JPS63305938A - Catalyst for purifying exhaust gas - Google Patents

Abstract

PURPOSE:To enhance the purification capacity of CO, hydrocarbon and NOx by carrying composite oxide having a specified perovskite type structure on a carrier consisting of compds. having the perovskite type structure and forming a catalyst for purifying exhaust gas. CONSTITUTION:The following aq. soln. is added to the powder of a marketing carrier wherein nitrate of metal constituting composite oxide La1-xSrxMO3 (0<x<0.5, M is V, Cr, Mn, Co, Fe, Ni and Cu) having a perovskite type structure being a catalytic component is mixed at a prescribed stoichiometric ratio. Then the mixture is dried at about 100 deg.C for 5-12hr in the atmosphere and thereafter calcined at 700-800 deg.C for 5-10hr in the atmosphere. The nitrate is pyrolyzed by this heat treatment and perovskite composite oxide is carried on the carrier. The amount of the catalytic component to be carried is regulated to 1-80wt.% preferably to 5-30wt.%.

Description

Detailed Description of the Invention [Industrial Application Field] The present invention is directed to carbon monoxide (C
O) This invention relates to an exhaust gas purifying catalyst that has excellent performance in purifying hydrocarbons (HC) and nitrogen oxides (NOX).

[Prior art and problems]

A complex oxide with a perovskite structure consisting of rare earth metals, alkaline earth metals, and transition metals is Co, H
Catalysts that have excellent C and NoX purification properties and contain these substances as catalyst components are expected to be put into practical use as exhaust gas catalysts for automobiles, etc. as inexpensive catalysts that do not contain precious metals.
Patent application (JP-A-59-87046.6O-82138
) has also been done. However, until now, when exposed to exhaust gas at temperatures of 900°C or higher for a long period of time, there have been problems with the carrier that supports the catalyst components, resulting in a phenomenon in which the catalyst's ability to purify Co, HC, and NO is significantly reduced.

Conventionally, heat-resistant oxides such as 717203, Tio, and 15IO□ have been used as carriers for supporting catalyst components. However, when /Vz03 and the like coexist with a composite oxide having a perovskite structure as a catalyst component, they react with each other at temperatures above 900°C.

The catalyst components were decomposed and the catalyst activity decreased.

In addition, the catalyst components easily move on the surface of the carrier N20's, etc., causing migration and adhering to each other.
As a result, the effective surface area of the catalyst components decreases.

Catalytic activity decreased. In this way, composite oxides having a perovskite structure can be used as carriers for long periods of time at temperatures of 900°C or higher.
As long as oxides such as No. 3 were used, there was a problem with the durability of the catalyst activity, and it was impossible to put it to practical use.

Therefore, the inventors of the present invention conducted various studies on carriers that do not react with catalyst components, and have completed the present invention.

[Description of the invention]

The present invention uses the general formula Lad-xSrXMo3 (0< x < 0.5
, M=V, Cr, Mn, Co, Fe, N
i, one or more selected from Cu) and the following three groups which are carriers, ■ General formula ABO3+ having a perovskite structure (where A is an alkaline earth metal, B is Ti, Zr A compound represented by one or more of the following.

■General formula LnAZO3 (with perovskite structure)
However, Ln is a compound represented by a rare earth metal.

■ General formula n2B2cJ with pyrochlore type structure
) (where Ln is a rare earth metal and B is one or more of Ti and Zr).

The present invention relates to an exhaust gas purifying catalyst characterized by being composed of one or more selected compounds.

The important point of the present invention is that the general formula ABO3 (where A is an alkaline earth metal) has a perovskite structure instead of the conventionally widely used carrier such as M2O3.

B is that a compound represented by one or both of Ti and Zr is used. These carrier compounds are 90
It is thermally stable at temperatures above 0°C.

Also, as with the case of using Alt03 etc., it does not contribute to improving the catalytic activity, but A! , 03, etc.

It does not react with the catalyst component, a composite oxide having a perovskite structure, and will not reduce the catalyst activity. Also 1
The catalyst component and the support used in the present invention both have rare earth metals or alkaline earth metals with similar chemical properties.1 These metals form a slight solid solution in the contact area between the two, and the catalyst component firmly adheres to the support. It comes to be in close contact with. Therefore, migration of catalyst components on the carrier is suppressed.

Decrease in catalyst activity due to decrease in surface area is effectively prevented.

This effect is particularly remarkable when the catalyst is manufactured by a method in which catalyst components are supported on a carrier. In addition, when using a mixture of pre-produced catalyst component powder and carrier powder, the catalytic acid component can be present between the carrier particles, so sintering and migration between the catalyst components can be suppressed, and as a result, the surface area A decrease in activity due to reduction is prevented, and exhaust gas purification ability is maintained for a long period of time. Further, when a mixed powder of the catalyst component and the carrier is made into a slurry and used by coating it on a base material, the same effect as when using the mixed powder can be obtained. Therefore, the catalyst according to the present invention has a temperature of 900"C
CO, HC and NOX used for a long time in the above
It is extremely effective as a three-way catalyst for purification.

[Explanation of implementation/modes]

Embodiments of the present invention will be described in detail.

The catalyst component used in the catalyst according to the present invention has a general formula of La+-
xSrxMo3(0<x<0.5.M=V,
Cr, Mn.

one or more selected from Co, Fe, Ni, Cu)
It is a composite oxide with a perovskite structure shown in It is desirable that the value of In particular, the catalytic activity is high in the range of 0.1 to 0.3. The shape, particle size, purity, specific surface area, etc. of the composite oxide may be in a state normally used as a catalyst component.

As the carrier, one or more compounds selected from the following groups are used.

■ General formula ABO3 having a perovskite structure (where A is an alkaline earth metal, such as Sr or Ca).

B is a compound represented by one or more of Ti and Zr.

■General formula LnAZO3 (with perovskite structure)
However, Ln is a rare earth metal such as La, Ce, Pr, Nd, Pm
, Sm, Eu.

Gd, Tb, Dy, Ho, Er, Tm, Y
b, Lu, Y, Sc).

(2) A compound having a pyrochlore type structure and represented by the general formula LnJz07 (wherein Ln is the above-mentioned rare earth metal, and B is one or both of Ti and Zr).

All of the compounds included in the above groups do not deteriorate or decompose themselves even when heated at temperatures of 900° C. or higher for a long period of time, nor do they react with each other and have excellent heat resistance. These compounds may be used in the same state (shape, particle size, purity, specific surface area, etc.) as Al 203, etc., which are widely used as carriers for catalyst components. For example, the specific surface area is desirably 10 m/g or more in order to maintain highly dispersed catalyst components. It is usually sufficient to use commercially available materials.

The catalyst according to the present invention is manufactured by a method normally used for manufacturing catalysts. Next, one example of the manufacturing method will be explained.

As a method for producing a catalyst component by supporting it on a carrier, a composite oxide Lad-xSrxMo3 (M = V, C
An aqueous solution of metal nitrates constituting Mn, Co, Fe, Ni, and Cu) mixed in a predetermined stoichiometric ratio was added and dried in the air at about 100°C for 5 to 12 hours.

Thereafter, it is further fired in the air at 700-800°C for 5-10 hours. Through this heat treatment, the nitrate is thermally decomposed, and the perovskite composite oxide is supported on the carrier. The supported amount of the catalyst component is 1 to 80% by weight, preferably 5 to 30% by weight.
Weight%.

Further, when mixing catalyst component powder and carrier powder, first, the catalyst component powder is manufactured. Composite oxide Lal-) (SrxMo3 (M=V,
A predetermined amount of an alkali salt such as sodium carbonate is added to an aqueous solution in which nitrates of each metal (Cr, Mn, Co, Fe, Ni, Cu) are mixed at a predetermined stoichiometric ratio to obtain a coprecipitate. . Next, after drying the precipitate, 5
After firing in air at 00~600°C, 700~800'
The mixture is further calcined in the air for 3 to 5 hours at C to obtain a composite oxide powder having a perovskite structure, which is a catalyst component. Thereafter, a predetermined amount of commercially available carrier powder is mixed with the catalyst component powder and used as a mixed powder, the mixed powder is molded into a predetermined shape and used, or water is added to the mixed powder to form a slurry. Use by applying it to a base material.

The amount of catalyst component powder added is preferably 10 to 80%.

Next, the present invention will be explained with reference to Examples, but the present invention is not limited thereto.

Example 1 90 g of commercially available 5rZrO:+ powder with a specific surface area of 18rd/g and a purity of 99% or higher was prepared as a carrier, and 14.69 g of lanthanum nitrate (La(NO3)3JH20) was added to this.
, strontium nitrate (sr(No3)z) 1.
79 g and cobalt nitrate (Co(NO3)2.6H
20) 40 ml of an aqueous solution containing 12.35 g was added and mixed, followed by drying in the air at 110°C for 10 hours. After that, it was fired in the atmosphere at 800°C for 93 hours to thermally decompose the nitrates and form a composite oxide (Lao, aSr) having a perovskite structure containing Co on 5rZr03.
o, zCOO3) supported catalyst (sample No. 1)
I got it.

Example 2 Commercially available purity 99 was used instead of 5rZr03 powder as a carrier.
．． A composite oxide with a perovskite structure containing Co on 5rZr03 (Lao, 5Sro, zCoO:
+ ) supported catalyst (sample No. 2) was prepared.

Example 3 Lanthanum nitrate (La(NO3)3.6H20) 69.
28 g and cobalt nitrate (Co(NO3)2-6H20
) 58.2 g and strontium nitrate (Sr(NO3
)z) A 2N aqueous solution was prepared by dissolving 8.48 g. Next, a coprecipitation neutralizer was prepared by dissolving 70 g of sodium carbonate (NazCO3) in 700 ml of distilled water.

The coprecipitation neutralizing agent was added dropwise to the above aqueous solution to obtain a coprecipitate. After filtration and thorough washing with water, vacuum drying was performed. Next, it was fired at 600°C in the atmosphere, and after being crushed, it was further
After baking at 00°C for 23 hours, composite oxides Lao, 5sro, 2COO3 with perovskite structure were prepared.
was synthesized.

−10= The specific surface area of this powder was 8.5 n(/g).

This powder was mixed with 5rZr(h) or 5rTiOi in a weight ratio of 1:1, and water was added to form a slurry. These were dried and formed into catalysts Lao, 5sro,
2COO3/5rZrO1 (sample No. 3) and Lao, asro, 2COO3/5rTi (h
(Sample No. 4) was obtained.

Example 4 90 g of commercially available 99% pure CaTiO3 powder as carrier
Lanthanum nitrate (La(NO3):+・6H20)
11.74 g + strontium nitrate (Sr(N03)
z) 3.83 g and manganese nitrate (Mn(NO3)2
・6H20) 40ml of an aqueous solution containing 12.97g
After mixing, the mixture was dried in the air at 110° C. for 110 hours. Thereafter, the compound oxide La (1,6Sro,
The catalyst supporting 4Mn03 (sample No. 5) was
I made arrangements.

Example 5 An aqueous solution added to 90 g of CaTi03 powder was 13.31 g of lanthanum nitrate (La(NO3)3-6820).
, Strontium nitrate (sr (No3L) 2.79
g, cobalt nitrate (Co(NO3)z・6)1zO
) 2.56 g, iron nitrate (Fe (NO3)s・9
)1zo) 40ml of an aqueous solution containing 14.19 g
CaTiO was prepared in the same manner as in Example 4 except that
Composite oxide with perovskite structure containing Co and Fe on 3 powder Lao, Jro, 3COO,z
Catalyst supporting Fe (1,803) (sample No. 6)
adjusted.

Example 6 Lanthanum nitrate (La(NO:+)3.6Hzo) 77
．． 9 g, strontium nitrate (Sr(NCh)z)
4.23 g, iron nitrate (Fe(NO3)3.98z
o) Aqueous solution in which 80.8 g of 2! was prepared, and 600 d of 10% ammonia water was dropped thereto to obtain a coprecipitate. After washing and filtering.

Drying was carried out in air at 110°C for 15 hours. Next, it is fired at 600°C in the air, and then further heated to 800°C after pulverization.
The composite oxides having a perovskite structure, ao, qSro, and 1FeO3, were synthesized by firing in the air for 5 hours.

Next, a composite oxide having a perovskite structure containing M as a carrier was synthesized by the method described below.

100g of commercially available T-Nz(h (99% purity) was added to lanthanum nitrate (La(No:+)3.68zO) 425
The mixture was added to 400 g of an aqueous solution containing 400 g of the solution, mixed, and then evaporated to dryness.

After that, it was heated in the air at 600°C for 3 hours.

After thermally decomposing lanthanum nitrate, it was calcined in the air at 900°C for 8 hours to synthesize LaAlO3.

The above Lao, qSro, +FeO3 powder and LaAl
A catalyst (sample No.
, 7) were adjusted.

Example 7 An example of a catalyst using a composite oxide having a pyrochlore structure as a carrier will be described. Lanthanum nitrate (La(NO3)
)3.6tlzO) 86.6 g and zirconyl nitrate (
Aqueous solution 2 in which 53.45 g of ZrO(NO3)2.2H20) was dissolved! 700 d of 10% ammonia water was added dropwise to obtain a coprecipitate. After washing with water and filtering, vacuum drying was performed. Next, it was calcined at 900°C for 5 hours in the air to synthesize LazZrzO7, which is a pyrochlore type compound.

The LaJr20t was used as the catalyst prepared in Example 4 (Lao,
A catalyst (Sample No. 8) was prepared in the same manner as in Example 4, except that CaTiO3 was used instead of CaTiO3, which is the carrier of bsro, 4Mno:+/CaTi03).

Example 8 Further, an example of a catalyst using a composite oxide having a pyrochlore structure as a carrier will be described.

Chromium nitrate (Cr(No:+) 3.911zo) 8
0 g and lanthanum nitrate (La(NO3)3.6H20
) 65 g and strontium nitrate (Sr(N031z
) Aqueous solution 70 in which 70 g of sodium carbonate (NazCO+) was dissolved in aqueous solution 21 in which 10.6 g of sodium carbonate (NazCO+) was dissolved.
0 ml was added dropwise to obtain a coprecipitate. After washing with water and filtration, it was vacuum dried and further calcined in the air at 800°C for 5 hours to synthesize compounds having a perovskite structure, Lao, 7ssro, and 25Cro3, which were catalyst components.

Next, 95.9 g of commercially available titania (T+Oz) powder was prepared. Next, yttrium nitrate was heated to 600°C for 1 hour in the air and pyrolyzed to obtain yttrium 112.
Add 9g to the above titanium powder and mix thoroughly.

It was baked in the air for 5 hours. After pulverization, it was further calcined in the air at 900°C for 10 hours to synthesize a composite oxide YzTizOi having a pyrochlore structure as a carrier.

The above Lao, 7SsrO, z5cr03 powder and YzT
Mix izO7 powder at a weight ratio of 3:2 to prepare a catalyst (sample No.
, 9) was obtained.

[Comparative Example 1] Lao, BSro, zcoOJ synthesized in Example 3
The l powder was used as a comparative catalyst (sample No. 10).

[Comparative Example 2] Commercially available 99.5% α-A was used instead of 5rZr03, which is the carrier in the catalyst of Example 1 (sample No. 1).
! A comparative catalyst (sample No. 11) was prepared in the same manner as in Example 1, except that the sample No. 203 was used.

[Comparative Example 3] Catalyst of Example 3 (Sample No. 3 and No. 4
) as carriers in 5rZrOs and 5rTi0
Commercially available 99.5% α-A instead of 3! A comparative catalyst (
Sample Nα12) was adjusted.

[Comparative Example 4] The catalyst of Example 4 (Sample No. 5) except that CaTiO3 powder as a carrier was replaced with commercially available SiO□ powder.

A comparative catalyst (sample Nα
13) was adjusted.

[Comparative Example 5] A comparative catalyst (sample No. 14) was prepared in the same manner as in Example 8 except that YzTizQt, the carrier in the catalyst of Example 8 (sample No. 9), was replaced with TiO□.
) was adjusted.

[Test Example 1] As a heat resistance test, each of the catalysts prepared in Examples and Comparative Examples was heated in the air at 1000°C for 5 hours.

[Test Example 2] For each of the catalysts prepared in Examples and Comparative Examples, a purification activity durability test was conducted for 250 hours in exhaust gas at an inlet gas temperature of 750°C. The gas composition is COI.

0%, CJaO, 1%, CO□ 10%, 820
With the fluctuation conditions of 1% and 0□, the remainder is N2.

〔evaluation〕

5oo'c for the catalysts subjected to the above heat resistance and durability tests.
Carbon monoxide (CO) and propylene (C3) in
) was measured. The gas composition is the same as in Test Example 2.

As shown in Tables 1 and 2, the catalyst of the present invention maintains a higher purification rate after the heat resistance and durability tests than the comparative example.

[Test Example 3] Lao, esro, z to evaluate the No purification rate
A catalyst prepared by mixing cooa and 5rZrO in a weight ratio of 1:1 (sample N).

3) and as comparative catalysts Lao, eSro,
2COO:1 (sample No. 10) was prepared. Both catalysts were heated to 1000'C.

After heating in the atmosphere for 3 hours, using the exhaust gas used in Test Example 2 with 50 ppm NO added, the gas concentration was 70.
The purification properties for NO were investigated at 0°C.

As a result, the No purification rate was 50% for the comparison catalyst, but was excellent at 72% for the catalyst according to the present invention.

Claims (1)

[Claims] General formula L having a perovskite structure as a catalyst component
a_1_−_xSr_xMo_3(0<x<0.5, M
= one or more selected from V, Cr, Mn, Co, Fe, Ni, Cu) and the following (
An exhaust gas purifying catalyst comprising one or more compounds selected from groups 1) to (3). (1) General formula ABO_3 with perovskite structure
(However, A is an alkaline earth metal, and B is one or more of Ti and Zr). (2) General formula LnAlO with perovskite structure
A compound represented by _3 (Ln is a rare earth metal). (3) General formula Ln_2B_ having a pyrochlore type structure
2O_7 (Ln is a rare earth metal, B is Ti, Zr 1
A compound represented by a species or two or more species.