Nickel-based silicate composite catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of heterogeneous catalysis, and particularly relates to a nickel-based silicate composite catalyst as well as a preparation method and application thereof. The preparation method comprises the following steps: hydrolyzing silicate ester to form a silicon dioxide shell layer on the surface of carbon nanofiber by adopting a microemulsion method, then synthesizing a nickel-based silicate nanotube on the surface of the silicon dioxide shell layer by adopting a hydrothermal method, taking the nickel-based silicate nanotube as an active component, and sequentially roasting in protective gas and carrying out reduction reaction in a reducing atmosphere to obtain the nickel-based silicate composite catalyst. The preparation method is simple, and the nickel-based silicate composite catalyst with high catalytic activity and excellent carbon deposition resistance and sintering resistance can be prepared under the condition of high nickel load.

Description

Technical Field

[0001] The present invention belongs to the technical field of heterogeneous catalysis, and particularly relates to a nickel-based silicate composite catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] Nickel-based catalysts have received extensive attention due to their low price and reforming activity. When applied to the dry reforming reaction of methane and carbon dioxide (CH 4 +CO 2 →CO+H 2 ), nickel-based catalysts are prone to high-temperature sintering, which promotes the methane cracking reaction (CH 4 →C+H 2 ) and disproportionation reaction (2CO→C+CO 2 ), resulting in serious carbon deposition on the catalyst surface area, which causes catalyst deactivation. Generally, by enhancing the metal-support interaction to improve the dispersion of nickel, the anti-sintering and anti-carbon deposition properties of nickel-based catalysts can be improved. However, when the nickel loading is relatively large (≥15 wt%), it is difficult to disperse, and the formed nickel particles are relatively large, which easily reduces the catalytic activity and generates carbon deposition. Summary of the Invention

[0003] In view of this, the purpose of the present invention is to provide a nickel-based silicate composite catalyst, a preparation method thereof, and an application thereof. The method prepares a nickel-based silicate composite catalyst with high catalytic activity, excellent anti-sintering and anti-carbon deposition capabilities under high nickel loading conditions.

[0004] To achieve the above purpose, the present invention provides the following technical solutions:

[0005] The present invention provides a preparation method of a nickel-based silicate composite catalyst, including the following steps:

[0006] Mix carbon nanofibers, quaternary ammonium base cationic surfactants, and an alcohol aqueous solution, adjust the pH value of the obtained mixed solution to alkaline, then mix with silicate esters, and subject the obtained reaction solution to hydrolysis and polycondensation reactions to obtain carbon nanofibers coated with silica;

[0007] Mix the dispersion of the carbon nanofibers coated with silica, a solution of metal salts, a silicate compound, and an alkaline substance, and subject the obtained hydrothermal precursor solution to hydrothermal reactions to obtain carbon nanofibers coated with silica loaded with nickel-based silicate nanotubes; the metal salts include nickel salts, or nickel salts and metal promoter salts; the metal elements in the metal promoter salts include one or more of iron, cobalt, copper, manganese, lanthanum, cerium, and magnesium;

[0008] The mass concentration of the silicon dioxide-coated carbon nanofibers in the hydrothermal precursor solution is 1-22 g / L, the mass concentration of the nickel salt is 1-22 g / L, the mass concentration of the metal promoter salt is 0-12% of the mass concentration of the nickel salt, and the mass concentration of the silicate compound is 1-2 times the mass concentration of the nickel salt;

[0009] After calcining the silicon dioxide-coated carbon nanofibers loaded with nickel-based silicate nanotubes in a protective gas, the obtained calcined product is subjected to a reduction reaction in a reducing atmosphere to obtain a nickel-based silicate composite catalyst.

[0010] Preferably, the nickel salt is nickel chloride and / or nickel nitrate; the metal promoter salt is one or more of nitrates, chlorides, and acetates.

[0011] Preferably, the quaternary ammonium base cationic surfactant is one or more of cetyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide.

[0012] Preferably, the mass concentration of the carbon nanofibers in the reaction solution is 1-10 g / L, the mass concentration of the quaternary ammonium base cationic surfactant is 0.5-3 g / L, and the mass concentration of the silicate ester is 0.5-10 g / L.

[0013] Preferably, the temperature of the hydrothermal reaction is 150-220 °C; the time of the hydrothermal reaction is 12-48 h.

[0014] Preferably, the temperature of the calcination is 300-550 °C; the time of the calcination is 1-3 h.

[0015] Preferably, the reducing atmosphere is hydrogen; the temperature of the reduction reaction is 500-600 °C; the time of the reduction reaction is 1-3 h.

[0016] The present invention also provides a nickel-based silicate composite catalyst prepared by the preparation method described in the above technical solution, including carbon nanofibers, a silicon dioxide shell layer coated on the surface of the carbon nanofibers, nickel-based silicate nanotubes loaded on the surface of the silicon dioxide shell layer, and metallic nickel doped in the nickel-based silicate nanotubes, or metallic nickel doped in the nickel-based silicate nanotubes, elemental metal promoters, and alloys formed by metallic nickel and elemental metal promoters; the nickel-based silicate includes nickel silicate, or nickel silicate and silicates of metal promoters;

[0017] The mass ratio of carbon, nickel, and silicon elements in the nickel-based silicate composite catalyst is 1-20:1-3:1; the mass percentage content of the metal promoter in the nickel-based silicate composite catalyst is 0-6%.

[0018] The present invention also provides an application of the nickel-based silicate composite catalyst described in the above technical solution in the dry reforming reaction of methane and carbon dioxide.

[0019] The present invention also provides a method for the dry reforming reaction of methane and carbon dioxide, comprising the following steps:

[0020] Under atmospheric pressure, a mixed gas containing CH 4 , CO 2 and N 2 is mixed with the catalyst to carry out the dry reforming reaction to obtain syngas; the syngas includes hydrogen and carbon monoxide;

[0021] The catalyst is the nickel-based silicate composite catalyst described in the above technical solution.

[0022] The present invention provides a preparation method of a nickel-based silicate composite catalyst, comprising the following steps: mixing carbon nanofibers, a quaternary ammonium base cationic surfactant and an aqueous alcohol solution, adjusting the pH value of the obtained mixed solution to be alkaline, and then mixing with a silicate ester, and subjecting the obtained reaction solution to a hydrolysis polycondensation reaction to obtain carbon nanofibers coated with silica; mixing the dispersion of the carbon nanofibers coated with silica, a solution of a metal salt, a silicate compound and an alkaline substance, and subjecting the obtained hydrothermal precursor solution to a hydrothermal reaction to obtain carbon nanofibers coated with silica loaded with nickel-based silicate nanotubes; the metal salt includes a nickel salt, or a nickel salt and a metal promoter salt; the metal element in the metal promoter salt includes one or more of iron, cobalt, copper, manganese, lanthanum, cerium and magnesium; the mass concentration of the carbon nanofibers coated with silica in the hydrothermal precursor solution is 1-22 g / L, the mass concentration of the nickel salt is 1-22 g / L, the mass concentration of the metal promoter salt is 0-12% of the mass concentration of the nickel salt, and the mass concentration of the silicate compound is 1-2 times the mass concentration of the nickel salt; after calcining the carbon nanofibers coated with silica loaded with nickel-based silicate nanotubes in a protective gas, the obtained calcined product is subjected to a reduction reaction in a reducing atmosphere to obtain the nickel-based silicate composite catalyst.

[0023] The present invention uses the microemulsion method, and SiO generated by hydrolysis of the silicate ester 2A uniform silica shell layer is formed on the surface of carbon nanofibers. Then, under alkaline conditions using the hydrothermal method, nickel-based silicate nanotubes are in-situ synthesized on the surface of the silica shell layer with nickel salts, or nickel salts and metal promoter salts and silicate compounds as raw materials. In an alkaline medium, the layered structure of nickel-based silicate releases surface tension and self-curls to form nanotubes. After that, the structure and morphology of the metal silicate nanotubes are fixed by calcination in a protective gas to promote the interaction between nickel and the metal promoter. Finally, a reduction reaction is carried out in a reducing atmosphere to reduce the metal silicate on the surface of the nickel-based silicate nanotubes to active metallic nickel and the elemental form of the metal promoter, or to form an alloy of the metal promoter and nickel. The nickel-based silicate nanotubes prepared by the present invention have an excellent nano-scale pore size distribution, which inhibits the aggregation of nickel metal particles; the metal promoter improves the nickel metal dispersion through metal-metal interaction, enhancing the anti-sintering performance of the catalyst. At the same time, the carbon nanofibers have high thermal conductivity and chemical inert stability, reducing the carbonization reaction and inhibiting carbon deposition, and improving the strong interaction between the support and the metal in the form of silica-coated carbon nanofibers, preventing the growth of nickel metal particles and enhancing the catalytic activity. The preparation method of this nickel-based silicate composite catalyst is simple, and it can prepare nickel-based silicate with a nanotube morphology at a high nickel loading, enhancing the metal-support interaction and improving the catalytic activity, anti-sintering and anti-carbon deposition capabilities of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 X-ray powder diffraction pattern of the hydrothermal reaction product in Example 1;

[0025] Figure 2 Transmission electron microscope (TEM) morphology characterization diagram of the hydrothermal reaction product in Example 1;

[0026] Figure 3 X-ray powder diffraction pattern of the hydrothermal reaction product in Example 2;

[0027] Figure 4 Transmission electron microscope (TEM) morphology characterization diagram of the hydrothermal reaction product in Example 2;

[0028] Figure 5 X-ray powder diffraction pattern of the hydrothermal reaction product in Example 4;

[0029] Figure 6 Transmission electron microscope (TEM) morphology characterization diagram of the hydrothermal reaction product in Example 4;

[0030] Figure 7 Point scanning energy spectrum characterization EDX diagram of the hydrothermal reaction product in Example 4;

[0031] Figure 8 Transmission electron microscope (TEM) morphology characterization diagram of the hydrothermal reaction product in Comparative Example 1;

[0032] Figure 9 BJH adsorption average pore size diagram of the nickel-based silicate composite catalyst prepared in Example 1;

[0033] Figure 10 BJH desorption average pore size diagram of the nickel-based silicate composite catalyst prepared in Example 1. Detailed implementation manners

[0034] The present invention provides a preparation method of a nickel-based silicate composite catalyst, comprising the following steps:

[0035] Mix carbon nanofibers, a quaternary ammonium base cationic surfactant and an alcohol aqueous solution, adjust the pH value of the obtained mixed solution to be alkaline, then mix with a silicate ester, and subject the obtained reaction solution to a hydrolysis polycondensation reaction to obtain carbon nanofibers coated with silica;

[0036] Mix the dispersion of the carbon nanofibers coated with silica, a solution of a metal salt, a silicate compound and an alkaline substance, and subject the obtained hydrothermal precursor solution to a hydrothermal reaction to obtain carbon nanofibers coated with silica and loaded with nickel-based silicate nanotubes; the metal salt includes a nickel salt, or a nickel salt and a metal promoter salt; the metal element in the metal promoter salt includes one or more of iron, cobalt, copper, manganese, lanthanum, cerium and magnesium;

[0037] In the hydrothermal precursor solution, the mass concentration of the carbon nanofibers coated with silica is 1-22 g / L, the mass concentration of the nickel salt is 1-22 g / L, the mass concentration of the metal promoter salt is 0-12% of the mass concentration of the nickel salt, and the mass concentration of the silicate compound is 1-2 times the mass concentration of the nickel salt;

[0038] After calcining the carbon nanofibers coated with silica and loaded with nickel-based silicate nanotubes in a protective gas, subject the obtained calcined product to a reduction reaction in a reducing atmosphere to obtain a nickel-based silicate composite catalyst.

[0039] Unless otherwise specified, the present invention has no special requirements on the sources of the raw materials used, and commercially available products well-known to those skilled in the art can be used.

[0040] The present invention mixes carbon nanofibers, a quaternary ammonium base cationic surfactant and an alcohol aqueous solution, adjusts the pH value of the obtained mixed solution to be alkaline, then mixes with a silicate ester, and subject the obtained reaction solution to a hydrolysis polycondensation reaction to obtain carbon nanofibers coated with silica.

[0041] As an implementation manner, the outer diameter of the carbon nanofibers is 50-300 nm, specifically 50-200 nm in specific embodiments, and the length is 1-20 μm, specifically 1-15 μm in specific embodiments. The carbon nanofibers are one-dimensional materials, having characteristics such as high strength, light weight, good thermal conductivity, and high conductivity. The carbon nanofibers act as carriers to load, disperse, and stabilize the morphology and structure of the catalyst.

[0042] As an implementation manner, before mixing the carbon nanofibers, quaternary ammonium base cationic surfactant, and aqueous alcohol solution, it further includes: performing acid pretreatment on the carbon nanofibers to obtain purified carbon nanofibers.

[0043] As an implementation manner, the acid solution includes nitric acid and sulfuric acid; the volume ratio of the nitric acid to the sulfuric acid is 1-3:1-3, specifically 1-2:2-3 in specific embodiments; the mass concentration of the nitric acid is 65%; the mass concentration of the sulfuric acid is 98%; the dosage ratio of the carbon nanofibers to the acid solution is 1 g:(20-100) mL, specifically 1 g:(30-50) mL in specific embodiments.

[0044] As an implementation manner, the temperature of the acid pretreatment is 80-90 °C, specifically 90 °C in specific embodiments; the time of the acid pretreatment is 1-3 h, specifically 2 h in specific embodiments.

[0045] The present invention uses the strong oxidizing property of the acid solution to perform acid pretreatment on the carbon nanofibers, and oxygen-containing functional groups can be formed on the surface of the carbon nanofibers: carboxyl group (COOH), hydroxyl group (OH), carbonyl group (C=O); SiO generated by subsequent hydrolysis of silicate 2 is more likely to react with the oxygen-containing functional groups to form a uniformly coated silica shell layer. At the same time, the acid pretreatment can remove impurities in the carbon nanofiber sample and improve its purity.

[0046] As an implementation manner, after the acid pretreatment, it further includes: after cooling the carbon nanofibers pretreated with acid to room temperature, successively performing washing, solid-liquid separation, and drying to obtain purified carbon nanofibers; the washing is water washing; the washing is until the pH value of the washed solution is neutral; the solid-liquid separation is centrifugation; the rotation speed of the centrifugation is 10000-12000 rpm, specifically 10000-11000 rpm in specific embodiments; the time of the centrifugation is 10-30 min, specifically 10-20 min in specific embodiments; the temperature of the drying is 70-80 °C, specifically 70-75 °C in specific embodiments; the time of the drying is 12-24 h, specifically 12-20 h in specific embodiments.

[0047] As an embodiment, the quaternary ammonium hydroxide cationic surfactant is one or more of cetyltrimethylammonium bromide (CTAB), dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide, and octadecyltrimethylammonium bromide, and in a specific embodiment, it is cetyltrimethylammonium bromide. The surfactant molecular film distributed between the alcohol aqueous solution interfaces of the quaternary ammonium hydroxide cationic surfactant has a high interface area and stable thermodynamic properties, and the particles are not easily agglomerated, which plays a role in stabilizing the interface and promoting the hydrolysis of silicate esters on the surface of carbon nanofibers to produce a uniform silica shell layer.

[0048] As an embodiment, the alcohol aqueous solution includes organic alcohol and water; the organic alcohol is ethanol; the volume ratio of water to organic alcohol is 1:2 to 6, and in a specific embodiment, it is 1:2 to 5; the dosage ratio of carbon nanofibers to the alcohol aqueous solution is 1 g:(200 - 400) mL, and in a specific embodiment, it is 1 g:(300 - 350) mL. The present invention adopts the microemulsion method, and the alcohol aqueous solution forms a microemulsion under the action of a surfactant, and by controlling the reaction conditions, a nanomaterial with high dispersion and uniformity is prepared.

[0049] As an embodiment, the mixing is carried out under the condition of ultrasonic dispersion; the power of the ultrasonic dispersion is 200 - 500 W, and in a specific embodiment, it is 400 W; the temperature of the ultrasonic dispersion is room temperature; the time of the ultrasonic dispersion is 20 - 30 min, and in a specific embodiment, it is 30 min. The present invention disperses the purified carbon nanofibers uniformly in the alcohol aqueous solution through ultrasonic dispersion.

[0050] As an embodiment, the alkalinity is pH = 8 - 12, and in a specific embodiment, it is 8 - 11; the reagent used to adjust the pH value of the obtained mixed solution to alkalinity is ammonia water; the adjustment of the pH value of the obtained mixed solution to alkalinity is carried out under the condition of stirring; the stirring rate is 200 - 600 rpm, and in a specific embodiment, it is 300 - 500 rpm; the stirring is magnetic stirring.

[0051] As an embodiment, the silicate ester is tetraethyl orthosilicate and / or tetramethyl orthosilicate, and in a specific embodiment, it is tetraethyl orthosilicate.

[0052] As an embodiment, the mass concentration of carbon nanofibers in the reaction solution is 1 - 10 g / L, and in a specific embodiment, it is 2 - 5 g / L, the mass concentration of the quaternary ammonium hydroxide cationic surfactant is 0.5 - 3 g / L, and in a specific embodiment, it is 0.7 - 2 g / L, and the mass concentration of the silicate ester is 0.5 - 10 g / L, and in a specific embodiment, it is 2 - 9.5 g / L.

[0053] As an implementation manner, the temperature of the hydrolysis polycondensation reaction is 10 to 30 °C, specifically 15 to 20 °C in specific embodiments; the time of the hydrolysis polycondensation reaction is 12 to 24 h, specifically 12 to 20 h in specific embodiments; the hydrolysis polycondensation reaction is carried out under stirring; the rate of the stirring is 200 to 600 rpm, specifically 300 to 500 rpm in specific embodiments; the stirring is magnetic stirring.

[0054] During the hydrolysis polycondensation reaction, the quaternary ammonium base cationic surfactant hydrolyzes to generate organic ammonium cations in the alkaline system of the alcohol aqueous solution. After adding the silicate ester, the alcohol and water form a system similar to "oil-in-water". The hydrophilic segment of the quaternary ammonium base cationic surfactant is dispersed in water, and the hydrophobic end is at the oil-water interface of the system. By reducing the free energy of the system, it plays a key role in stabilizing the oil phase. The silicate ester in the oil phase can diffuse to the oil-water interface. Under the condition that the pH value in the water phase is alkaline, it promotes the hydrolysis polycondensation reaction of the silicate ester at the oil-water interface. Under magnetic stirring, a layer of SiO 2 coating layer is formed on the surface of the carbon nanofibers.

[0055] As an implementation manner, after the hydrolysis polycondensation reaction, it further includes: sequentially subjecting the product obtained from the hydrolysis polycondensation reaction to solid-liquid separation, washing and drying to obtain silica-coated carbon nanofibers; the solid-liquid separation is centrifugation; the rotation speed of the centrifugation is 10000 to 12000 rpm, specifically 10000 to 11000 rpm in specific embodiments; the time of the centrifugation is 10 to 30 min, specifically 10 to 20 min in specific embodiments; the washing is water washing; the washing is carried out until the pH value of the washed solution is neutral; the drying temperature is 70 to 80 °C, specifically 70 to 75 °C in specific embodiments; the drying time is 12 to 24 h, specifically 12 to 20 h in specific embodiments.

[0056] After obtaining the silica-coated carbon nanofibers, the present invention mixes the dispersion of the silica-coated carbon nanofibers, the solution of the metal salt, the silicate compound and the alkaline substance to obtain a hydrothermal precursor solution for hydrothermal reaction, and obtains silica-coated carbon nanofibers loaded with nickel-based silicate nanotubes; the metal salt includes nickel salt, or nickel salt and metal promoter salt; the metal elements in the metal promoter salt include one or more of iron, cobalt, copper, manganese, lanthanum, cerium and magnesium.

[0057] As an implementation method, the preparation method of the dispersion of silica-coated carbon nanofibers is as follows: Mix the silica-coated carbon nanofibers and water and perform ultrasonic dispersion to obtain the dispersion of silica-coated carbon nanofibers; the dosage ratio of the silica-coated carbon nanofibers to water is (0.4 - 0.7) g : (10 - 30) mL, specifically (0.5 - 0.6) g : (20 - 25) mL in specific embodiments; the power of the ultrasonic dispersion is 200 - 500 W, specifically 400 W in specific embodiments; the temperature of the ultrasonic dispersion is room temperature; the time of the ultrasonic dispersion is 20 - 30 min, specifically 30 min in specific embodiments.

[0058] As an implementation method, the metal salt includes nickel salt, or nickel salt and metal promoter salt; the nickel salt is nickel chloride and / or nickel nitrate, specifically nickel chloride in specific embodiments; the metal promoter salt is one or several of metal nitrates, metal chlorides, and metal acetates, specifically copper chloride, or lanthanum chloride, or cobalt nitrate and magnesium nitrate, or manganese acetate tetrahydrate and magnesium nitrate in specific embodiments; the metal elements in the metal promoter salt include one or several of iron, cobalt, copper, manganese, lanthanum, cerium, and magnesium, specifically copper, or lanthanum, or cobalt and magnesium, or manganese and magnesium in specific embodiments; the mass ratio of the nickel salt to the metal promoter salt is 0.3 - 0.6 : 0.03 - 0.05, specifically 0.5 - 0.6 : 0.03 - 0.04 in specific embodiments; the preparation method of the solution of the metal salt is: Mix the metal salt and water and perform ultrasonic dispersion to obtain the solution of the metal salt; the dosage ratio of the metal salt to water is (0.3 - 0.7) g : (10 - 30) mL, specifically (0.4 - 0.6) g : (20 - 25) mL in specific embodiments; the power of the ultrasonic dispersion is 200 - 500 W, specifically 400 W in specific embodiments; the temperature of the ultrasonic dispersion is room temperature; the time of the ultrasonic dispersion is 20 - 30 min, specifically 30 min in specific embodiments.

[0059] As an implementation method, the silicate compound is tetraethyl orthosilicate and / or sodium silicate, specifically sodium silicate in specific embodiments; the silicate compound is used in the form of an aqueous solution; the concentration of the sodium silicate aqueous solution is 0.5 mol / L.

[0060] As an implementation method, the alkaline substance is one or several of sodium hydroxide, urea, and ammonia water, specifically sodium hydroxide in specific embodiments; the mass concentration of the ammonia water is 25 - 28%, specifically 25 - 27% in specific embodiments.

[0061] The function of adding the alkaline substance in the present invention is: On the one hand, SiO is more likely to dissolve to form SiO under hydrothermal conditions under alkaline conditions. 2 Under alkaline conditions, it is easier to dissolve to form SiO. 3 2- , and on the other hand, the alkaline condition in the hydrothermal reaction is more conducive to the reaction of metal ions with SiO.3 2- React to form nickel silicate nanotubes. When adding NaOH, Ni 2+ reacts with SiO 3 2- , OH - to produce nickel silicate. When adding ammonia water, Ni 2+ or nickel ammonia ions react with SiO 3 2- , OH - to produce nickel silicate.

[0062] As an implementation manner, the mass concentration of silica-coated carbon nanofibers in the hydrothermal precursor solution is 1-22 g / L, specifically 1-20 g / L in specific embodiments, the mass concentration of nickel salt is 1-22 g / L, specifically 1-20 g / L in specific embodiments, the mass concentration of metal auxiliary salt is 0-12% of the mass concentration of the nickel salt, specifically 0-10% in specific embodiments, the mass concentration of silicate compound is 1-2 times the mass concentration of the nickel salt, specifically 1.0-1.5 times in specific embodiments, and the mass concentration of alkaline substance is 1-22 times the mass concentration of the nickel salt, specifically 1-20 times in specific embodiments.

[0063] As an implementation manner, mixing the dispersion of silica-coated carbon nanofibers, the solution of metal salt, silicate compound and alkaline substance is as follows: mixing the dispersion of silica-coated carbon nanofibers and the solution of metal salt for the first stirring, then adding the silicate compound for the second stirring, and finally adding the alkaline substance for the third stirring; the first stirring, the second stirring and the third stirring are magnetic stirrings; the rates of the first stirring, the second stirring and the third stirring are independently 200-600 rpm, specifically 300-500 rpm in specific embodiments; the times of the first stirring, the second stirring and the third stirring are independently 5-20 min, specifically 10-15 min in specific embodiments.

[0064] As an implementation manner, the equipment used for the hydrothermal reaction is a hydrothermal reaction kettle; the temperature of the hydrothermal reaction is 150-220 °C, specifically 200-210 °C in specific embodiments, and the time of the hydrothermal reaction is 12-48 h, specifically 24-48 h in specific embodiments.

[0065] Under alkaline conditions, a SiO coating layer is formed on the surface of carbon nanofibers 2 to form SiO 3 2- ions, and the following reaction occurs under hydrothermal conditions:

[0066] Ni 2+ +SiO 3 2- +OH - →Ni3 Si 2 O 5 (OH) 4 nanotube

[0067] In an alkaline medium, the nickel-based silicate layered structure releases surface tension and self-curls to form nanotubes.

[0068] As an implementation, after the hydrothermal reaction, it further includes: after cooling the hydrothermal reaction product to room temperature, successively performing solid-liquid separation, washing, and drying to obtain silica-coated carbon nanofibers loaded with nickel-based silicate nanotubes; the solid-liquid separation is centrifugation; the rotation speed of the centrifugation is 10,000 - 12,000 rpm, specifically 10,000 - 11,000 rpm in specific embodiments; the centrifugation time is 10 - 30 min, specifically 10 - 20 min in specific embodiments; the washing is water washing; the washing is until the pH value of the washed solution is neutral; the drying temperature is 70 - 80 °C, specifically 70 - 75 °C in specific embodiments; the drying time is 12 - 24 h, specifically 12 - 20 h in specific embodiments.

[0069] After obtaining the silica-coated carbon nanofibers loaded with nickel-based silicate nanotubes, the present invention calcines the silica-coated carbon nanofibers loaded with nickel-based silicate nanotubes in a protective gas, and then performs a reduction reaction on the obtained calcined product in a reducing atmosphere to obtain a nickel-based silicate composite catalyst.

[0070] As an implementation, the protective gas is nitrogen; the calcination temperature is 300 - 550 °C, specifically 500 - 550 °C in specific embodiments; the calcination time is 1 - 3 h, specifically 2 - 3 h in specific embodiments.

[0071] The present invention calcines the silica-coated carbon nanofibers loaded with nickel-based silicate nanotubes in a protective gas and has the following effects: 1. Remove moisture and impurities. During the hydrolysis of silicate esters on the surface of quaternary ammonium base cationic surfactants under alkaline conditions and the process of coating a silica shell layer on the surface of carbon nanofibers, unreacted completely organic substances and unstable components, etc., can be removed by calcination in a protective gas, improving the purity of the sample. 2. The protective gas can prevent the carbon nanofibers from undergoing an oxidation reaction with oxygen at high temperatures. 3. Fix the morphology of the metal silicate structure during the calcination of the sample. 4. Calcination can play an activating component role, promoting the interaction between the active metal of the metal silicate and the additives.

[0072] As an implementation, the reducing atmosphere is hydrogen; the temperature of the reduction reaction is 500 - 600 °C, specifically 500 °C, 550 °C, or 600 °C in specific embodiments; the time of the reduction reaction is 1 - 3 h, specifically 2 - 3 h in specific embodiments.

[0073] In the present invention, a part of the metal silicate is reduced to active metallic nickel and copper, cobalt, iron, etc. in the metal promoter in a reducing atmosphere during roasting.

[0074] The preparation method provided by the present invention is simple, and can realize the controllable preparation of a nickel-based catalyst with a nanotube morphology structure, with a high nickel loading, high catalytic activity, and excellent anti-coking and anti-sintering capabilities.

[0075] The present invention also provides a nickel-based silicate composite catalyst prepared by the preparation method described in the above technical solution, including carbon nanofibers, a silica shell layer coated on the surface of the carbon nanofibers, nickel-based silicate nanotubes loaded on the surface of the silica shell layer, and metallic nickel doped in the nickel-based silicate nanotubes, or metallic nickel doped in the nickel-based silicate nanotubes, elemental metals of the metal promoter, and alloys formed by the elemental metals of metallic nickel and the metal promoter; the nickel-based silicate includes nickel silicate, or nickel silicate and silicates of the metal promoter;

[0076] In the nickel-based silicate composite catalyst, the mass ratio of carbon, nickel, and silicon elements is 1-20:1-3:1; the mass percentage content of the metal promoter in the nickel-based silicate composite catalyst is 0-6%.

[0077] As an implementation manner, the metal promoter includes one or more of iron, cobalt, copper, manganese, lanthanum, cerium, and magnesium, specifically copper, or lanthanum, or cobalt and magnesium, or manganese and magnesium in specific embodiments.

[0078] As an implementation manner, the average pore diameter of the nickel-based silicate composite catalyst is 12-16 nm, specifically 13-15 nm in specific embodiments; the diameter of the metal silicate nanotubes is 10-25 nm, specifically 10-20 nm, 15-25 nm, or 10-25 nm in specific embodiments, and the wall thickness is 1-10 nm, specifically 1-7 nm, 1-8 nm, or 1-10 nm in specific embodiments. In the present invention, the wall of the nanotube is a layered structure.

[0079] As an implementation manner, the mass ratio of carbon, nickel, and silicon elements in the nickel-based silicate composite catalyst is 1-20:1-3:1, specifically 2-20:1-2:1 in specific embodiments; the mass percentage content of the metal promoter in the nickel-based silicate composite catalyst is 0-6%, specifically 0-5% in specific embodiments.

[0080] The present invention also provides an application of the nickel-based silicate composite catalyst described in the above technical solution in the dry reforming reaction of methane and carbon dioxide.

[0081] The present invention also provides a dry reforming reaction method of methane and carbon dioxide, including the following steps: under normal pressure, a gas containing CH 4 、CO 2and N 2 The mixture of and the catalyst are mixed to carry out dry reforming reaction to obtain syngas; the syngas includes hydrogen and carbon monoxide;

[0082] The catalyst is the nickel-based silicate composite catalyst described in the above technical solution.

[0083] As an implementation manner, the CH 4 、CO 2 and N 2 have a volume ratio of 1:1:1 to 2, and in a specific embodiment, it is 1:1:1; the mixing is to introduce the mixture gas containing CH 4 、CO 2 and N 2 into a fixed-bed reactor containing the catalyst; the space velocity of the mixture gas introduction is 20 - 50 L / (g catalyst·h), and in a specific embodiment, it is 25 - 36 L / (g catalyst·h); the temperature of the dry reforming reaction is 650 - 850 °C, and in a specific embodiment, it is 700 - 750 °C, and the time is 1 - 30 h, and in a specific embodiment, it is 10 - 20 h.

[0084] As an implementation manner, the conversion rate of methane ≥ 85%, and in a specific embodiment, it is 85.5 - 89.6%; the conversion rate of carbon dioxide ≥ 88%, and in a specific embodiment, it is 88.6 - 92.8%.

[0085] Under the catalytic action of the nickel-based silicate composite catalyst, methane and carbon dioxide undergo dry reforming reaction: CH 4 +CO 2 →CO+H 2 .

[0086] Next, the technical solutions in the present invention will be clearly and completely described in combination with the embodiments in the present invention, but they cannot be understood as limiting the protection scope of the present invention.

[0087] Example 1

[0088] (1) 1 g of carbon nanofibers (with a diameter of 50 - 200 nm and a length of 1 - 15 μm) was added to a mixed solution of 10 mL of 65 wt% nitric acid and 30 mL of 98 wt% sulfuric acid, and acidification pretreatment was carried out at 90 °C for 2 h. After cooling to room temperature, it was washed with water multiple times until the washed aqueous solution was neutral, centrifuged at 10000 rpm for 20 min, and dried at 70 °C for 12 h to obtain purified carbon nanofibers. The above purified carbon nanofibers and 0.36 g of cetyltrimethylammonium bromide were added to a mixed solution of 50 mL of water and 300 mL of ethanol, ultrasonically dispersed at 400 W for 30 min at room temperature, then ammonia water was added under magnetic stirring at 500 rpm to adjust the pH value to 8, 2 mL of tetraethyl orthosilicate was added, and hydrolysis polycondensation reaction was carried out at 20 °C for 18 h. After centrifugal separation at 10000 rpm for 20 min and washing with water multiple times until the washed aqueous solution was neutral, it was dried at 70 °C for 12 h to obtain carbon nanofibers coated with silica.

[0089] (2) 0.5 g of the above carbon nanofibers coated with silica was added to 20 mL of water and ultrasonically dispersed at 400 W for 30 min at room temperature, and 0.5 g of nickel chloride hexahydrate was added to 20 mL of water and ultrasonically dispersed at 400 W for 30 min at room temperature. After the two solutions were mixed and magnetically stirred at 500 rpm for 10 min, 10 mL of 0.5 mol / L sodium silicate aqueous solution was added, magnetically stirred at 500 rpm for 10 min, 6 g of sodium hydroxide was added, magnetically stirred at 500 rpm for 10 min, and the solution was transferred to a hydrothermal reaction kettle. Hydrothermal reaction was carried out at 200 °C for 48 h. After the reaction was completed, it was cooled to room temperature, centrifuged at 10000 rpm for 20 min, washed with water multiple times until the washed aqueous solution was neutral, dried at 70 °C for 12 h, calcined at 500 °C for 2 h in a nitrogen atmosphere, and reduced at 550 °C for 3 h in a hydrogen atmosphere to obtain a nickel-based silicate composite catalyst.

[0090] Example 2

[0091] (1) Add 1 g of carbon nanofibers (with a diameter of 50 - 200 nm and a length of 1 - 15 μm) to a mixed solution of 30 mL of 65 wt% nitric acid and 10 mL of 98 wt% sulfuric acid, and conduct acid pretreatment at 90 °C for 2 h. Cool to room temperature, wash with water multiple times until the washed aqueous solution is neutral, centrifuge at 10000 rpm for 20 min, and dry at 70 °C for 12 h to obtain purified carbon nanofibers; Add the above purified carbon nanofibers and 0.42 g of cetyltrimethylammonium bromide to a mixed solution of 100 mL of water and 200 mL of ethanol, ultrasonically disperse at 400 W for 30 min at room temperature, then add ammonia water to adjust the pH value to 10 under the condition of magnetic stirring at 500 rpm, add 1 mL of tetraethyl orthosilicate, and conduct hydrolysis and polycondensation reaction at 20 °C for 12 h. Centrifuge at 10000 rpm for 20 min, wash with water multiple times until the washed aqueous solution is neutral, and dry at 70 °C for 12 h to obtain carbon nanofibers coated with silica;

[0092] (2) Add 0.4 g of carbon nanofibers coated with silica to 10 mL of water and ultrasonically disperse at 400 W for 30 min at room temperature. Add 0.3 g of nickel chloride hexahydrate and 0.03 g of copper chloride dihydrate to 20 mL of water and ultrasonically disperse at 400 W for 30 min at room temperature; After mixing the two solutions, stir magnetically at 500 rpm for 10 min, then add 5 mL of 0.5 mol / L sodium silicate aqueous solution, stir magnetically at 500 rpm for 10 min, add 10 mL of concentrated ammonia water (with a concentration of 25 wt%) and 1 g of urea, stir magnetically at 500 rpm for 10 min, transfer the solution into a hydrothermal reaction kettle, conduct hydrothermal reaction at 210 °C for 36 h. After the reaction is completed, cool to room temperature, centrifuge at 10000 rpm for 20 min, wash with water multiple times until the washed aqueous solution is neutral, dry at 70 °C for 12 h, calcine at 550 °C for 3 h under a nitrogen atmosphere, and conduct reduction reaction at 600 °C for 2 h under a hydrogen atmosphere to obtain a nickel-based silicate composite catalyst.

[0093] Example 3

[0094] (1) 1 g of carbon nanofibers (with a diameter of 50 - 200 nm and a length of 1 - 15 μm) was added to a mixed solution of 5 mL of 65 wt% nitric acid and 35 mL of 98 wt% sulfuric acid, and acidification pretreatment was carried out at 90 °C for 2 h. After cooling to room temperature, it was washed with water multiple times until the washed aqueous solution was neutral, centrifuged at 10000 rpm for 20 min, and dried at 70 °C for 12 h to obtain purified carbon nanofibers. The above purified carbon nanofibers and 0.25 g of cetyltrimethylammonium bromide were added to a mixed solution of 100 mL of water and 200 mL of ethanol, ultrasonically dispersed at 400 W for 30 min at room temperature, then ammonia water was added under magnetic stirring at 500 rpm to adjust the pH value to 9, 2.5 mL of tetraethyl orthosilicate was added, and hydrolysis polycondensation reaction was carried out at 20 °C for 20 h, centrifuged at 10000 rpm for 20 min, washed with water multiple times until the washed aqueous solution was neutral, and dried at 70 °C for 12 h to obtain carbon nanofibers coated with silica.

[0095] (2) 0.6 g of carbon nanofibers coated with silica was added to 25 mL of water and ultrasonically dispersed at 400 W for 30 min at room temperature. 0.5 g of nickel chloride hexahydrate, 0.03 g of lanthanum chloride tetrahydrate and 25 mL of water were ultrasonically dispersed at 400 W for 30 min at room temperature. After mixing the two solutions, magnetic stirring was carried out at 500 rpm for 10 min, 10 mL of 0.5 mol / L sodium silicate aqueous solution was added, magnetic stirring was carried out at 500 rpm for 10 min, 7 g of sodium hydroxide was added, magnetic stirring was carried out at 500 rpm for 10 min, the solution was transferred into a hydrothermal reaction kettle, and hydrothermal reaction was carried out at 200 °C for 48 h. After the reaction ended, it was cooled to room temperature, centrifuged at 10000 rpm for 20 min, washed with water multiple times until the washed aqueous solution was neutral, dried at 70 °C for 12 h, calcined at 550 °C for 2 h in a nitrogen atmosphere, and reduced at 500 °C for 3 h in a hydrogen atmosphere to obtain a nickel-based silicate composite catalyst.

[0096] Example 4

[0097] (1) Add 1 g of carbon nanofibers (with a diameter of 50 - 200 nm and a length of 1 - 15 μm) to a mixed solution of 20 mL of 65 wt% nitric acid and 20 mL of 98 wt% sulfuric acid, and perform acid pretreatment at 90 °C. After refluxing for 2 h, cool to room temperature, wash with water multiple times until the washed aqueous solution is neutral, centrifuge at 10000 rpm for 20 min, and dry at 70 °C for 12 h to obtain purified carbon nanofibers; add the above purified carbon nanofibers and 0.32 g of cetyltrimethylammonium bromide to a mixed solution of 50 mL of water and 250 mL of ethanol, ultrasonically disperse at 400 W for 30 min at room temperature, then add ammonia water to adjust the pH value to 11 under magnetic stirring at 500 rpm, add 1.5 mL of tetraethyl orthosilicate, and perform hydrolysis and polycondensation reaction at 20 °C for 16 h, centrifuge at 10000 rpm for 20 min, wash with water multiple times until the washed aqueous solution is neutral, and dry at 70 °C for 12 h to obtain carbon nanofibers coated with silica.

[0098] (2) Add 0.6 g of the above carbon nanofibers coated with silica to 20 mL of water and ultrasonically disperse at 400 W for 30 min at room temperature. Ultrasonically disperse 0.6 g of nickel chloride hexahydrate, 0.03 g of cobalt nitrate, 0.02 g of magnesium nitrate and 30 mL of water at 400 W for 30 min at room temperature; after mixing the two solutions, stir magnetically at 500 rpm for 10 min, add 10 mL of 0.5 mol / L sodium silicate aqueous solution, stir magnetically at 500 rpm for 10 min, add 8 g of sodium hydroxide, stir magnetically at 500 rpm for 10 min, transfer the solution into a hydrothermal reaction kettle, perform hydrothermal reaction at 200 °C for 36 h, after the reaction is completed, cool to room temperature, centrifuge at 10000 rpm for 20 min, wash with water multiple times until the washed aqueous solution is neutral, dry at 70 °C for 12 h, calcine at 550 °C for 3 h in a nitrogen atmosphere, and perform reduction reaction at 500 °C for 3 h in a hydrogen atmosphere to obtain a nickel-based silicate composite catalyst.

[0099] Example 5

[0100] (1) Add 1 g of carbon nanofibers (with a diameter of 50 - 200 nm and a length of 1 - 15 μm) to a mixed solution of 5 mL of 65 wt% nitric acid and 35 mL of 98 wt% sulfuric acid, and perform acid pretreatment at 90 °C. After refluxing for 2 h, cool to room temperature, wash with water multiple times until the washed aqueous solution is neutral, centrifuge at 10000 rpm for 20 min, and dry at 70 °C for 12 h to obtain purified carbon nanofibers; Add the above purified carbon nanofibers and 0.45 g of cetyltrimethylammonium bromide to a mixed solution of 100 mL of water and 200 mL of ethanol, ultrasonically disperse at 400 W for 30 min at room temperature, then add ammonia water to adjust the pH value to 12 under magnetic stirring at 500 rpm, add 3 mL of tetraethyl orthosilicate, and carry out hydrolysis and polycondensation reaction at 20 °C for 24 h. Centrifuge at 10000 rpm for 20 min, wash with water multiple times until the washed aqueous solution is neutral, and dry at 70 °C for 12 h to obtain carbon nanofibers coated with silica;

[0101] (2) Add 0.7 g of the above carbon nanofibers coated with silica to 20 mL of water and ultrasonically disperse at 400 W for 30 min at room temperature. Add 0.6 g of nickel chloride hexahydrate, 0.02 g of manganese acetate tetrahydrate, and 0.02 g of magnesium nitrate to 40 mL of water and ultrasonically disperse at 400 W for 30 min at room temperature; After mixing the two solutions, stir magnetically at 500 rpm for 10 min, then add 10 mL of 0.5 mol / L sodium silicate aqueous solution, stir magnetically at 500 rpm for 10 min, add 7 g of sodium hydroxide, stir magnetically at 500 rpm for 10 min, transfer the solution into a hydrothermal reaction kettle, carry out hydrothermal reaction at 200 °C for 48 h. After the reaction is completed, cool to room temperature, centrifuge at 10000 rpm for 20 min, wash with water multiple times until the washed aqueous solution is neutral, dry at 70 °C for 12 h, calcine at 550 °C for 2 h in a nitrogen atmosphere, and carry out reduction reaction at 500 °C for 3 h in a hydrogen atmosphere to obtain a nickel-based silicate composite catalyst.

[0102] Comparative Example 1

[0103] (1) Add 1 g of carbon nanofibers (with a diameter of 50 - 200 nm and a length of 1 - 15 μm) to a mixed solution of 10 mL of 65 wt% nitric acid and 30 mL of 98 wt% sulfuric acid, perform acid pretreatment at 90 °C for 2 h, then cool to room temperature, wash with water multiple times until the washed aqueous solution is neutral, centrifuge at 10000 rpm for 20 min, and dry at 70 °C for 12 h to obtain purified carbon nanofibers;

[0104] (2) Add 0.5 g of the above-mentioned silica-coated carbon nanofibers to 20 mL of water and ultrasonically disperse them at 400 W for 30 min at room temperature. Add 0.5 g of nickel chloride hexahydrate to 20 mL of water and ultrasonically disperse them at 400 W for 30 min at room temperature. After mixing the two solutions, stir them magnetically at 500 rpm for 10 min, then add 10 mL of 0.5 mol / L sodium silicate aqueous solution, stir magnetically at 500 rpm for 10 min, add 6 g of sodium hydroxide, stir magnetically at 500 rpm for 10 min, transfer the solution into a hydrothermal reaction kettle, carry out hydrothermal reaction at 200 °C for 48 h. After the reaction is completed, cool it to room temperature, centrifuge it at 10000 rpm for 20 min, wash it with water multiple times until the washed aqueous solution is neutral, dry it at 70 °C for 12 h, calcine it at 500 °C for 2 h in a nitrogen atmosphere, and carry out reduction reaction at 550 °C for 3 h in a hydrogen atmosphere to obtain the nickel-based composite catalyst.

[0105] Application Examples 1-5 and Comparative Application Example 1

[0106] Under atmospheric pressure, mix CH 4 , CO 2 and N 2 in a volume ratio of 1:1:1. Pass the obtained mixed gas into a fixed-bed reactor containing the nickel-based silicate composite catalyst prepared in Examples 1-5 and the nickel-based composite catalyst prepared in Comparative Example 1 at a space velocity of 36 L / (g catalyst·h) and carry out dry reforming reaction at 750 °C for 20 h to obtain syngas containing hydrogen and carbon monoxide.

[0107] Performance Test

[0108] (1) Figure 1 is the X-ray powder diffraction pattern of the hydrothermal reaction product in Example 1. As Figure 1 can be seen, the hydrothermal reaction product in Example 1 is identified as nickel silicate Ni 3 Si 2 O 5 (OH) 4 .

[0109] Figure 2 is the transmission electron microscope (TEM) morphology characterization diagram of the hydrothermal reaction product in Example 1. As Figure 2 can be seen, at a size of 50 nm, nanotubes are synthesized on the surface of the carbon nanofibers. The diameter of the nanotubes is 10-20 nm, the tube wall is a layered structure, and the wall thickness is 1-7 nm.

[0110] Combining Figure 1 and Figure 2 it can be seen that nickel-based silicate nanotubes are successfully synthesized on the surface of the carbon nanofibers.

[0111] (2) Figure 3 is the X-ray powder diffraction pattern of the hydrothermal reaction product in Example 2. AsFigure 3 It can be seen that the hydrothermal reaction product in Example 2 was identified as nickel silicate Ni 3 Si 2 O 5 (OH) 4 .

[0112] Figure 4 It is the transmission electron microscope (TEM) morphology characterization diagram of the hydrothermal reaction product in Example 2. From Figure 4 it can be seen that at a size of 20 nm, nanotubes were synthesized on the surface of carbon nanofibers. The diameter of the nanotubes was 15 - 25 nm, the tube wall was a layered structure, and the wall thickness was 1 - 8 nm.

[0113] Combined with Figure 3 and Figure 4 it can be seen that nickel copper silicate nanotubes were successfully synthesized on the surface of carbon nanofibers.

[0114] (3) Figure 5 It is the X-ray powder diffraction pattern of the hydrothermal reaction product in Example 4. From Figure 5 it can be seen that the hydrothermal reaction product in Example 4 was identified as nickel silicate Ni 3 Si 2 O 5 (OH) 4 .

[0115] Figure 6 It is the transmission electron microscope (TEM) morphology characterization diagram of the hydrothermal reaction product in Example 4. From Figure 6 it can be seen that at a size of 200 nm, nanotubes were synthesized on the surface of carbon nanofibers. The diameter of the nanotubes was 10 - 25 nm, the tube wall was a layered structure, and the wall thickness was 1 - 10 nm.

[0116] Combined with Figure 5 and Figure 6 it can be seen that nickel-based silicate nanotubes were successfully synthesized on the surface of carbon nanofibers.

[0117] Perform energy dispersive X-ray spectroscopy (EDX) point scanning on the surface of the sample in Figure 6 , and the results are as shown in Figure 7 . From Figure 7 it can be seen that the sample was mainly composed of carbon, oxygen, nickel, silicon, cobalt, magnesium, and copper elements, and the copper element came from the copper mesh of the transmission electron microscope grid.

[0118] (4) Use a transmission electron microscope (TEM) to analyze the morphology of the hydrothermal reaction product in Comparative Example 1, and the results are as shown in Figure 8 . From Figure 8 it can be seen that no nanotubes were observed to form on the surface of carbon nanofibers in the sample prepared in Comparative Example 1.

[0119] (5) Under normal pressure, CH 4 , CO2 and N 2 Mix them in a volume ratio of 1:1:1 and feed them into a fixed-bed reactor containing a catalyst at a space velocity of 36 L / (g catalyst·h) for reaction at 750 °C for 20 h. The catalysts are the nickel-based silicate composite catalysts prepared in Examples 1 to 5 and the nickel-based composite catalyst prepared in Comparative Example 1. Measure the methane conversion rate and carbon dioxide conversion rate. The results are shown in Table 1.

[0120] Table 1 Methane and carbon dioxide conversion rates under different catalysts

[0121] Serial number Methane conversion rate / % Carbon dioxide conversion rate / % Example 1 85.5 88.6 Example 2 87.2 90.1 Example 3 86.6 89.3 Example 4 89.6 92.8 Example 5 88.9 91.6 Comparative example 1 75.5 82.3

[0122] Comparison Figure 3 and Figure 1 It can be seen that in Example 2, when metal copper is added, the X-ray diffraction peaks of the sample do not show obvious changes, Figure 3 and no diffraction peaks related to copper appear, indicating that the copper species are in a highly dispersed state. The highly dispersed copper species are conducive to the formation of strong interactions between metals, improving the catalytic activity and anti-coking ability of the catalyst. Comparing the catalytic activity test data of the samples in Example 2 and Example 1 in Table 1, the results show that after adding metal copper, the catalytic activity and thermal stability of the catalyst are both significantly improved, and the catalyst has good anti-sintering and anti-coking abilities.

[0123] The catalytic activity test data of the sample in Example 3 in Table 1 show that after adding metal lanthanum, the catalytic activity and thermal stability of the catalyst are both significantly improved, and the catalyst has good anti-sintering and anti-coking abilities.

[0124] Comparison Figure 5 and Figure 1 It can be seen that in Example 4, when metal cobalt and metal magnesium are added, the X-ray diffraction peaks of the sample do not show obvious changes, Figure 5 and no diffraction peaks related to cobalt and magnesium appear, indicating that the cobalt species and magnesium species are in a highly dispersed state. The highly dispersed cobalt species and magnesium species are conducive to the formation of strong interactions between metals, thereby improving the catalytic activity, anti-sintering ability and anti-coking ability of the catalyst. Comparing the catalytic activity test data of Example 4 and Example 1 in Table 1, the results show that after adding metal cobalt and metal magnesium, the catalytic activity and thermal stability of the catalyst are both significantly improved, and the catalyst has good anti-sintering and anti-coking abilities.

[0125] The catalytic activity test data of the sample in Example 5 in Table 1 show that after adding metal manganese and magnesium, the catalytic activity and thermal stability of the catalyst are both significantly improved, and the catalyst has good anti-sintering and anti-coking abilities.

[0126] From Figure 8It can be seen that in Comparative Example 1, the carbon nanofibers were not coated with silica, and no rice tube structure morphology was formed on the carbon nanofibers in the prepared sample. In Example 1, a silicate nanotube morphology was formed after coating the carbon nanofibers with silica. Comparing the catalytic activity test results of the samples in Example 1 and Comparative Example 1 in Table 1, it shows that the catalytic activity and stability of the catalyst prepared in Example 1 are superior to those in Comparative Example 1, indicating that the catalyst with a nanotube morphology structure has higher catalytic activity and stability, and the catalyst has better anti-sintering and anti-coking capabilities.

[0127] (6) The pore sizes of the nickel-based silicate composite catalyst prepared in Example 1 were tested by the BET method and the BJH method respectively. The adsorption and desorption curves of the BJH method are shown in Figure 9 and Figure 10 respectively.

[0128] The measured results of the BET method adsorption and desorption average pore sizes (4V / A) of the nickel-based silicate composite catalyst were 15.8881 nm and 12.4677 nm respectively.

[0129] From Figure 9 and Figure 10 , it can be known that the measured results of the BJH adsorption and desorption average pore sizes (4V / A) of the nickel-based silicate composite catalyst were 15.9152 nm and 13.1977 nm respectively.

[0130] Although the above embodiments have described the present invention in detail, they are only a part of the embodiments of the present invention rather than all embodiments. People can also obtain other embodiments without creative efforts based on these embodiments, and these embodiments all fall within the protection scope of the present invention.

Claims

1. A method for preparing a nickel-based silicate composite catalyst, characterized in that: The following steps are involved: The carbon nanofibers, quaternary ammonium base cationic surfactant and alcohol aqueous solution are mixed, the pH value of the obtained mixed solution is adjusted to alkaline, and then mixed with silicate, and the obtained reaction solution is subjected to hydrolysis and polycondensation reaction to obtain silicon dioxide-coated carbon nanofibers; The dispersion of the silicon dioxide-coated carbon nanofibers, a solution of a metal salt, a silicic acid compound and an alkaline substance are mixed, and the obtained hydrothermal precursor solution is subjected to a hydrothermal reaction to obtain the silicon dioxide-coated carbon nanofibers loaded with nickel-based silicate nanotubes; the metal salt includes a nickel salt, or a nickel salt and a metal auxiliary salt; the metal element in the metal auxiliary salt includes one or more of iron, cobalt, copper, manganese, lanthanum, cerium and magnesium; The mass concentration of the silicon dioxide-coated carbon nanofibers in the hydrothermal precursor solution is 1-22 g / L, the mass concentration of the nickel salt is 1-22 g / L, the mass concentration of the metal additive salt is 0-12% of the mass concentration of the nickel salt, and the mass concentration of the silicate compound is 1-2 times the mass concentration of the nickel salt; The silicon dioxide-coated carbon nanofiber loaded with nickel-based silicate nanotubes is calcined in a protective gas, and the obtained calcined product is subjected to a reduction reaction in a reducing atmosphere to obtain a nickel-based silicate composite catalyst.

2. The preparation method according to claim 1, characterized in that: The nickel salt is nickel chloride and / or nickel nitrate; the metal additive salt is one or more of nitrate, chloride and acetate.

3. The preparation method according to claim 1, characterized in that: The quaternary ammonium base cationic surfactant is one or more of hexadecyltrimethylammonium bromide, dodecyltrimethylammonium bromide, tetradecyltrimethylammonium bromide and octadecyltrimethylammonium bromide.

4. The preparation method according to claim 1 or 3, characterized in that: The mass concentration of carbon nanofibers in the reaction solution is 1-10 g / L, the mass concentration of quaternary ammonium base cationic surfactant is 0.5-3 g / L, and the mass concentration of silicate is 0.5-10 g / L.

5. The preparation method according to claim 1, characterized in that: The temperature of the hydrothermal reaction is 150-220° C.; the time of the hydrothermal reaction is 12-48 hours.

6. The preparation method according to claim 1, characterized in that: The calcination temperature is 300-550° C. and the calcination time is 1-3 hours.

7. The preparation method according to claim 1, characterized in that: The reducing atmosphere is hydrogen; the temperature of the reducing reaction is 500-600° C.; and the time of the reducing reaction is 1-3 hours.

8. The nickel-based silicate composite catalyst prepared by the preparation method according to any one of claims 1 to 7, characterized in that: The invention comprises carbon nanofibers, a silicon dioxide shell layer coated on the surface of the carbon nanofibers, a nickel-based silicate nanotube loaded on the surface of the silicon dioxide shell layer, and metal nickel doped in the nickel-based silicate nanotubes, or metal nickel doped in the nickel-based silicate nanotubes, a single substance of a metal auxiliary agent, and an alloy formed by the single substance of metal nickel and the single substance of the metal auxiliary agent; the nickel-based silicate comprises nickel silicate, or a silicate of nickel silicate and a metal auxiliary agent; The mass ratio of carbon element, nickel element and silicon element in the nickel-based silicate composite catalyst is 1-20:1-3:1; the mass percentage of metal additive in the nickel-based silicate composite catalyst is 0-6%.

9. Use of the nickel-based silicate composite catalyst according to claim 8 in the dry reforming reaction of methane and carbon dioxide.

10. A dry reforming reaction method of methane and carbon dioxide, characterized in that: The following steps are involved: Under normal pressure, a mixed gas containing CH4, CO2 and N2 is mixed with a catalyst to perform a dry reforming reaction to obtain a synthesis gas; the synthesis gas includes hydrogen and carbon monoxide; The catalyst is the nickel-based silicate composite catalyst as claimed in claim 8.

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