JP2008023428A - Catalyst for exhaust gas purification - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a catalyst for an exhaust gas purification, which suppresses an aggregation and sintering of a catalytic metal, and at the same time, enables an increase in purification capability of an exhaust gas at a low temperatures, in particular, NOx and HC. <P>SOLUTION: The catalyst for the exhaust gas purification has a constitution that a permanent magnet or a magnetic field generating device is arranged on the periphery of a honeycomb carrier, and at the same time, a catalyst layer 12 formed on the honeycomb carrier includes a magnetic material 14 and a catalytic metal 13. The catalyst is characterized in that the catalyst layer includes further a porous material 15 provided with a fine pore 16 having a specific pore size, and the magnetic material and the catalytic metal are coexistently supported by the fine pore of the porous material. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to an exhaust gas purifying catalyst for purifying exhaust gas.

  For example, in vehicles such as automobiles, an exhaust gas purifying catalyst is used in an engine to purify exhaust gas containing air pollutants such as HC (hydrocarbon), CO (carbon monoxide), NOx (nitrogen oxide). Is provided in the exhaust system. Then, using the exhaust gas purification catalyst, HC and CO are oxidized and purified, and NOx is reduced and purified.

  Conventionally, as such an exhaust gas purifying catalyst, for example, a catalyst metal such as Pt is highly dispersed on the surface of an oxide carrier such as alumina having a high specific surface area or a CeZr-based composite oxide having oxygen storage / release capability. A supported exhaust gas purification catalyst is used to purify the exhaust gas.

  However, the exhaust gas purifying catalyst has a problem that the catalyst metal gradually aggregates and sinters when exposed to high temperature exhaust gas. When the catalyst metal is sintered, the specific surface area of the catalyst metal is reduced and the catalyst metal is deactivated, thereby deteriorating the exhaust gas purification performance.

On the other hand, it is known to contain a magnetic material in the exhaust gas purification catalyst to suppress sintering of the catalyst metal. For example, Patent Document 1 discloses a ferromagnetic particle that generates a magnetic force acting on the catalyst metal particle. And an exhaust gas purification device including a permanent magnet band on the outer periphery of the exhaust gas purification catalyst. Further, for example, Patent Document 2 discloses an exhaust gas purification apparatus for an internal combustion engine in which a magnetic field is present around an exhaust gas purification catalyst.
JP 2006-29138 A JP 2003-301715 A

  However, Patent Document 1 discloses an exhaust gas purification catalyst in which the catalyst metal is attracted by the magnetic force of the magnetic particles. However, the exhaust gas purification catalyst is magnetic when exposed to high-temperature exhaust gas. There is a possibility that the magnetic force of the particles gradually weakens its effectiveness and a predetermined purification performance cannot be obtained.

  Further, in Patent Document 2, an exhaust gas purification catalyst in which NOx in the exhaust gas is removed by a magnetic field existing around the exhaust gas purification catalyst is disclosed, but in the exhaust gas purification catalyst, In addition to NOx, improvement in purification performance is also required for HC. In particular, when the temperature of the exhaust gas is low, such as when the engine is started, the purification performance of the exhaust gas purification catalyst is not sufficiently exerted. Therefore, further improvement of the exhaust gas purification performance in such a case is desired.

  Therefore, the present invention has been made in view of the above technical problem, and suppresses the aggregation and sintering of the catalyst metal and improves the purification performance of exhaust gas, particularly NOx and HC, at low temperatures. It is an object of the present invention to provide an exhaust gas purifying catalyst.

  Therefore, in the exhaust gas purifying catalyst according to claim 1 of the present application, a permanent magnet or a magnetic field generator is disposed on the outer periphery of the honeycomb carrier, and a magnetic material and a catalyst are formed on the catalyst layer formed on the honeycomb carrier. An exhaust gas purifying catalyst containing a metal, wherein the catalyst layer further contains a porous material having pores having a specific pore diameter, and the magnetic material and the catalyst metal are: It is characterized by being coexistingly supported in the pores of the porous material.

  The invention according to claim 2 of the present application is characterized in that, in the invention according to claim 1, the porous material is zeolite or mesoporous silica.

According to the exhaust gas purifying catalyst according to claim 1 of the present application, the magnetic material and the catalytic metal are coexistingly supported in the pores of the porous material contained in the catalyst layer, so that the magnetic material is magnetized. Since the catalyst metal is sucked to suppress the movement of the catalyst metal and the movement of the catalyst metal between the pores is suppressed by the pore walls, the catalyst metal can be prevented from aggregating and sintering.
The exhaust gas purifying catalyst traps unburned hydrocarbon (HC) components contained in a large amount of exhaust gas at a low temperature in the pores of the porous material, and removes NO components in the exhaust gas from magnetic materials and catalytic metals. The exhaust gas at low temperatures, particularly NOx and HC purification performance can be enhanced. Such NO component reacts with the unburned hydrocarbon component (HC component) desorbed from the pore walls when the temperature of the exhaust gas rises, and is reduced to N ₂ and oxidatively purifies the HC component. .

  Further, according to the invention of claim 2 of the present application, the porous material can be provided with a porous material that can effectively realize the above-described effect by being zeolite or mesoporous silica.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
FIG. 1 is a schematic explanatory view schematically showing an exhaust gas purifying catalyst device according to a first embodiment of the present invention. As shown in FIG. 1, an exhaust system for purifying exhaust gas for purifying exhaust gas G flowing in the direction of the arrow (rightward in FIG. 1) is disposed in an exhaust system of a vehicle such as an automobile, for example. .

  The exhaust gas purification catalyst device 1 includes an exhaust gas purification catalyst 10 in which a catalyst layer for purifying the exhaust gas G is formed on a honeycomb carrier, and an interlam mat 20 that covers the outer periphery of the exhaust gas purification catalyst 10. A permanent magnet 30 is disposed on the outer periphery of the exhaust gas purification catalyst 10, specifically, on the outer periphery of the interram mat 20 via a nonmagnetic heat-resistant alloy canning case 21.

  The interlam mat 20 is formed from, for example, ceramic fiber, etc. so as to keep the exhaust gas purification catalyst 10 warm, hold and fix, and suppress the heat from the exhaust gas G from being transferred to the permanent magnet 30. Further, it is wound around the outer periphery of the exhaust gas purifying catalyst 10, specifically, the outer periphery of the honeycomb carrier. Further, the interlam mat 20 holds the honeycomb carrier in the exhaust gas purification catalyst device 1.

  As the permanent magnet 30 disposed on the outer periphery of the interlam mat 20, for example, a cast magnet such as a Fe—Al—Ni—Co magnet, a Fe—Cr—Co magnet, or a Cu—Ni—Co magnet, for example, a Ba ferrite magnet or Ferrite magnets such as Sr ferrite magnets, for example, rare earth magnets such as Sm—Co magnets or Nd—Fe—B magnets can be used. The permanent magnet 30 may be provided over the entire outer periphery of the honeycomb carrier, or may be provided on a part of the outer periphery of the honeycomb carrier.

FIG. 2 is a cross-sectional view of a main part of the exhaust gas purifying catalyst according to the present embodiment. As shown in FIG. 2, in the exhaust gas purifying catalyst 10, a catalyst layer 12 is formed on a honeycomb carrier 11 formed from, for example, cordierite. In the present embodiment, the catalyst layer 12 contains a catalyst metal, a magnetic material, and a porous material. Pt is used as the catalyst metal, Fe ₂ O ₃ is used as the magnetic material, and zeolite is used as the porous material. The catalyst layer 12 may contain an oxygen storage material such as alumina or CeZr-based composite oxide.

When preparing the exhaust gas purification catalyst 10, first, an aqueous solution containing a catalytic metal Pt and an aqueous solution containing an Fe component are mixed, and after impregnating the mixed solution into a porous material zeolite, for example, 250 ° C to The magnetic material Fe ₂ O ₃ and the catalyst are formed in the pores of the porous zeolite by performing heating and drying at a temperature of 400 ° C. and the like, followed by firing, for example, holding at a temperature of 500 ° C. for 2 hours. A catalyst powder in which the metal Pt is co-supported is obtained.

Next, the catalyst powder is mixed with a binder and water, and in this embodiment, alumina and an oxygen storage material are further mixed to prepare a slurry. The honeycomb carrier is immersed in this slurry, the honeycomb carrier is pulled up, and excess slurry is removed by air blowing. Then, the honeycomb carrier is heated to a temperature of, for example, 250 ° C. to 400 ° C. and dried. The catalyst for exhaust gas purification in which the catalyst layer 12 containing at least the catalyst metal Pt, the porous material zeolite, and the magnetic material Fe ₂ O ₃ is formed on the honeycomb carrier 11 by performing the firing for 2 hours. 10 is obtained.

  In the exhaust gas purification catalyst 10, the catalyst metal is preferably contained in a range of, for example, about 0.1 to 1.0 g / L, and the magnetic material is contained in a range of, for example, about 10 to 80 g / L. The porous material is contained, for example, in the range of about 80 to 150 g / L. Moreover, the porous material has a specific pore diameter, and the pore diameter is preferably about 0.5 nm to 10 nm.

  The interlam mat 20 is wound around the outer periphery of the exhaust gas purification catalyst 10 thus obtained, specifically, the outer periphery of the honeycomb carrier 11, and is housed in the canning case 21, and the permanent magnet 30 is disposed on the outer periphery thereof. Is disposed. In the exhaust gas purifying catalyst 10, the method of causing the catalyst layer 12 to contain the catalyst metal, the porous material, and the magnetic material is not limited to the method described above.

  FIG. 3 is an explanatory view schematically showing the main part of the porous material contained in the exhaust gas purification catalyst. As described above, in the exhaust gas purifying catalyst 10 according to the present embodiment, the catalyst layer 12 is formed on the honeycomb carrier 11, and the catalyst layer 12 contains the catalyst metal 13 and the magnetic material 14 and is porous. A material 15 is contained. As shown in FIG. 3, the catalyst metal 13 and the magnetic material 14 are co-supported on the pores 16 of the porous material 15.

In the exhaust gas purification catalyst 10, the NO component having a small molecular size contained in the exhaust gas G enters the pores 16 of the porous material 15, and the magnetic material 14 or catalyst supported in the pores 16. It is sucked into the metal 13. This is because the NO component is paramagnetic. Such NO component is adsorbed as NO ₂ on the magnetic material 14 and adsorbed as NO ₃ ⁻ on the catalyst metal 13. Thereby, for example, the NO component contained in the exhaust gas G in a low temperature state such as when the engine is started can be suppressed from being discharged into the atmosphere.

Further, in the exhaust gas purifying catalyst 10, unburned hydrocarbon (HC) components contained in the exhaust gas G, particularly benzene (C ₆ H) contained in the exhaust gas G in a low temperature state such as when the engine is started. ₆ ), HC components such as toluene (C ₆ H ₅ CH ₃ ) or methane (CH ₄ ) are trapped by the pore walls 17 of the porous material 15, and the HC components contained in the exhaust gas G in a low temperature state are Exhaust into the atmosphere can be suppressed.

Thus, in the exhaust gas purifying catalyst 10 in which the HC component is trapped in the pore wall 17 of the porous material 15 and the NO component is sucked into the magnetic material 14 or the catalytic metal 13, when the temperature of the exhaust gas G rises, The HC component trapped in the pore wall 17 is desorbed from the pore wall 17. The HC component reacts with NO ₂ adsorbed on the magnetic material 14 and / or NO ₃ ⁻ adsorbed on the catalytic metal 13, whereby the NO component is reduced and purified as N _2. The HC component is oxidized and purified as CO ₂ .

  In the present embodiment, the catalyst layer 12 formed on the honeycomb carrier 11 contains zeolite as the porous material 15. As such zeolite, MFI type (ZSM-5) zeolite, β-zeolite, Y type are used. Zeolite such as zeolite can be used. As another porous material, mesoporous silica having a relatively large pore diameter can be used. Table 1 below shows an example of the HC component trapped by the porous material having the pore diameter and the pores having the pore diameter.

As shown in Table 1, when using MFI type (ZSM-5) zeolite as the porous material, for example, one having a pore diameter of 0.5 nm can be used. By using such zeolite, for example, propylene _{(C 3 H} 6), can be trapped propane _{(C 3} H 8), n- butane and _{(n-C 4 H 10)} or n- heptane _{(n-C 7 H 16)} in the pores . In addition, when β-zeolite is used, for example, those having a long diameter of 0.7 nm and a short diameter of 0.55 nm can be used, for example, C ₆ H ₆ , isobutane (iso _{-C 4 H 10), C 6} H 5 CH 3 or cyclohexane _{(C 6 H 12)} can be trapped in the pores and the like. Further, when using a Y-type zeolite, for example, the pore diameter can be used those which are 0.7 nm, for example, _{C 6 H 6, iso-C} 4 H 10, C 6 H 5 CH 3 or cyclohexane Can be trapped in the pores.

On the other hand, when mesoporous silica is used as the porous material, for example, FSM-16 having a pore diameter of 2.7 nm (Toyota Central R & D Review, Vol. 36, NO. 2, p57-62 (2001.6 For example, 1,3,5-triethylbenzene (C ₆ H ₃ (C ₂ H ₅ ) ₃ ), or benzene in which a plurality of benzene rings are bonded to each other by using such mesoporous silica. Multi-membered rings can be trapped in the pores. Further, as mesoporous silica, for example, MCM-41 (refer to Toyota Central R & D Review, Vol. 36, No. 2, p57-62 (2001.6)) having a pore diameter of 8.0 to 10.0 nm, etc. For example, a benzene multi-membered ring can be trapped in the pores.

  In Table 1, an example of the pore size and trappable HC component is shown for the porous material. However, the present invention is not limited to this, and a porous material having other pore size should be used. HC components having a molecular size smaller than the pore diameter can be trapped in the pores. Further, as the porous material, other suitable porous materials capable of trapping HC components can be used.

In this embodiment, Pt is used as the catalyst metal, but a catalyst metal such as Pd or Rh may be used. In particular, it is preferable to use Pt or Pd as the catalyst metal in order to adsorb the NO component in the exhaust gas in the pores of the porous material in an oxidized state. The magnetic material is preferably a ferrite material, specifically γ-ferrite (γ-Fe ₂ O ₃ ), but other magnetic materials can also be used.

Thus, according to the exhaust gas purifying catalyst 10 according to the present embodiment, the magnetic material 14 and the catalytic metal 13 are co-supported on the pores 16 of the porous material 15 contained in the catalyst layer 12. As a result, the magnetic material attracts the catalytic metal by magnetic force and suppresses the movement of the catalytic metal, and the pore wall suppresses the movement of the catalytic metal between the pores. Can be suppressed.
In the exhaust gas purifying catalyst, unburned hydrocarbon (HC) components contained in the exhaust gas at a low temperature are trapped in the pores of the porous material, and NO components in the exhaust gas are trapped in the magnetic material Fe ₂ O. ₃ and the catalyst metal Pt, and can be adsorbed in the state of NO ₂ on the magnetic material Fe ₂ O ₃ , and adsorbed in the state of NO ₃ ⁻ on the catalyst metal. The purification performance of NOx and HC can be enhanced. Such NO ₂ and / or NO ₃ ⁻ reacts with the unburned hydrocarbon component (HC component) desorbed from the pore walls when the temperature of the exhaust gas rises, and is reduced to N ₂ and converts the HC component. It can be oxidized and purified.
The magnetic material Fe ₂ O ₃ is considered to have O atoms on its surface because Fe is in a trivalent state and is in an oxidized state. There is adsorbed as NO ₂ by NO approaches. On the other hand, since the catalytic metal Pt has a higher oxygen decomposition capability than Fe ₂ O ₃ , it tends to be in a state of NO ₃ ⁻ in which oxygen is further bonded.

  Moreover, the porous material 15 can provide the porous material which can implement | achieve the said effect effectively because it is a zeolite or mesoporous silica.

  In addition, since the permanent magnet 30 is disposed on the outer periphery of the exhaust gas purifying catalyst device 1, the deterioration of the magnetic force of the magnetic material 14 contained in the catalyst layer 12 formed on the honeycomb carrier 11 is suppressed. And the purification performance of the exhaust gas purification catalyst can be ensured.

  FIG. 4 is a schematic explanatory view schematically showing an exhaust gas purifying catalyst device according to a second embodiment of the present invention. In the following description, components having the same configuration as those of the first embodiment and having the same functions are denoted by the same reference numerals, and further description thereof is omitted.

  As shown in FIG. 4, the exhaust gas purification catalyst device 40 includes the exhaust gas purification catalyst 10 and the interlam mat 20 as in the first embodiment. On the outer periphery, specifically, a magnetic field generator 50 is disposed on the outer periphery of the interlam mat 20 via a canning case 21 instead of the permanent magnet 30.

  The magnetic field generator 50 includes an iron core 51 that has a substantially U-shaped cross section and applies a magnetic force to the magnetic material 14 contained in the exhaust gas purification catalyst 10, and an excitation circuit 53 that includes a coil 52 wound around the iron core 51. And a power supply 54 for supplying a current to the excitation circuit 53. In the magnetic field generator 50, when a current flows from the power source 54 to the coil 52, the iron core 51 is magnetized, and magnetic poles 55 a and 55 b are formed at the ends of the iron core 51, and a magnetic force is applied to the magnetic material 14. In addition, not only when using the magnetic field generator 50 but also when using the permanent magnet 30 described above, the catalyst metal 13 is in the form of ultrafine particles and close to the magnetic material 14. Thus, when a magnetic field is applied, it has a magnetic force.

  A cooling pipe 41 for cooling the exhaust gas purifying catalyst 10 is disposed between the magnetic field generator 50 and the canning case 21. The cooling pipe portion 41 includes, for example, an introduction portion 42 that introduces a cooling medium such as air and water, a discharge portion 43 that discharges the cooling medium, and a hollow portion provided between the introduction portion 42 and the discharge portion 43. 44, and is formed in a substantially cylindrical double tube structure. The canning case 21 itself may have the cooling structure.

  Further, the cooling pipe portion 41 is made of a nonmagnetic material and is configured not to affect the magnetic field formed by the magnetic field generator 50. When the exhaust gas purification catalyst 10 is in a high temperature state, the cooling pipe portion 41 prevents the overheating of the exhaust gas purification catalyst 10 by flowing the cooling medium in the cavity 44, thereby providing a magnetic material. 14 can be suppressed.

  Thus, also in the exhaust gas purifying catalyst according to the second embodiment, the magnetic field generator 50 is disposed on the outer periphery of the exhaust gas purifying catalyst 10, so that the same effect as in the first embodiment is obtained. Can play. Further, in the exhaust gas purification catalyst according to the second embodiment, the magnetic field generator 50 can more effectively suppress the deterioration of the magnetic force of the magnetic material, and more effectively ensure the purification performance of the exhaust gas purification catalyst. can do.

  In this embodiment, in order to give a magnetic force to the magnetic material contained in the exhaust gas purification catalyst, a permanent magnet or a magnetic force generator is disposed on the outer periphery of the exhaust gas purification catalyst. A magnetic field may be applied to the exhaust gas purifying catalyst using a suitable magnetizing means to apply a magnetic force to the magnetic material.

  As described above, the present invention is not limited to the illustrated embodiments, and it goes without saying that various improvements and design changes can be made without departing from the gist of the present invention.

  The present invention is an exhaust gas purifying catalyst in which a magnetic layer and a catalytic metal are contained in a catalyst layer formed on a honeycomb carrier and a porous material is further contained. For example, in an exhaust system of a vehicle such as an automobile. It can be suitably applied.

1 is a schematic explanatory diagram schematically showing an exhaust gas purifying catalyst device according to a first embodiment of the present invention. It is principal part sectional drawing of the exhaust gas purification catalyst which concerns on this embodiment. It is explanatory drawing which showed typically the principal part of the porous material contained in the said exhaust gas purification catalyst. It is a schematic explanatory drawing which shows roughly the exhaust gas purification catalyst apparatus which concerns on the 2nd Embodiment of this invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 10 Exhaust gas purification catalyst 11 Honeycomb carrier 12 Catalyst layer 13 Catalyst metal 14 Magnetic material 15 Porous material 16 Pore 30 Permanent magnet 50 Magnetic field generator

Claims (2)

A catalyst for purifying exhaust gas, wherein a permanent magnet or a magnetic field generator is disposed on the outer periphery of the honeycomb carrier, and a magnetic material and a catalyst metal are contained in a catalyst layer formed on the honeycomb carrier,
The catalyst layer further contains a porous material having pores having a specific pore diameter,
The magnetic material and the catalyst metal are co-supported in the pores of the porous material,
An exhaust gas purifying catalyst characterized by that.   The exhaust gas purification catalyst according to claim 1, wherein the porous material is zeolite or mesoporous silica.

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