CARRIER FOR EXHAUST GAS PURIFICATION CATALYST AND EXHAUST GAS PURIFICATION CATALYST

Abstract

Provide is a new carrier for exhaust gas purification catalyst which exhibits excellent catalytic activity, particularly catalytic activity at a low temperature. Proposed is a carrier for exhaust gas purification catalyst composed of particles which contain a silicate or phosphate containing one kind or two or more kinds among the elements belonging to Group 1 and Group 2 in the periodic table.

Claims

1. A carrier for exhaust gas purification catalyst comprising particles containing a silicate containing one kind or two or more kinds among elements belonging to Group 1 and Group 2 in the periodic table, wherein the silicate is A.sub.2SiO.sub.4 (A is an element including Ca, Sr, or Ba or two or more kinds of these), ASiO.sub.3 (A is an element including Ca, Sr, or Ba or two or more kinds of these), or a mixture of these.

2-3. (canceled)

4. A carrier for exhaust gas purification catalyst comprising particles containing a phosphate containing one kind or two or more kinds among elements belonging to Group 1 and Group 2 in the periodic table, wherein the phosphate is A.sub.xPO.sub.4 (x=2 or 1.5, A in the case of x=2 is a combination of any one kind of monovalent element or two or more kinds of monovalent elements among Li, Na, K, and Cs with any one kind of divalent element or two or more kinds of divalent elements among Mg, Ca, Sr, and Ba, A in the case of x=1.5 is any one kind of divalent element or two or more kinds of divalent elements among Mg, Ca, Sr, and Ba).

5. The carrier for exhaust gas purification catalyst according to claim 1, wherein the silicate is a silicate containing Ba.

6. An exhaust gas purification catalyst comprising the carrier for exhaust gas purification catalyst according to claim 1 and a catalytically active component.

7. The carrier for exhaust gas purification catalyst according to claim 4, wherein the phosphate is a phosphate containing Ba.

8. An exhaust gas purification catalyst comprising the carrier for exhaust gas purification catalyst according to claim 4 and a catalytically active component.

9. An exhaust gas purification catalyst comprising the carrier for exhaust gas purification catalyst according to claim 5 and a catalytically active component.

Description

EXAMPLES

[0102] Hereinafter, the invention will be described in more detail with reference to Examples and Comparative Examples.

Comparative Example 1

[0103] A commercially available alumina powder (specific surface area: 159.6 m.sup.2/g) was introduced into an aqueous solution of Pt(NH.sub.3).sub.2(NO.sub.2).sub.2 and stirred for 2 hours to impregnate the catalyst carrier with Pt, and then evaporated to dryness, and subsequently held for 3 hours at 600° C. in the air, thereby obtaining a precious metal-supporting catalyst (sample).

[0104] The amount of precious metal supported in the precious metal-supporting catalyst (sample) thus obtained was 1 mass %.

Example 1

[0105] Ba carbonate (BaCO.sub.3) and silicon oxide (SiO.sub.2) were mixed together at a proportion of 2:1 in a molar ratio, and the mixture was introduced into ethanol, wet-mixed by stirring for 24 hours, then dried by holding for 12 hours at 60° C. (product temperature), and then calcined for 36 hours at 1350° C. in the air, thereby obtaining a catalyst carrier.

[0106] The catalyst carrier obtained in this manner had a specific surface area of 0.4 m.sup.2/g and a peak indicating the single phase of Ba.sub.2SiO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

[0107] The catalyst carrier (Ba.sub.2SiO.sub.4) obtained in this manner was introduced into an aqueous solution of Pt(NH.sub.3).sub.2(NO.sub.2).sub.2 and stirred for 2 hours to impregnate the catalyst carrier with Pt, and then dried by holding the resultant for one hour at 600° C. (product temperature), and subsequently held for 3 hours at 600° C. in the air, thereby obtaining a precious metal-supporting catalyst (sample).

[0108] The amount of precious metal supported in the precious metal-supporting catalyst (sample) thus obtained was 1 mass %.

[0109] <C.sub.3H.sub.6—O.sub.2 Reaction (Light-Off Test)>

[0110] As a pre-treatment of the test for C.sub.3H.sub.6 oxidation activity evaluation test, a gas of 1.5% O.sub.2/He (600° C.) was allowed to flow over 0.1 g of the precious metal-supporting catalyst (sample) at a gas flow rate of 500 cm.sup.3/min for 10 minutes, thereby conducting the pre-treatment.

[0111] The purification performance of the respective precious metal-supporting catalysts (samples) obtained in Comparative Example 1 and Example 1 by a simulated exhaust gas was evaluated by using a fixed bed flow type reactor.

[0112] In other words, 0.1 g of each of the precious metal-supporting catalysts (samples) was set in the reaction tube such that quartz wool was respectively packed in front of and behind the precious metal-supporting catalyst (sample) as well as quartz wool was respectively packed in front of and behind the catalyst so as to sandwich the catalyst.

[0113] Thereafter, a simulated exhaust gas having a composition consisting of C.sub.3H.sub.6 at 1500 ppm, O.sub.2 at 9000 ppm, and He as the balance was introduced into the reaction tube at a total flow rate of 500 cm.sup.3/min after the pre-treatment, the temperature was continuously raised from 100° C. to 600° C. at 10° C./min, and the exhaust gas at the outlet of the reaction tube was analyzed by using a quadrupole mass spectrometer to determine the component composition in the reaction gas.

[0114] (Results)

[0115] It was possible to confirm that the catalyst carrier of Example 1 exerts superior propylene activating ability or oxygen activating ability even though it has a significantly smaller specific surface area as compared to the catalyst carrier of Comparative Example 1. Among them, it was possible to confirm that the catalyst carrier of Example 1 exhibits excellent propylene activating ability or oxygen activation ability at a low temperature.

Example 2

[0116] Ca carbonate (CaCO.sub.3) and silicon oxide (SiO.sub.2) were mixed together at a proportion of 2:1 in a molar ratio, and the mixture was introduced into deionized water, wet-mixed by stirring for 24 hours, then dried by holding for 12 hours at 120° C. (product temperature), and then calcined for 24 hours at 1350° C. in the air, thereby obtaining a catalyst carrier.

[0117] The catalyst carrier obtained in this manner had a specific surface area of 8.8 m.sup.2/g and a peak indicating the single phase of Ca.sub.2SiO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

[0118] The catalyst carrier (Ca.sub.2SiO.sub.4) obtained in this manner was introduced into an aqueous solution of Pt(NH.sub.3).sub.2(NO.sub.2).sub.2 and stirred for 2 hours to impregnate the catalyst carrier with Pt, and then evaporated to dryness, and subsequently held for 3 hours at 600° C. in the air, thereby obtaining a precious metal-supporting catalyst (sample).

[0119] The amount of precious metal supported in the precious metal-supporting catalyst (sample) thus obtained was 1 mass %.

Example 3

[0120] A catalyst carrier and a precious metal-supporting catalyst (sample) were obtained in the same manner as in Example 2 except that Ca carbonate was changed to Sr carbonate in Example 2.

[0121] Incidentally, the catalyst carrier obtained in this manner had a specific surface area of 9.6 m.sup.2/g and a peak indicating the single phase of Sr.sub.2SiO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

Example 4

[0122] A catalyst carrier and a precious metal-supporting catalyst (sample) were obtained in the same manner as in Example 2 except that Ca carbonate (CaCO.sub.3), Sr carbonate (SrCO.sub.3), and silicon oxide (SiO.sub.2) were mixed together at a proportion of 1:1:1 in a molar ratio instead of mixing Ca carbonate (CaCO.sub.3) and silicon oxide (SiO.sub.2) together at a proportion of 2:1 in a molar ratio in Example 2.

[0123] Incidentally, the catalyst carrier obtained in this manner had a specific surface area of 1.9 m.sup.2/g and a peak indicating the single phase of (Sr.sub.0.5Ca.sub.0.5).sub.2SiO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

Example 5

[0124] A catalyst carrier and a precious metal-supporting catalyst (sample) were obtained in the same manner as in Example 2 except that Sr carbonate (SrCO.sub.3), Mg carbonate (MgCO.sub.3), and silicon oxide (SiO.sub.2) were mixed together at a proportion of 1:1:1 in a molar ratio instead of mixing Ca carbonate (CaCO.sub.3) and silicon oxide (SiO.sub.2) together at a proportion of 2:1 in a molar ratio in Example 2.

[0125] Incidentally, the catalyst carrier obtained in this manner had a specific surface area of 3.1 m.sup.2/g and a peak indicating the single phase of (Sr.sub.0.5Mg.sub.0.5).sub.2SiO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

Example 6

[0126] A catalyst carrier and a precious metal-supporting catalyst (sample) were obtained in the same manner as in Example 2 except that Ca carbonate (CaCO.sub.3), Mg carbonate (MgCO.sub.3), and silicon oxide (SiO.sub.2) were mixed together at a proportion of 1:1:1 in a molar ratio instead of mixing Ca carbonate (CaCO.sub.3) and silicon oxide (SiO.sub.2) together at a proportion of 2:1 in a molar ratio in Example 2.

[0127] Incidentally, the catalyst carrier obtained in this manner had a specific surface area of 2.2 m.sup.2/g and a peak indicating the single phase of (Ca.sub.0.5Mg.sub.0.5).sub.2SiO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

Example 7

[0128] A catalyst carrier and a precious metal-supporting catalyst (sample) were obtained in the same manner as in Example 2 except that Ba carbonate (BaCO.sub.3) and silicon oxide (SiO.sub.2) were mixed together at a proportion of 1:1 in a molar ratio instead of mixing Ca carbonate (CaCO.sub.3) and silicon oxide (SiO.sub.2) together at a proportion of 2:1 in a molar ratio in Example 2.

[0129] Incidentally, the catalyst carrier obtained in this manner had a specific surface area of 1.7 m.sup.2/g and a peak indicating the single phase of BaSiO.sub.3 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

Example 8

[0130] A catalyst carrier and a precious metal-supporting catalyst (sample) were obtained in the same manner as in Example 2 except that an aqueous solution of Pt(NH.sub.3).sub.2(NO.sub.2).sub.2 was changed to an aqueous solution of Pd nitrate as well as Ca carbonate (CaCO.sub.3) was changed to Ba carbonate (BaCO.sub.3) in Example 2.

[0131] Incidentally, the catalyst carrier obtained in this manner had a specific surface area of 3.9 m.sup.2/g and a peak indicating the single phase of Ba.sub.2SiO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

[0132] <Measurement of Degree of Dispersion (%) of Pt or Pd>

[0133] The degree of dispersion (%) of Pt (Pd) was measured by a CO pulse adsorption method.

[0134] Incidentally, the degree of dispersion of Pt (Pd) presented in Table 1 and Table 2 is a value calculated by Equation (1).

Degree of dispersion of Pt (Pd) (%)=(amount of Pt (Pd) corresponding to amount of CO adsorbed (mole)/total amount of Pt (Pd) contained (mole))×100

[0135] <C.sub.3H.sub.6—O.sub.2 Reaction (Light-Off Test)>

[0136] As a pre-treatment of the test for C.sub.3H.sub.6 oxidation activity evaluation test, a gas of 1.5% O.sub.2/He (600° C.) was allowed to flow over 0.1 g of the precious metal-supporting catalyst (sample) at a gas flow rate of 500 cm.sup.3/min for 10 minutes, thereby conducting the pre-treatment.

[0137] The purification performance of the respective precious metal-supporting catalysts (samples) obtained in Comparative Example 1 and Examples 2 to 7 by a simulated exhaust gas was evaluated by using a fixed bed flow type reactor.

[0138] In other words, 0.1 g of each of the precious metal-supporting catalysts (samples) was set in the reaction tube such that quartz wool was respectively packed in front of and behind the precious metal-supporting catalyst (sample) as well as quartz wool was respectively packed in front of and behind the catalyst so as to sandwich the catalyst.

[0139] Thereafter, a simulated exhaust gas having a composition consisting of C.sub.3H.sub.6 at 1500 ppm, O.sub.2 at 9000 ppm, and He as the balance was introduced into the reaction tube at a total flow rate of 500 cm.sup.3/min after the pre-treatment, the temperature was continuously raised from 100° C. to 600° C. at 10° C./min, and the exhaust gas at the outlet of the reaction tube was analyzed by using a quadrupole mass spectrometer to determine the component composition in the reaction gas.

[0140] <NO-C.sub.3H.sub.6—O.sub.2 Reaction (Light-Off Test)>

[0141] As a pre-treatment of the test for NO reduction activity evaluation test, a gas of 1.5% O.sub.2/He (600° C.) was allowed to flow over 0.1 g of the precious metal-supporting catalyst (sample) at a gas flow rate of 500 cm.sup.3/min for 10 minutes to conduct the pre-treatment, and the temperature was lowered to the temperature at which the reaction was started.

[0142] The purification performance of the respective precious metal-supporting catalysts (samples) obtained in Comparative Example 1 and Examples 2 to 8 by a simulated exhaust gas was evaluated by using a fixed bed flow type reactor.

[0143] In other words, 0.1 g of each of the precious metal-supporting catalysts (samples) was set in the reaction tube such that quartz wool was respectively packed in front of and behind the precious metal-supporting catalyst (sample) as well as quartz wool was respectively packed in front of and behind the catalyst so as to sandwich the catalyst.

[0144] Thereafter, a simulated exhaust gas having a composition consisting of NO at 1000 ppm, C.sub.3H.sub.6 at 1500 ppm, O.sub.2 at 9000 ppm, and He as the balance was introduced into the reaction tube at a total flow rate of 500 cm.sup.3/min after the pre-treatment, the temperature was continuously raised from 200° C. to 600° C. at 10° C./min, and the exhaust gas at the outlet of the reaction tube was analyzed by using a quadrupole mass spectrometer to determine the component composition in the reaction gas.

TABLE-US-00001 TABLE 1 Specific Degree of C.sub.3H.sub.6—O.sub.2 C.sub.3H.sub.6—NO—O.sub.2 reaction surface dispersion reaction NO Compositional area of Pt (Pd) HC HC T-20 η η formula (m.sup.2/g) (%) T-50 T-50 (NO) 400(NO) 500(NO) Comparative Pt/Al.sub.2O.sub.3 159.6 28.2 348 409 398 21 21 Example 1 Example 2 Pt/Ca.sub.2SiO.sub.4 8.8 2.6 310 379 370 35 26 Example 3 Pt/Sr.sub.2SiO.sub.4 9.6 3 330 380 375 37 27 Example 4 Pt/(Sr.sub.0.5Ca.sub.0.5).sub.2SiO.sub.4 1.9 2.5 321 387 378 35 22 Example 5 Pt/(Sr.sub.0.5Mg.sub.0.5).sub.2SiO.sub.4 3.1 0.9 316 374 364 37 26 Example 6 Pt/(Ca.sub.0.5Mg.sub.0.5).sub.2SiO.sub.4 2.2 1.2 342 398 384 29 29 Example 7 Pt/BaSiO.sub.3 1.7 3 329 391 390 29 26 Example 8 Pd/Ba.sub.2SiO.sub.4 3.9 1.4 — 361 367 21 7

DISCUSSION

[0145] From the results for the C.sub.3H.sub.6—O.sub.2 reaction (Light-off test), it was revealed that T-50 of THC is on the lower temperature side in Examples as compared to Comparative Example 1 in which alumina is the carrier, and higher low-temperature activity is exerted in Examples as compared to the alumina carrier.

[0146] In addition, from the results for the NO—C.sub.3H.sub.6—O.sub.2 reaction (Light-off test), it was revealed that T-50 of THC is on the lower temperature side in Examples even in the coexistence with NO as compared to Comparative Example 1 in which alumina is the carrier, and higher low-temperature activity is exerted in Examples as compared to the alumina carrier. Furthermore, a tendency was revealed that T-20 of NO is also on the lower temperature side as T-50 of THC is on the lower temperature side.

[0147] It can be said that such a tendency is obtained in the case of phosphate particles as well.

[0148] Incidentally, the results on the low-temperature activity are superior in Examples to Comparative Example 1 although alumina used in Comparative Example 1 has a higher degree of dispersion as compared to the silicate particles used in Examples. With regard to this, it is presumed, for example, in consideration of the results for the C.sub.3H.sub.6—O.sub.2 reaction, C.sub.3H.sub.6 is activated on the catalyst carrier, namely, the surface of silicate particles so that a state in which the reaction of the HC-activated species with O.sub.2 or NO is likely to take place from the low temperature region is obtained and thus superior low-temperature activity is exerted in both reactions in Examples even though the specific surface area or the degree of dispersion of precious metal is significantly smaller as compared to that in Comparative Example 1.

[0149] In addition, it was found that the conversion ratio of C.sub.3H.sub.6 increases and the combustion of C.sub.3H.sub.6 is dominant in the high temperature region in Examples. Meanwhile, it was found that a higher η 500 is exhibited in Examples as compared to Comparative Example 1 although the conversion ratio of NO decreases along with an increase in temperature.

[0150] In addition, as presented in Example 8, it was possible to confirm that the present catalyst carrier can exert the propylene activating ability or oxygen activating ability as compared to the case of using an Al.sub.2O.sub.3 carrier although it has a smaller surface area in the same manner as in the case of supporting Pt even though the precious metal to be supported is a precious metal other than Pt, and the conversion ratio of NOx at a high temperature up to about 400° C. can be maintained at the equivalent level.

[0151] In addition, with regard to the active species to be supported on the present catalyst carrier, it was also confirmed that the NO conversion ability in a high temperature region is exerted in addition to the low-temperature activity by combining the present catalyst carrier with Pt or Pd rather than Rh.

[0152] It is possible to expect to obtain the same effect as in Examples described above from a carrier for exhaust gas purification catalyst composed of particles which contain a silicate containing one kind or two or more kinds among the elements belonging to Group 1 and Group 2 in the periodic table when Examples described above, the tests which have been so far carried out in the invention, and the common general technical knowledge that the elements belonging to Group 1 in the periodic table have common chemical properties and the elements belonging to Group 2 in the periodic table also have common chemical properties are taken into consideration.

Example 9

[0153] Ba carbonate (BaCO.sub.3) and K dihydrogen phosphate (KH.sub.2PO.sub.4) were mixed together at a proportion of 1:1 in a molar ratio, and the mixture was introduced into ethanol, wet-mixed by stirring for 24 hours, then dried by holding for 12 hours at 60° C. (product temperature), then temporarily calcined for 3 hours at 600° C. in the air, and calcined for 3 hours at 1300° C., thereby obtaining a catalyst carrier.

[0154] The catalyst carrier obtained in this manner had a specific surface area of 1.0 m.sup.2/g and a peak indicating the single phase of KBaPO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

[0155] A precious metal-supporting powder using the catalyst carrier described above was obtained by the same procedure as in Example 2.

Example 10

[0156] Sr carbonate (SrCO.sub.3) and K dihydrogen phosphate (KH.sub.2PO.sub.4) were mixed together at a proportion of 1:1 in a molar ratio, and the mixture was introduced into ethanol, wet-mixed by stirring for 24 hours, then dried by holding for 12 hours at 60° C. (product temperature), and then calcined for 12 hours at 1200° C. in the air, thereby obtaining a catalyst carrier.

[0157] The catalyst carrier obtained in this manner had a specific surface area of 0.9 m.sup.2/g and a peak indicating the single phase of KSrPO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

[0158] A precious metal-supporting powder using the catalyst carrier described above was obtained by the same procedure as in Example 2.

Example 11

[0159] Ba acetate (Ba(CH.sub.3COO).sub.2) and Na dihydrogen phosphate (NaH.sub.2PO.sub.4.2H.sub.2O) were mixed at a proportion of 1.5:1 in a molar ratio, and the mixture was introduced into nitric acid, subsequently the pH thereof was adjusted to 13 with Na hydroxide, the resultant mixture was aged for 12 hours at 90° C., and the suspension thus obtained was filtered, the residue was then dried for 12 hours at 60° C., thereby obtaining a catalyst carrier.

[0160] The catalyst carrier obtained in this manner had a specific surface area of 3.0 m.sup.2/g and a peak indicating the single phase of Ba.sub.1.5PO.sub.4 was confirmed as a result of the analysis thereof by an X-ray diffraction (XRD) method.

[0161] A precious metal-supporting powder using the catalyst carrier described above was obtained by the same procedure as in Example 2.

[0162] <Measurement of Specific Surface Area and Degree of Dispersion of Pt>

[0163] The specific surface area (m.sup.2/g) and the degree of dispersion (%) of Pt were measured in the same manner as described above.

[0164] <C.sub.3H.sub.6—O.sub.2 Reaction (Light-Off Test)>

[0165] The C.sub.3H.sub.6—O.sub.2 reaction (Light-off test) was measured in the same manner as described above.

TABLE-US-00002 TABLE 2 Specific Degree of C.sub.3H.sub.6—O.sub.2 Compositional surface area dispersion of reaction HC formula (m.sup.2/g) Pt (%) T-50 Example 1 Pt/Ba.sub.2SiO.sub.4 0.4 2 280 Example 9 Pt/KBaPO.sub.4 1.0 N.D. 260 Example 10 Pt/KSrPO.sub.4 0.9 2 227 Example 11 Pt/Ba.sub.1.5PO.sub.4 3.0 7 220

[0166] It has been confirmed that a carrier for exhaust gas purification catalyst composed of particles which contain a phosphate containing one kind or two or more kinds among the elements belonging to Group 1 and Group 2 in the periodic table has the same mechanism of action and can have the same effect as a carrier for exhaust gas purification catalyst composed of particles which contain a silicate containing one kind or two or more kinds among the elements belonging to Group 1 and Group 2 in the periodic table when Examples 9 to 11 and the results of the tests which the present inventors have so far carried out are taken into consideration.