A confined ruthenium single-atom catalyst, its preparation method, and its application in the hydrochlorination of acetylene.

Abstract

This invention relates to a confined ruthenium single-atom catalyst, its preparation method, and its application in the hydrochlorination of acetylene. The catalyst primarily consists of ruthenium single atoms as active sites, supported by a covalent organic framework linked by amide bonds, wherein the ruthenium single atoms account for 0.1% to 1.0% of the catalyst's weight. The catalyst preparation mainly involves three steps: 1) preparation of a nitrogen-containing covalent organic framework support; 2) mixing the support prepared in step 1) with a ruthenium source in a solvent, and loading the ruthenium active species onto the support through stirring, centrifugation, filtration, and drying; 3) subjecting the ruthenium single-atom catalyst prepared in step 2) to a simple dechlorination step to obtain the low-coordinate chlorine-modified ruthenium single-atom catalyst. Compared with existing technologies, this invention, by confining the ruthenium single-atom catalyst within a covalent organic framework, suppresses the migration and loss of catalytic active sites during the reaction.

Description

Technical Field

[0001] This invention relates to the fields of catalyst preparation and green chemical technology, and in particular to a confined ruthenium single-atom catalyst, its preparation method, and its application in the acetylene hydrochlorination reaction. Background Technology

[0002] Polyvinyl chloride (PVC) is the world's second most widely used general-purpose resin, with extensive applications in industrial production, communication technology, agriculture, and construction engineering, making it an indispensable basic material in the modern chemical industry. Vinyl chloride monomer (VCM), the core raw material for PVC synthesis, is typically produced industrially using three main process routes: ethane oxychlorination, ethylene oxychlorination, and acetylene hydrochlorination. Considering my country's energy resources are characterized by abundant coal, scarce oil, and limited gas, over 70% of domestic vinyl chloride production currently relies on the acetylene hydrochlorination process. This process commonly uses activated carbon-supported mercuric chloride (HgCl2 / AC) as a catalyst; however, the volatility and high toxicity of mercury severely impact the environment, hindering the sustainable development of this technology. Furthermore, the international Minamata Convention on Mercury and the domestic "Opinions on Further Strengthening the Prevention and Control of Heavy Metal Pollution" explicitly prohibit the use of mercury-containing catalysts in PVC manufacturing from 2020 onwards. Faced with these dual international and domestic challenges, developing efficient and stable mercury-free catalysts has become a key issue in promoting the development of the acetylene hydrochlorination process for vinyl chloride production.

[0003] Currently, research on catalysts for the hydrochlorination of acetylene mainly focuses on two types of materials: precious metals (such as gold, platinum, palladium, ruthenium, rhodium, iridium, etc.) and non-precious metals (such as tin, bismuth, manganese, copper, zinc, etc.). Precious metals are favored by researchers due to the following advantages: (1) high catalytic activity and stability; (2) easy formation of hybrid orbitals, thereby accepting lone pairs of electrons provided by heteroatoms; (3) their unsaturated d orbitals are conducive to forming covalent bonds with heteroatoms. Although the international academic community generally regards gold-based catalysts as the most promising mercury-free alternative, their limited reserves in the Earth's crust lead to high costs, which restricts their large-scale industrial promotion. In contrast, ruthenium metal is not only more affordable, but also has many similarities with gold in terms of catalytic performance, and is therefore regarded as one of the important development directions for replacing mercury catalysts. Currently, commonly used ruthenium-based catalysts generally use activated carbon and nitrogen-containing carbon with open sites as supports, and the above supports usually expose the ruthenium active components to the catalytic environment. Due to the harsh reaction conditions of the acetylene hydrochlorination reaction, ruthenium metal sites are gradually chlorinated in the hydrogen chloride gas stream, inevitably leading to their gradual loss during the reaction. Therefore, it is currently urgent to find a way to anchor the ruthenium active sites in a confined support to prevent their loss and to promote their long-term stable operation in the acetylene hydrochlorination reaction.

[0004] Patent application CN202310645290.4 discloses a ruthenium-based catalyst modified with pyridine ligands for the hydrochlorination of acetylene. This catalyst uses activated carbon as a catalyst support. The pyridine ligands are one or more selected from pyridine, 2-methylpyridine, 3-methylpyridine, 4-methylpyridine, 3-ethylpyridine, 3-isobutylpyridine, 4-ethylpyridine, 4-tert-butylpyridine, and 3,5-dimethylpyridine. The molar ratio of ruthenium salt to organic ligand is 1:0.5~10, and ruthenium accounts for 0.05~1.0 wt% of the total catalyst weight. This invention solves the problem of easy aggregation of active sites in current ruthenium-based catalysts, thereby effectively improving the catalytic activity of the catalyst. Furthermore, the various organic ligands added to this catalyst have a short-term (<100 h) stabilizing effect on the active species, but significant metal loss still occurs during long-term operation (>100 h) of the ruthenium-based catalyst.

[0005] Patent application CN202411278992.4 discloses a ruthenium-erbium-cerium trimetallic composite catalyst for the hydrochlorination of acetylene. This catalyst uses alumina as a support and ruthenium, erbium, and cerium as active components. The porous alumina has an average particle size of 3–4 mm and a specific surface area of ​​1000–1200 m². 2 / g; and the loading of ruthenium relative to the support is 0.5~0.6 wt.%. This invention improves the activity and stability of the catalyst by adding erbium and cerium, while simultaneously reducing the ruthenium content to below 1 wt.%, effectively lowering the catalyst preparation cost. However, the principle by which this catalyst stabilizes ruthenium metal and prevents its loss relies on the synergistic effect of erbium and cerium, and does not fundamentally solve the problem of ruthenium-based catalysts easily losing ruthenium during the reaction.

[0006] Patent application CN116139904B discloses a ruthenium-indium composite catalyst, its preparation method, and its application. The catalyst is prepared through the following steps: S1: Preparation of the support: A nitrogen-containing compound is dissolved in an acidic aqueous solution and cooled; subsequently, the mixture is added to a pre-cooled ammonium persulfate solution to complete the polymerization process, followed by filtration and washing; the resulting product is vacuum dried and then carbonized to obtain a nitrogen-containing activated carbon support; S2: Preparation of the ruthenium-indium dual-active-site composite material: A formic acid compound and an indium source are dissolved in an organic solvent and stirred in an oil bath. After heating, washing, centrifugation, and vacuum drying, the indium-containing organometallic framework material is collected. A ruthenium source is added to the nitrogen-containing activated carbon support prepared in step S1 and mixed. The mixture is then subjected to in-situ precipitation and vacuum drying to synthesize a ruthenium-doped nitrogen-containing activated carbon material. The prepared indium-containing organometallic framework material and the prepared ruthenium-doped nitrogen-containing activated carbon material are homogeneously mixed to form a ruthenium-indium dual-active-site composite material. S3: Preparation of the ruthenium-indium composite catalyst: The ruthenium-indium dual-active-site composite material prepared in step S2 is calcined to obtain the ruthenium-indium composite catalyst. This catalyst overcomes the Lewis strong acidity of ruthenium metal itself, fundamentally solving the problem of poor catalytic activity and stability caused by large-scale carbon deposition during the reaction. However, this technology uses open-type nitrogen-containing activated carbon, making ruthenium sites easily exposed and lost. The ruthenium single atoms are fixed through pore confinement and amide bond anchoring. Competition among the ruthenium-indium bimetallic composite active sites easily leads to ruthenium species aggregation.

[0007] Patent application CN119899082B discloses a method for using a low-content ruthenium-based catalyst modified with nitrogen and oxygen ligands for the hydrochlorination reaction of acetylene. The catalyst is prepared by the following steps: (1) Preparing the precursor solution: First, weigh ruthenium trichloride solid, dissolve it in distilled water, shake and sonicate, and then dilute it to a flask to obtain RuCl3 mother liquor; (2) Dissolve 2-pyridinecarboxylic acid in H2O for dispersion, stir at room temperature, then add hydrochloric acid, stir at room temperature to obtain 2-pyridinecarboxylic acid salt, and finally add RuCl3 mother liquor, cover the beaker with a sealing film, then cover it with tin foil, and stir at room temperature; (3) Preparing the catalyst by impregnation: Spread activated carbon evenly in a mortar; take the solution obtained in step (2) and add it evenly to the activated carbon support, and grind the catalyst thoroughly in a clockwise direction until the surface is smooth; (4) Place the ground catalyst in a forced-air drying oven to dry. The catalyst significantly improves the catalytic activity and stability of the catalyst through the interaction between nitrogen (oxygen) and active ruthenium species. However, its core principle is to stabilize the active species by forming a coordination bond between the nitrogen-oxygen ligand (2-pyridine carboxylate) and ruthenium. Its stability depends on the coordination between the ligand and ruthenium, focusing on short-term stability under low loading, but it cannot solve the problem of excessive chlorination loss of ruthenium sites.

[0008] Therefore, there is an urgent need in this field for a catalyst that can solve the cost and long-term stability problems in the acetylene hydrochlorination reaction. Summary of the Invention

[0009] The purpose of this invention is to solve at least one of the above-mentioned problems by providing a confined ruthenium single-atom catalyst, its preparation method, and its application in the acetylene hydrochlorination reaction.

[0010] The objective of this invention can be achieved through the following technical solutions: The first objective of this invention is to overcome the technical difficulties of existing ruthenium-based catalysts and provide a ruthenium single-atom catalyst with high catalytic activity and strong catalytic stability for the synthesis of vinyl chloride from acetylene hydrochlorination. This catalyst mainly consists of ruthenium single atoms as active sites and a covalent organic framework linked by amide bonds as a support. Specifically, it includes the following components: a nitrogen-containing covalent organic framework material as a support, on which 0.1~3 wt% of ruthenium single-atom active sites are loaded.

[0011] The second objective of this invention is to provide a method for preparing a low-coordinate chlorine-modified confined ruthenium single-atom catalyst for the synthesis of vinyl chloride from acetylene hydrochlorination, comprising the following steps: 1) Preparation of nitrogen-containing covalent organic framework: The nitrogen-containing precursor is added to a reactor containing organic solvent a, and after ultrasonic treatment, an organic acid catalyst is added; the resulting mixture is degassed by multiple freeze-vacuum-thaw cycles and then sealed (generally 2 to 4 freeze-vacuum-thaw cycles), and then heated in an oven; after cooling to room temperature, the supernatant is filtered off, and the solid precipitate is washed with a cleaning solvent until the solvent is colorless and then vacuum dried to obtain the nitrogen-containing covalent organic framework; 2) Preparation of confined covalent organic framework ruthenium single-atom material: The nitrogen-containing covalent organic framework support prepared in step 1) above is mixed with a ruthenium source solution, and ruthenium-doped nitrogen-containing covalent organic framework material is synthesized by in-situ precipitation followed by vacuum drying; finally, the covalent organic framework material is washed with a washing reagent 4 to 6 times to obtain confined covalent organic framework ruthenium single-atom material. 3) Preparation of confined ruthenium single-atom catalyst: The confined covalent organic framework ruthenium single-atom material prepared in step 2) is dispersed in organic solvent b under ice bath conditions. Sodium borohydride solution is added under vacuum conditions and stirred to achieve dechlorination treatment, and finally confined ruthenium single-atom catalyst is synthesized.

[0012] Furthermore, the confined ruthenium single-atom catalyst comprises a nitrogen-containing covalent organic framework material as a support, on which 0.1~3 wt% of ruthenium single-atom active sites are loaded; during the synthesis of the ruthenium single-atom catalyst, the nitrogen defects and regular covalent organic framework pore structure on the support enable the metallic ruthenium to be firmly fixed in the pores of the support, thereby completing the anchoring of the active component.

[0013] Further, the nitrogen-containing precursor in step 1) comprises 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline in a molar ratio of 1:(0.5~5); The organic solvent a is one or more selected from o-xylene, m-xylene, p-xylene, methanol, ethanol, propanol, and butanol; The organic acid catalyst is one or more of formic acid, acetic acid, propionic acid, and butyric acid; The mass ratio of the nitrogen-containing precursor, organic solvent a, and organic acid catalyst is 1:15~25:0.5~1.5, preferably 1:20:1; The cleaning solvent used for solid-phase precipitation washing is at least one of methanol, ethanol, tetrahydrofuran, dioxane, acetonitrile, acetone, and diethyl ether.

[0014] Furthermore, in step 1), the freezing temperature of the freezing-vacuum-thawing cycle is -190~-170 ℃, preferably -180 ℃, the vacuum degree is 15~25 Pa, preferably 20 Pa, and the thawing temperature is room temperature.

[0015] The oven temperature is 100~150 ℃, and the heating time is 100~200 h.

[0016] Further, the ruthenium source in step 2) is one of ruthenium oxide, ruthenium trichloride, ruthenium acetylacetone, ruthenium acetate, and ruthenium carbonyl chloride, and the molar ratio of the nitrogen-containing covalent organic framework support to the ruthenium source is 1:(1~5). The cleaning agent used for cleaning covalent organic framework materials is a mixture of at least two of N,N-dimethylformamide, ethanol, methanol, acetonitrile, acetone, and diethyl ether.

[0017] The in-situ deposition temperature described in step 2) is 50~100 ℃. In-situ deposition utilizes the nitrogen defects of the nitrogen-containing covalent organic framework carrier to first deposit ruthenium on its surface.

[0018] Furthermore, in step 3), organic solvent b is one of tetrahydrofuran, ethanol, methanol, acetonitrile, acetone, and diethyl ether; The concentration of the sodium borohydride solution is 0.01~0.1 mmol / L, preferably 0.05 mmol / L; the sodium borohydride solution is added at a rate of 0.1~2.0 mL / min.

[0019] Furthermore, in steps 1) to 2), the vacuum drying temperature is 50 to 100 ℃, and the vacuum drying time is 24 to 72 h.

[0020] Furthermore, during the synthesis of ruthenium single-atom catalysts, the nitrogen defects and regular covalent organic framework pore structure on the support allow metallic ruthenium to be firmly fixed within the support pores, resulting in confined ruthenium single-atom catalysts.

[0021] The third objective of this invention is to provide an application of a confined ruthenium single-atom catalyst for the synthesis of vinyl chloride from acetylene hydrochlorination.

[0022] Furthermore, the acetylene hydrochlorination reaction is carried out according to the following steps: Acetylene and hydrogen chloride, the reactant gases, are introduced into a fixed-bed reactor containing a catalyst at a molar ratio of 1:(1~1.2). The amount of catalyst used is 1~3g. The bed temperature is controlled at 160~200℃ and the acetylene space velocity is 160~200h⁻¹. -1 The reaction pressure is atmospheric pressure.

[0023] Compared with the prior art, the present invention has the following beneficial effects: 1. The catalyst of this invention uses a covalent organic framework linked by amide bonds as a confined support and a single ruthenium atom as the active site, and is designed to address the problem of excessive chlorination loss of ruthenium active sites. A confined ruthenium single-atom catalyst with low coordination chlorine modification is prepared by dechlorination treatment. Long-term stability is achieved by relying on the confined anchoring of the support and the regulation of the chemical environment of the active site. The catalyst is designed from the perspective of overcoming the easy loss of ruthenium metal during the catalytic reaction, and fundamentally solves the problem of poor catalytic activity and stability caused by large-scale loss of ruthenium sites due to excessive chlorination during the reaction.

[0024] 2. The ruthenium single-atom composite catalyst of the present invention promotes high dispersion of active components due to the introduction of covalent organic framework, and the regular pore structure and strong anchoring sites make it difficult to lose. At the same time, the strong interaction between ruthenium and the support significantly promotes electron separation and electron transfer during the reaction process, and inhibits the large-scale reduction of high-valence ruthenium to ensure its long-term catalysis.

[0025] 3. The catalyst prepared in this invention exhibits good catalytic activity and vinyl chloride selectivity, as well as excellent stability. In the reaction of acetylene hydrochlorination to vinyl chloride, the vinyl chloride selectivity remains above 99%, and the conversion rate reaches 98.31%. Compared with other catalysts under the same reaction conditions, the conversion rate of acetylene remains essentially unchanged after long-term reaction. It is expected to be a direct replacement for mercury-based catalysts in hydrochlorination reactions, reducing environmental problems caused by mercury pollution. Its preparation conditions are milder, requiring no high-temperature calcination, resulting in lower energy consumption and avoiding ruthenium species aggregation, while achieving higher catalytic efficiency (conversion rate 98.31%). Detailed Implementation

[0026] The present invention will now be described in detail with reference to specific embodiments. These embodiments are based on the technical solution of the present invention and provide detailed implementation methods and specific operating procedures. However, the scope of protection of the present invention is not limited to the following embodiments.

[0027] For simplicity, this application only explicitly discloses some numerical ranges. However, any lower limit can be combined with any upper limit to form a range not explicitly stated; and any lower limit can be combined with other lower limits to form a range not explicitly stated, just as any upper limit can be combined with any other upper limit to form a range not explicitly stated. Furthermore, although not explicitly stated, each point or individual value between the endpoints of a range is included within that range. Therefore, each point or individual value can be used as its own lower or upper limit and combined with any other point or individual value, or combined with other lower or upper limits, to form a range not explicitly stated. In the description of this application, it should be noted that, unless otherwise stated, "above" includes the stated number, and "multiple" in "one or more" means two or more.

[0028] The foregoing description of this application is not intended to describe every disclosed implementation or method. Instead, the following description provides more specific examples of exemplary embodiments. Throughout the application, guidance is provided through a series of embodiments that can be used in various combinations. The examples listed are representative only and should not be construed as exhaustive.

[0029] Numerous details are explored in the following description to provide a more thorough explanation of embodiments of this application; however, it will be apparent to those skilled in the art that embodiments of this application may be practiced without these specific details.

[0030] To address the issue of ruthenium-based catalysts being easily lost during reactions, this invention designs a novel catalyst, primarily composed of ruthenium single atoms as active sites, supported by a covalent organic framework linked by amide bonds, wherein the ruthenium single atoms account for 0.1% to 1.0% of the catalyst weight. The catalyst preparation mainly involves three steps: 1) preparation of a nitrogen-containing covalent organic framework support; 2) mixing the support prepared in step 1) with ruthenium-based solvents, and loading the ruthenium active species onto the support through stirring, centrifugation, filtration, and drying; 3) subjecting the ruthenium single-atom catalyst prepared in step 2) to a simple dechlorination step to obtain the low-coordinate chlorine-modified ruthenium single-atom catalyst.

[0031] This invention promotes high dispersion of the active component by introducing a covalent organic framework. The regular pore structure and strong anchoring sites prevent leaching. Simultaneously, the strong interaction between ruthenium and the support significantly promotes electron separation and transfer during the reaction, inhibiting the large-scale reduction of high-valence ruthenium to ensure long-term catalysis. The catalyst is designed to overcome the tendency of ruthenium metal to leak during catalytic reactions, fundamentally solving the problem of poor catalytic activity and stability caused by large-scale ruthenium loss due to excessive chlorination of ruthenium sites during the reaction. The catalyst prepared in this application exhibits good catalytic activity and vinyl chloride selectivity, and demonstrates excellent stability. Compared with other catalysts under the same reaction conditions, the acetylene conversion rate remains essentially unchanged after long-term reaction. In the catalytic hydrochlorination of acetylene, the vinyl chloride selectivity remains above 99%, and the conversion rate reaches 98.31%. Furthermore, it shows promise as a direct alternative to mercury-based catalysts for hydrochlorination, reducing environmental problems caused by mercury pollution.

[0032] To further understand the present invention, the following embodiments are provided. It is worth noting that, unless otherwise specified, all raw materials used in the present invention are commercially available; and all methods and equipment used are common in the art. In the embodiments, 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine was sourced from Sinopharm Chemical Reagent Co., Ltd.; and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline was sourced from Sinopharm Chemical Reagent Co., Ltd.

[0033] Example 1 (1) Preparation of nitrogen-containing covalent organic framework support: A nitrogen-containing precursor (in this example, 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline in a molar ratio of 1:1) was placed in a glass tube containing organic solvent a (in this example, p-xylene and methanol in a volume ratio of 1:5). After ultrasonic treatment, an organic acid catalyst (in this example, a 6 M acetic acid solution) was added to the tube, so that the mass ratio of nitrogen-containing precursor, organic solvent a, and organic acid catalyst was 1:20:1. The resulting mixture was degassed by three cycles of freezing (-180℃) - vacuum (20 Pa) - thawing (room temperature) and then sealed, and subsequently heated in an oven at 120℃ for 150 h. After cooling to room temperature, the supernatant was filtered off, and the solid precipitate was repeatedly washed with methanol until the solvent was colorless and then dried under vacuum (60 °C, 72 h) to obtain a nitrogen-containing covalent organic framework support. (2) Preparation of confined covalent organic framework ruthenium single-atom material: The nitrogen-containing covalent organic framework support prepared in step 1) above was mixed with RuCl3 solution in a 1:1 molar ratio. Ruthenium-doped nitrogen-containing covalent organic framework material was synthesized by in-situ precipitation followed by vacuum drying. Finally, the nitrogen-containing covalent organic framework material was washed 5 times with methanol and ethanol (volume ratio of 1:1) to obtain confined covalent organic framework ruthenium single-atom material. (3) Preparation of confined ruthenium single-atom catalyst: The confined covalent organic framework ruthenium single-atom material prepared in step 2) was dispersed in methanol under ice bath conditions. 0.05 mmol / L NaBH4 solution was added under vacuum at a rate of 0.1~2.0 mL / min and stirred for 2 h to achieve dechlorination treatment, and finally the confined ruthenium single-atom catalyst was synthesized.

[0034] Example 2 The molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetraphenyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline was adjusted to 1:2, and the rest was the same as in Example 1, as detailed below: (1) Preparation of nitrogen-containing covalent organic framework support: A nitrogen-containing precursor (in this example, 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline in a molar ratio of 1:2) was added to a glass tube containing organic solvent a (p-xylene and methanol in a volume ratio of 1:5). After ultrasonic treatment, an organic acid catalyst (6 M acetic acid solution) was added to the tube to make the mass ratio of nitrogen-containing precursor, organic solvent a and organic acid catalyst 1:20:1. The resulting mixture was degassed by three cycles of freezing (-180℃)-vacuum (20 Pa)-thawing (room temperature) and then sealed, and subsequently heated in an oven at 120℃ for 150 h. After cooling to room temperature, the supernatant was filtered off, and the solid precipitate was repeatedly washed with methanol until the solvent was colorless and then dried under vacuum (60 °C, 72 h) to obtain a nitrogen-containing covalent organic framework support. (2) Preparation of confined covalent organic framework ruthenium single-atom material: The nitrogen-containing covalent organic framework support prepared in step 1) above was mixed with RuCl3 solution in a 1:1 molar ratio, and ruthenium-doped nitrogen-containing covalent organic framework material was synthesized by in-situ precipitation followed by vacuum drying; finally, the covalent organic framework material was washed 5 times with methanol and ethanol (volume ratio of 1:1) to obtain confined covalent organic framework ruthenium single-atom material. (3) Preparation of confined ruthenium single-atom catalyst: The confined covalent organic framework ruthenium single-atom material prepared in step 2) was dispersed in methanol under ice bath conditions. 0.05 mmol / L NaBH4 solution was added under vacuum at a rate of 0.1~2.0 mL / min and stirred for 2 h to achieve dechlorination treatment, and finally the confined ruthenium single-atom catalyst was synthesized.

[0035] Example 3 The molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline was adjusted to 1:3, and the rest was basically the same as in Example 1, as detailed below: (1) Preparation of nitrogen-containing covalent organic framework support: A nitrogen-containing precursor (in this example, 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline in a molar ratio of 1:3) was added to a glass tube containing organic solvent a (p-xylene and methanol in a volume ratio of 1:5). After ultrasonic treatment, an organic acid catalyst (6 M acetic acid solution) was added to the tube, so that the mass ratio of nitrogen-containing precursor, organic solvent a and organic acid catalyst was 1:20:1. The mixture was degassed by three cycles of freezing (-180℃)-vacuum (20 Pa)-thawing (room temperature) and then sealed, and subsequently heated in an oven at 120℃ for 150 h. After cooling to room temperature, the supernatant was filtered off, and the solid precipitate was repeatedly washed with methanol until the solvent was colorless and then dried under vacuum (60 °C, 72 h) to obtain a nitrogen-containing covalent organic framework support. (2) Preparation of confined covalent organic framework ruthenium single-atom material: The nitrogen-containing covalent organic framework support prepared in step 1) above was mixed with ruthenium acetylacetone solution in a 1:1 molar ratio. The ruthenium-doped nitrogen-containing covalent organic framework material was synthesized by in-situ precipitation followed by vacuum drying. Finally, the covalent organic framework material was washed 5 times with methanol and ethanol (volume ratio of 1:1) to obtain confined covalent organic framework ruthenium single-atom material. (3) Preparation of confined ruthenium single-atom catalyst: The confined covalent organic framework ruthenium single-atom material prepared in step 2) was dispersed in methanol under ice bath conditions. 0.05 mmol / L NaBH4 solution was added under vacuum at a rate of 0.1~2.0 mL / min and stirred for 2 h to achieve dechlorination treatment, and finally the confined ruthenium single-atom catalyst was synthesized.

[0036] Example 4 The molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline was adjusted to 1:4, and the rest was basically the same as in Example 1, as detailed below: (1) Preparation of nitrogen-containing covalent organic framework support: A nitrogen-containing precursor (in this example, 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline in a molar ratio of 1:4) was added to a glass tube containing organic solvent a (p-xylene and methanol in a volume ratio of 1:5). After ultrasonic treatment, an organic acid catalyst (6 M acetic acid solution) was added to the tube, so that the mass ratio of nitrogen-containing precursor, organic solvent a and organic acid catalyst was 1:20:1. The resulting mixture was degassed by three cycles of freezing (-180℃)-vacuum (20 Pa)-thawing (room temperature) and then sealed, and subsequently heated in an oven at 120℃ for 150 h. After cooling to room temperature, the supernatant was filtered off, and the solid precipitate was repeatedly washed with methanol until the solvent was colorless and then dried under vacuum (60 °C, 72 h) to obtain a nitrogen-containing covalent organic framework support. (2) Preparation of confined covalent organic framework ruthenium single-atom material: The nitrogen-containing covalent organic framework support prepared in step 1) above was mixed with ruthenium acetylacetone solution in a 1:1 molar ratio. The ruthenium-doped nitrogen-containing covalent organic framework material was synthesized by in-situ precipitation followed by vacuum drying. Finally, the covalent organic framework material was washed 5 times with methanol and ethanol (volume ratio of 1:1) to obtain confined covalent organic framework ruthenium single-atom material. (3) Preparation of confined ruthenium single-atom catalyst: The confined covalent organic framework ruthenium single-atom material prepared in step 2) was dispersed in methanol under ice bath conditions. 0.05 mmol / L NaBH4 solution was added under vacuum at a rate of 0.1~2.0 mL / min and stirred for 2 h to achieve dechlorination treatment, and finally the confined ruthenium single-atom catalyst was synthesized.

[0037] Example 5 The molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline was adjusted to 1:5, and the rest was basically the same as in Example 1, as detailed below: (1) Preparation of nitrogen-containing covalent organic framework support: A nitrogen-containing precursor (in this example, 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline in a molar ratio of 1:5) was added to a glass tube containing organic solvent a (p-xylene and methanol in a volume ratio of 1:5). After ultrasonic treatment, an organic acid catalyst (6 M acetic acid solution) was added to the tube to make the mass ratio of nitrogen-containing precursor, organic solvent a and organic acid catalyst 1:20:1. The resulting mixture was degassed by three cycles of freezing (-180℃)-vacuum (20 Pa)-thawing (room temperature) and then sealed, and subsequently heated in an oven at 120℃ for 150 h. After cooling to room temperature, the supernatant was filtered off, and the solid precipitate was repeatedly washed with methanol until the solvent was colorless and then dried under vacuum (60 °C, 72 h) to obtain a nitrogen-containing covalent organic framework support. (2) Preparation of confined covalent organic framework ruthenium single-atom material: The nitrogen-containing covalent organic framework support prepared in step 1) above was mixed with ruthenium nitrate solution in a 1:1 molar ratio. The ruthenium-doped nitrogen-containing covalent organic framework material was synthesized by in-situ precipitation followed by vacuum drying. Finally, the covalent organic framework material was washed 5 times with methanol and ethanol (volume ratio of 1:1) to obtain confined covalent organic framework ruthenium single-atom material. (3) Preparation of confined ruthenium single-atom catalyst: The confined covalent organic framework ruthenium single-atom material prepared in step 2) was dispersed in methanol under ice bath conditions. 0.05 mmol / L NaBH4 solution was added under vacuum at a rate of 0.1~2.0 mL / min and stirred for 2 h to achieve dechlorination treatment, and finally the confined ruthenium single-atom catalyst was synthesized.

[0038] Comparative Example 1 The molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetraphenyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline was adjusted to 1:4, and no dechlorination was performed. The rest was the same as in Example 4, as detailed below: (1) Preparation of nitrogen-containing covalent organic framework support: A nitrogen-containing precursor (in this example, 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline in a molar ratio of 1:4) was added to a glass tube containing organic solvent a (p-xylene and methanol in a volume ratio of 1:5). After ultrasonic treatment, an organic acid catalyst (6 M acetic acid solution) was added to the tube, so that the mass ratio of nitrogen-containing precursor, organic solvent a and organic acid catalyst was 1:20:1. The resulting mixture was degassed by three cycles of freezing (-180℃)-vacuum (20 Pa)-thawing (room temperature) and then sealed, and subsequently heated in an oven at 120℃ for 150 h. After cooling to room temperature, the supernatant was filtered off, and the solid precipitate was repeatedly washed with methanol until the solvent was colorless and then dried under vacuum (60 °C, 72 h) to obtain a nitrogen-containing covalent organic framework support. (2) Preparation of confined covalent organic framework ruthenium single-atom material: The nitrogen-containing covalent organic framework support prepared in step 1) above was mixed with ruthenium acetylacetone solution in a 1:1 molar ratio. The ruthenium-doped nitrogen-containing covalent organic framework material was synthesized by in-situ precipitation followed by vacuum drying. Finally, the covalent organic framework material was washed 5 times with methanol and ethanol (volume ratio of 1:1) to obtain confined covalent organic framework ruthenium single-atom material. Comparative Example 2 The non-restricted framework material was synthesized using only 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline, with the rest of the process being basically the same as in Example 4, as detailed below: (1) Preparation of nitrogen-containing framework support: The nitrogen-containing precursor 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline was added to a glass tube containing organic solvent a (p-xylene and methanol in a volume ratio of 1:5). After ultrasonic treatment, an organic acid catalyst (6 M acetic acid solution) was added to the tube, so that the mass ratio of nitrogen-containing precursor, organic solvent a and organic acid catalyst was 1:20:1. The resulting mixture was degassed by three cycles of freezing (-180℃)-vacuum (20 Pa)-thawing (room temperature) and then sealed. It was then heated in an oven at 120℃ for 150 h. After cooling to room temperature, the supernatant was filtered off, and the solid precipitate was repeatedly washed with methanol until the solvent was colorless and then vacuum dried (60℃, 72 h) to obtain the framework support; (2) Preparation of unrestricted covalent organic framework ruthenium single-atom material: The nitrogen-containing covalent organic framework support prepared in step 1) above was mixed with ruthenium acetylacetone solution in a 1:1 molar ratio. The ruthenium-doped nitrogen-containing covalent organic framework material was synthesized by in-situ precipitation followed by vacuum drying. Finally, the covalent organic framework material was washed 5 times with methanol and ethanol (volume ratio of 1:1) to obtain unrestricted covalent organic framework ruthenium single-atom material. (3) Preparation of confined ruthenium single-atom catalyst: The confined covalent organic framework ruthenium single-atom material prepared in step 2) was dispersed in methanol under ice bath conditions. 0.05 mmol / L NaBH4 solution was added under vacuum at a rate of 0.1~2.0 mL / min and stirred for 2 h to achieve dechlorination treatment, and finally the confined ruthenium single-atom catalyst was synthesized.

[0039] The catalysts prepared in Examples 1-5 were used for the hydrochlorination reaction of acetylene, and the steps were as follows: Acetylene and hydrogen chloride (molar ratio of acetylene to hydrogen chloride was 1:1.1) were introduced into a fixed-bed reactor containing the catalyst. The amount of catalyst was 1.5 g, the bed temperature was controlled at 180 °C, and the acetylene space velocity was 180 h⁻¹. -1 The reaction pressure is atmospheric pressure.

[0040] The evaluation results of the catalyst of this invention in the acetylene hydrochlorination reaction are as follows: In Examples 1-5, the selectivity of vinyl chloride remained above 99%. The catalyst activity was compared based on the acetylene conversion rate at steady state, as shown in Table 1. Table 1 shows that as the precursor molar ratio (i.e., the molar ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetraphenyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline) increased, the catalytic activity of the confined ruthenium single-atom catalyst first increased and then decreased, reaching a maximum conversion rate of 98.3% when the precursor molar ratio was 1:4.

[0041] Table 1 Performance test results of Examples 1-5 As can be seen from the table above, the confined single-atom catalyst designed in this invention has a conversion rate of over 90%, and the conversion rate can still be maintained above 80% after 100 hours of reaction, with a selectivity of over 99%, exhibiting good catalytic activity and stability. It can be further applied in pilot-scale tests under industrial catalytic conditions. This invention prepares a confined ruthenium single-atom catalyst with low coordination chlorine modification through dechlorination treatment. It achieves long-term stability by relying on the confined anchoring of the support and the regulation of the chemical environment of the active site. The catalyst is designed from the perspective of overcoming the easy loss of ruthenium metal during the catalytic reaction. The conversion rate of Comparative Example 1, which underwent dechlorination treatment, is much lower than that of Example 4, which also underwent dechlorination treatment. Moreover, this invention and last year used a specific ratio of 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)benzene]. Using 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline as a nitrogen-containing precursor, the resulting nitrogen-containing covalent organic framework support has a regular pore structure and nitrogen defects, which allows the active ingredient ruthenium to be firmly fixed in the pores of the support, forming a single-atom distribution. This achieves good results with a low amount of ruthenium. In contrast, Comparative Example 2 only uses 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline for the synthesis of unrestricted framework materials. Even though the synthesis process is basically the same as in Example 4, its activity and stability are far lower than those in Example 4.

[0042] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention based on the technical solution and inventive concept should be covered within the scope of protection of the present invention.

Claims

1. A confined ruthenium single-atom catalyst, characterized in that, It includes the following components: a nitrogen-containing covalent organic framework material as a support, on which 0.1~3 wt% of ruthenium single-atom active sites are loaded.

2. A method for preparing a confined ruthenium single-atom catalyst as described in claim 1, characterized in that, Prepare according to the following steps: 1) Preparation of nitrogen-containing covalent organic framework support: The nitrogen-containing precursor was added to a reactor containing organic solvent a, and after ultrasonic treatment, an organic acid catalyst was added; the resulting mixture was degassed by multiple freeze-vacuum-thaw cycles and then sealed, and then heated in an oven; after cooling to room temperature, the supernatant was filtered off, the solid phase was precipitated and washed until the solvent was colorless and then vacuum dried to obtain the nitrogen-containing covalent organic framework support; 2) Preparation of confined covalent organic framework ruthenium single-atom material: The nitrogen-containing covalent organic framework support prepared in step 1) above is mixed with a ruthenium source solution, and ruthenium-doped nitrogen-containing covalent organic framework material is synthesized by in-situ precipitation followed by vacuum drying; the obtained covalent organic framework material is cleaned to obtain confined covalent organic framework ruthenium single-atom material. 3) Preparation of confined ruthenium single-atom catalyst: The confined covalent organic framework ruthenium single-atom material prepared in step 2) is dispersed in organic solvent b under ice bath conditions. Sodium borohydride solution is added under vacuum conditions and stirred to achieve dechlorination treatment, and finally confined ruthenium single-atom catalyst is synthesized.

3. The method for preparing a confined ruthenium single-atom catalyst according to claim 2, characterized in that, Step 1) The nitrogen-containing precursor comprises 4,4',4'',4'''-(pyrene-1,3,6,8-tetramethyl)tetraphenylamine and 3,8-bis[4-(5,5-dimethyl-1,3-dioxane-2-yl)phenyl]-1,10-phenanthroline in a molar ratio of 1:(0.5~5). The organic solvent a is one or more selected from o-xylene, m-xylene, p-xylene, methanol, ethanol, propanol, and butanol; The organic acid catalyst is one or more of formic acid, acetic acid, propionic acid, and butyric acid; The mass ratio of the nitrogen-containing precursor, organic solvent a, and organic acid catalyst is 1:15~25:0.5~1.

5. The cleaning solvent used for solid-phase precipitation washing is at least one of methanol, ethanol, tetrahydrofuran, dioxane, acetonitrile, acetone, and diethyl ether.

4. The method for preparing a confined ruthenium single-atom catalyst according to claim 2, characterized in that, In step 1), the freezing temperature of the freezing-vacuum-thawing cycle is -190~-170℃, the vacuum degree is 15~25 Pa, and the thawing temperature is room temperature; The oven temperature is 100~150 ℃, and the heating time is 100~200 h.

5. The method for preparing a confined ruthenium single-atom catalyst according to claim 2, characterized in that, Step 2) The ruthenium source is one of ruthenium oxide, ruthenium trichloride, ruthenium acetylacetone, ruthenium acetate, and ruthenium carbonyl chloride, and the molar ratio of nitrogen-containing covalent organic framework support to ruthenium source is 1:(1~5). The cleaning agent used for cleaning covalent organic framework materials is a mixture of at least two of N,N-dimethylformamide, ethanol, methanol, acetonitrile, acetone, and diethyl ether.

6. The method for preparing a confined ruthenium single-atom catalyst according to claim 2, characterized in that, The in-situ deposition temperature described in step 2) is 50~100 ℃. In-situ deposition utilizes the nitrogen defects of the nitrogen-containing covalent organic framework carrier to first deposit ruthenium on its surface.

7. The method for preparing a confined ruthenium single-atom catalyst according to claim 2, characterized in that, In step 3), organic solvent b is one of tetrahydrofuran, ethanol, methanol, acetonitrile, acetone, and diethyl ether. The concentration of the sodium borohydride solution is 0.01~0.1 mmol / L; the sodium borohydride solution is added at a rate of 0.1~2.0 mL / min.

8. The method for preparing a confined ruthenium single-atom catalyst according to claim 2, characterized in that, In steps 1) to 2), the vacuum drying temperature is 50 to 100 ℃, and the vacuum drying time is 24 to 72 h.

9. The method for preparing a confined ruthenium single-atom catalyst according to claim 2, characterized in that, In the process of synthesizing ruthenium single-atom catalysts, the nitrogen defects and regular covalent organic framework pore structure on the support allow metallic ruthenium to be firmly fixed in the support pores, resulting in confined ruthenium single-atom catalysts.

10. An application of the confined ruthenium single-atom catalyst as described in claim 1, characterized in that, The confined ruthenium single-atom catalyst was applied to the acetylene hydrochlorination reaction.

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