JPH03196842A - Catalyst for purification of exhaust gas and method for using the same - Google Patents

Abstract

PURPOSE:To obtain a catalyst for purification of exhaust gas contg. excess oxygen with high activity and long service life by incorporating cobalt and an alkaline earth metal into zeolite having a certain ratio of SiO2 to Al2O3. CONSTITUTION:A zeolite catalyst for removal of NOx, CO and hydrocarbon from exhaust gas contg. excess oxygen is made of zeolite having >=15 molar ratio of SiO2 to Al2O3, and cobalt and an alkaline earth metal such as Be or Mg are incorporated into the zeolite. When the resulting catalyst is used, NOx, CO and hydrocarbon are simultaneously removed from exhaust gas contg. excess oxygen. The catalyst hardly causes heat deterioration and has superior durability and high activity.

Description

Detailed Description of the Invention (Industrial Application Field) The present invention relates to an exhaust gas purification catalyst that removes nitrogen oxides, carbon oxides, and hydrocarbons from exhaust gas discharged from an internal combustion engine such as an automobile engine. In particular, it relates to a method for purifying oxygen-excess fuel exhaust gas.

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

Furthermore, in recent years, gasoline engines have become required to perform lean combustion in order to improve fuel efficiency and reduce carbon dioxide emissions. However, since the exhaust gas of this lean-burn gasoline engine is an oxygen-rich atmosphere, the conventional three-way catalyst as described above cannot be used, and no method for removing harmful components has been put into practical use.

There are also known methods for removing nitrogen oxides, especially nitrogen oxides, from such oxygen-excess exhaust gas, such as adding a reducing agent such as ammonia, and removing nitrogen oxides by absorbing them in alkali. This method is not an effective method for use with automobiles, which are mobile sources, and its applicability is limited.

It is known that a theolite catalyst with ion-exchanged transition metals can be used in the same way as a conventional three-way catalyst. For example, Japanese Patent Application Laid-Open No. 1-130735 discloses that M[ is proposed.

However, the activity of this conventionally proposed catalyst deteriorates significantly when used at high temperatures for long periods of time, and there is still room for further improvement in terms of durability, catalytic performance, etc., and it has yet to be put into practical use. (Problem to be Solved by the Invention) The purpose of the present invention was to solve the problems of the prior art as described above. The purpose of the present invention is to provide a catalyst that simultaneously removes carbon monoxide, 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.

(Means for Solving the Problems) As a result of intensive study on the above-mentioned problems, the inventors have found that
The present invention has now been completed.

That is, the present invention provides a theolite catalyst for removing nitrogen oxides, carbon monoxide, and hydrocarbons from oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbons,
An exhaust gas purification catalyst characterized by being a zeolite having a molar ratio of at least 15 to iO□/8920 and containing cobalt and an alkaline earth metal, and the jJ
Provided is a method for removing nitrogen oxides, carbon monoxide, and hydrocarbons in exhaust gas, the method comprising bringing combustion exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbons into contact with a residue purification catalyst. It is.

The present invention will be explained in detail below.

The above zeolite is generally XM>yIIO'Alxo3'MSIO2'ZH20
(However, 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 must have a molar ratio of 5i (h/A4203 of 15 or more. 5i02
Ha perfect. The upper limit of the 5r02/Altos molar ratio is not particularly limited, but if the 5r02/Altos molar ratio is less than 15, the heat resistance and durability of the zeolite itself will be low, making it difficult to obtain sufficient heat resistance and durability of the catalyst. I can't do it. -Numerically 5i0
Those having a 2/^92o3 molar ratio of about 10 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, ZSM-12,
Zeolites such as zSM-20 and mordenite can be used. In addition, these zeolites can be converted into NH4'' type or H
It can also be used as a catalyst in the present invention after being ion-exchanged into a mold.

It is essential that the zeolite used in the present invention contains cobalt and alkaline earth metals. The method for incorporating cobalt and alkaline earth metals is not particularly limited, and ion exchange, impregnation and support, etc. can be used, but ion exchange is most preferred.

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

Ion exchange methods include adding alkaline earth metal salts to a zeolite slurry and stirring, or adding zeolite to an aqueous solution of alkaline earth metal salts and stirring.
Numerical ion exchange methods such as these may be used. In other words, the liquid temperature is preferably 20 to 100°C, preferably 40 to 90°C. The concentration of alkaline earth metal salt in the aqueous solution is 0.01
~5 moR/L, preferably 0.1-2 mol/
L is good. The solid-liquid ratio between the zeolite and the aqueous solution is not particularly limited, as long as sufficient stirring is performed, and the solid content concentration of the slurry is preferably 5 to 50%.

In the ion exchange of cobalt, the salts may be aqueous salts, preferably divalent acetates. In cobalt ion exchange, there is no particular restriction on the number of times of exchange, and it is sufficient as long as the exchange rate is high, or if the exchange rate is low, ion exchange may be repeated two or more times. There is no particular upper limit to the number of times of ion exchange, but it may be 2 to 5 times.

The ion exchange method may be the same as that for alkaline earth metals. The concentration of cobalt acetate in aqueous solution is 0.0
1-1 moR/L, preferably 0.1-1 mol
/' is good. If it is less than 0.01 moi/L, a large amount of solution is required, resulting in poor operability. Also, 1 mo
If it is larger than Ll/L, the ion exchange rate will not improve to the extent commensurate with the amount of reagent added.

There is no particular restriction on the order in which alkaline earth metals and cobalt are contained, but when they are contained using ion exchange, the order of alkaline earth metals and cobalt is preferred.

As for the content of alkaline earth metals and cobalt, the molar ratio of alkaline earth metals to the number of moles of alumina in the zeolite is 0.1 to 1 times, cobalt 0.5 to 1.7 times,
Preferably, the total amount of alkaline earth metal and cobalt is 1.0 to 2.5 times. Alkaline earth metal content is 0.1
If the amount is less than 1, the effect of improving durability and catalytic activity may be small, and if the amount is more than 1, it is difficult to obtain an effect commensurate with the amount added. If the amount of cobalt is less than 0.5 times, it may not be suitable for use as a catalyst;
If the amount is more than double, it will be difficult to obtain durability and activity commensurate with the amount added.

Furthermore, alkaline earth metals and cobalt may be supported by evaporation to dryness or the like. The evaporation to dryness may be carried out by any conventional method, such as by immersing the zeolite in an aqueous solution containing an alkaline earth metal or cobalt, and then evaporating water as a solvent in a dryer or the like. The concentrations of alkaline earth metals and cobalt salts in the aqueous solution are not particularly defined, but
The alkaline earth metal or cobalt may be deposited evenly, usually in an amount of 0.01 to 1 moJl/L.

After the ion-exchanged sample is solid-liquid separated, washed, and dried,
Used as a catalyst. It can also be used after being fired if necessary.

The 5i (h/AQ2 (h molar ratio) of the exhaust gas purification catalyst of the present invention is 5i02/Affi20 of the zeolite base material used.
3 molar ratio is substantially unchanged. 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 zeolite can be molded in advance and cobalt can be contained in the molded product by ion exchange. Examples of binders used when molding this zeolite include kaolin,
Clay minerals such as attapulgite, montmorillonite, bentonite, allophane, sepiolite, or silica sol,
Examples include alumina sol. Alternatively, it may be a binderless zeolite molded body synthesized directly without using a binder.

Furthermore, zeolite can also be wash-coated onto a honeycomb-shaped substrate made of cordierite or metal.

Removal of nitrogen oxides, carbon monoxide, and hydrocarbons in oxygen-excess exhaust gas is achieved by using the exhaust gas purification catalyst of the present invention, nitrogen oxides,
This can be carried out by contacting oxygen-rich exhaust gas containing carbon monoxide and hydrocarbons. 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. Specific examples of such exhaust gas include exhaust gas discharged from internal combustion engines such as automobiles, particularly exhaust gas in a state where the air-fuel ratio is high (so-called lean region).

Note that even if the above-mentioned exhaust gas catalyst is used for exhaust gas containing carbon monoxide, hydrocarbons, and hydrogen and not in excess of oxygen, its performance will not change in any way.

EXAMPLES Hereinafter, the present invention will be explained in more detail with reference to Examples, but the present invention is not limited to these Examples.

(Example) Example 1 Preparation of catalyst 1> Ammonium type X with a SiO2/AN203 molar ratio of 40
20 g of 5M-5 was immersed in 180 g of an aqueous solution of barium chloride with a concentration of 1.09 moN/L, and stirred at 80° C. for 16 hours. After solid-liquid separation, wash thoroughly with water and continue to 0.23 m
Og/L aqueous solution of cobalt(II) acetate tetrahydrate 18
0 g 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 Catalyst 1. When the barium and cobalt contents of this catalyst were investigated by chemical analysis, barium was 0.44 times the number of moles of AQ20s of zeolite, and cobalt was 1 times as divalent.
．． It contained 13 times more.

Example 2 Preparation of Catalyst 2> Ion exchange was performed in the same manner as in Example 1, or strontium was used as the alkaline earth metal. This catalyst is used as catalyst 2.
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 3 <Preparation of Catalyst 3> Ion exchange was performed in the same manner as in Example 1, or magnesium was used as the alkaline earth metal.

This catalyst was designated as Catalyst 3, and the magnesium and cobalt contents of this catalyst were investigated by chemical analysis, and it was found that magnesium was 0.18% of the number of A4□03 moles of zeolite.
The amount of cobalt and cobalt was 1.08 times as divalent.

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 cobalt contents of this catalyst were investigated by chemical analysis, it was found that the calcium and cobalt contents were 0.16 times and divalent cobalt 10,404 times the number of A4203 moles of zeolite.

Example 5 Preparation of catalyst 5> Ammonium type 2 with a 5i02/Ap2Q8 molar ratio of 40
Add 20g of 5M to 180g of Cobalt acetate (11) tetrahydrate solution 78 with a concentration of 1.23moR/L.
Stirred at 0°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. Continue to increase the concentration to 1.09 mofl/
immersed in 180 g of barium chloride aqueous solution and heated to 80°C.
The mixture was stirred for 16 hours.

After solid-liquid separation, the catalyst was thoroughly washed with water and dried at 110°C for 10 hours, and this catalyst was designated as Catalyst 5. When the barium and cobalt contents of this catalyst were determined by chemical analysis, it was found that barium was contained 058 times and cobalt was contained 1.22 times as divalent compared to 20 times as much as the zeolite AU203.

Example 6 Preparation of Catalyst 6> 20 g of ammonium type ZSM-5 with a 5i02/A4zO++ molar ratio of 40 was mixed with a concentration of 0.23 [1lo9. /L
(7) Aqueous solution of cobalt acetate (11) tetrahydrate 180
g 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.The cobalt content of this zeolite was determined by chemical analysis, and it was found that the cobalt content was 1 as divalent cobalt per 20 on AP203 of the zeolite.
．． It contained 40 times more. Further, 20 g of the zeolite was added to 29 mL of a barium nitrate aqueous solution to 0.05 moL containing a barium amount corresponding to 1 wt% as metallic barium.
and heated at 85℃ for 10 hours, then at 110℃ for 10 hours.
Evaporation to dryness was performed by drying for hours.

This catalyst was designated as Catalyst 6.

Comparative Example 1 Preparation of Comparative Catalyst 1>s; o2/AR2 (h) 20 g of ammonium type ZSM-5 with a molar ratio of 40 was mixed with 180 g of an aqueous solution of cobalt (II) acetate tetrahydrate with a concentration of 0.23 moN/L. put it into
The mixture was 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,
The catalyst was dried at 10° C. for 10 hours and designated as Comparative Catalyst 1. When the cobalt content of this catalyst was investigated by chemical analysis, it was found that it contained 1.39 times as divalent cobalt compared to the number of moles of zeolade.

Comparative Example 2 <Preparation of Comparative Catalyst 2> 20g of ammonium type ZSM-5 with a 5i(h/Al2O3 molar ratio of 40) was weighed so as to be twice the number of moles of alumina contained therein. Concentration 0.1
The mixture was poured into an aqueous solution of copper (II) acetate hydrate of moLl/L, and immediately 2.5% aqueous ammonia was added to adjust the pH of the aqueous solution to 1O35, followed by stirring at room temperature for 16 hours. After solid-liquid separation,
The catalyst was thoroughly washed with water and dried at 110° C. for 10 hours, and this catalyst was designated as Comparative Catalyst 2. When the copper content of this catalyst was investigated by chemical analysis, it was found that 2 copper per mole of ARz03 of zeolite.
The value was 1.04 times higher.

Comparative Example 3 Preparation of Comparative Catalyst 3> 20 g of ammonium type ZSM-5 with a SiO2/8, Q, 03 molar ratio of 40 was added to 180 g of an aqueous solution of barium chloride at a concentration of 1.09 moLl, and the mixture was heated at 80°C. Stirred for 16 hours. After solid-liquid separation, thoroughly washed with water and heated at 110°C for 10
The catalyst was dried for a period of time to obtain Comparative Catalyst 3. When the barium content of this catalyst was investigated by chemical analysis, it was found that the AMz of zeolite (
The barium content was 07,676 times the h mole number.

Example 7 <Catalyst activity evaluation> Catalysts 1 to 6 prepared in Examples 1 to 6 were press-molded and then crushed and sized into 12 to 20 meshes, and 0.65 g of the catalysts were placed in an atmospheric fixed bed reaction tube. Filled. A gas having the composition shown below (hereinafter referred to as reaction gas) was circulated at a rate of 600 m/min, heated to 500° C., and held for 05 hours to serve as pretreatment. Thereafter, the temperature was lowered to 200°C, and the temperature was increased to 800°C at a temperature increase rate of 5°C/win (reaction 1). Continue to hold at 800℃ for 5 hours, change the circulating gas to nitrogen,
It was left to cool. Cool to room temperature, use the circulating gas as a reaction gas,
The temperature was raised to 200° C. and held for 0.5 hours as a pretreatment. Thereafter, the temperature was raised to 800°C at a rate of 5°C/min (reaction 2). Table 1 shows the results of evaluating the durability of the catalyst based on the change in the maximum activity value in Reaction 1 and Reaction 2, using NO as nitrogen oxide, which is a harmful component in the reaction gas. The N0 purification rate is expressed by the following formula.

NO purification rate (%) = (N0In N0out) / NOl, x
10 ONo, ・Fixed bed reaction tube population NO concentration N0
0ut: Fixed bed reaction tube ratio NO concentration reaction gas composition No.
700 ppm02 4 zero (:0 1000 ppm (38,400 ppm H2O3!k N2 Balance Comparative Example 4 <Comparative catalyst activity evaluation> Comparative catalysts 1 to 3 obtained in Comparative Examples 1 to 3 were subjected to the same method as Example 7. Table 1 shows the results of evaluating the activity.

Table 1 Catalyst activity evaluation results The effect of being able to do this is obtained.

Other 4 people (effects of the invention) From Table 1, it is clear that the catalyst of the present invention has 80%
Both the activity after holding at 0° C. for 5 hours and the ability to purify oxygen-rich exhaust gas in oxygen-excessive exhaust gas are higher than those of the comparative catalyst, and the catalyst exhibits extremely excellent heat resistance and durability.

Claims (1)

[Scope of Claims] 1. A zeolite catalyst for removing nitrogen oxides, carbon monoxide and hydrocarbons from oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, which comprises SiO_2/Al
An exhaust gas purification catalyst characterized by being a zeolite having a _2O_3 molar ratio of at least 15 or more, and containing cobalt and an alkaline earth metal. 2. A method for removing nitrogen oxides, carbon monoxide, and hydrocarbons from exhaust gas, which comprises bringing combustion exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbons into contact with the exhaust gas purification catalyst of claim 1. .