Bismuth-based catalyst with core-shell structure for enhancing gas-solid phase mass transfer, method and application

Abstract

The invention discloses a bismuth-based catalyst with a core-shell structure for strengthening gas-solid phase mass transfer and a method and application, and belongs to the technical field of bismuth-based catalyst preparation, and the method comprises the following steps: adding a bismuth source, a reducing agent and a dispersing agent into a solvent, and carrying out stirring reaction, centrifugation, washing and drying to obtain a bismuth-based material core; and adding the bismuth-based material core into a carbon source solution, and carrying out hydrothermal reaction and carbonization reaction to form a porous carbon shell, thereby obtaining the bismuth-based catalyst with the core-shell structure for enhancing gas-solid phase mass transfer, or adding the bismuth-based material core into a silicon source solution, and carrying out hydrolytic polycondensation reaction under the action of the catalyst to form a porous silicon dioxide shell, thereby obtaining the bismuth-based catalyst with the core-shell structure for enhancing gas-solid phase mass transfer. The catalyst shows high activity, high selectivity and good stability in preparation of formic acid through electrochemical reduction of CO2, and the gas-solid phase mass transfer efficiency is effectively improved. The high Faraday efficiency, formic acid energy efficiency and formic acid yield per unit electrolysis area are shown, and the method is suitable for efficient conversion and utilization of CO2.

Description

Technical Field

[0001] The present invention belongs to the technical field of bismuth-based catalyst preparation, and specifically relates to a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, a method for the same, and an application thereof. Background Art

[0002] With the acceleration of global industrialization, carbon dioxide (CO2) emissions are increasing, leading to serious environmental problems such as the greenhouse effect and climate change. Converting CO2 into high-value-added chemicals, such as formic acid, is an effective solution that not only reduces CO2 emissions but also achieves the recycling of carbon resources. Electrochemical reduction of CO2 to formic acid has become a highly promising method due to its advantages such as cleanliness, controllability, and simple reaction modules. However, this method faces problems such as insufficient catalyst activity, poor selectivity, and low stability, which limit its large-scale application. Among many catalysts, bismuth-based catalysts have attracted widespread attention due to their low price, environmental friendliness, and high selectivity for formic acid.

[0003] At present, a variety of bismuth-based catalysts have been reported for use in the electroreduction of CO2 to produce formic acid. For example, some studies have modified bismuth-based materials by doping, such as sulfur-doped bismuth oxide, to regulate the electronic structure and morphology of the materials and improve the activity and selectivity of the catalyst. However, these methods often have problems such as complex preparation process, high cost, and low gas-solid mass transfer efficiency, resulting in the catalyst performance still needs to be further improved. In terms of gas-solid mass transfer, traditional bismuth-based catalysts have the problem of low mass transfer efficiency, which makes it difficult for the reactant CO2 to reach the active sites of the catalyst quickly and effectively, thereby affecting the reaction rate and product selectivity. In addition, the stability of the catalyst is also an important issue. During a long reaction process, the catalyst is prone to agglomeration and deactivation, resulting in a shortened service life.

[0004] Therefore, the development of a bismuth-based catalyst with efficient gas-solid mass transfer performance, high activity, high selectivity and good stability and its preparation method are of great significance for the industrial application of CO2 electroreduction to formic acid. Summary of the Invention

[0005] In order to overcome the shortcomings of the above-mentioned prior art, the purpose of the present invention is to provide a bismuth-based catalyst with a core-shell structure to enhance gas-solid mass transfer, as well as a method and application, so as to solve the technical problems of low gas-solid mass transfer efficiency, insufficient activity, poor selectivity and low stability of existing bismuth-based catalysts in the process of CO2 electroreduction to formic acid.

[0006] In order to achieve the above object, the present invention adopts the following technical solutions: The present invention discloses a method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer, comprising: 1) adding a bismuth source, a reducing agent, and a dispersant to a solvent, stirring, reacting, centrifuging, washing, and drying to obtain a bismuth-based material core; 2) The bismuth-based material core is added to a carbon source solution, and after hydrothermal reaction and carbonization reaction, a porous carbon shell is formed to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer; Alternatively, a bismuth-based material core is added to a silicon source solution, and under the action of a catalyst, a hydrolysis and condensation reaction is carried out to form a porous silica shell, thereby obtaining a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer.

[0007] Preferably, in step 1), the usage ratio of the bismuth source, the reducing agent, the dispersant, and the solvent is (5-30) g: (1-10) g: (1-10) g: (50-400) mL.

[0008] Preferably, in step 1), the bismuth source is any one of bismuth nitrate and bismuth chloride; the reducing agent is any one of sodium borohydride and hydrazine hydrate; the dispersant is any one of polyvinyl pyrrolidone, sodium lauryl sulfate, polyethylene glycol and polyvinyl alcohol; and the solvent is any one of methanol, ethanol, propanol, ethylene glycol and deionized water.

[0009] Preferably, in step 1), the stirring reaction temperature is 30-100° C. and the time is 3-15 h; the drying conditions are: vacuum drying at 60-130° C. for 6-25 h.

[0010] Preferably, the mass ratio of the bismuth source to the carbon source solution is (5-30): (5-25); the carbon source solution is glucose or phenolic resin; The mass ratio of the bismuth source solution to the silicon source solution is (5-30): (8-30); the silicon source solution is ethyl orthosilicate; and the catalyst is aqueous ammonia.

[0011] Preferably, in step 2), the temperature of the hydrothermal reaction is 100-180°C and the time is 2-24 hours; the temperature of the carbonization reaction is 700-1000°C and the time is 2-5 hours; the temperature of the hydrolysis and polycondensation reaction is room temperature to 100°C and the time is 18-48 hours.

[0012] Preferably, step 2) further comprises calcining the bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer, wherein the calcination temperature is 500-800° C. and the calcination time is 2-5 hours.

[0013] The present invention also discloses a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer, which is prepared using the above-mentioned method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer. The bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer comprises: a core and an outer shell; the core is a bismuth-based material; and the outer shell is porous carbon or porous silica.

[0014] Preferably, the bismuth-based material is at least one of metallic bismuth, bismuth oxide and bismuth oxycarbonate.

[0015] The present invention also discloses the use of the bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer in the production of formic acid. In the electrochemical reduction of carbon dioxide to produce formic acid, a three-electrode system is used, with the bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer as the working electrode, a saturated calomel electrode or a silver / silver chloride electrode as the reference electrode, a platinum sheet as the counter electrode, and a KHCO3 solution or a NaHCO3 solution as the electrolyte. The reaction potential is -0.5 to -1.5 V, the reaction temperature is 10-50° C., the Faraday efficiency of formic acid is 82% to 90%, the energy efficiency of formic acid is 58% to 65%, and the formic acid yield per unit electrolysis area is 0.18 to 0.3 mmol / (h·cm 2 ).

[0016] Compared with the prior art, the present invention has the following beneficial effects: The present invention discloses a method for preparing a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer. The bismuth-based material core is synthesized by a reduction reaction, the particle morphology is controlled by combining a dispersant, and the reaction kinetics are optimized by a solvent system. The bismuth-based material core provides catalytic active sites, and the porous carbon shell or porous silica shell promotes gas diffusion through the pores, while protecting the core and reducing the deactivation of the active sites. Porous carbon has excellent electrical conductivity and is suitable for electrochemical reduction; silica is highly chemically inert and can enhance stability under acidic conditions. The hierarchical pore structure of the porous carbon shell and the porous silica shell shortens the CO2 diffusion path and enriches CO2 molecules through capillary action, thereby increasing their contact frequency with the bismuth-based active sites; the shell prevents the bismuth-based core from dissolving or oxidizing during the electrochemical cycle. Through the triple strategy of core morphology control, shell pore design, and core-shell coordinated optimization, a breakthrough in the mass transfer efficiency, selectivity, and stability of CO2 electrochemical reduction catalysts has been achieved. The flexible choice of porous carbon shell and porous silica shell further broadens the application scenarios, and the low-cost large-scale preparation process also provides a reliable technical path for industrial-grade CO2 resource utilization.

[0017] Furthermore, the optimization of dispersant dosage can regulate the particle size distribution of bismuth-based core to avoid agglomeration; the mass ratio of bismuth source to reducing agent is optimized to ensure Bi 3+ It is completely reduced to metallic bismuth or bismuth oxide, with low residual ion concentration, reducing the interference of impurities on catalytic activity.

[0018] Furthermore, the mass ratio of glucose to bismuth source is optimized to ensure that the thickness of the carbon layer is controllable, forming a conductive network after carbonization and reducing the charge transfer resistance; the mass ratio of ethyl orthosilicate to bismuth source is optimized to generate a mesoporous silica shell with a large specific surface area and high CO2 adsorption capacity.

[0019] Furthermore, high-temperature carbonization graphitizes the carbon skeleton, improving the efficiency of electron conduction, while forming micropores to adsorb CO2 and mesopores to promote mass transfer.

[0020] The present invention also discloses a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, produced by the aforementioned preparation method. The porous carbon shell and porous silica shell have a hierarchical pore structure, significantly increasing the specific surface area and providing abundant CO2 diffusion channels. The metallic bismuth or bismuth oxide in the core of the bismuth-based material provides highly active sites, while the porous shell physically isolates the core, preventing bismuth particle aggregation or dissolution. The catalyst maintains high activity even after repeated use.

[0021] The present invention also discloses the use of the bismuth-based catalyst with a core-shell structure to enhance gas-solid mass transfer in the production of formic acid. The reaction potential can be between -0.5V and -1.5V (vs. RHE), the Faraday efficiency of formic acid is 82% to 90%, the energy efficiency of formic acid is 58% to 65%, and the formic acid yield per unit electrolysis area is 0.18 to 0.3 mmol / (h·cm 2 ). It achieves high selectivity, high energy efficiency, and high yield in formic acid production, and the operating conditions are mild, which is suitable for industrial needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 This is a flow chart of the preparation method of the bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer disclosed in the present invention. DETAILED DESCRIPTION

[0023] The technical solution of the present invention will be described clearly and completely below. Obviously, the embodiments described are only some embodiments of the present invention, not all embodiments. All other embodiments derived by persons of ordinary skill in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0024] In the present invention, unless otherwise specified, all the embodiments and preferred implementation methods mentioned herein can be combined with each other to form a new technical solution.

[0025] In the present invention, unless otherwise specified, all technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0026] In the present invention, unless otherwise specified, percentages (%) or parts refer to percentages by weight or parts by weight relative to the composition.

[0027] In the present invention, unless otherwise specified, the components involved or their preferred components can be combined with each other to form a new technical solution.

[0028] In this disclosure, unless otherwise specified, the numerical range "a-b" is an abbreviation for any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "6-22" indicates that all real numbers between "6-22" are listed herein, and "6-22" is merely an abbreviation for these numerical combinations.

[0029] The "range" disclosed in the present invention is in the form of lower limit and upper limit, which can be one or more lower limits, and one or more upper limits respectively.

[0030] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0031] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in accordance with the order. Preferably, the reaction method herein is carried out sequentially.

[0032] Unless otherwise indicated, the professional and scientific terms used herein are the same as those familiar to those skilled in the art. In addition, any method or material similar or equivalent to the described content can also be applied to the present invention.

[0033] The present invention provides a method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer, comprising the following steps: Add 5-30g of a bismuth source, 1-10g of a reducing agent, and 1-10g of a dispersant to 50-400mL of solvent and stir thoroughly to form a mixed solution. The bismuth source can be one or more bismuth salts such as bismuth nitrate and bismuth chloride; the reducing agent can be one or more of sodium borohydride and hydrazine hydrate; the dispersant can be one or more of polyvinyl pyrrolidone (PVP), sodium dodecyl sulfate (SDS), polyethylene glycol (PEG), and polyvinyl alcohol (PVA); and the solvent can be any of methanol, ethanol, propanol, ethylene glycol, and deionized water. The mixed solution is stirred and reacted at 30-100°C for 3-15 hours. The mixture is then centrifuged, washed, and vacuum-dried at 60-130°C for 6-25 hours to obtain the bismuth-based material as the core.

[0034] A solution containing a shell material precursor is mixed with the core material, and the precursor reacts on the core surface to form a porous shell. For example, if the shell material is porous carbon, the core material can be added to 5-25g of a solution containing a carbon source such as glucose or phenolic resin. The reaction is hydrothermally reacted at 100-180°C for 2-24 hours, followed by a carbonization reaction at 700-1000°C for 2-5 hours to form a porous carbon shell, resulting in a core-shell structure for a bismuth-based catalyst with enhanced gas-solid mass transfer. If the shell material is porous silica, the core material can be added to 8-30g of a solution containing a silicon source such as ethyl orthosilicate. The catalyst, such as aqueous ammonia, is hydrolyzed and polycondensed at room temperature to 100°C for 18-48 hours to form a porous silica shell, resulting in a core-shell structure for a bismuth-based catalyst with enhanced gas-solid mass transfer.

[0035] The prepared core-shell structured bismuth-based catalyst for enhanced gas-solid mass transfer is calcined at 500-800° C. for 2-5 hours to further improve the performance of the catalyst.

[0036] The core-shell structure-enhanced bismuth-based catalyst prepared by the present invention is applied to the CO2 electroreduction reaction to produce formic acid. In the electrochemical reaction, a three-electrode system is adopted, with the core-shell structure-enhanced bismuth-based catalyst of the present invention serving as the working electrode, a saturated calomel electrode (SCE) or a silver / silver chloride electrode (Ag / AgCl) serving as the reference electrode, a platinum sheet serving as the counter electrode, and an electrolyte comprising a bicarbonate solution such as KHCO3 or NaHCO3. By controlling the reaction potential, temperature, and other conditions, efficient CO2 electroreduction to formic acid is achieved. The reaction potential can be between -0.5V and -1.5V (vs. RHE), and the reaction temperature between 10-50°C. The Faradaic efficiency of formic acid is 82%-90%, the energy efficiency of formic acid is 58%-65%, and the formic acid yield per unit electrolysis area is 0.18-0.3mmol / (h·cm 2 ).

[0037] The core-shell structured bismuth-based catalyst for enhancing gas-solid mass transfer provided by the present invention has a core-shell structure, comprising a core and an outer shell. The core is a bismuth-based material, and the outer shell is a material with a porous structure, and the outer shell is coated on the surface of the core. The bismuth-based material can be one or more bismuth compounds such as metallic bismuth, bismuth oxide, and bismuth oxycarbonate. The porous material can be one or more of porous carbon and porous silica.

[0038] The core-shell structure bismuth-based catalyst for enhancing gas-solid mass transfer disclosed in the present invention, as well as the method and application thereof, has the following advantages: 1) Enhanced gas-solid mass transfer: The core-shell structure design, especially the presence of a porous shell, provides abundant gas transmission channels, greatly increasing the contact opportunities between CO2 and the active sites of the catalyst, effectively improving the gas-solid mass transfer efficiency, and thus accelerating the reaction rate.

[0039] 2) High activity and selectivity: The bismuth-based core provides the main catalytic active sites, while the modification and protection of the shell make the catalyst more active and selective for the reduction of CO2 to formic acid, and can effectively inhibit the occurrence of side reactions such as hydrogen evolution.

[0040] 3) Good stability: The porous shell protects the core, reduces the agglomeration and deactivation of the catalyst during the reaction, improves the stability of the catalyst, and extends its service life.

[0041] 4) Simple preparation method: The preparation method of the present invention is simple to operate, has mild conditions, is easy to control, and is suitable for large-scale preparation.

[0042] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings herein can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without making creative work are within the scope of protection of the present invention.

[0043] Figure 1 This is a flow chart of the preparation method for the core-shell bismuth-based catalyst with enhanced gas-solid mass transfer disclosed in the present invention. As can be seen from the figure, the preparation method for the core-shell bismuth-based catalyst with enhanced gas-solid mass transfer includes: adding a bismuth source, a reducing agent, and a dispersant to a solvent, stirring the reaction, centrifuging, washing, and drying to obtain a bismuth-based core; adding the bismuth-based core to a carbon source solution, and subjecting it to a hydrothermal reaction and carbonization reaction to form a porous carbon shell, thereby obtaining a core-shell bismuth-based catalyst with enhanced gas-solid mass transfer; or adding the bismuth-based core to a silicon source solution, and subjecting it to a hydrolysis and polycondensation reaction in the presence of a catalyst to form a porous silica shell, thereby obtaining a core-shell bismuth-based catalyst with enhanced gas-solid mass transfer. This method achieves efficient mass transfer, high selectivity, and long life for the bismuth-based catalyst in CO2 electrochemical reduction. The introduction of the porous shell solves the core issue of limited mass transfer in traditional gas-solid catalysis, while the mildness and scalability of the preparation method lay the foundation for its industrial application.

[0044] Example 1 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 5g of bismuth nitrate in 50mL of ethylene glycol, add 1g of polyvinyl pyrrolidone (PVP) as a dispersant, and stir until uniform. Then, slowly add an ethylene glycol solution containing 1g of sodium borohydride dropwise. The mixture is allowed to react at 30°C for 3 hours. After the reaction, centrifuge to obtain a black precipitate, which is then washed repeatedly with ethanol and deionized water and dried in a vacuum at 60°C for 6 hours to obtain the bismuth-based material core.

[0045] The bismuth-based core prepared above was added to an aqueous solution containing 5g of glucose, stirred evenly, and then subjected to a hydrothermal reaction at 100°C for 12 hours. The product was then carbonized at 700°C for 2 hours under a nitrogen atmosphere to form a core-shell bismuth-based catalyst with enhanced gas-solid mass transfer, namely a bismuth-based core-shell catalyst encapsulated by a porous carbon shell.

[0046] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A three-electrode system was used, with a saturated calomel electrode as the reference electrode and a platinum sheet as the counter electrode, to carry out CO2 electroreduction in a 0.5M KHCO3 electrolyte. At a potential of -1.0V (vs. RHE) and 10°C, the Faradaic efficiency of formic acid reached 85%, the formic acid energy efficiency was 60%, and the formic acid production per unit electrolysis area was 0.2mmol / (h·cm 2 ).

[0047] Example 2 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 10g of bismuth nitrate in 100mL of ethylene glycol, add 3g of polyvinyl pyrrolidone (PVP) as a dispersant, and stir until uniform. Then, slowly add an ethylene glycol solution containing 3g of sodium borohydride dropwise, and react at 50°C for 5h. After the reaction, centrifuge to obtain a black precipitate, which is then washed repeatedly with ethanol and deionized water and dried in a vacuum at 80°C for 8h to obtain the bismuth-based material core.

[0048] The bismuth-based core prepared above was added to an aqueous solution containing 10g of glucose, stirred evenly, and then hydrothermally reacted at 120°C for 16 hours. The product was then carbonized at 800°C for 3 hours under a nitrogen atmosphere to form a core-shell bismuth-based catalyst with enhanced gas-solid mass transfer, namely a bismuth-based core-shell catalyst encapsulated by a porous carbon shell.

[0049] The prepared core-shell structure of the bismuth-based catalyst with enhanced gas-solid mass transfer was used as a working electrode. A three-electrode system was used, with a saturated calomel electrode as the reference electrode and a platinum sheet as the counter electrode, to carry out CO2 electroreduction in a 0.5M KHCO3 electrolyte. At a potential of -1.0V (vs. RHE) and 10°C, the Faradaic efficiency of formic acid reached 87%, the formic acid energy efficiency was 62%, and the formic acid production per unit electrolysis area was 0.23mmol / (h·cm2 ).

[0050] Example 3 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 6g of bismuth chloride in 80mL of ethanol, add 2g of sodium dodecyl sulfate (SDS) as a dispersant, and stir until uniform. Then, add dropwise an ethanol solution containing 2g of hydrazine hydrate. Incubate at 40°C for 4 hours. After the reaction, centrifuge, wash with ethanol and deionized water, and vacuum dry at 70°C for 8 hours to obtain the bismuth-based core.

[0051] The bismuth-based core was added to an ethanol solution containing 8g of tetraethyl orthosilicate, followed by an appropriate amount of aqueous ammonia as a catalyst. The reaction was stirred at room temperature for 18 hours to form a porous silica shell. The resulting catalyst was then calcined at 500°C for 2 hours to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer. This is a porous silica-coated bismuth-based core-shell catalyst.

[0052] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 0.5M NaHCO3 electrolyte in a three-electrode system. At a potential of -1.1 V (vs. RHE) and 20°C, the Faradaic efficiency of formic acid was 88%, the formic acid energy efficiency was 62%, and the formic acid production per unit electrolysis area was 0.25 mmol / (h·cm 2 ).

[0053] Example 4 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 12g of bismuth chloride in 120mL of ethanol, add 4g of sodium dodecyl sulfate (SDS) as a dispersant, and stir until uniform. Then, add dropwise an ethanol solution containing 4g of hydrazine hydrate. The mixture is reacted at 60°C for 6 hours. After the reaction, centrifuge, wash with ethanol and deionized water, and vacuum dry at 90°C for 10 hours to obtain the bismuth-based material core.

[0054] The bismuth-based core was added to an ethanol solution containing 12g of tetraethyl orthosilicate, followed by an appropriate amount of aqueous ammonia as a catalyst. The reaction was stirred at 50°C for 24 hours to form a porous silica shell. The resulting catalyst was then calcined at 600°C for 3 hours to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer. This is a porous silica-coated bismuth-based core-shell catalyst.

[0055] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 0.5M NaHCO3 electrolyte in a three-electrode system. At a potential of -1.1 V (vs. RHE) and 20°C, the Faradaic efficiency of formic acid was 89%, the formic acid energy efficiency was 64%, and the formic acid production per unit electrolysis area was 0.28 mmol / (h·cm 2 ).

[0056] Example 5 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: 8g of bismuth nitrate and 3g of ammonium carbonate were dissolved in 100mL of deionized water, stirred, and reacted at 50°C for 5h to form a bismuth oxycarbonate precipitate. The precipitate was then centrifuged, washed, and dried at 80°C for 10h to obtain a bismuth oxycarbonate core material.

[0057] The bismuth oxycarbonate core material was added to an ethanol solution containing 10g of phenolic resin, stirred evenly, and cured at 130°C for 2 hours. Then, it was carbonized at 800°C for 3 hours under a nitrogen atmosphere to form a porous carbon shell. This was then calcined at 500°C for 1 hour to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer, namely a porous carbon-encapsulated bismuth oxycarbonate core-shell catalyst.

[0058] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 1.0M KHCO3 electrolyte in a three-electrode system. At a potential of -0.9 V (vs. RHE) and at 30°C, the Faradaic efficiency of formic acid was 82%, the energy efficiency of formic acid was 58%, and the formic acid production per unit electrolysis area was 0.18 mmol / (h·cm 2 ).

[0059] Example 6 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 15g of bismuth nitrate and 6g of ammonium carbonate in 150mL of deionized water, stir, and react at 70°C for 8h to form a bismuth oxycarbonate precipitate. This precipitate is then centrifuged, washed, and dried at 100°C for 12h to obtain a bismuth oxycarbonate core material.

[0060] The bismuth oxycarbonate core material was added to an ethanol solution containing 15g of phenolic resin, stirred evenly, and cured at 150°C for 3 hours. Then, it was carbonized at 900°C under a nitrogen atmosphere for 4 hours to form a porous carbon shell. This was then calcined at 500°C for 2 hours to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer, namely a porous carbon-encapsulated bismuth oxycarbonate core-shell catalyst.

[0061] In the preparation methods of Examples 5 and 6, the main function of ammonium carbonate is to act as a precipitant to provide CO3 2- Ions and Bi 3+ The reaction generates bismuth oxycarbonate (BiOCO3) precipitation. The ion reaction achieves the precipitation and fixation of the bismuth element, providing the core material for the subsequent construction of the core-shell structure.

[0062] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 1.0M KHCO3 electrolyte in a three-electrode system. At a potential of -0.9 V (vs. RHE) and at 30°C, the Faradaic efficiency of formic acid was 84%, the formic acid energy efficiency was 60%, and the formic acid production per unit electrolysis area was 0.19 mmol / (h·cm 2 ).

[0063] Example 7 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 10g of bismuth chloride in 150mL of propanol, add 4g of polyethylene glycol (PEG) as a dispersant, and stir until uniform. Then, add a propanol solution containing 3g of sodium borohydride dropwise. The mixture is reacted at 60°C for 6 hours. After the reaction, centrifuge, wash with propanol and deionized water, and vacuum dry at 90°C for 12 hours to obtain the bismuth-based core.

[0064] The bismuth-based core was added to an ethanol solution containing 12g of ethyl orthosilicate and an appropriate amount of hydrochloric acid. The reaction was stirred at 60°C for 24 hours to form a porous silica shell. The shell was then calcined at 600°C for 3 hours to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer, namely a porous silica-coated bismuth-based core-shell catalyst.

[0065] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 1.0M NaHCO3 electrolyte in a three-electrode system. At a potential of -1.2 V (vs. RHE) and 40°C, the Faradaic efficiency of formic acid was 88%, the formic acid energy efficiency was 63%, and the formic acid production per unit electrolysis area was 0.28 mmol / (h·cm 2 ).

[0066] Example 8 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 20g of bismuth chloride in 200mL of propanol, add 8g of polyethylene glycol (PEG) as a dispersant, and stir until uniform. Then, add a propanol solution containing 6g of sodium borohydride dropwise. The mixture is reacted at 80°C for 10 hours. After the reaction, centrifuge, wash with propanol and deionized water, and vacuum dry at 110°C for 15 hours to obtain the bismuth-based core.

[0067] The bismuth-based core was added to an ethanol solution containing 20g of tetraethyl orthosilicate and an appropriate amount of hydrochloric acid. The reaction was stirred at 80°C for 36 hours to form a porous silica shell. The shell was then calcined at 700°C for 4 hours to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer, namely a porous silica-coated bismuth-based core-shell catalyst.

[0068] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 1.0M NaHCO3 electrolyte in a three-electrode system. At a potential of -1.2 V (vs. RHE) and at 40°C, the Faradaic efficiency of formic acid was 90%, the formic acid energy efficiency was 65%, and the formic acid production per unit electrolysis area was 0.3 mmol / (h·cm 2 ).

[0069] Example 9 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 12g of bismuth nitrate and 5g of urea in 200mL of deionized water, stir, and react at 70°C for 8h to generate a bismuth oxide precipitate. This precipitate is then centrifuged, washed, and dried at 100°C for 15h to obtain a bismuth oxide core material.

[0070] The bismuth oxide core material was added to an aqueous solution containing 15g of glucose, stirred evenly, and then hydrothermally reacted at 150°C for 18 hours. The product was then carbonized at 900°C for 4 hours under a nitrogen atmosphere to form a porous carbon shell. This was then calcined at 500°C for 2 hours to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer, namely a porous carbon-encapsulated bismuth oxide core-shell catalyst.

[0071] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 0.5M KHCO3 electrolyte in a three-electrode system. At a potential of -1.0 V (vs. RHE) and 50°C, the Faradaic efficiency of formic acid was 86%, the formic acid energy efficiency was 63%, and the formic acid production per unit electrolysis area was 0.22 mmol / (h·cm 2 ).

[0072] Example 10 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 25g of bismuth nitrate and 10g of urea in 300mL of deionized water, stir, and react at 90°C for 12h to produce a bismuth oxide precipitate. This precipitate is then centrifuged, washed, and dried at 120°C for 20h to obtain a bismuth oxide core material.

[0073] The bismuth oxide core material was added to an aqueous solution containing 25g of glucose, stirred evenly, and then hydrothermally reacted at 180°C for 24 hours. The product was then carbonized at 1000°C for 5 hours under a nitrogen atmosphere to form a porous carbon shell. This was then calcined at 600°C for 3 hours to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer, namely a porous carbon-encapsulated bismuth oxide core-shell catalyst.

[0074] In the preparation methods of Examples 9 and 10, the main function of urea is to generate NH3 and CO2 through hydrolysis, increase the pH of the solution and provide OH - ions, promoting Bi 3+ Hydrolysis generates a bismuth oxide (Bi2O3) precipitate. Urea functions as a precipitant and pH regulator. The slow-release properties of urea help control the precipitation process, improving the uniformity and purity of the core material and laying the foundation for the subsequent construction of the core-shell structure.

[0075] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 0.5M KHCO3 electrolyte in a three-electrode system. At a potential of -1.0 V (vs. RHE) and 50°C, the Faradaic efficiency of formic acid was 87%, the formic acid energy efficiency was 64%, and the formic acid production per unit electrolysis area was 0.24 mmol / (h·cm 2 ).

[0076] Example 11 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: Dissolve 15g of bismuth chloride in 250mL of methanol, add 6g of polyvinyl alcohol (PVA) as a dispersant, and stir until uniform. Then, add dropwise a methanol solution containing 5g of hydrazine hydrate. The mixture is reacted at 80°C for 10 hours. After the reaction, centrifuge, wash with methanol and deionized water, and vacuum dry at 110°C for 20 hours to obtain the bismuth-based core.

[0077] The bismuth-based core was added to an ethanol solution containing 18g of ethyl orthosilicate and an appropriate amount of ammonia. The reaction was stirred at 80°C for 36 hours to form a porous silica shell. The shell was then calcined at 700°C for 4 hours to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer. This is a porous silica-coated bismuth-based core-shell catalyst.

[0078] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 1M NaHCO3 electrolyte in a three-electrode system. At a potential of -1.1 V (vs. RHE) and at 30°C, the Faradaic efficiency of formic acid was 89%, the formic acid energy efficiency was 64%, and the formic acid production per unit electrolysis area was 0.28 mmol / (h·cm 2 ).

[0079] Example 12 A method for preparing a bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, comprising: 30g of bismuth chloride was dissolved in 400mL of methanol, and 10g of polyvinyl alcohol (PVA) was added as a dispersant, followed by stirring. A methanol solution containing 10g of hydrazine hydrate was then added dropwise, and the mixture was reacted at 100°C for 15 hours. After the reaction, the mixture was centrifuged, washed with methanol and deionized water, and vacuum-dried at 130°C for 25 hours to obtain the bismuth-based core.

[0080] The bismuth-based core was added to an ethanol solution containing 30g of ethyl orthosilicate and an appropriate amount of ammonia. The reaction was stirred at 100°C for 48 hours to form a porous silica shell. The shell was then calcined at 800°C for 5 hours to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer. This is a porous silica-coated bismuth-based core-shell catalyst.

[0081] The prepared core-shell structure of the bismuth-based catalyst for enhanced gas-solid mass transfer was used as a working electrode. A silver / silver chloride electrode was used as a reference electrode and a platinum sheet was used as a counter electrode. The CO2 electroreduction reaction was carried out in a 1M NaHCO3 electrolyte in a three-electrode system. At a potential of -1.1 V (vs. RHE) and at 30°C, the Faradaic efficiency of formic acid was 89.5%, the formic acid energy efficiency was 65%, and the formic acid production per unit electrolysis area was 0.29 mmol / (h·cm 2 ).

[0082] The above examples demonstrate that the core-shell bismuth-based catalyst with enhanced gas-solid mass transfer prepared by the present invention exhibits excellent performance in the CO2 electroreduction reaction to formic acid, with high Faradaic efficiency, formic acid energy efficiency, and formic acid yield per unit electrolysis area. Different preparation conditions and material combinations affect catalyst performance and can be adjusted and optimized based on actual needs.

[0083] In summary, the present invention discloses a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer for the production of formic acid, as well as its preparation method and application. The catalyst has a core-shell structure, with a core composed of a bismuth-based material (such as metallic bismuth or bismuth oxide) and a shell composed of a porous material (such as porous carbon or porous silica). The preparation method includes preparing the core material, forming a porous shell on the core surface, and an optional calcination step. The core material is obtained by reacting a bismuth source, a reducing agent, and a dispersant in a solvent, while the shell material is formed by reacting a precursor on the core surface. The catalyst exhibits high activity, high selectivity, and good stability in the electrochemical reduction of CO2 to formic acid, effectively improving gas-solid mass transfer efficiency. Specific examples demonstrate that catalyst performance varies under different preparation conditions and material combinations, but all exhibit high Faradaic efficiency, formic acid energy efficiency, and formic acid yield per unit electrolysis area, making it suitable for the efficient conversion and utilization of CO2.

[0084] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer, characterized in that: include: 1) adding a bismuth source, a reducing agent, and a dispersant to a solvent, stirring, reacting, centrifuging, washing, and drying to obtain a bismuth-based material core; 2) The bismuth-based material core is added to a carbon source solution, and after hydrothermal reaction and carbonization reaction, a porous carbon shell is formed to obtain a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer; Alternatively, a bismuth-based material core is added to a silicon source solution, and under the action of a catalyst, a hydrolysis and condensation reaction is carried out to form a porous silica shell, thereby obtaining a bismuth-based catalyst with a core-shell structure that enhances gas-solid mass transfer.

2. The method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer according to claim 1, characterized in that: In step 1), the usage ratio of the bismuth source, reducing agent, dispersant and solvent is (5-30) g: (1-10) g: (1-10) g: (50-400) mL.

3. The method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer according to claim 1, characterized in that: In step 1), the bismuth source is any one of bismuth nitrate and bismuth chloride; the reducing agent is any one of sodium borohydride and hydrazine hydrate; the dispersant is any one of polyvinyl pyrrolidone, sodium lauryl sulfate, polyethylene glycol and polyvinyl alcohol; and the solvent is any one of methanol, ethanol, propanol, ethylene glycol and deionized water.

4. The method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer according to claim 1, characterized in that: In step 1), the stirring reaction temperature is 30-100° C. and the time is 3-15 hours; the drying conditions are: vacuum drying at 60-130° C. for 6-25 hours.

5. The method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer according to claim 1, characterized in that: The mass ratio of the bismuth source to the carbon source solution is (5-30): (5-25); the carbon source solution is glucose or phenolic resin; The mass ratio of the bismuth source to the silicon source solution is (5-30): (8-30); the silicon source solution is ethyl orthosilicate; and the catalyst is aqueous ammonia.

6. The method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer according to claim 1, characterized in that: In step 2), the temperature of the hydrothermal reaction is 100-180°C and the time is 2-24 hours; the temperature of the carbonization reaction is 700-1000°C and the time is 2-5 hours; the temperature of the hydrolysis and polycondensation reaction is room temperature to 100°C and the time is 18-48 hours.

7. The method for preparing a bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer according to claim 1, characterized in that: Step 2) further includes calcining the bismuth-based catalyst with a core-shell structure for enhanced gas-solid mass transfer, wherein the calcination temperature is 500-800° C. and the calcination time is 2-5 hours.

8. A bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer, characterized in that: The bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer is prepared by the preparation method of any one of claims 1 to 7. The core-shell structure for enhancing gas-solid mass transfer comprises: a core and an outer shell; the core is a bismuth-based material; and the outer shell is porous carbon or porous silica.

9. The bismuth-based catalyst with a core-shell structure for enhancing gas-solid mass transfer according to claim 8, characterized in that: The bismuth-based material is at least one of metallic bismuth, bismuth oxide, and bismuth oxycarbonate.

10. Use of the bismuth-based catalyst with a core-shell structure for enhancing gas-solid phase mass transfer prepared by the method for preparing the bismuth-based catalyst with a core-shell structure for enhancing gas-solid phase mass transfer according to any one of claims 1 to 7 in the production of formic acid, characterized in that: In the electrochemical reduction of carbon dioxide to formic acid, a three-electrode system is used, with the bismuth-based catalyst with the core-shell structure enhancing gas-solid mass transfer as the working electrode, a saturated calomel electrode as the reference electrode, or a silver / silver chloride electrode as the reference electrode, a platinum sheet as the counter electrode, and a KHCO3 solution or a NaHCO3 solution as the electrolyte. The reaction potential is -0.5 to -1.5 V, the reaction temperature is 10-50°C, the Faradaic efficiency of formic acid is 82%-90%, the formic acid energy efficiency is 58%-65%, and the formic acid yield per unit electrolysis area is 0.18-0.3 mmol / (h·cm 2 ).

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