Molybdenum carbide-based thermal catalyst as well as preparation method and application thereof

Abstract

According to the molybdenum carbide-based thermal catalyst and the preparation method and application thereof, orthosilicate is hydrolyzed and converted into SiO2 in the alkaline environment, meanwhile, the alkaline environment is the condition needed by the complexation reaction of dopamine hydrochloride and molybdate, the two reactions are combined, preparation of the molybdenum carbide-based thermal catalyst precursor is achieved, and the molybdenum carbide-based thermal catalyst is prepared. And further performing high-temperature carbonization treatment on the catalyst precursor to obtain the molybdenum carbide-based thermal catalyst. In the molybdenum carbide-based thermal catalyst, SiO2 and Mo2C are uniformly mixed, so that efficient contact between catalytic active sites and reactants is ensured while hydrophobic performance is achieved, the shielding effect of SiO2 coating on the active sites is effectively avoided, and the catalytic efficiency is improved. The molybdenum carbide-based thermal catalyst prepared in the invention shows excellent reverse water gas catalytic activity, and can realize CO selectivity of 99% or more and CO2 conversion rate close to thermodynamic equilibrium.

Description

Technical Field

[0001] This application relates to the technical field of coal chemical conversion, and particularly relates to a molybdenum carbide-based thermal catalyst, a preparation method thereof, and an application thereof. Background Art

[0002] The development of clean energy technologies has provided an important path for the resource utilization of CO2. Green hydrogen, with its potential in terms of price and application scenarios, has become a key carrier for realizing CO2 emission reduction. Through the Reverse Water-Gas Shift (RWGS) reaction, green hydrogen can convert CO2 into syngas (CO and H2). This not only directly reduces CO2 emissions, but the generated syngas can further be used to prepare industrial products through processes such as Fischer-Tropsch synthesis, forming a closed-loop industrial chain of "carbon capture-conversion-utilization". However, the chemical stability of CO2 molecules is extremely high, and its hydrogenation reaction is limited by the thermodynamic equilibrium and kinetic barriers, resulting in a relatively large driving energy required for the reaction. At the same time, side reactions such as methanation (formation of CH4) or methanol synthesis are prone to occur during the CO2 hydrogenation process, causing the product gas components to be complex, increasing the separation difficulty and cost. Therefore, developing a catalyst with both high catalytic activity and high single-product selectivity has become the core requirement for improving the energy conversion efficiency and economy of the RWGS reaction.

[0003] Molybdenum carbide (Mo2C), as a typical metal interstitial compound, due to the electron modulation effect of interstitial carbon atoms on its metal molybdenum sites, exhibits an electronic structure similar to that of noble metals, endowing it with excellent catalytic activity and showing application potential in the fields of photocatalysis, electrocatalysis, and thermal catalysis. In the thermal catalytic RWGS reaction, Mo2C-based catalysts have become one of the research hotspots due to their strong ability to adsorb and activate CO2. To improve the atomic utilization rate, related technologies usually prepare Mo2C into nanoparticles to increase the exposure of active sites. In addition, in view of the influence of a large amount of water generated during the RWGS reaction on the catalyst performance, some studies coat the surface of Mo2C with inert materials such as SiO2 to improve the hydrophobicity of the catalyst, reduce the retention of water molecules at the active sites, and promote the reversible reaction to proceed in the direction of syngas generation.

[0004] Although Mo2C-based catalysts have potential advantages in RWGS reactions, their practical application still faces significant challenges: on the one hand, nanoscale Mo2C particles are prone to Ostwaldripening under high temperature reaction conditions, resulting in particle agglomeration and sintering, causing loss of active sites and catalyst deactivation, making it difficult to meet the needs of long-term stable operation; on the other hand, although the strategy of improving hydrophobicity through SiO2 coating can reduce water adsorption, the physical barrier of the surface coating layer to the active sites significantly reduces the contact efficiency between the reactants and the Mo2C active center, resulting in a decrease in catalytic activity. How to ensure the hydrophobicity of the catalyst while avoiding the shielding of the active sites and effectively inhibiting the sintering behavior of Mo2C nanoparticles has become a technical bottleneck that needs to be solved in the current application of Mo2C-based catalysts in RWGS reactions. Summary of the invention

[0005] In view of the problems existing in the background technology, the present application provides a molybdenum carbide-based thermal catalyst, a preparation method and its application. The present application simultaneously carries out the complexation reaction of dopamine hydrochloride and molybdate on the basis of the hydrolysis reaction of orthosilicates, and realizes the regulation and matching of the two reactions by regulating the alkalinity of the solution, the concentration of the reactants and the reaction temperature. After a one-step high-temperature carbonization treatment, the complex is converted into molybdenum carbide, and the orthosilicate is converted into SiO2 to obtain a molybdenum carbide-based thermal catalyst. Through the excellent active sites provided by highly dispersed molybdenum carbide and the hydrophobic effect of SiO2, the formed molybdenum carbide-based thermal catalyst exhibits an excellent catalytic reverse water gas conversion effect.

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

[0007] According to a first aspect of the present application, a method for preparing a molybdenum carbide-based thermal catalyst is provided, and the preparation method specifically comprises the following steps:

[0008] S1, stirring and mixing orthosilicate, deionized water and ethanol to form a first mixed system, and then adding an appropriate amount of ammonia water to hydrolyze the orthosilicate in an alkaline environment;

[0009] S2, adding an appropriate amount of molybdate solution to the first mixed system, and stirring to form a second mixed system;

[0010] S3, adding an appropriate amount of dopamine hydrochloride solution to the second mixed system, stirring for reaction, and collecting to obtain a catalyst precursor;

[0011] S4, placing the catalyst precursor in an inert atmosphere and performing a high-temperature carbonization treatment to obtain the molybdenum carbide-based thermal catalyst;

[0012] Among them, in the first mixed system, the molar concentration of orthosilicate is 0.01 - 0.3 mol / L, and the volume ratio of deionized water to ethanol is 1:1 - 1:3;

[0013] In the dopamine hydrochloride solution and the molybdate solution, the molar ratio of dopamine hydrochloride to molybdate is 1:1 - 8:1.

[0014] Optionally, the orthosilicate is one or more of methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate.

[0015] Optionally, the addition amount of ammonia water keeps the pH of the first mixed system at 12 - 14.

[0016] Optionally, the molybdate solution is selected from ammonium molybdate solution or sodium molybdate solution;

[0017] The molar amount of molybdenum element in the molybdate solution is 5 - 20 mmol.

[0018] Optionally, in the orthosilicate and the molybdate solution, the molar ratio of silicon to molybdenum is 1:1 - 5:1.

[0019] Optionally, steps S1 - S3 are all carried out at 20°C - 60°C.

[0020] Optionally, the temperature of the high-temperature carbonization treatment is 800°C - 1000°C.

[0021] According to the second aspect of the present application, a molybdenum carbide-based thermal catalyst is provided, and the molybdenum carbide-based thermal catalyst is obtained according to the above preparation method.

[0022] Optionally, the molybdenum carbide-based thermal catalyst is spherical nanoparticles with a particle size of 70 - 110 nm; the spherical nanoparticles are composed of SiO2, carbon, and molybdenum carbide. Among them, the mass ratio of SiO2 to molybdenum carbide in the molybdenum carbide-based thermal catalyst is 2:1 - 6:1, and the particle size of molybdenum carbide is 1 nm - 5 nm.

[0023] According to the third aspect of the present application, an application of a molybdenum carbide-based thermal catalyst is provided. Using CO2 and H2 with a volume ratio of 1:1 - 1:3 as reaction raw materials, at 300°C - 600°C, the molybdenum carbide-based thermal catalyst catalyzes the reverse water-gas shift reaction of CO2 hydrogenation;

[0024] Among them, the reaction space velocity is 6000 mL / g·h - 8000 mL / g·h, the conversion efficiency of CO2 is greater than 3.78%, and the selectivity of CO is greater than 96%.

[0025] Compared with the prior art, the present application has the following advantages:

[0026] The present application provides a molybdenum carbide-based thermal catalyst, a preparation method thereof, and an application thereof. The preparation method includes the following steps: stirring and mixing orthosilicates, deionized water, and ethanol to form a first mixed system, and then adding an appropriate amount of ammonia water to hydrolyze the orthosilicates in an alkaline environment; adding an appropriate amount of molybdate solution to the first mixed system and stirring to form a second mixed system; adding an appropriate amount of hydrochloric acid dopamine solution to the second mixed system, stirring and reacting, and collecting to obtain a catalyst precursor; placing the catalyst precursor in an inert atmosphere and performing high-temperature carbonization treatment to obtain the molybdenum carbide-based thermal catalyst. The molybdenum carbide-based thermal catalyst obtained by the above preparation method is used to catalyze the reverse water gas shift reaction of CO2 hydrogenation of CO2 and H2.

[0027] In the preparation method of the molybdenum carbide-based thermal catalyst provided by the present application, orthosilicates are hydrolyzed and converted into SiO2 in an alkaline environment, and at the same time, this alkaline environment is the condition required for the complexation reaction of hydrochloric acid dopamine and molybdate. The present application combines the two reactions to realize the preparation of the molybdenum carbide-based thermal catalyst precursor, and further performs high-temperature carbonization treatment on the catalyst precursor to obtain the molybdenum carbide-based thermal catalyst. In the complexation reaction of molybdate-hydrochloric acid dopamine, the organic matter of hydrochloric acid dopamine and molybdenum are in a coordination form. After carbonization treatment, the hydrochloric acid dopamine-molybdate complex is directly converted into Mo2C, realizing the uniform nano-dispersion of Mo2C, and the carbon substrate can effectively anchor the nanoparticles to prevent aggregation; at the same time, during the high-temperature carbonization heat treatment process, the surface hydroxyl groups of SiO2 are removed, and the molybdate-hydrochloric acid dopamine complex is converted into Mo2C, and the two proceed synchronously, so that the molybdenum carbide-based thermal catalyst can finally exhibit excellent hydrophobic effect, effectively reducing the adsorption of product water on the catalyst surface in the thermal reaction and improving the conversion rate of the reversible reaction. In the molybdenum carbide-based thermal catalyst, SiO2 and Mo2C are uniformly mixed rather than simply wrapped, ensuring the efficient contact between the catalytic active sites and the reactants, effectively avoiding the shielding effect of SiO2 coating on the active sites, and improving the catalytic efficiency. Compared with the existing Mo2C catalyst, the molybdenum carbide-based thermal catalyst prepared by the present application exhibits more excellent reverse water gas catalytic activity, and can achieve a CO selectivity of more than 99% and a CO2 conversion rate close to the thermodynamic equilibrium.

[0028] In addition, the preparation method has simple process, high controllability of the product composition and morphology, large single reaction output, and is suitable for large-scale batch production. Brief Description of the Drawings

[0029] To more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the accompanying drawings required for the description of the embodiments or the prior art. Obviously, the accompanying drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, without creative work, other accompanying drawings can also be obtained based on these drawings.

[0030] Figure 1 The flowchart showing the preparation method of the molybdenum carbide-based thermal catalyst provided by the embodiment of the present application is shown;

[0031] Figure 2 The SEM image of the molybdenum carbide-based thermal catalyst provided by the embodiment of the present application is shown. Detailed implementation manners

[0032] The following will clearly and completely describe the technical solutions in the embodiments of the present application in conjunction with the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present application and its application or use. Based on the embodiments in the present application, any product identical or similar to the present application obtained by anyone under the inspiration of the present application or by combining the features of the present application with other prior art features falls within the protection scope of the present application. And all other embodiments obtained by those of ordinary skill in the art without creative work also belong to the protection scope of the present application.

[0033] For 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 a part of the specification of the present application.

[0034] Moreover, the technical features involved in different embodiments of the present application described below can be combined with each other as long as they do not conflict with each other.

[0035]

[0036] ​In view of the problems of catalyst particle agglomeration and active site shielding in the catalyst of the related art, in the first aspect, the present application provides a method for preparing a molybdenum carbide-based thermal catalyst. Figure 1 The flow chart of the preparation method of the molybdenum carbide-based thermal catalyst provided in the embodiment of the present application is shown as follows: Figure 1 As shown, the preparation method specifically comprises the following steps:

[0037] S1, stirring and mixing orthosilicate, deionized water and ethanol to form a first mixed system, and then adding an appropriate amount of ammonia water to hydrolyze the orthosilicate in an alkaline environment;

[0038] S2, adding an appropriate amount of molybdate solution to the first mixed system, and stirring to form a second mixed system;

[0039] S3, adding an appropriate amount of dopamine hydrochloride solution to the second mixed system, stirring for reaction, and collecting to obtain a catalyst precursor;

[0040] S4, placing the catalyst precursor in an inert atmosphere and performing a high-temperature carbonization treatment to obtain the molybdenum carbide-based thermal catalyst;

[0041] Wherein, in the first mixed system, the molar concentration of orthosilicate is 0.01-0.3 mol / L, and the volume ratio of deionized water to ethanol is 1:1-1:3;

[0042] In the dopamine hydrochloride solution and the molybdate solution, the molar ratio of dopamine hydrochloride to molybdate is 1:1 to 8:1.

[0043] It should be noted that the purity of orthosilicates is greater than or equal to 98%. Deionized water can avoid impurities in water, such as Cl-, Ca 2 + Interfere with the hydrolysis and polycondensation process. Excess deionized water is required to ensure complete hydrolysis of the alkoxy groups. If the amount of water is insufficient, the residual alkoxy groups will lead to incomplete condensation and affect the integrity of the SiO2 structure. Ethanol is anhydrous ethanol, which reduces the effect of water in ethanol on the hydrolysis reaction. Ethanol not only acts as a co-solvent, but also can adjust the polarity of the system and control the hydrolysis rate.

[0044] It should also be noted that the reaction process of steps S1-S3 requires constant stirring, which can be magnetic stirring or mechanical stirring, to ensure that the orthosilicate, water, ethanol and 25% ammonia water are fully mixed to avoid local uneven concentrations that lead to agglomeration of SiO2 gel particles or uneven coating.

[0045] It should also be noted that in the first mixed system, the volume ratio of deionized water to ethanol needs to be maintained at 1:1 to 1:3. Below this volume ratio, molybdate does not dissolve during the subsequent reaction process, and the reaction cannot proceed; above this volume ratio, tetraethyl orthosilicate in the tetraethyl orthosilicate group does not dissolve, and the reaction also cannot proceed. In addition, too high an ethanol content will dilute the reactants and slow down the reaction; too low may lead to phase separation.

[0046] It should be noted that the molar ratio of dopamine hydrochloride to molybdate is 1:1 to 8:1. Excess molybdate may cause precipitation; while dopamine is easily oxidized. Maintaining an excess of dopamine can reduce the exposed active sites, inhibit the oxidation reaction, and at the same time prevent particle aggregation, achieving a high dispersion of nanoparticles. In this reaction system, molybdate needs to be added first and stirred evenly, and then dopamine hydrochloride solution is added. If added simultaneously, the reaction will be too fast and the product will agglomerate.

[0047] It should also be noted that molybdate and dopamine hydrochloride form a complex. The organic ligand in the complex is the carbon source. Due to the complexation of the organic ligand, Mo is better dispersed.

[0048] During specific implementation, the dopamine hydrochloride solution is added using a peristaltic pump at an addition rate of 0.5 mL / min to 2 mL / min to avoid agglomeration caused by too high a local concentration.

[0049] During specific implementation, tetraethyl orthosilicate group and deionized water undergo hydrolysis under alkaline catalysis. The molar concentration of tetraethyl orthosilicate group is 0.01 to 0.3 mol / L, generating silicic acid intermediates and methanol. Silicic acid forms a Si-O-Si network structure through dehydration condensation under alkaline conditions, and finally a three-dimensional network structure of silica gel is formed. Then, the molybdate solution is first added to the first mixed system and stirred evenly, and then the dopamine hydrochloride solution is added drop by drop. Stir and react at room temperature for 24 h, and centrifuge to collect the solid product to obtain the catalyst precursor.

[0050] In this embodiment, orthosilicates are hydrolyzed and converted into SiO2 in an alkaline environment, and this alkaline environment is the condition required for the complexation reaction of dopamine hydrochloride and molybdate. This application combines the two reactions to realize the preparation of a molybdenum carbide-based thermal catalyst precursor, and further performs high-temperature carbonization treatment on the catalyst precursor to obtain a molybdenum carbide-based thermal catalyst. In the complexation reaction of molybdate-dopamine hydrochloride, the dopamine hydrochloride organic matter and molybdenum are in a coordination form. After carbonization treatment, the dopamine hydrochloride-molybdate complex is directly converted into Mo2C, realizing the uniform nano-dispersion of Mo2C, and the carbon substrate can effectively anchor the nanoparticles to prevent agglomeration. At the same time, during the high-temperature carbonization heat treatment process, the surface hydroxyl groups of SiO2 are removed, and the molybdate-dopamine hydrochloride complex is converted into Mo2C, and the two proceed synchronously, so that the molybdenum carbide-based thermal catalyst can finally exhibit excellent hydrophobic effects, effectively reducing the adsorption of product water on the catalyst surface in the thermal reaction and improving the conversion rate of the reversible reaction. In the molybdenum carbide-based thermal catalyst, SiO2 and Mo2C are uniformly mixed rather than simply wrapped, ensuring the efficient contact between the catalytic active sites and the reactants, effectively avoiding the shielding effect of SiO2 coating on the active sites, and improving the catalytic efficiency.

[0051] In some embodiments, the orthosilicates are one or more of methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate.

[0052] It should be noted that when the orthosilicate is methyl orthosilicate, the hydrolysis rate of methyl orthosilicate is the fastest. When forming a molybdenum carbide-based thermal catalyst, the structure is that Mo2C is wrapped by SiO2 on the outer layer; when the orthosilicate is a mixture of methyl orthosilicate and ethyl orthosilicate, the hydrolysis rate of ethyl orthosilicate is slower, and when forming a molybdenum carbide-based thermal catalyst, a part of Mo2C is embedded in the SiO2 nanospheres.

[0053] In this embodiment, the orthosilicates are used as the silicon source precursor, and after hydrolysis, they provide the SiO2 skeleton. By controlling the type of orthosilicate (such as methyl ester, ethyl ester, propyl ester), the particle size, morphology, porosity, and coating uniformity of SiO2 can be controlled. The SiO2 formed by the hydrolysis of orthosilicates can form a mesoporous structure, providing a smoother diffusion path for the reactants (CO2, H2), and at the same time restricting the generation space of by-products (such as CH4, methanol), and improving the selectivity of the target product, namely syngas.

[0054] In some embodiments, the addition amount of ammonia water is such that the pH of the first mixed system is maintained at 12 to 14.

[0055] In specific implementation, in the reaction system of the present application, the addition amount of ammonia water is 3 mL to 8 mL, aiming to maintain the pH of the first mixed system at 12 to 14. If the pH is too high, the hydrolysis will be too fast, forming irregular gels; if the pH is too low, the hydrolysis will be incomplete and the condensation reaction will be difficult to proceed; at the same time, this pH also provides an alkaline condition for the reaction between molybdate and dopamine, and fixes molybdenum atoms in the complex through coordination bonds. The present application does not specifically limit the addition amount of ammonia water, as long as the pH of the system is maintained in the alkaline environment of 12 to 14.

[0056] In this embodiment, the hydrolysis reaction of orthosilicate esters and the complexation reaction of molybdate and dopamine may affect each other. By maintaining the pH at 12 to 14, the rates and processes of these two reactions can be synergistically regulated, enabling the two reactions to cooperate better, facilitating the molybdenum carbide-based thermal catalyst after carbonization treatment to have better activity, selectivity, and stability.

[0057] In some embodiments, the molybdate solution is selected from ammonium molybdate solution or sodium molybdate solution;

[0058] The molar amount of molybdenum element in the molybdate solution is 5 to 20 mmol.

[0059] In specific implementation, when the molar amount of molybdenum element is 5 to 20 mmol, too high molybdate concentration may lead to excessive cross-linking of the complex, hindering the growth of silica; too low concentration results in insufficient functional components.

[0060] In this embodiment, ammonium molybdate solution or sodium molybdate solution can provide a molybdenum source for the reaction, form a stable complex with dopamine, and facilitate the formation of molybdenum carbide through carbonization treatment.

[0061] In some embodiments, in the orthosilicate esters and the molybdate solution, the molar ratio of silicon to molybdenum is 1:1 to 5:1.

[0062] In this embodiment, under the silicon-molybdenum ratio of the present application, the hydrolysis and complexation reactions can proceed synergistically, which is beneficial to the formation of a catalyst precursor with uniform structure and stable performance.

[0063] In some embodiments, steps S1 - S3 are all carried out at 20 °C to 60 °C.

[0064] In specific implementation, the reaction temperature is at room temperature or low temperature, and the preferred temperature is 25 °C to 40 °C. Increasing the temperature can accelerate hydrolysis and condensation, but may lead to a decrease in the gel pore size and densification of the structure. However, high temperature (greater than 60 °C) may cause the gel to form too fast or particle agglomeration, and high temperature will also cause dopamine to oxidize rapidly.

[0065] In this embodiment, by regulating the reaction temperature, the regulation and matching of the two reactions are achieved, and the uniform distribution of different phases in the product is realized.

[0066] In some embodiments, the temperature of the high-temperature carbonization treatment is 800°C to 1000°C.

[0067] In this example, the interface between SiO2 and the organic ligand may be combined through chemical bonds (such as Si-O-C) or physical adsorption to stabilize the overall structure. When the high-temperature carbonization treatment temperature is greater than 800°C, the specific surface area and pore volume of the organic ligand 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 example, the temperature of the high-temperature carbonization treatment is selected to be 800°C to 1000°C, preferably 820 - 880°C.

[0068] In a second aspect, the present application provides a molybdenum carbide-based thermal catalyst, which is obtained according to the above preparation method.

[0069] In some embodiments, the molybdenum carbide-based thermal catalyst is spherical nanoparticles with a particle size of 70 - 110 nm; the spherical nanoparticles are composed of SiO2, carbon, and molybdenum carbide. Among them, the mass ratio of SiO2 to molybdenum carbide in the molybdenum carbide-based thermal catalyst is 2:1 to 6:1, and the particle size of molybdenum carbide is 1 nm to 5 nm.

[0070] Figure 2 The SEM image of the molybdenum carbide-based thermal catalyst provided by the embodiment of the present application is shown, as Figure 2 shown, the obtained morphology of the molybdenum carbide-based thermal catalyst is independent nanospheres with uniform sphere sizes and a diameter of about 100 nm, that is, the prepared catalyst is spherical nanoparticles.

[0071] Specifically, during the implementation, the molybdate reacts with dopamine hydrochloride to form a complex. The organic ligand in the complex is a carbon source, and the carbon source and the molybdenum source are carbonized to form molybdenum carbide. During the reaction process, the molybdenum source will not be completely converted into molybdenum carbide, and the remaining unconsumed carbon source will remain in the catalyst. As an oxide, silicon dioxide is stable at high temperatures and does not participate in the carbonization reaction. However, the silanol groups or the binding sites with dopamine on its surface provide sites for Mo, enabling the in-situ growth or attachment of nanoscale molybdenum carbide particles on the surface of SiO2 to avoid agglomeration. Therefore, the spherical nanoparticles are composed of SiO2, carbon, and molybdenum carbide.

[0072] It should be noted that the mass ratio of SiO2 to molybdenum carbide in the molybdenum carbide-based thermal catalyst is 2:1 to 6:1, preferably 3:1 to 5:1. The SiO2 carrier dominates, and molybdenum carbide is uniformly dispersed on the surface or in the pores of SiO2 in the form of nanoparticles. The particle size of molybdenum carbide is 1 nm to 5 nm, preferably 2 nm to 5 nm. That is, molybdenum carbide is distributed in the nanospheres in the form of ultra-fine nanoparticles, which is convenient for exposing more active edge sites, improving the activity of the catalyst, and taking into account both the number and dispersion of active sites.

[0073] It should also be noted that the addition amount of ethanol will affect the particle size of the nanospheres. Specifically, when the ethanol content is relatively high, the particle size of the nanospheres is relatively small; when the ethanol content decreases, the particle size of the nanospheres becomes larger.

[0074] In a third aspect, the present application provides an application of a molybdenum carbide-based thermal catalyst. Using a mixture of CO2 and H2 with a volume ratio of 1:1 to 1:3 as reaction raw materials, at 300°C to 600°C, the molybdenum carbide-based thermal catalyst catalyzes the reverse water-gas shift reaction of CO2 hydrogenation with H2;

[0075] wherein, the reaction space velocity is 6000 mL / g·h to 8000 mL / g·h, the conversion efficiency of CO2 is greater than 3.78%, and the CO selectivity is greater than 96%.

[0076] In specific implementation, an appropriate amount of the molybdenum carbide-based thermal catalyst is loaded into the constant temperature zone of a fixed bed reactor. The reaction raw materials use a mixture of CO2 and H2, and the volume ratio of the CO2 to the H2 is 1:1 to 1:3. Pass the CO2 / H2 through the catalyst bed layer at a certain flow rate. The reaction temperature is gradually increased to the set temperature to start the reaction. The reaction pressure is set to atmospheric pressure. The space velocity of the flow rate is 6000 mL / g·h to 8000 mL / g·h. The reaction temperature of the catalyst bed layer is 300°C to 600°C. The product directly enters 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 specific calculation is carried out according to the following calculation formula:

[0077] CO2 conversion rate = (CO 2进口 –CO 2出口 ) / CO 2进口 × 100%;

[0078] CO selectivity = (CO 出口 × number of carbon atoms) / (∑ products 出口 × number of carbon atoms) × 100%;

[0079] It should be noted that the product conversion rate and selectivity involved in the present application 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, 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 of all products at the outlet after the reaction.

[0080] In this embodiment, the activity of the molybdenum carbide-based thermal catalyst was tested by the conversion efficiency of CO2 and the selectivity of CO, indicating that the molybdenum carbide-based thermal catalyst exhibited excellent activity and stability during the RWGS process, demonstrating its potential for practical applications and having industrial application prospects.

[0081] To enable those skilled in the art to understand this application more clearly, the following examples are now used to elaborate in detail on a molybdenum carbide-based thermal catalyst, its preparation method, and its application described in this application.

[0082] Example 1

[0083] 50 mL of deionized water and 50 mL of absolute ethanol were stirred and mixed evenly to form a mixed solution. Then, 3.5 mL of methyl orthosilicate (the molar concentration of methyl orthosilicate was 0.23 mol / L) was added dropwise to the above mixed solution, and stirred and mixed evenly at room temperature for 3 - 10 min to form a first mixed system. Then, 6 mL of 25% ammonia water was added dropwise to maintain the pH of the first mixed system at 12 - 14, so that the methyl orthosilicate underwent a hydrolysis reaction in the alkaline environment to form SiO2;

[0084] 3 g of ammonium molybdate (the molar amount of ammonium molybdate was 15 mmol) was dissolved in 20 mL of deionized water to form an ammonium molybdate solution; the above ammonium molybdate solution was added to the first mixed system, and stirred at room temperature to form a second mixed system;

[0085] 0.3 g of dopamine hydrochloride (the molar amount of dopamine hydrochloride was 1.9 mmol) was dissolved in 5 mL of deionized water to form a dopamine hydrochloride solution. The above dopamine hydrochloride solution was added to the second mixed system using a peristaltic pump at a flow rate of 1 mL / min, and stirred and reacted at room temperature for 24 h. After the reaction, the solid product was collected by centrifugation to obtain a catalyst precursor;

[0086] The catalyst precursor was placed in an inert atmosphere and subjected to high-temperature carbonization treatment at 850 °C to obtain the molybdenum carbide-based thermal catalyst. Its morphological results are as Figure 2 shown. The morphology of the obtained molybdenum carbide-based thermal catalyst was independent nanospheres with uniform sphere sizes and a diameter of about 100 nm.

[0087] Example 2

[0088] Compared with Example 1, the differences are as follows:

[0089] (1) In this embodiment, different alcohol-water ratios were used, and 30 mL of deionized water and 70 mL of absolute ethanol were stirred and mixed evenly to form a mixed solution;

[0090] (2) The addition amount of 25% ammonia water in this embodiment was 3 mL;

[0091] The remaining steps and dosages are the same as those in Example 1, and a molybdenum carbide-based thermal catalyst is obtained.

[0092] The SEM image of the molybdenum carbide-based thermal catalyst obtained in this example is the same as that of Figure 2 and is not shown again here.

[0093] Example 3

[0094] Compared with Example 1, the difference is that:

[0095] In this example, different types of tetraethyl orthosilicates are used, and 1.5 mL of methyl orthosilicate and 2.0 mL of ethyl orthosilicate are added dropwise into the above-mentioned mixed solution.

[0096] The remaining steps and dosages are the same as those in Example 1, and a molybdenum carbide-based thermal catalyst is obtained.

[0097] The SEM image of the molybdenum carbide-based thermal catalyst obtained in this example is the same as that of Figure 2 and is not shown again here.

[0098] Example 4

[0099] Compared with Example 1, the difference is that:

[0100] In this example, the molybdate solution used is a sodium molybdate solution formed by dissolving 3 g of sodium molybdate (the molar amount of sodium molybdate is 14.5 mmol) in 20 mL of deionized water.

[0101] The remaining steps and dosages are the same as those in Example 1, and a molybdenum carbide-based thermal catalyst is obtained.

[0102] The SEM image of the molybdenum carbide-based thermal catalyst obtained in this example is the same as that of Figure 2 and is not shown again here.

[0103] Example 5

[0104] Compared with Example 1, the difference is that:

[0105] In this example, the tetraethyl orthosilicate used is ethyl orthosilicate, and 3.5 mL of ethyl orthosilicate (the molar concentration of ethyl orthosilicate is 0.15 mol / L) is added dropwise into the above-mentioned mixed solution.

[0106] The remaining steps and dosages are the same as those in Example 1, and a molybdenum carbide-based thermal catalyst is obtained.

[0107] The SEM image of the molybdenum carbide-based thermal catalyst obtained in this example is the same as that of Figure 2 and is not shown again here.

[0108] Catalyst activity test

[0109] Take 0.2 g of the molybdenum carbide-based thermal catalyst obtained in Examples 1-5, mix it with 0.4 g of quartz sand, and load it into the isothermal zone of a fixed-bed reactor. The reaction raw materials are a mixed gas of CO2 and H2, and the volume ratio of CO2 to H2 is 1:1. Pass CO2 / H2 through the catalyst bed at a certain flow rate, and the space velocity of the flow rate is set to 7500 mL / g·h. The reaction temperatures are set to 400 °C, 500 °C, and 600 °C respectively to start the reaction. The reaction pressure is set to atmospheric pressure, and the products directly enter a gas chromatograph for detection and analysis. Among them, the contents of the raw material gases H2 and CO2 and the 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.

[0110] The results in Table 1 show that for the molybdenum carbide-based thermal catalyst obtained in Example 1, the selectivity of CO reaches over 99% at different reaction temperatures; the conversion rate of CO2 reaches over 12%. For the molybdenum carbide-based thermal catalyst obtained in Example 2, the selectivity of CO reaches over 96% at different reaction temperatures; the conversion rate of CO2 reaches over 5.84%. For the molybdenum carbide-based thermal catalyst obtained in Example 3, the selectivity of CO reaches over 99% at different reaction temperatures; the conversion rate of CO2 reaches over 11%. For the molybdenum carbide-based thermal catalyst obtained in Example 4, the selectivity of CO reaches over 99% at different reaction temperatures; the conversion rate of CO2 reaches over 3.78%. For the molybdenum carbide-based thermal catalyst obtained in Example 5, the selectivity of CO reaches over 99% at different reaction temperatures; the conversion rate of CO2 reaches over 10%.

[0111] The molybdenum carbide-based thermal catalyst obtained by the preparation method of this application can exhibit excellent CO2 conversion efficiency and CO selectivity at an appropriate space velocity. Side reactions are effectively inhibited, and the product purity is extremely high, demonstrating its potential for large-scale industrial applications.

[0112] Evaluation conditions and results of the examples in Table 1

[0113]

[0114]

[0115] In the description of this specification, the descriptions referring to terms such as "one embodiment", "some embodiments", "examples", "specific examples", 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 this application. In this specification, the schematic descriptions 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.

[0116] For method embodiments, for the sake of simple description, they are all expressed as a series of combinations of actions. However, those skilled in the art should know that this application is not limited by the described order of actions, because according to this application, certain steps can be carried out in other orders 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 this application.

[0117] The above has introduced in detail a molybdenum carbide-based thermal catalyst, its preparation method and its application provided by this application. Specific examples are used herein to elaborate on the principle and implementation manner of this application. The description of the above embodiments is only used to help understand the method and its core idea of this application; at the same time, for those of ordinary skill in the art, according to the idea of this application, 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 this application.

Claims

1. A preparation method of a molybdenum carbide-based thermal catalyst, characterized in that, The preparation method specifically includes the following steps: S1. Stir and mix orthosilicate esters, deionized water, and ethanol to form a first mixed system, and then add an appropriate amount of ammonia water to cause the orthosilicate esters to hydrolyze in an alkaline environment; S2. Add an appropriate amount of molybdate solution to the first mixed system and stir to form a second mixed system; S3. Add an appropriate amount of hydrochloric acid dopamine solution to the second mixed system, stir and react, and collect to obtain a catalyst precursor; S4. Place the catalyst precursor in an inert atmosphere and perform high-temperature carbonization treatment to obtain the molybdenum carbide-based thermal catalyst; Wherein, in the first mixed system, the molar concentration of orthosilicate esters is 0.01 - 0.3 mol / L, and the volume ratio of deionized water to ethanol is 1:1 - 1:3; In the hydrochloric acid dopamine solution and the molybdate solution, the molar ratio of molybdate to hydrochloric acid dopamine is 1:1 - 8:

1.

2. The preparation method according to claim 1, characterized in that, The orthosilicate esters are one or more of methyl orthosilicate, ethyl orthosilicate, and propyl orthosilicate.

3. The preparation method according to claim 1, wherein The added amount of ammonia water keeps the pH of the first mixed system at 12 - 14.

4. The preparation method according to claim 1, characterized in that, The molybdate solution is selected from ammonium molybdate solution or sodium molybdate solution; The molar amount of molybdenum element in the molybdate solution is 5 - 20 mmol.

5. The preparation method according to claim 1, wherein In the orthosilicate esters and the molybdate solution, the molar ratio of silicon to molybdenum is 1:1 - 5:

1.

6. The preparation method according to claim 1, wherein, Steps S1 - S3 are all carried out at 20°C - 60°C.

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-based thermal catalyst, characterized in that, The molybdenum carbide-based thermal catalyst is obtained according to the preparation method described in any one of claims 1 - 7.

9. The molybdenum carbide-based thermal catalyst according to claim 8, wherein, The molybdenum carbide-based thermal catalyst is spherical nanoparticles with a particle size of 70 - 110 nm; the spherical nanoparticles are composed of SiO2, carbon, and molybdenum carbide. Among them, the mass ratio of SiO2 to molybdenum carbide in the molybdenum carbide-based thermal catalyst is 2:1 - 6:1, and the particle size of molybdenum carbide is 1 nm - 5 nm.

10. Use of the molybdenum carbide-based thermal catalyst according to any one of claims 8-9, characterized in that, Using CO2 and H2 with a volume ratio of 1:1 - 1:3 as reaction raw materials, at 300°C - 600°C, the molybdenum carbide-based thermal catalyst catalyzes the reverse water-gas shift reaction of CO2 hydrogenation; Wherein, the reaction space velocity is 6000 mL / g·h - 8000 mL / g·h, the conversion efficiency of CO2 is greater than 3.78%, and the selectivity of CO is greater than 96%.

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