JPH0481509A - Catalyst converter for purifying exhaust gas of automobile - Google Patents

Abstract

PURPOSE:To heat exhaust gas at the time of a low temperature, and ensure exhaust gas purifying performance at the time of cold starting by setting a honeycomb and a heater upstream and downstream of a main monolith catalyst. CONSTITUTION:In a honeycomb heater, a plurality of slits 11 serving as a resistance adjusting mechanism are provided on a honeycomb structure 10 having multiple penetration holes 12, and two electrodes 13 are provided on the outer wall thereof. The honeycomb heater or heater catalysts 14 are provided forward (an exhaust gas upstream side) and backward (an exhaust gas downstream side) of a main monolith catalyst 15. It is thus possible to ensure exhaust gas purifying performance at the time of a low temperature of exhaust gas. And it is also possible to prevent a metal carrier itself from corroding.

Description

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

[Prior art] Catalytic converters used to purify automobile exhaust scum need to be heated to a predetermined temperature or higher in order for the catalyst to exert its catalytic action. If the temperature of the catalyst has not risen sufficiently, it will be necessary to heat the catalyst.

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

[Question 8 to be solved by the invention] However, since catalyst components such as a monolith catalyst deteriorate from the upstream side of the exhaust residue, in the catalytic converter described in Utility Model Application Publication No. 63-67609, the main monolith catalyst The catalyst component of the metal monolith catalyst as a preheater placed close to the upstream side deteriorates first, and the exhaust gas purification ability at low temperature of the exhaust gas decreases. Another problem is that there is a large risk that the metal carrier itself will corrode.

[Means for Solving the Problems] Therefore, as a result of various studies, the inventors of the present invention solved the problem by arranging heaters on the upstream and downstream sides of the main monolith catalyst.
The inventors have discovered that the above drawbacks can be overcome, and have arrived at the present invention.

That is, according to the present invention, there is provided a catalyst for purifying automobile exhaust gas, characterized in that a honeycomb heater comprising a honeycomb structure provided with at least two energized electrodes is disposed on the upstream and downstream sides of the main monolithic catalyst. converter, or provided.

Further, in the present invention, it is preferable that the honeycomb heater disposed at least on the downstream side of the upstream side and the downstream side of the main monolithic catalyst has a catalyst supported on the honeycomb structure.

Furthermore, as a honeycomb heater, one having a resistance adjustment mechanism such as a slit between electrodes is preferable because it has excellent heat generation characteristics. Note that it is preferable that the honeycomb structure of the present invention is formed by extruding metal powder into a honeycomb shape and sintering it.

Further, in the case of the present invention, two or more honeycomb heaters may be provided on the upstream side and the downstream side of the main monolith catalyst.

[Function] The present invention is characterized in that honeycomb heaters each having a honeycomb structure provided with at least two electrodes for supplying electricity are disposed upstream and downstream of the main monolithic catalyst.

If a honeycomb heater is provided only upstream of the main monolithic catalyst, the catalyst on the honeycomb heater will deteriorate during actual use, and the purification performance at cold start will deteriorate.

On the other hand, if a honeycomb heater is installed only on the downstream side of the main monolithic catalyst, the heat capacity of the main monolithic catalyst on the upstream side is large at the time of a cold start, so the exhaust gas temperature does not rise easily, and the catalyst rises slowly, resulting in power consumption. becomes larger.

Therefore, by installing honeycomb heaters on the upstream and downstream sides of the main monolithic catalyst as in the present invention, the above-mentioned problems do not occur and the exhaust gas can be heated at low temperatures such as when starting the engine. , and by having two or more honeycomb heaters, it is possible to adjust the heating as necessary.

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 made of metal or ceramic, but metal is preferred because of its high mechanical strength. . In the case of metals, for example, stainless steel, Fe-Cr-Al, Fe-Cr, Fe
-A, material having a composition such as Fe-N1, W-Co, Ni-Cr, etc. may be mentioned. Of the above, F
eCr-An, Fe-Cr, and Fe-AfL are preferable because they have excellent heat resistance, oxidation resistance, and corrosion resistance, and are inexpensive.

The honeycomb structure may be porous or non-porous, but when supporting a catalyst, the adhesion to the catalyst layer is strongly determined by the difference in thermal expansion between the porous honeycomb structure and the catalyst layer. This is preferable because it hardly causes peeling of the catalyst.

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, 1, for example, Fe powder, AM 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 polyhinyl alcohol, and water, and then this mixture is extruded into a desired honeycomb shape.

Next, the extruded honeycomb molded body is fired at 1000 to 1450°C in a non-oxidizing atmosphere. If firing is performed in a non-oxidizing atmosphere containing hydrogen, the organic binder or Fe etc. will be used as a catalyst to decompose and remove the material, resulting in a good sintered body (
A honeycomb structure) can be obtained, which is preferable.

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.

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

Next, desirably, regarding the obtained honeycomb structure,
A resistance adjustment mechanism is provided between the electrodes in various ways, 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

The metallic honeycomb structure obtained in the manner described above is usually provided with electrodes on the outer peripheral partition wall or inside thereof by brazing, welding, or the like to produce a honeycomb heater.

Note that the term "electrode" as used herein is a general term for terminals for applying voltage to the heater, and includes terminals such as those directly connected to the outer periphery of the heater such as a can, 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 o, ooiΩ to 0.5Ω.

Further, by further supporting a catalyst on the surface of the above-mentioned metallic honeycomb structure, it is possible to expect a temperature increase due to the purification reaction of the exhaust residue (heat of # conversion reaction, etc.), which is preferable.

The catalyst supported on the surface of the metallic honeycomb structure is a carrier having a large surface area that supports a catalytically active substance. Here, examples of carriers having a large surface area include γ-A203 series, TlO2 series, 5iO2-A203 series, and 5iO2-A203 series.
Typical examples include the 3-series and belovskite-series. Examples of catalytically active substances include Pt, P
Examples include noble metals such as dRh, and base metals such as Cu, Ni, Cr, and Co. Among the above, y A l
It is preferable to use 203 series with Pt or Pd supported at 10 to 100 g/ft3.

The honeycomb shape of the honeycomb 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 g.

Further, as mentioned above, the honeycomb structure may be porous or non-porous, and its porosity is not limited, but may range from 0 to
From the viewpoint of strength, oxidation resistance, and corrosion resistance, it is desirable that the content be within the range of 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 described in more detail based on illustrated embodiments, but the present invention is not limited to these embodiments.

FIG. 1 is a plan view showing an example of a honeycomb heater supporting a catalyst of the present invention.
and two electrodes 13 are installed on its outer wall to form a honeycomb heater.

FIGS. 2 to 4 are explanatory diagrams showing the construction of an embodiment of a catalytic converter for purifying automobile waste according to the present invention.

FIG. 2 shows an example in which honeycomb heaters or heater catalysts 14 are arranged in front of the main monolithic catalyst 15 (exhaust gas upstream side) and behind (exhaust gas downstream side).

FIG. 3 shows an example in which a honeycomb heater or heater catalyst 14 is arranged on the upstream and downstream sides of the main monolith catalyst 15, and a main monolith catalyst or ignition catalyst 16 is further arranged on the downstream side of the honeycomb heater or heater catalyst l4. and the fourth
The figure shows an example in which honeycomb heaters or heater catalysts 14 are disposed upstream and downstream of the main monolithic catalyst 15, and a main monolithic contact 117 is further disposed upstream of the honeycomb heater or heater catalyst 14.

Next, specific implementation results will be explained.

(Example) Fe powder, Fe-C to become Fe-20Cr-5Al
After mixing R powder and Fe-A powder, extrusion molding and baking in an H2 atmosphere resulted in an outer diameter of 935 mφ and a thickness of 1.
5. A honeycomb structure with a heat treatment, a cell wall (rif) thickness of 8 layers j1, and a through hole number of 300 cells/inch2 (CPI2) was obtained. As shown in FIG.
Slits 11 with a length of 0 mm (the slit length at both ends is about 50 mm) are provided at 6 locations in the axial direction of the through hole 12, and the number of cells between the slits 11 is 4 (about 8 + W door). Formed.

Further, this honeycomb structure 10 was coated with γ-alumina, and then precious metals PT and Pd were each coated at 20 g/ft.
' It was supported and calcined at 600°C to become a catalyst. Thereafter, as shown in FIG. 1, electrodes 13 were set at two locations on the outer wall to form a heater catalyst 14.

The obtained heater catalyst 14 was installed in front (upstream side of !i gas) and behind (downstream side of exhaust gas) a commercially available three-way catalyst 15, which is the main monolithic catalyst, as shown in FIG.

In order to check the performance of this system when starting the engine,
Increase the temperature of introduced waste waste A from lOOoC to 420°C 2
The temperature was raised at a constant rate for 1 minute, and then the temperature was kept at 420°C for 1 minute (ohm-up test), and the purification rate of Co, HC, and No was measured. The heater catalysts 14 installed in front and behind the main monolithic catalyst 15 were energized for 1 minute using a 12V battery so that the exhaust gas temperature was 350°C.

For comparison, an ohm-up test was conducted using a heater catalyst installed behind the main monolithic catalyst 15 under the same conditions as above.

These results are shown in Table 1.

Next, as a durability test, a test was conducted in which the exhaust gas temperature was raised from room temperature to 750°C, held at 750°C for 10 seconds, and a cycle of 60 seconds of operation and 5 seconds of fuel cut was repeated while the temperature was maintained at 750°C. The heater catalyst 14 continued to be energized one minute before the engine was started until the exhaust gas temperature reached 350°C in the same manner as described above.

After repeating this durability test 10 times, the above-mentioned ohm-up test was conducted to measure the purification rate of CO, HC, and NOx.

For comparison, a durability test was conducted under the same conditions as above for a device in which a heater catalyst was installed in front of the main monolithic catalyst 15, and then an ohm-up test was conducted.

The results are shown in Table 2.

Table 1 Average purification rate (2) (warm-up test) Table 2-v Average purification rate (2) (warm-up test after durability test) [Effects of the invention As explained above, according to the present invention, By installing honeycomb heaters upstream and downstream of the main monolith catalyst, it is possible to heat exhaust gas at low temperatures, such as when starting the engine. Additionally, even if the catalyst in the upstream heater deteriorates during actual use, the downstream honeycomb heater can ensure exhaust gas purification performance during a cold start.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing an example of a honeycomb heater supporting a catalyst of the present invention, and FIGS. 2 to 4 are configuration explanatory diagrams showing embodiments of a catalytic converter for purifying automobile exhaust gas according to the present invention. 10...Honeycomb structure, 11...Slit, 12
... Through hole, 13 ... Electrode, 14 ... Honeycomb heater or heater catalyst, 15 ... Main monolith catalyst,
16... Main monolith catalyst or ignition catalyst, 17...
Main monolith catalyst.

Claims (4)

[Claims] (1) A catalytic converter for purifying automobile exhaust gas, characterized in that a honeycomb heater having a honeycomb structure provided with at least two electrodes for supplying electricity is disposed upstream and downstream of a main monolithic catalyst. (2) The catalytic converter according to claim 1, wherein the catalyst is supported by a honeycomb heater or a honeycomb structure disposed at least on the upstream side and downstream side of the main monolithic catalyst. (3) The catalytic converter according to any one of claims 1 to 2, wherein the honeycomb heater is provided with a resistance adjustment mechanism between the electrodes. (4) The catalytic converter according to any one of claims 1 to 3, wherein the honeycomb structure is formed by molding metal powder into a honeycomb shape and sintering it.