High-loading metal monatomic catalyst and preparation method thereof

Abstract

This invention belongs to the field of single-atom catalyst preparation technology, and discloses a high-load metal single-atom catalyst and its preparation method. The catalyst uses nitrogen-doped carbon material as a support, and the metal is uniformly loaded on the support in the form of single atoms; the metal loading in the catalyst is 10~35 wt%. Preparation method: (1) Mix carbon dots, organic solvent, metal salt, S-source organic ligand and graphitic carbon nitride precursor uniformly to obtain a reaction solution, evaporate the organic solvent and dry to obtain a solid powder; (2) Heat the solid powder obtained in step (1) to the calcination temperature under a protective atmosphere, and after calcination, cool to room temperature to obtain the high-load metal single-atom catalyst of this invention. The preparation method of this invention has universality, improves metal utilization, reduces preparation cost, reduces pollution in the preparation process, has a simple preparation process, short cycle, low energy consumption, good reproducibility, is environmentally friendly, applicable to a variety of metals, and is suitable for large-scale production.

Description

Technical Field

[0001] This invention belongs to the field of single-atom catalyst preparation technology, specifically relating to a metal single-atom catalyst and its preparation method. Background Technology

[0002] Homogeneous and heterogeneous catalysts are widely used in the chemical industry, each with its own characteristics and advantages. Homogeneous catalysts have the advantages of uniform active sites, high atom utilization, and easy adjustment of active sites, but they are unstable and difficult to separate from reactants. Heterogeneous catalysts, on the other hand, are highly stable and easy to separate from reactants, but their atom utilization is low, with only surface atoms able to contact reactants and participate in the catalytic reaction. How to combine the advantages of both types of catalysts is a hot topic and a challenge in catalysis research.

[0003] Single-atom catalysts are considered a bridge between homogeneous and heterogeneous catalysts due to their advantages such as near 100% atomic utilization, easily tunable active sites, and ease of separation from reactants. In 2011, Professor Zhang Tao's research group at the Dalian Institute of Chemical Physics, Chinese Academy of Sciences, successfully prepared a single-atom Pt / FeOx catalyst and first proposed the concept of "single-atom catalysis" (Nat. Chem. 2011, 3, 634-640). This catalyst exhibited high catalytic activity and stability in CO oxidation and selective CO oxidation reactions. Subsequently, metal single-atom catalysts have received widespread attention and research in electrocatalytic hydrogen production, oxygen reduction, and CO2 conversion. In addition to their excellent catalytic performance, the simplicity and homogeneity of single-atom material structures facilitate the accurate identification and characterization of active sites, providing an ideal model and research platform for understanding the mechanism of catalytic reactions at the molecular level, and helping to achieve rational catalyst design for target reactions at the atomic scale. Single-atom catalysts are expected to become a new type of catalyst with potential for industrial catalytic applications.

[0004] Despite the numerous advantages of single-atom metal catalysts, a major challenge they face is the low concentration of single-atom active sites, which significantly limits their catalytic activity and applications. Due to the high reactivity and extremely high surface free energy of single atoms, isolated individual metal atoms readily migrate and aggregate into particles. Furthermore, the preparation of single-atom metal catalysts typically requires high temperatures (e.g., exceeding 700 °C), where metal atoms are more prone to migration and aggregation, and the number of stable single-atom sites in metal oxides is limited. Therefore, preparing single-atom catalysts with high metal loadings while maintaining the dispersion of metal atoms under practical synthesis and reaction conditions is extremely challenging. Summary of the Invention

[0005] In order to overcome the shortcomings of the existing technology, the purpose of this invention is to provide a high-loading metal single-atom catalyst and its preparation method.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A high-load metal single-atom catalyst is provided, which uses nitrogen-doped carbon material as a support and the metal is uniformly loaded on the support in the form of single atoms; the metal loading in the catalyst is 10~35 wt% (the mass percentage of the metal in the entire catalyst).

[0008] Preferably, the metal is a transition metal.

[0009] Preferably, the transition metal is Ni, Cu, Sc, Ti, Cr, Ga, Y, Zr, In, Sn, La, Ce, Dy, Er, Yb, Lu, or Pt.

[0010] The preparation method of the high-load metal single-atom catalyst includes the following steps:

[0011] (1) The carbon dots, organic solvent, metal salt, S-source organic ligand and graphitic carbon nitride precursor are mixed evenly to obtain a reaction solution. The organic solvent is evaporated and dried to obtain a solid powder.

[0012] (2) The solid powder obtained in step (1) is heated to the calcination temperature under a protective atmosphere, and then cooled to room temperature after calcination to obtain the high-load metal single-atom catalyst of the present invention.

[0013] Preferably, in step (1), the carbon point : organic solvent = (0.4~1) g : (80~200) mL, the molar concentration of the metal salt in the reaction solution is 0~0.2 mol / L, the molar concentration of the S-source organic ligand is 0~2 mol / L, and the mass ratio of the S-source organic ligand to the graphitic carbon nitride precursor is 1 : (3~10); wherein, the molar concentrations of both the metal salt and the S-source organic ligand in the reaction solution are not 0.

[0014] Preferably, in step (1), the main elements of the carbon dots are C, N and O, including but not limited to ethylenediamine citrate carbon dots, o-phenylenediamine citrate carbon dots or biomass carbon dots. In this invention, ethylenediamine citrate carbon dots refer to carbon dots prepared from citric acid and ethylenediamine as raw materials, o-phenylenediamine citrate carbon dots refer to carbon dots prepared from o-phenylenediamine and citric acid as raw materials, and biomass carbon dots refer to carbon dots prepared from biomass as raw materials. The preparation methods of these carbon dots are all existing technologies. The organic solvent is any organic solvent that can dissolve carbon dots, metal salts, S-source organic ligands and graphitic carbon nitride precursors, including but not limited to ethanol or dimethyl sulfoxide. The metal salt is any metal salt that can be dispersed in an organic solvent, including but not limited to one or more of metal chloride salts, metal nitrate salts, metal acetate salts and metal sulfate salts. The S-source organic ligands include but are not limited to thiourea, dibenzyl disulfide, thioacetamide or thiophene. The graphitic carbon nitride precursors include but are not limited to dicyandiamide, urea, biuret or melamine.

[0015] Preferably, in step (2), the calcination temperature is 800~1000 ℃ and the calcination time is 1~4 h.

[0016] Preferably, in step (1), the mixture is homogenized by stirring or ultrasonication, and the organic solvent is evaporated by water bath or oil bath.

[0017] Preferably, in step (2), the heating rate is 2~10 ℃ / min, the protective atmosphere is argon or nitrogen, and the temperature is naturally cooled to room temperature after calcination.

[0018] The preparation principle of this invention is as follows: This invention utilizes heteroatom functional groups such as -OH and -COOH on the surface of carbon dots to chelate metal ions during the mixing process, achieving a spatial confinement effect; then, during the heating process, metal sulfide intermediates are formed to prevent agglomeration into excessively large metal elemental particles and the escape of metal element molecules due to thermal motion, thereby reducing the loss of metal elements during heating and ensuring their maximum loading; finally, during the high-temperature holding process, the thermal migration of metal atoms and the anchoring effect of graphitic carbon nitride with ultra-high nitrogen content are used to induce the confined formation of a metal single-atom catalyst with high dispersion and high loading.

[0019] In the catalyst prepared by this invention, the active component is a metal. Therefore, based on the catalytic reactions in which this metal is commonly used as a catalyst in the prior art, the catalyst prepared by this invention can also be practically applied to the catalytic reactions. For example, when the metal is In, Sn, or Cu, the single-atom catalyst prepared by this invention is used for electrocatalytic carbon dioxide reduction; when the metal is Cr, Ga, Y, Zr, or Ce, the single-atom catalyst prepared by this invention is used for electrocatalytic oxygen reduction; when the metal is Pt, the single-atom catalyst prepared by this invention is used for electrocatalytic hydrogen evolution; and so on for other catalysts.

[0020] Beneficial Effects: The metal single-atom catalyst provided by this invention uses metal single atoms as the active component and nitrogen-doped carbon as the support. The loading of metal single atoms is 10-35 wt%, with the highest loading being 2-3 times that of existing technologies. This invention improves the dispersion of metal elements through the confinement effect of carbon dots, ensures the maximum loading of metal elements through the addition of S-source organic ligands, and induces the confined formation of metal single-atom catalysts with high dispersion and high loading through the thermal migration of metal elements and the anchoring effect of graphitic carbon nitride with ultra-high N content. This preparation method is universal and can be used to prepare various metal single-atom catalysts. The preparation method of this invention avoids the acid etching method commonly used in the preparation of single-atom catalysts, improves metal utilization, reduces catalyst preparation costs, and reduces pollution during catalyst preparation. Its preparation process is simple, has a short cycle, low energy consumption, good reproducibility, is environmentally friendly, applicable to various metals, and suitable for large-scale production. The Cu-SACs prepared by this invention have high selectivity and Faraday efficiency in the electrocatalytic production of methane from carbon dioxide. Attached Figure Description

[0021] Figure 1 This is the powder diffraction (XRD) pattern of the Ni-SACs catalyst.

[0022] Figure 2 This is a low-magnification transmission electron microscope (TEM) image of the Ni-SACs catalyst.

[0023] Figure 3 This is an aberration-corrected transmission electron microscope (HAADF-STEM) image of the Ni-SACs catalyst.

[0024] Figure 4 This is an elemental distribution (EDS Mapping) diagram of Ni-SACs catalysts.

[0025] Figure 5 The image shows the K-edge EXAFS Fourier transform spectrum of Ni in the Ni-SACs catalyst.

[0026] Figure 6 This is a Ni synchrotron radiation fitting diagram of the Ni-SACs catalyst.

[0027] Figure 7 The image shows the in-situ temperature-variable powder diffraction (XRD) pattern of the Ni-SACs catalyst preparation process.

[0028] Figure 8 This is an aberration-corrected transmission electron microscope (HAADF-STEM) image of the Cu-SACs catalyst.

[0029] Figure 9The graph shows the electrocatalytic performance of Cu-SACs catalysts for the production of methane from carbon dioxide.

[0030] Figure 10 Aberration-corrected transmission electron microscopy (HAADF-STEM) images of Sc-SACs, Ti-SACs, Cr-SACs, Ga-SACs, Y-SACs, Zr-SACs, In-SACs, Sn-SACs, La-SACs, Ce-SACs, Dy-SACs, Er-SACs, Yb-SACs, Lu-SACs, and Pt-SACs.

[0031] Figure 11 The images show a comparison of the XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1-2. Detailed Implementation

[0032] To make the present invention clearer and more explicit, the present invention will be further described in detail below. It should be understood that the specific embodiments described herein are only for explaining the present invention and are not intended to limit the present invention.

[0033] Example 1

[0034] The preparation method of high-load Ni single-atom catalyst is as follows:

[0035] (1) Take 1 g of ethylenediamine citrate carbon dots, 100 mL of anhydrous ethanol, 5 mmol of nickel chloride, 2 g of thiourea and 10 g of dicyandiamide and place them in a beaker and stir magnetically. Heat in a water bath until the ethanol is completely evaporated, dry and grind to obtain solid powder.

[0036] (2) The above solid powder was placed in a quartz boat and then placed in a tube furnace containing a quartz tube. The temperature was raised to 900 °C at a rate of 5 °C / min in a nitrogen atmosphere. The high-temperature carbonization treatment was carried out at this temperature for 2 h. After completion, it was naturally cooled to room temperature to obtain a high-load Ni single-atom catalyst, denoted as Ni-SACs. The loading of Ni metal in the Ni-SACs was found to be 20.9 wt.% by ICP-OES detection.

[0037] Figure 1 This is the powder diffraction (XRD) pattern of the Ni-SACs catalyst. Figure 1 It can be seen that only carbon peaks appeared in the XRD pattern of the synthesized Ni-SACs, indicating that Ni is highly dispersed.

[0038] Figure 2 This is a low-magnification transmission electron microscope (TEM) image of the Ni-SACs catalyst. (Source: [Insert image here]) Figure 2 It can be seen that the catalyst has a thin sheet structure and does not contain Ni elemental or its compound nanoparticles, which also indicates that Ni is highly dispersed in it.

[0039] Figure 3 This is an aberration-corrected transmission electron microscope (HAADF-STEM) image of the Ni-SAC catalysts. (Source: [Insert Source Here]) Figure 3 As can be seen, Ni exists in the form of individual atoms dispersed.

[0040] Figure 4 This is an elemental distribution (EDS Mapping) diagram of Ni-SACs catalysts. From... Figure 4 It can be seen that the prepared catalyst contains C, Ni, and N elements simultaneously, and the Ni element is uniformly distributed on the catalyst. Figure 1 Carbon peaks in the XRD pattern and Figure 2 The thin-film structure in the TEM image confirms that the raw material dicyandiamide was successfully converted into carbon nitride material.

[0041] Figure 5 The images show the K-edge EXAFS Fourier transform spectra of Ni in Ni-SACs catalysts and Ni-foil. Figure 5 It can be seen that only Ni-N bonds exist in the highly loaded Ni-SACs, and there are no Ni-Ni bonds, which further proves the existence of Ni single atoms.

[0042] Figure 6 This is a Ni synchrotron radiation fitting plot of the Ni-SACs catalyst. (Source: [Insert Source Here]) Figure 6 It can be seen that the EXAFS Fourier transform of Ni-SACs fits well with Ni-N4-C, further indicating that Ni exists as a single atom and its structure is Ni-N4-C coordination form.

[0043] Figure 7 This is the in-situ temperature-variable powder diffraction (XRD) pattern of the Ni-SACs catalyst preparation process. From... Figure 7 It can be seen that Ni S-oxides exist at 400~650 ℃. 0.96 The formation of S, and the subsequent heating of Ni 0.96 S disappears as thermal migration intensifies, anchoring itself as a single atom on the nitrogen-doped carbon support.

[0044] Example 2

[0045] The preparation method of a high-load Cu single-atom catalyst, with specific steps as follows:

[0046] (1) Take 0.8 g of o-phenylenediamine citrate carbon dots, 100 mL of anhydrous ethanol, 6 mmol of copper chloride, 3 g of dibenzyl disulfide and 12 g of urea and place them in a beaker and stir magnetically. Heat in a water bath until the ethanol is completely evaporated, dry and grind to obtain solid powder.

[0047] (2) The above solid powder is placed in a quartz boat and then placed in a tube furnace containing a quartz tube. The temperature is raised to 1000 ℃ at a rate of 5 ℃ / min in a nitrogen atmosphere. The high-temperature carbonization treatment is carried out at this temperature for 1.5 h. After completion, it is naturally cooled to room temperature to obtain a high-load Cu single-atom catalyst, denoted as Cu-SACs.

[0048] Figure 8 This is an aberration-corrected transmission electron microscope (HAADF-STEM) image of the Cu-SACs catalyst. From... Figure 8 It can be clearly seen that Cu exists in the form of single atoms.

[0049] The performance of the Cu-SACs catalyst was tested using a Shanghai Chenhua electrochemical workstation (CHI650) with a three-electrode system. A flow electrolytic cell was used, with Ag / AgCl as the reference electrode and a platinum sheet as the counter electrode. The working electrode was prepared as follows: 3.0 mg of Cu-SACs was weighed and mixed with 370 μL of ethanol, 200 μL of distilled water, and 30 μL of 5 wt% Nafion solution. The mixture was then sonicated for at least three consecutive hours while ensuring the water bath temperature did not exceed 25 ℃. The resulting slurry was dropped onto 0.5 cm × 0.5 cm × 2 cm carbon paper and dried to obtain the working electrode. Chorothermal potentiometry was performed in a 1 mol / L potassium hydroxide solution at a specific potential for 1 h. Throughout the test, CO2 was continuously introduced at a constant flow rate, and the electrolyte was stirred at 800 rpm. Gaseous products were continuously analyzed by chromatography, while liquid products were collected and analyzed by nuclear magnetic resonance after electrolysis. The experimental results are shown in Figure 9 ,Depend on Figure 9 It can be seen that the synthesized Cu-SACs catalyst has good electrocatalytic performance in reducing carbon dioxide to methane, with a Faraday efficiency of 62% for methane at -1.21 V.

[0050] Example 3-17

[0051] The difference from Example 1 is that in step (1), nickel chloride is replaced sequentially with chlorides of Sc, Ti, Cr, Ga, Y, Zr, In, Sn, La, Ce, Dy, Er, Yb, Lu, and Pt; all other steps are the same as in Example 1. The resulting catalysts are all single-atom catalysts, designated as Sc-SACs, Ti-SACs, Cr-SACs, Ga-SACs, Y-SACs, Zr-SACs, In-SACs, Sn-SACs, La-SACs, Ce-SACs, Dy-SACs, Er-SACs, Yb-SACs, Lu-SACs, and Pt-SACs. The Pt-SACs, as determined by thermogravimetric analysis, have a Pt content as high as 34.59%.

[0052] Figure 10 The images show aberration-corrected transmission electron microscopy (HAADF-STEM) images of Sc-SACs, Ti-SACs, Cr-SACs, Ga-SACs, Y-SACs, Zr-SACs, In-SACs, Sn-SACs, La-SACs, Ce-SACs, Dy-SACs, Er-SACs, Yb-SACs, Lu-SACs, and Pt-SACs. The white bright spots represent metal single atoms. It can be seen that the transition metals are dispersed in the form of single atoms on the surface and inside of nitrogen-doped carbon, indicating that the catalyst preparation method of the present invention has broad applicability.

[0053] Comparative Example 1

[0054] The difference from Example 1 is that no carbon dots were added in step (1), that is, the amount of ethylenediamine citrate carbon dots was 0, and everything else was the same as in Example 1.

[0055] Comparative Example 2

[0056] The difference from Example 1 is that in step (1), no S-source organic ligand was added, that is, the amount of thiourea was 0, and everything else was the same as in Example 1.

[0057] Figure 11 This is a comparison of XRD patterns of the catalysts prepared in Example 1 and Comparative Examples 1-2. Figure 11 As can be seen, the catalyst prepared without carbon dots (Comparative Example 1) has a significant Ni3S2 peak, and the catalyst prepared without S-source organic ligands (Comparative Example 2) has a significant Ni peak. This indicates that the confinement effect of carbon dots and the S-source organic ligands can prevent metal from agglomerating into excessively large metal elemental particles, which are essential for the preparation of highly loaded metal single-atom catalysts.

Claims

1. A method for preparing a high loading metal monatomic catalyst, characterized by, The steps are as follows: (1) A reaction solution is prepared by uniformly mixing carbon dots, organic solvent, metal salt, S-source organic ligand and graphitic carbon nitride precursor. The organic solvent is evaporated and dried to obtain a solid powder. The carbon dots: organic solvent = (0.4~1) g: (80~200) mL. The molar concentration of the metal salt in the reaction solution is 0~0.2 mol / L. The molar concentration of the S-source organic ligand is 0~2 mol / L. The mass ratio of the S-source organic ligand to the graphitic carbon nitride precursor is 1: (3~10). The molar concentrations of the metal salt and the S-source organic ligand in the reaction solution are not 0. The main elements of the carbon dots are C, N and O. The organic solvent is any organic solvent that can dissolve the carbon dots, metal salt, S-source organic ligand and graphitic carbon nitride precursor. The metal salt is any metal salt that can be dispersed in the organic solvent. The S-source organic ligand is thiourea, dibenzyl disulfide, thioacetamide or thiophene. (2) The solid powder obtained in step (1) is heated to a calcination temperature of 800~1000 ℃ under a protective atmosphere and calcined for 1~4 h; after calcination, it is cooled to room temperature to obtain a high-load metal single-atom catalyst.

2. The method for preparing a high-load metal single-atom catalyst as described in claim 1, characterized in that: In step (1), the carbon dots are ethylenediamine citrate carbon dots, o-phenylenediamine citrate carbon dots, or biomass carbon dots; the organic solvent is ethanol or dimethyl sulfoxide; the metal salt is one or more of metal chloride salts, metal nitrate salts, metal acetate salts, and metal sulfate salts; and the graphitic carbon nitride precursor is dicyandiamide, urea, biuret, or melamine.

3. The method for preparing a high-load metal single-atom catalyst as described in claim 1, characterized in that: In step (1), the mixture is stirred or ultrasonically mixed evenly, and the organic solvent is evaporated by a water bath or oil bath.

4. The method for preparing a high-load metal single-atom catalyst as described in claim 1, characterized in that: In step (2), the heating rate is 2~10 ℃ / min, the protective atmosphere is argon or nitrogen, and the temperature is naturally cooled to room temperature after calcination.

5. A high-load metal single-atom catalyst prepared by the preparation method according to any one of claims 1 to 4, characterized in that: The catalyst uses nitrogen-doped carbon material as a support, and the metal is uniformly loaded on the support in the form of single atoms; the loading amount of the metal in the catalyst is 10~35 wt%.

6. The high-loading metal single-atom catalyst as described in claim 5, characterized in that: The metal is Ni, Cu, Sc, Ti, Cr, Ga, Y, Zr, In, Sn, La, Ce, Dy, Er, Yb, Lu, or Pt.

Images