Molybdenum carbide-metal composite catalyst as well as preparation method and application thereof

Abstract

According to the molybdenum carbide-metal composite catalyst as well as the preparation method and the application thereof, phenol and a formaldehyde solution are subjected to a heating reaction in a system in which an alkaline sodium hydroxide solution and a surfactant exist to form phenolic resin, molybdate and transition metal salt are introduced in the auto-polymerization process of the phenolic resin, and the molybdenum carbide-metal composite catalyst is obtained through one-step high-temperature carbonization treatment. The molybdenum carbide-metal composite catalyst which takes mesoporous carbon as a carrier and is loaded with molybdenum carbide particles and transition metal in a high-dispersion manner is obtained, and tight combination between the transition metal and molybdenum carbide is realized. According to the preparation method, sintering of the catalyst at high temperature can be effectively limited, the number of catalytic active sites is increased, efficient and stable catalysis is achieved, and the obtained molybdenum carbide-metal composite catalyst shows excellent activity and stability in the RWGS process. Meanwhile, the preparation method is simple and convenient in process, high in product composition morphology controllability and suitable for batch production.

Description

Technical Field

[0001] The present invention relates to the technical field of coal chemical conversion, and particularly relates to a molybdenum carbide-metal composite catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] In the modern coal chemical industry chain, the conversion of C1 compounds (such as CO, CO2, CH4, etc.) is the core link for realizing the deep processing of coal. Among them, the reverse water-gas shift reaction (RWGS) of CO2 hydrogenation has double significance: on the one hand, it can convert CO2 into syngas (CO and H2) to provide raw materials for downstream chemical products such as methanol and olefins; on the other hand, it can achieve greenhouse gas emission reduction by capturing and converting CO2. However, the RWGS reaction faces the following technical challenges: (1) The chemical properties of CO2 molecules are stable, and the bond energy of its C=O bond is as high as 750 kJ / mol, resulting in a high reaction energy barrier and significant energy consumption; (2) Under thermal field conditions, CO2 may undergo multiple-step hydrogenation to generate CH4 (methanation reaction), competing with the RWGS reaction, resulting in a decrease in syngas selectivity and an increase in the cost of product separation.

[0003] Related technologies accelerate the CO2 activation and hydrogenation processes and inhibit the methanation side reaction by developing efficient catalysts. Research shows that the dispersion of the catalyst is crucial for its performance: highly dispersed active sites can increase the gas-solid interface contact area, improving the conversion efficiency of the feed gas and the heat utilization rate. However, traditional highly dispersed catalysts (such as supported noble metal or transition metal catalysts) are prone to particle agglomeration and sintering due to surface energy driving during high-temperature reactions, resulting in the loss of active sites and the attenuation of catalytic performance.

[0004] Molybdenum carbide (Mo2C) is a typical metal interstitial compound. Due to the influence of interstitial carbon atoms, the metal molybdenum sites have an electronic structure similar to that of noble metals, so transition metals have a strong affinity and are often used as carriers for metal-based catalysts. However, since Mo2C belongs to the orthorhombic or hexagonal crystal system, it has a high mass density and lacks pores, resulting in a dense filling of the reaction bed, which affects the heat transfer and mass transfer processes of the reaction. In addition, Mo2C is also prone to grain coarsening and the collapse of the carrier structure at high temperatures, exacerbating the loss of active sites; Mo2C itself also shows a certain catalytic activity for the conversion process of C1 products. In Chinese Patent CN 115228491B, molybdenum carbide is only used as a carrier material, which is not conducive to the full exposure of active sites; moreover, the industrial catalytic CO2 hydrogenation reaction flux is large, making it difficult to meet the large-scale industrial demand. Summary of the Invention

[0005] In view of the problems existing in the background art, the present invention provides a molybdenum carbide-metal composite catalyst, a preparation method thereof, and an application thereof. By utilizing the electrostatic interaction during the self-polymerization process of phenolic resin, the adsorption of molybdate and transition metal salt is realized, and then through one-step carbonization treatment, it is transformed into a highly dispersed molybdenum carbide-metal composite catalyst supported on porous carbon.

[0006] The specific content of the invention is as follows:

[0007] According to the first aspect of the present invention, a preparation method of a molybdenum carbide-metal composite catalyst is provided.

[0008] The preparation method specifically includes the following steps:

[0009] S1. Mix phenol, formaldehyde solution and sodium hydroxide solution, and then add an appropriate amount of surfactant, and mix well to form a first mixed system;

[0010] S2. Within 2 h after the first mixed system starts to turn red, slowly add an appropriate amount of molybdate solution and stir to form a second mixed system;

[0011] S3. After the second mixed system starts to change from red to green, continue to add an appropriate amount of transition metal salt solution, stir and react for 24-72 h, and collect the solid to obtain a catalyst precursor;

[0012] S4. Place the catalyst precursor in an inert atmosphere and perform high-temperature carbonization treatment to obtain the molybdenum carbide-metal composite catalyst;

[0013] Wherein, in the solution, the molar ratio of phenol to formaldehyde is 1:2-1:10;

[0014] The surfactant is cetyltrimethylammonium bromide or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer;

[0015] In the molybdate solution and the transition metal salt solution, the molar ratio of molybdenum to transition metal is 5-25:0.1-1;

[0016] Steps S1-S3 are all carried out at 30-85 °C.

[0017] Optionally, the transition metal contained in the transition metal salt solution is selected from one or more of Cu, Fe, Co, Ni, and Ru.

[0018] Optionally, the transition metal salt solution is formed by dissolving a transition metal salt in an organic acid solution, and the organic acid is selected from acetic acid or propionic acid;

[0019] The volume ratio of the organic acid in the organic acid solution is 0.5%-5%.

[0020] Optionally, the transition metal salt is selected from transition metal-containing acetates, nitrates or chlorides.

[0021] Optionally, the molybdate solution is selected from ammonium molybdate solution or sodium molybdate solution.

[0022] Optionally, when the molybdate solution is sodium molybdate solution, the molybdate solution is formed by mixing sodium molybdate solution with ammonia water;

[0023] The volume ratio of ammonia water in the molybdate solution is 1% - 5%.

[0024] Optionally, the temperature of the high-temperature carbonization treatment is 800°C - 1000°C.

[0025] According to the second aspect of the present invention, there is provided a molybdenum carbide-metal composite catalyst prepared by the above preparation method; in the molybdenum carbide-metal composite catalyst, the loading amount of molybdenum carbide is 5wt% - 20wt%, the transition metal loading amount is 0.5wt% - 5wt%, and the rest is a mesoporous carbon carrier.

[0026] Optionally, the molybdenum carbide-metal composite catalyst has a spherical morphology, and the particle size is 100nm - 1μm; the particle size of the molybdenum carbide is less than 20nm.

[0027] According to the third aspect of the present invention, there is provided an application of the molybdenum carbide-metal composite catalyst. Using CO2 and H2 with a volume ratio of 1:1 - 1:3 as reaction raw materials, at 250°C - 600°C, the molybdenum carbide-metal composite catalyst catalyzes the reverse water gas shift reaction of CO2 hydrogenation of CO2 and H2;

[0028] wherein, the reaction space velocity is 7000mL / g·h - 60000mL / g·h, the CO2 conversion rate is greater than 16%, and the CO selectivity is greater than 96%.

[0029] Compared with the prior art, the present invention has the following advantages:

[0030] The present invention provides a molybdenum carbide-metal composite catalyst, a preparation method thereof and an application thereof. The preparation method includes the following steps: After mixing phenol, formaldehyde solution and sodium hydroxide solution evenly, an appropriate amount of surfactant is added, and after mixing evenly, a first mixed system is formed; within 2 hours after the first mixed system starts to turn red, an appropriate amount of molybdate solution is slowly added, and stirring is carried out to form a second mixed system; after the second mixed system starts to change from red to green, an appropriate amount of transition metal salt solution is continuously added, and after stirring and reacting for 24 to 72 hours, the solid is collected to obtain a catalyst precursor; the catalyst precursor is placed in an inert atmosphere for high-temperature carbonization treatment to obtain the molybdenum carbide-metal composite catalyst. The molybdenum carbide-metal composite catalyst obtained by the above preparation method is used for catalyzing the reverse water gas shift reaction of CO2 hydrogenation of CO2 and H2.

[0031] The preparation method of the molybdenum carbide-metal composite catalyst provided by the present invention is to carry out a heating reaction through phenol and formaldehyde solution in a system with alkaline sodium hydroxide solution and surfactant to form phenolic resin, and the first mixed system changes from colorless to red; on this basis, adding molybdate solution to carry out a complexation reaction to form a negatively charged group. At this time, the second mixed system changes from red to green, and transition metal cations are introduced by electrostatic adsorption and heated to react to form a catalyst precursor. After one-step high-temperature carbonization treatment, a molybdenum carbide-metal composite catalyst is obtained. In the present invention, molybdate and transition metal salts are introduced during the self-polymerization process of phenolic resin, and a mesoporous structure is formed under the guidance of surfactant. After one-step high-temperature carbonization treatment, phenolic resin serves as a carbon source, enabling Mo2C to be dispersed in the three-dimensional network structure of phenolic resin, realizing the preparation of high dispersion of Mo2C; after the carbonization treatment of phenolic resin, mesoporous channels are left, and the prepared catalyst has a porous structure, increasing the number of catalytic active sites, realizing efficient and stable catalysis as well as efficient mass and heat transfer; the present invention uses carbon as the substrate, effectively restricting the sintering of the catalyst at high temperature, and the catalyst is not easily agglomerated to affect the catalytic activity. Finally, a molybdenum carbide-metal composite catalyst with mesoporous carbon as the catalyst carrier, highly dispersed molybdenum carbide particles and transition metals is prepared, realizing the tight combination between the metal and molybdenum carbide. Compared with the impregnation method, the preparation method of the present invention can effectively achieve the nano-level dispersion and anchoring of Mo2C, and the obtained molybdenum carbide-metal composite catalyst shows excellent activity and stability in the RWGS process.

[0032] In addition, the raw materials of phenolic resin are easy to obtain, the preparation method has simple process, and the controllability of the product composition and morphology is high, which is suitable for large-scale industrial batch production. Description of the Drawings

[0033] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the accompanying drawings required in the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present invention. For those of ordinary skill in the art, without creative efforts, other accompanying drawings can also be obtained based on these drawings.

[0034] Figure 1 Shows the flowchart of the preparation method of the molybdenum carbide-metal composite catalyst provided by the embodiment of the present invention;

[0035] Figure 2 Shows the SEM image of the Cu-Mo₂C catalyst provided by the embodiment of the present invention;

[0036] Figure 3 Shows the catalytic activity performance graph of the Cu-Mo₂C catalyst provided by the embodiment of the present invention. Detailed implementation manners

[0037] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments of the present invention, any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with those of other prior arts falls within the protection scope of the present invention. And all other embodiments obtained by those of ordinary skill in the art without creative efforts also belong to the protection scope of the present invention.

[0038] For the technologies, methods and equipment known to those of ordinary skill in the relevant fields, they may not be discussed in detail, but under appropriate circumstances, the said technologies, methods and equipment should be regarded as part of the specification of the present invention.

[0039]

[0040] ​In addition, the technical features involved in different embodiments of the present invention described below can be combined with each other as long as they do not conflict with each other.

[0041] In the related art, there are problems such as low catalyst dispersibility, low mass transfer and heat transfer efficiency, and high preparation cost. In view of this, on the one hand, the present invention provides a method for preparing a molybdenum carbide-metal composite catalyst; Figure 1 The flowchart of the method for preparing the molybdenum carbide-metal composite catalyst provided by the present invention is shown in Figure 1 As shown, the preparation method specifically includes the following steps:

[0042] S1. After mixing phenol, formaldehyde solution and sodium hydroxide solution, an appropriate amount of surfactant is added, and after mixing, a first mixed system is formed;

[0043] S2. Within 2 h after the first mixed system starts to turn red, an appropriate amount of molybdate solution is slowly added and stirred to form a second mixed system;

[0044] S3. After the second mixed system starts to change from red to green, an appropriate amount of transition metal salt solution is continuously added, and after stirring and reacting for 24-72 h, the solid is collected to obtain a catalyst precursor;

[0045] S4. The catalyst precursor is placed in an inert atmosphere and subjected to high-temperature carbonization treatment to obtain the molybdenum carbide-metal composite catalyst;

[0046] Among them, in the solution, the molar ratio of phenol to formaldehyde is 1:2-1:10;

[0047] The surfactant is cetyltrimethylammonium bromide (abbreviated as CTAB) or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer (abbreviated as F127);

[0048] In the molybdate solution and the transition metal salt solution, the molar ratio of molybdenum to transition metal is 5-25:0.1-1;

[0049] Steps S1-S3 are all carried out at 30-85 °C.

[0050] It should be noted that the concentration of the sodium hydroxide solution is 0.1 mol / L; too high a concentration may lead to too fast a reaction rate and too high a cross-linking degree of the product; too low a concentration may result in incomplete reaction.

[0051] It should also be noted that the addition amount of the surfactant is 1.0 g to 5.0 g. The surfactant can guide the growth of polymers inside or on the surface of micelles to form nanoscale structures such as mesopores or nanoparticles; change the polarity of the reaction interface, promote the dispersion and mass transfer of reactants, thereby affecting the crosslinking degree and molecular weight distribution of the resin; and can also adsorb on the surface of phenolic resin particles to prevent particle agglomeration and improve the dispersion and stability of the product. The templating effect of surfactants CTAB or F127 can guide the formation of mesoporous structures in phenolic resins with pore diameters of 2 to 50 nm.

[0052] In specific implementation, phenol (C6H5OH) and formaldehyde (HCHO) undergo a polycondensation reaction under alkaline conditions (i.e., catalyzed by NaOH) to form phenolic resin. Specifically, NaOH, as an alkaline catalyst, promotes the deprotonation of the phenolic hydroxyl group of phenol to generate phenoxide anions; the phenoxide anions undergo a nucleophilic addition reaction with formaldehyde to form hydroxymethylphenol; hydroxymethylphenols further condense with each other or with phenol to form a polymer connected by methylene bridges (-CH2-) or ether bonds (-O-), namely [-C6H4OCH2-]. n . In the solution, the molar ratio of phenol to formaldehyde is 1:2 to 1:10; an excess of formaldehyde is beneficial for the formation of more hydroxymethylated products and promotes crosslinking. If the molar ratio of phenol to formaldehyde is less than 1:2, a three-dimensional crosslinked network cannot be formed. At the same time, phenolic resin serves as both a carbon source and a carrier throughout the reaction process. Therefore, an excess of phenolic resin needs to be generated for the next reaction. The molar ratio of phenol to formaldehyde is preferably 1:5 to 1:7. After the first mixed system starts to turn red from colorless, when the solution shows sol characteristics, start timing for 0 to 2 h and start dropwise adding the molybdate solution. When the molybdate solution is added within 0 to 1 h from the start of timing, the final formed catalyst molybdenum element is wrapped inside the nanospheres; when the molybdate solution is added within 1 to 2 h in the middle of the timing, the final formed catalyst molybdenum element is on the outer surface of the nanospheres. After the second mixed system starts to change from red to green, the interaction between the hydroxyl groups (-OH) in the phenolic resin and the molybdate ions (MoO4 2- ) is achieved to form a green complex. At this time, the complex as a whole is negatively charged and can adsorb transition metal cations through electrostatic adsorption. Continue heating the reaction, centrifuge to collect the solid, obtain the catalyst precursor, and obtain the molybdenum carbide-metal composite catalyst through carbonization treatment.

[0053] In specific implementation, a peristaltic pump is used to add the molybdate solution and the transition metal salt solution, and the addition rate is 0.5 mL / min to 2 mL / min.

[0054] In specific implementation, steps S1 - S3 are all carried out at 30 - 85 °C, preferably 50 - 60 °C. The synthesis of phenolic resin needs to be carried out under heating conditions. High temperature can accelerate the reaction, but too high temperature may cause over - crosslinking of the resin. Therefore, in this invention, the reaction temperature is controlled between 30 - 85 °C.

[0055] The preparation method of the molybdenum carbide - metal composite catalyst provided by this invention is as follows: phenol and formaldehyde solution react under heating in a system with alkaline sodium hydroxide solution and surfactant present, and the first mixed system changes from colorless to red; on this basis, molybdate solution is added to carry out a complexation reaction to form a negatively charged group, and at this time the second mixed system changes from red to green. Then, transition metal cations are introduced by electrostatic adsorption and heated to react to form a catalyst precursor, and through one - step high - temperature carbonization treatment, the molybdenum carbide - metal composite catalyst is obtained. In this invention, during the self - polymerization process of phenolic resin, electrostatic interaction is used to achieve the adsorption of molybdate and transition metal salts. The surfactant is used to guide the formation of a mesoporous structure. After one - step high - temperature carbonization treatment, phenolic resin serves as a carbon source, enabling Mo2C to be dispersed in the three - dimensional network structure of phenolic resin, realizing the preparation of high - dispersion of Mo2C; after the carbonization treatment of phenolic resin, mesoporous channels are left, and the prepared catalyst has a porous structure, which increases the number of catalytic active sites, realizing efficient and stable catalysis as well as efficient mass and heat transfer; this invention uses carbon as the substrate, which can effectively limit the sintering of the catalyst at high temperature, and the catalyst is not easy to agglomerate and affect the catalytic activity. Finally, a molybdenum carbide - metal composite catalyst with mesoporous carbon as the catalyst carrier, highly dispersed and loaded with molybdenum carbide particles and transition metals is prepared, realizing the tight combination between the metal and molybdenum carbide. Compared with the impregnation method, the preparation method of this invention can effectively achieve the nano - scale dispersion and anchoring of Mo2C, and the obtained molybdenum carbide - metal composite catalyst shows excellent activity and stability in the RWGS process. In addition, the raw material of phenolic resin is easily available, and the reaction process is simple, which is suitable for large - scale industrial batch production.

[0056] In some embodiments, the transition metal contained in the transition metal salt solution is selected from one or more of Cu, Fe, Co, Ni, and Ru.

[0057] In this embodiment, the addition of transition metals can improve the catalytic activity. The transition metals, as active centers, can adsorb reactant molecules (such as H2, CO, etc.) and directly participate in the CO2 hydrogenation catalytic reaction. Mo2C has an electronic structure similar to noble metals, which can activate reactants (such as dissociating H2 and adsorbing CO), and cooperate with transition metals to reduce the reaction energy barrier, significantly improving the catalytic efficiency. In addition, the strong electronic interaction between transition metals and Mo2C can change the electron density of the metal, avoiding the poisoning of active sites caused by over - adsorption.

[0058] In some embodiments, the transition metal salt solution is formed by dissolving a transition metal salt in an organic acid solution, and the organic acid is selected from acetic acid or propionic acid; the volume ratio of the organic acid in the organic acid solution is 0.5% to 5%.

[0059] In specific implementation, if 100 mL of the organic acid solution needs to be prepared, the organic acid is added to deionized water to form the organic acid solution, and the addition amount of the organic acid is 0.5 mL to 5 mL.

[0060] In this embodiment, after the transition metal salt is dissolved in the organic acid, metal cations are dissociated, which is convenient for electrostatic adsorption with the negatively charged groups after the reaction of phenolic resin and molybdate. The weak acidity of the organic acid (acetic acid or propionic acid) can maintain the pH stability of the reaction system, avoid premature hydrolysis of metal ions to form precipitates (such as hydroxides), affect the pH value of the reaction system, and thus disturb the formation of phenolic resin.

[0061] In some embodiments, the transition metal salt is selected from acetate, nitrate or chloride containing a transition metal.

[0062] In this embodiment, the transition metal salt is selected from acetate, nitrate or chloride containing a transition metal, such as copper acetate, cobalt acetate, nickel acetate, iron nitrate or ruthenium trichloride, etc. The acetate, nitrate or chloride of the transition metal has good solubility, low cost and good biodegradability, which is beneficial to the separation of the subsequent system.

[0063] In some embodiments, the molybdate solution is selected from ammonium molybdate solution or sodium molybdate solution.

[0064] In this embodiment, the molybdate solution is selected from ammonium molybdate solution or sodium molybdate solution. The ammonium molybdate solution or sodium molybdate solution can provide a molybdenum source for the reaction, which is convenient for forming molybdenum carbide through carbonization treatment.

[0065] In some embodiments, when the molybdate solution is sodium molybdate solution, the molybdate solution is formed by mixing sodium molybdate solution with ammonia water; the volume ratio of ammonia water in the molybdate solution is 1% to 5%.

[0066] It should be noted that if 100 mL of sodium molybdate solution is needed, sodium molybdate is dissolved in deionized water to form sodium molybdate solution, and the addition amount of ammonia water is 1 mL to 5 mL.

[0067] In this embodiment, for the sodium molybdate solution, an appropriate amount of ammonia water needs to be added to reduce its influence on the polymerization process of phenolic resin.

[0068] In some embodiments, the temperature of the high-temperature carbonization treatment is 800 °C to 1000 °C.

[0069] In this embodiment, when the high-temperature carbonization treatment temperature is greater than 800 °C, the specific surface area and pore volume of the mesoporous carbon increase significantly, and the formed mesopores can significantly reduce the mass transfer resistance and improve the performance of the catalyst; when the high-temperature carbonization treatment temperature is greater than 1000 °C, the pore channels may collapse due to excessive shrinkage. Therefore, in this embodiment, the high-temperature carbonization treatment temperature is selected to be 800 °C to 1000 °C, preferably 820 °C to 880 °C.

[0070] In a second aspect, the present invention provides a molybdenum carbide-metal composite catalyst, which is obtained according to the above preparation method;

[0071] Among them, in the molybdenum carbide-metal composite catalyst, the loading amount of molybdenum carbide is 5 wt% - 20 wt%, the loading amount of transition metal is 0.5 wt% - 5 wt%, and the rest is the mesoporous carbon carrier.

[0072] Specifically, when implemented, the phenolic resin serves as both the carbon source and the catalyst carrier. The phenolic resin is carbonized to form mesoporous carbon. At this time, the mesoporous carbon is the carrier of the catalyst. The carbon source of the phenolic resin and the molybdenum source of the molybdate are reduced at high temperature to form molybdenum carbide. The loading amount of molybdenum carbide is between 5 wt% - 20 wt%. When the loading amount of molybdenum carbide is less than 5 wt%, the active sites of the catalyst are fewer and the catalytic performance is reduced; when the loading amount of molybdenum carbide is greater than 20 wt%, the morphology of the catalyst cannot form a spherical shape. Therefore, when the loading amount of molybdenum carbide is 5 wt% - 20 wt%, the molybdenum carbide nanoparticles are highly dispersed on the surface of the mesoporous carbon, exposing more active sites and being better dispersed in the mesoporous carbon. It not only uses the pore confinement effect to inhibit agglomeration but also maintains the pore channels open to ensure the diffusion of reactants / products, that is, improves the mass transfer efficiency.

[0073] Specifically, when implemented, molybdenum carbide and transition metal are loaded on the mesoporous carbon. When the loading amount of the transition metal is less than 0.5 wt%, the active sites of the catalyst are fewer and the catalyst performance is reduced; when the loading amount of the transition metal is greater than 5 wt%, the transition metal particles are prone to agglomeration, covering the active sites of Mo2C and blocking the pores, resulting in a decrease in activity. Therefore, an appropriate loading amount of the transition metal can achieve the best match between the active site density and the mass transfer efficiency, significantly improving the overall catalytic performance.

[0074] In some embodiments, the molybdenum carbide-metal composite catalyst has a spherical morphology, and the particle size is 100 nm to 1 μm; the particle size of the molybdenum carbide is less than 20 nm.

[0075] Figure 2 The SEM image of the Cu-Mo2C catalyst provided by the embodiment of the present invention is shown, as Figure 2As shown, the molybdenum carbide-metal composite catalyst has a spherical morphology. There is no large-scale agglomeration between the spheres, and the particle size distribution is in the range of 100 nm to 1 μm, that is, the prepared catalyst is nanosphere particles.

[0076] It should be noted that the size of the nanosphere particles changes with the incorporation amount of the transition metal. Specifically, when the incorporation amount of the transition metal is small, the particle size of the nanosphere is small, 200 nm; when the incorporation amount of the transition metal is large, the particle size of the nanosphere becomes larger, 1 μm. That is, within a certain range, the particle size of the nanosphere increases with the increase of the incorporation amount of the transition metal.

[0077] In addition, the prepared molybdenum carbide has a particle size less than 20 nm, preferably less than 5 nm, which can achieve the uniform dispersion of molybdenum carbide in the three-dimensional network structure of mesoporous carbon, has a high active site density, and at the same time enhances the interaction between the transition metal and the mesoporous carbon support, improving the catalyst performance.

[0078] In the third aspect, the present invention provides an application of the molybdenum carbide-metal composite catalyst. Using CO2 and H2 with a volume ratio of 1:1 to 1:3 as reaction raw materials, at 250 °C to 600 °C, the molybdenum carbide-metal composite catalyst catalyzes the reverse water gas shift reaction of CO2 hydrogenation;

[0079] Among them, the reaction space velocity is 7000 mL / g·h to 60000 mL / g·h, the CO2 conversion rate is greater than 16%, and the CO selectivity is greater than 96%.

[0080] Specifically in implementation, an appropriate amount of the molybdenum carbide-metal composite catalyst is loaded into the isothermal zone of a fixed-bed reactor. The reaction raw materials are a mixture of CO2 and H2, and the volume ratio of CO2 to H2 is 1:1 to 1:3. Pass CO2 / H2 through the catalyst bed layer at a certain flow rate. The reaction temperature is gradually raised to the set temperature to start the reaction. The reaction pressure is set to atmospheric pressure. The space velocity of the flow rate is 7000 mL / g·h to 60000 mL / g·h. The reaction temperature of the catalyst bed layer is 250 °C to 600 °C. The product directly enters a gas chromatograph for detection and analysis. Among them, the content of H2, CO2 raw material gas and reaction product gases such as CO and CH4 in the mixed gas is analyzed by a TCD detector. The specific calculation is carried out according to the following calculation formula:

[0081] CO2 conversion rate = (CO 2进口 –CO 2出口 ) / CO 2进口 ×100%;

[0082] CO selectivity = (CO 出口 × number of carbon atoms) / (∑ products 出口 × number of carbon atoms)×100%;

[0083] It should be noted that the product conversion rate and selectivity involved in the present invention are calculated based on the carbon-based molar ratio. For example, CO 2进口 is the amount of substance of carbon atoms (mol) in CO2 before the reaction, and CO 2出口 is the amount of substance of carbon atoms (mol) in the unreacted CO2 after the reaction, and ∑ products 出口 is the molar amount of the carbon-based groups of all products at the outlet after the reaction.

[0084] In this example, the activity of the molybdenum carbide-metal composite catalyst was tested by the conversion efficiency of CO2 and the selectivity of CO, indicating that the molybdenum carbide-metal composite catalyst exhibits excellent activity and stability in the RWGS process, demonstrating its potential for practical applications and having industrial application prospects.

[0085] To make those skilled in the art understand the present invention more clearly, the following examples are now used to describe in detail a molybdenum carbide-metal composite catalyst, its preparation method, and its application according to the present invention.

[0086] Example 1

[0087] Dissolve 1 g of the surfactant F127 in a certain amount of deionized water to form an F127 solution. Dissolve 1 g of phenol (the molar amount of phenol is 0.010 mol) and 5 mL of 37 wt% formaldehyde solution (the molar amount of formaldehyde is 0.062 mol) in 0.1 mol / L NaOH solution and mix well. Heat and stir at 60 °C for 10 min; then add the F127 solution thereto and mix well to form a first mixed system;

[0088] Dissolve 1 g of ammonium molybdate (the molar amount of molybdenum is 5 mmol) in 10 mL of deionized water to form an ammonium molybdate solution; after the first mixed system starts to turn red, at this time the solution shows sol characteristics and starts to form phenolic resin. Start timing, and the timing time is 0 - 2 h. During the timing process, use a peristaltic pump to slowly add the above-mentioned ammonium molybdate solution to the above first mixed system at a flow rate of 1 mL / min, and heat and stir to form a second mixed system;

[0089] Dissolve 0.02 g of copper acetate (the molar amount of copper is 0.1 mmol) in 1% acetic acid solution to form a transition metal salt solution; after the second mixed system starts to change from red to green, at this time the phenolic resin and ammonium molybdate form a green complex. Add the transition metal salt solution dropwise to the above second mixed system at a flow rate of 1 mL / min by a peristaltic pump, and react at 60 °C with heating and stirring for 48 h. After the reaction ends, collect the solid product by centrifugation to obtain a catalyst precursor;

[0090] The catalyst precursor is placed in an inert atmosphere and subjected to high-temperature carbonization treatment at 850 °C to obtain the molybdenum carbide-metal composite catalyst, i.e., the Cu-Mo₂C catalyst. The morphological results are as Figure 2 shown. The morphology of the obtained Cu-Mo₂C catalyst is spherical, and the particle size ranges from 100 nm to 1 μm.

[0091] Example 2

[0092] Compared with Example 1, the difference lies in:

[0093] The transition metal salt solution used in this example is formed by dissolving 0.05 g of cobalt acetate (the molar amount of cobalt is 0.28 mmol) in 3% acetic acid solution;

[0094] The remaining steps and dosages are the same as those in Example 1 to obtain the Co-Mo₂C catalyst.

[0095] The SEM image of the Co-Mo₂C catalyst obtained in this example is similar to that of Figure 2 which is not shown again here.

[0096] Example 3

[0097] Compared with Example 1, the difference lies in:

[0098] (1) The surfactant used in this example is CTAB, and 3 g of CTAB is dissolved in a certain amount of deionized water to form a CTAB solution;

[0099] (2) The transition metal salt solution used in this example is formed by dissolving 0.08 g of nickel acetate (the molar amount of nickel is 0.45 mmol) in 3% propionic acid solution;

[0100] The remaining implementation steps and dosages are the same as those in Example 1 to obtain the Ni-Mo₂C catalyst. The SEM image of the Ni-Mo₂C catalyst obtained in this example is similar to that of Figure 2 which is not shown again here.

[0101] Example 4

[0102] Compared with Example 1, the difference lies in:

[0103] The transition metal salt solution used in this example is formed by dissolving 0.10 g of iron nitrate (the molar amount of iron is 0.41 mmol) in 4% acetic acid solution;

[0104] The remaining implementation steps and dosages are the same as those in Example 1 to obtain the Fe-Mo₂C catalyst.

[0105] The SEM image of the Fe-Mo₂C catalyst obtained in this example is similar to that of Figure 2Similar, not shown again here.

[0106] Example 5

[0107] Compared with Example 1, the differences are as follows:

[0108] The transition metal salt solution used in this example is formed by dissolving 0.01 g of ruthenium trichloride (the molar amount of ruthenium is 0.048 mmol) and 0.02 g of copper acetate in 5% acetic acid solution;

[0109] The remaining implementation steps and dosages are the same as those in Example 1 to obtain a Cu-Ru-Mo2C catalyst.

[0110] The SEM image of the Cu-Ru-Mo2C catalyst obtained in this example is similar to Figure 2 Similar, not shown again here.

[0111] Example 6

[0112] Compared with Example 1, the differences are as follows:

[0113] (1) The molybdate solution used in this example is formed by dissolving 2 g of sodium molybdate (the molar amount of molybdenum is 9.7 mmol) in 10 mL of deionized water and adding 2% ammonia water;

[0114] (2) In this example, when the transition metal salt solution is added dropwise to the above second mixed system, it is heated and stirred at 60 °C for 24 h;

[0115] The remaining implementation steps and dosages are the same as those in Example 1 to obtain a Cu-Mo2C-1 catalyst.

[0116] The SEM image of the Cu-Mo2C-1 catalyst obtained in this example is similar to Figure 2 Similar, not shown again here.

[0117] Example 7

[0118] Compared with Example 1, the differences are as follows:

[0119] The raw materials used in this example are quadrupled on the basis of Example 1, namely 4 g of surfactant F127, 4 g of phenol (the molar amount of phenol is 0.040 mol), 20 mL of 37 wt% formaldehyde solution (the molar amount of formaldehyde is 0.248 mol), 4 g of ammonium molybdate (the molar amount of molybdenum is 20 mmol), and 0.08 g of copper acetate (the molar amount of copper is 0.4 mmol);

[0120] The remaining implementation steps are the same as those in Example 1 to obtain a Cu-Mo2C-2 catalyst.

[0121] The SEM image of the Cu-Mo2C-2 catalyst obtained in this example is similar to Figure 2 which is not shown again here.

[0122] Calculated based on a solution volume of 100 mL, the yield of the catalyst prepared each time can reach more than 5 g. Tests show that the preparation method of the present invention has the feasibility of large-scale preparation.

[0123] Catalyst activity test

[0124] Take 0.2 g of the Cu-Mo2C catalyst prepared in Example 1 and mix it with 0.4 g of quartz sand, then load it into the constant temperature zone of a fixed-bed reactor. The reaction raw materials are a mixture of CO2 and H2, and the volume ratio of CO2 to H2 is 1:3. Pass CO2 / H2 through the catalyst bed layer at a certain flow rate, and the space velocities of the flow rate are set to 7500 mL / g·h, 15000 mL / g, and 60000 mL / g·h respectively. Start the reaction at reaction temperatures of 400 °C, 500 °C, and 600 °C respectively, and set the reaction pressure to atmospheric pressure. The products directly enter a gas chromatograph for detection and analysis. Among them, the contents of H2, CO2 raw material gas and reaction product gases such as CO and CH4 in the mixed gas are analyzed by a TCD detector. The results of the activity tests of each catalyst are shown in Table 1.

[0125] The results in Table 1 show that in Example 1 of the present invention, the catalytic activity of the Cu-Mo2C catalyst at different space velocities and different reaction temperatures was explored. When at a high space velocity, the CO2 conversion rate remained above 16%. When the space velocity was appropriate (7500 mL / g·h), the CO2 conversion rate was relatively high; when the space velocity was increased to 15000 mL / g·h, the selectivity of CO could still be maintained above 96%.

[0126] Further, the catalysts prepared in Examples 2-7 were subjected to catalyst activity tests (reaction conditions: the volume ratio of CO2 to H2 is 1:3, the space velocity is 7500 mL / g·h, the reaction temperatures are 400 °C, 500 °C, and 600 °C, and the reaction pressure is atmospheric pressure). The results of the activity tests are shown in Table 1.

[0127] Figure 3 Shows the catalytic activity performance diagram of the Cu-Mo2C catalyst obtained in Example 1 of the present invention (reaction conditions: the volume ratio of CO2 to H2 is 1:3, the space velocity is 7500 mL / g·h, the reaction temperatures are 300 °C, 350 °C, 400 °C, 450 °C, 500 °C, 550 °C, and 600 °C, and the reaction pressure is atmospheric pressure. Among them, the bar graph represents the CO selectivity at different temperatures; the curve with dots represents the CO2 conversion rate at different temperatures; the curve without dots is the corresponding CO2 equilibrium conversion rate at different temperatures); as Figure 3As shown, as the reaction temperature gradually increases, the selectivity of CO shows an upward trend. However, when the temperature is between 400 °C and 600 °C, the selectivity of CO tends to be stable, maintaining above 99%. As the reaction temperature gradually increases, the conversion rate of CO2 also shows a gradually increasing trend, and it can be seen from the figure that the conversion rate of CO2 at different temperatures is close to the equilibrium conversion rate of CO2 at different temperatures. The test results show that the Cu-Mo2C catalyst obtained in this application exhibits a conversion efficiency of CO2 close to the thermodynamic equilibrium and a CO selectivity of more than 99%, proving its advantage in catalyzing the RWGS reaction.

[0128] The test results show that: for the Co-Mo2C catalyst at different reaction temperatures, the selectivity of CO reaches above 99%; the conversion rate of CO2 reaches above 16%.

[0129] The catalyst obtained by the preparation method of the present invention can exhibit excellent conversion efficiency of CO2 and CO selectivity at an appropriate space velocity, and the scale-up preparation does not affect the catalytic activity of the catalyst, proving its potential for large-scale industrial applications.

[0130] Table 1 Evaluation conditions and results of the examples

[0131]

[0132] In the description of this specification, the descriptions with reference to terms such as "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. mean that the specific features, structures, materials or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in a suitable manner in any one or more embodiments or examples. In addition, those skilled in the art can combine and combine the different embodiments or examples described in this specification.

[0133] For method embodiments, for the sake of simple description, they are all expressed as a series of action combinations. However, those skilled in the art should know that the present invention is not limited by the described action sequence, because according to the present invention, certain steps can be performed in other sequences or simultaneously. Secondly, those skilled in the art should also know that the embodiments described in the specification are all preferred embodiments, and the actions and components involved are not necessarily essential to the present invention.

[0134] The above has introduced in detail a molybdenum carbide-metal composite catalyst, a preparation method thereof and an application thereof. Specific examples are used in this article to elaborate on the principle and implementation manner of the present invention. The description of the above embodiments is only used to help understand the method and its core idea of the present invention; at the same time, for those of ordinary skill in the art, according to the idea of the present invention, there will be changes in the specific implementation manner and application scope. In summary, the content of this specification should not be construed as a limitation to the present invention.

Claims

1. A method for preparing a molybdenum carbide-metal composite catalyst, characterized in that, The preparation method specifically includes the following steps: S1. After mixing phenol, formaldehyde solution and sodium hydroxide solution, an appropriate amount of surfactant is added, and after mixing, a first mixed system is formed; S2. Within 2 h after the first mixed system starts to turn red, an appropriate amount of molybdate solution is slowly added and stirred to form a second mixed system; S3. After the second mixed system starts to change from red to green, an appropriate amount of transition metal salt solution is continuously added, and after stirring and reacting for 24 - 72 h, the solid is collected to obtain a catalyst precursor; S4. The catalyst precursor is placed in an inert atmosphere for high-temperature carbonization treatment to obtain the molybdenum carbide-metal composite catalyst; Among them, in the solution, the molar ratio of phenol to formaldehyde is 1:2 - 1:10; The surfactant is cetyltrimethylammonium bromide or polyoxyethylene-polyoxypropylene-polyoxyethylene triblock copolymer; In the molybdate solution and the transition metal salt solution, the molar ratio of molybdenum to the transition metal is 5 - 25:0.1 - 1; Steps S1 - S3 are all carried out at 30 - 85 °C.

2. The preparation method according to claim 1, characterized in that, The transition metal contained in the transition metal salt solution is selected from one or more of Cu, Fe, Co, Ni, and Ru; 3. The preparation method according to claim 2, wherein The transition metal salt solution is formed by dissolving a transition metal salt in an organic acid solution, and the organic acid is selected from acetic acid or propionic acid; The volume ratio of the organic acid in the organic acid solution is 0.5% - 5%; 4. The preparation method according to claim 3, characterized in that, The transition metal salt is selected from acetate, nitrate or chloride containing a transition metal; 5. The preparation method according to claim 1, wherein The molybdate solution is selected from ammonium molybdate solution or sodium molybdate solution; 6. The preparation method according to claim 5, wherein When the molybdate solution is sodium molybdate solution, the molybdate solution is formed by mixing sodium molybdate solution and ammonia water; The volume ratio of ammonia water in the molybdate solution is 1% - 5%; 7. The preparation method according to claim 1, characterized in that, The temperature of the high-temperature carbonization treatment is 800 °C - 1000 °C; 8. A molybdenum carbide-metal composite catalyst, characterized in that, The molybdenum carbide-metal composite catalyst is obtained according to the preparation method described in any one of claims 1 - 7; Among them, in the molybdenum carbide-metal composite catalyst, the loading amount of molybdenum carbide is 5 wt% - 20 wt%, the transition metal loading amount is 0.5 wt% - 5 wt%, and the rest is a mesoporous carbon carrier; 9. The molybdenum carbide-metal composite catalyst according to claim 8, wherein The molybdenum carbide-metal composite catalyst has a spherical morphology, and the particle size is 100 nm - 1 μm; the particle size of the molybdenum carbide is less than 20 nm; 10. Use of the molybdenum carbide-metal composite catalyst according to claim 8 or 9, characterized in that, Using CO2 and H2 with a volume ratio of 1:1 - 1:3 as reaction raw materials, at 250 °C - 600 °C, the molybdenum carbide-metal composite catalyst catalyzes the reverse water gas shift reaction of CO2 hydrogenation of CO2 and H2; Among them, the reaction space velocity is 7000 mL / g·h - 60000 mL / g·h, the CO2 conversion rate is greater than 16%, and the CO selectivity is greater than 96%.

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