JP5822682B2 - Exhaust gas purification catalyst - Google Patents

Description

  The present invention relates to an exhaust gas purification catalyst, and more particularly to an exhaust gas purification catalyst for purifying exhaust gas discharged from an internal combustion engine or the like.

Exhaust gas discharged from internal combustion engines such as automobiles contains hydrocarbons (HC), carbon monoxide (CO), nitrogen oxides (NO _x ), etc., for exhaust gas purification to purify these Catalysts are known.

  As a catalyst for purifying these, noble metal elements (Rh (rhodium), Pd (palladium), Pt (platinum), etc.) as active components are supported or dissolved in heat-resistant oxides such as perovskite complex oxides. Various exhaust gas purifying catalysts are known.

Specifically, for example, the general formula A _x B _(1-y) Pd _y O _{3 + δ} (wherein A represents at least one element selected from rare earth elements and alkaline earth metals, and B represents a transition) Element (excluding rare earth elements and Pd), at least one element selected from Al and Si, x represents an atomic ratio of 1 <x, and y represents an atomic ratio of 0 <y ≦ 0.5 And δ represents an excess amount of oxygen), an exhaust gas purifying catalyst containing a perovskite complex oxide is proposed (see, for example, Patent Document 1).

International publication pamphlet WO2005 / 090238

  However, noble metals such as Pd (palladium) contained in such an exhaust gas purification catalyst are expensive. In order to achieve sufficient exhaust gas purification performance in the catalyst carrier described in Patent Document 1, There is a problem that it requires precious metals and is inferior in cost.

  An object of the present invention is to provide an exhaust gas purifying catalyst capable of reducing the amount of noble metal used and exhibiting more excellent gas purifying performance.

  In order to achieve the above object, the exhaust gas purifying catalyst of the present invention is characterized by containing a perovskite complex oxide represented by the following general formula (1).

La (Fe _1-x Cu _x ) O ₃ (1)
(In the formula, x represents an atomic ratio of 0 <x <0.3.)

  Since the exhaust gas purifying catalyst of the present invention does not contain expensive noble metals, the cost can be reduced, and lanthanum is contained in the A site of the perovskite complex oxide, and iron and copper are contained in the B site. In addition, since the atomic ratio x of copper is in the range of 0 <x <0.3 at the B site, the exhaust gas can be purified efficiently.

It is a graph which shows the exhaust gas purification rate of the catalyst for exhaust gas purification of Examples 1-2 and Comparative Examples 1-3. It is a graph which shows the exhaust gas purification rate of the catalyst for exhaust gas purification of Example 2 and Comparative Examples 4-5.

  The exhaust gas purifying catalyst of the present invention contains a perovskite complex oxide represented by the following general formula (1).

La (Fe _1-x Cu _x ) O ₃ (1)
(In the formula, x represents an atomic ratio of 0 <x <0.3.)
This perovskite complex oxide is a complex oxide having a crystal structure represented by the general formula ABO ₃ (theoretical composition ratio A: B: O = 1: 1: 3). Lanthanum (La) is arranged at the site, and iron (Fe) and copper (Cu) are arranged at the B site.

  In the general formula (1), the atomic ratio x of copper in the B site is more than 0 and less than 0.3, preferably 0.05 or more and 0.2 or less.

  Further, the atomic ratio of iron in the B site is the remainder of copper contained in the B site, which exceeds 0.7 and is less than 1, preferably 0.8 or more and 0.95 or less.

  Such a perovskite complex oxide is not particularly limited, and can be produced by an appropriate method for preparing the complex 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 a salt of each of the above elements, that is, a salt (raw material) of lanthanum (La), iron (Fe) and copper (Cu) in the above stoichiometric ratio is prepared. A neutralizing agent is added to the mixed salt aqueous solution to cause coprecipitation, and 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. Moreover, the mixed salt aqueous solution can be prepared, for example, by adding the salt of each element to water at a ratio that achieves the above stoichiometric ratio and stirring and mixing.

  Thereafter, a neutralizing agent is added to the mixed salt aqueous solution to cause coprecipitation. Examples of the neutralizing agent include ammonia, for example, organic bases such as amines such as triethylamine and pyridine, and inorganic bases such as caustic soda, caustic potash, potassium carbonate, and ammonium carbonate.

  The neutralizing agent is added so that the pH of the solution after adding the neutralizing agent is about 6 to 10.

  The obtained coprecipitate is washed with water as necessary, and dried by, for example, vacuum drying or ventilation drying, and then heat-treated at, for example, about 500 to 1000 ° C., preferably about 600 to 950 ° C. A perovskite complex oxide can be obtained.

  In the citric acid complex method, for example, citric acid and a salt (raw material) of each element described above are mixed with a citric acid mixed salt aqueous solution that is contained so that the salt of each element described above has the above stoichiometric ratio. After preparing and drying this citric acid mixed salt aqueous solution to form a citric acid complex of each element described above, 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 quickly 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 can be formed.

  The formed citric acid complex is subjected to heat treatment after calcination. Pre-baking may be performed by heating at 250 ° C. or higher in a vacuum or an inert atmosphere, for example. Thereafter, a perovskite complex oxide can be obtained by heat treatment at about 300 to 1000 ° C., preferably about 600 to 950 ° C., for example.

  In the alkoxide method, for example, a mixed alkoxide solution containing the alkoxide (raw material) of each element described above excluding copper in the above stoichiometric ratio is prepared, and a copper salt (raw material) is added to the mixed alkoxide solution. After adding the aqueous solution containing and making it precipitate by hydrolysis, the obtained deposit is dried and heat-processed.

  Examples of the alkoxide of each element include an alcoholate formed from each element and an alkoxy such as methoxy, ethoxy, propoxy, isopropoxy, butoxy, and an alkoxy alcoholate of each element represented by the following general formula (2). Can be mentioned.

_{^{E [OCH (R 1) -}} (CH 2) i-OR 2] j (2)
(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 3 Integer, j represents an integer of 2 to 3)
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. For example, aromatic hydrocarbons, aliphatic hydrocarbons, alcohols, ketones, esters and the like are used. Preferably, aromatic hydrocarbons such as benzene, toluene and xylene are used.

  Thereafter, an aqueous solution containing a copper salt at the above stoichiometric ratio is added to the mixed alkoxide solution to cause precipitation. Examples of the aqueous solution containing a copper salt include nitrate aqueous solution, chloride aqueous solution, hexaammine chloride aqueous solution, dinitrodiammine nitric acid aqueous solution, hexachloro acid hydrate, potassium cyanide salt and the like.

  The resulting precipitate is dried by, for example, vacuum drying or ventilation drying, and then heat-treated at, for example, about 500 to 1000 ° C., preferably about 500 to 850 ° C., so that the perovskite complex oxide Can be obtained.

  Further, in such an alkoxide method, for example, a mixed solution containing copper organometallic salt (raw material) is mixed with the above mixed alkoxide solution to prepare a uniform mixed solution, and water is added thereto to cause precipitation. Thereafter, the obtained precipitate can be dried and then heat-treated.

  Examples of copper organometallic salts include copper carboxylates formed from acetates, propionates, and the like, such as diketone compounds represented by the following general formula (3) or the following general formula (4). Copper metal chelate complexes such as copper diketone complexes.

R ³ COCHR ⁵ COR ⁴ (3)
(In the formula, R3 is an alkyl group having 1 to 4 carbon atoms, a fluoroalkyl group having 1 to 4 carbon atoms or a reel group, R4 is an alkyl group having 1 to 4 carbon atoms, and a fluoroalkyl group having 1 to 4 carbon atoms. , An aryl group or an alkyloxy group having 1 to 4 carbon atoms, and R5 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.)
CH ₃ CH (COR ⁶ ) ₂ (4)
(In the formula, R6 represents a hydrogen atom or an alkyl group having 1 to 4 carbon atoms.)
In the general formula (3) and the general formula (4), examples of the alkyl group having 1 to 4 carbon atoms of R3, R4, R5, and R6 include methyl, ethyl, propyl, isopropyl, n-butyl, s- Examples include butyl and t-butyl. Moreover, as a C1-C4 fluoroalkyl group of R3 and R4, trifluoromethyl etc. are mentioned, for example. Moreover, as an aryl group of R3 and R4, a phenyl is mentioned, for example. Moreover, as a C1-C4 alkyloxy group of R3, a methoxy, an ethoxy, a propoxy, an isopropoxy, n-butoxy, s-butoxy, t-butoxy etc. are mentioned, for example.

  More specific examples of the diketone compound include 2,4-pentanedione, 2,4-hexanedione, 2,2-dimethyl-3,5-hexanedione, 1-phenyl-1,3-butanedione, -Trifluoromethyl-1,3-butanedione, hexafluoroacetylacetone, 1,3-diphenyl-1,3-propanedione, dipivaloylmethane, methyl acetoacetate, ethyl acetoacetate, t-butyl acetoacetate It is done.

  Moreover, the solution containing the organic metal salt of copper can be prepared, for example, by adding the organic metal salt of copper to the organic solvent so as to have the above stoichiometric ratio and stirring and mixing. Examples of the organic solvent include the organic solvents described above.

  Thereafter, the solution containing the organometallic salt of copper thus prepared is mixed with the mixed alkoxide solution described above to prepare a uniform mixed solution, and then water is added thereto to cause precipitation. The resulting precipitate is dried by, for example, vacuum drying or ventilation drying, and then heat-treated at, for example, about 400 to 1000 ° C., preferably about 500 to 850 ° C., thereby obtaining a perovskite complex oxide. Can be obtained.

  In addition, the perovskite complex oxide of the present invention is obtained by first converting the perovskite complex oxide from the elements other than copper at the above stoichiometric ratio by the coprecipitation method, the citric acid complex method, and the alkoxide method. It can also be obtained by preparing and then supporting copper on the obtained perovskite complex oxide at the above stoichiometric ratio.

  There is no particular limitation on supporting copper on the perovskite complex oxide, and a known method can be used. For example, a salt solution containing copper is prepared, and the salt-containing solution is impregnated in a perovskite complex oxide, followed by firing.

  As the salt-containing solution, the above-described salt solutions may be used, and practically, an aqueous nitrate solution, a dinitrodiammine nitric acid solution, an aqueous chloride solution, and the like may be used.

  More specifically, examples of the copper salt solution include an aqueous copper nitrate solution. Moreover, after impregnating copper with the perovskite type complex oxide, for example, it is dried at 50 to 200 ° C. for 1 to 48 hours, and further fired at 350 to 1000 ° C. for 1 to 12 hours.

  Thereby, the perovskite complex oxide represented by the above formula (1) can be obtained.

  In the perovskite complex oxide thus obtained, the copper content is more than 0% by mass and less than 7.78% by mass, preferably 1.31% by mass with respect to the total amount of the perovskite complex oxide. % Or more and 5.20% by mass or less.

The specific surface area (BET method) of the perovskite complex oxide is, for example, 0.5 to 40 m ² / g, preferably 5 to 40 m ² / g.

  The perovskite complex oxide thus obtained is prepared in an appropriate form by a known method such as being supported on a catalyst carrier and used as an exhaust gas purifying catalyst.

  As the catalyst carrier, for example, a known catalyst carrier such as a honeycomb monolith carrier made of cordierite or the like is used.

  In order to support on the catalyst carrier, for example, first, water is added to the perovskite type complex oxide to form a slurry, which is then coated on the catalyst carrier and dried, and then about 300 to 800 ° C., preferably, It heat-processes at about 300-600 degreeC.

  Since the exhaust gas purifying catalyst thus obtained does not contain expensive noble metals, the cost can be reduced, lanthanum is present at the A site of the perovskite complex oxide, iron and iron is present at the B site. Since copper is contained and the atomic ratio x of copper is in the range of 0 <x <0.3 at the B site, the exhaust gas can be purified efficiently.

  In such a case, other known catalyst components (for example, a catalyst containing alumina or a catalyst containing other known composite oxides) may be used in combination with the perovskite composite oxide as appropriate. it can.

  Next, although this invention is demonstrated based on a manufacture example, an Example, and a comparative example, this invention is not limited by the following Example.

Example 1 (La _1.00 Fe _0.95 Cu _0.05 O ₃ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
Iron ethoxyethylate 30.7g (0.095 mol)
Copper ethoxyethylate 1.21 g (0.005 mol)
The above components were added to a 500 mL round bottom flask, and 200 mL of toluene was added and dissolved by stirring to prepare a homogeneous mixed solution containing La, Fe and Cu.

  Next, 200 mL of deionized water was dropped into the round bottom flask over about 15 minutes. As a result, a brown viscous precipitate was formed by hydrolysis.

  Then, after stirring at room temperature for 2 hours, toluene and water were distilled off under reduced pressure to obtain a precursor of LaFeCu composite oxide. Next, the precursor was transferred to a petri dish, dried by ventilation at 60 ° C. for 24 hours, and then heat-treated in the atmosphere at 800 ° C. for 1 hour using an electric furnace to obtain a blackish brown powder.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a composite oxide having a perovskite structure of La _1.00 Fe _0.95 Cu _0.05 O ₃ . The specific surface area was 18 m ² / g.

Example 2 (La _1.00 Fe _0.88 Cu _0.12 O ₃ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
28.4 g (0.088 mol) of iron ethoxyethylate
Copper ethoxyethylate 2.90 g (0.012 mol)
A blackish brown powder was obtained in the same manner as in Example 1 except that the above components were used.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a composite oxide having a perovskite structure of La _1.00 Fe _0.88 Cu _0.12 O ₃ . The specific surface area was 10 m ² / g.

Comparative Example 1 (La _1.00 Fe _1.00 O ₃ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
Iron ethoxyethylate 32.3g (0.100mol)
A blackish brown powder was obtained in the same manner as in Example 1 except that the above components were used.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a complex oxide having a perovskite structure of La _1.00 Fe _1.00 O ₃ . The specific surface area was 8 m ² / g.

Comparative Example 2 (La _1.00 Fe _0.70 Cu _0.30 O ₃ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
22.6 g (0.070 mol) of iron ethoxyethylate
7.25 g (0.030 mol) of copper ethoxyethylate
A blackish brown powder was obtained in the same manner as in Example 1 except that the above components were used.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a complex oxide having a perovskite structure of La _1.00 Fe _0.70 Cu _0.30 O ₃ . Its specific surface area was 11 m ² / g.

Comparative Example 3 (La _2.00 Cu _1.00 O ₄ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
Copper ethoxyethylate 12.1 g (0.050 mol)
A blackish brown powder was obtained in the same manner as in Example 1 except that the above components were used.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a complex oxide having a layered perovskite structure of La _2.00 Cu _1.00 O ₄ . Its specific surface area was 0.8 m ² / g.

Comparative Example 4 (La _1.00 Ni _0.88 Cu _0.12 O ₃ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
20.9 g (0.088 mol) of nickel-1-methoxy-2-propylate
Copper ethoxyethylate 2.90 g (0.012 mol)
A blackish brown powder was obtained in the same manner as in Example 1 except that the above components were used.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a composite oxide having a perovskite structure of La _1.00 Ni _0.88 Cu _0.12 O ₃ . The specific surface area was 6 m ² / g.

Comparative Example 5 (La _1.00 Co _0.88 Cu _0.12 O ₃ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
Cobalt ethoxyethylate 20.8 g (0.088 mol)
Copper ethoxyethylate 2.90 g (0.012 mol)
A blackish brown powder was obtained in the same manner as in Example 1 except that the above components were used.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a composite oxide having a perovskite structure of La _1.00 Co _0.88 Cu _0.12 O ₃ . The specific surface area was 5 m ² / g.

Comparative Example 6 (La _1.00 Mn _0.88 Cu _0.12 O ₃ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
Manganese ethoxyethylate 20.5 g (0.088 mol)
Copper ethoxyethylate 2.90 g (0.012 mol)
A blackish brown powder was obtained in the same manner as in Example 1 except that the above components were used.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a complex oxide having a perovskite structure of La _1.00 Mn _0.88 Cu _0.12 O ₃ . Its specific surface area was 11 m ² / g.

Comparative Example 7 (La _1.00 Fe _0.80 Ni _0.20 O ₃ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
Iron ethoxyethylate 25.9g (0.080 mol)
4.75 g (0.020 mol) of nickel-1-methoxy-2-propylate
A blackish brown powder was obtained in the same manner as in Example 1 except that the above components were used.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a composite oxide having a perovskite structure of La _1.00 Fe _0.80 Ni _0.20 O ₃ . The specific surface area was 9 m ² / g.

Comparative Example 8 (La _1.00 Fe _0.88 Co _0.20 O ₃ )
Lanthanum ethoxyethylate 40.6 g (0.100 mol)
Iron ethoxyethylate 25.9g (0.080 mol)
Cobalt ethoxyethylate 4.74 g (0.020 mol)
A blackish brown powder was obtained in the same manner as in Example 1 except that the above components were used.

As a result of powder X-ray diffraction analysis of this powder, it was identified as a single crystal phase composed of a composite oxide having a perovskite structure of La _1.00 Fe _0.88 Co _0.20 O ₃ . The specific surface area was 7 m ² / g.

  Table 1 shows the copper content and the specific surface area (BET method) with respect to the total amount of the perovskite complex oxides of the perovskite complex oxides obtained in the examples and comparative examples.

(Evaluation)
Exhaust gas purifying catalyst powders obtained in each Example and each Comparative Example were molded into pellets having a size of 0.5 to 1.0 mm to prepare test pieces.

Using a model gas having the composition shown in Table 2, each exhaust gas (temperature: 600 ° C., flow rate: 2.5 L / min) exhausted by combustion of this model gas (air-fuel ratio A / F = 14.5) is supplied to the test piece, HC of each specimen (THC: total hydrocarbon), NO: it was measured purification rate (NO _x nitrogen oxides) and CO (carbon monoxide).

  The exhaust gas purification rates of the exhaust gas purification catalysts of Examples 1-2 and Comparative Examples 1-3 are shown in FIG.

Moreover, the exhaust gas purification rates of the exhaust gas purification catalysts of Example 2 and Comparative Examples 4 to 5 are shown in FIG.
(Discussion)
From FIG. 1 and FIG. 2, in the perovskite type complex oxide containing lanthanum at the A site, when iron and copper are contained at the B site, only iron or copper is contained, or iron or copper and other elements are included. It was confirmed that the catalyst purification performance was superior compared to the case containing

Further, from FIG. 1, in the perovskite type complex oxide, if the B site contains iron and copper and the copper content at the B site exceeds 0 and less than 0.3, the copper content is within the above range. It was confirmed that the catalyst purification performance was particularly excellent as compared with the case where it was not.

Claims (1)

An exhaust gas-purifying catalyst comprising a perovskite complex oxide represented by the following general formula (1):
La (Fe _1-x Cu _x ) O ₃ (1)
(In the formula, x represents an atomic ratio of 0.05 to 0.12 .)

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