Pd content: 0.6 wt%, BET specific surface area 70 m ² / g). In Example 5, the supporting efficiency of Pd with respect to the precursor oxide was 100%.

Example 6 (Particle FPd content: 0.8 wt% BET specific surface area 70 m ² / g)
A slurry of complex oxide particles (precursor oxide) composed of cerium, zirconium and yttrium is added to an aqueous solution of palladium nitrate in an amount such that the Pd content is 0.8 wt% in the particles F described later. Produced particles F by the same method as in Example 4 (Pd content: 0.8 wt%, BET specific surface area 70 m ² / g). In Example 6, the supporting efficiency of Pd with respect to the precursor oxide was 89%.

Comparative Example 1 (Particle G Pd content: 1.1 wt% BET specific surface area 100 m ² / g)
A slurry of complex oxide particles (precursor oxide) composed of cerium, zirconium and yttrium is added to an aqueous solution of palladium nitrate in an amount such that the Pd content is 1.1 wt% in particles G described later. Produced particles G in the same manner as in Example 1 (Pd content: 1.1 wt%, BET specific surface area 100 m ² / g). In Comparative Example 1, the supporting efficiency of Pd with respect to the precursor oxide was 91%.

Comparative Example 2 (Particle H Pd content: 1.6 wt% BET specific surface area 100 m ² / g)
A slurry of complex oxide particles (precursor oxide) composed of cerium, zirconium and yttrium is added to an aqueous solution of palladium nitrate in an amount such that the Pd content is 1.6% by weight in particles H described later. Produced particles H by the same method as in Example 1 (Pd content: 1.6 wt%, BET specific surface area 100 m ² / g). In Comparative Example 2, the supporting efficiency of Pd with respect to the precursor oxide was 68%.

Comparative Example 3 (Particle I Pd content: 2.6% by weight BET specific surface area 100 m ² / g)
A slurry of complex oxide particles (precursor oxide) composed of cerium, zirconium and yttrium is added to an aqueous solution of palladium nitrate in an amount such that the content of Pd is 2.6% by weight in particles I described later. Produced particles I by the same method as in Example 1 (Pd content: 2.6 wt%, BET specific surface area 100 m ² / g). In Comparative Example 3, the loading efficiency of Pd with respect to the precursor oxide was 42%.

Comparative Example 4 (Particle J Pd content: 1.2% by weight BET specific surface area 70 m ² / g)
A slurry of complex oxide particles (precursor oxide) composed of cerium, zirconium and yttrium is added to an aqueous solution of palladium nitrate in an amount such that the Pd content is 1.2% by weight in particles J described later. Produced particles J by the same method as in Example 4 (Pd content: 1.2 wt%, BET specific surface area 70 m ² / g). In Comparative Example 4, the loading efficiency of Pd with respect to the precursor oxide was 68%.

Comparative Example 5 (Particle K Pt content: 0.5% by weight BET specific surface area 90 m ² / g)
Cerium nitrate 0.050 mol in terms of Ce Zirconium oxynitrate 0.045 mol in terms of Zr Yttrium nitrate 0.005 mol in terms of Y A mixed salt aqueous solution was prepared. Next, a 10% by weight ammonium hydroxide aqueous solution was gradually added dropwise to the mixed salt aqueous solution at room temperature to form a coprecipitate in the mixed salt aqueous solution. Subsequently, the mixed salt aqueous solution in which the coprecipitate was generated was stirred for 60 minutes, and then this aqueous solution was filtered to obtain a coprecipitate.

Subsequently, the coprecipitate is thoroughly washed with deionized water, vacuum dried at 110 ° C., and the coprecipitate is pulverized into particles. The particles are fired at 700 ° C. for 1 hour in the atmosphere (primary firing). ) To obtain particles of a composite oxide (precursor oxide) made of cerium, zirconium and yttrium. The precursor oxide had a BET specific surface area of 90 m ² / g.
Next, 50 g of the particles were added to a round bottom flask, and 500 mL of deionized water was added and stirred for 10 minutes to prepare a slurry by dispersing in deionized water.

Subsequently, this slurry was added to the dinitrodiamine platinum nitric acid aqueous solution in such an amount that the content of Pt was 0.5% by weight in particles K described later.
Then, the total amount of Pt contained in the dinitrodiamine platinum nitric acid aqueous solution is obtained by evaporating and drying the solution to which the slurry (precursor oxide) is added and baking it at 500 ° C. for 1 hour in the air atmosphere (secondary baking). As a result, precursor oxide particles on which was supported were obtained. In addition, of the total amount of Pt contained in the dinitrodiamine platinum nitric acid aqueous solution, the proportion adsorbed and supported on the precursor oxide (Pt loading efficiency) was 95%.

  Barium acetate was then added to the round bottom flask and 100 mL of deionized water was added and dissolved. Next, 50 g of Pt-supported precursor oxide particles were added to an aqueous barium acetate solution to prepare a slurry. The concentration of the barium acetate aqueous solution was adjusted so that the atomic ratio of barium was 10 with respect to the sum 100 of atomic ratios of cerium, zirconium, and yttrium in particles K described later.

Next, this slurry was vacuum-dried to remove moisture, thereby further supporting barium on the precursor oxide supporting Pt.
Then, by firing (final firing) at 1000 ° C. for 3 hours in the air atmosphere, the composite oxide particles K containing Ce, Zr and Y in which Pt is dissolved and / or supported and Ba is supported are obtained. (Pt content: 0.5% by weight BET specific surface area 90 m ² / g).
Test Example 1 (Evaluation of Pd loading efficiency)
In each of Examples and Comparative Examples 1 to 4, the solution to which the precursor oxide slurry was added was allowed to stand at 60 ° C. for 120 minutes, and then the supernatant of the solution was collected and measured by ICP emission spectroscopy. The amount of Pd remaining in the solution was calculated. From the obtained calculated value, the loading efficiency (%) of Pd was calculated. The results are shown in FIG. That is, the graph shown in FIG. 1 represents the change in the loading efficiency when the content of Pd is changed for the composite oxide particles A to J having a BET specific surface area of 100 m ² / g and 70 m ² / g. .
Test example 2 (activity evaluation)
1) Durability test 3 cycles of inert atmosphere, 3 minutes of oxidizing atmosphere, 3 minutes of inert atmosphere, and 3 minutes of reducing atmosphere are defined as 1 cycle, and this cycle is repeated for 250 cycles for a total of 50 hours. The particles obtained in each comparative example were alternately exposed to an oxidizing atmosphere and a reducing atmosphere, and then cooled to room temperature in the reducing atmosphere.

The inert atmosphere, the oxidizing atmosphere, and the reducing atmosphere correspond to exhaust gas atmospheres that are exhausted when the stoichiometric, lean, and rich air-fuel mixtures are burned, respectively.
Each atmosphere was prepared by supplying a gas having a composition shown in Table 1 including high-temperature steam at a flow rate of 300 × 10 ⁻³ m ³ / hr. The ambient temperature was maintained at about 1050 ° C.

２）Ｐｄの粒子サイズの測定（実施例１〜３および比較例１〜３）
耐久試験後の実施例１〜３および比較例１〜３の粒子におけるＰｄの粒子サイズ（粒径）を、ＣＯパルス法により測定した。結果を図２に示す。すなわち、図２に示すグラフは、ＢＥＴ比表面積１００ｍ²／ｇの複合酸化物粒子Ａ〜Ｃ、Ｇ〜Ｉに関して、Ｐｄの含有量を変化させたときの、Ｐｄの粒子サイズの変化を表わしている。
３）２０％浄化温度（実施例１〜３および比較例１〜３，５）
耐久試験後の実施例１〜３および比較例１〜３，５の粒子（粉末）を、０．５ｍｍ〜１．０ｍｍのサイズのペレットに成型して試験片を調製した。表２に示すモデルガス組成を用いて、このモデルガスの燃焼によって排出される排気ガスの温度を、室温から４５０℃まで、２０℃／分の割合で上昇させつつ、モデルガスを各試験片に供給し、排ガス中のＨＣ、ＮＯ_xおよびＣＯが、２０％浄化されるときの温度（２０％浄化温度：℃）を測定した。結果を表３および図３に示す。なお、図３に示すグラフは、表３に示される結果のうち、実施例１〜３および比較例１〜３の結果を表わしている。すなわち、図３に示すグラフは、ＢＥＴ比表面積１００ｍ²／ｇの複合酸化物粒子Ａ〜Ｃ、Ｇ〜Ｉに関して、Ｐｄの含有量を変化させたときの、ＨＣ、ＮＯ_xおよびＣＯそれぞれの２０％浄化温度の変化を表わしている。

2) Measurement of Pd particle size (Examples 1 to 3 and Comparative Examples 1 to 3)
The particle size (particle size) of Pd in the particles of Examples 1 to 3 and Comparative Examples 1 to 3 after the durability test was measured by a CO pulse method. The results are shown in FIG. That is, the graph shown in FIG. 2 represents the change in the particle size of Pd when the content of Pd is changed with respect to the composite oxide particles A to C and G to I having a BET specific surface area of 100 m ² / g. Yes.
3) 20% purification temperature (Examples 1-3 and Comparative Examples 1-3, 5)
The test pieces were prepared by molding the particles (powder) of Examples 1 to 3 and Comparative Examples 1 to 3 and 5 after the durability test into pellets having a size of 0.5 mm to 1.0 mm. Using the model gas composition shown in Table 2, the temperature of the exhaust gas exhausted by the combustion of the model gas is increased from room temperature to 450 ° C. at a rate of 20 ° C./min. The temperature at which HC, NO _x and CO in the exhaust gas were purified by 20% was measured (20% purification temperature: ° C.). The results are shown in Table 3 and FIG. In addition, the graph shown in FIG. 3 represents the result of Examples 1-3 and Comparative Examples 1-3 among the results shown in Table 3. That is, the graph shown in FIG. 3 shows 20 for each of HC, NO _x, and CO when the Pd content is changed for the composite oxide particles A to C and G to I having a BET specific surface area of 100 m ² / g. It represents the change in% purification temperature.

４）考察
図２に示すように、実施例１〜３の粒子では、耐久試験後のＰｄの粒子サイズが、それぞれ８ｎｍ、９ｎｍおよび１０ｎｍであった。一方、比較例１〜３の粒子では、耐久試験後のＰｄの粒子サイズが、それぞれ１８ｎｍ、２５ｎｍおよび３０ｎｍであった。これにより、Ｐｄの含有量が０．３〜０．８重量％である複合酸化物粒子では、長期使用においても、パラジウムの粒成長が効果的に抑制され、パラジウムの複合酸化物に対する分散状態が、良好に保持されることが確認された。

4) Discussion As shown in FIG. 2, in the particles of Examples 1 to 3, the particle sizes of Pd after the durability test were 8 nm, 9 nm, and 10 nm, respectively. On the other hand, in the particles of Comparative Examples 1 to 3, the particle sizes of Pd after the durability test were 18 nm, 25 nm, and 30 nm, respectively. Thereby, in the composite oxide particles having a Pd content of 0.3 to 0.8% by weight, palladium grain growth is effectively suppressed even in long-term use, and the dispersion state of the palladium composite oxide is reduced. It was confirmed that it was held well.

Further, as shown in Table 3, in the particles of Example 2 (Pd content: 0.6% by weight), the 20% purification temperatures of HC, NO _x and CO after the durability test were 260 ° C. and 263 ° C., respectively. And 248 ° C. On the other hand, in the particles of Comparative Example 5 (Pt content: 0.5% by weight) containing almost the same amount of noble metal as Example 2, the 20% purification temperatures of HC, NO _x and CO after the durability test were respectively 293 ° C, 310 ° C and 280 ° C.

Furthermore, as shown in Table 3 and FIG. 3, in the particles of Example 1 (Pd content: 0.3% by weight), the 20% purification temperature of HC, NO _x and CO after the durability test was 269 ° C., respectively. It is 272 ° C. and 259 ° C., and sufficiently excellent exhaust gas purification performance is expressed with a small Pd content.
According to Table 3 and FIG. 3, in the composite oxide particles in which the noble metal contained is Pd and the content is 0.3 to 0.8% by weight, the cost performance is excellent, and even in long-term use, It was confirmed that the grain growth of palladium was effectively suppressed and the dispersion state with respect to the composite oxide of palladium was well maintained.

Respect composite oxide particles A~J a BET specific surface area of 100 m ² / g and 70m ² / g, when varying the content of Pd, which is a graph showing a change in supporting efficiency. It is a graph which shows the change of the particle size of Pd when content of Pd is changed regarding the composite oxide particles A to C and G to I having a BET specific surface area of 100 m ² / g. FIG. 6 is a graph showing changes in 20% purification temperatures of HC, NO _x, and CO when the content of Pd is changed for composite oxide particles A to C and G to I having a BET specific surface area of 100 m ² / g. is there.

Claims (1)

Pd is dissolved and / or supported only in a heat-resistant oxide containing cerium, zirconium and / or rare earth elements (excluding cerium),
In addition, alkaline earth metals are supported,
A catalyst composition for exhaust gas purification , wherein the content of Pd is 0.3 to 0.8% by weight.

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