Silicon tetrachloride hydrogenation catalyst as well as preparation method and application thereof

Abstract

The invention relates to the technical field of polycrystalline silicon production, and particularly discloses a silicon tetrachloride hydrogenation catalyst as well as a preparation method and application thereof. The catalyst comprises a carbon nanotube matrix and a copper-silicon alloy loaded on the surface of the carbon nanotube matrix, and the carbon nanotube matrix further comprises a transition metal filling phase, and the transition metal filling phase exists in the internal cavity of the carbon nanotube matrix in a continuous or discontinuous nanowire form. When the catalyst is applied to a cold hydrogenation process, the conversion rate of silicon tetrachloride is relatively high.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of polysilicon production, and particularly relates to a silicon tetrachloride hydrogenation catalyst, a preparation method and application thereof. BACKGROUND

[0002] In the process of producing polysilicon by improved Siemens method, the conversion of industrial silicon into trichlorosilane through hydrochlorination reaction is a key step. Compared with the traditional hot hydrogenation process without catalyst, the cold hydrogenation process with anhydrous cuprous chloride (CuCl) as catalyst has significant advantages in energy consumption, reaction efficiency and atomic utilization, and is widely used by mainstream industrial enterprises. How to further optimize the process has become the focus of research, and the development of high-activity catalyst is particularly crucial. The main reaction equation of cold hydrogenation is as follows:

[0003] It is generally believed that the reaction mechanism (with CuCl as catalyst) includes the following steps: (1) Silicon tetrachloride and hydrogen gas are cooperatively adsorbed on the active sites of the catalyst surface; (2) The adsorbate reacts on the surface to generate trichlorosilane and hydrogen chloride; (3) The product trichlorosilane desorbs from the surface; (4) The desorbed hydrogen chloride continues to react with silicon to generate new trichlorosilane and hydrogen; (5) The trichlorosilane desorption completes the product release; (6) The copper species diffuses on the catalytic surface to regenerate the active center and complete the catalytic cycle.

[0004] Although the current industrial process is relatively mature in terms of process and parameter control, the CuCl catalyst still faces the challenge of low conversion rate of silicon tetrachloride, and the reasons mainly include: (1) The CuCl catalyst lacks carrier support and protection, resulting in poor dispersion of active sites, uneven particle size, and limited number of effective active sites; (2) The catalyst is prone to sintering and poisoning under high temperature conditions, significantly reducing its catalytic activity and service life. SUMMARY

[0005] The purpose of the present application is to overcome the problems of low conversion rate of silicon tetrachloride and easy sintering and poisoning of CuCl catalyst under high temperature conditions in the prior art, and to provide a silicon tetrachloride hydrogenation catalyst and a preparation method thereof. The catalyst has high silicon tetrachloride conversion rate and excellent thermal stability.

[0006] In order to achieve the above purpose, the present application provides a silicon tetrachloride hydrogenation catalyst, which comprises: a carbon nanotube matrix and a copper-silicon alloy loaded on the surface of the carbon nanotube matrix. And, the carbon nanotube matrix further comprises a transition metal filler phase, which is in a continuous or discontinuous nanowire form inside the internal cavity of the carbon nanotube matrix.

[0007] The second aspect of the present application provides a preparation method of the silicon tetrachloride hydrogenation catalyst of the first aspect of the present application, which comprises: S1: performing first contact treatment on the carbon nanotube matrix with a transition metal salt solution, and then sequentially performing first drying treatment and first calcination treatment to obtain a first intermediate A; S2: performing second contact treatment on the first intermediate A with a copper complex precursor solution, adding a reducing agent to perform reduction reaction, and then performing second drying treatment to obtain a second intermediate B; S3: performing third contact treatment on the second intermediate B with a silicon hydrolysis solution, and then sequentially performing third drying treatment and second calcination treatment to prepare the silicon tetrachloride hydrogenation catalyst.

[0008] The third aspect of the present application provides an application of the silicon tetrachloride hydrogenation catalyst of the first aspect of the present application in the field of polysilicon production.

[0009] The silicon tetrachloride hydrogenation catalyst prepared by the above technical solution utilizes the unique geometric and electronic structure of carbon nanotubes to confine transition metals to the inside of the nanotube of the carbon nanotube, which can effectively inhibit sintering of the transition metals at high temperatures; at the same time, the confined structure can promote rapid transportation of hydrogen species from the inside of the carbon nanotube to the outer surface through the hydrogen overflow effect, thereby improving the catalytic reaction activity; in addition, the intrinsic active center of the catalyst required by the present application is a copper-silicon alloy supported on the outer surface of the carbon nanotube, and Si as a guest component can block continuous copper sites, which can effectively inhibit Cu particle agglomeration at high temperatures, thereby making the catalyst exhibit excellent thermal stability; Si transfers part of the electrons to Cu, making the d-band center of Cu closer to the Fermi level, thereby reducing the adsorption energy of the substrate, and combining the hydrogen species transported by the hydrogen overflow effect, thereby effectively improving the catalytic activity of the cold hydrogenation reaction. BRIEF DESCRIPTION OF DRAWINGS

[0010] Figure 1 is the thermal stability evaluation result of the catalyst prepared in Example 1 in the specific embodiment. DETAILED DESCRIPTION

[0011] The endpoints of the ranges and any values disclosed herein are not limited to the precise values stated. The ranges or values should be construed to be approximations that allow for significant variation. Various ranges of values that are explicitly delineated between the endpoints, between a endpoint and a single value, and between single values, can be combined to form one or more new ranges of values that are also expressly disclosed.

[0012] The present application provides a silicon tetrachloride hydrogenation catalyst, which comprises: a carbon nanotube matrix and a copper-silicon alloy loaded on the surface of the carbon nanotube matrix. In addition, the carbon nanotube matrix further comprises a transition metal filling phase, which exists in the form of continuous or discontinuous nanowires in the internal cavity of the carbon nanotube matrix.

[0013] The present application can effectively inhibit sintering of the transition metal at high temperature by confining the transition metal to the inside of the nanotube of the carbon nanotube, thereby improving the catalytic reaction activity, and the copper-silicon alloy loaded on the outer surface of the carbon nanotube can make the catalyst exhibit excellent thermal stability, thereby effectively improving the catalytic activity of the cold hydrogenation reaction.

[0014] In the present application, the introduction of oxygen-containing functional groups such as carboxyl (-COOH), hydroxyl (-OH), carbonyl (C=O) and the like on the surface and end cap of the carbon nanotube can serve as excellent anchoring sites, strongly adsorb metal cations in the solution through electrostatic interaction or coordination bond, and can make the surface of the carbon nanotube hydrophilic and carry a charge, thereby better dispersing in water or polar solvents and avoiding agglomeration. Therefore, in some optional embodiments, the carbon nanotube matrix is a carbon nanotube modified with an oxygen-containing functional group.

[0015] In the present application, optionally, the performance parameters of the carbon nanotube matrix include: an outer diameter of 10-100 nm, a length of 2-20 μm, and a specific surface area of 30-160 m 2 / g; in other optional embodiments, the performance parameters of the carbon nanotube matrix include: an outer diameter of 40-60 nm, a length of 5-15 μm, and a specific surface area of 40-70 m 2 / g.

[0016] In the present application, the transition metal filling phase exists in the form of continuous or discontinuous nanowires in the internal cavity of the carbon nanotube matrix, which can inhibit sintering of the catalyst at high temperature, thereby improving the catalytic reaction activity. The inventors have found that further improving the reaction activity of the catalyst can be achieved by limiting the content of the transition metal filling phase in the carbon nanotube. Therefore, in optional cases, the content of the transition metal filling phase accounts for 5-20 wt% of the mass of the carbon nanotube matrix.

[0017] In some optional embodiments, the transition metal in the transition metal filling phase is selected from at least one of Fe, Co, Ni, Ru, Rh, Pd, Ag and Pt.

[0018] The second aspect of the present application provides a preparation method of the silicon tetrachloride hydrogenation catalyst of the first aspect of the present application, which comprises: S1: The carbon nanotube matrix is ​​subjected to a first contact treatment with a transition metal salt solution, followed by a first drying treatment and a first calcination treatment to obtain the first intermediate A; S2: After the copper-containing complex precursor solution is subjected to a second contact treatment with the first intermediate A, a reducing agent is added to carry out a reduction reaction, followed by a second drying treatment to obtain the second intermediate B; S3: The silicon-containing hydrolysate is subjected to a third contact treatment with the second intermediate B, followed by a third drying treatment and a second calcination treatment, to prepare the silicon tetrachloride hydrogenation catalyst.

[0019] In some optional embodiments, the method further includes a pretreatment step, which includes acidifying the carbon nanotubes with an acidic reagent to prepare a carbon nanotube matrix.

[0020] The above pretreatment steps are to introduce oxygen-containing functional groups such as carboxyl (-COOH), hydroxyl (-OH), and carbonyl (C=O) on the surface and end caps of carbon nanotubes, so as to adsorb metal cations in the subsequent solution and avoid aggregation.

[0021] In some optional embodiments, the acidic reagent is selected from nitric acid and / or sulfuric acid, and may be a mixture of concentrated nitric acid and concentrated sulfuric acid (wherein, the volume ratio of concentrated nitric acid to concentrated sulfuric acid may be, for example, 1:2-6, or 1:3-5, such as 1:3, 1:4, 1:5, etc., and any range between these values). The concentration of the acidic reagent may be, for example, concentrated sulfuric acid with a mass fraction of 95-99% and / or concentrated nitric acid with a mass fraction of 60-70%.

[0022] In this invention, optionally, the solid-liquid ratio of carbon nanotubes to acidic reagent is 1:8-25 (g / mL), optionally 1:10-20 (g / mL), for example, 1:10, 1:15, 1:20, and any range between these values.

[0023] In this invention, optionally, the acidification treatment conditions include: a temperature of 40-90°C and a time of 2-8 hours; alternatively, the acidification treatment conditions include: a temperature of 50-80°C and a time of 3-6 hours.

[0024] In this invention, optionally, the pretreatment step includes: drying the acidified carbon nanotubes to prepare a carbon nanotube matrix. The drying conditions may include: a temperature of 50-90°C and a time of 8-18 hours; alternatively, the drying conditions may include: a temperature of 60-80°C and a time of 10-15 hours.

[0025] In some optional embodiments, step S1, the preparation of the transition metal salt solution includes the following steps: A transition metal salt is dissolved in deionized water, and an organic structural agent is added to prepare a transition metal salt solution. After adding the organic structural agent, the solution must be stirred at room temperature (25-40℃) until it becomes clear to obtain the transition metal salt solution.

[0026] In this invention, the addition of an organic structural agent during the preparation of the transition metal salt solution can reduce the surface tension of the solution, thereby achieving intratube loading of carbon nanotubes. Optionally, the organic structural agent is selected from ethylene glycol, ethanolamine, ethylenediamine, diethylene glycol, glycerol, methanol, and ethanol.

[0027] In this invention, the volume ratio of the organic structural agent to the transition metal salt solution is optionally 1:0.5-8, optionally 1:1-5, for example, 1:1, 1:2, 1:5 and any range between these values.

[0028] In some optional embodiments, the transition metal salt is selected from at least one of transition metal nitrates, transition metal chlorides, transition metal sulfates and transition metal organic acid salts, preferably at least one of nickel nitrate hexahydrate, silver nitrate, rubidium sulfate, platinum chloride hexahydrate and rhodium chloride trihydrate; wherein, the amount of transition metal salt used in preparing the transition metal salt solution is such that the content of the transition metal filling phase accounts for 5-20 wt% of the carbon nanotube matrix, and can be selected as 8-15 wt%.

[0029] In some alternative implementations, the volume of the transition metal salt solution is equal to the volume of the internal cavity of the carbon nanotube matrix.

[0030] In this invention, optionally, in step S1, the conditions for the first contact treatment include: a temperature of 25-40°C and a time of 8-12 hours.

[0031] In this invention, optionally, the conditions for the first drying treatment include: a temperature of 60-90°C and a time of 8-20 hours; in some optional embodiments, the conditions for the first drying treatment include: a temperature of 65-85°C and a time of 10-15 hours.

[0032] In this invention, optionally, the conditions for the first calcination treatment include: a temperature of 200-500°C and a time of 2-8 hours; for example, when the transition metal is Fe, Co, or Ni, the temperature is 300-500°C; when the transition metal is Ru, Rh, Pd, Ag, or Pt, the temperature is 200-400°C.

[0033] In this invention, optionally, the heating rate in the first calcination process is 1-10℃ / min, or optionally 1-5℃ / min.

[0034] In this invention, step S1 may involve uniformly spraying a transition metal salt solution onto a carbon nanotube substrate for a first contact treatment, then allowing it to stand at 25-40°C for 8-12 hours, transferring it to a vacuum drying oven for a first drying treatment, followed by a first calcination treatment under a reducing atmosphere, and then cooling it to 25-40°C under nitrogen protection to obtain the first intermediate A.

[0035] According to some optional embodiments, in step S2, the preparation of the copper-containing complex precursor solution includes the following steps: Copper salts are dissolved in deionized water to obtain a copper salt solution. A complexing agent is then added to the copper salt solution until the solution becomes clear, thus obtaining a copper-containing complex precursor solution.

[0036] In this invention, optionally, the copper salt is selected from at least one of copper sulfate, copper nitrate, copper chloride, and copper acetate; optionally, the amount of deionized water used is such that the concentration of the copper salt solution is 0.05-0.6 mol / L, for example, 0.1-0.5 mol / L.

[0037] In this invention, optionally, the complexing agent is selected from at least one of aminocarboxylic acid complexing agents, nitrogen-containing complexing agents and hydroxycarboxylic acid complexing agents, for example, it can be at least one of sodium citrate, ethylenediamine and ethylenediaminetetraacetic acid.

[0038] In this invention, optionally, the molar ratio of copper salt to complexing agent is 1:0.5-3, for example, 1:1-2.

[0039] In this invention, optionally, in step S2, the conditions for the second contact treatment include: a temperature of 25-40°C, a time of 8-15 hours, and a pH of 7.5-8.5.

[0040] In this invention, optionally, the conditions for the reduction reaction include: a temperature of 25-40°C and a time of 1-3 hours; the reducing agent is selected from at least one of sodium borohydride, hydrazine hydrate, formic acid, glucose, and ascorbic acid.

[0041] In this invention, optionally, the conditions for the second drying process include: a temperature of 80-130°C and a time of 5-12 hours; in some optional embodiments, the conditions for the second drying process include: a temperature of 90-120°C and a time of 6-9 hours.

[0042] In this invention, step S2 may involve placing the first intermediate A obtained in step S1 into a copper complex precursor solution, slowly adding ammonia to adjust the pH for a second contact treatment, adding a reducing agent dropwise for a reduction reaction until the solution no longer produces bubbles, continuing to stir for 1-3 hours, and then sequentially performing filtration and washing treatments (the washing agent may be, for example, deionized water and / or anhydrous ethanol) until the filtrate is neutral, and then performing a second drying treatment to obtain the second intermediate B.

[0043] In this invention, in order to improve the synergistic effect between the first intermediate A and the copper-containing complex precursor solution, the solid-liquid ratio of the first intermediate A to the copper-containing complex precursor solution may be 1:2-6 (g / mL).

[0044] In some optional embodiments, the solid-liquid ratio of the carbon nanotube matrix to the copper-containing complex precursor solution is 1:2-6 (g / mL), and optionally 1:3-5 (g / mL).

[0045] In this invention, optionally, in step S3, the preparation of the silicon-containing hydrolysate includes the following steps: Under acidic conditions, a silicon source is dissolved in a nonpolar solvent to obtain a silicon-containing solution. Then, a chelating agent, a dispersant, and deionized water are added sequentially to the silicon-containing solution to prepare a silicon-containing hydrolysate.

[0046] In this invention, the acidic conditions can optionally be obtained by adding an acidic reagent to adjust the pH, for example, by adding acetic acid to adjust the pH to 3-5.

[0047] In some alternative embodiments, the silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, trimethoxysilane, triethoxysilane, and tert-butyltrimethoxysilane.

[0048] In this invention, optionally, the nonpolar solvent is selected from at least one of toluene, xylene, cyclohexane, n-hexane and petroleum ether; optionally, the amount of nonpolar solvent used is such that the concentration of the silicon-containing solution is 0.05-0.1 mol / L.

[0049] In this invention, optionally, the chelating agent is selected from at least one of carboxylic acid chelating agents, nitrogen-containing carboxylic acid chelating agents, phenolic chelating agents, and organophosphonic acid chelating agents, for example, at least one of ethylenediaminetetraacetic acid, salicylic acid, and citric acid.

[0050] In this invention, optionally, the molar ratio of silicon source to chelating agent is 1:0.5-3, or optionally 1:1-2.

[0051] In this invention, optionally, the dispersant is at least one of polyolefins, polystyrene and its derivatives, and amphiphilic block / graft copolymers; the amount of dispersant added can be, for example, 4%-20% of the mass of the silicon source, optionally 5%-15%.

[0052] In this invention, optionally, in step S3, the conditions for the third contact treatment include: a temperature of 25-40°C and a time of 4-12 hours.

[0053] In this invention, optionally, the conditions for the third drying process include: a temperature of 60-90°C and a time of 8-15 hours; in some optional embodiments, the conditions for the third drying process include: a temperature of 70-80°C and a time of 10-12 hours.

[0054] In this invention, optionally, the conditions for the second calcination treatment include: a temperature of 250-600°C and a time of 4-12 hours. In some optional embodiments, the second calcination treatment is a stepwise calcination treatment, including: raising the temperature to a first temperature (250-350°C, heating rate of 1-10°C / min) under an inert atmosphere, switching to a reducing atmosphere, and maintaining this for 2-6 hours; raising the temperature to a second temperature (450-600°C, heating rate of 1-10°C / min), maintaining this for 2-6 hours, and then lowering the temperature to room temperature under an inert atmosphere to obtain a silicon tetrachloride hydrogenation catalyst. The inert atmosphere can be, for example, N2 or Ar, and the reducing atmosphere can be, for example, a mixture of H2 and an inert gas (H2 volume concentration, for example, 5%-10%).

[0055] In this invention, step S3 may be: placing the second intermediate B obtained in step S2 into a silicon-containing hydrolysate for a third contact treatment, followed by sequential filtration and washing (the washing agent may be, for example, ethanol), then performing a third drying treatment, and finally a second calcination treatment to prepare a silicon tetrachloride hydrogenation catalyst.

[0056] In this invention, optionally, in step S3, the solid-liquid ratio of the second intermediate B to the silicon-containing hydrolysate is 1:5-12 (g / mL).

[0057] In some optional embodiments, the solid-liquid ratio of the carbon nanotube matrix to the silicon-containing hydrolysate is 1:5-12 (g / mL), and optionally 1:6-9 (g / mL).

[0058] The third aspect of the present invention provides an application of the silicon tetrachloride hydrogenation catalyst of the first aspect of the present invention in the field of polysilicon production.

[0059] Through the above technical solutions, the silicon tetrachloride hydrogenation catalyst prepared by the present invention has excellent silicon tetrachloride conversion rate and thermal stability. In particular, in some preferred embodiments, the silicon tetrachloride conversion rate is not less than 30%.

[0060] The present invention will be described in detail below through embodiments.

[0061] In the following examples, the carbon nanotubes a1 (purchased from Shenzhen Nanoport Co., Ltd., brand name L-MWNT-4060 multi-walled carbon nanotubes) have an outer diameter of 40-60 nm, a length of 5-15 μm, and a specific surface area of ​​40-70 m². 2 / g.

[0062] Example 1 This embodiment illustrates a method for preparing a silicon tetrachloride hydrogenation catalyst, which includes: S1: At room temperature (25℃, the same below), 9 mL of transition metal salt solution 1# was uniformly sprayed onto 10 g of carbon nanotube matrix CNT-1, stirred for the first contact treatment for 10 h, and then allowed to stand at 25℃ for 10 h. After that, it was transferred to a vacuum drying oven and dried at 70℃ for 15 h. Then, in H2 atmosphere, it was heated to 350℃ at a heating rate of 5℃ / min and kept at the temperature for 4 h for the first calcination treatment. After that, it was cooled to 25℃ under nitrogen protection to obtain the first intermediate A1. The preparation of the carbon nanotube matrix CNT-1 includes: slowly mixing 30 mL of concentrated nitric acid (65% by mass) and 120 mL of concentrated sulfuric acid (98% by mass), cooling to room temperature (25℃, the same below), adding 10 g of carbon nanotubes a1, heating to 65℃, and refluxing for 4 h for acidification treatment; after the reaction is completed, filtering to collect the solid product, and repeatedly washing with deionized water until the filtrate is neutral; drying the solid product at 70℃ for 12 h to obtain the carbon nanotube matrix CNT-1; The preparation of transition metal salt solution 1# includes: dissolving 4.94 g of nickel nitrate hexahydrate (purchased from Aladdin Company, grade N108891) in 6 mL of deionized water, adding 3 mL of ethanolamine, and stirring at room temperature (25℃, the same below) until the solution is clear to prepare transition metal salt solution 1#; S2: At room temperature, the first intermediate A1 obtained in step S1 was placed into 40 mL of copper complex precursor solution 1#, and ammonia was slowly added dropwise to adjust the pH to 8. The mixture was then stirred and subjected to a second contact treatment for 10 h. Ascorbic acid was added dropwise to carry out a reduction reaction until no more bubbles were produced in the solution. The mixture was stirred for another 2 h. Then, the mixture was filtered and washed (using deionized water and anhydrous ethanol) until the filtrate was neutral. Finally, the mixture was dried at 100 °C for 9 h to obtain the second intermediate B1. The preparation of copper-containing complex precursor solution 1# includes: dissolving 2.046 g of copper chloride dihydrate (purchased from Aladdin Company, brand name C111678) in 40 mL of deionized water, adding 1.082 g of ethylenediamine, and stirring at room temperature (25℃, the same below) until the solution is clear to obtain copper-containing complex precursor solution 1#. S3: At room temperature, the second intermediate B1 obtained in step S2 was placed into 80 mL of silicon-containing hydrolysate 1#, stirred for 9 h for the third contact treatment, and then filtered, washed (washing agent was anhydrous ethanol), dried at 70 °C for 12 h and calcined for the second time to prepare silicon tetrachloride hydrogenation catalyst 1#. The preparation of silicon-containing hydrolysate 1# includes: dissolving 1.334 g of tetraethyl orthosilicate (purchased from Aladdin Company, brand name T110593) in 80 mL of toluene to obtain a silicon-containing solution; then adding 3.573 g of ethylenediaminetetraacetic acid, 0.133 g of polystyrene (purchased from Maclean Company, brand name P728974), and 0.173 g of deionized water to the silicon-containing solution in sequence, and adjusting the pH to 4 with acetic acid; stirring at room temperature (25℃, the same below) for 45 min to obtain silicon-containing hydrolysate 1#; Furthermore, the conditions for the second calcination treatment include: first, heating to 300°C at a heating rate of 5°C / min under nitrogen protection, switching to 8% H2 / N2, and holding at that temperature for 4 h; then heating to 500°C at a heating rate of 5°C / min, holding at that temperature for 4 h, and then cooling to room temperature under nitrogen protection.

[0063] Example 2 S1: 9 mL of transition metal salt solution 2# was uniformly sprayed onto 10 g of carbon nanotube matrix CNT-2 and stirred at 40 °C for the first contact treatment for 12 h. After standing at 25 °C for 12 h, it was transferred to a vacuum drying oven and dried at 80 °C for 10 h. Then, in a 5% H2 / N2 atmosphere, it was heated to 200 °C at a heating rate of 1 °C / min and kept at the temperature for 6 h for the first calcination treatment. Finally, it was cooled to 25 °C under nitrogen protection to obtain the first intermediate A2. The preparation of the carbon nanotube matrix CNT-2 includes: slowly mixing 50 mL of concentrated nitric acid (70% by mass) and 150 mL of concentrated sulfuric acid (99% by mass), cooling to room temperature (25℃, the same below), adding 10 g of carbon nanotubes a1, heating to 50℃, and refluxing for 6 h for acidification treatment; after the reaction is completed, filtering to collect the solid product, and repeatedly washing with deionized water until the filtrate is neutral; drying the solid product at 60℃ for 15 h to obtain the carbon nanotube matrix CNT-2; The preparation of transition metal salt solution 2# includes: dissolving 2.78 g of silver nitrate (purchased from Aladdin Company, brand name S433974) in 7.5 mL of deionized water, adding 1.5 mL of ethanolamine, and stirring at room temperature (25℃, the same below) until the solution is clear to prepare transition metal salt solution 2#; S2: At room temperature, the first intermediate A2 obtained in step S1 was placed into 50 mL of copper complex precursor solution 2#, and ammonia was slowly added dropwise to adjust the pH to 8.5. The mixture was then stirred and subjected to a second contact treatment for 8 h. Hydrazine hydrate was added dropwise to carry out a reduction reaction until no more bubbles were produced in the solution. The mixture was stirred for another 2 h, and then filtered and washed (using deionized water and anhydrous ethanol) until the filtrate was neutral. Finally, the mixture was dried at 120 °C for 6 h to obtain the second intermediate B2. The preparation of copper-containing complex precursor solution 2# includes: dissolving 0.998 g of copper acetate monohydrate (purchased from Aladdin Company, brand name C665013) in 50 mL of deionized water, adding 2.581 g of sodium citrate, and stirring at room temperature until the solution is clear to obtain copper-containing complex precursor solution 2#. S3: At room temperature, the second intermediate B2 obtained in step S2 was placed into 100 mL of silicon-containing hydrolysate 2#, stirred for a third contact treatment for 12 h, and then filtered, washed (washing agent was anhydrous ethanol), dried at 80 °C for 10 h and calcined for a second time to prepare silicon tetrachloride hydrogenation catalyst 2#. The method for preparing silicon-containing hydrolysate 2# is as follows: 0.681 g of trimethoxysilane (purchased from Aladdin Company, brand name T106658) was dissolved in 100 mL of toluene to obtain a silicon-containing solution. Then, 1.381 g of salicylic acid, 0.102 g of polyacrylic acid-grafted polystyrene (purchased from Aladdin Company, brand name P487736) and 0.18 g of deionized water were added to the silicon-containing solution in sequence. Acetic acid was added to adjust the pH to 5, and the mixture was stirred at room temperature for 60 min to prepare silicon-containing hydrolysate 2#. Furthermore, the conditions for the second calcination treatment include: first, heating to 350°C at a heating rate of 10°C / min under nitrogen protection, switching to 10% H2 / N2, and holding at that temperature for 2 h; then heating to 600°C at a heating rate of 5°C / min, holding at that temperature for 2 h, and then cooling to room temperature under nitrogen protection.

[0064] Examples 3-5 The method is similar to that in Example 1, except that in step S1, a transition metal salt solution different from that in Example 1 is used. Example 3 uses the same volume of transition metal salt solution 3# to replace transition metal salt solution 1# to prepare silicon tetrachloride hydrogenation catalyst 3#; The preparation of transition metal salt solution 3# includes the following steps: following a similar preparation method to transition metal salt solution 1#, except that 1.56 g of rubidium sulfate (purchased from Aladdin Company, grade R112820) is used instead of 4.94 g of nickel nitrate hexahydrate to prepare transition metal salt solution 3#. Example 4 uses the same volume of transition metal salt solution 4# to replace transition metal salt solution 1# to prepare silicon tetrachloride hydrogenation catalyst 4#; The preparation of transition metal salt solution 4# includes the following steps: following a similar preparation method to transition metal salt solution 1#, except that 2.65 g of platinum chloride hexahydrate (purchased from Aladdin Company, grade C110574) is used instead of 4.94 g of nickel nitrate hexahydrate to prepare transition metal salt solution 4#. Example 5 uses the same volume of transition metal salt solution 5# to replace transition metal salt solution 1# to prepare silicon tetrachloride hydrogenation catalyst 5#; The preparation of transition metal salt solution 5# involves a similar method to that used for transition metal salt solution 1#, except that 2.56 g of rhodium chloride trihydrate (purchased from Aladdin Company, grade R190691) is used instead of 4.94 g of nickel nitrate hexahydrate to prepare transition metal salt solution 5#.

[0065] In Example 6, 5 mL of transition metal salt solution 1# was used to replace 9 mL of transition metal salt solution 1# to prepare silicon tetrachloride hydrogenation catalyst 12#.

[0066] Examples 7-8 The method is similar to that in Example 1, except that in step S2, a copper-containing complex precursor solution different from that in Example 1 is used. Example 7 uses the same volume of copper-containing complex precursor solution 3# to replace copper-containing complex precursor solution 1# to prepare silicon tetrachloride hydrogenation catalyst 7#; The preparation of copper-containing complex precursor solution 3# includes: dissolving 2.416 g of copper nitrate trihydrate (purchased from Aladdin Company, brand name C431149) in 20 mL of deionized water, adding 2.922 g of ethylenediaminetetraacetic acid, and stirring at room temperature until the solution is clear to obtain copper-containing complex precursor solution 3#; In Example 8, 20 mL of copper-containing complex precursor solution 1# was used to replace 40 mL of copper-containing complex precursor solution 1# to prepare silicon tetrachloride hydrogenation catalyst 8#.

[0067] Examples 9-10 The method is similar to that in Example 1, except that in step S3, a different silicon-containing hydrolysate is used than that in Example 1. Example 9 uses the same volume of silicon-containing hydrolysate 3# instead of silicon-containing hydrolysate 1# to prepare silicon tetrachloride hydrogenation catalyst 9#; The preparation of silicon-containing hydrolysate 3# includes: dissolving 0.761 g of tetraethyl orthosilicate in 20 mL of toluene to obtain a silicon-containing solution; then adding 10.961 g of citric acid, 0.038 g of polyethylene (purchased from Merck Life Sciences, brand number 427772) and 0.09 g of deionized water in sequence to the silicon-containing solution; adjusting the pH to 3 with acetic acid; and stirring at room temperature for 30 min to obtain silicon-containing hydrolysate 3#.

[0068] In Example 10, 50 mL of silicon-containing hydrolysate 1# was used to replace 80 mL of silicon-containing hydrolysate 1# to prepare silicon tetrachloride hydrogenation catalyst 10#.

[0069] The silicon tetrachloride hydrogenation catalysts prepared in Examples 1-10 above were characterized, and the specific results are shown in Table 1, including: the content of transition metal packed phase in the silicon tetrachloride hydrogenation catalyst was tested by XRF, and the specific results are shown in Table 1. Table 1

[0070] Comparative Example 1 Following a similar method to Example 1, except that in step S1, the same volume of metal salt solution 1'# is used instead of transition metal salt solution 1# to prepare catalyst 1'#; Preparation method of metal salt solution 1'#: The preparation method is similar to that of transition metal salt solution 1#, except that 3.92g of magnesium chloride (purchased from Aladdin Company, grade M140788) is used instead of 4.34g of nickel nitrate tetrahydrate to prepare metal salt solution 1'#.

[0071] Comparative Example 2 Following a similar method to Example 1, except that in step S1, the same volume of zinc-containing complex precursor solution 1'# is used instead of copper-containing complex precursor solution 1# to prepare catalyst 2'#; The preparation of zinc complex precursor solution 1'# includes: dissolving 1.64 g of zinc chloride (purchased from Aladdin Company, brand name Z112526) in 40 mL of deionized water, adding 1.082 g of ethylenediamine, and stirring at room temperature until the solution is clear to obtain zinc complex precursor solution 1'#.

[0072] Comparative Example 3 Following a similar method to Example 1, except that in step S1, the same volume of silicon-containing hydrolysate 1'# is used to replace silicon-containing hydrolysate 1# to prepare catalyst 3'#; The preparation of silicon-containing hydrolysate 1'# includes: following a similar preparation method to silicon-containing hydrolysate 1#, except that 1.334 g of tetraethyl orthosilicate is dissolved in 80 mL of deionized water and stirred at room temperature for 45 min to obtain silicon-containing hydrolysate 1'.

[0073] Comparative Example 4 Following a similar method to Example 1, except that in step S1, activated carbon was used to replace the carbon nanotube matrix CNT-1 in the same weight proportion to prepare catalyst 4'#.

[0074] Test Example 1 This test example is used to evaluate the activity of the catalysts prepared in the above examples and comparative examples, including the calculation of silicon tetrachloride conversion rate, as shown in Table 2. Test method: A fixed-bed evaluation device was used, with 8g of catalyst and 80g of silicon powder loaded. The reaction pressure was 2.1MPa, the H2 / SiCl4 molar ratio was 20, and the gas hourly space velocity was 2400h. -1 The reaction temperature was 550℃, and the reaction time was 6 hours. The formula for the conversion rate of silicon tetrachloride is: silicon tetrachloride

[0075] Table 2

[0076] Test Example 2 This test example is used to test the thermal stability of the silicon tetrachloride hydrogenation catalyst 1# prepared in Example 1, specifically as follows: Figure 1 As shown; Test method: Using a method similar to that used in Test Example 1, the conversion rate of silicon tetrachloride in silicon tetrachloride hydrogenation catalyst 1# was statistically analyzed within the range of 0-50h.

[0077] As can be seen from the results in Table 1, compared with the comparative examples, the silicon tetrachloride hydrogenation catalysts prepared by Examples 1-10 of the present invention have good catalytic activity, with a silicon tetrachloride conversion rate of not less than 25%, especially in some preferred Examples 1-5, the silicon tetrachloride conversion rate is not less than 30%.

[0078] In addition, according to Figure 1 It can be seen that the conversion rate of Example 1 increased from the initial value to 33.24% within 1-5 h, and remained stable at 32.51%-33.24% between 5-50 h. It decreased by only 0.73% at 50 h, showing a typical trend of "rapid activation - long-term stability - slow decay", which proves that the catalyst has both high activity and excellent thermal stability.

[0079] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A silicon tetrachloride hydrogenation catalyst, characterized in that, The catalyst comprises: a carbon nanotube matrix and a copper-silicon alloy supported on the surface of the carbon nanotube matrix; Furthermore, the carbon nanotube matrix also includes a transition metal filling phase, which exists in the internal cavity of the carbon nanotube matrix in the form of continuous or discontinuous nanowires.

2. The silicon tetrachloride hydrogenation catalyst according to claim 1, wherein, The carbon nanotube matrix is ​​a carbon nanotube modified with oxygen-containing functional groups.

3. The silicon tetrachloride hydrogenation catalyst according to claim 1 or 2, wherein, The performance parameters of the carbon nanotube matrix include: outer diameter of 10-100 nm, length of 2-20 μm, and specific surface area of ​​30-160 m². 2 / g; Preferably, the performance parameters of the carbon nanotube matrix include: an outer diameter of 40-60 nm, a length of 5-15 μm, and a specific surface area of ​​40-70 m². 2 / g.

4. The silicon tetrachloride hydrogenation catalyst according to any one of claims 1-3, wherein, The content of the transition metal filler phase accounts for 5-20 wt% of the mass of the carbon nanotube matrix, preferably 8-15 wt%. And / or, the transition metal in the transition metal-filled phase is selected from at least one of Fe, Co, Ni, Ru, Rh, Pd, Ag and Pt.

5. A method for preparing the silicon tetrachloride hydrogenation catalyst according to any one of claims 1-4, wherein, The method includes: S1: The carbon nanotube matrix is ​​subjected to a first contact treatment with a transition metal salt solution, followed by a first drying treatment and a first calcination treatment to obtain the first intermediate A; S2: After the copper-containing complex precursor solution is subjected to a second contact treatment with the first intermediate A, a reducing agent is added to carry out a reduction reaction, and then a second drying treatment is carried out to obtain the second intermediate B; S3: The silicon-containing hydrolysate is subjected to a third contact treatment with the second intermediate B, followed by a third drying treatment and a second calcination treatment, to prepare the silicon tetrachloride hydrogenation catalyst.

6. The preparation method according to claim 5, wherein, In step S2, the solid-liquid ratio of the first intermediate A to the copper-containing complex precursor solution is 1:2-6 (g / mL). In step S3, the solid-liquid ratio of the second intermediate B to the silicon-containing hydrolysate is 1:5-12 (g / mL).

7. The preparation method according to claim 5 or 6, wherein, The method further includes a pretreatment step, which includes: acidifying the carbon nanotubes with an acidic reagent to prepare the carbon nanotube matrix.

8. The preparation method according to any one of claims 5-7, wherein, The acidic reagent is selected from nitric acid and / or sulfuric acid; And / or, the acidification treatment conditions include: a temperature of 40-90°C and a time of 2-8 hours.

9. The preparation method according to any one of claims 5-8, wherein, In step S1, the preparation of the transition metal salt solution includes the following steps: The transition metal salt was dissolved in deionized water, and an organic structural agent was added to prepare the transition metal salt solution.

10. The preparation method according to claim 9, wherein, The transition metal salt is selected from at least one of transition metal nitrates, transition metal chlorides, transition metal sulfates and transition metal organoacid salts, preferably at least one of nickel nitrate hexahydrate, silver nitrate, rubidium sulfate, platinum chloride hexahydrate and rhodium chloride trihydrate; And / or, the organic structural additive is selected from at least one of ethylene glycol, ethanolamine, ethylenediamine, diethylene glycol, glycerol, methanol, and ethanol.

11. The preparation method according to any one of claims 5-10, wherein, In step S1, the conditions for the first contact treatment include: a temperature of 25-40°C and a time of 8-12 hours. And / or, the conditions for the first drying treatment include: a temperature of 60-90°C and a time of 8-20 hours; And / or, the conditions for the first calcination treatment include: a temperature of 200-500℃ and a time of 2-8h.

12. The preparation method according to any one of claims 5-11, wherein, In step S2, the preparation of the copper-containing complex precursor solution includes the following steps: Copper salt is dissolved in deionized water to obtain a copper salt solution. A complexing agent is then added to the copper salt solution until the solution becomes clear, thus obtaining the copper-containing complex precursor solution.

13. The preparation method according to any one of claims 5-12, wherein, The copper salt is selected from at least one of copper sulfate, copper nitrate, copper chloride, and copper acetate; And / or, the complexing agent is selected from at least one of aminocarboxylic acid complexing agents, nitrogen-containing complexing agents, and hydroxycarboxylic acid complexing agents.

14. The preparation method according to any one of claims 5-13, wherein, In step S2, the conditions for the second contact treatment include: a temperature of 25-40°C, a time of 8-15 hours, and a pH of 7.5-8.

5. And / or, the conditions for the reduction reaction include: a temperature of 25-40°C and a time of 1-3 hours; the reducing agent is selected from at least one of sodium borohydride, hydrazine hydrate, formic acid, glucose, and ascorbic acid; And / or, the conditions for the second drying process include: a temperature of 80-130°C and a time of 5-12 hours.

15. The preparation method according to any one of claims 5-14, wherein, In step S3, the preparation of the silicon-containing hydrolysate includes the following steps: Under acidic conditions, a silicon source is dissolved in a nonpolar solvent to obtain a silicon-containing solution. A chelating agent, a dispersant, and deionized water are then added sequentially to the silicon-containing solution to prepare the silicon-containing hydrolysate.

16. The preparation method according to claim 15, wherein, The silicon source is selected from at least one of methyl orthosilicate, ethyl orthosilicate, trimethoxysilane, triethoxysilane, and tert-butyltrimethoxysilane; And / or, the nonpolar solvent is selected from at least one of toluene, xylene, cyclohexane, n-hexane, and petroleum ether; And / or, the chelating agent is selected from at least one of carboxylic acid chelating agents, nitrogen-containing carboxylic acid chelating agents, phenolic chelating agents, and organophosphonic acid chelating agents; And / or, the dispersant is at least one of polyolefins, polystyrene and its derivatives, and amphiphilic block / graft copolymers.

17. The preparation method according to any one of claims 5-16, wherein, In step S3, the conditions for the third contact treatment include: a temperature of 25-40°C and a time of 4-12 hours. And / or, the conditions for the third drying process include: a temperature of 60-90°C and a time of 8-15 hours; And / or, the conditions for the second calcination treatment include: a temperature of 250-600°C and a time of 4-12 hours.

18. The application of the silicon tetrachloride hydrogenation catalyst according to any one of claims 1-4 in the field of polysilicon production.

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