JP2003200063A - Exhaust gas purification catalyst, method for producing the same, and exhaust gas purification system - Google Patents

Abstract

[PROBLEMS] To provide an exhaust gas purification catalyst capable of efficiently purifying cold HC, a method for producing the same, and an exhaust gas purification system. SOLUTION: A catalyst coat portion including a stacked body of an HC adsorbent layer and a catalyst component layer is provided on a monolithic carrier, and an area ratio of the catalyst coat portion per unit cell pitch is larger than an area ratio of a space portion. It is a gas purification catalyst. The corners of the cell are coated with a refractory inorganic oxide. The refractory inorganic oxide contains platinum, palladium, rhodium, and the like in a content of 1/5 or less of the total amount of noble metals contained in the catalyst component layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst, a method for manufacturing the same, and an exhaust gas purifying system. More specifically, the present invention purifies exhaust gas discharged from an internal combustion engine, and in particular, the exhaust gas is discharged when the engine is started. TECHNICAL FIELD The present invention relates to an exhaust gas purifying catalyst capable of efficiently removing high concentration hydrocarbons (HC), a manufacturing method thereof, and an exhaust gas purifying system.

[0002]

2. Description of the Related Art In recent years, for the purpose of purifying a large amount of HC (cold HC) discharged in a low temperature range at the time of engine startup of an internal combustion engine, an HC adsorption type three-way catalyst (HC adsorption) using zeolite as an HC adsorbent A functional three-way catalyst) has been developed.
The catalyst temporarily adsorbs a large amount of discharged HC in a low temperature range when the engine is started, in which the three-way catalyst is not activated.
Then, the HC is gradually desorbed and purified when the three-way catalyst is activated by the rise in exhaust gas temperature.

As a catalyst for purifying HC desorbed from an adsorbent, there has been conventionally used a specification in which noble metal species such as rhodium (Rh), platinum (Pt) and palladium (Pd) coexist in the same layer, or a Rh layer. A specification in which the Pd layer is separately coated has been proposed. For example, JP-A-2-56247 proposes an exhaust gas purifying catalyst in which a second layer containing a precious metal such as Pt, Pd and Rh as a main component is provided on a first layer containing a zeolite as a main component. Has been done.

The invention using the HC adsorbent is disclosed in, for example, Japanese Patent Application Laid-Open Nos. 6-74019 and 7-1441.
19, JP-A-6-142457, JP-A-5
-59942, JP-A-7-102957,
JP-A-7-96183 and JP-A-11-8199.
No. 9 publication and the like.

In Japanese Unexamined Patent Publication No. 6-74019, a bypass is provided in the exhaust passage so that HC discharged during cold immediately after the engine is started is once adsorbed by the HC adsorbent arranged in the bypass passage, and then the passage is opened. After switching and activating the downstream three-way catalyst, some of the exhaust gas is passed to the HC adsorption catalyst,
A system has been proposed in which desorbed HC is gradually purified by a three-way catalyst in the subsequent stage. Further, JP-A-7-144119 discloses that the heat efficiency of a three-way catalyst in the front stage is taken during cold to improve the adsorption efficiency of the HC adsorbing catalyst in the middle stage, and after activation of the three-way catalyst in the front stage, the middle stage is arranged in tandem. A system has been proposed in which the heat of reaction is easily transferred to the three-way catalyst in the latter stage via the HC adsorption catalyst and the purification of the three-way catalyst in the latter stage is promoted. Further, in Japanese Patent Laid-Open No. 6-142457, cold HC that promotes purification by a three-way catalyst by preheating exhaust gas containing desorbed HC in a heat exchanger when HC adsorbed in a low temperature range is desorbed. Adsorption removal systems have been proposed.

On the other hand, Japanese Patent Laid-Open No. 5-59942 discloses that
A system has been proposed in which the catalyst arrangement and the flow path of exhaust gas by a valve are switched to slow the temperature rise of the HC adsorbent and improve the adsorption efficiency of cold HC. Further, in Japanese Patent Laid-Open No. 7-102957, in order to improve the purification performance of the latter-stage oxidation / three-way catalyst, the former three-way catalyst and the middle H
A system has been proposed in which air is supplied between C adsorbents to promote the oxidation and activation of the three-way catalyst in the latter stage. Further, in Japanese Patent Laid-Open No. 7-96183, from the viewpoint of suppressing deterioration of the catalyst layer (mainly composed of Pd and Al ₂ O ₃ ) in contact with zeolite at high temperature, it is provided between the adsorbent layer and the catalyst layer. The average particle size of the Pd-supported Al ₂ O ₃ particles is 15 in order to provide the porous barrier layer and to suppress the lowering of the adsorption capacity of the lower adsorbent layer.
-25 μm, the average particle size of the refractory inorganic particles is 5 to 15
It has been proposed to use a μm one. Furthermore,
Japanese Patent Application Laid-Open No. 11-104462 discloses a catalyst layer having a thickness of 10 to 120 μm and a sum of the catalyst layer and the adsorption layer from the viewpoint of obtaining a good balance between the purification ability of the catalyst layer and the HC adsorption ability of the adsorption layer. By using the thing of 15-350 μm,
It has been proposed that the catalyst-adsorbent as a whole be improved in HC purification ability. Further, in JP-A-11-81999, in order to slow the desorption of HC captured by the adsorbent at the time of cold, to sufficiently delay the temperature rise of the HC adsorption catalyst, the upstream three-way catalyst and the downstream adsorption A method has been proposed in which the exhaust pipe in the exhaust passage connecting the heat capacity with the catalyst is made thicker or a carrier or the like is installed to make the exhaust pipe larger than the heat capacity of the exhaust manifold.

[0007]

When zeolite is used as the adsorbent, the cold HC adsorption performance has a correlation between the composition of the HC species in the exhaust gas and the pore size of the zeolite, so the optimum pore size and distribution are , It is necessary to use zeolite with skeletal structure. Conventionally, zeolite mainly having MFI type and having other pore size (for example, USY)
Were used alone or in combination to adjust the pore size distribution. However, since the pore size strain and the adsorption / desorption characteristics differ depending on the zeolite species after the endurance, there is a problem that the adsorption of exhaust gas HC species is insufficient.

From the viewpoint of heat resistance, zeolite having a high Si / 2Al ratio is generally used as an adsorbent for automobile catalysts. However, between the catalyst layer containing a relatively hydrophilic refractory inorganic oxide (such as alumina) on the particle surface and the adsorbent layer containing a highly hydrophobic zeolite on the particle surface, the particles that are in direct contact Weak bonding between interfaces. For this reason, the adsorbent layer and the catalyst layer are easily separated, and when exposed to high temperature for a long time, the catalyst layer laminated on the upper part of the adsorbent layer is separated and missing, and the purification function of the catalyst layer is significantly reduced. There was a problem.

When a three-way catalyst is used as the purification catalyst, the purification performance of HC desorbed from the adsorbent depends on the composition of the HC species desorbed when the purification catalyst is not sufficiently activated and the purification catalyst component species ( Noble metal species), the state of contact between the desorbed HC and the purification catalyst, and the temperature of the purification catalyst layer and the atmosphere in which the purification reaction takes place.
It is preferable to use an HC adsorption catalyst having a sequentially laminated structure. However, in the conventional catalyst structure in which the adsorbent layer and the catalyst layer are sequentially laminated, in order to obtain the ability to purify desorbed HC without impairing the adsorption ability of the adsorbent in the film thickness of each laminated layer, Although the film thickness of the purification catalyst layer has been studied, in the actual exhaust gas containing various HC components, the desorption suppression or desorption delay of the adsorbed HC is insufficient and the adsorbed H
There was a problem that the purification ability of C was low.

Further, in the conventional exhaust gas purifying catalyst provided with the HC adsorbent layer and the purifying catalyst layer, the cold HC adsorbed on the HC adsorbent in the exhaust gas low temperature region immediately after the start of the internal combustion engine has a higher exhaust gas temperature. It cannot be purified because it is desorbed before it rises, and when the adsorbed HC is desorbed, the atmosphere of the purification catalyst layer becomes an oxygen deficient state, so it is a three-way catalyst effective for purification in the theoretical air-fuel ratio range. Then, HC, CO and NOx
There was also a problem that the purification of the adsorbed HC could not be sufficiently performed because the purification could not be performed in a well-balanced manner.

On the other hand, as an exhaust gas purifying apparatus using a conventional adsorption catalyst, in order to suppress desorption of adsorbed HC trapped by an adsorbent such as zeolite, the three-way catalyst can be sufficiently operated by switching the exhaust passage. After activation, the adsorbed HC is desorbed and purified with a three-way catalyst, a method for early activation of the three-way catalyst by an electric heater, a method for introducing air from the outside to accelerate the start of activation of the three-way catalyst , And a method of increasing the heat capacity of the exhaust pipe in front of the adsorption catalyst. However, in reality, desorption of adsorbed HC is greatly affected by not only the temperature rise but also the amount of exhaust gas passing through the adsorbent layer and diffusing into the zeolite structure, and the exhaust gas flow velocity.
In the conventional method, the system configuration becomes complicated, and the sufficient effect of reducing cold HC cannot be obtained, the cost is high, the long-term use cannot be endured, and the activation start of the three-way catalyst is too late to be desorbed. There was a problem that HC could not be sufficiently purified.

On the other hand, in the production of a catalyst structure in which an adsorbent layer and a catalyst layer are successively laminated on a honeycomb carrier, when the slurry is applied to the cells, the adsorbent layer is affected by the surface tension of the slurry, It is thickly applied to the corners and thinly applied to the flat ends of the cells. For this reason, the adsorbed HC is desorbed earlier in the flat end portion of the cell than in the cell corner portion, and thus it is difficult to obtain sufficient purification performance of desorbed HC. Therefore, in order to delay desorption of adsorbed HC as much as possible and improve purification of desorbed HC, it has been proposed to make the thickness of the adsorbent layer uniform by using an undercoat layer. However, when a large amount of the undercoat layer is applied to make the thickness of the adsorbent layer uniform, there is a problem that the heat capacity of the entire catalyst increases and desorption purification of adsorbed HC deteriorates.

The present invention has been made in view of the above problems of the prior art, and an object thereof is to provide an exhaust gas purifying catalyst capable of efficiently purifying cold HC, a method for producing the same, and an exhaust gas. To provide a purification system.

[0014]

As a result of intensive studies to solve the above problems, the present inventor has found that the above problems can be solved by providing a catalyst coating layer in a desired area ratio. The present invention has been completed.

That is, the exhaust gas purifying catalyst of the present invention is an exhaust gas purifying catalyst in which a catalyst coat portion is provided on a monolith carrier, and the catalyst coat portion is formed by sequentially stacking an HC adsorbent layer and a catalyst component layer. It is characterized in that it comprises a laminated body, and the area ratio of the catalyst coat part per unit cell pitch is larger than the area ratio of the space part.

In a preferred embodiment of the exhaust gas purifying catalyst of the present invention, the weight ratio of the HC adsorbent layer and the catalyst component layer is 1: 0.01 to 0.5. It is characterized by

Further, according to another preferred embodiment of the exhaust gas purifying catalyst of the present invention, the layer thickness of the HC adsorbent layer and the layer thickness of the catalyst component layer are 1: 0.01-0. 5 is satisfied.

Still another preferred embodiment of the exhaust gas purifying catalyst of the present invention is characterized in that a corner of the cell is coated with a refractory inorganic oxide.

Further, in another preferred embodiment of the exhaust gas purifying catalyst of the present invention, the catalyst component layer comprises a noble metal, alumina, cerium oxide and zirconium oxide, an alkali metal compound and / or an alkaline earth metal compound. Wherein the alumina contains at least two elements selected from the group consisting of platinum, palladium and rhodium, and at least two elements selected from the group consisting of cerium, zirconium and lanthanum, The cerium compound contains at least two elements selected from the group consisting of praseodymium, neodymium and zirconium, and the zirconium oxide contains at least two elements selected from the group consisting of praseodymium, neodymium and cerium. , Is characterized.

Furthermore, in the method for producing an exhaust gas purifying catalyst of the present invention, in producing the exhaust gas purifying catalyst, a slurry containing a compound that can be eliminated by the elimination treatment in the refractory inorganic oxide is applied to the corners of the cells. Coating, and then the compound is eliminated by using at least one treatment method selected from the group consisting of baking, drying, dissolving, pressurizing / depressurizing, and freezing, and an inner diameter of 2 μm or more and coating of the undercoat layer. It is characterized in that the undercoat layer is provided with pores having a thickness of half or less.

Furthermore, the exhaust gas purifying system of the present invention is characterized in that two or more of the above exhaust gas purifying catalysts are arranged in series.

In a preferred embodiment of the exhaust gas purification system of the present invention, a three-way catalyst is disposed as a heat capacity body between the exhaust gas purification catalysts, and the number of cells / geometrical surface area (G
SA) is larger than the exhaust gas purification catalysts on the upstream side and the downstream side.

[0023]

The function of the exhaust gas purifying catalyst of the present invention is high concentration HC (hereinafter referred to as "cold H
The details of exerting an excellent purification performance with respect to (C)) are not necessarily clear, but at the present time, it is presumed as follows. That is, when the exhaust gas containing O ₂ , HC and NOx flows into the two-layer structure main catalyst at a low temperature immediately after the engine is started, HC is adsorbed in the lower HC adsorbent layer, and O ₂ in the exhaust gas is exhausted. The partial pressure increases. Where N
Since the Ox adsorption property is proportional to the O ₂ partial pressure, a large amount of NOx is adsorbed in the upper catalyst component layer at this time. Therefore, cold HC and unpurified NOx are simultaneously adsorbed on the catalyst. After that, when the exhaust gas becomes high temperature and the upper catalyst component layer having the three-way purification function is activated, HC is desorbed from the lower HC adsorbent layer and reacts with NOx adsorbed in the catalyst component layer. As a result, the exhaust gas can be efficiently purified.

[0024]

BEST MODE FOR CARRYING OUT THE INVENTION The exhaust gas purifying catalyst of the present invention will be described in detail below. In addition, in this specification, "%" shows a mass percentage unless otherwise specified.

As described above, the exhaust gas purifying catalyst (HC adsorption type three-way catalyst) of the present invention comprises a monolithic carrier provided with a catalyst coating portion, and the catalyst coating portion comprises the HC adsorption material layer and the catalyst component layer. And a laminated body in which the layers are sequentially laminated. Examples of the HC adsorbent layer include β-zeolite, mordenite, USY, and MFI, and examples of the catalyst component layer include those containing Pd and an alkali metal and / or an alkaline earth metal. Can be mentioned. By providing such an HC adsorbent layer and a catalyst component layer, it is possible to match the temperature and / or the time at which the start of desorption of adsorbed HC and the start of activation of the catalyst component layer are matched, and cold HC can be efficiently purified. Becomes

Further, in the above exhaust gas purifying catalyst,
The area ratio of the catalyst coat portion per unit cell pitch,
It should be larger than the area ratio of the space. From this, the cell shape in the monolith carrier, in other words, the number of cells and GSA
(Geometric Surface Area Are
a: Geometrical surface area), the flow velocity of exhaust gas that passes through the HC adsorbent layer without increasing, and H
It serves as a catalyst that reduces the amount and flow rate of exhaust gas that diffuses into the C adsorbent layer and delays the desorption of adsorbed HC. Further, the catalyst component layer easily exchanges heat of the exhaust gas, and the catalyst is activated early. For example, the desorption start temperature at which the adsorbed HC desorbs from the zeolite layer (HC adsorbent layer) is made to coincide with the activation start temperature of the catalyst component layer, or the activation start temperature is made lower than the desorption start temperature. As a result, cold HC can be efficiently purified. In order to exert these effects efficiently, the area ratio of the above-mentioned space portion is 1 with respect to the entire cell area.
It is suitable to be 0% or more and less than 50%. If it is less than 10%, the exhaust gas passage resistance is large, so the drivability of the engine is likely to deteriorate, and if it exceeds 50%, the amount of exhaust gas that diffuses through the adsorbent layer and the flow velocity cannot be sufficiently reduced, so cold HC can be efficiently produced. Sometimes it cannot be purified. Also,
It is preferable to increase the area ratio of the space portion along the downstream side of the exhaust gas purification catalyst. At this time, the contact efficiency with the exhaust gas can be adjusted to accelerate the activation start of the three-way catalyst component layer. In addition, as shown in FIG.
The “single cell pitch” means each cell of the honeycomb carrier, and the “space portion” means a portion where the coat layer is not applied. In addition, the above-mentioned “GSA” represents the surface area per unit volume, and the unit is cm ² / c.
m ³ .

The weight ratio of the HC adsorbent layer and the catalyst component layer is 1: 0.01 to 0.5.
It is preferable to satisfy. As a result, the diffusion resistance of the catalyst component layer is reduced, and cold HC is sufficiently diffused in the HC adsorbent layer and can be efficiently adsorbed. Further, with this weight ratio, the activation start temperature of the catalyst component layer can be further lowered. If it is less than 0.01, the desorbed adsorbed HC cannot sufficiently contact the purification catalyst component layer, and cold H
C cannot be purified efficiently. Cold H above 0.5
The diffusion resistance of C when it passes through the catalyst component layer is large, and the adsorption efficiency of cold HC may deteriorate.

Further, it is preferable that the layer thickness of the HC adsorbent layer and the layer thickness of the catalyst component layer satisfy a layer thickness ratio of 1: 0.01 to 0.5. As a result, the diffusion resistance of the catalyst component layer is reduced, and cold HC is sufficiently diffused in the HC adsorbent layer and can be efficiently adsorbed. Further, with this film thickness, the activation start temperature of the catalyst component layer can be further lowered. If it is less than 0.01, the desorbed adsorbed HC cannot sufficiently contact the purification catalyst component layer, and cold HC cannot be efficiently purified. If it exceeds 0.5, the diffusion resistance of cold HC when passing through the purification catalyst component layer is large, and the adsorption efficiency of cold HC may deteriorate.

Furthermore, in the catalyst coating layer, the cell flat portion is 100 to 300 μm, and the cell corner portion is 300 to 700 μm.
It is desirable that it is m. As a result, the catalyst activity after deterioration in thermal durability can be further improved. That is, when the layer thickness ratio of the catalyst coat layer is within the above range, the balance between the heat capacity of the carrier and the catalyst activity tends to be good. Further, when the thickness of the catalyst coat layer is within the above range, the catalyst component arranged in the cell flat portion is likely to exhibit sufficient activity. On the other hand, when the layer thickness ratio and the layer thickness of the catalyst coat layer are not within the above ranges, the increase or decrease in the purification activity due to uneven distribution of the catalyst component may be reduced. In addition,
The thickest part of the cell angle and the thinnest part of the flat part, for example,
Refers to a portion as shown in FIG.

Further, at least the corners of the cells can be coated with a refractory inorganic oxide to form an undercoat layer. In this case, the HC adsorbent layer and the catalyst component layer can be easily adjusted to the above-mentioned thickness. So effective. Further, the space portion can have an arbitrary shape. For example, as shown in FIG. 2, it is possible to coat the refractory inorganic oxide and laminate the HC adsorbent layer and the catalyst component layer in a desired layer thickness ratio. As long as the thickness of the catalyst coat layer can be made uniform and the space has a desired size, the undercoat layer may be coated not only on the corners of the cell but also on the flat end of the cell.

It is preferable that the undercoat layer contains alumina and has a plurality of pores partially or entirely. The size of the holes is such that the inner diameter is 2 μm or more and half or less of the coating thickness of the undercoat layer (2
It is preferably about 6 μm). In this case, H
It is possible to make the C adsorbent layer (such as the zeolite coat layer) uniform and easily adjust the aperture ratio of the coating portion. Further, when the exhaust gas passes through the adsorbent layer, it easily passes through the undercoat layer, so that desorption of the adsorbed HC is delayed.
The desorption HC purification capacity is improved. If the size of the holes is outside the above range, the desorption of the adsorbed HC may not be delayed sufficiently. Further, in the above undercoat layer, the volume per coat weight of the portion provided with pores is preferably 1.5 to 3.0 times that in the case where no pore is provided. In this case, It is possible to easily adjust the area of the coat layer coating portion through which the exhaust gas undergoes pressure loss and passes through. Further, since the weight of the undercoat layer used is reduced, the heat capacity can be reduced and the desorption HC purification ability can be improved. If the bulkiness ratio is out of the above range, the effect of adjusting the area of the coated portion of the coat layer may not be sufficiently obtained.
The above "bulk" refers to the thickness of the undercoat layer per constant volume. Further, the pores (inner diameter of 2 μm or more and half or less of the coating thickness of the refractory inorganic oxide) are
5 for the total volume of holes present in the undercoat layer
It is suitable to be contained in a ratio of ˜20%. In this case, the gas is more easily diffused into the undercoat layer, the desorption of the adsorbed HC is delayed, and the desorbed HC purification performance is improved. When the porosity is not the above, gas diffusion into the undercoat layer may be difficult to occur.

Further, the refractory inorganic oxide forming the undercoat layer preferably contains platinum (Pt), palladium (Pd) or rhodium (Rh), and a noble metal according to any combination thereof. is there. Than this,
The heat transferred from the exhaust gas can be efficiently used to further reduce the activation start temperature of the catalyst component layer. The content of these noble metals is preferably 1/5 or less of the total amount of noble metals contained in the catalyst component layer. At this time, since the desorbed adsorbed HC sufficiently contacts the catalyst component layer, the cold HC can be efficiently purified. If it exceeds 1/5, the purification efficiency of cold HC may deteriorate.

Further, the HC adsorbent layer contains β-zeolite as a main component and contains USY, Y-type, MFI or mordenite, and a zeolite according to any combination thereof. SiO ₂ / Al ₂ O ₃ Those having a ratio of 15 to 100 can be preferably used. In this case, it is effective from the initial stage to the endurance period, since excellent adsorbing ability, adsorbing HC holding force and heat resistance can be obtained. In addition, SiO ₂ / Al ₂ O
_{If the 3} ratio is less than 15, the heat resistance tends to be insufficient, and 100
If it exceeds, the holding power of the adsorbed HC may gradually decrease.

Furthermore, as the catalyst component layer, a layer containing a noble metal, alumina, cerium oxide and zirconium oxide and an alkali metal compound and / or an alkaline earth metal compound can be preferably used. Specifically, the alumina includes platinum (Pt), palladium (Pd) and rhodium (Rh), or two elements arbitrarily selected from these, cerium (Ce), zirconium (Zr) and lanthanum (La). ), Or 2 arbitrarily selected from these
And a seed element. The cerium compound is praseodymium (Pr), neodymium (Nd).
And zirconium (Zr), or two elements arbitrarily selected from these are preferably contained. Furthermore, the zirconium oxide preferably contains Pr, Nd, and Ce, or two kinds of elements arbitrarily selected from them. In this case, the durability of the catalyst component layer is remarkably improved, and high purification efficiency of adsorbed HC desorbed from the adsorbent can be obtained from the initial stage to the end stage. In the present invention, the above HC
The adsorbent layer functions as an HC trapper, and the catalyst component layer has a NOx adsorption / three-way purification function. Therefore, the exhaust gas purifying catalyst of the present invention sufficiently functions as a three-way catalyst, and can reduce emissions not only in the cold region but also in the hot region.

The exhaust gas purifying catalyst of the present invention comprises a monolith carrier (integral structure type carrier) provided with the above catalyst coating layer. The monolith carrier may be a honeycomb carrier or a metal carrier made of a heat resistant material. Is preferred. In particular, in purifying the exhaust gas of automobiles, by using a honeycomb-shaped carrier, the contact area between the catalyst component and the exhaust gas is increased, pressure loss is easily suppressed, and vibration and friction are strong. More effective.
As this honeycomb-shaped carrier, generally, a cordierite-based material such as ceramics is often used.
It is also possible to use a honeycomb carrier made of a metal material such as ferritic stainless steel, and further, the catalyst material powder itself may be formed into a honeycomb shape.

Next, the method for producing the exhaust gas purifying catalyst of the present invention will be described in detail. In such a manufacturing method, by coating the corners of the cell with the slurry and then performing the disappearance treatment, pores having an inner diameter of 2 μm or more and half or less of the coating thickness of the undercoat layer are provided in the undercoat layer. . Further, an exhaust gas purifying catalyst is obtained by sequentially stacking the HC adsorbent layer and the catalyst component layer. Here, the slurry contains a compound that can be eliminated by the elimination treatment in the refractory inorganic oxide, and voids are formed when the compound disappears. Examples of such compounds include activated carbon, resin beads, and starch. Further, as the disappearance treatment, baking, drying, dissolving, pressurizing / depressurizing or freezing,
And the processing which combined these arbitrarily is performed. Than this,
Voids of a desired size can be easily formed in the undercoat layer, the desorption of adsorbed HC can be delayed, and the desorbed HC purification performance is improved.

Next, the exhaust gas purification system of the present invention will be described in detail. Such an exhaust gas purification system
Two or more of the above exhaust gas purifying catalysts are arranged in series. Specifically, a configuration as shown in FIG. 3 can be exemplified.
With such a configuration, a series of cold HC adsorption-holding-desorption processes that occur in one HC adsorption type three-way catalyst (main exhaust gas purification catalyst) can be repeated multiple times. The purification efficiency of cold HC is further improved.

Further, it is preferable that the exhaust gas purifying catalyst used in the exhaust gas purifying system has a larger area ratio of the space as the installation position is on the downstream side. In other words, by changing the area ratio of the space (opening), the exhaust gas passes through all the HC adsorption type three-way catalysts (main exhaust gas purification catalyst) arranged upstream and downstream without pressure loss (resistance). By doing so, the purification efficiency of cold HC of the exhaust gas purification catalyst installed on the downstream side can be improved.

Further, a three-way catalyst can be arranged as a heat capacity body between the exhaust gas purification catalysts, and the number of cells / geometrical surface area (GSA) of the three-way catalyst is upstream and downstream exhaust gas purification. It is preferably larger than the catalyst. Than this,
The purification efficiency of cold HC of the exhaust gas purification catalyst installed on the downstream side can be improved. Typical three-way catalysts are alumina, cerium, zirconium and Pt, Pd, R.
A catalyst containing h or the like can be used. The three-way catalyst is not limited to being between the exhaust gas purifying catalysts, and may be installed in the most upstream or the most downstream.

[0040]

EXAMPLES The present invention will now be described in more detail with reference to the drawings and examples, but the present invention is not limited to these examples.

<Catalyst example 1> β- with Si / 2Al ratio of 40
Zeolite powder 800g, silica sol 1333.3g
(Solid content concentration 15 wt%) and 1000 g of pure water were put into an alumina ball mill pot and pulverized for 60 minutes to obtain a slurry liquid. This slurry liquid was attached to a monolith carrier (300 cells / 6 mils, catalyst capacity 0.75 L), excess slurry in the cells was removed by an air flow, and the mixture was dried for 30 minutes under air flow at 50 ° C., then After drying under air flow at 150 ° C for 15 minutes, it was baked at 400 ° C for 1 hour. At this time, the coating operation was repeated until the coating amount became 400 g / L after firing, to obtain a catalyst-a. Ce3
Alumina powder (Al 97 mol%) containing mol%,
An aqueous palladium nitrate solution was impregnated or sprayed under high-speed stirring, dried at 150 ° C. for 24 hours, and then calcined at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain a Pd-supported alumina powder (powder a). The Pd concentration of this powder a is 4.
It was 0%. A cerium oxide powder (Ce67 mol%) containing 1 mol% La and 32 mol% Zr was impregnated with an aqueous palladium nitrate solution or sprayed under high-speed stirring to obtain 150
After drying at ℃ for 24 hours, at 400 ℃ for 1 hour, then
It was baked at 600 ° C. for 1 hour to obtain a Pd-supporting cerium oxide powder (powder b). The Pd concentration of this powder b was 2.0%. The Pd-supported alumina powder (powder a) 400
g, Pd-supporting cerium oxide powder (powder b) 141, nitric acid acidic alumina sol 240 g (boehmite alumina 10
% In the sol obtained by adding 10% nitric acid to 24% in terms of Al ₂ O ₃ ) and barium carbonate 100 g
2000 g of pure water (67 g as BaO) was put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid is attached to the above-mentioned coated catalyst-a, the excess slurry in the cell is removed by an air flow and dried, and the temperature is 400 ° C.
The coated layer was baked for 1 hour at a coating layer weight of 66.5 g / L to obtain a catalyst-b. Alumina powder containing 3 mol% Zr (97 mol% Al) was impregnated with an aqueous rhodium nitrate solution or sprayed under high-speed stirring, dried at 150 ° C. for 24 hours, and then calcined at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour. Rh-supported alumina powder (powder c) was obtained. The Rh concentration of this powder c was 2.0%. Alumina powder (Al 97 mol%) containing 3 mol% Ce was impregnated with an aqueous dinitrodiammine platinum solution or sprayed under high-speed stirring,
After drying at 150 ° C. for 24 hours, it was baked at 400 ° C. for 1 hour and then at 600 ° C. for 1 hour to obtain a Pt-supported alumina powder (powder d). The Pt concentration of this powder d was 3.0%. A zirconium oxide powder containing 1 mol% La and 20 mol% Ce was impregnated with an aqueous dinitrodiammine platinum solution or sprayed under high-speed stirring, dried at 150 ° C. for 24 hours, and then at 400 ° C. for 1 hour, and then at 600 ° C. 1
Firing was carried out for a time to obtain a Pt-supported alumina powder (powder e).
The Pt concentration of this powder d was 3.0%. 118 g of the above Rh-supported alumina powder (powder c), 118 g of Pt-supported alumina powder (powder d), 118 g of Pt-supported zirconium oxide powder (powder e), nitric acid-acidified alumina sol 160
g was put into a magnetic ball mill and mixed and pulverized to obtain a slurry liquid. This slurry liquid was attached to the above coated catalyst-b, the excess slurry in the cell was removed by an air flow, and the mixture was dried and baked at 400 ° C. for 1 hour to give a coat layer weight of 37 g /
L was applied to obtain a catalyst. The amount of precious metal supported on the catalyst is Pt.
0.71 g / L, Pd 1.88 g / L, Rh0.24 g
Was / L.

<Catalyst Example 2> 530 g of powder a, 118 g of powder b and 120 g of nitric acid-acidified alumina sol (a sol obtained by adding 10% nitric acid to 10% boehmite alumina, 12 g in terms of Al ₂ O ₃ ). Then, 40 g of barium carbonate (27 g as BaO) was added to 1000 g of pure water in a magnetic ball mill, and mixed and ground to obtain a slurry liquid. This slurry liquid was attached to a monolith carrier (900 cells / 2 mils, catalyst volume 0.5 L), excess slurry in the cells was removed by an air stream, dried, and calcined at 400 ° C. for 1 hour. 70 g / L was applied, and catalyst-c
Got 235 g of powder e, 100 g of zirconium oxide powder containing 1 mol% of La and 20 mol% of Ce, and 150 g of nitric acid acidic alumina sol (boehmite alumina 10
% In the 15 g) in terms _{of Al} 2 _{O 3} sol obtained by adding 10% nitric acid were charged pure water 1000g into a magnetic ball mill to obtain a slurry which mixing and grinding. This slurry liquid was adhered to the catalyst-c, excess slurry in the cell was removed by an air stream, dried, and baked at 400 ° C. for 1 hour to apply a coat layer weight of 35 g / L. The amount of noble metal supported on the catalyst is Pd 2.35 g / L, Rh 0.47 g
Was / L.

<Catalyst Examples 3 to 15> As shown in Table 1, the same operation as in Catalyst Example 1 was repeated except that at least one of the number of cells, the wall thickness and the opening ratio was changed, and the exhaust gas of this example was exhausted. A gas purification catalyst was obtained. In Catalyst Example 9, the alumina layer was applied before applying the HC adsorbent layer containing zeolite, and in Catalyst Example 10, the intermediate layer composed of the alumina layer was applied on the HC adsorbent layer.

<Catalyst example 16> 850 g of γ-alumina, 500 g of nitric acid-acidified alumina sol (boehmite alumina 10
% In a sol obtained by adding 10% nitric acid to 50% in terms of Al ₂ O ₃ ) and having an average particle diameter of 2 to 3 μm.
100 g of activated carbon and 1000 g of pure water were put into a magnetic ball mill and pulverized for 60 minutes to obtain a slurry liquid. This slurry liquid was attached to a monolith carrier (300 cells / 6 mils, catalyst capacity 0.75 L), excess slurry in the cells was removed by an air flow, and the mixture was dried for 30 minutes under air flow at 50 ° C., then After drying for 15 minutes under air flow at 150 ° C, it was calcined at 600 ° C for 1 hour. The operation was repeated until the coating amount at this time was 70 g / L after firing, and catalyst-aa was obtained. By repeating the same operation as in Catalyst Example 1,
A slurry liquid containing zeolite is attached to the catalyst-aa,
Excess slurry in the cell is removed by air flow,
After being dried for 30 minutes under air circulation at 150 ° C. and then for 15 minutes under air circulation at 150 ° C., it was baked at 400 ° C. for 1 hour. At this time, the coating operation was repeated until the coating amount became 350 g / L after firing to obtain catalyst-d.
Further, the same operation as in Catalyst Example 1 was repeated to apply the catalyst component layer to the catalyst-f, and the applied amount was 103.
The coating operation was repeated until the amount became 5 g / L to obtain catalyst-h. A photograph and a histogram of this catalyst are shown in FIGS. 4 and 5.

<Catalyst Example 17> A catalyst was obtained by repeating the same operation as in Catalyst Example 16 except that an acrylic resin powder was used instead of the activated carbon.

<Catalyst Example 18> The same operation as in Catalyst Example 16 was repeated except that starch was used instead of activated carbon,
A catalyst was obtained.

<Catalyst example 19> After the first layer containing alumina was applied, it was rapidly cooled at a temperature of -40 ° C or lower, and the water contained in the coating layer was instantaneously frozen and expanded to discontinue. A catalyst was obtained by repeating the same operation as in Catalyst Example 9 except that voids of 2 μm or more were formed.

<Catalyst Example 20> A catalyst was obtained by repeating the same operation as in Catalyst Example 16 except that a filler made of an organic material was used instead of the activated carbon.

[0049]

[Table 1]

[Durability Conditions] The catalysts obtained in Catalyst Examples 1 to 20 were subjected to a durability test at the following engine displacement, fuel, exhaust gas catalyst inlet temperature and durability time.・ Engine displacement 3000cc ・ Fuel Nisseki Dash Gasoline (Pb =
0 mg / usg, S = 30 ppm or less) -Catalyst inlet gas temperature 650 ° C-Durability time 100 hours

(Examples 1 to 20 and Comparative Examples 1 to 5) Using the catalysts obtained in the above catalyst examples 1 to 20, FIG.
The exhaust gas purification systems of Examples 1 to 20 and Comparative Examples 1 to 5 were obtained with the configuration shown in.

[0052]

[Table 2]

Under the following evaluation conditions, HC purification characteristic evaluation (LA
-4 A-bag). The results are shown in Table 2.

[0054]

From Tables 1 and 2, the exhaust gas purification systems of Examples 1 to 20 can delay the desorption of adsorbed HC,
Moreover, since the activation of the purification catalyst component layer is promoted, it can be seen that the adsorption rate and desorption purification rate of cold HC are superior to those of the exhaust gas purification systems of Comparative Examples 1 to 5.

Although the present invention has been described in detail with reference to Examples and Comparative Examples, the present invention is not limited to these Examples, and various modifications can be made within the scope of the gist of the present invention. For example, the HC adsorbent layer and the catalyst component layer may be composed of a plurality of layers, or the HC adsorbent and catalyst component may be mixed and used. Further, the cell shape of the honeycomb carrier can be not only quadrangular but also triangular and hexagonal.

[0057]

As described above, according to the present invention, since the catalyst coating layer is provided in a desired area ratio, an exhaust gas purifying catalyst capable of efficiently purifying cold HC, a method for producing the same, and an exhaust gas. A gas purification system can be provided.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of a single cell pitch.

FIG. 2 is an enlarged view showing an example of a catalyst coat layer.

FIG. 3 is a schematic diagram showing an example of an exhaust gas purification system (vehicle system).

FIG. 4 is a photograph showing Catalyst Example 16.

5 is a histogram showing the ratio of pore distribution in catalyst example 16. FIG.

[Explanation of symbols]

1, 3 way catalyst 2,4 HC adsorption three-way catalyst

Front page continuation (51) Int.Cl. ⁷ Identification code FI theme code (reference) B01J 37/00 F01N 3/10 A F01N 3/08 3/24 E 3/10 3/28 301B 3/24 301P 3 / 28 301 B01D 53/36 104Z ZAB F term (reference) 3G091 AB03 AB10 BA15 BA39 FB02 FC07 GB06W GB09Y GB10W GB17W HA19 4D048 AA18 BA03X BA08X BA11X BA15X BA18X BA41X BA41X BA41X BA41X BB01XBA41X BA41X BB41XBB41XBB41XBB41XBB41XBA41XBA41XBB41XBB41XBB41XBB41XBB41XBB41XBB41XBB41XBB41XBBX BA05A BA05B BA07A BA07B BB04A BB04B BC13B BC32A BC33A BC42A BC42B BC44A BC71A BC71B BC72A BC72B BC75A BC75B CA03 CA15 DA06 EA19 EB06 EB15X EB15A ZA15 FC05 ZA30 FC08A ZA30 FC08A FB30A FB30A FB30AFB30A

Claims (15)

[Claims] 1. An exhaust gas purifying catalyst comprising a catalyst coating portion provided on a monolithic carrier, wherein the catalyst coating portion comprises a laminate in which an HC adsorbent layer and a catalyst component layer are sequentially laminated, and a single cell pitch. The exhaust gas purifying catalyst is characterized in that the area ratio of the catalyst coating portion per unit is larger than the area ratio of the space portion. 2. The exhaust gas purifying catalyst according to claim 1, wherein the area ratio of the space is 10% or more and less than 50% with respect to the entire cell area. 3. The layered amount of the HC adsorbent layer and the layered amount of the catalyst component layer satisfy a weight ratio of 1: 0.01 to 0.5, wherein the weight ratio is 1: 0.01 to 0.5. Exhaust gas purification catalyst. 4. The layer thickness ratio of the HC adsorbent layer and the catalyst component layer satisfies 1: 0.01 to 0.5 in terms of layer thickness. The exhaust gas purifying catalyst according to any one of the items. 5. The exhaust gas purifying catalyst according to claim 1, further comprising an undercoat layer formed by coating a refractory inorganic oxide on at least a corner of the cell. 6. The refractory inorganic oxide is at least one selected from the group consisting of platinum, palladium and rhodium.
The exhaust gas purifying catalyst according to claim 5, wherein the exhaust gas purifying catalyst comprises a kind of noble metal, and the content thereof is 1/5 or less of the total amount of the noble metal contained in the catalyst component layer. 7. The HC adsorbent layer contains β-zeolite as a main component and at least one zeolite selected from the group consisting of USY, Y type, MFI and mordenite, and SiO ₂ / Al ₂ O The exhaust gas purifying catalyst according to any one of claims 1 to 6, wherein the ₃ ratio is 15 to 100. 8. The catalyst component layer comprises a noble metal, alumina,
Cerium oxide and zirconium oxide, and an alkali metal compound and / or an alkaline earth metal compound, wherein the alumina is at least two elements selected from the group consisting of platinum, palladium and rhodium, and cerium. ,
At least two elements selected from the group consisting of zirconium and lanthanum, and the cerium compound contains at least two elements selected from the group consisting of praseodymium, neodymium and zirconium, and the zirconium oxide is 8. At least two elements selected from the group consisting of, praseodymium, neodymium, and cerium are included.
Exhaust gas purifying catalyst according to one section. 9. The undercoat layer contains alumina, and a part or the whole thereof has a plurality of pores having an inner diameter of 2 μm or more and half or less of a coating thickness of the undercoat layer. The exhaust gas purifying catalyst according to item 5. 10. The undercoat layer, wherein the volume per coat weight of the portion provided with pores is 1.5 to 3.0 times that of the case where no pore is provided. Item 9. An exhaust gas purification catalyst according to item 9. 11. The proportion of pores having an inner diameter of 2 μm or more and half or less of the coating thickness of the refractory inorganic oxide with respect to the total volume of pores existing in the undercoat layer is 5 to 20%. It is included, It is characterized by the above-mentioned.
The exhaust gas purifying catalyst according to 1. 12. In manufacturing the exhaust gas purifying catalyst according to any one of claims 9 to 11, a slurry containing a compound that can be eliminated by the elimination treatment in the refractory inorganic oxide is added to a corner portion of a cell. Coated and then fired,
The compound is eliminated by using at least one treatment method selected from the group consisting of drying, dissolution, pressurization / depressurization and freezing, and the inner diameter is 2 μm or more and half or less of the coating thickness of the undercoat layer. A method for producing an exhaust gas purification catalyst, characterized in that pores are provided in the undercoat layer. 13. An exhaust gas purification system comprising two or more exhaust gas purification catalysts according to any one of claims 1 to 11 arranged in series. 14. The exhaust gas purification system according to claim 13, wherein the area ratio of the space portion is larger as the installation position of the exhaust gas purification catalyst is on the downstream side. 15. A three-way catalyst as a heat capacity body is disposed between the exhaust gas purification catalysts, and the number of cells / geometrical surface area (GSA) of the three-way catalyst is larger than that of the upstream and downstream exhaust gas purification catalysts. The exhaust gas purification system according to claim 13 or 14, characterized in that.