JPH04219147A - 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, Cu and/or Rh. CONSTITUTION:The zeolite having an SiO2/Al2O3 molar ratio of at least 15 contains Co, rare earth metals, such as La, and Cu and/or Rh, preferably, in a Co amount of 10-150mol%, in a rare earth metal amount of 10-100mol%, in a Cu and/or Rh in an amount of 5 to 150mol%, and in the total amounts of 100-250mol% of the 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 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, the activity of these conventionally proposed catalysts deteriorates significantly when used at high temperatures for long periods of time.
Improvements were needed 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 even higher nitrogen oxide purification ability at lower temperatures.

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
It has been discovered that nitrogen oxide purification ability at low temperatures can be improved by further containing copper and/or rhodium in an exhaust gas purification catalyst that is a zeolite with a /Al2O3 molar ratio of at least 15 and contains cobalt and rare earth metals. , we have completed the present invention.

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 copper and/or rhodium, 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 copper and/or rhodium and having a SiO2/Al2O3 molar ratio of at least 15.

[0015] The above zeolite generally has xM2/nO
・The composition of Al2O3・ySiO2・zH2O (where n is the valence of the cation M, x is a number in the range of 0.8 to 1.2, y is a number of 2 or more, and z is a number of 0 or more) Among them, 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 if the SiO2/Al2O3 molar ratio is less than 15, the heat resistance and durability of the zeolite itself will be low. is not obtained. Generally, the SiO2/Al2O3 molar ratio is 15 to 10.
A value of about 00 is 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 copper and/or rhodium. Copper and rhodium may be contained at the same time, but only one of them may be contained. The method of incorporating cobalt, rare earth metals, and copper and/or rhodium 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 copper and/or rhodium, the concentrations of cobalt and rare earth metals and copper and/or rhodium ions in the aqueous solution are as follows:
It can be arbitrarily set depending on the ion exchange rate of the target catalyst. Rare earth metal ions include La, Ce
, Pr, Nd, Y, etc. can be used. Further, cobalt and rare earth metals and copper and/or rhodium 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 and rare earth metals and copper and/or rhodium is a molar ratio to the number of moles of alumina in the zeolite, and the content of cobalt is 0.1 to 0.1.
1.5 times, rare earth metals 0.1 to 1 times, copper or rhodium 0.05 to 1.5 times, and the total amount of cobalt and rare earth metals and copper and/or rhodium is 1
．． 0 to 2.5 times is preferable.

Samples containing cobalt and rare earth metals and copper and/or rhodium 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. Alternatively, zeolite may be formed in advance and the formed body may contain cobalt, rare earth metals, and copper and/or rhodium. 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・40SiO
2 Ammonium type ZSM-5 prepared by ion exchange with ammonium chloride aqueous solution; 200 g was mixed with a concentration of 1.
The mixture was poured into 1,800 ml of an aqueous solution of 0.09 mol/l 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 cobalt acetate (I
I) The mixture was poured into 1800 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, 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 lanthanum content was 0.0% relative to the number of moles of Al2O3 in the zeolite.
33 times more cobalt was contained as divalent 1.13 times more.

Example 1 <Preparation of Catalyst 1> 200 g of ammonium type ZSM-5 obtained in Comparative Example 1 was prepared at a concentration of 1.09.
The mixture was poured into 1800 ml of a 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.
Pour into 1800 ml of an aqueous solution of tetrahydrate and heat at 80°C for 16
Stir for hours. After solid-liquid separation of slurry, zeolite cake
The same operation was carried out by putting the sample into the aqueous solution having the above composition prepared again. After solid-liquid separation, wash thoroughly with water and incubate at 110°C for 20
After drying for hours, cobalt and lanthanum-containing ZSM-5 was obtained. Obtained cobalt and lanthanum-containing ZSM-5;1
5g to 43ml of copper acetate aqueous solution with a concentration of 0.05mol/l.
1, and dried under reduced pressure while stirring, and further dried at 110° C. for 16 hours to obtain catalyst 1. This catalyst lanthanum,
When the content of cobalt and copper was investigated by chemical analysis, it was found that the content of lanthanum was 0.0% compared to the number of moles of Al2O3 in zeolite.
32 times, cobalt is 0.42 times as divalent, copper is 0.4
twice included.

Example 2 <Preparation of Catalyst 2> Catalyst 2 was prepared in the same manner as in Example 1 except that copper acetate was replaced with rhodium nitrate. When the content of lanthanum, cobalt and rhodium in this catalyst was investigated by chemical analysis, it was found that lanthanum is 0.32 times the Al2O3 mole of zeolite, cobalt is 0.42 times as divalent, and rhodium is 0.4 times.
twice included.

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 3 <Preparation of Catalyst 3> 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 aqueous copper nitrate solution, dried under reduced pressure while stirring, and further dried at 110° C. for 16 hours to obtain catalyst 3. When the content of cerium, cobalt, and copper in this catalyst was investigated by chemical analysis, it was found that cerium was 0.13 times the number of moles of Al2O3 in the zeolite, and cobalt was 1 times as divalent.
．． It contained 12 times more copper, and 0.4 times more copper.

Example 4 <Preparation of Catalyst 4> Catalyst 4 was prepared in the same manner as in Example 3 except that copper nitrate was replaced with rhodium nitrate. When the content of cerium, cobalt, and rhodium in this catalyst was investigated by chemical analysis, it was found that cerium is 0.13 times the Al2O3 mole of zeolite, cobalt is 1.12 times as divalent, and rhodium is 0.4 times.
twice included.

Example 5 <Evaluation of catalyst activity> Catalyst 1~
4 and Comparative Catalysts 1 and 2 were crushed after press molding 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 250°C and 450°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.

[0033]

[Formula 1] Note that with the comparative catalyst, carbon monoxide was hardly detected at temperatures above 450°C and hydrocarbons were hardly detected at temperatures above 400°C.
In the example catalyst, carbon monoxide was hardly detected at temperatures of 400°C or higher, and hydrocarbons were hardly detected at temperatures of 350°C or higher.

[0034]

[0035]

[Table 1]

[0036]

Effects of the Invention From Table 1, the catalyst of the present invention has a higher ability to purify oxygen-excess exhaust gas, especially nitrogen oxides at low temperatures, than the comparative catalyst. Therefore, by bringing the catalyst of the present invention into contact with exhaust gas, even if the exhaust gas contains excess oxygen, the exhaust gas can be purified at a lower temperature.

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 copper and/or rhodium 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.