Porphyrin-based n-heterocyclic carbene framework immobilized metal nanoparticle catalysts, methods of making and use thereof

Abstract

The application discloses a kind of porphyrin-based azacyclic carbene framework immobilized metal nanoparticles catalyst and its preparation method and application, belong to the technical field of heterogeneous catalytic material.The metal nanoparticles catalyst contains porphyrin-based azacyclic carbene framework, and the metal nanoparticles is anchored by azacyclic carbene and porphyrin unit in the porphyrin-based azacyclic carbene framework.The preparation method includes: bromomethyl porphyrin derivative and triimidazolyl organic monomer are synthesized porphyrin-based azacyclic carbene precursor framework by quaternary ammonium reaction;Porphyrin-based azacyclic carbene precursor framework and metal salt are deprotonated reaction, immobilize metal active component, synthesize porphyrin-based metal azacyclic carbene framework;Porphyrin-based metal azacyclic carbene framework is synthesized metal nanoparticles catalyst by reduction reaction.The metal nanoparticles catalyst is used for nitroaromatics catalytic hydrogenation reaction preparation aromatic amine.The metal nanoparticles catalyst of the application has narrow particle size distribution, high metal loading, and good thermal stability.

Description

Technical Field

[0001] This invention belongs to the field of heterogeneous catalytic materials technology, specifically relating to a porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst, its preparation method, and its application. Background Technology

[0002] Metal nanoparticles are widely used as highly efficient heterogeneous catalysts in various important chemical transformations such as hydrogenation, oxidation, and coupling due to their excellent catalytic activity, selectivity, and stability. However, rare metals are scarce and expensive, and ultrafine metal nanoparticles have extremely high surface energy, making them prone to agglomeration, sintering, and loss of active components during preparation and use. This leads to a sharp decline in catalytic activity, severely limiting their industrial application.

[0003] Currently, strategies for preparing highly dispersed metal nanoparticles mainly fall into two categories: one is to utilize high specific surface area supports to mediate nucleation and growth; the other is to use stabilizers to protect pre-synthesized metal nanoparticles. However, the former often faces problems such as nanoparticle aggregation, loss of active components, uneven distribution, particle growth, and weak metal-support interactions, leading to decreased structural stability and catalytic performance. Although the latter can inhibit aggregation, excessive surface capping agents can introduce steric hindrance, restricting the diffusion of reactants to active sites, thereby reducing catalytic efficiency.

[0004] In recent years, utilizing the confinement effect of porous materials to precisely control the size, morphology, and dispersion of metal nanoparticles has become an emerging strategy. However, traditional porous supports (such as MOFs, COFs, and porous organic cages) still suffer from the inherent defect of weak metal-support interactions, which easily leads to irreversible aggregation, loss, and sintering of metal nanoparticles, severely reducing long-term catalytic performance. In existing technologies, nitrogen heterocyclic carbenes (NHCs) are used to stabilize metal nanoparticles due to their strong coordination ability with metals.

[0005] However, single NHC functionalized supports suffer from insufficient structural rigidity, low metal loading, and poor particle size control precision. Furthermore, the NHC functionalization framework often employs a single-structure triimidazolium monomer, limiting the tunability of the support structure and the optimization space for catalytic performance. Porphyrin compounds possess rigid macrocyclic structures and abundant coordination sites, but their metal anchoring ability is limited when used alone as a support. Summary of the Invention

[0006] To address the aforementioned problems in the prior art, this invention provides a porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst, its preparation method, and its application.

[0007] The technical problem to be solved by this invention is achieved through the following technical solution: In a first aspect, the present invention provides a metal nanoparticle catalyst immobilized on a porphyrin-based nitrogen heterocyclic carbene framework, wherein the metal nanoparticle catalyst contains a porphyrin-based nitrogen heterocyclic carbene framework, and the metal nanoparticles are anchored to the nitrogen heterocyclic carbene and porphyrin units through the porphyrin-based nitrogen heterocyclic carbene framework.

[0008] In one embodiment of the present invention, the structure of the metal nanoparticle catalyst is shown in general formula I:

[0009] Ⅰ In the general formula I, M represents metal nanoparticles.

[0010] In one embodiment of the present invention, the metal nanoparticles include one or more of platinum, palladium, gold, and copper.

[0011] Secondly, the present invention provides a method for preparing the above-mentioned porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst, comprising the steps of: S1. A porphyrin-based nitrogen-heterocyclic carbene precursor framework is synthesized by dissolving bromomethylporphyrin derivatives and triimidazole organic monomers in a polar aprotic solvent and then reacting them with a quaternization reaction. S2. The porphyrin-based nitrogen heterocyclic carbene precursor framework and metal salt are dissolved in a polar aprotic solvent and deprotonated under alkaline conditions to immobilize the metal active component and synthesize the porphyrin-based metal nitrogen heterocyclic carbene framework. S3. The porphyrin-based metal-nitrogen heterocyclic carbene framework is used to synthesize a porphyrin-based nitrogen-nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst via a reduction reaction.

[0012] In one embodiment of the present invention, in step S1: the molar ratio of the bromomethylporphyrin derivative to the triimidazole organic monomer is 1:(0.5~1.5), the reaction temperature is 60~140℃, and the reaction time is 1~2h.

[0013] In one embodiment of the present invention, the bromomethylporphyrin derivative includes one or more of meso-5,10,15,20-tetra(4-bromomethylphenyl)porphyrin, 5,15-dibromomethyl-10,20-diphenylporphyrin, 5,10,5,20-tetra(3,5-dibromomethylphenyl)porphyrin, 5,15-bis(4-bromomethylphenyl)porphyrin, and 5,15-bis(4-bromomethylphenyl)-10,20-diphenylporphyrin.

[0014] In one embodiment of the present invention, the triimidazolyl organic monomer includes one or more of 1,3,5-tris(4-imidazolylphenyl)benzene, 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine, 1,3,5-triimidazolylbenzene, tris-(4-imidazolylphenyl)amine, and tris-(4-imidazolylphenyl)methane.

[0015] In one embodiment of the present invention, in step S2: the molar ratio of the porphyrin-nitro-heterocyclic carbene precursor framework to the metal salt is 1:(0.5~3), the reaction temperature is 50~80℃, and the reaction time is 2~4h.

[0016] In one embodiment of the present invention, in step S3: the reducing agent for the reduction reaction is sodium citrate, sodium dithionite or lithium borohydride, the reaction temperature is 10~40℃, the reaction time is 0.5~2h, and the metal nanoparticle catalyst immobilized on the porphyrin-based nitrogen heterocyclic carbene framework is obtained after centrifugation, washing and drying.

[0017] Thirdly, this invention provides an application of a porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst in the catalytic hydrogenation of nitroaromatic hydrocarbons to prepare aromatic amines.

[0018] Compared with the prior art, the present invention has the following advantages: 1. The porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst provided by this invention constructs a synergistic system integrating NHC anchoring, porphyrin-assisted coordination, and stable covalent bridging. It solves the core problems of traditional supported metal nanoparticle catalysts from three dimensions: metal anchoring mechanism, electronic regulation, and structural stability. The particle size is precisely controlled at around 2.20 nm, with an extremely narrow particle size distribution and no obvious agglomeration. The metal loading is as high as 26~32.5 wt%, and the thermal stability is as high as 415~425℃. 2. The method for preparing metal nanoparticle catalysts supported by porphyrin-based nitrogen heterocyclic carbene frameworks provided by this invention integrates the strong covalent anchoring ability of nitrogen heterocyclic carbenes, the structural rigidity of porphyrins, and the π-conjugated electronic regulation effect of porphyrins by constructing porphyrin-based nitrogen heterocyclic carbene frameworks, achieving highly uniform dispersion and high loading of metal nanoparticles. Using triimidazolyl organic compounds with different structures as monomers, the pore size, specific surface area, and electronic properties of the support can be flexibly controlled by changing the central core (benzene ring, triazine ring, amino group, methaneyl group) and substituent positions of the monomers, thereby optimizing the loading, size distribution, and catalytic performance of metal nanoparticles to meet the needs of different reaction systems. A porphyrin-based nitrogen heterocyclic carbene precursor framework is synthesized by quaternization reaction of bromomethylporphyrin derivatives and triimidazolyl organic monomers, followed by deprotonation reaction with metal salts to immobilize the metal active component, and then synthesized by reduction reaction to synthesize the metal nanoparticle catalyst supported by the porphyrin-based nitrogen heterocyclic carbene framework, which improves the reaction rate and shortens the reaction time. 3. The metal nanoparticle catalyst supported on the porphyrin-based nitrogen heterocyclic carbene framework provided by this invention can be used for the catalytic hydrogenation reaction of nitroaromatics to prepare aromatic amines. It has high catalytic activity and broad applicability, and can exhibit excellent catalytic activity for a variety of substituted nitroaromatics. It can be widely used in the treatment of nitroaromatic wastewater and the green synthesis of aromatic amines.

[0019] The present invention will now be described in further detail with reference to the accompanying drawings. Attached Figure Description

[0020] Figure 1 This is a schematic flowchart of the preparation method of the metal nanoparticle catalyst immobilized on the porphyrin-based nitrogen heterocyclic carbene framework provided in the embodiments of the present invention. Figure 2 This is a schematic diagram of the synthetic route of the porphyrin-nitrogen heterocyclic carbene precursor framework (PImF-TIPT) in Example 1 of the present invention; Figure 3 These are the IR spectra of PImF-TIPT and its monomers prepared in Example 1 of this invention; Figure 4 It is the PImF-TIPT prepared in Example 1 of this invention. 13 C-CP-MAS NMR spectrum; Figure 5 This is a schematic diagram of the molecular skeleton structure of PImF-TIPT prepared in Example 1 of the present invention; Figure 6 This is the TGA spectrum of PImF-TIPT prepared in Example 1 of this invention; Figure 7 These are the BET adsorption spectra and pore size distribution diagrams of PImF-TIPT prepared in Example 1 of this invention, wherein... Figure 7(a) is the BET adsorption spectrum of PIMF-TIPT. Figure 7 (b) is the pore size distribution diagram of PImF-TIPT; Figure 8 This is the XPS spectrum of PImF-TIPT prepared in Example 1 of this invention, wherein... Figure 8 (a) is the XPS full spectrum. Figure 8 (b) is the high-resolution spectrum of C 1s. Figure 8 (c) is the high-resolution spectrum of N 1s. Figure 8 (d) is the high-resolution spectrum of Br 3d; Figure 9 This is a SEM image of the PImF-TIPT prepared in Example 1 of this invention, wherein, Figure 9 (a) is a low-magnification morphology image. Figure 9 (b) is a high-magnification morphology image; Figure 10 This is a synthetic route diagram of Pt-1@PNHCF-TIPT prepared in Example 1 of this invention; Figure 11 It is the Pt-1@PNHCF-TIPT prepared in Example 1 of this invention. 13 C-CP-MAS NMR spectrum; Figure 12 This is the XPS spectrum of Pt-1@PNHCF-TIPT prepared in Example 1 of this invention, wherein, Figure 12 (a) is the XPS full spectrum. Figure 12 (b) is the high-resolution spectrum of Pt 4f. Figure 12 (c) is the high-resolution spectrum of C 1s. Figure 12 (d) is the high-resolution spectrum of N 1s; Figure 13 This is the XRD pattern of Pt-1@PNHCF-TIPT prepared in Example 1 of this invention; Figure 14 This is the SEM spectrum of Pt-1@PNHCF-TIPT prepared in Example 1 of this invention, wherein, Figure 14 (a) is a low-magnification morphology image. Figure 14 (b) is a high-magnification morphology image; Figure 15 This is the TEM spectrum of Pt-1@PNHCF-TIPT prepared in Example 1 of this invention; Figure 16 This is a histogram of the particle size distribution of Pt-1@PNHCF-TIPT prepared in Example 1 of this invention. Detailed Implementation

[0021] The present invention will be further described in detail below with reference to specific embodiments, but the implementation of the present invention is not limited thereto.

[0022] To address the problems of easy aggregation, easy loss of active components, low catalytic efficiency and poor stability of existing rare metal nanocatalysts, as well as the limited selection of monomers for nitrogen heterocyclic carbene (NHC) functionalized frameworks, this invention provides a metal nanoparticle catalyst supported on a porphyrin-based NHC framework. This metal nanoparticle catalyst contains a porphyrin-based NHC framework, using the porphyrin-based NHC framework as a support, and anchors metal nanoparticles through NHC and porphyrin units.

[0023] The structure of the metal nanoparticle catalyst in this invention is shown in general formula I:

[0024] Ⅰ In Formula I, M represents a metal nanoparticle. This metal nanoparticle includes one or more of platinum, palladium, gold, and copper.

[0025] The metal nanoparticle catalyst of this invention is generated by deprotonation of a porphyrin-based heterocyclic carbene precursor framework to form a porphyrin-based heterocyclic carbene framework (PNHCF), and the metal nanoparticles are anchored through the dual-site synergistic interaction between the heterocyclic carbene (NHC) and the porphyrin unit. This porphyrin-based heterocyclic carbene framework uses bromomethylporphyrin derivatives and triimidazolyl organic monomers as building blocks, forming a methylene-bridged ionic organic framework through quaternization. The framework simultaneously contains a triazine ring, a porphyrin macrocycle, and a heterocyclic carbene active sites. The metal nanoparticles form covalent CM bonds with the carbene carbon atoms of the heterocyclic carbene and exhibit coordination interactions with the nitrogen atoms of the triazine ring and the porphyrin macrocycle, achieving high dispersion and stable immobilization.

[0026] Based on the same inventive concept, embodiments of the present invention also provide a method for preparing a porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst, referring to... Figure 1 The preparation method includes the following steps: S1. A porphyrin-based nitrogen-heterocyclic carbene precursor framework is synthesized by dissolving bromomethylporphyrin derivatives and triimidazole organic monomers in a polar aprotic solvent and then reacting them with a quaternization reaction. S2. Porphyrin-based nitrogen-heterocyclic carbene precursor framework and metal salt are dissolved in a polar aprotic solvent and deprotonated under alkaline conditions to immobilize the metal active component and synthesize a porphyrin-based metal nitrogen-heterocyclic carbene framework. S3, a porphyrin-based metal-nitrogen heterocyclic carbene framework, was used to synthesize porphyrin-based nitrogen-nitrogen heterocyclic carbene framework-supported metal nanoparticle catalysts via a reduction reaction.

[0027] In step S1 of this embodiment of the invention: the molar ratio of the bromomethylporphyrin derivative to the triimidazolyl organic monomer is 1:(0.5~1.5), the reaction temperature is 60~140℃, and the reaction time is 1~2h. The bromomethylporphyrin derivative includes one or more of meso-5,10,15,20-tetratetra(4-bromomethylphenyl)porphyrin, 5,15-dibromomethyl-10,20-diphenylporphyrin, 5,10,5,20-tetratetra(3,5-dibromomethylphenyl)porphyrin, 5,15-bis(4-bromomethylphenyl)porphyrin, and 5,15-bis(4-bromomethylphenyl)-10,20-diphenylporphyrin. Triimidazole organic monomers include one or more of 1,3,5-tris(4-imidazolylphenyl)benzene, 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine, 1,3,5-triimidazolelphenyl, tri-(4-imidazolylphenyl)amine, and tri-(4-imidazolylphenyl)methane.

[0028] In step S2 of this embodiment of the invention: the molar ratio of the porphyrin-nitro-heterocyclic carbene precursor framework to the metal salt is 1:(0.5~3), the reaction temperature is 50~80℃, and the reaction time is 2~4h.

[0029] In step S3 of this embodiment of the invention: the reducing agent for the reduction reaction is sodium citrate, sodium dithionite or lithium borohydride, the reaction temperature is 10~40℃, the reaction time is 0.5~2h, and the metal nanoparticle catalyst immobilized on the porphyrin-based nitrogen heterocyclic carbene framework is obtained after centrifugation, washing and drying.

[0030] The present invention preferably involves a reaction under an inert gas atmosphere, and a highly aprotic solvent can be selected. N , N Dimethylformamide, acetonitrile, or 1,4-dioxane, etc. The alkaline conditions in step S2 can be potassium carbonate, sodium hydride, sodium alkoxide, etc. The metal salts used in this embodiment of the invention can be platinum bromide, palladium bromide, cuprous iodide, tetrahydrothiophene gold chloride, etc.

[0031] The mechanism of this invention is as follows: 1. Mechanism of porphyrin-enhanced structural rigidity and thermal stability.

[0032] Traditional NHC-COFs are linked by imine bonds (C=N) (aldehyde + amino condensation), resulting in low bond energy, typically thermal stability below 300℃, and a tendency for framework deformation. In this invention, a porphyrin-reinforced nitrogen heterocyclic carbene ionic organic framework (PNHCF) is prepared by linking a methylene group (-CH2-) with an imidazolium cation (C=N... + Unit connection.

[0033] 1) Porphyrin macrocycles have rigid planar π-conjugated structures, which directly participate in framework construction as molecular skeletons, significantly improving the mechanical strength and thermal stability of the overall structure.

[0034] 2) Introducing stable structures such as benzene rings and triazine rings as three-node connecting units, forming a cross-conjugated network with porphyrin units, further inhibits the thermal degradation of the framework.

[0035] 3) The imine bond (C=N) has an extremely low heterolytic cleavage energy (350 kJ / mol), making it highly susceptible to nucleophilic addition-elimination reactions (hydrolysis) in the presence of water, acids, bases, or under heating conditions. This is the fundamental reason for the poor stability of traditional COFs. However, in the methylene (830 kJ / mol) and imidazolium units of the embodiments of this invention, the C=N... + All bonds (680 kJ / mol) are characterized by high heterolytic cleavage energy, strong chemical inertness, and stability far superior to imine bonds. The activation energy for the hydrolysis of imine bonds is only 40-60 kJ / mol, proceeding slowly at room temperature but rapidly accelerated under heating or acid / alkaline conditions. The activation energies for the hydrolysis of methylene and imidazolium units are both above 200 kJ / mol, and hydrolysis does not occur within a wide pH range of 1-14 and below 100°C. Experiments have shown that the PNHCF framework of this invention exhibits no skeletal decomposition below 420°C, exceeding the conventional NHC-COF by more than 120°C, and can withstand catalytic reactions at higher temperatures.

[0036] 2. Three-point synergistic metal anchoring and ultra-high dispersion mechanism.

[0037] Existing technologies rely solely on a single NHC coordination site to anchor metals, which easily leads to metal particle aggregation, low loading, and a wide particle size distribution. This invention employs a three-pronged stabilization mechanism: NHC anchoring, porphyrin-assisted coordination, and stable covalent bond bridging. The carbene carbon atom of the nitrogen-containing heterocyclic carbene forms a strong CM covalent bond with the metal, providing the primary anchoring effect and preventing metal particle migration and Ostwald ripening. The nitrogen atoms in the porphyrin macrocycle and bridging units (triazine ring, amine) exhibit weak coordination interactions with the surface of the metal nanoparticles, providing auxiliary anchoring and further limiting metal particle growth. This synergistic effect achieves a high metal loading while precisely controlling the particle size to around 2.20 nm, resulting in an extremely narrow particle size distribution and no significant aggregation.

[0038] 3. Porphyrin-mediated electronic regulation and catalytic activity enhancement mechanism.

[0039] The π-conjugated system of porphyrins not only provides structural support but also acts as an electron transport channel to regulate the electronic structure of metal nanoparticles. The electron-rich properties of porphyrins transfer electrons to metal nanoparticles, optimizing the d-band centers of the metal and enhancing its adsorption and activation capabilities for hydrogen species. The π-π stacking interaction between porphyrins and the substrate promotes the enrichment of reactants on the catalyst surface, accelerating the reaction rate.

[0040] 4. Mesoporous microsphere morphology enhances mass transfer mechanism.

[0041] PNHCF frameworks, prepared using a three-pronged stabilization mechanism of NHC anchoring, porphyrin-assisted coordination, and stable covalent bond bridging, spontaneously form monodisperse microspheres with rough nanotextures and mesoporous structures on their surfaces. The mesoporous structure facilitates rapid diffusion of reactants and products, preventing pore blockage. The spherical morphology ensures uniform dispersion of the catalyst in the reaction system, improves the utilization rate of active sites, and the microsphere structure facilitates the centrifugal recovery of the catalyst.

[0042] The porphyrin-based nitrogen heterocyclic carbene framework (PNHCF) constructed in this invention integrates the strong covalent anchoring ability of nitrogen heterocyclic carbene (NHC), the enhanced structural rigidity of porphyrin, and the π-conjugated electronic regulation effect. NHC firmly anchors metal nanoparticles through carbon-metal covalent bonds, effectively inhibiting particle migration, Ostwald ripening, and sintering. The nitrogen atoms in the porphyrin macrocycle and the triimidazole organic monomer framework (triazine ring, amine) provide auxiliary coordination sites as molecular scaffolds, enhancing the rigidity of the framework structure. Simultaneously, π-π interactions promote substrate adsorption, accelerate electron transfer, and optimize the electronic structure of the metal active component to improve catalytic activity.

[0043] Based on the same inventive concept, this invention also provides an application of a porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst in the catalytic hydrogenation of nitroaromatic hydrocarbons to prepare aromatic amines. This metal nanoparticle catalyst is prepared by a method for preparing a porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst according to this invention. The nitroaromatic hydrocarbons include 4-nitrophenol, 2-nitrophenol, 4-methyl-3-nitrophenol, and 4-nitroaniline. N One or more of 1,4-methyl-4-nitroaniline, 2,4-dinitrophenol, and 2,4,6-trinitrophenol.

[0044] In the catalytic hydrogenation of nitroaromatic hydrocarbons to prepare aromatic amines, the catalytic hydrogenation reaction can be carried out at room temperature and atmospheric pressure, using sodium citrate, sodium dithionite, or lithium borohydride as the hydrogen source, with a catalyst dosage of 1wt%~10wt%. In the hydrogenation reference reaction of 4-nitrophenol, the metal nanoparticle catalyst of this invention exhibits a pseudo-first-order rate constant of 2.154 min⁻¹. -1 It is 2.2 times that of catalysts containing only imidazolium framework and 36.7 times that of catalysts without porphyrin catalysts.

[0045] Example 1: Platinum nanoparticle catalyst (Pt-1@PNHCF-TIPT) was prepared using 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine (TIPT) as monomer.

[0046] The specific steps are as follows: S1. Synthesis of porphyrin-based nitrogen-heterocyclic carbene precursor framework (PImF-TIPT). See the schematic diagram of the synthetic route for PIMF-TIPT. Figure 2 .

[0047] In a 50 mL round-bottom flask, add 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine (TIPT) (0.349 g, 0.687 mmol), meso-5,10,15,20-tetra(4-bromomethylphenyl)porphyrin (TBPP) (0.509 g, 0.515 mmol), and zinc acetate (Zn(OAc)2). 2H₂O (0.157g, 0.858mmol) and 20mL anhydrous N , N Dimethylformamide (DMF) was magnetically stirred until completely dissolved. Argon gas was bubbled through the flask three times to purge the air. The flask was then sealed and heated in an oil bath at 120°C with stirring for 2 hours. During the reaction, a purplish-black precipitate gradually formed. After the reaction was complete, the flask was allowed to cool naturally to room temperature, filtered, and the precipitate was collected. The precipitate was washed three times with DMF (20 mL each time), then three times with anhydrous ethanol (20 mL each time), and dried under vacuum at 60°C overnight to obtain a purplish-black solid, PImF-TIPT, weighing 0.872 g, with a yield of 98%.

[0048] Detailed characterization data: FT-IR (KBr tablets, cm) -1 Fourier transform infrared (FTIR) spectroscopy tests confirmed that, referring to Figure 3 The carbon-bromine bond stretching vibration peak of TBPP in PImF material (731 cm⁻¹) -1 The disappearance of the 1617cm indicates that the quaternization reaction has been completed. -1 The presence of a distinct carbon-nitrogen double bond characteristic absorption peak at [location missing] confirms the successful formation of the imidazolium group; while the skeletal vibration peak of the porphyrin aromatic ring (1403 cm⁻¹) [is also present]. -1 This confirms that the porphyrin structure has been bonded to the material's framework. (3413cm) -1 The broad absorption band at this point originates from water molecules adsorbed by PImF-TIPT. This phenomenon is consistent with the inherent hydrophilicity of the material and is similar to the physicochemical properties of ionic liquids.

[0049] 13 CCP-MAS NMR: Reference Figure 4 In nuclear magnetic resonance (NMR), δThe characteristic peak at 142.6 ppm is attributed to the carbon atom at position 2 (C2) of the imidazolium ring, confirming the presence of a key functional group, the nitrogen heterocyclic carbene (NHC), which can be used for metal coordination. The signal at 168.9 ppm corresponds to a carbon atom in the triazine ring, indicating the presence of a triiodophenyltriazine (TIPT) structural unit in the molecule. The absorption peak at 52.9 ppm originates from the methylene bridge bond formed by the quaternization reaction of triiodophenyltriazine (TIPT) with tetrakis(4-bromophenyl)porphyrin (TBPP). CH2 This provides evidence that covalent bonds are formed between the two structural units. The broad peak in the 108–155 ppm range is attributed to the aromatic carbon atoms in the porphyrin and imidazole structures, further verifying the molecular framework structure of the material. (Refer to...) Figure 5 .

[0050] Thermogravimetric analysis (TGA) (N2 atmosphere, 10℃ / min): The thermal stability of PIMF-TIPT was characterized using thermogravimetric analysis (TGA) under a nitrogen atmosphere. (Reference) Figure 6 As can be seen from the thermogravimetric curve, the material has no mass loss below 144℃; subsequently, two obvious weight loss processes occur: (1) a mass loss of 11wt% occurs in the range of 144℃~420℃, which is due to the removal of physically adsorbed water and residual solvent, which is consistent with the hydrophilic characteristics brought by the imidazolium ion group in the material; (2) a significant weight loss occurs from 420℃, with a weight loss ratio of 38wt%, corresponding to the thermal decomposition of the framework structure. It is worth noting that PIMF-TIPT can maintain structural integrity below 420℃, and its thermal stability temperature is significantly better than that of imidazolium-based framework materials without porphyrin structure. This is because the porphyrin ring constitutes a rigid π-conjugated framework, which strengthens the main framework structure and thus inhibits thermal degradation. The excellent heat resistance can ensure that the catalyst can stably play a catalytic role in the high-temperature reaction system.

[0051] N2 adsorption-desorption isotherm: Nitrogen adsorption-desorption tests were used to characterize the pore structure of PImF-TIPT materials. BET adsorption spectra and pore size distribution maps are referenced. Figure 7 . Figure 7 (a) is the BET adsorption spectrum of PIMF-TIPT, referring to... Figure 7 (a) The adsorption isotherm exhibits Type IV isotherm characteristics, with a hysteresis loop appearing in the higher relative pressure range (P / P0 > 0.9), indicating that the material possesses a mesoporous structure; however, its BET specific surface area is low, only 2.7 m² / g. The low specific surface area stems from the flexible material framework and the presence of bromide ions (Br₂) filling the pores. - This hinders gas molecules from entering the pores and compresses the pore volume. Although the material has limited porosity, its ionic sites and metal coordination functional groups, provided by the imidazolyl and porphyrin structural units, play a more crucial role in immobilizing metal nanoparticles (MNPs) than its high specific surface area. Figure 7 (b) is the pore size distribution diagram of PImF-TIPT, referencing Figure 7 (b) The pore size distribution curves show that PIMF-TIPT is predominantly mesoporous. The most probable pore size corresponding to the main peak in the curve is approximately 20 nm, falling within the mesoporous pore size range (2–50 nm). This result is consistent with the average adsorption pore size (18.6 nm) and the average BJH adsorption pore size (26.4 nm) calculated by the BET method, further confirming that PIMF-TIPT is a mesoporous material. Furthermore, after the pore size exceeds 20 nm, the differential pore volume (dV / dw) gradually decreases with increasing pore size, indicating a wide range of mesoporous pore size distribution. This predominantly mesoporous pore structure is beneficial for mass transport during catalysis and adsorption processes, and the mesoporous channels can promote the diffusion and mass transfer of reactants and products.

[0052] XPS full spectrum: X-ray photoelectron spectroscopy (XPS) can characterize the surface elemental composition and chemical bonding environment of PImF-TIPT materials. The XPS spectrum of PImF-TIPT is shown below. Figure 8 . Reference Figure 8 (a) Full-spectrum XPS analysis clearly shows the characteristic peaks of all target elements in the synthesized framework material: the high-intensity peak at 284.8 eV belongs to the carbon 1s orbital, the peak at 398.8 eV to the nitrogen 1s orbital, the peak at 531.8 eV to the oxygen 1s orbital (mainly from water and oxygen physically adsorbed on the sample surface at room temperature), the peak at 67.8 eV to the bromine 3d orbital, and the characteristic peak of the zinc 3p orbital at 88.8 eV originates from the zinc porphyrin structural building unit. These results preliminarily prove that the target framework material with the predetermined elemental composition has been successfully synthesized. (Refer to...) Figure 8 (b) The high-resolution 1s carbon spectrum can be fitted with two characteristic peaks: the main peak at 284.8 eV originates from the sp² / sp³ hybridized carbon in the carbon-carbon and carbon-hydrogen bonds, corresponding to the aromatic skeleton of the porphyrin group, the benzene ring, and the alkyl linkage structure within the framework; the weaker characteristic peak at 286.2 eV is attributed to the imidazolium cation (C=N). + The positively charged carbon atom of the ion matched the nitrogen peaks corresponding to the like ionic group, directly confirming the successful construction of the cationic imidazolium structure. (Refer to...) Figure 8 (c) The nitrogen 1s spectrum contains two main characteristic peaks: the main peak at 401.5 eV is attributed to the imidazolium cation (C=N). + The peak at 398.8 eV corresponds to the positively charged nitrogen atom in the ionic structure; the peak at 398.8 eV corresponds to the neutral nitrogen atom within the imidazole ring and the porphyrin macrocycle, further confirming the successful formation of the imidazole-onium structure. (Refer to...) Figure 8 (d) The 3d spectrum of bromine shows a characteristic peak at 68.5 eV, which corresponds to the bromide ion (Br) introduced by the quaternization reaction. -The matching proves the presence of bromomethyl groups derived from TBPP and anions used to balance the charge within the framework.

[0053] FESEM: Field emission scanning electron microscopy (FESEM) characterization results visually reveal the microstructure characteristics of polyimidazolium organic framework material (PImF-TIPT), providing key morphological evidence for elucidating its structural advantages as a carrier of platinum nanoparticles (Pt NPs). Figure 9 This is a SEM image of PImF-TIPT. (Refer to...) Figure 9 (a) Low-magnification morphology images show that PImF-TIPT exhibits excellent monodispersity, regular spherical particles with a narrow particle size distribution and an average particle size of approximately 1.5 μm, without significant particle agglomeration or irregular aggregate formation. This result confirms that a one-step quaternization reaction of TBPP and TIPT followed by zinc ion coordination modification can precisely control the nucleation and growth kinetics of the material, enabling the reproducible preparation of uniformly morphological microspheres. (Refer to...) Figure 9 (b) The high-magnification morphology image further shows that the surface of a single PImF-TIPT microsphere is composed of a large number of closely packed secondary nanoparticles, exhibiting a rough nanoscale surface structure. This hierarchical porous structure can not only increase the density of surface active sites, but also provide sufficient physical anchoring points and spatial confinement environment for the immobilization and stable fixation of platinum nanoparticles.

[0054] S2: Synthesis of porphyrin-based platinum-nitrogen heterocyclic carbene framework (Pt 2+ @PNHCF-TIPT intermediate).

[0055] In a 50 mL round-bottom flask, add PimF-TIPT (43.2 mg, 0.100 mmol, based on imidazolium units), platinum bromide (PtBr2, 35.5 mg, 0.100 mmol), and anhydrous potassium carbonate (27.6 mg, 0.200 mmol), then add 20 mL of anhydrous acetonitrile and stir magnetically until homogeneous. Purge the air three times with argon gas, seal the flask, and heat and stir in an oil bath at 70 °C for 4 h to produce Pt. 2+ @PNHCF-TIPT intermediate.

[0056] S3: Synthesis of porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalysts (Pt-1@PNHCF-TIPT catalyst). A schematic diagram of the synthetic route from PIMF-TIPT to Pt-1@PNHCF-TIPT is shown below. Figure 10 .

[0057] The reaction system was cooled to room temperature, and 25 mL of freshly prepared sodium citrate (108 mg, 0.500 mmol) ethanol solution was slowly added dropwise using a syringe. During the addition, the solution rapidly turned black. After the addition was complete, the reaction was stirred for another 1 h at room temperature. After the reaction was complete, the solid was separated by centrifugation, and the precipitate was washed three times with anhydrous methanol (5 mL each time). It was then dried under vacuum at 60 °C to obtain a black solid powder, Pt-1@PNHCF-TIPT, weighing 55.2 mg.

[0058] Detailed characterization data: 13 C CP-MAS NMR (150MHz): Reference Figure 11 , δ The characteristic peak at 130.1 ppm is attributed to aromatic carbons on the porphyrin and benzene rings, confirming that the material's framework structure is preserved. The carbon signals at 50.6 ppm (C1) and the remaining carbon signals correspond to carbon atoms in different chemical environments within the cross-linked structure. These results indicate that the immobilized platinum nanoparticles do not disrupt the main chemical framework of PNHCF-TIPT and can retain various functional groups crucial for metal coordination.

[0059] XPS Full Spectrum: XPS spectrum of Pt-1@PNHCF-TIPT (refer to the original text) Figure 12 . Reference Figure 12 (a) The XPS spectra clearly show the characteristic diffraction peaks corresponding to carbon 1s, nitrogen 1s, platinum 4f, platinum 4d, and platinum 4p, proving that platinum species have been successfully doped into the PNHCF-TIPT framework. (Refer to...) Figure 12 (b) The high-resolution 4f spectrum of platinum clearly shows the chemical valence state of the immobilized platinum nanoparticles: the two characteristic peaks at 71.3 eV and 74.7 eV correspond to the 4f of zero-valent platinum, respectively. 7 / 2 With 4f 5 / 2 The orbital indicates that the divalent platinum precursor was successfully converted to zero-valent platinum after reduction with sodium borohydride. (Refer to...) Figure 12 (c) The high-resolution 1s carbon spectrum, after peak fitting, can be separated into three independent characteristic peaks, indicating that the chemical environment of carbon underwent subtle but crucial changes after platinum immobilization. The main peak at 284.8 eV belongs to sp bonds composed of carbon-carbon and carbon-hydrogen bonds. 2 / sp 3The hybrid carbon exhibits spectroscopic characteristics consistent with the raw material PImF-TIPT. The characteristic peak at 285.9 eV corresponds to carbon atoms in the nitrogen-heterocyclic carbene ring, triazine ring, and porphyrin macrocyclic structure, confirming the retention of these organic cyclic structures during platinum anchoring. Crucially, a new characteristic peak appears at 289.1 eV, clearly attributable to the carbon-platinum covalent bond formed between the carbene carbon atom of the nitrogen-heterocyclic carbene structure and metallic platinum. This direct covalent bonding firmly anchors platinum nanoparticles to the support surface, representing the core mechanism for inhibiting particle migration and Ostwald ripening during the catalytic reaction. (Reference) Figure 12 (d) The high-resolution 1s N spectrum further confirms the existence of the nitrogen heterocyclic carbene-platinum coordination interaction. The nitrogen 1s spectrum of the raw material PImF-TIPT contains two characteristic peaks: 398.8 eV corresponds to the nonionic nitrogen atom within the imidazolium ring and porphyrin macrocycle, and 401.5 eV corresponds to the cationic nitrogen in the imidazolium group; while the nitrogen 1s spectrum of the Pt-1@PNHCF-TIPT sample only shows a single main peak at 399.0 eV. This spectral change is caused by two coupled reactions: on the one hand, the imidazolium cation undergoes deprotonation to generate a neutral nitrogen heterocyclic carbene ligand, causing the characteristic peak of the high binding energy cationic nitrogen at 401.5 eV to completely disappear; on the other hand, the carbene carbon of the nitrogen heterocyclic carbene coordinates with platinum, causing the characteristic peak corresponding to neutral nitrogen to shift positively by 0.2 eV. This shift originates from the σ electron donor interaction of the carbene carbon to platinum, with electrons transferred through the conjugated imidazolium ring, reducing the electron cloud density of adjacent nitrogen atoms. The above spectroscopic changes directly demonstrate that there is a strong donor-acceptor interaction between nitrogen heterocyclic carbene and platinum, which can stabilize platinum nanoparticles and regulate the electronic structure of platinum, thereby improving hydrogenation catalytic performance.

[0060] XRD: Reference Figure 13 The X-ray diffraction (XRD) pattern of Pt-1@PNHCF showed sharp diffraction peaks at 39.7°, 46.1°, 67.4°, 81.3°, and 85.7°, which matched the (111), (200), (220), (311), and (222) crystal planes of face-centered cubic (FCC) platinum, respectively. These characteristic diffraction peaks confirmed that the product formed crystalline platinum nanoparticles with a regular face-centered cubic crystal structure. This characterization result not only verified the crystallinity and metallic valence state of the platinum nanoparticles, but also provided key evidence for the phase composition and structural integrity of the material.

[0061] FESEM (Field Emission Scanning Electron Microscopy): Figure 14 This is the SEM spectrum of Pt-1@PNHCF-TIPT. (Refer to...) Figure 14(a) Low-magnification field emission scanning electron microscopy (FESEM) images show that Pt-1@PNHCF-TIPT inherits the highly monodisperse spherical morphology of the precursor PIMF, with an average particle size of approximately 1.5 μm, and no obvious structural collapse or irregular aggregation. This result indicates that the entire platinum immobilization process, including deprotonation and cyclization of nitrogen heterocyclic carbene, coordination complexation of divalent platinum, and reduction by sodium borohydride, does not destroy the macroscopic spherical structure of the support framework. (Refer to...) Figure 14 (b) High-magnification field emission scanning electron microscope images further show that the surface roughness of PNHCF-TIPT microspheres is significantly improved after platinum is immobilized, and a large number of nanoscale protrusions are uniformly distributed on the entire surface of the particles. These protrusions are the immobilized platinum nanoparticles. The uniform dispersion of the particles also proves that the nitrogen heterocyclic carbene and porphyrin coordination sites on the surface of the support are uniformly exposed, which can provide sufficient anchoring points for the nucleation and growth of platinum.

[0062] ICP-MS: Inductively coupled plasma mass spectrometry (ICP-MS) analysis showed that the platinum loading was 26.4 wt%. This ratio achieves a good balance between performance and cost: it can provide sufficient active sites to ensure excellent catalytic activity, while avoiding excessive consumption of precious metals, thereby reducing preparation costs.

[0063] TEM: Reference Figure 15 Transmission electron microscopy (TEM) images allow for direct, high-resolution observation of platinum nanoparticles within the PNHCF-TIPT matrix: the platinum nanoparticles are discretely and uniformly dispersed within the support, without obvious particle aggregation or phase separation. (Reference) Figure 16 The results show that the platinum nanoparticles have an extremely narrow particle size distribution range, with an average particle size of 2.20 ± 0.02 nm. This ultrafine and highly uniform particle size characteristic originates from the synergistic stabilizing effect of the PNHCF-TIPT framework: the nitrogen heterocyclic carbene groups restrict the growth of platinum crystal nuclei through strong covalent bond anchoring, while the porphyrin units inhibit excessive particle growth through auxiliary coordination and spatial confinement effects.

[0064] EDX elemental mapping: The four elements C, N, Zn and Pt are uniformly distributed throughout the catalyst particles without local enrichment, proving that platinum nanoparticles are atomically uniformly dispersed on the support surface.

[0065] Example 2: Pt-1@PNHCF-TIPB was prepared using 1,3,5-tris(4-imidazolylphenyl)benzene (TIPB) as a monomer.

[0066] Except for replacing TIPT in step S1 of Example 1 with an equimolar amount of 1,3,5-tris(4-imidazolylphenyl)benzene (TIPB, 0.347 g, 0.687 mmol), the remaining steps were exactly the same as in Example 1, yielding a black solid powder Pt-1@PNHCF-TIPB.

[0067] Example 3: Preparation of Pt-1@PNHCF-TIB using 1,3,5-triimidazolylbenzene (TIB) as a monomer.

[0068] Except for replacing TIPT in step S1 of Example 1 with an equimolar amount of 1,3,5-triimidazolebenzene (TIB, 0.190 g, 0.687 mmol), the remaining steps were exactly the same as in Example 1, yielding a black solid powder Pt-1@PNHCF-TIB, weighing 47.8 mg.

[0069] Example 4: Preparation of Pt-1@PNHCF-TIPA using tri-(4-imidazolylphenyl)amine (TIPA) as monomer.

[0070] Except for replacing TIPT in step S1 of Example 1 with an equimolar amount of tri-(4-imidazolylphenyl)amine (TIPA, 0.305 g, 0.687 mmol), the remaining steps were exactly the same as in Example 1, yielding a black solid powder Pt-1@PNHCF-TIPA.

[0071] Example 5: Pt-1@PNHCF-TIPM was prepared using tri-(4-imidazolylphenyl)methane (TIPM) as a monomer.

[0072] Except for replacing TIPT in step S1 of Example 1 with an equimolar amount of tri-(4-imidazolylphenyl)methane (TIPM, 0.304 g, 0.687 mmol), the remaining steps were exactly the same as in Example 1, yielding a black solid powder Pt-1@PNHCF-TIPM.

[0073] Example 6: Pd-1@P2NHCF-TIPT was prepared using 5,15-dibromomethyl-10,20-diphenylporphyrin (P2) as a monomer.

[0074] In Example 1, meso-5,10,15,20-tetratetra(4-bromomethylphenyl)porphyrin in step S1 was replaced with an equimolar amount of 5,15-dibromomethyl-10,20-diphenylporphyrin (P2, 0.648 g, 1.031 mmol), and platinum bromide in step S2 was replaced with palladium bromide. The remaining main steps were the same as in Example 1, and a black solid powder Pd-1@P2NHCF-TIPT was obtained.

[0075] Example 7: Preparation of Cu-1@P3NHCF-TIPT using 5,15-bis(4-bromomethylphenyl)porphyrin (P3) as monomer.

[0076] In Example 1, meso-5,10,15,20-tetratetra(4-bromomethylphenyl)porphyrin in step S1 was replaced with an equimolar amount of 5,15-di(4-bromomethylphenyl)porphyrin (P3, 0.648 g, 1.031 mmol), and platinum bromide in step S2 was replaced with cuprous iodide. The remaining main steps were the same as in Example 1, and a black solid powder Cu-1@P3NHCF-TIPT was obtained, weighing 47.8 mg.

[0077] Example 8: Au-1@P4NHCF-TIPT was prepared using 5,15-bis(4-bromomethylphenyl)-10,20-diphenylporphyrin (P4) as a monomer.

[0078] In Example 1, meso-5,10,15,20-tetra(4-bromomethylphenyl)porphyrin in step S1 was replaced with an equimolar amount of 5,15-di(4-bromomethylphenyl)-10,20-diphenylporphyrin (P4, 0.825 g, 1.031 mmol), and platinum bromide in step S2 was replaced with tetrahydrothiophene gold chloride. The remaining main steps were the same as in Example 1, and a black solid powder Au-1@P4NHCF-TIPT was obtained.

[0079] Comparative Example 1: Synthesis of supportless platinum nanoparticles.

[0080] Without a support, the synthesized platinum nanoparticles undergo violent and irregular aggregation, forming large aggregates with sizes exceeding tens of nanometers and irregular morphologies. This phenomenon stems from the extremely high surface energy of the ultrafine platinum nanoparticles, which spontaneously fuse to reduce the total surface energy of the system. These results clearly demonstrate that unsupported platinum nanoparticles have poor thermodynamic stability and cannot be directly used as high-performance heterogeneous catalysts, thus confirming the crucial importance of using a stable support to immobilize platinum nanoparticles.

[0081] Comparative Example 2: Synthesis of Pt-1 / PImF-TIPT catalyst (without NHC covalent anchoring).

[0082] This comparative study investigated the effect of NHC covalent anchoring on the dispersibility and catalytic performance of platinum nanoparticles. Except for the absence of anhydrous potassium carbonate, the steps were identical to those in Example 1, yielding a black solid powder, Pt-1 / PImF-TIPT, weighing 48.7 mg. For Pt-1 / PImF-TIPT prepared without deprotonation of the imidazolium group using potassium carbonate, transmission electron microscopy (TEM) images showed that almost all platinum nanoparticles were aggregated on the surface of the PIMF-TIPT microspheres, with no dispersed individual nanoparticles observed. In this control sample, the platinum nanoparticles were immobilized only through weak physical adsorption and ionic interactions between platinum bromide and the cationic imidazolium framework, without forming strong N-heterocyclic carbene-platinum covalent bonds. Due to the lack of strong chemical anchoring sites, the nucleation and growth of platinum were unconstrained, ultimately leading to large-scale agglomeration of the nanoparticles. The above comparison results clearly confirm that the generation of nitrogen heterocyclic carbene ligands through imidazolium deprotonation is a necessary condition for achieving uniform dispersion of platinum nanoparticles. The strong carbon-platinum covalent bond can provide the main anchoring force, preventing the migration and aggregation of nanoparticles.

[0083] Comparative Example 3: Synthesis of Pt-1@NHCF-TIPT catalyst (without porphyrin structure enhancement).

[0084] This comparative study investigated the effects of porphyrin structure enhancement on the platinum nanoparticle loading, size control, and catalytic performance. A porphyrin-free nitrogen-containing heterocyclic carbene precursor framework (ImF-TIPT, prepared by the quaternization reaction of TIPT with 1,4-dibromomethylbenzene) was used instead of PImF-TIPT. The remaining steps were identical to those in Example 1, yielding a black solid powder, Pt-1@NHCF-TIPT. Surface scanning spectroscopy of platinum elements showed localized trace platinum enrichment, consistent with the results indicating a wider particle size distribution. Inductively coupled plasma mass spectrometry (ICP-MS) further revealed a significant difference in platinum loading between the two supports: under the same preparation conditions, Pt-1@PNHCF-TIPT achieved a platinum loading fraction of 26.4 wt%, while Pt-1@NHCF-TIPT only achieved 20.4 wt%. These differences demonstrate that the porphyrin structure not only provides auxiliary coordination sites for platinum atoms but also enhances the overall platinum adsorption capacity of the support framework, achieving higher metal loading while ensuring uniform particle dispersion. The lack of porphyrin structure causes the support to lose its rigid π-conjugated framework and additional nitrogen coordination sites, weakening the metal-support interaction. This makes it difficult to precisely control the nucleation and growth process of platinum particles, ultimately resulting in a wider particle size distribution and a decrease in metal loading.

[0085] Comparative Example 4: Synthesis of Pt-0.5@PNHCF-TIPT catalyst (low Pt immobilization).

[0086] This comparative study investigated the effect of Pt loading on catalytic performance. Except for changing the amount of platinum bromide to 17.7 mg (0.050 mmol), the remaining steps were identical to those in Example 1, yielding a black solid powder, Pt-0.5@PNHCF-TIPT, with a yield of 51.4 mg. The average particle size of the platinum nanoparticles was 1.85 ± 0.02 nm, but the particle density was low, resulting in insufficient active sites per unit area.

[0087] Comparative Example 5: Synthesis of Pt-3@PNHCF-TIPT catalyst (high Pt immobilization).

[0088] This comparative study investigated the effect of excess Pt support on catalytic performance. Except for changing the amount of platinum bromide to 106.5 mg (0.300 mmol) and the amount of sodium citrate to 216 mg (1.000 mmol), the remaining steps were identical to those in Example 1, yielding a black solid powder Pt-3@PNHCF-TIPT with a yield of 90.0 mg. The Pt support was 32.5 wt%. The average particle size of the platinum nanoparticles increased to 2.44 ± 0.02 nm, the size distribution broadened, and significant local agglomeration was observed, demonstrating that excess Pt leads to particle agglomeration.

[0089] Example 9: Catalytic hydrogenation performance test of 4-nitrophenol.

[0090] This embodiment details the performance evaluation method of the catalyst of the present invention in the hydrogenation reaction of nitroaromatics. Using 4-nitrophenol as a reference substrate, the catalytic activity of catalysts prepared with different triimidazole monomers and different immobilization methods was tested.

[0091] Experimental steps: In a 100 mL quartz cuvette, 40 mL of 0.050 mM 4-nitrophenol aqueous solution was added and magnetically stirred until homogeneous. 76 mg of sodium borohydride (2 mmol) was added and stirred until completely dissolved; the solution was then bright yellow with a strong characteristic absorption peak at 400 nm. 4 mg of the catalyst prepared in the above example was added to initiate the reaction. The initial spectrum was immediately scanned in the 250-600 nm wavelength range using a UV-Vis spectrophotometer. Scans were then performed every 30 s until the absorption peak at 400 nm completely disappeared, and the characteristic absorption peak of 4-aminophenol appeared at 317 nm. The catalytic performance comparison results of catalysts prepared with different triimidazole monomers and different immobilization methods are shown in Table 1.

[0092] Table 1

[0093] As shown in Table 1, all catalysts prepared using the technical solution of this invention exhibit excellent catalytic performance. Among them, Pt-1@PNHCF-TIPT, prepared using 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine as the monomer, shows the highest catalytic activity, with a rate constant of 2.017 min. -1 The activity of the catalyst prepared using 1,3,5-triimidazolebenzene as a monomer is 36.7 times that of the single NHC framework catalyst, fully demonstrating the advantages of electronic regulation. The catalyst prepared using 1,3,5-triimidazolebenzene as a monomer has slightly lower activity, but it is still far superior to the comparative catalyst. This fully demonstrates that the triimidazole monomers of this invention have a wide range of selection and can all achieve efficient and stable immobilization of platinum nanoparticles and excellent catalytic performance.

[0094] Example 10: Catalyst cycle stability test.

[0095] This embodiment uses Pt-1@PNHCF-TIPT prepared in Representative Example 1 as an example to evaluate the recycling performance of the catalyst of the present invention. The specific steps are as follows: The Pt-1@PNHCF-TIPT catalyst recovered from the reaction in Example 9 was centrifuged, washed three times with methanol (5 mL each time), and then washed three times with deionized water (5 mL each time). The recovered catalyst was then used for the next catalytic reaction under the same conditions as in Example 9, for a total of eight cycles. The time to complete conversion of 4-nitrophenol and the rate constant were recorded for each reaction.

[0096] The cycling stability test results of the Pt-1@PNHCF-TIPT catalyst are shown in Table 2. After 8 consecutive cycles, the Pt-1@PNHCF-TIPT catalyst retained 99.2% of the initial conversion and 98.1% of the initial rate constant. TEM characterization after cycling showed that the platinum nanoparticles remained uniformly dispersed with no significant change in average particle size; XPS characterization did not detect significant Pt. 2+ The signal; ICP-MS detection showed that the Pt content in the reaction solution was less than 0.01 ppm, proving that there was no significant loss of active components or oxidative inactivation.

[0097] Table 2

[0098] Example 11: Substrate universality test.

[0099] This example uses Pt-1@PNHCF-TIPT prepared in Representative Example 1 as an example to evaluate the catalytic applicability of the catalyst of the present invention to different substituted nitro aromatics. The same reaction conditions as in Example 9 were used, and the reaction progress was monitored at the characteristic absorption wavelength for each substrate.

[0100] Experimental results: Pt-1@PNHCF-TIPT exhibited excellent catalytic activity for a variety of substituted nitroaromatics with different structures. All substrates were completely converted to the corresponding aromatic amines without the formation of byproducts. Detailed test data on the performance of Pt-1@PNHCF-TIPT in catalyzing the hydrogenation of different nitroaromatics are shown in Table 3.

[0101] Table 3

[0102] As shown in Table 3, Pt-1@PNHCF-TIPT exhibits significantly higher catalytic activity for nitroaromatics containing electron-donating substituents than for substrates containing electron-withdrawing substituents, with 4-nitroaniline showing the highest catalytic activity. k 1 = 5.638 min -1 This is because the strong electron-donating effect of the amino group increases the electron density of the nitro group, which is beneficial for its nucleophilic reduction; the position of the substituent has a significant impact on the catalytic activity, with para-substituted 4-nitrophenol showing higher activity than ortho-substituted 2-nitrophenol, which is related to the steric hindrance effect; polynitro-substituted substrates have relatively low catalytic activity, among which 2,4-dinitrophenol has the lowest activity. k 1 = 0.019min -1 This is due to the combined effect of the strong electron-withdrawing effect of the two nitro groups and the large steric hindrance.

[0103] The above description, in conjunction with specific preferred embodiments, provides a further detailed explanation of the present invention. It should not be construed that the specific implementation of the present invention is limited to these descriptions. For those skilled in the art, various simple deductions or substitutions can be made without departing from the concept of the present invention, and all such modifications and substitutions should be considered within the scope of protection of the present invention.

Claims

1. A porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst, characterized in that, The metal nanoparticle catalyst contains a porphyrin-based nitrogen heterocyclic carbene framework, in which metal nanoparticles are anchored to the nitrogen heterocyclic carbene and porphyrin units.

2. The porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst according to claim 1, characterized in that, The structure of the metal nanoparticle catalyst is shown in general formula I: Ⅰ In the general formula I, M represents metal nanoparticles.

3. The porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst according to claim 1, characterized in that, The metal nanoparticles include one or more of platinum, palladium, gold, and copper.

4. A method for preparing a metal nanoparticle catalyst immobilized on a porphyrin-based nitrogen heterocyclic carbene framework as described in claim 1, characterized in that, Including the following steps: S1. A porphyrin-based nitrogen-heterocyclic carbene precursor framework is synthesized by dissolving bromomethylporphyrin derivatives and triimidazole organic monomers in a polar aprotic solvent and then reacting them with a quaternization reaction. S2. The porphyrin-based nitrogen heterocyclic carbene precursor framework and metal salt are dissolved in a polar aprotic solvent and deprotonated under alkaline conditions to immobilize the metal active component and synthesize the porphyrin-based metal nitrogen heterocyclic carbene framework. S3. The porphyrin-based metal-nitrogen heterocyclic carbene framework is used to synthesize a porphyrin-based nitrogen-nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst via a reduction reaction.

5. The method for preparing the porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst according to claim 4, characterized in that, In step S1: the molar ratio of the bromomethylporphyrin derivative to the triimidazole organic monomer is 1:(0.5~1.5), the reaction temperature is 60~140℃, and the reaction time is 1~2h.

6. The method for preparing the porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst according to claim 4, characterized in that, The bromomethylporphyrin derivatives include one or more of meso-5,10,15,20-tetra(4-bromomethylphenyl)porphyrin, 5,15-dibromomethyl-10,20-diphenylporphyrin, 5,10,5,20-tetra(3,5-dibromomethylphenyl)porphyrin, 5,15-bis(4-bromomethylphenyl)porphyrin, and 5,15-bis(4-bromomethylphenyl)-10,20-diphenylporphyrin.

7. The method for preparing the porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst according to claim 4, characterized in that, The triimidazolyl organic monomers include one or more of 1,3,5-tris(4-imidazolylphenyl)benzene, 2,4,6-tris-(4-imidazolylphenyl)-1,3,5-triazine, 1,3,5-triimidazolylbenzene, tris-(4-imidazolylphenyl)amine, and tris-(4-imidazolylphenyl)methane.

8. The method for preparing a porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst according to claim 4, characterized in that, In step S2: the molar ratio of the porphyrin-nitrogen heterocyclic carbene precursor framework to the metal salt is 1:(0.5~3), the reaction temperature is 50~80℃, and the reaction time is 2~4h.

9. The method for preparing the porphyrin-based nitrogen heterocyclic carbene framework-supported metal nanoparticle catalyst according to claim 4, characterized in that, In step S3: the reducing agent for the reduction reaction is sodium citrate, sodium dithionite or lithium borohydride, the reaction temperature is 10~40℃, the reaction time is 0.5~2h, and the metal nanoparticle catalyst immobilized on the porphyrin-based nitrogen heterocyclic carbene framework is obtained after centrifugation, washing and drying.

10. The application of a metal nanoparticle catalyst supported on a porphyrin-nitro-heterocyclic carbene framework as described in any one of claims 1 to 3, or a metal nanoparticle catalyst supported on a porphyrin-nitro-heterocyclic carbene framework prepared by any one of claims 4 to 9, in the catalytic hydrogenation of nitroaromatic hydrocarbons to prepare aromatic amines.

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