Exhaust gas purifying catalyst

Abstract

The present disclosure is a catalyst for purifying exhaust gas. A catalyst for purifying exhaust gas having improved exhaust gas purification performance is provided. The catalyst for purifying exhaust gas of the present disclosure has a porous carrier, catalyst metal particles supported within pores of the porous carrier, and zirconium dioxide particles supported within the pores of the porous carrier, the zirconium dioxide particles being uniformly dispersedly supported within the pores of the porous carrier and being monoclinic or a mixed crystal of monoclinic and tetragonal, wherein uniformly dispersedly supported means that, when the catalyst for purifying exhaust gas is measured using an electron probe microanalyzer, the proportion of the proportion of the presence of zirconium in a surface region up to a depth of 1.5 μm from the surface of the catalyst for purifying exhaust gas to the proportion of the presence of zirconium in a region inside the surface region of the catalyst for purifying exhaust gas is 95 to 105 mol%.

Description

TECHNICAL FIELD

[0001] The present disclosure relates to an exhaust gas purification catalyst. BACKGROUND

[0002] An exhaust gas purification catalyst is disclosed in Patent Literature 1, which is characterized by containing at least one or more noble metals selected from the group consisting of Pt, Pd, and Rh, and a composite compound which is a composite compound of at least one or more metal elements selected from the group consisting of Al, Ce, La, Zr, Co, Mn, Fe, Mg, Ba, and Ti, dispersed substantially uniformly in at least one or more oxides selected from the group consisting of Al203, Zr02, and Ce02, in a state where a part of the surface area of the noble metal is covered with the composite compound, the noble metal being supported on the composite compound.

[0003] PRIOR ART DOCUMENTS

[0004] PATENT LITERATURE

[0005] Patent Literature 1: Japanese Patent Application Laid-Open No. 2006-198594 SUMMARY

[0006] As a problem to be solved by the present application, it is required to improve the exhaust gas purification performance.

[0007] An object of the present disclosure is to provide an exhaust gas purification catalyst in which the exhaust gas purification performance is improved.

[0008] The present inventors have found that the above problem can be solved by the following means.

[0009] [Solution 1]

[0010] An exhaust gas purification catalyst is an exhaust gas purification catalyst having a porous support, catalyst metal particles, and zirconia particles, the catalyst metal particles being supported in the pores of the porous support, the zirconia particles being supported in the pores of the porous support,

[0011] The zirconia particles are supported in the pores of the porous support uniformly dispersed, and are monoclinic crystals or mixed crystals of monoclinic crystals and tetragonal crystals,

[0012] Here, the uniformly dispersed supported means that, when the exhaust gas purification catalyst is measured using an electron beam microanalyzer, the ratio of the presence ratio of zirconium in the surface region up to a depth of 1.5 μm from the surface of the exhaust gas purification catalyst to the presence ratio of zirconium in the region inside the surface region of the exhaust gas purification catalyst is 95 to 105 mol%.

[0013] [Solution 2]

[0014] The exhaust gas purification catalyst according to the scheme 1, wherein the zirconium dioxide particles are monoclinic.

[0015] [Scheme 3]

[0016] The exhaust gas purification catalyst according to the scheme 1 or 2, wherein the ratio of the mass of the zirconium dioxide particles to the mass of the porous support is 0.1 to 5.0 mass%.

[0017] [Scheme 4]

[0018] The exhaust gas purification catalyst according to any one of the schemes 1 to 3, wherein the crystallite diameter of the zirconium dioxide particles is 6.0 to 8.0 nm.

[0019] [Scheme 5]

[0020] The exhaust gas purification catalyst according to any one of the schemes 1 to 4, wherein the secondary particle diameter (D50) of the zirconium dioxide particles is 40 nm or less.

[0021] [Scheme 6]

[0022] The exhaust gas purification catalyst according to any one of the schemes 1 to 5, wherein the catalyst metal particles are Rh particles.

[0023] [Scheme 7]

[0024] The exhaust gas purification catalyst according to any one of the schemes 1 to 6, wherein the ratio of the mass of the catalyst metal particles to the mass of the porous support is 0.5 to 2.0 mass%.

[0025] [Scheme 8]

[0026] The exhaust gas purification catalyst according to any one of the schemes 1 to 7, wherein the primary particle diameter (D50) of the catalyst metal particles is 1.0 to 9.0 nm.

[0027] [Scheme 9]

[0028] The exhaust gas purification catalyst according to any one of the schemes 1 to 8, wherein the porous support is a composite oxide containing Al and Zr.

[0029] [Scheme 10]

[0030] The exhaust gas purification catalyst according to any one of the schemes 1 to 9, wherein the initial specific surface area of the porous support is 45 to 115 m 2 / g.

[0031] According to the present disclosure, it is possible to provide an exhaust gas purification catalyst whose exhaust gas purification performance is improved. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 is a schematic view of a catalyst particle for exhaust gas purification based on an embodiment of the present disclosure.

[0033] Figure 2 is a scanning electron microscope (SEM) image of a catalyst particle for exhaust gas purification of Comparative Example 2 (a), and an image (b) in which a surface region and a region inside the specific surface region of the image are cut out.

[0034] Figure 3 is a Zr mapping image obtained using an electron beam microanalyzer (EMPA) of catalyst particles for exhaust gas purification of Example 1 (a) and Comparative Example 2 (b).

[0035] Figure 4 is a graph showing the temperature at which 50% NOx purification is achieved by the catalyst particles for exhaust gas purification of Examples 1 to 6 and Comparative Examples 1 to 6.

[0036] BRIEF DESCRIPTION OF DRAWINGS

[0037] 1 catalyst for exhaust gas purification

[0038] 11 surface region

[0039] 12 region inside the specific surface region DETAILED DESCRIPTION

[0040] Hereinafter, embodiments of the present disclosure will be described in detail. Furthermore, the present disclosure is not limited to the following embodiments, and can be implemented in various modifications within the scope of the gist of the present disclosure.

[0041] [Catalyst for exhaust gas purification]

[0042] The catalyst for exhaust gas purification of the present disclosure has a porous support, catalyst metal particles supported in the pores of the porous support, and zirconium dioxide (Zr02) particles supported in the pores of the porous support. The zirconium dioxide particles are supported in the pores of the porous support in a uniform dispersion. The zirconium dioxide particles are monoclinic crystals or mixed crystals of monoclinic crystals and tetragonal crystals.

[0043] Here, the so-called uniform dispersion supported means that, when the catalyst for exhaust gas purification is measured using an electron beam microanalyzer, as shown in Figure 1 the ratio of the presence of zirconium in the surface region 11 of the catalyst for exhaust gas purification 1 up to a depth of d = 1.5 μm from the surface is 95 to 105 mol% with respect to the ratio of the presence of zirconium in the region 12 inside the surface region 11 of the catalyst for exhaust gas purification 1.

[0044] While not limited by theory, it is believed that the principle of the improvement of the exhaust gas purification performance in the exhaust gas purification catalyst of the present disclosure is as follows.

[0045] Generally, the catalyst metal particles possessed by the exhaust gas purification catalyst have a tendency to be solid-solved and particulated in the carrier and diffuse into the gas phase during the repetition of the oxidation atmosphere and the reduction atmosphere at high temperatures in the exhaust gas purification process, and thus transferred to the honeycomb substrate of the exhaust gas purification catalyst provided with other carriers, and deactivated.

[0046] The exhaust gas purification catalyst of the present disclosure can suppress the diffusion of the catalyst metal particles into the gas phase due to solid-solution and particulation into the carrier, and improve the catalyst activity, by bringing the following zirconia particles, which are monoclinic or a mixed crystal of monoclinic and tetragonal, close to the catalyst metal particles.

[0047] Specifically, the zirconia particles, which are monoclinic or a mixed crystal of monoclinic and tetragonal, have a large surface energy compared to the carriers generally used in the exhaust gas purification catalyst, such as Al2O3, CeO2, and composite oxide particles containing Al, Ce, and Zr. In addition, the zirconia particles do not have a crystal lattice that matches the oxides of the catalyst metals such as rhodium oxide. Therefore, it is believed that the solid-solution and particulation of the catalyst metal particles during the purification of the exhaust gas using the exhaust gas purification catalyst can be suppressed.

[0048] In addition, the zirconia particles, which are monoclinic or a mixed crystal of monoclinic and tetragonal, can reduce the catalyst metal, particularly Rh, at a lower temperature compared to zirconia of cubic and tetragonal.

[0049] On the other hand, the zirconia particles, which are monoclinic or a mixed crystal of monoclinic and tetragonal, can agglomerate and grow particles under a high-temperature atmosphere because of the low heat resistance. In this regard, since the zirconia particles of the exhaust gas purification catalyst of the present disclosure are uniformly supported within the pores of the carrier, agglomeration of the zirconia particles is difficult to occur.

[0050] According to the above, the exhaust gas purification performance of the exhaust gas purification catalyst of the present disclosure is improved.

[0051] 〈Porous Carrier〉

[0052] The porous carrier possessed by the exhaust gas purification catalyst of the present disclosure is not particularly limited as long as it is a porous carrier that can be used for an exhaust gas purification catalyst, and for example, can be a metal oxide, specifically, an Al-containing metal oxide, more specifically, Al2O3, or a composite oxide containing Al and Zr, and further specifically, an Al2O3-ZrO2 composite oxide.

[0053] The porous support may, for example, be particulate. In the case where the porous support is particulate, the average primary particle diameter (D50) thereof may, for example, be 1 to 1000 μm.

[0054] The average primary particle diameter (D50) of the porous support may be 1 μm or more, 10 μm or more, 50 μm or more, or 100 μm or more, and may be 1000 μm or less, 500 μm or less, 200 μm or less, or 100 μm or less.

[0055] Further, the average primary particle diameter is obtained by observing primary particles of the porous support using a scanning electron microscope (SEM) for at least 200 or more, finding the equivalent circle diameter (equivalent circular diameter) when a right circle equal in area thereto is taken as an equal-area circle, and then calculating the number average from the equivalent circle diameters thereof.

[0056] The initial specific surface area of the porous support is preferably 45 to 115 m 2 / g.

[0057] The initial specific surface area of the porous support may be 45 m 2 / g or more, 50 m 2 / g or more, 60 m 2 / g or more, or 70 m 2 / g or more, and may be 115 m 2 / g or less, 110 m 2 / g or less, 100 m 2 / g or less, or 90 m 2 / g or less.

[0058] Here, the initial specific surface area of the porous support is the specific surface area of the porous support of the exhaust gas purifying catalyst of the present disclosure before use as a product. Further, the specific surface area can be found using, for example, a gas adsorption method.

[0059] The pore diameter of the pores possessed by the porous support is not particularly limited as long as it is a size that enables the catalyst metal particles and the zirconia particles to be supported within the pores. The pore diameter may, for example, be 10 nm or more, 50 nm or more, or 100 nm or more, and may be 1000 nm or less, 500 nm or less, or 200 nm or less.

[0060] 〈Catalyst Metal Particle〉

[0061] The catalyst metal particle is a metal particle having catalytic activity that enables exhaust gas, for example, CO, HC, and NOx, and the like, to be purified. As such a metal particle, a noble metal can be cited, and more specifically, Rh, Pt, and Pd, and the like, can be cited. The catalyst metal particle may, in particular, be Rh.

[0062] The ratio of the mass of the catalyst metal particles to the mass of the porous support can be 0.5 to 2.0 mass%. The ratio can be 0.5 mass% or more, 0.6 mass% or more, 0.7 mass% or more, or 0.8 mass% or more, and can be 2.0 mass% or less, 1.5 mass% or less, 1.3 mass% or less, or 1.0 mass% or less.

[0063] In addition, the primary particle diameter (D50) of the catalyst metal particles can be 1.0 to 9.0 nm. The primary particle diameter (D50) can be 1.0 nm or more, 2.0 nm or more, 3.0 nm or more, or 4.0 nm or more, and can be 9.0 nm or less, 8.0 nm or less, 7.0 nm or less, or 6.0 nm or less.

[0064] Further, the catalyst metal particles can also be in contact with the zirconia particles within the pores of the porous support.

[0065] 〈Zirconia particles〉

[0066] The zirconia particles of the exhaust gas purifying catalyst of the present disclosure are monoclinic or a mixed crystal of monoclinic and tetragonal, but are particularly preferably monoclinic.

[0067] The ratio of the mass of the zirconia particles to the mass of the porous support is preferably 0.1 to 5.0 mass%. When the ratio of the mass of the zirconia particles to the mass of the porous support is 0.1 mass% or more, the number of zirconia particles that can act on the catalyst metal particles can be significantly increased. On the other hand, when the ratio of the mass of the zirconia particles to the mass of the porous support is 5.0 mass% or less, the dispersibility of the zirconia particles within the pores of the porous support is particularly good.

[0068] The ratio of the mass of the zirconia particles to the mass of the porous support can be 0.1 mass% or more, 0.5 mass% or more, 1.0 mass% or more, or 1.5 mass% or more, and can be 5.0 mass% or less, 4.0 mass% or less, 3.0 mass% or less, or 2.0 mass% or less.

[0069] The crystallite diameter of the zirconia particles is preferably 6.0 to 8.0 nm.

[0070] When the crystallite diameter of the zirconia particles is 6.0 nm or more, the effect of suppressing sintering of the catalyst metal particles and the like is particularly good. On the other hand, when the crystallite diameter of the zirconia particles is 8.0 nm or less, the heat resistance of the zirconia particles is particularly good, and in particular, the aggregation of the zirconia particles due to heating is suppressed.

[0071] The crystallite diameter of the zirconia particles can be 6.0 nm or more, 6.2 nm or more, 6.4 nm or more, or 6.8 nm or more, and can be 8.0 nm or less, 7.8 nm or less, 7.6 nm or less, or 7.4 nm or less.

[0072] The secondary particle diameter (D50) of the zirconia particles is preferably 40 nm or less. If the secondary particle diameter (D50) of the zirconia particles is such a size, the dispersibility of the zirconia particles within the pores of the porous support can be further improved.

[0073] The secondary particle diameter (D50) of the zirconia particles can be 40 nm or less, 35 nm or less, 30 nm or less, or 25 nm or less, and can be more than 0 nm, 5 nm or more, 10 nm or more, or 15 nm or more.

[0074] [Method for manufacturing exhaust gas purification catalyst]

[0075] The manufacturing method of the present disclosure is a method for manufacturing the exhaust gas purification catalyst of the present disclosure.

[0076] The manufacturing method of the present disclosure successively has the steps of: supporting the zirconia particles within the pores of the porous support by dispersing the porous support and the zirconia particles in an acidic dispersion medium, and then performing drying and calcination; and supporting the catalyst metal particles on the porous support. Here, the zirconia particles are monoclinic crystals or mixed crystals of monoclinic crystals and tetragonal crystals.

[0077] In the manufacturing method of the present disclosure, by setting the dispersion medium under an acidic condition, the aggregation of the zirconia particles in the dispersion liquid is suppressed, whereby the particle diameter of the secondary particles can be adjusted so as not to become too large, and the zirconia particles are supported within the pores of the porous support. Thus, the dispersibility of the zirconia particles within the pores of the porous support can be further improved.

[0078] The pH of the dispersion medium can be, for example, 1.0 or more, 1.5 or more, or 2.0 or more, and can be 5.0 or less, 4.5 or less, or 4.0 or less. The pH is particularly preferably 2.5 to 3.5.

[0079] The method for supporting the catalyst metal particles within the pores of the porous support is not particularly limited, but by adding the catalyst metal to the dispersion medium in which the porous support having the zirconia supported within the pores is dispersed, and stirring, and then performing drying and calcination, the catalyst metal can be supported within the pores of the porous support.

[0080] As for the porous support, the catalyst metal particles, and the zirconia particles, the same as described in the above "Exhaust gas purification catalyst" applies.

[0081] Example

[0082] [Examples 1 to 6 and Comparative Examples 1 to 6]

[0083] Preparation of Catalyst for Purification of Exhaust Gas

[0084] (Comparative Example 1)

[0085] A dispersion liquid in which Al2O3-ZrO2 powder as a porous support was dispersed in water and a dispersion liquid in which Rh particles (average primary particle diameter (D50) = 2 nm) were dispersed were mixed, and stirred for 1 hour.

[0086] Then, the mixed liquid was heated on a hot stirrer to evaporate water, and a precipitate was obtained. Next, the precipitate was dried at 120°C for one day, and further calcination was performed at 500°C in air, to obtain the catalyst for purification of exhaust gas of Comparative Example 1.

[0087] (Example 1)

[0088] To a dispersion liquid in which Al2O3-ZrO2 powder as a porous support was dispersed in water, nitric acid was added so that the pH value became 3. The dispersion liquid was mixed with a dispersion liquid of ZrO2 particles (mixed crystal of monoclinic crystal and tetragonal crystal, secondary particle diameter (D50) of ZrO2 particles in liquid = 15 nm) having a pH value of 3, and stirred for 1 hour. Further, the amount of ZrO2 particles in the mixed liquid was 4.0 mass% with respect to the Al2O3-ZrO2 powder.

[0089] Then, the mixed liquid was heated on a hot stirrer to evaporate water, and a precipitate was obtained. Next, the precipitate was dried at 120°C for one day, and further calcination was performed at 500°C in air, to obtain the Al2O3-ZrO2 powder having ZrO2 particles supported in the fine pores.

[0090] Next, using the Al2O3-ZrO2 powder having ZrO2 particles supported in the fine pores, Rh particles were supported in the fine pores of the Al2O3-ZrO2 powder in the same manner as in Comparative Example 1, to thereby obtain the catalyst for purification of exhaust gas of Example 1.

[0091] (Examples 2 to 4)

[0092] In the process of obtaining the Al2O3-ZrO2 powder having ZrO2 particles supported in the fine pores, the amount of ZrO2 particles in the mixed liquid was set to 0.5 mass%, 1.0 mass%, and 2.0 mass%, respectively, with respect to the Al2O3-ZrO2 powder, and the same was performed as in Example 1 except for this, to thereby obtain the catalysts for purification of exhaust gas of Examples 2 to 4.

[0093] (Example 5)

[0094] Except for using monoclinic ZrO2 particles (secondary particle diameter (D50) of ZrO2 particles in liquid = 38 nm), the same procedure as in Example 1 was performed to obtain the exhaust gas purifying catalyst of Example 5.

[0095] (Example 6)

[0096] Except for using Al2O3 powder as the porous support, the same procedure as in Example 5 was performed to obtain the exhaust gas purifying catalyst of Example 6.

[0097] (Comparative Example 2)

[0098] In the process of obtaining the Al2O3-ZrO2 powder having ZrO2 particles supported in the fine pores, ammonia was added to the ZrO2 particle dispersion liquid and the dispersion liquid in which the Al2O3-ZrO2 powder was dispersed in water, respectively, and after both were made to have a pH of 7, they were mixed and stirred for 1 hour, and the same procedure as in Example 1 was performed except for this to obtain the exhaust gas purifying catalyst of Comparative Example 2. Further, by making the pH of the ZrO2 particle dispersion liquid 7, the ZrO2 particles in the dispersion liquid coagulated to have a secondary particle diameter (D50) of 60 nm.

[0099] (Comparative Example 3)

[0100] To the dispersion liquid in which zirconium was dispersed in water, an amount of citric acid equivalent to the zirconium was added, and the zirconium was dissolved by sufficiently stirring. Next, zirconyl nitrate dihydrate was added to obtain an aqueous zirconium nitrate solution. Then, the prepared aqueous zirconium nitrate solution was added dropwise to tetraethylammonium hydroxide (10% aqueous solution) to obtain a solution of zirconium hydroxide (secondary particle diameter (D50) of ZrO2 = 10 nm).

[0101] Except for using the solution of zirconium hydroxide instead of the ZrO2 particle dispersion liquid, the same procedure as in Example 1 was performed to obtain the exhaust gas purifying catalyst of Comparative Example 3. In the exhaust gas purifying catalyst of Comparative Example 3, the zirconium dioxide supported in the fine pores of the porous support was amorphous.

[0102] (Comparative Example 4)

[0103] In the process of obtaining the Al2O3-ZrO2 powder having ZrO2 particles supported in the fine pores, a ZrO2 dispersion liquid in which cubic ZrO2 particles were dispersed (secondary particle diameter (D50) of ZrO2 particles in liquid = 6 nm) was used, and the same procedure as in Example 1 was performed except for this to obtain the exhaust gas purifying catalyst of Comparative Example 4.

[0104] (Comparative Example 5)

[0105] In the process of obtaining the Al2O3-ZrO2 powder having the ZrO2 particles supported in the fine pores, the amount of the ZrO2 particles in the mixed solution was made 8.0 mass% relative to the Al2O3-ZrO2 powder, and otherwise the same as in Example 1 to obtain the exhaust gas purification catalyst of Comparative Example 5.

[0106] (Comparative Example 6)

[0107] Except that the porous support was made of Al2O3, the same as in Comparative Example 1 was performed to obtain the exhaust gas purification catalyst of Comparative Example 6.

[0108] 〈Electron Probe Micro Analyzer Analysis〉

[0109] For the exhaust gas purification catalysts of Comparative Examples 2 to 5 and Examples 1 to 6, the distribution of the zirconia particles in the fine pores of the porous support was measured by an electron probe micro analyzer (EPMA) (Shimadzu Corporation, EPMA-8050G, beam current conditions: 15 kV, 50 nA). At the time of measurement, first, as shown in FIG. 1, a surface region up to a depth of 1.5 μm from the surface of the porous support and a region inside the surface region were cut out of the obtained image. Then, the EPMA detection amount (counts) per unit area of Zr and Al contained in the porous support was calculated for each region, and the Zr / Al ratio was calculated. Specifically, the following formula was used for the calculation. Figure 2

[0110] Uniformity (%) = (Zr / Al in the surface region) / (Zr / Al in the region inside the surface region) x 100

[0111] Further, in the case where the uniformity (%) is 95 to 105 mol%, it was regarded as uniform, and the case other than this was regarded as non-uniform.

[0112] Further, FIGS. 2 to 5 are Zr mapping results of the exhaust gas purification catalysts of Example 1 (a) and Comparative Examples 2 to 5 (b). Figure 3 Figure 3 Figure 3

[0113] The exhaust gas purification catalyst of Example 1 had a uniformity of 97 mol%, and the amount of the zirconia particles in the surface region and the region inside was almost constant and was uniformly supported. Similarly, as for Comparative Examples 3 and 4 and Examples 2 to 6, the zirconia particles were also uniformly supported in the fine pores of the porous support.

[0114] ​​​​On the other hand, the exhaust gas purifying catalyst of Comparative Example 2 had a uniformity of 108 mol%, and it was confirmed that the zirconium dioxide particles were carried in the surface region, i.e., were not uniformly carried. Also, in Comparative Example 5, the zirconium dioxide particles were not uniformly carried in the pores of the porous support.

[0115] It is thought that in Comparative Example 2, because the zirconium dioxide particles were carried in the porous support in a state of being aggregated in the liquid, the zirconium dioxide particles were not introduced to the deep portions of the pores of the porous support, and thus the amount of the particles carried in the surface region was more than in the internal region.

[0116] Also, it is thought that in Comparative Example 5, because the amount of the zirconium dioxide particles in the mixed liquid was 8 mass% in the process of obtaining the Al2O3-ZrO2 powder having the zirconium dioxide particles carried in the pores, the amount of the zirconium dioxide particles filled in the pores of the porous support was excessive, and thus the amount of the particles carried in the surface region was more than in the internal region.

[0117] < Evaluation of Exhaust Gas Purifying Performance >

[0118] The exhaust gas purifying performance (three-way purification catalyst performance) of the catalysts of each of the examples and each of the comparative examples was evaluated.

[0119] To simulate the actual coated catalyst, the powder of each of the examples and each of the comparative examples was mixed with the powders of Al2O3, Al2O3-CeO2-ZrO2, and CeO2-ZrO2, and pressure-molded using a cold isostatic press (CIP) at a pressure of 1 ton, and then, while being pulverized, sieved to obtain a pellet catalyst.

[0120] Next, 2 g of the pellet catalyst was placed in a flow-type reaction furnace, and heated to 500°C at a temperature increase rate of 50°C / minute in an evaluation model gas, and after being maintained at this temperature for 10 minutes, cooled to 100°C. Next, heating was performed at a temperature increase rate of 20°C / minute, and the three-way purification catalyst performance at the time of temperature increase was measured, and the temperature at which 50% of the NOx in the gas was purified was calculated.

[0121] Further, the composition of the evaluation model gas was NO 1600 ppm, O2 6100 ppm, CO2 10000 ppm, CO 5000 ppm, H2O 30000 ppm, and the balance N2. Also, the gas flow rate was 20 L / minute.

[0122] < Results >

[0123] In Figure 4 The manufacturing conditions of the exhaust gas purifying catalysts of each of the examples and the evaluation results of the exhaust gas purifying performance are shown in Table 1.

[0124] Table 1

[0125]

[0126] As Figure 4 As shown in Table 1, it is considered that by increasing the content of zirconia from 0.5 mass% to 8 mass% (Examples 1 to 4 and Comparative Example 5), the amount of Rh approaching zirconia particles increases, the sintering of Rh is inhibited, and this brings about a decrease in the temperature (°C) at which 50% of NOx is purified. However, it is considered that when the content of zirconia is 8.0 mass% as in Comparative Example 5, the thermal resistance of zirconia particles decreases due to deterioration of the uniformity of zirconia particles in the pores of the porous support, and the effect of inhibiting Rh degradation cannot be sufficiently obtained.

[0127] In addition, as shown in Example 5, when the crystal structure of zirconia particles is monoclinic, the temperature (°C) at which 50% of NOx is purified can be more decreased than when it is a mixed crystal.

[0128] In addition, as shown in Example 5 and Example 6, when the porous support uses Al2O3-ZrO2 composite oxide, the temperature (°C) at which 50% of NOx is purified can be more decreased than when the porous support is Al2O3 (Example 6).

Claims

1. An exhaust gas purification catalyst which is an exhaust gas purification catalyst having a porous carrier, catalyst metal particles, and zirconia particles, the catalyst metal particles being supported within pores of the porous carrier, the zirconia particles being supported within the pores of the porous carrier, the catalyst metal particles being Rh particles, the zirconia particles being supported within the pores of the porous carrier in a uniformly dispersed manner, and being monoclinic or a mixed crystal of monoclinic and tetragonal, the zirconia particles being supported within the pores of the porous carrier in a uniformly dispersed manner being such that, when the exhaust gas purification catalyst is measured using an electron probe microanalyzer, the proportion of the proportion of the presence of zirconium in a surface region up to a depth of 1.5 μm from the surface of the exhaust gas purification catalyst to the proportion of the presence of zirconium in a region inside the surface region of the exhaust gas purification catalyst is 95 to 105 mol%.

2. The exhaust gas purification catalyst according to claim 1, the zirconia particles being monoclinic.

3. The exhaust gas purification catalyst according to claim 1 or 2, the proportion of the mass of the zirconia particles to the mass of the porous carrier being 0.1 to 5.0 mass%. wherein 4. The exhaust gas purification catalyst according to claim 1 or 2, the crystallite diameter of the zirconia particles being 6.0 to 8.0 nm.

5. The exhaust gas purification catalyst according to claim 1 or 2, the secondary particle diameter D50 of the zirconia particles being 40 nm or less.

6. The exhaust gas purification catalyst according to claim 1 or 2, the proportion of the mass of the catalyst metal particles to the mass of the porous carrier being 0.5 to 2.0 mass%.

7. The exhaust gas purification catalyst according to claim 1 or 2, the primary particle diameter D50 of the catalyst metal particles being 1.0 to 9.0 nm.

8. The exhaust gas purification catalyst according to claim 1 or 2, the porous carrier being a composite oxide containing Al and Zr.

9. The exhaust gas purification catalyst according to claim 1 or 2, the porous carrier being a composite oxide containing Al and Zr. ​ ​ ​ ​ ​ ​ ​ ​ ​ ​ The initial specific surface area of the porous carrier is 45 to 115 m 2 / g.

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