JP3156577B2 - Material for exhaust gas purification catalyst and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst material and a method for producing the same, and more particularly to an alumina-based composite oxide containing cobalt, nickel and zinc at a fixed composition ratio and having a spinel structure. And its manufacturing method.

[0002]

2. Description of the Related Art Activated alumina, cerium oxide, and the like have been used as a base material for supporting a noble metal. In order to produce a metal aluminate, active alumina contains an aqueous solution of an additive element. A precipitation method in which a precipitation agent is added to a water-soluble salt of a raw material or a raw material is used.

[0003] Examples of such an exhaust gas purifying catalyst using activated alumina or cerium oxide are disclosed in Japanese Patent Publication No. 58-20307, Japanese Patent Application Laid-Open Nos. 5-305236 and 6-378. There are things that are. Japanese Patent Publication No. 58-20307 discloses an exhaust gas purifying catalyst in which a composition comprising platinum, rhodium and cerium is supported on a refractory carrier, and specifically, platinum, palladium and the like are prepared on alumina and cerium oxide. It has a structure in which a platinum group element such as rhodium is supported, and this is coated on a monolithic carrier.

Japanese Patent Application Laid-Open No. 5-305236 discloses that
An exhaust gas purification catalyst in which hexaaluminate containing no noble metal is mixed and dispersed in a noble metal-supported alumina such as platinum, rhodium, and palladium has been disclosed.Specifically, a hexaaluminate composition having a certain composition and platinum, rhodium And a mixture of alumina supporting at least one noble metal selected from the group consisting of palladium at a constant weight ratio.

JP-A-6-378 discloses that activated alumina and cerium oxide are mixed with at least one of platinum and palladium as catalyst components, potassium as a basic element,
Exhaust gas purification catalysts supporting an oxide of at least one metal selected from the group consisting of cesium, strontium and barium have been proposed, in other words, conventional catalyst components such as platinum group elements, activated alumina and cerium oxide. And a combination of at least one of a basic compound such as a potassium compound, a cesium compound, a strontium compound, and a barium compound.

Conventionally, in producing an alumina-based composite oxide containing cobalt, nickel and zinc,
After dissolving or dispersing one kind selected from the group consisting of cobalt, nickel and zinc and a water-soluble salt of aluminum in water, it is selected from the group consisting of ammonia water, ammonium carbonate, ammonium hydrogen carbonate, ammonium sulfate and ammonium hydrogen sulfate. A method is used in which at least one aqueous solution is added, water is removed, dried, and then fired.

[0007]

However, in the conventional exhaust gas purifying catalyst, when noble metal is supported on activated alumina, the noble metal is highly dispersed since activated alumina is porous and has a large specific surface area. Although the performance is improved, there is no activation promoting action between the noble metal and the activated alumina, so when the amount of the noble metal is reduced, the durability at high temperatures is insufficient, and after the high temperature durability, the catalyst at low temperatures There was a problem that activity and purification performance might be deteriorated.

Further, in the above-mentioned conventional method for producing an alumina-based composite oxide, the raw material cost is high for the oxide to be produced, and it is difficult to treat exhaust gas and waste water for NO _x roots and ammonium nitrate derived from raw material salts. Further, since the stirring / mixing state of the precipitate is insufficient, there is a problem that a part of cobalt, nickel and zinc forms a single oxide and the spinel type crystal structure becomes non-uniform.

Accordingly, an object of the present invention is to improve the low-temperature activity from the initial stage to the end of durability when used as a supporting substrate of a noble metal, compared with activated alumina as a conventional supporting substrate, and to achieve a stoichiometric air-fuel ratio. (hereinafter, referred to as "stoichiometric") insufficient oxygen concentration around the reducing atmosphere (hereinafter, referred to as "rich") cobalt which may be also HC, CO, enhancing the purification rate of the NO _x in, nickel and An object of the present invention is to provide an alumina-based composite oxide containing zinc and a method for producing the same.

[0010]

Means for Solving the Problems The present inventor has solved the above problems.
As a result of intensive research to determine _Two
O_Three) Instead of cobalt, nickel and zinc
Noble metal bearing alumina-based composite oxide
Activation of precious metals is promoted by using as a support material
It improves low-temperature activity from the initial stage to after
In the rich region where oxygen concentration is insufficient, especially in the toiki region
Even HC, CO, NO_xFound that the purification rate of
Then, the present invention has been reached.

Further, when producing the alumina-based composite oxide of the present invention, fine-particle alumina hydrate colloid (hereinafter referred to as “colloid”) is used.
By using "alumina sol"), the present inventors have found that the crystal structure is uniform, the structure stability at high temperatures is excellent, and the activity of promoting the activation of the noble metal is also excellent.

The exhaust gas purifying catalyst material of the present invention is a metal aluminate containing at least one selected from the group consisting of cobalt, nickel and zinc.

In order to increase the structural stability and specific surface area of the metal aluminate at high temperatures, the metal aluminate is
The following general formula; [X] in _a Al _b O _c (wherein, X is cobalt, and at least one element selected from the group consisting of nickel and zinc, a, b and c are atomic of each element Represents the ratio, and when b = 2.0, a = 0.
1 to 0.8, and c is the number of oxygen atoms necessary to satisfy the valence of each component described above), and is characterized by being an alumina-based composite oxide having a spinel structure.

The material for an exhaust gas purifying catalyst of the present invention is characterized in that when a metal aluminate containing at least one selected from the group consisting of cobalt, nickel and zinc comes into close contact with a noble metal species, lattice oxygen in the metal aluminate and Oxygen adsorbed on the surface is easily transferred and released, thereby improving low-temperature activity and contact performance such as purification performance in an oxygen-deficient atmosphere.

In the alumina-based composite oxide, when the composition of the metal aluminate is b = 2.0 in the above formula, a = 0.1
~ 0.8. If a is less than 0.1, the effect of the transition metal element selected from the group consisting of Co, Ni and Zn added to the alumina-based composite oxide is small, and a sufficient improvement effect cannot be obtained, which is the same as alumina. Also, a = 0.
If it exceeds 8, the physical properties of the alumina-based composite oxide, such as the BET specific surface area and the thermal stability, decrease, so that the dispersibility of the noble metal is poor. It promotes the ring, and conversely deteriorates the performance after durability.

By using an alumina-based composite oxide containing Co, Ni, and Zn in specific composition ratios as described above, compared to a stoichiometric ratio of metal aluminate ([X] ₁ Al ₂ O ₄ ), the temperature is higher. Is sufficient in structural stability and specific surface area, and the added element forms a solid solution in the crystal structure of alumina, so that sufficient performance can be obtained.

The alumina-based composite oxide of the present invention improves the thermal stability of the crystal structure at high temperatures and the activity of accelerating the activation of precious metals in the stoichiometric and rich regions. And a water-soluble salt of at least one element selected from the group consisting of zinc.

Further, the alumina-based composite oxide of the present invention comprises:
After dissolving alumina sol in water and dissolving a water-soluble salt of at least one element selected from the group consisting of cobalt, nickel and zinc in the dispersion, ammonia water, ammonium carbonate, ammonium hydrogen carbonate, ammonium sulfate and sulfuric acid It is obtained by adding at least one aqueous solution selected from the group consisting of ammonium hydrogen, removing water, drying and then firing.

Specifically, an aqueous solution obtained by dissolving a water-soluble salt of at least one element selected from the group consisting of cobalt, nickel and zinc in pure water is added to a dispersion obtained by adding the above alumina sol to pure water. Stir. At this time, a liquid in which each raw material is dissolved simultaneously or separately may be added. Next, aqueous ammonia, ammonium carbonate,
An aqueous solution of at least one compound selected from the group consisting of ammonium bicarbonate, ammonium sulfate and ammonium hydrogen sulfate is gradually added to adjust the pH of the solution to 7.0 to 9.
After adjusting to be in the range of 0, moisture is removed, and the residue is heat-treated to obtain an alumina-based composite oxide.

In producing the alumina-based composite oxide, the pH of the colloidal alumina hydrate having a size of 5 μm to 200 μm is maintained in a stable colloidal state.
To 2.0 to 7.0.

Cobalt, nickel and zinc can be used in any combination as nitrates, carbonates, ammonium salts, acetates, etc. In particular, the use of water-soluble salts makes it possible to obtain uniform crystal structure and heat resistance. To improve
Further, it is preferable from the viewpoint of improving the activation promoting action of the noble metal.

The method for preparing the alumina-based composite oxide is not limited to a special method, and may be any of various known methods such as an evaporation to dryness method, a precipitation method, and an impregnation method, unless there is a significant uneven distribution of components. Can be selected and used as appropriate,
After dispersing or dissolving the raw materials of the above elements in water,
The use of a precipitation method in which an aqueous solution of at least one compound selected from the group consisting of ammonia water, ammonium carbonate, ammonium hydrogen carbonate, ammonium sulfate and ammonium hydrogen sulfate is used as a precipitant, provides a sufficient BET ratio of the alumina-based composite oxide. This is preferable because uniformity of the surface area and the crystal structure is ensured and the noble metal is uniformly dispersed.

The exhaust gas purifying catalyst material according to the present invention comprises:
The alumina-based composite oxide obtained by the precipitation method of agglomerating the hydroxides of cobalt, nickel and zinc with the alumina sol of fine particles as the nucleus of precipitation has a fine pore structure and a large specific surface area. The uniform dispersion state of the active phase and the crystal structure having a uniform composition ratio play an important role in exhibiting the activation promoting action of the noble metal.

By using the above-mentioned ammonia water or an ammonium compound as a precipitant used in the precipitation method, no metal element remains even if the precipitation cake is insufficiently washed, and an ammonium compound (mainly ammonium nitrate after dropping) is used. Even if remains, the ammonium compound can be easily decomposed and removed in the subsequent baking. Furthermore, in order to use instead alumina sol aluminum nitrate, when drying and firing the precipitate, gas and wastewater treatment for NO _x and ammonium nitrate-derived materials is greatly reduced.

In carrying out the above precipitation method, precipitates of various metal salts can be formed by adjusting the pH of the solution to a range of 7.0 to 9.0. When the pH is lower than 7.0, various elements do not sufficiently form a precipitate, and conversely, the pH increases.
If it is higher than 9.0, some of the precipitated components may be redissolved.

The removal of water can be appropriately selected from known methods such as a filtration method and an evaporation to dryness method.
Although the first heat treatment for obtaining the alumina-based composite oxide of the present invention is not particularly limited, it is preferably performed, for example, in a temperature range of 600 to 1200 ° C. in the air and / or under the flow of air.

In the method for producing a material for an exhaust gas purifying catalyst of the present invention, the use of fine-particle alumina sol as a raw material for aluminum makes it possible to achieve a uniform crystal structure and a higher crystallinity than an alumina-based composite oxide using an aqueous solution of aluminum. The durability performance (thermal stability and the like) is further improved, and the specific surface area for carrying the noble metal in a highly dispersed state can be sufficiently secured. Therefore, the noble metal and the active phase can be more closely contacted with each other, so that the activation promoting action of the noble metal is increased, and the contact performance such as the low-temperature activity and the purification performance of the exhaust gas purifying catalyst is improved.

[0028]

The present invention will be described with reference to the following examples and comparative examples.

Example 1 An aqueous solution in which 485 parts of nickel nitrate was dissolved in 1000 parts of pure water was used.
20% by weight of alumina sol 1 in terms of alumina (Al ₂ O ₃ )
After adding 700 parts to a suspension in which 2500 parts of pure water were dispersed, 5% aqueous ammonia was added with stirring to adjust the pH to 8.0. The solution was dried at 150 ° C. for 24 hours, and calcined at 400 ° C. for 2 hours, at 600 ° C. for 2 hours, and then at 800 ° C. for 4 hours to obtain Ni _0.5 Al _2.0 O _x .

Example 2 Co _0.3 Al _2.0 O _x was obtained in the same manner as in Example 1 except that 291 parts of cobalt nitrate was used instead of nickel nitrate.

Example 3 Zn _0.3 Al _2.0 O _x was obtained in the same manner as in Example 1 except that 299 parts of zinc nitrate was used instead of nickel nitrate.

Comparative Example 1 Ni _0.5 Al _2.0 O _{x was} prepared in the same manner as in Example 1 except that 2500 parts of aluminum nitrate were used in place of the alumina sol.
I got

Comparative Example 2 Al _2.0 O _3.0 was obtained in the same manner as in Example 1, except that nickel nitrate was not used.

Comparative Example 3 Co _0.3 Al _2.0 O _{x was prepared in the same} manner as in Example 2 except that 2500 parts of aluminum nitrate were used instead of alumina sol.
I got

Comparative Example 4 Zn _0.3 Al _2.0 O _{x was} prepared in the same manner as in Example 3 except that 2500 parts of aluminum nitrate were used instead of the alumina sol.
I got

Example 4 692 parts of powder (powder A) having 1.0% by weight of palladium supported on Ni _0.5 Al _2.0 O _x obtained in Example 1 and 1 mol% of lanthanum (converted to La ₂ O ₃₎ 480 parts of powder (powder B) carrying 0.75 parts by weight of palladium on a cerium oxide powder containing ₂ % by weight of zirconium and 32% by mole of zirconium (25% by weight in terms of ZrO ₂ ) and 1200 parts of nitric acid aqueous solution It was put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells) and calcined at 400 ° C. for 1 hour to obtain a coat layer weight of 160 g / L and a palladium loading of 40 g / L.
A catalyst of cf (1.42 g / L) was obtained. Next, a barium acetate solution was applied to the cordierite-based monolithic carrier supporting the catalyst component, and then calcined at 400 ° C. for 1 hour to obtain BaO 15.
g / L.

Example 5 A coat layer having a weight of 160 was prepared in the same manner as in Example 4 except that Co _0.3 Al _2.0 O _x was used instead of Ni _0.5 Al _2.0 O _x.
g / L and a catalyst having a palladium carrying amount of 40 g / cf (1.42 g / L) were obtained. Then, after a barium acetate solution was applied in the same manner as in Example 4, it was baked at 400 ° C. for 1 hour,
It contained 15 g / L.

Example 6 A coating layer having a weight of 160 was prepared in the same manner as in Example 4 except that Zn _0.3 Al _2.0 O _x was used instead of Ni _0.5 Al _2.0 O _x.
g / L and a catalyst having a palladium carrying amount of 40 g / cf (1.42 g / L) were obtained. Then, after a barium acetate solution was applied in the same manner as in Example 4, it was baked at 400 ° C. for 1 hour,
It contained 15 g / L.

Comparative Example 5 The procedure of Example 4 was repeated except that Ni _0.5 Al _2.0 O _x of Comparative Example 1 was used, except that the coat layer weight was 160 g / L and the palladium carrying amount was 40 g / cf (1.42 g / L). A catalyst was obtained. Next, a barium acetate solution was applied in the same manner as in Example 4 and then calcined at 400 ° C. for 1 hour to contain BaO 15 g / L.

COMPARATIVE EXAMPLE 6 A coat layer weight of 160 g / L and a supported amount of palladium were carried out in the same manner as in Example 4 except that Al _2.0 O _3.0 of Comparative Example 2 was used.
40 g / cf (1.42 g / L) of the catalyst were obtained. Next, after a barium acetate solution was applied in the same manner as in Example 4, 40
It was baked at 0 ° C. for 1 hour to contain 15 g / L of BaO.

COMPARATIVE EXAMPLE 7 The procedure of Example 4 was repeated except that Co _0.3 Al _2.0 O _x was used, except that the coat layer weight was 160 g / L and the palladium carrying amount was 40 g / cf (1.42 g / L). A catalyst was obtained. Next, a barium acetate solution was applied in the same manner as in Example 4 and then calcined at 400 ° C. for 1 hour to contain BaO 15 g / L.

Comparative Example 8 The procedure of Example 4 was repeated, except that Zn _0.3 Al _2.0 O _x was used, except that the coat layer weight was 160 g / L and the palladium carrying amount was 40 g / cf (1.42 g / L). A catalyst was obtained. Next, a barium acetate solution was applied in the same manner as in Example 4 and then calcined at 400 ° C. for 1 hour to contain BaO 15 g / L.

Test Example Test Example 1 Ni _0.5 Al _2.0 obtained in Example 1 and Comparative Example 1
X-ray diffraction of O _x was performed, and the results are shown in FIG. Compared to Comparative Example 1, the X-ray diffraction of Example 1 showed impurities (free Ni).
O) peak is not observed, and a structure with high crystallinity is obtained.

Test Example 2 Ni _0.5 Al _2.0 obtained in Example 1 and Comparative Example 1
The crystallite diameter of O _x was measured, and the results are shown in Table 1. Even when firing was performed under the same conditions, Example 1 was compared with Comparative Example 1.
Ni _0.5 Al _2.0 O _x has a small crystallite diameter and is excellent in thermal stability of the crystal structure.

[0045]Test example 3 Ni obtained in Example 1 and Comparative Example 1_0.5Al_2.0
O_xAnd Al of Comparative Example 2._2.0O_3.0Was fired at each temperature
BET surface area and crystallite diameter at the time of measurement
2 is shown. Compared with Comparative Example 1 or 2, Ni of Example 1
_0.5Al_2.0O _xIs the heat shrinkage of the BET surface area and the crystallite diameter.
Growth (sintering) is suppressed and thermal stability of crystal structure
Is excellent.

Test Example 4 Co _0.3 Al _2.0 obtained in Example 2 and Comparative Example 3
The crystallite diameter of O _x was measured, and the results are shown in Table 1. Even in the case of firing under the same conditions, Example 2 was compared with Comparative Example 3.
Co _0.3 Al _2.0 O _x has a small crystallite diameter and is excellent in the thermal stability of the crystal structure.

Test Example 5 Zn _0.3 Al _2.0 obtained in Example 3 and Comparative Example 4
The crystallite diameter of O _x was measured, and the results are shown in Table 1. Even in the case of firing under the same conditions, Example 3 was compared with Comparative Example 4.
Zn _0.3 Al _2.0 O _x has a small crystallite diameter and is excellent in thermal stability of the crystal structure.

[0048]

[Table 1]

[0049] Ni _0.5 Al _2.0 O _x powder Test Example 6 Example 1, the powder 1 wt% on the palladium Ni _0.5 Al _2.0 O _x powder of Example 1, Al _2.0 O _3.0 powder of Comparative Example 2 The oxygen release characteristics of a powder having 1% by weight of palladium supported thereon were measured, and the results are shown in FIG. This indicates that oxygen is released from the low-temperature side via the noble metal.

Test Example 7 The exhaust gas purifying catalysts of Examples 4 to 6 and Comparative Examples 5 to 7 were endured under the following endurance conditions, and then evaluated for catalytic activity under the following evaluation conditions.

Endurance conditions Engine displacement 4400cc Fuel unleaded gasoline Catalyst inlet gas temperature 750 ° C Endurance time 100 hours Inlet gas composition CO 0.5 ± 0.1% O ₂ 0.5 ± 0.1% HC Approx.1100ppm NO 1300ppm CO ₂ 15%

[0052] Evaluation Condition 1: The low-temperature activity Engine displacement 2000cc fuel low-temperature activity of the exhaust gas purifying catalyst after unleaded petrol heating rate 10 ° C. / min measurement temperature range 150 to 500 ° C. durability, HC, the CO and NO _x Temperature at which the conversion reaches 50% (T50 / ℃)
And the results are shown in Table 2.

[0053] The purifying performance of the exhaust gas purifying catalyst after the durability test was determined using the following equation using the average conversion of HC, CO and NO _x in stoichiometric atmosphere (%) The results are shown in Table 2.

(Equation 1)

(Equation 2)

(Equation 3)

[0054]

[Table 2]

[0055]

The exhaust gas purifying catalyst material of the present invention has excellent durability at high temperatures, suppresses sintering of noble metal species, and can promote activation of noble metal species.

Further, the stability of the crystal structure at a high temperature can be improved.

According to a second aspect of the present invention, there is provided a method for producing an exhaust gas purifying catalyst material having a uniform crystal structure, improving structural stability at a high temperature, and further enhancing a dispersed state of an active phase to promote activation of a precious metal. Can be improved.

[Brief description of the drawings]

FIG. 1 is an X-ray diffraction diagram of an example of a material for an exhaust gas purifying catalyst of the present invention and a conventional material.

FIG. 2 is a diagram showing a BET surface area and a crystallite diameter of an example of the material for an exhaust gas purifying catalyst of the present invention and a conventional material.

FIG. 3 is a diagram showing oxygen release characteristics of an example of a material for an exhaust gas purifying catalyst of the present invention and a conventional material.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁷ Identification code FI B01J 23/89 C01G 9/00 B 37/04 102 51/00 A C01G 9/00 53/00 51/00 B01J 23/74 311A 53/00 B01D 53/36 104A (58) Fields investigated (Int. Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86 B01D 53/94

Claims (3)

(57) [Claims] 1. A metal aluminate, the following general formula; [X] in _a Al _b O _c (wherein, X is cobalt, and at least one element selected from the group consisting of nickel and zinc, a , B and c represent the atomic ratio of each element, and when b = 2.0, a = 0.
1 to 0.8, c is the number of oxygen atoms required to satisfy the valence of each of the above components), and is an alumina-based composite oxide having a spinel structure. Catalyst material. 2. In producing the alumina-based composite oxide according to claim 1, a fine particle alumina hydrate colloid;
A method for producing an exhaust gas purifying catalyst material, comprising using at least one water-soluble salt of cobalt, nickel and zinc. 3. In producing the alumina-based composite oxide according to claim 1, fine particle alumina hydrate colloid is dispersed in water, and at least one water-soluble salt of cobalt, nickel and zinc is added to the dispersion. After dissolving, ammonia water, ammonium carbonate, ammonium hydrogen carbonate,
A method for producing a material for an exhaust gas purifying catalyst, comprising adding at least one aqueous solution selected from the group consisting of ammonium sulfate and ammonium hydrogen sulfate, removing water, drying, and then calcining.