Exhaust gas purification catalyst and method for manufacturing the same

Abstract

To provide an exhaust gas purification catalyst in which Rh is supported on alumina, and which exhibits high Rh dispersion and a large BET specific surface area even when exposed to high temperatures. [Solution] A carrier comprising heat-resistant alumina containing 0.5 to 4 mass% La2O3 with 0.5 to 9 mass% MgO supported on it, and a material containing 0.05 to 5 mass% Rh supported on the carrier, An exhaust gas purification catalyst characterized in that, after a heat resistance test at 1050°C for 5 hours, the three strong lines (2θ = 35.16°, 43.37°, and 57.52°) attributed to α-Al2O3 are not detected in the X-ray diffraction pattern measured using CuKα rays as the X-ray source.

Description

[Technical Field]

[0001] The present invention relates to an exhaust gas purification catalyst and a method for producing the same, and more particularly to an exhaust gas purification catalyst in which Rh is supported on alumina and a method for producing the same. [Background technology]

[0002] Various exhaust gas purification catalysts have been conventionally used to effectively remove harmful components such as hydrocarbons (HC) and nitrogen oxides (NOx) contained in exhaust gases from internal combustion engines such as automobile engines. Among such exhaust gas purification catalysts, catalysts in which noble metals such as Rh are supported on a metal oxide support such as alumina are well known.

[0003] For example, Japanese Patent Publication No. 2002-153734 (Patent Document 1) discloses a catalyst in which Mg and Rh are supported on an alumina support as a catalyst for decomposing nitrous oxide. Furthermore, as a catalyst in which Mg and Rh are supported on alumina, Japanese Patent Publication No. 2009-34663 (Patent Document 2) discloses a catalyst in which Mg is supported on activated alumina, and then Rh is further supported on activated alumina. [Prior art documents] [Patent Documents]

[0004] [Patent Document 1] Japanese Patent Publication No. 2002-153734 [Patent Document 2] Japanese Patent Publication No. 2009-34663 [Overview of the project] [Problems that the invention aims to solve]

[0005] However, the catalysts described in Patent Documents 1 and 2 do not contain La and have poor heat resistance. Furthermore, the inventors have found that even when La2O3 is post-supported on the catalysts described in Patent Documents 1 and 2, the heat resistance does not improve sufficiently, and there are problems such as low Rh dispersion after exposure to high temperatures and a small BET specific surface area.

[0006] The present invention has been made in view of the problems of the prior art described above, and aims to provide an exhaust gas purification catalyst in which Rh is supported on alumina, which exhibits high Rh dispersion and a large BET specific surface area even when exposed to high temperatures, and a method for producing the same. [Means for solving the problem]

[0007] The present inventors, through diligent research to achieve the above objective, have discovered that by supporting an Mg salt on La-containing heat-resistant alumina containing a predetermined amount of La2O3, and then heat-treating it at a specific temperature to prepare a support on which a predetermined amount of MgO is supported, and then supporting a predetermined amount of Rh on this support, an exhaust gas purification catalyst can be obtained that exhibits high Rh dispersion and a large BET specific surface area even when exposed to high temperatures, thus completing the present invention.

[0008] In other words, the present invention provides the following embodiments. [1] A carrier comprising La-containing heat-resistant alumina containing 0.5 to 4 mass% La2O3 on which 0.5 to 9 mass% MgO is supported, and a carrier comprising 0.05 to 5 mass% Rh supported on the carrier, An exhaust gas purification catalyst in which, after a heat resistance test at 1050°C for 5 hours, the X-ray diffraction pattern measured using CuKα radiation as the X-ray source does not detect any of the three strong lines (2θ = 35.16°, 43.37°, and 57.52°) attributed to α-Al2O3. [2] The exhaust gas purification catalyst according to [1], wherein, after a heat resistance test at 1050°C for 5 hours, the three strong lines (2θ = 36.85°, 65.24°, and 44.81°) attributed to MgAl2O4 are not detected in the X-ray diffraction pattern measured using CuKα rays as the X-ray source. [3] The exhaust gas purification catalyst according to [1] or [2], wherein 0.5 to 2% by mass of La2O3 is further supported on the La-containing heat-resistant alumina. [4] A step of preparing a support in which 0.5 to 9 mass% of MgO is supported on La-containing heat-resistant alumina containing 0.5 to 4 mass% of La2O3, followed by heat treatment at a temperature of 900 to 1050°C, A step of supporting 0.05 to 5% by mass of Rh on the carrier, A method for producing an exhaust gas purification catalyst, including the present invention. [5] The method for producing an exhaust gas purification catalyst according to [4], wherein in the step of preparing the carrier, Mg salt and La salt are supported on the La-containing heat-resistant alumina, and then heat-treated at a temperature of 900 to 1050°C to prepare a carrier on which 0.5 to 9% by mass of MgO is supported and 0.5 to 2% by mass of La2O3 is further supported.

[0009] In this invention, "La-containing heat-resistant alumina" refers to alumina in which the phase change to the α phase (alpha-adsorption) can be suppressed by the uniform distribution of La2O3 in the alumina (Al2O3).

[0010] Furthermore, in this invention, "three strong lines in the X-ray diffraction pattern" refers to the three diffraction lines (diffraction peaks) with the strongest intensity among the peaks used to identify a substance (compound) based on the X-ray diffraction peak position and its intensity.

[0011] Furthermore, although the reason why the exhaust gas purification catalyst of the present invention exhibits high Rh dispersion and a large BET specific surface area even when exposed to high temperatures is not entirely clear, the inventors surmise the following: Rh (Rh), the active species of the exhaust gas purification catalyst, dissolves as an oxide in alumina (Al2O3) in a high-temperature oxidizing atmosphere, making activation, or metallization, difficult, which can lead to a decrease in exhaust gas purification performance. Since the dissolution of Rh into alumina occurs when Rh substitutes for defect sites in alumina, it is necessary to reduce the number of defect sites in alumina in order to suppress the dissolution of Rh into alumina. α-alumina is an alumina with few defect sites, and although the dissolution of Rh into alumina is suppressed, its specific surface area is extremely small. Therefore, at high temperatures, the grain growth of Rh particles progresses, reducing the active surface area and decreasing exhaust gas purification performance.

[0012] In this invention, by using heat-resistant alumina containing La to suppress the alpha-gelatinization of alumina at high temperatures, the reduction in specific surface area is suppressed, thereby inhibiting Rh grain growth, and Mg is introduced into the defect sites of the alumina. 2+ By substituting this compound, the solid solution of Rh into alumina is suppressed, enabling high dispersion and retention of Rh. As a result, it is presumed that the exhaust gas purification catalyst of the present invention maintains high levels of Rh dispersion and BET specific surface area even when exposed to high temperatures. [Effects of the Invention]

[0013] According to the present invention, it is possible to obtain an exhaust gas purification catalyst that has a high degree of Rh dispersion and a large BET specific surface area, even when exposed to high temperatures. [Brief explanation of the drawing]

[0014] [Figure 1] This graph shows the relationship between the amount of MgO supported and the degree of Rh dispersion of the catalysts obtained in Examples 1-4 and Comparative Examples 1-2. [Figure 2] This graph shows the relationship between the amount of MgO supported and the degree of Rh dispersion of the catalysts obtained in Examples 1-5 and Comparative Examples 1-6. [Figure 3] It is a graph showing the X-ray diffraction patterns of the catalysts obtained in Examples 3 to 4 and Comparative Examples 2 to 6.

Mode for Carrying Out the Invention

[0015] Hereinafter, the present invention will be described in detail according to its preferred embodiments.

[0016] 〔Catalyst for Exhaust Gas Purification〕 First, the catalyst for exhaust gas purification of the present invention will be described. The catalyst for exhaust gas purification of the present invention contains a carrier in which 0.5 to 9% by mass of MgO is supported on La-containing heat-resistant alumina containing 0.5 to 4% by mass of La2O3, and 0.05 to 5% by mass of Rh supported on the carrier.

[0017] In the La-containing heat-resistant alumina used in the present invention, the content of La2O3 is 0.5 to 4% by mass with respect to the entire La-containing heat-resistant alumina. When the content of La2O3 is less than the above lower limit, the heat resistance of alumina is insufficient, and when the catalyst for exhaust gas purification is exposed to high temperature, the BET specific surface area decreases and the Rh dispersion degree decreases. On the other hand, when the content of La2O3 exceeds the above upper limit, the metallization of the supported Rh active species tends to be insufficient. Also, from the viewpoint that the heat resistance of alumina is sufficiently exhibited and the decrease in BET specific surface area and the decrease in Rh dispersion degree are suppressed when the catalyst for exhaust gas purification is exposed to high temperature, the content of La2O3 is preferably 0.7 to 3% by mass, more preferably 0.9 to 2% by mass.

[0018] The catalyst for exhaust gas purification of the present invention contains a carrier (Mg-supported La-containing heat-resistant alumina carrier) in which MgO is supported on such La-containing heat-resistant alumina. The supported amount of MgO is 0.5 to 9% by mass with respect to the entire carrier. When the supported amount of MgO is within the above range, a catalyst for exhaust gas purification with high Rh dispersion degree can be obtained. Also, from the viewpoint that the Rh dispersion degree becomes even higher, the supported amount of MgO is preferably 0.5 to 7% by mass, more preferably 0.8 to 6% by mass, still more preferably from 1.5 to 5.5% by mass, and particularly preferably 2 to 5% by mass.

[0019] Furthermore, the exhaust gas purification catalyst of the present invention contains Rh supported on such a carrier. The amount of Rh supported is 0.05 to 5% by mass relative to the entire exhaust gas purification catalyst. If the amount of Rh supported falls below the lower limit, the exhaust gas purification performance of the exhaust gas purification catalyst decreases. On the other hand, if the amount of Rh supported exceeds the upper limit, the activity tends to saturate, and the Rh particle growth tends to progress. Also, from the viewpoint of improving the exhaust gas purification performance of the exhaust gas purification catalyst, the amount of Rh supported is preferably 0.10 to 2% by mass, more preferably 0.11 to 1% by mass, and even more preferably 0.12 to 0.5% by mass.

[0020] In the exhaust gas purification catalyst of the present invention, it is necessary that, after a heat resistance test at 1050°C for 5 hours, the three strong lines (2θ = 35.16°, 43.37°, and 57.52°) attributed to α-Al2O3 are not detected in the X-ray diffraction pattern measured using CuKα rays as the X-ray source. This means that even when the exhaust gas purification catalyst of the present invention is exposed to high temperatures, the α-gelatinization of the alumina constituting the support is suppressed, thereby suppressing the decrease in specific surface area, and as a result, the grain growth of Rh is suppressed, and a high degree of Rh dispersion is maintained.

[0021] Furthermore, in the exhaust gas purification catalyst of the present invention, it is preferable that, after a heat resistance test at 1050°C for 5 hours, the three strong lines (2θ = 36.85°, 65.24°, and 44.81°) attributed to MgAl2O4 are not detected in the X-ray diffraction pattern measured using CuKα rays as the X-ray source. This means that the Al and Mg constituting the support do not form a 1:1 spinel structure (MgAl2O4), and as a result, an exhaust gas purification catalyst having a high degree of Rh dispersion and a large BET specific surface area can be obtained.

[0022] Furthermore, in the exhaust gas purification catalyst of the present invention, from the viewpoint of further increasing the degree of Rh dispersion, it is preferable that 0.5 to 2% by mass (more preferably 0.8 to 1.5% by mass) of La2O3 is further supported on the La-containing heat-resistant alumina. The amount of La2O3 supported is the amount supported on the entire support (Mg / La-supported La-containing heat-resistant alumina support) on which MgO and La2O3 are supported on the La-containing heat-resistant alumina.

[0023] In the exhaust gas purification catalyst of the present invention, the Rh dispersion after a heat resistance test at 1050°C for 5 hours is preferably 43% or higher, more preferably 44% or higher, and particularly preferably 45% or higher. An exhaust gas purification catalyst having such an Rh dispersion maintains high exhaust gas purification performance even when exposed to high temperatures. The upper limit of the Rh dispersion after a heat resistance test at 1050°C for 5 hours is 100% or less, and an Rh dispersion of 100% means that Rh is dispersed atomically.

[0024] Furthermore, in the exhaust gas purification catalyst of the present invention, the BET specific surface area after a heat resistance test at 1050°C for 5 hours is 75 m². 2 Preferably 80-150 m 2 / g is more preferable, 90-120m 2 A BET specific surface area of ​​ / g is particularly preferred. Exhaust gas purification catalysts having such a BET specific surface area maintain high exhaust gas purification performance even when exposed to high temperatures.

[0025] [Method for manufacturing a catalyst for exhaust gas purification] Next, the method for producing the exhaust gas purification catalyst of the present invention will be described. The method for producing the exhaust gas purification catalyst of the present invention includes the steps of: preparing a carrier on which a predetermined amount of MgO is supported by supporting an Mg salt on La-containing heat-resistant alumina containing a predetermined amount of La2O3 [carrier preparation step], and heat-treating the La-containing heat-resistant alumina at a temperature of 900 to 1050°C; and supporting a predetermined amount of Rh on the carrier [Rh supporting step].

[0026] Furthermore, in the process of preparing the carrier, it is preferable to support the Mg salt and La salt on the La-containing heat-resistant alumina, and then heat-treat it at a temperature of 900 to 1050°C to prepare a carrier on which a predetermined amount of MgO is supported and a predetermined amount of La2O3 is further supported.

[0027] (Carrier preparation process) The La-containing heat-resistant alumina used in the method for producing the exhaust gas purification catalyst of the present invention is La-containing heat-resistant alumina containing the same predetermined amount (within the range described in the section on exhaust gas purification catalyst) as described in the section on exhaust gas purification catalyst.

[0028] In the method for producing the exhaust gas purification catalyst of the present invention, first, a magnesium salt is supported on such La-containing heat-resistant alumina. Examples of magnesium salts include acetate, nitrate, and chloride. Such magnesium salts can be supported on the La-containing heat-resistant alumina by, for example, dissolving them in water to prepare an aqueous solution, dispersing the La-containing heat-resistant alumina in this aqueous solution containing magnesium salt, and then evaporating it to dryness. The amount of magnesium salt supported is adjusted as appropriate so that the amount of magnesium oxygen supported on the resulting carrier is within a predetermined range (within the range described in the section on exhaust gas purification catalysts).

[0029] Furthermore, in this carrier preparation step, it is preferable to support the La salt on the La-containing heat-resistant alumina together with the Mg salt, or after supporting the Mg salt. Examples of La salts include acetate, nitrate, and chloride. Such a La salt can be supported on the La-containing heat-resistant alumina together with the Mg salt by, for example, dissolving it together with the Mg salt in water to prepare an aqueous solution, dispersing the La-containing heat-resistant alumina in this aqueous solution containing the Mg salt and La salt, and then evaporating it to dryness. Alternatively, the Mg salt and La salt may be supported on the La-containing heat-resistant alumina by dispersing the La-containing heat-resistant alumina in an aqueous solution containing the Mg salt, evaporating it to dryness, and then scattering the resulting dry material or a calcined version thereof in an aqueous solution containing the La salt and evaporating it to dryness. The amounts of Mg salt and La salt supported are adjusted as appropriate so that the amount of MgO and La2O3 supported on the resulting carrier is within a predetermined range (within the range described in the section on [exhaust gas purification catalyst] above).

[0030] Next, the dry material in which the Mg salt (preferably the Mg salt and the La salt) is supported on the La-containing heat-resistant alumina is heat-treated at a temperature of 900 to 1050°C. This yields a support (Mg-supported La-containing heat-resistant alumina support (preferably Mg / La-supported La-containing heat-resistant alumina support)) on which a predetermined amount of MgO (preferably MgO and La2O3) is supported on the La-containing heat-resistant alumina. If the heat treatment temperature falls below the lower limit, MgO, La2O3, LaCO3, etc. tend to form on the surface of the support. On the other hand, if the heat treatment temperature exceeds the upper limit, a decrease in specific surface area is a concern. From the above viewpoint, a heat treatment temperature of 900 to 1000°C is more preferable. There are no particular restrictions on the duration of the heat treatment, but from the viewpoint of reaction with the support and substitution at defect sites, 3 hours or more is preferable, and 5 hours or more is more preferable.

[0031] (Rh loading process) Next, a predetermined amount of Rh is supported on the carrier obtained in the carrier preparation step. There are no particular restrictions on the method of supporting Rh, and known methods can be used. For example, the carrier is dispersed in water, and then an Rh salt is added to support the Rh salt on the carrier, after which it is evaporated to dryness, and the resulting dry material is heat-treated to obtain an exhaust gas purification catalyst (Rh / Mg-supported La-containing heat-resistant alumina catalyst (preferably Rh / Mg / La-supported La-containing heat-resistant alumina catalyst)) on which a predetermined amount of Rh is supported on the Mg-supported La-containing heat-resistant alumina carrier (preferably the Mg / La-supported La-containing heat-resistant alumina carrier). The amount of Rh salt supported is adjusted as appropriate so that the amount of Rh supported in the obtained exhaust gas purification catalyst is within a predetermined range (within the range described in the section on [Exhaust Gas Purification Catalyst]).

[0032] There are no particular restrictions on the temperature of the heat treatment, but from the viewpoint of decomposing the Rh salt, 300 to 600°C is preferred, and 400 to 500°C is more preferred. There are no particular restrictions on the duration of the heat treatment, but from the viewpoint of sufficient decomposition of the Rh salt, 1 hour or more is preferred, and 2 hours or more is more preferred. [Examples]

[0033] The present invention will be described more specifically below based on examples and comparative examples, but the present invention is not limited to the following examples.

[0034] (Example 1) 1.86 g of magnesium acetate tetrahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 130-00095) was added to 100 ml of deionized water and dissolved by stirring without heating using a magnetic stirrer with a hot plate. 34.79 g of La-containing heat-resistant alumina containing 1% by mass of La2O3 was added to the resulting aqueous solution and dispersed. Heating was then started using a magnetic stirrer with a hot plate, and the mixture was evaporated to dryness while stirring. The resulting dry material was dried overnight in a dryer set to 120°C, and then heated to 1000°C over 2 hours in a 10% O2 / 90% N2 mixed gas, and held at 1000°C for 10 hours to react Mg with the La-containing heat-resistant alumina, thereby obtaining a Mg-supported La-containing heat-resistant alumina support in which 1.00% by mass of MgO was supported on the La-containing heat-resistant alumina.

[0035] 14.79 g of this carrier was added to 100 ml of deionized water and dispersed. Then, 0.827 g of a rhodium nitrate solution with an Rh concentration of 2.75% by mass was added and mixed. The mixture was stirred for 1 hour without heating using a magnetic stirrer with a hot plate, and then heated to evaporate to dryness. The resulting dry material was dried overnight in a dryer set to 120°C, then heated to 500°C in air over 2 hours, and held at 500°C for another 2 hours to obtain an Rh / Mg-supported La-containing heat-resistant alumina catalyst in which 0.153% by mass of Rh was supported on the carrier.

[0036] (Example 2) A Mg-supported La-containing heat-resistant alumina support was obtained in which 2.04% by mass of MgO was supported on the La-containing heat-resistant alumina, in the same manner as in Example 1, except that the amount of magnesium acetate tetrahydrate was changed to 3.72 g and the amount of the La-containing heat-resistant alumina was changed to 33.90 g. Using 14.41 g of this support, a Rh / Mg-supported La-containing heat-resistant alumina catalyst was obtained in which 0.156% by mass of Rh was supported on the support, in the same manner as in Example 1, except that the amount of the rhodium nitrate solution was changed to 0.818 g.

[0037] (Example 3) Except for changing the amount of magnesium acetate tetrahydrate to 2.11 g and the amount of the La-containing heat-resistant alumina to 19.6 g, and not performing a 24-hour drying treatment, a Mg-supported La-containing heat-resistant alumina support was obtained in which 2.00 mass% of MgO was supported on the La-containing heat-resistant alumina, in the same manner as in Example 1. Using 15.00 g of this support, and except for changing the amount of the rhodium nitrate solution to 0.819 g, an Rh / Mg-supported La-containing heat-resistant alumina catalyst was obtained in which 0.150 mass% of Rh was supported on the support, in the same manner as in Example 1.

[0038] (Example 4) Except for changing the amount of magnesium acetate tetrahydrate to 4.21 g and the amount of the La-containing heat-resistant alumina to 19.2 g, a Mg-supported La-containing heat-resistant alumina support was obtained in which 4.00 mass% of MgO was supported on the La-containing heat-resistant alumina, in the same manner as in Example 3. Except for using 15.00 g of this support, an Rh / Mg-supported La-containing heat-resistant alumina catalyst was obtained in which 0.150 mass% of Rh was supported on the support, in the same manner as in Example 3.

[0039] (Example 5) Except for changing the amount of magnesium acetate tetrahydrate to 2.11 g, and further using an aqueous solution in which 0.526 g of lanthanum nitrate hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 122-01735) was dissolved, the amount of La-containing heat-resistant alumina was changed to 19.4 g, and a 24-hour drying treatment was omitted, in the same manner as in Example 1, to obtain an Mg / La-supported La-containing heat-resistant alumina support in which 2.00 mass% of MgO was supported on the La-containing heat-resistant alumina, and 1.00 mass% of La2O3 was further supported. Using 15.00 g of this support, and except for changing the amount of rhodium nitrate solution to 0.819 g, an Rh / Mg / La-supported La-containing heat-resistant alumina catalyst was obtained in which 0.150 mass% of Rh was supported on the support, in the same manner as in Example 1.

[0040] (Comparative Example 1) 15.16 g of La-containing heat-resistant alumina containing 1% by mass of La2O3, the same as used in Examples 1-5, was dispersed in 80 ml of deionized water. Then, 0.835 g of rhodium nitrate solution with a Rh concentration of 2.75% by mass was added and mixed. The mixture was stirred for 1 hour without heating using a magnetic stirrer with a hot plate, and then heated to evaporate to dryness. The resulting dry material was dried overnight in a dryer set to 120°C, then heated to 500°C in air over 2 hours, and held at 500°C for another 2 hours to obtain an Rh-supported La-containing heat-resistant alumina catalyst in which 0.151% by mass of Rh was supported on the carrier.

[0041] (Comparative Example 2) Except for changing the amount of magnesium acetate tetrahydrate to 10.54 g and the amount of the La-containing heat-resistant alumina to 18.0 g, a Mg-supported La-containing heat-resistant alumina support was obtained in which 10.00 mass% of MgO was supported on the La-containing heat-resistant alumina, in the same manner as in Example 3. Except for using 15.00 g of this support, an Rh / Mg-supported La-containing heat-resistant alumina catalyst was obtained in which 0.150 mass% of Rh was supported on the support, in the same manner as in Example 3.

[0042] (Comparative Example 3) 106.15 g of magnesium acetate tetrahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 130-00095) and 367.63 g of aluminum nitrate nonahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 018-01945) were dissolved in 1 L of deionized water. The resulting aqueous solution was added to a neutralization solution containing 544 g of 25% aqueous ammonia (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 013-03173) and 1.2 L of deionized water, while being stirred with a propeller, to obtain a coprecipitation. The coprecipitation was centrifuged to remove the supernatant, and then dried overnight in a drying oven set to 120°C. The resulting dried material was heated to 500°C in air over 2 hours, and then held at 500°C for another 2 hours to obtain a precursor of MgAl2O4 at the initial composition. This precursor was crushed in a mortar and classified to a size of 150 μm or less. Then, it was heated to 900°C in air over 2 hours, and held at 900°C for 5 hours to obtain a spinel support with the initial composition of MgAl2O4.

[0043] 15.00 g of this spinel support was dispersed in 80 ml of deionized water, and 0.819 g of rhodium nitrate solution with an Rh concentration of 2.75% by mass was added and mixed. The mixture was stirred for 1 hour without heating using a magnetic stirrer with a hot plate, and then heated and evaporated to dryness. The resulting dry material was dried overnight in a dryer set to 120°C, then heated to 500°C in air over 2 hours, and held at 500°C for another 2 hours to obtain an Rh-supported spinel catalyst in which 0.150% by mass of Rh was supported on the spinel support.

[0044] (Comparative Example 4) Except for changing the amount of magnesium acetate tetrahydrate to 10.54 g and using 18.00 g of alumina (Showa Denko K.K. "UA-5605") instead of the La-containing heat-resistant alumina, a Mg-supported alumina support was obtained in the same manner as in Example 3, in which 10.00 mass% of MgO was supported on the alumina. Except for using 15.00 g of this support, an Rh / Mg-supported alumina catalyst was obtained in the same manner as in Example 3, in which 0.150 mass% of Rh was supported on the support.

[0045] (Comparative Example 5) 12.47 g of magnesium nitrate hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 131-00265) was added to 100 ml of deionized water and dissolved by stirring without heating using a magnetic stirrer with a hot plate. 17.80 g of alumina (manufactured by Showa Denko K.K., "UA-5605") was dispersed in the resulting aqueous solution, and then heated to evaporate to dryness. The resulting dry material was dried overnight in a drying oven set to 120°C, then heated to 400°C in air over 2 hours, and held at 400°C for 30 minutes. The obtained solid was crushed in a mortar and classified to a size of 150 μm or less. Then, under a nitrogen gas flow, it was heated to 400°C over 2 hours, held at 400°C for 3 hours, and then heated to 650°C over 1 hour in air, and held at 650°C for 3 hours to obtain a Mg-supported alumina carrier in which 10.10 mass% of MgO was supported on alumina.

[0046] 15.00 g of this carrier was dispersed in 100 ml of deionized water, and 0.819 g of a rhodium nitrate solution with an Rh concentration of 2.75% by mass was added and mixed. The mixture was stirred for 1 hour without heating using a magnetic stirrer with a hot plate, and then heated to evaporate to dryness. The resulting dry material was dried overnight in a dryer set to 120°C, and then heated to 400°C over 1 hour under a flow of a 3% H2 / 97% N2 mixed gas, and held at 400°C for 3 hours to obtain an Rh / Mg-supported alumina catalyst in which 0.150% by mass of Rh was supported on the carrier.

[0047] 13.02 g of this catalyst was dispersed in an aqueous solution prepared by dissolving 0.347 g of lanthanum nitrate hexahydrate in 100 ml of deionized water. The solution was heated and evaporated to dryness while stirring with a magnetic stirrer with a hot plate. The resulting dry material was heated to 650°C in air over 2 hours, and then held at 650°C for 3 hours to obtain a La / Rh / Mg-supported alumina catalyst in which 1.00 mass% of La2O3 and 0.149 mass% of Rh were supported on the Mg-supported alumina carrier.

[0048] (Comparative Example 6) 9.89 g of magnesium chloride hexahydrate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 132-00175) was added to 100 ml of deionized water and dissolved by stirring without heating using a magnetic stirrer with a hot plate. 17.80 g of alumina (manufactured by Showa Denko K.K., "UA-5605") was dispersed in the resulting aqueous solution, and 25% aqueous ammonia (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 013-03173) was added dropwise to adjust the pH to 13. After holding the solution overnight, it was heated and evaporated to dryness. The resulting dry material was dried overnight in a drying oven set to 120°C, then heated to 400°C in the air over 2 hours, and held at 400°C for 30 minutes. The obtained solid was crushed in a mortar and classified to a size of 150 μm or less. Then, under air circulation, the temperature was raised to 600°C over 1 hour, and the mixture was held at 600°C for 24 hours to obtain a Mg-supported alumina carrier in which 10.19% by mass of MgO was supported on alumina.

[0049] 15.00 g of this carrier was dispersed in 100 ml of deionized water, and 0.819 g of a rhodium nitrate solution with an Rh concentration of 2.75% by mass was added and mixed. The mixture was stirred for 1 hour without heating using a magnetic stirrer with a hot plate, and then heated to evaporate to dryness. The resulting dry material was heated to 500°C in air over 2 hours, and then held at 500°C for another 2 hours to obtain an Rh / Mg-supported alumina catalyst in which 0.149% by mass of Rh was supported on the carrier.

[0050] 13.02 g of this catalyst was dispersed in an aqueous solution prepared by dissolving 0.347 g of lanthanum nitrate hexahydrate in 100 ml of deionized water. The solution was heated and stirred using a magnetic stirrer with a hot plate, and evaporated to dryness. The resulting dry material was heated to 650°C in air over 2 hours, and then held at 650°C for 3 hours to obtain a La / Rh / Mg-supported alumina catalyst in which 1.00 mass% of La2O3 and 0.149 mass% of Rh were supported on the Mg-supported alumina carrier.

[0051] (Comparative Example 7) Except for using 4.47 g of barium acetate (manufactured by Fujifilm Wako Pure Chemical Industries, Ltd., product code: 026-00065) instead of magnesium acetate tetrahydrate and changing the amount of La-containing heat-resistant alumina to 33.90 g, a Ba-supported La-containing heat-resistant alumina support was obtained in which 7.33 mass% of BaO was supported on the La-containing heat-resistant alumina, in the same manner as in Example 1. Using 14.41 g of this support, and except for changing the amount of rhodium nitrate solution to 0.774 g, an Rh / Ba-supported La-containing heat-resistant alumina catalyst was obtained in which 0.147 mass% of Rh was supported on the support, in the same manner as in Example 1.

[0052] <Heat resistance test> Each catalyst obtained in the examples and comparative examples was vacuum-packed and molded at 1000 kg / cm² using an isostatic molding machine. 2Pelletizing was carried out under the pressure of , and the obtained molded body was crushed and sized to obtain catalyst pellets with a particle size of 0.5 mm to 1.0 mm. 2.5 g of the obtained catalyst pellets were filled into a quartz reaction tube with an inner diameter of 11 mm, and while alternately flowing a reducing gas [H2 (2 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (the rest)] for 1 minute and an oxidizing gas [O2 (1 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (the rest)] for 9 minutes at a flow rate of 0.5 L / min, the temperature was raised to 1050 °C over 1 hour, and further, a heat resistance test was carried out by holding at 1050 °C for 5 hours.

[0053] <Rh Dispersion Measurement> Approximately 0.3 g of the catalyst pellets after the heat resistance test were set in a low-temperature CO pulse adsorption measurement device (manufactured by Hemmi Slide Rule Co., Ltd.), and pre-reducing treatment was carried out by heating at 400 °C for 15 minutes while flowing H2 (100%). While cooling the catalyst pellets after the pre-treatment to -78 °C with dry ice, a mixed gas of 20% CO / 80% He was pulsed and flowed through the catalyst pellets multiple times until the adsorption of CO to the catalyst pellets was saturated, and the adsorption amount of CO was measured. Assuming that CO molecules adsorb to Rh atoms on the catalyst pellets in a 1:1 ratio, the following formula: Rh Dispersion [%] = Adsorption amount of CO [mol] / Rh loading amount [mol] × 100 was used to calculate the Rh dispersion. The results are shown in Table 1 and Figures 1 to 2. The Rh dispersion means that the larger the value, the larger the surface amount of Rh particles contributing as active sites for the exhaust gas purification reaction. Rh dispersion = 100% means that Rh is atomically dispersed on the catalyst pellets.

[0054] <Specific Surface Area Measurement> Approximately 0.25 g of the catalyst pellets after the Rh dispersion measurement were set in a fully automatic specific surface area measurement device (「MS4232」 manufactured by Micro Data Co., Ltd.), and pre-treatment was carried out at 250 °C for 15 minutes in a nitrogen atmosphere. Then, a mixed gas of 30% N2 / 70% He was flowed through to measure the nitrogen adsorption amount at liquid nitrogen temperature (-196 °C), and the BET specific surface area was determined from the obtained nitrogen adsorption amount. The results are shown in Table 1.

[0055]

Table 1

[0056] <X-ray diffraction measurement> After measuring the Rh dispersion, the catalyst pellets were pulverized in a mortar to prepare a sample for X-ray diffraction measurement. This sample was set in a sample horizontal multi-purpose X-ray diffractometer ("Ultima IV" manufactured by Rigaku Corporation), and using CuKα rays as the X-ray source, at a voltage of 40 kV, a current of 40 mA, a scan speed of 10° / min, and a sampling width of 0.01°, an X-ray diffraction pattern in the range of 2θ = 10° to 80° was measured. The results are shown in Fig. 3. In Fig. 3, the ■ mark represents the diffraction peak (PDF04-010-6476) attributed to α-Al2O3, the ▲ mark represents the diffraction peak (PDF00-035-0121) attributed to θ-Al2O3, the 〇 mark represents the diffraction peak (PDF04-005-4662) attributed to γ-Al2O3, and the * mark represents Mg 0.349 Al 2.428 The diffraction peak (PDF04-009-7688) attributed to O4 is represented, and the ● mark represents the diffraction peak (PDF98-000-0407) attributed to MgAl2O4.

[0057] As shown in Fig. 3, for the Rh / Mg-supported La-containing heat-resistant alumina catalysts (Examples 3 and 4) in which a predetermined amount of MgO and Rh were supported on the La-containing heat-resistant alumina, in the X-ray diffraction pattern measured using CuKα rays as the X-ray source, the three strongest lines (2θ = 35.16°, 43.37°, and 57.52°) attributed to α-Al2O3 and the three strongest lines (2θ = 36.85°, 65.24°, and 44.81°) attributed to MgAl2O4 were not detected. For the Rh / Mg-supported La-containing heat-resistant alumina catalysts obtained in Examples 1 and 2 and the Rh / Mg / La-supported La-containing heat-resistant alumina catalyst obtained in Example 5, the three strongest lines (2θ = 35.16°, 43.37°, and 57.52°) attributed to α-Al2O3 and the three strongest lines (2θ = 36.85°, 65.24°, and 44.81°) attributed to MgAl2O4 were also not detected in the X-ray diffraction pattern measured using CuKα rays as the X-ray source.

[0058] On the other hand, for the Rh / Mg-supported La-containing heat-resistant alumina catalyst (Comparative Example 2) in which excessive MgO was supported on La-containing heat-resistant alumina, the three strong lines (2θ = 35.16°, 43.37°, and 57.52°) attributed to α-Al2O3 and the three strong lines (2θ = 36.85°, 65.24°, and 44.81°) attributed to MgAl2O4 were not detected, but a diffraction peak attributed to Mg 0.349 Al 2.428 O4 was detected.

[0059] Also, for the Rh-supported spinel catalyst (Comparative Example 3) in which MgO and Al2O3 were coprecipitated, the three strong lines (2θ = 35.16°, 43.37°, and 57.52°) attributed to α-Al2O3 were not detected, but the three strong lines (2θ = 36.85°, 65.24°, and 44.81°) attributed to MgAl2O4 were detected.

[0060] Furthermore, for the Rh / Mg-supported alumina catalyst (Comparative Example 4) and the La / Rh / Mg-supported alumina catalysts (Comparative Examples 5 and 6) in which MgO was supported on alumina, the three strong lines (2θ = 36.85°, 65.24°, and 44.81°) attributed to MgAl2O4 were not detected, but the three strong lines (2θ = 35.16°, 43.37°, and 57.52°) attributed to α-Al2O3 were detected.

[0061] As shown in Table 1 and FIG. 1, the Rh / Mg-supported La-containing heat-resistant alumina catalysts (Examples 1 to 4) in which a predetermined amount of MgO and Rh were supported on La-containing heat-resistant alumina and the three strong lines attributed to α-Al2O3 and the three strong lines attributed to MgAl2O4 were not detected were found to have a high Rh dispersion degree after the heat resistance test and a large BET specific surface area after the heat resistance test. In particular, it was found that as the supported amount of MgO increased, the Rh dispersion degree after the heat resistance test tended to increase.

[0062] Furthermore, as shown in Table 1 and Figure 2, it was found that the Rh / Mg / La-supported La-containing heat-resistant alumina catalyst with a predetermined amount of La2O3 (Example 5) exhibited an even higher degree of Rh dispersion after the heat resistance test compared to the Rh / Mg-supported La-containing heat-resistant alumina catalyst without La2O3 (Examples 1-4).

[0063] On the other hand, as shown in Table 1 and Figure 1, it was found that the Rh-supported La-containing heat-resistant alumina catalyst (Comparative Example 1), in which MgO was not supported on the La-containing heat-resistant alumina, and the Rh / Mg-supported La-containing heat-resistant alumina catalyst (Comparative Example 2), in which excess MgO was supported on the La-containing heat-resistant alumina, showed a lower degree of Rh dispersion after the heat resistance test compared to the Rh / Mg-supported La-containing heat-resistant alumina catalyst (Examples 1-4), in which a predetermined amount of MgO and Rh were supported on the La-containing heat-resistant alumina.

[0064] Furthermore, as shown in Table 1 and Figure 2, the Rh / Mg-supported alumina catalyst (Comparative Example 4) and La / Rh / Mg-supported alumina catalysts (Comparative Examples 5 and 6), in which triples attributed to α-Al2O3 were detected, had similar MgO loads. Compared to the Rh / Mg-supported La-containing heat-resistant alumina catalyst (Comparative Example 2), in which no triples attributed to α-Al2O3 or MgAl2O4 were detected, the Rh dispersion after the heat resistance test was lower, and the BET specific surface area after the heat resistance test was also smaller.

[0065] Furthermore, as shown in Table 1 and Figure 2, the Rh-supported spinel catalyst (Comparative Example 3), in which triples attributed to MgAl2O4 were detected, showed significantly lower Rh dispersion after the heat resistance test and significantly smaller BET specific surface area after the heat resistance test compared to the Rh / Mg-supported La-containing heat-resistant alumina catalysts (Examples 1-4), in which neither triples attributed to α-Al2O3 nor triples attributed to MgAl2O4 were detected.

[0066] Furthermore, as shown in Table 1, compared to the Rh / Mg-supported La-containing heat-resistant alumina catalysts (Examples 1-4), in which a predetermined amount of MgO and Rh are supported on La-containing heat-resistant alumina, the Rh-supported catalysts (Comparative Examples 3-6), which have a smaller BET specific surface area after the heat resistance test, exhibit a lower degree of Rh dispersion after the heat resistance test. It is presumed that the decrease in BET specific surface area after the heat resistance test is one of the factors contributing to the decrease in the degree of Rh dispersion after the heat resistance test.

[0067] Furthermore, as shown in Table 1 and Figure 2, the Rh / Ba-supported La-containing heat-resistant alumina catalyst (Comparative Example 7), in which BaO and Rh are supported on La-containing heat-resistant alumina, showed significantly lower Rh dispersion after the heat resistance test compared to the Rh / Mg-supported La-containing heat-resistant alumina catalysts (Examples 1-4), in which MgO and Rh are supported on La-containing heat-resistant alumina. [Industrial applicability]

[0068] As described above, according to the present invention, it is possible to obtain an exhaust gas purification catalyst with a high degree of Rh dispersion and a large BET specific surface area, even when exposed to high temperatures. Therefore, the exhaust gas purification catalyst of the present invention is an exhaust gas purification catalyst with excellent heat resistance, having a large surface amount of Rh particles that contribute to the reaction even after exposure to high temperatures, and is useful as a catalyst for removing harmful components such as hydrocarbons (HC) and nitrogen oxides (NOx) contained in exhaust gas from internal combustion engines such as automobile engines.

Claims

1. 0.5 to 4 mass% La ２ O ３ A carrier comprising heat-resistant alumina containing La, on which 0.5 to 9% by mass of MgO is supported, and a carrier comprising 0.05 to 5% by mass of Rh supported on the carrier, In the X-ray diffraction pattern measured using CuKα radiation as the X-ray source after a heat resistance test at 1050°C for 5 hours, α-Al ２ O ３ An exhaust gas purification catalyst characterized in that the three strong lines (2θ = 35.16°, 43.37°, and 57.52°) belonging to the same region are not detected.

2. In the X-ray diffraction pattern measured using CuKα radiation as the X-ray source after a heat resistance test at 1050°C for 5 hours, MgAl ２ O ４ The exhaust gas purification catalyst according to claim 1, characterized in that three strong lines (2θ = 36.85°, 65.24°, and 44.81°) belonging to the same region are not detected.

3. The La-containing heat-resistant alumina contains 0.5 to 2% by mass of La ２ O ３ The exhaust gas purification catalyst according to claim 1, characterized in that the material is further supported.

4. 0.5 to 4% by mass of La ２ O ３ After supporting a Mg salt on the La-containing heat-resistant alumina containing the same, heat treatment is performed at a temperature of 900 to 1050 ° C to prepare a carrier on which 0.5 to 9% by mass of MgO is supported on the La-containing heat-resistant alumina; A step of supporting 0.05 to 5% by mass of Rh on the carrier. A method for producing an exhaust gas purification catalyst, characterized by containing [the specified ingredient].

5. In the process of preparing the carrier, after supporting the Mg salt and La salt on the La-containing heat-resistant alumina, the carrier is heat-treated at a temperature of 900 to 1050°C so that 0.5 to 9% by mass of MgO is supported on the La-containing heat-resistant alumina, and 0.5 to 2% by mass of La ２ O ３ A method for producing an exhaust gas purification catalyst according to claim 4, characterized in that a carrier is further supported thereon.

Images