Supported catalyst for producing hydrogen peroxide through electrocatalytic oxygen reduction and preparation method and application thereof

Abstract

The invention relates to the technical field of electrosynthesis of high-added-value products, in particular to a supported catalyst for producing hydrogen peroxide through electrocatalytic oxygen reduction and a preparation method and application of the supported catalyst. The catalyst is represented by a formula NiTPP (at) CNT-ox, an oxygen-doped carbon nanotube CNT-ox is used as a carrier, and nickel tetraphenylporphyrin NiTPP is used as an active site. According to the preparation method, NiTPP is adsorbed on CNT-ox through a dispersion-adsorption method, and the supported catalyst NiTPP coated CNT-ox is obtained. The NiTPP-CNT-ox prepared by the method has relatively high catalytic activity, selectivity and excellent stability in the process of preparing hydrogen peroxide by electrocatalytic oxygen reduction, and has a potential application prospect.

Description

Technical Field

[0001] The present invention relates to the technical field of electrosynthetic high value-added products, and in particular to a supported catalyst for electrocatalytic oxygen reduction to produce hydrogen peroxide, and a preparation method and application thereof. Background Art

[0002] Hydrogen peroxide is a potential green chemical that is used in many fields such as medicine, textiles, papermaking, caprolactam technology, semiconductors and aerospace industries. The traditional production process is the anthraquinone method, which has many disadvantages such as high equipment and production costs, environmental pollution caused by the use of organic solvents, and safety hazards in the transportation and storage of high-concentration hydrogen peroxide caused by centralized production. The electrochemical synthesis of hydrogen peroxide has mild reaction conditions, is green and environmentally friendly, has high product purity, and low production costs. The hydrogen and oxygen separation design and decentralized equipment avoid some difficulties and dangers in production, transportation and storage, and have the potential for practical application.

[0003] Electrocatalytic oxygen reduction to produce hydrogen peroxide can be divided into acidic, neutral and alkaline according to the pH value of the reaction system. The kinetics of oxygen reduction reaction under acidic conditions are slow and the hydrogen evolution side reaction is serious. Hydrogen peroxide under alkaline conditions has a narrower application and is more prone to self-decomposition reaction, exothermic and gas production, which increases the danger during transportation and storage. Neutral hydrogen peroxide has flexible uses and is easy to store, which is conducive to large-scale application.

[0004] Catalysts are the key to the industrial application of electrocatalytic oxygen reduction to produce hydrogen peroxide. Catalyst performance also shows a correlation with the pH value of the reaction system, which is specifically reflected in (including but not limited to): 1) Reaction mechanism: Acidity is O2+2H + +2e - →H2O2; alkaline is O2+H2O+2e - →HO2 - . 2) Reaction pathway: The reduction of oxygen can be achieved through four electrons (4e - ) or two electrons (2e - ) transfer pathways to generate water or H2O2 respectively. Changes in pH value will affect the adsorption mode of oxygen molecules on the catalyst surface, thus determining the reaction path. 3) Reaction kinetics: Changes in pH value will affect the electrochemical double layer (EDL) structure and surface adsorption energy, thereby affecting the kinetics of the entire electrochemical process. Therefore, the design principles and performance of catalysts in different systems vary greatly, and it is necessary to specifically study and invent catalysts for use under neutral conditions. Summary of the invention

[0005] In order to solve the above technical problems, the present invention provides a supported catalyst for electrocatalytic oxygen reduction to produce hydrogen peroxide and a preparation method thereof. A transition metal-nitrogen-carbon catalyst with high activity is obtained through a simple and environmentally friendly preparation process, which is used for highly selective electrocatalytic oxygen reduction to produce hydrogen peroxide under neutral conditions. The present invention improves the spin state and charge distribution of nickel atoms in tetraphenylporphyrin nickel molecules adsorbed on the surface of carbon nanotubes by oxygen doping on the surface of carbon nanotubes, adjusts the adsorption energy of key oxygen reduction intermediates, and thus improves the production performance of H2O2. The prepared catalyst has a high selectivity at 1000mAcm -2 The Faradaic efficiency is 85.3% at a high current density.

[0006] In order to achieve the above object, the technical solution of the present invention is as follows:

[0007] On one hand, the present invention provides a supported catalyst, which is an oxygen-doped carbon nanotube-supported nickel tetraphenylporphyrin; the catalyst is represented by the formula NiTPP@CNT-ox, wherein the oxygen-doped carbon nanotube CNT-ox is a carrier and the nickel tetraphenylporphyrin NiTPP is an active site.

[0008] In the above technical solution, further, the loading amount of nickel in the catalyst is 1-3wt%.

[0009] Another aspect of the present invention provides a method for preparing the above catalyst, wherein oxygen-doped carbon nanotubes are dispersed in a solvent, nickel tetraphenylporphyrin is added, ultrasonically dispersed uniformly, and the dispersion is separated and dried to obtain a supported catalyst NiTPP@CNT-ox.

[0010] In the above technical solution, further, the mass ratio of the oxygen-doped carbon nanotubes to tetraphenylporphyrin nickel is 1:1 to 10:1; and the solvent is N,N-dimethylformamide.

[0011] In the above technical solution, further, the preparation method of the oxygen-doped carbon nanotubes is as follows:

[0012] Step S1: adding carbon nanotubes into a nitric acid solution and dispersing them evenly to obtain a dispersion;

[0013] Step S2: adding the dispersion obtained in step S1 into the polytetrafluoroethylene liner and placing it into a hydrothermal kettle;

[0014] Step S3: heating the hydrothermal kettle containing the dispersion obtained in step S2 to 120-200° C. and keeping the temperature for 1-8 hours to obtain a dispersion after hydrothermal treatment;

[0015] Step S4: The dispersion obtained in step S3 is centrifuged, washed with water, and vacuum dried to obtain oxygen-doped carbon nanotubes.

[0016] In the above technical solution, further, in step S1, the ratio of the mass of the carbon nanotubes to the volume of nitric acid is 1-30 mg:1 mL; and the concentration of the nitric acid is 0.1-3 mol / L.

[0017] In the above technical solution, further, in step S2, the filling degree of the dispersion in the polytetrafluoroethylene liner is 30-80%.

[0018] The present invention also provides an application of the above catalyst in an electrocatalytic oxygen reduction reaction to produce hydrogen peroxide, wherein the electrolyte system in the electrocatalytic oxygen reduction reaction to produce hydrogen peroxide is a neutral solution.

[0019] The beneficial effects of the present invention are:

[0020] (1) The present invention uses oxygen-doped carbon nanotube carriers to improve the spin state and charge distribution of nickel atoms in the adsorbed active molecule NiTPP, adjust the adsorption energy of key ORR intermediates, avoid the problem of slow reaction rate caused by weak adsorption energy, and avoid the problem of low selectivity caused by difficult desorption of strong adsorption intermediates, thereby improving the production performance of H2O2 in neutral electrolyte. The supported catalyst NiTPP@CNT-ox was tested in a rotating ring disk electrode system in a neutral electrolyte (0.1M K2SO4). The test results showed that the selectivity of NiTPP@CNT-ox was 82.7-99.7% in the potential range of 0.1-0.4V (vs RHE), proving that it has a high selectivity for hydrogen peroxide.

[0021] (2) The active adsorbed molecule NiTPP of the catalyst of the present invention has a low activity in catalyzing the reduction of hydrogen peroxide, which makes the selectivity of hydrogen peroxide higher. In addition, NiTPP has a high turnover efficiency and can maintain a high Faradaic efficiency at a high current density. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 Linear sweep voltammetric curves of the catalysts prepared in Example 1 and Comparative Example 1 in a neutral electrolyte (0.1M K2SO4) obtained by rotating ring disk testing;

[0023] Figure 2 The hydrogen peroxide selectivity-potential curves of the catalysts prepared in Example 1 and Comparative Example 1 in a neutral electrolyte (0.1M K2SO4) obtained by rotating ring disk testing;

[0024] Figure 3 is the total spectrum of the X-ray photoelectron spectra of NiTPP@CNT-ox and CNT-ox in Example 1;

[0025] Figure 4Ni 2p fine spectra of X-ray photoelectron spectroscopy of NiTPP@CNT-ox in Example 1, NiTPP@CNT-re and NiTPP in Comparative Example 1;

[0026] Figure 5 Linear sweep voltammetric curves of the catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3 in a neutral electrolyte (0.1M K2SO4) obtained by rotating ring disk testing;

[0027] Figure 6 The hydrogen peroxide selectivity-potential curves of the catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3 in a neutral electrolyte (0.1M K2SO4) obtained by the rotating ring disk test;

[0028] Figure 7 Linear sweep voltammetric curves of the catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3 in a 10 mM H2O2 + 0.1 M K2SO4 mixed solution under nitrogen saturation obtained by rotating ring disk test;

[0029] Figure 8 Linear sweep voltammetric curves of the catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3 in alkaline electrolyte (0.1 M KOH) obtained by rotating ring disk test;

[0030] Fig. 9 The hydrogen peroxide selectivity-potential curves of the catalysts prepared in Example 1, Comparative Example 2 and Comparative Example 3 in an alkaline electrolyte (0.1 M KOH) obtained by the rotating ring disk test;

[0031] Fig.10 The change of the Faradaic efficiency of NiTPP@CNT-ox in Example 1 at different current densities in the flow electrolytic cell test. DETAILED DESCRIPTION

[0032] The above contents of the present invention are further described in detail below through examples, but this should not be understood as the scope of the above subject matter of the present invention being limited to the following examples, and all technologies implemented based on the above contents of the present invention belong to the scope of the present invention.

[0033] Unless otherwise specified, the materials used in the embodiments of the present invention can be obtained through commercial channels or prepared according to conventional methods well known to those skilled in the art.

[0034] Example 1

[0035] (1) adding 1 g of carbon nanotubes into 60 ml of nitric acid solution with a concentration of 2 M and dispersing them evenly to obtain a dispersion;

[0036] (2) adding the dispersion obtained in step (1) into a polytetrafluoroethylene liner with a volume of 100 mL and placing it in a hydrothermal kettle;

[0037] (3) heating the hydrothermal reactor containing the dispersion obtained in step (2) to 120° C. and keeping the temperature for 2 h to obtain a dispersion after hydrothermal treatment;

[0038] (4) subjecting the dispersion obtained in step (3) to centrifugation, water washing, and vacuum drying to obtain oxygen-doped multi-walled carbon nanotubes (CNT-ox);

[0039] (5) 300 mg of the CNT-ox obtained in step (4) was dispersed in N,N-dimethylformamide solvent, 100 mg of nickel tetraphenylporphyrin (NiTPP) was added, and ultrasonic dispersion was performed to obtain a supported catalyst NiTPP@CNT-ox after separation and drying.

[0040] Comparative Example 1

[0041] (1) adding 1 g of carbon nanotubes into 60 ml of nitric acid solution with a concentration of 2 M and dispersing them evenly to obtain a dispersion;

[0042] (2) adding the dispersion obtained in step (1) into a polytetrafluoroethylene liner with a volume of 100 mL and placing it in a hydrothermal kettle;

[0043] (3) heating the hydrothermal reactor containing the dispersion obtained in step (2) to 120° C. and keeping the temperature for 2 h to obtain a dispersion after hydrothermal treatment;

[0044] (4) subjecting the dispersion obtained in step (3) to centrifugation, water washing, and vacuum drying to obtain oxygen-doped multi-walled carbon nanotubes (CNT-ox);

[0045] (5) 300 mg of CNT-ox obtained in step (4) was placed in a quartz tube of a tubular furnace, and a hydrogen-argon mixture was introduced, with a hydrogen volume content of 5%. The tubular furnace was heated to 900° C. and kept warm for 1 hour. After the tubular furnace was cooled, the sample was taken out and named CNT-re;

[0046] (6) Take 300 mg of CNT-re obtained in step (5) and disperse it in solvent N,N-dimethylformamide, add 100 mg of nickel tetraphenylporphyrin (NiTPP), and disperse it evenly by ultrasonication. The dispersion is separated and dried to obtain the supported catalyst NiTPP@CNT-re.

[0047] Comparative Example 2

[0048] (1) adding 1 g of carbon nanotubes into 60 ml of nitric acid solution with a concentration of 2 M and dispersing them evenly to obtain a dispersion;

[0049] (2) adding the dispersion obtained in step (1) into a polytetrafluoroethylene liner with a volume of 100 mL and placing it in a hydrothermal kettle;

[0050] (3) heating the hydrothermal reactor containing the dispersion obtained in step (2) to 120° C. and keeping the temperature for 2 h to obtain a dispersion after hydrothermal treatment;

[0051] (4) subjecting the dispersion obtained in step (3) to centrifugation, water washing, and vacuum drying to obtain oxygen-doped multi-walled carbon nanotubes (CNT-ox);

[0052] (5) 300 mg of the CNT-ox obtained in step (4) was dispersed in N,N-dimethylformamide solvent, 100 mg of cobalt tetraphenylporphyrin (CoTPP) was added, and ultrasonic dispersion was performed to obtain a supported catalyst CoTPP@CNT-ox after separation and drying.

[0053] Comparative Example 3

[0054] (1) adding 1 g of carbon nanotubes into 60 ml of nitric acid solution with a concentration of 2 M and dispersing them evenly to obtain a dispersion;

[0055] (2) adding the dispersion obtained in step (1) into a polytetrafluoroethylene liner with a volume of 100 mL and placing it in a hydrothermal kettle;

[0056] (3) heating the hydrothermal reactor containing the dispersion obtained in step (2) to 120° C. and keeping the temperature for 2 h to obtain a dispersion after hydrothermal treatment;

[0057] (4) subjecting the dispersion obtained in step (3) to centrifugation, water washing, and vacuum drying to obtain oxygen-doped multi-walled carbon nanotubes (CNT-ox);

[0058] (5) 300 mg of the CNT-ox obtained in step (4) was dispersed in a solvent of N,N-dimethylformamide, 100 mg of tetraphenylporphyrin iron (FeTPP) was added, and ultrasonic dispersion was performed to obtain a supported catalyst FeTPP@CNT-ox after separation and drying.

[0059] from Figure 1 From the linear sweep voltammetric curves of Example 1 and Comparative Example 1, it can be seen that the NiTPP@CNT-ox prepared by using oxygen-doped carbon nanotubes as carriers to load NiTPP has the highest hydrogen peroxide oxidation current (j ring ), which indicates that it has the highest activity in catalyzing the production of hydrogen peroxide. Figure 2From the hydrogen peroxide selectivity-potential curves of Example 1 and Comparative Example 1, it can be seen that NiTPP@CNT-ox has the highest hydrogen peroxide selectivity, with a selectivity of 82.7-99.7% in the potential range of 0.1-0.4 V (vs RHE).

[0060] from Figure 3 From the X-ray photoelectron spectrum, we can see that NiTPP@CNT-ox has more N1s and Ni 2p peaks than CNT-ox, indicating that NiTPP is successfully adsorbed on CNT-ox. Figure 4 Comparison of the Ni2p fine spectra of Example 1 and Comparative Example 1 shows that the binding energy of Ni in NiTPP@CNT-ox is higher, indicating that the oxygen atoms in CNT-ox have an electronic regulation effect on Ni. Figure 7 The reaction activity of NiTPP@CNT-ox, CoTPP@CNT-ox and FeTPP@CNT-ox in catalytic hydrogen peroxide reduction (H2O2RR) was tested, among which NiTPP@CNT-ox had the lowest activity, proving that the reaction rate of the generated hydrogen peroxide being further reduced on its surface was the lowest, which also explains the high selectivity of NiTPP@CNT-ox in producing hydrogen peroxide. Figure 5 and Figure 6 The performance of FeTPP and CoTPP as active molecules was compared and they showed lower catalytic selectivity. Figure 8 and Fig. 9 The catalytic performance of NiTPP@CNT-ox, CoTPP@CNT-ox and FeTPP@CNT-ox under alkaline conditions (0.1M KOH solution) is shown in Figure 2. The selectivity is lower than that under neutral conditions under low potential conditions (0.1~0.3V). Fig.10 The Faradaic efficiency of NiTPP@CNT-ox varies with current density in the flow cell test. The Faradaic efficiency of NiTPP@CNT-ox is between 200 and 600 mA cm -2 Range above 93.2%, 1000mA cm -2 It can also reach 85.3%.

[0061] Table 1 shows the element contents of CNT-ox, NiTPP@CNT-ox, CNT-re, NiTPP@CNT-re and NiTPP obtained by X-ray photoelectron spectroscopy and inductively coupled plasma-optical emission spectroscopy (ICP-OES) tests. It can be seen from Table 1 that compared with CNT-ox, the oxygen content of CNT-re treated with high-temperature hydrogen reduction is significantly reduced. Figure 2 , due to the lack of interaction between oxygen and nickel, the hydrogen peroxide selectivity of NiTPP@CNT-re decreased.

[0062] Table 1

[0063]

[0064] In summary, on the one hand, compared with NiTPP@CNT-re after reduction treatment, the method of the present invention regulates the spin state and charge distribution of nickel atoms by incorporating oxygen atoms, thereby achieving the goal of adjusting the adsorption energy of key ORR intermediates, thereby obtaining a catalyst NiTPP@CNT-ox with high H2O2 production efficiency, which proves the importance of oxygen doping; on the other hand, compared with CoTPP@CNT-ox and FeTPP@CNT-ox with CoTPP and FeTPP as active centers, NiTPP@CNT-ox has the lowest reaction activity for catalytic hydrogen peroxide reduction (H2O2RR), which proves the importance of selecting NiTPP as the active center.

[0065] The above embodiments are only preferred embodiments of the present invention and are not intended to limit the implementation methods. The protection scope of the present invention shall be subject to the scope defined in the claims. Other different forms of changes or modifications may be made based on the above description. Obvious changes or modifications derived therefrom are still within the protection scope of the present invention.

Claims

1. A supported catalyst, characterized in that The catalyst is oxygen-doped carbon nanotube-supported tetraphenylporphyrin nickel.

2. The catalyst according to claim 1, characterized in that In the catalyst, the loading amount of nickel is 1-3 wt %.

3. A method for preparing the catalyst according to claim 1 or 2, characterized in that: The oxygen-doped carbon nanotubes are dispersed in a solvent, and nickel tetraphenylporphyrin is added and dispersed uniformly by ultrasonication. The dispersion is separated and dried to obtain a supported catalyst NiTPP@CNT-ox.

4. The preparation method according to claim 3, characterized in that: The mass ratio of the oxygen-doped carbon nanotubes to tetraphenylporphyrin nickel is 1:1 to 10:

1.

5. The preparation method according to claim 3, characterized in that: The solvent is N,N-dimethylformamide.

6. The preparation method according to claim 3, characterized in that: The preparation method of the oxygen-doped carbon nanotubes is as follows: Step S1: adding carbon nanotubes into a nitric acid solution and dispersing them evenly to obtain a dispersion; Step S2: adding the dispersion obtained in step S1 into the polytetrafluoroethylene liner and placing it into a hydrothermal kettle; Step S3: heating the hydrothermal kettle containing the dispersion obtained in step S2 to 120-200° C. and keeping the temperature for 1-8 hours to obtain a dispersion after hydrothermal treatment; Step S4: The dispersion obtained in step S3 is centrifuged, washed with water, and vacuum dried to obtain oxygen-doped carbon nanotubes.

7. The preparation method according to claim 6, characterized in that: In step S1, the ratio of the mass of the carbon nanotubes to the volume of nitric acid is 1-30 mg:1 mL; The concentration of the nitric acid is 0.1-3 mol / L.

8. The preparation method according to claim 6, characterized in that: In step S2, the filling degree of the dispersion in the polytetrafluoroethylene liner is 30-80%.

9. Use of the catalyst according to any one of claims 1 to 2 or the catalyst prepared by the preparation method according to any one of claims 3 to 8 in the electrocatalytic oxygen reduction reaction to produce hydrogen peroxide, characterized in that: The electrolyte system in the electrocatalytic oxygen reduction reaction to produce hydrogen peroxide is a neutral solution.

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