A sulfur-doped cobalt-based material with a core-shell porous structure, and a preparation method and application thereof

Abstract

The present application relates to the technical field of non-noble metal catalysts, and provides a sulfur-doped cobalt-based material with a core-shell porous structure, which has Co nanoparticles as an inner core, and a porous carbon layer containing Co9S8 coated on the surface of the Co nanoparticles. The present application significantly enhances the catalytic capacity of the material by regulating the micro-morphology and surface active site composition and structure of the material through sulfur doping. On the one hand, the metal sulfide obtained by S doping improves the electrical conductivity of the catalyst, and on the other hand, the S element can regulate the microstructure and morphology of the material due to its strong reducing effect, so that S doping is beneficial to promoting the exposure of active sites and the diffusion of target molecule, thereby significantly enhancing the oxygen molecule activation efficiency and improving the benzyl alcohol oxidation activity and selectivity.

Description

Technical Field

[0001] This invention relates to the field of non-precious metal catalyst technology, and in particular to a sulfur-doped cobalt-based material with a core-shell porous structure, its preparation method, and its application. Background Technology

[0002] Benzaldehyde is a crucial raw material for the synthesis of various pharmaceuticals and fine chemicals, with a huge demand. The production of benzaldehyde is primarily based on chemical synthesis, typically using toluene as a raw material and high-valence metal salts (such as potassium permanganate and potassium dichromate) as oxidants. This synthesis process requires large quantities of oxidants and organic solvents, leading to high costs and secondary pollution. In contrast, catalytic oxidation technology based on molecular oxygen (O2) activation is a greener and more environmentally friendly emerging technology. It boasts numerous advantages, including being green, clean, and producing no toxic or harmful byproducts, and has been successfully used for the oxidation of benzyl alcohol to benzaldehyde.

[0003] However, most existing reaction systems require high temperature and high pressure environments (~100℃, ~1MPa), and are prone to excessive oxidation, affecting their yield and product purity. Although noble metal catalysts such as Pt and Pd can achieve highly selective and controllable conversion of benzyl alcohol at room temperature, these materials are expensive and generally have poor desorption capabilities, thus limiting their large-scale application. Summary of the Invention

[0004] In view of this, the technical problem to be solved by the present invention is to provide a sulfur-doped cobalt-based material with a core-shell porous structure, its preparation method and application, which can be used as a catalyst for the oxidation of benzyl alcohol to benzaldehyde, and can achieve high conversion rate and selectivity.

[0005] To achieve the above objectives, the present invention provides a sulfur-doped cobalt-based material with a core-shell porous structure, wherein Co nanoparticles are used as the core and the surface of the Co nanoparticles is coated with a porous carbon layer containing Co9S8.

[0006] This invention uses Co / Zn-ZIFs material as a precursor and doespes its surface with sulfur. The sulfur combines with cobalt on the surface of the Co / Zn-ZIFs material to form Co9S8 nanoparticles, which in turn form a porous carbon layer coating the surface of the Co nanoparticles, creating a core-shell porous structure. The prepared catalyst has a large specific surface area and abundant active sites, which can effectively promote the enrichment and diffusion of reactant molecules, thereby enhancing the O2 activation effect.

[0007] This invention significantly enhances the catalytic activity of materials by controlling the microstructure and composition and structure of surface active sites through sulfur (S) doping. On the one hand, the metal sulfides obtained through S doping improve the conductivity of the catalyst; on the other hand, S, due to its strong reducing properties, can control the microstructure and morphology of the material. Therefore, S doping promotes the exposure of active sites and the diffusion of target molecules, thereby significantly enhancing the activation efficiency of oxygen molecules and improving the oxidation activity and selectivity of benzyl alcohol.

[0008] Optionally, the sulfur-doped cobalt-based material has a dodecahedral structure with an average particle size of 800 nm.

[0009] Optionally, in the sulfur-doped cobalt-based material, the sulfur doping amount is 1 wt% to 15 wt%, preferably 5 wt%.

[0010] As the sulfur doping concentration increases, the porous carbon layer covering the outer layer becomes thicker. Experimental results show that the sulfur-doped cobalt-based material prepared with a sulfur doping concentration of 5% exhibits the best catalytic performance.

[0011] Optionally, the Co nanoparticles have a particle size of 30-40 nm, preferably 30 nm.

[0012] Optionally, the thickness of the porous carbon layer containing Co9S8 is 40-50 nm, preferably 40 nm.

[0013] This invention provides a method for preparing the above-mentioned sulfur-doped cobalt-based material with a core-shell porous structure, comprising the following steps:

[0014] Using Co / Zn-ZIFs material as a precursor, a sulfur-doped cobalt-based material with a core-shell porous structure is obtained by first surface sulfidation treatment and then pyrolysis carbonization.

[0015] The present invention does not have any particular limitation on the source of the above-mentioned Co / Zn-ZIFs material, which can be commercially available or prepared according to methods known to those skilled in the art.

[0016] Optionally, the Co / Zn-ZIFs material has a porous dodecahedral structure.

[0017] In some specific embodiments of the present invention, the Co / Zn-ZIFs material is prepared according to the following method:

[0018] Cobalt nitrate hexahydrate and zinc nitrate hexahydrate were dissolved in a methanol solution of dimethylimidazole, reacted with vigorous stirring at room temperature, centrifuged, and dried to obtain Co / Zn-ZIFs material.

[0019] The molar ratio of cobalt nitrate hexahydrate to zinc nitrate hexahydrate is preferably 1:2. The total molar concentration of cobalt nitrate hexahydrate and zinc nitrate hexahydrate is preferably 37.5–75 mmol / L.

[0020] The preferred mass concentration of the dimethylimidazole is 15–35 g / L.

[0021] The preferred amount of methanol used is 40-80 mL.

[0022] The stirring time is preferably 6 to 12 hours.

[0023] Optionally, the surface vulcanization treatment specifically includes:

[0024] The surface of the Co / Zn-ZIFs material is doped with sulfur by mixing Co / Zn-ZIFs material and trithiocyanate in a solvent and reacting them.

[0025] The solvent is preferably methanol.

[0026] The preferred temperature for the reaction is 0–40°C, and the preferred reaction time is 0.5–1 h.

[0027] The preferred amount of trithiocyanate added is 1-15 mg / 100 mg Co / Zn-ZIFs, more preferably 5 mg / 100 mg Co / Zn-ZIFs.

[0028] After the reaction is complete, the system can be centrifuged and dried.

[0029] The centrifugal speed is preferably 10,000 to 13,000 rpm.

[0030] The drying process can be any drying method known to those skilled in the art, and is preferably vacuum drying. The vacuum drying time is preferably 6 to 12 hours.

[0031] The preferred temperature for pyrolysis carbonization is 700–900°C; more preferably 800°C.

[0032] The preferred time for pyrolysis carbonization is 2 to 4 hours, more preferably 3 hours.

[0033] The heating rate of the pyrolysis carbonization is preferably 1-10℃ / min, more preferably 5℃ / min.

[0034] The pyrolysis carbonization is preferably carried out in an inert gas atmosphere. The inert gas is preferably argon.

[0035] This invention provides the application of the sulfur-doped cobalt-based material with a core-shell porous structure or the sulfur-doped cobalt-based material with a core-shell porous structure prepared by the above preparation method as a catalyst for the reaction of benzyl alcohol oxidation to benzaldehyde.

[0036] Preferably, the amount of the sulfur-doped cobalt-based material with the core-shell porous structure used as a catalyst in the reaction system is preferably 0.1 to 1.5 g / L, more preferably 1 g / L.

[0037] Specifically, the sulfur-doped cobalt-based material with the core-shell porous structure mentioned above is added to an acetonitrile / water solution to activate O2 to selectively oxidize benzyl alcohol to benzaldehyde.

[0038] The aeration time during the reaction process is preferably 10 to 30 minutes, more preferably 20 minutes.

[0039] The preferred temperature for the above-mentioned reaction of benzyl alcohol oxidizing to benzaldehyde is 20-60°C, more preferably 60°C.

[0040] The reaction is preferably carried out under normal pressure.

[0041] The sulfur-doped cobalt-based material with a core-shell porous structure provided by this invention can be used as a catalyst to achieve efficient and selective oxidation of benzyl alcohol to benzaldehyde through molecular oxygen activation under low temperature, normal pressure and without the addition of chemical oxidants. The conversion rate is ~95% and the selectivity is ~100% within 2 hours, which effectively reduces the operating cost of the benzyl alcohol oxidation process.

[0042] In the above reaction of benzyl alcohol oxidation to benzaldehyde, the initial concentration of benzyl alcohol is preferably less than or equal to 0.1 mM.

[0043] Compared with the prior art, the present invention provides a sulfur-doped cobalt-based material with a core-shell porous structure, with Co nanoparticles as the core and the surface of the Co nanoparticles coated with a porous carbon layer containing Co9S8.

[0044] The sulfur-doped cobalt-based material with a core-shell porous structure provided by this invention exhibits a synergistic catalytic effect between Co nanoparticles in the inner layer and Co9S8 nanoparticles in the outer layer, enabling highly active and selective conversion of benzyl alcohol. Specifically, the Co9S8 nanoparticles in the outer layer dominate the rapid adsorption of hydroxyl radicals (·OH). ads The formation and stabilization of the oxidizing agent on the catalyst surface, with its moderate oxidizing power, enhances the selectivity of benzaldehyde in the benzyl alcohol oxidation reaction. This then follows the singlet oxygen pathway dominated by the inner Co nanoparticles, jointly achieving highly active and selective conversion of benzyl alcohol. Compared to existing catalysts that selectively oxidize benzyl alcohol using activated O2, this method primarily employs a free radical mechanism, achieving efficient and highly selective conversion through multiple reaction pathways involving the combination of adsorbed free radicals and non-free radicals.

[0045] Furthermore, the catalyst exhibits excellent chemical stability, retaining over 95% of its activity after 10 repeated uses in the selective oxidation of benzyl alcohol with activated O2. Moreover, its performance can be fully restored after long-term degradation through organic solvent washing and centrifugation. Even under continuous flow operation for 500 minutes, its catalytic performance remains stable. This demonstrates the material's excellent reusability and significant potential for industrial applications. Attached Figure Description

[0046] Figure 1 CoN / S X Schematic diagram of the catalyst structure;

[0047] Figure 2 CoN / S X XRD pattern of the catalyst;

[0048] Figure 3 CoN / S X SEM image of the catalyst;

[0049] Figure 4 CoN / S X TEM-EDS image of the catalyst;

[0050] Figure 5 CoN / S X The selective oxidation effect of the catalyst on 0.1 mM benzyl alcohol under O2 conditions;

[0051] Figure 6 Comparison of selective oxidation of benzyl alcohol during 10 cycles of CoN / S5 catalyst;

[0052] Figure 7 This is a schematic diagram of a continuous flow fixed-bed reactor as described in the technical content;

[0053] Figure 8 The effect of continuous flow fixed bed reaction with catalyst supported on polyurethane sponge. Detailed Implementation

[0054] To further illustrate the present invention, the following detailed description, in conjunction with embodiments, describes the highly efficient sulfur-doped core-shell porous cobalt-based catalyst for activating molecular oxygen, its preparation method, and its applications.

[0055] Example 1

[0056] Preparation of core-shell cobalt-based ZIF catalyst CoN / S X :

[0057] 1): Weigh 0.546g of cobalt nitrate hexahydrate and 1.116g of zinc nitrate hexahydrate and dissolve them in 40mL of methanol solution containing dimethylimidazole (content 30g / L). After stirring vigorously at room temperature for 6h, centrifuge and dry to obtain Co / Zn-ZIFs.

[0058] 2) 1 mg, 3 mg, 5 mg, 10 mg, and 15 mg of trithiocyanate (TCA) were added to 10 mL of methanol solution containing 100 mg of Co / Zn-ZIFs, respectively. The mixture was stirred vigorously at 25 °C for 0.5 h, centrifuged, and dried to obtain Co / Zn-ZIFs@TCA.

[0059] 3) CoN / S was obtained after calcination under an argon atmosphere. X Particles, with x values ​​of 1, 3, 5, 10, and 15 respectively. Calcination conditions: calcination at 800℃ for 3 hours, with a heating rate of 5℃ / min.

[0060] The above-synthesized CoN / S X Material properties were characterized and analyzed.

[0061] Material morphology and structure characterization: After homogenization, the material was characterized by X-ray diffraction (XRD) and transmission electron microscopy (TEM). Comparison with standard cards revealed that the XRD diffraction spectrum of this material corresponds to the characteristic peak of Co9S8 (…). Figure 2 This indicates that the Co9S8 nanoparticles in the outer shell were successfully loaded, and the peak intensity is proportional to the S doping amount. SEM images show that the synthesized material has a uniform dodecahedral ZIF structure. With increasing S doping amount, the surface gradually roughens, indicating the successful synthesis of the outer shell, with an average diameter of approximately 800 nm. TEM-EDS images further show the presence of a distinct double shell and Co nanoparticles. Figure 1 , Figures 3-4 ).

[0062] Test of the performance and mechanism of selective oxidation of benzyl alcohol to benzaldehyde by activated molecular oxygen in the material prepared in Example 1:

[0063] Selective oxidation of benzyl alcohol to benzaldehyde: Weigh out 1 g / L of catalyst CoN / S X The benzyl alcohol was added to a solution containing 0.1 mM benzyl alcohol. The reaction solution was acetonitrile:water = 1:1 (v / v). The mixture was pre-exposed to O2 for 30 min, and the reaction was initiated when the solution was heated to 60℃. During the reaction, a certain amount of methanol was added to the reaction solution to terminate the reaction. The conversion rate of benzyl alcohol and the yield of benzaldehyde were tested by liquid chromatography. The results showed that the best-performing CoN / S5 solution achieved a conversion rate of ~95% and a selectivity of ~100% within 2 h. Figure 5 ).

[0064] The used catalyst was washed multiple times with ethanol and water, centrifuged, and dried. O2 was introduced into a reaction solution containing 0.05 mM benzyl alcohol, and 1 g / L of the used catalyst was weighed and added to the reactor. After 10 cycles, the reaction system still maintained a selectivity of >90%, indicating that the material has good stability. Figure 6 ).

[0065] Catalytic reaction pathway analysis: Electron paramagnetic resonance (EPR) spectroscopy results showed that adsorbed hydroxyl radicals (·OH) were generated in this system. ads ) and singlet oxygen ( 1 The presence of O2 indicates that the reaction system achieves efficient selective conversion of benzyl alcohol primarily via a non-radical pathway.

[0066] Example 2

[0067] The effect of selective oxidation of benzyl alcohol in a continuous flow fixed-bed reactor with catalyst

[0068] The catalyst was repeatedly impregnated and dried onto a polyurethane sponge at a loading of approximately 0.5 g / g, and then packed into a custom-designed fixed-bed reactor (400 mm × 25 mm). The feed solution was an acetonitrile / water mixture containing 0.05 mM benzyl alcohol, with an acetonitrile:water ratio of 1:1 (v / v). O2 was continuously pumped into the catalyst-loaded fixed bed at a flow rate of 200 mL / min, and the reaction was initiated when the temperature was maintained at 60 °C by heating the circulating water. This system can achieve highly efficient and selective oxidation of benzyl alcohol under continuous flow conditions. The CoN / S5 conversion rate and selectivity gradually increased within 500 min, and the selectivity remained above ~95% after 200 min. This indicates that the system has the potential for highly efficient and selective oxidation applications under continuous flow conditions. Figure 7-8 ).

[0069] Comparative Example 1

[0070] Preparation of core-shell cobalt-based ZIF catalyst Co-N4:

[0071] 1): Weigh 0.546g of cobalt nitrate hexahydrate and 1.116g of zinc nitrate hexahydrate and dissolve them in 40mL of methanol solution containing dimethylimidazole (content 30g / L). After stirring vigorously at room temperature for 6h, centrifuge and dry to obtain Co / Zn-ZIFs.

[0072] 2) Co-N4 particles were obtained after calcination under an argon atmosphere. The calcination conditions were: calcination at 800℃ for 3 hours, with a heating rate of 5℃ / min.

[0073] Depend on Figure 3 It can be seen that Co-N4 has a smooth dodecahedral structure without obvious shell encapsulation, and an average diameter of about 800 nm.

[0074] Test the performance of the material prepared in Comparative Example 1 in selectively oxidizing benzyl alcohol to benzaldehyde using activated molecular oxygen:

[0075] Selective oxidation of benzyl alcohol to benzaldehyde: 1 g / L of catalyst Co-N4 was added to a solution containing 0.1 mM benzyl alcohol. The reaction solution was acetonitrile:water = 1:1 (v / v). The mixture was pre-exposed to O2 for 30 min, and the reaction was initiated when the solution was heated to 60℃. During the reaction, a certain amount of methanol was added to the reaction solution to terminate the reaction. The conversion rate of benzyl alcohol and the yield of benzaldehyde were tested by liquid chromatography. The results showed that the conversion rate of Co-N4 was <80% and the selectivity was <80% within 2 h, which was significantly lower than that of the sulfur-doped material. This indicates that sulfur doping significantly improved both the conversion rate and selectivity.

[0076] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

Claims

1. Application of sulfur-doped cobalt-based materials with core-shell porous structures as catalysts for the oxidation of benzyl alcohol to benzaldehyde; The sulfur-doped cobalt-based material with a core-shell porous structure has Co nanoparticles as its core, and the surface of the Co nanoparticles is coated with a porous carbon layer containing Co9S8.

2. The application according to claim 1, characterized in that, The sulfur-doped cobalt-based material has a dodecahedral structure.

3. The application according to claim 1, characterized in that, In the sulfur-doped cobalt-based material, the sulfur doping amount is 1wt%~15wt%.

4. The application according to claim 1, characterized in that, The average particle size of the material is 800 nm; The Co nanoparticles have a particle size of 30-40 nm; The thickness of the porous carbon layer containing Co9S8 is 40-50 nm.

5. The application according to claim 1, characterized in that, The preparation method of the sulfur-doped cobalt-based material with a core-shell porous structure includes the following steps: Using Co / Zn-ZIFs material as a precursor, a sulfur-doped cobalt-based material with a core-shell porous structure is obtained by first surface sulfidation treatment and then pyrolysis carbonization.

6. The application according to claim 5, characterized in that, The surface sulfidation treatment is as follows: The surface of the Co / Zn-ZIFs material is doped with sulfur by mixing Co / Zn-ZIFs material and trithiocyanate in a solvent and reacting them.

7. The application according to claim 6, characterized in that, The reaction temperature for the surface vulcanization treatment is 0~40℃, and the reaction time is 0.5~1h.

8. The application according to claim 5, characterized in that, The temperature for pyrolysis carbonization is 700~900℃; The pyrolysis carbonization time is 2-4 hours; The heating rate of the pyrolysis carbonization is 1-10℃ / min; The pyrolysis carbonization is carried out in an inert gas atmosphere.

9. The application according to claim 1, characterized in that, The reaction of benzyl alcohol to benzaldehyde by oxidation is carried out at a temperature of 20-60°C and under normal pressure.

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