Pickering emulsion electrocatalysis method for nitro compound hydrogenation

Abstract

The invention discloses an electro-catalysis method of Pickering emulsion for nitro compound hydrogenation, and relates to the technical field of catalytic hydrogenation, the Pickering emulsion is composed of an oil phase, a water phase and a platinum-loaded hydrophilic carbon nanotube catalyst; wherein based on the weight of the carbon nanotubes in the catalyst, the platinum accounts for 5.0 wt%-10.0 wt%; in the emulsion system, the particle concentration of the platinum-loaded hydrophilic carbon nanotube catalyst is 0.05 wt%-10 wt%; in the emulsion system, the hydrophilic carbon nanotubes have certain hydrophilicity and can be well dispersed in a water phase. According to the Pickering emulsion electro-catalysis method for nitro-compound hydrogenation, in a platinum-loaded hydrophilic carbon nanotube catalyst, the hydrogenation reaction of the nitro-compound can be effectively catalyzed when platinum is in a specific proportion range of 5.0 wt%-10.0 wt%.

Description

Technical Field

[0001] The invention relates to the technical field of catalytic hydrogenation, in particular to a Pickering emulsion electrocatalytic method for hydrogenation of nitro compounds. Background Art

[0002] Aniline is an important organic chemical substance that is widely used in the chemical industry and in daily life. It is mainly used in the production of dyes, especially the synthesis of azo dyes, which are widely used in textiles and other fields. In addition, aniline is also used as an intermediate in the pharmaceutical industry for the synthesis of a variety of drugs, such as antibiotics, anesthetics and analgesics, such as the production of acetaminophen (paracetamol). Aniline is also used in the rubber industry as an accelerator to improve the vulcanization efficiency of rubber and enhance its quality and performance. In some industrial applications, aniline is used as a preservative and antioxidant to extend the shelf life and stability of products. At the same time, aniline is also used in the synthesis of plastics, resins and other polymer materials, and participates in the production of some chemicals. It can also play an important role as a catalyst or reactant in organic synthesis.

[0003] As an important organic chemical, nitrobenzene has low water solubility, which limits its solubility in the aqueous phase, thus limiting its reactivity in the aqueous medium, especially its efficiency in the electrocatalytic hydrogenation reaction. Electrocatalytic hydrogenation reactions usually require the reactants to be well dissolved in the electrolyte solution so as to effectively contact the catalyst surface. Due to the low water solubility of nitrobenzene, its electrocatalytic hydrogenation process often faces the problems of insufficient reactant supply and reduced catalyst activity. Therefore, finding a suitable strategy to improve the effective contact of nitrobenzene in the aqueous phase is the key to improving its electrocatalytic hydrogenation reaction efficiency. An effective solution is to use Pickering emulsions with electrocatalytic nitrobenzene hydrogenation capabilities. Pickering emulsions are emulsions stabilized by solid particles. They form a stable oil-water interface through the interfacial adsorption of solid particles, and can effectively disperse nitrobenzene in the aqueous phase in the form of an oil phase. This emulsion system not only improves the solubility of nitrobenzene, but also promotes the contact between nitrobenzene molecules and catalysts, improving the transfer rate of reactants and the efficiency of catalytic reactions. Pickering emulsion can optimize the effect of electrocatalytic hydrogenation reaction by adjusting the stability of the emulsion, the type and size of the particles. In addition, the formation of the emulsion may also reduce the accumulation problem caused by hydrophobicity on the electrode surface, allowing the catalyst to continue to function. Therefore, the use of Pickering emulsion in the electrocatalytic hydrogenation reaction can not only solve the problem of poor water solubility of nitrobenzene, but also improve the selectivity and conversion rate of the reaction. In this way, the hydrogenation reaction of nitrobenzene can be achieved more efficiently, providing a more feasible technical path for its application in environmental protection, chemical synthesis and other fields. Summary of the invention

[0004] To achieve the above objectives, the present invention is implemented through the following technical scheme: a Pickering emulsion system with electrocatalytic nitrobenzene hydrogenation capability, the emulsion system consisting of an oil phase, an aqueous phase and a hydrophilic carbon nanotube catalyst loaded with platinum.

[0005] Among them, based on the weight of carbon nanotubes in the catalyst, platinum accounts for 5.0wt%-10.0wt%.

[0006] Preferably, in the emulsion system, the particle concentration of the hydrophilic carbon nanotube catalyst loaded with platinum is 0.05 wt % to 10 wt %.

[0007] Preferably, in the emulsion system, the volume fraction of the oil phase is 1-50%, and the rest is the water phase.

[0008] Preferably, in the emulsion system, the hydrophilic carbon nanotubes have a certain hydrophilicity and can be well dispersed in the water phase.

[0009] Preferably, in the emulsion system, the oil phase is selected from one or more of n-hexane, toluene, dodecane, tetradecane, petroleum ether and ethyl acetate.

[0010] A method for preparing a nitrobenzene hydrogenation electrocatalyst based on a Pickering emulsion electrocatalytic system comprises the following steps: Step S1, adding carbon nanotubes to a mixed liquid consisting of nitric acid and sulfuric acid for pretreatment to obtain hydrophilic carbon nanotubes; Step S2, adding a platinum precursor to a solution A prepared by oleylamine and oleic acid to obtain a solution B; Solution B is heated, reduced, cooled, separated, washed, and dried to obtain platinum-containing nanoparticles, which are referred to as Pt-NPs; Step S3, subjecting the platinum-containing nanoparticles Pt-NPs prepared in step S2 to ultrasonic treatment in n-hexane, which is recorded as solution C; Ultrasonic dispersion of the hydrophilic carbon nanotubes obtained in step S1 in isopropanol is recorded as solution D; Solution C is slowly added dropwise to solution D, and the resulting solution is filtered, washed, and dried to obtain a nitrobenzene hydrogenation electrocatalyst based on a Pickering emulsion electrocatalytic system.

[0011] Preferably, in step S1, the volume ratio of nitric acid to sulfuric acid is 0.5-10:1, the pretreatment temperature is 120-140° C., and the treatment time is 4-10 h.

[0012] Preferably, in step S2, the volume ratio of oleylamine to oleic acid is 10-40:1, the heating temperature of solution B is 240-350° C., and the reducing agent used to reduce the platinum nanoparticles is selected from one of citric acid, sodium borohydride, stannous chloride, vitamin C, and lithium triethylborohydride.

[0013] Preferably, in step S3, the volume ratio of solution C to solution D is 1:2-10, and the drying temperature is 60-120°C.

[0014] The present invention provides a Pickering emulsion electrocatalytic method for hydrogenation of nitro compounds. It has the following beneficial effects: 1. The Pickering emulsion electrocatalytic method for hydrogenation of nitro compounds can effectively catalyze the hydrogenation reaction of nitro compounds by loading platinum in a hydrophilic carbon nanotube catalyst, where the platinum is within a specific proportion range of 5.0wt%-10.0wt%.

[0015] Second, the Pickering emulsion electrocatalytic method for hydrogenation of nitro compounds uses a Pickering emulsion system consisting of a platinum-loaded hydrophilic carbon nanotube catalyst in a specific concentration range, an oil phase with a volume fraction of 1-50%, and a water phase, and the components work synergistically. The hydrophilic carbon nanotube catalyst can be stably adsorbed on the oil-water interface, preventing the emulsion from agglomerating and demulsifying, so that the emulsion maintains a stable dispersed state during the reaction, which is conducive to the continuous progress of the reaction, ensuring that the reactants can fully contact the catalyst, and improving the conversion rate and selectivity of the reaction. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] Figure 1 Schematic diagram of transmission electron microscopy (TEM) of the hydrophilic carbon nanotube electrocatalyst loaded with platinum according to the present invention; Figure 2 It is a schematic diagram of an optical microscope image of the Pickering emulsion having the electrocatalytic nitrobenzene hydrogenation capability of the present invention; Figure 3 It is a schematic diagram of the Pickering emulsion three-electrode cell electrocatalytic device of the present invention.

[0017] In the figure: 2, working electrode; 3, air inlet; 4, reference electrode; 5, counter electrode; 6, air outlet pipe. DETAILED DESCRIPTION

[0018] The present invention will be further described in detail below in conjunction with specific embodiments. The embodiments of the present invention are provided for the purpose of illustration and description, and are not intended to be exhaustive or to limit the present invention to the disclosed forms. Many modifications and variations will be apparent to those of ordinary skill in the art. The embodiments are selected and described to better illustrate the principles and practical applications of the present invention, and to enable those of ordinary skill in the art to understand the present invention and thereby design various embodiments with various modifications suitable for specific uses.

[0019] Gas chromatography analysis conditions: Agilent 7890B, chromatographic column: HP-5 (30m*530μm*1.5μm), automatic sampler, injection port temperature: 280℃, septum purge flow: 3m1 / min, split ratio: 10:1, injection volume: 0.8u1; Program temperature rise: 50℃ for 1 min, increase the temperature to 150℃ at 5℃ / min, maintain for 2 min, increase the temperature to 160℃ at 10℃ / min, maintain for 1 min, increase the temperature to 200℃ at 15℃ / min, maintain for 0 min, increase the temperature to 280℃ at 20℃ / min, maintain for 5 min; Detector: 280℃, hydrogen flow rate: 40mL / min, air flow rate: 400mL / min, tail gas flow rate: 25mL / min.

[0020] The specific surface area and pore size were analyzed using American Micromeritics ASAP2020 at an ambient temperature of 300°C and a pressure of 760 mmHg.

[0021] Metal content test method: 0.1 catalyst was added with 1.4g lithium hydroxide and 0.1g boric acid and melted at 750° for 1h, and then dissolved with 5%wt HCl aqueous solution.

[0022] The samples were tested using an inductively coupled plasma optical emission spectrometer (Agilent 700 Series ICP-OES) with the following analysis conditions: spray pressure 200 kPa, power 1.20 kW, and auxiliary purge flow rate 1.5 L / min.

[0023] In the first embodiment, the present invention provides a method for electrocatalytic hydrogenation of nitrobenzene using a Pickering emulsion electrocatalytic system, and the specific steps are as follows: 1000 ml of sulfuric acid (98%) and 1000 ml of nitric acid (68%) were mixed evenly, and stirred at 50°C for 2 hours to obtain solution A; 50 g of carbon nanotubes were added to solution A and stirred for 0.5 hours to obtain suspension B; suspension B was heated at 120°C for 5 hours, and after cooling to room temperature, solid products were separated by filtration, washed with water for multiple times, and dried at 80°C for 60 hours to obtain hydrophilic carbon nanotubes; 500 ml of oleylamine and 50 ml of oleic acid were mixed evenly, Ar gas was introduced, stirred at 60°C for 0.5 h, and then heated to 120°C and stirred for 2 h to obtain solution C; 500 mg of acetylacetonate platinum was added to solution C, and the solution was heated to 220°C to obtain solution D; solution D was vigorously stirred, 30 ml of lithium triethylborohydride (1.0 M in THF) was added, and the solution was quickly transferred to a pre-heated 350°C heating table, and heated at 350°C for 3 h. When cooled to room temperature, the solid product was obtained by centrifugation, washed three times with ethanol and water, and dried at 60°C for 10 h to obtain Pt NPs.

[0024] Take 250 mg of the prepared Pt NPs, add it to 100 ml of n-hexane and ultrasonicate for 1 hour to obtain solution E; take 5 g of the prepared hydrophilic carbon nanotubes, add it to 400 ml of isopropanol and ultrasonicate for 2 hours to obtain solution F; stir solution F at 25°C, and add solution E to solution F at a rate of 5 ml / min, and when the addition of solution E is completed, solution G is obtained; after stirring solution G for 5 hours, filter to obtain a solid product, wash it three times with ethanol and water, and dry it at 80°C for 12 hours to obtain a nitrobenzene hydrogenation electrocatalyst based on the Pickering emulsion electrocatalytic system.

[0025] 500 mg of hydrophilic carbon nanotubes loaded with platinum were added into 200 ml of 0.5 M H2SO4 solution and dispersed evenly by ultrasonication for 1 h to obtain solution H; 80 ml of n-hexane were added with 10 mmol of nitrobenzene to obtain solution I; solution H and solution I were mixed evenly, and after vigorous stirring for 3 h, a Pickering emulsion with electrocatalytic nitrobenzene hydrogenation ability was obtained.

[0026] Take the H-type electrolytic cell as the container, add 300ml of 0.5M H2SO4 solution to each of the anode parts of the electrolytic cell, add the prepared Pickering emulsion to the cathode part, and put a silver sheet as the cathode current collector working electrode. Use a platinum sheet as the counter electrode and Ag / AgCl as the reference electrode. Connect to the electrochemical workstation. First, measure the linear scanning curves of reduced water and reduced nitrobenzene, and compare the performance. Select a constant voltage of -0.8V (Vs. Ag / AgCl) for it. When the power consumption is about 3860C or the curve drops to a platform, it means that 10mmol nitrobenzene has been completely reduced. Take out the cathode emulsion, put it in an 80℃ oven and heat it for 0.5h to break the Pickering emulsion and separate it into oil and water phases. Take out the upper oil phase, filter out the carbon nanotube particles therein, and then use nuclear magnetic resonance and gas-mass spectrometry for qualitative analysis, and gas chromatography for quantitative analysis, and the yield of aniline is about 93.5%.

[0027] In the second embodiment, the present invention provides a method for electrocatalytic hydrogenation of nitrobenzene using a Pickering emulsion electrocatalytic system, and the specific steps are as follows: Mix 500 ml of sulfuric acid (98%) and 100 ml of nitric acid (68%) evenly, and stir at 80°C for 2 h to obtain solution A; add 10 g of carbon nanotubes to solution A and stir for 0.5 h to obtain suspension B; heat suspension B at 150°C for 3 h, and after cooling to room temperature, filter and separate to obtain a solid product, wash with water for several times, and dry at 80°C for 60 h to obtain hydrophilic carbon nanotubes.

[0028] 500 ml of oleylamine and 100 ml of oleic acid were mixed evenly, Ar gas was introduced, stirred at 60°C for 0.5 h, and then heated to 120°C and stirred for 2 h to obtain solution C; 500 mg of acetylacetonate platinum was added to solution C, and the solution was heated to 300°C to obtain solution D; solution D was vigorously stirred, 30 ml of lithium triethylborohydride (1.0 M in THF) was added, and the solution was quickly transferred to a pre-heated 350°C heating table, and heated at 350°C for 3 h. When cooled to room temperature, the solid product was obtained by centrifugation, washed with ethanol and water three times, and dried at 60°C for 10 h to obtain Pt NPs.

[0029] Take 250 mg of the prepared Pt NPs, add it to 100 ml of n-hexane and ultrasonicate for 1 hour to obtain solution E; take 5 g of the prepared hydrophilic carbon nanotubes, add it to 400 ml of isopropanol and ultrasonicate for 2 hours to obtain solution F; stir solution F at 25°C, and add solution E to solution F at a rate of 5 ml / min, and when the addition of solution E is completed, solution G is obtained; after stirring solution G for 5 hours, filter to obtain a solid product, wash it three times with ethanol and water, and dry it at 80°C for 12 hours to obtain a nitrobenzene hydrogenation electrocatalyst based on the Pickering emulsion electrocatalytic system.

[0030] 100 mg of hydrophilic carbon nanotubes loaded with platinum were added into 200 ml of 0.5 M H2SO4 solution and dispersed evenly by ultrasonication for 1 h to obtain solution H; 120 ml of ethyl acetate were added with 10 mmol of nitrobenzene to obtain solution I; solution H and solution I were mixed evenly, and after vigorous stirring for 3 h, a Pickering emulsion with electrocatalytic nitrobenzene hydrogenation ability was obtained.

[0031] A three-electrode electrolytic cell is used as a container, the anode part of the electrolytic cell is connected to the water phase, the cathode part is inserted into the prepared Pickering emulsion layer for neutralization, and a silver sheet is placed as the cathode current collector working electrode. A platinum sheet is used as the counter electrode, and Ag / AgCl is used as the reference electrode. Connect to an electrochemical workstation. First, the linear scanning curves of reduced water and reduced nitrobenzene are measured, and the performance is compared. A constant current of 200mA is selected for high current it. When the power consumption is about 3860C or the timing voltage curve drops to a platform, it indicates that 10mmol nitrobenzene has been completely reduced. 50ml of ethanol is added to the electrolytic cell to cause the Pickering emulsion to break and melt into a uniform layer. The carbon nanotube particles therein are filtered out and then qualitatively analyzed by nuclear magnetic resonance and gas-mass spectrometry, and quantitatively analyzed by gas chromatography, and the yield of aniline is about 89.6%.

[0032] In the third embodiment, the present invention provides a method for electrocatalytic hydrogenation of nitrobenzene using a Pickering emulsion electrocatalytic system, and the specific steps are as follows: 100 ml of sulfuric acid (98%) and 500 ml of nitric acid (68%) were mixed evenly, and stirred at 80°C for 2 h to obtain solution A; 20 g of carbon nanotubes were added to solution A and stirred for 0.5 h to obtain suspension B; suspension B was heated at 150°C for 6 h, and after cooling to room temperature, the solid product was separated by filtration, washed with water for multiple times, and dried at 80°C for 60 h to obtain hydrophilic carbon nanotubes.

[0033] 500 ml of oleylamine and 100 ml of oleic acid were mixed evenly, Ar gas was introduced, stirred at 60°C for 0.5 h, and then heated to 120°C and stirred for 2 h to obtain solution C; 500 mg of acetylacetonate platinum was added to solution C, and the solution was heated to 300°C to obtain solution D; solution D was vigorously stirred, 30 ml of lithium triethylborohydride (1.0 M in THF) was added, and the solution was quickly transferred to a pre-heated 350°C heating table, and heated at 350°C for 3 h. When cooled to room temperature, the solid product was obtained by centrifugation, washed with ethanol and water three times, and dried at 60°C for 10 h to obtain Pt NPs.

[0034] Take 250 mg of the prepared Pt NPs, add it to 100 ml of n-hexane and ultrasonicate for 1 hour to obtain solution E; take 5 g of the prepared hydrophilic carbon nanotubes, add it to 400 ml of isopropanol and ultrasonicate for 2 hours to obtain solution F; stir solution F at 25°C, and add solution E to solution F at a rate of 5 ml / min, and when the addition of solution E is completed, solution G is obtained; after stirring solution G for 5 hours, filter to obtain a solid product, wash it three times with ethanol and water, and dry it at 80°C for 12 hours to obtain a nitrobenzene hydrogenation electrocatalyst based on the Pickering emulsion electrocatalytic system.

[0035] 100 mg of hydrophilic carbon nanotubes loaded with platinum were added into 200 ml of 0.5 M H2SO4 solution and dispersed evenly by ultrasonication for 1 h to obtain solution H; 80 ml of toluene were added with 10 mmol of nitrobenzene to obtain solution I; solution H and solution I were mixed evenly, and after vigorous stirring for 3 h, a Pickering emulsion with electrocatalytic nitrobenzene hydrogenation ability was obtained.

[0036] A three-electrode electrolytic cell was used as a container. The anode part of the electrolytic cell was connected to the water phase, and the cathode part was inserted into the prepared Pickering emulsion layer for neutralization. A silver sheet was placed as the cathode current collector working electrode. A platinum sheet was used as the counter electrode and Ag / AgCl as the reference electrode. Connected to an electrochemical workstation. In order to obtain a higher current density, inhibit the hydrogen evolution side reaction and enhance mass transfer. The Pickering emulsion should be intermittently homogenized to make it undergo a demulsification-uniform distribution-emulsification process. First, the linear scanning curves of reduced water and reduced nitrobenzene were measured and the performance was compared. A constant current of 800mA was selected for high current it, and it was intense for 30s every 4-8min. When the power consumption was about 386000C or the timing voltage curve dropped to a platform, it indicated that 1 mol of nitrobenzene had been completely reduced. The Pickering emulsion was taken out and placed in an 80℃ oven for closed heating for 0.5h to cause the Pickering emulsion to demulsify and separate into oil and water phases. The upper oil phase was taken out, the carbon nanotube particles therein were filtered out, and then qualitative analysis was performed by NMR and GC-MS, and quantitative analysis was performed by gas chromatography, and the yield of aniline was about 84.3%.

[0037] Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field and related fields without creative work should fall within the scope of protection of the present invention. The structures, devices and operating methods not specifically described and explained in the present invention are implemented according to the conventional means in the field unless otherwise specified and limited.

Claims

1. A Pickering emulsion system for hydrogenation of nitro compounds, characterized in that: It consists of an oil phase, a water phase and a hydrophilic carbon nanotube catalyst loaded with platinum; Wherein, based on the weight of the carbon nanotubes in the catalyst, platinum accounts for 5.0wt%-10.0wt%.

2. A Pickering emulsion system for hydrogenation of nitro compounds according to claim 1, characterized in that: The particle concentration of the hydrophilic carbon nanotube catalyst loaded with platinum in the emulsion system is 0.05wt%-10wt%, the volume fraction of the oil phase is 1-50%, and the rest is the water phase.

3. A Pickering emulsion system for hydrogenation of nitro compounds according to claim 1, characterized in that: The oil phase is specifically selected from one or more of n-hexane, toluene, dodecane, tetradecane, petroleum ether, and ethyl acetate.

4. A method for preparing a Pickering emulsion system for hydrogenation of nitro compounds, characterized in that: The steps include: Step A1, taking the hydrophilic carbon nanotubes loaded with platinum and the aqueous phase, stirring, ultrasonicating and dispersing them to obtain a uniform dispersion; Step A2, mixing the dispersion obtained in step A1 with the oil phase, and stirring to obtain the Pickering emulsion having the electrocatalytic nitrobenzene hydrogenation ability.

5. A Pickering emulsion electrocatalytic method for hydrogenating nitro compounds, characterized in that: The following steps are involved: Step S1, adding carbon nanotubes to a mixed liquid consisting of nitric acid and sulfuric acid for pretreatment to obtain hydrophilic carbon nanotubes; Step S2, adding a platinum precursor to a solution A prepared by oleylamine and oleic acid to obtain a solution B; Solution B is heated, reduced, cooled, separated, washed, and dried to obtain platinum-containing nanoparticles, which are referred to as Pt-NPs; Step S3, subjecting the platinum-containing nanoparticles Pt-NPs prepared in step 2 to ultrasonic treatment in n-hexane, which is recorded as solution C; Ultrasonic dispersion of the hydrophilic carbon nanotubes obtained in step 1 in isopropanol is recorded as solution D; Solution C is slowly added dropwise to solution D, and the resulting solution is filtered, washed, and dried to obtain a nitrobenzene hydrogenation electrocatalyst based on a Pickering emulsion electrocatalytic system.

6. A Pickering emulsion electrocatalytic method for hydrogenation of nitro compounds according to claim 5, characterized in that: The volume ratio of nitric acid to sulfuric acid in step S1 is 0.5-10:

1.

7. A Pickering emulsion electrocatalytic method for hydrogenation of nitro compounds according to claim 5, characterized in that: In step S2, the volume ratio of oleylamine to oleic acid is 10-40:

1.

8. The Pickering emulsion electrocatalytic method for hydrogenation of nitro compounds according to claim 5, characterized in that: In step S3, the volume ratio of solution C to solution D is 1:2-10.

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