Fe-doped NiO catalyst nano material as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalytic materials, and discloses a Fe-doped NiO catalyst nano material as well as a preparation method and application thereof. The preparation method comprises the following steps: dissolving nickel nitrate, ferric nitrate, anhydrous sodium acetate and polyvinylpyrrolidone in a mixed solution of isopropanol and ethylene glycol, and stirring until the raw materials are completely dissolved; the preparation method comprises the following steps: adding NiO into a reaction kettle, reacting at 200 DEG C for 8 hours, washing and centrifuging the reaction product, drying and grinding the obtained precipitate into powder, and calcining in a muffle furnace to obtain the Fe-doped NiO catalyst nano material. The preparation method is low in cost, simple in equipment, simple and efficient in preparation process and good in industrial production potential. The catalyst material shows excellent catalytic performance in the process of preparing aromatic chemicals through electro-catalytic conversion of lignin, and particularly, the selectivity to aromatic monomers is remarkably improved. A new way is provided for high-value utilization of lignin, and an important breakthrough is achieved in the field of preparation of aromatic chemicals through electro-catalytic conversion.

Description

Technical Field

[0001] The present invention belongs to the technical field of catalytic materials, and particularly relates to an Fe-doped NiO catalyst nanomaterial, a preparation method thereof, and an application thereof. Background Art

[0002] With the rapid growth of global energy demand and the increasing depletion of fossil fuel resources such as coal and oil, the energy crisis has become a major challenge restricting social and economic development. Developing green and sustainable energy conversion technologies has become the key to solving this problem. In this context, biomass resources have received extensive attention due to their renewability and environmental friendliness. As one of the most abundant biomass resources on the earth, lignocellulose, among which lignin is considered an important raw material for preparing high-value chemicals by replacing fossil resources due to its unique aromatic ring structure and rich natural aromatic hydrocarbon reserves. Lignin has the characteristics of high energy density, low cost, and renewability, and can be directly converted into a variety of high-value chemicals through efficient catalytic conversion technologies. In particular, depolymerizing lignin into aromatic chemicals can not only replace the traditional petrochemical route but also significantly reduce the dependence on fossil resources, which has important strategic significance. However, although traditional lignin degradation methods (such as photothermal catalysis, chemical hydrolysis, and enzymatic hydrolysis, etc.) can achieve partial depolymerization, they generally have problems such as high energy consumption, low efficiency, and serious environmental pollution, which severely restrict the high-value utilization of lignin resources.

[0003] As a green and efficient conversion means, electrocatalytic technology provides a new way for the high-value utilization of lignin. Through electrocatalytic reactions, lignin can be efficiently converted into aromatic chemicals under mild conditions, while achieving efficient energy utilization and environmental sustainable development. Electro-catalysts such as noble metals (Ru, Pt, Pd, and Rh), and bimetals of non-noble metals (for example, Ni–Cu, Ni–Fe, Ni–Co) have been widely studied. For example, Ru catalysts can catalyze the hydrogenolysis of the C α -OH internal hydrogen source of lignin model compounds for the C β -O bond; there is also a team that prepared Ni-Mo X C / C and Co-Mo X C / C for the C-O bond cleavage of dimer model compounds and the depolymerization of lignin, showing significantly different activities in terms of product distribution; in addition, other teams can also achieve C α -C β and C βDirected cleavage of the -O bond; in another study, atomically dispersed Mo centers and Al Lewis acid sites were combined on a MgO substrate (Mo1Al / MgO) to depolymerize eucalyptus lignin by breaking the β-aryl ether bond, with a monophenol monomer yield of 46%; in addition, the NiZnAl ternary metal catalyst achieved 99% vanillin conversion and 99% 2-methoxy-4-methylphenol selectivity within 4 hours, which benefited from the increased acidity of the catalyst introduced by Zn, thus improving the deoxygenation efficiency. Although inexpensive transition metal catalysts have shown significant advantages in the selective regulation of lignin electrocatalytic conversion products, there are still many challenges in practical applications. For example, problems such as easy deactivation of the catalyst, low reaction efficiency, and long reaction time are common, so the overall conversion rate of lignin is mostly limited to the range of 50%-60%. Summary of the Invention

[0004] In order to overcome the disadvantages and deficiencies in the prior art such as low efficiency of non-noble metal catalysts, complex synthesis steps, instability of active components, and excessive reaction time during the electrocatalytic conversion of lignin, the primary object of the present invention is to provide a preparation method of an Fe-doped NiO catalyst nanomaterial; this method synthesizes the precursor of the Fe-doped NiO catalyst by a solvothermal method, and then calcines the precursor in air to obtain the final product.

[0005] Another object of the present invention is to provide an Fe-doped NiO catalyst nanomaterial prepared by the above preparation method; this bimetallic catalyst material is a uniformly distributed porous nanosphere or a three-dimensional nanoflower morphology composed of small-sized nanoparticles.

[0006] Another object of the present invention is to provide an application of the above Fe-doped NiO catalyst nanomaterial; this bimetallic catalyst material can be applied to the electrocatalytic conversion of lignin into high-value aromatic chemicals, with excellent lignin conversion rate and monomer selectivity.

[0007] The object of the present invention is achieved by the following technical solutions:

[0008] A preparation method of an Fe-doped NiO catalyst nanomaterial, comprising the following operating steps:

[0009] (1) Add the raw materials into a mixed solution of isopropanol and ethylene glycol and stir to obtain a homogeneous solution; react at 200 °C for 8 h. After the reaction is completed, wash and centrifuge, and dry the obtained precipitate to obtain a Fe-doped NiO catalyst precursor; the raw materials are nickel nitrate, iron nitrate, anhydrous sodium acetate and polyvinylpyrrolidone, where the molar ratio of nickel nitrate, iron nitrate and anhydrous sodium acetate is (2.9 - 1):(2 - 0.1):2, and the dosage of polyvinylpyrrolidone is calculated according to 50 mg of polyvinylpyrrolidone when the total molar amount of nickel nitrate and iron nitrate is 3 mmol;

[0010] (2) Grind the Fe-doped NiO catalyst precursor obtained in step (1) into powder, put it into a muffle furnace for calcination, and heat it up to 300 - 500 °C at a rate of 1 - 5 °C / min -1 and hold for 1 - 3 h. After the reaction is completed, a Fe-doped NiO catalyst nanomaterial is obtained.

[0011] In step (1), the molar volume ratio of nickel nitrate, ethylene glycol and isopropanol is (2.9 - 1) mmol:10 mL:50 mL; the molar volume ratio of iron nitrate, ethylene glycol and isopropanol is (2 - 0.1) mmol:10 mL:50 mL.

[0012] Preferably, the molar volume ratio of nickel nitrate, ethylene glycol and isopropanol is 2.8 mmol:10 mL:50 mL; the molar volume ratio of iron nitrate, ethylene glycol and isopropanol is 0.2 mmol:10 mL:50 mL.

[0013] In step (1), the molecular weight of polyvinylpyrrolidone is 10000; the drying is carried out at 65 - 120 °C for 24 - 32 h, preferably at 80 °C for 24 h.

[0014] In step (1), the stirring time is 60 min; the reaction is carried out in a 100 ml polytetrafluoroethylene reaction kettle in a constant temperature oven; the washing and centrifugation are carried out by washing with deionized water and anhydrous ethanol in sequence and then centrifuging, and the washing and centrifugation operations are repeated 3 - 5 times.

[0015] In step (2), the calcination is carried out at a rate of 1 - 5 °C / min -1 to heat up to 300 - 500 °C and hold for 1 - 3 h, preferably at a rate of 2 °C / min -1 to heat up to 400 °C and hold for 2 h.

[0016] A Fe-doped NiO catalyst nanomaterial prepared by the above preparation method, the Fe-doped NiO catalyst is a three-dimensional nanoflower-like morphology assembled by nanoparticles, and the petal thickness of the Fe-doped NiO catalyst material nanoflower is 5 - 20 nm.

[0017] The application of the above-mentioned Fe-doped NiO catalyst nanomaterial in the electrocatalytic conversion of lignin to prepare aromatic compounds is characterized in that the application comprises the following steps: dispersing lignin in 50 mL of 1 mol / L potassium hydroxide solution containing 5 wt% methanol as the anode electrolyte in an H-type three-electrode cell; using 50 mL of 1 mol / L potassium hydroxide solution in the cathode chamber; using nickel foam coated with the Fe-doped NiO catalyst nanomaterial as the anode electrode and a graphite rod as the cathode electrode; immersing the anode electrode in the anode electrolyte, applying an external voltage and starting stirring to enable the Fe-doped NiO catalyst nanomaterial to be in full contact with lignin, thereby realizing the electrocatalytic conversion of lignin to obtain aromatic monomers; the mass ratio of lignin to the Fe-doped NiO catalyst nanomaterial is 1:5. -1 in potassium hydroxide solution, as the anode electrolyte in an H-type three-electrode cell; the cathode chamber uses 50 mL of 1 mol / L -1 potassium hydroxide solution; nickel foam coated with the Fe-doped NiO catalyst nanomaterial is used as the anode electrode, and a graphite rod is used as the cathode electrode; the anode electrode is immersed in the anode electrolyte, an external voltage is applied and stirring is started to enable the Fe-doped NiO catalyst nanomaterial to be in full contact with lignin, thereby realizing the electrocatalytic conversion of lignin to obtain aromatic monomers; the mass ratio of lignin to the Fe-doped NiO catalyst nanomaterial is 1:5.

[0018] The present invention has the following advantages and effects compared with the prior art:

[0019] (1) Among noble metal and non-noble transition metal catalysts, compared with Pb, Pt, and Co systems, the raw material cost of the Fe-doped NiO catalyst material of the present invention is low and easy to obtain, and it has better electrocatalytic stability in the electrocatalytic conversion of lignin.

[0020] (2) The preparation conditions of traditional transition metal oxide catalysts are relatively high, and they need to be calcined in an H 2 atmosphere or at a high temperature of 800 °C to synthesize the catalyst, and the obtained nanomaterials have uneven morphologies, large particles, and limited specific surface areas. In contrast, the present invention combines the solvothermal method and low-temperature sintering technology, reducing the calcination temperature to 300 °C - 500 °C, which not only simplifies the preparation process but also achieves the purpose of low-carbon environmental protection.

[0021] (3) The synthesis process of the Fe-doped NiO catalyst nanomaterial of the present invention is simple, and nanocatalyst materials with different morphological structures can be obtained by changing the ratio of nickel nitrate and iron nitrate, having good potential for industrial production.

[0022] (4) The present invention can prepare Fe-doped NiO catalyst nanomaterials with excellent electrochemical properties by controlling the time and temperature of the solvothermal reaction and air calcination, and the catalyst nanomaterials are porous and loose nanoparticles or nanoflower morphologies assembled from nanoparticles, having a large specific surface area and more active sites, effectively improving the conversion rate and selectivity of the electrocatalytic conversion of lignin to aromatic chemicals.

[0023] (5) The Fe-doped NiO catalyst nanomaterial of the present invention can be at 25 mA cm -2At a current density, a conversion rate of more than 96.2% of the lignin model compound was achieved, and yields of 51.3% of benzoic acid and 44.6% of phenol were obtained respectively. Compared with other non-noble metal catalysts, the selectivity was increased by 15% - 50%. The catalytic performance of the Fe-doped NiO catalyst nanomaterial of the present invention is better. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] Figure 1 It is the XRD spectrum of the Fe-doped NiO catalyst nanomaterial prepared in Example 1 of the present invention.

[0025] Figure 2 It is the SEM (a) and TEM photos (b) of the Fe-doped NiO catalyst nanomaterial prepared in Example 1 of the present invention.

[0026] Figure 3 It is the chromatogram (the abscissa is time in min, and the ordinate is the peak intensity) of the liquid product after the reaction of the lignin model compound 2-phenoxy-1-phenylethanol catalyzed by the Fe-doped NiO catalyst nanomaterial prepared in Example 1 of the present invention, as well as the calculation of the yield and selectivity.

[0027] Figure 4 It is the chromatogram (the abscissa is time in min, and the ordinate is the peak intensity) of the gas chromatograph-mass spectrometer analysis of the liquid product after the enzymatic lignin degradation reaction catalyzed by the Fe-doped NiO catalyst nanomaterial prepared in Example 1 of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0028] The present invention will be further described in detail below in conjunction with the examples, but the implementation manners of the present invention are not limited thereto.

[0029] The raw materials in the examples can all be obtained commercially; unless otherwise specified, the reagents, methods, and equipment used in the present invention are conventional reagents, methods, and equipment in the technical field.

[0030] Example 1:

[0031] (1) Weigh 0.8120 g of Ni(NO 3 ) 3 ·6H 2 O, 0.0808 g of Fe(NO 3 ) 3 ·6H 2 O, 2.46 g of anhydrous CH 3 COONa and 0.050 g of polyvinylpyrrolidone (PVP K15-18) Dissolve it in 10 mL of ethylene glycol and 50 mL of isopropanol, stir vigorously for 60 min, transfer the solution to a 100 mL polytetrafluoroethylene reaction kettle, place it in a constant temperature oven, and react at 200 °C for 8 h;

[0032] (2) Take out the reaction product, wash it with deionized water and absolute ethanol respectively and centrifuge it 3 - 5 times to obtain a precipitate; Place the precipitate in an oven and dry it for 24 h at a temperature of 80 °C, and collect the brown product;

[0033] (3) Calcinate the brown product in a muffle furnace, heat it up to 400 °C at a rate of 2 °C / min and hold for 2 h; After the temperature cools down to room temperature, collect the product to obtain the Fe-doped NiO catalyst nanomaterial of the present invention, named Fe -1 -NiO. 0.2

[0034] See Figure 1 , the X-ray powder diffraction analysis (XRD) pattern of the Fe 0.2 -NiO catalyst material prepared by the method described in Example 1. The peak positions in the figure correspond one by one to all the diffraction crystal planes of the JCPDF standard card (78 - 0643), and no impure diffraction peaks are found.

[0035] See Figure 2 , where Figure 2 a in 0.2 is the scanning electron microscope (SEM) photograph of the Fe Figure 2 -NiO catalyst material prepared by the method described in Example 1, 0.2 b in 0.2 is the transmission electron microscope (TEM) photograph of the Fe 0.2 -NiO catalyst. It can be seen from the figure that the Fe

[0036] Example 2

[0037] (1) Weigh 0.8410 g of Ni(NO 3 ) 3 ·6H 2 O, 0.0404 g of Fe(NO 3 ) 3 ·6H 2 O, 2.46 g of anhydrous CH 3 COONa and 0.050 g of PVP K15-18Dissolve it in 10 mL of ethylene glycol and 50 mL of isopropanol, stir vigorously for 60 min, transfer the solution to a 100 mL polytetrafluoroethylene reaction kettle, place it in a constant temperature oven, and react at 200 °C for 8 h;

[0038] (2) Take out the reacted product, wash it with deionized water and absolute ethanol respectively and centrifuge 3 - 5 times to obtain a precipitate; place the precipitate in an oven and dry it at 80 °C for 24 h, and collect the obtained yellowish-brown product;

[0039] (3) Put the yellowish-brown product into a muffle furnace for calcination, heat it up to 400 °C at a rate of 2 °C / min and hold for 2 h; after the temperature cools down to room temperature, collect the product to obtain the Fe-doped NiO catalyst nanomaterial of the present invention, named Fe -1 -NiO. 0.1 -NiO.

[0040] The Fe 0.1 -NiO catalyst material prepared by the method described in Example 2 is observed to have a nanoflower-like morphology in SEM and TEM tests.

[0041] Example 3

[0042] (1) Weigh 0.783 g of Ni(NO 3 ) 2 ·6H 2 O, 0.1212 g of Fe(NO 3 ) 2 ·6H 2 O, 2.46 g of anhydrous CH 3 COONa and 0.050 g of PVP K15-18 Dissolve them in 10 mL of ethylene glycol and 50 mL of isopropanol, stir vigorously for 60 min, transfer the solution to a 100 mL polytetrafluoroethylene reaction kettle, place it in a constant temperature oven, and react at 200 °C for 8 h;

[0043] (2) Take out the reacted product, wash it with deionized water and absolute ethanol respectively and centrifuge 3 - 5 times to obtain a precipitate; place the precipitate in an oven and dry it at 80 °C for 24 h, and collect the obtained brown product;

[0044] (3) Put the brown product into a muffle furnace for calcination, heat it up to 400 °C at a rate of 2 °C / min and hold for 2 h; after the temperature cools down to room temperature, collect the product to obtain the Fe-doped NiO catalyst nanomaterial of the present invention, named Fe -1 -NiO. 0.3 -NiO.

[0045] The Fe 0.3-NiO catalyst nanomaterial, observed as nanoflower-like morphology in SEM and TEM tests.

[0046] Example 4

[0047] (1) Weigh 0.7540 g of Ni(NO 3 ) 2 ·6H 2 O, 0.1616 g of Fe(NO 3 ) 2 ·6H 2 O, 2.46 g of anhydrous CH 3 COONa and 0.050 g of PVP K15-18 Dissolve them in 10 mL of ethylene glycol and 50 mL of isopropanol, stir vigorously for 60 min, transfer the solution to a 100 mL polytetrafluoroethylene reaction kettle, place it in a constant temperature oven, and react at 200 °C for 8 h;

[0048] (2) Take out the reaction product, wash it with deionized water and anhydrous ethanol respectively and centrifuge 3 - 5 times to obtain a precipitate; place the precipitate in an oven and dry it for 24 h at a temperature of 80 °C, and collect the brown product;

[0049] (3) Calcinate the brown product in a muffle furnace, heat it to 400 °C at a rate of 2 °C / min and hold for 2 h; after the temperature cools to room temperature, collect the product to obtain the Fe-doped NiO catalyst nanomaterial of the present invention, named Fe -1 -NiO. 0.4

[0050] The Fe 0.4 -NiO catalyst nanomaterial prepared by the method described in Example 4 is observed as nanoflower-like morphology in SEM and TEM tests.

[0051] Example 5

[0052] (1) Weigh 0.2900 g of Ni(NO 3 ) 2 ·6H 2 O, 0.4040 g of Fe(NO 3 ) 2 ·6H 2 O, 2.46 g of anhydrous CH 3 COONa and 0.050 g of PVP K15-18 Dissolve them in 10 mL of ethylene glycol and 50 mL of isopropanol, stir vigorously for 60 min, transfer the solution to a 100 mL polytetrafluoroethylene reaction kettle, place it in a constant temperature oven, and react at 200 °C for 8 h;

[0053] (2) Take out the product after the reaction, wash it with deionized water and absolute ethanol respectively and centrifuge 3 - 5 times to obtain a precipitate; place the precipitate in an oven and dry it at 80 °C for 24 h, and collect the obtained yellowish-brown product;

[0054] (3) Put the yellowish-brown product into a muffle furnace for calcination, and heat it up to 400 °C at a rate of 2 °C / min and hold for 2 h; after the temperature cools down to room temperature, collect the product to obtain the Fe-doped NiO catalyst nanomaterial of the present invention, named NiFe -1 O 2 O 4 .

[0055] The NiFe 2 O 4 spinel catalyst material prepared by the method described in Example 2 was observed as a uniformly dispersed nanoparticle morphology in SEM and TEM tests.

[0056] Comparative Example 1

[0057] Except that PVP K15-18 in Example 1 was replaced with cetyltrimethylammonium bromide (CTAB), other conditions for preparing the Fe-doped NiO catalyst nanomaterial were the same as those in Example 1. It was found by SEM observation that there were obvious differences in its nanoflower shape from that in Example 1, the size and shape were uneven, and there was partial overlap, indicating that there might be a phenomenon of insufficient particle dispersion during the formation process. The close arrangement and overlap of the nanoflowers might limit the exposure of active sites, thus affecting the efficiency of the material in the electrocatalytic conversion reaction of lignin.

[0058] Example 6

[0059] Disperse the Nafion117 solution in ethanol and deionized water, and the volume ratio of Nafion117, ethanol and deionized water is 3:40:40, and ultrasonicate for 30 min to obtain a solvent. Then uniformly disperse 0.05 g of the Fe 0.2 -NiO catalyst nanomaterial prepared in Example 1 in 1.5 mL or more of the above solvent, and ultrasonicate for 10 min to obtain a catalyst material dispersion. Pretreat the nickel foam with acetone, ethanol and deionized water, and uniformly spray the catalyst material dispersion on the nickel foam. The loading amount of the catalyst is about 5.56 mg / cm -2 . Use an H-type electrochemical reaction cell, and use the nickel foam loaded with the catalyst as the working electrode and a graphite rod as the cathode electrode. Use a mixed solution of 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide and 2.5 mL of methanol as the anodic electrolyte, and 50 mL of mol / L potassium hydroxide as the cathodic electrolyte, and set the current density to 25 mA / cm -2, react for 10 h with stirring throughout the process; after the reaction, the electrolyte is neutralized with hydrochloric acid, the precipitate is separated by centrifugation, the supernatant is retained, and the organic phase is collected after extraction with dichloromethane for product analysis. Qualitative analysis is carried out on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometer in the United States, and quantitative analysis is carried out on an Agilent GC6890 gas chromatograph in the United States after adding an internal standard. The chromatographic column uses an HP-5ms, 30 m×0.25 mm×0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin)×100%.

[0060] See Figure 3 , according to the method described in Example 6, through the qualitative analysis results of each product in the total ion chromatogram, monophenols (vanillin, acetyl vanillone, p-hydroxyacetophenone, p-hydroxybenzaldehyde, etc.). The liquid products obtained within the detection range are aromatic products. As Figure 4 shown, the products obtained are small molecule phenols such as p-hydroxyacetophenone and p-hydroxybenzaldehyde.

[0061] Example 7

[0062] Disperse the Nafion117 solution in ethanol and deionized water. The volume ratio of Nafion117, ethanol and deionized water is 3:40:40, and ultrasonicate for 30 min to obtain a solvent. Then disperse 0.05 g of the Fe 0.1 -NiO catalyst material prepared in Example 2 uniformly in 1.5 mL or more of the solvent, and ultrasonicate for 10 min to obtain a catalyst material dispersion. Pretreat the nickel foam with acetone, ethanol and deionized water, and uniformly spray the catalyst material dispersion on the nickel foam. The loading amount of the catalyst is about 5.56 mg cm -2 . Use an H-type electrochemical reaction cell, and use the nickel foam loaded with the catalyst as the working electrode and a graphite rod as the cathode electrode. Use a mixed solution of 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide and 2.5 mL of methanol as the anodic electrolyte, and 50 mL of mol / L potassium hydroxide as the cathodic electrolyte, and set the current density to 25 mA cm -2, react for 10 h with stirring throughout the process; after the reaction, the electrolyte is neutralized with hydrochloric acid, the precipitate is separated by centrifugation, the supernatant is retained, and the organic phase is collected after extraction with dichloromethane for product analysis. Qualitative analysis is carried out on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometry instrument in the United States, and quantitative analysis is carried out on an Agilent GC6890 gas chromatograph in the United States after adding an internal standard. The chromatographic column uses an HP-5ms, 30 m×0.25 mm×0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin)×100%. The liquid products obtained within the detection range are aromatic products.

[0063] Example 8

[0064] Disperse the Nafion117 solution in ethanol and deionized water. The volume ratio of Nafion117, ethanol, and deionized water is 3:40:40, and ultrasonicate for 30 min to obtain a solvent. Then, 0.05 g of the Fe 0.3 -NiO catalyst material prepared in Example 3 is uniformly dispersed in more than 1.5 mL of the solvent, and ultrasonicate for 10 min to obtain a catalyst material dispersion. Pretreat the nickel foam with acetone, ethanol, and deionized water, and uniformly spray the catalyst material dispersion on the nickel foam. The loading amount of the catalyst is about 5.56 mg cm -2 . Use an H-type electrochemical cell, and use the nickel foam loaded with the catalyst as the working electrode and a graphite rod as the cathode electrode. Use a mixed solution of 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide, and 2.5 mL of methanol as the anodic electrolyte, and 50 mL of mol / L potassium hydroxide as the cathodic electrolyte. Set the current density to 25 mA cm -2 , react for 10 h with stirring throughout the process; after the reaction, the electrolyte is neutralized with hydrochloric acid, the precipitate is separated by centrifugation, the supernatant is retained, and the organic phase is collected after extraction with dichloromethane for product analysis. Qualitative analysis is carried out on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometry instrument in the United States, and quantitative analysis is carried out on an Agilent GC6890 gas chromatograph in the United States after adding an internal standard. The chromatographic column uses an HP-5ms, 30 m×0.25 mm×0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin)×100%. The liquid products obtained within the detection range are aromatic products.

[0065] Example 9

[0066] Disperse the Nafion 117 solution in ethanol and deionized water. The volume ratio of Nafion 117, ethanol, and deionized water is 3:40:40. Ultrasonic for 30 min to obtain the solvent. Then, 0.05 g of the Fe 0.4 -NiO catalyst prepared in Example 4 is uniformly dispersed in more than 1.5 mL of the solvent, and ultrasonic for 10 min to obtain the catalyst material dispersion. Pretreat the nickel foam with acetone, ethanol, and deionized water, and uniformly spray the catalyst material dispersion on the nickel foam. The loading amount of the catalyst is about 5.56 mg cm -2 . Use an H-type electrochemical reaction cell, and use the nickel foam loaded with the catalyst as the working electrode and the graphite rod as the cathode electrode. Take a mixed solution of 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide, and 2.5 mL of methanol as the anolyte, and 50 mL of mol / L potassium hydroxide as the catholyte. Set the current density to 25 mA cm -2 , react for 10 h with stirring throughout the process; after the reaction is completed, the electrolyte is neutralized with hydrochloric acid, the precipitate is separated by centrifugation, the supernatant is retained, and the organic phase is collected after extraction with dichloromethane for product analysis. Qualitative analysis is carried out on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometer in the United States, and quantitative analysis is carried out on an Agilent GC6890 gas chromatograph in the United States after adding the internal standard. The chromatographic column uses an HP-5ms, 30 m×0.25 mm×0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin)×100%. The liquid products obtained within the detection range are aromatic products.

[0067] Example 10

[0068] Disperse the Nafion 117 solution in ethanol and deionized water. The volume ratio of Nafion 117, ethanol, and deionized water is 3:40:40. Ultrasonic for 30 min to obtain the solvent. Then, 0.05 g of the NiFe 2 O 4 catalyst material is uniformly dispersed in more than 1.5 mL of the solvent, and ultrasonic for 10 min to obtain the catalyst material dispersion. Pretreat the nickel foam with acetone, ethanol, and deionized water, and uniformly spray the catalyst material dispersion on the nickel foam. The loading amount of the catalyst is about 5.56 mg cm -2 . Use an H-type electrochemical reaction cell, and use the nickel foam loaded with the catalyst as the working electrode and the graphite rod as the cathode electrode. Take a mixed solution of 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide, and 2.5 mL of methanol as the anolyte, and 50 mL of mol / L potassium hydroxide as the catholyte. Set the current density to 25 mA cm -2, react for 10 h with stirring throughout the process; after the reaction is completed, the electrolyte is neutralized with hydrochloric acid, the precipitate is separated by centrifugation, the supernatant is retained, and the organic phase is collected after extraction with dichloromethane for product analysis. Qualitative analysis is carried out on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometer in the United States, and quantitative analysis is carried out on an Agilent GC6890 gas chromatograph in the United States after adding an internal standard. The chromatographic column uses an HP-5ms, 30 m×0.25 mm×0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin)×100%. The liquid products obtained within the detection range are aromatic products.

[0069] Example 11

[0070] Disperse the Nafion117 solution in ethanol and deionized water. The volume ratio of Nafion117, ethanol, and deionized water is 3:40:40, and ultrasonicate for 30 min to obtain a solvent. Then, 0.05 g of the Fe 0.2 -NiO catalyst material prepared in Example 1 is uniformly dispersed in more than 1.5 mL of the solvent, and ultrasonicate for 10 min to obtain a catalyst material dispersion. Pretreat the nickel foam with acetone, ethanol, and deionized water, and uniformly spray the catalyst material dispersion on the nickel foam. The loading amount of the catalyst is about 5.56 mg cm -2 . Use an H-type electrochemical cell, and use the nickel foam loaded with the catalyst as the working electrode and a graphite rod as the cathode electrode. Use a mixed solution of 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide, and 2.5 mL of methanol as the anodic electrolyte, and 50 mL of mol / L potassium hydroxide as the cathodic electrolyte, and set the current density to 25 mA cm -2 , react for 6 h with stirring throughout the process; after the reaction is completed, the electrolyte is neutralized with hydrochloric acid, the precipitate is separated by centrifugation, the supernatant is retained, and the organic phase is collected after extraction with dichloromethane for product analysis. Qualitative analysis is carried out on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometer in the United States, and quantitative analysis is carried out on an Agilent GC6890 gas chromatograph in the United States after adding an internal standard. The chromatographic column uses an HP-5ms, 30 m×0.25 mm×0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin)×100%. The liquid products obtained within the detection range are aromatic products.

[0071] Example 12

[0072] Disperse the Nafion 117 solution in ethanol and deionized water. The volume ratio of Nafion 117, ethanol, and deionized water is 3:40:40. Ultrasonicate for 30 min to obtain the solvent. Then, disperse 0.05 g of the Fe 0.2 -NiO catalyst material prepared in Example 1 evenly in more than 1.5 mL of the solvent. Ultrasonicate for 10 min to obtain the catalyst material dispersion. Pretreat the nickel foam with acetone, ethanol, and deionized water, and evenly spray the catalyst material dispersion on the nickel foam. The loading amount of the catalyst is about 5.56 mg cm -2 . Use an H-type electrochemical reaction cell, and use the nickel foam loaded with the catalyst as the working electrode and a graphite rod as the cathode electrode. Use a mixed solution of 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide, and 2.5 mL of methanol as the anodic electrolyte, and 50 mL of mol / L potassium hydroxide as the cathodic electrolyte. Set the current density to 25 mA cm -2 . React for 18 h with stirring throughout the process. After the reaction, neutralize the electrolyte with hydrochloric acid, centrifuge to separate the precipitate, retain the supernatant, extract with dichloromethane, and collect the organic phase for product analysis. Perform qualitative analysis on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometry instrument in the United States, and perform quantitative analysis on an Agilent GC6890 gas chromatograph in the United States after adding an internal standard. The chromatographic column uses an HP-5ms, 30 m × 0.25 mm × 0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin) × 100%. The liquid products obtained within the detection range are aromatic products.

[0073] Example 13

[0074] Disperse the Nafion 117 solution in ethanol and deionized water. The volume ratio of Nafion 117, ethanol, and deionized water is 3:40:40. Ultrasonicate for 30 min to obtain the solvent. Then, disperse 0.05 g of the Fe 0.2 -NiO catalyst material prepared in Example 1 evenly in more than 1.5 mL of the solvent. Ultrasonicate for 10 min to obtain the catalyst material dispersion. Pretreat the nickel foam with acetone, ethanol, and deionized water, and evenly spray the catalyst material on the nickel foam. The loading amount of the catalyst is about 5.56 mg cm -2 . Use an H-type electrochemical reaction cell, and use the nickel foam loaded with the catalyst as the working electrode and a graphite rod as the cathode electrode. Use 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide, and 2.5 mL of methanol as the anodic electrolyte, and 50 mL of mol / L potassium hydroxide as the cathodic electrolyte. Set the current density to 25 mA cm -2React for 24 h with continuous stirring throughout the process. After the reaction is completed, the electrolyte is neutralized with hydrochloric acid, and the precipitate is separated by centrifugation. The supernatant is retained, extracted with dichloromethane, and the organic phase is collected for product analysis. Qualitative analysis is carried out on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometry instrument in the United States, and quantitative analysis is carried out on an Agilent GC6890 gas chromatograph in the United States after adding an internal standard. The chromatographic column used is an HP-5ms, 30 m×0.25 mm×0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin)×100%. The liquid product obtained within the detection range is an aromatic product.

[0075] Example 14

[0076] Disperse the Nafion117 solution in ethanol and deionized water. The volume ratio of Nafion117, ethanol, and deionized water is 3:40:40, and ultrasonicate for 30 min to obtain a solvent. Then, uniformly disperse 0.05 g of the Fe 0.2 -NiO catalyst material prepared in Example 1 in more than 1.5 mL of the above solvent and ultrasonicate for 10 min. Pretreat the nickel foam with acetone, ethanol, and deionized water, and uniformly spray the catalyst material onto the nickel foam. The loading amount of the catalyst is about 5.56 mg cm -2 . Use an H-type electrochemical cell, and use the nickel foam loaded with the catalyst as the working electrode and a graphite rod as the cathode electrode. Use a mixed solution of 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide, and 2.5 mL of methanol as the anodic electrolyte, and 50 mL of mol / L potassium hydroxide as the cathodic electrolyte. Set the current density to 50 mA cm -2 React for 10 h with continuous stirring throughout the process. After the reaction is completed, the electrolyte is neutralized with hydrochloric acid, and the precipitate is separated by centrifugation. The supernatant is retained, extracted with dichloromethane, and the organic phase is collected for product analysis. Qualitative analysis is carried out on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometry instrument in the United States, and quantitative analysis is carried out on an Agilent GC6890 gas chromatograph in the United States after adding an internal standard. The chromatographic column used is an HP-5ms, 30 m×0.25 mm×0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin)×100%. The liquid product obtained within the detection range is an aromatic product.

[0077] Comparative Example 2

[0078] Disperse the Nafion 117 solution in ethanol and deionized water. The volume ratio of Nafion 117, ethanol, and deionized water is 3:40:40, and ultrasonicate for 30 min to obtain the solvent. Then, disperse 0.05 g of the Fe 0.2 -NiO catalyst material prepared in Comparative Example 1 with CTAB as the dispersant uniformly in more than 1.5 mL of the solvent, and ultrasonicate for 10 min. Pretreat the nickel foam with acetone, ethanol, and deionized water, and uniformly spray the catalyst material onto the nickel foam. The loading amount of the catalyst is about 5.56 mg cm -2 . Use an H-type electrochemical reaction cell, and use the nickel foam loaded with the catalyst as the working electrode and a graphite rod as the cathode electrode. Take a mixed solution of 0.05 g of enzymatically hydrolyzed lignin, 47.5 mL of 1 mol / L potassium hydroxide, and 2.5 mL of methanol as the anodic electrolyte, and 50 mL of mol / L potassium hydroxide as the cathodic electrolyte. Set the current density to 25 mA cm -2 , react for 10 h with stirring throughout the process; after the reaction, neutralize the electrolyte with hydrochloric acid, centrifuge to separate the precipitate, retain the supernatant, extract with dichloromethane, and collect the organic phase for product analysis. Perform qualitative analysis on an Agilent 7890B-7000C gas chromatography-tandem mass spectrometry instrument in the United States, and perform quantitative analysis on an Agilent GC6890 gas chromatography instrument in the United States after adding an internal standard. The chromatographic column uses an HP-5ms, 30 m×0.25 mm×0.25 μm capillary column. The phenolic yield (wt.%) is calculated as (mass of phenols) / (mass of lignin)×100%. The liquid products obtained within the detection range are aromatic products. Analysis found that when using the Fe 0.2 -NiO catalyst material prepared in Comparative Example 1 with CTAB as the dispersant as the lignin electrocatalyst, fewer products were obtained. It is speculated that the dispersion stability of CTAB is poor, and its hydrophobic chains may cause enhanced interaction between particles, thus exacerbating the agglomeration phenomenon, resulting in fewer active sites exposed on the catalyst, thereby reducing the reaction activity.

[0079] As shown in Table 1, from Effect Examples 6-14 and Comparative Example 2, according to the technical solution of the invention, by adjusting the raw material ratio, selecting a suitable dispersant, or changing the reaction time and current density, the electrocatalytic conversion of lignin can be achieved, and aromatic chemical products can be obtained.

[0080] Table 1. Dispersants used in the Fe-doped NiO catalyst materials prepared in Examples 1-14 and Comparative Examples 1-2 and their electrocatalytic conversion reaction conditions

[0081]

[0082]

[0083] The above embodiments are preferred embodiments of the present invention, but the embodiments of the present invention are not limited to the above embodiments. Any other changes, modifications, substitutions, combinations, or simplifications made without departing from the spirit and principle of the present invention shall be equivalent replacement methods and are all included in the protection scope of the present invention.

Claims

1. A method for preparing Fe-doped NiO catalyst nanomaterial, characterized in that The steps include: (1) adding raw materials to a mixed solution of isopropanol and ethylene glycol and stirring to obtain a uniform solution; reacting at 200° C. for 8 hours, washing and centrifuging after the reaction is completed, and drying the obtained precipitate to obtain an Fe-doped NiO catalyst precursor; the raw materials are nickel nitrate, ferric nitrate, anhydrous sodium acetate and polyvinyl pyrrolidone, wherein the molar ratio of nickel nitrate, ferric nitrate and anhydrous sodium acetate is (2.9-1): (2-0.1): 2, and the amount of polyvinyl pyrrolidone is calculated based on the use of 50 mg of polyvinyl pyrrolidone when the total molar amount of nickel nitrate and ferric nitrate is 3 mmol; (2) Grinding the Fe-doped NiO catalyst precursor obtained in step (1) into powder, placing it in a muffle furnace for calcination, heating it to 300-500° C. at a rate of 1-5° C. / min and maintaining it for 1-3 h, and obtaining Fe-doped NiO catalyst nanomaterials after the reaction is completed.

2. The method for preparing a Fe-doped NiO catalyst nanomaterial according to claim 1, characterized in that: The molar volume ratio of the nickel nitrate, ethylene glycol and isopropanol in step (1) is (2.9-1) mmol:10 mL:50 mL; the molar volume ratio of the iron nitrate, ethylene glycol and isopropanol is (2-0.1) mmol:10 mL:50 mL.

3. The method for preparing a Fe-doped NiO catalyst nanomaterial according to claim 2, characterized in that: The molar volume ratio of the nickel nitrate, ethylene glycol and isopropanol is 2.8 mmol:10 mL:50 mL; the molar volume ratio of the iron nitrate, ethylene glycol and isopropanol is 0.2 mmol:10 mL:50 mL.

4. The method for preparing a Fe-doped NiO catalyst nanomaterial according to claim 1, characterized in that: The molecular weight of the polyvinyl pyrrolidone in step (1) is 10,000; and the drying is performed at 65 to 120° C. for 24 to 32 hours.

5. The preparation method according to claim 4, characterized in that: The drying is carried out at 80° C. for 24 hours.

6. The preparation method according to claim 1, characterized in that: The stirring time in step (1) is 60 minutes; the reaction is carried out in a 100 ml polytetrafluoroethylene reactor in a constant temperature oven; the washing and centrifugation are washing with deionized water and anhydrous ethanol in sequence and then centrifuging, and the washing and centrifugation operations are repeated 3 to 5 times.

7. The preparation method according to claim 1, characterized in that: The calcination in step (2) is carried out by heating the temperature to 300-500°C at a rate of 1-5°C / min and maintaining the temperature for 1-3h.

8. The preparation method according to claim 7, characterized in that: The calcination was carried out by heating the temperature to 400°C at a rate of 2°C / min and maintaining the temperature for 2h.

9. An Fe-doped NiO catalyst nanomaterial prepared by the preparation method according to any one of claims 1 to 8, characterized in that: The Fe-doped NiO catalyst is a three-dimensional nano-flower-like morphology assembled from nano-particles, and the thickness of the nano-flowers of the Fe-doped NiO catalyst material is 5-20 nm.

10. The use of the Fe-doped NiO catalyst nanomaterial according to claim 9 in the electrocatalytic conversion of lignin to prepare aromatic compounds, characterized in that: The application is carried out according to the following steps: dispersing lignin in 50 mL of a 1 mmol / L potassium hydroxide solution containing 5 wt% methanol as an anode electrolyte in an H-type three-electrode battery; using 50 mL of a 1 mmol / L potassium hydroxide solution in a cathode chamber; using a nickel foam coated with a Fe-doped NiO catalyst nanomaterial as an anode electrode, and a graphite rod as a cathode electrode; immersing the anode electrode in the anode electrolyte, turning on an external power supply and a stirrer, allowing the Fe-doped NiO catalyst nanomaterial to fully contact and react with the lignin, thereby achieving electrocatalytic conversion of the lignin to obtain an aromatic monomer; and the mass ratio of the lignin to the Fe-doped NiO catalyst nanomaterial is 1:5.

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