Modified palladium selenium catalyst, preparation thereof and application thereof in electrolysis of seawater for hydrogen production and magnesium production coupled with methane production for methanol production

Abstract

The application provides a modified palladium selenium catalyst and its preparation and application in electrolysis of seawater to produce hydrogen, magnesium extraction and co-production of methane to produce methanol. The preparation includes precursor dispersion system construction, solvothermal reduction nucleation and other steps, and can be used for electrolysis of seawater or brine in a proton exchange membrane electrolysis cell to produce hydrogen, extract magnesium and prepare methane. The catalyst optimizes the electronic structure of the palladium surface by selenium modification, precisely adjusts the position of the palladium d band center, changes the adsorption energy of the key intermediate, inhibits the excessive rupture of the C-O bond, blocks the deep oxidation path of methanol, and greatly improves the selectivity of methanol. The process innovation lies in using PEM electrolysis hydrogen as a "cocatalyst" to promote the generation of hydrogen peroxide intermediate in the low-temperature oxidation of methane to activate the C-H bond, and the by-product oxygen in electrolysis is directly used in the downstream reaction to improve the atomic utilization rate and optimize the material circulation. The PEM technology provides a high-purity hydrogen and oxygen gas stream, which can be reacted without purification, and the equipment is compact and occupies a small area, which is suitable for space-limited scenes such as offshore platforms, and provides a new solution for offshore chemical industry.

Description

Technical Field

[0001] This invention belongs to the interdisciplinary technical fields of new energy utilization, marine chemical resource development and C1 chemical synthesis, specifically the modified palladium selenide catalyst and its preparation and its application in the electrolysis of seawater to produce hydrogen, extract magnesium and produce methane to methanol. Background Technology

[0002] As the global energy structure shifts towards cleaner and lower-carbon energy sources, hydrogen energy, as a clean and efficient secondary energy source, is considered a key carrier for achieving this goal. Breakthroughs in its large-scale production technology have become a core requirement for industry development. Oceans cover approximately 71% of the Earth's surface and contain virtually unlimited water resources. Producing hydrogen from seawater eliminates the need to consume precious freshwater resources and can be coupled with fluctuating renewable energy sources such as offshore wind power, achieving efficient storage and utilization of green electricity. This has significant strategic importance and promising application prospects.

[0003] In seawater electrolysis for hydrogen production, proton exchange membrane (PEM) electrolysis offers significant advantages over traditional alkaline electrolysis, including higher current density, higher gas purity (hydrogen purity up to 99.999%), compact structure, and shorter dynamic response time (less than 200 milliseconds). This makes it better suited to the volatility of renewable energy sources such as offshore wind power, and it has become a key development direction in the current seawater electrolysis hydrogen production field. This technology uses a proton exchange membrane as the diaphragm and operates at 30-100℃ and 3-10 A / cm². 2 High-efficiency electrolysis can be achieved under certain conditions, with an electrolysis efficiency of 85%-95%. However, its performance is highly dependent on the activity, selectivity and stability of the electrode catalyst. Among them, palladium (Pd)-based catalysts have certain hydrogen evolution and oxygen evolution catalytic activities and have potential application value in methane oxidation reaction, and are widely used in related research and practice in this field.

[0004] Currently, existing palladium-based catalysts for seawater electrolysis mainly fall into two categories: one is pure palladium catalysts, which are often supported as nanoparticles on carbon-based supports to form Pd / C catalysts, accelerating the electrolysis reaction through the inherent catalytic activity of palladium metal; the other is noble metal-modified palladium-based catalysts. To improve the performance defects of pure palladium catalysts, researchers often introduce other noble metals such as gold (Au) to form alloy structures with palladium, or use composite structures such as Pd-doped Co NPs@C shell, which are doped with transition metals (such as Co, Ni, Fe, etc.) and coated with a graphite carbon shell. These attempts aim to regulate the d-band center of palladium through electronic effects, strain effects, and synergistic effects to optimize catalytic performance. In addition, some existing palladium-based catalysts also attempt to improve their adaptability to seawater environments through axial coordination engineering, support modification, or protective coating, but overall, they have not yet broken through the current technological bottlenecks.

[0005] Although existing palladium-based catalysts have been applied in PEM seawater electrolysis systems, they suffer from several insurmountable drawbacks that severely restrict the large-scale industrial application of the technology. These drawbacks are as follows: First, poor catalytic selectivity. Pure palladium catalysts exhibit excessive adsorption of intermediate products from the electrolysis reaction, which not only intensifies competition between the chlorine evolution reaction and oxygen evolution reaction at the anode during seawater electrolysis, reducing hydrogen production efficiency, but also leads to deep oxidation of products in the subsequent methane oxidation reaction, affecting the selectivity of the target product. Second, insufficient stability. High concentrations of chloride ions in seawater (approximately 0.5 mol / L) have strong coordination capabilities, forming soluble complexes with the metal active sites on the surface of the palladium-based catalyst, leading to the dissolution and loss of active components. Furthermore, the bubbles generated during electrolysis induce mechanical stress, and the catalyst's nanoparticle size further contributes to this problem. The palladium structure is prone to aggregation and phase transition, which further leads to catalyst structural collapse and activity decay. In addition, sulfur ions, heavy metal ions, and microbial metabolites in seawater can also cause catalyst poisoning and deactivation, forming a vicious cycle of "corrosion-exposure-re-corrosion". Third, the cost is high. Pure palladium is a precious metal with scarce reserves and high price. Although the scheme of introducing other precious metals such as gold for modification can improve the catalytic performance to a certain extent, it further increases the preparation cost of the catalyst, making it difficult to meet the economic requirements of large-scale industrial applications. Fourth, the catalytic performance is still lacking. Under the mild conditions required for PEM electrolysis of seawater, the existing palladium-based catalysts have high hydrogen evolution and oxygen evolution overpotentials, making it difficult to achieve efficient electrolysis. Moreover, the catalytic activity for methane activation is insufficient and cannot be adapted to subsequent methane conversion processes.

[0006] Meanwhile, existing methods for treating seawater or brine using palladium-based catalysts combined with proton exchange membranes suffer from extremely low comprehensive utilization rates of process byproducts, resulting in severe waste of resources and energy. In the PEM (Polymer Electrolysis) process for producing hydrogen from seawater, hydrogen evolution occurs at the cathode to generate hydrogen, while oxygen evolution occurs at the anode to generate oxygen. Furthermore, the hydrogen evolution reaction at the cathode leads to a localized increase in pH, creating a natural precipitation environment for magnesium extraction from seawater. Theoretically, this could achieve co-production of hydrogen, magnesium, and oxygen, significantly improving the process's economic efficiency. However, in practical applications, the oxygen produced at the anode is usually treated as a byproduct and directly released into the atmosphere, failing to achieve effective utilization and wasting valuable chemical energy and material resources. Simultaneously, existing technologies lack a corresponding recycling scheme for the magnesium precipitates formed at the cathode during electrolysis, further reducing the overall resource utilization rate and economic benefits of the process.

[0007] On the other hand, methane, as a major component of natural gas, shale gas, and combustible ice, is an extremely abundant carbon resource. Converting methane into liquid fuel methanol not only solves the problem of inconvenient methane gas transportation but also provides an important raw material for the production of high-value-added chemicals, possessing extremely high industrial value. However, the methane molecule has a highly symmetrical tetrahedral structure with a CH bond energy as high as 439 kJ / mol, making it extremely difficult to activate. Moreover, once the methane molecule is activated, the resulting methanol product is more reactive than methane, readily undergoing deep oxidation in an oxidizing environment to produce carbon dioxide. This leads to a significant reduction in the selectivity and yield of methanol, which has become the core bottleneck in the development of direct methane oxidation to methanol technology.

[0008] Current methane-to-methanol processes primarily employ a high-temperature, high-pressure "syngas" route. This route requires first reforming methane into a mixture of carbon monoxide and hydrogen, followed by subsequent synthesis reactions to produce methanol. The entire process is lengthy, energy-intensive, and involves high equipment investment costs, making it difficult to achieve energy conservation, emission reduction, and economic improvements. Although the industry generally recognizes the direct oxidation of methane to methanol using oxygen under mild conditions as the most promising technological route, often referred to as the "holy grail" reaction, and palladium (Pd)-based catalysts have been shown to have certain catalytic activity for this reaction, as mentioned earlier, existing pure palladium catalysts exhibit extremely poor selectivity. Furthermore, modifications using precious metals such as gold are prohibitively expensive, hindering industrial application.

[0009] In summary, existing palladium-based catalysts for seawater electrolysis suffer from drawbacks such as poor selectivity, insufficient stability, high cost, and inadequate catalytic performance. When using these palladium-based catalysts in conjunction with proton exchange membranes to treat seawater or brine, the process products (especially oxygen and magnesium resources) are not fully utilized, resulting in significant resource and energy waste. Furthermore, existing methane-to-methanol processes suffer from lengthy processes, high energy consumption, and low methanol selectivity, and are difficult to synergistically couple with seawater electrolysis. Therefore, developing a high-performance, cost-effective palladium-based catalyst to achieve comprehensive utilization of products from proton exchange membrane treatment of seawater or brine, and effectively couple it with the direct oxidation of methane to methanol process, thereby overcoming existing technological bottlenecks and achieving technological upgrades, has significant scientific, application, and industrial potential. Summary of the Invention

[0010] This application aims to solve the problems existing in the above-mentioned background art. The present invention provides a method for preparing a modified palladium-based catalyst, comprising the following steps: (1) Construction of a precursor dispersion system: 30-40 mg palladium acetylacetonate, 10-20 mg dimethyl diselenide, 30-40 mg ascorbic acid as a reducing agent, and 10-100 mg polyvinylpyrrolidone as a surfactant are added to 10-20 mL of ethylene glycol as a solvent; (2) Solvothermal reduction nucleation: The dispersion obtained in step (1) is placed in a closed or semi-closed container and subjected to a solvothermal reaction under constant heating conditions of 150-200℃. During this process, ethylene glycol and ascorbic acid act together to cause palladium ions to co-reduction with selenium precursors. Through the confinement effect of surfactants, Pd-Se alloy nanocrystal nuclei with uniform size and good dispersion are induced.

[0011] Furthermore, step (3) product purification and separation is also included: after the reaction is completed, the product is cooled to room temperature, and the solid product is collected by centrifugation at 8000-12000 r / min for 5-15 minutes. The product is then washed multiple times with the organic solvent ethanol to remove excess organic matter and unreacted precursors adsorbed on the surface.

[0012] Furthermore, it also includes step (4) liquid phase loading process: it also includes step (4) liquid phase loading process: the purified Pd-Se nanoparticles and 50-100mg carbon powder are dispersed together in 10-50mL n-hexane, and the metal nanoparticles are uniformly anchored on the carbon support surface by magnetic stirring for 12h to form a precursor complex. The magnetic stirring speed is 200-500 r / min.

[0013] Furthermore, it also includes step (5) high-temperature atmosphere activation: the precursor complex obtained in step (4) is vacuum filtered and dried at 60-80℃ and then placed in a tube furnace. Under the protection of inert gas, the temperature is raised to 250-400℃ at a rate of 2-10℃ / min and held for 30-120 minutes to finally obtain a structurally stable Pd-Se / C catalyst.

[0014] Furthermore, in step (1), ultrasonic treatment is used to make each component uniformly dispersed at the molecular or nanoscale in the solvent. The ultrasonic working frequency is 20-40 kHz, the ultrasonic power is 100-300W, and the processing time is 30-60 minutes.

[0015] Naturally, the catalyst of the present invention, prepared by the above method, has changed from the catalyst of the prior art. Therefore, the catalyst prepared by the above method is also within the scope of protection of the present invention.

[0016] The present invention also provides applications of the catalyst, including its use in proton exchange membrane electrolyzers for hydrogen production from seawater or brine, extraction of metallic magnesium, and preparation of methane.

[0017] Furthermore, the application method includes the following steps: (1) Electrolytic coupling magnesium extraction: pretreated seawater or brine is electrolyzed using a proton exchange membrane electrolyzer. The pretreatment refers to reducing the total concentration of divalent and higher metal ions such as calcium and magnesium in the treated seawater to below 0.1 mg / L and the conductivity to below 10 μS / cm. Anode side: Produces high-purity oxygen; Cathode side: Raw material gas preparation: The oxygen generated at the anode of the electrolytic cell, the hydrogen generated at the cathode, and the methane gas introduced from the outside are mixed according to the molar ratio of oxygen:hydrogen:methane (1-2): (1-3): (5-10) to construct the reaction raw material gas; (2) Three-phase catalytic conversion: The catalyst is dispersed in deionized water, the solid-liquid ratio of the catalyst to the reaction medium is 2 mg / mL, and placed in a high-pressure reactor. The mixed gas obtained in step (1) is introduced, and a multiphase catalytic reaction is carried out at 30-80℃. In the reaction system, hydrogen and oxygen generate active oxygen species H2O2* intermediate in situ on the catalyst surface. The intermediate then oxidizes methane to produce methanol.

[0018] In summary, by adopting the above-mentioned innovative technical solutions, the beneficial effects obtained by this invention are specifically reflected in the following aspects: In terms of catalyst electronic structure optimization, the electronic control capability of the catalyst was significantly improved by introducing the non-metallic element selenium (Se) to modify the surface of palladium (Pd). Selenium, with its unique electronegativity, can precisely adjust the d-band center position on the palladium surface, thereby effectively altering the catalyst's response to key reaction intermediates (especially CH3O). - and OH - The adsorption energy of methanol is significantly improved. This subtle electronic effect not only inhibits the excessive breaking of CO bonds, but more importantly, it blocks the reaction pathway of methanol to deep oxidation of carbon dioxide, thus greatly improving methanol selectivity.

[0019] This technology is highly innovative in its process coupling, utilizing hydrogen generated during PEM electrolysis as a "co-catalyst" to achieve efficient synergy between energy and chemical processes. Research has confirmed that the presence of an appropriate amount of hydrogen in the low-temperature methane oxidation reaction system promotes the formation of hydrogen peroxide intermediates, which play a crucial role in activating the CH bonds in methane. This technology directly utilizes the oxygen byproduct from electrolysis and the hydrogen, the main product, in downstream chemical reactions, maximizing atom utilization and achieving optimized material recycling.

[0020] PEM technology exhibits significant advantages. Compared to traditional diaphragm electrolysis technology, it can provide a higher purity hydrogen and oxygen stream, which can be directly delivered to the chemical reactor for reaction without complex purification processes. Furthermore, this technology features a compact structure and small footprint, making it particularly suitable for space-constrained applications such as offshore platforms, providing a new technological solution for offshore chemical production.

[0021] The preparation method has broad applicability. The "synthesis-then-support" strategy combined with high-temperature calcination ensures the uniformity of catalyst particle size and its stability on the support. This method effectively solves the problems of particle agglomeration and loss of active components commonly encountered in traditional impregnation methods, providing a reliable technical route for the large-scale preparation of high-performance catalysts. Attached Figure Description

[0022] Figure 1 The transmission electron microscope (TEM) image of the Pd-Se alloy nanoparticles prepared in Example 1 of this invention shows clear lattice fringes and a regular morphology.

[0023] Figure 2 The bar chart shows the changes in methane conversion, methanol yield, and selectivity of the catalyst in Example 1 of this invention at different reaction times.

[0024] Figure 3 This is a flowchart of the integrated process of "PEM electrolysis of seawater-magnesium extraction-methane conversion" of the present invention. Detailed Implementation

[0025] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments will be clearly and completely described below with reference to the accompanying drawings. The following embodiments are used to illustrate the present invention, but are not intended to limit the scope of the present invention.

[0026] Example 1: Preparation of Pd-Se / C catalyst Preparation of precursor solution: Accurately weigh 30.5 mg of palladium acetylacetone as palladium source, measure 17.5 mg of dimethyl diselenide as selenium source, weigh 36 mg of ascorbic acid as reducing agent, and add 100 mg of polyvinylpyrrolidone (molecular weight 29000 Daltons) to a container containing 10 mL of ethylene glycol.

[0027] Ultrasonic dispersion: The mixed solution is placed in an ultrasonic cleaner for long-term ultrasonic treatment until the solution appears uniform, transparent or semi-transparent to the naked eye, with no obvious precipitate. The ultrasonic wave operates at a frequency of 20kHz, has a power of 100W, and a processing time of 60 minutes.

[0028] Solvent-thermal synthesis: The well-dispersed precursor solution was transferred to a clean single-necked round-bottom flask and vigorously stirred for several minutes using a vortex mixer to ensure homogeneity. The flask was then immersed in an oil bath preheated to 180°C. The reaction was carried out at this temperature for 5 hours under magnetic stirring. During the reaction, the solution gradually darkened in color, indicating the formation and growth of nanocrystal nuclei.

[0029] Washing and purification: After the reaction is complete, allow the reaction solution to cool naturally to room temperature. Transfer the suspension to a centrifuge tube and centrifuge at 8000 r / min for 15 min, collecting the solid product. Discard the supernatant, add ethanol to redisperse the precipitate, and centrifuge again. Repeat this washing step until the supernatant is colorless to completely remove excess PVP and ethylene glycol.

[0030] Carbon support loading: Weigh 100 mg of conductive carbon powder and disperse it in 50 mL of n-hexane solvent. Add the prepared Pd-Se nanoparticles. Stir magnetically for 12 h to allow the metal particles to be fully adsorbed into the pores and surface of the carbon support. The magnetic stirring speed is 200 r / min.

[0031] Calcination and activation: The carbon powder loaded with metal particles was separated by vacuum filtration and dried under vacuum at 60°C. The dried powder was placed in a quartz tube of a tube furnace, and high-purity argon gas was introduced to purge the air. Under the protection of the argon gas flow, the temperature was increased to 300°C at a rate of 5°C / min and held for 30 minutes. After cooling, the final Pd-Se / C catalyst was obtained.

[0032] The prepared catalyst Figure 1 TEM tests showed that after calcination at 300℃ with argon gas, the nanoparticles were tightly bound to the carbon support and maintained good dispersibility after multiple cycles of reaction, with no obvious agglomeration, proving the reliability of the preparation process.

[0033] Figure 2 It is evident that the Pd-Se / C catalyst prepared in this invention exhibits significant methane conversion capability under mild conditions. Within the test potential range (-0.15 V to 0.45 V), the methanol yield shows a trend of first increasing and then decreasing. When the potential is near 0 V (vs. RHE), the total yield reaches its highest value, with the methanol CH3OH yield exceeding 6 mmol·g. pd -1 ·h -1 This fully demonstrates the significant promoting effect of Pd-Se alloying on the activation of CH bonds in methane.

[0034] Example 2: Electrolysis and Methanol Synthesis Process Based on PEM Device This example demonstrates how to use a PEM device to achieve the combined use of water electrolysis and methane conversion. The catalyst used is the one prepared in Example 1. The process is as follows: Figure 3 As shown.

[0035] PEM electrolysis system operation: Construct an electrolysis cell containing a perfluorosulfonic acid proton exchange membrane. The anode chamber is circulated with purified and hardness-reduced seawater (or enriched brine). The total concentration of divalent and higher-valence metal ions such as calcium and magnesium in the treated seawater is reduced to below 0.1 mg / L, and the conductivity is below 10 μS / cm.

[0036] Electrolysis is performed by connecting a DC power supply.

[0037] Under the influence of an electric field, protons migrate through the PEM film toward the cathode.

[0038] High-purity oxygen is collected at the anode exhaust port.

[0039] High-purity hydrogen gas is collected at the cathode exhaust port.

[0040] Meanwhile, a settling zone is set at the bottom of the cathode chamber to collect the magnesium hydroxide-rich slurry generated due to the increase in interface pH. The magnesium product is then obtained through subsequent filtration and separation.

[0041] Methane oxidation reaction: Loading: In a stainless steel high-pressure reactor with a polytetrafluoroethylene liner, the Pd-Se / C catalyst (20 mg) prepared in Example 1 and deionized water (10 mL) were added as the reaction medium, i.e., the solid-liquid ratio of the catalyst to the reaction medium was 2 mg / mL.

[0042] Gas filling: Connect the gas outlet pipe of the PEM electrolyzer to the gas inlet of the reactor, and introduce gas according to the molar ratio of oxygen:hydrogen:methane of 1:1:5.

[0043] Reaction: Magnetic stirring was turned on, and the reactor was heated to 30°C. Under these conditions, the Pd-Se active sites on the catalyst surface catalyze the reaction of H2 and O2 to generate surface-active oxygen species, which in turn oxidize methane dissolved in water to methanol.

[0044] Product detection: After 1 hour of reaction, the mixture was cooled and samples were taken. Gas phase products (CO2, etc.) were detected using gas chromatography (GC), and hydrogen nuclear magnetic resonance (NMR) spectroscopy was used for analysis. 1 H-NMR) and liquid chromatography are used to detect liquid products (methanol, formic acid, etc.).

[0045] Performance verification: Under the above experimental conditions, the Pd-Se / C catalyst prepared in this invention exhibits excellent catalytic performance.

[0046] Table 1 compares the performance of the Pd-Se catalyst in this work with other typical noble metal catalysts (Pd / C, Pt / C, Au, IrO2) in the electrochemical selective oxidation of methane to methanol. The results show that the Pd-Se catalyst in this work exhibits the best overall performance at the optimal potential of 0 V vs. RHE: the CH3OH yield is as high as 6.5 ± 1.5 mmol·g. -1 ·h -1 Accompanied by 1.5 ± 0.5 mmol·g -1 ·h -1 The yield of CH3OOH was ~10.5 mA·cm⁻¹. -2 The current density was significantly higher than that of commercial Pd / C (2.8 mmol·g⁻¹). -1 ·h -1 Pt / C (1.6 mmol·g) -1 ·h -1 Au-based catalyst (2.1 mmol·g) -1 ·h -1 ) and IrO2 (1.1 mmol·g -1 ·h -1 The advantages are 2.3–6 times. Se modification not only significantly improves methanol yield and current density, but also effectively suppresses competition from deep oxidation and OER, fully demonstrating that Pd-Se is one of the most outstanding systems for the electrocatalytic production of methanol from methane among the noble metal catalysts reported to date.

[0047] Example 3: Preparation of Pd-Se / C catalyst Preparation of precursor solution: Accurately weigh 30 mg of palladium acetylacetone as palladium source, measure 10 mg of dimethyl diselenide as selenium source, weigh 30 mg of ascorbic acid as reducing agent, and add 10 mg of polyvinylpyrrolidone (molecular weight 29000 Daltons) to a container containing 20 mL of ethylene glycol.

[0048] Ultrasonic dispersion: The mixed solution is placed in an ultrasonic cleaner for long-term ultrasonic treatment until the solution appears uniform, transparent or semi-transparent to the naked eye, with no obvious precipitate. The ultrasonic wave operates at a frequency of 40kHz, has a power of 300W, and takes 30 minutes to process.

[0049] Solvent-thermal synthesis: The well-dispersed precursor solution was transferred to a clean single-necked round-bottom flask and vigorously stirred for several minutes using a vortex mixer to ensure homogeneity. The flask was then immersed in an oil bath preheated to 150°C. The reaction was carried out at this temperature for 5 hours under magnetic stirring. During the reaction, the solution gradually darkened in color, indicating the formation and growth of nanocrystal nuclei.

[0050] Washing and purification: After the reaction is complete, allow the reaction solution to cool naturally to room temperature. Transfer the suspension to a centrifuge tube and centrifuge at 12000 r / min for 5 min, collecting the solid product. Discard the supernatant, add ethanol to redisperse the precipitate, and centrifuge again. Repeat this washing step until the supernatant is colorless to completely remove excess PVP and ethylene glycol.

[0051] Carbon support loading: Weigh 50 mg of conductive carbon powder and disperse it in 10 mL of n-hexane solvent. Add the prepared Pd-Se nanoparticles. Stir magnetically for 12 h to allow the metal particles to be fully adsorbed into the pores and surface of the carbon support. The magnetic stirring speed is 500 r / min.

[0052] Calcination and activation: Carbon powder loaded with metal particles was separated by vacuum filtration and dried under vacuum at 80°C. The dried powder was placed in a quartz tube of a tube furnace, and high-purity argon gas was introduced to purge the air. Under the protection of the argon gas flow, the temperature was increased to 250°C at a rate of 2°C / min and held for 60 minutes. After cooling, the final Pd-Se / C catalyst was obtained.

[0053] This embodiment demonstrates how to use a PEM device to combine water electrolysis and methane conversion.

[0054] PEM electrolysis system operation: Construct an electrolysis cell containing a perfluorosulfonic acid proton exchange membrane. The anode chamber is circulated with purified and hardness-reduced seawater (or enriched brine). The total concentration of divalent and higher-valence metal ions such as calcium and magnesium in the treated seawater is reduced to below 0.1 mg / L, and the conductivity is below 10 μS / cm.

[0055] Electrolysis is performed by connecting a DC power supply.

[0056] Under the influence of an electric field, protons migrate through the PEM film toward the cathode.

[0057] High-purity oxygen is collected at the anode exhaust port.

[0058] High-purity hydrogen gas is collected at the cathode exhaust port.

[0059] Meanwhile, a settling zone is set at the bottom of the cathode chamber to collect the magnesium hydroxide-rich slurry generated due to the increase in interface pH. The magnesium product is then obtained through subsequent filtration and separation.

[0060] Methane oxidation reaction: Loading: In a stainless steel high-pressure reactor with a polytetrafluoroethylene liner, the Pd-Se / C catalyst (20 mg) prepared in Example 3 and a solution of water and methanol (10 mL) were added as the reaction medium, i.e., the solid-liquid ratio of the catalyst to the reaction medium was 2 mg / mL.

[0061] Gas filling: Connect the gas outlet pipe of the PEM electrolyzer to the gas inlet of the reactor, and introduce gas according to the molar ratio of oxygen:hydrogen:methane of 2:3:10.

[0062] Reaction: Magnetic stirring was turned on, and the reactor was heated to 80°C. Under these conditions, the Pd-Se active sites on the catalyst surface catalyze the reaction of H2 and O2 to generate surface-active oxygen species, which in turn oxidize methane dissolved in water to methanol.

[0063] Product detection: After 1 hour of reaction, the mixture was cooled and samples were taken. Gas phase products (CO2, etc.) were detected using gas chromatography (GC), and hydrogen nuclear magnetic resonance (NMR) spectroscopy was used for analysis. 1 H-NMR) and liquid chromatography are used to detect liquid products (methanol, formic acid, etc.).

[0064] Example 4: Preparation of Pd-Se / C catalyst Preparation of precursor solution: Accurately weigh 40 mg of palladium acetylacetone as palladium source, measure 20 mg of dimethyl diselenide as selenium source, weigh 40 mg of ascorbic acid as reducing agent, and add 50 mg of polyvinylpyrrolidone (molecular weight 29000 Daltons) to a container containing 15 mL of ethylene glycol.

[0065] Ultrasonic dispersion: The mixed solution is placed in an ultrasonic cleaner for long-term ultrasonic treatment until the solution appears uniform, transparent or semi-transparent to the naked eye, with no obvious precipitate. The ultrasonic working frequency is 30kHz, the ultrasonic power is 200W, and the processing time is 45 minutes.

[0066] Solvent-thermal synthesis: The well-dispersed precursor solution was transferred to a clean single-necked round-bottom flask and vigorously stirred for several minutes using a vortex mixer to ensure homogeneity. The flask was then immersed in an oil bath preheated to 200°C. The reaction was carried out at this temperature for 5 hours under magnetic stirring. During the reaction, the solution gradually darkened in color, indicating the formation and growth of nanocrystal nuclei.

[0067] Washing and purification: After the reaction is complete, allow the reaction solution to cool naturally to room temperature. Transfer the suspension to a centrifuge tube and centrifuge at 10,000 r / min for 10 min, collecting the solid product. Discard the supernatant, add ethanol to redisperse the precipitate, and centrifuge again. Repeat this washing step until the supernatant is colorless to completely remove excess PVP and ethylene glycol.

[0068] Carbon support loading: Weigh 70 mg of conductive carbon powder and disperse it in 30 mL of n-hexane solvent. Add the prepared Pd-Se nanoparticles. Stir magnetically for 12 h to allow the metal particles to be fully adsorbed into the pores and surface of the carbon support. The magnetic stirring speed is 400 r / min.

[0069] Calcination and activation: Carbon powder loaded with metal particles was separated by vacuum filtration and dried under vacuum at 70°C. The dried powder was placed in a quartz tube of a tube furnace, and high-purity argon gas was introduced to purge the air. Under the protection of the argon gas flow, the temperature was increased to 400°C at a rate of 10°C / min and held for 120 minutes. After cooling, the final Pd-Se / C catalyst was obtained.

[0070] This embodiment demonstrates how to use a PEM device to combine water electrolysis and methane conversion.

[0071] PEM electrolysis system operation: Construct an electrolysis cell containing a perfluorosulfonic acid proton exchange membrane. The anode chamber is circulated with purified and hardness-reduced seawater (or enriched brine). The total concentration of divalent and higher-valence metal ions such as calcium and magnesium in the treated seawater is reduced to below 0.1 mg / L, and the conductivity is below 10 μS / cm.

[0072] Electrolysis is performed by connecting a DC power supply.

[0073] Under the influence of an electric field, protons migrate through the PEM film toward the cathode.

[0074] High-purity oxygen is collected at the anode exhaust port.

[0075] High-purity hydrogen gas is collected at the cathode exhaust port.

[0076] Meanwhile, a settling zone is set at the bottom of the cathode chamber to collect the magnesium hydroxide-rich slurry generated due to the increase in interface pH. The magnesium product is then obtained through subsequent filtration and separation.

[0077] Methane oxidation reaction: Loading: In a stainless steel high-pressure reactor with a polytetrafluoroethylene liner, the Pd-Se / C catalyst (20 mg) prepared in Example 4 and a solution of water and methanol (10 mL) were added as the reaction medium, i.e., the solid-liquid ratio of the catalyst to the reaction medium was 2 mg / mL.

[0078] Gas filling: Connect the gas outlet pipe of the PEM electrolyzer to the gas inlet of the reactor, and introduce gas according to the molar ratio of oxygen:hydrogen:methane of 1.5:2:7.

[0079] Reaction: Magnetic stirring was turned on, and the reactor was heated to 60°C. Under these conditions, the Pd-Se active sites on the catalyst surface catalyze the reaction of H2 and O2 to generate surface-active oxygen species, which in turn oxidize methane dissolved in water to methanol.

[0080] Product detection: After 1 hour of reaction, the mixture was cooled and samples were taken. Gas phase products (CO2, etc.) were detected using gas chromatography (GC), and hydrogen nuclear magnetic resonance (NMR) spectroscopy was used for analysis. 1H-NMR) and liquid chromatography are used to detect liquid products (methanol, formic acid, etc.).

[0081] It should be noted that since the performance of other embodiments of the present invention is within the range of the data in Table 1 above, they will not be described one by one in order to avoid unnecessary repetition.

[0082] The above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention in any way. Although the present invention has been disclosed above with reference to preferred embodiments, it is not intended to limit the present invention. Any person skilled in the art can make some modifications or alterations to the above-described technical content to create equivalent embodiments without departing from the scope of the present invention. Any simple modifications, equivalent changes, and alterations made to the above embodiments based on the technical essence of the present invention without departing from the scope of the present invention shall still fall within the scope of the present invention.

Claims

1. A method for preparing a modified palladium-based catalyst, characterized in that, The following steps are included: (1) Construction of precursor dispersion system: 30-40 mg palladium acetylacetonate, 10-20 mg dimethyl diselenide, 30-40 mg ascorbic acid reducing agent and 10-100 mg polyvinylpyrrolidone surfactant are added to 10-20 mL of ethylene glycol solvent; (2) Solvothermal reduction nucleation: The dispersion obtained in step (1) is placed in a closed or semi-closed container and subjected to a solvothermal reaction under constant heating conditions of 150-200℃. During this process, ethylene glycol and ascorbic acid act together to cause palladium ions to co-reduction with selenium precursors. Through the confinement effect of surfactants, Pd-Se alloy nanocrystal nuclei with uniform size and good dispersion are induced.

2. The method according to claim 1, characterized in that, It also includes step (3) product purification and separation: After the reaction is completed, the product is cooled to room temperature, and the solid product is collected by centrifugation at 8000-12000 r / min for 5-15 minutes. The product is then washed multiple times with the organic solvent ethanol to remove excess organic matter and unreacted precursors adsorbed on the surface.

3. The method according to claim 1, characterized in that, It also includes step (4) liquid phase loading process: the purified Pd-Se nanoparticles and 50-100mg carbon powder are dispersed together in 10-50mL n-hexane, and the metal nanoparticles are uniformly anchored on the carbon support surface by magnetic stirring for 12h to form a precursor complex. The magnetic stirring speed is 200-500 r / min.

4. The method according to claim 1, characterized in that, It also includes step (5) high temperature atmosphere activation: after the precursor complex obtained in step (4) is vacuum filtered and dried at 60-80℃, it is placed in a tube furnace and heated to 250-400℃ at a rate of 2-10℃ / min under inert gas protection, and held for 30-120 minutes to finally obtain a structurally stable Pd-Se / C catalyst.

5. The method according to claim 1, characterized in that, In step (1), ultrasonic treatment is used to make each component uniformly dispersed at the molecular or nanoscale in the solvent. The ultrasonic working frequency is 20-40 kHz, the ultrasonic power is 100-300W, and the processing time is 30-60 minutes.

6. A modified palladium-based catalyst, characterized in that, The catalyst was prepared by any one of claims 1-5.

7. The application of the catalyst according to claim 6, characterized in that, This catalyst is applied to the electrolysis of seawater or brine in proton exchange membrane electrolyzers for hydrogen production, extraction of metallic magnesium, and methane preparation.

8. The application according to claim 7, characterized in that, The application method includes the following steps: (1) Electrolytic coupling magnesium extraction: pretreated seawater or brine is electrolyzed using a proton exchange membrane electrolyzer. The pretreatment refers to reducing the total concentration of divalent and higher metal ions such as calcium and magnesium in the treated seawater to below 0.1 mg / L and the conductivity to below 10 μS / cm. Anode side: Produces high-purity oxygen; Cathode side: Raw material gas preparation: The oxygen generated at the anode of the electrolytic cell, the hydrogen generated at the cathode, and the methane gas introduced from the outside are mixed according to the molar ratio of oxygen:hydrogen:methane (1-2): (1-3): (5-10) to construct the reaction raw material gas; (2) Three-phase catalytic conversion: The catalyst is dispersed in deionized water, the solid-liquid ratio of the catalyst to the reaction medium is 2 mg / mL, and placed in a high-pressure reactor. The mixed gas obtained in step (1) is introduced, and a multiphase catalytic reaction is carried out at 30-80℃. In the reaction system, hydrogen and oxygen generate active oxygen species H2O2* intermediate in situ on the catalyst surface. The intermediate then oxidizes methane to produce methanol.

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