A Ru / C cluster catalyst for the electrocatalytic PTA-to-CHDA reaction, its preparation method and application

Abstract

This invention relates to a Ru / C cluster catalyst for the electrocatalytic PTA-to-CHDA reaction, its preparation method, and its application. The method employs a molten salt electrolyte containing carbonate; a Ru-containing compound and a morphology control agent are mixed with the molten salt electrolyte; heating is performed to form an ion-conducting molten electrolyte system; electrolysis at constant potential or constant current allows the Ru element in the precursor and the C element in the carbonate to be co-electrodeposited on the cathode surface, forming a supported metal catalyst; after electrolysis, cooling is performed, and the catalyst is collected from the cathode, washed, and dried to obtain the supported metal catalyst. This invention provides a one-step in-situ generation of amorphous carbon-supported supported Ru / C catalysts, effectively simplifying the complex multi-step preparation process of traditional catalysts, reducing energy consumption and production costs, and solving the problem of existing technologies struggling to prepare Ru-group cluster catalysts with uniform size, good dispersibility, and high stability.

Description

Technical Field

[0001] This invention relates to the fields of electrochemical catalysis and fine chemical technology, and more specifically to a Ru / C cluster catalyst for the electrocatalytic PTA to CHDA reaction, its preparation method and application. Background Technology

[0002] Cyclohexanedicarboxylic acid (CHDA), especially 1,4-cyclohexanedicarboxylic acid, is a core monomer for the synthesis of high-performance polyesters, environmentally friendly plasticizers, and high-end coatings. Currently, the mainstream preparation method for cyclohexanedicarboxylic acid is the selective hydrogenation of terephthalic acid (PTA). This method can be industrialized using terephthalic acid feedstocks obtained through biomass or petrochemical processes and is the core process route in the industry.

[0003] Existing technologies for the hydrogenation of terephthalic acid to cyclohexanedicarboxylic acid mostly rely on heterogeneous catalytic hydrogenation processes, typically employing supported noble metal catalysts such as Ru / C, Pd / C, and Rh / C, and carrying out the reaction under high-pressure hydrogen gas of 2-10 MPa and high-temperature conditions of 100-150 °C. Although this process has been industrially applied, it suffers from several insurmountable technical drawbacks: First, the reaction requires a harsh high-temperature and high-pressure hydrogen environment, placing extremely high demands on the pressure and temperature resistance of the production equipment, posing safety hazards such as hydrogen leakage and explosion, while also resulting in enormous energy consumption. Second, to ensure catalytic activity, the process requires the use of high-load metal nanoparticle catalysts, which can easily lead to over-hydrogenation reactions, generating byproducts such as cyclohexane and methanol, significantly reducing the selectivity and yield of cyclohexanedicarboxylic acid, and increasing the steps and costs of subsequent product separation and purification. Third, traditional catalysts are prepared using an impregnation-calcination-reduction method, where the active components are mostly in the form of large-sized nanoparticles, with a large number of precious metal atoms encapsulated inside the particles, unable to participate in surface catalytic reactions, resulting in low utilization of precious metal atoms and poor cost-effectiveness of the catalyst.

[0004] To address these issues, researchers began developing atomically dispersed catalysts (such as single-atom catalysts) to improve the utilization rate of precious metal atoms. However, in complex aromatic ring hydrogenation reactions such as the hydrogenation of terephthalic acid, single-atom catalysts lack adjacent metal atom sites, making it impossible to synergistically adsorb and activate H2 molecules and benzene rings. Consequently, their hydrogenation activity is limited, making it difficult to achieve efficient continuous hydrogenation processes.

[0005] Electrocatalytic hydrogenation technology, as an emerging green synthesis method, uses water as a hydrogen source and carries out the reaction under ambient temperature and pressure through an external electric field, fundamentally avoiding the use of high-pressure hydrogen. It boasts significant advantages such as high safety, mild reaction conditions, and environmental friendliness. However, the core bottleneck for the industrial application of this technology lies in developing a matching high-performance cathode catalyst. An ideal catalyst must simultaneously meet three requirements: high intrinsic activity to efficiently catalyze the hydrogenation reaction of the benzene ring in terephthalic acid; high selectivity to precisely control the degree of hydrogenation, producing only cyclohexanedicarboxylic acid and avoiding over-reduction; and high atom utilization to achieve optimal catalytic performance with minimal use of precious metals.

[0006] Metal clusters are aggregates of several to dozens of atoms, with sizes between single atoms and nanoparticles. They maintain near 100% metal atom utilization and possess multiple active sites composed of metal atoms. They can synergistically catalyze reactions requiring multiple sites, such as the dissociation of H₂O to generate active hydrogen atoms (H*) and the adsorption and hydrogenation of benzene rings. Therefore, they are ideal catalytic materials for the efficient electrocatalytic hydrogenation of aromatic rings in terephthalic acid. However, the preparation of metal cluster catalysts currently faces core technical challenges: the high surface energy of metal clusters makes it difficult to stably anchor them on a support using simple, controllable, and scalable methods. They are prone to migration and aggregation during preparation and use, leading to a decline in catalytic performance. Traditional wet chemical methods for preparing metal cluster catalysts cannot precisely control the size and distribution of clusters, and the preparation process is complex, hindering industrialization. Summary of the Invention

[0007] To address the problems of harsh PTA hydrogenation conditions, low catalyst activity, poor selectivity, low utilization of precious metals, and difficulty in stable preparation of cluster catalysts in the prior art, this invention aims to provide a Ru / C cluster catalyst for the electrocatalytic PTA to CHDA reaction, its preparation method, and its application.

[0008] The method for preparing a Ru / C cluster catalyst for the electrocatalytic PTA-to-CHDA reaction according to the present invention comprises the following steps: S1, providing an electrolytic reaction apparatus, wherein a molten salt electrolyte containing carbonate is disposed in the container of the electrolytic reaction apparatus; S2, mixing a Ru-containing compound and a morphology control agent as precursors with the molten salt electrolyte; S3, heating the electrolytic reaction apparatus to above the melting point of the molten salt electrolyte under a protective atmosphere to form an ion-conducting molten electrolyte system; S4, applying a DC voltage or a pulse voltage between the anode and cathode of the electrolytic reaction apparatus to perform constant potential or constant current electrolysis, so that the Ru element in the precursor and the C element in the carbonate are co-electrodeposited on the cathode surface to form a supported metal catalyst; S5, after electrolysis, cooling, collecting from the cathode, washing, and drying to obtain the supported metal catalyst.

[0009] In a preferred embodiment, in step S1, the carbonate is one or more of sodium carbonate (Na2CO3), potassium carbonate (K2CO3), and lithium carbonate (Li2CO3); the molten salt electrolyte is a chloride, fluoride, carbonate, or a eutectic mixture thereof.

[0010] In a preferred embodiment, the chloride is one or more of lithium chloride (LiCl), sodium chloride (NaCl), and potassium chloride (KCl); the fluoride is one or more of sodium fluoride (NaF), potassium fluoride (KF), and lithium fluoride (LiF).

[0011] In a preferred embodiment, in step S2, the precursor is one or more of RuCl3 and Ru(NO3)3; the morphology control agent is one or more of lithium hydroxide (LiOH), sodium hydroxide (NaOH), and potassium hydroxide (KOH).

[0012] In a preferred embodiment, in step S2, the precursor accounts for 0.1wt%-2wt% of the total electrolyte mass; the morphology control agent accounts for 5wt%-30wt% of the total electrolyte mass.

[0013] In a preferred embodiment, in step S3, the heating temperature is 425°C to 800°C.

[0014] In a preferred embodiment, in step S4, the current density of the constant current electrolysis is 5 mA / cm². 2 Up to 50mA / cm 2 .

[0015] The Ru / C catalyst obtained by the above preparation method according to the present invention is a supported catalyst, wherein the amorphous carbon formed by co-deposition is used as the support, Ru is the supported metal, and the Ru loading is 0.5-50 wt%.

[0016] In a preferred embodiment, the Ru in the Ru / C catalyst has a mixed structure consisting mainly of clusters and containing a small number of nanoparticles with a size of less than 2 nm.

[0017] The application of the Ru / C catalyst described above according to the present invention in the aqueous phase electrocatalytic hydrogenation reaction of PTA to prepare CHDA.

[0018] This invention employs a molten salt electrolyte system containing carbonates, where a Ru-containing precursor is co-mixed with a morphology control agent to form a molten electrolyte. A constant potential or constant current electrolysis is performed between the anode and cathode using a DC voltage or pulsed voltage, allowing Ru and carbon obtained from carbonate reduction to co-deposit simultaneously on the cathode surface. This enables one-step in-situ generation of amorphous carbon-supported Ru / C catalysts, effectively simplifying the complex multi-step preparation process of traditional catalysts and reducing energy consumption and production costs. By controlling the precursor, morphology control agent, and electrolysis conditions, the deposition morphology of Ru can be precisely controlled, ensuring that Ru in the catalyst is predominantly in cluster form. The catalyst contains a small number of nanoparticles smaller than 2 nm, which significantly increases the specific surface area and the number of catalytic active sites. At the same time, the carbon support generated in situ is firmly bonded to Ru, effectively inhibiting the loss and aggregation of active components during the reaction process, and greatly improving the stability and service life of the catalyst. This solves the problem that it is difficult to prepare Ru group cluster catalysts with uniform size, good dispersibility and high stability in the existing technology. When this catalyst is applied to the reaction of PTA aqueous phase electrocatalytic hydrogenation to prepare CHDA, it can achieve higher PTA conversion rate, CHDA yield and current efficiency, and has excellent catalytic performance and good prospects for industrial application. Attached Figure Description

[0019] Figure 1 This is the XRD pattern of the sample prepared according to Example 1 of the present invention.

[0020] Figure 2 This is the XAFS spectrum of the sample prepared according to Example 1 of the present invention.

[0021] Figure 3 This is the XAFS spectrum of the sample prepared according to Comparative Example 1 of the present invention.

[0022] Figure 4 This is the XAFS spectrum of the sample prepared according to Comparative Example 2 of the present invention.

[0023] Figure 5 This is the XAFS spectrum of the sample prepared according to Comparative Example 3 of the present invention. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to the accompanying drawings and embodiments. The described embodiments are only some embodiments of the present invention and are not intended to limit the scope of protection of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0025] Molten salt electrochemistry is an advanced material synthesis method that has shown great potential in the preparation of atomically dispersed catalysts in recent years. By applying an electric field in a high-temperature molten salt system, it enables atomic-level etching and controllable deposition of metal precursors, providing a new approach for the preparation of metal cluster catalysts. In existing technologies, this technique is mainly applied to the preparation of single-atom catalysts, and its use in preparing metal cluster catalysts with uniform size and high stability has not yet been observed. Based on this, this invention, relying on the principle of molten salt electrochemical co-deposition, provides a Ru / C cluster catalyst for the electrocatalytic PTA-to-CHDA reaction, its preparation method, and its application.

[0026] The method for preparing a Ru / C cluster catalyst for the electrocatalytic PTA-to-CHDA reaction according to the present invention firstly includes providing an electrolytic reaction apparatus, wherein a molten salt electrolyte containing a carbonate is disposed within the container of the electrolytic reaction apparatus. In a preferred embodiment, the container is a graphite crucible. In a preferred embodiment, the carbonate is one or more selected from sodium carbonate (Na₂CO₃), potassium carbonate (K₂CO₃), and lithium carbonate (Li₂CO₃). In a preferred embodiment, the molten salt electrolyte is a chloride, fluoride, carbonate, or a eutectic mixture thereof. In a preferred embodiment, the chloride is one or more selected from lithium chloride (LiCl), sodium chloride (NaCl), and potassium chloride (KCl); the fluoride is one or more selected from sodium fluoride (NaF), potassium fluoride (KF), and lithium fluoride (LiF). In one preferred embodiment, the molten salt electrolyte is a lithium chloride-potassium chloride mixed salt with a molar ratio of 1:1. In another preferred embodiment, the molten salt electrolyte is a lithium fluoride-potassium fluoride-sodium fluoride mixed salt with a molar ratio of 46.5:11.5:42.0. In a preferred embodiment, the anode of the electrolytic reactor is a graphite rod. In a preferred embodiment, the cathode of the electrolytic reactor is a metal, alloy, or conductive ceramic. In a preferred embodiment, the cathode is a sheet material of nickel, copper, or carbon.

[0027] The method for preparing a Ru / C cluster catalyst for the electrocatalytic PTA-to-CHDA reaction according to the present invention further includes mixing a Ru-containing compound as a precursor and a morphology control agent with the molten salt electrolyte. In a preferred embodiment, the precursor is one or more of RuCl3 and Ru(NO3)3. In a preferred embodiment, the morphology control agent is a strong base. In a preferred embodiment, the morphology control agent is one or more of lithium hydroxide (LiOH), sodium hydroxide (NaOH), and potassium hydroxide (KOH), used to control the size and morphology of the deposited catalyst particles. In a preferred embodiment, the precursor accounts for 0.1 wt%-2 wt% of the total electrolyte mass (carbonate mass + chloride / fluoride molten salt mass + precursor mass + morphology control agent mass). In a preferred embodiment, the precursor accounts for 1 wt%-1.4 wt% of the total electrolyte mass. In a preferred embodiment, the precursor accounts for 1.2 wt% of the total electrolyte mass. In a preferred embodiment, the morphology control agent accounts for 5 wt%-30 wt% of the total electrolyte mass. In a preferred embodiment, the morphology control agent accounts for 18 wt% of the total electrolyte mass.

[0028] The method for preparing the Ru / C cluster catalyst for the electrocatalytic PTA-to-CHDA reaction according to the present invention further includes heating the electrolytic reaction apparatus to above the melting point of the molten salt electrolyte under a protective atmosphere to form an ion-conducting molten electrolyte system. In a preferred embodiment, the protective atmosphere is argon. In a preferred embodiment, the heating temperature is 425°C to 800°C. In a preferred embodiment, the heating temperature is 450°C to 550°C.

[0029] The method for preparing the Ru / C cluster catalyst for the electrocatalytic PTA-to-CHDA reaction according to the present invention further includes applying a DC voltage or pulsed voltage between the anode and cathode to perform constant potential or constant current electrolysis, so that the Ru element in the precursor and the C element in the carbonate are co-electrodeposited on the cathode surface to form a supported metal catalyst. In a preferred embodiment, the current density of the constant current electrolysis is 5 mA / cm². 2 Up to 50mA / cm 2 In a preferred embodiment, the current density is 15 mA / cm². 2 In a preferred embodiment, the electrolysis time is 0.5 h to 5 h. In one preferred embodiment, the electrolysis time is 2 h.

[0030] The method for preparing the Ru / C cluster catalyst for the electrocatalytic PTA to CHDA reaction according to the present invention finally includes cooling after electrolysis, collecting from the cathode, washing and drying to obtain a supported metal catalyst.

[0031] The Ru / C catalyst prepared according to the above method is a supported catalyst, in which amorphous carbon formed by co-deposition serves as the support, Ru is the supported metal, and the Ru loading is 0.5-50 wt%. In a preferred embodiment, the Ru loading in the Ru / C cluster catalyst is 5-5.5 wt%. The Ru in the Ru / C catalyst has a mixed structure with clusters as the main body and containing a small amount of nanoparticles with a size of less than 2 nm, and has a high specific surface area and abundant catalytic active sites.

[0032] The present invention also provides the application of the above-mentioned Ru / C catalyst in the aqueous phase electrocatalytic hydrogenation of PTA to prepare CHDA.

[0033] Example 1

[0034] Take 49g of lithium carbonate, 6g of ruthenium chloride, 90g of potassium hydroxide, and 360g of a lithium chloride-potassium chloride mixed salt with a molar ratio of 1:1. After thoroughly mixing the above raw materials, place them in a graphite crucible and then place the graphite crucible in an electrolytic reaction device. Introduce argon gas into the electrolytic reaction device to form a protective atmosphere, and heat the device to 450°C to melt the mixed raw materials and form an ion-conducting molten electrolyte system.

[0035] A graphite rod was used as the anode for the electrolytic reaction, and a 1cm × 1cm nickel sheet was used as the cathode. An A / cm current was applied between the anode and the cathode. 2 Constant current electrolysis is performed for 2 hours, allowing Ru in the precursor and C in the carbonate to be simultaneously reduced and deposited on the cathode surface, forming a supported Ru / C metal catalyst.

[0036] After the electrolysis reaction is completed, heating is stopped and argon gas is turned off. The electrolysis reaction device is allowed to cool naturally to room temperature. The catalyst product obtained is collected from the surface of the cathode nickel sheet. The product is washed and dried in sequence to obtain the Ru / C cluster catalyst for the electrocatalytic hydrogenation of PTA to prepare CHDA.

[0037] The samples prepared in this embodiment were characterized for phase and structure, and the results were obtained. Figure 1 The XRD pattern of the sample prepared for this embodiment is obtained from... Figure 1 As can be observed, the XRD pattern of the sample only shows the characteristic diffraction peaks of amorphous carbon, and no characteristic diffraction peaks of metallic Ru are present. This characterization result indicates that the particle size of metallic Ru in the sample prepared in this embodiment is extremely small and uniformly distributed on the surface of the carbon support, with no obvious Ru particle agglomeration. The elemental content analysis of the sample by ICP-OES detection method determined that the Ru element loading in the Ru / C cluster catalyst prepared in this embodiment is 5 wt%.

[0038] Figure 2The extended-edge X-ray absorption fine structure spectrum (XAFS) of the Ru / C catalyst prepared in this embodiment is shown, with characteristic peak positions of Ru-C / O, Ru-Ru, and Ru-O-Ru marked. Figure 2 The K-edge absorption spectrum of Ru clearly shows that the Ru element in the Ru / C catalyst prepared in this embodiment is not a single morphology, but a mixed structure with Ru clusters as the main body and containing a small number of ultrafine nanoparticles with a size of less than 2 nm. This structure exposes a large number of Ru atoms on the support surface, forming abundant catalytic active sites, which verifies that the preparation method can successfully prepare cluster-type Ru / C catalysts with both high specific surface area and abundant active sites.

[0039] Example 2

[0040] Take 49g of lithium carbonate, 6g of ruthenium chloride, 90g of potassium hydroxide and 360g of a mixed salt of lithium fluoride-potassium fluoride-sodium fluoride with a molar ratio of 46.5:11.5:42.0, mix them thoroughly and place them in a graphite crucible. Place the crucible in an electrolysis reaction device and introduce argon gas to form a protective atmosphere. Heat to 550℃ to form a molten electrolyte system.

[0041] A graphite rod is used as the anode, and a 1cm × 1cm nickel sheet is used as the cathode, with an applied current of 15mA / cm. 2 A constant current electrolysis was applied for 2 hours to allow Ru and C elements to co-deposit on the cathode surface to form a supported Ru / C metal catalyst.

[0042] After electrolysis, a cooling device is used to collect the cathode products, which are then washed and dried to obtain the Ru / C cluster catalyst.

[0043] ICP-OES analysis confirmed that the Ru loading in the Ru / C cluster catalyst prepared in this embodiment was 5.5 wt%.

[0044] Example 3

[0045] The preparation steps, raw material types, and process parameters of this embodiment are the same as those of Example 1. The only difference is the amount of ruthenium chloride added as a precursor. In this embodiment, the amount of ruthenium chloride added is 10g. All other operations are the same as in Example 1, and a Ru / C cluster catalyst is finally obtained.

[0046] Example 4

[0047] The preparation steps, raw material types, and process parameters of this embodiment are the same as those of Example 1. The only difference is the amount of ruthenium chloride added as a precursor. In this embodiment, the amount of ruthenium chloride added is 0.5 g. All other operations are the same as in Example 1, and a Ru / C cluster catalyst is finally obtained.

[0048] Example 5

[0049] The preparation steps, raw material types, and raw material addition amounts in this embodiment are the same as in Example 1. The only difference is the reaction temperature of the molten electrolysis. In this embodiment, the electrolysis reaction device is heated to 800°C to form a molten electrolyte system. All other operations are the same as in Example 1, and finally, a Ru / C cluster catalyst is obtained.

[0050] Example 6

[0051] The preparation steps, raw material types, and raw material addition amounts in this embodiment are the same as in Example 1. The only difference is the reaction temperature of the molten electrolysis. In this embodiment, the electrolysis reaction device is heated to 425°C to form a molten electrolyte system. All other operations are the same as in Example 1, and finally, a Ru / C cluster catalyst is obtained.

[0052] Example 7

[0053] The preparation steps, raw material types, and raw material addition amounts are the same as in Example 1, except that the electrolysis current density is changed. In this example, 50 mA / cm² is applied between the anode and cathode. 2 Electrolysis was performed using a constant current for 2 hours, with all other operations being the same as in Example 1, ultimately yielding a Ru / C cluster catalyst.

[0054] Example 8

[0055] The preparation steps, raw material types, and raw material addition amounts are the same as in Example 1, except that the electrolysis current density is changed. In this example, 5 mA / cm² is applied between the anode and cathode. 2 Electrolysis was performed using a constant current for 2 hours, with all other operations being the same as in Example 1, ultimately yielding a Ru / C cluster catalyst.

[0056] Example 9

[0057] The preparation steps, raw material types, and raw material addition amounts are the same as in Example 1, except that the electrolysis duration is changed. In this example, 15 mA / cm is applied. 2 The constant current was continuously electrolyzed for 5 hours, and the remaining operations were the same as in Example 1, finally yielding the Ru / C cluster catalyst.

[0058] Example 10

[0059] The preparation steps, raw material types, and raw material addition amounts are the same as in Example 1, except that the electrolysis duration is changed. In this example, 15 mA / cm is applied. 2 The constant current was continuously electrolyzed for 0.5 h, and the remaining operations were the same as in Example 1, finally yielding the Ru / C cluster catalyst.

[0060] Example 11

[0061] The preparation steps, raw material types, and process parameters of this embodiment are the same as those of Example 1. The only difference is the addition mass of potassium hydroxide as the morphology control agent. In this embodiment, the addition mass of potassium hydroxide is 175g. All other operations are the same as those of Example 1, and the Ru / C cluster catalyst is finally obtained.

[0062] Example 12

[0063] The preparation steps, raw material types, and process parameters of this embodiment are the same as those of Example 1. The only difference is the addition mass of potassium hydroxide as the morphology control agent. In this embodiment, the addition mass of potassium hydroxide is 23g. All other operations are the same as those of Example 1, and the Ru / C cluster catalyst is finally obtained.

[0064] Comparative Example 1

[0065] This comparative example is a sample prepared using a carbonate-free molten salt system. The preparation steps, raw material addition amounts, and process parameters are basically the same as those in Example 1. The core difference is that no carbonate was added to the molten salt system used in this comparative example. The other raw material types, addition amounts, electrolysis, and post-treatment operations are the same as those in Example 1, and the final comparative sample is obtained.

[0066] The structure of the sample prepared in this comparative example was characterized, and the results were obtained. Figure 3 The XAFS spectrum of the sample prepared in this comparative example shows that the Ru element in the sample is mainly composed of Ru-Ru bonds of large Ru particles, with no obvious Ru cluster characteristic peaks. This indicates that the molten salt system without carbonates cannot achieve the co-deposition of Ru and C, and cannot prepare Ru / C cluster catalysts.

[0067] Comparative Example 2

[0068] This comparative example uses samples prepared under ultra-high current density and long electrolysis time. The preparation steps, raw material types, and amounts are basically the same as in Example 1. The key difference is that in this comparative example, a current density of 200 mA / cm² is applied between the anode and cathode. 2 A constant current was applied, and electrolysis was continued for 12 hours. All other operations were the same as in Example 1, and a comparative sample was finally obtained.

[0069] The structure of the sample prepared in this comparative example was characterized, and the results were obtained. Figure 4 The XAFS spectrum of the sample prepared in this comparative example shows that the Ru element in the sample is mainly composed of Ru-Ru bonds in large Ru particles, without obvious Ru cluster characteristics. This indicates that excessively high current density and excessively long electrolysis time will cause Ru particles to grow and aggregate rapidly, and fail to form cluster structures.

[0070] Comparative Example 3

[0071] This comparative example directly uses a commercially available Ru / C catalyst as a control sample. The structure of this commercial sample was characterized, and... Figure 5The XAFS spectrum of the commercial Ru / C sample is shown in this comparative example. In the commercial Ru / C sample, Ru exists in the form of large-sized nanoparticles, with significant Ru-Ru bond characteristic peaks and no Ru cluster structure characteristics. This is the core reason for the low atom utilization and poor catalytic activity of the commercial Ru / C catalyst.

[0072] Application Example 1

[0073] To verify the catalytic performance of the samples / commercial samples prepared in Examples 1-12 and Comparative Examples 1-3 in the electrocatalytic reaction of terephthalic acid to cyclohexanedicarboxylic acid, the reaction performance of all samples in the aqueous phase electrocatalytic hydrogenation of PTA to CHDA was tested using a performance testing system.

[0074] Prepare the electrolytic reaction solution: Dissolve 0.1g PTA in 100mL of 0.5mol / L KOH aqueous solution as the cathode electrolyte; at the same time, prepare a 0.5mol / L KOH aqueous solution as the anode electrolyte.

[0075] Preparation of working electrode: The samples of each embodiment and comparative example are thoroughly mixed with binder and dispersant, and the mixed slurry is uniformly dripped onto the surface of carbon paper. After drying, it is used as the cathode of electrocatalytic reaction. Nickel foam is used as anode, and an anion exchange membrane is used as diaphragm to separate the anode and cathode chambers, thus constructing a complete electrolytic reaction device.

[0076] Electrocatalytic reaction: The electrolysis reactor was placed in a constant temperature environment of 45°C, with an input current of 5 mA / cm². 2 The current density was continuously electrolyzed for 12 hours, driving the cathode to undergo a PTA electrocatalytic hydrogenation reaction to prepare CHDA.

[0077] Product separation and detection: After the electrolysis reaction was completed, a reaction solution containing 1,4-cyclohexanedicarboxylic acid was obtained in the cathode electrolysis chamber. 100 mL of 0.5 mol / L H2SO4 was added to the reaction solution to precipitate 1,4-cyclohexanedicarboxylic acid from the solution. The precipitated solid product was collected and analyzed. The PTA conversion rate, CHDA yield and current efficiency of each sample were calculated. The specific detection results are shown in Table 1.

[0078] Table 1

[0079]

[0080] Clearly, the Ru / C cluster catalysts prepared in Examples 1-12 of this invention all exhibit excellent PTA electrocatalytic hydrogenation performance, with the lowest PTA conversion rate at 78% and the lowest CHDA yield at 75%, significantly higher than the comparative samples. This indicates that the preparation method of this invention can effectively produce high-performance catalysts suitable for PTA electrocatalytic hydrogenation to CHDA. In particular, Example 1 achieved a PTA conversion rate of 99%, a CHDA yield of 95%, and a current efficiency of 38%, demonstrating the best catalytic performance. Comparative Example 1, lacking carbonate, could not achieve Ru-C co-deposition, resulting in extremely poor catalytic performance. Comparative Example 2, due to its ultra-high current density and excessively long electrolysis time, led to Ru particle agglomeration, resulting in a lack of cluster structure and a significant decrease in catalytic activity. The commercial Ru / C catalyst of Comparative Example 3, dominated by large-sized Ru particles, had low atom utilization and almost no effective PTA electrocatalytic hydrogenation performance, further demonstrating the significant performance advantages of the Ru / C cluster catalyst prepared by this invention.

[0081] This invention reduces carbonates and ruthenium ions in molten salt to carbon and ruthenium atoms by applying voltage or current. The driving force of the reduction reaction is controlled by the cathode potential; for example, a lower overpotential is achieved by controlling the current density, which facilitates the formation of numerous small nucleation sites rather than allowing existing nuclei to grow rapidly. The surface of the co-deposited carbon material typically has abundant defects and functional groups, which are high-energy sites and can serve as preferred nucleation sites, promoting the uniform distribution of Ru clusters. Under electrochemical conditions, the reduction reaction occurs simultaneously and rapidly at multiple active sites on the surface, instantaneously forming a large number of tiny Ru nuclei. Subsequently, due to the decrease in reactant concentration or potential control, the growth of these nuclei is limited, thus forming uniformly sized nanoclusters (typically composed of several to tens of atoms). Simultaneously, the stirring effect of gas generated by the reduction of KOH in the molten salt, for example, improves the dispersion of single atoms on the support surface, preventing agglomeration.

[0082] The Ru / C cluster catalyst prepared by this invention has many significant and beneficial effects:

[0083] (1) Process integration and simplification: The synthesis and loading of catalysts are achieved in one step by molten salt electrolysis, integrating the traditional multi-step preparation (such as support pretreatment, metal impregnation, reduction activation) into a single continuous process, which significantly simplifies the process flow, improves preparation efficiency, and reduces energy consumption and production costs.

[0084] (2) Precise and controllable catalyst structure: By adjusting electrolysis parameters (such as voltage, current density, and temperature) and electrolyte composition (such as adding morphology control agents), the deposition morphology of metallic ruthenium (Ru) can be precisely controlled, successfully obtaining a unique hybrid structure dominated by highly active clusters and containing ultrafine nanoparticles (<2nm). This structure endows the catalyst with a high specific surface area and abundant active sites, providing a foundation for efficient catalysis.

[0085] (3) Excellent catalytic performance: The Ru / C catalyst prepared by this method is specifically designed for the aqueous hydrogenation of terephthalic acid (PTA) to cyclohexanedicarboxylic acid (CHDA). Its unique cluster / nanoparticle hybrid structure significantly enhances catalytic activity and selectivity, thereby achieving higher PTA conversion (≈99%), higher CHDA yield (≈95%), and higher current efficiency (≈38%).

[0086] (4) In-situ generation and strong bonding of the support: During the electrolysis process, an amorphous carbon support is generated in situ, which makes the metal Ru and the carbon support interact strongly. This helps to prevent the loss and aggregation of active components of the catalyst during the reaction process, and significantly improves the stability and service life of the catalyst.

[0087] (5) Morphology control agents promote cluster formation: The strong alkaline environment of hydroxides such as KOH helps to introduce oxygen-containing functional groups such as hydroxyl (-OH) and carboxyl (-COOH) groups onto the carbon support surface. These functional groups can strongly bind metal atoms through metal-oxygen bonds (MOC), preventing them from moving and agglomerating; and KOH and the like will violently etch the carbon surface, generating a large number of defects, pores and edge sites. These sites have high surface energy and are excellent sites for anchoring individual metal atoms.

[0088] (6) Raw material applicability and economy: The ruthenium precursors used (such as RuCl3) are common and relatively inexpensive, and the molten salt electrolyte can be recycled, which conforms to the principles of green chemistry and atom economy, making this method have good industrial application potential and economy.

[0089] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a Ru / C cluster catalyst for the electrocatalytic PTA-to-CHDA reaction, characterized in that, The preparation method includes the following steps: S1, an electrolysis reaction apparatus is provided, wherein the container of the electrolysis reaction apparatus is provided with a molten salt electrolyte containing carbonate; S2, the Ru-containing compound and morphology control agent, which serve as precursors, are mixed with the molten salt electrolyte; S3, Under a protective atmosphere, the electrolysis reaction device is heated to above the melting point of the molten salt electrolyte to form an ion-conducting molten electrolyte system; S4. Apply a DC voltage or pulse voltage between the anode and cathode of the electrolysis reactor to perform constant potential or constant current electrolysis, so that the Ru element in the precursor and the C element in the carbonate are jointly electrodeposited on the cathode surface to form a supported metal catalyst. S5, after electrolysis, is cooled and collected from the cathode. After washing and drying, a supported metal catalyst is obtained.

2. The preparation method according to claim 1, characterized in that, In step S1, the carbonate is one or more of Na2CO3, K2CO3, and Li2CO3; the molten salt electrolyte is a chloride, fluoride, carbonate, or a eutectic mixture thereof.

3. The preparation method according to claim 2, characterized in that, The chloride is one or more of LiCl, NaCl, and KCl; the fluoride is one or more of NaF, KF, and LiF.

4. The preparation method according to claim 1, characterized in that, In step S2, the precursor is one or more of RuCl3 and Ru(NO3)3; the morphology control agent is one or more of LiOH, NaOH and KOH.

5. The preparation method according to claim 1, characterized in that, In step S2, the precursor accounts for 0.1wt%-2wt% of the total electrolyte mass; the morphology control agent accounts for 5wt%-30wt% of the total electrolyte mass.

6. The preparation method according to claim 1, characterized in that, In step S3, the heating temperature is 425°C to 800°C.

7. The preparation method according to claim 1, characterized in that, In step S4, the current density of the constant current electrolysis is 5 mA / cm². 2 Up to 50mA / cm 2 .

8. The Ru / C catalyst obtained by the preparation method according to any one of claims 1-7, characterized in that, This Ru / C catalyst is a supported catalyst, with co-deposited amorphous carbon as the support and Ru as the supported metal, and the Ru loading is 0.5-50 wt%.

9. The Ru / C catalyst according to claim 8, characterized in that, In the Ru / C catalyst, Ru has a mixed structure consisting mainly of clusters and containing a small number of nanoparticles with a size of less than 2 nm.

10. The application of the Ru / C catalyst according to claim 8 or 9 in the aqueous phase electrocatalytic hydrogenation of PTA to prepare CHDA.

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