Hollow cobalt phosphide catalyst for oxidation of 5-hydroxymethylfurfural and preparation of hollow cobalt phosphide catalyst

Abstract

The invention provides a hollow cobalt phosphide catalyst for oxidation of 5-hydroxymethylfurfural and preparation of the hollow cobalt phosphide catalyst. A preparation method comprises the following steps: (1) dispersing ZIF-67 in an ethanol-water solution for reflux heating etching; and (2) carrying out low-temperature phosphorization on the ZIF-67 (at) Co (OH) 2 to obtain the hollow cobalt phosphide catalyst. The MOF-derived hollow cobalt phosphide catalyst disclosed by the invention is used for electrocatalytic oxidation of 5-hydroxymethylfurfural into 2, 5-furandicarboxylic acid, has a hollow structure, fully exposes Co sites, induces conversion to Co < 3 + > and Co < 4 + > to a greater extent, remarkably improves catalytic activity and promotes reaction kinetics. The synthesis method disclosed by the invention is simple, convenient, green and environment-friendly, solves the problem that the whole catalytic efficiency is limited due to the fact that phase change only occurs at Co sites on the surface and the interior is not fully utilized due to a compact microstructure of a traditional cobalt-based nano material, and has a good application prospect.

Description

Technical Field

[0001] The invention belongs to the technical field of new energy material synthesis and electrochemistry, and particularly relates to a hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation and a preparation thereof. Background Art

[0002] Transition metal phosphides (TMPs) have been widely studied due to their advantages such as high conductivity and tunable electronic structure. Among the many transition metal phosphides, cobalt phosphide (CoP) stands out due to its unique electronic structure. CoP is a compound with intrinsic metal-like conductivity, in which phosphorus atoms are doped in the metal lattice. This structural feature is conducive to improving charge transfer ability and exhibits good bifunctional electrocatalytic activity for the 5-hydroxymethylfurfural oxidation reaction (HMFOR) and hydrogen evolution reaction (HER). When applied to the HMFOR / / HER electrolysis system, it has unlimited potential to achieve dual optimization of energy efficiency and product value.

[0003] Metal organic framework (MOF) materials are excellent precursors for the synthesis of cobalt phosphide due to their significant advantages such as highly controllable composition and structure. Existing studies have shown that CoOOH (Co 3+ ) and CoOOHx(Co 4 + ) is considered the true active species in the catalysis of HMFOR. Patents CN105688958A and CN109411736A, for example, produce CoP by phosphating ZIF-67. However, due to the limitations of the dense microstructure, only surface cobalt sites are activated, while internal sites are underutilized, resulting in a limited phase transition and constrained overall catalytic efficiency. Therefore, optimizing the structure of cobalt-based nanomaterials to promote more efficient conversion and, in turn, the formation of more active species, is an effective strategy for improving catalytic system performance. Summary of the Invention

[0004] The purpose of the present invention is to provide a hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation and its preparation, so as to solve the problem mentioned in the background art that the traditional cobalt-based nanomaterials have a dense microstructure that restricts the overall catalytic efficiency.

[0005] To achieve the above object, the present invention provides a method for preparing a hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation, the specific steps of which are as follows:

[0006] (1) Pour the methanol solution of cobalt salt into the methanol solution of 2-methylimidazole, stir rapidly and then allow to stand for aging, then centrifuge and rinse and dry to obtain a ZIF-67 precursor;

[0007] (2) The ZIF-67 precursor obtained in step (1) is uniformly dispersed in an ethanol-water mixed solution, placed in an oil bath, refluxed and continuously stirred, cooled to room temperature, and then centrifuged and rinsed and dried to obtain a ZIF-67@Co(OH)2 intermediate;

[0008] (3) The ZIF-67@Co(OH)2 intermediate obtained in step (2) is placed in a tubular electric furnace and phosphated in an inert gas atmosphere with sodium hypophosphite monohydrate as a phosphorus source to obtain a black powder hollow structure cobalt phosphide H-CoP.

[0009] Preferably, in step (1), the cobalt salt is cobalt nitrate hexahydrate.

[0010] Preferably, in step (2), the volume ratio of ethanol to water in the ethanol-water mixed solution is (1-5): (4-0).

[0011] Preferably, in step (2), the reflux heating temperature is 65-105°C.

[0012] Preferably, in step (2), the reflux heating time is 5 to 50 minutes.

[0013] Preferably, in step (2), the rinsing of the ZIF-67@Co(OH)2 intermediate is performed using ethanol, which serves to exchange water to prevent the ZIF-67 precursor from being further etched.

[0014] Preferably, in step (3), the mass ratio of the ZIF-67@Co(OH)2 intermediate to sodium hypophosphite monohydrate is 1:(10-15); and the inert gas is argon or nitrogen.

[0015] Preferably, in step (3), the temperature of the phosphating treatment is 250-400° C., the time of the phosphating treatment is 1-5 h, and the heating rate is 2-5° C. / min.

[0016] The present invention also provides a hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation. The hollow cobalt phosphide catalyst is prepared by the above-mentioned preparation method of the hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation.

[0017] Compared with the prior art, the present invention has the following beneficial effects:

[0018] (1) Based on the highly tunable composition and structure of MOF materials, hollow cobalt phosphide H-CoP was prepared using ZIF-67 as a precursor through simple heating reflow etching and low-temperature phosphating. This method not only inherits the structural stability of the MOF framework but also introduces a hollow structure to improve mass transfer efficiency. The preparation method is simple and environmentally friendly, and the prepared hollow cobalt phosphide H-CoP exhibits excellent HMFOR catalytic performance.

[0019] (2) Hollow cobalt phosphide was prepared based on the hollow structure engineering of the Kirkendall effect. Compared with traditional cobalt-based nanomaterials, the hollow structure provides a larger specific surface area, which is conducive to fully exposing Co sites and inducing their conversion to high-valent cobalt species to a greater extent, significantly improving the electrocatalytic activity of HMFOR and promoting the oxidation reaction kinetics of catalytic HMF.

[0020] In addition to the above-described objects, features and advantages, the present invention has other objects, features and advantages. The present invention is further described in detail below. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] The accompanying drawings, which constitute part of this application, are intended to provide a further understanding of the present invention. The exemplary embodiments of the present invention and their descriptions are intended to explain the present invention and do not constitute an undue limitation of the present invention. In the accompanying drawings:

[0022] Figure 1 The scanning electron microscope image and transmission electron microscope image of the 1#H-CoP catalyst prepared in Example 1;

[0023] Figure 2 The X-ray powder diffraction patterns of the 1#H-CoP catalyst prepared in Example 1 and the 3#S-CoP catalyst prepared in Example 3 are shown;

[0024] Figure 3 Linear sweep voltammetry curves of the H-CoP catalyst #1 prepared in Example 1 in 1.0 M KOH electrolyte with or without 50 mM HMF;

[0025] Figure 4 Linear sweep voltammetry curves of the 3# S-CoP catalyst prepared in Example 3 in 1.0 M KOH electrolyte with or without 50 mM HMF;

[0026] Figure 5 The single potentiostat chronoamperometry curve and single potentiostat cumulative charge method curve of the 1#H-CoP catalyst prepared in Example 1 in 10 mL of 1.0 M KOH electrolyte containing 10 mM HMF at a constant potential of 1.45 V;

[0027] Figure 6This is a graph showing the concentration variation of each substance in the electrolyte as the charge accumulation value changes when the 1#H-CoP catalyst prepared in Example 1 is in 10 mL of 1.0 M KOH electrolyte containing 10 mM HMF and the constant potential is 1.45 V;

[0028] Figure 7 The electricity consumed by the 1#H-CoP catalyst prepared in Example 1 as a bifunctional catalyst to produce hydrogen in HMFOR / / HER and traditional water electrolysis system OER / / HER respectively. DETAILED DESCRIPTION

[0029] The embodiments of the present invention are described in detail below. The specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0030] Example 1

[0031] This embodiment provides a method for preparing a MOF-derived hollow cobalt phosphide catalyst, comprising the following steps:

[0032] 4.36 g of cobalt nitrate hexahydrate was dispersed in 375 mL of methanol to form a cobalt nitrate solution. 4.92 g of 2-methylimidazole was evenly dispersed in 375 mL of methanol to form a 2-methylimidazole solution. The cobalt nitrate solution was then quickly poured into the 2-methylimidazole solution and stirred at 40 rpm for 2 minutes to produce a purple mixed solution. The solution was then allowed to stand at room temperature for 24 hours before centrifugation at 4000 rpm for 5 minutes to recover a purple solid sample. The sample was washed three times with methanol and dried overnight in a 50°C electric constant-temperature forced-air drying oven. The resulting purple solid powder was the ZIF-67 precursor. 0.08 g of the ZIF-67 precursor was evenly dispersed in 160 mL of ethanol. 20 mL of water was then added and stirred at 40 rpm for 10 seconds to homogenize the solution. The mixture was then heated to reflux in an oil bath at 95°C with continuous stirring at 15 rpm for 15 minutes. After cooling to room temperature, the sample was centrifuged at 4000 rpm for 5 minutes to recover a purple-black solid sample, which was then washed three times with ethanol and dried overnight in an electric constant-temperature forced-air drying oven at 50°C. The resulting purple-black solid powder sample was the ZIF-67@Co(OH)2 intermediate. 0.04 g of the ZIF-67@Co(OH)2 intermediate and 0.4 g of sodium hypophosphite monohydrate were placed in two quartz boats. The quartz boat containing NaH2PO2·H2O was placed upstream of the airflow, while the quartz boat containing ZIF-67@Co(OH)2 was placed downstream. The distance between the two samples was approximately 2.5 cm. A tubular furnace was first purged with Ar at room temperature for 30 minutes, then heated to 300°C at a rate of 2°C / min and maintained at this temperature for 1 hour under a continuous Ar atmosphere. The tubular furnace was allowed to cool naturally to room temperature. The resulting black solid powder sample was the hollow cobalt phosphide catalyst H-CoP.

[0033] Figure 1 The scanning electron microscope image and transmission electron microscope image of the 1#H-CoP catalyst prepared in this Example 1 can clearly be seen from the scanning electron microscope image that the outer surface of the nanosheet 1#H-CoP is rough and disordered granular matter is formed; according to the transmission electron microscope image, it can be clearly seen that 1#H-CoP has an internal hollow structure and a large amount of disordered granular matter exists.

[0034] Example 2

[0035] This embodiment provides a method for preparing a MOF-derived hollow cobalt phosphide catalyst, comprising the following steps:

[0036] 4.36 g of cobalt nitrate hexahydrate was dispersed in 375 mL of methanol to form a cobalt nitrate solution. 4.92 g of 2-methylimidazole was evenly dispersed in 375 mL of methanol to form a 2-methylimidazole solution. The cobalt nitrate solution was then quickly poured into the 2-methylimidazole solution and stirred at 40 rpm for 2 minutes to produce a purple mixed solution. The solution was then allowed to stand at room temperature for 24 hours before centrifugation at 4000 rpm for 5 minutes to recover a purple solid sample. The sample was washed three times with methanol and dried overnight in a 50°C electric constant-temperature forced-air drying oven. The resulting purple solid powder was the ZIF-67 precursor. 0.08 g of the ZIF-67 precursor was evenly dispersed in 160 mL of ethanol. 20 mL of water was then added and stirred at 40 rpm for 10 seconds to homogenize the solution. The mixture was then heated to reflux in an oil bath at 95°C with continuous stirring at 15 rpm for 15 minutes. After cooling to room temperature, the sample was centrifuged at 4000 rpm for 5 minutes to recover a purple-black solid sample, which was then washed three times with ethanol and dried overnight in an electric constant-temperature forced-air drying oven at 50°C. The resulting purple-black solid powder sample was the ZIF-67@Co(OH)2 intermediate. 0.04 g of the ZIF-67@Co(OH)2 intermediate and 0.4 g of sodium hypophosphite monohydrate were placed in two quartz boats. The quartz boat containing NaH2PO2·H2O was placed upstream of the airflow, while the quartz boat containing ZIF-67@Co(OH)2 was placed downstream. The distance between the two samples was approximately 2.5 cm. A tubular furnace was first purged with Ar at room temperature for 30 minutes, then heated at a rate of 2°C / min to 300°C and maintained at this temperature for 2 hours under a continuous Ar atmosphere. The tubular furnace was allowed to cool naturally to room temperature. The resulting black solid powder sample was the hollow cobalt phosphide catalyst H-CoP.

[0037] Example 3

[0038] This embodiment provides a method for preparing a MOF-derived solid cobalt phosphide catalyst, comprising the following steps:

[0039] 4.36 g of cobalt nitrate hexahydrate was dispersed in 375 mL of methanol to form a cobalt nitrate solution. 4.92 g of 2-methylimidazole was evenly dispersed in 375 mL of methanol to form a 2-methylimidazole solution. The cobalt nitrate solution was then rapidly poured into the 2-methylimidazole solution and stirred at 40 rpm for 2 minutes to produce a purple mixed solution. The mixture was then allowed to stand at room temperature for 24 hours before centrifugation at 4000 rpm for 5 minutes to recover a purple solid sample. The sample was washed three times with methanol and dried overnight in a 50°C electric constant-temperature forced-air drying oven. The resulting purple solid powder sample was the ZIF-67 precursor. 0.04 g of the ZIF-67 precursor and 0.4 g of sodium hypophosphite monohydrate were placed in two separate quartz boats. The quartz boat containing NaH2PO2·H2O was placed upstream of the airflow, while the quartz boat containing ZIF-67 was placed downstream. The distance between the two samples was approximately 2.5 cm. The tubular furnace was first purged with Ar at room temperature for 30 minutes. The temperature was then raised to 300°C at a rate of 2°C / min and maintained at this temperature under a continuous Ar atmosphere for 1 hour. The tubular furnace was then allowed to cool naturally to room temperature. The resulting black solid powder sample was the solid cobalt phosphide catalyst S-CoP.

[0040] Figure 2 The X-ray powder diffraction patterns of the 1#H-CoP catalyst prepared in Example 1 and the 3#S-CoP catalyst prepared in Example 3 show that both the 1#H-CoP catalyst and the 3#S-CoP catalyst match the characteristic diffraction peaks of CoP, indicating that the main phases of the 1#H-CoP catalyst and the 3#S-CoP catalyst are CoP.

[0041] Example 4

[0042] The HMFOR, OER, and HER catalytic performance of the 1#H-CoP catalyst prepared in Example 1 or the 3#S-CoP catalyst prepared in Example 3 were tested in a typical three-electrode system. The working electrode was composed of a glassy carbon electrode sandwiching a raw carbon cloth loaded with the catalyst, the counter electrode was a stone mill rod electrode, and the reference electrode was filled with 1 mol L -1 (1.0M) KOH solution of mercury / mercury oxide (Hg / HgO) electrode. The potential E of the reference electrode collected during the test is converted to Reaction Converted to the potential E relative to the reversible hydrogen electrode (RHE) RHE :

[0043] In the above formula, R is the ideal gas constant (8.31432 J·K -1 ·mol -1), T is the ambient temperature during the test (298.15K at 25°C), F is the Faraday constant (96485C mol -1 ), pH of 1.0M KOH is 13.8, E Θ (Hg / HgO) is the standard electrode potential of the Hg / HgO electrode, which is 0.098 V.

[0044] The HER / / HMFOR coupling system test uses a two-electrode system. The cathode and anode are both glassy carbon electrodes sandwiching raw carbon cloth loaded with catalysts, and the catalysts used for the cathode and anode are the same. The reference electrode is filled with 1.0 mol L -1 Mercury / mercury oxide (Hg / HgO) electrode in (1.0 M) KOH solution.

[0045] The working electrode is composed of a glassy carbon electrode sandwiched between raw carbon cloth loaded with catalyst. Take 400 μL of 5wt% Nafion TM The perfluororesin solution was diluted to 8 mL with ethanol and mixed evenly to form a catalyst fixative. 1 mg of the 1#H-CoP catalyst prepared in Example 1 or the 3#S-CoP catalyst prepared in Example 3 was accurately weighed and evenly dispersed in 250 μL of the catalyst fixative by ultrasonication. The catalyst dispersion was evenly applied to a 1×1 cm -2 The raw carbon cloth surface is coated with an infrared baking lamp to accelerate the drying process; the raw carbon cloth loaded with the catalyst is fixed on the glassy carbon electrode.

[0046] Electrocatalytic HMFOR and HER products of H-CoP catalyst #1, prepared in Example 1, were detected using an H-type electrolytic cell: the anolyte was 10 mL of 1.0 M KOH containing 10 mM HMF, and the catholyte was 10 mL of 1.0 M KOH. Electrolysis was performed at a constant voltage of 1.45 V. At 10C charge accumulation intervals, 10 μL of the electrolyte was sampled from the anodic chamber, diluted and filtered, and then analyzed by a high-performance liquid chromatograph. 1 mL of gas was sampled from the cathodic chamber and analyzed by a gas chromatograph.

[0047] Figure 3 The linear sweep voltammetry curves of the 1#H-CoP catalyst prepared in Example 1 in 1.0 M KOH electrolyte with or without 50 mM HMF are shown. The LSV curves of the 1#H-CoP catalytic OER and HMFOR reached 10 mA cm -2 The required potentials for the current density are 1.26 and 1.50 V vs. RHE, respectively.

[0048] Figure 4The linear sweep voltammetry curves of the 3#S-CoP catalyst prepared in Example 3 in 1.0 M KOH electrolyte with or without 50 mM HMF are shown. The LSV curves of the 3#S-CoP catalytic OER and HMFOR reached 10 mA cm -2 The required potentials for the current density are 1.37 and 1.53 V vs. RHE, respectively.

[0049] Figure 5 The single potentiostat chronoamperometry curve and the single potentiostat cumulative charge method curve of the 1#H-CoP catalyst prepared in Example 1 were measured at a constant potential of 1.45V in 10mL of 1.0M KOH electrolyte containing 10mM HMF. The time taken for the 1#H-CoP to completely oxidize HMF to reach the theoretically required charge of 57.89C was approximately 19.55h.

[0050] Figure 6 The concentration of each substance in the electrolyte of the H-CoP catalyst #1 prepared in Example 1 is changed as the charge accumulation value changes in 10 mL of 1.0 M KOH electrolyte containing 10 mM HMF at a constant potential of 1.45 V. The conversion rate of HMF is 99.5%, while the yield of FDCA and the total FE are 98.6% and 97.5%, respectively.

[0051] Figure 7 The power consumed by the 1#H-CoP catalyst prepared in Example 1 as a bifunctional catalyst to produce hydrogen in HMFOR / / HER and conventional water electrolysis system OER / / HER, respectively. The 1#H-CoP catalyst as a bifunctional catalyst drives the current density of the HMFOR / / HER electrolysis system to reach 10 mA cm -2 Only about 3.59kWh of electricity is required per cubic meter of H2, which saves 10.25% energy compared to the traditional water electrolysis system OER / / HER (4.00kWh).

[0052] The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments, and the specific implementation of the present invention should not be considered to be limited to these descriptions. For those skilled in the art of the present invention, several simple deductions and substitutions can be made without departing from the concept of the present invention, and all of these should be considered to fall within the scope of protection of the present invention.

Claims

1. A method for preparing a hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation, characterized in that: The specific steps are as follows: (1) Pour the methanol solution of cobalt salt into the methanol solution of 2-methylimidazole, stir rapidly and then allow to stand for aging, then centrifuge and rinse and dry to obtain a ZIF-67 precursor; (2) The ZIF-67 precursor obtained in step (1) is uniformly dispersed in an ethanol-water mixed solution, placed in an oil bath, refluxed and continuously stirred, cooled to room temperature, and then centrifuged and rinsed and dried to obtain a ZIF-67@Co(OH)2 intermediate; (3) The ZIF-67@Co(OH)2 intermediate obtained in step (2) is placed in a tubular electric furnace and phosphated in an inert gas atmosphere with sodium hypophosphite monohydrate as a phosphorus source to obtain a black powder hollow structure cobalt phosphide H-CoP.

2. The preparation method of the hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation according to claim 1, wherein In step (1), the cobalt salt is cobalt nitrate hexahydrate.

3. The preparation method of the hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation according to claim 1, wherein In step (2), the volume ratio of ethanol to water in the ethanol-water mixed solution is (1-5): (4-0).

4. The preparation method of the hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation according to claim 1, wherein In step (2), the reflux heating temperature is 65-105°C.

5. The preparation method of the hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation according to claim 1, wherein In step (2), the reflux heating time is 5 to 50 minutes.

6. The preparation method of the hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation according to claim 1, wherein In step (2), the ZIF-67@Co(OH)2 intermediate is rinsed with ethanol to exchange water to prevent the ZIF-67 precursor from being further etched.

7. The preparation method of the hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation according to claim 1, wherein In step (3), the mass ratio of the ZIF-67@Co(OH)2 intermediate to sodium hypophosphite monohydrate is 1:(10-15); and the inert gas is argon or nitrogen.

8. The preparation method of the hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation according to claim 1, wherein In step (3), the temperature of the phosphating treatment is 250-400° C., the time of the phosphating treatment is 1-5 hours, and the heating rate is 2-5° C. / min.

9. A hollow cobalt phosphide catalyst for the oxidation of 5-hydroxymethylfurfural, characterized in that: The hollow cobalt phosphide catalyst is prepared by the preparation method of the hollow cobalt phosphide catalyst for 5-hydroxymethylfurfural oxidation according to any one of claims 1 to 8.

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