Pipe-shaped catalyst construction for exhaust gas purification

Abstract

 The present invention intends to provide a pipe-shaped catalyst construction 10 which has high catalyst ability and which is excellent in high temperature resisting character, in a pipe-shaped catalyst construction. It is comprised of a pipe-shaped supporting body including a metallic pipe 11 and a cylindrical metallic foil 12 contained therein and provided with plural concaved portions 13 formed circumferentially, and a catalyst material 19 supported on the metallic foil.
In such catalyst construction, the metallic foil 12 is disposed along an inner peripheral surface of the pipe 11 except for a central portion of the metallic pipe in section. Also, rate of a central sectional area portion where the metallic foil 2 is not disposed to a whole sectional area of the pipe 11 defined by the inner peripheral surface of the pipe is selected to be 20 % to 60 %.

Description

BACKGROUND OF THE INVENTION

Field of the Invention

[0001] This invention relates to a pipe-shaped catalyst construction for exhaust gas purification used to purify an exhausted gas discharged from a motorbike or an automobile. Related Background Art

[0002] With increased interest to a recent environmental problem, measurements to an exhausted gas discharged from an internal combustion engine of a motorbike or an automobile has attracted much attention in industrial world. In view of this, the exhausted gas discharged from the motorbike etc., after having been purified harmful components such as carbon monoxide (CO), hydrocarbon (HC) and nitrogen oxide (NOx) contained therein is discharged to an atmosphere. Various kinds of catalysts for exhaust gas purification has been known, one sample of which is a pipe-shaped catalyst construction.

[0003] The pipe-shaped catalyst construction used in the motorbike etc. is comprised by supporting or bearing catalyst on an inner peripheral surface of a metallic pipe. Although, the pipe-shaped catalyst construction has simple construction, it can hardly perform the exhaust gas purification sufficiently due to small contacting area of the catalyst with the exhaust gas. In view of this, the catalyst has been supported on a metal foil or a metal sheet contained within a hollow portion of the pipe to broaden contacting area of the catalyst with the exhaust gas.

[0004] As such kinds of conventional art, a catalyst construction disclosed in Japanese Patent Publication No. 55-51624 and a catalyst construction disclosed Patent National Laid-open No. 11-510872 have been known. The former catalyst construction 50 shown in Fig. 5 is comprised of a cylindrical pipe 51, a metallic sheet 54 contained within the pipe 51, and catalysts (only partially shown) coated on an inner peripheral surface of the pipe 51 and an outer and on inner surfaces of the metallic sheet 54. The metallic sheet 54 is continuously formed plural concaved portions 53 circumferentially by plural section V-shaped portions 52 extending outwardly and inwardly in radial direction, to resultantly have a star shape. The pipe 51 and the metallic sheet 54 constructs a pipe-shaped supporting body.

[0005] The latter catalyst construction 60 shown in Fig. 6 is comprised of a cylindrical pipe 61 made of metal, a metallic film (foil) 62 contained within the pipe 61, and catalysts (only partially shown) 64 supported on the metallic film 62. The metallic film 62 is continuously formed plural concaved portions 63 circumferentially by plural section U-shape portions, constructing a pipe-shaped supporting body together with the pipe 61.

[0006] In the catalyst construction 50 shown in Fig. 5, a circle defined by connecting opened portions of the section V-shaped portion 52 ie top portions of the concaved portions 53 has smaller diameter, so that the opened portions extend radially near to a central portion of the pipe 51. As a result, a rate of a sectional area portion where the metallic sheet 54 does not exist to whole sectional area of the pipe 51 is very small. Increased contacting area of the catalyst 55 on the metallic sheet 54 with the exhaust gas improves the purifying ability of the exhaust gas. However, the exhaust gas flows faster at a central portion of the pipe 5 with receiving small resistance than at a surrounding portion with receiving larger resistance. Also, temperature of the exhaust gas rises higher at the central portion with radiating smaller heat than the surrounding portion with radiating larger heat. Accordingly, the opened portions of the section V-shaped portion 52 located near to the central portion of the pipe 51 have been exposed in the exhaust gas of high pressure and high temperature. In this way, a part of the metallic sheet 54 may crack and damaged by pressure and heat of the exhaust gas.

[0007] To the contrary, in the catalyst construction 60 shown in Fig. 6, the metallic film 63 is disposed only at a surrounding portion of a pipe 61, not being disposed at a central portion of the pipe 61. So, the metallic film 63 is hardly damaged by heat and pressure of the exhaust gas flowing at the central portion of the pipe 61. However, in this catalyst construction, rate of a surrounding sectional area where the metallic film 63 existed to a whole sectional area defined by an inner peripheral surface of the pipe 61 is very small. Thus, small contacting area of the catalyst 64 of the metallic film 63 with the exhaust gas hinders sufficient exhaust gas purification.

[0008] As mentioned above, a high catalyst ability to purify the exhaust gas efficiently and a high temperature resisting character not to be damaged by heat of high temperature, contradicting to each other, are required for the pipe-shaped catalyst construction. Whereas, no catalyst construction which can satisfy the both requirements has not been known.

Summary of the Invention

[0009] The present invention has ben made in view of the above circumstances and intends to provide a pipe-shaped catalyst construction which has high catalyst ability and which is excellent in high temperature resisting character.

[0010] Inventor of this application has hit on, for realizing such pipe-shaped catalyst construction to dispose a metal foil or a metal sheet as small as possible at a central portion of the pipe. This is because at the central portion, the exhaust gas flows in high speed with receiving small flowing resistance from the pipe and holds high temperature with small heat radiation through the pipe. In other words, the metallic foil etc. is preferably disposed at a surrounding portion of the pipe along an inner surface thereof. As a result of eager studying, the inventor has found out the most suitable rate of the central sectional area portion where the metallic foil etc. is not disposed to the whole sectional area of the pipe.

[0011] That is, a pipe-shaped catalyst construction for exhaust gas purification is comprised of (a) a pipe-shaped supporting body including a metallic pipe and a cylindrical metallic foil or a metallic sheet contained in the metallic pipe and provided with concaved portions formed continuously in circumferential direction to be concaved inwardly and outwardly in radial direction, and (b) a catalyst material supported at least on the metallic foil or the metallic sheet of the supporting body. In such catalyst construction, the metallic foil or the metallic sheet is disposed along an inner peripheral surface of the metallic pipe except for a central portion of the metallic pipe in section, and rate of a central sectional area portion where the metallic foil or the metallic sheet is not disposed to a whole sectional area of the metallic pipe defined by the inner peripheral surface of the pipe is selected to be 20 % to 60 %.

[0012] In the pipe-shaped catalyst construction according to the present invention, the metallic foil etc. is not disposed at the central portion (a cylindrical space having distance smaller than a predetermined value from a centre) of the pipe to leave a space at the central portion. In other words, the metallic foil etc. is disposed at the surrounding portion of the pipe along the inner peripheral surface thereof. As a result, the metallic foil etc. is hardly exposed to the exhaust gas of high speed and high temperature at the central portion of the pipe, which prevents damage of the metallic foil etc., and holds shape stability of it.

[0013] In addition, the surrounding sectional area has the larger rate (40 % to 80 %) to the whole sectional area of the pipe. Accordingly, the exhaust gas flowing at the surrounding portion of the pipe in relatively low speed is purified by the catalyst supported on the metallic foil etc. effectively, whereby the purifying ability of the catalyst construction is maintained.

[0014] When the rate of the central sectional area portion to the whole sectional area defined by the inner peripheral surface of the pipe decreases under 20 %, there is fear the part of the metallic foil etc. disposed at the central portion being damaged by high heat of the exhaust gas. On the other hand, when this rate increases over 60 %, there is fear the purifying ability by the catalyst on the metallic foil etc. being insufficient.

[0015] Next, embodying modes of the pipe-shaped catalyst construction for exhaust gas purification of the present invention will be explained.

[0016] The catalyst construction can be used to purify the exhaust gas discharged from an internal combustion engine of a motorbike or an automobile.

[0017] Various kinds of metals having heat resisting character and pressure resisting character can be used to construct the pipe of the pipe-shaped supporting body. For example, a stainless steel is suitably used. The pipe can have a cylindrical shape, elliptical shape or polygonal shape.

[0018] As metals constructing the metallic foil or the metallic sheet for the pipe-shaped supporting body, various kinds of metals excellent in the heat resisting character can be used. For example, 20Cr-5Al is preferably used. Here, the metallic foil and the metallic foil are distinguished by thickness thereof, but this distinction is not essential since both of them are included in the present invention.

[0019] Each of concaved portions continuously formed on the metallic foil or the metallic sheet circumferentially can be comprised of, for example, two section U-shaped portions being adjacent and protruding outwardly in radial direction, and a connecting portion connecting them. Also, concaved portion can be formed by two adjacent section V-shaped portions protruding outwardly radially or can be formed by two adjacent section V-shaped portions protruding outwardly in radial direction and a connecting portion connecting them.

[0020] The rate of the central sectional area portion to the whole sectional area defined by the inner peripheral surface can be selected in a range from 20 % to 60 %, more preferably it can be selected in a range from 31 % to 52 %. In connection with this, a rate of radius of the pipe central portion where the metallic foil etc. is not disposed (distance from a center of the cylindrical space to outer surface thereof) to radius of the pipe, can be selected in range from 45 % to 77 %, more preferably it can be selected in range from 55 % to 72 %.

[0021] The number of the concaved portions of the metallic foil is determined depending on circumferential length of the concave portion. It does not directly affect the rate of the central sectional area portion to the whole sectional area, and therefore can be freely selected. The number of the concaved portions changes size of each concaved portion. However, there is suitable size (height) of the concave portion to increase the purifying efficiency of the exhaust gas, to be explained later.

[0022] The concaved portions of the metallic foil etc. are joined, at the opened ends (radially outward ends) thereof, to the inner peripheral surface of the pipe. In the joined state, cavities of the concaved portions preferably form together with the pipe flowing paths (cells) allowing the exhaust gas flow at the surrounding portion of the pipe. With supporting the catalyst on the inner peripheral surface of the pipe and on the inner surfaces of the recessed portions defining the cells, the exhaust gas flowing through the cells is efficiently purified by the catalyst. When the cell size is too small due to small height of the concaved portions, most of the exhaust gas flows in the pipe central portion, resulting in low purifying ability of the exhaust gas. On the other hand, when the cells are too large due to large height of the concaved portions, the cells tend to be expanded by heat and pressure of the exhaust gas. As a result, the concaved portions may be deformed, or crack may be generated at a part of the concaved portion or at connected part between the concaved portion and the pipe.

[0023] Various kinds of catalysts such as a oxidizing catalyst, reducing catalyst and three-way catalyst can be supported on the supporting body. As well known, the oxidizing catalyst oxidizes harmful carbon monoxide and hydrocarbon in the exhaust gas to harmless carbon dioxide and steam, respectively. The reducing catalyst reduces harmful nitrogen oxide to nitrogen. The three-way catalyst oxidizes carbon monoxide and hydrocarbon and reduces nitrogen oxide. Using catalyst is selected in view of harmful component(s) required to be purified especially.

[0024] The catalyst is sufficiently supported at least on the metallic foil or the metallic sheet of the pipe-shaped supporting body, but can be supported on the pipe inner surface as occasion demands. The catalyst can be supported on the inner surface and/or the outer surface of the metallic foil etc.. Supporting the catalyst on broad area of the supporting body surface is preferable to increase the purifying ability of the catalyst. Part or area of the supporting body where the catalyst is supported is determined in view of the rate of the central cross-sections member to the surrounding sectional area, and the number of the concaved portions.

[0025] Above embodying modes of each component of the present invention can be selectively combined.

Brief Explanation of the Drawings

[0026] 

Fig. 1 is a sectional view of a pipe-shaped catalyst construction of the first embodiment according to the present invention;

Fig. 2 is a sectional view along a line 2- 2 in Fig. 1;

Fig. 3 is a sectional view of a pipe-shaped catalyst construction of the second embodiment according to the present invention;

Fig. 4 is a sectional view of a pipe-shaped catalyst construction of the third embodiment according to the present invention;

Fig. 5 is a sectional view of the first conventional pipe-shaped catalyst construction; and

Fig. 6 is a sectional view of the second conventional pipe-shaped catalyst construction.

Preferred Embodiment of the Invention

[0027] A preferred embodiment of the present invention will be explained reference to attached drawings.

<Embodiment 1>

[0028] Here, three (embodiment 1, comparative sample 1 and comparative sample 2) pipe-shaped catalyst construction have been produced to be tested.

[0029] The pipe-shaped catalyst construction 10 of the embodiment 1 is shown in Figs. 1 and 2. It is comprised of a pipe-shaped supporting body including a metallic pipe 11 and a metallic foil 12, and a catalyst 19 supported on a surface of the metallic foil 12. The pipe 11 made of a stainless steel has a cylindrical shape of which inner diameter is 25.4 mm, thickness is 1.2 mm and length is 170 mm, respectively. Thus, whole sectional area S1 of the pipe 11 is about 506.5 mm ².

[0030] The metallic foil 12 made of 20Cr-5Al having foil thickness of about 200 µm is formed plural recessed portion 13 circumferentially and has a cylindrical shape. Each of the concaved portions 13 includes two section U-shaped potions 16 extending outwardly in radial direction and a connecting portion connecting them. All of the section U-shaped portions 14 have same construction, each including a pain of stand-up portions 14a and a top portion 14b connecting them. The stand-up portion 14a has height of about 4 mm, which means distance between the connecting portions 15 opposing in diameter direction, ie diameter of the central portion 16 where the metallic foil 12 is not disposed is of about 17.4 mm. As a result, the rate of central portion diameter to the pipe diameter is of about 69 %. Also, the area of the central portion (central sectional area) S2 is of about 237.7 mm ², the rate to the above whole sectional area S1 of the pipe 11 being of about 47 %. Here, the surrounding sectional area portion S3 is of about 268.8 mm ², and has the rate to the whole sectional area S1 being of about 53 %.

[0031] The section U-shaped portion 14 has circumferential length smaller than distance between the adjacent section U-shaped portions 14. The metallic foil 12 is joined to the inner surface of the pipe at the opened ends of each concaved portion 13 (joined portion 17), so that the pipe 11 and the concaved portions 13 form flowing passages 18 each having section trapezoidal shape at the the surrounding portion. The three-way catalysts 19 (only partially shown) are coated on inner and outer surfaces of the concaved portions 13, and on inner and outer surfaces of the connecting portions 15.

<Comparative Sample 1>

[0032] A pipe-shaped catalyst construction of a comparative sample 1 is comprised of a pipe similar to the pipe 11 of the embodiment 1, a metallic foil having concaved portions of which size differs from the metallic foil 12 of the embodiment 1, and a catalyst similar to the catalyst 19 of the embodiment 1. Each of the concaved portions has radial height of about 8 mm, resulting in distance between the connecting portions opposed in diameter direction is of about 9.4 mm.

[0033] As a result, the rate of central portion diameter to the pipe diameter is of about 37 %. Also, the area of the central portion S2 is of about 69.4 mm ², the rate to the above whole sectional area S1 of the pipe 11 being of about 14 %. So, rate of the surrounding sectional area portion S3 to the whole sectional area Sl is of about 86 %. Another points such as the metallic foil material, the number of the concaved portions etc.are similar to the catalyst construction of the embodiment 1.

<Comparative Sample 2>

[0034] A pipe-shaped catalyst construction of a comparative sample 2 is comprised of a pipe similar to the pipe 11 of the embodiment 1, a metallic foil having concaved portions of which size differs from the metallic foil 12 of the embodiment 1, and a catalyst similar to the catalyst 19 of the embodiment 1.

[0035] Each of the concaved portions has radial height of about 2 mm, resulting in distance between the connecting portions opposed in diameter direction is of about 21.4 mm. As a result, the rate of central portion diameter to the pipe diameter is of about 84 %. Also, the area of the central portion S2 is of about 359.5 mm ², the rate to the above whole sectional area S1 of the pipe 11 being of about 71 %. So, rate of the surrounding sectional area portion S3 to the whole sectional area S1 is of about 29 %. Another points such as the metallic foil material, the number of the concaved portions etc. are similar to the catalyst construction of the embodiment 1.

[0036] An exhaust gas purifying test has been carried out by using the pipe-shaped catalyst construction of the embodiment 1 and the comparative samples 1 and 2, result of which are shown in Tables 1 and 2. In the Table 1 showing the purifying character, "HC purifying rate" is calculated by dividing ((HC density in exhaust gas not passed thorough catalyst) - (HC density in exhaust gas passed through catalyst)) by (HC density in exhaust gas not passed through catalyst), and multiplying 100. Also, "CO purifying rate" is calculated by dividing ((CO density in exhaust gas not passed thorough catalyst) - (CO density in exhaust gas passed through catalyst)) by (CO density in exhaust gas not passed through catalyst), and multiplying 100.

[0037] The Table 2 shows shape stability character of the metallic foil which is judged by observing deformation visually. Here, "cool and heat test" is carried out by repeating heating the catalyst construction at 950 °C in 10 min. and cooling them at room temperature in 10 min. by using a 2-stroke engine.

[Table 1]

	HC purified rate	CO purified rate
Embodiment 1	45 %	58 %
Comparative Sample 1	50 %	65 %
Comparative Sample 2	20 %	35 %

[0038] As apparent from the Table 1, the catalyst construction of the comparative sample 1 is excellent in both of the HC purifying ability and CO purifying ability, the catalyst construction of the embodiment 1 is secondary excellent, and catalyst construction of the comparative sample 2 is most poor. These results can be expected since the exhaust purifying ability depends on the rate of the surrounding sectional area portion where the metallic foil is disposed to the whole sectional area (53 % in the embodiment 1, 86 % in the comparative sample 1, and 29 % in the comparative sample 2).

[Table 2]

	metallic foil deformation after heat-cool test
Embodiment 1	no deformation
Comparative Sample 1	large deformation, partial crack
Comparative Sample 2	no deformation

[0039] As apparent from Table 2, deformation has not occurred in the metallic foil of the catalyst construction of the embodiment 1 and the comparative sample 2, but deformation and partial crack have occurred in the metallic foil of the catalyst construction of the comparative sample 2. This may results from large rate (47 % and 71 %) of the central sectional area portion in the catalyst construction of the embodiment 1 and comparative sample 2, and small rate (14 %) of the same in the catalyst construction of the comparative sample 2.

[0040] Here, quality of pipe-shaped catalyst construction is evaluated by the purifying ability and shape stability of the metallic foil. The catalyst construction of the embodiment 1 is excellent in the both aspects. To the contrary, the catalyst construction of the comparative sample 1 excellent in the catalyst ability is poor in the shape stability, while the catalyst construction in the comparative sample 2 excellent in the shape stability is poor in the catalyst ability. Judging them from totally, the catalyst construction of the embodiment 1 is most excellent.

[0041] Generally speaking, as selecting the rate of the surrounding sectional area portion to the whole sectional area larger, the purifying ability by the catalyst becomes higher while the shape stability of the metallic foil becomes poorer. How they are balanced is important.

[0042] In the catalyst construction in the comparative sample 1, size of the central portion is set extremely small by selecting the rate of radius of the central portion to radius of the pipe is 37 %, that is, by selecting the rate of the central sectional area portion to the whole sectional area is 14 %. However, it has only the HC purifying rate and the CO purifying rate corresponding to about 1.1 times that of the catalyst construction in the embodiment 1. Judging from this fact, excessive heightening of radial height (4 mm) of the concaved portion 13 does not contribute to purifying ability increase, but deteriorates the shape stability. In view of the both requirements, the concaved portion having height of about 5 mm seems to have the purifying ability of high level by the catalyst, and to maintain shape stability of the concaved portion. When the concaved portion has height of 5 mm, the rate of radius of the central portion to radius of the pipe is 61 %, which means the rate of the central sectional area portion to the whole sectional area is 37 %.

[0043] On the other hand, in the catalyst construction of the comparative sample 2, both of the HC purifying rate and the CO purifying rate have been inferior to that of the catalyst construction 10 of the embodiment 1. Judging from this fact, decreasing radial height (4 mm) of the concaved portion 13 greatly is not preferable. The concaved portion 13 having radial height down to 3.5 mm seems to perform the equivalent purifying ability to the concaved portion having radial height of 4 mm. In this case, the rate of radius of the central portion to radius of the pipe is 72 %, which means g the rate of the central sectional area portion to the whole sectional area is 52 %.

[0044] Value of the rate of the central portion radius to the pipe radius selected within range of 45 % to 77 %, and the value of the rate of the central sectional area portion to the whole sectional area selected within range of 20 % to 60 %, depend on shape and size of the metallic foil, shape and the number of the concaved portions, and supported area of the catalyst onto the supporting body.

[0045] In the pipe-shaped catalyst construction of the embodiment 1, different from the conventional catalyst construction 50 shown in Fig. 5, the metallic foil 12 does not have any part located radially inside of the connecting portion 13. Therefore, there is no fear the metallic foil 12 is damaged by the exhaust gas of high temperature and high pressure flowing through the central portion of the pipe 11.

<Embodiment 2>

[0046] A pipe-shaped catalyst construction 20 of the embodiment 2 shown in Fig. 3 differs from the catalyst construction 10 of the embodiment 1 in shape of concaved portions of metallic foil.

[0047] In the catalyst construction 20, each of concaved portions 23 of metallic foil 22 contained in a pipe 21 is comprised of two adjacent section V-shaped portions formed continuously in circumferential direction. Each of the section V-shaped portions 24 is joined to an outer peripheral surface of a cylindrical portion 25 of the metallic foil at opened ends thereof, and joined to an inner peripheral surface of the pipe 21 at top portion thereof.

[0048] Sizes of the catalyst construction 20 such as inner diameter of the pipe 21 and radial height of the concaved portion 23 of the metallic foil 22 are selected same as that of the catalyst construction of the embodiment 1. Accordingly, the rate of radius of the central portion to radius of the pipe is 69 %, which means the rate of the central sectional area portion to the whole sectional area is 47 %.

[0049] The pipe-shaped catalyst construction 20 can render the purifying ability by the catalyst and the shaped stability of the metallic foil 22, same as the above catalyst construction of the embodiment 1.

<Embodiment 3>

[0050] A pipe-shaped catalyst construction 30 of the embodiment 3 shown in Fig. 4 differs from the catalyst construction of the embodiment 1 in shape of concaved portions of metallic foil.

[0051] In the catalyst construction 30, each of concaved portions 33 of a metallic foil 32 contained in pipe 31 is comprised of two adjacent section V-shaped portions 34 each protruding outwardly in radial direction, and a connecting portion 35 disposed therebetween to connect them. That is, each section V-shaped portion 34 is comprised of a pair of stand-up portions 34a, so that the concaved portion 33 is defined by the stand-up portion 34a of the section V-shaped portion 34, the connecting portion 35 and the stand-up portion 34a of the adjacent section V-shaped portion 34. Each concaved portion 33 is joined to the inner peripheral surface of the pipe at opened ends thereof, ie at a bottom portion of the section V-shaped portion 34.

[0052] Sizes of the catalyst construction 30 such as inner diameter of the pipe 31 and radial height of the concaved portion 33 of the metallic foil 32 are selected same as that of the catalyst construction of the embodiment 1. Accordingly, the rate of radius of the central portion to radius of the pipe is 69 %, which means the rate of the central sectional area portion to the whole sectional area is 47 %.

[0053] The pipe-shaped catalyst construction 30 can render the purifying ability by the catalyst and the shaped stability of the metallic foil 32, same as the above catalyst construction of the embodiment 1.

[0054] The present invention intends to provide a pipe-shaped catalyst construction 10 which has high catalyst ability and which is excellent in high temperature resisting character, in a pipe-shaped catalyst construction. It is comprised of a pipe-shaped supporting body including a metallic pipe 11 and a cylindrical metallic foil 12 contained therein and provided with plural concaved portions 13 formed circumferentially, and a catalyst material 19 supported on the metallic foil.

[0055] In such catalyst construction, the metallic foil 12 is disposed along an inner peripheral surface of the pipe 11 except for a central portion of the metallic pipe in section. Also, rate of a central sectional area portion where the metallic foil 2 is not disposed to a whole sectional area of the pipe 11 defined by the inner peripheral surface of the pipe is selected to be 20 % to 60 %.

Claims

1. A pipe-shaped catalyst construction for exhaust gas purification comprising (a) a pipe-shaped supporting body including a metallic pipe 11 and a cylindrical metallic foil 12 or a metallic sheet contained in the metallic pipe and provided with concaved portions 13 formed continuously in circumferential direction to be concaved inwardly and outwardly in radial direction, and (b) a catalyst material 19 supported at least on the metallic foil 12 or the metallic sheet of the supporting body,
   characterized by that the metallic foil 12 or the metallic sheet is disposed along an inner peripheral surface of the metallic pipe 11 except for a central portion of the metallic pipe in section, and rate of a central sectional area portion where the metallic foil 12 or the metallic sheet is not disposed to a whole sectional area of the metallic pipe 11 defined by the inner peripheral surface of the pipe is selected to be 20 % to 60 %.

2. A pipe-shaped catalyst construction for exhaust gas purification according to claim 1, wherein a rate of radius of central portion in section where the metallic foil or the metallic sheet is not disposed to radius of the pipe is selected to be 45 % to 77 %.

3. A pipe-shaped catalyst construction for exhaust gas purification according to claim 1, wherein a rate of a central sectional area portion where the metallic foil or the metallic sheet is not disposed to a whole sectional area is selected to be 31 % to 52 %.

4. A pipe-shaped catalyst construction for exhaust gas purification according to claim 2, wherein a rate of radius of central portion in section where the metallic foil or the metallic sheet is not disposed to radius of the pipe is selected to be 55 % to 72 %.

5. A pipe-shaped catalyst construction for exhaust gas purification according to claim 2, wherein each of the concaved portions of the metallic foil or the metallic sheet has two adjacent section U-shaped portions each protruding outwardly in radial direction, and a connecting portion connecting the section U-shaped portions.

6. A pipe-shaped catalyst construction for exhaust gas purification according to claim 2, wherein each of the concaved portions of the metallic foil or the metallic sheet has two adjacent section V-shaped portions each protruding outwardly in radial direction.

7. A pipe-shaped catalyst construction for exhaust gas purification according to claim 2, wherein each of the concaved portions of the metallic foil or the metallic sheet has two adjacent section V-shaped portions each protruding outwardly in radial direction, and a connecting portion connecting the section V-shaped portions.

8. A pipe-shaped catalyst construction for exhaust gas purification according to claim 5, 6 or 7, wherein the catalyst material is supported on the inner peripheral surface of the metallic pipe, and on an inner surface and an outer surface of the metallic foil or the metallic sheet.

9. A pipe-shaped catalyst construction for exhaust gas purification according to claim 5, 6 or 7, wherein the concaved portions of the metallic foil or the metallic sheet are joined to the inner surface of the metallic pipe at opened ends thereof so that a recess in the concaved portion forms a flowing path at surrounding portion of the metallic pipe.

10. A pipe-shaped catalyst construction for exhaust gas purification according to claim 8 or 9, wherein the opened ends of the concave portions are joined to the inner peripheral surface of the metallic pipe so that cavities in the concaved portions form together with the metallic pipe flowing paths at the surrounding portion of the metallic pipe.

Drawing