Preparation method and application of fluorine-doped carbon-loaded cobalt-based catalyst

Abstract

The invention provides a preparation method and application of a fluorine-doped carbon-loaded cobalt-based catalyst, and belongs to the field of catalysts. The preparation method of the catalyst comprises the following steps: dissolving a certain amount of cobalt salt, citric acid and villiaumite in a solvent, drying to obtain a catalyst precursor, and performing high-temperature carbonization and grinding to obtain the fluorine-doped carbon-loaded cobalt-based catalyst. The invention also provides application of the catalyst in catalyzing selective hydrogenation of quinoline to prepare 1, 2, 3, 4-tetrahydroquinoline. The fluorine-doped carbon-loaded cobalt-based catalyst disclosed by the invention is used for selective hydrogenation reaction of quinoline, and has the advantages of high catalytic activity, good selectivity, easiness in recovery and reutilization, mild reaction conditions, green and environment-friendly reaction solvent and the like, the selectivity of a target product is as high as 99%, and meanwhile, the conversion rate of quinoline can also be as high as 99%; the preparation process of the catalyst and the target product is simple, the raw materials are easy to obtain, the production cost is low, and the industrial application value is good.

Description

Technical Field

[0001] The invention belongs to the field of catalysts, and in particular relates to a preparation method of a fluorine-doped carbon-supported cobalt-based catalyst and application thereof. Background Art

[0002] 1,2,3,4-tetrahydroquinoline and its derivatives are a class of nitrogen-containing heterocyclic compounds with important biological activities, and therefore have received extensive attention in the study of new synthetic methods. These compounds have shown great application potential as biologically active building blocks and key intermediates in the production of medicines, alkaloids, pesticides and many fine chemicals.

[0003]

[0004] Due to the wide application of 1,2,3,4-tetrahydroquinoline compounds, it is particularly important to develop new synthetic methods to improve their synthesis efficiency and selectivity. 1,2,3,4-tetrahydroquinoline derivatives are synthesized through hydrogenation reduction strategies, ring-closing transformation reaction strategies, and multi-molecular condensation reaction strategies, and more efficient and environmentally friendly synthetic routes are constantly explored. In the synthesis process, the selection of a suitable catalyst is crucial to improving the reaction efficiency and selectivity. Therefore, a new, high-performance heterogeneous catalyst is developed to achieve the selective hydrogenation of quinoline compounds to obtain high-purity 1,2,3,4-tetrahydroquinoline.

[0005] In the quinoline hydrogenation reaction, different types of catalysts are usually selected to improve the reaction efficiency, selectivity and catalyst stability. Precious metal catalysts, such as ruthenium (Ru), rhodium (Rh), platinum (Pt), palladium (Pd) and iridium (Ir), are widely used due to their high activity and selectivity. However, the high cost of these precious metals limits their use in large-scale industrial applications.

[0006] To reduce costs, non-precious metal catalysts, such as those based on cobalt (Co), copper (Cu), molybdenum (Mo), and iron (Fe), have become the focus of research. These catalysts are not only lower in cost, but in some cases, their catalytic performance can be comparable to that of precious metal catalysts.

[0007] Chinese invention patent application CN202211096958.6 discloses a method for synthesizing 1,2,3,4-tetrahydroquinoline by catalytic hydrogenation of a metal sub-nano cluster and a single atom coexisting catalyst, comprising the following specific steps: 1) adding a metal oxide-supported sub-nano cluster and a single atom coexisting catalyst, quinoline and a solvent into a reactor as a reaction solution; 2) reacting under the condition of passing hydrogen to obtain the product 1,2,3,4-tetrahydroquinoline. In this invention, in the metal oxide-supported sub-nano cluster and a single atom coexisting catalyst, the carrier is a metal oxide, and the active component is a metal sub-nano cluster and a single atom coexisting state; the metal oxide is selected from one or more of aluminum oxide, titanium oxide, magnesium oxide, cerium oxide, and iron oxide; the active component is selected from Pt, Pd, Rh, Ru or Co. The preparation method of the metal oxide-supported sub-nano cluster and single atom coexistence catalyst comprises the following steps: 11) drying the metal oxide at high temperature and in vacuum to obtain a dried metal oxide powder without free water and bound water for standby use; 12) dissolving glucose in deionized water and ultrasonically dispersing to obtain a glucose solution; then slowly adding the dried oxide powder obtained in step 11) into the glucose solution and stirring evenly to obtain a slurry; 13) in a water bath, stirring and evaporating the slurry obtained in step 12), vacuum drying, and grinding; then calcining the ground powder in an inert atmosphere to obtain a carbon-modified oxide carrier; 14) adding the carbon-modified oxide carrier obtained in step 13) into an active metal salt solution, stirring evenly, evaporating to dryness, vacuum drying, cooling, grinding into powder, and calcining in an inert atmosphere to obtain the product of the invention, the sub-nano cluster and single atom coexistence catalyst. Compared with the existing technology, the biggest feature of the inventive method is the use of sub-nano clusters and single-atom coexisting metals as catalysts, which greatly improves the atomic utilization rate, reduces the catalyst cost, and has good catalyst reproducibility and high product selectivity, making it possible to realize industrial production.

[0008] However, the inventors have found through experiments on the selective hydrogenation of quinoline to synthesize 1,2,3,4-tetrahydroquinoline that when using different catalysts or different hydrogenation reaction conditions, it is not difficult to improve the selectivity of the product 1,2,3,4-tetrahydroquinoline, and its selectivity can easily reach more than 99%, but it is quite difficult to improve the conversion rate of quinoline. In other words, the conversion performance of quinoline, the raw material of the reaction, is likely to be poor; but the above patent application does not mention the raw material conversion rate of the selective hydrogenation reaction of quinoline catalyzed by its catalyst at all, let alone the reusability of the catalyst. And the catalyst preparation method in the patent application is relatively cumbersome.

[0009] Those skilled in the art can make more efforts to improve the catalyst performance of the selective hydrogenation of quinoline to 1,2,3,4-tetrahydroquinoline, in order to obtain a non-precious metal catalyst with excellent catalytic reaction performance and lower cost, wherein the catalytic reaction performance includes the conversion rate of quinoline, the selectivity of the product and the reusability of the catalyst. Summary of the invention

[0010] Therefore, the present invention provides a method for preparing a fluorine-doped carbon-supported cobalt-based catalyst, the method comprising the following steps:

[0011] S1. Dissolve a certain proportion of cobalt salt, citric acid and fluoride salt in a solvent, and stir until dissolved to obtain a mixed solution;

[0012] S2, drying the mixed solution to obtain a catalyst precursor;

[0013] S3, carbonizing the catalyst precursor under a protective atmosphere and high temperature, and grinding the solid obtained after carbonization to obtain the catalyst.

[0014] In a specific embodiment, the cobalt salt in step S1 is at least one of cobalt nitrate, cobalt chloride, cobalt acetate and cobalt sulfate, the fluoride salt is at least one of ammonium fluoride, sodium fluoride, potassium fluoride and calcium fluoride, the solvent is at least one of methanol, ethanol, isopropanol and water, and the molar ratio of the cobalt salt to the citric acid is 0.05-0.5:1, preferably 0.1-0.3:1, and the molar ratio of the fluoride salt to the citric acid is 0.15-0.8:1, preferably 0.2-0.7:1, and more preferably 0.3-0.6:1.

[0015] In a specific embodiment, the drying temperature in step S2 is 80-120°C.

[0016] In a specific embodiment, the protective atmosphere in step S3 is at least one of nitrogen and argon, the high temperature is above 550°C, and the carbonization calcination temperature is preferably 600-700°C.

[0017] In a specific embodiment, the carbonization calcination time in step S3 is 1 to 3 hours.

[0018] The present invention also provides a fluorine-doped carbon-supported cobalt-based catalyst, the catalyst structure is a fluorine-doped carbon substrate supporting cobalt nanoparticles, and the cobalt element and the fluorine element in the catalyst are uniformly distributed on the carbon-based carrier.

[0019] The present invention also provides an application of a fluorine-doped carbon-supported cobalt-based catalyst prepared by the preparation method, wherein the catalyst is used for catalyzing the selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline.

[0020] In a specific embodiment, the step of preparing 1,2,3,4-tetrahydroquinoline by selective hydrogenation of quinoline comprises: adding reaction substrate quinoline and catalyst in an autoclave and a solvent environment, the reaction gas atmosphere is hydrogen, the reaction temperature is 60-120° C., the hydrogen pressure is 2-4 MPa, and the reaction time is 4-8 h.

[0021] In a specific embodiment, the solvent for selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline is at least one of ethanol, methanol, isopropanol, acetonitrile, water, tetrahydrofuran, n-hexane and toluene, preferably at least one of ethanol, methanol and tetrahydrofuran.

[0022] The present invention also provides a catalyst for catalyzing the selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline.

[0023] In the application of the present invention, the substrate of the selective hydrogenation reaction can be not only quinoline but also its derivatives, including 8-chloroquinoline, 8-fluoroquinoline, 8-methylquinoline, 8-bromoquinoline and 8-hydroxyquinoline.

[0024] The beneficial effects of the present invention include: the fluorine-doped carbon-supported cobalt-based catalyst of the present invention is used for the selective hydrogenation reaction of quinoline, and has the advantages of high catalytic activity, good selectivity, easy recovery and reuse, mild reaction conditions, and green reaction solvents, wherein the selectivity of the target product is as high as 99%, and the conversion rate of quinoline can also be as high as 99%; and the preparation process of the catalyst and the target product is simple, the raw materials are easily available, the production cost is low, and it has good industrial application value. Fluorine doping in the catalyst of the present invention is conducive to the redistribution of electrons on the surface of the carbon carrier, can enhance the electron transfer between the metal and the carrier, and is used to improve the activity and stability of the catalyst. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 The XRD diagrams of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1 are shown.

[0026] Figure 2 This is a diagram of the catalyst stability cycle catalytic performance in Example 1.

[0027] Figure 3 N2 physical adsorption-desorption curves of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1.

[0028] Figure 4 The pore size distribution curves of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1 are shown.

[0029] Figure 5The SEM images of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1 are shown.

[0030] Figure 6 TEM images of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1. Specific implementation plan

[0031] The present invention is further described below in conjunction with specific embodiments, but the protection scope of the present invention is not limited thereto.

[0032] Example 1

[0033] This example is the preparation and performance evaluation of Co / CF catalyst.

[0034] First, weigh 0.3g of cobalt nitrate (cobalt nitrate hexahydrate, the same below), 1g of citric acid and 0.1g of ammonium fluoride in a 50mL beaker for later use. Then, add 20mL of methanol to the beaker and stir at room temperature until it is completely dissolved. Then, pour the dissolved liquid in small amounts into a porcelain boat that has been placed in an oven at 100℃ for 1h. After drying for 1h, the porcelain boat containing the solid is calcined at 600℃ in a tube furnace for 2h, taken out, and ground into powder. The final catalyst is named Co / CF-0.5. Catalyst stability evaluation is shown in Figure 2 .

[0035] Example 2

[0036] Weigh 0.3 g of cobalt nitrate, 1 g of citric acid and 0.02 g of ammonium fluoride into a 50 mL beaker for later use. Then, add 20 mL of methanol into the beaker and stir at room temperature until it is completely dissolved. Subsequently, pour the dissolved liquid in small amounts into a porcelain boat that has been placed in an oven at 100 °C for 1 hour. After drying for 1 hour, the porcelain boat containing the solid is calcined in a tubular furnace at 600 °C for 2 hours, taken out, and ground into powder. The final catalyst is named Co / CF-0.1.

[0037] Example 3

[0038] Weigh 0.3 g of cobalt nitrate, 1 g of citric acid and 0.2 g of ammonium fluoride into a 50 mL beaker for later use. Then, add 20 mL of methanol into the beaker and stir at room temperature until it is completely dissolved. Subsequently, pour the dissolved liquid in small amounts into a porcelain boat that has been placed in an oven at 100 °C for 1 h and dry it. After that, calcine the porcelain boat containing the solid at 600 °C in a tubular furnace for 2 h, take it out, grind it into powder, and the resulting catalyst is named Co / CF-1.

[0039] Comparative Example 1

[0040] Weigh 0.3 g of cobalt nitrate, 1 g of citric acid and 0 g of ammonium fluoride into a 50 mL beaker for later use. Then, add 20 mL of methanol into the beaker and stir at room temperature until it is completely dissolved. Subsequently, pour the dissolved liquid in small amounts into a porcelain boat that has been placed in an oven at 100 °C for 1 h and dry it. After that, calcine the porcelain boat containing the solid at 600 °C in a tubular furnace for 2 h, take it out, grind it into powder, and the resulting catalyst is named Co / CF-0.

[0041] Example 4

[0042] Weigh 0.3 g of cobalt nitrate, 1 g of citric acid and 0.1 g of ammonium fluoride into a 50 mL beaker for later use. Then, add 20 mL of methanol into the beaker and stir at room temperature until it is completely dissolved. Subsequently, pour the dissolved liquid in small amounts several times into a porcelain boat that has been placed in an oven at 100 °C in advance and dry it for 1 hour. After that, calcine the porcelain boat containing the solid at 500 °C in a tubular furnace for 2 hours, take it out, grind it into powder, and finally obtain the catalyst.

[0043] Example 5

[0044] Weigh 0.3 g of cobalt nitrate, 1 g of citric acid and 0.1 g of ammonium fluoride into a 50 mL beaker for later use. Then, add 20 mL of methanol into the beaker and stir at room temperature until it is completely dissolved. Subsequently, pour the dissolved liquid in small amounts several times into a porcelain boat that has been placed in an oven at 100 °C and dry for 1 h. After that, calcine the porcelain boat containing the solid at 700 °C in a tubular furnace for 2 h, take it out, grind it into powder, and finally obtain the catalyst.

[0045] Example 6

[0046] This example is a study on the catalytic performance of catalysts with different fluorine-to-carbon ratios during the catalyst preparation process.

[0047] The Co / CF catalysts prepared in Examples 1 to 3 and Comparative Example 1 were used in the hydrogenation reaction of quinoline, and the specific implementation conditions were as follows: 30 mg of the Co / CF catalyst was weighed into a 50 mL polytetrafluoroethylene-lined stainless steel autoclave equipped with a magnetically driven stirrer, and then 0.5 mmol of the substrate quinoline and 15 mL of methanol were added for reaction, and the reaction conditions were: T = 100°C, P = 3 MPa, t = 6 h. The conversion rate of quinoline and the selectivity of the product 1,2,3,4-tetrahydroquinoline were detected by gas chromatography, and the measured conversion rate of quinoline and the selectivity of the product 1,2,3,4-tetrahydroquinoline are shown in Table 1 below.

[0048] Table 1

[0049] catalyst Fluorocarbon content Conversion rate (%) Selectivity (%) Example 1 0.5：1 99 99 Example 2 0.1：1 42.3 99 Example 3 1：1 20 99 Comparative Example 1 0：1 11.5 99

[0050] It can be seen from Table 1 that compared with Examples 2 to 3 and Comparative Example 1, the appropriate fluorine-carbon ratio in the catalyst of Example 1 can significantly improve the catalytic reaction effect of the catalyst, and the conversion rate of quinoline can reach 99% while the selectivity of the selective hydrogenation product 1,2,3,4-tetrahydroquinoline reaches 99%. That is, in the process of preparing the catalyst, the molar ratio of ammonium fluoride to the carbon source citric acid is preferably 0.2 to 0.7:1, and more preferably 0.3 to 0.6:1.

[0051] Example 7

[0052] This example is a study on the catalytic performance of catalysts calcined at different temperatures during the catalyst preparation process.

[0053] The Co / CF-0.5 catalyst prepared in Examples 1, 4 to 5 was used in the hydrogenation reaction of quinoline, and the specific implementation conditions were as follows: 30 mg of the Co / CF-0.5 catalyst was weighed into a 50 mL polytetrafluoroethylene-lined stainless steel autoclave equipped with a magnetically driven stirrer, and then 0.5 mmol of the substrate quinoline and 15 mL of methanol were added for reaction, and the reaction conditions were: T = 100°C, P = 3 MPa, t = 6 h. The conversion rate of quinoline and the selectivity of the product 1,2,3,4-tetrahydroquinoline were detected by gas chromatography, and the measured conversion rate of quinoline and the selectivity of the product 1,2,3,4-tetrahydroquinoline are shown in Table 2 below.

[0054] Table 2

[0055] catalyst Calcination temperature (℃) Conversion rate (%) Selectivity (%) Example 1 600 99 99 Example 4 500 25 99 Example 5 700 99 99

[0056] It can be seen from Table 2 that the appropriate calcination temperature during the catalyst preparation process is conducive to improving the effect of the catalyst on the selective hydrogenation of quinoline, and the calcination temperature is preferably above 550° C. In particular, when the calcination temperature is 600-700° C., while the selectivity of the selective hydrogenation product 1,2,3,4-tetrahydroquinoline reaches 99%, the conversion rate of quinoline can also reach 99%.

[0057] Example 8

[0058] This example is a study on the catalytic performance of different solvents in the process of selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline.

[0059] Table 3

[0060] Solvents Conversion rate (%) Selectivity (%) Methanol 99 99 Toluene 89 99 n-Hexane 11.25 99 Acetonitrile 6.18 99 water 65.5 99 Isopropyl alcohol 25 99 Tetrahydrofuran 99 99 Ethanol 99 99

[0061] The Co / CF-0.5 catalyst prepared in Example 1 was used in the hydrogenation reaction of quinoline, and the specific implementation conditions were as follows: 30 mg of the Co / CF-0.5 catalyst was weighed into a 50 mL polytetrafluoroethylene-lined stainless steel autoclave equipped with a magnetically driven stirrer, and then 0.5 mmol of the substrate quinoline and 15 mL of an organic solvent were added for reaction, and the reaction conditions were: T = 100°C, P = 3 MPa, t = 6 h. The conversion rate of quinoline and the selectivity of the product 1,2,3,4-tetrahydroquinoline were detected by gas chromatography, and the measured conversion rate of quinoline and the selectivity of the product 1,2,3,4-tetrahydroquinoline are shown in Table 3.

[0062] It can be seen from Table 3 that when Co / CF-0.5 catalyst is used to catalyze the reaction in the process of selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline, the catalytic results of using different solvents are quite different. When one or more of ethanol, methanol and tetrahydrofuran is used as the solvent, while the selectivity of the selective hydrogenation product 1,2,3,4-tetrahydroquinoline reaches 99%, the conversion rate of quinoline can also reach 99%.

[0063] also, Figure 1 The XRD diagrams of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1 are shown. Figure 2 The figure is a diagram of the catalyst stability cyclic catalytic performance in Example 1; it can be seen from the figure that when the catalyst of the present invention catalyzes the selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline, the selectivity of the product 1,2,3,4-tetrahydroquinoline is maintained at 99% after the catalyst is recycled for 5 times, and the conversion rate of quinoline is still as high as 80% after the catalyst is recycled for 5 times. Figure 3 N2 physical adsorption-desorption curves of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1. Figure 4 The pore size distribution curves of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1 are shown. Figure 5 These are SEM images of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1, wherein Figures a to d are SEM images of the catalysts in Examples 1 to 3 and Comparative Example 1, respectively. Figure 6 TEM images of Co / CF catalysts with different fluorine-carbon ratios in Examples 1 to 3 and Comparative Example 1, wherein Figures a to d are TEM images of the catalysts in Examples 1 to 3 and Comparative Example 1, respectively, and Figure e is a line scan of the catalyst in Example 1. Figures 4 to 6 It can be seen that in the present invention, there is an interaction between the cobalt atoms and the fluorine atoms in the catalyst, and the fluorine element is fixed on the carbon substrate in the form of a CF bond. The carbon substrate has a multi-level porous structure, including mesopores and micropores, and the average pore size is 6-17nm; the active center of the catalyst is cobalt nanoparticles, and the particle size is 2-3nm.

[0064] It will be easily understood by those skilled in the art that the above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions and improvements made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for preparing a fluorine-doped carbon-supported cobalt-based catalyst, characterized in that: The method comprises the following steps: S1. Dissolve a certain proportion of cobalt salt, citric acid and fluoride salt in a solvent, and stir until dissolved to obtain a mixed solution; S2, drying the mixed solution to obtain a catalyst precursor; S3, carbonizing the catalyst precursor under a protective atmosphere and high temperature, and grinding the solid obtained after carbonization to obtain the catalyst.

2. The method for preparing a fluorine-doped carbon-supported cobalt-based catalyst according to claim 1, characterized in that: In step S1, the cobalt salt is at least one of cobalt nitrate, cobalt chloride, cobalt acetate and cobalt sulfate, the fluoride salt is at least one of ammonium fluoride, sodium fluoride, potassium fluoride and calcium fluoride, the solvent is at least one of methanol, ethanol, isopropanol and water, and the molar ratio of the cobalt salt to the citric acid is 0.05 to 0.5:1, preferably 0.1 to 0.3:1, and the molar ratio of the fluoride salt to the citric acid is 0.15 to 0.8:1, preferably 0.2 to 0.7:1, and more preferably 0.3 to 0.6:

1.

3. The method for preparing a fluorine-doped carbon-supported cobalt-based catalyst according to claim 1, characterized in that: The drying temperature in step S2 is 80 to 120°C.

4. The method for preparing a fluorine-doped carbon-supported cobalt-based catalyst according to claim 1, characterized in that: In step S3, the protective atmosphere is at least one of nitrogen and argon, the high temperature is above 550°C, and the preferred carbonization calcination temperature is 600-700°C.

5. The method for preparing a fluorine-doped carbon-supported cobalt-based catalyst according to claim 4, characterized in that: The carbonization calcination time in step S3 is 1 to 3 hours.

6. A fluorine-doped carbon-supported cobalt-based catalyst, characterized in that: The catalyst structure is fluorine-doped carbon substrate loaded with cobalt nanoparticles, and the cobalt element and fluorine element in the catalyst are uniformly distributed on the carbon-based carrier.

7. Use of a fluorine-doped carbon-supported cobalt-based catalyst prepared by the preparation method according to any one of claims 1 to 5, characterized in that: The catalyst is used for catalyzing the selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline.

8. The use according to claim 7, characterized in that: The step of preparing 1,2,3,4-tetrahydroquinoline by selective hydrogenation of quinoline comprises: adding reaction substrate quinoline and catalyst into an autoclave and a solvent environment, the reaction gas atmosphere is hydrogen, the reaction temperature is 60-120° C., the hydrogen pressure is 2-4 MPa, and the reaction time is 4-8 hours.

9. The use according to claim 8, characterized in that: The solvent for preparing 1,2,3,4-tetrahydroquinoline by selective hydrogenation of quinoline is at least one of ethanol, methanol, isopropanol, acetonitrile, water, tetrahydrofuran, n-hexane and toluene, preferably at least one of ethanol, methanol and tetrahydrofuran.

10. A use of the fluorine-doped carbon-supported cobalt-based catalyst as claimed in claim 6, characterized in that: The catalyst is used for catalyzing the selective hydrogenation of quinoline to prepare 1,2,3,4-tetrahydroquinoline.

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