A carrier-free nickel-cobalt composite oxide catalyst, a preparation method and application thereof

Abstract

This invention discloses a carrier-free nickel-cobalt composite oxide catalyst, its preparation method, and its application, belonging to the field of catalyst technology. Using nickel acetylacetonate and cobalt acetylacetonate as starting materials, this invention synthesizes a series of NiO-Co3O4 composite oxide catalysts through a combination of planetary ball milling and air calcination. The ball milling process parameters are as follows: the total mass of the precursors (i.e., nickel acetylacetonate and cobalt acetylacetonate) is fixed at 12.5 g, the ball milling speed is set at 400 rpm, and the ball milling time is 10 hours. The calcination process parameters are as follows: calcination is carried out in an air environment at 2℃·min. ‑1 The catalyst was calcined at a rate of 400°C and held at this temperature for 2 hours to obtain a supportless nickel-cobalt composite oxide catalyst. This invention provides a new approach for developing green, inexpensive, and efficient non-precious metal catalysts for naphthalene hydrogenation.

Description

Technical Field

[0001] This invention belongs to the field of catalyst technology, and particularly relates to a supportless nickel-cobalt composite oxide catalyst, its preparation method, and its application. Background Technology

[0002] As the global energy landscape transitions towards sustainable development, hydrogen energy is widely recognized as a key renewable energy carrier. However, its large-scale storage and transportation remain challenging. Liquid organic hydrogen carriers (LOHCs) have emerged as a promising solution for safe, long-term hydrogen storage using existing fuel infrastructure. Among LOHC candidates, naphthalene stands out due to its low cost, abundant coal-based sources, stable molecular structure, and high hydrogen storage capacity (7.3 wt%). Its hydrogenation product, decahydronaphthalene, is liquid at room temperature, making it ideal for transportation. Therefore, the reversible naphthalene-decahydronaphthalene system is considered one of the most feasible approaches to achieving large-scale hydrogen storage.

[0003] Noble metal catalysts (Pt, Pd, Ru, Rh) exhibit excellent activity in the low-temperature hydrogenation of naphthalene. However, their high cost, limited reserves, and susceptibility to sulfur and nitrogen poisoning hinder their industrial application. To overcome these drawbacks, efforts have been made to develop non-noble metal catalysts as cost-effective alternatives. Nickel-based catalysts offer a cost-effective option, but typically require harsh conditions or pre-reduction treatments. The forced high-temperature H2 pre-reduction step increases process complexity and energy consumption. Therefore, developing catalysts capable of spontaneously generating active sites under reaction conditions is highly desirable.

[0004] Recently, NiO-Co3O4 composite oxides have attracted considerable research interest due to their synergistic effect in enhancing catalytic performance. However, their application in the hydrogenation of naphthalene, particularly as an unsupported catalyst, remains largely unexplored. Traditional preparation methods, such as impregnation and co-precipitation, are typically cumbersome and generate waste. Summary of the Invention

[0005] To address the aforementioned technical problems, this invention proposes a carrier-free nickel-cobalt composite oxide catalyst, its preparation method, and its application.

[0006] To achieve the above objectives, the present invention provides the following technical solution: This invention provides a method for preparing a carrierless nickel-cobalt composite oxide catalyst, which uses nickel acetylacetonate and cobalt acetylacetonate as starting materials and is synthesized by a combination of planetary ball milling and air calcination. The mass ratio of nickel acetylacetonate to cobalt acetylacetonate is 2:(1~4). During the air calcination, the calcination temperature is 400°C.

[0007] Ball milling provides a green, simple, and scalable route for catalyst synthesis. This invention synthesizes a series of unsupported NiO-Co3O4 catalysts via ball milling and air calcination. This invention systematically studies the effects of the Ni / Co ratio and calcination temperature on the catalyst structure and properties using various characterization techniques. This invention employs in-situ XRD and Raman spectroscopy to elucidate the dynamic structural evolution of the catalyst under a reducing atmosphere. The catalyst of this invention undergoes a unique in-situ activation process, spontaneously forming highly active bimetallic clusters without external pre-reduction, which is key to its excellent performance in the hydrogenation of naphthalene under mild conditions.

[0008] Furthermore, the mass ratio of nickel acetylacetonate to cobalt acetylacetonate is 2:3.

[0009] Furthermore, the preparation method of the carrier-free nickel-cobalt composite oxide catalyst includes the following steps: mixing nickel acetylacetonate and cobalt acetylacetonate, first performing planetary ball milling, and then calcining the ball-milled product in air to obtain the carrier-free nickel-cobalt composite oxide catalyst.

[0010] Furthermore, the ball mill is operated at a speed of 400 rpm for 10 hours.

[0011] Furthermore, the calcination time is 2 hours, and the heating rate is 2°C·min. -1 .

[0012] The present invention also provides a supportless nickel-cobalt composite oxide catalyst prepared according to the above method.

[0013] The present invention also provides an application of the above-mentioned carrierless nickel-cobalt composite oxide catalyst in the hydrogenation of naphthalene to decahydronaphthalene.

[0014] The present invention also provides a method for catalytic hydrogenation of naphthalene to produce decahydronaphthalene, wherein naphthalene, n-dodecane and the above-mentioned unsupported nickel-cobalt composite oxide catalyst are mixed and reacted by stirring at 3.0~4.0 MPa and 150~180°C, preferably at 3.0 MPa and 150°C.

[0015] Furthermore, the ratio of naphthalene, n-dodecane, and the above-mentioned unsupported nickel-cobalt composite oxide catalyst is 0.1g:0.7g:5mL.

[0016] Compared with the prior art, the present invention has the following advantages and technical effects: This invention synthesizes a series of unsupported NiO-Co3O4 composite oxides using nickel acetylacetonate and cobalt acetylacetonate as precursors via simple processes such as ball milling and air calcination. The structure and properties of these oxides were systematically characterized using XRD, BET, SEM, TEM, XPS, H2-TPR, NH3-TPD, Raman spectroscopy, and thermogravimetric analysis. The results show that the BM-NiCo(2:3)-400 catalyst exhibits the best performance, achieving complete conversion of naphthalene at 150℃ and 3 MPa H2, with a selectivity of up to 100% for decahydronaphthalene. A small amount of Ni is generated during the calcination stage of this catalyst. 0 Subsequently, further bulk reduction occurs under a H2 atmosphere, forming highly dispersed bimetallic clusters, which is the core reason for its high performance. Simultaneously, mesoporous characteristics, suitable specific surface area, uniform elemental distribution, significant metal synergistic effect, and moderate acid content and strength collectively ensure high conversion and high selectivity. This invention provides a new approach for developing green, inexpensive, and efficient non-precious metal catalysts for naphthalene hydrogenation. Attached Figure Description

[0017] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 The XRD characterization results are for the NiO-Co3O4 series catalysts in Examples 1-4, Comparative Examples 1-3, and Comparative Examples 6-7. UBM-NiCo(2:3)-400 refers to the used BM-NiCo(2:3)-400 catalyst. Figure 2 Thermogravimetric diagrams of the catalysts prepared in Example 1 and Comparative Example 2 under nitrogen conditions; Figure 3 The in-situ reduction XRD pattern of BM-NiCo(2:3)-400 catalyst under isothermal conditions; Figure 4 For characterizing the structure and performance of the NiO-Co3O4 series catalysts in Examples 1-4 and Comparative Examples 1-3, A is the N2 adsorption-desorption isotherm, and B is the BJH pore size distribution curve. Figure 5Images representing the microstructure and elemental distribution of the BM-NiCo(2:3)-400 catalyst are shown below. A~B are SEM images of the BM-NiCo(2:3)-400 catalyst at different magnifications. C~D are TEM and high-resolution TEM (HRTEM) images of the BM-NiCo(2:3)-400 catalyst. E~F are STEM images of the BM-NiCo(2:3)-400 catalyst. G~J are EDS plots of Co, Ni, O and C elements in the corresponding regions. K is the intensity curve of local lattice fringes and interplanar spacing of NiO and Co3O4. Figure 6 Raman spectra of catalysts prepared by different processes are shown. A is PM-(NiO+Co3O4)-400 prepared by physical mixing method, and B is a comparison of the Raman spectra of BM-NiCo(2:3)-400 catalyst prepared by ball milling before and after reaction. Figure 7 The XPS spectra of BM-NiCo(2:3)-400 catalyst before and after reaction are compared. A is the high-resolution XPS spectrum of Ni 2p before and after reaction, B is the high-resolution XPS spectrum of CO2 before and after reaction, C is the high-resolution XPS spectrum of O 1s before and after reaction, and D is the high-resolution XPS spectrum of C 1s before and after reaction. Figure 8 Characterization of the reduction performance and surface acidity of BM-NiCo(2:3)-400 catalyst, A is a brief introduction to H2-TPR, and B is the NH3-TPD curve; Figure 9 To compare the naphthalene hydrogenation performance of NiO-Co3O4 catalysts prepared under different conditions, A represents the reaction performance of catalysts with different Ni / Co ratios (2:1~2:4), B represents the reaction performance of catalysts prepared at different calcination temperatures (200~500℃), and C represents the reaction performance of catalysts with different active components and ball milling treatments. Figure 10 The effect of reaction conditions on the naphthalene hydrogenation performance of BM-NiCo(2:3)-400 catalyst is shown in Figure A, where A represents the effect of reaction temperature on naphthalene conversion and decahydronaphthalene selectivity, and B represents the effect of hydrogen pressure on naphthalene conversion and decahydronaphthalene selectivity. Figure 11 Cyclic performance of BM-NiCo(2:3)-400 catalyst; Figure 12 Comparison of space-time yields for the hydrogenation of naphthalene to decahydronaphthalene using different catalysts; Figure 13 This describes the evolution of naphthalene, tetrahydronaphthalene, and decahydronaphthalene during hydrogenation; Figure 14 A schematic diagram of the mechanism for the hydrogenation of naphthalene to produce decahydronaphthalene. Detailed Implementation

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention.

[0019] It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the invention. Furthermore, with respect to numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included in this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0020] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0021] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0022] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0023] An embodiment of the present invention provides a method for preparing a carrier-free nickel-cobalt composite oxide catalyst, comprising the following steps: mixing nickel acetylacetonate and cobalt acetylacetonate, first performing planetary ball milling, and then calcining the ball-milled product in air to obtain a carrier-free nickel-cobalt composite oxide catalyst; The mass ratio of nickel acetylacetone to cobalt acetylacetone is 2:(1~4). When calcining in air, the calcination temperature is 400℃.

[0024] In a preferred embodiment of the present invention, the mass ratio of nickel acetylacetonate to cobalt acetylacetonate is 2:3.

[0025] In a preferred embodiment of the present invention, the preparation method of the supportless nickel-cobalt composite oxide catalyst is described. In a preferred embodiment of the invention, the ball mill rotates at 400 rpm for 10 hours.

[0026] In a preferred embodiment of the present invention, the calcination time is 2 hours and the heating rate is 2°C·min. -1 .

[0027] The present invention also provides a supportless nickel-cobalt composite oxide catalyst prepared according to the above method.

[0028] Embodiments of the present invention also provide an application of the above-mentioned supportless nickel-cobalt composite oxide catalyst in the hydrogenation of naphthalene to decahydronaphthalene.

[0029] The embodiments of the present invention also provide a method for catalytic hydrogenation of naphthalene to produce decahydronaphthalene, wherein naphthalene, n-dodecane and the above-mentioned unsupported nickel-cobalt composite oxide catalyst are mixed and reacted by stirring at 3.0~4.0 MPa and 150~180°C.

[0030] In a preferred embodiment of the present invention, in the method of catalytic hydrogenation of naphthalene to produce decahydronaphthalene, the reaction is preferably carried out under stirring at a temperature of 3.0 MPa and 150 °C.

[0031] In a preferred embodiment of the present invention, the ratio of naphthalene, n-dodecane and the above-mentioned unsupported nickel-cobalt composite oxide catalyst is 0.1g:0.7g:5mL.

[0032] This invention synthesizes a series of NiO-Co3O4 composite oxide catalysts using nickel acetylacetonate and cobalt acetylacetonate as starting materials via a combination of planetary ball milling and air calcination. The ball milling process parameters are as follows: the total mass of the precursors (i.e., nickel acetylacetonate and cobalt acetylacetonate) is fixed at 12.5 g, the ball milling speed is set at 400 rpm, and the ball milling time is 10 hours. The calcination process parameters are as follows: calcination is carried out in air at 2℃·min⁻¹. -1 The temperature was increased to 400℃ and calcined at this rate, and held at this temperature for 2 hours to obtain a supportless nickel-cobalt composite oxide catalyst. In this invention, the Ni:Co ratio is defined as the mass ratio of nickel acetylacetone to cobalt acetylacetone, and is set to 2:1, 2:2, 2:3, and 2:4, respectively. The naming rules for related samples are explained as follows: BM-NiCo(x:y)-400: Two precursors are mixed uniformly at a specified mass ratio of x:y (x=2, y=1~4, i.e. x:y=2:1, 2:2, 2:3 and 2:4), ball-milled, and then calcined at 400℃ to obtain the final product.

[0033] For comparison, the following materials were also prepared: BM-NiO-400 and BM-Co3O4-400: Both are prepared using a single precursor and following the same ball milling and calcination process.

[0034] PM-(NiO+Co3O4)-400: Two single-component catalysts, BM-NiO-400 and BM-Co3O4-400, are physically mixed by manual grinding for 5 minutes, based on the metal molar ratio calculated according to the precursor mass ratio of 2:3.

[0035] NBM-NiCo(2:3)-400: The two precursors are directly mixed in a mass ratio of 2:3, and the ball milling step is omitted before calcination.

[0036] UBM-NiCo(2:3)-400: Used BM-NiCo(2:3)-400 catalyst.

[0037] Unless otherwise specified, the room temperature in this invention is 25±2℃.

[0038] All raw materials used in the embodiments of this invention were purchased commercially. Nickel acetylacetonate (98% purity, the same below), Energy Chemical, cobalt acetylacetonate (96.3%, Bide Pharmaceutical), naphthalene (98%, Energy Chemical), decahydronaphthalene (97%, Energy Chemical), tetrahydronaphthalene (98%, Energy Chemical), and hydrogen (99%, industrial grade) were all used directly.

[0039] It should be noted that any aspects not described in detail in this invention are conventional practices in the field and are not the focus of this invention.

[0040] The technical solution of the present invention will be further illustrated by the following embodiments.

[0041] Example 1 A method for preparing a supportless nickel-cobalt composite oxide catalyst, wherein the catalyst is synthesized using nickel acetylacetonate and cobalt acetylacetonate as starting materials by a combination of planetary ball milling and air calcination, the steps of which are as follows: The total mass of the precursors (i.e., nickel acetylacetone and cobalt acetylacetone) was fixed at 12.5 g, the mass ratio of nickel acetylacetone to cobalt acetylacetone was 2:3, the ball milling speed was set to 400 rpm, and the ball milling time was 10 hours. The calcination process parameters were as follows: calcination at 2℃·min in air. -1 The temperature was increased to 400℃ and calcined at this rate, and held at this temperature for 2 hours to obtain a supportless nickel-cobalt composite oxide catalyst, denoted as BM-NiCo(2:3)-400.

[0042] Example 2 A method for preparing a carrier-free nickel-cobalt composite oxide catalyst is the same as in Example 1, except that the mass ratio of nickel acetylacetonate to cobalt acetylacetonate is 2:1. The resulting carrier-free nickel-cobalt composite oxide catalyst is denoted as BM-NiCo(2:1)-400.

[0043] Example 3 A method for preparing a carrier-free nickel-cobalt composite oxide catalyst is the same as in Example 1, except that the mass ratio of nickel acetylacetonate to cobalt acetylacetonate is 2:2. The resulting carrier-free nickel-cobalt composite oxide catalyst is denoted as BM-NiCo(2:2)-400.

[0044] Example 4 A method for preparing a carrier-free nickel-cobalt composite oxide catalyst is the same as in Example 1, except that the mass ratio of nickel acetylacetonate to cobalt acetylacetonate is 2:4. The resulting carrier-free nickel-cobalt composite oxide catalyst is denoted as BM-NiCo(2:4)-400.

[0045] Comparative Example 1 Same as Example 1, except that the calcination temperature is 200℃, and the resulting catalyst is denoted as BM-NiCo(2:3)-200.

[0046] Comparative Example 2 Same as Example 1, except that the calcination temperature is 300℃, and the resulting catalyst is denoted as BM-NiCo(2:3)-300.

[0047] Comparative Example 3 Same as Example 1, except that the calcination temperature is 500℃, and the resulting catalyst is denoted as BM-NiCo(2:3)-500.

[0048] Comparative Example 4 Using nickel acetylacetonate as a single precursor (the amount was the same as the total mass of the precursor in Example 1), the same ball milling and calcination process as in Example 1 was followed to obtain a catalyst, denoted as BM-NiO-400.

[0049] Comparative Example 5 Using cobalt acetylacetone as a single precursor (the amount was the same as the total mass of the precursor in Example 1), the same ball milling and calcination process as in Example 1 was followed to obtain a catalyst, denoted as BM-Co3O4-400.

[0050] Comparative Example 6 Two single-component catalysts, BM-NiO-400 and BM-Co3O4-400, were physically mixed by manual grinding for 5 minutes based on the metal molar ratio calculated from the precursor (i.e., nickel acetylacetonate and cobalt acetylacetonate) mass ratio of 2:3. The resulting catalyst was denoted as PM-(NiO+Co3O4)-400.

[0051] Comparative Example 7 Nickel acetylacetone and cobalt acetylacetone were directly mixed at a mass ratio of 2:3 (total mass of both was 12.5 g). After omitting the ball milling step in Example 1, the mixture was calcined in the manner described in Example 1. The resulting catalyst was denoted as NBM-NiCo-400 or NBM-NiCo(2:3)-400.

[0052] X-ray diffraction (XRD) tests were performed on a LabX-XRD-6100 diffractometer using CuKα radiation (λ=0.15406nm), with an operating voltage of 40 kV, a current of 30 mA, a scanning range of 10° to 80°, and a scanning rate of 2° / min. N₂ adsorption-desorption tests were performed on a Micromeritics-ASAP-2020Plus physical adsorption system at -196℃. Samples were degassed under vacuum at 200℃ for 4 hours. Specific surface area was calculated using the BET method, and pore structure was determined using the BJH method. Scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) elemental distribution analysis were performed on a ZEISS-Gemini-SEM 300 to observe morphology and elemental distribution. Transmission electron microscopy (TEM) analysis was performed using a JEOL-JEM-2100F model with an accelerating voltage of 200 kV. Samples were dispersed in ethanol, dropped onto a copper mesh carbon film, dried, and then observed. High-resolution imaging (HRTEM), selected area electron diffraction (SAED), scanning transmission electron microscopy-high-angle annular dark-field (STEM-HAADF), and energy dispersive spectroscopy (EDS-mapping) were performed. H2-TPR and NH3-TPD were conducted on a Xianquan 5080B chemisorption analyzer equipped with a Hiden-DECRA mass spectrometer and a TCD detector. X-ray photoelectron spectroscopy (XPS) was used to analyze the valence states of surface elements, with binding energy calibrated using C1s (284.8 eV). Inductively coupled plasma atomic emission spectrometry (ICP-OES) was used to determine the actual content of Ni and Co. Thermogravimetric analysis (TG) was performed on a NETZSCH-STA-449F5 simultaneous thermal analyzer, with a testing range of 20℃ to 800℃ and a heating rate of 10℃ / min. An Al2O3 crucible was used as a reference, and the sample mass change with temperature was recorded in real time. Raman spectroscopy measurements were performed on a Horiba LabRAM HR Evolution confocal Raman spectrometer, with a scanning range of 100–4000 cm⁻¹. -1 After baseline correction, the D and G peaks of oxide lattice vibrations and surface carbon species were analyzed to investigate the interactions between the metallic phases. In-situ XRD was performed on the Bruker D8 ADVANCE in-situ stage using Cu Kα rays in a 10 vol% H2 / Ar atmosphere, and segmented isothermal spectra were collected to observe the phase transition of the oxide reduction products.

[0053] Catalytic performance evaluation: Catalytic performance evaluation was conducted in a 25 mL high-pressure reactor, which was loaded with 0.1 g catalyst, 0.7 g naphthalene, and 5 mL n-dodecane. Before the reaction, the reactor was purged three times with 1 MPa high-purity hydrogen to remove residual air, and then pressurized to the required pressure with hydrogen. Subsequently, the reaction was carried out at 130, 150, and 180 °C with stirring at 800 rpm for 6 hours.

[0054] After the reaction was complete, the reactor was cooled to room temperature, and the supernatant was collected and filtered through an organic filter membrane. Product analysis was performed using a Carian 456c gas chromatograph. The conversion rate of naphthalene and the selectivity of decahydronaphthalene were calculated according to formulas (1) and (2): (1) X naphthalene : Conversion rate of naphthalene (%) n 0 naphthalene Initial amount of naphthalene (mol) before reaction. n naphthalene : The amount of unreacted naphthalene after the reaction (mol).

[0055] (2) S decalin Selectivity of decahydronaphthalene (%) n decalin : Amount of decahydronaphthalene produced (mol) ∑n products Total amount of all products (mol).

[0056] 3 Results and Discussion 3.1 Phase Composition and Structure Analysis The crystal structure of the NiO-Co3O4 catalyst was investigated by XRD. For the samples calcined at 400℃, characteristic diffraction peaks of pure NiO (PDF#04-007-9781) and Co3O4 (PDF#00-043-1003) were observed at all Ni / Co ratios. The BM-NiCo(2:3)-400 sample showed clear and symmetrical two-phase diffraction peaks, indicating its good crystallinity and balanced phase composition. A weak metallic Ni peak was also detected. Figure 1 This indicates that partial self-reduction occurred during calcination. Calcination temperature significantly affects phase formation. Combined with TG analysis ( Figure 2 It was found that the precursor did not decompose completely at 300℃, while 400℃ ensured complete decomposition and the formation of a well-crystallized oxide phase with excellent thermal stability. Further increasing the temperature to 500℃ led to significant grain growth and agglomeration, which was detrimental to the exposure of active sites. Figure 1 It is worth noting that the diffraction peaks of the composite oxide are broader than those of pure NiO or Co3O4. Figure 1 Furthermore, according to the Scherrer equation, the grain size of the ball-milled sample (BM-NiCo) is smaller than that of the un-ball-milled sample (NBM-NiCo). This grain refinement is a direct result of mechanochemical effects, increasing grain boundaries and defects, shortening the diffusion path of reduction, and facilitating the construction of highly active interfaces under mild conditions.

[0057] A key finding from the XRD analysis was the comparison of the spectra before and after the catalytic reaction. The post-reaction spectrum showed a significant increase in the intensity of the corresponding peak in the Ni-Co alloy, confirming that the catalyst underwent substantial in-situ reduction during the hydrogenation reaction. Importantly, no new impurity phases were detected, indicating its excellent structural stability. To track this dynamic evolution in real time, in-situ XRD was performed on the BM-NiCo(2:3)-400 catalyst under a 10% H2 / Ar atmosphere. Figure 3 From room temperature to 130 °C, only peaks for NiO and Co3O4 were observed. At 200 °C, the intensity of these oxide peaks decreased, and new, unassigned diffraction signals appeared, which were attributed to low-valence transition intermediates. When the temperature reached 300 °C, these intermediate peaks disappeared, and three sets of clear peaks corresponding to metallic Ni and Co appeared. This in-situ XRD experiment clearly demonstrates the stepwise reduction pathway of the BM-NiCo(2:3)-400 catalyst and precisely indicates the temperature threshold for the formation of metal active sites, providing direct structural evidence for its in-situ activation capability.

[0058] Texture properties and microstructure: N2 physisorption analysis showed that all samples exhibited a type IV isotherm and an H2-type hysteresis loop, which are characteristic of mesoporous materials. Figure 4 (A). The BM-NiCo(2:3)-400 catalyst exhibits the most favorable pore structure with a narrow pore size distribution. Figure 4 (Medium B), with a specific surface area of ​​46.53 m² / g and a pore volume of 0.132 cm³. 3 / g. Imbalanced metal ratios or suboptimal calcination temperatures both lead to poor pore characteristics. After the reaction, the specific surface area decreased to 15.12 m² / g, and the average pore size increased, indicating the presence of carbon deposits and pore blockage.

[0059] SEM and TEM analyses showed that the BM-NiCo(2:3)-400 catalyst consisted of regularly aggregated nanoparticles (7~16 nm) with abundant surface pores and no sintering phenomenon. Figure 5(A~D, K). HRTEM images clearly show the coexistence of NiO and Co3O4 lattice fringes within the same particle, indicating close contact at the nanoscale. STEM-EDS surface scan ( Figure 5 The study (E~J) demonstrated a uniform distribution of Ni, Co, O, and C without elemental segregation. This compact and uniform microstructure facilitates electron transfer between Ni and Co species and promotes the formation of highly dispersed bimetallic clusters during reduction, which is crucial for deep hydrogenation.

[0060] Surface chemical environment and reduction behavior: Raman spectroscopy provides further insights into metal-metal oxide interactions. The physically mixed sample PM-(NiO+ Co3O4)-400 shows Co3O4 at ~190, 470, 525, and 690 cm⁻¹. -1 (at ~560 and 1080 cm⁻¹) and NiO (at ~560 and 1080 cm⁻¹) -1 The obvious characteristic peaks of (location) Figure 6 (A). In contrast, the ball-milled BM-NiCo(2:3)-400 catalyst exhibited significant peak broadening and shift, indicating enhanced molecular-level mixing and stronger bimetallic electronic interactions. This mechanochemical effect lowers the reduction temperature of the oxide, as seen in H2-TPR ( Figure 8 As confirmed in (A), this is beneficial for the in-situ formation of active Ni-Co clusters. Furthermore, the D, G, and 2D carbon peak intensities of the ball-milled sample are much lower, indicating less carbon residue from precursor decomposition. After the reaction, the Raman spectrum of the spent catalyst (…) Figure 6 (B) shows a significant increase in the 2D peak intensity, confirming the deposition of graphitic carbon, which is consistent with the loss of activity and surface area.

[0061] XPS analysis was used to investigate the surface chemical state before and after the reaction. Figure 7 For the fresh BM-NiCo(2:3)-400 sample, the Ni 2p spectrum shows main peaks at 855.8 eV and 873.2 eV, which are the Ni values ​​in NiO. 2+ The characteristic is that it also has a value at ~852.5 eV belonging to Ni. 0 weak signal ( Figure 7 (A) After the reaction, Ni 0 The peak intensity increases sharply, and the Ni2p3 / 2 main peak shifts to higher binding energies (from 854.9 eV to 855.8 eV). This clearly indicates that, under a reducing reaction atmosphere, the surface and bulk NiO are converted in situ into metallic nickel. Similarly, the Co 2p spectrum ( Figure 7 (B) shows that although cobalt in fresh catalysts is in the form of Co 2+ and Co 3+It exists in a mixture form, but its signal intensity decreases significantly after the reaction, and a signal at ~778.2 eV attributed to Co appears. 0 The new peak indicates that the presence of Ni promoted the low-temperature reduction of Co3O4, likely forming Ni-Co alloy clusters or strongly interacting interfaces. (O 1s spectrum) Figure 7 The XRD (C) results show that the lattice oxygen signal (529.5 eV) weakens after the reaction, while the peaks corresponding to oxygen vacancies or hydroxyl groups (~531.5 eV) strengthen, confirming the loss of lattice oxygen and the formation of defects during the reduction process. Essentially, the combination of XPS results and in-situ XRD clearly depicts the "pre-activation and reconstruction" process: a small amount of Ni is formed during calcination. 0 These hydrogens serve as nucleation sites for H2 dissociation. The dissociated hydrogens then promote the reduction of surrounding NiO and Co3O4, forming a cascade reaction that ultimately creates electron-rich bimetallic sites and oxygen vacancies, which synergistically enhance the adsorption of naphthalene and the activation of hydrogen.

[0062] H2-TPR curve of BM-NiCo(2:3)-400 ( Figure 8 NiO (A) exhibits a single, sharp reduction peak at ~350℃, significantly lower than that of pure NiO or Co3O4. This confirms a strong synergistic effect, where Ni promotes Co3O4 reduction while Co inhibits Ni particle agglomeration, resulting in highly dispersed bimetallic sites. NH3-TPD curve ( Figure 8 Figure B) shows two desorption peaks, located at 198℃ (weak acid site) and 611℃ (medium-strong acid site), respectively, with no strong acid sites (>700℃). This acidity distribution is ideal: the weak acid sites are conducive to the adsorption and diffusion of naphthalene, while the medium-strong acid sites activate the aromatic ring and promote deep hydrogenation to form decahydronaphthalene; the absence of strong acid sites inhibits side reactions such as cracking and coking.

[0063] Catalytic performance and optimization: The relationship between catalytic performance and Ni / Co ratio, calcination temperature, and ball milling treatment was systematically evaluated. Figure 9 The BM-NiCo(2:3)-400 catalyst exhibited the highest activity, achieving complete conversion of naphthalene and 100% selectivity for decahydronaphthalene. Figure 9 (A). This confirms the existence of an optimal bimetallic synergistic effect at this specific ratio. A calcination temperature of 400℃ has been proven to be optimal. Figure 9 (B) Lower temperatures lead to incomplete crystallization, while higher temperatures cause particle sintering, both of which are detrimental to performance. The ball-milled catalyst performs significantly better than the unmilled sample and the single-component oxide (B). Figure 9The study (C) demonstrated the crucial role of mechanochemical treatment in enhancing intermetallic interactions and accessibility of active sites. The catalyst maintained excellent performance even at high and low concentrations, indicating its promising potential for industrial applications.

[0064] The reaction conditions were optimized. Figure 10 At 150 °C and 3 MPa H2, the catalyst achieved complete conversion and 100% selectivity for decahydronaphthalene, demonstrating its "mild yet efficient" characteristics. Lower temperatures or pressures limited the reaction kinetics, while more demanding conditions promoted side reactions and reduced selectivity.

[0065] This invention also evaluated the reusability of the catalyst ( Figure 11 In the first two cycles, it maintained 100% conversion and selectivity. However, a sharp decline in activity was observed in the third cycle, with the conversion plummeting to 13.99%. XRD, BET, SEM, and EDX analyses of the spent catalyst indicated that deactivation was primarily caused by carbon deposits covering active sites, pore blockage, and metal particle agglomeration.

[0066] Comparative analysis with literature data highlights the superior performance of the BM-NiCo(2:3)-400 catalyst of this invention. Figure 12 It exhibits high specific activity (STY) under mild conditions. mol = 9.1 mmol·g -1 ·h -1 It outperforms most reported non-precious metal catalysts and does not require an energy-intensive pre-reduction step, making it comparable to some precious metal systems.

[0067] Figure 12 The following are the references: [1]ZHANG M, SONG Q, HE Z, et al. Tuning the mesopore-acid-metalbalance in Pd / HY for efficient deep hydrogenation saturation of naphthalene[J]. International Journal of Hydrogen Energy, 2022, 47(48):20881-20893. [2]LIANG Y, ZHAO B, TANG Q, et al. Adjusting Pt Nanoparticle Size onSBA-15 by a Sol-Immobilisation Method Towards Naphthalene Hydrogenation[J].Catalysis Letters, 2022, 152(11):3489-3497. [3]ZHU L, ZHANG H, ZHONG L, et al. RuNiCo-based nanocatalysts withdifferent nanostructures for naphthalene selective hydrogenation[J]. Fuel,2018, 216:208-217. [4]ENCARNACIóN-GóMEZ C, CORTéS-JáCOME M A, MEDINA-MENDOZA A K, et al.Uniformly sized Pt nanoparticles dispersed at high loading on Titaniananotubes[J]. Applied Catalysis A: General, 2020, 600. [5]LI P, WANG L, ZHANG X, et al. Deep Hydrogenation Saturation ofNaphthalene Facilitated by Enhanced Adsorption of the Reactants on Micro-Mesoporous Pd / HY[J]. ChemistrySelect, 2021, 6(22):5524-5533. [6]ZHU L, CUI J, RUAN L, et al. Tiny Ruthenium‐Cobalt‐CobaltHydroxide Nanoparticles Supported on Graphene for Efficiently CatalyzingNaphthalene Complete Hydrogenation[J]. Chemistry Select, 2019, 4(29):8394-8397. [7]LIU Z, WANG E, MEI J, et al. Hierarchical porous Pt / Hβ catalystwith controllable acidity for efficient hydrogenation of naphthalene[J].Chemical Engineering Journal, 2024, 481:148763-148776. [8]LIU Z, MEI J, WANG D, et al. Ultrafine Pt particles on hollowhierarchical porous β zeolites for selective hydrogenation of naphthalene[J].Fuel, 2024, 368:131642-131654. [9]WANG E, SONG Y, MEI J, et al. Highly Dispersed Pt Catalysts onHierarchically Mesoporous Organosilica@Silica Nanoparticles with a Core-ShellStructure for Polycyclic Aromatic Hydrogenation[J]. ACS Applied Materials&Interfaces, 2023, 15(8):10761-10773.

[10] TéLLEZ-ROMERO J G, CUEVAS-GARCíA R, RAMíREZ J, et al.Simultaneous naphthalene and thiophene hydrogenation over Ni(X)-Pt / HMORcatalysts[J]. Catalysis Today, 2015, 250:12-20.

[11] CUAUHTéMOC-LóPEZ I, JIMéNEZ-VáZQUEZ A, ESTUDILLO-WONG L A, et al.Naphthalene hydrogenation using Rh / Fe2O3-TiO2magnetic catalysts[J]. CatalysisToday, 2021, 360:176-184.

[12] KIM H J, SONG C. A refined design concept for sulfur-tolerant Pdcatalyst supported on zeolite by shape-selective exclusion and hydrogenspillover for hydrogenation of aromatics[J]. Journal of Catalysis, 2021, 403:203-214.

[13] DU M, QIN Z, GE H, et al. Enhancement of Pd-Pt / Al2O3catalystperformance in naphthalene hydrogenation by mixing different molecular sievesin the support[J]. Fuel Processing Technology, 2010, 91(11):1655-1661.

[14] LI Z, JING J-Y, QIE Z-Q, et al. Influence of ReductionTemperature on the Structure and Naphthalene Hydrogenation SaturationPerformance of Ni2P / Al2O3Catalysts. Crystals. 2022:318.

[15] ZHANG

[16] YIN C, WU T, DONG C, et al. Preparation of highly activeunsupported Ni-Si-Mo catalyst for the deep hydrogenation of aromatics[J]. Journal of Alloys and Compounds, 2020, 834:155076.

[17] Fu Rao, Yang Lina, Ma Qipeng, et al. Effect of HY molecular sieve on the performance of NiO / SBA-16 naphthalene hydrogenation catalyst [J]. Petrochemical Technology and Application, 2022, 40(4):233-137.

[18] ZHAO A, ZHANG X, CHEN

[19] NARES RN, RAMı´REZ J, GUTIE´RREZ-ALEJANDRE AD, et al.Characterization and Hydrogenation Activity of Ni / Si(Al)-MCM-41 CatalystsPrepared by Deposition-Precipitation[J]. American Chemical Society, 2009, 48:1154-1162.

[20] An Juanjuan, Wang Shun, Wang Shanmin, et al. Multi-level porous Ni / SAPO-5 naphthalene hydrogenation catalyst to decahydronaphthalene[J]. Molecular Catalysis, 2017, 31(5):438-445.

[21] Xi Zhiqiang, Zhang Ziyi, Jing Jieying, et al. Effect of Ni2P loading on the structure of Ni2P / Ce-Al2O3 catalyst and naphthalene hydrogenation performance[J]. Journal of Fuel Chemistry, 2018, 47(6):718-724.

[22] JIANG C, WANG Y, ZHANG H, et al. Effect of PDADMAC with different molecular weight regulating Hβ Properties on hydrogenation performance ofNiMoC / Hβ catalysts[J]. Fuel Processing Technology, 2021, 213:106704.

[23] CUI S, WANG Z, WANG G, et al. A Novel Approach to PreparingHighly Porous and Dispersed Supported Nickel Catalyst[J]. ChemistrySelect, 2017, 2(35):11497-11502.

[24] SONG

[25] HU D, DUAN A, XU C, et al. Ni2P promotes the hydrogenationactivity of naphthalene on wrinkled silica nanoparticles with tunablehierarchical pore sizes in a large range[J]. Nanoscale, 2019, 11(33):15519-15529.

[26] GUAN Q, YUN G, LI W. Tuning hydrodearomatization performance ofinterstitial NixW alloy catalyst by controlling the doping of a small amountof tungsten[J]. Catalysis Today, 2021, 364:202-210.

[27] YUN G, GUAN Q, LI W. The synthesis and mechanistic studies of ahighly active nickel phosphide catalyst for naphthalene hydrodearomatization[J]. RSC Advances, 2017, 7(14):8677-8687.

[28] DAVTYAN D, AGHOYAN A, AKOPYAN A, et al. Microwave AssistedSynthesis and Catalytic Activity of Nano Sized Molybdenum Carbide inNaphthalene Hydrogenation[J]. Engineering village, 2024, 12:156-161.

[29] WANG M, QIAN

[30] Li Guofeng, Sun Qingguo, Gulinar Tursun, et al. Study on the hydrogenation performance of naphthalene by NiW / γ-Al2O3 catalyst in suspension bed[J]. Energy and Chemical Engineering, 2022, 41(5):34-38.

[31] VARGAS H, MORALES JC, BOKHIMI To elucidate the reaction pathway of naphthalene hydrogenation on the BM-NiCo(2:3)-400 catalyst, the product composition at different reaction times was analyzed, and the results are as follows: Figure 13 As shown, after 1 hour of reaction, naphthalene was still the dominant component in the system (88.93%), with only 11.07% tetrahydronaphthalene detected, indicating that the naphthalene hydrogenation reaction had begun, but only preliminary hydrogenation had occurred. As the reaction time was extended to 2 hours, the selectivity for tetrahydronaphthalene rapidly increased to 94.71%, while decahydronaphthalene accounted for only 5.29%, indicating that naphthalene first underwent partial hydrogenation to form tetrahydronaphthalene, and that tetrahydronaphthalene accumulated in large quantities during this stage.

[0068] When the reaction time was further extended to 3 h, the selectivity of tetrahydronaphthalene decreased to 45.48%, while the selectivity of decahydronaphthalene increased to 54.52%, indicating that tetrahydronaphthalene began to be further hydrogenated to decahydronaphthalene. Continuing the reaction for another 4 h, the selectivity of decahydronaphthalene further increased to 91.69%, while only 8.31% of tetrahydronaphthalene remained. When the reaction time reached 5 h, tetrahydronaphthalene completely disappeared, ultimately achieving 100% selectivity for decahydronaphthalene.

[0069] The above results clearly reveal that the naphthalene hydrogenation reaction follows a continuous hydrogenation pathway: naphthalene is first hydrogenated to tetrahydronaphthalene, which is then further hydrogenated to decahydronaphthalene. During the reaction, tetrahydronaphthalene is first generated and accumulates in large quantities, then gradually consumed and converted to decahydronaphthalene, providing direct experimental evidence for tetrahydronaphthalene as a key reaction intermediate. Simultaneously, the BM-NiCo(2:3)-400 catalyst can efficiently promote both the naphthalene to tetrahydronaphthalene and tetrahydronaphthalene to decahydronaphthalene consecutive hydrogenation steps, indicating that the in-situ activated Ni-Co active sites possess excellent hydrogen activation ability and deep aromatic ring hydrogenation capability.

[0070] Based on XPS, H2-TPR, and in-situ XRD results, as well as the product's behavior over time, a possible hydrogenation pathway is proposed: naphthalene is first hydrogenated on one side of the benzene ring to generate a tetrahydronaphthalene intermediate, which is then further hydrogenated to yield cis and trans-decahydronaphthalene stereoisomers. Figure 14 ).

[0071] In summary, this invention successfully developed a series of unsupported NiO-Co3O4 composite oxide catalysts using a green and simple ball milling-air calcination method. The optimized BM-NiCo(2:3)-400 catalyst achieved 100% naphthalene conversion and 100% decahydronaphthalene selectivity under mild conditions (150 °C, 3 MPa H2) without the need for a separate pre-reduction step. This superior performance is attributed to a unique in-situ activation mechanism, namely, the formation of a small amount of Ni during calcination. 0 Under the given reaction conditions, a cascade reduction of NiO and Co3O4 is initiated, forming a highly dispersed, electron-rich Ni-Co bimetallic cluster, which has been confirmed by XPS and in-situ XRD. The catalyst's mesoporous structure, optimal surface area, uniform elemental distribution, strong bimetallic synergistic effect, and suitable acidity (weak to moderately strong) collectively suppress side reactions and promote deep hydrogenation. This work not only provides a highly efficient and economical catalyst for the naphthalene-decahydronaphthalene LOHC system but also offers a new paradigm for designing non-noble metal catalysts for clean energy applications using in-situ activation.

[0072] The above are merely preferred embodiments of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a supportless nickel-cobalt composite oxide catalyst, characterized in that, It was synthesized using nickel acetylacetonate and cobalt acetylacetonate as starting materials by a combination of planetary ball milling and air calcination. The mass ratio of nickel acetylacetonate to cobalt acetylacetonate is 2:(1~4). During the air calcination, the calcination temperature is 400°C.

2. The method for preparing the supportless nickel-cobalt composite oxide catalyst according to claim 1, characterized in that, The mass ratio of nickel acetylacetone to cobalt acetylacetone is 2:

3.

3. The method for preparing the supportless nickel-cobalt composite oxide catalyst according to claim 1, characterized in that, The process includes the following steps: mixing nickel acetylacetonate and cobalt acetylacetonate, first performing planetary ball milling, and then calcining the ball-milled product in air to obtain the carrier-free nickel-cobalt composite oxide catalyst.

4. The method for preparing the supportless nickel-cobalt composite oxide catalyst according to claim 3, characterized in that, The ball mill was operated at 400 rpm for 10 hours.

5. The method for preparing the supportless nickel-cobalt composite oxide catalyst according to claim 3, characterized in that, The calcination time is 2 hours, and the heating rate is 2℃·min. -1 .

6. A supportless nickel-cobalt composite oxide catalyst, characterized in that, It is prepared according to any one of claims 1 to 5.

7. The application of the carrierless nickel-cobalt composite oxide catalyst as described in claim 6 in the hydrogenation of naphthalene to decahydronaphthalene.

8. A method for catalytic hydrogenation of naphthalene to produce decahydronaphthalene, characterized in that, Naphthalene, n-dodecane, and the carrier-free nickel-cobalt composite oxide catalyst according to claim 6 are mixed and reacted under stirring at 3.0~4.0 MPa and 150~180°C.

9. The method for catalytic hydrogenation of naphthalene to decahydronaphthalene according to claim 8, characterized in that, Naphthalene, n-dodecane, and the carrier-free nickel-cobalt composite oxide catalyst of claim 6 were mixed and reacted under stirring at 3.0 MPa and 150 °C.

10. The method for catalytic hydrogenation of naphthalene to decahydronaphthalene according to claim 8, characterized in that, The ratio of naphthalene, n-dodecane, and the carrier-free nickel-cobalt composite oxide catalyst of claim 6 is 0.1 g: 0.7 g: 5 mL.

Images