Cerium-zirconium-praseodymium-based composite material, preparation method and application thereof

Abstract

The application belongs to the technical field of catalysts, and particularly relates to a cerium-zirconium-praseodymium-based composite material and a preparation method and application thereof. The application provides a preparation method of a cerium-zirconium-praseodymium-based composite material, which comprises the following steps: mixing soluble cerium salt, soluble zirconium salt, soluble praseodymium salt, water and an oxidizing agent, and performing co-precipitation under alkaline conditions to obtain a precursor slurry; performing solid-liquid separation on the precursor slurry, mixing the obtained precipitate with water, and performing primary calcination on the obtained slurry to obtain the cerium-zirconium-praseodymium-based composite material; or mixing the precursor slurry with a structure-directing agent, and then sequentially performing drying and secondary calcination to obtain the cerium-zirconium-praseodymium-based composite material. The application can improve the effective contact efficiency of the composite material and carbon soot particulate matters, and further improve the purification catalytic efficiency of the composite material on the carbon soot particulate matters.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalysts, and particularly relates to a cerium-zirconium-praseodymium-based composite material and a preparation method and application thereof. BACKGROUND

[0002] The solid-solid catalytic reaction of the catalyst and the solid reactant (soot particles) is a solid-solid catalytic reaction of soot particles, and the contact efficiency between the catalyst and the soot particles directly affects the efficiency of the catalyst in catalyzing and purifying soot particles. Therefore, improving the contact efficiency between the catalyst and the soot particles is an effective way to improve the performance of the catalyst in catalyzing and purifying soot particles.

[0003] In the industry, a spray drying-calcination process is often used to synthesize catalysts. The catalyst obtained by the above process is in the form of spherical and irregular block particles formed by the accumulation of nanoparticles, has a small pore structure, and has a low contact efficiency between the catalyst and soot particles, which leads to a decrease in the efficiency of the catalyst in catalyzing and purifying soot particles. SUMMARY

[0004] The application aims to provide a cerium-zirconium-praseodymium-based composite material and a preparation method and application thereof. The cerium-zirconium-praseodymium-based composite material obtained by the preparation method provided by the application can improve the effective contact efficiency with soot particles, and thus improve the catalytic efficiency of the cerium-zirconium-praseodymium-based composite material in purifying soot particles.

[0005] To achieve the above-mentioned purpose, the application provides the following technical scheme:

[0006] The application provides a preparation method of a cerium-zirconium-praseodymium-based composite material, which comprises the following steps:

[0007] The soluble cerium salt, the soluble zirconium salt, the soluble praseodymium salt, water and the oxidizing agent are mixed, and co-precipitation is performed under alkaline conditions to obtain a precursor slurry;

[0008] The precursor slurry is subjected to solid-liquid separation, the obtained precipitate is mixed with water, and the obtained slurry is subjected to primary calcination to obtain the cerium-zirconium-praseodymium-based composite material;

[0009] or the precursor slurry is mixed with a structure-directing agent, and then is subjected to drying and secondary calcination in sequence to obtain the cerium-zirconium-praseodymium-based composite material.

[0010] Preferably, the soluble cerium salt comprises one or more of cerium nitrate, cerium acetate, cerium carbonate, cerium ammonium nitrate, cerium ammonium acetate and cerium ammonium carbonate; the soluble zirconium salt comprises one or more of zirconium nitrate, zirconium acetate, zirconium oxynitrate, zirconium carbonate, zirconium ammonium carbonate and zirconium potassium carbonate; the soluble praseodymium salt comprises one or more of praseodymium nitrate, praseodymium hydroxide, praseodymium chloride, praseodymium iodide, praseodymium acetate, praseodymium sulfate, praseodymium perchlorate, praseodymium phosphate and praseodymium carbonate.

[0011] The oxidizing agent comprises hydrogen peroxide.

[0012] Preferably, in the precursor slurry, the molar amount of cerium accounts for 20% to 70% of the total molar amount of metal elements, the molar amount of zirconium accounts for 20% to 60% of the total molar amount of metal elements, and the molar amount of praseodymium accounts for 5% to 20% of the total molar amount of metal elements.

[0013] Preferably, the mass ratio of the total mass of the soluble cerium salt, the soluble zirconium salt and the soluble praseodymium salt to the mass of water is less than 0.6.

[0014] The mass ratio of the total mass of the soluble cerium salt, the soluble zirconium salt and the soluble praseodymium salt to the mass of the oxidizing agent is less than 28.

[0015] Preferably, the pH value of the alkaline condition is 7 to 10.

[0016] The temperature of the co-precipitation is 25 to 70℃.

[0017] Preferably, the solid content of the slurry is 2% to 25%.

[0018] The temperature of the first-stage calcination is 300 to 800℃, and the holding time is greater than or equal to 1.5h; the first-stage calcination is performed in an air atmosphere, an oxygen atmosphere or an oxygen-containing nitrogen atmosphere.

[0019] Preferably, the structure-directing agent comprises one or more of lauric acid, oleic acid, ethanol, urea and starch.

[0020] Preferably, the mass ratio of the precursor slurry to the structure-directing agent is less than 10.

[0021] The temperature of the second-stage calcination is 300 to 800℃, and the holding time is greater than or equal to 1.5h; the second-stage calcination is performed in an air atmosphere, an oxygen atmosphere or an oxygen-containing nitrogen atmosphere.

[0022] The present application also provides a cerium-zirconium-praseodymium-based composite material prepared by the preparation method.

[0023] The cerium-zirconium-praseodymium-based composite material has a porous structure.

[0024] The average pore diameter of the cerium-zirconium-praseodymium-based composite material is 13.7 nm; the average pore volume is 0.33 cm 3 / g.

[0025] The application further provides application of the cerium-zirconium-praseodymium-based composite material as a catalyst for purifying soot particles in exhaust gas of diesel vehicles.

[0026] The application provides a preparation method of a cerium-zirconium-praseodymium-based composite material, which comprises the following steps: mixing soluble cerium salt, soluble zirconium salt, soluble praseodymium salt, water and an oxidizing agent, and performing co-precipitation under alkaline conditions to obtain a precursor slurry; performing solid-liquid separation on the precursor slurry, mixing the obtained precipitate with water, and performing primary calcination on the obtained slurry to obtain the cerium-zirconium-praseodymium-based composite material; or mixing the precursor slurry with a structure directing agent, and then sequentially performing drying and secondary calcination to obtain the cerium-zirconium-praseodymium-based composite material. By controlling the boiling calcination state in the primary calcination process of the precursor slurry, the pore structure of the composite material is adjusted, or by adding a structure directing agent in the drying and secondary calcination process, the pore structure of the composite material is adjusted, so that the pore structure of the composite material obtained by the application is obviously optimized, and the pore volume is large; the pore diameter can make soot particles effectively enter the inner pores of the composite material, so that the effective contact efficiency with soot particles is improved, and the purification and catalysis efficiency of the cerium-zirconium-praseodymium-based composite material on soot particles is improved. BRIEF DESCRIPTION OF DRAWINGS

[0027] Figure 1 XRD spectra of the composite materials obtained in Examples 1-3 and Comparative Example 1;

[0028] Figure 2 SEM images of the composite materials obtained in Examples 1-3;

[0029] Figure 3 TEM images of the composite materials obtained in Examples 1-3;

[0030] Figure 4 N2 adsorption-desorption isotherms of the composite materials obtained in Examples 1-3 and Comparative Example 1;

[0031] Figure 5 Pore size distribution diagrams of the composite materials obtained in Examples 1-3 and Comparative Example 1;

[0032] Figure 6 Particle size distribution diagrams of the composite materials obtained in Examples 1-3;

[0033] Figure 7 a Carbon dioxide concentration-temperature change curve of the composite materials obtained in Examples 1-4; Figure 7b is a soot particle purification efficiency curve of the composite material obtained in Example 1-4;

[0034] Figure 8 a SEM image of the composite material obtained in Comparative Example 1;

[0035] Figure 9 a TEM image of the composite material obtained in Comparative Example 1;

[0036] Figure 10 a carbon dioxide concentration curve of the composite material obtained in Comparative Example 1-4 with temperature change; Figure 10 b is a soot particle purification efficiency curve of the composite material obtained in Comparative Example 1-4. DETAILED DESCRIPTION

[0037] The present application provides a preparation method of a cerium-zirconium-praseodymium-based composite material, comprising the following steps:

[0038] Mixing soluble cerium salt, soluble zirconium salt, soluble praseodymium salt, water and oxidizing agent, and co-precipitating under alkaline conditions to obtain a precursor slurry;

[0039] Carrying out solid-liquid separation on the precursor slurry, mixing the obtained precipitate with water, and carrying out primary calcination on the obtained slurry to obtain the cerium-zirconium-praseodymium-based composite material;

[0040] Or mixing the precursor slurry with a structure-directing agent, and then sequentially carrying out drying and secondary calcination to obtain the cerium-zirconium-praseodymium-based composite material.

[0041] In the present application, all the preparation raw materials are commercially available products well known to those skilled in the art, unless otherwise specified.

[0042] In the present application, soluble cerium salt, soluble zirconium salt and soluble praseodymium salt are all preferably hydrated salts.

[0043] In the present application, the soluble cerium salt preferably includes one or more of cerium nitrate, cerium acetate, cerium carbonate, cerium ammonium nitrate, cerium ammonium acetate and cerium ammonium carbonate; the cerium nitrate is preferably added in the form of cerium nitrate hexahydrate; the soluble zirconium salt preferably includes one or more of zirconium nitrate, zirconium acetate, zirconium oxynitrate, zirconium carbonate, zirconium ammonium carbonate and zirconium potassium carbonate; the zirconium nitrate is preferably added in the form of zirconium nitrate pentahydrate; the soluble praseodymium salt preferably includes one or more of praseodymium nitrate, praseodymium hydroxide, praseodymium chloride, praseodymium iodide, praseodymium acetate, praseodymium sulfate, praseodymium perchlorate, praseodymium phosphate and praseodymium carbonate; the praseodymium nitrate is preferably added in the form of praseodymium nitrate hexahydrate.

[0044] In the present application, the oxidizing agent preferably comprises hydrogen peroxide; the mass concentration of the hydrogen peroxide is preferably 30%.

[0045] In the present application, in the precursor slurry, the molar amount of cerium element preferably accounts for 20% to 70% of the total molar amount of metal elements, the molar amount of zirconium element preferably accounts for 20% to 60% of the total molar amount of metal elements, and the molar amount of praseodymium element preferably accounts for 5% to 20% of the total molar amount of metal elements, in terms of the molar amount of Ce, Zr and Pr.

[0046] In the present application, the water is preferably ultrapure water. In the present application, the mass ratio of the total mass of the soluble cerium salt, the soluble zirconium salt and the soluble praseodymium salt to the mass of water is preferably less than 0.6, and further preferably 0.2. In the present application, the mass ratio of the total mass of the soluble cerium salt, the soluble zirconium salt and the soluble praseodymium salt to the mass of the oxidizing agent is preferably less than 28, and further preferably 14.

[0047] In the present application, the mixing process preferably comprises: after mixing and dissolving the soluble cerium salt, the soluble zirconium salt, the soluble praseodymium salt and the water, the oxidizing agent is added for stirring and mixing; the stirring and mixing time is preferably 0.5 h.

[0048] In the present application, the pH value of the alkaline condition is preferably 7 to 10, and further preferably 7 to 8. In the present application, an aqueous ammonia solution is preferably used to provide the alkaline condition. In the present application, the aqueous ammonia solution is configured from concentrated ammonia water and ultrapure water, and the mass ratio of the concentrated ammonia water to the ultrapure water is preferably 1:8 to 15.

[0049] In the present application, the co-precipitation process preferably comprises:

[0050] Under stirring conditions, the mixed solution obtained by mixing and the aqueous ammonia solution are dropped into a container.

[0051] The present application does not have special limitations on the stirring conditions, and any conditions known to those skilled in the art can be used. In the present application, the dropping rate of the mixed solution is preferably 3 to 10 mL / min, and the dropping rate of the aqueous ammonia solution is preferably 5 to 15 mL / min. In the present application, the volume ratio of the mixed solution to the aqueous ammonia solution is preferably 1:2 to 2:1. In the present application, the co-precipitation temperature is preferably 40°C. In the present application, the co-precipitation occurs when the mixed solution and the aqueous ammonia solution come into contact.

[0052] After obtaining the precursor slurry, the precursor slurry is subjected to solid-liquid separation in the present application, the obtained precipitate is mixed with water, the obtained slurry is subjected to primary calcination, and the cerium-zirconium-praseodymium-based composite material is obtained (hereinafter referred to as method one);

[0053] or mixing the precursor slurry and the structure-directing agent, and then sequentially drying and secondary calcining to obtain the cerium-zirconium-praseodymium-based composite material (hereinafter referred to as method two).

[0054] In the present application, when method one is adopted, before the solid-liquid separation, the precursor slurry is preferably subjected to sealed stirring; the temperature of the sealed stirring is preferably 90°C, and the time is preferably 3h. After the heating stirring, the obtained slurry is preferably cooled to room temperature.

[0055] In the present application, the solid-liquid separation is preferably centrifugal separation. The present application does not have special limitations on the process of the centrifugal separation, and any process known to those skilled in the art can be adopted.

[0056] After the solid-liquid separation, the present application further preferably includes water washing of the obtained solid; the number of times of the water washing is preferably 2-3 times.

[0057] In the present application, the water is preferably ultrapure water. In the present application, the precipitation and the water are mixed under stirring. The present application does not have special limitations on the parameters of the stirring conditions, and any parameter known to those skilled in the art can be adopted. In the present application, the solid content of the slurry is preferably 2%-25%, and further preferably 5-6%.

[0058] In the present application, the temperature of the primary calcination is 300-800°C, further 400-700°C, and more preferably 500-600°C; the holding time is preferably ≥1.5h, and further preferably 3h; the primary calcination is preferably carried out in an air atmosphere, an oxygen atmosphere, or an oxygen-containing nitrogen atmosphere.

[0059] In the present application, when method two is adopted, the structure-directing agent preferably includes one or more of lauric acid, oleic acid, ethanol, urea, and starch. In the present application, the mass ratio of the precursor slurry to the structure-directing agent is preferably less than 10.

[0060] In the present application, when the structure-directing agent is lauric acid and / or oleic acid, the structure-directing agent is preferably added in the form of a structure-directing agent organic solution. In the present application, the organic solvent in the structure-directing agent organic solution is preferably N,N-dimethylformamide; the concentration of the structure-directing agent organic solution is preferably 0.4g / mL.

[0061] In the present application, the mixing of the precursor slurry and the structure-directing agent is preferably carried out under stirring; the temperature of the stirring is preferably 40°C, the rotation speed is preferably 45rpm, and the time is preferably 3h; the stirring is carried out under sealed conditions.

[0062] After the mixing, the present application further preferably includes cooling the obtained slurry to room temperature.

[0063] In the present application, the drying method is preferably spray drying. The process of the spray drying is not particularly limited in the present application, and any process known to those skilled in the art can be used.

[0064] In the present application, the temperature of the secondary calcination is preferably 300-800℃, further preferably 400-700℃, and more preferably 500-600℃; the holding time is preferably ≥1.5h, and further preferably 3h; the secondary calcination is preferably carried out in an air atmosphere, an oxygen atmosphere, or an oxygen-containing nitrogen atmosphere.

[0065] The cerium-zirconium-praseodymium-based composite material prepared by the preparation method described in the above technical solution has a particle size of 25-2000nm, and further preferably 643nm.

[0066] The cerium-zirconium-praseodymium-based composite material preferably has a porous structure.

[0067] The average pore size of the cerium-zirconium-praseodymium-based composite material is preferably 13.7nm; and the average pore volume is preferably 0.33cm 3 / g.

[0068] The present application also provides the application of the cerium-zirconium-praseodymium-based composite material described in the above technical solution as a catalyst for purifying diesel vehicle exhaust soot particulate matter.

[0069] In order to further illustrate the present application, the cerium-zirconium-praseodymium-based composite material, the preparation method and the application thereof provided by the present application are described in detail below in conjunction with the accompanying drawings and examples, but they should not be regarded as limiting the scope of protection of the present application.

[0070] Example 1

[0071] Ce(NO3)3·6H2O (11.76g), Zr(NO3)4·5H2O (13.31g), and Pr(NO3)3·6H2O (2.95g) were dissolved in 150mL of ultrapure water; then 7mL of 30% H2O2 was added, and stirring was continued for 0.5h to prepare a green, clear and transparent mixed solution; under stirring, the mixed solution was dropped into a container at a dropping rate of 5.3mL / min, and an ammonia solution (in which the mass ratio of concentrated ammonia water to ultrapure water was 1:14) was dropped at a dropping rate of 8.3mL / min, and the pH value was controlled at 7-8, and co-precipitation was carried out at 40℃ to obtain a precursor slurry;

[0072] The precursor slurry was sealed and stirred at 90℃ for 3h to obtain a light yellow slurry; the obtained slurry was cooled to room temperature and then centrifuged at low speed, and the precipitate was obtained after water washing for 3 times;

[0073] The obtained precipitate and ultrapure water are stirred uniformly at a ratio of 100 mL / g, and the obtained slurry is calcined at a temperature of 600°C in an air atmosphere, with a holding time of 3h, to obtain the cerium-zirconium-praseodymium-based composite material.

[0074] Example 2

[0075] Ce(NO3)3·6H2O (11.76g), Zr(NO3)4·5H2O (13.31g), Pr(NO3)3·6H2O (2.95g) are dissolved in 150 mL of ultrapure water; then 7 mL of 30% H2O2 by mass is added, and stirring is continued for 0.5h, to obtain a green, clear and transparent mixed solution; under stirring, the obtained mixed solution is co-precipitated by dropwise adding ammonia solution (in which the mass ratio of concentrated ammonia water to ultrapure water is 1:14) at a dropwise adding rate of 8.3 mL / min and ammonia solution at a dropwise adding rate of 5 mL / min into a container, with pH controlled at 7-8, at 40°C, to obtain a precursor slurry;

[0076] 4g of lauric acid is dissolved in 10 mL of DMF to obtain a transparent solution, and the obtained transparent solution is added to the precursor slurry, which is sealed and stirred at 40°C for 3h; after cooling, spray drying is performed, and the obtained powder is calcined at a temperature of 600°C in an air atmosphere, with a holding time of 3h, to obtain the cerium-zirconium-praseodymium-based composite material.

[0077] Example 3

[0078] Ce(NO3)3·6H2O (11.76g), Zr(NO3)4·5H2O (13.31g), Pr(NO3)3·6H2O (2.95g) are dissolved in 150 mL of ultrapure water; then 7 mL of 30% H2O2 by mass is added, and stirring is continued for 0.5h, to obtain a green, clear and transparent mixed solution; under stirring, the obtained mixed solution is co-precipitated by dropwise adding ammonia solution (in which the mass ratio of concentrated ammonia water to ultrapure water is 1:14) at a dropwise adding rate of 8.3 mL / min and ammonia solution at a dropwise adding rate of 5 mL / min into a container, with pH controlled at 7-8, at 40°C, to obtain a precursor slurry;

[0079] 4g of lauric acid is dissolved in 10 mL of DMF to obtain a transparent solution, and the obtained transparent solution is added to the precursor slurry, which is sealed and stirred at 40°C for 3h; after cooling, spray drying is performed, and the obtained powder is calcined at a temperature of 600°C in an air atmosphere, with a holding time of 3h, to obtain the cerium-zirconium-praseodymium-based composite material.

[0080] Example 4

[0081] Ce(NO3)3.6H2O (11.76 g), Zr(NO3)4.5H2O (13.31 g), Pr(NO3)3.6H2O (2.95 g) were dissolved in 150 mL ultrapure water; then 7 mL of 30% H2O2 was added, and stirring was continued for 0.5 h to obtain a green clear transparent mixed solution; the obtained mixed solution was added dropwise into a container at a rate of 5 mL / min, and ammonia solution (the mass ratio of concentrated ammonia and ultrapure water was 1:14) was added dropwise at a rate of 8.3 mL / min under stirring, and the pH value was controlled at 7-8, and co-precipitation was carried out at 40°C to obtain a precursor slurry;

[0082] The obtained precursor slurry was mixed with an equal volume of anhydrous ethanol, and stirring was carried out at 40°C for 3 h in a sealed state; after cooling, spray drying was carried out, and the obtained powder was dried in an air atmosphere at a temperature of 600°C for 3 h to obtain the cerium-zirconium-praseodymium-based composite material.

[0083] Comparative Example 1

[0084] CeO2-ZrO2-PrO2 composite material catalyst prepared by a commonly used co-precipitation method in industry;

[0085] Raw materials Ce(NO3)3.6H2O (47 g), Zr(NO3)4.5H2O (58 g) and Pr(NO3)3.6H2O (12 g) were dissolved in 800 mL pure water at 45°C and stirred for 30 min to obtain a mixed solution; 1400 mL of ammonia water was measured and added dropwise into a beaker together with the obtained mixed solution at 45-50°C, and the pH value of the mixed system was accurately controlled at 8-9 during the dropwise addition; 16 mL of hydrogen peroxide was added to the obtained mixed system and stirring was continued for 10 min, and then the stirring reaction was carried out at 95°C for 3 h, and after cooling, the precipitate was collected by washing and filtration; the precipitate was calcined in air at 600°C for 3 h to obtain the composite material.

[0086] Comparative Example 2

[0087] Comparative Example 2: CeO2-ZrO2 catalyst prepared by a traditional co-precipitation method.

[0088] Ce(NO3)3.6H2O (47 g), Zr(NO3)4.5H2O (58 g) and Pr(NO3)3.6H2O (12 g) were dissolved in 600 mL pure water at room temperature, and then 28 mL hydrogen peroxide was added after stirring for 30 min to obtain a mixed solution. 300 mL ammonia was diluted to 1500 mL at 40°C and then added dropwise into a beaker with the mixed solution. The pH value of the mixed system was accurately controlled at 7-8 during the dropwise addition. Then the mixed solution was stirred at 90°C for 3 h. After cooling, the precipitate was collected by washing and centrifugation. The precipitate was calcined at 600°C in air for 3 h to obtain a composite material.

[0089] Comparative Example 3

[0090] CeO2-ZrO2-PrO2 catalyst prepared by a conventional coprecipitation method;

[0091] Ce(NO3)3.6H2O (47 g), Zr(NO3)4.5H2O (58 g) and Pr(NO3)3.6H2O (12 g) were dissolved in 600 mL pure water at room temperature, and then 28 mL hydrogen peroxide was added after stirring for 30 min to obtain a mixed solution. 300 mL ammonia was diluted to 1500 mL at 40°C and then added dropwise into a beaker with the mixed solution. The pH value of the mixed system was accurately controlled at 7-8 during the dropwise addition. Then the mixed solution was stirred at 90°C for 3 h. After cooling, the precipitate was collected by washing and centrifugation. The precipitate was calcined at 600°C in air for 3 h to obtain a composite material.

[0092] Comparative Example 4

[0093] CeO2-ZrO2-LaO2-TiO2-PrO2 catalyst prepared by a conventional coprecipitation method;

[0094] Ce(NO3)3.6H2O (47 g), Zr(NO3)4.5H2O (58 g) and Pr(NO3)3.6H2O (12 g) were dissolved in 600 mL pure water at room temperature, and then 28 mL hydrogen peroxide was added after stirring for 30 min to obtain a mixed solution. 300 mL ammonia was diluted to 1500 mL at 40°C and then added dropwise into a beaker with the mixed solution. The pH value of the mixed system was accurately controlled at 7-8 during the dropwise addition. Then the mixed solution was stirred at 90°C for 3 h. After cooling, the precipitate was collected by washing and centrifugation. The precipitate was calcined at 600°C in air for 3 h to obtain a composite material.

[0095] Performance test

[0096] Test example 1

[0097] Figure 1 is the XRD spectrum of the composite material obtained from Examples 1-3 and Comparative Example 1;

[0098] From Figure 1 It can be seen that the crystal phase structure of the obtained composite material, the main peak presents the face-centered cubic fluorite structure of Ce 0.4 Zr 0.6 O2(ICDD-PDF#38-1439); the main peak does not shift, and the position is basically consistent with the standard card, and there is no diffraction peak related to Pr in the XRD spectrum, indicating that Pr does not enter the face-centered cubic fluorite structure of the composite material;

[0099] Test example 2

[0100] Figure 2 is the SEM image of the composite material obtained from Examples 1-3, wherein Examples 1 (a1, a2), Example 2 (b1, b2), and Example 3 (c1, c2);

[0101] From Figure 2 It can be seen that Example 1 is in granular and a small amount of block structure under the micron scale, the particle dispersion of the composite material is good, Examples 2-3 are in spherical and block structure under the micron scale, and the dispersion of the composite material is obviously improved after the introduction of the structure directing agent in Examples 2-3; under the nanometer scale, there are more pore structures in Example 1, and the pore becomes larger and the number of pore structures increases after the introduction of the structure directing agent in Examples 2-3;

[0102] Figure 8 is the SEM image of the composite material obtained from Comparative Example 1, from Figure 8 It can be seen that under the micron scale, it is mainly a close-packed particle agglomerate; further magnification still presents a similar particle aggregate morphology, and the agglomeration degree is still obvious, and no obvious porous structure is observed;

[0103] Figure 3 is the TEM image of the composite material obtained from Examples 1-3, wherein (a, b) is Example 1, (c, d) is Example 2, and (e, f) is Example 3; from Figure 3 It can be seen that the large particles of each catalyst in the example are stacked by smaller nanocrystals;

[0104] Figure 9 is the TEM image of the composite material obtained from Comparative Example 1, from Figure 9 It can be seen that the structure of the obtained composite material is composed of nanocrystalline grains, but the agglomeration degree of the nanocrystalline grains is obviously higher than that of Examples 1-3.

[0105] Test Example 3

[0106] Figure 4 N2 adsorption-desorption isotherm of the composite material obtained in Example 1-3 and Comparative Example 1, Figure 5 pore size distribution of the composite material obtained in Example 1-3 and Comparative Example 1, and the specific test results are shown in Table 1;

[0107] Table 1 Specific surface area, pore volume and pore size of the composite material obtained in Example 1-3 and Comparative Example 1

[0108] Sample S BET / (m 2 ·g -1 )]]> V total (cm 3 ·g -1 )]]> D pore / nm Example 1 90 0.33 13.7 Example 2 35 0.13 12.9 Example 3 40 0.15 13.6 Comparative Example 1 75 0.1 4.8

[0109] From Figures 4-5 and Table 1, it can be seen that the pore size and pore volume of Comparative Example 1 are small, while the pore size and pore volume of Examples 1-3 are obviously larger than that of Comparative Example 1, the distribution range is wide, which indicates that Examples 1-3 have more pore structures of different sizes; and the N2 adsorption-desorption amount of Examples 1-3 is much larger than that of Comparative Example 1; the above test results confirm that the preparation method provided by the present application can improve the texture properties and pore structure of the composite material compared with the commonly used coprecipitation process (Comparative Example 1) in industry.

[0110] Figure 6 Particle size distribution of the composite material obtained in Example 1-3; from Figure 5 it can be seen that the particle size of Examples 1-3 shows unimodal distribution, which indicates that the preparation method provided by the present application can make the particle size distribution of the composite material tend to be uniform, so that the particle dispersion of the composite material is better.

[0111] Test Example 4

[0112] The composite materials obtained in Examples 1-4 and Comparative Examples 1-4 are used as catalysts for soot particle purification reaction of diesel vehicle exhaust, and the test curves and test results are shown in Figure 7 、 10 and Tables 2 and 3, Figure 7 a is the carbon dioxide concentration curve of Examples 1-4 with temperature change, Figure 7 b is the soot particle purification efficiency curve of Examples 1-4, Figure 10 a is the carbon dioxide concentration curve of Comparative Examples 1-4 with temperature change, Figure 10 b is the soot particle purification efficiency curve of Comparative Examples 1-4;

[0113] Table 2 Catalytic performance of the composite material obtained in Examples 1-4

[0114] Sample Example 1 Example 2 Example 3 Example 4 CO2 peak temperature (°C) 368 392 388 444 Soot burn-off 10% temperature (°C) 339 353 348 374 Soot burn-off 50% temperature (°C) 372 391 384 426 Soot burn-off 90% temperature (°C) 404 427 416 460

[0115] Table 3 Catalytic performance of the composite material obtained in Comparative Examples 1-4

[0116] Sample Comparative Example 1 Comparative Example 2 Comparative Example 3 Comparative Example 4 CO2 peak temperature (°C) 494 483 515 499 Soot burn-off 10% temperature (°C) 415 415 380 438 Soot burn-off 50% temperature (°C) 478 471 495 499 Soot burn-off 90% temperature (°C) 516 510 550 548

[0117] From Figure 7 , 10 and Tables 2, 3, it can be seen that Examples 1-4 have better low-temperature catalytic performance for purification of diesel engine exhaust soot particles. Compared with the comparative examples, the composite material obtained by the present application can more efficiently catalyze and purify diesel engine exhaust soot particles at a lower temperature.

[0118] Although the above examples have made a detailed description of the present application, it is only a part of the embodiments of the present application, not all the embodiments, and other embodiments can be obtained according to the present embodiments without creativity, which all belong to the protection scope of the present application.

Claims

1. The application of a cerium-zirconium-praseodymium-based composite material as a catalyst for purifying particulate matter in diesel vehicle exhaust; The preparation method of the cerium-zirconium-praseodymium-based composite material includes the following steps: 11.76 g of Ce(NO3)3·6H2O, 13.31 g of Zr(NO3)4·5H2O, and 2.95 g of Pr(NO3)3·6H2O were dissolved in 150 mL of ultrapure water. Then, 7 mL of 30% H2O2 was added, and the mixture was stirred continuously for 0.5 h to obtain a green, clear, and transparent mixed solution. Under stirring conditions, the obtained mixed solution was added dropwise to a container at a rate of 5.3 mL / min and an ammonia solution at a rate of 8.3 mL / min. The mass ratio of concentrated ammonia to ultrapure water was 1:14, and the pH value was controlled at 7-8. Co-precipitation was carried out at 40 °C to obtain the precursor slurry. The precursor slurry was sealed and stirred at 90°C for 3 hours to obtain a light yellow slurry. After cooling the obtained slurry to room temperature, centrifuge it at low speed and wash it with water three times to obtain the precipitate. The precipitate and ultrapure water were stirred evenly at a ratio of 100 mL / g. The resulting slurry was then calcined in air at 600°C for 3 hours to obtain the cerium-zirconium-praseodymium-based composite material.

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