JPH04219150A - Exhaust gas purification catalyst - Google Patents

Abstract

PURPOSE:To remove nitrogen oxide, CO, and hydrocarbon at the same time from the exhaust gas excess in oxygen 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 Mn and alkaline earth metals. CONSTITUTION:The zeolite having an SiO2/Al2O3 molar ratio of at least 15 contains Mn and alkaline earth metals, such as Ca, preferably, in an amount of alkaline earth metal of 10-100mol% and in an amount of Mn of 30-200mol%, and in the total amounts of 80-250mol% of the alumina in the zeolite, thus permitting nitrogen oxide, CO, and hydrocarbon to be removed efficiently at the same time 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

[Industrial Application Field] The present invention relates to nitrogen oxides in exhaust gas emitted from internal combustion engines such as automobile engines,
The present invention relates to an exhaust gas purification catalyst that removes carbon monoxide and hydrocarbons, and particularly relates to a catalyst that purifies oxygen-excess combustion exhaust gas.

0002

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

[0003] Also, in recent gasoline engines,
Lean combustion has become necessary for the purpose of improving fuel efficiency and reducing carbon dioxide emissions. However, the exhaust gas of this lean-burn gasoline engine is an oxygen-rich atmosphere, so the conventional three-way catalyst described above cannot be used.
No method has been put into practical use to remove harmful components.

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

It is known that a zeolite catalyst obtained by ion-exchanging transition metals can be used in the same manner as a conventional three-way catalyst. For example, Japanese Patent Application Laid-Open No. 1-130735 discloses a catalyst that can selectively reduce nitrogen oxides even in oxygen-excess exhaust gas that contains trace amounts of unburned carbon monoxide and reducing agents such as hydrocarbons. is proposed.

However, the activity of the conventionally proposed catalyst deteriorates significantly when used at high temperatures for a long period of time.
There are still points to be improved in terms of durability, catalytic performance, etc., and it has not yet been put into practical use.

[0007]

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art as described above.
The present invention provides a catalyst that simultaneously removes nitrogen oxides, carbon monoxide, and hydrocarbons, is resistant to thermal deterioration, has excellent durability, and has high catalytic activity.

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

[0009]

[Means for Solving the Problems] The present inventors have completed the present invention as a result of intensive study on the above-mentioned problems.

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 zeolite catalyst having a silica/alumina molar ratio. An exhaust gas purification catalyst characterized by being a zeolite of at least 15 or more and containing manganese and an alkaline earth metal, 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.

[0012] 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) However, the zeolite used in the present invention must have a silica/alumina molar ratio of 15 or more. The upper limit of the silica/alumina molar ratio is not particularly limited, but if the silica/alumina molar ratio is less than 15, the heat resistance and durability of the zeolite itself will be low, and the catalyst will not have sufficient heat resistance and durability. I can't. Generally, the silica/alumina 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, mordenite, Y ,ZSM-5,ZS
Zeolites such as M-11, ZSM-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.

[0014] It is essential that the zeolite used in the present invention contains manganese and alkaline earth metals. The method for incorporating manganese and alkaline earth metals is not particularly limited, and ion exchange, impregnating and supporting, etc. can be used, but ion exchange is most preferred.

In the ion exchange of manganese, the salts may be divalent water-soluble salts, such as nitrates, chlorides, acetates or sulfates, preferably acetates. In the ion exchange of manganese, there is no particular restriction on the number of exchanges, and if the exchange rate is low, the ion exchange may be repeated two or more times. There is no particular upper limit to the number of ion exchanges, but 2
~5 times is enough.

The ion exchange method may be a general ion exchange method such as adding manganese salt to a zeolite slurry and stirring it, or adding zeolite to an aqueous solution of manganese salt and stirring it. In other words, the liquid temperature is preferably 20 to 100°C, preferably 40 to 90°C. The concentration of manganese salt in the aqueous solution is 0.01 to 1 mol/l,
Preferably it is 0.1 to 1 mol/l. 0.01mo
If it is less than 1/1, a large amount of solution is required, resulting in poor operability. Moreover, if it is larger than 1 mol/l, the ion exchange rate will not improve to the extent commensurate with the amount of reagent added.

The solid-liquid ratio between the zeolite and the aqueous solution is not particularly limited, but it is sufficient that sufficient stirring is performed, and the solid content concentration of the slurry is preferably 5 to 50%.

The salts used in the ion exchange of alkaline earth metals may be water-soluble, preferably nitrates and chlorides, which have high solubility. As an alkaline earth metal, Be
, Mg, Ca, Sr, Ba, and Ra, preferably Sr or Ba.

The ion exchange method may be the same as that for manganese, and the concentration of the alkaline earth metal salt in the aqueous solution is 0.01 to 5 mol/l, preferably 0.1 to 2 mol/l.
l/l is good.

The ion-exchanged sample is subjected to solid-liquid separation, washing,
After drying, it is used as a catalyst. It can also be used after being fired if necessary.

[0021]Alkaline earth metals and manganese can also be supported by evaporation to dryness or the like. The evaporation to dryness may be carried out by any conventional method, such as by introducing the zeolite into an aqueous solution containing an alkaline earth metal or manganese, and evaporating water as a solvent in a dryer or the like. The concentration of the alkaline earth metal and manganese salt in the aqueous solution is not particularly determined, but it is sufficient that the alkaline earth metal or manganese is uniformly deposited, and is usually 0.01 to 1 mol/l.

There is no particular restriction on the order in which the alkaline earth metal and manganese are added, but when they are added using ion exchange, the order of the alkaline earth metal and manganese is preferred. Further, ion exchange may be performed simultaneously in the coexistence of manganese ions and alkaline earth metal ions.

The content of alkaline earth metals and manganese is such that the molar ratio of alkaline earth metals to the number of moles of alumina in the zeolite is 0.1 to 1 times, manganese 0.3 to 2 times, and alkaline It is preferable that the total amount of earth metal and manganese is 0.8 to 2.5 times. When the amount of alkaline earth metal is less than 0.1 times, the effect of improving durability and catalytic activity may be small, and when it is more than 1 times, it is difficult to obtain an effect commensurate with the amount added. If the amount of manganese is less than 0.3 times, it may not be suitable for use as a catalyst, and if it is more than 2 times, it is difficult to obtain durability and activity commensurate with the amount added.

The silica/alumina molar ratio of the exhaust gas purification catalyst of the present invention is substantially the same as the silica/alumina molar ratio of the zeolite base material used. Furthermore, the crystal structure of the exhaust gas purification catalyst is not essentially different before and after ion exchange.

The exhaust gas purification catalyst of the present invention can be used by being mixed with a binder such as a clay mineral and molded, or by molding zeolite in advance and incorporating manganese into the molded product through ion exchange. You can also do that. Examples of binders used when molding this zeolite include clay minerals such as kaolin, attapulgite, montmorillonite, bentonite, allophane, and sepiolite;
Examples include metal oxides such as silica, alumina, and silica-alumina. Alternatively, a binderless zeolite molded body synthesized directly without using a binder may be used. Furthermore, zeolite can be wash-coated onto a honeycomb-shaped substrate made of cordierite or metal.

The removal of nitrogen oxides, carbon monoxide, and hydrocarbons from the oxygen-excess exhaust gas is achieved by contacting the oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbons with the exhaust gas purification catalyst of the present invention. This can be done by letting The oxygen-excessive exhaust gas targeted by 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. This refers to gas, and examples of such exhaust gas include:
A specific example is exhaust gas emitted from an internal combustion engine such as an automobile, particularly exhaust gas in a state where the air-fuel ratio is high (so-called lean region).

[0027] The above exhaust gas catalyst does not change its performance in any way even if it is applied to exhaust gas containing carbon monoxide, hydrocarbons and hydrogen and not in excess of oxygen.

[0028]

[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.

Example 1 <Preparation of catalyst 1> Ammonium type ZSM-5 with a silica/alumina molar ratio of 40; 20
g was added to 180 g of an aqueous solution of barium chloride having a concentration of 1.09 mol/l, and the mixture was stirred at 80° C. for 16 hours. After solid-liquid separation of the slurry, the zeolite cake was poured into a barium aqueous solution of the above concentration prepared again, and the same operation was repeated twice. After solid-liquid separation, wash thoroughly with water, and then add 0.23 mol/
1 of an aqueous solution of manganese(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 manganese 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 Catalyst 1.

When the barium and manganese contents of this catalyst were investigated by chemical analysis, it was found that barium was contained 0.66 times and manganese was contained 0.87 times as divalent, relative to the number of moles of alumina in the zeolite.

Example 2 <Preparation of Catalyst 2> Ion exchange was performed in the same manner as in Example 1, except that strontium was used as the alkaline earth metal. This catalyst was designated as Catalyst 2, and when the strontium and manganese contents of this catalyst were investigated by chemical analysis, it was found that strontium was contained 0.53 times, and manganese was contained 0.85 times as divalent, relative to the number of moles of alumina in the zeolite. Ta.

Example 3 <Preparation of Catalyst 3> Ion exchange was carried out in the same manner as in Example 1, except that magnesium was used as the alkaline earth metal. This catalyst was designated as Catalyst 3, and when the magnesium and manganese contents of this catalyst were investigated by chemical analysis, magnesium was 0.31 times the number of moles of alumina in the zeolite, and manganese was 0.8 as divalent.
It contained three times as much.

Example 4 <Preparation of Catalyst 4> Ion exchange was carried out in the same manner as in Example 1, except that calcium was used as the alkaline earth metal. This catalyst was designated as Catalyst 4, and when the calcium and manganese contents of this catalyst were investigated by chemical analysis, it was found that calcium was contained 0.29 times and manganese was contained 0.82 times as divalent, relative to the number of moles of alumina in the zeolite. Ta.

Example 5 <Preparation of catalyst 5> Ammonium type ZSM-5 with a silica/alumina molar ratio of 40; 20
g of manganese(II) acetate at a concentration of 0.23 mol/l.
The mixture was poured into 180 g 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, wash thoroughly with water and continue to reduce the concentration to 1.09.
Pour into 180 g of a mol/l aqueous solution of barium chloride,
The mixture was stirred at 80°C for 16 hours. After solid-liquid separation, wash thoroughly with water,
The catalyst was dried at 110° C. for 10 hours and designated as Catalyst 5.

When the barium and manganese contents of this catalyst were investigated by chemical analysis, it was found that barium was contained 0.58 times and manganese was contained 0.82 times as divalent, relative to the number of moles of alumina in the zeolite.

Example 6 <Preparation of catalyst 6> Ammonium type ZSM-5 with a silica/alumina molar ratio of 40; 20
g of manganese(II) acetate at a concentration of 0.23 mol/l.
The mixture was poured into 180 g 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, and the manganese content of this zeolite was investigated by chemical analysis, and it was found that it contained 1.03 times the manganese divalent content compared to the number of moles of alumina in the zeolite. . Further, 20 g of the zeolite was added to 29 ml of a 0.05 mol/l barium nitrate aqueous solution containing an amount of barium equivalent to 1 wt% as metallic barium, and dried at 85 ° C. for 10 hours and then at 110 ° C. for 10 hours. Evaporation to dryness was performed. This catalyst was designated as Catalyst 6.

Comparative Example 1 <Preparation of Comparative Catalyst 1> Ammonium type ZSM-5 with a silica/alumina molar ratio of 40;
20g of manganese acetate (I) with a concentration of 0.23mol/l.
I) Pour into 180 g 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, thoroughly washed with water and heated at 110°C for 10
This catalyst was designated as Comparative Catalyst 1.

When the manganese content of this catalyst was investigated by chemical analysis, it was found that the manganese content was 1.02 times the number of moles of alumina in the zeolite as divalent manganese.

Comparative Example 2 <Preparation of Comparative Catalyst 2> Ammonium type ZSM-5 with a silica/alumina molar ratio of 40;
20g was added to an aqueous solution of copper(II) acetate hydrate with a concentration of 0.1 mol/l, which was weighed so that it was twice the number of moles of alumina contained therein, and immediately 2.5
% ammonia water was added to adjust the pH of the aqueous solution to 10.5,
Stirred at room temperature for 16 hours. After solid-liquid separation, wash thoroughly with water,
The catalyst was dried at 10° C. for 10 hours and designated as Comparative Catalyst 2.

When the copper content of this catalyst was investigated by chemical analysis, it was found that it contained 1.04 times the number of moles of alumina in the zeolite as divalent copper.

Comparative Example 3 <Preparation of Comparative Catalyst 3> Ammonium type ZSM-5 with a silica/alumina molar ratio of 40;
20 g was added to 180 g of an aqueous solution of barium chloride with a concentration of 1.09 mol/l, and the mixture was stirred at 80° C. for 16 hours. After solid-liquid separation of the slurry, the zeolite cake was poured into a barium aqueous solution of the above concentration prepared again, and the same operation was repeated twice. After solid-liquid separation, it was thoroughly washed with water and dried at 110° C. for 10 hours to obtain Comparative Catalyst 3. When the barium content of this catalyst was investigated by chemical analysis, it was found that the barium content was 0.86 times the number of moles of alumina in the zeolite.

Example 7 <Evaluation of catalyst activity> Example 1
The catalysts 1 to 6 prepared in steps 1 to 6 were press-molded and then crushed to obtain 12
The particles were sized to ~20 mesh, and 0.65 grams thereof was filled into an atmospheric fixed bed reaction tube. Gases with the composition shown below (hereinafter referred to as
(referred to as reaction gas) at 600 ml/min. distributed in 5
The temperature was raised to 00° C. and held for 0.5 hours as a pretreatment. After that, the temperature was lowered to 200°C, and the temperature was lowered to 5°C/min. The temperature was raised to 800°C at a heating rate of
). The temperature was continued to be maintained at 800° C. for 5 hours, the circulating gas was changed to nitrogen, and the mixture was allowed to cool. The mixture was cooled to room temperature, and the temperature was raised to 200° C. using the flowing gas as a reaction gas, and maintained for 0.5 hours as a pretreatment. After that, 5°C/min. The temperature was raised to 800°C at a heating rate of
. Table 1 summarizes the results of evaluating the durability of the catalyst based on the change in the maximum purification rate in Reaction 1 and Reaction 2, using NO as nitrogen oxide, which is a harmful component in the reaction gas. It can be said that a catalyst with a smaller decrease in the maximum purification rate in Reaction 1 and Reaction 2, that is, a catalyst with a higher maximum purification rate in Reaction 2, has higher heat resistance and durability. The NO purification rate is expressed by the following formula.

[0043]

Comparative Example 4 <Evaluation of activity of comparative catalyst> Table 1 shows the results of evaluating the activity of comparative catalysts 1 to 3 obtained in Comparative Examples 1 to 3 using the same method as in Example 7.

[0044]

[Table 1]

[0045]

Effects of the Invention From Table 1, the catalyst of the present invention has a higher exhaust gas purifying ability in oxygen-excess exhaust gas than the comparative catalyst in both the initial activity and the activity after being held at 800°C for 5 hours in the reaction gas.
It has the effect of exhibiting extremely excellent heat resistance and durability. Therefore, by bringing the catalyst of the present invention into contact with exhaust gas, it is possible to purify nitrogen oxides, carbon monoxide, and hydrocarbons even in an oxygen-excess state.

Claims (1)

[Claims] Claim 1: A zeolite catalyst for removing nitrogen oxides, carbon monoxide and hydrocarbons from oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, the zeolite catalyst comprising silica/
An exhaust gas purification catalyst characterized by being a zeolite having an alumina molar ratio of at least 15 or more, and containing manganese and an alkaline earth metal.