High-entropy porous boric acid multi-metal catalyst, preparation method thereof and application of high-entropy porous boric acid multi-metal catalyst in photocatalytic reduction of CO2

Abstract

The invention discloses a high-entropy porous boric acid multi-element metal catalyst and a preparation method thereof and application in photocatalytic reduction of CO2, the catalyst is composed of H (Al alpha Cu beta Fe gamma Co delta Ga lambda) 3B6O12 (OH) 4, alpha: beta: gamma: delta: lambda = (1-4): (1-4): (1-4): (1-4): (1-4), and alpha + beta + gamma + delta + lambda = 1, the preparation method of the catalyst comprises the following steps: boric acid is added into a hydrothermal solution containing cobalt salt, aluminum salt, copper salt, iron salt and gallium salt for a reaction, and the reaction liquid is cooled to room temperature to obtain the high-entropy porous boric acid multi-element metal catalyst. And then washing and drying. The obtained catalyst has high thermodynamic and chemical stability, and has the advantages of being long in service life and excellent in CO2 photocatalytic reduction performance as a CO2 photocatalytic reduction catalyst.

Description

Technical Field

[0001] The present invention belongs to the technical field of inorganic functional materials, and specifically relates to a high-entropy porous borate multi-metal catalyst, a preparation method thereof, and an application thereof in photocatalytic reduction of CO2. Background Art

[0002] With the acceleration of global industrialization, carbon dioxide (CO2) emissions have increased dramatically, leading to increasingly serious greenhouse effect and climate change problems. Converting CO2 into high-value-added chemicals or fuels not only helps mitigate the greenhouse effect, but also enables the recycling of carbon resources, which has important environmental and energy significance. Photocatalytic reduction of CO2 technology uses solar energy to convert CO2 into useful products such as CO, CH4, and CH3OH, and is considered a green and sustainable solution. However, traditional photocatalytic materials face problems such as narrow light absorption range, high recombination rate of photogenerated carriers, and insufficient CO2 adsorption and activation capacity during the CO2 reduction process, which limits their practical application.

[0003] Porous aluminum borate is a new type of porous catalytic material. Unlike traditional silica-alumina molecular sieves, the porous aluminum borate framework is composed of AlO6 octahedrons and BO clusters, forming a three-dimensional open pore structure with rich structure and adjustable pore size, which avoids the diffusion limitation problem of traditional molecular sieves; more importantly, the surface of the three-dimensional open pore structure is rich in terminal hydroxyl groups, which can selectively adsorb CO2 molecules through weak hydrogen bonds, and can achieve efficient enrichment even under low concentration conditions. At the same time, this type of material has a certain photocatalytic CO2 conversion activity, especially by taking advantage of its adjustable structure. After introducing photocatalytic active components such as Ga and Fe into its framework structure, its photocatalytic conversion activity is significantly enhanced. But in general, the photocatalytic conversion activity of this type of material in CO2 is relatively low.

[0004] In recent years, high-entropy materials (HEMs) have shown tremendous potential in catalysis due to their unique multi-element synergistic effects, tunable electronic structures, and excellent physicochemical properties. Composed of five or more principal elements, HEMs possess complex crystal structures and multiple active sites that can effectively optimize light absorption, enhance charge separation efficiency, and improve catalytic activity. Furthermore, confined structures, by confining active materials to nanoscale spaces, can significantly improve catalyst stability and reactivity while suppressing side reactions.

[0005] The preparation of porous aluminum borate into a high-entropy material significantly enhances its performance in photocatalytic reduction of CO2. The advantages of high-entropy materials, such as multi-factor synergistic effects, optimized energy band structures, enhanced light absorption, efficient charge separation, and abundant surface active sites, make them highly efficient, stable, and environmentally friendly photocatalytic materials suitable for CO2 reduction. Summary of the Invention

[0006] In order to address the deficiencies of the prior art, the purpose of the present invention is to provide a high-entropy porous borate multi-metal catalyst, a preparation method thereof, and an application in the photocatalytic reduction of CO2. The catalyst has high thermodynamic and chemical stability, and as a photocatalytic reduction of CO2 catalyst has the characteristics of long service life and excellent photocatalytic reduction of CO2 performance.

[0007] In order to achieve the above objectives, the present invention adopts the following technical solutions: A high entropy porous borate multi-metal catalyst, the chemical formula of the catalyst is H(Al α Cu β Fe γ Co δ Ga λ )3B6O 12 (OH)4, where α:β:γ:δ:λ=(1~4):(1~4):(1~4):(1~4):(1~4), and α+β+γ+δ+λ=1.

[0008] The preparation method of the above-mentioned catalyst specifically comprises the following steps: adding boric acid to a hydrothermal solution containing cobalt salt, aluminum salt, copper salt, iron salt and gallium salt for reaction, and then washing and drying to obtain a high-entropy porous boric acid multi-metal catalyst.

[0009] Preferably, in the aforementioned hydrothermal solution, the concentrations of cobalt salt, aluminum salt, copper salt, iron salt and gallium salt are respectively 0.05-5 mol / L.

[0010] Preferably, the aforementioned cobalt salt, aluminum salt, copper salt, iron salt and gallium salt are at least one of nitrates, sulfates and acetates containing cobalt, aluminum, copper, iron or gallium, respectively.

[0011] Preferably, the molar ratio of the total molar amount of cobalt salt, aluminum salt, copper salt, iron salt and gallium salt to boric acid is 1:40 to 1:240, calculated on the basis of cobalt, aluminum, copper, iron and gallium.

[0012] Preferably, the hydrothermal solution is prepared by mixing cobalt salt, aluminum salt, copper salt, iron salt and gallium salt, and hydrothermaling the mixture at 50-120° C. for 4-20 h.

[0013] Preferably, the reaction temperature after boric acid is added to the hydrothermal solution is 180-250°C, and the reaction time is 5-10 days.

[0014] Preferably, the drying temperature is 30-90°C and the drying time is 6-48 hours.

[0015] Application of the above catalyst in photocatalytic reduction of CO2.

[0016] The present invention is beneficial in that: (1) The catalyst of the present invention has high thermodynamic and chemical stability, and as a photocatalytic reduction catalyst for CO2, it has the characteristics of long service life and excellent performance; the catalyst raw materials are abundant, non-toxic, low-priced, and have a high raw material conversion rate; the preparation method is simple and has high production efficiency, and the product is obtained by a single hydrothermal step without the need for other complex steps; (2) The present invention uses boric acid as a boron source to participate in the reaction. On the one hand, it jointly constructs the skeleton structure of the material with metal elements to form a stable boric acid multi-metal framework; on the other hand, boric acid decomposes at high temperature to produce gas, which helps to form pores in the material; the simultaneous addition of multiple metal ions forms a high-entropy structure, reduces the Gibbs free energy of the system, and enhances stability; the multi-metal synergistic effect can optimize the electronic structure and catalytic activity of the material, improve the efficiency of photocatalytic reduction of CO2, and at the same time, it can also form a heterojunction or energy level gradient, promote the separation and transmission of photogenerated electron-hole pairs, and improve the efficiency of photocatalytic reduction of CO2. BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 Schematic diagram of the photocatalytic reduction of CO2 by porous borate multi-metal catalyst; Figure 2 This is a scanning electron microscope image of the catalyst prepared in Example 1; Figure 3 The XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1 to 5 are shown; Figure 4 This is a BET comparison chart of the catalysts prepared in Example 1 and Comparative Example 5; Figure 5 This is a comparison chart of the photocatalytic reduction of CO2 performance of the catalysts prepared in Example 1 and Comparative Examples 1 to 5; Figure 6 This is a test chart of the cyclic stability of the catalysts prepared in Example 1 and Comparative Examples 1 to 5. DETAILED DESCRIPTION

[0018] The present invention will be described in detail below with reference to the accompanying drawings and specific embodiments.

[0019] A high entropy porous borate multi-metal catalyst, the chemical formula of the catalyst is H(Al α Cu β Fe γ Co δ Ga λ )3B6O 12 (OH)4, where α:β:γ:δ:λ=(1~4):(1~4):(1~4):(1~4):(1~4), and α+β+γ+δ+λ=1.

[0020] Example 1: A method for preparing a high-entropy porous borate multi-metal catalyst, comprising the following steps: 2 mmol aluminum nitrate, 1 mmol copper nitrate, 0.75 mmol iron nitrate, 0.75 mmol cobalt nitrate and 0.6 mmol gallium nitrate were placed in a reactor and reacted at 80°C for 6 hours. Then, 125 mmol boric acid was placed in the above reactor and reacted at 180°C for 5 days. After the reaction, the precipitate was washed three times with deionized water and then three times with ethanol. Finally, the precipitate was dried at 80°C for 6 hours to obtain a high-entropy porous boric acid multi-metal catalyst, and the product was labeled HE-PKU-1.

[0021] Comparative Example 1: The difference between this comparative example and Example 1 is that only metallic aluminum salt is added. The preparation method is as follows: 5 mmol of aluminum nitrate and 125 mmol of boric acid were placed in a reactor and reacted at 180°C for 5 days. After the reaction, the precipitate was washed 3 times with deionized water, then washed 3 times with ethanol, and finally dried at 80°C for 6 hours to obtain a porous aluminum borate catalyst. The product was labeled PKU-1.

[0022] Comparative Example 2: This comparative example differs from Example 1 in that only metallic aluminum salt and copper salt are added. The preparation method is as follows: 1 mmol of copper nitrate and 4 mmol of aluminum nitrate were placed in a reactor and reacted at 80°C for 6 hours. Then, 125 mmol of boric acid was placed in the above reactor and reacted at 180°C for 5 days. After the reaction, the precipitate was washed three times with deionized water, then washed three times with ethanol, and finally dried at 80°C for 6 hours to obtain a porous boric acid multi-metal catalyst. The product was labeled PKU-2.

[0023] Comparative Example 3: This comparative example differs from Example 1 in that only metallic aluminum salt and iron salt are added. The preparation method is as follows: 1 mmol of ferric nitrate and 5 mmol of aluminum nitrate were placed in a reactor and reacted at 80°C for 6 hours. Then, 125 mmol of boric acid was placed in the above reactor and reacted at 180°C for 5 days. After the reaction, the precipitate was washed three times with deionized water, then washed three times with ethanol, and finally dried at 80°C for 6 hours to obtain a porous boric acid multi-metal catalyst. The product was labeled PKU-3.

[0024] Comparative Example 4: This comparative example differs from Example 1 in that no metal cobalt salt is added. The preparation method is as follows: 2 mmol of aluminum nitrate, 1 mmol of copper nitrate, 0.75 mmol of iron nitrate, and 0.6 mmol of gallium nitrate were placed in a reactor and reacted at 80°C for 6 h. Subsequently, 125 mmol of boric acid was added and the reaction was carried out at 180°C for 5 days. After the reaction, the precipitate was washed three times with deionized water and then three times with ethanol. Finally, the precipitate was dried at 80°C for 6 hours to obtain catalyst PKU-4.

[0025] Comparative Example 5: This comparative example differs from Example 1 in that no metal gallium salt is added. The preparation method is as follows: 2 mmol of aluminum nitrate, 1 mmol of copper nitrate, 0.75 mmol of iron nitrate, and 0.75 mmol of cobalt nitrate were placed in a reactor and reacted at 80°C for 6 h. Subsequently, 125 mmol of boric acid was added and reacted at 180°C for 5 days. After the reaction, the precipitate was washed three times with deionized water and then three times with ethanol. Finally, the precipitate was dried at 80°C for 6 hours to obtain catalyst PKU-5.

[0026] Performance testing (1) Figure 2 This is a scanning electron microscope image of the catalyst prepared in Example 1. Figure 2 As shown, the morphology of the catalyst shows that it presents a highly ordered nanowire structure with uniform diameter distribution and good orientation consistency.

[0027] (2) Figure 3 The XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1 to 5 are as follows: Figure 3 As shown, its characteristic peaks are basically consistent with the PKU-1 standard card, but compared with other samples, the diffraction peaks of HE-PKU-1 show a significant weakening, indicating that with the increase of metal content, the catalyst transitions to an amorphous state, thereby reducing the crystallinity.

[0028] (3) The specific surface area and pore size distribution of the catalysts in Example 1 and Comparative Example 5 were analyzed by nitrogen adsorption-desorption test. The results are as follows: Figure 4 As shown. Compared with Comparative Example 5, HE-PKU-1 in Example 1 has a larger specific surface area, more active sites and a larger pore size. The specific surface area and pore size of the catalyst in Comparative Example 5 are both lower, indicating that the absence of gallium will lead to pore collapse or structural densification, and gallium may maintain an open pore structure by occupying skeleton nodes. It can be seen that gallium in the HE-PKU-1 catalyst acts as a structural stabilizer or electron regulator, which can optimize the lattice structure or electron distribution of the catalyst, optimize the energy band structure of the catalyst, and promote the separation and transmission of photogenerated carriers by regulating the electronic structure of other metals.

[0029] (4) Photocatalytic CO2 reduction activity test: A 300 W xenon lamp was used as the light source for the photocatalytic reaction. First, 5 mg of the photocatalyst prepared in Example 1 and Comparative Examples 1 to 5 were weighed and placed in a photocatalytic reactor. 12 mL of ultrapure water and 4 mL of triethanolamine were added and ultrasonically dispersed uniformly. The reactor was then evacuated and high-purity CO2 was introduced to maintain the pressure at around 85 kPa. This operation was repeated three times before the photocatalytic CO2 reduction test was performed. After 5 hours of illumination, the content of the generated gas products was detected using a gas chromatograph equipped with TCD and FID. See the specific results for details. Figure 5 .

[0030] like Figure 5 As shown, the efficiency of the photocatalytic reduction of CO2 of the catalyst prepared in Example 1 is significantly higher than that of Comparative Examples 1 to 5. Specifically, by comparing Comparative Example 1 and Comparative Example 2, it can be seen that metallic copper is added to Comparative Example 2, and the efficiency of the photocatalytic reduction of CO2 is higher than that of Comparative Example 1, wherein the yield of CH4 is significantly improved. This is because the d orbital electrons of copper can effectively adsorb and activate CO2 molecules, and are active centers for CO2 reduction, especially for generating products such as CH4. It can be seen from Comparative Example 1 and Comparative Example 3 that after adding metallic iron, the yields of CO and CH4 of the catalyst in Comparative Example 3 are significantly improved. This is because iron, as a co-catalyst, can provide redox active sites, promote the transfer of photogenerated electrons, enhance the catalyst's ability to absorb visible light, and improve the photocatalytic efficiency through synergy with other metals. By comparing Example 1 and Comparative Example 4, it can be seen that the yields of CO and CH4 of the catalyst in Comparative Example 4 without the addition of metallic cobalt are lower than those in Example 1. This is because cobalt has excellent light-to-heat conversion ability, can adjust the reaction path, and improve reaction efficiency.

[0031] Therefore, Al, Ga, Fe, Cu, and Co were simultaneously introduced into the porous aluminum borate framework, leveraging the synergistic effect of multiple metals and the cocktail effect of their high-entropy catalysts to significantly improve their photocatalytic conversion efficiency. Omitting any of these metal elements would destroy this synergistic effect, leading to fundamental changes in the catalyst's structure and electronic properties, thereby reducing its ability to photocatalytically reduce CO2. The HE-PKU-1 catalyst has a highly ordered nanowire structure, providing a large specific surface area and abundant surface active sites. This significantly increases the adsorption and activation capacity of CO2 molecules, shortens the diffusion distance of photogenerated carriers from the bulk to the surface, and reduces the probability of charge recombination. Furthermore, the highly ordered nanowire structure can suppress phase transitions and agglomeration, maintaining the long-term stability of the catalyst. At the same time, the synergistic effect of multiple metal elements in HE-PKU-1 can optimize the electronic structure and further promote charge separation and transport.

[0032] (5) Catalyst cycle stability test To evaluate the cyclic stability of Example 1 (HE-PKU-1) and Comparative Examples 1-5 (PKU-1-5), the following experiment was designed: 5 mg of each catalyst was dispersed in 12 mL of ultrapure water and 4 mL of triethanolamine, loaded into a photoreactor, evacuated, and introduced with CO2 to 85 kPa. Illumination was performed continuously with a 300 W xenon lamp for 5 hours, constituting one cycle. After each reaction, the catalyst was recovered by centrifugation, washed three times with deionized water and once with ethanol, dried at 80°C for 2 hours, and reused for a total of five cycles. After each cycle, the yields of CO and CH4 were quantified by gas chromatography (GC-TCD / FID), and the activity retention rate was calculated (yield at the nth time / yield at the first time × 100%). The specific results are shown in Table 2. Figure 6 .

[0033] like Figure 6 As shown, the activity retention rates of CH4 and CO in Example 1 (HE-PKU-1) after 5 cycles are both higher than 90%, which is significantly better than all the comparative examples, indicating that its high entropy multi-metal synergistic effect (Al / Cu / Fe / Co / Ga) can inhibit the deactivation of active sites and structural collapse: Comparative Example 1 (only Al) has poor structural stability due to the lack of multi-metal synergy, and its activity loses nearly 50% after 5 cycles; Comparative Example 4 (without Co) lacks the photothermal regulation ability of cobalt, and the temperature fluctuation of the reaction system is large, resulting in sintering of the catalyst surface and reduced activity retention rate; Comparative Example 5 (without Ga) lacks gallium, resulting in pore structure collapse (BET specific surface area decreases), reduced active sites, and significant performance degradation after cycling; Comparative Example 2 (Al+Cu) and Comparative Example 3 (Al+Fe) have improved stability due to partial metal combinations, but no electronic cooperative network of the high entropy system is formed, and there are still problems such as high charge recombination rate and metal dissolution. In summary, the high entropy porous structure of HE-PKU-1, the photothermal enhancement effect of cobalt and the skeleton stabilization of gallium are the core reasons why its cyclic stability is significantly better than that of the control.

Claims

1. A high entropy porous borate multi-metal catalyst, characterized in that: The chemical formula of the catalyst is H(Al α Cu β Fe γ Co δ Ga λ )3B6O 12 (OH)4, where α:β:γ:δ:λ=(1~4):(1~4):(1~4):(1~4):(1~4), and α+β+γ+δ+λ=1.

2. The method for preparing the catalyst according to claim 1, wherein The specific steps are: adding boric acid to a hydrothermal solution containing cobalt salt, aluminum salt, copper salt, iron salt and gallium salt to react, and then washing and drying to obtain a high-entropy porous boric acid multi-metal catalyst.

3. The method for preparing the catalyst according to claim 2, wherein In the hydrothermal solution, the concentrations of cobalt salt, aluminum salt, copper salt, iron salt and gallium salt are respectively 0.05-5 mol / L.

4. The method for preparing the catalyst according to claim 2, wherein The cobalt salt, aluminum salt, copper salt, iron salt and gallium salt are respectively at least one of nitrates, sulfates and acetates containing cobalt, aluminum, copper, iron or gallium.

5. The method for preparing the catalyst according to claim 2, wherein: Calculated on the basis of cobalt, aluminum, copper, iron and gallium, the molar ratio of the total molar amount of cobalt salt, aluminum salt, copper salt, iron salt and gallium salt to boric acid is 1:40 to 1:

240.

6. The method for preparing the catalyst according to claim 2, wherein: The preparation method of the hydrothermal solution is: mixing cobalt salt, aluminum salt, copper salt, iron salt and gallium salt, and hydroheating at 50-120° C. for 4-20 hours.

7. The method for preparing the catalyst according to claim 2, wherein: The reaction temperature after boric acid is added to the hydrothermal solution is 180~250℃, and the reaction time is 5~10 days.

8. The method for preparing the catalyst according to claim 2, wherein: The drying temperature is 30~90℃ and the time is 6~48h.

9. Use of the catalyst according to claim 1 in photocatalytic reduction of CO2.

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