JPH04219148A - 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 motorcars 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, rare earth metals, Ni and/or Zn. CONSTITUTION:The zeolite having an SiO2/Al2O3 molar ratio of at least 15 contains Co, rare earth metals, such as La, and Ni and/or Zn, preferably, in a Co amount of 10-150mol%, in a rare earth meal amount of 10-100mol%, in a Ni and/or Zn in an amount of 5-200mol%, and in the total amounts of 100-250mol% of the alumina in the zeolite, thus permitting nitrogen oxide, CO, and hydrocarbon to be removed efficiently at the same time in a comparatively wide temperature range from the exhaust gas exhausted from the internal combustion engines of motorcars 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 characterized by being a zeolite having a SiO2/Al2O3 molar ratio of at least 15 and containing cobalt and rare earth metals. (Patent Application No. 149203/1999).

[0008]

[Problems to be Solved by the Invention] However, although the exhaust gas purification catalyst proposed in Japanese Patent Application No. 2-149203 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 SiO2
/Al2O3 molar ratio of at least 15 or more and an exhaust gas purification catalyst containing cobalt and rare earth metals has been found to improve nitrogen oxide purification ability by further containing nickel and/or zinc,
The present invention has now been 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 and rare earth metals and nickel and/or zinc, and a combustion 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 bringing the exhaust gases into contact with each other.

The present invention will be explained in detail below.

The exhaust gas purification catalyst according to the present invention is a zeolite containing cobalt and rare earth metals, and nickel and/or zinc and having a SiO2/Al2O3 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.

The zeolite used in the present invention contains cobalt and rare earth metals as well as nickel and/or zinc. Nickel and zinc may be contained at the same time, but only one of them may be contained. The method of incorporating cobalt, rare earth metals, and nickel and/or zinc into zeolite is not particularly limited, but generally includes ion exchange using a water-soluble salt, impregnation support method, evaporation drying method, etc. I can do it. When containing each element, each element may be contained sequentially or all at once.

[0018] When containing cobalt and rare earth metals and nickel and/or zinc, the concentrations of cobalt and rare earth metals and nickel and/or zinc ions in the aqueous solution can be arbitrarily set depending on the desired ion exchange rate of the catalyst. I can do it. Rare earth metal ions include La,
Ce, Pr, Nd, Y, etc. can be used. Further, cobalt and rare earth metals and nickel and/or zinc ions can be used in the form of soluble salts, and nitrates, acetates, oxalates, hydrochlorides, etc. can be preferably used as the soluble salts.

[0019] The content of cobalt, rare earth metals, and nickel and/or zinc is a molar ratio relative to the number of moles of alumina in the zeolite, and the content of cobalt is 0.1.
~1.5 times, preferably 0.1 to 1 times for rare earth metals, and 0.05 to 2 times for nickel or zinc, and the total amount of cobalt and rare earth metals and nickel and/or zinc is 1.0 to 2 times. .5 times is preferable.

Samples containing cobalt and rare earth metals and nickel and/or zinc are generally subjected to solid-liquid separation,
Used after 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. Alternatively, zeolite may be formed in advance and the formed body may contain cobalt, rare earth metals, and nickel and/or zinc. 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. Moreover, zeolite can be wash-coated onto a cordierite or metal honeycomb base material.

[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;
1 of an aqueous solution of lanthanum chloride, and
Stirred at ℃ 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 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 lanthanum and cobalt contents of this catalyst were investigated by chemical analysis, it was found that the zeolite A
The amount of lanthanum was 0.33 times the number of moles of 12O3, and the amount of cobalt was 1.13 times as divalent.

Example 1 <Preparation of Catalyst 1> 15 g of Comparative Catalyst 1 prepared in Comparative Example 1 was added to 43 ml of an aqueous nickel nitrate solution with a concentration of 0.05 mol/l, dried under reduced pressure while stirring, and further heated at 110°C. After drying for 16 hours, Catalyst 1 was obtained. When the content of lanthanum, cobalt and nickel in this catalyst was investigated by chemical analysis, it was found that Al2O3 of zeolite
Lanthanum is 0.33 times the number of moles, cobalt is 2 times
It contained 1.13 times the value and 0.4 times the nickel content.

Example 2 <Preparation of Catalyst 2> 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 lanthanum 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 2 was prepared in the same manner as in Example 1. When the content of lanthanum, cobalt and nickel in this catalyst was investigated by chemical analysis, it was found that Al2O3 of zeolite
Lanthanum is 0.32 times the number of moles, cobalt is 2 times
It contained 0.42 times the value and 0.4 times the nickel content.

Example 3 <Preparation of Catalyst 3> Catalyst 3 was prepared in the same manner as in Example 2 except that nickel nitrate was replaced with nickel chloride. When the content of lanthanum, cobalt and nickel in this catalyst was investigated by chemical analysis, it was found that the content of lanthanum was 0.5% compared to the number of moles of Al2O3 in the zeolite.
32 times as much, cobalt as divalent 0.42 times, and nickel as 0.4 times.

Example 4 <Preparation of Catalyst 4> Catalyst 4 was prepared in the same manner as in Example 2 except that nickel nitrate was replaced with nickel acetate. When the content of lanthanum, cobalt and nickel in this catalyst was investigated by chemical analysis, it was found that the content of lanthanum was 0.5% compared to the number of moles of Al2O3 in the zeolite.
32 times as much, cobalt as divalent 0.42 times, and nickel as 0.4 times.

Comparative Example 2 <Preparation of Comparative Catalyst 2> 200 g of ammonium type ZSM-5 obtained in Comparative Example 1 was added to 1800 ml of an aqueous solution of cerium 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 1800 ml of an aqueous solution of 0.23 mol/l cobalt (II) acetate tetrahydrate, and
Stirred at ℃ 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,
It was dried at ℃ for 10 hours to obtain Comparative Catalyst 2. When the cerium and cobalt contents of this catalyst were investigated by chemical analysis, it was found that cerium was contained 0.13 times and cobalt was contained 1.12 times as divalent relative to the number of moles of Al2O3 in the zeolite.

Example 5 <Preparation of catalyst 5> Comparative catalyst 2; 15 g prepared in Comparative Example 2 was mixed into a concentration of 0.05 mol/
1 of nickel nitrate aqueous solution, dried under reduced pressure while stirring, and further dried at 110°C for 16 hours.
I got it. When the cerium, cobalt and nickel contents of this catalyst were investigated by chemical analysis, it was found that the zeolite Al2O
With respect to 3 moles, cerium was contained 0.13 times, cobalt was contained 1.12 times as divalent, and nickel was contained 0.4 times.

Comparative Example 3 <Preparation of Comparative Catalyst 3> Comparative Catalyst 3 was prepared in the same manner as Comparative Example 2 except that yttrium was used as the rare earth metal. When the yttrium and cobalt contents of this catalyst were investigated by chemical analysis, it was found that yttrium is 0.2% of the number of moles of Al2O3 in zeolite.
It contained 8 times more cobalt, and 0.98 times more cobalt as divalent.

Example 6 <Preparation of catalyst 6> Comparative catalyst 3; 15 g prepared in Comparative Example 3 was mixed into a concentration of 0.05 mol/
1 of nickel nitrate aqueous solution, dried under reduced pressure while stirring, and further dried at 110°C for 16 hours.
I got it. When the yttrium, cobalt and nickel contents of this catalyst were investigated by chemical analysis, it was found that the zeolite Al
With respect to the number of moles of 2O3, yttrium was contained 0.28 times, cobalt was contained 0.98 times as divalent, and nickel was contained 0.4 times.

Comparative Example 4 <Preparation of Comparative Catalyst 4> Comparative Catalyst 4 was prepared in the same manner as Comparative Example 2 except that praseodymium was used as the rare earth metal. When the praseodymium and cobalt contents of this catalyst were investigated by chemical analysis, it was found that praseodymium was contained 0.14 times and cobalt was contained 1.04 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 4 prepared in Comparative Example 4 was mixed at a concentration of 0.05 mol/
1 of nickel nitrate aqueous solution, dried under reduced pressure while stirring, and further dried at 110°C for 16 hours.
I got it. When the praseodymium, cobalt and nickel contents of this catalyst were investigated by chemical analysis, it was found that the zeolite A
With respect to the number of moles of l2O3, praseodymium is 0.14 times, cobalt is 1.04 times as divalent, and nickel is 0.4 times.
twice included.

Comparative Example 5 <Preparation of Comparative Catalyst 5> 20 g of ammonium type ZSM-5 obtained in Comparative Example 1 was
．． 23 mol/l aqueous solution of nickel acetate tetrahydrate 18
0ml and stirred at 80°C for 16 hours. Slurry
After solid-liquid separation, the zeolite cake was again put into 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.
I got it. When the nickel content of this catalyst was investigated by chemical analysis, it was found that the nickel content was 1.40 times as divalent compared to the number of moles of Al2O3 in the zeolite.

Example 8 <Preparation of Catalyst 8> Catalyst 8 was prepared in the same manner as in Example 1 except that nickel nitrate was replaced with zinc nitrate. When the content of lanthanum, cobalt and zinc in this catalyst was investigated by chemical analysis, it was found that the zeolite A
With respect to the number of moles of 12O3, lanthanum was contained 0.33 times, cobalt was contained 1.13 times as divalent, and zinc was contained 0.4 times.

Example 9 <Preparation of Catalyst 9> Catalyst 9 was prepared in the same manner as in Example 2 except that nickel nitrate was replaced with zinc nitrate. When the content of lanthanum, cobalt and zinc in this catalyst was investigated by chemical analysis, it was found that the zeolite A
With respect to the number of moles of 12O3, lanthanum was contained 0.32 times, cobalt was contained 0.42 times as divalent, and zinc was contained 0.4 times.

Example 10 <Preparation of Catalyst 10> Catalyst 10 was prepared in the same manner as in Example 5 except that nickel nitrate was replaced with zinc nitrate. When the cerium, cobalt, and zinc contents of this catalyst were investigated by chemical analysis, the cerium content was 0.13 times the Al2O3 mole number of the zeolite.
Cobalt was contained 1.12 times as divalent, and zinc was contained 0.4 times.

Example 11 <Evaluation of catalyst activity> Catalyst 1
-10 and Comparative Catalysts 1 to 5 were each press-molded and crushed to size 12 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. The temperature was raised to 500° C. and maintained for 0.5 hours while circulating at a temperature of 500° C. for 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.

[0042]

[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.

[0043]

[0044]

[Table 1] Example 12 <Durability evaluation of catalyst> For each catalyst,
After carrying out a durability treatment at 800° C. for 5 hours while flowing the reaction gas shown above, the catalytic activity was measured in the same manner as in Example 11. Table 2 shows the NO purification rate after reaching steady state at each temperature.
Shown below.

[0045]

[Table 2]

[0046]

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. An oxygen-enriched zeolite containing nitrogen oxides, carbon monoxide and hydrocarbons, characterized in that it contains cobalt and rare earth metals and nickel and/or zinc in a zeolite with a SiO2/Al2O3 molar ratio of at least 15. Exhaust gas purification catalyst that removes nitrogen oxides, carbon monoxide, and hydrocarbons from exhaust gas.