JP2000093799A - Catalyst for cleaning exhaust gas and preparation thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a catalyst for cleaning an exhaust gas which shows an outstanding low temperature activity and an likewise outstanding catalytic activity under all automotive exhaust composition atmospheres, even at the sacrifice of a significant reduction in the usage of a noble metal, compared to a conventional catalyst as well as a method for manufacturing this catalyst for cleaning an exhaust gas. SOLUTION: In a monolithically structured catalyst with a catalytic component bearing layer, its catalytic components are at least, palladium and metal aluminate powder, and the metal aluminate powder is an alumina compound oxide represented by [X]a[Y]bAlcOd (wherein, X is at least, one kind of element selected from the group of cobalt, nickel and zinc; Y is cerium and/or zirconium; a, b, c and d show the atomic ratio of each of elements and a=0.1-0.8, b=0.001-0.3 and d is the number of oxygen atoms required for satisfying the atomic value of each of the described components when it is c=2.0).

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 a hydrocarbon (hereinafter referred to as "HC") in exhaust gas discharged from an internal combustion engine such as an automobile.
), Carbon monoxide (hereinafter, referred to as “CO”) and nitrogen oxides (hereinafter, referred to as “NO _x ”) can be efficiently purified even at a low temperature, and have excellent low-temperature activity, and The present invention relates to an exhaust gas purifying catalyst having excellent purifying performance under all exhaust gas composition atmospheres 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 reaction is started from a low temperature because exhaust gas purification performance is not sufficient. Exhaust gas purification catalysts are expected to be developed.

As such an exhaust gas purifying catalyst, for example, JP-B-58-20307 and JP-A-5-305 are disclosed.
236 and JP-A-6-378. 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.

Japanese Patent Application Laid-Open No. 5-305236 discloses that
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, and palladium has been disclosed.Specifically, a hexaaluminate composition having a certain composition and platinum have been disclosed. , Rhodium, and palladium are mixed at a certain weight ratio with alumina supporting at least one noble metal selected from the group consisting of rhodium and palladium.

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,
There has been proposed an exhaust gas purifying catalyst in which an oxide of at least one metal selected from the group consisting of cesium, strontium and barium is supported. That is, the catalyst is at least one of a basic element, a potassium compound, a cesium compound, a strontium compound, and a barium compound, in addition to those conventionally used as catalyst components such as a platinum group element, activated alumina, and cerium oxide. It is a combination of one kind.

[0006]

However, in order to obtain a sufficient catalytic activity from a low temperature, the conventional butterfly described in the above publication discloses a large amount of precious metal which is not rich in resources and expensive. I use it. Therefore, the development of a catalyst that has sufficient purification ability even with a small amount of precious metal based on palladium, which is relatively inexpensive among precious metals, or a butterfly that uses as little as possible even when rhodium is used, is expected. Have been. However, when palladium is used alone, there is a problem in that the purification ability is reduced when the exhaust gas is brought into a reducing atmosphere, and when the amount of palladium is reduced, the low-temperature activity and the purification performance itself are deteriorated.

Further, the exhaust gas purifying catalyst must treat the exhaust gas of an automobile whose composition varies widely over a wide temperature range from a low temperature range to a high temperature range and at a high purification rate. However, in purifying exhaust gas with palladium, at low temperatures immediately after starting the engine or in a reducing atmosphere where the hydrocarbon concentration is high and the oxygen concentration is low, some of the hydrocarbons remain without being purified, and the remaining hydrocarbons remain on the palladium. Due to strong adsorption, activity is reduced or active sites are reduced, resulting in reduced purification performance.In an oxidizing atmosphere with high oxygen concentration and low hydrocarbon concentration, oxygen is adsorbed on palladium and nitrogen oxides are adsorbed. However, there is a disadvantage that the purification performance of nitrogen oxides is greatly reduced.

Further, when the amount of palladium is reduced,
There is also a problem that the above-mentioned influence appears remarkably and the purification performance is further reduced.

Accordingly, an object of the present invention is to provide an exhaust gas purifying catalyst having excellent low-temperature activity and catalytic activity under all exhaust composition atmospheres of automobiles even if the amount of noble metal used is significantly reduced as compared with conventional catalysts. And a method for manufacturing the same.

[0010]

Means for Solving the Problems As a result of research for solving the above problems, the present inventors have found that an alumina-based composite oxide containing a transition metal element in a fixed composition ratio together with palladium in a catalyst component-supporting layer is obtained. The present invention has been found to be able to improve the catalytic performance of palladium, to significantly improve and maintain the catalytic activity in the low-temperature range and the low-temperature activity and purification performance after durability under all exhaust gas composition atmospheres. Reached.

The exhaust gas purifying catalyst according to claim 1 of the present invention is an integrated catalyst having a catalyst component-supporting layer, wherein at least palladium and a metal aluminate powder are contained as catalyst components, and the metal aluminate powder is , The following general formula:

[X] _a [Y] _b Al _C O _d (wherein X is at least one element selected from the group consisting of cobalt, nickel and zinc, and Y is cerium and / or zirconium. Yes, a, b, c and d
Represents the atomic ratio of each element, and when c = 2.0, a =
0.1 to 0.8, b = 0.001 to 0.3, and d is the number of oxygen atoms necessary to satisfy the valence of each of the above components.)
Characterized in that it is an alumina-based composite oxide represented by the formula:

Further, in order to further enhance the catalytic activity of the exhaust gas purifying catalyst according to the first aspect in the rich region, the exhaust gas purifying catalyst according to the second aspect is further selected from the group consisting of lanthanum, neodymium and zirconium. The exhaust gas purifying catalyst contains a cerium oxide containing at least one selected from the group consisting of 1 to 40 mol% in terms of metal and cerium in the range of 60 to 98 mol% in terms of metal.

Further, in order to further enhance the low-temperature activity of the exhaust gas purifying catalyst according to the first or second aspect, the exhaust gas purifying catalyst according to the third aspect includes a total amount of palladium contained in the catalyst component supporting layer. 30% to 80% by weight of palladium in terms of metal is contained in the alumina-based composite oxide.

Further, in order to further enhance the low-temperature activity of the exhaust gas purifying catalyst according to any one of claims 1 to 3, the exhaust gas purifying catalyst according to claim 4 further comprises rhodium and alumina. It is characterized by being contained in a purification catalyst.

Further, in order to further enhance the catalytic activity of the exhaust gas purifying catalyst according to the fourth aspect in a rich atmosphere, the exhaust gas purifying catalyst according to the fifth aspect further comprises a lanthanum, neodymium and cerium. The exhaust gas purifying catalyst contains a zirconium oxide containing 1 to 40 mol% of at least one selected metal in terms of metal and 60 to 98 mol% of zirconium in terms of metal.

Further, in order to further enhance the catalytic activity of palladium and rhodium, the catalyst for purifying exhaust gas according to claim 6 further comprises a rhodium-containing layer comprising a palladium-containing layer. Same layer and / or
Alternatively, the palladium-containing layer is disposed above the palladium-containing layer.

Further, in order to improve the purification performance of the exhaust gas purifying catalyst according to any one of claims 1 to 6 in a rich region, the exhaust gas purifying catalyst according to claim 7 further comprises an alkali metal and At least one selected from the group consisting of alkaline earth metals is contained in the exhaust gas purifying catalyst.

Further, in the method for producing an exhaust gas purifying catalyst according to the present invention, there is provided a method for producing the alumina-based composite oxide according to any one of the first to seventh aspects, wherein fine-particle alumina hydrate colloid and cobalt are used. , A water-soluble salt of at least one element selected from the group consisting of nickel and zinc, and a water-soluble salt of cerium and / or zirconium are dissolved or dispersed in water, and formic acid, acetic acid and succinic acid are added to the mixture. After adding at least one aqueous solution selected from the group consisting of and adjusting the pH to be in the range of 3.0 to 7.0, pressurizing to 1 to 10 atm and heating to 50 to 200 ° C, It is characterized by being obtained by removing moisture, drying and then firing.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The noble metal contained at least in the catalyst component supporting layer of the exhaust gas purifying catalyst of the present invention is palladium. The content of the palladium is 0.1 to 20 g / L in 1 L of the catalyst. If the amount is less than 0.1 g, the low-temperature activity and purification performance are not sufficiently exhibited, and if the amount exceeds 20 g, the dispersibility of palladium deteriorates, the catalyst performance is not significantly improved, and it is not economically effective.

The composition of the metal aluminate in the catalyst component is represented by the following general formula:

[X] _a [Y] _b Al _c O _d (wherein X is at least one element selected from the group consisting of cobalt, nickel and zinc, and Y is cerium and / or zirconium. Yes, a, b, c and d
Represents the atomic ratio of each element, and when c = 2.0, a =
0.1 to 0.8, b = 0.001 to 0.3, and d is the number of oxygen atoms necessary to satisfy the valence of each of the above components.)
It is represented by

As the substrate on which the palladium is supported, an alumina-based composite oxide is suitable for improving the catalytic performance of palladium. In particular, in order to enhance the low-temperature activity and purification performance of palladium (particularly, NOx steady-state conversion performance in an oxygen-deficient atmosphere and in the vicinity of a stoichiometric air-fuel ratio), the alumina-based composite oxide is selected from the group consisting of cobalt, nickel, and zinc. Cerium and / or zirconium are contained in order to suppress at least one selected from particles growth due to palladium sink ring and to improve purification performance after durability.

The amount of the alumina-based composite oxide used is as follows:
It is 10 to 200 g per liter of the catalyst. If the amount is less than 10 g, a sufficient effect of improving the catalytic performance that the alumina-based composite oxide activates palladium cannot be obtained.
Even when the value exceeds 3, the effect of improving the catalyst performance is saturated or, conversely, the catalyst performance is lowered.

In the composition of the metal aluminate, c =
At 2.0, a = 0.1 to 0.8. a = 0.1 ~
The value of 0.8 enhances the structural stability and the BET specific surface area of the alumina-based composite oxide at high temperatures, and fully demonstrates the effect of improving the catalyst performance due to the interaction between palladium and the alumina-based composite oxide. It is to make it. If a = less than 0.1, Co, Ni added to the alumina-based composite oxide
And the effect of the transition metal selected from the group consisting of Zn and Zn was small, and a sufficient improvement effect was not obtained.
₂ O ₃ ).

On the other hand, when a exceeds 0.8, the BET specific surface area of the alumina-based composite oxide and the structural stability at high temperatures are reduced, so that the dispersibility of the noble metal is poor and sufficient performance can be obtained at the initial stage. Or promotes sinking of true metal during durability, conversely deteriorating performance after durability.

Further, in the above equation, when c = 2.0, b =
It is 0.001-0.3. The reason for setting b = 0.001 to 0.3 is that the effect of suppressing palladium sinking on the alumina-based composite oxide is further maintained while the catalyst performance improving effect resulting from the interaction between palladium and the alumina-based composite oxide is maintained. Is added.

If b is less than 0.001, the effect of cerium and / or zirconium added to the alumina-based composite oxide is small and a sufficient improvement effect cannot be obtained, and the alumina-based composite oxide ([X] _a Al ₂ O _c ). On the other hand, if c exceeds 0.3, Ce or Zr which does not form a solid solution in the alumina-based composite oxide coats the surface of the alumina-based composite shoe, and N has a co-catalytic effect on palladium.
The function of the Ox adsorption activation point is deteriorated.

As described above, by supporting palladium on an alumina-based composite oxide powder having a specific composition ratio, an alumina-based composite oxide powder containing at least one selected from the group consisting of cobalt, nickel and zinc can be obtained. The palladium is in close contact, so that the lattice oxygen in the alumina-based composite oxide and the adsorbed oxygen on the surface are easily transferred and released via the palladium, thereby improving the low-temperature activity of the palladium. Stoichiometric metal aluminate ([X] ₁ Al ₂ O ₄ )
Structural stability at high temperature and specific surface area are sufficient compared to
The added element forms a solid solution in the alumina crystal structure and does not exist as an oxide on the surface, so that sufficient performance can be obtained.

Further, cobalt in solid solution alumina-based composite oxide, at least one element selected from the group consisting of nickel and zinc, and functions as an adsorption active sites, such as NO _x, oxygen-deficient atmosphere and Theory This improves the catalytic performance of palladium in the vicinity of the air-fuel ratio. In addition,
By adding cerium and / or zirconium, cerium and / or zirconium and palladium are in close contact on the surface of the alumina-based composite oxide, sintering of palladium is suppressed, and durability and low-temperature activity of palladium are improved. It will be.

Further, the exhaust gas purifying catalyst according to claim 2 further contains cerium oxide in addition to the catalyst components in the exhaust gas purifying catalyst according to claim 1. The cerium oxide contains at least one element selected from the group consisting of lanthanum, neodymium, and zirconium in an amount of 1 to 40 mol% in terms of metal and 60 to 98 mol% of cerium.

The content of 1 to 40 mol% is determined by adding at least one element selected from the group consisting of lanthanum, neodymium and zirconium to cerium oxide (CeO ₂ ), and BET specific surface area,
This is because the thermal stability is significantly improved. If it is less than 1 mol%, the effect of adding the lanthanum and / or neodymium and / or zirconium elements does not appear as in the case of only cerium oxide, and if it exceeds 40 mol%, this effect is saturated or conversely decreases.

As described above, since the cerium oxide containing at least one selected from the group consisting of lanthanum, neodymium and zirconium is further contained in the catalyst component supporting layer, the cerium oxide having a high oxygen storage capacity is reduced. (Oxygen deficiency) Since lattice oxygen and adsorbed oxygen are released in the atmosphere and near the stoichiometric air-fuel ratio to make the oxidation state of palladium suitable for purifying exhaust gas, it is possible to suppress a decrease in catalytic ability due to reduction of palladium. . Further, by contact with the alumina-based composite oxide in the catalyst component supporting layer,
It is also possible to suppress a decrease in catalytic ability due to the reduction of the alumina-based composite oxide.

The exhaust gas purifying catalyst according to a third aspect of the present invention is the catalyst component in the exhaust gas purifying catalyst according to the first or second aspect, wherein the total palladium amount is from 30 to 30 in terms of metal.
80% by weight of palladium is supported on the alumina-based composite oxide powder.

As a substrate on which palladium is supported, in order to enhance the dispersibility of palladium and improve the catalytic performance,
Metal aluminates, especially alumina-based composite oxides, are suitable. In particular, palladium sintering can be suppressed because the structural stability of alumina after high-temperature durability is enhanced and the phase transition to α-alumina and a decrease in the BET specific surface area are suppressed.

By supporting palladium on the alumina-based composite oxide powder, the alumina-based composite oxide powder and palladium come into close contact with each other, and lattice oxygen in the alumina-based composite oxide and adsorbed oxygen on the surface are mediated by palladium. Move
It is easy to be released, and the low-temperature activity of palladium is improved, so that the purification performance from the initial stage to after the endurance can be improved. Further, cobalt and / or nickel and / or zinc dissolved in the alumina-based composite oxide and cerium and / or
Or a zirconium, effectively function as adsorption active points such as NO _x, and thus to improve the catalytic performance of the palladium in an oxygen deficient atmosphere and near stoichiometric air-fuel ratio.

[0035] In the amount of palladium carried on an alumina-based composite oxide powder is less than 30 wt%, without low-temperature activity improving effect and the like is sufficiently expressed, even beyond 80 wt% conversely, NO _x steady turning performance improving effect Is saturated and not effective.

As described above, by supporting 30 to 80% by weight of palladium in terms of metal in the total amount of palladium contained in the catalyst component-supporting layer on the alumina-based composite oxide, the effect of improving the low-temperature activity of palladium is improved. NO _x steady turning performance improving effect and can be obtained sufficiently.

The catalyst for purifying exhaust gas according to claim 4 can further contain rhodium and alumina in the catalyst component supporting layer. Rhodium content is
0.001 to 5 g in 1 L of catalyst, 0.001 g
If the amount is less than 5, the effect of improving the low-temperature activity by rhodium is not sufficiently exhibited. Conversely, if the amount exceeds 5 g, the catalytic activity of rhodium is saturated, which is not economically effective.

As the substrate on which the rhodium is supported,
In order to increase the dispersibility of rhodium and improve catalyst performance,
Alumina containing zirconium is suitable. In particular,
In order to suppress rhodium from forming a solid solution with alumina at a high temperature and increase durability, the alumina powder contains zirconium in an amount of 0.1 mol% to 10 mol% in terms of metal.
If zirconium is less than 0.1 mol%, the effect of improving zirconium added to alumina cannot be obtained, and A1 ₂ O ₃
If it exceeds 10 mol%, the physical properties such as the specific surface area of alumina will decrease, so that the dispersibility of the noble metal will deteriorate and sufficient performance will not be obtained. The amount of the alumina powder used is 1 to 100 g per liter of the catalyst. 1
If the amount is less than 100 g, sufficient dispersibility of the noble metal cannot be obtained.
No significant performance improvement is seen with more.

By including such rhodium and alumina, the activity at low temperatures and the purification performance in an oxygen-deficient atmosphere can be further improved.

Further, the exhaust gas purifying catalyst according to the fifth aspect further comprises a zirconium oxide in addition to the catalyst component in the exhaust gas purifying catalyst according to the fourth aspect. The zirconium oxide contains at least one element selected from the group consisting of lanthanum, neodymium and cerium in an amount of 1 to 40 mol% in terms of metal, and zirconium as 60%.
９８98 mol%.

The reason why the content is set to 1 to 40 mol% is that at least one element selected from the group consisting of lanthanum, neodymium and cerium is added to zirconium oxide (ZrO ₂ ), and the oxygen storage capacity of zirconium oxide and This is to significantly improve the BET specific surface area and the thermal stability. If it is less than 1 mol%, the effect of adding the lanthanum and / or neodymium and / or cerium elements does not appear as in the case of zirconium oxide alone, and if it exceeds 40 mol%, the added element is completely solidified in the zirconium oxide. It becomes difficult to form a dissolved composite oxide, and physical properties of the zirconia oxide, such as thermal stability, decrease.

By containing the zirconium oxide containing at least one selected from the group consisting of lanthanum, neodymium and cerium, the rhodium oxidation state is made suitable for purifying the exhaust gas. It is possible to suppress a decrease in catalytic ability due to reduction.

Further, in the exhaust gas purifying catalyst according to the present invention, the rhodium-containing catalyst component layer is formed of the same layer as the palladium-containing layer and / or the palladium-containing layer in order to efficiently exhibit the synergistic action of palladium and rhodium. It is arranged above the catalyst component layer. As a result, it is possible to sufficiently secure the poisoning resistance to poisonous substances such as lead and sulfur and the purification performance in a rich region.

Further, the exhaust gas purifying catalyst according to claim 7 further contains at least one selected from the group consisting of alkali and alkaline earth metals. The alkali metals and alkaline earth metals used include, for example, lithium,
Potassium, cerium, magnesium, calcium, strontium, barium and the like are included. Its content is 1 to 40 g per liter of catalyst. If less than 1 g, adsorption poisoning of hydrocarbon species and sintering of palladium are not suppressed,
Even if the amount exceeds 40 g, the effect of addition is saturated, a significant increase effect cannot be obtained, and it is not economically effective.

The purification performance is improved by the close contact of the above-mentioned palladium, alumina-based composite oxide powder, and cerium oxide and zirconium oxide, which are added as required, with alkali metals and / or alkaline earth metals. The effect is obtained. Alkali metals and / or alkaline earth metals have the ability to mitigate the adsorption and poisoning of hydrocarbons in a rich atmosphere. When they are contained in the catalyst component-supporting layer, they suppress palladium and sintering, reduce the temperature in the low-temperature region and The activity in an oxygen-deficient atmosphere can be further improved.

Further, according to the method for producing an exhaust gas purifying catalyst according to the eighth aspect, in producing the alumina-based composite oxide according to any one of the first to seventh aspects, first, a fine-particle alumina hydrate colloid (hereinafter referred to as a colloid) is used. , "Alumina sol")
And a water-soluble salt of at least one element selected from the group consisting of cobalt, nickel and zinc, cerium and / or
Alternatively, a water-soluble salt of zirconium is dissolved or dispersed in water, followed by stirring and mixing. At this time, a liquid in which each catalyst material is dissolved simultaneously or separately may be added.

Next, at least one selected from the group consisting of formic acid, acetic acid, and succinic acid as a reaction accelerator is gradually added to the mixture to adjust the pH to a range of 3.0 to 7.0. After adjusting, 100 ℃ in autoclave
To 400 ° C. and boil for 1 to 12 hours.
After cooling, the mixed solution is obtained by removing water with a spray drier and then firing. This method is preferable because a sufficient BET specific surface area and uniformity of the crystal structure of the alumina-based composite oxide are ensured, and the noble metal is uniformly dispersed. However, the preparation method of the alumina-based composite oxide is not limited to a special method, and may be appropriately selected from various methods such as a known evaporative drying method and a precipitation method, unless accompanied by a significant uneven distribution of components. Can be used.

The pH of the mixed solution of the catalyst raw materials is adjusted to 3.0 to 7.0.
By adjusting to a range of 0, alumina forms an organic salt complex and reacts with other additional elements to form a composite oxide. When the pH is lower than 3.0, various elements are eluted and alumina does not form an organic salt complex.
If it is higher than 0, a part of the organic salt complex of alumina will form a hydroxide, and it will be difficult for alumina to react with other elements, and complex formation will not proceed and a uniform structure cannot be obtained.

By using formic acid, acetic acid, succinic acid or the like for adjusting the pH, no metal element remains even if the precipitation cake is not sufficiently cleaned. Can be decomposed and removed.

The obtained mixed solution is heated to 100 to 400 ° C. and boiled for 1 to 12 hours. To do this,
This is because pulverization of highly crystalline alumina promotes the formation of an organic salt complex, and also causes the organic salt complex to react with other additional elements.

By producing such an alumina-based composite oxide, the BET specific surface area of the alumina-based composite oxide is increased, and the additive element is uniformly dispersed and dissolved in a crystal structure (spinel type structure). Can be.

The raw material of each element used in the exhaust gas purifying catalyst of the present invention can be produced by arbitrarily combining nitrates, carbonates, acetates, oxides and the like of each element.

The alumina-based composite oxide containing cobalt and / or nickel and / or zinc, cerium and / or zirconium and aluminum used in the production of the exhaust gas purifying catalyst of the present invention comprises nitrate of each of the above elements, It is prepared by first preparing a mixed solution by arbitrarily combining carbonates, ammonium salts, acetates and the like with alumina sol or boehmite alumina. It is particularly preferable to use a water-soluble salt and fine-particle alumina sol from the viewpoint of improving the catalytic performance. Unlike aluminum nitrate, since alumina sol or boehmite alumina is used, exhaust gas and wastewater treatment for NO _x and ammonium nitrate derived from the raw material are significantly reduced when the precipitate is dried and calcined.

The removal of water can be appropriately selected from known methods such as an evaporation to dryness method and a spray drier method. In order to obtain the alumina-based composite oxide used in the present invention, the alumina-based composite oxide is not particularly limited, but forms an alumina-based composite oxide in which the added element is dissolved, and has a large specific surface area for supporting palladium with good dispersibility. In order to obtain, it is preferable to use a spray dryer. Furthermore, in order to form an alumina-based composite oxide in which the added element forms a solid solution and obtain a large specific surface area, the calcination may be performed, for example, at 600 ° C. to 1100 ° C. in the air and / or under air flow. preferable.

The method of supporting palladium on the alumina-based composite oxide can be appropriately selected from known methods such as an impregnation method and a kneading method. In particular, it is preferable to use the impregnation method. preferable. As a raw material compound of palladium, any compound can be used as long as it is a water-soluble compound such as an ammonium salt, a chloride or a nitrate.

The heat treatment of the palladium-supported alumina-based composite oxide of the present invention is not particularly limited, but is carried out after impregnation and drying, for example, at a temperature in the range of 400 ° C. to 700 ° C. in air and / or under an air stream. Is preferred.

Preferably, a catalyst for purifying exhaust gas according to claim 2 is obtained by adding cerium oxide powder to said alumina powder. The cerium oxide powder contains at least one selected from the group consisting of lanthanum, neodymium, and zirconium.

Further, by adding rhodium and alumina, the exhaust gas purifying catalyst according to claim 4 can be obtained. As the raw material compound of rhodium, any compound can be used as long as it is water-soluble, such as nitrate, halide, acetate and the like.

The alumina may contain zirconium, and the method for preparing such zirconium-containing alumina is not limited to a special method, and may be a known evaporating dry solid as long as there is no significant uneven distribution of components. Method, precipitation method, impregnation method and the like can be appropriately selected and used. However, the impregnation method using an aqueous solution in which zirconium acetate is dissolved in water can be used. This is preferable because the specific surface area can be sufficiently ensured and the supported noble metal can be uniformly dispersed.

The method for supporting rhodium on the alumina can be appropriately selected from, for example, an impregnation method and a kneading method, and it is particularly preferable to use the impregnation method. The subsequent removal of water can be appropriately selected from known methods such as an evaporation to dryness method. The heat treatment of the rhodium-supported alumina powder used in the present invention is not particularly limited, but after impregnation and drying, for example, 400 ° C. to 70 ° C.
It is preferably carried out at a temperature in the range of 0 ° C. in air and / or under air flow.

Preferably, an exhaust gas purifying catalyst according to claim 5 is obtained by adding zirconium oxide powder to the rhodium-supported alumina powder. The zirconium oxide powder contains at least one selected from the group consisting of lanthanum, neodymium and cerium.

When cerium oxide powder is added to the exhaust gas purifying catalyst according to the fourth aspect, the cerium oxide strongly holds rhodium in an oxidized state, and consequently the purifying performance is reduced. In contrast, by adding such zirconium oxide powder, rhodium can be more effectively maintained in an oxidation state suitable for exhaust gas purification.

The removal of water can be appropriately selected from known methods such as an evaporation to dryness method and a spray drier method. In order to obtain the alumina-based composite oxide used in the present invention, although not particularly limited, a large specific surface area for forming an alumina-based composite oxide in which the added element forms a solid solution, and for supporting palladium with good dispersibility. In order to obtain, it is preferable to use a spray dryer. Furthermore, in order to form an alumina-based composite oxide in which the added element forms a solid solution and obtain a large specific surface area, the calcination may be performed, for example, at 600 ° C. to 1100 ° C. in the air and / or under air flow. preferable.

The exhaust gas purifying catalyst according to the present invention thus obtained can be effectively used without a carrier. However, it is pulverized / slurried, coated on a catalyst carrier, and heated at 400 to 900 ° C. It is preferable to use it after firing. The catalyst carrier can be appropriately selected from known catalyst carriers and used, and examples thereof include a monolith carrier made of a refractory material and a metal carrier.

The shape of the catalyst carrier is not particularly limited, but it is usually preferable to use the catalyst carrier in the form of a honeycomb. A catalyst powder is applied to various honeycomb base materials.
As the honeycomb material, cordierite materials such as ceramics are generally used in general, but it is also possible to use many honeycomb materials made of a metal material such as ferrite stainless steel, and further, the catalyst powder itself is formed into a honeycomb shape. May be. By making the shape of the catalyst into a honeycomb shape, the contact area between the catalyst and the exhaust gas is increased and the pressure loss can be suppressed, which is extremely effective when used as an exhaust gas purifying catalyst for automobiles.

The amount of the catalyst component coat layer adhered to the honeycomb material is determined by the total amount of the catalyst components per liter of the catalyst.
50-400 g is preferred. The more catalyst components is preferable from the viewpoint of catalytic activity and catalyst life, when the coating layer becomes too thick, HC, CO, since the reaction gas such as NO _x becomes poor diffusion, these gases sufficiently catalyst Contact cannot be achieved, and the effect of increasing the amount of activity is saturated, and further, the gas passage resistance increases. Therefore, the coat layer amount is
The amount is preferably 50 g to 400 g per liter of the catalyst.

More preferably, the obtained catalyst for purifying exhaust gas may be impregnated and supported with an alkali metal and / or an alkaline earth metal. Examples of the alkali metal and alkaline earth metal that can be used include one or more elements selected from the group consisting of lithium, sodium, potassium, cesium, magnesium, calcium, strontium, barium, and the like.

The alkali metal and / or alkaline earth metal compounds which can be used are water-soluble compounds such as oxides, acetates, hydroxides, nitrates and carbonates. This makes it possible to carry the alkali metal and / or alkaline earth metal as a basic element in the vicinity of palladium with good dispersibility. At this time, the starting compounds of the alkali metal and / or the alkaline earth metal may be contained simultaneously or separately.

That is, an aqueous solution of a powder comprising an alkali metal compound and / or an alkaline earth metal compound is impregnated into the above-mentioned carrier carrying a washcoat component, dried, and then dried in air and / or under a stream of air. ° C to 600
It is baked at ℃. This is because, once a raw material compound of an alkali metal and / or an alkaline earth metal is heat-treated at a low temperature and contained in the coat layer in the form of an oxide, it becomes difficult to form a composite oxide even when exposed to a high temperature later. is there. If the calcination temperature is less than 200 ° C., the alkali metal compound and / or the alkaline earth metal compound cannot be sufficiently converted into an oxide form, and if it exceeds 600 ° C., the raw material salt is rapidly separated. However, it is not preferable because the security may be cracked.

[0070]

The present invention will be described with reference to the following examples and comparative examples. Unless otherwise specified, “parts” means “parts by weight”.

Example 1 An aqueous solution prepared by dissolving 198 parts of nickel carbonate, 79 parts of cerium acetate, and 26 parts of zirconium oxyacetate in 1000 parts of pure water was converted to alumina (Al ₂ O ₃ ) 20% by weight of crystalline fine-particle alumina sol 1700. Was added to a suspension in which 2500 parts of pure water had been dispersed, and then a 10% by weight aqueous solution of acetic acid was added with stirring to adjust the pH to 4.0. After boiling this solution at 250 ° C. for 4 hours, water was removed.
And then calcined at 400 ° C. for 2 hours, 600 ° C. for 2 hours, and 800 ° C. for 4 hours to obtain Ni _0.5 Ce
_0.02 Zr _0.01 Al _2.0 O _x (powder A) was obtained. This powder A is impregnated with an aqueous solution of palladium nitrate, dried and then dried.
By baking at 0 ° C. for 2 hours, a Pd-supported cerium / zirconium-added nickel aluminate powder (powder B) was obtained. The Pd-supporting concentration of the powder B was 1.0% by weight.

700 parts of the above powder (powder B) supporting 1.0% by weight of palladium, and a powder obtained by supporting 0.75 part by weight of palladium on a cerium oxide powder containing 1% by mole of lanthanum and 32% by mole of zirconium. (Powder C) 480 parts, activated alumina 20 parts, and nitric acid aqueous solution 1200 parts were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was adhered to a cordierite-based monolith carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried, baked at 400 ° C. for 1 hour, and a coat layer weight of 160 g / An L-carrier and a cordierite-based monolithic carrier carrying a catalyst component having a palladium carrying amount of 40 g / cf (1.41 g / L-catalyst) were obtained. Then
After a barium acetate solution was adhered to the above-mentioned catalyst component-carrying cordierite-based monolithic carrier, it was calcined at 400 ° C. for 1 hour to contain 15 g / L of BaO to obtain an exhaust gas purifying catalyst.

Example 2 Instead of powder A, Ni _0.3 Ce _0.02 Zr _0.01 Al _2.0
Except that O _x (powder D) was used, an exhaust gas purifying catalyst was obtained in the same manner as in Example 1.

Example 3 Instead of powder A, Ni _0.7 Ce _0.02 Zr _0.01 Al _2.0
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that O _x (powder E) was used.

Example 4 Instead of powder A, Co _0.3 Ce _0.02 Zr _0.01 Al _2.0
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that O _x (powder F) was used.

Example 5 Instead of powder A, Zn _0.3 Ce _0.02 Zr _0.01 Al _2.0
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that O _x (powder G) was used.

Example 6 Instead of powder A, Ni _0.3 Co _0.1 Zn _0.1 Ce _0.02
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that Zr _0.01 Al _2.0 O _x (powder H) was used.

Example 7 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that a 10% by weight aqueous solution of formic acid was used instead of the 10% by weight aqueous solution of acetic acid.

Example 8 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that a 10% by weight aqueous solution of succinic acid was used instead of the 10% by weight aqueous solution of acetic acid.

Example 9 An aqueous solution obtained by dissolving 485 parts of nickel nitrate, 9 parts of cerium acetate, and 26 parts of zirconium oxyacetate in 1000 parts of pure water was mixed with 1700 parts of boehmite alumina sol at 20% by weight in terms of alumina (Al ₂ O ₃ ). To the suspension dispersed in 2500 parts of pure water, a 10% by weight aqueous solution of acetic acid was added with stirring to adjust the pH to 3.5. 250 ° C
After boiling for 4 hours, remove water and then
And then calcined at 400 ° C. for 2 hours, 600 ° C. for 2 hours, and 800 ° C. for 4 hours to obtain Ni _0.5 Ce
It was obtained _0.02 Zr _0.01 A1 _2.0 O _x (powder K). This powder K is impregnated with an aqueous solution of palladium nitrate, dried and then dried.
By baking at 0 ° C. for 2 hours, a Pd-supported cerium / zirconium-added nickel aluminate powder (powder L) was obtained. The Pd-supporting concentration of the powder L was 1.0% by weight.

700 parts by weight of the above powder (powder L) carrying 1.0% by weight of palladium and 0.75 parts by weight of palladium on cerium oxide powder containing 1 mol% of lanthanum and 32 mol% of zirconium (Powder C) 480 parts,
20 parts of activated alumina and 1200 parts of a nitric acid aqueous solution were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid.
This slurry liquid was used as a cordierite monolithic carrier (1.
3L, 400 cells), baked at 400 ° C. for 1 hour, and a cordierite monolithic carrier carrying a catalyst component having a coat layer weight of 160 g / L-support and a palladium carrying amount of 40 g / cf (1.41 g / L-catalyst). I got

137 parts of zirconium oxyacetate was added to pure water 5
The resulting mixture was dissolved in 00 parts and impregnated into 1000 parts of activated alumina.
This was dried at 150 ° C. for 24 hours, and calcined at 400 ° C. for 2 hours and then at 1000 ° C. for 2 hours to obtain alumina powder (powder M) containing 3 mol% of Zr. The Zr3 mol% added alumina powder (powder M) is impregnated with an aqueous rhodium nitrate solution, dried and calcined at 400 ° C. for 2 hours to obtain a Rh-supported Zr3.
A mole% added alumina powder (powder N) was obtained. This powder N
Was 1.06% by weight.

Zr having 1.06% by weight of the above rhodium supported thereon
135 parts of alumina powder (powder N) added with 3 mol% of r, 450 parts of alumina powder (powder M) added with 3 mol% of Zr, and zirconium oxide powder (powder O) 400 containing 1 mol% of lanthanum and 20 mol% of cerium Parts, 15 parts of activated alumina and 1000 parts of nitric acid aqueous solution were put into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid a. Weight of the coat layer obtained in Example 1 175 g / L-supported (160 g / L-supported palladium-containing coat layer, palladium supported amount 4
0 g / cf (1.41 g / L-catalyst), BaO 15 g /
L-catalyst), the slurry liquid a
And calcined at 400 ° C. for 1 hour to obtain a total coating layer weight of 225 g / L-carrier (rhodium-containing catalyst component supporting layer 50).
g / L-carrier), palladium carrying amount 40 g / cf (1.
41 g / L-catalyst), rhodium loading 2 g / cf (0.
071 g / L-catalyst) was obtained.

Example 10 The weight of the coat layer obtained in the same manner as in Example 1 was 160 g / L—the carrier and the amount of palladium carried was 40 g / cf (1.41 g / L—
The rhodium-containing slurry solution a obtained in Example 9 was adhered to a catalyst component-supporting cordierite monolithic carrier (1.3 L, 400 cells) containing the catalyst), and baked at 400 ° C. for 1 hour. Weight 210 g / L (rhodium-containing total weight 50 g / L-catalyst), palladium carrying amount 40 g / L
cf (1.41 g / L-catalyst), rhodium supported amount 2 g /
A cf (0.071 g / L-catalyst) catalyst component-carrying cordierite monolith carrier was obtained. Next, a barium acetate solution was attached to the above-mentioned catalyst component-supporting cordierite-based monolithic carrier, and then calcined at 400 ° C. for 1 hour.
g / L-catalyst was obtained to obtain an exhaust gas catalyst.

Comparative Example 1 Ni _0.5 Ce _0.02 Zr _0.01 Al obtained by using 2500 parts of aluminum nitrate instead of the crystalline fine-particle alumina sol
_{2.0 Ox} was used as exhaust gas.

Comparative Example 2 Instead of the crystalline fine-particle alumina sol, activated alumina (A
Exhaust gas purification catalyst was obtained in the same manner as in Example 1 except that Ni _0.5 Ce _0.02 Zr _0.01 A1 _2.0 O _x obtained using 1700 parts of (1 ₂ O ₃ ) and 485 parts of nickel nitrate was used.

Comparative Example 3 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that activated alumina (A1 ₂ O ₃ ) was used instead of Ni _0.5 Ce _0.02 Zr _0.01 A1 _2.0 O _x .

Comparative Example 4 1164 parts of nickel nitrate and 20% by weight alumina sol 17
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1, except that Ni _1.2 Al _2.0 O _x obtained using 00 parts was used.

Comparative Example 5 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that cerium oxide (CeO ₂ ) powder was used instead of the zirconium-containing cerium oxide powder.

Comparative Example 6 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that BaO was not contained.

Comparative Example 7 The same procedure as in Example 9 was carried out except that a rhodium-containing component layer was disposed in the inner layer and a palladium-containing component layer was disposed in the surface layer to obtain an exhaust gas purifying catalyst.

Table 1 shows the composition of metal aluminate in the exhaust gas purifying catalysts of Examples 1 to 10 and Comparative Examples 1 to 7.

[0093]

[Table 1]

Test Examples The exhaust gas purifying catalysts of Examples 1 to 10 and Comparative Examples 1 to 7 were subjected to durability under the following durability conditions.
The catalyst activity was evaluated under the following evaluation conditions.

Endurance conditions Engine displacement 4400cc Fuel unleaded gasoline Catalyst inlet gas temperature 700 ° 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% A / F fluctuation 5500 times (cycle 65 seconds / time) Cycle: A / F = 14.655 seconds Fuel cut 5 seconds Rich spike 5 seconds

Evaluation condition 1: Low-temperature active engine displacement : 2000 cc fuel Unleaded gasoline Heating rate: 10 ° C./min Measurement temperature range: 150 to 500 ° C. The low-temperature activity of each exhaust gas purifying catalyst after endurance was measured by HC, C
O and NO _x temperature when the conversion reached 50% (T5
0 / ° C.), and the results are shown in Table 2.

[0097] The purifying performance of the exhaust gas purifying catalyst after the durability test was determined HC, the average conversion rate (%) The following equation for CO and NO _x at stoichiometric atmosphere, and the results are shown in Table 2.

[0098]

(Equation 4)

(Equation 5)

(Equation 6)

[0099]

[Table 2]

[0100]

The exhaust gas purifying catalyst according to claim 1 is
It has excellent low-temperature activity and can improve the catalytic performance of palladium in an oxygen-deficient atmosphere and near the stoichiometric air-fuel ratio.

The exhaust gas purifying catalyst according to claim 2 can suppress the sinking of palladium carried on the alumina-based composite oxide and improve the durability and low-temperature activity of palladium, in addition to the above effects. it can.

The exhaust gas purifying catalyst according to the third aspect has the effect of improving the low-temperature activity of palladium and the NO.
x The effect of improving the steady-state conversion performance can be sufficiently obtained.

In the exhaust gas purifying catalyst according to the fourth aspect, in addition to the above-mentioned effects, the purifying performance in a low-temperature activity and an oxygen-deficient atmosphere can be further improved by the aid of rhodium.

The exhaust gas purifying catalyst according to claim 5, in addition to the above-mentioned effects, is suitable for purifying exhaust gas with an oxidized state of rhodium, and can suppress a decrease in catalytic ability due to reduction of rhodium.

The exhaust gas purifying catalyst according to claim 6 is suitable for purifying palladium and rhodium in addition to the above-mentioned effects.
It is possible to suppress a decrease in catalytic ability due to poisoning of palladium or rhodium.

The exhaust gas purifying catalyst according to claim 7 can reduce the effect of adsorbing and poisoning hydrocarbons and suppress sintering of palladium, in addition to the above effects.

The method for producing an exhaust gas purifying catalyst according to claim 8 can efficiently produce the exhaust gas purifying catalyst of the present invention. An exhaust gas purifying catalyst which can be formed and has a large specific surface area for supporting palladium with good dispersibility can be obtained.

 ──────────────────────────────────────────────────続 き Continued on the front page F-term (reference) 4D048 AA06 AA13 AA18 AB05 BA03X BA08X BA18X BA19X BA31X BA33X BA37X BA38X BA42X BB04 4G069 AA03 BA01A BA01B BB06A BB06B BC08A BC35A BC35B BC41A BCBC BCB BC BC BC BC BC BC BC BC CA03 CA09 DA06 EA19 FA01 FC08 FC09

Claims (8)

[Claims] 1. A monolithic catalyst having a catalyst component-supporting layer, comprising at least palladium and a metal aluminate powder as catalyst components, wherein the metal aluminate powder has the following general formula: _a [Y] _b Al _c O _d (where X is at least one element selected from the group consisting of cobalt, nickel and zinc, Y is cerium and / or zirconium, and a, b, c And d
Represents the atomic ratio of each element, and when c = 2.0, a =
0.1 to 0.8, b = 0.001 to 0.3, and d is the number of oxygen atoms necessary to satisfy the valence of each component.)
An exhaust gas purifying catalyst characterized by being an alumina-based composite oxide represented by the formula: 2. The exhaust gas purifying catalyst according to claim 1,
An exhaust gas purifying catalyst characterized by further containing a cerium oxide containing at least one selected from the group consisting of lanthanum, neodymium and zirconium in terms of metal at 1 to 40 mol% and cerium at 60 to 98 mol%. . 3. The exhaust gas purifying catalyst according to claim 1, wherein the total palladium amount is 30 to 8 in terms of metal.
An exhaust gas purifying catalyst, wherein 0% by weight of palladium is contained in an alumina-based composite oxide. 4. An exhaust gas purifying catalyst according to any one of claims 1 to 3, further comprising rhodium and alumina. 5. The exhaust gas purifying catalyst according to claim 4,
Further, at least one selected from the group consisting of lanthanum, neodymium and cerium is 1 to 40 mol% in terms of metal,
An exhaust gas purifying catalyst comprising a zirconium oxide containing 60 to 98 mol% of zirconium. 6. The exhaust gas purifying catalyst according to claim 4, wherein the rhodium-containing layer is arranged on the same layer as palladium and / or above the palladium-containing layer. 7. The exhaust gas purifying catalyst according to claim 1, further comprising at least one selected from the group consisting of alkali metals and alkaline earth metals. Gas purification catalyst. 8. In producing the exhaust gas purifying catalyst according to any one of claims 1 to 7, the alumina-based composite oxide is selected from the group consisting of a fine particle alumina hydrate colloid and cobalt, nickel and zinc. After dissolving or dispersing a water-soluble salt of at least one selected element and a water-soluble salt of cerium and / or zirconium in water, the mixture is selected from the group consisting of formic acid, acetic acid and succinic acid. At least one aqueous solution is added to adjust the pH to 3.0 to 7.0.
The method for producing an exhaust gas purifying catalyst is characterized in that the catalyst is adjusted to be in the range described above, heated to 100 to 400 ° C., dried by removing moisture, and then calcined.