Preparation method and application of porous carbon-based catalyst for nitrogen reduction

A catalyst and porous carbon technology, applied in the field of ammonia synthesis, can solve the problems of high cost and low catalytic activity of nitrogen reduction catalysts, and achieve the effects of enhanced nitrogen reduction performance, high catalytic activity and low cost

Pending Publication Date: 2020-01-03
SHENZHEN UNIV
6 Cites 6 Cited by

AI-Extracted Technical Summary

Problems solved by technology

[0007] The technical problem to be solved by the present invention is to provide a method for preparing a porous carbon-based nitrogen reduction catalyst in view of the above-mentioned defects...
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Method used

Fig. 2 and Fig. 4 are respectively the linear sweep voltage of chitin porous carbon-based nitrogen reduction catalyst prepared in embodiment 1 and embodiment 2 and cyclodextrin porous carbon-based nitrogen reduction catalyst under nitrogen and argon atmosphere security curve. Fig. 5 is a linear sweep voltammetry curve of a commercial Pt/C catalyst under nitrogen and argon atmospheres. It can be seen from Fig. 2, Fig. 4 and Fig. 5 that the prepared chitin porous carbon-based nitrogen reduction catalyst and cyclodextrin porous carbon-based nitrogen reduction catalyst compared with the existing commercial Pt/C catalyst in nitrogen and argon atmosphere It has a larger initial potential and limiting current density. However, due to the addition of a pore-forming agent when the chitin porous carbon-based nitrogen reduction catalyst is prepared, its initial potential and limiting current density are better than those of the cyclodextrin porous carbon-based nitrogen reduction catalyst.
In a specific embodiment, in the present embodiment, also add pore-forming agent in the macromolecule material after pretreatment, make to form micropore and mesopore in porous carbon material, thereby improve the porous carbon-based nitrogen that prepares The specific surface area of ​​the reduction catalyst, when used as a nitrogen reduction catalyst, the reactant can penetrate into the interior of the catalyst through micropores and mesopores, which greatly improves the catalytic activity of the catalyst. In a specific embodiment, the pore forming agent is one of zinc chloride and potassium hydroxide, for example, when the pore forming agent is potassium hydroxide, the pore forming agent potassium hydroxide etches the porous carbon material at a high temperature to form Carbon dioxide and carbon monoxide create micropores and mesopores.
In a specific embodiment, raw material pretreatment also can not adopt hydrothermal method, and use directly pre-oxidation method in air, make raw material oxidative cross-linking, rearrangement between heated molecules in air, to improve its Stability during the subsequent high-temperature carbonization process. In a specific embodiment, the pre-oxidation temperature is 200-220° C., and the pre-oxidation time is 5-6 hours. Under this condition, carbon with a higher degree of aromatization can also be formed to improve its performance in the subsequent high-temperature carbonization process. in the stability.
In a specific embodiment, the present invention adopts hydrothermal method to carry out pretreatment to raw material, the macromolecular raw material containing glucose unit is pretreated for a period of time under hydrothermal condition, makes raw material molecule carry out appropriate under heated condition Cross-linking and rearrangement to improve its stability in the subsequent high-temperature carbonization process. In a specific embodiment, the hydrothermal temperature is 200-220° C., and the hydrothermal time is 5-6 hours. Under this condition, carbon with a higher degree of aromatization can be formed, which improves its performance in the subsequent high-temperature carbonization process. stability.
In sum, the present invention discloses a kind of preparation method and application of porous carbon-based nitrogen reduction catalyst, described preparation method comprises carrying out pretreatment to the polymer raw material containing glucose unit, obtains the polymer material after pretreatment material; after the pretreated polymer material is mixed with a pore-forming agent and a catalyst, carbonizat...
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Abstract

The invention discloses a preparation method and application of a porous carbon-based catalyst for nitrogen reduction. The preparation method includes the steps: pretreating a glucose unit-containingpolymer raw material so as to obtain a pretreated polymer material, mixing the pretreated polymer material and a pore-forming agent and a catalyst, performing carbonization under the protection actionof inert gas so as to obtain a porous carbon material, washing the porous carbon material sequentially with an acid and deionized water, and then performing forced air drying so as to obtain the carbon-based nitrogen-reduction catalyst. The glucose unit-containing polymer raw material is adopted as a raw material, single atoms are formed through coordinate anchoring of transition metal so as to obtain multiple active centers, and baking carbonization is perfomed in the pore-form agent so as to obtain the porous carbon-based nitrogen-reduction catalyst with a high specific surface area, so that the nitrogen reduction performance of the carbon-material non-noble metal catalyst is enhanced, and the nitrogen reduction catalyst with low cost and high catalytic activity is prepared under mild,safe and environment-friendly conditions.

Application Domain

Physical/chemical process catalystsElectrodes

Technology Topic

Non noble metalActive center +10

Image

  • Preparation method and application of porous carbon-based catalyst for nitrogen reduction
  • Preparation method and application of porous carbon-based catalyst for nitrogen reduction
  • Preparation method and application of porous carbon-based catalyst for nitrogen reduction

Examples

  • Experimental program(2)

Example Embodiment

[0061] Example 1
[0062] Preparation method of chitin porous carbon-based nitrogen reduction catalyst:
[0063] (1) Take 3 g of commercial chitin, put it in a porcelain boat, and pre-oxidize it in an air atmosphere of 250 ° C for 2 hours. After the reaction is completed, the temperature of the reaction system is lowered to room temperature to obtain the pre-oxidized chitin-based carbon material;
[0064] (2) According to ZnCl 2 , CoCl 3 mixed with the pre-oxidized chitin-based carbon material in a mass ratio of 1:3:1, under N 2 Heating at a heating rate of 5 °C/min to a constant temperature of 800 °C for 2 h in an atmosphere to obtain a carbonized chitin-based carbon material;
[0065] (3) when cooling to room temperature, remove Co and Zn metal compounds in the chitin-based porous carbon with HCl with a concentration of 2M, and use deionized water to clean 5 times, and dry to obtain a chitin-based porous carbon-based nitrogen reduction catalyst;
[0066] Performance test of chitin porous carbon-based nitrogen reduction catalyst:
[0067] (4) In a 10ml strain bottle, mix the chitin porous carbon-based nitrogen reduction catalyst and anhydrous ethanol dispersant and then ultrasonicate for 30min, then add 50μl of the film-forming agent Nafion and ultrasonicate for 20min to obtain a nitrogen reduction catalyst suspension;
[0068] (5) Use a pipette to measure 10 μl of the nitrogen reduction catalyst suspension prepared in proportion and evenly drop it on the cutting area of ​​1*1cm -2 On the commercial carbon cloth, bake with infrared light for 1-2min, using Na concentration of 0.05M 2 SO 4 The solution was used as the electrolyte to prepare a three-electrode system. The linear sweep voltammetry curves of the prepared chitin porous carbon-based nitrogen reduction catalysts were tested under the condition of potential window of 0.4~-0.8V and scanning speed of 5mV/s.
[0069](6) Take 2 ml of the electrolyte solution after the chitin porous carbon-based nitrogen reduction catalyst runs for 2 hours, add 2 ml of 1 mol/L sodium hydroxide solution (which contains 5wt% salicylic acid and 5wt% sodium citrate dihydrate), and then add 0.05 1ml of mol/L sodium hypochlorite solution, finally add 0.2ml of 5wt% sodium nitroprusside dihydrate solution, stand for 2h at room temperature and dark for color development, use UV-Vis spectrophotometer to perform spectral scanning in the wavelength range of 550-750nm, and record The absorbance value at 655nm is combined with the working curve to finally obtain the concentration of ammonia. After data processing and calculation, the ammonia production rate and Faradaic efficiency of electrocatalytic ammonia production are obtained.

Example Embodiment

[0070] Example 2
[0071] Preparation method and performance test of cyclodextrin porous carbon-based nitrogen reduction catalyst:
[0072] (1) Weigh 2g of β-cyclodextrin, 120ml of deionized water, mix and stir, place it in 50ml of polytetrafluoroethylene lining for hydrothermal pretreatment, and treat at a hydrothermal temperature of 220°C for 6 hours, and wait for the reaction to end After the reaction system temperature is lowered to room temperature, the pretreated cyclodextrin-based carbon material is obtained;
[0073] (2) According to CoCl 3 mixed with the pretreated cyclodextrin-based carbon material in a mass ratio of 1:1, in N 2 Heating at a heating rate of 5 °C/min to a constant temperature of 800 °C for 2 h in an atmosphere to obtain a carbonized cyclodextrin-based carbon material;
[0074] (3) when cooling to room temperature, remove the metal compound in the cyclodextrin-based carbon material with HCl with a concentration of 2M, and use deionized water to wash 5 times, and dry to obtain a cyclodextrin porous carbon-based nitrogen reduction catalyst;
[0075] Performance test of cyclodextrin porous carbon-based nitrogen reduction catalyst:
[0076] (4) Mix the cyclodextrin-based carbon material and the anhydrous ethanol dispersant in a 10ml strain bottle and ultrasonicate for 30min, then add 50μl of the film-forming agent Nafion and ultrasonicate for 20min to obtain a nitrogen reduction catalyst suspension;
[0077] (5) Use a pipette to measure 10 μl of the nitrogen reduction catalyst suspension prepared in proportion and evenly drop it on the cutting area of ​​1*1cm -2 On the commercial carbon cloth, bake with infrared light for 1-2min, using Na concentration of 0.05M 2 SO 4 The solution was used as the electrolyte to prepare a three-electrode system. The linear sweep voltammetry curve of the prepared cyclodextrin porous carbon-based nitrogen reduction catalyst was tested under the condition of potential window of 0.4~-0.8V and scanning speed of 5mV/s.
[0078] (6) Take 2ml of the electrolyte after the cyclodextrin porous carbon-based nitrogen reduction catalyst has been operated for 2h, add 2ml of 1mol/L sodium hydroxide solution (which contains 5wt% salicylic acid and 5wt% sodium citrate dihydrate), and then add 1ml of 0.05mol/L sodium hypochlorite solution, finally add 0.2ml of 5wt% sodium nitroprusside dihydrate solution, stand for 2 hours at room temperature and dark for color development, and then use a UV-Vis spectrophotometer to perform spectral scanning in the wavelength range of 550-750nm, and Record the absorbance value at 655nm and combine it with the working curve to finally get the ammonia concentration. After data processing and calculation, the ammonia production rate and Faradaic efficiency of electrocatalytic ammonia production are obtained.
[0079] figure 1 and image 3 The scanning electron microscope images of the chitin porous carbon-based nitrogen reduction catalyst and the cyclodextrin porous carbon-based nitrogen reduction catalyst prepared in Example 1 and Example 2, respectively, are represented by figure 1 It can be seen that the chitin porous carbon-based nitrogen reduction catalyst after adding the pore-forming agent contains a large number of micropores and mesopores; image 3 It can be seen that the cyclodextrin porous carbon-based nitrogen reduction catalyst prepared in Example 2 is carbon spherical, but because no pore-forming agent is added, it cannot be seen that there are micropores and mesopores in the cyclodextrin porous carbon-based nitrogen reduction catalyst. .
[0080] figure 2 and Figure 4 The linear sweep voltammetry curves of the chitin porous carbon-based nitrogen reduction catalyst and the cyclodextrin porous carbon-based nitrogen reduction catalyst prepared in Example 1 and Example 2 under nitrogen and argon atmospheres, respectively. Figure 5 Linear sweep voltammograms of commercial Pt/C catalysts under nitrogen and argon atmospheres. from figure 2 , Figure 4 as well as Figure 5 It can be seen that the prepared chitin porous carbon-based nitrogen reduction catalyst and cyclodextrin porous carbon-based nitrogen reduction catalyst have larger initial potential and limit under nitrogen and argon atmosphere compared to the existing commercial Pt/C catalysts. current density. However, the initial potential and limiting current density of the chitin porous carbon-based nitrogen reduction catalyst were better than those of the cyclodextrin porous carbon-based nitrogen reduction catalyst due to the addition of a pore-forming agent.
[0081] Image 6 with ammonium chloride as the standard reagent in 0.05M Na 2 SO 4 The solution was prepared with 0, 0.25, 0.5, 1 μg/ml ammonium chloride standard solution, respectively, and the ultraviolet spectrum of the test after color reaction. Figure 7 It is a standard curve obtained by plotting the absorbance at 655nm with the concentration of 0, 0.25, 0.5, 1μg/ml ammonium chloride standard solution after color reaction.
[0082] Figure 8 These are the UV spectra of the chitin porous carbon-based nitrogen reduction catalyst prepared in Example 1 and Example 2, the cyclodextrin porous carbon-based nitrogen reduction catalyst and the commercial Pt/C catalyst after running for 2 hours. Figure 9 The ammonia production rate and Faradaic efficiency of the chitin porous carbon-based nitrogen reduction catalyst and the cyclodextrin porous carbon-based nitrogen reduction catalyst prepared in Example 1 and Example 2, as well as the commercial Pt/C catalyst. from Figure 9 It can be seen that, after calculation, the ammonia production rate and Faradaic efficiency of the chitin porous carbon-based nitrogen reduction catalyst and the cyclodextrin porous carbon-based nitrogen reduction catalyst prepared in Example 1 and Example 2 are compared with those of the commercial Pt/C catalyst. higher. Among them, the chitin porous carbon-based nitrogen reduction catalyst has an ammonia production rate of up to 26ug due to the addition of a pore-forming agent. NH3 h -1 mg -1 cat , the Faraday efficiency is 9%.
[0083] To sum up, the present invention discloses a preparation method and application of a porous carbon-based nitrogen reduction catalyst. The preparation method includes pretreating a macromolecular raw material containing glucose units to obtain a pretreated macromolecular material; After the pretreated polymer material is mixed with a pore-forming agent and a catalyst, carbonization is carried out under the protection of an inert gas to obtain a porous carbon material; the porous carbon material is washed with acid and deionized water in sequence, and then dried by blasting , a carbon-based nitrogen reduction catalyst was obtained. In the invention, the macromolecule containing glucose unit is used as the raw material, and the transition metal is coordinatively anchored to form a single atom to obtain multiple active centers; the pore-forming agent is calcined and carbonized to obtain a high specific surface area porous carbon-based nitrogen reduction catalyst, which enhances the non-toxicity of the carbon material. The nitrogen reduction performance of the noble metal catalyst enables the preparation of a low-cost, high catalytic activity nitrogen reduction catalyst under relatively mild, safe and environmentally friendly conditions.

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