A method for preparing CeO2 microsphere composite catalytic material
By constructing oxygen vacancy defects on CeO2 microspheres to achieve strong chemical anchoring of noble metals, the problem of high-temperature sintering of noble metals was solved, the stability and lifespan of the catalyst were improved, and high-efficiency catalytic performance was achieved.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- NANCHANG MEDICAL COLLEGE
- Filing Date
- 2026-04-13
- Publication Date
- 2026-06-02
AI Technical Summary
In existing technologies, noble metal nanoparticles are prone to sintering at high temperatures on CeO2 supports, leading to rapid decay of catalyst activity and shortened lifespan. The lack of strong chemical anchoring sites results in insufficient bonding between the support and the noble metal, making it impossible to achieve long-term stability and efficient utilization.
High-quality CeO2 microsphere carriers were prepared by hydrothermal synthesis, and oxygen vacancy defects were constructed on their surface. These defect sites were used to form strong chemical bonds with noble metal ions, achieving precise anchoring and efficient immobilization of noble metal nanoparticles and inhibiting high-temperature sintering.
This significantly improves the long-term stability and catalytic lifetime of the catalyst. The noble metal nanoparticles remain highly dispersed at high temperatures, reducing costs and enhancing catalytic performance.
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Figure CN122124783A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalytic material preparation technology containing rare earth metal compounds. Specifically, it is a method for preparing CeO2 microsphere composite catalytic materials, particularly an integrated preparation method that combines the controllable preparation of high-quality CeO2 microsphere supports with the surface defect anchoring functionalization of noble metals, for high-temperature catalytic reactions and with super strong anti-sintering properties. Background Technology
[0002] In heterogeneous catalysis, supported noble metal-based catalytic systems are crucial in environmental protection and fine chemical industries. These catalysts exhibit excellent activity and selectivity in automotive exhaust purification, industrial VOCs elimination, and high-temperature catalytic conversion, with cerium dioxide (CeO2)-based systems attracting particular attention. CeO2, with its unique crystal structure and excellent oxygen storage and release capabilities, can provide a highly dispersed platform for noble metal nanoparticles and participate in redox cycles, significantly enhancing catalytic performance. Therefore, constructing high-performance noble metal / CeO2 composite catalytic materials has become a research hotspot in the field of catalysis.
[0003] In technological development, the conventional impregnation method has long dominated the noble metal loading process. This method involves mixing a noble metal precursor solution with a support, drying, and calcining it to transform the noble metal compound into nanoparticles dispersed on the support surface. Its design philosophy is to maximize the dispersion of noble metal active sites by utilizing the high specific surface area of the support, thereby improving utilization efficiency and reducing costs. In the early stages of catalysis technology, the impregnation method provided an economical and effective solution for industrial catalysis due to its advantages such as simple operation, wide applicability, and ease of large-scale production, promoting the widespread application of supported catalysts and enabling expensive noble metals to efficiently exert their catalytic functions.
[0004] However, with technological advancements and increasing performance requirements in application scenarios, the inherent characteristics of the impregnation method have gradually revealed its limitations, creating deep-seated technical contradictions. Since the noble metal nanoparticles supported by the impregnation method primarily rely on van der Waals forces or weak physical adsorption to bind with the CeO2 support, this binding force becomes extremely fragile at temperatures exceeding several hundred degrees Celsius. At this point, the high surface energy noble metal nanoparticles spontaneously migrate and merge, leading to an increase in particle size—a phenomenon known as "sintering." This directly results in a reduction of the active sites of the noble metals, a decrease in the effective surface area of the catalyst, triggering rapid catalytic activity decay and irreversible deactivation, shortening the catalyst's lifespan, increasing the operating costs of industrial plants, and impacting production efficiency and environmental benefits.
[0005] A deeper contradiction lies in the fact that existing technologies treat CeO2 support preparation and noble metal loading as relatively independent steps, lacking an integrated design concept centered on solving high-temperature sintering. Although hydrothermal synthesis and other methods have been used for CeO2 morphology control and crystal form optimization, most support preparation methods do not actively introduce or directionally construct anchoring sites that can form strong chemical bonds with noble metals at the microscopic level. The surface structure and chemical properties of the support fail to organically synergize with the noble metal immobilization strategy. This results in even the preparation of CeO2 supports with regular morphology and large specific surface area, whose surfaces may lack a sufficient number and intensity of high-energy defect sites, making it difficult to form a truly strong support-metal interaction (SMSI). Therefore, under the traditional technical system, optimizing the support morphology or changing the loading conditions cannot fundamentally overcome the bottleneck of high-temperature sintering of noble metals. The core mechanism remains at the level of passive physical adsorption or weak chemical adsorption, failing to achieve active and persistent locking of the atomic-level dispersion state of noble metals. This trade-off between sacrificing high-temperature stability for improving initial dispersion is unacceptable in modern industrial applications with stringent requirements for catalyst lifetime and stability.
[0006] Therefore, how to go beyond the traditional loading mode and construct an integrated preparation method that can actively regulate the surface defects of the support to achieve strong chemical anchoring of noble metals, fundamentally inhibit the high-temperature sintering of noble metals and improve the long-term stability of catalysts has become a key challenge and an urgent technical problem for those skilled in the art. Summary of the Invention
[0007] To achieve the aforementioned objectives, and addressing the dual technical challenges of high-temperature sintering and deactivation of heterogeneous catalysts and the disconnect between high-quality support preparation and noble metal functionalization in the prior art, this invention provides a method for preparing CeO2 microsphere composite catalytic materials. This invention integrates sophisticated materials engineering design and preparation processes, organically combining the controllable preparation of high-quality CeO2 microsphere supports with a precise noble metal anchoring strategy based on their surface defects, forming a complete technical solution with inherent synergistic effects. This method enables the formation of inherently strong chemical bonds between noble metal nanoparticles and the CeO2 support, thereby fundamentally inhibiting the migration, coalescence, and sintering of noble metals under extreme high-temperature conditions, significantly improving the long-term stability and catalytic lifetime of the catalyst, and ensuring the efficient utilization of active sites.
[0008] To achieve the above-mentioned objectives, the present invention adopts the following technical solution: A method for preparing a CeO2 microsphere composite catalytic material includes the following steps: (1) First stage: Controllable preparation of CeO2 microsphere carriers, including: S1. Precursor preparation: Cerium salt is mixed with carbonate solution to prepare precursor solution of cerium carbonate complex; S2. Hydrothermal synthesis: The precursor solution is transferred to a high-purity gold tube, sealed, and placed in a high-temperature and high-pressure reactor. The reaction is carried out at 200-500℃ and 200MPa for 24 hours. The reaction product is then post-treated to obtain CeO2 microsphere particle carrier. Under these hydrothermal conditions, the cerium carbonate precursor gradually transforms into a more thermodynamically stable CeO2 crystal structure through mechanisms such as dissolution-reprecipitation, directional attachment, and Ostwald ripening. Water exhibits unique solvent properties under high temperature and pressure, which can promote the transformation of CeO2 into a more thermodynamically stable crystal structure. 3+ Ions to Ce 4+ Oxidation of ions and CO3 2- The decomposition of CeO2 nuclei can be controlled by precisely regulating the growth rate and aggregation behavior of CeO2 nuclei, thereby forming micron- or submicron-sized particles with well-defined crystal faces and regular spherical morphology.
[0009] The inventors have discovered that, in order to stably obtain a regular spherical structure with a polydispersity index of less than 0.2, it is preferable to control the hydrothermal synthesis temperature between 300℃ and 400℃. When the temperature is below 250℃, the product has poor crystallinity and irregular morphology; while when the temperature is above 450℃, it is easy to cause excessive growth and aggregation of particles, which destroys the regularity of the spherical shape.
[0010] (2) Second stage: precious metal anchoring based on surface defects, including: S3. Directional construction of surface defects: The CeO2 microsphere particle carrier obtained in step S2 is subjected to high-temperature treatment in a reducing atmosphere before loading noble metals, so as to controllably create oxygen vacancy defects on the surface of the CeO2 microsphere particle carrier. The oxygen vacancy serves as the anchoring point for subsequent noble metal ions. S4. Defect-guided anchoring and in-situ reduction: The CeO2 microsphere particle carrier, which has undergone surface functionalization treatment in step S3, is dispersed in ultrapure water or ethanol to form a suspension. A noble metal precursor solution is added to anchor the noble metal at the oxygen vacancy defect sites. Subsequently, the anchored noble metal precursor is converted into noble metal nanoparticles in situ under reduction conditions, and finally the noble metal / CeO2 microsphere composite catalytic material is obtained.
[0011] Further, in step S1, the cerium salt is cerium chloride (CeCl3), and the carbonate solution is an aqueous solution of sodium carbonate (Na2CO3); the concentration range of the precursor solution is 0.05-0.4 mol / L, and its solution volume accounts for 40%-60% of the total volume of the gold tube.
[0012] Further, in step S2: the gold tube is pretreated by being shortened, acid-boiled, washed and quenched before use; the high-temperature and high-pressure reactor is connected to a high-precision ultra-high-pressure gauge, a vent pipe and a shut-off valve; the high-temperature and high-pressure reactor has a metal shell, and a strong acid and strong alkali resistant liner is provided in the metal shell, and the strong acid and strong alkali resistant liner is polytetrafluoroethylene.
[0013] Further, in step S2, the post-processing includes: rapidly cooling the reactor with ice water or compressed air, collecting the precipitate adhering to the liner, washing it 2-3 times sequentially with deionized water and anhydrous ethanol, and storing it after natural air drying.
[0014] Furthermore, the CeO2 microsphere carrier prepared in step S2 possesses the following characteristics: an average particle size range of 200 nm-800 nm, a narrow particle size distribution, and a polydispersity index below 0.2; a specific surface area of 30-120 m² / g; and a pore volume of 0.1-0.5 cm³ / g. These characteristics work synergistically to provide an ideal carrier platform for the subsequent high dispersion and anchoring of noble metals.
[0015] Further, in step S3, the reducing atmosphere is a mixture of hydrogen and argon or nitrogen inert gas, wherein the volume fraction of hydrogen is controlled at 5%-20%; the total flow rate of the reducing gas is 50-200 mL / min; the high-temperature treatment temperature is 300℃-600℃, and the time is 1-4 hours; the CeO2 microsphere particle carrier is cooled to room temperature under continuous inert atmosphere to avoid the generated oxygen vacancies being re-oxidized in the air.
[0016] Within this temperature range, some oxygen atoms in the CeO2 lattice are removed under the influence of a reducing atmosphere, resulting in the formation of oxygen vacancies, accompanied by Ce... 4+ The ions are reduced to Ce 3+ Ions maintain charge balance. The reaction equation can be expressed as: 2CeO2 + xH2 → Ce2O 4-x + xH2O. This process is a controllable thermodynamically driven process. By adjusting the processing temperature, the concentration of reducing gas, and the processing time, the density and distribution of oxygen vacancies can be precisely controlled.
[0017] The formation mechanism of these oxygen vacancies lies in the fact that high temperature provides the activation energy for lattice oxygen diffusion and desorption, while the reducing atmosphere acts as an oxygen scavenger, combining the desorbed oxygen into water molecules, thereby driving the reaction towards oxygen vacancy generation. These oxygen vacancies are not simple gaps, but rather involve significant changes in local electronic structure and charge density, causing neighboring Ce ions to exhibit Ce0 properties. 3+ Price states, these Ce 3+Together with oxygen vacancies, these regions form high-energy electron-rich regions. These regions are strongly electrophilic and can serve as Lewis basic or reducing sites, exhibiting extremely strong chemisorption and capture capabilities for subsequently introduced noble metal ions.
[0018] Further, in step S4: the concentration of the suspension is 10-50 g / L; the noble metal precursor is selected from at least one of chloroplatinic acid, palladium nitrate, chloroauric acid, or chlororhodium acid; the concentration of noble metal ions in the noble metal precursor solution is 0.001-0.05 mol / L; the noble metal precursor solution is added dropwise to the suspension at a constant rate of 0.1-1.0 mL / min, the dropwise addition is carried out under continuous stirring, the reaction temperature is controlled between 25℃ and 60℃, and the pH value of the solution is maintained between 5.0 and 7.0 to optimize the adsorption efficiency of noble metal ions.
[0019] During this anchoring phase, noble metal ions (e.g., PtCl6) 2- Pd 2+ Through electrostatic interactions, coordination, and interaction with Ce 3+ Direct chemical bonding at the site, by oxygen vacancies and adjacent Ce 3+ Cation capture is effective. These defect sites provide high-affinity adsorption capabilities, enabling noble metal ions to be stably immobilized on the CeO2 surface, rather than through simple physical adsorption in the traditional sense. This anchoring effect is essentially the formation of strong chemical bonds, such as covalent or ionic covalent bonds between the noble metal and the Ce-O lattice, or through electron transfer induced by defect sites.
[0020] Furthermore, the in-situ reduction is achieved through chemical reduction, which includes adding a reducing agent to the anchored suspension; the reducing agent is selected from at least one of sodium borohydride, hydrazine hydrate, sodium formate, or ascorbic acid; the reduction reaction is carried out at room temperature with stirring for 30-120 minutes.
[0021] For example, when NaBH4 is used as a reducing agent, it can be prepared into an aqueous solution of 0.01-0.1 mol / L and added dropwise at a rate of 0.5-2.0 mL / min.
[0022] This process reduces noble metal ions anchored at defect sites in situ to zero-valent noble metal nanoparticles. Due to the anchoring effect, these nanoparticles grow tightly at the defect sites, forming a nanoscale dispersion.
[0023] Furthermore, the in-situ reduction is achieved through thermal reduction, which includes: heating the solid obtained after centrifugation of the anchored suspension to 200℃-400℃ in a hydrogen / inert gas mixed atmosphere for 1-4 hours.
[0024] At this temperature, oxygen vacancies and Ce 3+ As reducing sites, these sites can reduce noble metal ions to metal nanoparticles, enabling the immobilization of these particles at defect sites. This method further enhances the interaction between the noble metal and the support, forming a tighter interface.
[0025] After the reduction reaction, the resulting solid product needs to be washed multiple times to remove all unreacted species and byproducts. The washing solvent is typically ultrapure water and / or ethanol. Finally, the washed composite catalyst is dried at low temperature (80°C, 12 hours) in a vacuum drying oven.
[0026] Another objective of this invention is to provide a CeO2 microsphere composite catalytic material, wherein the average size of the noble metal nanoparticles in the catalytic material is 1-5 nm, and the noble metal nanoparticles form a strong support-metal interaction bond with the CeO2 microsphere support. This strong interaction significantly inhibits the Ostwald ripening and agglomeration sintering of the noble metal nanoparticles at high temperatures.
[0027] The beneficial effects of this invention are: (1) Enhanced resistance to high-temperature sintering: Through the surface defect-oriented construction strategy introduced in the second stage, high-density high-energy anchoring sites such as oxygen vacancies are pre-set on the surface of CeO2 microsphere support. These defect sites can form inherently strong chemical bonds with noble metal ions, rather than traditional van der Waals forces or weak physical adsorption. This strong immobilization effect fundamentally inhibits the migration, aggregation, and size growth (sintering) of noble metal nanoparticles at hundreds of degrees Celsius or even higher temperatures. In simulated catalytic reactions or thermal aging tests, the catalyst prepared by this invention can still maintain a highly dispersed state of noble metal nanoparticles, and the particle size growth rate is significantly lower than that of catalysts prepared by traditional methods, thereby ensuring the long-term stability of the catalyst under harsh conditions.
[0028] (2) Long-lasting high catalytic activity and lifespan: Due to the effective and long-lasting stability of the noble metal active sites at high temperatures, the composite catalytic material prepared in this invention exhibits significantly extended lifespan and more stable catalytic performance. In long-term catalytic activity evaluation experiments, the conversion rate retention rate of the catalyst of this invention can still be maintained at a high level after long-term operation, which significantly reduces the catalyst replacement frequency and operating costs in industrial applications and improves production efficiency.
[0029] (3) Strong controllability and universality of the preparation method: The method system of this invention has a high degree of controllability. By adjusting the temperature, time, and hydrogen concentration of the reducing atmosphere treatment in the second stage, the density and distribution of oxygen vacancy defects on the CeO2 surface can be controlled. This controllability of defect density directly affects the loading and dispersion of noble metals, enabling this method to prepare high-performance catalysts with controllable noble metal loading and dispersion according to different catalytic requirements. At the same time, this method has good universality for different noble metals (such as Pt, Pd, Au, Rh, etc.).
[0030] (4) Improved utilization of precious metals and reduced costs: This invention achieves ultra-high dispersion and excellent stability of precious metal nanoparticles through strong chemical anchoring, ensuring that more precious metal atoms are exposed at the active sites of the catalytic reaction and effectively avoiding agglomeration and deactivation at high temperatures. This means that the actual amount of precious metals used can be significantly reduced while achieving the same or higher catalytic effect. Precious metals are rare and expensive resources, and reducing their usage can significantly reduce the production cost of catalysts, thereby bringing significant economic benefits to environmental protection and industrial production. At the same time, the extended catalyst life also reduces the generation of waste catalysts, which is in line with the concept of sustainable development. Attached Figure Description
[0031] Figure 1 This is a schematic flowchart of a method for preparing a CeO2 microsphere composite catalytic material according to the present invention. Detailed Implementation
[0032] To enable those skilled in the art to better understand the technical solutions of this invention, the present application will be further described in detail below with reference to embodiments.
[0033] Example 1 This embodiment aims to prepare a Pt / CeO2 composite catalytic material using the method of the present invention.
[0034] S1. Preparation of high-quality CeO2 microsphere carriers: a. Precursor preparation: Weigh 0.3g of cerium chloride (CeCl3) and dissolve it in 5ml of 0.75mol / L Na2CO3 to obtain a 0.25mol / L NaCe(CO3)2 solution.
[0035] b. Hydrothermal Synthesis: 2 ml of the prepared precursor solution is poured into a 4 ml gold tube and sealed (the precursor solution volume occupies 50% of the gold tube volume). The gold tube is then placed in a high-temperature, high-pressure reactor, and deionized water is injected as the medium. After tightening the reactor, argon gas is injected into the reactor through the vent pipe to a pressure of 60 MPa as the initial pressure. The shut-off valve is closed to stop the gas injection. The reactor is then heated in a furnace until the temperature reaches 350°C. o After step C, open the shut-off valve and continue to inject argon gas until the pressure reaches 200 MPa. Maintain the reaction time for 24 hours. After the reaction is completed, use ice water to rapidly cool the reactor to room temperature. Open the reactor and collect the precipitate adhering to the liner. Wash the precipitate three times in sequence with deionized water and anhydrous ethanol. After natural air drying, obtain high-quality CeO2 microsphere particle carrier.
[0036] The prepared CeO2 microsphere particle carrier was tested and found to have an average particle size of 613 nm, a polydispersity index of 0.14, a specific surface area of 79 m² / g, and a pore volume of 0.36 cm³ / g.
[0037] S2, Directional Construction of Surface Defects: 1.0 g of the CeO2 microspheres prepared above were uniformly spread in an alumina boat and placed inside a tubular furnace quartz tube. A 10% H2 / Ar mixed gas was introduced (total flow rate 100 mL / min, H2 flow rate 10 mL / min, Ar flow rate 90 mL / min). The temperature was increased to 400 °C at a rate of 5 °C / min and held for 2 hours. Subsequently, it was naturally cooled to room temperature under an Ar atmosphere.
[0038] S3, Pt Anchoring and In-situ Restoration: 0.5 g of defect-constructed CeO2 microspheres were dispersed in 20 mL of ultrapure water to obtain a suspension with a concentration of 25 g / L, and ultrasonically dispersed for 15 min. 0.0097 g of H2PtCl6·6H2O was dissolved in 5 mL of ultrapure water to obtain a noble metal ion concentration of 0.0035 mol / L in the noble metal precursor solution. The Pt precursor solution was added dropwise to the CeO2 suspension at a rate of 0.5 mL / min under continuous stirring (600 rpm), and stirred at 40 °C for 2 hours (during which the pH was maintained at 6.0 by adding 0.1 mol / L NaOH aqueous solution). Subsequently, a 0.08 mol / L NaBH4 aqueous solution (0.015 g NaBH4 dissolved in 5 mL of water) was prepared. This NaBH4 solution was added dropwise to the Pt-loaded CeO2 suspension at a rate of 1.0 mL / min, and stirred at room temperature for 60 min. After the reaction was completed, the sample was centrifuged, washed with water and ethanol, and finally dried under vacuum at 80°C for 12 hours. The resulting sample was a Pt / CeO2 composite catalyst.
[0039] Example 2 This embodiment aims to prepare a Pd / CeO2 composite catalytic material using the method of the present invention.
[0040] S1. Preparation of high-quality CeO2 support: a. Precursor preparation: Weigh 0.06g of cerium chloride (CeCl3) and dissolve it in 5ml of 0.75mol / L Na2CO3 to obtain a 0.05mol / L NaCe(CO3)2 solution.
[0041] b. Hydrothermal synthesis: The volume of the precursor solution was 40% of the volume of the gold tube, the reaction temperature was 200℃, and the remaining steps were the same as in Example 1, to prepare high-quality CeO2 microspheres.
[0042] The prepared CeO2 microsphere particle carrier was tested and found to have an average particle size of 316 nm, a polydispersity index of 0.11, a specific surface area of 42 m² / g, and a pore volume of 0.15 cm³ / g.
[0043] S2. Surface defect construction: Introduce a 5% H2 / N2 mixture (total flow rate 50 mL / min, H2 flow rate 2.5 mL / min, N2 flow rate 47.5 mL / min), treat at 300℃ for 1 h, and then allow to cool naturally to room temperature under N2 atmosphere.
[0044] S3, Pd Anchoring and Reduction: 0.2 g of defective CeO2 was dispersed in 20 mL of ethanol (concentrated 10 g / L). 0.012 g of palladium nitrate (Pd(NO3)2) was dissolved in 5 mL of ethanol to prepare a precursor solution with a noble metal ion concentration of 0.001 mol / L (dropping rate 0.1 mL / min). The solution was stirred at 25 °C for 2 h (during which time the pH value of the solution was maintained at 5.0 by adding 0.1 mol / L NaOH aqueous solution). Subsequently, it was reduced with 0.1 mol / L hydrazine hydrate (reaction at room temperature for 90 min). After the reaction was completed, the sample was centrifuged, washed with water and ethanol, and finally dried under vacuum at 80 °C for 12 h. The obtained sample was a Pt / CeO2 composite catalyst.
[0045] Example 3 This embodiment aims to prepare a Rh / CeO2 composite catalytic material using the method of the present invention.
[0046] S1. Preparation of high-quality CeO2 support: a. Precursor preparation: Weigh 0.49g of cerium chloride (CeCl3) and dissolve it in 5ml of 0.75mol / L Na2CO3 to obtain a 0.4mol / L NaCe(CO3)2 solution.
[0047] b. Hydrothermal synthesis: The volume of the precursor solution is 60% of the volume of the gold tube, the reaction temperature is 500℃, and the remaining steps are the same as in Example 1, to prepare a high-quality CeO2 support.
[0048] The prepared CeO2 microsphere particle carrier was tested and found to have an average particle size of 519 nm, a polydispersity index of 0.17, a specific surface area of 93 m² / g, and a pore volume of 0.42 cm³ / g.
[0049] S2. Surface defect construction: 1.0 g CeO2 support was placed in a tube furnace and a 20% H2 / Ar mixed gas (total flow rate 200 mL / min, H2 flow rate 40 mL / min, Ar flow rate 160 mL / min) was introduced. The furnace was heated to 600℃ for 4 h and then naturally cooled to room temperature under an Ar atmosphere.
[0050] S3, Rh Anchoring and In-situ Reduction: 1.0 g of defective CeO2 microspheres were dispersed in 20 mL of ultrapure water and sonicated for 20 min (200 W) to prepare a suspension with a concentration of 50 g / L. 0.106 g of rhodium chloroacetic acid (H3RhCl6・3H2O) was weighed and dissolved in 5 mL of ultrapure water to prepare a precursor solution with a noble metal ion concentration of 0.05 mol / L. Under stirring at 600 rpm, the Rh precursor solution was added dropwise to the CeO2 suspension at a rate of 1 mL / min, and the reaction was carried out at 60 °C for 2 h (during which time the pH of the solution was maintained at 7.0 by adding 0.1 mol / L NaOH aqueous solution). Subsequently, a thermal reduction method was adopted: after centrifugation of the suspension, the solid was heated to 300℃ at 3℃ / min in a 20% H2 / Ar mixed gas (flow rate 150 mL / min) and kept at this temperature for 2 h to complete the in-situ reduction. After vacuum drying at 80℃ for 12 h, the Rh / CeO2 composite catalyst material was obtained.
[0051] Comparative Example 1 This comparative example uses Pt / CeO2 catalytic materials prepared by the traditional impregnation method.
[0052] 1. Preparation of conventional CeO2 supports: CeO2 powder (non-microsphere structure) was prepared by precipitation method: 0.5 mol / L CeCl3 solution was mixed with 0.5 mol / L NaOH solution to pH=10, allowed to stand for precipitation, filtered, and calcined at 600℃ for 2 h to obtain irregular CeO2 powder (average particle size 1-2 μm, specific surface area 25 m² / g, non-oriented morphology).
[0053] 2. Load and restore order: Following the process of "loading Pt first, then reducing": after performing the same operation steps as S2 in Example 1, the material is directly dried by rotary evaporation, and then calcined in air at 400°C for 2 hours (simulating conventional reduction) to obtain the Pt / CeO2 composite catalyst.
[0054] Comparative Example 2 1. High-quality CeO2 carrier: The original CeO2 microspheres used are exactly the same as those in Example 1, but without defect construction treatment.
[0055] 2. Load and restore order: The key sequence was changed to "first load Pt, then reduce": 0.5g of the CeO2 microspheres of the present invention were dispersed in 20mL of water, Pt precursor solution was added and stirred for 2h, then directly dried and calcined in air at 400℃ for reduction (i.e. steps S2 and S3 in Example 1 were not performed first).
[0056] Comparative Example 3 1. Preparation of conventional CeO2 support: The same conventional raw CeO2 microspheres as in Comparative Example 1 were used.
[0057] 2. Loading and Restoration Sequence: Follow the sequence of the present invention: "first restore, then load Pt, then restore": that is, adopt the same steps as S2-S3 in Example 1.
[0058] Performance Comparison With "carrier structure optimization + surface defect anchoring" as the core innovation, this invention's "integrated preparation strategy" (high-quality CeO2 microsphere carrier + directional surface defect construction + defect-guided noble metal anchoring) is compared with traditional methods by controlling a single variable. The effects are compared quantitatively through five key performance indicators. All samples are tested under the same experimental conditions to ensure data comparability.
[0059] (1) Size of precious metal nanoparticles: Particle size of fresh samples and after aging (simulating high temperature conditions), reflecting dispersibility and anti-sintering ability.
[0060] (2) Size growth rate: (Aging size - Fresh size) / Fresh size × 100%, which directly reflects the degree of particle agglomeration at high temperature.
[0061] (3) CO oxidation T 50 Temperature: The temperature at which the conversion rate reaches 50% in the catalytic reaction, as tested by temperature programmed oxidation (TPO), reflects the level of catalytic activity.
[0062] (4) CO oxidation T after aging 50 Temperature: T measured after high-temperature aging treatment 50 This reflects the ability to maintain activity under high-temperature conditions.
[0063] (5) 50h conversion rate retention rate: The proportion of catalytic conversion rate maintained after 50 hours of continuous use, reflecting long-term stability.
[0064] Table 1 As shown in Table 1, by comparing the key performance indicators of Examples 1-3 and Comparative Examples 1-3, the significant advantages of the present invention in terms of anti-sintering properties, catalytic activity, and stability are fully verified, as detailed below: (1) The ability to resist high-temperature sintering is significantly enhanced. High-temperature sintering of noble metal nanoparticles is the core reason for catalyst deactivation. The data in Table 1, namely "size of noble metal after aging" and "size growth rate", intuitively demonstrate the breakthrough of this invention: a. Superior initial dispersion: In the fresh state, the average size of the noble metal nanoparticles in the embodiments of the present invention is only 2.0-2.3 nm, which is much smaller than that of Comparative Example 1 (8.2 nm), Comparative Example 2 (5.1 nm) and Comparative Example 3 (4.8 nm), indicating that the present invention achieves ultra-high dispersion of noble metals through defect anchoring.
[0065] b. Enhanced High-Temperature Stability: After aging treatment, the size of the precious metal particles in the example only slightly increased to 2.4-2.8 nm, with a size growth rate of only 19.0%-21.7%; while in the comparative example, the particle size increased dramatically to 14.2-25.6 nm after aging, with a growth rate as high as 195.8%-212.2%, a difference of more than 10 times. This confirms that the present invention, through the strategy of "strong chemical anchoring of surface oxygen vacancies," fundamentally inhibits the migration and agglomeration of precious metal particles, significantly improving anti-sintering performance.
[0066] (2) Significant advantages in catalytic activity and high-temperature activity retention. T of CO oxidation reaction 50 (The temperature at which the conversion rate reaches 50%) is the core indicator of catalytic activity. Data shows that this invention maintains high activity in both fresh and aged states: a. Higher activity with freshness: Example: Fresh CO oxidation T 50 The temperature was 85-91℃, which is much lower than that of Comparative Example 1 (128℃), Comparative Example 2 (100℃) and Comparative Example 3 (105℃), indicating that the catalyst prepared by the present invention has more initial active sites and higher catalytic efficiency.
[0067] b. Minimal activity degradation after aging: After aging, Example T 50 It only rose slightly to 92-99℃, while the comparative T 50 The temperature rises significantly to 148-187℃. This indicates that the catalyst of this invention can still maintain effective exposure of active sites under high-temperature conditions, solving the problem of rapid activity decay of traditional catalysts at high temperatures.
[0068] (3) Long-term stability is greatly improved The 50-hour conversion retention rate directly reflects the catalyst's lifespan, and the present invention has a particularly prominent advantage in stability: The conversion rate of all examples exceeded 92% after 50 hours (Example 1 > 95%, Example 2 > 94%, Example 3 > 92%), indicating that the catalyst can maintain high catalytic performance for a long time.
[0069] The highest retention rate among the comparative examples was only 68% (Comparative Example 3), and the lowest was only 45% (Comparative Example 1), which was far lower than that of the examples. This is due to the persistent locking of the noble metal active sites by the "strong support-metal interaction" of the present invention, which reduces deactivation caused by particle sintering or detachment and significantly extends the catalyst lifetime.
[0070] The comparison between Examples 1-3 and Comparative Examples 1 and 3 shows that the high-quality CeO2 microsphere carrier (average particle size 200-800 nm, narrow particle size distribution, specific surface area 30-120 m² / g) prepared by hydrothermal synthesis in this invention provides a better physical platform for the dispersion of precious metals due to its regular spherical structure, high specific surface area and controllable pore volume. It significantly improves the initial dispersion and high temperature stability of precious metals and is the basic guarantee for performance improvement.
[0071] The comparison between Examples 1-3 and Comparative Example 2 shows that "directional construction of surface oxygen vacancy defects" is the core technical feature that enables the performance breakthrough of this invention. The high-density oxygen vacancies introduced on the surface of CeO2 microspheres through reducing atmosphere treatment serve as strong chemical anchoring sites for noble metal ions, which can significantly enhance the chemical bonding between noble metals and the support, fundamentally inhibiting the migration and aggregation of noble metal particles. This mechanism cannot be achieved by traditional defect-free supports.
[0072] The comparison between Examples 1-3 and Comparative Examples 2 and 3 shows that the "preparation of high-quality CeO2 microsphere carriers" and "directional construction of surface oxygen vacancy defects" of the present invention are not isolated technical steps. The two form a synergistic effect. The high specific surface area and regular structure of the microsphere carriers provide a physical basis for the uniform distribution of defect sites, while the surface defects accurately fix the noble metal to the surface of the microspheres through strong chemical anchoring. Together, they achieve a comprehensive performance improvement of "high dispersibility, strong anti-sintering properties, and stability". This synergistic mechanism cannot be achieved by traditional technical systems.
[0073] This invention successfully solves the core problems of traditional supported catalysts, such as easy sintering at high temperatures and rapid activity decay, through an integrated strategy of "controllable preparation of CeO2 microspheres - directional construction of surface oxygen vacancies - anchoring of noble metal defects". It achieves a synergistic improvement of "high resistance to sintering - high catalytic activity - long lifespan" and provides a high-performance material solution for high-temperature catalysis fields (such as automobile exhaust purification and VOCs elimination).
Claims
1. A method for preparing a CeO2 microsphere composite catalytic material, characterized in that, Includes the following steps: (1) First stage: Controllable preparation of CeO2 microsphere particle carriers, including: S1. Precursor preparation: Cerium salt is mixed with carbonate solution to prepare precursor solution of cerium carbonate complex; S2. Hydrothermal synthesis: The precursor solution is transferred to a high-purity gold tube, sealed, and placed in a high-temperature and high-pressure reactor. The reaction is carried out at 200-500℃ and 200MPa for 24 hours. The reaction product is then post-treated to obtain CeO2 microsphere particle carrier. (2) Second stage: precious metal anchoring based on surface defects, including: S3. Directional construction of surface defects: The CeO2 microsphere particle carrier obtained in step S2 is subjected to high-temperature treatment in a reducing atmosphere before loading noble metals, so as to controllably create oxygen vacancy defects on the surface of the CeO2 microsphere particle carrier. The oxygen vacancy serves as the anchoring point for subsequent noble metal ions. S4. Defect-guided anchoring and in-situ reduction: The CeO2 microsphere particle carrier, which has undergone surface functionalization treatment in step S3, is dispersed in ultrapure water or ethanol to form a suspension. A noble metal precursor solution is added to anchor the noble metal at the oxygen vacancy defect sites. Subsequently, the anchored noble metal precursor is converted into noble metal nanoparticles in situ under reduction conditions, and finally the noble metal / CeO2 microsphere composite catalytic material is obtained.
2. The preparation method according to claim 1, characterized in that, In step S1, the cerium salt is cerium chloride (CeCl3), and the carbonate solution is sodium carbonate (Na2CO3) aqueous solution; the concentration range of the precursor solution is 0.05-0.4 mol / L, and its solution volume accounts for 40%-60% of the total volume of the gold tube.
3. The preparation method according to claim 1, characterized in that, In step S2: The gold tube is pretreated by cutting, acid boiling, washing and quenching before use; The high-temperature and high-pressure reactor is connected to a high-precision ultra-high-pressure pressure gauge, a venting pipe, and a shut-off valve. The high-temperature and high-pressure reactor has a metal shell, and a strong acid and strong alkali resistant liner is provided in the metal shell. The strong acid and strong alkali resistant liner is made of polytetrafluoroethylene.
4. The preparation method according to claim 1, characterized in that, In step S2, the post-processing includes: rapidly cooling the reactor with ice water or compressed air, collecting the precipitate adhering to the liner, washing it 2-3 times sequentially with deionized water and anhydrous ethanol, and storing it after natural air drying.
5. The preparation method according to claim 1, characterized in that, The CeO2 microsphere particle carrier prepared by step S2 has the following characteristics: the average particle size ranges from 200 nm to 800 nm, the particle size distribution is narrow, and the polydispersity index is less than 0.2; the specific surface area is 30-120 m² / g; and the pore volume is 0.1-0.5 cm³ / g.
6. The preparation method according to claim 1, characterized in that, In step S3, the reducing atmosphere is a mixture of hydrogen and argon or nitrogen inert gas, wherein the volume fraction of hydrogen is controlled at 5%-20%; the total flow rate of the reducing gas is 50-200 mL / min; the high-temperature treatment is at 300℃-600℃ for 1-4 hours; the CeO2 microsphere carrier is cooled to room temperature under continuous inert atmosphere to prevent the generated oxygen vacancies from being re-oxidized in the air.
7. The preparation method according to claim 1, characterized in that, In step S4: the concentration of the suspension is 10-50 g / L; the noble metal precursor is selected from at least one of chloroplatinic acid, palladium nitrate, chloroauric acid, or chlororhodium acid; the concentration of noble metal ions in the noble metal precursor solution is 0.001-0.05 mol / L; the noble metal precursor solution is added dropwise to the suspension at a constant rate of 0.1-1.0 mL / min, the dropwise addition is carried out under continuous stirring, the reaction temperature is controlled between 25℃ and 60℃, and the pH value of the solution is maintained between 5.0 and 7.
0.
8. The preparation method according to claim 1, characterized in that, The in-situ reduction is achieved by chemical reduction, which includes adding a reducing agent to the anchored suspension; the reducing agent is selected from at least one of sodium borohydride, hydrazine hydrate, sodium formate, or ascorbic acid; the reduction reaction is carried out at room temperature with stirring for 30-120 minutes.
9. The preparation method according to claim 7, characterized in that, The in-situ reduction is achieved by thermal reduction, which includes: heating the solid obtained after centrifugation of the anchored suspension to 200℃-400℃ in a hydrogen / inert gas mixed atmosphere for 1-4 hours.
10. A CeO2 microsphere composite catalytic material, prepared by the method according to any one of claims 1-9, characterized in that, The average size of the noble metal nanoparticles in the catalytic material is 1-5 nm.