Hydrophobically modified copper-based monatomic catalyst as well as preparation method and application thereof

Abstract

The invention discloses a preparation method of a hydrophobic modified copper-based monatomic catalyst. The preparation method comprises the following steps: S1, dissolving Cu (NO3) 2 and L-alanine in deionized water; dissolving trimesic acid in an ethanol solution; s2, mixing the two solutions, and stirring at regular time at normal temperature to obtain a Cu-BTC precursor; s3, grinding and uniformly mixing the Cu-BTC precursor and dicyandiamide, and then putting the mixture into a tubular furnace for high-temperature pyrolysis treatment to obtain Cu-N-C-Pre powder; s4, the Cu-N-C-Pre powder is subjected to acid leaching impurity removal treatment in an acid solution, and the copper-based monatomic catalyst is obtained; and S5, dissolving the Cu-N-C catalyst and triacetylene benzene in an organic solvent, adding pyridine, uniformly stirring, and carrying out a hydrothermal reaction to obtain the hydrophobic modified copper-based monatomic catalyst. Hydrophobic modification is performed on the surface of the Cu-N-C monatomic catalyst, so that the hydrophobicity of the surface of the catalyst is enhanced, the catalytic activity of the catalyst in a reaction for preparing phenol by activating a benzene C-H bond by taking H2O2 as an oxidizing agent is improved, and the yield of phenol is increased.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of nanomaterials, in particular to a hydrophobic modified copper-based single-atom catalyst and a preparation method and application thereof. BACKGROUND

[0002] Phenol is an important raw material and intermediate in the chemical industry, and is widely used in the production of plastics, dyes, medicines, pesticides, etc. Direct activation of the C-H bond of benzene to synthesize phenol using green oxidants such as hydrogen peroxide (H2O2) is an ideal atom-economic route. However, the direct hydroxylation of benzene usually faces challenges such as low activity and difficulty in controlling selectivity, so it is necessary to develop catalysts to promote the oxidation reaction. Currently, single-atom catalysts (SACs), especially metal-nitrogen-carbon (M-N-C) materials, have attracted much attention in the field of heterogeneous catalysis due to their high atom utilization efficiency, unique coordination environment and catalytic performance.

[0003] The mismatch between the wettability and affinity of the catalyst surface and the reactants is a key factor limiting the reaction efficiency. In the benzene hydroxylation reaction, hydrophobic benzene molecules are difficult to effectively enrich and contact the active sites on the surface of hydrophilic or weakly hydrophobic catalysts, especially in the presence of aqueous media. The surface of traditional Cu-N-C single-atom catalysts is less hydrophobic, which leads to insufficient effective contact and enrichment of the catalyst with benzene molecules, and the catalytic activity needs to be improved.

[0004] Therefore, it is urgent to modify the surface of Cu-N-C single-atom catalysts to enhance the hydrophobicity of the catalyst surface, improve the wettability and affinity between the catalyst surface and the reactants, and thus improve the catalytic efficiency. SUMMARY

[0005] The present application discloses a hydrophobic modified copper-based single-atom catalyst and a preparation method and application thereof. By hydrophobically modifying the surface of the Cu-N-C single-atom catalyst, the hydrophobicity of the catalyst surface is enhanced, the catalytic activity of the catalyst in the benzene C-H bond activation reaction to synthesize phenol using H2O2 as the oxidant is improved, and the yield of phenol is improved.

[0006] The first object of the present application is to provide a preparation method of a hydrophobic modified copper-based single-atom catalyst, which comprises:

[0007] S1 dissolving Cu(NO3)2 and L-alanine in deionized water to obtain a first mixed solution; dissolving trimesic acid in an ethanol solution to obtain a second mixed solution;

[0008] S2 pouring the second mixed solution into the first mixed solution, stirring at room temperature for a certain time, separating out a blue solid product, and washing and drying the blue solid product to obtain a Cu-BTC precursor;

[0009] S3, the Cu-BTC precursor and dicyandiamide are mixed uniformly to obtain a first mixture, and the first mixture is placed in a tube furnace for high-temperature pyrolysis treatment to obtain Cu-N-C-Pre powder;

[0010] S4, the Cu-N-C-Pre powder is subjected to acid leaching impurity removal treatment in an acidic solution to obtain a copper-based single-atom catalyst, denoted as Cu-N-C catalyst;

[0011] S5, the Cu-N-C catalyst and triethynylbenzene are dissolved in an organic solvent, pyridine is added, and after uniform stirring, the mixture is placed in a hydrothermal synthesis reactor for hydrothermal reaction, and after the reaction is completed, the product is subjected to washing and drying treatment to obtain a hydrophobic modified copper-based single-atom catalyst, denoted as Cu-N-C-Phobic catalyst.

[0012] Specifically, in step S1, the mass ratio of Cu(NO3)2, L-alanine and trimesic acid is (1.3-2):(0.7-1):(0.8-1.2).

[0013] Specifically, in step S2, the time for the timed stirring is 6-8h.

[0014] Specifically, in step S3, the mass ratio of the Cu-BTC precursor and dicyandiamide is 1:10.

[0015] Specifically, step S3 further comprises: pyrolyzing the first mixture at 800℃ under an argon environment, with a heating rate of 5℃ / min and a pyrolysis time of 3h, and then naturally cooling to room temperature to obtain Cu-N-C-Pre powder.

[0016] Specifically, step S4 further comprises: subjecting the Cu-N-C-Pre powder to acid leaching impurity removal treatment in an oxygen-saturated 10%aq.HCl acidic solution for 4-6h.

[0017] Specifically, in step S5, the mass ratio of the Cu-N-C catalyst and triethynylbenzene is 10:(0.5-2); and the organic solvent is toluene.

[0018] Specifically, in step S5, the reaction temperature of the hydrothermal reaction is 120-140℃, and the reaction time is 4-6h; and the washing and drying treatment specifically comprises: sequentially washing the product with ethanol and acetone for 3 times each, and then drying in a 60℃ vacuum oven for 4-6h.

[0019] The second object of the present application is to provide a hydrophobic modified copper-based single-atom catalyst prepared by the preparation method.

[0020] The third object of the present application is to provide an application of the hydrophobic modified copper-based monatomic catalyst in the preparation of phenol from hydrogen peroxide, wherein benzene, hydrogen peroxide and the hydrophobic modified copper-based monatomic catalyst are mixed to perform an oxidation reaction in acetonitrile at 35-40 DEG C, and phenol is obtained by extraction.

[0021] Compared with the prior art, the present application has the following beneficial technical effects:

[0022] (1) The present application forms a hydrophobic layer on the surface of a Cu-N-C monatomic catalyst synthesized in advance by using triethynylbenzene as a modifier through a hydrothermal reaction, thereby obtaining a hydrophobic modified copper-based monatomic catalyst Cu-N-C-Phobic; the catalyst treated by modification has the advantages of significantly improved catalytic activity, enhanced substrate affinity, controllable surface hydrophobicity and mild reaction conditions of the catalytic reaction.

[0023] (2) The amount of the hydrophobic modifier (1,3,5-triethynylbenzene) can be adjusted to conveniently control the hydrophobicity (water contact angle 60-150 DEG) of the catalyst surface, thereby providing the possibility of optimizing a specific reaction system; the high hydrophobicity of the catalyst surface is conducive to the enrichment of hydrophobic benzene substrate molecules on the catalyst surface and near the active sites, thereby promoting the mass transfer process and improving the reaction efficiency.

[0024] (3) The catalyst has a turnover frequency (TOF) of 3 times that of the unmodified Cu-N-C catalyst in the direct hydroxylation of benzene with hydrogen peroxide as the oxidant; at the same time, the catalytic reaction can be effectively performed at a lower temperature, the benzene conversion rate is more than 92%, the phenol selectivity is more than 98.3%, and the catalytic efficiency is significantly improved. BRIEF DESCRIPTION OF DRAWINGS

[0025] Figure 1 SEM image of the hydrophobic modified copper-based monatomic catalyst prepared in Example 1 of the present application;

[0026] Figure 2 Water contact angle test comparison chart of the catalysts prepared in Example 1 and Comparative Example 1 of the present application;

[0027] Figure 3 Performance comparison chart of the catalysts prepared in Example 1 and Comparative Example 1 of the present application in the oxidation of benzene with hydrogen peroxide to prepare phenol. DETAILED DESCRIPTION

[0028] The technical solutions in the embodiments of the present application will be clearly and completely described in combination with the contents in the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments. Based on the embodiments in the present application, all the other embodiments obtained by a person of ordinary skill in the art without creative effort belong to the scope of protection of the present application. Unless otherwise defined, all the technical and scientific terms used in the specification have the same meanings as those commonly understood by a person of ordinary skill in the art to which the present application belongs. The terms used in the specification of the present application are only for the purpose of describing the specific embodiments, and are not used to limit the present application. The term "and / or" used in the specification includes any and all combinations of one or more related listed items. It should be understood that, unless otherwise specified, the various raw materials in the present application can be obtained commercially.

[0029] Embodiment 1

[0030] Preparation of hydrophobic-modified copper-based single-atom catalyst

[0031] S1 1.3 g of Cu(NO3)2 and 1 g of L-alanine were dissolved in 500 ml of deionized water to obtain a first mixed solution a; 1.2 g of trimesic acid was dissolved in an ethanol solution to obtain a second mixed solution a; wherein the ethanol solution was mixed by deionized water (250 ml) and ethanol (100 ml);

[0032] S2 The second mixed solution a was poured into the first mixed solution a, and after stirring at room temperature for 6 h, a blue solid product was separated out, and the blue solid product was washed with deionized water and dried in a vacuum oven at 60°C for 4 h to obtain a Cu-BTC precursor a;

[0033] S3 0.2 g of the Cu-BTC precursor a was uniformly ground mixed with 2.0 g of dicyandiamide to obtain a first mixture a, and the first mixture a was placed in a tube furnace and pyrolyzed at 800°C under an argon atmosphere, with a heating rate of 5°C / min and a high-temperature pyrolysis time of 3 h, and after natural cooling to room temperature, a Cu-N-C-Pre powder a was obtained;

[0034] S4 The Cu-N-C-Pre powder a was subjected to acid leaching impurity removal treatment in an oxygen-saturated 10% aq. HCl acidic solution for 6 h to remove free metal residues, to obtain a Cu-N-C catalyst a;

[0035] S5 100 mg of Cu-N-C catalyst a and 10 mg of 1,3,5-triethynylbenzene were dissolved in 10 mL of toluene, 2 mL of pyridine was added, and stirred at room temperature at 600 rpm for 2 h, and placed in a hydrothermal synthesis reactor at 120 °C for 4 h of hydrothermal reaction. After the reaction was completed, it was cooled to room temperature, and the product was washed with ethanol, acetone, and the solid product was washed 3 times, and dried in a vacuum oven at 60 °C for 6 h to obtain Cu-N-C-Phobic catalyst a.

[0036] Preparation of phenol

[0037] 0.5 mmol of benzene, 2 mL of acetonitrile (solvent), 1 mL of 30% aqueous H2O2 (oxidant), and 10 mg of Cu-N-C-Phobic catalyst a were mixed, and the oxidation reaction was carried out at a reaction temperature of 35 °C for 140 h. After the reaction was completed, the reaction product was filtered with a filter membrane, and the phenol a was extracted and extracted.

[0038] Example 2

[0039] Preparation of hydrophobically modified copper-based single-atom catalyst

[0040] S1 2 g of Cu(NO3)2 and 0.7 g of L-alanine were dissolved in 500 ml of deionized water to obtain a first mixed solution b; 0.8 g of trimesic acid was dissolved in an ethanol solution to obtain a second mixed solution b; wherein the ethanol solution was mixed by deionized water (250 ml) and ethanol (100 ml);

[0041] S2 The second mixed solution b was poured into the first mixed solution b, and after stirring at room temperature for 8 h, a blue solid product was separated, and the blue solid product was washed with deionized water, and dried in a vacuum oven at 60 °C for 4 h to obtain a Cu-BTC precursor b;

[0042] S3 0.2 g of Cu-BTC precursor b was mixed with 2.0 g of dicyandiamide to obtain a first mixture b, and the first mixture b was placed in a tube furnace and pyrolyzed at 800 °C under an argon atmosphere, with a heating rate of 5 °C / min, and a high-temperature pyrolysis time of 3 h. After natural cooling to room temperature, Cu-N-C-Pre powder b was obtained;

[0043] S4 The Cu-N-C-Pre powder b was subjected to acid leaching impurity removal treatment in an oxygen-saturated 10% aq. HCl acid solution for 6 h to remove free metal residues to obtain Cu-N-C catalyst b;

[0044] S5 100 mg of Cu-N-C catalyst b and 20 mg of 1,3,5-triethynylbenzene were dissolved in 10 mL of toluene, 3 mL of pyridine was added, and the mixture was stirred at room temperature at 600 rpm for 2 h, and then placed in a hydrothermal synthesis reactor and subjected to hydrothermal reaction at 140 °C for 6 h. After the reaction was completed, the product was cooled to room temperature, and the solid product was washed with ethanol and acetone three times each, and then dried in a vacuum oven at 60 °C for 4 h to obtain Cu-N-C-Phobic catalyst b.

[0045] Preparation of phenol

[0046] 0.5 m mol of benzene, 2 mL of acetonitrile (solvent), 1 mL of 30% aqueous H2O2 (oxidant), and 10 mg of Cu-N-C-Phobic catalyst b were mixed and subjected to oxidation reaction at a reaction temperature of 35 °C for 140 h. After the reaction was completed, the reaction product was filtered with a filter membrane, and the phenol b was extracted and extracted.

[0047] Example 3

[0048] Preparation of hydrophobically modified copper-based single-atom catalyst

[0049] S1 1.5 g of Cu(NO3)2 and 0.8 g of L-alanine were dissolved in 500 mL of deionized water to obtain a first mixed solution c; 1 g of trimesic acid was dissolved in an ethanol solution to obtain a second mixed solution c; wherein the ethanol solution was obtained by mixing deionized water (250 mL) and ethanol (100 mL);

[0050] S2 The second mixed solution c was poured into the first mixed solution c, and after stirring at room temperature for 7 h, a blue solid product was separated, washed with deionized water, and dried in a vacuum oven at 60 °C for 4 h to obtain a Cu-BTC precursor c;

[0051] S3 0.2 g of the Cu-BTC precursor c was uniformly mixed with 2.0 g of dicyandiamide to obtain a first mixture c, which was placed in a tube furnace and subjected to pyrolysis at 800 °C under an argon atmosphere, with a heating rate of 5 °C / min and a high-temperature pyrolysis time of 3 h. After natural cooling to room temperature, a Cu-N-C-Pre powder c was obtained.

[0052] S4 The Cu-N-C-Pre powder c was subjected to acid pickling treatment with an oxygen-saturated 10% aq. HCl acidic solution for 5 h to remove free metal residues, to obtain a Cu-N-C catalyst c;

[0053] S5: 100 mg Cu-N-C catalyst c and 5 mg of 1,3,5-triethynylbenzene were dissolved in 10 mL of toluene, 2 mL of pyridine was added, and stirred at room temperature at 600 rpm for 2 h, and placed in a hydrothermal synthesis reactor at 130 °C for 5 h of hydrothermal reaction. After the reaction was completed, it was cooled to room temperature, and the product was washed with ethanol, acetone, and the solid product was washed 3 times at 60 °C in a vacuum oven for 5 h to obtain Cu-N-C-Phobic catalyst c.

[0054] Preparation of phenol

[0055] 0.5 mmol of benzene, 2 mL of acetonitrile (solvent), 1 mL of 30% H2O2 aqueous solution (oxidant) and 10 mg of Cu-N-C-Phobic catalyst c were mixed, and the oxidation reaction was carried out at a reaction temperature of 35 °C for 140 h. After the reaction was completed, the reaction product was filtered with a filter membrane, and the phenol c was extracted and extracted.

[0056] Comparative Example 1

[0057] The Cu-N-C catalyst A was prepared by steps S1-S4 in Example 1; the only difference is that the Cu-N-C catalyst was not modified by hydrophobic modification in step S5.

[0058] The phenol was prepared by the steps in Example 1, and the only difference is that the catalyst is Cu-N-C catalyst A which is not modified by hydrophobic modification.

[0059] Performance test

[0060] Figure 1 SEM images of the hydrophobically modified copper-based monatomic catalyst prepared in Example 1 of the present application from different perspectives; from Figure 1 As can be seen from the SEM images of the Cu-N-C-Phobic catalyst a, the morphology presents an ultra-thin, highly wrinkled sheet structure, and the wrinkles are randomly distributed, indicating the presence and high uniform distribution of C, N elements and Cu atoms.

[0061] Figure 2 The water contact angle test comparison chart of the catalysts prepared in Example 1 and Comparative Example 1 of the present application. From Figure 2 As can be seen from the static water contact angle characterization, the contact angle of the Cu-N-C-Phobic catalyst a after the traditional Cu-N-C catalyst A is modified by hydrophobic modification is increased from 27.8° to 151.8°, which confirms that the surface energy is significantly reduced, and shows high hydrophobicity, which is beneficial to the enrichment of the hydrophobic benzene substrate molecules on the catalyst surface and near the active sites, promotes the mass transfer process, and thus improves the reaction efficiency.

[0062] In the embodiments of the present invention, gas chromatography-mass spectrometry (GC-MS) was used to quantitatively analyze the conversion rate of benzene and the selectivity / yield of phenol in Example 1 and Comparative Example 1, and the TOF value was calculated. Figure 3 This is a performance comparison diagram of the catalysts prepared in Example 1 and Comparative Example 1 of this invention in the oxidation of benzene to phenol using hydrogen peroxide. Figure 3 (a) is a comparison diagram of the performance of the catalysts prepared in Example 1 and Comparative Example 1 of the present invention in the oxidation of benzene to phenol by H2O2; Figure 3 (b) is a comparison graph showing the cyclic stability test of the catalysts prepared in Example 1 and Comparative Example 1 of this invention in the oxidation of benzene to phenol using H2O2. Figure 3 As can be seen, the hydrophobically modified Cu-NC-Phobic catalyst a exhibits significantly improved catalytic performance. After 4 hours of reaction, compared with Cu-NC catalyst A in Comparative Example 1, the benzene conversion rate of the Cu-NC-Phobic catalyst a prepared in Example 1 increased from 46% to 92%, and the benzene oxidation selectivity increased from 76.5% to 98.3%. Furthermore, the Cu-NC-Phobic catalyst a prepared in Example 1 maintained stable catalytic activity (no conversion decay) during four consecutive cycles, and the surface contact angle remained >150° (superhydrophobic state) after cycling, confirming the excellent stability of its hydrophobic modification layer. Simultaneously, using the Cu-NC-Phobic catalyst prepared in this invention in the reaction of direct oxidation of benzene to phenol with hydrogen peroxide significantly improves the benzene oxidation selectivity and hydrogen peroxide utilization.

[0063] The Cu-NC-Phobic catalyst prepared in this invention is applied to the catalytic CH bond activation / hydroxylation reaction of benzene (or other hydrophobic aromatics) to prepare phenol, and has the following advantages: Significantly improved catalytic activity: The hydrophobically modified Cu-NC-Phobic catalyst exhibits excellent performance in the direct hydroxylation reaction of benzene, with significantly improved catalytic activity and a turnover frequency (TOF) three times that of the unmodified Cu-NC catalyst. Enhanced substrate affinity: The high hydrophobicity of the catalyst surface enhances the affinity for hydrophobic benzene substrate molecules, which is beneficial for substrate enrichment near the active site and optimizes the mass transfer process. Controllable surface hydrophobicity: The degree of hydrophobicity of the catalyst surface (water contact angle 60°-150°) can be controlled by adjusting the amount of hydrophobic modifier, providing the possibility for optimization of specific reaction systems. Mild reaction conditions: This catalyst can catalyze efficiently at a relatively low temperature of 35℃, achieving a benzene conversion rate of over 92% and a phenol selectivity of up to 98.3%. It also has good cycle stability, with its activity and hydrophobicity remaining stable after four uses, effectively improving the oxidation selectivity of benzene and the utilization rate of hydrogen peroxide.

[0064] The above described embodiments are only to illustrate the preferred modes of the present application, and are not intended to limit the scope of the present application. Any modification and improvement made by those skilled in the art to the technical solutions of the present application without departing from the design spirit of the present application shall fall within the protection scope of the present application as defined by the claims.

Claims

1. A method for preparing a hydrophobically-modified copper-based single-atom catalyst, characterized in that, The preparation method comprises: S1: dissolving Cu(NO3)2 and L-alanine in deionized water to obtain a first mixed solution; dissolving trimesic acid in an ethanol solution to obtain a second mixed solution; S2: pouring the second mixed solution into the first mixed solution, stirring at room temperature for a certain period of time, separating a blue solid product, and washing and drying the blue solid product to obtain a Cu-BTC precursor; S3: uniformly grinding and mixing the Cu-BTC precursor and dicyandiamide to obtain a first mixture, and placing the first mixture in a tube furnace for high-temperature pyrolysis treatment to obtain a Cu-N-C-Pre powder; S4: performing acid leaching impurity removal treatment on the Cu-N-C-Pre powder in an acidic solution to obtain a copper-based single-atom catalyst, denoted as Cu-N-C catalyst; S5: dissolving the Cu-N-C catalyst and triethylbenzene in an organic solvent, adding pyridine, stirring uniformly, and then placing in a hydrothermal synthesis reactor for hydrothermal reaction, and after the reaction is completed, washing and drying the product to obtain a hydrophobic modified copper-based single-atom catalyst, denoted as Cu-N-C-Phobic catalyst.

2. The production method according to claim 1, characterized by, In step S1, the mass ratio of Cu(NO3)2, L-alanine and trimesic acid is (1.3-2):(0.7-1):(0.8-1.2).

3. The preparation method according to claim 1, characterized in that, In step S2, the stirring time is 6-8h.

4. The method of claim 1, wherein, In step S3, the mass ratio of the Cu-BTC precursor and dicyandiamide is 1:

10.

5. The preparation method according to claim 1, characterized in that, Step S3 further comprises: pyrolyzing the first mixture at 800℃ under an argon environment, with a heating rate of 5℃ / min and a pyrolysis time of 3h, and then naturally cooling to room temperature to obtain the Cu-N-C-Pre powder.

6. The method of claim 1, wherein, Step S4 further comprises: performing acid leaching impurity removal treatment on the Cu-N-C-Pre powder in an oxygen-saturated 10%aq.HCl acidic solution for 4-6h.

7. The preparation method according to claim 1, characterized in that, In step S5, the mass ratio of the Cu-N-C catalyst and triethylbenzene is 10:(0.5-2); and the organic solvent is toluene.

8. The method of claim 1, wherein, In step S5, the reaction temperature of the hydrothermal reaction is 120-140℃, and the reaction time is 4-6h; and the washing and drying treatment specifically comprises: sequentially washing the product with ethanol and acetone for 3 times each, and then drying in a 60℃ vacuum oven for 4-6h.

9. A hydrophobic modified copper-based single-atom catalyst prepared by the preparation method of any one of claims 1-8.

10. Use of a hydrophobically modified copper-based monatomic catalyst as claimed in claim 9 above for the production of phenol from hydrogen peroxide, characterized in that, After mixing benzene, hydrogen peroxide and the hydrophobic modified copper-based single-atom catalyst, performing an oxidation reaction in acetonitrile, and extraction, phenol is obtained.

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