JP2000157865A - Gas purifying catalyst carrier - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve the heat resistance of a composite oxide carrier by using a composite oxide carrier composed of a TiO2-Al2O3 catalyst as a main component for purifying exhaust gas from an automobile and containing therein the specified amount of Si based on the SiO2 conversion. SOLUTION: A composite oxide carrier composed of TiO2-Al2O3 as a main component is used as an exhaust gas purifying catalyst carrier and the composite oxide carrier containing 0.5-10 wt.% Si based on the SiO2 conversion is used. Si is used together with either one of TiO2 or Al2O3 so that a composite oxide is constituted. The carrier can be manufactured by mixing a composite powder composed of TiO2-Al2O3 as a main component mixed with an SiO2 powder, and preferably an Al source and an Si source are formed as organic metal compounds soluble in an organic solvent respectively and fed into the organic solvent, agitated, mixed and then hydrolyzed therein to form a composite oxide carrier by the sol gel process burning the organic metal compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a carrier used for an exhaust gas purifying catalyst for purifying exhaust gas from automobiles, and more particularly to a composition of a carrier optimal for a NOx storage reduction catalyst.

[0002]

2. Description of the Related Art In recent years, global warming due to carbon dioxide has become a problem, and reducing carbon dioxide emissions has become an issue. In automobiles, reduction of the amount of carbon dioxide in exhaust gas has become an issue, and lean burn engines have been developed in which fuel is burned lean in an oxygen-excess atmosphere. According to the lean burn engine, the amount of fuel used is reduced, so that the emission of carbon dioxide can be suppressed.

[0003] When purifying harmful components in the exhaust gas from lean-burn engines, the reduction purification is an oxygen-rich atmosphere because NO _x becomes difficult. Therefore,
No. 317652, etc., include alkali metals with precious metals,
A NO _x storage reduction catalyst supporting a NO _x storage material selected from alkaline earth metals and rare earth elements is disclosed. Using this NO _x storage-and-reduction type catalyst, by controlling the mixture composition as a stoichiometric-rich atmosphere in a pulsed manner during the lean atmosphere, to proceed efficiently and reduction of HC and CO oxidation and NO _x And high purification performance can be obtained.

[0004] That NO _x becomes oxidized is NO in the exhaust gas in a lean atmosphere, because it is occluded in _the NO _x storage material NO _x
Emission is suppressed. When the the stoichiometric-rich atmosphere, NO _x from _the NO _x storage material is released, it is to be reduced by reaction with reducing components such as HC present in the exhaust gas, NO _x emissions can be suppressed. Therefore it is possible to suppress the emission of the NO _x in all atmosphere rich-lean.

However, exhaust gas contains fuel.
SO generated by combustion of sulfur (S) _xIs included
SO oxidized by catalytic metals in an oxygen-rich atmosphere_ThreeTona
You. And that is also the water vapor contained in the exhaust gas
It becomes sulfuric acid more easily and these are NO_xReacts with the occlusion material
Since sulfites and sulfates are generated, NO_xOcclusion material is poorly poisoned
It became clear that it became. In addition, many materials such as alumina
The porous carrier is SO_xHas the property of easily absorbing
There is also a problem that the above-mentioned sulfur poisoning is promoted.

[0006] Thus, NO_xThe storage material is sulfite
And sulfate, NO_xIs difficult to absorb
As a result, with the above catalyst, NO_xPurification
There was a problem that performance deteriorated. Therefore, JP-A-8-
No. 099034 discloses TiO_Two−Al_TwoO_Three, ZrO_Two−Al_TwoO_ThreeAnd Si
O_Two−Al _TwoO_ThreeAt least one complex oxide selected from
NO used as carrier_xNo storage reduction type catalyst is disclosed.
You. By using such a composite oxide carrier, Al
_TwoO_ThreeEarly NO due to the advantages of_xPurification rate increases. Also Ti
O_Two, ZrO_Two, SiO_TwoIs Al_TwoO _ThreeSO compared to_xHard to absorb
Good and absorbed SO_xIs NO_xWhen absorbed by occlusion material
Sulfur poisoning is prevented because it is easier to desorb at lower temperatures than
You. Therefore, when the above composite oxide carrier is used, the initial
NO_xDurability test due to high purification ability and prevention of sulfur poisoning
Later NO_xPurification rate is also improved.

[0007]

Problems to be Solved by the Invention Improvement of engine performance,
Due to an increase in high-speed running and the like, the temperature of exhaust gas emitted from automobiles in recent years has become extremely high. However, it has been found that in the catalyst using the composite oxide carrier disclosed in JP-A-8-099034, sintering occurs in the composite oxide carrier when used at a high temperature. This sintering occurs from the grain boundary interface of the outer surface of the composite oxide support, the grain growth in the noble metal and _the NO _x storage material that is supported decreases the purification performance due to a decrease in surface area occurs accordingly.

[0008] The present invention has been made in view of such circumstances, TiO ₂ disclosed in Japanese Patent Laid-Open No. 8-099034 -
An object is to improve the heat resistance of a composite oxide carrier containing Al ₂ O ₃ as a main component.

[0009]

According to a first aspect of the present invention, there is provided an exhaust gas purifying catalyst carrier comprising a TiO ₂ -Al
A composite oxide carrier containing ₂ O ₃ as a main component, wherein Si is SiO ₂
0.5 to 10% by weight in conversion. The feature of the exhaust gas purifying catalyst carrier according to claim 2 is that, in the exhaust gas purifying catalyst carrier according to claim 1, Si is composed of TiO ₂ and Al ₂ O _3.
At least one of them forms a composite oxide.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION In the carrier for an exhaust gas purifying catalyst of the present invention, Si is used for a composite oxide carrier containing TiO ₂ -Al ₂ O ₃ as a main component.
It contains 0.5 to 10% by weight in terms of SiO ₂ . By including Si in the above range, the heat resistance of the support is remarkably improved, and even if a catalyst using the support is used at a high temperature, the reduction in purification performance is extremely small. Although the reason for this is unknown, it is considered that the heat resistance is improved as a whole because SiO ₂ is excellent in heat resistance.

If the Si content is less than 0.5% by weight in terms of SiO ₂ , the effect of containing Si cannot be obtained, and no improvement in heat resistance can be seen. If the Si content exceeds 10% by weight in terms of SiO ₂ , the NO _x purification ability tends to decrease when the catalyst is a NO _x storage-reduction catalyst. Therefore, in the present invention, the content of Si
0.5 to 10% by weight in terms of O ₂ . It is particularly desirable that the content be in the range of 1 to 5% by weight in terms of SiO ₂ .

The carrier of the present invention comprises TiO ₂ -Al ₂ O ₃ powder and SiO ₂
Although it may be produced by mixing with a powder, it is desirable that Si forms a composite oxide with at least one of TiO ₂ and Al ₂ O ₃ . By doing so, the heat resistance is improved with a smaller amount of Si, so that when the catalyst is a NO _x storage-reduction catalyst, the heat resistance can be improved without lowering the NO _x purification ability. Although the reason for this is not clear, Si forms a composite oxide containing bonds such as TiOSi and AlOSi with Ti or Al, and since these bonds are stable, the effect of improving the heat resistance by Si is more remarkable. It is considered to be played.

The compounding ratio of TiO ₂ and Al ₂ O ₃ is as follows:
And Ti / Al = 5/95 to 50/50 in molar ratio converted to metal Al
It is preferable to set it in the range. When Ti / Al is smaller than 5/95, when a NO _x storage reduction type catalyst is used, after the durability test,
When the NO _x purification rate decreases and becomes greater than 50/50, the initial NO
_{The x} purification rate decreases, and the NO _x purification rate after the durability test also decreases according to the value. A particularly desirable range is Ti / Al = 20 /
It is 80-30 / 70.

To produce the support of the present invention, TiO ₂ —Al ₂ O
It can be produced by mixing a composite oxide powder containing ₃ as a main component and a SiO ₂ powder. In this case, however, it is difficult to improve the heat resistance does not contain a relatively high SiO ₂ as described above, the inclusion lot of SiO ₂
The NO _x purifying ability when used as a NO _x storage reduction catalyst is reduced.

Therefore, the Ti source, the Al source and the Si source are each supplied as an organic metal compound soluble in an organic solvent, stirred and mixed in an organic solvent, then hydrolyzed, and then calcined, and the composite oxide carrier is baked. It is desirable to form Thereby compounding the metal elements at an atomic level, since heat resistance with less amount of Si as described above is improved, when the NO _x storage-and-reduction type catalyst, the heat resistance without decreasing the _the NO _x purification performance Can be improved.

[0016] The carrier of the present invention may be a NO _x storage-and-reduction type catalyst by carrying _the NO _x storage material and a noble metal. Platinum as the noble metal (Pt), rhodium (Rh), palladium (Pd), iridium (Ir), etc. are exemplified, NO _x
As the occlusion material, at least one selected from alkali metals, alkaline earth metals, and rare earth elements can be used. As alkali metals lithium, sodium,
Potassium, rubidium, cesium, and francium. Further, the alkaline earth metal refers to an element of Group 2A of the periodic table, and examples thereof include barium, beryllium, magnesium, calcium, and strontium. Examples of the rare earth element include scandium, yttrium, lanthanum, cerium, praseodymium, and neodymium.

The content of the NO _x occluding material depends on the composite oxide carrier 1
The range of 0.05 to 1.0 mol per 20 g is desirable. If the content is less than 0.05 mol, the NO _x storage capacity is small and the NO _x purification performance is reduced. Even if the content exceeds 1.0 mol, the effect is saturated and a problem occurs due to a decrease in the amount of other components. As the noble metal, one or more of Pt, Rh, Pd, and Ir can be used. In the case of Pt and Pd, the supporting amount is preferably 0.1 to 20.0 g, more preferably 0.5 to 10.0 g, per 120 g of the carrier. In the case of Rh, the amount is preferably 0.01 to 80 g, particularly preferably 0.05 to 5.0 g, per 120 g of the composite oxide carrier. Converted to 1 liter of carrier volume, Pt and Pd
In this case, the amount is preferably 0.1 to 20 g, particularly preferably 0.5 to 10 g. In the case of Rh, 0.01 to 10 g is preferable, and 0.05 to 5 g.
g is particularly preferred.

[0018]

The present invention will be specifically described below with reference to examples and comparative examples. (Example 1) 400 g of isopropyl alcohol was placed in a flask equipped with a reflux device for sol-gel synthesis, and kept at 82 ° C. Then, while stirring, a 75% propanol solution of ethyl acetoacetate aluminum diisopropylate 20
9.6 g and tetraisopropoxy titanium (Ti OCH (CH ₃ ) _2
4 ) and 40.8 g of tetraethoxysilicon (Si (C ₂ H
₅ O) ₄ ) 4.3 g are mixed and stirring is continued at 82 ° C. for 2 hours.

Thereafter, while stirring the solution at 82 ° C., 12
8.5 g of ion-exchanged water is added dropwise, and after the addition, stirring is continued at 82 ° C. for 5 hours. After aging for one day and night at room temperature, the water and alcohol were removed using a rotary evaporator, air-dried, forced dried at 110 ° C, and calcined at 800 ° C for 2 hours to obtain the composite oxide carrier of this example. Prepared. The content of SiO ₂ is about 3% by weight.

(Example 2) Isopropyl alcohol 412
and g, 75% and propanol solution 226.2g of ethyl acetoacetate aluminum diisopropylate, tetraisopropoxytitanium _{(Ti OCH (CH 3) 2} 4) and 44.0g of tetraethoxy silicon _{(Si (C 2 H 5 O} ) ₄ ) A composite oxide carrier of Example 2 was prepared in the same manner as in Example 1 except that 1.04 g and 135 g of ion-exchanged water were used. The content of SiO ₂ is about 0.67% by weight.

(Example 3) Isopropyl alcohol 40
And 5.8 g, 75% and propanol solution 221.4g of ethyl acetoacetate aluminum diisopropylate, tetraisopropoxytitanium the _{(Ti OCH (CH 3) 2} 4) 43.1g
And 1.9 g of tetraethoxysilicon (Si (C ₂ H ₅ O) ₄ )
A composite oxide carrier of Example 3 was prepared in the same manner as in Example 1 except that 133.2 g of ion-exchanged water was used. SiO ₂
Is about 1.3% by weight.

Example 4 Isopropyl alcohol 37
And 3.7 g, 75% and propanol solution 195.7g of ethyl acetoacetate aluminum diisopropylate, tetraisopropoxytitanium the _{(Ti OCH (CH 3) 2} 4) 38.1g
Then, a composite oxide carrier of Example 4 was prepared in the same manner as in Example 1 except that 7.0 g of tetraethoxysilicon (Si (C ₂ H ₅ O) ₄ ) was used. The content of SiO ₂ is about 5% by weight.

(Example 5) Isopropyl alcohol 35
And 2.9 g, 75% and propanol solution 179.0g of ethyl acetoacetate aluminum diisopropylate, tetraisopropoxytitanium the _{(Ti OCH (CH 3) 2} 4) 34.8g
And 10.2 g of tetraethoxysilicon (Si (C ₂ H ₅ O) ₄ )
A composite oxide carrier of Example 5 was prepared in the same manner as in Example 1 except that 116.6 g of ion-exchanged water was used. SiO ₂
Is about 10% by weight.

Comparative Example 1 Isopropyl alcohol 32
And 3.6 g, 75% and propanol solution 155.5g of ethyl acetoacetate aluminum diisopropylate, tetraisopropoxytitanium the _{(Ti OCH (CH 3) 2} 4) 30.26g
And 14.8 g of tetraethoxysilicon (Si (C ₂ H ₅ O) ₄ )
A composite oxide carrier of Comparative Example 1 was prepared in the same manner as in Example 1 except that 107.4 g of ion-exchanged water was used. SiO ₂
Is about 30% by weight.

Comparative Example 2 Isopropyl alcohol 41
And 8.7 g, 75% and propanol solution 231.6g of ethyl acetoacetate aluminum diisopropylate, tetraisopropoxytitanium the _{(Ti OCH (CH 3) 2} 4) 45.1g
Example 1 except that 137.1 g of ion-exchanged water was used.
In the same manner as in the above, a composite oxide carrier of Comparative Example 2 was prepared.
SiO ₂ is not contained.

Comparative Example 3 20.4 g of γ-Al ₂ O ₃ powder and TiO ₂
The carrier of Comparative Example 3 was prepared by mixing 8 g of the powder and 1.5 g of the SiO ₂ powder. The content of SiO ₂ is 5% by weight. (Comparative Example 4) 20.4 g of γ-Al ₂ O ₃ powder, 8 g of TiO ₂ powder,
The carrier of Comparative Example 4 was prepared by mixing 3.2 g of SiO ₂ powder. The content of SiO ₂ is 10% by weight.

Comparative Example 5 20.4 g of γ-Al ₂ O ₃ powder and TiO ₂
The carrier of Comparative Example 5 was prepared by mixing 8 g of the powder and 12.2 g of the SiO ₂ powder. The content of SiO ₂ is 30% by weight. (Comparative Example 6) 20.4 g of γ-Al ₂ O ₃ powder, 8 g of TiO ₂ powder,
The carrier of Comparative Example 6 was prepared by mixing 28.4 g of SiO ₂ powder. The content of SiO ₂ is 50% by weight.

Test Example 1 Each of the above carriers was placed in an electric furnace and subjected to a heat treatment of heating at 1000 ° C. for 5 hours in the atmosphere. Then, the specific surface area after the heat treatment was measured by the BET method, and the results are shown in FIG. 2 and 3 show electron micrographs of the carrier of Example 1 and the carrier of Comparative Example 2 after the heat treatment.

As shown in FIG. 1, the carriers of Examples 1 to 4 are Comparative Example 2
It is apparent that the specific surface area after the heat treatment is larger than that of the carrier and the heat resistance is excellent. Also, comparing FIG. 2 with FIG. 3, the carrier of Comparative Example 2 has a larger particle size, and the carrier of Comparative Example 2 has grown due to the heat treatment.
It can be seen that the carrier has a fine particle size even after the heat treatment. It is clear that these effects are the effects of further complexing SiO ₂ to the complex oxide carrier containing TiO ₂ —Al ₂ O ₃ as a main component.

Further, in both of the examples and the comparative examples, it can be seen that as the content of SiO ₂ increases, the specific surface area increases and the heat resistance further improves. However, the carrier of the example can secure a higher specific surface area with a smaller amount of SiO ₂ than the comparative example. <Test Example 2> Next, using each of the above carriers, NO
_{An x-} reduction catalyst was produced. Specifically, 20 g of each carrier powder before heat treatment was put into 200 cc of ion-exchanged water and stirred, and a predetermined concentration of dinitrodiammineplatinum nitric acid aqueous solution was added dropwise, stirred for 1 hour, and filtered and washed.
After drying at ℃ for 1 hour, it was baked at 250 ℃. Thereafter, each powder was again put into 200 cc of ion-exchanged water and stirred. A predetermined concentration of rhodium chloride aqueous solution was added dropwise, stirred for 1 hour, filtered and washed, dried at 120 ° C. for 1 hour, and dried at 250 ° C.
Was fired. Each powder contains Pt for 20g of carrier
0.2 g and Rh 0.01 g.

Further, the total amount of each powder carrying Pt and Rh was poured into 200 cc of ion-exchanged water and stirred, and 8.5 g of barium acetate and 0.76 g of lithium nitrate were added and dissolved by stirring. The mixture was evaporated to dryness, dried at 120 ° C. for 1 hour, and calcined at 500 ° C. for 1 hour to prepare each catalyst powder. After compression molding, pulverize, 0.5 ~ 1.7
A pellet catalyst having a size of mm was used.

Each of the obtained pellet catalysts was filled in an endurance test apparatus, and a rich model gas of A / F = 14.1 and a lean model gas of A / F = 15.1 shown in Table 1 were alternately arranged. An endurance test was carried out by heating at 800 ° C. for 5 hours while flowing for 1 minute.

[0033]

[Table 1] Then, each of the pellet catalysts after the endurance test was filled in an evaluation test apparatus, and the above-described rich model gas and lean model gas gas were alternately flowed at a gas temperature of 350 ° C. for 2 minutes while NO _x when the lean model gas was flowing. The purification rate was measured. FIG. 4 shows the results.

FIG. 4 shows that the catalyst using the carrier of each example was
Higher even after endurance test compared to catalyst using carrier of comparative example
NO_xIt turns out that it shows the purification rate. This is TiO_Two−
Al_TwoO _ThreeSiO as a composite oxide carrier containing_TwoMore
It is clear that this is a combined effect. And examples
No. after the endurance test_xPurification rate is over 60%
Is SiO_TwoContent in the range of 0.5 to 10% by weight
I understand.

[0035]

According to the exhaust gas purifying catalyst carrier of the Effect of the Invention] The present invention, since the excellent heat resistance, high after exposure to high temperatures when used as a NO _x storage-and-reduction type catalyst
The catalyst exhibits NO _x purification ability and is excellent in durability.

[Brief description of the drawings]

FIG. 1 is a graph showing the specific surface area after heat treatment of carriers of Examples and Comparative Examples of the present invention.

FIG. 2 is a micrograph showing the particle structure of a carrier of Example 1 after heat treatment.

FIG. 3 is a micrograph showing the particle structure of a carrier of Comparative Example 2 after heat treatment.

FIG. 4 is a graph showing NO _x purification rates after endurance tests of NO _x storage-reduction catalysts produced from carriers of Examples and Comparative Examples.

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[Procedure amendment]

[Submission date] December 3, 1998 (1998.12.
3)

[Procedure amendment 1]

[Document name to be amended] Drawing

[Correction target item name] Figure 2

[Correction method] Change

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FIG. 2

[Procedure amendment 2]

[Document name to be amended] Drawing

[Correction target item name] Figure 3

[Correction method] Change

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FIG. 3

 ────────────────────────────────────────────────── ─── Continued on the front page F-term (reference) 4D048 AA06 AA13 AA18 AB01 AB02 AB05 BA03X BA06X BA07X BA30X BA33X BA41X BB01 4G069 AA01 AA03 AA08 BA01A BA01B BA02A BA02B BA03A BA04A BA04B BB02B BB06ABBC BCBC BCB BCBC EC03Y FA01 FB05 FB30 FB31 FB57 FC08

Claims (2)

[Claims] 1. An exhaust gas purifying catalyst carrier comprising a composite oxide carrier containing TiO ₂ —Al ₂ O ₃ as a main component, comprising 0.5 to 10% by weight of Si in terms of SiO ₂ . 2. The exhaust gas purifying catalyst carrier according to claim 1, wherein Si forms a composite oxide with at least one of TiO ₂ and Al ₂ O ₃ .