Oxidation catalyst and method for producing the same, and method for producing 2,5-furandicarboxylic acid

Abstract

The application relates to the chemical technology field and discloses an oxidation catalyst, a preparation method of the oxidation catalyst, and a preparation method of 2,5-furan dicarboxylic acid. The catalyst comprises a carrier and an active metal component loaded on the carrier, the active metal component is at least one of Ru and optionally Pt, Pd and Au, and the carrier is a nitrogen-doped nanometer carbon cage; wherein the nitrogen-doped nanometer carbon cage has a hollow cage structure, the diameter of the nitrogen-doped nanometer carbon cage is 2-200 nm, the molar content of pyrrole nitrogen and / or pyridine nitrogen in the surface nitrogen of the nitrogen-doped nanometer carbon cage is greater than 80% as measured by X-ray photoelectron spectroscopy with the total molar amount of nitrogen as a reference, and the BET specific surface area of the nitrogen-doped nanometer carbon cage is greater than 400 m 2 / g. The catalyst has good activity, greatly simplifies the process flow in the preparation of 2,5-furan dicarboxylic acid, does not need to use alkaline compounds and acidification treatment, and has excellent industrial prospects.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of chemical technology, in particular to an oxidation catalyst, a preparation method thereof, and a preparation method of 2,5-furan dicarboxylic acid. BACKGROUND

[0002] Currently, fuels and chemicals required by society are mainly derived from fossil fuels, and the impact of fossil fuels on the environment has aroused widespread interest in sustainable alternative energy and chemical raw materials, especially biomass resources, which are widely available and have a high carbohydrate content, and can produce liquid fuels and organic chemicals through various chemical catalytic processes. 5-hydroxymethylfurfural (HMF) is one of the important biomass-based platform compounds, which can be prepared by acid-catalyzed dehydration of carbohydrates such as fructose, glucose and cellulose. 2,5-furan dicarboxylic acid (FDCA) is obtained by catalytic oxidation of HMF. FDCA is used to synthesize bio-based macromolecular materials, which can effectively improve their heat resistance and mechanical properties, and is considered to be an ideal substitute for petroleum-based monomer terephthalic acid (PTA), which can be widely used in the synthesis of bio-based polymers such as polyesters, polyamides and epoxy resins. Therefore, developing a synthesis method of 2,5-furan dicarboxylic acid has important application value and significance for sustainable utilization of biomass.

[0003] In the process of preparing FDCA by selective oxidation of HMF, since the solubility of FDCA in water is low (<1 g / 100 mL water, 100℃), researchers often add basic compounds to the reaction process to generate FDCA-soluble salt compounds with the product FDCA, in order to improve the single-pass processing capacity of the process method. However, the salt compounds of FDCA obtained by these methods cannot be directly used in the production of polymers and other processes, and must be treated by acidification (pH about 1) to convert them back to FDCA products, which undoubtedly increases the complexity of the overall FDCA production process and reduces its environmental friendliness. Patent application CN108779088A discloses a method for preparing FDCA from HMF in one or two steps without introducing basic compounds. This method effectively improves the solubility of FDCA by using a mixed solvent of water and an organic solvent. The catalyst used in this method is a supported metal catalyst, in which the metal component is Pt or Au. Since Pt and Au are expensive, the overall process method is correspondingly high in cost, making it difficult to be practically applied.

[0004] It should be noted that the information disclosed in the foregoing background section is only used to strengthen the understanding of the background of the present application, and therefore it can include information that does not constitute prior art known to those of ordinary skill in the art. SUMMARY

[0005] The purpose of this invention is to overcome the problems existing in the prior art and provide an oxidation catalyst and its preparation method, as well as a method for preparing 2,5-furandicarboxylic acid. The oxidation catalyst uses nitrogen-doped nano-carbon cages with a hollow cage-like structure and a high specific surface area as a support to load specific active metal components, exhibiting good activity. This oxidation catalyst is used to prepare 2,5-furandicarboxylic acid, which greatly simplifies the process flow, eliminates the need for alkaline compounds and acidification treatment, reduces costs, and has excellent industrialization potential.

[0006] To achieve the above objectives, a first aspect of the present invention provides an oxidation catalyst, wherein the catalyst comprises a support and an active metal component supported on the support, the active metal component being Ru and optionally at least one selected from Pt, Pd, and Au, and the support being a nitrogen-doped carbon nanocage; wherein the nitrogen-doped carbon nanocage has a hollow cage-like structure, and the diameter of the nitrogen-doped carbon nanocage is 2-200 nm; based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 80%; and the BET specific surface area of ​​the nitrogen-doped carbon nanocage is greater than 400 m². 2 / g.

[0007] Preferably, the active metal component is Ru.

[0008] Preferably, based on the total amount of catalyst, the content of the nitrogen-doped carbon nanocage is 80-99% by mass, and the content of the active metal component, calculated as an element, is 1-20% by mass.

[0009] Preferably, the nitrogen-doped carbon nanocage has a BET specific surface area of ​​400-800 m². 2 / g.

[0010] A second aspect of the present invention provides a method for preparing the oxidation catalyst described in the first aspect, wherein the method comprises:

[0011] S1. An active metal component is introduced into the support by impregnation and then dried to obtain the catalyst precursor;

[0012] S2. The catalyst precursor obtained in step S1 is calcined in a calcining atmosphere and then treated in a reducing atmosphere to obtain an oxidation catalyst.

[0013] The active metal component is Ru and optionally at least one of Pt, Pd and Au;

[0014] The carrier is a nitrogen-doped carbon nanocage; the nitrogen-doped carbon nanocage has a hollow cage-like structure, and its diameter is 2-200 nm; based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 80%; the BET specific surface area of ​​the nitrogen-doped carbon nanocage is greater than 400 m². 2 / g.

[0015] A third aspect of the present invention provides a method for preparing 2,5-furandicarboxylic acid, wherein the method comprises: reacting 5-hydroxymethylfurfural with an oxygen-containing gas in the presence of the oxidation catalyst described in the first aspect, in the presence of a mixed solvent containing an organic solvent and / or water, to obtain 2,5-furandicarboxylic acid.

[0016] In this invention, nitrogen-doped carbon nanocages with a hollow cage-like structure and high specific surface area are selected as the support to load specific active metal components to obtain an oxidation catalyst. By selecting the above support, on the one hand, the rich pore structure of the hierarchical porous carbon material increases its specific surface area and improves its intrinsic activity; on the other hand, the three-dimensional interconnected channels it constructs can provide multi-directional, high-flux mass transfer channels, thereby accelerating the kinetics of surface / interface catalytic reactions. In summary, this enables the oxidation catalyst to have good activity.

[0017] The inventors of this invention discovered in their research that, using the oxidation catalyst of this invention, the reaction process for preparing 2,5-furandicarboxylic acid by oxidation of 5-hydroxymethylfurfural can be realized under alkali-free conditions in a mixed solvent composed of water and organic solvent. Compared with the methods in the prior art, this method greatly simplifies the process flow, eliminates the need for acidification treatment, and reduces costs. It is a method for preparing 2,5-furandicarboxylic acid with great industrial potential. Attached Figure Description

[0018] Figure 1 This is a TEM image of the nitrogen-doped carbon nanocage prepared in Example 1;

[0019] Figure 2 This is the XPS image of the nitrogen-doped carbon nanocage prepared in Example 1;

[0020] Figure 3 The XPS N1s peak spectrum of the nitrogen-doped carbon nanocage prepared in Example 1 is shown.

[0021] Figure 4 The BJH pore size distribution curve of the nitrogen-doped carbon nanocage prepared in Example 1 is shown.

[0022] Figure 5 This is the N1s peak spectrum of XPS for the nitrogen-doped carbon nanocage prepared in Example 2.

[0023] Figure 6 This is the N1s peak spectrum of XPS for the nitrogen-doped carbon nanocage prepared in Example 3. Detailed Implementation

[0024] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0025] The first aspect of this invention provides an oxidation catalyst, comprising a support and an active metal component supported on the support, said active metal component being Ru and optionally at least one selected from Pt, Pd, and Au, wherein the support is a nitrogen-doped carbon nanocage; wherein the nitrogen-doped carbon nanocage has a hollow cage-like structure, and the diameter of the nitrogen-doped carbon nanocage is 2-200 nm; based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 80%; and the BET specific surface area of ​​the nitrogen-doped carbon nanocage is greater than 400 m². 2 / g.

[0026] The oxidation catalyst provided by this invention selects a support with specific structure and properties to support a specific active metal component. This catalyst has excellent activity and can be used to prepare 2,5-furandicarboxylic acid, showing excellent industrial prospects.

[0027] In this invention, "optionally at least one of Pt, Pd, and Au" means that the active metal component may or may not contain at least one of Pt, Pd, and Au. In a preferred embodiment, the active metal component is Ru. The advantage of this preferred embodiment is that Ru is inexpensive and exhibits the best selectivity for the target product in the reaction.

[0028] In this invention, the content of each substance in the catalyst is not specifically limited. Preferably, based on the total amount of catalyst, the content of the nitrogen-doped carbon nanocage is 80-99% by mass, and the content of the active metal component, calculated as an element, is 1-20% by mass; more preferably, based on the total amount of catalyst, the content of the nitrogen-doped carbon nanocage is 85-95% by mass, and the content of the active metal component, calculated as an element, is 5-15% by mass. The advantage of this preferred embodiment is that the catalyst exhibits the best activity and selectivity for the target product within the preferred composition range.

[0029] In this invention, the "hollow cage-like structure" of the nitrogen-doped nano-carbon cage refers to a hollow sphere or quasi-sphere formed by a graphitized carbon layer surrounding it.

[0030] In a preferred embodiment, the diameter of the nitrogen-doped carbon nanocage is 2-200 nm, preferably 2-100 nm, more preferably 5-50 nm, and even more preferably 5-20 nm.

[0031] In this invention, the surface morphology of the material is characterized by high-resolution transmission electron microscopy (HRTEM). The HRTEM used is a JEM-2100 (Japan Electronics Corporation), and the HRTEM testing conditions are: accelerating voltage of 200 kV. The diameter of the nitrogen-doped carbon nanocage can be measured from the HRTEM images.

[0032] In this invention, the term "nitrogen-doped carbon nanocage" refers to the element nitrogen. Specifically, this term refers to the nitrogen element that exists in various forms within the nitrogen-doped carbon nanocage during the preparation process of the nitrogen-doped carbon nanocage.

[0033] In this invention, the terms "pyrrole nitrogen," "pyridine nitrogen," "graphite nitrogen," and "oxidized nitrogen" have their conventional meanings in the art, specifically referring to: pyridine nitrogen as a nitrogen species identified by characteristic spectral peaks corresponding to binding energies of 398.7-399.1 eV in X-ray photoelectron spectroscopy; pyrrole nitrogen as a nitrogen species identified by characteristic spectral peaks corresponding to binding energies of 398.8-400.2 eV in X-ray photoelectron spectroscopy; graphite nitrogen as a nitrogen species identified by characteristic spectral peaks corresponding to binding energies of 401.2-409.8 eV in X-ray photoelectron spectroscopy; and oxidized nitrogen as a nitrogen species identified by characteristic spectral peaks corresponding to binding energies of 402.8-403.6 eV in X-ray photoelectron spectroscopy.

[0034] In this invention, X-ray photoelectron spectroscopy analysis was performed on an ESCALab250 X-ray photoelectron spectrometer from Thermo Scientific equipped with ThermoAvantage V5.926 software. The excitation source was monochromatic Al Kα X-rays with an energy of 1486.6 eV and a power of 150 W. The transmission energy used for narrow scanning was 30 eV, and the baseline vacuum during analysis was 6.53 × 10⁻⁶. -9 mbar, electron binding energy was corrected using the C1s peak (284.6 eV) of elemental carbon, data processing was performed on ThermoAvantage software, and quantitative analysis was performed using the sensitivity factor method in the analysis module.

[0035] In a preferred embodiment, based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 80%, preferably greater than 90%.

[0036] In a preferred embodiment, the molar ratio of pyrrole nitrogen to pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage, as measured by X-ray photoelectron spectroscopy, is greater than 2, preferably greater than 3.

[0037] In a preferred embodiment, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is 85.8-100%, and the molar content of pyridine nitrogen is 0-14.2%. More preferably, the molar content of pyrrole nitrogen is 100%.

[0038] The nitrogen species on the surface of the nitrogen-doped nanocarbon cage provided by this invention are pyridine nitrogen and pyrrole nitrogen, which is beneficial to improving the activity of the oxidation catalyst in the oxidation reaction of 5-hydroxymethylfurfural (HMF).

[0039] In a preferred embodiment, the nitrogen-doped carbon nanocage may also contain oxygen, which may be formed in the nitrogen-doped carbon nanocage in various forms during the preparation process.

[0040] In this invention, the content of each element on the surface of the nitrogen-doped carbon nanocage is not particularly limited. Preferably, the molar content of carbon on the surface of the nitrogen-doped carbon nanocage, as measured by X-ray photoelectron spectroscopy, is 89-92%, the molar content of nitrogen is 1-3%, and the molar content of oxygen is 5-10%.

[0041] According to a preferred embodiment of the present invention, the nitrogen-doped carbon nanocage may contain doping elements known to those skilled in the art that can be applied to carbon materials. Preferably, the nitrogen-doped carbon nanocage does not contain elements such as nickel, sulfur, boron, phosphorus, fluorine, chlorine, bromine, or iodine.

[0042] In a particularly preferred embodiment, the nitrogen-doped carbon nanocage has a BET specific surface area of ​​400-800 m². 2 / g. The advantage of this preferred embodiment is that it can better disperse the metal components, promote mass transfer in the reaction process, and effectively improve catalyst activity and target product selectivity.

[0043] In a preferred embodiment, the total pore volume of the nitrogen-doped carbon nanocage is greater than 0.6 cm³. 3 / g, further preferably greater than 0.9cm 3 / g.

[0044] In a preferred embodiment, the nitrogen-doped carbon nanocage has a dual mesoporous distribution peak, which corresponds to a first most probable pore size and a second most probable pore size, respectively. The first most probable pore size is 3.5-4 nm, and the second most probable pore size is 6-9.5 nm. In this preferred embodiment, the small pore size further provides a large specific surface area for the material, increasing active sites, while the large pore size provides diffusion channels for molecules or ions, accelerating mass transfer and providing higher stability.

[0045] In this invention, the term "mesopore" is defined as a pore with a diameter in the range of 2-50 nm.

[0046] In this invention, the pore structure properties of nitrogen-doped carbon nanocages are detected using the BET test method. Specifically, a Quantachrome AS-6B analyzer is used for measurement. The BET specific surface area and pore volume of the nitrogen-doped carbon nanocages are obtained by the Brunauer-Emmett-Taller (BET) method, and the mesopore distribution curve is calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0047] In a preferred embodiment, in the Raman curve of the nitrogen-doped carbon nanocage, I D / I G The value ranges from 0.2 to 1, preferably from 0.3 to 0.8. The nitrogen-doped carbon nanocage of the present invention has obvious D and G peaks and exhibits a certain degree of graphitization.

[0048] In this invention, the degree of graphitization of nitrogen-doped carbon nanocages is characterized by Raman spectroscopy at 1355 cm⁻¹. -1 The peak (D peak) is attributed to structural defects, consisting of amorphous carbon, at 1585 cm⁻¹. -1 The peak (G peak) is attributed to carbon in a planar structure. I0 is typically used. D / I G The degree of graphitization of a material is characterized by the intensity ratio of the D peak to the G peak. D / I G The higher the value, the more defects and the lower the degree of graphitization. The Raman spectrum of the material was obtained using an RM2000 microconfocal Raman spectrometer (Reinshaw product). Technical specifications: The excitation source was a He-Ne laser with a wavelength of 525 nm.

[0049] In a preferred embodiment, the nitrogen-doped carbon nanocage is prepared by the following method:

[0050] (1) A solution containing a transition metal salt, a nitrogen-containing organic carboxylic acid and a solvent is provided, and then dried to obtain a precursor, wherein the nitrogen-containing organic carboxylic acid is ethylenediaminetetraacetic acid; the molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid, calculated based on the transition metal element, is 1:0.6-1;

[0051] (2) Under an inert or reducing atmosphere, the precursor obtained in step (1) is subjected to high-temperature pyrolysis to obtain pyrolysis products;

[0052] (3) The pyrolysis product is acid washed, then solid-liquid separation, washing and drying are performed.

[0053] In a preferred embodiment, the nitrogen-doped carbon nanocage is prepared by using a specific nitrogen-containing organic carboxylic acid and by controlling a specific ratio of transition metal salt to the specific nitrogen-containing organic carboxylic acid. The nitrogen-doped carbon nanocage has a hollow cage-like structure with a diameter of 2-200 nm. Based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 80%. The preparation method uses simple equipment and is easy to operate. In some embodiments, the nitrogen-doped carbon nanocage can be obtained under pure aqueous phase and atmospheric pressure conditions through simple mixing, pyrolysis, and acid washing.

[0054] In this invention, there is no particular limitation on the amount of each substance used in step (1) during the preparation of nitrogen-doped carbon nanocages. Preferably, in step (1), the molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid, calculated as a transition metal element, is 1:0.6-1, more preferably 1:0.6-0.9. A molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid within the above-mentioned range is beneficial for controlling the nitrogen content and the types of nitrogen species, so that the nitrogen on the surface of the prepared nitrogen-doped carbon nanocage exists in the form of pyrrole nitrogen and / or pyridine nitrogen.

[0055] In a preferred embodiment, the amount of the transition metal salt and the nitrogen-containing organic carboxylic acid is such that the molar content of carbon on the surface of the nitrogen-doped nanocage is 89-92%, the molar content of nitrogen is 1-3%, and the molar content of oxygen is 5-10%.

[0056] In a preferred embodiment, the amount of the transition metal salt and nitrogen-containing organic carboxylic acid is such that the nitrogen on the surface of the nitrogen-doped carbon nanocage is mainly in the form of pyrrole nitrogen and / or pyridine nitrogen. Based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and / or pyridine nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 80%, preferably greater than 90%.

[0057] In this invention, the preparation process of nitrogen-doped carbon nanocages does not particularly limit the type of transition metal salt in step (1), and all transition metal salts conventionally defined in the art are applicable to this invention. Preferably, in step (1), the transition metal salt is selected from at least one of organic acid salts of transition metals, carbonates of transition metals, and basic carbonates of transition metals, and more preferably carbonates of transition metals and / or basic carbonates of transition metals.

[0058] In this invention, the nitrogen-doped carbon nanocage preparation process allows for a wide range of choices for the transition metal in step (1). Preferably, the transition metal is a Group VIII metal element, more preferably at least one of iron, cobalt, nickel, and copper, and even more preferably nickel.

[0059] In a preferred embodiment, the transition metal salt is selected from basic nickel carbonate and / or nickel acetate.

[0060] In this invention, during the preparation process of nitrogen-doped carbon nanocages, step (1) does not particularly limit the method of forming the solution. For example, it can be formed by heating, and more preferably by heating and stirring. This invention also does not particularly limit the heating temperature or the stirring rate, as long as the solution can be formed.

[0061] According to a preferred embodiment of the present invention, in step (1), the precursor is obtained by dissolving a transition metal salt and a nitrogen-containing organic carboxylic acid in a solvent to form a homogeneous solution, and then removing the solvent from the homogeneous solution. The present invention does not particularly limit the type of solvent, as long as it can form a homogeneous solution. Preferably, the solvent is water and / or ethanol, more preferably water; the present invention also does not particularly limit the amount of solvent used, again as long as it can form a homogeneous solution. The solvent in the homogeneous solution can be removed by direct evaporation. The evaporation temperature and process can adopt existing techniques known to those skilled in the art, for example, the solvent in the homogeneous solution can be removed by heating to dryness.

[0062] In this invention, the nitrogen-doped carbon nanocage preparation process allows for a wide range of selection for the high-temperature pyrolysis conditions in step (2). Preferably, the high-temperature pyrolysis conditions are: a heating rate of 0.5-30℃ / min, a high-temperature pyrolysis temperature of 850-1000℃, and a holding time of 20-600min; more preferably, the high-temperature pyrolysis conditions are: a heating rate of 1-20℃ / min, a high-temperature pyrolysis temperature of 850-950℃, and a holding time of 60-480min. Using the above-mentioned high-temperature pyrolysis conditions can adjust the types of nitrogen species and the removal rate of transition metals. For example, if the temperature is too low, it is not conducive to the removal of transition metals from the material, while if the temperature is too high, nitrogen-doped carbon nanocages containing other nitrogen species are easily generated.

[0063] According to a preferred embodiment of the present invention, in the nitrogen-doped carbon nanocage preparation process, step (2) involves a two-stage heating method to reach the high-temperature pyrolysis temperature. Specifically, the temperature is first increased to 400-800℃, preferably 500-700℃, at a rate of 1-20℃ / min, preferably 5-10℃ / min, and held at this temperature for 20-600min, preferably 60-480min. Then, the temperature is further increased to the high-temperature pyrolysis temperature at a rate of 1-20℃ / min, preferably 5-10℃ / min, and held at this temperature for 20-600min, preferably 60-480min. In this invention, the two-stage heating method is beneficial for forming nitrogen-doped carbon nanocages containing only pyrrole nitrogen or only pyrrole nitrogen and pyridine nitrogen in the nitrogen species.

[0064] In this invention, the type of inert atmosphere in step (2) of the nitrogen-doped carbon nanocage preparation process is not particularly limited, and any inert atmosphere conventionally defined in the art is applicable to this invention. Preferably, in step (2), the inert atmosphere is selected from at least one of nitrogen, argon, neon, and helium.

[0065] In this invention, the type of reducing atmosphere in step (2) of the nitrogen-doped carbon nanocage preparation process is not particularly limited, and any reducing atmosphere conventionally defined in the art is applicable to this invention. Preferably, the reducing atmosphere is provided by hydrogen and optionally an inert gas, wherein the inert gas is selected from at least one of nitrogen, argon, neon and helium.

[0066] In this invention, during the preparation process of nitrogen-doped carbon nanocages, step (3) involves acid washing the pyrolysis product using an acid washing agent. Specifically, this can be achieved by mixing the pyrolysis product with the acid washing agent. This invention does not impose any particular limitation on the mixing method; ultrasonic or stirring methods can be used. The acid washing agent can be any acid commonly used in the art, as long as it can remove the transition metals from the pyrolysis product. Preferably, the acid washing agent is an aqueous solution of an inorganic acid and / or an aqueous solution of an organic acid, more preferably at least one of an aqueous solution of hydrochloric acid, an aqueous solution of sulfuric acid, an aqueous solution of nitric acid, and an aqueous solution of citric acid, and even more preferably an aqueous solution of hydrochloric acid.

[0067] In this invention, during the preparation process of nitrogen-doped carbon nanocages, the concentration of the acid washing agent in step (3) is not particularly limited. Preferably, the concentration of the inorganic acid aqueous solution and / or organic acid aqueous solution is 0.1-10 mol / L.

[0068] In this invention, during the preparation process of nitrogen-doped carbon nanocages, the pH of the pickling agent in step (3) is not particularly limited. Preferably, the pH of the inorganic acid aqueous solution and / or organic acid aqueous solution is less than 7. This invention does not have specific requirements on the amount of the pickling agent used, as long as it is sufficient to remove transition metals from the pyrolysis products.

[0069] In a preferred embodiment, in the nitrogen-doped carbon nanocage preparation process, in step (3), the acid washing temperature is 20-120℃ and the time is 0.1-48h; more preferably, the temperature is 60-100℃ and the time is 4-12h.

[0070] In the nitrogen-doped carbon nanocage preparation process, step (3) does not have any particular limitation on the solid-liquid separation method. It can be carried out by solid-liquid separation methods known in the art, such as filtration.

[0071] In a preferred embodiment, in the nitrogen-doped carbon nanocage preparation process, in step (3), the washing is used to remove the acid and metal ions remaining on the nitrogen-doped carbon nanocage during the acid washing process. Therefore, various water washing methods that can wash the nitrogen-doped carbon nanocage to neutrality are applicable to the present invention.

[0072] In a preferred embodiment, during the preparation process of nitrogen-doped carbon nanocages, step (3) involves drying to remove water from the nitrogen-doped carbon nanocages. For example, atmospheric pressure drying or reduced pressure drying can be used. Preferably, the drying conditions may include a temperature of 80-140°C and a time of 6-10 hours.

[0073] The nitrogen-doped carbon nanocages prepared by the above method have a BET specific surface area greater than 400 m². 2 / g.

[0074] A second aspect of the present invention provides a method for preparing the oxidation catalyst described in the first aspect, wherein the method comprises:

[0075] S1. An active metal component is introduced into the support by impregnation and then dried to obtain the catalyst precursor;

[0076] S2. The catalyst precursor obtained in step S1 is calcined in a calcining atmosphere and then treated in a reducing atmosphere to obtain an oxidation catalyst.

[0077] The active metal component is Ru and optionally at least one of Pt, Pd and Au;

[0078] The carrier is a nitrogen-doped carbon nanocage; the nitrogen-doped carbon nanocage has a hollow cage-like structure, and its diameter is 2-200 nm; based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 80%; the BET specific surface area of ​​the nitrogen-doped carbon nanocage is greater than 400 m². 2 / g.

[0079] This method is simple to operate and easy to implement. It uses nitrogen-doped carbon nanocages as a support to load specific active metal components to obtain an oxidation catalyst.

[0080] In this invention, there is no particular limitation on the amount of each substance in the catalyst. Preferably, the amount of nitrogen-doped carbon nanocage and active metal component is such that, based on the total amount of catalyst, the content of nitrogen-doped carbon nanocage is 80-99% by mass, and the content of active metal component (based on elemental composition) is 1-20% by mass; more preferably, the amount of nitrogen-doped carbon nanocage and active metal component is such that, based on the total amount of catalyst, the content of nitrogen-doped carbon nanocage is 85-95% by mass, and the content of active metal component (based on elemental composition) is 5-15% by mass.

[0081] In this invention, in step S1, "optionally at least one of Pt, Pd, and Au" means that the active metal component may contain at least one of Pt, Pd, and Au, or may not contain at least one of Pt, Pd, and Au. In a preferred embodiment, in step S1, the active metal component is Ru.

[0082] In this invention, the active metal components are provided by their respective precursors. Preferably, the active metal component precursors are selected from chlorides and / or nitrates of the respective active metal components.

[0083] In a preferred embodiment, the precursor of Ru is selected from ruthenium chloride and / or ruthenium nitrate.

[0084] In a preferred embodiment, the precursor of Pt is selected from chloroplatinic acid and / or platinum nitrate.

[0085] In a preferred embodiment, the precursor of Pd is selected from palladium chloride and / or palladium nitrate.

[0086] In a preferred embodiment, the precursor of Au is selected from gold chloride and / or gold nitrate.

[0087] In this invention, the properties of nitrogen-doped carbon nanocages, such as the choice of diameter, have been described in the first aspect and will not be repeated here.

[0088] In this invention, the types and contents of each species in the nitrogen-doped nano-carbon cage have been described in the first aspect and will not be repeated here.

[0089] In this invention, the BET surface area, total pore volume, pore distribution, and I of nitrogen-doped carbon nanocages are analyzed. D / I G As already explained in the first aspect, it will not be repeated here.

[0090] In this invention, the preparation method of nitrogen-doped carbon nanocages has been described in the first aspect and will not be repeated here.

[0091] In this invention, the drying conditions in step S1 can be selected within a wide range; for example, drying under normal pressure is acceptable. Preferably, the drying conditions include a temperature of 100-140°C and a time of 6-24 hours.

[0092] In this invention, there is no particular limitation on the type of calcination atmosphere in step S2; any calcination atmosphere conventionally defined in the art is applicable to this invention. Preferably, the calcination atmosphere is selected from at least one of nitrogen, argon, neon, and helium, with nitrogen being the most preferred.

[0093] In this invention, the calcination conditions in step S2 can be selected within a wide range. Preferably, the calcination conditions include a temperature of 300-800℃ and a time of 2-8 hours; more preferably, the calcination conditions include a temperature of 400-600℃ and a time of 3-6 hours. The advantage of this preferred embodiment is that it effectively removes impurities such as Cl from the metal component precursor.

[0094] In this invention, the type of reducing atmosphere in step S2 is not particularly limited, and any reducing atmosphere conventionally defined in the art is applicable to this invention. Preferably, the reducing atmosphere is hydrogen and optionally an inert gas, wherein the inert gas is selected from at least one of nitrogen, argon, neon, and helium.

[0095] In a preferred embodiment, the reducing atmosphere is hydrogen and nitrogen.

[0096] In a preferred embodiment, the reducing atmosphere contains 5-30% hydrogen by volume and 70-95% nitrogen by volume.

[0097] In this invention, the reduction conditions in step S2 can be selected over a wide range. Preferably, the reduction conditions include: a temperature of 200-600℃, a time of 1-5 h, and a volume hourly space velocity (VHSV) of 1-100 h⁻¹. -1 More preferably, the reduction conditions include: a temperature of 400-500℃, a time of 2-4 hours, and a volume hourly space velocity (VHSV) of 5-50 h⁻¹. -1 .

[0098] In this field, conventionally defined preparation methods for catalysts are applicable to this invention, such as isochoric impregnation, initial wet impregnation, ion exchange, deposition-precipitation, or vacuum impregnation. According to a specific embodiment of this invention, the catalyst can be prepared by initial wet impregnation, specifically: a solution containing an active metal precursor is introduced into a support and impregnated at room temperature for 1-12 hours, followed by drying in an oven at 100-140°C for 6-24 hours. The resulting catalyst precursor is then calcined in an inert gas (e.g., nitrogen) at 300-800°C for 2-8 hours, and then reduced in a reducing atmosphere (e.g., a mixture of hydrogen and nitrogen) at 200-600°C for 1-5 hours to obtain the oxidation catalyst.

[0099] According to one specific embodiment of the present invention, the present invention provides an oxidation catalyst prepared by the preparation method described in the second aspect.

[0100] A third aspect of the present invention provides a method for preparing 2,5-furandicarboxylic acid, wherein the method comprises: reacting 5-hydroxymethylfurfural with an oxygen-containing gas in the presence of the oxidation catalyst described in the first aspect, in the presence of a mixed solvent containing an organic solvent and / or water, to obtain 2,5-furandicarboxylic acid.

[0101] This invention increases the solubility of the product 2,5-furandicarboxylic acid by using a mixture of water and organic solvent in an appropriate ratio as the reaction solvent, thus avoiding the introduction of alkaline compounds. It also simplifies the post-processing steps of the product and avoids the generation of large amounts of waste acid and wastewater in the subsequent acidification process. In addition, this invention uses a Ru-based catalyst supported on a nitrogen-doped nano-carbon cage as the oxidation catalyst. The catalyst has high oxidation activity, high yield of 2,5-furandicarboxylic acid, and the reaction process is green and simple.

[0102] In this invention, there is no particular limitation on the type of organic solvent; organic solvents conventionally defined in the art are all applicable. Preferably, the organic solvent is selected from at least one of tetrahydrofuran, 1,4-dioxane, γ-valerolactone, and dimethyl sulfoxide, and more preferably 1,4-dioxane. Using the above-mentioned organic solvent has the advantage of significantly improving the saturated solubility of FDCA after forming a mixture with water.

[0103] In a preferred embodiment, the mass ratio of organic solvent to water in the mixed solvent is 5:1-0.2:1, preferably 3:1-0.5:1.

[0104] In a preferred embodiment, based on the total amount of the solution formed by the 5-hydroxymethylfurfural and the mixed solvent, the content of the 5-hydroxymethylfurfural is 0.1-30% by mass, preferably 0.5-20% by mass, and more preferably 1-10% by mass. The advantage of this preferred embodiment is that the concentration of the generated FDCA is controlled within the saturated solubility of FDCA corresponding to the reaction conditions, thus avoiding the crystallization of FDCA during the reaction.

[0105] In a preferred embodiment, the molar ratio of the active metal component to 5-hydroxymethylfurfural in the oxidation catalyst is 1:1-1000, preferably 1:5-250, and more preferably 1:5-30. The advantage of this preferred embodiment is that the suitable ratio range can accelerate the conversion of intermediate species during the reaction process while controlling the amount of precious metal used, thus avoiding side reactions.

[0106] In this invention, the range of oxygen-containing gases is relatively wide, as long as oxygen can be provided. Preferably, the oxygen-containing gas is selected from pure oxygen, air, and a mixture of oxygen and an inert gas, wherein the inert gas is selected from at least one of nitrogen, argon, neon, and helium.

[0107] In a preferred embodiment, the partial pressure of the oxygen-containing gas is 0.2-4 MPa, preferably 1-3 MPa.

[0108] In this invention, there are no particular limitations on the reaction conditions, as long as 2,5-furandicarboxylic acid can be prepared. Preferably, the reaction temperature is 50-170℃ and the time is 1-30h, and more preferably, the temperature is 90-150℃ and the time is 5-15h.

[0109] In this invention, the reaction is carried out under stirring conditions, and the stirring conditions are not particularly limited. Preferably, the stirring speed is 500-1000 rpm.

[0110] In a preferred embodiment, the reaction products are separated into solid and liquid components after the reaction is completed. The method of solid-liquid separation is not particularly limited in this invention; any method known in the art can be used, such as filtration.

[0111] In a preferred embodiment, the filter cake obtained after solid-liquid separation of the washing reaction product is treated with a washing solvent. The type of washing solvent is not particularly limited in this invention. Preferably, the mixed solvent used in the reaction process is selected as the washing solvent. Similarly, the washing method is not particularly limited in this invention; methods conventionally defined in the art are applicable to this invention.

[0112] In this invention, high-performance liquid chromatography (HPLC) is used to analyze the reaction products. Preferably, the HPLC conditions include using an Alltech OA-1000 organic acid column, a UV detector, a mobile phase of 0.005 mol / L H₂SO₄ aqueous solution, a flow rate of 0.6 mL / min, and a column temperature of 70 °C.

[0113] The present invention will be described in detail below through embodiments.

[0114] Unless otherwise specified, all reagents used in this invention are of analytical grade and are commercially available.

[0115] The surface morphology of the material was characterized by high-resolution transmission electron microscopy (HRTEM). The HRTEM used was a JEM-2100 (Nippon Electron Ltd.), and the testing conditions were: accelerating voltage of 200 kV. The diameter of the nitrogen-doped carbon nanocages was measured from the HRTEM images.

[0116] The pore structure properties of the material were detected using the BET test method. Specifically, a Quantachrome AS-6B analyzer was used for measurement. The specific surface area and pore volume of the material were obtained by the Brunauer-Emmett-Taller (BET) method, and the mesopore distribution curve was calculated from the desorption curve using the Barrett-Joyner-Halenda (BJH) method.

[0117] The elemental content of the material surface was determined by X-ray photoelectron spectroscopy (XPS). X-ray photoelectron spectroscopy analysis was performed on an ESCALab250 X-ray photoelectron spectrometer from Thermo Scientific equipped with ThermoAvantage V5.926 software. The excitation source was monochromatic Al Kα X-rays with an energy of 1486.6 eV and a power of 150 W. The narrow scan passthrough energy was 30 eV, and the baseline vacuum during analysis was 6.53 × 10⁻⁶. -9 mbar, electron binding energy was corrected using the C1s peak (284.6 eV) of elemental carbon, data processing was performed on ThermoAvantage software, and quantitative analysis was performed using the sensitivity factor method in the analysis module.

[0118] The degree of graphitization of the material was characterized by Raman spectroscopy at 1355 cm⁻¹. -1 The peak (D peak) is attributed to structural defects, consisting of amorphous carbon, at 1585 cm⁻¹. -1 The peak (G peak) is attributed to carbon in a planar structure. I0 is typically used. D / I G The degree of graphitization of a material is characterized by the intensity ratio of the D peak to the G peak. D / I G The higher the value, the more defects and the lower the degree of graphitization. The Raman spectrum of the material was obtained using an RM2000 microconfocal Raman spectrometer (Reinshaw product). Technical specifications: The excitation source was a He-Ne laser with a wavelength of 525 nm.

[0119] In this invention, high performance liquid chromatography (HPLC) is used to analyze the reaction products of 2,5-furandicarboxylic acid. The HPLC conditions include using an Alltech OA-1000 organic acid column, a UV detector, a mobile phase of 0.005 mol / L H2SO4 aqueous solution, a flow rate of 0.6 mL / min, and a column temperature of 70 °C.

[0120] Preparation Examples 1-3 are used to illustrate the preparation of nitrogen-doped carbon nanocages.

[0121] Preparation Example 1

[0122] (1) Weigh 15g of basic nickel carbonate and 20.9g of ethylenediaminetetraacetic acid (molar ratio 1:0.7), add them to a beaker containing 40mL of deionized water, stir and mix evenly at 80℃, and continue to heat and evaporate to dryness to obtain a solid precursor.

[0123] (2) Place the precursor obtained in step (1) into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas with a flow rate of 80 mL / min, and heat it to 600℃ at a rate of 10℃ / min. After holding the temperature for 1 hour, continue to heat it to 900℃ at a rate of 10℃ / min and hold the temperature for 2 hours. Stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the pyrolysis product.

[0124] (3) Add the pyrolysis product obtained in step (2) to an aqueous solution containing 2M hydrochloric acid and stir at 90°C for 8 hours. Then filter, collect the filtrate, wash with deionized water until the filtrate is neutral, and then dry the filter cake in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nano carbon cage Z1.

[0125] Figure 1 The image shows a TEM image of the nitrogen-doped carbon nanocage. As can be seen from the image, the nitrogen-doped carbon nanocage is a hollow cage-shaped carbon nanomaterial with a diameter of 5-20 nm.

[0126] Figure 2 The XPS spectrum of the nitrogen-doped carbon nanocage shows that, in addition to carbon, oxygen and nitrogen are present on the surface of the nitrogen-doped carbon nanocage. The atomic molar percentage of each element can be calculated from the peak area, where carbon is 90.06%, oxygen is 8.4%, and nitrogen is 1.54%.

[0127] Figure 3The XPS N1s peak spectrum of the nitrogen-doped carbon nanocage shows that the nitrogen on the surface of the nitrogen-doped carbon nanocage exists in the form of pyrrole nitrogen, and there are no other forms of nitrogen species. Based on the total molar amount of nitrogen, the content of pyrrole nitrogen is 100%.

[0128] BET testing showed that the nitrogen-doped carbon nanocage had a BET specific surface area of ​​466.24 m². 2 / g, pore volume is 0.978cm³ 3 / g. Figure 4 The figure shows the BJH pore size distribution curve of the nitrogen-doped carbon nanocage. As can be seen from the figure, there are two mesoporous distribution peaks at 3.68 nm and 6.15 nm.

[0129] Raman spectroscopy analysis revealed that the nitrogen-doped carbon nanocage exhibited distinct D and G peaks, I... D / I G The value is 0.5266, indicating that the nitrogen-doped carbon nanocage has a certain degree of graphitization.

[0130] Preparation Example 2

[0131] (1) Weigh 15g of basic nickel carbonate and 20.9g of ethylenediaminetetraacetic acid (molar ratio 1:0.7), add them to a beaker containing 40mL of deionized water, stir and mix evenly at 80℃, and continue to heat and evaporate to dryness to obtain a solid precursor.

[0132] (2) Place the precursor obtained in step (1) into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas with a flow rate of 80 mL / min, and heat it to 600℃ at a rate of 10℃ / min. After holding the temperature for 1 h, continue to heat it to 850℃ at a rate of 10℃ / min and hold the temperature for 2 h. Stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the pyrolysis product.

[0133] (3) Add the pyrolysis product obtained in step (2) to an aqueous solution containing 2M hydrochloric acid and stir at 100°C for 8 hours. Then filter, collect the filtrate, wash with deionized water until the filtrate is neutral, and then dry the filter cake in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nano carbon cage Z2.

[0134] High-resolution transmission electron microscopy (HRTEM) observation and measurement revealed that the nitrogen-doped carbon nanocage has a hollow cage-like structure with a diameter of 5-20 nm.

[0135] XPS measurements revealed that the surface of this nitrogen-doped carbon nanocage contained not only carbon but also oxygen and nitrogen. The atomic percentage of each element could be calculated from the peak areas: carbon 91.05%, oxygen 7.48%, and nitrogen 1.47%. Nitrogen peaks in this nitrogen-doped carbon nanocage were further analyzed. Figure 5 As shown in the figure, the nitrogen on the surface of the nitrogen-doped carbon nanocage exists in two forms: pyrrole nitrogen and pyridine nitrogen. Based on the total molar amount of nitrogen, the content of pyrrole nitrogen is 92.01%, and the content of pyridine nitrogen is 7.99%.

[0136] BET testing showed that the nitrogen-doped carbon nanocage had a BET specific surface area of ​​713.17 m². 2 / g, pore volume is 1.482cm³ 3 / g. In the BJH pore size distribution curve of this nitrogen-doped carbon nanocage, two mesopore distribution peaks exist at 3.71 nm and 6.25 nm.

[0137] Raman spectroscopy analysis revealed that the nitrogen-doped carbon nanocage exhibited distinct D and G peaks, I... D / I G The value is 0.703, indicating that the nitrogen-doped carbon nanocage has a certain degree of graphitization.

[0138] Preparation Example 3

[0139] (1) Weigh 15g of nickel acetate and 22.3g of ethylenediaminetetraacetic acid (molar ratio of 1:0.9), add them to a beaker containing 40mL of deionized water, stir and mix evenly at 80℃, and continue to heat and evaporate to dryness to obtain a solid precursor.

[0140] (2) Place the precursor obtained in step (1) into a ceramic boat, then place the ceramic boat in the constant temperature zone of a tube furnace, introduce nitrogen gas with a flow rate of 150 mL / min, and heat it to 950 °C at a rate of 20 °C / min. After holding the temperature for 2 hours, stop heating and cool it to room temperature under a nitrogen atmosphere to obtain the pyrolysis product.

[0141] (3) Add the pyrolysis product obtained in step (2) to an aqueous solution containing 2M nitric acid and stir at 100°C for 8 hours. Then filter, collect the filtrate, wash with deionized water until the filtrate is neutral, and then dry the filter cake in a constant temperature oven at 120°C for 6 hours to obtain nitrogen-doped nano carbon cage Z3.

[0142] High-resolution transmission electron microscopy (HRTEM) observation and measurement revealed that the nitrogen-doped carbon nanocage has a hollow cage-like structure with a diameter of 5-20 nm.

[0143] XPS measurements revealed that the surface of this nitrogen-doped carbon nanocage contained not only carbon but also oxygen and nitrogen. The atomic percentage of each element could be calculated from the peak areas: carbon 89.96%, oxygen 7.97%, and nitrogen 2.07%. Nitrogen peaks in this nitrogen-doped carbon nanocage were further analyzed. Figure 6 As shown in the figure, the nitrogen on the surface of the nitrogen-doped carbon nanocage exists in two forms: pyrrole nitrogen and pyridine nitrogen. Based on the total molar amount of nitrogen, the content of pyrrole nitrogen is 85.80% and the content of pyridine nitrogen is 14.20%.

[0144] BET testing showed that the nitrogen-doped carbon nanocage had a BET specific surface area of ​​512.17 m². 2 / g, pore volume is 1.123cm³ 3 / g. In the BJH pore size distribution curve of this nitrogen-doped carbon nanocage, two mesopore distribution peaks exist at 3.59 nm and 9.25 nm.

[0145] Raman spectroscopy analysis revealed that the nitrogen-doped carbon nanocage exhibited distinct D and G peaks, I... D / I G The value of 0.324 indicates that the nitrogen-doped carbon nanocage has a certain degree of graphitization.

[0146] Examples 1-8 and Comparative Examples 1-4 are used to illustrate the preparation of oxidation catalysts.

[0147] Example 1

[0148] Preparation of nitrogen-doped carbon nanocage-supported Ru-based oxidation catalyst (10% Ru / C) by initial wet impregnation method:

[0149] Weigh out 0.1 g of RuCl3 solution and 10.0 mL of deionized water according to the mass of Ru, mix well, and then add 0.9 g of nitrogen-doped carbon nanocage (Z2) obtained in Preparation Example 2 to the mixture. After stirring and impregnation at room temperature for 10 hours, evaporate the water using a rotary evaporator, and then dry in an oven at 110 °C for 12 hours to obtain the catalyst precursor. The Ru loading is 10% (mass percentage). Place the precursor prepared in the above steps in a quartz tube, calcine it at 500 °C for 4 h in nitrogen, and then reduce it at 500 °C for 3 h in a reducing atmosphere of 20 vol% H2 + 80 vol% N2 with a volume hourly space velocity of 10 h⁻¹. -1 Catalyst A1 with a loading of 10% Ru / C was obtained (where the loading is based on the total amount of catalyst).

[0150] Example 2

[0151] Following the method of Example 1, a RuCl3 solution containing 0.05 g of Ru was weighed and mixed with 10 mL of deionized water using a Ru mass meter. The mixture was stirred until homogeneous. Then, 0.95 g of the nitrogen-doped carbon nanocage (Z2) obtained in Preparation Example 2 was added to the mixture. After stirring and impregnation at room temperature for 10 hours, the water was evaporated using a rotary evaporator, and then dried in an oven at 110 °C for 12 hours to obtain the catalyst precursor. The Ru loading was 5% (mass percentage). The precursor prepared in the above steps was placed in a quartz tube and calcined at 400 °C for 6 hours in nitrogen atmosphere, followed by reduction at 400 °C for 4 hours in a reducing atmosphere of 20 vol% H2 + 80 vol% N2 with a reducing atmosphere volume hourly space velocity of 10 h⁻¹. -1 Catalyst A2 with a loading of 5% Ru / C was obtained (where the loading is based on the total amount of catalyst).

[0152] Example 3

[0153] Following the method of Example 1, a RuCl3 solution containing 0.15 g of Ru was weighed and mixed with 10 mL of deionized water using a Ru mass meter. The mixture was stirred until homogeneous. Then, 0.85 g of the nitrogen-doped carbon nanocage (Z2) obtained in Preparation Example 2 was added to the mixture. After stirring and impregnation at room temperature for 10 hours, the water was evaporated using a rotary evaporator, and then dried in an oven at 110 °C for 12 hours to obtain the catalyst precursor. The Ru loading was 15% (mass percentage). The precursor prepared in the above steps was placed in a quartz tube and calcined at 600 °C for 4 hours in nitrogen atmosphere, followed by reduction at 500 °C for 4 hours in a reducing atmosphere of 20 vol% H2 + 80 vol% N2 with a reducing atmosphere volume hourly space velocity (VHSV) of 20 h⁻¹. -1 Catalyst A3 with a loading of 15% Ru / C was obtained (where the loading is based on the total amount of catalyst).

[0154] Example 4

[0155] Following the method of Example 1, except that the nitrogen-doped carbon nanocage (Z1) obtained in Example 1 was used as the support, and all other conditions were the same, a catalyst A4 with a Ru loading of 10% by mass was prepared (wherein, the loading is based on the total amount of catalyst).

[0156] Example 5

[0157] Following the method of Example 1, except that the nitrogen-doped carbon nanocage (Z3) obtained in Preparation Example 3 was used as the support, and all other conditions were the same, a catalyst A5 with a Ru loading of 10% by mass was prepared (wherein the loading is based on the total amount of catalyst).

[0158] Example 6

[0159] Preparation of oxidation catalyst 5% Ru-5% Pt / C by initial wet impregnation method:

[0160] Weigh out a RuCl3 solution containing 0.05 g of Ru according to the mass of Ru, and weigh out an H2PtCl6 solution containing 0.05 g of Pt according to the mass of Pt. Mix the solutions with 10.0 mL of deionized water and stir until homogeneous. Then, add 0.9 g of nitrogen-doped carbon nanocages (Z2) obtained in Preparation Example 2 to the mixture. After stirring and impregnation at room temperature for 10 hours, evaporate the water using a rotary evaporator and then dry in an oven at 110 °C for 12 hours to obtain the catalyst precursor. The loading of Ru is 5% (mass percentage), and the loading of Pt is 5% (mass percentage). Place the precursor prepared in the above steps in a quartz tube and calcine it at 500 °C for 4 hours in nitrogen atmosphere, then reduce it at 500 °C for 3 hours in a reducing atmosphere of 20 vol% H2 + 80 vol% N2 with a volume hourly space velocity of 10 h⁻¹. -1 A supported 5% Ru-5% Pt / C catalyst A6 was obtained (wherein, the loading is based on the total amount of catalyst).

[0161] Example 7

[0162] Following the method of Example 5, a RuCl3 solution containing 0.08 g of Ru and an H2PtCl6 solution containing 0.02 g of Pt were weighed according to the mass of Pt and mixed with 10.0 mL of deionized water. The mixture was stirred until homogeneous. Then, 0.9 g of nitrogen-doped carbon nanocages (Z2) obtained in Preparation Example 2 were added to the mixture. After stirring and impregnation at room temperature for 10 hours, the water was evaporated using a rotary evaporator, and then dried in an oven at 110°C for 12 hours to obtain the catalyst precursor. The Ru loading was 8% (mass percentage), and the Pt loading was 2% (mass percentage). The precursor prepared in the above steps was placed in a quartz tube and calcined at 500°C for 4 hours in nitrogen atmosphere, followed by reduction at 500°C for 3 hours in a reducing atmosphere of 20 vol% H2 + 80 vol% N2 with a volume hourly space velocity (VHSV) of 10 h⁻¹. -1 The supported 8%Ru-2%Pt / C catalyst A7 was obtained (wherein the loading is based on the total amount of catalyst).

[0163] Example 8

[0164] Following the method of Example 5, a RuCl3 solution containing 0.05 g of Ru and a PdCl2 solution containing 0.05 g of Pd were weighed according to the mass of Ru and 10.0 mL of deionized water, respectively. The mixture was stirred until homogeneous. Then, 0.9 g of nitrogen-doped carbon nanocages (Z2) obtained in Preparation Example 2 were added to the mixture. After stirring and impregnation at room temperature for 10 hours, the water was evaporated using a rotary evaporator, and then dried in an oven at 110°C for 12 hours to obtain the catalyst precursor. The loading of Ru was 5% (mass percentage), and the loading of Pd was 5% (mass percentage). The precursor prepared in the above steps was placed in a quartz tube and calcined at 500°C for 4 hours in nitrogen atmosphere, followed by reduction at 500°C for 3 hours in a reducing atmosphere of 20 vol% H2 + 80 vol% N2 with a volume hourly space velocity (VHSV) of 10 h⁻¹. -1 A supported 5% Ru-5% Pd / C catalyst A8 was obtained (wherein the loading is based on the total amount of catalyst).

[0165] Comparative Example 1

[0166] Following the method of Example 1, a solution containing 0.1 g of Pt in H2PtCl6 and 10.0 mL of deionized water were weighed and mixed thoroughly. Then, 0.9 g of nitrogen-doped carbon nanocages (Z2) obtained in Preparation Example 2 were added to the mixture. After stirring and impregnation at room temperature for 10 hours, the water was evaporated using a rotary evaporator, and then dried in an oven at 110°C for 12 hours to obtain the catalyst precursor. The Pt loading was 10% (mass percentage). The precursor prepared in the above steps was placed in a quartz tube and calcined at 500°C for 4 hours in nitrogen atmosphere, followed by reduction at 500°C for 3 hours in 20 vol% H2 + 80 vol% N2 atmosphere to obtain catalyst D1 with a Pt / C loading of 10% (wherein, the loading is based on the total amount of catalyst).

[0167] Comparative Example 2

[0168] Following the method of Example 1, a PdCl2 solution containing 0.1 g of Pd was weighed and mixed with 10.0 mL of deionized water according to the mass of Pd. The mixture was stirred until homogeneous. Then, 0.9 g of nitrogen-doped carbon nanocages (Z2) obtained in Preparation Example 2 was added to the mixture. After stirring and impregnation at room temperature for 10 hours, the water was evaporated using a rotary evaporator, and then dried in an oven at 110 °C for 12 hours to obtain the catalyst precursor. The Pd loading was 10% (mass percentage). The precursor prepared in the above steps was placed in a quartz tube and calcined at 500 °C for 4 hours in nitrogen atmosphere, and then reduced at 500 °C for 3 hours in 20 vol% H2 + 80 vol% N2 atmosphere to obtain catalyst D2 with a Pd / C loading of 10% (wherein, the loading is based on the total amount of catalyst).

[0169] Comparative Example 3

[0170] Following the method of Example 1, a solution containing 0.1 g of Au and 10.0 mL of deionized water were weighed and mixed, stirred until homogeneous, and then 0.9 g of nitrogen-doped carbon nanocages (Z2) obtained in Preparation Example 2 were added to the mixture. After stirring and impregnation at room temperature for 10 hours, the water was evaporated using a rotary evaporator, and then dried in an oven at 110°C for 12 hours to obtain the catalyst precursor. The Au loading was 10% (mass percentage). The precursor prepared in the above steps was placed in a quartz tube, calcined at 500°C for 4 hours in nitrogen, and then reduced at 500°C for 3 hours in 20 vol% H2 + 80 vol% N2 to obtain catalyst D3 with a loading of 10% Au / C (wherein, the loading is based on the total amount of catalyst).

[0171] Comparative Example 4

[0172] Following the method of Example 1, except that the carrier was commercially available Cabot VXC72 activated carbon product, and all other conditions were the same, catalyst D4 with a loading of 10% Ru / C was obtained (wherein the loading is based on the total amount of catalyst).

[0173] Test Examples 1-18 and Comparative Test Examples 1-4 are used to illustrate the preparation of 2,5-furandicarboxylic acid.

[0174] The conversion rate of 5-hydroxymethylfurfural and the yield of 2,5-furandicarboxylic acid were obtained by the following formula:

[0175] The conversion rate of 5-hydroxymethylfurfural = (1 - the molar amount of 5-hydroxymethylfurfural remaining after the reaction / the molar amount of 5-hydroxymethylfurfural added before the reaction) × 100%.

[0176] Yield of 2,5-furandicarboxylic acid = (molar amount of 2,5-furandicarboxylic acid produced in the reaction) / (molar amount of 5-hydroxymethylfurfural added before the reaction) × 100%.

[0177] Test Example 1

[0178] In a 50 mL high-pressure reactor, 0.5 g of 5-hydroxymethylfurfural, 0.2 g of the A1 catalyst from Example 1, and 10 g of a mixed solvent consisting of 1,4-dioxane and water (1,4-dioxane to water mass ratio 1:1) were added. After sealing the reactor, 1 MPa of oxygen was introduced to replace the residual air in the reactor. This process was repeated three times. Then, 1 MPa of oxygen was introduced into the reactor, and the reactor was placed on a furnace and heated to the reaction temperature of 100 °C. The reaction was stirred at 700 rpm for 10 hours. After the reaction was completed, the reactor was removed from the furnace, cooled to room temperature, filtered, and the filter cake was washed with the same mixed solvent as the reaction solvent. The final volume was adjusted to 100 mL, and the liquid sample was taken for high-performance liquid chromatography analysis. The reaction results are listed in Table 1.

[0179] Test Example 2

[0180] The method was the same as in Test Example 1, except that 0.4 g of the A2 catalyst from Example 2 was used as the oxidation catalyst. The reaction results are listed in Table 1.

[0181] Test Example 3

[0182] The method was the same as in Test Example 1, except that 0.1 g of the A3 catalyst from Example 3 was used as the oxidation catalyst. The reaction results are listed in Table 1.

[0183] Test Example 4

[0184] The method was the same as in Test Example 1, except that 0.2 g of the A4 catalyst from Example 4 was used as the oxidation catalyst. The reaction results are listed in Table 1.

[0185] Test Example 5

[0186] The method was the same as in Test Example 1, except that 0.2 g of the A5 catalyst from Example 5 was used as the oxidation catalyst. The reaction results are listed in Table 1.

[0187] Test Example 6

[0188] The method was the same as in Test Example 1, except that 0.2 g of the A6 catalyst from Example 6 was used as the oxidation catalyst. The reaction results are listed in Table 1.

[0189] Test Example 7

[0190] The method was the same as in Test Example 1, except that 0.2g of the A7 catalyst from Example 7 was used as the oxidation catalyst. The reaction results are listed in Table 1.

[0191] Test Example 8

[0192] The method was the same as in Test Example 1, except that 0.2 g of the A8 catalyst from Example 8 was used as the oxidation catalyst. The reaction results are listed in Table 1.

[0193] Test Example 9

[0194] The method was the same as in Test Example 1, except that the oxygen pressure introduced into the reactor at the beginning of the reaction was 2 MPa. The reaction results are listed in Table 1.

[0195] Test Case 10

[0196] The method was the same as in Test Example 1, except that the oxygen pressure introduced into the reactor at the beginning of the reaction was 3 MPa. The reaction results are listed in Table 1.

[0197] Test Example 11

[0198] The method was the same as in Test Example 1, except that the reaction temperature was 120℃. The reaction results are listed in Table 1.

[0199] Test Example 12

[0200] The method was the same as in Test Example 1, except that the reaction temperature was 140℃. The reaction results are listed in Table 1.

[0201] Test Example 13

[0202] The method was the same as in Test Example 1, except that the reaction solvent was a mixed solvent of γ-valerolactone and water (the mass ratio of γ-valerolactone to water was 1:1), and the total amount of the mixed solvent was 10g. The reaction results are listed in Table 2.

[0203] Test Example 14

[0204] The method was the same as in Test Example 1, except that the reaction solvent was a mixed solvent of 1,4-dioxane and water (the mass ratio of 1,4-dioxane to water was 3:1), and the total amount of the mixed solvent was 10g. The reaction results are listed in Table 2.

[0205] Test Example 15

[0206] The method was the same as in Test Example 1, except that the reaction solvent was a mixed solvent of 1,4-dioxane and water (the mass ratio of 1,4-dioxane to water was 0.5:1), and the total amount of the mixed solvent was 10g. The reaction results are listed in Table 2.

[0207] Test Example 16

[0208] The method was the same as in Test Example 1, except that the reaction solvent was only water, with a total amount of 10g. The reaction results are listed in Table 2.

[0209] Test Example 17

[0210] The method was the same as in Test Example 1, except that the reaction solvent was only 1,4-dioxane, with a total amount of 10g. The reaction results are listed in Table 2.

[0211] Test Example 18

[0212] The method was the same as in Test Example 1, except that the reaction solvent was only γ-valerolactone, with a total amount of 10g. The reaction results are listed in Table 2.

[0213] Test Comparison Example 1

[0214] The method was the same as in Test Example 1, except that 0.2 g of catalyst D1 from Comparative Example 1 was used as the oxidation catalyst. All other conditions were the same. The reaction results are listed in Table 1.

[0215] Test Comparison Example 2

[0216] The method was the same as in Test Example 1, except that 0.2 g of the D2 catalyst prepared in Comparative Example 2 was used as the oxidation catalyst. All other conditions were the same. The reaction results are listed in Table 1.

[0217] Test Comparison Example 3

[0218] The method was the same as in Test Example 1, except that 0.2 g of the D3 catalyst from Comparative Example 3 was used as the oxidation catalyst. All other conditions were the same. The reaction results are listed in Table 1.

[0219] Test Case Comparison 4

[0220] The method was the same as in Test Example 1, except that 0.2 g of the D4 catalyst from Comparative Example 4 was used as the oxidation catalyst. All other conditions were the same. The reaction results are listed in Table 1.

[0221] Table 1

[0222]

[0223]

[0224] Table 2

[0225]

[0226] According to the data in Table 1, 1. The oxidation catalyst obtained by supporting active metal components on the nitrogen-doped nano-carbon cage support of this invention can achieve efficient conversion of HMF to FDCA under the conditions described in this method, with an FDCA yield as high as 91%. 2. As can be seen from the test examples and comparative test examples 1-4, the oxidation catalysts prepared by supporting only Pt, Pd, or Au active metal components on the nitrogen-doped nano-carbon cage support all exhibit significantly lower catalytic performance than the Ru-based oxidation catalyst supported by the nitrogen-doped nano-carbon cage. This indicates that the high specific surface area nitrogen-doped nano-carbon cage supported Ru-based oxidation catalyst involved in this invention has a special catalytic effect on the reaction of HMF oxidation to FDCA.

[0227] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. An oxidation catalyst, wherein, The catalyst comprises a support and an active metal component supported on the support, wherein the active metal component is Ru, and the support is a nitrogen-doped carbon nanocage; wherein the nitrogen-doped carbon nanocage has a hollow cage-like structure, and the diameter of the nitrogen-doped carbon nanocage is 5-20 nm; based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy shows that the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 80%; the BET specific surface area of ​​the nitrogen-doped carbon nanocage is greater than 400 m². 2 / g; The nitrogen-doped carbon nanocage has a dual mesoporous distribution peak, and the dual mesoporous distribution peaks correspond to the first most probable pore size and the second most probable pore size, respectively. The first most probable pore size is 3.5-4 nm, and the second most probable pore size is 6-9.5 nm. The nitrogen-doped carbon nanocage was prepared by the following method: (1) A solution containing a transition metal salt, a nitrogen-containing organic carboxylic acid and a solvent is provided, and then dried to obtain a precursor, wherein the nitrogen-containing organic carboxylic acid is ethylenediaminetetraacetic acid; the molar ratio of the transition metal salt to the nitrogen-containing organic carboxylic acid, calculated based on the transition metal element, is 1:0.6-1; (2) Under an inert or reducing atmosphere, the precursor obtained in step (1) is subjected to high-temperature pyrolysis to obtain pyrolysis products; (3) The pyrolysis product is acid-washed, then subjected to solid-liquid separation, washing and drying; In step (2), the high-temperature pyrolysis conditions are: heating rate of 0.5-30℃ / min, high-temperature pyrolysis temperature of 850-1000℃, and constant temperature time of 20-600min; The transition metal is nickel.

2. The catalyst according to claim 1, wherein, Based on the total amount of catalyst, the content of the nitrogen-doped nano-carbon cage is 80-99% by mass, and the content of the active metal component by element is 1-20% by mass.

3. The catalyst according to claim 2, wherein, Based on the total amount of catalyst, the content of the nitrogen-doped nano-carbon cage is 85-95% by mass, and the content of the active metal component by element is 5-15% by mass.

4. The catalyst according to any one of claims 1-3, wherein, Based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy determined that the molar content of pyrrole nitrogen and / or pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage is greater than 90%.

5. The catalyst according to any one of claims 1-3, wherein, X-ray photoelectron spectroscopy revealed that the molar ratio of pyrrole nitrogen to pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage was greater than 2.

6. The catalyst according to claim 5, wherein, X-ray photoelectron spectroscopy revealed that the molar ratio of pyrrole nitrogen to pyridine nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage was greater than 3.

7. The catalyst according to claim 4, wherein, Based on the total molar amount of nitrogen, X-ray photoelectron spectroscopy determined that the molar content of pyrrole nitrogen in the nitrogen on the surface of the nitrogen-doped carbon nanocage was 85.8-100%, and the molar content of pyridine nitrogen was 0-14.2%.

8. The catalyst according to claim 7, wherein, X-ray photoelectron spectroscopy revealed that the molar content of carbon on the surface of the nitrogen-doped carbon nanocage was 89-92%, the molar content of nitrogen was 1-3%, and the molar content of oxygen was 5-10%.

9. The catalyst according to any one of claims 1-3, wherein, The nitrogen-doped carbon nanocage has a BET specific surface area of ​​400-800 m². 2 / g.

10. The catalyst according to any one of claims 1-3, wherein, The total pore volume of the nitrogen-doped carbon nanocage is greater than 0.6 cm³. 3 / g.

11. The catalyst according to any one of claims 1-3, wherein, The total pore volume of nitrogen-doped carbon nanocages is greater than 0.9 cm³. 3 / g.

12. The catalyst according to any one of claims 1-3, wherein, In the Raman curve of the nitrogen-doped carbon nanocage, I D / I G The range is 0.2-1.

13. The catalyst according to claim 12, wherein, In the Raman curve of the nitrogen-doped carbon nanocage, I D / I G The range is 0.3-0.

8.

14. The catalyst according to claim 1 or 2, wherein, In step (1), the transition metal salt is selected from at least one of the following: organic acid salts of transition metals, carbonates of transition metals, and basic carbonates of transition metals. And / or, in step (1), the solvent is water; And / or, in step (2), the inert atmosphere is selected from at least one of nitrogen, argon, neon and helium; And / or, in step (2), the reducing atmosphere is hydrogen and optionally an inert gas; And / or, in step (3), the pickling agent used to pickle the pyrolysis product is an aqueous solution of inorganic acid and / or an aqueous solution of organic acid; And / or, in step (3), the pickling temperature is 20-120℃ and the time is 0.1-48h.

15. The catalyst according to claim 14, wherein, The transition metal salt is a carbonate of a transition metal and / or a basic carbonate of a transition metal.

16. The catalyst according to claim 1 or 2, wherein, The high-temperature pyrolysis conditions are as follows: heating rate of 1-20℃ / min, high-temperature pyrolysis temperature of 850-950℃, and isothermal time of 60-480min.

17. The catalyst according to claim 1 or 2, wherein, The high-temperature pyrolysis process includes: first, heating to 400-800℃ at a rate of 1-20℃ / min, holding at that temperature for 20-600min, and then continuing to heat to the high-temperature pyrolysis temperature at a rate of 1-20℃ / min, holding at that temperature for 20-600min.

18. The catalyst according to claim 17, wherein, The high-temperature pyrolysis process includes: first, heating to 500-700℃ at a rate of 5-10℃ / min, holding at that temperature for 60-480min, and then continuing to heat to the high-temperature pyrolysis temperature at a rate of 5-10℃ / min, holding at that temperature for 60-480min.

19. The catalyst according to claim 14, wherein, In step (3), the acid washing agent used to wash the pyrolysis product is at least one of hydrochloric acid aqueous solution, sulfuric acid aqueous solution, nitric acid aqueous solution and citric acid aqueous solution.

20. The catalyst according to claim 19, wherein, In step (3), the acid washing agent used to wash the pyrolysis product is an aqueous solution of hydrochloric acid.

21. The catalyst according to claim 14, wherein, In step (3), the pickling temperature is 60-100℃ and the time is 4-12h.

22. A method for preparing the oxidation catalyst according to any one of claims 1-21, wherein, The method includes: S1. An active metal component is introduced into the support by impregnation and then dried to obtain the catalyst precursor. S2. The catalyst precursor obtained in step S1 is calcined in a calcining atmosphere and then treated in a reducing atmosphere to obtain an oxidation catalyst.

23. The method according to claim 22, wherein, In step S1, the drying conditions include: a temperature of 100-140℃ and a time of 6-24h.

24. The method according to claim 22, wherein, In step S2, the calcination atmosphere is selected from at least one of nitrogen, argon, neon and helium; And / or, the reducing atmosphere is hydrogen and optionally an inert gas.

25. The method according to claim 22, wherein, The calcination conditions include: a temperature of 300-800℃ and a time of 2-8 hours.

26. The method of claim 25, wherein, The calcination conditions include: a temperature of 400-600℃ and a time of 3-6 hours.

27. The method according to claim 22, wherein, The processing conditions under the reducing atmosphere include: a temperature of 200-600℃, a time of 1-5 hours, and a volume hourly space velocity (VHSV) of 1-100 h⁻¹. -1 .

28. The method according to claim 27, wherein, The processing conditions under the reducing atmosphere include: a temperature of 400-500℃, a time of 2-4 hours, and a volume hourly space velocity (VHSV) of 5-50 h⁻¹. -1 .

29. A method for preparing 2,5-furandicarboxylic acid, wherein, The method comprises reacting 5-hydroxymethylfurfural with an oxygen-containing gas in the presence of an oxidation catalyst as described in any one of claims 1-21, in the presence of a mixed solvent containing an organic solvent and water, to obtain 2,5-furandicarboxylic acid.

30. The method according to claim 29, wherein, The organic solvent is selected from at least one of tetrahydrofuran, 1,4-dioxane, γ-valerol, and dimethyl sulfoxide; And / or, in the mixed solvent, the mass ratio of organic solvent to water is 5:1 to 0.2:

1.

31. The method according to claim 30, wherein, The organic solvent is 1,4-dioxane.

32. The method according to claim 30, wherein, In the mixed solvent, the mass ratio of organic solvent to water is 3:1 to 0.5:

1.

33. The method according to any one of claims 29-32, wherein, Based on the total volume of the solution formed by the 5-hydroxymethylfurfural and the mixed solvent, the content of the 5-hydroxymethylfurfural is 0.1-30% by mass. And / or, the molar ratio of the active metal component in the oxidation catalyst to 5-hydroxymethylfurfural is 1:1-1000; And / or, the oxygen-containing gas is selected from pure oxygen, air, and a mixture of oxygen and an inert gas; And / or, the partial pressure of the oxygen-containing gas is 0.2-4 MPa; And / or, the reaction temperature is 50-170℃ and the time is 1-30h.

34. The method according to claim 33, wherein, Based on the total amount of the solution formed by the 5-hydroxymethylfurfural and the mixed solvent, the content of the 5-hydroxymethylfurfural is 0.5-20% by mass.

35. The method according to claim 34, wherein, Based on the total amount of the solution formed by the 5-hydroxymethylfurfural and the mixed solvent, the content of the 5-hydroxymethylfurfural is 1-10% by mass.

36. The method according to claim 33, wherein, The molar ratio of the active metal component in the oxidation catalyst to 5-hydroxymethylfurfural is 1:5-250.

37. The method of claim 36, wherein, The molar ratio of the active metal component in the oxidation catalyst to 5-hydroxymethylfurfural is 1:5-30.

38. The method according to claim 33, wherein, The partial pressure of the oxygen-containing gas is 1-3 MPa.

39. The method according to claim 33, wherein, The reaction temperature is 90-150℃, and the time is 5-15h.

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