JPH11197506A - Catalyst for purification of exhaust gas and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To promote activation of noble metals and to improve low temp. activity from the initial stage after long-term use by using an alumina-based multiple oxide containing at least one kind of lanthanum, nickel and cobalt in a specified compsn. ratio as the carrier base of noble metals. SOLUTION: This catalyst for purification of exhaust gas consists of an alumina multiple oxide containing at least one kind selected from lanthanum, nickel and cobalt. The alumina-based multiple oxide is prepared by dispersing or dissolving fine particles of alumina hydrate colloid (alumina sol), a water-soluble salt of at least one kind of element selected from cobalt and nickel, and a water-soluble salt of lanthanum in water, adding at least one kind of aq. soln. selected from ammonia water, aluminum carbonate, ammonium hydrogen carbonate, ammonium sulfate and ammonium hydrogen sulfate, then removing water, drying and calcining.

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 and a method for producing the same, and more particularly, to hydrocarbons (hereinafter referred to as "HC") and monoxide in exhaust gas discharged from an internal combustion engine of an automobile or the like. Excellent low-temperature activity that can effectively purify carbon (hereinafter referred to as “CO”) and nitrogen oxides (hereinafter referred to as “NO _x ”) even at low temperatures, and excellent catalytic activity under all exhaust gas composition atmospheres The present invention relates to an exhaust gas purifying catalyst and a method for producing the same.

[0002]

2. Description of the Related Art Conventionally, during a low temperature period from the start of an internal combustion engine until the catalyst temperature reaches a reaction temperature for exhaust gas purification, the exhaust gas purification performance is not sufficient. The development of gas purification catalysts is expected.

[0003]

As such exhaust gas purifying catalysts, for example, JP-B-58-20307, JP-A-5-305236, and JP-A-6-378.
And Japanese Patent Application Laid-Open No. 8-323205. The exhaust gas purifying catalyst described in Japanese Patent Publication No. 58-20307 is a catalyst in which a composition comprising platinum, rhodium and cerium is supported on a refractory carrier, and specifically, platinum on alumina or cerium oxide. , Palladium, rhodium, and other platinum group elements, and a monolithic carrier coated with the element. JP-A-5-305236 discloses an exhaust gas purifying catalyst in which hexaaluminate containing no noble metal is mixed and dispersed in a noble metal-supported alumina such as platinum, rhodium, or palladium. Is a mixture of a hexaaluminate composition having the following composition and alumina carrying at least one noble metal selected from the group consisting of platinum, rhodium and palladium at a constant weight ratio. JP-A-6-378 discloses that activated alumina and cerium oxide include at least one of platinum and palladium as catalyst components and at least one selected from the group consisting of basic elements potassium, cesium, strontium and barium. There has been proposed an exhaust gas purifying catalyst in which an oxide of a metal is supported. In other words, the catalyst is a platinum group element, activated alumina, cerium oxide, etc., in addition to those conventionally used as a catalyst component, and a basic element such as a potassium compound, a cesium compound, a strontium compound and a barium compound. At least one of them is combined. Further, Japanese Unexamined Patent Publication No.
Japanese Patent Publication No. 323205 proposes an exhaust gas purifying catalyst characterized by containing at least palladium and metal aluminate as catalyst components.

[0004]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems, and as a result, have found that an alumina-based composite oxide containing at least one selected from lanthanum, nickel and cobalt in a fixed composition ratio. By using as a noble metal-supporting substrate, activation of the noble metal is promoted, low-temperature activity is improved from the initial stage to endurance, and H is increased even in a rich region where the oxygen concentration is insufficient mainly in the stoichiometric region.
It has been found that the purification rates of C, CO and NO _X are improved.
Further, in producing this alumina-based composite oxide, a fine particle alumina hydrate colloid (alumina sol) and at least one water-soluble salt selected from lanthanum, nickel and cobalt are dissolved or dispersed in water. Water, ammonium carbonate, ammonium bicarbonate, ammonium sulfate, and at least one aqueous solution selected from the group consisting of ammonium hydrogensulfate are added, water is removed, dried, and then calcined to obtain lanthanum and nickel and cobalt. It has been found that at least one selected from the group consisting of (1) and (2) is in a state of being very highly dispersed, has excellent structural stability at a high temperature, and has an excellent action of promoting the activation of the noble metal, and has reached the present invention.

[0005] The exhaust gas purifying catalyst according to claim 1 is characterized by being an alumina-based composite oxide containing at least one selected from lanthanum, nickel and cobalt. Further, in order to increase the structural stability and the specific surface area of the alumina-based composite oxide according to claim 1 at a high temperature, the exhaust gas purifying catalyst according to claim 2 is characterized in that: The following general formula: [X] a [Y] b Alc Od (where X is a lanthanum element, Y is at least one element selected from the group consisting of cobalt and nickel, and a, b , C and d represent the atomic ratio of each element, and when c = 2.0, a = 0.01 to less than 0.1, b =
0.1 to 0.7, d is the number of oxygen atoms necessary to satisfy the valence of each component described above). Further, in the alumina-based composite oxide according to claim 2, when the composition of the alumina-based composite oxide according to claim 1 is c = 2.0 in the above formula, b =
0.1 to 0.7. If a is less than 0.01,
The effect of the lanthanum element added to the alumina-based composite oxide is small, and a sufficient improvement effect cannot be obtained, which is the same as a composite oxide composed of aluminum and at least one element selected from nickel and cobalt. Also, a = 0.1
Exceeds the physical properties of the alumina-based composite oxide, such as the BET specific surface area and thermal stability, so that the dispersibility of the noble metal is poor. And, on the contrary, the performance after the durability is deteriorated.

Further, the alumina-based composite oxide according to claim 1 or 2 further improves the thermal stability of the crystal structure at a high temperature and the activity of accelerating the activation of the noble metal in the stoichiometric region and the rich region. After dissolving or dispersing a fine particle alumina hydrate colloid (alumina sol), a water-soluble salt of at least one element selected from the group consisting of cobalt and nickel, and a water-soluble salt of lanthanum in water, ammonia water, ammonium carbonate Adding at least one aqueous solution selected from the group consisting of ammonium hydrogen carbonate, ammonium sulfate and ammonium hydrogen sulfate, removing water and drying,
Then, it is obtained by firing.

In producing the alumina-based composite oxide according to the third aspect, the pH is adjusted to 2.0 to 7.0 in order to keep alumina hydrate having a colloidal size of 5 μm to 200 μm in a stable colloidal state. The prepared alumina sol can be produced by arbitrarily combining nickel, cobalt, and lanthanum nitrates, carbonates, ammonium salts, acetates, and the like. It is preferable from the viewpoint of improving the properties and further enhancing the activation promoting action of the noble metal.

The method of preparing the alumina-based composite oxide is not limited to a special method, and may be any of various known methods such as evaporation to dryness, precipitation, impregnation, etc., unless significant uneven distribution of components is involved. Can be selected and used from
After dissolving or dispersing the core material 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.

In producing the exhaust gas purifying catalyst of the present invention, an aqueous solution in which a water-soluble salt of at least one element selected from nickel and cobalt is dissolved in pure water is added to a dispersion obtained by adding alumina sol to pure water. And stir. At this time, a liquid in which each raw material is dissolved simultaneously or separately may be added. Next, at least one compound selected from the group consisting of aqueous ammonia, ammonium carbonate, ammonium hydrogen carbonate, ammonium sulfate and ammonium hydrogen sulfate is gradually added to the raw material mixed solution, and the pH of the solution is adjusted to 7.0 to 9.0. After adjusting to be in the range of 0,
Heat treatment of this mixed solution at 100 to 300 ° C (boiling)
Then, moisture is removed and dried, and the residue is heat-treated to obtain an alumina-based composite oxide.

[0010] The alumina-based composite oxide, which is the catalyst for purifying exhaust gas according to the present invention, has a fine pore structure and a large specific surface area. The crystal structure having an appropriate composition ratio plays an important role in expressing the activation promoting action of the noble metal.

If the above-mentioned aqueous ammonia or ammonium compound is used as a precipitating agent in the precipitating method, no metal element remains even if the precipitation cake is insufficiently washed, and an ammonium compound (mainly ammonium nitrate after dropping) is used.
Can be easily decomposed and removed in the subsequent firing. Furthermore, since alumina sol is used instead of aluminum nitrate, when the precipitate is dried and fired, N
Exhaust gas and wastewater treatment for O _X or ammonium nitrate is significantly 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. pH 7
When the pH is lower than 0, various elements do not sufficiently form a precipitate, and when the pH 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 700 to 1200 ° C. in air and / or under air flow.

[0014]

The exhaust gas purifying catalyst according to claim 1 is characterized in that when at least one selected from nickel and cobalt and lanthanum-containing alumina-based composite oxide come into intimate contact with a noble metal species, the alumina-based composite oxide becomes Lattice oxygen and oxygen adsorbed on the surface are easily transferred and released, and catalytic performance such as low-temperature activity and purifying performance in an oxygen-deficient atmosphere is improved.

Further, the method for producing an exhaust gas purifying catalyst according to the third aspect of the present invention uses fine-particle alumina sol as a raw material of aluminum, thereby making it possible to use a crystalline alumina sol as compared with an alumina-based composite oxide using a water-soluble salt of aluminum. The uniformity of the structure and the durability performance (thermal stability, etc.) are further improved, and the specific surface area for highly dispersing and supporting the noble metal can be sufficiently secured. Therefore, the noble metal and the active phase can be brought into more intimate contact with each other, so that the activation promoting action of the noble metal is increased, and the catalytic performance such as the low-temperature activity and the purification performance of the exhaust gas purifying catalyst is improved.

[0016]

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

Example 1 An aqueous solution obtained by dissolving 42.7 g of lanthanum acetate and 485 g of nickel nitrate in 1000 g of pure water was dispersed in 2500 g of pure water with 1700 g of alumina sol of 20% by weight in terms of alumina (Al ₂ O ₃ ). After adding to the suspension, 5% aqueous ammonia was added with stirring, and p
H was adjusted to 8.0. This solution was boiled at 150 ° C. for 4 hours, dried with a spray dryer, and then dried at 400 ° C. for 2 hours.
Time, 2 hours at 600 ° C., and then calcined 4 hours at 800 ° C., to obtain a La0.03Ni0.5Al2.0O _X. Here, X is the number of oxygen atoms necessary to satisfy the valence of each component. The same applies to Examples 2 to 10 and Comparative Examples 1 to 10.

<Example 2> An aqueous solution in which 14.2 g of lanthanum acetate and 485 g of nickel nitrate were dissolved in 1000 g of pure water was dispersed in 2500 g of pure water with 1700 g of alumina sol of 20% by weight in terms of alumina (Al ₂ O ₃ ). After adding to the suspension, 5% aqueous ammonia was added with stirring, and p
H was adjusted to 8.0. This solution was boiled at 150 ° C. for 4 hours, dried with a spray dryer, and then dried at 400 ° C. for 2 hours.
Calcination was performed at 600 ° C. for 2 hours and then at 800 ° C. for 4 hours to obtain La0.01Ni0.5Al2.0O _x .

<Example 3> Lanthanum acetate 128.1 g,
An aqueous solution prepared by dissolving 485 g of nickel nitrate in 1000 g of pure water was added to a suspension in which 1700 g of 20 wt% alumina sol in terms of alumina (Al ₂ O ₃ ) was dispersed in 2500 g of pure water. Add water,
The pH was adjusted to 8.0. After boiling for 4 hours at a solution 0.99 ° C., dried in a spray drier, 2 hours at 400 ° C., and calcined for 4 hours at 2 hours, then 800 ° C. at 600 ° C., to obtain a La0.09Ni0.5Al2.0O _X .

Example 4 An aqueous solution obtained by dissolving 42.7 g of lanthanum acetate and 291 g of cobalt nitrate in 1000 g of pure water was dispersed in 2500 g of pure water with 1700 g of 20 wt% alumina sol in terms of alumina (Al ₂ O ₃ ). After adding to the suspension, 5% aqueous ammonia was added with stirring, and p
H was adjusted to 8.0. This solution was boiled at 150 ° C. for 4 hours, dried with a spray dryer, and then dried at 400 ° C. for 2 hours.
Time, 2 hours at 600 ° C., and then calcined 4 hours at 800 ° C., to obtain a La0.03Ni0.3Al2.0O _X.

<Example 5> 42.7 g of lanthanum acetate, 97 g of cobalt nitrate and 388 g of nickel nitrate were added to 100 parts of pure water.
0 g of an aqueous solution dissolved in alumina (Al ₂ O ₃ ) was converted to 20 wt% of alumina sol (1700 g) in pure water (2,500).
After adding to the suspension dispersed in g, 5% aqueous ammonia was added with stirring to adjust the pH to 8.0. This solution was boiled at 150 ° C. for 4 hours, dried with a spray drier, baked at 400 ° C. for 2 hours, 600 ° C. for 2 hours, and then at 800 ° C. for 4 hours to obtain La0.03Ni0.4Co.
It was obtained 0.1Al2.0O _X.

Comparative Example 1 An aqueous solution in which 7.1 g of lanthanum acetate and 485 g of nickel nitrate were dissolved in 1000 g of pure water was dispersed in 2500 g of pure water with 1700 g of 20 wt% alumina sol in terms of alumina (Al ₂ O ₃ ). After adding to the suspension, 5% aqueous ammonia was added with stirring, and p
H was adjusted to 8.0. This solution was boiled at 150 ° C. for 4 hours, dried with a spray dryer, and then dried at 400 ° C. for 2 hours.
Time, 2 hours at 600 ° C., and then calcined 4 hours at 800 ° C., to obtain a La0.005Ni0.5Al2.0O _X.

<Comparative Example 2> 284.6 g of lanthanum acetate,
An aqueous solution prepared by dissolving 485 g of nickel nitrate in 1000 g of pure water was added to a suspension in which 1700 g of 20 wt% alumina sol in terms of alumina (Al ₂ O ₃ ) was dispersed in 2500 g of pure water. Add water,
The pH was adjusted to 8.0. This solution was boiled at 150 ° C. for 4 hours, dried with a spray drier, and calcined at 400 ° C. for 2 hours, 600 ° C. for 2 hours, and then at 800 ° C. for 4 hours to obtain La0.2Ni0.5Al2.0O _X. .

Comparative Example 3 An aqueous solution obtained by dissolving 485 g of nickel nitrate in 1000 g of pure water was mixed with alumina (Al ₂ O).
₃ ) 1700 g of a 20% by weight alumina sol was converted to a suspension of 2500 g of pure water dispersed in 2500 g of pure water.
% Ammonia water was added to adjust the pH to 8.0. After drying this solution at 150 ° C. for 24 hours, it was baked at 400 ° C. for 2 hours, 600 ° C. for 2 hours, and then at 800 ° C. for 4 hours to obtain Ni0.5Al2.0O _X.

<Comparative Example 4> An aqueous solution in which 291 g of cobalt nitrate was dissolved in 1000 g of pure water was converted to alumina (Al ₂ O).
₃ ) 1700 g of a 20% by weight alumina sol was converted to a suspension of 2500 g of pure water dispersed in 2500 g of pure water.
% Ammonia water was added to adjust the pH to 8.0. After drying this solution at 150 ° C. for 24 hours, it was baked at 400 ° C. for 2 hours, at 600 ° C. for 2 hours, and then at 800 ° C. for 4 hours to obtain Co0.3Al2.0O _x .

Comparative Example 5 An aqueous solution obtained by dissolving 42.7 g of lanthanum acetate in 1000 g of pure water was mixed with alumina (Al ₂ O).
₃ ) After adding 1700 g of alumina sol of 20% by weight in terms of a dispersion in 2500 g of pure water, the pH was adjusted to 8.0 by adding 5% aqueous ammonia with stirring.
The solution was boiled at 150 ° C. for 4 hours, dried with a spray drier, baked at 400 ° C. for 2 hours, 600 ° C. for 2 hours, and then at 800 ° C. for 4 hours to obtain La0.03Al.
2.0O _X was obtained.

Example 6 La 0.03 obtained in Example 1
The palladium in Ni0.5Al2.0O _X 1.0% by weight
692 g of the supported powder (powder A) and 1 mol% of lanthanum
( ₂ % by weight in terms of La ₂ O ₃ ) and zirconium
To 480 g of powder (powder B) carrying 0.75 weight g of palladium on cerium oxide powder containing 2 mol% (25 weight% in terms of ZrO ₂ ), 1200 g of an aqueous nitric acid solution was put into a magnetic ball mill, and mixed and pulverized. Thus, a slurry liquid was obtained. 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 carrying amount of 40 g / cf (1.42 g / L). A catalyst was obtained. Next, a barium acetate solution was applied to the cordierite monolithic carrier supporting the catalyst component, and then calcined at 400 ° C. for 1 hour to contain 15 g / L of BaO.

<Example 7> La 0.01 obtained in Example 2
Except for using Ni0.5Al2.0O _X was obtained a catalyst coating layer weight 160 g / L in the same manner as in Example 6, palladium weight 40g / cf (1.42g / L) . Next, a barium acetate solution was applied in the same manner as in Example 6, and then baked at 400 ° C. for 1 hour to contain 15 g / L of BaO.

Example 8 La 0.09 obtained in Example 3
Except for using Ni0.5Al2.0O _X was obtained a catalyst coating layer weight 160 g / L in the same manner as in Example 6, palladium weight 40g / cf (1.42g / L) . Next, a barium acetate solution was applied in the same manner as in Example 6, and then baked at 400 ° C. for 1 hour to contain 15 g / L of BaO.

Example 9 La 0.03 obtained in Example 4
Except for using Ni0.3Al2.0O _X was obtained a catalyst coating layer weight 160 g / L in the same manner as in Example 6, palladium weight 40g / cf (1.42g / L) . Next, a barium acetate solution was applied in the same manner as in Example 6, and then baked at 400 ° C. for 1 hour to contain 15 g / L of BaO.

Example 10 La0.0 obtained in Example 5
Except for using 3Ni0.4Co0.1Al2.0O _X is coat layer weight in the same manner as in Example 6 160 g / L,
A catalyst having a palladium loading of 40 g / cf (1.42 g / L) was obtained. Next, after a barium acetate solution was applied in the same manner as in Example 6, it was baked at 400 ° C. for 1 hour to obtain BaO
It contained 15 g / L.

Comparative Example 6 La0.05Ni of Comparative Example 1
Except for using 0.5Al2.0O _X is coating layer weight 160 g / L in the same manner as in Example 6, palladium amount 4
0 g / cf (1.42 g / L) of the catalyst was obtained. Then
After depositing a barium acetate solution in the same manner as in Example 6, it was baked at 400 ° C. for 1 hour to contain 15 g / L of BaO.

Comparative Example 7 La0.2Ni of Comparative Example 2
Except for using 0.5Al2.0O _X is coating layer weight 160 g / L in the same manner as in Example 6, palladium amount 4
0 g / cf (1.42 g / L) of the catalyst was obtained. Then
After depositing a barium acetate solution in the same manner as in Example 6, it was baked at 400 ° C. for 1 hour to contain 15 g / L of BaO.

Comparative Example 8 Ni0.5Al of Comparative Example 3
Except for using 2.0O _X is coating layer weight 160 g / L in the same manner as in Example 6, palladium weight 40 g / cf
(1.42 g / L) of the catalyst was obtained. Next, a barium acetate solution was applied in the same manner as in
For 1 hour, and contained 15 g / L of BaO.

<Comparative Example 9> Co0.3Al of Comparative Example 4
Except for using 2.0O _X is coating layer weight 160 g / L in the same manner as in Example 6, palladium weight 40 g / cf
(1.42 g / L) of the catalyst was obtained. Next, a barium acetate solution was applied in the same manner as in
For 1 hour, and contained 15 g / L of BaO.

Comparative Example 10 La 0.03 A of Comparative Example 5
except for using L2.0O _X is coating layer weight 160 g / L in the same manner as in Example 6, palladium weight 40 g / c
f (1.42 g / L) of the catalyst was obtained. Then, Example 6
After depositing a barium acetate solution in the same manner as in
It was baked at 1 ° C. for 1 hour to contain 15 g / L of BaO.

<Test Examples> The exhaust gas purifying catalysts of the above Examples and Comparative Examples were endured under the following endurance conditions, and then evaluated under the following evaluation conditions.

[0038]

Evaluation condition 1: Low-temperature activity Engine displacement 2000 cc Fuel unleaded gasoline Heating rate 10 ° C./min Measurement temperature range 150 ° C. to 500 ° C. The low-temperature activity of each exhaust gas purifying catalyst after endurance was determined by HC, C
O and NO _X temperature when the conversion reached 50% (T5
0 / ° C.), and the results are shown in FIG.

[0040] The average conversion of the HC purifying performance in stoichiometric atmosphere of the exhaust gas purifying catalyst, CO and NO _X after durability (%)
Is determined by the following Equations 1 to 3, and the result is shown in FIG.
Shown in

[0041]

[Formula 1]

[0042]

[Formula 2]

[0043]

[Equation 3]

[0044]

The exhaust gas purifying catalyst obtained by the present invention has excellent durability at high temperatures, suppresses sintering of noble metal species, and can promote activation of noble metal species. In addition, the crystal structure can be made uniform, the structural stability at a high temperature can be improved, and the dispersed state of the active phase can be increased to enhance the activation promoting action of the noble metal.

[Brief description of the drawings]

FIG. 1 is a diagram showing an evaluation of catalytic activity of exhaust gas purifying catalysts of Examples and Comparative Examples of the present invention.

Claims (3)

[Claims] 1. An exhaust gas purifying catalyst having an integral structure having a catalyst component-supporting layer, comprising at least palladium and an alumina-based composite oxide as a catalyst component, wherein the alumina-based composite oxide comprises lanthanum, cobalt and nickel. An exhaust gas purifying catalyst comprising at least one selected from the group consisting of: 2. The exhaust gas purifying catalyst according to claim 1, wherein the alumina-based composite oxide has the following general formula: [X] a [Y] bAlcOd (where X is a lanthanum element La) Y is at least one element selected from the group consisting of cobalt and nickel, and a, b, c and d represent the atomic ratio of each element. When c = 2.0, a = 0 .01 to less than 0.1,
b = 0.1 to 0.7, and d is the number of oxygen atoms necessary to satisfy the valence of each component described above.) Catalyst. 3. A method for producing the alumina-based composite oxide according to claim 1 or 2, wherein at least one of colloidal alumina hydrate (hereinafter referred to as “alumina sol”), a water-soluble salt of lanthanum, cobalt and nickel. After dissolving or dispersing one kind of water-soluble salt in water, at least one kind of aqueous solution selected from the group consisting of aqueous ammonia, ammonium carbonate and ammonium hydrogen carbonate is added, and the pH is adjusted to 7.
After adjusting so as to be in the range of 0 to 9.0, the mixed solution is further heat-treated (boiled) at 100 ° C to 300 ° C,
A method for producing an exhaust gas purifying catalyst, characterized in that the catalyst is obtained by removing water, drying and then calcining.