A thermal catalyst for CO hydrogenation to CO, its preparation method, and its application in the two-step CO2 to methanol process.

Abstract

This invention belongs to the field of carbon dioxide conversion application and catalyst fine synthesis technology, specifically relating to a thermal catalyst for CO2 hydrogenation to CO, its preparation method, and its application in the two-step CO2 to methanol process. The thermal catalyst comprises an S- and N-doped reduced graphene oxide support and MoS2 and Fe2O3 supported on the S- and N-doped reduced graphene oxide support. x N; Mo and Fe in the MoS2 x The molar ratio of Fe in N is (0.5–3.0):1; the Fe x N includes FeN and / or Fe3N2. The key to this invention lies in the design and synthesis of a MoS2 / Fe... x The N / S,N-rGO thermal catalyst, with its Mo and Fe ratio adjusted, effectively leverages the synergistic effect of Mo and Fe. Combined with the S,N-rGO support, it lowers the CO2 activation energy, increases CO2 conversion, and promotes CO formation. This enables highly efficient catalytic hydrogenation of CO2 to produce high-concentration CO with high CO selectivity. When combined with the CO-to-methanol process, it significantly improves the methanol yield of the two-step CO2-to-methanol process.

Description

Technical Field

[0001] This invention belongs to the field of carbon dioxide conversion application and catalyst fine synthesis technology, specifically relating to a thermal catalyst for CO2 hydrogenation to CO, its preparation method, and its application in the two-step CO2 to methanol production process. Background Technology

[0002] CO2 resource utilization has become a key pathway to solving the dual challenges of emission reduction and energy transition. Among these technologies, CO2 hydrogenation thermocatalytic methanol production stands out due to its potential for "carbon negativity"—synthesizing methanol through green hydrogen energy and industrially captured CO2 under the action of a catalyst. This approach can both scale up the consumption of renewable energy power and produce high-value-added chemical feedstocks and clean fuels. Current research focuses primarily on enhancing catalyst activity and optimizing reaction mechanisms, providing a new fulcrum for global carbon neutrality and technological competition.

[0003] Thermocatalytic reduction is a relatively mature method. There are two main pathways for the hydrogenation of CO2 to methanol: one is a one-step direct synthesis of methanol from CO2 hydrogenation, and the other is a two-step synthesis of methanol from the product gas (CO + H2O) generated by reverse water-gas reaction (RWGS), followed by condensation, dehydration, and compression. The CO2 hydrogenation to CO reaction can be carried out at atmospheric pressure with high conversion rates. The CO-to-methanol hydrogenation technology after water removal is mature; studies have shown that the yield of methanol from CO2 via the two-step method is three times that of the one-step method. Currently, catalysts for CO2 hydrogenation to CO production mostly employ Cu-based catalysts and noble metal catalysts, but they still face core challenges such as activity-selectivity balance, anti-sintering, methane side reactions, cost, and compatibility with green hydrogen. Noble metal catalysts (such as Pt, Ru, and Rh) typically have high hydrogen dissociation capabilities, but their high price limits their large-scale application. Current research mainly focuses on reducing dependence on noble metals by precisely controlling metal-support interactions to overcome the bottlenecks in catalyst industrialization.

[0004] Researchers at the University of Illinois at Chicago (UIC) have identified molybdenum disulfide as a promising and cost-effective alternative to noble metal catalysts for the electrochemical reduction of carbon dioxide, but their thermocatalytic performance in reducing carbon dioxide to carbon monoxide has not been investigated. Sameer et al. at the Petroleum Research Institute of India (CSIR) investigated the performance of molybdenum disulfide-based sulfur incorporated into mesoporous nitrogen-doped carbon as a noble metal-free catalyst for the conversion of CO2 to CO using a two-step sequential synthesis method with molybdenum-doped SBA-15 as a template. However, this method involves multiple steps including template synthesis, impregnation, carbonization, and etching, which is not conducive to large-scale production. Furthermore, the embedding of MoS2 may restrict pore size, resulting in some MoS2 remaining unutilized. The redox properties and low cost of Fe make it a core component of RWGS catalysts, but issues such as carbon deposition and insufficient low-temperature activity persist. Summary of the Invention

[0005] The purpose of this invention is to overcome the shortcomings of existing catalysts in the low catalytic activity and low CO selectivity of CO2 hydrogenation to CO, which leads to low methanol yield in the two-step CO2 to methanol process. This invention provides a MoS2 / Fe... x The N / S,N-rGO thermal catalyst has high CO2 conversion efficiency and high CO selectivity. The high CO concentration gas obtained is then reacted with H2 to synthesize methanol, thereby improving the methanol yield.

[0006] In a first aspect, the present invention provides a thermal catalyst for the hydrogenation of CO2 to CO. The thermal catalyst comprises an S- and N-doped reduced graphene oxide support and MoS2 and Fe2O3 supported on the S- and N-doped reduced graphene oxide support. x N; Mo and Fe in the MoS2 x The molar ratio of Fe in N is (0.5~3.0):1; the Fe x N includes FeN and / or Fe3N2.

[0007] Secondly, the present invention provides a method for preparing a thermal catalyst for the hydrogenation of CO2 to CO. The preparation method includes the following steps: S1. Performing a first mixing treatment on graphene oxide, an iron source, and a nitrogen source; sintering the resulting iron-nitrogen-based precursor material under a nitrogen source gas atmosphere to obtain Fe... x N / N-rGO material; S2. Fe x The N / N-rGO material is mixed with a molybdenum source and a sulfur source in a second mixing process. The resulting mixture undergoes a hydrothermal reaction under inert gas protection. The reaction products are then washed with water and dried to obtain a thermal catalyst.

[0008] Thirdly, the present invention provides a thermal catalyst for the hydrogenation of CO2 to CO prepared by the above method.

[0009] Fourthly, the present invention provides the application of the above-mentioned thermal catalyst for CO2 hydrogenation to CO in the CO2 hydrogenation to CO process and / or the CO2 two-step methanol production process.

[0010] Fifthly, the present invention provides a two-step method for producing methanol from CO2. The method includes the following steps: S1. Using the above-mentioned MoS2 / Fe... xThe N / S,N-rGO catalyst catalyzes the first reaction of CO2 and H2 at a first temperature to obtain a first mixed gas containing CO. After cooling the first mixed gas and separating the liquid water, a first exhaust gas containing CO is obtained. S2'. The catalyst is used to catalyze the CO and H2 in the first exhaust gas at a second temperature to obtain a second mixed gas containing methanol. After cooling the second mixed gas, liquid methanol and a second exhaust gas are obtained.

[0011] Beneficial effects: The key to this invention lies in the design and synthesis of a MoS2 / Fe... x The N / S,N-rGO thermal catalyst, with its Mo and Fe ratio precisely controlled, effectively leverages the synergistic effect of Mo and Fe. Combined with the S,N-rGO support, it lowers the CO2 activation energy, increases CO2 conversion, and promotes CO formation. This results in highly efficient catalytic CO2 hydrogenation to high-concentration CO with high CO selectivity. Furthermore, when integrated into the CO-to-methanol process, it significantly improves the methanol yield of the two-step CO2-to-methanol process. The reason for this improvement may be due to: Fe... x N includes FeN and / or Fe3N2, wherein Fe 2+ Assists in H2 dissociation, providing active H and Fe 3+ Adsorption and activation of CO2, Mo edge sites (Mo 4+ It can act as a Lewis acidic site to adsorb and activate CO2, and its high reactivity can also be attributed to the large number of bridging S2 groups. 2- And the existence of its vacancies, at the same time, Fe 3+ / Fe 2+ Redox pairs and Mo 4+ The presence of sulfur also plays a role in regulating electron density and inhibiting excessive hydrogenation (avoiding the formation of CH4), thereby improving CO selectivity. Furthermore, the sulfur-vacancy-rich MoS2 nanosheets help to lower the CO2 activation energy and improve CO2 conversion. Unlike other high specific surface area carbon supports, N,S co-doped reduced graphene oxide (N,S-rGO) effectively promotes electron transfer of the active metal components (Fe, Mo) and helps to lower the CO2 activation energy barrier by altering the electron distribution of graphene due to pyridine nitrogen and graphitic nitrogen. On the other hand, thiophene sulfur (or CSC) can form local electron-deficient regions, promoting H2 dissociation and inhibiting carbon deposition. In addition, the lone pair electrons of sulfur can stabilize the metal nanoparticles (Fe, Mo), prevent sintering, and improve catalytic stability. Attached Figure Description

[0012] Figure 1 This is a schematic diagram of the process flow for the two-step CO2 methanol production method in Example 1. Detailed Implementation

[0013] The thermal catalyst for CO2 hydrogenation to CO provided by this invention comprises an S- and N-doped reduced graphene oxide support and MoS2 and Fe supported on the S- and N-doped reduced graphene oxide support. x N, denoted as MoS2 / Fe x N / S, N-rGO. Mo and Fe in the MoS2 x The molar ratio of Fe in N is (0.5~3.0):1, such as 0.5:1, 0.8:1, 1.0:1, 1.2:1, 1.5:1, 1.8:1, 2.2:1, 2.5:1, 2.8:1, 3.0:1, or any value between them. This exhibits the advantage of synergistically optimizing the electronic and structural effects of the catalyst, regulating active sites and structural stability, and optimizing the kinetic matching of each step in the entire reaction chain of CO2 adsorption-activation-H2 dissociation-intermediate conversion-product desorption, thereby improving CO2 conversion and CO selectivity. The Fe... x N includes FeN and / or Fe3N2.

[0014] In this invention, the total content of Mo and Fe in the thermal catalyst is preferably 10-30 wt%, such as 10 wt%, 15 wt%, 20 wt%, 25 wt%, 30 wt%, or any value between them. This provides advantages such as balancing the density and dispersion of active sites on the support, enhancing electron transfer efficiency and interfacial synergistic effects, and improving mass transfer. This is because the bimetallic particles at this loading are highly dispersed on the S,N-rGO surface, forming single-atom or sub-nano clusters, maximizing the exposure of active sites, thus contributing to excellent catalytic performance. If the metal loading is increased, the metal particles easily agglomerate to form micron-sized crystals, the active sites are easily buried, and the conductive network of the support is covered by the metal, inhibiting electron transfer.

[0015] The method for preparing a thermal catalyst for CO2 hydrogenation to CO provided by this invention includes the following steps:

[0016] S1. Graphene oxide, an iron source, and a nitrogen source are subjected to a first mixing treatment. The resulting iron-nitrogen-based precursor material is then sintered in a nitrogen source gas atmosphere to obtain Fe. x N / N-rGO materials;

[0017] S2. Fe x N / N-rGO material was subjected to a second mixing treatment with a molybdenum source and a sulfur source. The resulting mixture underwent a hydrothermal reaction under inert gas protection. The reaction product was then washed with water and dried to obtain MoS2 / Fe. x N / S, N-rGO thermal catalyst.

[0018] In the above preparation process, iron ions and nitrogen ions from the iron source are first loaded onto graphene oxide. Then, during sintering, urea pyrolysis generates active nitrogen species that are doped into the graphene framework. Nitrogen source gas reduces benzene oxide and promotes Fe... x N generation: During the hydrothermal reaction, the sulfur source reacts with the molybdenum source to generate MoS2, and the sulfur atoms in the sulfur source can also be doped into N-rGO to form S,N-rGO.

[0019] In this invention, in step S1, the iron source can be any compound capable of providing an iron-nitrogen-based precursor material obtained by mixing Fe with graphene oxide and a nitrogen source. The iron source is preferably at least one of ferric nitrate, ferric chloride, ferric sulfate, and ferric acetate.

[0020] In this invention, in step S1, the nitrogen source can be any compound capable of providing nitrogen to be mixed with graphene oxide and an iron source to obtain an iron-nitrogen-based precursor material. The nitrogen source is preferably at least one of urea, ethylenediamine, hydrazine hydrate, and melamine.

[0021] In this invention, in step S1, the nitrogen source gas is a type of nitrogen-containing gas with reducing properties, which can reduce graphene oxide to Fe during the sintering process. x The formation of N and / or nitrogen doping of graphene oxide provides a nitrogen source, preferably from at least one of ammonia, hydrazine (N2H4) vapor, and N2-H2 mixture.

[0022] In this invention, in step S1, the first mixing treatment can be solid-phase mixing or liquid-phase mixing, preferably liquid-phase mixing. The liquid-phase mixing treatment can be mechanical stirring or ultrasonic mixing. The first mixing treatment preferably includes: mixing graphene oxide, an iron source, a nitrogen source, and water, followed by ultrasonic treatment. The preferred ratio of graphene oxide to nitrogen source is 1g:(0.005~0.05)mol, such as 1g:0.005mol, 1g:0.008mol, 1g:0.01mol, 1g:0.02mol, 1g:0.03mol, 1g:0.04mol, 1g:0.05mol, or any value between them. The preferred ultrasonic treatment time is 5~10h, such as 5h, 6h, 7h, 8h, 9h, 10h, or any value between them.

[0023] In this invention, the sintering conditions in step S1 preferably include: a temperature of 400~700℃, such as 400℃, 500℃, 600℃, 700℃ or any value between them; and a time of 1~3h, such as 1h, 1.5h, 2h, 2.5h, 3h or any value between them. Sintering temperatures below 400℃ tend to produce cubic pure FeN, while high temperatures (above 700℃) tend to produce hexagonal Fe3N nanosheets and may lead to phase deterioration. Therefore, controlling the sintering temperature at 400~700℃ is more conducive to forming a mixed phase of FeN and Fe3N2, enhancing the synergistic effect of CO2 adsorption and activation on FeN, H2 dissociation on Fe3N2, and electron transfer from Fe3N to FeN, thereby improving the conversion rate and selectivity of CO2 reduction to CO.

[0024] In this invention, in step S2, the molybdenum source can be any compound capable of reacting Mo with a sulfur source to generate MoS2. The molybdenum source is preferably at least one of ammonium molybdate, sodium molybdate, potassium molybdate, molybdenum acetylacetonate, ammonium tetrathiomolybdate, and ammonium phosphomolybdate.

[0025] In this invention, in step S2, the sulfur source can be any compound capable of providing S to react with a molybdenum source to generate MoS2 and to provide S for sulfur doping of N-rGO. The sulfur source is preferably at least one of carbon disulfide, thiourea, sodium thiocyanate, potassium thiocyanate, sodium sulfide, potassium sulfide, ammonium tetrathiomolybdate, and hydrogen sulfide.

[0026] In this invention, in step S2, the Fe... x The mixing order of N / N-rGO material with the molybdenum source and sulfur source is not specifically limited. The second mixing process preferably includes: mixing Fe... x The N / N-rGO material is dispersed in water, a molybdenum source is added to form a homogeneous solution, and then a sulfur source is added to form a homogeneous mixture. The molar ratio of the molybdenum source to the sulfur source is preferably 1:(30~200), such as 1:30, 1:40, 1:50, 1:60, 1:80, 1:100, 1:120, 1:150, 1:180, 1:200 or any value between them.

[0027] In this invention, the hydrothermal reaction conditions in step S2 preferably include: a temperature of 300~500℃, such as 300℃, 350℃, 400℃, 450℃, 500℃ or any value between them; and a time of 2~4h, such as 2h, 2.5h, 3h, 3.5h, 4h or any value between them.

[0028] In this invention, step S2, the hydrothermal reaction process specifically includes: reacting Fe... xThe mixture obtained by second mixing treatment of N / N-rGO material with molybdenum source and sulfur source is sealed in an autoclave and subjected to hydrothermal reaction at 300~500℃ for 2~4 hours under the protection of inert gas. The inert gas is preferably at least one of nitrogen, argon, neon and xenon.

[0029] In this invention, in step S2, the hydrothermal reaction product is preferably treated with an alkaline solution before water washing. This alkaline solution treatment not only removes unreacted raw materials, intermediates, and byproducts, exposing more active MoS2 edges, but also partially passivates sulfur vacancies at the edges of rGO and MoS2 to suppress side reactions, promotes the exfoliation of the layered structures of rGO and MoS2, further increases the specific surface area, exposes more catalytic active sites, and thus improves catalytic activity.

[0030] In this invention, in step S2, the concentration of the alkaline substance in the alkaline solution is preferably 4~8M (mol / L), such as 4M, 5M, 6M, 7M, 8M or any value between them. The alkaline substance is preferably potassium hydroxide and / or sodium hydroxide.

[0031] In this invention, the molar ratio of Fe in the iron source to Mo in the molybdenum source is preferably 1:(0.5~3.0), such as 1:0.5, 1:0.8, 1:1.0, 1:1.2, 1:1.5, 1:1.8, 1:2.0, 1:2.2, 1:2.5, 1:2.8, 1:3.0 or any value between them.

[0032] In this invention, the amounts of the iron source and the molybdenum source are preferably such that the MoS2 / Fe ratio is [missing value]. x The total Fe and Mo content in N / S, N-rGO thermal catalysts is 10~30wt%, such as 10wt%, 15wt%, 20wt%, 25wt%, 30wt%, or any value between them.

[0033] The two-step method for producing methanol from CO2 provided by this invention includes the following steps:

[0034] S1`. Using the above MoS2 / Fe x The N / S,N-rGO thermal catalyst catalyzes the first reaction of CO2 and H2 at a first temperature to obtain a first mixed gas containing CO. After cooling the first mixed gas and separating the liquid water, a first exhaust gas containing CO is obtained.

[0035] S2'. A catalyst is used to catalyze the CO and H2 in the first exhaust gas to undergo a second reaction at a second temperature, obtaining a second mixed gas containing methanol. The second mixed gas is then cooled to obtain liquid methanol and the second exhaust gas. The catalyst mentioned in step S2' can be any catalyst capable of catalyzing the reaction of CO and H2 to synthesize methanol. This invention does not limit its specific type or source; it can be a commercially available catalyst or a catalyst prepared according to existing methods. This invention preferably uses a commercially available CuO / ZnO / Al2O3 catalyst.

[0036] In this invention, in step S1`, the first temperature is preferably 400~700℃, such as 400℃, 500℃, 600℃, 700℃ or any value between them. The molar ratio of CO2 to H2 is preferably (0.5~1):3, such as 0.5:3, 0.6:3, 0.7:3, 0.8:3, 0.9:3, 1:3 or any value between them.

[0037] In this invention, step S1' preferably includes, before the first reaction of CO2 and H2, heat exchange between CO2 and H2 and a first mixed gas and a second mixed gas. Since the first and second mixed gases have higher temperatures, heat exchange with the CO2 and H2 mixture facilitates full heat recovery and utilization, improving the energy efficiency of the entire reaction system.

[0038] In this invention, in step S2`, the second reaction temperature is preferably 200~300℃, such as 200℃, 220℃, 250℃, 280℃, 300℃, or any value between them. The molar ratio of CO to H2 in the first exhaust gas is preferably 1:(2~3), such as 1:2, 1:2.2, 1:2.5, 1:2.8, 1:3, or any value between them.

[0039] Furthermore, the terms "first" and "second" are used for descriptive purposes and should not be construed as a particular limitation on the composition or content of the technical features.

[0040] The present invention will be described in detail below through specific embodiments. These embodiments are intended to explain the invention and should not be construed as limiting it. Where specific techniques or conditions are not specified in the embodiments, they are performed according to the techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments whose manufacturers are not specified are all conventional products that can be obtained commercially.

[0041] Preparation Example 1

[0042] This preparation example illustrates the preparation of a CuO / ZnO / Al2O3 catalyst, and the specific preparation process is as follows:

[0043] Dissolve 2.9 g (0.012 mol) Cu(NO3)2·3H2O, 1.1 g (0.005 mol) Zn(NO3)2·2H2O, and 0.7 g (0.002 mol) Al(NO3)3·9H2O in 20 mL of deionized water to obtain a mixed metal salt solution.

[0044] Add 200 mL of deionized water to a 500 mL three-necked flask, stir and heat to 65 °C, while simultaneously adding the mixed metal salt solution obtained in the above steps and 15 mL of 1.5 M Na2CO3 solution (precipitant). Control the pH of the reaction system at 7.0 using ammonia.

[0045] After the addition is complete, continue stirring for 1 hour for aging, then filter and separate, wash repeatedly with deionized water, and then place in an oven to dry at 120°C for 6 hours.

[0046] After drying, the material is ground and then calcined in a muffle furnace at 400°C for 4 hours to obtain the CuO / ZnO / Al2O3 catalyst.

[0047] Preparation Example 2

[0048] This preparation example illustrates the preparation of a Ru / Al2O3 catalyst, and the specific preparation process is as follows:

[0049] Dissolve 0.27g RuCl3 hydrate in 20mL of deionized water and stir until completely dissolved (the solution turns orange-red) to obtain solution 1; add 1.9g of pretreated Al2O3 to 20mL of deionized water and sonicate for 30min to form a uniform suspension to obtain solution 2.

[0050] Slowly add solution 1 dropwise to solution 2 while mechanically stirring (400 rpm), and adjust the pH to 8.0~8.5 with 0.1M NaOH solution (keep it constant). Control the temperature at 60℃ and react for 2 hours.

[0051] After the reaction was completed, the mixture was stirred and aged for another 1 hour, then cooled to room temperature, filtered, washed, and dried to obtain the precursor powder.

[0052] The precursor was placed in a muffle furnace and heated to 350°C at a rate of 10°C / min. It was then calcined in air for 4 hours and naturally cooled to room temperature to obtain a black Ru / Al2O3 catalyst.

[0053] Example 1

[0054] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0055] (1) MoS2 / Fe x Preparation of N / S, N-rGO catalysts:

[0056] S1. Take 0.6 g of graphene oxide and disperse it in 10 mL of water. Add 0.81 g (0.002 mol) of ferric nitrate (Fe(NO3)3•9H2O) and 1.20 g of urea (CH4N2O, 0.02 mol) to the dispersion and continue sonication for 8 h. Centrifuge at 6000 rpm, wash the precipitate with water and ethanol, and vacuum dry at 60 °C for 6 h to obtain the iron-nitrogen-based precursor material. Place the iron-nitrogen-based precursor material in a crucible and place it in a tube furnace. Heat to 600 °C and calcine for 2 h under a flowing NH3 atmosphere. Finally, cool the system to room temperature under a flowing NH3 gas to obtain Fe. x N / N-rGO.

[0057] S2. The prepared Fe x N / N-rGO was redispersed in water, and 0.35g of ammonium molybdate ((NH4)6Mo7O) was added. 24 After forming a homogeneous solution by adding 4H₂O and 0.002 mol Mo, 8 mL of 0.0963 mol CS₂ was added. The mixture was then sealed in a stainless steel autoclave and reacted at 400 °C for 3 h under Ar protection. After the reaction was completed, the solid and liquid phases were separated. The resulting product was stirred with 5 mL of 6M KOH solution at 60 °C for 3 h, then washed several times with pure water and anhydrous ethanol, and finally dried at 80 °C to obtain MoS₂ / Fe. x The N / N,S-rGO catalyst, designated MFC-1, has a total Mo and Fe content of approximately 28 wt%.

[0058] (2) Two-step CO2 method for methanol production: The process flow of this method is as follows Figure 1 As shown.

[0059] S1. The CO2 feed gas is compressed to 30 bar in multiple stages by a compressor unit (the cooler is cooled during the multi-stage compression). The compressed CO2 and H2 are adiabatically and isobarically mixed in mixer 1, and the molar ratio of CO2 to H2 in the resulting mixture is 1:3. The mixture is initially heated in a heat exchanger by a second mixed gas containing methanol from catalytic reactor 2, and then reheated by a first mixed gas containing CO produced by catalytic reactor 1. The mixed feed gas after the two heatings enters a heater and is heated to the reaction temperature of 500°C, and then enters catalytic reactor 1. The MoS2 / Fe prepared in step (1) is then heated. x The reaction proceeded against water gas under the action of N / N,S-rGO catalyst (MFC-1, 3g, 15~20 mesh) at a space velocity of 20000 mL / g. cat / h. The first mixed gas containing CO obtained from the catalytic reactor 1 is separated into liquid water and the first exhaust gas containing CO after the heat is recovered by the heat exchanger. The refrigerant of the separation and purification unit 1 is atmospheric pressure water, and the inlet temperature is 70℃.

[0060] S2'. The first exhaust gas containing CO separated from the purification unit is compressed to 70 bar by compressor 2, and then adiabatically mixed with H2 (compressed by compressor 1 at the same pressure as CO) in mixer 2. The resulting mixture has a CO to H2 molar ratio of 1:2 and a temperature of 250°C. The mixture enters catalytic reactor 2 and undergoes a methanol synthesis reaction in the presence of a CuO / ZnO / Al2O3 catalyst (from Preparation Example 1, 3g, 15-20 mesh) at a space velocity of 20000 mL / g. cat / h. The second mixed gas containing methanol obtained from catalytic reactor 2, after heat recovery via a heat exchanger, enters separation and purification unit 2 for separation to obtain liquid methanol and a second exhaust gas (CO and H2). The refrigerant in separation and purification unit 2 is atmospheric pressure water, with an inlet temperature of 70°C. The second exhaust gas is supplied to the gas turbine for power generation or directly burned to provide heat to the system.

[0061] Samples were taken from mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas was detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield were calculated according to the method of the test example.

[0062] Example 2

[0063] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0064] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that the amount of graphene oxide used in step S1 was 2.5 g, and the other conditions were the same as in step (1) of Example 1. Thus, MoS2 / Fe2O3 catalyst was prepared. x The N / S, N-rGO catalyst, designated MFC-2, has a total Mo and Fe content of approximately 10 wt%.

[0065] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst MFC-2 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0066] Example 3

[0067] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0068] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that in step S2, ammonium molybdate ((NH4)6Mo7O) was used. 24 The amount of ·4H2O was 0.17 g (Mo-0.001 mol), and all other conditions were the same as in step (1) of Example 1, thereby preparing MoS2 / Fe x The N / S,N-rGO catalyst, designated MFC-3, has a total Mo and Fe content of approximately 20 wt%.

[0069] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst MFC-3 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0070] Example 4

[0071] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0072] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that the amount of graphene oxide used in step S1 was 1.4 g, and the amount of ammonium molybdate ((NH4)6Mo7O) in step S2 was different. 24The amount of ·4H2O was 1.6 g (Mo-0.006 mol), and all other conditions were the same as in step (1) of Example 1, thereby preparing MoS2 / Fe x The N / S,N-rGO catalyst, designated MFC-4, has a total Mo and Fe content of approximately 28 wt%.

[0073] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst MFC-4 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0074] Example 5

[0075] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0076] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: MoS2 / Fe was prepared according to step (1) in Example 1. x The N / S,N-rGO catalyst, designated MFC-1, has a total Mo and Fe content of approximately 28 wt%.

[0077] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1, the mixed raw material gas is heated to the reaction temperature of 600°C in the heater, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0078] Example 6

[0079] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0080] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: MoS2 / Fe was prepared according to step (1) in Example 1. xThe N / S,N-rGO catalyst, designated MFC-1, has a total Mo and Fe content of approximately 28 wt%.

[0081] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1, the mixed raw material gas is heated to the reaction temperature of 700°C in the heater, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0082] Example 7

[0083] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0084] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that in step S1, the iron-nitrogen-based precursor material was heated to 400°C and calcined for 2 hours in a flowing NH3 atmosphere. All other conditions were the same as in step (1) of Example 1, thus obtaining MoS2 / Fe x The N / S,N-rGO catalyst, designated MFC-5, has a total Mo and Fe content of approximately 28 wt%.

[0085] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst MFC-5 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0086] Example 8

[0087] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0088] (1) MoS2 / Fe xPreparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that in step S1, the iron-nitrogen-based precursor material was heated to 700°C and calcined for 2 hours in a flowing NH3 atmosphere. All other conditions were the same as in step (1) of Example 1, thus obtaining MoS2 / Fe x The N / S, N-rGO catalyst, designated MFC-6, has a total Mo and Fe content of approximately 28 wt%.

[0089] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst MFC-5 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0090] Example 9

[0091] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0092] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that in step S1, the iron-nitrogen-based precursor material was heated to 250°C and calcined for 2 hours in a flowing NH3 atmosphere. All other conditions were the same as in step (1) of Example 1, thus obtaining MoS2 / Fe x The N / S, N-rGO catalyst, designated MFC-7, has a total Mo and Fe content of approximately 28 wt%.

[0093] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst MFC-7 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0094] Example 10

[0095] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0096] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that in step S1, the iron-nitrogen-based precursor material was heated to 850°C and calcined for 2 hours in a flowing NH3 atmosphere. All other conditions were the same as in step (1) of Example 1, thus obtaining MoS2 / Fe x The N / S,N-rGO catalyst, designated MFC-8, has a total Mo and Fe content of approximately 28 wt%.

[0097] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst MFC-8 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0098] Example 11

[0099] This embodiment is used to illustrate a MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0100] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that the amount of graphene oxide used in step S1 was 0.3 g, and the other conditions were the same as in step (1) of Example 1. Thus, MoS2 / Fe2O3 catalyst was prepared. x The N / S,N-rGO catalyst, designated MFC-9, has a total Mo and Fe content of approximately 40 wt%.

[0101] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst MFC-9 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0102] Example 12

[0103] This embodiment is used to illustrate a MoS2 / Fe xThe preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0104] (1) MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that in step S2, the reaction product was not treated with 5 mL of 6 M KOH solution, but was washed several times with pure water and anhydrous ethanol and then dried. All other conditions were the same as in step (1) of Example 1. Thus, MoS2 / Fe2O3 catalyst was prepared. x The N / S,N-rGO catalyst, designated MFC-10, has a total Mo and Fe content of approximately 28 wt%.

[0105] (2) Two-step CO2 methanol production method: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst MFC-10 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0106] Comparative Example 1

[0107] This comparative example is used to illustrate a reference MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0108] (1) Reference MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that in step S2, ammonium molybdate ((NH4)6Mo7O) was used. 24 The amount of ·4H2O was 0.07 g (Mo-0.0004 mol), and all other conditions were the same as in step (1) of Example 1, thereby preparing the reference MoS2 / Fe. x The N / S, N-rGO catalyst, designated D-MFC-1, has a total Mo and Fe content of approximately 18 wt%.

[0109] (2) Two-step method for producing methanol from CO2: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst D-MFC-1 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0110] Comparative Example 2

[0111] This comparative example is used to illustrate a reference MoS2 / Fe x The preparation process of N / S,N-rGO catalyst and a two-step CO2 method for methanol production are as follows:

[0112] (1) Reference MoS2 / Fe x Preparation of N / S,N-rGO catalyst: The catalyst was prepared according to step (1) in Example 1, except that the amount of graphene oxide used in step S1 was 2.1 g and the amount of ammonium molybdate ((NH4)6Mo7O) in step S2 was different. 24 The amount of ·4H2O was 1.75 g (Mo-0.01 mol), and all other conditions were the same as in step (1) of Example 1, thereby preparing the reference MoS2 / Fe. x The N / S, N-rGO catalyst, designated D-MFC-2, has a total Mo and Fe content of approximately 28 wt%.

[0113] (2) Two-step CO2 to methanol production method: The method is carried out according to step (2) in Example 1, except that in step S1', catalyst D-MFC-2 is used instead of catalyst MFC-1, and the other conditions are the same as in step (2) in Example 1. Samples are taken after mixer 1, separation and purification unit 1 and separation and purification unit 2 respectively, and the concentration of each component in the gas is detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield are calculated according to the method of the test example.

[0114] Comparative Example 3

[0115] This comparative example illustrates a two-step method for producing methanol from CO2, the specific process of which is as follows:

[0116] The procedure was carried out according to step (2) of Example 1, except that in step S1', the catalyst Ru / Al2O3 obtained in Preparation Example 2 was used instead of catalyst MFC-1, and all other conditions were the same as in step (2) of Example 1. Samples were taken after mixer 1, separation and purification unit 1 and separation and purification unit 2, and the concentration of each component in the gas was detected by gas chromatography. The CO2 conversion rate, CO selectivity and methanol yield were calculated according to the method of the test example.

[0117] Comparative Example 4

[0118] This comparative example illustrates a two-step method for producing methanol from CO2, the specific process of which is as follows:

[0119] The CO2 feed gas is compressed to 30 bar in multiple stages by a compressor unit (cooling is performed during the multi-stage compression). The compressed CO2 and H2 are adiabatically and isobarically mixed in mixer 1, resulting in a CO2 to H2 molar ratio of 1:3. The mixed feed gas is then heated to the reaction temperature of 250°C in a heater and directly enters catalytic reaction 2. The reaction proceeds to synthesize methanol from CO2 under the action of a CuO / ZnO / Al2O3 catalyst (from preparation example 1, 3g, 15-20 mesh) at a space velocity of 20000 mL / g. cat / h. The second mixed gas containing methanol obtained from catalytic reaction 2 is separated into liquid methanol and a second exhaust gas (CO and H2) after heat recovery by a heat exchanger. The refrigerant of the separation and purification unit 2 is atmospheric pressure water, and the inlet temperature is 70℃.

[0120] Test case

[0121] (1) The CO2 conversion rate (X) of each of the above embodiments and comparative examples was calculated according to the following method. CO2 ), methanol selectivity (S CH3OH ) and methanol yield (X CH3OH The results are shown in Table 1.

[0122] Formula (1)

[0123] In formula (1), A CO2 in and A CO2 out These are the peak areas of CO2 detected by a gas chromatograph, representing the raw gas (molar ratio CO2:H2=1:3) before catalytic reaction 1 and the mixed gas obtained from separation and purification unit 1 after catalytic reaction 1.

[0124] Formula (2)

[0125] In formula (2), n COn is the number of carbon moles of CO in the mixture obtained from separation and purification unit 1 after catalytic reaction 1. total It is the total number of carbon moles of all products in the mixed gas obtained from the separation and purification unit 1 after catalytic reaction 1.

[0126] Formula (3)

[0127] In formula (3), n CH3OH n represents the number of moles of methanol in the mixture obtained from the separation and purification unit 2 after catalytic reaction 2. CO2 This represents the number of moles of CO2 in the feed gas before catalytic reaction 1.

[0128] (2) Catalytic activity stability test: The catalytic reaction time of each of the above examples and comparative examples was extended to 50h, 100h, and 300h, and the CO2 conversion rate (X) was calculated at this time. CO2 ) and methanol selectivity (S CH3OH The results are shown in Table 1.

[0129] Table 1

[0130]

[0131]

[0132] As shown in Table 1, compared with Comparative Examples 1-4, the MoS2 / Fe provided in Examples 1-12 of this invention... x N / S,N-rGO catalysts exhibit higher CO2 conversion and CO selectivity, and also provide better methanol yield in the two-step methanol synthesis process.

[0133] Although embodiments of the present invention have been shown and described above, it is understood that the above embodiments are exemplary and should not be construed as limiting the present invention. Those skilled in the art can make changes, modifications, substitutions and variations to the above embodiments within the scope of the present invention without departing from the principles and spirit of the present invention.

Claims

1. A thermal catalyst for the hydrogenation of CO2 to CO, characterized in that, The thermal catalyst comprises an S- and N-doped reduced graphene oxide support and MoS2 and Fe2O3 supported on the S- and N-doped reduced graphene oxide support. x N; Mo and Fe in the MoS2 x The molar ratio of Fe in N is (0.5~3.0):1; the Fe x N includes FeN and Fe3N2; the total content of Mo and Fe in the thermal catalyst is 10~30wt%; the preparation method of the thermal catalyst includes the following steps: S1. Graphene oxide, an iron source, and a nitrogen source are subjected to a first mixing treatment. The resulting iron-nitrogen-based precursor material is then sintered in a nitrogen source gas atmosphere, wherein the nitrogen source gas is a reducing nitrogen-containing gas, to obtain Fe. x N / N-rGO materials; S2. Fe x The N / N-rGO material is mixed with a molybdenum source and a sulfur source in a second mixing process. The resulting mixture is subjected to a hydrothermal reaction under inert gas protection. The reaction product is then washed with water and dried to obtain a thermal catalyst. The sintering temperature is 400~700℃; the hydrothermal reaction product is further treated with an alkaline solution before being washed with water.

2. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 1, characterized in that, The preparation method includes the following steps: S1. Graphene oxide, an iron source, and a nitrogen source are subjected to a first mixing treatment. The resulting iron-nitrogen-based precursor material is then sintered in a nitrogen source gas atmosphere, wherein the nitrogen source gas is a reducing nitrogen-containing gas, to obtain Fe. x N / N-rGO materials; S2. Fe x The N / N-rGO material is mixed with a molybdenum source and a sulfur source in a second mixing process. The resulting mixture undergoes a hydrothermal reaction under inert gas protection. The reaction products are then washed with water and dried to obtain a thermal catalyst.

3. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 2, characterized in that, In step S1, the iron source is selected from at least one of ferric nitrate, ferric chloride, ferric sulfate, and ferric acetate; The nitrogen source is selected from at least one of urea, ethylenediamine, hydrazine hydrate, and melamine; The nitrogen source gas is selected from at least one of ammonia, hydrazine vapor, and N2-H2 mixture.

4. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 2, characterized in that, In step S1, the first mixing process includes: mixing graphene oxide, iron source, nitrogen source and water and then subjecting the mixture to ultrasonic treatment; the ultrasonic treatment time is 5~10h.

5. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 2, characterized in that, The ratio of graphene oxide to nitrogen source is 1 g:(0.005~0.05) mol.

6. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 2, characterized in that, The sintering process takes 1 to 3 hours.

7. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 2, characterized in that, In step S2, the molybdenum source is selected from at least one of ammonium molybdate, sodium molybdate, potassium molybdate, molybdenum acetylacetonate, ammonium tetrathiomolybdate, and ammonium phosphomolybdate. The sulfur source is selected from at least one of carbon disulfide, thiourea, sodium thiocyanate, potassium thiocyanate, sodium sulfide, potassium sulfide, ammonium tetrathiomolybdate, and hydrogen sulfide.

8. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 2, characterized in that, The molar ratio of Mo in the molybdenum source to S in the sulfur source is 1:(30~200).

9. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 2, characterized in that, The conditions for the hydrothermal reaction include: a temperature of 300~500℃ and a time of 2~4h.

10. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 2, characterized in that, The molar ratio of Fe in the iron source to Mo in the molybdenum source is 1:(0.5~3.0).

11. The method for preparing the thermal catalyst for CO2 hydrogenation to CO according to claim 2, characterized in that, The amount of iron source and molybdenum source used is such that the total content of Fe and Mo in the thermal catalyst is 10~30wt%.

12. The thermal catalyst for CO2 hydrogenation to CO prepared by the method according to any one of claims 2 to 11.

13. The application of the thermal catalyst according to any one of claims 1 and 12 in the process of CO2 hydrogenation to CO or the two-step process of CO2 to methanol.

14. A two-step method for producing methanol from CO2, characterized in that, The method includes the following steps: S1. Using the thermal catalyst described in any one of claims 1 and 12, CO2 and H2 are catalyzed to undergo a first reaction at a first temperature to obtain a first mixed gas containing CO. After cooling the first mixed gas and separating out liquid water, a first exhaust gas containing CO is obtained. S2'. A catalyst is used to catalyze the CO and H2 in the first exhaust gas to undergo a second reaction at a second temperature to obtain a second mixed gas containing methanol. The second mixed gas is then cooled to obtain liquid methanol and the second exhaust gas.

15. The two-step CO2 method for producing methanol according to claim 14, characterized in that, The first temperature is 400~700℃; the second reaction temperature is 200~300℃.

16. The two-step CO2 method for producing methanol according to claim 14, characterized in that, In step S1', the molar ratio of CO2 to H2 is (0.5~1):

3.

17. The two-step CO2 method for producing methanol according to claim 14, characterized in that, In step S2', the molar ratio of CO to H2 in the first exhaust gas is 1:(2~3).

18. The two-step CO2 method for producing methanol according to claim 14, characterized in that, In step S1`, before the CO2 and H2 undergo the first reaction, the process includes: exchanging heat between CO2 and H2 and the first mixed gas and the second mixed gas.

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