JP3091201B2 - Catalytic converter for automotive exhaust gas purification - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a catalytic converter that can be suitably used for purifying automobile exhaust gas.

[Prior Art] A catalytic converter used for purifying exhaust gas of an automobile needs to be heated to a predetermined temperature or higher in order for the catalyst to exert a catalytic action. If the temperature of the catalyst has not been sufficiently raised, it is necessary to heat the catalyst.

Conventionally, as a proposal for heating such a catalyst,
For example, the technique described in Japanese Utility Model Laid-Open No. 63-67609 is known. Japanese Utility Model Application Laid-Open No. 63-67609 discloses a catalytic converter in which an electrically conductive metal monolith catalyst in which a metal carrier is coated with alumina is disposed close to the upstream side of a ceramic main monolith catalyst.

[Problems to be Solved by the Invention] However, since the catalyst components such as the monolith catalyst deteriorate from the upstream side of the exhaust gas, in the catalytic converter described in Japanese Utility Model Application Laid-Open No. 63-67609, the upstream side of the main monolith catalyst is used. The catalyst component of the metal monolith catalyst as a pre-heater disposed in close proximity first deteriorates, and the exhaust gas purification ability at low exhaust gas temperatures is reduced. Further, there is a problem that the metal carrier itself is likely to be corroded.

[Means for Solving the Problems] Thus, as a result of various studies, the present inventors have found that the above-mentioned disadvantage can be solved by disposing a heater on the downstream side of the main monolith catalyst, and reached the present invention.

That is, according to the present invention, the catalyst is supported on the honeycomb structure having a large number of through holes made of a material which generates heat by energization, and the catalyst is supported downstream of the main monolith catalyst or between the main monolith catalyst and the main monolith catalyst. And providing slits between the electrodes in various directions, positions, and lengths, changing the length of the partition wall in the through-axis direction, and forming the partition wall thickness of the honeycomb structure. (A wall thickness) or a cell density of a through hole, and a slit is provided in a partition wall of the honeycomb structure. The present invention provides a catalytic converter for purifying automobile exhaust gas, wherein the catalytic converter is provided.

Further according to the invention, downstream of the main monolith catalyst,
Alternatively, between the main monolith catalyst and the main monolith catalyst, at least two electrodes for energization are provided in a honeycomb structure made of a material that generates heat by energization and having a large number of through holes, and slits are formed between the electrodes by various kinds of slits. Direction, position,
Providing the length, changing the partition wall length in the through-axis direction, changing the thickness (wall thickness) of the partition walls of the honeycomb structure, or changing the cell density of the through holes, and the honeycomb A slit is provided in the partition of the structure, and a honeycomb heater provided with a resistance adjusting mechanism, which is one of the above, is provided, and a monolith catalyst for ignition is provided downstream of the honeycomb heater. And a catalytic converter for purifying automobile exhaust gas.

Further, since the honeycomb heater is provided with a resistance adjusting mechanism such as a slit between the electrodes, the honeycomb heater is excellent in heat generation characteristics and is preferable. It is preferable that the honeycomb structure of the present invention is formed by extruding a metal powder into a honeycomb shape and sintering it.

Further, according to the present invention, for supplying electricity to a honeycomb structure having a large number of through holes made of a material which generates heat by energization, between an upstream side or a downstream side of the main monolith catalyst, or between the main monolith catalyst and the main monolith catalyst. And providing slits between the electrodes in various directions, positions, and lengths, changing the length of the partition wall in the through-axis direction, and the thickness of the partition wall of the honeycomb structure ( A honeycomb heater and a monolith for ignition, each of which is provided with a resistance adjusting mechanism, which is one of changing a wall thickness) or changing a cell density of a through-hole, and providing a slit in a partition wall of the honeycomb structure. A catalytic converter for purifying automobile exhaust gas, wherein a module formed of a catalyst and a catalyst is detachably provided.

[Operation] In the present invention, the main monolith catalyst is arranged at least on the upstream side of the exhaust gas flow path, and on the downstream side of the main monolith catalyst, a honeycomb structure having a large number of through holes made of a material that generates heat when energized is energized. And a honeycomb heater having a resistance adjusting mechanism provided between the electrodes.

Thus, by installing the honeycomb heater on the downstream side of the main monolith catalyst, it is possible to heat exhaust gas at a low temperature such as at the time of starting the engine, and to reduce the exhaust gas even after the exhaust gas becomes hot. Since the main monolith catalyst is disposed on the upstream side, metal corrosion of the honeycomb heater and deterioration of the catalyst carried on the honeycomb heater are suppressed as much as possible.

Further, in the present invention, when a module formed of a honeycomb heater and a monolithic catalyst for ignition is disposed on the upstream or downstream side of the main monolith catalyst, or when the module is detachably disposed between the main monolith catalyst and the main monolith catalyst, Usually, the honeycomb heater or the ignition catalyst deteriorates earlier than the main monolith catalyst, and accordingly, the life of the entire catalytic converter can be extended only by appropriately replacing the module in accordance with the deterioration.

The constituent material of the honeycomb structure serving as the base of the present invention is not limited as long as it is made of a material that generates heat when energized, and may be metallic or ceramic, but metallic is preferable because of its high mechanical strength. In the case of metal, for example, stainless steel or Fe-Cr-Al, Fe-Cr, Fe-Al, Fe-Ni,
A material made of a material having a composition such as W-Co, Ni-Cr or the like may be used. Among the above, Fe-Cr-Al, Fe-Cr, and Fe-Al are preferable because they are excellent in heat resistance, oxidation resistance, and corrosion resistance, and are inexpensive. The honeycomb structure may be porous or non-porous, but when carrying a catalyst, the porous honeycomb structure has a strong adhesion to the catalyst layer and the catalyst has a large thermal expansion difference. This is preferable because peeling hardly occurs.

Next, an example of a method for manufacturing a metallic honeycomb structure among the honeycomb structures of the present invention will be described.

First, a metal powder raw material is prepared from, for example, an Fe powder, an Al powder, a Cr powder, or an alloy powder thereof so as to have a desired composition. Next, after mixing the thus prepared metal powder raw material, an organic binder such as methyl cellulose and polyvinyl alcohol, and water, the mixture is extruded into a desired honeycomb shape.

Next, the extruded honeycomb formed body is fired at 1000 to 1450 ° C. in a non-oxidizing atmosphere. Here, when firing is carried out in a non-oxidizing atmosphere containing hydrogen, the organic binder becomes
It is preferable because it can be decomposed and removed using Fe or the like as a catalyst to obtain a good sintered body (honeycomb structure).

If the firing temperature is lower than 1000 ° C., the compact is not sintered, and if the firing temperature is higher than 1450 ° C., the obtained sintered body is undesirably deformed.

Preferably, the surfaces of the partition walls and pores of the obtained honeycomb structure are coated with a heat-resistant metal oxide.

Next, desirably, in the obtained honeycomb structure, a resistance adjusting mechanism is provided between the electrodes described below in various modes.

As the resistance adjusting mechanism provided in the honeycomb structure, for example, providing slits in various directions, positions, and lengths,
Changing the partition wall length in the through-axis direction, changing the thickness (wall thickness) of the partition walls of the honeycomb structure, or changing the cell density of the through holes, and providing slits in the partition walls of the honeycomb structure And the like are preferred.

The metallic honeycomb structure obtained as described above,
Usually, a honeycomb heater is manufactured by providing an electrode on a partition wall or an inner portion thereof by brazing, welding, or the like.

The term “electrode” as used herein means a general term for terminals for applying a voltage to the heater, and includes a terminal directly connected to the outer peripheral portion of the heater and the can body, and a terminal such as a ground.

When this metal honeycomb structure is used as a heater, it is preferable to form the metal honeycomb structure so that the resistance value as a whole is in the range of 0.001Ω to 0.5Ω.

In addition, it is preferable that a catalyst is further supported on the surface of the metallic honeycomb structure, because a temperature rise due to a purification reaction (such as heat of oxidation reaction) of exhaust gas can be expected.

The catalyst supported on the surface of the metallic honeycomb structure is obtained by supporting a catalytically active substance on a carrier having a large surface area. Here, as a carrier having a large surface area,
For example, γ-Al ₂ O ₃ type, TiO ₂ type, SiO ₂ —Al ₂ O ₃ type and perovskite type are typical examples.
As the catalytically active substance, for example, noble metals such as Pt, Pd, Rh,
Base metals such as Cu, Ni, Cr, and Co can be used.
Among the above, those in which Pt and Pd are supported on the γ-Al ₂ O ₃ system at 10 to 100 g / ft ³ are preferable.

As the ignition catalyst disposed behind the honeycomb heater (downstream of the gas), the same catalyst as the catalyst supported on the surface of the metallic honeycomb structure may be used, or the same catalyst as the main monolith catalyst may be used. May be used.

Although the honeycomb shape of the honeycomb structure of the present invention is not particularly limited, specifically, for example, 6 to 1500
It is preferable to form the cell so as to have a cell density in the range of cells / In ² (0.9 to 233 cells / cm ² ). The thickness of the partition is 50
The range of -2000 μm is preferred.

As described above, the honeycomb structure may be porous or non-porous, and the porosity is not limited.
It is desirably in the range of 50% to 50%, preferably less than 25% from the viewpoint of strength properties, oxidation resistance, and corrosion resistance. When a catalyst is supported, the catalyst preferably has a porosity of 5% or more from the viewpoint of adhesion to the catalyst layer.

In the present invention, the term “honeycomb structure” refers to an integrated structure having a large number of through-holes partitioned by partition walls. For example, the cross-sectional shape (cell shape) of the through-hole may be any of various shapes such as a circle, a polygon, and a corrugated shape. Various shapes can be used.

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

FIG. 1 is a plan view showing an example of a honeycomb heater supporting a catalyst of the present invention. A honeycomb structure 10 having a large number of through holes 12 is provided with a plurality of slits 11 as a resistance adjusting mechanism, and the outer wall thereof is provided with a plurality of slits 11. In this example, three electrodes 13 are provided to form a honeycomb heater.

FIGS. 2 to 5 are explanatory diagrams each showing an embodiment of a catalytic converter for purifying automobile exhaust gas according to the present invention.

FIG. 2 shows that between the main monolith catalyst 15 and the ignition catalyst 16,
FIG. 3 shows an example in which a honeycomb heater or heater catalyst 14 is inserted downstream of the main monolith catalyst 15 and upstream of the ignition catalyst 16 through flow paths 17 and 18, respectively. An example in which is disposed is shown.

FIG. 4 shows an example in which a heater catalyst 14 serving also as an ignition catalyst is disposed adjacent to the downstream side of the main monolith catalyst 15, and FIG. 5 shows a flow path 17 and a flow path 17 between the two main monolith catalysts 15. 18
This shows an example in which a honeycomb heater or a heater catalyst 14 and an ignition catalyst 16 arranged close to the downstream side of the honeycomb heater or heater catalyst 14 are provided via the heater.

 Next, specific results will be described.

(Example) Fe powder, Fe-Cr powder, Fe-Al so as to become Fe-20Cr-5Al
After mixing the powder, extrusion molding and baking in H ₂ atmosphere, outer diameter 93mmφ, thickness 15mm, cell wall (rib) thickness 8m
A honeycomb structure having il and a through-hole number of 300 cells / inch ² (CPI ² ) was obtained. The obtained honeycomb structure 10 has a length of about 70 mm as shown in FIG. 1 (a slit length at both ends is about 50 mm).
The slits 11 were formed at six locations in the axial direction of the through-hole 12 and the number of cells between the slits 11 was 7 (about 10 mm).

Further, the honeycomb structure 10 was coated with γ-alumina, and then each of the precious metals Pt and Pd was supported at 20 g / ft ³ and 600 g
C. and catalyzed. Thereafter, as shown in FIG. 1, electrodes 13 were set at two places on the outer wall of the electrode 13 to form a heater catalyst 14.

As shown in FIG. 2, the obtained heater catalyst 14 is installed behind (a downstream side of exhaust gas) a commercial three-way catalyst 15 which is a main monolith catalyst, and an ignition catalyst 16 which is an oxidation catalyst is further installed behind the catalyst. did.

In order to confirm the performance of this system when starting the engine, the temperature of the introduced exhaust gas A was raised from 100 ° C to 420 ° C at a constant speed in 2 minutes, and then kept at 420 ° C for 1 minute (warm-up test). , HC and NO _x purification rates were measured.
The heater catalyst 14 was energized with a 12 V battery for one minute, and was energized so that the exhaust gas temperature became 350 ° C.

Next, as an endurance test, a test was performed in which the exhaust gas temperature was raised from room temperature to 750 ° C., and the temperature was maintained at 750 ° C. for 10 hours. The heater catalyst 14 has an exhaust gas temperature of 350
C. for 1 minute.

After this durability test was repeated 10 times, and performing the warm-up test, CO, HC, the purification rate of the NO _x were measured.

For comparison, an endurance test was performed on a system in which the heater catalyst 14 was installed in front of the main monolith catalyst 15 as shown in FIG.

Table 1 shows the average purification rate before and after the durability test of the present invention and the average purification rate after the durability test of the comparative example.

[Effects of the Invention] As described above, according to the present invention, by installing a honeycomb heater downstream of the main monolith catalyst,
Since the exhaust gas can be heated at low temperatures such as when starting the engine, and even after the exhaust gas has become hot, the main monolithic catalyst is disposed upstream of the exhaust gas, so the metal of the honeycomb heater can be heated. Corrosion and deterioration of the catalyst carried on the honeycomb heater are minimized.

Further, in the present invention, when using a module formed from a honeycomb heater and a monolithic catalyst for ignition,
In response to the deterioration of the module, the life of the entire catalytic converter can be extended only by appropriately replacing the module.

[Brief description of the drawings]

FIG. 1 is a plan view showing an example of a honeycomb heater supporting the catalyst of the present invention, and FIGS. 2 to 5 are explanatory views showing the construction of an embodiment of a catalytic converter for purifying automobile exhaust gas according to the present invention. The figure is a configuration explanatory view showing an example of a catalytic converter for comparison. 10: honeycomb structure, 11: slit, 12: through hole, 13: electrode, 14: honeycomb heater or heater catalyst, 15: main monolith catalyst, 16: ignition catalyst, 17, 1
8 …… Flow path.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) F01N 3/24 F01N 3/20

Claims (5)

(57) [Claims] The present invention relates to a method for supporting a catalyst on a honeycomb structure having a large number of through-holes, which is made of a material that generates heat when energized, downstream of the main monolith catalyst or between the main monolith catalyst and the main monolith catalyst. At least two electrodes are provided, slits are provided between the electrodes in various directions, positions, and lengths, the length of the partition wall in the through-axis direction is changed, and the thickness of the partition wall of the honeycomb structure (wall Thick)
Or by changing the cell density of the through-holes, and providing slits in the partition walls of the honeycomb structure, a honeycomb heater provided with a resistance adjusting mechanism, which is provided. Automotive exhaust gas purification catalytic converter. 2. At least two electrodes for supplying electricity to a honeycomb structure having a large number of through holes made of a material which generates heat when electricity is supplied downstream of the main monolith catalyst or between the main monolith catalyst and the main monolith catalyst. And providing slits between the electrodes in various directions, positions, and lengths, changing the partition wall length in the through-axis direction, and changing the thickness (wall thickness) of the partition walls of the honeycomb structure. Or let
Or changing the cell density of the through-holes, and providing slits in the partition walls of the honeycomb structure, and disposing a honeycomb heater provided with a resistance adjusting mechanism, and downstream of the honeycomb heater. A catalytic converter for purifying automobile exhaust gas, characterized in that a monolithic catalyst for ignition is provided in the vehicle. 3. The catalytic converter according to claim 2, wherein the honeycomb heater has a catalyst supported on a honeycomb structure. 4. The catalytic converter according to claim 1, wherein the honeycomb structure is formed by molding metal powder into a honeycomb shape and sintering the metal powder. 5. A honeycomb structure having a large number of through-holes made of a material which generates heat when energized is provided between the main monolith catalyst and an upstream or downstream side of the main monolith catalyst or between the main monolith catalyst and at least two of the main monolith catalysts. Providing two electrodes, providing slits in various directions, positions, and lengths between the electrodes, changing the partition wall length in the through-axis direction, and the thickness (wall thickness) of the partition walls of the honeycomb structure. Or to change the cell density of the through-hole,
And a slit formed in a partition wall of the honeycomb structure, wherein a module formed of a honeycomb heater provided with a resistance adjusting mechanism and an ignition monolith catalyst is detachably disposed. Catalytic converter for automotive exhaust gas purification.