Preparation method and application of high-load copper monatomic catalyst

Abstract

The invention discloses a preparation method and application of a high-load copper monatomic catalyst, copper nitrate trihydrate and small biological molecule guanine are used as raw materials, and a series of copper monatomic catalysts are directly synthesized through a self-assembly and high-temperature carbonization method. The synthesis process is simple to operate, low in manufacturing cost and high in sustainability. The obtained material has curled two-dimensional morphology, high nitrogen content (-30 at%) and high metal loading capacity (the highest copper content can reach 33.2 wt%). The synthesized catalyst has excellent catalytic activity in a benzene hydroxylation reaction.

Description

Technical Field

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

[0002] The concept of single atom catalysts (SACs) was proposed in 2011, that is, all active sites are dispersed in the form of atoms on the support, thus achieving a catalyst system with theoretically 100% atomic utilization (Acc. Chem. Res. 2013, 46, 8,1740–1748). Unlike nanoparticle-based catalysts, the isolated single atoms of single atom catalysts are usually anchored to the heteroatoms of the support. The strong interaction between the catalyst and the support can ensure the uniform dispersion of metal atoms, so the selection of support materials is crucial to achieve the excellent catalytic activity and stability of SACs. So far, metal atoms have been effectively anchored on various supports such as metals, metal oxides, zeolites and even nanocarbon materials (especially nitrogen-doped carbon-based materials) (Adv. Funct. Mater. 2021, 31, 2008318). Two-dimensional (2D) nitrogen-doped carbon nanosheets provide a large number of reaction sites for SACs due to their extremely high specific surface area, and effectively shorten the distance between the active sites and the reaction molecules, thereby accelerating the catalytic process. In addition, nitrogen doping can not only change the chemical and electronic structure of carbon nanosheets, enhance their electronic conductivity and promote efficient electron transfer in the catalytic process, but also introduce additional active centers such as edge defects and nitrogen active sites, which significantly affect the path and efficiency of the catalytic reaction.

[0003] Given the unique electronic structure, extreme atomic utilization and enhanced intrinsic catalytic activity of SACs, they have shown great application potential in a variety of catalytic fields, covering key processes such as oxidation, reduction, pollutant degradation, CO2 electrochemical conversion and hydrogen generation (Nat Commun, 2019, 10, 4290). However, in contrast to the zero-valent properties of bulk metals, individual metal atoms often present a positive charge state due to the transfer of electrons from the central metal site to the substrate, depriving them of the metallic properties required for effective adsorption and activation of specific catalytic reactions. At the same time, the inherent adsorption-energy balance mechanism of SACs may also pose challenges to reaction kinetics and thermodynamics, especially for complex reactions involving multiple intermediates.

[0004] To address the above problems, recent research has focused on the development of high-density SACs, which are unique in geometry and electronic structure and aim to optimize the efficiency of large-scale industrial applications by improving mass-specific activity. High-density SACs may not only promote electron transfer, spin coupling or charge redistribution between sites, thereby fine-tuning the local environment of the active site, but may also stimulate the synergistic effect of adjacent metal centers, allowing reaction intermediates to be adsorbed simultaneously on multiple sites, breaking the constraints of the traditional adsorption-energy balance mechanism (ACS Catal. 2023, 13, 1316−1325).

[0005] The current methods for preparing single-atom catalysts mainly face the following disadvantages: metal atoms tend to agglomerate to form nanoparticles at high loadings, making it difficult to maintain high dispersion of single atoms; the binding force between the metal and the carrier is insufficient, which can easily lead to single-atom migration and deactivation; some preparation methods have complex conditions and high requirements for the surface chemistry and structure of the carrier; it is difficult to balance the stability and activity of the catalyst while achieving high loadings. These problems limit the large-scale development of single-atom catalysts in practical applications (Prog. Chem. 2020, 32(1): 23-32). Therefore, the development of a simple and efficient synthesis method is of great practical significance. Summary of the invention

[0006] The purpose of the present invention is to provide a preparation method of a high-load copper single-atom catalyst and its application. In order to explore a better preparation method of a high-load copper single-atom catalyst, the present invention uses copper nitrate trihydrate and biological small molecule guanine as raw materials and successfully prepares a high-load copper single-atom catalyst through a simple two-step method.

[0007] In order to achieve the above object, the present invention adopts the following technical solution: A method for preparing a high-load copper single-atom catalyst comprises the following steps: (1) Dispersing copper nitrate trihydrate and biological small molecule guanine in deionized water, stirring in an oil bath to obtain a precursor solution, and freeze-drying to obtain a precursor; (2) Grinding the precursor obtained in step (1) into powder, heating it to a specific temperature under a protective atmosphere and then keeping it warm for reaction, then naturally cooling it to room temperature, and grinding it to obtain a copper single atom catalyst.

[0008] Furthermore, the mass ratio of the biological small molecule guanine to copper nitrate trihydrate in step (1) is 3:(0.21-1.63).

[0009] Furthermore, the volume of the deionized water in step (1) is 50 mL.

[0010] Furthermore, the temperature of the oil bath in step (1) is 100o C, the stirring time was 12 h and the stirring speed was 500 rpm.

[0011] Furthermore, the protective atmosphere in step (2) is N2.

[0012] Furthermore, the heating rate in step (2) is 1 o C / min, specific temperature is 700 o C, the holding time is 2h.

[0013] A high-load copper single-atom catalyst obtained by the above preparation method.

[0014] Application of the above-mentioned high-load copper single-atom catalyst in the selective oxidation of benzene to produce phenol.

[0015] Conditions: Heating rate is 1 o C / min; high temperature carbonization temperature is 700 o C; carbonization time is 2 h.

[0016] Compared with the prior art, the present invention has the following beneficial effects: This patent innovatively uses biological small molecules guanine and copper nitrate trihydrate as precursors, and through a "bottom-up" simple chemical synthesis strategy, successfully prepares a high-load copper single-atom catalyst through only two steps of self-assembly and high-temperature carbonization. The synthesis process is simple to operate, low in production cost, and highly sustainable. The resulting catalyst has a curled two-dimensional morphology, a high nitrogen content (~30 at%) and a metal loading (the copper content can reach up to 33.2 wt%). In addition, in the selective oxidation of benzene to phenol, this series of catalysts exhibits excellent catalytic activity and stability, and the mechanism of H2O2 decomposition and benzene oxidation to phenol is revealed through experiments and theoretical calculations.

[0017] Guanine has shown significant advantages as a precursor in the preparation of high-load single-atom catalysts. Its high nitrogen content can form stable nitrogen coordination sites (such as MN x structure), effectively anchoring metal atoms, preventing agglomeration, and improving the stability and activity of the catalyst. At the same time, the guanine molecule has a strong self-assembly ability, forming an ordered structure through hydrogen bonding, and providing an ideal platform for uniformly distributed metal single atoms after pyrolysis. The amino and carbonyl groups in its molecules have good coordination properties and can form stable complexes with metal precursors, further improving the metal loading and dispersibility. In addition, the tunability of guanine's structure and function allows for flexible regulation of material properties by optimizing pyrolysis conditions to meet different catalytic needs. As a green and environmentally friendly biomolecular raw material, the preparation process of guanine is environmentally friendly, providing an efficient, economical and sustainable way to develop high-performance single-atom catalysts, and has important application potential. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 Schematic diagram of the synthesis of copper single-atom catalysts.

[0019] Figure 2 is Cu in Example 5 30 Scanning electron microscopy (SEM) image of G.

[0020] Figure 3 is Cu in Example 5 30 Aberration-corrected high-angle annular dark-field scanning transmission electron microscopy (AC HAADF-STEM) of G.

[0021] Figure 4 The X-ray photoelectron spectra of the catalysts obtained in Examples 1-5 are shown in FIG.

[0022] Figure 5 The X-ray absorption near edge structure spectra (XANES) of the catalysts obtained in Examples 1-5.

[0023] Figure 6 The catalytic activity of the catalysts obtained in Examples 1-5 for selective oxidation of benzene to produce phenol.

[0024] Figure 7 is Cu in Example 5 30 Cyclic stability test of G-catalyzed selective oxidation of benzene to phenol.

[0025] Figure 8 This is the reaction mechanism diagram of the decomposition of H2O2 and oxidation of benzene to phenol catalyzed by copper single atom catalyst. DETAILED DESCRIPTION

[0026] The technical solutions in the embodiments of the present invention will be described clearly and completely below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0027] Example 1 Cu5G (1) Weigh 0.21 g of copper nitrate trihydrate and 5 g of guanine and disperse them in a beaker containing 50 mL of deionized water. o The mixture was stirred at 500 rpm for 12 h in an oil bath and freeze-dried to obtain the precursor; (2) Grind the precursor and transfer it to a corundum crucible. o C / min heating rate to 700 o C, keep warm for 2 h, and then cool naturally to room temperature. Then grind to obtain copper single atom catalyst, named Cu5G.

[0028] Example 2 Cu 10 G (1) Weigh 0.42 g of copper nitrate trihydrate and 5 g of guanine and disperse them in a beaker containing 50 mL of deionized water. o C oil bath was stirred for 12 h, and the precursor was obtained after freeze drying; (2) Grind the precursor and transfer it to a corundum crucible. o C / min heating rate to 700 o C, keep warm for 2 h, and cool naturally to room temperature after the end of the heat treatment. Then grind to obtain the copper single atom catalyst, named Cu 10 G.

[0029] Example 3 Cu 15 G (1) Weigh 0.67 g of copper nitrate trihydrate and 5 g of guanine and disperse them in a beaker containing 50 mL of deionized water. o C oil bath was stirred for 12 h, and the precursor was obtained after freeze drying; (2) Grind the precursor and transfer it to a corundum crucible. o C / min heating rate to 700 o C, keep warm for 2 h, and cool naturally to room temperature after the end of the heat treatment. Then grind to obtain the copper single atom catalyst, which is marked as Cu 15 G.

[0030] Example 4 Cu 20 G (1) Weigh 0.95 g of copper nitrate trihydrate and 5 g of guanine and disperse them in a beaker containing 50 mL of deionized water. o C oil bath was stirred for 12 h, and the precursor was obtained after freeze drying; (2) Grind the precursor and transfer it to a corundum crucible. o C / min heating rate to 700 o C, keep warm for 2 h, and cool naturally to room temperature after the end of the heat treatment. Then grind to obtain the copper single atom catalyst, named Cu 20 G.

[0031] Example 5 Cu 30 G (1) Weigh 1.63 g of copper nitrate trihydrate and 5 g of guanine and disperse them in a beaker containing 50 mL of deionized water. o C oil bath was stirred for 12 h, and the precursor was obtained after freeze drying; (2) Grind the precursor and transfer it to a corundum crucible.o C / min heating rate to 700 o C, keep warm for 2 h, and cool naturally to room temperature after the end of the heat treatment. Then grind to obtain the copper single atom catalyst, named Cu 30 G.

[0032] Figure 1 Schematic diagram of the synthesis of copper single atom catalyst.

[0033] Figure 2 Cu 30 The SEM image of G shows that Cu 30 G has a layered nanosheet morphology at the microscale.

[0034] Figure 3 Cu 30 AC HAADF-STEM image of G, the results show that metallic Cu is dispersed on the support in the form of single atoms.

[0035] The C, N, O, and Cu element contents of the copper single atom catalysts synthesized in Examples 1-5 are shown in Table 1. As can be seen from Table 1, the catalysts obtained by this preparation method have a high nitrogen content (~30 at%) and a metal loading (the copper content can reach up to 33.2wt%).

[0036] Table 1 C, N, O, Cu element contents of Examples 1-5 Figure 4 This is the XPS spectrum of the copper single atom catalyst synthesized in Examples 1-5. It can be seen from the figure that all samples are composed of Cu, C, N, and O elements, and the characteristic peak of Cu increases with the increase of the loading amount.

[0037] Figure 5 The X-ray absorption near-edge structure spectra of the copper single-atom catalysts synthesized in Examples 1-5 show that the absorption edge energies of all samples are between Cu foil and CuO, indicating that the oxidation state of the Cu atom center is between 0 and +2. At the same time, it can also be observed that with the increase of Cu content, the edge absorption energy of the sample moves to a lower energy, indicating that the average valence state of the Cu center decreases with the increase of Cu content.

[0038] Application Examples The catalyst obtained in Example 1-5 was used for the selective oxidation of benzene to produce phenol. The specific conditions were as follows: 0.3 mL of benzene, 5 mL of H2O2, 6 mL of acetonitrile and 5 mg of catalyst were mixed in a 48 mL thick-walled pressure bottle and heated at 60 o The reaction was carried out in an oil bath at C for 1 h. The concentrations of reactants and products were analyzed by GC-MS (GCMS-QP2010 SE) using tetradecane as the internal standard. The results are shown in Figure 6 As shown, the catalyst Cu 30 The benzene conversion rate of G can be as high as 78.7%.

[0039] Figure 7 is Cu in Example 5 30 The cyclic stability test of Cu G catalyzed the selective oxidation of benzene to phenol showed that 30 The conversion rate and selectivity of G did not change much during the 6 catalytic cycle tests.

[0040] Figure 8 The reaction mechanism diagram of the copper single atom catalyst catalyzing the decomposition of H2O2 and the oxidation of benzene to phenol. The reaction first starts from H2O2 in the Cu-N x The adsorption of C6H6 molecules on the active sites begins, which is conducive to its activation to form O-Cu-Nx intermediates (step I). Subsequently, C6H6 molecules are adsorbed on the Cu-O sites (step II) and form Cu-Nx through hydrogen transfer reaction. x - C6H5OH intermediate (step III). Finally, through the desorption of C6H5OH molecules and the Cu-N x Regeneration of the site completes the catalytic cycle (step IV).

[0041] The above description is only a preferred embodiment of the present invention. All equivalent changes and modifications made according to the scope of the patent application of the present invention should fall within the scope of the present invention.

Claims

1. A method for preparing a high-load copper single-atom catalyst, characterized in that: The following steps are involved: (1) Dispersing copper nitrate trihydrate and biological small molecule guanine in deionized water, stirring in an oil bath to obtain a precursor solution, and freeze-drying to obtain a precursor; (2) Grinding the precursor obtained in step (1) into powder, heating it to a specific temperature under a protective atmosphere and then keeping it warm for reaction, then naturally cooling it to room temperature, and grinding it to obtain a copper single atom catalyst.

2. The method for preparing a high-load copper single-atom catalyst according to claim 1, characterized in that: The mass ratio of the biological small molecule guanine to copper nitrate trihydrate in step (1) is 3:(0.21-1.63).

3. The method for preparing a high-load copper single-atom catalyst according to claim 1, characterized in that: The volume of deionized water in step (1) is 50 mL.

4. The method for preparing a high-load copper single-atom catalyst according to claim 1, characterized in that: The temperature of the oil bath in step (1) is 100 o C, the stirring time was 12 h and the stirring speed was 500 rpm.

5. The method for preparing a high-load copper single-atom catalyst according to claim 1, characterized in that: The protective atmosphere in step (2) is N2.

6. The method for preparing a high-load copper single-atom catalyst according to claim 1, characterized in that: The heating rate in step (2) is 1 o C / min, specific temperature is 700 o C, the holding time is 2 h.

7. A high-load copper single-atom catalyst obtained by the preparation method according to any one of claims 1 to 6.

8. Use of the high-load copper single-atom catalyst as claimed in claim 7 in the selective oxidation of benzene to produce phenol.

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