WO2006054404A1

WO2006054404A1 - Exhaust gas purification catalyst and method for production thereof

Info

Publication number: WO2006054404A1
Application number: PCT/JP2005/018605
Authority: WO
Inventors: Hiroto Kikuchi; Masanori Nakamura; Hironori Wakamatsu; Toru Sekiba; Katsuo Suga
Original assignee: Nissan Motor Co., Ltd.
Priority date: 2004-11-16
Filing date: 2005-10-07
Publication date: 2006-05-26
Also published as: JP2006142137A

Abstract

A method for producing an exhaust gas clarification catalyst, which comprises providing a substrate (4) containing alumina and ceria, allowing the substrate (4) to carry noble metal particles (13, 23) containing a noble metal selected from platinum, palladium and rhodium, and then covering at least a part of the above noble metal particles (13, 23) with a metal oxide (14, 24). The method can be suitably used for inhibiting the sintering of noble metal particles and for retaining high catalyst activity also under a high temperature and oxidizing circumstance.

Description

Specification

Exhaust gas purification catalyst and method for producing the same

Technical field

TECHNICAL FIELD [0001] The present invention relates to an exhaust gas purification catalyst for purifying exhaust gas from a vehicle and a method for producing the same.

Background art

[0002] Vehicles that contain harmful components such as unburned hydrocarbons (HC) or carbon monoxide (CO) in the exhaust gas have a purification mechanism that removes those harmful components and purifies the exhaust gas. Equipped exhaust gas purifier is provided.

[0003] On the other hand, noble metals such as platinum (Pt), palladium (Pd), and rhodium (Rh) come into contact with the exhaust gas of a vehicle, and harmful components therein are harmless gas or water (H 0). Convert to component

2

And has a catalytic action to purify the exhaust gas.

[0004] Therefore, carrier particles such as alumina (A1 0) carrying noble metal particles are exhausted.

twenty three

An exhaust gas purification device having a purification mechanism dispersedly supported on the wall surface of a passage has been developed.

[0005] In this respect, the carrier particle has both a side surface as a supporting element and a side surface as a supported element, and is also called a "base material" in order to prevent confusion. When the carrier particles are called a base material, a member that defines the exhaust gas passage is called a “carrier”. The base material supporting the noble metal particles, the carrier supporting the base material, the purification mechanism including them, and the exhaust gas purification device are collectively referred to as “exhaust gas purification catalyst”. In either case, the noble metal particles are supported on the base material.

[0006] When the total surface area per unit amount of the noble metal particles, that is, the specific surface area of the exhaust gas purification catalyst is increased, the exhaust gas purification performance is improved.

[0007] Precious metal particles can be increased in specific surface area by being finely divided.

[0008] Japanese Unexamined Patent Application Publication No. 2000-42411 discloses a reverse micelle method as a technique for forming fine particles of noble metal particles.

[0009] In this reverse micelle method, a noble metal-containing aqueous solution and a surfactant are mixed in an organic solvent, and the reverse micelle of the surfactant is dispersed in the solvent, and the noble metal-containing is contained inside the reverse micelle. An emulsion of an aqueous solution is prepared, and the noble metal is precipitated, reduced, or insoluble, and precipitated in reverse micelles to atomize the noble metal. Disclosure of the invention

[0010] By this method, the noble metal is adjusted to an ultrafine particle size of several nm or less.

[0011] However, when the exhaust gas purification catalyst is exposed to a high-temperature (about 500 ° C to 600 ° C) acid atmosphere for a long time, the surface of the precious metal particles is not only oxidized but also in the vicinity. Particles sinter together and coalesce. The combined precious metal particles are enlarged to about several tens of particles, and the specific surface area is reduced accordingly, and the exhaust gas purification performance is reduced.

[0012] The present invention was made to solve this problem, and an exhaust gas purification catalyst that suppresses sintering of noble metal particles even when exposed to a high-temperature oxidizing atmosphere, and maintains the purification performance correspondingly. It is an object to provide a manufacturing method thereof.

[0013] An exhaust gas purifying catalyst according to one aspect of the present invention includes a base material containing alumina and ceria that achieves the above-mentioned problem, and a noble metal selected from platinum, nodium and rhodium, It has noble metal particles carried on the substrate, and a metal oxide covering at least a part of the noble metal particles.

[0014] A method for producing an exhaust gas purifying catalyst according to another aspect of the present invention provides a base material containing alumina and ceria that can achieve the above-mentioned problems, and a precious metal in which the intermediate forces of platinum, noradium and rhodium are also selected. The noble metal particles containing are supported on the base material, and at least a part of the noble metal particles is covered with a metal oxide.

[0015] According to the above aspects of the present invention, since at least a part of the noble metal particles is covered with the metal oxide, sintering of the noble metal particles is suppressed, and accordingly, the purification of the exhaust gas purification catalyst.匕 performance is maintained.

The above-mentioned and other problems, features, and effects of the present invention will be clarified by reading the description of the best mode for carrying out the invention made with reference to the accompanying drawings. . Brief Description of Drawings

[0017] [Fig. 1] Fig. 1 (a) is a cross-sectional view of the main part of an exhaust gas purification catalyst according to an embodiment of the present invention, Fig. 1 (b) is a detailed view of the lb portion of Fig. 1 (a), 1 (c) is a cross-sectional view of Ic Ic of FIG. 1 (b).

[Fig.2] Fig. 2 (a) is a cross-sectional view of Ila-Ila in Fig. 1 (c), and Fig. 2 (b) is a cross-sectional view of lib-lib in Fig. 1 (c).

FIG. 3 is a flowchart showing a method for manufacturing the exhaust gas purification catalyst of FIGS. 1 and 2. [FIG. 4] FIG. 4 is a graph showing the results of the purification performance test of the exhaust gas purification catalyst according to the example of the production method of FIG. 3 and the comparative example.

[FIG. 5] FIG. 5 (a) is a TEM observation photograph of the alumina substrate of the exhaust gas purification catalyst according to the embodiment of FIG. 4, and FIGS. 5 (b) and 5 (c) are EDX (energy) of the substrate. (Dispersive X-ray fluorescence analyzer) Analysis image.

BEST MODE FOR CARRYING OUT THE INVENTION

Next, an exhaust gas purification catalyst according to an embodiment of the present invention will be described with reference to FIGS. 1 and 2.

[0019] Fig. 1 (a) shows a cross section of the main part of the exhaust gas purification catalyst 1 according to the embodiment of the present invention, and Fig. 1 (b) shows details of its lb portion, and shows its Ic Ic cross section. It is shown in Fig. 1 (c). The cross sections 11 & 11 & and 111 111) of FIG. 1 (c) are shown in FIGS. 2 (a) and 2 (b), respectively.

[0020] As shown in Fig. 1 (a), the exhaust gas purification catalyst 1 includes a carrier 2 as a ceramic monolith that defines a number of exhaust gas passages 2a communicating with exhaust gas pipes (not shown) of a vehicle, It is composed of at least a single-layer coating layer 3 that uniformly covers the inner surface of the exhaust gas passage 2a. If necessary, different types of coating layers are formed on the coating layer 3 (for example, slurry R described later). (Not shown) is applied.

[0021] As shown in FIG. 1 (b), the coating layer 3 is a coating material as a binder having a net-like shape, a porous shape, a film shape, or a shape in which they are mixed and fixed on the inner surface of the exhaust gas passage 2a. 3a and a large number of base materials 4 as spongy porous fine particles dispersed and held by the coating material 3a. Each base material 4 is formed as a catalyst carrier 4a having an embedded portion fixed by being embedded in the coating material 3a and a protruding portion protruding from the outer surface 3b of the coating material 3a to the exhaust gas passage 2a. Ultra-thin exhaust gas purification catalyst active layer 4b is formed on the body

[0022] As shown in Fig. 1 (c) and Fig. 2 (a), the catalytically active layer 4b has a part of the surface 13a of the noble metal particle 13 in a net-like shape, a porous shape, a membrane shape, or a mixture thereof. The catalyst exposed part 10 is mostly composed of a metal oxide 14 shaped like this, and the remainder of the surface 13a is exposed to the exhaust gas passage 2a, as shown in Fig. 1 (c) and Fig. 2 (b). In addition, the surface 23a of the noble metal particle 23 It also includes a catalyst coating portion 20 in which the body is covered with a metal oxide 24 having a net shape, a porous shape, a film shape, or a shape in which they are mixed.

[0023] As illustrated in FIG. 1 (c), the oxides 14 and 24 are scattered in the form of archipelago or connected to the surface of the base material 4 (that is, the outer surface of the carrier 4a). As a layer, it is fixed on the base material 4 and covers and holds at least a part of the corresponding noble metal particles 13 and 23 as shown in FIGS. 2 (a) and 2 (b). As a result, a large number of noble metal particles 13 and 23 are dispersed and arranged relatively uniformly over the entire surface of the base material 4, and are anchored and supported on the base material 4 through the oxide 14 and 24 layers.

[0024] Therefore, the exhaust gas purification catalyst 1 is used for a long period of time in a high-temperature acid atmosphere, with the advantage that the uniform dispersion of the noble metal particles 13 and 23 contributes to the improvement of the catalyst performance of the entire catalytic active layer 4b. Even in this case, since the sintering between adjacent noble metal particles 13, 13; 13, 23; or 23, 23 is greatly suppressed, the initial specific surface area of the noble metal particles 13, 23 is effectively maintained, and the catalyst There are advantages to maintaining performance.

[0025] In the above configuration, the base material 4 may be a composition or composite containing alumina and ceria, and the noble metal particles 13, 23 may be made of one or more kinds of noble metals selected from platinum, palladium, and rhodium. The metal oxides 14, 24 comprise the medium strength of one or more metals selected from Co, Ni, Fe, Cu, Sn, Mn, Ce and Zr.

[0026] The catalytically active layer 4b has an average molar ratio of metal in the metal oxides 14 and 24 to the noble metal particles 13 and 23 (atomic ratio in the case of atomic ratio) in the range of 0.005 to 6. It is desirable to set the material mixing ratio so that When this value is less than 0.005, the sintering suppressing effect of the noble metal particles 13 and 23 is weakened. Conversely, when the value exceeds 6, the catalyst activity of the noble metal particles 13 and 23 is lowered from the useful range. In this regard, the average value of the molar ratio is more preferably set such that the material mixing ratio is in the range of 0.1 to 3.

[0027] At least a part of the noble metal particles 13, 23 is covered with island-shaped metal oxides 14, 24 as shown in Fig. 2 (a) and Fig. 2 (b), and is simply anchored on the substrate 4. However, the ability to prevent the individual displacements of the noble metal particles 13 and 23 and suppress their sintering. The metal oxides 14 and 24 are formed as a continuous layer as illustrated in Fig. 1 (c). When fixed on material 4, it acts as a physical barrier, preventing the relative displacement of precious metal particles 13, 23 and suppressing sintering. Complement effectively.

[0028] Note that the coating layer 3 of the exhaust gas purification catalyst 1 shown in FIG. 1 (a) may be laminated by applying a plurality of layers to the carrier 2 and firing the substrate. 4b may be laminated with a coating layer 3 having a different composition or structure.

Next, a method for manufacturing the exhaust gas purification catalyst 1 will be described with reference to FIG.

FIG. 3 is a flowchart showing a method for manufacturing the exhaust gas purification catalyst 1.

[0031] The exhaust gas purification catalyst 1 includes at least one of an adjustment step S1 for adjusting the base material 4, a support step S2 for supporting the noble metal particles 13 and 23 on the adjusted base material 4, and the noble metal particles 13 and 23 supported. Coating step S3 for covering the part with metal oxides 14, 24, and coating step S4 for slurrying base material 4 supporting noble metal particles 13, 23 covered with metal oxides 14, 24 and applying them to carrier 2 Manufactured by the method of inclusion.

[0032] In the adjustment step S1, the adjustment of the alumina base material containing alumina and the adjustment of the ceria base material containing ceria are performed separately.

[0033] In the supporting step S2, noble metal particles 13 and 23 are supported on the adjusted alumina base material and ceria base material by an impregnation method, and dried and fired.

[0034] In the coating step S3, a predetermined metal is deposited on the surfaces 13a, 23a of the supported noble metal particles 13, 23 or a part thereof by a selective deposition method, and baked to oxidize the deposited metal and oxidize its metal. Cover at least part of the noble metal particles 13 and 23 with the objects 14 and 24.

[0035] The selective deposition method is preferably an electroless plating method. The electroless plating method uses Co, Ni, Fe, Cu, or Sn as a selective metal among the forces applicable to the selective deposition of Co, Ni, Fe, Cu, Sn, Mn, Ce, and Zr. Is preferred. More preferably, an individual base material is prepared (S1), and Pt particles are supported by the impregnation method (S2), pulverized, immersed in a Co solution, stirred, and then sodium borohydride is added. By reducing Co, it is deposited on the Pt particles, and the precipitated Co is baked and oxidized to cover at least a part of the Pt particles (S3).

[0036] In the coating step S4, different types of substrates are overcoated on the carrier 2.

[0037] Hereinafter, more detailed examples will be shown, but the present invention is not limited to these examples.

Example

[0038] ¾fine Alumina base material composed of γ-alumina compounded with 9% acid cerium, 6% acid zirconium, and 6% lanthanum oxide (hereinafter referred to as “1S1-alumina” in the sense of the alumina base in step S1 of the first embodiment) The ceria base material (hereinafter referred to as “1S1-ceria base material”) was individually adjusted (Sl).

[0039] The alumina substrate -1S1 is impregnated with a dinitrodiammine platinum aqueous solution, dried, calcined at 400 ° C, and loaded with 0.44% Pt (hereinafter referred to as "1S2-alumina substrate") Was obtained (S2).

[0040] 150 g of 1S2-alumina substrate was added to a cobalt solution containing 0.002 g of cobalt nitrate dissolved in 200 g of water and stirred for 1 hour at room temperature, and then 0.0% of sodium borohydride was added. Stir OOlmol, stir for another hour, filter, wash, dry this cobalt solution, calcinate at 400 ° C, PtO.44% alumina base material containing 0.01 atomic ratio of Co to Pt. This was called “1S3-Alumina substrate” (S3).

[0041] Further, the above 1S1-ceria base material is impregnated with a dinitrodiammine platinum aqueous solution, dried, calcined at 400 ° C, and loaded with 0.375% Pt (hereinafter referred to as "1S2-ceria base material"). Was obtained (S2).

[0042] 100 g of 1S2-ceria base material was added to a cobalt solution containing 0.001 lg of cobalt dissolved in 200 g of water in cobalt nitrate hexahydrate, stirred at room temperature for 1 hour, and then sodium borohydride was added to 0.000. Stir 058mol, stir for another hour, filter, wash, dry this cobalt solution, calcinate at 400 ° C, and contain Pt 0.375% ceria substrate (hereinafter referred to as "1S3 -Called “Celer base material.”) (S3).

[0043] 124.8 g of 1S3-alumina base material, 48.6 g of 1S3-ceria base material, and 1.6 g of bermite alumina are placed in a ball mill, and 307.5 g of water and 17.5 g of 10% nitric acid aqueous solution are added to form a powder. Was pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry A”) (S4).

[0044] Next, a composite of γ-alumina containing 3% zirconium and zirconium oxide was impregnated with rhodium nitrate to obtain a powder base material carrying 0.6% rhodium.

[0045] Further, a zirconium base material obtained by combining 24% of cerium oxide with zirconium oxide was obtained.

[0046] 116.55 g of the rhodium 0.6% base material, 44.45 g of the zirconia base material, llg of the alumina base material, and 3 g of boehmite alumina were added to a ball mill, and further 307.5 g of water and a 10% nitric acid aqueous solution 1 7.5 g was added and pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry R”). (S4) In this slurry R, the noble metal supported on the base material is not covered with the metal oxide.

[0047] 36 mm diameter, 400 cell, 6 mil Hercame carrier (capacity 0.04L), coated with 141g / L of slurry A and dried, and further coated with 59g / L of slurry R, dried, 400 ° The sample of Example 1 was obtained by baking with C (S4). This sample is a catalyst which carries Pt 0.587g / L, Rh 0.236g / L and contains Co in an atomic ratio of 0.01 with respect to Pt.

[0048] Example 2

Add 150 g of 1S2-alumina substrate (Pt 0.44% alumina substrate) to cobalt solution containing cobalt nitrate hexahydrate dissolved in 200 g of water and cobalt in O.Olg, and stir at room temperature for 1 hour. Add 0.0005 mol of sodium borohydride and stir for an additional hour. The cobalt solution is filtered, washed, dried, calcined at 400 ° C, and PtO.44% Al containing 0.05 by atomic ratio of Co to Pt. A Mina base material (hereinafter referred to as “2S3-alumina base material”) was obtained (S3).

[0049] Further, 100 g of 1S2-ceria base material (Pt 0.375% ceria base material) was added to a cobalt solution in which cobalt nitrate hexahydrate was dissolved in 200 g of water and 0.0057 g of cobalt was added. After stirring for 1 hour, 0.00029 mol of sodium borohydride was added, and the mixture was further stirred for 1 hour, and this cobalt solution was filtered, washed, dried, calcined at 400 ° C, and Co contained in an atomic ratio of 0.05 to Pt. Pt 0.37 5% ceria base material (hereinafter referred to as “2S3-ceria base material”) was obtained (S3).

[0050] 124.8 g of 2S3-alumina base material, 48.6 g of 2S3-ceria base material, and 1.6 g of bermite alumina are placed in a ball mill, and 307.5 g of water and 17.5 g of a 10% nitric acid aqueous solution are added to the powder. Was pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry B”). (S4).

[0051] A 36-millimeter, 400-cell, 6-mil Hercam carrier (capacity 0.04 L) was coated with 141 g / L of slurry B and dried, and further coated with 59 g / L of slurry R (see Example 1). After drying, baking was performed at 400 ° C. to obtain a sample of Example 2 (S4). This sample is a catalyst that supports Pt at 0.587 g / L, Rh at 0.236 g / L, and contains Co in an atomic ratio of 0.05 with respect to Pt.

[0052] Example 3

Add 150 g of 1S2-alumina substrate (Pt 0.44% alumina substrate) to a cobalt solution containing cobalt nitrate hexahydrate dissolved in 200 g of water and 0.02 g of cobalt, and stir at room temperature for 1 hour. O.OOlmol power of sodium boronide! ] Stir for an additional hour and filter this cobalt solution , Washed, dried, and fired at 400 ° C to obtain a PtO.44% alumina substrate (hereinafter referred to as "3S3-alumina substrate") containing Co in an atomic ratio of 0.1 to Pt (S3). ).

[0053] Further, 100 g of 1S2-ceria base material (Pt 0.375% ceria base material) was added to a cobalt solution containing 0.0113 g of cobalt dissolved in 200 g of water and dissolved in 200 g of water at room temperature. After stirring for 1 hour, 0.00058 mol of sodium borohydride was added, and the mixture was further stirred for 1 hour. The cobalt solution was filtered, washed, dried, and calcined at 400 ° C. Co contained in an atomic ratio of 0.1 to Pt. A Pt 0.375% ceria substrate (hereinafter referred to as “3S3-ceria substrate”) was obtained (S3).

[0054] 124.8 g of 3S3-alumina base material, 48.6 g of 3S3-ceria base material, and 1.6 g of bermite alumina are placed in a ball mill, and 307.5 g of water and 17.5 g of a 10% nitric acid aqueous solution are added to form a powder. Was pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry C”). (S4).

[0055] A 36-millimeter, 400-cell, 6-mil Hercam carrier (capacity 0.04 L) was coated with 141 g / L of slurry C and dried, and further coated with slurry R (see Example 1) 59 g / L. After drying, baking was performed at 400 ° C. to obtain a sample of Example 3 (S4). This sample is a catalyst that carries 0.587 g / L of Pt, 0.236 g / L of Rh, and contains Co in an atomic ratio of 0.1 with respect to Pt.

[0056] Example 4

Using the same method as in Example 1, a quantitative operation was performed to obtain an alumina base material supporting 0.441% Pt (hereinafter referred to as “4S2-alumina base material”) and a ceria base material supporting 0.3756% Pt ( Hereinafter, referred to as “4S2-ceria substrate”) (S2).

[0057] Cobalt nitrate hexahydrate was dissolved in 200 g of water and cobalt solution containing 0.20 g of cobalt was charged with 149.72 g of 4S2-alumina substrate (Pt 0.441% alumina substrate). After stirring for a period of time, add 0.0102 mol of sodium borohydride, stir for an additional hour, and filter, wash, dry this condensate solution, calcinate at 400 ° C, and contain Co in an atomic ratio of 1 to Pt. A Pt 0.44% alumina substrate (hereinafter referred to as “4S3-alumina substrate”) was obtained (S3).

[0058] Further, 99.84 g of 4S2-ceria base material (Pt 0.3756% ceria base material) was added to a cobalt solution containing cobalt nitrate 0.1132 g dissolved in water 200 g of cobalt nitrate, and room temperature. After stirring for 1 hour, add 0.0058 mol of sodium borohydride and stir for an additional hour. The cobalt solution is filtered, washed, dried, calcined at 400 ° C, and contains Co in an atomic ratio of 1 to Pt. A Pt 0.375% ceria substrate (hereinafter referred to as “4S3-ceria substrate”) was obtained (S3). [0059] 4S3-alumina base material 124.8g, 4S3-ceria base material 48.6g, and bermite alumina 1.6g were placed in a ball mill, and further water 307.5g and 10% nitric acid aqueous solution 17.5g were added. Was pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry D”). (S4).

[0060] A 36 mm diameter, 400 cell, 6 mil Hercame carrier (capacity 0.04 L) was coated with 141 g / L of slurry D and dried, and further coated with 59 g / L of slurry R (see Example 1). After drying, baking was performed at 400 ° C. to obtain a sample of Example 4 (S4). This sample is a catalyst that carries 0.587 g / L of Pt, 0.236 g / L of Rh, and contains Co in an atomic ratio of 1 to Pt.

[0061] Example 5

Using the same method as in Example 1, a quantitative operation was performed to obtain an alumina base material supporting 0.442% Pt (hereinafter referred to as “5S2-alumina base material”) and a ceria base material supporting 0.3762% Pt ( Hereinafter, it is referred to as “5S2-ceria substrate”) (S2).

[0062] Cobalt nitrate hexahydrate dissolved in 200 g of water and cobalt solution containing 0.3987 g of cobalt was added 149.44 g of 5S2-alumina substrate (Pt 0.442% alumina substrate) at room temperature. After stirring for 1 hour, add 0.0203 mol of sodium borohydride, stir for an additional hour, filter, wash, dry this Conoleto solution, calcinate at 400 ° C, and Co at an atomic ratio of 2 to Pt. A Pt0.4 containing 4% alumina substrate (hereinafter referred to as “5S3-alumina substrate”) was obtained (S3).

[0063] Further, 99.68 g of 5S2-ceria base material (Pt 0.3762% ceria base material) was added to a cobalt solution containing cobalt nitrate hexahydrate dissolved in 200 g of water and 0.2265 g of cobalt at room temperature. After stirring for 1 hour, add 0.012 mol of sodium borohydride and stir for an additional hour. This cobalt solution is filtered, washed, dried, calcined at 400 ° C, and contains Co in an atomic ratio of 2 to Pt. Pt 0.375% ceria base material (hereinafter referred to as “5S3-ceria base material”) was obtained (S3).

[0064] 12Sg of 5S3-alumina base material, 48.6g of 5S3-ceria base material, and 1.6g of bermite alumina are placed in a ball mill, and 307.5g of water and 17.5g of 10% nitric acid aqueous solution are added to the powder. Was pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry E”). (S4).

[0065] A 36-millimeter, 400-cell, 6-mil Hercam carrier (capacity 0.04 L) was coated with 141 g / L of slurry E, dried, and then coated with 59 g / L of slurry R (see Example 1). After drying, baking was performed at 400 ° C. to obtain a sample of Example 5 (S4). This sample is a catalyst that carries 0.587 g / L of Pt, 0.236 g / L of Rh, and contains Co in an atomic ratio of 2 with respect to Pt. [0066] Example 6

Using the same method as in Example 1, a quantitative operation was performed to obtain an alumina substrate supporting 0.4425% Pt (hereinafter referred to as “6S2-alumina substrate”) and a ceria substrate supporting 0.3768% Pt ( Hereinafter, referred to as “6S2-ceria substrate”) (S2).

[0067] 149.16g of 6S2-alumina base material (Pt 0.4425% alumina base material) was added to a cobalt solution in which cobalt nitrate hexahydrate was dissolved in 200g of water and 0.5981g of cobalt was added. After stirring, 0.0304 mol of sodium borohydride was added, and the mixture was further stirred for 1 hour, and this solution was filtered, washed and dried, calcined at 400 ° C, and Co contained in an atomic ratio of 3 to Pt. .4 A 4% alumina substrate (hereinafter referred to as “6S3-alumina substrate”) was obtained (S3).

[0068] Also, 99.52g of 6S2-ceria base material (Pt 0.3768% ceria base material) was added to a cobalt solution containing 0.3396g of cobalt dissolved in 200g of water. After stirring for 1 hour, 0.0173 mol of sodium borohydride was added, and further stirred for 1 hour. This cobalt solution was filtered, washed, dried, calcined at 400 ° C, and Co contained in an atomic ratio of 3 to Pt. A Pt 0.375% ceria substrate (hereinafter referred to as “6S3-ceria substrate”) was obtained (S3).

[0069] 12Sg of 6S3-alumina base material, 48.6g of 6S3-ceria base material, and 1.6g of bermite alumina were placed in a ball mill, and 307.5g of water and 17.5g of 10% nitric acid aqueous solution were added to powder. Was pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry F”). (S4).

[0070] 36 g diameter, 400 cell, 6 mil Hercame carrier (capacity 0.04L) was coated with 141g / L of slurry F, dried, and then coated with slurry R (see Example 1) 59g / L. After drying, baking was performed at 400 ° C. to obtain a sample of Example 6 (S4). This sample is a catalyst that supports 0.587 g / L of Pt, 0.236 g / L of Rh, and contains Co in an atomic ratio of 3 with respect to Pt.

[0071] Example 7

Using the same method as in Example 1, a quantitative operation was performed to obtain an alumina substrate carrying 0.443% Pt (hereinafter referred to as “7S2-alumina substrate”) and a ceria substrate carrying 0.3774% Pt ( Hereinafter, referred to as “7S2-ceria substrate”) was obtained (S2).

[0072] Cobalt nitrate hexahydrate dissolved in 200 g of water and 0.7974 g of cobalt was added to a cobalt solution containing 148.88 g of 7S2-alumina substrate (Pt 0.443% alumina substrate) at room temperature. After stirring for 1 hour, add 0.041 mol of sodium borohydride and stir for another 1 hour. The liquid was filtered, washed, dried, and fired at 400 ° C. to obtain a Pt 0.44% alumina base material (hereinafter referred to as “7S3-alumina base material”) containing Co in an atomic ratio of 4 to Pt. (S3).

[0073] Also, 99.36g of 7S2-ceria base material (Pt 0.3774% ceria base material) was added to a cobalt solution containing cobalt nitrate hexahydrate dissolved in 200g of water and 0.4528g of cobalt at room temperature. After stirring for 1 hour, add 0.0231 mol of sodium borohydride and stir for an additional hour. This cobalt solution is filtered, washed, dried, calcined at 400 ° C, and contains Co in an atomic ratio of 4 to Pt. A Pt 0.375% ceria substrate (hereinafter referred to as “7S3-ceria substrate”) was obtained (S3).

[0074] 7S3-alumina base material 124.8g, 7S3-ceria base material 48.6g, and bermite alumina 1.6g were placed in a ball mill, and water 307.5g and 10% nitric acid aqueous solution 17.5g were added, and powdered. Was pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry G”). (S4).

[0075] A 36-millimeter, 400-cell, 6-mil Hercam carrier (capacity 0.04 L) was coated with 141 g / L of slurry G and dried, and further coated with 59 g / L of slurry R (see Example 1). After drying, baking was performed at 400 ° C. to obtain a sample of Example 7 (S4). This sample is a catalyst that carries 0.587 g / L of Pt, 0.236 g / L of Rh, and contains Co in an atomic ratio of 4 with respect to Pt.

[0076] Example 8

Using the same method as in Example 1, a quantitative operation was performed to obtain an alumina base material supporting 0.444% Pt (hereinafter referred to as “8S2-alumina base material”) and a ceria base material supporting 0.378% Pt ( Hereinafter, referred to as “8S2-ceria substrate”) was obtained (S2).

[0077] Add 148.60g of 8S2-alumina base material (Pt 0.444% alumina base material) to cobalt solution containing 0.997g of cobalt nitrate dissolved in 200g of water for 1 hour at room temperature. After stirring, add 0.051 mol of sodium borohydride and stir for an additional hour. Filter, wash and dry this solution of condensate, calcinate at 400 ° C, and contain Co in an atomic ratio of 5 to Pt. A Pt0.44% alumina substrate (hereinafter referred to as “8S3-alumina substrate”) was obtained (S3).

[0078] Further, 99.20 g of 8S2-ceria base material (Pt 0.378% ceria base material) was added to a cobalt solution in which cobalt nitrate hexahydrate was dissolved in 200 g of water and 0.566 g of cobalt was contained, and at room temperature. After stirring for 1 hour, 0.029 mol of sodium borohydride was added and further stirred for 1 hour, and this cobalt solution was filtered, washed, dried, calcined at 400 ° C, and Co contained in an atomic ratio of 5 to Pt. A Pt 0.375% Celer substrate (hereinafter referred to as “8S3-ceria substrate”) was obtained (S3). [0079] 124.8 g of 8S3-alumina base material, 48.6 g of 8S3-ceria base material, and 1.6 g of bermite alumina were placed in a ball mill, and 307.5 g of water and 17.5 g of a 10% nitric acid aqueous solution were added to form a powder. Was pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry H”). (S4).

[0080] A 36-millimeter, 400-cell, 6-mil Herkam carrier (capacity 0.04 L) was coated with 141 g / L of slurry H and dried, and further coated with slurry R (see Example 1) 59 g / L. After drying, baking was performed at 400 ° C. to obtain a sample of Example 8 (S4). This sample is a catalyst that supports Pt at 0.587 g / L, Rh at 0.236 g / L, and contains Co in an atomic ratio of 5 to Pt.

[0081] Example 9

Add 150 g of 1S2-alumina base (Pt 0.44% alumina base) to a cobalt solution containing cobalt nitrate hexahydrate dissolved in 200 g of water and cobalt in O.OOlg, and stir at room temperature for 1 hour. Add 0.00005 mol of sodium borohydride and stir for an additional hour, then filter, wash, dry this cobalt solution, calcinate at 400 ° C, and contain Co in an atomic ratio of 0.005 to Pt 0.44% An alumina substrate (hereinafter referred to as “9S3-alumina substrate”) was obtained (S3).

[0082] Further, 100 g of 1S2-ceria base material (Pt 0.375% ceria base material) was added to a cobalt solution containing 0.0006 g of cobalt dissolved in 200 g of water and cobalt nitrate hexahydrate at room temperature. After stirring for 1 hour, add 0.00003mol of sodium borohydride and stir for an additional hour, then filter, wash, dry this cobalt solution, calcinate at 400 ° C and contain Co in an atomic ratio of 0.005 to Pt Pt 0.3 75% ceria base material (hereinafter referred to as “9S3-ceria base material”) was obtained (S3).

[0083] 124.8 g of 9S3-alumina base material, 48.6 g of 9S3-ceria base material, and 1.6 g of bermite alumina were placed in a ball mill, and 307.5 g of water and 17.5 g of a 10% nitric acid aqueous solution were added to form a powder. Was pulverized to obtain a slurry having an average particle size of 3 μm (hereinafter referred to as “slurry I”). (S4).

[0084] A 36-millimeter, 400-cell, 6-mil Hercam carrier (capacity 0.04 L) was coated with 141 g / L of slurry I and dried, and further coated with 59 g / L of slurry R (see Example 1). After drying, baking was performed at 400 ° C. to obtain a sample of Example 9 (S4). This sample is a catalyst that supports 0.587 g / L of Pt, 0.236 g / L of Rh, and contains Co in an atomic ratio of 0.005 to Pt.

[0085] Example 10

Using the same method as in Example 1, a quantitative operation was performed to obtain an alumina substrate carrying 0.445% Pt (hereinafter referred to as “10S2-alumina substrate”) and a ceria substrate carrying 0.3786% Pt ( Less than Hereinafter referred to as “10S2-ceria substrate”. ) Was obtained (S2).

[0086] Cobalt nitrate hexahydrate was dissolved in 200 g of water and 1.196 g of cobalt was added, and 148.32 g of 10S2-alumina substrate (Pt 0.445% alumina substrate) was added at room temperature. After stirring for 1 hour, add 0.061 mol of sodium borohydride, stir for an additional hour, filter, wash, dry this condensate solution, calcinate at 400 ° C, and Co in atomic ratio to Pt. A Pt 0.44% alumina substrate containing 6 (hereinafter referred to as “10S3-alumina substrate”) was obtained (S3).

[0087] Further, 99.04 g of 10S2-ceria base material (Pt 0.3786% ceria base material) was added to a cobalt solution in which cobalt nitrate hexahydrate was dissolved in 200 g of water and 0.679 g of cobalt was contained. After stirring for 1 hour, add 0.035 mol of sodium borohydride and stir for an additional hour. Filter, wash, and dry this conorate solution, calcinate at 400 ° C, and contain Co in an atomic ratio of 6 to Pt. A Pt 0.375% ceria substrate (hereinafter referred to as “10S3-ceria substrate”) was obtained (S3).

[0088] Add 124.8 g of 10S3-alumina base material, 48.6 g of 10S3-ceria base material, and 1.6 g of bermite alumina to the ball mill, and then add 307.5 g of water and 17.5 g of 10% nitric acid aqueous solution to grind the powder. Thus, a slurry having an average particle diameter of 3 m (hereinafter referred to as “slurry J”) was obtained. (S4).

[0089] A 36 mm diameter, 400 cell, 6 mil Hercame carrier (capacity 0.04 L) was coated with 141 g / L of slurry J, dried, and further coated with 59 g / L of slurry R (see Example 1). After drying, baking was performed at 400 ° C. to obtain a sample of Example 10 (S4). This sample is a catalyst that supports 0.587 g / L of Pt, 0.23 6 g / L of Rh, and contains Co in an atomic ratio of 6 with respect to Pt.

[0090] Comparative Example 1

1S2-alumina substrate (see Example 1) 124.8g, 1S2-ceria substrate (see Example 1) 48.6g, and bermite alumina 1.6g are added to the ball mill, followed by 307.5g water and 10% aqueous nitric acid solution 17.5 g was added and the powder was pulverized to obtain a slurry having an average particle size of 3 / zm (hereinafter referred to as “slurry X”).

[0091] A 36-millimeter, 400-cell, 6-mil Hercam carrier (capacity 0.04L) was coated with 141g / L of slurry X and dried, and further coated with 59g / L of slurry R (see Example 1). After drying, the sample of Comparative Example 1 was obtained by baking at 400 ° C. This sample is a normal catalyst in which Pt is supported on a substrate at 0.587 g / L and Rh is 0.23 6 g / L, and it is not coated with a metal oxide. [0092] Each of the catalysts obtained as samples in Examples 1 to 10 and Comparative Example 1 was subjected to the durability test described below, and then the purification performance of each catalyst was examined.

[0093] (Durability test)

Each of the catalysts in Examples 1 to 10 and Comparative Example 1 above was installed in a 3500cc V-type engine exhaust system, 5 each per bank, using Japanese regular gasoline, and the catalyst inlet temperature was 650 Durability test was performed to observe the thermal history when operating at 30 ° C for 30 hours o

[0094] (Evaluation of purification performance)

After the endurance test, each catalyst is incorporated into a simulated exhaust gas distribution device, and simulated exhaust gas as a reaction gas is circulated through this device at a space velocity (SV) of 60000 / h, and the catalyst temperature is set at a rate of 30 ° C / min. Purification temperature T (° C) at which NOx, HC (CH and CO purification rate is 50% when the temperature is raised

3 6

A purification performance test was conducted. The composition of the reaction gas is shown in Table 1, the measurement results of the purification temperature of each catalyst are shown in Table 2, and the HC (CH) purification temperature (HCT50) of each catalyst is shown in FIG. Na

3 6

In Table 2, HC means HC (C H).

3 6

[table 1]

Space velocity SV = 60000 / h

[Table 2] Purification temperature T (° C)

Atomic ratio of Go to Pt

NOx 50% HC 50% CO 50%

Example 1 0.01 288 291 251 Example 2 0.05 286 287 247 Example 3 0.1 283 285 245 Example 4 1 279 280 240 Example 5 2 275 278 238 Example 6 3 280 281 244 Example 7 4 285 287 249 Example Example 8 5 288 291 252 Example 9 0.005 289 291 253 Example 10 6 289 292 254 Comparative Example 1-290 293 255

[0095] In the catalyst of Comparative Example 1, the Pt particles are not coated with Co oxide, that is, the atomic ratio of Co to Pt is 0. As shown in Table 2, NOx, HC ( CH) and CO

3 6

The conversion temperature is also higher than other catalysts.

[0096] In this regard, each catalyst of Examples 1 to 10 containing Co in an atomic ratio with respect to Pt in the range of 0.005 to 6 covers at least a part of the Pt particles is NOx, HC ( CH) and CO

3 6

The displacement purification temperature was also lower than that of Comparative Example 1.

[0097] In particular, the catalysts of Examples 3 to 6 containing Co in an atomic ratio of 0.1 to 3 with respect to Pt have a purification temperature lower than those of Examples 1-2 and 7-10. Excellent performance.

[0098] This is considered to be the result of the Co oxide layer that covers at least a part of the Pt particles and that is deposited on the substrate physically hinders the movement of the Pt particles and suppresses sintering of the Pt particles. .

[0099] The catalyst of Example 9 has a smaller amount of Co relative to Pt than the other examples. Pt particles are not sufficiently covered with Co oxide, and purification performance is improved by sintering. This is thought to have declined.

[0100] Further, in the catalyst of Example 10, the amount of Co relative to Pt is larger than in the other examples. Pt particles are excessively coated with Co oxide, which acts as a barrier to inhibit diffusion of the reaction gas. Therefore, it is considered that the reaction gas could not sufficiently contact the Pt particles, and it was a force that did not bring out the catalyst purification performance well.

[0101] (Amount of reducing agent)

Although sodium borohydride was used as a reducing agent for precipitating Co in step S3, An experiment was conducted to determine a suitable range of the addition amount.

[0102] In this experiment, a 6S2-alumina substrate (Pt 0.4425% supported alumina substrate: see Example 6) was used as a reference substrate, and the target amount of precipitation of Co relative to the amount of Pt supported was defined as 3 in atomic ratio. . Then, in Step S3, a catalyst was prepared by changing the addition amount of the reducing agent.

◦ Quantitative investigation was conducted to determine whether the amount of precipitation reached the specified amount.

[0103] More specifically, the amount of sodium borohydride added was adjusted to 0.5, 1, 2, 3, 4, and 5 times the specified mol number of Co. C supported on the alumina substrate

The amount of 0 was quantified by ICP (plasma emission spectroscopy).

[0104] As a result, when the amount of the reducing agent is in the range of 3 times mol or more of Co, the amount of Co supported reaches 100% as a percentage of the above specified amount, and slightly less than 97% at 2 times mol. In mol, it dropped to about 65%, and it became 23% in 0.5 times mol.

[0105] From the above experiment, when sodium borohydride is used as the reducing agent in step S3, the addition amount should be 3 times mol or more of the target amount of Co precipitation, and therefore 4 mol or 5 times mol. I understand.

[0106] If a large amount of sodium borohydride is added while pressing, the decomposition product of sodium borohydride (eg, boron, sodium) remains on the substrate when the substrate is washed after Co deposition. Absent.

[0107] Therefore, it is desirable to set the amount of sodium borohydride added to 3 times the target amount of Co precipitation.

In this regard, in Step S3 of Examples 1 to 10, 3 times mol of sodium borohydride as a target amount of Co precipitation is added.

[0109] Note that the sample of Comparative Example 1 is a catalyst in which a base material is impregnated with a Pt solution, but the samples of Examples 1 to 10 are selectively coated with Co on a base material impregnated with Pt. This is a catalyst supported by precipitation. That is, in Examples 1 to 10, after adding Pt-supported powder to a solution in which Co is dissolved and stirring, sodium borohydride is added and Co is reduced and precipitated.

[0110] For confirmation, Example 1 to: When a LO sample was observed with a TEM (transmission electron microscope), Co was present at the place where Pt was supported.

[0111] Figure 5 (a) shows a 4S3-alumina substrate (Pt 0.441% alumina containing Co in an atomic ratio of 1 to Pt). Substrate: See Example 4) TEM observation result (HAADF image: x800K times) is shown.

[0112] FIGS. 5 (b) and 5 (c) show the analysis results of the sample of Example 4 using EDX (energy dispersive X-ray fluorescence spectrometer). Co particles 7 (see Fig. 5 (c)) coexist in a region where many white-pointed Pt particles 6 (see Fig. 5 (b)) exist. More specifically, Co is present at the location where Pt exists. This is thought to be a result of the Pt particles supported on the substrate becoming nuclei during the reduction of Co, and the Co being selectively deposited on the surface of the Pt particles. In step S3, since the base material is fired after the Co deposition, Co in the alumina base material is considered to be an oxide.

[0113] Although the conventional reverse micelle method is suitable for precious metal fine particles, it is not suitable for mass production of precious metal particles. In this respect, it will be understood that the embodiment described above can be applied to mass production of precious metal particles.

[0114] This application claims priority based on Japanese Patent Application No. 2004-332196 filed on Nov. 16, 2004, which is incorporated herein by reference in its entirety.

[0115] Although the best mode and embodiments for carrying out the present invention have been described above, this description is illustrative and can be easily changed by those skilled in the art, and the present invention is not limited thereto. It is not limited, and shall be interpreted according to the description of the claims.

Industrial applicability

[0116] According to the present invention, it is possible to obtain an exhaust gas purification catalyst in which sintering of noble metal particles is suppressed and high catalytic activity can be maintained even in a high-temperature oxidizing environment.

Claims

The scope of the claims

[1] a substrate (4) containing alumina and ceria;

Noble metal particles (13, 23) comprising a noble metal selected from platinum, noradium and rhodium and supported on the substrate (4);

An exhaust gas purifying catalyst comprising: a metal oxide (14, 24) covering at least a part of the noble metal particles (13, 23).

[2] The exhaust gas purification according to claim 1, wherein the metal oxide (14, 24) is made of a selected metal oxide of Co, Ni, Fe, Cu, Sn, Mn, Ce and Zr. catalyst.

[3] The metal molar ratio of the metal oxide (14, 24) to the noble metal particles (13, 23) is

The exhaust gas purification catalyst according to claim 1, which is in the range of 0.005 to 6.

[4] The exhaust gas purifying catalyst according to claim 1, comprising a layer of the metal oxide (14, 24) to be deposited on the base material (4).

[5] Prepare a substrate (4) containing alumina and ceria,

Carrying the noble metal particles (13, 23) containing a noble metal selected from platinum, palladium and rhodium on the substrate (4);

A method for producing an exhaust gas purification catalyst, wherein at least a part of the noble metal particles (13, 23) is covered with a metal oxide (14, 24).

[6] The metal oxide (14, 24) is a medium force selected from the group consisting of Co, Ni, Fe, Cu, Sn, Mn, Ce and Zr.

By selectively depositing the selected metal on the noble metal particles (13, 23) and firing the base material (4) supporting the noble metal particles (13, 23), the deposited gold Oxidize genus

6. A method for producing an exhaust gas purifying catalyst according to claim 5.

7. The method for producing an exhaust gas purification catalyst according to claim 5, wherein the base material (4) is a powder power containing alumina and ceria.