JP3131630B2 - Method for oxidizing and removing carbon fine particles in diesel engine exhaust gas and catalyst used therefor - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for oxidizing and removing carbon fine particles contained in diesel engine exhaust gas and a catalyst used for the method.

[0002]

2. Description of the Related Art In recent years, the problem of environmental pollution due to carbon fine particles contained in exhaust gas from diesel engines has become more serious. As a countermeasure against this problem, a filter trap method, a catalytic combustion method, and the like have been proposed. Catalytic combustion method, a high-temperature exhaust gas produced from the engine in contact with the catalyst, a method of converting into CO ₂ by oxidative combustion of carbon particles of the exhaust gas. Oxide-based, chloride-based, precious metal-based catalysts and the like have been proposed as catalysts for this purpose, but none of these catalysts has been satisfactory in terms of catalytic activity and stability.

[0003]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for effectively oxidizing and removing carbon fine particles contained in diesel engine exhaust gas and a catalyst used therefor.

[0004]

Means for Solving the Problems The present inventors have conducted intensive studies to solve the above-mentioned problems, and as a result, have completed the present invention. That is, according to the present invention, in a method of contacting a diesel engine exhaust gas with a catalyst to oxidize and remove carbon fine particles in the exhaust gas, the catalyst comprises at least one metal oxide selected from tantalum oxide and tin oxide. The above method is provided, wherein a catalyst comprising platinum supported on a substance is used. According to the present invention, there is provided a method for oxidizing and removing carbon fine particles in a diesel engine exhaust gas by contacting the exhaust gas with a catalyst,
As the catalyst, titanium oxide supported on silicon carbide, zirconium oxide or aluminum oxide supported with platinum, wherein the titanium oxide, zirconium oxide and aluminum oxide are each a titanium salt of an inorganic acid, zirconium. The method is provided, wherein a salt and an aluminum salt are formed by firing in air. Further, according to the present invention, there is provided a catalyst for oxidizing and removing carbon fine particles in exhaust gas of a diesel engine, the catalyst comprising platinum supported on at least one metal oxide selected from tantalum oxide and tin oxide. Is provided. Furthermore, according to the present invention, in a catalyst for oxidizing and removing carbon fine particles in diesel engine exhaust gas, titanium oxide containing inorganic acid radicals supported on silicon carbide, zirconium oxide or aluminum oxide is supported with platinum. Wherein the titanium oxide, zirconium oxide and aluminum oxide are each formed by calcining a titanium salt, a zirconium salt and an aluminum salt of an inorganic acid in the air. Is provided.

[0005]

DETAILED DESCRIPTION OF THE INVENTION One embodiment of the catalyst of the present invention is tantalum oxide (Ta ₂ O ₅ ) and tin oxide (SnO ₂ ).
At least one kind of metal oxide selected from the above is used as a carrier, and platinum is supported on the carrier. As the carrier metal oxide, a metal hydroxide obtained by calcining a corresponding metal hydroxide at 300 to 800 ° C, preferably 500 to 600 ° C in the air can be used. The carrier made of the metal oxide can be in various shapes such as a powder or a pellet. The specific surface area measured by the BET method is 1 to 400 m ² / g, preferably 1 to 50 m ² / g.
² / g.

To support platinum on a metal oxide, a water-soluble platinum compound, for example, Pt (NH ₃ ) ₄ (O
H) Impregnating the metal oxide with an aqueous solution of ₂ and then drying, then in air at 500-800 ° C., preferably 500 ° C.
Bake at ~ 600 ° C. Thus, a catalyst in which platinum is supported on a carrier metal oxide can be obtained. Platinum in the catalyst is usually present in a metal state, and its content is 0.05 to 20% by weight, preferably 0.1 to 5% by weight in the catalyst.

[0007] Another embodiment of the catalyst of the present invention is titanium oxide (TiO ₂ ) supported on silicon carbide (SiC),
Zirconium oxide (ZrO ₂ ) or aluminum oxide (Al ₂ O ₃ ) is used as a carrier, and platinum is supported on the carrier. The titanium oxide, zirconium oxide, and aluminum oxide are each a titanium salt of an inorganic acid, It is formed by firing a zirconium salt and an aluminum salt in air. These metal oxides impregnate silicon carbide with an inorganic acid salt of a metal,
It can be prepared by a method of baking at 〜800 ° C., preferably 500-600 ° C. As the inorganic acid,
Sulfuric acid, nitric acid, phosphoric acid, hydrochloric acid and the like can be mentioned. In the calcined products of these inorganic acid metal salts, a small amount of an inorganic acid radical bonded to the metal remains in the metal oxide, and the obtained metal oxide is acidified. The carrier obtained by supporting the metal oxide on silicon carbide can be in various shapes such as a powder or a pellet. The specific surface area measured by the BET method is 1 to 400 m ² / g, preferably 1 to ² m ² / g.
0 m ² / g.

To support platinum on a metal oxide containing an inorganic acid group supported on silicon carbide, an aqueous solution of a water-soluble platinum compound, for example, Pt (NH ₃ ) ₄ (OH) ₂ is subjected to metal oxidation. And then dried, and then dried at 250-600 ° C., preferably 3 ° C. in a nitrogen stream containing hydrogen.
Hydrogen reduction treatment at 00 to 500 ° C and then 50
The firing is performed at 0 to 800 ° C, preferably 500 to 600 ° C. In this manner, a catalyst in which platinum is supported on a metal oxide supported on a silicon carbide carrier can be obtained. Platinum in the catalyst is usually present in a metal state, and its content is 0.05 to 20% by weight, preferably 0.1 to 20% by weight in the catalyst.
~ 5% by weight. The ratio of the metal oxide per 100 parts by weight of silicon carbide is 1 to 50 parts by weight, preferably 5 to 50 parts by weight.
-20 parts by weight.

[0009] The catalyst obtained as described above is slightly acidified due to the inorganic acid radicals remaining in the metal oxide. The content of the inorganic acid radical in the metal oxide is Ti
For O _2, Ti1 mol per 1 to 10 millimoles, preferably at a rate of 1-6 mmol. In the case of Al ₂ O ₃ ,
1 to 15 mmol, preferably 1 to 10 per mol of Al
It is a mmol ratio. For ZrO _2, Zr1 mol per 1 to 10 millimoles, preferably at a rate of 1 to 5 millimoles.

[0010] In order to remove carbon fine particles in diesel engine exhaust gas by oxidation using the catalyst of the present invention, the exhaust gas may be brought into contact with the catalyst. The contact temperature in this case is 200 to 700 ° C., preferably 250 to 50 ° C.
0 ° C. and the contact time is 10 ³ to 1 expressed in GHSV.
0 ⁵ hr ^-1, preferably ¹⁰ 4 ^~4 × ¹⁰ 4 ^{hr -1}
It is. The catalyst of the present invention has a relatively low temperature of 500 ° C. or less,
Particularly, it has high activity even at a temperature of about 250 to 480 ° C., and is suitable for treating engine exhaust gas in an exhaust gas exhaust pipe.

The reason why the catalyst according to the present invention has a high catalytic activity for oxidizing combustion of carbon fine particles in exhaust gas of a diesel engine is considered as follows. That is, NO, SO _2, and H ₂ O coexist in the exhaust gas in addition to O ₂ , and it is considered that the coexisting components keep the catalyst at high activity. That is, it is considered that NO ₂ generated by oxidizing NO on the catalyst oxidizes the carbon fine particles, and SO ₂ (or SO ₃ ) and water promote this reaction.

[0012]

Next, the present invention will be described in more detail with reference to examples.

Example 1 2 mol% of a platinum precursor [Pt (NH ₃ ) ₄ (OH) ₂ ]
20 g of the carrier shown in Table 1 was immersed in 3 cc of the contained aqueous solution at a temperature of 25 ° C., and the carrier was impregnated with the aqueous solution, dried, and fired in air at 600 ° C. for 1 hour. However, in Comparative Examples 5 to 7, reduction firing was performed at 400 ° C. for 4 hours in 3% He / N ₂ before performing air firing. To 0.5 g of the catalyst containing 0.3 wt% of Pt thus obtained, 0.005 g of commercially available carbon black was dry-mixed, and an oxidative combustion test of the carbon black was performed using this mixture. In this test, 10% O ₂ /7% H was used to approximate the diesel engine exhaust gas composition.
_A mixed gas consisting of ₂ O / 1000 ppm NO / 100 ppm SO ₂ / balance N ₂ was passed through a reaction tube (diameter: 10 mm) containing the mixture. In this case, the flow rate of the mixed gas is 0.5 liter / min (0 ° C., 1 atm conversion).
The reaction tube is set at 10 ° C in the region from 80 ° C to 700 ° C.
/ Min. Then, the concentrations of CO and CO ₂ generated by burning the carbon black were measured.
Table 1 shows the results.

[0014]

[Table 1]

From the results shown in Table 1, all of the catalysts of the present invention have a temperature (peak temperature) at which the generated CO ₂ concentration becomes the highest in relation to the reaction temperature and the CO ₂ concentration generated by carbon oxidation. ) Is low and shows high catalytic activity at low temperatures.

Incidentally, the specific contents of the properties, starting temperature, peak temperature and final temperature of each carrier shown in Table 1 are as follows. (1) Ta ₂ O ₅ particle size: 150 to 250 μm specific surface area (BET): 2.5 m ² / g (2) SnO ₂ particle size: 150 to 250 μm specific surface area (BET): 3m ² / g (3) ZrO ₂ particle size: 150 to 250 μm Specific surface area (BET): 44 m ² / g (4) Al ₂ O ₃ particle size: 150 to 250 μm Specific surface area (BET ): 200 m ² / g (5) TiO ₂ particle size: 150 to 250 μm Specific surface area (BET): 29 m ² / g (6) Starting temperature (° C.) CO ₂ concentration generated after carbon black starts burning Is 1
Meaning temperatures above 00 ppm. (7) Peak temperature (° C.) It means the temperature at which the generated CO ₂ concentration becomes maximum. (8) Final temperature (° C) Combustion reaction is completed and generated CO ₂ concentration is 100ppm
It means the temperature below.

Example 2 In Experiment No. 1 of Example 1, the reaction temperature was 35
The experiment was carried out in the same manner except that carbon black was burned at 0 ° C. As a result, the entire amount of carbon black was oxidized and removed in about one hour.

EXAMPLE 3 An aqueous solution of zirconium sulfate tetrahydrate, Zr (SO ₄ ) ₂ .4H ₂ O, was mixed with silicon carbide (SiC) having a particle size of 150 to 250 μm.
It was impregnated with 0.5 mm · mol of Zr per 1 g, dried, and fired at 600 ° C. for 1 hour. The resulting carrier (Zr
O ₂ / SiC) 20 g with a platinum precursor Pt (NH ₃ )
₄ (OH) ₂ in 3 cc of an aqueous solution containing 2 mol% at a temperature of 25
The carrier was impregnated at 400 ° C. for 4 hours in hydrogen (3% H ₂ / N ₂ ) and in air at 600 ° C. for 1 hour. 0.3wt% P
t / ZrO ₂ / SiC). This catalyst contained 4 mmol of sulfate (SO ₄ ) per mole of Zr.

Example 4 Platinum was supported in the same manner as in Example 3 except that aluminum sulfate (Al ₂ (SO ₄ ) ₃ .18H ₂ O) was used instead of zirconium sulfate tetrahydrate. This catalyst (0.
3 wt% Pt / Al ₂ O ₃ / SiC). The catalyst contained 8 mmol of sulfate (SO ₄ ) per mole of Al.

Example 5 Platinum was supported in the same manner as in Example 3 except that titanium sulfate (Ti (SO ₄ ) ₂ .4H ₂ O) was used instead of zirconium sulfate tetrahydrate. (0.3wt% P
t / TiO ₂ / SiC). The catalyst contained 5 mmol of sulfate (SO ₄ ) per mole of Ti.

Example 6 Commercial carbon black (0.00 g) was added to 0.5 g of the catalyst containing 0.3 wt% of Pt obtained as described above.
5 g was dry-blended, and the carbon black was subjected to an oxidation combustion test using the mixture. In this test,
To approximate the diesel engine exhaust gas composition, 10
% O ₂ /7% H ₂ O / 1000 ppm NO / 100 pp
A mixed gas consisting of mSO ₂ / remainder N ₂ was passed through a reaction tube (diameter: 10 mm) containing the mixture. In this case, the flow rate of the mixed gas is 0.5 liter / min (0 ° C.,
The reaction tube was heated at a rate of 10 ° C./min from 80 ° C. to 700 ° C. Then, the concentrations of CO and CO ₂ generated by burning the carbon black were measured. Table 2 shows the results.

[0022]

[Table 2]

[0023]

According to the catalyst of the present invention, carbon fine particles in the exhaust gas of a diesel engine can be efficiently oxidized and removed at a low temperature.

────────────────────────────────────────────────── (5) References JP-A-10-33985 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) B01D 53 / 86,53 / 94 B01J 21 / 00-38/74

Claims (4)

(57) [Claims] 1. A method for oxidizing and removing carbon fine particles in an exhaust gas of a diesel engine by contacting the exhaust gas with a catalyst, wherein the catalyst comprises at least one metal oxide selected from tantalum oxide and tin oxide. The method according to claim 1, characterized in that a catalyst is used. 2. A method for oxidizing and removing carbon fine particles in a diesel engine exhaust gas by contacting the exhaust gas with a catalyst, wherein platinum is supported on titanium oxide, zirconium oxide or aluminum oxide supported on silicon carbide as the catalyst. Wherein the titanium oxide, zirconium oxide and aluminum oxide are each formed by calcining a titanium salt, a zirconium salt and an aluminum salt of an inorganic acid in the air. Method. 3. A catalyst for oxidizing and removing carbon fine particles in exhaust gas of a diesel engine, wherein platinum is supported on at least one metal oxide selected from tantalum oxide and tin oxide. 4. A catalyst for oxidizing and removing carbon fine particles in exhaust gas of a diesel engine, the catalyst comprising platinum supported on titanium oxide, zirconium oxide or aluminum oxide supported on silicon carbide,
The above-mentioned catalyst, wherein the titanium oxide, zirconium oxide and aluminum oxide are each formed by calcining a titanium salt, a zirconium salt and an aluminum salt of an inorganic acid in the air.