JPH0655076A - Catalyst for purification of exhaust gas and method for purifying exhaust gas - Google Patents

Abstract

(57) [Abstract] [Purpose] A catalyst for removing nitrogen oxides, carbon monoxide and hydrocarbons in exhaust gas with a high purification rate from oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons. And a purification method. [Composition] A catalyst for removing nitrogen oxides, carbon monoxide and hydrocarbons from an oxygen-excessive exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, wherein the zeolite contains manganese and palladium. An exhaust gas purifying catalyst, and an exhaust gas purifying method using the catalyst.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst and method for purifying exhaust gas discharged from an internal combustion engine, and more particularly to a catalyst and method for removing nitrogen oxides, carbon monoxide and hydrocarbons in exhaust gas in excess of oxygen. It is about the method.

[0002]

2. Description of the Related Art At present, purification of nitrogen oxides, carbon monoxide, hydrocarbons and the like is regarded as important because of serious environmental problems. Nitrogen oxides are also found in large quantities from various mobile sources such as internal combustion engines such as automobile gasoline engines, and fixed sources such as internal combustion engines such as boilers in plant plants, gas engines in cogeneration systems, and gas turbines. It is discharged to the United States and its purification is an urgent and serious social issue.

Currently, a three-way catalyst in which Pt, Rh, Pd, etc. are carried on a carrier is used as a purification catalyst for exhaust gas discharged from an internal combustion engine. The three-way catalyst is nitrogen in exhaust gas with excess oxygen. Since it cannot purify oxides, it is used together with a system for controlling the ratio of air to fuel (so-called air-fuel ratio).

On the other hand, a lean burn system has been developed for the purpose of reducing fuel consumption and reducing carbon dioxide emissions. However, since lean burn exhaust gas contains excess oxygen, the three-way catalyst removes nitrogen oxides. Can not do it.

As a method for removing nitrogen oxides from an oxygen-excess exhaust gas, reductive denitration by adding ammonia has been carried out, but its range of use is limited due to the large size of the apparatus and the danger of ammonia.

Recently, a zeolite-based catalyst has been proposed which can purify nitrogen oxides in exhaust gas with excess oxygen without adding a special reducing agent such as ammonia. For example, JP-A-63-283727 and JP-A-1-13073.
Japanese Patent Laid-Open No. 5 proposes that a zeolite catalyst ion-exchanged with a transition metal can purify nitrogen oxides by using unburned hydrocarbons contained in a small amount in oxygen-rich exhaust gas as a reducing agent.

However, JP-A-63-283727
The conventional zeolite-based catalysts proposed in JP-A No. 1-130735 and JP-A No. 1-130735 have not reached the practical range.

Further, in the case of an internal combustion engine using a gaseous fuel such as a gas engine or a gas turbine, the trace hydrocarbons contained in the exhaust gas are hydrocarbons having a carbon number of 1 as a main component, and zeolites that have been conventionally proposed. Nitrogen oxide purification performance was particularly poor with the system catalyst. Therefore, Japanese Patent Application No. 3-42
No. 310 catalyst for efficiently removing nitrogen oxides, carbon monoxide, and hydrocarbons from oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide, and hydrocarbons even if the main component of the hydrocarbons is 1. As these, manganese-containing zeolites have been proposed.

[0009]

[Patent Document 1] Japanese Patent Application No. 3-42310
In the manganese-containing zeolite catalyst shown in No. 6, even if the main component of the hydrocarbon is a hydrocarbon having 1 carbon,
Nitrogen oxides can be efficiently removed from exhaust gas with excess oxygen. However, a higher nitrogen oxide purification capacity is required as an exhaust gas purification catalyst.

An object of the present invention is to provide a method for efficiently removing nitrogen oxides, carbon monoxide and hydrocarbons from an oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons. An object of the present invention is to provide a catalyst having an exhaust gas purifying ability higher than that of the catalyst disclosed in Japanese Patent No. 42310 and an exhaust gas purifying method using the same.

[0011]

Means for Solving the Problems As a result of intensive studies for solving the above problems, the present inventors have found that the use of zeolite containing manganese and palladium as a catalyst results in excess oxygen in the presence of hydrocarbons. From the exhaust gas,
It was found that nitrogen oxides, carbon monoxide, and hydrocarbons can be efficiently removed, and that the purification rate of nitrogen oxides can be particularly increased by adding hydrocarbons to the exhaust gas, and the present invention has been completed. Came to do.

That is, the present invention contains manganese and palladium as a catalyst for efficiently removing nitrogen oxides, carbon monoxide and hydrocarbons from oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons. The present invention further provides a zeolite catalyst described above, and further provides an exhaust gas purification method characterized in that a hydrocarbon is added to the exhaust gas using the catalyst.

The present invention will be described in more detail below.

[0014] Zeolite to be used in the present invention, _{generally, xM 2 / n O · Al} 2 O 3 · ySiO 2 · zH 2 O ( where, n is the valence of the cation M, x is 0.8 to 1.2
, Y is a number greater than or equal to 2, and z is a number greater than or equal to 0)
It is a crystalline aluminosilicate having the following composition, and many kinds are known as natural products and synthetic products. The type of zeolite used in the present invention is not particularly limited, but it is desirable that the silica / alumina molar ratio is 10 or more. Typically, ferrierite, Y, mordenite, ZSM-5, ZSM-11 and the like can be mentioned. Of these, ZSM-5 is most preferred. Moreover, these zeolites may be used as they are, but
There is no problem even if it is used as NH ₄ type or H type ion-exchanged with H ₄ Cl, NH ₄ NO ₃ , (NH ₄ ) ₂ SO _4, etc. Further, it does not matter even if it contains cations such as alkali metals and alkaline earth metals.

The exhaust gas purifying catalyst of the present invention is characterized by containing manganese and palladium. The method of incorporating manganese and palladium into zeolite is not particularly limited, and it may be carried out by an ion exchange method, an impregnation supporting method, or the like.

[0016] For example, when manganese is ion-exchanged, zeolite is added to a solution containing manganese ions, and 20 to 20 is added.
It suffices to stir at 100 ° C. for several hours. Examples of the manganese salt used include acetate, nitrate, oxalate, and chloride.

The manganese and palladium contents are not particularly limited, but the manganese content is MnO / Al ₂ O.
_The molar ratio is preferably 0.2 to 2.5, and is 0.8.
~ 1.2 is more preferable. Pd content is Pd
The O / Al ₂ O ₃ molar ratio is preferably 0.01 to 1.0, more preferably 0.05 to 0.4. (PdO + M
The nO) / Al ₂ O ₃ molar ratio is preferably 0.2 to 3.5, and more preferably 0.8 to 1.5. MnO / Al ₂ O
_{If the 3} molar ratio is lower than 0.2, sufficient activity cannot be obtained. Further, even if the MnO / Al ₂ O ₃ molar ratio is higher than 2.5, it is difficult to obtain the effect of increasing manganese. P
When the dO / Al ₂ O ₃ molar ratio is lower than 0.01, sufficient activity cannot be obtained. Further, even if the PdO / Al ₂ O ₃ molar ratio is higher than 1.0, the effect of increasing the amount of palladium cannot be obtained.

The sample containing manganese and palladium may be subjected to a pretreatment such as drying or calcination before use as a catalyst.

The catalyst containing manganese and palladium according to the present invention may have any shape, structure, etc., such as powder, pellets, and honeycombs. Further, the introduction of the metal element can be performed after the molding.

The exhaust gas purifying catalyst of the present invention is molded into a predetermined shape by adding a binder such as alumina sol, silica sol or clay, or is made into a slurry by adding water, and alumina, magnesia, cordierite or the like in the shape of a honeycomb, etc. It may be used after being coated on the refractory base material.

The exhaust gas targeted by the catalyst of the present invention is an oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons. Exhaust gas with excess oxygen means exhaust gas containing oxygen in excess of the amount of oxygen required to completely oxidize reducing components such as carbon monoxide and hydrocarbons contained in the exhaust gas. Further, the hydrocarbon contained in the exhaust gas is not particularly limited, but the catalyst of the present invention can efficiently purify the exhaust gas even for the exhaust gas whose main component of the hydrocarbon is carbon number 1. Generally, most of the hydrocarbons contained in the exhaust gas discharged from an engine using liquid fuel such as an automobile are hydrocarbons having 2 or more carbon atoms. On the other hand, the main component of hydrocarbons contained in exhaust gas discharged from an engine using a gaseous fuel such as a gas engine has 1 carbon atom. Usually, the reactivity of hydrocarbon tends to increase as the carbon number increases, and the reactivity is particularly low when the carbon number is 1.

Here, the term "exhaust gas having a carbon number of 1 as the main component of hydrocarbons" refers to an exhaust gas in which 80% or more of the hydrocarbons contained in the exhaust gas have a carbon number of 1. Examples of such exhaust gas include exhaust gas discharged from a lean-burn gas engine using city gas as fuel.

The hydrocarbon to be added is not particularly limited, but the catalyst of the present invention efficiently purifies the exhaust gas even if the hydrocarbon is methane or a mixed gas of hydrocarbons containing methane as a main component. can do. The mixed gas of hydrocarbons containing methane as a main component means a mixed gas in which 80% or more of the hydrocarbons in the mixed gas are methane. The concentration of the added hydrocarbon is not particularly limited and may be 50
It may be about ppm to 1%. Although the addition amount may be increased, it is not preferable because it causes a decrease in economic efficiency and a reduction rate of hydrocarbons. Further, if the hydrocarbon concentration in the exhaust gas is sufficiently high, the hydrocarbon need not be added.

[0024]

The present invention will be described in more detail below with reference to examples, but the present invention is not limited to these examples.

Example 1 <Preparation of catalyst 1> 200 g of NH ₄ type ZSM-5 zeolite having a silica / alumina ratio of 40 was mixed with a 0.25 M manganese acetate aqueous solution 18
It was put into 00 ml and stirred at 80 ° C. for 20 hours to carry out ion exchange. After the solid-liquid separation of the slurry, the zeolite cake was again put into an aqueous solution having the same composition as above, and the ion exchange operation was performed again. After solid-liquid separation, it was washed with 20 liters of pure water and dried at 110 ° C. for 10 hours. As a result of elemental analysis, manganese was 1.02 times that of alumina.

10 g of this catalyst was added to contain 0.1 times more palladium than alumina in the zeolite [Pd (NH
₃ ) ₄ ] Cl ₂ · H ₂ O was poured into 100 ml of an aqueous solution, dried under reduced pressure at 80 ° C to contain palladium, and then dried at 110 ° C for 20 hours to obtain a catalyst 1. As a result of elemental analysis, manganese was 1.02 times that of alumina and palladium was 0.1 times.

Comparative Example 1 <Preparation of Comparative Catalyst 1> 200 g of NH ₄ type ZSM-5 zeolite having a silica / alumina ratio of 40 was mixed with a 0.25 M manganese acetate aqueous solution 18
It was put into 00 ml and stirred at 80 ° C. for 20 hours to carry out ion exchange. After the solid-liquid separation of the slurry, the zeolite cake was again put into an aqueous solution having the same composition as above, and the ion exchange operation was performed again. After solid-liquid separation, it was washed with 20 liters of pure water and dried at 110 ° C. for 10 hours to obtain Comparative Catalyst 1. As a result of elemental analysis, manganese is 1.
It was 02 times.

Example 2 <Preparation of Catalyst 2> Zeolite is added to 100 ml of an aqueous solution in which [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O containing 0.2 times more palladium than alumina in zeolite is dissolved. Example 1 except
A catalyst was prepared in the same manner as above to obtain a catalyst 2. As a result of elemental analysis, manganese is 1.02 times that of alumina in zeolite,
Palladium was 0.2 times the amount of alumina in the zeolite.

Example 3 <Preparation of catalyst 3> 10 g of the catalyst of Comparative Example 1 was taken, and the amount of palladium contained in the zeolite was 0.1 times the amount of [Pd (N
H ₃ ) ₄ ] Cl ₂ · H ₂ O was added to 100 ml of an aqueous ammonia solution having a pH of 10.5 and stirred at 30 ° C. for 2 hours to carry out an ion exchange treatment. After the solid-liquid separation of the slurry, the slurry was washed with 1 liter of pure water and dried at 110 ° C. for 20 hours to obtain a catalyst 3. As a result of elemental analysis, manganese was 1.02 times that of alumina and palladium was 0.1 times.

Comparative Example 2 <Preparation of Comparative Catalyst 2> Comparative catalyst 2 was prepared in the same manner as in Example 1 except that the manganese acetate aqueous solution was changed to the manganese nitrate aqueous solution.
As a result of elemental analysis, manganese was 0.54 times that of alumina.

Comparative Example 3 <Preparation of Comparative Catalyst 3> NH ₄ type ZSM-5, 20 having a silica / alumina ratio of 40.
0 g was added to 1800 ml 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, it is thoroughly washed with water, and then continuously poured into 700 ml of a 0.23 mol / L manganese acetate aqueous solution, and the mixture is kept at 80 ° C. for 16 minutes.
Stir for hours. Zeolite case after solid-liquid separation of slurry
The same operation was performed by throwing Ki into the aqueous solution of the above composition prepared again. After solid-liquid separation, wash thoroughly with water and hold at 110 ° C for 10
After drying for an hour, Comparative Catalyst 3 was obtained. As a result of elemental analysis, barium was 0.66 times that of alumina and manganese was 0.87 times.

Example 4 <Catalyst Evaluation 1> Catalysts 1 to 3 and comparative catalysts 1 to 3 were crushed after tableting, respectively, and crushed to 12 to 20 mesh, 1.2 g of which was fixed under atmospheric pressure. Filled. 1 at 500 ° C under air flow
After the pretreatment for an hour, a gas having the composition shown in Table 1 (hereinafter referred to as a reaction gas) was passed at 500 ml / min to give 40.
The catalytic activity at 0 ° C and 500 ° C was measured. Table 2 shows the purification rates of NOx and methane when the temperature reached a steady state. The purification rates of hydrocarbons other than CO and methane were almost 100% for all the catalysts. The NOx purification rate is the value obtained from the following equation, and the methane purification rate is the value obtained accordingly.

NOx purification rate (%) = (NOxin−NOxout) / NOxin × 100 NOxin: Reaction tube inlet NO concentration NOxout: Reaction tube outlet NO concentration

[0034]

[Table 1]

[0035]

[Table 2] Example 5 <Catalyst Evaluation 2> To the reaction gas shown in Table 3, 5000 ppm of a mixed gas of hydrocarbons containing methane as a main component shown in Table 4 was further added, and catalytic activity was increased in the same manner as in Example 4. It was measured. Table 5 shows the purification rates of NOx and methane when the temperature reaches a steady state.
It was shown to. The purification rate of hydrocarbons other than CO and methane was almost 100% for all the catalysts.

[0036]

[Table 3]

[0037]

[Table 4]

[0038]

[Table 5] Example 6 <Catalyst evaluation 3> The catalyst activity was measured in the same manner as in Example 4 except that the reaction gas having the composition shown in Table 6 was used instead. Table 7 shows the NOx purification rates when the temperature reached a steady state. In addition, CO
The purification rates of propane and propane were almost 100% for all the catalysts.

[0039]

[Table 6]

[0040]

[Table 7] Example 7 <Catalyst evaluation 4> The catalytic activity was measured in the same manner as in Example 4 except that the reaction gas having the composition shown in Table 8 was used instead of the reaction gas, and the amount of the catalyst was 2.5 g. Table 9 shows the NOx purification rate when the temperature reached the steady state. The purification rates of CO and propylene were almost 100% for all the catalysts.

[0041]

[Table 8]

[0042]

[Table 9]

[0043]

From the results of Table 2, Table 5, Table 7 and Table 9, the zeolite catalyst containing manganese and palladium of the present invention was used to add nitrogen and nitrogen oxide by a method of adding hydrocarbon. Nitrogen oxides can be removed at a higher purification rate from an oxygen-excessive exhaust gas containing carbon and a hydrocarbon whose main component is carbon number 1. Further, by using the catalyst of the present invention, hydrocarbons can be removed. It is clear that the nitrogen oxide can be purified at a very high purification rate by the addition thereof, and therefore the present invention is extremely significant in terms of environmental protection.

Claims (5)

[Claims] 1. A catalyst for removing nitrogen oxides, carbon monoxide and hydrocarbons from an oxygen-rich exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, wherein the zeolite contains manganese and palladium. An exhaust gas purifying catalyst characterized in that 2. The exhaust gas purifying catalyst according to claim 1, in removing nitrogen oxides, carbon monoxide and hydrocarbons from oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons. An exhaust gas purification method characterized by using. 3. The exhaust gas purification method according to claim 2, wherein the main component of the hydrocarbon is a hydrocarbon having 1 carbon atom. 4. When removing nitrogen oxides, carbon monoxide and hydrocarbons from oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, further adding hydrocarbons to the exhaust gas. The exhaust gas purification method according to claim 2, wherein 5. The exhaust gas purification method according to claim 4, wherein the added hydrocarbon is methane or a mixed gas of hydrocarbons containing methane as a main component.