Exhaust gas purification catalyst composition and exhaust gas purification catalyst

Abstract

Provided is a new catalyst that can have heightened purification performance for NOx under lean conditions. Proposed is an exhaust gas purification catalyst composition provided with: a carrier (A) comprising zirconium phosphate; a catalyst active component (a) supported on the carrier (A); a carrier (B) comprising an inorganic oxide porous body; and a catalyst active component (b) supported on the carrier (B).

Claims

1. An exhaust gas purification catalyst composition comprising: a carrier A comprising a zirconium phosphate; a catalytically active component (a) supported on the carrier A; a carrier B comprising an inorganic oxide porous material; and a catalytically active component (b) supported on the carrier B, wherein the carrier B is one or more inorganic oxide porous materials selected from a group consisting of silica, silica-alumina, ceria-zirconia, lanthanum, alumina, alumino-silicate, alumina-zirconia, alumina-chromia, alumina-ceria titania, and titania, the catalytically active component (a) comprises Rh, 50% or more of the catalytically active component (a) is supported on the carrier A, and 50% or more of the catalytically active component (b) is supported on the carrier B.

2. The exhaust gas purification catalyst composition according to claim 1, wherein the carrier B contains an oxide porous material having a Hammett acidity function H.sub.0max of 10<H.sub.0max<15.

3. The exhaust gas purification catalyst composition according to claim 1, wherein the catalytically active component (b) supported on the carrier B is Pt.

4. The exhaust gas purification catalyst composition according to claim 1, wherein the catalytically active component (a) supported on the carrier A consists of Rh.

5. An exhaust gas purification catalyst having a structure in which the exhaust gas purification catalyst composition according to claim 1 is supported on a substrate.

6. An exhaust gas purification catalyst having a structure in which the exhaust gas purification catalyst composition according to claim 1 is formed into a pellet shape.

7. The exhaust gas purification catalyst composition according to claim 1, wherein the carrier B is one or more inorganic oxide porous materials selected from a group consisting of ceria-zirconia, lanthanum, alumina-zirconia, alumina-chromia, and alumina-ceria titania.

Description

EXAMPLES

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

(2) <Synthesis of Zirconium Phosphate (ZrP.sub.2O.sub.7)>

(3) After zirconium oxynitrate dehydrate of 203.6 g was dissolved in deionized water, aqueous ammonia of 4 mol/L was slowly added dropwise to a solution charged with 85%-phosphate of 173.9 g to obtain a value of pH 8, and the obtained gel-like product was washed and filtered with deionized water and was then subjected to drying at 120 C. through the night. After the drying, the product was calcined at 900 C. for five hours in the air to obtain zirconium phosphate (ZrP.sub.2O.sub.7).

Example 1

(4) The zirconium phosphate (ZrP.sub.2O.sub.7) and La-stabilized alumina (H.sub.0max: 7.1) obtained as described above were individually made into a slurry by a wet grinding treatment. The specific surface area (BET) of the zirconium phosphate (ZrP.sub.2O.sub.7) after the grinding was m.sup.2/g (the specific surface area (BET) of zirconium phosphate (ZrP.sub.2O.sub.7) used in the following Examples is also the same). The zirconium phosphate slurry was added with an Rh salt solution and was then stirred for two hours. Meanwhile, the La-stabilized alumina was dispersed into the deionized water to obtain a slurry, and the resulting slurry was added with a Pt salt solution and was then stirred for two hours. Thereafter, the stirred mixture was added to the Rh-containing zirconium phosphate slurry and was then stirred for one hour, and then a hinder component was added thereto.

(5) With respect to various components contained in the slurry, when the zirconium phosphate was set to be 73 parts by mass, the slurry contained the La-stabilized alumina of 21 parts by mass, and the binder of 6 parts by mass, Rh of 0.14 wt % with respect to the total mass of the zirconium phosphate, and Pt of 0.24 wt % with respect to the total mass of the La-stabilized alumina.

(6) The resulting slurry was dried and calcined in a state of being coated on a ceramic honeycomb substrate by 100 g/L to obtain a catalyst layer formed on the ceramic honeycomb substrate and the resultant was used as a honeycomb catalyst for activity evaluation.

(7) In the catalyst layer, Rh of 0.10 g/L was supported on a carrier consisting of the zirconium phosphate and Pt of 0.05 g/L was supported on the La-stabilized alumina.

Example 2

(8) The zirconium phosphate (ZrP.sub.2O.sub.7) obtained as described above and a ceria-zirconia composite oxide (CeO.sub.2ZrO.sub.2) were individually made into a slurry by a wet grinding treatment. The zirconium phosphate slurry was added with an Rh salt solution and was then stirred for two hours. Meanwhile, the ceria-zirconia composite oxide (CeO.sub.2ZrO.sub.2) was dispersed into deionized water to obtain a slurry, and the resulting slurry was added with a Pt salt solution and was then stirred for two hours. Thereafter, the stirred mixture was added to the Rh-containing zirconium phosphate slurry and was then stirred for one hour, and then a binder component was added thereto.

(9) With respect to various components contained in the slurry, when the zirconium phosphate was set to be 73 parts by mass, the slurry contained the ceria-zirconia composite oxide (CeO.sub.2) of 21 parts by mass, and the binder of 6 parts by mass, Rh of 0.14 wt %, respect to the total mass of the zirconium phosphate, and Pt of 0.24 wt % with respect to the total mass of the ceria-zirconia composite oxide (CeO.sub.2ZrO.sub.2).

(10) The resulting slurry was dried and calcined in a state of being coated on a ceramic honeycomb substrate by 100 g/L to obtain a catalyst layer formed on the ceramic honeycomb substrate and the resultant was used as a honeycomb catalyst for activity evaluation.

(11) In the catalyst layer, Rh of 0.10 g/L was supported on a carrier consisting of the zirconium phosphate and Pt of 0.05 g/L was supported on the ceria-zirconia composite oxide (CeO.sub.2ZrO.sub.2).

Example 3

(12) The zirconium phosphate (ZrP.sub.2O.sub.7) obtained as described above was made into a slurry by a wet grinding treatment. The zirconium phosphate slurry was added with an Rh salt solution and was then stirred for two hours. Meanwhile, CeO.sub.2 was dispersed into deionized water to obtain a slurry, and the resulting slurry was added with a Pt salt solution and was then stirred for two hours. Thereafter, the stirred mixture was added to the Rh-containing zirconium phosphate slurry and was then stirred for one hour, and then a binder component was added thereto.

(13) With respect to various components contained in the slurry, when the zirconium phosphate was set to be 7 parts by mass, the slurry contained CeO.sub.2 of 21 parts by mass, the binder of 6 parts by mass, Rh of 0.14 wt % with respect to the total mass of the zirconium phosphate, and Pt of 0.24 wt % with respect to the total mass of CeO.sub.2.

(14) The resulting slurry was dried and calcined in a state of being coated on a ceramic honeycomb substrate by 100 g/L and the resultant was used as a honeycomb catalyst for activity evaluation.

(15) In the catalyst layer, Rh of 0.10 q/L was supported on a carrier consisting of the zirconium phosphate and Pt of 0.05 g/L was supported on CeO.sub.2.

Example 4

(16) The zirconium phosphate (ZrP.sub.2O.sub.7) obtained as described above was made into a slurry by a wet grinding treatment. The zirconium phosphate slurry was added with an Rh salt solution and was then stirred for two hours. Meanwhile, ZrO.sub.2 (H.sub.0max: 9.3) was dispersed into deionized water to obtain a slurry, and the resulting slurry was added with a Pt salt solution and was then stirred for two hours. Thereafter, the stirred mixture was added to the Rh-containing zirconium phosphate slurry and was then stirred for one hour, and then a binder component was added thereto.

(17) With respect to various components contained in the slurry, when the zirconium phosphate was set to be 73 parts by mass, the slurry contained ZrO.sub.2 of 21 parts by mass, and the binder of 6 parts by mass, Rh of 0.14 wt % with respect to the total mass of the zirconium phosphate, and Pt of 0.24 wt % with respect to the total mass of ZrO.sub.2.

(18) The resulting slurry was dried and calcined in a state of being coated on a ceramic honeycomb substrate by 100 g/L and the resultant was used as a honeycomb catalyst for activity evaluation.

(19) In the catalyst layer, h of 0.10 g/L was supported on a carrier consisting of the zirconium phosphate and Pt of 0.05 g/L was supported on ZrO.sub.2.

Example 5

(20) The zirconium phosphate (ZrP.sub.2O.sub.7) obtained as described above was made into slurry by a wet grinding treatment. The zirconium phosphate slurry was added with an Rh salt solution and was then stirred for two hours. Meanwhile, TiO.sub.2 (H.sub.0max: 4.3) was dispersed into deionized water to obtain a slurry, and the resulting slurry was added with a Pt salt solution and was then stirred for two hours. Thereafter, the stirred mixture was added to the Rh-containing zirconium phosphate slurry and was then stirred for one hour, and then a binder component was added thereto.

(21) With respect to various components contained in the slurry, when the zirconium phosphate was set to be 73 parts by mass, the slurry contained TiO.sub.2 of 21 parts by mass, and the binder of 6 parts by mass, Rh of 0.14 wt % with respect to the total mass of the zirconium phosphate, and Pt of 0.24 wt % with respect to the total mass of TiO.sub.2.

(22) The resulting slurry was dried and calcined in a state of being coated on a ceramic honeycomb substrate by 100 g/L and the resultant was used as a honeycomb catalyst for activity evaluation.

(23) In the catalyst layer, Rh of 0.10 q/L was supported on a carrier consisting of the zirconium phosphate and Pt of 0.05 g/L was supported on TiO.sub.2.

Example 6

(24) The zirconium phosphate (ZrP.sub.2O.sub.7) obtained as described above was made into a slurry by a wet grinding treatment. The zirconium phosphate slurry was added with an Rh salt solution and was the a stirred for two hours. Meanwhile, SiO.sub.2 (H.sub.0max: 3.3) was dispersed into deionized water to obtain a slurry, and the resulting slurry was added with a Pt salt solution and was then stirred for two hours. Thereafter, the stirred mixture was added to the Rh-containing zirconium phosphate slurry and was then stirred for one hour, and then a binder component was added thereto.

(25) With respect to various components contained in the slurry, when the zirconium phosphate was set to be 73 parts by mass, the slurry contained SiO.sub.2 of 21 parts by mass, and the binder of 6 parts by mass, Rh of 0.14 wt % with respect to the total mass of the zirconium phosphate, and Pt of 0.24 wt % with respect to the total mass of SiO.sub.2.

(26) The resulting slurry was dried and calcined in a state of being coated on a ceramic honeycomb substrate by 100 g/L and the resultant was used as a honeycomb catalyst for activity evaluation.

(27) In the catalyst layer, h of 0.10 g/L was supported on a carrier consisting of the zirconium phosphate and Pt of 0.05 g/L was supported on SiO.sub.2.

Comparative Example 1

(28) The zirconium phosphate (ZrP.sub.2O.sub.7) and La-stabilized alumina obtained as described above were individually made into a slurry by a wet grinding, treatment. After the zirconium phosphate slurry was added with an Rh salt solution and was then stirred for two hours, the stirred mixture was added with the La-stabilized alumina slurry and was then stirred for one hour, and then a binder component was added thereto.

(29) Rh was set to contain 0.21 wt % with respect to the total mass of the zirconium phosphate.

(30) The resulting slurry was dried and calcined in a state of being coated on a ceramic honeycomb substrate by 100 g/L and the resultant was used as a honeycomb catalyst for activity evaluation.

(31) In the catalyst layer, Rh of 0.15 g/L was supported on a carrier consisting of the zirconium phosphate.

(32) <Evaluation Method of Catalyst Performance>

(33) A/F scanning evaluation of the honeycomb catalyst was performed in the following manner: complete-combustion-simulated exhaust gas consisting of CO, CO.sub.2, C.sub.3H.sub.6, O.sub.2, NO, and H.sub.2O, the balance being N.sub.2 was subjected to scanning until A/F was 15.0 to 15.3 (until CO and O.sub.2 concentration was changed) and flowed through the ceramic honeycomb catalyst at an SV of 100,000 h.sup.1; and an outlet gas component was measured at 400 C. using a CO/HC/NO analyzer (MOTOR EXHAUST GAS ANALYZER MEXA9100 made by HORIBA Ltd.) to compare the performance of each Rh-supporting catalyst.

(34) By the A/F scanning evaluation of the honeycomb catalyst, the performance comparison was performed on the catalyst after the simulated exhaust gas was used for a long period. With respect to endurance condition of the simulated exhaust gas, a catalyst was placed in an electric furnace maintained at 800 C., and to the furnace accommodating the catalyst, a gas mixture (for 20 s) of C.sub.3H.sub.6 and CO or C.sub.3H.sub.6 and O.sub.2 (complete combustion ratio), and air (for 10 s) were alternately and periodically fed for 50 hours.

(35) A purification rate (%) of NO.sub.x in an A/F sweep test of C.sub.3H.sub.6CONO reaction for each catalyst was indicated in Table 1, a purification rate (%) of NO.sub.x in an sweep test of C.sub.3H.sub.6NO reaction for each catalyst was indicated in Table 2, and a purification rate (%) of NO.sub.x in an A/F sweep test of CONO reaction for each catalyst was indicated in Table 3.

(36) In Tables 1 to 3, Al.sub.2O.sub.3 indicates La-stabilized alumina, MO.sub.x indicates an inorganic oxide, and ZPO indicates zirconium phosphate (ZrP.sub.2O.sub.7).

(37) TABLE-US-00001 TABLE 1 A/F Cat. 15.0 15.1 15.2 15.3 Comparative Rh/ZPO + Al.sub.2O.sub.3 47.6 34.3 25.6 17.3 Example 1 Rh/ZPO + Pt/MO.sub.x Example 1 MO.sub.xAl.sub.2O.sub.3 (7.1) 54.7 48.5 41.5 35.3 Example 2 MO.sub.xCeO.sub.2ZrO.sub.2 50.0 40.2 34.2 27.9 Example 3 MO.sub.xCeO.sub.2 32.7 24.9 20.3 14.5 Example 4 MO.sub.xZrO.sub.2 (9.3) 21.0 19.9 18.9 16.9 Example 5 MO.sub.xTiO.sub.2 (4.3) 62.1 53.2 46.3 37.8 Example 6 MO.sub.xSiO.sub.2 (3.3) 53.0 47.6 42.7 36.3 * Numeric values in parenthesis indicate Hammett acidity functions.

(38) TABLE-US-00002 TABLE 2 A/F Cat. 15.0 15.1 15.2 15.3 Comparative Rh/ZPO + Al.sub.2O.sub.3 16.3 9.9 5.4 3.2 Example 1 Rh/ZPO + Pt/MO.sub.x Example 1 MO.sub.xAl.sub.2O.sub.3 29.6 27.4 24.7 23.7 Example 5 MO.sub.xTiO.sub.2 34.0 29.0 24.6 21.4 Example 6 MO.sub.xSiO.sub.2 45.9 33.7 27.0 22.4

(39) TABLE-US-00003 TABLE 3 A/F Cat. 15.0 15.1 15.2 15.3 Comparative Rh/ZPO + Al.sub.2O.sub.3 43.3 33.4 28.1 22.2 Example 1 Rh/ZPO + Pt/MO.sub.x Example 1 MO.sub.xAl.sub.2O.sub.3 55.3 43.8 36.9 29.3 Example 5 MO.sub.xTiO.sub.2 66.2 54.7 47.7 39.6 Example 6 MO.sub.xSiO.sub.2 53.5 45.5 40.3 34.0

(40) (Results of Evaluation)

(41) As seen from Table 1, purification performance for NO.sub.x was significantly improved under lean conditions in Example 1 compared with Comparative Example 1, and excellent purification performance for NO.sub.x was shown in an area of 15.0A/F15.3 when an Rh/zirconium phosphate was added with an Pt-supported inorganic oxide.

(42) In Examples 1 to 6 in Table 1, the purification performance for NO was reduced when a basic metal oxide having a value of Hammett acidity function higher than that of Al.sub.2O.sub.3 was added. However, purification capability for NO.sub.x equal to or higher than that of Example 1 was shown when a metal oxide having a value of Hammett acidity function equal to or lower than that of Al.sub.2O.sub.3 was added. In particular, higher purification performance for NO.sub.x was observed in a lean area of 15.0A/F15.3 in Example 5 compared with Comparative Example 1.

(43) In C.sub.3H.sub.6NO reaction in Table 2, the improvement in purification capability for NO.sub.x was observed in Examples 1, 5, and 6 compared with Comparative Example 1, and particularly, the same level of purification capability for NO.sub.x was shown in an area of A/F15.2 regardless of kinds of metal oxides. This is considered because the effect of Pt is remarkable for the C.sub.3H.sub.6NO reaction in a lean area of A/F15.2.

(44) In CONO reaction in Table 3, the improvement in purification capability for NO.sub.x was observed in Examples 1, 5, and 6 compared with Comparative Example 1 The purification capability for NO.sub.x was greatly varied depending on kinds of metal oxides, and particularly, the purification capability for NO was significantly improved is Example 5.

(45) From the above, it is considered that performance is specifically improved due to acceleration of the C.sub.3H.sub.6NO reaction by addition of Pt and improvement of CONO reactivity by addition of TiO.sub.2 in Example 5 in Table 1.