Metal-doped Tin Oxide and Its Preparation Method and Application

Abstract

The present invention discloses a metal-doped tin oxide, a preparation method thereof and an application thereof. First, a hydrothermal method is used to synthesize a tin oxide with a nanosheet array structure on a conductive substrate, and then a metal-doped tin oxide with a nanosheet array structure is obtained by an impregnation method, and the metal-doped tin oxide is applied to the electrocatalytic reduction of HMF to produce DHMF. The tin oxide doped with heteroatoms prepared by the present invention has a more stable structure, improved performance, has a nanosheet array structure, can provide a large electrochemical current density, and is used as a cathode catalyst in the reaction of electrocatalytic hydrogenation of HMF, and can promote HMF to achieve a high Faraday efficiency within a wide voltage range.

Description

Technical Field

[0001] The present invention belongs to the technical field of nanomaterial synthesis and application, and particularly relates to a metal-doped tin oxide, a preparation method thereof, and an application thereof. Background Art

[0002] The catalytic hydrogenation of unsaturated aldehydes / ketones, especially biomass-derived aldehydes / ketones, to produce unsaturated alcohols is an important reaction in industry at present. Alcohols have a wide range of applications in the production of commodity chemicals such as flavors, fragrances, and pharmaceuticals. For example, the selective hydrogenation of 5-hydroxymethylfurfural (HMF) can produce 2,5-bis(hydroxymethyl)furan (BHMF), which is an important high-value diol used in fine chemical synthesis, the preparation of novel functionalized polyethers, polyurethanes, and their pharmaceutical polyheterocyclic compounds. At present, the industrial hydrogenation of aldehydes / ketones mainly relies on the thermal catalytic process of homogeneous or heterogeneous catalysts. Although relatively high reaction rates and selectivities can be obtained, the homogeneous system requires the use of unstable and expensive hydride donors such as LiAlH4 and NaBH4, which are difficult to separate and reuse, and are environmentally unfriendly. The thermal catalytic hydrogenation of heterogeneous catalysts is the most commonly used method, but usually requires high pressure (0.1 - 1 MPa), high temperature (100 - 500 °C), and H2 raw materials, which have certain safety hazards. Therefore, it is necessary to develop a green and sustainable hydrogenation method for aldehyde and ketone compounds to eliminate safety hazards.

[0003] Electrocatalytic hydrogenation (ECH) driven by clean energy (such as solar energy and wind energy) is considered an environmentally friendly upgrading route for aldehydes / ketones. ECH is similar to traditional thermal catalytic hydrogenation. The key difference is that adsorbed hydrogen (H*) is in-situ electrochemically generated from protons or water on the electrode surface, rather than through the dissociation of molecular H2. By this method, the huge kinetic barrier of H2 dissociation in traditional thermal catalysis is avoided, so that ECH can be carried out under mild temperature and pressure. So far, various biomass-derived aldehydes and ketones, such as acetaldehyde, acetone, benzaldehyde, acetophenone, 5-hydroxymethylfurfural, and ethyl pyruvate, have been successfully electrocatalytically hydrogenated to the corresponding alcohols using relatively inexpensive metals such as Ag and Cu. However, the current research still has problems such as low reaction rate, low selectivity, or a narrow voltage window for the target product due to multiple reaction paths and competitive hydrogen evolution reactions, which hinder its practical application. Therefore, it is a great challenge to find a catalyst that can achieve high activity and high selectivity for the ECH of unsaturated aldehydes and ketones. Summary of the Invention

[0004] The present invention is proposed to solve the problem of the narrow voltage window of the target product in the electrocatalytic hydrogenation of aldehyde and ketone compounds in the existing research. Its purpose is to provide a metal-doped tin oxide, a preparation method thereof, and an application thereof to improve the efficiency of electrocatalytic reduction of aldehydes and ketones.

[0005] The present invention is achieved through the following technical solutions:

[0006] A metal-doped tin oxide, wherein the tin oxide is a nanosheet array, and the metal is dispersed on the sheet structure of the tin oxide; the metal is any one or more of silver, gold, copper, platinum, palladium, rhodium, tin, iridium, ruthenium, cobalt, nickel, copper, manganese or iron; the size of the nanosheets is 100 nm to 500 nm; the particle size range of the metal is 1 nm to 5 nm; the doping amount range of the metal is 0.3% to 0.7% of the mass of the tin oxide.

[0007] A preparation method of a metal-doped tin oxide, comprising the following steps:

[0008] (i) Immerse the conductive substrate in a tin precursor solution by hydrothermal method to synthesize tin oxide with a nanosheet array structure on the conductive substrate;

[0009] (ii) Immerse the conductive substrate loaded with tin oxide obtained in the previous step in a metal ion salt solution, adsorb metal cations, then rinse, and electro-reduce at a fixed voltage to obtain a metal-doped tin oxide with a nanosheet array structure.

[0010] In the above technical solution, the preparation method of the tin precursor solution is: dissolve the tin salt in water, stir until fully dissolved, add ammonium fluoride, and stir until fully dissolved to obtain the tin precursor solution; the tin salt is any one or more of tin nitrate, tin chloride or tin sulfate; the concentration range of the tin salt in the tin precursor solution is 0.1 mol / L to 0.5 mol / L; the concentration range of ammonium fluoride is 0.2 mol / L to 0.5 mol / L. The addition of ammonium fluoride enables the formation of a nanosheet array structure of tin oxide.

[0011] In the above technical solution, the reaction conditions of the hydrothermal method are to react under a constant temperature condition of 160°C to 200°C for 20 h to 24 h, take out and rinse, and dry under the condition of 60°C to 80°C.

[0012] In the above technical solution, the metal ions in step (ii) are any one or more of silver, gold, copper, platinum, palladium, rhodium, tin, iridium, ruthenium, cobalt, nickel, copper, manganese or iron; more preferably, the metal salt solution is any one of silver nitrate, silver sulfate, copper sulfate, cobalt chloride, copper nitrate or cobalt nitrate.

[0013] In the above technical solution, the concentration of the metal ion salt solution in step (ii) is 0.01 mol / L to 0.05 mol / L; the soaking time is 5 s to 30 s; the conditions for electroreduction are that the conductive substrate loaded with tin oxide is used as the cathode, the platinum electrode is used as the counter electrode, and the Ag / AgCl electrode is used as the reference electrode, and reduction is carried out at a voltage of -0.5 to -1.2 V vs. RHE for 10 min to 30 min.

[0014] In the above technical solution, the conductive substrate is any one of carbon cloth, carbon paper, nickel foam, nickel sheet, copper mesh, copper sheet, copper foam, titanium mesh, stainless steel, iron sheet or FTO conductive glass.

[0015] Application of a metal-doped tin oxide in electrocatalytic reduction of aldehydes and ketones, wherein the metal-doped tin oxide is used as a cathode catalyst.

[0016] In the above technical solution, in the electrocatalytic reduction of aldehydes and ketones, the metal-doped tin oxide loaded on the conductive substrate is used as the cathode, and an electrolytic cell is assembled with the anode and the electrolyte. HMF is added to the electrolyte, and HMF is electrocatalytically reduced to generate DHMF on the cathode at a voltage of -0.5 V to -1.2 V vs. RHE.

[0017] In the above technical solution, the electrolyte is a solution of any one or more of lithium hydroxide, potassium hydroxide, sodium hydroxide, potassium bicarbonate, potassium carbonate, sodium bicarbonate, sodium carbonate, sodium sulfate or potassium sulfate; the concentration of the electrolyte is 0.1 M to 1 M; the concentration of HMF is 0.03 M to 0.05 M; the anode is an oxygen evolution catalyst loaded on the conductive substrate, and the oxygen evolution catalyst is one or more of metal iridium / carbon catalyst, metal ruthenium / carbon catalyst, iridium dioxide, ruthenium dioxide, nickel iron hydrotalcite or nickel hydroxide.

[0018] The beneficial effects of the present invention are:

[0019] The present invention provides a metal-doped tin oxide, a preparation method thereof, and an application thereof. The metal-doped tin oxide obtained in the present invention is specifically a nanosheet array structure, which can provide a large electrochemically active area and promote the enrichment of aldehydes and ketones on the electrode surface during the electrocatalytic reduction reaction. The tight binding between the oxide as a catalyst and the conductive substrate can accelerate electron transfer and increase the current density. The tin / heteroatom dual-metal structure in the tin oxide can effectively regulate the charge distribution of the lamellar and improve the intrinsic activity of the catalyst. The heteroatoms in the tin oxide can promote the decomposition of water to generate H*, thereby promoting the hydrogenation reaction of aldehydes and ketones, providing a new type of catalyst for the efficient conversion and utilization of aldehydes and ketones to prepare high-value-added chemicals. At the same time, a tin oxide doped with heteroatoms, with stable structure and improved performance, is generated, providing new ideas for the design and controllable preparation of tin-based nanomaterials. Description of the Drawings

[0020] Figure 1 is the SEM image of the tin oxide supported on carbon cloth prepared in Example 1 of the present invention;

[0021] Figure 2 is the SEM image of the silver-doped tin oxide supported on carbon cloth prepared in Example 1 of the present invention;

[0022] Figure 3 is the TEM image of the silver-doped tin oxide supported on carbon cloth prepared in Example 1 of the present invention;

[0023] Figure 4 is the XRD pattern of the tin oxide supported on carbon cloth and the silver-doped tin oxide supported on carbon cloth prepared in Example 1 of the present invention;

[0024] Figure 5 is the electrochemical (time-current) test data graph of HMF hydrogenation in Example 1 of the present invention;

[0025] Figure 6 is the Faraday efficiency result of the DHMF product prepared by electrocatalytic HMF hydrogenation in Example 1 and Comparative Example 1 of the present invention;

[0026] Figure 7 is the schematic diagram of the principle of using the carbon cloth-supported silver-doped layered tin oxide for HMF hydrogenation to prepare DHMF in Example 1 of the present invention.

[0027] For those of ordinary skill in the art, without creative efforts, other related drawings can be obtained based on the above drawings. Detailed Embodiments

[0028] In order to enable those skilled in the art to better understand the technical solutions of the present invention, the technical solutions of the present invention will be further described below in conjunction with the drawings in the specification and through specific embodiments.

[0029] Example 1

[0030] (Ⅰ)Synthesis of silver-doped tin oxide (nanosheet array electrode) supported on carbon cloth:

[0031] (ⅰ)Soak the appropriately cut carbon cloth in 0.15 M (mol / L) potassium permanganate solution for half an hour, take it out, wash it with deionized water, and dry it.

[0032] (ⅱ)Dissolve 5 mmol of SnCl2·2H2O in 35 mL of deionized water, stir at room temperature for 30 min to form a transparent solution, add 10 mmol of NH4F, and continue to stir for 30 min to obtain a tin precursor solution.

[0033] (ⅲ)Soak the carbon cloth in a high-pressure reaction kettle containing the tin precursor solution, hydrothermally grow it at 180 °C for 24 h, take out the carbon cloth, rinse it with water and ethanol to remove other residues, and dry it at 80 °C to obtain tin oxide supported on carbon cloth.

[0034] The SEM image of the prepared silver-doped tin oxide (nanosheet array electrode) supported on carbon cloth is as Figure 1 shown. It can be seen from Figure 1 that the tin oxide on the carbon cloth is a uniform sheet array structure.

[0035] The XRD characterization result of the tin oxide supported on carbon paper is as Figure 4 shown, proving that the synthesized catalyst is tin oxide.

[0036] (ⅳ)Soak the above-prepared tin oxide nanosheet array supported on carbon cloth in a 10 mM solution containing silver nitrate for 10 s to adsorb silver ions; rinse it with deionized water and electro-reduce it at -0.92 V vs. RHE for 10 min to obtain silver-doped tin oxide supported on carbon cloth.

[0037] The conditions for the electro-reduction are: the conductive substrate of the supported tin oxide serves as the cathode, the platinum electrode serves as the counter electrode, and the Ag / AgCl electrode serves as the reference electrode.

[0038] The SEM image of the prepared silver-doped tin oxide (nanosheet array electrode) supported on carbon cloth is as Figure 2 shown. It can be seen from Figure 2 that the silver-doped tin oxide supported on carbon cloth is a uniform sheet array structure, and there is no obvious difference in morphology from the undoped tin oxide.

[0039] The TEM image of the silver-doped tin oxide (nanosheet array electrode) supported on carbon cloth is as Figure 3 shown. It can be seen from Figure 3It can be seen that the carbon cloth supported silver-doped tin oxide has a nanosize of 5 nm.

[0040] The XRD characterization results of the carbon paper supported silver-doped tin oxide are as Figure 4 shown, proving that the synthesized catalyst is silver-doped tin oxide.

[0041] (II) Using the carbon cloth supported silver-doped layered tin oxide (nanosheet array electrode) for the hydrogenation of HMF to prepare DHMF:

[0042] (i) Using the prepared carbon cloth supported silver-doped tin oxide (nanosheet array) as the cathode, the conductive substrate loaded with the oxygen evolution catalyst as the anode, the platinum sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode to build a three-electrode system; the oxygen evolution catalyst used at the anode is cobalt-nickel hydrotalcite.

[0043] (ii) During the electrochemical performance test, using 0.5 M potassium bicarbonate solution as the electrolyte solution, reacting at -0.92 V vs. RHE voltage for 1 h.

[0044] (iii) Performing liquid-phase testing on the solution after the reaction to measure the products.

[0045] The electrochemical (time-current) test of the HMF hydrogenation is as Figure 5 shown. It can be seen from Figure 5 that the carbon cloth supported silver-doped tin oxide has a relatively large current density and excellent stability.

[0046] The Faraday efficiency results of the DHMF product prepared by the electrocatalytic hydrogenation of HMF are as Figure 6 shown. It can be seen from Figure 6 that a high Faraday efficiency of >95% for DHMF is exhibited within a wide potential window of -0.62 V to -1.12 V vs. RHE.

[0047] Comparative Example 1

[0048] (i) Using the carbon cloth supported tin oxide (nanosheet array) prepared in Example 1 as the cathode, the platinum sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode to build a three-electrode system; the conductive substrate loaded with the oxygen evolution catalyst is the anode, and the oxygen evolution catalyst used at the anode is cobalt-nickel hydrotalcite.

[0049] (ii) During the electrochemical performance test, using 0.5 M potassium bicarbonate solution as the electrolyte solution, reacting at -0.92 V vs. RHE voltage for 1 h.

[0050] (iii) Performing liquid-phase testing on the solution after the reaction to measure the products.

[0051] The Faraday efficiency results of the DHMF product prepared by electrocatalytic hydrogenation of HMF are as follows Figure 6 shown. It can be seen from Figure 6 that the Faraday efficiency of DHMF is relatively low at both low and high voltages.

[0052] The reaction rate of carbon cloth supported silver-doped tin oxide for the selective electrochemical reduction of other aldehydes / ketones to the corresponding alcohols (including furfural, benzaldehyde derivatives, pyruvic acid, acetophenone) is also 1.5 - 3 times higher than that of tin oxide, indicating that carbon cloth supported silver-doped tin oxide has a general promoting effect on the hydrogenation of aldehydes / ketones.

[0053] Example 2

[0054] (I) Synthesis of nickel foam supported cobalt-doped tin oxide (nanosheet array electrode)

[0055] (i) Cut the appropriate nickel foam and wash it in ethanol, 35% dilute sulfuric acid, and deionized water for half an hour each, then take it out and dry it.

[0056] (ii) Dissolve 5 mmol of SnCl2·2H2O in 35 mL of deionized water, stir at room temperature for 30 min to form a transparent solution, add 10 mmol of NH4F, and continue stirring for 30 min to obtain a tin precursor solution.

[0057] (iii) Immerse the nickel foam in a high-pressure reaction kettle containing the tin precursor solution, hydrothermally grow it at 180 °C for 24 h, then take out the nickel foam, wash it with water and ethanol to remove other residues, and dry it at 80 °C to obtain nickel foam supported tin oxide.

[0058] (iii) Immerse the above-prepared carbon cloth supported tin oxide nanosheet array in a 10 mM solution containing cobalt nitrate for 10 s to adsorb cobalt ions, wash it with deionized water, and electroreduce it at -0.92 V vs. RHE for 10 min to obtain nickel foam supported cobalt-doped tin oxide.

[0059] The conditions for the electroreduction are as follows: the conductive substrate of the supported tin oxide is used as the cathode, the platinum electrode is used as the counter electrode, and the Ag / AgCl electrode is used as the reference electrode.

[0060] (II) Nickel foam supported cobalt-doped tin oxide (nanosheet array electrode) is used for the reduction of HMF to prepare DHMF:

[0061] (i) Use the prepared nickel foam supported cobalt-doped tin oxide (nanosheet array electrode) as the cathode, the platinum sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode to build a three-electrode system. Among them, the oxygen evolution catalyst used at the anode is cobalt-nickel hydrotalcite.

[0062] (ii) During the electrochemical performance test, a 0.5 M sodium bicarbonate solution was used as the electrolyte solution, and the reaction was carried out at a voltage of -0.92 V vs. RHE for 1 h.

[0063] (iii) The solution after the reaction was subjected to liquid-phase testing to measure the products.

[0064] The Faraday efficiency of the DHMF product prepared by electrocatalytic hydrogenation of HMF can reach 95%.

[0065] Example 3

[0066] (I) Synthesis of carbon paper supported copper-doped tin oxide (nanosheet array electrode):

[0067] (i) The appropriately cut carbon paper was immersed in a 0.15 M potassium permanganate solution for half an hour, taken out, washed with deionized water, and dried.

[0068] (ii) 5 mmol of SnCl2·2H2O was dissolved in 35 mL of deionized water, stirred at room temperature for 30 min to form a transparent solution, 10 mmol of NH4F was added, and stirring was continued for 30 min to obtain a tin precursor solution.

[0069] (iii) The carbon paper supported tin oxide nanosheet array prepared above was immersed in a 10 mM solution containing silver nitrate for 10 s to adsorb copper ions, rinsed with deionized water, and electrochemically reduced at -0.92 V vs. RHE for 10 minutes to obtain carbon cloth supported copper-doped tin oxide.

[0070] The conditions for the electroreduction were as follows: the conductive substrate of the supported tin oxide was used as the cathode, the platinum electrode was used as the counter electrode, and the Ag / AgCl electrode was used as the reference electrode.

[0071] (II) Carbon paper supported copper-doped tin oxide nanosheet array electrode for electrocatalytic hydrogenation of HMF to prepare DHMF:

[0072] (i) Using the prepared carbon paper supported copper-doped tin oxide nanosheet array (catalyst) as the cathode, the platinum sheet as the counter electrode, and the Ag / AgCl electrode as the reference electrode, a three-electrode system was constructed. Among them, the oxygen evolution catalyst used at the anode was cobalt-nickel hydrotalcite.

[0073] (ii) During the electrochemical performance test, a 0.1 M (mol / L) potassium sulfate solution was used as the electrolyte solution, and the reaction was carried out at a voltage of -0.92 V vs. RHE for 12 h.

[0074] (iii) The solution after the reaction was subjected to liquid-phase testing to measure the products.

[0075] The Faraday efficiency of the DHMF product prepared by electrocatalytic hydrogenation of HMF can reach over 95%.

[0076] Reaction principle of the present invention (taking Example 1 as an example):

[0077] As Figure 5 shown, the present invention constructs a carbon cloth supported silver-doped tin oxide (nanosheet array electrode) as the cathode electrocatalyst, using hydrogen atoms / oxygen atoms in water as the [H] / [O] source in the redox reaction. During the electrolysis process, water generates [H], and [H] undergoes electrocatalytic hydrogenation with the C=O in HMF to produce DHMF.

[0078] Meanwhile, water is oxidized to oxygen at the anode.

[0079] The reaction equation is:

[0080]

[0081] It should be noted that, without conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.

[0082] The applicant declares that the above is only the specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Those skilled in the art should understand that any changes or substitutions that can be easily thought of by those skilled in the art within the technical scope disclosed by the present invention fall within the protection scope and the disclosure scope of the present invention.

Claims

1. A preparation method of metal-doped tin oxide, characterized in that: It includes the following steps: (i) Immerse the conductive substrate in a tin precursor solution and synthesize tin oxide with a nanosheet array structure on the conductive substrate by hydrothermal method; (ii) Immerse the conductive substrate loaded with tin oxide obtained in the previous step in a metal ion salt solution, adsorb metal cations, then rinse and electro-reduce at a fixed voltage to obtain metal-doped tin oxide with a nanosheet array structure; The tin oxide is a nanosheet array, and the metal is dispersed on the tin oxide flake structure; the metal is any one or more of silver, gold, copper, platinum, palladium, rhodium, tin, iridium, ruthenium, cobalt, nickel, copper, manganese or iron; the size of the nanosheets is 100 nm to 500 nm; the particle size range of the metal is 1 nm to 5 nm; the doping amount of the metal is 0.3% to 0.7% of the mass of the tin oxide.

2. The preparation method of the metal-doped tin oxide according to claim 1, wherein: The preparation method of the tin precursor solution is: dissolve the tin salt in water, stir until fully dissolved, add ammonium fluoride, and stir until fully dissolved to obtain the tin precursor solution; the tin salt is any one or more of tin nitrate, tin chloride or tin sulfate; the concentration range of the tin salt in the tin precursor solution is 0.1 mol / L to 0.5 mol / L; the concentration range of ammonium fluoride is 0.2 mol / L to 0.5 mol / L.

3. The preparation method of the metal-doped tin oxide according to claim 2, characterized in that: The reaction conditions of the hydrothermal method are to react at a constant temperature of 160°C to 200°C for 20 h to ~24 h, take out and rinse and dry at 60°C to 80°C.

4. The preparation method of the metal-doped tin oxide according to claim 1, characterized in that: The metal ions in step (ii) are any one or more of silver, gold, copper, platinum, palladium, rhodium, tin, iridium, ruthenium, cobalt, nickel, copper, manganese or iron; The concentration of the metal ion salt solution is 0.01 mol / L to 0.05 mol / L; The immersion time is 5 s to 30 s.

5. The preparation method of the metal-doped tin oxide according to claim 1, characterized in that: The conditions for electro-reduction are: the conductive substrate loaded with tin oxide is used as the cathode, the platinum electrode is used as the counter electrode, the Ag / AgCl electrode is used as the reference electrode, and it is reduced at a voltage of -0.5 V to -1.2 V vs. RHE for 10 min to 30 min.

6. The preparation method of the metal-doped tin oxide according to claim 1, characterized in that: The conductive substrate is any one of carbon cloth, carbon paper, nickel foam, nickel sheet, copper mesh, copper sheet, copper foam, titanium mesh, stainless steel, iron sheet or FTO conductive glass.

7. Use of a metal-doped tin oxide prepared by the method according to claim 1, characterized in that: It is applied to electrocatalytic reduction of aldehyde or ketone, and the metal-doped tin oxide is used as the cathode catalyst.

8. Use of the metal-doped tin oxide according to claim 7, characterized in that: In the electrocatalytic reduction of aldehyde or ketone, the conductive substrate loaded with the metal-doped tin oxide prepared by the method of claim 1 is used as the cathode, assembled with the anode and the electrolyte into an electrolytic cell, add HMF to the electrolyte, and electrocatalytically reduce HMF to generate DHMF at the cathode at a voltage of -0.5 V to -1.2 V vs.RHE.

9. The application of the metal-doped tin oxide according to claim 8, characterized in that: The electrolyte is a solution of any one or more of lithium hydroxide, potassium hydroxide, sodium hydroxide, potassium bicarbonate, potassium carbonate, sodium bicarbonate, sodium carbonate, sodium sulfate or potassium sulfate; The concentration of the electrolyte is 0.1 M to 1 M; the concentration of HMF is 0.03 M to 0.05 M; The anode is an oxygen evolution catalyst supported on a conductive substrate, and the oxygen evolution catalyst is one or more of metal iridium / carbon catalyst, metal ruthenium / carbon catalyst, iridium dioxide, ruthenium dioxide, nickel-iron hydrotalcite or nickel hydroxide.

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