Preparation method and application of bifunctional catalyst for direct conversion of carbon dioxide

Abstract

The invention relates to the technical field of catalysts, and discloses a preparation method and application of a bifunctional catalyst for direct conversion of carbon dioxide, and the preparation method comprises the following steps: (1) dispersing carbon nanotubes and amino micromolecules in an organic solvent, with the mixing mass ratio of SWCNTs to MWCNTs in the carbon nanotubes being 1: 3-3: 1, and the mixing mass ratio of SWCNTs to MWCNTs in the organic solvent being 1: 3-3: 1; the amino micromolecule is one or more of glutathione, cysteine and lysine; (2) adding copper salt, and stirring at-5 to 5 DEG C for 24 hours or more; then adding a sodium borohydride aqueous solution at the temperature of-5 to 5 DEG C, standing and aging for 2 to 4 hours, and finally performing post-treatment to obtain the bifunctional catalyst. The Cu nanocluster bifunctional catalyst with high dispersion and high conductivity is obtained by adopting the carbon nano tube as a carrier and loading the Cu nanocluster on the carrier, low-concentration CO2 can be directly catalytically converted to obtain methanol after being adsorbed and captured, and meanwhile, high methanol selectivity can be achieved.

Description

Technical Field

[0001] The present invention relates to the technical field of catalysts, and in particular to a preparation method and application of a bifunctional catalyst for direct conversion of carbon dioxide. Background Art

[0002] The chemical production process will emit a large amount of CO 2 , causing a series of ecological and environmental problems. It is worth noting that CO 2 The concentrations are generally low (5-30%), and there is an urgent need to develop advanced and efficient CCUS technology (CO 2 Capture, utilization and storage) can achieve carbon emission reduction in chemical processes, but this technology still faces many challenges. 2 In terms of capture, absorption and adsorption are currently the most effective methods for large-scale capture of low-concentration CO. 2 Potential technical route, but currently CO 2 The regeneration energy consumption of absorbent / adsorbent material is high, and the system operation energy consumption is as high as 4.0~6.0 MJ / kg CO 2 , which seriously hinders CO 2 Large-scale application of capture and utilization technology. 2 In terms of catalytic conversion, the main technology currently used is to 2 Hydrogenation thermal catalysis to produce methanol and olefins, as well as CO 2 and methane dry reforming to produce synthesis gas, etc. For example, the patent with publication number CN106622252A discloses a method for CO 2 Catalyst for hydrogenation to methanol, designed to overcome CO 2 CO in the process of hydrogenation to methanol 2 To solve the problems of low conversion rate and low methanol selectivity, a Cu, ZnO, ZrO 2 The catalyst with graphene oxide (GO) as the main components is prepared by co-precipitation. However, the catalyst is used for thermal catalytic conversion to produce methanol, the reaction temperature is 200~300℃, and the pressure is 4.0~12.0MPa, so the reaction conditions are harsh (high temperature and high pressure conditions are required), resulting in high energy consumption and cost.

[0003] In addition, most existing CCUS technologies are based on CO 2 Collectors and CO 2 Catalyst development. By developing higher CO 2 Adsorption capacity and low CO 2 Regeneration energy consumption of the collector, such as using amine solution absorbent to replace alkali solution absorbent to reduce CO 2Regeneration energy consumption. At the same time, strategies such as the morphology effect, crystal plane effect, valence state effect, and defect effect of the catalyst are used to design and prepare thermal / electrical catalysts with higher selectivity and efficiency. Such a two-step process faces the problem of high CO 2 regeneration energy consumption, complex process flow, and high equipment investment and maintenance costs, resulting in the inability to widely promote and use existing CO 2 capture and conversion technologies. SUMMARY OF THE INVENTION

[0004] To solve the problems of complex process flow, high energy consumption for CO 2 regeneration and compression, long time cycle and low efficiency in the two-step process, the present invention provides a preparation method and application of a bifunctional catalyst for direct conversion of carbon dioxide. By using carbon nanotubes as a carrier and loading Cu nanoclusters thereon, a highly dispersed and highly conductive Cu nanocluster catalyst is obtained. This catalyst can directly catalytically convert low-concentration CO 2 after adsorption and capture to methanol, thus realizing the dual functions of a CO 2 capturing agent and a CO 2 catalyst.

[0005] The object of the present invention is achieved by the following technical solutions: In a first aspect, the present invention provides a preparation method of a bifunctional catalyst for direct conversion of carbon dioxide, comprising the following steps: (1) Disperse carbon nanotubes and amino small molecules in an organic solvent, where the mixed mass ratio of SWCNTs and MWCNTs in the carbon nanotubes is 1:3 to 3:1, and the amino small molecules are one or more of glutathione, cysteine, and lysine; (2) Then add a copper salt and stir at -5 to 5 °C for 24 h or more; subsequently add an aqueous sodium borohydride solution at -5 to 5 °C, let it stand for aging for 2 to 4 h, and finally obtain a bifunctional catalyst through post-treatment.

[0006] In existing CCUS technologies, the capture and conversion of CO 2 are carried out independently in two steps. Low-concentration CO 2 is first absorbed by an alkali solution / amine solution, then heated for CO 2 regeneration, and finally, after compression, it is electro-thermally catalytically converted into high-value chemicals and fuels. Such a two-step process has problems of complex process flow, high energy consumption for CO 2 regeneration and compression, long time cycle and low efficiency. Therefore, to address this problem, the bifunctional catalyst prepared in the present invention can convert low-concentration CO 2 into methanol after adsorption and capture, thus 2Direct catalytic conversion after adsorption and capture to obtain methanol, thereby achieving high energy utilization efficiency and process intensiveness.

[0007] The bifunctional catalyst is obtained by using carbon nanotubes as a support and loading Cu nanoclusters on it to obtain a highly dispersed and highly conductive Cu nanocluster catalyst. Among them, the carbon nanotubes have a hollow tubular structure, providing a channel for mass transfer. There are a large number of atoms on its surface, providing rich and uniform adsorption sites and having a high specific surface area, which is conducive to the adsorption of Cu nanoclusters, enhancing the stability and uniformity of loading. Moreover, the carbon nanotubes have a large aspect ratio, and when loaded on the surface of carbon paper, they can form a 3D intertwined network structure, enhancing the binding force and support, and the 3D intertwining can also form a pore structure, thus realizing the efficient adsorption and enrichment of low-concentration CO 2 of.

[0008] At the same time, the carbon nanotubes include SWCNTs and MWCNTs. SWCNTs have a relatively large specific surface area, which can provide more adsorption sites for Cu nanoclusters. Due to its smaller tube diameter, the dispersion of Cu nanoclusters on the surface of single-walled carbon nanotubes is relatively uniform. When SWCNTs are mixed with MWCNTs, the presence of MWCNTs can play a role of spacing and support. The multi-layer structure of MWCNTs can prevent the aggregation of Cu nanoclusters because the clusters can be better dispersed between the multi-layers or in the voids between MWCNTs and SWCNTs. From the perspective of surface chemistry, there are functional groups (such as carboxyl groups, hydroxyl groups, etc.) on the surface of CNTs that can interact with Cu nanoclusters through chemical bonding (such as coordination bonds). The distribution and properties of surface functional groups on SWCNTs and MWCNTs are slightly different. Under the condition of an appropriate mixing ratio, this difference can be utilized to enhance the adsorption and dispersion of Cu nanoclusters. The dispersion of Cu nanoclusters on the surface of carbon nanotubes is better, which is more conducive to acting as the "node" of electron transport and further enhancing the conductivity of the entire system.

[0009] Amino small molecules can coordinate with Cu(II) to form chelates, acting as capping agents for Cu(II) to form Cu nanoclusters of different sizes. However, the amino molecular chain cannot be too large, otherwise a large steric hindrance effect will be generated, resulting in the formation of very large Cu clusters or even the inability to form clusters. In addition, coordinating large amino molecules around Cu(II) will hinder the contact between CO 2 molecules and the Cu cluster catalyst to participate in the reaction. CO 2 The mechanism of electroreduction is that CO 2 is first activated and hydrogenated to intermediate, and further hydrogenated to , and if hydrogenation continues, it will reach methanol / methane, but if Dimerization produces multi-carbon products such as ethylene / ethanol, etc. By controlling the dosages of amino small molecules and Cu salts, Cu nanocluster catalysts with appropriate sizes can be prepared, thereby controlling the appropriate number and distance of Cu active sites. At the same time, by introducing amino groups, the adsorption behavior of CO 2 electroreduction intermediates can be synergistically regulated, thereby regulating the selectivity of Cu nanoclusters and highly selectively generating methanol products.

[0010] Sodium borohydride is used to reduce Cu(II). At the same time, the aging process can promote sufficient reaction, optimize the composition and structure of the reaction products, and can also promote the crystal growth and particle maturation of the generated metal nanoparticles, and there is enough time for lattice rearrangement and perfection, improving the crystallinity of the products. When highly crystalline metal nanocrystals are used as catalysts, the activity and stability of their surface atoms will be better. A good crystalline structure can provide a more suitable atomic arrangement and electronic structure, thereby improving the catalytic efficiency.

[0011] Preferably, the carbon nanotubes are pretreated with an acid solution; the acid is one of a hydrochloric acid solution, a sulfuric acid solution, and a nitric acid solution with a concentration of 0.6 mol / L; the pretreatment time is 24 - 48 h.

[0012] The acid solution pretreatment is used to remove impurities.

[0013] Preferably, the mixing mass ratio of SWCNTs and MWCNTs in the carbon nanotubes is 1:3, 1:1, or 3:1.

[0014] SWCNTs itself has excellent electrical properties and fast electron transport. When SWCNTs are mixed with MWCNTs, a good conductive channel can be formed at the interface between the two. Electrons can be conducted from the Cu nanoclusters to the CNTs surface through chemical bonds (such as Cu - C bonds), and then quickly transported in the CNTs network. The multi-layer structure of MWCNTs also helps to increase the path diversity of electron transport.

[0015] When the mixing mass ratio of SWCNTs and MWCNTs is 1:3, the relative content of MWCNTs is higher. Its internal multi-layer structure can provide more electron transport channels, and the synergistic effect between SWCNTs and MWCNTs can be utilized to better improve the overall conductivity.

[0016] Preferably, the addition ratio of the carbon nanotubes, amino small molecules, and copper salt is 20 mg: 0.0625 - 1.0 mmol: 0.1 - 0.3 mmol; more preferably, the addition ratio of the carbon nanotubes, amino small molecules, and copper salt is 20 mg: 0.2 - 1.0 mmol: 0.1 - 0.3 mmol.

[0017] Preferably, the SWCNTs are single-walled carbon nanotubes with a diameter of 0.4 to 2 nm; the MWCNTs are multi-walled carbon nanotubes with a diameter of 2 to 50 nm.

[0018] Preferably, the copper salt contains Cu 2+ ions of nitrate, chloride, carbonate, acetylacetonate or acetate.

[0019] Preferably, the ratio of the addition amount of the carbon nanotubes to the organic solvent is 20 mg: 30 to 50 mL.

[0020] Preferably, the volume ratio of the sodium borohydride aqueous solution to the organic solvent is 1: 4 to 8.

[0021] Preferably, the concentration of the sodium borohydride aqueous solution is 0.1 to 1 mol / L.

[0022] Preferably, the organic solvent includes one or more of methanol, ethanol, ethylene glycol, acetone and N, N-dimethylformamide.

[0023] Preferably, the post-treatment includes centrifugation, washing and freeze-drying in sequence.

[0024] Preferably, the rotation speed of the centrifugation is 8000 to 12000 rpm, and the centrifugation time is 5 to 15 min.

[0025] In the second aspect, the present invention also provides an application of the bifunctional catalyst prepared by the above preparation method in the catalytic conversion of carbon dioxide to methanol.

[0026] Preferably, the bifunctional catalyst can directly catalytically convert methanol in industrial waste gas with a volume content of CO 2 of 5 to 30%.

[0027] Compared with the prior art, the present invention has the following beneficial effects: (1) The bifunctional catalyst uses carbon nanotubes as a carrier and loads Cu nanoclusters on it to obtain a highly dispersed and highly conductive Cu nanocluster catalyst, which can adsorb and capture low-concentration CO 2 and directly catalytically convert it to methanol, thereby realizing the high efficiency of energy utilization and the intensiveness of the process flow; (2) The carbon nanotubes include SWCNTs and MWCNTs. The distribution and properties of the surface functional groups of SWCNTs and MWCNTs are slightly different, and this difference can be used to enhance the adsorption and dispersion of Cu nanoclusters. The dispersion of Cu nanoclusters on the surface of the carbon nanotubes is better, which is more conducive to being used as the "node" of electron transport and further enhancing the conductivity of the whole system; (3) Amino small molecules can coordinate with Cu(II) to form chelates, acting as capping agents for Cu(II) to form Cu nanoclusters of different sizes. Utilizing the size effect of the nanocatalyst and the introduction of amino groups, the adsorption behavior of CO 2 electroreduction intermediates is synergistically regulated, thereby controlling the selectivity of Cu nanoclusters and highly selectively generating methanol products. Description of the Drawings

[0028] Figure 1 SEM image of the catalyst without loaded Cu nanoclusters prepared in Example 1.

[0029] Figure 2 SEM image of the catalyst loaded with Cu nanoclusters prepared in Example 1. Specific Embodiments

[0030] The following specific examples are used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto.

[0031] The preparation of the bifunctional catalyst for the direct conversion of carbon dioxide in the present invention includes the following steps: (1) Immerse the carbon nanotubes in an acid solution for pretreatment for 24 - 48 h to remove impurities, and then wash with deionized water and freeze-dry for standby; (2) Disperse the pretreated carbon nanotubes and amino small molecules in an organic solvent. The addition ratio of carbon nanotubes to the organic solvent is 20 mg: 30 - 50 mL. The mixing mass ratio of single-walled carbon nanotubes (SWCNTs, with a diameter of 0.4 - 2 nm) and multi-walled carbon nanotubes (MWCNTs, with a diameter of 2 - 50 nm) in the carbon nanotubes is 1:3 - 3:1. The amino small molecules are one or more of glutathione, cysteine, lysine, and proline; (3) Then add copper salt. The addition ratio of carbon nanotubes, amino small molecules, and copper salt is 20 mg: 0.0625 - 1.0 mmol: 0.1 - 0.3 mmol. Stir at -5 - 5 °C for 24 h or more; subsequently, add an aqueous sodium borohydride solution with a concentration of 0.1 - 1 mol / L at -5 - 5 °C. The volume ratio of the aqueous sodium borohydride solution to the organic solvent is 5: 20 - 40, and let it stand for aging for 2 - 4 h; (4) Finally, after post-treatment, centrifuge at a rotation speed of 8000 - 12000 rpm for 5 - 15 min, and then wash and freeze-dry in sequence to obtain the bifunctional catalyst.

[0032] In the specific embodiments of the present invention, the diameter of the single-walled carbon nanotubes (SWCNTs) used is 1 - 2 nm, and the diameter of the multi-walled carbon nanotubes (MWCNTs) used is 30 - 50 nm.

[0033] In a specific embodiment of the present invention, the acid solution used is one of hydrochloric acid solution, sulfuric acid solution and nitric acid solution with a concentration of 0.6 mol / L.

[0034] In a specific embodiment of the present invention, the organic solvent includes one or more of methanol, ethanol, ethylene glycol, acetone and N,N-dimethylformamide.

[0035] In a specific embodiment of the present invention, the copper salt contains Cu 2+ ions of nitrate, chloride, carbonate, acetylacetonate or acetate.

[0036] Example 1 (1) Pretreat the carbon nanotubes with hydrochloric acid solution with a concentration of 0.6 mol / L for 24 h; (2) Add 20 mg of the pretreated carbon nanotubes (a mixture of 5 mg of single-walled carbon nanotubes (SWCNTs) and 15 mg of multi-walled carbon nanotubes (MWCNTs), SWCNTs:MWCNTs = 1:3) and 0.5 mmol of amino small molecule (glutathione) into 40 mL of methanol solution and disperse them by ultrasonic wave; (3) Subsequently, add 0.2 mmol of copper acetate, place the well-mixed solution at 0 °C and stir it vigorously for 24 h, then slowly dropwise add 8 mL of sodium borohydride solution with a concentration of 0.2 mol / L (at 0 °C), and let it stand for aging for 2 h; (4) Finally, after multiple centrifugation, washing and freeze-drying treatments, a bifunctional catalyst is obtained.

[0037] The prepared bifunctional catalyst is hot-pressed and loaded on the proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode is used as the reference electrode, and a commercial iridium-plated titanium mesh is used as the counter electrode; 1 M sulfuric acid solution is used as the electrolyte for the anode, and 1 M KHCO 3 solution is used as the electrolyte for the cathode; simulated natural gas with a CO 2 volume content of 15% is used as the raw material gas, and electroreduction of CO 2 testing is carried out at a constant potential. Gas chromatography is used to detect the gas-phase products, and nuclear magnetic resonance hydrogen spectrum is used to detect the liquid-phase products.

[0038] Example 2 (1) Pretreat the carbon nanotubes with nitric acid solution with a concentration of 0.6 mol / L for 24 h; (2) Add 20 mg of pretreated carbon nanotubes (a mixture of 10 mg of single-walled carbon nanotubes (SWCNTs) and 10 mg of multi-walled carbon nanotubes (MWCNTs), SWCNTs:MWCNTs = 1:1) and 0.3 mmol of amino small molecule (cysteine) into 30 mL of N,N-dimethylformamide (DMF) solution and disperse them by ultrasonic wave; (3) Subsequently, add 0.2 mmol of copper acetylacetonate, place the well-mixed solution at 0 °C and stir it vigorously for 24 h, then slowly dropwise add 6 mL of sodium borohydride solution with a concentration of 0.5 mol / L (at 0 °C), and let it age for 2 h; (4) Finally, after centrifugation, washing, and freeze-drying for many times, a bifunctional catalyst is obtained.

[0039] The prepared bifunctional catalyst is hot-pressed and loaded on the proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode is used as the reference electrode, and a commercial iridium-coated titanium mesh is used as the counter electrode; 1 M sulfuric acid solution is used as the electrolyte for the anode, and 1 M KHCO 3 solution is used as the electrolyte for the cathode; A simulated natural gas with a CO 2 volume content of 10% is used as the raw material gas, and the electroreduction of CO 2 is tested under constant potential. Gas chromatography is used to detect gas-phase products, and nuclear magnetic resonance hydrogen spectrum is used to detect liquid-phase products.

[0040] Example 3 (1) Pretreat the carbon nanotubes with a hydrochloric acid solution with a concentration of 0.6 mol / L for 24 h; (2) Add 20 mg of pretreated carbon nanotubes (a mixture of 5 mg of single-walled carbon nanotubes (SWCNTs) and 15 mg of multi-walled carbon nanotubes (MWCNTs), SWCNTs:MWCNTs = 1:3) and 0.8 mmol of amino small molecule (glutathione) into 40 mL of ethylene glycol solution and disperse them by ultrasonic wave; (3) Subsequently, add 0.3 mmol of copper acetylacetonate, place the well-mixed solution at 0 °C and stir it vigorously for 24 h, then slowly dropwise add 10 mL of sodium borohydride solution with a concentration of 0.4 mol / L (at 0 °C), and let it age for 2 h; (4) Finally, after centrifugation, washing, and freeze-drying for many times, a bifunctional catalyst is obtained.

[0041] The prepared bifunctional catalyst is hot-pressed and loaded on the proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode is used as the reference electrode, and a commercial iridium-coated titanium mesh is used as the counter electrode; 1 M sulfuric acid solution is used as the electrolyte for the anode, and 1 M KHCO 3The solution is used as the electrolyte; CO 2 simulated natural gas with a volume content of 15% is used as the raw material gas, and electroreduction of CO is carried out at a constant potential 2 testing. Gas chromatography is used to detect the gas-phase products, and nuclear magnetic resonance hydrogen spectrum is used to detect the liquid-phase products.

[0042] Example 4 The difference from Example 1 is that SWCNTs:MWCNTs = 1:1.

[0043] (1) The carbon nanotubes are pretreated with a hydrochloric acid solution with a concentration of 0.6 mol / L for 24 h; (2) 20 mg of the pretreated carbon nanotubes (a mixture of 10 mg of single-walled carbon nanotubes (SWCNTs) and 10 mg of multi-walled carbon nanotubes (MWCNTs), SWCNTs:MWCNTs = 1:1) and 0.5 mmol of amino small molecule (glutathione) are added to 40 mL of methanol solution and ultrasonically dispersed; (3) Subsequently, 0.2 mmol of copper acetate is added, and the uniformly mixed solution is placed under vigorous stirring at 0 °C for 24 h, then 8 mL of a sodium borohydride solution with a concentration of 0.2 mol / L (0 °C) is slowly added dropwise, and it is left to age for 2 h; (4) Finally, after multiple centrifugation, washing, and freeze-drying treatments, a bifunctional catalyst is obtained.

[0044] The prepared bifunctional catalyst is hot-pressed and loaded on a proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode is used as the reference electrode, and a commercial iridium-plated titanium mesh is used as the counter electrode; 1 M sulfuric acid solution is used as the electrolyte for the anode, and 1 M KHCO 3 The solution is used as the electrolyte; CO 2 simulated natural gas with a volume content of 15% is used as the raw material gas, and electroreduction of CO is carried out at a constant potential 2 testing. Gas chromatography is used to detect the gas-phase products, and nuclear magnetic resonance hydrogen spectrum is used to detect the liquid-phase products.

[0045] Example 5 The difference from Example 1 is that SWCNTs:MWCNTs = 3:1.

[0046] (1) The carbon nanotubes are pretreated with a hydrochloric acid solution with a concentration of 0.6 mol / L for 24 h; (2) Add 20 mg of pretreated carbon nanotubes (a mixture of 15 mg of single-walled carbon nanotubes (SWCNTs) and 5 mg of multi-walled carbon nanotubes (MWCNTs), SWCNTs:MWCNTs = 3:1) and 0.5 mmol of amino small molecule (glutathione) into 40 mL of methanol solution and disperse them by ultrasonic treatment; (3) Subsequently, add 0.2 mmol of copper acetate, place the well-mixed solution at 0 °C and stir it vigorously for 24 h, then slowly dropwise add 8 mL of sodium borohydride solution with a concentration of 0.2 mol / L (at 0 °C), and let it age for 2 h; (4) Finally, after centrifugation, washing, and freeze-drying for multiple times, a bifunctional catalyst is obtained.

[0047] The prepared bifunctional catalyst is hot-pressed and loaded on the proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode is used as the reference electrode, and a commercial iridium-coated titanium mesh is used as the counter electrode; 1 M sulfuric acid solution is used as the electrolyte for the anode, and 1 M KHCO 3 solution is used as the electrolyte for the cathode; Using simulated natural gas with a CO 2 volume content of 15% as the raw material gas, and perform electroreduction of CO 2 testing under constant potential. Gas chromatography is used to detect gas-phase products, and nuclear magnetic resonance hydrogen spectrum is used to detect liquid-phase products.

[0048] Comparative Example 1 The difference from Example 1 is that only SWCNTs are used for the carbon nanotubes.

[0049] (1) Pretreat the carbon nanotubes with a hydrochloric acid solution with a concentration of 0.6 mol / L for 24 h; (2) Add 20 mg of pretreated carbon nanotubes (single-walled carbon nanotubes (SWCNTs)) and 0.5 mmol of amino small molecule (glutathione) into 40 mL of methanol solution and disperse them by ultrasonic treatment; (3) Subsequently, add 0.2 mmol of copper acetate, place the well-mixed solution at 0 °C and stir it vigorously for 24 h, then slowly dropwise add 8 mL of sodium borohydride solution with a concentration of 0.2 mol / L (at 0 °C), and let it age for 2 h; (4) Finally, after centrifugation, washing, and freeze-drying for multiple times, a bifunctional catalyst is obtained.

[0050] The prepared bifunctional catalyst is hot-pressed and loaded on the proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode is used as the reference electrode, and a commercial iridium-coated titanium mesh is used as the counter electrode; 1 M sulfuric acid solution is used as the electrolyte for the anode, and 1 M KHCO 3 solution is used as the electrolyte; Using CO2 Simulated natural gas with a volume content of 15% was used as the feed gas, and electroreduction of CO was carried out at a constant potential. 2 Testing was performed. Gas chromatography was used to detect the gas-phase products, and nuclear magnetic resonance hydrogen spectroscopy was used to detect the liquid-phase products.

[0051] Comparative Example 2 The difference from Example 1 was that only MWCNTs were used for the carbon nanotubes.

[0052] (1) The carbon nanotubes were pretreated with a hydrochloric acid solution with a concentration of 0.6 mol / L for 24 h; (2) 20 mg of the pretreated carbon nanotubes (multi-walled carbon nanotubes (MWCNTs)) and 0.5 mmol of the amino small molecule (glutathione) were added to 40 mL of methanol solution and ultrasonically dispersed; (3) Subsequently, 0.2 mmol of copper acetate was added, and the uniformly mixed solution was placed at 0 °C and vigorously stirred for 24 h. Then, 8 mL of a sodium borohydride solution with a concentration of 0.2 mol / L (at 0 °C) was slowly added dropwise, and it was left to age for 2 h; (4) Finally, after multiple centrifugation, washing, and freeze-drying treatments, a bifunctional catalyst was obtained.

[0053] The prepared bifunctional catalyst was hot-pressed and loaded on a proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode was used as the reference electrode, and a commercial iridium-coated titanium mesh was used as the counter electrode; 1 M sulfuric acid solution was used as the electrolyte at the anode, and 1 M KHCO 3 solution was used as the electrolyte at the cathode; with CO 2 Simulated natural gas with a volume content of 15% was used as the feed gas, and electroreduction of CO was carried out at a constant potential. 2 Testing was performed. Gas chromatography was used to detect the gas-phase products, and nuclear magnetic resonance hydrogen spectroscopy was used to detect the liquid-phase products.

[0054] Comparative Example 3 The difference from Example 1 was that no amino small molecule was added.

[0055] (1) The carbon nanotubes were pretreated with a hydrochloric acid solution with a concentration of 0.6 mol / L for 24 h; (2) 20 mg of the pretreated carbon nanotubes (a mixture of 5 mg of single-walled carbon nanotubes (SWCNTs) and 15 mg of multi-walled carbon nanotubes (MWCNTs), SWCNTs:MWCNTs = 1:3) were added to 40 mL of methanol solution and ultrasonically dispersed; (3) Subsequently, 0.2 mmol of copper acetate was added, and the uniformly mixed solution was placed under vigorous stirring at 0 °C for 24 h. Then, 8 mL of a sodium borohydride solution with a concentration of 0.2 mol / L (at 0 °C) was slowly added dropwise, and it was left to age for 2 h; (4) Finally, after multiple centrifugation, washing, and freeze-drying treatments, a bifunctional catalyst was obtained.

[0056] The prepared bifunctional catalyst was hot-pressed and loaded on a proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode was used as the reference electrode, and a commercial iridium-plated titanium mesh was used as the counter electrode; 1 M sulfuric acid solution was used as the electrolyte for the anode, and 1 M KHCO 3 solution was used as the electrolyte for the cathode; simulated natural gas with a CO 2 volume content of 15% was used as the feed gas, and electroreduction of CO 2 testing was carried out at a constant potential. Gas chromatography was used to detect the gas-phase products, and nuclear magnetic resonance hydrogen spectroscopy was used to detect the liquid-phase products.

[0057] Comparative Example 4 The difference from Example 1 was that the amino small molecule was proline.

[0058] (1) The carbon nanotubes were pretreated with a hydrochloric acid solution with a concentration of 0.6 mol / L for 24 h; (2) 20 mg of the pretreated carbon nanotubes (a mixture of 5 mg of single-walled carbon nanotubes (SWCNTs) and 15 mg of multi-walled carbon nanotubes (MWCNTs), SWCNTs:MWCNTs = 1:3) and 0.5 mmol of the amino small molecule (proline) were added together to 40 mL of methanol solution and ultrasonically dispersed; (3) Subsequently, 0.2 mmol of copper acetate was added, and the uniformly mixed solution was placed under vigorous stirring at 0 °C for 24 h. Then, 8 mL of a sodium borohydride solution with a concentration of 0.2 mol / L (at 0 °C) was slowly added dropwise, and it was left to age for 2 h; (4) Finally, after multiple centrifugation, washing, and freeze-drying treatments, a bifunctional catalyst was obtained.

[0059] The prepared bifunctional catalyst was hot-pressed and loaded on a proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode was used as the reference electrode, and a commercial iridium-plated titanium mesh was used as the counter electrode; 1 M sulfuric acid solution was used as the electrolyte for the anode, and 1 M KHCO 3 solution was used as the electrolyte for the cathode; simulated natural gas with a CO 2 volume content of 15% was used as the feed gas, and electroreduction of CO 2 testing was carried out at a constant potential. Gas chromatography was used to detect the gas-phase products, and nuclear magnetic resonance hydrogen spectroscopy was used to detect the liquid-phase products.

[0060] Comparative Example 5 The difference from Example 5 is that the dosages of amino small molecules and Cu salts are excessive.

[0061] (1) The carbon nanotubes were pretreated with a hydrochloric acid solution with a concentration of 0.6 mol / L for 24 h; (2) 20 mg of the pretreated carbon nanotubes (a mixture of 15 mg of single-walled carbon nanotubes (SWCNTs) and 5 mg of multi-walled carbon nanotubes (MWCNTs), SWCNTs:MWCNTs = 3:1) and 1.5 mmol of amino small molecules (glutathione) were added to 40 mL of methanol solution and ultrasonically dispersed; (3) Subsequently, 0.8 mmol of copper acetate was added, and the uniformly mixed solution was vigorously stirred at 0 °C for 24 h, then 8 mL of a sodium borohydride solution with a concentration of 0.2 mol / L (at 0 °C) was slowly added dropwise, and it was left to age for 2 h; (4) Finally, after multiple centrifugation, washing, and freeze-drying treatments, a bifunctional catalyst was obtained.

[0062] The prepared bifunctional catalyst was hot-pressed and loaded on a proton membrane as the working cathode, a standard solid-state Ag / AgCl electrode was used as the reference electrode, and a commercial iridium-plated titanium mesh was used as the counter electrode; 1 M sulfuric acid solution was used as the electrolyte for the anode, and 1 M KHCO 3 solution was used as the electrolyte for the cathode; simulated natural gas with a CO 2 volume content of 15% was used as the raw material gas, and electroreduction of CO 2 was tested under a constant potential. Gas chromatography was used to detect gas-phase products, and nuclear magnetic resonance hydrogen spectroscopy was used to detect liquid-phase products.

[0063] Table 1 Catalytic activities of catalysts in different examples

[0064] Note: The "C 2+ " products include ethanol, ethylene, isopropanol, and acetic acid; the sum of the product selectivities is less than 100% due to certain systematic errors in the detection process.

[0065] As Figure 1 shown are the scanning electron microscope images of carbon nanotubes (including single-walled carbon nanotubes and multi-walled carbon nanotubes), and there are no Cu nanoclusters loaded on their surfaces. As Figure 2 shown are the scanning electron microscope images of carbon nanotubes after loading Cu nanoclusters, indicating that the Cu nanocluster catalyst loaded on carbon nanotubes was successfully prepared in Example 1 using the method of the present invention.

[0066] As shown in Table 1, the Cu nanocluster bifunctional catalyst supported on carbon nanotubes prepared in Examples 1-5 can directly catalytically convert low-concentration CO 2 after adsorption and capture, showing high activity and methanol selectivity in the reaction of catalytically converting to methanol. Specifically, the present invention proposes a synergistic strategy of support regulation and catalyst design: the carbon nanotube support synergistically composed of SWCNTs and MWCNTs can adsorb low-concentration CO 2 and improve the dispersion and conductivity of Cu nanoclusters; amino small molecules can regulate the size and electronic structure of Cu nanoclusters, making the adsorption of intermediates moderate, thereby improving methanol selectivity.

[0067] In Comparative Example 1, only SWCNTs are used as the carbon nanotube support. Due to the insufficient sites for SWCNTs to adsorb CO 2 , the supply of reactants is insufficient, resulting in a decrease in the selectivity of methanol products and a serious hydrogen evolution side reaction. In Comparative Example 2, only MWCNTs are used as the carbon nanotube support. Since Cu nanoclusters are highly dispersed on the surface of MWCNTs, the carrier carbon sites catalyze CO 2 to be reduced to CO, resulting in a decrease in methanol selectivity.

[0068] In Comparative Example 3, no amino small molecules are added. Since there is no amino small molecule as a capping agent, Cu atoms agglomerate, resulting in the reduction of CO 2 to multi-carbon (C 2+ ) products and a decrease in methanol selectivity. In Comparative Example 4, the molecular chain steric hindrance of the amino small molecule used is too large. Proline contains a five-membered ring. Compared with the linear configurations of glutathione, cysteine, and lysine, it has a larger steric hindrance when coordinating with Cu atoms, resulting in too large or agglomerated Cu nanoclusters, which will also cause the reduction of CO 2 to multi-carbon (C 2+ ) products and a decrease in methanol selectivity.

[0069] In Comparative Example 5, the dosages of amino small molecules and Cu salts exceed the scope defined in the claims. Since there are insufficient amino small molecules coordinating with Cu atoms and some uncoordinated Cu atoms agglomerate, part of the CO 2 is reduced to multi-carbon (C 2+ ) products, resulting in a decrease in methanol selectivity.

[0070] The above are only the preferred embodiments of the present invention, and do not limit the patent scope of the present invention accordingly. Any equivalent structural or equivalent process transformation made using the description of the present invention, or directly or indirectly applied in other related technical fields, shall be included in the patent protection scope of the present invention by the same token.

Claims

1. A method for preparing a bifunctional catalyst for direct conversion of carbon dioxide, characterized in that: The steps include: (1) dispersing carbon nanotubes and amino small molecules in an organic solvent, wherein the mixing mass ratio of SWCNTs and MWCNTs in the carbon nanotubes is 1:3-3:1, and the amino small molecules are one or more of glutathione, cysteine ​​and lysine; (2) Then, copper salt is added and stirred at -5 to 5°C for 24 hours or more; then, sodium borohydride aqueous solution at -5 to 5°C is added, and the solution is allowed to stand for 2 to 4 hours, and finally, a bifunctional catalyst is obtained through post-treatment.

2. The method for preparing the bifunctional catalyst for direct conversion of carbon dioxide according to claim 1, characterized in that: The ratio of the added amounts of the carbon nanotubes, the amino small molecules and the copper salt is 20 mg: 0.0625-1.0 mmol: 0.1-0.3 mmol.

3. The method for preparing the bifunctional catalyst for direct conversion of carbon dioxide according to claim 1, characterized in that: The SWCNTs are single-walled carbon nanotubes with a diameter of 0.4-2 nm; the MWCNTs are multi-walled carbon nanotubes with a diameter of 2-50 nm.

4. The method for preparing the bifunctional catalyst for direct conversion of carbon dioxide according to claim 1, characterized in that: The copper salt contains Cu 2+ ion nitrate, chloride, carbonate, acetylacetonate or acetate.

5. The method for preparing the bifunctional catalyst for direct conversion of carbon dioxide according to claim 1, characterized in that: The ratio of the added amount of the carbon nanotubes to the organic solvent is 20 mg: 30-50 mL.

6. The method for preparing the bifunctional catalyst for direct conversion of carbon dioxide according to claim 1, characterized in that: The volume ratio of the sodium borohydride aqueous solution to the organic solvent is 1:4-8.

7. The method for preparing the bifunctional catalyst for direct conversion of carbon dioxide according to claim 1, characterized in that: The concentration of the sodium borohydride aqueous solution is 0.1-1 mol / L.

8. The method for preparing the bifunctional catalyst for direct conversion of carbon dioxide according to claim 1, characterized in that: The organic solvent includes one or more of methanol, ethanol, ethylene glycol, acetone and N,N-dimethylformamide.

9. The method for preparing the bifunctional catalyst for direct conversion of carbon dioxide according to claim 1, characterized in that: The post-treatment includes centrifugation, washing and freeze-drying in sequence.

10. Use of the bifunctional catalyst prepared by the preparation method according to any one of claims 1 to 9 in catalytic conversion of carbon dioxide to produce methanol.

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