JP3488999B2 - Exhaust gas purification catalyst composition, method for producing the same, and exhaust gas purification catalyst - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purification catalyst.
Medium composition, method for producing the same, and exhaust gas purification catalyst
Regarding the medium , in particular, hydrocarbons (hereinafter referred to as “HC”), carbon monoxide (hereinafter referred to as “CO”), and nitrogen oxides (hereinafter referred to as “CO”) in exhaust gas discharged from an internal combustion engine of an automobile or the like.
The present invention relates to an exhaust gas purification catalyst that can efficiently purify (NO _x )) even at low temperatures, has excellent low-temperature activity, and has excellent purification performance in all exhaust gas composition atmospheres.

[0002]

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

As such an exhaust gas purifying catalyst, for example, Japanese Examined Patent Publication (Kokoku) No. 58-20307 and Japanese Unexamined Patent Publication No. 5-305 can be used.
There are those disclosed in Japanese Patent Laid-Open No. 236 and Japanese Patent Laid-Open No. 6-378. The exhaust gas purifying catalyst described in Japanese Patent Publication No. 58-20307 is a composition in which a composition comprising platinum, rhodium and cerium is supported on a refractory carrier, and specifically, alumina or cerium oxide is used for platinum. Platinum group elements such as palladium, rhodium and the like are supported and coated on a monolith carrier.

Further, in Japanese Patent Laid-Open No. 5-305236,
Disclosed is an exhaust gas purification catalyst in which hexaaluminate containing no noble metal is mixed and dispersed in noble metal-supported alumina such as platinum, rhodium or palladium. Specifically, a hexaaluminate composition having a certain composition and platinum are disclosed. , Alumina carrying at least one noble metal selected from the group consisting of rhodium and palladium at a fixed weight ratio.

Japanese Unexamined Patent Publication (Kokai) No. 6-378 discloses that activated alumina and cerium oxide are mixed with at least one of platinum and palladium as a catalyst component and potassium as a basic element.
There has been proposed an exhaust gas purifying catalyst carrying an oxide of at least one metal selected from the group consisting of cesium, strontium and barium. That is, the catalyst, in addition to those conventionally used as a catalyst component such as platinum group elements, activated alumina, cerium oxide, etc., is a basic element, at least of potassium compounds, cesium compounds, strontium compounds and barium compounds. It is a combination of one type.

[0006]

However, the conventional catalyst described in the above publication uses a large amount of precious metal which is not rich in resources and is expensive in order to obtain sufficient catalytic activity even at a low temperature. is doing. Therefore, it is expected to develop a catalyst that has a sufficient purification capacity even if the amount of precious metal used is relatively low, based on palladium, which is relatively inexpensive among precious metals, or a catalyst that uses rhodium at the lowest possible amount. ing. However, when palladium is used alone, there is a problem that the purifying ability is deteriorated when the exhaust gas is in a reducing atmosphere, and the low temperature activity and the purifying performance itself are deteriorated when the amount of palladium is reduced.

Further, the exhaust gas purifying catalyst must treat exhaust gas of an automobile whose composition fluctuates widely in a wide temperature range from a low temperature range to a high temperature range and with a high purification rate. However, in exhaust gas purification with palladium, a portion of the hydrocarbons remains unpurified in the low temperature immediately after the engine is started or in a reducing atmosphere where the hydrocarbon concentration is high and the oxygen concentration is low, and the residual hydrocarbons remain on the palladium. Strong adsorption leads to a decrease in activity or a decrease in active sites, resulting in a decrease in purification performance.In an oxidizing atmosphere with a high oxygen concentration and a low hydrocarbon concentration, oxygen is adsorbed on palladium and nitrogen oxides are adsorbed. However, there is a drawback in that the purification performance of nitrogen oxides is significantly reduced.

Further, when the amount of palladium is reduced,
There is also a problem that the above-mentioned effect is prominent and the purification performance is further deteriorated.

Therefore, an object of the present invention is to provide an exhaust gas purifying catalyst having excellent low temperature activity and catalytic activity in all exhaust gas composition atmospheres of automobiles, even if the amount of precious metal used is greatly reduced as compared with conventional catalysts. And to provide a manufacturing method thereof.

[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 at a constant composition ratio together with palladium in a catalyst component supporting layer. By including palladium, it is possible to improve the catalytic performance of the palladium, and it has been found that the catalytic activity in the low temperature range and the low temperature activity and purification performance after endurance in all exhaust gas composition atmospheres are significantly improved and maintained, and the present invention Arrived

The present invention has 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 required to satisfy the valences of the above components)
An exhaust gas-purifying composition, a method for producing the same, and an exhaust gas-purifying catalyst, which is a spinel-type metal aluminate represented by

Further, in order to further enhance the catalytic activity in the rich region of the exhaust gas purifying catalyst according to claim 2 or 3 , the exhaust gas purifying catalyst according to claim 4 further comprises a group consisting of lanthanum, neodymium and zirconium. The exhaust gas purifying catalyst is characterized in that cerium oxide containing at least one selected from the group of 1 to 40 mol% in terms of metal and 60 to 98 mol% of cerium in terms of metal is contained in the exhaust gas purifying catalyst.

Furthermore, in order to further increase the low-temperature activity of the exhaust gas purifying catalyst according to claim 2, wherein
The exhaust gas purifying catalyst according to item 5 is 30% by weight to 80% by metal in terms of the total amount of palladium contained in the catalyst component supporting layer.
% Of palladium is contained in the alumina-based composite oxide.

Furthermore, in order to further increase the claims 2 to 5 either low-temperature activity of the exhaust gas purifying catalyst according to claim, wherein
The exhaust gas purifying catalyst according to Item 6 is characterized in that rhodium and alumina are further contained in the exhaust gas purifying catalyst.

Further, in order to further enhance the catalytic activity of the exhaust gas purifying catalyst according to any one of claims 2 to 6 in a rich atmosphere, the exhaust gas purifying catalyst according to claim 7 further comprises lanthanum and neodymium. And at least one selected from the group consisting of cerium and zirconium oxide containing 1 to 40 mol% in terms of metal and 60 to 98 mol% of zirconium in terms of metal are contained in the exhaust gas purifying catalyst. And

Furthermore, in the exhaust gas purifying catalyst according to claim 6 or 7 , in order to further enhance the catalytic activity of palladium and rhodium, the exhaust gas purifying catalyst according to claim 8 further comprises a rhodium-containing layer and palladium. Same layer and /
Alternatively, it is arranged on the palladium-containing layer.

Furthermore, in order to improve the purification performance of the exhaust gas purifying catalyst according to any one of claims 2 to 8 in a rich region, the exhaust gas purifying catalyst according to claim 9 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 the exhaust gas purifying catalyst composition of the present invention, in producing the metal aluminate according to claim 1 , fine particle alumina hydrate colloid and cobalt, nickel and zinc are used. After dissolving or dispersing a water-soluble salt of at least one element selected from the group consisting of and a water-soluble salt of cerium and / or zirconium in water, the mixture is preferably mixed with formic acid, acetic acid and succinic acid. At least one aqueous solution selected from the group consisting of
Adjust the H to be in the range of 3.0 to 7.0, 100
It is characterized in that it is obtained by heating to ˜400 ° C., removing water, drying, and then firing.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION At least the noble metal contained in the catalyst component carrying layer of the exhaust gas purifying catalyst of the present invention is palladium. The content of palladium is 0.1 to 20 g / L in 1 L of the catalyst. If it is less than 0.1 g, low-temperature activity and purification performance are not sufficiently exerted, and conversely if it exceeds 20 g, the dispersibility of palladium is deteriorated, 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 required to satisfy the valences of the above components)
It is represented by.

As the base material on which the palladium is carried, an alumina-based composite oxide is suitable in order to improve the catalytic performance of palladium. In particular, in order to improve the low-temperature activity and purification performance of palladium (particularly, the NOx steady conversion performance in an oxygen-deficient atmosphere and near the stoichiometric air-fuel ratio), the above-mentioned alumina-based composite oxide is selected from the group consisting of cobalt, nickel and zinc. At least one selected from the group contains cerium and / or zirconium in order to suppress particle growth due to a palladium sink ring and improve purification performance after endurance.

The amount of the alumina-based composite oxide used is
It is 10 to 200 g per 1 L of the catalyst. If it is less than 10 g, it is not possible to obtain a sufficient catalytic performance improving effect that the alumina-based composite oxide activates palladium.
Even if it exceeds, the effect of improving the catalyst performance is saturated or, conversely, the catalyst performance is deteriorated.

In the composition of the metal aluminate, c =
When 2.0, a = 0.1 to 0.8. a = 0.1
The value of 0.8 enhances the structural stability and BET specific surface area of the alumina-based composite oxide at high temperature, and sufficiently exerts the catalyst performance improving effect due to the interaction between palladium and the alumina-based composite oxide. This is to allow it. When a is less than 0.1, Co and Ni added to the alumina-based composite oxide
The effect of the transition metal selected from the group consisting of Zn and Zn is small, and a sufficient improvement effect cannot be obtained.
₂ O ₃ ).

If a = 0.8 is exceeded, the BET specific surface area of the alumina-based composite oxide and the structural stability at high temperature are reduced, so that the dispersibility of the noble metal is poor and sufficient performance is obtained in the initial stage. If you do not, or promote the sinking of a true metal during endurance, the performance after endurance deteriorates.

Further, in the above equation, when c = 2.0, b =
It is 0.001-0.3. b = 0.001 to 0.3 means that while maintaining the catalytic performance improving effect resulting from the interaction between palladium and the alumina-based composite oxide, the alumina-based composite oxide further suppresses the sinking of palladium. This is for adding.

When 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 ). Further, when c is larger than 0.3, Ce or Zr which is not solid-dissolved in the alumina-based composite oxide coats the surface of the alumina-based composite oxide, and NOx adsorption activity that plays a co-catalyst function for palladium. It deteriorates the function of the point of conversion.

As described above, by supporting palladium on the 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 is obtained. Palladium comes into close contact with each other, and lattice oxygen in the alumina-based composite oxide and adsorbed oxygen on the surface are easily transferred and released through the palladium, which improves the low-temperature activity of palladium. Stoichiometric metal aluminate ([X] ₁ Al ₂ O ₄ )
The structural stability and specific surface area at high temperature are sufficient compared to
The added element forms a solid solution in the alumina crystal structure, does not exist as an oxide on the surface, and sufficient performance can be obtained.

Further, at least one element selected from the group consisting of cobalt, nickel and zinc, which is solid-dissolved in the alumina-based composite oxide, functions as an adsorption active point for NO _x, etc. The catalytic performance of palladium near the air-fuel ratio will be improved. Furthermore, in advance,
By adding cerium and / or zirconium, cerium and / or zirconium and palladium are in close contact with each other on the surface of the alumina-based composite oxide, the sintering of palladium is suppressed, and the durability and low-temperature activity of palladium are improved. It will be.

The exhaust gas purifying catalyst according to claim 4 is a contractor.
In addition to the catalyst component in the exhaust gas purifying catalyst according to claim 2, cerium oxide is further contained. 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% and 60 to 98 mol% of cerium in terms of metal.

The amount 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 ) to obtain oxygen storage capacity of cerium oxide and BET specific surface area,
This is to significantly improve the thermal stability. If it is less than 1 mol%, the effect of adding the lanthanum and / or neodymium and / or zirconium element does not appear as in the case of only cerium oxide, and if it exceeds 40 mol%, this effect is saturated or conversely decreases.

Thus, the catalyst component-supporting layer further contains the cerium oxide containing at least one selected from the group consisting of lanthanum, neodymium and zirconium, whereby the cerium oxide having a high oxygen storage capacity is reduced. (Lack of oxygen) 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 purification of exhaust gas, so that reduction in catalytic ability due to reduction of palladium can be suppressed. . Further, by contacting 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 claim 5 is a contractor.
In the exhaust gas purifying catalyst according to any one of claims 2 to 4,
Of the total amount of palladium in the catalyst component, 3 in terms of metal
The metal aluminate powder carries 0 to 80% by weight of palladium.

As the base material on which palladium is supported, in order to improve the dispersibility of palladium and improve the catalytic performance,
Metal aluminates, especially alumina-based complex oxides, are suitable. In particular, the structural stability of alumina after high-temperature durability is increased, and the phase transition to α-alumina and the decrease in BET specific surface area are suppressed, so that sintering of palladium can be suppressed.

By supporting palladium on the alumina-based composite oxide powder, the alumina-based composite oxide powder and palladium are in 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 becomes easy to be released and the low temperature activity of palladium is improved, and the purification performance from the initial stage to the endurance period can be improved. Further, cobalt and / or nickel and / or zinc and cerium and / or which are solid-dissolved in the alumina-based composite oxide.
Alternatively, zirconium effectively functions as an adsorption active site for NO _{x and the} like, and improves the catalytic performance of palladium in an oxygen-deficient atmosphere and near the stoichiometric air-fuel ratio.

When the amount of palladium supported on the alumina-based composite oxide powder is less than 30% by weight, the low temperature activity improving effect is not sufficiently exhibited, and conversely, when it exceeds 80% by weight, the NO _x steady state conversion improving effect is improved. Is saturated and not effective.

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

The exhaust gas purifying catalyst according to claim 6 can further contain rhodium and alumina in the catalyst component supporting layer. Rhodium content is catalyst 1
It is 0.001 to 5 g in the L capacity, and if it is less than 0.001 g, the low temperature activity improving effect by rhodium is not sufficiently exerted, and conversely if it exceeds 5 g, the catalytic activity of rhodium is saturated,
Not economically effective.

As the base material on which the rhodium is carried,
In order to improve the dispersibility of rhodium and improve the catalytic performance,
Alumina containing zirconium is suitable. In particular,
In order to suppress solid solution of rhodium in alumina at high temperature and enhance durability, zirconium is contained in the alumina powder in an amount of 0.1 mol% to 10 mol% in terms of metal.
If the content of zirconium is less than 0.1 mol%, the effect of improving the 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 are deteriorated, so that the dispersibility of the noble metal is deteriorated and sufficient performance cannot be obtained. The amount of such alumina powder used is 1 to 100 g of catalyst 1L. 1
If it is less than g, sufficient noble metal dispersibility cannot be obtained, and 100 g
No significant improvement in performance can be seen even if the amount is larger.

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

Further, the exhaust gas purifying catalyst according to claim 7 further comprises zirconium oxide in addition to the catalyst component in the exhaust gas purifying catalyst according to any one of claims 2 to 6. It is contained. 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% and 60 to 98 mol% of zirconium in terms of metal.

The amount of 1 to 40 mol% is determined by adding at least one element selected from the group consisting of lanthanum, neodymium and cerium to zirconium oxide (ZrO ₂ ) to obtain oxygen storage capacity of zirconium oxide. This is to significantly improve the BET specific surface area and thermal stability. If it is less than 1 mol%, it is the same as the case of only zirconium oxide, and the effect of adding the above-mentioned lanthanum and / or neodymium and / or cerium elements does not appear. 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 the physical properties of the zirconia oxide such as thermal stability deteriorate.

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

Further, in the exhaust gas purifying catalyst according to claim 8 , the rhodium-containing catalyst component layer is the same layer as the palladium-containing layer in order to efficiently exhibit the synergistic action of palladium and rhodium. And / or placed on top of the palladium-containing catalyst component layer. This makes it possible to sufficiently secure the poisoning resistance to poisonous substances such as lead and sulfur and the purification performance in the rich region.

The exhaust gas purifying catalyst according to claim 9 further contains at least one selected from the group consisting of alkali and alkaline earth metals. Alkali metals and alkaline earth metals used include, for example, lithium,
It includes potassium, cerium, magnesium, calcium, strontium and barium. The content is 1 to 40 g in 1 L of the catalyst. If it is less than 1 g, adsorption poisoning of hydrocarbon species and sintering of palladium are not suppressed,
Even if it exceeds 40 g, the effect of addition is saturated, a significant amount increasing effect cannot be obtained, and it is not economically effective.

The palladium, the alumina-based composite oxide powder, and the cerium oxide and the zirconium oxide, which are optionally added, are in intimate contact with the alkali metal and / or the alkaline earth metal to improve the purification performance. The effect is obtained. Alkali metals and / or alkaline earth metals have the ability to alleviate the adsorption and poisoning of hydrocarbons in a rich atmosphere, and when these are contained in the catalyst component-supporting layer, they suppress palladium and sintering, and The activity in an oxygen-deficient atmosphere can be further improved.

Further, the exhaust gas purifying catalyst composition and the exhaust gas purifying catalyst of the present invention, in the production of a metal aluminate, first include fine particle alumina hydrate colloid (hereinafter referred to as "alumina sol"), A water-soluble salt of at least one element selected from the group consisting of cobalt, nickel and zinc and a water-soluble salt of cerium and / or zirconium are dissolved or dispersed in water and stirred and mixed. At this time, a liquid in which each catalyst raw material is dissolved simultaneously or separately may be added.

Then, at least one selected from the group consisting of formic acid, acetic acid and succinic acid as a reaction accelerator is gradually added to this mixed solution so that the pH is in the range of 3.0 to 7.0. After adjustment, 100 ℃ in an autoclave
To 400 ° C. and boil for 1 to 12 hours.
After cooling, this mixed solution is obtained by removing water using a spray dryer and then calcining. This method is preferable because it ensures a sufficient BET specific surface area and crystal structure uniformity of the alumina-based composite oxide and uniformly disperses the noble metal. However, the method for preparing the alumina-based composite oxide is not limited to a special method, and may be appropriately selected from various methods such as a known evaporation-drying method and a precipitation method unless significant uneven distribution of the components is involved. Can be used.

The pH of the mixed solution of the catalyst raw material is 3.0 to 7.
By adjusting to the range of 0, alumina can form an organic salt complex and react with other additive elements to form a complex oxide. When the pH is lower than 3.0, various elements are eluted and alumina does not form an organic salt complex, and conversely, the pH is 7.
When it is higher than 0, a part of the organic salt complex of alumina forms a hydroxide, which makes it difficult for the alumina to react with other elements, and the complexing does not proceed to obtain a uniform structure.

By using formic acid, acetic acid, succinic acid or the like for adjusting the pH, the metal element does not remain even if the precipitation cake is not sufficiently cleaned, and even if these acids remain, they can be easily baked in a later step. 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 for the purpose of deflocculating highly crystalline alumina, promoting the formation of an organic salt complex, and reacting this organic salt complex with other additive 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 solid-dissolved in the crystal structure (spinel structure). You can

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

The metal aluminate containing cobalt and / or nickel and / or zinc, cerium and / or zirconium and aluminum used for producing the exhaust gas purifying catalyst composition of the present invention is a nitrate of each of the above elements,
It is prepared by optionally combining carbonates, ammonium salts, acetates and the like with alumina sol or boehmite alumina to prepare a mixed solution. Particularly, it is 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 raw materials is significantly reduced when the precipitate is dried and calcined.

The water can be removed by appropriately selecting from known methods such as an evaporation dryness method and a spray dryer 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 supporting palladium with good dispersibility In order to obtain the above, it is preferable to carry out with a spray dryer. Further, the calcination may be performed in air and / or under air circulation, for example, at 600 ° C. to 1100 ° C. in order to form an alumina-based composite oxide in which the added element forms a solid solution and to obtain a large specific surface area. preferable.

The method for 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, the impregnation method is used. preferable. As a raw material compound of palladium, any water-soluble compound such as an ammine salt, a chloride or a nitrate can be used.

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

Preferably, a catalyst for purifying exhaust gas according to claim 4 is obtained by adding cerium oxide powder to the alumina powder. The cerium oxide powder contains at least one selected from the group consisting of lanthanum, neodymium and zirconium.

Further, by containing rhodium and alumina, the exhaust gas purifying catalyst according to claim 6 can be obtained. As the raw material compound of rhodium, any compound can be used as long as it is a water-soluble compound such as nitrate, halide and acetate.

Further, zirconium may be contained in the alumina, and the method for preparing such zirconium-containing alumina is not limited to a special method, and any known evaporation to dryness may be used unless significant uneven distribution of the components is accompanied. Can be appropriately selected from various methods such as a precipitation method, an impregnation method and an impregnation method, but the impregnation method using an aqueous solution in which zirconium acetate is dissolved in water is used. It is preferable because a sufficient specific surface area can be secured and the supported precious metal can be uniformly dispersed.

The method for supporting rhodium on the alumina may be appropriately selected from, for example, an impregnation method and a kneading method, but the impregnation method is particularly preferable. The removal of water to be carried out next can be appropriately selected from known methods such as evaporation to dryness. 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 preferable to carry out at a temperature in the range of 0 ° C. in air and / or under air flow.

Preferably, a zirconium oxide powder is added to the rhodium-supported alumina powder to obtain a contract.
The exhaust gas purifying catalyst according to claim 7 is obtained. 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 sixth aspect, the cerium oxide strongly holds rhodium in an oxidized state, so that the purifying performance is deteriorated. On the other hand, by adding such zirconium oxide powder, rhodium can be more effectively maintained in an oxidized state suitable for exhaust gas purification.

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

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

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

The amount of the catalyst component coating layer adhered to the honeycomb material is the total amount of all the catalyst components per 1 L of the catalyst.
50 to 400 g is preferable. The more the catalyst component is, the more preferable it is from the viewpoint of catalytic activity and catalyst life. However, if the coating layer is too thick, the reaction gas such as HC, CO, NO _x, etc. will be poorly diffused, so these gases are sufficient for the catalyst. It becomes impossible to contact, the effect of increasing the amount of activity is saturated, and further the gas passage resistance becomes large. Therefore, the coat layer amount is
It is preferably 50 g to 400 g per liter of the catalyst.

More preferably, an alkali metal and / or an alkaline earth metal can be impregnated and carried on the obtained exhaust gas purifying catalyst. The alkali metal and alkaline earth metal that can be used are, for example, one or more elements selected from the group consisting of lithium, sodium, potassium, cesium, magnesium, calcium, strontium and barium.

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 support the alkaline metal and / or alkaline earth metal, which is a basic element, in the vicinity of palladium with good dispersibility. At this time, the raw material compounds of alkali metal and / or alkaline earth metal may be contained simultaneously or separately.

That is, an aqueous solution of a powder of an alkali metal compound and / or an alkaline earth metal compound is impregnated into the above carrier carrying a washcoat component, dried, and then dried in air and / or under air flow to obtain 200 ℃ ~ 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 to be contained in the coating layer in an oxide form, it becomes difficult to form a composite oxide even if it is subsequently exposed to a high temperature. is there. If the firing temperature is lower than 200 ° C., the alkali metal compound and / or the alkaline earth metal compound cannot be sufficiently converted into an oxide form. On the contrary, if the firing temperature is higher than 600 ° C., the raw material salt is rapidly separated. However, it is not preferable because the collateral may crack.

[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 used as a fine particle alumina sol 1700 of 20% by weight in terms of alumina (Al ₂ O ₃ ). Parts was added to a suspension prepared by dispersing 2500 parts of pure water, and a 10 wt% acetic acid aqueous solution was added with stirring to adjust the pH to 4.0. After boiling this solution at 250 ° C for 4 hours, remove the water and
After drying for 12 hours at 400 ° C. for 2 hours, at 600 ° C. for 2 hours, and then at 800 ° C. for 4 hours, Ni _0.5 Ce
_0.02 Zr _0.01 Al _2.0 O _x (powder A) was obtained. This powder A was impregnated with an aqueous solution of palladium nitrate and dried, then 40
The mixture was calcined at 0 ° C. for 2 hours to obtain a Pd-supported cerium / zirconium-added nickel aluminate powder (powder B). The concentration of Pd supported on this powder B was 1.0% by weight.

700 parts by weight of the above powder (powder B) supporting 1.0% by weight of palladium, and 0.75 parts by weight of palladium in a cerium oxide powder containing 1 mol% of lanthanum and 32 mol% of zirconium. 480 parts of (powder C), 20 parts of activated alumina, and 1200 parts of nitric acid aqueous solution were put into a magnetic ball mill, and mixed and pulverized to obtain a slurry liquid. This slurry liquid was attached to a cordierite monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried, and baked at 400 ° C. for 1 hour to give a coat layer weight of 160 g / A cordierite-based monolithic carrier supporting a catalyst component having an L-carrier and a palladium loading of 40 g / cf (1.41 g / L-catalyst) was obtained. Then
A barium acetate solution was attached to the above-mentioned catalyst component-supporting cordierite monolithic carrier, followed by firing at 400 ° C. for 1 hour to contain BaO in an amount of 15 g / L-catalyst 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
An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that O _x (powder D) was used.

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 purification 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 wt% formic acid aqueous solution was used instead of the 10 wt% acetic acid aqueous solution.

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

Example 9 An aqueous solution prepared 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 added with 1700 parts of boehmite alumina sol of 20% by weight in terms of alumina (Al ₂ O ₃ ). To the suspension dispersed in 2500 parts of pure water, 10% by weight acetic acid aqueous solution was added with stirring to adjust the pH to 3.5. This solution is 250 ℃
After boiling for 4 hours, remove water and then 150 ℃
After drying for 12 hours at 400 ° C. for 2 hours, at 600 ° C. for 2 hours, and then at 800 ° C. for 4 hours, Ni _0.5 Ce
_0.02 Zr _0.01 A1 _{2.0 Ox} (powder K) was obtained. The powder K was impregnated with an aqueous solution of palladium nitrate and dried, and then 40
It was calcined at 0 ° C. for 2 hours to obtain a Pd-supported cerium / zirconium-added nickel aluminate powder (powder L). The concentration of Pd supported on this powder L was 1.0% by weight.

700 parts of the above powder (powder L) carrying 1.0% by weight of palladium and 0.75 part 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 nitric acid aqueous solution were put into a magnetic ball mill and mixed and ground to obtain a slurry liquid.
This slurry liquid was used as a cordierite monolith carrier (1.
(3 L, 400 cells) and calcined at 400 ° C. for 1 hour, and a catalyst component-supporting cordierite monolith carrier having a coat layer weight of 160 g / L-support and a palladium loading of 40 g / cf (1.41 g / L-catalyst). Got

137 parts of zirconium oxyacetate was added to pure water 5
It was dissolved in 100 parts and impregnated in 1000 parts of activated alumina.
This was dried at 150 ° C. for 24 hours, then calcined at 400 ° C. for 2 hours and then at 1000 ° C. for 2 hours to obtain a Zr 3 mol% -added alumina powder (powder M). This Zr3 mol% -added alumina powder (powder M) was impregnated with an aqueous rhodium nitrate solution, dried, and then calcined at 400 ° C. for 2 hours to obtain Rh-supporting Zr3.
A mol% added alumina powder (powder N) was obtained. This powder N
The supported Rh concentration of was 1.06% by weight.

Z containing 1.06% by weight of the above rhodium
135 parts of r3 mol% added alumina powder (powder N), 450 parts of Zr3 mol% added alumina powder (powder M), 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 ground to obtain a slurry liquid a. Weight of coat layer obtained in Example 1 175 g / L-support (160 g / L-support of palladium-containing coat layer, palladium support amount 4
0 g / cf (1.41 g / L-catalyst), BaO 15 g /
This slurry liquid a is used as an exhaust gas purifying catalyst (L-catalyst).
And baked for 1 hour at 400 ° C. to give a total coat layer weight of 225 g / L-carrier (rhodium-containing catalyst component-supporting layer 50).
g / L-carrier), palladium loading 40 g / cf (1.
41 g / L-catalyst), rhodium supported amount 2 g / cf (0.
(071 g / L-catalyst) was obtained as an exhaust gas purifying catalyst.

Example 10 Coat layer weight obtained according to Example 1 160 g / L-Carrier, palladium loading 40 g / cf (1.41 g / L-
The rhodium-containing slurry liquid a obtained in Example 9 was adhered to a catalyst component-supporting cordierite-based monolithic carrier (1.3 L, 400 cells) containing a catalyst, and the mixture was baked at 400 ° C. for 1 hour to make the total coat total. Weight 210 g / L (rhodium-containing total weight 50 g / L-catalyst), palladium loading 40 g /
cf (1.41 g / L-catalyst), rhodium supported amount 2 g /
A cf (0.071 g / L-catalyst) cordierite-based monolithic support carrying a catalyst component was obtained. Then, a barium acetate solution was adhered to the above-mentioned catalyst component-supporting cordierite monolithic carrier, followed by firing at 400 ° C. for 1 hour to obtain BaO15.
An exhaust gas catalyst was obtained by containing g / L-catalyst.

Example 11 Ni _0.5 Ce _0.02 Zr _0.01 Al obtained by using 2500 parts of aluminum nitrate in place of the crystalline fine particle alumina sol.
_{2.0 Ox} was used .

Example 12 Instead of the crystalline fine particle alumina sol, activated alumina (A
The catalyst for exhaust gas purification was obtained in the same manner as in Example 1 except that Ni _0.5 Ce _0.02 Zr _0.01 Al _2.0 O _x obtained by using 1700 parts of 1 ₂ O ₃ ) and 485 parts of nickel nitrate was used.

Comparative Example 1 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 2 1164 parts of nickel nitrate and 20 wt% 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 by using 100 parts was used.

Example 13 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.

Example 14 An exhaust gas purifying catalyst was obtained in the same manner as in Example 1 except that BaO was not contained.

Example 15 The same procedure as in Example 9 was carried out, except that the rhodium-containing component layer was placed in the inner layer and the palladium-containing component layer was placed in the surface layer to obtain an exhaust gas purifying catalyst.

Table 1 shows the composition of the metal aluminate of the exhaust gas purifying catalysts of Examples 1 to 15 and Comparative Examples 1 and 2 .

[0093]

[Table 1]

Test Example The exhaust gas purifying catalysts of Examples 1 to 15 and Comparative Examples 1 and 2 were subjected to durability under the following durability conditions, and then,
The catalytic activity was evaluated under the following evaluation conditions.

Endurance conditions Engine displacement 4400 cc 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 Approx. 1100 ppm NO 1300 ppm CO ₂ 15% A / F fluctuation 5500 times (cycle 65 seconds / cycle) cycle: A / F = 14.6 55 seconds Fuel cut 5 seconds Rich spike 5 seconds

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

[0097] With respect to the purification performance of each exhaust gas purification catalyst after endurance, the average conversion rate (%) of HC, CO and NO _x in a stoichiometric atmosphere was determined by the following formula, and the results are shown in Table 2.

[0098]

[Equation 4]

[Equation 5]

[Equation 6]

[0099]

[Table 2]

[0100]

According to the exhaust gas purifying catalyst of claim 2 ,
It excels in low-temperature activity and can improve the catalytic performance of palladium in an oxygen-deficient atmosphere and near the stoichiometric air-fuel ratio.

In addition to the above effects, the catalyst for purifying exhaust gas according to claim 4 can suppress the sink ring of palladium carried on the alumina-based composite oxide to improve the durability and low temperature activity of palladium. it can.

In addition to the above effects, the exhaust gas purifying catalyst according to claim 5 has the effect of improving the low temperature activity of palladium and NO.
x It is possible to sufficiently obtain the effect of improving the steady conversion performance.

In addition to the above effects, the catalyst for purifying exhaust gas according to claim 6 can further improve the low-temperature activity and the purification performance in an oxygen-deficient atmosphere due to the promoter action of rhodium.

In addition to the above effects, the catalyst for purifying exhaust gas according to claim 7 is suitable for purifying exhaust gas by changing the oxidation state of rhodium, and can suppress deterioration of catalytic ability due to reduction of rhodium.

In addition to the above effects, the exhaust gas purifying catalyst according to claim 8 is suitable for purifying palladium and rhodium,
It is possible to suppress a decrease in catalytic ability due to poisoning of palladium or rhodium.

In addition to the above effects, the exhaust gas purifying catalyst according to claim 9 can alleviate the adsorption and poisoning action of hydrocarbons and suppress palladium sintering.

An exhaust gas purifying catalyst composition according to claim 10.
The method for producing a product is the exhaust gas purifying catalyst composition of the present invention.
A catalyst composition for exhaust gas purification, which can efficiently produce a substance, can form an alumina-based composite oxide in which an added element forms a solid solution, and has a large specific surface area for supporting palladium with good dispersibility. Obtainable.

─────────────────────────────────────────────────── ─── Continuation of the front page (58) Fields surveyed (Int.Cl. ⁷ , DB name) B01J 21/00-38/74 B01D 53/86 B01D 53/94

Claims (13)

(57) [Claims] 1. A catalyst composition for purifying exhaust gas , comprising the following general formula: [X] _a [Y] _b Al _c O _d (wherein X is a group consisting of cobalt, nickel and zinc). At least one element selected from Y, 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 required to satisfy the valences of the above components)
A catalyst composition for purifying exhaust gas , which is a spinel-type metal aluminate represented by: 2. A monolithic structure type catalyst having a catalyst component supporting layer, comprising at least palladium and a metal aluminate as a catalyst component, the metal aluminate having 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, 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 required to satisfy the valences of the above components)
An exhaust gas purifying catalyst characterized by being a spinel-type metal aluminate represented by. 3. The exhaust gas purifying catalyst according to claim 2, wherein the metal aluminate is a powder. 4. The exhaust gas purifying catalyst according to claim 2 or 3, further comprising at least one selected from the group consisting of lanthanum, neodymium and zirconium in terms of metal.
An exhaust gas purifying catalyst containing 40 mol% of cerium oxide containing 60 to 98 mol% of cerium. 5. The exhaust gas purifying catalyst according to claim 2, wherein the metal aluminate contains 30 to 80% by weight of palladium based on the total amount of palladium in terms of metal. Exhaust gas purification catalyst. 6. An exhaust gas purifying catalyst, wherein the exhaust gas purifying catalyst according to claim 2 further contains rhodium and alumina. 7. The exhaust gas purifying catalyst according to claim 2, further comprising at least one selected from the group consisting of lanthanum, neodymium and cerium in an amount of 1 to 40 mol% in terms of metal and zirconium. An exhaust gas purifying catalyst comprising 60 to 98 mol% of zirconium oxide. 8. The exhaust gas purifying catalyst according to claim 6 or 7, wherein the rhodium-containing layer is arranged in the same layer as palladium and / or above the palladium-containing layer. . 9. An exhaust gas, wherein the exhaust gas purifying catalyst according to claim 2 further contains at least one selected from the group consisting of alkali metals and alkaline earth metals. Gas purification catalyst. 10. In producing an exhaust gas purifying catalyst composition, a fine particle alumina hydrate colloid , a salt of at least one element selected from the group consisting of cobalt, nickel and zinc, and cerium and / or zirconium are used. A salt and a salt are dissolved or dispersed in a solution, and then the pH of this mixed solution is adjusted to be in the range of 3.0 to 7.0, followed by firing to obtain a metal aluminate having a spinel structure. A method for producing an exhaust gas purifying catalyst composition. 11. The method for producing an exhaust gas purifying catalyst composition according to claim 10, wherein at least one selected from the group consisting of formic acid, acetic acid and succinic acid is added to the mixed solution to adjust the pH. A method for producing an exhaust gas-purifying catalyst composition, comprising: 12. The method for producing an exhaust gas purifying catalyst composition according to claim 10, wherein the mixed solution is adjusted to pH.
A method for producing an exhaust gas purifying catalyst composition, which is obtained by adjusting, heating to 100 to 400 ° C., removing water, drying, and then firing. 13. The metal aluminate is a water-soluble salt of fine particle alumina hydrate colloid and at least one element selected from the group consisting of cobalt, nickel and zinc.
When process according to claim 10 to 12 exhaust gas purifying catalyst composition according to the water-soluble salts of cerium and / or zirconium characterized by using the mixture dissolved or dispersed in water.