Preparation method of double-site cobalt-based nitrogen-doped carbon catalyst derived by template-free method and application of double-site cobalt-based nitrogen-doped carbon catalyst to room-temperature catalytic oxidation of 5-hydroxymethylfurfural

Abstract

The invention provides a double-active-site cobalt-based nitrogen-doped carbon catalyst which is low in cost, easy to prepare, stable and efficient and is used for a catalytic oxidation reaction of 5-hydroxymethylfurfural under light-driven or room-temperature and normal-pressure conditions. And a set of complete catalyst amplified preparation and 5-hydroxymethylfurfural oxidation reaction separation and purification system is developed. According to the invention, the use of a template agent which is difficult to remove, dangerous and toxic raw material reagents and the like is avoided, and the prepared metal active site carbon material has an ideal porous and ultrathin structure, controllable surface characteristics and excellent structural stability. And the unique microstructure on the surface of the catalyst shows high selectivity and excellent cycle stability when being used for catalytic oxidation of biomass derived alcohol under the conditions of room temperature and normal pressure, and large-scale preparation in a laboratory stage is realized. The efficient, stable, cheap and easy-to-prepare catalyst realizes oxidation of 5-hydroxymethylfurfural under mild conditions.

Description

Technical Field

[0001] The present invention relates to a cobalt-based nitrogen-doped carbon catalyst with dual active sites that can be controllably prepared by a cheap and easy-to-prepare hard template-free method, and in particular to a catalyst preparation method using high-temperature pyrolysis of carbon nitride chelated metal-based ligand molecules and the application of the obtained catalyst in the preparation of high-purity 2,5-furandicarboxylic acid by light-driven catalytic oxidation of 5-hydroxymethylfurfural in room temperature air. Background Art

[0002] The rapid growth of global resource consumption and the depletion of fossil fuels have stimulated people's great interest in exploring renewable resources. Countries around the world have actively proposed sustainable development strategies, and developing biomass, the only renewable organic carbon resource, to produce high-value-added chemicals and fuels has become a promising strategy for the transition from traditional petrochemicals to green and renewable resources.

[0003] It is estimated that by 2030, about 35% of the world's chemicals and other industrial products will come from biomanufacturing. The conversion of biomass and biomass platform molecules has become a research hotspot because it provides a green and feasible way to reduce the heavy dependence on traditional fossil chemicals. However, the direct use of biomass and its derivatives to produce high value-added chemicals and fuels remains challenging due to the lack of economically competitive upgrading technologies. Oxidation reactions are a key way to achieve value-added conversion of biomass platform molecules by introducing oxygen species. And in the industrial production of chemical reactions, it is crucial to develop an efficient, low-cost and inexpensive catalyst. In the oxidation process of the biomass platform molecule 5-hydroxymethylfurfural, the separation and purification of the product 2,5-furandicarboxylic acid and the by-products caused by harsh reaction conditions are a key issue. Summary of the invention

[0004] The purpose of the present invention is to overcome the deficiencies in the above-mentioned prior art and to provide a cheap, easy-to-prepare, stable and efficient dual-active site cobalt-based nitrogen-doped carbon catalyst for the catalytic oxidation reaction of 5-hydroxymethylfurfural driven by light or under room temperature and atmospheric pressure; and to develop a complete set of catalyst scale-up preparation and oxidation reaction separation and purification system for 5-hydroxymethylfurfural.

[0005] The invention uses a preheating process to achieve strong and effective combination of carbon nitride and the chelate through the mass ratio of the industrialized cheap ligand molecule o-phenylenediamine chelate to the carrier carbon nitride, and finally prepares the target catalyst through high-temperature pyrolysis.

[0006] In order to achieve the above object, the present invention proposes a method for preparing a bifunctional, biactive site cobalt-based nitrogen-doped carbon catalyst using a template-free method, comprising the following steps:

[0007] (1) Two-dimensional carbon nitride nanosheets are obtained by calcining urea in air in a muffle furnace. Urea is calcined in air at 500-600°C for 2-4 hours. The yield of carbon nitride is 4.5-6.5wt.%, and the by-product is mainly ammonia.

[0008] (2) Adding carbon nitride nanosheets, ligand molecule o-phenylenediamine and cobalt chloride metal salt in a certain mass ratio into an ethanol solvent and stirring and dispersing the mixture, removing the ethanol solvent by vacuum distillation to obtain a brown powder precursor.

[0009] (3) The obtained powder precursor is placed in a tubular furnace and subjected to high-temperature pyrolysis in a circulating nitrogen atmosphere until the reaction is completed.

[0010] In step (1), the obtained carbon nitride nanosheets can be used directly without further treatment.

[0011] In step (2), the mass ratio of carbon nitride nanosheets, ligand molecule o-phenylenediamine and cobalt chloride metal salt is 7:2:1, 7:1:1 or 7:2:1.

[0012] In step (2), the temperature of the reduced pressure distillation is below 60° C. to remove the ethanol solvent, and the ethanol can be recovered and reused.

[0013] In step (3), the catalyst is preheated at 150-300°C for 1 h by a programmed temperature method, and then heated to 700-900°C and kept warm for 2 h. The catalyst yield is 14-17 wt.%, and the by-products are nitrogen and carbon dioxide.

[0014] In order to verify the efficient catalytic oxidation activity of the catalyst, the present invention proposes a method for preparing 2,5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural under room temperature and atmospheric pressure air conditions, comprising the following steps:

[0015] (1) adding sodium hydroxide in a molar amount of 1-2 times the molar amount of 5-hydroxymethylfurfural into distilled water to form an alkaline solution, and adjusting the solution pH to 11-13 by further water content;

[0016] (2) adding a certain mass of cobalt-based nitrogen-doped carbon catalyst into the reaction system;

[0017] (3) At room temperature, air is introduced into the reactor and stirring is continued, and the catalyst is filtered after the reaction is completed;

[0018] (4) Control the temperature of the filtrate at 0-2°C, and add concentrated hydrochloric acid dropwise to acidify the filtrate to a pH of 2.5-3;

[0019] (5) The solution acidified in step (4) is grown in a cold room at 0-2° C. for more than 12 hours, filtered, rinsed with ice water to obtain a wet product of 2,5-furandicarboxylic acid, and freeze-dried for 5-8 hours to obtain a white or light yellow crystalline powder of 2,5-furandicarboxylic acid.

[0020] The beneficial effects of the present invention are as follows:

[0021] (1) The present invention uses no template and no complicated separation means during or after the catalyst synthesis process, and can achieve large-scale production of the catalyst simply and efficiently.

[0022] (2) The cobalt-based nitrogen-doped carbon catalyst with controllable dual-active site metal cobalt nanoparticles and single-atom cobalt sites exhibits excellent catalytic activity for 5-hydroxymethylfurfural under room temperature and air conditions, and the performance of the scaled-up catalyst does not change significantly. When the reaction system is driven by light, the performance is further improved, showing a special dual functionality.

[0023] (3) Based on the characteristics of the catalyst being cheap and easy to prepare, an integrated system for catalyst preparation and catalytic reaction purification of 2,5-furandicarboxylic acid was developed.

[0024] The present invention avoids the use of difficult-to-remove templates and dangerous and toxic raw materials and reagents, and the prepared metal active site carbon material has an ideal porous and ultra-thin structure, controllable surface properties and excellent structural stability. The unique microstructure on the catalyst surface shows high selectivity and excellent cyclic stability when used as a catalytic oxidation of biomass-derived alcohols under room temperature and normal pressure conditions, realizing large-scale preparation at the laboratory stage. In addition, no complex experimental equipment and cumbersome experimental steps are used in the synthesis process, which is conducive to larger-scale preparation and has high application prospects and use value. This highly efficient, stable, cheap and easy-to-prepare catalyst realizes the oxidation of 5-hydroxymethylfurfural under mild conditions. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 A schematic diagram of a laboratory-scale synthesis system of a dual-active-site cobalt-based nitrogen-doped carbon catalyst obtained in Example 1 of the present invention is shown.

[0026] Figure 2 A schematic diagram of a catalytic oxidation reaction purification system for 5-hydroxymethylfurfural in Example 3 of the present invention is shown. DETAILED DESCRIPTION

[0027] In order to explain the present invention more clearly, the present invention is further described below in conjunction with preferred embodiments. It should be understood by those skilled in the art that the content described below is illustrative rather than restrictive, and should not be used to limit the scope of protection of the present invention.

[0028] The preparation methods in the present invention are conventional methods unless otherwise specified. The raw materials used can be obtained from public commercial channels unless otherwise specified.

[0029] Example 1

[0030] A method for preparing a high-performance cobalt-based nitrogen-doped carbon catalyst with dual active sites comprises the following steps:

[0031] (1) Urea is placed in a crucible and wrapped with multiple layers of tin foil. The crucible is placed in a muffle furnace for subsequent pyrolysis process. The temperature is raised to 500-600°C and calcined to obtain a light yellow powder which is carbon nitride.

[0032] (2) Adding carbon nitride nanosheets, ligand molecule o-phenylenediamine and cobalt chloride metal salt in a certain mass ratio into an ethanol solvent and stirring and dispersing the mixture, removing the ethanol solvent by vacuum distillation to obtain a brown powder precursor.

[0033] (3) The obtained solid powder is placed in a tubular furnace and subjected to high-temperature pyrolysis in a circulating nitrogen atmosphere until the reaction is completed. The temperature is then kept at 150-300° C. for 1 h, and then raised to 700-900° C. for 2 h to obtain the target catalyst.

[0034] The preparation process of the dual-active site cobalt-based nitrogen-doped carbon catalyst prepared in Example 1 is simple; compared with the prior art, the present invention adopts a carbon nitride-induced pyrolysis strategy to prepare a bifunctional dual-active site cobalt-based nitrogen-doped carbon catalyst, which comprises metal cobalt nanoparticles and single-atom cobalt active sites; it does not require traditional acid-washing templates and crystal growth methods, and is more green and efficient.

[0035] Example 2

[0036] A method for preparing 2,5-furandicarboxylic acid by oxidizing 5-hydroxymethylfurfural under room temperature and atmospheric pressure air conditions, comprising the following steps:

[0037] (1) In a reactor, 5-hydroxymethylfurfural and sodium hydroxide in a molar ratio of 1:2 are added to distilled water to form an alkaline solution, and the pH of the solution is adjusted to 11-13 by adjusting the water content;

[0038] (2) adding a certain mass of cobalt-based nitrogen-doped carbon catalyst into the reactor;

[0039] (3) At room temperature, air is introduced into the reaction flask and stirring is continued. After the reaction is completed, the catalyst is filtered out;

[0040] (4) The temperature of the filtrate is controlled at 0-2°C, and the pH of the filtrate is adjusted to 2.5-3 with hydrochloric acid;

[0041] (5) The solution acidified in step (4) was grown in a cold room at 0-2°C for more than 12 hours, filtered, rinsed with ice water to obtain a wet product of 2,5-furandicarboxylic acid, and freeze-dried for 5-8 hours to obtain a white or light yellow crystalline powder of 2,5-furandicarboxylic acid. The production rate of the product FDCA at room temperature was 4.43 mmol g cat -1 h -1 ;

[0042] (6) A series of comparative characterizations were performed on the white or light yellow crystalline powder 2,5-furandicarboxylic acid obtained in step (5) and the commercial FDCA product.

[0043] Example 3

[0044] A method for preparing 2,5-furandicarboxylic acid by efficient oxidation of 5-hydroxymethylfurfural under room temperature and atmospheric pressure air conditions promoted by light, comprising the following steps:

[0045] (1) In a reactor with a quartz window, 5-hydroxymethylfurfural and sodium hydroxide in a molar ratio of 1:2 are added to distilled water to form an alkaline solution, and the pH of the solution is adjusted to 11-13 by adjusting the water content;

[0046] (2) adding a certain amount of cobalt-based nitrogen-doped carbon catalyst into a reactor with a quartz window; placing the reactor under ultraviolet and visible light of different light intensities for illumination;

[0047] (3) Keeping the reaction bottle at room temperature, introduce air into the reaction bottle and continue stirring. After the reaction, filter the catalyst; (4) Control the temperature of the filtrate at 0-2°C, and adjust the pH of the filtrate to 2.5-3 with hydrochloric acid;

[0048] (5) The solution acidified in step (4) was grown in a cold room at 0-2°C for more than 12 hours, filtered, rinsed with ice water to obtain a wet product of 2,5-furandicarboxylic acid, and freeze-dried for 5-8 hours to obtain a white or light yellow crystalline powder of 2,5-furandicarboxylic acid; the generation rate of the product FDCA under light-driven room temperature conditions was significantly better than that under dark conditions, which was 9.32 mmol g cat -1 h -1 ;

[0049] (6) A series of comparative characterizations were performed on the white or light yellow crystalline powder 2,5-furandicarboxylic acid obtained in step (5) and the commercial FDCA product.

[0050] Example 4

[0051] A method for preparing 5-hydroxymethyl-2-furancarboxylic acid by light-promoted efficient oxidation of 5-hydroxymethylfurfural under nitrogen conditions at room temperature and normal pressure, comprising the following steps:

[0052] (1) In a reactor with a quartz window, 5-hydroxymethylfurfural and sodium hydroxide in a molar ratio of 1:2 are added to distilled water to form an alkaline solution, and the pH of the solution is adjusted to 11-13 by adjusting the water content;

[0053] (2) adding a certain amount of cobalt-based nitrogen-doped carbon catalyst into a reactor with a quartz window; placing the reactor under ultraviolet and visible light of different light intensities for illumination;

[0054] (3) The reaction was maintained at room temperature, nitrogen was introduced into the reaction flask and stirring was continued, and the catalyst was filtered after the reaction was completed;

[0055] (4) detecting the obtained product by high performance liquid chromatography;

[0056] (5) The rate of production of 5-hydroxymethyl-2-furancarboxylic acid (1.15 mmol g) under light-driven nitrogen conditions at room temperature cat -1 h -1 ) was also significantly better than that under dark conditions (0.52 mmol g cat -1 h -1 ).

[0057] In summary, in the prior art, the oxidation reaction in the conversion of 5-hydroxymethylfurfural to 2,5-furandicarboxylic acid in a cobalt-based carbon-based material catalyst requires a relatively high reaction temperature and pressure; compared with the prior art, the present invention uses a cobalt-based nitrogen-doped carbon catalyst with dual active sites, which can achieve highly selective generation of 2,5-furandicarboxylic acid at room temperature and atmospheric pressure. In addition, under light-driven room temperature conditions, the generation rate of oxidation products in the reaction system is greatly improved. At the same time, the selective conversion of the product can also be achieved by regulating the reaction atmosphere, confirming the excellent controllable catalytic oxidation activity and stability of this bifunctional catalyst.

[0058] Obviously, the above embodiments of the present invention are only examples for clearly illustrating the present invention, and are not limitations on the implementation methods of the present invention. For ordinary technicians in the relevant field, other different forms of changes or modifications can be made on the basis of the above description. It is impossible to list all the implementation methods here. All obvious changes or modifications derived from the technical solution of the present invention are still within the protection scope of the present invention.

Claims

1. A method for preparing a dual-site cobalt-based nitrogen-doped carbon catalyst derived by a template-free method, characterized in that The preparation method comprises the following steps: (1) obtaining two-dimensional carbon nitride nanosheets by calcining urea under air conditions, placing a crucible containing urea in a muffle furnace and calcining it under air at 500-600° C. for 2-4 h to obtain light yellow carbon nitride nanosheets; (2) adding a certain mass ratio of carbon nitride nanosheets, ligand molecule o-phenylenediamine and cobalt chloride hexahydrate to an ethanol solvent, respectively, and mixing and stirring for 30-180 minutes to make them dispersed and complexed uniformly, and removing the ethanol solvent by reduced pressure distillation at a temperature of less than 60° C. to obtain a brown powder precursor; (3) The brown powder precursor obtained in step (2) is placed in a tubular furnace and subjected to high-temperature pyrolysis in a circulating nitrogen atmosphere. It is preheated at 150°C-300°C for 1 h through a programmed temperature rising process, and then heated to 900°C and kept warm for 2 h until the reaction is completed to obtain the target catalyst.

2. The method for preparing a dual-site cobalt-based nitrogen-doped carbon catalyst derived by a template-free method according to claim 1, characterized in that: In step (1), the byproduct of the thermal decomposition of urea under air conditions is ammonia.

3. The method for preparing a dual-site cobalt-based nitrogen-doped carbon catalyst derived by a template-free method according to claim 1, characterized in that: In step (2), the mass ratio of the carbon nitride nanosheets, the ligand molecule o-phenylenediamine and cobalt chloride hexahydrate is 7:2:1, 7:1:1 or 7:1:2, wherein the ethanol solvent is separated under reduced pressure distillation conditions and recycled for catalyst preparation.

4. The method for preparing a dual-site cobalt-based nitrogen-doped carbon catalyst derived by a template-free method according to claim 1, characterized in that: The cobalt-based nitrogen-doped carbon catalyst component is nitrogen-doped carbon-supported cobalt nanoparticles and single-atom cobalt sites, wherein the cobalt nanoparticles are graphite carbon-coated structures, and single-atom cobalt is coordinated with nitrogen atoms on the carbon carrier. The ratio of nanoparticles to single atoms is controlled to be in the range of 2:8 to 7:3 according to the ratio of ligand molecules.

5. The dual-active-site cobalt-based nitrogen-doped carbon catalyst prepared in any ratio according to claim 3 is applied to the catalytic oxidation of 5-hydroxymethylfurfural, characterized in that: The obtained dual-site cobalt-based nitrogen-doped carbon catalyst is used to catalyze 5-hydroxymethylfurfural to prepare 2,5-furandicarboxylic acid under room temperature and air conditions, comprising the following steps: (1) adding sodium hydroxide having a molar amount twice that of 5-hydroxymethylfurfural into distilled water to form an alkaline solution in a reactor, and controlling the water content to a solution pH of 12-13; (2) adding a certain mass of cobalt-based nitrogen-doped carbon catalyst into the reactor; (3) At room temperature, air is introduced into the reactor and stirring is continued, and the catalyst is filtered after the reaction is completed; (4) adding concentrated hydrochloric acid dropwise to the filtrate obtained in step (3) to acidify the filtrate to a pH of 2.5-3; (5) The solution acidified in step (4) is grown in a cold storage room at 0-2° C. for more than 12 hours, filtered, rinsed with ice water to obtain a wet product of 2,5-furandicarboxylic acid, and then freeze-dried for 5-8 hours to obtain a white or light yellow crystalline powder of 2,5-furandicarboxylic acid.

6. The dual-active-site cobalt-based nitrogen-doped carbon catalyst prepared in any ratio according to claim 3 is applied to the catalytic oxidation of 5-hydroxymethylfurfural, characterized in that: The obtained dual-site cobalt-based nitrogen-doped carbon catalyst is used to realize the photo-driven catalytic preparation of 2,5-furandicarboxylic acid from 5-hydroxymethylfurfural under room temperature and air conditions, comprising the following steps: (1) In a reactor with a quartz window, sodium hydroxide in an amount twice the molar amount of 5-hydroxymethylfurfural is added to distilled water to form an alkaline solution, and the water content is controlled to a solution pH of 12-13; (2) adding a certain amount of cobalt-based nitrogen-doped carbon catalyst into the reactor; placing the reactor under ultraviolet and visible light of different light intensities for illumination; (3) At room temperature, air is introduced into the reactor and stirring is continued, and the catalyst is filtered after the reaction is completed; (4) adding concentrated hydrochloric acid dropwise to the filtrate obtained in step (3) to acidify the filtrate to a pH of 2.5-3; (5) The solution acidified in step (4) is grown in a cold storage room at 0-2° C. for more than 12 hours, filtered, rinsed with ice water to obtain a wet product of 2,5-furandicarboxylic acid, and then freeze-dried for 5-8 hours to obtain a white or light yellow crystalline powder of 2,5-furandicarboxylic acid.

7. The dual-active-site cobalt-based nitrogen-doped carbon catalyst prepared in any ratio according to claim 3 is applied to the catalytic oxidation of 5-hydroxymethylfurfural, characterized in that: Using the obtained dual-site cobalt-based nitrogen-doped carbon catalyst to realize the photo-driven catalysis of 5-hydroxymethylfurfural to efficiently prepare 5-hydroxymethyl-2-furancarboxylic acid under room temperature nitrogen conditions, the steps include: (1) In a reactor with a quartz window, sodium hydroxide in an amount twice the molar amount of 5-hydroxymethylfurfural is added to distilled water to form an alkaline solution, and the water content is controlled to a solution pH of 12-13; (2) adding a certain amount of cobalt-based nitrogen-doped carbon catalyst into the reactor; placing the reactor under ultraviolet and visible light of different light intensities for illumination; (3) At room temperature, nitrogen was introduced into the reactor and stirring was continued, and the catalyst was filtered after the reaction; (4) The selectivity of the product 5-hydroxymethyl-2-furancarboxylic acid in the solution is greater than 97%.

8. The use according to any one of claims 5, 6 and 7, characterized in that: The cobalt-based nitrogen-doped carbon catalyst with controllable dual active sites achieved the catalytic oxidation of 5-hydroxymethylfurfural at room temperature and atmospheric pressure. The purity of 2,5-furandicarboxylic acid after simple separation was greater than 99% by infrared, high-performance liquid chromatography and nuclear magnetic resonance. In addition, the light-driven production rate of the product 2,5-furandicarboxylic acid under room temperature oxygen conditions was 9.32 mmol g cat -1 h -1 Obviously better than 4.43mmol g cat -1 h -1 The photo-driven production rate of the product 5-hydroxymethyl-2-furancarboxylic acid under room temperature nitrogen conditions was 1.15 mmol g cat -1 h -1 It is also significantly better than 0.52mmol g cat -1 h -1 .

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