JPH0975736A - Catalyst for purification of exhaust gas from diesel engine and method for purifying exhaust gas from diesel engine with the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a novel catalyst capable of efficiently decomposing and removing NOx and capable of burning and removing even harmful components such as particulates, unburnt hydrocarbons and CO. SOLUTION: Platinum and an alkali metallic sulfate, together with fireproof inorg. oxide powder, are carried on a fireproof three-dimensional structure to obtain the objective catalyst having high NOx decomposing ability at high temp. and excellent in durability. The temp. range in which the catalyst has activity can be varied by varying the amt. of the alkali metallic sulfate added.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a diesel engine exhaust gas purifying catalyst. Specifically, nitrogen oxides (NO _x ) among harmful components in diesel engine exhaust gas
Decomposes and reduces the amount of carbon-based fine particles, unburned hydrocarbon
The present invention relates to a catalyst capable of burning and removing carbon monoxide and the like.

[0002]

2. Description of the Related Art NO _x contained in exhaust gas from diesel engines causes photochemical smog and acid rain.
Emissions of O _x has become a social problem. In addition, diesel engine exhaust gas contains particulate matter, unburned hydrocarbons, carbon monoxide, etc. that are harmful to health, and it is important to remove these components by burning them.

On the other hand, although a three-way catalyst has been conventionally used for purifying exhaust gas from an automobile, oxygen is excessive in the exhaust gas of a diesel engine, and thus a normal three-way catalyst sufficiently reduces NO _x. I can't.

A method using platinum as a main catalyst has also been proposed, such as the method described in JP-A-5-137963. However, such a platinum-containing catalyst is
_Since it has a strong activity to oxidize ₂ , it has a problem that when it is used for the treatment of exhaust gas from a diesel engine, SO ₂ is oxidized to increase sulfates, which rather increases the particulate matter in the exhaust gas.

Further, Japanese Patent Application Laid-Open No. 6-31139 discloses that
A method for purifying exhaust gas using a catalyst in which an alkali metal oxide and platinum are supported on a carrier made of a porous body is described. This catalyst is a NO in lean condition when processing exhaust gas of gasoline lean burn engine.
_An alkali metal oxide is used to enhance the _x- adsorption capacity, and the adsorbed NO _x can be decomposed by stoichiometry due to the action of platinum. However, the effect of alkali metal oxides is not high in diesel engine exhaust gas that is always lean and SO ₂ is present, and there is a problem in durability, and when it is used at high temperatures, it gradually disappears due to thermal decomposition and formation of sulfate salts. I will live it.

In the methods proposed so far, the temperature at which NO _x can be efficiently decomposed is limited to a relatively narrow range, but the actual exhaust gas temperature changes depending on the type of engine and running conditions. There is a demand for catalysts that can handle various temperatures.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above problems of the prior art. The object of the present invention is to efficiently decompose and remove NO _x , and to remove fine particles and unburned substances. It is an object of the present invention to provide a novel catalyst for purifying diesel engine exhaust gas, which can burn and remove harmful components such as hydrocarbons and carbon monoxide, and an exhaust gas purification method using the same.

Another object of the present invention is to provide a diesel engine exhaust gas purification catalyst which has a high NO _x resolution at high temperatures and is excellent in durability.

Still another object of the present invention is to provide a diesel engine exhaust gas purifying catalyst which can cope with various exhaust gas temperatures.

[0010]

The above objects are achieved by a diesel engine exhaust gas purifying catalyst comprising a refractory inorganic oxide powder and platinum and an alkali metal sulfate supported on a refractory three-dimensional structure. It

The present invention is also the above-mentioned diesel engine exhaust gas-purifying catalyst, wherein the alkali metal sulfate is potassium sulfate.

[0012] The above-mentioned various purposes are also related to HC / N in exhaust gas.
O _x ratio is achieved by the method for purifying a diesel engine exhaust gas comprising contacting the exhaust gas from a diesel engine is a 0.5 to 20 molar ratio to the diesel engine exhaust gas purifying catalyst.

The present invention is also the method for purifying diesel engine exhaust gas, characterized by injecting a reducing agent into the exhaust gas on the upstream side of the diesel engine exhaust gas purifying catalyst.

The present invention is also the method for purifying the exhaust gas of the diesel engine, wherein the reducing agent is light oil.

[0015]

BEST MODE FOR CARRYING OUT THE INVENTION In the present invention, platinum and alkali metal sulfate are supported on a refractory three-dimensional structure together with refractory inorganic oxide powder to form a diesel engine exhaust gas purifying catalyst. .

In the present invention, the amount of platinum carried is
0.1 to 5.0 g per liter of the fire resistant three-dimensional structure,
It is preferably 0.1 to 2.0 g. When the loading amount of platinum is less than 0.1 g / l, the NO _x decomposing activity is low, which is not preferable. On the other hand, when the loading amount exceeds 5.0 g / l, the NO _x decomposing activity is no more improved corresponding to the loading amount. Not economically disadvantageous. As a starting material of platinum, there are inorganic salts such as platinum nitrate, sulfate, chloride, etc., and organic acid salts such as ammine complex salts, etc., for example, chloroplatinic acid, dinitrodiaminoplatinum, potassium chloroplatinate, sodium chloroplatinate. , Platinum tetramine chloride, platinum sulfide complex salt and the like can be used.

The alkali metal sulfates include lithium sulfate, sodium sulfate, potassium sulfate, rubidium sulfate,
Cesium sulfate etc. are mentioned. The amount of the alkali metal sulfate supported is 0.5 to 2 per liter of the refractory three-dimensional structure.
0 g, preferably 1-10 g. When the amount of the alkali metal sulfate supported is less than 0.5 g / l, the effect of suppressing the oxidation of SO ₂ is insufficient and it is disadvantageous because sulfate radicals tend to be generated, while the supported amount is 20 g / l. When it exceeds 1, the effect of suppressing the oxidation of SO ₂ is not improved even if it is increased more, and NO _x decomposition may be rather inhibited, which is not preferable.

Examples of the refractory inorganic oxide powder used in the present invention include activated alumina such as γ-alumina, δ-alumina, η-alumina and θ-alumina, α-alumina, titania, silica, zirconia, garia or Examples of these composite oxides include alumina-titania, alumina-zirconia, titania-zirconia, and the like, or a mixture thereof, but preferably activated alumina, titania, silica, zirconia, alumina-silica or silica-alumina or a mixture thereof. A mixture is good. These refractory inorganic oxides are usually in powder form, and their Bru
nauer-Emmett-Teller (hereinafter BE
Surface area (referred to as T) is 5 to 400 m ² / g, preferably 1
0 to 300 m ² / g, the average particle size is 0.1 to 150 μ
m, preferably 0.2 to 100 μm.

The amount of the refractory inorganic oxide powder used is 20 to 300 g, preferably 50 to 200 g, per liter of the refractory three-dimensional structure. If it is less than 20 g / l, sufficient performance cannot be obtained, while if it exceeds 300 g / l, performance commensurate with the amount used cannot be obtained.

In the present invention, if necessary, the second refractory inorganic oxide powder may be coated on the refractory three-dimensional structure together with the platinum-carrying refractory inorganic oxide powder. In this case, the material, BET surface area and average particle size of the second refractory inorganic oxide powder are the same as those of the refractory inorganic oxide. The platinum-supported refractory inorganic oxide powder and the second
The ratio of the platinum-carrying refractory inorganic oxide powder to the catalyst composition consisting of the refractory inorganic oxide powder (1) is 1 to 99% by weight, preferably 10 to 90% by weight. The ratio is 1
When the amount is less than 10% by weight, when the amount of platinum required to obtain sufficient activity is used, the second refractory inorganic oxide is used in an unnecessarily large amount, which is economically and complicated in catalyst adjustment. On the other hand, it is disadvantageous for the reason. On the other hand, if the ratio exceeds 99% by weight, it is disadvantageous because it is difficult to maintain the balance of expressing the NO _x resolution of platinum and suppressing the SO ² oxidation ability.

Examples of the refractory three-dimensional structure used in the present invention include pellets and monolith carriers.
A monolith carrier is preferable. Examples of the monolith carrier include ceramic foam, open flow type ceramic honeycomb, wall flow type honeycomb monolith, open flow type metal honeycomb, metal foam, and metal mesh. Among them, the open flow type ceramic honeycomb is included. Alternatively, a metal honeycomb is preferably used. As the ceramic honeycomb carrier, cordierite, mullite, α-alumina,
Zirconia, titania, titanium phosphate, aluminum titanate, betalite, spodumene, aluminosilicate, magnesium silicate and the like are preferable, and cordierite is particularly preferable. Further, as the metal honeycomb carrier, one having an integrated structure made of a heat resistant metal having oxidation resistance such as stainless steel or Fe—Cr—Al alloy is preferably used.

These monolith carriers are manufactured by an extrusion molding method, a method of winding and solidifying a sheet-shaped element, or the like. The shape of the gas passage (cell shape) may be any of a hexagon, a quadrangle, a triangle, and a corrugation. A cell density (number of cells / unit cross-sectional area) of 150 to 600 cells / square inch is sufficient for use, and preferably 200.
~ 500 cells / in2.

In the present invention, in order to further suppress the formation of sulfate, rhodium is separately supported on the refractory inorganic oxide powder on the catalyst component layer formed on the refractory three-dimensional structure. May be coated with a rhodium-bearing refractory inorganic oxide. The rhodium-supporting refractory inorganic oxide coating layer may be a single layer or a plurality of layers. In this case, the amount of rhodium used per liter of the refractory three-dimensional structure is 0.01 to 0.5 g, preferably 0.05 to 0.3 g. If the amount of rhodium used is less than this, the effect is small, while if the amount used is more than this, the effect corresponding to the amount used is not improved. As a starting material for rhodium, inorganic acid salts and organic acid salts such as rhodium nitrate, rhodium chloride, rhodium chloride hexaammine rhodium chlorite, and rhodium sulfide complex salts can be used.

In the present invention, the method of supporting the catalyst component is not particularly limited, but a usual impregnation method is preferably used.

In the present invention, examples of the method for adjusting the catalyst include the following methods.

(1) The above platinum source, alkali metal sulfate and refractory inorganic oxide are combined into an aqueous slurry, the monolith carrier is coated with the aqueous slurry, and then dried.
A method of firing to obtain a finished catalyst, if necessary.

(2) The above platinum source and the refractory inorganic oxide are put together into an aqueous slurry, the monolith carrier is coated with the aqueous slurry, then dried and, if necessary, calcined, and the carrier is an alkali metal sulfate. Method of immersing in the above aqueous solution, drying, and then calcination if necessary to obtain a finished catalyst.

(3) The alkali metal sulfate and the refractory inorganic oxide are collectively made into an aqueous slurry, and the aqueous slurry is coated on a monolith carrier, then dried and, if necessary, calcined, and the carrier is platinum. A method in which the catalyst is completed by immersing it in an aqueous solution of the source, drying it, and then baking it if necessary.

(4) A refractory inorganic oxide is added to an aqueous solution of a platinum source, thoroughly mixed, dried, and fired if necessary,
A platinum-supported refractory inorganic oxide powder is obtained. This is an aqueous slurry, the monolith carrier is coated with the aqueous slurry,
Next, a method of drying, firing if necessary, further immersing the carrier in an aqueous solution of an alkali metal sulfate, drying, and then firing if necessary to obtain a finished catalyst.

(5) A refractory inorganic oxide carrying an alkali metal or alkaline earth metal sulfate is added to a solution of alkali metal sulfate in which a refractory inorganic oxide is added, thoroughly mixed, dried, and fired if necessary. A powder of the product is obtained. This is an aqueous slurry, the monolith carrier is coated with the aqueous slurry,
Next, it is dried, and the carrier is further immersed in an aqueous solution of a platinum source,
A method of drying, and if necessary, calcining to obtain a finished catalyst.

(6) The above platinum source and alkali metal sulfate are thoroughly mixed together with the refractory inorganic oxide, and then dried and, if necessary, calcined to obtain a platinum-supported refractory inorganic oxide powder. Then, the platinum-supported refractory inorganic oxide powder is made into an aqueous slurry, and the aqueous slurry is coated on a monolithic carrier, then dried and, if necessary, calcined to obtain a finished catalyst.

The catalyst component, refractory inorganic oxide, platinum-supported refractory inorganic oxide, etc. may be made into an aqueous slurry by any method that can be usually used as an aqueous slurry. Can be mentioned.

In any of the above methods (1) to (6), the catalyst component layer formed on the refractory three-dimensional structure may be further coated with a rhodium-supporting refractory inorganic oxide. .

Among the above methods (1) to (6), the method (4) or (6) is preferable in view of the viscosity of the preparation liquid and the convenience of handling during preparation of the catalyst.

An example of the method (6) of the above-mentioned catalyst preparation is as follows. First, in an aqueous solution containing a predetermined amount of platinum and an alkali metal sulfate,
After adding refractory inorganic oxide powder and impregnating it, 80
To 250 ° C, preferably 100-150 ° C, then 300-850 ° C, preferably 400-70 ° C.
By burning at a temperature of 0 ° C. for 0.5 to 5 hours, preferably 1 to 2 hours, a platinum-supported refractory inorganic oxide powder in which platinum and an alkali metal sulfate are dispersed is obtained.

Next, the platinum-supported refractory inorganic oxide powder and, if necessary, the second refractory inorganic oxide powder are mixed, wet-milled into a slurry, and the catalyst thus obtained. The refractory three-dimensional structure is immersed in the slurry of the composition to remove excess slurry, and then 80 to 250 ° C.
Preferably it is dried at a temperature of 100 to 150 ° C., then 3
0.5 at 00 to 800 ° C, preferably 400 to 700 ° C
The refractory three-dimensional structure is coated with the catalyst composition by firing for ~ 3 hours, preferably 1-2 hours.

Further, if necessary, a refractory inorganic oxide powder is added to and impregnated in an aqueous solution containing a predetermined amount of a rhodium compound, and then impregnated, then at 80 to 250 ° C., preferably 1
Dry at a temperature of 00-150 ° C, then 300-800
The rhodium-supported refractory inorganic oxide powder in which rhodium is dispersed in the refractory inorganic oxide powder is obtained by calcining at 0.5 ° C., preferably 400 to 700 ° C. for 0.5 to 5 hours, preferably 1 to 2 hours. obtain.

Next, this powder is wet pulverized to form a slurry, and the coated refractory three-dimensional structure which is obtained by impregnating the catalyst composition into the refractory three-dimensional structure, supporting and firing it is dipped in the obtained slurry. , After removing the excess slurry, 80
To 250 ° C, preferably 100 to 150 ° C, and then 300 to 850 ° C, preferably 400 to 70 ° C.
The catalyst is obtained by calcining at 0 ° C. for 0.5 to 3 hours, preferably 1 to 2 hours.

In the present invention, a diesel engine exhaust gas having a molar ratio of HC / NO _x of 0.5 to 20 (where HC is the total carbon concentration in terms of methane), preferably 1 to 10 is contacted with the catalyst. By doing so, nitrogen oxides in the exhaust gas are removed. That is, when the HC / NO _x ratio is lower than the above range, sufficient NO _x decomposing activity cannot be obtained. On the other hand, when the HC / NO _x ratio exceeds the above range, the activity can no longer be improved, and HC Is not preferable because it is exhausted without being completely burned.

Further, in the present invention, HC is contained in the exhaust gas.
Less, if it is the the NO _x decomposition activity is not sufficiently obtained, the temperature is 200 to 500 ° C., preferably 220 to
By injecting a reducing agent on the upstream side of the catalyst in the exhaust gas at 450 ° C., the HC / NO _x ratio can be adjusted to an appropriate value for the reaction.

Ammonia, hydrogen, various hydrocarbons, etc. are known as reducing agents for reducing nitrogen oxides, but light oil is a simple and economical system to be mounted on an automobile. Therefore, light oil is preferably used in the present invention. As a method of injecting light oil,
Although not particularly limited, for example, a method of introducing in a liquid state by using a single tube or a method of spraying with air and adding in a mist state is suitably used.

[0042]

EXAMPLES The present invention will be described in more detail with reference to examples.

[Example 1] BET specific surface area of 150 m ²
3,000 g of alumina powder and 150 g of potassium sulfate are put into a chloroplatinic acid aqueous solution containing 30 g of platinum, thoroughly mixed, dried at a temperature of 150 ° C. for 2 hours, and further heated at a temperature of 500 ° C. for 1 hour. Firing was performed to obtain an alumina powder carrying platinum and potassium sulfate in a dispersed state.

Next, 3000 g of this powder was wet pulverized to form a slurry. A cylindrical cordierite honeycomb carrier having a diameter of 5.66 inches and a length of 6.00 inches having about 400 open flow gas flow cells per square inch of cross section was immersed in this slurry to remove excess slurry. After removing, dry at 150 ℃ for 2 hours, then 500 ℃
It was baked for 1 hour. The catalyst thus obtained contained 1 g of platinum, 5 g of potassium sulfate (2.2 g as potassium), and 100 g of alumina per liter of the carrier.

Example 2 A catalyst was prepared in the same manner as in Example 1 except that 300 g of potassium sulfate was used instead of 150 g of potassium sulfate. The catalyst thus obtained contained 1 g of platinum, 10 g of potassium sulfate and 100 g of alumina per liter of the carrier.

[Example 3] A BET specific surface area of 80 m ² /
2000 g of titania powder and 1 g of potassium sulfate
Pour 00 g into a chloroplatinic acid aqueous solution containing 20 g of platinum, mix thoroughly, dry for 2 hours at a temperature of 150 ° C., and further calcine for 1 hour at a temperature of 500 ° C. to carry platinum and potassium sulfate in a dispersed state. A titania powder was obtained.

Next, 2120 g of this powder and 1000 g of titania powder having a BET specific surface area of 20 m ² / g were wet-milled together to form a slurry. A cylindrical cordierite honeycomb carrier having a diameter of 5.66 inches and a length of 6.00 inches having about 400 open flow gas flow cells per square inch of cross section was immersed in this slurry to remove excess slurry. After removing, it was dried at 150 ° C. for 2 hours and then calcined at 500 ° C. for 1 hour. The catalyst thus obtained was 1 g of platinum, 5 g of potassium sulfate and 10 parts of titania having a BET surface area of 80 m ² / g per liter of the carrier.
It contained 0 g and 50 g of titania having a BET surface area of 20 m ² / g.

[Example 4] In Example 3, 200 g of potassium sulfate was used instead of 100 g of potassium sulfate.
A catalyst was prepared in the same manner as in Example 3 except that 2220 g of titania having the same BET surface area was used instead of 2120 g of titania having an ET surface area of 80 m ² / g. Thus catalyst obtained by the carrier per liter of platinum 1g, potassium sulfate 10 g, titania 100g of BET surface area 80 m ² / g, titania 50g of BET surface area 20 m ² / g
Was included.

Comparative Example 1 A catalyst was prepared in the same manner as in Example 1 except that potassium sulfate was not used. The catalyst obtained was 1 platinum per liter of carrier.
g, and 100 g of alumina.

[Comparative Example 2] A catalyst was prepared in the same manner as in Example 1, except that 900 g of potassium sulfate was used instead of 150 g of potassium sulfate. The catalyst thus obtained contained 1 g of platinum, 30 g of potassium sulfate, and 100 g of alumina per liter of the carrier.

Comparative Example 3 A catalyst was prepared in the same manner as in Example 1 except that 9 g of potassium sulfate was used instead of 150 g of potassium sulfate in Example 1. The catalyst thus obtained contained 1 g of platinum, 0.3 g of potassium sulfate, and 100 g of alumina per liter of the carrier.

Comparative Example 4 Titania 21 having a BET surface area of 80 m ² / g was used without using potassium sulfate in Example 3.
Titania 2020 with the same BET surface area instead of 20 g
A catalyst was prepared in the same manner as in Example 3 except that g was used. The catalyst thus obtained was 1 g of platinum per liter of carrier and 10 parts of titania having a BET surface area of 80 m ² / g.
It contained 0 g and 50 g of titania having a BET surface area of 20 m ² / g.

Comparative Example 5 A catalyst was prepared in the same manner as in Example 1 except that 174 g of potassium nitrate (67 g as potassium) was used in place of 150 g of potassium sulfate (67 g as potassium) in Example 1. The catalyst thus obtained contained 1 g of platinum, 2.2 g of potassium and 100 g of alumina per liter of the carrier.

[Example 5] (Evaluation of catalyst) The diesel engine exhaust gas purification performance of the catalysts obtained in Examples 1 to 4 and Comparative Examples 1 to 4 was evaluated by the following method. In this method, a supercharged direct injection diesel engine (4 cylinders, 2800 cc) and diesel fuel having a sulfur content of 0.05% by weight were used as fuel.

The catalyst was attached to the exhaust gas pipe from the engine, and a durability test was carried out for 100 hours under the conditions of an engine speed of 2500 rpm, a full load, and a catalyst inlet temperature of 700 ° C.

Next, the engine speed is 2000 rpm,
After ventilating the catalyst for 1 hour under the condition of the catalyst inlet 200 ° C.,
By changing the torque, the engine speed is 2000 rpm, the catalyst inlet temperature is 300 ° C., NO _x in the exhaust gas before entering the catalyst bed (inlet) and after exiting the catalyst bed (outlet), particulate matter, SOF, gaseous The contents of hydrocarbons, carbon monoxide and sulfur dioxide were measured and the respective purification rates and conversion rates were obtained.

[0057] Incidentally, a light oil is used as a reducing agent for NO _x, and injected into the inlet of the catalyst as HC / NO _x ratio is 5 molar ratio. The purification rate was obtained from the ratio with the actual outlet concentration based on the inlet concentration when the light oil was not added in this way.

The above results are shown in Table 1 above.

[0059]

[Table 1]

[0060]

According to the diesel engine exhaust gas catalyst for the present invention, the NO _x in diesel engine exhaust gas HC / NO _x ratio is in the proper range to efficiently decompose and remove,
At the same time, harmful substances such as particulate matter, unburned hydrocarbons and carbon monoxide can be burned and removed.

That is, in the present invention, the addition of the alkali metal sulfate suppresses the SO ₂ oxidation activity and suppresses the formation of sulfate, which is advantageous for suppressing the particulate matter.

Further, by adding the alkali metal sulfate, the NO _x decomposing ability on the high temperature side is improved, and a diesel engine exhaust gas purifying catalyst excellent in high temperature durability can be obtained.

Furthermore, by changing the addition amount of the alkali metal sulfate, the temperature range in which the obtained catalyst is active can be changed, and a catalyst for purifying exhaust gas of diesel engine which can cope with various exhaust gas temperatures can be obtained. You can

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Claims (5)

[Claims] 1. A catalyst for purifying a diesel engine exhaust gas, comprising a refractory inorganic oxide powder and platinum and alkali metal sulfate supported on a refractory three-dimensional structure. 2. The catalyst for purifying exhaust gas from a diesel engine according to claim 1, wherein the alkali metal sulfate is potassium sulfate. 3. A diesel engine exhaust gas having a HC / NO _x ratio in the exhaust gas of 0.5 to 20 in molar ratio, which is brought into contact with the diesel engine exhaust gas-purifying catalyst according to claim 1. How to purify engine exhaust gas. 4. The method for purifying diesel engine exhaust gas according to claim 3, wherein a reducing agent is injected into the exhaust gas on the upstream side of the diesel engine exhaust gas purification catalyst. 5. The method for purifying diesel engine exhaust gas according to claim 4, wherein the reducing agent is light oil.