Preparation method and application of layered lanthanum oxide with high specific surface area

Abstract

The invention discloses a preparation method of layered lanthanum oxide with a high specific surface area. The preparation method comprises the following steps: (1) mixing granular lanthanum oxide with an average particle size of 1-2 m with deionized water so as to uniformly wet the surface of the granular lanthanum oxide; (2) standing the material obtained in the step (1) at 24-26 DEG C until a white, loose and popcorn-like intermediate is formed; and (3) calcining the intermediate obtained in the step (2) at a constant temperature of 450-550 DEG C to obtain the product. The lanthanum oxide with extremely high specific surface area and a unique layered microstructure can be efficiently prepared through a unique'top-to-bottom 'rupture mechanism, so that the lanthanum oxide has huge potential in the application fields of catalysis, adsorption, energy storage and the like, and the practical application value of the material is remarkably improved.

Description

Technical Field

[0001] This invention belongs to the field of rare earth functional materials technology, specifically relating to a method for preparing high specific surface area layered lanthanum oxide and its application. Background Technology

[0002] Lanthanum oxide (La₂O₃), as an important rare earth oxide, possesses unique basicity, oxygen storage capacity, and thermal stability, playing a crucial role in numerous industrial fields. Particularly in heterogeneous catalysis, lanthanum oxide with its high specific surface area is widely used as a catalyst or promoter in applications such as automotive exhaust purification (e.g., CO oxidation catalysts), fluidized bed catalytic cracking (FCC), methane oxidative coupling, and hydrogen storage materials. The specific surface area of ​​a material is one of the core factors affecting its catalytic activity; a higher specific surface area exposes more active sites, thereby significantly improving the efficiency of catalytic reactions.

[0003] Therefore, developing efficient and low-cost methods for preparing high specific surface area layered lanthanum oxide has always been a research hotspot in materials science and chemical engineering. Currently, the mainstream preparation methods mainly employ a bottom-up wet chemical route. Specifically, these methods include the following:

[0004] (1) Precipitation method: Using soluble lanthanum salts such as lanthanum nitrate or lanthanum chloride as raw materials, precipitants such as ammonia, sodium hydroxide or urea are added to an aqueous solution to precipitate lanthanum ions in the form of hydroxides or carbonates. The resulting gel or powder precursor needs to undergo multiple steps such as filtration, washing, drying and high-temperature calcination to obtain the final lanthanum oxide. This method is relatively mature, but it has problems such as a long process flow, consumption of a large amount of chemical reagents and pure water, generation of a large amount of saline wastewater, and difficulty in accurately controlling the morphology and particle size of the final product.

[0005] (2) Sol-gel method: Using organometallic compounds such as lanthanum alkoxides as precursors, a three-dimensional network structure gel is formed through hydrolysis and condensation reactions, followed by drying and calcination to obtain oxides. This method can prepare materials with highly uniform composition, but the precursors are expensive and require a large amount of organic solvents, which has an adverse impact on the environment.

[0006] (3) Template method: Soft templates such as surfactants and polymers, or hard templates such as silica and carbon spheres, are used as structure guiding agents to induce the precursor to form an ordered porous structure. This method can produce materials with uniform pore size, but the introduction and subsequent removal of the templates significantly increase the complexity and cost of the process.

[0007] (4) Hydrothermal method: The reaction is carried out in a closed reactor under high temperature and high pressure, which can produce nanomaterials with good crystallinity. However, this method has high requirements for equipment and high energy consumption, and is not suitable for large-scale industrial production.

[0008] In summary, existing methods for preparing high-specific-surface-area layered lanthanum oxide generally face challenges such as complex processes, high costs, high energy consumption, or environmental unfriendliness. These issues limit the widespread industrial application of high-performance lanthanum oxide materials. Therefore, there is an urgent need to develop a new technology that is simple, economical, environmentally friendly, and easy to scale up to meet the growing industrial demand for high-performance lanthanum oxide materials. Summary of the Invention

[0009] The purpose of this invention is to overcome the shortcomings of the prior art and provide a method for preparing high specific surface area layered lanthanum oxide and its application.

[0010] The technical solution of the present invention is as follows:

[0011] A method for preparing layered lanthanum oxide with high specific surface area includes the following steps:

[0012] (1) Mix granular lanthanum oxide with an average particle size of 1-2 µm with deionized water to uniformly wet the surface of the granular lanthanum oxide;

[0013] (2) Let the material obtained in step (1) stand at 20-30 ℃ for 10 min-2 h until a white, loose and popcorn-like intermediate is formed;

[0014] (3) The intermediate obtained in step (2) is calcined at a constant temperature of 450-550 °C for 1-4 h. The heating rate before constant temperature calcination is 2-10 °C / min, thus obtaining the high specific surface area layered lanthanum oxide.

[0015] In a preferred embodiment of the present invention, in step (1), the mass ratio of the granular lanthanum oxide to deionized water is 1:0.2-1.

[0016] More preferably, the mass ratio of the granular lanthanum oxide to deionized water is 1:0.4.

[0017] In a preferred embodiment of the present invention, the settling temperature in step (2) is 25 °C and the settling time is 30 min.

[0018] In a preferred embodiment of the present invention, the isothermal calcination in step (3) is carried out at a temperature of 500 °C for 2 h.

[0019] More preferably, the heating rate before isothermal calcination in step (3) is 5 °C / min.

[0020] The beneficial effects of this invention are:

[0021] 1. The entire process of this invention includes only three main steps: mixing, settling, and calcination. This avoids the cumbersome operations of precise pH control, filtration, and repeated washing in traditional precipitation methods, thereby significantly reducing the complexity of operation and time costs.

[0022] 2. The starting material of this invention is inexpensive industrial-grade granular lanthanum oxide, and the only reaction reagent is water. There is no need to use expensive lanthanum salts, organic alkoxides or template agents, which greatly reduces the production cost and facilitates industrial promotion.

[0023] 3. The reaction process of this invention does not involve any organic solvents or acid / base reagents, does not produce saline wastewater or harmful pollutants, is environmentally friendly, and meets the requirements of sustainable development.

[0024] 4. This invention utilizes a unique "top-down" fracture mechanism to efficiently prepare lanthanum oxide with extremely high specific surface area and a unique layered microstructure. High specific surface area means the material has a larger exposed surface area per unit mass, providing more active sites for chemical reactions and thus greatly improving its catalytic efficiency. It can be applied to automotive exhaust purification (such as CO oxidation catalysts) and fluidized catalytic cracking (FCC), significantly enhancing the material's application value. Attached Figure Description

[0025] Figure 1 This is a SEM image of the "popcorn-like" lanthanum hydroxide intermediate formed after hydration and self-decomposition in Example 1 of the present invention.

[0026] Figure 2 This is a SEM image of the high specific surface area layered lanthanum oxide obtained in Example 1 of the present invention. Detailed Implementation

[0027] The technical solution of the present invention will be further explained and described below with reference to specific embodiments and accompanying drawings.

[0028] Example 1

[0029] (1) Weigh 100 g of commercially available granular lanthanum oxide with an average particle size of 1-2 µm, place it in an open container, slowly add 40 g of deionized water (the mass ratio of water to lanthanum oxide is 0.4:1), and stir simply to ensure that the water evenly wets the surface of the particles.

[0030] (2) The material obtained in step (1) was left to stand at room temperature (25 °C) for 30 min. It was observed that the particles gradually emitted a slight crackling sound after absorbing water and underwent significant volume expansion, transforming into the following state: Figure 1 The white, loose, popcorn-like solid shown is an intermediate of lanthanum hydroxide (La(OH)3).

[0031] (3) The lanthanum hydroxide intermediate obtained in step (2) is transferred to a muffle furnace and heated to 500 °C at a heating rate of 5 °C / min. It is then calcined at this temperature for 2 h and naturally cooled to room temperature to obtain the high specific surface area layered lanthanum oxide.

[0032] According to the BET method, the specific surface area of ​​the high specific surface area layered lanthanum oxide in this embodiment is 115 m². 2 / g. Scanning electron microscopy (SEM) revealed that the product consists of numerous stacked, layered particles with a rich porous structure (e.g., ...). Figure 2 (As shown).

[0033] Comparative Example 1 (Insufficient Water)

[0034] The steps of Example 1 were repeated, but the amount of deionized water added was changed to 20 g (the mass ratio of water to lanthanum oxide was 0.2:1). Reactions were observed on some particle surfaces, but no large-scale "popcorn" bursting occurred; a large number of unreacted hard particle cores remained. After calcining the product at 500 °C for 2 h, its BET specific surface area was measured to be 48 m². 2 / g.

[0035] Comparative Example 2 (Excessive Water)

[0036] The steps of Example 1 were repeated, but the amount of deionized water added was changed to 200 g (the mass ratio of water to lanthanum oxide was 1:2). The particles were observed to be completely submerged in water, forming a sparse slurry. No obvious particle breakage or volume expansion was observed during the reaction. The slurry was dried at 110 °C and then calcined at 500 °C for 2 h. The BET specific surface area of ​​the final product was measured to be 27 m². 2 / g.

[0037] Comparative Example 3 (Raw material particle size too fine)

[0038] The steps of Example 1 were repeated, but the starting material in step (1) was changed to nano-lanthanum oxide powder with an average particle size of 0.1 µm. After adding 40 g of water, the powder quickly formed a uniform paste without any "popcorn" phenomenon. After calcination under the same conditions, the BET specific surface area of ​​the product was measured to be 42 m². 2 / g.

[0039] Comparative Example 4 (Raw material with larger particle size)

[0040] The steps of Example 1 were repeated, but the starting material in step (1) was changed to large lanthanum oxide particles with an average particle size of 3-5 µm. After adding 40 g of water, a more vigorous bursting phenomenon was observed. After calcination under the same conditions, the BET specific surface area of ​​the product was measured to be 98 m². 2 / g, SEM observation showed that it also has a layered porous structure.

[0041] Comparative Example 5 (calcination temperature too high)

[0042] The "popcorn-like" lanthanum hydroxide intermediate obtained in Example 1 was calcined at 800 °C for 2 h. The BET specific surface area of ​​the final product was measured to be only 18 m². 2 / g. SEM observation showed obvious melting and sintering at the particle edges, with a large amount of pore structure collapsing.

[0043] Comparative Example 6 (Prior Art: Precipitation Method)

[0044] 43.3 g of lanthanum nitrate hexahydrate (La(NO3)3·6H2O) was dissolved in 1 L of deionized water to form a 0.1 mol / L solution. Under vigorous stirring, 2 mol / L ammonia solution was added dropwise until the pH reached 10. After stirring for 3 h, the resulting gel-like precipitate was filtered. The precipitate was washed five times with deionized water and twice with ethanol to remove residual nitrate and ammonium ions. The washed precipitate was dried at 80 °C for 24 h to obtain lanthanum hydroxide precursor powder. Finally, the powder was calcined at 500 °C for 2 h. The BET specific surface area of ​​the final product was measured to be 65 m². 2 / g. This method involves numerous steps, is time-consuming, and generates a large amount of harmful wastewater.

[0045] Comparative Example 7 (Prior Art: Excessive Hydration)

[0046] 100 g of commercially available granular lanthanum oxide with an average particle size of 1 µm was weighed and added to 500 g of deionized water to form a suspension slurry. The mixture was stirred at room temperature for 24 h. After filtration, the resulting solid was dried at 110 °C and then calcined at 500 °C for 2 h. The BET specific surface area of ​​the final product was measured to be 13 m². 2 / g.

[0047] The key parameters and results of the above embodiments and comparative examples are summarized in Table 1 below.

[0048] Table 1

[0049] serial number Starting materials <![CDATA[Water / La2O3 mass ratio]]> Hydration Calcination temperature (°C) BET specific surface area (m² / g) Final morphology (SEM) Example 1 <![CDATA[Granular La2O3 (1 - 2 µm)]]> 0.4 Violent "popcorn"-like bursting 500 115 Layered, porous sheets Comparative Example 1 <![CDATA[Granular La2O3 (1 - 2 µm)]]> 0.2 Incomplete reaction, slight cracking 500 48 Partially reacted particles Comparative Example 2 <![CDATA[Granular La2O3 (1 - 2 µm)]]> 0.6 Forms a slurry without cracking. 500 27 Aggregated fine particles Comparative Example 3 <![CDATA[Powder La2O3 (<0.1 µm)]]> 0.4 Forms a paste-like substance without breaking. 500 42 Aggregated fine particles Comparative Example 4 <![CDATA[Granular La2O3 (3 - 5 µm)]]> 0.4 Incomplete reaction, slight cracking 500 58 Partially reacted particles Comparative Example 5 <![CDATA[Granular La2O3 (1 - 2 µm)]]> 0.4 Violent "popcorn"-like bursting 800 18 Sintered particles Comparative Example 6 <![CDATA[La(NO3)3 solution]]> N / A Gel precipitation 500 65 Nanorod-shaped fine powder Comparative Example 7 <![CDATA[Granular La2O3 (1-2 µm)]]> 5.0 (slurry) No cracks 500 13 Low porosity particles

[0050] The data comparison in Table 1 clearly shows that:

[0051] 1. The criticality of water quantity: The comparison between Example 1, Comparative Example 1, and Comparative Example 2 shows that there is an optimal water quantity range (around 0.4:1). Too little water results in insufficient reaction, while too much water fails to accumulate stress, neither of which can effectively achieve the preparation of a high specific surface area.

[0052] 2. Importance of raw material form: The comparison between Example 1 and Comparative Examples 3 and 4 shows that the starting raw material must be "particles" of a certain size, rather than fine or coarse powder, which is a prerequisite for mechanical fracture.

[0053] 3. Control of calcination temperature: The comparison between Example 1 and Comparative Example 5 shows that low-temperature calcination (500 °C) is crucial for maintaining the high specific surface area of ​​the material, while high temperature will lead to severe sintering.

[0054] 4. Advantages over existing technologies: Compared with Comparative Example 6 (precipitation method) and Comparative Example 7 (excess water hydration), Example 1 not only greatly simplifies the process, but also significantly increases the specific surface area of ​​the final product.

[0055] In summary, this invention, by ingeniously utilizing a long-neglected physicochemical phenomenon, opens up a completely new, efficient, and low-cost technical route for preparing high-performance lanthanum oxide materials, possessing extremely high scientific value and promising industrial application prospects.

[0056] The above description is merely a preferred embodiment of the present invention, and therefore should not be construed as limiting the scope of the present invention. All equivalent changes and modifications made in accordance with the scope of the patent and the contents of the specification should still fall within the scope of the present invention.

Claims

1. A method for preparing high specific surface area layered lanthanum oxide, characterized in that: Includes the following steps: (1) Mix granular lanthanum oxide with an average particle size of 1-2 µm with deionized water to uniformly wet the surface of the granular lanthanum oxide; (2) Let the material obtained in step (1) stand at 24-26 ℃ until it forms a white, loose and popcorn-like intermediate; (3) The intermediate obtained in step (2) is calcined at a constant temperature of 450-550 °C to obtain the final product.

2. The preparation method according to claim 1, characterized in that: In step (1), the mass ratio of the granular lanthanum oxide to deionized water is 1:0.2-1.

3. The preparation method according to claim 2, characterized in that: The mass ratio of the granular lanthanum oxide to deionized water is 1:0.

4.

4. The preparation method according to claim 1, characterized in that: The settling temperature in step (2) is 25 ℃ and the settling time is 30 min.

5. The preparation method according to claim 1, characterized in that: The constant temperature calcination in step (3) is 500℃ and the time is 2 h.

6. The preparation method according to claim 5, characterized in that: The heating rate before isothermal calcination in step (3) is 5 °C / min.

7. The preparation method according to claim 1, characterized in that: The mass ratio of the granular lanthanum oxide to deionized water is 1:0.4; the settling temperature in step (2) is 25 ℃ and the time is 30 min; the isothermal calcination temperature in step (3) is 500 ℃ and the time is 2 h, and the heating rate before isothermal calcination is 5 ℃ / min.

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