JP2002013412A - Exhaust emission control system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide an exhaust emission control system capable of sufficiently enjoying a fuel consumption improving effect by travelling mainly in an oxygen excessive region (for example, in a lean state) and effectively using H2 contained in exhaust gas as a reducer. SOLUTION: The exhaust emission control system is constituted by arranging at least an NOx removing catalyst to reduce and treat nitrogen oxides with hydrogen as a reducer as well as an H2 diffusion control material to control diffusivity of hydrogen in an exhaust passage of an internal combustion engine or combustion equipment to be mainly driven in the oxygen excessive region and it increases H2 density in the exhaust gas to be supplied at the time when the NOx removing catalyst reduces and treats the nitrogen oxides by controlling diffusing speed of H2 by the H2 diffusion control material. The H2 diffusion control material and the NOx removing catalyst are laminated on an integral structured catalyst support and make a multilayer structure, and either one or both of an inner surface and an outer surface of this NOx removing catalyst layer makes or make contact with the H2 diffusion control layer. The H2 diffusion control material contains more than two kinds of fire resistance inorganic matters modes of pore diameter distribution of which are less than 4A and less than 10A.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a system for purifying exhaust gas discharged from an internal combustion engine, a combustor or the like.
In particular, it relates to an exhaust gas purification system that purifies nitrogen oxides (NOx) in exhaust gas with high efficiency.

[0002]

2. Description of the Related Art Conventionally, catalysts for purifying carbon monoxide (CO), hydrocarbons (HC), nitrogen oxides (NOx) and the like contained in exhaust gas discharged from internal combustion engines such as automobiles include: There are known three-way catalysts that operate at a stoichiometric air-fuel ratio and an exhaust gas purification system using the same. Further, as a method for purifying nitrogen oxides in a case where purification of nitrogen oxides is impossible with a three-way catalyst, such as when the exhaust gas of an internal combustion engine is in excess of oxygen, a method disclosed in Japanese Patent Publication No. 2640029 is disclosed. As described above, an exhaust gas purification system that absorbs NOx when the exhaust gas is in excess of oxygen, and reduces the concentration of oxygen in the exhaust gas flowing into the NOx absorbent to release the absorbed NOx to perform a purification process. Used.

However, in such an exhaust gas purifying system using a three-way catalyst or an exhaust gas purifying system as disclosed in Japanese Patent Publication No. 2640029, when the absorbed NOx is desorbed and purified, a reduction is required. HC and C as agents
O is used, and in these conventional technologies, it is necessary to supply HC and CO to the NOx purification catalyst in order to purify NOx by reaction. For this reason, a part of HC and CO may remain in the NOx purification catalyst, and it has been difficult to purify exhaust gas at a higher level. As a method of purifying HC and CO that have not been consumed, NOx
A method of simultaneously performing an oxidation reaction on the catalyst and a method of disposing a three-way catalyst after the NOx purification catalyst have been adopted.
Since the Ox purification catalyst and the three-way catalyst at the subsequent stage are arranged at positions away from the engine in the exhaust passage, the exhaust gas temperature of the exhaust gas decreases, and sufficient HC and CONOx purification performance cannot be obtained. In particular, there is a problem that it is difficult to purify HC and CO components discharged immediately after the engine is started.

Further, as a catalyst using hydrogen for NOx reaction purification, as disclosed in Japanese Patent Application Laid-Open No. 6-126174, hydrogen stored in a hydrogen storage alloy is used to reduce a reducing gas in a lean region. N in exhaust gas containing no
An exhaust gas purifying catalyst for purifying Ox has been proposed.

On the other hand, as a method of controlling gas diffusivity in exhaust gas in a catalyst, Japanese Patent Application Laid-Open No. H10-43588 discloses a method for controlling two or more types of refractory having different pore diameter distribution modes on a noble metal catalyst layer. HC that is coated at the time of cold start of the engine by coating a hydrocarbon desorption suppressing layer made of a volatile inorganic substance
Describes an exhaust gas purifying catalyst that temporarily adsorbs and controls the diffusivity of HC at the time of desorption to delay the desorption of HC. Also, JP-A-11-22645 discloses that
The use of two or more types of hydrocarbon adsorbents having a pore size distribution of 4 to 9 ° and different pore size peaks (modes) as a multilayer structure also provides excellent hydrocarbon adsorption efficiency at cold start. And a catalyst for delaying the desorption of adsorbed hydrocarbons.

[0006]

However, such a catalyst has the following problems. That is, as disclosed in JP-A-6-126174, an exhaust gas purifying catalyst for purifying NOx in exhaust gas not containing a reducing gas in a lean region using hydrogen stored in a hydrogen storage alloy. Thus, there is a problem that sufficient catalytic performance cannot be obtained in order to purify NOx in a lean region by the NOx purification function of the hydrogen storage alloy itself.

Further, in the catalysts described in JP-A-10-43588 and JP-A-11-22645, the target for controlling the gas diffusivity is a hydrocarbon, and therefore, the material used for the diffusion layer is fine. Those having a pore size distribution suitable for the adsorption performance of hydrocarbons and having a pore distribution capable of suppressing desorption of hydrocarbons are selected. However, the diffusivity of H2 gas, which has a smaller molecular diameter than that of hydrocarbons, cannot be sufficiently controlled, and appropriate H2 gas diffusion in exhaust gas in which H2 exists as a reducing agent for NOx purification. There was a problem that control could not be performed and sufficient NOx purification performance could not be obtained.

The present invention has been made in view of the above-mentioned problems of the prior art, and an object of the present invention is to sufficiently improve the fuel efficiency by running in an oxygen-excess region (for example, in a lean state). It is an object of the present invention to provide an exhaust gas purification system that can effectively utilize H2 contained in exhaust gas as a reducing agent.

[0009]

The inventor of the present invention has made intensive studies to solve the above-mentioned problems, and as a result, the NOx purification catalyst purifies NOx by controlling the diffusion rate of hydrogen by a predetermined H2 diffusion control material. By increasing the hydrogen concentration at the time,
The inventors have found that the above-mentioned problems can be solved, and have completed the present invention.

That is, the exhaust gas purifying system of the present invention comprises:
H2 for controlling the diffusivity of hydrogen in the exhaust passage of an internal combustion engine or a combustion device mainly operated in an oxygen excess region
A diffusion control material, and a NOx purification catalyst for reducing nitrogen oxides by using at least hydrogen as a reducing agent. The H2 concentration in the exhaust gas supplied when the NOx purification catalyst reduces nitrogen oxides Is increased by controlling the diffusion rate of H2 by the H2 diffusion control material.

In a preferred embodiment of the exhaust gas purifying system of the present invention, a hydrogen supply source is added to the upstream side of the H2 diffusion control material, and the hydrogen supply source is a hydrogen generation exhaust gas purifying catalyst. The operation is performed in the stoichiometric air-fuel ratio or the excess fuel region.

Further, in another preferred embodiment of the exhaust gas purifying system of the present invention, the H2 diffusion control material and the NOx purifying catalyst form an H2 diffusion control layer and a NOx purifying catalyst layer, respectively. The H2 diffusion control layer is in contact with one or both of the inner surface and the outer surface of the NOx purification catalyst layer by being laminated on a carrier.

Still another preferred embodiment of the exhaust gas purifying system according to the present invention is characterized in that the H2 diffusion control material comprises a refractory inorganic substance having a pore diameter distribution peak of 4 ° or less;
It is characterized by containing two or more kinds of refractory inorganic substances including the following refractory inorganic substances.

[0014]

According to the present invention, an H2 diffusion control material for controlling the diffusivity of hydrogen is disposed in an exhaust passage of an internal combustion engine or a combustion apparatus to control the diffusion rate of H2 in exhaust gas.
The hydrogen concentration of the exhaust gas is increased when the NOx purification catalyst reduces the nitrogen oxides. Further, a NOx purification catalyst is arranged near or downstream of the H2 diffusion control material, so that NOx purification processing can be performed using at least hydrogen as a reducing agent. Further, if necessary, a hydrogen supply source is added to the upstream side of the H2 diffusion control material, and a short-time operation in the stoichiometric air-fuel ratio or the excess fuel region is added. Thus, in the exhaust gas purification system of the present invention, the H2 diffusion control material and the NOx
The purifying catalyst and the NOx purifying catalyst are arranged in a desired configuration.
By appropriately controlling H2 used as a reducing agent in the purification of Ox with the H2 diffusion control material, it is possible to purify the exhaust gas at a higher level.

Here, HC, CO and H2 are known as the main reducing components contained in the exhaust gas. According to the method described in Japanese Patent Publication No. 2600429, NOx is absorbed in a lean region, HC is mainly used as a reducing agent in the case of releasing NOx in the air-fuel ratio or excess fuel region and reducing and purifying with a reducing agent. Also,
In a catalyst for reducing and purifying NOx in a lean region, HC is mainly used as a reducing agent.

However, from the point of view of air quality conservation,
Recently, there is a need to further purify exhaust gas components discharged from an internal combustion engine. For this purpose, improvement of the internal combustion engine and improvement of the exhaust gas purifying catalyst are being promoted. However, if the reducing components of HC and CO are reduced too much, the reducing component for purifying NOx disappears, and sufficient NO
x Purification cannot be performed. Therefore, it is necessary to discharge HC and CO to the NOx purification catalyst in a state where they are left in the exhaust gas to some extent, but it has been difficult to purify the exhaust gas at a higher level. On the other hand, in the present invention, since H2 is used as the reducing agent as described above, such a problem can be avoided.

[0017]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, an exhaust gas purification system of the present invention will be described in detail. As described above, the exhaust gas purification system of the present invention is one in which the H2 diffusion control material and the NOx purification catalyst are arranged in the exhaust passage of an internal combustion engine or a combustion device that is operated mainly in an oxygen excess region.

Here, as the H2 diffusion controlling material, N 2
It can be used as long as it can control the diffusivity of hydrogen (H2) as a reducing agent when purifying Ox. In particular, the exhaust gas purification system of the present invention contains two or more types of refractory inorganic substances. As the refractory inorganic material, an H2 diffusion control material containing at least a refractory inorganic material having a pore size distribution peak (mode value) of 4 ° or less and a refractory inorganic material having a pore size distribution of 10 ° or less may be used. preferable.
The distance between H—H bonds in H 2 gas is 0.74
Since it is about Å, it can be estimated that the adsorption and desorption of H2 by molecular sieving can be performed theoretically if the pore diameter is 0.74Å or more. If at least two or more types of H2 diffusion controlling materials having such pore diameters are used, H2 will perform more appropriate adsorption / desorption, and the diffusion rate will be suitably controlled. The diffusion speed is controlled by delaying the diffusion speed, and a difference in diffusion speed is given to H2 molecules, so that the time during which H2 is supplied to the NOx purification catalyst can be extended.

Further, as the refractory inorganic substance, specifically, zeolite, alumina, silica, silica-alumina or alumina silicate and any combination thereof can be used.

On the other hand, it is sufficient for the NOx purifying catalyst to be able to reduce and purify NOx with a reducing component containing at least H2. However, in the present exhaust gas purifying system, this reducing component is reduced by the action of the H2 diffusion controlling material. The main component is H2.

As such a NOx purifying catalyst, a NOx adsorbing / occluding type purifying catalyst, a NOx selective reduction catalyst or a predetermined three-way catalyst is suitable.
NOx is temporarily adsorbed / absorbed in an oxygen-excess region (lean state, etc.), and NOx is released in a stoichiometric air-fuel ratio (stoichiometric) and / or in a fuel-excess region (rich state, etc.) to purify NOx by a reducing component. The selective reduction catalyst purifies by selectively reacting NOx with a reducing component in a lean state, and the predetermined three-way catalyst has a function of reducing and purifying NOx under lean conditions near stoichiometry.

In the exhaust gas purifying system of the present invention, cesium (C) is used as the NOx adsorbing / occluding type purifying catalyst.
s), barium (Ba), sodium (Na), potassium (K), magnesium (Mg), lanthanum (La) or calcium (Ca) and mixed metal elements thereof, and platinum (Pt), palladium (Pd) or Rhodium (R
h) and a catalyst containing these mixed noble metal elements can be used.

Further, in the exhaust gas purifying system of the present invention, as the NOx selective reduction catalyst, copper (Cu), cobalt (Co), nickel (Ni), iron (Fe), gallium (Ga), lanthanum (La) are used. , Cerium (Ce), zinc (Zn), titanium (Ti), calcium (Ca), barium (Ba) or silver (Ag) and mixed elements thereof,
And / or a catalyst using platinum (Pt), iridium (Ir), palladium (Pd) or rhodium (Rh) and a zeolite or alumina containing a mixed noble metal element thereof can be used.

Further, in the exhaust gas purifying system of the present invention, Pt, Pd or Rh and a mixed metal element thereof, lanthanum (La), cerium (Ce), praseodymium (Pr), Neodymium (N
Catalysts comprising d) or samarium (Sm) and mixed rare earths thereof, Zr or Ba and any combination thereof can be used.

The amount of the noble metal contained in the above-mentioned NOx purification catalyst is not particularly limited as long as the functions of these catalysts can be sufficiently obtained.
It is preferable that noble metal is contained in a ratio of 0.5 to 10 g per 1 L of the integral structure type carrier including the x purification catalyst.

In the exhaust gas purifying system of the present invention, it is preferable that a hydrogen supply source is added to the exhaust passage on the upstream side of the H2 diffusion controlling material. This allows
The NOx purification catalyst can sufficiently supply a reducing agent required for NOx purification. Examples of such a hydrogen supply source include a hydrogen generation exhaust gas purifying catalyst capable of generating hydrogen from exhaust gas and a hydrogen cylinder capable of supplying H2 from the outside. When using a hydrogen generation exhaust gas purification catalyst,
It is preferable to add a short-time operation in the stoichiometric air-fuel ratio or the excess fuel region, so that the supply amount of hydrogen can be increased.

Further, in the exhaust gas purifying system of the present invention, the above-mentioned H2 diffusion controlling material controls the diffusion speed of H2, and the above-mentioned NOx purifying catalyst supplies the exhaust gas with which the NOx purifying catalyst reduces the nitrogen oxides. By increasing the H2 concentration, NOx can be efficiently purified. That is, the H2 diffusion controlling material has a certain pore size corresponding to the molecular size of H2 gas, and the molecular size of H2 gas is HC or C.
Since it is much smaller than the molecular diameter of O, H2 gas is preferentially selected by molecular sieve action and adsorbed on the H2 diffusion controlling material, and H2 is desorbed and released at a desired diffusion rate. Thus, the NOx purification catalyst purifies NOx.

The timing of the NOx purification catalyst for reducing the nitrogen oxides varies depending on the type and amount of the NOx purification catalyst. The NOx purification catalyst releases or desorbs the stored or adsorbed NOx, or the stored NOx is saturated. Or when a reducing agent is required for NOx purification.

More specifically, “Hydrogen-producing exhaust gas purifying catalyst—
In the case of the "H2 diffusion control material-NOx purification catalyst", when a NOx adsorbing / occluding catalyst is used, when a rich spike enters, NOx is desorbed from the catalyst and reduced.
In the NOx selective reduction catalyst, a reduction process is performed using H2 or HC as a reducing agent after entering a lean state after a rich spike has entered. When a three-way catalyst is used, the reduction treatment is mainly performed when a rich spike enters, but the reduction treatment is also performed using H2, HC, or CO as a reducing agent even in a partially lean state. When the H2 storage alloy is disposed upstream of the H2 diffusion control material, the timing at which the reducing agent runs short in the NOx purification catalyst, the time when the rich spike ends in the NOx adsorption / storage catalyst, and the lean time in the NOx selective reduction catalyst During operation, when the amount of reducing agents such as HC, H2, and CO is low, and when the three-way catalyst has a small amount of reducing agents such as HC, H2, and CO relative to NOx, regardless of the rich and lean operating conditions. To release H2 to NOx
Can be reduced.

Further, the diffusion rate of H2 is determined by measuring the amount of the material having a pore diameter, which uses the materials having different pore diameters of the H2 diffusion controlling material, chemically modifies the surface state of the material having the pores. (By changing the amount of coating), and by controlling the distribution ratio of different cell diameters.

Further, H2 adsorbed on the H2 diffusion controlling material is H2 in the exhaust gas, and HC and CO in the exhaust gas are reformed by a catalyst for purifying hydrogen-producing exhaust gas installed on the upstream side.
Examples include H2 obtained by generation and H2 supplied from a hydrogen supply device installed on the upstream side. The catalyst for purifying hydrogen-producing exhaust gas may be, for example, an oxidation catalyst or a three-way catalyst. Furthermore, a hydrogen storage material such as a hydrogen storage alloy (La-Ni-based, Mg-Ni-based, Ti-Fe-based, Pd-Ce-based alloy, etc.) or a carbon nanotube may be provided upstream of the H2 diffusion controlling material or the hydrogen supply. If added between the source and this H2 diffusion control material, H2
H2 relating to the diffusion control material can be increased, and the diffusion rate of H2 can be more effectively controlled.

Further, in the present exhaust gas purification system, H2
The diffusion control material controls the diffusion of H2. As a result, the exhaust gas supplied to the NOx purification catalyst is converted into the following equation (A) H2 amount / TR amount ≧ 0.3 (A) (TR in the equation) The amount indicates the amount of all reducing components in the exhaust gas.)
It is desirable to control so as to satisfy the gas composition represented by If this relationship is satisfied, the NOx purification catalyst realizes a suitable NOx purification rate.

Further, the NOx purifying catalyst and the H2 diffusion control material are at least simultaneous (H2 diffusion control material first).
In addition, the diffusion speed of H2 is not controlled unless it comes into contact with the exhaust gas. From such a viewpoint, in the exhaust gas purification system of the present invention, the H2 diffusion control material can be disposed separately from or mixed with the NOx purification catalyst. At this time, the arrangement ratio or the mixing ratio between the H2 diffusion control material and the NOx purification catalyst is H2 diffusion control material / NOx purification catalyst = 1/9 to 4
/ 6 is preferable.

When the H2 diffusion controlling material and the NOx purifying catalyst are separately arranged, for example, an H2 diffusion controlling material, which is an example of the H2 diffusion controlling material, is provided on a monolithic carrier such as a honeycomb-shaped carrier.
It is possible to have a multilayer structure in which a diffusion control layer and a NOx purification catalyst layer which is an example of a NOx purification catalyst material are laminated.
At this time, at least one of the two layers may be arbitrarily laminated, and may have a two-layer structure or a sandwich structure. However, either one of the inner surface and the outer surface of the NOx purification catalyst layer or It is preferable that the H2 diffusion control layer is in contact with both. In addition, it is desirable to have a structure having four layers or less in total, especially in consideration of economy and productivity.

The H2 diffusion control layer is more preferably a laminate of H2 diffusion control materials having the same or different components and pore diameters, so that the H2 diffusion rate can be more accurately controlled. The uppermost layer or the lowermost layer in the above-mentioned multilayer structure may be either an H2 diffusion control layer or a NOx purification catalyst layer. In particular, the uppermost exhaust gas contact layer is an H2 diffusion control layer. Then, H in the exhaust gas
2 is more efficiently performed, and if the lowermost carrier-supporting layer is a NOx purifying catalyst layer, it is less susceptible to poisoning components in exhaust gas.

Further, the H2 diffusion controlling material and the NOx purification catalyst are separately arranged on one carrier, and
(2) It is also possible to arrange the diffusion control material and the NOx purification catalyst in separate carriers in tandem independently of each other. In this case, it is possible to select a carrier (cell density, cell shape, etc.) and the thickness of the coat layer suitable for each catalytic reaction, which is preferable.

On the other hand, the H2 diffusion control material and the NOx purification catalyst can be mixed and arranged. Specifically, each component can be made into a granular form or a pellet form, and these can be mixed and placed in the exhaust passage. However, in order to improve the reaction efficiency, it is desirable to dispose the H2 diffusion control material and the NOx purification catalyst on the monolithic carrier in the same manner as when disposing the H2 diffusion control material and the NOx purification catalyst separately.

Here, as such a monolithic carrier,
Examples include a monolithic carrier and a metal carrier made of a heat-resistant material. In particular, when used for purifying exhaust gas from automobiles, a honeycomb-shaped carrier is coated with H
(2) The contact area (reaction surface area) between the diffusion control material or the NOx purification catalyst and the exhaust gas can be increased, and the pressure loss can be reduced, which is more effective. Note that, as such a honeycomb-shaped carrier, generally, cordierite materials such as ceramics are often used, but it is also possible to use a honeycomb material made of a metal material such as ferrite stainless steel, and further, an H2 diffusion control material or The powder itself of the NOx purification catalyst may be formed into a honeycomb shape.

The amount of the H2 diffusion control material or NOx purification catalyst carried when coating the honeycomb-shaped carrier is 30 to 30 H2 / diffusion control material per 1 L of the integral structure type carrier.
Preferably, 100 g and the NOx purification catalyst are 50 to 300 g. This is because the catalyst component supporting layer is preferably thick (the supporting amount is large) from the viewpoint of catalytic activity and catalyst life, but if the coating layer is too thick, the reaction gas will be poorly diffused, and the catalyst inside the coating layer will be insufficient. Lose contact with
In other words, the effect of increasing the amount of activity is saturated, and the passage resistance of the exhaust gas is increased.

[0040]

EXAMPLES Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples, but the present invention is not limited to these Examples.

Example 1 First, an exhaust gas purifying catalyst (H
2 diffusion control material and NOx purification catalyst), and an exhaust gas purification system was constructed using the obtained exhaust gas purification catalyst.

[Construction of exhaust gas purification system] Pd nitrate
The aqueous solution is impregnated with activated alumina powder, dried and then dried in air.
It was calcined at 0 ° C. for 1 hour to obtain Pd-supported alumina powder (powder B). The Pd concentration of this powder was 5.0% by weight. An activated alumina powder was impregnated with an aqueous solution of Rh nitrate, dried, and calcined in air at 400 ° C. for 1 hour to obtain a Rh-supported alumina powder (powder C). The Rh concentration of this powder was 3.0% by weight. 347 g of powder B, 58 g of powder C, 496 g of activated alumina powder, and 900 g of water were charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. The grinding time was 1 hour. This slurry solution was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by air flow, dried at 130 ° C., baked at 400 ° C. for 1 hour, and coated. Layer weight 200g
/ L-carrier was obtained. Further, the coated carrier was impregnated and supported by using barium acetate aqueous solution,
After drying at 400C, the mixture was calcined at 400C to obtain a NOx purification catalyst layer.

500 g of activated alumina prepared by an alkoxide method or the like so that the peak (mode) of the pore diameter is 10 ° or less, 500 g of A-type zeolite having a pore diameter of 4 ° or less, and 1000 g of a 2% nitric acid solution It was put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. The grinding time was 1 hour. This slurry liquid was adhered to the NOx purification catalyst layer, excess slurry in the cell was removed by an air stream, dried at 130 ° C., and calcined at 400 ° C. for 1 hour to obtain a coat layer weight of 50 g / L. A system (No. 1) using this catalyst was constructed as an exhaust gas purification catalyst. Table 1 shows the configuration of the stacked H2 diffusion control layer and NOx purification catalyst layer.

(Example 2) MF without using activated alumina
The same operation as in Example 1 was repeated except that I zeolite was used, and an exhaust gas purification catalyst was used to construct a system (No. 2) using this catalyst. Table 1 shows the configuration of the stacked H2 diffusion control layer and NOx purification catalyst layer.

(Example 3) As the H2 diffusion control layer, M
An exhaust gas purification system (No. 3) was constructed by repeating the same operations as in Example 1 except that FI zeolite was used. The method for preparing the exhaust gas purifying catalyst will be described below. Table 1 shows the configurations of the stacked H2 diffusion control layer and NOx purification catalyst layer.

[Adjustment of Exhaust Gas Purifying Catalyst] 400 g of activated alumina prepared by an alkoxide method or the like so that the peak of the pore diameter becomes 10 ° or less, 300 g of MFI zeolite (peak of the pore diameter distribution 5.8 °), and the pore diameter Is 4
(3) 300 g of the following type A zeolite and silica sol 2
00g and 1000g of water are put into a magnetic ball mill,
The slurry was mixed and pulverized to obtain a slurry liquid. The grinding time was 1 hour. This slurry liquid is adhered to the NOx purification catalyst layer, and the excess slurry in the cell is removed by an air flow to remove the slurry.
After drying at 0 ° C., it was baked at 400 ° C. for 1 hour to obtain an exhaust gas purifying catalyst in which the H 2 diffusion control layer had a coat layer weight of 50 g / L.

Example 4 500 g of activated alumina prepared by an alkoxide method or the like so that the peak of the pore diameter becomes 10 ° or less, 500 g of A-type zeolite having a pore diameter of 4 ° or less, and 1000 g of a 2% nitric acid solution It was put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. The grinding time was 1 hour. This slurry solution was adhered to a cordierite-based monolithic carrier (1.3 L, 400 cells), excess slurry in the cells was removed by an air stream, dried at 130 ° C., and baked at 400 ° C. for 1 hour to form a coating layer. Weight 50g /
L is a diffusion control layer of H2.

347 g of powder B, 58 g of powder C, 496 g of activated alumina powder and 90 g of water used in Example 1 were used.
0 g was charged into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. The grinding time was 1 hour. This slurry solution was adhered to the H2 diffusion control layer, excess slurry in the cell was removed by air flow, dried at 130 ° C., and calcined at 400 ° C. for 1 hour.
00 g / L-carrier was obtained. Further, the coated carrier was impregnated and supported with an aqueous barium acetate solution, dried at 120 ° C., and calcined at 400 ° C. to obtain an exhaust gas purifying catalyst. A system using this catalyst (N0.4)
Was built. Table 1 shows the configuration of the stacked H2 diffusion control layer and NOx purification catalyst layer.

Example 5 25 g / L of the inner layer of Example 4
Further, the H2 diffusion control layer was coated on the NOx purification catalyst layer so that the H2 diffusion control layer became 25 g / L in the same manner as in the inner layer of Example 4, to obtain an exhaust gas purification catalyst, and a system using this catalyst (No. .5) was constructed. Table 1 shows the configuration of the stacked H2 diffusion control layer and NOx purification catalyst layer.

Example 6 Activated alumina containing γ-alumina as a main component was impregnated with a cerium nitrate solution and a barium nitrate solution, dried, and fired at 500 ° C. for 1 hour. At this time, the cerium carrying concentration was 7% by weight, and the barium concentration was 5% by weight. The powder thus obtained was impregnated with an aqueous solution of palladium nitrate, dried and calcined at 400 ° C. for 1 hour to obtain a Pd-supported activated alumina powder. The loading concentration of Pd was 1.00% by weight. A slurry obtained by mixing and pulverizing 700 g of this powder, 300 g of cerium oxide powder, and 1000 g of alumina sol with a ball mill is adhered to a monolith carrier base material (1.3 L, 400 cells) and fired (40).
0 ° C., 1 hour). At this time, the adhesion amount is 200 g / L.
Set to. Thus, a NOx purification catalyst layer was obtained.

Further, the same operation as in Example 1 was repeated on this NOx purification catalyst layer so that the H2 diffusion control layer was adhered so that the adhesion amount after firing became 50 g / L, and this was used as an exhaust gas purification catalyst. , A system using this catalyst (No. 6)
Was built. Table 1 shows the configuration of the stacked H2 diffusion control layer and NOx purification catalyst layer.

(Comparative Example 1) Without stacking the H2 diffusion control layer,
The same operation as in Example 1 was repeated except that only the NOx purification catalyst layer was used, and a system using this catalyst was constructed as an exhaust gas purification catalyst. Table 1 shows the configuration of the NOx purification catalyst layer.

(Comparative Example 2) Without stacking the H2 diffusion control layer,
The same operation as in Example 6 was repeated except that only the NOx purification catalyst layer was used, and a system using this catalyst was constructed as an exhaust gas purification catalyst. Table 1 shows the configuration of the NOx purification catalyst layer.

[0054]

[Table 1]

[Performance Evaluation Method] The catalyst directly under the manifold obtained by the above method (Pd / Rh-2.82 g / L catalyst 0.8.
7L) and a NOx purification catalyst, and into an exhaust passage of a passenger car equipped with a 1.8L direct injection gasoline engine,
Immediately after the exhaust of the engine, the catalyst directly below the manifold is
A NOx purification catalyst was arranged at the subsequent stage, and the performance was evaluated. The performance evaluation (vehicle evaluation) was performed by traveling in the LA4-CH mode (FTP-75 mode), which is a test mode in North America, and measuring the emissions at that time. Table 2 shows the results.

The residual rate shown in Table 2 is expressed by the following equation: Residual rate = (1−H in the exhaust gas at the outlet of the NOx purifying catalyst.
C, CO, and NOx emissions / HC, CO, and NOx emissions in engine-out exhaust gas) × 100. The HC, CO, and NOx emissions in the exhaust gas indicate the emissions when the vehicle travels in the above-described vehicle evaluation mode. The ratio of NOx / HC in Table 2 indicates the running portion immediately after the start while running in the vehicle evaluation mode, specifically, FT.
This is a value calculated using the average concentration of each component of NOx and HC in the portion excluding the running portion up to about 200 seconds after the start of the P-75 mode. The HC concentration also indicates the average concentration calculated in the same manner. The reason why the running portion immediately after the start is excluded is that the HC concentration is high due to the discharge of unburned HC immediately after the start of the engine.

[0057]

[Table 2]

As described above, the present invention has been described in detail with reference to preferred examples and comparative examples. Examples 1 to 6, which are within the preferred range of the present invention, show that exhaust gas components are smaller than those of the comparative examples as shown in Table 2. Is high and the residual ratios of HC, CO and NOx are low, indicating that H2 is supplied from the H2 diffusion control layer to the NOx purification catalyst layer at an appropriate diffusion rate and exhibits excellent exhaust gas purification performance. . On the other hand, Comparative Examples 1 and 2
It can be seen that the residual rates of C, CO and NOx are high, and the NOx conversion rate is low because the H2 diffusion control layer is not particularly laminated.

[0059]

As described above, according to the present invention, the predetermined H2 diffusion controlling material controls the diffusion speed of adsorbed H2, and the predetermined NOx purification catalyst increases the H2 concentration in the exhaust gas. Therefore, it is possible to provide an exhaust gas purifying system which sufficiently enjoys an effect of improving fuel efficiency mainly by traveling in an oxygen excess region (for example, a lean state) and can effectively utilize H2 contained in exhaust gas as a reducing agent. Can be.

──────────────────────────────────────────────────続 き Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) F01N 3/10 F01N 3/28 301C 3/28 301 301G F02D 41/04 305A F02D 41/04 305 B01D 53 / 36 104A F-term (reference) 3G091 AA02 AA12 AB01 AB03 AB05 AB06 AB08 AB09 BA14 BA33 CA19 CA26 CB02 DB10 FB10 FB12 FC02 GA06 GA16 GB01W GB01X GB02W GB03W GB04W GB05W GB06W GB07W GB09X GB09Y GB10X GB16A GB18 JA4 GB18A GB18 AA13 AA18 AB01 AB02 BA01Y BA02Y BA03X BA07Y BA08Y BA10X BA14Y BA16Y BA30Y BA31Y BA33Y BA35Y BA36Y BA38Y BA41Y BB02 EA04 4G069 AA03 AA08 AA09 BC01B BC13A BC13A BC13A BC13A BCBC BC BC CA07 CA08 CA09 DA06 EA19 EE06 FA02 FA03 FB14

Claims (11)

[Claims] 1. An H2 diffusion control material for controlling the diffusivity of hydrogen in an exhaust passage of an internal combustion engine or a combustion device mainly operated in an oxygen excess region, and NOx for reducing nitrogen oxides using at least hydrogen as a reducing agent. A purification catalyst is arranged, and the concentration of H2 in the exhaust gas supplied when the NOx purification catalyst reduces nitrogen oxides is increased by controlling the H2 diffusion rate by the H2 diffusion control material. And exhaust gas purification system. 2. The exhaust gas purification system according to claim 1, wherein a hydrogen supply source is added upstream of the H2 diffusion control material in the exhaust passage. 3. The exhaust gas purification system according to claim 1, wherein the hydrogen supply source is a hydrogen generation exhaust gas purification catalyst, and the operation is performed in a short period of time in a stoichiometric air-fuel ratio or an excess fuel region. 4. A hydrogen storage material is added upstream of the H2 diffusion control material or between the hydrogen supply source and the H2 diffusion control material. An exhaust gas purification system according to one of the above paragraphs. 5. The H2 diffusion control material and the NOx purification catalyst form an H2 diffusion control layer and a NOx purification catalyst layer, respectively. These two layers are laminated on a monolithic carrier to form a multilayer structure. The exhaust gas purification system according to any one of claims 1 to 4, wherein the H2 diffusion control layer is in contact with one or both of an inner surface and an outer surface of the layer. 6. The exhaust gas supplied to the NOx purifying catalyst when the nitrogen oxide is subjected to a reduction treatment is represented by the following formula (A): H2 amount / TR amount ≧ 0.3 (A) The exhaust gas purification system according to any one of claims 1 to 5, wherein the amount satisfies an exhaust gas composition represented by the following formula: 7. The H2 diffusion controlling material contains at least two types of refractory inorganic substances including a refractory inorganic substance having a mode of pore diameter distribution of 4 ° or less and a refractory inorganic substance of 10 ° or less. The exhaust gas purification system according to any one of claims 1 to 6, characterized in that: 8. The exhaust gas purification system according to claim 7, wherein said refractory inorganic substance is at least one selected from the group consisting of zeolite, alumina, silica, silica alumina and alumina silicate. . 9. The NOx purification catalyst is selected from the group consisting of at least one metal element selected from the group consisting of cesium, barium, sodium, potassium, magnesium, lanthanum and calcium, and the group consisting of platinum, palladium and rhodium. And at least one noble metal element,
2. The catalyst according to claim 1, wherein the catalyst is a NOx storage type purification catalyst.
An exhaust gas purification system according to any one of Items 1 to 8. 10. The NOx purification catalyst according to claim 1, wherein the NOx purification catalyst is at least one element selected from the group consisting of copper, cobalt, nickel, iron, gallium, lanthanum, cerium, zinc, titanium, calcium, barium and silver, and / or 9. A NOx selective reduction catalyst containing zeolite or alumina containing at least one noble metal element selected from the group consisting of platinum, iridium, palladium and rhodium, characterized in that it is a NOx selective reduction catalyst. The exhaust gas purification system according to the paragraph. 11. The NOx purification catalyst according to claim 1, wherein the NOx purification catalyst is at least one selected from the group consisting of platinum, palladium and rhodium.
At least one rare earth element selected from the group consisting of lanthanum, cerium, praseodymium, neodymium and samarium, at least one selected from the group consisting of zirconium and barium, 3. A three-way catalyst,
Item 8. The exhaust gas purification system according to any one of Items 8.