JPH08257405A - Catalyst for decomposition of nitrogen oxide and method for removing nitrogen oxide in exhaust gas from diesel engine by using the same - Google Patents

Abstract

PURPOSE: To decrease NOx and to burn and remove carbonaceous particulates, unburned hydrocarbon and carbon monoxide or the like, by using a catalyst for decomposition of nitrogen oxide, made by combining a catalyst layer containing platinum and a catalyst layer containing copper. CONSTITUTION: At first, a refractory inorganic oxide powder carrying platinum is formed by making carry a catalytically active oxide of at least one metal selected from the group consisting of tungsten, antimony, molybdenum, nickel, vanadium, manganese, iron, bismuth, cobalt, zinc and alkaline earth metals together with platinum into a 1st refractory inorganic oxide powder. A 1st catalytic composition consisting of the refractory inorganic oxide powder carrying platinum and the 2nd refractory inorganic oxide powder is coated on a refractory three dimensional structure. Thus, the catalyst for decomposing nitrogen oxide is obtained by applying coating of a 2nd catalytic composition carrying copper and rhodium to a 3rd refractory inorganic oxide powder onto the layer carrying a catalytic component thus formed. This catalyst suppresses a particulate substance and is excellent in durability at high temperatures.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a catalyst for decomposing nitrogen oxides and a method for purifying diesel engine exhaust gas using the same. More specifically, among harmful components in diesel engine exhaust gas, especially nitrogen oxides (N
The present invention relates to a catalyst capable of decomposing and reducing O _x ) and burning and removing carbonaceous fine particles, unburned hydrocarbons, carbon monoxide and the like, and a method for purifying diesel engine exhaust gas using the same.

[0002]

2. Description of the Related Art Nitrogen oxides (hereinafter, also referred to as NO _x ) in exhaust gas of diesel engines cause photochemical smog and acid rain. In recent years, particularly in urban areas, the emission of NO _x from a diesel engine has become a social problem, and it is important to reduce the emission amount. Therefore, research on exhaust gas treatment catalysts is being conducted. . Also,
Since diesel engine exhaust gas contains particulate matter that is harmful to health, it is desired that such an exhaust gas treatment catalyst has a capability of suppressing particulate matter as well as NO _x decomposing ability.

Conventionally, a three-way catalyst has been used to purify the exhaust gas of an automobile. However, in the exhaust gas of the diesel engine, NO _x cannot be sufficiently reduced by the ordinary three-way catalyst because of excess oxygen.

A catalyst effective for removing NO _x in exhaust gas containing a large amount of oxygen, such as exhaust gas of a diesel engine or exhaust gas of a gasoline lean burn engine, is described in, for example, JP-A-63-100919. As described above, a catalyst in which copper is supported on a porous carrier such as zeolite, alumina or silica has been proposed. However, such a catalyst has a problem that it has poor heat resistance and is easily poisoned by sulfur oxides.

Further, for example, as described in JP-A-5-137963, there has been proposed a method of removing NO _x by using platinum as a main catalyst and coexisting with a sulfur oxide. However, since such a platinum-containing catalyst has a high activity of oxidizing SO ₂ , when it is used for treating diesel engine exhaust gas, it increases sulfate radicals due to the oxidation of SO ₂ , which is disadvantageous in reducing particulate matter. , But it may even increase it.

As described above, the nitrogen oxide removing catalysts proposed so far have a problem in practical use for purifying exhaust gas of a diesel engine.

[0007]

SUMMARY OF THE INVENTION Therefore, an object of the present invention is to provide a novel catalyst for decomposing nitrogen oxides and a method for purifying diesel engine exhaust gas using the same.

Another object of the present invention is to use a catalyst layer containing platinum and a catalyst layer containing copper in combination so that NO _{x in} a wide temperature range can be accommodated in order to cope with the actual temperature change of exhaust gas. It is to provide a catalyst having a decomposition performance.

Still another object of the present invention is to burn and remove harmful components such as unburned hydrocarbons and carbon monoxide, and at the same time suppress the formation of sulfate radicals due to the oxidation of SO ₂ and reduce the particulate matter. It is to provide a catalyst to be obtained.

[0010]

The above-mentioned various purposes are (A) platinum, tungsten, antimony, molybdenum, nickel, vanadium, manganese, iron, bismuth, cobalt,
A platinum-supported refractory inorganic oxide powder, comprising a first refractory inorganic oxide powder and a catalytically active oxide of at least one metal selected from the group consisting of zinc and alkaline earth metals, and (B ) A refractory three-dimensional structure is coated with a first catalyst composition comprising a second refractory inorganic oxide powder, and (C) copper and rhodium are deposited on the catalyst component-supporting layer thus formed. This is achieved by a catalyst for decomposing nitrogen oxides, which is obtained by coating a second catalyst composition supported on a third refractory inorganic oxide powder.

The present invention also provides 0.01 to 3 g of platinum, 0.01 to 4 g of the catalytically active oxide and 0.01 to 4 g of platinum in the platinum-supported refractory inorganic oxide powder per liter of the refractory three-dimensional structure. The above-mentioned catalyst for decomposing nitrogen oxides, which carries 0.02 to 25 g of the refractory inorganic oxide powder of No. 1. The present invention is also the catalyst for decomposing nitrogen oxide, wherein the platinum-carrying refractory inorganic oxide powder (A) is used in an amount of 0.1 to 50% by weight with respect to the first catalyst composition. The present invention provides 0.01 to 10 parts of rhodium per liter of the refractory three-dimensional structure.
0.5 g and 4 to 50 g of copper, the amount of rhodium used was 0.1 to 10 times that of platinum and 0.01 to 0.
The catalyst for decomposing nitrogen oxide is 2 times by weight. The present invention also provides gallium oxide per liter of the refractory three-dimensional structure in a carrier layer of at least one catalyst composition selected from the group consisting of a first catalyst composition and a second catalyst composition. The catalyst for decomposing nitrogen oxides is contained in an amount of 0.1 to 15 g. The present invention provides the nitrogen oxidation, wherein the first and second refractory inorganic oxide powders are at least one selected from the group consisting of alumina, zirconia, titania, silica, alumina-zirconia and silica-alumina. It is a catalyst for material decomposition. The present invention is also the catalyst for decomposing nitrogen oxides, wherein the refractory three-dimensional structure is an open-flow ceramic honeycomb or metal honeycomb.

The above-mentioned objects are to contact a diesel engine exhaust gas in which the HC / NO _x ratio in the exhaust gas is 0.5 to 20 (HC is a methane equivalent concentration) in a molar ratio with the catalyst. It is also achieved by the method for removing nitrogen oxides in exhaust gas.

The present invention is also the method for removing nitrogen oxides, wherein the temperature of the exhaust gas into which the reducing agent is injected is 200 to 500 ° C. The present invention is also the method for removing nitrogen oxides, wherein the reducing agent is gas oil.

[0014]

The catalyst for decomposing nitrogen oxides according to the present invention is (A)
A first refractory material containing platinum and a catalytically active oxide of at least one metal selected from the group consisting of tungsten, antimony, molybdenum, nickel, vanadium, manganese, iron, bismuth, cobalt, zinc and alkaline earth metals. A refractory three-dimensional structure is coated with a first catalyst composition composed of a platinum-supported refractory inorganic oxide powder supported on a refractory inorganic oxide powder and (B) a second refractory inorganic oxide powder, On the catalyst component-supporting layer thus formed,
(C) A second catalyst composition in which copper and rhodium are supported on a third refractory inorganic oxide powder and coated.

First, the catalytically active oxides used in the present invention are tungsten, antimony, molybdenum, nickel, vanadium, manganese, iron, bismuth, cobalt,
It is an oxide of at least one metal selected from the group consisting of zinc and alkaline earth metals, preferably oxides of alkaline earth metals, antimony, vanadium, cobalt, tungsten and the like. As alkaline earth metal,
Examples include calcium, magnesium, strontium, and barium.

The catalytically active oxide is supported together with platinum on the first refractory inorganic oxide powder to form platinum-supported refractory inorganic oxide powder (A).

The platinum-supported refractory inorganic oxide powder (A)
Forms the first catalyst composition with the second refractory inorganic oxide powder (B) and is coated on the refractory three-dimensional structure.

The amount of platinum supported is the refractory three-dimensional structure 1
0.01 to 3 g, preferably 0.1 to 2 per liter
g. That is, when the supported amount of platinum is less than 0.01 g / l, the NO _x decomposition activity is low, which is not preferable. On the other hand, when the supported amount of platinum exceeds 3 g / l, NO is no longer commensurate with the supported amount. _There is no improvement in _x- degrading activity, which is 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 amount of the catalytically active oxide of at least one metal supported together with platinum is 0.01 to 4 g, preferably 0.1 to 2 per liter of the refractory three-dimensional structure.
g. That is, the supported amount of the catalytically active oxide was 0.
If it is less than 1 g / liter, the effect of suppressing the oxidation of SO ₂ is insufficient, and there is a tendency that sulfate radicals tend to be generated, which is disadvantageous. The effect of catalytically active oxides did not improve and NO
_X decomposition may be rather inhibited, which is not preferable. As the starting material of the catalytically active oxide, there are inorganic acid salts such as nitrates, sulfates, carbonates, phosphates, chlorides, hydroxides and oxides of the above metals, and organic acid salts such as acetates. is there.

As the first refractory inorganic oxide powder, γ
-Alumina, δ-alumina, η-alumina, θ-alumina and other activated alumina, α-alumina, titania, silica, zirconia, garia, and their composite oxides such as alumina-titania, alumina-zirconia, titania-zirconia, etc. But preferably at least one selected from the group consisting of activated alumina, titania, silica, zirconia, alumina-silica and silica-alumina.
It is a seed. The refractory inorganic oxide is usually in the form of powder, and its Brunauer-Emmett-Te
Leller (hereinafter referred to as BET) surface area is 5 to 400
m ² / g, preferably from 10 to 300 m ² / g. The average particle size is 0.1 to 150 μm, preferably 0.2
˜100 μm.

The amount of the first refractory inorganic oxide powder used is 0.02 to 2 per liter of the refractory three-dimensional structure.
It is 5 g, preferably 0.1 to 2 g. That is, 0.
If it is less than 02 g / liter, sufficient performance cannot be obtained, while if it exceeds 25 g / liter, performance commensurate with the amount used cannot be obtained.

The material, BET surface area and average particle size of the second refractory inorganic oxide powder (B) are the same as those of the first refractory inorganic oxide.

The platinum-supported refractory inorganic oxide powder (A) for the first catalyst composition comprising the platinum-supported refractory inorganic oxide powder (A) and the second refractory inorganic oxide powder (B). ) Is 0.1 to 50% by weight, preferably 1 to
It is 20% by weight. That is, when the ratio is less than 0.1% by weight, the second refractory inorganic oxide (B) is used in an unnecessarily large amount when the amount of platinum required to obtain sufficient activity is used. However, it is disadvantageous for economic reasons and convenience of catalyst preparation. On the other hand, when the ratio exceeds 50% by weight, it is disadvantageous because it is difficult to maintain the balance of expressing the NO _x decomposing ability of platinum and suppressing the SO ₂ oxidizing ability.

The refractory three-dimensional structure used in the present invention includes pellets, monolith carriers, etc., preferably monolith carriers. The monolithic carrier may be any one generally called a ceramic honeycomb carrier, and particularly cordierite, mullite, α-alumina, zirconia, titania, titanium phosphate, aluminum titanate, betalite, spodumene, aluminosilicate, magnesium silicate. Honeycomb carriers made of, for example, are preferable, and cordierite-based ones are particularly preferable. In addition, stainless steel, Fe-Cr-Al
An integrated structure made of a heat-resistant metal such as an alloy that is resistant to oxidation is also 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 shape. If the cell density (the number of cells / unit cross-sectional area) is 150 to 600 cells / square inch, it can be sufficiently used, and preferably 200 to
500 cells / square inch.

In the catalyst according to the present invention, the first catalyst composition is coated on the refractory three-dimensional structure to form a catalyst component supporting layer. The catalyst component-supporting layer is coated with the second catalyst composition in which copper and rhodium are supported on the third refractory inorganic oxide powder (C). This second
The coating layer of the catalyst composition may be a single layer or a plurality of layers.

The material, BET surface area and average particle size of the third refractory inorganic oxide powder (C) are the same as those of the first refractory inorganic oxide.

In the second catalyst composition, copper is usually present in the oxide form and rhodium is present in the metal form.

The amount of copper used per liter of the refractory three-dimensional structure is 4 to 50 g, preferably 8 to 25 g as metal. Further, rhodium is 0.01 to 0.5 g, preferably 0.05 to 0.3 g as metal.
And 0.1 to 10 times by weight of platinum, preferably 0.1.
It is 1 to 1 times by weight, and 0.001 to 0.1 times by weight, and preferably 0.005 to 0.05 times by weight that of copper. That is, if the amount of copper and rhodium used is less than this, the effect is small, while if the amount of copper and rhodium is greater than this, the effect commensurate with the amount used is not improved.

As a starting material for copper, water-soluble salts such as copper nitrate and acetate, copper oxide and the like can be used. Also,
As the starting material of rhodium, inorganic acid salts and organic acid salts such as rhodium nitrate, rhodium chloride, rhodium chloride hexaammine rhodium chloride and rhodium sulfide complex salts can be used.

Since the second catalyst composition is a copper-containing catalyst layer, it has the ability to decompose NO _x efficiently, especially at relatively high temperatures.

Further, in the present invention, the catalytically active oxide of at least one metal and rhodium supported together with platinum have the effect of suppressing the formation of sulfate.

Further, in the present invention, gallium oxide may be blended in the platinum-supported refractory inorganic oxide or the second or third refractory inorganic oxide powder. Gallium oxide is used as a water-soluble compound such as gallium oxide powder or gallium nitrate. The amount of gallium oxide used is 0.1 per liter of the refractory three-dimensional structure.
-15 g, preferably 0.5-5 g. Thereby, the NO _x decomposition activity can be improved.

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

The catalyst according to the present invention can be prepared, for example, by the following method.

First, the first refractory inorganic oxide powder is added to and impregnated in an aqueous solution containing a predetermined amount of platinum and a compound of at least one other metal.
Drying at a temperature of 50 ° C, preferably 100-150 ° C,
Then 300-850 ° C, preferably 400-700 ° C
By firing at a temperature of 0.5 to 5 hours, preferably 1 to 2 hours, a platinum-supported refractory inorganic oxide powder in which platinum and a metal oxide are dispersed can be obtained.

Next, the platinum-supported refractory inorganic oxide powder (A) and the second refractory inorganic oxide powder (B) are mixed and wet pulverized to form a slurry, which is thus obtained. After immersing the refractory three-dimensional structure in the slurry of the first catalyst composition and removing the excess slurry, 80 to 25
Said first catalyst by drying at a temperature of 0 ° C., preferably 100-150 ° C. and then calcining at 300-800 ° C., preferably 400-700 ° C. for 0.5-3 hours, preferably 1-2 hours. The composition is coated on a refractory three-dimensional structure.

Further, after the third refractory inorganic oxide powder (C) is put into an aqueous solution containing a predetermined amount of a compound of copper and rhodium to impregnate it, the temperature is 80 to 250 ° C., preferably 100 to 150. Dry at a temperature of ℃, then 30
By firing at a temperature of 0 to 800 ° C., preferably 400 to 700 ° C. for 0.5 to 5 hours, preferably 1 to 2 hours, copper oxide and rhodium are the third refractory inorganic oxide powder (C). A second catalyst composition dispersed in is obtained.

Next, the second catalyst composition is wet pulverized to form a slurry, and the slurry thus obtained is impregnated with the first catalyst composition in a refractory three-dimensional structure, supported and fired. The three-dimensional structure is dipped to remove excess slurry, and then 80 to 250 ° C., preferably 100 to
The catalyst is obtained by drying at a temperature of 150 ° C. and then calcining at 300 to 850 ° C., preferably 400 to 700 ° 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, if the HC / NO _x ratio is lower than the above range, sufficient NO _x decomposing activity cannot be obtained, while if the HC / NO _x ratio exceeds the above range, no further improvement in activity can be obtained. Is not preferable because it is exhausted without being completely burned.

Further, in the present invention, HC is contained in the exhaust gas.
When the NO _x decomposing activity is not sufficiently obtained as it is, the temperature is 200 to 500 ° C., preferably 220 to 500 ° C.
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. However, when mounted on an automobile, diesel oil is a simple and economical system. 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.

[0043]

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

Example 1 Titania powder 10 having a BET specific surface area of 10 m ² / g
0 g was put into a chloroplatinic acid aqueous solution containing 42.2 g of calcium nitrate and 10.0 g of platinum, thoroughly mixed, dried at a temperature of 150 ° C. for 2 hours, and further baked at a temperature of 500 ° C. for 1 hour. As a result, titania powder carrying platinum and calcium oxide dispersed therein was obtained.

Next, 120 g of this powder, 1000 g of the same titania powder as used above, 400 g of alumina having a BET specific surface area of 145 m ² / g and 20 g of gallium oxide were wet-milled together to form a slurry. . A cylindrical honeycomb carrier made of cordierite having a diameter of 5.66 inches and a length of 6.00 inches and having about 400 open flow gas flow cells per square inch in cross section was immersed in this slurry to remove excess slurry. Later, 1
By drying at 50 ° C. for 2 hours and then baking at 500 ° C. for 1 hour, a three-dimensional structure coated with a platinum-containing catalyst layer was obtained.

Next, 900 g of zirconia powder having a specific surface area of 110 m ² / g was added to an aqueous solution prepared by dissolving 608 g of rhodium nitrate containing 1.0 g of rhodium and copper nitrate in deionized water and thoroughly stirred. 2 at 150 ° C
It was dried for an hour and then calcined at 500 ° C. for 1 hour to obtain a zirconia powder in which rhodium and copper were dispersed and supported. This powder was wet pulverized into a slurry.

The three-dimensional structure prepared as described above is dipped in the thus obtained slurry to remove excess slurry, and then dried at 150 ° C. for 1 hour and then 5
The catalyst was obtained by calcining at 00 ° C. for 1 hour.

Example 2 A catalyst was prepared in the same manner as in Example 1 except that 304 g of copper nitrate and 600 g of zirconia were used.

Example 3 In the same manner as in Example 1 except that 10.0 g of antimony trioxide powder was used instead of 42.2 g of calcium nitrate in Example 1 and the amount of slurry impregnated in the honeycomb carrier was changed. A catalyst was prepared.

Example 4 A catalyst was prepared in the same manner as in Example 1 except that vanadium pentoxide (8.0 g) was used instead of calcium nitrate (42.2 g).

Example 5 140 g of titania powder having a specific surface area of 10 m ² / g
Was added to an aqueous solution prepared by dissolving dinitrodiaminoplatinum containing 29.0 g of cobalt nitrate and 10 g of platinum in deionized water, thoroughly mixed, and then dried at a temperature of 150 ° C. for 3 hours, and further at 500 ° C. It was fired for 2 hours to obtain a titania powder carrying platinum and cobalt oxide in a dispersed manner.
Next, 158 g of the obtained powder and 800 g of titania powder
And zirconia 200 having a specific surface area of 83 m ² / g
g was mixed, wet-milled, and made into a slurry. 5.66 inch diameter with about 400 open flow gas flow cells per square inch cross section in the resulting slurry x
A 6.00-inch long cylindrical cordierite honeycomb carrier was dipped, excess slurry was removed, dried at 150 ° C. for 2 hours, and then calcined at 500 ° C. for 1 hour to form a tertiary coating coated with a platinum-containing catalyst layer. The original structure is obtained.

On the other hand, zirconia powder 9 having a specific surface area of 110 m ² / g in an aqueous solution of rhodium nitrate containing 1.0 g of rhodium and 608 g of copper nitrate in deionized water.
00 g and 20 g of gallium oxide were added and mixed sufficiently, dried at 150 ° C. for 2 hours, and then calcined at 500 ° C. for 1 hour to obtain zirconia powder in which rhodium and copper were dispersed and supported. This powder was wet pulverized into a slurry.
The three-dimensional structure prepared as described above is dipped in the obtained slurry to remove excess slurry, and then at 150 ° C.
Then, the three-dimensional structure covered with the platinum-containing catalyst layer was prepared by drying for 2 hours and then firing at 500 ° C. for 1 hour.

Example 6 A titania powder carrying platinum and iron oxide dispersed therein was obtained in the same manner as in Example 1 except that 202 g of iron nitrate was used instead of 42.2 g of calcium nitrate in Example 1.

Next, 150 g of this powder and alumina 4
00 g and zirconia 800 g were mixed and wet-milled to form a slurry. The resulting slurry has a cross-sectional area of 1
A cylindrical cordierite honeycomb carrier having a diameter of 5.66 inches and a length of 6.00 inches having approximately 400 open flow gas flow cells per square inch was immersed in the honeycomb carrier to remove excess slurry, and then at 2 ° C at 150 ° C. A three-dimensional structure coated with a platinum-containing catalyst layer was prepared by drying for an hour and then firing at 500 ° C. for 1 hour.

Then, a second stage catalyst layer was prepared in the same manner as in Example 5.

Comparative Example 1 In the same manner as in Example 1, a titania powder carrying platinum and calcium oxide dispersed therein was obtained. Next, add rhodium to 1.0
After adding 400 g of alumina to an aqueous solution of rhodium nitrate containing g in deionized water and thoroughly stirring, 1
It was dried at 50 ° C. for 2 hours and then calcined at 500 ° C. for 1 hour to obtain an alumina powder carrying rhodium dispersed therein.

120 g of titania powder carrying platinum and calcium oxide dispersed therein, and alumina powder 4 carrying rhodium dispersed therein
01 g, titania powder 1000 g and gallium oxide 2
0 g was mixed and wet pulverized to form a slurry. 5.66 inch diameter with about 400 open flow gas flow cells per square inch cross section in the resulting slurry x
After immersing a 6.00 inch long cylindrical cordierite honeycomb carrier to remove excess slurry, 150
A catalyst was prepared by drying at 2 ° C. for 2 hours and then calcining at 500 ° C. for 1 hour.

Comparative Example 2 800 g of zirconia powder having a specific surface area of 110 m ² / g
Was added to an aqueous solution prepared by dissolving 540 g of copper nitrate in deionized water, thoroughly stirred, dried at 150 ° C. for 2 hours, and further calcined at 500 ° C. for 1 hour to obtain a zirconia powder carrying copper dispersed therein. Obtained. The powder thus obtained was wet pulverized into a slurry.

A cylindrical honeycomb carrier made of cordierite having a diameter of 5.66 inches and a length of 6.00 inches having approximately 400 open-flow gas flow cells per square inch in cross section was dipped in this slurry to make an excess. After removing the slurry, it was dried at 150 ° C for 2 hours and then 500 ° C.
It was calcined for 1 hour to obtain a catalyst.

Comparative Example 3 A catalyst was prepared in the same manner as in Example 1 except that calcium, gallium and rhodium were not used.

Comparative Example 4 A catalyst was prepared in the same manner as in Comparative Example 2 except that an aqueous chloroplatinic acid solution containing 8.9 g of platinum was used in addition to zirconia and copper nitrate.

The compositions of the catalysts obtained in the above Examples 1 to 6 and Comparatives 1 to 4 are shown in Tables 1 and 2. In addition, Table 1
The numerical values in Table 2 represent the amount used (g) per liter of the three-dimensional structure.

[0063]

[Table 1]

[0064]

[Table 2]

Example 7 (Evaluation of catalyst) The diesel engine exhaust gas purification performance of the catalysts obtained in Examples 1 to 6 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 0.06 wt% were used as fuel.

The catalyst was attached to the exhaust gas pipe from the above engine, and a durability test was carried out for 100 hours under the conditions of an engine speed of 2500 rpm 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.,
Exhaust gas before entering the catalyst bed (inlet) and after exiting the catalyst bed (outlet) when the engine speed is 2000 rpm and the catalyst inlet temperature is 250 ° C, 300 ° C, 350 ° C, 400 ° C and 450 ° C by changing the torque. The contents of NO _x and fine particles in the powder were measured and the respective purification rates were obtained.

Light oil used as a NO _x reducing agent was injected into the catalyst inlet at a rate of 3% of the amount consumed as fuel. The purification rates of NO _x and particulate matter were obtained from the ratio with the actual outlet concentration based on the inlet concentration in the case where light oil was not added in this way.

The above results are shown in Tables 3 to 4 and FIGS.

[0070]

[Table 3]

[0071]

[Table 4]

[0072]

INDUSTRIAL APPLICABILITY In the present invention, by using a platinum-containing catalyst layer and a copper-containing catalyst layer in combination, NO _x can be efficiently decomposed and reduced in a wide temperature range as shown in FIGS. Since it has an effect, it is practically advantageous. Moreover, since these catalysts suppress particulate matter and have excellent durability at high temperatures, they are extremely useful as catalysts for purifying diesel engine exhaust gas.

The catalyst of Comparative Example 1 has no copper-containing layer,
In that case, the NO _x purification capacity on the high temperature side is low.

The catalyst of Comparative Example 2 does not use the platinum-containing layer, and therefore has a low NO _x purification ability on the low temperature side.

In the catalyst of Comparative Example 3, the additive component used with platinum and rhodium were not used. Therefore, the generation of sulfate is not suppressed, and the purification rate of the particulate matter is low.

In the catalyst of Comparative Example 4, platinum and copper are contained in the same catalyst layer and used, but the NO _x purification rate is low.

As described above, the inventors of the present invention have found that when platinum and copper are present in the vicinity of each other,
Since it has been found that the NO _x decomposition activity decreases, the platinum-containing layer and the copper-containing layer are decomposed and used in the present invention.

[Brief description of drawings]

FIG. 1 is a graph showing the relationship between the catalyst inlet temperature and the NO _x purification rate in the catalysts of Examples and Comparative Examples of the present invention.

FIG. 2 is a graph showing the relationship between the catalyst inlet temperature and the particulate matter purification rate in the catalysts of Examples and Comparative Examples of the present invention.

FIG. 3 is a graph showing the relationship between the catalyst inlet temperature and the NO _x purification rate in the catalysts of other examples and comparative examples of the present invention.

FIG. 4 is a graph showing the relationship between the catalyst inlet temperature and the particulate matter purification rate in the catalysts of other examples and comparative examples of the present invention.

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Internal reference number FI Technical display location B01J 23/60 ZAB B01J 37/02 ZAB 23/64 ZAB 301L 37/02 ZAB B01D 53/36 ZAB 301 102B 102A

Claims (7)

[Claims] 1. (A) platinum and tungsten, antimony, molybdenum, nickel, vanadium, manganese,
Platinum-supported refractory inorganic material comprising a first refractory inorganic oxide powder and a catalytically active oxide of at least one metal selected from the group consisting of iron, bismuth, cobalt, zinc and alkaline earth metals. A first catalyst composition comprising an oxide powder and (B) a second refractory inorganic oxide powder is coated on a refractory three-dimensional structure, and a catalyst component-supporting layer thus formed is C) A catalyst for decomposing nitrogen oxides, which is obtained by coating a second catalyst composition in which copper and rhodium are supported on a third refractory inorganic oxide powder. 2. The decomposition of nitrogen oxides according to claim 1, wherein the platinum-supported refractory inorganic oxide powder (A) is used in an amount of 0.1 to 50% by weight based on the first catalyst composition. catalyst. 3. Gallium oxide per liter of the refractory three-dimensional structure in a carrier layer of at least one catalyst composition selected from the group consisting of a first catalyst composition and a second catalyst composition. The catalyst for decomposing nitrogen oxides according to claim 1 or 2, which comprises 0.1 to 15 g. 4. The catalyst according to claim 1, wherein a diesel engine exhaust gas having a molar ratio of HC / NO _x in the exhaust gas of 0.5 to 20 (HC is a methane conversion concentration) is used. A method for removing nitrogen oxides from exhaust gas of a diesel engine, which is characterized by bringing them into contact with each other. 5. A method for removing nitrogen oxides, which comprises injecting a reducing agent into the exhaust gas of a diesel engine and bringing the exhaust gas into contact with the catalyst according to any one of claims 1 to 3. 6. The temperature of the exhaust gas injected with the reducing agent is 20.
The method for removing nitrogen oxides according to claim 5, which is 0 to 500 ° C. 7. The method for removing nitrogen oxides according to claim 4, wherein the reducing agent is light oil.