Calcium-based bifunctional material based on calcium cycle CO2 capture and fuel self-supply synergism as well as preparation method and application of calcium-based bifunctional material

Abstract

The invention relates to the technical field of CO2 capture and CH4 supply, in particular to a calcium-based bifunctional material based on calcium cycle CO2 capture and fuel self-supply cooperation as well as a preparation method and application of the calcium-based bifunctional material. The invention provides a calcium-based bifunctional material. The calcium-based bifunctional material comprises a calcium adsorbent and a metal catalyst, the calcium adsorbent is inert metal oxide doped calcium carbonate, and the metal catalyst is a cerium oxide carrier and metal oxide loaded on the surface of the cerium oxide carrier; the mass ratio of the calcium adsorbent to the metal catalyst is (1-9): 1. According to the invention, the adaptability of the calcium-based bifunctional material in a low-temperature low-CO2-concentration ship tail gas environment is improved through doping of the inert metal oxide, and efficient CO2 capture is realized; and the generated CH4 can be used as fuel for reinjection and utilization while the energy consumption required by CaO regeneration is reduced.

Description

Technical Field

[0001] This invention relates to the field of CO2 capture and CH4 supply technology, specifically to a calcium-based bifunctional material based on calcium cycle CO2 capture and synergistic fuel self-supply, its preparation method and application. Background Technology

[0002] Global climate change has become a major challenge facing humanity, with carbon emissions being the core factor exacerbating the greenhouse effect. In recent years, the frequency of extreme weather events triggered by the greenhouse effect has increased significantly, and global sea levels are rising at an accelerated pace. These chain reactions pose a serious threat to global ecosystems. The international community generally believes that if warming is not limited to within 1.5°C, humanity will face an irreversible ecological crisis.

[0003] Ocean-going vessels handle over 80% of global cargo transport. Due to their long-term reliance on high-carbon fuels such as heavy oil and diesel, the shipping industry has become a key emission sector facing significant challenges in emissions reduction. While LNG ships, fueled by liquefied natural gas (LNG), can reduce CO2 emissions by about a quarter compared to traditional fuel oil ships, their overall emission reduction effect still falls short of increasingly stringent carbon reduction targets. The widely used amine absorption method, although highly efficient, suffers from problems such as large equipment size and high regeneration energy consumption. Furthermore, the captured CO2 needs to be compressed and stored, occupying valuable cargo space on ships. More importantly, existing technologies primarily focus on CO2 storage rather than resource utilization, making it difficult to build a sustainable circular economy model.

[0004] Calcium Looping (CaL) technology offers a new approach to addressing the aforementioned challenges. This technology utilizes the reversible reaction between CaO and CO2 to achieve carbon capture. Its theoretical adsorption capacity is as high as 17.8 mmol / g, and the raw material, limestone, is abundant and inexpensive. In the treatment of carbon-containing flue gas from stationary sources such as power plant flue gas, calcium looping technology has shown promising application prospects. However, its adaptability in ship exhaust gas treatment still needs to be improved. The main challenges are: (1) The temperature of exhaust gas from dual-fuel LNG ships is usually around 300~400℃, which is lower than the optimal temperature range for CaO to capture CO2. (2) The CO2 concentration of exhaust gas from dual-fuel LNG ships is relatively low, usually around 5%. (3) CaO regeneration requires temperatures above 800℃, relying on fossil fuels for heating, which contradicts the original intention of emission reduction. (4) Calcium-based materials are prone to deactivation due to sintering after multiple cycles, which exacerbates the performance degradation.

[0005] Therefore, under the conditions of low temperature and low CO2 concentration in ship exhaust gas treatment, it is difficult for ordinary calcium-based materials to achieve calcium cycling. How to solve the problem of ship exhaust gas treatment is another current dilemma. Summary of the Invention

[0006] This invention provides a calcium-based bifunctional material based on calcium-cycle CO2 capture and synergistic fuel self-supply, along with its preparation method and applications. This invention improves the adaptability of the calcium-based bifunctional material to low-temperature, low-CO2-concentration ship exhaust environments through inert metal oxide doping, achieving highly efficient CO2 capture; while reducing the energy consumption required for CaO regeneration, the generated CH4 can be reused as fuel for reinjection.

[0007] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a calcium-based bifunctional material, comprising a calcium adsorbent and a metal catalyst; the calcium adsorbent is calcium carbonate doped with an inert metal oxide, and the metal catalyst is a cerium oxide support and a metal oxide supported on its surface; the mass ratio of calcium carbonate in the calcium adsorbent to the metal catalyst is (1.8~16):1.

[0008] This invention breaks with conventional thinking by using CaCO3 instead of CaO and doping it with inert metal oxides as stabilizing agents. The adsorbent is assembled with the catalyst in the form of inert metal oxide-doped CaCO3. Subsequently, hydrogen reduction is used to obtain inert metal oxide-doped CaO and elemental metal. The advantage of this structure is that, under the hydrogen spillover effect generated by the catalyst, the doping of inert metal oxides reduces CaCO3 to smaller CaO particles. The CaO produced by the hydrogen spillover reaction has a stronger CO2 capture capacity than directly prepared CaO.

[0009] Preferably, the inert metal oxide is at least one of aluminum oxide, cerium oxide, magnesium oxide, and zirconium oxide.

[0010] Preferably, the metal oxide is nickel oxide.

[0011] This invention provides a method for preparing a calcium-based bifunctional material, comprising: S3.1 An inert metal salt, calcium salt, citric acid and water are mixed, heated and stirred continuously to obtain a gel, which is then dried and calcined at ≤600℃ to obtain a calcium adsorbent; S3.2 Cerium salt and sodium hydroxide were mixed separately in solution, and then hydrothermally heated to obtain cerium oxide; cerium oxide was mixed with a metal salt solution, stirred and dried to obtain a metal catalyst. S3.3 A calcium-based bifunctional material was obtained by mixing calcium adsorbent and metal catalyst.

[0012] In calcium adsorbents obtained by calcination at ≤600℃, calcium exists in the form of calcium carbonate; in calcium adsorbents obtained by calcination at >600℃, calcium exists in the form of calcium oxide.

[0013] Preferably, in S3.1, the inert metal salt is at least one of aluminum salt, cerium salt, magnesium salt, and zirconium salt.

[0014] Preferably, the molar ratio of the inert metal in the inert metal salt to the calcium in the calcium salt is (0.1~0.3):1.

[0015] Preferably, the heating temperature is 80~90℃.

[0016] Preferably, the stirring time is 6-8 hours.

[0017] Preferably, the drying temperature is 120~150℃.

[0018] Preferably, the calcination temperature is 400~600℃ and the calcination time is 4~5 h.

[0019] Preferably, in step S3.2, the hydrothermal temperature is 100~120℃, and the hydrothermal time is at least 24 hours.

[0020] Preferably, the metal salt solution is a nickel salt solution; Preferably, the molar ratio of the metal salt to the cerium in the cerium salt in the metal salt solution is 1:(5~20). Preferably, cerium oxide is suspended in a metal salt solution and stirred for 6-8 h, followed by evaporation of the metal salt solution at 60-80 °C to obtain the catalyst.

[0021] This invention provides a method for CO2 capture and co-fuel self-supply based on the calcium cycle, comprising: S6.1 Pre-reduction: Hydrogen gas is introduced, and the metal oxide in the calcium-based bifunctional material is reduced to the metal element and active hydrogen atoms are generated. The active hydrogen atoms react with calcium carbonate to generate calcium oxide. S6.2 CO2 capture: When CO2-containing waste gas is mixed in, calcium oxide captures the CO2 and produces calcium carbonate; S6.3 Methane Conversion: Hydrogen gas is introduced again, and calcium carbonate reacts with hydrogen gas to produce methane and calcium oxide; The calcium oxide cycle is involved in CO2 capture and methane conversion.

[0022] This application utilizes hydrogen reduction to reduce the metal oxide catalyst in a calcium-based bifunctional material to a metallic state catalyst. The active hydrogen atoms (H*) generated from the cracking of hydrogen gas react with CaCO3 to produce CaO, which has a rich porous structure and small grain size. CaO can continuously participate in the reaction, continuously capturing CO2 to generate CaCO3, and CaCO3 further reacts with H2 to generate CH4.

[0023] The reaction formulas involved are as follows: MO + H2 → M + H2O (M is a metallic element, MO is a metal oxide) (1). CaCO3+H2→CaO+CO+H2O(2); CaO + CO2 → CaCO3 (reversible reaction) (3); CaCO3+4H2→CH4+2H2O+CaO (4).

[0024] Preferably, in step S6.1, the concentration of hydrogen gas introduced is 15~100% vol.

[0025] Preferably, in S6.2, the CO2-containing exhaust gas is LNG ship exhaust gas.

[0026] Doping with inert metal oxides can improve the adaptability of calcium-based bifunctional materials to low-temperature, low-CO2-concentration ship exhaust environments, achieving efficient CO2 capture. This application can be referenced when applying it to LNG ship exhaust gases. Figure 1 The proposed approach utilizes the renewable energy production capacity of islands along the route to couple CaO regeneration with CO2 methanation. This reduces the energy consumption required for CaO regeneration while the generated CH4 can be reinjected into the ship's fuel system. This closed-loop design not only solves the problems of large space occupation and high energy consumption for carbon capture on ships, but also transforms ships from pure carbon emitters into participants in the carbon cycle through the ingenious conversion of CO2 to CH4.

[0027] Preferably, in S6.2, the CO2 concentration in the CO2-containing waste gas is 3~20% vol.

[0028] Preferably, the temperature for capturing CO2 is 350~450℃.

[0029] The calcium-based bifunctional material provided by the hydrogen reduction application can achieve efficient CO2 capture in environments with CO2 concentrations of 3~20%vol (low CO2 concentration) and 350~450℃ (low temperature), while converting CO2 into CH4.

[0030] Therefore, in addition to the exhaust gas from LNG ships with low temperature and low CO2 concentration, other exhaust gases with low temperature and low CO2 concentration can also be treated using the calcium-based bifunctional material of this application in accordance with the specific method provided in this application.

[0031] Preferably, in step S6.3, the temperature at which methane is generated is 400~550℃.

[0032] Preferably, the concentration of hydrogen gas introduced is 100% vol.

[0033] Therefore, the present invention has the following beneficial effects: (1) The calcium-based bifunctional material composition structure designed in this invention breaks through the traditional calcium-based material, and introduces inert metal oxides to improve the long-term cycle stability of the calcium-based bifunctional material and the CO2 capture ability at low temperature and low concentration CO2.

[0034] (2) In the method of CO2 capture and fuel self-supply based on calcium cycle provided by the present invention, the decomposition of CaCO3 in calcium-based bifunctional material is promoted by hydrogen overflow, which reduces the energy consumption of CaO regeneration and obtains CaO with smaller grain size, thereby making the CO2 capture capacity of the method stronger at low temperature and low concentration of CO2.

[0035] (3) This invention proposes a CO2 capture and fuel self-supply system process that combines in-situ carbon capture of ship exhaust gas with the conversion of CaCO3 to CH4 by hydrogenation on coastal islands. This process realizes the transformation of CO2 pollutants into CH4 fuel and achieves low-carbon fuel self-supply.

[0036] (4) This invention abandons the traditional amine absorption method for ship CO2 treatment and adopts solid adsorption method to remove CO2 from ship exhaust gas, saving the space occupied by carbon capture devices on ships.

[0037] (5) The method of CO2 capture and fuel self-supply based on calcium cycle provided by the present invention forms a CO2 treatment mode of low carbon fuel self-supply for dual-fuel LNG ships throughout the entire life cycle, which has good industrial and commercial application value. Attached Figure Description

[0038] Figure 1 A schematic diagram of a CO2 capture and co-fuel self-supply system for dual-fuel LNG vessels throughout their entire lifecycle.

[0039] Figure 2 The images show SEM images of calcium-based bifunctional materials after hydrogen reduction, where a is the calcium-based bifunctional material with hydrogen overflow decomposition promoted after reduction (Comparative Example 1), b is the calcium-based bifunctional material with Al2O3 modified after reduction with hydrogen overflow decomposition promoted after reduction (Example 1), c is the calcium-based bifunctional material with conventional synthesis after reduction (Comparative Example 2), and d is the calcium-based bifunctional material with Al2O3 modified after reduction (Comparative Example 3).

[0040] Figure 3 Figure 1 shows the CO2 capture and CH4 production performance of different calcium-based bifunctional materials.

[0041] Figure 4 Figure 1 shows the results of long-cycle CO2 capture performance of different calcium-based bifunctional materials.

[0042] Figure 5 Figure 1 shows the long-cycle CH4 production performance of different calcium-based bifunctional materials. Detailed Implementation

[0043] The present invention will be further described below with reference to specific embodiments. Those skilled in the art will be able to implement the present invention based on these descriptions. Furthermore, the embodiments of the present invention described below are generally only some, not all, of the embodiments of the present invention. Therefore, all other embodiments obtained by those skilled in the art based on the embodiments of the present invention without inventive effort should fall within the scope of protection of the present invention.

[0044]

Example

[0045] (2) Dissolve 4.325 g Ce(NO3)3·6H2O and 50.0 g NaOH in 25 mL and 175 mL of deionized water, respectively. Add the cerium nitrate solution to the sodium hydroxide solution and stir for 30 min at room temperature. Then transfer the solution to two 100 mL stainless steel autoclaves and maintain the temperature at 100 °C for 24 h. After cooling to room temperature, filter the solution using a Buchner funnel and wash the precipitate with deionized water until the pH reaches 7. Then dry the precipitate at 80 °C overnight to obtain CeO2 nanorods.

[0046] (3) 0.8 g of CeO2 nanorods were suspended in 16 mL of 0.085 mol / L Ni(NO3)2·6H2O solution and stirred at room temperature for 8 h. The suspension was evaporated and dried overnight at 80 °C to obtain the catalyst (cerium oxide supported nickel oxide).

[0047] (4) The adsorbent and catalyst obtained in steps (1) and (3) are physically mixed uniformly according to the ratio of calcium oxide content to catalyst mass of 9:1 to obtain calcium-based bifunctional material.

[0048] (5) The calcium-based bifunctional material was placed in a vertical fixed bed and heated to 500°C at a rate of 5°C / min under N2 conditions. 100% vol H2 was introduced for pre-reduction at the target temperature for 120 min.

[0049] (6) Switch the atmosphere to N2 and cool to 350℃ for CO2 capture. Introduce 5% vol CO2, with N2 as the equilibrium gas, and react for 120 min; then switch the atmosphere to N2 and heat to 500℃; then introduce pure H2 and react for 60 min.

[0050] Example 2 This embodiment is basically the same as Embodiment 1, except that: (6) Switch the atmosphere to N2 and cool to 400℃ for CO2 capture. Introduce 5% vol CO2, with N2 as the equilibrium gas, and react for 120 min; then switch the atmosphere to N2 and heat to 450℃; then introduce pure H2 and react for 60 min.

[0051] Example 3 This embodiment is basically the same as Embodiment 1, except that: (6) Switch the atmosphere to N2 and cool to 350℃ for CO2 capture. Introduce 20% vol CO2, with N2 as the equilibrium gas, and react for 120 min; then switch the atmosphere to N2 and heat to 500℃; then introduce pure H2 and react for 60 min.

[0052] Example 4 This embodiment is basically the same as Embodiment 1, except that: (6) Switch the atmosphere to N2 and cool to 350℃ for CO2 capture. Introduce 3% vol CO2, with N2 as the equilibrium gas, and react for 120 min; then switch the atmosphere to N2 and heat to 500℃; then introduce pure H2 and react for 60 min.

[0053] Example 5 This embodiment is basically the same as Embodiment 1, except that: (6) Switch the atmosphere to N2 and cool to 450℃ for CO2 capture. Introduce 5% vol CO2, with N2 as the equilibrium gas, and react for 120 min; then switch the atmosphere to N2 and heat to 500℃; then introduce pure H2 and react for 60 min.

[0054] Comparative Example 1 (1) Mix 8.4223 g of Ca(NO3)2·4H2O and 7.4947 g of C6H8O7·H2O with 26 mL of deionized water. Stir in an oil bath at 90°C for 6 h to form a transparent gel. Then dry in an oven at 130°C for 12 h. A foamy solid material is then obtained. Crush the material and place it in a muffle furnace. Calcine at 400°C for 4 h in air atmosphere to obtain the adsorbent (calcium carbonate).

[0055] (2) Dissolve 4.325 g Ce(NO3)3·6H2O and 50.0 g NaOH in 25 mL and 175 mL of deionized water, respectively. Add the cerium nitrate solution to the sodium hydroxide solution and stir for 30 min at room temperature. Then transfer the solution to two 100 mL stainless steel autoclaves and maintain the temperature at 100 °C for 24 h. After cooling to room temperature, filter the solution using a Buchner funnel and wash the precipitate with deionized water until the pH reaches 7. Then dry the precipitate at 80 °C overnight to obtain CeO2 nanorods.

[0056] (3) 0.8 g of CeO2 nanorods were suspended in 16 mL of 0.085 mol / L Ni(NO3)2·6H2O solution and stirred at room temperature for 8 h. The suspension was evaporated and dried overnight at 80 °C to obtain the catalyst (cerium oxide supported nickel oxide).

[0057] (4) The adsorbent and catalyst obtained in steps (1) and (3) are physically mixed uniformly according to the ratio of calcium oxide content to catalyst mass of 9:1 to obtain calcium-based bifunctional material.

[0058] (5) The calcium-based bifunctional material was placed in a vertical fixed bed and heated to 500°C at a rate of 5°C / min under N2 conditions. 100% vol H2 was introduced for pre-reduction at the target temperature for 120 min.

[0059] (6) Switch the atmosphere to N2 and cool to 350℃ for CO2 capture. Introduce 5% vol CO2, with N2 as the equilibrium gas, and react for 120 min; then switch the atmosphere to N2 and heat to 500℃; then introduce pure H2 and react for 60 min.

[0060] Comparative Example 2 This comparative example is basically the same as Comparative Example 1, except that: (1) Mix 8.4223 g of Ca(NO3)2·H2O and 7.4947 g of C6H8O7·H2O with 26 mL of deionized water. Stir in an oil bath at 90 °C for 6 h to form a transparent gel. Then dry in an oven at 130 °C for 12 h. A foamy solid material is then obtained. Crush the material and place it in a muffle furnace. Calcine at 900 °C for 4 h in air atmosphere to obtain the adsorbent (calcium oxide).

[0061] Comparative Example 3 This comparative example is basically the same as Example 1, except that: (1) Mix 8.4223 g of Ca(NO3)2·H2O, 2.6758 g of Al(NO3)·9H2O, and 9.012 g of C6H8O7·H2O with 31 mL of deionized water. Stir in an oil bath at 90 °C for 6 h to form a transparent gel. Dry in an oven at 130 °C for 12 h to obtain a foamy solid material. Crush the material and calcine it in a muffle furnace at 900 °C for 4 h in air atmosphere to obtain an adsorbent (alumina doped with calcium oxide).

[0062] Comparative Example 4 This comparative example is basically the same as Comparative Example 1, except that: (6) Switch the atmosphere to N2 and cool to 450℃ for CO2 capture. Introduce 5% vol CO2, with N2 as the equilibrium gas, and react for 120 min; then switch the atmosphere to N2 and heat to 500℃; then introduce pure H2 and react for 60 min.

[0063] [Performance Testing] 1. Structural characterization The calcium-based bifunctional materials of Example 1 and Comparative Examples 1-3 after hydrogen reduction were characterized by SEM, and the results are as follows: Figure 2 As shown in the figure, observation reveals that the Al2O3-modified calcium-based bifunctional material successfully generated CaO with a rich porous structure and small grain size after hydrogen reduction. In Example 1 (… Figure 2 b) Comparative Example 1 Figure 2 a) Comparative Example 2 ( Figure 2 c) and Comparative Example 3 Figure 2 d) Among the four calcium-based bifunctional materials with different compositions, the grain size of Example 1 after hydrogen reduction was smaller than that of Comparative Examples 1 to 3, indicating that Al can promote the formation of CaO with smaller grain size.

[0064] 2. CO2 capture and methane conversion performance This section simulates CO2 capture under ship exhaust conditions of low temperature and low CO2 concentration, followed by the introduction of hydrogen to achieve in-situ conversion, simulating the conversion process on an island. The specific reaction process and conditions are as follows: (1) Heating stage: Under N2 conditions, the temperature is increased / decreased from the hydrogen-rich reduction temperature to 350 / 400 / 450 ℃, with a heating / decreasing rate of 5 ℃ / min; (2) CO2 capture stage: 3 / 5 / 20% vol CO2, N2 as equilibrium gas, reaction time 120 min; (3) Heating / cooling stage: Under N2 conditions, the temperature is increased / decreased from the CO2 capture temperature to 450 / 500 ℃, with a heating / cooling rate of 5 ℃ / min; (4) Methanation conversion stage: pure H2, reaction time 60 min; (5) Purge with N2 for 5 min.

[0065] The flow rate of all processes was kept constant at 100 mL / min, and the amount of calcium-based bifunctional material used was 0.3 g.

[0066] Loop testing method: (1) Heating stage: Under N2 conditions, the temperature is reduced from the hydrogen-rich reduction temperature to 450 °C at a rate of 5 °C / min; (2) CO2 capture stage: 5% vol CO2, N2 as equilibrium gas, reaction time 120 min; (3) Heating stage: Under N2 conditions, the temperature is increased from the CO2 capture temperature to 500 ℃ at a rate of 5 ℃ / min; (4) Methanation conversion stage: pure H2, reaction time 60 min; (5) Purge with N2 for 5 min.

[0067] Then, repeat steps (2) to (5) 9 times.

[0068] The flow rate of all processes was kept constant at 100 mL / min, and the amount of calcium-based bifunctional material used was 0.3 g.

[0069] Table 1. Performance test results of calcium-based bifunctional materials in Examples 1-5 and Comparative Examples 1-4

[0070] Table 2. Cyclic stability test results of calcium-based bifunctional materials in Example 5 and Comparative Example 4

[0071] Combining Table 1 and Figure 3 It can be seen that the performance of Example 1 is significantly better than that of Comparative Examples 1, 2, and 3, and Comparative Example 1 is significantly better than that of Comparative Examples 2 and 3. This indicates that promoting the decomposition of CaCO3 into CaO through hydrogen overflow has better activity than CaO obtained directly through high-temperature calcination. Al species doping reduces the grain size and improves the low-to-medium temperature CO2 capture performance of the calcium-based bifunctional material. Examples 2-4 demonstrate that the optimized calcium-based bifunctional material exhibits excellent CO2 capture performance and in-situ methanation performance under low CO2 concentration (~3%) and low temperature (350℃) and low-to-medium CO2 concentration (20%) and medium temperature (450℃) conditions. Furthermore, Table 2 and... Figure 4 , Figure 5Cyclic stability test data show that the optimized calcium-based bifunctional material in the examples exhibits excellent stability, with a CO2 capture decay rate of only 11.8% and a methanation decay rate of only 6.6% after 10 cycles. The comparison results between Example 5 and Comparative Example 4 demonstrate that Al species are key to improving cyclic stability.

[0072] Therefore, the calcium-based bifunctional material provided in this application possesses excellent performance and recyclability, and can be widely used in processes such as in-situ CO2 capture on ships and in-situ hydrogenation conversion on coastal islands. Furthermore, this calcium-based bifunctional material is also suitable for flue gas treatment from stationary sources such as coal-fired power plants (CO2 concentration ~20%).

Claims

1. A calcium-based bifunctional material, characterized in that, The calcium adsorbent is inert metal oxide doped calcium carbonate, and the metal catalyst is a cerium oxide carrier and a metal oxide loaded on the surface of the carrier; the mass ratio of the calcium carbonate in the calcium adsorbent to the metal catalyst is (1.8-16):

1.

2. The calcium-based bifunctional material of claim 1, wherein, The inert metal oxide is at least one of aluminum oxide, cerium oxide, magnesium oxide and zirconium oxide; Preferably, the metal oxide is nickel oxide.

3. The method for producing a calcium-based bifunctional material according to claim 1 or 2, characterized by, The preparation method comprises the following steps: S3.1 mixing an inert metal salt, a calcium salt, citric acid and water, heating, continuously stirring to obtain a gel, and then drying and calcining the gel at ≤600 ℃ to obtain the calcium adsorbent; S3.2 mixing a cerium salt and sodium hydroxide in the form of a solution, and then hydrothermally obtaining cerium oxide; mixing the cerium oxide and a metal salt solution, stirring and drying to obtain the metal catalyst; S3.3 mixing the calcium adsorbent and the metal catalyst to obtain the calcium-based bifunctional material.

4. The preparation method of claim 3, wherein In S3.1, the inert metal salt is at least one of an aluminum salt, a cerium salt, a magnesium salt and a zirconium salt; Preferably, the molar ratio of the inert metal in the inert metal salt to calcium in the calcium salt is (0.1-0.3):1; Preferably, the heating temperature is 80-90 ℃; Preferably, the stirring time is 6-8 h; Preferably, the drying temperature is 120-150 ℃; Preferably, the calcining temperature is 400-600 ℃, and the calcining time is 4-5 h.

5. The production method according to claim 3, wherein In S3.2, the hydrothermal temperature is 100-120 ℃, and the hydrothermal time is at least 24 h; Preferably, the metal salt solution is a nickel salt solution; Preferably, the molar ratio of the metal salt in the metal salt solution to cerium in the cerium salt is 1:(5-20); Preferably, the cerium oxide is suspended in the metal salt solution, stirred for 6-8 h, and then evaporated at 80-100 ℃ to obtain the catalyst.

6. A method for CO2 capture and fuel self-supply based on calcium circulation, comprising: The calcium-based bifunctional material is prepared by using the calcium-based bifunctional material of claim 1 or 2 or the preparation method of any one of claims 3-5; and the method comprises the following steps: S6.1 pre-reduction: hydrogen is introduced, the metal oxide in the calcium-based bifunctional material is reduced to a metal element, active hydrogen atoms are generated, and the active hydrogen atoms react with calcium carbonate to generate calcium oxide; S6.2 CO2 capture: CO2-containing exhaust gas is mixed, the calcium oxide captures CO2 and generates calcium carbonate; S6.3 methane conversion: hydrogen is introduced again, the calcium carbonate reacts with hydrogen to generate methane and calcium oxide; The calcium oxide is recycled to participate in CO2 capture and methane conversion.

7. The method of claim 6, wherein, In S6.1, the concentration of the introduced hydrogen is 15-100%vol.

8. The method of claim 6 or 7, wherein, In S6.2, the CO2-containing exhaust gas is LNG ship exhaust gas.

9. The method of claim 6, wherein, In S6.2, the CO2 concentration in the CO2-containing exhaust gas is 3-20%vol; Preferably, the temperature for capturing CO2 is 350-450 ℃.

10. The method of claim 6, wherein, In S6.3, the temperature for generating methane is 400-550 ℃; Preferably, the concentration of the introduced hydrogen is 100%vol.

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