Cerium-based sub-nanocrystalline electrocatalyst, preparation method thereof and application of cerium-based sub-nanocrystalline electrocatalyst in production of 1, 6-hexanediol through electrocatalysis of HMF

Abstract

The invention discloses an application of a cerium-based sub-nanocrystalline electrocatalyst and a preparation method thereof in production of 1, 6-hexanediol through electrocatalysis of HMF, and relates to the technical field of catalyst material synthesis and biomass value materials.The preparation method comprises the steps that a carbon nano-carrier is dispersed in absolute ethyl alcohol, then cerium salt is added for ultrasonic treatment, and the cerium-based sub-nanocrystalline electrocatalyst is obtained; and after the treatment is completed, obtaining a precipitate, calcining the precipitate in an air atmosphere at 300-500 DEG C for 2 hours, and calcining the precipitate in an H2 / Ar atmosphere at 500-800 DEG C for 5-10 hours, so as to obtain the cerium-based sub-nanocrystalline electrocatalyst. According to the present invention, the cerium-based sub-nanocrystalline has the ultra-small scale characteristic, can expose the high-density Ce active site (Ce < 3 + > / Ce < 4 + >), can accurately regulate and control the conversion of HMF to 1, 6-hexanediol, and provides the efficient green synthesis platform for biomass value, such that the sustainable chemical synthesis is easily achieved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of catalyst material synthesis and biomass valorization, in particular to a cerium-based sub-nanocrystal electrocatalyst, a preparation method thereof and application thereof in electrocatalytic production of 1,6-hexanediol from HMF. BACKGROUND

[0002] Lignin is an important component of lignocellulosic biomass, accounting for 15-30% of its total mass, and is rich in aromatic ring structures, making it a potential source of renewable aromatic chemicals. However, the complex three-dimensional network structure of lignin (mainly connected by β-O-4, α-O-4, and other ether bonds and C-C bonds) makes it difficult to depolymerize. Currently, it is mainly used as low-value fuel or waste, causing resource waste and environmental pollution. Among them, 5-hydroxymethylfurfural (HMF) as a core "platform compound" connecting biomass resources and high-end fine chemicals is a key hub in the utilization system of renewable carbon resources; lignin, as the second largest biomass component in nature, can realize the directional generation of HMF through mild catalytic depolymerization (such as acid catalytic directional conversion, enzymatic assisted degradation). With the breakthrough of lignin resource technology, the annual output of HMF from lignin has broken through the million-ton level, successfully breaking through the conversion link of "agricultural and forestry waste → lignin → HMF", and becoming the core bridge to promote the upgrading of lignin from "low-value fuel" to "high-value chemical precursor".

[0003] 1,6-hexanediol, as an important straight-chain aliphatic diol, is widely used in the synthesis of high molecular materials (such as high-performance polyurethane elastomers, environmentally friendly polyesters PCTG), high-end coatings (automobile original paint, food contact ink), and pharmaceutical intermediates (anti-ulcer drug synthesis), with a global annual demand of over 500,000 tons. Currently, its industrial synthesis mainly relies on petroleum-based routes (such as high-pressure hydrogenation of adipic acid, condensation of ethylene oxide and hydrogenation), which not only faces the risk of raw material supply due to the increasing depletion of fossil resources, but also is accompanied by high energy consumption and high carbon emissions in the high-temperature and high-pressure reaction process. Therefore, developing a green alternative synthesis path based on renewable biomass resources has become an urgent demand in the chemical industry.

[0004] The conversion of lignin-derived HMF to 1,6-hexanediol through catalytic reduction not only realizes the high-value utilization of lignin resources, but also provides a sustainable synthesis route for 1,6-hexanediol. It is an important research direction in the field of sustainable chemistry, which is in line with the low-carbon transformation direction of chemical industry under the "double carbon" strategy. However, this conversion process still faces multiple key challenges. First, the lignin-derived HMF raw material system is complex, containing not only target HMF but also lignin degradation residues such as phenolic compounds (e.g. phenol, guaiacol), furan derivatives (e.g. furfural, 2,5-dimethylfuran) and carboxylic acid impurities (e.g. p-hydroxybenzoic acid, acetic acid). These impurities are easily adsorbed on the active sites of the catalyst, on the one hand leading to catalyst deactivation due to poisoning, on the other hand causing side reaction pathways of HMF, such as excessive reduction to generate 2,5-dihydroxymethylfuran (DHF), 1,2,6-hexanetriol, or disordered ring-opening of furan ring to generate low-carbon alcohols (e.g. 1,4-butanediol, ethanol), which seriously reduces the selectivity of 1,6-hexanediol. Second, traditional catalytic reduction routes (such as thermal catalytic hydrogenation) require high temperature (150-220℃) and high pressure hydrogen (3-8MPa), which not only has safety risks in hydrogen storage and transportation, but also makes it difficult to control the product distribution due to the harsh reaction conditions. In addition, the high energy consumption further limits its industrial application.

[0005] Electrocatalysis technology provides a new direction for solving the selectivity and mildness of HMF reduction, with the advantages of room temperature and atmospheric pressure reaction conditions, and precise control of reaction pathways through electrode potential. However, the current electrocatalytic HMF reduction system to produce 1,6-hexanediol still has significant technical gaps. On the one hand, existing catalysts are difficult to adapt to the complex substrate of lignin-derived HMF. For example, noble metal catalysts (such as Pt, Pd, Ru) have certain activity for the reduction of aldehyde groups in HMF, but they easily cause excessive hydrogenation or disordered ring-opening of furan ring to generate some low-carbon chain alcohols, and the high cost limits their large-scale application. Non-noble metal catalysts (such as Ni, Co, Cu-based alloys) have the problems of poor activity site dispersion and low electron transfer efficiency, which easily leads to rapid stability decay in complex impurity systems due to surface carbon or metal ion dissolution. On the other hand, the reaction of HMF reduction to produce 1,6-hexanediol involves multiple electron transfer and precise functional group transformation (aldehyde group -CHO reduction to hydroxymethyl group -CH2OH, selective ring-opening of furan ring, and preservation of carbon chain integrity), which requires the catalyst to have three core capabilities: efficient electron transfer capability to support the continuous progress of multi-step reduction reaction, precise adsorption and activation capability for intermediate products (such as 5-hydroxymethyl-2-furfuryl alcohol HMFOL, 2,5-dihydroxymethyl tetrahydrofuran DHMTHF), and the ability to control the ring-opening pathway of furan ring to avoid carbon chain breakage. Traditional single-phase catalysts or micron-sized particle catalysts cannot meet these requirements at the same time, which leads to the fact that electrocatalytic reduction of HMF to produce 1,6-hexanediol has not been realized.

[0006] Therefore, providing an electrocatalyst suitable for complex matrix, realizing high selectivity, high stability and high activity is a technical problem to be solved in the field. SUMMARY

[0007] In order to solve the above problems, the present application provides a cerium-based sub-nanocrystalline electrocatalyst, a preparation method and application thereof. The cerium-based sub-nanocrystalline has an ultra-small size feature, can expose a high-density Ce active site (Ce 3+ / Ce 4+ ), precisely regulates the conversion of HMF to 1,6-hexanediol, provides a high-efficiency green synthesis platform for biomass valueization, and thus helps sustainable chemical synthesis.

[0008] In order to achieve the above purpose, the technical scheme is as follows: A cerium-based sub-nanocrystalline electrocatalyst, the electrocatalyst is a carbon nanocarrier loaded with cerium-based sub-nanocrystalline, wherein the Ce of the cerium-based sub-nanocrystalline accounts for 15-30% of the mass of the electrocatalyst.

[0009] Preferably, the preparation method of the carbon nanocarrier is: 1) Preparation of precursor: after adjusting the pH value of MgSO4 aqueous solution to 8-10, reacting at 160-240℃ for 12-24h, and obtaining the precipitate after the reaction is completed, the precipitate is the precursor; 2) After grinding the precursor, calcining at 900-1100℃ for 2-10min in a carbon-containing atmosphere, and using HF etching on the product, the carbon nanocarrier is obtained.

[0010] Preferably, the concentration of the MgSO4 aqueous solution in step 1) is 0.5-1.0M; the pH value is adjusted by using NH4·H2O; In step 2), the carbon-containing atmosphere is methane or gaseous acetonitrile; the heating rate of calcination is 2-10℃ / min; the HF etching is etching with 1M HF for 10-30h.

[0011] Preferably, in step 2), the carbon-containing atmosphere is 10-50sccm of methane or gaseous acetonitrile mixed with 100-500sccm of argon.

[0012] According to the preparation method of the cerium-based sub-nanocrystalline electrocatalyst, the following specific steps are included: The carbon nanocarrier is dispersed in anhydrous ethanol, then cerium salt is added and ultrasonic treated, the precipitate obtained after the treatment is calcined at 300-500℃ for 2h in an air atmosphere and calcined at 500-800℃ for 5-10h in a H2 / Ar atmosphere, and the cerium-based sub-nanocrystalline electrocatalyst is obtained.

[0013] Preferably, the mass-volume ratio of the carbon nanocarrier, anhydrous ethanol and cerium salt is 100-500 mg:20-100 mL:50-200 mg.

[0014] Preferably, the cerium salt is at least one of cerium chloride, cerium sulfate and cerium nitrate.

[0015] Preferably, the ultrasonic time is 48-96 h; the rate of the calcination temperature rise is 2-10 ℃ / min; The volume ratio of H2 / Ar is 5:95, and the flow rate of H2 / Ar is 20-100 sccm.

[0016] The present application realizes a directional breakthrough on the traditional catalytic bottleneck by constructing a cerium-based sub-nanocrystal catalyst system and combining the reaction mechanism of HMF electrocatalytic reduction to produce 1,6-hexanediol (multi-step electron transfer, intermediate precise conversion, and selective ring-opening of furan ring). a) Precise adaptation of the site requirement of the multi-step reaction of HMF reduction and carbon chain regulation, the ultra-small scale characteristics of cerium-based sub-nanocrystal (size about 1 nm) can expose high-density Ce active sites (Ce 3+ / Ce 4+ ), and a "gradient adsorption-conversion" site system is formed through surface hydroxyl modification: the outer layer of hydroxyl sites preferentially selectively adsorb the aldehyde group (-CHO) of the HMF molecule to avoid the competitive adsorption of impurity molecules (such as phenols); the inner layer of Ce active sites mediate the first step of reduction of aldehyde group to hydroxymethyl group (-CH2OH) (to generate HMFOL), and the intermediate layer of sites further activate the furan ring and regulate the ring-opening path (to avoid carbon chain rupture), finally realizing the directional conversion of "aldehyde group reduction→furan ring opening→carbon chain saturation" through synergistic effect, solving the problem of traditional single-phase catalysts that the adsorption of intermediates is too strong (leading to excessive reduction to DHF) or too weak (leading to disordered ring-opening of furan ring); b) Strengthening the dynamic response of cerium-based valence state cycle and the electron transfer efficiency, the quantum size effect of cerium-based sub-nanocrystal can significantly improve the Ce 3+ / Ce 4+ valence state conversion rate, and its redox potential can be matched with the reaction requirement in real time through the potential regulation of the electrocatalytic system: in the low potential range, Ce 4+ is quickly converted to Ce 3+ to provide electrons and promote the efficient reduction of the aldehyde group of HMF; in the medium potential range, Ce 3+ / Ce 4+ maintains a dynamic balance, precisely activates the C-O bond of the furan ring (reduces the ring-opening energy barrier) while inhibiting the hydrogenation of the double bond; this dynamic adaptability effectively solves the defects of traditional non-noble metal catalysts, such as electron transfer lag and loss of control of the reaction path; c) To resist interference from complex matrices of lignin-derived HMF and improve long-term stability, the Ce-O-Ce bonds on the surface of the cerium-based subnanocrystalline material of this invention have excellent chemical stability, which can resist the coordination poisoning of phenolic impurities (avoiding the active sites from being occupied by phenolic hydroxyl groups); at the same time, the hydrophilic hydroxyl groups (-OH) modified on the crystal surface can preferentially bind to HMF molecules through hydrogen bonds (compared to hydrophobic phenols and furan derivatives), achieving selective adsorption and transformation of HMF in complex matrices; in addition, the high dispersibility of the subnanocrystalline material can avoid the agglomeration and deactivation of traditional particulate catalysts, solving the problem of poor catalyst stability in complex matrices; d) Breaking through the inherent balance bottleneck of "activity-selectivity", the interfacial charge transfer effect formed by the cerium-based sub-nanocrystalline material and the support (such as carbon nanotubes or graphene) can accelerate the transfer of electrons from the support to the Ce active site, significantly improving the reaction kinetics. At the same time, by controlling the electron cloud density on the crystal surface (such as doping with a small amount of Ni or Co atoms), the interaction between 1,6-hexanediol molecules and the active site can be weakened, promoting rapid desorption of the product and preventing its further reduction to lower alcohols (such as 1,4-butanediol). This achieves a simultaneous improvement in catalytic activity and 1,6-hexanediol selectivity, breaking the limitation that high activity in traditional catalysts necessarily means low selectivity.

[0017] Application of the cerium-based sub-nanocrystalline electrocatalyst described above or the cerium-based sub-nanocrystalline electrocatalyst prepared by the above preparation method in the electrocatalytic reduction of HMF to 1,6-hexanediol.

[0018] Preferably, the specific method is as follows: using the cerium-based sub-nanocrystalline electrocatalyst as the working electrode, a platinum sheet as the counter electrode, Hg / HgO as the reference electrode, KOH solution as the electrolyte, adding HMF to the cathode electrolyte, and using a constant voltage electrolysis method.

[0019] Preferably, the specific method is as follows: the cerium-based sub-nanocrystalline electrocatalyst is prepared into a dispersion at a ratio of 1 mg dispersed in 200 μL of isopropanol, and a slurry is prepared by adding 0.5 μL of Nafion 117 membrane solution to every 200 μL of dispersion. The slurry is then dispersed at a ratio of 1 cm... 2 A working electrode was fabricated by spraying 200 μL of slurry onto a titanium fiber felt electrode; HMF was dissolved in 1M KOH aqueous solution at a concentration of 500 mM as the cathode electrolyte and 1M KOH aqueous solution as the anolyte; a platinum sheet electrode was used as the counter electrode and a mercury oxide electrode was used as the reference electrode. The working electrode was subjected to electrochemical testing in a commercial H-type electrolytic cell; constant potential electrolysis was performed at a potential of (-0.6)-(-1.2V) (vs. RHE), and the electrolysis products were detected by liquid chromatography.

[0020] Compared with the prior art, the present invention has the following beneficial effects: (1) The cerium-based sub-nanocrystalline electrocatalyst provided by the present invention, with its high specific surface area and abundant hydroxyl / oxygen vacancy defects due to its ultra-small size (around 1 nm), can expose high-density Ce 3+ / Ce 4+ The active site significantly enhances the specific adsorption and activation ability of HMF molecules' aldehyde group (-CHO) and furan ring, laying the foundation for subsequent reduction reactions; (2) The Ce inside the cerium-based subnanocrystalline material of the present invention 3 With / Ce 4+ The dynamic valence cycle and the interfacial charge transfer effect with the support can precisely optimize the electronic structure of the active site, effectively reduce the reaction energy barrier of HMF aldehyde reduction (generating HMFOL) and selective ring opening of furan ring, and simultaneously improve the electrocatalytic reaction rate and the selectivity of 1,6-hexanediol formation. (3) The cerium-based sub-nano crystals of the present invention form a stable Ce-O bond framework through a two-step process of air pre-calcination-hydrogen reduction. Combined with its strong interaction with the support (such as carbon-based support), it can suppress crystal agglomeration, metal ion dissolution and structural collapse during the reaction process, and significantly improve the catalyst’s resistance to deactivation and long-term cycle stability in complex HMF matrix. (4) The Ce-based subnanocrystalline material of the present invention 3+ / Ce 4+ The ratio can be precisely controlled by adjusting the flow rate of the calcination atmosphere (5% H2 + 95% Ar). Its adjustable redox properties can efficiently construct an "electron transfer channel", accelerate the transfer efficiency of electrons from the support to the HMF intermediate (such as DHMTHF), and promote the orderly progress of multi-step reduction reactions. (5) The “gradient adsorption-conversion” site system of the cerium-based sub-nanocrystalline material of the present invention (the outer layer hydroxyl adsorbs aldehyde groups and the inner layer Ce active site activates furan rings) can accurately identify and activate the C=O bond and the CO bond of furan ring of HMF, while inhibiting side reactions such as excessive reduction of aldehyde groups (generating DHF) and disordered ring opening of furan ring (generating low-carbon alcohols), and directionally improving the selectivity of 1,6-hexanediol generation. Attached Figure Description

[0021] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. The drawings in this description are merely embodiments of the present invention.

[0022] Figure 1 This is a STEM image of a cerium-based subnano cluster of the present invention; Figure 2 This is an X-ray diffraction pattern of a cerium-based subnano cluster according to the present invention; Figure 3 This is a liquid chromatogram of HMF, the electrocatalytic substrate of this invention; Figure 4 The liquid chromatogram of 1,6-hexanediol, the electrocatalytic product of this invention; Figure 5 This is a liquid chromatogram of the electrolyte after electrolytic reduction of 1,6-hexanediol by the catalyst of this invention. Detailed Implementation

[0023] Embodiments of the present invention are described below, examples of which are shown in the accompanying drawings. The embodiments described with reference to the drawings are exemplary and intended to explain the present invention, but are not to be construed as limiting the present invention.

[0024] Example 1 This invention provides a method for preparing a cerium-based subnanocrystalline electrocatalyst, specifically including the following steps; (1) Synthesis of precursor magnesium oxide nanorods Weigh a certain amount of MgSO4 and dissolve it in deionized water to prepare a 0.5M MgSO4 aqueous solution, then use 1M NH3. Titrate with H2O until the pH value equals 8; transfer the titrated solution to a hydrothermal reactor, then transfer the hydrothermal reactor to an oven and react at 160℃ for 12 hours; after the reaction is complete, cool to room temperature, filter out the precipitate in the liner and wash it, wash it twice with deionized water, then wash it twice with anhydrous ethanol, and then wash it once with deionized water. Place the washed precipitate in a vacuum oven at 60℃ to dry, and the precursor is obtained.

[0025] (2) Preparation of the carrier The dried precursor was taken out and weighed 100 mg. It was then ground thoroughly in an agate mortar. The ground powder was spread evenly in a corundum crucible and transferred to a vacuum tube furnace. The furnace was purged with a mixture of 10 sccm methane and 100 sccm argon. The temperature was increased from room temperature to 900℃ for 2 minutes at a rate of 2℃ / min, and then cooled to room temperature. After the reaction was completed, the product was taken out and etched with 1M HF for 10 hours. The etched product was washed 5 times with deionized water and then dried in a vacuum oven to obtain carbon nanocarriers. (3) Preparation of cerium-based sub-nanocrystalline electrocatalysts Take out the dried carbon nanocarrier, weigh 100 mg, disperse it in 20 mL of anhydrous ethanol, then weigh 50 mg of cerium chloride and dissolve it in the above solution; stir the solution for two days and filter it, then transfer the filtered solid to a vacuum oven to dry; the powder obtained after vacuum drying is placed in an alumina crucible and spread out, then transferred to a vacuum tube furnace, and calcined at 300 °C for 2 hours at a heating rate of 2 °C / min under air atmosphere, then cooled to room temperature, and calcined again at 500 °C for 5 hours at a heating rate of 2 °C / min under a flow rate of 20 sccm and an atmosphere of 5% H2 + 95% Ar; after the reaction is completed, take out the product, wash it twice with deionized water and then twice with anhydrous ethanol, and dry it in a vacuum oven at 60 °C to obtain the cerium-based sub-nanocrystalline electrocatalyst, with ICP analysis showing that Ce accounts for 21.4% of the total mass.

[0026] Example 2 This invention provides a method for preparing a cerium-based subnanocrystalline electrocatalyst, specifically including the following steps; (1) Synthesis of precursor magnesium oxide nanorods Weigh a certain amount of MgSO4 and dissolve it in deionized water to prepare a 0.75M MgSO4 aqueous solution, then use 1M NH3. Titrate with H2O until the pH value equals 9; transfer the titrated solution to a hydrothermal reactor, then transfer the hydrothermal reactor to an oven and react at 200℃ for 18 hours; after the reaction is complete, cool to room temperature, filter out the precipitate in the liner and wash it, wash it twice with deionized water, then wash it twice with anhydrous ethanol, and then wash it once with deionized water. Place the washed precipitate in a vacuum oven at 60℃ to dry, and the precursor is obtained.

[0027] (2) Preparation of the carrier The dried precursor was taken out and weighed 300 mg. It was then ground thoroughly in an agate mortar. The ground powder was spread evenly in a corundum crucible and transferred to a vacuum tube furnace. The atmosphere was introduced into the tube furnace with a mixture of 30 sccm methane and 300 sccm argon. The temperature was increased from room temperature to 1000℃ at a rate of 6℃ / min and calcined for 6 minutes. Then it was cooled to room temperature. After the reaction was completed, the product was taken out and etched with 1M HF for 20 hours. The etched product was washed 5 times with deionized water and then dried in a vacuum oven to obtain carbon nanocarriers. (3) Preparation of cerium-based sub-nanocrystalline electrocatalysts Take out the dried carbon nanocarrier, weigh 300 mg, disperse it in 60 mL of anhydrous ethanol, then weigh 125 mg of cerium chloride and dissolve it in the above solution; stir the solution for two days and filter it, then transfer the filtered solid to a vacuum oven to dry; the powder obtained after vacuum drying is placed in a corundum crucible and leveled, then transferred to a vacuum tube furnace, and calcined at 400 °C for 2 hours at a heating rate of 6 °C / min under air atmosphere, then cooled to room temperature, and calcined again at 650 °C for 7.5 hours at a heating rate of 6 °C / min under a flow rate of 50 sccm and an atmosphere of 5% H2 + 95% Ar; after the reaction is completed, take out the product, wash it twice with deionized water and then twice with anhydrous ethanol, and dry it in a vacuum oven at 60 °C to obtain the cerium-based sub-nanocrystalline electrocatalyst, with ICP analysis showing that Ce accounts for 25.6% of the total mass.

[0028] Example 3 This invention provides a method for preparing a cerium-based subnanocrystalline electrocatalyst, specifically including the following steps; (1) Synthesis of precursor magnesium oxide nanorods Weigh a certain amount of MgSO4 and dissolve it in deionized water to prepare a 1M MgSO4 aqueous solution, then use 1M NH3... Titrate with H2O until the pH value equals 10; transfer the titrated solution to a hydrothermal reactor, then transfer the hydrothermal reactor to an oven and react at 240℃ for 24 hours; after the reaction is complete, cool to room temperature, filter out the precipitate in the liner and wash it, wash it twice with deionized water, then wash it twice with anhydrous ethanol, and then wash it once with deionized water. Place the washed precipitate in a vacuum oven at 60℃ to dry, and the precursor is obtained.

[0029] (2) Preparation of the carrier The dried precursor was taken out and weighed 500 mg. It was then ground thoroughly in an agate mortar. The ground powder was spread evenly in a corundum crucible and transferred to a vacuum tube furnace. The atmosphere was introduced into the tube furnace with 50 sccm of methane mixed with 500 sccm of argon. The temperature was increased from room temperature to 1100℃ at a heating rate of 10℃ / min and calcined for 10 minutes. Then it was cooled to room temperature. After the reaction was completed, the product was taken out and etched with 1M HF for 30 h. The etched product was washed 5 times with deionized water and then dried in a vacuum oven to obtain carbon nanocarriers. (3) Preparation of cerium-based sub-nanocrystalline electrocatalysts Take out the dried carbon nanocarrier, weigh 500 mg, disperse it in 100 mL of anhydrous ethanol, then weigh 200 mg of cerium chloride and dissolve it in the above solution; stir the solution for two days and filter it, then transfer the filtered solid to a vacuum oven to dry; the powder obtained after vacuum drying is placed in a corundum crucible and leveled, then transferred to a vacuum tube furnace, and calcined at 500 °C for 2 hours at a heating rate of 10 °C / min under air atmosphere, then cooled to room temperature, and calcined again at 800 °C for 10 hours at a heating rate of 100 sccm under a 5% H2 + 95% Ar atmosphere, from room temperature to 100 °C; after the reaction is completed, take out the product, wash it twice with deionized water and then twice with anhydrous ethanol, and dry it in a vacuum oven at 60 °C to obtain the cerium-based sub-nanocrystalline electrocatalyst, with ICP analysis showing that Ce accounts for 24.6% of the total mass.

[0030] Example 4 This invention provides a method for preparing a cerium-based subnanocrystalline electrocatalyst, specifically including the following steps; (1) Synthesis of precursor magnesium oxide nanorods Weigh a certain amount of MgSO4 and dissolve it in deionized water to prepare a 0.5M MgSO4 aqueous solution, then use 1M NH3. Titrate with H2O until the pH value equals 8; transfer the titrated solution to a hydrothermal reactor, then transfer the hydrothermal reactor to an oven and react at 160℃ for 12 hours; after the reaction is complete, cool to room temperature, filter out the precipitate in the liner and wash it, wash it twice with deionized water, then wash it twice with anhydrous ethanol, and then wash it once with deionized water. Place the washed precipitate in a vacuum oven at 60℃ to dry, and the precursor is obtained.

[0031] (2) Preparation of the carrier The dried precursor was taken out and weighed 100 mg. It was then ground thoroughly in an agate mortar. The ground powder was spread evenly in a corundum crucible and transferred to a vacuum tube furnace. The furnace was purged with a mixture of 10 sccm methane and 100 sccm argon. The temperature was increased from room temperature to 900℃ for 2 minutes at a rate of 2℃ / min, and then cooled to room temperature. After the reaction was completed, the product was taken out and etched with 1M HF for 10 hours. The etched product was washed 5 times with deionized water and then dried in a vacuum oven to obtain carbon nanocarriers. (3) Preparation of cerium-based sub-nanocrystalline electrocatalysts Take out the dried carbon nanocarrier, weigh 100 mg, disperse it in 20 mL of anhydrous ethanol, then weigh 50 mg of cerium sulfate and dissolve it in the above solution; stir the solution for two days and filter it, then transfer the filtered solid to a vacuum oven to dry; place the powder obtained after vacuum drying into an alumina crucible and spread it evenly, transfer it to a vacuum tube furnace, and calcine it at a heating rate of 2 °C / min from room temperature to 300 °C for 2 hours in an air atmosphere, then cool it to room temperature, and calcine it again at a heating rate of 2 °C / min from room temperature to 500 °C for 5 hours in an atmosphere of 5% H2 + 95% Ar at a flow rate of 20 sccm; after the reaction is completed, take out the product, wash it twice with deionized water and then twice with anhydrous ethanol, and dry it in a vacuum oven at 60 °C to obtain the cerium-based sub-nanocrystalline electrocatalyst, which was found to contain 28.1% Ce by ICP.

[0032] Example 5 This invention provides a method for preparing a cerium-based subnanocrystalline electrocatalyst, specifically including the following steps; (1) Synthesis of precursor magnesium oxide nanorods Weigh a certain amount of MgSO4 and dissolve it in deionized water to prepare a 0.75M MgSO4 aqueous solution, then use 1M NH3. Titrate with H2O until the pH value equals 9; transfer the titrated solution to a hydrothermal reactor, then transfer the hydrothermal reactor to an oven and react at 200℃ for 18 hours; after the reaction is complete, cool to room temperature, filter out the precipitate in the liner and wash it, wash it twice with deionized water, then wash it twice with anhydrous ethanol, and then wash it once with deionized water. Place the washed precipitate in a vacuum oven at 60℃ to dry, and the precursor is obtained.

[0033] (2) Preparation of the carrier The dried precursor was taken out and weighed 300 mg. It was then ground thoroughly in an agate mortar. The ground powder was spread evenly in a corundum crucible and transferred to a vacuum tube furnace. The atmosphere was introduced into the tube furnace with a mixture of 30 sccm methane and 300 sccm argon. The temperature was increased from room temperature to 1000℃ at a rate of 6℃ / min and calcined for 6 minutes. Then it was cooled to room temperature. After the reaction was completed, the product was taken out and etched with 1M HF for 20 hours. The etched product was washed 5 times with deionized water and then dried in a vacuum oven to obtain carbon nanocarriers. (3) Preparation of cerium-based sub-nanocrystalline electrocatalysts Take out the dried carbon nanocarrier, weigh 300 mg, disperse it in 60 mL of anhydrous ethanol, then weigh 125 mg of cerium sulfate and dissolve it in the above solution; stir the solution for two days and filter it, then transfer the filtered solid to a vacuum oven to dry; the powder obtained after vacuum drying is placed in an alumina crucible and spread out, then transferred to a vacuum tube furnace, and calcined at 400 °C for 2 hours at a heating rate of 6 °C / min under air atmosphere, then cooled to room temperature, and calcined again at 650 °C for 7.5 hours at a heating rate of 6 °C / min under a flow rate of 100 sccm and an atmosphere of 5% H2 + 95% Ar, from room temperature; after the reaction is completed, take out the product, wash it twice with deionized water and then twice with anhydrous ethanol, and dry it in a vacuum oven at 60 °C to obtain the cerium-based sub-nanocrystalline electrocatalyst, with ICP analysis showing that Ce accounts for 19.8% of the total mass.

[0034] Example 6 This invention provides a method for preparing a cerium-based subnanocrystalline electrocatalyst, specifically including the following steps; (1) Synthesis of precursor magnesium oxide nanorods Weigh a certain amount of MgSO4 and dissolve it in deionized water to prepare a 1M MgSO4 aqueous solution, then use 1M NH3... Titrate with H2O until the pH value equals 10; transfer the titrated solution to a hydrothermal reactor, then transfer the hydrothermal reactor to an oven and react at 240℃ for 24 hours; after the reaction is complete, cool to room temperature, filter out the precipitate in the liner and wash it, wash it twice with deionized water, then wash it twice with anhydrous ethanol, and then wash it once with deionized water. Place the washed precipitate in a vacuum oven at 60℃ to dry, and the precursor is obtained.

[0035] (2) Preparation of the carrier The dried precursor was taken out and weighed 500 mg. It was then ground thoroughly in an agate mortar. The ground powder was spread evenly in a corundum crucible and transferred to a vacuum tube furnace. The atmosphere was introduced into the tube furnace with 50 sccm of methane mixed with 500 sccm of argon. The temperature was increased from room temperature to 1100℃ at a heating rate of 10℃ / min and calcined for 10 minutes. Then it was cooled to room temperature. After the reaction was completed, the product was taken out and etched with 1M HF for 30 h. The etched product was washed 5 times with deionized water and then dried in a vacuum oven to obtain carbon nanocarriers. (3) Preparation of cerium-based sub-nanocrystalline electrocatalysts Take out the dried carbon nanocarrier, weigh 500 mg, disperse it in 100 mL of anhydrous ethanol, then weigh 200 mg of cerium sulfate and dissolve it in the above solution; stir the solution for two days and filter it, then transfer the filtered solid to a vacuum oven to dry; the powder obtained after vacuum drying is placed in a corundum crucible and leveled, then transferred to a vacuum tube furnace, and calcined at 500 °C for 2 hours at a heating rate of 10 °C / min under air atmosphere, then cooled to room temperature, and calcined again at 800 °C for 10 hours at a heating rate of 10 °C / min under a flow rate of 50 sccm and an atmosphere of 5% H2 + 95% Ar, from room temperature; after the reaction is completed, take out the product, wash it twice with deionized water and then twice with anhydrous ethanol, and dry it in a vacuum oven at 60 °C to obtain the cerium-based sub-nanocrystalline electrocatalyst, with ICP analysis showing that Ce accounts for 20.0% of the total mass.

[0036] Example 7 This invention provides a method for preparing a cerium-based subnanocrystalline electrocatalyst, specifically including the following steps; (1) Synthesis of precursor magnesium oxide nanorods Weigh a certain amount of MgSO4 and dissolve it in deionized water to prepare a 0.6M MgSO4 aqueous solution, then use 1M NH3. Titrate with H2O until the pH value equals 8.5; transfer the titrated solution to a hydrothermal reactor, then transfer the hydrothermal reactor to an oven and react at 180°C for 16 hours; after the reaction is complete, cool to room temperature, filter out the precipitate from the liner and wash it, wash it twice with deionized water, then wash it twice with anhydrous ethanol, and then wash it once with deionized water. Place the washed precipitate in a vacuum oven at 60°C to dry, thus obtaining the precursor.

[0037] (2) Preparation of the carrier The dried precursor was taken out and weighed 200 mg. It was then ground thoroughly in an agate mortar. The ground powder was spread evenly in a corundum crucible and transferred to a vacuum tube furnace. The furnace was purged with a mixture of 20 sccm methane and 200 sccm argon. The temperature was increased from room temperature to 950°C at a rate of 4°C / min and calcined for 4 minutes. The furnace was then cooled to room temperature. After the reaction was completed, the product was taken out and etched with 1 M HF for 15 hours. The etched product was washed five times with deionized water and then dried in a vacuum oven to obtain carbon nanocarriers. (3) Preparation of cerium-based sub-nanocrystalline electrocatalysts Take out the dried carbon nanocarrier, weigh 200 mg, disperse it in 40 mL of anhydrous ethanol, then weigh 80 mg of cerium nitrate and dissolve it in the above solution; stir the solution for two days and filter it, then transfer the filtered solid to a vacuum oven to dry; the powder obtained after vacuum drying is placed in an alumina crucible and spread out, then transferred to a vacuum tube furnace, and calcined at 350 °C for 2 hours at a heating rate of 4 °C / min under air atmosphere, then cooled to room temperature, and calcined again at 550 °C for 6 hours at a heating rate of 4 °C / min under a flow rate of 100 sccm and an atmosphere of 5% H2 + 95% Ar, from room temperature to 550 °C; after the reaction is completed, take out the product, wash it twice with deionized water and then twice with anhydrous ethanol, and dry it in a vacuum oven at 60 °C to obtain the cerium-based sub-nanocrystalline electrocatalyst, with ICP analysis showing that Ce accounts for 25.2% of the total mass.

[0038] Example 8 This invention provides a method for preparing a cerium-based subnanocrystalline electrocatalyst, specifically including the following steps; (1) Synthesis of precursor magnesium oxide nanorods Weigh a certain amount of MgSO4 and dissolve it in deionized water to prepare a 0.9M MgSO4 aqueous solution, then use 1M NH3. Titrate with H2O until the pH value equals 9.5; transfer the titrated solution to a hydrothermal reactor, then transfer the hydrothermal reactor to an oven and react at 220℃ for 22 hours; after the reaction is complete, cool to room temperature, filter out the precipitate in the liner and wash it, wash it twice with deionized water, then wash it twice with anhydrous ethanol, and then wash it once with deionized water. Place the washed precipitate in a vacuum oven at 60℃ to dry, thus obtaining the precursor.

[0039] (2) Preparation of the carrier The dried precursor was taken out and weighed 400 mg. It was then ground thoroughly in an agate mortar. The ground powder was spread evenly in a corundum crucible and transferred to a vacuum tube furnace. The atmosphere was introduced into the tube furnace with a mixture of 40 sccm methane and 400 sccm argon. The temperature was increased from room temperature to 1050℃ at a rate of 8℃ / min and calcined for 8 minutes. Then it was cooled to room temperature. After the reaction was completed, the product was taken out and etched with 1M HF for 25 hours. The etched product was washed 5 times with deionized water and then dried in a vacuum oven to obtain carbon nanocarriers. (3) Preparation of cerium-based sub-nanocrystalline electrocatalysts 400 mg of dried carbon nanocarrier was weighed and dispersed in 80 mL of anhydrous ethanol. Then, 180 mg of cerium nitrate was weighed and dissolved in the above solution. After stirring the solution for two days, it was filtered. The filtered solid was transferred to a vacuum oven for drying. The powder obtained after vacuum drying was placed in an alumina crucible and spread evenly. It was then transferred to a vacuum tube furnace and calcined at 450 °C for 2 hours at a heating rate of 8 °C / min under air atmosphere. After cooling to room temperature, it was calcined again at 750 °C for 9 hours at a heating rate of 4 °C / min under a flow rate of 20 sccm and an atmosphere of 5% H2 + 95% Ar. After the reaction was completed, the product was taken out, washed twice with deionized water and then twice with anhydrous ethanol. It was then dried in a vacuum oven at 60 °C to obtain the cerium-based sub-nanocrystalline electrocatalyst. ICP analysis showed that Ce accounted for 22.3% of the total mass.

[0040] Example 9 This invention provides a method for preparing a cerium-based subnanocrystalline electrocatalyst, specifically including the following steps; (1) Synthesis of precursor magnesium oxide nanorods Weigh a certain amount of MgSO4 and dissolve it in deionized water to prepare a 1.0M MgSO4 aqueous solution, then use 1M NH3. Titrate with H2O until the pH value equals 10; transfer the titrated solution to a hydrothermal reactor, then transfer the hydrothermal reactor to an oven and react at 240℃ for 24 hours; after the reaction is complete, cool to room temperature, filter out the precipitate in the liner and wash it, wash it twice with deionized water, then wash it twice with anhydrous ethanol, and then wash it once with deionized water. Place the washed precipitate in a vacuum oven at 60℃ to dry, and the precursor is obtained.

[0041] (2) Preparation of the carrier The dried precursor was taken out and weighed 500 mg. It was then ground thoroughly in an agate mortar. The ground powder was spread evenly in a corundum crucible and transferred to a vacuum tube furnace. The atmosphere was introduced into the tube furnace with 50 sccm of methane mixed with 500 sccm of argon. The temperature was increased from room temperature to 1100℃ at a heating rate of 10℃ / min and calcined for 10 minutes. Then it was cooled to room temperature. After the reaction was completed, the product was taken out and etched with 1M HF for 30 h. The etched product was washed 5 times with deionized water and then dried in a vacuum oven to obtain carbon nanocarriers. (3) Preparation of cerium-based sub-nanocrystalline electrocatalysts Take out the dried carbon nanocarrier, weigh 500 mg, disperse it in 80 mL of anhydrous ethanol, then weigh 200 mg of cerium nitrate and dissolve it in the above solution; stir the solution for two days and filter it, then transfer the filtered solid to a vacuum oven to dry; the powder obtained after vacuum drying is placed in a corundum crucible and spread out, then transferred to a vacuum tube furnace, and calcined at 500 °C for 2 hours at a heating rate of 10 °C / min under air atmosphere, then cooled to room temperature, and calcined again at 800 °C for 10 hours at a heating rate of 10 °C / min under a flow rate of 50 sccm and an atmosphere of 5% H2 + 95% Ar; after the reaction is completed, take out the product, wash it twice with deionized water and then twice with anhydrous ethanol, and dry it in a vacuum oven at 60 °C to obtain the cerium-based sub-nanocrystalline electrocatalyst, with ICP analysis showing that Ce accounts for 24.0% of the total mass.

[0042] in, Figure 1 This is a STEM image of a cerium-based sub-nano cluster from Example 5 of the present invention. As can be seen from the image, the average grain size is 1 nm. Figure 2 The image shows an X-ray diffraction pattern of a cerium-based sub-nano cluster in Example 5 of this invention. As can be seen from the image, it exhibits broadened diffraction peaks of an ultra-small crystal form, proving that the synthesized crystal is a sub-nano crystal.

[0043] Application examples The catalytic performance of the cerium-based subnanocrystalline electrodes prepared in Examples 1-9 was tested using the following methods: The cerium-based subnanocrystalline materials prepared in Examples 1-9 were dispersed in 200 μL of isopropanol to form a dispersion. A slurry was prepared by adding 0.5 μL of Nafion 117 membrane solution to every 200 μL of dispersion. The slurry was then dispersed in a concentration of 1 cm³. 2 The titanium fiber felt electrode was fabricated by spraying 200 microliters of slurry onto it, resulting in a titanium fiber felt electrode with an effective area of ​​1 cm * 1 cm loaded with catalyst. HMF was dissolved in 1M KOH aqueous solution at a concentration of 500 mmol / L as the cathode electrolyte and 1M KOH aqueous solution as the anolyte. 25 mL of electrolyte was added to both the cathode and anolyte. Electrochemical tests were performed in a commercial H-type electrolytic cell using a platinum sheet electrode as the counter electrode, a mercury oxide electrode as the reference electrode, and a titanium fiber felt electrode with a catalyst supported on a 1 cm × 1 cm effective area as the working electrode. Potentiostatic electrolysis was performed at a potential of (-0.6)–(-1.0) V (vs. RHE). 10 μL of electrolyte was taken, and 10 μL of 1M HCl solution was added to neutralize the KOH in the electrolyte. Then, 180 μL of ultrapure water was added to dilute it 9 times. The solution was filtered through a 0.22 μm aqueous filter membrane and then placed in a liquid chromatography vial for qualitative and quantitative analysis. The injection volume was 10 μL, and the detection method was separation using an organic acid column at 40 °C with a 5 mM mobile phase. Elute with H2SO4 aqueous solution at a flow rate of 0.6 ml / min; Figure 3 Here is the liquid chromatogram of the electrocatalytic substrate HMF. Figure 4 Liquid chromatogram of the electrocatalytic product 1,6-hexanediol. Figure 5 The figure shows the liquid chromatograms of the electrolyte after electrolysis at different potentials for the electrocatalytic reduction of HMF to 1,6-hexanediol using cerium-based subnanocrystalline materials of the present invention. The substrate in the reaction is HMF, the product is 1,6-hexanediol, and the byproduct is 1,2,6-hexanetriol. As can be seen from the figure, cerium-based subnanocrystalline materials can be used as electrocatalytic materials for the reduction of HMF to 1,6-hexanediol, with 1,2,6-hexanetriol as a byproduct.

[0044] Table 1 shows the Faradaic efficiency (FE) of the catalysts synthesized in Examples 1-9 for the electrocatalytic production of 1,6-hexanediol from HMF; Example 5 is the optimal scheme, with an FE of 84.6% for 1,6-hexanediol and 12.8% for 1,2,6-hexanetriol at 500 mmol / L and a potential of -0.6 V vs. RHE.

[0045] Table 1. Faraday efficiency results of catalysts used in Examples 1-9 for electrocatalysis

[0046]

[0047] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A cerium-based sub-nanocrystalline electrocatalyst, characterized in that, The electrocatalyst is carbon nanocarrier loaded cerium-based sub-nanocrystal, wherein the Ce of the cerium-based sub-nanocrystal accounts for 15-30% of the mass of the electrocatalyst.

2. The cerium-based sub-nanocrystalline electrocatalyst according to claim 1, wherein, The preparation method of the carbon nanocarrier is: 1) Preparation of a precursor: after adjusting the pH value of a MgSO4 aqueous solution to 8-10, reacting at 160-240℃ for 12-24h, and obtaining a precipitate after the reaction, the precipitate is the precursor; 2) After grinding the precursor, calcining at 900-1100℃ for 2-10min in a carbon-containing atmosphere, and etching the product with HF, the carbon nanocarrier is obtained.

3. The cerium-based sub-nanocrystalline electrocatalyst according to claim 2, wherein the cerium-based sub-nanocrystalline electrocatalyst is CeO2. In step 1), the concentration of the MgSO4 aqueous solution is 0.5-1.0M; the pH value is adjusted by using NH4·H2O; In step 2), the carbon-containing atmosphere is methane or gaseous acetonitrile; the heating rate of calcination is 2-10℃ / min; the HF etching is etching with 1M HF for 10-30h.

4. The cerium-based sub-nanocrystalline electrocatalyst according to claim 3, wherein the cerium-based sub-nanocrystalline electrocatalyst is CeO2. In step 2), the carbon-containing atmosphere is 10-50sccm of methane or gaseous acetonitrile mixed with 100-500sccm of argon.

5. The method for preparing a cerium-based subnanocrystalline electrocatalyst according to any one of claims 1-4, characterized in that, The method comprises the following specific steps: The carbon nanocarrier is dispersed in anhydrous ethanol, then cerium salt is added and ultrasonic treatment is performed, and after the treatment is completed, the precipitate is calcined in an air atmosphere and an H2 / Ar atmosphere in sequence, thereby obtaining a cerium-based sub-nanocrystal electrocatalyst.

6. The method for preparing a cerium-based subnanocrystalline electrocatalyst according to claim 5, characterized in that, The mass-volume ratio of the carbon nanocarrier, anhydrous ethanol and cerium salt is 100-500mg:20-100mL:50-200mg; The cerium salt is at least one of cerium chloride, cerium sulfate and cerium nitrate.

7. The method for preparing a cerium-based subnanocrystalline electrocatalyst according to claim 5, characterized in that, The calcination in the air atmosphere is at 300-500℃ for 2h, and the calcination in the H2 / Ar atmosphere is at 500-800℃ for 5-10h.

8. The method for preparing a cerium-based subnanocrystalline electrocatalyst according to claim 5, characterized in that, The ultrasonic treatment time is 48-96h; the heating rate of calcination is 2-10℃ / min; The volume ratio of H2 / Ar is 5:95, and the flow rate of H2 / Ar is 20-100sccm.

9. Application of the cerium-based sub-nanocrystal electrocatalyst according to any one of claims 1-4 or the cerium-based sub-nanocrystal electrocatalyst prepared by the method according to any one of claims 5-8 in electrocatalytic reduction of HMF to produce 1,6-hexanediol.

10. Use according to claim 9, characterized in that, Specifically, the cerium-based sub-nanocrystal electrocatalyst is used as a working electrode, a platinum sheet is used as a counter electrode, Hg / HgO is used as a reference electrode, a KOH solution is used as an electrolyte, HMF is added to the cathode electrolyte, and a constant voltage electrolysis method is used.

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