LDHs (Layered Double Hydroxides) bifunctional catalyst for preparing CO through CO2 selective absorption in-situ relay coupling low-energy-consumption conversion as well as preparation method and application of LDHs bifunctional catalyst

Abstract

The invention relates to an LDHs (Layered Double Hydroxides) bifunctional catalyst for preparing CO through CO2 selective absorption in-situ relay coupling low-energy-consumption conversion as well as a preparation method and application of the LDHs bifunctional catalyst. Controlling the thickness of a laminate to prepare an ultrathin NO3-intercalated LDHs carrier, adding a metal salt solution in N2 atmosphere, and reducing metal to obtain the catalyst. The method comprises the following steps of: applying the LDHs to a reaction device, introducing CO2-containing feed gas, realizing the trapping process that CO2 is stored between the LDHs in the form of CO3 < 2-> in the presence of water vapor, and then performing low-temperature in-situ conversion on the CO3 < 2-> in the interlayer into a high-added-value product in an H2 atmosphere. After the reaction, the catalyst continues to selectively capture CO2 and is repeatedly used, and CO2 capture-in-situ conversion integration is achieved. According to the invention, H < + > transfer and interlayer carbonate reduction are promoted; meanwhile, desorption of a CO intermediate on the surface of the catalyst is accelerated, subsequent reaction steps are prevented, and therefore the process of preparing CO from CO2 at low temperature is achieved, energy consumption is low, efficiency is high, and selectivity is high.

Description

Technical Field

[0001] The present invention relates to a CO 2 LDHs bifunctional catalyst for selective absorption in-situ relay coupling low-energy conversion to CO, and preparation method and application thereof. Background Art

[0002] At present, the impact of excessive carbon dioxide gas emissions on global climate change cannot be ignored, and it is necessary to find an effective carbon dioxide capture and utilization system. 2 and CO 2 Hydrogenation to fuels and chemicals is the key to achieving CO 2 However, due to the difficulty of capturing carbon dioxide and its thermodynamic stability, this remains a challenging step. 2 Integrated capture-in-situ conversion bifunctional catalyst to convert carbon dioxide into other value-added products.

[0003] Most of the materials reported so far use solid capture materials based on alkali metal oxides and active metals as catalytic hydrogenation sites to achieve capture and conversion. 2 It is a strongly endothermic reaction, requires high energy input, and captures CO 2 The later generated Na 2 CO 3 MgCO 3 、CaCO 3 Carbonates such as Ni-CaO are relatively stable, and the conversion temperature is often above 500°C. 2 Capture and conversion.Chem Eng J, 2022, 428: 132110. Using Ni-CaO dual-functional materials for integrated CO in flue gas environments 2 Capture and conversion to generate CO, the capture and conversion temperature is up to 650°C. In addition, alkali metal oxides directly capture CO from industrial waste gas 2 When SO x 、NO x Acidic gases such as Na-Ru / Al-2 not only affect the capture selectivity, but also poison and deactivate the bifunctional catalyst to a certain extent; Reference 2 on Sulfur tolerance and self-regeneration mechanism of Na-Ru / Al-22 O 3 dual function material during the cyclic CO 2 A metal oxide bifunctional material containing Na and Ru was used to test CO capture and catalytic methanation under simulated flue gas conditions. 2 The results show that the presence of 1% water vapor can poison the catalyst, making CO 2 The capture capacity is reduced by about 20%; only 10ppm SO 2 The presence of impurity gases can cause competitive adsorption, making CO 2 Capture ability reduced by approximately 10%.

[0004] On this basis, the development of suitable CO 2 The selective absorption of low-energy in-situ conversion bifunctional catalyst plays an important role in simplifying the process and reducing energy input. At the same time, for the conversion product, CO is the "building block molecule" of C1 chemistry. Almost all basic carbon-based chemicals can be obtained from CO, but CO 2 Hydrogenation to CO is an endothermic reaction, and the production of CO is thermodynamically more favorable at higher temperatures. It is undeniable that high temperature conditions are more likely to cause catalyst deactivation and generate more energy consumption. Therefore, the preparation of CO 2 The bifunctional catalyst that selectively absorbs and couples in-situ relay to generate CO with low energy consumption can improve the efficiency of the entire process and reduce costs, thus realizing the efficient utilization of industrial gas emissions.

[0005] Layered composite metal hydroxides are a type of anionic clay with a two-dimensional structure, referred to as hydrotalcite (LDHs), and are a new type of basic carbonate inorganic material. According to the stability order of anions between layers: CO 3 2- >SO 4 2- >HPO 4 2- >F - >Cl - >NO 3 - It can be seen that LDHs materials have the ability to selectively convert CO 2 Captured in the interlayer to form CO 3 2- The interlayer confinement effect of LDHs and the ion polarization effect can anchor the metal with hydrogenation activity on the surface of the metal layer to realize H2 CO in the atmosphere 3 2- Efficient in-situ conversion of CO 2 The process coupling of capture and in-situ conversion. The controllable thickness of LDHs material also provides a basis for the interlayer CO 3 2- The in-situ conversion process provides convenience for product regulation. By changing the concentration of the added formamide solution to control the thickness of LDHs, ultra-thin layered LDHs with limited stacking degree of the layers are obtained. + On the other hand, it accelerates the desorption of CO intermediates on the catalyst surface, preventing the subsequent reaction steps from occurring, thereby achieving CO 2 The integrated process of selective absorption and in-situ relay coupling to produce CO with low energy consumption provides new ideas and approaches for the efficient and comprehensive utilization of carbon resources.

[0006] Therefore, the present invention uses hydrotalcite as a carrier to load metals to prepare a basic carbonate bifunctional catalyst in a flow reaction system to complete CO 2 Selective absorption and in-situ conversion reaction. The dual-functional catalyst is used for the adsorption and capture process of flue gas emissions, and then hydrogenation is carried out in-situ to generate high value-added products CO. After the reaction, the catalyst enters the adsorption and capture process again to achieve the reuse of industrial emissions and efficient use of resources. The whole method and device are simple in design, CO 2 The improvement of reduction efficiency provides a new idea and direction for industrial carbon dioxide capture and utilization (CCU); at the same time, producing CO at low temperature reduces the energy consumption of producing CO at high temperature in the past, and also provides more economic benefits for energy utilization and recovery. Summary of the invention

[0007] The object of the present invention is to provide a CO 2 LDHs bifunctional catalyst for selective absorption in-situ relay coupling low-energy conversion to CO, and preparation method and application thereof.

[0008] The catalyst prepared by the present invention has a chemical formula of N / NO 3 - -M 2+ M 3+ -LDHs, where N represents precious metals such as Pt, Pd, and Ru; M 2+ For Co 2+ 、Ni 2+ 、Zn 2+ , Cu 2+ Mg 2+ One or two of M 3+ For Al 3+ , Fe 3+ , Ga3+ Cr 3+ One of the 2 + :M 3+ The molar ratio of is 2 to 4:1; compared with the prior art, this catalyst can be used to selectively capture CO in air and industrial waste gas such as cement, steel, and lime kilns. 2 At 100℃~300℃, the 2 The bifunctional catalyst of the present invention is used to convert CO into high value-added product CO in situ in the atmosphere. 2 The capture capacity is 0.3-1.4 mmol / g, the conversion rate is 90%, and the CO selectivity is 2%-35%. During the reaction, the carbonate between the LDHs nanosheets is continuously consumed and converted into the reduction product CO at low temperature. After the reaction, it can selectively absorb CO in the mixed atmosphere. 2 Converted to interlayer CO 3 2- It can be restored and reused many times to achieve CO 2 Integrated capture and in-situ conversion.

[0009] The present invention provides a CO 2 LDHs bifunctional catalyst for selective absorption in-situ relay coupling low energy conversion to CO and its preparation method and application, the specific preparation steps are as follows:

[0010] A. Soluble M 2+ 、M 3+ Nitrates dissolve in the CO 2 Prepare mixed solution A, M in deionized water 2+ :M 3+ The molar ratio is 2 to 4:1, where M 2+ The molar concentration is 0.05mol / L~0.10mol / L;

[0011] The M 2+ For Co 2+ 、Ni 2+ 、Zn 2+ , Cu 2+ Mg 2+ One or two of M 3+ For Al 3+ , Fe 3+ , Ga 3+ Cr 3+ One of;

[0012] B. Use alkali to remove CO 2 Prepare a precipitant solution B in deionized water, wherein the alkali is NaOH or KOH, and the concentration of the alkali solution is 0.425 mol / L to 1.05 mol / L;

[0013] C. Add a solution with a volume percentage of 5% to 30% formamide to the three-necked flask to remove all CO. 2 Deionized water solution, in a hot water bath at 80℃, stirring at 500rpm and under nitrogen protection, solution A and solution B were dripped into a three-necked flask. The pH of the solution was kept at 9-11 during the titration process by controlling the amount of alkaline solution B added until the addition of solution A was completed. After the addition was completed, the sample was directly centrifuged and washed until the supernatant was neutral, and freeze-dried for 12 hours. The thickness of the obtained sample was 1.2nm-8.5nm, expressed as B-NO 3 - -M 2+ M 3+ -LDHs, B is the concentration of the formamide solution contained in the solution of equal volume to solution A in the three-necked flask;

[0014] D. Dissolve the precipitate obtained in step D in 2 Place the deionized water solution in a nitrogen atmosphere, add another metal N salt solution dropwise thereto, the amount of metal N salt solution added should make the mass ratio of metal N to LDHs in the final catalyst be 1-5%, stir for 1-2h; add NaBH 4 Liquid phase reduction of metallic N, NaBH 4 The molar amount added is 5 times that of the metal N salt, stirred for 1 to 2 hours, and the resulting solution was filtered and the CO 2 The solid was washed with deionized water until the supernatant was neutral, and the solid was placed in a freeze dryer and vacuum dried for 12 h to obtain NO loaded with metal N 3 - Intercalation of hydrotalcite with different thicknesses, finally expressed as N / B-NO 3 - -M 2+ M 3+ -LDHs;

[0015] The metal N salt is H 2 PtCl 4 、Na 2 PdCl 4 、RuCl 3 ·3H 2 O, and the metal N salt loading is the mass percentage of the N salt in the catalyst.

[0016] The present invention provides a CO 2The LDHs bifunctional catalyst, which selectively absorbs and couples the in-situ low-energy conversion to produce CO, can continuously complete the capture and conversion of carbon dioxide from air and industrial waste gas such as cement, steel, and lime kilns in the reactor. The specific application process of this catalyst includes two stages: (1) adsorption and capture stage: the bifunctional catalyst absorbs CO in the raw gas 2 Selective capture of CO in the presence of water vapor 2 CO 3 2- Stored in the LDHs interlayer in the form of; (2) Gasification reaction stage: interlayer CO 3 2- In H 2 The consumed CO in the atmosphere is converted into high value-added products in situ, achieving CO 2 Integrated capture and in-situ conversion to produce CO.

[0017] The present invention also provides a CO 2 A reactor device using a dual-function catalyst for selective absorption in-situ relay coupling and low-energy conversion to produce CO is provided. A raw gas inlet, a hydrogen device and a gas purge port are arranged at the top of the reactor, an exhaust port is arranged at the bottom of the reactor, and the interior of the reactor is filled with a reaction medium.

[0018] The flue gas flow completes the capture process under the condition of water vapor, and after purging with nitrogen for five minutes, the hydrogen device is turned on and introduced into the reactor to generate CO 2 In-situ conversion reaction process. The catalyst after the reaction enters the adsorption capture process for recycling.

[0019] A CO 2 The application process of the dual-function catalyst for selective absorption in-situ relay coupling low-energy conversion to produce CO is characterized by applying it in a simulated flue gas atmosphere according to the following steps:

[0020] (1) N / B-NO 3 - -M 2+ M 3+ -LDHs catalyst basic carbonate and quartz sand are uniformly mixed and loaded into a steel tube reactor as a reaction medium;

[0021] (2) 15% CO 2 +75% N 2 +200ppm NO 2 The simulated flue gas passes through a material bottle filled with water and enters the reactor to complete the capture process. Subsequently, the flue gas in the reactor is purged with an inert gas flow and 0.1 MPa H 2 The process is closed and the airflow is circulated by a peristaltic pump. The reaction temperature is 100 to 300°C and the reaction is carried out at a constant temperature for 1 to 3 hours.

[0022] (3) After the reaction, the CO in the raw gas is purged with an inert gas stream in the presence of water vapor. 2 Selectively capture CO 2 CO 3 2- in the form of stored between the basic carbonate LDHs layers and used in the next reaction.

[0023] The product obtained in the above steps was characterized as follows:

[0024] Figure 1 The XRD spectra of the final catalysts obtained by the above steps in Example 1 were respectively added with 5%, 15%, and 25% formamide solutions. The synthesized catalysts all had the characteristic peaks of LDHs, indicating that NO was successfully synthesized. 3 - For the NiMgFe-LDHs, after loading metal Pt, the positions of the diffraction peaks (003), (006), and (009) of the LDHs did not change, and no obvious characteristic diffraction peaks of Pt particles were observed, indicating that the crystal structure type and interlayer spacing of the LDHs did not change significantly after loading metal Pt. The (003) peak of the final catalyst after adding 30% formamide solution shifted to the right, indicating that the lattice contracted and the interlayer spacing became smaller.

[0025] Figure 2 The morphologies of the three groups of final catalysts obtained in Example 1, to which 5%, 15% and 25% formamide solutions were added respectively, were analyzed. The high-resolution electron microscope structure showed that after Pt was loaded on the layer plate by the liquid phase reduction method, the LDHs layer plate structure was still maintained, laying the foundation for the capture and conversion of carbon dioxide.

[0026] Figure 3 The three catalysts with different thicknesses obtained in Example 1 were respectively introduced with 15% CO 2 +75%N 2 +200ppmNO 2 After the simulated flue gas passes through a material bottle filled with water and enters the reactor to complete the capture process, the flue gas in the reactor is purged with an inert gas flow and 0.1 MPa H 2 The reaction was closed and the air flow was circulated by a peristaltic pump. The reaction temperature was 250°C and the reaction was kept at a constant temperature for 2 hours. It was found that the final catalyst with the addition of 15% formamide solution had the best capture conversion performance.

[0027] Figure 4 The curve of the final catalyst performance obtained in Example 1 by adding 15% formamide solution as a function of temperature shows that in pure H 2Under the atmosphere, LDHs-based bifunctional materials can achieve in-situ reduction of interlayer carbonates at low temperatures of 100°C to 300°C to generate CO. It is worth noting that the yield of hydrogenation products of the catalyst in the reaction temperature range presents a volcano-shaped curve, among which the hydrogenation performance is optimal at 150°C to 250°C.

[0028] Figure 5 The final catalyst obtained in Example 1 was added with 15% formamide solution and CO was introduced into the 2 Mixed gas (15% CO 2 +85% N 2 , 15% CO 2 +75% N 2 +200ppm NO 2 , 15% CO 2 +75%N 2 +200ppm SO 2 ), CO in the presence of water vapor 2 The results show that the catalyst can still selectively capture CO at the reaction temperature under mixed gases containing nitrogen oxides or sulfur oxides. 2 , with a selectivity greater than 97%, and NO 2 Atmosphere for CO 2 The selectivity of capture has little effect.

[0029] Figure 6 The final catalyst B-Pt / NO obtained by adding 15% formamide solution obtained in Example 1 3 2- -NiMgFe-LDHs was bubbled with 15% CO 2 +75% N 2 +200ppm NO 2 The simulated flue gas passes through a material bottle filled with water and enters the reactor to complete the capture process. Subsequently, the flue gas in the reactor is purged with an inert gas flow and 0.1 MPa H 2 The system was closed and the air flow was circulated using a peristaltic pump. The reaction temperature was 250°C and the reaction was kept at a constant temperature for 2 hours. The system was reused 7 times. The results showed that the catalyst still had good stability after seven repeated uses.

[0030] Beneficial effects of the present invention:

[0031] 1. The present invention provides a CO 2 A bifunctional catalyst for selective absorption and in-situ relay coupling to produce CO with low energy consumption, using the characteristics of LDHs basic carbonates, NO between LDHs 3 - Capable of absorbing CO from flue gas 2, so that the catalyst can be supplemented with carbon source from flue gas, so as to achieve the purpose of repeated use, with high selectivity, reducing carbon emissions and achieving CO 2 Resource utilization.

[0032] 2. The present invention provides a CO 2 The preparation method and application of a bifunctional catalyst for selective absorption in-situ relay coupling and low-energy conversion to produce CO can be used to selectively capture CO in air and industrial waste gas such as cement, steel, and lime kilns. 2 At 100℃~300℃, the 2 The conversion of CO into high value-added products in situ in the atmosphere can not only achieve CO 2 The capture and utilization of CO2 can be greatly reduced, and the reaction process temperature is greatly reduced, and the energy consumption is lower than that of traditional CO2 2 Capture technology helps reduce costs and investment.

[0033] 3. The integrated design of the present invention occupies a small area, has a simple process and low loss, and converts the waste gas generated in the industrial production process. It is worth mentioning that high-value-added product CO is generated at low temperature, which improves energy utilization efficiency and meets different industrial manufacturing needs. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 The XRD spectra of the three groups of samples in Example 1.

[0035] Figure 2 HRTEM photos of three groups of catalysts prepared in Example 1.

[0036] Figure 3 The capture conversion performance of the three groups of catalysts prepared in Example 1 under the same conditions.

[0037] Figure 4 Pt / 15%-NO prepared in Example 1 3 2- -NiMgFe-LDHs catalyst, according to the conditions of the application example, in 15% CO 2 +75% N 2 +200ppm NO 2 After capture in a simulated flue gas atmosphere, pure H 2 Catalytic performance obtained after reaction for 2 h at different temperatures under atmosphere.

[0038] Figure 5 Pt / 15%-NO prepared in Example 1 3 2- -NiMgFe-LDHs second group of catalysts were used in different CO 2 CO obtained under mixed gas2 Capture selectivity.

[0039] Figure 6 (a) Pt / 15%-NO prepared in Example 1 3 2- -NiMgFe-LDHs catalyst was fed with 15% CO according to the conditions of the application example 2 +75% N 2 +200ppm NO 2 The simulated flue gas passed through a material bottle filled with water and then entered the reactor, and the capture process was repeated seven times; Figure 6 (b) 0.1 MPa H is introduced into the catalyst. 2 The reaction was closed and the air flow was circulated by a peristaltic pump. The reaction temperature was 250°C and the reaction was carried out at a constant temperature for 2 hours. The conversion performance was repeated seven times.

[0040] Figure 7 For a CO 2 Diagram of the application device of bifunctional catalyst for producing CO by selective absorption and in-situ relay coupling with low energy consumption conversion. DETAILED DESCRIPTION

[0041] Example 1

[0042] A: Weigh 0.0045 mol of Ni(NO 3 ) 2 6H 2 O, 0.0045 mol Mg(NO 3 ) 2 6H 2 O solid and 0.0045 mol Fe(NO 3 ) 3 9H 2 O solid, dissolve the three salts in 100 mL of water to remove all CO 2 Prepare mixed salt solution A in a beaker of deionized water.

[0043] B: Weigh 0.045 mol of NaOH solid and dissolve it in 100 ml of water to remove CO 2 Prepare alkaline solution B in a beaker of deionized water.

[0044] C: Synthesize NiMgFe-LDHs by coprecipitation method. Add 5%, 15% or 25% formamide (volume percentage) equal to solution A into a three-necked flask to remove all CO 2Deionized water solution, in a hot water bath at 80℃, stirring at 500rpm and under nitrogen protection, solution A and solution B were dripped into a three-necked flask. The pH of the solution was kept at 10 during the titration process by controlling the amount of alkaline solution B added until the addition of solution A was completed. After the addition was completed, the samples were directly centrifuged and washed until the supernatant was neutral, and freeze-dried for 12h. The three groups of samples were expressed as 5%-NO 3 - -NiMgFe-LDHs, 15%-NO 3 - -NiMgFe-LDHs, 25%-NO 3 - -NiMgFe-LDHs;

[0045] D: Weigh 0.300 g of the three groups of samples obtained in step C and dissolve them in 30.0 mL of 1% CO 2 In a beaker of deionized water, 1.44 mL and 50 mmol / L H 2 PtCl 4 The solution was stirred for 1 hour; 5 times the molar amount of metal Pt NaBH 4 The liquid phase reduction was stirred for 1 h, and the resulting solution was filtered and the CO 2 The solid was washed with deionized water until the supernatant was neutral, and the solid was placed in a freeze dryer and vacuum dried for 12 h to obtain Pt-loaded NO 3 - The intercalated hydrotalcite is finally expressed as Pt / 5%-NO 3 2- -NiMgFe-LDHs, Pt / 15%-NO 3 2- -NiMgFe-LDHs, Pt / 25%-NO 3 2- -NiMgFe-LDHs;

[0046] Example 2

[0047] A: Weigh 0.018 mol of Zn(NO 3 ) 2 6H 2 O solid and 0.009 mol Ga(NO 3 ) 3 9H 2 O solid, dissolve the two salts in 100 mL of water to remove all CO 2 Prepare mixed salt solution A in a beaker of deionized water.

[0048] B: Weigh 0.045 mol of NaOH solid and dissolve it in 100 ml of water to remove CO 2Prepare alkaline solution B in a beaker of deionized water.

[0049] C: Synthesize ZnGa-LDHs by coprecipitation method. Add an equal volume of 10% formamide to solution A in a three-necked flask to remove all CO. 2 Deionized water solution, in a hot water bath at 80℃, stirring at 500rpm and under nitrogen protection, solution A and solution B were dripped into a three-necked flask. The pH of the solution was kept at 10 during the titration process by controlling the amount of alkaline solution B added until the addition of solution A was completed. After the addition was completed, the solution was directly centrifuged and washed until the supernatant was neutral, and freeze-dried for 12h, which was expressed as 10%-NO 3 - -ZnGa-LDHs;

[0050] D: Weigh 0.300 g of 10% -NO obtained in step C 3 - -ZnGa-LDHs catalyst was dissolved in 30.0 mL of CO 2 In a beaker of deionized water, 1.13 mL of 50 mmol / L RuCl was added dropwise to the solution. 3 ·3H 2 O solution, stirred for 1 hour; weigh 5 times the molar amount of metal Ru NaBH 4 The liquid phase reduction was stirred for 1 h, and the resulting solution was filtered and the CO 2 The solid was washed with deionized water until the supernatant was neutral, and the solid was placed in a freeze dryer and vacuum dried for 12 h to obtain Ru-loaded NO 3 - The intercalated hydrotalcite is finally expressed as Ru / 10%-NO 3 2- -ZnGa-LDHs.

[0051] Example 3

[0052] A: Weigh 0.003 mol of Ni(NO 3 ) 2 6H 2 O solid, 0.003 mol Co(NO 3 ) 2 6H 2 O solid and 0.003 mol Al(NO 3 ) 3 9H 2 O solid. Dissolve the three salts in 100 mL of water to remove all CO 2 Prepare mixed salt solution A in a beaker of deionized water.

[0053] B: Weigh 0.064 mol of NaOH solid and dissolve it in 100 ml of water to remove all CO2 Prepare alkaline solution B in a beaker of deionized water.

[0054] C: Synthesis of NiCoAl-LDHs by coprecipitation method: Add an equal volume of solution A to a three-necked flask containing 20% ​​formamide to remove all CO 2 Deionized water solution was added to a three-necked flask in a hot water bath at 80°C, stirred at 500 rpm and protected by nitrogen. The pH of the solution was kept at 10 during the titration process by controlling the amount of alkaline solution B added until the addition of solution A was completed. After the addition was completed, the solution was directly centrifuged and washed until the supernatant was neutral, and freeze-dried for 12 hours to obtain a hydrotalcite carrier, expressed as 20%-NO 3 - -NiCoAl-LDHs;

[0055] D: Weigh 0.300 g of 20%-NO obtained in step C 3 - -NiCoAl-LDHs catalyst was dissolved in 30.0 mL of CO 2 In a beaker of deionized water, 1.13 mL of 50 mmol / L Na 2 PdCl 4 The solution was stirred for 1 hour; 5 times the molar amount of metal Pd was weighed, and NaBH 4 The liquid phase reduction was stirred for 1 h, and the resulting solution was filtered and the CO 2 The solid was washed with deionized water until the supernatant was neutral, and the solid was placed in a freeze dryer and vacuum dried for 12 h to obtain Pd-loaded NO 3 - The intercalated hydrotalcite is finally expressed as Pd / 20%-NO 3 2- -NiCoAl-LDHs.

[0056] Example 4

[0057] A: Weigh 0.01 mol of Zn(NO 3 ) 2 6H 2 O solid and 0.005 mol Al(NO 3 ) 3 9H 2 O solid. Dissolve the two salts in 100 mL of water to remove all CO 2 Prepare mixed salt solution A in a beaker of deionized water.

[0058] B: Weigh 1.8% NaOH solid and dissolve it in 100ml of water to remove CO 2 Prepare alkaline solution B in a beaker of deionized water.

[0059] C: Synthesize ZnAl-LDHs by coprecipitation method. Add an equal volume of solution A to a three-necked flask and remove all CO. 2 Deionized water solution was added to a three-necked flask in a hot water bath at 80°C, stirred at 500 rpm and protected by nitrogen. The pH of the solution was kept at 11 during the titration process by controlling the amount of alkaline solution B added until the addition of solution A was completed. After the addition was completed, the solution was directly centrifuged and washed until the supernatant was neutral, and freeze-dried for 12 hours to obtain a hydrotalcite carrier, which was expressed as 0%-NO 3 2- -ZnAl-LDHs.

[0060] D: Weigh 0.300 g of 0%-NO obtained in step C 3 2- -ZnAl-LDHs catalyst was dissolved in 30.0 mL of 2 In a beaker of deionized water, add 1.13 mL of 50 mmol / L Na 2 PdCl 4 After stirring for 1 h, weigh 5 times the molar amount of NaBH 4 The liquid phase reduction was stirred for 1 h, and the resulting solution was filtered and the CO 2 The solid was washed with deionized water until the supernatant was neutral, and the solid was placed in a freeze dryer and dried for 12 h to obtain Pd-loaded NO 3 - The intercalated hydrotalcite is finally expressed as Pd / 0%-NO 3 2- -ZnAl-LDHs.

[0061] Example 5

[0062] A: Weigh 0.01 mol of Zn(NO 3 ) 2 6H 2 O solid and 0.005 mol Al(NO 3 ) 3 9H 2 O solid. Dissolve the two salts in 100 mL of water to remove all CO 2 Prepare mixed salt solution A in a beaker of deionized water.

[0063] B: Weigh 1.8% NaOH solid and dissolve it in 100ml of water to remove CO 2 Prepare alkaline solution B in a beaker of deionized water.

[0064] C: Synthesis of ZnAl-LDHs by coprecipitation method: In a hot water bath at 80°C, stirring at 500 rpm and under nitrogen protection, 30% formamide equal in volume to solution A was added to a three-necked flask to remove all CO. 2 Deionized water solution was added, and solution A and solution B were dripped into a three-necked flask. The pH of the solution was kept at 11 during the titration process by controlling the amount of alkaline solution B added until solution A was added. After the addition was completed, the solution was directly centrifuged and washed until the supernatant was neutral, and freeze-dried for 12 hours to obtain a hydrotalcite carrier, which was expressed as 30%-NO 3 2- -ZnAl-LDHs.

[0065] D: Weigh 0.300 g of 30% -NO obtained in step C 3 2- -ZnAl-LDHs catalyst was dissolved in 30.0 mL of 2 In a beaker of deionized water, add 1.13 mL of 50 mmol / L Na 2 PdCl 4 After stirring for 1 h, weigh 5 times the molar amount of NaBH 4 The liquid phase reduction was stirred for 1 h, and the resulting solution was filtered and the CO 2 The solid was washed with deionized water until the supernatant was neutral, and the solid was placed in a freeze dryer and dried for 12 h to obtain Pd-loaded NO 3 - The intercalated hydrotalcite is finally expressed as Pd / 30%-NO 3 2- -ZnAl-LDHs.

[0066] Application Example 1

[0067] The catalysts prepared in Examples 1-5 were used for CO 2 Selective absorption in situ relay coupling low energy conversion reaction:

[0068] The reaction conditions are as follows: 0.2000 g of catalyst powder and 1.8000 g of quartz sand with a particle size of 40-70 mesh were uniformly mixed and filled into the middle section of the reactor. Inert gas was introduced to replace the air in the device. Then, 0.1 MPa of H 2 The gas was sealed and heated to the reaction temperature (100-300°C) at a heating rate of 10°C / min, and the gas flow was circulated using a peristaltic pump. After the reaction started, 1 mL of gas was taken every 1 hour using a stainless steel gas-tight needle and injected into a gas chromatograph for detection. The concentration of the product in the gas was detected to evaluate the catalyst reaction activity.

[0069] After the reaction is completed, use N 2Purify the reaction system and introduce 0.1MPa CO 2 Mixed gas (15% CO 2 +85% N 2 , 15% CO 2 +75% N 2 +200ppm NO 2 , 15% CO 2 +75% N 2 +200ppm SO 2 ), CO in the presence of water vapor 2 The capture reaction lasts for 10 hours. After the capture is completed, the above steps are repeated to perform the in-situ conversion reaction.

[0070] The dual-functional materials obtained according to the methods of Examples 1-4 were used to seed CO 2 In the selective absorption in-situ relay coupling low energy conversion process, the results are shown in Table 1. It can be seen from Table 1 that the bifunctional catalyst basic carbonate of the present invention has a significant effect on CO 2 The capture capacity is 0.3-1.4 mmol / g, the conversion rate is 90%, and the CO selectivity is 2%-35%. 2 The captured CO 2 Can be almost completely converted into CH 4 and CO, further realizing the carbon dioxide capture and utilization (CCU) reaction under mild conditions.

[0071] Table 1

[0072]

Claims

1. A method for preparing a LDHs bifunctional catalyst for selective CO2 absorption and in-situ relay coupling low-energy conversion to CO, characterized by: A : Soluble metal salt M 2+ and M 3+ Dissolve in deionized water from which CO2 has been completely removed to prepare a mixed solution A, wherein the soluble metal salt refers to M 2+ 、M 3+ Nitrate, M 2+ For Co 2+ 、Ni 2+ 、Zn 2+ , Cu 2+ Mg 2+ One or two of M 3+ For Al 3+ , Fe 3+ , Ga 3+ Cr 3+ One of the 2+ :M 3+ The molar ratio is 2 to 4:1; wherein M 2+ The molar concentration is 0.05mol / L~0.10mol / L; B: Prepare precipitant solution B by dissolving alkali in deionized water from which CO2 has been completely removed, wherein the alkali is NaOH or KOH, and the concentration of the alkali solution is 0.425 mol / L to 1.05 mol / L; C: Add a deionized water solution containing 5% to 30% formamide in a volume percentage concentration equal to that of solution A to a three-necked flask, and drip solution A and solution B into the three-necked flask in a hot water bath at 80°C, stirring at 500 rpm and under nitrogen protection. Keep the pH of the solution at 9 to 11 during the titration process by controlling the amount of alkaline solution B added until solution A is added dropwise; after the addition is completed, centrifuge and wash directly until the supernatant is neutral, and freeze-dry for 12 hours. The thickness of the obtained sample is 1.2nm to 8.5nm, expressed as B-NO3 - -M 2+ M 3+ -LDHs, B is the concentration of the formamide solution contained in the solution of equal volume to solution A in the three-necked flask; D: The precipitate obtained in step C is dissolved in a deionized water solution from which CO2 has been completely removed and placed under a nitrogen atmosphere, and another metal N salt solution is added dropwise thereto. The amount of the metal N salt solution added should make the mass ratio of metal N to LDHs in the final catalyst be 1-5%. After stirring for 1-2 hours, NaBH4 is added to carry out liquid phase reduction of the metal N. The molar amount of NaBH4 added is 5 times that of the metal N salt added. The mixture is stirred for 1-2 hours. The obtained solution is filtered and washed with deionized water from which CO2 has been completely removed until the supernatant is neutral. The solid is placed in a freeze dryer and vacuum dried for 12 hours to obtain NO3 loaded with metal N. - Intercalated hydrotalcite with different thickness, expressed as N / B-NO3 - -M 2+ M 3+ -LDHs; The metal N salt is one of H2PtCl4, Na2PdCl4 and RuCl3·3H2O.

2. The LDHs-based bifunctional catalyst prepared by the method of claim 1 is characterized in that The catalyst is used to selectively capture CO2 in industrial waste gas from air, cement, steel or lime kilns and convert it into CO in situ in a H2 atmosphere at a temperature of 100°C to 300°C.

3. The use of the LDHs-based bifunctional catalyst according to claim 2, characterized in that The catalyst application process includes two stages: (1) Adsorption capture stage: The bifunctional catalyst selectively captures CO2 in the feed gas in the presence of water vapor, converting CO2 into CO3 2- Stored in the LDHs interlayer; (2) Gasification reaction stage: interlayer CO3 2- It is consumed in H2 atmosphere and converted into high value-added product CO in situ; achieving integrated CO2 capture and in-situ conversion to produce CO.

4. A reactor device for the application of a dual-function catalyst for the production of CO by in-situ relay coupling of CO2 selective absorption and low-energy conversion, wherein a raw gas inlet, a hydrogen device and a gas purge port are arranged at the top of the reactor, an exhaust port is arranged at the bottom of the reactor, and the interior of the reactor is filled with a reaction medium; The flue gas flow completes the capture process in the presence of water vapor, and after purging with nitrogen for five minutes, the hydrogen device is turned on and introduced into the reactor, and an in-situ conversion reaction of CO2 occurs; the catalyst after the reaction enters the adsorption capture process for recycling.

5. The use according to claim 4, characterized in that Follow these steps: (1) N / NO3 - -M 2+ M 3+ -LDHs catalyst basic carbonate and quartz sand are uniformly mixed and loaded into a steel tube reactor as a reaction medium; (2) A simulated flue gas of 15% CO2+75% N2+200ppm NO2 is introduced through a material bottle filled with water into the reactor to complete the capture process. Subsequently, the flue gas in the reactor is purged with an inert gas flow, and 0.1MPa H2 is introduced to seal the reactor. The gas flow is circulated by a peristaltic pump. The reaction temperature is 100-300°C, and the reaction is carried out at a constant temperature for 1-3 hours. (3) After the reaction, the inert gas flow is purged to selectively capture the CO2 in the raw gas in the presence of water vapor to convert the CO2 into CO3 2- in the form of stored between the basic carbonate LDHs layers and used in the next reaction.

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