CN109046349B

CN109046349B - Monoatomic palladium catalyst, preparation method thereof and method for preparing 2,5-FDCA by catalytic oxidation of 5-HMF

Info

Publication number: CN109046349B
Application number: CN201810864499.9A
Authority: CN
Inventors: 廖雪梅; 侯金豆; 王娅; 刘长炆; 袁永俊; 包清彬
Original assignee: Xihua University
Current assignee: Xihua University
Priority date: 2018-08-01
Filing date: 2018-08-01
Publication date: 2021-07-23
Anticipated expiration: 2038-08-01
Also published as: CN109046349A

Abstract

The invention relates to a monoatomic palladium catalyst, a preparation method thereof and a method for preparing 2,5-FDCA by catalytic oxidation of 5-HMF, belonging to the field of preparation of 2,5-FDCA by selective oxidation of 5-HMF. The structure of the monatomic palladium catalyst is as follows: the active component palladium is highly dispersed and uniformly distributed on the surface of the manganese dioxide in a monoatomic mode; wherein the content of palladium is 0.2-3 wt%, and the content of manganese dioxide is 97-99.8 wt%. The catalyst provided by the invention is simple in preparation method, is used for preparing 2,5-FDCA by catalytic oxidation of 5-HMF, is simple in use method, and is good in selectivity and reusability during catalytic oxidation.

Description

Monoatomic palladium catalyst, preparation method thereof and method for preparing 2,5-FDCA by catalytic oxidation of 5-HMF

Technical Field

The invention relates to a monoatomic palladium catalyst, a preparation method thereof and a method for preparing 2,5-FDCA by catalytic oxidation of 5-HMF, belonging to the field of preparation of 2,5-FDCA by selective oxidation of 5-HMF.

Background

The energy problem is a worldwide problem, and nowadays, the society has an increasing demand for fossil energy, and many organic materials in life are derived from the fossil energy, and in addition, due to the non-renewable property of the fossil energy such as coal, petroleum and natural gas and environmental problems caused by the heavy use, the search for alternatives of the energy is inevitably a focus of common attention of all countries in the world. The biomass energy source is wide and can be regenerated, and the biomass energy source has good potential value in the aspect of replacing fossil energy, and becomes a hot spot of research in recent years.

5-hydroxymethylfurfural, converted from glucose or fructose, is considered a versatile platform compound that can be used to prepare a range of furan compounds by catalytic oxidation, such as 2, 5-furandicarboxylic acid, 2-formyl-furan-2-carboxylic acid, 2, 5-diformylfuran, and the like.

2, 5-furandicarboxylic acid is used as a high value-added product obtained by selective oxidation of 5-hydroxymethylfurfural, can be used as a raw material to synthesize some polyester materials with excellent performance, and further can be widely used in the fields of packaging material engineering plastics and the like. Many organic materials synthesized by using stone resources such as petroleum and the like as raw materials are difficult to degrade, waste gas and waste residues generated in the synthesis process can cause environmental pollution to a great extent, and the polyester material synthesized by using FDCA (fully drawn yarn) derived from biomass and 2, 5-furandicarboxylic acid as a monomer can be degraded, so that the requirements of sustainable development and environmental protection are met.

In an organic reaction for preparing 2, 5-furandicarboxylic acid (i.e., 2,5-FDCA) by catalytic oxidation of 5-hydroxymethylfurfural (i.e., 5-HMF), often accompanied by the formation of some by-products, catalytic oxidation of 5-hydroxymethylfurfural using a noble metal catalyst is a method effective for increasing the conversion of reactants and the yield of the desired product.

Patent publication No. CN106749130A discloses a method for preparing 2, 5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural with a Pt catalyst. However, the preparation method of the catalyst is complex, the catalyst needs to be prepared under the condition of high temperature of 280 ℃, and ozone is used as a precursor. The oxygen pressure required by the catalyst in the process of preparing 2, 5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural is 0.4Mpa, which is higher than the normal pressure reaction condition of the invention.

Patent publication No. CN104277020A discloses the use of Pd/Bi₂O₃A process for preparing 2, 5-furandicarboxylic acid by catalytic oxidation of 5-hydroxymethylfurfural and Pd/Bi are disclosed₂O₃The preparation method of the catalyst is a deposition precipitation method. But the Pd/Bi₂O₃The using method of the catalyst is complex, the catalyst needs to be reduced for 1-5 hours at 150-250 ℃ in a hydrogen atmosphere before use, the complexity of operation is increased, andthe safety risk is increased due to the need to handle in a high temperature hydrogen atmosphere.

Disclosure of Invention

The first technical problem to be solved by the invention is to provide a monoatomic palladium catalyst. When the monatomic palladium catalyst is used for preparing 2,5-FDCA by catalytic oxidation of 5-HMF, the problem of environmental pollution caused by the need of strong alkali (sodium hydroxide, potassium hydroxide and the like) in the oxidation reaction process of 5-hydroxymethylfurfural catalyzed by the traditional catalyst is solved, and the conversion rate of 5-HMF and the yield of 2,5-FDCA are improved.

A monatomic palladium catalyst, the catalyst structure being: the active component palladium is highly dispersed and uniformly distributed on the surface of the manganese dioxide in a monoatomic mode; wherein the content of palladium is 0.2-3 wt%, and the content of manganese dioxide is 97-99.8 wt%. The monoatomic palladium catalyst prepared by the invention can be Pd/MnO₂To indicate.

The second technical problem to be solved by the invention is to provide a preparation method of the monatomic palladium catalyst, which is simple and low in cost, and can ensure that the active component palladium is highly dispersed and uniformly distributed on the surface of manganese dioxide in a monatomic manner without agglomeration.

The preparation method of the monoatomic palladium catalyst comprises the following steps: taking raw materials according to the weight ratio of 5-7: 2-3: 0.05-0.08: 1-2 of ammonium sulfate, ammonium persulfate, palladium nitrate and manganese sulfate, adding water, stirring to obtain a mixture, placing the mixture at 120-160 ℃, reacting for 9-14 h, cooling, filtering, washing to neutrality to obtain black precipitates, drying and crushing the black precipitates to obtain the monatomic palladium catalyst.

Preferably: the weight ratio of ammonium sulfate to ammonium persulfate to palladium nitrate to manganese sulfate is 5.24-6.24: 2.36-2.86: 0.066-0.077: 1.56-1.81; more preferably, the weight ratio of the ammonium sulfate to the ammonium persulfate to the palladium nitrate to the manganese sulfate is 5.24-6.08: 2.36-2.74: 0.066-0.077: 1.56-1.81; further preferably, the weight ratio of ammonium sulfate, ammonium persulfate, palladium nitrate and manganese sulfate is 6.08:2.74:0.077: 1.81.

Preferably: the mixture was left to react at 140 ℃ for 12 h.

Preferably: the drying temperature of the black precipitate is 120 ℃, and the drying time is 12 h.

The third technical problem to be solved by the invention is the application of the monatomic palladium catalyst, and the monatomic palladium catalyst prepared by the invention is used for preparing 2,5-FDCA by catalytic oxidation of 5-HMF, and the method is simple and easy to operate. The method does not require the addition of strong base (sodium hydroxide, potassium hydroxide, etc.).

The method for preparing 2,5-FDCA by catalytic oxidation of 5-HMF by using the monoatomic palladium catalyst comprises the following steps: and mixing the prepared monoatomic palladium catalyst, anhydrous potassium carbonate and an aqueous solution of 5-HMF, and reacting at 80-110 ℃ in an oxygen atmosphere to obtain the 2, 5-FDCA.

Preferably: the weight ratio of the monoatomic palladium catalyst to the anhydrous potassium carbonate to the 5-HMF is 0.9-1.1: 3-4: 0.7-0.9; preferably, the weight ratio of the monoatomic palladium catalyst to the potassium carbonate to the 5-HMF is 1-1.1: 3.35-3.5: 0.77-0.8; more preferably, the weight ratio of the monatomic palladium catalyst, potassium carbonate, and 5-HMF is 1.1:3.5: 0.8.

Preferably: the oxygen flow rate was 25 ml/min.

Preferably: the reaction temperature is 90-110 ℃; further preferably, the reaction temperature is 110 ℃.

Preferably: the reaction time is at least 3 h; the preferred reaction time is 5 h.

The invention has the beneficial effects that:

1. the monoatomic palladium catalyst Pd/MnO of the invention₂The structure is unique, the active component palladium is highly dispersed and uniformly distributed on the surface of manganese dioxide in a monoatomic mode, and the problem of poor catalytic performance caused by the agglomeration of noble metal atoms into atomic groups with different particle sizes is solved.

2. Pd/MnO of the invention₂Medium Pd and carrier MnO₂The acting force between the catalyst and the carrier is strong, and the defect of poor reusability caused by weak acting force between the traditional supported catalyst and the carrier is overcome. The palladium catalyst is adopted to catalyze and oxidize 5-HMF to prepare 2,5-FDCA, the 5-HMF can be oxidized in a short time, the conversion rate reaches more than 98 percent, the yield of the 2,5-FDCA reaches more than 90 percent, and the catalyst is reusableAnd the 5-HMF oxidation reaction conversion rate is basically kept unchanged, and the yield of the 2,5-FDCA is reduced by only 2 percent after the 5-HMF oxidation reaction is repeatedly used.

3. In the process of catalyzing the oxidation reaction of the 5-hydroxymethylfurfural by adopting the palladium catalyst, strong alkali (sodium hydroxide, potassium hydroxide and the like) is not needed, so that the conversion rate of the 5-hydroxymethylfurfural is high, the yield of the 2, 5-furandicarboxylic acid is high, and the problems of equipment corrosion and environmental pollution caused by the strong alkali needed in the traditional catalyst catalysis are solved.

4. The palladium catalyst of the invention has simple preparation method, does not need any treatment before use, is simple and convenient to use, can be used under normal pressure, and has wide application prospect.

Drawings

FIG. 1 is a graph showing the oxidation conversion of 5-hydroxymethylfurfural and the yield of p-2, 5-furandicarboxylic acid with time in example 1.

FIG. 2 is a graph of the reusability of catalyst A1 in example 1.

FIG. 3 is an electron microscope structural view of the catalyst A1 in example 1.

Detailed Description

The conversion and yield of the invention are calculated as follows:

wherein, the 5-HMF is 5-hydroxymethylfurfural; 2,5-FDCA is 2, 5-furandicarboxylic acid.

The monatomic palladium catalyst has the following structure: the active component palladium is highly dispersed and uniformly distributed on the surface of the manganese dioxide in a monoatomic mode; wherein the content of palladium is 0.2-3 wt%, and the content of manganese dioxide is 97-99.8 wt%. The monoatomic palladium catalyst of the invention can be Pd/MnO₂To indicate.

The preparation method of the monoatomic palladium catalyst comprises the following steps: taking raw materials according to the weight ratio of 5-7: 2-3: 0.05-0.08: 1-2 of ammonium sulfate, ammonium persulfate, palladium nitrate and manganese sulfate, adding water, magnetically stirring to obtain a mixture, placing the mixture at 120-160 ℃, reacting for 9-14 h, naturally cooling, taking out, filtering, washing filtrate to neutrality to obtain black precipitate, drying and crushing the black precipitate to obtain the monatomic palladium catalyst Pd/MnO₂。

In order to improve the performance of the catalyst, it is preferable that: the weight ratio of ammonium sulfate to ammonium persulfate to palladium nitrate to manganese sulfate is 5.24-6.24: 2.36-2.86: 0.066-0.077: 1.56-1.81; more preferably, the weight ratio of the ammonium sulfate to the ammonium persulfate to the palladium nitrate to the manganese sulfate is 5.24-6.08: 2.36-2.74: 0.066-0.077: 1.56-1.81; when the weight ratio of ammonium sulfate to ammonium persulfate to palladium nitrate to manganese sulfate is 6.08:2.74:0.077:1.81, the prepared monatomic palladium catalyst has the best performance, when the monatomic palladium catalyst is used for preparing 2,5-FDCA by catalytic oxidation of 5-HMF, the conversion rate of 5-HMF is high, the yield of 2,5-FDCA is high, and the reusability of the catalyst is the best.

To improve the performance of the monatomic palladium catalyst, it is preferable that: the mixture was left to react at 140 ℃ for 12 h.

The method for preparing 2,5-FDCA by catalytic oxidation of 5-HMF by using the monoatomic palladium catalyst is characterized by comprising the following steps: and mixing the prepared monoatomic palladium catalyst, anhydrous potassium carbonate and an aqueous solution of 5-HMF, and reacting at 80-110 ℃ in an oxygen atmosphere to obtain the 2, 5-FDCA.

In the prior art, strong base (sodium hydroxide, potassium hydroxide and the like) is needed to reduce the loss of active components of the catalyst in the catalytic oxidation reaction process of the 5-HMF, the basic salt potassium carbonate is used for replacing the strong base to provide an alkaline environment for the conversion of the 5-HMF, and the problems of equipment corrosion and environmental pollution caused by the use of the strong base are avoided because the strong base is not used.

To improve the performance of the monatomic palladium catalyst, it is preferable that: the weight ratio of the monoatomic palladium catalyst to the anhydrous potassium carbonate to the 5-HMF is 0.9-1.1: 3-4: 0.7-0.9; more preferably, the weight ratio of the monoatomic palladium catalyst to the potassium carbonate to the 5-HMF is 1-1.1: 3.35-3.5: 0.77-0.8; further preferably, the weight ratio of the monatomic palladium catalyst, potassium carbonate, and 5-HMF is 1.1:3.5: 0.8.

Preferably: the oxygen flow rate was 25 ml/min.

The following examples are provided to further illustrate the embodiments of the present invention and are not intended to limit the scope of the present invention.

Example 1

Step 1, preparation of a catalyst: 6.08g of ammonium sulfate, 2.74g of ammonium persulfate, 77mg of palladium nitrate and 1.81g of manganese sulfate are weighed into a reaction kettle, and 43ml of deionized water is added. Adding magnetons, stirring for 10min, taking out the magnetons, and putting the reaction kettle into an oven at 140 ℃ for reaction for 12 h. Taking out after naturally cooling, filtering and washing the filtrate to be neutral. The resulting black precipitate was dried in an oven at 120 ℃ for 12 h. The block solid was ground to a powder during the drying process to give a black powder catalyst A1 for use. In the catalyst, the palladium content was 1.5 wt%, and the manganese dioxide content was 98.5 wt%. The scanning electron micrograph of A1 is shown in FIG. 3. As can be seen from fig. 3, the palladium atoms are highly uniformly dispersed on the surface of the manganese dioxide without agglomeration.

Step 2, using the monatomic palladium catalyst for catalytic oxidation of 5-HMF to prepare 2, 5-FDCA: weighing the prepared catalyst 110mg, 5-HMF80mg and anhydrous potassium carbonate 350mg, adding into a three-neck flask, adding deionized water 40ml, introducing oxygen at the flow rate of 25ml/min, reacting at 110 ℃, and testing the conversion rate of 5-HMF and the yield of 2,5-FDCA under different reaction times. The reaction results are shown in Table 1 and FIG. 1.

TABLE 1

Catalytic oxidation time/h	Conversion of 5-HMF/%)	Yield of 2, 5-FDCA/%)
			1	38.2	17.1
2	64.0	42.5
			3	98.1	85.3
4	100	89.2
			5	100	94.2

The catalyst after 5 hours of reaction was recovered by filtration and reused 4 more times according to the above procedure 2 for 5 hours of reaction each time, and the results are shown in FIG. 2. The conversions of 5-HMF at 4 times were all 100% and the yields of 2,5-FDCA were 93.8%, 93.2%, 93.0%, 92.2%, respectively.

Example 2

Step 1, preparation of a catalyst: 5.24g of ammonium sulfate, 2.36g of ammonium persulfate, 66mg of palladium nitrate and 1.56g of manganese sulfate are weighed into a reaction kettle, and 37ml of deionized water is added. Adding magnetons, stirring for 10min, taking out the magnetons, and putting the reaction kettle into an oven at 140 ℃ for reaction for 12 h. Taking out after naturally cooling, filtering and washing the filtrate to be neutral. The resulting black precipitate was dried in an oven at 120 ℃ for 12 h. And grinding the blocky solid into powder in the drying process to obtain the black powder catalyst for later use. In the catalyst, the palladium content was 1.42 wt%, and the manganese dioxide content was 98.58 wt%.

Step 2, using the monatomic palladium catalyst for catalytic oxidation of 5-HMF to prepare 2, 5-FDCA: 110mg of the prepared catalyst, 5-HMF80mg and 350mg of anhydrous potassium carbonate are weighed and added into a three-neck bottle, and then 40ml of deionized water is added. Oxygen was then introduced at a flow rate of 25ml/min and the reaction was carried out at 110 ℃ for 5 hours, whereby the conversion of 5-HMF was 100% and the yield of 2,5-FDCA was 95.1%. The catalyst was recovered by filtration and reused 4 more times as described above for 5h each time. The conversions of 5-HMF at 4 times were all 100% and the yields of 2,5-FDCA were 94.2%, 94.0%, 93.5%, 90.7%, respectively.

Example 3

Step 1, preparation of a catalyst: 6.24g of ammonium sulfate, 2.86g of ammonium persulfate, 77mg of palladium nitrate and 1.67g of manganese sulfate are weighed into a reaction kettle, and 45ml of deionized water is added. Adding magnetons, stirring for 10min, taking out the magnetons, and putting the reaction kettle into an oven at 140 ℃ for reaction for 12 h. Taking out after naturally cooling, filtering and washing the filtrate to be neutral. The resulting black precipitate was dried in an oven at 120 ℃ for 12 h. And grinding the blocky solid into powder in the drying process to obtain the black powder catalyst for later use. In the catalyst, the palladium content was 1.03 wt%, and the manganese dioxide content was 98.97 wt%.

Step 2, using the monatomic palladium catalyst for catalytic oxidation of 5-HMF to prepare 2, 5-FDCA: 100mg of the prepared catalyst, 5-HMF77mg and 335mg of anhydrous potassium carbonate were weighed into a three-necked flask, and 39ml of deionized water was added thereto. Then, oxygen gas was introduced at a flow rate of 25ml/min, and the reaction was carried out at 110 ℃ for 5 hours. The conversion of 5-HMF was found to be 98% and the yield of 2,5-FDCA was found to be 90.1%.

The catalyst was recovered by filtration and reused 4 more times as described above for 5h each time. The conversions of 5-HMF at 4 times were determined to be 98%, 98.3%, 97.5%, 97.2%, 97.6%, respectively, and the yields of 2,5-FDCA were 90.1%, 89.5%, 89.4%, 88.9%, respectively.

Example 4

Step 1, preparation of a catalyst: 5.24g of ammonium sulfate, 2.36g of ammonium persulfate, 66mg of palladium nitrate and 1.56g of manganese sulfate are weighed into a reaction kettle, and 37ml of deionized water is added. Adding magnetons, stirring for 10min, taking out the magnetons, and putting the reaction kettle into an oven at 130 ℃ for reaction for 14 h. Taking out after naturally cooling, filtering and washing the filtrate to be neutral. The resulting black precipitate was dried in an oven at 120 ℃ for 12 h. And grinding the blocky solid into powder in the drying process to obtain the black powder catalyst for later use. In the catalyst, the content of palladium was 0.92 wt%, and the content of manganese dioxide was 99.08 wt%.

Step 2, using the monatomic palladium catalyst for catalytic oxidation of 5-HMF to prepare 2, 5-FDCA: 90mg of the prepared catalyst, 90mg of 5-HMF and 400mg of anhydrous potassium carbonate are weighed and added into a three-necked bottle, and then 40ml of deionized water is added. Then, oxygen gas was introduced at a flow rate of 25ml/min, and the reaction was carried out at 110 ℃ for 5 hours. The conversion of HMF was found to be 95.8% with a yield of FDCA of 86.1%.

Example 5

Step 1, preparation of a catalyst: 5.24g of ammonium sulfate, 2.36g of ammonium persulfate, 66mg of palladium nitrate and 1.56g of manganese sulfate are weighed into a reaction kettle, and 37ml of deionized water is added. Adding magnetons, stirring for 10min, taking out magnetons, and placing the reaction kettle into an oven at 150 ℃ for reaction for 10 h. Taking out after naturally cooling, filtering and washing the filtrate to be neutral. The resulting black precipitate was dried in an oven at 120 ℃ for 12 h. And grinding the blocky solid into powder in the drying process to obtain the black powder catalyst for later use. In the catalyst, the palladium content was 1.38 wt% and the manganese dioxide content was 98.62 wt%.

Step 2, using the monatomic palladium catalyst for catalytic oxidation of 5-HMF to prepare 2, 5-FDCA: 110mg of the prepared catalyst, 5-HMF90mg and 300mg of anhydrous potassium carbonate are weighed and added into a three-neck flask, and then 40ml of deionized water is added. Then, oxygen gas was introduced at a flow rate of 25ml/min, and the reaction was carried out at 90 ℃ for 5 hours. The conversion of 5-HMF was found to be 98.6% with a yield of FDCA of 88.4%.

Claims

1. A monatomic palladium catalyst useful in the catalytic oxidation of 5-HMF to produce 2,5-FDCA, wherein the catalyst structure is: the active component palladium is highly dispersed and uniformly distributed on the surface of the manganese dioxide in a monoatomic mode; wherein the content of palladium is 0.2-3 wt%, and the content of manganese dioxide is 97-99.8 wt%;

2. The monatomic palladium catalyst for the catalytic oxidation of 5-HMF to 2,5-FDCA according to claim 1, characterized in that: the weight ratio of the ammonium sulfate to the ammonium persulfate to the palladium nitrate to the manganese sulfate is 5.24-6.24: 2.36-2.86: 0.066-0.077: 1.56-1.81.

3. The monatomic palladium catalyst for the catalytic oxidation of 5-HMF to 2,5-FDCA according to claim 2, characterized in that: the weight ratio of the ammonium sulfate to the ammonium persulfate to the palladium nitrate to the manganese sulfate is 5.24-6.08: 2.36-2.74: 0.066-0.077: 1.56-1.81.

4. The monatomic palladium catalyst for the catalytic oxidation of 5-HMF to 2,5-FDCA according to claim 3, characterized in that: the weight ratio of ammonium sulfate, ammonium persulfate, palladium nitrate and manganese sulfate is 6.08:2.74:0.077: 1.81.

5. The monatomic palladium catalyst for the catalytic oxidation of 5-HMF to 2,5-FDCA according to claim 1, characterized in that: the mixture was left to react at 140 ℃ for 12 h.

6. The monatomic palladium catalyst for the catalytic oxidation of 5-HMF to 2,5-FDCA according to claim 1, characterized in that: the drying temperature of the black precipitate is 120 ℃, and the drying time is 12 h.

7. The method for preparing 2,5-FDCA by catalytic oxidation of 5-HMF by using the monoatomic palladium catalyst is characterized by comprising the following steps: mixing the monoatomic palladium catalyst according to any one of claims 1 to 6, anhydrous potassium carbonate and an aqueous solution of 5-HMF, and reacting at 80-110 ℃ in an oxygen atmosphere to obtain 2, 5-FDCA.

8. The method of claim 7 for preparing 2,5-FDCA by the catalytic oxidation of 5-HMF with a monoatomic palladium catalyst, wherein: the weight ratio of the monoatomic palladium catalyst to the anhydrous potassium carbonate to the 5-HMF is 0.9-1.1: 3-4: 0.7-0.9.

9. The method of claim 8 for preparing 2,5-FDCA by the catalytic oxidation of 5-HMF with a monoatomic palladium catalyst, wherein: the weight ratio of the monoatomic palladium catalyst to the potassium carbonate to the 5-HMF is 1-1.1: 3.35-3.5: 0.77-0.8.

10. The method of claim 7 for preparing 2,5-FDCA by the catalytic oxidation of 5-HMF with a monoatomic palladium catalyst, wherein: the weight ratio of the monatomic palladium catalyst, potassium carbonate, and 5-HMF was 1.1:3.5: 0.8.

11. The method of claim 7 for preparing 2,5-FDCA by the catalytic oxidation of 5-HMF with a monoatomic palladium catalyst, wherein: the oxygen flow rate was 25 ml/min.

12. The method of claim 7 for preparing 2,5-FDCA by the catalytic oxidation of 5-HMF with a monoatomic palladium catalyst, wherein: the reaction temperature is 90-110 ℃.

13. The process for the preparation of 2,5-FDCA by the catalytic oxidation of 5-HMF with a monoatomic palladium catalyst according to claim 12, wherein: the reaction temperature was 110 ℃.

14. The method of claim 7 for preparing 2,5-FDCA by the catalytic oxidation of 5-HMF with a monoatomic palladium catalyst, wherein: the reaction time is at least 3 h.

15. The process for the preparation of 2,5-FDCA by the catalytic oxidation of 5-HMF with a monoatomic palladium catalyst according to claim 14, wherein: the reaction time was 5 h.