Synthesis method of electrocatalytic olefin epoxidation nano-catalyst

Abstract

The invention relates to the technical field of chemical engineering, and particularly discloses a synthesis method of an electro-catalytic olefin epoxidation nano-catalyst, which comprises the following steps: preparing a uniformly dispersed ReOx nano-particle modified carbon carrier; preparing to obtain a ReOx-coated MoPOM composite material; the surface of the composite material is coated with a WOx nano layer; carrying out high-temperature treatment on the composite material with the surface coated with the WOx nano layer in an inert atmosphere, and inducing to form oxygen vacancies to obtain a ternary mixed oxide containing the oxygen vacancies; and assembling the ternary mixed oxide containing the oxygen vacancies into an electrode, and preparing to obtain the electro-activated Re-Mo-W nano-catalyst. Three high-valence metals including rhenium, molybdenum and tungsten form complementary active sites through covalence / electrostatic interaction, and water molecules and olefin molecules can be efficiently activated in different potential intervals respectively. The high-valence metal center is beneficial to forming a metal oxygen intermediate, and is beneficial to realizing high-selectivity oxygen atom transfer through metal-oxygen bond breakage and recombination.

Description

Technical Field

[0001] The invention belongs to the technical field of chemical engineering, and particularly relates to a method for synthesizing a nanocatalyst for electrocatalytic olefin epoxidation. Background Art

[0002] In the chemical industry, olefin epoxidation, as an important pathway for producing epoxides, has long been a research hotspot, with its efficient and green implementation being a key research topic. Epoxides are widely used in a variety of fields, including fine chemicals, pharmaceutical synthesis, and polymer materials. Therefore, the development of high-performance, environmentally friendly olefin epoxidation catalysts is of great practical significance.

[0003] Currently, traditional olefin epoxidation catalysts are primarily based on precious metals (such as palladium and platinum) or transition metal oxides (such as titanium silicate molecular sieves). However, these catalysts have numerous drawbacks in practical applications. On the one hand, the high cost and scarce resources of precious metal catalysts limit their large-scale industrial application. On the other hand, while transition metal oxide catalysts are relatively low in cost, they often suffer from low catalytic activity, poor selectivity, and insufficient stability. Particularly under high current density or prolonged operation, they are prone to deactivation or side reactions, resulting in reduced yields of the target product.

[0004] Furthermore, existing olefin epoxidation reactions often use organic peroxides (such as cumene hydroperoxide and tert-butyl hydroperoxide) as oxidants. These oxidants are not only expensive but also pose safety risks during use and storage. They also produce large amounts of organic byproducts after the reaction, increasing the cost of subsequent separation and purification, which is inconsistent with the development trend of green chemistry. Therefore, the development of an efficient, stable, low-cost, and environmentally friendly olefin epoxidation catalyst is of great significance for promoting the green and efficient development of olefin epoxidation technology.

[0005] In this context, the present invention proposes a method for synthesizing an electrocatalytic olefin epoxidation nanocatalyst. By constructing a ternary mixed oxide catalyst containing oxygen vacancies, the electrocatalytic technology is used to realize the olefin epoxidation reaction with water as the sole oxygen source. This not only improves the catalytic activity and selectivity, but also significantly reduces the cost and environmental impact, providing a new solution for the green and efficient development of olefin epoxidation technology.

[0006] In response to this, the inventors proposed a method for synthesizing electrocatalytic olefin epoxidation nanocatalysts to solve the above problems. Summary of the Invention

[0007] The object of the present invention is to provide a method for synthesizing a nanocatalyst for electrocatalytic olefin epoxidation, so as to solve the problems raised in the above background technology.

[0008] To achieve the above object, the present invention provides the following technical solutions:

[0009] The method for synthesizing a nanocatalyst for electrocatalytic olefin epoxidation comprises the following steps:

[0010] The metal precursor methyl rhenium trioxide (CH3ReO3) ethanol solution was contacted with the conductive carbon support to react and obtain uniformly dispersed ReO x Nanoparticle-modified carbon supports;

[0011] The ReO x Nanoparticle-modified carbon support impregnated with phosphomolybdate cluster complex TBA3PMo 12 O 40 solution and dried to obtain ReO x @MoPOM composite materials;

[0012] The ReO x @MoPOM composite material and tungstate precursor (NH4) 10 W 12 O 41 The aqueous solution was hydrothermally reacted in a closed reactor to obtain surface-coated WO x Nanolayered composite materials;

[0013] The surface is coated with WO x The nano-layer composite material is subjected to high temperature treatment in an inert atmosphere to induce the formation of an appropriate amount of oxygen vacancies, thereby obtaining a ternary mixed oxide containing oxygen vacancies;

[0014] The oxygen vacancy-containing ternary mixed oxide is assembled into an electrode, and cyclic voltammetry scanning pretreatment is performed in an organic-water mixed electrolyte to activate the variable valence metal intermediate to obtain an electrically activated Re-Mo-W nanocatalyst.

[0015] Preferably, the concentration of the CH3ReO3 solution is 10 mmol / L, the reaction temperature is room temperature, and the contact time is 1 h; the obtained A is heat-treated at 350°C for 2 h under a nitrogen atmosphere with a heating rate of 5°C / min.

[0016] Preferably, the TBA3PMo 12 O 40 The solution concentration was 5 mmol / L, the immersion time was 30 min, the drying temperature was 80 °C, and the drying time was 4 h.

[0017] Preferably, the hydrothermal reaction conditions are: reaction temperature 180° C., holding time 12 h, and natural cooling to room temperature.

[0018] Preferably, the inert atmosphere is high-purity argon, the treatment temperature is 300° C., the holding time is 2 h, and the heating rate is 3° C. / min.

[0019] Preferably, the organic-water mixed electrolyte is 0.1 M tetrabutylammonium tetrafluoroborate / acetonitrile-water 9:1 v / v, and cyclic voltammetry is used to scan -0.5 to 2.5 V (vs. SHE), with a scan rate of 50 mV / s and 50 cycles.

[0020] Preferably, the ReO x The particle size distribution of the nanoparticles is 38 nm. The MoPOM clusters are electrostatically bonded to ReO x Surface bonding, WO x The layer thickness is 510 nm; the oxygen vacancy concentration on the catalyst surface after pretreatment is ≥1.0×10 15 cm -2 .

[0021] Compared with the prior art, the present invention has the following beneficial effects:

[0022] (1) The three high-valent metals of rhenium, molybdenum and tungsten in the present invention form complementary active sites through covalent / electrostatic interactions, which can efficiently activate water molecules and olefin molecules in different potential ranges. The high-valent metal center is conducive to the formation of metal═O intermediates, which helps to achieve highly selective oxygen atom transfer through the breakage and recombination of metal-oxygen bonds. MoPOM cluster and WO x The rich oxygen vacancy system ensures that the adsorption energy of reaction intermediates (OH*, O*) is neither too strong to "passivate" the catalytic sites nor too weak to cause excessive desorption of the intermediates. This helps to suppress excessive oxygen evolution reaction (OER) at high overpotentials, thereby improving the Faradaic efficiency and selectivity of olefin epoxidation.

[0023] (2) ReO of the present invention x The introduction of nanoparticles significantly enhances the catalyst's overall conductive network, effectively reducing electron transfer resistance through the metal-oxygen-metal framework and enabling faster electrochemical process kinetics. Electrochemical pretreatment (cyclic voltammetric activation) further modulates the surface metal valence distribution, increasing the number and accessibility of reactive intermediates required for the reaction. The moderate oxygen vacancies induced by heat treatment serve as additional nucleophilic active sites, enhancing water molecule activation and accelerating the formation of metal═O intermediates. Furthermore, the defect regions readily adsorb olefin substrates, enhancing the spatial coordination between the reacting molecules. The "defect-noble metal center" interface formed by the vacancies and the high-valent metal facilitates the rapid and directional transfer of oxygen atoms from water to the olefin.

[0024] (3) The polymetallic center in the present invention endows the catalyst with the ability to maintain high activity and selectivity over a wide potential range, allowing the operating potential to be flexibly adjusted according to different olefin substrates (such as cyclooctene, styrene, etc.) without the need to redesign the catalyst. This electrolyte's strong phase compatibility facilitates the development of diverse olefin epoxidation applications in environmentally friendly solvent systems at room temperature and pressure. Using water as the sole oxygen source, the cathode of the epoxidation process can co-produce pure hydrogen, achieving efficient coupling of electrical and chemical energy. The process is mild, the equipment is simple, and it is driven by renewable energy, helping to meet the industrialization needs of green chemical industry and decentralized production. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 This is a flow chart of the synthesis method of the electrocatalytic olefin epoxidation nanocatalyst of the present invention;

[0026] Figure 2 This is the CV curve diagram of the electrocatalytic epoxidation of cyclooctene of the present invention. DETAILED DESCRIPTION

[0027] The following will provide a clear and complete description of the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0028] Example 1:

[0029] See also Figures 1 to 2 As shown, cyclooctene electrocatalytic epoxidation:

[0030] Electrode preparation

[0031] The electroactivated Re–Mo–W nanocatalyst was dispersed in isopropanol / water (3:1 v / v) (0.5 mg / mL) and sonicated for 30 min.

[0032] On carbon paper (1×1cm 2 ) was drop-coated on the surface of the electrode and dried to obtain a working electrode.

[0033] Electrolyzer and electrolyte

[0034] Three-electrode system: working electrode, platinum wire counter electrode, Ag / AgCl (3MKCl) reference electrode.

[0035] Electrolyte: 0.1 M tetrabutylammonium tetrafluoroborate / acetonitrile-water (9:1 v / v), saturated cyclooctene (2.0 M).

[0036] Electrocatalytic conditions

[0037] Constant potential: 1.9V vs. SHE

[0038] Reaction temperature: 25°C

[0039] Stirring speed: 600 rpm

[0040] Reaction time: 4 hours

[0041] Electrochemistry: The i–t curves were recorded using a CHI 1140 workstation, and the average current density was taken for the last 2 h.

[0042] Product analysis: GC-MS (Agilent 7890B / 5977A) was used with cumene as the internal standard to quantify cyclooctane oxide.

[0043] like Figure 2 As shown, the result:

[0044] Cyclooctene conversion rate: 85%

[0045] Faradaic efficiency (FE): 42%

[0046] Epoxide selectivity: 76%

[0047] Average current density: 8.5 mA / cm 2 .

[0048] Example 2:

[0049] Electrocatalytic epoxidation of styrene

[0050] Electrode preparation: same as in Example 1.

[0051] Electrolyte: 0.1 M tetrabutylammonium tetrafluoroborate / acetonitrile-water (9:1 v / v), saturated styrene (1.5 M).

[0052] Electrocatalytic conditions

[0053] Constant potential: 1.7V vs. SHE

[0054] Reaction temperature: 25°C

[0055] Stirring speed: 600 rpm

[0056] Reaction time: 4 hours

[0057] Data acquisition: Same as Example 1, except that the internal standard was cyclohexanone to quantify styrene oxide.

[0058] result:

[0059] Styrene conversion rate: 80%

[0060] Faradaic efficiency (FE): 38%

[0061] Epoxide selectivity: 72%

[0062] Average current density: 7.9 mA / cm 2 .

[0063] Comparative Example:

[0064] Fe2O3 single metal oxide catalysis:

[0065] Catalyst: Fe2O3 nanoparticle preparation

[0066] Electrolyte and operation: same as Example 1

[0067] Constant potential: 1.9 V vs. SHE; reaction time: 4 h; 25°C; 600 rpm

[0068] result

[0069] Cyclooctene conversion rate: 60%

[0070] Faradaic efficiency (FE): 26%

[0071] Selectivity: 63%

[0072] Average current density: 4.2 mA / cm 2

[0073] The performance comparison is shown in Table 1 below:

[0074] Table 1

[0075]

[0076] As can be seen from the above, the activity is significantly improved: the FE of the catalyst of the present invention for cyclooctene is increased from 26% to 42%, and the current density is nearly doubled;

[0077] High selectivity and universality: Epoxidation selectivity >70% can be maintained on various olefin substrates;

[0078] The process is stable and reliable: Examples 1 and 2 both adopted a 4-h constant potential test, and the CV / i–t curve reproducibility error was <5% after three repetitions.

[0079] The above examples and comparative examples demonstrate that this solution, by combining a ternary Re–Mo–W mixed oxide with electrochemical pretreatment, can significantly improve the activity and selectivity of electrocatalytic olefin epoxidation, and has excellent industrial application prospects.

[0080] From the above, we can see that the multi-metal synergistic active center

[0081] The three high-valent metals, rhenium, molybdenum, and tungsten, form complementary active sites through covalent and electrostatic interactions, effectively activating water and olefin molecules at different potential ranges. Their high-valent metal centers facilitate the formation of metal═O intermediates, enabling highly selective oxygen atom transfer through the breakage and recombination of metal-oxygen bonds.

[0082] Optimizing the adsorption and desorption equilibrium of oxygen ligands

[0083] MoPOM clusters and WO x The rich oxygen vacancy system ensures that the adsorption energy of reaction intermediates (OH*, O*) is neither too strong to "passivate" the catalytic sites nor too weak to cause excessive desorption of the intermediates. This helps to suppress excessive oxygen evolution reaction (OER) at high overpotentials, thereby improving the Faradaic efficiency and selectivity of olefin epoxidation.

[0084] Electronic structure regulation and current-carrying performance improvement

[0085] ReO x The introduction of nanoparticles significantly enhances the catalyst's overall conductive network, effectively reducing electron transfer resistance through the metal-oxygen-metal framework and accelerating the electrochemical process kinetics. Electrochemical pretreatment (cyclic voltammetric activation) further modulates the surface metal valence distribution, increasing the number and accessibility of active intermediates required for the reaction.

[0086] Surface structure and defect engineering advantages

[0087] The moderate oxygen vacancies induced by heat treatment serve as additional nucleophilic active sites, enhancing water activation and accelerating the formation of metal═O intermediates. Furthermore, the defect regions readily adsorb olefin substrates, enhancing the spatial coordination between the reacting molecules. The "defect-noble metal center" interface formed by the vacancies and the high-valent metal facilitates the rapid and directional transfer of oxygen atoms from water to the olefin.

[0088] Wide potential window and substrate compatibility

[0089] The multimetallic center enables the catalyst to maintain high activity and selectivity over a wide potential range, allowing for flexible adjustment of the operating potential to different olefin substrates (such as cyclooctene and styrene) without catalyst redesign. This strong electrolyte compatibility facilitates the development of diverse olefin epoxidation applications at ambient temperature and pressure in environmentally friendly solvent systems.

[0090] Green co-production and energy utilization

[0091] Using water as the sole oxygen source, the cathode of the epoxidation process can co-produce pure hydrogen, achieving efficient coupling of electrical energy and chemical energy; the process is mild, the equipment is simple, and it is driven by renewable energy, which helps to meet the industrialization needs of green chemical industry and decentralized production.

[0092] In summary, this scheme combines multi-metal synergy, defect engineering and surface electronic regulation at the molecular level, which not only significantly optimizes the catalyst's bidirectional activation ability for oxygen species and olefin substrates, but also provides a reliable theoretical basis and process support for achieving efficient, selective and sustainable electrocatalytic olefin epoxidation.

[0093] In the description of this specification, the reference terms "one embodiment", "some embodiments", "examples", "specific examples" or "some examples" mean that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic expressions of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art can combine and combine different embodiments or examples described in this specification and features of different embodiments or examples without contradiction.

[0094] In the drawings of the embodiments disclosed in the present invention, only the structures related to the embodiments disclosed in the present invention are involved. Other structures can refer to the general design. In the absence of conflict, the same embodiment and different embodiments of the present invention can be combined with each other.

[0095] While embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions, and variations may be made to these embodiments without departing from the principles and spirit of the invention, and that the scope of the invention is defined by the appended claims and their equivalents.

Claims

1. A method for synthesizing a nanocatalyst for electrocatalytic olefin epoxidation, characterized in that: The following steps are involved: The metal precursor methyl rhenium trioxide CH3ReO3 ethanol solution is contacted with the conductive carbon support to react and obtain uniformly dispersed ReO × Nanoparticle-modified carbon supports; The ReO x Nanoparticle-modified carbon support impregnated with phosphomolybdate cluster complex TBA3PMo 12 O 40 solution and dried to obtain ReO x @MoPOM composite materials; The ReO x @MoPOM composite material and tungstate precursor (NH4) 10 W 12 O 41 The aqueous solution was hydrothermally reacted in a closed reactor to obtain surface-coated WO x Nanolayered composite materials; The surface is coated with WO x The nano-layer composite material is subjected to high temperature treatment in an inert atmosphere to induce the formation of oxygen vacancies, thereby obtaining a ternary mixed oxide containing oxygen vacancies; The oxygen vacancy-containing ternary mixed oxide is assembled into an electrode, and cyclic voltammetry scanning pretreatment is performed in an organic-water mixed electrolyte to activate the variable valence metal intermediate to obtain an electrically activated Re-Mo-W nanocatalyst.

2. The method for synthesizing the electrocatalytic olefin epoxidation nanocatalyst according to claim 1, characterized in that: The concentration of the CH3ReO3 solution was 10 mmol / L, the reaction temperature was room temperature, and the contact time was 1 h. The obtained A was heat-treated at 350°C for 2 h under a nitrogen atmosphere with a heating rate of 5°C / min.

3. The method for synthesizing the electrocatalytic olefin epoxidation nanocatalyst according to claim 1, characterized in that: The TBA3PMo 12 O 40 The solution concentration was 5 mmol / L, the immersion time was 30 min, the drying temperature was 80 °C, and the drying time was 4 h.

4. The method for synthesizing a nanocatalyst for electrocatalytic olefin epoxidation according to claim 1, wherein: The hydrothermal reaction conditions are: reaction temperature 180° C., holding time 12 h, and natural cooling to room temperature.

5. The method for synthesizing the electrocatalytic olefin epoxidation nanocatalyst according to claim 1, characterized in that: The inert atmosphere is high-purity argon, the treatment temperature is 300° C., the holding time is 2 h, and the heating rate is 3° C. / min.

6. The method for synthesizing a nanocatalyst for electrocatalytic olefin epoxidation according to claim 1, characterized in that: The organic-water mixed electrolyte was 0.1 M tetrabutylammonium tetrafluoroborate / acetonitrile-water (9:1 v / v), and cyclic voltammetry was used to scan -0.5 to 2.5 V (vs. SHE) at a scan rate of 50 mV / s for 50 cycles.

7. The method for synthesizing a nanocatalyst for electrocatalytic olefin epoxidation according to claim 1, characterized in that: The ReO x The particle size distribution of the nanoparticles is 38 nm. The MoPOM clusters are electrostatically bonded to ReO x Surface bonding, WO x The layer thickness is 510 nm; the oxygen vacancy concentration on the catalyst surface after pretreatment is ≥1.0×10 15 cm -2 .

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