Trace ruthenium modified cobalt-based nanocage catalyst and preparation and application thereof

Abstract

The invention discloses a method for synthesizing a trace ruthenium modified cobaltosic oxide nanocage catalyst by an ion exchange method, which comprises the following steps: dropwise adding a methanol solution of dimethylimidazole into a methanol solution containing cobalt nitrate hexahydrate, and reacting to obtain a precursor ZIF67; dropwise adding the ethanol solution of ruthenium chloride into the ethanol solution containing the ZIF67 to obtain ruthenium modified ZIF67; and calcining the ruthenium modified ZIF67 to prepare the trace ruthenium modified cobaltosic oxide nanocage catalyst. The invention also discloses an application of the catalyst in preparation of 2-bromoethanol by electro-catalytic oxidation of ethylene, and the catalyst shows high intrinsic activity and high catalytic activity. A trace amount of metal ruthenium is introduced into the cobalt-based catalyst to form abundant Ru-O-Co asymmetric active sites, and meanwhile, the electronic structure on the surface of the catalyst and the activation energy barrier of bromide ions in the electro-catalytic reaction process are changed through dissimilar metal doping, so that the catalytic performance is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of catalytic material preparation, and particularly relates to a trace ruthenium-modified cobalt tetroxide nanocatalyst and its preparation and application. Background Art

[0002] 2-Bromoethanol is an organic compound and is important in the field of organic synthesis. It can synthesize a variety of important organic compounds such as ethylene glycol, diethylene glycol, and haloethers through substitution, elimination, oxidation and other reactions. These compounds are widely used in chemical production, such as for manufacturing polyester fibers, plastics, solvents, etc. 2-Bromoethanol is also an important raw material for synthesizing a variety of drugs and can be used to synthesize some antiviral drugs, antitumor drugs, etc., which is of great significance to pharmaceutical research and production.

[0003] In recent years, the electrocatalytic ethylene oxidation (EOR) for the preparation of high-value chemicals has attracted increasing attention. Compared with the traditional chemical method of direct oxidation with hypochlorous acid, the one-step electrocatalytic synthesis of high-value 2-bromoethanol provides an environmentally friendly and sustainable low-cost route. It has advantages such as low transportation and processing costs and less pollution compared with the traditional chemical method. Among various paths of electrocatalytic ethylene oxidation, the electrocatalytic ethylene oxidation to produce 2-bromoethanol has the following advantages: (1) The potential of bromine evolution (BrER) is relatively low. Therefore, from a thermodynamic perspective, BrER has higher efficiency at a low cell voltage. (2) Br2 is moderately soluble in water (34 g / L at room temperature). The Br2 reactant is still easily available in the aqueous phase to promote the reaction of ethylene to 2-bromoethanol. (3) All bromine-derived products (including 2-bromoethanol, bromoethane, etc.) and bromine itself are moderately to highly soluble in the aqueous electrolyte. If the oxygen evolution reaction does not occur at the anode, the reactant ethylene can be fed in excess in the circulation loop without any downstream purification steps, thereby inhibiting the formation of by-products such as 1,2-dibromoethane (Br2Et). However, the existing electrocatalytic ethylene oxidation system for producing 2-bromoethanol faces three major bottlenecks: (1) Mass transfer limitation. Ethylene has a low solubility in the aqueous electrolyte (35 g / L), and the Faraday efficiency drops sharply at high current densities. (2) Over-oxidation. A high anodic potential will cause over-oxidation of ethylene to produce by-products such as CO2. It is necessary to operate at a low current density (<100 mA / cm 2 ) to maximize the maintenance of high selectivity and high Faraday efficiency, but the low current density leads to a sharp increase in the required electrolyzer area, significantly increasing the industrialization cost. (3) Cost limitation. The high cost of currently well-performing noble metal catalysts (such as dimensionally stable anodes with high Ru and / or Ir content (~30%)) makes their industrial application a challenge. Therefore, developing highly efficient, low-cost and highly stable catalysts is still the key problem to be solved at present.

[0004] Co3O4 is a typical AB2O4-type spinel oxide, which has attracted much attention due to its low cost, high elemental abundance, and controlled geometric Co sites. However, for the electrocatalytic ethylene oxidation to 2-bromoethanol system, Co3O4 still needs to overcome the limitations of slow kinetics and its stability. In recent years, studies have shown that highly dispersed single-atom catalysts are beneficial to improving the electrocatalytic ethylene oxidation to 2-bromoethanol activity while reducing the use of precious metals Ru, Ir, and Pt. At present, there are many synthesis methods for noble metal-loaded cobalt tetroxide-based catalysts. For example, in the Chinese patent document with the patent number CN118976514A, in order to prepare a catalyst with coexisting Pt single atoms and nanoparticles, this method first mixes ZIF-67 with water to obtain a suspension; after mixing the platinum source with the suspension evenly, a platinum aqueous solution is obtained; the obtained platinum aqueous solution is heated, rotary evaporated, first dried, and calcined to obtain the catalyst with coexisting Pt single atoms and nanoparticles. This method can achieve the dual activation of lattice oxygen and molecular oxygen, further improving the catalytic efficiency, but the preparation process is relatively complex. At the same time, the preferred noble metal loading is 4-6 wt%, and the catalyst cost is relatively high. Therefore, a simpler and more effective method is needed to have cost-effectiveness while ensuring the improvement of the intrinsic properties and electrocatalytic activity of the catalyst. Summary of the Invention

[0005] Based on the above problems in the prior art, the present invention studies the preparation of a trace ruthenium-modified cobalt tetroxide nanocage catalyst by a simple ion adsorption method. By introducing trace metal ruthenium into the cobalt-based catalyst, Ru-O-Co asymmetric bimetallic sites are formed. At the same time, the surface electronic structure of the catalyst and the activation energy barrier of bromide ions during the electrocatalytic ethylene oxidation to prepare 2-bromoethanol are changed by hetero-metal doping, thereby improving the catalytic performance of electrocatalytic ethylene oxidation to prepare 2-bromoethanol.

[0006] To achieve the above invention purpose, the present invention adopts the following technical solutions.

[0007] The present invention first provides a preparation method of a trace ruthenium-modified cobalt-based nanocage catalyst. This method can obtain a cobalt tetroxide nanocage catalyst by a simple ion adsorption method, and introduce trace ruthenium into the cobalt tetroxide to modify it, obtaining a trace ruthenium-modified cobalt tetroxide nanocage catalyst with high electrocatalytic ethylene oxidation to 2-bromoethanol activity.

[0008] A preparation method of a trace ruthenium-modified cobalt tetroxide nanocage catalyst, comprising:

[0009] (1) Add cobalt nitrate hexahydrate and dimethylimidazole to methanol respectively, and continuously stir until completely dissolved to obtain a methanol solution of cobalt nitrate hexahydrate and a methanol solution of dimethylimidazole respectively.

[0010] (2) The above-mentioned methanol solution of dimethylimidazole was added dropwise to the methanol solution of cobalt nitrate hexahydrate, and stirred at room temperature to obtain a turbid purple solution.

[0011] (3) The product obtained in step (2) is washed with methanol and anhydrous ethanol in sequence, filtered, dried in a vacuum oven, and ground to obtain the precursor ZIF67.

[0012] (4) Add ZIF67 and ruthenium chloride into ethanol respectively, and continue stirring until they are evenly dispersed to obtain an ethanol solution of ruthenium chloride and an ethanol solution containing ZIF67 respectively.

[0013] (5) Add the ruthenium chloride ethanol solution dropwise to the ethanol solution containing ZIF67, stir thoroughly to allow the ruthenium ions in the solution to be fully adsorbed on the surface of ZIF67, then wash with anhydrous ethanol, filter and dry in a vacuum oven, take out and grind to obtain trace ruthenium-modified ZIF67. At this time, the ruthenium ions are adsorbed on the surface of ZIF67 to form trace ruthenium-modified ZIF67.

[0014] (6) calcining the ruthenium-modified ZIF67 in a muffle furnace to obtain the trace ruthenium-modified cobalt tetroxide nanocage catalyst. During the high-temperature calcination process, ZIF67 is calcined to form a hollow polyhedron composed of cobalt tetroxide nanoparticles, namely cobalt tetroxide nanocages, and at the same time, the ruthenium ions originally adsorbed on the surface of ZIF67 are oxidized to ruthenium oxide nanoparticles during the calcination process and loaded on the surface of the cobalt tetroxide nanocages.

[0015] The present invention introduces metallic ruthenium into a cobalt-based catalyst by a simple ion adsorption method to form a Ru-O-Co asymmetric bimetallic site, and at the same time, heterogeneous metal doping changes the electronic structure of the catalyst surface and the activation energy barrier of bromide ions in the process of electrocatalytic ethylene oxidation to prepare 2-bromoethanol, thereby improving the catalytic performance of electrocatalytic ethylene oxidation to prepare 2-bromoethanol.

[0016] In step (1), the amount of cobalt nitrate hexahydrate and dimethylimidazole added satisfies the molar ratio of 1:2 to 1:4, and the preferred molar ratio of cobalt nitrate hexahydrate to dimethylimidazole ensures that the two are fully coordinated and crystal nuclei grow to obtain the precursor ZIF67. The total volume of methanol used in the methanol solution of cobalt nitrate hexahydrate and the methanol solution of dimethylimidazole formed in step 1) satisfies: relative to the molar amount of cobalt nitrate hexahydrate added in step (1), the ratio is 40 to 120 mL: 3 to 9 mmol. The ZIF67 prepared under this condition is a regular polyhedron, which is conducive to the formation of the subsequent hollow cage framework.

[0017] In steps (4)-(5), the mass of ruthenium chloride added is 4-16 wt% of the mass of ZIF67 added. Limiting the added mass of ruthenium within a suitable range, in the prepared trace ruthenium-modified cobalt tetroxide nanocage catalyst, if the doping amount of ruthenium is too low, the change in the surface electronic structure of the catalyst by ruthenium is not obvious, and sufficient Ru-O-Co asymmetric sites cannot be formed, thus affecting the catalytic activity and selectivity; if the doping amount of ruthenium is too high, it may cause the aggregation and inactivation of ruthenium oxide particles adsorbed on the surface of cobalt tetroxide nanocages.

[0018] In step (6), in order to ensure the full oxidation of the catalyst precursor, it is selected to be calcined in a muffle furnace at 300-400 °C for 1-2 hours. The prepared trace ruthenium-modified cobalt tetroxide nanocage catalyst further improves the catalytic activity and selectivity of the main product 2-bromoethanol while ensuring good performance in inhibiting oxygen evolution.

[0019] The present invention also provides a trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared by the above method. The trace ruthenium-modified cobalt tetroxide nanocage catalyst is composed of two components, cobalt tetroxide and trace ruthenium oxide. The microscopic morphology of the trace ruthenium-modified cobalt tetroxide nanocage catalyst shows that several cobalt tetroxide nanoparticles form the framework and enclose to form several hollow polyhedrons, namely cobalt tetroxide nanocages; ruthenium oxide nanoparticles are adsorbed on the surface of the cobalt tetroxide nanocages. The ruthenium loading is 0.22-0.56 wt%, and the ruthenium loading refers to the mass percentage of ruthenium element contained in the catalyst in the catalyst.

[0020] The present invention also provides the application of the above trace ruthenium-modified cobalt tetroxide nanocage catalyst in the electrocatalytic preparation of 2-bromoethanol from ethylene, as follows.

[0021] Attach the trace ruthenium-modified cobalt tetroxide nanocage catalyst of the present invention to carbon paper as the working electrode, and its loading is 0.25-1.0 mg cm -2 , using 0.1 mol / L potassium bromide solution as the electrolyte, the ethylene bubbling rate is 15 mL / min, and at the same time, using Ag / AgCl as the reference electrode and a platinum sheet as the counter electrode, a three-electrode system is formed in an H-type electrolytic cell to carry out the electrocatalytic reaction of ethylene to 2-bromoethanol.

[0022] The present invention prepares the above-mentioned trace ruthenium-modified cobalt tetroxide nanocage catalyst by a simple ion adsorption method, introduces metal ruthenium into the cobalt-based catalyst, and forms a trace ruthenium-modified cobalt tetroxide nanocage catalyst through surface modification. The doping of ruthenium changes the electronic structure of the catalytic material and reduces the activation energy barrier of bromide ions during the electrocatalytic reaction of ethylene to 2-bromoethanol. At the same time, a rich Ru-O-Co asymmetric site is formed, improving the catalytic activity and selectivity of the electrocatalytic reaction of ethylene to 2-bromoethanol.

[0023] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0024] (1) By a simple ion adsorption method, a cobalt tetroxide nanocage catalyst modified with trace ruthenium is prepared. The preparation method is simple, has good reproducibility, and is suitable for industrial production.

[0025] (2) By the simple ion adsorption method of the present invention, the cobalt tetroxide nanocage catalyst modified with trace ruthenium is obtained, in which the Ru loading is 0.22 - 0.56 wt%, the noble metal loading is small, and it has a cost advantage compared with other noble metal catalysts.

[0026] (3) The cobalt tetroxide nanocage catalyst modified with trace ruthenium prepared in the present invention has a hollow nanocage structure that improves the conductivity and intrinsic electrocatalytic performance of the catalyst. For example, the catalyst has a large current density and a low overpotential within the test potential range, showing excellent electrocatalytic potential.

[0027] (4) In the cobalt tetroxide nanocage catalyst modified with trace ruthenium prepared in the present invention, metallic ruthenium is successfully introduced into the cobalt-based catalyst, forming abundant Ru - O - Co asymmetric active sites, changing the electronic structure of the catalyst such as the electron cloud density and the activation energy of bromide ions in the electrocatalytic oxidation of ethylene to 2 - bromoethanol, and thus improving the catalytic performance of the oxidation of ethylene to 2 - bromoethanol. For example, at 1.4 V vs. RHE, compared with the cobalt tetroxide nanocage catalyst without ruthenium modification, the Faraday efficiency of 2 - bromoethanol increases from 84.4% to 93.9%.

[0028] (5) The present invention realizes the efficient preparation of 2 - bromoethanol, an important chemical and pharmaceutical intermediate, using clean and renewable electric energy, which conforms to the concept of green, environmental - friendly and sustainable development. Description of the Drawings

[0029] Figure 1 SEM image of the cobalt tetroxide nanocage catalyst modified with trace ruthenium prepared in Example 1 of the present invention before calcination.

[0030] Figure 2 TEM image of the cobalt tetroxide nanocage catalyst modified with trace ruthenium prepared in Example 1 of the present invention.

[0031] Figure 3 XRD pattern of the catalyst prepared in Example 1 of the present invention.

[0032] Figure 4 Electrochemical polarization curve of the catalysts prepared in Example 1, Comparative Example 1 and Comparative Example 2 of the present invention in a three - electrode reaction cell with 0.1 M potassium bromide electrolyte.

[0033] Figure 5 Tafel slope diagrams of the catalysts prepared in Example 1 of the present invention, Comparative Example 1, and Comparative Example 2 in a three-electrode reaction cell with 0.1 M potassium bromide electrolyte.

[0034] Figure 6 Faradaic efficiency diagrams of 2-bromoethanol of the catalysts prepared in Example 1 of the present invention, Comparative Example 1, and Comparative Example 2 in a three-electrode reaction cell with 0.1 M potassium bromide electrolyte. Detailed implementation manners

[0035] The present invention will be further described below in conjunction with the accompanying drawings and specific embodiments. It should be understood that these embodiments are only used to illustrate the present invention and not to limit the scope of the present invention. The experimental methods without specific conditions indicated in the following embodiments are usually carried out under conventional conditions or according to the conditions recommended by the manufacturer.

[0036] Example 1

[0037] Preparation steps of a trace ruthenium-modified cobalt tetroxide nanocage catalyst:

[0038] Step 1: Weigh 0.873 g (about 3 mmol) of cobalt nitrate hexahydrate and 0.984 g of dimethylimidazole on an electronic balance, that is, the molar ratio of the addition amounts of cobalt nitrate and dimethylimidazole is 1:4, and dissolve them separately in 30 ml and 10 ml of methanol under magnetic stirring.

[0039] Step 2: Slowly add the above-prepared methanol solution of dimethylimidazole drop by drop to the methanol solution of cobalt nitrate hexahydrate, and react fully for 24 hours under magnetic stirring at a speed of 600 rpm to obtain a turbid purple solution product.

[0040] Step 3: Wash the product in Step 2 successively with methanol and absolute ethanol, filter by suction, and then dry in a vacuum oven at 60 °C for 12 h, take out and grind to obtain the product ZIF67.

[0041] Step 4: Weigh 100 mg of the product ZIF67 in Step 3 on an electronic balance and disperse it fully in 75 ml of ethanol under magnetic stirring. Weigh 8 mg of ruthenium chloride on an electronic balance and dissolve it fully in 5 ml of ethanol under magnetic stirring.

[0042] Step 5: Slowly add the above-prepared ethanol solution of ruthenium chloride drop by drop to the ethanol solution of ZIF67, and react fully for 2 hours under magnetic stirring at a speed of 600 rpm.

[0043] Step 6: Wash the product in Step 2 with absolute ethanol, filter by suction, and then dry in a vacuum oven at 60 °C for 12 h, take out and grind to obtain ruthenium ion-loaded ZIF67, that is, trace ruthenium-modified ZIF67.

[0044] Step 6: Calcinate the product in Step 6 in a muffle furnace at 300 °C for 2 hours to finally obtain a trace ruthenium-modified cobalt tetroxide nanocage catalyst.

[0045] Example 2

[0046] Preparation steps of a trace ruthenium-modified cobalt tetroxide nanocage catalyst:

[0047] Step 1: Weigh 1.746 g (about 6 mmol) of cobalt nitrate hexahydrate and 1.968 g of dimethylimidazole on an electronic balance, that is, the molar ratio of the addition amounts of cobalt nitrate and dimethylimidazole is 1:4. Under magnetic stirring, dissolve them separately in 60 and 20 ml of methanol.

[0048] Step 2: Slowly add the above-prepared methanol solution of dimethylimidazole drop by drop to the methanol solution of cobalt nitrate hexahydrate, and react fully for 24 hours under magnetic stirring at a speed of 600 rpm to obtain a turbid purple solution product.

[0049] Step 3: Wash the product in Step 2 with methanol and absolute ethanol, filter it by suction, and then dry it in a vacuum oven at 60 °C for 12 h. Take it out and grind it to obtain product ZIF67.

[0050] Step 4: Weigh 100 mg of ZIF67 prepared in Step 3 on an electronic balance and disperse it fully in 75 ml of ethanol under magnetic stirring. Weigh 4 mg of ruthenium chloride and dissolve it fully in 5 ml of ethanol under magnetic stirring.

[0051] Step 5: Slowly add the above-prepared ethanol solution of ruthenium chloride drop by drop to the ethanol solution of ZIF67, and react fully for 2 hours under magnetic stirring at a speed of 600 rpm.

[0052] Step 6: Wash the product in Step 2 with absolute ethanol, filter it by suction, and then dry it in a vacuum oven at 60 °C for 12 h. Take it out and grind it to obtain a trace ruthenium-modified ZIF67.

[0053] Step 6: Calcinate the product in Step 6 in a muffle furnace at 350 °C for 2 hours to finally obtain a trace ruthenium-modified cobalt tetroxide nanocage catalyst.

[0054] Example 3

[0055] Preparation steps of a trace ruthenium-modified cobalt tetroxide nanocage catalyst:

[0056] Step 1: Weigh 2.619 g (about 9 mmol) of cobalt nitrate hexahydrate and 2.952 g of dimethylimidazole on an electronic balance, that is, the molar ratio of the addition amounts of cobalt nitrate and dimethylimidazole is 1:4. Under magnetic stirring, dissolve them separately in 90 and 30 ml of methanol.

[0057] Step 2: Slowly and dropwise add the above-prepared methanol solution of 2-methylimidazole into the methanol solution of cobalt nitrate hexahydrate, and react fully for 24 hours under magnetic stirring at a speed of 600 rpm to obtain a turbid purple solution product.

[0058] Step 3: Wash the product in Step 2 with methanol and absolute ethanol, filter it by suction, and then dry it in a vacuum oven at 60 °C for 12 h. Take it out and grind it to obtain the product ZIF67.

[0059] Step 4: Weigh 50 mg of the product ZIF67 in Step 3 on an electronic balance and disperse it fully in 38 ml of ethanol under magnetic stirring. Weigh 8 mg of ruthenium chloride on an electronic balance and dissolve it fully in 2 ml of ethanol under magnetic stirring.

[0060] Step 5: Slowly and dropwise add the above-prepared ethanol solution of ruthenium chloride into the ethanol solution of ZIF67, and react fully for 2 hours under magnetic stirring at a speed of 600 rpm.

[0061] Step 6: Wash the product in Step 2 with absolute ethanol, filter it by suction, and then dry it in a vacuum oven at 60 °C for 12 h. Take it out and grind it to obtain ZIF67 modified with trace ruthenium.

[0062] Step 6: Calcine the product in Step 6 in a muffle furnace at 400 °C for 2 hours to finally obtain a trace ruthenium-modified cobalt tetroxide nanocage catalyst.

[0063] Example 4

[0064] Compared with Example 1, in this example, the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole added in Step 1 was adjusted to 1:2, and the rest was the same.

[0065] Example 5

[0066] Compared with Example 1, in this example, the molar ratio of cobalt nitrate hexahydrate to 2-methylimidazole added in Step 1 was adjusted to 1:3, and the rest was the same.

[0067] Example 6

[0068] Compared with Example 1, in this example, the calcination time in Step 6 was adjusted to 1 h. The rest was the same as in Example 1.

[0069] Example 7

[0070] Compared with Example 1, the first step of this example is as follows: Weigh 0.873 g (about 3 mmol) of cobalt nitrate hexahydrate and 0.984 g of dimethylimidazole on an electronic balance. That is, the molar ratio of the addition amounts of cobalt nitrate and dimethylimidazole is 1:4. Under magnetic stirring, they are respectively dissolved in 90 and 30 ml of methanol. The rest is the same as in Example 1.

[0071] Example 8

[0072] Compared with Example 1, the first step of this example is as follows: Weigh 2.619 g (about 9 mmol) of cobalt nitrate hexahydrate and 2.952 g of dimethylimidazole on an electronic balance. That is, the molar ratio of the addition amounts of cobalt nitrate and dimethylimidazole is 1:4. Under magnetic stirring, they are respectively dissolved in 30 and 10 ml of methanol. The rest is the same as in Example 1.

[0073] Through SEM and TEM analysis, the trace ruthenium-modified cobalt tetroxide nanocage catalysts prepared in each example show a hollow cage-like structure composed of several cobalt tetroxide nanoparticles in terms of microscopic morphology, and ruthenium oxide nanoparticles are loaded on the surface of the cage-like structure; among them, several cobalt tetroxide nanoparticles enclose several hollow polyhedrons, which constitute the cobalt tetroxide nanocage, and ruthenium oxide nanoparticles are loaded on the surface of the cobalt tetroxide nanocage. As Figure 1 and Figure 2 , where Figure 1 is the SEM image of the trace ruthenium-modified cobalt tetroxide nanocage catalyst before calcination prepared in Example 1, that is, the SEM image of the catalyst precursor, trace ruthenium-modified ZIF67, obtained at the end of Step 5 of Example 1;

[0074] Figure 2 The TEM image of the trace ruthenium-modified cobalt tetroxide nanocage catalyst finally prepared in Example 1. From Figure 1 it can be seen that the trace ruthenium-modified ZIF67 before calcination is a regular polyhedron, and several nanoparticles are loaded on the outer surface of ZIF67. These nanoparticles are adsorbed ruthenium ions. Further from Figure 2 it can be seen that after calcination, ZIF67 is transformed into cobalt tetroxide nanoparticles, inheriting the regular polyhedron morphology of the original ZIF67. The regular polyhedron of ZIF67 forms a hollow polyhedron with a framework composed of cobalt tetroxide nanoparticles after calcination, that is, the cobalt tetroxide nanocage; the ruthenium ions originally adsorbed on the surface of ZIF67 are oxidized to ruthenium oxide nanoparticles after calcination and are loaded on the surface of the cage-like structure enclosed by cobalt tetroxide nanoparticles.

[0075] Through XRD detection, it is confirmed that the main phase of the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in each example is Co3O4, and the mainly exposed crystal plane is the Co(311) crystal plane. The trace Ru is not shown in the XRD, and its content is accurately measured by ICP-OES, and the content of ruthenium in the catalyst is 0.22 - 0.56 wt%. For example, Figure 3 records the XRD pattern of the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in Example 1. It can be seen from the figure that the main component of the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in Example 1 is Co3O4. Due to its ultra-low loading amount in the catalyst, the presence of trace Ru is not shown in this XRD. After further detection by ICP-OES, among the components of the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in each example, the mass fraction of ruthenium satisfies the range of 0.22 - 0.56 wt%. For example, in the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in Example 1, the mass fraction of ruthenium element in the catalyst is ~0.41 wt%; in the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in Example 2, the mass fraction of ruthenium element in the catalyst is ~0.22 wt%; in the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in Example 3, the mass fraction of ruthenium element in the catalyst is ~0.56 wt%.

[0076] The trace ruthenium-modified cobalt tetroxide nanocage catalysts prepared in each example are applied to the electrocatalytic oxidation of ethylene to prepare 2-bromoethanol, and all show excellent Faraday efficiency. For example, Application Example 1 below shows the specific application of the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in Example 1 in the electrocatalytic oxidation of ethylene to prepare 2-bromoethanol with a catalyst loading of 0.5 mg cm -2 The following is the specific application situation. For the catalysts prepared in other examples in the electrocatalytic oxidation of ethylene to prepare 2-bromoethanol with a catalyst loading of 0.25 - 1.0 mg cm -2 Under the catalyst loading, the trace ruthenium-modified cobalt tetroxide nanocage catalysts of each example all show application effects comparable to those in Application Example 1 below.

[0077] Application Example 1

[0078] Application of the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in Example 1 as an anode material for the electrocatalytic oxidation of ethylene to prepare 2-bromoethanol, and related test methods and test results.

[0079] Step 1: Weigh 10 mg of the catalyst prepared in Example 1 with an analytical balance. At the same time, take 100 μL of isopropanol and 20 μL of 0.5 wt.% Nafion solution. After uniformly mixing the three, put them into a sample bottle and ultrasonicate for 2 h.

[0080] Step 2: Cut out a 1×3 cm2 For the carbon paper, wind an insulating tape around the middle position for one circle, and leave a space of 1×1 cm 2 to dropwise coat the catalyst. Measure the catalyst solution prepared in the first step and add it dropwise onto the carbon paper in the 1×1 cm 2 area. The catalyst loading is 0.5 mg cm -2 . Dry it at room temperature or under infrared light to obtain the working electrode.

[0081] Step 3: Use Ag / AgCl as the reference electrode and a platinum sheet as the counter electrode. Together with the working electrode, form a three-electrode system and place it in an H-shaped electrolytic cell. Use 0.1 M potassium bromide as the electrolyte solution and conduct tests at different potentials. Analyze the yields of the product 2-bromoethanol and the by-product ethylene glycol through nuclear magnetic resonance hydrogen spectroscopy.

[0082] The application effect of the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in Example 1 is as follows Figures 4 - 6 . Among them Figure 4 is the electrochemical polarization curve of the catalysts prepared in Example 1 (marked as "Example" in the figure), Comparative Example 1, and Comparative Example 2 in a three-electrode reaction cell with 0.1 M potassium bromide electrolyte. It can be seen from the figure that the current density of the trace ruthenium-modified cobalt tetroxide nanocage catalyst prepared in Example 1 at different potentials. At the same potential, this catalyst has the maximum current density, and at the same time its overpotential is the lowest. When the current density reaches 10 mA cm -2 , its overpotential is reduced by 106 mV and 34 mV compared with Comparative Example 1 and Comparative Example 2 respectively, indicating its good conductivity and catalytic potential. Figure 5 is the Tafel slope diagram of the catalysts prepared in Example 1 (marked as "Example" in the figure), Comparative Example 1, and Comparative Example 2 in a three-electrode reaction cell with 0.1 M potassium bromide electrolyte. It can be seen from Figure 5 that the Tafel slope of the catalyst in Example 1 is the smallest, which is 55.9 mV dec -1 , lower than that of Comparative Example 1 (104.4 mV dec -1 ) and Comparative Example 2 (66.3 mV dec -1 ), indicating that its reaction kinetics is the fastest and its catalytic activity is the highest. Figure 6 is the Faraday efficiency diagram of 2-bromoethanol of the catalysts prepared in Example 1 (marked as "Example" in the figure), Comparative Example 1, and Comparative Example 2 in a three-electrode reaction cell with 0.1 M potassium bromide electrolyte. It can be seen from Figure 6It can be seen that the Faraday efficiency of 2-bromoethanol of this catalyst at 1.4 V vs. RHE, compared with Comparative Example 1, the Faraday efficiency of 2-bromoethanol in Example 1 increased from 84.4% in Comparative Example 1 to 93.9%; compared with the ruthenium oxide nanoparticle catalyst with a large noble metal loading in Comparative Example 2, the Faraday efficiency of 2-bromoethanol in Comparative Example 2 was only 80.0%, and the 93.9% Faraday efficiency of Example 1 also showed significant advantages.

[0083] Comparative Example 1

[0084] In this comparative example, a cobalt-based catalyst without noble metal modification, namely a pure cobalt tetroxide nanocage catalyst, was prepared. The preparation steps of the cobalt tetroxide nanocage catalyst are as follows:

[0085] Step 1: Weigh 0.873 g of cobalt nitrate hexahydrate and 0.984 g of dimethylimidazole on an electronic balance, that is, the molar ratio of the addition amounts of cobalt nitrate and dimethylimidazole is 1:4. Under magnetic stirring, they are respectively fully dissolved in 30 and 10 ml of methanol.

[0086] Step 2: Slowly and dropwise add the above-prepared methanol solution of dimethylimidazole to the methanol solution of cobalt nitrate hexahydrate, and react fully for 24 hours under magnetic stirring at a speed of 600 rpm to obtain a turbid purple solution product.

[0087] Step 3: Wash the product in Step 2 with methanol and absolute ethanol, filter by suction, and then dry it in a vacuum oven at 60 °C for 12 h, take it out and grind it to obtain the product ZIF67.

[0088] Step 4: Calcinate the product ZIF67 in Step 3 in a muffle furnace at 300 °C for 2 hours to finally obtain the cobalt tetroxide nanocage catalyst of this comparative example.

[0089] The cobalt tetroxide nanocage catalyst prepared in Comparative Example 1 was applied to the electrocatalytic oxidation of ethylene to prepare 2-bromoethanol. This cobalt-based catalyst was used as the anode material for the electrocatalytic oxidation of ethylene to prepare 2-bromoethanol. Except for the different anode materials, other method steps and parameters were the same as those in Application Example 1. The test showed that, as Figure 4 , compared with the cobalt-based catalyst in Comparative Example 1 and the cobalt tetroxide nanocage catalyst modified with trace ruthenium in Example 1, the current density in the test interval of the cobalt-based catalyst in Comparative Example 1 was lower than that of the cobalt tetroxide nanocage catalyst modified with trace ruthenium, and its conductivity and catalytic potential were significantly lower than those of the cobalt tetroxide nanocage catalyst modified with trace ruthenium. As Figure 5 , compared with the cobalt-based catalyst in Comparative Example 1 and the cobalt tetroxide nanocage catalyst modified with trace ruthenium in Example 1, the Tafel slope of the cobalt-based catalyst in Comparative Example 1 was larger, indicating that its reaction kinetics was slow. As Figure 6The test results show that when the cobalt-based catalyst of Comparative Example 1 is used as the anode material, the Faraday efficiency of electrocatalytic ethylene oxidation to prepare 2-bromoethanol is significantly lower than that of Example 1. At 1.4 V vs. RHE, the Faraday efficiencies of 2-bromoethanol in Comparative Example 1 and Example 1 are 84.4% and 93.9% respectively.

[0090] Comparative Example 2

[0091] The commercially available ruthenium oxide nanoparticles were applied as Comparative Example 2 to electrocatalytic ethylene oxidation to prepare 2-bromoethanol. Ruthenium oxide was used as the anode material for electrocatalytic ethylene oxidation to prepare 2-bromoethanol. Except for the different anode materials, the other method steps and parameters were the same as those in Application Example 1. The test results showed that Figure 4 , compared with the trace ruthenium-modified cobalt tetroxide nanocage catalyst of Example 1, the current density of the commercial ruthenium oxide catalyst of Comparative Example 2 was lower than that of the trace ruthenium-modified cobalt tetroxide nanocage catalyst in the test range, and it was significantly lower than the trace ruthenium-modified cobalt tetroxide nanocage catalyst in terms of conductivity and catalytic potential. As Figure 5 the test results in showed that its reaction kinetics was also relatively slow. As Figure 6 the test results showed that when the commercial ruthenium oxide catalyst of Comparative Example 2 was used as the anode material, the Faraday efficiency of electrocatalytic ethylene oxidation to prepare 2-bromoethanol was about 80.0%, and its catalytic performance was significantly lower than that of Example 1. It shows that the trace ruthenium-modified cobalt tetroxide nanocage catalyst of Example 1 can combine the advantages of cost and performance.

[0092] It should be noted that the above specific implementation methods have described the technical solutions and application results of the present invention in detail. Please understand that the above examples are only the most preferred examples and are not used to limit the present invention. Modifications or equivalent replacements made by relevant technicians within the core theory scope of the present invention should all fall within the protection scope of the present invention.

Claims

1. A trace ruthenium-modified cobalt-based nanocage catalyst, characterized in that: The trace ruthenium-modified cobalt-based nanocage catalyst is a trace ruthenium-modified cobalt tetroxide nanocage catalyst; The trace ruthenium-modified cobalt tetroxide nanocage catalyst is composed of two components, cobalt tetroxide and trace ruthenium oxide; The microscopic morphology of the trace ruthenium-modified cobalt tetroxide nanocage catalyst is as follows: several cobalt tetroxide nanoparticles form a framework and enclose several hollow polyhedra, that is, the cobalt tetroxide nanocage, and several ruthenium oxide nanoparticles are dispersedly adsorbed on the surface of the cobalt tetroxide nanocage.

2. The trace ruthenium-modified cobalt-based nanocage catalyst according to claim 1, characterized in that: The ruthenium loading of the catalyst is 0.22 - 0.56 wt%, and the ruthenium loading refers to the mass percentage of ruthenium element contained in the catalyst in the catalyst.

3. A method for preparing a trace ruthenium-modified cobalt-based nanocage catalyst according to claim 1 or 2, characterized in that, The ion adsorption method is adopted, and the steps are as follows: 1) Cobalt nitrate hexahydrate and dimethylimidazole are respectively added to methanol, and continuously stirred until completely dissolved to obtain a methanol solution of cobalt nitrate hexahydrate and a methanol solution of dimethylimidazole respectively; 2) The above-mentioned methanol solution of dimethylimidazole is gradually added dropwise to the methanol solution of cobalt nitrate hexahydrate, and stirred at room temperature to obtain a turbid purple solution as the product; 3) The product obtained in step 2) is washed successively with methanol and absolute ethanol, filtered by suction, dried in a vacuum oven, and ground to obtain the precursor ZIF67; 4) The precursor ZIF67 and ruthenium chloride are respectively added to ethanol, and continuously stirred until evenly dispersed to obtain an ethanol solution of ruthenium chloride and an ethanol solution containing ZIF67 respectively; 5) The ethanol solution of ruthenium chloride is gradually added dropwise to the ethanol solution containing ZIF67, and fully stirred to make the ruthenium ions in the solution fully adsorbed on the surface of ZIF67, and then washed with absolute ethanol, filtered by suction, dried in a vacuum oven, and ground to obtain trace ruthenium-modified ZIF67; 6) The ruthenium-modified ZIF67 is placed in a muffle furnace and calcined to obtain the trace ruthenium-modified cobalt tetroxide nanocage catalyst.

4. The preparation method of a trace ruthenium-modified cobalt-based nanocage catalyst according to claim 3, characterized in that: In step 1), the addition amounts of cobalt nitrate hexahydrate and dimethylimidazole satisfy a molar ratio of 1:2 to 1:

4.

5. The preparation method of a trace ruthenium-modified cobalt-based nanocage catalyst according to claim 3, characterized in that: The total volume of methanol used in the methanol solution of cobalt nitrate hexahydrate and the methanol solution of dimethylimidazole formed in step 1) satisfies: relative to the molar amount of cobalt nitrate hexahydrate added in step (1), it is in a ratio of 40 - 120 mL: 3 - 9 mmol.

6. The preparation method of a trace ruthenium-modified cobalt-based nanocage catalyst according to claim 3, characterized in that: In step 4), the added mass of ruthenium chloride is 4 - 16 wt% of the added mass of ZIF67.

7. The preparation method of a trace ruthenium-modified cobalt-based nanocage catalyst according to claim 3, characterized in that: In step 6), in order to ensure the full oxidation of the catalyst precursor, it is selected to be calcined in a muffle furnace at a temperature of 300 - 400 °C for 1 - 2 hours.

8. The application of the trace ruthenium-modified cobalt-based nanocage catalyst according to claim 1 or 2, wherein the catalyst is applied to electrocatalytically prepare 2-bromoethanol from ethylene.

9. Use of a cobalt-based nanocage catalyst modified with trace ruthenium according to claim 8, characterized in that: Attach the trace ruthenium-modified cobalt tetroxide nanocage catalyst to the carbon paper as the working electrode, use potassium bromide solution as the electrolyte, Ag / AgCl as the reference electrode, and a platinum sheet as the counter electrode to form a three-electrode system for the electrocatalytic reaction of ethylene to 2-bromoethanol in an H-type electrolytic cell.

10. Use of a cobalt-based nanocage catalyst modified with trace ruthenium according to claim 8, characterized in that: The loading amount of the trace ruthenium-modified cobalt tetroxide nanocage catalyst attached to the carbon paper is 0.25 - 1.0 mg cm -2 .

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