Preparation method of cobalt-based nano-foam hybrid catalyst and application of cobalt-based nano-foam hybrid catalyst in electro-catalytic synthesis of urea

Abstract

The invention discloses a preparation method of a cobalt-based nano-foam hybrid catalyst and application of the cobalt-based nano-foam hybrid catalyst in electrocatalytic synthesis of urea, and the preparation method comprises the following steps: dissolving glucose, urea, cobalt nitrate and other metal salts in deionized water, and stirring to form a uniform solution; heating the solution to form porous foam; and putting the porous foam into a tubular furnace, heating in an air atmosphere, cooling to room temperature, and carrying out heat treatment in argon-hydrogen mixed gas to form the cobalt-based nano-foam hybrid catalyst. According to the preparation method of the cobalt-based nano-foam hybrid catalyst, the material synthesis method is simple and convenient, CoCr < 1% > has the optimal Faraday efficiency and yield under-0.3 V (RHE), 23% of urea Faraday efficiency and 60 mmoL g <-1 > cat h <-1 > urea yield are achieved under the condition that CO2 is saturated in 0.2 M KHCO3 and 20 mM KNO2 electrolyte, the current density reaches 16 mA cm <-2 >, and compared with the same type of catalysts, the cobalt-based nano-foam hybrid catalyst has the advantages that the cobalt-based nano-foam hybrid catalyst has the advantages that the cobalt-based nano-foam hybrid catalyst is low in cost and good in performance. The device has the advantages of potential correction and lower energy consumption.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic materials, and particularly relates to a preparation method of a cobalt-based nanofoam hybrid catalyst and its application in electrocatalytic synthesis of urea. Background Art

[0002] Urea is a high-concentration nitrogen fertilizer and is widely used in agriculture. Currently, urea is synthesized industrially through the reaction of ammonia and CO 2 under high temperature and high pressure conditions, and the raw material ammonia needs to be obtained through the Haber-Bosch process. The synthesis of urea consumes 80% of the global ammonia production and 2% of the world's energy.

[0003] Therefore, there is an urgent need to explore methods for green synthesis of urea, such as photocatalysis, electrocatalysis, etc.; among them, electrocatalysis has attracted much attention due to its mild conditions, low energy consumption, and clean and green nature.

[0004] So far, the electro-synthesis of urea using NO x - and CO 2 as raw materials still has problems of low current density and low Faraday efficiency. In addition, the applied potential range for the electro-synthesis of urea reported in the literature in recent years is -0.2 to -1.5 V (RHE), which is much smaller than its thermodynamic potential (0.48 V). At such negative potentials, kinetically favorable competitive side reactions are likely to occur, such as the generation of H 2 generation, CO 2 reduction and NO 2 - and NH 3 generation, and reduce the selectivity of urea electro-synthesis. Summary of the Invention

[0005] The purpose of this part is to outline some aspects of the embodiments of the present invention and briefly introduce some preferred embodiments. Some simplifications or omissions may be made in this part, as well as in the abstract and title of the present application, to avoid obscuring the purpose of this part, the abstract, and the title, and such simplifications or omissions shall not be used to limit the scope of the present invention.

[0006] In view of the above and / or problems existing in the prior art, the present invention is proposed.

[0007] Therefore, the purpose of the present invention is to overcome the deficiencies in the prior art and provide a preparation method of a cobalt-based nanofoam hybrid catalyst.

[0008] To solve the above technical problems, the present invention provides the following technical solution: A preparation method of a cobalt-based nanofoam hybrid catalyst, comprising,

[0009] Dissolve glucose, urea, cobalt nitrate, and other metal salts in deionized water and stir to form a homogeneous solution;

[0010] Heat the solution to form a porous foam;

[0011] Place the porous foam in a tubular furnace, heat it in an air atmosphere, cool it to room temperature, and then heat-treat it in a mixed argon-hydrogen gas to form a cobalt-based nano-foam hybrid catalyst;

[0012] Among them, the other metal salts include vanadium salts, chromium salts, manganese salts, molybdenum salts, and tungsten salts.

[0013] As a preferred embodiment of the preparation method of the present invention, wherein: the ratio of cobalt nitrate to other metal salts is 0.75 mmol: 0.00375 - 0.015 mmol.

[0014] As a preferred embodiment of the preparation method of the present invention, wherein: the ratio of glucose, urea, and cobalt nitrate is 5 g: 1 g: 0.75 mmol.

[0015] As a preferred embodiment of the preparation method of the present invention, wherein: when heating to form the porous foam, the heating temperature is 140 - 160 °C and the heating time is 6 - 8 h.

[0016] As a preferred embodiment of the preparation method of the present invention, wherein: when heating in an air atmosphere, the heating temperature is 500 °C, the heating time is 10 - 12 h, and the heating rate is 5 °C / min.

[0017] As a preferred embodiment of the preparation method of the present invention, wherein: when heat-treating in a mixed argon-hydrogen gas, the heat-treatment temperature is 300 - 400 °C, the heat-treatment time is 2 - 4 h, and the heating rate is 2 - 5 °C / min.

[0018] As a preferred embodiment of the preparation method of the present invention, wherein: for the mixed argon-hydrogen gas, the volume ratio of argon to hydrogen is 5%: 95%.

[0019] Another object of the present invention is to overcome the deficiencies in the prior art and provide a cobalt-based nano-foam hybrid catalyst.

[0020] Another object of the present invention is to overcome the deficiencies in the prior art and provide an application of a cobalt-based nano-foam hybrid catalyst in the electrocatalytic synthesis of urea.

[0021] Advantages of the present invention:

[0022] The invention provides a method for preparing a cobalt-based nano foam hybrid catalyst. The material synthesis method is simple. CoCr1% has the best Faraday efficiency and yield at -0.3V (RHE). 3 and 20 mM KNO 2 Saturated CO in electrolyte 2 Under the conditions of 23% urea Faradaic efficiency and 60mmoL g -1 cat h -1 The urea yield was as high as 16 mA cm -2 Compared with the same type of catalysts, it has the advantages of more positive potential and lower energy consumption. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the technical solutions of the embodiments of the present invention, the following briefly introduces the drawings required for describing the embodiments. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without creative labor. Among them:

[0024] Figure 1 This is a scanning electron microscope image of CoCr0% in an embodiment of the present invention.

[0025] Figure 2 This is a scanning electron microscope image of CoCr0.5% in an embodiment of the present invention.

[0026] Figure 3 This is a scanning electron microscope image of CoCr1% in an embodiment of the present invention.

[0027] Figure 4 This is a scanning electron microscope image of CoCr2% in an embodiment of the present invention.

[0028] Figure 5 This is the TEM image of CoCr1% in the embodiment of the present invention.

[0029] Figure 6 This is the HRTEM image of CoCr1% in the embodiment of the present invention.

[0030] Figure 7 This is the CoCr1% Mapping diagram in the embodiment of the present invention.

[0031] Figure 8 This is the XRD diagram of CoCr1% in the embodiment of the present invention.

[0032] Figure 9 This is a comparison chart of the urea production performance of CoCr1% in the embodiments of the present invention.

[0033] Figure 10 Performance graph of other metal doping in the embodiments of the present invention for urea production.

[0034] Figure 11 Graph of catalyst stability test in the embodiments of the present invention.

[0035] Figure 12 Graph comparing the performance of the CoCr1% catalyst in Example 3 of the present invention with the catalysts reported in the literature.

[0036] Figure 13 Graph comparing the quantitative results of urea production by chromium-doped cobalt nanofoam CoCr1% with the blank control in the embodiments of the present invention. Detailed implementation manners

[0037] To make the above objects, features, and advantages of the present invention more obvious and understandable, the following describes the detailed implementation manners of the present invention in conjunction with the embodiments of the specification.

[0038] Many specific details are set forth in the following description to facilitate a thorough understanding of the present invention, but the present invention may be practiced in other ways different from those described herein. Those skilled in the art can make similar extensions without departing from the connotation of the present invention. Therefore, the present invention is not limited by the specific embodiments disclosed below.

[0039] Secondly, the so-called "one embodiment" or "embodiment" herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation manner of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a separate or alternative embodiment that is mutually exclusive with other embodiments.

[0040] Electrochemical tests in the embodiments of the present invention:

[0041] The electrochemical tests were carried out in a 50 mL H-type electrolytic cell, using Nafion 117 as the electrolytic cell diaphragm to ensure that the redox products in the cathode electrolyte and the anode electrolyte do not come into contact with each other and interfere.

[0042] Both the cathode electrolyte and the anode electrolyte were 30 mL of a mixed solution of 0.2 M KHCO 3 and 20 mM KNO 2 mixed solution.

[0043] The working electrode was made by dropping the catalyst on carbon paper. First, 2 mg of the catalyst was evenly dispersed in 950 μL of ethanol, then 50 μL of Nafion aqueous solution was added, and the mixture was sonicated for another 10 min to obtain a uniform catalyst slurry.

[0044] 50 μL of the catalyst slurry was dropped on the carbon paper and air-dried to be used as the working electrode.

[0045] The working electrode area is 1.0 x 0.5 cm 2 , and the catalyst loading is 0.2 mg·cm 2 ;

[0046] The reference electrode is an Ag / AgCl electrode (filled with saturated KCl solution), and the working electrode and the reference electrode are placed in the cathode electrolytic cell; the counter electrode is nickel foam and is placed on the anode side.

[0047] Before the electrochemical test, CO gas is first introduced into the cathode electrolyte at a gas flow rate of 50 sccm for 30 min to saturate it. 2 The gas is saturated for 30 minutes.

[0048] The test is carried out using an electrochemical workstation (BioLogic 4-channel electrochemical workstation from France). During the test, the gas is continuously introduced at a flow rate of 30 sccm to keep the gas saturated at all times. At the same time, mechanical stirring (rotation speed of about 800 rpm) is added to the cathode chamber to enhance mass transfer.

[0049] Note: In this invention, the electrochemical test refers to the performance test of electrocatalytic synthesis of urea, which is all constant potential electrolysis. Constant potential electrolysis is carried out under different potential conditions, and the solution in the cathode chamber after the reaction is taken for product analysis to calculate the Faraday efficiency and yield of urea.

[0050] Quantification of products in the examples of this invention:

[0051] The by-product ammonia is quantified by the indophenol blue method. In an alkaline environment, ammonia reacts with salicylic acid and sodium hypochlorite to form a characteristic blue-green substance catalyzed by sodium nitroprusside. The characteristic absorption peak of this substance is at 652 nm.

[0052] Urease indirect method is used to qualitatively and quantitatively detect urea in the solution. Utilizing the characteristics of the specific catalytic hydrolysis of urea by the enzyme to release ammonia and carbon dioxide, the urea concentration is indirectly determined by detecting the difference in ammonia concentration in the solution before and after urease hydrolysis.

[0053] Note: Ammonia is a by-product. After quantification of urea through the standard curve, the content of the solution in the cathode chamber is obtained, and then the Faraday efficiency and urea yield are calculated.

[0054] Example 1

[0055] (1) Take 5 g of glucose, 1 g of urea, and 0.75 mmol of cobalt nitrate and dissolve them in 5 mL of deionized water, and stir for 20 min to form a homogeneous solution;

[0056] (2) Place this solution in an oven and heat it at 160 °C for 6 hours to form a porous foam;

[0057] (3) Place the porous foam in a tube furnace and heat it at 500 °C for 10 hours in an air atmosphere with a heating rate of 5 °C / min;

[0058] (4) After cooling to room temperature, heat-treat it at 400 °C for 4 h in a 5% argon-hydrogen mixed gas with a heating rate of 2 °C / min to form chromium-doped cobalt nanofoam CoCr0%.

[0059] Example 2

[0060] (1) Take 5 g of glucose, 1 g of urea, 0.75 mmol of cobalt nitrate, and 0.00375 mmol of chromium nitrate, dissolve them in 5 mL of deionized water, and stir for 20 min to form a homogeneous solution;

[0061] (2) Place this solution in an oven and heat it at 160 °C for 6 hours to form a porous foam;

[0062] (3) Place the porous foam in a tube furnace and heat it at 500 °C for 10 hours in an air atmosphere with a heating rate of 5 °C / min;

[0063] (4) After cooling to room temperature, heat-treat it at 400 °C for 4 h in a 5% argon-hydrogen mixed gas with a heating rate of 2 °C / min to form chromium-doped cobalt nanofoam CoCr0.5%.

[0064] Example 3

[0065] (1) Take 5 g of glucose, 1 g of urea, 0.75 mmol of cobalt nitrate, and 0.0075 mmol of chromium nitrate, dissolve them in 5 mL of deionized water, and stir for 20 min to form a homogeneous solution;

[0066] (2) Place this solution in an oven and heat it at 160 °C for 6 hours to form a porous foam;

[0067] (3) Place the porous foam in a tube furnace and heat it at 500 °C for 10 hours in an air atmosphere with a heating rate of 5 °C / min;

[0068] (4) After cooling to room temperature, heat-treat it at 400 °C for 4 h in a 5% argon-hydrogen mixed gas with a heating rate of 2 °C / min to form chromium-doped cobalt nanofoam CoCr1%.

[0069] Example 4

[0070] (1) Take 5 g of glucose, 1 g of urea, 0.75 mmol of cobalt nitrate, and 0.015 mmol of chromium nitrate, dissolve them in 5 mL of deionized water, and stir for 20 min to form a homogeneous solution;

[0071] (2) Place this solution in an oven and heat it at 160 °C for 6 hours to form a porous foam;

[0072] (3) Place the porous foam in a tubular furnace and heat it at 500 °C for 10 hours in an air atmosphere with a heating rate of 5 °C / min;

[0073] (4) After cooling to room temperature, heat-treat it at 400 °C for 4 h in a 5% argon-hydrogen mixed gas with a heating rate of 2 °C / min to form chromium-doped cobalt nanofoam CoCr2%.

[0074] SEM characterization was performed on the synthesized CoCrx% (x = 0, 0.5, 1, 2), see Figures 1 to 4 , it can be seen that it exhibits a porous two-dimensional sheet structure, has a large specific surface area, and the doping of chromium does not change its morphology.

[0075] TEM characterization was performed on CoCr1%, see Figure 5 , it can be seen that the size of the individual particles constituting its nanofoam is about 40 nm;

[0076] The HRTEM image of CoCr1% is shown in Figure 6 , the high-resolution results show that its lattice corresponds to cobalt oxide, cobalt, and chromium oxide; The Mapping image of CoCr1% is shown in Figure 7 , the Mapping results show that the four elements C, O, Co, and Cr are evenly distributed.

[0077] XRD characterization was performed on CoCr1%, see Figure 8 , the results show that it is mainly metallic cobalt and contains a small amount of cobalt oxide.

[0078] Example 5 (CoV1%)

[0079] Dissolve 5 g of glucose, 1 g of urea, 0.75 mmol of cobalt nitrate, and 0.00375 mmol of ammonium metavanadate in 5 mL of deionized water and stir for 20 min to form a homogeneous solution;

[0080] All other steps are the same as in Example 3 to obtain CoV1%.

[0081] Example 6 (CoMn1%)

[0082] Dissolve 5 g of glucose, 1 g of urea, 0.75 mmol of cobalt nitrate, and 0.00375 mmol of manganese nitrate in 5 mL of deionized water and stir for 20 min to form a homogeneous solution;

[0083] All other steps are the same as in Example 3 to obtain CoMn1%.

[0084] Example 7 (CoMo1%)

[0085] Dissolve 5 g of glucose, 1 g of urea, 0.75 mmol of cobalt nitrate, and 0.00375 mmol of ammonium molybdate in 5 mL of deionized water, and stir for 20 min to form a homogeneous solution;

[0086] All the remaining steps are the same as those in Example 3 to obtain CoMo1%.

[0087] Example 8 (CoW1%)

[0088] Dissolve 5 g of glucose, 1 g of urea, 0.75 mmol of cobalt nitrate, and 0.00375 mmol of ammonium tungstate in 5 mL of deionized water, and stir for 20 min to form a homogeneous solution;

[0089] All the remaining steps are the same as those in Example 3 to obtain CoW1%.

[0090] Performance of electrocatalytic urea synthesis:

[0091] Performance tests of electrocatalytic urea synthesis were carried out for different hybrid metals. See Figure 10 , it can be seen that chromium exhibits more excellent performance in electrocatalytic urea synthesis.

[0092] The Faraday efficiency and yield at different potentials were tested respectively. See Figure 9 , and the results show that CoCr1% has the best performance in electrocatalytic urea synthesis. It has the best Faraday efficiency and yield at -0.3 V (RHE). It has a urea Faraday efficiency of 24% and a urea yield of 60 mmol g 3 in an electrolyte of 0.2 M KHCO 2 and 20 mM KNO 2 under the condition of saturated CO -1 cat h -1 , and the current density reaches 16 mA / cm 2 , and it remains stable during ten cycles (under the electrochemical test conditions described above, electrolyze at a constant potential of -0.3 V RHE for 20 min, change the electrolyte, and electrolyze again, and perform cyclic tests ten times. See Figure 11 ).

[0093] See Figure 12 , compared with catalysts of the same type, it has the advantages of more positive potential and lower energy consumption. Among them, the source of catalysts of the same type can be found in the literature:

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[0097] [4]Leverett, J.; Tran - Phu, T.; Yuwono, J. A.; Kumar, P.; Kim, C.; Zhai, Q.; Han, C.; Qu, J.; Cairney, J.; Simonov, A. N.; et al. Tuning the Coordination Structure of Cu - N - C Single Atom Catalysts for Simultaneous Electrochemical Reduction of CO2 and NO3– to Urea. Adv. Energy Mater. 2022, 12(32), 2201500.

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[11] Yuan, M.; Chen, J.; Zhang, H.; Li, Q.; Zhou, L.; Yang, C.; Liu, R.; Liu, Z.; Zhang, S.; Zhang, G. Host–guest Molecular Interaction Promoted Urea Electrosynthesis over a Precisely Designed Conductive Metal–organic Framework. Energy Environ. Sci. 2022, 15(5), 2084 - 2095.

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[12] Pan, L.; Wang, J.; Lu, F.; Liu, Q.; Gao, Y.; Wang, Y.; Jiang, J.; Sun, C.; Wang, J.; Wang, X. Single-Atom or Dual-Atom in TiO2 Nanosheet: Which is the Better Choice for Electrocatalytic Urea Synthesis? Angew. Chem., Int. Ed. 2023, 62(8), e202216835

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[0107] The quantitative results of urea production from the cobalt chromium nano-foam CoCr1% prepared in Example 3 and the blank control are shown in Figure 13 , where the urea quantification is carried out by decomposing urea with urease to produce ammonia, and calculating the difference in ammonia concentration before and after. Ammonia is quantified by measuring the ultraviolet absorbance by the indophenol blue method. It can be seen that the increase in absorbance after decomposition proves the production of urea. Control experiments were carried out on the carbon source alone, the nitrogen source alone, and the blank carbon paper, and urea could not be detected in all of them. However, in the test of the co-reduction of carbon dioxide and nitrite, there was an obvious change in the ammonia absorbance before and after decomposition, confirming the production of urea.

[0108] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to the preferred embodiments, those of ordinary skill in the art should understand that the technical solutions of the present invention can be modified or equivalently replaced without departing from the spirit and scope of the technical solutions of the present invention, and they should all be covered within the scope of the present invention.

Claims

1. A method for preparing a cobalt-based nano-foam hybrid catalyst, characterized in that: include, Dissolve glucose, urea, cobalt nitrate, and other metal salts in deionized water and stir to form a uniform solution; heating the solution to form a porous foam; The porous foam is placed in a tube furnace, heated in an air atmosphere, cooled to room temperature, and then heat treated in an argon-hydrogen mixed gas to form a cobalt-based nano-foam hybrid catalyst; Among them, other metal salts include vanadium salts, chromium salts, manganese salts, molybdenum salts, and tungsten salts.

2. The preparation method according to claim 1, characterized in that: The ratio of the cobalt nitrate to other metal salts is 0.75 mmol: 0.00375-0.015 mmol.

3. The preparation method according to claim 1 or 2, characterized in that: The ratio of glucose, urea and cobalt nitrate is 5g:1g:0.75mmol.

4. The preparation method according to claim 3, characterized in that: The heating forms the porous foam, wherein the heating temperature is 140-160° C. and the heating time is 6-8 hours.

5. The preparation method according to claim 1 or 4, characterized in that: The heating in air atmosphere has a heating temperature of 500° C., a heating time of 10 to 12 hours, and a heating rate of 5° C. / min.

6. The preparation method according to claim 5, characterized in that: The heat treatment in the argon-hydrogen mixed gas has a heat treatment temperature of 300-400° C., a heat treatment time of 2-4 hours, and a heating rate of 2-5° C. / min.

7. The preparation method according to claim 6, characterized in that: The argon-hydrogen mixed gas has a volume ratio of argon to hydrogen of 5%:95%.

8. The cobalt-based nano-foam hybrid catalyst prepared by the preparation method according to any one of claims 1 to 7.

9. Use of the cobalt-based nano-foam hybrid catalyst as claimed in claim 8 in electrocatalytic synthesis of urea.

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