Praseodymium copper hetero catalyst for efficient electroreduction of carbon dioxide to synthesize multi-carbon alcohol products and preparation method thereof

Abstract

The application discloses a praseodymium-copper heterogeneous catalyst for efficiently electro-reducing carbon dioxide to synthesize a multi-carbon alcohol product and a preparation method thereof. The praseodymium-copper heterogeneous catalyst is a composite material of praseodymium oxide and copper oxide, wherein praseodymium, copper and oxygen are uniformly distributed in the praseodymium-copper heterogeneous catalyst; the praseodymium oxide is an oxide with a praseodymium-oxygen molar ratio of 6:11; and the molar ratio of praseodymium to copper is not less than 2. The application provides a method for electro-catalytically reducing carbon dioxide to prepare a multi-carbon alcohol product, which comprises the following steps: taking a mercury / mercury oxide electrode as a reference electrode, taking a nickel foam electrode as a counter electrode, taking the praseodymium-copper heterogeneous catalyst as a working electrode, and performing electrochemical reduction in a gas diffusion type flow electrolytic cell to obtain the multi-carbon alcohol product. The praseodymium-copper heterogeneous catalyst material is designed, the interaction relationship between metals and carriers and between the metal-carrier and reaction intermediates in the catalyst is adjusted by introducing the rare earth element praseodymium, so that the reaction activity and the selectivity of the target product are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to a praseodymium-copper heterogeneous catalyst for efficient electro-reduction of carbon dioxide to synthesize multi-carbon alcohol products and a preparation method thereof, belonging to the field of electrochemical catalysis. BACKGROUND

[0002] Carbon dioxide is a major greenhouse gas and an important renewable carbon resource. So far, there are many methods for converting carbon dioxide into high-value chemicals, including electrocatalysis, photocatalysis, thermal catalysis and other means. Among the many conversion technologies, electrocatalysis using renewable surplus electricity is of great concern due to its controllable reaction conditions, environmentally friendly reaction system, simple operation, and mild conditions. Producing fuels and chemicals from carbon dioxide reduction reactions through electrochemical methods is expected to become a sustainable process to reduce the current dependence on fossil energy and complete the artificial carbon cycle. However, this conversion process faces several key challenges, especially the low conversion efficiency and poor selectivity, which seriously restrict the value-added and selective conversion of carbon dioxide.

[0003] Multi-carbon alcohol products such as ethanol and n-propanol are important products of carbon dioxide reduction reactions, which have high energy density and can be fully integrated with the current infrastructure. Copper-based catalysts are considered to be effective catalysts for the electrocatalytic reduction of carbon dioxide to produce multi-carbon alcohol products. However, compared with multi-carbon hydrocarbon products such as ethylene, multi-carbon alcohol products have more saturated and more polar molecular structures, and the intermediate products in the production process are more difficult to stabilize on the surface of copper-based catalysts. This makes the paths of generating multi-carbon hydrocarbon products and multi-carbon alcohol products coexist and compete, making it difficult to control the selectivity of the products. Therefore, it is very important to optimize and design advanced copper-based catalysts to achieve high-selectivity electro-synthesis of multi-carbon alcohol products at industrial current density. SUMMARY

[0004] The purpose of the present application is to provide a praseodymium-copper heterogeneous catalyst for efficient electro-reduction of carbon dioxide to synthesize multi-carbon alcohol products, which is a praseodymium-copper heterogeneous catalyst prepared by a step-by-step precipitation and step-by-step calcination method, and the praseodymium oxide and copper oxide are uniformly distributed. The electrocatalytic reduction of carbon dioxide to prepare multi-carbon alcohol products shows high activity and selectivity.

[0005] The praseodymium-copper heterogeneous catalyst provided by the present application is a composite material of praseodymium oxide and copper oxide, wherein praseodymium, copper and oxygen are uniformly distributed in the praseodymium-copper heterogeneous catalyst.

[0006] The praseodymium oxide is an oxide with a praseodymium-oxygen molar ratio of 6:11.

[0007] In the praseodymium-copper heterogeneous catalyst of the present application, the molar ratio of praseodymium to copper is not less than 2, preferably 2-5, and more preferably 4.

[0008] The application also provides a preparation method of the praseodymium-copper heterogeneous catalyst, comprising the following steps:

[0009] S1, preparing a mixed solution of praseodymium acetate and copper acetate;

[0010] S2, adding a precipitant 1 to the mixed solution obtained in the step S1 to obtain a precipitate 1; the precipitant 1 is an aqueous ammonium carbonate solution;

[0011] S3, adding a precipitant 2 to the precipitate 1 obtained in the step S2 to obtain a precipitate 2; the precipitant 2 is an aqueous potassium hydroxide solution;

[0012] S4, removing the solvent in the precipitate 2 to obtain a solid mixture; the solid mixture is dried and ground, and then calcined in a flowing air atmosphere and an inert atmosphere in sequence, so that the praseodymium-copper heterogeneous catalyst is obtained.

[0013] In the preparation method, in the step S1, the mixed solution is prepared by using a mixed solution of deionized water and ethanol; in the mixed solution, the molar concentration of praseodymium acetate is 20-50 mM, and the molar concentration of copper acetate is 5-20 mM;

[0014] In the step S2, the precipitant 1 is prepared by using deionized water; in the precipitant 1, the molar concentration of ammonium carbonate is 0.500-0.800 M;

[0015] In the step S3, the precipitant 2 is prepared by using deionized water; in the precipitant 2, the molar concentration of potassium hydroxide is 0.5-3 M.

[0016] In the preparation method, the step S1 further comprises a step of stirring at 50-65 ℃ for 15-45 min, so that the two metal precursors are fully mixed and dissolved;

[0017] The step S2 further comprises a step of stirring the precipitate 1 for 20-40 min and then heating to 70-90 ℃, so that the precipitates of praseodymium and copper (mainly the precipitate of praseodymium) are sequentially and fully formed;

[0018] In the step S3, the precipitate 1 is stirred for 90-150 min after being added to obtain the precipitate 2, so that the precipitates of praseodymium and copper (mainly the precipitate of copper) are sequentially and fully formed.

[0019] In the preparation method, in the step S4, after removing the solvent in the precipitate 2, the precipitate 2 is cleaned by using deionized water and ethanol respectively, and then vacuum dried at 120 ℃ for 12 h.

[0020] In the preparation method, in the step S4, the calcination condition in the air atmosphere is as follows:

[0021] temperature is 475-525℃, time is 1-3h, and the heating rate is 8-15℃ / min;

[0022] The product calcined in the air atmosphere is washed with deionized water and ethanol, and after vacuum drying, it is calcined in an inert atmosphere again;

[0023] The calcination conditions in the inert atmosphere are as follows:

[0024] temperature is 550-650℃, time is 1-4h, and the heating rate is 1-2.5℃ / min.

[0025] The praseodymium-copper heterogeneous catalyst can be used for electrocatalytic reduction of carbon dioxide to prepare multi-carbon alcohol products, wherein the praseodymium-copper heterogeneous catalyst as a cathode material can improve the selectivity of multi-carbon alcohol products.

[0026] The multi-carbon alcohol products include ethanol and n-propanol.

[0027] The application further provides a method for electrocatalytic reduction of carbon dioxide to prepare multi-carbon alcohol products, comprising the following steps:

[0028] With a mercury / mercury oxide electrode as a reference electrode, a nickel foam electrode as a counter electrode, and the praseodymium-copper heterogeneous catalyst as a working electrode, electrochemical reduction is carried out in a gas diffusion type flow electrolytic cell to obtain multi-carbon alcohol products.

[0029] In the gas diffusion type flow electrolytic cell, the anode electrolyte is a potassium hydroxide aqueous solution, and the cathode electrolyte is a potassium hydroxide aqueous solution.

[0030] Carbon dioxide gas is continuously introduced during the electrochemical reduction process.

[0031] The reduction current of the electrochemical reduction process is set to 100-900 milliamps, preferably 700 milliamps.

[0032] The praseodymium-copper heterogeneous catalyst is prepared by a step-by-step precipitation-distributed calcination method, which is simple, low in cost, good in repeatability, and friendly to the environment. The application utilizes the combination of praseodymium oxide and copper oxide to prepare a high-efficiency praseodymium-copper bimetallic catalyst, which exhibits excellent multi-carbon alcohol product selectivity under industrial-grade current density and has high catalytic stability, providing a new idea for designing catalysts with customized selectivity in multi-electron carbon dioxide reduction reactions.

[0033] The praseodymium-copper heterogeneous catalytic material is designed, the interaction between the metal and the carrier in the catalyst and the metal-carrier and the reaction intermediates is adjusted by introducing the rare earth element praseodymium, so as to improve the reaction activity and the selectivity of the target product. BRIEF DESCRIPTION OF DRAWINGS

[0034] Figure 1 Scanning electron microscope image of praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 4 prepared in Example 1 of the present application.

[0035] Figure 2 X-ray diffraction pattern of praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 4 prepared in Example 1 of the present application.

[0036] Figure 3 Elemental distribution map of praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 4 prepared in Example 1 of the present application.

[0037] Figure 4 Scanning electron microscope image of praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 2 prepared in Example 2 of the present application.

[0038] Figure 5 Scanning electron microscope image of praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 2.5 prepared in Example 3 of the present application.

[0039] Figure 6 Scanning electron microscope image of praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 3 prepared in Example 4 of the present application.

[0040] Figure 7 Scanning electron microscope image of praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 5 prepared in Example 5 of the present application.

[0041] Figure 8 Carbon dioxide electrochemical reduction performance graph of praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 4 prepared in Example 1 of the present application.

[0042] Figure 9 Effect of praseodymium-copper heterogeneous catalysts with different copper-praseodymium molar ratios on carbon dioxide reduction performance graph, with a test current of 700 milliampere.

[0043] Figure 10 Performance stability curve of praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 4 in the preparation of multi-carbon alcohol products by carbon dioxide electrochemical reduction, with a test current of 700 milliampere.

[0044] Figure 11 Scanning electron microscope image of copper oxide single metal catalyst. DETAILED DESCRIPTION

[0045] The present application will be further described in conjunction with the specific embodiments, and the examples given are only to illustrate the present application, and are not intended to limit the scope of the present application. The examples provided below can serve as a guide for further improvement by those of ordinary skill in the art, and do not in any way constitute a limitation on the present application.

[0046] The experimental methods in the following examples are all conventional methods, and are carried out according to the techniques or conditions described in the literature in the art or according to the product instructions, unless otherwise specified. The materials, reagents, etc. used in the following examples are commercially available, unless otherwise specified.

[0047] Example 1. Preparation of Pr-Cu heterogeneous catalyst with Pr-Cu molar ratio of 4

[0048] a) 4 mmol of praseodymium acetate and 1 mmol of copper acetate were dissolved in 30 ml of a mixture of deionized water and 70 ml of ethanol by using an ultrasonic instrument. The mixture was heated to 55°C and stirred vigorously for 15 minutes.

[0049] b) 3 mmol of ammonium carbonate was dissolved in 5 ml of deionized water to form precipitant 1. Precipitant 1 was slowly dripped into the mixture prepared in step a), and the temperature was increased to 85°C after stirring for 30 minutes.

[0050] c) 10 mmol of potassium hydroxide was dissolved in 10 ml of deionized water to form precipitant 2. Precipitant 2 was slowly dripped into the precipitate solution prepared in step b), and the precipitation was completed after stirring for 2 hours.

[0051] d) The obtained solid mixture was recovered after the solvent was evaporated by using a rotary evaporator, and was washed with deionized water and ethanol, and vacuum dried at 120°C for 12 hours.

[0052] e) The dried solid was carefully ground, and the obtained powder was calcined at 500°C for 3 hours in a flowing air with a heating rate of 10°C per minute. Subsequently, it was washed with deionized water and ethanol, and vacuum dried at 80°C for 12 hours.

[0053] f) The dried solid powder was calcined at 600°C for 2 hours in an argon atmosphere with a heating rate of 2°C per minute.

[0054] The scanning electron microscope image of the obtained Pr-Cu heterogeneous catalyst with Pr-Cu molar ratio of 4 is shown in Figure 1 、 X The X-ray diffraction pattern is shown in Figure 2 , and the element distribution map is shown in Figure 3 .

[0055] It can be seen from Figure 1 that the obtained Pr-Cu heterogeneous catalyst with Pr-Cu molar ratio of 4 presents a nano-sized spherical block structure.

[0056] It can be seen from Figure 2 that the main crystal forms are praseodymium oxide and copper oxide. Further analysis by X-ray diffraction and inductively coupled plasma element analysis determined that the actual molar ratio of praseodymium, copper and oxygen is 4.0:1.0:6.4.

[0057] From Figure 3 It can be seen that copper, praseodymium and oxygen are uniformly distributed in the catalytic material.

[0058] Example 2, preparation of praseodymium copper heterogeneous catalyst with praseodymium copper molar ratio of 2

[0059] The amount of substance of praseodymium acetate in Example 1 is changed to 2 mmol, and the amount of substance of ammonium carbonate is changed to 2.5 mmol. Finally, a praseodymium copper heterogeneous catalyst with a praseodymium copper molar ratio of 2 can be obtained, and the scanning electron microscope image thereof is as shown in Figure 4 It can be seen that the finally obtained praseodymium copper heterogeneous catalyst with a praseodymium copper molar ratio of 2 presents a rod-like structure.

[0060] Example 3, preparation of praseodymium copper heterogeneous catalyst with praseodymium copper molar ratio of 2.5

[0061] The amount of substance of praseodymium acetate in Example 1 is changed to 2.5 mmol, and the amount of substance of ammonium carbonate is changed to 2.5 mmol. Finally, a praseodymium copper heterogeneous catalyst with a praseodymium copper molar ratio of 2.5 can be obtained, and the scanning electron microscope image thereof is as shown in Figure 5 It can be seen that the finally obtained praseodymium copper heterogeneous catalyst with a praseodymium copper molar ratio of 2.5 presents a rod-like structure.

[0062] Example 4, preparation of praseodymium copper heterogeneous catalyst with praseodymium copper molar ratio of 3

[0063] The amount of substance of praseodymium acetate in Example 1 is changed to 3 mmol, and the amount of substance of ammonium carbonate is changed to 3 mmol. Finally, a praseodymium copper heterogeneous catalyst with a praseodymium copper molar ratio of 3 can be obtained, and the scanning electron microscope image thereof is as shown in Figure 6 It can be seen that the finally obtained praseodymium copper heterogeneous catalyst with a praseodymium copper molar ratio of 3 presents a ball-rod-like structure.

[0064] Example 5, preparation of praseodymium copper heterogeneous catalyst with praseodymium copper molar ratio of 5

[0065] The amount of substance of praseodymium acetate in Example 1 is changed to 5 mmol, and the amount of substance of ammonium carbonate is changed to 4 mmol. Finally, a praseodymium copper heterogeneous catalyst with a praseodymium copper molar ratio of 5 can be obtained, and the scanning electron microscope image thereof is as shown in Figure 7 It can be seen that the finally obtained praseodymium copper heterogeneous catalyst with a praseodymium copper molar ratio of 5 presents a block layer structure with rough surface.

[0066] Example 6,

[0067] The three-electrode system is used to test the performance of the praseodymium copper heterogeneous catalyst in the present application in electrochemical reduction of carbon dioxide.

[0068] The reference electrode is a mercury / mercury oxide electrode, the counter electrode is a nickel foam electrode, and the working electrode is the praseodymium copper heterogeneous catalyst prepared in Examples 1-5.

[0069] The test was carried out in a gas diffusion flow electrolysis cell, the anolyte was a 1 mol / L potassium hydroxide solution, the catholyte was a 1 mol / L potassium hydroxide solution, the reduction current was set to 100, 300, 500, 600, 700, 800, 900 mA, the reduction time was 10 minutes, and carbon dioxide gas was continuously introduced into the catholyte during the electro-reduction process.

[0070] The carbon dioxide electrochemical reduction performance of the praseodymium-copper heterogeneous catalyst with a praseodymium-copper molar ratio of 4 in the present application is shown in Figure 8 . Figure 8 It can be seen that the distribution of carbon dioxide reduction products changes significantly with the working current (the test time for each working current is 10 minutes), and when the working current is 700 mA, the faradic efficiency of the multi-carbon alcohol product can reach 71.3%, of which the faradic efficiency of ethanol is 58.6% and the faradic efficiency of n-propanol is 12.7%.

[0071] The performance of praseodymium-copper heterogeneous catalysts with different praseodymium-copper molar ratios at a working current of 700 mA is shown in Figure 9 .

[0072] It can be seen from Figure 9 that adjusting the molar ratio of praseodymium and copper can effectively regulate the efficiency of carbon dioxide reduction to produce multi-carbon alcohol products. The praseodymium-copper heterogeneous catalyst with a praseodymium-copper molar ratio of 4 can effectively promote the carbon-carbon asymmetric coupling and hydrogenation of reaction intermediates, thereby improving the selectivity of multi-carbon alcohol products, including ethanol and n-propanol.

[0073] Example 7,

[0074] The catalytic performance stability of the praseodymium-copper heterogeneous catalyst was tested using the carbon dioxide reduction test device in Example 6. The praseodymium-copper heterogeneous catalyst with a praseodymium-copper molar ratio of 4 (prepared in Example 1) was selected as the working electrode, and the stability test was carried out at a working current of 700 mA. The current, faradic efficiency of multi-carbon alcohol products, and time variation curves are shown in Figure 10 . It can be seen from Figure 10 that the catalyst can better maintain the catalytic activity and selectivity for multi-carbon alcohol products, and remains almost unchanged for 12 hours.

[0075] Comparative Example 1,

[0076] Referring to the operation of Example 1, the difference is that no praseodymium acetate is added to the solution in step a).

[0077] The single-metal catalyst of copper oxide was obtained, and the scanning electron microscope image is shown in Figure 11 . It can be seen that the final single-metal catalyst of copper oxide presents a rod-like and block layer structure.

[0078] The Faradaic efficiency of the production of multi-carbon alcohol products from the electrocatalytic reduction of carbon dioxide by this comparative catalyst was only 25.4% at a working current of 700 mA, with a Faradaic efficiency of 18.8% for ethanol and 6.6% for n-propanol, which is much lower than the product performance of Example 1, confirming the importance of the large amount of praseodymium oxide species introduced.

Claims

1. A method for preparing a praseodymium-copper heterocatalyst, comprising the following steps: S1. Prepare a mixed solution of praseodymium acetate and copper acetate; S2. Add precipitant 1 to the mixed solution obtained in step S1 to obtain precipitate 1; precipitant 1 is an aqueous solution of ammonium carbonate. S3. Add precipitant 2 to the precipitate 1 obtained in step S2 to obtain precipitate 2; the precipitant 2 is an aqueous solution of potassium hydroxide. S4. After removing the solvent from the precipitate 2, a solid mixture is obtained; the solid mixture is dried and ground, and then calcined in a flowing air atmosphere and an inert atmosphere in sequence to obtain the praseodymium copper heterocatalyst.

2. The preparation method according to claim 1, characterized in that: In step S1, the mixed solution is prepared using a mixture of deionized water and ethanol; in the mixed solution, the molar concentration of praseodymium acetate is 20-50 mM and the molar concentration of copper acetate is 5-20 mM. In step S2, deionized water is used to prepare the precipitant 1; the molar concentration of ammonium carbonate in the precipitant 1 is 0.500-0.800 M; In step S3, deionized water is used to prepare the precipitant 2; the molar concentration of potassium hydroxide in the precipitant 2 is 0.5-3 M.

3. The preparation method according to claim 1 or 2, characterized in that: Step S1 also includes stirring at 50-65 °C for 15-45 min; Step S2 also includes stirring the precipitate 1 for 20-40 min and then heating it to 70-90 °C; In step S3, after adding the precipitant 1, the mixture is stirred for 90-150 min to obtain the precipitate 2.

4. The preparation method according to claim 1 or 2, characterized in that: In step S4, the calcination conditions in the air atmosphere are as follows: The temperature was 475-525 °C, the time was 1-3 h, and the heating rate was 8-15 °C / min. The calcination conditions in the inert atmosphere are as follows: The temperature was 550-650 °C, the time was 1-4 h, and the heating rate was 1-2.5 °C / min.

5. The praseodymium-copper heterocatalyst prepared by the method according to any one of claims 1-4; The praseodymium-copper heterocatalyst is a composite material of praseodymium oxide and copper oxide, wherein, Praseodymium, copper, and oxygen are uniformly distributed in the praseodymium-copper heterocatalyst; The praseodymium oxide is an oxide with a praseodymium-oxygen molar ratio of 6:11; In the praseodymium-copper heterocatalyst, the molar ratio of praseodymium to copper is not less than 2.

6. The application of the praseodymium-copper heterocatalyst according to claim 5 in the electrocatalytic reduction of carbon dioxide to prepare polyol products; The praseodymium-copper heterocatalyst is used as the cathode material; The polyol product is ethanol, n-propanol, or a mixture of both.

7. A method for preparing polyol products by electrocatalytic reduction of carbon dioxide, comprising the following steps: Using a mercury / mercury oxide electrode as the reference electrode, a nickel foam electrode as the counter electrode, and the praseodymium copper heterocatalyst described in claim 5 as the working electrode, electrochemical reduction is carried out in a gas diffusion-type flow electrolytic cell to obtain the polycarbon alcohol product.

8. The method according to claim 7, characterized in that: In the gas diffusion type flow electrolytic cell, the anolyte is an aqueous solution of potassium hydroxide, and the cathode electrolyte is an aqueous solution of potassium hydroxide. Carbon dioxide gas is continuously introduced during the electrochemical reduction process; The reduction current set in the electrochemical reduction process is 100–900 mA.

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