Catalysts for exhaust gas purification and their manufacturing methods

Abstract

This invention relates to a catalyst for exhaust gas purification and its manufacturing method. The catalyst for exhaust gas purification comprises Pd-based nanoparticles supported on a composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide, and using the formula CeO₂. 2‑x (0≤x<0.5) represents cerium dioxide nanoparticles, with a molar ratio (Ce / Pd) of 1 to 8 for Ce and Pd supported on the carrier. Based on the distribution map of Pd and Ce in the elemental mapping image obtained by energy-dispersive X-ray analysis, the proximity α between Pd and Ce calculated by the following formula (1) is 0.15 to 0.50. While circulating concentrated gas (H2(2vol%) + CO2(10vol%) + H2O(3vol%) + N2(balance)) and dilute gas (O2(1vol%) + CO2(10vol%) + H2O(3vol%) + N2(balance)) at a flow rate of 0.5 L / min every 5 minutes, the Pd dispersion after a heat resistance test at 1050°C for 25 hours is 0.8% or higher.

Description

Technical Field

[0001] This invention relates to a catalyst for exhaust gas purification and a method for manufacturing the same, and more specifically, to a catalyst for exhaust gas purification supported on a composite metal oxide support containing alumina, cerium dioxide and zirconium oxide, and a method for manufacturing the same. Background Technology

[0002] Three-way catalysts, which oxidize carbon monoxide (CO) and hydrocarbons (HC) contained in exhaust gases from internal combustion engines such as automobile engines while reducing nitrogen oxides (NOx), are widely known as exhaust purification catalysts. These catalysts utilize precious metals such as platinum, rhodium, and palladium supported on metal oxide supports composed of alumina, titanium dioxide, silicon dioxide, zirconium oxide, and cerium dioxide. Furthermore, in such exhaust purification catalysts, materials with oxygen storage capacity (OSC)—capable of absorbing oxygen when the oxygen concentration in the exhaust is high and releasing oxygen when the oxygen concentration is low—are used as catalyst supports and co-catalysts to enhance exhaust purification capabilities by absorbing variations in oxygen concentration in the exhaust.

[0003] As an exhaust gas purification catalyst using such an oxygen storage material, for example, Japanese Patent Application Publication No. 2010-12397 (Patent Document 1) discloses an exhaust gas purification catalyst material containing alumina particles, CeZr-based composite metal oxide particles with oxygen storage and release capabilities, and Pd. In this exhaust gas purification catalyst material, by doping and fixing only the CeZr-based composite metal oxide particles with Pd, the oxygen storage and release capability is improved. Furthermore, by dispersing the CeZr-based composite metal oxide particles on the surface of the alumina particles, the sintering of the CeZr-based composite metal oxide particles with each other is suppressed. Therefore, excellent purification performance can be maintained even when exposed to high-temperature exhaust gas. Moreover, Patent Document 1 also describes that such an exhaust gas purification catalyst material is obtained by mixing a co-precipitate containing Ce, Zr, and Pd with an Al-containing precipitate, followed by drying and calcination.

[0004] Furthermore, Japanese Patent Application Publication No. 2007-105633 (Patent Document 2) discloses an exhaust gas purification catalyst comprising: a support composed of a metal oxide containing at least one of Al2O3, ZrO2, SiO2, TiO2, and CeO2; palladium oxide (PdO) particles supported on the support; and rare earth oxide (LnOx) particles supported on the support in contact with the palladium oxide (PdO) particles. In this exhaust gas purification catalyst, metallization from PdO to Pd is suppressed by having PdO particles and LnOx particles coexist on the support, preventing the aggregation of Pd particles, thereby maintaining high catalyst activity even at high temperatures. Moreover, Patent Document 2 also describes that such an exhaust gas purification catalyst is obtained by calcining the dried powder obtained by evaporating water from an aqueous solution containing the support, Pd precursor, and Ln precursor. Summary of the Invention

[0005] However, in the exhaust purification catalysts described in Patent Documents 1-2, hydrocarbons (HC) adsorb onto the surface of Pd and poison it in the low-temperature region immediately after the start-up of an internal combustion engine such as a car engine, thus failing to achieve sufficient catalyst activity. In addition, the oxygen absorption and release performance after exposure to high temperatures is also insufficient.

[0006] The present invention was made in view of the problems existing in the prior art, and its object is to provide an exhaust gas purification catalyst and a method thereof that have excellent catalytic activity at low temperature and excellent oxygen absorption and release performance after exposure to high temperature.

[0007] To achieve the above objectives, the inventors conducted repeated and intensive research and discovered that by supporting cerium dioxide nanoparticles on a composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide in a specific molar ratio of Ce to Pd, and then supporting Pd-containing nanoparticles, an exhaust gas purification catalyst can be obtained in which Pd-containing nanoparticles are dispersedly supported, and the cerium dioxide nanoparticles and Pd-containing nanoparticles are supported in approximately the same manner. This exhaust gas purification catalyst exhibits excellent catalytic activity at low temperatures and excellent oxygen absorption and release performance after exposure to high temperatures, thus completing the present invention.

[0008] That is, the present invention provides the following solution.

[0009] [1] A catalyst for exhaust gas purification, wherein Pd nanoparticles composed of Pd or Pd oxide are supported on a composite metal oxide support containing alumina, cerium dioxide and zirconium oxide, and the catalyst is composed of CeO 2-x (0≤x<0.5) represents cerium dioxide nanoparticles.

[0010] The molar ratio (Ce / Pd) of Ce and Pd supported on the composite metal oxide support is 1 to 8.

[0011] Based on the Pd and Ce distribution maps obtained from the elemental mapping images by energy-dispersive X-ray analysis, the proximity α between Pd and Ce, calculated using the following equation (1), is 0.15–0.50.

[0012]

[0013] In equation (1), I(i,j) represents the luminance value in region (i,j) that is the i-th region in the horizontal direction and the j-th region in the vertical direction when the Pd distribution map is divided into M horizontal sections and N vertical sections. ave T represents the average luminance value in the Pd distribution map, and T(i,j) represents the luminance value in the region (i,j) that is the i-th region in the horizontal direction and the j-th region in the vertical direction when the Ce distribution map is divided into M horizontal and N vertical sections. ave This represents the average luminance value in the Ce distribution map.

[0014] While alternating between concentrated gas (H2 (2 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (balance)) and dilute gas (O2 (1 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (balance)) at a flow rate of 0.5 L / min every 5 minutes, the Pd dispersion after a heat resistance test at 1050°C for 25 hours was greater than 0.8%.

[0015] [2] According to the exhaust gas purification catalyst described in [1],

[0016] Based on the elemental mapping image obtained by energy-dispersive X-ray analysis, the Ce concentration β near the Pd-based nanoparticles, calculated using the following equation (2), is greater than 16%.

[0017]

[0018] In equation (2), n is the total number of regions of 162.0 nm x 162.0 nm randomly selected from the elemental mapping image, centered on the Pd-based nanoparticles, and C Ce C Pd C Al C M These represent the concentrations of Ce, Pd, Al, and other metal M in the extracted regions, respectively.

[0019] [3] According to the exhaust gas purification catalyst described in [1],

[0020] The dispersion of Pd in ​​the atmosphere after heating at 500°C for 5 hours is greater than 15%.

[0021] [4] According to the exhaust gas purification catalyst described in [2],

[0022] The dispersion of Pd in ​​the atmosphere after heating at 500°C for 5 hours is greater than 15%.

[0023] [5] A method for manufacturing a catalyst for exhaust gas purification,

[0024] The composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide is supported by a CeO2 composition. 2-x After cerium dioxide nanoparticles (0≤x<0.5) are loaded with Pd-based nanoparticles composed of Pd or Pd oxide, the molar ratio (Ce / Pd) of Ce and Pd loaded on the composite metal oxide carrier is 1 to 8.

[0025] [6] According to the method for manufacturing the catalyst for exhaust gas purification described in [5],

[0026] Cerium dioxide nanoparticles are loaded onto the composite metal oxide carrier by impregnating the composite metal oxide carrier containing alumina, cerium dioxide, and zirconium oxide with a compound containing tetravalent Ce.

[0027] [7] According to the method for manufacturing the catalyst for exhaust gas purification described in [6],

[0028] The compound containing tetravalent Ce is a tetravalent Ce nitrate.

[0029] [8] According to the method for manufacturing the catalyst for exhaust gas purification described in [5],

[0030] The Pd-based nanoparticles are loaded onto the composite metal oxide carrier by impregnating it with palladium nitrate.

[0031] [9] According to the method for manufacturing the catalyst for exhaust gas purification described in [6],

[0032] The Pd-based nanoparticles are loaded onto the composite metal oxide carrier by impregnating it with palladium nitrate.

[0033]

[10] According to the method for manufacturing the catalyst for exhaust gas purification described in [7],

[0034] The Pd-based nanoparticles are loaded onto the composite metal oxide carrier by impregnating it with palladium nitrate.

[0035] Furthermore, the reason why the exhaust gas purification catalyst of the present invention exhibits excellent catalytic activity at low temperatures and excellent oxygen uptake and release performance after exposure to high temperatures is not necessarily clear, but the inventors speculate as follows. That is, in exhaust gas purification catalysts obtained by conventional loading methods such as supporting a co-precipitate of cerium dioxide and Pd on a composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide, or physically mixing a composite metal oxide powder supported on Pd with cerium dioxide powder, or simultaneously supporting cerium dioxide and Pd, Pd is embedded in cerium dioxide, or Pd and CeO2 are... 2-x The junctions are insufficient, therefore the interaction between cerium dioxide and Pd cannot be fully achieved (Pd and CeO). 2-x Oxygen acceptor at the interface, hydrocarbons (HC) adsorb onto the surface of Pd-based nanoparticles, causing them to become poisoned and not exhibit sufficient catalytic activity at low temperatures.

[0036] Furthermore, when cerium dioxide nanoparticles are replaced with nanoparticles containing metal atoms such as Ba, La, Fe, and Co that have HC poisoning inhibition and HC oxidation promotion effects to suppress HC adsorption poisoning on the surface of Pd-based nanoparticles, the metal atoms undergo solid-phase reactions with alumina and zirconium oxide under high-temperature conditions, thus reducing the oxygen storage and release performance after exposure to high temperatures.

[0037] On the other hand, in the exhaust gas purification catalyst of the present invention, since cerium dioxide nanoparticles are supported on a composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide, and then Pd-containing nanoparticles are supported on it, cerium dioxide nanoparticles and Pd-based nanoparticles are supported in close proximity. Thus, it is presumed that in the exhaust gas purification catalyst in which cerium dioxide nanoparticles and Pd-based nanoparticles are supported in close proximity, the interaction between cerium dioxide nanoparticles and Pd, specifically, the interaction between Pd and CeO... 2-x At the oxygen donation and acceptance interface, Ce is reduced, generating oxygen vacancies and free oxygen. Thus, Pd and CeO... 2-x The HC oxidation activity at the three-phase interface of the gas phase is improved, and the adsorption poisoning of HC on the surface of Pd nanoparticles is suppressed, exhibiting excellent catalytic activity even at low temperatures.

[0038] Furthermore, it is speculated that in the exhaust gas purification catalyst of the present invention, even when exposed to high temperatures, cerium dioxide nanoparticles and Pd-based nanoparticles do not react, thus maintaining excellent oxygen uptake and release performance. Moreover, even when a portion of the cerium dioxide nanoparticles reacts with the oxygen uptake and release material (cerium dioxide-zirconia solid solution), they still maintain excellent oxygen uptake and release performance. In addition, by remaining near the Pd-based nanoparticles, they suppress the adsorption and poisoning of HC onto the surface of the Pd-based nanoparticles. Therefore, in the exhaust gas purification catalyst of the present invention, excellent catalytic activity is exhibited even at low temperatures.

[0039] According to the present invention, an exhaust gas purification catalyst with excellent catalytic activity at low temperatures and excellent oxygen absorption and release performance after exposure to high temperatures can be obtained. Attached Figure Description

[0040] Figure 1 This is a graph showing the proximity α of Pd and Ce supported on the metal oxide support in the catalyst powders obtained in the examples and comparative examples.

[0041] Figure 2 This is a graph showing the Ce concentration β near the Pd-based nanoparticles of the catalyst powders obtained in the examples and comparative examples.

[0042] Figure 3 This is a graph showing the Pd dispersion of the catalyst powders obtained in the examples and comparative examples after a heat resistance test.

[0043] Figure 4 This is a diagram showing the X-ray diffraction patterns of the catalyst powders obtained in Examples 2, 6 and Comparative Examples 4, 5 after heat resistance tests.

[0044] Figure 5 This is a graph showing the oxygen release rate of the catalyst powders obtained in the examples and comparative examples at 400°C.

[0045] Figure 6 This is a graph showing the C3H6 purification rate of the catalyst powders obtained in the examples and comparative examples at 400°C.

[0046] Figure 7 This is a graph showing the relationship between the proximity α of Pd and Ce and the Pd dispersion after the heat resistance test.

[0047] Figure 8 This is a graph showing the relationship between the oxygen release rate and the C3H6 purification rate at 400℃. Detailed Implementation

[0048] The present invention will now be described in detail with reference to its preferred embodiments.

[0049] [Catalyst for exhaust gas purification]

[0050] First, the exhaust gas purification catalyst of the present invention will be described. The exhaust gas purification catalyst of the present invention comprises Pd-based nanoparticles composed of Pd or Pd oxides supported on a composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide, and using the formula CeO₂. 2-x (0≤x<0.5) represents a catalyst for exhaust gas purification using cerium dioxide nanoparticles.

[0051] As a carrier used in this invention, conventionally known composite metal oxide carriers containing alumina, cerium dioxide, and zirconium oxide, used in exhaust gas purification catalysts, can be cited as examples. The alumina content in such a composite metal oxide carrier is preferably 20-40% by mass. If the alumina content is lower than the aforementioned lower limit, the specific surface area of ​​the composite metal oxide carrier decreases, tending to reduce catalyst activity at low temperatures. On the other hand, if it exceeds the aforementioned upper limit, the oxygen storage capacity (OSC capacity) of the composite metal oxide carrier decreases, tending to reduce catalyst activity at low temperatures.

[0052] The preferred molar ratio of cerium dioxide to zirconium oxide in the composite metal oxide support is cerium dioxide:zirconium oxide = 2:8 to 5:5. If the molar ratio of cerium dioxide to zirconium oxide is lower than the lower limit, the oxygen storage capacity (OSC capacity) of the composite metal oxide support decreases, and it tends to have reduced catalyst activity at low temperatures. On the other hand, if it exceeds the upper limit, the heat resistance of the cerium dioxide-zirconium oxide composite metal oxide decreases, and the phase separation and specific surface area of ​​the cerium dioxide-zirconium oxide composite metal oxide decrease significantly, tending to have reduced catalyst activity at low temperatures.

[0053] Furthermore, in the composite metal oxide support used in this invention, other metal oxides may include oxides of Sc, Ti, Y, or Hf, as well as lanthanide oxides such as La, Pr, Nd, and Sm. Among these metal oxides, oxides of Y, La, Nd, and Pr are preferred.

[0054] The Pd-based nanoparticles used in this invention are nanoparticles composed of Pd or Pd oxide (PdO), i.e., Pd nanoparticles, Pd oxide nanoparticles, or mixtures thereof, which serve as active sites in the exhaust gas purification catalyst of this invention. At these active sites, oxidation reactions of oxygen, hydrocarbons (HC), etc., occur from the adjacent cerium dioxide nanoparticles.

[0055] The cerium dioxide nanoparticles used in this invention are composed of the formula CeO. 2-xThe nanoparticles represented by (0≤x<0.5) function as oxygen storage materials (OSC materials). In the exhaust gas purification catalyst of the present invention, since the cerium dioxide nanoparticles are close to the Pd-based nanoparticles, oxygen transfer and acceptance can be fully carried out between the Pd-based nanoparticles and the cerium dioxide nanoparticles, HC adsorption poisoning is suppressed, and excellent catalytic activity is exhibited even at low temperatures.

[0056] In the exhaust gas purification catalyst of the present invention, the molar ratio (Ce / Pd) of Ce and Pd supported on the composite metal oxide support is 1 to 8. If Ce / Pd is within this range, an interface between Pd-based nanoparticles and cerium dioxide nanoparticles can be sufficiently formed, and oxygen transfer between the Pd-based nanoparticles and cerium dioxide nanoparticles is sufficiently facilitated, suppressing HC adsorption poisoning and exhibiting excellent catalytic activity even at low temperatures. On the other hand, if Ce / Pd is below the lower limit, an interface between Pd-based nanoparticles and cerium dioxide nanoparticles cannot be sufficiently formed, making oxygen transfer to suppress HC adsorption poisoning difficult, and insufficient catalytic activity is not exhibited at low temperatures. Conversely, if Ce / Pd exceeds the upper limit, the interface between Pd-based nanoparticles and cerium dioxide nanoparticles increases, but Pd is coated on the surface, reducing contact with the reactant gas. The specific surface area decreases due to the pore closure of the support, and therefore, insufficient catalytic activity is not exhibited at low temperatures. Furthermore, from the viewpoint of further suppressing HC adsorption poisoning and improving catalyst activity at low temperatures, the Ce / Pd ratio is preferably 1 to 5, more preferably 2 to 5, and particularly preferably 2 to 4.

[0057] Furthermore, in the exhaust gas purification catalyst of the present invention, the proximity α between Pd and Ce, obtained by the following formula (1), is 0.15 to 0.50, based on the Pd distribution map and Ce distribution map in the elemental mapping image (EDX elemental mapping image) obtained by energy dispersive X-ray analysis (EDX).

[0058]

[0059] In equation (1), I(i,j) represents the luminance value in region (i,j) that is the i-th region in the horizontal direction and the j-th region in the vertical direction when the Pd distribution map is divided into M horizontal sections and N vertical sections. ave T represents the average luminance value in the Pd distribution map, and T(i,j) represents the luminance value in the region (i,j) that is the i-th region in the horizontal direction and the j-th region in the vertical direction when the Ce distribution map is divided into M horizontal and N vertical sections. ave This represents the average luminance value in the Ce distribution map.

[0060] If the proximity α between Pd and Ce is within the aforementioned range, the adsorption poisoning of HC onto the surface of Pd-based nanoparticles is suppressed through the interaction between cerium dioxide and Pd, and the metallization of Pd is not hindered. Therefore, excellent catalytic activity is exhibited even at low temperatures. On the other hand, if the proximity α between Pd and Ce is below the aforementioned lower limit, the interaction between cerium dioxide and Pd is not fully manifested, and HC adsorbs onto the surface of Pd-based nanoparticles, poisoning them and resulting in insufficient catalytic activity at low temperatures. On the other hand, if the proximity α between Pd and Ce exceeds the aforementioned upper limit, the interface between Pd-based nanoparticles and cerium dioxide nanoparticles increases, but Pd will be coated on them, thus reducing contact with the reactant gas. Alternatively, the specific surface area may decrease due to the closure of the pores of the support, sometimes resulting in insufficient catalytic activity at low temperatures. Furthermore, based on the view that the catalyst activity is improved at low temperatures because the adsorption poisoning of HC is further suppressed and the metallization of Pd becomes more difficult to hinder, the proximity α between Pd and Ce is preferably 0.18 to 0.45, more preferably 0.20 to 0.40, and particularly preferably 0.25 to 0.35.

[0061] Furthermore, the EDX elemental mapping image can be, for example, displayed using a scanning transmission electron microscope equipped with an energy-dispersive X-ray analysis device at a field of view magnification of 1.2 × 10⁻⁶. 6 The Pd-Ce proximity α is obtained by performing EDX analysis under the condition of multiples. Furthermore, the proximity α between Pd and Ce can be obtained by calculating the zero-mean normalized cross-correlation (ZNCC) coefficient using image processing software such as ImageJ or Matlab on the Pd and Ce distribution maps in the EDX element mapping image.

[0062] Furthermore, in the exhaust gas purification catalyst of the present invention, the dispersion of Pd after a heat resistance test conducted at 1050°C for 25 hours is 0.8% or higher, achieved by alternately circulating concentrated gas (H2 (2 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (balance)) and dilute gas (O2 (1 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (balance) at a flow rate of 0.5 L / min every 5 minutes. If the dispersion of Pd after the heat resistance test is within the above range, the surface area of ​​the active Pd-based nanoparticles for the purification reaction can be ensured, and the catalyst activity at low temperatures can be guaranteed. On the other hand, if the dispersion of Pd after the heat resistance test is lower than the above lower limit, the surface area of ​​the active Pd-based nanoparticles for the purification reaction is insufficient, and the catalyst activity at low temperatures decreases. In addition, there are cases where Pd-based nanoparticles are coated or buried by cerium dioxide nanoparticles. In such cases, the contact between the Pd-based nanoparticles and the reactant gas is reduced, and there is a tendency for the catalyst activity to decrease at low temperatures. Furthermore, from the viewpoint of improving catalyst activity at low temperatures, the dispersion of Pd after the heat resistance test is preferably 0.8% to 50%, more preferably 0.9% to 50%, and particularly preferably 1% to 50%.

[0063] Furthermore, the dispersion of Pd can be used to determine the CO adsorption amount of catalysts used for exhaust gas purification. The CO adsorption amount and Pd loading obtained can be calculated using the following formula.

[0064] Pd dispersibility [%] = CO adsorption capacity [mol] / Pd loading capacity [mol] × 100

[0065] Furthermore, in the exhaust gas purification catalyst of the present invention, the Ce concentration β near the Pd-based nanoparticles, calculated by the following formula (2) based on the elemental mapping image obtained by energy-dispersive X-ray analysis, is preferably 16% or more.

[0066]

[0067] In equation (2), n is the total number of regions of 162.0 nm x 162.0 nm randomly selected from the elemental mapping image, centered on the Pd-based nanoparticles, and C Ce C Pd C Al C M These represent the concentrations of Ce, Pd, Al, and other metal M in the extracted regions, respectively.

[0068] If the Ce concentration β near the Pd-based nanoparticles is within the aforementioned range, an interface between the Pd-based nanoparticles and cerium dioxide nanoparticles can be sufficiently formed, and oxygen transfer between the Pd-based nanoparticles and cerium dioxide nanoparticles can be sufficiently carried out. HC adsorption poisoning is suppressed, and excellent catalytic activity is easily exhibited even at low temperatures. On the other hand, if the Ce concentration β near the Pd-based nanoparticles is below the aforementioned lower limit, an interface between the Pd-based nanoparticles and cerium dioxide nanoparticles is not sufficiently formed. Oxygen transfer to suppress HC adsorption poisoning between the Pd-based nanoparticles and cerium dioxide nanoparticles becomes difficult, and there is a tendency for sufficient catalytic activity to be difficult to exhibit at low temperatures. Furthermore, from the viewpoint that HC adsorption poisoning is further suppressed and catalytic activity is improved at low temperatures, the Ce concentration β near the Pd-based nanoparticles is preferably 16–50%, more preferably 18–40%, and particularly preferably 20–30%.

[0069] Furthermore, the Ce concentration β near the Pd nanoparticles can be obtained by randomly selecting n = 50 to 100 regions centered on the Pd nanoparticles with a vertical dimension of 162.0 nm and a horizontal dimension of 162.0 nm from the EDX elemental mapping image. Based on the EDX elemental mapping data, the concentrations of Pd, Al, Ce and other metal M in each selected region can be calculated. Using the obtained concentrations of each element, the above formula (2) can be used to obtain the concentrations.

[0070] Furthermore, in the exhaust gas purification catalyst of the present invention, the dispersion of Pd in ​​the atmosphere after heating at 500°C for 5 hours (initial (initial) Pd dispersion) is preferably 15% or more. If the initial Pd dispersion is within the above range, the surface area of ​​the active Pd-based nanoparticles for the purification reaction can be ensured, and the catalyst activity at low temperatures can be easily ensured. On the other hand, if the initial Pd dispersion is lower than the above lower limit, the surface area of ​​the active Pd-based nanoparticles for the purification reaction is insufficient, and there is a tendency for the catalyst activity to decrease at low temperatures. In addition, there are cases where Pd-based nanoparticles are coated or buried by cerium dioxide nanoparticles. In this case, the contact between the Pd-based nanoparticles and the reactant gas is reduced, and there is a tendency for the catalyst activity to decrease at low temperatures. Furthermore, from the viewpoint of improving the catalyst activity at low temperatures, the initial Pd dispersion is preferably 15% to 80%, more preferably 15% to 60%, and particularly preferably 20% to 60%. Moreover, the method for calculating the Pd dispersion is as described above.

[0071] [Manufacturing method of catalyst for exhaust gas purification]

[0072] Next, the method for manufacturing the exhaust gas purification catalyst of the present invention will be described. The method for manufacturing the exhaust gas purification catalyst of the present invention involves loading cerium dioxide nanoparticles onto a composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide, such that the molar ratio (Ce / Pd) of Ce and Pd supported on the composite metal oxide support is 1 to 8 (preferably 1 to 5, more preferably 2 to 5, particularly preferably 2 to 4), followed by loading Pd-based nanoparticles composed of Pd or Pd oxides. By loading Pd-based nanoparticles after loading cerium dioxide nanoparticles, it is possible to prevent the Pd-based nanoparticles from being buried within the cerium dioxide nanoparticles, resulting in the exhaust gas purification catalyst of the present invention in which cerium dioxide nanoparticles and Pd-based nanoparticles are supported approximately in close proximity on the composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide, and the Pd-based nanoparticles are dispersedly supported. On the other hand, when cerium dioxide nanoparticles and Pd-based nanoparticles are simultaneously loaded, the Pd-based nanoparticles will be buried in the cerium dioxide nanoparticles. Therefore, the Pd-based nanoparticles and the reactant gas cannot be in sufficient contact, and the catalyst activity of the obtained exhaust gas purification catalyst is reduced at low temperatures.

[0073] There are no particular limitations on the methods for supporting cerium dioxide nanoparticles and Pd-based nanoparticles. For example, conventionally known supporting methods such as impregnation, neutralization precipitation, sol-gel method, alkoxide hydrolysis, and nitrate aqueous solution combustion can be used.

[0074] In the method for manufacturing the exhaust gas purification catalyst of the present invention, it is preferable to impregnate the composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide with a compound containing tetravalent Ce (more preferably a tetravalent Ce nitrate), and then dry and calcine it under an oxidizing atmosphere, such as in the atmosphere, to support cerium dioxide nanoparticles on the composite metal oxide support. This allows cerium dioxide nanoparticles to be supported as CeO2, which is difficult to react with alumina in the solid phase, and enables the high dispersion of cerium dioxide nanoparticles while maintaining the fine structure of the composite metal oxide support.

[0075] Furthermore, in the method for manufacturing the exhaust gas purification catalyst of the present invention, it is preferable to load cerium dioxide nanoparticles onto the composite metal oxide support using the above-described method, and then impregnate it with palladium nitrate to load the Pd-based nanoparticles. This allows for the acquisition of an exhaust gas purification catalyst that exhibits excellent catalytic activity even at low temperatures. Additionally, this exhaust gas purification catalyst can accelerate the activation of the HC purification reaction at low temperatures, and the generated heat of the purification reaction also promotes the activation of other noble metal active sites and co-catalysts (OSC materials, etc.).

[0076] Example

[0077] The present invention will be described in more detail below based on embodiments and comparative examples, but the present invention is not limited to the following embodiments.

[0078] (Example 1)

[0079] 4.33 g of diammonium cerium nitrate was dissolved in 50.00 g of deionized water. 19.64 g of alumina-cerium dioxide-zirconia composite metal oxide powder (ACZ powder, Al₂O₃:CeO₂:ZrO₂:other metal oxides = 30 wt%: 23 wt%: 39 wt%: 8 wt%) was added to the resulting aqueous solution and stirred for at least 30 minutes. The resulting dispersion was then heated on a hot stirrer to remove the solvent, followed by calcination at 400 °C for 5 hours to obtain alumina-cerium dioxide-zirconia composite metal oxide powder (Ce-supported ACZ powder) loaded with cerium dioxide nanoparticles.

[0080] Next, 0.4 g of palladium nitrate (based on Pd atomic conversion) was added to 50.00 g of ion-exchanged water. Then, 20.00 g of the Ce-supported ACZ powder was added to the resulting aqueous solution, and the mixture was stirred for at least 30 minutes. The resulting dispersion was then heated on a hot stirrer to remove the solvent, and finally calcined at 400°C for 5 hours to obtain a catalyst powder (Pd-2Ce / ACZ powder) in which cerium dioxide nanoparticles and Pd-based nanoparticles were sequentially supported on an alumina-cerium dioxide-zirconia composite metal oxide support. In this catalyst powder, the molar ratio of Ce to Pd supported on the ACZ powder was Ce / Pd = 2.

[0081] (Example 2)

[0082] Except for changing the amount of diammonium nitrate cerium to 8.66 g and the amount of ACZ powder to 18.28 g, the process was carried out in the same manner as in Example 1, resulting in a catalyst powder (Pd-4Ce / ACZ powder) in which cerium dioxide nanoparticles and Pd-based nanoparticles were sequentially supported on an alumina-cerium dioxide-zirconia composite metal oxide support. In this catalyst powder, the molar ratio of Ce to Pd supported on the ACZ powder was Ce / Pd = 4.

[0083] (Example 3)

[0084] Except for changing the amount of diammonium nitrate cerium to 17.32 g and the amount of ACZ powder to 16.92 g, the process was carried out in the same manner as in Example 1, resulting in a catalyst powder (Pd-8Ce / ACZ powder) in which cerium dioxide nanoparticles and Pd-based nanoparticles were sequentially supported on an alumina-cerium dioxide-zirconia composite metal oxide support. In this catalyst powder, the molar ratio of Ce to Pd supported on the ACZ powder was Ce / Pd = 8.

[0085] (Comparative Example 1)

[0086] Palladium nitrate (equivalent to 0.4 g of Pd atoms) was added to 50.00 g of ion-exchanged water. Then, 17.41 g of alumina-cerium dioxide-zirconia composite metal oxide powder (ACZ powder, Al₂O₃:CeO₂:ZrO₂:other metal oxides = 30 wt%: 23 wt%: 39 wt%: 8 wt%) was added to the resulting aqueous solution and stirred for at least 30 minutes. The resulting dispersion was then heated on a hot stirrer to remove the solvent, followed by calcination at 400°C for 5 hours to obtain alumina-cerium dioxide-zirconia composite metal oxide powder (Pd / ACZ powder) loaded with Pd-based nanoparticles. This Pd / ACZ powder and 2.59 g of cerium dioxide powder were mixed by stirring in a mortar for at least 5 minutes, and then calcined at 400°C for 5 hours to obtain a catalyst powder (Pd / ACZ+4Ce powder) composed of a physical mixture of Pd / ACZ powder and cerium dioxide powder. In this catalyst powder, the molar ratio of Pd supported in ACZ powder to Ce in cerium dioxide powder is Ce / Pd = 4.

[0087] (Comparative Example 2)

[0088] Except for changing the amount of ACZ powder to 15.82 g and the amount of cerium dioxide powder to 5.18 g, the same procedure as Comparative Example 1 was performed to obtain a catalyst powder (Pd / ACZ+8Ce powder) composed of a physical mixture of Pd / ACZ powder and cerium dioxide powder. In this catalyst powder, the molar ratio of Pd supported in ACZ powder to Ce in cerium dioxide powder is Ce / Pd = 8.

[0089] (Comparative Example 3)

[0090] Palladium nitrate aqueous solution was prepared by adding 0.4 g of palladium nitrate (equivalent to Pd atoms) to 20.00 g of ion-exchanged water. Conversely, cerium diammonium nitrate aqueous solution was prepared by dissolving 8.66 g of cerium diammonium nitrate in 30.00 g of ion-exchanged water. These aqueous solutions were mixed and stirred to prepare a precursor aqueous solution containing palladium (Pd) and cerium (Ce).

[0091] Next, the above-mentioned precursor aqueous solution was added dropwise to an aqueous solution prepared by mixing 13.00 g of 25% ammonia and 50.00 g of ion-exchanged water to prepare a sol solution. The obtained sol was filtered, washed, and then redispersed in 300 g of ion-exchanged water. 17.41 g of alumina-cerium dioxide-zirconia composite metal oxide powder (ACZ powder, Al2O3:CeO2:ZrO2:other metal oxides = 30 wt%:23 wt%:39 wt%:8 wt%) was added to the obtained dispersion, and the mixture was stirred for more than 30 minutes. The obtained dispersion was heated on a hot stirrer while stirring to remove the solvent, and then calcined at 400°C for 5 hours to obtain a catalyst powder (Pd+4Ce / ACZ powder) supported on an alumina-cerium dioxide-zirconia composite metal oxide support, which is a coprecipitate of palladium (Pd) and cerium dioxide. In this catalyst powder, the molar ratio of Pd to Ce supported on ACZ powder is Ce / Pd = 4.

[0092] (Comparative Example 4)

[0093] Except for replacing cerium diammonium nitrate with 6.84 g of barium acetate and changing the amount of ACZ powder to 17.55 g, the process was carried out in the same manner as in Example 1, resulting in a catalyst powder (Pd-4Ba / ACZ powder) in which barium oxide (BaO) nanoparticles and Pd-based nanoparticles were sequentially supported on an alumina-cerium dioxide-zirconia composite metal oxide support. In this catalyst powder, the molar ratio of Ba to Pd supported on the ACZ powder was Ba / Pd = 4.

[0094] (Comparative Example 5)

[0095] Except for replacing cerium diammonium nitrate with 4.03 g of lanthanum nitrate hexahydrate and changing the amount of ACZ powder to 17.42 g, the process was the same as in Example 1, resulting in a catalyst powder (Pd-4La / ACZ powder) in which lanthanum oxide (La₂O₃) nanoparticles and Pd-based nanoparticles were sequentially supported on an alumina-cerium dioxide-zirconia composite metal oxide support. In this catalyst powder, the molar ratio of La to Pd supported on the ACZ powder was La / Pd = 4.

[0096] (Comparative Example 6)

[0097] Palladium nitrate, equivalent to 0.42 g of Pd atoms, was added to 50.00 g of ion-exchanged water. Then, 17.41 g of alumina-cerium dioxide-zirconia composite metal oxide powder (ACZ powder, Al₂O₃:CeO₂:ZrO₂:other metal oxides = 30 wt%: 23 wt%: 39 wt%: 8 wt%) was added to the resulting aqueous solution, and the mixture was stirred for at least 30 minutes. The resulting dispersion was then heated on a hot stirrer to remove the solvent, followed by calcination at 400 °C for 5 hours to obtain a catalyst powder (Pd / ACZ powder) supported on an alumina-cerium dioxide-zirconia composite metal oxide support using Pd nanoparticles. In this catalyst powder, the molar ratio of Ce to Pd supported on the ACZ powder was Ce / Pd = 0.

[0098] (Comparative Example 7)

[0099] 8.66 g of diammonium nitrate (Cerium) and 0.4 g of palladium nitrate (equivalent to 0.4 g of Pd atoms) were dissolved in 50.00 g of ion-exchanged water. 18.28 g of alumina-cerium dioxide-zirconia composite metal oxide powder (ACZ powder, Al₂O₃:CeO₂:ZrO₂:other metal oxides = 30 wt%: 23 wt%: 39 wt%: 8 wt%) was added to the resulting aqueous solution, and the mixture was stirred for at least 30 minutes. The resulting dispersion was heated at 150 °C for 24 hours to remove the solvent, and then calcined at 400 °C for 5 hours to obtain a catalyst powder (Pd-4Ce co-supported / ACZ powder) containing both cerium dioxide nanoparticles and Pd-based nanoparticles simultaneously supported on an alumina-cerium dioxide-zirconia composite metal oxide support. In this catalyst powder, the molar ratio of Ce to Pd supported on the ACZ powder was Ce / Pd = 4.

[0100] (Comparative Example 8)

[0101] Except that 18.28 g of alumina powder was used instead of ACZ powder, the process was carried out in the same manner as in Example 2 to obtain a catalyst powder (Pd-4Ce / Al powder) in which cerium dioxide nanoparticles and Pd-based nanoparticles were sequentially supported on an alumina support. In this catalyst powder, the molar ratio of Ce to Pd supported on the alumina powder was Ce / Pd = 4.

[0102] <Energy Dispersion Type X-ray Analysis>

[0103] Regarding the catalyst powders obtained in the examples and comparative examples, a scanning transmission electron microscope (JEM-ARM200F NEOARM, manufactured by Nippon Electron Ltd.) equipped with an energy-dispersive X-ray analysis device was used with an accelerating voltage of 200 kV and a field of view magnification of 1.2 × 10⁻⁶. 6Under the condition of [X] times, energy-dispersive X-ray (EDX) analysis was performed to obtain an EDX elemental mapping image of 512 pixels in length × 512 pixels in width, and distribution maps of each element of Al, Ce, Zr, Pd, and O were obtained.

[0104] <Proximity α of Pd-Ce>

[0105] Based on the Pd distribution map and the Ce distribution map obtained through the above EDX analysis, the proximity α (Pd-Ce proximity α) of Pd and Ce supported on the metal oxide support was calculated using the following formula (1).

[0106]

[0107] In formula (1), I(i, j) represents the luminance value of the pixel that is the i-th in the horizontal direction and the j-th in the vertical direction in the Pd distribution map (M = 512, N = 512), and I ave represents the average luminance value in the Pd distribution map, T(i, j) represents the luminance value of the pixel that is the i-th in the horizontal direction and the j-th in the vertical direction in the Ce distribution map (M = 512, N = 512), and T ave represents the average luminance value in the Ce distribution map.

[0108] Specifically, the coefficient value of zero-mean normalized cross-correlation (ZNCC: Zero-means Normarized Cross-Correlation) calculated using image processing software ImageJ or Matlab for the Pd distribution map and the Ce distribution map was used as the Pd-Ce proximity α. The results are shown in Table 1 and Figure 1 .

[0109] <Ce concentration β near Pd-based nanoparticles>

[0110] In the EDX elemental mapping image obtained through the above EDX analysis, n = 50 to 100 regions of 162.0 nm in length × 162.0 nm in width centered on Pd-based nanoparticles were randomly selected, and the concentrations of each element of Pd, Al, Ce, and other metal M in the selected regions were calculated based on the EDX elemental mapping data. Using the concentrations of each element obtained, the Ce concentration β [%] near the Pd-based nanoparticles was calculated using the following formula (2).

[0111]

[0112] In formula (2), n is the total number of selected regions, C Ce , C Pd , C Al , C MThe concentrations of Ce, Pd, Al, and other metal M in each extracted region are represented, respectively. The results are shown in Table 1 and... Figure 2 .

[0113] <Initial Pd Dispersion>

[0114] The catalyst powders obtained in the examples and comparative examples were calcined in the atmosphere at 500°C for 5 hours. 0.5 g of the calcined catalyst powder was filled into a U-shaped quartz sample tube and pretreated by heating at 300°C for 15 minutes while allowing O2 (100%) to flow through, followed by heating at 400°C for 15 minutes while allowing H2 (100%) to flow through. While cooling the pretreated catalyst powder to -78°C with dry ice, CO was pulsed multiple times at a pulse rate of 0.0188 ml / pulse. During this period, the amount of CO not adsorbed by the catalyst powder was measured using a thermal conductivity detector, and the number of pulses and the amount of CO adsorbed at adsorption saturation were determined. The initial Pd dispersion was calculated from the obtained CO adsorption amount and Pd loading using the following formula: Pd dispersion [%] = CO adsorption amount [mol] / Pd loading [mol] × 100. In addition, the initial average particle size of the Pd nanoparticles was calculated using the following formula (3). These results are shown in Table 1.

[0115]

[0116] In equation (3), f m M represents the shape factor (=6). Pd The atomic weight of Pd is ρ = 106.4 g / mol. Pd This indicates the density of Pd (=12.02 g / cm³). 3 ), N A R represents Avogadro's constant. Pd This represents the atomic radius of Pd (=1.37×10). -8 (cm), where D represents the initial Pd dispersion.

[0117] <Heat Resistance Test>

[0118] 10g of the catalyst powder obtained in the examples and comparative examples was subjected to cold pressing (CIP) for 1 minute at a pressure of 1 ton using a hydrostatic pressing device (Nikkiso Co., Ltd. "CK4-22-60"). The resulting molded body was then pulverized to form granules with a diameter of 0.5 to 1.0 mm. 2.0g of this catalyst granules was filled into a reaction tube, and a heat resistance test was conducted by alternating flow of concentrated gas (H2 (2 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (balance)) and dilute gas (O2 (1 vol%) + CO2 (10 vol%) + H2O (3 vol%) + N2 (balance)) at a flow rate of 0.5 L / min every 5 minutes, while heating at 1050°C for 25 hours.

[0119] <Pd dispersion after heat resistance test>

[0120] 0.5 g of the catalyst powder after the heat resistance test was filled into a U-shaped quartz sample tube. Pretreatment was performed by heating at 300°C for 15 minutes while allowing O2 (100%) to flow through, followed by heating at 400°C for 15 minutes while allowing H2 (100%) to flow through. The pretreated catalyst powder was then cooled to -78°C using dry ice, and CO was pulsed multiple times at 0.0188 ml / pulse under a He (100%) atmosphere. During this time, the amount of CO not adsorbed by the catalyst powder was measured using a thermal conductivity detector, and the number of pulses and the amount of CO adsorbed at adsorption saturation were determined.

[0121] The Pd dispersion after the heat resistance test was calculated using the obtained CO adsorption amount and Pd loading amount, according to the following formula: Pd dispersion [%] = CO adsorption amount [mol] / Pd loading amount [mol] × 100. The results are shown in Table 1 and Figure 3 .

[0122] In addition, the average particle size of the Pd-based nanoparticles after the heat resistance test was calculated using the following formula (3). The results are shown in Table 1.

[0123]

[0124] In equation (3), f m M represents the shape factor (=6). Pd The atomic weight of Pd is ρ = 106.4 g / mol. Pd This indicates the density of Pd (=12.02 g / cm³). 3 ), N A R represents Avogadro's constant. Pd This represents the atomic radius of Pd (=1.37×10). -8 (cm), where D represents the Pd dispersion.

[0125] <Solid reactants after heat resistance test>

[0126] Powder X-ray diffraction was performed on the catalyst powder after the heat resistance test to identify the solid reactants formed during the test. The results are presented below. Figure 4 See Table 1.

[0127] <Oxygen release rate>

[0128] 0.5 g of the catalyst powder after the heat resistance test was sealed into a 10 mm diameter sample holder and installed in a fixed-bed flow-through catalyst activity evaluation device (CATA-5000-7SP, manufactured by Best Tester Co., Ltd.). Pretreatment was performed by alternating between a concentrated gas (CO (2 vol%) + N2 (balance)) and a dilute gas (O2 (1 vol%) + N2 (balance)) at a flow rate of 10 L / min every 3 minutes, while heating the catalyst bed at a gas temperature of 600°C for 12 minutes. Subsequently, the gas temperature was maintained at 400°C, and the CO2 production was measured when the flow-through gas was switched from dilute to concentrated under steady-state conditions. The oxygen release rate was calculated from this CO2 production. The results are shown in Table 2 and... Figure 5 .

[0129] <Catalyst activity during cold start (C3H6 purification rate)>

[0130] 1.5g of the catalyst powder after the heat resistance test was sealed into a sample holder with a diameter of 18mm and installed in a fixed-bed flow-through catalyst activity evaluation device (CATA-5000-7SP manufactured by Best Tester Co., Ltd.). While alternating between concentrated gas (CO2 (10 vol%) + O2 (0.646 vol%) + CO (1.121 vol%) + NO (1200 ppm) + C3H6 (1600 ppm C) + H2 (0.374 vol%) + H2O (3 vol%) + N2 (balance)) and dilute gas (CO2 (10 vol%) + O2 (0.748 vol%) + CO (0.7 vol%) + NO (1200 ppm) + C3H6 (1600 ppm C) + H2 (0.233 vol%) + H2O (3 vol%) + N2 (balance)) at a flow rate of 20 L / min every 10 seconds, the catalyst bed is pretreated by heating it at a temperature of 600°C for 5 minutes, and then cooled by circulating N2 gas until the catalyst temperature reaches 50°C.

[0131] Next, an activity evaluation gas (CO2 (14 vol%) + O2 (0.55 vol%) + CO (0.52 vol%) + NO (3000 ppm) + C3H6 (3000 ppm C) + H2O (3 vol%) + N2 (balance)) heated to 750 °C was passed through the catalyst bed at a flow rate of 20 L / min. The concentration of C3H6 in the gas exiting the catalyst was measured at the time point when the catalyst temperature reached 400 °C, and the C3H6 purification rate was calculated. The results are shown in Table 2 and... Figure 6 .

[0132]

[0133] Table 2

[0134]

[0135] As shown in Table 1 and Figures 1-3 As shown, it was confirmed that in the catalysts (Examples 1-3) in which cerium dioxide nanoparticles and Pd-based nanoparticles were successively supported on ACZ powder, the Pd-Ce proximity α, the Ce concentration β near the Pd-based nanoparticles, and the Pd dispersion after the initial and heat resistance tests were all within the specified range.

[0136] On the other hand, it was found that the catalysts formed by physically mixing Pd / ACZ powder and cerium dioxide powder (Comparative Examples 1-2), the catalysts in which BaO nanoparticles and Pd-based nanoparticles were sequentially supported on ACZ powder (Comparative Example 4), the catalysts in which La2O3 nanoparticles and Pd-based nanoparticles were sequentially supported on ACZ powder (Comparative Example 5), the catalysts in which only Pd-based nanoparticles were supported on ACZ powder (Comparative Example 6), the catalysts in which both cerium dioxide nanoparticles and Pd-based nanoparticles were simultaneously supported on ACZ powder (Comparative Example 7), and the catalysts in which cerium dioxide nanoparticles and Pd-based nanoparticles were sequentially supported on alumina powder (Comparative Example 8) all exhibited a smaller Pd-Ce proximity α and a smaller Ce concentration β near the Pd-based nanoparticles. Furthermore, it was found that the initial Pd dispersion was smaller in the catalysts in which BaO nanoparticles and Pd-based nanoparticles were sequentially supported on ACZ powder (Comparative Example 4) and in the catalysts in which only Pd-based nanoparticles were supported on ACZ powder (Comparative Example 6). In addition, it is known that when cerium dioxide nanoparticles and Pd-based nanoparticles are simultaneously supported on ACZ powder catalyst (Comparative Example 7), the Pd dispersion decreases both initially and after the heat resistance test.

[0137] In addition, it can be seen that: although the Pd-Ce proximity α and the Ce concentration β near the Pd nanoparticles are within the specified range in the catalyst supported on ACZ powder (Comparative Example 3) with co-precipitate of cerium dioxide and Pd, the Pd dispersion is smaller in the initial and heat resistance tests.

[0138] As shown in Table 1 and Figure 4 As shown, the following catalysts were prepared: catalysts in which cerium dioxide nanoparticles and Pd-based nanoparticles were sequentially supported on ACZ powder (Examples 1-3); catalysts prepared by physically mixing Pd / ACZ powder and cerium dioxide powder (Comparative Examples 1-2); catalysts in which a co-precipitate of cerium dioxide and Pd was supported on ACZ powder (Comparative Example 3); catalysts in which only Pd-based nanoparticles were supported on ACZ powder (Comparative Example 6); and catalysts in which both cerium dioxide nanoparticles and Pd-based nanoparticles were simultaneously supported on ACZ powder (Comparative Example 7). In the catalyst where cerium dioxide nanoparticles and Pd-based nanoparticles were sequentially supported on alumina powder (Comparative Example 8), no solid-phase reactants were formed even after heat resistance tests. However, in the catalysts where BaO nanoparticles and Pd-based nanoparticles were sequentially supported on ACZ powder (Comparative Example 4) and La2O3 nanoparticles and Pd-based nanoparticles were sequentially supported on ACZ powder (Comparative Example 5), solid-phase reactions of Ba and La with the supported alumina and zirconium oxide occurred after heat resistance tests, generating BaAlO. x BaZrO3, LaAlO3.

[0139] As shown in Table 2 and Figure 5 As shown, the catalysts in which cerium dioxide nanoparticles and Pd-based nanoparticles are sequentially supported on ACZ powder (Examples 1-3) exhibit a faster oxygen release rate compared to catalysts formed by physically mixing Pd / ACZ powder and cerium dioxide powder (Comparative Examples 1-2), catalysts in which a co-precipitate of cerium dioxide and Pd is supported on ACZ powder (Comparative Example 3), catalysts in which BaO nanoparticles and Pd-based nanoparticles are sequentially supported on ACZ powder (Comparative Example 4), catalysts in which La2O3 nanoparticles and Pd-based nanoparticles are sequentially supported on ACZ powder (Comparative Example 5), catalysts in which cerium dioxide nanoparticles and Pd-based nanoparticles are simultaneously supported on ACZ powder (Comparative Example 7), and catalysts in which cerium dioxide nanoparticles and Pd-based nanoparticles are sequentially supported on alumina powder (Comparative Example 8).

[0140] Additionally, as shown in Table 2 and Figure 6As shown, the catalysts with cerium dioxide nanoparticles and Pd-based nanoparticles sequentially supported on ACZ powder (Examples 1-3) exhibit superior catalytic activity during cold start compared to catalysts formed by physically mixing Pd / ACZ powder and cerium dioxide powder (Comparative Examples 1-2), catalysts with a co-precipitate of cerium dioxide and Pd supported on ACZ powder (Comparative Example 3), catalysts with BaO nanoparticles and Pd-based nanoparticles sequentially supported on ACZ powder (Comparative Example 4), catalysts with La2O3 nanoparticles and Pd-based nanoparticles sequentially supported on ACZ powder (Comparative Example 5), catalysts with only Pd-based nanoparticles supported on ACZ powder (Comparative Example 6), catalysts with both cerium dioxide nanoparticles and Pd-based nanoparticles simultaneously supported on ACZ powder (Comparative Example 7), and catalysts with cerium dioxide nanoparticles and Pd-based nanoparticles sequentially supported on alumina powder (Comparative Example 8).

[0141] Based on the above results, a graph was plotted showing the Pd dispersion after the heat resistance test relative to the Pd-Ce similarity α. The results are shown below. Figure 7 Additionally, a graph was plotted showing the C3H6 purification rate at 400℃ relative to the oxygen release rate. The results are presented below. Figure 8 .contrast Figure 7 and Figure 8 It is evident that catalysts with high Pd-Ce proximity α and high Pd dispersion after heat resistance test (Example) exhibit superior oxygen release rate and C3H6 purification rate compared to catalysts with low Pd-Ce proximity α and low Pd dispersion after heat resistance test (Comparative Example).

[0142] As explained above, according to the present invention, an exhaust gas purification catalyst exhibiting excellent catalytic activity at low temperatures and excellent oxygen uptake and release performance after exposure to high temperatures can be obtained. Therefore, the exhaust gas purification catalyst of the present invention is useful as a catalyst for purifying harmful components such as hydrocarbons (HC) contained in gases emitted from internal combustion engines such as automobile engines.

Claims

1. A catalyst for exhaust gas purification, comprising a component of the formula CeO supported on a composite metal oxide carrier containing alumina, cerium dioxide, and zirconium oxide. 2-x The cerium dioxide nanoparticles are followed by Pd-based nanoparticles composed of Pd or Pd oxides, wherein... 0≤x<0.5， The molar ratio of Ce to Pd supported on the composite metal oxide carrier, i.e., Ce / Pd, is 1 to 8. Based on the Pd and Ce distribution maps obtained from the elemental mapping images by energy-dispersive X-ray analysis, the proximity α between Pd and Ce, calculated using the following equation (1), is 0.15–0.

50. In equation (1), I(i,j) represents the luminance value in region (i,j) that is the i-th region in the horizontal direction and the j-th region in the vertical direction when the Pd distribution map is divided into M horizontal sections and N vertical sections. ave T represents the average luminance value in the Pd distribution map, and T(i,j) represents the luminance value in the region (i,j) that is the i-th region in the horizontal direction and the j-th region in the vertical direction when the Ce distribution map is divided into M horizontal and N vertical sections. ave This represents the average luminance value in the Ce distribution map. While alternating between concentrated and dilute gases at a flow rate of 0.5 L / min every 5 minutes, the Pd dispersion after a heat resistance test at 1050°C for 25 hours was greater than 0.8%. The concentrated gas consisted of 2 vol% H2 + 10 vol% CO2 + 3 vol% H2O + balance N2, and the dilute gas consisted of 1 vol% O2 + 10 vol% CO2 + 3 vol% H2O + balance N2. Cerium dioxide nanoparticles are loaded onto the composite metal oxide carrier by impregnating the composite metal oxide carrier containing alumina, cerium dioxide, and zirconium oxide with a compound containing tetravalent Ce.

2. The catalyst for exhaust gas purification according to claim 1, Based on the elemental mapping image obtained by energy-dispersive X-ray analysis, the Ce concentration β near the Pd-based nanoparticles, calculated using the following equation (2), is greater than 16%. In equation (2), n is the total number of regions of 162.0 nm x 162.0 nm randomly selected from the elemental mapping image, centered on the Pd-based nanoparticles, and C Ce C Pd C Al C M These represent the concentrations of Ce, Pd, Al, and other metal M in the extracted regions, respectively.

3. The catalyst for exhaust gas purification according to claim 1, The dispersion of Pd in ​​the atmosphere after heating at 500°C for 5 hours is greater than 15%.

4. The catalyst for exhaust gas purification according to claim 2, The dispersion of Pd in ​​the atmosphere after heating at 500°C for 5 hours is greater than 15%.

5. A method for manufacturing a catalyst for exhaust gas purification according to any one of claims 1-4, The composite metal oxide support containing alumina, cerium dioxide, and zirconium oxide is supported by a CeO2 composition. 2-x After representing cerium dioxide nanoparticles, Pd-based nanoparticles composed of Pd or Pd oxides are supported, such that the molar ratio of Ce to Pd supported on the composite metal oxide carrier, i.e., Ce / Pd, is 1 to 8, wherein... 0≤x<0.5， Cerium dioxide nanoparticles are loaded onto the composite metal oxide carrier by impregnating the composite metal oxide carrier containing alumina, cerium dioxide, and zirconium oxide with a compound containing tetravalent Ce.

6. The method for manufacturing the catalyst for exhaust gas purification according to claim 5, The compound containing tetravalent Ce is a tetravalent Ce nitrate.

7. The method for manufacturing the catalyst for exhaust gas purification according to claim 5, The Pd-based nanoparticles are loaded onto the composite metal oxide carrier by impregnating it with palladium nitrate.

8. The method for manufacturing the catalyst for exhaust gas purification according to claim 6, The Pd-based nanoparticles are loaded onto the composite metal oxide carrier by impregnating it with palladium nitrate.

Images