JP2006281118A - Metallic catalyst carrier - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metallic catalyst carrier without causing any difference in the exhaust gas cleaning performance of a metallic honeycomb body all over the exhaust gas outlet of the metallic honeycomb body even when the metallic honeycomb body has high cell density of >200 cells/in<SP>2</SP>. <P>SOLUTION: The metallic honeycomb body 2 obtained by winding metallic flat foil 4 and metallic corrugated foil 5 is used in the metallic/catalytic carrier 1. The metallic honeycomb body 2 has a center hole 7 penetrating the metallic honeycomb body in the central part of the axis thereof. An insert 8 through which exhaust gas is hindered from flowing is arranged in the center hole 7. As a result, the amount of exhaust gas passing through the center hole 7 can be made extremely small and the cleaning performance of the exhaust gas passing near the central part of the axis of the metallic honeycomb body can be made nearly equal to that of the exhaust gas passing through any part other than the central part of the axis. Furthermore, the oxygen concentration in exhaust gas can normally be detected stably by an oxygen sensor and the catalysis can be controlled stably. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a metal catalyst carrier used for the purpose of purifying exhaust gas of an internal combustion engine.

For the purpose of purifying the exhaust gas of the internal combustion engine, a catalytic converter carrying a catalyst is disposed in the exhaust gas path. Also, a methanol reformer that steam-reforms a hydrocarbon compound such as methanol to produce a hydrogen-rich gas, a CO remover that reforms and removes CO to CO ₂ , or H ₂ is burned to produce H ₂ O. In the H ₂ combustion apparatus that removes the catalyst in the same manner, a carrier carrying a catalyst is similarly used. These catalyst carriers have a large number of cells through which gas passes, and the walls of each cell are coated with the catalyst, so that the gas passing through and the catalyst can come into contact with each other with a wide contact area.

  Examples of the catalyst carrier used for these purposes include a ceramic catalyst carrier and a metal catalyst carrier. As shown in FIG. 3, the metal catalyst carrier is formed into a cylindrical metal honeycomb body 2 by alternately laminating and winding flat foils 4 and corrugated foils 5 each having a thickness of several tens of μm using a heat-resistant alloy. The metal honeycomb body 2 is inserted into a cylindrical metal outer cylinder 3 to form a metal carrier. For example, a porous γ-alumina layer called a washcoat layer is coated on the surface of the metal foil of the cell 6 of the honeycomb body that becomes the gas passage of the metal carrier. Next, a catalyst support layer is formed by a method of impregnating a catalyst made of noble metal or the like into this wash coat layer, or a method of coating a metal support with a wash coat layer containing a catalyst in advance, and a metal catalyst support 1 supporting the catalyst. And

Since the catalytic reaction when the gas passes through the catalyst carrier proceeds at the interface between the catalyst carrier layer and the gas, the reaction is promoted as the surface area of the catalyst carrier layer contacting the gas in the catalyst carrier increases. In the cross section perpendicular to the passage through which the gas of the catalyst carrier passes, the number of cells per unit cross-sectional area of the honeycomb body is called cell density and is expressed in cells / in ² . As the cell density is higher, the surface area where the catalyst and the gas are in contact with each other per unit cross-sectional area of the catalyst carrier is increased, so that the purification rate is expected to be improved. For example, in an exhaust gas purification catalyst carrier for automobiles, a metal carrier having a cell density of about 200 to 600 cells / in ² , particularly about 400 cells / in ² has been used.

In recent years, there has been a demand for further reduction in catalyst reaction efficiency while reducing the size and weight of the catalyst carrier. In the invention described in Patent Document 1, a metal catalyst carrier having a cell density of more than 600 cells / in ² , further 800 cells / in ² or more, or 1000 cells / in ² or more is employed, and the catalyst is supported. By reducing the thickness of the layer 5 as compared with the conventional one, the catalytic reaction efficiency similar to the conventional one can be maintained even in a metal catalyst carrier that is smaller and lighter than the conventional one, or the same size as the conventional one A metal catalyst carrier capable of increasing the catalytic reaction efficiency is disclosed.

  When purifying exhaust gas from an internal combustion engine using a catalyst carrier, catalytic reaction control may be performed. In the exhaust gas path, an oxygen sensor is placed immediately after passing through the catalyst carrier, the oxygen concentration in the exhaust gas after the catalytic reaction is measured, and the degree of catalytic reaction (catalytic efficiency) is detected from the measured value. A device has been devised to highly stabilize the catalyst efficiency by feeding back data to the engine control system and performing electronic control such as fuel injection valve timing. It is important that the measured oxygen concentration value to be obtained here is a representative value (average value) of the exhaust gas oxygen concentration after passing through the catalyst in order to achieve the above-mentioned object efficiently.

JP 2002-119869 A

In a metal catalyst carrier in which a metal honeycomb body is formed by winding a metal flat foil and a corrugated foil, and a catalyst support layer is formed on the cell surface through which the gas of the metal honeycomb body passes, the cell density is about 200 cells / in. ^When a metal honeycomb body having a high cell density exceeding ² was used, it was found that the catalyst purification performance varies depending on the radial direction position of the honeycomb body outlet. That is, it is clear that the degree of purification of exhaust gas that has passed through the vicinity of the axial center of the honeycomb body is somewhat lower than the degree of purification of exhaust gas that has passed through other parts of the honeycomb body. It was.

  In addition, in an exhaust gas purification system for an internal combustion engine using a metal catalyst carrier, when performing a catalytic reaction control, the measurement of the oxygen concentration sensor placed immediately after the catalyst carrier in the exhaust gas path becomes unstable, and the catalytic reaction control becomes impossible. It may not be possible to perform stably.

It is an object of the present invention to provide a metal catalyst carrier in which the purification performance does not vary across the exhaust gas outlet of the honeycomb body even in the case of a high cell density metal honeycomb body having a cell density exceeding 200 cells / in ^2. Objective. Another object of the present invention is to stabilize the measurement of the exhaust gas oxygen concentration in catalytic reaction control and to enable stable catalytic reaction control.

When the metal flat foil 4 and the corrugated foil 5 are wound to form the metal honeycomb body 2, the flat foil 4 and the corrugated foil 5 are joined around the metal winding shaft 21 as shown in FIG. A honeycomb body is formed by winding. When the formation of the metal honeycomb body 2 having a predetermined diameter is completed, the winding shaft 21 is removed from the honeycomb body. As a result, a central hole 7 having an inner diameter substantially equal to the diameter of the winding shaft 21 and penetrating the metal honeycomb body 2 is formed in the axial center portion of the honeycomb body (FIG. 3). The diameter of the winding shaft 21 requires a diameter of about 3 to 5 mm in order to maintain the rigidity required when the metal flat foil 4 and the corrugated foil 5 are wound to form the metal honeycomb body 2. Therefore, for example, when the winding shaft diameter is 5 mm, the inner diameter of the center hole 7 is about 5 mm, and in this case, the cross-sectional area of the center hole 7 is about 20 mm ² .

For example, in the case of a high cell density metal honeycomb body with a cell density exceeding 900 cells / in ² , the cross-sectional area of each cell 6 is less than 0.7 mm ² . That is, the sectional area of the center hole 7 is much larger than the sectional area of the cell 6. For this reason, the exhaust gas passing through the metal honeycomb body 2 flows preferentially to the center hole 7 over the cells 6 other than the center hole, and although the catalyst is also carried on the inner wall of the center hole 7, it is highly purified. Although it is a high-density cell honeycomb catalyst intended for performance, the catalyst purification performance is not sufficiently exhibited in the vicinity of the center hole.

  When high density cells were formed using a conventional metal honeycomb body, it was found that this central hole 7 was responsible for the difference in catalyst purification performance depending on the radial position of the honeycomb body.

  The oxygen sensor arranged for controlling the catalytic reaction is usually arranged so as to measure the exhaust gas oxygen concentration in the position immediately after the catalyst carrier and near the radial center of the exhaust gas path. The vicinity of the center in the radial direction immediately after the catalyst carrier is exactly the position where the exhaust gas that has passed through the center hole of the metal honeycomb body flows. In the exhaust gas flow that flows out from the so-called large central hole of the high-density cell metal honeycomb body, the oxygen concentration in the exhaust gas is increased due to the lean catalytic reaction in the middle of the path, and the amount of gas passing through Since there are many, the pulsation width of an oxygen concentration absolute value also becomes large. That is, in an exhaust gas purification system of an internal combustion engine using this type of metal catalyst carrier, when performing a catalytic reaction control, the measured oxygen concentration by an oxygen concentration sensor placed immediately after the catalyst carrier in the exhaust gas path is increased and undesired. Become stable. It has been found that the above is the reason why the catalytic reaction control has not been performed stably in the high-density cell catalyst.

  Furthermore, this unstable control has resulted in problems such as a reduction in fuel consumption and engine output.

This invention is made | formed based on the said knowledge, The place made into the summary is as follows.
(1) In a metal catalyst carrier 1 using a metal honeycomb body 2 formed by winding a metal flat foil 4 and a corrugated foil 5, the metal honeycomb body 2 penetrates the metal honeycomb body 2 at the axial center portion thereof. A metal catalyst carrier characterized by comprising a central hole 7 and an insert 8 disposed in the central hole 7 for inhibiting the flow of gas.
(2) The metal catalyst carrier according to (1) above, wherein the insert 8 is a metal plug 9.
(3) The metal catalyst carrier according to (2) above, wherein the metal plug 9 has a through hole 10.
(4) The metal catalyst carrier according to any one of (1) to (3) above, wherein the cell density of the metal honeycomb body 2 is 200 / in ² or more.

  The present invention relates to a metal catalyst carrier using a metal honeycomb body formed by winding a metal flat foil and a corrugated foil, and the metal honeycomb body has a central hole penetrating the metal honeycomb body at its axial center. And an insert that inhibits the flow of gas is disposed in the center hole, so that the exhaust gas that passes through the honeycomb body does not pass through the center hole at all, or an extremely small amount of exhaust gas passes through the center hole. Therefore, the purification performance of exhaust gas that has passed through the vicinity of the axial center of the honeycomb body can be made comparable to the purification performance of exhaust gas that has passed through other portions. In addition, the exhaust gas oxygen concentration can be normally and stably detected by an oxygen sensor disposed immediately after the catalyst carrier for catalytic reaction control, and the catalytic reaction control can be stabilized.

The present invention can exhibit particularly excellent effects when applied to a high cell density metal honeycomb body having a cell density exceeding 200 cells / in ² .

  As shown in FIG. 2, the metal honeycomb body 2 uses a heat-resistant stainless steel flat foil 4 and a corrugated foil 5 obtained by corrugating the flat foil, and a metal winding shaft 21. By laminating a flat foil and a corrugated foil around the axis. As shown in FIG. 2 (a), the winding shaft 21 is composed of two winding shaft members (21a, 21b) each having a half of a metal cylinder having a diameter of about 5 mm. Is sandwiched between the halves. As a result of sandwiching, as shown in FIG. 2B, the two winding shaft members (21a, 21b) are combined to form a cylindrical winding shaft 21 shape. By rotating the winding shaft 21, as shown in FIG. 2 (c), the flat foil 4 and the corrugated foil 5 are alternately wound in a spiral shape and laminated to form a metal honeycomb body. After the winding is completed, the winding shaft 21 is removed from the metal honeycomb body 2. As a result, as shown in FIG. 3, a center hole 7 penetrating the metal honeycomb body 2 is formed in the axial center portion of the metal honeycomb body 2, and the inner diameter of the center hole 7 is substantially equal to the outer diameter of the winding shaft 21. It becomes a dimension. A number of cells 6 surrounded by the flat foil 4 and the corrugated foil 5 are formed in the honeycomb body that has been wound, and a catalyst is supported on the surface of the foil that constitutes the cells 6, and the gas As it passes, the gas is purified, reformed or removed by a catalytic reaction.

  After the flat foil 4 and the corrugated foil 5 are laminated to form the metal honeycomb body 2, the metal honeycomb body 2 is accommodated in the stainless steel outer cylinder 3 and the flat foil 4 and the corrugated foil 5 are in contact with each other. Part or all of these are joined by brazing or diffusion joining to form the metal catalyst carrier 1 before carrying the catalyst. After forming the honeycomb body as described above, the surface of the metal foil of the cell 6 is coated with a washcoat solution. Next, the washcoat solution is baked onto the support by high-temperature heat treatment, and further, a catalyst species such as noble metal is coated to form a catalyst support layer on the metal foil surface of each cell 6.

  The present invention is characterized in that an insert 8 that inhibits the flow of gas is disposed in the center hole 7 located in the axial center portion of the metal honeycomb body 2. The insert 8 is made of metal, and the contact portion between the metal honeycomb body 2 and the insert 8 is brazed simultaneously when the metal honeycomb body 2 is brazed. As a result of the arrangement of the insert 8, the exhaust gas passing through the honeycomb body 2 does not pass through the central hole 7, or the exhaust gas passing through the central hole 7 can be made extremely small amount, and the exhaust gas is By passing through the cell 6, good purification performance can be realized. Further, in the conventional honeycomb body, the exhaust gas flow flowing through the center hole 7 is unstable due to the high oxygen concentration. However, in the present invention, the fluctuation of the oxygen concentration is minimized, so the oxygen concentration sensor disposed immediately after the catalyst carrier. Measurement can be stabilized, and the catalytic reaction can be controlled stably.

  A metal plug 9 can be used as the insert 8 disposed in the center hole 7 of the metal honeycomb body 2. The metal plug 9 means a metal plug that can block the gas flow through the center hole 7. The metal plug 9 may have any shape as long as it can block the gas flow through the central hole 7 or minimize the gas flow. Further, the metal plug 9 does not need to extend over the entire length of the metal honeycomb body 2, and is preferably disposed at least at a part of the exhaust gas inlet side. As a material of the metal plug 9, it is preferable to use a metal having heat resistance equivalent to that of the metal constituting the metal honeycomb body 2. For example, in the case of use in an automobile exhaust gas purification catalyst carrier, a heat-resistant material such as high heat-resistant stainless steel and Ni-base superalloy that can withstand use at a high temperature of about 1000 ° C. is suitable, and more preferably rapid heating, In order to cope with the thermal stress caused by cooling, a material having a thermal expansion coefficient equivalent to that of the catalyst carrier is desirable. Specifically, 20Cr-5Al stainless steel generally used for a catalyst support for automobiles can be used.

  It is more preferable that the metal plug 9 used in the present invention has the through hole 10. As described above, the metal plug 9 is disposed in the center hole 7 of the metal honeycomb body, and the contact portion between the center hole 7 and the metal plug 9 is brazed, and then the washcoat liquid is applied to the metal foil surface of the honeycomb body 2. Coating. Specifically, the honeycomb body 2 is dipped in the washcoat liquid, and then the honeycomb body 2 is pulled up from the washcoat liquid, and the excess washcoat liquid is discharged to coat the washcoat liquid on the surface of the metal foil. In a preferred embodiment of the present invention, if the through hole 10 is formed in the metal plug 9, the excess washcoat liquid filled in the center hole 7 is discharged through the through hole 10, so that the inner peripheral surface of the center hole is discharged. It is preferable that no excess washcoat solution remains.

  In addition, when the shape of the metal plug 9 used in the present invention is tapered, it becomes easy to insert the plug into the central hole in manufacturing the product of the present invention, thereby improving the production efficiency and the product. It is more preferable because it has a yield improving effect.

In the metal catalyst carrier 1 to which the present invention is applied, the cell density of the metal honeycomb body is preferably 200 / in ² or more. Thus, in the metal catalyst carrier 1 having the high-density cells 6, the effect of preventing the adverse effect of the central hole 7 existing in the axial center portion of the metal honeycomb body 2 is great, and the effect of improving the catalyst purification performance of the metal catalyst carrier This is because the effect of improving the catalytic reaction control accuracy in the exhaust gas purification system is large. The higher the cell density of the metal honeycomb body, the greater the effect of the present invention, and the more preferable the cell density of the metal honeycomb body is 400 / in ² or more. More preferably, the cell density of the metal honeycomb body is 600 / in ² or more.

  The reason for laminating the flat foil 4 and the corrugated foil 5 in the present invention is that the cells formed by laminating the wave 1 wavelength portion of the corrugated foil and the flat foil by laminating the flow path of the exhaust gas There is in point to do. If such a cell is formed, the purpose is achieved, and the flat foil 4 does not need to be completely flat as long as it is within the range to achieve such purpose. The flat foil 4 may have a corrugated shape in which the corrugated wave height is smaller than the wave height of the corrugated foil 5. By stacking the flat foil 4 and the corrugated foil 5, the formation of the cells as the exhaust gas flow path is the same as in the case of the flat foil 4 having no corrugated shape. The corrugated wave wavelength of the flat foil 4 may be smaller than the wave wavelength of the wave foil 5 or may be larger than the wave wavelength of the wave foil 5. Preferably, the corrugated wave wavelength of the flat foil 4 is 85% or less of the wave wavelength of the corrugated foil 5, and the corrugated wave height of the flat foil 4 is 50% or less of the wave height of the corrugated foil 5, A honeycomb body having a good cell shape can be formed. When the flat foil 4 has such a corrugated shape, it is possible to obtain an effect of increasing the elasticity of the flat foil 4 and improving the life of the honeycomb body.

  The present invention was applied as a metal catalyst carrier installed directly under the engine of a 3000 cc gasoline engine vehicle. The metal honeycomb body shown in FIG. 1 is used, and the diameter is 100 mm and the length is 120 mm. The inner diameter of the center hole is 5 mm.

As the cell density of the metal honeycomb body, No. 1: 200 / in ² (h = 1.80 mm, P = 3.60 mm), No. 1 2: 400 / in ² (h = 2.50 mm, P = 1.25 mm), No. 2 3: 600 / in ² (h = 2.00 mm, P = 1.00 mm), no. 4: Four types of 900 / in ² (h = 1.70 mm, P = 0.85 mm) were used.

  As the insert 8 disposed in the center hole 7, the material is 20Cr-5Al-Fe ferritic stainless steel, the shape is a round bar shape having a diameter of 5 mm, and has a tapered outer shape. A 1 mm one was used.

  HORIBA, Ltd.'s MEXA series was installed as a high-precision gas analyzer in the exhaust path downstream of the metal catalyst carrier, and emissions of HC, CO, and NOx in the exhaust gas were measured.

  The cell density is no. For each of 1-4, the emission measurement was performed for each of the cases with and without the insert 8, and relative emission was calculated based on the analysis value of HC and without the insert 8. The results are shown in Table 1.

  As is apparent from Table 1, the metal catalyst carrier of the present invention was able to improve the exhaust gas purification performance by using the insert 8 in its central hole. The higher the cell density of the metal honeycomb body, the greater the improvement effect could be obtained.

It is a perspective sectional view showing the metal catalyst carrier of the present invention. It is a perspective view which shows the condition which winds flat foil and a corrugated foil using a winding axis, (a) is the condition before combining a half winding shaft member, (b) is a half winding shaft member. (C) is the figure which shows the condition which winds flat foil and a corrugated foil around a winding axis | shaft. It is a perspective sectional view showing a conventional metal catalyst carrier. It is a perspective sectional view showing the metal catalyst carrier of the present invention.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Metal catalyst carrier 2 Metal honeycomb body 3 Outer cylinder 4 Flat foil 5 Wave foil 6 Cell 7 Center hole 8 Insert 9 Metal plug 10 Through-hole 21 Winding shaft

Claims (4)

  In a metal catalyst carrier using a metal honeycomb body formed by winding a metal flat foil and a corrugated foil, the metal honeycomb body has a central hole penetrating the metal honeycomb body at its axial center, and A metal catalyst carrier characterized in that an insert for inhibiting gas flow is disposed in the central hole.   2. The metal catalyst carrier according to claim 1, wherein the insert is a metal plug.   The metal catalyst carrier according to claim 2, wherein the metal plug has a through hole. The metal catalyst carrier according to any one of claims 1 to 3, wherein a cell density of the metal honeycomb body is 200 / in ² or more.

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