JPH06254403A - Exhaust gas purification device - Google Patents

Abstract

PURPOSE:To provide an exhaust gas purification catalyst which is capable of shortening the time required until catalytic activity appears without supplying energy during engine start, especially during the second round of the start. CONSTITUTION:One end of plane sheet 4 of SUS430 to which aluminum is flame-sprayed, is brazed to a pipe 2 of SUS304, then a corrugated sheet 5 of SUS 430 to which aluminum is flame-sprayed is rolled into an area between the pipe 2 and the plane sheet 4 in a swirl from, and the outer peripheral end is brazed to form a honeycomb carrier. Further, this honeycomb carrier is thermally treated at 800 deg.C, then is wash-coated using activated alumina, and baked at 550 deg.C. After that, the honeycomb carrier is soaked in an aqueous palladium nitrate solution, and is again baked at 550 deg.C. Next, zirconia balls are charged in the pipe 2 as a heat accumulator. Consequently, time required until catalytic activity appears during the second and following round of engine start, and exhaust gas purification performance at the time of start is enhanced.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an exhaust gas purifying catalyst, and particularly to various kinds of hydrocarbons in exhaust gas discharged from various industries such as automobile exhaust gas, for example, chemical plants.
The present invention relates to an exhaust gas purifying catalyst for removing combustible harmful substances such as carbon monoxide.

[0002]

2. Description of the Related Art In recent years, exhaust gas regulations of automobiles have become more and more strict, and improvement in performance of exhaust gas purifying catalysts has been strongly demanded. A ceramic honeycomb catalyst is known as an exhaust gas purifying catalyst for an automobile using an internal combustion engine as a power source, for example. By the way, in the case of engines such as automobiles and generators where cold start is unavoidable, the temperature of the engine can be increased from the start of operation to the ignition temperature of fuel.
The fuel supplied to the engine is prone to incomplete combustion. Moreover, since the exhaust gas purifying catalyst has not reached a sufficiently high temperature, the exhaust gas passing through the catalyst is discharged to the atmosphere without being substantially processed. Therefore, in such a cold-start engine, a large amount of unburned harmful components are easily discharged at the time of startup. This tendency becomes even stronger when a ceramic honeycomb catalyst having a low thermal conductivity is used as the exhaust gas purifying catalyst.

On the other hand, in order to prevent such an adverse effect,
Metal honeycomb catalysts with high thermal conductivity have been developed. FIG. 3 is a perspective view of a conventional metal honeycomb catalyst. In the figure, there is shown a metal honeycomb catalyst in which a catalyst component is carried on a honeycomb catalyst carrier in which a corrugated metal plate and a flat metal plate are superposed and spirally wound. Such a metal honeycomb catalyst has a high thermal conductivity, and the time required from starting to reaching the temperature at which the catalyst activity is exhibited becomes short. In addition, such a self-heatable catalyst in which an electrode is built into the metal honeycomb catalyst can significantly reduce the time required from the start-up to the manifestation of catalytic activity by rapidly increasing the catalyst temperature immediately after the start of operation. Therefore, it is attracting attention as being able to improve the exhaust gas purification performance immediately after the start of operation.

[0004]

However, the above-mentioned metallic honeycomb catalyst has a problem that the cooling rate after the engine is stopped is high as a characteristic opposite to the characteristic that the thermal conductivity is high, and therefore the second engine after the engine is stopped once is stopped. At the time of start-up, it becomes a cold start state again, and starts and stops repeatedly. For example, it is not satisfactory as an exhaust gas purifying catalyst for automobiles.

On the other hand, a metal honeycomb catalyst having a built-in electrode is intended to shorten the time required for the catalytic activity to be exhibited.
A current of several hundred amperes is required, and there is a problem that the electric system and the battery are overloaded. An object of the present invention is to solve the above-mentioned problems of the prior art, and to significantly shorten the time required from the start to the activation of the catalyst without the need to replenish energy when starting from the second time. An object of the present invention is to provide an exhaust gas purifying catalyst that can effectively improve the exhaust gas purifying performance at startup.

[0006]

The above object can be achieved by filling the central portion of the catalyst substrate with a heat storage material or a material having a heat storage effect. That is, the first invention of the present application is an exhaust gas purifying catalyst in which a catalytically active component is supported on a honeycomb catalyst carrier composed of a corrugated metal plate and a flat metal plate, and a hermetically sealed container is arranged at the center of the honeycomb catalyst carrier. The present invention also relates to an exhaust gas purifying catalyst, characterized in that the closed container is filled with a heat storage material.

A second aspect of the present invention is an exhaust gas purifying catalyst comprising a honeycomb catalyst carrier in which a corrugated stainless steel plate and a flat stainless steel plate are superposed and spirally wound to carry a catalytically active component. The exhaust gas purifying catalyst is characterized in that a pipe that can be sealed is arranged in a portion, and the pipe is filled with a heat storage material.

[0008]

[Function] By filling the central portion of the metal honeycomb catalyst with a heat storage material so as to have a heat storage function, the high temperature is maintained even after the engine is stopped, and the temperature reaches the temperature at which the catalyst activity is exhibited at the time of starting from the second time. Since the time required up to is shortened, it becomes easier to purify the exhaust gas discharged from the automobile engine at the time of startup, which contains a large amount of unburned components. Also,
By filling the heat storage material in the airtight container, the outer portion of the airtight container acts as a heat radiation suppressing member, so that a higher heat storage effect can be obtained.

In the present invention, for example, a heat storage material-filled pipe is used as the closed container arranged in the central portion of the honeycomb catalyst carrier, but the diameter of the pipe is not particularly limited as long as the activity of the catalyst is not deteriorated. Not done. That is, the pipe diameter can be set to about 10% of the effective cross-sectional area of the catalyst if the allowable range for the catalyst activity to fall is set to about 10%. Therefore, for example, the diameter of the metal honeycomb catalyst is 70 to 1
When the length is 00 mm, the allowable diameter of the heat storage material filled pipe is about 25 mm.

In the present invention, the heat storage material is preferably one having a large specific heat and a large specific gravity and a large physical strength, for example, a so-called heat storage material such as cast iron, zirconia or cermet is used. Further, as a material for enhancing the heat storage effect, a porous material having a large number of minute spaces, such as a foam material, can be used. In the present invention, the honeycomb catalyst carrier is preferably used by spirally winding a corrugated stainless steel thin plate and a flat plate-shaped stainless steel thin plate, and its structure, for example, the number of cells, the thickness of the thin plate, etc. There is no particular limitation. Further, the type of metal may be other than stainless steel. Further, the material of the heat storage material filled pipe which is a closed container, it is preferable to use the same kind of the honeycomb catalyst carrier, for example,
Stainless steel is used.

In the present invention, it is preferable to provide the honeycomb catalyst carrier with heating means, for example, a heating electrode. As a result, not only at the second and subsequent startups, but also at the first startup and the startup after a long period of rest, it is possible to shorten the time until the catalytic activity is expressed. In addition,
In the present invention, the heat capacity of the catalyst itself in the honeycomb catalyst can be made relatively small by relatively increasing the diameter of the closed container filled with the heat storage material, for example, the pipe, so that the temperature rising rate of the catalyst becomes faster. The secondary effect is obtained. In addition, the weight of the heat storage material filled in the closed container is preferably about 20 to 40% of the total weight of the catalyst, whereby a sufficient heat storage effect can be obtained. If the diameter of the pipe filled with the heat storage material is about 25% of the catalyst diameter as described above, even if the heat storage material having a specific gravity of 6 is densely packed, the weight of the pipe is 20 to 20% of the total weight of the catalyst. It can be within the range of 40%.

[0012]

EXAMPLES Next, the present invention will be described in more detail by way of examples. 1 is an explanatory view showing an embodiment of the present invention, FIG.
FIG. 11 is a sectional view taken along line II-II of FIG. This exhaust gas purifying catalyst is different from the conventional technique of FIG. 3 in that a heat storage material filling pipe 2 is arranged as a closed container in the center of a spiral metal honeycomb catalyst body 1, and the heat storage material 3 is placed in the heat storage material filling pipe 2.
Is the point filled.

Example 1 SU having a diameter of 25 mm, a wall thickness of 0.5 mm and a length of 130 mm
A heat storage material filled pipe 2 made of S304, SUS4 having a thickness of 0.2 mm and a width of 100 mm formed by spraying aluminum on both surfaces.
One end of a flat plate 4 made of 30 is brazed and then expanded between the heat storage material filled pipe 2 and the flat plate 4 and then sprayed with aluminum and corrugated to a height of about 2.5 mm. Thickness 0.2mm, width 100m
m corrugated sheet 5 made of SUS430 was wound, wound in a spiral shape, and brazed so that the outermost circumferences of the flat plates 4 overlap each other to obtain a honeycomb structure having a diameter of 80 mm and a length of 100 mm. The apparent volume of this honeycomb structure is 470 m.
It is l. Next, this honeycomb structure was once heat-treated at 800 ° C. to oxide the aluminum sprayed layer, wash-coated with activated alumina, and then fired at 550 ° C. Then, it was immersed in an aqueous solution of palladium nitrate to prepare a palladium content of about 1 g / l, dried, and finally calcined again at 550 ° C. Then, a zirconia ball having a diameter of 1 mm is filled as a heat storage material into the heat storage material-filled pipe 2 in the central portion, and then both ends of the pipe 2 are SU
The exhaust gas purifying catalyst was brazed with an S304 lid.

According to the present embodiment, the pipe 2 filled with the heat storage material 3 is arranged in the central portion, so that the heat storage effect is obtained and, for example, the temperature drop during cooling after the engine of the automobile is stopped is reduced. Therefore, the exhaust gas purification rate at the time of restart is improved. Further, since it is possible to prevent moisture from adhering to the catalyst during cooling after the engine is stopped, it is possible to avoid heat loss due to latent heat due to evaporation of moisture during restart.

Example 2 An exhaust gas purifying catalyst was constructed in the same manner as in Example 1 except that a flat plate made of SUS430 having a thickness of 1 mm was welded to the flat plate 4 on the outer peripheral portion of the exhaust gas purifying catalyst as an energizing electrode.
The exhaust gas purifying catalyst can generate heat by passing an electric current between the heat storage material filled pipe 2 in the central portion and the electrode in the outer peripheral portion. The electric resistance between both electrodes was 0.07Ω.

According to the present embodiment, the exhaust gas purifying catalyst provided with the current-carrying electrode is filled with the heat storage material in the central portion,
It is possible to remarkably shorten the temperature rising time from the start-up to the manifestation of catalytic activity. The shortening of the temperature raising time directly leads to the reduction of the amount of electric power used, and the burden on the battery and the electric system can be reduced. Further, according to this embodiment,
By relatively increasing the diameter of the heat storage material-filled pipe 2 arranged in the center of the catalyst, the catalyst center and the outer periphery due to the imbalance between heat generation and heat radiation, as seen in the conventional energization type catalyst, are formed. The temperature difference is extremely small, and the catalyst temperature during energization tends to be uniform in the radial direction. Therefore, the catalyst performance is uniformly exhibited, and the exhaust gas purification rate is improved.

Comparative Example 1 An exhaust gas purifying catalyst was constructed in the same manner as in Example 1 except that the heat storage material-filled pipe 2 in the central portion was not filled with the heat storage material. The exhaust gas purifying catalysts of Examples 1 and 2 and Comparative Example 1 were each connected to an exhaust gas line of an automobile engine, operated for 30 minutes under a constant condition, and then the engine was stopped.
After 0 minutes, the engine was started again under the same conditions, and the temperature rising / cooling curve of the exhaust gas purifying catalyst was obtained. However, in the performance test of the exhaust gas purifying catalyst of Example 2, a voltage of 12 V was applied between both electrodes for 30 seconds at the same time when the engine was started to heat the catalyst.

The test results are shown in FIG. 4, in Examples 1 and 2, the cooling rate after the engine is stopped is slower than that in Comparative Example 1, and the temperature rising rate after the engine is restarted is high. Particularly, the temperature rising rate in Example 2 is remarkably high. I understand. Since the temperature at which the activity of a normal three-way catalyst for exhaust gas purification is expressed is 250 to 400 ° C., the exhaust gas purification catalyst of the present example until the temperature at which the catalytic activity is expressed is reached at the time of starting from the second time. The time required for
It can be shortened to / 2-1 / 4.

[0019]

According to the invention described in claim 1 of the present application, in the apparatus in which the start and stop is repeated by disposing the closed container filled with the heat storage material in the center of the exhaust gas purifying catalyst,
Since the time required for the catalyst activity to appear at the second and subsequent startups can be significantly shortened, the exhaust gas purification performance at the initial stage of operation can be improved.

According to the invention of claim 2 of the present application, the heat storage material is filled in the central portion of the exhaust gas purifying catalyst in which the catalytically active component is carried on the honeycomb catalyst carrier composed of the corrugated stainless steel thin plate and the flat plate-shaped stainless steel thin plate. By disposing the pipe and filling the heat storage material in the pipe, it is possible to improve the exhaust gas purification performance at the beginning of the operation at the time of starting the device that repeats the start and stop, for example, the automobile engine from the second time.

[Brief description of drawings]

FIG. 1 is an explanatory diagram of an exhaust gas purifying catalyst showing an embodiment of the present invention.

FIG. 2 is a sectional view taken along the line II-II of FIG.

FIG. 3 is a perspective view showing a conventional technique.

FIG. 4 is a view showing a result of a performance test of an exhaust gas purifying catalyst.

[Explanation of symbols]

1 ... Metal honeycomb catalyst body, 2 ... Heat storage material filling pipe, 3
... Heat storage material, 4 ... Flat plate, 5 ... Corrugated plate.

Claims (2)

[Claims] 1. An exhaust gas purifying catalyst comprising a catalytically active component supported on a honeycomb catalyst carrier comprising a corrugated metal plate and a flat metal plate, wherein a hermetically sealed container is arranged at the center of the honeycomb catalyst carrier. An exhaust gas purifying catalyst having a heat storage material filled therein. 2. An exhaust gas purifying catalyst in which a catalytically active component is supported on a honeycomb catalyst carrier, which is formed by superposing a corrugated stainless steel plate and a flat stainless steel plate and wound in a spiral shape, and can be hermetically sealed at the center of the honeycomb catalyst carrier. An exhaust gas purifying catalyst, characterized in that a simple pipe is arranged and a heat storage material is filled in the pipe.