Preparation method and application of nitrogen-doped carbon nanotube supported rhodium catalyst

Abstract

The present application relates to a kind of preparation methods of nitrogen-doped carbon nanotube supported rhodium catalyst, which comprises the following steps: (1) after mixing and stirring carbon nanotube and excess mixed acid solution, washing, drying is obtained after processing carbon nanotube;The treated carbon nanotube is dispersed in ethanol aqueous solution, and carbon nanotube ethanol aqueous solution with concentration of 4~8g / L is formed;(2) water-soluble rhodium salt, melamine, formaldehyde solution and deionized water are mixed and stirred uniformly, and white transparent rhodium complex solution is formed;(3) carbon nanotube ethanol aqueous solution is added dropwise to rhodium complex solution, and after stirring at 80~100 ℃ for 3~6h, washing, drying is obtained rhodium precursor;(4) rhodium precursor is high-temperature calcined in argon, and nitrogen-doped carbon nanotube supported rhodium catalyst is obtained.Simultaneously, the application of the catalyst is also disclosed.The preparation process of the present application is simple, easy to scale production, and the obtained catalyst structure and property are stable, with excellent catalytic activity in catalytic olefin hydroformylation reaction.

Description

Technical Field

[0001] This invention relates to the field of rhodium-based catalyst technology, and in particular to a method for preparing a rhodium catalyst supported on nitrogen-doped carbon nanotubes and its application. Background Technology

[0002] The hydroformylation of olefins is one of the most important homogeneous catalytic reactions in industry, boasting 100% atom economy. This process can produce over 10 million tons of aldehydes annually, which can be further converted into alcohols, acids, esters, amines, and other valuable chemical substances, finding wide application in the production of high-value-added fine chemicals. Chem. Rev. , 2012, 112, 5675-5732; Eur. J. Org. Chem. , 2012, 6309-6320.).

[0003] Many metals, including rhodium, cobalt, ruthenium, iridium, and palladium, can catalyze the hydroformylation of olefins, but only rhodium-based and cobalt-based catalysts are used in industrial production, while other metals remain in the basic research stage. Furthermore, while cobalt catalysts exhibit high tolerance to toxic substances in the feedstock, the demanding reaction conditions and high investment costs have gradually diminished their advantages. Rhodium catalysts show significantly higher catalytic activity than cobalt catalysts for the hydroformylation of high-carbon-chain olefins, and the reaction conditions are milder. Therefore, the commonly used rhodium-based catalytic system has become a hot topic for the optimization and improvement of hydroformylation processes. However, homogeneous catalysts face severe challenges in recovery and separation, and the loss of rhodium metal and the emission of phosphorus-containing ligands during the reaction process pose significant drawbacks. In particular, when high-carbon olefins (C5 and above) are used as substrates, homogeneous rhodium-based catalysts are more prone to deactivation during high-temperature separation and distillation due to the high boiling point of the products. Chem. Sus. Chem. , 2018, 11: 2310-2314).

[0004] In contrast, heterogeneous catalysts are easier to separate, recover, and reuse, making them a more attractive option for industrial applications. In recent years, carbon-based materials have attracted widespread attention due to their high activity, large specific surface area, controllable pore structure, good stability, and environmental friendliness, and are considered ideal supports for heterogeneous catalysts. However, currently, only a few studies have focused on carbon-based materials as supports for hydroformylation reactions; furthermore, these carbon-supported rhodium-based catalysts suffer from drawbacks such as cumbersome preparation steps, low reactivity, and poor stability. Multi-walled carbon nanotubes (MWCNTs) are widely used in these catalytic applications due to their ease of large-scale production. For example, Chinese invention patent CN202210604725.6 reports the successful synthesis of a heterogeneous catalyst for the catalytic oxidation of cyclohexene to cyclohexanone by loading palladium acetate onto modified MWCNTs; palladium nanoparticles supported on MWCNTs (Pd / MWCNTs) have also been found to be an effective catalyst for the hydrogenation of biomass-derived levulinic acid. Furthermore, the interaction strength between the catalyst support and the metal phase can be altered by electronically modifying carbon nanotubes with heteroatoms (such as nitrogen). Nitrogen doping leads to the formation of defect sites in the carbon nanotube structure. These defects also act as anchoring sites for well-dispersed catalytically active metals, enabling nitrogen-doped carbon nanotubes to support various metal catalysts. These nitrogen-doped carbon nanotube-supported catalysts have been applied in various reactions, such as hydrogenation and dehydrogenation processes, oxidation reactions, and Fischer-Tropsch synthesis. However, the preparation of supported rhodium-based catalysts by loading rhodium metal onto nitrogen-doped carbon nanotubes for the hydroformylation of olefins has not yet been reported. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a simple method for preparing a nitrogen-doped carbon nanotube supported rhodium catalyst with stable catalyst structure and properties.

[0006] Another technical problem to be solved by the present invention is to provide the application of the nitrogen-doped carbon nanotube supported rhodium catalyst.

[0007] To address the above problems, the present invention provides a method for preparing a rhodium catalyst supported on nitrogen-doped carbon nanotubes, comprising the following steps: (1) Mix carbon nanotubes with an excess of mixed acid solution, stir at 50-70℃ for 3-5 hours, filter and wash with deionized water until neutral, and dry to obtain the treated carbon nanotubes; disperse the treated carbon nanotubes in an ethanol aqueous solution to form a carbon nanotube ethanol aqueous solution with a concentration of 4-8 g / L. (2) Mix water-soluble rhodium salt, melamine, formaldehyde solution and deionized water, and stir evenly at 60~80℃ to form a white transparent rhodium complex solution; (3) Add the carbon nanotube ethanol aqueous solution dropwise to the rhodium complex solution, stir at 80~100℃ for 3~6h, filter and wash with deionized water, and dry to obtain the rhodium precursor; the volume ratio of the rhodium complex solution to the carbon nanotube ethanol aqueous solution is 4:5. (4) The rhodium precursor is calcined in argon at a rate of 2℃ / min at 700~1000℃ for 2~6h to obtain a nitrogen-doped carbon nanotube supported rhodium catalyst.

[0008] In step (1), the mixed acid solution is prepared by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1.

[0009] In step (1), the volume ratio of anhydrous ethanol to water in the ethanol-water solution is 3:1.

[0010] In step (2), the molar ratio of rhodium to melamine in the water-soluble rhodium salt is 1:400~430; the volume ratio of formaldehyde solution to deionized water is 1:10~20; and the ratio of melamine to formaldehyde solution is 1~2g:2mL.

[0011] The water-soluble rhodium salt is one of rhodium trichloride, ammonium hexachlororhodium, rhodium nitrate, and rhodium acetate.

[0012] A nitrogen-doped carbon nanotube-supported rhodium catalyst prepared by the method described above.

[0013] The application of a nitrogen-doped carbon nanotube-supported rhodium catalyst as described above is characterized in that: the catalyst is used to catalyze the hydroformylation reaction of olefins to synthesize aldehyde compounds; the amount of the catalyst, calculated in rhodium, is 0.14% to 0.7% of the molar amount of the olefin compound.

[0014] The structural formula of the olefin compound is: R1 is one of butyl, pentyl, hexyl, cyclobutyl, and phenyl.

[0015] The conditions for the hydroformylation reaction are as follows: the solvent is toluene, the reaction temperature is 90~120℃, the reaction pressure is 3~6MPa, and the reaction time is 1~7h.

[0016] Compared with the prior art, the present invention has the following advantages: 1. The nitrogen-doped carbon nanotube supported rhodium catalyst of the present invention is prepared by a one-step pyrolysis process. The precursors of melamine, carbon nanotubes and rhodium source are uniformly mixed and polymerized, and then calcined under a non-oxidizing atmosphere to synthesize the catalyst.

[0017] 2. This invention does not require operation under anhydrous and oxygen-free conditions, and the preparation process is simple and easy to scale up for production.

[0018] 3. The catalyst obtained by the method of this invention has a stable structure and properties, exhibits excellent catalytic activity in the hydroformylation of olefins, and there is no loss of rhodium active components or structural damage during the reaction. After the catalytic reaction, the mixture can be separated and recovered by simple centrifugation, and the catalytic performance does not significantly decrease after multiple recycling, showing good application prospects. Attached Figure Description

[0019] The specific embodiments of the present invention will be described in further detail below with reference to the accompanying drawings.

[0020] Figure 1 This is a synthetic route diagram for the present invention.

[0021] Figure 2 This is an HR-TEM image of catalyst A of the present invention.

[0022] Figure 3 This is a TEM image of catalyst A of the present invention. Detailed Implementation

[0023] like Figure 1 As shown, a method for preparing a rhodium catalyst supported on nitrogen-doped carbon nanotubes includes the following steps: (1) Mix carbon nanotubes with an excess of mixed acid solution, stir at 50-70℃ for 3-5 hours, filter and wash with deionized water until neutral, and dry to obtain the treated carbon nanotubes; disperse the treated carbon nanotubes in an ethanol aqueous solution to form a carbon nanotube ethanol aqueous solution with a concentration of 4-8 g / L.

[0024] The volume ratio (mL / mL) of anhydrous ethanol to water in the ethanol-water solution is 3:1.

[0025] The mixed acid solution is made by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 (mL / mL).

[0026] (2) Mix water-soluble rhodium salt, melamine, formaldehyde solution and deionized water, and stir evenly at 60~80℃ to form a white transparent rhodium complex solution.

[0027] Among them: the molar ratio of rhodium to melamine in water-soluble rhodium salt is 1:400~430; the volume ratio (mL / mL) of formaldehyde solution to deionized water is 1:10~20; and the ratio of melamine to formaldehyde solution is 1~2g:2mL.

[0028] The water-soluble rhodium salt is one of rhodium trichloride, ammonium hexachlororhodiumate, rhodium nitrate, and rhodium acetate, with rhodium trichloride being preferred.

[0029] (3) Add carbon nanotube ethanol aqueous solution dropwise to the rhodium complex solution, with a volume ratio (mL / mL) of 4:5 between the rhodium complex solution and the carbon nanotube ethanol aqueous solution. After stirring at 80~100℃ for 3~6h, filter and wash with deionized water, and dry to obtain the rhodium precursor.

[0030] (4) The rhodium precursor is calcined in argon at a rate of 2℃ / min at 700~1000℃ for 2~6h to obtain the nitrogen-doped carbon nanotube supported rhodium catalyst.

[0031] Application of a nitrogen-doped carbon nanotube supported rhodium catalyst: This catalyst is used to catalyze the hydroformylation of olefins to synthesize aldehydes; the amount of catalyst used is 0.14% to 0.7% of the molar amount of the olefin compound, calculated in rhodium.

[0032] The structural formula of the olefin compound is: R1 is one of butyl, pentyl, hexyl, cyclobutyl, and phenyl.

[0033] The conditions for hydroformylation are as follows: the solvent is toluene, the reaction temperature is 90~120℃, the reaction pressure is 3~6MPa, and the reaction time is 1~7h.

[0034] Example 1 A method for preparing a rhodium catalyst supported on nitrogen-doped carbon nanotubes: (1) Mix carbon nanotubes with an excess of mixed acid solution, stir at 50-70℃ for 3-5 hours, filter and wash with deionized water until neutral, and dry to obtain the treated carbon nanotubes; take 200mg of the treated carbon nanotubes and disperse them in 40mL of ethanol aqueous solution to form carbon nanotube ethanol aqueous solution.

[0035] The volume ratio (mL / mL) of anhydrous ethanol to water in the ethanol-water solution is 3:1.

[0036] The mixed acid solution is made by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 (mL / mL).

[0037] (2) Add 4 mg RhCl3·3H2O, 1.0 g melamine, 2 mL formaldehyde solution and 30 mL deionized water to a 100 mL round-bottom flask and stir vigorously at 70 °C for 15 min to form a white, uniform and transparent rhodium complex solution.

[0038] (3) Add carbon nanotube ethanol aqueous solution dropwise to the rhodium complex solution, stir evenly, rapidly heat to 100℃ and maintain for 3h, filter and wash with deionized water, and finally dry the obtained solid at 60℃ for 12h to obtain the rhodium precursor.

[0039] (4) The rhodium precursor was calcined in argon at 900°C for 2 h at a rate of 2 °C / min to obtain the nitrogen-doped carbon nanotube supported rhodium catalyst, denoted as catalyst A.

[0040] Catalyst A was observed using high-resolution transmission electron microscopy and conventional transmission electron microscopy, and the results are as follows: Figures 2-3 As shown. By Figures 2-3 It can be seen that the tubular structure is still present after high-temperature calcination, and the carbon nanotube structure has not been destroyed. In addition, no obvious Rh metal particles were found in the catalyst, indicating that Rh is uniformly dispersed on the support surface.

[0041] Catalyst evaluation: In an 80 mL stainless steel reactor equipped with magnetic stir bar, 10 mmol of 1-octene, 5 mL of toluene, and 20 mg of catalyst were added. After sealing, the reactor was purged three times, then pressurized with syngas (CO:H2 = 1:1) to 6 MPa. The reactor was heated to 120 °C and maintained for 5 h. After the reaction was completed, the reactor was cooled to room temperature and the pressure was slowly released. 5 mmol of n-hexadecane was added to the mixture as an internal standard, and 5 mL of ethyl acetate was added for dilution. The solid catalyst was removed by centrifugation, and the reaction solution was quantitatively analyzed by gas chromatography (Agilent 7890A GC). The conversion and yield were calculated using the internal standard method and NMR quantification.

[0042] Example 2 In Example 2, except that 700°C was used as the catalyst calcination temperature, the rest of the implementation process was the same as in Example 1, and the resulting nitrogen-doped carbon nanotube supported rhodium catalyst was designated as catalyst B.

[0043] Catalyst evaluation and product analysis were the same as in Example 1.

[0044] Example 3 In Example 3, except that 800°C was used as the catalyst calcination temperature, the rest of the implementation process was the same as in Example 1, and the resulting nitrogen-doped carbon nanotube supported rhodium catalyst was denoted as catalyst C.

[0045] Catalyst evaluation and product analysis were the same as in Example 1.

[0046] Example 4 In Example 4, except that 1000°C was used as the catalyst calcination temperature, the rest of the implementation process was the same as in Example 1, and the resulting nitrogen-doped carbon nanotube supported rhodium catalyst was denoted as catalyst D.

[0047] Catalyst evaluation and product analysis were the same as in Example 1.

[0048] Example 5 In Example 5, except that the amount of melamine was changed to 2.0g, the rest of the implementation process was the same as in Example 1, and the resulting nitrogen-doped carbon nanotube supported rhodium catalyst was denoted as catalyst E.

[0049] Catalyst evaluation and product analysis were the same as in Example 1.

[0050] Example 6 In Examples 6-19, the hydroformylation reaction performance under different temperatures, pressures, times, and solvents was evaluated using catalyst A from Example 1 as an example.

[0051] Catalyst evaluation: In Example 6, except that the reactor temperature was heated to 110°C, the rest of the catalyst evaluation and product analysis process was the same as in Example 1.

[0052] Example 7 Catalyst evaluation: In Example 7, except that the reactor temperature was heated to 100°C, the rest of the catalyst evaluation and product analysis process was the same as in Example 1.

[0053] Example 8 Catalyst evaluation: In Example 8, except that the reactor temperature was heated to 90°C, the rest of the catalyst evaluation and product analysis process was the same as in Example 1.

[0054] Example 9 Catalyst evaluation: In Example 9, except that the syngas pressure (CO:H2 = 1:1) was increased to 5 MPa, the rest of the catalyst evaluation and product analysis process was the same as in Example 1.

[0055] Example 10 Catalyst evaluation: In Example 10, except that the syngas pressure (CO:H2 = 1:1) was increased to 4 MPa, the rest of the catalyst evaluation and product analysis process was the same as in Example 1.

[0056] Example 11 Catalyst evaluation: In Example 11, except that the syngas pressure (CO:H2 = 1:1) was increased to 3 MPa, the rest of the catalyst evaluation and product analysis process was the same as in Example 1.

[0057] Example 12 Catalyst evaluation: In Example 12, the catalyst evaluation and product analysis process were the same as in Example 1, except that the reaction time was changed to 4 hours.

[0058] Example 13 Catalyst evaluation: In Example 13, the catalyst evaluation and product analysis process were the same as in Example 1, except that the reaction time was changed to 3 hours.

[0059] Example 14 Catalyst evaluation: In Example 14, the catalyst evaluation and product analysis process were the same as in Example 1, except that the reaction time was changed to 2 hours.

[0060] Example 15 Catalyst evaluation: In Example 15, the catalyst evaluation and product analysis process were the same as in Example 1, except that the reaction time was changed to 1 hour.

[0061] Example 16 Catalyst evaluation: In Example 16, the catalyst evaluation and product analysis process were the same as in Example 1, except that the solvent was changed to tetrahydrofuran.

[0062] Example 17 Catalyst evaluation: In Example 17, the catalyst evaluation and product analysis process were the same as in Example 1, except that the reaction time was changed to acetonitrile.

[0063] Example 18 Catalyst evaluation: In Example 18, the catalyst evaluation and product analysis were the same as in Example 1, except that the reaction time was changed to N,N-dimethylformamide.

[0064] Example 19 Catalyst evaluation: In Example 19, the catalyst evaluation and product analysis process were the same as in Example 1, except that the reaction time was changed to 1,4-dioxane.

[0065] Table 1. Reaction performance of nitrogen-doped carbon nanotube-supported rhodium catalysts As can be seen from Table 1, the nitrogen-doped carbon nanotube-supported rhodium catalyst prepared in this invention exhibits excellent catalytic performance. Among them, the catalyst calcined at 900℃ showed excellent 1-octene conversion (100%) and aldehyde yield (98%) under optimized conditions (120℃, 6MPa, 5h).

[0066] Example 20 Taking catalyst A from Example 1 as an example, a recycling performance test was conducted: the catalyst after reaction was washed three times with toluene, dried in a vacuum drying oven, and the dried catalyst was used for the next cycle. Other operations and product analysis were the same as in Example 1, and the reaction data for catalyst reuse are shown in Table 2.

[0067] Table 2 Reusability of Catalyst A in Example 1 Hydroformylation As can be seen from Table 2, the nitrogen-doped carbon nanotube-supported rhodium catalyst prepared in this invention can be reused multiple times, and the catalytic activity and aldehyde yield are well maintained.

[0068] Example 21 In Examples 21-31, the procedures were identical to those of Example 1, except that 10 mmol of a different olefin substrate was added instead of 10 mmol of 1-octene. The reaction results for different olefin substrates are shown in Table 3.

[0069] Table 3 Catalytic performance of catalyst A in various olefin hydroformylation reactions in Example 1 As can be seen from Table 3, the nitrogen-doped carbon nanotube-supported rhodium catalyst prepared in this invention can be applied to the hydroformylation reaction of various olefins, and all of them exhibit excellent catalytic activity and yield.

[0070] The above description uses only specific examples to illustrate the principles and implementation methods of the present invention and is not intended to limit the present invention in any way. It should be noted that those skilled in the art will recognize variations and modifications in specific implementation methods and application scope without departing from the principles of the present invention, and these variations and modifications should also be considered within the scope of protection of the present invention.

Claims

1. An application of a nitrogen-doped carbon nanotube-supported rhodium catalyst, characterized in that: This catalyst is used to catalyze the hydroformylation of olefins to synthesize aldehydes; the preparation method of the catalyst includes the following steps: (1) Mix carbon nanotubes with an excess of mixed acid solution, stir at 50-70℃ for 3-5 hours, filter and wash with deionized water until neutral, and dry to obtain the treated carbon nanotubes; disperse the treated carbon nanotubes in an ethanol aqueous solution to form a carbon nanotube ethanol aqueous solution with a concentration of 4-8 g / L. (2) Mix water-soluble rhodium salt, melamine, formaldehyde solution and deionized water, and stir evenly at 60~80℃ to form a white transparent rhodium complex solution; (3) Add the carbon nanotube ethanol aqueous solution dropwise to the rhodium complex solution, stir at 80~100℃ for 3~6h, filter and wash with deionized water, and dry to obtain the rhodium precursor; the volume ratio of the rhodium complex solution to the carbon nanotube ethanol aqueous solution is 4:

5. (4) The rhodium precursor is calcined in argon at a rate of 2℃ / min at 800~1000℃ for 2~6h to obtain a nitrogen-doped carbon nanotube supported rhodium catalyst.

2. The application of the nitrogen-doped carbon nanotube-supported rhodium catalyst as described in claim 1, characterized in that: In step (1), the mixed acid solution is prepared by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:

1.

3. The application of the nitrogen-doped carbon nanotube-supported rhodium catalyst as described in claim 1, characterized in that: In step (1), the volume ratio of anhydrous ethanol to water in the ethanol-water solution is 3:

1.

4. The application of the nitrogen-doped carbon nanotube-supported rhodium catalyst as described in claim 1, characterized in that: In step (2), the molar ratio of rhodium to melamine in the water-soluble rhodium salt is 1:400~430; the volume ratio of formaldehyde solution to deionized water is 1:10~20; and the ratio of melamine to formaldehyde solution is 1~2g:2mL.

5. The application of the nitrogen-doped carbon nanotube-supported rhodium catalyst as described in claim 4, characterized in that: The water-soluble rhodium salt is one of rhodium trichloride, ammonium hexachlororhodium, and rhodium nitrate.

6. The application of the nitrogen-doped carbon nanotube-supported rhodium catalyst as described in claim 1, characterized in that: The structural formula of the olefin is: R1 is one of butyl, pentyl, hexyl, cyclobutyl, and phenyl.

7. The application of the nitrogen-doped carbon nanotube-supported rhodium catalyst as described in claim 1, characterized in that: The conditions for the hydroformylation reaction are as follows: the solvent is toluene, the reaction temperature is 90~120℃, the reaction pressure is 3~6MPa, and the reaction time is 1~7h.

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