Praseodymium-copper heterogeneous catalyst for synthesizing multi-carbon alcohol product through efficient electroreduction of carbon dioxide and preparation method of praseodymium-copper heterogeneous catalyst

Abstract

The invention discloses a praseodymium-copper heterogeneous catalyst for synthesizing a multi-carbon alcohol product through efficient electroreduction of carbon dioxide and a preparation method of the praseodymium-copper heterogeneous catalyst. The praseodymium-copper heterogeneous catalyst is a composite material of praseodymium oxide and copper oxide, and praseodymium, copper and oxygen are uniformly distributed in the praseodymium-copper heterogeneous catalyst; the praseodymium oxide is an oxide with the praseodymium-oxygen molar ratio of 6: 11; the molar ratio of praseodymium to copper is not less than 2. The invention provides a method for preparing a multi-carbon alcohol product by electrocatalytic reduction of carbon dioxide, which comprises the following steps: by taking a mercury / mercuric oxide electrode as a reference electrode, a foamed nickel electrode as a counter electrode and a praseodymium-copper heterogeneous catalyst as a working electrode, carrying out electrochemical reduction in a gas diffusion type flowing electrolytic tank to obtain the multi-carbon alcohol product. The praseodymium-copper heterogeneous catalytic material is designed, and the interaction relationship between metal and a carrier and between the metal and the carrier and a reaction intermediate in the catalyst is adjusted by introducing the rare earth element praseodymium, so that the reaction activity and the target product selectivity are improved.

Description

Technical Field

[0001] The invention relates to a praseodymium-copper heterogeneous catalyst for efficiently electroreducing carbon dioxide to synthesize polyol products and a preparation method thereof, belonging to the field of electrochemical catalysis. Background Art

[0002] Carbon dioxide is a major greenhouse gas and an important renewable carbon resource. To date, there are many methods for converting carbon dioxide into high-value-added chemicals, including electrocatalysis, photocatalysis, and thermal catalysis. Among the many conversion technologies, the use of renewable surplus electricity for electrocatalysis has attracted much attention due to its advantages such as controllable reaction conditions, environmentally friendly reaction system, simple operation, and mild conditions. The production of fuels and chemicals from carbon dioxide reduction reactions by electrochemical methods is expected to become a sustainable process to reduce the current dependence on fossil energy and complete the artificial carbon cycle process. However, this conversion process faces several key challenges, especially the problems of low conversion efficiency and insufficient selectivity, which seriously restrict the value enhancement of carbon dioxide and the improvement of its selective conversion capabilities.

[0003] Polyol products such as ethanol and n-propanol are important products of the carbon dioxide reduction reaction. They have high energy density and can be fully integrated with the current infrastructure. Copper-based catalysts are considered to be effective catalysts for the preparation of polyol products by electrocatalytic carbon dioxide reduction reaction. However, compared with polyol products such as ethylene, polyol products have more saturated and polar molecular structures, and the intermediates in the production process are more difficult to stabilize on the surface of copper-based catalysts. This makes the pathways for generating polyol products and polyol products coexist and compete, and the selectivity of the products is difficult to control. Therefore, optimizing and designing advanced copper-based catalysts to achieve highly selective electrosynthesis of polyol products at industrial current density is one of the very important solutions. Summary of the invention

[0004] The purpose of the present invention is to provide a praseodymium-copper heterogeneous catalyst for efficient electroreduction of carbon dioxide to synthesize polyol products, which is a praseodymium-copper heterogeneous catalyst prepared by step-by-step precipitation and step-by-step calcination method and in which praseodymium oxide and copper oxide are evenly distributed. The catalyst exhibits high activity and selectivity in the electrocatalytic reduction of carbon dioxide to prepare polyol products.

[0005] The praseodymium-copper heterogeneous catalyst provided by the present invention 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 to oxygen molar ratio of 6:11.

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

[0008] The present invention also provides a method for preparing the praseodymium-copper heterogeneous catalyst, comprising the following steps:

[0009] S1. preparing a mixed solution of praseodymium acetate and cupric acetate;

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

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

[0012] S4, removing the solvent from 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 to obtain the praseodymium-copper heterogeneous catalyst.

[0013] In the preparation method of the present invention, in step S1, a mixed solution of deionized water and ethanol is used to prepare the mixed solution; in the mixed solution, the molar concentration of praseodymium acetate is 20-50mM, and the molar concentration of copper acetate is 5-20mM;

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

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

[0016] In the preparation method of the present invention, step S1 also includes the step of stirring at 50-65° C. for 15-45 min, the purpose of which is to fully mix and dissolve the two metal precursors;

[0017] Step S2 also includes the step of stirring the precipitate 1 for 20-40 minutes and then heating it to 70-90° C., so that precipitates of praseodymium and copper (mainly precipitates of praseodymium) are formed sequentially and fully;

[0018] In step S3, the precipitant 1 is added and stirred for 90-150 minutes to obtain the precipitate 2, so as to form praseodymium and copper precipitates (mainly copper precipitates) in sequence and fully.

[0019] In the preparation method of the present invention, in step S4, after removing the solvent in the precipitate 2, the precipitate is washed with deionized water and ethanol respectively, and then vacuum dried at 120° C. for 12 h.

[0020] In the preparation method of the present invention, in step S4, the calcination conditions in the air atmosphere are as follows:

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

[0022] The product calcined in air atmosphere was washed with deionized water and ethanol, and then calcined in an inert atmosphere after vacuum drying;

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

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

[0025] The praseodymium-copper heterogeneous catalyst of the present invention can be used for preparing polyol products by electrocatalytic reduction of carbon dioxide, wherein the praseodymium-copper heterogeneous catalyst is used as a cathode material to improve the selectivity of polyol products;

[0026] The polyol products include ethanol and n-propanol.

[0027] The present invention further provides a method for preparing polyol products by electrocatalytic reduction of carbon dioxide, comprising the following steps:

[0028] Using 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 flow electrolysis cell to obtain a polyol product.

[0029] Wherein, in the gas diffusion type flow electrolytic cell, the anolyte is a potassium hydroxide aqueous solution, and the catholyte is a potassium hydroxide aqueous solution;

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

[0031] The reduction current set in the electrochemical reduction process is 100-900 mA, preferably 700 mA.

[0032] The present invention adopts a step-by-step precipitation-distributed calcination method to prepare a praseodymium-copper heterogeneous catalyst, which is simple, low-cost, reproducible and environmentally friendly. The present invention uses a combination of praseodymium oxide and copper oxide to prepare a highly efficient praseodymium-copper bimetallic catalyst, which exhibits excellent selectivity for multi-carbon alcohol products at 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 present invention designs a praseodymium-copper heterogeneous catalytic material, and by introducing the rare earth element praseodymium, the interaction relationship between the metal and the carrier and between the metal-carrier and the reaction intermediate in the catalyst is adjusted, thereby improving the reaction activity and the selectivity of the target product. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 This is a scanning electron microscope image of the praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 4 in Example 1 of the present invention.

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

[0036] Figure 3 This is an element distribution diagram of the praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 4 prepared in Example 1 of the present invention.

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

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

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

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

[0041] Figure 8 This is a graph showing the electrochemical reduction performance of carbon dioxide of a praseodymium-copper heterogeneous catalyst having a copper-praseodymium molar ratio of 4 prepared in Example 1 of the present invention.

[0042] Fig. 9 This is a graph showing the effect of praseodymium-copper heterogeneous catalysts with different copper-praseodymium molar ratios on carbon dioxide reduction performance of the present invention, and the test current is 700 mA.

[0043] Fig.10 This is a performance stability curve of the praseodymium-copper heterogeneous catalyst with a copper-praseodymium molar ratio of 4 in the preparation of polyol products by electrochemical reduction of carbon dioxide, and the test current is 700 mA.

[0044] Fig.11 This is a scanning electron microscope image of copper oxide single metal catalyst. DETAILED DESCRIPTION

[0045] The present invention is further described in detail below in conjunction with specific embodiments, and the examples provided are only for illustrating the present invention, rather than for limiting the scope of the present invention. The examples provided below can be used as a guide for further improvements by those of ordinary skill in the art, and do not constitute a limitation of the present invention in any way.

[0046] The experimental methods in the following examples, unless otherwise specified, are all conventional methods, and are performed according to the techniques or conditions described in the literature in the field or according to the product instructions. The materials, reagents, etc. used in the following examples, unless otherwise specified, can all be obtained from commercial channels.

[0047] Example 1. Preparation of a praseodymium-copper heterogeneous catalyst having a praseodymium-copper molar ratio of 4

[0048] a) 4 mmol of praseodymium acetate and 1 mmol of copper acetate were dissolved in a mixed solvent of 30 ml of deionized water and 70 ml of ethanol by ultrasonication, and the mixture was heated to 55 degrees Celsius 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. The precipitant 1 was slowly dripped into the mixed solution prepared in step a), and the mixture was stirred for 30 minutes and then the temperature was raised to 85 degrees Celsius.

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

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

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

[0053] f) calcining the dried solid powder at 600 degrees Celsius in an argon atmosphere for 2 hours at a heating rate of 2 degrees Celsius per minute.

[0054] The scanning electron microscope image of the praseodymium-copper heterogeneous catalyst with a praseodymium-copper molar ratio of 4 is as follows: Figure 1 , X X-ray diffraction pattern Figure 2 , element distribution diagram Figure 3 .

[0055] from Figure 1 It can be seen that the final praseodymium-copper heterogeneous catalyst with a praseodymium-copper molar ratio of 4 presents a nanoscale spherical block structure.

[0056] from Figure 2 It can be seen that its main crystal forms are praseodymium oxide and copper oxide. Further X-ray diffraction analysis and inductively coupled plasma elemental 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 evenly distributed in the catalytic material.

[0058] Example 2: Preparation of a praseodymium-copper heterogeneous catalyst having a praseodymium-copper molar ratio of 2

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

[0060] Example 3: Preparation of a praseodymium-copper heterogeneous catalyst having a praseodymium-copper molar ratio of 2.5

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

[0062] Example 4: Preparation of a praseodymium-copper heterogeneous catalyst having a praseodymium-copper molar ratio of 3

[0063] The amount of praseodymium acetate in Example 1 was replaced with 3 mmol, and the amount of ammonium carbonate was replaced with 3 mmol, and finally a praseodymium-copper heterogeneous catalyst with a praseodymium-copper molar ratio of 3 was obtained. The scanning electron microscope image thereof is shown in FIG. Figure 6 It can be seen that the praseodymium-copper heterogeneous catalyst with a praseodymium-copper molar ratio of 3 finally obtained exhibits a ball-and-stick structure.

[0064] Example 5. Preparation of a praseodymium-copper heterogeneous catalyst having a praseodymium-copper molar ratio of 5

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

[0066] Embodiment 6,

[0067] The electrochemical reduction performance of carbon dioxide of the praseodymium-copper heterogeneous catalyst of the present invention was tested using a three-electrode system:

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

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

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

[0071] The performance of the Pr-Cu heterogeneous catalysts with different Pr-Cu molar ratios at a working current of 700 mA is shown in Figure 2. Fig. 9 .

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

[0073] Embodiment 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 (prepared in Example 1) with a praseodymium-copper molar ratio of 4 was selected as the working electrode, and the stability test was performed at a working current of 700 mA to obtain the change curves of the current, the Faraday efficiency of the polyol product and time as shown in FIG. Fig.10 .from Fig.10 It can be seen that the catalyst can maintain its catalytic activity and selectivity for polyol products well, with almost no attenuation for 12 hours.

[0075] Comparative Example 1

[0076] The operation is similar to that of Example 1, except that praseodymium acetate is not added to the solution in step a).

[0077] The single metal catalyst of copper oxide was obtained, and its scanning electron microscope image is as follows Fig.11 It can be seen that the final copper oxide single metal catalyst presents a rod-shaped and block-layer structure.

[0078] At an operating current of 700 mA, the Faradaic efficiency of the polyol products produced by the electrocatalytic carbon dioxide reduction reaction of this comparative catalyst is only 25.4%, of which the Faradaic efficiency of ethanol is 18.8% and the Faradaic efficiency of n-propanol is 6.6%, which are much lower than the product performance of Example 1, confirming the importance of introducing a large amount of praseodymium oxide species.

Claims

1. A praseodymium-copper heterogeneous catalyst, which is a composite material of praseodymium oxide and copper oxide, wherein: Praseodymium, copper and oxygen are uniformly distributed in the praseodymium-copper heterogeneous catalyst.

2. The praseodymium-copper heterogeneous catalyst according to claim 1, characterized in that: The praseodymium oxide is an oxide with a praseodymium to oxygen molar ratio of 6:

11.

3. The praseodymium-copper heterogeneous catalyst according to claim 1 or 2, characterized in that: In the praseodymium-copper heterogeneous catalyst, the molar ratio of praseodymium to copper is not less than 2.

4. The method for preparing the praseodymium-copper heterogeneous catalyst according to any one of claims 1 to 3, comprising the following steps: S1. preparing a mixed solution of praseodymium acetate and cupric acetate; S2, adding precipitant 1 to the mixed solution obtained in step S1 to obtain precipitate 1; the precipitant 1 is an aqueous solution of ammonium carbonate; S3, adding precipitant 2 to the precipitate 1 obtained in step S2 to obtain precipitate 2; the precipitant 2 is a potassium hydroxide aqueous solution; S4, removing the solvent from 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 to obtain the praseodymium-copper heterogeneous catalyst.

5. The preparation method according to claim 4, characterized in that: In step S1, the mixed solution is prepared by 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, the precipitant 1 is prepared with deionized water; the molar concentration of ammonium carbonate in the precipitant 1 is 0.500-0.800M; In step S3, the precipitant 2 is prepared with deionized water; the molar concentration of potassium hydroxide in the precipitant 2 is 0.5-3M.

6. The preparation method according to claim 4 or 5, characterized in that: Step S1 also includes the step of stirring at 50-65° C. for 15-45 min; Step S2 also includes the step of stirring the precipitate 1 for 20-40 minutes and then heating it to 70-90° C.; In step S3, the precipitant 1 is added and stirred for 90-150 minutes to obtain the precipitate 2.

7. The preparation method according to any one of claims 4 to 6, characterized in that: In step S4, the calcination conditions in the air atmosphere are as follows: The temperature is 475-525℃, the time is 1-3h, and the heating rate is 8-15℃ / min; The conditions for calcination in the inert atmosphere are as follows: The temperature is 550-650℃, the time is 1-4h, and the heating rate is 1-2.5℃ / min.

8. Use of the praseodymium-copper heterogeneous catalyst according to any one of claims 1 to 3 in the electrocatalytic reduction of carbon dioxide to produce polyol products; The praseodymium-copper heterogeneous catalyst is used as a cathode material; The polyol product is ethanol, n-propanol or a mixture of the two.

9. A method for preparing a polyol product by electrocatalytic reduction of carbon dioxide, comprising the following steps: Using a mercury / mercury oxide electrode as a reference electrode, a nickel foam electrode as a counter electrode, and the praseodymium-copper heterogeneous catalyst described in any one of claims 1 to 3 as a working electrode, electrochemical reduction is carried out in a gas diffusion flow electrolytic cell to obtain a polyol product.

10. The method according to claim 9, characterized in that: In the gas diffusion type flow electrolytic cell, the anolyte is a potassium hydroxide aqueous solution, and the catholyte is a potassium hydroxide aqueous solution; Continuously introducing carbon dioxide gas during the electrochemical reduction process; The reduction current set in the electrochemical reduction process is 100 to 900 mA.

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