Calcium-based bifunctional material, method for preparing same and use thereof

Abstract

The application provides a calcium-based bifunctional material and a preparation method and application thereof, and the preparation method comprises the following steps: mixing a calcium salt solution and an organic template agent, stirring under heating conditions, forming a gel, and then drying and calcining to obtain a calcium carbonate adsorption component; preparing a rare earth metal oxide by using a hydrothermal method, and then loading a transition metal on the rare earth metal oxide by using an impregnation method to obtain a transition metal supported catalytic component; and placing the adsorption component and the catalytic component in a hydrogen-rich atmosphere after physical mixing and calcining to obtain the calcium-based bifunctional material. According to the method, the preparation process of the adsorption component is controlled, the calcium carbonate is first generated by using a sol-gel method and low-temperature calcining, and the calcium carbonate is mixed with the catalytic component and then hydrogen-rich calcining is performed to generate porous calcium oxide, so that the sintering of the calcium oxide in the high-temperature preparation process is avoided; the method has the advantages of simple process, excellent performance, low energy consumption and good industrial application value.

Description

Technical Field

[0001] This invention belongs to the field of CO2 capture and utilization technology, and relates to a calcium-based bifunctional material, its preparation method and uses, especially a calcium-based bifunctional material, its preparation method and its application in the field of CO2 capture and conversion. Background Technology

[0002] In recent years, with the annual increase in CO2 emissions, serious environmental problems have arisen. Therefore, controlling CO2 emissions to achieve sustainable development of human civilization is a common goal worldwide. Integrated CO2 capture and conversion technology (ICCU) is an efficient way to reduce CO2 emissions. This technology couples CO2 capture and CO2 conversion technologies to achieve CO2 capture and in-situ conversion in the same reactor at the same temperature, significantly reducing industrial energy consumption and showing promising application prospects.

[0003] Based on the CO2 capture temperature, CO2 adsorbents can be classified into high-temperature adsorbents (>400℃), medium-temperature adsorbents (200~400℃), and low-temperature adsorbents (<200℃). The reactions occurring during the conversion stage include methanation, which is exothermic, while CO2 adsorption is an endothermic process. Coupled, these two processes are more conducive to heat replenishment and reduce energy consumption. Based on the reversible reaction of CaO with CO2 to form CaCO3, calcium oxide is commonly chosen as a CO2 adsorbent due to its excellent theoretical capture capacity and low cost, and is widely used in cement, dehumidification, energy storage, and waste gas purification.

[0004] Because the Taman temperature of calcium carbonate is approximately 533℃, while the optimal operating temperature range for calcium-based materials is typically above 650℃, sintering is a common problem, leading to gradual deactivation. Therefore, when using calcium oxide as an adsorbent to synthesize bifunctional materials, CO2 is first adsorbed, followed by CO2 conversion and calcium oxide regeneration with the aid of a catalyst. However, the significant volume change from calcium oxide to calcium carbonate during cycling accelerates sintering, causing the activity of the bifunctional material to gradually decrease with increasing cycle count. Current research has explored increasing porosity and inhibiting sintering by doping calcium-based adsorbents with inert supports exhibiting high Taman temperatures, such as MgO, ZrO2, and Al2O3, but these methods have not enabled calcium oxide to achieve its optimal reactivity.

[0005] CN 114377679A discloses a bifunctional catalyst integrating carbon dioxide capture and conversion, its preparation method, and its application. The bifunctional catalyst comprises an adsorbent component, a catalytic component, and a support component. The adsorbent component includes one or a combination of MgO, CaO, and BaO; the catalytic component includes one or a combination of Ni, Fe, Cu, Co, Ir, Pt, Ru, Rh, or oxides of the above elements; and the support component includes Al2O3. The method includes: preparing an aqueous solution of an active metal soluble salt; preparing a precipitant solution; mixing the solutions for a co-precipitation reaction, controlling the pH value to obtain a co-precipitate slurry; aging; centrifuging and washing the aged co-precipitate slurry to obtain a precipitate; drying the precipitate, grinding, and calcining to obtain the bifunctional catalyst. Although this bifunctional catalyst discloses the support component, it does not clearly define whether it acts on the adsorbent or catalytic component. Furthermore, the selection of the adsorbent component includes medium- and high-temperature adsorbents, requiring high energy consumption, and the temperature conditions may not be suitable for the CO2 conversion reaction, easily leading to unsatisfactory conversion results.

[0006] CN 115445622A discloses a porous adsorption and catalysis bifunctional material, its preparation method, and its application. The chemical formula of this bifunctional material is Ni. a M b / N c CaO, where M is any one of Fe, Mo, Co, Zr, or Mg, and N is an alkali metal; adsorption active component N c CaO and catalytically active component Ni a M b The mass ratio between the components is 1:0.05–0.3. The adsorbent and catalytic components in this material are prepared together using a one-step sol-gel method. A porous composite material is prepared by adding an organic template agent. The role of the alkali metal in this bifunctional material is only to provide basic sites, not to modify calcium oxide. This bifunctional material is used for high-temperature flue gas carbon dioxide capture and in-situ dry reforming of methane. Both adsorption and dry reforming reactions are high-temperature endothermic processes, and the capture performance of CaO adsorbent under mesophilic conditions is not addressed.

[0007] In summary, regarding the composition and preparation process of calcium-based bifunctional materials, based on their functions and applications of CO2 adsorption and catalytic methane conversion, it is necessary to improve the synthesis process of calcium oxide to reduce sintering problems, enhance its adsorption and reaction performance under medium-temperature conditions, and reduce energy consumption. Summary of the Invention

[0008] To address the problems existing in the prior art, the present invention aims to provide a calcium-based bifunctional material, its preparation method, and its applications. The method is based on the composition of the calcium-based bifunctional material and controls the preparation process of the adsorbent component. First, calcium carbonate is generated by sol-gel method and low-temperature calcination. After mixing with the catalytic component, porous calcium oxide is generated by hydrogen-rich calcination, avoiding the sintering of calcium oxide, improving the reactivity, and the reaction process has low energy consumption. It has excellent performance when used for CO2 capture and conversion.

[0009] To achieve this objective, the present invention adopts the following technical solution:

[0010] In a first aspect, the present invention provides a method for preparing a calcium-based bifunctional material, the method comprising the following steps:

[0011] (1) Mix calcium salt solution and organic template agent, stir under heating conditions to form a gel, and then dry and calcine at a temperature of 400-500℃ to obtain calcium carbonate adsorbent component; for example, 400℃, 420℃, 450℃, 480℃ or 500℃, but not limited to the listed values, other unlisted values ​​within the range are also applicable;

[0012] (2) Rare earth metal oxides were prepared by hydrothermal method, and then transition metals were loaded onto rare earth metal oxides by impregnation method to obtain transition metal supported catalytic components.

[0013] (3) The calcium carbonate adsorption component described in step (1) and the transition metal supported catalytic component described in step (2) are physically mixed and then calcined in a hydrogen-rich atmosphere to obtain the calcium-based bifunctional material.

[0014] In this invention, to achieve the coupling of CO2 capture and conversion, the material needs to possess both adsorption and catalytic functions. Therefore, this invention prepares a calcium-based bifunctional material, which includes an adsorption component and a catalytic component. The adsorption component is mainly calcium oxide. Calcium oxide is first prepared using a sol-gel method and low-temperature calcination, while a transition metal-supported catalytic component is prepared simultaneously. The two are then mixed and calcined in a hydrogen-rich atmosphere. Hydrogen is used to reduce the transition metal, and then the transition metal catalytic component catalyzes the decomposition reaction of calcium carbonate, generating calcium oxide with a porous structure and high activity, avoiding the sintering in the traditional high-temperature preparation process of calcium oxide. At the same time, calcining calcium carbonate to calcium oxide in a hydrogen-rich atmosphere can shorten the existence time of metastable calcium oxide in the transition stage from calcium carbonate to calcium oxide, reduce the degree of calcium oxide sintering, and improve the reactivity. The method is simple, has excellent performance, low energy consumption, and has good industrial application value.

[0015] The following are preferred technical solutions of the present invention, but are not intended to limit the technical solutions provided by the present invention. The technical objectives and beneficial effects of the present invention can be better achieved and realized through the following technical solutions.

[0016] As a preferred technical solution of the present invention, the calcium salt in step (1) includes any one or a combination of at least two of calcium nitrate, calcium chloride or calcium acetate. Typical but non-limiting examples of such combinations include: a combination of calcium nitrate and calcium chloride, a combination of calcium chloride and calcium acetate, a combination of calcium nitrate, calcium chloride and calcium acetate, etc.

[0017] Preferably, the organic template agent in step (1) includes any one or a combination of at least two of citric acid, acetic acid, ethylenediaminetetraacetic acid (EDTA) or urea. Typical but non-limiting examples of such combinations include: a combination of citric acid and acetic acid, a combination of acetic acid and EDTA, a combination of citric acid, acetic acid and urea, a combination of citric acid, acetic acid and EDTA, etc.

[0018] Preferably, the raw materials mixed in step (1) further include alkali metal salts.

[0019] Preferably, the alkali metal salt includes alkali metal nitrates and / or alkali metal carbonates.

[0020] Preferably, the alkali metal includes any one or a combination of at least two of lithium, sodium, or potassium. Typical but non-limiting examples of such combinations include combinations of lithium and sodium, combinations of lithium and potassium, and combinations of lithium, sodium, and potassium.

[0021] Preferably, the molar ratio of the calcium salt to the alkali metal salt is (4 to 19):1, for example, 4:1, 5:1, 6:1, 8:1, 10:1, 12:1, 14:1, 15:1, 17:1 or 19:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0022] In this invention, alkali metal salts are added during the preparation of the adsorbent component to modify the calcium-based adsorbent component. This effectively improves the CO2 capture performance of calcium oxide under intermediate temperature conditions. Specifically, by forming a molten liquid film on the surface of calcium oxide, CO2 diffusion into the adsorbent is promoted, and CO3 diffusion is also promoted. 2- The formation of ions can also hinder the formation of a hard carbonate product layer and promote the mass transfer of hydrogen and calcium carbonate formed by adsorbed CO2.

[0023] Preferably, the molar ratio of total metal ions to organic template agent in the mixed raw materials is 1:1 to 1:2, such as 1:1, 1:1.2, 1:1.5, 1:1.8 or 1:2, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0024] In this invention, the role of the organic template agent in the calcium carbonate preparation process is to chelate metal ions.

[0025] As a preferred technical solution of the present invention, the mixture in step (1) is heated and stirred under oil bath conditions.

[0026] Preferably, the heating temperature in step (1) is 80-90°C, such as 80°C, 82°C, 85°C, 88°C or 90°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The heating time is 6-8h, such as 6h, 6.5h, 7h, 7.5h or 8h, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0027] Preferably, the stirring rate in step (1) is 200 to 500 r / min, such as 200 r / min, 250 r / min, 300 r / min, 350 r / min, 400 r / min, 450 r / min or 500 r / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0028] Preferably, the gel in step (1) is transparent.

[0029] As a preferred technical solution of the present invention, the drying temperature in step (1) is 110 to 130°C, such as 110°C, 115°C, 120°C, 125°C or 130°C, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable. The drying time is 8 to 16 hours, such as 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, 15 hours or 16 hours, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0030] Preferably, the drying process in step (1) yields a foam-like solid material.

[0031] Preferably, the calcination in step (1) is carried out in an air atmosphere.

[0032] Preferably, the calcination time in step (1) is 3 to 6 hours, such as 3 hours, 3.5 hours, 4 hours, 4.5 hours, 5 hours, 5.5 hours or 6 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0033] Preferably, the heating rate of the calcination in step (1) is 4 to 6 °C / min, such as 4 °C / min, 4.5 °C / min, 5 °C / min, 5.5 °C / min or 6 °C / min, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0034] As a preferred technical solution of the present invention, the hydrothermal method in step (2) includes: mixing a rare earth metal salt solution and an alkaline solution and then carrying out a hydrothermal reaction, cooling after the reaction, separating the solid and liquid, washing, and drying to obtain a rare earth metal oxide carrier.

[0035] Preferably, the rare earth metal salt solution includes a cerium salt solution, which includes any one or a combination of at least two of cerium nitrate solution, cerium chloride solution, or cerium sulfate solution. Typical but non-limiting examples of such combinations include: a combination of cerium nitrate solution and cerium chloride solution, a combination of cerium chloride solution and cerium sulfate solution, a combination of cerium nitrate solution, cerium chloride solution, and cerium sulfate solution, etc.

[0036] Preferably, the alkaline solution comprises sodium hydroxide solution and / or potassium hydroxide solution, and the mass fraction of the alkaline solution is 20-40 wt%, such as 20 wt%, 25 wt%, 30 wt%, 35 wt%, or 40 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0037] Preferably, the temperature of the hydrothermal reaction is 100–110°C, such as 100°C, 102°C, 105°C, 108°C, or 110°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The time is 24–30 hours, such as 24 hours, 25 hours, 26 hours, 27 hours, 28 hours, 29 hours, or 30 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0038] Preferably, the solid-liquid separation includes filtration or centrifugation, and more preferably, vacuum filtration.

[0039] Preferably, the washing is a water wash, washing the reaction product until it is neutral.

[0040] Preferably, the rare earth metal oxide includes cerium dioxide.

[0041] In this invention, the rare earth metal salt and the alkali are dissolved in water to form solutions. The rare earth metal salt solution is added to the alkali solution and stirred at room temperature for 0.5 to 1 hour, for example, 0.5 hours, 0.67 hours, 0.75 hours, 0.8 hours, 0.9 hours, or 1 hour. The solution is then transferred to a high-pressure hydrothermal reactor. After the hydrothermal reaction, the solution is cooled to room temperature, filtered or vacuum filtered to separate the precipitate, and washed with deionized water until the pH value reaches about 7. After drying, nano-sized rare earth metal oxide carriers are obtained.

[0042] As a preferred technical solution of the present invention, the impregnation method in step (2) includes: adding rare earth metal oxides into a transition metal precursor solution, stirring thoroughly, evaporating and drying to obtain a transition metal supported catalytic component.

[0043] Preferably, the transition metal precursor solution comprises any one or a combination of at least two of the following: transition metal chloride, transition metal nitrate, and transition metal acetate. Typical but non-limiting examples of such combinations include: a combination of transition metal chloride and transition metal nitrate, a combination of transition metal nitrate and transition metal acetate, and a combination of transition metal chloride, transition metal nitrate, and transition metal acetate.

[0044] Preferably, the transition metal includes any one or a combination of at least two of nickel, ruthenium, or rhodium. Typical but non-limiting examples of such combinations include: a combination of nickel and ruthenium, a combination of rhodium and nickel, a combination of ruthenium, rhodium, and nickel, etc.

[0045] In this invention, the rare earth metal oxide, such as cerium dioxide, is added to the transition metal precursor solution and suspended in the solution. After thorough stirring for 8 to 24 hours, such as 8 hours, 10 hours, 12 hours, 14 hours, 16 hours, 18 hours, 20 hours, 22 hours, or 24 hours, a suspension is formed.

[0046] Preferably, the evaporation drying temperature is 80–120°C, such as 80°C, 85°C, 90°C, 95°C, 100°C, 105°C, 110°C, 115°C, or 120°C, but is not limited to the listed values; other unlisted values ​​within this range are also applicable. The time is 6–12 hours, such as 6 hours, 7 hours, 8 hours, 9 hours, 10 hours, 11 hours, or 12 hours, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0047] Preferably, the loading of transition metal in the catalytic component is 0.5 to 10 wt%, such as 0.5 wt%, 1 wt%, 2 wt%, 3 wt%, 5 wt%, 6 wt%, 8 wt%, or 10 wt%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0048] In this invention, the catalytic component is selected as a transition metal supported catalyst, with rare earth metal oxides as the support. It has high catalytic activity and, when used for CO2 capture and conversion, helps to improve CO2 conversion rate and methane selectivity, thereby increasing methane production.

[0049] As a preferred technical solution of the present invention, the mass ratio of the calcium carbonate adsorbent component and the transition metal supported catalytic component in step (3) is (1-2):1, for example 1:1, 1.2:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1 or 2:1, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0050] Preferably, the physical mixing method in step (3) includes grinding or ball milling.

[0051] In this invention, when the adsorption component and the catalytic component are mixed, the mass of the calcium carbonate adsorption component is calculated based on the mass of calcium oxide it contains, and the mass of calcium oxide contained in the calcium carbonate adsorption component is 56% of the actual mass. Furthermore, the physical mixing method used in this invention can control the distance between the adsorption sites and the catalytic sites to maintain the stability of the cycle.

[0052] Preferably, the calcination in step (3) includes: the physically mixed components are first heated to 400-550°C in a protective atmosphere, for example, 400°C, 420°C, 450°C, 480°C, 500°C, 520°C or 550°C, and then a hydrogen-containing atmosphere is introduced for reduction calcination to obtain a calcium-based bifunctional material.

[0053] Preferably, the protective atmosphere includes nitrogen and / or an inert gas.

[0054] Preferably, the heating rate is 5 to 10 °C / min, such as 5 °C / min, 6 °C / min, 7 °C / min, 8 °C / min, 9 °C / min or 10 °C / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0055] Preferably, the hydrogen-containing atmosphere is a mixture of hydrogen and a protective gas, wherein the volume fraction of hydrogen in the mixture is 15% to 100%, such as 15%, 30%, 40%, 50%, 60%, 70%, 80%, or 100%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0056] Preferably, the flow rate of the hydrogen-containing atmosphere is 80 to 200 mL / min, such as 80 mL / min, 100 mL / min, 120 mL / min, 140 mL / min, 160 mL / min, 180 mL / min or 200 mL / min, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0057] Preferably, the reduction calcination time is 2 to 4 hours, such as 2 hours, 2.5 hours, 3 hours, 3.5 hours or 4 hours, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0058] Preferably, after the reduction and calcination, the calcium carbonate in the adsorbent component is decomposed into calcium oxide, which has a porous structure, and the oxidized transition metal in the catalytic component is reduced to its elemental state.

[0059] Secondly, the present invention provides a calcium-based bifunctional material obtained by the above preparation method, the calcium-based bifunctional material comprising an adsorption component and a catalytic component, the adsorption component comprising porous calcium oxide, and the catalytic component comprising a transition metal active component and a rare earth metal oxide support.

[0060] As a preferred technical solution of the present invention, the mass ratio of the adsorbent component to the catalytic component is (1-2):1, for example 1:1, 1.2:1, 1.4:1, 1.5:1, 1.6:1, 1.8:1 or 2:1, but is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0061] Preferably, the adsorbent component further includes an alkali metal salt, wherein the alkali metal salt accounts for 5 to 20% of the molar fraction of the adsorbent component, such as 5%, 6%, 8%, 10%, 12%, 15%, 18%, or 20%, but is not limited to the listed values; other unlisted values ​​within this range are also applicable.

[0062] Preferably, the specific surface area of ​​the adsorbent component is 10–20 m². 2 / g, for example, 10m 2 / g、12m 2 / g、14m 2 / g, 16m 2 / g、18m 2 / g or 20m 2 / g, etc., but not limited to the listed values; other unlisted values ​​within this range also apply.

[0063] Preferably, the particle size of the calcium-based bifunctional material is 80 to 100 mesh, such as 80 mesh, 85 mesh, 90 mesh, 95 mesh or 100 mesh, but it is not limited to the listed values. Other unlisted values ​​within this range are also applicable.

[0064] Thirdly, the present invention provides an application of the above-mentioned calcium-based bifunctional material, wherein the calcium-based bifunctional material is used for CO2 capture and CO2 conversion.

[0065] Preferably, the conversion of CO2 includes the methanation reaction of CO2.

[0066] In this invention, when the calcium-based bifunctional material is used for CO2 capture and conversion, different compositions can be selected depending on the application temperature. Typically, the calcium oxide adsorption component adsorbs CO2 at temperatures above 400°C, such as 400°C, 450°C, 500°C, 550°C, or 600°C. However, by modifying calcium oxide with alkali metal salts, the CO2 capture temperature can be lowered to a medium-temperature condition of 200–400°C, such as 200°C, 250°C, 300°C, 350°C, or 400°C. In specific applications, the CO2 capture and methanation conversion stages can be carried out continuously and alternately within the catalyst's lifespan.

[0067] Compared with the prior art, the present invention has the following beneficial effects:

[0068] (1) The method described in this invention is based on the composition of calcium-based bifunctional materials. By controlling the preparation process of the adsorbent components, calcium carbonate is first generated by sol-gel method and low-temperature calcination. After being mixed with the catalytic components, porous calcium oxide is generated by hydrogen-rich calcination, thus avoiding the sintering in the traditional high-temperature preparation process of calcium oxide.

[0069] (2) The present invention calcines calcium carbonate to produce calcium oxide in a hydrogen-rich atmosphere, which can shorten the existence time of metastable calcium oxide in the transition stage from calcium carbonate to calcium oxide, reduce the degree of calcium oxide sintering, and improve the reactivity; when used for CO2 capture and conversion, it helps to increase the CO2 capture capacity and CH4 production.

[0070] (3) The method described in this invention is simple, has excellent performance, low energy consumption, and has good industrial application value. Attached Figure Description

[0071] Figure 1 This is a SEM image of the calcium-based bifunctional material provided in Embodiment 1 of the present invention;

[0072] Figure 2 This is a SEM image of the calcium-based bifunctional material provided in Comparative Example 1 of this invention. Detailed Implementation

[0073] To better illustrate the present invention and facilitate understanding of its technical solutions, the present invention is further described in detail below. However, the following embodiments are merely simplified examples of the present invention and do not represent or limit the scope of protection of the present invention. The scope of protection of the present invention is determined by the claims.

[0074] The following are typical but non-limiting embodiments of the present invention:

[0075] Example 1:

[0076] This embodiment provides a method for preparing a calcium-based bifunctional catalyst, the method comprising the following steps:

[0077] (1) Calcium nitrate solution and citric acid are mixed, wherein the molar ratio of calcium nitrate and citric acid is 1:1.3. The mixture is heated and stirred in an oil bath at a temperature of 80°C for 8 hours and a stirring rate of 300 r / min to form a transparent gel. The gel is then dried and calcined at a temperature of 120°C for 12 hours to obtain a foamy solid material. The calcination is carried out in an air atmosphere at a temperature of 450°C for 4 hours and a heating rate of 5°C / min to obtain a calcium carbonate adsorbent component.

[0078] (2) Cerium dioxide was prepared by hydrothermal method, which included: mixing cerium nitrate solution and sodium hydroxide solution and stirring for 30 min, wherein the mass fraction of sodium hydroxide solution was 28.5 wt%, and carrying out hydrothermal reaction at a temperature of 100 °C for 24 h, cooling after reaction, separating by filtration, washing with water until neutral, and drying at 80 °C for 10 h to obtain cerium dioxide nanorods;

[0079] Then, the metallic nickel is loaded onto cerium dioxide using an impregnation method. The impregnation method includes: taking 1.0 g of cerium dioxide and adding it to 17 mL of 0.01 mol / L nickel nitrate solution, stirring for 8 h to obtain a suspension, and then evaporating and drying it at a temperature of 100 °C for 8 h to obtain a metallic nickel-loaded cerium dioxide catalytic component.

[0080] (3) Grind and mix the calcium carbonate adsorption component described in step (1) and the nickel-supported cerium dioxide catalyst component described in step (2) at a mass ratio of 1:1. Then, heat the mixture to 550°C in a nitrogen atmosphere at a heating rate of 5°C / min. At this temperature, introduce a hydrogen-containing atmosphere for reduction calcination. The hydrogen-containing atmosphere is a mixture of hydrogen and nitrogen, wherein the volume fraction of hydrogen is 50%, the flow rate of the hydrogen-containing atmosphere is 120 mL / min, and the reduction calcination time is 2 h to obtain the calcium-based bifunctional material.

[0081] Example 2:

[0082] This embodiment provides a method for preparing a calcium-based bifunctional material, the method comprising the following steps:

[0083] (1) Calcium nitrate solution and citric acid are mixed, wherein the molar ratio of calcium nitrate and citric acid is 1:1, and the mixture is heated and stirred in an oil bath at a temperature of 85°C for 7 hours and a stirring rate of 400 r / min to form a transparent gel. The gel is then dried and calcined at a temperature of 130°C for 8 hours to obtain a foamy solid material. The calcination is carried out in an air atmosphere at a temperature of 400°C for 6 hours and a heating rate of 4°C / min to obtain a calcium carbonate adsorbent component.

[0084] (2) Cerium dioxide was prepared by hydrothermal method, which included: mixing cerium nitrate solution and sodium hydroxide solution and stirring for 40 min, wherein the mass fraction of sodium hydroxide solution was 30 wt%, and carrying out hydrothermal reaction at a temperature of 105 °C for 27 h, cooling after reaction, separating by filtration, washing with water to neutral, and drying at 85 °C for 7 h to obtain cerium dioxide nanorods;

[0085] Then, ruthenium metal was loaded onto cerium dioxide using an impregnation method. The impregnation method included: adding 1.0 g of cerium dioxide to 20 mL of 0.01 mol / L nickel chloride solution, stirring for 10 h to obtain a suspension, and then evaporating and drying at a temperature of 120 °C for 6 h to obtain a nickel-loaded cerium dioxide catalytic component.

[0086] (3) Grind and mix the calcium carbonate adsorption component described in step (1) and the nickel-supported cerium dioxide catalyst component described in step (2) at a mass ratio of 1.5:1. Then, heat the mixture to 450°C in a nitrogen atmosphere at a heating rate of 7°C / min. At this temperature, introduce a hydrogen-containing atmosphere for reduction calcination. The hydrogen-containing atmosphere is a mixture of hydrogen and nitrogen, wherein the volume fraction of hydrogen is 80%, the flow rate of the hydrogen-containing atmosphere is 80 mL / min, and the reduction calcination time is 3 h to obtain the calcium-based bifunctional material.

[0087] Example 3:

[0088] This embodiment provides a method for preparing a calcium-based bifunctional material, the method comprising the following steps:

[0089] (1) A calcium chloride solution was mixed with ethylenediaminetetraacetic acid (EDTA), wherein the molar ratio of calcium chloride to EDTA was 1:1.5. The mixture was heated and stirred in an oil bath at a temperature of 90°C for 6 hours and a stirring rate of 200 r / min to form a transparent gel. The gel was then dried and calcined at a temperature of 110°C for 16 hours to obtain a foamy solid material. The calcination was carried out in an air atmosphere at a temperature of 470°C for 4 hours and a heating rate of 5.5°C / min to obtain a calcium carbonate adsorbent component.

[0090] (2) Cerium dioxide was prepared by hydrothermal method, which included: mixing cerium chloride solution and potassium hydroxide solution and stirring for 50 min, wherein the mass fraction of potassium hydroxide solution was 35 wt%, and carrying out hydrothermal reaction at 110 °C for 30 h, cooling after reaction, separating by filtration, washing with water to neutral, and drying at 90 °C for 8 h to obtain cerium dioxide nanorods;

[0091] Then, ruthenium metal was loaded onto cerium dioxide using an impregnation method. The impregnation method included: adding 1.0 g of cerium dioxide to 3.4 mL of 0.05 mol / L ruthenium chloride solution, stirring for 8 h to obtain a suspension, and then evaporating and drying at a temperature of 80 °C for 12 h to obtain a ruthenium metal-loaded cerium dioxide catalytic component.

[0092] (3) The calcium carbonate adsorption component described in step (1) and the ruthenium-supported cerium dioxide catalytic component described in step (2) are ball-milled and mixed at a mass ratio of 2:1. Then, the mixture is heated to 400°C in an argon atmosphere at a heating rate of 8°C / min. At this temperature, a hydrogen-containing atmosphere is introduced for reduction calcination. The hydrogen-containing atmosphere is a mixture of hydrogen and argon, wherein the volume fraction of hydrogen is 20%, the flow rate of the hydrogen-containing atmosphere is 200 mL / min, and the reduction calcination time is 4 h to obtain the calcium-based bifunctional material.

[0093] Example 4:

[0094] This embodiment provides a method for preparing a calcium-based bifunctional material, the method comprising the following steps:

[0095] (1) A calcium nitrate solution, citric acid and potassium nitrate solution are mixed, wherein the molar ratio of calcium nitrate, citric acid and potassium nitrate is 0.9:1:0.1. The mixture is heated and stirred in an oil bath at a temperature of 90°C for 6.5 h and a stirring rate of 500 r / min to form a transparent gel. The gel is then dried and calcined at a temperature of 115°C for 14 h to obtain a foamy solid material. The calcination is carried out in an air atmosphere at a temperature of 480°C for 3 h and a heating rate of 6°C / min to obtain a potassium nitrate modified calcium carbonate adsorbent component.

[0096] (2) Cerium dioxide was prepared by hydrothermal method, which included: mixing cerium chloride solution and sodium hydroxide solution and stirring for 60 min, wherein the mass fraction of sodium hydroxide solution was 25 wt%, and carrying out hydrothermal reaction at a temperature of 106 °C for 24 h, cooling after reaction, centrifuging, washing with water to neutral, and drying at 80 °C for 12 h to obtain cerium dioxide nanorods;

[0097] Then, the metallic nickel is loaded onto cerium dioxide using an impregnation method. The impregnation method includes: taking 1.0 g of cerium dioxide and adding it to 3.4 mL of 0.05 mol / L nickel chloride solution, stirring for 12 h to obtain a suspension, and then evaporating and drying it at a temperature of 90 °C for 10 h to obtain a metallic nickel-loaded cerium dioxide catalytic component.

[0098] (3) The potassium nitrate modified calcium carbonate adsorbent component described in step (1) and the nickel-supported cerium dioxide catalytic component described in step (2) are ground and mixed at a mass ratio of 1:1. Then, the mixture is heated to 400°C in an argon atmosphere at a heating rate of 10°C / min. At this temperature, a hydrogen atmosphere is introduced for reduction calcination at a flow rate of 150 mL / min and a reduction calcination time of 3.5 h to obtain the calcium-based bifunctional material.

[0099] Example 5:

[0100] This embodiment provides a method for preparing a calcium-based bifunctional material. The preparation method is the same as that in Example 4, except that potassium nitrate is not added in step (1).

[0101] Comparative Example 1:

[0102] This comparative example provides a method for preparing a calcium-based bifunctional material. The preparation method is the same as that in Example 1, except that the calcination temperature in step (1) is 800°C.

[0103] The calcium-based bifunctional materials prepared in Example 1 and Comparative Example 1 were characterized using scanning electron microscopy, and their SEM images are shown below. Figure 1 and Figure 2 As shown.

[0104] Depend on Figure 1 It can be seen that the calcium-based bifunctional material described in Example 1 has a porous coral-like structure, and the CaO particles have a small particle size; Figure 2 It can be seen that the traditional high-temperature calcination method used in Comparative Example 1 is prone to sintering, and its morphology is a blocky aggregate structure with large CaO particle size and agglomeration.

[0105] The calcium-based bifunctional materials prepared in Example 1 and Comparative Example 1 were characterized using an N2 adsorption analyzer. The specific surface area, pore volume, and pore size were calculated using the BET model and the BJH method, respectively. The results are shown in Table 1.

[0106] Table 1

[0107] sample <![CDATA[BET surface area (m 2 / g)]]> <![CDATA[Pore volume (cm 3 / g)]]> Aperture (nm) Example 1 18.98 0.151 27.0 Comparative Example 1 1.74 0.008 24.9

[0108] As shown in Table 1, the calcium-based bifunctional material described in Example 1 has a large specific surface area and abundant pore structure; while the material synthesized by the traditional high-temperature calcination method in Comparative Example 1 has a small specific surface area and no obvious pore structure, which is not conducive to the adsorption reaction.

[0109] The calcium-based bifunctional materials prepared in Examples 1-5 and Comparative Example 1 were used in the coupled process of CO2 capture and methanation conversion to evaluate the performance of the catalyst. The reaction process and conditions during application were as follows: (1) Heating stage: N2 atmosphere, heating from room temperature to 350-550℃, heating rate 5℃ / min; (2) CO2 capture stage: 20% CO2, nitrogen as the balance gas, reaction time 60min; (3) N2 purging for 5min; (4) Methanation conversion stage: pure H2, reaction time 60min; (5) N2 purging for 5min.

[0110] The test temperature in Examples 1-3 and Comparative Example 1 was 550℃, and the test temperature in Examples 4-5 was 400℃. After this process was performed once, steps (2) to (5) were repeated 4 times, and the test results are shown in Table 2.

[0111] Table 2

[0112]

[0113]

[0114] As shown in Table 2, when the above-mentioned calcium-based bifunctional materials are used for CO2 capture and methanation conversion, the calcium-based bifunctional materials in Examples 1-3 show significantly higher CO2 capture and CH4 production compared to Comparative Example 1. This indicates that by sequentially using low-temperature calcination and hydrogen-rich calcination during the preparation of the adsorbent components, calcium oxide with a porous structure can be obtained, exhibiting strong adsorption performance and high activity. The CO2 conversion rate and CH4 selectivity can both reach over 97%, which is higher than the corresponding results in Comparative Example 1. In contrast, the high-temperature calcination method used in Comparative Example 1 easily causes sintering of calcium oxide, resulting in a smaller specific surface area and weakened adsorption performance.

[0115] Example 4 modifies the calcium oxide adsorption component using alkali metal salts. Compared with Example 5, which does not use alkali metal salts for modification, the former can effectively improve the adsorption performance of calcium-based bifunctional materials at a medium temperature of 400°C. This helps to maintain consistency with the suitable temperature for the methanation conversion reaction, increase the yield of methane, and reduce the energy consumption of the reaction.

[0116] As can be seen from the above embodiments and comparative examples, the method of the present invention is based on the composition of calcium-based bifunctional materials. By controlling the preparation process of the adsorbent components, calcium carbonate is first generated by sol-gel method and low-temperature calcination. After mixing with the catalytic components, porous calcium oxide is generated by hydrogen-rich calcination, avoiding the sintering in the traditional high-temperature preparation process of calcium oxide. The present invention calcines calcium carbonate to calcium oxide in a hydrogen-rich atmosphere, which can shorten the existence time of metastable calcium oxide in the transition stage from calcium carbonate to calcium oxide, reduce the degree of calcium oxide sintering, and improve the reactivity. When used for CO2 capture and conversion, it helps to improve the CO2 capture capacity and CH4 yield. The method is simple, has excellent performance, low energy consumption, and has good industrial application value.

[0117] The applicant declares that the present invention is illustrated through the above embodiments to describe the detailed products and methods of the present invention, but the present invention is not limited to the detailed products and methods described above, that is, it does not mean that the present invention must rely on the detailed products and methods described above to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the products of the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

Claims

1. A method for preparing a calcium-based bifunctional material, characterized in that, The preparation method includes the following steps: (1) Mix calcium salt solution and organic template agent, stir under heating conditions to form a gel, and then dry and calcine at a temperature of 400~500℃ to obtain calcium carbonate adsorption component; (2) Rare earth metal oxides are prepared by hydrothermal method, and then transition metals are loaded onto rare earth metal oxides by impregnation method to obtain transition metal supported catalytic components; (3) The calcium carbonate adsorption component described in step (1) and the transition metal supported catalytic component described in step (2) are physically mixed and then calcined in a hydrogen-rich atmosphere to obtain the calcium-based bifunctional material. The organic template agent in step (1) includes any one or a combination of at least two of citric acid, acetic acid, ethylenediaminetetraacetic acid, or urea; The raw materials mixed in step (1) also include alkali metal salts; Alkali metals include any one or a combination of at least two of lithium, sodium, or potassium; The rare earth metal oxide includes cerium dioxide; The transition metal includes any one or a combination of at least two of nickel, ruthenium, or rhodium; The calcination in step (3) includes: the physically mixed components are first heated to 400~550℃ in a protective atmosphere, and then a hydrogen-containing atmosphere is introduced for reduction calcination to obtain calcium-based bifunctional materials; After reduction and calcination, the calcium carbonate in the adsorbent component is decomposed into calcium oxide, which has a porous structure, and the oxidized transition metal in the catalytic component is reduced to its elemental state.

2. The preparation method according to claim 1, characterized in that, The calcium salt in step (1) includes any one or a combination of at least two of calcium nitrate, calcium chloride, or calcium acetate.

3. The preparation method according to claim 1, characterized in that, The alkali metal salts include alkali metal nitrates and / or alkali metal carbonates.

4. The preparation method according to claim 1, characterized in that, The molar ratio of the calcium salt to the alkali metal salt is (4~19):

1.

5. The preparation method according to claim 1, characterized in that, The molar ratio of total metal ions to organic template agent in the mixed raw materials is 1:1 to 1:

2.

6. The preparation method according to claim 1, characterized in that, After mixing in step (1), heat and stir in an oil bath.

7. The preparation method according to claim 1, characterized in that, The heating temperature in step (1) is 80~90℃ and the heating time is 6~8h.

8. The preparation method according to claim 1, characterized in that, The stirring rate in step (1) is 200~500 r / min.

9. The preparation method according to claim 1, characterized in that, The gel in step (1) is transparent.

10. The preparation method according to claim 1, characterized in that, The drying temperature in step (1) is 110~130℃, and the drying time is 8~16h.

11. The preparation method according to claim 1, characterized in that, After drying in step (1), a foam-like solid material is obtained.

12. The preparation method according to claim 1, characterized in that, The calcination in step (1) is carried out in an air atmosphere.

13. The preparation method according to claim 1, characterized in that, The calcination time in step (1) is 3 to 6 hours.

14. The preparation method according to claim 1, characterized in that, The heating rate of calcination in step (1) is 4~6℃ / min.

15. The preparation method according to claim 1, characterized in that, The hydrothermal method in step (2) includes: mixing a rare earth metal salt solution and an alkaline solution and then carrying out a hydrothermal reaction, cooling after the reaction, separating the solid and liquid, washing, and drying to obtain a rare earth metal oxide carrier.

16. The preparation method according to claim 15, characterized in that, The rare earth metal salt solution includes a cerium salt solution, which includes any one or a combination of at least two of cerium nitrate solution, cerium chloride solution, or cerium sulfate solution.

17. The preparation method according to claim 15, characterized in that, The alkaline solution includes sodium hydroxide solution and / or potassium hydroxide solution, and the mass fraction of the alkaline solution is 20~40wt%.

18. The preparation method according to claim 15, characterized in that, The hydrothermal reaction is carried out at a temperature of 100-110℃ for 24-30 hours.

19. The preparation method according to claim 15, characterized in that, The solid-liquid separation includes filtration separation or centrifugal separation.

20. The preparation method according to claim 15, characterized in that, The solid-liquid separation includes vacuum filtration.

21. The preparation method according to claim 15, characterized in that, The washing is a water wash, which washes the reaction product until it is neutral.

22. The preparation method according to claim 1, characterized in that, The impregnation method in step (2) includes: adding rare earth metal oxides to a transition metal precursor solution, stirring thoroughly, evaporating and drying to obtain a transition metal supported catalytic component.

23. The preparation method according to claim 22, characterized in that, The transition metal precursor solution includes any one or a combination of at least two of the following: transition metal chloride, transition metal nitrate, or transition metal acetate.

24. The preparation method according to claim 22, characterized in that, The evaporation drying temperature is 80~120℃, and the time is 6~12h.

25. The preparation method according to claim 22, characterized in that, The loading of transition metals in the catalytic component is 0.5~10wt%.

26. The preparation method according to claim 1, characterized in that, The mass ratio of the calcium carbonate adsorbent component and the transition metal supported catalytic component in step (3) is (1~2):

1.

27. The preparation method according to claim 1, characterized in that, The physical mixing method described in step (3) includes grinding and mixing.

28. The preparation method according to claim 1, characterized in that, The protective atmosphere includes nitrogen and / or an inert gas.

29. The preparation method according to claim 1, characterized in that, The heating rate is 5~10℃ / min.

30. The preparation method according to claim 1, characterized in that, The hydrogen-containing atmosphere is a mixture of hydrogen and a protective gas, wherein the volume fraction of hydrogen in the mixture is 15-100%.

31. The preparation method according to claim 1, characterized in that, The flow rate of the hydrogen-containing atmosphere is 80~200 mL / min.

32. The preparation method according to claim 1, characterized in that, The reduction calcination time is 2-4 hours.

33. The calcium-based bifunctional material obtained by the preparation method according to any one of claims 1-32, characterized in that, The calcium-based bifunctional material includes an adsorption component and a catalytic component. The adsorption component includes porous calcium oxide, and the catalytic component includes a transition metal active component and a rare earth metal oxide support.

34. The calcium-based bifunctional material according to claim 33, characterized in that, The mass ratio of the adsorption component to the catalytic component is (1~2):

1.

35. The calcium-based bifunctional material according to claim 33, characterized in that, The adsorbent component also includes an alkali metal salt, which accounts for 5-20% of the molar fraction of the adsorbent component.

36. The calcium-based bifunctional material according to claim 33, characterized in that, The specific surface area of ​​the adsorbed component is 10~20m². 2 / g.

37. The calcium-based bifunctional material according to claim 33, characterized in that, The particle size of the calcium-based bifunctional material is 80-100 mesh.

38. The use of the calcium-based bifunctional material according to any one of claims 33-37, characterized in that, The calcium-based bifunctional material is used for CO2 capture and CO2 conversion.

39. The use according to claim 38, characterized in that, The CO2 conversion includes the methanation of CO2.

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