Ionized molecular cage supported palladium catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of ammonia preparation through electrocatalytic reduction of nitrate radicals, and particularly discloses an ionized molecular cage supported palladium catalyst and a preparation method and application thereof.The ionized molecular cage supported palladium catalyst comprises a carrier and an active component, and the carrier comprises an amorphous ionized molecular cage; the active component comprises a palladium nanocluster with the particle size of 0.6-1.4 nm, and the palladium nanocluster is packaged in an inner cavity of the ionized molecular cage; the particle size of the ionized molecular cage palladium catalyst is 200-2000 nm, and the loading capacity of palladium is 0.3-2.5 wt%. The catalyst provided by the invention can realize efficient electroreduction of nitrate and selective synthesis of ammonia, can ensure the yield of ammonia and the Faraday efficiency of the ammonia preparation process, and can improve the repeated utilization rate of the catalyst, thereby controlling the cost.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic reduction of nitrate to ammonia technology, specifically relating to an ionized molecular cage supported palladium catalyst, its preparation method, and its application. Background Technology

[0002] With the energy crisis worsening, the search for sustainable alternatives to fossil fuels is becoming increasingly urgent. Ammonia (NH3) has attracted widespread attention due to its extensive applications in agriculture, medicine, and the textile industry. However, industrial production of NH3 is generally achieved through the high-temperature, high-pressure Haber-Bosch process. Electrochemical nitrogen reduction reaction (NRR) is a new technology that utilizes atmospheric N2 and water to generate NH3, but it suffers from problems such as low N2 solubility and the difficulty in breaking the inert nitrogen-nitrogen triple bond. Compared to NRR, electrocatalytic nitrate reduction reaction (NO3RR) has relatively lower N=O bond dissociation energy, higher nitrate solubility in water, and faster liquid-solid interface kinetics, making it more practical for industrial application. Meanwhile, NO3... - As an environmental pollutant, NO3RR is widely present in low-level radioactive wastewater, industrial wastewater, and contaminated groundwater. Therefore, the NO3RR process not only provides a green route for ammonia synthesis but also solves the environmental pollution problem. However, NO3RR has complex 8e-phase flow characteristics. - The process and other competing reactions result in poor activity and selectivity for NO3RR. Therefore, it is necessary to investigate suitable catalysts for NO3RR to improve Faraday efficiency and ammonia selectivity.

[0003] To date, noble metal-based materials (Au, Pd, Rh, etc.) have been considered effective catalysts for NO3RR. However, noble metals and materials suffer from low atom utilization due to their stable large-particle metal properties, while single-atom noble metals provide ample active sites but are prone to aggregation and difficult to reuse. Therefore, it is necessary to develop a new catalyst to improve reusability while ensuring ammonia yield and Faraday efficiency. Summary of the Invention

[0004] The purpose of this invention is to provide an ionized molecular cage supported palladium catalyst, its preparation method, and its application. In-situ encapsulation of Pd nanoclusters is achieved within the large-sized cavity of the molecular cage. This catalyst can achieve efficient electroreduction of nitrate and selective synthesis of ammonia under ambient temperature and pressure argon atmosphere, ensuring ammonia yield and Faradaic efficiency in the ammonia production process, and improving the reusability of the catalyst, thereby controlling costs.

[0005] To achieve the above objectives, the present invention employs the following technical solution: According to a first aspect of the present invention, an ionized molecular cage supported palladium catalyst is provided, comprising a support and an active component; the support comprises an ionized molecular cage, the ionized molecular cage being amorphous; the active component is palladium nanoclusters, the palladium nanoclusters having a particle size of 0.6-1.4 nm, the palladium nanoclusters being encapsulated in the internal cavity of the ionized molecular cage; The ionized molecular cage palladium catalyst has a particle size of 200-2000 nm and a palladium loading of 0.3-2.5 wt%.

[0006] According to one embodiment of the present invention, the ionized molecular cage supported palladium catalyst has the molecular formula Pd. QA-Cage 24+ -24Cl (abbreviated as Pd) QA-Cage 24+ The molecular formula of the ionized molecular cage is QA-Cage. 24+ -24Cl (abbreviated as QA-Cage) 24+ ).

[0007] Using the above technical solution, an ionized molecular cage supported palladium catalyst Pd is provided. QA-Cage 24+ Palladium nanoclusters are encapsulated in QA-Cage 24+ The internal cavity not only restricts the size of the nanoclusters but also isolates individual clusters, making them difficult to aggregate during the reaction process. This ensures the stability of efficient utilization of active metal sites and thus improves the reusability of the catalyst.

[0008] In the process of reducing nitrate to produce ammonia, QA-Cage 24+ Free radicals can be generated under electroinduced conditions, catalyzing water splitting to produce H•. The H• overflows to nearby Pd sites, promoting NO3- production. - The hydrogenation, and QA-Cage 24+ It can also regulate the electronic structure of Pd clusters and promote NO3- production. - Enrichment on the Pd surface enables an increase in the yield and Faradaic efficiency of the reduced nitrate to ammonia reaction under ambient temperature and pressure conditions; furthermore, this catalyst Pd QA-Cage 24+ Even after repeated use, the reaction process can still maintain its yield and Faraday efficiency, resulting in high reusability and helping to reduce cost input.

[0009] According to one embodiment of the present invention, the ionized molecular cage is obtained by reducing and ionizing an organic cage precursor; the organic cage precursor is obtained by amine-aldehyde condensation reaction of tris(4-formylphenyl)amine and (R,R)cyclohexanediamine.

[0010] According to a second aspect of the present invention, a method for preparing an ionized molecular cage supported palladium catalyst is provided, comprising the following steps: Synthetic organic cage precursor imine Cage 1; The organic cage precursor imine Cage 1 was reduced to obtain the reduced organic cage material amine Cage 1. The reduced organic cage material amine Cage1 after reduction treatment was ionized to obtain ionized molecular cages QA-Cage. 24+ ; Using an ionized molecular cage as a carrier and palladium nanoclusters as the active component, palladium nanoclusters are encapsulated in the internal cavity of the ionized molecular cage to obtain an ionized molecular cage supported palladium catalyst.

[0011] According to one embodiment of the present invention, the step of synthesizing the organic cage precursor imine Cage 1 includes: Tris(4-formylphenyl)amine was dissolved in dichloromethane to obtain an aldehyde solution; (R,R)cyclohexanediamine was dissolved in dichloromethane to obtain an amine solution. The amine solution is injected into the aldehyde solution, allowed to stand, and an amine-aldehyde condensation reaction is carried out to obtain an organic cage precursor. The molar ratio of tris(4-formylphenyl)amine to (R,R)cyclohexanediamine is 0.8-4:1.2-6.

[0012] According to one embodiment of the present invention, after the amine-aldehyde condensation reaction is completed, the process further includes the steps of filtering to obtain crystals, washing and drying the crystals, wherein dichloromethane is used in the washing process and the drying temperature is 0-40 °C.

[0013] Preferably, during the amine-aldehyde condensation reaction, the reaction temperature is 0-25 ℃ and the standing time is 12-72 h.

[0014] Preferably, during the washing and drying process of the crystals, dichloromethane is used for washing 3-5 times, and the drying temperature is 0-40 ℃.

[0015] According to one embodiment of the present invention, in the step of reducing the organic cage precursor imine Cage 1, NaBH4 is used as a reducing agent; the mass ratio of NaBH4 to the organic cage precursor is 1.6-5:7-22.

[0016] According to one embodiment of the present invention, before reducing the organic cage precursor, the method further includes a step of dissolving the organic cage precursor in a mixture of chloroform and methanol to obtain a precursor suspension. The mass-to-volume ratio of the organic cage precursor to chloroform was 10-35 mg: 1-4 mL; the volume ratio of chloroform to methanol was 1: 1-5.

[0017] Preferably, the reduction process of the organic cage precursor imine Cage 1 is carried out under a nitrogen or argon atmosphere at a reaction temperature of 0-30 °C.

[0018] Specifically, the steps of reducing the organic cage precursor amine Cage 1 to obtain the reduced organic cage precursor, i.e., the reduced organic cage material amine Cage 1, include: At room temperature, imine Cage 1 was dissolved in a mixture of chloroform and methanol to obtain a precursor suspension; the volume ratio of chloroform to methanol was 1:1-3. NaBH4 was slowly added to the obtained precursor suspension, and the mixture was stirred and reacted overnight. After the reaction was completed, the sample was extracted, washed, dried and filtered to obtain crystals. After washing and drying, the reduced organic cage material amineCage 1 was obtained.

[0019] Further, after the reaction is complete, chloroform and water with a volume ratio of 1-3:1 are added to the reaction system, and the mass-volume ratio of imineCage 1 to water is 5-10 mg: 1 mL. After stirring for 10-40 min, the mixture is separated using a separatory funnel. The aqueous layer is extracted with chloroform, and the organic layer is washed with water, dried with anhydrous Na2SO4, filtered, and vacuum dried at 40-60 ℃ for 4-8 h to obtain the reduced imine Cage 1, i.e., amine Cage 1, which is a pale yellow powder.

[0020] According to one embodiment of the present invention, in the step of ionizing the reduced organic cage precursor, hydrochloric acid solution is used to acidify the reduced organic cage precursor to achieve ionization. The hydrochloric acid solution is concentrated hydrochloric acid; the mass-to-volume ratio of the reduced organic cage material amine Cage 1 to the hydrochloric acid solution is 1-4 mg: 3-10 μL.

[0021] Specifically, the ionization treatment step for the reduced organic cage material amine Cage 1 includes: A reduced organic cage material, amine Cage 1, was ultrasonically dispersed in water to obtain a reduced organic cage suspension. Hydrochloric acid was added to the reduced organic cage suspension, stirred, and then freeze-dried to obtain QA-Cage. 24+ The obtained QA-Cage 24+ It is a yellow powder.

[0022] Preferably, in the process of preparing the reduced organic cage suspension, the mass-to-volume ratio of the reduced organic cage material amine Cage 1 to water is 50-200 mg: 3-10 mL.

[0023] Furthermore, in the process of preparing the reduced organic cage suspension, the reduced organic cage material amine Cage 1 is added to water and dispersed at 20-30 ℃ under ultrasonic treatment with a power of 50-100 W for 15-30 min to form a reduced organic cage suspension.

[0024] According to one embodiment of the present invention, the step of encapsulating palladium nanoclusters within the internal cavity of an ionized molecular cage includes: The ionized molecular cage is dissolved in water to obtain a cage solution; potassium chloropalladium is dissolved in water to obtain a metal solution; A metal solution is injected into a cage solution to obtain a mixture; NaBH4 solution was slowly added to the mixture under vortex conditions to reduce the metal and obtain an ionized molecular cage supported palladium catalyst. The mass ratio of ionized molecular cages to potassium chloropalladate is 10-30:1.2-3.7; The mass-to-volume ratio of the ionized molecular cage to the NaBH4 solution was 10-30 mg: 1-4 mL; the concentration of the NaBH4 solution was 0.25-4 mg / mL.

[0025] Furthermore, after the metal solution is injected into the cage solution to obtain a mixture, a settling process is also included, with a settling time of 5-30 minutes.

[0026] According to a third aspect of the present invention, the above-described ionized molecular cage supported palladium catalyst, or the ionized molecular cage supported palladium catalyst obtained by the above preparation method, is used in the reduction of nitrate to produce ammonia.

[0027] Compared with the prior art, the present invention has at least the following beneficial effects: 1. This invention provides an ionized molecular cage supported palladium catalyst, wherein the ionized molecular cage QA-Cage serves as the support. 24+ Completely soluble in water, which helps improve catalytic efficiency. The Pd of this invention... QA-Cage 24+ Palladium nanoclusters are encapsulated in QA-Cage 24+ The internal cavity ensures the stability and high efficiency of active metal sites, thereby improving the catalyst's reusability. On the other hand, QA-Cage... 24+As a carrier of the active component, regulating the size and electronic state of the active component (metal Pd in ​​this invention) also helps to improve the efficiency and selectivity of the catalyst, and increase the reaction yield and Faraday efficiency.

[0028] 2. The ionized molecular cage QA-Cage prepared in this invention 24+ Free radicals can be generated under electroinduced conditions, catalyzing water splitting to produce H•. The H• overflows to nearby Pd sites, promoting NO3- production. - The hydrogenation, and QA-Cage 24+ It can also regulate the electronic structure of Pd clusters and promote NO3- production. - The enrichment of Pd on the surface enables it to be used as a catalyst for electrocatalytic nitrate reduction under mild conditions of ambient temperature and pressure, thereby increasing the yield of ammonia, reducing reaction conditions, and facilitating industrial applications.

[0029] 3. This invention uses tris(4-formylphenyl)amine and (R,R)-cyclohexanediamine as raw materials to synthesize an organic cage precursor. Through an imine condensation reaction, the organic cage material imine Cage 1 is synthesized, which is completely soluble in water after reduction and ionization. The completely dissolved organic cage QA-Cage is then presented. 24+ The catalyst, which complexes the support and metal precursor and is reduced in situ to active metal clusters, has a simple preparation process that is easy to implement, and the resulting solid catalyst is easy to recycle and reuse.

[0030] 4. The catalyst of this invention exhibits excellent catalytic activity and cycle stability when used for the electrocatalytic reduction of nitrate to ammonia. Under ambient temperature and pressure with an argon atmosphere, the ammonia yield reaches 25.70 mg / h after 1 h of reaction. -1 mg cat -1 The Faraday efficiency reached 95.44%; after 30 cycles, the yield and Faraday efficiency did not change significantly. Attached Figure Description

[0031] The accompanying drawings, which are included to provide a further understanding of embodiments of the invention and form part of this application, do not constitute a limitation thereof. In the drawings: Figure 1 QA-Cage in Example 1 24+ NMR spectrum of -24Cl; Figure 2 For Comparative Example 1, QA-Cage 12+ NMR spectrum of -12Cl; Figure 3 For Comparative Example 2, QA-Cage 6+ NMR spectrum of -6Cl; Figure 4QA-Cage in Example 1 24+ SEM image of -24Cl; Figure 5 For Comparative Example 1, QA-Cage 12+ SEM image of -12Cl; Figure 6 For Comparative Example 2, QA-Cage 6+ SEM image of -6Cl; Figure 7 QA-Cage in Example 1 24+ HAADF plot of -24Cl; Figure 8 For Comparative Example 1, QA-Cage 12+ HAADF plot of -12Cl; Figure 9 For Comparative Example 2, QA-Cage 6+ HAADF plot of -6Cl; Figure 10 The above are the Pd 3d XPS spectra of the catalysts obtained in Example 1 and Comparative Examples 1-2. Figure 11 This is a schematic diagram of the H-type electrolytic cell structure used in the electrocatalytic reduction of nitrate to produce ammonia in the application example; Figure 12 The LSV curves of the catalysts obtained in Example 1 and Comparative Examples 1 and 2 are shown. Figure 13 The NH3 yields of the catalysts obtained in Example 1 and Comparative Examples 1 and 2 at different potentials; Figure 14 The Faraday efficiency of the catalysts obtained in Example 1 and Comparative Examples 1 and 2 at different potentials; Figure 15 Pd in ​​Example 1 QA-Cage 24+ NH3 yield and Faraday efficiency of 30-cycle stability of -24Cl; Figure 16 Pd in ​​Example 1 QA-Cage 24+ -24Cl Cl 2p and N 1s spectra before and after the generation of free radicals by potential stimulation; Figure 17 The EPR diagrams of free radicals generated by the catalysts obtained in Example 1 and Comparative Examples 1 and 2 under potential stimulation are shown. Figure 18 The above are quasi-in-situ EPR spectra of H• generated before and after Pd encapsulation and H• consumed after Pd encapsulation in Example 1. Figure 19Bode phase diagram and CV curve of the catalyst obtained in Example 1, whether or not the reduced organic cage material was ionized during the preparation process; Figure 20 The OCP curves of the catalyst obtained in Example 1 are shown, depending on whether the reduced organic cage material was ionized during the preparation process. Detailed Implementation

[0032] The present invention will now be described in detail with reference to the accompanying drawings and embodiments. It should be noted that, unless otherwise specified, the embodiments and features described herein can be combined with each other.

[0033] The following detailed description is exemplary and intended to provide further detailed explanation of the invention. Unless otherwise specified, all technical terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art. The terminology used in this invention is for describing particular embodiments only and is not intended to limit the scope of exemplary embodiments according to the invention.

[0034] Example 1 Pd QA-Cage 24+ Preparation of -24Cl composite catalyst S1. Preparation of the carrier.

[0035] S1-1. Synthesize organic cage precursors.

[0036] Tris(4-formylphenyl)amine powder was dissolved in dichloromethane to obtain an aldehyde solution with a concentration of 0.02 mol / L; simultaneously, (R,R)cyclohexanediamine was dissolved in dichloromethane to obtain an amine solution with a concentration of 0.03 mol / L.

[0037] The amine solution was injected into the aldehyde solution and allowed to stand at room temperature (25°C) for 48 h to carry out the amine-aldehyde condensation reaction. The volume ratio of the amine solution to the aldehyde solution was 1:1, that is, the molar ratio of tris(4-formylphenyl)amine to (R,R)cyclohexanediamine was 2:3.

[0038] After the reaction, a clear, pale yellow solution was observed, containing a large amount of water. Colorless, cubic crystals floated on top of the solution. The crystals were obtained by filtration and then washed three times with dichloromethane. During each wash, the volume ratio of dichloromethane to the amine or aldehyde solution was 1:8. After washing, the resulting crystals were dried at 40 °C to obtain pure imine Cage 1.

[0039] S1-2. Reduce the organic cage precursor to prepare reduced organic cage material.

[0040] Under a nitrogen atmosphere, imine Cage 1 obtained in S1-1 was dissolved in a mixture of chloroform and methanol to obtain a precursor suspension. The resulting suspension became clear after stirring at room temperature for 10 min. The volume ratio of chloroform to methanol in the chloroform and methanol mixture was 1:5; the mass-to-volume ratio of imine Cage 1 to chloroform was 35 mg:3 mL.

[0041] NaBH4 was slowly added to the above precursor suspension at a mass ratio of 37:70 to imine Cage 1. The reaction mixture was then stirred overnight at room temperature under a N2 atmosphere until a clear solution was formed. After the reaction was complete, chloroform and water were added to the clear solution, and the mixture was stirred for 30 min, then allowed to stand in a separatory funnel. The volume ratio of chloroform to water was 2:1; the mass-volume ratio of imine Cage 1 to water was 7 mg:1 mL. After the solution separated into layers, the aqueous layer was extracted with chloroform, and the organic layers were combined. The organic layers were dried over Na2SO4, filtered, and then dried in a vacuum drying oven at 40 °C for 8 h to obtain a yellow powder, which is the reduced organic cage material amine Cage 1.

[0042] S1-3. Ionize the reduced organic cage material to obtain ionized molecular cages.

[0043] Water was added to amine Cage 1 and dispersed under ultrasonication to obtain an organic cage suspension, wherein the mass-to-volume ratio of amine Cage 1 to water was 100 mg:9 mL. The ultrasonication conditions were 25 °C, ultrasonic power 75 W, and ultrasonication time 20 min.

[0044] Hydrochloric acid was added to the reduced organic cage suspension to form a transparent pale yellow solution. After stirring at 25 °C for 2 h, the solution was freeze-dried in the temperature range of -20 °C to -50 °C to obtain QA-Cage. 24+ The resulting QA-Cage 24+ It is a yellow powder. The hydrochloric acid used is undiluted concentrated hydrochloric acid, and the mass-to-volume ratio of amine Cage 1 to concentrated hydrochloric acid is 2 mg: 7 μL.

[0045] S2. Preparation of palladium catalyst supported on ionized molecular cages.

[0046] Palladium nanoclusters are encapsulated in the internal cavity of an ionized molecular cage.

[0047] Specifically, the QA-Cage obtained in step S1 is heated at 25°C. 24+ -24Cl dissolves in water to form a cage solution, QA-Cage 24 +The mass-to-volume ratio of -24Cl to water is 5 mg: 3 mL; potassium chloropalladium (K2PdCl6) is dissolved in water to obtain a metal solution, with a mass-to-volume ratio of K2PdCl6 to water of 187 mg: 50 mL.

[0048] A mixture is obtained by injecting molten metal into a cage solution, with a volume ratio of cage solution to molten metal solution of 18:1; this is known as QA-Cage. 24+ The mass ratio of -24Cl to K2PdCl6 is 1500:187.

[0049] After allowing the above mixture to stand for 10 min, NaBH4 solution was slowly added to it under vortex conditions to reduce the metal, thus obtaining the ionized molecular cage supported palladium catalyst Pd. QA-Cage 24+ -24Cl.

[0050] Specifically, the concentration of the NaBH4 solution is 1 mg / mL. (QA-Cage) 24+ The mass-to-volume ratio of -24Cl to NaBH4 solution was 15 mg:2 mL. During the procedure, NaBH4 solution was added dropwise to the mixture to reduce the metal. The resulting transparent solution was freeze-dried at temperatures ranging from -20°C to -50°C to separate solid Pd. QA-Cage 24+ -24Cl.

[0051] Example 2 The difference between this embodiment and Embodiment 1 is that: In step S1-1, the molar ratio of tris(4-formylphenyl)amine to (R,R)cyclohexanediamine is 0.8:6; During the amine-aldehyde condensation reaction, the reaction temperature was 15 ℃ and the standing time was 12 h. During the washing and drying process of the crystals, they were washed five times with dichloromethane, and the drying temperature was 0℃. In steps S1-2, the reaction temperature for reducing the organic cage precursor imine Cage 1 is 30 °C. In the mixture of chloroform and methanol, the volume ratio of chloroform to methanol is 1:5; the mass-to-volume ratio of imine Cage 1 to chloroform is 35 mg:4 mL. The mass ratio of NaBH4 to imine Cage 1 is 1.6:7; During the extraction process, the volume ratio of chloroform to water was 1:1, and the mass-volume ratio of amine Cage 1 to water was 5 mg: 1 mL. The mixture was stirred for 40 min. After filtration, it was vacuum dried at 50 °C for 6 h to obtain amine Cage 1.

[0052] In steps S1-3, during the preparation of the organic cage suspension, the mass-to-volume ratio of amine Cage 1 to water is 50 mg: 3 mL, and the conditions for ultrasonic treatment are 20°C, ultrasonic power 50 W, and ultrasonic time 30 min. During the acidification process using hydrochloric acid, the mass-to-volume ratio of amine Cage 1 to concentrated hydrochloric acid was 1 mg: 3 μL.

[0053] In step S2, when the metal solution is injected into the cage solution to obtain a mixture, QA-Cage 24+ The mass ratio of -24Cl to K2PdCl6 was 25:3; the settling time was 5 min.

[0054] Preparation of ionized molecular cage supported palladium catalyst Pd QA-Cage 24+ At -24Cl, the concentration of NaBH4 solution is 0.25 mg / mL; QA-Cage 24+ The mass-to-volume ratio of -24Cl to NaBH4 solution is 15 mg: 2 mL.

[0055] All other steps and conditions are the same.

[0056] Example 3 The difference between this embodiment and Embodiment 1 is that: In step S1-1, the molar ratio of tris(4-formylphenyl)amine to (R,R)cyclohexanediamine is 1:0.3; The reaction temperature during the amine-aldehyde condensation reaction was 0 ℃ and the standing time was 72 h. During the washing and drying process of the crystals, they were washed three times with dichloromethane, and the drying temperature was 20℃.

[0057] In steps S1-2, the reaction temperature for reducing the organic cage precursor imine Cage 1 is 0 °C; In the mixture of chloroform and methanol, the volume ratio of chloroform to methanol is 1:1; the mass-to-volume ratio of imine Cage 1 to chloroform is 10 mg:1 mL. The mass ratio of NaBH4 to imine Cage 1 is 1.6:22; During the extraction process, the volume ratio of chloroform to water was 3:1, and the mass-volume ratio of amine Cage 1 to water was 10 mg: 1 mL. The mixture was stirred for 10 min. After filtration, it was vacuum dried at 60 °C for 4 h to obtain amine Cage 1.

[0058] In steps S1-3, during the preparation of the organic cage suspension, the mass-to-volume ratio of amine Cage 1 to water is 5 mg:1 mL, and the conditions for ultrasonic treatment are 30°C, ultrasonic power 100 W, and ultrasonic time 15 min. During the acidification process using hydrochloric acid, the mass-to-volume ratio of amine Cage 1 to concentrated hydrochloric acid was 1 mg: 10 μL.

[0059] In step S2, when the metal solution is injected into the cage solution to obtain a mixture, QA-Cage 24+ The mass ratio of -24Cl to K2PdCl6 was 100:37; the settling time was 30 min.

[0060] Preparation of ionized molecular cage supported palladium catalyst Pd QA-Cage 24+ At -24Cl, the concentration of NaBH4 solution is 2 mg / mL; QA-Cage 24+ The mass-to-volume ratio of -24Cl to NaBH4 solution is 5 mg: 2 mL.

[0061] All other steps and conditions are the same.

[0062] Example 4 The difference between this embodiment and Embodiment 1 is that: In steps S1-2, the volume ratio of chloroform to methanol in the mixture of chloroform and methanol is 1:1; the mass-volume ratio of imine Cage1 to chloroform is 5 mg: 2 mL. The mass ratio of NaBH4 to imine Cage 1 is 5:7.

[0063] In steps S1-3, during the preparation of the organic cage suspension, the mass-to-volume ratio of amine Cage 1 to water is 200 mg: 3 mL, and the conditions for ultrasonic treatment are 25°C, ultrasonic power 60 W, and ultrasonic time 25 min. During the acidification process using hydrochloric acid, the mass-to-volume ratio of amine Cage 1 to concentrated hydrochloric acid was 4 mg: 3 μL.

[0064] In step S2, when the metal solution is injected into the cage solution to obtain a mixture, QA-Cage 24+ The mass ratio of -24Cl to K2PdCl6 was 25:1; the settling time was 15 min.

[0065] Preparation of ionized molecular cage supported palladium catalyst Pd QA-Cage 24+At -24Cl, the concentration of NaBH4 solution is 4 mg / mL; QA-Cage 24+ The mass-to-volume ratio of -24Cl to NaBH4 solution is 10 mg: 1 mL.

[0066] All other steps and conditions are the same.

[0067] Example 5 The difference between this embodiment and Embodiment 1 is that: In steps S1-2, the volume ratio of chloroform to methanol in the mixture of chloroform and methanol is 1:1; the mass-volume ratio of imine Cage1 to chloroform is 35 mg:1 mL; and the mass ratio of NaBH4 to imine Cage1 is 5:22.

[0068] In steps S1-3, during the preparation of the organic cage suspension, the mass-to-volume ratio of amine Cage 1 to water is 20 mg:1 mL, and the conditions for ultrasonic treatment are 20°C, ultrasonic power 50 W, and ultrasonic time 15 min. During the acidification process using hydrochloric acid, the mass-to-volume ratio of amine Cage 1 to concentrated hydrochloric acid was 2 mg: 5 μL.

[0069] In step S2, when the metal solution is injected into the cage solution to obtain a mixture, QA-Cage 24+ The mass ratio of -24Cl to K2PdCl6 was 300:37; the settling time was 20 min.

[0070] Preparation of ionized molecular cage supported palladium catalyst Pd QA-Cage 24+ At -24Cl, the concentration of NaBH4 solution is 0.25 mg / mL; QA-Cage 24+ The mass-to-volume ratio of -24Cl to NaBH4 solution is 30 mg: 1 mL.

[0071] All other steps and conditions are the same.

[0072] Comparative Example 1 The difference between this comparative example and Example 1 is that: The specific steps for synthesizing the organic cage precursor in step S1-1 are as follows: Dichloromethane was slowly added to 1,3,5-trimethylbenzene, and then trifluoroacetic acid was added as a catalyst to the mixture to obtain a first mixture. The mass-to-volume ratio of 1,3,5-trimethylbenzene to dichloromethane was 50 mg:1 mL, and the volume ratio of trifluoroacetic acid to dichloromethane was 1:1000.

[0073] (R,R)-1,2-diaminocyclohexane was dissolved in dichloromethane to obtain an amine solution. The mass-to-volume ratio of (R,R)-1,2-diaminocyclohexane to dichloromethane was 53 mg: 1 mL. An amine solution was added to the first mixture to obtain a second mixture. The mass ratio of 1,3,5-trimethylbenzene to (R,R)-1,2-diaminocyclohexane was 50:53. The second mixture was capped and allowed to stand for one week, during which time transparent prism-like crystals formed in the solution.

[0074] The crystallized product was filtered and washed three times (50 mL each time) with dichloromethane / methanol solution (v / v=5 / 95), and finally dried under vacuum at 80 °C for 24 h to obtain the organic cage precursor imine Cage 2, which is a white powder.

[0075] The specific steps for preparing the reduced organic cage material in step S1-2 are as follows: In a vortex state, the imine Cage 2 molecular cage was dissolved in a dichloromethane / methanol solution (v / v=1 / 1); the mass-to-volume ratio of imine Cage 2 to dichloromethane / methanol solution was 20 mg: 1 mL.

[0076] After the solution becomes transparent, NaBH4 is added directly, and the reaction is carried out at 25°C for 15 h; the mass ratio of mine Cage 2 to NaBH4 is 1:1.

[0077] Then, water was added, and the solution was stirred for another 9 hours. The mass-to-volume ratio of mine Cage 2 to water was 500 mg: 1 mL.

[0078] Finally, the solution was removed under vacuum. The residue was washed with plenty of water until the decomposition products of NaBH4 were completely removed, with a mass-to-volume ratio of amine Cage 2 to water of 5 mg:1 mL per wash. If the pH of the product suspension was higher than 7, the washing procedure was continued until it became neutral. The resulting sample was then vacuum-dried at 80 °C for 24 h to obtain the reduced organic cage material amine Cage 2 as a white powder.

[0079] In steps S1-3, amine Cage 1 in Example 1 is replaced with amine Cage 2 as described above, and ionization treatment is performed to obtain an ionized molecular cage QA-Cage. 12+ -12Cl (abbreviated as QA-Cage) 12+ ).

[0080] In step S2, the above-mentioned QA-Cage is used. 12+ Instead of QA-Cage in Example 124 The ionized molecular cage supported palladium catalyst was obtained as Pd. QA-Cage 12+ .

[0081] All other steps and conditions are the same.

[0082] Comparative Example 2 The difference between this comparative example and Example 1 is that: The specific steps for synthesizing the organic cage precursor in step S1-1 are as follows: 4,4',4″-tricarboxytriphenylphosphine oxide and ethylenediamine were dissolved in chloroform and stirred at room temperature for 48 h. Methanol and NaBH4 were then added. The mass ratio of 4,4',4″-tricarboxytriphenylphosphine oxide to ethylenediamine was 180:43; the mass-to-volume ratio of 4,4',4″-tricarboxytriphenylphosphine oxide to chloroform was 900 mg:52 mL; the volume ratio of methanol to chloroform was 1:1; and the mass-to-volume ratio of NaBH4 to methanol was 3.95 g:52 mL.

[0083] After stirring for another 12 hours, water was added at a volume ratio of 1:1 to the chloroform. The mixture was then extracted with dichloromethane at a volume ratio of 1:1 to the chloroform. After three extractions, the organic layers were combined and washed with water and 26% NaCl solution, respectively. The layers were then dried with anhydrous sodium sulfate and the solvent was removed by vacuum evaporation to obtain the organic cage precursor imine Cage 3.

[0084] The specific steps for preparing the reduced organic cage material in step S1-2 are as follows: In a vortex state, the imine Cage 3 molecular cage was dissolved in a dichloromethane / methanol solution (v / v=1 / 1); the mass-to-volume ratio of imine Cage 2 to the dichloromethane / methanol solution was 20 mg: 1 mL.

[0085] After the solution becomes transparent, NaBH4 is added directly, and the reaction is carried out at 25 °C for 15 h; the mass ratio of mine Cage 2 to NaBH4 is 1:1.

[0086] Then, water was added, and the solution was stirred for another 9 hours. The mass-to-volume ratio of mine Cage 2 to water was 500 mg: 1 mL.

[0087] Finally, the solution was removed under vacuum. The residue was washed with plenty of water until the decomposition products of NaBH4 were completely removed, with a mass-to-volume ratio of amine Cage 2 to water of 5 mg:1 mL per wash. If the pH of the product suspension was higher than 7, the washing procedure was continued until it became neutral. The resulting sample was then vacuum-dried at 80 °C for 24 h to obtain the reduced organic cage material amine Cage 3 as a white powder.

[0088] In steps S1-3, amine Cage 1 in Example 1 is replaced with amine Cage 3 as described above, and ionization treatment is performed to obtain an ionized molecular cage QA-Cage. 6+ -6Cl (abbreviated as QA-Cage) 6+ ).

[0089] In step S2, the above-mentioned QA-Cage is used. 6+ Instead of QA-Cage in Example 1 24+ The ionized molecular cage supported palladium catalyst was obtained as Pd. QA-Cage 6+ .

[0090] All other steps and conditions are the same.

[0091] Comparative Example 3 The difference between this comparative example and Example 1 is that: Steps S1-3 are omitted, and the reduced organic cage material amine Cage 1 obtained in step S1-2 is directly used to load palladium in step S2.

[0092] All other steps and conditions are the same.

[0093] The molecular formula of the unionized molecular cage supported palladium catalyst prepared in this comparative example is abbreviated as Pd. A-Cage.

[0094] Test case Structural testing QA-Cage in Example 1 24+ -24Cl, QA-Cage of Comparative Example 1 12+ -12Cl and QA-Cage of Comparative Example 2 6+ The NMR spectrum of -6Cl is shown below. Figure 1-3 SEM image (see) Figure 4-6 See HAADF chart Figure 7-9 .

[0095] Combination Figure 1-3 QA-Cage in Example 1 24+ -24Cl compared to QA-Cage in Comparative Example 112+ -12Cl and QA-Cage of Comparative Example 2 6+ For -6Cl, there are differences in molecular structure type, QA-Cage 24+ -24Cl is a polycyclic supramolecular substance containing multiple benzene rings and saturated chains; and the chemical environment of the hydrogen atom exhibits diversity, with negative chemical shift peaks present, which may be due to the spatial magnetic anisotropy of the molecule.

[0096] Combination Figure 4-6 Pd in ​​Example 1 QA-Cage 24+ -24Cl, Pd from Comparative Example 1 QA-Cage 12+ -12Cl and Pd in ​​Comparative Example 2 QA-Cage 6+ -6Cl all exhibit irregular structures with dimensions on the order of hundreds of nanometers. Among them, Pd in ​​Example 1... QA-Cage 24+ -24Cl exhibits an irregular blocky structure with a rough surface and protrusions; Pd in ​​Comparative Example 1 QA-Cage 12+ -12Cl exhibits an irregular, sheet-like structure with wrinkled edges and a finely textured surface; Comparative Example 2's Pd QA-Cage 6+ -6Cl also has a plate-like structure with clear edges and a relatively flat surface.

[0097] Combination Figure 7-9 Pd in ​​Example 1 QA-Cage 24+ The bright spot particles of -24Cl are relatively uniformly distributed, with extremely small particle sizes and clear outlines for each individual particle. Furthermore, the size of the bright spot particles is significantly larger than that of Pd in ​​Comparative Example 1. QA-Cage 12+ -12Cl and Pd in ​​Comparative Example 2 QA-Cage 6+ -6Cl. Pd in ​​Example 1 QA-Cage 24+ The particle size of -24Cl is concentrated at 0.96 ± 0.09 nm, with a narrow distribution, indicating that Pd QA-Cage 24+ -24Cl nanoparticles exhibit good size uniformity, with particle sizes in the range of nearly 1 nm and low dispersion.

[0098] Pd in ​​Example 1 QA-Cage 24+ -24Cl, Pd from Comparative Example 1 QA-Cage 12+ -12Cl and Pd in ​​Comparative Example 2 QA-Cage 6+ The Pd 3d XPS spectrum of -6Cl is shown below. Figure 10 Examples 1 and Comparative Examples 1-2 exhibit characteristic 3d values ​​at 335.8 eV, 335.6 eV, and 335.2 eV, respectively. 5 / 2 The peak corresponds to the zero-valent Pd species. Compared to Comparative Example 2, Example 1 showed a positive shift of approximately 0.6 eV, and compared to Comparative Example 1, Example 1 showed a positive shift of approximately 0.2 eV, demonstrating the positive shift of the QA-Cage. x+ (x = 6, 12, 24) can tune the electronic structure of the Pd cluster surface.

[0099] Application examples 1. Electrocatalytic nitrate reduction reaction (ENO3RR) In a typical H-type electrolyzer, NO3 is processed using a Nafion 117 membrane. - Reduction experiment.

[0100] The tests were conducted using a Shanghai Chenhua CHI660E workstation. All electrochemical measurements were performed at room temperature in an H-type electrolytic cell with Naion 117 membrane separation, using a three-electrode configuration: a catalyst-coated carbon paper as the working electrode, a Pt sheet electrode as the counter electrode, and Ag / AgCl as the reference electrode. The catalyst used was Pd from Example 1. QA-Cage 24+ -24Cl, Pd from Comparative Example 1 QA-Cage 12+ -12Cl and Pd in ​​Comparative Example 2 QA-Cage 6+ -6Cl; the electrolyte is 0.5 M Na₂SO₄ + 0.1 M NaNO₃. In the specific procedure, the 0.5 M Na₂SO₄ + 0.1 M NaNO₃ solution is purified with Ar for 20-30 minutes before being purified with NO₃⁻. - Reduction experiment. Before each ENO3RR experiment, [the sample was] tilted at 20-30 cm [a pressure / pressure]. 3 min -1 The gas flow rate is first blew into Ar for 15-30 minutes to remove air from the pool.

[0101] LSV curves were obtained in Ar-saturated 0.5 M Na₂SO₄ and 0.5 M Na₂SO₄ + 0.1 M NaNO₃ at a rate of 10 mV s⁻¹. -1 The scan rate was used.

[0102] Time-ampere tests were performed at -0.2 to -0.9 V vs. RHE for 1 hour.

[0103] Stability testing was performed at -0.8 V vs. RHE for 30 cycles of time-ampere testing, with each electrolysis time being 1 h.

[0104] The schematic diagram of the H-type electrolytic cell structure used in ENO3RR is shown below. Figure 11 The LSV curves for Example 1 and Comparative Examples 1-2 are shown below. Figure 12 For the NH3 yields of Example 1 and Comparative Examples 1-2 at different potentials, please refer to [reference needed]. Figure 13 For Faraday efficiency, see [link / reference]. Figure 14 The stability of Example 1 is shown in [reference needed]. Figure 15 .

[0105] Combination Figures 12-15 The test results showed that, under normal temperature and pressure and an argon atmosphere, the ammonia yield reached 25.70 mg / h in the example after 1 hour of reaction. -1 mg cat -1 The Faraday efficiency reached 95.44%, while the ammonia yield of Comparative Example 1 was 11.82 mg / h. - 1 mg cat -1 The Faraday efficiency was 93.2%, and the ammonia yield of Comparative Example 2 was 2.66 mg h. -1 mg cat -1 The Faraday efficiency was 90.34%; and after 30 cycles, the yield and Faraday efficiency of Example 1 did not change significantly.

[0106] 2. Mechanism Verification For Pd in ​​Example 1 QA-Cage 24+ -24Cl powder was subjected to a potential application of -0.8V vs. RHE and then subjected to XPS (PHI Quantera II; ESCALAB 250Xi, Thermo Fisher, monochromatized Al Kα source, all XPS spectra were calibrated to the C 1s peak at 284.6 eV).

[0107] For Pd in ​​Example 1 QA-Cage 24+ -24Cl, Pd from Comparative Example 1 QA-Cage 12+ -12Cl and Pd in ​​Comparative Example 2 QA-Cage 6+ EPR (EMXplus-6 / 1, Bruker) testing was performed using -6Cl. The EPR test conditions were: operation at 20°C and an X-band frequency (9.84 GHz), with the temperature controlled by a circulating water system. The spectrometer was set to: scan width 100 GHz, center field 3505 GHz, scan time 30 seconds, modulation amplitude 1 GHz, receiver gain 30 dB, microwave power 0.6325 mW, conversion time 12.64 ms, and time constant 5.12 ms.

[0108] For Pd in ​​Example 1 QA-Cage 24+ Quasi-in-situ EPR measurements were performed using -24Cl. The measurements were conducted at room temperature in an H-type cell separated by a Nafion 117 membrane, using a three-electrode setup with a platinum plate (1 × 1 cm²). 2 A catalyst-coated carbon paper was used as the working electrode, Ag / AgCl (saturated KCl) as the counter electrode, and catalyst-coated carbon paper as the reference electrode. In NO3... - Prior to reduction, 6 mL of Ar-saturated 0.5 M Na₂SO₄ or 0.5 M Na₂SO₄ + 0.1 M NaNO₃ electrolyte was mixed with 60 μL of 5,5-dimethyl-1-pyrrolidine-N-oxide (DMPO). Ar was bubbled in throughout the experiment. After electrocatalysis at a potential of -0.8 V vs. RHE, 30 μL of solution was collected, transferred to a quartz EPR sample tube, sealed at the bottom with wax, and then placed in a spectrometer for hydrogen radical (H•) detection.

[0109] For Pd in ​​Example 1 QA-Cage 24+ -24Cl and Pd in ​​Comparative Example 3 H-current testing was performed on the A-Cage using a Shanghai Chenhua CHI660E workstation. Bode measurements were taken with a 5 mV disturbance at frequencies from 10 kHz to 0.01 Hz, and the CV curve was measured at 100 mV s⁻¹. 1 The scan frequency of D was used for testing in the potential range of -0.4 to 0.6 V vs. RHE. The electrolyte was 0.5 M Na2SO4 + 0.1 M NaNO3.

[0110] For Pd in ​​Example 1 QA-Cage 24+ -24Cl and Pd in ​​Comparative Example 3 OCP testing was performed on the A-Cage. The test conditions were as follows: the test was conducted on a Shanghai Chenhua CHI660E workstation, the test time was 600s, the sampling frequency was 0.05 s, the initial electrolyte was 0.5 M Na2SO4, and after 300s the electrolyte was changed to 0.5 M Na2SO4 + 0.1 M NaNO3.

[0111] Figure 16 Pd in ​​Example 1 QA-Cage 24+ The Cl 2p and N 1s spectra of -24Cl before and after the generation of free radicals by potential stimulation were obtained. According to the Cl 2p spectrum, in addition to the characteristic peak of chloride ions maintaining the positive charge of the cage, two new characteristic peaks appeared, belonging to the neutral Cl atom (Cl•) signal. According to the N 1s spectrum, after applying a potential, a characteristic peak belonging to the stable quaternary ammonium free radical (N•) appeared at 398.4 eV, and... Figure 17 EPR tests showed that, after applying a potential, both Example 1 and Comparative Examples 1-2 exhibited a radical peak at g = 2.0046, collectively confirming the presence of a free radical peak at g = 2.0046 after applying a potential. x+ N• is produced.

[0112] Figure 18 Implementing column 1 of Pd QA-Cage 24+ The quasi-in-situ EPR spectrum of -24Cl, quasi-in-situ EPR testing confirms that QA-Cage was obtained after applying a potential. 24+ The generated N• can catalyze water splitting to produce H•, which can then be used for subsequent NO3 production. - Reduction hydrogenation.

[0113] Figure 19 In the Bode phase diagram, compared to the unionized Example 1, Example 1 showed a smaller phase angle at a lower frequency and a stronger H resolution peak in the CV curve, proving the presence of hydrogen spillover.

[0114] Figure 20 Pd in ​​Example 1 QA-Cage 24+ The OCP test for whether -24Cl is ionized was performed by adding NaNO3 to the electrolyte, compared to Pd without ionization. QA-Cage 24+ -24Cl, the open-circuit voltage of Example 1 was increased by 7 mV, thus proving that the ionized molecular cage framework is beneficial to NO3. - Enrichment.

[0115] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the protection scope of the claims of the present invention.

Claims

1. An ionized molecular cage supported palladium catalyst, characterized in that, The device includes a carrier and an active component; the carrier includes an ionized molecular cage, which is amorphous; the active component includes palladium nanoclusters with a particle size of 0.6-1.4 nm, which are encapsulated in the internal cavity of the ionized molecular cage. The ionized molecular cage palladium catalyst has a particle size of 200-2000 nm and a palladium loading of 0.3-2.5 wt%.

2. The ionized molecular cage supported palladium catalyst according to claim 1, characterized in that, The ionized molecular cage is obtained by reducing and ionizing the organic cage precursor. The organic cage precursor is obtained by amine-aldehyde condensation reaction of tris(4-formylphenyl)amine and (R,R)cyclohexanediamine.

3. The ionized molecular cage supported palladium catalyst according to claim 1, characterized in that, The molecular formula of the ionized molecular cage supported palladium catalyst is Pd. QA-Cage 24+ -24Cl.

4. A method for preparing an ionized molecular cage supported palladium catalyst, characterized in that, Includes the following steps: Synthetic organic cage precursors; The organic cage precursor was reduced. The reduced organic cage precursor was ionized to obtain an ionized molecular cage. Using an ionized molecular cage as a carrier and palladium nanoclusters as the active component, palladium nanoclusters are encapsulated in the internal cavity of the ionized molecular cage to obtain an ionized molecular cage supported palladium catalyst.

5. The preparation method according to claim 4, characterized in that, The step of synthesizing the organic cage precursor includes: Tris(4-formylphenyl)amine was dissolved in dichloromethane to obtain an aldehyde solution; (R,R)cyclohexanediamine was dissolved in dichloromethane to obtain an amine solution. The amine solution is injected into the aldehyde solution to carry out an amine-aldehyde condensation reaction, thereby obtaining an organic cage precursor; The molar ratio of tris(4-formylphenyl)amine to (R,R)cyclohexanediamine is 0.8-4:1.2-6.

6. The preparation method according to claim 5, characterized in that, After the amine-aldehyde condensation reaction is completed, the steps also include filtration, washing, and drying. The washing process uses dichloromethane, and the drying temperature is 0-40 ℃.

7. The preparation method according to claim 4, characterized in that, Before reducing the organic cage precursor, the process further includes a step of dissolving the organic cage precursor in a mixture of chloroform and methanol to obtain a precursor suspension; the mass-to-volume ratio of the organic cage precursor to chloroform is 10-35 mg: 1-4 mL; and the volume ratio of chloroform to methanol is 1: 1-5. In the step of reducing the organic cage precursor, NaBH4 is used as the reducing agent; the mass ratio of organic cage precursor to NaBH4 is 7-22:1.6-5.

8. The preparation method according to claim 4, characterized in that, In the ionization process of the reduced organic cage precursor, hydrochloric acid solution is used to acidify the reduced organic cage precursor to achieve ionization. The mass-to-volume ratio of the reduced organic cage precursor to the hydrochloric acid solution was 1-4 mg: 3-10 μL.

9. The preparation method according to claim 4, characterized in that, The step of encapsulating palladium nanoclusters within the internal cavity of an ionized molecular cage includes: The ionized molecular cage is dissolved in water to obtain a cage solution; potassium chloropalladium is dissolved in water to obtain a metal solution; A metal solution is injected into a cage solution to obtain a mixture; A NaBH4 solution was added to the mixture under vortex conditions to reduce the metal, resulting in an ionized molecular cage supported palladium catalyst. The mass ratio of ionized molecular cages to potassium chloropalladate is 10-30:1.2-3.7; The mass-to-volume ratio of the ionized molecular cage to the NaBH4 solution was 10-30 mg: 1-4 mL; the concentration of the NaBH4 solution was 0.25-4 mg / mL.

10. The application of the ionized molecular cage supported palladium catalyst according to any one of claims 1-3 or the ionized molecular cage supported palladium catalyst obtained by the preparation method according to any one of claims 4-9 in the reduction of nitrate to ammonia.

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