JPH0460107A - Resistance adjusting type heater and catalyst converter - Google Patents

Abstract

PURPOSE:To obtain effective purification function by so forming a resistance adjusting means as to be substantially even to a sectional face of a main monorice catalyst on which a sectional face of a heating part of a heater is also provided. CONSTITUTION:Slits 11 as resistance adjusting mechanisms are formed on a honeycomb structure 10, while an inorganic adhesive is charged in an outer peripheral part for insulation. After the honeycomb structure 10 is coated with gamma-alumina, Pd and Pt are respectively held, to prepare a catalyst through burning. Electrodes 13 are set at two portions of an outer wall of the thus obtained honeycomb structure 10 with catalyst. The structure is then arranged in front of a marketed catalytic converter rhodium 14 as a main monorice catalyst, that is, on an upstream side of gas.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a resistance-adjustable heater and a catalytic converter that can be suitably used for purifying automobile exhaust gas.

[Prior art and problems to be solved by the invention] Recently, nitrogen oxides (NOx), -carbon oxides (Co), and hydrogen chloride (HC) in exhaust gas emitted from internal combustion engines of automobiles, etc. In addition to the conventionally known porous ceramic honeycomb structures, metal honeycomb structures or pillars have come to be used as catalysts, catalyst carriers, etc. for purification.

On the other hand, as exhaust gas regulations become stricter, there is a strong need for the development of heaters, catalytic converters, etc. that reduce emissions during cold starts.

As such a honeycomb structure, for example,
A technique described in Japanese Patent No. 67609 is known. This Japanese Utility Model Application Publication No. 63-67609 discloses a catalytic converter in which a metal monolithic catalyst capable of conducting electricity is disposed in close proximity to the upstream side of a main monolithic catalyst made of ceramic and has a metal carrier coated with alumina. .

However, in the catalytic converter described in Japanese Utility Model Application Publication No. 63-67609, the metal monolith catalyst serving as a preheater disposed close to the upstream side of the main monolith catalyst is simply a foil-type metal honeycomb structure. Electricity is passed from the inner circumference to the outer circumference to generate heat, and its resistance is not adjusted (that is, the material, dimensions, and thickness of the rift are only specified, and the desired resistance is not adjusted).
Moreover, since the cross-sectional diameters of the metal monolith catalyst and the main monolith catalyst are substantially the same, there was a problem in that the temperature increase characteristics were insufficient.

Therefore, the present applicant previously proposed a heater and a catalytic converter in which a honeycomb structure is provided with at least two electrodes for energizing, and a resistance adjustment means is provided between the electrodes (Japanese Patent Application No. 2-96866). issue).

The present invention provides further improvements to this heater and catalytic converter.

[Means for Solving the Problems] That is, according to the present invention, there is provided a heater in which a honeycomb structure is provided with at least two electrodes for energization, and a resistance adjustment means is provided between the electrodes, the heater having a There is also provided a resistance-adjustable heater, characterized in that the resistance-adjusting means is formed so that the cross-section of the heat-generating portion is substantially the same as the cross-section of the main monolithic catalyst.

Further, according to the present invention, at least two electrodes for supplying electricity to the honeycomb structure are provided upstream of the main monolithic catalyst or between the main monolithic catalysts, and
A heater having a resistance adjusting means between the electrodes, wherein the resistance adjusting means is formed such that a cross section of a heat generating part of the heater is substantially the same as a cross section of a main monolithic catalyst downstream of the heater. A catalytic converter is characterized in that a type heater is provided, and at least two electrodes are provided downstream of the main monolithic catalyst in which the catalyst is supported on a honeycomb structure and for conducting electricity, and a resistor is provided between the electrodes. The heater is characterized in that a resistance-adjustable heater is provided, the resistance-adjusting means being formed such that the cross-section of the heat-generating portion of the heater is substantially the same as the cross-section of the main monolithic catalyst. A catalytic converter is provided.

Further, it is preferable that the heater is formed so that its cross-sectional diameter (outer diameter dimension) is larger than the cross-sectional diameter of the main monolithic catalyst.

[Function] The present invention provides at least two
The heater is provided with two electrodes and has a resistance adjustment means such as a slit between the electrodes, and the resistance adjustment means is formed so that the cross section of the heat generating part of the heater is substantially the same as the cross section of the main monolithic catalyst to which it is attached. This is a resistance-adjustable heater.

By adjusting the resistance in this way, heat generation can be controlled.

In Japanese Patent Application No. 2-96866, which is the applicant's earlier application, the examples suggest that the cross-sectional shapes of the honeycomb heater as a preheater and the main monolith catalyst are approximately concave. In that case, it has been found that no matter how the resistance adjusting means is provided, the heating of the outer circumference of the honeycomb heater tends to be insufficient, and as a result, the catalytic action of the outer circumference of the heater tends to become insufficient. Furthermore, there is also the problem that the electrode section, which is usually installed on the outer periphery of the heater, is easily corroded by high-temperature exhaust gas.

In the present invention, the cross section of the heat generating part of the heater is made to be substantially the same as the cross section of the main monolith catalyst to which it is attached,
This solves the above problem.

In the present invention, it is preferable to seal the inflow of the gas fluid to the parts other than the heat generating part of the heater with a heat insulating material or the like, and allow the gas fluid to flow only into the heat generating part of the heater, since the gas fluid can be heated quickly. In this case, since the electrode does not come into direct contact with the gas fluid, the problem of corrosion from the gas fluid can be avoided, which is preferable.

The constituent material of the honeycomb structure, which is 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 metal or ceramic, and metal is preferable because of its high mechanical strength. . In the case of metals, for example, stainless steel, FeCr-Al, Fe-Cr, Fe-
Materials having compositions such as A, Fe--Ni, W--Co, and Ni--Cr may be mentioned. Of the above, Fe
-Cr-A! ; L, Fe-Cr, Fe-A, heat resistant;
It is preferable because it has excellent oxidation resistance and corrosion resistance, and is inexpensive.

The honeycomb structure may be porous or non-porous, but when supporting a catalyst, the porous honeycomb structure has strong adhesion to the catalyst layer, and the catalyst is not easily supported due to the difference in thermal expansion. This is preferable because there is almost no peeling.

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

First, to obtain the desired composition, for example, Fe powder, AI powder, etc.
A metal powder raw material is prepared from a granular Cr powder or an alloy powder thereof. Next, the metal powder raw material prepared in this manner is mixed with an organic binder such as methyl cellulose or polyvinyl alcohol, and water, and then this mixture is extruded into a desired honeycomb shape.

Next, the extruded honeycomb molded body is fired at 100° C. to 1450° C. in a non-oxidizing atmosphere. When firing is performed in a non-oxidizing atmosphere containing hydrogen, the organic binder is decomposed and removed using Fe as a catalyst, resulting in a good sintered body (
It is preferable to obtain a honeycomb structure).

If the firing temperature is less than 1000°C, the molded body will not be sintered, and if the firing temperature exceeds 1450°C, the resulting sintered body will be deformed, which is not preferable.

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

Next, in the obtained honeycomb structure, a resistance adjustment mechanism is provided in various ways between the electrodes, which will be described later.

Examples of resistance adjustment mechanisms provided in the honeycomb structure include: (1) providing slits in various directions, positions, and lengths;
Changing the length of the partition wall in the through-axis direction, ■ Changing the thickness of the partition wall (wall thickness) of the honeycomb structure or changing the cell density of the through hole, and ■ Adding slits to the partition wall of the honeycomb structure. Preferable examples include providing a Among these, the formation of slits (3) is particularly preferred as a method for easily adjusting the heat generating portion.

The metallic honeycomb structure obtained as described above is usually provided with electrodes on the outer peripheral partition wall or inside thereof by means such as brazing or welding, thereby producing a honeycomb type heater.

Note that the term "electrode" here refers to a general term for terminals for applying voltage to the heater, and includes terminals such as those in which the outer circumference of the heater and the can body are directly connected, and terminals such as ground terminals.

When this metallic honeycomb structure is used as a heater, it is preferably formed so that its overall resistance value is in the range of 0.001Ω to 0.5Ω.

Further, by further supporting a catalyst on the surface of the above-mentioned metallic honeycomb structure, a temperature increase due to the exhaust gas purification reaction (oxidation reaction heat, etc.) can be expected, which is preferable.

The catalyst supported on the surface of the metallic honeycomb structure is one in which a catalytically active substance is supported on a carrier having a large surface area. Here, examples of the carrier having a large surface area include γ-AM, 03 series, TiO2 series, 5jO2-A structure,
Typical examples include the 03 series and perovskite series. Examples of catalytically active substances include Pt,
Examples include noble metals such as PdRh, and base metals such as Cu, Ni, Cr, and Co. Among the above, γ-A sentence,
It is preferable to use 03 series with Pt or Pd supported at 10 to 100 g/ft3.

The honeycomb shape of the mucocam structure in the present invention is not particularly limited, but specifically, for example, 6 to 150
Preferably, the cell density is in the range of 0 cell/In2 (0.9 to 233 cells/C2).

Further, the thickness of the partition wall is preferably in the range of 50 to 2000 JL.

Further, as mentioned above, the honeycomb structure may be porous or non-porous, and the porosity is not limited or is 0 to 0.
From the viewpoint of strength properties, oxidation resistance, and corrosion resistance, it is desirable that the range is less than 50%, preferably less than 25%. Further, when supporting a catalyst, it is preferable to have a porosity of 5% or more from the viewpoint of adhesion with the catalyst layer.

In the present invention, the honeycomb structure refers to an integral structure having a large number of through holes partitioned by partition walls, and the cross-sectional shape (cell shape) of the through holes may be any arbitrary shape such as circular, polygonal, corrugated, etc. You can use any shape.

[Examples] Hereinafter, the present invention will be explained in more detail based on illustrated embodiments, but the present invention is not limited to these embodiments.

FIGS. 1(a) and 1(b) are schematic plan views showing examples of two types of honeycomb type heaters with outer diameters of 90 mm and 120 mm, respectively. A plurality of slits 11 are provided as a resistance adjustment mechanism, and the outer peripheral portion 12 of the slit 11 is filled with an inorganic adhesive to insulate it.
Two electrodes are installed on the outer wall of the heater, creating a honeycomb-shaped heater.

Figure 2 (a) and (b) have outer diameters of 90mm and 12mm, respectively.
This shows a catalytic converter in which two types of honeycomb heaters 10 of 0 m-φ are installed on the upstream side of the exhaust gas A of the main monolith catalyst 14. Note that 16 is an outer frame.

Next, specific implementation results will be explained.

(Example) Fe powder, Fe-C so that it becomes Fe-20Cr-5A pattern
After mixing R powder and Fe-An powder, extrusion molding and firing in H2 atmosphere resulted in partition walls (ribs) with a thickness of 4 cm (11 mm).
400 cells/inch2 (cp
i2), outer diameter 90mm, made of 15cm thick, diameter φ
Two types of honeycomb structures with diameters of 1 and 120 mm were obtained.

A slit 11 is made in the obtained honeycomb structure 10 as shown in FIGS. 1(a) and 1(b), and a ZrO
It was filled with two types of inorganic adhesive and insulated. The slit 11 is
The number of partition walls (ribs) between the slits and the slits was 8, that is, there were 7 cells between the slits.

Furthermore, 8 wt of CeO2 was added to this honeycomb structure lO.
It was coated with γ-alumina containing 1z 20 g/ft3, and then Pd and pt were supported at 1z 20 g/ft3 each, and catalyzed by firing at 600°C. Obtained honeycomb structure with catalyst lO
Electrodes 13 were set in two places on the outer wall of the
As shown in b), outer diameter 90111φ, length 100m■
A commercially available three-way catalyst (rib thickness 611,
The number of through holes was 400 tons/inch2) 14 (on the gas upstream side).

In addition, the heater with an outer diameter of 120 mφ is as shown in Figure 3.
The outer circumferential portion 15 10 mm from the outer circumference was sealed with a heat insulating material to prevent exhaust gas from flowing.

The heat generating portion of the heater having an outer diameter of 90 mmφ formed as described above was approximately 70 mmφ, and the heat generating portion of the heater having an outer diameter of 120+mφ was approximately 90 mmφ.

In order to check the performance of this system when starting the engine, the exhaust gas from the engine (A/F = 14.6) is heated to 100°C.
to 420°C for 2 minutes (constant temperature increase), then 420°C
The temperature was kept at °C for 1 minute, and the purification rate of each emission was measured. Power the heater at 24V for 5 seconds, then turn on 12V so that the heater temperature reaches 450'C.
On-off control was performed. Show the results on your robe.

The catalyst on top of the catalyst also showed an effective purification effect because the temperature reached a wider range, resulting in a high purification rate.

[Effects of the Invention] As explained above, according to the heater and catalytic converter of the present invention, the resistance adjusting means is formed so that the cross section of the heat generating part of the heater is substantially the same as the cross section of the main monolith catalyst attached thereto. The heater heats the entire main monolith catalyst relatively uniformly, and the catalyst on the heater also reaches a high temperature over a wider area, so it exhibits an effective purification effect.

As is clear from the results in the table, the heater with an outer diameter of 120 lφ has almost the same heat generation area as the main monolith catalyst at the rear (downstream side of the gas), so it can heat the entire main monolith catalyst relatively uniformly and at the same time. , Hi

[Brief explanation of the drawing]

@ Figure 1 (a) (b) is a schematic plan view showing examples of two types of honeycomb heaters with different outer diameters, Figure 2 (a) (b)
) is a cross-sectional view showing a type of catalytic converter in which two types of honeycomb heaters with different outer diameters are installed upstream of the main monolith catalyst, and Figure 3 is a perspective view showing an example in which the outer periphery is sealed with a heat insulating material. be. lO...Honeycomb structure, 11...Slit, 12
...Outer peripheral part, 13... Electrode, 14... Main monolith catalyst, 15... Outer peripheral part, 16... Outer frame. Figure 2 (a)

Claims (9)

[Claims] (1) A heater in which a honeycomb structure is provided with at least two electrodes for energizing, and a resistance adjustment means is provided between the electrodes, and the cross section of the heat generating part of the heater is substantially the same as the cross section of the main monolithic catalyst. A resistance adjustment type heater characterized in that the resistance adjustment means is formed so that the resistance adjustment means is formed so as to be. (2) The resistance-adjustable heater according to claim 1, wherein the cross-sectional diameter of the heater is larger than the cross-sectional diameter of the main monolithic catalyst. (3) The resistance-adjustable heater according to claim 1, wherein the heater supports a catalyst. (4) The resistance-adjustable heater according to claim 1, wherein the resistance-adjusting means is formed by forming slits. (5) The heater is provided with at least two electrodes for supplying electricity to the honeycomb structure on the upstream side of the main monolithic catalyst or between the main monolithic catalysts, and has a resistance adjustment means between the electrodes. A catalyst characterized in that a resistance-adjustable heater is disposed in which the resistance-adjusting means is formed so that the cross-section of the heat-generating portion of the heater is substantially the same as the cross-section of the main monolithic catalyst downstream of the heater. converter. (6) A heater in which a honeycomb structure supports a catalyst and at least two electrodes for energization are provided on the downstream side of the main monolithic catalyst, and a resistance adjustment means is provided between the electrodes, and the heater generates heat. A catalytic converter characterized in that a resistance-adjustable heater is disposed in which the resistance-adjusting means is formed so that a partial cross-section thereof is substantially the same as a cross-section of the main monolithic catalyst. (7) The catalytic converter according to claim 5 or 6, wherein the cross-sectional diameter of the heater is larger than the cross-sectional diameter of the main monolith catalyst. (8) The catalytic converter according to claim 5, wherein the heater supports a catalyst. (9) The catalytic converter according to claim 5 or 6, wherein the resistance adjusting means is formed by forming slits.