Method for preparing monatomic catalyst from pd porphyrin precursor and application thereof in hydrogenation deoxidization of vanillin
By combining Pd porphyrin complexes with H-ZSM-5 molecular sieves, a Pd1/H-ZSM-5 single-atom catalyst was prepared, which solved the problems of low noble metal utilization and insufficient stability of existing Pd-based catalysts. It achieved highly efficient hydrodeoxygenation reaction of lignin derivatives, especially high selectivity and stability in the conversion of vanillin to 2-methoxy-4-methylphenol.
Patent Information
- Application Number
- CN202611329829.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-08-31
- Publication Date
- 2026-11-06
AI Technical Summary
Existing Pd-based catalysts suffer from problems such as low utilization of precious metals, easy sintering and agglomeration of metal particles, uneven distribution of active sites, and insufficient catalytic stability in the hydrodeoxygenation reaction of lignin derivatives. Furthermore, the preparation method of Pd single atoms is complex and costly.
Using Pd porphyrin complexes as metal precursors and combining them with the confinement effect of H-ZSM-5 molecular sieves, Pd1/H-ZSM-5 single-atom catalysts were prepared. Stable Pd single-atom structures were formed through high-temperature carbonization, and the acidic sites of H-ZSM-5 were used to form a metal-acid synergistic catalytic effect with Pd.
High dispersion and anchoring of Pd single atoms on the H-ZSM-5 surface was achieved, which improved the stability of the catalyst and the selectivity of the target product. The utilization rate of precious metals was close to 100%, and the catalytic activity and selectivity were significantly improved. Moreover, the preparation process was simple and low in cost.
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Figure CN123038868A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of heterogeneous catalysis and biomass catalytic conversion technology, and relates to a method for preparing a Pd single-atom catalyst, particularly a method for preparing a Pd1 / H-ZSM-5 single-atom catalyst using a Pd porphyrin complex as a metal precursor, and its application in the hydrodeoxygenation reaction of the lignin derivative vanillin. Background Technology
[0002] With the increasing depletion of fossil resources and the continuous advancement of green and low-carbon development, the high-value utilization of renewable biomass resources has become an important research direction in the energy and chemical industry. Lignin is the only abundant renewable aromatic polymer resource in nature, possessing rich aromatic ring structures and oxygen-containing functional groups, making it an important raw material for the preparation of high-value-added aromatic chemicals. Vanillin, as an important platform compound for lignin degradation, is often used as a model compound in lignin catalytic conversion research. Through hydrodeoxygenation, vanillin can be converted into high-value-added products such as 2-methoxy-4-methylphenol, which is of great significance for the efficient utilization of biomass resources.
[0003] Currently, Pd-based catalysts are widely used in the hydrodeoxygenation reaction of lignin derivatives due to their excellent hydrogenation performance. Existing catalysts mostly employ Pd nanoparticles supported on carriers such as activated carbon, alumina, and silica. While these catalysts exhibit high catalytic activity, they still suffer from problems such as low utilization of precious metals, easy sintering and agglomeration of metal particles, uneven distribution of active sites, and insufficient catalytic stability. Furthermore, the presence of multiple active sites on the surface of Pd nanoparticles can easily trigger side reactions, affecting the selectivity of the target product.
[0004] In recent years, single-atom catalysts have exhibited excellent catalytic performance in reactions such as hydrodeoxygenation due to their near 100% metal atom utilization, uniform active centers, and unique electronic structure. However, Pd single atoms possess high surface free energy, making them prone to migration and aggregation during preparation and reaction, and difficult to maintain a stable single-atom dispersion. Currently used preparation methods such as atomic layer deposition, strong electrostatic adsorption, and coprecipitation generally suffer from problems such as complex processes, high costs, demanding equipment requirements, or insufficient single-atom stability, which limit their widespread application.
[0005] H-ZSM-5 molecular sieves possess a regular microporous structure, high specific surface area, excellent thermal stability, and abundant acidic sites, providing good confinement and anchoring effects for metal active components, which is beneficial for improving catalyst dispersibility and stability. However, when using traditional palladium salts as precursors, Pd species still tend to aggregate into nanoparticles during calcination, making it difficult to obtain stable single-atom structures. Therefore, developing a Pd single-atom catalyst using Pd porphyrin complexes as metal precursors combined with the confinement effect of H-ZSM-5 molecular sieves and applying it to the hydrogenation deoxygenation reaction of vanillin has significant application value for improving noble metal utilization efficiency, enhancing catalyst stability, and improving the selectivity of target products. Summary of the Invention
[0006] The purpose of this invention is to provide a method for preparing Pd1 / H-ZSM-5 single-atom catalyst from Pd porphyrin precursor, and to demonstrate excellent reactivity, conversion rate, selectivity and stability in the hydrogenation and deoxygenation of lignin derivative vanillin to 2-methoxy-4-methylphenol.
[0007] The above-mentioned objectives of the present invention are achieved through the following technical solutions:
[0008] A method for preparing a single-atom catalyst from a Pd porphyrin precursor includes the following steps:
[0009] (1) Benzaldehyde and pyrrole react in propionic acid solvent to form 5,10,15,20-tetraphenylporphyrin;
[0010] (2) The 5,10,15,20-tetraphenylporphyrin obtained in step (1) is reacted with palladium chloride to obtain 5,10,15,20-tetraphenylporphyrin palladium;
[0011] (3) Dissolve the 5,10,15,20-tetraphenylporphyrin palladium obtained in step (2) in an organic solvent, stir until completely dissolved, add dried H-ZSM-5, mix and stir, and dry to obtain a solid mixture;
[0012] (4) The solid mixture obtained in step (3) is carbonized at high temperature in an inert gas atmosphere and cooled to room temperature to obtain Pd1 / H-ZSM-5 single-atom catalyst;
[0013] In the Pd1 / H-ZSM-5 single-atom catalyst, Pd is dispersed in single-atom form on the surface of H-ZSM-5 molecular sieve with acidic sites.
[0014] Further, in step (1), the reaction is carried out by stirring and heating under reflux at 150 °C for 2 h; the molar ratio of benzaldehyde to pyrrole is 1:1.
[0015] Furthermore, in step (2), the reaction is carried out under argon protection and stirred and heated under reflux at 150 °C for 6 h; the amount of palladium chloride used is 5 times the equivalent of 5,10,15,20-tetraphenylporphyrin.
[0016] Further, in step (2), after the reaction is completed and cooled to room temperature, the organic phase is extracted and purified using dichloromethane and saturated NaCl aqueous solution. The organic phase is collected, dried with anhydrous sodium sulfate, filtered, and the filtrate is evaporated to obtain crude product. Then, it is purified by silica gel column chromatography to obtain 5,10,15,20-tetraphenylporphyrin palladium.
[0017] Further, the specific operation of step (3) is as follows: 5,10,15,20-tetraphenylporphyrin palladium obtained from step (2) is dissolved in N,N-dimethylformamide, stirred until completely dissolved, then dried H-ZSM-5 is added, stirred at room temperature for 12 h, and the resulting mixture is dried by rotary evaporation to obtain a solid mixture.
[0018] Furthermore, the Pd loading in the Pd1 / H-ZSM-5 single-atom catalyst is 0.3 wt%, and the loading is expressed as a percentage of the mass of Pd element to the total mass of the final catalyst.
[0019] Furthermore, in step (4), the inert gas is nitrogen or argon; the high-temperature carbonization is achieved by heating to 800 ℃ at a rate of 10 ℃ / min and holding at that temperature for 2 h.
[0020] The Pd1 / H-ZSM-5 single-atom catalyst prepared by the method of the present invention has a bifunctional active center composed of a Pd single-atom metal center and an H-ZSM-5 acidic site.
[0021] The present invention relates to the application of the single-atom catalyst prepared by the method of the present invention in the selective hydrodeoxygenation of lignin derivatives. The application is the hydrodeoxygenation of vanillin to prepare 2-methoxy-4-methylphenol. A batch stainless steel high-pressure reactor is used. The single-atom catalyst, vanillin, and solvent are added to the reactor. The gas inside the reactor is replaced with hydrogen five times. The reaction is carried out for 1 h at 1 MPa H2, 100 °C, and 500 rpm. After centrifugation, the supernatant is collected to obtain the reaction product. The solvent is tetrahydrofuran, ethanol, or isopropanol. The mass / molar ratio of vanillin to catalyst is 50 mg: 1 mmol.
[0022] Compared with the prior art, the present invention has the following innovative features and beneficial effects:
[0023] (1) In the prior art, when inorganic palladium salts (such as Na2PdCl4) or simple palladium complexes (such as ammonia / ethylenediamine palladium complex) are used as precursors, Pd species lack effective spatial confinement and coordination stabilization during heat treatment, and are prone to migration and aggregation, forming Pd nanoparticles, which leads to destruction of single-atom structure and decay of catalytic performance. This invention innovatively selects 5,10,15,20-tetraphenylporphyrin palladium as a metal precursor, making full use of the rigid planar conjugated structure of porphyrin macrocyclic molecules and the stable Pd-N4 coordination structure. During high-temperature carbonization (800 °C), it plays a dual stabilizing role of "anchoring-confining" for Pd atoms. At the same time, the high bond energy of Pd-N4 coordination bonds significantly and effectively inhibits the thermal migration of Pd atoms at high temperatures, achieving high dispersion and anchoring of Pd single atoms on the surface of H-ZSM-5 molecular sieve, avoiding the metal sintering and agglomeration problem that is easily caused by traditional precursors. Characterization by aberration-corrected transmission electron microscopy (AC HAADFSTEM) showed that Pd in the catalyst of the present invention was uniformly dispersed in the form of isolated bright spots, with no Pd nanoparticles or clusters present; no Pd or PdO crystal phase diffraction peaks were observed in the X-ray diffraction (XRD) pattern, further confirming that Pd was in a single-atom dispersed state.
[0024] (2) Existing Pd single-atom catalysts (such as Pd1 / WO) 2.72 Although Pd / SAPO-31 shows some activity for the hydrodeoxygenation of vanillin, its support (WO3) 2.72 Lacking sufficient Brønsted acidic sites, the catalytic process of Pd single atoms (such as SAPO-31 or N-doped carbon) relies mainly on the metal active centers of Pd single atoms, making it difficult to effectively promote CO bond breaking and intermediate dehydration steps, resulting in limited reaction activity or target product selectivity. This invention uses H-ZSM-5 molecular sieve as a support. Its abundant Brønsted acidic sites and regular microporous structure not only provide a stable confined environment for Pd single atoms but also form a metal-acid synergistic catalytic effect with Pd active centers, promoting C=O bond activation and selective C-O bond breaking in vanillin, thus improving the hydrodeoxygenation reaction activity and target product selectivity. Under mild conditions of 1 MPa H2, 100 °C, and 500 rpm for 1 h, the vanillin conversion rate is close to 100%, and the selectivity and yield of 2-methoxy-4-methylphenol are both greater than 99%.
[0025] (3) Compared with traditional Pd catalysts prepared using palladium salt precursors, the preparation process of this invention is simple. Stable Pd single-atom catalysts can be obtained by impregnation, drying and high-temperature carbonization. There is no need for complex equipment such as atomic layer deposition. It has good repeatability and industrial scale-up potential.
[0026] (4) When traditional Pd-based catalysts exist in the form of Pd nanoparticles, only surface atoms participate in the catalytic reaction, while bulk atoms are embedded and cannot be utilized, resulting in a noble metal atom utilization rate that is usually less than 30%. In the Pd1 / H-ZSM-5 catalyst prepared in this invention, each Pd atom is dispersed on the support surface as an isolated single atom, and all Pd atoms can participate in the catalytic reaction as active sites, achieving a noble metal atom utilization rate of nearly 100%. Under the condition of a metal loading of only 0.3 wt%, the catalyst of this invention exhibits excellent catalytic activity, significantly reducing the amount of noble metal required per unit of catalytic activity, greatly reducing the catalyst production cost, and has important economic value for the industrial promotion of noble metal catalysts.
[0027] (5) In the hydrodeoxygenation reaction, traditional Pd nanoparticle catalysts are prone to Pd particle sintering, migration, or loss during the reaction due to the weak interaction between the metal particles and the support, resulting in a rapid decline in catalytic activity with increasing cycle number. In this invention, Pd single atoms form a strong coordination-confined dual stable structure with H-ZSM-5 molecular sieve through porphyrin-derived nitrogen species, and the regular microporous structure of H-ZSM-5 provides physical confinement protection for Pd single atoms, effectively preventing the migration and aggregation of Pd atoms during the reaction. After five consecutive cycles, the vanillin conversion rate of the catalyst of this invention remains close to 100%, and the selectivity of 2-methoxy-4-methylphenol remains greater than 99%, without obvious activity decay or metal loss, demonstrating excellent cycle stability and service life. Attached Figure Description
[0028] Figure 1 Aberration-corrected transmission electron microscopy (ACHAADFSTEM) image of the Pd1 / H-ZSM-5 single-atom catalyst prepared for Example 1.
[0029] Figure 2 Transmission electron microscopy (TEM) image of the Pd1 / H-ZSM-5 single-atom catalyst prepared for Example 1.
[0030] Figure 3 The image shows the X-ray diffraction (XRD) pattern of the Pd1 / H-ZSM-5 single-atom catalyst prepared in Example 1.
[0031] Figure 4 The image shows the X-ray photoelectron spectroscopy (XPS) spectrum of the Pd1 / H-ZSM-5 single-atom catalyst prepared in Example 1.
[0032] Figure 5 The Pd1 / H-ZSM-5 single-atom catalyst prepared in Example 1, commercial Pd / C and Pd nmComparison of the catalytic performance of / H-ZSM-5 nanocatalysts in the hydrogenation and deoxygenation reaction of vanillin.
[0033] Figure 6 Cyclic stability of the Pd1 / H-ZSM-5 single-atom catalyst prepared in Example 1 in the hydrogenation deoxygenation reaction of vanillin. Detailed Implementation
[0034] The present invention will be further described below with reference to the embodiments, but the scope of protection of the present invention is not limited to the scope shown in the embodiments.
[0035] Example 1: Preparation of Pd1 / H-ZSM-5 single-atom catalyst
[0036] This embodiment provides a method for preparing Pd1 / H-ZSM-5 single-atom catalysts from Pd porphyrin precursors. The specific steps are as follows:
[0037] (1) Synthesis of 5,10,15,20-tetraphenylporphyrin: In a 1000 mL round-bottom flask, 50 mL (0.8 mol) of benzaldehyde and an equimolar amount of freshly distilled pyrrole were added, followed by 50 mL of propionic acid. The entire reaction mixture was refluxed at 150 °C for 2 h with stirring to stop the reaction. After the reaction solution cooled naturally to room temperature, it was filtered using a sintered glass funnel and washed three times each with distilled water and methanol solvent to obtain the purple solid compound 5,10,15,20-tetraphenylporphyrin.
[0038] (2) Synthesis of 5,10,15,20-tetraphenylporphyrin palladium: 5,10,15,20-tetraphenylporphyrin (50 mg) obtained in step (1) and five equivalents of palladium chloride were dissolved in N,N-dimethylformamide (100 mL). The mixture was purged with argon to remove dissolved oxygen. Under argon protection, the above reaction mixture was stirred and refluxed at 150 °C for 6 h. A small amount of the reflux liquid was then picked up with a capillary tube and plated onto a TLC plate. If no fluorescent band appeared under a 365 nm UV lamp, the reaction could be terminated. The reaction was stopped and cooled to room temperature. The product was purified by extraction using a 500 mL separatory funnel and dichloromethane solution and saturated NaCl aqueous solution as the extractant. The organic phase was collected by standing and separating the layers. The operation was repeated 6 times. The product was dried with anhydrous sodium sulfate and filtered. The obtained filtrate was evaporated to dryness to obtain a crude product. The crude product was then separated and purified by silica gel column chromatography to obtain 5,10,15,20-tetraphenylporphyrin palladium.
[0039] (3) Based on the Pd loading of 0.3 wt% in the final catalyst, weigh 5,10,15,20-tetraphenylporphyrin palladium obtained in step (2) and dissolve it in N,N-dimethylformamide (10 mL). After stirring until completely dissolved, add dried H-ZSM-5 (2 g) and stir at room temperature for 12 h. Then, rotary evaporate the mixture and dry it at 60 ℃ for 12 h to obtain a solid mixture.
[0040] (4) The solid mixture obtained in step (3) is placed in an alumina ceramic boat, and the air inside the tube is replaced with nitrogen five times. In a nitrogen atmosphere, it is carbonized at high temperature in a tube furnace. The temperature program is to increase the temperature by 10 °C / min to 800 °C and hold for 2 h. After cooling to room temperature, the Pd1 / H-ZSM-5 single-atom catalyst is obtained.
[0041] Example 2: Hydrogenation and deoxygenation reaction of vanillin
[0042] The Pd1 / H-ZSM-5 single-atom catalyst prepared in Example 1 was applied to the hydrogenation and deoxygenation of vanillin to prepare 2-methoxy-4-methylphenol. In a 50 mL stainless steel high-pressure reactor, 50 mg of the catalyst obtained in Example 1, 1 mmol of vanillin, and 8 mL of tetrahydrofuran solvent were added. After sealing, the gas inside the reactor was purged with hydrogen five times, and the reaction was carried out for 1 h at 1 MPa H2, 100 °C, and 500 rpm. After the reaction was completed, the reactor was cooled to room temperature, and the catalyst was recovered by centrifugation. The product was analyzed using an Agilent gas chromatograph equipped with an HP-5 capillary column. The conversion rate of vanillin and the selectivity for 2-methoxy-4-methylphenol were analyzed. The results showed that under mild conditions and a short reaction time, the conversion rate of vanillin was close to 100%, and the selectivity and yield of 2-methoxy-4-methylphenol were both >99%. Furthermore, the Pd1 / H-ZSM-5 single-atom catalyst prepared in Example 1 maintained good stability in vanillin conversion and 2-methoxy-4-methylphenol selectivity after five cycles, such as... Figure 6 As shown.
[0043] Methods for calculating conversion rate, selectivity, and yield:
[0044] .
Claims
1. A method for preparing a single-atom catalyst from a Pd porphyrin precursor, characterized in that, Includes the following steps: (1) Benzaldehyde and pyrrole react in propionic acid solvent to form 5,10,15,20-tetraphenylporphyrin; (2) The 5,10,15,20-tetraphenylporphyrin obtained in step (1) is reacted with palladium chloride to obtain 5,10,15,20-tetraphenylporphyrin palladium; (3) Dissolve the 5,10,15,20-tetraphenylporphyrin palladium obtained in step (2) in an organic solvent, stir until completely dissolved, add dried H-ZSM-5, mix and stir, and dry to obtain a solid mixture; (4) The solid mixture obtained in step (3) is carbonized at high temperature in an inert gas atmosphere and cooled to room temperature to obtain Pd1 / H-ZSM-5 single-atom catalyst; In the Pd1 / H-ZSM-5 single-atom catalyst, Pd is dispersed in single-atom form on the surface of H-ZSM-5 molecular sieve with acidic sites.
2. The method of claim 1, wherein, In step (1), the reaction is carried out by stirring and heating under reflux at 150 °C for 2 h; the molar ratio of benzaldehyde to pyrrole is 1:
1.
3. The method of claim 1, wherein, In step (2), the reaction is carried out under argon protection and stirred and heated under reflux at 150 °C for 6 h; the amount of palladium chloride used is 5 equivalents of 5,10,15,20-tetraphenylporphyrin.
4. The method of claim 1, wherein, In step (2), after the reaction is completed, the mixture is cooled to room temperature and purified by extraction with dichloromethane and saturated NaCl aqueous solution. The organic phase is collected, dried with anhydrous sodium sulfate, filtered, and the filtrate is evaporated to dryness to obtain the crude product. The crude product is then purified by silica gel column chromatography to obtain 5,10,15,20-tetraphenylporphyrin palladium.
5. The method of claim 1, wherein, The specific operation of step (3) is as follows: 5,10,15,20-tetraphenylporphyrin palladium obtained from step (2) is dissolved in N,N-dimethylformamide and stirred until completely dissolved. Then, dried H-ZSM-5 is added and stirred at room temperature for 12 h. The resulting mixture is then dried by rotary evaporation to obtain a solid mixture.
6. The method according to claim 1, characterized in that, The Pd loading in the Pd1 / H-ZSM-5 single-atom catalyst is 0.3 wt%, which is expressed as a percentage of the mass of Pd element to the total mass of the final catalyst.
7. The method according to claim 1, characterized in that, In step (4), the inert gas is nitrogen or argon; the high-temperature carbonization is achieved by heating to 800 ℃ at a rate of 10 ℃ / min and holding for 2 h.
8. The Pd1 / H-ZSM-5 single-atom catalyst prepared by the method according to any one of claims 1-7, wherein the catalyst has a bifunctional active center composed of a Pd single-atom metal center and an H-ZSM-5 acidic site.
9. The application of the Pd1 / H-ZSM-5 single-atom catalyst prepared by the method according to any one of claims 1-7 in the selective hydrodeoxygenation of lignin derivatives.
10. The application according to claim 9, characterized in that, The application is the preparation of 2-methoxy-4-methylphenol by hydrogenation and deoxygenation of vanillin. An intermittent stainless steel high-pressure reactor is used. The single-atom catalyst, vanillin, and solvent are added to the reactor. The gas inside the reactor is replaced with hydrogen five times. The reaction is carried out for 1 hour at 1 MPa H2, 100 °C, and 500 rpm. After centrifugation, the supernatant is collected to obtain the reaction product. The solvent is tetrahydrofuran, ethanol, or isopropanol. The mass / molar ratio of vanillin to catalyst is 50 mg: 1 mmol.