JPH06296869A - Catalyst for exhaust gas purification - Google Patents

Abstract

PURPOSE:To enhance the purification performance of the catalyst for purification of an exhaust gas, which is discharged from an internal combustion engine of an automobile, including palladium as a catalytic component. CONSTITUTION:The subject catalyst for exhaust gas purification is of a monolithic structure with a catalytic component-carrying layer which contains at least, at least, palladium as a precious metal, and activated alumina powder and cerium oxide powder as catalytic components. In addition, the cerium oxide contains, at least, one kinds selected from the group of iron, cobalt and nickel, and zirconium.

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 for purifying hydrocarbons (HC), carbon monoxide (CO) and nitrogen oxides (NO _x ) in exhaust gas discharged from internal combustion engines such as automobiles. Regarding

[0002]

2. Description of the Related Art A conventional exhaust gas purifying catalyst is a combination of noble metals such as platinum (Pt), palladium (Pd) and rhodium (Rh) as a catalyst component, and these noble metals and activated alumina, cerium oxide and the like are contained. , Hydrocarbon (H
A three-way catalyst that removes C), carbon monoxide (CO), and nitrogen oxides (NO _x ) at once has been widely used.

[0003]

However, among these precious metals, rhodium is not particularly abundant in terms of resources and the price is expensive. Therefore, there is a demand for the development of a catalyst that does not use rhodium as a three-way catalyst for the purpose of purifying exhaust gas, particularly a catalyst having a sufficient purifying ability only with palladium.

However, when palladium is used alone, there is a problem that the purification capacity is insufficient when the exhaust gas is in a reducing atmosphere. This is because in a reducing atmosphere where the oxygen concentration is insufficient for purification of hydrocarbons, some of the hydrocarbons remain unpurified, and the remaining hydrocarbons are strongly adsorbed on the palladium and the activity decreases or the active sites decrease. ,
As a result, it is considered that the purification performance decreases.

[0005]

Means for Solving the Problems As a result of intensive studies to solve the above problems, the present inventors have found that when an iron group metal such as iron, cobalt, or nickel, zirconium, and cerium coexist in the catalyst, reduction is achieved. The inventors have found that the catalytic activity of palladium in the atmosphere is improved, and have accomplished the present invention.

That is, the exhaust gas-purifying catalyst of the present invention contains a cerium oxide powder containing zirconium and at least one palladium selected from the group consisting of iron, cobalt and nickel as a catalytically active component. It is characterized by including.

The present invention is characterized in that at least one selected from the group consisting of iron, cobalt and nickel is in close contact with zirconium and cerium. When these are in close contact with each other, the purification performance improving effect can be obtained, which is suitable for the purpose.

The method for producing the catalyst of the present invention will be described below.

The method for producing a cerium oxide containing zirconium and at least one selected from the group consisting of iron, cobalt and nickel in the present invention is, for example, a salt of at least one of iron, cobalt and nickel and zirconium. There is a method in which a solution containing is impregnated and supported on cerium oxide, and dried and baked.

As another method, ammonia is previously added to an acidic aqueous solution containing salts of cerium and zirconium.
A precipitate is obtained by adding an alkaline aqueous solution of ammonium carbonate, sodium carbonate, sodium hydroxide or the like to carry out a precipitation forming reaction. This precipitate or a product obtained by once calcining the precipitate is used for at least one of iron, cobalt and nickel. There is a method of impregnating and supporting a solution containing a salt, drying and firing.

As another method, a cerium precipitate, a zirconium precipitate, and a precipitate containing at least one of iron, cobalt and nickel obtained separately by the same method as above are mixed and dried. , There is a method of firing.

As a method for producing the catalyst of the present invention using the above-mentioned oxide powder, for example, activated alumina powder and the oxide powder are pulverized and mixed by a wet method to prepare a water-soluble slurry. There is a method in which a monolithic carrier made of metal is coated, dried, calcined, further immersed in an aqueous solution containing palladium, and dried and calcined again.

As another method for producing the catalyst, an alumina powder carrying palladium in advance and the oxide powder are wet mixed to prepare a water-soluble slurry, which is coated on a ceramic or metal monolith carrier. There is a method of drying, baking.

Further, the catalyst of the present invention is at least selected from the group consisting of alkali metals and alkaline earth metals such as lithium, sodium, potassium, cesium, strontium and barium in order to further improve the activity in a reducing atmosphere. You may further include 1 type. This is because alkali metals and alkaline earth metals are generally known to have the ability to absorb and absorb hydrocarbons. As a method for adding these, for example, there is a method in which compounds such as oxides, hydroxides, nitrates and carbonates of the above-mentioned metals are simultaneously added to and mixed with a slurry containing a washcoat component to coat the monolith carrier. As another manufacturing method, for example, there is a method in which an aqueous solution containing the salt of the above metal is impregnated and supported in advance on any of the washcoat component powders. Another manufacturing method is, for example, a method in which a washcoat component is coated on a monolith carrier and then the monolith carrier is dipped in an aqueous solution containing the above metal salt to carry it. When the above-mentioned alkali metal or alkaline earth metal is contained in the catalyst coating layer, it is 1 to 30% by weight per 1 L of the catalyst.
The range is. Within this range, the activity in the reducing atmosphere can be further improved.

The cerium oxide powder containing zirconium and at least one selected from the group consisting of iron, cobalt and nickel in the present invention is 1 per 1 L of the catalyst.
It is 0 to 100 g. If it is less than 10 g, the effect of improving the purification performance cannot be sufficiently obtained, and if it exceeds 100 g, no significant amount increasing effect is observed even if it is added.

The oxide contains 1 to 20 of at least one selected from the group consisting of iron, cobalt and nickel.
Mol%, zirconium 1 to 20 mol%, cerium 6
Contains 0 to 98 mol%. With at least one selected from the group consisting of iron, cobalt and nickel and zirconium, if the amount is less than the above value, the effect of improving the purification performance is not sufficiently obtained, and if added more than the above value, a significant amount increasing effect is recognized. Absent.

The oxide is, in addition to at least one selected from the group consisting of iron, cobalt and nickel, zirconium and cerium, other rare earth elements such as lanthanum and neodymium slightly contained in the cerium raw material, and zirconium raw material. Hafnium, which is contained in a small amount, may be included.

[0018]

The exhaust gas purifying catalyst has to treat exhaust gas whose composition varies widely, but palladium has a drawback that it greatly reduces in an exhaust gas purifying atmosphere in which the hydrocarbon concentration is high and the oxygen concentration is low. It was

According to the present invention, the cerium oxide powder containing zirconium and at least one selected from the group consisting of iron, cobalt and nickel donates oxygen and electrons to palladium, and as a result, palladium is obtained even in an oxygen-deficient atmosphere. The oxidation state of is suitable for exhaust gas purification, and the deterioration of catalytic performance due to the reduction of palladium, which has been reported so far, can be suppressed, and further contains an alkali metal and / or an alkaline earth metal. This further improves the activity in the reducing atmosphere.
With such an action, the present invention meets the purpose.

[0020]

EXAMPLES The present invention will be described below with reference to Examples, Comparative Examples and Test Examples.

Example 1 Activated alumina powder was impregnated with an aqueous palladium nitrate solution, dried and calcined at 400 ° C. for 1 hour to obtain palladium-supported activated alumina powder (powder A). The palladium concentration of powder A was 2.0% by weight.

Cerium oxide powder was impregnated with a mixed aqueous solution of an aqueous solution of iron nitrate and an aqueous solution of zirconium nitrate, dried in air at 150 ° C. for 12 hours, and then calcined in air at 600 ° C. for 2 hours to contain iron and zirconium. Cerium oxide powder (powder B) was obtained. This powder contained 10 mol% of iron (5.0 wt% as Fe ₂ O ₃ ) and 5 mol% of zirconium (3.8 wt% as ZrO ₂ ) in terms of metal.

A magnetic ball mill was charged with 630 g of powder A, 270 g of powder B, and 900 g of an aqueous nitric acid solution, and the mixture was pulverized to obtain a slurry liquid. This slurry liquid was attached to a cordierite monolith carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air flow, and the slurry was dried.
It was baked at 00 ° C. for 1 hour. This operation was performed twice to obtain a catalyst having a coat layer weight of 200 g / L-support.

Example 2 Instead of iron nitrate in Example 1, an aqueous solution of cobalt nitrate was used, and 10 mol% of cobalt (Co ₃ O) in terms of metal was used.
₄ , 5.0% by weight) and 5 mol% zirconium (Z
A catalyst was obtained in the same manner as in Example 1 except that a cerium oxide powder containing 3.8% by weight as rO ₂ ) was used.

Example 3 In place of iron nitrate in Example 1, an aqueous solution of nickel nitrate was used, and nickel was 10 mol% (4.6% by weight as NiO) and zirconium was 5 mol% (ZrO in terms of metal).
_A catalyst was obtained in the same manner as in Example 1 except that cerium oxide powder containing 3.8% by weight as ₂ ) was used.

Example 4 A 1N aqueous ammonia solution was gradually added dropwise to a mixed aqueous solution of cerium nitrate aqueous solution and zirconium nitrate aqueous solution (containing 0.400 mol of cerium and 0.024 mol of zirconium per 1 L of aqueous solution) to adjust the pH of the solution. It was set to 9.0 and stirred for 1 hour. The formed hydroxide precipitate was filtered, and the precipitate was dried in air at 150 ° C. for 12 hours and then calcined at 300 ° C. for 12 hours. This powder was impregnated with an aqueous iron nitrate solution (1 kg of powder was loaded with 53 g of Fe ₂ O ₃ ) and was heated to 150 ° C.
After being dried in air for 12 hours, it was baked in air at 600 ° C. for 2 hours to obtain a cerium oxide powder containing iron and zirconium. This powder contained 10 mol% of iron and 5 mol% of zirconium in terms of metal. This powder was used in Example 1.
A catalyst was obtained in the same manner as in Example 1, except that the powder B was used instead of the powder B.

Example 5 Example 4 was repeated except that an aqueous solution of cobalt nitrate was used in place of the iron nitrate in Example 4, and a cerium oxide powder containing 10 mol% of cobalt and 5 mol% of zirconium in terms of metal was used. A catalyst was obtained in the same manner as in.

Example 6 Example 4 was repeated, except that an aqueous solution of nickel nitrate was used in place of iron nitrate in Example 4, and a cerium oxide powder containing 10 mol% of nickel and 5 mol% of zirconium in terms of metal was used. A catalyst was obtained in the same manner as in.

Example 7 A mixed aqueous solution of an aqueous cerium nitrate solution, an aqueous zirconium nitrate solution and an aqueous iron nitrate solution (0.4 cerium was added per 1 L of the aqueous solution).
00 mol, zirconium 0.024 mol, iron 0.0
(Containing 47 mol), a 1N aqueous ammonia solution was gradually added dropwise to adjust the pH of the solution to 9.0, and the mixture was stirred for 1 hour. The generated hydroxide precipitate was filtered to obtain a hydroxide precipitate of cerium, zirconium and iron. The obtained precipitate was dried in air at 150 ° C. for 12 hours and then calcined at 300 ° C. for 12 hours to obtain a cerium oxide powder containing iron and zirconium. This powder contained 10 mol% of iron and 5 mol% of zirconium in terms of metal.

A catalyst was obtained in the same manner as in Example 1 except that this powder was used instead of the powder B in Example 1.

Example 8 An aqueous solution of cobalt nitrate was used in place of the aqueous solution of iron nitrate in Example 7, an aqueous solution of ammonia bicarbonate was used in place of the aqueous solution of ammonia in Example 7, and 10 mol% of cobalt and zirconium in terms of metal were used. A cerium oxide powder containing 5 mol% was obtained. A catalyst was obtained in the same manner as in Example 7, except that this was used instead of the cerium oxide powder in Example 7.

Example 9 An aqueous solution of nickel nitrate was used in place of the aqueous solution of iron nitrate in Example 7, an aqueous solution of oxalic acid was used in place of the aqueous solution of ammonia in Example 7, and nickel was converted to 1 in terms of metal.
Cerium oxide powder containing 0 mol% and zirconium of 5 mol% was obtained. A catalyst was obtained in the same manner as in Example 7, except that this was used instead of the cerium oxide powder in Example 7.

Comparative Example 1 A catalyst was obtained in the same manner as in Example 1 except that cerium oxide powder was used instead of powder B in Example 1.

Comparative Example 2 An aqueous zirconium nitrate solution was impregnated and supported on cerium oxide,
Dry in air at 150 ° C for 12 hours and then at 600 ° C for 2 hours.
The powder was calcined in air for a period of time to obtain a zirconium-containing cerium oxide powder. This powder contained 5 mol% (3.6% by weight) of zirconium in terms of metal. A catalyst was obtained in the same manner as in Example 1 except that the above powder was used instead of the powder B in Example 1.

Comparative Example 3 An aqueous iron nitrate solution was impregnated and supported on cerium oxide, dried in air at 150 ° C. for 12 hours, and then calcined in air at 600 ° C. for 2 hours to obtain an iron-containing cerium oxide powder. This powder contains 10 mol% of iron in terms of metal (5.0% as Fe ₂ O _3).
% By weight). A catalyst was obtained in the same manner as in Example 1 except that the above powder was used instead of the powder B in Example 1.

Comparative Example 4 An aqueous cobalt nitrate solution was impregnated and supported on cerium oxide to give 15
After drying in air at 0 ° C. for 12 hours, it was baked in air at 600 ° C. for 2 hours to obtain a cobalt-containing cerium oxide powder. This powder contains 10 mol% of cobalt (Co
₃ O ₄ as a 4.9 wt%) was contained at. Example 1 except that the above powder was used instead of the powder B in Example 1.
A catalyst was obtained in the same manner as in.

Comparative Example 5 An aqueous solution of nickel nitrate was impregnated and supported on cerium oxide to obtain 15
After drying in air at 0 ° C. for 12 hours, it was baked in air at 600 ° C. for 2 hours to obtain a nickel-containing cerium oxide powder. This powder contains nickel in an amount of 10 mol% (Ni
O was 4.6% by weight). A catalyst was obtained in the same manner as in Example 1 except that the above powder was used instead of the powder B in Example 1.

Comparative Example 6 The composition of the cerium oxide powder containing iron and zirconium in Example 1 was 30 mol% iron (18.5 as Fe ₂ O _3).
% By weight), 30 mol% zirconium ( ₂ as ZrO 2
A catalyst was obtained in the same manner as in Example 1 except that the cerium oxide powder of 8.5% by weight) was used.

Comparative Example 7 The composition of the cerium oxide powder containing cobalt and zirconium in Example 2 was changed to 30 mol% of cobalt (Co ₃ O ₄
18.5% by weight), zirconium 30 mol% (Z
A catalyst was obtained in the same manner as in Example 2 except that the cerium oxide powder having rO ₂ of 28.5% by weight) was used.

Comparative Example 8 The composition of the cerium oxide powder containing nickel and zirconium in Example 3 was changed to 30 mol% of nickel (17.4% by weight) and 30 mol% of zirconium ( ₂ as ZrO ₂ ).
A catalyst was obtained in the same manner as in Example 3 except that the cerium oxide powder (8.9% by weight) was used.

Comparative Example 9 The same as Example 1 except that a mixture of iron oxide powder, zirconium oxide powder and cerium oxide powder (equivalent to 10 mol% of iron and 5 mol% of zirconium in terms of metal) was used in place of powder B. The method gave the catalyst.

Comparative Example 10 Same as Example 1 except that a mixture of cobalt oxide powder, zirconium oxide powder and cerium oxide powder (corresponding to 10 mol% of cobalt and 5 mol% of zirconium in terms of metal) was used in place of powder B. The method gave the catalyst.

Comparative Example 11 Same as Example 1 except that a mixture of nickel oxide powder, zirconium oxide powder and cerium oxide powder (corresponding to 10 mol% of nickel and 5 mol% of zirconium in terms of metal) was used in place of powder B. The method gave the catalyst.

Example 10 The catalyst obtained in Example 9 was further immersed in an aqueous solution of lithium nitrate, the excess was removed by an air stream, dried, and calcined at 400 ° C. for 1 hour to obtain Li ₂ O of 10 g / L. A catalyst was obtained by supporting lithium.

Example 11 The catalyst obtained in Example 9 was further immersed in an aqueous sodium nitrate solution, the excess was removed with an air stream, and the mixture was dried at 400 ° C.
It was calcined for 1 hour to carry 10 g / L of sodium as Na ₂ O to obtain a catalyst.

Example 12 The catalyst obtained in Example 9 was further immersed in an aqueous potassium nitrate solution, the excess was removed with an air stream, dried, and calcined at 400 ° C. for 1 hour to give K ₂ O of 10 g / L potassium. Was carried to obtain a catalyst.

Example 13 The catalyst obtained in Example 9 was further immersed in an aqueous strontium nitrate solution, the excess portion was removed with an air stream and dried.
The catalyst was obtained by carrying out calcination at 0 ° C. for 1 hour, carrying 10 g / L of strontium as SrO.

Example 14 The catalyst obtained in Example 9 was further immersed in an aqueous barium acetate solution, the excess was removed by an air stream, dried, and calcined at 400 ° C. for 1 hour to obtain 10 g / L of barium as BaO. It was carried to obtain a catalyst.

Example 15 Pd-supported activated alumina powder was obtained by impregnating activated alumina powder with an aqueous palladium nitrate solution, drying and firing at 400 ° C. for 1 hour. The Pd concentration of this powder was 1.4% by weight.

The cerium oxide powder in Example 9 was impregnated with an aqueous solution of palladium nitrate, dried and then calcined at 400 ° C. for 1 hour to obtain powder C. The Pd concentration of the powder C was 1.4% by weight.

630 g of Pd-supported alumina powder, powder C2
70 g and 900 g of an aqueous nitric acid solution were charged into a magnetic ball mill, and a catalyst was obtained by the same method as in Example 1.

Test Example The catalysts of Examples 1 to 15 and Comparative Examples 1 to 11 were subjected to activity evaluation after endurance under the following conditions.

[0053]

[Table 1] <Durability conditions> Engine displacement 4400cc Catalyst inlet gas temperature 850 ° C Endurance time 100 hours Inlet gas composition CO 0.5 ± 0.1% O ₂ 0.5 ± 0.1% HC About 1100ppm NO 1300ppm CO ₂ 15%

[0054]

[Table 2] <Evaluation conditions> Engine displacement 2000 cc Fuel smokeless gasoline Catalyst inlet gas temperature 400 ° C Stoke amplitude ± 1.0 A / F center A / F = 14.6 Rich amplitude ± 0.2 A / F center A / F = 14.2A / F

Table 3 shows the measurement results of the conversion rates of the catalyst after being durable, in stoichiometry and rich.

[0056]

[Table 3]

[0057]

As described above, according to the present invention, at least palladium among noble metals, at least one selected from the group consisting of iron, cobalt and nickel, and zirconium are contained as catalytically active components. Since it contains cerium oxide, the purification performance at the theoretical air fuel consumption is impaired and the catalytic performance in the reducing atmosphere is improved.

This is because the intimate contact of at least one selected from the group consisting of iron, cobalt and nickel with zirconium and cerium causes an interaction which cannot be obtained by simply mixing individual oxides. It is considered to improve the purifying action of palladium. Further, by further supporting the alkali metal and / or the alkaline earth metal on the catalyst component supporting layer, the effect that the activity in the reducing atmosphere can be further improved can be obtained.

Further, as is clear from the examples, the component composition of the cerium oxide containing zirconium and at least one selected from the group consisting of iron, cobalt and nickel used in the present invention has a preferable range. is there.

Claims (3)

[Claims] 1. A monolithic structure type catalyst having a catalyst component supporting layer, wherein the catalyst component supporting layer contains at least palladium among noble metals as a catalyst component, activated alumina powder and cerium oxide powder, and the cerium oxide is iron. An exhaust gas purifying catalyst comprising at least one selected from the group consisting of cobalt, nickel and zirconium. 2. The cerium oxide powder, in terms of metal,
1 to 20 mol% of at least one selected from the group consisting of iron, cobalt and nickel, and 1 to 2 of zirconium
0 mol%, containing 60 to 98 mol% of cerium, catalyst 1L
The catalyst according to claim 1, wherein the catalyst is supported in an amount of 10 to 100 g per unit. 3. The catalyst component-supporting layer further comprises at least one selected from the group consisting of lithium, sodium, potassium, barium and strontium per 1 L of catalyst.
The catalyst according to claim 1 or 2, which comprises 30% by weight.