Multi-metal LDHs (layered double hydroxides) bifunctional catalyst as well as preparation method and application thereof
By designing a multi-metal LDHs catalyst, the problems of low efficiency and poor stability in low-concentration CO2 capture and low-temperature in-situ hydrogenation conversion were solved, realizing efficient CO2 capture, conversion and recycling, which is suitable for industrial applications.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-24
- Publication Date
- 2026-04-10
AI Technical Summary
In existing technologies, bifunctional catalysts are inefficient in the process of capturing low-concentration CO2 and converting it into hydrogen at low temperatures in situ. They are also susceptible to O2 poisoning, have poor catalyst stability, and are difficult to balance efficient capture and conversion.
A bifunctional multimetallic LDH catalyst was prepared by selecting at least two divalent and trivalent metal ions to create a metal plate with variable valence. By utilizing the dynamic changes in a redox atmosphere, the CO2 capture capacity was improved and in-situ hydrogenation methanation was carried out under low temperature conditions for recycling.
The catalyst significantly improved CO2 capture capacity and hydrogenation methanation rate under low-temperature conditions, reduced energy consumption, and enhanced catalyst stability, achieving efficient CO2 capture, conversion, and recycling, making it suitable for industrial applications.
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Figure CN121819904A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of catalysts, and more particularly to a multi-metal LDHs bifunctional catalyst, its preparation method, and its application. Background Technology
[0002] The ever-increasing demand for energy and rapid industrialization have significantly increased greenhouse gas emissions, leading to a series of environmental problems that threaten human health and survival. Currently, the concentration of carbon dioxide in the atmosphere has reached 420 ppm, and it is projected to increase to 500 ppm by 2050. Therefore, direct air capture of carbon dioxide (DAC), as a promising "carbon-negative" technology, has attracted increasing attention from researchers. DAC technology can actively capture low concentrations of carbon dioxide from ambient air, thereby reducing the CO2 concentration in the atmosphere. Furthermore, direct air capture of carbon dioxide is not limited by geographical location, offering greater flexibility and solving the problems of point sources and distributed sources. Therefore, DAC technology is an important and feasible option for reducing greenhouse gas levels and has significant practical implications for mitigating global warming.
[0003] In recent years, carbon dioxide capture and utilization (CCU) has played an important role in limiting atmospheric CO2 concentration as a relatively mature technology. However, due to the sparse nature of atmospheric CO2, the capture process is often accompanied by slow adsorption kinetics, which significantly reduces the capture capacity of CO2 under low concentration conditions. Meanwhile, the presence of O2 (~21%) in the air not only competes with CO2 for adsorption at active sites but may also cause problems such as catalyst oxidation and active site poisoning, thus affecting reaction performance and catalyst stability. Furthermore, CO2, as an inert molecule, exhibits high thermodynamic stability at low temperatures, with a C=O bond energy as high as 750 kJ / mol, making C=O bond breaking and hydrogenation difficult. Bifunctional catalytic materials can serve as both solid adsorbents for CO2 capture and catalysts for hydrocarbon production, effectively coupling the two processes of direct air capture and conversion of CO2, thus reducing energy consumption to some extent. However, while bifunctional catalytic materials with strong adsorption properties are beneficial for achieving high-capacity CO2 capture, they may inhibit the desorption of intermediates and subsequent hydrogenation reactions. Conversely, while bifunctional catalytic materials with weak adsorption properties facilitate intermediate migration and transformation, they significantly reduce CO2 capture efficiency, making effective enrichment difficult. Therefore, how to rationally design suitable bifunctional catalytic materials to overcome the kinetic limitations under low-temperature conditions while efficiently capturing CO2 from the air, and further improve CO2 conversion rate and product yield, is an urgent problem to be solved. Reference 1 uses Ru+Na2O / Al2O3 as a bifunctional catalyst in Dual function materials (Ru+Na2O / Al2O3) for direct air capture of CO2 and in situ catalytic methanation: The impact of realistic ambient conditions. Appl. Catal. B Environ. 2022,307:120990. to directly capture CO2 from the air (DAC) and convert it to methane in situ. The capture and conversion capabilities of this bifunctional catalyst are significantly improved compared to traditional thermal catalysts. However, the CO2 capture and conversion efficiency of this catalyst is low, and it cannot achieve efficient combination of CO2 capture and in situ conversion under low temperature conditions, resulting in high economic costs.Reference 2, in "How the presence of O2 and NOxin influences the alternate cycles of CO2 adsorption and hydrogenation to CH4 on Ru-Na-Ca / Al2O3 dual function material. Journal of CO2 Utilization," states that during the CO2 capture and conversion process, the presence of O2 intensifies competitive adsorption, inhibiting CO2 capture and thus reducing the yield of CH4. Furthermore, the catalyst's catalytic sites are prone to deactivation, resulting in poor cycle stability, which is detrimental to industrial applications.
[0004] In summary, there is an urgent need for a bifunctional catalyst material capable of efficiently capturing and in-situ hydrogenating low-concentration CO2 from the air. Therefore, developing a bifunctional catalyst for direct air capture of CO2 coupled with in-situ hydrogenation, resistant to O2 poisoning, is of great importance for the efficient utilization of CO2 in the air and for reducing energy consumption and costs.
[0005] Layered double hydroxides (LDHs), also known as hydrotalcite, are two-dimensional layered inorganic functional materials with a magnesia-like structure. They possess high specific surface area, adjustable layer metals, adjustable interlayer anions, and good resistance to CO32-. 2- It possesses characteristics such as extremely high affinity. Theoretically, LDHs can directly capture CO2 in the air and convert it into CO3 through ion exchange. 2- The CO3 is stored in the interlayer in the form of [a substance]; then it undergoes in-situ conversion under an H2 atmosphere, consuming the interlayer CO3. 2- To generate high-value-added chemicals; the reacted LDHs can again replenish interlayer CO3 through direct air capture of CO2. 2- This allows for recycling. However, no LDH-based bifunctional catalysts have been successfully applied to the efficient capture and low-temperature in-situ hydrogenation conversion of low-concentration CO2, and key technical issues such as catalyst poisoning in the presence of O2 and the imbalance between capture and conversion performance have not been resolved. Summary of the Invention
[0006] To address the problems of existing technologies, this invention provides a multi-metal LDHs bifunctional catalyst that achieves integrated efficient capture of CO2 from the air coupled with in-situ hydrogenation and methanation. Compared with existing technologies, this catalyst efficiently and selectively captures low-concentration CO2 from the air in an oxidizing atmosphere and converts it in-situ to CH4 under low-temperature conditions in a H2 / N2 reducing atmosphere. During the low-temperature reaction, the valence state of the variable-valence metals in the LDHs layers decreases, weakening the interaction with interlayer CO3. 2- The binding force between LDH layers, CO3 2- The CO2 is continuously consumed and converted into the reduction product CH4. After the reaction, CO2 is again captured directly in the air in a mixed gas of 400 ppm CO2 (400 ppm CO2 + 20% O2 + N2). The valence state of the variable-valence metals in the LDHs layers increases, and the increase in positive charge density promotes the increase in CO2 capture. The captured CO2 is then converted back into interlayer CO3. 2- It can restore the anions between the layers of hydrotalcite, and can be recycled to realize the direct air capture of CO2 coupled with in-situ hydrogenation and methanation cycle process.
[0007] The technical solution of the present invention is as follows: This invention provides a multi-metal LDHs bifunctional catalyst with the chemical formula P / NO3. - -M2M3-LDHs, where: P is a precious metal, selected from one of Pt, Pd, Ru, and Ir; M2 is a divalent metal ion selected from Cu. 2+ Co 2+ Fe 2+ Mn 2+ At least two of them; Laminates formed with a single M2 ion tend to have dense lattice arrangement and limited pores. However, the differences in ionic radii between two or more divalent metal ions increase the interlayer spacing, providing more space for CO2 molecules to be captured. Furthermore, the formation of a hierarchical pore structure improves gas mass transfer efficiency, addressing the problem of low CO2 capture efficiency at low concentrations. The differences in redox potentials among different divalent metal ions allow for a stepped valence state cycle when multiple M2 ions coexist. During the oxidative capture phase, metal ions with lower oxidation potentials are preferentially oxidized by O2, rapidly increasing the oxidative properties of the laminate, allowing more CO2 to be captured as CO32. 2- The metal ions are stored in the interlayer to balance the positive charge of the plates, thereby enhancing the ability to capture low concentrations of CO2. During the reductive conversion stage, metal ions with higher oxidation potentials are preferentially reduced by H2, while the plate metal cations react with CO3. 2-The decreased binding force of interlayer anions drives rapid interlayer desorption and their participation in the reaction. This synergistic effect significantly improves the valence state cycling rate, solving the problems of slow valence state transformation kinetics and the disconnect between capture and conversion processes caused by single M2 ions. Furthermore, single M2 ions have a limited affinity for LDHs and are easily affected by O2 competitive adsorption. When multiple divalent metal ions coexist, they exhibit complementarity, forming multiple adsorption sites and improving CO2 capture capacity and efficiency. The different interactions between different divalent metal ions and noble metal P can optimize the adsorption and dissociation capacity of hydrogen, improving the conversion rate of CO2 hydrogenation methanation under low-temperature conditions. LDHs with single M2 ions are prone to problems such as layer collapse and metal ion dissolution after multiple redox cycles, leading to catalyst deactivation. The synergistic effect of two or more divalent metal ions can avoid the loss of active centers caused by excessive oxidation or reduction of single metal ions, inhibit structural damage during cycling, and extend the catalyst's lifespan.
[0008] M3 is a trivalent metal ion selected from Al. 3+ Fe 3+ Ga 3+ Cr 3+ Mn 3+ Ce 3+ One of them.
[0009] Furthermore, the XRD pattern of the LDHs bifunctional catalyst showed characteristic diffraction peaks of (003), (006), (0009), (110), and (113). This indicates that the crystal structure type and interlayer spacing of the LDHs did not change significantly after loading with noble metals.
[0010] Furthermore, the molar ratio of M2 to M3 is 2 to 4:1.
[0011] Furthermore, the total ion concentration of M2 and M3 is 0.18 mol / L to 0.4 mol / L.
[0012] When the total concentration of M2 and M3 ions is too low, the collision probability and coordination driving force of metal ions in the solution are insufficient, making it impossible to complete ordered lamination. This leads to the potential for noble metal agglomeration during subsequent loading, reducing the utilization rate of hydrogenation active sites and affecting CO2 capture capacity and methane conversion. Conversely, when the total concentration of M2 and M3 ions is too high, it easily leads to a reduction in the interlayer spacing of LDHs, pore blockage, and difficulty for CO2 to diffuse to the interlayer adsorption sites, hindering efficient hydrogen contact with CO3. 2- This inhibits the continued progress of the hydrogenation methanation reaction, leading to a decrease in both capture and conversion efficiency.
[0013] Furthermore, the mass ratio of the noble metal P to LDHs is 1 to 5%.
[0014] Furthermore, the LDHs bifunctional catalyst exhibits a CO2 capture capacity of 1.142–1.858 mmol / g at room temperature and a CH4 yield of 1.131–1.802 mmol / g in a H2 / N2 reducing atmosphere at 100℃–300℃.
[0015] This invention provides an application of a multi-metal LDHs bifunctional catalyst, which can continuously complete the CO2 direct air capture coupled in-situ hydrogenation methanation cycle in an integrated reactor. The specific application process of this catalyst includes three stages: (1) ambient temperature oxidizing atmosphere capture stage: the supported LDHs bifunctional catalyst is introduced into a mixed gas containing 400 ppm CO2 (400 ppm CO2 + 20% O2 + N2) at room temperature to capture CO2 in the air. The valence state of the variable-valence metal in the plate increases, increasing the amount of CO2 captured, and converting CO2 into CO3. 2- (2) In-situ conversion stage of reducing atmosphere: interlayer CO3 2- In an H2 atmosphere, it is consumed and efficiently converted into CH4 by in-situ hydrogenation; (3) Cooling and recapture stage: After the reactor is cooled, the catalyst after the reaction is cooled to room temperature and then a mixed gas containing 400 ppm CO2 (400ppm CO2+20% O2+N2) is introduced, and water vapor is introduced at the same time. The variable valence metal is restored to its high oxidation state, and the LDHs bifunctional catalyst is used to capture CO2 again, storing the CO2 in the feed gas as CO3 again. 2- This enables a cyclical process of direct air capture of CO2 coupled with in-situ conversion.
[0016] This invention also provides a reactor device for an integrated LDHs bifunctional catalyst to achieve a CO2 direct air capture coupled in-situ conversion process based on metal valence state cycling. The reactor has an outlet at the top, and its interior contains steel pipes and quartz glass tubes to fill the reaction medium. The bottom of the reactor is equipped with a thermocouple, an exhaust port, a feed gas inlet, an inert gas inlet, and a hydrogen-nitrogen mixture device. The sides of the reactor are equipped with a flow meter, a valve control device, and a temperature control device.
[0017] The reactor temperature is set to room temperature using a temperature control device. The feed gas is a mixture of 400 ppm CO2 (400 ppm CO2 + 20% O2 + N2). CO2 is captured at room temperature while water vapor is introduced to complete the capture process. Subsequently, the valve control device and the hydrogen / nitrogen mixture device are opened to introduce an H2 / N2 mixture into the reactor, initiating an in-situ CO2 conversion reaction. The catalyst after the reaction is cooled to room temperature and then subjected to the same CO2 capture process described above, thus enabling recycling.
[0018] This invention provides a method for preparing the above-mentioned multimetallic LDHs bifunctional catalyst, the method comprising the following steps: S1: Dissolve soluble nitrates containing M2 and M3 in deionized water after CO2 removal to prepare mixed solution A, where M2 is a divalent metal ion selected from Cu. 2+ Co 2+ Fe 2+ Mn 2+ At least two of them; M3 is a trivalent metal ion selected from Al 3+ Fe 3+ Ga 3+ Cr 3+ Mn 3+ Ce 3+ One of them; the molar ratio of M2 to M3 is 2 to 4:1; S2: Dissolve the alkali in deionized water from which CO2 has been removed to prepare precipitant solution B, wherein the alkali is selected from NaOH or KOH; S3: Add no more than 1 / 3 of the container volume of deionized water (after removing CO2) to the reactor. Under a nitrogen atmosphere, add equal volumes of solution A and solution B dropwise into the reactor. During the titration, maintain the pH of the solution at 9-10. After titration, wash and centrifuge until the supernatant is neutral. Vacuum dry solid A to obtain the hydrotalcite precursor, denoted as NO3. - -M2M3-LDHs; S4: Dissolve the hydrotalcite precursor obtained in step S3 under an inert atmosphere, and add a metal P salt solution dropwise to it. The amount of metal P salt solution added should be such that the mass ratio of metal P to LDHs in the bifunctional catalyst is 1-5%. Add NaBH4 to reduce metal P in the liquid phase. The molar amount of NaBH4 added is 5 times that of the metal P salt added. After stirring for 1-2 hours, filter the resulting solution and wash it with deionized water until the supernatant is neutral. Vacuum dry solid B to obtain NO3 loaded with metal P. - Intercalated hydrotalcite, denoted as P / NO3 - -M2M3-LDHs; The metal P is one of Pt, Pd, Ru, and Ir.
[0019] Furthermore, the metal P salt is one of H2PtCl4, Na2PdCl4, RuCl3·3H2O, and Na2IrCl6.
[0020] Furthermore, the total ion concentrations of M2 and M3 are 0.18 mol / L to 0.4 mol / L.
[0021] Furthermore, the alkali concentration of solution B is 0.60 mol / L to 1.20 mol / L.
[0022] Furthermore, the mass ratio of P to LDHs is 1–5%.
[0023] Furthermore, the temperature is maintained at 70℃~90℃ during the titration process in step S3.
[0024] Furthermore, the vacuum drying time for solid A in step 3 is 18~24h.
[0025] Further, in step S4, after adding the metal P salt solution, stir for 1-2 hours.
[0026] Furthermore, the vacuum drying time for solid B in step S4 is 10~14h.
[0027] The multi-metal LDHs bifunctional catalyst was prepared according to the above method. The application of the multi-metal LDHs bifunctional catalyst in a real air atmosphere was simulated. The operation steps are as follows: (1) Mix the multi-metal LDHs bifunctional catalyst and quartz sand evenly, use it as a reaction medium, load it into the middle of a quartz glass tube, load it into a steel tube, and then load it into a reactor device. (2) First, a mixture of 400 ppm CO2 (400 ppm CO2 + 20% O2 + N2) is introduced into the reaction device at room temperature, and water vapor is introduced at the same time to capture CO2. After the capture is completed, the air in the reactor device is purged with an inert gas flow. The flow rate of the inert gas is controlled by a valve control device and a flow meter. Then, a 0.1 MPa H2 / N2 mixture is introduced into the reactor device and then sealed. The gas flow in the reactor device is circulated by a peristaltic pump. The reaction temperature is set to 100-300℃ and the reaction is carried out at a constant temperature for 2-2.5 h. (3) After the reaction, the reactor is cooled down to room temperature. Then, CO2 in the feed gas (400 ppm CO2 + 20% O2 + N2) is selectively captured in the presence of water vapor, and the CO2 is converted into CO32. 2- It is stored in the interlayer of LDHs in the form of [a substance] and used in the next reaction.
[0028] Then, the capture atmosphere was switched to 400 ppm CO2+N2, which does not contain oxygen. Under the same experimental conditions, a control experiment was conducted on capture under low concentration CO2 and in-situ hydrogenation conversion to reveal the effect of the presence or absence of O2 in the capture atmosphere on performance.
[0029] The present invention also provides a fixed bed device comprising the above-described multimetallic LDHs bifunctional catalyst.
[0030] The beneficial effects of this application are as follows: 1. Compared to flue gas and lime kiln gas, air has a lower CO2 concentration and a higher oxygen concentration. The presence of oxygen easily poisons the catalyst, making it more difficult for the catalyst to capture CO2 from the air. This invention selects at least two types of divalent and trivalent metal ions to prepare a bifunctional LDH catalyst, strictly controlling the total concentration of divalent and trivalent metal ions, thus solving the problem of O2 poisoning of the catalyst in the air and improving the CO2 capture capacity and hydrogenation methanation rate.
[0031] 2. This invention provides a multi-metal LDHs bifunctional catalyst, utilizing the dynamic changes in the valence state of the variable-valence metals in the LDHs layers under a redox atmosphere and the effect of LDHs on CO32-. 2- It has a high affinity for CO2, which increases the capture rate of low concentrations of CO2 in the air and converts it into CO3. 2- The catalyst is stored in the interlayer in the form of a medium, which enables in-situ hydrogenation methanation under low temperature conditions. At the same time, the catalyst after the reaction can be re-enhanced in an oxidizing atmosphere to increase the metal valence state, capture CO2 from the air to obtain carbon source replenishment, and restore the catalyst so as to be recycled. It has high selectivity, low energy consumption and realizes the reuse of CO2.
[0032] 3. This invention provides an application of a multi-metal LDHs bifunctional catalyst, which can be used to directly capture CO2 from the air and convert it into CH4 in situ in an H2 / N2 mixed atmosphere at a temperature of 100℃~300℃. The reaction conditions are mild, the energy consumption is lower than that of traditional CO2 capture technology, and it can efficiently realize the integration of CO2 capture coupled with in-situ hydrogenation and methanation, thereby reducing carbon dioxide emissions and having high economic benefits.
[0033] 4. The integrated design of CO2 direct air capture coupled with in-situ conversion in this invention features a simple and easy-to-operate reaction procedure and a small reactor footprint, which is conducive to industrialization. DACC technology gives the supported LDHs bifunctional catalyst the advantage of geographical freedom, allowing it to be appropriately placed near a hydrogen source to reduce gas transportation and storage issues. Attached Figure Description
[0034] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0035] Figure 1 The image shows the XRD pattern of the sample in Example 1.
[0036] Figure 2 HRTEM image of the catalyst prepared in Example 1.
[0037] Figure 3 The product methane yield was obtained at different temperatures under an H2 / N2 atmosphere using the catalyst prepared in Example 1, according to the conditions of the application example.
[0038] Figure 4 The catalyst prepared in Example 1 was subjected to the conditions of the application example after capture (T1 state), after reaction (T2 state), and after recapture (T1 state). R XPS spectra under three stages (state).
[0039] Figure 5 The reusability of the catalyst prepared in Example 1 under the conditions of the application example.
[0040] Figure 6 This is a diagram of an application device for LDHs bifunctional materials that utilize direct air capture coupled with in-situ conversion of CO2 driven by metal valence state cycles. Detailed Implementation
[0041] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.
[0042] Example 1 S1: Weigh 0.004 mol of Cu(NO3)2·3H2O solid, 0.008 mol of Co(NO3)2·6H2O solid, and 0.006 mol of Al(NO3)3·9H2O solid. Dissolve the three soluble metal salts in a beaker containing 100 mL of deionized water (after removing CO2) to prepare a mixed metal salt solution A.
[0043] S2: Weigh 0.072 mol NaOH solid and dissolve it in a beaker containing 100 mL of deionized water to remove CO2 to prepare precipitant solution B.
[0044] S3: CuCoAl-LDHs were synthesized using a co-precipitation method. The water bath temperature was set to 80℃. Under a N2 atmosphere, 100 mL of deionized water (with CO2 removed) was added to a three-necked flask. The two solutions from steps S1 and S2 were then added dropwise to a 500 mL three-necked flask. During the titration, the pH of the solution was maintained at 9, and the temperature was maintained at 80℃. After titration, the precipitate was washed with deionized water (with CO2 removed) and centrifuged until the supernatant was neutral. The solid was then vacuum-dried in a freeze dryer for 24 h to obtain the hydrotalcite precursor, denoted as NO3. - -CuCoAl-LDHs; S4: Weigh 0.3 g of the hydrotalcite precursor obtained in step S3 and dissolve it in deionized water to remove CO2. Under an inert atmosphere, add 0.625 mL of 0.04530 mol / L Na2PdCl4 dropwise, denoted as solution C. After stirring for 1 h, add 0.0053 g of NaBH4 to reduce the metal Pd salt in the liquid phase. The molar ratio of NaBH4 to metal Pd salt is 1:5. After stirring for 1 h, filter the resulting solution, wash with deionized water, and centrifuge until the supernatant is neutral. Place the solid in a freeze dryer and vacuum dry for 12 h to obtain NO3 loaded with metal Pd. - Intercalated hydrotalcite, denoted as Pd / NO3 - -CuCoAl-LDHs.
[0045] Example 2 S1: Weigh 0.006 mol of Cu(NO3)2·3H2O solid, 0.012 mol of Co(NO3)2·6H2O solid, and 0.006 mol of Ga(NO3)3·9H2O solid. Dissolve the three soluble metal salts in a beaker containing 100 mL of deionized water (after removing CO2) to prepare a mixed metal salt solution A.
[0046] S2: Weigh 0.054 mol of NaOH solid and dissolve it in a beaker containing 100 mL of deionized water to remove CO2 to prepare precipitant solution B.
[0047] S3: CuCoGa-LDHs were synthesized using a co-precipitation method. The water bath temperature was set to 80℃. Under a N2 atmosphere, 100 mL of deionized water (with CO2 removed) was added to a three-necked flask. The two solutions from steps A and B were then added dropwise to a 500 mL three-necked flask. During the titration, the pH of the solution was maintained at 10, and the temperature was maintained at 80℃. After titration, the precipitate was washed with deionized water (with CO2 removed) and centrifuged until the supernatant was neutral. The solid was then vacuum-dried in a freeze dryer for 24 h to obtain the hydrotalcite precursor, denoted as NO3. - -CuCoGa-LDHs; S4: Weigh 0.3 g of the hydrotalcite precursor obtained in step S3 and dissolve it in deionized water to remove CO2. Under an inert atmosphere, add 0.560 mL of 0.05306 mol / L RuCl3 dropwise, denoted as solution C. After stirring for 2 h, add 0.0056 g of NaBH4 to reduce the metallic Ru salt in the liquid phase. The molar ratio of NaBH4 to the metallic Ru salt is 1:5. After stirring for 2 h, filter the resulting solution, wash with deionized water, and centrifuge until the supernatant is neutral. Place the solid in a freeze dryer and vacuum dry for 12 h to obtain NO3 loaded with metallic Ru. - Intercalated hydrotalcite, denoted as Ru / NO3 - -CuCoGa-LDHs.
[0048] Example 3 S1: Weigh 0.004 mol of Cu(NO3)2·3H2O solid, 0.008 mol of Co(NO3)2·6H2O solid, and 0.006 mol of Fe(NO3)3·9H2O solid. Dissolve the three soluble metal salts in a beaker containing 100 mL of deionized water (after removing CO2) to prepare a mixed metal salt solution A.
[0049] S2: Weigh 0.064 mol of NaOH solid and dissolve it in a beaker containing 100 mL of deionized water to remove CO2 to prepare precipitant solution B.
[0050] S3: CuCoFe-LDHs were synthesized using a co-precipitation method. The water bath temperature was set to 80℃. Under a N2 atmosphere, 100 mL of deionized water (with CO2 removed) was added to a three-necked flask. The two solutions from steps A and B were then added dropwise to a 500 mL three-necked flask. During the titration, the pH of the solution was maintained at 0.5, and the temperature was kept at 80℃. After titration, the precipitate was washed with deionized water (with CO2 removed) and centrifuged until the supernatant was neutral. The solid was then vacuum-dried in a freeze dryer for 24 h to obtain the hydrotalcite precursor, denoted as NO3. - -CuCoFe-LDHs; S4: Weigh 0.3 g of the hydrotalcite precursor obtained in step S3 and dissolve it in deionized water to remove CO2. Under an inert atmosphere, add 0.320 mL of 0.04815 mol / L H2PtCl4 dropwise, denoted as solution C. After stirring for 2 h, add 0.0029 g of NaBH4 to reduce the metal Pt salt in the liquid phase. The molar ratio of NaBH4 to metal Pt salt is 1:5. After stirring for 1 h, filter the resulting solution, wash with deionized water, and centrifuge until the supernatant is neutral. Place the solid in a freeze dryer and vacuum dry for 12 h to obtain Pt-loaded NO3- intercalated hydrotalcite, denoted as Pt / NO3.- -CuCoFe-LDHs.
[0051] Example 4 S1: Weigh 0.006 mol of Co(NO3)2·6H2O solid, 0.006 mol of Fe(NO3)2·6H2O solid, and 0.006 mol of Al(NO3)3·9H2O solid. Dissolve the three soluble metal salts in a beaker containing 100 mL of boiled water (after removing all CO2) to prepare a mixed metal salt solution A.
[0052] S2: Weigh 0.062 mol of NaOH solid and dissolve it in a beaker containing 100 mL of deionized water to prepare precipitant solution B.
[0053] S3: CoFeAl-LDHs were synthesized using a co-precipitation method. The water bath temperature was set to 80℃. Under a N2 atmosphere, 100 mL of deionized water (with CO2 removed) was added to a three-necked flask. The two solutions from steps A and B were then added dropwise to a 500 mL three-necked flask. During the titration, the pH of the solution was maintained at 9, and the temperature was maintained at 80℃. After titration, the precipitate was washed with deionized water (with CO2 removed) and centrifuged until the supernatant was neutral. The solid was then vacuum-dried in a freeze dryer for 24 h to obtain the hydrotalcite precursor, denoted as NO3. - -CoFeAl-LDHs; S4: Weigh 0.3 g of the hydrotalcite precursor obtained in step S3 and dissolve it in deionized water to remove CO2. Under an inert atmosphere, add 0.560 mL of 0.05306 mol / L RuCl3 dropwise, denoted as solution C. After stirring for 2 h, add 0.0056 g of NaBH4 to reduce the metallic Ru salt in the liquid phase. The molar ratio of NaBH4 to the metallic Ru salt is 1:5. After stirring for 2 h, filter the resulting solution, wash with deionized water, and centrifuge until the supernatant is neutral. Place the solid in a freeze dryer and vacuum dry for 12 h to obtain NO3 loaded with metallic Ru. - Intercalated hydrotalcite, denoted as Ru / NO3 - -CoFeAl-LDHs.
[0054] Example 5 S1: Weigh 0.006 mol of Co(NO3)2·6H2O solid, 0.024 mol of Mn(NO3)2·6H2O solid, and 0.01 mol of Al(NO3)3·9H2O solid. Dissolve the three soluble metal salts in a beaker containing 100 mL of boiled water (after removing all CO2) to prepare metal salt mixed solution A.
[0055] S2: Weigh 0.09 mol of NaOH solid and dissolve it in a beaker containing 100 mL of deionized water to remove CO2 to prepare precipitant solution B.
[0056] S3: CoMnAl-LDHs were synthesized using a co-precipitation method. The water bath temperature was set to 80℃. Under a N2 atmosphere, 100 mL of deionized water (with CO2 removed) was added to a three-necked flask. The two solutions from steps A and B were then added dropwise to a 500 mL three-necked flask. During titration, the pH of the solution was maintained at 10, and the temperature was maintained at 80℃. After titration, the precipitate was washed with deionized water (with CO2 removed) and centrifuged until the supernatant was neutral. The solid was then vacuum-dried in a freeze dryer for 24 h to obtain the hydrotalcite precursor, denoted as NO3. - -CoMnAl-LDHs; S4: Weigh 0.3 g of the hydrotalcite precursor obtained in step S3 and dissolve it in deionized water to remove CO2. Under an inert atmosphere, add 0.560 mL of 0.05306 mol / L RuCl3 dropwise, denoted as solution C. After stirring for 2 h, add 0.0056 g of NaBH4 to reduce the metallic Ru salt in the liquid phase. The molar ratio of NaBH4 to the metallic Ru salt is 1:5. After stirring for 2 h, filter the resulting solution, wash with deionized water, and centrifuge until the supernatant is neutral. Place the solid in a freeze dryer and vacuum dry for 12 h to obtain NO3 loaded with metallic Ru. - Intercalated hydrotalcite, denoted as Ru / NO3 - -CoMnAl-LDHs.
[0057] Comparative Example 1 S1: Weigh 0.012 mol of Cu(NO3)2·3H2O solid and 0.006 mol of Al(NO3)3·9H2O solid. Dissolve the three soluble metal salts in a beaker containing 100 mL of deionized water to remove CO2 to prepare a mixed metal salt solution A.
[0058] S2: Weigh 0.072 mol NaOH solid and dissolve it in a beaker containing 100 mL of deionized water to remove CO2 to prepare precipitant solution B.
[0059] S3: CuAl-LDHs were synthesized using a co-precipitation method. The water bath temperature was set to 80℃. Under a N2 atmosphere, 100 mL of deionized water (with CO2 removed) was added to a three-necked flask. The two solutions from steps S1 and S2 were then added dropwise to a 500 mL three-necked flask. During the titration, the pH of the solution was maintained at 9, and the temperature was maintained at 80℃. After titration, the precipitate was washed with deionized water (with CO2 removed) and centrifuged until the supernatant was neutral. The solid was then vacuum-dried in a freeze dryer for 24 h to obtain the hydrotalcite precursor, denoted as NO3. - -CuAl-LDHs; S4: Weigh 0.3 g of the hydrotalcite precursor obtained in step S3 and dissolve it in deionized water to remove CO2. Under an inert atmosphere, add 0.625 mL of 0.04530 mol / L Na2PdCl4 dropwise, denoted as solution C. After stirring for 1 h, add 0.0053 g of NaBH4 to reduce the metal Pd salt in the liquid phase. The molar ratio of NaBH4 to metal Pd salt is 1:5. After stirring for 1 h, filter the resulting solution, wash with deionized water, and centrifuge until the supernatant is neutral. Place the solid in a freeze dryer and vacuum dry for 12 h to obtain NO3 loaded with metal Pd. - Intercalated hydrotalcite, denoted as Pd / NO3 - -CuAl-LDHs.
[0060] Comparative Example 2 S1: Weigh 0.01 mol of Cu(NO3)2·3H2O solid, 0.03 mol of Co(NO3)2·6H2O solid, and 0.02 mol of Al(NO3)3·9H2O solid. Dissolve the three soluble metal salts in a beaker containing 100 mL of deionized water (after removing CO2) to prepare a mixed metal salt solution A.
[0061] S2: Weigh 0.072 mol NaOH solid and dissolve it in a beaker containing 100 mL of deionized water to remove CO2 to prepare precipitant solution B.
[0062] S3: CuCoAl-LDHs were synthesized using a co-precipitation method. The water bath temperature was set to 80℃. Under a N2 atmosphere, 100 mL of deionized water (with CO2 removed) was added to a three-necked flask. The two solutions from steps S1 and S2 were then added dropwise to a 500 mL three-necked flask. During the titration, the pH of the solution was maintained at 9, and the temperature was maintained at 80℃. After titration, the precipitate was washed with deionized water (with CO2 removed) and centrifuged until the supernatant was neutral. The solid was then vacuum-dried in a freeze dryer for 24 h to obtain the hydrotalcite precursor, denoted as NO3. - -CuCoAl-LDHs; S4: Weigh 0.3 g of the hydrotalcite precursor obtained in step S3 and dissolve it in deionized water to remove CO2. Under an inert atmosphere, add 0.625 mL of 0.04530 mol / L Na2PdCl4 dropwise, denoted as solution C. After stirring for 1 h, add 0.0053 g of NaBH4 to reduce the metal Pd salt in the liquid phase. The molar ratio of NaBH4 to metal Pd salt is 1:5. After stirring for 1 h, filter the resulting solution, wash with deionized water, and centrifuge until the supernatant is neutral. Place the solid in a freeze dryer and vacuum dry for 12 h to obtain NO3 loaded with metal Pd. - Intercalated hydrotalcite, denoted as Pd / NO3 - -CuCoAl-LDHs.
[0063] Application example: Example 1 The bifunctional catalysts prepared in Examples 5 and 1-2 were applied under simulated real air atmosphere according to the following steps: The reaction conditions are as follows: 0.2000 g of bifunctional catalyst is uniformly mixed with 1.8000 g of quartz sand with a particle size of 40-70 mesh, and the mixture is packed into a quartz glass tube. The two ends of the reaction medium are fixed with quartz wool and placed in the middle of the reactor device. Then, an oxidizing capture atmosphere (400 ppm CO2 + 20% O2 + N2) is introduced to capture CO2 at a low concentration at room temperature. At the same time, water vapor is introduced to complete the capture process.
[0064] After capture, inert gas was introduced for 20 min to purge the air from the reactor. Then, a reducing atmosphere (H2 / N2 mixture) was introduced for 20 min. The reactor outlet was closed, and the H2 / N2 mixture pressure was raised to 0.1 MPa before the inlet was closed, bringing the entire reactor to a closed state. The temperature was increased to the reaction temperature of 100–300 °C at a rate of 15 °C / min, with the gas circulating within the reactor using a peristaltic pump. After the reactor reached the set temperature, 5 mL of gas was injected into a gas chromatograph every 1 h using a syringe for analysis. The catalyst activity was evaluated by detecting the concentration of the product in the gas.
[0065] After the reaction was complete, the reaction apparatus was purged with inert gas for 30 minutes to clean the reaction system. Once the apparatus temperature had cooled to room temperature, an oxidizing atmosphere (400 ppm CO2 + 20% O2 + N2) was introduced again, and the CO2 capture reaction was carried out in the presence of water vapor for 10 hours. After capture, the above steps were repeated for the in-situ conversion reaction. The capture atmosphere was switched to 400 ppm CO2+N2, which does not contain oxygen. Under the same experimental conditions, a control experiment was conducted on capture under low concentration CO2 and in-situ hydrogenation conversion to reveal the effect of the presence of O2 in the capture atmosphere.
[0066] The bifunctional catalysts prepared according to the methods of Examples 1-5 and Comparative Examples 1-2 were applied in the manner described above. The results are shown in Table 1. Table 1 shows that the bifunctional catalysts provided by this invention improved the capture capacity for low-concentration CO2 in an oxidizing capture atmosphere, with a CO2 capture capacity of 1.142–1.858 mmol / g. In a reducing conversion atmosphere, the yield of product CH4 was 1.131–1.802 mmol / g. However, in an oxygen-free capture atmosphere (400 ppm CO2 + N2), both the CO2 capture capacity and the yield of product CH4 decreased. This indicates that in an oxidizing capture atmosphere, O2 drives the change in the valence state of variable-valence metals, increasing the CO2 capture amount and, in the subsequent in-situ hydrogenation process, increasing the yield of product CH4. In the integrated reaction device, the bifunctional catalyst effectively couples the capture and conversion steps together, improving the CO2 capture amount and the yield of product CH4 at low concentrations, and promoting the carbon dioxide capture, utilization, and storage (CCUS) reaction.
[0067] Table 1
[0068] Characterization tests on the catalyst product obtained from the preparation steps of Example 1 show that: Figure 1 The XRD pattern of the sample obtained in Example 1 shows that the synthesized catalyst has characteristic peaks of LDHs, indicating that CuCoAl-LDHs were successfully synthesized. After loading metal Pd, the positions of the (003), (006), (009), (110) and (113) diffraction peaks of LDHs did not change, and no obvious characteristic diffraction peaks of Pd particles were observed, indicating that the crystal structure type and interlayer spacing of LDHs did not change significantly after loading metal Pd.
[0069] Figure 2 To analyze the morphology of the catalyst prepared in Example 1, high-resolution transmission electron microscopy images showed that after Pd was loaded onto the laminations by liquid-phase reduction, the LDH lamination structure was still maintained, laying the foundation for carbon dioxide capture and conversion.
[0070] Figure 3The bar chart shows the performance of the catalyst prepared in Example 1 as a function of temperature, indicating that the LDHs bifunctional material can achieve in-situ reduction of interlayer carbonate at low temperatures of 100℃ to 300℃ under H2 / N2 atmosphere, with CH4 as the main hydrogenation product. The methane yield shows a trend of first increasing and then decreasing, with the best hydrogenation performance at 200℃ to 260℃.
[0071] Figure 4 The Pd / NO3 prepared in Example 1 - -CuCoAl-LDHs catalyst after capture (T1 state), after reaction (T2 state), and after recapture (T1 state) R XPS spectra of the three stages (state) show that the variable valence metals in the plates increase in an oxidizing trap atmosphere, decrease in a reducing conversion atmosphere, and then recover to their high oxidation state during the recapture stage. The cycle of variable valence metals in the plates drives the CO2 direct air capture-in-situ conversion cycle.
[0072] Figure 5 The Pd / NO3 prepared in Example 1 - The performance of the CuCoAl-LDHs catalyst after six reuses was demonstrated, indicating that the catalyst still exhibits good stability after six reuses.
[0073] Figure 6 This diagram shows an application setup for a multi-metal LDH bifunctional catalyst. The reaction procedure is simple and easy to operate, and the reactor requires a small footprint, which is conducive to industrialization.
[0074] It should be understood that this application is not limited to the processes and structures described above and shown in the accompanying drawings, and various modifications and changes can be made without departing from its scope. The scope of this application is limited only by the appended claims.
Claims
1. A multi-metal LDHs bifunctional catalyst, characterized in that, The chemical formula is P / NO3 - -M2M3-LDHs, where: P is a precious metal, selected from one of Pt, Pd, Ru, and Ir; M2 is a divalent metal ion selected from Cu. 2+ Co 2+ Fe 2+ Mn 2+ At least two of them; M3 is a trivalent metal ion selected from Al. 3+ Fe 3+ Ga 3+ Cr 3+ Mn 3+ Ce 3+ One of them.
2. The multi-metal LDHs bifunctional catalyst according to claim 1, characterized in that, The XRD pattern of the LDHs bifunctional catalyst showed characteristic diffraction peaks of (003), (006), (009), (110) and (113).
3. The multi-metal LDHs bifunctional catalyst according to claim 1, characterized in that, The molar ratio of M2 to M3 is 2 to 4:
1.
4. The multi-metal LDHs bifunctional catalyst according to claim 1, characterized in that, The total ion concentration of M2 and M3 is 0.18 mol / L to 0.4 mol / L.
5. The multi-metal LDHs bifunctional catalyst according to claim 1, characterized in that, The mass ratio of P to LDHs is 1 to 5%.
6. The multi-metal LDHs bifunctional catalyst according to claim 1, characterized in that, The LDHs bifunctional catalyst exhibits a CO2 capture capacity of 1.142–1.858 mmol / g at room temperature and a CH4 yield of 1.131–1.802 mmol / g in a H2 / N2 reducing atmosphere at 100℃–300℃.
7. A method for preparing a multi-metal LDHs bifunctional catalyst according to any one of claims 1-6, characterized in that, The method includes the following steps: S1: Dissolve soluble nitrates containing M2 and M3 in deionized water after CO2 removal to prepare mixed solution A, where M2 is a divalent metal ion selected from Cu. 2+ Co 2+ Fe 2+ Mn 2+ At least two of them; M3 is a trivalent metal ion selected from Al 3+ Fe 3 + Ga 3+ Cr 3+ Mn 3+ Ce 3+ One of them; the molar ratio of M2 to M3 is 2 to 4:1; S2: Dissolve the alkali in deionized water from which CO2 has been removed to prepare precipitant solution B, wherein the alkali is selected from NaOH or KOH; S3: Add no more than 1 / 3 of the container volume of deionized water (after removing CO2) to the reactor. Under a nitrogen atmosphere, add equal volumes of solution A and solution B dropwise into the reactor. During the titration, maintain the pH of the solution at 9-10. After titration, wash and centrifuge until the supernatant is neutral. Vacuum dry solid A to obtain the hydrotalcite precursor, denoted as NO3. - -M2M3-LDHs; S4: The hydrotalcite precursor obtained in step S3 is placed under an inert atmosphere, and deionized water with CO2 removed is added and stirred. A metal P salt solution is added dropwise, with the amount of metal P salt solution added ensuring that the mass ratio of metal P to LDHs in the bifunctional catalyst is 1–5%. NaBH4 is added to perform liquid-phase reduction of metal P, with the molar amount of NaBH4 being 5 times that of the metal P salt. After stirring for 1–2 hours, the resulting solution is filtered and washed with deionized water until the supernatant is neutral. Solid B is then vacuum dried to obtain NO loaded with metal P. 3- Intercalated hydrotalcite, denoted as P / NO3 - -M2M3-LDHs; The metal P is one of Pt, Pd, Ru, and Ir.
8. The method for preparing the multi-metal LDHs bifunctional catalyst according to claim 7, wherein the total ion concentration of M2 and M3 is 0.18 mol / L to 0.4 mol / L.
9. The method for preparing the multi-metal LDHs bifunctional catalyst according to claim 7, wherein the alkali concentration of solution B is 0.45 mol / L to 1 mol / L.
10. A fixed bed device, characterized in that, The immobilization device comprises the multi-metal LDHs bifunctional catalyst according to any one of claims 1-6.