JP4924500B2 - Exhaust gas purification catalyst body - Google Patents

Description

The present invention relates to an exhaust gas purification catalyst body that purifies at least HC, CO, and NO _x harmful components contained in exhaust gas discharged from an engine.

Conventionally, in order to purify harmful components such as HC, CO, NOx and the like contained in automobile exhaust gas, oxide particles such as γ-alumina carrying catalyst components made of noble metals such as Pt, Pd, Rh, etc. An exhaust gas purification catalyst body carried on a porous substrate such as light is used.
In order to smoothly advance the oxidation-reduction reaction that is a catalytic reaction in the exhaust gas purification catalyst body, it is necessary to mitigate fluctuations in the air-fuel ratio of the catalyst environment due to exhaust gas pulsation and maintain an appropriate oxygen concentration. For this reason, it has become the mainstream to simultaneously carry the above-described catalyst component and a promoter having oxygen storage / release capability, such as a three-way catalyst for automobiles and a NO _x storage reduction catalyst.

However, the conventional exhaust gas purification catalyst body has the following problems.
That is, when the co-catalyst and the catalyst component made of a noble metal element such as Rh are used in combination, Rh is temporarily brought into an oxygen poisoning state, and the Rh activity is temporarily deactivated. was there.
In addition, there is a problem that the noble metal element and the promoter particles themselves move due to heat, or the particles associate with each other to be alloyed to lose their original functions.
Therefore, in the conventional exhaust gas purification catalyst body, in order to maintain the purification performance required in consideration of the above-mentioned deactivation and reduction in catalyst function in advance, about 70% is more than the required amount of catalyst at the time of a new vehicle. Measures for supporting noble metal elements and promoters have been taken, which has been a problem in terms of environmental burden and high cost.

Therefore, for example, in order to promote the NO _x purification reaction of the NO _x storage reduction catalyst, a plurality of monoliths having different functions are arranged, and on the upstream side, a monolith having a function of adjusting the CO concentration and the H ₂ concentration is arranged. a method of improving _the NO _x purification rate is disclosed (see Patent Document 1).
Also in the field of three-way catalysts that can simultaneously purify HC, CO, and NOx, for example, a plurality of monoliths with different functions are arranged, and a monolith that further assumes the HC purification function is arranged downstream of the monolith having the three-way catalyst. Is disclosed (see Patent Document 2).

Japanese Patent Laid-Open No. 2003-24749 Japanese Patent Laid-Open No. 11-226425

However, in the method of improving the NO _x purification rate, measures against the purification catalyst component of HC are insufficient.
In addition, in the method of separately arranging the monolith responsible for the HC purification function downstream of the monolith having the three-way catalyst, there is still concern about the deactivation of the Rh function due to the combined use of Rh and the cocatalyst. There was a possibility that the catalyst performance may be reduced due to alloying.

The present invention has been made in view of such conventional problems, and is capable of sufficiently purifying at least HC, CO, and NO _x harmful components contained in the exhaust gas and capable of suppressing deterioration in purification performance. The catalyst body is to be provided.

An exhaust gas purification catalyst body that purifies at least HC, CO, and NO _x harmful components contained in exhaust gas discharged from an engine,
The exhaust gas purification catalyst body has a porous base material in which porous partition walls are arranged in a polygonal lattice to form a large number of cells extending in the axial direction, and the cells form an exhaust gas flow path,
A reduction catalyst in which a reduced noble metal catalyst having a reducing ability is supported on either the upstream side or the downstream side of the exhaust gas passage without supporting a promoter having an oxygen concentration adjusting ability on the surface of the porous partition wall. An area is formed, and on the other side, an oxidation catalyst area in which a noble metal catalyst having an oxidizing ability and a promoter having an oxygen concentration adjusting ability are supported on the surface of the porous partition wall is formed,
Between the reduction catalyst region and the oxidation catalyst region, an oxygen concentration adjustment region in which a promoter having an oxygen concentration adjustment capability is supported on the surface of the porous partition wall without supporting a noble metal catalyst is formed. An exhaust gas purifying catalyst body characterized in that (claim 1).

In the exhaust gas purification catalyst body of the present invention, as described above, at least three regions having different functions (the reduction catalyst region, the oxygen gas, and the upstream side of the exhaust gas flow channel of the porous substrate, and between them. A concentration adjustment region and the oxidation catalyst region) are formed. That is, NO _x can be purified by the reduced noble metal catalyst in the reduction catalyst region, and CO and HC can be purified by the noble metal catalyst in the oxidation catalyst region. Further, in the oxygen concentration adjustment region, the above-described purification reaction can be smoothly advanced by adjusting the oxygen concentration by the promoter.

  In the exhaust gas purifying catalyst body, the reduced noble metal catalyst and the oxidized noble metal catalyst are arranged in different regions of the porous base material, the upstream side and the downstream side, respectively. Furthermore, the oxygen concentration adjustment region having the promoter is provided in a region different from the reduction catalyst region having the reduced noble metal catalyst. Therefore, in the exhaust gas purification catalyst body, the reduction action in the reduction catalyst area, the oxidation action in the oxidation catalyst area, and the oxygen concentration adjustment action in the oxygen concentration adjustment area can be sufficiently exerted without interfering with each other. it can.

  In particular, in the exhaust gas purifying catalyst body, the reduced noble metal catalyst that is susceptible to oxygen poisoning and reacts with the promoter to be deactivated is different from the oxidation catalyst region and the oxygen concentration adjusting region that contain the promoter. Formed in position. Therefore, direct contact between the reduced noble metal catalyst and the promoter can be avoided, and a decrease in the catalytic activity of the reduced noble metal catalyst can be suppressed. Furthermore, the reduction catalyst region having the reduced noble metal catalyst and the oxidation catalyst region having the oxidized noble metal catalyst are formed at different positions (the upstream side or the downstream side). Therefore, it is possible to avoid direct contact between the reduced noble metal catalyst and the oxidized noble metal catalyst, to prevent alloying thereof under a high temperature environment, and to suppress a decrease in catalytic activity. Therefore, the exhaust gas purifying catalyst body can exhibit a purifying action excellent in stability for a long period of time.

  As described above, the exhaust gas purification catalyst body can exhibit an excellent purification action stably for a long period of time as described above, and therefore exhibits an excellent purification action without using an excessive amount of the reduced precious metal catalyst and the oxidized precious metal catalyst. can do.

Further, in the exhaust gas purification catalyst body, even if the reduced noble metal catalyst, the oxidized noble metal catalyst, and the promoter are supported on one porous base material, it becomes a harmful component of HC, CO, and NO _x. On the other hand, an excellent purifying action can be stably exhibited for a long period of time. Therefore, it is not necessary to use a plurality of porous base materials, and the exhaust gas purification system can be prevented from being enlarged, and the degree of freedom in the exhaust pipe layout under the engine room or the vehicle floor can be increased.

Thus, according to the present invention, it is possible to provide an exhaust gas purification catalyst body that can sufficiently purify at least HC, CO, and NO _x harmful components contained in the exhaust gas, and can suppress a decrease in purification performance. .

Next, a preferred embodiment of the present invention will be described.
The exhaust gas purification catalyst body has a porous base material in which porous partition walls are arranged in a polygonal lattice to form a large number of cells extending in the axial direction. In the exhaust gas purification catalyst body, the cells have exhaust gas flow paths. Forming. The cross-sectional shape of the cell of the porous substrate can be a polygonal shape such as a triangle, a quadrangle, and a hexagon. Moreover, as a shape of the said porous base material, although various shapes are employable, it can be set as a cylindrical shape etc., for example.

A reduction catalyst region in which a reduced noble metal catalyst having a reducing ability is supported on the surface of the porous partition wall is formed on the upstream side or the downstream side of the exhaust gas passage.
The reduction catalyst region preferably does not contain the promoter.
In this case, in the reduction catalyst region, oxygen reduction of the reduced noble metal catalyst can be suppressed, and the reduced noble metal catalyst can exhibit excellent reducing ability stably for a long period of time.

The reduced noble metal catalyst preferably contains Rh (Claim 3).
In this case, the reducing noble metal catalyst utilizing an excellent reducing power of Rh may exhibit better reduction ability, it is possible to improve the purification effect for NO _x of the exhaust gas purifying catalyst. Specifically, as the reduced noble metal catalyst, for example, Rh, an oxide of Rh, a composite oxide of Rh and another metal element, or the like can be used.

Preferably, the reduced noble metal catalyst preferably contains only Rh as a metal element.
In this case, the reduction of the reducing ability of the reduced noble metal catalyst can be suppressed, and the exhaust gas purification catalyst body can exhibit a purification action for NO _{x in} a stable manner for a longer period of time.
That is, while Rh can exhibit excellent reducing ability, it reacts with other noble metals to form an alloy and is easily deactivated. By adopting only Rh as described above, alloying with other noble metals can be prevented, and the reduced noble metal catalyst can stably maintain excellent catalytic performance for a long period of time.

In addition, an oxidation catalyst region in which either a downstream side or an upstream side in the exhaust gas flow channel carries a noble metal oxide catalyst having an oxidizing ability and a promoter having an oxygen concentration adjusting ability on the surface of the porous partition wall. Is formed.
The precious metal oxide catalyst preferably contains Pt and / or Pd (Claim 5).
In this case, the precious metal oxide catalyst can exhibit a better oxidizing ability, and the purification action of the exhaust gas purification catalyst body on HC and CO can be improved.
Specifically, as the noble metal oxide catalyst, for example, Pt, Pd, Pt oxide, Pd oxide, a composite oxide of Pt and Pd, a composite oxide of Pt or Pd and other metal elements, or the like is used. Can do.

In addition, an oxygen concentration adjustment region is formed between the reduction catalyst region and the oxidation catalyst region, in which a promoter having an oxygen concentration adjustment capability is supported on the surface of the porous partition wall.
The cocatalyst preferably contains an oxide of an element selected from Ce, Zr, Al, Mg, Ti, and Si, or a composite oxide of these two or more elements.
In this case, the cocatalyst can exhibit an excellent oxygen storage / release capability.
Specifically, for example, CeO ₂ , ZrO ₂ , Al ₂ O ₃ , MgO, TiO ₂ , and SiO ₂ can be used as the oxide of the above-described element. In addition, as the above-described composite oxide, for example, a composite oxide containing two or more elements selected from Ce, Zr, Al, Mg, Ti, and Si, or Ce, Zr, Al, Mg, Ti, and A composite oxide of one or more elements selected from Si and other elements can be used.

More preferably, the promoter is composed of a CeO ₂ / ZrO ₂ solid solution.
In this case, the oxygen storage / release capability of the cocatalyst can be further improved, and the above purification in the reduction catalyst region and the oxidation catalyst region can be performed more efficiently.

One or more selected from Al ₂ O ₃ , MgO, Y ₂ O ₃ , TiO ₂ , SiO ₂ , Ni ₂ O ₃ , and W ₂ O ₃ is provided on the surface of the porous partition wall of the porous substrate. It is preferred that the reduced noble metal catalyst, the oxidized noble metal catalyst, and the promoter are supported on the supported layer.
In this case, the heat resistance of the reduced noble metal catalyst, the oxidized noble metal catalyst, and the promoter can be improved. Therefore, it is possible to improve the durability of the exhaust gas purification catalyst body that is exposed to a high temperature.
In forming the support layer on which each of the catalysts described above is formed, for example, the support layer can be formed in advance on the surface of the porous partition wall of the porous base material, and each catalyst can be supported on the support layer. . Further, each catalyst is supported on particles composed of the above-described Al ₂ O ₃ or the like forming the support layer, and the composite layer is supported on the surface of the porous partition wall of the porous substrate to form the support layer. You can also

More preferably, the carrier layer is made of Al ₂ O ₃ or SiO ₂ .
In the case of Al ₂ O ₃ , the support layer can support the reduced noble metal catalyst, the oxidized noble metal catalyst, and the cocatalyst with excellent binding force, and the porous base material made of, for example, cordierite. Can be tightly coupled to. In this case, the surface area of the support layer can be increased, and the exhaust gas can be purified more efficiently.
Further, when composed of SiO ₂ , the adhesion between the reduced noble metal catalyst, the oxidized noble metal catalyst, etc., and the promoter and the support layer is improved, and the catalyst component can be used even for a long time at high temperatures. Catalyst degradation due to aggregation of (reduced noble metal catalyst and oxidized noble metal catalyst), that is, sintering, can be suppressed. As a result, the activity of the catalyst component can be maintained at a high level, and durability at high temperatures can be improved. In particular, combinations that improve durability at high temperatures include SiO ₂ particles (the support) and CeO ₂ particles (the promoter), SiO ₂ particles (the support) and CeO ₂ —ZrO ₂ solid solution particles (the promoter). ) Etc.

The noble metal catalyst in the oxidation catalyst region is preferably supported on the promoter and / or the support layer (claim 9).
In this case, purification with the noble metal oxide catalyst can be performed more efficiently, and the purification action of the exhaust gas purification catalyst body can be improved.

The porous substrate is preferably made of cordierite ceramics.
In this case, the porous substrate has a low thermal expansion coefficient and excellent thermal shock resistance. Therefore, the exhaust gas purification catalyst body can exhibit excellent durability even when used at high temperatures.

Further, in the exhaust gas purification catalyst body, the reduction catalyst region or the oxidation catalyst region has a predetermined width in the axial direction from an end portion in the axial direction of the porous substrate (the end portion on the upstream side or the downstream side). It can be formed in the region. Further, the oxygen concentration adjustment region can be formed with a predetermined width in the axial direction of the porous substrate between the reduction catalyst region and the oxidation catalyst region.
Preferably, the reduction catalyst region, the oxidation catalyst region, and the oxygen concentration adjustment region are formed with a width of 1/10 to 1/2 of the total length of the porous substrate in the axial direction. .
When each region is less than 1/10 of the total length of the porous base material in the axial direction, the reducing ability, oxidizing ability, and oxygen concentration adjusting ability in each region may be insufficient. More preferably, it should be formed with a width of 1/4 or more. On the other hand, when at least one of the regions exceeds 1/2, the other regions are small, and there is a possibility that sufficient catalytic ability cannot be exhibited.
More specifically, for example, when a cylindrical monolith having a length of 100 mm and a diameter of φ100 mm is used as the porous substrate, each region is adjusted to have a width in the axial direction of the porous substrate of about 10 mm to 50 mm. Can do.

Next, an embodiment of the present invention will be described with reference to FIGS.
As shown in FIGS. 1 and 2, the exhaust gas purification catalyst body 1 of this example is used to purify at least HC, CO, and NO _x harmful components contained in the exhaust gas discharged from the engine. The exhaust gas purification catalyst body 1 has a porous base material 2 in which a plurality of cells 22 extending in the axial direction are formed by arranging porous partition walls 21 in a polygonal lattice shape. The cell 22 forms an exhaust gas passage 221 that is a passage for the exhaust gas.

As shown in FIG. 2 and FIG. 3A, the reduction catalyst region 11 in which the reduced noble metal catalyst 3 having the reducing ability is supported on the surface 200 of the porous partition wall 21 is formed on the upstream end 28 side of the exhaust gas passage 221. Has been.
Further, as shown in FIGS. 2 and 3B, on the downstream end 29 side of the exhaust gas passage 221, the noble metal oxide catalyst 4 having oxidation ability on the surface 200 of the porous partition wall 21 and the oxygen concentration adjusting ability are supported. An oxidation catalyst region 12 carrying the catalyst 5 is formed.
Further, as shown in FIG. 2 and FIG. 3C, the promoter 5 having an oxygen concentration adjusting ability is supported on the surface 200 of the porous partition wall 21 between the reduction catalyst region 11 and the oxidation catalyst region 12. An oxygen concentration adjustment region 13 is formed.
As shown in FIGS. 2, 3 (a), and 3 (b), on the upstream 28 side and the downstream 29 side of the exhaust gas flow path 221, different catalyst regions of the reduction catalyst region 11 and the oxidation catalyst region 12, respectively. Is formed.

Hereinafter, the exhaust gas purification catalyst body 1 of this example will be described in detail.
In this example, as shown in FIGS. 1 to 3, the porous substrate 2 is a cylindrical porous body made of cordierite ceramics and having a large number of pores. The porous partition walls 21 are arranged in a square lattice shape, and the cross-sectional shape of the cells 22 is a square shape.

In this example, as shown in FIGS. 3A to 3C, the support layer 6 made of alumina (Al ₂ O ₃ ) is formed on the surface 200 of the porous partition wall 22. In the reduction catalyst region 11, the oxidation catalyst region 12, and the oxygen concentration adjustment region 13, the reduced noble metal catalyst 3, the oxidized noble metal catalyst 4, and the promoter are supported on the surface of the porous partition wall 21 via the support layer 6.

In the reduction catalyst region 11, the reduced noble metal catalyst 3 made of Rh particles having a particle size of about 0.5 to 1 nm is supported on the support layer 6 made of alumina (Al ₂ O ₃ ) (FIG. 3A). reference).
In the oxidation catalyst region 12, a promoter 5 made of CeO ₂ / ZrO ₂ solid solution particles having a particle size of about 1 to ₂₀ nm and a particle size of about 0.5 to 0.5 on a support layer 6 made of alumina (Al ₂ O ₃ ). A precious metal oxide catalyst 4 made of 1 nm Pt particles is supported (see FIG. 3B). Part of the oxidized noble metal catalyst 4 is directly supported on the support layer 6, and the remaining part is supported on the promoter 5.
In the oxygen concentration adjusting region 13, the promoter 5 made of a solid solution having a particle size of about 1 to ₂₀ nm CeO ₂ / ZrO ₂ is supported on the support layer 6 made of alumina (Al ₂ O ₃ ) (FIG. 3C). reference).

  In this example, as shown in FIG. 2, the reduction catalyst region 11 is formed in a region that is 1/3 of the axial length of the porous substrate 2 from the upstream end 28 of the porous substrate 2. Further, the oxidation catalyst region 12 is formed in a region that is 1/3 of the axial length of the porous substrate 2 from the downstream end 29 of the porous substrate 2. Further, the oxygen concentration adjustment region 13 is formed between the reduction catalyst region 11 and the oxidation catalyst region 12, that is, a region of １ ／ of the axial length at the center of the porous substrate 2.

Hereinafter, the manufacturing method of the exhaust gas purifying catalyst body of this example will be described.
In this example, a supporting layer is formed on the porous partition wall of the porous base material, and then the promoter is supported in a region 2/3 from one end in the axial direction of the porous base material, and the same side. A noble metal oxide catalyst is supported in a region of 1/3 from the end of the metal. Next, a reduced noble metal catalyst is supported in a region 1/3 from the other end to produce an exhaust gas purification catalyst body.
Details will be described below.

First, a support layer 6 made of alumina was formed on the surface of a porous substrate (monolith).
That is, first, alumina particles (Nissan Chemical, alumina sol 520) were prepared, and about 100 ml of the alumina particles were dispersed in 500 ml of pure water to prepare an alumina particle-dispersed slurry. Next, the porous substrate (monolith) was impregnated in the alumina particle-dispersed slurry, and the entire porous substrate was uniformly coated with alumina particles (direct impregnation method). Thereafter, by carrying out calcination at a temperature of 400 ° C., a support layer 6 made of alumina covering the surface 200 of the porous substrate 2 was formed (see FIGS. 3A to 3C). The support layer 6 is formed on the entire surface of the porous partition wall 21 of the porous substrate 2.

Next, a slurry of cocatalyst precursor particles was prepared.
That is, first, 25 g of Ce—Zr composite oxide was added to 500 ml of a solvent composed of water or an organic solvent such as ethanol. Next, by irradiating ultrasonic waves of 25 kHz while stirring for 30 minutes, the Ce—Zr composite oxide was refined into nano-order, and a Ce—Zr composite oxide slurry dispersed in a solvent was obtained. This slurry was washed with a centrifuge (manufactured by Hitachi Koki, CR20G). In this way, a slurry of cocatalyst precursor particles was obtained.

Next, a slurry of noble metal oxide catalyst (Pt particles) was prepared.
That is, first, 0.1 g of PtCl ₂ (manufactured by Furuya Metal Co.) is dispersed in 250 ml of a solvent composed of water or an organic solvent such as ethanol, and alkanolamine (Wako Pure Chemical Industries), which is a PtCl ₂ reduction aid to Pt About 10 ml of Kogyo) was added. Next, the obtained slurry was set in an ultrasonic generator (Sono Reactor, manufactured by Honda Electronics Co., Ltd.), and irradiated with 25 kHz ultrasonic waves while stirring for 30 minutes. This ultrasonic irradiation reduces platinum chloride (PtCl ₂ ) into Pt particles.
Thereafter, the Pt particles in the slurry were washed with a centrifuge. In this way, a slurry of a precious metal oxide catalyst was obtained.

In addition, a slurry of reduced noble metal catalyst (Rh particles) was prepared.
Rh particles can be obtained by the same method as the above-described slurry of Pt particles. That is, RhCl ₃ was used in place of PtCl ₂ , and the other operations were performed in the same manner as the above-described method for producing Pt particles, thereby obtaining a slurry of Rh particles.

  In the preparation of the noble metal oxide catalyst, when supported on the porous substrate described later, the noble metal catalyst precursor and the cocatalyst precursor particles are dispersed in a solvent, and nitric acid is further added to reduce the pH of the dispersion. By adjusting to about 3, the slurry can be easily carried on the porous substrate.

  Next, the obtained slurry of precious metal oxide catalyst (Pt particles), the slurry of reduced precious metal catalyst (Rh particles), and the slurry of co-catalyst precursor particles are each again irradiated with ultrasonic waves of 25 kHz, thereby producing Pt particles. , Rh particles, and precursor particles were refined to nano-order.

Next, Pt particles, Rh particles, and precursor particles were supported on the porous substrate on which the support layer was formed as described above.
That is, first, a region from one end in the axial direction of the porous substrate to about 1/3 of the length of the porous substrate is immersed in the slurry of Rh particles, and the Rh particles are supported on the porous substrate. I let you. Next, hot air with a temperature of 150 ° C. was irradiated using a hot air generator and dried. This immersion and irradiation were repeated to carry 0.3 g / L of Rh particles. Thereby, the reduction catalyst area | region 11 was formed in the porous base material 2 (refer FIG. 2).

  Further, the region from the other end in the axial direction of the porous substrate, that is, the end opposite to the end immersed in the slurry of Rh particles, to about 2/3 of the length of the porous substrate. Was immersed in a slurry of cocatalyst precursor particles, and the precursor particles of the cocatalyst were supported on the porous substrate. Next, hot air with a temperature of 150 ° C. was irradiated using a hot air generator and dried. This dipping and irradiation were repeated to carry 80 g / L of cocatalyst precursor particles. In the immersion, the region where the Rh particles were already supported (reduction catalyst region) was not immersed.

Next, the region from the end of the cocatalyst precursor particle immersed in the slurry to about 1/3 of the length of the porous substrate is immersed in the Pt particle slurry, Pt particles were supported. Next, hot air with a temperature of 150 ° C. was irradiated using a hot air generator and dried. This immersion and irradiation were repeated to carry 1.4 g / L of Pt particles.
Thereafter, the porous substrate was baked at a temperature of 500 ° C. for 2 hours. As a result, a promoter composed of a CeO ₂ / ZrO ₂ solid solution was generated from the precursor particles of the promoter composed of Ce—Zr composite oxide.

In this way, as shown in FIGS. 1 to 3, the reduced noble metal catalyst 3 (Rh) is formed in a region about １ ／ of the axial length of the porous substrate 2 from the upstream end 28 of the porous substrate 2. Particles) are formed, and the noble metal oxide catalyst 4 (Pt particles) and the co-catalyst 5 (in the region of 1/3 of the axial length of the porous substrate 2 from the downstream end 29 are formed. The oxidation catalyst region 12 supporting the CeO ₂ / ZrO ₂ solid solution particles) is formed, and the promoter 5 (CeO ₂ / ZrO ₂ solid solution particles) is supported between the reduction catalyst region 11 and the oxidation catalyst region 12. An exhaust gas purification catalyst body 1 in which the oxygen concentration adjustment region 13 was formed was obtained.

As shown in FIGS. 1 to 3, in the exhaust gas purification catalyst body 1 of this example, at least three regions having different functions between the upstream 28 side and the downstream 29 side of the exhaust gas flow path 221 of the porous substrate 2 and between them. (Reduction catalyst region 11, oxygen concentration adjustment region 13, and oxidation catalyst region 12) are formed. That is, in the reduction catalyst region 11, NO _x can be purified by the reduced noble metal catalyst 3, and in the oxidation catalyst region 12, CO and HC can be purified by the oxidized noble metal catalyst 4. Further, in the oxygen concentration adjustment region 13, the above-described purification reaction can proceed smoothly by adjusting the oxygen concentration by the promoter 5.

Further, in the exhaust gas purification catalyst body 1, the reduced noble metal catalyst 3 and the oxidized noble metal catalyst 4 are arranged in different regions of the porous substrate 2, that is, the upstream 28 side and the downstream 29 side. Further, the oxygen concentration adjusting region 13 having the promoter 5 is provided in a region different from the reducing catalyst region 11 having the reduced noble metal catalyst 3.
Therefore, in the exhaust gas purification catalyst body 1, the reduction action in the reduction catalyst area 11, the oxidation action in the oxidation catalyst area 12, and the oxygen concentration adjustment action in the oxygen concentration adjustment area 13 can be sufficiently exhibited without interfering with each other. it can.

  In particular, in the exhaust gas purification catalyst body 1, the reduced noble metal catalyst 3 that is susceptible to oxygen poisoning and easily reacts with the promoter 5 to be deactivated, the oxidation catalyst region 12 containing the promoter 5, and the oxygen concentration adjusting region 13. Are formed at different positions, and the promoter 5 is not supported on the reduction catalyst region 11. Therefore, direct contact between the reduced noble metal catalyst 3 and the co-catalyst 5 can be avoided, and a reduction in the catalytic activity of the reduced noble metal catalyst 3 can be suppressed.

  Furthermore, the reduction catalyst region 11 having the reduced noble metal catalyst 3 and the oxidation catalyst region 12 having the oxidized noble metal catalyst 4 are formed at different positions (upstream 28 side or downstream 29 side). Therefore, direct contact between the reduced noble metal catalyst 3 and the oxidized noble metal catalyst 4 can be avoided, and alloying of these in a high temperature environment can be prevented. Therefore, a decrease in catalyst activity can be suppressed. Therefore, the exhaust gas purifying catalyst body 1 of this example can exhibit a purifying action excellent in stability for a long period of time.

  Since the exhaust gas purification catalyst body 1 can exhibit an excellent purification action stably for a long period of time as described above, the exhaust gas purification catalyst of this example can be used without using an excessive amount of the reduced precious metal catalyst 3 and the oxidized precious metal catalyst 4. The medium 1 can exhibit an excellent purification action.

Further, in the exhaust gas purification catalyst body 1 of this example, even if the reduced noble metal catalyst 3, the oxidized noble metal catalyst 4 and the promoter 5 are supported on one porous substrate 2, as described above, HC, CO, and excellent cleaning effect with respect to harmful components of the NO _x long period can be stably exhibited. Therefore, it is not necessary to use a plurality of porous base materials, and the exhaust gas purification system can be prevented from being enlarged, and the degree of freedom in the exhaust pipe layout under the engine room or the vehicle floor can be increased.

Thus, according to this example, it is possible to provide the exhaust gas purification catalyst body 1 that can sufficiently purify at least HC, CO, and NO _x harmful components contained in the exhaust gas, and can suppress a decrease in purification performance. it can.

  Further, in this example, an exhaust gas purification catalyst body (see FIG. 1) was prepared using a porous substrate having cells having a quadrangular cross section. However, as shown in FIG. The exhaust gas purification catalyst body 1 can also be produced by using the porous substrate 2 having the same. That is, even if the porous base material 2 in which the porous partition walls 21 are arranged in a hexagonal lattice shape to form a large number of cells 22 extending in the axial direction is used, the reduction catalyst region, the oxidation catalyst region, as in the above example. In addition, the exhaust gas purification catalyst body 1 can be manufactured by forming an oxygen concentration adjustment region.

Explanatory drawing which shows the mode of the whole exhaust gas purification catalyst body concerning an Example. Explanatory drawing which shows the cross-sectional structure of the axial direction of the exhaust gas purification catalyst body concerning an Example. It is a figure which shows the cross-sectional structure of the axial direction of an exhaust gas purification catalyst body concerning an Example, Comprising: Explanatory drawing (a) which shows a mode that the periphery of the porous partition in a reduction catalyst area | region was expanded, The axial direction of an exhaust gas purification catalyst body FIG. 2 is an explanatory view showing an enlarged view of the periphery of a porous partition wall in an oxidation catalyst region, and is a view showing an axial sectional structure of an exhaust gas purification catalyst body, in which an oxygen concentration Explanatory drawing (c) which shows a mode that the circumference | surroundings of the porous partition in the adjustment area | region were expanded. BRIEF DESCRIPTION OF THE DRAWINGS Explanatory drawing which shows the mode of the whole exhaust gas purification catalyst body provided with the porous base material of the cell of a hexagonal cross section concerning an Example.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Exhaust gas purification catalyst body 11 Reduction catalyst area | region 12 Oxidation catalyst area | region 13 Oxygen concentration adjustment area | region 2 Porous base material 21 Porous partition 22 Cell 221 Exhaust gas flow path 28 Upstream end 29 Downstream end 3 Reduction | restoration noble metal catalyst 4 Oxidation noble metal catalyst 5 Cocatalyst

Claims (10)

An exhaust gas purification catalyst body that purifies at least HC, CO, and NO _x harmful components contained in exhaust gas discharged from an engine,
The exhaust gas purification catalyst body has a porous base material in which porous partition walls are arranged in a polygonal lattice to form a large number of cells extending in the axial direction, and the cells form an exhaust gas flow path,
A reduction catalyst in which a reduced noble metal catalyst having a reducing ability is supported on either the upstream side or the downstream side of the exhaust gas passage without supporting a promoter having an oxygen concentration adjusting ability on the surface of the porous partition wall. An area is formed, and on the other side, an oxidation catalyst area in which a noble metal catalyst having an oxidizing ability and a promoter having an oxygen concentration adjusting ability are supported on the surface of the porous partition wall is formed,
Between the reduction catalyst region and the oxidation catalyst region, an oxygen concentration adjustment region in which a promoter having an oxygen concentration adjustment capability is supported on the surface of the porous partition wall without supporting a noble metal catalyst is formed. An exhaust gas purification catalyst body characterized by that.   In Claim 1, the said reduction | restoration catalyst area | region, the said oxidation catalyst area | region, and the said oxygen concentration adjustment area | region are formed with the width | variety of 1/10-1/2 of the said axial direction full length of the said porous base material. An exhaust gas purification catalyst body characterized by the above.   3. The exhaust gas purifying catalyst body according to claim 1, wherein the reduced noble metal catalyst contains Rh.   The exhaust gas purification catalyst body according to any one of claims 1 to 3, wherein the reduced noble metal catalyst contains only Rh as a metal element.   The exhaust gas purifying catalyst body according to any one of claims 1 to 4, wherein the noble metal oxide catalyst contains Pt and / or Pd.   6. The promoter according to claim 1, wherein the promoter contains an oxide of an element selected from Ce, Zr, Al, Mg, Ti, and Si, or a composite oxide of these two or more elements. An exhaust gas purifying catalyst body characterized in that: According to any one of claims 1 to 6, the cocatalyst, the exhaust gas purifying catalyst, characterized in that it consists CeO ₂ / ZrO ₂ solid solution. In any one of claims 1 to 7, on the surface of the porous partition walls of the porous _{substrate, Al 2 O 3, MgO,} Y 2 O 3, TiO 2, SiO 2, Ni 2 O 3, A supported layer containing one or more compounds selected from W ₂ O ₃ is formed, and the reduced noble metal catalyst, the oxidized noble metal catalyst, and the promoter are supported on the supported layer. Exhaust gas purification catalyst body.   9. The exhaust gas purifying catalyst body according to claim 8, wherein the precious metal catalyst in the oxidation catalyst region is supported on the promoter and / or the support layer.   The exhaust gas purification catalyst body according to any one of claims 1 to 9, wherein the porous base material is made of cordierite ceramics.

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