MgO-coated SiO2-loaded nickel catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and discloses an MgO-coated SiO2-loaded nickel catalyst as well as a preparation method and application thereof. The structure of the catalyst is Ni-MOx / SiO2 (at) MgO, Ni is an active component, SiO2 (at) MgO is a composite material formed by uniformly coating MgO on the surface of SiO2, and MOx is an auxiliary agent added in the catalyst; according to the preparation method, urea is slowly decomposed in a solution by regulating the temperature, concentration and other conditions of a synthesis system, so that the concentration of OH <-> is gradually increased, and the SiO2 (at) MgO composite material with high specific surface area and good structural uniformity is constructed by utilizing the relationship between the pH value and the isoelectric point and the electronegativity of particles. Compared with a traditional method, the method has the advantages that the specific surface area, water absorption loss resistance and CO2 activation capacity of MgO are remarkably improved. On the basis, metal Ni is loaded on the composite material, and the prepared catalyst shows excellent stability and catalytic performance in CO2 methanation reaction and has good industrial application potential.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalysts. Specifically, it relates to a catalyst with MgO-coated SiO2 material as a carrier and nickel as an active component, its preparation method, and its application in the field of CO2 methanation. Background Art

[0002] With the increasingly severe global climate change problem, carbon dioxide (CO2) emission reduction and energy transition have become key issues for the current social sustainable development. The CO2 methanation reaction, as an effective way to convert CO2 into methane, has attracted wide attention. This process can not only directly reduce the CO2 concentration in the atmosphere, thus alleviating the greenhouse effect, but also convert it into high-value clean energy methane to achieve efficient carbon recycling.

[0003] In addition, with the rapid development of renewable energy such as wind energy and solar energy, their intermittency and volatility have brought major challenges to energy storage. When the energy supply is excessive, using electrolyzed water to produce hydrogen and further methanating hydrogen with CO2 to generate methane can not only effectively store the excess electric energy, but also achieve large-scale transportation and distribution of methane through the existing natural gas pipeline network. This method provides seasonal and regional regulation capabilities for the utilization of renewable energy. At the same time, as an important energy carrier, the mature storage and transportation infrastructure of methane further enhances the practicality of this technology. Therefore, the CO2 methanation reaction has important strategic significance in achieving emission reduction, promoting energy structure optimization, and improving energy utilization efficiency.

[0004] In the CO2 methanation reaction, the choice of catalyst plays a decisive role in the reaction performance. At present, catalysts are mainly divided into two categories: precious metals and non-precious metals. Studies have shown that precious metal catalysts (such as Ru, Rh, Pd, etc.) have excellent catalytic activity and selectivity, but their high price and limited reserves limit their large-scale industrial application. Non-precious metal catalysts (such as Ni, Co, Fe, etc.) have attracted much attention due to their low cost and abundant resources. Among them, although Co catalysts show certain activity in the CO2 methanation reaction, their catalytic selectivity is low and they are prone to generate more by-products (such as CO), thereby reducing the yield of methane; secondly, Fe catalysts are more inclined to catalyze the Fischer-Tropsch synthesis reaction in CO2 methanation to generate long-chain hydrocarbon compounds rather than methane, which makes their application range in the field of CO2 methanation narrow; Ni catalysts have become a research hotspot due to their high activity, good selectivity and low cost. However, nickel-based catalysts are prone to sintering under high temperature conditions, which affects the long-term stability of the catalyst. At the same time, since the CO2 molecule has a highly stable chemical structure and the carbon element is in its highest oxidation state, how to effectively activate CO2 under low temperature conditions remains a scientific problem that needs to be solved. Therefore, developing a nickel-based catalyst with high activity, good selectivity and excellent stability, especially a catalyst that performs well at low temperatures, is one of the core issues in promoting the industrial application of CO2 methanation reactions.

[0005] Support materials play a vital role in catalyst performance. Common CO2 methanation catalyst supports include SiO2, Al2O3, TiO2, ZrO2, etc., among which SiO2 is widely used due to its low cost, good mechanical strength and large specific surface area. However, the chemical activity of SiO2 is relatively weak and lacks sufficient active adsorption sites, which limits its performance in CO2 methanation reactions. In order to improve the activity and stability of the catalyst, researchers began to explore strategies for compounding different support materials in order to improve the catalytic effect. Summary of the invention

[0006] The purpose of the present invention is to overcome the problems of low activity and poor stability of existing CO2 methanation catalysts, and to provide a MgO-coated SiO2-loaded nickel catalyst and a preparation method and application thereof. The catalyst preparation method controls the gradual decomposition of urea in a synthesis system to achieve uniform coating of MgO on the SiO2 surface by electrostatic adsorption in the form of slow precipitation of Mg(OH)2; not only does it avoid the dependence of traditional processes on expensive precursors, but it also obtains a SiO2@MgO composite material with uniform particle size, good dispersibility and large specific surface area by precisely controlling the reaction conditions, which significantly improves its performance as a catalyst carrier, and provides an efficient, economical and environmentally friendly solution for CO2 methanation reactions.

[0007] According to one aspect of the present invention, there is provided a MgO-coated SiO2-supported nickel catalyst, and its composition is Ni-MO x / SiO2@MgO; wherein: Ni is the active component of the catalyst, and MO x is an additive in the catalyst, and MO x is at least one of La2O3 and CeO2; SiO2@MgO is a composite material of MgO-coated SiO2 and is used as the carrier of the catalyst; the molar ratio of SiO2 to MgO in SiO2@MgO is (1.0-4.0):1; SiO2@MgO is prepared by a deposition method, and urea is used as a precipitating agent to uniformly coat MgO on the surface of SiO2 to form the SiO2@MgO composite material.

[0008] The SiO2@MgO material consists of a silica (SiO2) core and a magnesium oxide (MgO) coating layer. SiO2 serves as the main carrier and provides a high surface area. MgO can activate CO2 and can also interact with the supported metal nickel nanoparticles to inhibit the sintering of nickel. The molar ratio of SiO2 to MgO is maintained in the range of (1.0-4.0):1 to optimize the distribution of MgO on the surface of SiO2. The uniformly coated MgO is beneficial to the high dispersion of nano-metal nickel and is conducive to the activation of CO2.

[0009] Ni-MO x / SiO2@MgO catalyst uses urea as a precipitating agent to control the slow deposition formation process, so as to achieve uniform coating of MgO on the surface of SiO2 through electrostatic adsorption, thereby significantly improving the catalyst performance.

[0010] Furthermore, the mass fraction of Ni in the catalyst is 5-20%.

[0011] Nickel (Ni) is the active catalytic component of the catalyst. Nickel is loaded on the SiO2@MgO material to promote the methanation of CO2. The nickel component is uniformly distributed on the MgO-coated SiO2 carrier to maximize the catalytic efficiency.

[0012] Furthermore, in terms of molar ratio, Ni:MO x =1:(0-0.3).

[0013] According to another aspect of the present invention, there is provided a preparation method of the above MgO-coated SiO2-supported nickel catalyst, including the following process:

[0014] (1) Dissolve magnesium nitrate in deionized water under stirring until it is completely dissolved to obtain a uniform solution;

[0015] (2) Add fumed silica to the solution obtained in step (1) and perform ultrasonic dispersion until the silica is completely dispersed to form a uniform mixture;

[0016] (3) Add 1.0 - 5.0 mol / L urea to the mixture obtained in step (2), stir to dissolve it, then heat it in a water bath at 75 - 95 °C while continuously stirring to form a solid-liquid mixture;

[0017] (4) Filter the solid-liquid mixture obtained in step (3), separate the solid, and then dry the obtained solid;

[0018] (5) Calcinate the dried solid obtained in step (4) to prepare the SiO2@MgO support;

[0019] (6) Prepare an aqueous solution of nickel nitrate, or an aqueous solution of nickel nitrate and the corresponding nitrate of the promoter and citric acid, and uniformly impregnate the SiO2@MgO support prepared in step (5) by the equal-volume impregnation method; then seal the mixture, first dry it in an oven and then further dry it to obtain a dried product;

[0020] (7) Calcinate the dried product obtained in step (6) to obtain a catalyst precursor;

[0021] (8) Pass a reducing gas into the catalyst precursor prepared in step (7) for reduction treatment to obtain the catalyst Ni-MO x / SiO2@MgO.

[0022] In the preparation method of the present invention, urea is used as a precipitant, and its slow decomposition characteristic can precisely control the generation rate of OH- in the solution by regulating the temperature of the reaction system and the concentration of urea. Urea decomposes step by step under heating conditions, slowly releasing OH-, and gradually increasing the pH value of the solution. During this process, the free Mg 2+ in the solution gradually combines with OH- to form a precipitate of Mg(OH)2. Since Mg(OH)2 and SiO2 are in solution environments with pH values lower and higher than their respective isoelectric points, they are respectively positively and negatively charged, and under the influence of electrostatic interaction, they attract each other and uniformly coat on the surface of SiO2. After subsequent calcination treatment, the deposited Mg(OH)2 is transformed into uniformly distributed MgO, thus forming a structurally stable SiO2@MgO composite material.

[0023] This process makes full use of the slowness of urea decomposition and the electrostatic interaction of different substances with different isoelectric points having different charge properties in the same pH solution, ensuring the uniformity and continuity of the coating of MgO on the surface of SiO2. This method overcomes the defects of low specific surface area and easy loss of pure MgO, and ensures that the catalyst has high activation ability and excellent stability in the CO2 methanation reaction.

[0024] By controlling the gradual decomposition of urea in the synthesis system, the present invention realizes that MgO is uniformly coated on the surface of SiO2 by electrostatic adsorption in the form of slow precipitation of Mg(OH)2. This method not only avoids the dependence on expensive precursors in the traditional process, but also obtains SiO2@MgO composites with uniform particle size, good dispersion and large specific surface area by precisely controlling the reaction conditions, significantly improving its performance as a catalyst support and providing an efficient, economical and environmentally friendly solution for the CO2 methanation reaction.

[0025] Further, the concentration of magnesium nitrate in the solution obtained in step (1) is 0.05 - 0.20 mol / L.

[0026] Further, after the urea is stirred and dissolved in step (3), the pH value of the solution is 5.5 - 6.4.

[0027] Further, the stirring time of the water bath heating in step (3) is 5 - 6 h.

[0028] Further, the drying in step (4) is carried out in an oven with a temperature range of 60°C - 120°C for a duration of 6 - 24 h.

[0029] Further, the calcination temperature range in step (5) is 600 - 900°C, the calcination time is 2 - 6 h, and the heating rate is 1 - 10°C / min.

[0030] Further, the molar ratio of the sum of nickel nitrate and the corresponding nitrate of the promoter to citric acid in step (6) is 1:(1 - 3).

[0031] Further, the sealed standing time in step (6) is 12 - 48 h.

[0032] Further, the drying temperature in step (6) is 60°C - 90°C, and it is carried out in an oven for 5 - 7 h.

[0033] Further, the drying temperature range in step (6) is 100°C - 150°C, and it is carried out in an oven for 6 - 24 h.

[0034] Further, the calcination temperature range in step (7) is 600 - 900°C, the calcination time is 2 - 6 h, and the heating rate is 1 - 10°C / min.

[0035] Further, the flow rate of the reducing gas in step (8) is 10 - 30 mL / min, the reduction temperature range is 600 - 800°C, the heating rate is 1 - 10°C / min, and the reduction process lasts for 1 - 3 h.

[0036] Further, the reducing gas in step (8) includes at least one of hydrogen and carbon monoxide.

[0037] According to another aspect of the present invention, there is provided an application of the above-mentioned MgO-coated SiO2-supported nickel catalyst in the CO2 methanation reaction.

[0038] Further, the catalyst is added to a fixed-bed reactor, and carbon dioxide and hydrogen are introduced into the reactor at a temperature of 200-450 °C and a pressure of 0.1-5 MPa with a volumetric space velocity of 5000-60000 mL / (gcat·h), wherein the molar ratio of carbon dioxide to hydrogen is 1:(1-5), to obtain the target product methane.

[0039] The beneficial effects of the present invention are as follows:

[0040] (1) The MgO-coated SiO2-supported nickel catalyst of the present invention makes full use of the high specific surface area characteristics of SiO2. Through the electrostatic adsorption effect, it ensures that MgO can be uniformly coated on the surface of SiO2 to form a composite material with a high specific surface area. The Ni-based catalyst prepared in this way not only has a relatively large specific surface area, but also MgO is not easily lost and Ni is not easily sintered, and has higher activity, which effectively improves the catalytic performance and reaction efficiency of the catalyst.

[0041] (2) The preparation method of the MgO-coated SiO2-supported nickel catalyst of the present invention can control Mg in the solution by adjusting the temperature and solution concentration in the synthesis process. 2+ Mg(OH)2 is slowly formed, and at the same time, the electrostatic adsorption effect between positive and negative ions optimizes the coating effect of MgO and improves the surface properties of the catalyst and its stability in the catalytic reaction.

[0042] (3) When the MgO-coated SiO2-supported nickel catalyst of the present invention is used for the CO2 methanation reaction, it exhibits excellent catalytic activity and good thermal stability. The reaction conversion rate can reach 98%, and it has strong potential for industrial application, which can provide reliable technical support for the efficient conversion and utilization of CO2. Description of the Drawings

[0043] Figure 1 Zeta potentials of SiO2@MgO, SiO2, and MgO at different pH values in Example 1.

[0044] Figure 2 X-ray diffraction (XRD) patterns of SiO2@MgO and the catalyst precursor in Example 1.

[0045] Figure 3 STEM images and elemental distribution maps of SiO2@MgO in Example 1.

[0046] Figure 4Local enlarged STEM image and line scan of SiO2@MgO in Example 1.

[0047] Figure 5 Nitrogen adsorption - desorption isotherms and specific surface areas of SiO2@MgO and Ni / SiO2@MgO in Example 1.

[0048] Figure 6 Stability test results of the catalyst in the CO2 methanation reaction in Example 1. Detailed implementation manners

[0049] To make the objectives, technical solutions and advantages of the present invention clearer and more understandable, the following further elaborates the present invention in detail with reference to specific examples and drawings.

[0050] Example 1

[0051] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.05 mol / L.

[0052] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1, and use ultrasonic waves to stir until the silica is completely dispersed to obtain a uniform mixture. The molar concentration of silica is 0.05 mol / L.

[0053] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 1.5 mol / L. At this time, the pH of the system is 5.7. Stir in a water bath at 95°C for 5 hours to obtain a solid - liquid mixture.

[0054] 4. Filter the solid - liquid mixture obtained in step 3, and dry the filtered solid in an oven at 120°C for 24 h.

[0055] 5. Calcinate the solid dried in step 4 at 700°C for 5 hours, with a heating rate of 2°C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1, to obtain the SiO2@MgO composite material.

[0056] Test the zeta potential of SiO2@MgO, SiO2, and MgO at different pH values. Before the test, disperse the samples with a 2 mol / L KCl solution, and use 1 mol / L sodium hydroxide and hydrochloric acid to adjust the solution to different pH values respectively. According to Figure 1 As shown in the zeta potential results, the isoelectric points of SiO2@MgO, SiO2, and MgO are 9.1, 3.0, and 9.5 respectively, indicating that the isoelectric point of SiO2@MgO is close to that of MgO, and is quite different from that of SiO2, indicating that the outer surface of SiO2@MgO is mainly MgO, and MgO well coats the surface of SiO2.

[0057] According to Figure 2 the XRD pattern shown in Figure 2 , the grain size of MgO in SiO2@MgO is small, and the corresponding characteristic peaks can hardly be identified; according to Figure 3 the element distribution map shown in Figure 3 , the distribution of Mg element on the surface of SiO2@MgO is uniform, meeting the expectation. As Figure 4 shown, further line scan analysis indicates that the outer layer of the particle is mainly Mg element and the inner layer is Si element, indicating that SiO2@MgO has a structure with a MgO shell coating a SiO2 core.

[0058] The specific surface area of SiO2@MgO was measured: the sample was vacuum degassed at 300 °C for 4 hours to remove surface adsorbed substances, and then N2 adsorption was carried out in the range of relative pressure 0.05 - 0.30 to obtain the adsorption - desorption isotherm, and its specific surface area (SBET) was calculated by the BET equation. As Figure 5 shown, the specific surface area of SiO2@MgO is 190 m 2 / g, which is larger than the specific surface area of 105 m 2 / g of MgO particles synthesized by the microemulsion method found in the literature (MgO nanostructured microspheres synthesized by an interfacial reaction in a solid - stabilized emulsion[J / OL].Materials Letters,2006,60(29 - 30):3511 - 3513.DOI:10.1016 / j.matlet.2006.03.040.).

[0059] 6. A nickel nitrate solution with a concentration of 1.27 mol / L was added dropwise to the carrier obtained in step 5 by the equal - volume impregnation method. After sealing and standing for 24 hours, it was dried in an oven at 80 °C for 6 hours and then dried at 120 °C for 12 hours to obtain a dried product.

[0060] 7. The dried product obtained in step 6 was calcined at 800 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0061] According to Figure 2 the XRD pattern shown in Figure 2 , the crystal phase of NiO was observed, and as Figure 5 shown, its specific surface area is 158 m 2 / g.

[0062] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, and a heating rate of 2 °C / min, and reduce it at 650 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO with a mass fraction of Ni of 15%.

[0063] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor to conduct a CO2 methanation reaction test.

[0064] Under the conditions of a space velocity of 60000 mL / (g·cat·h) and a pressure of 0.1 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 4.15%, and the CH4 selectivity is 100%; at 350 °C, the CO2 conversion rate is 61.73%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 79.36%, and the CH4 selectivity is 99.36%.

[0065] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 6.87%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 73.38%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 97.95%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 96.05%, and the CH4 selectivity is 99.32%.

[0066] Under the conditions of a space velocity of 5000 mL / (g·cat·h) and a pressure of 5 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 11.32%, and the CH4 selectivity is 100%; at 350 °C, the CO2 conversion rate is 79.43%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 96.73%, and the CH4 selectivity is 100%.

[0067] Perform a stability test on the catalyst at 500 °C. The reaction conditions are: the reaction gas composition is H2:CO2 = 4:1, the reaction pressure is 3 MPa, the temperature is 550 °C; the reaction space velocity is 15000 mL / (g cat h). From Figure 6 It can be seen that the catalyst shows no tendency of activity decline within 100 hours and has excellent stability.

[0068] Example 2

[0069] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.05 mol / L.

[0070] 2. Add fumed silica to the magnesium nitrate solution obtained in Step 1, and use ultrasonic stirring until the silica is completely dispersed to obtain a uniform mixture. The molar concentration of silica is 0.05 mol / L.

[0071] 3. Add urea to the mixture obtained in Step 2 and stir evenly. The concentration of urea is 1.5 mol / L. At this time, the pH of the system is 5.7. Stir in a water bath at 95 °C for 6 hours to obtain a solid-liquid mixture.

[0072] 4. Filter the solid-liquid mixture obtained in Step 3 by suction filtration, and dry the filtered solid in an oven at 120 °C for 24 hours.

[0073] 5. Calcinate the solid dried in Step 4 at 700 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0074] 6. Drop the nickel nitrate solution with a concentration of 1.7 mol / L onto the support obtained in Step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 24 hours to obtain a dried product.

[0075] 7. Calcinate the dried product obtained in Step 6 at 600 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0076] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, with a heating rate of 2 °C / min, and reduce it at 650 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO, and the mass fraction of Ni is 20%. It can also be found through zeta potential, XRD spectra, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0077] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor for CO2 methanation reaction testing.

[0078] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 5.97%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 81.70%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 91.81%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 91.44%.

[0079] Example 3

[0080] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.05 mol / L.

[0081] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and use ultrasonic waves to stir until the silica is completely dispersed to obtain a homogeneous mixture. The molar concentration of silica is 0.05 mol / L.

[0082] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 1.5 mol / L. At this time, the pH of the system is 5.7. Stir in a water bath at 90 °C for 5 hours to obtain a solid-liquid mixture.

[0083] 4. Filter the solid-liquid mixture obtained in step 3 by suction filtration, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0084] 5. Calcinate the solid dried in step 4 at 800 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0085] 6. Drop a nickel nitrate solution with a concentration of 1.7 mol / L onto the support obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0086] 7. Calcinate the dried product obtained in step 6 at 700 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0087] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, with a heating rate of 2 °C / min, and reduce it at 650 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO. The mass fraction of Ni is 20%. It can also be found through zeta potential, XRD pattern, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0088] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor for CO2 methanation reaction testing.

[0089] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 12.01%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 91.79%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 93.55%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 91.68%.

[0090] Example 4

[0091] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.05 mol / L.

[0092] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and stir with ultrasonic waves until the silica is completely dispersed to obtain a uniform mixture. The molar concentration of the silica is 0.05 mol / L.

[0093] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 1.5 mol / L. At this time, the pH of the system is 5.7. Stir in a water bath at 85 °C for 5 hours to obtain a solid-liquid mixture.

[0094] 4. Filter the solid-liquid mixture obtained in step 3, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0095] 5. Calcinate the solid dried in step 4 at 900 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0096] 6. Drop a nickel nitrate solution with a concentration of 0.4 mol / L onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0097] 7. Calcinate the dried product obtained in step 6 at 900 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0098] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, heat it at a rate of 2 °C / min, and reduce it at 650 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO. The mass fraction of Ni is 5%. It can also be found through zeta potential, XRD spectra, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0099] 9. Feed a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor and conduct a CO2 methanation reaction test.

[0100] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 2.01%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 55.42%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 85.66%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 86.37%.

[0101] Example 5

[0102] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.05 mol / L.

[0103] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and use ultrasonic waves to stir until the silica is completely dispersed to obtain a uniform mixture. The molar concentration of silica is 0.05 mol / L.

[0104] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 3.5 mol / L. At this time, the pH of the system is 5.9. Stir in a water bath at 95 °C for 5 hours to obtain a solid-liquid mixture.

[0105] 4. Filter the solid-liquid mixture obtained in step 3, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0106] 5. Calcinate the solid dried in step 4 at 700 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0107] 6. Drop a nickel nitrate solution with a concentration of 0.85 mol / L onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0108] 7. Calcinate the dried product obtained in step 6 at 900 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0109] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, and a heating rate of 2 °C / min. Reduce it at 650 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO, with the mass fraction of Ni being 10%. It can also be found through zeta potential, XRD spectra, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0110] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor for the CO2 methanation reaction test.

[0111] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 3.44%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 59.17%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 89.47%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 88.12%.

[0112] Example 6

[0113] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.05 mol / L.

[0114] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and use ultrasonic stirring until the silica is completely dispersed to obtain a homogeneous mixture, with the molar concentration of silica being 0.05 mol / L.

[0115] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 2.5 mol / L, and the pH of the system is 5.7 at this time. Stir in a water bath at 95 °C for 5 hours to obtain a solid-liquid mixture.

[0116] 4. Filter the solid-liquid mixture obtained in step 3, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0117] 5. Calcinate the solid dried in step 4 at 800 °C for 5 hours, with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0118] 6. Drop the nickel nitrate solution with a concentration of 0.85 mol / L onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0119] 7. Calcinate the dried product obtained in step 6 at 800 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0120] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, and heat it at a rate of 2 °C / min. Reduce it at 650 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO, and the mass fraction of Ni is 10%. It can also be found through zeta potential, XRD patterns, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0121] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor for CO2 methanation reaction testing.

[0122] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 5.14%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 57.51%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 77.93%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 85.49%.

[0123] Example 7

[0124] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.05 mol / L.

[0125] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and use ultrasonic stirring until the silica is completely dispersed to obtain a uniform mixture, and the molar concentration of silica is 0.05 mol / L.

[0126] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 1.5 mol / L, and the pH of the system is 5.7 at this time. Stir in a water bath at 85 °C for 6 hours to obtain a solid-liquid mixture.

[0127] 4. Filter the solid-liquid mixture obtained in step 3, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0128] 5. Calcinate the solid dried in step 4 at 800 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0129] 6. The nickel nitrate solution with a concentration of 1.7 mol / L was added dropwise to the support obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, it was dried in an oven at 80 °C for 6 hours and then dried at 120 °C for 12 hours to obtain a dried product.

[0130] 7. The dried product obtained in step 6 was calcined at 900 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0131] 8. The obtained catalyst precursor was placed in a reactor, and H2 gas with a flow rate of 20 mL / min was introduced. The heating rate was 2 °C / min, and it was reduced at 650 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO with a Ni mass fraction of 20%. It was also found through zeta potential, XRD spectra, and specific surface area tests that MgO well coated the surface of SiO2 and had a high specific surface area.

[0132] 9. A mixed gas with a molar ratio of CO2 to H2 of 1:4 was introduced into the reactor for CO2 methanation reaction testing.

[0133] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction was as follows: at 200 °C, the CO2 conversion rate was 6.48% and the CH4 selectivity was 100%; at 300 °C, the CO2 conversion rate was 60.17% and the CH4 selectivity was 100%; at 400 °C, the CO2 conversion rate was 79.11% and the CH4 selectivity was 100%; at 450 °C, the CO2 conversion rate was 90.05%.

[0134] Example 8

[0135] 1. Magnesium nitrate was dissolved in deionized water and stirred evenly to obtain a magnesium nitrate solution with a concentration of 0.20 mol / L.

[0136] 2. Fumed silica was added to the magnesium nitrate solution obtained in step 1, and ultrasonic stirring was used until the silica was completely dispersed to obtain a uniform mixture with a silica molar concentration of 0.20 mol / L.

[0137] 3. Urea was added to the mixture obtained in step 2 and stirred evenly with a urea concentration of 2.5 mol / L. At this time, the pH of the system was 5.9, and it was stirred in a water bath at 75 °C for 6 hours to obtain a solid-liquid mixture.

[0138] 4. The solid-liquid mixture obtained in step 3 was filtered by suction, and the filtered solid was dried in an oven at 120 °C for 12 hours.

[0139] 5. Calcinate the solid after drying in step 4 at 800 °C for 4 hours, with a heating rate of 1 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0140] 6. Drop the nickel nitrate solution with a concentration of 1.7 mol / L onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 12 hours, dry it in an oven at 90 °C for 7 hours, and then dry it at 150 °C for 12 hours to obtain a dried product.

[0141] 7. Calcinate the dried product obtained in step 6 at 900 °C for 6 hours, with a heating rate of 1 °C / min, to obtain a catalyst precursor.

[0142] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 30 mL / min, with a heating rate of 1 °C / min, and reduce it at 800 °C for 3 hours to obtain the catalyst Ni / SiO2@MgO, with the mass fraction of Ni being 20%. It can also be found through zeta potential, XRD patterns, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0143] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor to conduct a CO2 methanation reaction test.

[0144] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 5.82%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 46.75%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 68.91%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 80.11%.

[0145] Example 9

[0146] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.10 mol / L.

[0147] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and use ultrasonic stirring until the silica is completely dispersed to obtain a uniform mixture, with the molar concentration of silica being 0.10 mol / L.

[0148] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 2.0 mol / L, and the pH of the system is 5.7 at this time. Stir in a water bath at 80 °C for 5 hours to obtain a solid-liquid mixture.

[0149] 4. Filter the solid-liquid mixture obtained in step 3, and dry the filtered solid in an oven at 100 °C for 10 hours.

[0150] 5. Calcinate the solid dried in step 4 at 600 °C for 5 hours with a heating rate of 5 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1, and the SiO2@MgO composite material is obtained.

[0151] 6. Drop the nickel nitrate solution with a concentration of 1.28 mol / L onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 36 hours, dry it in an oven at 85 °C for 5 hours, and then dry it at 140 °C for 6 hours to obtain a dried product.

[0152] 7. Calcinate the dried product obtained in step 6 at 900 °C for 5 hours with a heating rate of 8 °C / min to obtain a catalyst precursor.

[0153] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 15 mL / min, and reduce it at 700 °C for 2.5 hours with a heating rate of 5 °C / min to obtain the catalyst Ni / SiO2@MgO, and the mass fraction of Ni is 15%. It can also be found through zeta potential, XRD spectra, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0154] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:3 into the reactor for CO2 methanation reaction testing.

[0155] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 7.48%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 74.22%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 89.53%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 91.24%.

[0156] Example 10

[0157] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.15 mol / L.

[0158] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1, and stir it with ultrasonic waves until the silica is completely dispersed to obtain a uniform mixture, and the molar concentration of silica is 0.15 mol / L.

[0159] 3. Urea is added to the mixed solution obtained in step 2 and stirred evenly. The concentration of urea is 3.0 mol / L. At this time, the pH of the system is 5.8. It is stirred in a water bath at 90 °C for 5 hours to obtain a solid-liquid mixture.

[0160] 4. The solid-liquid mixture obtained in step 3 is filtered by suction, and the filtered solid is dried in an oven at 120 °C for 6 hours.

[0161] 5. The solid dried in step 4 is calcined at 800 °C for 5 hours, and the heating rate is 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1, and the SiO2@MgO composite material is obtained.

[0162] 6. A nickel nitrate solution with a concentration of 1.28 mol / L is added dropwise to the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, it is dried in an oven at 80 °C for 6 hours, and then dried at 120 °C for 12 hours to obtain a dried product.

[0163] 7. The dried product obtained in step 6 is calcined at 800 °C for 5 hours, and the heating rate is 2 °C / min to obtain a catalyst precursor.

[0164] 8. The obtained catalyst precursor is placed in a reactor, and H2 gas with a flow rate of 10 mL / min is introduced. The heating rate is 10 °C / min, and it is reduced at 600 °C for 1 hour to obtain the catalyst Ni / SiO2@MgO, and the mass fraction of Ni is 15%. It can also be found through zeta potential, XRD spectrum and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0165] 9. A mixed gas with a molar ratio of CO2 to H2 of 1:5 is introduced into the reactor for CO2 methanation reaction testing.

[0166] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 7.69%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 72.67%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 90.15%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 90.04%.

[0167] Example 11

[0168] 1. Magnesium nitrate is dissolved in deionized water and stirred evenly to obtain a magnesium nitrate solution with a concentration of 0.20 mol / L.

[0169] 2. Add fumed silica to the magnesium nitrate solution obtained in Step 1, and stir with ultrasonic waves until the silica is completely dispersed to obtain a homogeneous mixture. The molar concentration of silica is 0.20 mol / L.

[0170] 3. Add urea to the mixture obtained in Step 2 and stir evenly. The concentration of urea is 3.5 mol / L. At this time, the pH of the system is 6.0. Stir in a water bath at 75 °C for 6 hours to obtain a solid-liquid mixture.

[0171] 4. Filter the solid-liquid mixture obtained in Step 3 by suction filtration, and dry the filtered solid in an oven at 60 °C for 24 hours.

[0172] 5. Calcinate the solid dried in Step 4 at 600 °C for 5 hours with a heating rate of 8 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0173] 6. Drop the nickel nitrate solution with a concentration of 0.43 mol / L onto the support obtained in Step 5 by the equal-volume impregnation method. After sealing and standing for 36 hours, dry it in an oven at 70 °C for 6 hours, and then dry it at 100 °C for 24 hours to obtain a dried product.

[0174] 7. Calcinate the dried product obtained in Step 6 at 600 °C for 3 hours with a heating rate of 10 °C / min to obtain a catalyst precursor.

[0175] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, and heat it at a rate of 2 °C / min. Reduce it at 650 °C for 1 hour to obtain the catalyst Ni / SiO2@MgO, and the mass fraction of Ni is 5%. It can also be found through zeta potential, XRD patterns, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0176] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor to conduct a CO2 methanation reaction test.

[0177] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 2.11%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 55.28%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 67.97%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 70.35%.

[0178] Example 12

[0179] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.05 mol / L.

[0180] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and use ultrasonic waves to stir until the silica is completely dispersed to obtain a uniform mixture. The molar concentration of silica is 0.05 mol / L.

[0181] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 5.0 mol / L. At this time, the pH of the system is 6.4. Stir in a water bath at 95 °C for 5 hours to obtain a solid-liquid mixture.

[0182] 4. Filter the solid-liquid mixture obtained in step 3 by suction filtration, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0183] 5. Calcinate the solid dried in step 4 at 700 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0184] 6. Drop a nickel nitrate solution with a concentration of 1.70 mol / L onto the support obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 48 hours, dry it in an oven at 60 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0185] 7. Calcinate the dried product obtained in step 6 at 600 °C for 2 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0186] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, with a heating rate of 2 °C / min, and reduce it at 600 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO. The mass fraction of Ni is 20%. It can also be found through zeta potential, XRD patterns, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0187] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:2 into the reactor for CO2 methanation reaction testing.

[0188] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 9.43%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 81.12%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 91.88%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 92.36%.

[0189] Example 13

[0190] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.05 mol / L.

[0191] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and stir with ultrasonic waves until the silica is completely dispersed to obtain a uniform mixture. The molar concentration of the silica is 0.20 mol / L.

[0192] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 1 mol / L. At this time, the pH of the system is 5.5. Stir in a water bath at 95 °C for 5 hours to obtain a solid-liquid mixture.

[0193] 4. Filter the solid-liquid mixture obtained in step 3, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0194] 5. Calcinate the solid dried in step 4 at 900 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 4:1 to obtain the SiO2@MgO composite material.

[0195] 6. Drop a nickel nitrate solution with a concentration of 1.70 mol / L onto the support obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0196] 7. Calcinate the dried product obtained in step 6 at 900 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0197] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, heat it at a rate of 2 °C / min, and reduce it at 800 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO, and the mass fraction of Ni is 20%. It can also be found through zeta potential, XRD spectra, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0198] 9. Feed a mixed gas with a molar ratio of CO2 to H2 of 1:1 into the reactor and conduct a CO2 methanation reaction test.

[0199] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 8.16%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 79.64%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 90.48%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 89.44%.

[0200] Example 14

[0201] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.20 mol / L.

[0202] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and use ultrasonic waves to stir until the silica is completely dispersed to obtain a uniform mixture. The molar concentration of silica is 0.5 mol / L.

[0203] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 3.5 mol / L. At this time, the pH of the system is 5.8. Stir in a water bath at 95 °C for 6 hours to obtain a solid-liquid mixture.

[0204] 4. Filter the solid-liquid mixture obtained in step 3, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0205] 5. Calcinate the solid dried in step 4 at 900 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 2.5:1 to obtain the SiO2@MgO composite material.

[0206] 6. Drop a nickel nitrate solution with a concentration of 1.70 mol / L onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0207] 7. Calcinate the dried product obtained in step 6 at 900 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0208] 8. The obtained catalyst precursor was placed in a reactor, and H2 gas with a flow rate of 20 mL / min was introduced. The heating rate was 2 °C / min, and it was reduced at 700 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO, with the mass fraction of Ni being 20%. It was also found through zeta potential, XRD patterns, and specific surface area tests that MgO well coated the surface of SiO2 and had a relatively high specific surface area.

[0209] 9. A mixed gas with a molar ratio of CO2 to H2 of 1:4 was introduced into the reactor for the CO2 methanation reaction test.

[0210] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction was as follows: at 200 °C, the CO2 conversion rate was 6.14%, and the CH4 selectivity was 100%; at 300 °C, the CO2 conversion rate was 68.37%, and the CH4 selectivity was 100%; at 400 °C, the CO2 conversion rate was 80.15%, and the CH4 selectivity was 100%; at 450 °C, the CO2 conversion rate was 82.64%.

[0211] Example 14

[0212] 1. Magnesium nitrate was dissolved in deionized water and stirred evenly to obtain a magnesium nitrate solution with a concentration of 0.20 mol / L.

[0213] 2. Fumed silica was added to the magnesium nitrate solution obtained in step 1, and ultrasonic stirring was used until the silica was completely dispersed to obtain a uniform mixture, with the molar concentration of silica being 0.4 mol / L.

[0214] 3. Urea was added to the mixture obtained in step 2 and stirred evenly. The concentration of urea was 3.0 mol / L, and the pH of the system was 5.7 at this time. It was stirred in a water bath at 95 °C for 6 hours to obtain a solid-liquid mixture.

[0215] 4. The solid-liquid mixture obtained in step 3 was filtered by suction, and the filtered solid was dried in an oven at 120 °C for 12 hours.

[0216] 5. The solid dried in step 4 was calcined at 700 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO was 2:1 to obtain the SiO2@MgO composite material.

[0217] 6. A nickel nitrate solution with a concentration of 0.85 mol / L was added dropwise to the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, it was dried in an oven at 80 °C for 6 hours and then dried at 120 °C for 12 hours to obtain a dried product.

[0218] 7. Calcinate the dried product obtained in step 6 at 900 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0219] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, and reduce it at 600 °C for 2 hours with a heating rate of 2 °C / min to obtain the catalyst Ni / SiO2@MgO with a mass fraction of Ni of 10%. It can also be found through zeta potential, XRD patterns, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0220] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor for CO2 methanation reaction testing.

[0221] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 4.39% and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 64.92% and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 76.24% and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 74.92%.

[0222] Example 15

[0223] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.20 mol / L.

[0224] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and stir with ultrasonic waves until the silica is completely dispersed to obtain a homogeneous mixture with a molar concentration of silica of 0.3 mol / L.

[0225] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 1.5 mol / L. At this time, the pH of the system is 5.6, and stir in a water bath at 95 °C for 6 hours to obtain a solid-liquid mixture.

[0226] 4. Filter the solid-liquid mixture obtained in step 3, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0227] 5. Calcinate the solid dried in step 4 at 700 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1.5:1 to obtain the SiO2@MgO composite material.

[0228] 6. The nickel nitrate solution with a concentration of 0.43 mol / L was added dropwise to the support obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, it was dried in an oven at 80 °C for 6 hours and then dried at 120 °C for 12 hours to obtain a dried product.

[0229] 7. The dried product obtained in step 6 was calcined at 600 °C for 5 hours with a heating rate of 2 °C / min to obtain a catalyst precursor.

[0230] 8. The obtained catalyst precursor was placed in a reactor, and H2 gas with a flow rate of 20 mL / min was introduced. The heating rate was 2 °C / min, and it was reduced at 900 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO, with the mass fraction of Ni being 5%. It can also be found through zeta potential, XRD spectra, and specific surface area tests that MgO well coated the surface of SiO2 and had a relatively high specific surface area.

[0231] 9. A mixed gas with a molar ratio of CO2 to H2 of 1:4 was introduced into the reactor for CO2 methanation reaction testing.

[0232] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction was as follows: at 200 °C, the CO2 conversion rate was 1.89%, and the CH4 selectivity was 100%; at 300 °C, the CO2 conversion rate was 43.66%, and the CH4 selectivity was 100%; at 400 °C, the CO2 conversion rate was 75.12%, and the CH4 selectivity was 100%; at 450 °C, the CO2 conversion rate was 73.49%.

[0233] Example 16

[0234] 1. Magnesium nitrate was dissolved in deionized water and stirred evenly to obtain a magnesium nitrate solution with a concentration of 0.20 mol / L.

[0235] 2. Fumed silica was added to the magnesium nitrate solution obtained in step 1, and ultrasonic stirring was used until the silica was completely dispersed to obtain a uniform mixture, with the molar concentration of silica being 0.20 mol / L.

[0236] 3. Urea was added to the mixture obtained in step 2 and stirred evenly. The concentration of urea was 2.3 mol / L, and the pH of the system was 5.6 at this time. It was stirred in a water bath at 75 °C for 6 hours to obtain a solid-liquid mixture.

[0237] 4. The solid-liquid mixture obtained in step 3 was filtered by suction, and the filtered solid was dried in an oven at 120 °C for 12 hours.

[0238] 5. Calcinate the solid after drying in step 4 at 600 °C for 5 hours, with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1, obtaining the SiO2@MgO composite material.

[0239] 6. Drop the nickel nitrate solution with a concentration of 0.43 mol / L onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain the dried product.

[0240] 7. Calcinate the dried product obtained in step 6 at 800 °C for 5 hours, with a heating rate of 2 °C / min, to obtain the catalyst precursor.

[0241] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, with a heating rate of 2 °C / min, and reduce it at 650 °C for 2 hours to obtain the catalyst Ni / SiO2@MgO, with the mass fraction of Ni being 5%. It can also be found through zeta potential, XRD spectra, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0242] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor for the CO2 methanation reaction test.

[0243] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 2.05%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 56.15%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 76.82%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 77.14%.

[0244] Example 17

[0245] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.20 mol / L.

[0246] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and use ultrasonic stirring until the silica is completely dispersed to obtain a uniform mixture, with the molar concentration of silica being 0.20 mol / L.

[0247] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 2.3 mol / L, and the pH of the system is 5.6 at this time. Stir in a water bath at 75 °C for 6 hours to obtain a solid-liquid mixture.

[0248] 4. Filter the solid-liquid mixture obtained in step 3 by suction filtration, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0249] 5. Calcinate the solid dried in step 4 at 600 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1, and the SiO2@MgO composite material is obtained.

[0250] 6. Weigh the required drugs according to the molar ratio of nickel nitrate: lanthanum nitrate: citric acid = 1:0.3:1.3 to prepare an aqueous solution with a nickel nitrate concentration of 0.43 mol / L. Drop it onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0251] 7. Calcinate the dried product obtained in step 6 at 800 °C for 5 hours with a heating rate of 2 °C / min to obtain the catalyst precursor NiO-La2O3 / SiO2@MgO.

[0252] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, with a heating rate of 2 °C / min, and reduce it at 650 °C for 2 hours to obtain the catalyst Ni-La2O3 / SiO2@MgO with a Ni mass fraction of 5%. It can also be found through zeta potential, XRD spectra, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0253] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor for CO2 methanation reaction testing.

[0254] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 7.12%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 66.23%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 84.79%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 93.22%.

[0255] Example 18

[0256] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.20 mol / L.

[0257] 2. Add fumed silica into the magnesium nitrate solution obtained in step 1, and use ultrasonic stirring until the silica is completely dispersed to obtain a uniform mixture. The molar concentration of silica is 0.20 mol / L.

[0258] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 2.3 mol / L. At this time, the pH of the system is 5.6. Stir in a water bath at 75 °C for 6 hours to obtain a solid-liquid mixture.

[0259] 4. Filter the solid-liquid mixture obtained in step 3 by suction filtration, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0260] 5. Calcinate the solid dried in step 4 at 600 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0261] 6. Weigh the required drugs according to the molar ratio of nickel nitrate: cerium nitrate: citric acid = 1:0.125:3.375 to prepare an aqueous solution. The concentration of nickel nitrate is 0.43 mol / L. Drop it onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0262] 7. Calcinate the dried product obtained in step 6 at 800 °C for 5 hours with a heating rate of 2 °C / min to obtain the catalyst precursor NiO-CeO2 / SiO2@MgO.

[0263] 8. Place the obtained catalyst precursor in a reactor, introduce H2 gas with a flow rate of 20 mL / min, with a heating rate of 2 °C / min, and reduce it at 650 °C for 2 hours to obtain the catalyst Ni-CeO2 / SiO2@MgO, and the mass fraction of Ni is 5%. It can also be found through zeta potential, XRD spectrum and specific surface area tests that MgO well coats the surface of SiO2 and has a high specific surface area.

[0264] 9. Introduce a mixed gas with a molar ratio of CO2 to H2 of 1:4 into the reactor for CO2 methanation reaction testing.

[0265] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 6.32%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 63.38%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 82.47%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 91.16%.

[0266] Example 19

[0267] 1. Dissolve magnesium nitrate in deionized water and stir evenly to obtain a magnesium nitrate solution with a concentration of 0.20 mol / L.

[0268] 2. Add fumed silica to the magnesium nitrate solution obtained in step 1 and stir with ultrasonic waves until the silica is completely dispersed to obtain a homogeneous mixture. The molar concentration of silica is 0.20 mol / L.

[0269] 3. Add urea to the mixture obtained in step 2 and stir evenly. The concentration of urea is 2.3 mol / L. At this time, the pH of the system is 5.6. Stir in a water bath at 75 °C for 6 hours to obtain a solid-liquid mixture.

[0270] 4. Filter the solid-liquid mixture obtained in step 3, and dry the filtered solid in an oven at 120 °C for 12 hours.

[0271] 5. Calcinate the solid dried in step 4 at 600 °C for 5 hours with a heating rate of 2 °C / min. According to the molar ratio, the ratio of SiO2 to MgO is 1:1 to obtain the SiO2@MgO composite material.

[0272] 6. Weigh the required drugs according to the molar ratio of nickel nitrate: cerium nitrate: lanthanum nitrate: citric acid = 1:0.125:0.125:1.5 to prepare an aqueous solution. The concentration of nickel nitrate is 0.43 mol / L. Drop it onto the carrier obtained in step 5 by the equal-volume impregnation method. After sealing and standing for 24 hours, dry it in an oven at 80 °C for 6 hours, and then dry it at 120 °C for 12 hours to obtain a dried product.

[0273] 7. Calcinate the dried product obtained in step 6 at 800 °C for 5 hours with a heating rate of 2 °C / min to obtain the catalyst precursor NiO-CeO2-La2O3 / SiO2@MgO.

[0274] 8. The obtained catalyst precursor is placed in a reactor, and H2 gas with a flow rate of 20 mL / min is introduced. The heating rate is 2 °C / min, and it is reduced at 650 °C for 2 hours to obtain the catalyst Ni-CeO2-La2O3 / SiO2@MgO, with the mass fraction of Ni being 5%. It can also be found through zeta potential, XRD patterns, and specific surface area tests that MgO well coats the surface of SiO2 and has a relatively high specific surface area.

[0275] 9. A mixed gas with a molar ratio of CO2 to H2 of 1:4 is introduced into the reactor for CO2 methanation reaction testing.

[0276] Under the conditions of a space velocity of 15000 mL / (g·cat·h) and a pressure of 3 MPa, the catalytic performance of the CO2 hydrogenation methanation reaction is as follows: at 200 °C, the CO2 conversion rate is 6.38%, and the CH4 selectivity is 100%; at 300 °C, the CO2 conversion rate is 65.34%, and the CH4 selectivity is 100%; at 400 °C, the CO2 conversion rate is 86.89%, and the CH4 selectivity is 100%; at 450 °C, the CO2 conversion rate is 93.83%.

[0277] It can be seen that all the embodiments involved in the present invention can exhibit good catalytic performance in the CO2 methanation reaction, and the selectivity of the products is stable without obvious deactivation, showing excellent stability and having extremely high application value.

[0278] For the technical solutions disclosed and proposed in the present invention, those skilled in the art can achieve them by referring to the content herein and appropriately changing conditions, routes, and other aspects. Although the methods and preparation techniques of the present invention have been described through preferred embodiments, it is obvious that relevant technicians can make changes or recombinations to the methods and technical routes described herein without departing from the content, spirit, and scope of the present invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art, and they are all considered to be included in the spirit, scope, and content of the present invention.

Claims

1. A Ni catalyst supported on MgO-coated SiO2, characterized in that, Its composition is Ni-MO x / SiO2@MgO; wherein: Ni is the active component of the catalyst, and MO x is an additive added to the catalyst, and MO x is at least one of La2O3 and CeO2; SiO2@MgO is a composite material with MgO coating SiO2, used as the carrier of the catalyst; the molar ratio of SiO2 to MgO in SiO2@MgO is (1.0-4.0):1; SiO2@MgO is prepared by the deposition method, and urea is used as the precipitating agent to uniformly coat MgO on the surface of SiO2 to form the SiO2@MgO composite material.

2. The MgO-coated SiO2-supported nickel catalyst according to claim 1, wherein The mass fraction of Ni in the catalyst is 5-20%.

3. The MgO-coated SiO2-supported nickel catalyst according to claim 1, characterized in that, According to the molar ratio, Ni: MO x = 1: (0 to 0.3).

4. A method for preparing the MgO-coated SiO2-supported nickel catalyst according to any one of claims 1-3, characterized in that, It includes the following processes: (1) Dissolve magnesium nitrate in deionized water under stirring until it is completely dissolved to obtain a uniform solution; (2) Add fumed silica to the solution obtained in step (1) and perform ultrasonic dispersion until the silica is completely dispersed to form a uniform mixture; (3) Add 1.0-5.0 mol / L urea to the mixture obtained in step (2), stir and dissolve it, then heat it in a water bath at 75-95 °C while continuously stirring to form a solid-liquid mixture; (4) Filter the solid-liquid mixture obtained in step (3), separate the solid, and then dry the obtained solid; (5) Calcinate the dried solid obtained in step (4) to prepare the SiO2@MgO support; (6) Prepare an aqueous solution of nickel nitrate, or an aqueous solution of nickel nitrate and the corresponding nitrate of the promoter and citric acid, and uniformly impregnate the SiO2@MgO support prepared in step (5) by the equal-volume impregnation method; then seal the mixture, first dry it in an oven and then dry it to obtain a dried product; (7) Calcinate the dried product obtained in step (6) to obtain the catalyst precursor; (8) Introduce a reducing gas into the catalyst precursor prepared in step (7) for reduction treatment to obtain the catalyst Ni-MO x / SiO2@MgO.

5. The preparation method of an MgO-coated SiO2-supported nickel catalyst according to claim 4, characterized in that, The concentration of magnesium nitrate in the solution obtained in step (1) is 0.05-0.20 mol / L; after the urea is stirred and dissolved in step (3), the pH value of the solution is 5.5-6.4; the stirring time for heating in the water bath in step (3) is 5-6 h; the drying in step (4) is carried out in an oven at a temperature range of 60 °C to 120 °C for a duration of 6-24 h.

6. The preparation method of a nickel catalyst supported on MgO-coated SiO2 according to claim 4, characterized in that, In steps (5) and (7), the calcination temperature range is 600-900 °C, the calcination time is 2-6 h, and the heating rate is 1-10 °C / min.

7. The preparation method of an MgO-coated SiO2-supported nickel catalyst according to claim 4, characterized in that, In step (6), the molar ratio of the sum of nickel nitrate and the corresponding nitrate of the promoter to citric acid is 1:(1-3); the sealing and standing time in step (6) is 12-48 h; the drying temperature in step (6) is 60 °C to 90 °C and it is carried out in an oven for 5-7 h; the drying temperature range in step (6) is 100 °C to 150 °C and it is carried out in an oven for 6-24 h.

8. The preparation method of an MgO-coated SiO2-supported nickel catalyst according to claim 4, characterized in that, In step (8), the flow rate of the reducing gas is 10-30 mL / min, the reduction temperature range is 600-800 °C, the heating rate is 1-10 °C / min, and the reduction process lasts for 1-3 h; the reducing gas in step (8) includes at least one of hydrogen and carbon monoxide.

9. Use of the MgO-coated SiO2-supported nickel catalyst as described in any one of claims 1-3 in the CO2 methanation reaction.

10. Use of the MgO-coated SiO2-supported nickel catalyst according to claim 9 in the CO2 methanation reaction, characterized in that, Add the catalyst to a fixed-bed reactor, and under the conditions of a temperature of 200-450 °C and a pressure of 0.1-5 MPa, introduce carbon dioxide and hydrogen into the reactor at a volume space velocity of 5000-60000 mL / (gcat·h), wherein the molar ratio of carbon dioxide to hydrogen is 1:(1-5) to obtain the target product methane.

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