Three-way catalyst with hollow structure, preparation method of three-way catalyst and motor vehicle after-treatment catalyst

Abstract

The invention relates to the field of catalytic materials, and particularly provides a three-way catalyst with a hollow structure, a preparation method of the three-way catalyst and an after-treatment catalyst of a motor vehicle. The preparation method of the three-way catalyst with the hollow structure comprises the following steps: A, primary crystallization: uniformly mixing a noble metal precursor, a ligand and water to obtain a noble metal complexing solution; mixing a silicon source, an optional aluminum source, a first template agent, the precious metal complexing solution and water to obtain a first mixed solution; transferring the first mixed solution into a closed reaction kettle for primary crystallization reaction, and then separating and washing a product to obtain a solid; b, secondary crystallization: mixing the solid, a second template agent and water to obtain a second mixed solution; and transferring the second mixed solution into a closed reaction kettle for secondary crystallization reaction, and then separating and washing the product to obtain the three-way catalyst with the hollow structure. The catalyst provided by the invention has the advantages of low cost, high catalytic efficiency and long service life.

Description

Technical Field

[0001] The present invention relates to the field of catalytic materials, and in particular, to a hollow-structured three-way catalyst, a preparation method thereof, and a motor vehicle aftertreatment catalytic converter. Background Art

[0002] With the increasing global awareness of environmental protection and the rapid development of clean energy technologies, natural gas, as an important clean energy, has been widely used in the transportation field. In particular, the popularization of natural gas vehicles (NGVs) has provided strong support for reducing carbon emissions and improving air quality. Existing natural gas vehicles mainly adopt the technical route of stoichiometric combustion engines combined with three-way catalysts, and usually use noble metal / oxide catalytic materials as three-way catalysts to simultaneously remove carbon monoxide (CO), methane (CH4), and nitrogen oxides (NOx) in the exhaust gas.

[0003] Existing three-way catalytic materials face the following several technical problems. First, the methane oxidation reaction usually requires a relatively high temperature. Reducing the reaction temperature requires a relatively high content of noble metal catalysts, which increases the cost of the aftertreatment system. Second, the dispersion of noble metals on traditional catalyst carriers is low, the particle size is large, and the surface active sites are not fully exposed, which affects the catalytic efficiency. Finally, the exhaust gas of natural gas vehicles contains a relatively high water vapor concentration. In a high-temperature and high-humidity environment, the noble metal active sites are prone to physical and chemical changes, such as sintering and decomposition, resulting in rapid aging and inactivation of the catalyst and shortening the service life of the catalyst.

[0004] In view of this, the present invention is specifically proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a hollow-structured three-way catalyst, a preparation method thereof, and a motor vehicle aftertreatment catalytic converter to solve the problems of high cost, low catalytic efficiency, and short service life existing in the prior art.

[0006] To achieve the above object of the present invention, the following technical solutions are specifically adopted: In the first aspect, the present invention provides a preparation method of a hollow-structured three-way catalyst, including the following steps: A. Primary crystallization: Mix a noble metal precursor, a ligand, and water evenly to obtain a noble metal complex solution; Mix a silicon source, an optional aluminum source, a first template agent, the noble metal complex solution, and water to obtain a first mixed solution; Transfer the first mixed solution to a sealed reaction kettle for a primary crystallization reaction, and then separate and wash the product to obtain a solid; B. Secondary crystallization: Mix the solid, a second template agent, and water to obtain a second mixed solution; Transfer the second mixed solution into a sealed reaction kettle for secondary crystallization reaction, and then separate and wash the product to obtain a hollow-structured three-way catalyst.

[0007] As a further preferred technical solution, the primary crystallization duration is 6 to 96 h, and the crystallization temperature is 130 to 200 °C.

[0008] As a further preferred technical solution, the secondary crystallization duration is 6 to 48 h, and the crystallization temperature is the same as the primary crystallization temperature.

[0009] As a further preferred technical solution, in step B, the concentration after mixing the second template agent and the water is 0.1 to 1 M.

[0010] As a further preferred technical solution, the noble metal includes at least one of Pd, Pt, Rh or Ru.

[0011] In a second aspect, the present invention provides a hollow-structured three-way catalyst obtained by the above preparation method. The catalyst includes a hollow outer shell composed of molecular sieve and noble metal particles located inside the molecular sieve; the thickness of the hollow outer shell is 2 to 40 nm; the size of the noble metal particles is 1.5 to 30 nm.

[0012] As a further preferred technical solution, the molecular sieve structure is at least one of MFI, CHA, BEA, AEI, LTA and FAU.

[0013] As a further preferred technical solution, the molecular sieve contains silicon element, or contains both silicon element and aluminum element at the same time; when the molecular sieve contains aluminum element, the molar ratio of silicon element to aluminum element is not less than 6:1.

[0014] As a further preferred technical solution, the mass content of the noble metal in the catalyst is 0.5% to 3%.

[0015] In a third aspect, the present invention provides a motor vehicle aftertreatment catalytic converter, including the above hollow-structured three-way catalyst.

[0016] Compared with the prior art, the beneficial effects of the present invention are: The three-way catalyst with a hollow structure provided by the present application uses a molecular sieve material as the outer shell. The confinement effect of the pore structure of the molecular sieve reduces the size of individual noble metal particles formed during the primary crystallization, increases the dispersion degree of noble metal active sites, and improves the catalytic reaction efficiency. During the process of secondary crystallization to form a hollow structure, the noble metals in the molecular sieve accumulate to form small particles inside, which can effectively exert the synergistic effect between noble metal atoms. At the same time, the particle structure is loose, which is conducive to the transmission and transfer of gas molecules. The hollow structure increases the number of acidic sites of the molecular sieve material, promotes the adsorption and dissociation of reactant molecules, and the hollow internal structure provides sufficient space for the migration of noble metal active sites, thereby improving the catalytic activity. Under the protection of the molecular sieve outer shell, the influence of water vapor on the noble metal is inhibited, and at the same time, the active sites cannot escape to the outside of the molecular sieve under the structural restriction, effectively reducing the loss of noble metals at high temperatures, greatly improving the hydrothermal stability of the catalyst, and increasing the service life. And because not too much noble metal is needed, the cost is reduced.

[0017] In the preparation method of the three-way catalyst with a hollow structure of the present application, no organosilane needs to be introduced during the synthesis of the molecular sieve, and the surface of the synthesized hollow molecular sieve is smoother and more regular. The molecular sieve particles can better maintain the hollow and non-damaged morphology, which is beneficial to the stability of noble metals inside the molecular sieve and protects them from being easily lost to the outside of the molecular sieve. This method can obtain the required catalyst by two crystallizations, which is easy to implement industrially and has a low cost. Description of the Drawings

[0018] Figure 1 It is the transmission electron microscope (TEM) image of the catalyst in Example 1; Figure 2 It is the conversion rate curve of CH4 during the three-way catalytic reaction of the catalysts in Examples 1-2 and Comparative Examples 1-2; Figure 3 It is the conversion rate curve of CO during the three-way catalytic reaction of the catalysts in Examples 1-2 and Comparative Examples 1-2; Figure 4 It is the conversion rate curve of NO during the three-way catalytic reaction of the catalysts in Examples 1-2 and Comparative Examples 1-2; Figure 5 It is the conversion rate curve of CH4 during the three-way catalytic reaction of the catalysts in Examples 1-2 and Comparative Examples 1-2 after hydrothermal aging; Figure 6 It is the conversion rate curve of CO during the three-way catalytic reaction of the catalysts in Examples 1-2 and Comparative Examples 1-2 after hydrothermal aging; Figure 7 It is the conversion rate curve of NO during the three-way catalytic reaction of the catalysts in Examples 1-2 and Comparative Examples 1-2 after hydrothermal aging. Detailed Embodiments

[0019] The following will describe the implementation embodiments of the present invention in detail in conjunction with the embodiments. However, those skilled in the art will understand that the following embodiments are only used to illustrate the present invention and should not be regarded as limiting the scope of the present invention. For those not specified in the embodiments, they are carried out according to conventional conditions or conditions recommended by the manufacturer.

[0020] On the one hand, the present application provides a method for preparing a hollow-structured three-way catalyst, comprising the following steps: A. Primary crystallization: Mix the noble metal precursor, ligand and water evenly to obtain a noble metal complex solution; Mix the silicon source, optionally the aluminum source, the first template agent, the noble metal complex solution and water to obtain a first mixed solution; Transfer the first mixed solution to a closed reaction kettle for primary crystallization reaction, and then separate and wash the product to obtain a solid; B. Secondary crystallization: Mix the solid, the second template agent and water to obtain a second mixed solution; Transfer the second mixed solution to a closed reaction kettle for secondary crystallization reaction, and then separate and wash the product to obtain a hollow-structured three-way catalyst.

[0021] The above preparation method has low requirements for equipment and can be completed with conventional hydrothermal reaction equipment. It can accurately control the morphology and size of the catalyst by adjusting the raw material ratio and reaction time. By sequentially adding the noble metal complex solution, silicon source, optionally aluminum source, template agent and water, stirring and undergoing two crystallizations, the required catalytic material can be obtained. This material has the required structure and has good catalytic performance and hydrothermal stability.

[0022] In an alternative embodiment, the primary crystallization duration is 6 - 96 h, and the crystallization temperature is 130 - 200 °C. The primary crystallization duration is typically but not limited to 6, 12, 24, 26, 48, 60, 72, 84 or 96 h, preferably 60 - 72 h; the crystallization temperature is typically but not limited to 130, 140, 150, 160, 170, 180, 190 or 200 °C, preferably 140 - 170 °C. If the primary crystallization duration is less than 6 h, the crystallization degree of the catalyst is low, the yield is low, and the catalyst cost is high. If the primary crystallization duration is more than 96 h, the catalyst yield is high but the synthesis cycle is long, affecting the production efficiency.

[0023] In an alternative embodiment, the duration of the secondary crystallization is 6 to 48 h, and the crystallization temperature is the same as the primary crystallization temperature. The duration of the secondary crystallization is typically but not limited to 6, 12, 24, 26 or 48 h, preferably 6 to 24 h; the crystallization temperature is the same as the primary crystallization temperature. When the secondary crystallization time is less than 6 h, the hollow structure formed in the catalyst is not obvious. When the secondary crystallization time is greater than 48 h, the catalyst is overly dissolved, and the morphology of the formed hollow molecular sieve particles is irregular.

[0024] In an alternative embodiment, in step B, the concentration after mixing the second template agent and the water is 0.1 to 1 M. The above concentration is typically but not limited to 0.1, 0.2, 0.3, 0.4, 0.5, 0.6, 0.7, 0.8, 0.9 or 1 M, preferably 0.1 to 0.3 M. When the concentration of the secondary crystallization template agent is less than 0.1 M, the hollow structure formed in the catalyst is not obvious. When the concentration of the secondary crystallization template agent is greater than 1 M, the catalyst is overly dissolved, and the morphology of the formed hollow molecular sieve particles is irregular.

[0025] In an alternative embodiment, the noble metal includes at least one of Pd, Pt, Rh or Ru. The noble metal includes but is not limited to: Pd, Pt, Rh, Ru, combinations of Pd and Pt, combinations of Pt and Rh, combinations of Rh and Ru, combinations of Pd, Pt and Rh, combinations of Pt, Rh and Ru, combinations of Pd, Pt and Ru, or combinations of Pd, Pt, Rh and Ru, etc.

[0026] Optionally, the first template agent and the second template agent may be the same or different. The first template agent and the second template agent may be triethylamine, tetraethylammonium hydroxide, tetrapropylammonium hydroxide, cetyltrimethylammonium bromide, N,N,N-trimethyl-1-adamantylammonium hydroxide or polyvinylpyrrolidone.

[0027] Optionally, the noble metal precursor includes palladium chloride, palladium nitrate, chloroplatinic acid, platinum nitrate, rhodium chloride, rhodium nitrate, hexammine rhodium(III) chloride, ruthenium chloride or ruthenium nitrate.

[0028] Optionally, the ligand includes ethylenediamine, tetraethylenepentamine, pentaethylenehexamine or triethanolamine.

[0029] Optionally, the silicon source includes silica, tetraethyl orthosilicate, silica sol or pure silica molecular sieve.

[0030] Optionally, the aluminum source includes aluminum sulfate, aluminum nitrate, aluminum chloride, aluminum hydroxide, alumina, sodium aluminate, aluminum isopropoxide, aluminum sec-butoxide, aluminum powder or an organic complex of aluminum.

[0031] On the other hand, the present application provides a three-way catalyst with a hollow structure, which is obtained by the above preparation method. The catalyst includes a hollow outer shell composed of molecular sieve and noble metal particles located inside the molecular sieve; the thickness of the hollow outer shell is 2 - 40 nm; the size of the noble metal particles is 1.5 - 30 nm.

[0032] Among them, the thickness of the above-mentioned hollow outer shell is typically but not limited to 2, 5, 10, 15, 20, 25, 30, 35 or 40 nm, and preferably 2 - 15 nm. The size of the above-mentioned noble metal particles is typically but not limited to 1.5, 3, 5, 10, 15, 20, 25 or 30 nm, and preferably 15 - 25 nm.

[0033] In the present invention, by adjusting the process conditions of the first crystallization and the second crystallization, the thickness of the hollow outer shell and the size of the noble metal particles are precisely controlled. The thickness of the hollow outer shell is mainly affected by the template agent concentration and the crystallization time during the second crystallization. The higher the template agent concentration and the longer the crystallization time, the greater the dissolution degree of the molecular sieve outer shell, and the thinner the thickness of the hollow structure outer shell. By adjusting the template agent concentration (0.1 - 1 M) and the crystallization time (6 - 48 h), precise regulation of the outer shell thickness within the range of 2 - 40 nm can be achieved. The size of the noble metal particles is mainly affected by the dispersion degree of the noble metal complex solution, the noble metal content, and the crystallization temperature during the first crystallization. The higher the dispersion degree of the noble metal complex solution, the lower the noble metal content, and the lower the crystallization temperature, the smaller the size of the noble metal particles. By adjusting the crystallization temperature (130 - 200 °C) and the crystallization time (6 - 96 h), precise regulation of the noble metal particle size within the range of 1.5 - 30 nm can be achieved.

[0034] The above-mentioned three-way catalyst with a hollow structure uses a molecular sieve material as the outer shell. The confinement effect of the molecular sieve pore structure reduces the size of individual noble metal particles formed during the first crystallization, increases the dispersion degree of noble metal active sites, and improves the catalytic reaction efficiency; during the process of forming a hollow structure by the second crystallization, the noble metals in the molecular sieve accumulate to form small particles inside, as Figure 1 shown, which can effectively exert the synergistic effect between noble metal atoms; at the same time, the particle structure is loose, which is conducive to the transmission and transfer of gas molecules. The hollow structure increases the number of acidic sites of the molecular sieve material and promotes the adsorption and dissociation of reactant molecules. The hollow internal structure provides sufficient space for the migration of noble metal active sites, inhibits the influence of water vapor on noble metals under the protection of the molecular sieve outer shell, and at the same time, the active sites cannot escape to the outside of the molecular sieve under the structural restriction, effectively reducing the loss of noble metals at high temperatures and greatly improving the hydrothermal stability of the catalyst.

[0035] In an alternative embodiment, the molecular sieve structure is at least one of MFI, CHA, BEA, AEI, LTA, and FAU. The above molecular sieve structures include, but are not limited to, MFI, CHA, BEA, AEI, LTA, FAU, combinations of MFI and CHA, combinations of CHA and BEA, combinations of BEA and AEI, combinations of AEI and LTA, combinations of LTA and FAU, combinations of MFI, CHA, and BEA, combinations of CHA, BEA, and AEI, combinations of AEI, LTA, and FAU, combinations of MFI, CHA, BEA, and AEI, combinations of BEA, AEI, LTA, and FAU, etc.

[0036] In an alternative embodiment, the molecular sieve contains silicon element, or contains both silicon element and aluminum element; when the molecular sieve contains aluminum element, the molar ratio of silicon element to aluminum element is not less than 6:1. Since the silicon-based molecular sieve has good hydrophobic properties, the water resistance of the catalyst can be effectively improved by increasing the proportion of silicon element; while the aluminum element improves the acidic sites of the catalyst, provides more adsorption sites for the reaction gas, and promotes the catalytic reaction. If the molar ratio of silicon element to aluminum element is less than 6:1, the crystallization of the molecular sieve will be negatively affected.

[0037] In an alternative embodiment, the mass content of the noble metal in the catalyst is 0.5% - 3%. The mass content of the noble metal is typically but not limited to 0.5%, 0.7%, 1.9%, 1%, 1.5%, 2%, 2.5%, or 3%, preferably 1% - 1.5%. If the mass content of the noble metal is less than 0.5%, the three-way catalytic efficiency decreases. If the mass content of the noble metal is higher than 3%, the catalyst cost is relatively high.

[0038] On the other hand, the present invention provides a motor vehicle after-treatment catalytic converter, including the above-mentioned hollow structure three-way catalyst. This motor vehicle after-treatment catalytic converter includes the above-mentioned hollow structure three-way catalyst, and thus has at least the same advantages as this catalyst.

[0039] The present invention will be further described in detail below with reference to examples and comparative examples.

[0040] Example 1 A preparation method of a hollow structure three-way catalyst includes the following steps: A. Mix 0.0954 g of palladium chloride, 0.1617 g of ethylenediamine and 5 g of water evenly to obtain a noble metal complex solution; mix 15.18 g of tetraethyl orthosilicate, 23.71 g of tetrapropylammonium hydroxide (25% aqueous solution), the noble metal complex solution and 23.13 g of water, and stir to obtain a mixture; transfer the mixture to a closed reaction kettle for the first crystallization reaction, the crystallization reaction temperature is 170 °C, the reaction duration is 72 h, and separate and wash the product to obtain a solid; B. Mix 2 g of the solid obtained from the first crystallization with 20 mL of a 0.2 M tetrapropylammonium hydroxide solution (including water and the second template agent - tetrapropylammonium hydroxide), and stir to obtain a mixture; transfer the mixture to a closed reaction kettle for the second crystallization reaction, the crystallization reaction temperature is 170 °C, the reaction duration is 24 h, and separate and wash the product to obtain a three-way catalyst with a hollow structure, the Pd loading is 1.3 wt%, the thickness of the hollow outer shell is 16 nm, the Pd particle size is 21 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0 (that is, there is no aluminum element).

[0041] That is, Example 1 is a three-way catalyst with a hollow structure obtained through two crystallizations.

[0042] Example 2 A method for preparing a three-way catalyst with a hollow structure includes the following steps: A. Use the same method as in Example 1 to obtain the solid after the first crystallization.

[0043] B. The concentration of tetrapropylammonium hydroxide used is 0.1 M, and the others are the same as in Example 1.

[0044] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow outer shell is 18 nm, the Pd particle size is 20 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0.

[0045] Example 3 A method for preparing a three-way catalyst with a hollow structure includes the following steps: A. Use the same method as in Example 1 to obtain the solid after the first crystallization.

[0046] B. The concentration of tetrapropylammonium hydroxide used is 0.3 M, and the others are the same as in Example 1.

[0047] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow outer shell is 11 nm, the Pd particle size is 23 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0.

[0048] Example 4 A preparation method of a hollow-structured three-way catalyst, comprising the following steps: A. Using the same method as in Example 1, a solid after primary crystallization is obtained.

[0049] B. The concentration of tetrapropylammonium hydroxide used is 0.1 M, and the duration of the secondary crystallization reaction is 12 h. Other conditions are the same as in Example 1.

[0050] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow shell is 29 nm, the Pd particle size is 5 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0.

[0051] Example 5 A preparation method of a hollow-structured three-way catalyst, comprising the following steps: A. Using the same method as in Example 1, a solid after primary crystallization is obtained.

[0052] B. The duration of the secondary crystallization reaction is 12 h. Other conditions are the same as in Example 1.

[0053] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow shell is 24 nm, the Pd particle size is 9 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0.

[0054] Example 6 A preparation method of a hollow-structured three-way catalyst, comprising the following steps: A. Using the same method as in Example 1, a solid after primary crystallization is obtained.

[0055] B. The concentration of tetrapropylammonium hydroxide used is 0.3 M, and the duration of the secondary crystallization reaction is 12 h. Other conditions are the same as in Example 1.

[0056] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow shell is 21 nm, the Pd particle size is 7 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0.

[0057] Example 7 A preparation method of a hollow-structured three-way catalyst, comprising the following steps: A. The primary crystallization duration is 96 h, and the crystallization temperature is 130 °C.

[0058] B. The secondary crystallization duration is 48 h, and the crystallization temperature is 130 °C.

[0059] Other conditions are the same as in Example 1.

[0060] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow shell is 32 nm, the Pd particle size is 6 nm, the molecular sieve structure is MFI, and the molar ratio of silicon to aluminum in the molecular sieve is 1:0.

[0061] Example 8 A preparation method of a hollow-structured three-way catalyst, comprising the following steps: A. The primary crystallization duration is 6 h, and the crystallization temperature is 200 °C.

[0062] B. The secondary crystallization duration is 6 h, and the crystallization temperature is 200 °C.

[0063] Other conditions are the same as in Example 1.

[0064] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow shell is 22 nm, the Pd particle size is 18 nm, the molecular sieve structure is MFI, and the molar ratio of silicon to aluminum in the molecular sieve is 1:0.

[0065] Example 9 A preparation method of a hollow-structured three-way catalyst, comprising the following steps: A. Using the same method as in Example 1, a solid after primary crystallization is obtained.

[0066] B. The concentration of tetrapropylammonium hydroxide used is 1 M, and other conditions are the same as in Example 1.

[0067] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow shell is 8 nm, the Pd particle size is 25 nm, the molecular sieve structure is MFI, and the molar ratio of silicon to aluminum in the molecular sieve is 1:0.

[0068] Example 10 A preparation method of a hollow-structured three-way catalyst, comprising the following steps: A. 0.0367 g of palladium chloride, 0.1617 g of ethylenediamine and 5 g of water are mixed evenly to obtain a noble metal complex solution, and other conditions are the same as in Example 1.

[0069] B. Using the same method as in Example 1.

[0070] In the obtained catalyst: the Pd loading is 0.5 wt%, the thickness of the hollow shell is 18 nm, the Pd particle size is 1.8 nm, the molecular sieve structure is MFI, and the molar ratio of silicon to aluminum in the molecular sieve is 1:0.

[0071] Example 11 A preparation method of a hollow-structured three-way catalyst, comprising the following steps: A. Mix 0.2202 g of palladium chloride, 0.1617 g of ethylenediamine, and 5 g of water evenly to obtain a precious metal complex solution. The other steps are the same as in Example 1.

[0072] B. Use the same method as in Example 1.

[0073] In the obtained catalyst: the Pd loading is 3 wt%, the thickness of the hollow shell is 16 nm, the Pd particle size is 28 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0.

[0074] Example 12 A method for preparing a hollow-structured three-way catalyst includes the following steps: A. Mix 0.0954 g of palladium chloride, 0.1617 g of ethylenediamine, and 5 g of water evenly to obtain a precious metal complex solution; mix 13.01 g of tetraethyl orthosilicate, 0.812 g of aluminum hydroxide, 23.71 g of tetrapropylammonium hydroxide (25% aqueous solution), the precious metal complex solution, and 23.13 g of water, stir to obtain a mixed solution; transfer the mixed solution to a closed reaction kettle for the first crystallization reaction, the crystallization reaction temperature is 170 °C, the reaction duration is 72 h, and separate and wash the product to obtain a solid; B. Use the same method as in Example 1.

[0075] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow shell is 4 nm, the Pd particle size is 25 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 6:1.

[0076] Example 13 A method for preparing a hollow-structured three-way catalyst includes the following steps: A. Mix 0.0954 g of palladium chloride, 0.1617 g of ethylenediamine, and 5 g of water evenly to obtain a precious metal complex solution; mix 13.45 g of tetraethyl orthosilicate, 0.406 g of aluminum hydroxide, 23.71 g of tetrapropylammonium hydroxide (25% aqueous solution), the precious metal complex solution, and 23.13 g of water, stir to obtain a mixed solution; transfer the mixed solution to a closed reaction kettle for the first crystallization reaction, the crystallization reaction temperature is 170 °C, the reaction duration is 72 h, and separate and wash the product to obtain a solid; B. Use the same method as in Example 1.

[0077] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow shell is 11 nm, the Pd particle size is 23 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 12:1.

[0078] Example 14 A method for preparing a hollow-structured three-way catalyst includes the following steps: A. The primary crystallization duration is 100 h, and the crystallization temperature is 120 °C; B. The secondary crystallization duration is 60 h, and the crystallization temperature is 120 °C; The rest are the same as in Example 1.

[0079] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow outer shell is 23 nm, the Pd particle size is 17 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0.

[0080] Example 15 A method for preparing a hollow-structured three-way catalyst includes the following steps: A. The same as in Example 1; B. The concentration of the second template agent used is 1.5 M; the rest are the same as in Example 1.

[0081] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow outer shell is 5 nm, the Pd particle size is 28 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0.

[0082] Comparative Example 1 A method for preparing a three-way catalyst includes the following steps: Mix 0.0954 g of palladium chloride, 0.1617 g of ethylenediamine, and 5 g of water evenly to obtain a noble metal complex solution; mix 15.18 g of tetraethyl orthosilicate, 23.71 g of tetrapropylammonium hydroxide (25% aqueous solution), the noble metal complex solution, and 23.13 g of water and stir to obtain a mixed solution; transfer the mixed solution to a closed reaction kettle for the first crystallization reaction, the crystallization reaction temperature is 170 °C, the reaction duration is 72 h, and separate and wash the product to obtain a three-way catalyst with a Pd loading of 1.3 wt%.

[0083] That is, Comparative Example 1 is a non-hollow-structured three-way catalyst obtained by one crystallization.

[0084] Comparative Example 2 A method for preparing an impregnation-type three-way catalyst includes the following steps: 15.18 g of tetraethyl orthosilicate, 28.71 g of tetrapropylammonium hydroxide (25% aqueous solution), and 23.13 g of water were mixed and stirred to obtain a mixed solution; the mixed solution was transferred to a closed reaction kettle for the first crystallization reaction. The crystallization reaction temperature was 170 °C, and the reaction duration was 72 h. The product was separated and washed to obtain a molecular sieve support material. 5 g of the molecular sieve support material was added to 2.5 g of palladium nitrate solution, stirred and left standing for 2 h, then dried at 80 °C for 6 h, and then calcined at 550 °C for 3 h to obtain a three-way catalyst with a Pd loading of 1.3 wt%.

[0085] That is, Comparative Example 2 is a supported catalyst prepared by the impregnation method.

[0086] Comparative Example 3 A method for preparing a three-way catalyst, in which tetraethyl orthosilicate is replaced by 3-aminopropyltrimethoxysilane, and the others are the same as in Example 1.

[0087] In the obtained catalyst: the Pd loading is 1.3 wt%, the Pd particle size is 89 nm, and the molar ratio of silicon element to aluminum element in the catalyst is 1:0.

[0088] Comparative Example 4 A method for preparing a hollow-structured three-way catalyst, comprising the following steps: A. 15.18 g of tetraethyl orthosilicate, 23.71 g of tetrapropylammonium hydroxide (25% aqueous solution), and 28.13 g of water were mixed and stirred to obtain a mixed solution; the mixed solution was transferred to a closed reaction kettle for the first crystallization reaction. The crystallization reaction temperature was 170 °C, and the reaction duration was 72 h. The product was separated and washed to obtain a solid; B. 2 g of the solid obtained from the first crystallization was mixed and stirred with 20 mL of a tetrapropylammonium hydroxide solution with a concentration of 0.2 M (including water and the second template - tetrapropylammonium hydroxide) to obtain a mixed solution; the mixed solution was transferred to a closed reaction kettle for the second crystallization reaction. The crystallization reaction temperature was 170 °C, and the reaction duration was 24 h. The product was separated and washed to obtain a molecular sieve support with a hollow structure.

[0089] C. 5 g of the molecular sieve support material was added to 2.5 g of palladium nitrate solution, stirred and left standing for 2 h, then dried at 80 °C for 6 h, and then calcined at 550 °C for 3 h to obtain a three-way catalyst with a Pd loading of 1.3 wt%.

[0090] In the obtained catalyst: the Pd loading is 1.3 wt%, the thickness of the hollow outer shell is 18 nm; the Pd particle size is 28 nm, the molecular sieve structure is MFI, and the molar ratio of silicon element to aluminum element in the molecular sieve is 1:0.

[0091] Performance test 1. Catalyst activity test The catalysts prepared in Examples 1 - 15 and Comparative Examples 1 - 4 were evaluated for catalyst activity on a simulated atmosphere evaluation system. The activity test atmosphere was 1000 ppm CH4, 1000 ppm NO, 5000 ppm CO, 3500 ppm O2, 10 vol.% H2O, 10 vol.% CO2, and N2 was used as the balance gas, with a space velocity of 50000 h -1 . The activity test results are shown in Table 1, and some of the test results are as Figures 2 to 4 shown

[0092] 2. Catalyst hydrothermal aging treatment The catalysts prepared in Examples 1 - 15 and Comparative Examples 1 - 4 were subjected to hydrothermal aging treatment in a tube furnace. The hydrothermal aging treatment atmosphere was 10 vol. H2O, 15 vol.% O2, and N2 was used as the balance gas, and the aging treatment duration was 12 h. The aged catalysts were subjected to activity tests, and the results are shown in Table 1 and Figures 5 to 7 shown

[0093] Table 1 Activity test results of the catalysts in Examples 1 - 15 and Comparative Examples 1 - 4

[0094] Among them, the light-off temperature refers to the temperature at which the pollutant conversion rate reaches 50%. The better the activity of the catalyst, the lower the corresponding light-off temperature

[0095] From Table 1 and Figures 2 to 7It can be seen that Examples 1 to 15 prepared by the method of the present invention all have stable and efficient three-way catalytic effects. Comparative Example 1 is a molecular sieve catalyst that only undergoes one-step crystallization, and Examples 1 to 15 are catalysts with a hollow structure prepared by two-step crystallization. By comparing the performance of fresh samples, it can be seen that the hollow structure formed by two-step crystallization can improve the performance of the catalyst under certain conditions, especially showing better stability after hydrothermal aging. It shows that the formation of the hollow structure not only does not damage the catalytic effect of the catalyst, but also can further promote the synergy between active sites due to the loose structure formed by the active sites, improving the catalytic effect and reducing the light-off temperature under specific conditions. After aging, the three-way catalytic effects of Comparative Example 1 and Examples 1 to 15 were tested again. The catalyst of Comparative Example 1 showed obvious deactivation after aging, while Examples 1 to 15 showed excellent stability in the catalytic performance of CH4 and NO; especially for CH4, the change range of the CH4 light-off temperature after aging was less than 4 °C. It shows that the formed hollow structure can effectively improve the hydrothermal aging resistance of the three-way catalyst to CH4 and NO. In terms of the catalytic performance of CO, the light-off temperatures of some examples are higher than that of Comparative Example 1, which is related to the sensitivity of the CO catalytic reaction to the particle size and dispersion of noble metal particles. Nevertheless, Examples 1-15 are still superior to Comparative Example 1 in terms of overall catalytic performance and hydrothermal stability.

[0096] For the catalyst of Comparative Example 2, the method of first synthesizing hollow molecular sieve and then impregnating noble metal was adopted, and the catalytic performance of its fresh sample decreased significantly compared with Examples 1 to 15. After the catalyst of Comparative Example 2 was hydrothermally aged, the catalyst performance for CH4 and NO further decreased, indicating that the position and morphology of the noble metal in the hollow molecular sieve greatly affect the performance of the catalyst. By comparing the sum of the change ranges of the light-off temperatures of CH4, CO and NO before and after hydrothermal aging of the three-way catalyst, it was found that the range of the sum of the change ranges of the light-off temperatures of Examples 1 to 15 after hydrothermal aging compared with before aging was -11 to 28 °C, and the range of the sum of the change ranges of the light-off temperatures of Comparative Examples 1 to 4 after hydrothermal aging compared with before aging was 39 to 61 °C, indicating that the method adopted in the present invention can effectively utilize the protective effect of the hollow structure on the noble metal and improve the hydrothermal stability of the three-way catalyst.

[0097] Although the present invention has been illustrated and described with specific examples, it should be realized that many other changes and modifications can be made without departing from the spirit and scope of the present invention. Therefore, this means that all such changes and modifications within the scope of the present invention are included in the appended claims.

Claims

1. A preparation method of a hollow structure three-way catalyst, characterized in that, Comprising the following steps: A. Primary crystallization: Mix a noble metal precursor, a ligand, and water uniformly to obtain a noble metal complex solution; Mix a silicon source, optionally an aluminum source, a first template agent, the noble metal complex solution, and water to obtain a first mixed solution; Transfer the first mixed solution to a closed reaction kettle for a primary crystallization reaction, and then separate and wash the product to obtain a solid; B. Secondary crystallization: Mix the solid, a second template agent, and water to obtain a second mixed solution; Transfer the second mixed solution to a closed reaction kettle for a secondary crystallization reaction, and then separate and wash the product to obtain a hollow-structured three-way catalyst.

2. The preparation method of the hollow-structured three-way catalyst according to claim 1, characterized in that, The duration of the primary crystallization is 6 - 96 h, and the crystallization temperature is 130 - 200 °C.

3. The preparation method of the hollow structure three-way catalyst according to claim 2, characterized in that, The duration of the secondary crystallization is 6 - 48 h, and the crystallization temperature is the same as that of the primary crystallization.

4. The preparation method of the hollow structure three-way catalyst according to claim 1, characterized in that In step B, the concentration after mixing the second template agent and water is 0.1 - 1 M.

5. The preparation method of the hollow structure three-way catalyst according to claim 1, characterized in that, The noble metal includes at least one of Pd, Pt, Rh, or Ru.

6. A three-way catalyst with a hollow structure, characterized in that, Obtained by using the preparation method according to any one of claims 1 - 5, the catalyst comprises a hollow outer shell composed of molecular sieve and noble metal particles located inside the molecular sieve; the thickness of the hollow outer shell is 2 - 40 nm; the size of the noble metal particles is 1.5 - 30 nm.

7. The three-way catalyst with a hollow structure according to claim 6, characterized in that, The molecular sieve structure is at least one of MFI, CHA, BEA, AEI, LTA, and FAU.

8. The three-way catalyst with a hollow structure according to claim 6, wherein, The molecular sieve contains silicon element, or contains both silicon element and aluminum element; when the molecular sieve contains aluminum element, the molar ratio of silicon element to aluminum element is not less than 6:

1.

9. The three-way catalyst with a hollow structure according to any one of claims 6-8, characterized in that, The mass content of the noble metal in the catalyst is 0.5% - 3%.

10. An after-treatment catalytic converter for a motor vehicle, characterized in that, Comprising the hollow-structured three-way catalyst according to any one of claims 6 - 9.

Images