Catalysts for the low-energy-consumption, high-selectivity reduction of carbon dioxide to formic acid over a wide current density range, their preparation methods, and applications.

Abstract

The present application relates to a kind of catalyst for the low energy consumption, high selectivity reduction carbon dioxide to form formic acid in wide current density range and its preparation method and application, the preparation method of the catalyst includes: S1.palladium template is prepared: sodium chloropalladate, porous silicon and water are mixed, vacuum drying is carried out after adding reducing agent solution, centrifugal, washing, second vacuum drying, to obtain palladium template;S2.alloying: mix inorganic bismuth salt with palladium template, and calcine in reducing atmosphere;S3.etching: the reduction reaction product obtained in step S2 is placed in lye to etch porous silicon in ultrasonic, washing.The catalyst of the present application is uniform in size, the diameter is 118±0.4nm, bismuth palladium metal ratio is adjustable in wide range and there is good linear relationship between product metal ratio and feed metal ratio, surface atomic arrangement shows highly ordered light and dark atoms alternate periodic arrangement, and it shows excellent catalytic selectivity and energy efficiency to carbon dioxide electrochemical reduction to form formic acid in wide current density range.

Description

Technical Field

[0001] This application relates to the field of nanocatalyst technology, specifically to catalysts for the low-energy-consumption, high-selectivity reduction of carbon dioxide to formic acid over a wide current density range, as well as their preparation methods and applications. Background Technology

[0002] Among various CO2 conversion methods, utilizing green electricity to electrochemically reduce CO2 into value-added chemicals is considered an effective way to simultaneously achieve carbon cycling and renewable energy storage. Of the many products from the CO2 electrochemical reduction reaction, formic acid is the most commercially valuable. Furthermore, formic acid can not only be used as fuel in direct formic acid fuel cells, but also as a liquid hydrogen storage carrier to solve the challenges of hydrogen storage and transportation, and to build sustainable hydrogen storage systems geared towards carbon neutrality.

[0003] Linear CO2 molecules are chemically inert with low electron affinity, and a large energy gap (13.7 eV) exists between its lowest unoccupied molecular orbital and its highest occupied molecular orbital. Therefore, the electrochemical conversion of CO2 often requires a large electrical energy input. Furthermore, the electroreduction of CO2 is complex, producing up to 16 different products, resulting in low selectivity in the electroreduction of CO2 to formic acid. Simultaneously, the current density in the electrochemical CO2 reduction process directly impacts its future industrialization cost; currently, achieving low-energy consumption and high selectivity in the reduction of CO2 to formic acid over a wide and high current density range remains a significant challenge.

[0004] Currently, catalysts for the electrochemical reduction of CO2 to formic acid are typically p-block metals (Sn, Bi, etc.), which are poor catalysts for the hydrogen evolution reaction. However, due to their weak adsorption energies, the CO2 reduction process on the surface of these catalysts exhibits a high overpotential. In contrast, palladium is the only known metal that shows promise for achieving the reduction of CO2 to formic acid at near-zero overpotential; however, competition from CO poisoning and the hydrogen evolution reaction limits the application of palladium-based catalysts in CO2 conversion. Summary of the Invention

[0005] The technical problem to be solved by the present invention is the challenge mentioned in the background art. It provides an intermetallic alloy catalyst for reducing CO2 to formic acid with low energy consumption and high selectivity over a wide current density range. The surface atoms of the catalyst are arranged in a highly ordered periodic pattern and have a continuously adjustable metal ratio. Compared with single metal and alloy catalysts with disordered surface atoms, it exhibits lower power consumption and higher formic acid selectivity over a wider current density range.

[0006] To address the above problems, the present invention proposes the following technical solution:

[0007] In a first aspect, the present invention provides a method for preparing an intermetallic alloy catalyst for reducing CO2 to formic acid with low energy consumption and high selectivity over a wide current density range, comprising the following steps:

[0008] S1. Preparation of palladium template: Mix palladium chloride, porous silicon and water, vacuum dry and then add to a reducing agent solution to carry out a reduction reaction. Centrifuge, wash, and vacuum dry again to obtain palladium template;

[0009] S2. Alloying: Mixing inorganic bismuth salt with the palladium template and calcining in a reducing atmosphere to carry out a reduction reaction;

[0010] S3. Etching: The reduction reaction product obtained in step S2 is placed in an alkaline solution under ultrasonication to etch the porous silicon, followed by washing to obtain the ordered intermetallic catalyst for catalyzing the production of formic acid from carbon dioxide.

[0011] Optionally, in step S1, the reducing agent is selected from at least one of ascorbate, glucose, and sodium borohydride.

[0012] Optionally, in step S1, the mass ratio of the chloropalladium salt to porous silicon is 0.05-0.06:0.1-0.3.

[0013] Optionally, in step S1, the molar ratio of the chloropalladium salt to the reducing agent is 0.15-0.2:1-3.

[0014] Optionally, in step S2, the inorganic bismuth salt is bismuth chloride.

[0015] In this application, the molar ratio of inorganic bismuth salt to chloropalladium salt is 0.3-5:1.

[0016] Optionally, in step S2, the reducing atmosphere is selected from a hydrogen / argon mixture.

[0017] Optionally, in the hydrogen / argon mixture, the volume ratio of hydrogen to argon is 5-9:95-5.

[0018] Optionally, in step S2, the calcination temperature is 280-320 ℃, and the calcination time is 5-7 h.

[0019] Optionally, in step S3, the concentration of the alkaline solution is 1-3 mol / L.

[0020] Optionally, in step S3, the alkaline solution may be selected from sodium hydroxide solution, potassium hydroxide solution, or a combination thereof.

[0021] Optionally, in step S3, the etching time is 10-20 min.

[0022] Secondly, this application also provides a catalyst prepared according to the method described above.

[0023] Thirdly, this application also provides the use of the catalyst prepared according to the method described above in the catalytic oxidation of carbon dioxide to formic acid.

[0024] The beneficial effects of this invention are:

[0025] The preparation method of the present invention is simple, reproducible, suitable for large-scale production, and can meet the needs of large-scale use.

[0026] The ordered intermetallic catalyst of the present invention has uniform size with a diameter of 118 ± 0.4 nm. The bismuth-palladium metal ratio is adjustable over a wide range and there is a good linear relationship between the product metal ratio and the feed metal ratio. The surface atomic arrangement shows a highly ordered periodic arrangement of alternating light and dark atoms.

[0027] The ordered intermetallic catalyst of this invention exhibits excellent catalytic selectivity for the electrochemical reduction of carbon dioxide to formic acid over a wide current density range of 100-400 mA cm⁻¹. -2 Within the range, the formic acid faradaic efficiency remained at around 95%.

[0028] The ordered intermetallic catalyst of this invention exhibits significantly reduced voltage requirements and excellent energy efficiency for the electrochemical reduction of carbon dioxide to formic acid over a wide current density range, at a current density of 100 mA cm⁻¹. -2 At that time, the full cell voltage was only 2.37 V, and the energy efficiency of the formic acid product was as high as 57.5%. Attached Figure Description

[0029] Figure 1 The graph shows the relationship between the actual atomic ratio and the synthesis feed ratio of the palladium-bismuth intermetallic alloy catalysts prepared in Examples 1-6 of this invention.

[0030] Figure 2 This is a TEM image of the palladium-bismuth intermetallic alloy catalyst prepared in Example 4 of the present invention.

[0031] Figure 3 The image shows a HAADF-STEM image of the palladium-bismuth intermetallic alloy catalyst prepared in Example 4 of this invention.

[0032] Figure 4 The image shows the activity of the palladium-bismuth intermetallic alloy catalyst prepared in Example 4 of this invention during the electrochemical reduction catalysis of carbon dioxide.

[0033] Figure 5 This is an HRTEM image of the palladium-bismuth alloy catalyst prepared in Example 7 of the present invention.

[0034] Figure 6This is a comparison diagram of the activity of the catalysts prepared in Examples 4 and 7 of the present invention.

[0035] Figure 7 This is a comparison graph of the full-cell voltages of the catalysts prepared in Examples 4 and 7 of this invention.

[0036] Figure 8 This is a comparison chart of the energy efficiency of the catalysts prepared in Examples 4 and 7 of this invention. Detailed Implementation

[0037] The embodiments of the present invention will be described below with reference to the accompanying drawings and preferred embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention from the content disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and various details in this specification can also be modified or changed based on different viewpoints and applications without departing from the spirit of the present invention. It should be understood that the preferred embodiments are only for illustrating the present invention and not for limiting the scope of protection of the present invention.

[0038] It should be noted that the illustrations provided in the following embodiments are only schematic representations of the basic concept of the present invention. Therefore, the drawings only show the components related to the present invention and are not drawn according to the actual number, shape and size of the components in the actual implementation. In the actual implementation, the form, quantity and proportion of each component can be arbitrarily changed, and the layout of the components may also be more complex.

[0039] Numerous details are explored in the following description to provide a more thorough explanation of embodiments of the invention; however, it will be apparent to those skilled in the art that embodiments of the invention may be practiced without these specific details. Example 1

[0040] S1. 53.3 mg sodium chloropalladium and 0.2 g KIT-6 porous silica were added to 2 mL of water and dried under vacuum at 60 °C for 6 h. Then, 2 mL of 1 mol / L ascorbic acid aqueous solution was added, and the mixture was allowed to stand at room temperature for 12 h. After centrifugation, the precipitate was washed three times with water and dried under vacuum at 60 °C to obtain the palladium template.

[0041] S2. The palladium template obtained in step S1 was ground and mixed with 19 mg of bismuth chloride, and then placed in a hydrogen / argon mixed atmosphere with a volume ratio of 5:95 and calcined at 300 °C for 6 h.

[0042] S3. The calcined product was placed in 10 mL of a 2 mol / L sodium hydroxide aqueous solution, sonicated for 15 min, and centrifuged. This process was repeated 5 times. After replacing the sodium hydroxide solution with water, the washing steps were repeated. The product was then vacuum dried at 60 °C to obtain an intermetallic catalyst for the catalytic production of formic acid from carbon dioxide.

[0043] The bismuth-palladium atomic ratio (i.e., the actual bismuth-palladium atomic ratio) of the intermetallic catalyst prepared in this embodiment for catalyzing the production of formic acid from carbon dioxide was determined by energy dispersive X-ray spectroscopy.

[0044] The relationship between the bismuth-palladium atomic ratio (i.e., the actual bismuth-palladium atomic ratio) and the synthesis feed ratio of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment is as follows: Figure 1 As shown. Example 2

[0045] The difference between this embodiment and Embodiment 1 is that:

[0046] S2. The palladium template obtained in step S1 was ground and mixed with 57.1 mg of bismuth chloride, and then placed in a hydrogen / argon mixed atmosphere with a volume ratio of 5:95 and calcined at 300 °C for 6 h.

[0047] The atomic ratio of bismuth to palladium metals (i.e., the actual atomic ratio of bismuth to palladium metals) of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment was detected using the same method as in Example 1.

[0048] The relationship between the bismuth-palladium atomic ratio (i.e., the actual bismuth-palladium atomic ratio) and the synthesis feed ratio of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment is as follows: Figure 1 As shown. Example 3

[0049] The difference between this embodiment and Embodiment 1 is that:

[0050] S2. The palladium template obtained in step S1 was ground and mixed with 114.2 mg of bismuth chloride, and then placed in a hydrogen / argon mixed atmosphere with a volume ratio of 5:95 and calcined at 300 °C for 6 h.

[0051] The atomic ratio of bismuth to palladium metals (i.e., the actual atomic ratio of bismuth to palladium metals) of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment was detected using the same method as in Example 1.

[0052] The relationship between the bismuth-palladium atomic ratio (i.e., the actual bismuth-palladium atomic ratio) and the synthesis feed ratio of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment is as follows: Figure 1 As shown. Example 4

[0053] The difference between this embodiment and Embodiment 1 is that:

[0054] S2. The palladium template obtained in step S1 was ground and mixed with 171.4 mg of bismuth chloride, and then placed in a hydrogen / argon mixed atmosphere with a volume ratio of 5:95 and calcined at 300 °C for 6 h.

[0055] The atomic ratio of bismuth to palladium metals (i.e., the actual atomic ratio of bismuth to palladium metals) of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment was detected using the same method as in Example 1.

[0056] The relationship between the bismuth-palladium atomic ratio (i.e., the actual bismuth-palladium atomic ratio) and the synthesis feed ratio of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment is as follows: Figure 1 As shown.

[0057] TEM images of the palladium-bismuth intermetallic alloy catalyst prepared in the embodiments of the present invention are shown below. Figure 2 See HADDF-STEM diagram. Figure 3 .

[0058] Depend on Figure 2 and Figure 3 It can be seen that the palladium-bismuth intermetallic alloy catalyst prepared in Example 4 of the present invention has uniform size (118 ± 0.4 nm) and the surface atoms show a highly ordered periodic arrangement of alternating light and dark atoms.

[0059] The preparation of formic acid by electrochemical reduction of carbon dioxide using the prepared palladium-bismuth alloy catalyst was tested. The specific steps are as follows:

[0060] Weigh 10 mg of the palladium-bismuth intermetallic alloy catalyst prepared in this embodiment of the invention and 1 mg of XC-72 carbon, add them to 1 mL of a 1:1 volume ratio ethanol / water mixture, then add 30 μL of naphthol solution. After sonicating for 15 minutes, spray the mixture evenly onto the surface of carbon paper (1.25 cm × 1.25 cm) and dry it under an infrared lamp. The catalyst is tested for carbon dioxide reduction using a membrane electrode electrolytic cell. The anolyte is 1 M KOH, and the anolyte flow rate is 2 mL / min. The anode is an iridium dioxide-plated titanium mesh (2 cm × 2 cm), and the cathode uses CO2 gas at a flow rate of 50 sccm (corrected for by the exhaust gas flow rate).

[0061] The reaction process was carried out in constant current mode. Different current densities were set, and the voltage corresponding to each current density was recorded. Gas phase products were collected starting at 600 s, and the gas content was determined by gas chromatography. Liquid phase products were tested by nuclear magnetic resonance.

[0062] The Faradaic efficiency of the palladium-bismuth intermetallic alloy catalyst prepared in the embodiments of the present invention at various current densities is shown in the figure. Figure 4 .

[0063] Depend on Figure 4 It can be seen that in the range of 100 ~ 400 mA cm -2 Over a wide current density range, the formic acid faradaic efficiency of the intermetallic catalyst prepared in Example 4 for catalyzing the production of formic acid from carbon dioxide remained at around 95%.

[0064] The palladium-bismuth intermetallic alloy catalyst prepared in the embodiments of the present invention is at 200 mA cm⁻¹ -2 See the battery voltage corresponding to the current density. Figure 7 For the energy efficiency of formic acid products, please refer to [reference needed]. Figure 8 . Example 5

[0065] The difference between this embodiment and Embodiment 1 is that:

[0066] S2. The palladium template obtained in step S1 was ground and mixed with 228.5 mg of bismuth chloride, and then placed in a hydrogen / argon mixed atmosphere with a volume ratio of 5:95 and calcined at 300 °C for 6 h.

[0067] The atomic ratio of bismuth to palladium metals (i.e., the actual atomic ratio of bismuth to palladium metals) of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment was detected using the same method as in Example 1.

[0068] The relationship between the bismuth-palladium atomic ratio (i.e., the actual bismuth-palladium atomic ratio) and the synthesis feed ratio of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment is as follows: Figure 1 As shown. Example 6

[0069] The difference between this embodiment and Embodiment 1 is that:

[0070] S2. The palladium template obtained in step S1 was ground and mixed with 285.6 mg of bismuth chloride, and then placed in a hydrogen / argon mixed atmosphere with a volume ratio of 5:95 and calcined at 300 °C for 6 h.

[0071] The atomic ratio of bismuth to palladium metals (i.e., the actual atomic ratio of bismuth to palladium metals) of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment was detected using the same method as in Example 1.

[0072] The relationship between the bismuth-palladium atomic ratio (i.e., the actual bismuth-palladium atomic ratio) and the synthesis feed ratio of the intermetallic catalyst for the catalytic production of formic acid from carbon dioxide prepared in this embodiment is as follows: Figure 1 As shown. Example 7

[0073] 53.3 mg sodium chloropalladium and 150 mg XC-72 carbon were added to 2 mL of water and dried under vacuum at 60 °C for 6 h. Then, 2 mL of 1 M (mol / L) ascorbic acid aqueous solution was added, and the mixture was allowed to stand at room temperature for 12 h. After centrifugation, the mixture was washed three times with water and dried under vacuum at 60 °C to obtain the palladium template.

[0074] The obtained palladium template was thoroughly ground and mixed with 171.4 mg of bismuth chloride, and then calcined at 300°C for 6 h in a hydrogen / argon mixed atmosphere with a volume ratio of 5:95 to obtain an intermetallic alloy catalyst. Its HRTEM image is shown below. Figure 5 .

[0075] Depend on Figure 5 It can be seen that the atomic arrangement on the surface of the palladium-bismuth alloy catalyst prepared in Example 7 is not periodic.

[0076] The preparation of formic acid by electrochemical reduction of carbon dioxide using the prepared palladium-bismuth alloy catalyst was tested. The specific steps are as follows:

[0077] 20 mg of the palladium-bismuth alloy catalyst prepared in this embodiment of the invention was weighed and added to 1 mL of a 1:1 volume ratio ethanol / water mixture, followed by 30 μL of naphthol solution. After sonication for 15 minutes, the solution was evenly sprayed onto the surface of carbon paper (1.25 cm × 1.25 cm) and dried under an infrared lamp. The catalyst was tested for carbon dioxide reduction using a membrane electrode electrolytic cell. The anolyte was 1 M KOH solution, and the anolyte flow rate was 2 mL / min. The anode was a titanium mesh (2 cm × 2 cm) plated with iridium dioxide, and the cathode used CO2 gas at a flow rate of 50 sccm (corrected for by the exhaust gas flow rate).

[0078] The reaction process employed a constant current mode, setting different current densities and recording the corresponding voltages. Gaseous products were collected starting at 600 s, and their content was determined by gas chromatography. Liquid products were analyzed using nuclear magnetic resonance (NMR) at 200 mA cm⁻¹. -2 For the formic acid product Faradaic efficiency at the current density, see [reference needed]. Figure 6 For the corresponding battery voltage, please refer to [link / reference]. Figure 7 For the energy efficiency of formic acid products, please refer to [reference needed]. Figure 8 .

[0079] The relationship between the atomic ratio of the bismuth-palladium precursors used in the preparation of Examples 1-6 of this invention and the actual atomic ratio of the resulting palladium-bismuth intermetallic alloy catalysts is shown in the figure. Figure 1 .

[0080] Depend on Figure 1 It can be seen that there is a good linear relationship between the atomic ratio of the feed material and the atomic ratio of the actual sample.

[0081] The ordered palladium-bismuth intermetallic alloy catalyst and the disordered palladium-bismuth alloy catalyst prepared in Examples 4 and 7 of this invention were subjected to carbon dioxide electrochemical reduction tests, with a test current density of 200 mA cm⁻¹. -2 At this current density, the comparison results of the catalyst activity of different embodiments are as follows: Figure 6 As shown.

[0082] Depend on Figure 6 It can be seen that, compared with the palladium-bismuth alloy catalyst with disordered surface structure in Example 7, the palladium-bismuth intermetallic alloy catalyst with highly ordered surface atoms prepared in Example 4 showed a significant improvement in formic acid selectivity.

[0083] The ordered palladium-bismuth intermetallic alloy catalyst and the disordered palladium-bismuth alloy catalyst prepared in Examples 4 and 7 of this invention were subjected to carbon dioxide electrochemical reduction tests, with a test current density of 200 mA cm⁻¹. -2 At this current density, the cell voltage comparison results of catalysts from different embodiments are as follows: Figure 7 As shown, the energy efficiency comparison results are as follows: Figure 8 As shown.

[0084] Depend on Figure 7 and Figure 8 It can be seen that, compared with the palladium-bismuth alloy catalyst with disordered surface structure in Example 7, the palladium-bismuth intermetallic alloy catalyst with highly ordered surface atoms prepared in Example 4 exhibits lower energy consumption and higher energy efficiency.

[0085] In summary, the intermetallic alloy catalyst and its preparation method provided by this invention achieve low energy consumption and high selectivity in reducing CO2 to formic acid over a wide current density range. The arrangement of surface atoms is controlled by the nano-confinement effect of the template. The highly ordered periodic atomic arrangement optimizes the selectivity of formic acid products over a wide current density range and reduces the energy consumption required for the full cell.

[0086] The above embodiments are merely illustrative of the principles and effects of the present invention and are not intended to limit the invention. Any person skilled in the art can modify or alter the above embodiments without departing from the spirit and scope of the present invention. Therefore, all equivalent modifications or alterations made by those skilled in the art without departing from the spirit and technical concept disclosed in the present invention should still be covered by the claims of the present invention.

Claims

1. A method for preparing an ordered intermetallic catalyst for the reduction of carbon dioxide to formic acid with low energy consumption and high selectivity over a wide current density range, characterized in that, The method comprises the following steps: S1. Preparing a palladium template: mixing sodium chloropalladate, porous silicon and water, vacuum drying, adding a reducing agent solution to perform a reduction reaction, centrifuging, washing, vacuum drying twice, and obtaining the palladium template; S2. Alloying: mixing an inorganic bismuth salt with the palladium template, and calcining in a reducing atmosphere to perform a reduction reaction; S3. Etching: placing the reduction reaction product obtained in step S2 in a lye in ultrasonic waves to etch the porous silicon, and washing to obtain an ordered intermetallic catalyst for catalyzing carbon dioxide into formic acid.

2. The production method according to claim 1, wherein In step S1, the reducing agent is at least one selected from ascorbic acid, glucose and sodium borohydride.

3. The production method according to claim 1, wherein In step S1, the mass ratio of sodium chloropalladate to porous silicon is 0.05-0.06:0.1-0.

3.

4. The production method according to claim 1, wherein In step S1, the molar ratio of sodium chloropalladate to reducing agent is 0.15-0.2:1-3.

5. The production method according to claim 1, wherein In step S2, the inorganic bismuth salt is bismuth chloride.

6. The production method according to claim 1, wherein In step S2, the reducing atmosphere is selected from hydrogen / argon mixed gas.

7. The production method according to claim 1, characterized by, In step S2, the calcination temperature is 280-320℃, and the calcination time is 5-7 h.

8. The production method according to claim 1, wherein In step S3, the etching time is 10-20 min.

9. The catalyst prepared by the method according to any one of claims 1-8.

10. The catalyst prepared by the method according to any one of claims 1-8 for catalyzing carbon dioxide into formic acid.

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