Micron-sized macroporous cerium-zirconium-praseodymium composite material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and particularly relates to a micron-sized macroporous cerium-zirconium-praseodymium composite material as well as a preparation method and application thereof. According to the preparation method, the micron-sized macroporous CeO2-ZrO2-PrO2 composite material is constructed by using the starch which is low in price and wide in source as a template agent under an industrial coprecipitation process, and the micron-sized macroporous CeO2-ZrO2-PrO2 composite material is used as a catalyst, so that the contact efficiency between the catalyst and soot particles can be improved, and the performance of the catalyst for purifying the soot particles in the tail gas of the diesel engine is further improved.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, specifically relating to a micron-sized macroporous cerium-zirconium-praseodymium composite material, its preparation method, and its application. Background Technology

[0002] CeO2-ZrO2-based composite oxides are widely used in automotive exhaust purification, water-gas shift reactions, and toluene catalytic reforming due to their excellent oxygen storage capacity, thermal stability, and catalytic activity. Internal combustion engine exhaust (such as from automobiles, diesel vehicles, and ships) emits small and numerous particulate matter, posing a significant threat to human health and the environment. Installing particulate matter traps is the most effective means of reducing particulate matter emissions. However, particulate matter traps require surface coating with catalysts to maintain their high-efficiency trapping and regeneration performance; CeO2-ZrO2-based composite oxides are highly promising catalysts for particulate matter purification.

[0003] In the research of catalysts for purifying soot particles in internal combustion engine exhaust, two main strategies exist to address soot pollution in the exhaust. One approach is to regulate the chemical composition of the material to optimize its intrinsic properties; the other focuses on the macroscopic and microscopic structural design of the catalyst. Soot catalytic oxidation is a typical multiphase reaction interface between solid (catalyst), solid (sot), and gas (oxygen). Due to the large size of soot particles (up to micrometers), they typically cannot enter the internal pores (nanoscale mesopores) of traditional soot purification catalysts, resulting in low contact efficiency between them and the active sites of the catalyst. Currently, three-dimensional ordered macroporous materials (pore sizes down to the hundreds of nanometers) significantly improve the contact efficiency between soot and the catalyst due to their regular macroporous structure, thereby enhancing catalytic activity. However, the synthesis of three-dimensional ordered macroporous materials requires the extensive use of expensive template agents, and their preparation process is complex, which hinders the large-scale production and industrial application of macroporous catalysts. Summary of the Invention

[0004] The purpose of this invention is to provide a micron-sized macroporous cerium-zirconium-praseodymium composite material, its preparation method, and its application.

[0005] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing micron-sized macroporous cerium-zirconium-praseodymium composite material, comprising the following steps: A cerium source, zirconium source, praseodymium source, and oxidant are dissolved in water to obtain a metal source mixture. The metal source mixture and the starch solution are mixed to obtain a colloidal mixture; The colloidal mixture was mixed with an alkaline solution and co-precipitated to obtain a precipitate system. The precipitate system was subjected to aging, dehydration and calcination in sequence to obtain the micron-sized macroporous cerium-zirconium-praseodymium composite material.

[0006] Preferably, the cerium source includes at least one of cerium nitrate, cerium acetate, cerium carbonate, cerium ammonium nitrate, cerium ammonium acetate, and cerium ammonium carbonate; The zirconium source includes at least one of zirconium nitrate, zirconium acetate, zirconium oxynitrate, zirconium carbonate, ammonium zirconium carbonate, and potassium zirconium carbonate. The praseodymium source includes at least one of praseodymium nitrate, praseodymium hydroxide, praseodymium acetate, praseodymium chloride, praseodymium iodide, praseodymium acetate, praseodymium sulfate, praseodymium perchlorate, praseodymium phosphate, praseodymium oxalate, and praseodymium carbonate; The oxidant includes a first oxidant or a second oxidant; the first oxidant includes at least one of hydrogen peroxide, potassium permanganate, nitric acid, peroxy organic matter, and perchlorate; the second oxidant includes an oxidizing gas, which includes at least one of oxygen, ozone, and chlorine.

[0007] Preferably, the molar ratio of the cerium source, zirconium source, and praseodymium source, based on the amount of cerium, zirconium, and praseodymium, is 0.1~0.9:0.1~0.9:0.05~0.5; When the oxidant is the first oxidant, the content of the oxidant in the metal source mixture is 0.05~3 mol / L; when the oxidant is the second oxidant, the flow rate of the oxidant is 5~60 L / h, and the introduction time is 1~3h. The dissolution is carried out under stirring conditions, the stirring temperature is room temperature to 80°C, and the stirring time is 10 to 180 min; The dissolution process includes dissolving the cerium source, zirconium source and praseodymium source in water, and then adding an oxidant.

[0008] Preferably, the ratio of the total amount of cerium, zirconium, and praseodymium sources to the mass of starch in the starch solution is 1 mol: 10~500g, based on the amount of cerium, zirconium, and praseodymium.

[0009] Preferably, the alkaline solution includes at least one of ammonia solution, ammonium carbonate solution, urea solution, sodium hydroxide solution, and potassium hydroxide solution; The concentration of the alkaline solution is 10~500 mmol / L; During the mixing of the colloidal mixture and the alkaline solution, the pH value of the system is controlled to be 7~10; The process of mixing the colloidal mixture and the alkaline solution is as follows: the colloidal mixture and the alkaline solution are added dropwise to the reaction vessel using a two-phase co-current titration method; The temperature at which the drops are added is between room temperature and 80°C.

[0010] Preferably, the coprecipitation reaction is carried out at a temperature of room temperature to 80°C for a time of 0.5 to 5 hours.

[0011] Preferably, the aging temperature is 90~100℃ and the time is 0.5~5h; the aging is carried out under stirring and closed conditions; The dehydration temperature is 80~100℃; the dehydration is carried out under stirring and unsealed conditions.

[0012] Preferably, the roasting includes a first roasting, a second roasting, a third roasting, and a fourth roasting performed sequentially; The first roasting temperature is 80~120℃, and the holding time is 0.5~3h; The second roasting temperature is 250~350℃, and the holding time is 0.5~3h; The third roasting temperature is 450~550℃, and the holding time is 0.5~3h; The fourth roasting temperature is 550~650℃, and the holding time is 0.5~6h.

[0013] This invention also provides a micron-sized macroporous cerium-zirconium-praseodymium composite material prepared by the preparation method described above, wherein the micron-sized macroporous cerium-zirconium-praseodymium composite material has a mesoporous-macroporous hierarchical pore structure; wherein the pore size of the macropores is 0.1~25μm; and the specific surface area of ​​the mesopores is 24~35m². 2 ·g -1 The mesoporous pore volume is 0.06~0.07mL / g.

[0014] This invention also provides the application of the micron-sized macroporous cerium-zirconium-praseodymium composite material described above as a catalyst in the purification of soot in diesel vehicle exhaust.

[0015] This invention utilizes inexpensive and widely available starch as a template to construct a micron-sized macroporous CeO2-ZrO2-PrO2 composite material. As a catalyst, this composite material improves the contact efficiency between the catalyst and particulate matter, thereby enhancing the catalyst's performance in purifying particulate matter from diesel engine exhaust. The invention is prepared by utilizing the gelatinization and water absorption of the starch template material during the preparation process, which then disperses into the surrounding material, creating a network-like porous structure. The catalyst prepared using this starch template offers the following technical advantages in the catalytic purification reaction of particulate matter from diesel engine exhaust: (1) Structural advantages: The catalyst has a multi-level pore structure of macropores and mesopores, with excellent macropore structure with pore size up to micrometers (pore size range of 0.1~25μm), which significantly improves the diffusion efficiency of gas and heat and the contact area of ​​soot particles.

[0016] (2) The catalytic activity was significantly improved. The introduction of starch not only regulated the pore structure, but also optimized the surface chemical state, enhancing the activation and migration ability of oxygen.

[0017] (3) The preparation is simple and environmentally friendly. Starch is widely available, low in cost, and environmentally friendly. Moreover, its gelatinization properties make it easy to form a controllable macroporous structure, which is suitable for large-scale preparation.

[0018] (4) Good thermal stability. The introduction of starch did not destroy the cubic fluorite structure of CeO2-ZrO2-PrO2 catalyst. Instead, it regulated the crystallization process and improved thermal stability. The catalyst maintained a stable crystal structure and catalytic performance at high temperatures. Attached Figure Description

[0019] Figure 1 The XRD patterns of Comparative Example 1 and Examples 1-3 are shown below. Figure 2 Scanning electron microscope images of the composite materials obtained in the examples and comparative examples; Figure 3 Nitrogen elution desorption isotherms (a) and pore size distribution (b) of the composite materials obtained in the examples and comparative examples; Figure 4 The pore volume (left) and pore size distribution (right) of the composite materials obtained in the examples and comparative examples were determined by the mercury infiltration method. Figure 5 XPS spectra of the composite materials obtained in the examples and comparative examples; Figure 6 The test results for H2 temperature programmed reduction (H2-TPR (left)) and O2 temperature programmed oxidation (O2-TPD (right)) of the composite material; Figure 7 Results of carbon soot-TPR tests under close contact and loose contact conditions; Figure 8 The activity (a) and conversion rate (b) of the catalyst for removing soot particles under tight conditions; Figure 9 The graph (a) shows the CO2 concentration variation of Examples 1-3 and Comparative Example 1 with soot under loose contact conditions, and the soot conversion rate curve (b) shows the soot conversion rate curve. Figure 10 To compare Examples 2-4 with soot under loose contact conditions, see graph (a) showing the CO2 concentration change and soot conversion rate curve (b). Detailed Implementation

[0020] This invention provides a method for preparing micron-sized macroporous cerium-zirconium-praseodymium composite material, comprising the following steps: A cerium source, zirconium source, praseodymium source, and oxidant are dissolved in water to obtain a metal source mixture. The metal source mixture and the starch solution are mixed to obtain a colloidal mixture; The colloidal mixture was mixed with an alkaline solution and co-precipitated to obtain a precipitate system. The precipitate system was subjected to aging, dehydration and calcination in sequence to obtain the micron-sized macroporous cerium-zirconium-praseodymium composite material.

[0021] This invention dissolves a cerium source, a zirconium source, a praseodymium source, and an oxidant in water to obtain a metal source mixture.

[0022] In this invention, the cerium source preferably includes at least one of cerium nitrate, cerium acetate, cerium carbonate, cerium ammonium nitrate, cerium ammonium acetate, and cerium ammonium carbonate; the zirconium source preferably includes at least one of zirconium nitrate, zirconium acetate, zirconium oxynitrate, zirconium carbonate, zirconium ammonium carbonate, and potassium zirconium carbonate; and the praseodymium source preferably includes at least one of praseodymium nitrate, praseodymium hydroxide, praseodymium acetate, praseodymium chloride, praseodymium iodide, praseodymium acetate, praseodymium sulfate, praseodymium perchlorate, praseodymium phosphate, praseodymium oxalate, and praseodymium carbonate.

[0023] In this invention, the oxidant preferably includes a first oxidant or a second oxidant; the first oxidant preferably includes at least one selected from hydrogen peroxide, potassium permanganate, nitric acid, peroxyorganic compounds, and perchlorate; the second oxidant preferably includes an oxidizing gas, which preferably includes at least one selected from oxygen, ozone, and chlorine. In this invention, the water is preferably ordinary industrial water or ultrapure water.

[0024] In this invention, the molar ratio of the cerium source, zirconium source, and praseodymium source, based on the amount of cerium, zirconium, and praseodymium, is preferably 0.1~0.9:0.1~0.9:0.05~0.5; the total concentration of the cerium source, zirconium source, and praseodymium source in the metal source mixture is preferably 0.05~3 mol / L; when the oxidant is a first oxidant, the content of the oxidant in the metal source mixture is preferably 0.05~3 mol / L; when the oxidant is a second oxidant, the flow rate of the oxidant is preferably 5~60 L / h, and the introduction time is preferably 1~3 h.

[0025] In this invention, the dissolution is preferably carried out under stirring conditions, the stirring temperature is preferably room temperature to 80°C, and the time is 10 to 180 min; the dissolution process preferably includes: dissolving the cerium source, zirconium source and praseodymium source in water, and then adding an oxidant.

[0026] After obtaining the metal source mixture, the present invention mixes the metal source mixture with a starch solution to obtain a colloidal mixture.

[0027] In this invention, the water in the starch solution is preferably ultrapure water. In this invention, the ratio of the total amount of cerium, zirconium, and praseodymium sources to the mass of starch in the starch solution is preferably 1 mol: 10~500 g, based on the amount of cerium, zirconium, and praseodymium. This invention does not impose any special limitations on the mixing process; any process well-known to those skilled in the art can be used to mix the two components evenly.

[0028] After obtaining the colloidal mixture, the present invention mixes the colloidal mixture with an alkaline solution and performs co-precipitation to obtain a precipitate system.

[0029] In this invention, the alkaline solution preferably includes at least one selected from ammonia solution, ammonium carbonate solution, urea solution, sodium hydroxide solution, and potassium hydroxide solution; the concentration of the alkaline solution is preferably 10-500 mmol / L. In this invention, during the mixing of the colloidal mixture and the alkaline solution, the pH of the system is preferably controlled to be 7-10; the mixing process is preferably as follows: the colloidal mixture and the alkaline solution are added dropwise to the reaction vessel using a two-phase co-current titration method; the temperature of the system is controlled to be room temperature to 80°C during the addition; the coprecipitation is preferably carried out under stirring conditions.

[0030] In this invention, the temperature of the coprecipitation reaction is preferably room temperature to 80°C, and the time is preferably 0.5 to 5 hours (referring to the reaction time after the addition is completed).

[0031] After obtaining the coprecipitation system, the present invention sequentially ages, dehydrates and calcines the precipitate system to obtain the micron-sized macroporous cerium-zirconium-praseodymium composite material.

[0032] In this invention, the aging temperature is preferably 90-100°C, and the time is 0.5-5 hours; the aging is preferably carried out under stirring and sealed conditions. In this invention, after aging, it is also preferable to cool the resulting system to room temperature. In this invention, the dehydration temperature is preferably 80-100°C; the dehydration is preferably carried out under stirring and unsealed conditions.

[0033] In this invention, the roasting preferably includes a first roasting, a second roasting, a third roasting, and a fourth roasting performed sequentially; the temperature of the first roasting is preferably 80~120℃, and the holding time is preferably 0.5~3h; the temperature of the second roasting is preferably 250~350℃, and the holding time is preferably 0.5~3h; the temperature of the third roasting is preferably 450~550℃, more preferably 500℃, and the holding time is preferably 0.5~3h; the temperature of the fourth roasting is preferably 550~650℃, more preferably 600℃, and the holding time is preferably 0.5~6h.

[0034] This invention also provides a micron-sized macroporous cerium-zirconium-praseodymium composite material prepared by the preparation method described above, wherein the micron-sized macroporous cerium-zirconium-praseodymium composite material has a mesoporous-macroporous hierarchical pore structure; wherein the pore size of the macropores is 0.1~25μm; and the specific surface area of ​​the mesopores is 24~35m². 2 ·g -1 The mesoporous pore volume is 0.06~0.07mL / g.

[0035] This invention also provides the application of the micron-sized macroporous cerium-zirconium-praseodymium composite material described above as a catalyst in the purification of soot in diesel vehicle exhaust.

[0036] Unless otherwise specified, the materials and equipment used in this invention are all commercially available products in the field.

[0037] The technical solutions of this invention will be clearly and completely described below with reference to the embodiments thereof. Obviously, the described embodiments are only a part of the embodiments of this invention, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort are within the scope of protection of this invention.

[0038] Example 1 Weigh out the raw materials cerium salt (Ce(NO3)3∙6H2O, 11.75g), zirconium salt (Zr(NO3)4∙5H2O, 13.31g) and praseodymium salt (Pr(NO3)3·6H2O, 2.94g) according to the metal ion molar ratio (Ce:Zr:Pr=4:5:1). Dissolve the above substances completely in 100mL of ultrapure water at room temperature. After stirring thoroughly, add 7mL of H2O2, control the temperature at 40℃, and stir magnetically for 30min to obtain the metal source solution. Dissolve another 5g of starch in 200mL of ultrapure water to obtain a starch solution. Add the metal source solution to the starch solution to obtain a colloidal mixture. Take 20 mL of ammonia water and dilute it to 300 mL to obtain an ammonia solution; Two separatory funnels were used to hold the colloidal mixture and the ammonia solution, respectively, and a two-phase co-current titration was performed (the temperature of the titration solution was controlled at 40℃ and its pH was controlled between 8 and 9). After the titration was completed, the mixture was stirred at a constant temperature of 40℃ for 1 hour to complete the coprecipitation and obtain the coprecipitation system. The temperature of the coprecipitation system was then raised to 90°C and stirred at a constant temperature for 3 hours (under closed conditions to prevent water evaporation); after cooling to room temperature, it was stirred and cooked at 100°C for 2 hours until completely dehydrated. The dehydrated product was placed in a quartz beaker and subjected to gradient calcination in a muffle furnace. The product was calcined at 120℃ for 30 min, 350℃ for 1 h, 500℃ for 1 h, and 600℃ for 3 h to obtain the cerium-zirconium-praseodymium composite material.

[0039] Example 2 Cerium-zirconium-praseodymium composite material was prepared according to Example 1, wherein the amount of starch added was 10g.

[0040] Example 3 Cerium-zirconium-praseodymium composite material was prepared according to Example 1, wherein the amount of starch added was 20g.

[0041] Comparative Example 1 The cerium-zirconium-praseodymium composite material was prepared according to Example 1, wherein the amount of starch added was 0g, that is, no starch solution was added, and the metal source solution and ammonia solution were directly mixed.

[0042] Comparative Example 2 Pt / Al2O3. A commercially available Pt / Al2O3 catalyst for the purification of diesel vehicle exhaust pollution, with a Pt loading of 1 wt.%.

[0043] Comparative Example 3 CeO2. CeO2 catalyst prepared by co-precipitation: 80 g of Ce(NO3)3∙6H2O was dissolved in 650 mL of pure water at 40 °C and stirred for 30 minutes to obtain solution A. 300 mL of ammonia solution was measured and added dropwise to a large beaker along with solution A obtained in step 1 at 40 °C to prepare mixed solution B, with the pH of mixed solution B accurately controlled to 8-9 during the addition process. Mixed solution B was stirred at 95 °C for 2 hours to obtain a homogeneous mixed solution C. After cooling, mixed solution C was washed, filtered, and the solid D was collected. Solid D was calcined in air at 600 °C for 3 hours to obtain Comparative Example 3.

[0044] Comparative Example 4 CeO2-ZrO2. CeO2-ZrO2 catalyst prepared by co-precipitation method: 59 g of Ce(NO3)3∙6H2O and 25 g of Zr(NO3)4∙5H2O were dissolved in water and stirred in 650 mL of pure water at 540 °C for 30 minutes to obtain solution A. 30 mL of ammonia solution was added dropwise to a large beaker at 40 °C along with solution A obtained in step 1 to obtain mixed solution B, with the pH of mixed solution B accurately controlled to 8-9 during the addition process. Mixed solution B was stirred at 95 °C for 2 hours to obtain a homogeneous mixed solution C. After cooling, mixed solution C was washed, filtered, and the solid D was collected. Solid D was calcined in air at 600 °C for 3 hours to obtain Comparative Example 4.

[0045] Performance testing Test Example 1 Figure 1 The XRD patterns of Comparative Example 1 and Examples 1-3 are shown. It can be observed that all samples exhibit significant characteristic peaks at 29.3°, 34.0°, 48.8°, and 58.0°, corresponding to the Ce phase of the cubic fluorite, respectively. 0.45 Zr 0.45 Pr 0.1 O 1.85(PDF#97-016-1654) The (111), (200), (220), and (311) crystal planes of the solid solution. The diffraction peaks remained consistent with different starch addition amounts, indicating that the introduction of starch did not change the crystal structure of the material. Further analysis of the full width at half maximum (FWHM) of the (111) crystal plane showed that the FWHMs of Comparative Example 1, Example 1, Example 2, and Example 3 were 0.874, 0.791, 0.696, and 0.865, respectively, corresponding to grain sizes of 9.29, 10.26, 11.66, and 9.38 nm. Compared with Comparative Example 1, the improved crystal integrity of Examples 1-3 makes the crystals less prone to destruction at high temperatures, exhibiting excellent thermal stability, which in turn helps to improve catalytic performance.

[0046] Test Example 2 Figure 2 Scanning electron microscope (SEM) images of the composite materials obtained in the Examples and Comparative Examples are shown, where (b)-(f), (c)-(g), (d)-(h), and (a)-(e) correspond to successive magnified views of Examples 1, 2, 3, and Comparative Example 1, respectively. Experimental results show that the catalyst prepared by adding a starch template (obtained by adjusting the starch incorporation amount) (corresponding to...) Figure 1 (bf), Figure 1 (cg) Figure 1 (dh) all exhibited a distinct micron-sized pore structure. Comparative Example 1, however, clearly lacked a macroporous structure. As the amount of starch gradually increased, the pore size inside the material continued to expand, and the pore density also significantly increased. Especially when the mass of starch was twice the mass of the catalyst (i.e., Example 3, such as...) Figure 1 As shown in (d) and (h), the abundance of micron-sized pores forms a network-like porous structure. This implies that utilizing the gelatinization properties of starch to construct micron-sized porous bodies is a good approach for preparing macroporous diesel vehicle exhaust purification catalysts. The micron-sized porous structure facilitates soot adhesion, improving soot purification performance by increasing the contact efficiency between the material and soot. The study also found that micron-sized channels enhance the adsorption capacity of composite materials for soot particles, significantly improving particulate matter purification efficiency by increasing the effective contact area.

[0047] Test Example 3 Figure 3 Nitrogen elution desorption isotherms (a) and pore size distribution (b) of the composite materials obtained in the examples and comparative examples; like Figure 3As shown in (a), Examples 1, 2, 3, and Comparative Example 1 all exhibited an H3-type hysteresis loop, indicating that all composite materials possess slit-like mesoporous pores. Specifically, the adsorption capacity of Examples 1-3 continuously increased in the high-pressure region, suggesting that the presence of a macroporous structure enhanced the adsorption capacity in this region. Notably, Examples 1-3 performed significantly better than Comparative Example 1, a result consistent with Table 1. Analysis of the data in the table shows that with increasing starch content, the mesoporous specific surface area of ​​Example 1 reached 24 m². 2 ·g -1 The mesoporous specific surface area of ​​Example 2 is 32m². 2 ·g -1 The mesoporous specific surface area of ​​Example 3 is 35m². 2 ·g -1 The overall trend shows an increasing trend, while the mesopore volumes of Examples 1, 2, and 3 are 0.06 mL / g, 0.07 mL / g, and 0.07 mL / g, respectively, with no significant difference. The pore size of Example 1 is 7.4 nm, that of Example 2 is 6.7 nm, and that of Example 3 is 6.3 nm, also showing a decreasing trend. This change can be attributed to the collapse of adjacent macropores or micron-sized macropores during the structural reorganization process of material formation, forming smaller mesopores or even micropores.

[0048] Considering that in practical applications, the particle size of soot particles is usually greater than 25 nm, especially the soot agglomerates in diesel engine exhaust, which can even reach 500 nm to over 1 μm, and based on the specific surface area, volume, and pore size analysis of the examples and comparative examples, it is evident that soot particles within the mesoporous pore size range have difficulty entering the pores of the catalysts in the examples and comparative examples, resulting in insufficient contact with the active sites; improving this issue may be a key factor in improving catalytic purification performance. Figure 3 (b) Pore size distribution analysis showed that Examples 1, 2, and 3 still exhibited a significant and widespread peak distribution in the macropore region (>50 nm), while Comparative Example 1 showed no distribution in the macropore region. This further verifies that the materials of the present invention have a wider pore size distribution range and exhibit significant macropore signals.

[0049] It should be noted that the N2 adsorption-desorption experiment, by its very nature, cannot accurately detect the macroporous characteristics of catalyst materials; it can only reflect mesoporous features. Therefore, the specific surface area, pore volume, and pore size data from the N2 adsorption-desorption experiment fail to reflect the influence of the macroporous structure. To further and more accurately evaluate the macroporous pore size distribution characteristics of the materials of this invention, mercury intrusion porosimetry was used for supplementary analysis.

[0050] Test Example 4 Figure 4 The pore volume (left figure) and pore size distribution (right figure) of the composite materials obtained in the examples and comparative examples were determined by mercury infiltration method. like Figure 4 The left figure shows the relationship between cumulative mercury ingress and pore size. As pressure increases, mercury can enter pores with smaller radii, successively penetrating the macropores (0-50 psia), macropores (50-10000 psia), and mesopores (above 10000 psia) of the catalyst. Examples 1, 2, 3, and Comparative Example 1 all show clear distributions within both macropore and mesopore ranges. Comparative Example 1 did not show clear stepwise distribution within the macropore range; Examples 1, 2, and 3 all exhibited a multi-level pore system composed of mesopores, macropores, and micron-sized macropores. Example 3 showed higher cumulative pore volume than Examples 1 and 2 in pressure ranges of 8-40 psia and 40-2000 psia, respectively, combined with pore size distribution. Figure 3 (b) The pore volume of Example 3 is higher than that of Examples 1 and 2, which shows that the addition of starch can effectively construct a macroporous structure; and the amount of starch added can affect the number of pores in the material.

[0051] also, Figure 4 The right-hand figure further demonstrates that Examples 1-3 exhibit macropore-micropore structures with pore diameters ranging from 0.1 to 25 μm, while pore structures <0.1 μm are also present. Combined with SEM and N2 adsorption-desorption results, Examples 1-3 possess abundant macropore-micropore structures, with Example 3 exhibiting the highest abundance of macropore-micropore structures. Clearly, controlling the amount of starch added is a key factor in the formation of the hierarchical pore structure in Examples 1-3.

[0052] Test Example 5 Figure 5 XPS spectra of the composite materials obtained in the examples and comparative examples: (a) Ce 3d and (b) O 1s. The elemental chemical states of Ce and O in the composite material were analyzed by XPS. Figure 5 (a) shows that the unconvolution of the 3d5 / 2 and 3d3 / 2 XPS spectra of Ce in the composite material has 10 components. The V1-V4 peaks located at 881.3 eV, 884.6 eV, 899.1 eV, and 902.8 eV, respectively, are attributed to Ce. 3+ U1-U6, located at 882.3 eV, 888.6 eV, 898.1 eV, 900.8 eV, 907.0 eV, and 916.6 eV respectively, are Ce 4+ XPS peak. Based on fitted total Ce 3+ and Ce 4+ Calculate Ce using peak area 3+ / Ce 4+ The proportions and specific results are shown in Table 1, for Examples 1, 2, and 3, regarding Ce. 3+ / Ce 4+The area ratios are 0.22, 0.25, and 0.26, showing an increasing trend. Due to Ce... 3+ Closely related to oxygen vacancies, oxygen vacancies facilitate the activation of gaseous oxygen molecules, thus providing more active oxygen species for the catalytic oxidation of soot. Based on the above XPS results, it can be seen that the amount of starch added significantly alters the chemical state of Examples 1, 2, and 3. With increasing starch addition, the number of oxygen vacancies in Examples 1, 2, and 3 also increases sequentially. The number of oxygen vacancies in Examples 1, 2, and 3 is significantly better than that in Comparative Example 1. Considering both catalyst performance and relevant literature, compared to the grain size information obtained from XRD, the Ce content on the catalyst surface... 3+ / Ce 4+ The ratio may play a dominant role in performance regulation.

[0053] Figure 5 (b) is the O 1s XPS spectrum, fitted to lattice oxygen species (O) with a binding energy at 528.7 eV. 2- ), and surface-active oxygen species with binding energies at 531.0 eV and 532.4 eV ( , Three peaks. Table 2 lists the contents of different oxygen species for different catalysts, including the surface active oxygen of the catalyst ( , The results showed significant differences: Example 3 (31.1%) > Example 2 (27.9%) > Example 1 (25.5%), and the surface reactive oxygen species content in all examples was better than that in Comparative Example 1. Based on the Mars-van-Krevelen mechanism, surface reactive oxygen species play a dominant role in the catalytic oxidation of soot. After migrating to the soot surface, these reactive oxygen species can directly promote the oxidation of soot to CO2. Therefore, adding starch can provide more reactive oxygen species to participate in the catalytic oxidation of soot. In summary, the introduction of starch can effectively enhance the surface oxygen activity of the catalyst, thereby improving the catalytic oxidation efficiency of soot.

[0054] Test Example 6 H2-TPR testing procedure: Approximately 100 mg of the composite material (20-30 mesh) was weighed as a catalyst sample and placed in a quartz reaction tube. The sample was pretreated at 450 °C with a N2 flow rate of 40 mL / min for 30 min. After the sample cooled naturally to room temperature, the atmosphere was switched to a reducing atmosphere (5.0 vol.% H2-N2, flow rate 40 mL / min). Subsequently, the sample was heated to 900 °C at a constant heating rate (10 °C / min). The amount of hydrogen consumed during the reduction process was monitored and recorded using a thermal conductivity detector (TCD).

[0055] Figure 6 The test results for H2 temperature programmed reduction (H2-TPR (left)) and O2 temperature programmed oxidation (O2-TPD (right)) of the composite material.

[0056] like Figure 6 As shown in the left figure, the reduction peaks below 750℃ originate from the conversion of surface lattice oxygen. Surface lattice oxygen can generate highly active surface oxygen, effectively promoting the efficiency of soot oxidation. Hydrogen consumption was quantified by the integrated peak area (Table 2). The H2 consumption value of Example 3 reached 9324, significantly higher than that of Example 2 (area 8770) and Example 1 (area 8340). These results indicate that Example 3 possesses a stronger surface lattice oxygen supply capacity, thus exhibiting the best soot catalytic oxidation performance. O2-TPD analysis revealed the characteristics of catalyst oxygen activation and oxygen release (…). Figure 6 (See the right figure). Based on the characteristic peak assignments, the desorption peaks below 200℃ (peaks I and II) belong to physically adsorbed oxygen and weakly chemisorbed oxygen, the oxygen consumption peak in the range of 200~450℃ (peak III) belongs to chemisorbed oxygen, the desorption peak in the range of 450~650℃ (peak IV) originates from the migration of surface lattice oxygen, and the signal released above 750℃ is related to the release of bulk lattice oxygen. Since the combustion temperature of soot is usually higher than 250℃, and the catalyst is difficult to participate in the soot catalytic reaction at temperatures exceeding the diesel engine emission temperature (>650℃), the key oxygen species determining the catalytic activity of soot are peak III (chemisorbed oxygen) and peak IV (surface lattice oxygen). The chemisorbed oxygen desorption peak temperature of Example 3 (216℃) is significantly lower than that of Example 1 (258℃) and Example 2 (247℃). At the same time, Example 3 shows a lower oxygen vacancy desorption peak temperature and a larger peak area, indicating that it can provide a richer variety of active oxygen species at low temperatures. This characteristic provides favorable conditions for low-temperature carbon soot catalytic combustion, revealing that Example 3 has better low-temperature reactivity; in summary, the overall performance of Examples 1, 2 and 3 is better than that of Comparative Example 1.

[0057] Test Example 7 Soot-TPR testing procedure: 90 mg of the composite material was weighed as a catalyst and mixed with 10 mg of soot. After thorough grinding and mixing, the mixture was placed in a quartz reaction tube. First, He gas was introduced at 120 °C (flow rate 40 mL / min) for 1 h for pretreatment. Then, the sample was heated to 900 °C at a constant heating rate (10 °C / min) and held at this temperature for 1 h. The gas signal generated during the reduction process was monitored in real time using a thermal conductivity detector (TCD).

[0058] Figure 7 (a) and Figure 7(b) shows the soot-TPR test results under close contact and loose contact conditions, respectively. The reduction peak in the 400-750℃ range originates from the surface lattice oxygen reaction, while the peak above 750℃ represents the process of bulk lattice oxygen migrating to the catalyst surface and participating in the soot combustion reaction. In an N2 atmosphere, the oxygen species of the catalyst itself provide the only oxidant source for soot oxidation. Quantitative analysis based on Table 3 shows that the low-temperature peak area (3532) of Example 3 under close contact is significantly higher than that of Example 2 (3101) and Example 1 (2429); the same trend is observed under loose contact conditions, with the low-temperature peak area (3200) of Example 3 being significantly larger than that of Example 2 (2487) and Example 1 (1872). Therefore, under both contact modes, Example 3 shows a significant advantage in the amount of surface lattice oxygen involved; in summary, the overall performance of Examples 1, 2, and 3 is also superior to that of Comparative Example 1. Figure 5 (XPS), Figure 6 (O2-TPD) and Figure 7 The (H2-TPR) results show that Example 3 can decompose more reactive oxygen species at a lower temperature. Interestingly, compared with the catalysts of Example 2 and Example 1, the catalyst of Example 3 shows a smaller difference in low-temperature peak area between close and loose contact, demonstrating the superior mass transfer efficiency of the catalyst of Example 3, thus confirming that the structural design of the catalyst of Example 3 is most suitable for carbon soot oxidation. A comprehensive comparison of Examples 1, 2, 3 and Comparative Example 1 shows that the overall performance of the examples is superior to that of the comparative example.

[0059] Test Example 8 Various composite materials were used as catalysts for the catalytic oxidation (solid-solid) reaction of diesel engine exhaust soot. The test procedure was as follows: First, 90 mg of catalyst was uniformly ground in a mortar for 5 minutes, then mixed with 10 mg of soot for 2 minutes to obtain a loose sample; then, 90 mg of catalyst was uniformly ground in a mortar for 5 minutes, then 10 mg of soot particles were added and grinding was continued for 5 minutes to obtain a compact sample. During the activity test, the prepared mixed sample was loaded into a stainless steel tubular reactor. First, N2 (flow rate 50 mL / min) was introduced at 160 °C for pretreatment to remove surface adsorbed species. After pretreatment, the total reaction gas flow rate was switched to 500 mL / min (1000 ppm NO, 7.0 vol.% H2O, 10.0 vol.% O2, N2). Under this atmosphere, the reactor temperature was increased to 600 °C at a constant rate (2 °C / min). The CO2 concentration in the outlet gas flow generated during the reaction was monitored using a Fourier transform infrared spectroscopy (iS50 FT-IR).

[0060] T, which is used to statistically analyze the activity data of each catalyst p T 10% T 50% T 90%See Table 3.

[0061] Figure 8 The table shows the activity (a) and conversion rate (b) of the catalyst in removing soot particles under compacted conditions. Combined with the analysis in Table 3, the Tp values ​​of Examples 1, 2, and 3 decrease sequentially. Specifically, the Tp value of Example 3 is... p (372℃) lowest. Typically, the ignition temperature T10% is one of the key indicators for evaluating the intrinsic activity of a reaction catalyst. Data analysis shows (see Table 3 for details) that the T10% in Example 3... 10% (349°C) lower than Example 2 (T) 10% =350℃) and Example 1 (T 10% =369℃). This indicates that both Example 3 and Example 2 have superior intrinsic activity. Overall T p With T 10% As a result, the intrinsic activity order of the catalysts was Example 3 > Example 2 > Example 1. Given that under close contact conditions, the catalyst and soot are thoroughly mixed and contacted through prolonged grinding, the catalyst performance may be weakened by its morphological characteristics. Therefore, the contact mode will be changed subsequently to more closely simulate the actual exhaust gas atmosphere for performance evaluation. Figure 9 The figures show the catalyst activity (a) and conversion rate (b) for removing soot particles under loose conditions. Combined with Table 3, the T values ​​for Examples 1, 2, and 3 are analyzed. p The values ​​also decreased sequentially, consistent with the results under tight conditions. Among them, the T value of the catalyst in Example 3... p The lowest temperature was only 408°C. Furthermore, T50% is typically the most commonly used indicator for evaluating activity; all starch-doped Examples 1 (T50%)... 50% =432℃), Example 2 (T) 50% =428℃), Example 3 (T) 50% T = 414℃) 50% The values ​​all decreased sequentially. Particularly significant was the marked decrease in the conversion temperature of Example 3, with its Tconversion... 50% It dropped by 18°C. This trend is... Figure 9 (b) The conversion curve of Example 3 was also verified: Example 3 exhibited the highest reaction rate at a lower temperature. A comprehensive comparison of Examples 1, 2, 3, and Comparative Example 1, combined with the data listed in the table and the results of the above close-contact mode experiments, leads to the conclusion that using starch as a pore-forming agent to construct the macroporous structure of the catalyst is beneficial for improving catalytic activity. Examples 1, 2, and 3 generally outperformed Comparative Example 1; among Examples 1-3, Example 3 demonstrated the most excellent catalytic activity.

[0062] In addition, commonly used industrial carbon soot purification catalysts Pt / Al2O3, CeO2, and CeO2-ZrO2 were used for comparison. Comparative Examples 2, 3, and 4 are commonly used industrial Pt / Al2O3, CeO2, and CeO2-ZrO2 catalysts, respectively. The carbon soot purification performance of Comparative Examples 2, 3, and 4 is listed below. Figure 10 Detailed data are listed in Table 3. As can be seen from the figure, the purification performance of the catalysts in the series of embodiments developed in this invention is significantly better than that of the comparative catalysts.

[0063] Table 1. XPS test results of the composite materials obtained in the examples and comparative examples.

[0064] Note: a is the pore size of the sample; b is derived from the study of the XRD (111) crystal plane.

[0065] Table 2. Purification efficiency of composite materials for carbon soot from examples and comparisons.

[0066] Note: a represents the area of ​​peaks III and IV in the O2-TPD curve of each sample; b represents the peak area of ​​the H2-TPR curve of the sample; c represents the calculated peak area of ​​the soot-TPR curve of the sample.

[0067] Table 3. Purification efficiency of composite materials for carbon soot from examples and comparisons.

[0068] Although the above embodiments have provided a detailed description of the present invention, they are only some embodiments of the present invention, and not all embodiments. Other embodiments can be obtained based on these embodiments without creative effort, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a micron-sized macroporous cerium-zirconium-praseodymium composite material, characterized in that, Includes the following steps: A cerium source, zirconium source, praseodymium source, and oxidant are dissolved in water to obtain a metal source mixture. The metal source mixture and the starch solution are mixed to obtain a colloidal mixture; The colloidal mixture was mixed with an alkaline solution and co-precipitated to obtain a precipitate system. The precipitate system was subjected to aging, dehydration and calcination in sequence to obtain the micron-sized macroporous cerium-zirconium-praseodymium composite material.

2. The preparation method according to claim 1, characterized in that, The cerium source includes at least one of cerium nitrate, cerium acetate, cerium carbonate, cerium ammonium nitrate, cerium ammonium acetate, and cerium ammonium carbonate; The zirconium source includes at least one of zirconium nitrate, zirconium acetate, zirconium oxynitrate, zirconium carbonate, ammonium zirconium carbonate, and potassium zirconium carbonate. The praseodymium source includes at least one of praseodymium nitrate, praseodymium hydroxide, praseodymium acetate, praseodymium chloride, praseodymium iodide, praseodymium acetate, praseodymium sulfate, praseodymium perchlorate, praseodymium phosphate, praseodymium oxalate, and praseodymium carbonate; The oxidant includes a first oxidant or a second oxidant; the first oxidant includes at least one of hydrogen peroxide, potassium permanganate, nitric acid, peroxy organic matter, and perchlorate; the second oxidant includes an oxidizing gas, which includes at least one of oxygen, ozone, and chlorine.

3. The preparation method according to claim 2, characterized in that, The molar ratio of the cerium source, zirconium source, and praseodymium source, based on the amount of cerium, zirconium, and praseodymium, is 0.1~0.9:0.1~0.9:0.05~0.

5. When the oxidant is the first oxidant, the content of the oxidant in the metal source mixture is 0.05~3 mol / L; when the oxidant is the second oxidant, the flow rate of the oxidant is 5~60 L / h, and the introduction time is 1~3h. The dissolution is carried out under stirring conditions, the stirring temperature is room temperature to 80°C, and the time is 10 to 180 minutes; the dissolution process includes: dissolving the cerium source, zirconium source and praseodymium source in water, and then adding an oxidant.

4. The preparation method according to claim 1, characterized in that, The ratio of the total amount of cerium, zirconium, and praseodymium source to the mass of starch in the starch solution is 1 mol: 10~500 g, based on the amount of cerium, zirconium, and praseodymium.

5. The preparation method according to claim 1, characterized in that, The alkaline solution includes at least one of ammonia solution, ammonium carbonate solution, urea solution, sodium hydroxide solution, and potassium hydroxide solution; The concentration of the alkaline solution is 10~500 mmol / L; During the mixing of the colloidal mixture and the alkaline solution, the pH value of the system is controlled to be 7~10; The process of mixing the colloidal mixture and the alkaline solution is as follows: the colloidal mixture and the alkaline solution are added dropwise to the reaction vessel using a two-phase co-current titration method; The temperature at which the drops are added is between room temperature and 80°C.

6. The preparation method according to claim 1, characterized in that, The coprecipitation reaction was carried out at a temperature of room temperature to 80°C for a time of 0.5 to 5 hours.

7. The preparation method according to claim 1, characterized in that, The aging temperature is 90~100℃, and the time is 0.5~5h; the aging is carried out under stirring and closed conditions. The dehydration temperature is 80~100℃; the dehydration is carried out under stirring and unsealed conditions.

8. The preparation method according to claim 1, characterized in that, The roasting includes a first roasting, a second roasting, a third roasting, and a fourth roasting performed sequentially; The first roasting temperature is 80~120℃, and the holding time is 0.5~3h; The second roasting temperature is 250~350℃, and the holding time is 0.5~3h; The third roasting temperature is 450~550℃, and the holding time is 0.5~3h; The fourth roasting temperature is 550~650℃, and the holding time is 0.5~6h.

9. The micron-sized macroporous cerium-zirconium-praseodymium composite material prepared by the preparation method according to any one of claims 1 to 8, characterized in that, The micron-sized macroporous cerium-zirconium-praseodymium composite material has a mesoporous-macroporous hierarchical structure; wherein the pore size of the macropores is 0.1~25μm; and the specific surface area of ​​the mesopores is 24~35m². 2 ·g -1 The mesoporous pore volume is 0.06~0.07mL / g.

10. The application of the micron-sized macroporous cerium-zirconium-praseodymium composite material of claim 9 as a catalyst in the purification of soot in diesel vehicle exhaust.

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