Method for catalyzing selective conversion of furfural into 2-methylfuran

Abstract

The invention provides a method for catalyzing selective conversion of furfural into 2-methylfuran. According to the method, furfural is efficiently catalyzed to be converted into 2-methylfuran under mild conditions by using a carbon nanotube supported platinum-based bimetallic catalyst (3Pt3Fe / MWNT), and the method has high conversion rate and high selectivity. Wherein the 3Pt3Fe / MWNT catalyst uses isopropanol as a solvent in a fixed bed reactor at normal pressure and 200 DEG C, the furfural conversion rate exceeds 99%, the initial selectivity of 2-MF is 91%, and the conversion rate is reduced from 99.8% to 90.41% after stable operation for 60 hours. The preparation process of the catalyst is simple, the finished product is stable and reliable, additional auxiliaries are not needed in the catalysis process, additional separation of the catalyst and a reaction substrate is not needed, and the catalyst has high activity and stability. The technology not only has important application value in the fields of energy and chemical industry, but also plays a positive role in promoting sustainable development and green chemistry.

Description

Technical Field

[0001] The present invention relates to a method for catalytically converting furfural into 2-methylfuran selectively, belonging to the field of biomass energy catalysis. Background Art

[0002] With the global emphasis on sustainable chemical synthesis, the development of biomass-based chemicals has become a research hotspot. Furfural, as an important biomass-derived platform compound, has rich sources and diverse conversion paths. The hydrogenation of furfural to prepare 2-methylfuran is an important conversion process, which not only has potential industrial application value but also provides new ideas for the synthesis of biomass-based high-value-added chemicals.

[0003] The hydrogenation reaction of furfural is of great significance in the field of biomass conversion. Its reaction path usually involves the selective hydrogenation of C=O and C=C bonds, and the selectivity of the product depends on the nature of the catalyst and the reaction conditions. In recent years, researchers have conducted extensive studies on the catalytic hydrogenation of furfural, mainly focusing on the design and optimization of catalysts. For example, Cu-based catalysts have shown excellent performance in the study of furfural hydrogenation to furfuryl alcohol, and both their conversion rate and selectivity have reached relatively high levels. However, the synthesis of 2-methylfuran requires higher selectivity and milder reaction conditions, which pose higher requirements for the catalyst. In terms of catalyst research, multi-metal catalysts have attracted much attention due to their synergistic effect and adjustable active sites. For example, the Cu-Zn / Al2O3 catalyst has shown good activity and selectivity in the furfural hydrogenation reaction.

[0004] Nevertheless, there are still many challenges in the hydrogenation of furfural to prepare 2-methylfuran. First, by-products are easily generated during the reaction process, such as tetrahydrofurfural and 2-methyltetrahydrofuran, which reduces the selectivity of the target product. Second, the stability and reusability of the catalyst are still key issues to be solved. In addition, the optimization of reaction conditions, such as temperature, pressure, and solvent selection, is crucial for improving the reaction efficiency and product selectivity.

[0005] In summary, studying a reliable catalyst for the highly selective hydrogenation of furfural to prepare 2-methylfuran has important scientific significance and also provides a new way for the efficient utilization of biomass resources. Summary of the Invention

[0006] The problem solved by the present invention is to propose a method for catalytically converting furfural into 2-methylfuran selectively.

[0007] Under mild conditions, while achieving high conversion of furfural and high selectivity of 2-methylfuran, single-metal catalysts often struggle to simultaneously possess high activity and high selectivity. The present invention employs a fixed-bed reactor with a relatively low hydrogen pressure and does not require catalyst separation. Through a combination of bimetallic catalysts, furfural is catalytically hydrodeoxygenated to 2-methylfuran under atmospheric pressure in a fixed-bed reaction.

[0008] The present invention provides the following technical solution: A method for preparing 2-methylfuran using a platinum-based catalyst for furfural includes the following steps: The reaction for hydrogenating furfural to prepare 2-methylfuran is carried out in a temperature-controlled fixed bed. A certain mass of the platinum-based catalyst is added to a customized quartz tube reactor. By pumping in an isopropanol solution of furfural and introducing hydrogen gas, furfural is hydrogenated to 2-methylfuran under the action of the catalyst; The platinum-based catalyst is obtained using the co-impregnation method; The catalyst preparation steps are as follows: Weigh an appropriate amount of the platinum precursor salt tetraammineplatinum nitrate and the iron precursor salt iron nitrate, dissolve them in deionized water, stir and ultrasonically oscillate to uniformly disperse the metal ions; Gradually add the obtained metal precursor mixed solution dropwise onto a multi-walled carbon nanotube (MWNT) support treated with concentrated nitric acid, and thoroughly grind until the impregnation is uniform; Subsequently, place the mixture in a blast drying oven at 80 °C and dry for 8 - 12 hours; Transfer the dried catalyst to a tubular furnace, and calcine and reduce it under hydrogen at 250 - 450 °C for 2 - 4 hours; After cooling, take it out to obtain a multi-walled carbon nanotube-supported platinum-iron bimetallic catalyst 3Pt3Fe / MWNT, where both Pt and Fe have a mass fraction of 3%, and store it in a drying oven for later use.

[0009] Preferably, the reaction for hydrogenating furfural to prepare 2-methylfuran is carried out in a temperature-controlled fixed bed. A fixed-bed reactor is used as the reactor for furfural hydrodeoxygenation, and a quartz tube with a constriction is used as the filler for the catalyst bed. Hydrogen gas and the reaction liquid are respectively introduced from above through a gas flow meter and a high-pressure flow pump so that the two pass through the catalyst bed simultaneously; The two are separated by a condensation and gas-liquid separation device below, where the reaction liquid is manually collected and separated; Before the reaction, the air in the reaction device is replaced with nitrogen. The reaction liquid is a furfural isopropanol solution, pure hydrogen gas is used as the hydrogen source, the pressure during the reaction process is atmospheric pressure, and the reaction temperature is between 180 - 220 °C.

[0010] The specific steps are as follows: (1) Add 3 g of multi-walled carbon nanotubes and 300 mL of nitric acid to a round-bottom flask. Install the round-bottom flask in an oil bath, stir at 120 °C, and carry out condensation reflux for 4 hours. After the purification is completed, quickly add deionized water to cool down and dilute the acid concentration. Wash and filter the carbon nanotubes repeatedly until the pH of the final filtrate is 4. Subsequently, dry it in an oven at 80 °C for 12 hours. Take out the dried carbon nanotubes, put them in a mortar and grind them. After passing through a 100-mesh standard sieve, prepare the carbon nanotube support. (2) Weigh 282 mg of the multi-walled carbon nanotube support and evenly spread it on a mortar. Take 0.36 mL of a 25 mg / mL tetraammineplatinum nitrate solution, shake and ultrasonicate it before taking, then add 0.9 mL of a 10 mg / mL iron nitrate solution and an appropriate amount of deionized water, ultrasonicate for 5 min to make it mix evenly, and evenly drip the mixed solution onto the support prepared in step (1). Grind until the catalyst is fully impregnated, and place it in a 70 °C drying oven for 12 h; (3) Take out the impregnated and dried catalyst, grind it into uniform fine particles, and load it into a vertical tubular furnace. Quartz wool is installed above and below the catalyst bed layer. Then, introduce hydrogen into the tubular furnace at a flow rate of 50 mL / min. Heat it from room temperature to 400 °C at a heating rate of 5 °C / min, calcine and reduce it at 400 °C for 4 h. After cooling to room temperature, change to nitrogen to purge the pipeline, take it out, and obtain the 3Pt3Fe / MWNT catalyst; (4) The reaction for preparing 2-methylfuran by furfural hydrogenation is carried out in a fixed bed equipped with temperature control. The inner diameter of the quartz tube is 4 mm, the flow rate of the reaction liquid furfural is 0.05 mL / min, the flow rate of the hydrogen used in the reaction is 5 mL / min, the reaction solvent is isopropanol, the reaction temperature is 200 °C, and the reaction pressure is atmospheric pressure.

[0011] (1) Pretreatment of the support: Place 3 g of multi-walled carbon nanotubes, 300 mL of nitric acid, and a magnetic stirrer in a 500 mL round-bottom flask, heat it in an oil bath at 120 °C for 4 hours, condense and recover nitric acid during this period, and absorb the tail gas with water. Purify the carbon tubes and disperse them in two beakers. After precipitation, discard the supernatant. Wash the remaining carbon tubes with pure water, filter to obtain a filter cake, and repeat washing multiple times to obtain the filter cake. Dry the filter cake overnight at 80 °C and grind it to less than 100 mesh to obtain CNTs. This process removes metal impurities and amorphous carbon and introduces oxygen-containing functional groups, which is beneficial for the adsorption of metal precursors.

[0012] (2) Preparation of the bimetallic catalyst by impregnation method: Weigh appropriate amounts of the platinum precursor salt and the iron precursor salt (the mass is determined according to the catalyst loading), dissolve them with deionized water, stir and ultrasonically oscillate to make the metal ions evenly dispersed. Gradually add the obtained mixed metal precursor solution dropwise onto the multi-walled carbon nanotube (MWNT) support treated with concentrated nitric acid, and grind it thoroughly until the impregnation is uniform. Subsequently, place the mixture in a blast drying oven at 80 °C and dry it for 8 - 12 hours. Transfer the dried catalyst to a tubular furnace and calcine and reduce it under hydrogen at 250 - 450 °C for 2 - 4 hours. After cooling, take it out to obtain the multi-walled carbon nanotube-supported platinum-iron bimetallic catalyst PtFe / MWNT, and store it in a drying oven for standby.

[0013] (3) A fixed-bed reactor is used as the reactor for furfural hydrodeoxygenation, and a quartz tube with a constriction is used as the filler for the catalyst bed. Hydrogen and the reaction liquid are introduced from above through a gas flow meter and a high-pressure flow pump respectively, so that the two pass through the catalyst bed simultaneously. The two are separated by a condensing and gas-liquid separation device below, and the reaction liquid is manually collected and separated. Before the reaction, the air in the reaction device is replaced with nitrogen. The reaction liquid is a furfural isopropanol solution, and pure hydrogen is used as the hydrogen source. The pressure during the reaction process is atmospheric pressure, and the reaction temperature is between 60 - 240 °C.

[0014] Preferably, in step (1), the ratio of carbon nanotubes to nitric acid is 1 g:100 mL.

[0015] Preferably, in step (1), the purified carbon tubes are evenly dispersed into 2 500-mL beakers. After sufficient precipitation, the upper acid solution is poured out, and this is repeated twice. Thereafter, it is stirred and dispersed in 600 mL of ultrapure water, ultrasonicated for 10 min, and then filtered by suction. The obtained filter cake is operated three times. At this time, the pH of the filtrate is about 4.0.

[0016] A platinum-based bimetallic catalyst supported on carbon nanotubes, one is platinum metal and the other is a transition metal, with different contents, is supported on the carrier by the co-impregnation method. The transition metal is added to the platinum-based catalyst as a promoter, and the transition metal is one of Co, Fe, Cr, Cu, Ni, etc. The mass ratio of the two metals is between 1:1 - 1:5, based on the total weight of the catalyst. The precursor of platinum is an aqueous solution of tetraamineplatinum nitrate, and the precursors of the transition metals are all metal nitrate solutions.

[0017] The specific steps are as follows:

[0018] Step 1. Pretreatment of the carrier:

[0019] Add multi-walled carbon nanotubes and concentrated nitric acid to a round-bottom flask, add concentrated nitric acid according to the ratio of 100 mL of nitric acid per gram of carbon nanotubes, install the round-bottom flask in an oil bath, stir, and carry out reflux condensation. After the purification is completed, quickly add deionized water to cool down and dilute the acid concentration, repeatedly wash and filter the carbon nanotubes until the final filtrate is neutral, and dry at 80 °C for 8 - 12 h; take out the dried carbon nanotubes, put them into a mortar, grind them, and make a carbon nanotube carrier after sieving.

[0020] Step 2. Preparation of the platinum and transition metal precursor solutions:

[0021] Dissolve a certain amount of platinum salt and transition metal nitrate (the required mass is determined according to the loading amount of the catalyst) in an appropriate amount of deionized water, and under stirring, ultrasonically oscillate to make the metal ions disperse evenly in the solution. The actual metal content is determined by ICP (inductively coupled plasma spectroscopy).

[0022] Step 3. Preparation of supported platinum-based bimetallic catalyst:

[0023] Transfer a specific volume of metal precursor solution (Pt and Fe, Ni, Co, etc.) according to the actual metal combination, mix evenly by ultrasonic, weigh a specific weight of purified carbon nanotubes and spread them on a mortar, slowly drip to make the precursor solution completely cover the carbon nanotubes, grind until impregnation is sufficient, and then put them into a blast drying oven at 80 °C for drying for 8 - 12 h; load the dried catalyst into a tubular furnace, calcine and reduce it with hydrogen at 250 - 450 °C for 2 - 4 h, wait for it to cool down and take it out to obtain the supported platinum-based bimetallic catalyst, and then put it into a drying oven for storage.

[0024] Preferably, when Fe and metal Pt are the best metal combination, it shows better selectivity.

[0025] Preferably, the ratio of the metal precursor solution to the carrier carbon nanotubes is about 2 mL of precursor mixture per 300 mg of carbon nanotubes, and at this time, the precursor mixture is slowly dripped to be roughly equivalent to the volume of the carbon nanotubes.

[0026] Preferably, the mass ratio of Pt to Fe is 1:1, and the mass fraction of Pt is 3 wt%.

[0027] Preferably, in step 3, the reduction temperature of the catalyst is 400 °C and the reduction time is 4 h.

[0028] Application of the supported platinum-based bimetallic catalyst in the preparation of 2-methylfuran under mild conditions, used for catalytic conversion of furfural to 2-methylfuran in a fixed-bed reactor under atmospheric pressure. The specific steps are as follows

[0029] (1) Pretreatment of the carrier: Put 3 g of multi-walled carbon nanotubes, 300 mL of nitric acid and a magnetic stirrer into a 500 mL round-bottom flask, heat it in an oil bath at 120 °C for 4 hours, during which nitric acid is condensed and recovered, and the tail gas is absorbed by water. The purified carbon tubes are dispersed in two beakers, the supernatant is discarded after precipitation, and the remaining carbon tubes are washed with pure water, filtered to obtain a filter cake, and the washing is repeated many times to obtain the filter cake. The filter cake is dried overnight at 80 °C and ground to less than 100 mesh to obtain CNTs. This process removes metal impurities and amorphous carbon and introduces oxygen-containing functional groups, which is beneficial to the adsorption of metal precursors.

[0030] (2) Preparation of bimetallic catalyst by impregnation method: Weigh appropriate amounts of platinum precursor salt and iron precursor salt (the mass is determined according to the catalyst loading), dissolve them in deionized water, stir and ultrasonically oscillate to evenly disperse the metal ions. Add the obtained metal precursor mixed solution dropwise to the multi-walled carbon nanotube (MWNT) carrier treated with concentrated nitric acid, and grind thoroughly until the impregnation is uniform. Subsequently, place the mixture in an 80°C forced air drying oven and dry it for 8-12 hours. The dried catalyst is transferred to a tubular furnace and calcined and reduced with hydrogen at 250-450°C for 2-4 hours. After cooling, take it out to obtain a multi-walled carbon nanotube-loaded platinum-iron bimetallic catalyst PtFe / MWNT, which is stored in a drying oven for later use.

[0031] ① Atmospheric pressure reaction device such as Figure 10 As shown, first prepare the reaction solution 0.2 M furfural isopropanol solution, in which 1% volume fraction of dodecane is added as an internal standard. Then fill the catalyst: fill a small amount of quartz wool, quartz sand (about 3 mm height), 200 mg catalyst, quartz sand (about 3 mm height) in the custom quartz tube in sequence, and then tighten the nuts at both ends to press the sealing ring to seal. Then assemble the reaction device as shown in the figure.

[0032] Filling pump: Connect the reaction tank, turn on the reactor switch, turn on the feed pump switch, and use a syringe to extract liquid until no bubbles are generated;

[0033] Rinse the pipeline: Place the centrifuge tube at the tube mouth, put a plastic sealing bag underneath, press PURGE to rinse the pipeline. It needs to be connected with 7.5mL (i.e. rinse three times, 2.5mL each time). Press stop to stop and close the valve. Connect the receiving kettle while rinsing.

[0034] Connect the pipes and connect the pipes to the quartz tubes up and down

[0035] The temperature program was set so that the reactor was heated to 200 °C at 5 °C / min and kept at this temperature.

[0036] Wetting: Use a large flow rate (2 mL / min) to preferentially introduce about 1 mL of reaction solution to allow the catalyst to reach physical adsorption equilibrium first.

[0037] Start the reaction, introduce hydrogen into the reactor (5 mL / min), and use a high-pressure metering pump to introduce the reaction liquid (0.05 mL / min); and start timing, take samples from the bottom of the gas-liquid separator every hour, mark them as 0, 1, 2...10, and analyze the obtained samples using gas chromatography.

[0038] ② Non-normal pressure fixed bed reactor such as Figure 10As shown in the figure, different from the atmospheric pressure reaction that uses a quartz tube with a constriction, the high-pressure reaction uses a 304 stainless steel tube with nuts at both ends as the reaction vessel. During use, a special quartz sand core is supported by a steel needle at the bottom, and about 3 mm high quartz sand, 200 mg of catalyst, and 3 mm high quartz sand are filled on the sand core in sequence. Prepare a reaction solution of 0.2 M furfural in isopropanol solution, and add 1% by volume of dodecane as an internal standard. Then assemble the reaction device as shown in the figure.

[0039] Pump filling: Connect to the reaction tank, turn on the reactor switch, turn on the feed pump switch, and use a syringe to extract the liquid until no bubbles are generated.

[0040] Pipe rinsing: Place a centrifuge tube at the pipe opening, pad a plastic seal bag below, press PURGE to rinse the pipeline. It is necessary to connect 7.5 mL (that is, rinse three times, 2.5 mL each time), press stop to stop, and close the valve. While rinsing, connect the receiving kettle.

[0041] Connect the pipeline and connect the pipeline to the quartz tube up and down.

[0042] Set the heating program so that the reactor heats up to 200 °C at a rate of 5 °C / min and holds the temperature.

[0043] Infiltration: First, use a large flow rate (2 mL / min) to preferentially introduce about 1 mL of the reaction solution to enable the catalyst to reach physical adsorption equilibrium first.

[0044] Start the reaction. When starting the reaction, first close the back pressure valve, slowly introduce hydrogen into the reactor through the ball valve. When the hydrogen pressure is higher than the target pressure, slowly open the back pressure valve until the pressure is controlled at the target pressure. Then introduce hydrogen into the reactor (5 mL / min), and use a high-pressure metering pump to introduce the reaction solution (0.05 mL / min); and start timing. Take samples from below the gas-liquid separator every hour and mark them as 0, 1, 2... 10 respectively. The obtained samples are analyzed using gas chromatography.

[0045] Preferably, the optimal reaction pressure is atmospheric pressure.

[0046] Preferably, in the atmospheric pressure reaction, a quartz tube with a constriction and an inner diameter of 4 mm is used, and the catalyst bed height is about 7 mm at this time.

[0047] Preferably, the optimal reaction temperature is 200 °C.

[0048] Preferably, the hydrogen flow rate used in the reaction is 5 mL / min.

[0049] Beneficial effects:

[0050] The present invention provides an efficient method for the selective conversion of furfural to 2-methylfuran. Its technical superiority is reflected in mild reaction conditions, excellent catalyst activity and stability, high operation reliability, and significant benefits to energy and the environment, as follows:

[0051] 1. Mild reaction conditions: The present invention achieves the efficient conversion of furfural under mild conditions of atmospheric pressure and 200 °C, significantly reducing energy consumption and equipment requirements. Compared with traditional methods that require high-temperature and high-pressure conditions, the present invention not only reduces energy consumption but also lowers equipment costs and operation risks. In addition, the use of isopropanol as a solvent further enhances the environmental friendliness and economy of the reaction.

[0052] 2. High activity and high selectivity of the catalyst: Using a carbon nanotube-supported platinum-based bimetallic catalyst (such as 3Pt3Fe / MWNT), under optimized reaction conditions, the furfural conversion rate exceeds 99%, and the initial selectivity of 2-methylfuran is as high as 91%. The high activity of the catalyst stems from the synergistic effect of platinum and iron bimetals and the high specific surface area and abundant oxygen-containing functional groups provided by the carbon nanotube support, which effectively promote the adsorption and activation of reactants.

[0053] 3. Excellent catalyst stability: After the catalyst of the present invention is continuously operated for 60 hours, the furfural conversion rate only drops from 99.8% to 90.41%, showing excellent stability. This stability benefits from the pretreatment of the support (multi-walled carbon nanotubes) during the catalyst preparation process and the uniform dispersion of bimetallic active sites, effectively preventing the catalyst from deactivating due to carbon deposition or metal sintering during the reaction.

[0054] 4. Simple and reliable operation: The catalyst preparation process of the present invention is simple and easy. A highly active and stable catalyst can be obtained by the co-impregnation method. During the catalytic reaction process, no additional additives are required, and there is no need for complex separation of the catalyst and reaction substrates, significantly simplifying the operation process and reducing production costs. In addition, the use of a fixed-bed reactor makes the reaction process easy to control and scale up, suitable for industrial production.

[0055] 5. Benefits to energy and the environment: The present invention has significant advantages in green chemistry and sustainable development. First, the reaction conditions are mild and no toxic reagents are used, reducing energy consumption and environmental pollution. Second, the high efficiency and stability of the catalyst reduce the catalyst replacement frequency and resource waste. Finally, as an important chemical intermediate, the efficient preparation of 2-methylfuran helps to promote the utilization of biomass resources and reduce the dependence on fossil resources, in line with the development concepts of green chemistry and circular economy.

[0056] In summary, through the optimization of reaction conditions and catalyst design, the present invention realizes the efficient and highly selective conversion of furfural to 2-methylfuran, with advantages such as mild reaction conditions, excellent catalyst activity and stability, simple and reliable operation, and significant benefits to energy and the environment, providing important technical support for promoting green chemistry and sustainable development. Description of the Drawings

[0057] Figure 1 is the reaction equation

[0058] Figure 2 is the hydrogenation reaction results of different bimetallic combinations

[0059] Figure 3 Reaction results of different PtFe ratios

[0060] Figure 4 Reaction results of different pressures

[0061] Figure 5 、 Figure 6 Influence of reactor inner diameter and temperature on the reaction

[0062] Figure 7 Influence of H2 / FOR in the reaction on the reaction

[0063] Figure 8 Investigation on the stability of the catalyst during long-term operation

[0064] Figure 9 Influence of different solvents on the reaction

[0065] Figure 10 Schematic diagram of the fixed-bed reactor

[0066] Figure 11 TEM image of 3Pt3Fe / MWNT

[0067] Figure 13 XRD patterns of catalysts with different PtFe ratios

[0068] Figure 14 NH3-TPD characterization diagram

[0069] Figure 15 Comparison of this work with related works

[0070] Among them Figure 10 In it: 1. Gas cylinder, 2. Gas regulator, 3. Digital pressure detector, 4. Temperature indicator, 5. Temperature controller, 6. Stainless steel tubular reactor, 7. Electric tubular furnace, 8. Two-way valve, 9. Gas-liquid separator, 10. Two-way valve, 11. Back pressure valve, 12. Two-way valve, 13. Metering pump, 14. Feed tank. Detailed Description of the Invention

[0071] The present invention will be further described in detail below in conjunction with specific examples. These examples are only for illustrative purposes of the present invention, but the present invention is not limited to the following examples.

[0072] Example 1

[0073] (1) Add 3 g of multi-walled carbon nanotubes and 300 mL of nitric acid to a round-bottom flask. Install the round-bottom flask in an oil bath and stir at 120 °C for 4 hours with condensation reflux. After the purification is completed, quickly add deionized water to cool down and dilute the acid concentration. Wash and filter the carbon nanotubes repeatedly until the pH of the final filtrate is about 4. Then dry in an oven at 80 °C for 12 hours. Take out the dried carbon nanotubes, put them into a mortar and grind them. After sieving through a 100-mesh standard sieve, a carbon nanotube support is prepared.

[0074] (2) Weigh 282 mg of the multi-walled carbon nanotube support and spread it evenly on the mortar. Take 0.36 mL of the platinum precursor solution (25 mg / mL tetraammineplatinum nitrate solution), shake and ultrasonicate it before taking. Then add 0.9 mL of the iron precursor solution (10 mg / mL iron nitrate solution) and an appropriate amount of deionized water, and ultrasonicate for 5 min to make it mix evenly. Drop the mixed solution evenly onto the support prepared in step (1), grind until the catalyst is fully impregnated, and dry in a drying oven at 70 °C for 12 h.

[0075] (3) Take out the impregnated and dried catalyst, grind it into uniform fine particles, and load it into a vertical tubular furnace. Quartz wool is installed above and below the catalyst bed. Then introduce hydrogen into the tubular furnace at a flow rate of 50 mL / min. Heat from room temperature to 400 °C at a heating rate of 5 °C / min and calcine and reduce at 400 °C for 4 h. After cooling to room temperature, replace the nitrogen to purge the pipeline, take out, and obtain the 3Pt3Fe / MWNT catalyst.

[0076] (4) Measure the actual metal loading content by an inductively coupled plasma instrument.

[0077] Example 2

[0078] The high-pressure reaction device used in this example is as Figure 10 shown. First, prepare a reaction solution of 0.2 M furfural in isopropanol solution, and add 1% by volume of dodecane as an internal standard. For the high-pressure reaction, use a 304 stainless steel tube (inner diameter 4 mm) with nuts at both ends as the reaction vessel. When in use, support a special quartz sand core with a 20 cm steel needle at the bottom. On the sand core, successively fill about 3 mm height of quartz sand, 200 mg of 3Pt3Fe / MWNT catalyst (about 7 mm high), and 3 mm height of quartz sand. Then assemble the reaction device as shown in the figure.

[0079] Pump priming: Connect the reaction tank, turn on the reactor switch, turn on the feed pump switch, and draw liquid with a syringe until no bubbles are generated;

[0080] Rinse the pipeline: Place the centrifuge tube at the pipe opening, pad a plastic seal bag underneath, press PURGE to rinse the pipeline. It is necessary to connect 7.5 mL (i.e., rinse three times, 2.5 mL each time), press stop to stop, and close the valve. While rinsing, connect the receiving kettle.

[0081] Connect the pipeline and connect the pipeline to the quartz tube up and down.

[0082] Set the heating program so that the reactor heats up to 150 °C at a rate of 5 °C / min and holds the temperature.

[0083] Infiltration: At least 20 min before starting the reaction, first introduce about 1 mL of the reaction solution at a high flow rate (2 mL / min) to enable the catalyst to reach physical adsorption equilibrium first.

[0084] Start the reaction: When starting the reaction, we first close the back pressure valve, slowly introduce hydrogen into the reactor through the ball valve. When the hydrogen pressure is higher than the target pressure, slowly open the back pressure valve until the pressure is controlled at 0.1 MPa. Then introduce hydrogen into the reactor (5 mL / min), use a high-pressure metering pump to introduce the reaction solution (0.05 mL / min); and start timing. Take samples from below the gas-liquid separator every hour. When sampling, first open the upper needle valve for 1 min and then close it, and slowly open the lower needle valve to let the reaction solution flow out, and mark 0, 1, 2...

[0085] The samples after the reaction are analyzed using a flame ionization detector (FID) of a gas chromatograph (GC) equipped with an HP-5 capillary column. The by-products are analyzed by GC-MS (Agilent, 6890 N5973).

[0086] Example 3

[0087] The atmospheric pressure reaction device used in this example is as Figure 10 shown. First, prepare a reaction solution of 0.2 M furfural in isopropanol solution, and add 1% volume fraction of dodecane as an internal standard. Then load the catalyst prepared in Example 1: First fill a small amount of quartz wool, quartz sand (about 3 mm in height), 200 mg of 3Pt3Fe / MWNT catalyst (about 7 cm in height), and quartz sand (about 3 mm in height) into a customized quartz tube (4 mm inner diameter) in sequence. Then tighten the nuts at both ends to compress the sealing ring to play a sealing role. Then assemble the reaction device as shown in the figure.

[0088] Pump priming: Connect the reaction tank, turn on the reactor switch, turn on the feed pump switch, and draw liquid with a syringe until no bubbles are generated;

[0089] Rinse the pipeline: Place the centrifuge tube at the tube opening, pad a plastic seal bag underneath, press PURGE to rinse the pipeline. It is necessary to connect 7.5 mL (i.e., rinse three times, 2.5 mL each time), press stop to stop, and close the valve. While rinsing, connect the receiving kettle.

[0090] Connect the pipeline and connect the pipeline to the quartz tube vertically.

[0091] Set the heating program so that the reactor heats up to 200 °C at a rate of 5 °C / min and holds the temperature.

[0092] Infiltration: At least 20 min before starting the reaction, first introduce about 1 mL of the reaction solution at a large flow rate (2 mL / min) to enable the catalyst to reach physical adsorption equilibrium first.

[0093] Start the reaction, introduce hydrogen (5 mL / min) into the reactor, and use a high-pressure metering pump to introduce the reaction solution (0.05 mL / min); and start timing. Take samples from below the gas-liquid separator every hour and label them 0, 1, 2...

[0094] The samples after the reaction are analyzed using a flame ionization detector (FID) of a gas chromatograph (GC) equipped with an HP-5 capillary column. The by-products are analyzed by GC-MS (Agilent, 6890 N5973).

[0095] In the initial stage of the reaction, the furfural conversion rate is close to complete conversion (>99%), and the selectivity of 2-methylfuran (2-MF) is as high as 92.4%. After 60 hours of continuous and stable operation, the furfural conversion rate gradually decreases from the initial 99.25% to 90.41%, and the selectivity of 2-methylfuran also slightly decreases to 84%. This method shows excellent high activity and long-term stability under the condition of a space velocity of 0.29 h - ¹. At the same time, the lower hydrogen-to-aldehyde ratio and atmospheric pressure reaction conditions further reduce the energy consumption and equipment requirements, making this method have significant economic efficiency and operational convenience in industrial applications, showing broad application prospects (see the comparison data in Figure 15 ).

[0096] Comparative Example 1

[0097] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.6 mL of tetraammineplatinum nitrate (25 mg / mL) and an appropriate amount of water. The catalyst is named 5Pt / MWNT.

[0098] Comparative Example 1-2

[0099] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.6 mL of tetraammineplatinum nitrate (25 mg / mL), 0.3 mL of chromium nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 5Pt1Cr / MWNT.

[0100] Comparative Examples 1 - 3

[0101] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.6 mL of tetraammineplatinum nitrate (25 mg / mL), 0.3 mL of nickel nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 5Pt1Ni / MWNT.

[0102] Comparative Examples 1 - 4

[0103] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.6 mL of tetraammineplatinum nitrate (25 mg / mL), 0.3 mL of chromium cobalt solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 5Pt1Co / MWNT.

[0104] Comparative Examples 1 - 5

[0105] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.6 mL of tetraammineplatinum nitrate (25 mg / mL), 0.3 mL of copper nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 5Pt1Cu / MWNT.

[0106] Comparative Examples 1 - 6

[0107] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.6 mL of tetraammineplatinum nitrate (25 mg / mL), 0.3 mL of iron nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 5Pt1Fe / MWNT.

[0108] Comparative Examples 1 - 6

[0109] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.6 mL of tetraammineplatinum nitrate (25 mg / mL), 0.6 mL of iron nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 5Pt2Fe / MWNT.

[0110] Comparative Examples 1 - 7

[0111] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.12 mL of tetraammineplatinum nitrate (25 mg / mL), 0.3 mL of cobalt nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 1Pt1Fe / MWNT.

[0112] Comparative Examples 1-8

[0113] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.12 mL of tetraammineplatinum nitrate (25 mg / mL), 0.9 mL of cobalt nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 1Pt3Fe / MWNT.

[0114] Comparative Examples 1-9

[0115] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.12 mL of tetraammineplatinum nitrate (25 mg / mL), 1.5 mL of cobalt nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 1Pt5Fe / MWNT.

[0116] Comparative Examples 1-10

[0117] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.36 mL of tetraammineplatinum nitrate (25 mg / mL), 1.5 mL of cobalt nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 3Pt1Fe / MWNT.

[0118] Comparative Examples 1-11

[0119] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.36 mL of tetraammineplatinum nitrate (25 mg / mL), 1.5 mL of cobalt nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 3Pt5Fe / MWNT.

[0120] Comparative Examples 1-12

[0121] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.6 mL of tetraammineplatinum nitrate (25 mg / mL), 0.9 mL of cobalt nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 5Pt3Fe / MWNT.

[0122] Comparative Examples 1-13

[0123] The difference between this comparative example and Example 1 is that the impregnated mixed precursor solution is: 0.6 mL of tetraammineplatinum nitrate (25 mg / mL), 1.5 mL of cobalt nitrate solution (10 mg / mL), and an appropriate amount of water. The catalyst is named 5Pt5Fe / MWNT.

[0124] Comparative Example 2-1

[0125] The difference between this comparative example and Example 2 is that the pressure regulated by the pressure relief valve is 0.1 MPa.

[0126] Comparative Example 2-2

[0127] The difference between this comparative example and Example 2 is that the pressure regulated by the pressure-bearing valve is 0.2 MPa.

[0128] Comparative Example 2-3

[0129] The difference between this comparative example and Example 2 is that the pressure regulated by the pressure-bearing valve is 0.5 MPa.

[0130] Comparative Example 2-4

[0131] The difference between this comparative example and Example 2 is that the pressure regulated by the pressure-bearing valve is 0.8 MPa.

[0132] Comparative Example 2-5

[0133] The difference between this comparative example and Example 2 is that the pressure regulated by the pressure-bearing valve is 1 MPa.

[0134] Comparative Example 3-1

[0135] The difference between this comparative example and Example 3 is that the inner diameter of the quartz tube used is 8 mm, the hydrogen flow rate is 20 mL / min (at this time, the height of the catalyst layer is about 1.8 cm, and the hydrogen flow velocity is 9.95 cm / min), and the temperature is 150 °C.

[0136] Comparative Example 3-2

[0137] The difference between this comparative example and Example 3 is that the reactor is reacted for 1 h at 60, 80, 100... 240 °C respectively by programmed temperature rise, and samples are taken at each temperature (at this time, the height of the catalyst layer is about 7 cm, and the hydrogen flow velocity is 9.95 cm / min).

[0138] Comparative Example 3-3

[0139] The difference between this comparative example and Comparative Example 3-1 is that the inner diameter of the quartz tube used is 5 mm, and the hydrogen flow rate is 7.8 mL / min (at this time, the height of the catalyst layer is about 4.48 cm, and the hydrogen flow velocity is 9.95 cm / min).

[0140] Comparative Example 3-4

[0141] The difference between this comparative example and Comparative Example 3-1 is that the inner diameter of the quartz tube used is 6 mm, and the hydrogen flow rate is 11.25 mL / min (at this time, the height of the catalyst layer is about 3 cm, and the hydrogen flow velocity is 9.95 cm / min).

[0142] Comparative Example 3-5

[0143] The difference between this comparative example and Comparative Example 3-1 is that the inner diameter of the quartz tube used is 7 mm, and the hydrogen flow rate is 15.31 mL / min (at this time, the catalyst layer height is about 2.3 cm, and the hydrogen flow velocity is 9.95 cm / min).

[0144] Comparative Example 3-6

[0145] The difference between this comparative example and Comparative Example 3-1 is that the inner diameter of the quartz tube used is 8 mm, and the hydrogen flow rate is 20 mL / min (at this time, the catalyst layer height is about 1.8 cm, and the hydrogen flow velocity is 9.95 cm / min).

[0146] Comparative Example 3-6

[0147] The difference between this comparative example and Example 3 is that the hydrogen flow rate used in the starting reaction step is 2.5 mL / min, and at this time, H2 / FOR = 5.

[0148] Comparative Example 3-8

[0149] The difference between this comparative example and Example 3 is that the hydrogen flow rate used in the starting reaction step is 7.5 mL / min, and at this time, H2 / FOR = 20.

[0150] Comparative Example 3-9

[0151] The difference between this comparative example and Example 3 is that the hydrogen flow rate used in the starting reaction step is 10 mL / min, and at this time, H2 / FOR = 40.

[0152] Comparative Example 3-10

[0153] The difference between this comparative example and Example 3 is that the hydrogen flow rate used in the starting reaction step is 12.5 mL / min, and at this time, H2 / FOR = 50.

[0154] Comparative Example 3-11

[0155] The difference between this comparative example and Example 3 is that the hydrogen flow rate used in the starting reaction step is 15 mL / min, and at this time, H2 / FOR = 60.

[0156] Comparative Example 3-12

[0157] The difference between this comparative example and Example 3 is that the hydrogen flow rate used in the starting reaction step is 17.5 mL / min, and at this time, H2 / FOR = 70.

[0158] Comparative Example 3-13

[0159] The difference between this comparative example and Example 3 is that the hydrogen flow rate used in the starting reaction step is 20 mL / min, and at this time, H2 / FOR = 80.

[0160] Comparative Example 3-14

[0161] The difference between this comparative example and Example 3 is that: the reaction solution is an aqueous solution of 0.2 M furfural, in which 1% by volume of dodecane is added as an internal standard, and the reaction solution is extracted with ethyl acetate and then analyzed by gas chromatography.

[0162] Comparative Example 3-15

[0163] The difference between this comparative example and Example 3 is that: the reaction solution is a 1,4-epoxyhexane solution of 0.2 M furfural, in which 1% by volume of dodecane is added as an internal standard.

[0164] Comparative Example 3-16

[0165] The difference between this comparative example and Example 3 is that: the reaction solution is a methanol solution of 0.2 M furfural, in which 1% by volume of dodecane is added as an internal standard.

[0166] Comparative Example 3-17

[0167] The difference between this comparative example and Example 3 is that: the reaction solution is an ethanol solution of 0.2 M furfural, in which 1% by volume of dodecane is added as an internal standard.

[0168] Comparative Example 3-18

[0169] The difference between this comparative example and Example 3 is that: the reaction solution is a methyl isobutyl ketone solution of 0.2 M furfural, in which 1% by volume of dodecane is added as an internal standard.

[0170] Summary: The experimental results show that ( Figure 2 , the reaction conditions are the same as those in Comparative Example 3-1) under the action of 5Pt / MWNT, the product distribution is relatively wide and the selectivity for 2-MF is relatively low, while the introduction of Fe can very effectively limit the formation of products other than FOL and 2-MF. Among them, furfuryl alcohol is considered to be an intermediate product from furfural to 2-MF. Among them, metallic iron and metallic copper significantly improve the selectivity of 2-methylfuran. Compared with metallic copper, the introduction of iron does not reduce the conversion rate of the substrate. Continuing to increase the content of iron, the selectivity of 2-methylfuran is improved, which proves that the combination of metallic platinum and iron may be effective.

[0171] From Figure 3(The reaction conditions are the same as those in Comparative Example 3-1) It can be seen that when the mass fractions of both Pt and Fe are 3%, both the conversion rate and selectivity are relatively good. When the total loading is not high, the higher the iron content, the higher the selectivity of 2-methylfuran. However, when the total loading is relatively high, such as in 3Pt5Fe / MWNT, 5Pt3Fe / MWNT, and 5Pt5Fe / MWNT, the conversion rate of furfural decreases significantly. In particular, for 3Pt5Fe / MWNT, the selectivity of 2-methylfuran decreases. This may be due to the decrease in specific surface area and the reduction of the effective Pt surface area caused by the increase in the particle size of the metal nanoparticles formed when the total metal content increases. The actual Pt and Fe contents measured by ICP are found to be slightly different from the theoretical loading, which is in line with the theory (specific data are shown in Table 1).

[0172] Table 1 ICP measurement data of the metal loading of the catalyst

[0173]

[0174] From Figure 4 (Comparative Examples 2-1 to 2-5), it can be seen that both the selectivity of 2-methylfuran and the conversion rate of furfural decrease monotonically as the pressure increases from atmospheric pressure to 1 MPa. It should be noted in particular that the tetrahydrofurfuryl alcohol (THFA) and the solvation product (SP) in the steel pipe are higher than those in the quartz tube, because of the catalytic effect of the steel pipe itself.

[0175] We assume that increasing the height of the catalyst bed by changing the size of the fixed-bed reactor and thus extending the reaction time may be a simple method to improve the selectivity of 2-methylfuran. From Figure 5 、 Figure 6 It can be seen that at the same temperature, as the inner diameter of the reaction tube becomes thinner and the height of the catalyst bed increases, the selectivity of 2-methylfuran increases. In the higher temperature range, the temperature for the formation of by-products in the thinner tube reactor is also lower than that in the thicker tube part. However, due to problems such as pressure build-up and difficulty in loading the catalyst that may occur when the tube diameter is further reduced, a 4-mm reaction tube is selected as the optimal reactor size, and 200 °C is the optimal reaction temperature for this size of reactor.

[0176] In addition, it is found experimentally that the conversion rate of furfural is not sensitive to the change in the ratio of H2 / FOL within a certain range (almost complete conversion within 20 - 80). When the molar ratio of H2 / FOR is lower than 20, the substrate cannot be completely converted. However, too high a H2 / FOR may lead to a small amount of over-hydrogenation and the generation of some by-products. The optimal molar ratio of H2 / FOL is selected as 10 (at this time, the hydrogen flow rate is 5 mL / min). At this time, the conversion rate of furfural reaches 97.3%, and the selectivity of 2-methylfuran is 90%.

[0177] Figure 7The reaction results of different solvents are shown. When water is used as the solution, there are obvious differences in the product selectivity compared with other solvents. At this time, the main product is cyclopentanone, and no 2-methylfuran is formed. This is because the presence of water will inhibit the formation of 2-methylfuran from the intermediate product furfuryl alcohol. The cyclopentanone of methyl isobutyl ketone similar to water is the main product except for 2-methylfuran. And due to problems such as hydrogen dissolution, the furfural conversion rate of methyl isobutyl ketone and 1,4-epoxyhexane is relatively small. When alcohols (methanol, ethanol, isopropanol) are used as solvents, the furfural conversion rate is relatively high because protic solvents promote the hydrogenation reaction. Among them, isopropanol has the most obvious promoting effect on hydrogenation (isopropanol > methanol > ethanol), and the selectivity of 2-methylfuran shows the same law as the conversion rate. Therefore, isopropanol is selected as the ideal solvent for the system.

[0178] Figure 9 The excellent stability of the catalyst is shown. In the early stage of the reaction, furfural basically maintains a state of complete conversion, while the selectivity of 2-methylfuran slowly increases from the initial 92.4% to 95.3%, maintains for a period of time and then gradually decreases, and the conversion rate only starts to slowly decrease after 36 h. After 60 h, the conversion rate of the catalyst decreases from the initial 99.25% to 90.41%, and the selectivity of 2-methylfuran drops to 84%.

[0179] It can be seen from the high-resolution transmission electron microscope that almost every metal particle has a dark core, which is the Pt core with a high atomic number. Outside the Pt is a metal layer coexisting with Pt and Fe. At this time, Pt and Fe are arranged in a disordered interval. Pt@PtFe forms nanoparticles with uniform spatial distribution and relatively uniform size (average particle size 2.1 nm) ( Figure 11 ,12). The XRD pattern ( Figure 12 ) also proves that the introduction of Fe promotes the dispersion of Pt, and the particle size is significantly reduced, while Pt still exists as a single substance without alloy formation. The secret of high selectivity may lie in the appropriate acidic sites of 3Pt3Fe / WMNT ( Figure 13 ).

[0180] According to the reaction results, the present invention is a method for preparing pentanol by hydrogenating 2-methylfuran using a platinum-based catalyst, including the preparation of the catalyst and the corresponding catalytic reaction conditions. The catalyst synthesized by this method has the characteristics of simple synthesis and easy promotion, and at the same time has high activity and stability. The catalytic conditions are mild, there is no need to separate the catalyst and the reaction solution, and it also reduces the equipment cost and operation risk. The present invention has advantages such as significant benefits to energy and the environment, providing important technical support for promoting green chemistry and sustainable development. Therefore, the present invention has broad application potential in industrial production.

[0181] The present invention is not limited to the specific technical solutions described in the above embodiments. Any technical solutions formed by equivalent substitution are within the protection scope required by the present invention.

Claims

1. A method for catalyzing the selective conversion of furfural into 2-methylfuran, characterized in that: The reaction of furfural hydrogenation to prepare 2-methylfuran is carried out in a fixed bed equipped with a temperature control system. A certain mass of platinum-based catalyst is added to a customized quartz tube reactor, and furfural is hydrogenated to 2-methylfuran under the action of the catalyst by pumping in an isopropanol solution of furfural and passing in hydrogen. The platinum-based catalyst is obtained by a co-impregnation method. The catalyst preparation steps are as follows: weigh appropriate amounts of platinum precursor salt tetraammine platinum nitrate and iron precursor salt ferric nitrate, dissolve them in deionized water, stir and ultrasonically oscillate to evenly disperse the metal ions; the obtained metal The precursor mixed solution is added dropwise onto the multi-walled carbon nanotube MWNT carrier treated with concentrated nitric acid, and fully ground until the impregnation is uniform; then, the mixture is placed in an 80°C forced air drying oven for drying for 8-12 hours; the dried catalyst is transferred to a tubular furnace and calcined and reduced with hydrogen at 250-450°C for 2-4 hours; after cooling, it is taken out to obtain a multi-walled carbon nanotube-loaded platinum-iron bimetallic catalyst 3Pt3Fe / MWNT, in which Pt and Fe are both 3% by mass, and stored in a drying oven for future use.

2. The method for selectively converting furfural into 2-methylfuran according to claim 1, characterized in that: The reaction of furfural hydrogenation to prepare 2-methylfuran is carried out in a fixed bed equipped with a temperature control system. A fixed bed reactor is used as a reactor for furfural hydrogenation and deoxygenation. A quartz tube with a constricted mouth is used as a filler of a catalyst bed. Hydrogen and a reaction liquid are introduced from the top through a gas flow meter and a high-pressure flow pump respectively so that the two pass through the catalyst bed at the same time. The two are separated through a condensation and gas-liquid separation device below, wherein the reaction liquid is manually collected and separated. Before the reaction, the air in the reaction device is replaced by nitrogen, the reaction liquid is a furfural isopropanol solution, pure hydrogen is used as a hydrogen source, the pressure of the reaction process is normal pressure, and the reaction temperature is between 180-220°C.

3. The method for preparing 2-methylfuran using a platinum-based catalyst for furfural according to claim 1, characterized in that: The platinum precursor salt is a tetraamine platinum nitrate aqueous solution, and the iron precursor salt is Fe(NO3)3·9H2O. The mass ratio of platinum to iron in the platinum precursor salt and the iron precursor salt is 1:

1.

4. The method for preparing 2-methylfuran using a platinum-based catalyst for furfural according to claim 1, characterized in that: The multi-walled carbon nanotube carrier needs to be treated with concentrated nitric acid before use to remove impurities and introduce oxygen-containing functional groups to enhance the adsorption capacity of the metal precursor.

5. The method for preparing 2-methylfuran using a platinum-based catalyst for furfural according to claim 1, characterized in that: The catalyst reduction process is carried out under a hydrogen atmosphere, the hydrogen flow rate is maintained at 50 mL / min, the heating rate is 5°C / min, the calcination temperature is 300-450°C, and the time is 2-4 hours.

6. The method for preparing 2-methylfuran using a platinum-based catalyst for furfural according to claim 1, characterized in that: After the acidification is completed, deionized water is added to cool down and dilute the acid concentration. The carbon nanotubes are repeatedly washed and filtered until the final filtrate is weakly acidic with a pH of 4.0, and dried at 80 °C for 8-12 h. The dried carbon nanotubes are taken out, ground in a mortar, and sieved to make carbon nanotube carriers.

7. The method for preparing 2-methylfuran using a platinum-based catalyst for furfural according to claim 2, characterized in that: A quartz tube with a narrowed mouth was used as the reaction container. A small amount of quartz wool, quartz sand at a height of 3 mm, 200 mg of catalyst, and quartz sand at a height of 3 mm were sequentially filled into the customized quartz tube. The inner diameter of the quartz tube was adjusted so that the catalyst bed height was above 6 cm. After the reaction device was assembled, nitrogen was used to remove the air in the device. Before hydrogen was introduced, the catalyst was soaked in the reaction solution for more than 20 min to pre-adsorb the catalyst.

8. The method for preparing 2-methylfuran using a platinum-based catalyst for furfural according to claim 2, characterized in that: The inner diameter of the quartz tube is 4 mm, the flow rate of the reaction liquid furfural is 0.05 mL / min, the flow rate of hydrogen is 5 mL / min, the reaction solvent is isopropanol, the reaction temperature is 200 °C, and the reaction pressure is normal pressure.

9. The method for preparing 2-methylfuran using a platinum-based catalyst for furfural according to claim 2, characterized in that: The reaction is carried out in a roasting furnace equipped with a temperature sensor. During the reaction, the tail gas is connected to the atmosphere to make the reaction pressure normal pressure, and the reaction temperature is 200°C.

10. The method for catalyzing the selective conversion of furfural into 2-methylfuran according to claim 2, characterized in that: The specific steps are as follows: (1) Add 3 g of multi-walled carbon nanotubes and 300 mL of nitric acid to a round-bottom flask, place the round-bottom flask in an oil bath, stir at 120 °C, and reflux for 4 hours. After purification, quickly add deionized water to cool and dilute the acid concentration. Repeatedly wash and filter the carbon nanotubes until the final filtrate pH is 4, then dry in an oven at 80 °C for 12 hours, take out the dried carbon nanotubes, grind them in a mortar, and sieve through a 100-mesh standard sieve to prepare a carbon nanotube carrier; (2) Weigh 282 mg of multi-walled carbon nanotube carrier and spread it evenly on a mortar. Take 0.36 mL of 25 mg / mL tetraammine platinum nitrate solution, shake and sonicate it before, then add 0.9 mL of 10 mg / mL ferric nitrate solution and an appropriate amount of deionized water, sonicate for 5 min to mix them evenly, and evenly drop the mixed solution onto the carrier prepared in step (1). Grind until the catalyst is fully impregnated and dry it in a 70 °C drying oven for 12 h. (3) The impregnated and dried catalyst was taken out and ground into uniform fine particles, and then loaded into a vertical tube furnace. Quartz wool was placed above and below the catalyst bed. Then hydrogen was introduced into the tube furnace at a flow rate of 50 mL / min. The temperature was raised from room temperature to 400°C at a heating rate of 5°C / min. The catalyst was calcined and reduced at 400°C for 4 h. After cooling to room temperature, the pipeline was purged with nitrogen and the catalyst was taken out to obtain a 3Pt3Fe / MWNT catalyst. (4) The reaction of furfural hydrogenation to prepare 2-methylfuran was carried out in a fixed bed equipped with a temperature controller. The inner diameter of the quartz tube was 4 mm, the flow rate of the reaction liquid furfural was 0.05 mL / min, the flow rate of hydrogen used in the reaction was 5 mL / min, the reaction solvent was isopropanol, the reaction temperature was 200 °C, and the reaction pressure was atmospheric pressure.

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