JPH1128359A - Catalyst structure for purification of exhaust gas - Google Patents

Abstract

PROBLEM TO BE SOLVED: To make a catalyst structure not to be restricted in a shape and a size while it is excellent in high temperature corrosion resistance, has high adhesion strength to a base material of the catalyst, and can be manufactured without use of expensive equipment. SOLUTION: The catalyst structure has a ferrite stainless steel made base material composed of at most 0.2 wt.% C, 0.4 to 3.0 wt.% Si, at most 2.0 wt.% Mn, 13.0 to 20.0 wt.% Cr, 0.3 to 3.0 wt.% Mo, and balance consisting of Fe and impurities. In the catalyst, a metal selected from platinum and paradium as an active constituent and rhodium are supported on a support consisting of γ-alumina and cerium stabilized zirconia, and it is supported on a base material.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is used for purifying exhaust gas discharged from an internal combustion engine, a boiler, a gas turbine, etc., and has good heat resistance and corrosion resistance, and firmly adheres a catalyst to a substrate. The present invention relates to an exhaust gas purifying catalyst structure having excellent durability.

[0002]

2. Description of the Related Art Honeycomb materials having a small pressure loss are frequently used as a base material of a catalyst for purifying exhaust gas discharged from an internal combustion engine, a boiler, a gas turbine, and the like. It has been.

[0003] In recent years, metal-based substrates have begun to be used because they are resistant to vibration and impact, are less likely to be damaged, have lower pressure loss, and have a faster temperature rise.
In applications where the pressure loss needs to be further reduced, a metal cylindrical or conical shape having a large number of through holes in the side wall or a cross plate shape has been devised.

In such a catalyst structure in which an exhaust gas purifying catalyst is supported on such a metal base material, exhaust gas having a high temperature of 700 ° C. or more and corrosive substances such as water vapor, S0 _x and NO _x contained in the exhaust gas are used. Exposed to For this reason, the metal substrate constituting the catalyst structure is first required to have heat resistance and corrosion resistance, particularly high-temperature corrosion resistance.

Further, the catalyst structure is used for operation and
Thermal expansion / contraction occurs due to repetition of pauses, and vibrations during operation are received. For this reason, second, the catalyst structure is required that the metal substrate and the catalyst are firmly adhered so that the catalyst does not fall off from the metal substrate due to thermal expansion / contraction or vibration. .

However, in a conventional catalyst structure in which a catalyst is directly supported on a metal substrate, the substrate is oxidized and its oxides appear on the surface of the catalyst, particularly when exposed to an exhaust gas containing water vapor. In addition to the reduced activity, there were problems such as the catalyst layer easily falling off from the metal substrate due to the thermal expansion / contraction and vibration as described above.

Therefore, in order to solve these problems, a metal material containing chromium such as a nickel-chromium alloy or stainless steel is plasma-sprayed on a metal substrate, and a ceramic material such as alumina is further plasma-sprayed thereon. Thus, there has been proposed a method of providing a catalyst layer thereon after providing two intermediate layers (Automotive Technology Vol. 47, No. 5, 1993).

[0008]

However, the method of providing an intermediate layer by the above-described plasma spraying requires expensive processing equipment, difficulties in uniform processing, and the diameter of holes formed in a metal base material. When the diameter is small, it is difficult to spray the inner surface of the hole, so that the applicable shape is limited, and thus there is a problem that the application is limited.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the conventional catalyst structure in which an exhaust gas purifying catalyst is provided on a metal substrate, and its object is to excel in heat resistance and corrosion resistance. In addition to the high adhesion between the catalyst and the base material, which not only has excellent durability, but also can be manufactured without using expensive equipment, and has a catalyst structure for purifying exhaust gas which is not restricted by its shape and size. To provide.

[0010]

Means for Solving the Problems As a result of intensive studies, the present inventors have found that a catalyst structure comprising a stainless steel having a specific alloy composition as a base material and carrying a specific exhaust gas purifying catalyst on the base material has the above object. Was found to be achieved.

That is, the present invention relates to (A)
C: 0.2% or less, Si: 0.4% to 3.0%, Mn:
2.0% or less, Cr: 13.0 to 20.0%, Mo:
A metal selected from platinum and palladium as an active ingredient in a ferrite stainless steel base material containing 0.3 to 3.0%, balance Fe and impurities, and (B) a carrier made of γ-alumina and cerium-stabilized zirconia And rhodium is supported, a catalyst supported on the substrate,
The present invention provides an exhaust gas purifying catalyst structure comprising:

[0012]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, a catalyst structure according to the present invention will be described in detail. Substrate for supporting catalyst (A) Ferritic stainless steel used as a substrate in the present invention is, by weight%, C: 0.2% or less, Si: 0.4% to
3.0%, Mn: 2.0% or less, Cr: 13.0-2
0.0%, Mo: 0.3 to 3.0%, with the balance being Fe and impurities.

The content of the metal element in the ferritic stainless steel is limited for the following reasons. C is 0.20%
If it exceeds, the workability is reduced. If the Si content is less than 0.4%, the high-temperature corrosion resistance is insufficient, while if it exceeds 3.0%, the workability decreases. If the Mn content exceeds 2.0%, the curing becomes remarkable and the productivity decreases. If the Cr content is less than 13%, the effect of high-temperature corrosion resistance cannot be sufficiently obtained, and if it exceeds 20%, the workability deteriorates. If Mo is less than 0.3%, the effect of high-temperature corrosion resistance is small, and if it exceeds 3.0%, workability is reduced,
The cost also goes up.

The stainless steel substrate used in the present invention comprises:
Since the alloy composition has high heat resistance and corrosion resistance (especially oxidation resistance) and Si as a constituent element is easily oxidized, an oxide film containing more Si as a Si oxide than Si of the alloy composition itself is formed. Therefore, there is an advantage that the exhaust gas purifying catalyst adheres firmly. This oxide film can be formed under ordinary conditions such as annealing or pickling the stainless steel in air. It can also be formed by performing bright annealing in an atmosphere in which Si is selectively oxidized.

The shape of the substrate used in the present invention is not particularly limited. Any shape conventionally used as a base material of an exhaust gas purifying catalyst can be used. These substrates have various shapes and structures devised to achieve efficient contact with the exhaust gas. For example, a honeycomb shape, a cylindrical shape, a conical shape, a curved shape, a spiral shape, a plate shape, a cross plate shape, a ribbon shape, a ring shape, a net shape, a line shape, and the like can be given. The shape and size can be appropriately selected according to the use conditions.

Catalyst (B) The catalyst structure of the present invention comprises a specific exhaust gas purifying catalyst supported on the above-described substrate. The supported catalyst is such that rhodium and a metal selected from platinum and palladium as active components are supported on a support made of γ-alumina and cerium-stabilized zirconia. The catalyst uses a mixture of γ-alumina and cerium-stabilized zirconia as a carrier. The specific surface area of the γ-alumina used is preferably 50 to 250 m ² / g, and 100 to ² m ² / g.
00 m ² / g is more preferred. The cerium content of the cerium-stabilized zirconia used is preferably 5 to 50% by weight, more preferably 15 to 35% by weight.
Specific surface area of cerium stabilized zirconia is 20-100m
² / g are preferred, more preferably 40 to 80 m ² / g. The mixing ratio of γ-alumina and cerium-stabilized zirconia is not particularly limited, but the mixing ratio of cerium-stabilized zirconia is preferably 10 to 70% by weight, and preferably 3 to 70% by weight.
0-60% by weight is more preferred.

It is essential that the active component of the catalyst contains a metal selected from platinum and palladium and rhodium.
Either one of platinum and palladium may be included, or both may be included. The active component of the catalyst preferably contains an element selected from lanthanum and barium in addition to platinum and / or palladium and rhodium. When lanthanum and barium are contained, the adhesion strength of the catalyst to the base material is further improved, and the hydrocarbon (H
The purification performance of C) is further improved. Lanthanum and barium may be either one or both.

Therefore, the composition of the active ingredient can be various, and specifically, for example, platinum and rhodium;
Palladium, rhodium and lanthanum; platinum, rhodium and barium; palladium, rhodium and lanthanum; palladium, rhodium and barium;
Platinum, rhodium, lanthanum and barium; palladium,
It is a combination of rhodium, lanthanum and barium.

The loading amount of a metal selected from platinum and palladium is 1 to 20% by weight in terms of metal based on the total weight of the catalyst.
Is preferable, and 2 to 15% by weight is more preferable. The supported amount of rhodium is from 0.5 to 0.5 in terms of metal based on the total weight of the catalyst.
It is preferably 10% by weight, more preferably 1 to 5% by weight. The loading amount of a metal selected from lanthanum and barium is preferably 0.5 to 7% by weight, more preferably 1 to 5% by weight in terms of metal, based on the total weight of the catalyst.

[0020] Manufacturing Method Next, a method for manufacturing the catalyst structure of the present invention. In order to improve the adhesion between the substrate and the catalyst, it is preferable to sand the surface of the substrate and carry out a surface treatment with various blasts or the like before supporting the catalyst. Further, it is preferable to clean the surface of the substrate before supporting the catalyst. This cleaning treatment may be performed by degreasing with a commercially available neutral detergent, washing with pure water or the like, and drying at 80 to 110 ° C for 20 to 60 minutes.

Next, the catalyst is supported on a substrate. The catalyst is supported on at least the surface of the substrate that comes into contact with the exhaust gas. Depending on the actual use condition of the catalyst structure, it may be supported on the entire surface of the substrate or may be partially supported. For example, in the case of a honeycomb base material having a large number of holes in the flow direction of the exhaust gas, the catalyst is carried on the inner surface of the hole that contacts the exhaust gas.

The method of carrying the catalyst, in particular, a conventionally used method may be used. For example, the carrier component and the active component of the catalyst may be supported at the same time, or the carrier component may be supported first and then the active component. As a method of supporting, prepare a slurry containing the required components,
What is necessary is just to select suitably from the conventionally used methods, such as immersion, brush coating, flow coating, spray coating, etc. according to the shape and size of a base material. Thus, the catalyst structure of the present invention is obtained. The amount of the supported catalyst was 1 m
Usually, 20 to 100 g per ² is preferable.

The catalyst structure of the present invention is provided in a flow path of exhaust gas discharged from an internal combustion engine, a boiler, a gas turbine or the like, and purifies the gas by contacting the exhaust gas. The installation position may be selected at an optimum position such as a high-temperature region or a low-temperature region of the exhaust gas depending on the characteristics of the supported catalyst.

[0024]

EXAMPLES The present invention will be described more specifically with reference to the following examples, but the present invention is not limited to these examples. In the examples,% is% by weight. Example 1 Ferritic stainless steel NTK manufactured by Nippon Metal Industry Co., Ltd.
U-4B (C: 0.01%, Si: 2.15
%, Mn: 0.58%, Cr: 18.75%, Mo:
0.46%, the balance Fe), the outer diameter 30mm × length 100mm
x Process into a cylinder with a thickness of 1 mm, and add a hole diameter to the side wall of this cylinder.
A substrate having a large number of through-holes having a diameter of 2 mm and a center interval of the holes of 3 mm was used as a substrate. A particle size of 250 to 300
A μm alumina powder was blasted with compressed air for 1 minute. Next, this was degreased with a commercially available neutral detergent, washed with pure water, and then dried at 105 ° C. for 60 minutes.

Next, a slurry of the catalyst was prepared, and this was applied to the entire surface of the base material with a brush. The catalyst used was a commercially available γ-alumina powder (BET specific surface area 150 m ² / g, average particle size 30 μm) and a commercially available cerium stabilized zirconia powder (cerium content 25%, BET specific surface area 60 m ² / g, average particle size) (A diameter of 10 μm) (46% of γ-alumina and 48% of cerium-stabilized zirconia with respect to the total weight of the catalyst) supported 5% of platinum and 1% of rhodium in terms of metal with respect to the total weight of the catalyst. Was. Next, after drying at 105 ° C. for 2 hours, it was calcined in air at 400 ° C. for 30 minutes to obtain a catalyst structure (A-1) supporting 40 g of catalyst per 1 m ^{2 of} the base material.

Example 2 In Example 1, instead of the stainless steel NTK U-4B, a ferritic stainless steel NTK E-1 manufactured by Nippon Metal Industry Co., Ltd. (composition: C: 0.016%, Si:
0.51%, Mn: 0.33%, Cr: 18.50%,
Example 1 except that Mo: 0.57% and the balance Fe) were used.
In the same manner as in the above, a catalyst structure (A-2) was obtained.

Example 3 In Example 1, the amount of γ-alumina in the total weight of the catalyst was changed to 45%, and the active components were changed to 5% of palladium and 1% of rhodium in terms of metal instead of 5% of platinum and 1% of rhodium in terms of metal. Except having changed to 2%, it carried out similarly to Example 1, and obtained the catalyst structure (A-3).

Example 4 A catalyst structure was prepared in the same manner as in Example 1 except that the amount of γ-alumina in the total weight of the catalyst was changed to 43%, and lanthanum was further supported as an active component by 3% in terms of metal. A body (A-4) was obtained.

Example 5 A catalyst structure was prepared in the same manner as in Example 1 except that the amount of γ-alumina was changed to 43% based on the total weight of the catalyst, and 3% of barium was further supported as an active component in terms of metal. A body (A-5) was obtained.

Comparative Example 1 A base material was prepared in the same manner as in Example 1 using a commercially available ferritic stainless steel SUS430 (composition: C: 0.021%, Cr: 17.58%, balance Fe). Thereafter, a blast treatment and a cleaning treatment were similarly performed. The substrate was plasma sprayed with alumina. The thickness of the obtained alumina coating was about 30 μm on the outer surface of the substrate and about 5 μm on the inner surface. No pinholes, cracks, cracks, etc. were observed in the coating. Next, a catalyst was supported on this alumina-coated substrate in the same manner as in Example 1, to obtain a catalyst structure (B-1).

Comparative Example 2 A substrate was made in the same manner as in Example 1 using the stainless steel plate used in Comparative Example 1, and only the cleaning treatment was performed without blasting. This base material is immersed in a 13% m-xylene solution of polysilazane and coated with the solution, dried at 80 ° C. for 10 minutes, and then baked at 450 ° C. for 1 hour to form a thermally decomposed polysilazane on the base material. Was formed. The thickness of the film was about 1 μm, and no pinholes, cracks, cracks, etc. were observed in the film. Next, a catalyst was supported on the polysilazane pyrolyzate-coated substrate in the same manner as in Example 1, and the catalyst structure (B-2)
I got

Comparative Example 3 In Example 1, a commercially available ferritic stainless steel SUS463L was used instead of the stainless steel NTK U-4B.
(Composition: C: 0.005%, Cr: 17.02%, M
o: A catalyst structure (B-3) was obtained in the same manner as in Example 1 except that 1.03% and the balance Fe) were used.

Performance Evaluation Example 1 For the catalyst structures of Examples 1 to 5 and Comparative Examples 1 to 3,
Initial exhaust gas purification performance was evaluated using a motorcycle engine. Exhaust gas purification rate test is 30k when idling
Under operating conditions corresponding to m / h and 50 km / h, the concentrations of hydrocarbons (HC) and carbon monoxide (CO) were measured. Table 1 shows the results of the exhaust gas purification rate test.

[0034]

[Table 1]

Performance Evaluation Example 2 The catalyst structures obtained in Examples 1 to 5 and Comparative Examples 1 to 3 were tested for catalyst adhesion by the following method. Each catalyst structure was weighed before the test. The catalyst structure was placed in an electric furnace maintained at 300 ° C., and heated at 300 ° C. for 1 hour. The catalyst structure was taken out of the electric furnace, immediately put into water and cooled. This heating and cooling was repeated twice more.
Next, the catalyst structure was dried at 105 ° C. for 1 hour and weighed. In addition, each catalyst structure was weighed before and after supporting the catalyst, and the weight of the supported catalyst was measured in advance.
The peeling rate of the catalyst was determined by the following equation. In addition, it did not peel except the catalyst.

[0036] (A): Weight of catalyst structure before test (B): Weight of catalyst structure after test is shown in Table 2.

[0037]

[Table 2] As shown in Table 2, the catalyst structure (A-1 to A-5) of the present invention has a catalyst adhesion that significantly surpasses the catalyst structure (B-1) of Comparative Example 1 in which alumina was plasma-sprayed on a stainless steel substrate. It was found to have.

Performance Evaluation Example 3 For the catalyst structures of Examples 1 and 2 and Comparative Examples 1 to 3,
The high temperature corrosion resistance after durability was evaluated. As for the durability conditions, the catalyst structure was exposed to exhaust gas (A / F = 15.0) of a four-wheeled vehicle engine. . The center temperature of the catalyst structure was 950 ° C., and the surface temperature was 1000 ° C. The endurance time is every 20 hours,
It went up to a total of 100 hours. The catalyst structure was taken out every 20 hours and the degree of corrosion was visually observed. The durability of the catalyst structure having a high degree of corrosion was improved thereafter. The observation results were evaluated according to the following criteria. A: No corrosion. ：: Oxides are generated in the form of dots on the catalyst surface. Δ: Oxides are generated in a lump at a plurality of locations on the catalyst surface. ×: The oxide covers the entire surface of the catalyst. Table 3 shows the results.

[0039]

[Table 3] (Note) When the substrate of the catalyst structure was corroded, the oxide of the substrate penetrated the catalyst and reached the catalyst surface. Table 3 shows that the catalyst structures (A-1 to A-2) of the present invention have much better high-temperature corrosion resistance than the catalyst structures of Comparative Examples.

Performance Evaluation Example 4 With respect to the catalyst structures of Examples 1 and 2 and Comparative Example 1, the catalyst purification performance after durability was evaluated. The catalyst structures of Examples 1 and 2 were exposed to exhaust gas of a four-wheel engine for 100 hours in Performance Evaluation Example 3, and the catalyst structures of Comparative Example 1 were exposed for 20 hours. . The evaluation conditions were the same as in Performance Evaluation Example 1. Table 4 shows the results.

[0041]

[Table 4]

From Table 4, it can be seen that the catalyst structure of the present invention (A-1 to A-1)
It can be seen that A-2) has excellent purification performance even after 100 hours of durability. As described above, the catalyst structure of the present invention has a better adhesion between the base material and the catalyst than a catalyst structure obtained by plasma spraying alumina on a stainless steel substrate or a catalyst structure using stainless steel SUS436L as a base material. Excellent heat resistance and high temperature corrosion resistance.

[0043]

The exhaust gas purifying catalyst structure of the present invention has the following features.
It has excellent corrosion resistance (especially high-temperature corrosion resistance), and has high adhesion strength between the metal substrate and the catalyst. Furthermore, it can be manufactured without using expensive equipment, and has an advantage that it is not restricted by its shape and size.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI C22C 38/38 B01D 53/36 ZABC (72) Inventor Kiyoshi Inanaga 2-1-1 Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Metal Industry Co., Ltd. Inside the company (72) Inventor Kinji Saito 2-1-1, Nishi-Shinjuku, Shinjuku-ku, Tokyo Japan Metal Industry Co., Ltd.

Claims (2)

[Claims] (A) In weight%, C: 0.2% or less, S
i: 0.4% to 3.0%, Mn: 2.0% or less, Cr:
13.0 to 20.0%, Mo: 0.3 to 3.0%, base material made of ferritic stainless steel composed of Fe and impurities, and carrier composed of (B) γ-alumina and cerium-stabilized zirconia A catalyst selected from platinum and palladium as active components and rhodium supported thereon, and a catalyst supported on the substrate. 2. The catalyst structure according to claim 1, wherein said catalyst further contains a metal selected from lanthanum and barium as an active component.