JP2840054B2 - Heat-resistant oxide - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a catalyst for efficiently purifying carbon monoxide (CO), hydrocarbons (HC) and nitrogen oxides (NOx) contained in exhaust gas of an automobile engine or the like. Composite oxide to be obtained.

[0002]

2. Description of the Related Art Until now, carbon monoxide (CO) contained in exhaust gas has been used as an exhaust gas purifying catalyst for automobiles.
A three-way catalyst capable of simultaneously purifying hydrocarbons (HC) and nitrogen oxides (NOx) is being developed, and three-way catalysts using noble metals such as platinum, palladium, and rhodium as active substances are well known. .

In order to improve the activity of the three-way catalyst, attention is paid to the function of oxygen storage or release of oxygen in the gas phase of cerium oxide (CeO ₂ ). Cerium oxide is added to the gas to adjust the gas phase atmosphere in the oxidation reaction of CO and HC and the reduction reaction of NOx to improve the purification efficiency. For example, Japanese Patent Publication No. 59-41775, Kaisho 59-
No. 90695 and Japanese Patent Publication No. 58-20307 disclose techniques using cerium oxide.

[0004]

However, in some cases, the exhaust gas purifying catalyst is practically used at a high temperature of 800 ° C. or higher. At such a high temperature, cerium oxide grows (sinters) in a grain size. There was a problem that the surface area was reduced and the purification performance was reduced due to the reduced oxygen storage capacity on the cerium oxide surface.

For this reason, zirconium is added to cerium oxide,
It has been proposed to suppress grain growth of cerium oxide by adding lanthanum or the like (Japanese Patent Application Laid-Open No. 63-116741).
However, even in this case, the oxygen storage capacity after use in a high-temperature oxidation-reduction fluctuating atmosphere is significantly reduced as compared with the oxygen storage capacity in the initial stage of use. When designing the purification catalyst, it is necessary to design in advance how much the oxygen storage capacity will be reduced, which is very complicated and has a disadvantage that the quality is not constant.

[0006]

Means for Solving the Problems The inventors of the present invention have excellent heat resistance and exhibit an oxygen storage capacity almost equal to the oxygen storage capacity in the initial stage of use even in a high-temperature oxidation-reduction fluctuating atmosphere. After extensive investigations on the heat-resistant oxide that does not decrease, the cerium oxide, the zirconium oxide and the rare earth metal oxide, the atomic ratio of zirconium is 0.60 to 0.70, the atomic ratio of the rare earth metal is, 0.20 to 0.25, and a composite oxide configured such that the atomic ratio of zirconium and the rare earth metal is 0.80 to 0.95 in a high-temperature redox fluctuation atmosphere at about 1000 ° C. Have also been found to exhibit the same activity as the oxygen storage capacity at the beginning of use, and have completed the present invention. That is, the present invention provides:

[0007]

Embedded image Ce _{1- (x + y)} Zr _x R _y O _2-z

(Wherein, R represents a rare earth metal, _z represents the amount of oxygen vacancies, _x represents an atomic ratio of 0.60 to 0.70, and _y represents an atomic ratio of 0.20 to 0.25, respectively. , _{X + y}
Indicates a range of 0.80 to 0.95. (2) a heat-resistant oxide according to (1), at least a part of which is a composite oxide and / or solid solution; (3) a rare-earth metal represented by R is yttrium (Y (4) The heat-resistant oxide according to any one of (1) to (3), further comprising a noble metal, and (5) the noble metal is platinum. (6) The heat-resistant oxide according to any one of (1) to (5), which is a catalyst for purifying exhaust gas.

[0009]

BEST MODE FOR CARRYING OUT THE INVENTION In the heat-resistant oxide of the present invention,
The rare earth metals R useful for forming at least a part as a complex oxide and / or solid solution include yttrium, scandium, lanthanum, praseodymium, neodymium, promethium, samarium, eurobium, gadolinium, terbium, dysprosium, holmium, erbium. , Thulium, ytterbium, and lutetium. Yttrium (Y), which is easier to form as a composite oxide and / or solid solution, is preferably used. These rare earth metals R may be used alone or in combination of two or more.

[0010] The atomic ratio of the rare earth metal R represented by _y is in the range of 0.20 to 0.25. If it is less than 0.20, the stability of the heat-resistant oxide at high temperatures may be deteriorated. If it exceeds 0.25, the rare-earth metal R may form a different compound.

On the other hand, zirconium (Zr) represented by _x
Is in the range of 0.60 to 0.70. 0.
If it is less than 60, the grain growth of cerium oxide may not be effectively suppressed, and if it exceeds 0.70, zirconium may form a different compound.

Further, _{x + y} ranges from 0.80 to 0.95. If it is less than 0.80, it may not be possible to exhibit an oxygen storage capacity substantially equal to that in the initial stage of use in a high-temperature oxidation-reduction fluctuating atmosphere.
If it exceeds 95, the cerium content is too small, and the oxygen storage capacity cannot be effectively exhibited in practical use.

Therefore, the atomic ratio of cerium (Ce) is
It become a minus and the atomic ratio _y of the atomic ratio _x and a rare earth metal R zirconium _{(Zr) 1- (x + y} ).

_Z represents the amount of oxygen vacancies, which means the proportion of vacancies in the fluorite-type crystal lattice usually formed by oxides of cerium, zirconium and rare earth metals.

The heat-resistant oxide of the present invention can be produced by a known method. For example, a slurry is prepared by adding water to cerium oxide powder, and then a zirconium salt and a rare earth metal salt are added to the slurry. After adding an aqueous solution mixed at a stoichiometric ratio of, and sufficiently stirring, an oxidation treatment is performed to obtain a heat-resistant oxide of the present invention.

The cerium oxide powder may be any commercially available one, but preferably has a large specific surface area in order to enhance the oxygen storage capacity, and preferably has a crystal grain size of 0.1 μm or less. About 10 to 50 parts by weight of water is added to 1 part by weight of the cerium oxide powder to form a slurry.

The salts of zirconium salts and rare earth metal salts include inorganic salts such as sulfates, nitrates, hydrochlorides and phosphates;
Organic salts such as acetates and oxalates are mentioned, and nitrates are preferably used. These zirconium salts and rare earth metal salts are each in a stoichiometric ratio within a range of the above-mentioned predetermined atomic ratio of the present invention in a range of 0.1 part by weight to 1 part by weight.
Dissolve in 1 to 10 weight of water to obtain a mixed aqueous solution.

After the mixed aqueous solution is added to the above slurry and sufficiently stirred and mixed, an oxidation treatment is performed. This oxidation treatment is first performed under reduced pressure using a vacuum dryer or the like, and then preferably dried at about 50 ° C. to 200 ° C. for about 1 to 48 hours to obtain a dried product. ° C to 1000
C., preferably from about 400.degree. C. to 700.degree. C. for about 1 to 12 hours, preferably about 2 to 4 hours. In this firing, it is preferable that at least a part of the heat-resistant oxide be a composite oxide and / or a solid solution to enhance the heat resistance of the heat-resistant oxide. Suitable firing conditions for forming the composite oxide and / or the solid solution are appropriately determined by the composition of the heat-resistant oxide and its ratio.

The heat-resistant oxide of the present invention is prepared by adjusting a solution of a salt containing cerium, zirconium and a rare earth metal so as to have a predetermined stoichiometric ratio. After coprecipitating a salt containing zirconium and a rare earth metal, the coprecipitate is oxidized, or a mixed alkoxide solution containing cerium, zirconium and a rare earth metal is adjusted, and deionized water is added to the mixed alkoxide solution. In addition, this coprecipitate or hydrolysis product may be oxidized by coprecipitation or hydrolysis.

In this case, as the salt to be used, the salts exemplified above as salts of cerium salt, zirconium salt and rare earth metal salt are used. As the alkaline aqueous solution, alkali metal salts such as sodium and potassium and ammonia and the like are used. In addition to the aqueous solution, a known buffer may be used as appropriate,
The pH of the solution after adding the alkaline aqueous solution is 8 to 11
Preferably, it is about

On the other hand, mixed alkoxide solutions include cerium, zirconium and methoxide of rare earth metal,
Ethoxide, propoxide, butoxide and their ethylene oxide adducts are used, butbutoxide is preferably used.

When the obtained coprecipitate or hydrolysis product is subjected to oxidation treatment, the coprecipitate or hydrolysis product is filtered and washed, preferably at about 50 ° C. to 20 ° C.
It is dried at 0 ° C. for about 1 to 48 hours to obtain a dried product, and the obtained dried product is subsequently subjected to about 350 ° C. to 1000 ° C., preferably 400 to 1000 ° C.
The firing is performed at 700 ° C. for about 1 to 12 hours, preferably for about 2 to 4 hours. In this firing, it is preferable that at least a part of the heat-resistant oxide be a composite oxide and / or a solid solution to enhance the heat resistance of the heat-resistant oxide. Suitable firing conditions for forming the composite oxide and / or the solid solution are appropriately determined by the composition of the heat-resistant oxide and its ratio.

The heat-resistant oxide of the present invention thus obtained further contains a noble metal to impart catalytic activity.

As the noble metal, ruthenium (Ru),
Platinum group elements consisting of rhodium (Rh), palladium (Pd), osmium (Os), iridium (Ir) and platinum (Pt) are listed. As a three-way catalyst for purifying exhaust gas, platinum (Pt), rhodium ( Rh) and palladium (Pd) are preferable, and platinum (Pt) is particularly preferably used. These noble metals are used in an amount of 0.01 to 10 parts by weight, preferably 0.05 to 2 parts by weight, per 100 parts by weight of the heat-resistant oxide.
It is preferable that it be contained by weight.

The method of incorporating the noble metal into the heat-resistant oxide may be any known method. For example, a solution of a salt containing the noble metal is prepared, and this salt-containing solution is impregnated with the heat-resistant oxide. It is done by doing. In this case, as the salt-containing solution, a solution of any of the above-mentioned salts may be used, and practically, a nitrate aqueous solution, a dinitrodiammine nitric acid solution, a chloride aqueous solution, or the like is used. About 1 salt solution
After impregnating the refractory oxide with the precious metal salt of up to 20% by weight, it is preferably
Dried at about 350 ° C. to 1000 ° C. for about 1 to 1
It is carried out by firing for 2 hours and carrying the material.

As another method, in the above-mentioned step of producing a heat-resistant oxide, when a solution of a salt containing cerium, zirconium and a rare earth metal or a mixed alkoxide solution is coprecipitated or hydrolyzed, a noble metal salt is used. A method of adding a solution to coprecipitate a noble metal salt together with each component of the heat-resistant oxide, and then performing an oxidation treatment. In this method, the noble metal is uniformly dispersed in the heat-resistant oxide, and good catalytic activity can be obtained. Examples of the solution of the noble metal salt used in this case include the above-mentioned salt-containing solutions such as an aqueous nitrate solution, a dinitrodiammine nitric acid solution, and an aqueous chloride solution.Specifically, as a platinum salt solution, dinitrodiammine platinum Nitric acid solution, chloroplatinic acid solution, tetravalent platinum ammine solution, palladium salt solution: palladium nitrate aqueous solution, dinitrodiammine palladium nitrate solution, tetravalent palladium ammine nitric acid solution, rhodium salt solution: rhodium nitrate solution, rhodium chloride solution And the like, and preferably a dinitrodiammineplatinum nitrate solution is used. This salt solution is about 1-20% by weight
It is preferable to include a salt of

The oxidation treatment of the obtained coprecipitate is carried out by drying under reduced pressure using a vacuum dryer or the like, and preferably by drying at about 50 to 200 ° C. for about 1 to 48 hours. Is obtained, and the obtained dried product is subsequently cooled to about 350 ° C. to 1000
C., preferably at 400 to 700.degree. C. for about 1 to 12 hours, preferably about 2 to 4 hours.

The heat-resistant oxide of the present invention thus obtained, which further contains a noble metal, combines the oxygen storage capacity of cerium oxide with the excellent catalytic activity of a noble metal. Can be suitably used as an exhaust gas purifying catalyst for automobiles in which the oxidation-reduction atmosphere fluctuates due to fluctuations in the exhaust gas.

[0029]

EXAMPLES The present invention will be described below more specifically based on examples.

Comparative Example 1 33.1 g (0.077 mol) of cerium butoxide, 26.1 g (0.068 mol) of zirconium butoxide,
7.8 g (0.025 mol) of yttrium butoxide was placed in a 500 ml round bottom flask, and 200 ml of toluene was added.
Then, the resulting mixture was stirred and dissolved to prepare a mixed alkoxide solution. On the other hand, 600 ml of water was put into a 1 L round bottom flask and stirred, and about 10 times of the mixed alkoxide solution was dropped therein, and a large amount of white precipitate was formed. Then, the mixture was heated to remove most of the solvent, and Ce _0.45 Zr _0.40
A Y _0.15 Oxide precursor slurry dispersion was obtained.

Next, 0.534 g of a dinitrodiammine platinum nitrate solution (platinum content: 4.569% by weight) was added to 20 m of water.
l, and added to this solution with Ce _0.45 Zr _0.40 Y
_0.15 Oxide precursor slurry dispersion was added, and after stirring and mixing, water was distilled off under reduced pressure to obtain white viscous Ce _0.45.
A Zr _0.40 Y _0.15 Oxide / Pt precursor was obtained.

This Ce _0.45 Zr _0.40 Y _0.15
After drying the Oxide / Pt precursor with ventilation at 60 ° C. for 24 hours, it is baked at 450 ° C. for 3 hours in an electric furnace to obtain yellowish white powdery Ce _0.45 Zr _0.40 Y _0.15 Oxide.
A heat-resistant oxide 1 having a composition of / Pt was obtained.

As shown in Table 2, the obtained heat-resistant oxide 1 was aged at 1000 ° C. for 2 hours while repeating a reducing atmosphere, an inert atmosphere, and an oxidizing atmosphere.

Then, the oxygen storage capacity of the unheated initial heat-resistant oxide 1 and the aged heat-resistant oxide 1 was evaluated, and the change of the oxygen storage capacity between the initial sample and the sample after endurance at 1000 ° C. Was examined. Table 1 shows the results. The evaluation of the oxygen storage capacity was performed as follows.

Evaluation of Oxygen Storage Capacity (OSC) About 20 mg of powdery heat-resistant oxide 1 was sampled, and the weight change was measured with a thermobalance having the setting conditions shown in Table 3, and the results were obtained in steps 8 and 10. The change in weight during the period was estimated as the amount of oxygen absorbed and released, and expressed as the number of moles of oxygen in 1 mole of the sample.

The gas flow rate at the time of the measurement was set to 40 ml / min, which is almost the same as the actual flow rate of the exhaust gas of an automobile.

Comparative Example 2 29.4 g of cerium butoxide as alkoxide
(0.068 mol), zirconium butoxide 29.4
g (0.077 mol), yttrium butoxide 7.8
g (0.025 mol) as a solution of the noble metal salt,
The same operation as in Comparative Example 1 was carried out except that 0.525 g of dinitrodiammineplatinic nitric acid solution was used, and yellowish white powdery Ce _0.40 Zr _0.45 Y _0.15 Oxide / Pt was used.
Was obtained. This heat-resistant oxide 2 was aged at a temperature of 1000 ° C. in the same manner as in Comparative Example 1, and then the oxygen storage capacity was evaluated. Table 1 shows the results.

Example 1 Cerium ethoxyethylate as alkoxide
Using 9 g (0.034 mol), 45.7 g (0.102 mol) of zirconium ethoxyethylate and 12.1 g (0.034 mol) of yttrium ethoxyethylate,
The same operation as in Comparative Example 1 was performed except that 0.488 g of a dinitrodiammineplatinic nitric acid solution was used as the solution of the noble metal salt, and yellowish white powder Ce _0.20 Zr _0.60 Y
Heat resistant oxide 3 having composition of _0.20 Oxide / Pt 3
I got This heat-resistant oxide 3 was treated with 10 as in Comparative Example 1.
Aging was performed at a temperature of 00 ° C., and then the oxygen storage capacity was evaluated. Table 1 shows the results.

Example 2 5.5 g of cerium ethoxide as an alkoxide (0.
017 mol), 32.4 g of zirconium ethoxide
(0.119 mol), 7.6 g of yttrium ethoxide
(0.034 mol) and 0.468 g of dinitrodiammineplatinic nitric acid solution was used as the solution of the noble metal salt, and the same operation as in Comparative Example 1 was carried out.
e _0.10 Zr _0.70 Y _0.20 Oxide / Pt to obtain a heat-resistant oxide 4. This heat-resistant oxide 4
Was aged at a temperature of 1000 ° C. in the same manner as in Comparative Example 1, and then the oxygen storage capacity was evaluated. Table 1 shows the results.

Example 3 3.5 g of cerium isopropoxide as alkoxide
(0.009 mol), zirconium isopropoxide 3
Using 9.7 g (0.121 mol) and 12.0 g (0.045 mol) of yttrium isopropoxide, a dinitrodiammineplatinum nitric acid solution 0.4
The same operation as in Comparative Example 1 was performed except that 60 g was used.
Yellow-white powdery Ce _0.05 Zr _0.70 Y _0.25 O
A heat-resistant oxide 5 having a composition of xide / Pt was obtained. This heat-resistant oxide 5 was aged at a temperature of 1000 ° C. in the same manner as in Comparative Example 1, and then the oxygen storage capacity was evaluated. Table 1 shows the results.

Comparative Example 3 Cerium ethoxyethylate as alkoxide
8 g (0.068 mol), 30.5 g (0.068 mol) of zirconium ethoxyethylate, 13.8 g (0.034 mol) of lanthanum ethoxyethylate, and a dinitrodiammineplatinum nitrate solution 0 as a solution of the noble metal salt. The same operation as in Comparative Example 1 was carried out except that .565 g was used, and yellowish white powdery Ce _0.40 Zr _0.40 La was used.
Heat resistant oxide 6 having composition of _0.20 Oxide / Pt 6
I got This heat-resistant oxide 6 was treated with 10 as in Comparative Example 1.
Aging was performed at a temperature of 00 ° C., and then the oxygen storage capacity was evaluated. Table 1 shows the results.

Comparative Example 4 73.5 g of cerium butoxide as alkoxide
(0.170 mol), and the same operation as in Comparative Example 1 was carried out except that 0.641 g of dinitrodiammineplatinum nitric acid solution was used as the solution of the noble metal salt, to obtain CeO ₂ / Pt of yellow-white powder. A heat resistant oxide 7 having a composition was obtained. This heat-resistant oxide 7 was mixed with 1000 as in Comparative Example 1.
After aging at a temperature of ° C., the oxygen storage capacity was evaluated. Table 1 shows the results.

Comparative Example 5 35.4 g of cerium ethoxide as alkoxide
(0.111 mol), zirconium ethoxide 13.4
g (0.051 mol), yttrium ethoxide 1.9
g (0.009 mol) as a solution of a noble metal salt,
The same operation as in Comparative Example 1 was carried out except that 0.569 g of dinitrodiammineplatinic nitric acid solution was used, and yellowish white powdery Ce _0.65 Zr _0.30 Y _0.05 Oxide / Pt was used.
Was obtained. This heat-resistant oxide 8 was aged at a temperature of 1000 ° C. in the same manner as in Comparative Example 1, and then the oxygen storage capacity was evaluated. Table 1 shows the results.

Comparative Example 6 32.7 g of cerium ethoxide as alkoxide
(0.102 mol), zirconium ethoxide 13.9
g (0.051 mol), yttrium ethoxide 3.8
g (0.017 mol) as a solution of a noble metal salt,
The same operation as in Comparative Example 1 was carried out except that 0.505 g of dinitrodiammineplatinum nitric acid solution was used, and yellowish white powdery Ce _0.60 Zr _0.30 Y _0.10 Oxide / Pt was used.
Was obtained. This heat-resistant oxide 9 was aged at a temperature of 1000 ° C. in the same manner as in Comparative Example 1, and then the oxygen storage capacity was evaluated. Table 1 shows the results.

Comparative Example 7 36.8 g of cerium butoxide as alkoxide
(0.085 mol), zirconium butoxide 26.1
g (0.068 mol), yttrium butoxide 5.2
g (0.017 mol) as a solution of a noble metal salt,
The same operation as in Comparative Example 1 was carried out except that 0.545 g of dinitrodiammineplatinic nitric acid solution was used, and yellowish white powdery Ce _0.50 Zr _0.40 Y _0.10 Oxide / Pt was used.
Was obtained. This heat-resistant oxide 10 was aged at a temperature of 1000 ° C. in the same manner as in Comparative Example 1, and then the oxygen storage capacity was evaluated. Table 1 shows the results.

Comparative Example 8 48.9 g of zirconium butoxide as alkoxide
(0.128 mol), yttrium butoxide 13.1
g (0.043 mol) as a solution of a noble metal salt,
The same operation as in Comparative Example 1 was carried out except that 0.453 g of dinitrodiammineplatinum nitric acid solution was used, and white powdery Z
A heat-resistant oxide 11 having a composition of r _0.75 Y _0.25 O _1.875 / Pt was obtained. This heat-resistant oxide 11 was aged at a temperature of 1000 ° C. in the same manner as in Comparative Example 1, and then the oxygen storage capacity was evaluated. Table 1 shows the results.

[0047]

[0048]

[Table 2]

[0049]

[Table 3]

According to Table 1, the atomic ratio of cerium was 0.20.
( _{X + y} = 0.80) In Examples 1 to 3 or less, there was no difference from the initial sample, and the oxygen storage capacity was completely equal or higher.

[0051]

The heat-resistant oxide of the present invention has excellent heat resistance and exhibits an oxygen storage capacity almost equivalent to the oxygen storage capacity in the initial stage of use even in a high-temperature redox fluctuation atmosphere. It can be suitably used as a cocatalyst for purifying gas, and further contains other catalytically active components, for example, a noble metal, in combination with the oxygen storage ability of cerium oxide and the excellent catalytic activity of a noble metal,
It can be suitably used as it is as a three-way catalyst for purifying exhaust gas for automobiles.

Continued on the front page (51) Int.Cl. ⁶ Identification code FI B01J 23/56 301A

Claims (6)

(57) [Claims] 1. A compound of the general formula: Ce _{1- (x + y)} Zr _x R _y O
_2-z (where R represents a rare earth metal, _z represents the amount of oxygen vacancies, _x represents an atomic ratio of 0.60 to 0.70, and _y represents 0.2
_{X + y} represents an atomic ratio of 0 to 0.25, respectively.
The range is 0.80 to 0.95. A heat-resistant oxide represented by). 2. The heat-resistant oxide according to claim 1, wherein at least a part thereof is a composite oxide and / or a solid solution. 3. The heat-resistant oxide according to claim 1, wherein the rare earth metal represented by R is yttrium (Y). 4. The heat-resistant oxide according to claim 1, further comprising a noble metal. 5. The heat-resistant oxide according to claim 4, wherein the noble metal is platinum (Pt). 6. The exhaust gas purifying catalyst according to claim 1, wherein said catalyst is an exhaust gas purifying catalyst.
A heat-resistant oxide according to any one of the above.