Preparation method and application of high-dispersion cobalt-based heterogeneous catalyst

Abstract

The invention relates to a preparation method of a high-dispersion cobalt-based heterogeneous catalyst, which comprises the following steps: dropwise adding a carbon nanotube solution into a cobalt complex solution at 70 DEG C, stirring at 100 DEG C for 3 hours, and sequentially carrying out suction filtration, washing and drying to obtain a compound Co-CN-coated CNTs; and calcining the Co-CN (at) CNTs compound in a nitrogen atmosphere, so as to obtain the nitrogen-doped Co-based heterogeneous catalyst. Meanwhile, the invention also discloses application of the catalyst. The high-dispersion cobalt-based heterogeneous catalyst prepared by the invention has more uniformly distributed active sites and higher catalytic activity in olefin hydroformylation reaction; meanwhile, the preparation strategy of the catalyst has the advantages of simplicity, economy and environmental protection.

Description

Technical Field

[0001] The present invention relates to the technical field of hydroformylation, and in particular to a preparation method of a highly dispersed cobalt-based heterogeneous catalyst and application thereof. Background Art

[0002] As a typical catalytic component of Group VIII metals, cobalt exhibits unique performance advantages in industrial catalytic systems. It has both tunable electronic properties and significant economic benefits, showing great potential in replacing precious metal catalysts and has become an important direction of green chemistry research ( Res. Chem. Intermed. , 2017, 43: 1341-1353.). As global energy supply and demand intensify, Co-based catalysts, leveraging their unique physicochemical properties and cost advantages, are rapidly advancing from basic research to industrial applications. Current research focuses on the controlled preparation of cobalt nanoparticles. These nanocatalysts, leveraging ultrafine particle size and high surface area, fully expose active sites, enhancing catalytic efficiency. However, nanosized transition metal particles are highly complex, and even slight variations in their morphology and structure can significantly affect catalytic activity. Therefore, developing supported Co-based catalysts with stable dispersion properties has become a key path to overcoming technical bottlenecks in this field.

[0003] The main strategy to reduce the cost of the catalytic system is to optimize the structure-activity relationship of the components and design a more reasonable support structure to maximize the utilization of active sites. Non-precious metal Co-based catalytic systems have shown considerable application potential in the field of olefin hydroformylation, and their performance optimization paths have made breakthrough progress. For example, Wei et al. developed a Mo6C2-bonded cobalt cluster as the active center of the propylene hydroformylation reaction. Compared with traditional metal cobalt cluster catalysts, the Co / β-Mo2C catalyst not only has improved activity, but also shows good stability in long-term tests. In addition, cobalt catalysts have also achieved good research results in the hydroformylation reaction of long-chain α-olefins ( ACS Catal. , 2021, 11: 14319-14327.). Gong et al. successfully synthesized CoZrP-2.0 (P / Zr=2) catalyst by combining cobalt metal with phosphate groups on the surface of zirconium phosphate (ZrP). They achieved complete conversion in the hydroformylation of 1-octene with an aldehyde selectivity of up to 91.3% ( J. CatalDespite these advances, the industrial application of Co-based catalysts for the hydroformylation of long-chain olefins still faces numerous challenges. For one thing, their intrinsic activity remains significantly lower than that of precious metal Rh catalysts. Furthermore, deactivation due to leaching of active components during the reaction severely limits the catalyst's lifespan. Literature analysis indicates that existing Co-based catalytic systems generally suffer from insufficient cyclic stability and rapid decay of active sites, attributed to weak interactions between the Co species and the support. Therefore, enhancing the metal-support electronic synergy and constructing novel Co-based heterogeneous catalytic systems with both high activity and stability have become key research directions for addressing current scientific challenges. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to provide a method for preparing a highly dispersed cobalt-based heterogeneous catalyst.

[0005] Another technical problem to be solved by the present invention is to provide an application of the highly dispersed cobalt-based heterogeneous catalyst.

[0006] To solve the above problems, the present invention discloses a method for preparing a highly dispersed cobalt-based heterogeneous catalyst, characterized in that: a carbon nanotube solution is added dropwise to a cobalt complex solution at 70°C, stirred at 100°C for 3 hours, and then filtered, washed, and dried to obtain a composite Co-CN@CNTs; the Co-CN@CNTs composite is calcined under a nitrogen atmosphere to obtain a nitrogen-doped Co-based heterogeneous catalyst; the volume ratio of the carbon nanotube solution to the cobalt complex solution is 1:0.75.

[0007] The carbon nanotube solution is prepared by adding 200 mg of carbon nanotubes treated with mixed acid into a mixed solution of 30 mL of deionized water and 10 mL of anhydrous ethanol and stirring at room temperature.

[0008] The concentration of the carbon nanotubes in the mixed acid solution is 10 g / L; the mixed acid solution is a solution formed by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1.

[0009] The cobalt complex solution is a white transparent solution obtained by adding 120 mg of cobalt nitrate, 1.0 g of melamine, and 2 mL of formaldehyde solution into 30 mL of deionized water and reacting them at 70° C. for 15 minutes.

[0010] The suction filtration and washing are performed using deionized water and anhydrous ethanol respectively.

[0011] The calcination conditions are as follows: calcination in a tube furnace at a heating rate of 2°C / min, a calcination temperature of 700-1000°C, and a calcination time of 2h.

[0012] A highly dispersed cobalt-based catalyst prepared by the method described above.

[0013] The application of the highly dispersed cobalt-based catalyst as described above is characterized in that the catalyst is used to catalyze the hydroformylation reaction of olefin compounds to synthesize aldehyde compounds.

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

[0015] The conditions of the hydroformylation reaction are that the solvent is toluene, the reaction temperature is 110-160° C., the reaction pressure is 2-5 MPa, and the reaction time is 1-6 h.

[0016] Compared with the prior art, the present invention has the following advantages: 1. This invention achieves uniform anchoring of the active component on the surface of a carbon nanotube support through the coordination of a melamine-formaldehyde polymer with a Co species. Subsequently, a gradient high-temperature pyrolysis treatment under an inert atmosphere yields a composite catalyst with highly dispersed Co-Nx active sites within a nitrogen-doped carbon matrix.

[0017] 2. The present invention successfully prepared a highly dispersed Co-Nx species catalyst by thermally decomposing a cobalt-melamine complex adsorbed on a carbon nanotube carrier. The abundant nitrogen atoms in melamine coordinate with cobalt metal ions. At the same time, the porous properties of the carbon nanotube carrier and the nitrogen doping effectively isolate the cobalt atoms, avoiding the agglomeration of the metal during high-temperature pyrolysis, and ensuring that the catalyst has high dispersion and high stability. Therefore, the pre-construction of the cobalt-nitrogen coordination structure in the present invention not only significantly enhances the interaction between the metal precursor and the carrier, but more importantly, it effectively suppresses the agglomeration tendency of the metal particles during high-temperature treatment through the spatial confinement effect, thereby achieving precise regulation of the active sites at the atomic scale.

[0018] 3. The present invention does not need to be operated under anhydrous and oxygen-free conditions, and the preparation process is simple and easy to scale up. The cobalt metal in the obtained catalyst is in a highly dispersed state, which is a guarantee for improving catalytic activity.

[0019] 4. The catalyst obtained using the present method has a stable structure and properties, exhibiting excellent catalytic activity in olefin hydroformylation reactions without significant loss of active metal components or structural damage during the reaction. Compared to nitrogen-doped carbon-supported cobalt nanoparticle catalysts prepared by traditional impregnation methods, this catalyst offers significant performance and structural advantages, while significantly reducing costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The specific embodiments of the present invention will be further described in detail below with reference to the accompanying drawings.

[0021] Figure 1 HRTEM and element distribution diagram of the cobalt-based heterogeneous catalyst prepared in Example 1 of the present invention.

[0022] Figure 2 XRD patterns of the cobalt-based heterogeneous catalysts prepared in Examples 1 to 4 of the present invention.

[0023] Figure 3 This is the XPS graph of the cobalt-based heterogeneous catalyst prepared in Example 1 of the present invention.

[0024] Figure 4 This is a preparation flow chart of Example 1 of the present invention. DETAILED DESCRIPTION

[0025] A method for preparing a highly dispersed cobalt-based heterogeneous catalyst: The carbon nanotube solution was added dropwise to the cobalt complex solution at 70°C, stirred at 100°C for 3 hours, filtered and washed with deionized water and anhydrous ethanol, and dried at 70°C to constant weight to obtain the composite Co-CN@CNTs. The Co-CN@CNTs composite was calcined in a tubular furnace under a nitrogen atmosphere at a heating rate of 2°C / min, the calcination temperature was 700-1000°C, and the calcination time was 2 hours to obtain a nitrogen-doped Co-based heterogeneous catalyst. The volume ratio (mL / mL) of the carbon nanotube solution to the cobalt complex solution was 1:0.75.

[0026] The carbon nanotube solution is prepared by placing 200 mg of mixed-acid-treated carbon nanotubes in a mixture of 30 mL of deionized water and 10 mL of anhydrous ethanol and stirring at room temperature. The concentration of the carbon nanotubes in the mixed-acid solution is 10 g / L. The mixed-acid solution is a mixture of concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:1 (mL / mL).

[0027] The cobalt complex solution refers to a white transparent solution obtained by adding 120 mg of cobalt nitrate, 1.0 g of melamine, and 2 mL of formaldehyde solution into 30 mL of deionized water and reacting them at 70° C. for 15 minutes.

[0028] The invention discloses an application of a highly dispersed cobalt-based catalyst for catalyzing the hydroformylation reaction of olefin compounds, wherein the solvent is toluene, the reaction temperature is 110-160°C, the reaction pressure is 2-5 MPa, and the reaction time is 1-6 hours to synthesize aldehyde compounds.

[0029] The structural formula of olefin compounds is: ; Wherein R1 is one of butyl, pentyl, hexyl, nonyl and phenyl.

[0030] Example 1 A method for preparing a highly dispersed cobalt-based heterogeneous catalyst, such as Figure 4As shown: 1.0 g of melamine and 120 mg of Co(NO₃)₂·6H₂O were weighed, 2 mL of formaldehyde solution, and 30 mL of deionized water were added. The mixture was heated and stirred at 70°C until the solution became clear and transparent. Then, 200 mg of dispersed carbon nanotubes in ethanol (40 mL, v / v = 3:1) were added dropwise. After stirring, the mixture was rapidly heated to 100°C and stirred for 3 hours to ensure complete polymerization. After the reaction, the mixture was filtered, washed with deionized water and anhydrous ethanol, dried in an oven, and ground. A portion of the mixture was placed in a tube furnace and heated to 900°C under a nitrogen atmosphere at a heating rate of 2°C / min. This temperature was maintained for 2 hours. The resulting highly dispersed cobalt-based heterogeneous catalyst, Co-N / CNTs-900, was designated Catalyst A.

[0031] Catalyst A was observed by HRTEM, XRD and XPS respectively. The results are as follows: Figures 1-3 No cobalt nanoparticles were observed, and the element distribution diagram showed that C, N, O, and Co were uniformly distributed. The Co 2p fine spectrum showed that cobalt species always existed in a positive valence state. This highly dispersed Co-N x The active sites effectively prevented the aggregation of metal particles, providing a structural basis for the high activity of the catalyst. In addition, XRD showed that all samples exhibited a characteristic diffraction peak at 26.4°, which was confirmed to be a characteristic signal of the graphitic carbon (002) crystal plane by comparison with Co PDF#15-0806 card.

[0032] Catalyst Evaluation: A 30 mg sample of catalyst was added to an 8 mL toluene solution containing 1-octene (5 mmol, 0.56 g). The reactor was sealed and replaced three times with synthesis gas (CO / H2 = 1:1), followed by a 5 MPa charge. The reactor was placed in a heating block preheated to 150°C and stirred for 5 h. After the reaction, the reactor was cooled to room temperature and the pressure was slowly released. After the reaction was complete, the reactor was cooled in an ice bath, the remaining gas was slowly released, and hexadecane was added as an internal standard. The liquid product was qualitatively analyzed using a gas chromatograph (Agilent 7890 GC) equipped with a flame ionization detector (FID) and an SE-54 column (30 m × 0.25 mm × 0.25 μm). Conversion and yield were calculated using the internal standard method and nuclear magnetic resonance quantification.

[0033] 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 that of Example 1. The obtained highly dispersed cobalt-based heterogeneous catalyst Co-N / CNTs-700 was recorded as catalyst B.

[0034] Catalyst evaluation and product analysis were the same as in Example 1.

[0035] XRD observation of catalyst B showed the following results: Figure 2 As shown in the figure, no Co metal characteristic diffraction peak was observed under the lower temperature of 700℃.

[0036] 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 that of Example 1. The obtained highly dispersed cobalt-based heterogeneous catalyst Co-N / CNTs-800 was recorded as catalyst C.

[0037] Catalyst evaluation and product analysis were the same as in Example 1.

[0038] XRD observation of catalyst C showed the following results: Figure 2 As shown in the figure, no characteristic diffraction peak of Co metal is found under 800℃.

[0039] 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 that of Example 1. The obtained highly dispersed cobalt-based heterogeneous catalyst Co-N / CNTs-1000 was recorded as catalyst D.

[0040] Catalyst evaluation and product analysis were the same as in Example 1.

[0041] XRD observation of catalyst D showed the following results: Figure 2 As shown in the figure, no characteristic diffraction peaks of metallic cobalt or cobalt oxide were detected even when the temperature was raised to 1000°C.

[0042] In Examples 5-17, the hydroformylation reaction performance at different reaction temperatures, synthesis gas pressures, and reaction times was evaluated using Catalyst A of Example 1 as an example.

[0043] Example 5 Catalyst evaluation: In Example 5, except that the reactor temperature was heated to 110°C, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0044] Example 6 Catalyst evaluation: In Example 6, except that the reactor temperature was heated to 120°C, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0045] Example 7 Catalyst evaluation: In Example 7, except that the reactor temperature was heated to 130°C, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0046] Example 8 Catalyst evaluation: In Example 8, except that the reactor temperature was heated to 140°C, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0047] Example 9 Catalyst evaluation: In Example 9, except that the reactor temperature was heated to 160°C, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0048] Example 10 Catalyst evaluation: In Example 10, except that the synthesis gas pressure (CO:H2=1:1) was charged to 2 MPa, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0049] Example 11 Catalyst evaluation: In Example 11, except that the synthesis gas pressure (CO:H2=1:1) was charged to 3 MPa, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0050] Example 12 Catalyst evaluation: In Example 12, except that the synthesis gas pressure (CO:H2=1:1) was charged to 4 MPa, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0051] Example 13 Catalyst evaluation: In Example 13, except that the reaction time was changed to 5 h, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0052] Example 14 Catalyst evaluation: In Example 14, except that the reaction time was changed to 4 h, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0053] Example 15 Catalyst evaluation: In Example 15, except that the reaction time was changed to 3 h, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0054] Example 16 Catalyst evaluation: In Example 16, except that the reaction time was changed to 2 h, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0055] Example 17 Catalyst evaluation: In Example 17, except that the reaction time was changed to 1 h, the rest of the catalyst evaluation and product analysis procedures were the same as in Example 1.

[0056] The reaction performances of the catalysts of Examples 1 to 17 are shown in Table 1.

[0057] Table 1 Reaction performance of highly dispersed cobalt-based heterogeneous catalysts As can be seen from Table 1, the highly dispersed cobalt-based heterogeneous catalyst prepared in the present invention has excellent catalytic performance. Specifically, the catalyst calcined at 900°C exhibited excellent 1-octene conversion (100%) and aldehyde yield (79%) under optimized conditions (150°C, 5 MPa, 6 h).

[0058] Example 18 Catalyst A from Example 1 was used as an example for recycling performance testing: the catalyst was washed and dried after reaction and then used directly in the next cycle. Other operations and product analysis were consistent with those in Example 1. Reaction data for the catalyst's reuse are shown in Table 2.

[0059] Table 2 Reusability of Catalyst A in Example 1 in 1-octene hydroformylation As can be seen from Table 2, the highly dispersed cobalt-based heterogeneous catalyst prepared by the present invention exhibits excellent catalytic performance. After four cycles of reaction, the conversion rate of 1-octene remains at a high level, with little change compared to the initial conversion rate. Although the output of C9 aldehydes decreases slightly, the yield of aldehydes still reaches 63% after four cycles. ICP analysis results further indicate that only 33% of the cobalt species leach into the liquid phase during the four cycles.

[0060] Examples 19-23 In Examples 19-23, except that 5 mmol of a different olefin substrate was added instead of 5 mmol of 1-octene, the rest of the process was the same as in Example 1. The reaction results for different olefin substrates are shown in Table 3.

[0061] Table 3 Catalytic performance of catalyst A in Example 1 in various olefin hydroformylation reactions It can be seen from the experimental results in Table 3 that the highly dispersed cobalt-based heterogeneous catalyst prepared in the present invention can be applied to the hydroformylation reaction of various olefins, and exhibits good catalytic activity and yield.

[0062] It should be understood that these embodiments are only used to illustrate the present invention rather than to limit the scope of the present invention.

Claims

1. A method for preparing a highly dispersed cobalt-based heterogeneous catalyst, characterized in that: The carbon nanotube solution was added dropwise to the cobalt complex solution at 70°C, stirred at 100°C for 3 hours, and then filtered, washed, and dried to obtain a composite Co-CN@CNTs. The Co-CN@CNTs composite was calcined under a nitrogen atmosphere to obtain a nitrogen-doped Co-based heterogeneous catalyst. The volume ratio of the carbon nanotube solution to the cobalt complex solution was 1:0.

75.

2. The method for preparing a highly dispersed cobalt-based heterogeneous catalyst according to claim 1, wherein: The carbon nanotube solution is prepared by adding 200 mg of carbon nanotubes treated with mixed acid into a mixed solution of 30 mL of deionized water and 10 mL of anhydrous ethanol and stirring at room temperature.

3. The method for preparing a highly dispersed cobalt-based heterogeneous catalyst according to claim 2, wherein: The concentration of the carbon nanotubes in the mixed acid solution is 10 g / L; the mixed acid solution is a solution formed by mixing concentrated sulfuric acid and concentrated nitric acid in a volume ratio of 3:

1.

4. The method for preparing a highly dispersed cobalt-based heterogeneous catalyst according to claim 1, wherein: The cobalt complex solution is a white transparent solution obtained by adding 120 mg of cobalt nitrate, 1.0 g of melamine, and 2 mL of formaldehyde solution into 30 mL of deionized water and reacting them at 70° C. for 15 minutes.

5. The method for preparing a highly dispersed cobalt-based heterogeneous catalyst according to claim 1, wherein: The suction filtration and washing are performed using deionized water and anhydrous ethanol respectively.

6. The method for preparing a highly dispersed cobalt-based heterogeneous catalyst according to claim 1, wherein: The calcination conditions are as follows: calcination in a tube furnace at a heating rate of 2°C / min, a calcination temperature of 700-1000°C, and a calcination time of 2h.

7. A highly dispersed cobalt-based catalyst prepared by the method according to any one of claims 1 to 6.

8. The use of a highly dispersed cobalt-based catalyst according to claim 7, characterized in that: The catalyst is used for catalyzing the hydroformylation reaction of olefin compounds to synthesize aldehyde compounds.

9. The use of a highly dispersed cobalt-based heterogeneous catalyst according to claim 8, characterized in that: The structural formula of the olefin compound is: ; Wherein R1 is one of butyl, pentyl, hexyl, nonyl and phenyl.

10. The use of a highly dispersed cobalt-based heterogeneous catalyst according to claim 8, characterized in that: The conditions of the hydroformylation reaction are that the solvent is toluene, the reaction temperature is 110-160° C., the reaction pressure is 2-5 MPa, and the reaction time is 1-6 h.

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