JPH04219142A - Exhaust gas purification catalyst - Google Patents

Abstract

PURPOSE:To efficiently remove nitrogen oxide, CO, and hydrocarbon at the same time in a comparatively wide temperature range from the exhaust gas exhausted from the internal combustion engines of automobiles and the like by using the exhaust gas purification catalyst of zeolite having an SiO2/Al2O3 molar ratio of specified value or more and containing Co, alkaline earth metals and silver. CONSTITUTION:The zeolite having an SiO2/Al2O3 molar ratio of at least 15 contains Co, alkaline earth metals, such as Ca, and sliver; each preferably, in a Co amount of 10-150mol%, in an alkaline earth metal amount of 10-100mol% in a silver amount of 5-200mol%, and in the total amounts of 100-250mol% of alumina in the zeolite, thus permitting nitrogen oxide, CO, and hydrocarbon to be removed at the same time in a comparatively wide temperature range from the exhaust gas exhausted from the internal combustion engines of automobiles and the like by using this catalyst.

Description

[Detailed description of the invention]

0001

[Field of Industrial Application] The present invention relates to an exhaust gas purifying catalyst for removing nitrogen oxides, carbon monoxide, and hydrocarbons from exhaust gas emitted from internal combustion engines such as automobile engines, and in particular, to The present invention relates to a catalyst for purifying nitrogen oxides and a method for using the same.

0002

[Prior Art] The harmful substances nitrogen oxides, carbon monoxide, and hydrocarbons in the exhaust gas emitted from internal combustion engines are removed by a three-way catalyst in which, for example, Pt, Rh, Pd, etc. are supported on a carrier. ing. However, since diesel engine exhaust gas contains a large amount of oxygen, there is no effective catalyst for removing nitrogen oxides, and exhaust gas purification by catalysts has not been carried out.

[0003] Furthermore, in recent years, it has become necessary for gasoline engines to perform lean combustion for the purpose of improving fuel efficiency and reducing carbon dioxide emissions. However, since the exhaust gas of a lean-burn gasoline engine is an oxygen-rich atmosphere,
Conventional three-way catalysts such as those described above cannot be used, and methods for removing harmful components, particularly nitrogen oxides, have not been put to practical use.

[0004] As a method for removing nitrogen oxides from such oxygen-excess exhaust gas, there are known methods such as adding a reducing agent such as ammonia, and removing nitrogen oxides by absorption with alkali. It is not an effective method for use in automobiles, which are mobile sources, and its application is limited.

[0005] In recent years, it has been reported that a zeolite catalyst in which transition metals are ion-exchanged can remove nitrogen oxides from oxygen-excess exhaust gas without adding a special reducing agent such as ammonia. For example, in JP-A-63-283727 and JP-A-1-130735, nitrogen oxides are selected even in oxygen-excess exhaust gas that contains trace amounts of reducing agents such as unburned carbon monoxide and hydrocarbons. A zeolite-based catalyst has been proposed that can reduce the

However, these conventionally proposed catalysts suffer from significant deterioration in activity due to long-term use at high temperatures, and there is a need for improvement in terms of durability, catalytic performance, etc.

[0007] Therefore, as a catalyst to solve these problems, an exhaust gas purification catalyst has been proposed, which is a zeolite with a SiO2/Al2O3 molar ratio of at least 15 and contains cobalt and an alkaline earth metal. (Patent Application No. 1-337249).

[0008]

[Problems to be Solved by the Invention] However, although the exhaust gas purification catalyst proposed in Japanese Patent Application No. 1-337249 has improved durability, the temperature range in which nitrogen oxides can be purified is relatively high and narrow. Catalysts for purifying exhaust gas from internal combustion engines, particularly automobiles, are required to have higher nitrogen oxide purifying ability over a wider temperature range.

An object of the present invention is to simultaneously remove nitrogen oxides, carbon monoxide, and hydrocarbons from exhaust gas emitted from internal combustion engines of automobiles, etc., in order to solve the problems of the prior art as described above. Furthermore, the present invention aims to provide a catalyst that is resistant to thermal deterioration, has excellent durability, and has high catalytic performance.

Another object of the present invention is to provide a method for purifying exhaust gas using such a catalyst.

[0011]

[Means for Solving the Problems] As a result of intensive study on the above-mentioned problems, the present inventors have developed the previously proposed SiO
It has been discovered that nitrogen oxide purification ability is improved by further containing silver in an exhaust gas purification catalyst which is a zeolite having a 2/Al2O3 molar ratio of at least 15 and contains cobalt and alkaline earth metals, and has developed the present invention. It was completed.

That is, the present invention provides a zeolite catalyst for removing nitrogen oxides, carbon monoxide, and hydrocarbons from oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbons, the catalyst having a SiO2/Al2O3 molar ratio. is at least 1
An exhaust gas purification catalyst characterized by being a zeolite of 5 or more and containing cobalt, an alkaline earth metal, and silver, and a combustion exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbons in the exhaust gas purification catalyst. The present invention provides a method for removing nitrogen oxides, carbon monoxide, and hydrocarbons from exhaust gas, which comprises contacting the exhaust gas with nitrogen oxides, carbon monoxide, and hydrocarbons.

The present invention will be explained in detail below.

[0014] The exhaust gas purification catalyst according to the present invention is a SiO2/A catalyst containing cobalt, an alkaline earth metal, and silver.
A zeolite having an l2O3 molar ratio of at least 15.

[0015] The above zeolite generally has xM2/nO
・Al2O3・ySiO2・zH2O (where n is the valence of the cation, x is a number in the range of 0.8 to 2, y is a number of 2 or more, and z is a number of 0 or more). Among these, the zeolite used in the present invention has a SiO2/Al2O3 molar ratio of 15 or more. The upper limit of the SiO2/Al2O3 molar ratio is not particularly limited, but the SiO2/Al2O3 molar ratio is 1.
If it is less than 5, the heat resistance and durability of the zeolite itself will be low, making it impossible to obtain sufficient heat resistance and durability of the catalyst. Generally, those having a SiO2/Al2O3 molar ratio of about 15 to 1000 are used.

The zeolite constituting the catalyst of the present invention may be either a natural product or a synthetic product, and the method for producing these zeolites is not particularly limited, but typically ferrierite, Y, ZSM -5, ZSM-11, ZS
Zeolites such as M-12 and ZSM-20 can be used. Further, these zeolites can be used as the catalyst of the present invention either as they are or after being ion-exchanged into NH4 type or H type by treatment with ammonium salts, mineral acids, etc.

[0017] The zeolite used in the present invention contains cobalt,
Contains alkaline earth metals and silver. The method for incorporating cobalt, alkaline earth metals, and silver into zeolite is not particularly limited, and generally, they can be incorporated by ion exchange using a water-soluble salt, impregnation support method, evaporation drying method, etc. . When containing each element, each element may be contained sequentially or all at once.

The concentrations of cobalt, alkaline earth metal and silver ions in the aqueous solution when containing cobalt, alkaline earth metal and silver can be arbitrarily set depending on the desired ion exchange rate of the catalyst. As the alkaline earth metal ion, Ca, Mg, Sr, Ba, etc. can be used. Further, cobalt, alkaline earth metals, and silver ions can be used in the form of soluble salts, and nitrates, acetates, oxalates, hydrochlorides, etc. can be preferably used as the soluble salts.

The contents of cobalt, alkaline earth metals and silver are 0.1 to 1.5 times the mole of alumina in the zeolite, and 0.1 to 1.5 times the content of cobalt and 0.1 to 1.5 times the amount of alkaline earth metals. 1 times, silver is preferably 0.05 to 2 times, and the total amount of cobalt, alkaline earth metal, and silver is preferably 1.0 to 2.5 times.

Samples containing cobalt, alkaline earth metals and silver are generally used after solid-liquid separation, washing and drying. Moreover, it can also be used after baking if necessary.

The exhaust gas purification catalyst of the present invention can also be used by mixing it with a binder such as clay minerals and molding the mixture. In addition, by molding zeolite in advance, cobalt and
Alkaline earth metals and silver can also be included. The binder used when molding zeolite is not particularly limited, but clay minerals such as kaolin, attapulgite, montmorillonite, bentonite, allophane, sepiolite, silica, alumina, etc. can be used. Alternatively, it may be a binderless zeolite molded product that is directly synthesized without using a binder. Also,
Zeolite can also be wash-coated onto a honeycomb-shaped substrate made of cordierite or metal.

[0022] Removal of nitrogen oxides, carbon monoxide, and hydrocarbons from oxygen-excess exhaust gas can be carried out by bringing the exhaust gas into contact with the exhaust gas purification catalyst of the present invention. The oxygen-excessive exhaust gas that is the object of the present invention refers to exhaust gas that contains oxygen in excess of the amount of oxygen required to completely oxidize carbon monoxide, hydrocarbons, and hydrogen contained in the exhaust gas. Examples of such exhaust gas include exhaust gas emitted from internal combustion engines such as automobiles, especially when air and fuel consumption is high (
A specific example is exhaust gas in a so-called lean region.

[0023] Even if the above exhaust gas catalyst is applied to exhaust gas containing carbon monoxide, hydrocarbons and hydrogen and not in excess of oxygen, its performance will not change in any way.

[0024]

[Examples] The present invention will be explained in more detail with reference to Examples below, but the present invention is not limited to these Examples.

Comparative Example 1 <Preparation of Comparative Catalyst 1> ZSM was prepared according to the method of Example 5 of JP-A-59-54620.
-5 similar zeolite was synthesized. It had the following chemical composition, expressed as molar ratios of oxides on an anhydrous basis.

1.1Na2O・Al2O3・40SiO2 Ammonium type ZSM-5 prepared by ion exchange with ammonium chloride aqueous solution;
of barium chloride in 1,800 ml of an aqueous solution of 80
Stirred at ℃ for 16 hours. After solid-liquid separation, the mixture was thoroughly washed with water, then poured into 700 ml of an aqueous solution of 0.23 mol/l cobalt (II) acetate tetrahydrate, and stirred at 80° C. for 16 hours. After solid-liquid separation of the slurry, the zeolite cake was added to the prepared aqueous solution having the above composition and the same operation was performed. After solid-liquid separation, it was thoroughly washed with water and dried at 110°C for 10 hours to obtain Comparative Catalyst 1. When the barium and cobalt contents of this catalyst were investigated by chemical analysis, it was found that the Al of the zeolite
The amount of barium was 0.58 times the number of moles of 2O3, and the amount of cobalt was 0.49 times as divalent.

Example 1 <Preparation of Catalyst 1> 15 g of Comparative Catalyst 1 prepared in Comparative Example 1 was added to a concentration of 0.025 mol.
The mixture was poured into 22 ml of silver nitrate aqueous solution at a concentration of 1.2 ml, dried under reduced pressure while stirring, and further dried at 110° C. for 16 hours to obtain catalyst 1. When the content of barium, cobalt and silver in this catalyst was investigated by chemical analysis, it was found that barium is 0.58 times, cobalt is 0.49 times as divalent, and silver is 0.1 times the number of moles of Al2O3 in the zeolite. twice included.

Example 2 <Preparation of Catalyst 2> 15 g of Comparative Catalyst 1 prepared in Comparative Example 1 was added to a concentration of 0.05 mol/
The catalyst was poured into 43 ml of aqueous silver nitrate solution, dried under reduced pressure while stirring, and further dried at 110° C. for 16 hours to obtain catalyst 2. When the content of barium, cobalt and silver in this catalyst was investigated by chemical analysis, barium was 0.58 times the number of moles of Al2O3 in the zeolite, and cobalt was 0 as divalent.
．． 49 times, and silver was included 0.4 times.

Example 3 <Preparation of Catalyst 3> 15 g of Comparative Catalyst 1 prepared in Comparative Example 1 was added to a concentration of 0.05 mol/
The mixture was poured into 43 ml of silver nitrate aqueous solution and stirred at 80° C. for 16 hours. After solid-liquid separation of the slurry, it was thoroughly washed with water and
After drying at ℃ for 16 hours, catalyst 3 was obtained. Chemical analysis of the contents of barium, cobalt and silver in this catalyst revealed that barium was 0.57 times the Al2O3 mole of zeolite, cobalt was 0.48 times as divalent, and silver was 0.
．． It contained 13 times more.

Example 4 <Preparation of Catalyst 4> 20 g of ammonium type ZSM-5 obtained in Comparative Example 1 was mixed with a concentration of 1.0
The mixture was poured into 180 ml of a 9 mol/l aqueous solution of barium chloride, and stirred at 80° C. for 16 hours. After solid-liquid separation, it was thoroughly washed with water, and then 0.23 mol/l of cobalt(II) nitrate was added.
The mixture was poured into 180 ml of an aqueous solution of tetrahydrate, and stirred at 80° C. for 16 hours. After solid-liquid separation of the slurry, the zeolite cake was added to the prepared aqueous solution having the above composition and the same operation was performed. After solid-liquid separation, the mixture was thoroughly washed with water and dried at 110° C. for 10 hours, and then a catalyst 4 was prepared in the same manner as in Example 2. Chemical analysis of the contents of barium, cobalt, and silver in this catalyst revealed that, relative to the number of moles of Al2O3 in the zeolite, barium is 0.52 times, cobalt is 0.32 times as divalent, and silver is 0.4 times. twice included.

Example 5 <Preparation of Catalyst 5> 20 g of ammonium type ZSM-5 obtained in Comparative Example 1 was prepared at a concentration of 0.2
Pour into 180 ml of mol/l silver nitrate aqueous solution and heat at 80°C.
The mixture was stirred for 16 hours. After solid-liquid separation of the slurry, the zeolite cake was added to the prepared aqueous solution having the above composition and the same operation was performed. After solid-liquid separation, wash thoroughly with water, and then add 180 ml of an aqueous solution of barium chloride with a concentration of 1.09 mol/l.
1 and stirred at 80°C for 16 hours. After solid-liquid separation,
After thoroughly washing with water, it was poured into 180 ml of an aqueous solution of 0.23 mol/l cobalt (II) acetate tetrahydrate and heated at 80°C.
The mixture was stirred for 16 hours. After solid-liquid separation of the slurry, it was thoroughly washed with water and dried at 110°C for 20 hours to obtain catalyst 5. When the content of barium, cobalt and silver in this catalyst was investigated by chemical analysis, it was found that the content of barium, cobalt and silver was determined based on the number of moles of Al2O3 in the zeolite.
Barium is 0.67 times, cobalt is 0.58 as divalent
Silver was included 0.09 times.

Example 6 <Preparation of Catalyst 6> 20 g of ammonium type ZSM-5 obtained in Comparative Example 1 was prepared at a concentration of 1.0.
The mixture was poured into 180 ml of a 9 mol/l aqueous solution of barium chloride, and stirred at 80° C. for 16 hours. After solid-liquid separation, the mixture was subsequently poured into 180 ml of an aqueous silver nitrate solution with a concentration of 0.2 mol/l, and stirred at 80° C. for 16 hours. After solid-liquid separation, 0.
The mixture was poured into 180 ml of an aqueous solution of 1 mol/l cobalt (II) acetate tetrahydrate, and stirred at 80° C. for 16 hours. After separating the slurry into solid and liquid, it was thoroughly washed with water and dried at 110°C for 20 hours to obtain catalyst 6. When the content of barium, cobalt and silver in this catalyst was investigated by chemical analysis, barium was 0.56 times the Al2O3 mole number of zeolite, cobalt was 0.58 times as divalent, and silver was 0.21 times. twice included.

Comparative Example 2 <Preparation of Comparative Catalyst 2> 200 g of the ammonium type ZSM-5 obtained in Comparative Example 1 was added to an aqueous solution of strontium chloride with a concentration of 1.09 mol/l.
00ml and stirred at 80°C for 16 hours. After solid-liquid separation, the mixture was thoroughly washed with water, then poured into 1800 ml of an aqueous solution of 0.23 mol/l cobalt (II) acetate tetrahydrate, and stirred at 80° C. for 16 hours. After solid-liquid separation of slurry,
The zeolite cake was again put into the aqueous solution having the above composition and the same operation was performed. After solid-liquid separation, wash thoroughly with water,
Comparative catalyst 2 was obtained by drying at 110° C. for 10 hours. When the strontium and cobalt contents of this catalyst were investigated by chemical analysis, it was found that strontium was contained 0.23 times and cobalt was contained 1.12 times as divalent relative to the number of moles of Al2O3 in the zeolite.

Example 7 <Preparation of Catalyst 7> 15 g of Comparative Catalyst 2 prepared in Comparative Example 2 was added to a concentration of 0.05 mol/
The catalyst was poured into 43 ml of a silver nitrate aqueous solution, dried under reduced pressure while stirring, and further dried at 110° C. for 16 hours to obtain catalyst 7. When the strontium, cobalt and silver contents of this catalyst were investigated by chemical analysis, strontium was 0.23 times the Al2O3 mole number of the zeolite, and cobalt was 2 times the mole number of Al2O3 in the zeolite.
The price was 1.12 times higher, and silver was 0.4 times higher.

Example 8 <Evaluation of catalyst activity> Catalyst 1~
7 and Comparative Catalysts 1 to 2 were each press-molded and then crushed to obtain 1.
The particles were sized to 2 to 20 mesh, and 1 g of the particles was filled into an atmospheric fixed bed reaction tube. A gas having the composition shown below (hereinafter referred to as reaction gas) was supplied at a rate of 1000 ml/min. While circulating in 5
The temperature was raised to 00° C. and held for 0.5 hours as a pretreatment. Thereafter, the temperature was kept constant at every 50°C between 300°C and 500°C, and the catalytic activity at each temperature was measured. Table 1 shows the NO purification rate after reaching steady state at each temperature. The NO purification rate is a value determined by the following formula.

[0036]

[Equation 1] In addition, with any catalyst, carbon monoxide is heated at 450°C or higher,
Almost no hydrocarbons were detected at temperatures above 400°C.

[0037]

[0038]

[Table 1] Example 9 <Durability evaluation of catalyst> Catalyst 1 and comparative catalyst 1 were heated at 800°C while flowing the reaction gas shown in Table 1.
After carrying out a durability treatment for 5 hours, the catalyst activity was measured in the same manner as in Example 8. Table 2 shows the NO purification rate after reaching steady state at each temperature.

[0039]

[Table 2]

[0040]

Effects of the Invention From Tables 1 and 2, it is clear that the catalyst of the present invention has a higher ability to purify oxygen-excess exhaust gas, particularly nitrogen oxides, than the comparative catalyst. Therefore, by bringing the catalyst of the present invention into contact with exhaust gas, nitrogen oxides, carbon monoxide, and hydrocarbons can be purified at a high purification rate even if the exhaust gas contains excess oxygen.

Claims (1)

[Claims] 1. From an oxygen-rich exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, characterized in that it contains cobalt, alkaline earth metals and silver in a zeolite having a SiO2/Al2O3 molar ratio of at least 15. , exhaust gas purification catalyst that removes nitrogen oxides, carbon monoxide and hydrocarbons.