CO2 Electroreduction Catalyst for Ethylene Production, Its Preparation Method and Application

Abstract

The present invention relates to a CO2 electroreduction catalyst for ethylene production, its preparation method and application. The catalyst is prepared by in-situ calcination of cuprous oxide and a nitrogen-rich precursor, and has a CuO(111) crystal plane for catalyzing the electroreduction of CO2 to ethylene, as well as an oxygen vacancy structure and surface nitrogen-rich species for enhancing CO2 adsorption, activation and stabilization. The prepared catalyst has small particle size and high dispersion, increasing the catalytic active sites on the catalyst surface. When applied in the electroreduction of CO2 to ethylene, it can promote the adsorption of the key intermediate * CO. The oxygen vacancies can enhance the charge transfer on the catalyst surface, thereby reducing the activation energy barrier of CO2 and the C-C coupling barrier, being more beneficial to the formation of ethylene and having high product selectivity.

Description

Technical Field

[0001] The present invention relates to the technical field of electrocatalytic CO2 reduction, in particular to a catalyst for electro-reducing CO2 to ethylene, a preparation method thereof, and an application thereof. Background Art

[0002] In the context of current energy transformation and the demand for carbon neutrality, it is of great significance to convert CO2 into high-value chemicals and fuels using electrical energy generated from renewable energy sources such as wind energy and solar energy. Due to the wide application of high-value multi-carbon products (such as ethylene) in the chemical and energy fields, their preparation has also attracted much attention. Traditional thermal conversion of CO2, such as catalytic hydrogenation and catalytic reforming, must be carried out under high temperature and high pressure conditions. Disadvantages such as low conversion rate, low efficiency, and high energy consumption limit its large-scale application. Compared with traditional thermal catalytic CO2 reduction technology, electrocatalytic CO2 reduction is undoubtedly the most attractive. Electrocatalytic CO2 reduction is a method of driving the conversion of CO2 into high-value chemical products by applying a voltage between two electrodes at normal temperature and pressure.

[0003] However, due to the need to overcome the relatively high activation energy barrier of CO2 molecules and the complex reaction path (C-C coupling), the activity and selectivity of the electrocatalytic CO2 reaction are usually low, and appropriate catalysts are required to improve the reaction efficiency. Among many electrocatalysts, copper-based catalysts can effectively convert CO2 into high-value multi-carbon products. Among them, ethylene has received extensive attention from the scientific and commercial communities due to its high energy density, wide application range, easy storage and transportation, etc. Researchers have developed a series of catalyst regulation strategies to improve the selectivity and yield of ethylene. Nevertheless, the multiple reaction paths and the competition of by-products (such as methane and hydrogen) result in low selectivity and activity for the electrocatalytic reduction of CO2 to ethylene products.

[0004] Therefore, developing a catalyst with a simple preparation method and capable of significantly improving the selectivity and catalytic activity of electrocatalytic CO2 reduction to ethylene is one of the research focuses for the electro-reduction of CO2 to ethylene nowadays. Summary of the Invention

[0005] Aiming at the deficiencies of the prior art, the present invention provides a catalyst for electro-reducing CO2 to ethylene, a preparation method thereof, and an application thereof, with the aim of improving the selectivity and reaction activity of the catalyst to achieve efficient electrocatalytic reduction of CO2 to ethylene.

[0006] The technical solution adopted by the present invention is as follows:

[0007] On the one hand, the present invention provides a CO2 electroreduction catalyst for ethylene production. The catalyst is prepared by in-situ calcination of cuprous oxide and a nitrogen-rich precursor, and has a CuO(111) crystal plane for catalyzing the electroreduction of CO2 to ethylene, as well as an oxygen vacancy structure and surface nitrogen-rich species for enhancing CO2 adsorption, activation and stabilization.

[0008] The size of the catalyst is 100 - 500 nm, and it can be regulated by adjusting the mass ratio of cuprous oxide and the nitrogen-rich precursor during in-situ calcination and the calcination conditions.

[0009] On the second hand, the present invention provides a preparation method of the above-mentioned CO2 electroreduction catalyst for ethylene production, including:

[0010] Weigh a certain mass of cuprous oxide and the nitrogen-rich precursor, and grind and mix them evenly;

[0011] In an air atmosphere, perform in-situ calcination on the evenly mixed materials.

[0012] The mass ratio of the cuprous oxide to the nitrogen-rich precursor is 1:(5 - 50).

[0013] The temperature of the in-situ calcination is 400 - 600 °C, and the calcination time is 1 - 5 h.

[0014] The nitrogen-rich precursor is one of cyanamide, melamine, dicyandiamide, urea and thiourea.

[0015] On the third hand, the present invention provides an application of the above-mentioned CO2 electroreduction catalyst for ethylene production, including:

[0016] Disperse the catalyst evenly on the carbon paper, use it as the working electrode for CO2 electroreduction, and place it in the catholyte;

[0017] Pass CO2 into the catholyte for pre-saturation and activation of the working electrode, and then continuously pass CO2 and perform potentiostatic electrolysis, then it can catalyze the reduction of CO2 to produce ethylene.

[0018] The potentiostatic potential is -0.9 - -1.3 V (vs. RHE), and the electrolysis time is 40 - 240 min.

[0019] The catholyte is a KHCO3 solution or a KCl solution, and the concentration is 0.1 - 1 mol / L.

[0020] The flow rate of continuously passing CO2 is 1 - 100 mL / min.

[0021] The beneficial effects of the present invention are as follows:

[0022] 1. Different from the catalyst obtained by mechanically mixing copper oxide and graphitic carbon nitride in the prior art, the catalyst of the present invention is prepared by in-situ calcination of cuprous oxide and a nitrogen-rich precursor. The reducing gas generated during the calcination of the nitrogen-containing precursor in-situ reduces cuprous oxide to copper oxide, obtaining the CuO(111) crystal plane for catalytic electroreduction of CO2 to ethylene. Meanwhile, an oxygen vacancy structure and surface nitrogen-rich species that can enhance CO2 adsorption, activation, and stability are constructed. The preparation method is simple, the catalytic performance is excellent, and by changing the mass ratio of cuprous oxide and the nitrogen-containing precursor, the amount and rate of the gas released by the nitrogen-containing precursor during the in-situ calcination process can be changed, realizing the regulation of the nanoscale size of the catalyst.

[0023] 2. The competitive reactions in the existing electrocatalytic CO2 reduction process are intense. The key intermediate *CO for generating C2 products has a low adsorption energy and slow charge transfer on the catalyst surface, which limits the catalytic activity and selectivity of electrocatalytic CO2 reduction to produce ethylene. The catalyst obtained in the present invention has small particle size and high dispersion, increasing the catalytic active sites on the catalyst surface and promoting the adsorption of the key intermediate * CO. At the same time, the created oxygen vacancies enhance the charge transfer on the catalyst surface and lower the activation energy barrier of CO2 and the C-C coupling barrier, promoting the electrocatalytic CO2 reduction to produce high-value ethylene products.

[0024] 3. The existing thermal catalytic CO2 reaction system requires high temperature, high pressure, and hydrogen, but the product types are numerous and the distribution is wide, and the selectivity of ethylene is difficult to exceed 35%. Under the condition of using water as the hydrogen source at normal temperature and pressure in the present invention, the selectivity of ethylene can reach 55.97%, and the current density of the reaction can reach -12.8 mA / cm 2 , with very excellent performance.

[0025] Other features and advantages of the present invention will be described in the subsequent specification, and part of them will be obvious from the specification or understood by implementing the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0026] Figure 1 It is the SEM image of the A2 catalyst in Example 2 of the present invention.

[0027] Figure 2 It is the particle size distribution diagram of the A2 catalyst in Example 2 of the present invention.

[0028] Figure 3 It is the TEM image of the CuO(111) structure in the A2 catalyst in Example 2 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0029] The following describes the specific embodiments of the present invention with reference to the drawings.

[0030] On the one hand, the present application provides a CO2 electroreduction catalyst for ethylene production. The catalyst is prepared by in-situ calcination of cuprous oxide and a nitrogen-rich precursor, and has a CuO(111) crystal plane for catalyzing the electroreduction of CO2 to ethylene, as well as an oxygen vacancy structure and surface nitrogen-rich species for enhancing CO2 adsorption, activation and stabilization.

[0031] Among them, the size of the catalyst is 100 - 500 nm, and it can be regulated by adjusting the mass ratio of cuprous oxide and the nitrogen-rich precursor during in-situ calcination and the calcination conditions.

[0032] On the second hand, the present application provides a preparation method of the above-mentioned CO2 electroreduction catalyst for ethylene production, including:

[0033] Weigh a certain mass of cuprous oxide and the nitrogen-rich precursor, and grind and mix them evenly;

[0034] In an air atmosphere, perform in-situ calcination on the uniformly mixed materials.

[0035] Among them, the mass ratio of the cuprous oxide to the nitrogen-rich precursor is 1:(5 - 50).

[0036] Among them, the temperature of the in-situ calcination is 400 - 600 °C, and the calcination time is 1 - 5 h.

[0037] Among them, the nitrogen-rich precursor is one of cyanamide, melamine, dicyandiamide, urea and thiourea.

[0038] On the third hand, the present invention provides an application of the above-mentioned CO2 electroreduction catalyst for ethylene production, including:

[0039] Disperse the catalyst evenly on the carbon paper, use it as the working electrode for CO2 electroreduction, and place it in the catholyte;

[0040] Pass CO2 into the catholyte to pre-saturate and activate the working electrode, and then continuously pass CO2 and perform constant potential electrolysis, then it can catalyze the reduction of CO2 to produce ethylene.

[0041] Among them, the constant potential is -0.9 - -1.3 V (vs. RHE), and the electrolysis time is 40 - 240 min.

[0042] Among them, the catholyte is a KHCO3 solution or a KCl solution, and the concentration is 0.1 - 1 mol / L.

[0043] Among them, the flow rate of continuously passing CO2 is 1 - 100 mL / min.

[0044] The catalyst obtained by the preparation method of the present application has small particle size and high dispersion. The abundant catalytic active sites on the catalyst surface can promote the adsorption of *CO, the key intermediate for ethylene production, and solve the problems that the adsorption energy of *CO, the key intermediate for the production of C2 products in the electrocatalytic CO2 reduction process, is relatively low on the catalyst surface, and the slow charge transfer limits the catalytic activity and selectivity of electrocatalytic CO2 reduction for ethylene production. At the same time, the fabricated oxygen vacancy structure can enhance the charge transfer on the catalyst surface, thereby reducing the activation energy barrier of CO2 and the C-C coupling barrier, which is more beneficial to the production of ethylene and has high product selectivity.

[0045] The technical solution of the present application will be further described below with specific examples.

[0046] Examples 1 to 5 below are the preparation methods of the catalysts for electroreduction of CO2 to ethylene. The calcination in Examples 1 to 5 is carried out in an air atmosphere.

[0047] Example 1

[0048] Weigh cuprous oxide and cyanamide according to a mass ratio of 1:5, grind and mix them evenly, then put them into a ceramic crucible and calcine in a muffle furnace at 400 °C for 5 h to obtain a catalyst, denoted as A1.

[0049] Example 2

[0050] Weigh cuprous oxide and melamine according to a mass ratio of 1:10, grind and mix them evenly, then put them into a ceramic crucible and keep it at 450 °C for 4 h in a muffle furnace to obtain a catalyst, denoted as A2.

[0051] As Figure 1 and Figure 2 shown, they are the SEM image and particle size distribution diagram of catalyst A2 under a 200 nm scale, respectively. It can be seen that its particles are spherical-like, and the particle size is normally distributed from 50 nm to 200 nm, with an average particle size of 122.7 nm.

[0052] As Figure 3 shown, it is the TEM image of catalyst A2 under a 1.25 nm scale, showing an obvious CuO(111) crystal plane with a lattice spacing of 0.23 nm.

[0053] Example 3

[0054] Weigh cuprous oxide and dicyandiamide according to a mass ratio of 1:20, grind and mix them evenly, then put them into a ceramic crucible and keep it at 500 °C for 3 h in a muffle furnace to obtain a catalyst, denoted as A3.

[0055] Example 4

[0056] Weigh cuprous oxide and urea according to a mass ratio of 1:30, grind and mix them evenly, then put them into a ceramic crucible and keep them at 550 °C in a muffle furnace for 2 h to obtain a catalyst, denoted as A4.

[0057] Example 5

[0058] Weigh cuprous oxide and thiourea according to a mass ratio of 1:50, grind and mix them evenly, then put them into a ceramic crucible and keep them at 600 °C in a muffle furnace for 1 h to obtain a catalyst, denoted as A5.

[0059] Table 1 Statistical table of the working conditions of the preparation methods of Examples 1 - 5 and the average particle size of the obtained catalysts

[0060]

[0061] As shown in Table 1, by changing the mass ratio of the nitrogen-containing precursor to cuprous oxide and the calcination conditions, the nanosize of the obtained catalyst can be regulated. When the mass ratio of cuprous oxide to the nitrogen-containing precursor is 1:10, the calcination temperature is 450 °C, and the calcination time is 4 h, the nanosize of the obtained catalyst A2 is the smallest, and its average particle size is only 122.7 nm. The catalyst particles have a small size and a high dispersion degree, which not only increases the catalytic active sites on the catalyst surface but also is conducive to promoting the adsorption of the key intermediate * CO.

[0062] In the following Examples 6 - 10, the catalysts obtained in Examples 1 to 5 are respectively used in the electrocatalytic reduction of CO2 to prepare ethylene. The catalyst loading in Examples 6 - 10 is 1 mg / cm 2 , the carbon paper used as the working electrode is 1 cm × 1 cm, and the CO2 electroreduction reaction is carried out in an H-type electrolytic cell with a platinum electrode as the counter electrode and a saturated Ag / AgCl electrode as the reference electrode.

[0063] Example 6

[0064] Load the catalyst A1 on the carbon paper to make a working electrode, put it into a 0.1 mol / L KHCO3 electrolytic cell saturated with CO2, continuously introduce CO2 with a flow rate of 1 mL / min and carry out potentiostatic electrolysis. Electro-catalytically reduce CO2 at -0.9 V (vs. RHE) for 40 min, and measure its product composition by on-line GC. The result is: the Faraday efficiency of ethylene is 22.11%.

[0065] Example 7

[0066] The catalyst A2 was loaded on carbon paper to make a working electrode, which was placed in an electrolytic cell containing 0.5 mol / L KHCO3 pre-saturated with CO2. CO2 was continuously introduced at a flow rate of 20 mL / min and constant potential electrolysis was carried out. The CO2 was electrocatalytically reduced for 120 min at a voltage of -1.1 V (vs. RHE), and the product composition was determined by on-line GC. The result was that the Faraday efficiency of ethylene was 55.97%.

[0067] Example 8

[0068] The catalyst A3 was loaded on carbon paper to make a working electrode, which was placed in an electrolytic cell containing 1 mol / L KHCO3 pre-saturated with CO2. CO2 was continuously introduced at a flow rate of 100 mL / min and constant potential electrolysis was carried out. The CO2 was electrocatalytically reduced for 240 min at a voltage of -1.3 V (vs. RHE), and the product composition was determined by on-line GC. The result was that the Faraday efficiency of ethylene was 49.79%.

[0069] Example 9

[0070] The catalyst A4 was loaded on carbon paper to make a working electrode, which was placed in an electrolytic cell containing 0.5 mol / L KCl pre-saturated with CO2. CO2 was continuously introduced at a flow rate of 100 mL / min and constant potential electrolysis was carried out. The CO2 was electrocatalytically reduced for 240 min at a voltage of -1.1 V (vs. RHE), and the product composition was determined by on-line GC. The result was that the Faraday efficiency of ethylene was 40.66%.

[0071] Example 10

[0072] The catalyst A5 was loaded on carbon paper to make a working electrode, which was placed in an electrolytic cell containing 0.1 mol / L KCl pre-saturated with CO2. CO2 was continuously introduced at a flow rate of 100 mL / min and constant potential electrolysis was carried out. The CO2 was electrocatalytically reduced for 240 min at a voltage of -0.9 V (vs. RHE), and the product composition was determined by on-line GC. The result was that the Faraday efficiency of ethylene was 34.24%.

[0073] It can be seen from Examples 6 to 10 that the application of the catalyst of the present application in the electrocatalytic reduction of CO2 to prepare ethylene can reach a selectivity of ethylene of 55.97% and a current density of the reaction of -12.8 mA / cm 2 under the condition of using water as a hydrogen source at normal temperature and pressure, and has very excellent performance.

[0074] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements for some of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A CO2 electroreduction catalyst for ethylene production, characterized in that, The catalyst is prepared by in-situ calcination of cuprous oxide and a nitrogen-rich precursor, and has a CuO(111) crystal plane for catalytic electroreduction of CO2 to ethylene, as well as an oxygen vacancy structure and a nitrogen-rich surface species for enhancing CO2 adsorption, activation, and stabilization. The nitrogen-rich precursor is one of cyanamide, melamine, dicyandiamide, urea, and thiourea.

2. The CO2 electroreduction catalyst for ethylene production according to claim 1, wherein, The size of the catalyst is 100 - 500 nm and can be regulated by adjusting the mass ratio of cuprous oxide and the nitrogen-rich precursor during in-situ calcination and the calcination conditions.

3. A preparation method of the CO2 electroreduction catalyst for ethylene production as described in claim 1, characterized in that, It includes: Weigh a certain mass of cuprous oxide and the nitrogen-rich precursor, and grind and mix them evenly. In an air atmosphere, the evenly mixed materials are subjected to in-situ calcination.

4. The preparation method of the CO2 electroreduction catalyst for ethylene production according to claim 3, characterized in that, The mass ratio of the cuprous oxide to the nitrogen-rich precursor is 1:(5 - 50).

5. The preparation method of the CO2 electroreduction catalyst for ethylene production according to claim 3, characterized in that, The temperature of the in-situ calcination is 400 - 600 °C, and the calcination time is 1 - 5 h.

6. Use of the CO2 electroreduction catalyst for ethylene production according to claim 1, characterized in that, It includes: The catalyst is evenly dispersed on carbon paper, used as a working electrode for CO2 electroreduction, and placed in a catholyte. CO2 is introduced into the catholyte for pre-saturation and activation of the working electrode, and then CO2 is continuously introduced and constant potential electrolysis is carried out to catalytically reduce CO2 to prepare ethylene.

7. Use of the CO2 electroreduction catalyst for ethylene production according to claim 6, characterized in that, The constant potential is -0.9 to -1.3 V ( vs .RHE), and the electrolysis time is 40 to 240 min.

8. Use of the CO2 electroreduction catalyst for ethylene production according to claim 6, characterized in that, The catholyte is a KHCO3 solution or a KCl solution with a concentration of 0.1 - 1 mol / L.

9. Use of the CO2 electroreduction catalyst for ethylene production according to claim 6, characterized in that, The flow rate of continuously introducing CO2 is 1 - 100 mL / min.

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