JPH09253493A - Carrier for nox reducing catalyst - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a carrier for an NOx reducing catalyst with rich durability which reduces NOx in exhaust gas to decrease NOx. SOLUTION: This carrier for an NOx reducing catalyst has a basic structure of a shell-like porous body wherein nickel oxide is a main component to reduce and purify NOx in exhaust gas exhausted from a combustion room of a diesel engine and the NOx reducing catalyst with a brownmillerite type structure is carried in the pores which the shell-like porous body has. There exist fine pores with 0.20-0.05μm on the surface of the shell-like porous body and the shell-like porous body has pores with an internal diameter of 4-1μm.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to carrier of the NO _X reduction catalyst by reducing NO _X contained in the exhaust gas of the engine to purify the exhaust gas.

[0002]

2. Description of the Related Art Conventionally, catalysts for catalytic reduction and direct decomposition are known as NO _X decomposition catalysts. In gasoline engines, platinum, rhodium are used as catalysts, and HC, CO, H in exhaust gas are used as reducing agents. Three-way catalysts using ₂ are known. However, although a three-way catalyst is one in which a noble metal is supported on alumina, zeolite, or a carrier thereof, the NO _x reduction rate is low in a lean burn region with excess oxygen, that is, a lean burn region or a diesel engine, and the three-way catalyst is low. Was not effective in purifying the exhaust gas emitted from diesel engines. That is, in a diesel engine,
Since it is burned with excess air, O ₂ is present in the exhaust gas,
Nitrogen oxides NO _X is a large amount of discharge. On the contrary,
In gasoline engines are burned in stoichiometric, the exhaust gas does not exist remainder O _2, since NO is decomposed by reduction catalyst provided in flow after the engine, there is no of the NO _X problems. Conventionally, from diesel engines nitrogen oxides NO _x
Diesel particulate filters incorporating various catalysts have been known in order to suppress the emission of hydrogen to the outside. However, the exhaust gas of a diesel engine is
Since the catalyst contains a large amount of O ₂ , it has a drawback that the catalyst does not function.

Therefore, for purifying NO _{X in} the diesel engine and the lean burn region, that is, the lean burn region as described above, a perovskite catalyst has been developed, but it is said that the NO _X reduction rate is low. There was a problem (for example, Japanese Patent Laid-Open Nos. 6-100319 and 6-315).
634). Further, the exhaust gas purifying catalyst disclosed in Japanese Patent Application Laid-Open No. 63-77543 includes a catalyst carrier,
It comprises a perovskite-type composite oxide composed of an oxide of an alkaline earth metal, lanthanum oxide and cerium oxide supported on the surface of the catalyst carrier, and a noble metal catalyst component. Further, the exhaust gas purifying catalyst disclosed in JP-A-63-77543 has Pd as a catalyst component on a catalyst carrier having a layer containing a perovskite complex oxide and an O ₂ storage rare earth oxide on the surface. Alternatively, Pd and another noble metal are supported.

[0004]

In view of the situation as described above [0005], various the catalyst has been studied, as a catalyst for reducing NO _X, directly reducing and decomposing Brown mirrors that do not require a reducing agent therein A compound having a light type structure,
For example, there are compounds of Ba ₃ Y ₄ O ₉ and BaLa ₂ O ₄ .

Conventionally, the general formula A ₂ B ₂ O ₅ (where A is 2
The NO _x reduction catalyst having a brown-milarite type structure having a valent metal, B is a trivalent metal, synthesizes a metal carbonate or oxide at a high temperature of about 1400 ° C. For this reason,
During the production of the raw materials, there are drawbacks such that the raw materials are not uniformly mixed and the catalyst surface becomes small due to shrinkage during firing during synthesis. Further, when the NO _x reduction catalyst having the brown-milarite type structure is synthesized at a low temperature by the wet method, its surface area can be increased and the reduction rate of NO _x can be improved, but the strength of the calcined body is improved. It was weak, and if the NO _x reduction catalyst having the Brownmillerite type structure was simply attached to the surface of the porous carrier, the carrier itself was easily pulverized and there was a problem in durability. Therefore, the NO _x reduction catalyst having the brown-milarite type structure can directly reduce NO _x , but it was difficult to put it into practical use.

[0006]

The main object of the present invention is to reduce and purify NO _X in the exhaust gas discharged from the combustion chamber of a diesel engine, so that nickel oxide having fine pores as a carrier is used. Using a porous body consisting of
In the pores of the porous body, a NO _x reduction catalyst having a brown mirrorlite type structure fired at low temperature is carried, and further, a NO _x reduction catalyst having a brown mirrorlite type structure is used as a nitrate or a catalyst metal of barium or yttrium. Citric acid was added to an aqueous solution of acetate, which was heated to evaporate water,
Alternatively, it is precipitated with an aqueous ammonia solution or tetramethylammonium and heated to evaporate the water, and then 50
The object of the present invention is to provide a carrier for a NO _x reduction catalyst in which the specific surface area of the conventional brown millerite structure is dramatically increased by firing at a low temperature of 0 ° C to 1000 ° C.

In the present invention, a shell-like porous body containing nickel oxide as a main component is used as a basic structure, and in the pores of the shell-like porous body, a general formula A showing an order-disorder transition of oxygen defects at a predetermined temperature. carrier of the NO _X reduction catalyst NO _X reduction catalyst is characterized in that it is carried with brownmillerite type structure having a ₂ B ₂ O ₅ about. Here, A in the general formula A ₂ B ₂ O ₅ is a divalent metal, and B is a trivalent metal.

Further, in this NO _x reduction catalyst carrier, the basic structure of the shell-like porous material is 0.20 on the surface thereof.
To 0.05 μm, and the inside diameter of the shell-shaped porous body is 4 to 1 μm. Further, the nickel oxide forming the shell-like porous body is mainly
They are bonded by oxide ceramics containing aluminum and silicon.

As described above, the carrier for the NO _X reduction catalyst has a shell-like porous body mainly composed of nickel oxide as a basic structure, and the NO _X reduction catalyst having a Brown millerite type structure in its pores. since was supported, without the shell-like porous body is powdering even in long-term use, can improve durability, yet high reduction rate of the NO _X by the NO _X reduction catalyst, a large industrial value Will be things. That is, when the exhaust gas exhausted from the diesel engine is brought into contact with the carrier of the NO _x reduction catalyst, the temperature becomes high enough to activate the disordered oxygen defects, so that the NO _x existing in the exhaust gas is the catalyst is reduced, it can always maintain a high reducing action of the NO _X, to improve the NO _X reduction ratio, thereby reducing the abundance of the NO _X in the exhaust gas.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of a carrier for a NO _x reduction catalyst according to the present invention will be described below with reference to the drawings. FIG. 1 is an explanatory view showing one embodiment of a manufacturing process of a carrier of a NO _x reduction catalyst according to the present invention.

The carrier for the NO _x reduction catalyst is, for example,
The present invention is applied to an exhaust gas purification device that reduces and purifies NO _x in exhaust gas discharged from a diesel engine. Generally, a diesel engine has a cylinder head fixed to a cylinder block, intake and exhaust ports formed in the cylinder head, a cylinder liner provided in the cylinder block, and a piston that reciprocates within a cylinder bore formed in the cylinder liner. There is. The exhaust port is connected to the exhaust pipe, and the exhaust pipe is provided with an exhaust gas purification device. The carrier for the NO _x reduction catalyst can be used by being incorporated in the exhaust gas purifying device as described above, and reduces and reduces NO _x in the exhaust gas discharged from the diesel engine to convert it into N _2. Used for.

The carrier for the NO _x reduction catalyst according to the present invention has a shell-like porous body mainly composed of nickel oxide as a basic structure, and the oxygen vacancy order is established at a predetermined temperature in the pores of the shell-like porous body. - NO _X reduction catalyst having a brownmillerite type structure exhibiting disorder transition is supported. Here, the general formula of the brown mirror light type structure is A ₂ B ₂ O
₅ , A is a divalent metal and B is a trivalent metal. Further, the basic structure of the shell-shaped porous body has fine pores of 0.20 to 0.05 μm on the surface thereof, and the internal diameter of the shell-shaped porous body has pores of 4 to 1 μm. . Further, the nickel oxide forming the shell-like porous body is mainly bonded with an oxide ceramic containing aluminum and silicon.

The structure of the porous body is formed in a honeycomb shape, a foam shape, or a felt shape. In this example, the NO _x reduction catalyst having a Brownmillerite-type structure exhibiting an order-disorder transition of oxygen defects at a predetermined temperature is composed of barium, yttrium and oxygen, and for example, Ba ₃ Y ₄ O ₉ is used. You can In this example, BaLa ₂ O ₄ may be used as the compound having a brown-milarite structure.

Next, with reference to FIG. 1, an embodiment of the method for producing the carrier of the NO _x reduction catalyst will be described. This NO
_{In a} method for producing a carrier for an _X- reducing catalyst, a shell-like porous body having pores mainly composed of nickel oxide is prepared as a basic structure. First, graphite particles of 1 to 0.3 μm were put into a 20 wt% nickel nitrate aqueous solution, which was mixed and suspended. Sodium boron hydride (NaBH ₄ ) was added to this suspended solution and reduced to form a nickel coating on the surface of the graphite particles. The nickel film-forming graphite was filtered, and the graphite was removed as carbon dioxide in an air atmosphere furnace at 800 ° C. to convert nickel into nickel oxide. The nickel oxide powder produced in this manner was a powder having pores of about 1 μm formed inside and fine holes of about 0.2 μm on the surface of the nickel oxide particles.
Next, 15 wt% of clay mineral was added to the nickel oxide powder and fired at 1200 ° C. to prepare a shell-shaped nickel oxide porous body of the basic structure.

Next, as shown in FIG. 1, the mixture contains 0.14 mol of barium acetate Ba (CH ₃ COO) ₂ and 0.16 mol of yttrium nitrate Y (NO ₃ ) _3.
A 0 cc aqueous solution was prepared (step 1). The aqueous solutions were mixed (step 2) and the citric acid C ₆ H ₈ O ₇ was added to 0.
3 mol was added (step 3) and mixed (step 4). Next, 100 cc of a 3 wt% aqueous solution of carbomethylcellulose (CMC) was added to this mixed solution,
A viscous solution was made (step 5). The shell-shaped nickel oxide porous body produced by the above-mentioned manufacturing method was immersed in the mixed solution containing the CMC solution to impregnate the pores of the nickel oxide porous body with the mixed solution (step 6). Then, the nickel oxide porous body impregnated with the above mixed solution is added to 25
Heated at 0 ° C. and evaporated to dryness (step 7). Next, the dried nickel oxide porous body is heated to 1000 ° C.
The mixture impregnated into the pores of the nickel oxide porous body was baked for 2 hours at room temperature to form a Ba ₃ having a brown millerite structure.
The Y ₃ O ₄ O ₉ is converted into Y ₄ O ₉ , and the above Ba ₃ Y ₄ O ₉ is supported in the pores of the nickel oxide porous body, whereby the nickel oxide porous body carrying the NO _x reduction catalyst having the brown millerite type structure ( Hereinafter, a product of the present invention) was produced (step 8).

As a comparative product, the product of the present invention and a conventional cordierite porous body having a honeycomb structure supporting a NO _x reduction catalyst were prepared. A comparative product was prepared by adding barium carbonate to 0.
An aqueous solution containing 14 mol and 0.16 mol of yttrium oxide was mixed to prepare a mixed solution. A cordierite porous body having a honeycomb structure was immersed in this mixed solution to impregnate the pores of the cordierite porous body with the above mixed solution. Then, the cordierite porous body impregnated with the above mixed solution is dried at 1300 ° C. for 1 hour by a dry method, and N
A honeycomb-structured cordierite porous body carrying an O _X reduction catalyst was prepared.

Therefore, the specific surface area and the NO _x reduction rate of the powder of the present invention product and the comparative product were measured. Table 1 shows the results. As measurement conditions, the measurement temperature was 400 ° C., the gas concentration was NO _x 800 ppm / N ₂ , and the space velocity SV was 5 × 10 ⁴ / h.

[Table 1]

As can be seen from Table 1, the specific surface area of the product of the present invention was 8 m ² / g, whereas the specific surface area of the comparative product was 1.2 m ² / g. Further, the NO _x reduction rate of the product of the present invention was 38%, whereas the NO _x reduction rate of the comparative product was 25%.

Further, the basic structure of the nickel oxide porous body of the present invention had 0.2 μm pores on its surface, and 1 μm pores were formed inside the nickel oxide porous body. However, the conditions for the basic structure of the nickel oxide porous body can be arbitrarily changed depending on the graphite used, the thickness of the nickel coating and the oxidizing conditions. However, in consideration of the inflow of exhaust gas into the nickel oxide porous body and the scattering of the NO _x reducing powder, the optimum value of the surface pores and the internal pores of the nickel oxide porous body is 0.05 μm. From 0.2 to 0.2 μm, and it was found that the proper pore size inside the nickel oxide porous body was 1 to 4 μm.

In the above-mentioned Examples, the acetate radicals and nitrate radicals in the mixed solution were removed by thermal decomposition in the production process of the product of the present invention, but they are removed by reacting with an aqueous ammonia solution or another alkaline liquid having an ammonium group. However, the same effect can be obtained.

The increase in the NO _x reduction rate by the product of the present invention is due to the synthesis of powder having a large specific surface area from the homogeneous mixed solution, but the increase in the specific surface area is due to the fact that low temperature calcination is possible. is there. In this low temperature firing, the barium compound and the yttrium compound become a complex in the solution,
It is considered that this is because the mixing of barium and yttrium became uniform and the powder was formed. From the results of the X-ray diffraction analysis of the powders of the dry comparison product and the product of the present invention, the following was found. That is, the dry comparative product had a peak of barium carbonate and was not a compound having a brownmillerite type structure completely, whereas the product of the present invention was a compound having a brownmillerite type structure completely.

In the above embodiment according to the present invention, the nickel oxide porous body was used alone, but a heat resistant fiber such as
The same NO can be obtained even if it is adhered together with a binder to an inorganic fiber such as silicon carbide or alumina and formed into a felt-shaped carrier.
It was possible to form a carrier having an _X- reducing function.

[0023]

INDUSTRIAL APPLICABILITY As described above, the carrier of the NO _X reduction catalyst according to the present invention has NO having a Brown-Millalite type structure in the pores of the shell-like porous body of the basic structure mainly composed of nickel oxide. _{Since the X-} reducing catalyst is supported, the shell-like porous material itself does not become powdered even after long-term use, and the durability can be improved. Moreover, the support of the NO _X reduction catalyst because NO _X reduction catalyst has a full brownmillerite type structure, large specific surface area of the powder as compared with the conventional products, also reduction rate of the NO _X Is larger than that of the conventional product, NO _x contained in the exhaust gas is efficiently reduced, and NO _x is decomposed by the reducing action to be converted into N ₂ and O ₂ , and NO in the exhaust gas is reduced. _X can be reduced.

[Brief description of drawings]

FIG. 1 is a block diagram showing an embodiment of a production method for producing a carrier for a NO _x reduction catalyst according to the present invention.

Claims (3)

[Claims] 1. A general formula A ₂ which has a basic structure of a shell-shaped porous body containing nickel oxide as a main component, and which exhibits an order-disorder transition of oxygen defects at a predetermined temperature in the pores of the shell-shaped porous body.
N having a brown-milarite type structure having B ₂ O ₅
NO _x characterized by having an O _x reduction catalyst supported
A carrier for a reduction catalyst. 2. The basic structure of the shell-shaped porous body has micropores of 0.20 to 0.05 μm on its surface, and the internal diameter of the shell-shaped porous body has pores of 4 to 1 μm or less. The carrier for the NO _x reduction catalyst according to claim 1, which has. 3. The NO _x reduction catalyst according to claim 1, wherein the nickel oxide forming the shell-like porous body is bound mainly by oxide ceramics containing aluminum and silicon. Carrier.