A Pd@ZIF-8@C3N4 composite material, its preparation method, and its application in the catalytic reduction reaction of benzaldehyde.
By loading Pd nanoparticles onto the ZIF-8@C3N4 support, the problem of easy aggregation of metal Pd catalysts was solved, and the efficient and selective reduction of benzaldehyde to toluene was achieved. The catalyst has good stability and recyclability.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- LIAONING UNIVERSITY
- Filing Date
- 2026-03-31
- Publication Date
- 2026-07-03
Smart Images
Figure CN122321954A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalytic synthesis technology, and specifically relates to a Pd@ZIF-8@C3N4 composite material and a method for catalytic benzaldehyde reduction reaction based on the Pd@ZIF-8@C3N4 composite material. Background Technology
[0002] The reduction of benzaldehyde to toluene primarily refers to the process of completely reducing the aldehyde group of benzaldehyde to a methyl group through catalytic hydrogenation or chemical reduction. This reaction uses benzaldehyde as a substrate and proceeds under the action of a transition metal catalyst (such as palladium / carbon) or a specific reduction system (such as zinc amalgam / concentrated hydrochloric acid). Compared to the reduction pathways of other aromatic aldehydes, this deep reduction reaction can achieve the complete conversion of the aldehyde group to a methyl group with high efficiency and selectivity, and the reaction pathway is well-defined. The reaction conditions are relatively mature and have important applications in the synthesis of fine chemicals, pharmaceutical molecules, and fragrance intermediates, providing a key method for constructing toluene and its derivatives.
[0003] The reduction reaction of benzaldehyde commonly uses Pd nanoparticles as catalysts. However, Pd nanoparticles often undergo aggregation and self-oxidation during catalysis, leading to low catalytic efficiency and short lifespan. Metal-organic frameworks (MOFs), on the other hand, are porous coordination polymers formed by the self-assembly of inorganic metal nodes with nitrogen-, oxygen-, or aromatic acid-based multidentate organic ligands through coordination interactions. They possess characteristics such as large specific surface area, regular pore structure, high porosity, and abundant active sites, significantly enhancing substrate adsorption and mass transfer efficiency, making them ideal catalyst support materials. ZIF-8, as a typical zeolite imidazolium ester framework MOF material, is composed of Zn... 2+ When coordinated with imidazole ligands, it exhibits high crystallinity, high porosity, and excellent chemical and thermal stability. Its uniform microporous structure can effectively confine metal nanoparticles and inhibit aggregation, providing an ideal platform for efficient loading and stable dispersion of Pd active sites.
[0004] Meanwhile, C3N4 exhibits multiple unique advantages in thermocatalysis. Its skeleton, rich in tert-butyl nitrogen and amino sites, endows it with excellent basicity and nucleophilicity, enabling efficient activation of reactant molecules. The two-dimensional layered structure of C3N4 and its hexagonal surface pores, when combined with Pd nanoparticles, not only stabilize and disperse metal particles, but its electron-rich surface also allows for strong electronic interactions with the metal center, modulating the electron density of the metal and thus precisely optimizing the activity and selectivity of the catalytic reaction, achieving "catalyst customization." Furthermore, the material possesses excellent thermal and chemical stability, ensuring a long catalyst lifespan under high-temperature reaction conditions. Summary of the Invention
[0005] To address the aforementioned technical problems, one objective of this invention is to provide a Pd@ZIF-8@C3N4 composite material, in which Pd nanoparticles are loaded onto a ZIF-8@C3N4 composite support to construct a novel MOF-based composite catalyst. The microporous structure of ZIF-8 effectively confines the Pd nanoparticles, inhibiting their aggregation and sintering, achieving a high degree of dispersion of active sites. C3N4, through electronic regulation and structural stabilization, synergistically enhances the catalytic activity and stability of Pd. The composite material combines the advantages of high specific surface area and tunable pores found in MOFs with the electronic effects and structural stability of C3N4, effectively solving the problems of easy aggregation, poor stability, and low efficiency of pure Pd catalysts.
[0006] The second objective of this invention is to provide the application of Pd@ZIF-8@C3N4 composite material as a catalyst in the catalytic reduction reaction of benzaldehyde, thereby providing a high-performance catalytic system for the efficient and selective reduction of benzaldehyde to toluene.
[0007] To achieve the above-mentioned objectives, the technical solution adopted by this invention is: a Pd@ZIF-8@C3N4 composite material, the preparation method of which includes the following steps:
[0008] (1) C3N4 was dispersed in methanol and continuously stirred under ultrasonication to obtain a suspension. Zinc salt was added to the obtained suspension and stirred vigorously for 8 h - 10 h. After standing overnight at room temperature, 2-methylimidazole methanol solution was added under stirring and stirring was continued for 24 h - 25 h. After centrifugation, washing, and vacuum drying, ZIF-8@C3N4 was obtained.
[0009] (2) Mix and disperse ZIF-8@C3N4 and sodium chloropalladium solution (Na2PdCl4) evenly to obtain a mixed solution; add sodium borohydride to methanol solution, sodium borohydride and methanol release hydrogen gas, quickly take the upper layer of liquid with bubbles and add it to the obtained mixed solution and stir continuously for 30 min - 60 min, wash, vacuum dry to obtain Pd@ZIF-8@C3N4 composite material.
[0010] Further, in step (1), the C3N4 preparation method includes: placing urea in a muffle furnace, first keeping it at 323 K - 333 K for 6 h - 8 h, then heating it to 818 K - 828 K for 1 h - 2 h, and cooling it to room temperature to obtain C3N4.
[0011] Further, in step (1), the zinc salt is Zn(NO3)2·6H2O.
[0012] Further, in step (2), the method for preparing the sodium chloropalladium solution includes: mixing palladium chloride, sodium chloride and methanol until dissolved, and stirring overnight.
[0013] Furthermore, according to the feed-to-liquid ratio, palladium chloride: sodium chloride: methanol = (0.02 g - 0.04 g): (0.010 g - 0.015 g): 1 mL.
[0014] Furthermore, in step (2), the concentration of the sodium chloropalladium solution is 0.15 mol / L - 0.20 mol / L.
[0015] Further, in step (2), the molar ratio is 2-methylimidazole:zinc salt = (3-4):1.
[0016] This invention provides the application of a Pd@ZIF-8@C3N4 composite material as a catalyst in the catalytic reduction reaction of benzaldehyde.
[0017] A method for catalyzing the reduction reaction of benzaldehyde using a Pd@ZIF-8@C3N4 composite material as a catalyst, comprising: placing formic acid, benzaldehyde, and the catalyst in a reaction vessel and reacting at 378 K - 388 K for 12 h - 13 h. The reaction formula is as follows:
[0018]
[0019] The beneficial effects of this invention are:
[0020] 1. In the Pd@ZIF-8@C3N4 composite material provided by this invention, Pd nanoparticles are highly dispersed in the pores of ZIF-8@C3N4, effectively preventing the aggregation of Pd nanoparticles. C3N4 is a non-metallic polymer semiconductor with a graphene-like layered structure, visible light response, and good chemical stability. C3N4 can provide excellent binding sites for the in-situ growth of MOFs. ZIF-8 grows on the two-dimensional plane of C3N4, further promoting the dispersion of the catalyst and increasing the contact area of the Pd catalytic sites, thereby improving the stability of the catalyst. The combination of the two not only improves the reaction rate but also reduces the formation of by-products.
[0021] 2. The reduction of benzaldehyde typically occurs in a reaction system using formic acid as the hydrogen source. Firstly, the active hydrogen species generated from formic acid possess extremely high reactivity and can directly participate in the reduction of benzaldehyde. In the Pd@ZIF-8@C3N4 composite material catalyzing the reduction of benzaldehyde to toluene, the introduction of C3N4 significantly improves the electronic conductivity of the composite material, promoting rapid electron transfer within the catalyst and facilitating the reduction step, thereby greatly enhancing catalytic efficiency. Furthermore, the porous structure of ZIF-8 and the high electronic conductivity of C3N4 create a favorable synergistic effect in the Pd@ZIF-8@C3N4 composite material. This synergistic effect results in higher catalytic activity and selectivity in the benzaldehyde reduction reaction. Moreover, after five cycles of testing, the Pd@ZIF-8@C3N4 composite material maintains high catalytic activity, exhibiting high stability and recyclability. Attached Figure Description
[0022] Figure 1 This is a TEM image of the Pd@ZIF-8@C3N4 composite material of the present invention.
[0023] Figure 2 This is the FT-IR spectrum of the Pd@ZIF-8@C3N4 composite material of the present invention.
[0024] Figure 3 This is the PXRD spectrum of the Pd@ZIF-8@C3N4 composite material of the present invention.
[0025] Figure 4 This is a catalytic activity diagram of the Pd@ZIF-8@C3N4 composite material of the present invention after five cycles of catalytic reaction. Detailed Implementation
[0026] Example 1: A Pd@ZIF-8@C3N4 composite material
[0027] (I) Preparation method
[0028] 1. Synthesis of C3N4:
[0029] 15 g of urea was placed in a covered crucible and placed in a muffle furnace. It was first heated at 328 K for 6 h to allow for thermal polymerization in air. After cooling to room temperature, the yellow powder was collected, and then heated to 823 K for calcination for 1 h. After cooling to room temperature, a slightly yellow powder, namely C3N4, was obtained.
[0030] 2. Synthesis of ZIF-8@C3N4:
[0031] 1.00 g of C3N4 was dispersed in 40 mL of anhydrous methanol and stirred continuously under ultrasonication for 2 h to obtain a homogeneous and stable suspension. Zn(NO3)2·6H2O (0.194 g, 0.000652 mol) was added to this suspension, and the mixture was vigorously stirred on a magnetic stirrer for at least 8 h. Afterward, it was allowed to stand at room temperature overnight for aging to allow the Zn... 2+ Preferential adsorption was achieved on the C3N4 surface. Next, an organic ligand solution prepared by dissolving 0.183 g (0.0022 mol) of 2-methylimidazole in 10 mL of methanol was rapidly added under continuous stirring. The mixture gradually became turbid, indicating that ZIF-8 had begun nucleation. Vigorous stirring was continued for 24 h to ensure sufficient crystal growth and crystallization. After the reaction was complete, the resulting white suspension was centrifuged, and the precipitate was washed repeatedly with fresh anhydrous methanol at least three times until the supernatant was clear. Finally, the collected solid was placed in a vacuum drying oven and dried at 333 K for 12 h to obtain a white powder product, namely ZIF-8@C3N4, which was sealed and stored for later use.
[0032] 3. Synthesis of Pd@ZIF-8@C3N4
[0033] Accurately weigh 0.12 g of palladium chloride solid and 0.044 g of sodium chloride solid, pour them into a 10 mL glass bottle, add 4 mL of methanol to the bottle, heat slightly until completely dissolved, stir overnight to obtain a 0.17 mol / L brown sodium chloropalladium solution.
[0034] Accurately weigh 50 mg of ZIF-8@C3N4 and place it in a 5 mL glass bottle. Use a pipette to accurately transfer 0.05882 mL of sodium chloropalladium solution into the glass bottle in multiple portions to ensure even dispersion. Accurately weigh 8.62 mg of sodium borohydride solid and add it to 5 mL of methanol solution. The reaction of sodium borohydride and methanol releases hydrogen gas. Quickly pipette the bubbly upper layer of liquid into the glass bottle and stir continuously for 30 min. Wash the bottle three times with methanol, and finally dry it in a vacuum drying oven at 333 K for 6 h to obtain a yellow powder, which is Pd@ZIF-8@C3N4.
[0035] (II) Testing
[0036] Figure 1 This is a TEM image of the Pd@ZIF-8@C3N4 composite material of this invention. Figure 1 It is evident that the Pd@ZIF-8@C3N4 composite material retains both the layered structure of C3N4 and the geometric shape of ZIF-8 during the synthesis process. This demonstrates that the Pd@ZIF-8@C3N4 composite material exhibits good crystallinity and a complete structural morphology.
[0037] Figure 2 This is the Fourier transform infrared (FT-IR) spectrum of the Pd@ZIF-8@C3N4 composite material prepared in this embodiment. Figure 2 It can be seen that the infrared spectrum of Pd@ZIF-8@C3N4 retains the characteristic peaks of both C3N4 and ZIF-8, and at 500 cm⁻¹... -1 -800 cm -1 The new vibration peaks appearing within the range are Pd-N related vibration absorption peaks, indicating the formation of the Pd@ZIF-8@C3N4 composite material.
[0038] Figure 3 This is the XRD powder diffraction (PXRD) pattern of Pd@ZIF-8@C3N4 prepared in this embodiment. Figure 3 It is evident that the diffraction pattern of the modified sample is similar to that of the unmodified sample, indicating that the main framework of ZIF-8 in the synthesized composite material was not destroyed.
[0039] Example 2: A method for catalyzing the reduction reaction of benzaldehyde using Pd@ZIF-8@C3N4 composite material as a catalyst.
[0040] (a) The method is as follows
[0041] 30 mg of Pd@ZIF-8@C3N4 composite material and 5 mL of formic acid were added to a 10 mL three-necked reaction vessel, followed by 4.9 mmol of benzaldehyde. The reaction was carried out at 383 K for 12 h. The yield of the product was monitored by gas chromatography (GC).
[0042] During the reaction, the catalytic performance of the Pd@ZIF-8@C3N4 composite material as a catalyst for the reduction of benzaldehyde was tested by GC. As the reaction proceeded, the yield gradually increased. After 12 hours, the experimental results are shown in Table 1, and the conversion rate of benzaldehyde reached 91%.
[0043] (II) Reuse of Pd@ZIF-8@C3N4 composite materials
[0044] After the reaction was completed, the reaction mixture was centrifuged and filtered to separate it from the catalyst. The mixture was then washed with ethanol, filtered, and dried. The composite material was recovered.
[0045] The specific procedure for the cyclic experiment was as follows: the recovered catalyst was used to catalyze the reduction of benzaldehyde again, selectively preparing toluene, and the reaction was carried out at 383 K for 12 h. The experimental results are as follows: Figure 4 As shown, after five cycles of the cyclic experiment, the catalyst activity did not decrease significantly, and the recovered catalyst remained stable. This indicates that the Pd@ZIF-8@C3N4 composite material is recyclable.
[0046] (III) Effect of different catalysts on the catalytic reduction reaction of benzaldehyde
[0047] 30 mg of Pd@ZIF-8@C3N4 composite material, Pd@ZIF-8, Pd@C3N4, and 5 mL of formic acid were added to a 10 mL three-necked reaction vessel, followed by 4.9 mmol of benzaldehyde. The reaction was carried out at 383 K for 6-12 h. The yield of the product was monitored by gas chromatography (GC), and the results are shown in Table 1.
[0048] Table 1
[0049]
[0050] As shown in Table 1, under the same reaction time, the Pd@ZIF-8@C3N4 composite material exhibited the highest benzaldehyde conversion rate, reaching 35% at 6 h and 91% at 12 h; Pd@C3N4 showed the second highest conversion rate, while Pd@ZIF-8 showed the lowest. With the reaction time increasing from 6 h to 12 h, the benzaldehyde conversion rates of all three catalysts significantly improved, indicating that increasing the reaction time helps improve the reduction efficiency of benzaldehyde. The catalytic performance of the Pd@ZIF-8@C3N4 composite material was significantly better than that of the single-supported Pd@ZIF-8 and Pd@C3N4, demonstrating that the composite structure of ZIF-8 and C3N4 can effectively enhance the catalyst activity.
Claims
1. A Pd@ZIF-8@C3N4 composite material, characterized in that, The preparation method includes the following steps: (1) C3N4 was dispersed in methanol and continuously stirred under ultrasonication to obtain a suspension. Zinc salt was added to the obtained suspension and stirred vigorously for 8 h - 10 h. After standing overnight at room temperature, 2-methylimidazole methanol solution was added under stirring and stirring was continued for 24 h - 25 h. After centrifugation, washing, and vacuum drying, ZIF-8@C3N4 was obtained. (2) Mix ZIF-8@C3N4 and sodium chloropalladium solution evenly to obtain a mixed solution; add sodium borohydride to methanol solution, sodium borohydride and methanol release hydrogen gas, quickly take the upper layer of liquid with bubbles and add it to the obtained mixed solution and stir continuously for 30 min - 60 min, wash, vacuum dry to obtain Pd@ZIF-8@C3N4 composite material.
2. The Pd@ZIF-8@C3N4 composite material according to claim 1, characterized in that, In step (1), the C3N4 preparation method includes: placing urea in a muffle furnace, first keeping it at 323 K - 333 K for 6 h - 8 h, then heating it to 818 K - 828 K for 1 h - 2 h, and cooling it to room temperature to obtain C3N4.
3. The Pd@ZIF-8@C3N4 composite material according to claim 1, characterized in that, In step (1), the zinc salt is Zn(NO3)2·6H2O.
4. The Pd@ZIF-8@C3N4 composite material according to claim 1, characterized in that, In step (2), the method for preparing the sodium chloropalladium solution includes: mixing palladium chloride, sodium chloride and methanol until dissolved, and stirring overnight.
5. The Pd@ZIF-8@C3N4 composite material according to claim 4, characterized in that, According to the feed-to-liquid ratio, palladium chloride: sodium chloride: methanol = (0.02 g - 0.04 g): (0.010 g - 0.015 g): 1 mL.
6. The Pd@ZIF-8@C3N4 composite material according to claim 1, characterized in that, In step (2), the concentration of the sodium chloropalladium solution is 0.15 mol / L - 0.20 mol / L.
7. The Pd@ZIF-8@C3N4 composite material according to claim 1, characterized in that, In step (2), the molar ratio is 2-methylimidazole:zinc salt = (3 - 4):
1.
8. The application of the Pd@ZIF-8@C3N4 composite material according to any one of claims 1-7 as a catalyst in the catalytic reduction reaction of benzaldehyde.
9. A method for catalyzing the reduction reaction of benzaldehyde using a Pd@ZIF-8@C3N4 composite material as a catalyst, characterized in that, Using the Pd@ZIF-8@C3N4 composite material according to any one of claims 1-7 as a catalyst, the method includes: taking formic acid, benzaldehyde and the catalyst in a reaction vessel and reacting them at 378 K - 388 K for 12 h - 13 h.