Exhaust gas purification catalyst

Abstract

Provided is a novel exhaust gas purification catalyst, which uses a Cu-based delafossite oxide, capable of increasing the exhaust gas purification performance compared to the case of using the Cu-based delafossite oxide alone. Proposed is an exhaust gas purification catalyst comprising a delafossite-type oxide represented by a general formula ABO.sub.2 and an inorganic porous material, wherein Cu is contained in the A site of the general formula of the delafossite oxide, one or two or more elements selected from the group consisting of Mn, Al, Cr, Ga, Fe, Co, Ni, In, La, Nd, Sm, Eu, Y, V, and Ti are contained in the B site thereof, and Cu is contained in 3 to 30% relative to the total content (mass) of the delafossite-type oxide and the inorganic porous material.

Claims

1. An exhaust gas purification catalyst, comprising a delafossite-type oxide represented by a general formula ABO.sub.2 and an inorganic porous material, wherein Cu is comprised in the A site of the general formula of the delafossite-type oxide, one or two or more elements selected from the group consisting of Mn, Al, Cr, Ga, Fe, Co, Ni, In, La, Nd, Sm, Eu, Y, V, and Ti are comprised in the B site thereof, and Cu is comprised in 3 to 30% relative to the total content (mass) of the delafossite-type oxide and the inorganic porous material.

2. The exhaust gas purification catalyst according to claim 1, wherein the content (mass) ratio of the delafossite-type oxide to the inorganic porous material is 10:90 to 70:30.

3. The exhaust gas purification catalyst according to claim 1, wherein the ratio of an average particle diameter (D50) of the delafossite-type oxide to the average particle diameter (D50) of the inorganic porous material is 10:90 to 85:15.

4. The exhaust gas purification catalyst according to claim 1, wherein one or two or more elements selected from the group consisting of Mn, Al, Cr, and Ga are comprised in the B site of the general formula.

5. The exhaust gas purification catalyst according to claim 1, wherein only Mn is comprised in the B site of the general formula or Mn and one or two or more elements selected from the group consisting of Al, Cr, and Ga are comprised therein.

6. The exhaust gas purification catalyst according to claim 1, wherein Mn and one or two or more elements selected from the group consisting of Al, Cr, and Ga are comprised in the B site of the general formula, and the atomic ratio of the content of Mn to the total content of Al, Cr, and Ga in the B site is 10:90 to 90:10.

7. The exhaust gas purification catalyst, having a configuration in which the exhaust gas purification catalyst according to claim 1 is supported on a substrate made of metal or ceramics.

Description

EXAMPLES

(1) Hereinafter, the present invention will be described based on the following Examples. However the present invention is not limited to the following Examples.

Example 1

(2) Copper nitrate trihydrate corresponding to 53.6 parts by mass in terms of Cu metal and manganese nitrate hexahydrate corresponding to 46.4 parts by mass in terms of Mn metal were added to pure water and sufficiently stirred to obtain 1 mol/L of a transparent nitrate solution. 1 mol/L of a sodium hydroxide (NaOH) solution was dropped into the transparent nitrate solution to obtain a precipitate.

(3) The resultant precipitate was aged at room temperature for 24 hours, and then sufficiently washed with water, filtered, and dried at 120 C. to obtain a precursor. The precursor was then calcined at 900 C. for 10 hours in a nitrogen atmosphere to thereby obtain a Cu-based delafossite-type oxide powder (CuMnO.sub.2).

(4) Next, a alumina (Al.sub.2O.sub.3) particle powder (D50: 12.4 m, BET specific surface area: 105 m.sup.2/g) was prepared, and 11.2 parts by mass of the Cu-based delafossite-type oxide powder, 80.3 parts by mass of the alumina (Al.sub.2O.sub.3) particle powder, 8.5 parts by mass of a zirconia binder, and water were mixed and stirred for 2 hours using a propeller such that the content of Cu was 5.2% by mass relative to the total amount of the resultant Cu-based delafossite-type oxide powder and the alumina (Al.sub.2O.sub.3) particle powder, thereby producing a slurry.

(5) Next, a honeycomb substrate made of stainless (size: 4060 mm) was immersed into the slurry and pulled out therefrom, and then the excess slurry was blown off. Thereafter, the substrate was dried at 90 C. for 10 minutes and calcined at 500 C. for 1.5 hours to form a catalyst layer, thereby obtaining an exhaust gas purification catalyst (sample).

Example 2

(6) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 except that a alumina (Al.sub.2O.sub.3) particle powder of which the average particle diameter (D50) was 31.9 m and the BET specific surface area was 100 m.sup.2/g was used instead of the alumina (Al.sub.2O.sub.3) particle powder in Example 1.

Example 3

(7) Copper nitrate trihydrate corresponding to 52.9 parts by mass in terms of Cu metal, manganese nitrate hexahydrate corresponding to 46.2 parts by mass in terms of Mn metal, and silver nitrate corresponding to 0.9 parts by mass in terms of Ag metal were added to pure water and sufficiently stirred to obtain 1 mol/L of a transparent nitrate solution. 1 mol/L of a sodium hydroxide (NaOH) solution was dropped into the transparent nitrate solution to obtain a precipitate.

(8) The resultant precipitate was aged at room temperature for 24 hours, and then sufficiently washed with water, filtered, and dried at 120 C. to obtain a precursor. The precursor was then calcined at 850 C. for 10 hours in a nitrogen atmosphere to thereby obtain a Cu-based delafossite-type oxide powder (Cu.sub.0.99Ag.sub.0.01MnO.sub.2).

(9) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 by using the Cu-based delafossite-type oxide powder thus obtained.

Example 4

(10) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 except that the content of Cu relative to the total amount of the Cu-based delafossite-type oxide powder and the alumina (Al.sub.2O.sub.3) particle powder was changed to 10.4% by mass in Example 1.

Example 5

(11) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 except that the content of Cu relative to the total amount of the Cu-based delafossite-type oxide powder and the alumina (Al.sub.2O.sub.3) particle powder was changed to 20.8% by mass in Example 1.

Example 6

(12) Copper nitrate trihydrate corresponding to 53.2 parts by mass in terms of Cu metal and iron nitrate nonahydrate corresponding to 46.8 parts by mass in terms of Fe metal were added to pure water and sufficiently stirred to obtain 1 mol/L of a transparent nitrate solution. 1 mol/L of a sodium hydroxide (NaOH) solution was dropped into the transparent nitrate solution to obtain a precipitate.

(13) The resultant precipitate was aged at room temperature for 24 hours, and then sufficiently washed with water, filtered, and dried at 120 C. to obtain a precursor. The precursor was then calcined at 900 C. for 10 hours in a nitrogen atmosphere to thereby obtain a Cu-based delafossite-type oxide powder (CuFeO.sub.2).

(14) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 by using the Cu-based delafossite-type oxide powder thus obtained.

Example 7

(15) Copper nitrate trihydrate corresponding to 70.2 parts by mass in terms of Cu metal and aluminum nitrate nonahydrate corresponding to 29.8 parts by mass in terms of Al metal were added to pure water and sufficiently stirred to obtain 1 mol/L of a transparent nitrate solution. 1 mol/L of a sodium hydroxide (NaOH) solution was dropped into the transparent nitrate solution to obtain a precipitate.

(16) The resultant precipitate was aged at room temperature for 24 hours, and then sufficiently washed with water, filtered, and dried at 120 C. to obtain a precursor. The precursor was then calcined at 1,100 C. for 10 hours in a nitrogen atmosphere to thereby obtain a Cu-based delafossite-type oxide powder (CuAlO.sub.2).

(17) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 by using the Cu-based delafossite-type oxide powder thus obtained.

Example 8

(18) Copper nitrate trihydrate corresponding to 55.0 parts by mass in terms of Cu metal and chromium nitrate nonahydrate corresponding to 45.0 parts by mass in terms of Cr metal were added to pure water and sufficiently stirred to obtain 1 mol/L of a transparent nitrate solution. 1 mol/L of a sodium hydroxide (NaOH) solution was dropped into the transparent nitrate solution to obtain a precipitate.

(19) The resultant precipitate was aged at room temperature for 24 hours, and then sufficiently washed with water, filtered, and dried at 120 C. to obtain a precursor. The precursor was then calcined at 900 C. for 10 hours in a nitrogen atmosphere to thereby obtain a Cu-based delafossite-type oxide powder (CuCrO.sub.2).

(20) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 by using the Cu-based delafossite-type oxide powder thus obtained.

Example 9

(21) Copper nitrate trihydrate corresponding to 54.7 parts by mass in terms of Cu metal, manganese nitrate hexahydrate corresponding to 9.5 parts by mass in terms of Mn metal, and chromium nitrate nonahydrate corresponding to 35.8 parts by mass in terms of Cr metal were added to pure water and sufficiently stirred to obtain 1 mol/L of a transparent nitrate solution. 1 mol/L of a sodium hydroxide (NaOH) solution was dropped into the transparent nitrate solution to obtain a precipitate.

(22) The resultant precipitate was aged at room temperature for 24 hours, and then sufficiently washed with water, filtered, and dried at 120 C. to obtain a precursor. The precursor was then calcined at 900 C. for 10 hours in a nitrogen atmosphere to thereby obtain a Cu-based delafossite-type oxide powder (CuCr.sub.0.8Mn.sub.0.2O.sub.2).

(23) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 by using the Cu-based delafossite-type oxide powder thus obtained.

Example 10

(24) Copper nitrate trihydrate corresponding to 56.3 parts by mass in terms of Cu metal, manganese nitrate hexahydrate corresponding to 38.9 parts by mass in terms of Mn metal, and aluminum nitrate nonahydrate corresponding to 4.8 parts by mass in terms of Al metal were added to pure water and sufficiently stirred to obtain 1 mol/L of a transparent nitrate solution. 1 mol/L of a sodium hydroxide (NaOH) solution was dropped into the transparent nitrate solution to obtain a precipitate.

(25) The resultant precipitate was aged at room temperature for 24 hours, and then sufficiently washed with water, filtered, and dried at 120 C. to obtain a precursor. The precursor was then calcined at 950 C. for 10 hours in a nitrogen atmosphere to thereby obtain a Cu-based delafossite-type oxide powder (CuAl.sub.0.2Mn.sub.0.8O.sub.2).

(26) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 by using the Cu-based delafossite-type oxide powder thus obtained.

Example 11

(27) Copper nitrate trihydrate corresponding to 60.8 parts by mass in terms of Cu metal, manganese nitrate hexahydrate corresponding to 26.3 parts by mass in terms of Mn metal, and aluminum nitrate nonahydrate corresponding to 12.9 parts by mass in terms of Al metal were added to pure water and sufficiently stirred to obtain 1 mol/L of a transparent nitrate solution. 1 mol/L of a sodium hydroxide (NaOH) solution was dropped into the transparent nitrate solution to obtain a precipitate.

(28) The resultant precipitate was aged at room temperature for 24 hours, and then sufficiently washed with water, filtered, and dried at 120 C. to obtain a precursor. The precursor was then calcined at 950 C. for 10 hours in a nitrogen atmosphere to thereby obtain a Cu-based delafossite-type oxide powder (CuAl.sub.0.5Mn.sub.0.5O.sub.2).

(29) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 by using the Cu-based delafossite-type oxide powder thus obtained.

Example 12

(30) Copper nitrate trihydrate corresponding to 66.1 parts by mass in terms of Cu metal, manganese nitrate hexahydrate corresponding to 11.4 parts by mass in terms of Mn metal, and aluminum nitrate corresponding to 22.5 parts by mass in terms of Al metal were added to pure water and sufficiently stirred to obtain 1 mol/L of a transparent nitrate solution. 1 mol/L of a sodium hydroxide (NaOH) solution was dropped into the transparent nitrate solution to obtain a precipitate.

(31) The resultant precipitate was aged at room temperature for 24 hours, and then sufficiently washed with water, filtered, and dried at 120 C. to obtain a precursor. The precursor was then calcined at 950 C. for 10 hours in a nitrogen atmosphere to thereby obtain a Cu-based delafossite-type oxide powder (CuAl.sub.0.8Mn.sub.0.2O.sub.2).

(32) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 by using the Cu-based delafossite-type oxide powder thus obtained.

(33) Using an X-ray diffractometer (Mini Flex 600, target: Cu, accelerating voltage: 40 kV, manufactured by Rigaku Corporation), the peak pattern of the Cu-based delafossite-type oxide powder used in each of Examples 1 to 12 was measured, and as a result, it was confirmed that a crystal structure of a 3R-type delafossite-type oxide was obtained.

(34) Furthermore, the exhaust gas purification catalyst (sample) obtained in each of Examples 1 to 12 was observed by an electron microscope, and as a result, it was confirmed that the delafossite-type oxide particles and the inorganic porous particles were not supported with each other but were respectively present in a state of being mixed.

Comparative Example 1

(35) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 except that the alumina (Al.sub.2O.sub.3) particle powder was removed from the Cu-based delafossite-type oxide powder in Example 1.

Comparative Example 2

(36) An exhaust gas purification catalyst (sample) was obtained in the same manner as in Example 1 except that the content of Cu relative to the total amount of the Cu-based delafossite-type oxide powder and the alumina (Al.sub.2O.sub.3) particle powder was changed to 2.7% by mass in Example 1.

(37) <Measurement of Cu Content>

(38) With regard to the exhaust gas purification catalyst (sample) obtained in each of Examples and Comparative Examples, the content of Cu was measured by a calibration curve method using an X-ray fluorescence spectrometer (ZSX Primus II, manufactured by Rigaku Corporation).

(39) Each of the obtained contents of Cu was shown in Tables 1 and 2 as a mass ratio relative to the total content of the delafossite-type oxide and the inorganic porous material.

(40) <Measurement of Average Particle Diameter>

(41) With regard to the exhaust gas purification catalyst (sample) obtained in each of Examples and Comparative Examples, the average particle diameter (D50) of each of the delafossite-type oxide and the alumina was measured using a laser diffraction scattering-type particle size distribution, and the results were shown in Tables 1 and 2.

(42) Each of the samples (powders) was introduced into an aqueous solvent by using an automatic sample supply machine for a laser diffraction particle size distribution measuring device (Microtorac SDC, manufactured by Nikkiso Co., Ltd.), and the sample was irradiated with ultrasonic waves of 30 W at a flow rate of 50% for 360 seconds. Thereafter, the particle size distribution was measured by using a laser diffraction particle size distribution measuring device MT3000II manufactured by Nikkiso Co., LTD., and the D50 was then measured from the obtained volume-basis particle size distribution chart. In this case, it was determined under the conditions where the refractive index of the particle was 1.5, the particle shape was spherical, the refractive index of the solvent was 1.3, the zero-setting was 30 seconds, the measurement time was 30 seconds, and the average value was from two measurements.

(43) <Exhaust Gas Purification Performance Test>

(44) The catalytic activity was evaluated as follows after the exhaust gas purification catalyst (sample) obtained in each of Examples and Comparative Examples was aged. The durability condition was at 950 C. for 4 hours under air atmosphere.

(45) Using a catalyst evaluation device (SIGU-1000, manufactured by HORIBA, Ltd.), the exhaust gas purification catalyst (sample) was set in a reaction furnace thereof, and a model gas composed of CO: 1.4%, NO: 1,500 ppm, C.sub.3H.sub.6: 500 ppmC, O.sub.2: 0.7%, and the residual of N.sub.2 was circulated in the reaction furnace. Then, the outlet gas components were measured at 100 to 600 C. using an automobile exhaust gas measuring device (MEXA-7100, manufactured by HORIBA Ltd.). From the results of the light-off performance evaluation, the temperature (T50) ( C.) at which the model gas was purified to 50% and the purification rate (400) (%) of the model gas at 400 C. were determined, and the results were shown in Tables 3 and 4.

(46) TABLE-US-00001 TABLE 1 Average Particle Delafossite in Cu in Average Diameter of (Delafossite + (Delafossite + Particle Inorganic Inorganic Inorganic Diameter of Inorganic Porous Porous Porous Type of Delafossite Porous Material Material) Material) No. Delafossite (D50/m) Material (D50/m) (% by mass) (% by mass) Comparative CuMnO.sub.2 27.8 100.0 42.2 Example 1 Comparative CuMnO.sub.2 27.8 alumina 12.4 6.5 2.7 Example 2 Example 1 CuMnO.sub.2 27.8 alumina 12.4 12.3 5.2 Example 2 CuMnO.sub.2 27.8 alumina 31.9 12.3 5.2 Example 3 Cu.sub.0.99Ag.sub.0.01MnO.sub.2 40.0 alumina 12.4 12.5 5.2 Example 4 CuMnO.sub.2 27.8 alumina 12.4 24.6 10.4 Example 5 CuMnO.sub.2 27.8 alumina 12.4 49.2 20.8 Example 6 CuFeO.sub.2 36.4 alumina 12.4 12.4 5.2 Example 7 CuAlO.sub.2 24.3 alumina 12.4 10.0 5.2 Example 8 CuCrO.sub.2 3.2 alumina 12.4 12.1 5.2

(47) TABLE-US-00002 TABLE 2 Average Particle Delafossite in Cu in Average Diameter of (Delafossite + (Delafossite + Particle Inorganic Inorganic Inorganic Diameter of Inorganic Porous Porous Porous Type of Delafossite Porous Material Material) Material) No. Delafossite (D50/m) Material (D50/m) (% by mass) (% by mass) Example 1 CuMnO.sub.2 27.8 alumina 12.4 12.3 5.2 Example 9 CuCr.sub.0.8Mn.sub.0.2O.sub.2 3.7 alumina 12.4 12.1 5.2 Example 10 CuAl.sub.0.2Mn.sub.0.8O.sub.2 40.8 alumina 12.4 11.9 5.2 Example 11 CuAl.sub.0.5Mn.sub.0.5O.sub.2 52.0 alumina 12.4 11.2 5.2 Example 12 CuAl.sub.0.8Mn.sub.0.2O.sub.2 56.6 alumina 12.4 10.5 5.2

(48) TABLE-US-00003 TABLE 3 Type of T50 ( C.) 400 (%) No. Delafossite CO HC NO CO HC NO Compara- CuMnO.sub.2 578 600 600 16 1 0 tive Ex- or or ample 1 more more Compara- CuMnO.sub.2 386 470 448 57 33 11 tive Ex- ample 2 Example 1 CuMnO.sub.2 273 447 404 77 41 45 Example 2 CuMnO.sub.2 253 423 391 87 45 67 Example 3 Cu.sub.0.99Ag.sub.0.01MnO.sub.2 247 436 390 83 44 62 Example 4 CuMnO.sub.2 290 431 388 87 43 63 Example 5 CuMnO.sub.2 236 406 352 92 47 75 Example 6 CuFeO.sub.2 262 431 416 68 43 33 Example 7 CuAlO.sub.2 257 402 402 74 49 46 Example 8 CuCrO.sub.2 290 412 410 66 46 37

(49) TABLE-US-00004 TABLE 4 Type of T50 ( C.) 400 (%) No. Delafossite CO HC NO CO HC NO Example 1 CuMnO.sub.2 273 447 404 77 41 45 Example 9 CuCr.sub.0.8Mn.sub.0.2O.sub.2 255 410 398 78 48 54 Example 10 CuAl.sub.0.2Mn.sub.0.8O.sub.2 254 410 399 77 48 51 Example 11 CuAl.sub.0.5Mn.sub.0.5O.sub.2 262 419 413 70 46 35 Example 12 CuAl.sub.0.8Mn.sub.0.2O.sub.2 257 420 414 70 46 36

(50) From the results shown in Tables 1 and 3, it was found that when the content mass of Cu relative to the total mass of the Cu-based delafossite-type oxide powder and the alumina (Al.sub.2O.sub.3) particle powder in the exhaust gas purification catalyst (sample) was set to 3 to 30%, a three-way catalyst having excellent NO.sub.x purification performance could be obtained. Furthermore, it was found that when Cu is contained preferably in 5% or more or 25% or less, more preferably in 10% or more or 22% or less, a more excellent three-way catalyst could be obtained.

(51) Also, from the results shown in Tables 2 and 4, it was found that Mn and one or two or more elements selected from the group consisting of Al, Cr, and Ga were preferably contained in the B site of the exhaust gas purification catalyst (sample), and the atomic ratio of the content of Mn relative to the total content of Al, Cr, and Ga (Al+Cr+Ga) in the B site was preferably 10:90 to 90: 10, more preferably 30:70 to 90:10, even more preferably 40:60 to 90:10. Especially, it was found that the atomic ratio was preferably 50:50 to 90:10, the total content (atomic ratio) of Al, Cr, and Ga was more preferably smaller than the content (atomic ratio) of Mn in the B site, and the atomic ratio was even more preferably 70:30 to 90:10, from the viewpoint of improving the light-off performance of HC and NO.