Composite metal oxide catalyst, its preparation method and application

Abstract

This invention provides a composite metal oxide catalyst, its preparation method, and its application. The composite metal oxide catalyst is obtained by first forming a composite metal hydroxide from divalent and trivalent soluble metal salts through hydrothermal nucleation, precipitation crystallization, and vacuum drying, followed by calcination of the composite metal hydroxide. The composite metal oxide catalyst comprises divalent metal oxides, trivalent metal oxides, and spinel formed from divalent and trivalent metals. The composite metal oxide catalyst provided by this invention exhibits high reproducibility, which is beneficial for large-scale production. Furthermore, it requires no special protection and can be stored for a long time. When used for the catalytic electrochemical reduction of carbon dioxide to produce ethanol and ethylene, this composite metal oxide catalyst demonstrates ultra-durable electrochemical CO2RR performance, with only a slight decrease in the ethanol Faraday efficiency (<5%) during a 150-hour test.

Description

Technical Field

[0001] This invention relates to a composite metal oxide catalyst, its preparation method and application, belonging to the field of carbon dioxide reduction technology. Background Technology

[0002] Capturing carbon dioxide at its source and converting it into high-value-added products using renewable energy is an effective way to alleviate global ecological and environmental problems and the energy crisis. Therefore, the production of multi-carbon (C2+) products and chemical raw materials through electrocatalytic carbon dioxide reduction (CO2RR) has become a research hotspot. Currently, copper-based electrocatalysts have been proven to be the only catalysts that can effectively produce C2+ products via CO2RR. However, the selectivity of CO2RR for producing C2+ products via copper-based catalysts is still limited by its high overpotential, slow reaction kinetics, and low selectivity. In recent years, the design and preparation of various novel copper-based catalysts have developed rapidly. For example, Chinese patent CN112899709A prepared a copper-based compound / copper nanocatalyst with interface regulation function. It utilizes the synergistic effect of monovalent copper / zero-valent copper, divalent copper / zero-valent copper, and divalent copper / monovalent copper / zero-valent copper to lower the reaction energy barrier of CO intermediate dimerization, thus effectively suppressing the hydrogen evolution reaction during electrochemical carbon dioxide reduction and exhibiting good selectivity for multi-carbon products. However, the stability of the copper-based compound / copper nanocatalyst is poor and cannot meet the needs of long-term use.

[0003] Therefore, how to simultaneously achieve stabilization of high active sites in catalysts, high selectivity of C2 products in electrochemical CO2RR, and performance stability during long-term testing are technical problems that urgently need to be solved in the field of electrocatalytic CO2 reduction. Summary of the Invention

[0004] To address the aforementioned shortcomings and deficiencies, one objective of this invention is to provide a composite metal oxide catalyst.

[0005] Another object of the present invention is to provide a method for preparing the composite metal oxide catalyst described above.

[0006] Another object of the present invention is to provide the application of the above-described composite metal oxide catalyst in the catalytic electrochemical reduction of carbon dioxide to produce ethanol and ethylene.

[0007] To achieve the above objectives, on the one hand, the present invention provides a composite metal oxide catalyst, wherein the composite metal oxide catalyst is obtained by first forming a composite metal hydroxide by hydrothermal nucleation, precipitation crystallization and vacuum drying of divalent soluble metal salt and trivalent soluble metal salt, and then calcining the composite metal hydroxide; wherein the composite metal oxide catalyst includes divalent metal oxide, trivalent metal oxide and spinel formed by divalent metal and trivalent metal.

[0008] In a specific embodiment of the composite metal oxide catalyst described above in this invention, the divalent metal oxide, the trivalent metal oxide, and the spinel formed by the divalent and trivalent metals are all nanosheets, and the divalent metal oxide nanosheets and the spinel nanosheets formed by the divalent and trivalent metals are uniformly dispersed on the spinel nanosheets formed by the trivalent metal.

[0009] As a specific embodiment of the composite metal oxide catalyst described above in this invention, the total weight of spinel formed by divalent metal oxide and divalent metal and trivalent metal is 100%, and the weight percentage of spinel formed by trivalent metal is 1%-35%.

[0010] As a specific embodiment of the composite metal oxide catalyst described above in this invention, the divalent soluble metal salt includes soluble copper salt and / or soluble magnesium salt, the trivalent soluble metal salt includes one or a combination of soluble aluminum salt, soluble cobalt salt and soluble chromium salt, and the molar ratio of divalent soluble metal salt to trivalent soluble metal salt is 1:1-3:1.

[0011] In some embodiments of the present invention, the soluble copper salt and soluble aluminum salt may be chlorides, nitrates, sulfates or chlorates of copper and aluminum, respectively.

[0012] As a specific embodiment of the composite metal oxide catalyst described above in this invention, the hydrothermal nucleation conditions include first heating to 80-120°C at a heating rate of 5-10°C / min and holding at that temperature for 30-90min; preferably heating to 110°C and holding at that temperature for 30min.

[0013] As a specific embodiment of the composite metal oxide catalyst described above in this invention, the precipitation crystallization conditions include stirring in an oil bath at 50-80°C for 6-24 hours, wherein the stirring speed is 100-500 rpm; preferably, the precipitation crystallization conditions are stirring in an oil bath at 50°C for 12 hours.

[0014] In one specific embodiment of the composite metal oxide catalyst described above in this invention, the vacuum drying is performed at 40-70°C for 12-24 hours, preferably at 40-60°C for 24 hours.

[0015] In one specific embodiment of the composite metal oxide catalyst described above in this invention, the calcination is performed at 700-1000℃ for 4-6 hours.

[0016] Preferably, the calcination is performed by first heating from room temperature to 300-500℃ at a heating rate of 1-3℃ / min and holding for 1-2 hours, then heating to 550-650℃ at a heating rate of 5-10℃ / min and holding for 1-2 hours, and finally heating to 700-1000℃ at a heating rate of 5-10℃ / min and calcining for 4-6 hours.

[0017] In one specific embodiment of the composite metal oxide catalyst described above in this invention, the calcination atmosphere includes one or a mixture of oxygen, nitrogen, and argon.

[0018] In a specific embodiment of the composite metal oxide catalyst described above in this invention, when the divalent soluble metal salt and the trivalent soluble metal salt are soluble copper salt and soluble aluminum salt, respectively, the composite metal oxide catalyst includes CuO, CuAl2O4 and Al2O3.

[0019] On the other hand, the present invention also provides a method for preparing the above-described composite metal oxide catalyst, wherein the preparation method includes:

[0020] (1) After adding divalent soluble metal salt, trivalent soluble metal salt and precipitant to deionized water to prepare a solution, hydrothermal nucleation and precipitation crystallization reactions were carried out in sequence, and the product obtained from the reaction was dried under vacuum to obtain composite metal hydroxide.

[0021] (2) The composite metal hydroxide is calcined to obtain the composite metal oxide catalyst.

[0022] In a specific embodiment of the preparation method described above in this invention, the ratio of the total molar amount of the divalent soluble metal salt and the trivalent soluble metal salt to the molar amount of the precipitant is 1:7-1:12, preferably 1:10.

[0023] In one specific embodiment of the preparation method described above in this invention, the precipitant includes urea, ammonia, or hexamethylenetetramine.

[0024] In another aspect, the present invention also provides the application of the above-described composite metal oxide catalyst in the catalytic electrochemical reduction of carbon dioxide to produce ethanol and ethylene.

[0025] As a specific embodiment of the application described above in this invention, the use of the composite metal oxide catalyst for the catalytic electrochemical reduction of carbon dioxide to produce ethanol and ethylene, i.e., the efficient electrocatalytic reduction of carbon dioxide to ethylene and ethanol using the composite metal oxide catalyst, includes:

[0026] At room temperature, the composite metal oxide catalyst is coated on a gas diffusion electrode as the working electrode, mercury-mercury oxide is used as the reference electrode, a platinum sheet is used as the counter electrode, and an electrocatalytic carbon dioxide reduction reaction is carried out in a flowing electrolytic cell using potassium hydroxide solution as the electrolyte to obtain ethylene and ethanol.

[0027] The beneficial technical effects that the composite metal oxide catalyst provided by this invention can achieve include:

[0028] 1) The composite metal oxide catalyst provided by the present invention has high reproducibility, which is conducive to large-scale production, and it does not require special protection and can be stored for a long time.

[0029] 2) The composite metal oxide catalyst provided by this invention can be used to electrocatalyze the reduction of carbon dioxide to ethylene and ethanol. It can optimize active hydrogen transfer, accelerate the formation of COH intermediates, and reduce the CC coupling energy barrier, thus exhibiting excellent catalytic performance for the electrochemical reduction of carbon dioxide to produce ethanol and ethylene.

[0030] (3) When the composite metal oxide catalyst provided by the present invention is used to electrocatalyze the reduction of carbon dioxide to ethylene and ethanol, it can effectively stabilize the high active sites on the composite metal oxide catalyst and has ultra-durable electrochemical CO2RR performance. In the 150h test, the ethanol Faraday efficiency only decreased slightly (<5%). Attached Figure Description

[0031] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0032] Figure 1 This is a transmission electron microscope image of CuAl-LDHs prepared in Example 1 of the present invention.

[0033] Figure 2 This is a transmission electron microscope (TEM) image of CuO / CuAl2O4 / Al2O3 prepared in Example 1 of the present invention.

[0034] Figure 3 The image shows an HRTEM image of CuO / CuAl2O4 / Al2O3 prepared in Example 1 of this invention.

[0035] Figure 4 The image shows the HAADF-STEM image of CuO / CuAl2O4 / Al2O3 obtained in Example 1 of this invention.

[0036] Figures 5a-5c This is the energy dispersive spectroscopy (EDS) elemental mapping diagram of CuO / CuAl2O4 / Al2O3 prepared in Example 1 of this invention.

[0037] Figure 6 The image shows the X-ray powder diffraction (XRD) pattern of CuO / CuAl2O4 / Al2O3 prepared in Example 1 of this invention.

[0038] Figure 7 The image shows the XPS spectrum of Cu 2p in CuO / CuAl2O4 / Al2O3 prepared in Example 1 of this invention.

[0039] Figure 8 The Fourier transform infrared spectrum of CuO / CuAl2O4 / Al2O3 prepared in Example 1 of this invention is shown.

[0040] Figure 9 The image shows the H2-TPR diagram of CuO / CuAl2O4 / Al2O3 obtained in Example 1 of this invention.

[0041] Figure 10 The image shows the H2-TPR of CuO / CuAl2O4 / Al2O3-1 prepared in Example 2 of this invention.

[0042] Figure 11 The image shows the H2-TPR of CuO / CuAl2O4 / Al2O3-2 prepared in Example 3 of this invention.

[0043] Figure 12 The image shows the H2-TPR of CuO / CuAl2O4 / Al2O3-3 obtained in Example 4 of this invention.

[0044] Figure 13 The image shows the X-ray powder diffraction (XRD) pattern of CuO / CuAl2O4 / MgAl2O4 / Al2O3 prepared in Example 5 of this invention.

[0045] Figure 14 The image shows the X-ray powder diffraction (XRD) pattern of CuO / CuAl2O4 / CuCr2O4 / Al2O3 prepared in Example 6 of this invention.

[0046] Figure 15 The image shows the XRD pattern of CuO / Al2O3 prepared in Comparative Example 1.

[0047] Figure 16 The image shows the HRTEM image of CuO / Al2O3 prepared in Comparative Example 1.

[0048] Figure 17 This is a Faraday efficiency diagram of the ethylene and ethanol products obtained at different current densities when CuO / CuAl2O4 / Al2O3 catalyzes the electrochemical reduction of carbon dioxide to produce ethanol and ethylene in Example 1 of this invention.

[0049] Figure 18 When the CuO / CuAl2O4 / Al2O3 catalyst prepared in Example 1 of this invention was used to electrochemically reduce carbon dioxide to produce ethanol and ethylene, the current density was 200 mA / cm². -2 Stability test voltage-time curves and ethanol Faraday efficiency plot under the specified conditions. Detailed Implementation

[0050] It should be noted that the term "comprising" and any variations thereof in the specification, claims, and accompanying drawings of this invention are intended to cover non-exclusive inclusion. For example, a process, method, system, product, or device that includes a series of steps or units is not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such processes, methods, products, or devices.

[0051] The "range" disclosed in this invention is given in the form of a lower limit and an upper limit. It can be one or more lower limits and one or more upper limits, respectively. A given range is defined by selecting a lower limit and an upper limit. The selected lower and upper limits define the boundaries of the particular range. All ranges defined in this way are composable, meaning that any lower limit can be combined with any upper limit to form a range. For example, if ranges of 60-120 and 80-110 are listed for specific parameters, it is also expected that ranges of 60-110 and 80-120 are also expected. Furthermore, if the listed minimum range values ​​are 1 and 2, and the listed maximum range values ​​are 3, 4, and 5, then the following ranges are all expected: 1-3, 1-4, 1-5, 2-3, 2-4, and 2-5.

[0052] In this invention, unless otherwise specified, the numerical range "ab" represents a shortened representation of any combination of real numbers between a and b, where a and b are real numbers. For example, the numerical range "0-5" indicates that all real numbers between "0-5" have been listed in this invention, and "0-5" is simply a shortened representation of these numerical combinations.

[0053] In this invention, unless otherwise specified, all embodiments and preferred embodiments mentioned in this invention can be combined with each other to form new technical solutions.

[0054] In this invention, unless otherwise specified, all technical features and preferred features mentioned in this invention can be combined with each other to form new technical solutions.

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. The embodiments described below are some, but not all, embodiments of this invention, and are only used to illustrate the invention, and should not be considered as limiting the scope of the invention. Based on the embodiments of this invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this invention. Where specific conditions are not specified in the embodiments, conventional conditions or conditions recommended by the manufacturer shall apply. Reagents or instruments whose manufacturers are not specified are all conventional products that can be purchased commercially.

[0056] Example 1

[0057] This embodiment provides a composite metal oxide catalyst, which is prepared by a method including the following specific steps:

[0058] (1) Weigh 9.6641g Cu(NO3)2·3H2O, 7.5013g Al(NO3)3·9H2O, and 36g urea and add them to a 500mL beaker containing 200mL deionized water (copper-aluminum molar ratio of 2:1). After stirring for 30 minutes, transfer the resulting mixed solution to a 500mL polytetrafluoroethylene-lined reactor and place the reactor in a 110℃ oven for 30 minutes for hydrothermal nucleation. After cooling to room temperature, transfer the resulting reaction product to a three-necked flask and continue stirring in a 50℃ oil bath to precipitate and crystallize for 12 hours. Filter under reduced pressure, wash the solid product with deionized water until neutral, wash the solid product once with anhydrous ethanol, filter, and place the solid product in a vacuum oven at 60℃ for 24 hours to obtain a composite bimetallic hydroxide, denoted as CuAl-LDHs.

[0059] (2) Weigh 0.05g of CuAl-LDHs powder, spread it evenly on a quartz boat and place it in the high-temperature zone of a tube furnace. Calcination is carried out by segmented heating, i.e., first heating to 500℃ in O2 atmosphere at a heating rate of 1℃ / min and holding for 1h, then heating from 500℃ to 600℃ in O2 atmosphere at a heating rate of 5℃ / min and holding for 1h, and finally heating from 600℃ to 800℃ in O2 atmosphere at a heating rate of 10℃ / min and holding for 4h. In step (2), the flow rate of O2 is kept at 45sccm.

[0060] After maintaining the temperature for 4 hours, the system was cooled to room temperature to obtain the composite metal oxide catalyst, denoted as CuO / CuAl2O4 / Al2O3.

[0061] Example 2

[0062] This embodiment provides a composite metal oxide catalyst, which is prepared by a method including the following specific steps:

[0063] (1) Weigh 9.6641g Cu(NO3)2·3H2O, 7.5013g Al(NO3)3·9H2O, and 42g urea and add them to a 500mL beaker containing 200mL deionized water (copper-aluminum molar ratio of 2:1). After stirring for 30 minutes, transfer the resulting mixed solution to a 500mL polytetrafluoroethylene-lined reactor and place the reactor in a 110℃ oven for 30 minutes for hydrothermal nucleation. After cooling to room temperature, transfer the resulting reaction product to a three-necked flask and continue stirring in a 50℃ oil bath to precipitate and crystallize for 12 hours. Filter under reduced pressure, wash the solid product with deionized water until neutral, wash the solid product once with anhydrous ethanol, filter, and place the solid product in a vacuum oven at 60℃ for 24 hours to obtain a composite bimetallic hydroxide, denoted as CuAl-LDHs.

[0064] (2) Weigh 0.05g of CuAl-LDHs powder, spread it evenly on a quartz boat and place it in the high-temperature zone of a tube furnace. Calcination is carried out in a segmented heating method, namely: first, heat the powder to 500℃ in an O2 atmosphere at a heating rate of 1℃ / min and hold for 1h; then heat the powder to 600℃ in an O2 atmosphere at a heating rate of 5℃ / min and hold for 1h; finally, heat the powder to 900℃ in an O2 atmosphere at a heating rate of 10℃ / min and hold for 4h. In step (2), the O2 flow rate is kept at 45sccm.

[0065] After holding at the temperature for 4 hours, the system was cooled to room temperature to obtain the composite metal oxide catalyst, denoted as CuO / CuAl2O4 / Al2O3-1.

[0066] Example 3

[0067] This embodiment provides a composite metal oxide catalyst, which is prepared by a method including the following specific steps:

[0068] (1) Weigh 9.6641g Cu(NO3)2·3H2O, 7.5013g Al(NO3)3·9H2O, and 36g urea and add them to a 500mL beaker containing 200mL deionized water (copper-aluminum molar ratio of 2:1). After stirring for 30 minutes, transfer the resulting mixed solution to a 500mL polytetrafluoroethylene-lined reactor and place the reactor in a 110℃ oven for 30 minutes for hydrothermal nucleation. After cooling to room temperature, transfer the resulting reaction product to a three-necked flask and continue stirring in a 50℃ oil bath to precipitate and crystallize for 12 hours. Filter under reduced pressure, wash the solid product with deionized water until neutral, wash the solid product once with anhydrous ethanol, filter, and place the solid product in a vacuum oven at 60℃ for 24 hours to obtain a composite bimetallic hydroxide, denoted as CuAl-LDHs.

[0069] (2) Weigh 0.05g of CuAl-LDHs powder, spread it evenly on a quartz boat and place it in the high-temperature zone of a tube furnace. Calcination is carried out by segmented heating, i.e., first heating to 500℃ in an Ar atmosphere at a heating rate of 1℃ / min and holding for 1h, then heating from 500℃ to 600℃ in an Ar atmosphere at a heating rate of 5℃ / min and holding for 1h, and finally heating from 600℃ to 800℃ in an Ar atmosphere at a heating rate of 10℃ / min and holding for 4h. In step (2), the flow rate of Ar is kept at 45sccm.

[0070] After maintaining the temperature for 4 hours, the system was cooled to room temperature to obtain the composite metal oxide catalyst, denoted as CuO / CuAl2O4 / Al2O3-2.

[0071] Example 4

[0072] This embodiment provides a composite metal oxide catalyst, which is prepared by a method including the following specific steps:

[0073] (1) Weigh 9.6641g Cu(NO3)2·3H2O, 7.5013g Al(NO3)3·9H2O, and 36g urea and add them to a 500mL beaker containing 200mL deionized water (copper-aluminum molar ratio of 2:1). After stirring for 30 minutes, transfer the resulting mixed solution to a 500mL polytetrafluoroethylene-lined reactor and place the reactor in a 110℃ oven for 30 minutes for hydrothermal nucleation. After cooling to room temperature, transfer the resulting reaction product to a three-necked flask and continue stirring in a 50℃ oil bath to precipitate and crystallize for 12 hours. Filter under reduced pressure, wash the solid product with deionized water until neutral, wash the solid product once with anhydrous ethanol, filter, and place the solid product in a vacuum oven at 60℃ for 24 hours to obtain a composite bimetallic hydroxide, denoted as CuAl-LDHs.

[0074] (2) Weigh 0.05g of CuAl-LDHs powder, spread it evenly on a quartz boat and place it in the high-temperature zone of a tube furnace. Calcination is carried out by segmented heating, i.e., first heating to 500℃ in O2 atmosphere at a heating rate of 1℃ / min and holding for 1h, then heating from 500℃ to 600℃ in O2 atmosphere at a heating rate of 5℃ / min and holding for 1h, and finally heating from 600℃ to 1000℃ in O2 atmosphere at a heating rate of 10℃ / min and holding for 4h. In step (2), the flow rate of O2 is kept at 45sccm.

[0075] After maintaining the temperature for 4 hours, the system was cooled to room temperature to obtain the composite metal oxide catalyst, denoted as CuO / CuAl2O4 / Al2O3-3.

[0076] Example 5

[0077] This embodiment provides a composite metal oxide catalyst, which is prepared by a method including the following specific steps:

[0078] (1) Weigh 7.2480g Cu(NO3)2·3H2O, 2.5641g Mg(NO3)2·6H2O, 7.5013g Al(NO3)3·9H2O, and 36g urea and add them to a 500mL beaker containing 200mL deionized water (the total molar ratio of copper and magnesium to aluminum is 2:1). After stirring for 30 minutes, transfer the resulting mixed solution to a 500mL polytetrafluoroethylene-lined reactor and place the reactor in a 110℃ oven for 30 minutes to carry out hydrothermal nucleation. Then, cool it to room temperature and transfer the resulting reaction product to a three-necked flask. Continue stirring and crystallizing in a 50℃ oil bath for 12 hours. The solid product was filtered under reduced pressure, washed with deionized water until neutral, and then washed once with anhydrous ethanol. After filtration, the solid product was placed in a vacuum oven and dried under vacuum at 60°C for 24 hours to obtain a composite trimetallic hydroxide, denoted as CuMgAl-LDHs.

[0079] (2) Weigh 0.05g CuMgAl-LDHs powder, spread it evenly on a quartz boat and place it in the high-temperature zone of a tube furnace. Calcination is carried out in a segmented heating method, namely: first, heat the powder to 500℃ in an O2 atmosphere at a heating rate of 1℃ / min and hold for 1h; then heat the powder to 600℃ in an O2 atmosphere at a heating rate of 5℃ / min and hold for 1h; finally, heat the powder to 800℃ in an O2 atmosphere at a heating rate of 10℃ / min and hold for 4h. In step (2), the flow rate of O2 is kept at 45sccm.

[0080] After maintaining the temperature for 4 hours, the system was cooled to room temperature to obtain the composite metal oxide catalyst, denoted as CuO / CuAl2O4 / MgAl2O4 / Al2O3.

[0081] Example 6

[0082] This embodiment provides a composite metal oxide catalyst, which is prepared by a method including the following specific steps:

[0083] (1) Weigh 9.6641g Cu(NO3)2·3H2O, 4.0015g Cr(NO3)3·9H2O, 3.7513g Al(NO3)3·9H2O, and 36g urea and add them to a 500mL beaker containing 200mL deionized water (the molar ratio of copper to the total molar ratio of aluminum and chromium is 2:1). After stirring for 30 minutes, transfer the resulting mixed solution to a 500mL polytetrafluoroethylene-lined reactor and place the reactor in a 110℃ oven for 30 minutes to carry out hydrothermal nucleation. After cooling to room temperature, transfer the resulting reaction product to a three-necked flask and continue stirring in a 50℃ oil bath to precipitate and crystallize for 12 hours. The solid product was filtered under reduced pressure, washed with deionized water until neutral, and then washed once with anhydrous ethanol. After filtration, the solid product was placed in a vacuum oven and dried under vacuum at 60°C for 24 hours to obtain a composite trimetallic hydroxide, denoted as CuCrAl-LDHs.

[0084] (2) Weigh 0.05g CuCrAl-LDHs powder, spread it evenly on a quartz boat and place it in the high-temperature zone of a tube furnace. Calcination is carried out by segmented heating, i.e., first heating to 500℃ in O2 atmosphere at a heating rate of 1℃ / min and holding for 1h, then heating from 500℃ to 600℃ in O2 atmosphere at a heating rate of 5℃ / min and holding for 1h, and finally heating from 600℃ to 800℃ in O2 atmosphere at a heating rate of 10℃ / min and holding for 4h. In step (2), the flow rate of O2 is kept at 45sccm.

[0085] After maintaining the temperature for 4 hours, the system was cooled to room temperature to obtain the composite metal oxide catalyst, denoted as CuO / CuAl2O4 / CuCr2O4 / Al2O3.

[0086] Example 7

[0087] This embodiment provides a composite metal oxide catalyst, which is prepared by a method including the following specific steps:

[0088] (1) Weigh 7.2480g Cu(NO3)2·3H2O, 2.9103g Co(NO3)3·6H2O, 7.5013g Al(NO3)3·9H2O, and 36g urea and add them to a 500mL beaker containing 200mL deionized water (the molar ratio of copper to the total molar ratio of cobalt and aluminum is 1:1). After stirring for 30 minutes, transfer the resulting mixed solution to a 500mL polytetrafluoroethylene-lined reactor and place the reactor in a 110℃ oven for 30 minutes to carry out hydrothermal nucleation. Then, cool it to room temperature and transfer the resulting reaction product to a three-necked flask. Continue stirring and crystallizing in a 50℃ oil bath for 12 hours. The solid product was filtered under reduced pressure, washed with deionized water until neutral, and then washed once with anhydrous ethanol. After filtration, the solid product was placed in a vacuum oven and dried under vacuum at 60°C for 24 hours to obtain a composite trimetallic hydroxide, denoted as CuCoAl-LDHs.

[0089] (2) Weigh 0.05g of CuCoAl-LDHs powder, spread it evenly on a quartz boat and place it in the high-temperature zone of a tube furnace. Calcination is carried out by segmented heating, i.e., first heating to 500℃ in O2 atmosphere at a heating rate of 1℃ / min and holding for 1h, then heating from 500℃ to 600℃ in O2 atmosphere at a heating rate of 5℃ / min and holding for 1h, and finally heating from 600℃ to 800℃ in O2 atmosphere at a heating rate of 10℃ / min and holding for 4h. In step (2), the flow rate of O2 is kept at 45sccm.

[0090] After maintaining the temperature for 4 hours, the system was cooled to room temperature to obtain the composite metal oxide catalyst, denoted as CuO / CuAl2O4 / CuCo2O4 / Al2O3.

[0091] Comparative Example 1

[0092] This comparative example provides a composite metal oxide catalyst, which is prepared by a method including the following specific steps:

[0093] (1) Weigh 9.6641g Cu(NO3)2·3H2O, 7.5013g Al(NO3)3·9H2O, and 36g urea and add them to a 500mL beaker containing 200mL deionized water (copper-aluminum molar ratio of 2:1). After stirring for 30 minutes, transfer the resulting mixed solution to a 500mL polytetrafluoroethylene-lined reactor and place the reactor in a 110℃ oven for 30 minutes for hydrothermal nucleation. After cooling to room temperature, transfer the resulting reaction product to a three-necked flask and continue stirring in a 50℃ oil bath to precipitate and crystallize for 12 hours. Filter under reduced pressure, wash the solid product with deionized water until neutral, wash the solid product once with anhydrous ethanol, filter, and place the solid product in a vacuum oven at 60℃ for 24 hours to obtain a composite bimetallic hydroxide, denoted as CuAl-LDHs.

[0094] (2) Weigh 0.05g of CuAl-LDHs powder, spread it evenly on a quartz boat and place it in the high-temperature zone of a tube furnace. Calcination is carried out in a segmented heating method, namely: first, heat the powder to 500℃ in an Ar atmosphere at a heating rate of 1℃ / min and hold for 1h; then heat the powder to 600℃ in a mixed H2 and Ar (1v% H2) atmosphere at a heating rate of 5℃ / min and hold for 1h; finally, heat the powder to 800℃ in an Ar atmosphere at a heating rate of 10℃ / min and hold for 4h. In step (2), the gas flow rate is kept at 45sccm.

[0095] After maintaining the temperature for 4 hours, the system was cooled to room temperature to obtain the composite metal oxide catalyst, denoted as CuO / Al2O3.

[0096] Comparative Example 2

[0097] This comparative example provides a metal oxide catalyst, which is prepared by a method including the following specific steps:

[0098] (1) Weigh 9.6641g Cu(NO3)2·3H2O, 7.5013g Al(NO3)3·9H2O, and 36g urea and add them to a 500mL beaker containing 200mL deionized water (copper-aluminum molar ratio of 2:1). After stirring for 30 minutes, transfer the resulting mixed solution to a 500mL polytetrafluoroethylene-lined reactor and place the reactor in a 110℃ oven for 30 minutes for hydrothermal nucleation. After cooling to room temperature, transfer the resulting reaction product to a three-necked flask and continue stirring in a 50℃ oil bath to precipitate and crystallize for 12 hours. Filter under reduced pressure, wash the solid product with deionized water until neutral, wash the solid product once with anhydrous ethanol, filter, and place the solid product in a vacuum oven at 60℃ for 24 hours to obtain a composite bimetallic hydroxide, denoted as CuAl-LDHs.

[0099] (2) Weigh 0.05g of CuAl-LDHs powder, spread it evenly on a quartz boat and place it in the high-temperature zone of a tube furnace. Calcination is carried out in a segmented heating manner, namely: first, heat the material to 500℃ in an O2 atmosphere at a heating rate of 1℃ / min and hold for 1h; then heat the material to 600℃ in an O2 atmosphere at a heating rate of 5℃ / min and hold for 1h; finally, heat the material to 800℃ in an O2 atmosphere at a heating rate of 10℃ / min and hold for 4h. In step (2), the flow rate of O2 is kept at 45sccm. After holding for 4h, the system is cooled to room temperature to obtain the composite metal oxide catalyst, denoted as CuO / CuAl2O4 / Al2O3.

[0100] (3) CuO / CuAl2O4 / Al2O3 was stirred with dilute hydrochloric acid (1 mol / L) at room temperature for 12 h to remove CuO and Al2O3. Then, the product was filtered and washed with deionized water until neutral, and then dried at 60 °C for 24 h to obtain the metal oxide catalyst, which is CuAl2O4.

[0101] Characterization Test Example 1

[0102] This test example performs transmission electron microscopy (TEM) analysis on the CuAl-LDHs obtained in Example 1 of this invention. The obtained TEM image is shown below. Figure 1 As shown. From Figure 1 As can be seen, CuAl-LDHs nanosheets have a smooth surface and their lateral dimensions are about 100-200 nm.

[0103] This test example also involves transmission electron microscopy (TEM), high-resolution TEM (HRTEM), high-angle annular dark-field scanning TEM (HAADF-STEM), energy dispersive spectroscopy (EDS), X-ray powder diffraction (XRD), XPS, and Fourier transform infrared spectroscopy (FTIR) analyses of the CuO / CuAl2O4 / Al2O3 obtained in Example 1 of this invention. The obtained TEM images, HRTEM images, HAADF-STEM images, EDS, XRD patterns, XPS spectra of Cu 2p, and FTIR spectra are shown below. Figures 2-4 , Figures 5a-5c , Figures 6-8 As shown.

[0104] from Figure 2 It can be clearly seen that in CuO / CuAl2O4 / Al2O3, CuO nanosheets and CuAl2O4 nanosheets are highly dispersed on amorphous Al2O3 nanosheets. Figure 3 The HRTEM image shown indicates that the main growth crystal plane orientations are CuO(111) and CuAl2O4(311). Figure 4 and Figures 5a-5c The HAADF-STEM image (with line scan image overlaid) and energy dispersive spectroscopy elemental mapping diagram shown demonstrate that the composite metal oxide catalyst provided in Example 1 of this invention contains both CuO and CuAl2O4, and both are uniformly dispersed without any agglomeration. Figure 6 As can be seen, after the CuAl-LDHs precursor was calcined in a segmented high-temperature atmosphere in an O2 atmosphere, the new peaks (31.26°, 36.83°, 44.82°, and 55.67°) that appeared corresponded to the CuAl2O4 (220), (311), (400), and (422) crystal planes, respectively; and the peaks of 32.51°, 35.42°, 35.54°, 38.71°, 38.90°, 48.72°, and 61.52° corresponded to the CuO (110), (002), (11-1), (111), (200), (20-2), and (11-3) crystal planes, respectively. Furthermore, Figure 6 The absence of an Al2O3 peak indicates that Al2O3 exists in an amorphous state. Figure 7 The XPS spectrum of Cu 2p shown further confirms that Cu in the composite metal oxide catalyst provided in Example 1 of this invention... 2+ The existence of species. Figure 8 The Fourier transform infrared spectrum shown further demonstrates the presence of CuAl4O2 species in the composite metal oxide catalyst provided in Example 1 of this invention.

[0105] This test example also included X-ray powder diffraction (XRD) analysis of the composite metal oxide catalysts prepared in Examples 5-6 of this invention. The obtained XRD patterns are shown below. Figures 13-14 As shown. From Figure 13 and Figure 14 As can be seen from the above, the composite metal oxide catalyst prepared in Example 5 of the present invention contains CuO, CuAl2O4 and MgAl2O4, and the composite metal oxide catalyst prepared in Example 6 of the present invention contains CuO, CuAl2O4 and CuCr2O4. Figure 13 and Figure 14 The absence of Al2O3 peaks indicates that Al2O3 exists in an amorphous state; furthermore, Figure 13 No MgO peak was observed. Figure 14 The absence of a Cr2O3 peak may be due to the fact that under high temperature conditions, MgO is more likely to react with Al2O3 to form MgAl2O4 spinel, while Cr2O3 is more likely to react with CuO to form CuCr2O4 spinel.

[0106] Characterization Test Example 2

[0107] In this test example, H2-TPR analysis was performed on CuO / CuAl2O4 / Al2O3, CuO / CuAl2O4 / Al2O3-1, CuO / CuAl2O4 / Al2O3-2, and CuO / CuAl2O4 / Al2O3-3 to further determine the CuAl4O2 content in these composite metal oxide catalysts. The obtained H2-TPR chromatograms are shown below. Figures 9-12 As shown.

[0108] The following uses CuO / CuAl2O4 / Al2O3 and Figure 9 The calculation process of CuAl4O2 content is explained in detail using an example: First, according to... Figure 9 The H2-TPR diagram shown determines the molar ratio of H2 consumption, i.e., η = (CuAl2O4). 氢气 / (CuO+CuAl2O4) 氢气 This corresponds to the molar ratio of CuAl2O4 phase to total Cu in CuO / CuAl2O4 / Al2O3; then according to Figure 9 The H2-TPR diagram shown determines the amount of H2 consumed, and the mass percentage of CuAl4O2 is calculated using the following formula:

[0109] W=n×182 / [(1-n)×80+n×182];

[0110] In the formula, W is the weight percentage of CuAl2O4 calculated based on the total weight of CuO and CuAl2O4, in %;

[0111] η=(CuAl2O4) 氢气 / (CuO+CuAl2O4) 氢气 ,%; of which, (CuAl2O4) 氢气 The peak area represents the amount of H2 consumed (i.e., the peak area) corresponding to CuAl2O4 in the H2-TPR diagram; (CuO+CuAl2O4) 氢气 This represents the total H2 consumption (i.e., the total peak area) corresponding to CuO+CuAl2O4 in the H2-TPR diagram.

[0112] 182 is the molar mass of CuAl2O4, in g / mol;

[0113] 80 is the molar mass of CuO, in g / mol.

[0114] Based on this, the mass percentage content of CuAl2O4 phase in CuO / CuAl2O4 / Al2O3, CuO / CuAl2O4 / Al2O3-1, CuO / CuAl2O4 / Al2O3-2, and CuO / CuAl2O4 / Al2O3-3 were calculated to be 13.3%, 25.2%, 1.7%, and 33.1%, respectively.

[0115] Therefore, comparing Examples 1-2 and Example 4 and combining the CuAl2O4 phase mass percentage data calculated above, it can be seen that under the same calcination atmosphere, the higher the calcination temperature, the greater the CuAl2O4 phase mass percentage. Comparing Examples 1 and Example 3 and combining the CuAl2O4 phase mass percentage data calculated above, it can be seen that under the same calcination temperature, the calcination atmosphere also has a significant impact on the CuAl2O4 phase mass percentage. The CuAl2O4 phase mass percentage in the catalyst calcined in an oxygen atmosphere is significantly higher than that in the catalyst calcined in an argon atmosphere.

[0116] Characterization Test Example 3

[0117] In this test example, the CuO / Al2O3 prepared in Comparative Example 1 was subjected to XRD and HRTEM analyses, respectively. The obtained XRD and HRTEM patterns are shown below. Figure 15 and Figure 16 As shown. From Figure 15 and Figure 16 As can be seen from the results, CuO is present in the CuO / Al2O3 prepared in Comparative Example 1, but CuAl2O4 species are not present.

[0118] Application test cases

[0119] In this test example, CuO / CuAl2O4 / Al2O3, CuO / CuAl2O4 / Al2O3-1, CuO / CuAl2O4 / Al2O3-2, CuO / CuAl2O4 / Al2O3-3 provided in Examples 1-4, and CuO / Al2O3 and CuAl2O4 provided in Comparative Examples 1-2 were used as catalysts for the electrochemical reduction of carbon dioxide to produce ethanol and ethylene, and their catalytic performance was tested. The specific steps are as follows:

[0120] The electrochemical reduction of carbon dioxide to produce ethanol and ethylene is carried out in a flow electrolytic cell with an anion exchange membrane as the diaphragm. The electrolyte in the cathode / anodine chamber is a 30 mL volume of 1 M KOH solution. A platinum sheet electrode is used as the anode, a mercury-mercury oxide electrode is used as the reference electrode, and the effective area of ​​the working electrode (cathode) is 1 cm². 2The working electrode was prepared as follows: 5 mg of the catalyst described above was mixed with 323 μL of isopropanol and 157 μL of deionized water, and the resulting mixture was sonicated at room temperature for 1 h to form a homogeneous solution. Then, 20 μL of 5 wt% Nafion solution was added dropwise to the homogeneous solution, and sonication was continued for 40 min to obtain a catalyst slurry. Subsequently, 100 μL of the catalyst slurry was drop-coated onto a gas diffusion electrode using a pipette and dried under an infrared lamp to complete the fabrication of the working electrode. The catalyst loading in the working electrode was 1 mg / cm³. -2 .

[0121] Subsequently at 10-300mA cm -2 The reaction was conducted at a constant current, a CO2 flow rate of 50 sccm throughout the process, a cathode electrolyte circulation rate of 10 sccm, an anolyte circulation rate of 100 sccm, and a test temperature of 25℃ for 1 hour. After 1 hour of reaction, the products of electrochemical reduction of carbon dioxide to produce ethanol and ethylene were detected.

[0122] In Example 1 of this invention, the Faraday efficiency diagrams of the C2 (ethylene and ethanol) products obtained under different current densities during the catalytic electrochemical reduction of carbon dioxide to produce ethanol and ethylene using CuO / CuAl2O4 / Al2O3 were prepared. Figure 17 As shown. From Figure 17 As can be seen, the Faraday efficiency of the C2 product significantly improves with increasing current density, and this improvement is particularly evident at a current density of 200 mA / cm². -2 At that time, the total Faraday efficiency of C2 products was greater than 70%, with ethanol having a Faraday efficiency as high as 40%.

[0123] In Example 1 of this invention, the CuO / CuAl2O4 / Al2O3 catalyst was used for the electrochemical reduction of carbon dioxide to produce ethanol and ethylene, with a current density of 200 mA cm⁻¹. -2 The stability test voltage-time curve and ethanol Faraday efficiency plot under the specified conditions are shown in the figure. Figure 18 As shown. From Figure 18 As can be seen from the data, during the 150h test, the ethanol Faraday efficiency on the CuO / CuAl2O4 / Al2O3 catalyst decreased only slightly (<5%), indicating that the composite metal oxide catalyst provided in this embodiment of the invention has ultra-durable electrochemical CO2RR performance when electrocatalyzing the reduction of carbon dioxide to ethylene and ethanol.

[0124] For the CuO / CuAl2O4 / Al2O3-1 prepared in Example 2 of this invention, after reacting for 1 hour, at a current density of 200 mA / cm², -2 At that time, the total Faraday efficiency of C2 products was greater than 60%, with ethanol having a Faraday efficiency as high as 31%.

[0125] For the CuO / CuAl2O4 / Al2O3-2 prepared in Example 3 of this invention, after reacting for 1 hour, at a current density of 200 mA / cm², -2 At that time, the overall Faraday efficiency of the C2 products was greater than 33%, of which the Faraday efficiency of ethanol was 15%.

[0126] For the CuO / CuAl2O4 / Al2O3-3 prepared in Example 4 of this invention, after reacting for 1 hour, at a current density of 200 mA / cm², -2 At that time, the total Faraday efficiency of the C2 products was greater than 48%, of which the Faraday efficiency of ethanol was 24%.

[0127] For the CuO / Al2O3 prepared in Comparative Example 1, after reacting for 1 hour, at a current density of 200 mA cm⁻¹ -2 At that time, the overall Faraday efficiency of the C2 products was greater than 32%, of which the Faraday efficiency of ethanol was 14%.

[0128] For CuAl2O4 prepared in Comparative Example 2, after reacting for 1 hour, at a current density of 200 mA cm⁻¹ -2 At this time, only a small amount of CO is generated, and the overall Faraday efficiency of H2 is greater than 70%.

[0129] The experimental data above show that CuAl2O4 and its content in the catalyst affect the total Faradaic efficiency of C2 products and the Faradaic efficiency of ethanol. An appropriate amount of CuAl2O4 can provide more active hydrogen and participate in ethanol formation, thus helping to improve the total Faradaic efficiency of C2 products and the Faradaic efficiency of ethanol. That is, within a certain range of CuAl2O4 content, the total Faradaic efficiency of C2 products and the Faradaic efficiency of ethanol increase with increasing CuAl2O4 content. However, when the CuAl2O4 content is high, although it can produce more active hydrogen, the CuO content decreases with increasing CuAl2O4 content. Since CuO is an activation site for CO2, a decrease in CuO content reduces the number of CO2 activation sites, thereby weakening the formation of CO intermediates, leading to weakened CC coupling, and a decrease in the total Faradaic efficiency of C2 products and the Faradaic efficiency of ethanol.

[0130] In summary, the beneficial technical effects that the composite metal oxide catalyst provided in the embodiments of the present invention can achieve include:

[0131] 1) The composite metal oxide catalyst provided in the embodiments of the present invention has high reproducibility, which is conducive to large-scale production, and it does not require special protection and can be stored for a long time.

[0132] 2) The composite metal oxide catalyst provided by this invention can be used to electrocatalyze the reduction of carbon dioxide to ethylene and ethanol. It can optimize active hydrogen transfer, accelerate the formation of COH intermediates, and reduce the CC coupling energy barrier, thus exhibiting excellent catalytic performance for the electrochemical reduction of carbon dioxide to produce ethanol and ethylene.

[0133] (3) When the composite metal oxide catalyst provided in the present invention is used to electrocatalyze the reduction of carbon dioxide to ethylene and ethanol, it can effectively stabilize the high active sites on the composite metal oxide catalyst and has ultra-durable electrochemical CO2RR performance. In the 150h test, the ethanol Faraday efficiency only decreased slightly (<5%).

[0134] The above description is merely a specific embodiment of the present invention and should not be construed as limiting the scope of the invention. Therefore, any substitution of equivalent components or equivalent changes and modifications made within the scope of protection of this patent should still fall within the scope of this patent. Furthermore, the technical features, technical features and technical inventions, and technical inventions in this invention can be freely combined and used.

Claims

1. A composite metal oxide catalyst characterized by, The composite metal oxide catalyst is obtained by first subjecting an aqueous solution of divalent soluble metal salt, trivalent soluble metal salt, and precipitant to hydrothermal nucleation, precipitation crystallization, and vacuum drying to form a composite metal hydroxide, which is in the form of nanosheets, and then calcining the composite metal hydroxide. The composite metal oxide catalyst includes divalent metal oxides, trivalent metal oxides, and spinel formed from divalent and trivalent metals. All divalent metal oxides, trivalent metal oxides, and spinel formed from divalent and trivalent metals are nanosheets, and the divalent metal oxide nanosheets and the spinel nanosheets formed from divalent and trivalent metals are uniformly dispersed on the trivalent metal oxide. Wherein, the divalent soluble metal salt and the trivalent soluble metal salt are respectively soluble copper salt and soluble aluminum salt, and the divalent metal oxide, the trivalent metal oxide and the spinel formed by the divalent metal and the trivalent metal are respectively CuO, Al2O3 and CuAl2O4. The precipitant includes urea, ammonia, or hexamethylenetetramine. The hydrothermal nucleation conditions include heating to 80-120°C at a rate of 5-10°C / min and holding for 30-90 min. The precipitation crystallization conditions include stirring in an oil bath at 50-80°C for 6-24 h at a stirring speed of 100-500 rpm. The calcination involves heating from room temperature to 300-500°C at a rate of 1-3°C / min and holding for 1-2 h, then heating to 550-650°C at a rate of 5-10°C / min and holding for 1-2 h, and finally calcining at 700-1000°C at a rate of 5-10°C / min for 4-6 h.

2. The composite metal oxide catalyst according to claim 1, characterized by, The weight percentage of spinel formed by divalent metal oxides and divalent and trivalent metals is 1%-35%, with the total weight of divalent metal oxides and spinel formed by divalent and trivalent metals being 100%.

3. The composite metal oxide catalyst according to claim 1, characterized in that, The molar ratio of divalent soluble metal salts to trivalent soluble metal salts is 1:1 to 3:

1.

4. The composite metal oxide catalyst according to any one of claims 1-3, characterized in that, The conditions for hydrothermal nucleation include first heating to 110°C at a heating rate of 5-10°C / min and holding at that temperature for 30 min.

5. The composite metal oxide catalyst according to any one of claims 1-3, characterized in that, The precipitation and crystallization conditions were: stirring in an oil bath at 50°C for 12 hours.

6. The composite metal oxide catalyst according to any one of claims 1-3, characterized in that, The vacuum drying process involves vacuum drying at 40-70℃ for 12-24 hours.

7. The composite metal oxide catalyst according to claim 6, characterized in that, The vacuum drying process involves vacuum drying at 40-60℃ for 24 hours.

8. The composite metal oxide catalyst according to claim 1, characterized in that, The calcination atmosphere includes one or a mixture of oxygen, nitrogen, and argon.

9. The method for preparing the composite metal oxide catalyst according to any one of claims 1-8, characterized in that, The preparation method includes: (1) After adding divalent soluble metal salt, trivalent soluble metal salt and precipitant to deionized water to prepare a solution, hydrothermal nucleation and precipitation crystallization reactions were carried out in sequence, and the product obtained from the reaction was dried under vacuum to obtain composite metal hydroxide. (2) The composite metal hydroxide is calcined to obtain the composite metal oxide catalyst.

10. The preparation method according to claim 9, characterized in that, The ratio of the total molar amount of the divalent and trivalent soluble metal salts to the molar amount of the precipitant is 1:7 to 1:

12.

11. The preparation method according to claim 10, characterized in that, The ratio of the total molar amount of the divalent and trivalent soluble metal salts to the molar amount of the precipitant is 1:

10.

12. The use of the composite metal oxide catalyst according to any one of claims 1-8 in the catalytic electrochemical reduction of carbon dioxide to produce ethanol and ethylene.

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