Exhaust gas purification catalyst and exhaust gas purification catalyst structure

Abstract

A catalyst for exhaust gas purification includes a carrier and a platinum group element supported on the carrier. The carrier includes a modified aluminum borate which contains an aluminum borate and at least one of oxides of an element selected from the group consisting of Zr, Si, Fe, and Ti. The modified aluminum borate contains the oxide in a concentration of 0.06% to 18% by mass relative to the mass of the modified aluminum borate.

Claims

1. A catalyst for exhaust gas purification comprising a carrier and a platinum group element supported on the carrier, the carrier comprising a modified aluminum borate which contains aluminum borate and at least one oxide of an element selected from the group consisting of Zr, Si, Fe, and Ti, and the modified aluminum borate containing the oxide in a concentration of 0.06% to 18% by mass relative to the mass of the modified aluminum borate.

2. The catalyst for exhaust gas purification according to claim 1, wherein the platinum group element supported on the carrier is at least one of Pd, Pt, Rh, and Ru.

3. A catalyst structure for exhaust gas purification comprising: a catalyst support made of a ceramics or a metallic material; and a layer of the catalyst for exhaust gas purification according to claim 2 supported on the catalyst support.

4. A catalyst structure for exhaust gas purification comprising: a catalyst support made of a ceramics or a metallic material; and a layer of the catalyst for exhaust gas purification according to claim 1 supported on the catalyst support.

5. The catalyst structure for exhaust gas purification according to claim 4, wherein the platinum group element supported on the carrier comprises Pd.

6. The catalyst structure for exhaust gas purification according to claim 5, further comprising a second catalyst layer that comprises Rh overlying said layer comprising Pd.

7. The catalyst structure for exhaust gas purification according to claim 4, wherein the modified aluminum borate has a cage structure.

8. The catalyst structure for exhaust gas purification according to claim 4, wherein the modified aluminum borate is in the form of particles having a log differential pore volume distribution peak in a pore volume diameter range of from 20 nm to 100 nm in a pore size distribution measured with a mercury porosimeter.

9. The catalyst structure for exhaust gas purification according to claim 8, wherein said pore volume diameter range is from 25 nm to 70 nm.

10. The catalyst structure for exhaust gas purification according to claim 4, wherein the modified aluminum borate contains the oxide in a concentration of 0.10% to 10% by mass relative to the mass of the modified aluminum borate.

11. The catalyst structure for exhaust gas purification according to claim 4, wherein the platinum group element is present in an amount of 0.1% to 5% by mass relative to the mass of the carrier.

12. The catalyst structure for exhaust gas purification according to claim 4, wherein the platinum group element is present in an amount of 0.2% to 4% by mass relative to the mass of the carrier.

13. The catalyst for exhaust gas purification according to claim 1, wherein the platinum group element supported on the carrier comprises Pd.

14. The catalyst for exhaust gas purification according to claim 1, wherein the modified aluminum borate has a cage structure.

15. The catalyst for exhaust gas purification according to claim 1, wherein the modified aluminum borate is in the form of particles having a log differential pore volume distribution peak in a pore volume diameter range of from 20 nm to 100 nm in a pore size distribution measured with a mercury porosimeter.

16. The catalyst for exhaust gas purification according to claim 15, wherein said pore volume diameter range is from 25 nm to 70 nm.

17. The catalyst for exhaust gas purification according to claim 1, wherein the modified aluminum borate contains the oxide in a concentration of 0.10% to 10% by mass relative to the mass of the modified aluminum borate.

18. The catalyst for exhaust gas purification according to claim 1, wherein the platinum group element is present in an amount of 0.1% to 5% by mass relative to the mass of the carrier.

19. The catalyst for exhaust gas purification according to claim 1, wherein the platinum group element is present in an amount of 0.2% to 4% by mass relative to the mass of the carrier.

Description

EXAMPLES

(1) The invention will now be illustrated in greater detail with reference to Examples and Comparative Examples. Unless otherwise noted, all the parts and percents are by mass.

(2) Preparation of Aluminum Borate:

(3) In a three-necked flask supported in a water bath at 50 C. were put 1.5 l of 2-propanol, 200 g of aluminum isopropoxide having been ground using an agate mortar, and 40.9 g of boron n-propoxide and stirred while purging with nitrogen gas. After the aluminum isopropoxide dissolved completely (after the solution turned clear), 24.6 g of a 1:1 mixture of water and 2-propanol was slowly added thereto dropwise, whereupon the aluminum isopropoxide hydrolyzed gradually to form a white gelatinous sediment, which was washed successively with ethanol and pure water, followed by filtration. The filter cake was dried at 120 C. overnight (about 15 hours) and fired in air first at 300 C. for 3 hours and then at 1000 C. for 5 hours to yield aluminum borate as a white product. The resulting product was identified to be aluminum borate having formula: 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 by XRD.

Example 1

(4) The above prepared aluminum borate was immersed in an aqueous solution of zirconium oxynitrate. The zirconium oxynitrate concentration in the aqueous solution was such that the desired ZrO.sub.2-modified aluminum borate (10Al.sub.2O.sub.3.2B.sub.2O.sub.3) might have a ZrO.sub.2 content of 1%. The mixture was evaporated at 120 C. overnight (about 15 hours) to dryness, and the solid was fired in air at 600 C. for 3 hours to give modified aluminum borate having formula: 10Al.sub.2O.sub.3.2B.sub.2O.sub.3 modified with 1% ZrO.sub.2.

(5) Ninety-nine parts of the modified aluminum borate containing 1% ZrO.sub.2, palladium nitrate of an amount corresponding to 1 part in terms of metallic palladium, and an adequate amount of ion-exchanged water were mixed and stirred to prepare a slurry, which was dried and fired at 500 C. for 1 hour to make Pd-supporting modified aluminum borate.

Example 2

(6) The above prepare aluminum borate was immersed in colloidal silica (Snowtex 040) of such an amount that the desired SiO.sub.2-modified aluminum borate might have an SiO.sub.2 content of 1%. The mixture was processed in the same manner as in Example 1 to give Pd-supporting modified aluminum borate.

Example 3

(7) The above prepare aluminum borate was immersed in an aqueous iron nitrate solution. The iron nitrate concentration in the aqueous solution was such that the desired Fe.sub.2O.sub.3-modified aluminum borate might have an Fe.sub.2O.sub.3 content of 1%. The mixture was processed in the same manner as in Example 1 to give Pd-supporting modified aluminum borate.

Example 4

(8) The above prepare aluminum borate was immersed in an aqueous titanium (III) chloride solution. The titanium (III) chloride concentration in the aqueous solution was such that the desired TiO.sub.2-modified aluminum borate might have a TiO.sub.2 content of 1%. The mixture was processed in the same manner as in Example 1 to give Pd-supporting modified aluminum borate.

Example 5

(9) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 2, except that the SiO.sub.2 content of the SiO.sub.2-modified aluminum borate was changed to 0.06%.

Example 6

(10) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 2, except that the SiO.sub.2 content of the SiO.sub.2-modified aluminum borate was changed to 0.10%.

Example 7

(11) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 2, except that the SiO.sub.2 content of the SiO.sub.2-modified aluminum borate was changed to 0.50%.

Example 8

(12) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 2, except that the SiO.sub.2 content of the SiO.sub.2-modified aluminum borate was changed to 5.00%.

Example 9

(13) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 2, except that the SiO.sub.2 content of the SiO.sub.2-modified aluminum borate was changed to 10.00%.

Example 10

(14) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 2, except that the SiO.sub.2 content of the SiO.sub.2-modified aluminum borate was changed to 18.00%.

Example 11

(15) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 3, except that the Fe.sub.2O.sub.3 content of the Fe.sub.2O.sub.3-modified aluminum borate was changed to 0.06%.

Example 12

(16) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 3, except that the Fe.sub.2O.sub.3 content of the Fe.sub.2O.sub.3-modified aluminum borate was changed to 0.10%.

Example 13

(17) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 3, except that the Fe.sub.2O.sub.3 content of the Fe.sub.2O.sub.3-modified aluminum borate was changed to 0.50%.

Example 14

(18) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 3, except that the Fe.sub.2O.sub.3 content of the Fe.sub.2O.sub.3-modified aluminum borate was changed to 5.00%.

Example 15

(19) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 3, except that the Fe.sub.2O.sub.3 content of the Fe.sub.2O.sub.3-modified aluminum borate was changed to 10.00%.

Example 16

(20) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 3, except that the Fe.sub.2O.sub.3 content of the Fe.sub.2O.sub.3-modified aluminum borate was changed to 18.00%.

Comparative Example 1

(21) Ninety-nine parts of the above prepared aluminum borate, palladium nitrate of an amount corresponding to 1 part of metallic palladium, and an adequate amount of ion-exchanged water were mixed and stirred to prepare a slurry, which was dried and fired at 500 C. for 1 hour to make Pd-supporting aluminum borate.

Comparative Example 2

(22) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 2, except that the SiO.sub.2 content of the SiO.sub.2-modified aluminum borate was changed to 0.03%.

Comparative Example 3

(23) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 2, except that the SiO.sub.2 content of the SiO.sub.2-modified aluminum borate was changed to 20.00%.

Comparative Example 4

(24) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 3, except that the Fe.sub.2O.sub.3 content of the Fe.sub.2O.sub.3-modified aluminum borate was changed to 0.03%.

Comparative Example 5

(25) Palladium-supporting modified boron aluminum was prepared in the same manner as in Example 3, except that the Fe.sub.2O.sub.3 content of the Fe.sub.2O.sub.3-modified aluminum borate was changed to 20.00%.

(26) Method of Evaluating Catalyst Performance:

(27) The samples obtained in Examples and Comparative Examples were evaluated for the ability to purify simulated exhaust gas using a fixed bed flow reactor. In a reaction tube was placed 100 mg of the catalyst powder, and a simulated exhaust gas that simulated a complete combustion gas and consisted of CO, CO.sub.2, C.sub.3H.sub.6, H.sub.2, O.sub.2, NO, H.sub.2O, and the balance of N.sub.2 was introduced to the catalyst powder at a total flow rate of 1000 cc/min while heating the reaction tube and the catalyst powder up to 500 C. at a rate of 10 C./min. The gas composition was analyzed with time.

(28) The outlet gas composition was analyzed using a CO/NO analyzer (PG240, available from Horiba, Ltd.) and an HC analyzer (VMF-1000F, available from Shimadzu Corp.).

(29) Accelerated aging of each catalyst simulating sulfur poisoning was conducted at 250 C. for 20 hours at an O.sub.2 concentration of 20%, an H.sub.2O concentration of 10%, and an SO.sub.2 concentration of 100 ppm.

(30) Method for Evaluating Degree of Dispersion of Platinum Group Element:

(31) The degree of dispersion of Pd used as a platinum group element was determined by CO pulse chemisorption, which is a means known from T. Takeguchi, S. Manabe, R. Kikuchi, K. Eguchi, T. Kanazawa, and S. Matsumoto, Applied Catalysts A:293 (2005), 91. The degree of dispersion of Pd is calculated as a ratio of the amount of Pd (mol) corresponding to the CO adsorption to the total Pd content.

(32) Results of Evaluation of Catalyst Performance and Degree of Dispersion of Pd:

(33) In Table 1 below is shown T50, the temperature at which 50% of CO, HC, and NO were converted, of each catalyst having been subjected to sulfur poisoning aging. It is seen from these results that Examples 1 to 16 are superior in low-temperature (150 C.) activity to Comparative Example 1. With a modifying oxide content of 0.03% as in Comparative Examples 2 and 4, the difference in catalyst performance from Comparative Example 1 is not noticeable. The difference is remarkable when the modifying oxide content is 0.06% as in Examples 5 and 11. When the modifying oxide content is 20% as in Comparative Examples 3 and 5, in contrast, the low-temperature catalyst activity is lower than that in Comparative Example 1, proving that the modifying oxide content as high as 20% has the opposite effect of actually deteriorating the low-temperature activity. With a modifying oxide content of less than 20%, the low-temperature activity increases. Accordingly, the low-temperature activity in Examples 10 and 16, in which the modifying oxide content is 18%, is higher than that in Comparative Example 1.

(34) Sulfur poisoning was carried out in the same manner as in the evaluation of catalyst performance, i.e., at 250 C. for 20 hours at an O.sub.2 concentration of 20%, an H.sub.2O concentration of 10%, and an SO.sub.2 concentration of 100 ppm.

(35) The far right column in Table 1 shows the results of evaluation of degree of Pd dispersion after sulfur poisoning aging. It is seen that Examples 1 to 16 have a higher degree of Pd dispersion than Comparative Example 1. With a modifying oxide content of 0.03% as in Comparative Examples 2 and 4, the difference from Comparative Example 1 is not noticeable. The difference is remarkable when the modifying oxide content is 0.06% as in Examples 5 and 11. When the modifying oxide content is 20% as in Comparative Examples 3 and 5, in contrast, the low-temperature catalyst activity is equal to or lower than that in Comparative Example 1, proving that the modifying oxide content as high as 20% has the opposite effect of actually deteriorating the degree of Pd dispersion. With a modifying oxide content of less than 20%, the degree of Pd dispersion increases. Accordingly, the degree of Pd dispersion in Examples 10 and 16, in which the modifying oxide content is 18%, is higher than that in Comparative Example 1.

(36) TABLE-US-00001 TABLE 1 Catalyst Composition Aluminum Modifying Conversion Pd (wt % w.r.t. Borate Element Oxide Efficiency Degree catalyst-on- (wt % w.r.t. (wt % w.r.t. carrier) (T50) ( C.) of Pd carrier) carrier) ZrO.sub.2 SiO.sub.2 Fe.sub.2O.sub.3 TiO.sub.2 CO HC NO Dispersion Comparative. 1 100.00 343.0 350.1 391.9 0.05% Example 1 Example 1 1 99.00 1.00 331.7 339.6 373.6 0.16% Example 2 1 99.00 1.00 327.0 332.9 368.7 0.27% Example 3 1 99.00 1.00 331.2 340.7 380.9 4.52% Example 4 1 99.00 1.00 332.0 340.8 381.2 0.15% Comparative. 1 99.97 0.03 342.1 349.5 390.8 0.06% Example 2 Example 5 1 99.94 0.06 338.1 345.2 385.8 0.11% Example 6 1 99.90 0.10 337.9 345.0 385.4 0.10% Example 7 1 99.50 0.50 333.0 338.7 378.4 0.22% Example 8 1 95.00 5.00 332.0 339.2 378.7 0.21% Example 9 1 90.00 10.00 337.6 344.7 385.0 0.11% Example 10 1 82.00 18.00 338.0 344.9 385.2 0.10% Comparative. 1 80.00 20.00 353.0 362.9 410.1 0.02% Example 3 Comparative. 1 99.97 0.03 342.7 349.3 391.8 0.07% Example 4 Example 11 1 99.94 0.06 339.0 345.7 385.7 1.50% Example 12 1 99.90 0.10 338.9 345.5 385.9 2.52% Example 13 1 99.50 0.50 333.3 341.1 382.5 3.64% Example 14 1 95.00 5.00 333.7 342.5 383.1 3.78% Example 15 1 90.00 10.00 338.7 344.9 385.3 2.59% Example 16 1 82.00 18.00 339.0 345.6 385.7 2.30% Comparative. 1 80.00 20.00 353.7 361.9 412.1 0.05% Example 5