JP2003080081A - Catalyst for cleaning exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a catalyst for cleaning an exhaust gas, exhibiting a high oxidation performance and NOx-occlusion/reduction performances. SOLUTION: This exhaust gas cleaning catalyst has an oxidation catalyst section comprising a three dimensional structure having a fire-resistant property, a first support layer part formed from a first inorganic oxide and provided on the three dimensional structure and a first catalytic metal supported on the first support layer part, and a NOx-occlusion/reduction section comprising a second support layer part formed from a second inert oxide and provided on the three dimensional structure, a second catalytic metal supported on the second support layer part and a NOx-occlusion/reduction material supported on the second support layer part. The exhaust gas cleaning catalyst has the oxidation catalyst section and the NOx-occlusion/reduction section on the three dimensional structure, and thereby, the catalyst exhibits the high oxidation performance and the NOx-occlusion/reduction performances.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst, and more particularly to an exhaust gas purifying catalyst having high NOx storage reduction performance.

[0002]

Exhaust gas emitted from an internal combustion engine such as an automobile engine is a hydrocarbon (HC) or carbon monoxide (C).
O), nitrogen oxides (NOx) and other harmful components. If exhaust gas containing this harmful component is directly discharged into the atmosphere, pollution will occur and the environment will deteriorate. Therefore, the exhaust gas containing these components is
Hazardous components are purified by a purification means such as an exhaust gas purification catalyst and then discharged into the atmosphere.

Further, due to the growing interest in the global environment,
In particular, automobiles are required to have low fuel consumption and low pollution. Lean burn engines and diesel engines are being used as vehicle engines that meet this demand.

Since lean burn engines and diesel engines burn in an oxygen excess atmosphere, a large amount of NO is generated.
Discharge x. Therefore, as an exhaust gas purifying catalyst for purifying the exhaust gas of these engines, a storage reduction catalyst in which a NOx storage reducing material made of an alkali metal or alkaline earth metal element is added to a normal exhaust gas purifying catalyst is used. It is used.

However, it is known that the elements of alkali metal and alkaline earth metal have a function of significantly reducing the oxidizing function of the catalytic metal having a catalytic action. Therefore, the storage reduction catalyst has a problem that the oxidation performance of the catalyst metal is deteriorated by adding the NOx storage reduction material.

[0006]

The present invention has been made in view of the above circumstances, and an object thereof is to provide an exhaust gas purifying catalyst having high oxidation performance and NOx storage reduction performance.

[0007]

In order to solve the above-mentioned problems, the present inventors have found that an oxidation catalyst portion and NOx are formed on a three-dimensional structure.
It has been found that the above problem can be solved by using an exhaust gas purifying catalyst having an occlusion reduction section.

That is, the exhaust gas purifying catalyst of the present invention is
It has a three-dimensional structure having fire resistance, a first supporting layer portion made of a first inorganic oxide provided on the three-dimensional structure, and a first catalytic metal supported on the first supporting layer portion. Oxidation catalyst part, second supporting layer part made of a second inorganic oxide provided on the three-dimensional structure, second catalyst metal supported on the second supporting layer part, and supported on the second supporting layer part And a NOx storage / reduction unit including the stored NOx storage / reduction material.

The exhaust gas purifying catalyst of the present invention has the oxidation catalyst portion and the NOx storage reduction portion on the three-dimensional structure, so that the first catalyst metal of the oxidation catalyst portion and the Nx storage reduction portion of the NOx storage reduction portion.
The Ox storage reduction material does not come into contact with the first catalyst metal, and the oxidation function of the first catalyst metal does not deteriorate. That is, in the exhaust gas purifying catalyst of the present invention, the oxidation catalyst unit oxidizes and purifies the exhaust gas, and the NOx storage reduction unit purifies NOx by storage reduction. As a result, the exhaust gas purifying catalyst of the present invention is a catalyst having high oxidation performance and NOx storage reduction performance.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas-purifying catalyst of the present invention has a three-dimensional structure, an oxidation catalyst portion, and a NOx storage reduction portion.

The three-dimensional structure is a member having fire resistance and having an oxidation catalyst portion and a NOx storage reduction portion formed on its surface. That is, the three-dimensional structure retains the catalyst component on the surface. Further, since the three-dimensional structure has fire resistance, it is possible to purify high temperature exhaust gas.

The oxidation catalyst portion has a first supporting layer portion made of a first inorganic oxide provided on the three-dimensional structure, and a first catalytic metal supported on the first supporting layer portion. That is, since the oxidation catalyst portion has the first supporting layer portion and the first catalyst metal, the exhaust gas purifying catalyst of the present invention can oxidize and purify exhaust gas.

The NOx occlusion reduction section comprises a second supporting layer section made of a second inorganic oxide provided on the three-dimensional structure, a second catalytic metal supported on the second supporting layer section, and a second supporting layer. And a NOx storage-reduction material carried on the layer portion. That is, the NOx occlusion reduction section has the second support layer section, the second catalytic metal, and the NOx occlusion reduction material, so that the exhaust gas purifying catalyst of the present invention occlusion-reduces NOx in the exhaust gas. You can

Since the exhaust gas purifying catalyst of the present invention has the oxidation catalyst portion and the NOx occlusion reduction portion, it is an exhaust gas purifying catalyst having a high NOx occlusion reduction performance without impairing the oxidation function. Specifically, the oxidation catalyst part oxidizes and purifies harmful components in the exhaust gas, and the NOx storage reduction part reduces and purifies NOx components. Therefore, the exhaust gas purification catalyst of the present invention has a high NOx storage capacity without impairing oxidation performance. It is a catalyst for exhaust gas purification that has reducing performance.

It is preferable that the oxidation catalyst portion and the NOx occlusion reduction portion are provided on the three-dimensional structure side by side in the exhaust gas flow direction. That is, since the oxidation catalyst portion and the NOx storage / reduction portion are arranged side by side, the oxidation catalyst portion and the NOx storage / reduction portion do not coexist, so that the catalyst performance of the first catalyst metal by the NOx storage / reduction material is The decrease is suppressed.

Further, since the oxidation catalyst portion and the NOx occlusion reduction portion are arranged side by side along the flow direction of the exhaust gas, the exhaust gas purified by the NOx occlusion reduction portion or the oxidation catalyst portion is oxidized. Alternatively, it is purified by the NOx storage reduction unit. Therefore, a high NOx storage reduction performance can be exhibited without impairing the oxidation performance.

The oxidation catalyst portion and the NOx occlusion reduction portion may be arranged in a line in the exhaust gas flow direction, and their relative positions are not particularly limited. Specifically, when the oxidation catalyst portion and the NOx storage reduction portion are provided on the three-dimensional structure in a line along the flow direction of the exhaust gas, either the oxidation catalyst portion or the NOx storage reduction portion is provided upstream. You may make money.

Further, the oxidation catalyst portion and the NOx occlusion reduction portion, which are arranged side by side along the flow direction of the exhaust gas, may each be a plurality of portions. That is, the oxidation catalyst part and N
Ox storage reduction units may be provided alternately.

Further, in the exhaust gas purifying catalyst of the present invention, the oxidation catalyst portion and the NOx storage reduction portion may be provided on the same three-dimensional structure, but may be provided on different three-dimensional structures. Good.

It is preferable that the oxidation catalyst portion and the NOx occlusion reduction portion are laminated on the three-dimensional structure. That is, since the oxidation catalyst portion and the NOx storage reduction portion are stacked and provided, the oxidation catalyst portion and the NOx storage reduction portion do not coexist, and therefore the deterioration of the catalytic performance of the first catalyst metal by the NOx storage reduction material is suppressed. Has been.

Since the oxidation catalyst portion and the NOx occlusion reduction portion are stacked and provided on the three-dimensional structure, N
The exhaust gas purified by the Ox storage reduction section or the oxidation catalyst section is purified by the oxidation catalyst section or the NOx storage reduction section. Therefore, a high NOx storage reduction performance can be exhibited without impairing the oxidation performance.

The oxidation catalyst portion and the NOx occlusion reduction portion only need to be stacked on the three-dimensional structure, and their relative positions are not particularly limited. Specifically, the oxidation catalyst part and NOx on the three-dimensional structure
When the storage reduction unit is stacked and provided, either the oxidation catalyst unit or the NOx storage reduction unit may be provided in the upper layer.

Further, the oxidation catalyst portion and the NOx occlusion reduction portion, which are stacked on the three-dimensional structure, may be plural in number. That is, the oxidation catalyst portion and the NOx storage reduction portion may be alternately stacked on the three-dimensional structure.

Further, in the exhaust gas purifying catalyst of the present invention, the oxidation catalyst portion and the NOx storage / reduction portion may be lined up in the exhaust gas flow direction and laminated.

The first inorganic oxide and the first catalytic metal forming the oxidation catalyst portion are not particularly limited, and the materials used for conventional exhaust gas purifying catalysts can be used.

The first inorganic oxide is preferably made of at least one of alumina, silica, titania, zirconia, ceria and zeolite. When the first inorganic oxide is composed of at least one of these, a supporting layer having excellent heat resistance and a large specific surface area can be formed.

The first catalytic metal is Pt, Pd, Rh, A
It is preferably made of at least one of g, Au and Ir. That is, when the first catalyst metal is made of at least one of these, the oxidation catalyst part can purify the exhaust gas.

The second inorganic oxide, NOx storage-reducing material and second catalyst metal forming the NOx storage-reduction part are not particularly limited, and are materials used in conventional NOx storage-reduction type exhaust gas purifying catalysts. Can be used.

The second inorganic oxide is preferably made of at least one of alumina, silica, titania, zirconia, ceria and zeolite. When the second inorganic oxide is composed of at least one of these, a supporting layer having excellent heat resistance and a large specific surface area can be formed.

The second catalytic metal is Pt, Pd, Rh, A
It is preferably made of at least one of g, Au and Ir. That is, when the second catalytic metal is made of at least one of these, the NOx storage reduction unit can purify the exhaust gas.

The NOx occlusion reducing material is preferably made of at least one selected from alkali metals and alkaline earth metals. That is, since the NOx storage / reduction material is made of at least one of these, the NOx storage / reduction portion has N
It becomes possible to store Ox.

The first inorganic oxide and the second inorganic oxide may be the same inorganic oxide or different inorganic oxides. Inorganic oxides of the same kind are preferable because the number of kinds of materials does not increase. Further, when the same kind of inorganic oxide is used, the first supporting layer and the second supporting layer can be formed at the same time depending on the arrangement of the oxidation catalyst part and the NOx storage reduction part, and the increase in cost required for production can be suppressed. You can

The first catalytic metal and the second catalytic metal may be the same kind of metal or different kinds of metal. It is preferable to use the same kind of catalytic metal because the number of kinds of materials does not increase. Furthermore, if the same kind of catalytic metal is used,
Depending on the arrangement of the oxidation catalyst part and the NOx storage reduction part, it becomes possible to support the first catalyst metal and the second catalyst metal at the same time, and it is possible to suppress an increase in manufacturing cost.

The three-dimensional structure is preferably an open flow honeycomb or a wall flow DPF.

The three-dimensional structure is preferably made of ceramics or metal. Examples of ceramics or metals that form the three-dimensional structure include cordierite, silicon carbide (SiC), stainless steel, and ceramic fibers.

The supported amounts of the first and second inorganic oxides in the first supporting layer and the second supporting layer provided on the three-dimensional structure are not particularly limited. That is, it is sufficient that the catalyst metal and the storage reduction component to be supported on the respective support layers can be supported.

The amount of the first catalytic metal supported on the first supporting layer part is 100 wt% of the entire first supporting layer part.
It is preferably contained in an amount of 0.01 to 10 wt%. That is, the first support layer portion contains 0.01 to 10 w of the first catalyst metal.
By having the content of t%, exhaust gas can be sufficiently purified.
If the amount of the first catalytic metal is less than 0.01 wt%, the amount of the first catalytic metal will be small and the purification of the exhaust gas will be insufficient. Further, if the first catalytic metal exceeds 10 wt%, the improvement in the effect of exhaust gas purification with respect to the increase in the carried amount of the catalytic metal becomes small. More preferably, it is in the range of 0.1 to 5 wt%.

The amount of NOx occlusion-reducing material loaded on the second carrier layer part is 100 wt% of the entire second carrier layer part.
It is preferably contained in an amount of 0.5 to 30 wt%. That is, the second support layer portion contains 0.5 to 30 w of the NOx storage reducing material.
By having t%, the NOx storage reduction unit can reduce and purify NOx. It should be noted that the NOx occlusion reducing material is less than 0.
If it is less than 5 wt%, the amount of NOx storage-reducing material is small and purification of NOx in exhaust gas is insufficient. Further, when the NOx storage / reduction material exceeds 30 wt%, the improvement of the NOx purification effect against the increase in the carried amount of the NOx storage / reduction material becomes small. More preferably, it is in the range of 1 to 20 wt%.

The amount of the second catalytic metal supported on the second supporting layer portion is preferably 0.1 to 10 wt% when the entire second supporting layer portion is 100 wt%. That is, the second support layer portion contains the second catalyst metal in an amount of 0.1 to 10
By having it at t%, the purification of NOx is sufficiently performed.
If the amount of the second catalytic metal is less than 0.1 wt%, the amount of the second catalytic metal will be small and the purification of NOx in the exhaust gas will be insufficient. Further, when the content of the second catalytic metal exceeds 10 wt%, the improvement in the effect of NOx purification with respect to the increase in the carried amount of the catalytic metal becomes small. More preferably, it is in the range of 1 to 5 wt%.

The ratio between the oxidation catalyst portion and the NOx storage reduction portion is not particularly limited and can be appropriately determined depending on the components of the exhaust gas to be purified. Further, it can be appropriately determined depending on the amounts of the catalyst metal and the NOx storage-reduction material carried on each.

The exhaust gas purifying catalyst of the present invention is not particularly limited as long as it has a three-dimensional structure, an oxidation catalyst portion, and a NOx storage reduction portion, and its manufacturing method is not particularly limited.

The exhaust gas purifying catalyst of the present invention has the oxidation catalyst part and the NOx storage reduction part on the three-dimensional structure, so that the first catalyst metal of the oxidation catalyst part and the Nx storage reduction part of the NOx storage reduction part.
The Ox storage reduction material does not come into contact with the first catalyst metal, and the oxidation function of the first catalyst metal does not deteriorate. That is, in the exhaust gas purifying catalyst of the present invention, the oxidation catalyst unit oxidizes and purifies the exhaust gas, and the NOx storage reduction unit purifies NOx by storage reduction. As a result, the exhaust gas purifying catalyst of the present invention is a catalyst having high oxidation performance and NOx storage reduction performance.

[0043]

EXAMPLES The present invention will be described below with reference to examples.

As an example, an exhaust gas purifying catalyst was manufactured.

Example 1 First, 100 parts by weight of alumina powder was dispersed in 140 parts by weight of deionized water, and then 3 parts by weight of alumina sol in terms of alumina was added and wet pulverized to prepare an alumina slurry.

The prepared alumina slurry had a wall flow gas distribution cell having a cell number of 47 cells / cm ² (about 300 cells / inch ² ) in diameter of 12.9 cm and axial length of 15.0 cm. Was coated on a cylindrical DPF carrier made of cordierite, dried at 250 ° C. for 1 hour, and then calcined at 500 ° C. for 1 hour to obtain an alumina-coated cordierite DPF.

The amount of alumina in the obtained alumina-coated cordierite DPF was 100 g per liter of the refractory three-dimensional structure.

The obtained alumina-coated cordierite DPF was impregnated with an aqueous solution of platinum nitrate, dried at 250 ° C. for 1 hour, then impregnated with an aqueous solution of rhodium nitrate and dried at 250 ° C. for 1 hour, and then the catalyst-coated alumina-coated cordierite carrying a noble metal was used. I got a light DPF. Amount of supported catalytic precious metal of alumina coated cordierite DPF carrying supported catalytic precious metal is D
5 g of platinum and 0.1 of rhodium per liter of PF carrier.
It was 1 g.

Alumina-coated cordierite DP supporting catalyst noble metal was immersed in deionized water and then suctioned to carry out alumina-coated cordierite DP supporting catalyst noble metal.
The water absorption per F was determined. The catalytic noble metal supported on the catalytic noble metal-supported alumina-coated cordierite DPF does not dissolve in deionized water because it is calcined even when immersed in deionized water. In addition, the water absorption is measured by measuring the weight of the catalyst noble metal-supported alumina-coated cordierite DPF in advance and immersing it in deionized water and sucking it to measure the weight difference between the two. The water absorption was obtained from

Barium acetate and lithium nitrate were dissolved in deionized water in an amount half the water absorption obtained, and the catalyst-precious metal-supported alumina-coated cordierite DPF was immersed in the solution only from one end surface. At this time, the solution is
It was immersed in a portion from one end face to half the axial length of the DPF carrier. Then, it was dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour to obtain a gas purifying catalyst of Example 1. The NOx storage material amount of the exhaust gas purifying catalyst of Example 1 was 1 barium per one three-dimensional structure.
3.5 g and 1.4 g of lithium.

In the exhaust gas purifying catalyst of Example 1, the part carrying barium and lithium was used as the NOx storage reduction part.
The portion not supported is the oxidation catalyst portion.

Specifically, the exhaust gas-purifying catalyst of Example 1 comprises a cordierite DPF carrier, an alumina coat layer portion provided on the DPF carrier, and platinum and rhodium supported on the alumina coat layer portion. NOx occlusion reduction section having an oxidation catalyst section, an alumina coating layer section provided on a DPF carrier, platinum and rhodium supported on the alumina coating layer section, and barium and lithium supported on the alumina coating layer section. And a catalyst having

(Example 2) The exhaust gas purifying catalyst of Example 2 is the same as the exhaust gas purifying catalyst of Example 1 except that the supporting layer is made of titania and potassium is further supported in the NOx occlusion reduction section. Is.

First, 100 parts by weight of titania was dispersed in 67 parts by weight of deionized water, 83 parts by weight of titania sol was added, and wet pulverization was performed to prepare a titania slurry.

The titania slurry prepared was used in Example 1.
Apply to a cordierite DPF carrier similar to
It was dried at 0 ° C. for 1 hour and then baked at 500 ° C. for 1 hour to obtain a titania-coated cordierite DPF.

The titania amount of the obtained titania-coated cordierite DPF was 100 g per liter of the fire-resistant three-dimensional structure.

The resulting titania-coated cordierite DPF was impregnated with an aqueous solution of platinum nitrate, dried at 250 ° C. for 1 hour, then impregnated with an aqueous solution of rhodium nitrate and dried at 250 ° C. for 1 hour, and the titania-coated cordierite carrying catalyst noble metal was used. I got a light DPF.

The amount of the catalyst noble metal supported on the obtained catalyst noble metal-supported titania-coated cordierite DPF was determined by the DPF.
5 g of platinum and 0.1 g of rhodium per liter of carrier
Met.

After the obtained catalyst precious metal-supporting titania coat cordierite DPF was immersed in deionized water,
Suction was performed to determine the amount of water absorbed per one piece of the catalyst precious metal-supporting titania coat cordierite DPF.

Barium acetate, lithium nitrate and potassium acetate were dissolved in deionized water in an amount half the water absorption obtained,
The catalyst precious metal-supporting titania coat cordierite DPF was immersed in the solution only from one end surface. At this time, the dissolution liquid was immersed in a portion from one end surface to half the axial length of the DPF carrier. After that, 250 ℃
It was dried for 1 hour and then calcined at 500 ° C. for 1 hour to obtain an exhaust gas purifying catalyst of Example 2. The NOx storage material amount of the exhaust gas purifying catalyst of Example 2 was 13.5 g for barium, 1.4 g for lithium, and 3.8 g for potassium per one three-dimensional structure.

(Example 3) The exhaust gas purifying catalyst of Example 3 is the same exhaust gas purifying catalyst as that of Example 2 except that the supporting layer is formed of zeolite composed of H-type mordenite.

In Example 3, 100 parts by weight of H-type mordenite zeolite was dispersed in 87 parts by weight of deionized water, 63 parts by weight of silica sol was further added, and the mixture was wet pulverized to prepare a zeolite slurry of titania slurry. It is a catalyst for purifying exhaust gas manufactured in place of.

In the exhaust gas-purifying catalyst of Example 3, the amount of zeolite was 100 g per liter of DPF carrier, and the amount of noble metal catalyst was 5 g of platinum and 0.1 g of rhodium per liter of DPF carrier. The amount of NOx storage material was 13.5 g for barium, 1.4 g for lithium, and 3.8 g for potassium per DPF carrier.

(Example 4) The exhaust gas purifying catalyst of Example 4 has a cell number of 62 cells / cm ² (40
0x / inch ² ) using a cylindrical cordierite honeycomb carrier having a diameter of 12.9 cm and a length of 15.0 cm having an open flow gas flow cell, and NOx
The catalyst for purifying exhaust gas is the same as in Example 1, except that potassium is further supported in the storage reduction section.

The exhaust gas-purifying catalyst of Example 4 was manufactured in the same manner as in the manufacturing method of Examples 1 and 2.

The amount of alumina in the exhaust gas purifying catalyst of Example 4 was 100 g per liter of the honeycomb carrier, and the amount of catalytic noble metal was 5 g of platinum and 0.1 g of rhodium per liter of the honeycomb carrier. The amount of NOx storage material is 13.5 barium per honeycomb carrier.
g, lithium was 1.4 g, and potassium was 3.8 g.

Example 5 First, barium acetate 29.5
Part by weight is dissolved in 200 parts by weight of deionized water, 100 parts by weight of alumina powder is added to this solution, stirred for 1 hour, dried at 250 ° C. for 12 hours, calcined at 500 ° C. for 1 hour, and barium-loaded alumina. A powder was prepared.

100 parts by weight of this barium-supported alumina powder was dispersed in 140 parts by weight of deionized water, and then 19 parts by weight of aluminum nitrate 9-hydrate and 3 parts by weight of alumina hydrate manufactured by Condia were added and wet-milled. To prepare a barium alumina slurry.

The barium-alumina slurry thus obtained was used to obtain a wall flow having a cell number of 47 cells / cm ² (approximately 300 cells / inch ² ) having a diameter of 12.9 cm and an axial length of 15.
Barium-alumina-coated cordierite D was coated on a 0 cm cylindrical DPF carrier made of cordierite, dried at 250 ° C for 1 hour, and then baked at 500 ° C for 1 hour.
PF was obtained.

The amount of barium alumina in the obtained barium alumina-coated cordierite DPF was determined by the DPF carrier 1
It was 50 g per liter.

Subsequently, 100 parts by weight of alumina powder was dispersed in 140 parts by weight of deionized water, and then 3 parts by weight of alumina sol in terms of alumina was added and wet pulverized to prepare an alumina slurry.

The prepared alumina slurry was applied to barium alumina-coated cordierite DPF to obtain a multilayer alumina-coated cordierite DPF. Here, the amount of alumina deposited in the upper layer was 50 g per liter of the DPF carrier.

Then, the multilayer alumina-coated cordierite DPF was impregnated with an aqueous solution of platinum nitrate, dried at 250 ° C. for 1 hour, and then impregnated with an aqueous solution of rhodium nitrate to give 250
After drying at 0 ° C. for 1 hour, an exhaust gas purifying catalyst of Example 5 was obtained. The catalyst noble metal amounts in the exhaust gas purifying catalyst of Example 5 were 5 g of platinum and 0.1 g of rhodium per liter of DPF carrier.

(Embodiment 6) The exhaust gas purifying catalyst of Embodiment 6 is an exhaust gas purifying catalyst in which an oxidation catalyst portion and a NOx storage reduction portion are provided on different carriers.

Specifically, the exhaust gas-purifying catalyst of Example 6 had a cell number of 62 cells / cm ² (about 400 cells / inc).
h ² ), a diameter of 12.9 cm, an axial length of 7.5 cm, and an oxidation catalyst in which only an oxidation catalyst portion is formed on a cylindrical honeycomb structure, and the number of cells is 47 cells / cm ² ( About 30
0x / inch ² ), diameter 12.9 cm, axial length 7.5 cm, and NOx on a cylindrical honeycomb structure.
An NOx storage reduction catalyst in which only the storage reduction section is formed, and the oxidation catalyst section and the NOx storage reduction section are the same catalysts as the oxidation catalyst section and the NOx storage reduction section of the first embodiment.

More specifically, the exhaust gas purifying catalyst of Example 6 was an oxidation catalyst in which the surface of a honeycomb structure having 62 cells / cm ² was coated with alumina, and the alumina was loaded with a catalytic noble metal. The surface of a honeycomb structure having a cell number of 62 cells / cm ² is coated with alumina, and this alumina comprises a NOx storage reduction catalyst in which a catalytic noble metal, barium, and lithium are carried.

The oxidation catalyst and the NOx occlusion reduction catalyst were produced by the same method as the method for producing the oxidation catalyst part and the NOx occlusion reduction part of Example 1.

The exhaust gas purifying catalyst of Example 6 is used by being held in the same container in a state where the oxidation catalyst is arranged in the front stage and the NOx storage reduction catalyst is arranged in close proximity to the rear stage.

In the exhaust gas purifying catalyst of Example 6, the oxidation catalyst is formed on the high-density carrier, so that the catalytic reaction in the NOx storage reduction catalyst arranged in the subsequent stage is promoted.
That is, since the catalytic reaction in the oxidation catalyst is an exothermic reaction, heat is generated when the exhaust gas is purified by the high-density oxidation catalyst. The heat generated in the oxidation catalyst is transferred to the NOx storage reduction catalyst located in the subsequent stage, and this heat is converted into NO.
x The catalytic reaction of the occlusion reduction catalyst is promoted.

Comparative Example A comparative example is an exhaust gas purifying catalyst in which a conventional NOx storage-reducing material is carried in a state of being mixed with a catalyst metal.

First, 100 parts by weight of alumina powder was dispersed in 140 parts by weight of deionized water, 19 parts by weight of aluminum nitrate 9 hydrate and 3 parts by weight of alumina hydrate were added, and wet pulverized to obtain an alumina slurry. Prepared.

The obtained alumina slurry had a cell number of 4
7 pieces / cm ² (about 300 pieces / inch ² ) of wall flow having a diameter of 12.9 cm and an axial length of 15.0 cm are applied to a cylindrical cordierite DPF carrier,
It was dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour to obtain an alumina-coated cordierite DPF. Here, the amount of alumina supported on the alumina-coated cordierite DPF was 50 g per liter of the DPF carrier.

Alumina-coated cordierite DPF
Was impregnated with an aqueous solution of platinum nitrate, dried at 250 ° C. for 1 hour, then impregnated with an aqueous solution of rhodium nitrate and dried at 250 ° C. for 1 hour to obtain a catalyst noble metal-supported alumina-coated cordierite DPF. The catalyst noble metal amount of the noble metal-supported alumina-coated cordierite DPF was 5 g of platinum and 0.1 g of rhodium per liter of DPF carrier.

The catalyst noble metal-supported alumina-coated cordierite DPF was immersed in deionized water and then suctioned to determine the amount of water absorbed per noble metal-supported alumina-coated cordierite DPF.

Barium acetate, lithium nitrate and potassium nitrate were dissolved in deionized water having the determined water absorption amount, and noble metal-supported alumina-coated cordierite DP was dissolved in the solution.
F was immersed. This immersion was performed by immersing the solution from the both end surfaces of the noble metal-supported alumina-coated cordierite DPF. Then, it was dried at 250 ° C. for 1 hour and then calcined at 500 ° C. for 1 hour to obtain an exhaust gas purifying catalyst of a comparative example. NO of the exhaust gas purifying catalyst of the comparative example
x The amount of storage material is 26.9 for barium per DPF carrier.
g, lithium 2.7 g, potassium 7.7 g.

(Evaluation) As an evaluation of the catalysts of Examples 1 to 6 and Comparative Example, the exhaust gas from the diesel engine was actually purified and the purification performance was measured.

The purification performance was evaluated in a state where each catalyst was made durable (deteriorated). This durability (deterioration) was performed by baking at 650 ° C. for 50 hours using an oven.

A direct injection diesel engine with a supercharger (4 cylinders, 2000 cc) was used, and the diesel engine was operated under operating conditions in which the catalyst bed temperature rose from 100 ° C. to 450 ° C. Hydrocarbon (HC), carbon monoxide (CO), nitrogen oxides (N
The concentration of Ox) was measured to obtain the purification rate. In addition, in the multistage exhaust gas purifying catalysts of Examples 1 to 6, the exhaust gas was purified in a state where the oxidation catalyst portion was located on the upstream side of the exhaust gas flow. The concentration of each component was measured using a gas analyzer (MEXA9100) manufactured by Horiba Ltd. The diesel engine is operated at a rotational speed of 2
The temperature is kept constant at 100 rpm and the catalyst temperature rise is 100 to 45
It was done by changing the load (torque) so that it became 0 ° C. Here, in the catalyst of Example 6, since the two honeycomb carriers are arranged in the same container in a close state, the catalyst bed temperatures of the two catalyst parts are substantially the same. From this, the catalyst bed temperature of Example 6 was the catalyst bed temperature of one of the honeycomb-supported catalysts.

Further, the purification rate was measured by measuring the gas concentration at both ends of the catalyst inlet and outlet and determining the purification rate from the gas concentration with the incoming gas concentration.

Further, the concentration of particulate matter (PM) discharged in this test was measured by the small tunnel dilution sampling method. Moreover, the purification rate of the particulate matter was calculated from the measured values. Table 1 shows the measurement results of the respective purification rates.

[0091]

[Table 1]

In Table 1, the purification rates of HC, CO and NOx are as follows: Purification rate (%) = {(inlet gas component concentration (%))-(outlet gas component concentration (%))} × 100 / (inlet gas In the component concentration (%)), the PM purification rate is the purification rate (%) = {(inlet gas PM mass (mg))-(outlet gas P
M mass (mg)} × 100 / (containing gas PM mass (m
g)).

From Table 1, the exhaust gas purifying catalysts of Examples 1 to 6 are higher in HC and C than the exhaust gas purifying catalysts of Comparative Examples.
The purification rates of both O and NOx are high. That is, in the exhaust gas purifying catalysts of Examples 1 to 6, since the oxidation catalyst portion and the NOx storage reduction portion are provided separately,
Since the catalytic noble metal carried on the oxidation catalyst portion is not deteriorated in the oxidation function by the NOx storage reduction material, the exhaust gas purifying catalyst has high NOx storage reduction performance without impairing the oxidation performance.

[0094]

The exhaust gas purifying catalyst of the present invention has the oxidation catalyst part and the NOx storage reduction part on the three-dimensional structure, so that the first catalyst metal of the oxidation catalyst part and the Nx storage reduction part of the NOx storage reduction part.
The Ox storage reduction material does not come into contact with the first catalyst metal, and the oxidation function of the first catalyst metal does not deteriorate. That is, in the exhaust gas purifying catalyst of the present invention, the oxidation catalyst unit oxidizes and purifies the exhaust gas, and the NOx storage reduction unit purifies NOx by storage reduction. As a result, the exhaust gas purifying catalyst of the present invention is a catalyst having high oxidation performance and NOx storage reduction performance.

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) F01N 3/08 F01N 3/10 A 3/10 3/24 E 3/24 3/28 301C 3/28 301 B01D 46/42 B // B01D 46/42 53/36 102B 104A 104B (72) Inventor Daisuke Oki 7800, Chihama, Daito-cho, Ogasa-gun, Shizuoka Prefecture F-term (reference) 3G090 AA01 AA02 AA03 BA01 EA01 EA05 3G091 AA02 AA12 AA17 AA18 AB02 AB06 AB09 AB13 BA00 BA14 BA15 BA19 GA06 GA20 GB01W GB01X GB02Y GB05W GB06W GB07W GB10X GB16X GB17X HA11 4D048 AA06 AA13 BA34 BA31 BA31 BA31 BA33 BA08 BA31 BA03 BA08BA30 BA08 BA31 BA08BA30 BA08BA30 BA08BA03 BA08X BB14 BB16 CC32 CC47 EA04 4D058 JA32 JB06 MA44 SA08 4G069 AA03 BA01A BA01B BA02A BA04A BA04B BA05A BA07A BA13A BA13B BA17 BB04A BB04B BC01A BC03B BC04B BC08A BC13B BC32A BC33A BC43A BC71A BC71B BC72A BC74A BC75A BC75B CA03 CA09 CA18 EA18 EA19 EA27 EB12Y EB14Y EC28 EC29 EE09

Claims (10)

[Claims] 1. A three-dimensional structure having fire resistance, a first support layer part made of a first inorganic oxide provided on the three-dimensional structure, and a first support layer part supported on the first support layer part. An oxidation catalyst part having one catalytic metal, a second supporting layer part made of a second inorganic oxide provided on the three-dimensional structure, and a second catalytic metal supported on the second supporting layer part. An exhaust gas purifying catalyst comprising: a NOx storage-reduction portion having the NOx storage-reduction material supported on the second support layer portion. 2. The exhaust gas purifying catalyst according to claim 1, wherein the oxidation catalyst portion and the NOx storage reduction portion are provided in a state of being arranged on the three-dimensional structure in a flow direction of exhaust gas. 3. The exhaust gas purifying catalyst according to claim 1, wherein the oxidation catalyst portion and the NOx storage reduction portion are stacked on the three-dimensional structure. 4. The exhaust gas-purifying catalyst according to claim 1, wherein the first inorganic oxide comprises at least one of alumina, silica, titania, zirconia, ceria, and zeolite. 5. The first catalytic metal is Pt, Pd, R
The exhaust gas purifying catalyst according to claim 1, comprising at least one of h, Ag, Au, and Ir. 6. The exhaust gas purifying catalyst according to claim 1, wherein the second inorganic oxide is at least one of alumina, silica, titania, zirconia, ceria, and zeolite. 7. The second catalyst metal is Pt, Pd, R
The exhaust gas purifying catalyst according to claim 1, comprising at least one of h, Ag, Au, and Ir. 8. The exhaust gas-purifying catalyst according to claim 1, wherein the NOx storage-reducing material comprises at least one selected from alkali metals and alkaline earth metals. 9. The exhaust gas purifying catalyst according to claim 1, wherein the three-dimensional structure is an open flow honeycomb or a wall flow DPF. 10. The exhaust gas purifying catalyst according to claim 1, wherein the three-dimensional structure is made of ceramics or metal.