A silver-copper double single-atom catalyst and its preparation method and application

Abstract

The invention discloses a silver-copper double single-atom catalyst and a preparation method and application thereof, belonging to the technical field of catalysts, and comprising the following steps: step S1, dissolving cyanamide in colloidal silicon dioxide, drying and grinding, and then calcining at high temperature, and cooling to obtain g-C3N4@SiO2; step S2, dispersing the g-C3N4@SiO2 in water, and then dropping a silver nitrate solution and a copper nitrate solution in sequence, stirring for 12 hours under dark conditions, and then centrifuging, washing the precipitate, and vacuum drying to obtain a precursor; step S3, soaking the precursor in an ammonium bifluoride aqueous solution, filtering, washing, vacuum drying, and annealing to obtain the silver-copper double single-atom catalyst; the preparation method of the invention is simple and easy to operate, and the prepared catalyst exhibits excellent catalytic activity and selectivity in a CO2 cycloaddition reaction, and has good industrial application prospects.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and in particular relates to a silver-copper double single-atom catalyst and a preparation method and application thereof. Background Art

[0002] Cyclic carbonates are valuable chemicals and are crucial in the chemical and polymer industries because they are precursors for making polycarbonates and polyurethanes. Using greenhouse gas carbon dioxide (CO2) as a carbon source, in the presence of a catalyst, a cycloaddition reaction selectively occurs with propargyl alcohol to generate α-alkylene cyclic carbonates that are widely used in organic synthesis; this synthesis reaction is a typical CO2 cycloaddition reaction. Due to the thermodynamic stability and kinetic inertness of CO2, a catalyst is required to react under relatively mild conditions.

[0003] Many supported metal catalysts have been developed in the prior art for this CO2 cycloaddition reaction, such as silver (Ag) nanoparticles supported on porous polymers or covalent organic frameworks (COFs), Ag porous polymers or Cu metal organic framework materials, etc. However, the activity and selectivity of catalysts prepared by loading metal nanoparticles or single metal elements are low, and their stability in the catalytic cycle is also poor; therefore, the development of catalysts with high activity, high selectivity and cyclic stability is a technical problem that urgently needs to be solved. Summary of the invention

[0004] The purpose of the present invention is to provide a silver-copper double single-atom catalyst and a preparation method and application thereof, so as to solve the problems in the background technology.

[0005] The purpose of the present invention can be achieved through the following technical solutions:

[0006] A method for preparing a silver-copper double single-atom catalyst comprises the following steps:

[0007] Step S1, dissolving cyanamide in colloidal silica under vigorous stirring, and then continuing to stir at 100° C. for 3 hours to completely remove water, then grinding into powder and pouring into a crucible, transferring into a muffle furnace for high-temperature calcination, and cooling to room temperature with the furnace to obtain yellow powder g-C3N4@SiO2;

[0008] Step S2, ultrasonically dispersing g-C3N4@SiO2 in deionized water, then dropping an aqueous solution containing silver nitrate and an aqueous solution containing copper nitrate in sequence, vigorously stirring for 12 hours in the dark, then centrifuging and separating the precipitate, washing the precipitate with water and ethanol, and then vacuum drying at 25°C for 12 hours to obtain a powdery precursor AgNO3+Cu(NO3)2@g-C3N4@SiO2;

[0009] Step S3, soak the precursor AgNO3+Cu(NO3)2@g-C3N4@SiO2 in an aqueous solution of ammonium bifluoride for 2 days to remove silica, filter, wash with distilled water, and vacuum dry at 100°C, then pour into a magnetic boat, and place the magnetic boat in a tubular furnace for annealing to obtain a silver-copper double single-atom catalyst (Ag1Cu1 / mpg-C3N4).

[0010] Furthermore, the usage ratio of the cyanamide to the colloidal silica is 5 g:10-15 mL; the colloidal silica is commercially available LUDOX AS-40 colloidal silica.

[0011] Furthermore, the high-temperature calcination temperature is 550° C., the heating rate is 2° C. / min, and the calcination time is 4 hours.

[0012] Furthermore, the mass ratio of the silver nitrate, copper nitrate and g-C3N4@SiO2 is 0.05-0.15:0.07-0.21:3.

[0013] Furthermore, the dosage ratio of the precursor AgNO3+Cu(NO3)2@g-C3N4@SiO2 to the aqueous solution of ammonium bifluoride is 0.5g:100mL; the concentration of the aqueous solution of ammonium bifluoride is 4mol / L.

[0014] Furthermore, the annealing treatment is carried out in a nitrogen or argon atmosphere with a gas flow rate of 10-100 mL / min, heating to 300° C. at a heating rate of 5° C. / min and keeping the temperature for 2-4 hours.

[0015] A silver-copper double single-atom catalyst is prepared by the above preparation method.

[0016] Furthermore, the mass fraction of silver in the silver-copper double single-atom catalyst is 0.5-1.5%, and the mass fraction of copper in the silver-copper double single-atom catalyst is 0.3-1%.

[0017] Application of a silver-copper double single-atom catalyst in the cycloaddition reaction of alkynol compounds and CO2.

[0018] Furthermore, the alkynol compound is any one of 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynylcyclopentan-1-ol, and 2-phenyl-3-butyn-2-ol.

[0019] Beneficial effects of the present invention:

[0020] (1) The present invention first uses cyanamide and colloidal silica as precursor raw materials, and obtains graphite phase carbon nitride g-C3N4@SiO2 loaded with silica particles after mixing and high-temperature calcination, and then mixes the graphite phase carbon nitride loaded with silica with silver ions and copper ions, and uniformly loads the silver ions and copper ions on the surface of g-C3N4@SiO2 to obtain a precursor AgNO3+Cu(NO3)2@g-C3N4@SiO2, and then soaks it in an ammonium bifluoride aqueous solution to remove the silica ions, thereby obtaining the silver-copper double single-atom catalyst Ag1Cu1 / mpg-C3N4 of the present invention; the preparation method of the present invention is simple and easy to operate, the raw materials are easy to obtain, and the metal loading and ratio of silver-copper are adjustable;

[0021] (2) The silver-copper double single-atom catalyst prepared by the present invention combines silver atoms and copper atoms at the characteristic N / C coordination vacancies of mesoporous graphite phase carbon nitride at the same time. The single-atom silver and single-atom copper can interact with each other, and show better activity for CO2 activation than single silver or copper. In addition, the mesoporous structure of mesoporous graphite phase carbon nitride can fully expose the active sites, and can also promote the mass transfer of substrate molecules and the enrichment of CO2. Therefore, the silver-copper double single-atom catalyst prepared by the present invention can realize the cycloaddition reaction of CO2 and alkynol compounds under low additive and low temperature conditions, showing the advantages of high activity and high selectivity, and has good industrial application prospects;

[0022] (3) The present invention constructs atomically dispersed silver-copper sites on mesoporous graphitic carbon nitride, which can effectively improve the utilization rate of metal atoms while ensuring the uniformity of active sites. In addition, the synergistic effect of the silver-copper double single-atom metal sites significantly exhibits better activity than single-atom silver or copper sites in the present invention. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] The present invention will be further described below in conjunction with the accompanying drawings.

[0024] Figure 1 is a transmission electron microscope (TEM) image of the silver-copper double single-atom catalyst prepared in Example 2 of the present invention;

[0025] Figure 2 is a transmission electron microscope (TEM) image of the silver single atom catalyst prepared in Comparative Example 1 of the present invention;

[0026] Figure 3 is a transmission electron microscope (TEM) image of the copper single atom catalyst prepared in Comparative Example 2 of the present invention;

[0027] Figure 4 X-ray powder diffraction characterization (XRD) diagrams of the catalysts prepared in Example 2, Comparative Example 1 and Comparative Example 2 of the present invention;

[0028] Figure 5 This is an extended edge X-ray absorption fine structure spectrum (XAFS) diagram of the silver-copper double single-atom catalyst prepared in Example 2 of the present invention. DETAILED DESCRIPTION

[0029] The following will be combined with the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0030] Example 1

[0031] This embodiment provides a silver-copper double single-atom catalyst, which is prepared by the following preparation method:

[0032] Step S1, dissolving 5 g of cyanamide in 10 mL of LUDOXAS-40 colloidal silica under vigorous stirring, then continuing to stir at 100 ° C for 3 h to remove water, then grinding into powder and pouring into a crucible, transferring the crucible into a muffle furnace, heating to 550 ° C at a heating rate of 2 ° C / min for high-temperature calcination for 4 h, and cooling to room temperature with the furnace to obtain yellow powder g-C3N4@SiO2;

[0033] Step S2, ultrasonically dispersing 3 g of g-C3N4@SiO2 in 50 mL of deionized water, then sequentially adding 10 mL of an aqueous solution containing 0.05 g of silver nitrate and 10 mL of an aqueous solution containing 0.07 g of copper nitrate, stirring vigorously for 12 h in the dark, then centrifuging and separating the precipitate, washing the precipitate with water and ethanol, and then vacuum drying at 25 ° C for 12 h to obtain powdered AgNO3+Cu(NO3)2@g-C3N4@SiO2;

[0034] Step S3, soaking 0.5g AgNO3+Cu(NO3)2@g-C3N4@SiO2 in 100mL of 4mol / L ammonium bifluoride aqueous solution for 2 days, filtering, washing with distilled water, and vacuum drying at 100°C, then pouring the obtained powder into a magnetic boat, and then placing the magnetic boat in a tube furnace, heating to 300°C at a heating rate of 5°C / min in a nitrogen or argon atmosphere with a gas flow rate of 10mL / min, and annealing for 2h to obtain a silver-copper double single-atom catalyst Ag1Cu1 / mpg-C3N4;

[0035] The mass fraction of silver in the silver-copper double single-atom catalyst prepared in this example is 0.54%, and the mass fraction of copper is 0.33%.

[0036] Example 2

[0037] This embodiment provides a silver-copper double single-atom catalyst, which is prepared by the following preparation method:

[0038] Step S1, dissolving 5 g of cyanamide in 12.5 mL of LUDOXAS-40 colloidal silica under vigorous stirring, then continuing to stir at 100 ° C for 3 h to remove water, then grinding into powder and pouring into a crucible, transferring the crucible into a muffle furnace, heating to 550 ° C at a heating rate of 2 ° C / min for high-temperature calcination for 4 h, and cooling to room temperature with the furnace to obtain yellow powder g-C3N4@SiO2;

[0039] Step S2, ultrasonically dispersing 3 g of g-C3N4@SiO2 in 50 mL of deionized water, then sequentially adding 10 mL of an aqueous solution containing 0.1 g of silver nitrate and 10 mL of an aqueous solution containing 0.17 g of copper nitrate, stirring vigorously for 12 h in the dark, then centrifuging and separating the precipitate, washing the precipitate with water and ethanol, and then vacuum drying at 25 ° C for 12 h to obtain powdered AgNO3+Cu(NO3)2@g-C3N4@SiO2;

[0040] Step S3, soaking 0.5g AgNO3+Cu(NO3)2@g-C3N4@SiO2 in 100mL of 4mol / L ammonium bifluoride aqueous solution for 2 days, filtering, washing with distilled water, and vacuum drying at 100°C, then pouring the obtained powder into a magnetic boat, and then placing the magnetic boat in a tube furnace, heating to 300°C at a heating rate of 5°C / min in a nitrogen or argon atmosphere with a gas flow rate of 50mL / min, and annealing for 3h to obtain a silver-copper double single-atom catalyst Ag1Cu1 / mpg-C3N4;

[0041] The mass fraction of silver in the silver-copper double single-atom catalyst prepared in this example is 0.98%, and the mass fraction of copper is 0.68%.

[0042] Example 3

[0043] This embodiment provides a silver-copper double single-atom catalyst, which is prepared by the following preparation method:

[0044] Step S1, dissolving 5 g of cyanamide in 15 mL of LUDOX AS-40 colloidal silica under vigorous stirring, then continuing to stir at 100 ° C for 3 h to remove water, then grinding into powder and pouring into a crucible, transferring the crucible into a muffle furnace, heating to 550 ° C at a heating rate of 2 ° C / min for high-temperature calcination for 4 h, and cooling to room temperature with the furnace to obtain yellow powder g-C3N4@SiO2;

[0045] Step S2, ultrasonically dispersing 3 g of g-C3N4@SiO2 in 50 mL of deionized water, then sequentially adding 10 mL of an aqueous solution containing 0.15 g of silver nitrate and 10 mL of an aqueous solution containing 0.21 g of copper nitrate, vigorously stirring for 12 h in the dark, then centrifuging and separating the precipitate, washing the precipitate with water and ethanol, and then vacuum drying at 25 ° C for 12 h to obtain powdered AgNO3+Cu(NO3)2@g-C3N4@SiO2;

[0046] Step S3, soaking 0.5g AgNO3+Cu(NO3)2@g-C3N4@SiO2 in 100mL of 4mol / L ammonium bifluoride aqueous solution for 2 days, filtering, washing with distilled water, and vacuum drying at 100°C, then pouring the obtained powder into a magnetic boat, and then placing the magnetic boat in a tube furnace, heating to 300°C at a heating rate of 5°C / min in a nitrogen or argon atmosphere with a gas flow rate of 100mL / min, and annealing for 4h to obtain a silver-copper double single-atom catalyst Ag1Cu1 / mpg-C3N4;

[0047] The mass fraction of silver in the silver-copper double single-atom catalyst prepared in this example is 1.4%, and the mass fraction of copper is 0.99%.

[0048] Comparative Example 1

[0049] Compared with Example 2, the difference between this comparative example is that in step S2, "10 mL of aqueous solution containing 0.2 g of silver nitrate" is used instead of "10 mL of aqueous solution containing 0.1 g of silver nitrate and 10 mL of aqueous solution containing 0.17 g of copper nitrate", and the amounts of other materials and steps are the same, and finally the silver single atom catalyst Ag / mpg-C3N4 is obtained.

[0050] Comparative Example 2

[0051] Compared with Example 2, the difference between this comparative example is that in step S2, "10 mL of aqueous solution containing 0.28 g of copper nitrate" is used instead of "10 mL of aqueous solution containing 0.1 g of silver nitrate and 10 mL of aqueous solution containing 0.17 g of copper nitrate", and the amounts of other materials and steps are the same, and finally the copper single atom catalyst Cu / mpg-C3N4 is prepared.

[0052] Example 4

[0053] This embodiment provides a method for synthesizing a cyclic carbonate, comprising the following steps:

[0054] 1mmol 3-methyl-1-butyn-3-ol, 30mg Ag1Cu1 / mpg-C3N4 prepared in Example 1, 0.2mmol tetrabutylammonium bromide and 3mL acetonitrile were mixed evenly in a 10mL Schlenk tube, and then the Schlenk tube was connected to a CO2 balloon, and the reaction was stirred at 30°C for 12h. After the reaction was completed, the CO2 balloon was removed to complete the synthesis of cyclic carbonate.

[0055] Example 5

[0056] This embodiment provides a method for synthesizing a cyclic carbonate, comprising the following steps:

[0057] 1mmol 3-methyl-1-butyn-3-ol, 30mg Ag1Cu1 / mpg-C3N4 prepared in Example 2, 0.2mmol tetrabutylammonium bromide and 3mL acetonitrile were mixed evenly in a 10mL Schlenk tube, and then the Schlenk tube was connected to a CO2 balloon, and the reaction was stirred at 30°C for 12h. After the reaction was completed, the CO2 balloon was removed to complete the synthesis of the cyclic carbonate.

[0058] Example 6

[0059] This embodiment provides a method for synthesizing a cyclic carbonate, comprising the following steps:

[0060] 1mmol 3-methyl-1-butyn-3-ol, 30mg Ag1Cu1 / mpg-C3N4 prepared in Example 3, 0.2mmol tetrabutylammonium bromide and 3mL acetonitrile were mixed evenly in a 10mL Schlenk tube, and then the Schlenk tube was connected to a CO2 balloon, and the reaction was stirred at 30°C for 12h. After the reaction was completed, the CO2 balloon was removed to complete the synthesis of the cyclic carbonate.

[0061] Example 7

[0062] This embodiment provides a method for synthesizing a cyclic carbonate, comprising the following steps:

[0063] 1mmol 3-methyl-1-pentyn-3-ol, 30mg Ag1Cu1 / mpg-C3N4 prepared in Example 2, 0.2mmol tetrabutylammonium bromide and 3mL acetonitrile were mixed evenly in a 10mL Schlenk tube, and then the Schlenk tube was connected to a CO2 balloon, and the reaction was stirred at 30°C for 12h. After the reaction was completed, the CO2 balloon was removed to complete the synthesis of cyclic carbonate.

[0064] Example 8

[0065] This embodiment provides a method for synthesizing a cyclic carbonate, comprising the following steps:

[0066] 1mmol 3,5-dimethyl-1-hexyn-3-ol, 30mg Ag1Cu1 / mpg-C3N4 prepared in Example 2, 0.2mmol tetrabutylammonium bromide and 3mL acetonitrile were mixed evenly in a 10mL Schlenk tube, and then the Schlenk tube was connected to a CO2 balloon, and the reaction was stirred at 30°C for 12h. After the reaction was completed, the CO2 balloon was removed to complete the synthesis of the cyclic carbonate.

[0067] Example 9

[0068] This embodiment provides a method for synthesizing a cyclic carbonate, comprising the following steps:

[0069] 1mmol 1-ethynylcyclopentan-1-ol, 30mg Ag1Cu1 / mpg-C3N4 prepared in Example 2, 0.2mmol tetrabutylammonium bromide and 3mL acetonitrile were mixed evenly in a 10mL Schlenk tube, and then the Schlenk tube was connected to a CO2 balloon, and the reaction was stirred at 30°C for 12h. After the reaction was completed, the CO2 balloon was removed to complete the synthesis of the cyclic carbonate.

[0070] Example 10

[0071] This embodiment provides a method for synthesizing a cyclic carbonate, comprising the following steps:

[0072] 1mmol 2-phenyl-3-butyn-2-ol, 30mg Ag1Cu1 / mpg-C3N4 prepared in Example 2, 0.2mmol tetrabutylammonium bromide and 3mL acetonitrile were mixed evenly in a 10mL Schlenk tube, and then the Schlenk tube was connected to a CO2 balloon, and the reaction was stirred at 30°C for 12h. After the reaction was completed, the CO2 balloon was removed to complete the synthesis of the cyclic carbonate.

[0073] Comparative Example 3

[0074] Compared with Example 5, this comparative example is different in that the "Ag / mpg-C3N4 prepared in Comparative Example 1" is used to replace the "Ag1Cu1 / mpg-C3N4 prepared in Example 2" in equal amounts, and the other materials and steps are the same.

[0075] Comparative Example 4

[0076] The difference between this comparative example and Example 5 is that the "Cu / mpg-C3N4 prepared in Comparative Example 2" is used to replace the "Ag1Cu1 / mpg-C3N4 prepared in Example 2" in equal amounts, and the other materials and steps are the same.

[0077] The cyclic carbonate products obtained in Examples 4 to 10 and Comparative Examples 3 to 4 were tested respectively. The liquid phase was diluted with 10 mL of acetonitrile, and 20 mg of biphenyl was added as an internal standard. The conversion rate of the product and the selectivity of the reaction were determined by gas chromatography (GC). The results are shown in Table 1:

[0078] Table 1

[0079]

[0080] It can be seen from the data in Table 1 that the silver-copper double single-atom catalysts prepared in Examples 1 to 3 of the present invention have excellent catalytic activity and selectivity in catalyzing the cycloaddition reaction of alkynol compounds with CO2; they have significant catalytic activity advantages over silver or copper single-atom catalysts; and the present invention cycles the synthesis process of Example 5 for 5 times, and can still achieve 100% conversion rate and 100% selectivity, indicating that the silver-copper double single-atom catalyst of the present invention also has excellent cycle stability. It should be further explained that, compared with the data of Example 5, Example 6 uses the Ag1Cu1 / mpg-C3N4 prepared in Example 3 with higher silver and copper contents, but when the silver and copper content standards of the Ag1Cu1 / mpg-C3N4 prepared in Example 2 are reached, its catalytic performance can already achieve the optimal effect, and further increasing its content will only increase the material cost of the catalyst, so there is no need to pursue excessively high silver and copper contents.

[0081] See also Figure 1-Figure 3 As shown, the mesoporous structure of g-C3N4 is presented, and the pore size is about 10-15nm. No obvious metal nanoparticles are found on the g-C3N4 carrier, indicating that the metal species therein are presented in a single-atom distribution state.

[0082] See also Figure 4 As shown, none of the three catalysts have peaks related to metal elements and oxides of Ag and Cu, and the peak appearing at 28° is attributed to the characteristic peak of g-C3N4.

[0083] See also Figure 5 As shown, a) the K-edge absorption spectrum of Ag proves that Ag is distributed in a single atom in the silver-copper double single atom catalyst, and b) the K-edge absorption spectrum of Cu proves that Cu is distributed in a single atom in the silver-copper double single atom catalyst.

[0084] It should be noted that, in this article, relational terms such as first and second, etc. are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any such actual relationship or order between these entities or operations. Moreover, the terms "include", "comprise" or any other variants thereof are intended to cover non-exclusive inclusion, so that a process, method, article or device including a series of elements includes not only those elements, but also other elements not explicitly listed, or also includes elements inherent to such process, method, article or device.

[0085] Although embodiments of the present invention have been shown and described, it will be appreciated by those skilled in the art that various changes, modifications, substitutions and variations may be made to the embodiments without departing from the principles and spirit of the present invention, and that the scope of the present invention is defined by the appended claims and their equivalents.

Claims

1. Application of a silver-copper double single-atom catalyst in the cycloaddition reaction of an alkynol compound and CO2, characterized in that: The preparation method of the silver-copper double single-atom catalyst comprises the following steps: Step S1, dissolving cyanamide in colloidal silica under vigorous stirring, then continuing to stir at 100° C. for 3 h, grinding into powder and calcining at high temperature, and cooling to room temperature to obtain g-C3N4@SiO2; Step S2, ultrasonically dispersing g-C3N4@SiO2 in deionized water, then dropping an aqueous solution containing silver nitrate and an aqueous solution containing copper nitrate in sequence, vigorously stirring for 12 hours in the dark, then centrifuging and separating the precipitate, washing the precipitate, and vacuum drying to obtain a precursor; the mass ratio of the silver nitrate, copper nitrate and g-C3N4@SiO2 is 0.05-0.15:0.07-0.21:3; Step S3, soaking the precursor in an aqueous solution of ammonium bifluoride for 2 days, filtering, washing, vacuum drying, and then annealing in a tubular furnace to obtain a silver-copper double single atom catalyst.

2. The use of a silver-copper double single-atom catalyst according to claim 1, characterized in that: The usage ratio of the cyanamide to the colloidal silicon dioxide is 5g:10-15mL.

3. The use of a silver-copper double single-atom catalyst according to claim 1, characterized in that: The high temperature calcination temperature is 550° C., the heating rate is 2° C. / min, and the calcination time is 4 hours.

4. The use of a silver-copper double single-atom catalyst according to claim 1, characterized in that: The usage ratio of the precursor to the aqueous solution of ammonium bifluoride is 0.5 g:100 mL.

5. The use of a silver-copper double single-atom catalyst according to claim 1, characterized in that: The annealing treatment is carried out in a nitrogen or argon atmosphere with a gas flow rate of 10-100 mL / min, heating to 300° C. at a heating rate of 5° C. / min and keeping the temperature for 2-4 hours.

6. The use of a silver-copper double single-atom catalyst according to claim 1, characterized in that: The mass fraction of silver in the silver-copper double single atom catalyst is 0.5-1.5%, and the mass fraction of copper in the silver-copper double single atom catalyst is 0.3-1%.

7. The use of a silver-copper double single-atom catalyst according to claim 1, characterized in that: The alkynol compound is any one of 3-methyl-1-butyn-3-ol, 3-methyl-1-pentyn-3-ol, 3,5-dimethyl-1-hexyn-3-ol, 1-ethynylcyclopentan-1-ol, and 2-phenyl-3-butyn-2-ol.

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