Catalyst composition for exhaust gas purification and catalyst for exhaust gas purification

Abstract

The invention relates to a catalyst composition using other metals different from precious metals as a catalytically active component and is to propose a novel catalyst composition for exhaust gas purification which has excellent catalytic activity, in particular, excellent treatment activity of HC even after a thermal durability treatment. The invention is to propose a catalyst composition for exhaust gas purification comprising catalyst particles having a constitution in which Cu and a transition metal A including at least one of Cr, Fe, Mn, Co, Ni, Zr, and Ag are supported on ceria (CeO.sub.2) particles and a catalyst using the same.

Claims

1. A catalyst composition for exhaust gas purification comprising catalyst particles having a constitution in which Cu and a transition metal A including at least one of Ni and Zr are supported on ceria (CeO.sub.2) particles by an arc plasma method.

2. The catalyst composition for exhaust gas purification according to claim 1, wherein a content ratio of the transition metal A to the ceria particles obtained by the following Formula (2) is 0.05 to 20 mass %,
Content ratio of transition metal A={amount of transition metal A/(amount of ceria particles+amount of Cu+amount of transition metal A)}100.(2)

3. The catalyst composition for exhaust gas purification according to claim 1, wherein a content ratio of the Cu to the ceria (CeO.sub.2) particles obtained by the following formula (1) is 0.05 to 20 mass % and a content ratio of the transition metal A to the ceria (CeO.sub.2) particles obtained by the following formula (2) is 0.05 to 20 mass %,
Content ratio of Cu={amount of Cu/(amount of ceria particles+amount of Cu+amount of transition metal A)}100(1)
Content ratio of transition metal A={amount of transition metal A/(amount of ceria particles+amount of Cu+amount of transition metal A)}100.(2)

4. A catalyst for exhaust gas purification comprising a constitution in which the catalyst composition for exhaust gas purification according to claim 1 is supported on a honeycomb substrate.

5. A catalyst for exhaust gas purification comprising a constitution in which the catalyst composition for exhaust gas purification according to claim 1 is formed in a pellet shape.

6. The catalyst composition for exhaust gas purification according to claim 1, wherein Cu, Ni and Zr are supported on the ceria (CeO.sub.2) particles.

7. The catalyst composition for exhaust gas purification according to claim 1, wherein Cu and Ni are supported on the ceria (CeO.sub.2) particles.

8. The catalyst composition for exhaust gas purification according to claim 1, wherein Cu and Zr are supported on the ceria (CeO.sub.2) particles.

9. The catalyst composition for exhaust gas purification according to claim 1, wherein Cu and the transition metal A are supported on the ceria (CeO.sub.2) particles in a state of a composite oxide of Cu and the transition metal A.

10. The catalyst composition for exhaust gas purification according to claim 1, further comprising another catalyst particle in which a precious metal is supported on an inorganic porous particle, the another catalyst particle being different from the catalyst particles having the constitution in which Cu and the transition metal A including at least one of Ni and Zr are supported on ceria (CeO.sub.2) particles by the arc plasma method.

11. A catalyst composition for exhaust gas purification containing catalyst particles having a constitution in which Cu and a transition metal A including at least one of Ni and Zr are supported on ceria (CeO.sub.2) particles by an arc plasma method, wherein the Cu and the transition metal A of the catalyst particles are supported on the ceria (CeO.sub.2) particles in a state of an each oxide or a metal or in a state of a composite oxide thereof.

12. The catalyst composition for exhaust gas purification according to claim 11, wherein a content ratio of the transition metal A to the ceria particles obtained by the following Formula (2) is 0.05 to 20 mass %,
Content ratio of transition metal A={amount of transition metal A/(amount of ceria particles+amount of Cu+amount of transition metal A)}100.(2)

13. The catalyst composition for exhaust gas purification according to claim 11, wherein a content ratio of the Cu to the ceria (CeO.sub.2) particles obtained by the following formula (1) is 0.05 to 20 mass % and a content ratio of the transition metal A to the ceria (CeO.sub.2) particles obtained by the following formula (2) is 0.05 to 20 mass %,
Content ratio of Cu={amount of Cu/(amount of ceria particles+amount of Cu+amount of transition metal A)}100(1)
Content ratio of transition metal A={amount of transition metal A/(amount of ceria particles+amount of Cu+amount of transition metal A)}100.(2)

14. A catalyst for exhaust gas purification comprising a constitution in which the catalyst composition for exhaust gas purification according to claim 11 is supported on a honeycomb substrate.

15. A catalyst for exhaust gas purification comprising a constitution in which the catalyst composition for exhaust gas purification according to claim 11 is formed in a pellet shape.

16. The catalyst composition for exhaust gas purification according to claim 11, wherein Cu, Ni and Zr are supported on the ceria (CeO.sub.2) particles.

17. The catalyst composition for exhaust gas purification according to claim 11, wherein Cu and Ni are supported on the ceria (CeO.sub.2) particles.

18. The catalyst composition for exhaust gas purification according to claim 11, wherein Cu and Zr are supported on the ceria (CeO.sub.2) particles.

19. The catalyst composition for exhaust gas purification according to claim 11, wherein Cu and the transition metal A are supported on the ceria (CeO.sub.2) particles in a state of a composite oxide of Cu and the transition metal A.

20. The catalyst composition for exhaust gas purification according to claim 1, further comprising an OSC material particle including at least one selected from a group consisting of a cerium compound particle, a zirconium compound particle and a ceria-zirconia composite oxide particle, the OSC material particle being different from the catalyst particles having the constitution in which Cu and the transition metal A including at least one of Ni and Zr are supported on ceria (CeO.sub.2) particles by the arc plasma method.

Description

EXAMPLES

(1) Hereinafter, the invention will be described in detail based on the following Examples and Comparative Examples.

Comparative Example 1

(2) A catalyst composition (Fresh) including a constitution in which Cu oxide was supported on ceria particles was obtained in such a manner that 99 parts by mass of CeO.sub.2, 1 part by mass of copper acetate monohydrate in terms of Cu metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(3) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

(4) An XRD measurement was performed on the catalyst composition (Aged), and, as a result, a peak of CuO was detected simultaneously with a peak of CeO.sub.2.

Comparative Example 2

(5) A catalyst composition (Fresh) including a constitution in which Cu oxide was supported on ceria particles was obtained in such a manner that 90 parts by mass of CeO.sub.2, 10 parts by mass of copper acetate monohydrate in terms of Cu metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(6) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

(7) An XRD measurement was performed on the catalyst composition (Aged), and, as a result, a peak of CuO was detected simultaneously with a peak of CeO.sub.2.

Example 1

(8) A catalyst composition (Fresh) including a constitution in which Cu oxide and Mn oxide were supported on ceria particles was obtained in such a manner that 95 parts by mass of CeO.sub.2, 2.5 parts by mass of copper acetate monohydrate in terms of Cu metal, 2.5 parts by mass of manganese nitrate hexahydrate in terms of Mn metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(9) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

(10) An XRD measurement was performed on the catalyst composition (Aged), and, as a result, a peak of Cu.sub.1.5Mn.sub.1.5O.sub.4 and Mn.sub.2O.sub.3 was detected simultaneously with a peak of CeO.sub.2.

Example 2

(11) A catalyst composition (Fresh) including a constitution in which Cu oxide and Mn oxide were supported on ceria particles was obtained in such a manner that 95 parts by mass of CeO.sub.2, 4 parts by mass of copper acetate monohydrate in terms of Cu metal, 1 part by mass of manganese nitrate hexahydrate in terms of Mn metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(12) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

(13) An XRD measurement was performed on the catalyst composition (Aged), and, as a result, a peak of Cu.sub.1.5Mn.sub.1.5O.sub.4 and Mn.sub.2O.sub.3 was detected simultaneously with a peak of CeO.sub.2.

Example 3

(14) A catalyst composition (Fresh) including a constitution in which Cu oxide and Mn oxide were supported on ceria particles was obtained in such a manner that 95 parts by mass of CeO.sub.2, 1 part by mass of copper acetate monohydrate in terms of Cu metal, 4 parts by mass of manganese nitrate hexahydrate in terms of Mn metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(15) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

(16) An XRD measurement was performed on the catalyst composition (Aged), and, as a result, a peak of Cu.sub.1.5Mn.sub.1.5O.sub.4 and Mn.sub.2O.sub.3 was detected simultaneously with a peak of CeO.sub.2.

Example 4

(17) A catalyst composition (Fresh) including a constitution in which Cu oxide and Ni oxide were supported on ceria particles was obtained in such a manner that 95 parts by mass of CeO.sub.2, 2.5 parts by mass of copper acetate monohydrate in terms of Cu metal, 2.5 parts by mass of nickel nitrate hexahydrate in terms of Ni metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(18) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

(19) An XRD measurement was performed on the catalyst composition (Aged), and, as a result, a peak of CuO and NiO was detected simultaneously with a peak of CeO.sub.2.

Example 5

(20) A catalyst composition (Fresh) including a constitution in which Cu oxide and Ni oxide were supported on ceria particles was obtained in such a manner that 95 parts by mass of CeO.sub.2, 4 parts by mass of copper acetate monohydrate in terms of Cu metal, 1 part by mass of nickel nitrate hexahydrate in terms of Ni metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(21) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

(22) An XRD measurement was performed on the catalyst composition (Aged), and, as a result, a peak of CuO and NiO was detected simultaneously with a peak of CeO.sub.2.

Example 6

(23) A catalyst composition (Fresh) including a constitution in which Cu oxide and Ni oxide were supported on ceria particles was obtained in such a manner that 95 parts by mass of CeO.sub.2, 1 part by mass of copper acetate monohydrate in terms of Cu metal, 4 parts by mass of nickel nitrate hexahydrate in terms of Ni metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(24) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

(25) An XRD measurement was performed on the catalyst composition (Aged), and, as a result, a peak of CuO and NiO was detected simultaneously with a peak of CeO.sub.2.

Example 7

(26) A catalyst composition (Fresh) including a constitution in which Cu oxide, Ag oxide, and Ag metal were supported on ceria particles was obtained in such a manner that 95 parts by mass of CeO.sub.2, 2.5 parts by mass of copper acetate monohydrate in terms of Cu metal, 2.5 parts by mass of silver nitrate in terms of Ag metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(27) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

Example 8

(28) A catalyst composition (Fresh) including a constitution in which Cu oxide and Co oxide were supported on ceria particles was obtained in such a manner that 95 parts by mass of CeO.sub.2, 2.5 parts by mass of copper acetate monohydrate in terms of Cu metal, 2.5 parts by mass of cobalt nitrate hexahydrate in terms of Co metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(29) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

Example 9

(30) A catalyst composition (Fresh) including a constitution in which Cu oxide and Co oxide were supported on ceria particles was obtained in such a manner that 95 parts by mass of CeO.sub.2, 2.5 parts by mass of copper acetate monohydrate in terms of Cu metal, 2.5 parts by mass of iron nitrate nonahydrate in terms of Fe metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(31) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 800 C. for five hours under air atmosphere.

(32) An XRD measurement was performed on the catalyst composition (Aged), and, as a result, a peak of CuFe.sub.2O.sub.4 was detected simultaneously with a peak of CeO.sub.2.

(33) (Catalyst Performance Evaluation)

(34) With respect to the catalyst compositions (Aged) obtained in Comparative Examples 1 and 2 and Examples 1 to 9, purification performance of a simulation exhaust gas was measured using a fixed bed flow type reactor.

(35) A catalyst composition (powder) of 0.1 g was set in a reaction tube, and then the simulation exhaust gas was introduced into the catalyst powder at the following state, that is, 10 C./min, CO: 500 ppm, C.sub.3H.sub.6: 500 ppmC, NO: 200 ppm, O.sub.2: 4.8%, CO.sub.2: 10%, H.sub.2O: 10%, N.sub.2: balance, and a total flow rate of 1000 cc/min.

(36) After a temperature was raised up to 500 C. at a temperature rising rate of 10 C./min, a pre-treatment was carried out by holding the temperature of 500 C. for 10 minutes. Thereafter, the purification performance of the simulation exhaust gas was measured by raising a temperature from 100 C. to 500 C. at the temperature rising rate of 10 C./min after once cooling, outlet gas components were measured using HC analyzer (VMF-1000F manufactured by Shimadzu Co.), and a temperature (T20) at which HC was purified by 20% was measured.

(37) TABLE-US-00001 TABLE 1 HC (T20): C. Comparative 1 wt % Cu/CeO.sub.2 474.0 Example 1 Comparative 10 wt % Cu/CeO.sub.2 442.2 Example 2 Example 1 (2.5 wt % Cu + 2.5 wt % Mn)/CeO.sub.2 323.8 Example 2 (4 wt % Cu + 1 wt % Mn)/CeO.sub.2 371.7 Example 3 (1 wt % Cu + 4 wt % Mn)/CeO.sub.2 402.2 Example 4 (2.5 wt % Cu + 2.5 wt % Ni)/CeO.sub.2 433.4 Example 5 (4 wt % Cu + 1 wt % Ni)/CeO.sub.2 409.1 Example 6 (1 wt % Cu + 4 wt % Ni)/CeO.sub.2 424.9 Example 7 (2.5 wt % Cu + 2.5 wt % Ag)/CeO.sub.2 396.1 Example 8 (2.5 wt % Cu + 2.5 wt % Co)/CeO.sub.2 376.1 Example 9 (2.5 wt % Cu + 2.5 wt % Fe)/CeO.sub.2 430.8

(38) From Table 1, as compared to the case where only Cu was supported on the ceria (CeO.sub.2) particles, it was found that the purification performance of HC was improved in the case where a combination of Cu and other transition metals was supported on the ceria (CeO.sub.2) particles.

(39) When the catalyst particles obtained in Examples 1 to 9 were measured by an XRD, Cu and the other transition metals were supported on the ceria (CeO.sub.2) particles in a state of an each oxide or a metal before the thermal durability treatment.

(40) Meanwhile, when heating and thermal durability treatment were carried out under a reducing atmosphere, it was found that Cu and other transition metals were supported on the ceria (CeO.sub.2) particles in a state of a delafossite-type oxide.

(41) In addition, when the heating and thermal durability treatment were carried out under an oxidizing atmosphere, it was found that Cu and Mn were supported on the ceria (CeO.sub.2) particles in a state of a non-stoichiometry spinel (Cu.sub.1.5Mn.sub.1.5O.sub.4); Cu and Fe were supported on the ceria (CeO.sub.2) particles in a state of a spinel-type oxide (CuFe.sub.2O.sub.4); Cu and Ni were supported on the ceria (CeO.sub.2) particles in a state of an each oxide (CuONiO); and Cu and Ag were supported on the ceria (CeO.sub.2) particles in a state of an each oxide (CuOAg.sub.2O) and a metal (CuOAg).

(42) Even in any case, it was also found that excessive quantities of Cu and transition metal A exist in the state of an oxide or a metal.

(43) Furthermore, from the above test results and test results which have been made, with respect to the content (that is, supported amount) of Cu, it was considered that the content ratio of Cu to the ceria (CeO.sub.2) particles obtained by the following Formula (1) was preferably 0.05 to 20 mass %, more preferably 0.10 mass % or more or 15 mass % or less, and most preferably 0.15 mass % or more or 10 mass % or less.
Content ratio of Cu={amount of Cu/(amount of ceria particles+amount of Cu+amount of transition metal A)}100(1)

(44) On the other hand, with respect to the content (that is, supported amount) of the transition metal A, it was considered that the content ratio of transition metal A to the ceria (CeO.sub.2) particles obtained by the following Formula (2) was preferably 0.05 to 20 mass %, more preferably 0.1 mass % or more or 10 mass % or less, and most preferably 0.2 mass % or more or 5 mass % or less.
Content ratio of transition metal A={amount of transition metal A/(amount of ceria particles+amount of Cu+amount of transition metal A)}100(2)

(45) Above all, with respect to the content (that is, supported amount) of Mn, it was considered that the content ratio of transition metal A to the ceria (CeO.sub.2) particles obtained by the following Formula (2) was preferably 0.05 to 20 mass %, more preferably 0.1 mass % or more or 10 mass % or less, and most preferably 0.5 mass % or more or 1.5 mass % or less.

(46) With respect to the content (that is, supported amount) of Ni, it was considered that the content ratio of transition metal A to the ceria (CeO.sub.2) particles obtained by the following Formula (2) was preferably 0.05 to 20 mass %, more preferably 0.1 mass % or more or 10 mass % or less, and most preferably 0.2 mass % or more or 1.0 mass % or less.

Comparative Examples 3 to 7 and Examples 10 to 13

(47) In Comparative Examples 3 to 7 and Examples 10 to 13, a catalyst composition was prepared by arc plasma (AP) method.

(48) Using an arc plasma (AP) generator (ARL-300 manufactured by Ulvac Inc.) attached with various cylindrical metal cast body (10 mm17 mm, purity of 99.9% or more, manufactured by Furuya Metal Co., Ltd.) as a cathode, CeO.sub.2 as a carrier was put in a container in a vacuum chamber and a gas was exhausted by an oil rotary vacuum pump (RP) and a turbo molecular pump (TMP) under conditions indicated in Table 2. Under plasma irradiation, the container was rotated and thus powders (samples) were stirred by scraper. Further, CeO.sub.2 powders having a specific surface area of 120 m.sup.2/g was used.

(49) In order to precipitate a predetermined amount of metal nanoparticles onto the carrier, the preparation was made at a room temperature by generating an arc discharge at a frequency of 1 Hz or 2 Hz with a peak current of 2 kA and a pulse width of 0.2 ms while stirring the powders by rotating each container.

(50) After the plasma irradiation is finished, the vacuum chamber was opened to atmospheric pressure and the catalyst composition (Fresh) prepared while stirring the powders by rotating each container was taken from the container. Thereafter, a catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at a temperature of 900 C. for 25 hours under water vapor of 10%/air atmosphere using an electric furnace. Detailed conditions refer to Table 2 described below.

(51) TABLE-US-00002 TABLE 2 Capacity of Discharge Number of Stirring speed capacitor/ Discharge frequency/ discharges/ Irradiation of carrier Cathode Carrier F voltage/V Hz shot time/h powder/kpa Comparative Fe CeO.sub.2 (2 g) 360 125 1 26000 7.2 60 Example 3 Comparative Cu CeO.sub.2 (2 g) 363 125 1 26000 7.2 60 Example 4 Comparative Ni CeO.sub.2 (2 g) 360 125 1 26000 7.2 60 Example 5 Comparative Cr CeO.sub.2 (2 g) 360 125 1 26000 7.2 60 Example 6 Comparative Zr CeO.sub.2 (2 g) 360 125 1 26000 7.2 60 Example 7 Example 10 FeCu CeO.sub.2 (2 g) 360 125 1 20000 5.6 60 Example 11 NiCu CeO.sub.2 (2 g) 360 125 1 20000 5.6 60 Example 12 CrCu CeO.sub.2 (2 g) 360 125 1 20000 5.6 60 Example 13 ZrCu CeO.sub.2 (2 g) 360 125 1 20000 5.6 60

(52) TABLE-US-00003 TABLE 3 Amount supported on carrier/wt % Comparative Example 3 Fe/CeO.sub.2 0.70 Comparative Example 4 Cu/CeO.sub.2 0.74 Comparative Example 5 Ni/CeO.sub.2 0.74 Comparative Example 6 Cr/CeO.sub.2 0.70 Comparative Example 7 Zr/CeO.sub.2 1.04 Example 10 FeCu/CeO.sub.2 0.18 (Fe) 0.11 (Cu) Example 11 NiCu/CeO.sub.2 0.17 (Ni) 0.13 (Cu) Example 12 CrCu/CeO.sub.2 0.20 (Cr) 0.10 (Cu) Example 13 ZrCu/CeO.sub.2 0.22 (Zr) 0.13 (Cu)

(53) In each of Examples, the supported amount of each element was calculated from analytical values of the XRF.

(54) (Catalyst Performance Evaluation)

(55) With respect to each of the catalyst compositions (Fresh) and the catalyst compositions (Aged) obtained in Comparative Examples 3 to 7 and Examples 10 to 13, purification performance of a simulation exhaust gas was measured using a fixed bed flow type reactor.

(56) A catalyst powder of 0.1 g was set in a reaction tube, and then the simulation exhaust gas was introduced into the catalyst powder at the following state, that is, 10 C./min, CO: 1000 ppm, O.sub.2: 1.25%, He: balance, and W/F of 5.010.sup.4 g/min.Math.cm.sup.3.

(57) After a temperature was raised up to 500 C. at a temperature rising rate of 10 C./min, a pre-treatment was carried out by holding the temperature of 500 C. for 10 minutes. Thereafter, the purification performance of the simulation exhaust gas was measured by raising a temperature from 100 C. to 500 C. at the temperature rising rate of 10 C./min after once cooling, outlet gas components were measured using CO/NO analyzer (PG240 manufactured by Horiba Ltd.), and a temperature (T50) at which CO was purified by 50% was measured.

(58) TABLE-US-00004 TABLE 4 CO (T50): C. Fresh Aged Comparative Example 3 Fe/CeO.sub.2 332 400> Comparative Example 4 Cu/CeO.sub.2 155 252 Comparative Example 5 Ni/CeO.sub.2 150 220 Comparative Example 7 Zr/CeO.sub.2 254 400> Example 10 FeCu/CeO.sub.2 290 152 Example 11 NiCu/CeO.sub.2 190 146 Example 12 CrCu/CeO.sub.2 296 117 Example 13 ZrCu/CeO.sub.2 279 150

(59) From the results indicated in Table 4, as compared to the case where only Cu or one element of the transition metals was supported on the ceria (CeO.sub.2) particles, it was found that the purification performance of CO was improved in the case where a combination of Cu and other transition metals was supported on the ceria (CeO.sub.2) particles.

(60) Even more surprisingly, it was found that the purification performance of CO after the thermal durability treatment (Aged) was improved compared to that before thermal durability treatment (Fresh) when the combination of Cu and other transition metals was supported on the ceria (CeO.sub.2) particles by the arc plasma (AP) method.

(61) In addition, it was found that an oxide of Cu and an oxide of the transition metal A were supported on the ceria (CeO.sub.2) particles in proximity to each other when the present catalyst composition is prepared by the arc plasma (AP) method.

Example 14

(62) A catalyst composition (Fresh) including a constitution in which Cu oxide and Fe oxide were supported on ceria particles was obtained in such a manner that 99.6 parts by mass of CeO.sub.2, 0.2 parts by mass of iron nitrate in terms of Cu metal, 0.2 parts by mass of iron nitrate nonahydrate in terms of Fe metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(63) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 900 C. for 25 hours under water vapor of 10%/air atmosphere using an electric furnace.

Example 15

(64) A catalyst composition (Fresh) including a constitution in which Cu oxide and Fe oxide were supported on ceria particles was obtained in such a manner that 80 parts by mass of CeO.sub.2, 10 parts by mass of iron nitrate in terms of Cu metal, 10 parts by mass of iron nitrate nonahydrate in terms of Fe metal, and an appropriate amount of ion exchange water were mixed and stirred to make slurry and then the slurry was subjected to drying.

(65) A catalyst composition (Aged) was obtained in such a manner that the catalyst composition (Fresh) was subjected to a thermal durability treatment so as to be calcined at 900 C. for 25 hours under water vapor of 10/air atmosphere using an electric furnace.

(66) (Catalyst Performance Evaluation)

(67) With respect to the catalyst compositions (Aged) obtained in Examples 14 and 15 and Comparative Examples 3 and 4, purification performance of a simulation exhaust gas was measured using a fixed bed flow type reactor.

(68) A catalyst powder of 0.1 g was set in a reaction tube, and then the simulation exhaust gas was introduced into the catalyst powder at the following state, that is, 10 C./min, CO: 1000 ppm, O.sub.2: 1.25%, He: balance, and W/F of 5.010.sup.4 g/min.Math.cm.sup.3.

(69) After a temperature was raised up to 500 C. at a temperature rising rate of 10 C./min, a pre-treatment was carried out by holding the temperature of 500 C. for 10 minutes. Thereafter, the purification performance of the simulation exhaust gas was measured by raising a temperature from 100 C. to 500 C. at the temperature rising rate of 10 C./min after once cooling, outlet gas components were measured using CO/NO analyzer (PG240 manufactured by Horiba Ltd.), and a temperature (T50) at which CO was purified by 50% was measured.

(70) TABLE-US-00005 TABLE 5 CO (T50): C. Example 14 (0.2 wt % Cu + 0.2 wt % Fe)/CeO.sub.2 220 Example 15 (10 wt % Cu + 10 wt % Fe)/CeO.sub.2 242 Comparative Example 3 Fe/CeO.sub.2 400> Comparative Example 4 Cu/CeO.sub.2 252

(71) From the results indicated in Table 5, it was found that the catalyst compositions (Aged) obtained in Examples 14 and 15 had excellent purification performance of CO as compared to that of the catalyst compositions (Aged) obtained in Comparative Examples 3 and 4.

(72) Thus, with respect to the catalyst composition containing the catalyst particles having the constitution in which Cu and the transition metal A including at least one of Cr, Fe, Mn, Co, Ni, Zr, and Ag are supported on the ceria (CeO.sub.2) particles, it was found that the catalytic activity was high in the range where the Cu and the transition metal A was supported with high concentration.