JPH08150339A - Exhaust gas purification catalyst and its production - Google Patents

Abstract

PURPOSE: To obtain a catalyst by which exhaust gas is stably and efficiently purified by feeding a reducing agent such as light oil even in the presence of water by carrying a specified amt. of a noble metal such as Pt or Pd on a phosphoric acid compd. CONSTITUTION: Aluminum phosphate powder is mixed with a silica sol and water to prepare a slurry for wash coating and a honeycomb monolithic carrier 11 is dipped in the slurry and fired under atmospheric pressure to form an aluminum phosphate layer 12 on the surface of the carrier 11. This carrier 11 is then dipped in an aq. soln. of chloroplatinic acid, etc., dried and fired in a reducing atmosphere to carry 0.01-5wt.% noble metal selected from among Pt, Pd, Rh and Ir. Since the resultant noble metal carried phosphoric acid compd. has a relatively large amt. of a solid acid activating a catalyst, NOx is efficiently diminished in the presence of NO, hydrocarbons and oxygen.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for reducing nitrogen oxides (hereinafter referred to as NOx) contained in exhaust gas of automobile engines and a method for producing the same. More specifically, it relates to a catalyst for purifying exhaust gas and a method for producing the same.

[0002]

2. Description of the Related Art A copper ion-exchanged zeolite catalyst is known as a monolith catalyst for reducing NOx of this type.
When oxygen and hydrocarbons are present on this copper ion-exchanged zeolite catalyst, N in the temperature range of 300 to 500 ° C.
The selective reduction of Ox proceeds catalytically with high efficiency, and it becomes possible to purify exhaust gas from diesel engines, lean-burn gasoline engines and the like. This copper ion exchange zeolite catalyst is N
It is a substance in which Na ions of a-type ZSM-5 zeolite are ion-exchanged with Cu ions. Conventionally, a copper ion-exchanged zeolite catalyst is constructed by coating Cu-ZSM-5 zeolite on the surface of a monolith carrier made of a ceramic such as cordierite.

[0003]

However, while the conventional copper ion-exchanged zeolite catalyst has a high NOx selective reduction function, it has a molecular structure that adsorbs water in the presence of water and NOx in the presence of water. There was a problem that the reduction function declined. Further, the above conventional catalyst has a drawback that the crystal structure of zeolite is easily destroyed when water is present and the exhaust gas temperature becomes high.

The object of the present invention is, even in the presence of water,
An object of the present invention is to provide a catalyst for purifying exhaust gas capable of reducing NOx contained in the exhaust gas stably and with high efficiency by supplying a reducing agent such as light oil, and a method for producing the same.
Another object of the present invention is to provide a catalyst for purifying exhaust gas that is not affected by sulfur contained in the exhaust gas and that can stably reduce NOx even at high temperatures, and a method for producing the same.

[0005]

[Means for Solving the Problems]

(a) Catalyst for Purifying Exhaust Gas The first catalyst for purifying exhaust gas of the present invention is a phosphoric acid compound selected from the group consisting of Pt, Pd, Rh and Ir 1.
0.01 to 5% by weight of one kind or two or more kinds of noble metals is supported. In the second exhaust gas purifying catalyst of the present invention, as shown in FIG. 1, a phosphoric acid compound layer 12 is formed on the surface of a monolith carrier 11 made of ceramics or metal, and Pt, Pd, Rh is formed on the phosphoric acid compound layer 12. And at least one noble metal selected from the group consisting of Ir and Ir.
It is a monolith catalyst loaded with 01 to 5% by weight. A third catalyst for purifying exhaust gas of the present invention is a monolith carrier or a pellet carrier obtained by sintering a phosphoric acid compound.
0.01 to 5% by weight of one or more noble metals selected from the group consisting of d, Rh and Ir are supported. In the first to third catalysts, the phosphoric acid compound is preferably aluminum phosphate, zirconium phosphate or silicoaluminophosphate.

A fourth exhaust gas purifying catalyst of the present invention is
Pt in a mixture of sulfuric acid compound and oxide ceramics,
1 or 2 selected from the group consisting of Pd, Rh and Ir
0.01 to 5% by weight of at least one precious metal is supported. In a fifth exhaust gas purifying catalyst of the present invention, a layer made of a mixture of a sulfuric acid compound and an oxide type ceramic is formed on the surface of a monolithic carrier made of ceramics or metal, and Pt, Pd, Rh and One or more precious metals selected from the group consisting of Ir are 0.0
It is a monolith catalyst supported by 1 to 5% by weight. The sixth catalyst for purifying exhaust gas of the present invention is selected from the group consisting of Pt, Pd, Rh and Ir in a monolith carrier or pellet carrier obtained by sintering a mixture of a sulfuric acid compound and oxide ceramics. 0.01 to 1 or 2 or more precious metals
5% by weight is carried. In the fourth to sixth catalysts, the sulfuric acid compound is Al ₂ (SO ₄ ) ₃ , Zr (SO ₄ ) ₂ or FeSO ₄ , and the mixture of the sulfuric acid compound and the oxide ceramics is Al ₂ (SO ₄ ) _3- Al ₂ O ₃ , Zr (S
O ₄₎ is preferably ₂ -Al ₂ O ₃ or FeSO ₄ -Al ₂ O _3. Further, since the sulfuric acid compounds of the fourth to sixth catalysts have a relatively small specific surface area, it is preferable to use a mixture with oxide ceramics having a large specific surface area such as γ-Al ₂ O ₃ . As a result, Pt, Pd, Rh or I
The noble metal of r can be highly dispersed.

(B) Method for Producing Catalyst for Purifying Exhaust Gas The first method for producing a catalyst for purifying exhaust gas of the present invention comprises a step of preparing a slurry by mixing phosphoric acid compound powder, a binder and water. A step of immersing the monolith carrier made of ceramics or metal in the slurry, a step of drying and calcining the monolith carrier immersed in the slurry, and immersing the calcined monolith carrier in an aqueous metal salt solution of Pt, Pd, Rh or Ir. And a step of drying the immersion product and firing it in a reducing atmosphere.

In the first production method of the present invention, a slurry for washcoat is prepared by using phosphoric acid compound powder,
The slurry is coated on the surface of a known monolithic carrier made of ceramics or metal and fired, and one or more metals of Pt, Pd, Rh or Ir are supported on this coating layer. Examples of the ceramic monolith carrier include honeycomb carriers made of cordierite, alumina and the like, and examples of the metal monolith carrier include carriers made of Fe—Cr—Al alloy. The metal carrier is formed into a tubular shape by alternately laminating corrugated metal foils and flat metal foils. The slurry is prepared by mixing the composite oxide powder, a binder such as silica sol, and water. After sufficiently dipping the monolith carrier in this slurry, the monolith carrier dipped in this slurry is dried under atmospheric pressure to obtain a temperature of 500-
Baking at 800 ° C. for 1 to 10 hours. Then, the calcined monolithic carrier is impregnated with an aqueous solution of chloroplatinic acid, an aqueous solution of dinitrodiaminoplatinum, an aqueous solution of rhodium chloride, an aqueous solution of palladium chloride or an aqueous solution of iridium chloride, and after drying, the impregnated product is subjected to a reducing atmosphere, for example, Baking is performed in hydrogen gas at 500 to 700 ° C. for 1 to 3 hours. The content of the noble metal in the aqueous solution of the noble metal salt or the concentration of the aqueous solution is 0.01 to 5% by weight of the noble metal in the catalyst after firing.
However, the amount of the carrier is preferably 0.1 to 3% by weight, and more preferably 1 to 2% by weight.

The second method for producing a catalyst for purifying exhaust gas according to the present invention comprises a step of kneading a phosphoric acid compound powder, a binder and water, a step of molding the kneaded product into a predetermined shape, and a drying of the molded product. And then firing, a step of immersing the sintered body obtained by firing the molded article in an aqueous solution of a metal salt of Pt, Pd, Rh, or Ir, and a step of drying the soaked article and firing in a reducing atmosphere. Is.

In the second production method of the present invention, a phosphoric acid compound powder is kneaded together with a binder and water, the kneaded product is molded into a predetermined shape, and the molded body is dried and fired to form a monolith carrier. , P the monolithic carrier of this sintered body
It is dipped in an aqueous solution of a noble metal salt of t, Pd, Rh or Ir and dried and baked. Examples of the binder include one or more binders selected from the group consisting of kaolin, talc, aluminum nitrate, silica sol and the like. Also, polyvinyl alcohol (P
VA), propylene glycol, methyl cellulose (M
C), carboxymethyl cellulose (CMC), polyethylene glycol (PEG), and the like, and 1 or 2 or more molding auxiliary agents selected from the group. In order to further improve the moldability and the strength of the molded product, when the solid content of the kneaded product is 100% by weight, the kneaded product contains 7% of the composite oxide.
It is preferable to contain 0 to 90% by weight and a binder of 20 to 30% by weight.

The kneading is performed by a kneader so that the respective components are uniformly mixed. The kneaded product is molded using an extrusion molding machine so that the molded product has a honeycomb shape in which a large number of regular through holes such as squares, triangles, and hexagons are formed in the exhaust gas flowing direction. Further, the kneaded product can be molded into pellets. The molded body is dried under atmospheric pressure and then calcined under atmospheric pressure at 500 to 800 ° C. for 1 to 5 hours to produce a monolith carrier. The monolithic carrier of this sintered body is further immersed in the same aqueous solution of chloroplatinic acid, an aqueous solution of dinitrodiaminoplatinum, an aqueous solution of rhodium chloride, an aqueous solution of palladium chloride or an aqueous solution of iridium chloride, which is the same as in the first production method. By drying and firing in the same manner as in the first manufacturing method, Pt, Pd, Rh or I
r is supported. The content of the above-mentioned noble metal in the aqueous solution of the noble metal salt or the concentration of this aqueous solution is the same as in the first production method.

A third method for producing a catalyst for purifying exhaust gas according to the present invention comprises a step of preparing a slurry by mixing a powder comprising a mixture of a sulfuric acid compound and an oxide-based ceramic, a binder and water, and a ceramic or A step of immersing the metal monolith carrier in the slurry, a step of drying and firing the monolith carrier immersed in the slurry, and a step of immersing the fired monolith carrier in an aqueous metal salt solution of Pt, Pd, Rh or Ir. And a step of drying the immersion product and firing it in a reducing atmosphere. The third manufacturing method is the same as the first manufacturing method except that a powder made of a mixture of a sulfuric acid compound and oxide-based ceramics is used instead of the phosphoric acid compound powder.

A fourth method for producing a catalyst for purifying exhaust gas according to the present invention comprises a step of kneading a powder made of a mixture of a sulfuric acid compound and an oxide-based ceramic, a binder and water, and shaping the kneaded material into a predetermined shape. A step of molding, a step of drying and firing the molded article, and a sintered body obtained by firing the molded article being Pt, Pd,
It is a method including a step of immersing in a metal salt aqueous solution of either Rh or Ir, and a step of drying the immersed material and firing in a reducing atmosphere. The fourth manufacturing method is the same as the second manufacturing method except that a powder made of a mixture of a sulfuric acid compound and an oxide ceramic is used instead of the phosphoric acid compound powder.

In the first to fourth manufacturing methods, Pt and P are used.
When two or more kinds of noble metals of d, Rh or Ir are carried, the aqueous solution of two or more kinds of noble metal salts may be mixed, the monolith carrier may be dipped in the mixed solution and dried, and then baked in a reducing atmosphere. It is preferable to first immerse the monolith carrier in the first aqueous solution of the noble metal salt, dry it, and fire it in a reducing atmosphere, and then immerse the monolith carrier in the second aqueous solution of the precious metal salt, dry it, and fire it in a reducing atmosphere. .

[0015]

In the first catalyst, since the Pt, Pd, Rh or Ir-supported phosphoric acid compound has a relatively large amount of solid acid that activates the catalyst, NOx in the presence of NO, hydrocarbons and oxygen. It can be reduced with high efficiency. Further, since the above-mentioned phosphoric acid compound has a large mechanical strength, even against high-temperature exhaust gas,
Even in the presence of water, there is little change in the catalyst, and NOx contained in the exhaust gas can be reduced with high efficiency. In particular, the NOx reduction function is not impaired even when high-temperature exhaust gas is passed for a long time. In the fourth catalyst, the sulfuric acid compound exhibits solid acidity with strong electron withdrawing property. As a result, Pt, P
The sulfuric acid compound carrying d, Rh or Ir cracks hydrocarbons and can highly reduce NOx in the presence of NO and oxygen. Further, the NOx contained in the exhaust gas can be reduced with high efficiency even with respect to the high-temperature exhaust gas, in the presence of water, and even when the exhaust gas contains sulfur. In particular, the NOx reduction function is not impaired even when high-temperature exhaust gas is passed for a long time.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following examples. <Example 1> Aluminum phosphate powder, silica sol, and water were uniformly mixed to prepare a slurry for washcoat. After the honeycomb-shaped monolithic carrier 11 made of cordierite is sufficiently dipped in this slurry, the monolithic carrier 11 dipped in this slurry is dried, and under atmospheric pressure.
It was baked at 700 ° C. for 3 hours. A layer 12 of aluminum phosphate was formed on the surface of the monolith carrier 11. Next, the monolith carrier 11 on which the aluminum phosphate layer 12 is formed
Is immersed in a chloroplatinic acid aqueous solution (chloroplatinic acid concentration 2%),
After drying, the immersion product was calcined in a reducing atmosphere, for example, hydrogen gas at 500 ° C. for 3 hours to obtain a monolith catalyst 10. The aluminum phosphate layer 11 supported 1% by weight of Pt.

Example 2 100 g of γ-Al ₂ O ₃ powder
Aluminum sulfate aqueous solution (aluminum sulfate concentration 5
%), Mixed and dried, and then baked at 300 ° C. under atmospheric pressure for 5 hours to form Al ₂ (SO ₄ ) ₃ -Al ₂ O ₃
Of powder was obtained. This Al ₂ (SO ₄ ) ₃ -Al ₂ O ₃ powder, silica sol and water were uniformly mixed to prepare a wash coat slurry. A honeycomb-shaped monolithic carrier made of cordierite was sufficiently dipped in this slurry, and then the monolithic carrier dipped in this slurry was dried and calcined under atmospheric pressure at 600 ° C. for 3 hours. A layer of Al ₂ (SO ₄ ) ₃ —Al ₂ O ₃ was formed on the surface of the monolith carrier. Then, the monolith carrier on which the Al ₂ (SO ₄ ) ₃ -Al ₂ O ₃ layer is formed is immersed in a chloroplatinic acid aqueous solution (chloroplatinic acid concentration of 2%) and dried, and then the immersion product is subjected to a reducing atmosphere, It was calcined in hydrogen gas at 600 ° C. for 3 hours to obtain a monolith catalyst. The Al ₂ (SO ₄ ) ₃ -Al ₂ O ₃ layer contains 1% by weight of P.
carried t.

Comparative Example 1 A monolithic carrier composed of cordierite having the same shape and size as the monolithic carrier of Example 1 contains a copper ion-exchanged zeolite in which Na ions of Na-type ZSM-5 zeolite are ion-exchanged with Cu ions. After immersing in the wash coat slurry and drying, under atmospheric pressure, 5
It was calcined at 00 ° C for 3 hours to obtain a monolith catalyst.

<Evaluation Test> Regarding the monolith catalysts of Examples 1, 2 and Comparative Example 1, part of the exhaust gas of the following diesel engine was introduced into the catalytic reaction tube to carry out NOx catalytic reduction to reduce NOx. Examined. Test gas is NO 1
000ppm, HC 100ppm, SO ₂ 10pp
An engine exhaust gas containing m, O ₂ of 10% and H ₂ O of 6% was used. As a reducing agent, light oil ((light oil /
NO) = 2 was added. Test gas is 20 by electric furnace
0 ° C, 250 ° C, 300 ° C, 350 ° C, 400 ° C and 4
It is controlled to the temperature of 50 ° C., the space velocity (S of 20000Hr ^-1 reduction rate of NOx in the each temperature
V). The result is shown in FIG. The NOx reduction rate was calculated by the following equation, where C _{1 is} the NO concentration before passing the monolith catalyst and C ₂ is the NO concentration after passing the monolith catalyst. NOx reduction rate = {(C ₁ -C ₂ ) / C ₁ } × 100 (%) (1) As is apparent from FIG. 2, the test gas contained 6% of H ₂ O. The NOx reduction rate of the monolith catalyst was 15% at 400 ° C., whereas the NOx reduction rate of the catalysts of Example 1 and Example 2 showed values of about 24% and about 26% at 250 ° C., respectively. Values of about 18% and about 15% were obtained at 400 ° C, respectively. In particular, the NOx reduction rate of the monolith catalyst of Comparative Example 1 decreased relatively early over time, whereas the monolith catalysts of Example 1 and Example 2 maintained substantially the same NOx reduction rate for a long period of time. .

[0020]

As described above, according to the present invention, the monolith carrier or pellet carrier formed of a phosphoric acid compound or the ceramic carrier or metal carrier coated with the phosphoric acid compound layer is relatively solid. Has an acid. The catalyst of the present invention has Pt, Pd, Rh or Ir on the surface of the phosphoric acid compound which acts as the solid acid catalyst.
Since NOx is supported, NOx can be highly efficiently reduced in the presence of NO, hydrocarbons and oxygen. Further, since the above-mentioned phosphoric acid compound has a large mechanical strength, even against high-temperature exhaust gas,
Even in the presence of water, there is little change in the catalyst, and there is an excellent effect of reducing NOx contained in exhaust gas with high efficiency. In addition, a monolith carrier or pellet carrier formed of a mixture of a sulfuric acid compound and oxide-based ceramics, or a ceramic carrier or a metal carrier coated with a layer of the above-mentioned sulfuric acid compound or the like has a strong electron withdrawing property when a compound is formed with oxygen. Solid acidity is developed under the condition. Since the catalyst of the present invention carries Pt, Pd, Rh or Ir on the surface of a sulfuric acid compound or the like which acts as this solid acid catalyst,
NOx in the presence of NO, hydrocarbons and oxygen as above
Can be reduced with high efficiency. Also for high temperature exhaust gas,
Even in the presence of water, even if sulfur is contained in the exhaust gas, NOx contained in the exhaust gas can be reduced with high efficiency with little change in the catalyst.

[Brief description of drawings]

FIG. 1 is a configuration diagram of a catalyst for purifying exhaust gas according to a first embodiment of the present invention.

FIG. 2 is a graph showing changes in NOx reduction rates of catalysts of Examples 1 and 2 of the present invention and Comparative Example 1 depending on the catalyst inlet temperature.

[Explanation of symbols]

 10 monolith catalyst (catalyst) 11 monolith carrier 12 phosphoric acid compound layer

─────────────────────────────────────────────────── ───

[Procedure amendment]

[Submission date] March 22, 1995

[Procedure Amendment 1]

[Document name to be amended] Statement

[Correction target item name] 0016

[Correction method] Change

[Correction content]

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Next, embodiments of the present invention will be described in detail with reference to the drawings. The present invention is not limited to the following examples. <Example 1> Aluminum phosphate powder, silica sol, and water were uniformly mixed to prepare a slurry for washcoat. After the honeycomb-shaped monolithic carrier 11 made of cordierite is sufficiently dipped in this slurry, the monolithic carrier 11 dipped in this slurry is dried, and under atmospheric pressure.
It was baked at 700 ° C. for 3 hours. A layer 12 of aluminum phosphate was formed on the surface of the monolith carrier 11. Next, the monolith carrier 11 on which the aluminum phosphate layer 12 is formed
Is immersed in a chloroplatinic acid aqueous solution (chloroplatinic acid concentration 2%),
After drying, the immersion product was calcined in a reducing atmosphere, for example, hydrogen gas at 500 ° C. for 3 hours to obtain a monolith catalyst 10. The aluminum phosphate layer 1 2 1 wt% of Pt was supported.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B01J 27/053 ZAB A F01N 3/28 ZAB 301 Z B01D 53/36 102 A

Claims (13)

[Claims] 1. A phosphoric acid compound containing Pt, Pd, Rh and I.
A catalyst for purifying exhaust gas carrying 0.01 to 5% by weight of one or more precious metals selected from the group consisting of r. 2. A phosphoric acid compound layer (12) is formed on the surface of a monolithic carrier (11) composed of ceramics or metal, and the phosphoric acid compound layer (12) is selected from the group consisting of Pt, Pd, Rh and Ir. 0.0% of one or more precious metals
A catalyst for purifying exhaust gas supported by 1 to 5% by weight. 3. A monolith carrier or a pellet carrier obtained by sintering a phosphoric acid compound contains 0.0 or more of one or more noble metals selected from the group consisting of Pt, Pd, Rh and Ir.
A catalyst for purifying exhaust gas supported by 1 to 5% by weight. 4. The catalyst for purifying exhaust gas according to claim 1, wherein the phosphoric acid compound is aluminum phosphate, zirconium phosphate or silicoaluminophosphate. 5. Exhaust gas in which 0.01 to 5% by weight of one or more noble metals selected from the group consisting of Pt, Pd, Rh and Ir is carried in a mixture of a sulfuric acid compound and an oxide ceramic. Catalyst to purify. 6. A layer (12) made of a mixture of a sulfuric acid compound and an oxide type ceramic is formed on the surface of a monolith carrier made of ceramics or metal, and P is formed in the mixture layer.
A catalyst for purifying exhaust gas carrying 0.01 to 5% by weight of one or more noble metals selected from the group consisting of t, Pd, Rh and Ir. 7. A monolith carrier or pellet carrier obtained by sintering a mixture of a sulfuric acid compound and an oxide-based ceramic is selected from the group consisting of Pt, Pd, Rh and Ir.
A catalyst for purifying exhaust gas carrying 0.01 to 5% by weight of one or two or more noble metals. 8. The sulfuric acid compound is Al ₂ (SO ₄ ) ₃ , Zr.
The catalyst for purifying exhaust gas according to any one of claims 5 to 7, which is (SO ₄ ) ₂ or FeSO ₄ . 9. A mixture of a sulfuric acid compound and oxide-based ceramics is Al ₂ (SO ₄ ) ₃ -Al ₂ O ₃ , Zr (SO ₄ ) ₂
The catalyst for purifying exhaust gas according to claim 5, which is —Al ₂ O ₃ or FeSO ₄ —Al ₂ O ₃ . 10. A step of mixing a phosphoric acid compound powder, a binder and water to prepare a slurry, a step of immersing a monolith carrier made of ceramics or a metal in the slurry, and a step of drying the monolith carrier immersed in the slurry. And calcining, and Pt, Pd, Rh or Ir for the calcined monolith support.
A method for producing a catalyst for purifying exhaust gas, which comprises a step of immersing the metal salt aqueous solution in any one of the above, and a step of drying the soaked product and firing in a reducing atmosphere. 11. A step of kneading a phosphoric acid compound powder, a binder, and water, a step of molding the kneaded product into a predetermined shape, a step of drying and firing the molded article, and a firing of the molded article. Sinter the sintered body with Pt, Pd, Rh or I
A method for producing a catalyst for purifying exhaust gas, which comprises a step of immersing in any one of the aqueous metal salt solutions of r and a step of drying the soaked product and firing in a reducing atmosphere. 12. A step of preparing a slurry by mixing a powder made of a mixture of a sulfuric acid compound and an oxide ceramics, a binder and water, and a step of immersing a monolithic carrier made of ceramics or metal in the slurry. A step of drying and calcining the monolith carrier immersed in the slurry; and Pt, Pd, Rh or Ir of the calcined monolith carrier.
A method for producing a catalyst for purifying exhaust gas, which comprises a step of immersing the metal salt aqueous solution in any one of the above, and a step of drying the soaked product and firing in a reducing atmosphere. 13. A step of kneading a powder made of a mixture of a sulfuric acid compound and an oxide-based ceramics, a binder and water, a step of molding the kneaded material into a predetermined shape, and a step of drying and firing the molded material. And a sintered body obtained by firing the molded product, Pt, Pd, Rh or I
A method for producing a catalyst for purifying exhaust gas, which comprises a step of immersing in any one of the aqueous metal salt solutions of r and a step of drying the soaked product and firing in a reducing atmosphere.