A bifunctional Ni1Co3Al2 composite oxide catalyst, its preparation method and its application

Abstract

This invention discloses a method for preparing a Ni1Co3Al2 composite oxide bifunctional catalyst and its application. In the preparation process, Ni, Co, and Al sources are dissolved, urea is added and stirred, and a hydrothermal reaction is carried out to obtain the double hydroxide precursor Ni1Co3Al2-LDH. The catalyst is then calcined sequentially under air and reducing atmospheres to obtain the Ni1Co3Al2 composite oxide bifunctional catalyst. The beneficial effects of this invention are that the catalyst exhibits good cycle stability and magnetic properties. When applied to the supercritical ethanol depolymerization reaction of lignin model compounds, the main product is a high-value monocyclic aromatic hydrocarbon. Under optimized conditions, the conversion rate of the model compound BOB can reach 100%, and the total yield of aromatic hydrocarbons reaches 171.3 mol%, demonstrating high reactivity and aromatic hydrocarbon selectivity. Ethanol simultaneously serves as a solvent and in-situ hydrogen donor, eliminating the need for external high-pressure hydrogen, thus reducing equipment requirements and safety risks.

Description

Technical Field

[0001] This invention relates to the field of catalysts for the preparation of aromatics by alcoholysis, and particularly to a bifunctional Ni1Co3Al2 composite oxide catalyst, its preparation method, and its application. Background Technology

[0002] Against the backdrop of increasingly depleted fossil resources and prominent environmental pollution problems, the development and utilization of renewable biomass resources has become an important strategic direction for global sustainable development. Lignin, as the most abundant renewable aromatic polymer in nature, is crucial for the high-value utilization of biomass through efficient depolymerization into monophenols or aromatics. Among numerous conversion pathways, catalytic alcoholysis or hydrogenolysis is an effective means of breaking ether bonds in lignin. However, traditional catalytic hydrogenation deoxygenation processes typically rely on external high-pressure hydrogen, resulting in harsh reaction conditions and a tendency for excessive hydrogenation saturation of aromatic rings, generating cycloalkanes with low economic value. Therefore, developing a green conversion process that does not require external hydrogen, can selectively break CO bonds while preserving the aromatic ring structure, has become an urgent need for the targeted upgrading of lignin. In this context, lignin alcoholysis technology, utilizing alcohol solvents as reaction media and in-situ hydrogen donors, avoids the direct use of hydrogen and offers mild reaction conditions. It also holds promise for precise control of product selectivity through catalyst design, demonstrating significant necessity and application potential.

[0003] Based on the thermodynamic principles of traditional hydrodeoxygenation (HDO) processes, conventional catalysts tend to saturate and hydrogenate high-value aromatic rings during deoxygenation, generating low-value cycloalkanols (such as cyclohexanol). Therefore, how to achieve precise CO bond cleavage while preserving the aromatic ring structure, and how to regulate the reaction pathway to directionally prepare high-value aromatics (such as toluene and ethylbenzene) to improve the economic grade of the products, has always been a core challenge for the high-value utilization of lignin. Summary of the Invention

[0004] This invention discloses a bifunctional Ni1Co3Al2 composite oxide catalyst, its preparation method, and its applications. Utilizing the synergistic effect of the metal active sites and acidic sites of the Ni1Co3Al2 composite oxide bifunctional catalyst, and leveraging the in-situ hydrogen donation capability of supercritical ethanol, it achieves efficient depolymerization of lignin model compounds into small organic molecules, thus solving problems in existing technologies such as the need for an external hydrogen source, low product selectivity, and harsh reaction conditions.

[0005] To achieve the above objectives, the present invention adopts the following technical solution:

[0006] A method for preparing a Ni1Co3Al2 composite oxide bifunctional catalyst includes the following steps:

[0007] a. Ni source, Co source and Al source are dissolved together in deionized water at a molar ratio of 1:3:2. A certain amount of urea is added and stirred to mix. After mixing, the mixture is transferred to a polytetrafluoroethylene liner for hydrothermal reaction. The reaction temperature is 80~120℃ and the reaction time is 20~26h to obtain the layered double hydroxide precursor Ni1Co3Al2-LDH.

[0008] b. Place the precursor Ni1Co3Al2-LDH obtained in step a in a muffle furnace and perform a first calcination treatment in air. The heating rate is 5℃ / min, the calcination temperature is 550~650℃, and the calcination time is 1~3h.

[0009] c. Grind the product obtained from the first calcination treatment into powder, place it in a tube furnace, and carry out a second calcination treatment under a reducing atmosphere. The heating rate is 3℃ / min, the temperature is 550~650℃, and the reduction time is 1~3h, thus obtaining the Ni1Co3Al2 composite oxide bifunctional catalyst.

[0010] Further, in step a, the Ni source is nickel nitrate hexahydrate or anhydrous nickel nitrate, the Co source is cobalt nitrate hexahydrate or anhydrous cobalt nitrate, and the Al source is aluminum nitrate nonahydrate or anhydrous aluminum nitrate.

[0011] Furthermore, in step a1, the ratio of urea to water is (0.8-1.2) g : (20-26) ml.

[0012] Secondly, the present invention also discloses a bifunctional Ni1Co3Al2 composite oxide catalyst prepared by the above preparation method.

[0013] Thirdly, this disclosure also discloses the application of this Ni1Co3Al2 composite oxide bifunctional catalyst in the supercritical alcoholysis of lignin model compounds to prepare aromatics, the specific process of which is as follows:

[0014] (1) A certain ratio of lignin model compound, alcohol solvent and Ni1Co3Al2 composite oxide bifunctional catalyst are added together into a high-pressure reactor and the reaction is carried out in a supercritical state.

[0015] (2) Replace the air in the high-pressure reactor three times with N2, fill with N2, heat, and the reaction temperature is 220~320℃, and the reaction time is 1~3 h;

[0016] (3) After the reaction is complete, stop heating and allow the high-pressure reactor to cool naturally to room temperature. Then remove the reaction mixture and analyze the filtrate using gas chromatography / mass spectrometry (GC / MS).

[0017] Further, in step (1), the lignin model compound is a model containing a β-O-4 ether bond, selected from at least one of benzylphenyl ether and phenethoxybenzene, and the alcohol solvent is selected from at least one of methanol, ethanol or isopropanol, and the amount used is 150~250ml.

[0018] Furthermore, in step (1), the mass ratio of the Ni1Co3Al2 composite oxide bifunctional catalyst to the lignin model compound is (0.8~1.2) g: (0.8~1.3) g.

[0019] The beneficial effects of this invention are:

[0020] (1) The bifunctional catalyst of Ni1Co3Al2 composite oxide was applied to the supercritical ethanol depolymerization reaction of lignin model compounds, which has excellent ability to selectively hydrogenate CO bonds and retain aromatic rings.

[0021] (2) Supercritical ethanol is used as both a solvent and an in-situ hydrogen donor, eliminating the need for external high-pressure hydrogen, which reduces equipment requirements and safety risks, making the process greener and more economical.

[0022] (3) The main product is a high-value monocyclic aromatic hydrocarbon (such as toluene). Under optimized conditions, the conversion rate of the model compound benzylphenyl ether (BOB) can reach 100%, and the total yield of aromatic hydrocarbons reaches 171.3 mol%, showing high reactivity and aromatic hydrocarbon selectivity.

[0023] (4) The Ni1Co3Al2 composite oxide bifunctional catalyst has good cycle stability and magnetism, and can be easily separated and recovered by an external magnet, which is convenient for continuous or cyclic processes. Attached Figure Description

[0024] Figure 1 The XRD pattern of the catalyst prepared in Example 1 of this invention;

[0025] Figure 2 The SEM image of the catalyst prepared in Example 1 of this invention;

[0026] Figure 3 The HAADF-TEM spectrum of the catalyst prepared in Example 1 of this invention;

[0027] Figure 4 XPS spectrum of the Ni1Co3Al2 composite oxide bifunctional catalyst prepared in Example 1 of this invention;

[0028] Figure 5 The H2-TPR spectrum of the Ni1Co3Al2 composite oxide bifunctional catalyst prepared in Example 1 of this invention;

[0029] Figure 6The NH3-TPD spectrum of the Ni1Co3Al2 composite oxide bifunctional catalyst prepared in Example 1 of this invention;

[0030] Figure 7 This is a single-factor plot showing the ethanololysis of BOB under different conditions using the Ni1Co3Al2 composite oxide bifunctional catalyst prepared in Example 1 of this invention.

[0031] Figure 8 This is a comparison chart of the ethanololysis of BOB under different atmospheres when Ni1Co3Al2 is used as a catalyst in the application example.

[0032] Figure 9 This is a comparison chart of the ethanololysis of BOB in different solvents when Ni1Co3Al2 is used as a catalyst in the application example.

[0033] Figure 10 This is a graph showing the recycling performance of Ni1Co3Al2 as a catalyst in the BOB alcoholysis reaction in the application example. Detailed Implementation

[0034] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] Example 1

[0036] A method for preparing a Ni1Co3Al2 composite oxide bifunctional catalyst includes the following steps:

[0037] 0.29 g Ni(NO3)2·6H2O, 0.87 g Co(NO3)2·6H2O, and 0.75 g Al(NO3)3·9H2O were dissolved in 50 mL of deionized water, and then 2.25 g urea was added. The mixture was stirred for a certain period of time, and the solution was transferred to a polytetrafluoroethylene liner. The mixture was heated at 100 °C for 24 h. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The resulting crystals were washed with deionized water until neutral, and then dried overnight in a vacuum drying oven at 90 °C to obtain a layered double hydroxide precursor, denoted as Ni1Co3Al2-LDH.

[0038] The obtained precursor Ni1Co3Al2-LDH was placed in a muffle furnace for the first calcination at a heating rate of 5 °C / min and calcined at 600 °C for 2 h.

[0039] The obtained solid sample was ground into powder and calcined at 600℃ for 2 h under H2 atmosphere. The black powder was collected, which is the Ni1Co3Al2 composite oxide bifunctional catalyst.

[0040] The X-ray diffraction pattern of the prepared Ni1Co3Al2 composite oxide bifunctional catalyst is shown in the figure. Figure 1 As shown in the figure, the Ni1Co3Al2-LDH precursor underwent a significant structural topological transformation after calcination at 600℃. Its original characteristic diffraction peaks almost completely disappeared, while clear characteristic diffraction peaks appeared at 2θ = 44.3°, 51.6°, and 76.4°. These diffraction peaks are typical of Ni-Co elemental alloys, confirming that Ni and Co successfully formed a metallic elemental alloy phase after calcination. Furthermore, it is noteworthy that Al appears amorphous in XRD, primarily forming a spinel-structured composite oxide during calcination.

[0041] SEM images of the prepared Ni1Co3Al2 composite oxide bifunctional catalyst are shown below. Figure 2 As shown in the scanning electron microscope (SEM) images, the Ni1Co3Al2 catalyst exhibits a multi-layered snowflake / plate-like microstructure with a uniformly distributed layer structure. This unique morphological feature provides sufficient exposure area for active sites in the catalytic reaction, which is beneficial for the full contact between the reaction substrate and the active sites.

[0042] High-angle annular dark-field scanning transmission electron microscopy (HAADF-TEM) and the corresponding elemental distribution map show, as Figure 3 As shown, O, Co, Ni, and Al elements exhibit a uniform distribution within the catalyst nanoparticles. This result indicates good dispersion of the components in the catalyst, suggesting the possible formation of a uniform alloy or composite structure among them. This uniform elemental distribution, combined with the specific morphological structure, synergistically enhances the catalyst's activity and stability by optimizing the distribution of active sites.

[0043] X-ray photoelectron spectroscopy (XPS) analysis of the prepared Ni1Co3Al2 composite oxide bifunctional catalyst is as follows: Figure 4As shown, XPS further confirmed the presence of elements O, Al, Ni, and Co in Ni1Co3Al2, consistent with the EDS results. Specifically, in the O 1s spectrum, the peak near 530.4 eV is attributed to lattice oxygen, the peak at 531.5 eV can be attributed to abundant −OH groups on the catalyst surface, while the peak near 532.6 eV is related to chemisorbed oxygen species (such as H2O); a higher proportion of chemisorbed oxygen usually indicates abundant oxygen vacancies on the material surface, which is beneficial to the activation of reactant molecules. In the Al 2p spectrum, peaks at 73.0 eV, 74.2 eV, and 75.5 eV, belonging to Al2O3, NiAl2O4, and CoAl2O3, respectively, were observed, indicating that Al exists in multiple chemical states. Notably, the binding energy of Al 2p in CoAl2O4 is between that of Al2O3 and NiAl2O4, indicating that Ni... 2+ Co 2+ With Al 3+ There are interactions between them, thus regulating the electron binding energy of Al 2p. The Ni 2p and Co 2p spectra show that both Ni and Co simultaneously exist in a metallic state (Ni... 0 Co 0 ) and oxide state (Ni 2+ Co 2+ / Co 3+ The mixed valence state indicates that some metal oxides have been reduced, enhancing the chemical bonding between the metal and the support. The formation of the oxide state is mainly due to two reasons: (1) oxidation of the NiO surface exposed to air, and (2) unreduced NiO. X Species.

[0044] The H2-TPR diagram of the prepared Ni1Co3Al2 composite oxide bifunctional catalyst is shown in the figure. Figure 5 As shown, the H2-TPR curves of the Ni1Co3Al2 catalyst exhibit three distinct reduction peaks at 306℃, 410℃, and 784℃. Compared with the reported reduction peaks of Ni1Al2 (at 360℃ and 788℃) and Co3Al2 (at 411℃ and 798℃), the reduction peak temperatures are significantly lower, indicating a significant synergistic effect between Ni and Co, which weakens the interaction between the active metal and the Al support. The reduction peaks in the low-temperature region (306℃ and 410℃) correspond to the transformation process of Ni / Co oxides to the metallic state, while the reduction peak in the high-temperature region (784℃) is attributed to NiO and CoO. X Species are deeply reduced to metallic Ni 0 and Co 0 The process.

[0045] The NH3-TPD diagram of the prepared Ni1Co3Al2 composite oxide bifunctional catalyst is shown in Figure 1. Figure 6 As shown in the NH3-TPD spectrum of the Ni1Co3Al2 catalyst, the ammonia desorption temperatures are mainly distributed in two ranges: 100–320 °C and 320–650 °C, corresponding to weak and strong acid sites, respectively. This is mainly due to the strong interaction between the highly dispersed Ni and Co oxide species and the Al2O3 support. The intensity of the fitted desorption peak at 427 °C is significantly higher than other peaks, indicating that the strong acid sites are the main acidic centers of this catalyst. This acidic characteristic plays a crucial role in enhancing the catalytic activity.

[0046] Example 2

[0047] A method for preparing a Ni1Co3 composite oxide bifunctional catalyst includes the following steps:

[0048] 0.29 g Ni(NO3)2·6H2O and 0.87 g Co(NO3)2·6H2O were dissolved in 50 mL of deionized water, with a molar ratio of Ni to Co of 1:3. 2.25 g urea was then added, and the mixture was stirred for a certain period of time. The mixed solution was transferred to a polytetrafluoroethylene liner and heated at 100 °C for 24 h. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The resulting crystals were washed with deionized water until neutral and then dried overnight in a vacuum drying oven at 90 °C to obtain the precursor, denoted as Ni1Co3-LDH.

[0049] The obtained precursor Ni1Co3-LDH was placed in a muffle furnace for the first calcination at a heating rate of 5 °C / min and calcined at 600 °C for 2 h.

[0050] The obtained solid sample was ground into powder and calcined at 600℃ for 2 h under H2 atmosphere. The black powder was collected, which is the Ni1Co3 catalyst.

[0051] Example 3

[0052] A method for preparing a Co3Al2 composite oxide bifunctional catalyst includes the following steps:

[0053] 0.87 g Co(NO3)2·6H2O and 0.75 g Al(NO3)3·9H2O were dissolved in 50 mL of deionized water, with a molar ratio of Co to Al of 3:2. 2.25 g of urea was then added, and the mixture was stirred for a certain period of time. The mixed solution was then transferred to a polytetrafluoroethylene liner and heated at 100 °C for 24 h. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The resulting crystals were washed with deionized water until neutral and then dried overnight in a vacuum drying oven at 90 °C to obtain the precursor, denoted as Co3Al2-LDH.

[0054] The obtained precursor Co3Al2-LDH was placed in a muffle furnace for the first calcination at a heating rate of 5 °C / min and calcined at 600 °C for 2 h.

[0055] The obtained solid sample was ground into powder and calcined at 600℃ for 2 h under H2 atmosphere. The black powder was collected, which is the Co3Al2 catalyst.

[0056] Example 4

[0057] A method for preparing a Ni1Al2 composite oxide bifunctional catalyst includes the following steps:

[0058] 0.29 g Ni(NO3)2·6H2O and 0.75 g Al(NO3)3·9H2O were dissolved in 50 mL of deionized water, with a molar ratio of Ni to Al of 1:2. 2.25 g urea was then added, and the mixture was stirred for a certain period of time. The mixed solution was then transferred to a polytetrafluoroethylene liner and heated at 100 °C for 24 h. After the hydrothermal reaction was completed, the mixture was cooled to room temperature. The resulting crystals were washed with deionized water until neutral and then dried overnight in a vacuum drying oven at 90 °C to obtain the precursor, denoted as Ni1Al2-LDH.

[0059] The obtained precursor Ni1Al2-LDH was placed in a muffle furnace for the first calcination at a heating rate of 5 °C / min and calcined at 600 °C for 2 h.

[0060] The obtained solid sample was ground into powder and calcined at 600℃ for 2 h under H2 atmosphere. The black powder was collected, which is the Ni1Al2 catalyst.

[0061] Example 5

[0062] A Ni 0.5 The preparation method of the Co3Al2 composite oxide bifunctional catalyst includes the following steps:

[0063] 0.15 g Ni(NO3)2·6H2O, 0.87 g Co(NO3)2·6H2O, and 0.75 g Al(NO3)3·9H2O were dissolved in 50 mL of deionized water, with a molar ratio of Ni:Co:Al of 0.5:3:2. Then, 2.25 g urea was added, and the mixture was stirred for a certain period. The resulting solution was transferred to a polytetrafluoroethylene liner and heated at 100 °C for 24 h. After the hydrothermal reaction was complete, the mixture was cooled to room temperature. The resulting crystals were washed with deionized water until neutral and then dried overnight in a vacuum drying oven at 90 °C to obtain a layered double hydroxide precursor, denoted as Ni. 0.5 Co3Al2-LDH.

[0064] The obtained precursor Ni 0.5Co3Al2-LDH was placed in a muffle furnace for the first calcination, with a heating rate of 5 °C / min, and calcined at 600 °C for 2 h.

[0065] The obtained solid sample was ground into powder, calcined at 600℃ for 2 h under H2 atmosphere, and the black powder was collected, which is Ni. 0.5 Co3Al2 composite oxide bifunctional catalyst.

[0066] Example 6

[0067] A Ni 1.5 The preparation method of the Co3Al2 composite oxide bifunctional catalyst includes the following steps:

[0068] 0.44 g Ni(NO3)2·6H2O, 0.87 g Co(NO3)2·6H2O, and 0.75 g Al(NO3)3·9H2O were dissolved in 50 mL of deionized water, with a molar ratio of Ni, Co, and Al of 1.5:3:2. Then, 2.25 g urea was added, and the mixture was stirred for a certain period of time. The resulting solution was transferred to a polytetrafluoroethylene liner and heated at 100 °C for 24 h. After the hydrothermal reaction was complete, the mixture was cooled to room temperature. The resulting crystals were washed with deionized water until neutral and then dried overnight in a vacuum drying oven at 90 °C to obtain a layered double hydroxide precursor, denoted as Ni. 1.5 Co3Al2-LDH.

[0069] The obtained precursor Ni 1.5 Co3Al2-LDH was placed in a muffle furnace for the first calcination, with a heating rate of 5 °C / min, and calcined at 600 °C for 2 h.

[0070] The obtained solid sample was ground into powder, calcined at 600℃ for 2 h under H2 atmosphere, and the black powder was collected, which is Ni. 1.5 Co3Al2 composite oxide bifunctional catalyst.

[0071] Application examples

[0072] The catalysts prepared in Examples 1-6 were applied to the alcoholysis reaction of the lignin model compound benzylphenyl ether (BOB). The specific process is as follows:

[0073] (1) Place 0.5 g BOB, 0.5 g of each catalyst prepared in Examples 1-6 and 200 mL of ethanol into a 1000 mL stainless steel high-pressure reactor;

[0074] (2) After purging the high-pressure reactor with N2 three times, pressurize it with 1 MPa N2 at room temperature;

[0075] (3) Subsequently, the high-pressure reactor is heated to 220-300℃ and maintained at the set temperature for 30-150 min;

[0076] (4) After the reaction is completed, the high-pressure reactor is cooled to room temperature and the reaction mixture is removed. The filtrate is then analyzed by GC / MS.

[0077] When Ni1Co3Al2 is used as a catalyst in Example 1, the single-factor plots of BOB ethanol hydrolysis under different conditions are shown below. Figure 7 As shown, the effects of catalysts on the conversion and yield of BOB ethanol hydrolysis under different reaction conditions were investigated. With increasing reaction temperature from 220℃ to 300℃, the BOB conversion significantly increased, reaching complete conversion at 300℃; the aromatic yield also increased with increasing temperature, reaching its highest value (171.3 mol%) at 300℃. The by-product yield showed a trend of first increasing and then decreasing with increasing temperature, partly due to the further improvement of the catalyst's selectivity for aromatics, and partly due to the further reaction of intermediate products into aromatics. Therefore, increasing the temperature is beneficial to the activation of ethanol and the formation of aromatics. With prolonged reaction time, the BOB conversion gradually increased, achieving complete conversion at 120 min; the main product yield first increased rapidly with time and then tended to stabilize. The Ni1Co3Al2 catalyst can activate ethanol to release H· free radicals, which then attack the >C–O– bridging bond. Simultaneously, CH3CH2O· and H· produced by ethanol cracking can also attack (ethoxymethyl)benzene, promoting the formation of the corresponding aromatics. Therefore, 2 h is the optimal reaction time.

[0078] In the application example, when Ni1Co3Al2 is used as a catalyst, the atmospheric comparison diagram of the ethanololysis of BOB under different atmospheres is shown below. Figure 8 As shown, the BOB conversion rate follows the order: INP (0 MPa) < INP (1 MPa). This confirms that although ethanol solvent can act as an in-situ hydrogen donor, a moderate inert atmosphere can not only effectively maintain the stability of the reaction system and suppress gas-phase free radical side reactions, but also promote the activation of ethanol at Ni-Co active sites and the hydrogen transfer process, thereby optimizing the synergistic catalytic pathway of C–O bond breaking and hydrogen deoxygenation. This demonstrates the key regulatory role of the reaction atmosphere in the selectivity of lignin alcoholysis.

[0079] In the application example, when Ni1Co3Al2 is used as a catalyst, the comparison diagram of the ethanololysis of BOB in different solvents is shown below. Figure 9As shown in the figure, the effects of different protic solvents (methanol, ethanol, and isopropanol) on the reaction of BOB under N2 atmosphere were investigated. The conversion rates of BOB in the three solvents were 76.6%, 100%, and 100%, respectively, indicating that no additional hydrogen is needed during alcoholysis. The lower conversion rate in the methanol system may be related to its poor hydrogen donation stability and insufficient thermal stability due to its molecular structure. Furthermore, the product distribution differed significantly under different solvents. In isopropanol, the reaction favored a stable hydrogen donation pathway, with products mainly consisting of monomeric alkanes (47.7 mol%) and aromatics (91.5 mol%). In the methanol and ethanol systems, the main products were monocyclic aromatics, with yields of 96.4 mol% and 171.3 mol%, respectively. This is because, under mild conditions, the acidic sites on the catalyst surface can effectively activate alcohol molecules; the hydroxyl oxygen in the activated alcohol molecule carries a lone pair of electrons, becoming a strong nucleophile, which then attacks the oxygen-containing bridge bonds in the lignin model compound, causing them to break. Lignin is a three-dimensional amorphous aromatic polymer formed by random cross-linking of three phenylpropane structural units through ether and carbon-carbon bonds, and its structure endows it with high chemical stability. Alcohol solvents can penetrate the porous structure of lignin, causing swelling and disrupting non-covalent interactions, thereby increasing the yield of the target product. In summary, ethanol has greater application potential due to its moderate nucleophilicity, steric hindrance effect, and controllable cost; methanol and isopropanol also exhibit good reaction performance in this catalytic hydrocracking system due to their respective solvent properties.

[0080] In the application example, when Ni1Co3Al2 is used as a catalyst, the cycle stability test is as follows: Figure 10 As shown in the figure, the cyclic stability of the Ni1Co3Al2 catalyst in the BOB catalytic hydrocracking reaction was evaluated under the conditions of 1 MPa N2, 300 °C, and 2 h of reaction. After three cycles, the catalyst still maintained high catalytic activity: the BOB conversion decreased from 100% to 95.75%, and the aromatic yield decreased from 171.3 mol% to 144.3 mol%. The results indicate that the catalyst has good cyclic stability and can be easily separated and recovered from the reaction solution using an external magnet. Furthermore, the composition and distribution of the products did not change significantly with increasing cycle number.

[0081] The results of the application of the catalysts prepared in Examples 1-6 in the alcoholysis reaction of the lignin model compound benzylphenyl ether (BOB) are compared and the results are shown in Table 1 below.

[0082] Table 1

[0083]

[0084] As shown in the table above, although other catalysts exhibited good catalytic hydrocracking (CHC) activity for BOB, Ni1Co3Al2 showed the highest conversion (100%) and total aromatic yield (171.3 mol%), with the main product, toluene, reaching a yield of 139.0 mol%. In contrast, the conversions of Ni1Al2 and Co3Al2 were 78.1% and 85.4%, respectively, while the conversion of Ni1Co3 was only 56.9%, indicating that the introduction of Al significantly improved catalytic activity. This suggests a synergistic effect among Ni, Co, and Al, which can jointly enhance hydrogen activation and C–O bond breaking. Furthermore, both excessively high and low Ni proportions are detrimental to the formation of the target product: Ni... 0.5 The low Ni content in Co3Al2 results in insufficient deoxidation capacity; while Ni 1.5 Excessive Ni content in Co3Al2 can easily lead to the aggregation of nickel nanoparticles (NNPs), resulting in a decrease in catalyst activity. Therefore, Ni1Co3Al2 is the optimal composition.

[0085] The reaction system of this invention is carried out in a closed high-pressure reactor. When the ethanol used is heated to 220-320 °C, its temperature is already higher than the critical temperature of ethanol (243 °C). Simultaneously, the autogenous pressure generated by solvent vaporization within the reactor exceeds the critical pressure of ethanol (6.4 MPa), thus the reaction system is actually in a supercritical ethanol state. In this state, ethanol possesses a high diffusion coefficient similar to a gas and a high solubility similar to a liquid, effectively penetrating and swelling the lignin model compound. More importantly, supercritical ethanol can release active hydrogen species at the active sites of the Ni1Co3Al2 catalyst, thus eliminating the need for external hydrogen supply. The supercritical environment also inhibits excessive hydrogenation of aromatic rings, promoting the formation of high-value aromatics. The catalyst prepared by this method has two advantages: firstly, the Ni-Co alloy nanoclusters in the catalyst act as metal hydrogenation active sites, efficiently activating hydrogen species in alcohol solvents (especially supercritical ethanol), achieving in-situ hydrogen supply and transfer; secondly, Al exists in the form of a spinel-structured composite oxide, providing abundant acidic sites that can effectively adsorb and break the CO ether bonds in the lignin model compound. The synergistic effect of these two aspects enables the catalyst to selectively break CO bonds and avoid excessive hydrogenation of aromatic rings without the need for external hydrogen, thereby obtaining aromatic hydrocarbon products in high yield.

[0086] This method utilizes the unique properties of the Ni1Co3Al2 composite oxide bifunctional catalyst in a specific ethanol depolymerization system to successfully resolve the contradiction between the difficulty in breaking CO bonds and the ease of over-hydrogenation, thus locking the main product to aromatics. When the prepared Ni1Co3Al2 composite oxide bifunctional catalyst is applied to a supercritical ethanol system without external hydrogenation, it can promote the saturated transformation of aromatic rings to highly selective catalytic hydrogenolysis of CO bonds while retaining the aromatic ring, thereby achieving a highly efficient conversion from lignin model compounds to high-yield aromatic hydrocarbons.

[0087] This invention proposes a novel strategy for lignin conversion. Unlike the traditional hydrodeoxygenation route that relies on external hydrogen, this method utilizes the in-situ hydrogen-donating properties of ethanol in a supercritical ethanol and N2 atmosphere system to achieve highly selective cleavage of CO bonds in lignin model compounds, yielding aromatic hydrocarbons such as toluene and ethylbenzene in high yields. Experiments show that in the ethanol system, introducing H2 actually inhibits the catalyst's activity for CO bond cleavage, while an N2 atmosphere is more conducive to aromatic hydrocarbon formation. This invention avoids the use of high-pressure H2, ensuring high safety, and the product distribution is more favorable for the preparation of aromatic chemicals.

[0088] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A method for preparing a Ni1Co3Al2 composite oxide bifunctional catalyst, characterized in that, Includes the following steps: a. Ni source, Co source and Al source are dissolved together in deionized water at a molar ratio of 1:3:

2. A certain amount of urea is added and stirred to mix. After mixing, the mixture is transferred to a polytetrafluoroethylene liner for hydrothermal reaction. The reaction temperature is 80~120℃ and the reaction time is 20~26h to obtain the layered double hydroxide precursor Ni1Co3Al2-LDH. b. Place the precursor Ni1Co3Al2-LDH obtained in step a in a muffle furnace and perform a first calcination treatment in air. The heating rate is 5℃ / min, the calcination temperature is 550~650℃, and the calcination time is 1~3h. c. Grind the product obtained from the first calcination treatment into powder, place it in a tube furnace, and carry out a second calcination treatment under a reducing atmosphere. The heating rate is 3℃ / min, the temperature is 550~650℃, and the reduction time is 1~3h, thus obtaining the Ni1Co3Al2 composite oxide bifunctional catalyst.

2. The preparation method of the Ni1Co3Al2 composite oxide bifunctional catalyst as described in claim 1, characterized in that, In step a, the Ni source is nickel nitrate hexahydrate or anhydrous nickel nitrate, the Co source is cobalt nitrate hexahydrate or anhydrous cobalt nitrate, and the Al source is aluminum nitrate nonahydrate or anhydrous aluminum nitrate.

3. The preparation method of the Ni1Co3Al2 composite oxide bifunctional catalyst as described in claim 2, characterized in that, In step a, the ratio of urea to water is (0.8-1.2) g : (20-26) ml.

4. A bifunctional Ni1Co3Al2 composite oxide catalyst prepared by the preparation method described in claim 3.

5. The application of the Ni1Co3Al2 composite oxide bifunctional catalyst as described in claim 4 in the supercritical alcoholysis of lignin model compounds to prepare aromatics, characterized in that, Specific process: (1) A certain ratio of lignin model compound, alcohol solvent and Ni1Co3Al2 composite oxide bifunctional catalyst are added together into a high-pressure reactor and the reaction is carried out in a supercritical state. (2) Replace the air in the high-pressure reactor three times with N2, fill with N2, heat, and the reaction temperature is 220~320℃, and the reaction time is 1~3 h; (3) After the reaction is complete, stop heating and allow the high-pressure reactor to cool naturally to room temperature. Then remove the reaction mixture and analyze the filtrate using gas chromatography / mass spectrometry.

6. The application of the Ni1Co3Al2 composite oxide bifunctional catalyst as described in claim 5 in the supercritical alcoholysis of lignin model compounds to prepare aromatics, characterized in that, In step (1), the lignin model compound is a model containing a β-O-4 ether bond, selected from at least one of benzylphenyl ether and phenethoxybenzene, and the alcohol solvent is selected from at least one of methanol, ethanol or isopropanol, and the amount used is 150~250ml.

7. The application of the Ni1Co3Al2 composite oxide bifunctional catalyst as described in claim 6 in the supercritical alcoholysis of lignin model compounds to prepare aromatics, characterized in that, In step (1), the mass ratio of the Ni1Co3Al2 composite oxide bifunctional catalyst to the lignin model compound is (0.8~1.2) g: (0.8~1.3) g.

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