Nano-catalyst for preparing methane through carbon dioxide hydrogenation as well as preparation method and application of nano-catalyst

Abstract

The invention relates to the technical field of catalysts, in particular to a nano-catalyst for preparing methane through hydrogenation of carbon dioxide, the nano-catalyst is prepared from a eutectic solvent as a carrier precursor through a coprecipitation method, the nano-catalyst comprises a carrier, and NiO is loaded on the carrier; on the basis of the total mass of the nano-catalyst, the content of NiO is 5-20 wt%, and the content of the carrier is 80-95 wt%; the average particle size of the nano-catalyst is 5-10 nm; the carrier is selected from one or more of CeO2, ZrO2, MgO and Al2O3. According to the nano-catalyst, the dispersity and stability of NiO particles are effectively enhanced by using the eutectic solvent as a carrier precursor and a solvent, high-density Ni-OV interface sites are constructed in situ by using an alkali treatment method, the adsorption and activation of the catalyst on H2 and CO2 are promoted, the higher CO2 conversion rate is shown, and the catalyst has a good application prospect. The catalyst for efficiently obtaining a single product CH4 at a low temperature and with high selectivity has a higher application value.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of catalysts, in particular to a nano-catalyst for carbon dioxide hydrogenation to methane, and a preparation method and application thereof. BACKGROUND

[0002] With the development of global industrialization and technological progress, large-scale combustion of fossil fuels has led to a continuous increase in atmospheric CO2 concentration, triggering problems such as greenhouse effect and climate change. Therefore, efficient carbon dioxide capture, storage and utilization (CCSU) technology is crucial for achieving sustainable energy and environmental development. CO2 methanation reaction, also known as Sabatier reaction, has attracted widespread attention due to its contribution to CO2 recovery and optimization of energy systems. This reaction provides a practical approach to large-scale CO2 conversion using renewable hydrogen. Methane can be integrated into existing natural gas distribution pipelines as a clean energy carrier. And CO2 methanation reaction is an exothermic reaction, which is thermodynamically favorable.

[0003] However, CO2 methanation involves the reduction of fully oxidized carbon to methane, which is an eight-electron conversion, and there are significant kinetic constraints. Therefore, it is crucial to develop high-performance catalysts to achieve high methane selectivity and ideal reaction rate. Nickel (Ni) -based catalysts are widely studied for CO2 methanation reaction due to their low cost, easy availability and excellent catalytic performance. However, due to kinetic limitations, its activity is usually limited to higher temperatures. High temperature operation and the exothermic nature of the reaction promote the aggregation and sintering of Ni particles, leading to catalyst deactivation and decreased catalytic performance. Therefore, current research focuses on improving the activity of Ni catalysts at low temperatures to reduce the energy consumption of CO2 methanation reaction. The interaction between Ni and the support material has a significant impact on catalytic performance and resistance to metal sintering. A variety of Ni-based catalysts have been extensively studied in the literature, including catalysts with a-Al2O3, SiO2, TiO2, MgO and CeO2 materials as supports, and their catalytic activities have been systematically compared. Among them, Ni / CeO2 catalysts exhibit the highest activity, achieving nearly 100% methane selectivity under the same reaction conditions. The excellent catalytic performance of Ni / CeO2 can be attributed to the high dispersion of Ni, the rich oxygen vacancies on the surface of CeO2, and the enhanced surface coverage of CO2 derivatives.

[0004] The optimal reaction temperature of the Ni / CeO2 catalyst prepared by the traditional method is usually higher than 300℃. In addition, the morphology of CeO2 needs to be controlled by various techniques such as hard template method. Researchers have made unremitting efforts to optimize these methods. For example, Liu et al. successfully prepared a nickel catalyst with smaller average particle size and strong interaction with the support by decomposing the nickel precursor at low temperature using gas discharge plasma. Yao et al. used sol-gel method combined with organic materials (such as EDTA, PVP, etc.) to improve the dispersibility of metal precursors, and further optimized the catalytic performance by forming metal-organic complexes to promote the generation of smaller metal particles. However, how to achieve uniform and stable dispersion of Ni particles through rational design of Ni / CeO2 catalyst and significantly improve the CO2 conversion rate and CH4 selectivity at low temperature remains an important challenge in current research. SUMMARY

[0005] In view of the above-mentioned disadvantages of the prior art, the purpose of the present application is to provide a nano-catalyst for carbon dioxide hydrogenation to methane, as well as a preparation method and application thereof, so as to solve the problems of insufficient activity of the Ni / CeO2 catalyst at low temperature and poor stability of the catalyst due to easy agglomeration of Ni particles at high temperature in the prior art.

[0006] To achieve the above-mentioned purposes and other related purposes, the first aspect of the present application provides the use of a eutectic solvent as a carrier precursor in the preparation of a nano-catalyst for carbon dioxide hydrogenation to methane by coprecipitation method.

[0007] Preferably, the eutectic solvent is obtained by heating and mixing a hydrogen bond acceptor and a hydrogen bond donor, the hydrogen bond acceptor is an amino acid, and the hydrogen bond donor is a hydrate salt corresponding to the carrier.

[0008] Preferably, the use includes enhancing the dispersibility of the supported material on the carrier.

[0009] Preferably, the use includes reducing the reaction temperature of the nano-catalyst in carbon dioxide hydrogenation to methane.

[0010] The amino acid and the hydrate salt corresponding to the carrier are mixed and heated and stirred, the amino acid is a hydrogen bond acceptor, and the hydrate salt corresponding to the carrier is a hydrogen bond donor, to form a eutectic solvent as a carrier precursor, so that the supported material is better dispersed in the carrier precursor, so as to improve the dispersibility of the supported material on the carrier when the nano-catalyst is prepared by subsequent coprecipitation method.

[0011] The second aspect of the present application provides a nano-catalyst for carbon dioxide hydrogenation to produce methane, wherein the nano-catalyst is prepared by a coprecipitation method using a eutectic solvent as a carrier precursor, the nano-catalyst comprises a carrier, and the carrier is loaded with NiO; the content of the NiO is 5-20 wt%, and the content of the carrier is 80-95 wt% based on the total mass of the nano-catalyst; the average particle size of the nano-catalyst is 5-10 nm; and the carrier is selected from one or more of CeO2, ZrO2, MgO and Al2O3.

[0012] The content of the NiO can be 5-6.4 wt%, 6.4-8 wt%, 8-10 wt%, 10-12.7 wt%, 12.7-13 wt%, 13-15 wt%, 15-18 wt%, 18-19.1 wt% or 19.1-20 wt%.

[0013] The content of the carrier can be 80-80.9 wt%, 80.9-82 wt%, 82-85 wt%, 85-87.3 wt%, 87.3-90 wt%, 90-92 wt%, 92-93.6 wt% or 93.6-95 wt%.

[0014] The average particle size of the nano-catalyst can be 5-6 nm, 6-7 nm, 7-8 nm, 8-9 nm or 9-10 nm.

[0015] Preferably, the content of the NiO is 6.4-19.1 wt%.

[0016] Preferably, the content of the carrier is 80.9-93.6 wt%.

[0017] Preferably, the carrier is CeO2.

[0018] The third aspect of the present application discloses a preparation method of the nano-catalyst, and the preparation method comprises the following steps:

[0019] 1) mixing an amino acid with a hydrate salt corresponding to the carrier and heating and stirring to obtain a eutectic solvent, and then adding a hydrated nickel salt and heating and stirring to obtain a premix;

[0020] 2) adding a precipitant to the premix, performing solid-liquid separation and drying and calcining to obtain the nano-catalyst.

[0021] The amino acid is mixed with the hydrate salt corresponding to the carrier and heated and stirred, the amino acid is a hydrogen bond acceptor, the hydrate salt corresponding to the carrier is a hydrogen bond donor, and the eutectic solvent is formed as a carrier precursor and a solvent, so that the hydrated nickel salt is better dispersed in the eutectic solvent.

[0022] Preferably, in the step 1), the hydrated salt is selected from one or more of hydrated chloride salt, hydrated nitrate salt, hydrated sulfate salt.

[0023] More preferably, the hydrated salt corresponding to the carrier is hydrated nitrate salt. The hydrated nitrate salt is more conducive to forming hydrogen bond donors to form a eutectic solvent with amino acids as a carrier precursor and a solvent.

[0024] Preferably, in the step 1), the amino acid is selected from one or more of glycine, lysine, glutamic acid, alanine, proline.

[0025] More preferably, the amino acid is selected from one or more of glycine, lysine, glutamic acid.

[0026] Preferably, in the step 1), the molar ratio of the mixture of the amino acid and the hydrated salt corresponding to the carrier is 3:1-15. For example, the molar ratio of the mixture of the amino acid and the hydrated salt corresponding to the carrier can be 3:1-3, 3:3-6, 3:6-9, 3:9-12, 3:12-15.

[0027] Preferably, in the step 1), the heating temperature is 50-100℃. For example, the heating temperature can be 50-60℃, 60-70℃, 70-80℃, 80-90℃, 90-100℃. If the temperature is too low, the eutectic solvent cannot be formed, and if the temperature is too high, part of the components in the eutectic solvent will be decomposed.

[0028] Preferably, in the step 1), the heating and stirring time of the amino acid and the hydrated salt corresponding to the carrier is 0.5-6h. For example, the heating and stirring time of the amino acid and the hydrated salt corresponding to the carrier can be 0.5-1h, 1-2h, 2-3h, 3-4h, 4-5h, 5-6h.

[0029] Preferably, in the step 1), the mixing and heating and stirring time of the hydrated nickel salt is 0.5-4h. For example, the mixing and heating and stirring time of the hydrated nickel salt can be 0.5-1h, 1-2h, 2-3h, 3-4h.

[0030] In the present application, the amount of the hydrated nickel salt is calculated according to the content of NiO in the nano-catalyst, and the content of nickel in the hydrated nickel salt is the same as the content of nickel in NiO, based on the total mass of the carrier and NiO.

[0031] Preferably, in the step 2), the precipitant is an alkali solution, and the pH value of the alkali solution is 9-13. For example, the pH value of the alkali solution can be 9-10, 10-11, 11-12, 12-13.

[0032] More preferably, the alkali in the alkali solution is selected from one or more of Na2CO3, NaOH, NH3·H2O, K2CO3, (NH4)2CO3, (NH2)2CO, and KOH.

[0033] Further, the alkali is selected from one or more of Na2CO3, NaOH, and NH3·H2O.

[0034] More preferably, the concentration of the alkali solution is 0.5-5 mol / L. For example, the concentration of the alkali solution can be 0.5-1 mol / L, 1-2 mol / L, 2-3 mol / L, 3-4 mol / L, 4-5 mol / L.

[0035] Preferably, in the step 2), the drying temperature is 100-150℃. For example, the drying temperature can be 100-110℃, 110-120℃, 120-130℃, 130-140℃, 140-150℃.

[0036] Preferably, in the step 2), the drying time is 12-36 h. For example, the drying time can be 12-18 h, 18-20 h, 20-24 h, 24-28 h, 28-36 h.

[0037] Preferably, in the step 2), the calcination temperature is 200-600℃. For example, the calcination temperature can be 200-300℃, 300-400℃, 400-500℃, 500-600℃.

[0038] Preferably, in the step 2), the calcination time is 2-6 h. For example, the calcination time can be 2-3 h, 3-4 h, 4-5 h, 5-6 h.

[0039] Preferably, in the step 2), after the solid-liquid separation, a washing step is further included, and the washing liquid for the washing is water.

[0040] Preferably, in the step 2), the calcination is performed under an air atmosphere.

[0041] The fourth aspect of the present application discloses a use of the above-mentioned nano-catalyst in a reaction of preparing methane from carbon dioxide and hydrogen.

[0042] The nano-catalyst is used in the reaction of preparing methane from carbon dioxide and hydrogen, when the nano-catalyst comprises a carrier, the carrier is loaded with NiO, the content of the NiO is 19.1wt% based on the total mass of the nano-catalyst, the carrier is CeO2, and the average particle size of the catalyst is 6.0nm; under the conditions of H2 / CO2=4, normal pressure, 250℃, and 12000mL / g / h, the conversion rate of CO2 is up to 86.0%, and the conversion rate of CO2 can still be kept above 85% and the selectivity of methane is 98% after 60h continuous reaction.

[0043] The fifth aspect of the present application discloses a method for preparing methane from carbon dioxide and hydrogen by using the nano-catalyst as described above.

[0044] Preferably, the reaction gas of the reaction of preparing methane from carbon dioxide and hydrogen comprises H2 and CO2, and the volume ratio of H2 to CO2 is (1-4):1. For example, the volume ratio of H2 to CO2 is (1-2):1, (2-3):1, or (3-4):1.

[0045] More preferably, the volume ratio of H2 to CO2 is 4:1.

[0046] Preferably, the temperature of the reaction is 200-400℃. For example, the temperature of the reaction can be 200-225℃, 225-250℃, 250-275℃, 275-300℃, 300-325℃, 325-350℃, 350-375℃, or 375-400℃.

[0047] Preferably, the pressure of the reaction is normal pressure.

[0048] Preferably, the space velocity of the reaction is 12000-36000h -1 . For example, the space velocity of the reaction can be 12000-18000h -1 , 18000-24000h -1 , 24000-30000h -1 , or 30000-36000h -1 .

[0049] Preferably, the method further comprises a step of reducing the catalyst before the reaction.

[0050] More preferably, the reducing gas is hydrogen or a mixture of hydrogen and inert gas.

[0051] More preferably, the space velocity of the reduction is 6000-12000h -1 . For example, the space velocity of the reduction can be 6000-7000h -1 , 7000-8000h -1, 8000~9000h -1 9000~10000h -1 , 10000~11000h -1 11000~12000h -1 .

[0052] More preferably, the reduction temperature is 300-500° C. For example, the reduction temperature may be 300-325° C., 325-350° C., 350-375° C., 375-400° C., 400-425° C., 425-450° C., 450-475° C., or 475-500° C.

[0053] More preferably, the reduction time is 1 to 4 hours. For example, the reduction time can be 1 to 1.5 hours, 1.5 to 2 hours, 2 to 2.5 hours, 2.5 to 3 hours, 3 to 3.5 hours, or 3.5 to 4 hours.

[0054] Compared with the prior art, the present invention has the following beneficial effects:

[0055] (1) The nanocatalyst described in this application effectively enhances the dispersion and stability of NiO particles by using a low eutectic solvent as a carrier precursor and solvent, and constructs a high-density Ni-O in situ using an alkali treatment method. V The interfacial sites promote the adsorption and activation of H2 and CO2 on the catalyst, resulting in higher CO2 conversion rates. This catalyst, which achieves efficient and highly selective production of a single product, CH4, at low temperatures, has greater application value. Compared to traditional Ni / CeO2 catalysts that require high temperatures to achieve efficient CO2 conversion and CH4 selectivity, this method can achieve high CO2 conversion and CH4 selectivity at temperatures of 250-300°C, significantly enhancing catalyst stability and reducing reaction energy consumption.

[0056] (2) The nanocatalysts of the present invention have good preparation repeatability. The raw materials of the nanocatalysts of the present invention are relatively low in price, the preparation method is simple and easy to control, and it is easy to repeat the preparation to obtain products with the same quality and performance, thereby meeting the needs of large-scale stable industrial production.

[0057] (3) The nanocatalyst of the present invention has good catalytic activity, stability and performance repeatability. In the reaction system of carbon dioxide hydrogenation to methane, increasing the space velocity will lead to a decrease in CO2 conversion rate and CH4 selectivity. The nanocatalyst of the present invention can achieve a CO2 conversion rate of more than 80% and a CH4 selectivity of 95% for a long time at a high space velocity.

[0058] The above CH4 selectivity shows excellent catalytic stability, which makes industrial application possible. BRIEF DESCRIPTION OF THE DRAWINGS

[0059] Figure 1 The graph shows the results of the catalyst stability test in Example 1 of the present application. DETAILED DESCRIPTION

[0060] The present application will now be described in greater detail by way of specific embodiments thereof, which should not be construed as limiting the scope of the present application. Other advantages and benefits of the present application will be readily understood by persons skilled in the art upon review of the disclosure presented herein.

[0061] Before further description of the present application, it should be understood that the scope of the present application is not limited to the particular specific embodiments described below; also, the terminology used in the description is for the purpose of describing particular embodiments only and is not intended to limit the scope of the present application. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, although methods, devices, and materials similar or equivalent to those described herein can be used in the practice of the present application, the particular methods, devices, and materials described herein are illustrative only.

[0062] When numerical ranges are given, understand that every numerical range is a range of values including the endpoints, and any number within the range. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. In addition, although methods, devices, and materials similar or equivalent to those described herein can be used in the practice of the present application, the particular methods, devices, and materials described herein are illustrative only.

[0063] The reaction results of the catalysts described in the present application were obtained by the following methods:

[0064] 1) The types and contents of various components contained in the products were analyzed using a gas chromatograph (Agilent 8860);

[0065] 2) The CO2 conversion rate was calculated based on the number of carbon atoms, and the calculation formula was as follows:

[0066]

[0067] wherein CO2 inlet and CO2 outlet represent the number of moles of CO2 entering / leaving the reaction system, respectively.

[0068] 3) The CH4 selectivity calculation formula was:

[0069]

[0070] wherein represents the number of moles of CH4 flowing out of the reaction tube.

[0071] The component content of the actual catalyst in the following examples of the present application is quantitatively determined by a Jobin Yvon Ultima2 inductively coupled plasma emission spectrometer (ICP-OES) and the proportion is obtained by calculation.

[0072] The average particle size of the actual catalyst in the following examples of the present application is obtained by statistical analysis of the TEM characterization results of the catalyst.

[0073] It should be noted that the amount of the nano-catalyst can be adjusted according to the catalytically effective amount of the specific catalyst, the reaction conditions, the convenience and economy of actual operation, and the stability of long-term operation.

[0074] Example 1

[0075] The present embodiment provides a nano-catalyst for hydrogenation of carbon dioxide to methane, which comprises a carrier, and NiO loaded on the carrier; the content of the NiO is 12.7wt% based on the total mass of the nano-catalyst, the carrier is CeO2, and the average particle size of the catalyst is 6.0nm.

[0076] The present embodiment also provides a preparation method of a nano-catalyst for hydrogenation of carbon dioxide to methane, which comprises the following steps:

[0077] 1) 0.75g of glycine and 4.3412g of cerium nitrate hexahydrate were mixed in a molar ratio of 1:1 and added to a round-bottom flask, and 5g of the premixed solution was added to 0.8528g of nickel nitrate hexahydrate.

[0078] The mixture was sealed and stirred at 80℃ for 1h to obtain a colorless transparent eutectic solvent.

[0079] 2) Then, 5g of the premixed solution was added to 0.8528g of nickel nitrate hexahydrate, and the stirring was continued at 80℃ for another 30min to obtain a uniform light green transparent premixed solution. Subsequently, 3mL of 5mol / L sodium hydroxide solution was added dropwise for alkaline treatment, the pH was controlled at about 13, and the stirring reaction was carried out for 1h to produce a blue-white precipitate.

[0080] 3) The obtained precipitate was washed with deionized water for several times, and then dried in a 100℃ oven for 18h. Finally, the dried blue-white precipitate was placed in a muffle furnace, heated to 400℃, calcined for 2h, and cooled to room temperature to obtain the nano-catalyst. The content of NiO in the nano-catalyst was 12.7wt%, and the content of CeO2 was 87.3wt% obtained by determination with a Jobin Yvon Ultima2 inductively coupled plasma emission spectrometer (ICP-OES).

[0081] The embodiment also provides use of the nanocatalyst in carbon dioxide hydrogenation to prepare methane. The nanocatalyst in the embodiment is placed in a constant temperature section of a quartz reaction tube, and quartz wool is plugged into both ends to prevent powder loss, and then the performance of the catalyst is evaluated, specifically as follows:

[0082] 0.05 g of the nanocatalyst is weighed and placed in a constant temperature section of a quartz reaction tube, and quartz wool is plugged into both ends to prevent powder loss, and then the nanocatalyst is used in a carbon dioxide hydrogenation reaction to prepare methane, and a fixed bed reactor is used as a reaction device. The nanocatalyst is pre-reduced at 400 ℃ for 2 h in a pure H2 (10 mL / min) atmosphere, then purged with N2, and the temperature is lowered to the reaction temperature. Then, H2 and CO2 are injected into the reaction tube at a ratio of 4:1, the total flow rate is 30 mL / min, the space velocity (GHSV) is 36000 h-1, and the reaction is carried out at 400 ℃. -1 The reaction is carried out at 250 ℃. After the reaction is completed, a gas chromatograph (Agilent 8860) is used to analyze the types and contents of various components contained in the product, and the CO2 conversion rate and CH4 selectivity of the reaction are calculated accordingly, and the specific results are shown in Table 1.

[0083] Embodiment 2

[0084] The embodiment provides a nanocatalyst for carbon dioxide hydrogenation to prepare methane, the nanocatalyst comprising a carrier, and NiO loaded on the carrier; the content of the NiO is 6.4 wt% based on the total mass of the nanocatalyst, the carrier is CeO2, and the average particle size of the catalyst is 4.9 nm.

[0085] The embodiment also provides a preparation method of the nanocatalyst for carbon dioxide hydrogenation to prepare methane, and the preparation method comprises the following steps:

[0086] 1) 2.9238 g of lysine and 4.3412 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) are mixed into a round-bottom flask at a molar ratio of 2:1, and are sealed and stirred at 100 ℃ for 0.5 h to obtain a colorless transparent eutectic solvent.

[0087] 2) Then, 5 g of the premixed solution is taken and mixed with 0.4264 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), and stirring is continued at 100 ℃ for another 30 min to obtain a uniform light green transparent premixed solution. Subsequently, 5 mL of a 3 mol / L sodium hydroxide solution is added dropwise for alkaline treatment, the pH is controlled to be about 12, and stirring is performed for 2 h to generate a blue-white precipitate.

[0088] 3) The obtained precipitate was washed with deionized water by filtration several times, and then dried in an oven at 80°C for 18h. Finally, the dried blue-white precipitate was placed in a muffle furnace, heated to 500°C, calcined for 2 hours, and cooled to room temperature. The content of NiO in the nanocatalyst was 6.4wt%, and the content of CeO2 was 93.6wt% as determined by a Jobin Yvon Ultima2 inductively coupled plasma optical emission spectrometer (ICP-OES).

[0089] The present embodiment also provides the use of the nanocatalyst in the hydrogenation of carbon dioxide to produce methane. The nanocatalyst in the present embodiment was placed in the constant temperature section of a quartz reaction tube, with quartz wool plugged into both ends to prevent loss of powder, and the performance of the catalyst was evaluated. Specifically:

[0090] 0.05g of the nanocatalyst was weighed and placed in the constant temperature section of a quartz reaction tube, with quartz wool plugged into both ends to prevent loss of powder, and used to catalyze the hydrogenation of carbon dioxide to produce methane. The reaction device was a fixed bed reactor. The catalyst was pre-reduced at 450°C for 2h in a mixture of H2 / N2(1:1, 20mL / min), then purged with N2, and the temperature was allowed to drop to the reaction temperature. Then, H2 and CO2 were injected into the reaction tube at a ratio of 4:1, with a total flow rate of 15mL / min and a space velocity (GHSV) of 18000h -1 The reaction was carried out at a temperature range of 275°C. After the reaction was completed, the types and contents of various components contained in the products were analyzed using a gas chromatograph (Agilent 8860), and the CO2 conversion rate and CH4 selectivity of the reaction were calculated accordingly. The specific results are shown in Table 1.

[0091] Example 3

[0092] The present embodiment provides a nanocatalyst for the hydrogenation of carbon dioxide to produce methane, which comprises a carrier loaded with NiO; the content of the NiO is 19.1wt% based on the total mass of the nanocatalyst, the carrier is CeO2, and the average particle size of the catalyst is 7.6nm.

[0093] The present embodiment also provides a preparation method of a nanocatalyst for the hydrogenation of carbon dioxide to produce methane, which comprises the following steps:

[0094] 1) 1.4713g of glutamic acid (Glu) and 8.6824g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) were mixed in a molar ratio of 1:2 and added to a round-bottom flask, which was sealed and stirred at 60°C for 4h to obtain a colorless transparent eutectic solvent.

[0095] 2) Then, 5 g of the premix solution was added to 1.2792 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), and stirring was continued at 60°C for another 2 h to obtain a uniform light green transparent premix solution. Subsequently, 10 mL of 1 mol / L sodium hydroxide solution was added dropwise for alkaline treatment, the pH was controlled at about 11, and stirring was continued for 2 h to produce a bluish-white precipitate.

[0096] 3) The obtained precipitate was washed with deionized water by repeated filtration, and then dried in an oven at 120°C for 18 h. Finally, the dried bluish-white precipitate was placed in a muffle furnace, heated to 300°C, calcined for 6 h, and cooled to room temperature to obtain the nano-catalyst. The content of NiO in the nano-catalyst was determined by a Jobin Yvon Ultima2 inductively coupled plasma optical emission spectrometer (ICP-OES)

[0097] The content of NiO in the nano-catalyst was determined to be 19.1 wt%, and the content of CeO2 was 80.9 wt%.

[0098] The nano-catalyst in this example was also used for carbon dioxide hydrogenation to produce methane. The nano-catalyst was placed in the constant temperature section of a quartz reaction tube, and quartz wool was inserted into both ends to prevent powder loss. The performance of the catalyst was evaluated, specifically:

[0099] 0.05 g of the nano-catalyst was weighed and placed in the constant temperature section of a quartz reaction tube, and quartz wool was inserted into both ends to prevent powder loss. The catalyst was used in the reaction of carbon dioxide hydrogenation to produce methane, and the reaction device was a fixed bed reactor. The catalyst was pre-reduced in H2 (10 mL / min) at 500°C for 1 h, then purged with N2, and the temperature was allowed to drop to the reaction temperature. Then, H2 and CO2 were injected into the reaction tube at a ratio of 4:1, the total flow rate was 10 mL / min, the gas hourly space velocity (GHSV) was 12000 h -1 , and the reaction was carried out at 275°C. After the reaction was completed, the types and contents of various components contained in the products were analyzed using a gas chromatograph (Agilent 8860), and the CO2 conversion rate and CH4 selectivity of the reaction were calculated accordingly. The specific results are shown in Table 1.

[0100] Example 4

[0101] The nano-catalyst for carbon dioxide hydrogenation to produce methane provided in this example includes a carrier, and NiO is loaded on the carrier. The content of the NiO is 19.1 wt% based on the total mass of the nano-catalyst, the carrier is CeO2, and the average particle size of the catalyst is 7.9 nm.

[0102] The preparation method of the nano-catalyst for carbon dioxide hydrogenation to produce methane provided in this example includes the following steps:

[0103] 1) 2.2521 g of glycine and 4.3412 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) were weighed out in a molar ratio of 3:1 and mixed into a round-bottom flask, and stirred at 60°C for 2 h to obtain a colorless transparent deep eutectic solvent.

[0104] 2) Then, 5 g of the premixed solution was added to 1.2792 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), and stirring was continued at 80°C for another 30 min to obtain a uniform light green transparent premixed solution. 5 mL of a Na2CO3 solution (2 mol / L) was added

[0105] Alkaline treatment was performed, and the pH was controlled to be about 12, and stirring was performed for 2 h to produce a blue-white precipitate.

[0106] 3) The obtained precipitate was repeatedly filtered and washed with deionized water, and then dried in an oven at 150°C for 18 h. Finally, the dried blue-white precipitate was placed in a muffle furnace, heated to 450°, calcined for 4 hours, and cooled to room temperature to obtain the nano-catalyst. The content of NiO in the nano-catalyst was 19.1 wt%, and the content of CeO2 was 80.9 wt%, as determined by a Jobin Yvon Ultima2 inductively coupled plasma optical emission spectrometer (ICP-OES).

[0107] The example also provides the use of the nano-catalyst in the hydrogenation of carbon dioxide to produce methane. The nano-catalyst in this example was placed in the constant temperature section of a quartz reaction tube, and quartz wool was inserted into both ends to prevent loss of powder, and the performance of the catalyst was evaluated, specifically:

[0108] 0.05 g of the nano-catalyst was weighed out and placed in the constant temperature section of a quartz reaction tube, and quartz wool was inserted into both ends to prevent loss of powder, and used to catalyze the hydrogenation of carbon dioxide to produce methane, and the reaction device was a fixed bed reactor. The catalyst was pre-reduced in H2 (5 mL / min) at 300°C for 4 h, then purged with N2, and the temperature was allowed to drop to the reaction temperature. Then, H2 and CO2 were injected into the reaction tube in a ratio of 4:1, and the total flow rate was 30 mL / min, and the space velocity (GHSV) was 12000 h -1 The reaction was carried out at 300°C, and the specific results are shown in Table 1.

[0109] Example 5

[0110] The example provides a nano-catalyst for the hydrogenation of carbon dioxide to produce methane, which comprises a carrier, and NiO is loaded on the carrier; the content of the NiO is 12.7 wt% based on the total mass of the nano-catalyst, the carrier is CeO2, and the average particle size of the catalyst is 5.7 nm.

[0111] The embodiment also provides a preparation method of the nanocatalyst for carbon dioxide hydrogenation to methane, which comprises the following steps:

[0112] 1) 0.3754 g of glycine and 10.853 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) were weighed and mixed in a molar ratio of 1:5 and added to a round-bottom flask, and stirred at 100 °C for 2 h to obtain a colorless transparent eutectic solvent.

[0113] 2) Then, 5 g of the premixed solution was taken and mixed with 0.8528 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), and stirring was continued at 80 °C for another 30 min to obtain a uniform light green transparent premixed solution. Subsequently, 15 mL of 0.5 mol / L NH3·H2O solution was added for alkaline treatment, the pH was controlled at about 9, and stirring was performed for 3 h to produce a blue-white precipitate.

[0114] 3) The obtained precipitate was washed with deionized water for multiple times, and then dried in an oven at 150 °C for 18 h. Finally, the dried blue-white precipitate was placed in a muffle furnace, heated to 450 °C, calcined for 4 hours, and cooled to room temperature to obtain the nanocatalyst. The content of NiO in the nanocatalyst was 12.7 wt%, and the content of CeO2 was 87.3 wt%, which were determined by a Jobin Yvon Ultima2 inductively coupled plasma optical emission spectrometer (ICP-OES).

[0115] The embodiment also provides the use of the nanocatalyst in carbon dioxide hydrogenation to methane. The nanocatalyst in the embodiment was placed in the constant temperature section of a quartz reaction tube, and quartz wool was plugged into both ends to prevent powder loss, and then the performance of the catalyst was evaluated, specifically as follows:

[0116] 0.05 g of the nanocatalyst was weighed and placed in the constant temperature section of a quartz reaction tube, and quartz wool was plugged into both ends to prevent powder loss, and then used to catalyze the reaction of carbon dioxide hydrogenation to methane, and the reaction device was a fixed bed reactor. The catalyst was pre-reduced at 450 °C for 2 h in a mixed gas of H2 / N2 (1:1, 20 mL / min), and then purged with N2 and waited for the temperature to drop to the reaction temperature. Then, H2 and CO2 were injected into the reaction tube at a ratio of 4:1, the total flow rate was 30 mL / min, the space velocity (GHSV) was 36000 h -1 , and the reaction was carried out at 300 °C. After the reaction was completed, the types and contents of various components contained in the product were analyzed by gas chromatography (Agilent 8860), and the CO2 conversion rate and CH4 selectivity of the reaction were calculated accordingly, and the specific results are shown in Table 1.

[0117] Example 6

[0118] The embodiment provides a nano catalyst for preparing methane by carbon dioxide hydrogenation, the nano catalyst comprising a carrier, wherein NiO is loaded on the carrier; the content of the NiO is 19.1 wt% based on the total mass of the nano catalyst; the carrier is CeO2; and the average particle size of the catalyst is 8.3 nm.

[0119] The embodiment further provides a preparation method of the nano catalyst for preparing methane by carbon dioxide hydrogenation, the preparation method comprising the following steps:

[0120] 1) 0.75 g of glycine (Gly) and 4.3412 g of cerium nitrate hexahydrate (Ce(NO3)3·6H2O) are weighed in a molar ratio of 1:

[0121] 1) The mixture is added to a round-bottom flask, and stirring is performed at 80 DEG C for 3 h in a sealed state to obtain a colorless transparent eutectic solvent.

[0122] 2) Then, 5 g of the premixed solution is added to 1.2792 g of nickel nitrate hexahydrate (Ni(NO3)2·6H2O), and stirring is continued at 80 DEG C for 30 min to obtain a uniform light green transparent premixed solution. Subsequently, 3 mL of a 5 mol / L sodium hydroxide solution is added dropwise for alkaline treatment, the pH is controlled to be about 13 during the dropwise addition, and stirring is performed for 1 h to generate a blue-white precipitate.

[0123] 3) The obtained precipitate is washed by repeatedly filtering with deionized water, and then is dried in an oven at 100 DEG C for 18 h. Finally, the dried blue-white precipitate is placed in a muffle furnace, heated to 400 DEG C, calcined for 2 hours, and cooled to room temperature to obtain the nano catalyst. The content of NiO in the nano catalyst is 19.1 wt%, and the content of CeO2 is 80.9 wt% as measured by a Jobin Yvon Ultima2 inductively coupled plasma optical emission spectrometer (ICP-OES).

[0124] The embodiment further provides use of the nano catalyst in preparing methane by carbon dioxide hydrogenation. The nano catalyst in the embodiment is placed in a constant temperature section of a quartz reaction tube, quartz wool is plugged into both ends to prevent powder loss, and then the performance of the catalyst is evaluated, and the evaluation is specifically as follows:

[0125] 0.05 g of the nano catalyst is weighed, placed in a constant temperature section of a quartz reaction tube, quartz wool is plugged into both ends to prevent powder loss, and then the nano catalyst is used in a reaction of preparing methane by carbon dioxide hydrogenation, and a reaction device is a fixed bed reactor. The nano catalyst is pre-reduced in H2 (10 mL / min) at 400 DEG C for 2 h, then is purged with N2, and waits for the temperature to drop to a reaction temperature. Then, H2 and CO2 are injected into the reaction tube at a ratio of 4:1, the total flow rate is 20 mL / min, and the space velocity (GHSV) is 24000 h-1.-1 The reaction was carried out at 300°C. After the reaction, the types and contents of various components contained in the product were analyzed using a gas chromatograph (Agilent 8860), and the CO2 conversion rate and CH4 selectivity of the reaction were calculated accordingly, with the specific results shown in Table 1.

[0126] Example 1

[0127] The nanocatalyst obtained in Example 1 was used to catalyze the reaction of carbon dioxide hydrogenation to methane, and its stability was investigated, with the specific process being as follows,

[0128] 0.05 g of the nanocatalyst was weighed and placed in the constant temperature section of a quartz reaction tube, with quartz wool being inserted into both ends to prevent powder loss. The nanocatalyst was pre-reduced at 400°C for 2 h in a mixed gas of H2 / N2 (1:1, 20 mL / min), and then purged with N2 and waited for the temperature to drop to the reaction temperature. Then, H2 and CO2 were injected into the reaction tube at a ratio of 4:1, with the total flow rate being 30 mL / min and the space velocity being 12000 h-1. -1 The reaction was carried out at 250°C for 60 h. At each time period, the types and contents of various components contained in the product were analyzed using a gas chromatograph (Agilent 8860), and the CO2 conversion rate and CH4 selectivity of the reaction were calculated accordingly, with the specific results shown in Table 2. Figure 1

[0129] Comparative Example 1

[0130] This comparative example provides a catalyst for carbon dioxide hydrogenation to methane and a preparation method thereof, which comprises a carrier, and NiO is loaded on the carrier; the content of the NiO is 12.7 wt% based on the total mass of the nanocatalyst, the carrier is CeO2, and the average particle size of the catalyst is 10.4 nm.

[0131] The preparation method of the catalyst of this comparative example comprises the following steps: 0.8520 g of Ce(NO3)3·6H2O and 0.1855 g of Ni(NO3)2·6H2O are weighed and dissolved in 50 mL of deionized water, and stirred at room temperature for 12 hours. Subsequently, the solution is transferred to an oven for overnight drying, and the dried powder is heated to 450°C at a heating rate of 1°C / min in a muffle furnace, calcined for 2 h, and cooled to room temperature to obtain the catalyst.

[0132] The catalyst of this comparative example was placed in the constant temperature section of a quartz reaction tube, with quartz wool being inserted into both ends to prevent powder loss, and the performance of the catalyst was evaluated, specifically as follows:

[0133] ​Weigh 0.05g of the catalyst and place it in the constant temperature section of a quartz reaction tube. Insert quartz wool at both ends to prevent the loss of powder. Use it to catalyze the hydrogenation of carbon dioxide to methane. The reaction apparatus is a fixed bed reactor. Pre-reduction is carried out at 400°C for 2h in a pure H2 (10mL / min) atmosphere, followed by N2 purge, and wait for the temperature to drop to the reaction temperature. Then, H2 and CO2 are injected into the reaction tube in a ratio of 4:1, with a total flow rate of 30mL / min and a space velocity (GHSV) of 36000h -1 The reaction was carried out at 250° C. After the reaction, the types and contents of the various components in the product were analyzed using gas chromatography (Agilent 8860), and the CO2 conversion rate and CH4 selectivity of the reaction were calculated accordingly. The specific results are shown in Table 1.

[0134] Table 1 Catalyst reaction results of Examples 1 to 6 and Comparative Example 1

[0135] CO2 conversion (%) <![CDATA[CH4选择性(%)]]> Example 1 86.0 93.3 Example 2 45.7 95.1 Example 3 52.9 96.7 Example 4 55.8 98.0 Example 5 62.5 95.5 Example 6 60.8 98.2 Comparative Example 1 18.5 92.3

[0136] The above results show that the nanocatalyst described in this application exhibits high activity, high methane selectivity, and high stability in the CO2 hydrogenation to methane reaction at low temperatures of 250-300°C. Specifically, the nanocatalyst described in Example 1 of this application achieved a CO2 conversion rate of 86.0% under the conditions of H2 / CO2 = 4, atmospheric pressure, 250°C, and 12,000 mL / g / h. After 60 hours of continuous reaction, it can still maintain a CO2 conversion rate of over 85% and a methane selectivity of 98%. In contrast, the CO2 conversion rate of Comparative Example 1, which has the same catalyst components and the same catalytic reaction conditions, is only 18.5%.

[0137] The present invention effectively overcomes various shortcomings of the prior art and has high industrial utilization value.

[0138] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the present invention. Anyone skilled in the art may modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by one of ordinary skill in the art without departing from the spirit and technical principles disclosed herein are intended to be covered by the claims of the present invention.

Claims

1. Use of a deep eutectic solvent as a carrier precursor in the coprecipitation method for preparing a nanocatalyst for hydrogenation of carbon dioxide to methane.

2. The use according to claim 1, characterized in that The deep eutectic solvent is obtained by heating and mixing a hydrogen bond acceptor and a hydrogen bond donor, wherein the hydrogen bond acceptor is an amino acid and the hydrogen bond donor is a hydrated salt corresponding to the carrier; And / or, the use includes enhancing the dispersion of the load on the carrier; And / or, the use includes lowering the reaction temperature of the nanocatalyst in carbon dioxide hydrogenation to methane.

3. A nanocatalyst for hydrogenating carbon dioxide to produce methane, characterized in that: The nanocatalyst is prepared by a coprecipitation method using a low eutectic solvent as a carrier precursor. The nanocatalyst includes a carrier, and NiO is loaded on the carrier. Based on the total mass of the nanocatalyst, the content of NiO is 5 to 20 wt%, and the content of the carrier is 80 to 95 wt%. The carrier is selected from one or more of CeO2, ZrO2, MgO and Al2O3.

4. The nanocatalyst according to claim 1, characterized in that The content of NiO is 6.4-19.1wt%; and or, the content of the carrier is 80.9 to 93.6 wt %; And / or, the average particle size of the nanocatalyst is 5 to 10 nm; And / or, the carrier is CeO2.

5. The method for preparing a nanocatalyst according to any one of claims 3 to 4, characterized in that: The preparation method comprises the following steps: 1) The amino acid is first mixed with the hydrated salt corresponding to the carrier and heated and stirred to obtain a deep eutectic solvent, and then the hydrated nickel salt is added, mixed, heated and stirred to obtain a premixed solution; 2) adding a precipitant to the premixed liquid, performing solid-liquid separation, and drying and calcining to obtain the nanocatalyst.

6. The preparation method according to claim 5, characterized in that In step 1), the hydrated salt is selected from one or more of hydrated chloride, hydrated nitrate, and hydrated sulfate; And / or, in step 1), the amino acid is selected from one or more of glycine, lysine, glutamic acid, alanine, and proline; And / or, in step 1), the molar ratio of the amino acid and the hydrated salt corresponding to the carrier is 3:1 to 15; And / or, in step 1), the heating temperature is 50-100° C.; And / or, in step 1), the heating and stirring time of the hydrated salt corresponding to the amino acid and the carrier is 0.5 to 6 hours; and / or, the time for mixing, heating and stirring the hydrated nickel salt is 0.5 to 4 hours; And / or, in step 2), the precipitant is an alkali solution, and the pH value of the alkali solution is 9 to 13; And / or, in step 2), the drying temperature is 100-150°C; And / or, in step 2), the drying time is 12 to 36 hours; And / or, in step 2), the calcination temperature is 200-600°C; And / or, in step 2), the calcination time is 2 to 6 hours; And / or, in the step 2), a washing step is further included after the solid-liquid separation; And / or, in the step 2), the calcination is carried out in an air atmosphere.

7. The preparation method according to claim 6, characterized in that The hydrated salt is a hydrated nitrate; and / or, the amino acid is selected from one or more of glycine, lysine, and glutamic acid; and / or, the alkali in the alkali solution is selected from one or more of Na2CO3, NaOH, NH3·H2O, K2CO3, (NH4)2CO3, (NH2)2CO, and KOH; and / or, the concentration of the alkali solution is 0.5 to 5 mol / L; And / or, the washing liquid is water.

8. Use of the nanocatalyst according to any one of claims 3 to 4 in the reaction of hydrogenating carbon dioxide to produce methane.

9. A method for preparing methane by catalyzing carbon dioxide hydrogenation using the nanocatalyst according to any one of claims 3 to 4.

10. The method according to claim 9, characterized in that The reaction gas for the carbon dioxide hydrogenation reaction to prepare methane includes H2 and CO2, and the volume ratio of H2 to CO2 is (1-4):1; and / or, the reaction temperature is 200-400° C.; And / or, the reaction space velocity is 12000~36000h -1 ; And / or, the reaction further includes a step of reducing the catalyst before the reaction.

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