A praseodymium fluoride modified nickel cobalt oxide self-supporting electrocatalyst, a preparation method and application thereof

Abstract

The application relates to the technical field of electrocatalytic organic synthesis and nanomaterials, and discloses a praseodymium fluoride modified nickel cobalt oxide self-supporting electrocatalyst as well as a preparation method and application thereof. The electrocatalyst takes a foamed nickel as a conductive substrate, in-situ grows a porous nano array containing spinel type NiCo2O4 and PrF3 on the surface of the foamed nickel, and the PrF3 is distributed on the surface of the NiCo2O4 nano structure and forms a contact interface with the NiCo2O4 nano structure. Nickel salt, cobalt salt, praseodymium salt, urea and fluorine-containing precipitants are dispersed in a mixed solvent of water, ethanol and N, N-dimethylformamide, and the electrocatalyst is prepared through hydrothermal treatment, washing and air calcination. The electrocatalyst can electro-oxidize cyclohexanol, cyclohexanone or KA oil into adipate in an alkaline aqueous solution without adding a chemical oxidant, a surfactant or a homogeneous oxidation-reduction medium. In a representative KA oil experiment, the yield of adipic acid is about 69% to 74%, and the selectivity is about 78% to 85%; after acidification, concentration, decolorization and recrystallization, adipic acid with a purity greater than or equal to 97.2% can be obtained.

Description

Technical Field

[0001] This invention relates to the fields of electrocatalytic organic synthesis and nanomaterials technology, specifically to a praseodymium fluoride-modified nickel-cobalt oxide self-supporting electrocatalyst, an in-situ hydrothermal-calcination preparation method for the electrocatalyst, and its application in the direct electrocatalytic oxidation of cyclohexanol, cyclohexanone, and KA oil of different compositions in alkaline media to prepare adipate. Background Technology

[0002] Adipic acid is an important platform compound for the production of nylon 66, polyurethane, polyester, plasticizers, and lubricants. Existing industrial routes typically involve first producing KA oil (composed of cyclohexane alcohol and cyclohexanone) from cyclohexane, followed by oxidation using high-concentration nitric acid. While this route is technologically mature, it generates N2O and other nitrogen oxides and suffers from strong corrosion, high oxidant consumption, and a heavy burden of exhaust gas treatment. Utilizing renewable electricity and incorporating water and hydroxide ions in anodic oxidation, KA oil can be converted to adipic acid salts near ambient temperature and pressure, representing a potential green alternative to nitric acid oxidation.

[0003] However, cyclohexanol first needs to be dehydrogenated to cyclohexanone, which then undergoes further oxidation, ring-opening, and oxidation processes. Simultaneously, oxygen evolution reaction easily occurs at the anode, and the intermediate may further break down to form short-chain byproducts such as glutaric acid, succinic acid, malonic acid, or acetic acid. Therefore, the catalyst needs to balance cyclohexanol dehydrogenation, cyclohexanone activation, C6 skeleton retention, and oxygen evolution inhibition. Furthermore, the alcohol and ketone composition of actual KA oils varies depending on the source and process; electrodes optimized only for single cyclohexanol or single cyclohexanone may not be directly adaptable to KA oils with different compositions.

[0004] Chinese invention patent CN115747844A discloses a method for preparing adipic acid by electrocatalytic oxidation of cyclohexanol or cyclohexanone using metal oxide / hydroxide supported on foamed metal. The electrode is primarily obtained by treating the foamed metal with a hydrogen peroxide solution containing ferrous salts. This technology does not disclose the in-situ construction of a self-supporting catalytic layer containing spinel-type NiCo2O4 and PrF3 on the surface of the foamed nickel, nor does it provide compositional adaptability data for KA oil with different cyclohexanol / cyclohexanone ratios. Chinese invention patent CN113337836B uses an electrolyte containing manganese salts, nitriles, and quaternary ammonium bases and introduces nitrogen plasma to oxidize cyclohexanone; the reaction system and electrode structure are significantly different from the self-supporting electrode of this invention.

[0005] Furthermore, existing fluorinated NiCo2O4 or rare earth oxide modified catalysts are mostly used for oxygen evolution, energy storage, or electro-oxidation of other organic substrates; simple fluorine doping is not equivalent to introducing PrF3 modified species on the surface of NiCo2O4 nanostructures. Therefore, there is still a need for a self-supporting electrocatalyst that can act directly on KA oil, without the need for additional chemical oxidants and homogeneous mediators, and has good adipic acid generation capacity and adaptability to feedstock composition. Summary of the Invention

[0006] The purpose of this invention is to provide a praseodymium fluoride-modified nickel-cobalt oxide self-supporting electrocatalyst and its preparation method, so as to solve the problems of existing electrodes being dependent on a single substrate, exhibiting significant competitive oxygen evolution, and lacking adaptability to changes in the composition of KA oleyl alcohol ketones.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a self-supporting electrocatalyst. The electrocatalyst uses nickel foam as a conductive framework, with a porous nanoarray grown in situ on the surface of the nickel foam; the nanoarray comprises spinel-type NiCo2O4 and PrF3, with PrF3 distributed in the contact region of NiCo2O4 nanosheets, nanorods, or both. PrF3 can be observed in Pr 3d X-ray photoelectron spectroscopy. 3+ and Pr 4 + The relevant signals indicate that the praseodymium-containing species on the surface of the catalyst layer have a mixed chemical state, but this does not limit the formation of an independent praseodymium oxide crystal phase.

[0008] Secondly, the present invention provides a method for preparing the above-mentioned electrocatalyst: Cleaned nickel foam is vertically placed in a precursor solution containing nickel salt, cobalt salt, praseodymium salt, urea, and NH4F; a hydrothermal reaction is used to deposit the precursor containing nickel, cobalt, praseodymium, and fluorine in situ; followed by washing, drying, and air calcination to form a catalyst layer containing NiCo2O4 and PrF3. By adjusting the amount of praseodymium salt and NH4F added and the calcination temperature, a self-supporting electrode with good electro-oxidation performance of cyclohexanol and KA oil is obtained.

[0009] Thirdly, this invention provides the application of the above-mentioned electrocatalyst in the electro-oxidation of cyclohexanol, cyclohexanone, and KA oils of different compositions to produce adipate. The reaction can be carried out in 0.1~10 mol / L alkaline aqueous solution, at 5~80 °C, and under constant current conditions, without requiring the addition of nitric acid, peroxide, permanganate, surfactant, or homogeneous redox mediator.

[0010] Without being restricted by specific theories, NiCo2O4 can form a working surface containing high-valence Ni / Co species under alkaline anodic conditions, promoting the dehydrogenation of cyclohexanol to cyclohexanone and further activating cyclohexanone; PrF3 modification and related changes in the chemical state of praseodymium-containing surfaces may regulate the surface electronic environment and adsorption of oxygen-containing species around Ni and Co centers, thereby facilitating the oxidation of KA oil and reducing the impact of competitive oxygen evolution on adipic acid formation.

[0011] Compared with the prior art, the present invention has the following beneficial effects: (1) It is not simply fluorine doping, but PrF3 modified species are introduced on the surface of NiCo2O4 nanostructure; XRD and HRTEM results can mutually confirm the existence of NiCo2O4 and PrF3 crystal phases, and EDS surface distribution shows that praseodymium-containing and fluorine-containing components are in close contact with NiCo2O4 at the nanoscale.

[0012] (2) The catalyst layer is grown directly in situ on nickel foam without the need for polymer binders, and has a continuous conductive path and an open mass transfer structure.

[0013] (3) Adipic acid can be obtained from pure cyclohexanol, pure cyclohexanone, and KA oil with a molar ratio of cyclohexanol / cyclohexanone of 3:1, 1:1 and 1:3. The representative adipic acid yield is about 69%~74% and the selectivity is about 76%~85%, showing adaptability to changes in raw material composition.

[0014] (4) The anolyte does not require nitric acid, permanganate, peroxide, surfactant or homogeneous redox mediator; after acidification, concentration, activated carbon decolorization and recrystallization, the purity of adipic acid can reach 97.2% or above. Attached Figure Description

[0015] Figure 1 The images show the morphology and elemental distribution of the PrF3-NiCo2O4 / NF self-supporting electrocatalyst obtained in Example 1. In the images, A is a scanning electron microscope image, B is a transmission electron microscope image, C is a high-resolution transmission electron microscope image, and D is a scanning transmission electron microscope image and the surface distribution diagrams of Co, Ni, Pr, F and O elements.

[0016] Figure 2 The X-ray diffraction patterns are shown for the PrF3-NiCo2O4 composite powder obtained in Example 2, the PrF3-NiCo2O4 / NF self-supporting electrocatalyst obtained in Example 1, and the NiCo2O4 / NF control electrode. The NiCo2O4 standard card JCPDS #20-0781 and the PrF3 standard card JCPDS #06-0325 are also shown in the figure.

[0017] Figure 3 The images show the high-resolution X-ray photoelectron spectra of the PrF3-modified self-supporting electrocatalyst obtained in Example 1 and the NiCo2O4 / NF control electrode, where A is the Co 2p spectrum, B is the Ni 2p spectrum, and C is the Pr 3d spectrum of the PrF3-modified sample.

[0018] Figure 4 The values ​​are before the electro-oxidation reaction of cyclohexanol, after 4 hours of reaction, and after 24 hours of reaction. 1 The 1H NMR spectrum and the spectrum of adipic acid standard, where CHN represents cyclohexanone, AA represents adipic acid, GA represents glutaric acid, and SA represents succinic acid.

[0019] Figure 5 The graph shows the effects of catalyst composition, calcination temperature, and initial Pr source feed amount on the electro-oxidation performance of cyclohexanol. In this graph, A represents the PrF3-NiCo2O4 / NF self-supported electrocatalyst and the NiCo2O4 / NF control electrode at 40 mA·cm⁻¹. -2 and 70 mA·cm -2 A) Comparison of adipic acid Faradaic efficiency under different current densities; B) Graphs showing the conversion rate of cyclohexanol and the Faradaic efficiency of cyclohexanone and adipic acid at different calcination temperatures under a total current of 40 mA; C) Graphs showing the conversion rate of cyclohexanol and the Faradaic efficiency of cyclohexanone and adipic acid at different initial feed amounts of Pr source under a total current of 70 mA.

[0020] Figure 6 The graph shows the electro-oxidation performance of the self-supported electrocatalyst obtained in Example 1. In the graph, A is the Faradaic efficiency of cyclohexanone and adipic acid after electrolysis of 0.1 mol / L cyclohexanone for 4 h at different current densities. In the graph, B is the yield and selectivity of adipic acid in pure cyclohexanone, KA oil with different cyclohexanone / cyclohexanone molar ratios, and pure cyclohexanone system after electrolysis for 11 h at a total current of 70 mA. A represents cyclohexanone, and K represents cyclohexanone.

[0021] Figure 7 The diagram shows the continuous feed electrolysis and separation products. A represents the chronopotential curve and adipic acid Faraday efficiency curve after 24 hours of continuous electrolysis at a total current of 70 mA, with 3 mmol of cyclohexanol added every 4 hours during the electrolysis process. B shows the white adipic acid solid obtained after acidification, concentration, decolorization, crystallization, and recrystallization of the electrolyte. C shows the separation product and adipic acid standard. 1 The NMR spectrum is shown in Figure 1, and the high-performance liquid chromatograms of the adipic acid standard and the obtained adipic acid product are shown in Figure 2. Detailed Implementation

[0022] The specific embodiments of the present invention are described below to enable those skilled in the art to understand the present invention. However, it should be understood that the present invention is not limited to the scope of the specific embodiments. For those skilled in the art, various changes are obvious as long as they are within the spirit and scope of the present invention as defined and determined by the appended claims. All inventions utilizing the concept of the present invention are protected.

[0023] Example 1 This embodiment provides a method for preparing a PrF3-NiCo2O4 / NF self-supporting electrocatalyst, comprising the following steps: S1. The nickel foam with dimensions of 2 cm × 3 cm × 0.5 mm was ultrasonically washed sequentially with dilute hydrochloric acid for 15 min, ultrasonically washed with ethanol for 15 min, and ultrasonically washed with water for 15 min.

[0024] S2. Weigh 0.582 g (2 mmol) Ni(NO3)2·6H2O, 1.164 g (4 mmol) Co(NO3)2·6H2O, 0.174 g (0.4 mmol) Pr(NO3)3·6H2O, 0.600 g urea, and 0.186 g NH4F. Add them to a mixed solvent consisting of 6 mL N,N-dimethylformamide, 12 mL ethanol, and 18 mL deionized water. Sonicate and stir until a homogeneous precursor solution is formed. NH4F and Pr 3+ The process forms a Pr-F precursor component, while the slow hydrolysis of urea promotes the co-deposition of Ni, Co and Pr precursors on the surface of nickel foam.

[0025] S3. Place the nickel foam vertically in a polytetrafluoroethylene-lined reactor, immersing it in the precursor solution; perform a hydrothermal reaction at 120 °C for 6 h, then allow it to cool naturally to room temperature. Remove the electrode, wash it three times with water and three times with ethanol, and then dry it with a hair dryer for 5 min.

[0026] S4. Place the dried electrode in an air atmosphere furnace, heat it to 350 ℃ at 5 ℃ / min, hold it at that temperature for 2 h and then cool it naturally to obtain the PrF3-NiCo2O4 / NF self-supporting electrocatalyst.

[0027] Example 2 This embodiment provides a method for preparing PrF3-NiCo2O4 electrocatalyst composite powder, including the following steps: Weigh 0.582 g (2 mmol) Ni(NO3)2·6H2O, 1.164 g (4 mmol) Co(NO3)2·6H2O, 0.174 g (0.4 mmol) Pr(NO3)3·6H2O, 0.600 g urea, and 0.186 g NH4F. Add these to a mixed solvent consisting of 6 mL N,N-dimethylformamide, 12 mL ethanol, and 18 mL deionized water. Sonicate and stir until a homogeneous precursor solution is formed. NH4F and Pr³ + The reaction process forms a Pr-F precursor component. The reaction is carried out hydrothermally at 120 °C for 6 h, followed by natural cooling to room temperature. The powder is removed, centrifuged, washed three times with water and three times with ethanol, and then dried at 60 °C. The dried powder is placed in an air atmosphere furnace, heated to 350 °C at a rate of 5 °C / min, held at this temperature for 2 h, and then naturally cooled to obtain the PrF3-NiCo2O4 electrocatalyst composite powder.

[0028] Example 3 This embodiment provides a method for preparing a praseodymium fluoride-modified NiCo2O4 self-supporting electrocatalyst with low praseodymium feed. The same foamed nickel, Ni salt, Co salt, urea, NH4F, mixed solvent, hydrothermal and calcination conditions as in Example 1 were used, except that the amount of Pr(NO3)3·6H2O was adjusted to 0.130 g (0.3 mmol). The foamed nickel was vertically immersed in the precursor solution and hydrothermally heated at 120 °C for 6 h. After washing three times with water, three times with ethanol, and drying, the temperature was increased to 350 °C at 5 °C / min and held for 2 h to obtain the low praseodymium feed self-supporting catalyst, denoted as PrF3-NiCo2O4-0.3 / NF.

[0029] Example 4 This embodiment provides a method for preparing a praseodymium fluoride-modified NiCo2O4 self-supporting electrocatalyst with high praseodymium feed. The same foamed nickel, Ni salt, Co salt, urea, NH4F, mixed solvent, hydrothermal and calcination conditions as in Example 1 were used, except that the amount of Pr(NO3)3·6H2O was adjusted to 0.218 g (0.5 mmol). The resulting electrode, denoted as PrF3-NiCo2O4-0.5 / NF, was used to investigate the effect of Pr source feed amount on the electro-oxidation performance of cyclohexanol and KA oil.

[0030] Example 5 This embodiment investigates the effect of different calcination temperatures on the obtained self-supporting electrodes. The precursor was hydrothermally grown, washed, and dried according to Example 1; subsequently, it was heated to 450 °C, 550 °C, and 650 °C at a rate of 5 °C / min in air and held for 2 h, followed by natural cooling to obtain Pr / F-containing self-supporting electrodes calcined at different temperatures. The above high-temperature samples were used to compare the effects of calcination temperature on crystal phase, morphology, and electro-oxidation performance; however, this does not imply that all high-temperature samples maintain the same PrF3 surface structure as the 350 °C sample.

[0031] Comparative Example 1 This comparative example provides a method for preparing a NiCo2O4 / NF self-supporting electrode. Except for the absence of Pr(NO3)3·6H2O, the remaining steps are the same as in Example 1, yielding the NiCo2O4 / NF self-supporting electrode. NH4F is retained as a morphology modifier so that the comparative example primarily reflects the effect of the introduction of Pr-containing components on catalytic performance.

[0032] Test case 1. Scanning electron microscope (SEM) and transmission electron microscope (TEM) images and elemental distribution maps of the catalyst. Depend on Figure 1 As shown in A, the PrF3-NiCo2O4 / NF self-supporting electrocatalyst forms a continuous, rough catalytic layer with open pores on the surface of nickel foam. Figure 1As can be seen from B, the catalyst layer is mainly composed of overlapping sheet-like and rod-like nanostructures, which is beneficial to increasing the contact area between the catalyst and the electrolyte.

[0033] Depend on Figure 1 The high-resolution transmission electron microscope image shown in C reveals clear lattice fringes. In the NiCo2O4 region, the measured lattice spacing is approximately 0.204 nm, which can be attributed to the (400) and (040) crystal planes of NiCo2O4. The angle between the two sets of lattice fringes is approximately 90°. The measured lattice spacings are approximately 0.229 nm and 0.250 nm, which can be attributed to the (22-2) and (311) crystal planes of NiCo2O4, respectively. The angle between the two is approximately 59.7°, which is basically consistent with the theoretical angle of approximately 58.5°. In the PrF3 region, the measured lattice spacings were approximately 0.320 nm and 0.200 nm, which can be attributed to the (111) and (113) crystal planes of PrF3, respectively, with an angle of approximately 29.7° between them. In local areas, lattice fringes with spacings of approximately 0.349 nm and 0.208 nm were also observed, which can be attributed to the (110) and (300) crystal planes of PrF3, respectively, with an angle of approximately 30.7° between them, which is basically consistent with the theoretical angle of approximately 30.0°. The NiCo2O4 and PrF3 structural regions are adjacent to each other at the nanoscale, indicating a close contact between the PrF3 modified species and NiCo2O4. The absence of a clear long-range ordered lattice in some regions suggests the possible presence of low-crystallinity or amorphous praseodymium-containing surface species.

[0034] Figure 1 The D-array shows that Co, Ni, Pr, F, and O elements are all distributed within the selected region, and the distribution regions of Pr and F elements overlap well with those of Ni, Co, and O elements. This indicates that praseodymium-containing and fluorine-containing components have been successfully introduced into the NiCo2O4 catalyst layer and are in close contact with NiCo2O4 at the nanoscale. The elemental surface distribution reflects the spatial co-distribution relationship and is not used alone to determine Pr-O chemical bonds or independent praseodymium oxide phases.

[0035] 2. X-ray diffraction pattern of the catalyst from Figure 2 It can be seen that diffraction characteristics corresponding to the NiCo2O4 standard card JCPDS #20-0781 can be observed in the PrF3-NiCo2O4 composite powder, the PrF3-NiCo2O4 / NF self-supporting electrocatalyst, and the NiCo2O4 / NF control electrode. Diffraction characteristics corresponding to the PrF3 standard card JCPDS #06-0325 can also be observed in the praseodymium-containing and fluorine-containing samples, indicating that the obtained composite catalyst contains both NiCo2O4 and PrF3 crystalline phases.

[0036] 3. X-ray photoelectron spectroscopy of the catalyst Depend on Figure 3 A and Figure 3 As shown in B, compared with the NiCo2O4 / NF control electrode, the binding energy of the Co 2p characteristic peak of the PrF3 modified sample changed by about 0.21 eV, and the binding energy of the Ni 2p region changed by about 0.11 eV and 0.21 eV, which is consistent with the change in the surface electronic environment around the Ni and Co centers after the introduction of Pr / F components. Figure 3 Pr can be observed in C. 3+ and Pr 4+ The correlation fitting peaks and satellite peaks indicate that the praseodymium-containing species on the catalyst surface have a mixed chemical state, and some surface praseodymium species may be oxidized or hydroxylated.

[0037] 4. Performance testing of catalyst in the electro-oxidation of KA oil and cyclohexanol Depend on Figure 4 It was observed that the NMR spectrum before the reaction was dominated by cyclohexanol-related signals; after 4 h of reaction, cyclohexanone signals appeared, and characteristic signals corresponding to adipic acid standards began to appear; after 24 h of reaction, the characteristic signals of adipic acid were significantly enhanced, and small amounts of glutaric acid and succinic acid-related signals could also be observed. This indicates that cyclohexanol is first converted to cyclohexanone during electro-oxidation, and then further oxidized to adipic acid. Prolonged reaction times may be accompanied by the formation of small amounts of carbon chain cleavage byproducts.

[0038] Figure 5 The experiment investigated the effects of catalyst composition, calcination temperature, and initial Pr source feed amount on electro-oxidation performance by electrolysis in a 1.0 mol / L KOH and 0.1 mol / L cyclohexanol system for 4 h.

[0039] Depend on Figure 5 As can be seen from A, at 40 mA·cm -2 At current densities, the adipic acid Faradaic efficiencies of the PrF3-NiCo2O4 / NF self-supporting electrocatalyst obtained in Example 1 and the NiCo2O4 / NF control electrode are approximately 45% and 36%, respectively; at 70 mA·cm⁻¹ -2 The values ​​were approximately 72% and 59% respectively, indicating that the introduction of Pr-containing components is beneficial to improving the Faraday efficiency of adipic acid formation.

[0040] Electrodes were prepared using the method described in Example 1, with the only difference being the calcination temperature, which was adjusted to 350 °C, 450 °C, 550 °C, and 650 °C, and tests were conducted at a total current of 40 mA. Figure 5As can be seen from B, the conversion rate of cyclohexanol and the Faraday efficiency of adipic acid generally decrease with the increase of calcination temperature; the conversion rate of cyclohexanol and the Faraday efficiency of adipic acid in the sample calcined at 350 ℃ are about 80% and 45%, respectively, while the conversion rate of cyclohexanol and the Faraday efficiency of adipic acid in the sample calcined at 650 ℃ are reduced to about 30% and 28%, respectively, indicating that 350 ℃ is a more suitable calcination temperature.

[0041] Electrodes with initial Pr source feed amounts of 0.3 mmol, 0.4 mmol, and 0.5 mmol were prepared using the method in Example 1, and tested at a total current of 70 mA. Figure 5 As shown in Figure C, the cyclohexanol conversion rates of the three electrodes were approximately 90%, close to 100%, and 88%, respectively, while the adipic acid faradaic efficiencies were approximately 70%, 72%, and 60%, respectively. Among them, the electrode obtained with an initial Pr source feed amount of 0.4 mmol exhibited superior overall performance, indicating that a suitable Pr source feed is beneficial to improving the cyclohexanol conversion rate and the adipic acid faradaic efficiency.

[0042] Figure 6 A shows that in the 1.0 mol / L KOH and 0.1 mol / L cyclohexanol system, the current density has a significant impact on the Faradaic efficiency distribution of the two main oxidation products, cyclohexanone and adipic acid. When the current density is 70 mA·cm⁻¹... -2 At this time, the sum of the Faradaic efficiencies of cyclohexanone and adipic acid is approximately 100%, with the Faradaic efficiency of adipic acid being approximately 72.9% and the Faradaic efficiency of cyclohexanone being approximately 26.9%, indicating that under these conditions, the electro-oxidation of cyclohexanol mainly produces cyclohexanone and adipic acid.

[0043] Depend on Figure 6 As shown in section B, under electrolysis conditions of 1.0 mol / L KOH electrolyte, a total substrate concentration of 0.1 mol / L, and a total current of 70 mA for 11 h, pure cyclohexanol, KA oil with different cyclohexanol / cyclohexanone ratios, and pure cyclohexanone can all be converted to adipic acid. The adipic acid yields of pure cyclohexanol, KA-3:1, KA-1:1, KA-1:3, and pure cyclohexanone systems are approximately 71%, 69%, 74%, 70%, and 69%, respectively, with corresponding adipic acid selectivities of approximately 76%, 78%, 79%, 85%, and 82%. Among these, the KA-1:1 system exhibits the highest adipic acid yield, while the KA-1:3 system demonstrates the highest adipic acid selectivity, indicating that the catalyst prepared in this invention can adapt to KA oil feedstocks with different compositions. A represents cyclohexanol, K represents cyclohexanone, and KA-3:1, KA-1:1, and KA-1:3 represent the molar ratios of cyclohexanol to cyclohexanone as 3:1, 1:1, and 1:3, respectively.

[0044] 5. Catalyst stability testing and adipic acid product separation Depend on Figure 7As shown in Figure A, when electrolyzing continuously for 24 h in 30 mL of 1.0 mol / L KOH electrolyte at a total current of 70 mA, with 3 mmol of cyclohexanol added every 4 h, the electrode exhibited similar potential changes after each addition of cyclohexanol. Throughout the test, the operating potential remained within the range of 1.48–1.70 V (relative to the reversible hydrogen electrode), and the adipic acid Faradaic efficiency at each sampling point remained approximately 65%–76%. This indicates that the PrF3-NiCo2O4 / NF self-supporting electrocatalyst prepared in this invention can operate stably for 24 h under continuous feeding conditions and maintain good adipic acid production capacity.

[0045] After continuous electrolysis, acid is added to the anolyte containing adipic acid to adjust the pH to 1-3, converting adipic acid to adipic acid. The acidified electrolyte is then concentrated by rotary evaporation, decolorized with activated carbon, filtered, further concentrated, and cooled to crystallize. Finally, the resulting crystals are recrystallized. Figure 7 As shown in B, a white solid can be obtained after acidification, concentration, decolorization, crystallization, and recrystallization. Figure 7 From C, we can know that the obtained solid... 1 The H NMR characteristic signal and integral ratio were basically consistent with those of the adipic acid standard. Further determination using high-performance liquid chromatography (HPLC) with external standard method showed that the retention time of the obtained solid was consistent with that of the adipic acid standard. The RSDs of the peak areas of the sample and standard in three parallel injections were 0.21% and 0.23%, respectively. After correction for standard purity, the mass fraction of the obtained adipic acid product was 97.2%, and its chromatogram is shown below. Figure 7 As shown in Figure D. The above results indicate that the separated solid is adipic acid with high purity. This shows that the adipic acid obtained by this invention can not only be detected in the electrolyte, but can also be physically separated through steps such as acidification, concentration, decolorization, and crystallization.

[0046] It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered illustrative rather than restrictive, and the scope of protection of the present invention is defined by the appended claims.

[0047] Furthermore, it should be understood that although this specification describes embodiments, not every embodiment contains only one independent technical solution. Those skilled in the art can understand the specification as a whole, and the technical solutions in each embodiment can be appropriately combined without contradiction to form other possible embodiments.

Claims

1. A praseodymium fluoride-modified nickel-cobalt oxide self-supporting electrocatalyst, comprising a nickel foam substrate and a catalyst layer in situ supported on the surface of the nickel foam substrate, characterized in that, The catalyst layer comprises spinel-type NiCo2O4 and PrF3, wherein the PrF3 is distributed on the surface of the NiCo2O4 nanostructure and forms a contact interface with it.

2. The self-supporting electrocatalyst according to claim 1, characterized in that, The catalyst layer is in the form of a porous nanoarray consisting of nanosheets, nanorods, or a combination of both; it has a lattice spacing of approximately 0.250 nm corresponding to the NiCo2O4 crystal plane and approximately 0.320 nm corresponding to the PrF3 crystal plane in a high-resolution transmission electron microscope.

3. A method for preparing the self-supporting electrocatalyst according to any one of claims 1 to 2, characterized in that, include: S1, clean the nickel foam; S2, disperse nickel salt, cobalt salt, praseodymium salt, urea and fluorine-containing precipitant in a solvent to form a precursor solution, place the nickel foam in the precursor solution for hydrothermal reaction, so that the precursor containing nickel, cobalt, praseodymium and fluorine grows in situ on the surface of the nickel foam; S3, wash, dry and calcine the nickel foam after hydrothermal reaction in an air atmosphere to obtain a praseodymium fluoride modified nickel cobalt oxide self-supporting electrocatalyst.

4. The preparation method according to claim 3, characterized in that, The nickel salt, cobalt salt, and praseodymium salt are nitrates of their respective metals; the molar ratio of Ni, Co, and Pr elements in the precursor solution is 1:2:(0.15~0.25), preferably 1:2:0.20; the fluorine-containing precipitant is NH4F, and the molar ratio of NH4F to Pr is 10:1~17:1, preferably 25:2; the molar ratio of urea to the total amount of Ni, Co, and Pr is 1.53:1~1.59:1, preferably 1.56:

1.

5. The preparation method according to claim 3 or 4, characterized in that, The solvent is a mixture of water, ethanol, and N,N-dimethylformamide, or one of them; the hydrothermal temperature is 80~180 ℃, and the hydrothermal time is 1~12 h; the calcination temperature is 300~700 ℃, preferably 350 ℃, the calcination time is 1~10 h, and the heating rate is 1~10 ℃ / min.

6. The preparation method according to any one of claims 3 to 5, characterized in that, Nickel foam was used as the substrate; the precursor solution contained Ni(NO3)2·6H2O, Co(NO3)2·6H2O, Pr(NO3)3·6H2O, urea and NH4F, and the solvent was a mixture of N,N-dimethylformamide, ethanol and water or one of them; the hydrothermal reaction conditions were a hydrothermal temperature of 80~180 ℃ and a hydrothermal time of 1~12 h to obtain the catalyst precursor; then the temperature was increased to 300~700 ℃ at 1~10 ℃ / min and calcined for 1~10 h.

7. The use of the self-supporting electrocatalyst according to any one of claims 1 to 2 in the electrocatalytic oxidation of cyclohexanol, cyclohexanone or KA oil in alkaline aqueous solution to prepare adipate.

8. The application according to claim 7, characterized in that, When the substrate is KA oil, the cyclohexanol in the KA oil accounts for 5% to 95% of the total amount of cyclohexanol and cyclohexanone, preferably the molar ratio of cyclohexanol to cyclohexanone is 3:1, 1:1 or 1:

3.

9. The application according to claim 7 or 8, characterized in that, The alkaline aqueous solution is a KOH aqueous solution with a KOH concentration of 0.1–10 mol / L and a total concentration of cyclohexanol and cyclohexanone of 0.1–5.0 mol / L; the reaction temperature is 5–80 °C, and constant current electrolysis is used with a current density of 10–1000 mA·cm⁻¹. -2 The reaction time is 1~26 h.

10. The application according to any one of claims 7 to 9, characterized in that, No nitric acid, permanganate, peroxide-based external chemical oxidants, surfactants, or homogeneous redox mediators are added to the anolyte.

11. The application according to any one of claims 7 to 10, characterized in that, After electrolysis, the electrolyte containing adipic acid salt is acidified to pH 1-3, and then concentrated under reduced pressure, decolorized with activated carbon, filtered, cooled and crystallized, and recrystallized to obtain solid adipic acid.

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