Method and application of hydrothermal ammonolysis lignin carbon-based multi-metal catalyst

Abstract

The present application relates to a kind of preparation method of hydrothermal ammonia lignin carbon-based multi-metal catalyst and its application.The present application constructs Ni-N-C structure by hydrothermal nitrogen doping method to enhance the synergistic effect of catalytic active component and lignin carbon-based carrier, while doping Zn to regulate the electronic structure of Ni, effectively inhibit the hydrogenolysis of carbon-carbon bond and methanation in the reaction process, so as to improve the catalytic activity of catalyst and the selectivity of product.The catalyst obtained according to the preparation method of the present application can reach 69.4% ethanol conversion rate, the yield of higher alcohol can reach 50.3%, and the selectivity of gas byproduct is only 2.4%, the catalytic effect is good, and the problems of low ethanol conversion rate, complicated synthesis process and poor stability of existing traditional ethanol Guerbet coupling catalyst can be effectively solved.

Description

TECHNICAL FIELD

[0001] The present application belongs to the field of catalysis technology, and particularly relates to a hydrothermal ammonolysis lignin carbon-based multi-metal catalyst, a preparation method and application thereof. BACKGROUND

[0002] At present, bioethanol is gradually becoming a sustainable alternative fuel (or fuel additive) to traditional gasoline. However, ethanol as a biofuel has some significant limitations, such as low energy density, hydrophilicity, and corrosion to engines. Higher alcohols have higher octane number and energy density, hydrophobicity, better mixing stability and compression ignition performance, and have good environmental benefits, and therefore are potential biofuels.

[0003] At present, the high-efficiency catalysts applied to ethanol coupling experiments mainly include homogeneous iridium, ruthenium complex catalysts, hydroxyapatite catalysts, and metal-supported heterogeneous catalysts, which have the advantages of high specific surface area, controllable acid-base sites, and stable structure; however, these catalysts have the disadvantages of low catalytic activity, harsh reaction conditions, and the like, which further lead to low ethanol conversion rate, increased gas by-products, and the like. Since the metal active components such as Ru, Cu, Pt, Co, and Ni have excellent dehydrogenation performance, they have a wide application in the field of ethanol coupling and other catalysis-related fields. Compared with noble metals, metal nickel has the advantages of high yield and low cost, and the metal nickel supported on a homogeneous base carrier exhibits excellent catalytic activity in ethanol coupling.

[0004] Lignin has a high yield in nature, and is rich in phenolic hydroxyl groups, alcoholic hydroxyl groups, and carboxyl groups. The high carbon content of lignin makes it an ideal carbon material precursor. The catalyst with lignin porous carbon material as the carrier has the advantages of higher specific surface area, greater porosity, excellent electrical conductivity and stability, and easy processing. Therefore, a proper amount of nitrogen-doped modified lignin is used to increase the basic sites on the surface of lignin, and the metal active sites are anchored on the nitrogen-doped carbon material to prepare a catalyst, which has great application potential in ethanol coupling experiments.

[0005] Nickel-based multi-metal catalysts exhibit excellent ethanol coupling catalytic performance. Through nitrogen doping and multi-metal synergistic effect, the electronic environment and defect structure of Ni and the carbon carrier can be effectively improved, thereby increasing the stability of the catalyst and effectively inhibiting the generation of methane and other by-products, and therefore the nickel-based multi-metal catalysts become one of the research hotspots of high-efficiency catalysts for ethanol coupling. However, due to the strong metallic property of nickel, Ni has excellent dehydrogenation activity and C-C bond / C-O bond breaking ability, which leads to the generation of gas by-products in the process of ethanol coupling and affects the yield of higher alcohols. In addition, the low intrinsic activity, less active site exposure, and complex preparation process of the nickel-based single-metal catalyst also make it have no competitiveness in the application of ethanol coupling to prepare higher alcohols. SUMMARY

[0006] The present application aims to overcome the deficiencies and defects in the prior art, and provides a hydrothermal ammonia lignin carbon-based multi-metal catalyst, which can effectively enhance the interaction between the metal active component and the lignin-based carbon carrier through hydrothermal nitrogen doping and multi-metal synergistic effect, improve the electronic environment and defect structure of the nickel-based catalyst, effectively inhibit the hydrogenolysis and methanation of carbon-carbon bonds during the reaction process, and thus improve the catalytic activity of the catalyst and the selectivity of the product.

[0007] To solve the above technical problems, the present application is realized by the following technical scheme.

[0008] The present application provides a preparation method of a hydrothermal ammonia lignin carbon-based multi-metal catalyst, comprising the following steps:

[0009] (1) mixing a lignin solution, a nitrogen source, a nickel source and a metal salt solution, adjusting the pH and then performing a hydrothermal reaction to synthesize a nitrogen-doped metal-lignin precursor;

[0010] (2) performing centrifugal treatment and vacuum freeze-drying on the doped metal-lignin precursor obtained in step (1) to prepare a metal-lignin synthetic material;

[0011] (3) performing calcination on the metal-lignin synthetic material obtained in step (2) under a protective gas atmosphere to obtain a powder-shaped particle, and then performing sufficient grinding to obtain the hydrothermal ammonia lignin carbon-based multi-metal catalyst.

[0012] Preferably, the lignin in step (1) is selected from one or more of the following: Longli enzymatic lignin, sulfite lignin, alkali lignin, kraft lignin, and Russian sodium lignin.

[0013] Preferably, the nitrogen source in step (1) is selected from one or more of the following: melamine, cyanuric acid, disodium EDTA, N,N-dimethylformamide, hydroxylamine hydrochloride, diethylenetriamine, ethylenediamine, dicyandiamide, urea, and ammonia.

[0014] Preferably, the nickel source in step (1) is selected from one or more of the following: nickel chloride, nickel sulfate, nickel ammonium nitrate, nickel acetate, nickel oxalate, and nickel nitrate; most preferably, the nickel source is nickel nitrate.

[0015] As preferably, the metal salt solution in step (1) is selected from one or more of zinc chloride solution, zinc sulfate solution, copper chloride solution, molybdenum nitrate solution, iron chloride solution, copper sulfate solution, manganese sulfate solution, ruthenium chloride solution, copper nitrate solution, zinc nitrate solution, zinc acetate solution, zinc oxalate solution, zinc gluconate solution; more preferably, the metal salt solution is selected from one or more of zinc chloride solution, zinc sulfate solution, zinc nitrate solution, zinc acetate solution, zinc oxalate solution, zinc gluconate solution; most preferably, the metal salt solution is selected from zinc nitrate solution

[0016] As preferably, the molar ratio of nickel element in the nickel source to lignin in step (1) is 5-60:1.

[0017] As preferably, the molar ratio of nickel element in the nickel source to metal element in the metal salt solution in step (1) is 5-60:1.

[0018] As preferably, the amount of lignin in step (1) is 2-90wt% of the total mass of reactants, and the amount of nitrogen source is 2-90wt% of the total mass of reactants.

[0019] As preferably, the mass ratio of lignin to nitrogen source in step (1) is 1:0.1-4; more preferably, the mass ratio of lignin to nitrogen source is 1:0.5-3; most preferably, the mass ratio of lignin to nitrogen source is 1:0.5-1.5.

[0020] As preferably, the pH in step (1) is adjusted to 2-13; more preferably, the pH is adjusted to 7-11; most preferably, the pH is adjusted to 9.

[0021] As preferably, the temperature of the hydrothermal reaction in step (1) is 40-400℃, and the time is 1-64h; more preferably, the temperature of the hydrothermal reaction is 180-230℃, and the time is 6-10h; most preferably, the temperature of the hydrothermal reaction is 195-205℃, and the time is 7-9h.

[0022] As preferably, the speed of centrifugal treatment in step (2) is 3000-10000rpm, and the time is 5-30min.

[0023] As preferably, the temperature of vacuum freeze-drying in step (2) is -60~-40℃, and the time is 12-72h.

[0024] As preferably, the protective gas in step (3) is selected from one or more of ammonia, nitrogen, argon, air, hydrogen; most preferably, the protective gas is selected from nitrogen.

[0025] Preferably, the temperature of the calcination in step (3) is 300-1000℃, and the time is 2-12h; more preferably, the temperature of the calcination is 420-580℃, and the time is 1-3h; most preferably, the temperature of the calcination is 450-550℃, and the time is 1.5-2.5h.

[0026] The second aspect of the present application provides a hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared by the above preparation method.

[0027] The third aspect of the present application provides an application of the above hydrothermal ammonia lignin carbon-based multi-metal catalyst in the preparation of higher alcohols by ethanol coupling.

[0028] In the preparation of the nitrogen-doped metal-lignin precursor, the present application adopts one-pot hydrothermal treatment, and grafting reaction with melamine, ammonia and the like as the nitrogen source, so that the N element is uniformly distributed in the carbon material, and a modified lignin doped with N element is obtained. Subsequently, the modified lignin is subjected to coordination complexation with a metal active component to obtain a metal-lignin precursor. The catalytic performance of the hydrothermal ammonia lignin carbon-based multi-metal catalyst has a certain relationship with the content of the doped element. With the increase of the basic site, the selectivity of n-butanol increases. The present application subsequently performs centrifugal treatment and vacuum freeze-drying on the nitrogen-doped metal-lignin precursor to obtain a metal-lignin synthetic material; then, the prepared metal-lignin synthetic material is calcined in a protective gas atmosphere by using a tube furnace to obtain a hydrothermal ammonia lignin carbon-based multi-metal catalyst (Ni x M y @NC catalyst, x / y is the molar ratio of the metal nickel salt to the metal salt), and the metal M is selected from Zn. The hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared by the present application has a good catalytic effect, and the ethanol conversion rate of the catalyst can reach 69.4%, the yield of higher alcohols can reach 50.3%, and the selectivity of gaseous by-products is only 2.4%.

[0029] Compared with the prior art, the present application has the following advantages and beneficial effects:

[0030] (1) In the preparation of the nitrogen-doped metal-lignin precursor, the present application greatly enriches the N and O elements of the carbon material by hydrothermal ammonia treatment of the lignin, which helps to improve the precise coordination of the lignin with Ni, Zn, Cr, Co, Mn and the like ions, and further makes the metal uniformly dispersed in the carbon material, so as to improve the applicability of the functionalized lignin carbon-based multi-metal catalyst in the conversion of ethanol into higher alcohol materials.

[0031] (2) The present application uses lignin as a carbon source, and melamine as a nitrogen source, and the raw materials are abundant in source. The catalyst prepared by one-pot hydrothermal treatment is green and environmentally friendly, and the preparation process is simple and energy-saving. The present application creates conditions for the industrial application of a hydrothermal ammonolysis lignin carbon-based multi-metal catalyst, and by doping Zn and the like to regulate the electronic structure of Ni and increase the defect structure of carbon materials, hydrogenolysis of carbon-carbon bonds and methanation in the reaction process are effectively inhibited, thereby improving the catalytic activity of the catalyst and the selectivity of the product. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 A scanning electron microscope image of the hydrothermal ammonolysis lignin carbon-based multi-metal catalyst prepared in Example 2 of the present application.

[0033] Figure 2 A transmission electron microscope image of the hydrothermal ammonolysis lignin carbon-based multi-metal catalyst prepared in Example 2 of the present application.

[0034] Figure 3 A high-resolution transmission electron microscope image of the hydrothermal ammonolysis lignin carbon-based multi-metal catalyst prepared in Example 2 of the present application.

[0035] Figure 4 An EDS element map of nickel, nitrogen and carbon elements of the hydrothermal ammonolysis lignin carbon-based multi-metal catalyst prepared in Example 2 of the present application. DETAILED DESCRIPTION

[0036] In order to make the purpose, technical scheme and effect of the present application more clear and explicit, the present application will be further described in detail below with reference to examples. It should be understood that the specific examples described herein are only used to explain the present application, and are not intended to limit the present application.

[0037] Unless otherwise defined, all professional terms used in the following have the same meaning as generally understood by those skilled in the art. The professional terms used herein are only for the purpose of describing specific examples, and are not intended to limit the protection scope of the present application. Unless otherwise specified, the various raw materials, reagents, instruments and equipment used in the present application can be purchased from the market or can be prepared by existing methods.

[0038] Unless otherwise specifically indicated, all materials, reagents, solvents, and the like used in the application are available from commercial vendors and are prepared by conventional methods. In the examples and comparative examples of the present application, alkali lignin (AL) is used as an example of lignin, which is used as a raw material to provide a carbon source. It should be understood that the specific type of lignin has no significant effect on the properties of the catalyst product, and when other types of lignin such as one or more of Dragon King enzymatic lignin, sulfite lignin, kraft lignin, and Russian lignin are used to prepare the catalyst, the performance of the catalyst obtained has no significant difference compared to alkali lignin. Therefore, they are not listed one by one here.

[0039] Example 1

[0040] A hydrothermal ammonolysis lignin carbon-based multi-metal catalyst, the preparation method comprising the following steps:

[0041] (1) Dissolve lignin in ammonia water to obtain a lignin solution, then place the lignin solution, a nickel acetate solution, a zinc nitrate solution, and melamine in the inner container of a hydrothermal kettle, stir at room temperature for 30 min to fully mix, adjust the pH to 9, and hydrothermally react at 200°C for 8h to synthesize a black nitrogen-doped metal-lignin precursor; wherein the mass fractions of lignin, ammonia water, nickel acetate, zinc nitrate, and melamine are 2.71%, 1.36%, 2.14%, 0.14%, and 2.71%, respectively, and the balance is water.

[0042] (2) Centrifuge the doped metal-lignin precursor obtained in step (1) at 10,000 rpm for 10 min, and vacuum freeze-dry the solid precipitate at -50°C for 72h to obtain a metal-lignin synthetic material;

[0043] (3) Calcine the metal-lignin synthetic material obtained in step (2) at 500°C under a nitrogen atmosphere for 2h, and after natural cooling, obtain a powder-like particle, and then fully grind to obtain the product.

[0044] In the ethanol coupling experiment, the hydrothermal ammonolysis lignin carbon-based multi-metal catalyst prepared in this example is used, the ethanol conversion rate can reach 67.3%, the yield of higher alcohols can reach 47.2%, and the selectivity of gaseous by-products is 3.7%.

[0045] Example 2

[0046] A hydrothermal ammonolysis lignin carbon-based multi-metal catalyst, the preparation method comprising the following steps:

[0047] (1) Lignin was dissolved in ammonia water to obtain a lignin solution, and then the lignin solution, a nickel nitrate solution, a zinc nitrate solution and melamine were placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to mix them thoroughly, adjusted to pH 9, and then hydrothermally reacted at 200 ℃ for 8 h to obtain a black nitrogen-doped metal-lignin precursor; wherein the mass fractions of lignin, ammonia water, nickel nitrate, zinc nitrate and melamine were 2.71%, 1.36%, 2.14%, 0.14% and 2.71% respectively, and the rest was water.

[0048] (2) The nitrogen-doped metal-lignin precursor obtained in step (1) was centrifuged at 10,000 rpm for 10 min, and the solid precipitate was vacuum freeze-dried at -50 ℃ for 72 h to obtain a metal-lignin synthetic material;

[0049] (3) The metal-lignin synthetic material obtained in step (2) was calcined at 500 ℃ under a nitrogen atmosphere for 2 h, and then naturally cooled to obtain a powder, which was then fully ground to obtain the product.

[0050] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment was used, and the ethanol conversion rate could reach 69.4%, the yield of higher alcohols could reach 50.3%, and the selectivity of gaseous by-products was 2.4%.

[0051] The scanning electron microscope image and the transmission electron microscope image of the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment are shown in Figure 1 、 Figure 2 As can be seen from the figures, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment has a sheet-like thin layer structure and has a rich pore structure.

[0052] The high-resolution transmission electron microscope image and the pore size distribution graph of the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment are shown in Figure 3 As can be seen from the figures, the Ni of the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment is wrapped in amorphous carbon material, and the crystal lattice fringes with a crystal face spacing of 0.201 nm are exposed, which corresponds to the Ni(111) crystal face in the XRD spectrum. Figure 4 As can be seen from the figures, the Ni, N and C elements are uniformly distributed on the sample.

[0053] Example 3

[0054] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, and a preparation method thereof, are provided.

[0055] (1) lignin is dissolved in ammonia water to obtain a lignin solution, then the lignin solution, a nickel nitrate solution, a zinc acetate solution and melamine are placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, the pH is adjusted to 9, and a black nitrogen-doped metal-lignin precursor is synthesized by hydrothermal reaction at 200℃ for 8h; the mass fractions of the lignin, ammonia water, nickel nitrate, zinc acetate and melamine are 2.71%, 1.36%, 2.14%, 0.14% and 2.71% respectively, and the rest is water.

[0056] (2) the metal-lignin precursor obtained in step (1) is centrifuged at 10000 rpm for 10 min, the solid precipitate is vacuum freeze-dried at -50℃ for 72h to obtain a metal-lignin synthetic material;

[0057] (3) the metal-lignin synthetic material obtained in step (2) is calcined at 500℃ in a nitrogen atmosphere for 2h, and then naturally cooled to obtain a powder, which is fully ground to obtain the product.

[0058] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment has an ethanol conversion rate of 68.2%, a higher alcohol yield of 48.1%, and a gas byproduct selectivity of 3.6%.

[0059] Comparative Example 1

[0060] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, and a preparation method thereof, are provided.

[0061] (1) lignin is dissolved in ammonia water to obtain a lignin solution, then the lignin solution, a nickel nitrate solution, a zinc acetate solution and melamine are placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, the pH is adjusted to 9, and a black nitrogen-doped metal-lignin precursor is synthesized by hydrothermal reaction at 200℃ for 4h; the mass fractions of the lignin, ammonia water, nickel nitrate, zinc acetate and melamine are 2.71%, 1.36%, 2.14%, 0.14% and 2.71% respectively, and the rest is water.

[0062] (2) the metal-lignin precursor obtained in step (1) is centrifuged at 10000 rpm for 10 min, the solid precipitate is vacuum freeze-dried at -50℃ for 72h to obtain a metal-lignin synthetic material;

[0063] (3) the metal-lignin synthetic material obtained in step (2) is calcined at 500℃ in a nitrogen atmosphere for 2h, and then naturally cooled to obtain a powder, which is fully ground to obtain the product.

[0064] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment can achieve an ethanol conversion rate of 45.2%, a higher alcohol yield of 32.2%, and a gas by-product selectivity of 7.2%.

[0065] Comparative Example 2

[0066] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, the preparation method thereof comprising the following steps:

[0067] (1) lignin is dissolved in ammonia water to obtain a lignin solution, then the lignin solution, a nickel nitrate solution, a zinc nitrate solution and melamine are placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, the pH is adjusted to 9, and a black nitrogen-doped metal-lignin precursor is synthesized by hydrothermal reaction at 200℃ for 6h; wherein the mass fractions of lignin, ammonia water, nickel nitrate, zinc nitrate and melamine are 2.71%, 1.36%, 2.14%, 0.14% and 2.71% respectively, and the balance is water.

[0068] (2) the doped metal-lignin precursor obtained in step (1) is centrifuged at 10000 rpm for 10 min, and the solid precipitate is vacuum freeze-dried at -50℃ for 72h to obtain a metal-lignin synthetic material;

[0069] (3) the metal-lignin synthetic material obtained in step (2) is calcined at 500℃ under a nitrogen atmosphere for 2h, and then ground to obtain a powder.

[0070] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment can achieve an ethanol conversion rate of 51.3%, a higher alcohol yield of 38.2%, and a gas by-product selectivity of 5.1%.

[0071] Comparative Example 3

[0072] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, the preparation method thereof comprising the following steps:

[0073] (1) lignin is dissolved in ammonia water to obtain a lignin solution, then the lignin solution, a nickel nitrate solution, a zinc nitrate solution and melamine are placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, the pH is adjusted to 9, and a black nitrogen-doped metal-lignin precursor is synthesized by hydrothermal reaction at 200℃ for 10h; wherein the mass fractions of lignin, ammonia water, nickel nitrate, zinc nitrate and melamine are 2.71%, 1.36%, 2.14%, 0.14% and 2.71% respectively, and the balance is water.

[0074] (2) The doped metal-lignin precursor obtained in step (1) is centrifuged at 10,000 rpm for 10 min, and the solid precipitate is vacuum freeze-dried at -50°C for 72 h to obtain a metal-lignin synthetic material;

[0075] (3) The metal-lignin synthetic material obtained in step (2) is calcined at 500°C under a nitrogen atmosphere for 2 h, and after natural cooling, a powdery particle is obtained, which is then fully ground to obtain the product.

[0076] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment has an ethanol conversion rate of 49.4%, a higher alcohol yield of 37.4%, and a gas byproduct selectivity of 7.6%.

[0077] Comparative Example 4

[0078] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, and a preparation method thereof, are provided.

[0079] (1) Lignin is dissolved in ammonia water to obtain a lignin solution, and then the lignin solution, a nickel nitrate solution, a zinc nitrate solution, and melamine are placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, the pH is adjusted to 9, and a black nitrogen-doped metal-lignin precursor is synthesized by hydrothermal reaction at 180°C for 8 h; wherein the mass fractions of lignin, ammonia water, nickel nitrate, zinc nitrate, and melamine are 2.71%, 1.36%, 2.14%, 0.14%, and 2.71% respectively, and the balance is water.

[0080] (2) The doped metal-lignin precursor obtained in step (1) is centrifuged at 10,000 rpm for 10 min, and the solid precipitate is vacuum freeze-dried at -50°C for 72 h to obtain a metal-lignin synthetic material;

[0081] (3) The metal-lignin synthetic material obtained in step (2) is calcined at 500°C under a nitrogen atmosphere for 2 h, and after natural cooling, a powdery particle is obtained, which is then fully ground to obtain the product.

[0082] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment has an ethanol conversion rate of 62.1%, a higher alcohol yield of 45.6%, and a gas byproduct selectivity of 8.2%.

[0083] Comparative Example 5

[0084] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, and a preparation method thereof, are provided.

[0085] (1) lignin is dissolved in ammonia water to obtain a lignin solution, then the lignin solution, a nickel nitrate solution, a zinc nitrate solution and melamine are placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, the pH is adjusted to 9, and a black nitrogen-doped metal-lignin precursor is synthesized by hydrothermal reaction at 190 ℃ for 8 h; the mass fractions of the lignin, ammonia water, nickel nitrate, zinc nitrate and melamine are 2.71%, 1.36%, 2.14%, 0.14% and 2.71% respectively, and the rest is water.

[0086] (2) the metal-lignin precursor obtained in step (1) is centrifuged at 10,000 rpm for 10 min, the solid precipitate is vacuum freeze-dried at -50 ℃ for 72 h to obtain a metal-lignin synthetic material;

[0087] (3) the metal-lignin synthetic material obtained in step (2) is calcined at 500 ℃ in a nitrogen atmosphere for 2 h, and then naturally cooled to obtain a powder, which is fully ground to obtain the product.

[0088] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment has an ethanol conversion rate of 64.3%, a high alcohol yield of 47.3%, and a gas byproduct selectivity of 7.5%.

[0089] Comparative Example 6

[0090] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, and a preparation method thereof, are provided.

[0091] (1) lignin is dissolved in ammonia water to obtain a lignin solution, then the lignin solution, a nickel nitrate solution, a zinc nitrate solution and melamine are placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, the pH is adjusted to 9, and a black nitrogen-doped metal-lignin precursor is synthesized by hydrothermal reaction at 210 ℃ for 8 h; the mass fractions of the lignin, ammonia water, nickel nitrate, zinc nitrate and melamine are 2.71%, 1.36%, 2.14%, 0.14% and 2.71% respectively, and the rest is water.

[0092] (2) the metal-lignin precursor obtained in step (1) is centrifuged at 10,000 rpm for 10 min, the solid precipitate is vacuum freeze-dried at -50 ℃ for 72 h to obtain a metal-lignin synthetic material;

[0093] (3) the metal-lignin synthetic material obtained in step (2) is calcined at 500 ℃ in a nitrogen atmosphere for 2 h, and then naturally cooled to obtain a powder, which is fully ground to obtain the product.

[0094] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment can achieve an ethanol conversion rate of 64.5%, a higher alcohol yield of 46.5%, and a gas by-product selectivity of 9.1%.

[0095] Comparative Example 7

[0096] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, and a preparation method thereof, are provided.

[0097] (1) Lignin is dissolved in ammonia water to obtain a lignin solution, and then the lignin solution, a nickel nitrate solution, a zinc nitrate solution, and melamine are placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to mix them thoroughly, adjusted to a pH of 9, and then subjected to hydrothermal reaction at 200°C for 8 h to synthesize a black nitrogen-doped metal-lignin precursor; wherein the mass fractions of the lignin, the ammonia water, the nickel nitrate, the zinc nitrate, and the melamine are 2.71%, 1.36%, 2.14%, 0.14%, and 2.71% respectively, and the balance is water.

[0098] (2) The doped metal-lignin precursor obtained in step (1) is subjected to centrifugal treatment at 10,000 rpm for 10 min, and the solid precipitate is vacuum freeze-dried at -50°C for 72 h to obtain a metal-lignin synthetic material.

[0099] (3) The metal-lignin synthetic material obtained in step (2) is calcined at 400°C in a nitrogen atmosphere for 2 h, and then naturally cooled to obtain a powder-like particle, which is then fully ground to obtain the hydrothermal ammonia lignin carbon-based multi-metal catalyst.

[0100] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment can achieve an ethanol conversion rate of 43.2%, a higher alcohol yield of 35.5%, and a gas by-product selectivity of 9.8%.

[0101] Comparative Example 8

[0102] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, and a preparation method thereof, are provided.

[0103] (1) Lignin is dissolved in ammonia water to obtain a lignin solution, and then the lignin solution, a nickel nitrate solution, a zinc nitrate solution, and melamine are placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to mix them thoroughly, adjusted to a pH of 9, and then subjected to hydrothermal reaction at 200°C for 8 h to synthesize a black nitrogen-doped metal-lignin precursor; wherein the mass fractions of the lignin, the ammonia water, the nickel nitrate, the zinc nitrate, and the melamine are 2.71%, 1.36%, 2.14%, 0.14%, and 2.71% respectively, and the balance is water.

[0104] (2) The doped metal-lignin precursor obtained in step (1) is centrifuged at 10,000 rpm for 10 min, and the solid precipitate is vacuum freeze-dried at -50°C for 72 h to obtain a metal-lignin synthetic material;

[0105] (3) The metal-lignin synthetic material obtained in step (2) is calcined at 600°C under a nitrogen atmosphere for 2 h, and after natural cooling, a powder-like particle is obtained, which is then fully ground.

[0106] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment has an ethanol conversion rate of 42.5%, a higher alcohol yield of 32.3%, and a gas byproduct selectivity of 8.3%.

[0107] Comparative Example 9

[0108] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, and a preparation method thereof, includes the following steps:

[0109] (1) Lignin is dissolved in ammonia water to obtain a lignin solution, and then the lignin solution, a nickel nitrate solution, a zinc nitrate solution, and melamine are placed in a beaker in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, and then heated to 100°C and stirred until the water is completely evaporated to synthesize a black nitrogen-doped metal-lignin precursor; the mass fractions of lignin, ammonia water, nickel nitrate, zinc nitrate, and melamine are 2.7%, 1.4%, 2.1%, 0.1%, and 2.7%, respectively, and the balance is water.

[0110] (2) The doped metal-lignin precursor obtained in step (1) is placed in a 90°C oven to completely dry, and is ground into a powder to obtain a metal-lignin synthetic material;

[0111] (3) The metal-lignin synthetic material obtained in step (2) is calcined at 500°C under a nitrogen atmosphere for 2 h, and after natural cooling, a powder-like particle is obtained, which is then fully ground.

[0112] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in this embodiment has an ethanol conversion rate of 56.4%, a higher alcohol yield of 34.2%, and a gas byproduct selectivity of 8.9%.

[0113] Comparative Example 10

[0114] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, and a preparation method thereof, includes the following steps:

[0115] (1) lignin was dissolved in ammonia water to obtain a lignin solution, then the lignin solution, a nickel nitrate solution and a zinc nitrate solution were placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, the pH was adjusted to 9, and a black nitrogen-doped metal-lignin precursor was synthesized by hydrothermal reaction at 200 ℃ for 8 h; the mass fractions of the lignin, ammonia water, nickel nitrate and zinc nitrate were 2.79%, 1.4%, 2.2% and 0.14% respectively, and the rest was water.

[0116] (2) the metal-lignin synthetic material was prepared by centrifuging the metal-lignin precursor obtained in step (1) at 10,000 rpm for 10 min and vacuum freeze-drying the solid precipitate at -50 ℃ for 72 h;

[0117] (3) the metal-lignin synthetic material obtained in step (2) was calcined at 500 ℃ in a nitrogen atmosphere for 2 h, and then ground to obtain a powder.

[0118] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based multi-metal catalyst prepared in the present example had an ethanol conversion rate of 64.6%, a higher alcohol yield of 45.1%, and a gas by-product selectivity of 6.9%.

[0119] Example 11

[0120] A hydrothermal ammonia lignin carbon-based catalyst, and a preparation method thereof, the preparation method comprising the following steps:

[0121] (1) lignin was dissolved in ammonia water to obtain a lignin solution, then the lignin solution, a nickel nitrate solution and melamine were placed in the inner container of a hydrothermal kettle, stirred at room temperature for 30 min to fully mix, the pH was adjusted to 9, and a black nitrogen-doped metal-lignin precursor was synthesized by hydrothermal reaction at 200 ℃ for 8 h; the mass fractions of the lignin, ammonia water, nickel nitrate and melamine were 2.72%, 1.36%, 2.15% and 2.72% respectively, and the rest was water.

[0122] (2) the metal-lignin synthetic material was prepared by centrifuging the metal-lignin precursor obtained in step (1) at 10,000 rpm for 10 min and vacuum freeze-drying the solid precipitate at -50 ℃ for 72 h;

[0123] (3) the metal-lignin synthetic material obtained in step (2) was calcined at 500 ℃ in a nitrogen atmosphere for 2 h, and then ground to obtain a powder.

[0124] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based catalyst prepared in the present example was used, and the ethanol conversion rate was 41.6%, the yield of higher alcohols was 26.3%, and the selectivity of gaseous by-products was 8.1%.

[0125] Comparative Example 12

[0126] A hydrothermal ammonia lignin carbon-based multi-metal catalyst, the preparation method thereof comprising the following steps:

[0127] (1) Dissolve lignin in sodium hydroxide solution to obtain a lignin solution, then place the lignin solution, nickel nitrate solution, zinc nitrate solution and melamine in the inner container of a hydrothermal kettle, stir at room temperature for 30 min to fully mix, adjust the pH to 9, and hydrothermally react at 200°C for 8h to synthesize a black nitrogen-doped metal-lignin precursor; wherein the mass fractions of lignin, sodium hydroxide, nickel nitrate, zinc nitrate and melamine are 2.71%, 0.8%, 2.14%, 0.14% and 2.17% respectively, and the balance is water.

[0128] (2) Centrifuge the doped metal-lignin precursor obtained in step (1) at 10000 rpm for 10 min, and freeze-dry the solid precipitate at -50°C for 72h to obtain a metal-lignin synthetic material.

[0129] (3) Calcine the metal-lignin synthetic material obtained in step (2) at 500°C under a nitrogen atmosphere for 2h, and obtain a powder after natural cooling, then fully grind to obtain the product.

[0130] In the ethanol coupling experiment, the hydrothermal ammonia lignin carbon-based catalyst prepared in the present example was used, and the ethanol conversion rate was 41.6%, the yield of higher alcohols was 26.3%, and the selectivity of gaseous by-products was 8.1%.

[0131] Verification Example 1

[0132] Ni prepared by different raw material ratios x Zn yThe NC catalyst can catalyze the coupling conversion of ethanol into higher alcohols. The water phase product and the oil phase product generated in the ethanol coupling experiment are analyzed by GC, and the gas product generated in the ethanol coupling experiment is analyzed by TCD and FID, to obtain the data in Table 1. From the results in Table 1, it can be seen that when melamine and urea are used as the nitrogen source, nickel nitrate and zinc nitrate are used as the metal salt, the mass fractions of lignin, ammonia, melamine, nickel nitrate and zinc nitrate are 2.71%, 1.36%, 2.71%, 2.14% and 0.14% respectively, and the hydrothermal temperature is 200 DEG C, the hydrothermal time is 8h, and the calcination temperature is 500 DEG C, the catalyst has the best effect on the synthesis of higher alcohols, the ethanol conversion rate can reach 69.4%, the yield of higher alcohols can reach 50.3%, and the selectivity of the gas byproduct is 2.4%.

[0133] The present application finds through a large number of studies that selecting appropriate nitrogen-containing reagents to provide N doping can effectively disperse Ni grains and improve catalytic activity; at the same time, N doping is conducive to the generation of defect structures, and the construction of a Ni-N-C structure helps to improve the synergistic effect of the metal active component and the lignin-based carbon carrier, the doping of Zn can also improve the electronic structure of Ni, improve the stability of the metal on the carbon-based support through the bonding between N sites and Ni and Zn metal atoms, and increase the dispersion of the metal active component to provide more active sites; N doping can precisely regulate the electronic structure of Ni, promote the charge redistribution between the carrier and the NiZn catalyst, and make the metal cluster exhibit a less positive charge state, thereby weakening the excessive dehydrogenation of the metal active site, enhancing the desorption behavior of intermediates (such as CH3CHO*), ultimately promoting the C-C coupling reaction and inhibiting further dehydrogenation and C-C bond breaking; when applied to an ethanol coupling reaction, it can effectively inhibit C-C bond breaking and improve the selectivity of the target product. For the nitrogen source, melamine and ammonia are the best choices, ammonia also makes lignin disperse uniformly in the solution when used as a partial nitrogen source, which helps to better perform grafting reaction and metal loading, and with the addition of melamine, a large amount of volatile gas is generated during the pyrolysis of melamine, which destroys the dense carbon skeleton, forms a layered porous nanolayer structure and increases the specific surface area of the catalyst.

[0134] Meanwhile, the dosage of melamine has a significant impact on the performance of the catalyst. However, when the mass ratio of melamine to lignin is too high, the specific surface area of the catalyst will decrease significantly, which may be due to the excessive melamine inhibiting the growth of carbon nanostructures, resulting in a lower specific surface area. A high specific surface area provides enhanced metal anchoring sites, increases the dispersion of the metal, and is conducive to the exposure of active sites, which is conducive to the adsorption process, thereby providing the catalyst with the possibility of good catalytic activity. Mesopores of about 2 nm can provide a suitable path for the penetration and transport of reactants, making it easier for reactants to diffuse to active sites, which is conducive to the mass transfer process, promotes rapid diffusion on the catalyst, reduces the deposition of reactants and products on the catalyst, and reduces the occurrence of side reactions. Mesoporous materials can promote the fixed distribution of metal particles, and in addition, the metal particles wrapped in the carbon skeleton can effectively avoid particle aggregation and metal leaching due to inter-particle interactions, thereby greatly improving the stability and catalytic activity of the catalyst. When the mass ratio of melamine to lignin is too low, the loading of nickel-zinc active components will be less. By adjusting the mass of melamine to adjust the doping content of N, the metal loading and specific surface area can be improved, the defect structure of the catalyst and the dispersion degree of metal clusters can be improved, and the exposure of active sites and the mass transfer process can be promoted; and appropriate nitrogen doping may help to regulate the charge redistribution between the support and nickel, thereby inhibiting the generation of by-products in the decomposition reaction by hindering the interaction of reaction intermediates, so as to realize the high ethanol conversion rate and high C4+ higher alcohol yield of the lignin-derived carbon material catalyst for the coupling conversion of ethanol to higher alcohols.

[0135] In addition, factors such as hydrothermal reaction time, hydrothermal reaction temperature, and high-temperature calcination temperature also have a crucial impact on the performance of the catalyst. The time and temperature of the hydrothermal reaction significantly affect the nitrogen doping and metal loading effect: if the hydrothermal time is insufficient or the temperature is too low, the nitrogen doping effect will be poor, thereby reducing the metal loading and the number of acidic active sites, and significantly weakening the catalytic performance. High-temperature calcination plays a key role in the morphology and stability of the catalyst. During the calcination process, the lignin-based carbon support gradually forms a porous carbon sphere, and the metal is wrapped therein; an excessively low calcination temperature may result in incomplete wrapping, while an excessively high calcination temperature may cause the aggregation of metal active components, thereby affecting the performance and structural stability of the catalyst.

[0136] Meanwhile, the choice of metal salt has a key impact on the catalytic performance of the catalyst. For example, the catalyst prepared using nickel nitrate significantly improves the ethanol conversion rate and product selectivity compared to the catalyst prepared using nickel acetate. This is mainly due to the better solubility of nickel nitrate in water, which is conducive to the formation of a homogeneous solution with other reactants, promotes the uniform formation of the catalyst precursor, and facilitates the occurrence of homogeneous reactions during the catalytic process. At the same time, nitrate has higher thermal stability at high temperatures and is less likely to decompose, thereby causing less interference with the preparation of the catalyst and the catalytic reaction.

[0137] Table 1 Analysis results of Examples 1-3 and Comparative Examples 1-12

[0138]

[0139] The above detailed description of the analysis method involved in the present application is introduced in the above detailed embodiment part. It should be noted that the above introduction is only to help the technical personnel in the art better understand the method and idea of the present application, and is not a limitation on the related content. The technical personnel in the art can also make appropriate adjustments or modifications to the present application without departing from the principles of the present application, and the above adjustments and modifications should also belong to the protection scope of the present application.

Claims

1. A method for preparing a hydrothermal ammonolysis lignin carbon-based multimetallic catalyst, characterized in that, Includes the following steps: (1) The lignin solution, nitrogen source, nickel source and metal salt solution are thoroughly mixed, and the pH is adjusted to 9 before hydrothermal reaction to synthesize nitrogen-doped metal-lignin precursor; the nitrogen source is selected from melamine and ammonia; the nickel source is selected from nickel nitrate; the metal salt is selected from zinc nitrate; the hydrothermal reaction temperature is 200℃ and the time is 8h; (2) The metal-lignin precursor obtained in step (1) is centrifuged and freeze-dried in vacuum to obtain metal-lignin synthetic material; (3) The metal-lignin synthetic material obtained in step (2) is calcined in a protective gas atmosphere to obtain powder particles, which are then fully ground to obtain the final product; the calcination temperature is 500℃ and the time is 2h.

2. The preparation method according to claim 1, characterized in that, The molar ratio of nickel to lignin in the nickel source mentioned in step (1) is 5-60:

1.

3. The preparation method according to claim 1, characterized in that, The molar ratio of nickel in the nickel source to metal in the metal salt solution in step (1) is 5-60:

1.

4. The hydrothermal ammonolysis lignin carbon-based multimetallic catalyst prepared by the preparation method according to any one of claims 1-3.

5. The application of the hydrothermal ammonolysis lignin carbon-based multimetallic catalyst prepared according to any one of claims 1-3 in the coupling of ethanol to prepare higher alcohols.

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