CN113889629A

CN113889629A - Preparation method of platinum-ruthenium alloy catalyst for fuel cell anode

Info

Publication number: CN113889629A
Application number: CN202111142280.6A
Authority: CN
Inventors: 邓翔; 裴晓东; 骆艳华
Original assignee: Sinosteel Nanjing New Material Research Institute Co Ltd
Current assignee: Sinosteel New Materials Co Ltd
Priority date: 2021-09-28
Filing date: 2021-09-28
Publication date: 2022-01-04

Abstract

The invention discloses a preparation method of a platinum-ruthenium alloy catalyst for a fuel cell anode, which comprises the following steps: preparing a metal salt solution by adopting a platinum salt solution and a ruthenium salt solution; adding a carbon carrier and an additive into the obtained metal salt solution, stirring, homogenizing and dispersing to obtain a reaction solution; placing the obtained reaction solution in a bubbling reaction kettle, introducing reaction gas containing hydrogen and carbon monoxide, and carrying out bubbling reduction reaction; and after the bubbling reduction reaction is finished, discharging the obtained reaction liquid from the reaction kettle, filtering, and drying a filter cake to obtain the platinum-ruthenium alloy catalyst. The method can solve the two problems that two noble metals are mixed inhomogeneously to form a phase-splitting structure or generate serious agglomeration inhomogeneously in the process of preparing the PtRu alloy catalyst by dry or wet reduction, and does not need a high-temperature roasting alloying step, thereby obviously improving the quality of the PtRu/C catalyst product and reducing the cost.

Description

Preparation method of platinum-ruthenium alloy catalyst for fuel cell anode

Technical Field

The invention relates to the technical field of catalyst preparation, in particular to a preparation method of a platinum-ruthenium alloy catalyst for a fuel cell anode.

Background

In the anode of the proton exchange membrane fuel cell, pure hydrogen is needed as fuel gas, electrochemical reaction is carried out under the action of a catalyst to generate protons, and chemical energy can be directly converted into electric energy without fuel. However, at present, hydrogen produced on an industrial scale is generally obtained by steam reforming or partial oxidation of liquid hydrocarbon fuel such as methanol, ethanol, gasoline, etc. or natural gas, and these hydrogen production processes generate carbon monoxide (CO) impurities in the product in an amount of about 1-2%. Although the CO concentration after the two purifications of steam shift and selective oxidation can be reduced to below 100ppm in the subsequent hydrogen purification process within an acceptable cost range, the studies prove that even a few ppm CO concentration can generate strong poisoning effect on the platinum-carbon catalyst of the anode of the fuel cell, thereby causing the performance of the fuel cell to be rapidly reduced and be irreversible.

At present, the best solution to the problem of CO poisoning of the Pt/C catalyst of the anode of a proton exchange membrane fuel cell is to develop an anti-CO electrocatalyst. From the industrial point of view, the platinum ruthenium alloy catalyst (PtRu/C) is the most fully researched next-generation high-performance anode catalyst system with the best comprehensive performance, and has already been commercially applied. However, the preparation of a PtRu/C catalyst with a bimetallic component is much more difficult than a pure Pt/C catalyst with a single metal component. The preparation method of the PtRu/C catalyst with the bimetallic component generally needs to uniformly mix metal salt precursors of platinum and ruthenium, and then load the metal salt precursors on a carbon carrier with a high specific surface through dry impregnation or wet reduction, so as to obtain the platinum-ruthenium alloy nanocrystals highly dispersed on carbon particles. However, in the production by dry impregnation, it is difficult to uniformly disperse the impregnation solutions of the two metal components, resulting in non-uniformity of the two components and failure to smoothly alloy the two components. When wet reduction is used, the metal reduction potentials of platinum and ruthenium are different, and during the reduction process, generally, platinum is firstly reduced to form nucleus, and then ruthenium is attached to platinum particles, so that the platinum and the ruthenium are separated from each other. In order to compensate for the heterogeneity, the prepared PtRu/C catalyst often needs to be calcined at a high temperature to promote alloying, but this may significantly cause the catalyst particles to grow and agglomerate, and affect the electrochemical activity of the PtRu/C catalyst product.

Disclosure of Invention

The invention aims to provide a preparation method of a platinum-ruthenium alloy catalyst reduced by bubbling mixed gas, which can solve the two problems that two noble metals are mixed unevenly to form a phase-splitting structure or generate serious agglomeration and unevenness in the process of preparing the PtRu alloy catalyst by dry or wet reduction, and does not need a high-temperature roasting alloying step, thereby obviously improving the quality of the PtRu/C catalyst product and reducing the cost.

In order to achieve the purpose, the invention provides a preparation method of a platinum-ruthenium alloy catalyst through mixed gas bubbling reduction, which mainly comprises the following steps: (1) preparing a metal salt solution by adopting a platinum salt solution and a ruthenium salt solution; (2) adding a carbon carrier and an additive into the metal salt solution obtained in the step (1), stirring, homogenizing and dispersing to obtain a reaction solution; (3) placing the reaction liquid obtained in the step (2) into a bubbling reaction kettle, introducing reaction gas to carry out bubbling reduction reaction, wherein the reaction gas contains hydrogen and carbon monoxide; (4) and after the bubbling reduction reaction is finished, discharging reaction liquid obtained by the reaction from the reaction kettle, filtering and drying to obtain the platinum-ruthenium alloy catalyst.

In one embodiment of the present invention, the platinum salt is a water-soluble platinum salt, preferably, the water-soluble platinum salt is selected from one or more of chloroplatinic acid, potassium chloroplatinate, platinum nitrate and platinum acetylacetonate; and/or the ruthenium salt is water-soluble ruthenium salt, preferably, the water-soluble ruthenium salt is selected from one or more of ruthenium trichloride, ammonium chlororuthenate and potassium chlororuthenate.

In one embodiment of the present invention, the concentration of the metal salt ion in the metal salt solution is 0.05 to 0.5 mol/L.

In one embodiment of the present invention, the molar ratio of platinum ions to ruthenium ions in the metal salt solution is 1:0.1-1.

In one embodiment of the present invention, the carbon support is selected from one or more of XC-72R, ketjen black, furnace black; and/or the additive is polyalcohol and/or a high molecular surfactant; preferably, the polyhydric alcohol is selected from one or more of isopropanol, ethylene glycol and glycerol, and/or the high molecular surfactant is selected from one or more of polyvinylpyrrolidone (PVP), Cetyl Trimethyl Ammonium Bromide (CTAB) and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123).

In one embodiment of the invention, the mass ratio of the added amount of the carbon carrier to the total amount of the metal elements is 1:0.1-1.5, and/or the additive accounts for 0.1-10 wt% of the reaction solution.

In one embodiment of the present invention, the volume ratio of hydrogen to carbon monoxide in the reaction gas is 1: 0.1-1; preferably, the volume ratio of hydrogen to carbon monoxide in the reaction gas is 1: 0.5.

In one embodiment of the present invention, the reaction gas further contains an inert gas; preferably, the volume ratio of hydrogen to inert gas in the reaction gas is 1: 0-0.5; and/or the inert gas is selected from one or more of nitrogen, argon and carbon dioxide gas.

In one embodiment of the present invention, the gas flow rate of the reaction gas introduced in step (3) is 0.5-3L/min, and/or the temperature of the reaction solution is 60-90 ℃, and/or the reaction time is 2-10h, and/or the drying in step (4) is vacuum drying.

Compared with the prior art, the mixed gas bubbling reduction preparation method and the reaction kettle of the platinum-ruthenium alloy catalyst have the following advantages:

(1) by introducing carbon monoxide gas as a ligand in the reduction process of platinum and ruthenium ions in a liquid phase, the dynamic reaction process of the platinum and ruthenium ions in the reduction process of the platinum and ruthenium ions into ruthenium nanoparticles can be modulated, and the nucleation rate, crystal face formation tendency and dispersity of the platinum and ruthenium ions are adjusted, so that the morphology and distribution of the platinum and ruthenium ions are controlled in an auxiliary manner, the alloy type platinum and ruthenium catalyst with uniform element distribution is directly obtained, and the two problems that two noble metals are mixed and are not uniform to form a phase-splitting structure or seriously agglomerated and are not uniform in the process of preparing the PtRu alloy catalyst by dry or wet reduction are solved, and a high-temperature roasting alloying step is not needed, so that the quality of the PtRu/C catalyst product is obviously improved, and the cost is reduced.

(2) The platinum-ruthenium alloy catalyst prepared by the method has obviously reduced oxidation overpotential compared with commercial products, has good carbon monoxide poisoning resistance, and has excellent performance when being used as an anode of a proton exchange membrane fuel cell.

Drawings

FIG. 1 is a comparison of XRD images of sample #1-1 prepared in example 1 with commercial products of the same type;

FIG. 2 is a comparative XRD image of sample #1-1 prepared in example 1 and sample #1-2 prepared in comparative example 1;

FIG. 3 is a graph of carbon monoxide oxidation potential measurements for sample #2-1 of the platinum ruthenium carbon catalyst prepared in example 2;

figure 4 is a graph of carbon monoxide oxidation potential measurements for a sample of a commercially pure platinum carbon catalyst.

Detailed Description

The technical solution of the present invention will be described below by way of specific examples. It is to be understood that one or more of the steps mentioned in the present invention does not exclude the presence of other methods or steps before or after the combined steps, or that other methods or steps may be inserted between the explicitly mentioned steps. It should also be understood that these examples are intended only to illustrate the invention and are not intended to limit the scope of the invention. Unless otherwise indicated, the numbering of the method steps is only for the purpose of identifying the method steps, and is not intended to limit the arrangement order of each method or the scope of the implementation of the present invention, and changes or modifications of the relative relationship thereof may be regarded as the scope of the implementation of the present invention without substantial technical change.

The raw materials and apparatuses used in the examples are not particularly limited in their sources, and may be purchased from the market or prepared according to a conventional method well known to those skilled in the art.

Throughout the specification and claims, unless explicitly stated otherwise, the word "comprise", or variations such as "comprises" or "comprising", will be understood to imply the inclusion of a stated element or component but not the exclusion of any other element or component.

Example 1

Dissolving chloroplatinic acid 5.18g and ruthenium trichloride 2.07g in deionized water 200mL, dissolving completely, adding Ketjen black as carbon carrier and glycerol 10mL as dispersant, homogenizing completely with high-speed homogenizer to obtain slurry, pumping the slurry into a bubbling reaction kettle, and blowing hydrogen and carbon monoxide mixed gas (H)₂and/CO ═ 1:0.5), without using an inert gas as a diluent gas, the bubbling flow rate was 3L/min. In this process, the reaction solution was heated to 60 ℃ for 10 hours. And after the reaction is finished, discharging the reaction liquid from the reaction kettle, filtering and washing, and placing a filter cake in a vacuum drying oven for drying at 60 ℃ to obtain a catalyst product which is marked as # 1-1.

Comparative example 1

The method adopts the following specific processes that carbon monoxide gas is not introduced, and hydrogen gas is simply used for reduction to prepare the platinum-ruthenium alloy catalyst for comparison: dissolving chloroplatinic acid 5.18g and ruthenium trichloride 2.07g in deionized water 200mL, dissolving completely and uniformly, adding Ketjen black as carbon carrier and glycerol 10mL as dispersant, homogenizing completely with high-speed homogenizer to obtain slurry, pumping the slurry into a bubbling reaction kettle, and blowing hydrogen and argon gas mixture (H)₂and/Ar 1:0.5), the bubbling flow rate was 3L/min. In this process, the reaction solution was heated to 60 ℃ for 10 hours. And after the reaction is finished, discharging the reaction liquid from the kettle, filtering and washing, and placing a filter cake in a vacuum drying oven for drying at 60 ℃ to obtain a catalyst product which is marked as # 1-2.

Example 2

Dissolving platinum acetylacetonate 3.93g and ammonium ruthenate 1.75g in deionized water 100mL, adding furnace black 6g as carbon carrier and propanetriol 2mL as dispersant, homogenizing in high speed homogenizer to obtain slurry, pumping the slurry into bubbling reactor, and blowing hydrogen and carbon monoxide mixed gas (H)₂/CO＝1:0.5)，40% by volume of argon was used as a diluent gas, and the bubbling flow rate was 1.5L/min. In this process, the reaction solution was heated to 75 ℃ for 5 hours. And after the reaction is finished, discharging the reaction liquid from the kettle, filtering and washing, and placing a filter cake in a vacuum drying oven for drying overnight at 70 ℃ to obtain a catalyst product which is marked as # 2-1.

Example 3

Taking potassium chloroplatinate (K)₂PtCl₆)4.86g of potassium chlororuthenate 0.392g are dissolved in 25mL of deionized water, after the uniform dissolution, 2.5g of carbon carrier with the mark of XC-72R and 0.125g of PVP K-30 are added as dispersing agents, after the uniform dissolution is carried out by using a high-speed homogenizer, the slurry is fully homogenized by using a reaction liquid, the reaction liquid is pumped into a bubbling reaction kettle, and mixed gas (H) of hydrogen and carbon monoxide is bubbled into the bubbling reaction kettle₂1/CO ═ 0.1), nitrogen was used as the diluent gas, the volume ratio of hydrogen to nitrogen was 1: 0.2. the bubbling flow rate was 0.5L/min. In this process, the reaction solution was heated to 90 ℃ for 2 hours. And after the reaction is finished, discharging the reaction liquid from the kettle, filtering and washing, and placing a filter cake in a vacuum drying oven for drying overnight at 80 ℃ to obtain a catalyst product which is marked as # 3-1.

Example 4

3.19g of platinum nitrate and 1.04g of ruthenium trichloride are dissolved in 80mL of deionized water, and after the platinum nitrate and the ruthenium trichloride are fully and uniformly dissolved, 4g of furnace black is added to be used as a carbon carrier. Adding 9.3mL of isopropanol and 0.72g of P123 solid powder as dispersing agents, homogenizing the mixture into slurry by using a high-speed homogenizer, pumping the reaction solution into a bubbling reaction kettle, and blowing a mixed gas (H) of hydrogen and carbon monoxide₂1/CO), using a mixed gas of argon and carbon dioxide as an inert diluent gas, wherein the volume ratio of hydrogen to the inert diluent gas is 1: 0.1. the bubbling flow rate was 2.5L/min. In this process, the reaction solution was heated to 80 ℃ for 3 hours. And after the reaction is finished, discharging the reaction liquid from the kettle, filtering and washing, and placing the formed filter cake in a vacuum drying oven for drying overnight at 70 ℃ to obtain a catalyst product which is marked as # 4-1.

Example 5

Dissolving 3.19g of platinum nitrate and 1.04g of ruthenium trichloride in 30mL of deionized water, fully and uniformly dissolving,adding 2.5g Ketjen black (EC600J) as carbon carrier and 3mL ethylene glycol as dispersant, homogenizing with high speed homogenizer to obtain slurry, pumping the reaction solution into bubbling reaction kettle, and blowing hydrogen and carbon monoxide mixed gas (H)₂1/CO ═ 0.1), carbon dioxide was used as inert diluent gas, the volume ratio of hydrogen to inert diluent gas was 1: 0.05. the bubbling flow rate was 3.0L/min. In this process, the reaction solution was heated to 60 ℃ for 10 hours. And after the reaction is finished, discharging the reaction liquid from the kettle, filtering and washing, and placing a filter cake in a vacuum drying oven for drying overnight at 70 ℃ to obtain a catalyst product which is marked as # 5-1.

Example 6

4.86g of potassium chloroplatinate (K2PtCl6) and 0.784g of potassium chlororuthenate are dissolved in 70mL of deionized water, after the potassium chloroplatinate and the potassium chlororuthenate are fully and uniformly dissolved, 5.7g of Ketjen black (EC300J) serving as a carbon carrier and 0.2g of CTAB (cetyl trimethyl ammonium bromide) serving as a dispersing agent are added, after the mixture is fully homogenized into slurry by using a high-speed homogenizer, the reaction solution is pumped into a bubbling reaction kettle, and a mixed gas (H) of hydrogen and carbon monoxide is blown into the bubbling reaction kettle₂1/CO ═ 0.7), using a mixed gas of carbon dioxide and nitrogen as an inert diluent gas, the volume ratio of hydrogen to inert diluent gas being 1: 0.5. the bubbling flow rate was 1.2L/min. In this process, the reaction solution was heated to 90 ℃ for 3 hours. And after the reaction is finished, discharging the reaction liquid from the kettle, filtering and washing, and placing a filter cake in a vacuum drying oven for drying overnight at 70 ℃ to obtain a catalyst product, which is marked as # 6-1.

Example 7

Dissolving platinum acetylacetonate 3.93g and ammonium ruthenate 3.5g in 400mL of deionized water, fully and uniformly dissolving, adding furnace black 29.6g as a carbon carrier and glycerol 8mL as a dispersing agent, fully homogenizing by using a high-speed homogenizer to obtain slurry, pumping the slurry into a bubbling reaction kettle, and blowing hydrogen and carbon monoxide mixed gas (H)₂CO ═ 1:0.5), 40% by volume of argon was used as a diluent gas, and the bubbling flow rate was 1.5L/min. In this process, the reaction solution was heated to 75 ℃ for 5 hours. After the reaction is finished, discharging the reaction liquid from the kettle, filtering and washing, placing the filter cake in a vacuum drying oven for drying overnight at 70 ℃ to obtain a catalyst productAnd is denoted as # 7-1.

X-ray diffraction (XRD) analysis of example 1 and comparative example 1

Based on the noble metal charge ratio, #1-1 is a catalyst with a composition ratio of 60 wt% -PtRu/C, and the XRD pattern of the catalyst is shown in figure 1 in comparison with the curve of a commercial 60 wt% -PtRu/C catalyst of the same type. It can be seen that the XRD pattern shows only fcc diffraction peaks of the metal simple substance Pt, and no diffraction peaks corresponding to the metal Ru or its oxide appear, which can be attributed to two reasons, one is that the metal Ru forms an alloy with Pt, and the other is that Ru may exist in the form of amorphous oxide. The XRD peak position of the 60 wt% -PtRu/C catalyst prepared by #1-1 is completely consistent with that of a commercial PtRu/C sample, which indicates that pure-phase PtRu alloy nanoparticles are successfully obtained; the XRD peak width is wider, which shows that the PtRu alloy nano particles have smaller size and more uniform distribution. From the width of the diffraction peak calculated from the Bragg equation, it can be seen that the average particle diameter of PtRu in the sample #1-1 is 2.2-3.8nm, whereas that in the commercial sample is 3.5-6.9 nm. Compared with the traditional commercial dry synthesis preparation process, the hydrogen/carbon monoxide mixed bubbling reduction method can reduce the particle size of the nano alloy catalyst particles in the product and improve the alloying degree and the uniformity.

Based on the noble metal charge ratio, #1-2 was also 60 wt% -PtRu/C catalyst, and the preparation method was different from example 1 only in that a hydrogen and argon gas mixture was used instead of a hydrogen and carbon monoxide gas mixture. Comparing the XRD pattern of the catalyst #1-2 with that of the product #1-1 of example 1 (FIG. 2), it can be found that RuO occurred in the sample #1-2 in which carbon monoxide gas was not used as a ligand during the preparation process₂The PtRu alloy is not pure phase, and the XRD diffraction peak intensity of the PtRu alloy is higher than that of the PtRu alloy in a #1-1 mode, so that the PtRu alloy particles are agglomerated and are larger. This further shows that the carbon monoxide gas is used as the ligand of the noble metal in the liquid phase reduction, compared with the method of only using hydrogen gas for reduction, the method can adjust the process and the speed of the reduction nucleation, and inhibit the appearance of impurity phase and the agglomeration and growth of nano particles when the alloy is formed.

Carbon monoxide adsorption Oxidation potential test of platinum ruthenium carbon catalysts prepared in examples 2-7

The platinum-ruthenium-carbon catalysts prepared in examples 2 to 7 were subjected to a carbon monoxide adsorption oxidation potential test under the same conditions as the comparative commercial pure platinum-carbon catalyst by the following method: by exposing the working electrode to N containing high purity CO₂Saturated 0.5M H₂SO₄In solution, a low potential was applied to saturate the CO onto the Pt sites, after which the working electrode was immediately transferred to fresh 0.5M H₂SO₄The solution was neutralized and cyclic voltammetric scans were performed at a scan rate of 50mV s-1. The oxidation potential of carbon monoxide for platinum ruthenium carbon catalyst #2-1 is shown in FIG. 3, the oxidation potential of carbon monoxide for a commercial pure platinum carbon sample is shown in FIG. 4, and the oxidation potential of carbon monoxide for other example prepared samples are not shown. The results of the carbon monoxide adsorption oxidation potential tests performed on the platinum-ruthenium carbon catalysts #2-1, #3-1, #4-1, #5-1, #6-1, #7-1 prepared in examples 2-7 are shown in the following table:

sample numbering	Carbon monoxide oxidation potential (V)
		Commercial pure platinum carbon catalyst	0.73
#2-1	0.47
		#3-1	0.65
#4-1	0.52
		#5-1	0.44
#6-1	0.69
		#7-1	0.50

The carbon monoxide oxidation potential of the commercial pure platinum carbon sample is up to 0.73V vs 0.5M H₂SO₄Compared with the platinum-ruthenium carbon catalysts prepared by the method, the oxidation potentials of the carbon monoxide of the platinum-ruthenium carbon catalysts #2-1, #3-1, #4-1, #5-1, #6-1 and #7-1 are reduced to different degrees, the maximum reduction range of #5-1 is reduced to 0.44V, the reduction range reaches 40%, and the minimum reduction range of #6-1 is also reduced by more than 5%, so that the significant level is reached. The test results show that compared with a commercial pure platinum carbon sample, the platinum ruthenium carbon catalyst prepared by the method has good carbon monoxide poisoning resistance, and the method can be used for preparing the platinum ruthenium carbon catalyst with good carbon monoxide poisoning resistance.

The foregoing descriptions of specific exemplary embodiments of the present invention have been presented for purposes of illustration and description. It is not intended to limit the invention to the precise form disclosed, and obviously many modifications and variations are possible in light of the above teaching. The exemplary embodiments were chosen and described in order to explain certain principles of the invention and its practical application to enable one skilled in the art to make and use various exemplary embodiments of the invention and various alternatives and modifications as are suited to the particular use contemplated. It is intended that the scope of the invention be defined by the claims and their equivalents.

Claims

1. A preparation method of a platinum-ruthenium alloy catalyst for a fuel cell anode mainly comprises the following steps:

(1) preparing a metal salt solution by adopting a platinum salt solution and a ruthenium salt solution;

(2) adding a carbon carrier and an additive into the metal salt solution obtained in the step (1), stirring, homogenizing and dispersing to obtain a reaction solution;

(3) placing the reaction liquid obtained in the step (2) into a bubbling reaction kettle, introducing reaction gas to carry out bubbling reduction reaction, wherein the reaction gas contains hydrogen and carbon monoxide;

(4) and after the bubbling reduction reaction is finished, discharging reaction liquid obtained by the reaction from the reaction kettle, filtering and drying to obtain the platinum-ruthenium alloy catalyst.

2. The method of claim 1, wherein:

the platinum salt is water-soluble platinum salt; preferably, the water-soluble platinum salt is selected from one or more of chloroplatinic acid, potassium chloroplatinate, platinum nitrate and platinum acetylacetonate;

and/or, the ruthenium salt is water-soluble ruthenium salt; preferably, the water-soluble ruthenium salt is selected from one or more of ruthenium trichloride, ammonium chlororuthenate and potassium chlororuthenate.

3. The method of claim 1, wherein: the concentration of metal salt ions in the metal salt solution is 0.05-0.5 mol/L.

4. The method of claim 1, wherein: the molar ratio of the platinum ions to the ruthenium ions in the metal salt solution is 1:0.1-1.

5. The method of claim 1, wherein: the carbon carrier is selected from one or more of XC-72R, Ketjen black and furnace black;

and/or the additive is polyalcohol and/or a high molecular surfactant; preferably, the polyalcohol is selected from one or more of isopropanol, ethylene glycol and glycerol,

and/or the high molecular surfactant is selected from one or more of polyvinylpyrrolidone (PVP), Cetyl Trimethyl Ammonium Bromide (CTAB) and polyethylene oxide-polypropylene oxide-polyethylene oxide triblock copolymer (P123).

6. The preparation method according to claim 1, wherein the mass ratio of the addition amount of the carbon carrier to the total amount of the metal elements is 1: 0.1-1.5;

and/or the additive accounts for 0.1-10 wt% of the reaction liquid.

7. The production method according to claim 1, wherein the volume ratio of hydrogen to carbon monoxide in the reaction gas is 1: 0.1-1; preferably, the volume ratio of hydrogen to carbon monoxide in the reaction gas is 1: 0.5.

8. The production method according to claim 1, wherein the reaction gas further contains an inert gas;

preferably, the inert gas is selected from one or more of nitrogen, argon and carbon dioxide gas.

9. The production method according to claim 8, wherein the volume ratio of hydrogen gas to inert gas in the reaction gas is 1:0 to 0.5.

10. The production method according to claim 1, wherein the gas flow rate of the reaction gas introduced in the step (3) is 0.5 to 3L/min;

and/or the temperature of the reaction liquid is 60-90 ℃;

and/or the reaction time is 2-10 h;

and/or, the drying in the step (4) is vacuum drying.