JP3298133B2 - Method for producing zeolite containing cobalt and palladium and method for purifying exhaust gas - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a method for purifying exhaust gas discharged from an internal combustion engine and a method for producing a catalyst.
In particular, the present invention relates to a method for producing a cobalt and palladium-containing zeolite catalyst for removing nitrogen oxides, carbon monoxide and hydrocarbons in an oxygen-excess exhaust gas, and an exhaust gas purification method.

[0002]

2. Description of the Related Art At present, purification of nitrogen oxides, carbon monoxide, hydrocarbons, and the like has been regarded as important due to serious environmental problems. Nitrogen oxides represent various mobile sources, such as internal combustion engines such as gasoline engines of automobiles, and internal combustion engines, such as boilers in factory plants, gas engines in cogeneration systems, and gas turbines. It is also emitted in large quantities from stationary sources, and its purification is an urgent and important social issue.

At present, a three-way catalyst having Pt, Rh, Pd, etc. supported on a carrier is used as a catalyst for purifying exhaust gas discharged from an internal combustion engine. Since oxides cannot be purified, they are used together with a system that controls 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 the exhaust gas of the lean burn is excessive in oxygen, the three-way catalyst removes nitrogen oxides. Can not do it.

[0005] As a method for removing nitrogen oxides from an excess oxygen exhaust gas, reductive denitration by adding ammonia is performed.
Due to the size of the apparatus and the danger of ammonia, its use range is limited.

Recently, a zeolite-based catalyst has been proposed which can purify nitrogen oxides in an oxygen-excess exhaust gas without adding a special reducing gas such as ammonia. For example, JP-A-63-283727 and JP-A-1-13073.
No. 5 proposes that a zeolite catalyst ion-exchanged with a transition metal can purify nitrogen oxides by using unburned hydrocarbons contained in exhaust gas containing excess oxygen as a reducing agent. However, the conventional zeolite-based catalysts proposed in the above publication have not yet reached practical use.

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 mainly hydrocarbons having 1 carbon atom. With the catalyst, the purification performance of nitrogen oxides was particularly low.

[0008] In Japanese Patent Application No. 3-42311, Japanese Patent Application No. 3-42311 discloses that an exhaust gas containing an excess of oxygen containing nitrogen oxides, carbon monoxide and hydrocarbons contains nitrogen oxides and carbon monoxide even if the hydrocarbon has one carbon atom. And a catalyst and a method for efficiently removing hydrocarbons are provided. As a catalyst, cobalt and palladium-containing zeolites have been proposed. As a method for producing the catalyst, a method of adding an aqueous palladium solution to cobalt-containing zeolite and drying it under reduced pressure to contain palladium is described.

[0009]

Problems to be Solved by the Invention Japanese Patent Application No. 3-42311
It is clear that the zeolite catalyst containing cobalt and palladium provided in No. 1 can efficiently remove nitrogen oxides from an oxygen-excess exhaust gas even if the hydrocarbon is a hydrocarbon whose main component is one. However, an exhaust gas purifying catalyst is required to have a higher nitrogen oxide purifying ability.

[0010] An object of the present invention is to remove nitrogen oxides, carbon monoxide and hydrocarbons from an oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons in Japanese Patent Application No. 3-42311. An object of the present invention is to provide a method for producing a catalyst having a higher exhaust gas purification ability and an exhaust gas purification method using the same.

[0011]

Means for Solving the Problems The inventors of the present invention have conducted intensive studies to solve the above-mentioned problems. As a result, in producing cobalt and palladium-containing zeolite by adding palladium to cobalt-containing zeolite, the present inventors have found that cobalt-containing zeolites usually contain cobalt-containing zeolites. Neutral or acidic when zeolite and palladium compound coexist, but using a catalyst produced by coexisting cobalt-containing zeolite and palladium compound in an alkaline solution and solid-liquid separation, nitrogen oxidation from oxygen-excess exhaust gas It has been found that substances, carbon monoxide and hydrocarbons can be removed more efficiently, and the present invention has been completed.

That is, according to the present invention, in producing a zeolite containing cobalt and palladium, the cobalt-containing zeolite and the palladium compound are allowed to coexist in an alkaline solution, and thereafter, are obtained by solid-liquid separation. For producing nitrogen-containing zeolites, and for removing nitrogen oxides, carbon monoxide and hydrocarbons from exhaust gases containing excess oxygen containing nitrogen oxides, carbon monoxide and hydrocarbons, the zeolites containing cobalt and palladium produced by the above method Is used as a catalyst.

Hereinafter, the present invention will be described in detail.

The zeolite used in the present invention is generally xM ₂ /nO.ySiO ₂ .zH ₂ O (where n is the valency of the cation M, and x is 0.8 to 1.2)
, Y is a number of 2 or more, and z is a number of 0 or more. ) Is a crystalline aluminosilicate having the composition of (1), and many types are known as natural products and synthetic products. The type of zeolite used in the present invention is not particularly limited, but the silica / alumina molar ratio is desirably 10 or more. Typically, ferrierite, Y, mordenite, ZSM-5, ZSM-11 and the like can be mentioned. Of these, ZSM-5 is most preferred. Although these zeolites may be used as they are, they may be used as NH ₄ type or H type ion-exchanged with NH ₄ Cl, NH ₄ NO ₃ , (NH ₄ ) ₂ SO ₄ or the like. Further, even if it contains a cation such as an alkali metal or an alkaline earth metal, it does not matter at all.

In the production method of the present invention, first, the zeolite base material contains cobalt and then palladium. The method of impregnating the zeolite with cobalt is not particularly limited, and may be performed by an ion exchange method, an impregnation-supporting method, or the like. The ion exchange method is preferable as the method of containing cobalt. When ion exchange is not particularly limited, for example,
The zeolite is charged into the solution containing cobalt ions,
What is necessary is just to stir at -100 degreeC for several hours. Examples of the cobalt salt to be used include acetate, nitrate, oxalate, chloride and the like.

The production method of the present invention is characterized in that a cobalt-containing zeolite and a palladium compound are made to coexist in an alkaline solution, and then obtained by solid-liquid separation. In the present invention, alkaline means that the pH is 7.5 or more. The pH of the solution is preferably from 8 to 12. In order to make the solution alkaline, a normal alkaline reagent such as a hydroxide or carbonate of an alkali metal or an alkaline earth metal, or ammonia or urea may be used, with ammonia being preferred. The order in which the cobalt-containing zeolite and the palladium compound coexist in the alkaline solution is not particularly limited, as long as the pH of the solution in the state where the cobalt-containing zeolite and the palladium compound coexist is within the above range. The temperature and time for coexistence are not particularly limited.
The heat treatment may be performed at a temperature of 100 to 100 ° C. for 5 minutes to 50 hours. In the case of coexistence, stirring and circulation may be performed.
After the cobalt-containing zeolite and the palladium compound are made to coexist in an alkaline solution, solid-liquid separation is performed. The method for solid-liquid separation is not particularly limited, and may be filtration, centrifugation, or the like.
Palladium compounds include nitrates, chlorides, ammine complexes and the like.

The contents of cobalt and palladium are not particularly limited, but cobalt is 0.2 to 2.5 in terms of Co / Al ₂ O ₃ molar ratio, and palladium is Pd / Al ₂ O _3.
The molar ratio is preferably from 0.01 to 1.0. (PdO
+ CoO) / Al ₂ O ₃ molar ratio is preferably from 0.2 to 3.5. If the Co / Al ₂ O ₃ molar ratio is lower than 0.2, sufficient activity cannot be obtained, and even if it is higher than 2.5, the effect of increasing cobalt is difficult to obtain. In addition, PdO /
If the Al ₂ O ₃ molar ratio is lower than 0.01, sufficient activity cannot be obtained, and if it is higher than 1.0, the effect of increasing palladium cannot be obtained.

The sample containing cobalt and palladium may be used after being subjected to pretreatment such as drying and calcination when used as a catalyst.

The catalyst containing cobalt and palladium according to the present invention may be in any shape such as powder, pellet, honeycomb, etc., regardless of its shape and structure. Further, the introduction of the metal element can be performed after the molding.

The exhaust gas purifying catalyst of the present invention is formed into a predetermined shape by adding a binder such as alumina sol, silica sol, or clay, or is formed into a slurry by adding water, and is formed into an alumina, magnesia, or co-polymer having a honeycomb shape. -It may be used after being applied on a refractory substrate such as gelite.

The exhaust gas targeted by the catalyst of the present invention is an oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons. The oxygen-excess exhaust gas refers to an exhaust gas containing oxygen in excess of the amount of oxygen necessary to completely oxidize reducing components such as carbon monoxide and hydrocarbons contained in the exhaust gas.
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 when the main component of the hydrocarbon is an exhaust gas having 1 carbon atom. Here, the exhaust gas having a carbon number of 1 as a main component of the hydrocarbon indicates 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.

In the present invention, the purification of exhaust gas is carried out by bringing the above-mentioned exhaust gas into contact with the zeolite containing cobalt and palladium produced by the production method of the present invention. The temperature at that time may be 200 to 800 ° C, and 250 to 800 ° C.
700 ° C. is preferred. The space velocity is 1000-500
000 hr- ¹ . The space velocity is a value obtained by dividing the flow rate (cc / hr) of the exhaust gas by the volume (cc) of the catalyst.

Further, by using the purification catalyst of the present invention and adding hydrocarbons to the exhaust gas, the purification rate of nitrogen oxides can be further increased.

The exhaust gas purifying catalyst of the present invention may be used in combination with a conventional oxidation catalyst.

[0025]

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

The NH ₄ form ZSM-5 zeolite of Example 1 <Preparation of Catalyst 1> silica / alumina ratio of 40; the 200 g, 0.25M of _Co (CH 3 COO)
_An aqueous 2.4 H ₂ O solution was charged into 1800 ml, and stirred at 80 ° C. for 20 hours to perform ion exchange. After the slurry was subjected to solid-liquid separation, the zeolite cake was charged into an aqueous solution having the same composition as above, and the ion exchange operation was performed again. After solid-liquid separation,
After washing with 20 liters of pure water and drying at 110 ° C. for 10 hours, a cobalt-containing zeolite was obtained. Of these, 10 g was added to 90 ml of pure water. Thereafter, the pH was adjusted to 10.0 by adding 7% aqueous ammonia, and [Pd (N) was 0.05 times the number of moles of alumina in the zeolite.
H ₃ ) ₄ ] Cl ₂ .H ₂ O was added, at which time the solution pH was 9.80. Thereafter, the mixture was stirred at 30 ° C. for 2 hours to carry palladium. After this operation, washing, 1
After drying at 10 ° C. for 20 hours, Catalyst 1 was obtained.

As a result of elemental analysis, cobalt was 1.39 times that of alumina and palladium was 0.05 times that of alumina.

Example 2 <Preparation of Catalyst 2> Example 1 was repeated except that [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O was 0.1 times the number of moles of alumina in the zeolite. Prepared in the same manner as Catalyst 2. In addition,
The pH of the solution when [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O was added was 9.80. As a result of elemental analysis, cobalt was 1.39 times that of alumina and palladium was 0.1 times that of alumina.

Example 3 <Preparation of catalyst 3> [Pd (NH ₃ ) ₄ ] Example ₂ was repeated except that the amount of Cl ₂ · H ₂ O was 0.2 times the number of moles of alumina in the zeolite. Prepared in the same manner as Catalyst 3. In addition,
The pH of the solution when [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O was added was 9.80. As a result of elemental analysis, cobalt was 1.39 times that of alumina and palladium was 0.2 times that of alumina.

Example 4 <Preparation of Catalyst 4> Example 1 was repeated except that [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O was changed to 0.4 times the number of moles of alumina in the zeolite. Prepared in a similar manner to Catalyst 4. In addition,
The pH of the solution when [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O was added was 9.80. As a result of elemental analysis, cobalt was 1.39 times that of alumina and palladium was 0.4 times that of alumina.

Example 5 <Preparation of Catalyst 5> The procedure of Example 1 was repeated except that [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O was 0.025 times the number of moles of alumina in the zeolite. Prepared in the same manner as Catalyst 5. The pH of the solution when [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O was added was 9.80. As a result of elemental analysis,
Cobalt is 1.39 times that of alumina and palladium is 0.0
It was 25 times.

Comparative Example 1 <Preparation of Comparative Catalyst 1> Cobalt-containing zeolite of Example 1; 20 g of [P] was 0.05 times the mole number of alumina in the zeolite.
d (NH ₃ ) ₄ ] Cl ₂ .H ₂ O dissolved aqueous solution 10
0 cc. The pH of the solution was 7.3.
Then, after drying under reduced pressure at 80 ° C. to carry Pd,
After drying at 10 ° C. for 20 hours, Comparative Catalyst 1 was obtained. As a result of elemental analysis, cobalt was 1.39 times that of alumina and palladium was 0.05 times.

Comparative Example 2 <Preparation of Comparative Catalyst 2> Comparative Example 1 except that the amount of [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O was 0.1 times the number of moles of alumina in the zeolite. Prepared in the same manner as in Comparative Example 2 to obtain Comparative Catalyst 2. The pH of the solution in which the cobalt-containing zeolite and palladium coexisted was 7.3. As a result of elemental analysis, cobalt was 1.39 times that of alumina and palladium was 0.1 times that of alumina.

Comparative Example 3 <Preparation of Comparative Catalyst 3> Comparative Example 1 except that [Pd (NH ₃ ) ₄ ] Cl ₂ .H ₂ O was 0.2 times the number of moles of alumina in the zeolite. Prepared in the same manner as in Comparative Example 3 and used as Comparative Catalyst 3. The pH of the solution in which the cobalt-containing zeolite and palladium coexisted was 7.3. As a result of elemental analysis, cobalt was 1.39 times that of alumina and palladium was 0.2 times that of alumina.

Example 6 <Catalyst Evaluation 1> Catalysts 1 to 3 and Comparative Catalysts 1 to 3 were each crushed after tablet molding, sized to 12 to 20 mesh, and 1.2 g of the resulting mixture was subjected to a normal pressure fixed bed reactor. Was filled. 1 at 500 ° C under air circulation
After performing the time pretreatment, a gas having a composition shown in Table 1 (hereinafter referred to as a reaction gas) was passed at 500 ml / min.
And the catalyst activity at 500 ° C. Table 2 shows the purification rates of NOx and methane when the temperature reached a steady state at each temperature. Purification rates of CO and other hydrocarbons were almost 100% for all catalysts. The NOx purification rate is a value obtained from the following equation, and the methane purification rate is a value obtained according to the same.

NOx purification rate (%) = (NOxin−NOxout) / NOxin × 100 NOxin: NOx concentration at reaction tube inlet NOxout: NOx concentration at reaction tube outlet

[0037]

[Table 1]

[0038]

[Table 2] Example 7 <Catalyst evaluation 2> The catalytic activity was the same as in Example 6 except that the reaction gas was changed to the reaction gas having the composition shown in Table 3 and the catalysts to be evaluated were changed to Catalysts 1 to 5 and Comparative catalysts 1 to 3. Was measured. Table 4 shows the purification rates of NOx and methane when the steady state was reached at each temperature. The conversion of hydrocarbons other than CO and methane was almost 100% in each of the catalysts.

[0039]

[Table 3]

[0040]

[Table 4] Example 8 <Catalyst evaluation 3> The catalytic activity was measured in the same manner as in Example 6, except that the reaction gas was changed to the reaction gas having the composition shown in Table 5. Table 6 shows the NOx purification rates when the temperature reached a steady state at each temperature. In addition,
The purification rates of CO and propane were almost 100% for both catalysts.

[0041]

[Table 5]

[0042]

[Table 6] Example 9 <Catalyst evaluation 4> The catalytic activity was measured in the same manner as in Example 6, except that the reaction gas was changed to the reaction gas having the composition shown in Table 7 and the amount of the catalyst was changed to 5 g. Table 8 shows the NOx purification rates when the temperature reached a steady state at each temperature. The purification rates of CO and propylene were almost 100% for each of the catalysts.

[0043]

[Table 7]

[0044]

[Table 8]

[0045]

From the results shown in Tables 2, 4, 6 and 8, the zeolite catalyst containing cobalt and palladium produced by the method of the present invention shows that oxygen containing nitrogen oxides, carbon monoxide and hydrocarbons can be obtained. It is clear that nitrogen oxides, carbon monoxide and hydrocarbons can be removed from excess exhaust gas at a higher purification rate than the comparative catalyst. Therefore, the present invention provides a method for producing a catalyst having a high efficiency of removing nitrogen oxides, carbon monoxide and hydrocarbons from an oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons, and a method for purifying the exhaust gas. Useful.

Claims (3)

(57) [Claims] 1. A method for producing a cobalt- and palladium-containing zeolite, comprising allowing a cobalt-containing zeolite and a palladium compound to coexist in an alkaline solution, followed by solid-liquid separation. 2. The method according to claim 1, wherein the pH of the solution in which the cobalt-containing zeolite and the palladium compound coexist is 8 to 12. 3. A method for removing nitrogen oxides, carbon monoxide and hydrocarbons from an oxygen-excess exhaust gas containing nitrogen oxides, carbon monoxide and hydrocarbons. An exhaust gas purification method comprising using a palladium-containing zeolite as a catalyst.