JP2620624B2 - Exhaust gas purification catalyst - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to carbon monoxide (CO) used at 900 ° C. or higher,
The present invention relates to an exhaust gas purifying catalyst having excellent hydrocarbon (HC) and nitrogen oxide (NO _X ) purifying performance.

[Conventional technology and problems]

Complex oxide having a rare earth metal, a perovskite-type structure composed of alkaline earth metal preliminary transition metal has excellent characteristics of purification of CO, HC and NO _X, the catalyst comprising a substance catalyst component automobile as an inexpensive catalyst including no noble metal It is expected that the catalyst will be put to practical use as an exhaust gas catalyst, and patent applications (JP-A-59-87046, 60-82138) have been filed. However, there has been a problem with the carrier that carries the catalyst components when exposed to exhaust gas at 900 ° C or higher for a long time.
The phenomenon that the purification ability for C and NO _X was remarkably reduced was observed.

Conventionally, heat-resistant oxides such as Al ₂ O ₃ , TiO ₂ , and SiO ₂ have been used as supports for supporting catalyst components. However, when Al ₂ O _{3 and the} like and the composite oxide having a proovskite structure as a catalyst component coexisted, they reacted with each other at 900 ° C. or higher, and the catalyst component was decomposed, resulting in a decrease in catalytic activity. In addition, the catalyst component easily migrated on the surface of the carrier such as Al ₂ O ₃ and caused migration and adhered to each other, thereby decreasing the effective surface area of the catalyst component and decreasing the catalytic activity. As described above, when the composite oxide having a perovskite structure is used for a long time at a temperature of 900 ° C. or more, the durability of the catalytic activity is as long as the oxide such as Al ₂ O ₃ which has been conventionally used as a carrier is used. There was a problem and it was impossible to put it to practical use.

Therefore, the present inventors have made various studies on a carrier that does not react with the catalyst component and made the present invention.

[Description of the Invention]

The present invention relates to a catalyst component having a perovskite structure represented by a general formula La _1-X Sr _x MO ₃ (0 <x <0.5, M = V, Cr, Mn, Co, Fe,
A complex oxide represented by at least one selected from Ni and Cu) and the following three groups of carriers, represented by the general formula LnAlO ₃ (where Ln is a rare earth metal) having a perovskite structure of SiZrO ₃ and CaTiO ₃ Compound.

General formula Ln ₂ B ₂ O ₇ having pyrochlore structure (however, 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 comprising one or more compounds selected from the group consisting of:

An important point of the present invention is that SrZrO ₃ and CaTiO ₃ are used in place of Al ₂ O _{3 and the} like which have been widely used in the past. These carrier compounds are thermally stable at temperatures above 900 ° C.

Also, it does not contribute to the improvement of the catalytic activity as in the case of using Al ₂ O ₃ etc., but unlike the case of Al ₂ O ₃ etc., it reacts with the composite oxide having a perovskite type structure as the catalyst component and reacts with the catalytic activity Is not reduced. In addition, the catalyst component and the carrier used in the present invention have both a rare earth metal or an alkaline earth metal having similar chemical properties. To adhere firmly to Therefore, migration of the catalyst component on the carrier is suppressed, and a decrease in catalyst activity due to a decrease in surface area is effectively prevented. This effect is particularly remarkable when a catalyst is produced by a method in which a catalyst component is supported on a carrier. In addition, when the pre-produced catalyst component powder and the carrier powder are mixed and used, the catalyst component can be present between the carrier particles, so that sintering and migration of the catalyst components can be controlled, resulting in a reduction in surface area. Thus, the activity of the exhaust gas is prevented from lowering, and the exhaust gas purifying ability is maintained for a long time. In addition, when the mixed powder of the catalyst component and the carrier is made into a slurry and applied to a base material, the same effect can be obtained as when the powder is mixed and used.
Therefore, the catalyst according to the present invention is extremely effective as a three-way catalyst for purifying CO, HC and NO _X used for a long time at 900 ° C. or higher.

(Description of Embodiment)

 An embodiment 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 _1-X S
r _x MO ₃ is a composite oxide having a perovskite type structure represented by (0 <x <0.5, M = V, Cr, Mn, Co, Fe, Ni, 1 or more selected from Cu). The value of x is desirably in the range of 0 <x <0.5, and if it is larger than 0.5, the catalytic activity decreases, which is not preferable. Particularly, the catalytic activity is high in the range of 0.1 to 0.3.
The shape, particle size, purity, specific surface area and the like of the composite oxide may be in a state usually used as a catalyst component.

As the carrier, one or more compounds selected from each group described below are used.

General formula LnAlO ₃ having a perovskite structure of SrZrO ₃ and CaTiO ₃ (where Ln is a rare earth metal and is La, Ce, Pr, Nd, Pm, S
m, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Y, Sc).

General formula Ln ₂ B ₂ O ₇ having pyrochlore structure (however, Ln
Is a compound represented by the above-mentioned rare earth metals, and B is one or two of Ti and Zr).

The compounds contained in each of the above groups do not themselves degrade or decompose even when heated at a temperature of 900 ° C or more for a long time.
In addition, they have excellent heat resistance without reacting with each other.
These compounds may be used in the same state (shape, particle size, purity, specific surface area, etc.) as Al ₂ O ₃ and the like which are widely used as a carrier for the catalyst component. For example, the specific surface area is desirably 10 m ² / g or more in order to keep the catalyst component highly dispersed. It is usually sufficient to use commercially available materials.

The catalyst according to the present invention is produced by a method usually used for producing a catalyst. Next, one example of the manufacturing method will be described.

As a method for producing a catalyst component supported on a carrier, a composite oxide La _1-X Sr _x MO ₃ having a perovskite structure as a catalyst component (M = V, Cr, Mn, Co, Fe , Ni, C
Add an aqueous solution in which the metal nitrate constituting u) is mixed at a predetermined stoichiometric ratio, dry in air at about 100 ° C for 5 to 12 hours, and then in air at 700 to 800 ° C for 5 to 10 hours. Bake. By 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.

When mixing the catalyst component powder and the carrier powder,
First, a catalyst component powder is manufactured. Complex oxide La _1-X Sr _x MO ₃ having a perovskite structure (M = V, Cr, Mn, Co, Fe, N
A predetermined amount of an alkali salt such as sodium carbonate is added to an aqueous solution in which nitrates of the respective metals constituting i, Cu) are mixed in a predetermined stoichiometric ratio to obtain a coprecipitate. Next, the precipitate is dried, calcined in air at 500 to 600 ° C., and further calcined in air at 700 to 800 ° C. for 3 to 5 hours to obtain a composite oxide powder having a perovskite structure as a catalyst component. Get. Thereafter, a predetermined amount of a commercially available carrier powder is mixed with the catalyst component powder and used as a mixed powder, or the mixed powder is formed into a predetermined shape and used, or water is added to the mixed powder to form a slurry. It is used after being applied to a substrate. The addition amount of the catalyst component powder is desirably 10 to 80%.

Next, the present invention will be described with reference to examples, but the present invention is not limited to these examples.

Example 1 Commercially available SrZ having a specific surface area of 18 m ² / g and a purity of 99% or more as a carrier
Prepare 90g of rO ₃ powder and add lanthanum nitrate (La (NO ₃ )
₃ · 6H ₂ O) _14.69g, strontium nitrate (Sr (NO _{3) 2)}
1.79g and cobalt nitrate _{(Co (NO 3) 2 ·} 6H 2 O) 12.35g
40 ml of an aqueous solution in which was dissolved was added and mixed, and then dried at 110 ° C. in the atmosphere for 10 hours. Thereafter, the mixture is calcined in the air at 800 ° C for 3 hours to thermally decompose the nitrate and form a composite oxide having a perovskite structure containing Co on SrZrO ₃ (La _0.8 Sr _0.2 Co
O ₃ ) -supported catalyst (sample No. 1) was obtained.

Example 2 69.28 g of lanthanum nitrate (La (NO ₃ ) ₃ .6H ₂ O), 58.2 g of cobalt nitrate (Co (NO ₃ ) ₂ .6H ₂ O) and 8.48 g of strontium nitrate (Sr (NO) ₃ ) ₂ Was dissolved to prepare an aqueous solution 2. Next, 70 g of sodium carbonate (Na ₂ CO ₃ ) was dissolved in 700 ml of distilled water to prepare a coprecipitation neutralizer. The coprecipitating neutralizing agent was added dropwise to the aqueous solution to obtain a coprecipitate. After filtration and sufficient water washing, vacuum drying was performed. Next, it is fired in the air at 600 ° C, crushed, and then fired in the air at 800 ° C for 3 hours to obtain a composite oxide La _0.8 S having a perovskite structure.
r _0.2 CoO ₃ ) was synthesized.

The specific surface area of this powder was 8.5 m ² / g.

This powder was mixed with SrZrO ₃ at a weight ratio of 1: 1 and water was added to form a slurry. These are dried to form a catalyst
La _0.8 Sr _0.2 CoO ₃ / SrZrO ₃ (sample No. 2) was obtained.

Example 3 11.74 g of lanthanum nitrate (La (NO ₃ ) ₃ .6H ₂ O), 3.83 g of strontium nitrate (Sr (NO ₃ ) ₂ ) and manganese nitrate (90 g of commercially available 99% pure CaTiO ₃ powder as a carrier) Mn (NO ₃ ) ₂
・ 6H ₂ O) 40 ml of an aqueous solution in which 12.97 g is dissolved is added and mixed.
It was dried in air at 10 ℃ for 10 hours. Thereafter, further 800 ° C. in air and fired for 3 hours, the composite oxide La _0.6 Sr _0.4 MnO ₃ having a perovskite structure containing Mn on the CaTiO ₃
Was prepared (sample No. 3).

Example 4 An aqueous solution added to 90 g of CaTiO ₃ powder was treated with lanthanum nitrate (La
_{(NO 3) 3 · 6H 2} O) 13.31g, strontium nitrate (Sr (NO
_{3) 2)} 2.79g, cobalt nitrate _{(Co (NO 2) 3 ·} 6H 2 O) 2.56
g and iron nitrate (Fe (NO ₃ ) ₃ .9H ₂ O).
O ₃ onto the powder was adjusted catalyst carrying composite oxide _{La 0.7 Sr 0.3 Co 0.2 Fe 0.8} O 3 having a perovskite structure containing Co and Fe (Sample No.4).

Example 5 lanthanum nitrate _{(La (NO 3) 3 ·} 6H 2 O) 77.9g, strontium nitrate _{(Sr (NO 3) 2)} 4.23g, iron nitrate (Fe (NO _{3) 3}
・ 9H ₂ O) An aqueous solution 2 in which 80.8 g was dissolved was prepared.
600 ml of 0% ammonia water was added dropwise to obtain a coprecipitate. After washing and filtration, drying was performed in air at 110 ° C for 15 hours.
Next, calcination was performed in air at 600 ° C, and after pulverization, the mixture was further baked in air at 800 ° C for 5 hours to synthesize a composite oxide La _0.9 Sr _0.1 FeO ₃ having a perovskite structure.

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

100 g of commercially available γ-Al ₂ O ₃ (purity 99%) is lanthanum nitrate (L
_{a (NO 3) 3 · 6H} 2 O) 425g was added to an aqueous solution 400ml prepared by dissolving the mixture was evaporated to dryness. After that, it is heated at 600 ° C for 3 hours in the air to thermally decompose lanthanum nitrate.
After baking at 0 ℃ for 8 hours, LaAlO ₃ was synthesized.

The above La _0.9 Sr _0.1 FeO ₃ powder and LaAlO ₃ powder in a weight ratio of 2:
The resulting mixture was mixed to obtain water, water was added thereto, and the mixture was slurried and dried to prepare a catalyst (sample No. 5).

Example 6 An example of a catalyst using a composite oxide having a pyrochlore structure as a carrier will be described. Lanthanum nitrate (La (NO ₃ )
₃ · 6H ₂ O) _86.6g and zirconyl nitrate _{(ZrO (NO 3) 2 ·} 2H 2
O) 10% ammonia water 7 in aqueous solution 2 in which 53.45 g was dissolved
00 ml was added dropwise to obtain a coprecipitate. After washing with water and filtration, vacuum drying was performed. Next, bake in air at 900 ° C for 5 hours.
La ₂ Zr ₂ O ₇ which was a pyrochlore type compound was synthesized. Said La
₂ Zr ₂ O ₇ Catalyst prepared in Example 3 (La _0.6 Sr _0.4 MnO ₃ / CaT
A catalyst (Sample No. 6) was prepared in the same manner as in Example 3 except that CaTiO _{3 as} a carrier of iO ₃ ) was used.

Example 7 An example of a catalyst using a composite oxide having a pyrochlore structure as a carrier will be described.

Chromium nitrate _{(Cr (NO 3) 3 ·} 9H 2 O) 80g and lanthanum nitrate _{(La (NO 3) 3 ·} 6H 2 O) 65g and strontium nitrate (Sr
700 ml of an aqueous solution in which 70 g of sodium carbonate (Na ₂ CO ₃ ) was added dropwise to an aqueous solution 2 in which 10.6 g of (NO ₃ ) ₂ was dissolved, to obtain a coprecipitate. After washing with water, filtration, vacuum drying, and calcination in air at 800 ° C. for 5 hours, a compound La _0.75 Sr _0.25 CrO ₃ having a perovskite structure as a catalyst component was synthesized.

Next, 95.9 g of commercially available titania (TiO ₂ ) powder was prepared. Next, yttrium nitrate is heated to 600 ° C. for one hour in the atmosphere,
112.9 g of yttria obtained by pyrolysis was added to the titanium powder, mixed well, and calcined in the air for 5 hours. After pulverization, the mixture was calcined at 900 ° C for 10 hours in the air to synthesize a composite oxide Y ₂ Ti ₂ O ₇ having a pyrochlore structure.

The above La _0.75 Sr _0.25 CrO ₃ powder and Y ₂ Ti ₂ O ₇ powder in a weight ratio
The mixture was mixed at 3: 2 to obtain a catalyst (sample No. 7).

Comparative Example 1 The La _0.8 Sr _0.2 CrO ₃ powder synthesized in Example 2 was used as a comparative catalyst (sample No. 8).

[Comparative Example 2] SrZr as a carrier in the catalyst of Example 1 (sample No. 1)
Instead of O _3, except that a commercially available 99.5% alpha-Al ₂ O _3, the catalyst for comparison by the same operation as in Example 1 (Sample
No. 9) was adjusted.

[Comparative Example 3] Instead of SrZrO ₃ powder as a carrier, commercially available 99.7% pure
SrZrO ₃ was prepared in the same manner as in Example 1 except that SrTiO ₃ powder was used.
A catalyst (Sample No. 10) supporting a composite oxide having a perovskite structure containing Co (La _0.8 Sr _0.2 CrO ₃ ) containing Co thereon was prepared.

Comparative Example 4 A composite oxide (La _0.8 Sr _0.2 CrO ₃ ) having a perovskite structure synthesized in Example 2 was mixed with SrTiO ₃ at a weight ratio of 1: 1 and water was added to form a slurry. These were dried to obtain a catalyst La _0.8 Sr _0.2 CrO ₃ ) / SrTiO ₃ (sample No. 11).

[Comparative Example 5] SrZr as a carrier in the catalyst of Example 2 (sample No. 2)
Instead of O _3, except that a commercially available 99.5% alpha-Al ₂ O _3, the catalyst for comparison by the same operation as in Example 1 (Sample
No. 12) was adjusted.

[Comparative Example 6] CaTi as a support in the catalyst of Example 3 (sample No. 3)
A comparative catalyst (Sample No. 13) was prepared in the same manner as in Example 3, except that the commercially available SiO ₂ powder was used instead of the O ₃ powder.

[Comparative Example 7] Y ₂ Ti as a carrier in the catalyst of Example 7 (sample No. 7)
_A comparative catalyst (sample No. 14) was prepared in the same manner as in Example 7, except that ₂ O ₇ was replaced with TiO ₂ .

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

[Test Example 2] With respect to each of the catalysts prepared in Examples and Comparative Examples, a durability test of purification activity was performed in exhaust gas at an inlet gas temperature of 750 ° C for 250 hours. The gas composition is CO 1.0%, C ₃ H ₆ 0.1%, CO ₂ 10%, H ₂ O
1% and O ₂ are the fluctuation conditions, and the balance is N ₂ .

[Evaluation]

The purification rates of carbon monoxide (CO) and propylene (C ₃ H ₆ ) at 500 ° C. were measured for the catalysts subjected to the heat and durability tests described above. The gas composition was the same as in Test Example 2.

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

The La _0.8 Sr _0.2 CoO ₃ and SrZrO ₃ to evaluate the [Test Example 3] NO purification rate in a weight ratio of 1: La _0.8 Sr _0.2 CoO as mixed catalysts 1 catalyst for (sample No.2) and comparative ₃ (Sample No. 8) was prepared.
After heating both catalysts at 1000 ° C. for 3 hours in the air, the purification characteristics of NO at a gas concentration of 700 ° C. were examined using a gas obtained by adding 50 ppm of NO to the exhaust gas used in Test Example 2.

As a result, the NO purification rate was 50% for the comparative catalyst, but 72% for the catalyst according to the present invention.

──────────────────────────────────────────────────続 き Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical display location B01J 23/10 B01J 32/00 32/00 B01D 53/36 104Z (56) References JP-A-61 JP-18434 (JP, A) JP-A-61-274748 (JP, A) JP-A-48-55892 (JP, A) JP-A-48-55190 (JP, A) JP-A-61-97032 (JP, A) JP-A-63-4851 (JP, A) JP-A-63-302950 (JP, A)

Claims (1)

(57) [Claims] 1. A catalyst of the general formula La _1-X Sr _x MO ₃ having a perovskite structure (0 <x <0.5, M = V, Cr, Mn, Co, F
e, Ni and Cu) for exhaust gas purification, characterized by comprising a composite oxide represented by the formula (1) and a support and one or more compounds selected from the following groups: catalyst. General formula LnAlO ₃ having SiZrO ₃ and CaTiO ₃ perovskite structure (where Ln
Is a rare earth metal). General formula Ln ₂ B ₂ O ₇ having pyrochlore structure (however, Ln
Is a rare earth metal, and B is one or more of Ti and Zr).