US3928241A - Catalysts for purifying exhaust gas - Google Patents

Abstract

Exhaust gas purifying catalysts characterized in that alloys comprising 0.1-40% of Cu and the balance of Ni and/or Fe by weight as fundamental components are shaped as desired and are activated, at least partially, by providing their surfaces with oxidized enriched Cu layers thicker than 10 Beta in the oxidization atmosphere or by partially reducing the oxidized layers with hydrogen gas at high temperature.

Description

United States Patent Niimi et a1.

CATALYSTS FOR PURIFYING EXHAUST GAS Inventors:

Assignee:

Filed:

Appl. No.:

' Itaru Niimi, Nagoya; Yasuhisa Kaneko, Toyota; Akiyoshi Morita, Toyota; Yasuo Nemoto, Toyota; Mitsuyoshi Sato, Toyota, all of Japan Toyota Jidosha Kogyo Kabushiki Kaisha, Japan Feb. 12, 1973 US. Cl. Int. CL

......... 252/470; 252/474; 423/213.5 BOIJ 23/86; B01J 23/72 Field of Search 252/470, 474; 423/2132,

References Cited UNITED STATES PATENTS Hodge 252/470 X Dec. 23, 1975 3,206,414 9/1965 Gunther 252/474 3,565,574 2/1971 Kearby et a1. 252/474 x 3,699,683 10/1972 Tourtellotte et a] 423/2132 x 3,718,733 2/1973 061111 423/2132 3,773,894 11/1973 Bernstein et a1. 252/474 X FOREIGN PATENTS 0R APPLICATIONS 354,692 2/1930 United Kingdom 423/2132 Primary Examiner-W. J. Shine Attorney, Agent, or Firm-Connolly and Hutz [5 7] ABSTRACT Exhaust gas purifying catalysts characterized in that alloys comprising 01-40% of Cu and the balance of Ni and/or Fe by weight as fundamental components are shaped as desired and are activated, at least partially, by providing their surfaces with oxidized enriched Cu layers thicker than 10 1 in the oxidization atmosphere or by partially reducing the oxidized layers with hydrogen gas at high temperature.

3 Claims, 16 Drawing Figures US. Patent Dec. 23, 1975 Sheet 2 of4 3,928,241

After annealing Casted as is Fe-2. 8%Ni-O.5%Cu

(Specimen No. 1)

casted as is After annealing Fe-Q-SZCu (Specimen No. 16)

Ni-24.0ZCu (Specimen No. 18)

US. Patent Dec. 23, 1975 Sheet 3 of4 3,928,241

c d as i After annealing Fe32.0%Ni-l7.7%Cu-3.9ZA1 X 200 (Specimen No. 27)

casted u 1.

];5% C -1. 6181 (Specimen No. 22)

casted as is Fe-28-9ZCu-33.0ZCO gg s (Specimen N0. 33)

US. Patent Dec. 23, 1975 Sheet4 0f4 3,928,241

X 300 Fe-52.0ZNi-26. 4ZCu (Oxidized layer thickness 0.6mm

Oxidized at 900C. for 24 hours) X 1000 Surface of alloy without oxidized layer X 1000 X 3000 Fe-52.0ZNi-26. 4ZCu Fe52.0ZNi-26. rZCu (Oxidized layer thickness 0.6mm (Oxidized layer thickness 0.6mm

Oxidized at 900C. for 24 hours) Oxidized at 900C for 24 hours) CATALYSTS FOR PURIFYING EXHAUST GAS BACKGROUND OF THE INVENTION The present invention relates to a catalyst for purifying exhaust gas.

Conventional industrial catalysts suitable for purifying exhaust gas are agents which are generally made by allowing carriers such as alumina to carry noble metals such as Pt or Pd or carry or mix with oxides of Ni, Cu or Cr. But these are significantly disadvantageous in that catalytic agents comprising noble metals such as Pt or Pd are expensive, their resources are insufficiently available, inferiority in heat resistance and durability, and unsuitability for quantity production due to difficult manufacturing methods. Various other alloy system catalysts are known in addition to catalysts as mentioned above, but these do not demonstrate their effects if temperature is not high.

SUMMARY OF THE INVENTION Accordingly, it is an object of the present invention to provide a unique catalyst for purifying exhaust gas which avoids the drawbacks of the prior art and which functions in a highly beneficial and economical manher.

The present invention relates to exhaust gas purifying catalysts having characteristics for removing harmful nitrogen oxide (NOx) components contained in exhaust gases, particularly those from internal combustion engines, by reduction, and is characterized in that alloys comprising 01 40% of Cu and the balance of Ni and/or Fe by weightare provided with enriched Cu layers on their surface portions, or further, the oxidized layers are partially activated. I

BRIEF DESCRIPTION OF THE DRAWINGS Novel features and advantages of the present invention in addition to those mentioned above will become apparent to those skilled in the art from a reading of the following detailed description in conjunction with the accompanying drawings wherein similar reference characters refer to similar parts and in which:

FIG. 1 is a diagram of alloy composition ranges of the I catalysts according to the present invention;

FIG. 2 is a graph diagram showing therelationship between NO and CO purification rates and catalyst bed temperatures;

FIG. 3 through 8 are microscopic photographs of typical alloys and catalysts obtained in embodying Examples I through 6 according to the present invention;

FIG. 9 is a photograph made by a scanning-type electronic microscope illustrating the state of an alloy surface in the case where an oxidized layer is absent from the surface; and

FIG. 10 comprises photographs made by a scanningtype electronic microscope illustrating the state of an alloy surface in the case where an oxidized layer thicker than 10g. is present.

DETAILED DESCRIPTION OF TI-IEINVENTION The present invention is intended to provide catalysts for reducingand removingNOx contained'in exhaust gas discharged from internal combustion engines. The

dance with a wide range of applications. Compositions and manufacturing of exhaust gas purifying catalysts according to the present invention'are described below.

Asfor compositions of alloys according to the present invention, catalysts of this invention comprise a binary Fe-Cu or Ni-Cu or a ternary Fe-Ni-Cu system alloy (hereinafter referred to as this systems alloy) always containing less than 99.9% of Fe and Ni and the balance of Cu.

In this'case, it is possible to reduce contents of Fe and Ni as desired and instead, to add elements other than Fe, Ni and Cu less than 10% by weight.

The type of elements to be added is not particularly restricted, but since C0 and Cr efficiently achieve the catalytic effect, addition of those elements up to 40% by weight is acceptable. Co demonstrates the effect similar to that of Cu. Of course, nonmetallic elements such as C and Si which are contained in usual alloys also may be added.

A composition range of this systems alloy for the catalysts according to the present invention is given in FIG. 1. A portion rectangularly surrounded by ABCD is a standard composition range. Even in case other additive elements are contained, if the composition rate is within a diagonallylined range, that composition is acceptable. In the presentinvention, this system's alloy within the above composition range is obtained by the conventional method and is shaped in workable plasticity types such as a sheet, bar, pipe, line or alloy powder, casting materials, etc., according to alloy compositions and applications for use as catalysts.

It is an essential factor in producing alloy catalysts to place oxidized layers thicker than 10p. over the alloys. The catalysts according to the present invention, can function satisfactory with an oxidized layer only, but those are further improved by reducing the oxidized layers formed on alloys. Descriptions as to examples embodying the present invention are given below. In each of these examples only one-half of the specimen is reduced after oxidation to thereby provide a comparison between oxidation alone and reduction after oxidation.

EXAMPLE 1 After melting Fe-Ni-Cu ternary alloys with various compositions as given in Table 1 at l600C. by using a Tammann furnace, a casting was made in a stainless steel (SUS 27) mold coated with a sufficient thickness of graphite. After casting, casted cylindrical bars'obtained were machined tomake cuttings and were subjected to oxidization treatment in a high temperature atmosphere at 1000C. for six hours to obtain catalyst cuttings.

By producing the cuttings as described above, an apparent surface area per unit weight becomes wider. The dimensions of the cuttings vary with the material, but those within the range of 0.1 0.5mm in thickness, 2mm-20mm in length and lmm-3mm in width are desirable. The term Cuttings in this Example and hereinafter, represents granularity almost within the above range.

Further, half of the catalyst (after oxidization) obtained as above, was reduced at 800C. in hydrogen gas for two hours. Alloy compositions and purification rates of the catalyst obtained by the above process are given in Table 1. Chemical components given in the Table show alloy compositions after casting and the 3 purification rates are results of the test using 10ml of the catalyst. The above explanations are common in Table 2 and succeeding tables.

Table 1 Compositions and purification rates of Fe-Ni-Cu system allo The catalysts apparent surface area of 10ml is desped- Chemical component Npyurjficmion mite pendent on the catalyst components, but is almost 1 p i g i y ft within 100 l000cm Unless otherwise specified,- the Cu Ni Fe :f; surface area 15 identical to that in Example 1.

2 0.8 ba EXAMPLE 2 3 0.9 8.9 ba:

The binary alloy with a COmPOSIUOIIOOf Fe and Cu as 5 26 m bal 195 64.3 given in Table 2 was casted at 1650 C. in the same 6 4,4 50,8 bal 51.3 86.2 metal mold as in Example 1 after being melted in a high 3-; 2:: 2-3 23-? frequency f q 9 6:4 17:5 bal 313 800 Casted cylindrical bars obtained were machined to 1? g-g 2% make cuttings and the cuttings were subjected to oxldi- 12 5 4 zation treatment in an atmosphere at 1100 C. for three 13 10.9 42.1 bal 0 72.1 hours to obtain catalysts. Also, half of the cuttings were 14 223 bal 0 0 15 26.4 52.0 bal 0 78.5 reduced m hydrogen gas at 800 C. for two hours to obtain catalysts.

' 20 EXAMPLE 3 Table 2 A sheet-type catalyst was obtained by subjecting Compositions and purification rates of 0.5mm thickness of an Ni-Cu alloy to atmospheric System alloys N0 oxldlzatlon 800C l and 1 for Speci- Chemical Oxidation/Reduction purification 24, 12, 6 and 3 hours, respectively. men component rate This sheet-type catalyst had been shaped cylindri- Fe cally at 0.5mm in thickness, 2.5mm in width and 15mm 16 2 5 b l 0 6 8 an n in length. A half: of the catalyst was Sub ected to hydroa f f 2 gen gas reduction at 800C. for 2 hours. Apparent oxidization 70.0 surface area of a 10ml catalyst obtained by the above 17 bal process was approximately 100cm.

EXAMPLE 4 Fe-Ni-Cu alloy comprising other additive elements as Table 3 givenin Table 4 was made into cuttings and subjected Treatment conditions and purification to high temperature atmospheric oxidization at S Ch I I 6 9 7 yg C0 ecl- 8111108 Xl 1Z3 1011 1000C. for 6 hours, and a half was Subjec to y glen component Reduction purification purification gen gas reduction at 800C. for 2 hours. No. c N rate rate EXAMPLE 5 40 80.0%.

Fe-Cu binary alloy comprising other additive eleg 'g'fi g: ments as given in Table 5 was made into cuttings and after subjected to high temperature atmospheric oxidization 6323 at 1 100C. for three hours, and a half was subjected to oxidizatjon 763 hydrogen gas reduction at 800C. for 2 hours. Redactlon a er 18 24 66 oxidization 54.3 46.0 EXAMPLE 6 1990,?

Ni-Cu alloy comprising other additive elements as 0 0 eductlon given 111 Table 6 was formed into a 1.0mm thick sheet after and subjected to high temperature atmospheric oxidigggg 531 zation at 900C. for twelve hours to obtain a sheet-type oxidimion 0 1 catalyst, and a half was sub ected to hydrogen gas re- Redpction 0 8 181' duction at 800 C. for 2 hours. The sheet with dimenoxidizafion 62.0 482 810118 of 1.0mm X 2.5mm X 15mm, the same as m Example 3, was cylindrically formed. Apparent surface area of 10ml catalyst was approximately cm Table 4 Fe-Ni-Cu additive element system alloys and purification rates Chemical component NO purification rate Oxidization/Reduction Specimen Oxidization Reduction No. after Cu Ni Fe Others oxidization 19 8.8 30.4 bal C-l. Not 75.0

Si-2.2 measured Co-2l.4 20 9.8 18.4 bal C-2.1 72.1

Si-2.3 21 11.6 39.8 bal C-l.6 80.9

Table 4-continued Fe-Ni-Cu additive element system alloys and purification rates Chemical component N purification rate Oxidization/Reduction Specimen Oxidization Reduction No. after Cu Ni Fe Others oxidization Si-2.l 22 17.7 47.6 bal C-l.5 72.0

Si-l.6 23 17.7 32.0 bal Al-3.9 3.7 74.1 24 18.9 47.4 bal C1 .1 Not 72.0

Si- 1 .6 measured 25 27.9 17.3 bal Si-'4.3 75.3 26 24.3 39.1 bal I Ce-4.l 1.8 Not measured 27 29.7 3.7 bal Al-2.8 2.8 77.7 28 30.1 8.9 bal Si-3.l 0 70.4

using X-ray diffraction after subjecting same to reduc- Table tion treatment.

Fe-Cu additive element system alloys and purification rate Chemical component NO purification rate Reasons for restricting each component element in this systems alloy, which is a basis for the catalyst according to this invention, and its effect are presented below.

As for Cu, when this system s alloy has been oxidized and subsequently reduced to impart a catalyst effect, CuO* is formed on the alloy surface, and CuO* being diffused into FeO* and NiO* is presumed to play a significant role for catalytic effect.

CuO* herein represents oxidized Cu, but since the state of achieving the optimum catalytic effect is unknown and content of oxygen can not be determined, representation is made by 0*.

Catalytic activity is deemed to become present when 0* in oxides is almost nil. FeO* and NiO* denote the same as in CuO*.

When the surface of alloys subjected to oxidization treatment at high temperature was examined by utilizing X-ray diffraction to certify the above matters, compositions were proven as follows.

CuO* CuO FeO* Fe O (Hematite) NiO* NiO Moreover, the following compositions were also clarified when the surface of the alloy was examined by However, it can not be concluded that all of them are in the same state as mentionedabove.

The reason for restricting the Cu content is that when Cu exceeds 40% or becomes less than 0.1% by weight, diffusion of CuO* into NiO* and FeO* becomes dense and coarse respectively, and either case adversely affects the catalytic effect. In case Cu is excessive, it separates and deposits in the alloy provided that it does not form a solid solution or intermetallic compound.

This problem is caused due to the presence of Fe as seen from the Fe-Cu binary state diagram given in FIG. 1, and deposited Cu does not have catalytic effect.

Intermetallic compounds are difficult to oxidize, and even if oxidized, those compounds do not form oxidized layers having catalytic effect. Therefore, although Cu is contained therein, it adversely affects the catalytic effect. The more this systems alloy contains solid solution Fe-Ni-Cu or Fe-Cu, the greater the catalytic effect becomes. Now, as for Ni and Fe, it is felt that Ni and Fe act to promote the catalytic effect rather than to provide the direct reduction effect to NOx, that is, a dispersed state of CuO* is thereby made effective and the effect of adsorbing molecules such as CO and H useful for reduction of NO is excellent.

Meanwhile, Ni is effective for expanding a solid solution limit of Cu into Fe, which can be presumed from the binary state diagram of Ni-Cu and Fe-Ni given in FIG. 1. Coexistence and independent existence of Ni and Fe are acceptable.

1f additive elements satisfy the following conditions when added to this systems alloys of Fe-Ni-Cu, Fe-Cu or Ni-Cu, the catalytic effect will not be reduced much, that is;

1. Permeation into solid solution.

2. Non-production of intermetallic compound with 3. Non-deposition of Cu due to presence of additive elements.

Moreover, if additive elements less than 10% by weight satisfy the above conditions, the catalytic effect will be obtained. The less the degree of satisfying the conditions becomes, the lower the catalytic effect becomes, but as long as additive elements do not exceed 10% by weight, the catalytic effect will be substantially maintained.

Also, even if graphite is crystallized in the alloy structure by adding carbon or silicon, the catalytic effect will not be adversely effected. As for Co, it acts similarly to Cu as described previously and it is unnecessary to restrict the content of Co, but the upper limit is determined in relation to the coexistence with Fe and Ni. As for Cr, it does not considerably lower the catalytic effect and the content may widely be restricted. However, the content of Cr over 40% is undesirable from a standpoint of melting and subsequent workability.

In addition to the description as to component elements, microscopic photographs of casted and annealed structures of component elements given in Examples 1 through 6 are presented in FIGS. 3 through 8 in order to clarify the effect of each component. Annealed structures are those which are annealed by furnace cooling after heating at l000C. for 6 hours.

Then, actions of oxidized layers and reduced layers which are essential for obtaining optimum catalytic effect are described. Oxidized layers are formed by oxidizing in atmospheric conditions. Since thicknesses of oxidized layers vary with alloy compositions, surface condition, oxidizing temperature, and period of oxidizing time, treatment conditions can not be formulated, but desired thickness is obtainable by selecting conditions within temperatures ranging from 700 to 1 100C. and time periods ranging from 1/2 hour to 24 hours or temperatures ranging from 800 to 1300C and time periods ranging from 3 to 24 hours.

The thickness of oxidized layers are required to be at least 10p. and a thickness above 10p. is unlimitedly permissible, to the extreme of up to the center portion of the alloys.

On the contrary, as the thickness becomes less than 10 1., the catalytic effect is remarkably deteriorated and at last becomes unobtainable if the temperature is above 700C. This is considerably due to the effect of CuO*, NiO*, FeO*, etc., against the catalytic activity as previously described in the compositions. Also, the oxidized layer with a thickness of at least 10p. is necessary to provide oxidized layers with corrugation and to increase the surface area as will be described later. As a result of examining composition variations of oxidized layers by using an X-ray micro-analyzer, the following matters became clear, that is enriched Fe and Cu layers are formed at the top surface, and moreover, the enriched Cu layer is placed close to the surface more than the enriched Fe layer. This tendency becomes further obvious by providing a reduction treatment and the enriched Cu layer exists at the very top surface.

An enriched Ni layer is also formed at the portion near the surface, but slightly lower than the enriched Fe and Cu layers, and after subsequent reduction treatment, in the same position as that of the enriched Fe layer or slightly close to the surface. The enriched Cu layer formed near the top surface exists independent from other additive elements. Co displays an enriched state similar to that of Cu.

In case the oxidized layer is thinner than 10 1., the enriched oxidized layer, as described above, can not be formed. On the other hand, as the oxidized layer becomes thicker, the above tendency becomes considerably more, that is, Cu enriches in the surface and diffuses into Ni and Fe. This is an advantageous condition for catalytic effect. In Examples 1-6, since the thickness of all oxidized layers were made in 0.5 1.0mm,

the above condition was satisfied. As a result of observing oxidized layer surfaces by a scanning-type microscope, it became clearer that the oxidized layer surfaces were corrugated and porous, that this tendency became extreme when the oxidized layer thickness was less than 10a, and further, that this tendency became' obvious when the oxidized layer was subjected to a subsequent reduction treatment.

Thus, an oxidized layer thinner than 10p. apparently lowers its catalytic effect, as seen from the above surface observation results. This tendency is shown in FIGS. 9 and 10. FIG. 9 shows the surface when the oxidized layer is insufficiently formed and corrugation and porosity are not seen therein, but are apparent in FIG. 8 which shows the state of a sufficiently oxidized layer.

As described in the Examples, the reduction treatment of an oxidized layer is the processing in hydrogen gas and the treatment condition is determined within the treatment period of time ranging from 24 hours in accordance with the state of the subject oxidized layer, and at least, partial treatment is acceptable.

Thereafter, the test results on catalytic effects by catalysts according to the present invention are presented.

TEST EXAMPLE 1 The purification rate as to NO was measured under the following conditions in order to certify the effect of each catalyst obtained in the embodying Examples l6.

Devices employed:

Test gas:

Gas flow rate: Amount of catalyst: Type of catalyst:

S.V. (Space Velocity):

Catalyst bed temperature: Catalyst surface area:

2. Results The results are as given in Tables 1 through 6. Each result shows an excellent NO purification rate. Certain catalysts do not achieve sufficient purification ability with their oxidized layers only, but it has been known that the effect can be improved by providing same with reduction treatment. As a result of testing with alloy systems other than this system's alloy under the same conditions, neither one demonstrated a suffficient NO purification rate.

The catalysts according to the present invention also act effectively as an oxidization catalyst for hydrocarbon (HC) and carbon monoxide (CO) if an oxidization atmosphere is available.

g TEST EXAMPLE 2 TEST EXAMPLE 3 The test was made under the following conditions by This test proves that the catalysts according to this using the same analyzing devices as in. Test Example 1. invention are effective for purifying harmful NO com- 5 ponents contained in internal combustion engine exhaust gas.

The catalyst was made by machining this 'systems (1) Test alloy with various components, as given in Table 7, to

CO measuring meter was used.

Test gas: CQ produce cuttings by forming an oxidized layer, by reg gggg PP"! ducing, and then stuffing into the catalyst converter for N: the rest ,I purifying internal combustion engine exhaust gas.

(1) Test conditions Internal combustion engine: 1900cc four cylinder reciprocal gasoline engine Installation location of Just behind the exhaust manifold catalyst converter: and approximately 40cm back from the cylinder head Shape of catalyst converter: Cylindrical type with 70mm diameter and 300mm length. Capacity 1.2 lit. Type of catalyst: Catalysts with compositions given in Table 7. Stuffed compactly. Weight: Approx. 2.0kg Apparent surface area: Approx. 20000 cm Engine operation: Steady bench test operation Condition: A 2700 rpm 2.2kg rn B 2500 rpm 1.2kg m Catalyst bed temperature: A 660C. B 630C. S.V.: A 40,000 V/V,. hr B 27,000 V/V,,. hr

Gas flow rate: 2.5 l/minute Measurement was made by an exhaust gas analyzing Amount of catalyst: Sml meter Type of catalyst: Ni-24% Cu catal st in a bent sheet with 0 cm Results of pp surface area NO and CO were purified approximately 100% S.V.. 30,000 v/v,. hr r Catalyst bed temperature: 300 700C, and l 1% respectively, as shown in Table 7. As a result of testing with alloys other than this systems alloy, both achieved a slight purification rate.

Table 7 Alloy component Engine N0 C0 operapurifipurifi- Specimen ting cation cation condirate rate No. Cu Ni Fe Others tion 35- 9.4 45.0 bal A 58.3 10.7 B 98.0 5.0 36 9.0 43.3 bal Cr- 3.7 A 55.5 9.9 B 94.4 4.6 37 9.2 39.5 bal Co- 1.3 A 40.5 8.3 B 89.9 4.7 38 8.9 41.7 bal Co-I5.7 A 49.7 9.1 B 92.3 5.0 39 8.8 42.6 bal Co- 5.3 A 45.2 8.9

Cr- 4.1 Ce- 2.5 B 88.3 4.4

Note:

Average exhaust gas composition under operating condition A N0-2400 ppm C0-2.2% l-lC-l 10 ppm Average exhaust gas composition under operating condition B NO-600 ppm C0-4.5% I-IC-l ppm 2. Results As seen from the evaluations based on the above test Both NO and CO were remarkably purified from the examples, this systems alloy achieves an outstanding low temperature side as illustrated in FIG. 2. The term effect as reduction oxidization catalysts. Also as proven Oxidization" given in FIG. 2 denotes that an oxidized by embodying examples and test examples, the alloy is layer formed by treating in atmosphere at 900C. for 12 obtainable at low cost due to extensive selection range hours was present and the term Reduction after oxidiof alloys. Moreover, the alloy is a highly strong and zatlon denotes that it was subsequently subjected to excellent in plasticity, workability and castability as hydrogen gas reduction at 800C. for 2 hours. well as heat resistance and corrosion resistance. Therefore, it can advantageously be formed into cuttings, sheets, pipes, etc. according to application.

What is claimed is:

1. An exhaust gas purifying catalyst comprising an alloy consisting essentially of 01-40% Cu and the balance of at least one of the group consisting of Ni, Fe, and a combination of Ni and Fe by weight as fundamental components, and including a surface formed by first oxidizing the alloy by heating at 700C. 1100C. in an oxidizing atmosphere for k to 24 hours to provide an oxidized layer at least p. in thickness, and thereafter reducing the oxidized layer in a reducing atmosphere at approximately 800C. for about 2 hours.

sired containing 0.1 40% of Cu and the balance of at least one of Ni and Fe as fundamental components and forming an oxidized layer of more than lOp. in thickness on the surface of said shaped alloy by heating same at 800- l300C. in an oxidization atmosphere for 3 24 hours, and thereafter reducing the oxidizing layer by heating same in a reducing atmosphere at approximately 800C. for about 2 hours.

Claims (3)

1. AN EXHAUST GAS PURIFYING CATALYST COMPRISING AN ALLOY CONSISTING ESSENTIALLY OF 0.1-40% CU AND THE BALANCE OF AT LEAST ONE OF THE GROUP CONSISTING OF NI, FE, AND A COMBINATION OF NI AND FE BY WEIGHT AS FUNDAMENTAL COMPONENTS, AND INCLUDING A SURFACE FORMED BY FIRST OXIDIZING THE ALLOY BY HEATING AT 700*C.-1100*C. IN AN OXIDIZING ATMOSPHERE FOR 1/2 TO 24 HOURS TO PROVIDE AN OXIDIZED LAYER AT LEAST 10$ IN A THICKNESS, AND THEREAFTER REDUCING THE OXIDIZED LAYER IN A REDUCING TAMOSPHERE AT APPROXIMATELY 800*C. FOR ABOUT 2 HOURS.

2. An exhaust gas purifying catalyst according to claim 1 including 40% or less of at least one of the group consisting of Co and Cr.

3. A process of producing a catalyst for purifying exhaust gas which comprises shaping an alloy as desired containing 0.1 - 40% of Cu and the balance of at least one of Ni and Fe as fundamental components and forming an oxidized layer of more than 10 Mu in thickness on the surface of said shaped alloy by heating same at 800*- 1300*C. in an oxidization atmosphere for 3 - 24 hours, and thereafter reducing the oxidizing layer by heating same in a reducing atmosphere at approximately 800*C. for about 2 hours.

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