Catalyst for improving methane preparation through photo-thermal CO2 hydrogenation by constructing Mn monatomic on surface of nickel silicate nanotube and preparation method of catalyst

Abstract

The invention provides a catalyst for improving methane preparation through photo-thermal CO2 hydrogenation by constructing Mn monatomic on the surface of a nickel silicate nanotube and a preparation method of the catalyst, and belongs to the technical field of photo-thermal catalyst preparation. The preparation method of the catalyst comprises the following steps: loading manganese salt onto the multilayer nickel silicate nanotube by a wet impregnation method; and then calcining the nickel silicate nanotube into black powder, and carrying out reduction reaction in an H2 atmosphere to obtain the metal manganese regulated multilayer nickel silicate nanotube catalyst. According to the method, CO2 is efficiently reduced into the high-added-value product CH4 by utilizing the excellent performance of the multi-layer nickel silicate nanotubes and the Mn nanoparticles, the cost is low, the preparation is simple, and the catalyst has relatively high photo-thermal catalytic efficiency.

Description

Technical Field

[0001] The present invention belongs to the technical field of photothermal catalyst preparation, and in particular relates to a catalyst for constructing Mn single atoms on the surface of nickel silicate nanotubes to enhance photothermal CO2 hydrogenation to methane and a preparation method thereof. Background Art

[0002] Energy issues have always received widespread attention from all over the world. The continuous development of society requires a large amount of energy, most of which comes from the combustion of fossil fuels, and environmental pollution problems such as the greenhouse effect caused by these fossil fuels have become another serious crisis. CO2, as the main greenhouse gas, has a great impact on global climate change. Therefore, it is of great significance to develop catalysts that can convert CO2 into high value-added products and utilize new energy. In the prior art, photocatalysis has the advantage of being green and environmentally friendly, but its reaction efficiency is not ideal; thermal catalysis has a higher reaction efficiency but requires more energy consumption.

[0003] Therefore, there is an urgent need to provide a new catalyst for catalyzing CO2 photothermal hydrogenation methanation reaction and a preparation method thereof to solve the above-mentioned problems. Summary of the invention

[0004] In order to solve the above technical problems, the present invention proposes a catalyst for constructing Mn single atoms on the surface of nickel silicate nanotubes to enhance photothermal CO2 hydrogenation to methane and a preparation method thereof. The excellent properties of multilayer nickel silicate nanotubes and Mn nanoparticles are utilized to efficiently reduce CO2 to high value-added product CH4. The catalyst has low cost and simple preparation. The catalyst has high photothermal catalytic efficiency, stable catalytic activity and high CH4 yield.

[0005] To achieve the above object, the present invention provides the following technical solutions:

[0006] One of the technical solutions of the present invention:

[0007] A method for preparing a multilayer nickel silicate nanotube catalyst regulated by metal manganese, comprising: loading manganese salt onto the multilayer nickel silicate nanotube by a wet impregnation method; then calcining the multilayer nickel silicate nanotube into black powder, and then reducing the powder in a H2 atmosphere to obtain the metal manganese regulated multilayer nickel silicate nanotube catalyst.

[0008] The beneficial effects achieved by the above technical scheme are as follows: First, the multilayer nickel silicate nanotubes prepared by the present invention not only have a typical layered structure, but also have a good electron transfer effect due to the combination of the embedded structure of the nickel compound and the silicate layer structure. Moreover, after reduction, the nickel metal has an excellent activation effect on the H2 molecule, and can effectively crack the H2 molecule into active H atoms to participate in the reduction reaction of the CO2 molecule; further, the nanotube material has excellent properties of high thermal stability and mechanical strength as a one-dimensional semiconductor and a high specific surface area catalyst. Second, the present invention loads metal manganese onto the multilayer nickel silicate nanotubes. In addition to the abundant source of manganese materials and low cost, it also has good photothermal performance, which is mainly manifested in that the addition of Mn atoms forms a charge imbalance induced by the Si-O-Mn structure and the spin polarization of the material caused by the magnetic coupling effect, which improves the catalyst's adsorption and activation ability for CO2 and accelerates the transfer of electrons on the catalyst surface. The direction of the spin polarization electric field is consistent with the direction of the photogenerated electron transition, which inhibits the recombination of photogenerated electrons.

[0009] Preferably, the mass percentage of metal manganese in the metal manganese-regulated multilayer nickel silicate nanotube catalyst is 0.6-1.2%. When the mass fraction of metal Mn is less than 0.6%, or greater than 1.2%, the catalytic activity of the catalyst will be reduced.

[0010] Preferably, the outer diameter of the multilayer nickel silicate nanotube is 17-20 nm, and the inner diameter is 6-8 nm.

[0011] Preferably, the manganese salt is manganese nitrate or manganese chloride.

[0012] Preferably, the specific steps of loading the manganese salt onto the multilayer nickel silicate nanotubes by wet impregnation method are:

[0013] The multilayer nickel silicate nanotubes are added to the manganese salt solution, stirred for 4-8 hours, and heated at 80-90° C. until the water is completely evaporated.

[0014] Preferably, the preparation steps of the multilayer nickel silicate nanotubes are:

[0015] A soluble silicon salt solution is dropped into a nickel salt solution to form a light green precipitate, sodium hydroxide is added and stirred, and then the mixture is transferred to a polytetrafluoroethylene reactor for a hydrothermal reaction. The obtained product is then washed, dried, and calcined under a H2 atmosphere to finally obtain the multilayer nickel silicate nanotubes.

[0016] Further, the soluble silicon salt is sodium silicate;

[0017] The nickel salt is a soluble nickel salt, preferably nickel nitrate or nickel chloride.

[0018] Furthermore, the molar ratio of nickel atoms to silicon atoms in the soluble silicon salt and the nickel salt solution is 1.5-2.

[0019] Furthermore, the conditions of the hydrothermal reaction are: reaction temperature is 190-200° C., and reaction time is 12-48 h.

[0020] Furthermore, the calcination temperature during the calcination process under the H2 atmosphere is 300-400°C, and the calcination time is 0.5-2h.

[0021] Preferably, during the calcination process, the calcination temperature is 400-450° C. and the calcination time is 1-4 hours.

[0022] Preferably, during the reduction reaction, the reducing agent hydrogen concentration is 5% H2 (95% Ar), the reduction temperature is 300-400°C, and the time is 0.5-2h.

[0023] The second technical solution of the present invention:

[0024] A multilayer nickel silicate nanotube catalyst regulated by metal manganese is prepared by the above preparation method.

[0025] Preferably, the metal manganese-regulated multilayer nickel silicate nanotube catalyst is a supported catalyst, wherein nickel silicate is the main phase and metal manganese is the reinforcing phase;

[0026] Nickel nanoparticles are grown on the multilayer nickel silicate nanotubes; and the metal manganese is evenly dispersed on the multilayer nickel silicate nanotubes, wherein the nickel nanoparticles and the metal manganese are both distributed on the outer surface of the nanotubes.

[0027] The third technical solution of the present invention:

[0028] Application of metal manganese regulated multilayer nickel silicate nanotube catalyst in catalytic CO2 photothermal or thermal hydrogenation methanation reaction.

[0029] Preferably, the conditions for the CO2 photothermal hydrogenation methanation reaction are: the molar ratio of H2 to CO2 is 4:1; the reaction pressure is normal pressure; and the light source is a 300W xenon lamp.

[0030] Compared with the prior art, the present invention has the following advantages and technical effects:

[0031] (1) The Mn / NNSO catalyst in the present application utilizes the charge imbalance induced by the Si-O-Mn structure formed by the addition of Mn atoms and the material spin polarization caused by the magnetic coupling effect to improve the catalyst's ability to adsorb and activate CO2, accelerate the transfer of electrons on the catalyst surface, and thus improve the catalyst's reaction activity, selectivity and stability.

[0032] (2) The catalyst disclosed in the present invention combines the advantages of photocatalysis and thermal catalysis. Without using an additional heat source, it effectively converts light energy into thermal energy by using the photothermal effect of metal nanoparticles. Under the condition of ensuring low energy consumption, it realizes the effective conversion of CO2 into CH4 at normal pressure with a selectivity of more than 95%. Compared with traditional photocatalytic and thermal catalytic CO2 reduction, it has lower reaction energy consumption and higher energy utilization rate.

[0033] (3) The catalyst defined in the present invention has lower preparation cost than precious metal-supported catalysts, and provides a new approach for effectively converting CO2 into high value-added products.

[0034] (4) In the Mn / NNSO catalyst disclosed in the present invention, the Mn active center and the Ni active center work together, one for activating CO2 and the other for activating H2, and nickel silicate, as a reducible substrate material, has a strong hydrogen overflow effect during the reaction process, which accelerates the rapid transfer of active H on the catalyst surface, thereby accelerating the catalytic reaction.

[0035] (5) The catalyst can effectively absorb light energy and convert it into heat energy, thereby driving chemical reactions. Light energy is directly converted into heat energy, avoiding the energy loss that may occur in traditional thermal catalysis. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The drawings constituting a part of the present application are used to provide a further understanding of the present application. The illustrative embodiments and descriptions of the present application are used to explain the present application and do not constitute an improper limitation on the present application. In the drawings:

[0037] Figure 1 This is an XRD pattern of a Mn / NNSO catalyst prepared in Example 1 of the present invention;

[0038] Figure 2 TEM image of a Mn / NNSO catalyst prepared in Example 1 of the present invention;

[0039] Figure 3 This is a performance diagram of the CO2 photothermal hydrogenation reduction reaction in the effect example of the present invention. DETAILED DESCRIPTION

[0040] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as limiting the present invention, but should be understood as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0041] It should be understood that the terms described in the present invention are only for describing special embodiments and are not intended to limit the present invention. In addition, for the numerical range in the present invention, it should be understood that each intermediate value between the upper and lower limits of the scope is also specifically disclosed. Each smaller range between the intermediate value in any stated value or stated range and any other stated value or intermediate value in the described range is also included in the present invention. The upper and lower limits of these smaller ranges can be independently included or excluded in the scope.

[0042] Unless otherwise indicated, all technical and scientific terms used herein have the same meanings as those generally understood by those skilled in the art. Although the present invention describes only preferred methods and materials, any methods and materials similar or equivalent to those described herein may also be used in the implementation or testing of the present invention. All documents mentioned in this specification are incorporated by reference to disclose and describe the methods and / or materials associated with the documents. In the event of a conflict with any incorporated document, the content of this specification shall prevail.

[0043] It will be apparent to those skilled in the art that various modifications and variations may be made to the specific embodiments of the present invention description without departing from the scope or spirit of the present invention. Other embodiments derived from the present invention description will be apparent to those skilled in the art. The present invention description and examples are exemplary only.

[0044] The words “include,” “including,” “have,” “contain,” etc. used in this document are open-ended terms, meaning including but not limited to.

[0045] The present invention provides a method for preparing a multilayer nickel silicate nanotube catalyst (Mn / NNSO) regulated by metal manganese, comprising the following steps:

[0046] (1) Preparation of multilayer nickel silicate nanotubes (NNSO):

[0047] The nickel salt is dissolved in deionized water to obtain solution A, and the soluble silicate is dissolved in deionized water to obtain solution B, and then solution B is dripped dropwise into solution A to form a light green precipitate, and stirred. Then sodium hydroxide is added and stirred to adjust the pH of the solution to 10, and then the solution is transferred to a polytetrafluoroethylene reactor for hydrothermal reaction. The obtained light green precipitate is washed and dried, and calcined in a H2 atmosphere to finally obtain multilayer nickel silicate nanotubes.

[0048] (2) Preparation of multilayer nickel silicate nanotube catalyst (Mn / NNSO) regulated by metal manganese:

[0049] The manganese salt is dissolved in deionized water, the NNSO prepared as above is added, stirred, and then heated until the water is completely evaporated, the obtained powder is placed in a porcelain boat, calcined in a muffle furnace, and then reduced with H2 to finally obtain reduced Mn / NNSO, wherein the mass percentage of Mn is 0.6-1.2%.

[0050] In some preferred embodiments, in step (1), the nickel salt is a water-soluble nickel salt, preferably nickel nitrate or nickel chloride; the soluble silicate is sodium silicate;

[0051] Among them, the molar ratio of nickel and silicon atoms is 1.5-2; the concentration of sodium hydroxide is 2-10wt%; the hydrothermal reaction temperature is 190-200°C, and the reaction time is 12-48h; the calcination temperature in H2 atmosphere is 300-400°C, and the calcination time is 0.5-2h.

[0052] In some preferred embodiments, in step (2), the manganese salt is manganese nitrate or manganese chloride; the heating evaporation temperature is 80-90°C; the muffle furnace calcination temperature is 400-450°C, and the calcination time is 1-4h; the hydrogen reduction temperature is 300-400°C, and the H2 reduction time is 0.5-2h.

[0053] In addition, the present invention also provides an application of a multilayer nickel silicate nanotube catalyst regulated by metal manganese in a CO2 photothermal hydrogenation methanation reaction.

[0054] In some preferred embodiments, the conditions for the CO2 photothermal hydrogenation methanation reaction are: the raw gas composition is a molar ratio of H2:CO2 of 4:1; the reaction pressure is normal pressure; and the light source is a 300W xenon lamp.

[0055] All raw materials used in the examples of the present invention are commercially available.

[0056] The technical solution of the present invention is further illustrated by the following embodiments.

[0057] Example 1

[0058] (1) Preparation of multilayer nickel silicate nanotubes (NNSO):

[0059] 0.74g NiCl2·6H2O was dissolved in 30mL deionized water, Na2SiO3·9H2O was dissolved in water to form a solution with a concentration of 0.5mol / L, 4mL 0.5mol / L sodium silicate solution was quickly added to the nickel chloride solution to form a light green precipitate, stirred for 10min, 9.0wt% (3.6g) NaOH was added and stirred for 10min, then transferred to a polytetrafluoroethylene reactor, and hydrothermally reacted at 190-200℃ for 48h. The obtained light green precipitate was washed with deionized water and centrifuged several times, dried, and reduced with H2 at 400℃ for 2h, and finally multi-layer nickel silicate nanotubes were obtained. It is represented as NNSO.

[0060] (2) Preparation of 0.6% Mn / NNSO:

[0061] Dissolve 2.16 mg of MnCl2·4H2O in 10 mL of deionized water, add 100 mg of NNSO prepared in step (1), stir for 8 h, and let stand overnight. Heat at 80°C until the water is completely evaporated, place the resulting powder in a porcelain boat, and calcine at 400°C in a muffle furnace for 4 h. After calcination, reduce with H2 at 400°C for 2 h to finally obtain reduced Mn / NNSO. The mass percentage of Mn in Mn / NNSO is 0.6%.

[0062] Figure 1 The XRD pattern of a Mn / NNSO catalyst prepared in this embodiment shows that sharp peaks appear at 12.0°, 19.5°, 24.4°, 34.1°, 36.7°, and 60.5°, which are attributed to the characteristic peaks of Ni3Si2O5(OH)4 (JPCDS No.49-1859). At the same time, characteristic peaks of Ni(111), Ni(200), and Ni(220) appear at 44.5°, 51.8°, and 76.4° (JPCDS No.87-0712). Due to its high dispersibility and low loading, no relevant characteristic peaks of Mn were observed in the XRD spectrum.

[0063] Figure 2 This is a TEM image of a Mn / NNSO catalyst prepared in this example. Through transmission electron microscopy, it can be observed that the prepared nickel silicate material has a hollow tubular morphology, the inner diameter of the nanotube is about 8nm, the outer diameter is about 20nm, and the tube wall is a multi-layer structure. Nickel nanoparticles grow on the outer wall of the nanotube.

[0064] Example 2

[0065] The difference from Example 1 is that the amount of MnCl2·4H2O used in step (2) is 2.88 mg, and the mass percentage of Mn in the prepared Mn / NNSO is 0.8%. The rest is the same as Example 1.

[0066] Example 3

[0067] The difference from Example 1 is that the amount of MnCl2·4H2O used in step (2) is 3.60 mg, and the mass percentage of Mn in the prepared Mn / NNSO is 1.0%. The rest is the same as Example 1.

[0068] Example 4

[0069] The difference from Example 1 is that the amount of MnCl2·4H2O used in step (2) is 4.32 mg, and the mass percentage of Mn in the prepared Mn / NNSO is 1.2%. The rest is the same as Example 1.

[0070] Comparative Example

[0071] The difference from Example 1 is that step (2) is omitted, and multilayer nickel silicate nanotubes (NNSO) are prepared as catalysts; the rest are consistent with Example 1.

[0072] Effect verification

[0073] The performance of CO2 photothermal hydrogenation and methanation was tested on the multilayer nickel silicate nanotube catalyst regulated by metal manganese prepared in Examples 1-4 and the multilayer nickel silicate nanotube (NNSO) catalyst prepared in the comparative example. The test process was carried out in a fluid reaction bed. 30 mg of the catalyst was spread on the reaction bed layer. A mixture of H2 and CO2 (molar ratio of 4:1) was used as the reaction gas, a 300W xenon lamp was used as the light source, no additional heat source, and the pressure was normal pressure. Before the start of illumination, the reaction mixture was ventilated for 30 minutes to evacuate the air inside the reactor. After the internal air was evacuated, the illumination reaction was started. During the reaction, the volume flow rate of the reaction mixture was 20 mL / min, and the gas hourly space velocity (GHSV) was 40000 mL·g -1 ·h -1 The obtained gaseous products were analyzed by gas chromatography, such as Figure 3 The results are shown in Table 1. The relevant calculation formula is as follows:

[0074]

[0075]

[0076]

[0077] Note: Formula (1) is the calculation formula for gas hourly space velocity, Q in Indicates the volume flow rate of the mixed gas, m cat . represents the mass of the catalyst; Formula (2) is the CO2 conversion rate calculation formula, represents the CO2 concentration entering the reactor, It represents the CO2 concentration of the reactor; Formula (3) is the CH4 yield formula, S CH4 Indicates the selectivity of CH4.

[0078] Table 1 Photothermal catalytic performance of catalysts prepared in comparative examples and examples 1-4

[0079]

[0080] Conclusion: From Table 1 and Figure 3 It can be seen that the Mn / NNSO catalyst prepared by the present invention has excellent CO2 photothermal hydrogenation and methanation reaction activity. The catalytic activity of the multilayer nickel silicate nanotube material for CO2 photothermal hydrogenation and methanation reaction is not high, and the CH4 generation rate is only 0.91mmol·g -1 ·h -1 , the selectivity of methane is only 32%. When metal Mn is introduced, the methane generation rate is significantly improved. Specifically, the CH4 generation rate of the catalyst prepared in Example 1 of the present invention is 45.7 mmol·g -1 ·h -1 The selectivity of methane is 99.90%, and the CH4 generation rate of the catalyst prepared in Example 2 is 108.9 mmol·g -1 ·h -1 The selectivity of methane is 99.93%, and the CH4 generation rate of the catalyst prepared in Example 3 is 195.7 mmol·g -1 ·h -1 The selectivity of methane is 99.99%. The CH4 generation rate of the catalyst prepared in Example 4 is 59.6 mmol·g -1 ·h -1 , the selectivity for methane is 99.99%.

[0081] The above are only preferred specific implementations of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A method for preparing a multilayer nickel silicate nanotube catalyst regulated by metal manganese, characterized in that: The manganese salt is loaded onto the multilayer nickel silicate nanotubes by a wet impregnation method; then the multilayer nickel silicate nanotubes are calcined into black powder, and then reduced in a H2 atmosphere to obtain the metal manganese-regulated multilayer nickel silicate nanotube catalyst.

2. The method for preparing a multilayer nickel silicate nanotube catalyst regulated by metal manganese according to claim 1, characterized in that: The preparation steps of the multilayer nickel silicate nanotubes are as follows: A soluble silicon salt solution is dropped into a nickel salt solution to form a light green precipitate, sodium hydroxide is added and stirred, and then the mixture is transferred to a polytetrafluoroethylene reactor for a hydrothermal reaction. The obtained product is then washed, dried, and calcined under a H2 atmosphere to finally obtain the multilayer nickel silicate nanotubes.

3. The method for preparing a multilayer nickel silicate nanotube catalyst regulated by metal manganese according to claim 2, characterized in that: The molar ratio of nickel atoms to silicon atoms in the soluble silicon salt and the nickel salt solution is 1.5-2.

4. The method for preparing a multilayer nickel silicate nanotube catalyst regulated by metal manganese according to claim 2, characterized in that: The conditions of the hydrothermal reaction are: reaction temperature is 190-200° C., and reaction time is 12-48 hours.

5. The method for preparing a multilayer nickel silicate nanotube catalyst regulated by metal manganese according to claim 2, characterized in that: The calcination temperature in the calcination process is 300-400° C., and the calcination time is 0.5-2 h.

6. The method for preparing a multilayer nickel silicate nanotube catalyst regulated by metal manganese according to claim 1, characterized in that: During the calcination process, the calcination temperature is 400-450° C. and the calcination time is 1-4 hours.

7. The method for preparing a multilayer nickel silicate nanotube catalyst regulated by metal manganese according to claim 1, characterized in that: During the reduction reaction, the reduction temperature is 300-400° C. and the time is 0.5-2 h.

8. A multilayer nickel silicate nanotube catalyst regulated by metal manganese, characterized in that: The compound is prepared by the preparation method described in any one of claims 1 to 7.

9. The metal manganese-regulated multilayer nickel silicate nanotube catalyst according to claim 8, characterized in that: The mass percentage of metal manganese in the metal manganese-regulated multilayer nickel silicate nanotube catalyst is 0.6-1.2%.

10. Use of the metal manganese-regulated multilayer nickel silicate nanotube catalyst according to any one of claims 8 to 9 in catalyzing CO2 photothermal or thermal hydrogenation methanation reactions.

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