Cobalt-gallium alloy catalyst for guaiacol hydrodeoxygenation to cyclohexanol and preparation method and application thereof

Abstract

This invention belongs to the field of catalyst preparation technology, and provides a cobalt-gallium alloy catalyst for the hydrodeoxygenation of guaiacol to cyclohexanol, its preparation method, and its application. The preparation method includes the following steps: First, a mixed metal salt solution of cobalt and gallium sources is prepared, then carbon nanotubes are added, and the mixture is ultrasonically dispersed and refluxed. After the reaction, the catalyst is dried and reduced to obtain the catalyst CoGa / CNTs. Then, the CoGa / CNTs are mixed with an organophosphoric acid ligand solution and reacted at room temperature to obtain the organophosphonic acid ligand-modified carbon nanotube supported cobalt-gallium alloy catalyst R-PA@CoGa / CNTs. Applying the prepared catalyst R-PA@CoGa / CNTs to the hydrodeoxygenation of guaiacol to cyclohexanol achieves excellent guaiacol yield under milder reaction conditions and with a lower active metal content.

Description

Technical Field

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a cobalt-gallium alloy catalyst for the hydrogenation and deoxygenation of guaiacol to cyclohexanol, its preparation method, and its application. Background Technology

[0002] Lignin is an abundant renewable aromatic compound found in nature, and its targeted conversion is considered an important direction for the high-value utilization of biomass. Guaiacol, as a typical model molecule for lignin pyrolysis oil and lignin-derived phenolic compounds, contains both methoxy and hydroxyl functional groups. It can be selectively hydrogenated and deoxygenated to produce cyclohexanol, an important nylon precursor and fine chemical intermediate, which can be used in the preparation of high-value-added products such as adipic acid and cyclohexanone. Therefore, this reaction has significant scientific and practical value. However, the hydrogenation and deoxygenation of guaiacol to cyclohexanol is a typical multi-step tandem-parallel reaction process with a complex reaction pathway, usually requiring simultaneous aromatic ring hydrogenation, selective cleavage of the aryl methoxy group, and hydroxyl group retention. The reaction process is prone to the formation of phenol, methoxycyclohexanol, cyclohexanone, cyclohexane, and other deeply deoxygenated products, leading to a decrease in the selectivity of the target product.

[0003] Chinese patent application CN113731441A discloses a cobalt-reduced graphene oxide (Co / rGO) catalyst applicable to the preparation of cyclohexanol from guaiacol. This catalyst achieves a good cyclohexanol yield (95%), but its Co loading remains high, the preparation method is complex, and the reaction conditions are harsh (200°C). Therefore, achieving a balance between high conversion, high cyclohexanol selectivity, and high stability under milder conditions and with lower metal costs remains a pressing technical challenge in this field.

[0004] Therefore, it is necessary to develop a non-precious metal catalyst that is easy to prepare, low in cost, and can efficiently catalyze the hydrogenation and deoxygenation of guaiacol to cyclohexanol under mild conditions. Summary of the Invention

[0005] In view of this, the present invention provides a non-precious metal catalyst with controllable structure, simple preparation, low cost and excellent catalytic performance under mild conditions, and a method for preparing the same. In particular, the present invention achieves effective control over hydrogen activation, key intermediate adsorption configuration and reaction pathway selectivity in the hydrodeoxygenation reaction of guaiacol through the synergistic effect of cobalt-gallium alloy active center, carbon nanotube support and organophosphorus ligand surface modification, thereby improving the yield of cyclohexanol.

[0006] To achieve the above objectives, the technical solution of the present invention is as follows: A method for preparing a cobalt-gallium alloy catalyst for the hydrogenation of guaiacol to cyclohexanol includes the following steps: (1) Prepare a mixed metal salt solution of cobalt and gallium sources, then add carbon nanotubes, disperse by ultrasonication, and reflux at 60-90℃; after the reaction, dry and reduce to obtain a carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as CoGa / CNTs; the molar ratio of Co to Ga is 0.8-1.5:1, and the Co loading is 3.5-6.0 wt%; (2) Under an inert atmosphere, CoGa / CNTs and organophosphoric acid ligand solution are mixed and stirred thoroughly at room temperature to allow the organophosphoric acid ligand to undergo self-assembly modification with the surface of the cobalt-gallium alloy and the support surface, thereby obtaining a carbon nanotube-supported cobalt-gallium alloy catalyst modified with organophosphoric acid ligand, denoted as R-PA@CoGa / CNTs; the tail carbon chain length of the organophosphoric acid ligand is C10-C16, and its general formula is R-PO(OH)2, wherein R is a straight-chain C10-C16 alkyl group.

[0007] The present invention is further configured such that the molar ratio of Co to Ga is 0.8 to 1.2:1, for example 0.8:1, 0.9:1, 1:1, 1.1:1 or 1.2:1; preferably, the molar ratio of Co to Ga is 1:1.

[0008] The present invention is further configured such that the solvent of the mixed metal salt solution is an alcohol solution; preferably an aqueous ethanol solution, wherein the volume ratio of ethanol to water is (0.5~2.0):1.

[0009] The present invention is further configured such that the carbon nanotubes are carbon nanotubes that have undergone oxygen-containing functionalization treatment.

[0010] The present invention is further configured such that the oxygen-containing functionalization treatment includes the following process: adding carbon nanotubes to an H2O2 solution, stirring thoroughly at room temperature, and then filtering, washing, and drying to obtain carbon nanotubes with -OH / -CO- functional groups introduced on the surface.

[0011] The present invention is further configured such that, in step (1), hydrogen is used for reduction, and the reduction temperature is 600~750℃.

[0012] The present invention is further configured such that, in step (1), hydrogen reduction is used and the heating rate is 5~20℃ / min.

[0013] The present invention is further configured such that, in step (2), the organophosphonic acid ligand is selected from one of decylphosphonic acid, undecylphosphonic acid, dodecylphosphonic acid, tetradecylphosphonic acid or hexadecylphosphonic acid.

[0014] The present invention is further configured such that the mass ratio of the organophosphonic acid ligand to the carbon nanotube-supported cobalt-gallium alloy catalyst CoGa / CNTs is (0.5~40):1.

[0015] The present invention provides a cobalt-gallium catalyst for the hydrogenation of guaiacol to cyclohexanol prepared according to the above preparation method, which is a cobalt-gallium alloy supported on carbon nanotubes, wherein the surface of the carbon nanotubes is modified with organophosphonic acid.

[0016] The present invention is further configured such that the phosphorus content in the catalyst is 2.0 wt%-3.0 wt%.

[0017] The present invention also provides the application of the cobalt gallium catalyst in the hydrodeoxygenation of guaiacol to cyclohexanol, wherein the hydrodeoxygenation reaction conditions are: hydrogen pressure 2-4 MPa and temperature 140-160℃.

[0018] Compared with the prior art, the present invention has the following beneficial effects: This invention constructs cobalt-gallium alloy active centers, utilizes carbon nanotube carriers to achieve high dispersion and stable anchoring of active components, and introduces organophosphorus ligands with adjustable carbon chain lengths to finely regulate the microenvironment on the catalyst surface. This enables synergistic optimization of the electronic structure, geometric configuration, interfacial interactions, and steric hindrance of the active centers, improving hydrogen activation efficiency and the directional adsorption and activation capacity of key intermediates, suppressing excessive deoxygenation and other side reactions, and ultimately achieving efficient conversion of guaiacol and highly selective generation of cyclohexanol under relatively mild conditions, showing promising application prospects. Detailed Implementation

[0019] The technical solution of the present invention will be clearly and completely described below with reference to specific embodiments. It should be understood that the described embodiments are only some embodiments of the present invention, and not all embodiments. 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 the present invention. Unless otherwise defined, all technical and scientific terms used herein have the same meaning as those familiar with the art.

[0020] Example 1 An organophosphonic acid ligand-modified carbon nanotube-supported cobalt-gallium alloy catalyst comprises the following steps: (1) Vector pretreatment: Carbon nanotubes (CNTs) were selected from multi-walled carbon nanotubes (MWCNTs), with an outer diameter of 10-40 nm, a length of 5-20 μm, and a diameter of 200-400 m. 2 g -1Before use, oxygen-containing functionalization was performed: CNTs were added to 30 wt% H2O2 solution (solid-liquid ratio 1:40, g:mL), magnetically stirred at room temperature for 2 h, filtered, washed with deionized water until neutral, and vacuum dried at 80 °C for 12 h to obtain carbon nanotubes CNT-OH with -OH / -CO- functional groups introduced on the surface.

[0021] (2) Preparation of carbon nanotube-supported cobalt-gallium alloy catalysts: A mixed metal salt solution was prepared using cobalt nitrate hexahydrate as the cobalt source, gallium nitrate hydrate as the gallium source, and a mixed solution of ethylene glycol and water as the solvent; wherein the volume ratio of ethylene glycol to water was 1:1, and the molar ratio of Co / Ga was 1:1. Then, according to the target total metal loading of 5.0 wt%, the CNT-OH support treated in step (1) was added, and the resulting mixed system was ultrasonically dispersed for 30 min, and then refluxed in an 80°C water bath for 2 h to allow the metal precursor to be fully adsorbed on the surface of the support; subsequently, the solvent was removed by rotary evaporation, and then dried at 120°C for 4 h. The resulting solid was reduced in a 20% H2 / Ar mixed atmosphere (20% being the volume fraction of H2 in the mixed atmosphere), at a reduction temperature of 700°C, a holding time of 4 h, and a heating rate of 10°C. min -1 Thus, a carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as CoGa / CNTs, is obtained.

[0022] (3) Organophosphonic acid ligand-modified catalysts: Under an inert atmosphere, the organophosphonic acid ligand was dissolved in an organic solvent to prepare a solution with a concentration of 1.0 mol·L⁻¹. -1 The organophosphonic acid modified solution, wherein the organophosphonic acid ligand is decylphosphonic acid and the organic solvent is tetrahydrofuran (THF). 1.0 g of the CoGa / CNTs catalyst prepared in step (2) was weighed and added to 100 mL of a 1.0 mol·L⁻¹ solution. -1 In an organophosphonic acid-modified solution, the mixture was stirred at 0.05 MPa and room temperature for 24 h to allow the organophosphonic acid ligands to self-assemble and modify the cobalt-gallium alloy surface and the support surface. After the reaction, the resulting solid was centrifuged, washed with THF, and then vacuum dried at 80°C for 6 h to obtain the organophosphonic acid ligand-modified carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as C10-PA@CoGa / CNTs. The phosphorus content in the catalyst was determined by ICP to be P = 2.9 wt%.

[0023] Example 2 A method for preparing a carbon nanotube-supported cobalt-gallium alloy catalyst modified with an organophosphonic acid ligand is disclosed. The only difference from Example 1 is the organophosphonic acid ligand used; in this example, the organophosphonic acid ligand is undecylphosphonic acid. All other operations are the same. The resulting carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as C11-PA@CoGa / CNTs, was obtained. ICP analysis showed that the phosphorus content in the catalyst was P = 2.9 wt%.

[0024] Example 3 A method for preparing a carbon nanotube-supported cobalt-gallium alloy catalyst modified with an organophosphonic acid ligand is disclosed. The only difference from Example 1 is the organophosphonic acid ligand used; in this example, the organophosphonic acid ligand is dodecylphosphonic acid. All other operations are the same. The resulting carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as C12-PA@CoGa / CNTs, was obtained. ICP analysis showed that the phosphorus content in the catalyst was P = 2.6 wt%.

[0025] Example 4 A method for preparing a carbon nanotube-supported cobalt-gallium alloy catalyst modified with an organophosphonic acid ligand is disclosed. The only difference from Example 1 is the organophosphonic acid ligand used; in this example, the organophosphonic acid ligand is hexadecylphosphonic acid. All other operations are the same. The resulting carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as C16-PA@CoGa / CNTs, was obtained. ICP analysis showed that the phosphorus content in the catalyst was P = 2.2 wt%.

[0026] Example 5 A method for preparing a carbon nanotube-supported cobalt-gallium alloy catalyst modified with organophosphonic acid ligands is disclosed. The only difference from Example 1 is the amount of organophosphonic acid ligand used. In this example, the amount of hexadecylphosphonic acid is 100 mL, 0.50 mol·L⁻¹. -1 The remaining operations were the same. ICP analysis showed that the phosphorus content in the C16-PA@CoGa / CNTs catalyst was P=2.0 wt%.

[0027] Example 6 A method for preparing a carbon nanotube-supported cobalt-gallium alloy catalyst modified with organophosphonic acid ligands is disclosed. The only difference from Example 1 is the amount of organophosphonic acid ligand used. In this example, the amount of hexadecylphosphonic acid is 100 mL, 0.25 mol·L⁻¹. -1 The remaining operations were the same. ICP analysis showed that the phosphorus content in the C16-PA@CoGa / CNTs catalyst was P=2.2 wt%.

[0028] Comparative Example 1 A method for preparing a carbon nanotube-supported cobalt-gallium alloy catalyst modified with an organophosphonic acid ligand is disclosed. Compared with Example 1, the only difference is the organophosphonic acid ligand; in this example, the organophosphonic acid ligand is methylphosphonic acid. All other operations are the same. The resulting carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as Cl-PA@CoGa / CNTs, was obtained. ICP analysis showed that the phosphorus content in the catalyst was P = 2.5 wt%.

[0029] Comparative Example 2 A method for preparing a carbon nanotube-supported cobalt-gallium alloy catalyst modified with an organophosphonic acid ligand is disclosed. The only difference from Example 1 is the organophosphonic acid ligand used; in this example, the organophosphonic acid ligand is butylphosphonic acid. All other operations are the same. The resulting carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as C4-PA@CoGa / CNTs, was obtained. ICP analysis showed that the phosphorus content in the catalyst was P = 2.8 wt%.

[0030] Comparative Example 3 A method for preparing a carbon nanotube-supported cobalt-gallium alloy catalyst modified with an organophosphonic acid ligand is disclosed. Compared with Example 1, the only difference is the organophosphonic acid ligand; in this example, the organophosphonic acid ligand is octylphosphonic acid. All other operations are the same. The resulting carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as C8-PA@CoGa / CNTs, was obtained. ICP analysis showed that the phosphorus content in the catalyst was P = 2.1 wt%.

[0031] Comparative Example 4 A method for preparing an organophosphonic acid ligand-modified cobalt-gallium alloy catalyst, which differs from Example 4 only in the support.

[0032] In this comparative example, activated carbon (AC) was used as the support, and the catalyst obtained in step (2) was CoGa / AC. Then, 1.0 g of CoGa / AC was weighed and added to a THF solution containing hexadecylphosphonic acid (1.0 mol·L⁻¹). -1 The catalyst was prepared by stirring at 0.05 MPa (100 mL) at room temperature for 24 h under centrifugation, THF washing, and vacuum drying at room temperature. The catalyst was designated as C16-PA@CoGa / AC. The phosphorus content in the catalyst was determined to be P = 2.0 wt% by ICP.

[0033] Comparative Example 5 A method for preparing a carbon nanotube-supported cobalt-gallium alloy catalyst, which differs from Example 1 only in that the organophosphonic acid modification treatment in step (3) is not performed. The resulting catalyst is CoGa / CNTs.

[0034] Comparative Example 6 A method for preparing a cobalt catalyst supported on carbon nanotubes, which differs from Example 1 only in that there is no cobalt source in step (2) and the organophosphonic acid modification treatment in step (3) is not performed. The resulting catalyst is Co / CNTs.

[0035] Comparative Example 7 A method for preparing an organophosphonic acid ligand-modified cobalt-gallium alloy catalyst, which differs from Example 4 only in that the molar ratio of Co / Ga is 0.5:1.

[0036] Comparative Example 8 A method for preparing an organophosphonic acid ligand-modified cobalt-gallium alloy catalyst, which differs from Example 4 only in the molar ratio of Co / Ga, specifically 2:1.

[0037] Comparative Example 9 A method for preparing an organophosphonic acid ligand-modified cobalt catalyst, which differs from Example 4 only in that there is no gallium source in step (2). Co / CNTs are prepared in step (2) and then modified with organophosphonic acid in step (3). The resulting catalyst is C16-PA@Co / CNTs.

[0038] Catalyst performance evaluation The catalytic performance of the catalysts prepared in Examples 1-6 and Comparative Examples 1-9 was evaluated as follows: In a 100 mL stainless steel magnetically stirred autoclave, guaiacol-GUA (2.0 mmol), isopropanol (IPA 50 mL), and 15 mg of catalyst were added. After sealing, the autoclave was evacuated and hydrogen-purged three times, pressurized to 4.0 MPa H2, and heated to 150 °C with stirring (600 rpm) for 2 h. The autoclave was then cooled, depressurized, and centrifuged to separate the catalyst. The supernatant was analyzed quantitatively using GC-FID (polar capillary column), with n-propanol as an internal standard. The target product was cyclohexanol (CHOL); byproducts included phenol (PhOH), methoxycyclohexanol (MCHOL), cyclohexanone (CHONE), and cyclohexane (CHA), which were qualitatively analyzed by GC-MS.

[0039] Guaiacin conversion rate X (%) = (GUA0 – GUA) t ) / GUA0×100% Cyclohexanol selectivity S_CHOL (%) = CHOL t / ∑products t ×100% Cyclohexanol yield Y_CHOL (%) = X × S_CHOL / 100; After the reaction was completed and cooled to room temperature, the mixture was filtered after purging the air. The conversion rate of guaiacol and the selectivity of cyclohexanol were determined by GC external standard method. The hydrodeoxygenation reaction of guaiacol was analyzed online using an Agilent 8860 gas chromatograph equipped with an HP-5 capillary column (30 m long, 0.32 mm inner diameter, 0.5 μm film thickness). The results are shown in Table 1 below.

[0040] Table 1 Evaluation results of catalytic performance of cobalt gallium catalysts

[0041] As shown in Table 1, for the catalytic system of guaiacol hydrodeoxygenation to cyclohexanol, the conversion rate of the unmodified Co / CNTs catalyst supported by a single metal (Comparative Example 6) was only 21%, and the selectivity was 13.3%. After introducing an equimolar ratio of Ga, the conversion rate of the unmodified CoGa alloy catalyst (Comparative Example 5) was significantly increased to 55.0%, and the selectivity was also increased to 44.0%. This is because the introduction of Ga isolated the continuous Co active sites, inhibited the strong adsorption of Co atoms to guaiacol, alleviated the blockage of active sites, and promoted the rapid desorption of the product. In Comparative Example 7, due to the excessively high proportion of Ga, the activation of the catalyst for the reactants was reduced, and both the conversion rate and selectivity were reduced. In Comparative Example 8, the Ga content was insufficient to isolate the continuous Co sites, and the conversion rate was only 51%, with a selectivity of 69.9%. Furthermore, the experimental results also show that the organophosphonic acid modification of the CoGa alloy catalyst can further improve the conversion rate of guaiacol and the selectivity of cyclohexanol, and even achieve 100% cyclohexanol selectivity. For examples 5 and 6, which use lower concentrations of phosphonic acid solution for modification, the modification still achieves the desired effect on the support surface, with no impact on conversion and selectivity. In other words, for phosphonic acid solution modification, as long as the phosphonic acid content is sufficient, the difference in phosphorus content on the resulting catalyst is minimal. For Comparative Example 9, the catalyst modified with Ga-free 16-alkylphosphoric acid still exhibits low activity, similar to Comparative Example 6. This pattern is related to the combined regulation of interfacial hydrophobicity, steric hindrance, and substrate adsorption configuration. These results fully demonstrate that the coordination layer formed by organophosphoric ligand molecules on the catalyst surface can effectively suppress side reaction pathways such as deep hydrogenation and cracking through both electronic effects and steric hindrance, preferentially generating the target furanol product. Furthermore, for C6 catalysts modified with hexadecylphosphonic acid on different types of carbon supports… 16 - The PA@CoGa / AC catalyst (Comparative Example 4) showed a significant decrease in conversion rate to below 40%, indicating that the catalyst system of the present invention has high requirements for the support. Even commonly used activated carbon supports, which also use carbon as the main component, cannot achieve good results for this catalytic system.

[0042] The above embodiments are only for illustrating the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent transformations or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing a cobalt-gallium alloy catalyst for the hydrogenation of guaiacol to cyclohexanol, characterized in that, The process includes the following: (1) Prepare a mixed metal salt solution of cobalt and gallium sources, then add carbon nanotubes, disperse by ultrasonication, and reflux at 60-90℃; after the reaction, dry and reduce to obtain a carbon nanotube-supported cobalt-gallium alloy catalyst, denoted as CoGa / CNTs; the molar ratio of Co to Ga is 0.8-1.5:1, and the Co loading is 3.5-6.0 wt%; (2) Under an inert atmosphere, CoGa / CNTs and organophosphoric acid ligand solution are mixed and stirred thoroughly at room temperature to allow the organophosphoric acid ligand to undergo self-assembly modification with the surface of the cobalt-gallium alloy and the support surface, thereby obtaining a carbon nanotube-supported cobalt-gallium alloy catalyst modified with organophosphoric acid ligand, denoted as R-PA@CoGa / CNTs; the tail carbon chain length of the organophosphoric acid ligand is C10-C16, and its general formula is R-PO(OH)2, wherein R is a straight-chain C10-C16 alkyl group.

2. The preparation method according to claim 1, characterized in that, In step (1), the carbon nanotubes are carbon nanotubes that have undergone oxygen-containing functionalization treatment.

3. The preparation method according to claim 2, characterized in that, The oxygen-containing functionalization treatment includes the following process: adding carbon nanotubes to H2O2 solution, stirring thoroughly at room temperature, and then filtering, washing, and drying to obtain carbon nanotubes with -OH / -CO- functional groups introduced on the surface.

4. The preparation method according to claim 1, characterized in that, In step (1), hydrogen is used for reduction at a temperature of 600~750℃.

5. The preparation method according to claim 1, characterized in that, In step (2), the organophosphonic acid ligand is selected from one of decylphosphonic acid, undecylphosphonic acid, dodecylphosphonic acid, tetradecylphosphonic acid or hexadecylphosphonic acid.

6. A cobalt-gallium alloy catalyst for the hydrogenation of guaiacol to cyclohexanol, prepared by the method according to any one of claims 1 to 5, characterized in that, Cobalt-gallium alloy is loaded onto carbon nanotubes, the surface of which is modified with organophosphonic acid.

7. The cobalt-gallium alloy catalyst according to claim 6, characterized in that, The catalyst contains 2.0-3.0 wt% phosphorus.

8. The application of a cobalt-gallium alloy catalyst as described in claim 6 or 7 in the hydrodeoxygenation of guaiacol to cyclohexanol, characterized in that, The conditions for the hydrodeoxygenation reaction are: hydrogen pressure 2.0-4.0 MPa and temperature 140-160℃.

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