A hydrothermally constructed Co / Al2O3 catalyst, its preparation method, and its application in the hydrogenation of aromatic phenols to cyclohexanol.

Abstract

The present application relates to a kind of hydrothermal in-situ construction Co / Al2O3 Catalyst and its preparation method and application in aromatic phenol hydrogenation preparation cyclohexanol.The catalyst is Al2O3 as carrier, Co is only additional transition metal component, by in-situ introduction Co precursor during the formation of aluminum-containing precursor, by hydrothermal treatment, separation, washing, drying, calcination and hydrogen-containing atmosphere reduction is prepared.The catalyst is used for the selective hydrogenation of aromatic ring without methoxy aromatic phenol, can phenol, methyl phenol and ethyl phenol are converted into cyclohexanol and corresponding alkyl substituted cyclohexanol respectively.Co / Al2O3-450 ℃ Catalyst is at 120 ℃, 3 MPa hydrogen, 6 h and 500 r / min condition, realizes 99.9% phenol conversion and 99.8% cyclohexanol yield, and has good substrate applicability and cycle stability.

Description

Technical Field

[0001] This invention belongs to the technical field of industrial catalysis and high-value utilization of biomass resources, specifically relating to a hydrothermal in-situ constructed Co / Al2O3 catalyst, its preparation method, and its application in the hydrogenation of aromatic phenols to prepare cyclohexanol. Background Technology

[0002] Cyclohexanol is an important organic chemical intermediate, serving as a crucial raw material for the production of nylon-related chemicals such as adipic acid and caprolactam. It can also be used as a solvent and an intermediate in the synthesis of fine chemicals. Existing cyclohexanol production routes mainly include cyclohexane oxidation and catalytic hydrogenation of phenol. These processes place high demands on catalyst activity, target product selectivity, and recycling stability. Therefore, developing non-precious metal catalytic systems with well-defined compositions, readily available raw materials, and the ability to achieve highly selective hydrogenation of methoxylated aromatic phenols under relatively mild conditions is of great significance.

[0003] Lignin is an important natural aromatic component in lignocellulosic biomass, and through depolymerization and further conversion, it can yield various aromatic phenolic compounds. Phenol, as well as alkyl-substituted phenols such as methylphenol and ethylphenol, do not contain methoxy groups. Under hydrogen-containing conditions, they mainly undergo selective hydrogenation of the aromatic ring, retaining the CO bond corresponding to the phenolic hydroxyl group and the alkyl substituents on the aromatic ring. Specifically, phenol is hydrogenated to cyclohexanol, while methylphenol and ethylphenol are hydrogenated to the corresponding methylcyclohexanol and ethylcyclohexanol, respectively. These reactions belong to selective hydrogenation of the aromatic ring, without involving methoxy group removal or hydrodeoxygenation. Phenol can serve as a representative substrate with the simplest structure. Methylphenol and ethylphenol with different substitution positions can be used to evaluate the suitability of catalysts for changes in alkyl substitution position and alkyl carbon chain length. This type of reaction can be used to evaluate the catalyst's hydrogen activation ability, aromatic ring hydrogenation ability, target product selectivity, and ability to inhibit further hydrogenolysis or removal of the phenolic hydroxyl group.

[0004] Noble metal catalysts typically exhibit high activity in aromatic ring hydrogenation, but they are costly and relatively scarce. Non-noble metals such as Co possess hydrogen dissociation activation and aromatic ring hydrogenation capabilities, thus showing potential application in the selective hydrogenation of methoxy-free aromatic phenols. For supported Co catalysts, the distribution state of Co species, the degree of reduction, and the contact and interfacial interactions between Co and the support can all influence hydrogen activation, aromatic phenol substrate adsorption, and aromatic ring hydrogenation behavior.

[0005] In the preparation of Co / Al2O3 catalysts, the contact state between the Co precursor and aluminum-containing species, as well as the subsequent drying, calcination, and reduction conditions, can all affect the distribution of the resulting Co species on the Al2O3 support and the performance of the catalyst. Therefore, there is still room for improvement in how to promote sufficient contact between the Co precursor and aluminum-containing species during the formation of the aluminum-containing support precursor, and obtain a Co / Al2O3 catalyst suitable for the selective hydrogenation of phenol and alkyl-substituted phenols at lower temperatures.

[0006] This invention introduces a Co precursor simultaneously during the formation of an aluminum-containing precursor, ensuring sufficient contact between the Co and aluminum species during the hydrothermal treatment stage. Subsequent drying, calcination, and reduction treatments yield a hydrothermally constructed in-situ Co / Al₂O₃ single-metal catalyst. This preparation method improves the distribution of Co species on the Al₂O₃ support and its contact state with the support, enabling the resulting catalyst to catalyze the selective aromatic ring hydrogenation of phenol and alkyl-substituted phenols at relatively low reaction temperatures, respectively preparing cyclohexanol and the corresponding alkyl-substituted cyclohexanols. Summary of the Invention

[0007] The purpose of this invention is to provide a hydrothermally in-situ constructed Co / Al2O3 catalyst and its preparation method. By introducing a Co precursor in situ during the formation of an aluminum-containing precursor, the Co species and aluminum-containing species are fully contacted during the hydrothermal treatment stage, thereby improving the distribution of Co species on the obtained Al2O3 support and its contact state with the support. The obtained catalyst is then used for selective hydrogenation of methoxy aromatic phenols.

[0008] This invention involves treating an aluminum-containing precursor, a Co precursor, and a precipitant under hydrothermal conditions to obtain a Co–Al-containing hydrothermal precursor. After separation, washing, drying, calcination, and reduction in a hydrogen-containing atmosphere, a Co / Al₂O₃ catalyst is prepared. The obtained catalyst can be used for the selective hydrogenation of the aromatic rings of phenol and alkyl-substituted phenols. Phenol hydrogenation yields cyclohexanol, and alkyl-substituted phenol hydrogenation yields the corresponding alkyl-substituted cyclohexanol. The reaction retains the CO bond corresponding to the phenolic hydroxyl group and the alkyl substituents on the aromatic ring, without involving methoxy group removal or hydrogenation deoxygenation.

[0009] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0010] This invention provides a hydrothermally in-situ constructed Co / Al2O3 monometallic catalyst, wherein Co is the only added transition metal component and Al2O3 is the support.

[0011] The catalyst contains 10–30 wt% Co. The Co mass fraction refers to the percentage of Co by mass relative to the total mass of the catalyst.

[0012] The method for preparing the hydrothermally in-situ constructed Co / Al2O3 monometallic catalyst of the present invention includes the following steps:

[0013] 1) Dissolve aluminum nitrate nonahydrate in deionized water. The concentration of aluminum nitrate nonahydrate is 0.32-0.46 mol / L based on the initial volume of deionized water used. Stir until completely dissolved to obtain an aluminum-containing precursor solution.

[0014] 2) Under room temperature and stirring conditions, cobalt nitrate hexahydrate and urea are added to the aluminum-containing precursor solution, and stirring is continued until the mixture is homogeneous to obtain a mixed solution; wherein the molar ratio of cobalt nitrate hexahydrate to aluminum nitrate nonahydrate is (0.09~0.38):1, and the molar ratio of urea to aluminum nitrate nonahydrate is (1.37~1.60):1;

[0015] 3) The mixed solution is transferred to a hydrothermal reactor and subjected to hydrothermal treatment at 100~140 °C for 20~24 h to obtain a Co-Al-containing hydrothermal precursor;

[0016] 4) The hydrothermal precursor was filtered and washed with deionized water, and then dried at 56-64 °C for 10-14 h to obtain the dried precursor;

[0017] 5) The dried precursor is calcined and then reduced in a hydrogen-containing atmosphere to obtain a Co / Al2O3 single metal catalyst with a Co mass fraction of about 10-30 wt%.

[0018] In the preparation method of the hydrothermal in-situ constructed Co / Al2O3 monometallic catalyst, in step 5, the calcination temperature is 250~650 ℃, the calcination time is 4~6 h, and the heating rate is 4~6 ℃ / min;

[0019] In the preparation method of the hydrothermal in-situ constructed Co / Al2O3 monometallic catalyst, in step 5, the reducing atmosphere is a 2-8% H2 / N2 mixed gas, the reduction temperature is 250-650 ℃, the reduction time is 4-6 h, and the heating rate is 1-3 ℃ / min.

[0020] This invention also provides the application of the Co / Al2O3 catalyst in the hydrogenation of aromatic phenols to cyclohexanol, comprising the following steps:

[0021] a) Add the catalyst, aromatic phenol substrate and reaction solvent to a high-pressure reactor and mix thoroughly. After sealing, replace the gas in the reactor with hydrogen and fill with hydrogen until the initial pressure is 2-4 MPa.

[0022] b) Heat the reactor to 110–130 °C and react for 4–8 h with stirring at 450–550 r / min. After the reaction is complete, stop heating and stirring, and after the reactor cools to room temperature, release the pressure and open the reactor to separate the liquid reaction products and catalyst.

[0023] The aromatic phenol substrate is a methoxylated aromatic phenol selected from phenol, 2-methylphenol, 3-methylphenol, 4-methylphenol, 2-ethylphenol, 3-ethylphenol, and 4-ethylphenol. Phenol undergoes selective hydrogenation of its aromatic ring to generate cyclohexanol; 2-methylphenol, 3-methylphenol, and 4-methylphenol generate their respective methylcyclohexanols; and 2-ethylphenol, 3-ethylphenol, and 4-ethylphenol generate their respective ethylcyclohexanols. In this invention, "hydrogenation of aromatic phenols to prepare cyclohexanol" includes the hydrogenation of phenol to prepare cyclohexanol, and the hydrogenation of alkyl-substituted phenols to prepare their respective alkyl-substituted cyclohexanols.

[0024] The reaction solvent is n-hexane, and n-dodecane is used as an internal standard for quantitative gas chromatography.

[0025] The mass ratio of the catalyst to the aromatic phenol substrate is 1: (0.9~2.0).

[0026] After the reaction is complete, the solid catalyst and the liquid reaction product are separated by filtration, and the liquid reaction product is qualitatively and quantitatively analyzed by gas chromatography. The obtained product can be further separated and purified according to the requirements of use.

[0027] In this invention, the reduced Co species in the catalyst participate in the dissociation and activation of hydrogen and the selective hydrogenation of the aromatic ring of the aromatic phenol substrate. The Al2O3 support provides a basis for the dispersion and loading of the Co species, and the hydrothermal in-situ preparation method facilitates sufficient contact between the Co precursor and the aluminum-containing species. During the reaction, the aromatic ring of the aromatic phenol substrate undergoes hydrogenation, while the CO bond corresponding to the phenolic hydroxyl group and the alkyl substituents on the aromatic ring are retained. Under the conditions described in Example 4, the Co / Al2O3-450 °C catalyst achieved a phenol conversion of 99.9% and a cyclohexanol yield of 99.8% at 120 °C, an initial hydrogen pressure of 3 MPa, a reaction time of 6 h, and a stirring rate of 500 r / min.

[0028] The significant advantages and effects of this invention are as follows:

[0029] 1. The present invention introduces Co precursor in situ during the formation of aluminum precursor, so that Co species and aluminum species can fully contact each other during the hydrothermal treatment stage, which is beneficial to improving the distribution of Co species on Al2O3 support and its contact state with the support.

[0030] 2. The only externally added transition metal component in the catalyst of this invention is Co, the catalyst composition is well-defined, and the raw materials for preparation are readily available.

[0031] 3. Under the preferred reaction conditions shown in the examples, the Co / Al2O3-450 ℃ catalyst can achieve a phenol conversion rate of 99.9% and a cyclohexanol yield of 99.8% at 120 ℃, an initial hydrogen pressure of 3 MPa, a reaction time of 6 h, and a stirring rate of 500 r / min.

[0032] 4. The Co / Al2O3 catalyst described in this invention can be used for the selective hydrogenation of the aromatic rings of methylphenol and ethylphenol with different substitution positions, indicating that it has good substrate applicability to alkyl-substituted aromatic phenols without methoxy groups.

[0033] 5. In the cyclic stability test, after 10 cycles, the catalyst still achieved a phenol conversion rate of 99.9% and a cyclohexanol yield of 94.5%, indicating that it has good cyclic stability. Attached Figure Description

[0034] Figure 1 Microstructure, particle size distribution and elemental distribution of the Co / Al2O3 catalysts obtained in Examples 1-3.

[0035] (a1) Transmission electron microscopy (TEM) image of Co / Al2O3 catalyst at 250 ℃; (a2) High-resolution transmission electron microscopy (HRTEM) image of Co / Al2O3 catalyst at 250 ℃, with the inset being a magnified view of the boxed area; (a3) ​​Particle size distribution of Co particles in Co / Al2O3 catalyst at 250 ℃, with a statistical average particle size of approximately 10.0 nm;

[0036] (b1) TEM image of Co / Al2O3 at 450 ℃; (b2) HRTEM image of Co / Al2O3 at 450 ℃, with the inset showing a magnified view of the boxed area; (b3) Co particle size distribution of the Co / Al2O3 at 450 ℃ catalyst, with a statistically average particle size of approximately 8.5 nm; (c1) TEM image of Co / Al2O3 at 650 ℃ catalyst; (c2) HRTEM image of Co / Al2O3 at 650 ℃ catalyst, with the inset showing a magnified view of the boxed area; (c3) Co particle size distribution of the Co / Al2O3 at 650 ℃ catalyst, with a statistically average particle size of approximately 11.6 nm; (d1) High-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM) image of the Co / Al2O3 at 450 ℃ catalyst; (d2) Co / Al2O3 at 450 ℃ catalyst... Co elemental distribution of the catalyst at ℃; Al elemental distribution of the Co / Al2O3 catalyst at 450 ℃ (d3); O elemental distribution of the Co / Al2O3 catalyst at 450 ℃ (d4). The lattice fringe spacing observed in (a2), (b2) and (c2) is approximately 0.20 nm, which can be attributed to the (111) crystal plane of metallic Co. Detailed Implementation

[0037] To make the content of this invention easier to understand, the technical solution of this invention will be further described below with reference to specific embodiments, but this invention is not limited thereto.

[0038] Example 1: Preparation of Co / Al2O3 catalyst at -450 °C

[0039] 1. Weigh 7.3583 g Al(NO3)3·9H2O, add it to 50 mL of deionized water and stir until completely dissolved;

[0040] 2. Under room temperature and stirring conditions, add 1.2332 g Co(NO3)2·6H2O and 1.8768 g urea, and continue stirring to mix them evenly;

[0041] 3. Transfer the resulting mixed solution to a 100 mL hydrothermal reactor, seal it, and place it in a 120 ℃ rotary oven for hydrothermal treatment for 22 h;

[0042] 4. After hydrothermal treatment, the obtained solid was filtered, washed with deionized water, and dried at 60 °C for 12 h to obtain a dry precursor containing Co–Al;

[0043] 5. The dried precursor was heated to 450 °C at 5 °C / min and calcined for 5 h; then, in a H2 / N2 mixture with a H2 volume fraction of 5%, the temperature was increased to 450 °C at 2 °C / min and reduced for 5 h to obtain a Co / Al2O3-450 °C catalyst with a Co mass fraction of approximately 20 wt%.

[0044] Example 2 Preparation of Co / Al2O3 catalyst at -250 °C

[0045] 1. Weigh 6.1535 g Al(NO3)3·9H2O, add it to 50 mL of deionized water and stir until completely dissolved;

[0046] 2. Under room temperature and stirring conditions, add 0.4595 g Co(NO3)2·6H2O and 1.3564 g urea, and continue stirring to mix them evenly;

[0047] 3. Transfer the resulting mixed solution to a 100 mL hydrothermal reactor, seal it, and place it in a 100 °C rotary oven for hydrothermal treatment for 20 h;

[0048] 4. After the hydrothermal treatment, the obtained solid was filtered, washed with deionized water, and dried at 56 °C for 10 h.

[0049] 5. The obtained dry precursor was heated to 250 °C at 4 °C / min and calcined for 4 h; then it was reduced to 250 °C at 1 °C / min in a H2 / N2 mixture with a H2 volume fraction of 2% for 4 h to obtain a Co / Al2O3-250 °C catalyst with a Co mass fraction of approximately 10 wt%.

[0050] Example 3 Preparation of Co / Al2O3 catalyst at 650 °C

[0051] 1. Weigh 8.5160 g Al(NO3)3·9H2O, add it to 50 mL of deionized water and stir until completely dissolved;

[0052] 2. Under room temperature and stirring conditions, add 2.4522 g Co(NO3)2·6H2O and 1.97263 g urea, and continue stirring to mix them evenly;

[0053] 3. Transfer the resulting mixed solution to a 100 mL hydrothermal reactor, seal it, and place it in a 140 ℃ rotary oven for hydrothermal treatment for 24 h;

[0054] 4. After the hydrothermal treatment, the obtained solid was filtered, washed with deionized water, and dried at 64 °C for 14 h.

[0055] 5. The obtained dry precursor was heated to 650 °C at 6 °C / min and calcined for 6 h; then it was reduced to 650 °C at 3 °C / min in an H2 / N2 mixture with a H2 volume fraction of 8% for 6 h to obtain a Co / Al2O3-650 °C catalyst with a Co mass fraction of approximately 30 wt%.

[0056] The microstructure, particle size distribution, and elemental distribution of the Co / Al2O3 catalysts obtained in Examples 1-3 are as follows: Figure 1 As shown, lattice fringes of approximately 0.20 nm were observed locally, with a lattice spacing consistent with that of the relevant Co crystal planes; Co, Al, and O were relatively uniformly distributed within the observed region. The sample names Co / Al₂O₃-250 ℃, Co / Al₂O₃-450 ℃, and Co / Al₂O₃-650 ℃ are based on the primary heat treatment temperatures and do not indicate that the three samples differed only in terms of heat treatment temperature.

[0057] Example 4

[0058] Co / Al2O3 catalyst at -450 ℃ catalyzes the selective hydrogenation of phenol.

[0059] a) Add 0.10 g of the Co / Al2O3-450 ℃ catalyst obtained according to Example 1 and 10 mL of n-hexane solution containing 0.118 g of phenol and 0.213 g of n-dodecane internal standard to a high-temperature and high-pressure reactor;

[0060] b) Replace the air in the reactor with hydrogen three times, then fill the reactor with hydrogen until the initial pressure is 3 MPa, raise the temperature to 120°C, stir at 500 r / min, and react for 6 h.

[0061] c) After the reaction is complete, stop heating and stirring. After the reaction vessel has cooled to room temperature, release the pressure and open the vessel. Separate the liquid reaction products and catalyst. Use gas chromatography to perform qualitative and quantitative analysis on the liquid reaction products and calculate the phenol conversion rate and cyclohexanol yield.

[0062] The reaction results are shown in Table 1.

[0063] Table 1 Results of the selective hydrogenation of phenol catalyzed by Co / Al2O3 catalyst at -450 ℃

[0064]

[0065] Example 5

[0066] Co / Al2O3 catalyst at -250 ℃ catalyzes the selective hydrogenation of phenol.

[0067] a) Add 0.08 g of the Co / Al2O3-250 ℃ catalyst obtained according to Example 2 and 10 mL of n-hexane solution containing 0.118 g of phenol and 0.213 g of n-dodecane internal standard to a high-temperature and high-pressure reactor;

[0068] b) Replace the air in the reactor with hydrogen three times, then fill the reactor with hydrogen until the initial pressure is 2 MPa, raise the temperature to 110°C, stir at 450 r / min, and react for 4 h.

[0069] c) After the reaction is complete, stop heating and stirring. After the reaction vessel has cooled to room temperature, release the pressure and open the vessel. Separate the liquid reaction products and catalyst. Use gas chromatography to perform qualitative and quantitative analysis on the liquid reaction products and calculate the phenol conversion rate and cyclohexanol yield.

[0070] The reaction results are shown in Table 2.

[0071] Table 2 Results of the selective hydrogenation of phenol catalyzed by Co / Al2O3 catalyst at -250 ℃

[0072]

[0073] Example 6

[0074] Co / Al2O3 catalyst at 650 ℃ catalyzes the selective hydrogenation of phenol.

[0075] a) Add 0.12 g of the Co / Al2O3-650 ℃ catalyst obtained according to Example 3 and 10 mL of n-hexane solution containing 0.118 g of phenol and 0.213 g of n-dodecane internal standard to a high-temperature and high-pressure reactor;

[0076] b) Replace the air in the reactor with hydrogen three times, then fill the reactor with hydrogen until the initial pressure is 4 MPa, raise the temperature to 130°C, stir at 550 r / min, and react for 8 h.

[0077] c) After the reaction is complete, stop heating and stirring. After the reaction vessel has cooled to room temperature, release the pressure and open the vessel. Separate the liquid reaction products and catalyst. Use gas chromatography to perform qualitative and quantitative analysis on the liquid reaction products and calculate the phenol conversion rate and cyclohexanol yield.

[0078] The reaction results are shown in Table 3.

[0079] Table 3 Results of the selective hydrogenation of phenol catalyzed by Co / Al2O3 catalyst at -650 ℃

[0080]

[0081] Example 7

[0082] Co / Al₂O₃ catalyst at 450 °C catalyzes the selective hydrogenation of 2-methylphenol.

[0083] a) Add 0.10 g of the Co / Al2O3-450 ℃ catalyst obtained according to Example 1 and 10 mL of n-hexane solution containing 0.1352 g of 2-methylphenol and 0.213 g of n-dodecane internal standard to a high-temperature and high-pressure reactor;

[0084] b) Replace the air in the reactor with hydrogen three times, then fill the reactor with hydrogen until the initial pressure is 3 MPa, raise the temperature to 120°C, stir at 500 r / min, and react for 6 h.

[0085] c) After the reaction is complete, stop heating and stirring. After the reaction vessel has cooled to room temperature, release the pressure and open the vessel. Separate the liquid reaction products and catalyst. Use gas chromatography to perform qualitative and quantitative analysis on the liquid reaction products and calculate the conversion rate of 2-methylphenol and the yield of 2-methylcyclohexanol.

[0086] The reaction results are shown in Table 4.

[0087] Table 4 Results of the selective hydrogenation of 2-methylphenol catalyzed by Co / Al2O3 catalyst at -450 ℃

[0088]

[0089] Example 8

[0090] Co / Al₂O₃ catalyst at 250 °C catalyzes the selective hydrogenation of 3-methylphenol.

[0091] a) Add 0.08 g of the Co / Al2O3-250 °C catalyst obtained according to Example 2 and 10 mL of n-hexane solution containing 0.1352 g of 3-methylphenol and 0.213 g of n-dodecane internal standard to a high-temperature and high-pressure reactor;

[0092] b) Replace the air in the reactor with hydrogen three times, then fill the reactor with hydrogen until the initial pressure is 2 MPa, raise the temperature to 110°C, stir at 450 r / min, and react for 4 h.

[0093] c) After the reaction is complete, stop heating and stirring. After the reaction vessel has cooled to room temperature, release the pressure and open the vessel. Separate the liquid reaction products and catalyst. Use gas chromatography to perform qualitative and quantitative analysis on the liquid reaction products and calculate the conversion rate of 3-methylphenol and the yield of 3-methylcyclohexanol.

[0094] The reaction results are shown in Table 5.

[0095] Table 5 Results of the selective hydrogenation of 3-methylphenol catalyzed by Co / Al2O3 catalyst at -250 ℃

[0096]

[0097] Example 9

[0098] Co / Al₂O₃ catalyst at 650 °C catalyzes the selective hydrogenation of 4-methylphenol.

[0099] a) Add 0.12 g of the Co / Al2O3-650 ℃ catalyst obtained according to Example 3 and 10 mL of n-hexane solution containing 0.1352 g of 4-methylphenol and 0.213 g of n-dodecane internal standard to a high-temperature and high-pressure reactor;

[0100] b) Replace the air in the reactor with hydrogen three times, then fill the reactor with hydrogen until the initial pressure is 4 MPa, raise the temperature to 130°C, stir at 550 r / min, and react for 8 h.

[0101] c) After the reaction is complete, stop heating and stirring. After the reaction vessel has cooled to room temperature, release the pressure and open the vessel. Separate the liquid reaction products and catalyst. Use gas chromatography to perform qualitative and quantitative analysis on the liquid reaction products and calculate the conversion rate of 4-methylphenol and the yield of 4-methylcyclohexanol.

[0102] The reaction results are shown in Table 6.

[0103] Table 6 Results of the selective hydrogenation of 4-methylphenol catalyzed by Co / Al2O3 catalyst at -650 ℃

[0104]

[0105] Example 10

[0106] Co / Al₂O₃ catalyst at -450 °C catalyzes the selective hydrogenation of 2-ethylphenol.

[0107] a) Add 0.10 g of the Co / Al2O3-450 ℃ catalyst obtained according to Example 1 and 10 mL of n-hexane solution containing 0.1527 g of 2-ethylphenol and 0.213 g of n-dodecane internal standard to a high-temperature and high-pressure reactor;

[0108] b) Replace the air in the reactor with hydrogen three times, then fill the reactor with hydrogen until the initial pressure is 3 MPa, raise the temperature to 120°C, stir at 500 r / min, and react for 6 h.

[0109] c) After the reaction is complete, stop heating and stirring. After the reaction vessel has cooled to room temperature, release the pressure and open the vessel. Separate the liquid reaction products and catalyst. Use gas chromatography to perform qualitative and quantitative analysis on the liquid reaction products and calculate the conversion rate of 2-ethylphenol and the yield of 2-ethylcyclohexanol.

[0110] The reaction results are shown in Table 7.

[0111] Table 7 Results of the selective hydrogenation of 2-ethylphenol catalyzed by Co / Al2O3 catalyst at -450 ℃

[0112]

[0113] Example 11

[0114] Co / Al₂O₃ catalyst at 250 °C catalyzes the selective hydrogenation of 3-ethylphenol.

[0115] a) Add 0.08 g of the Co / Al2O3-250 °C catalyst obtained according to Example 2 and 10 mL of n-hexane solution containing 0.1527 g of 3-ethylphenol and 0.213 g of n-dodecane internal standard to a high-temperature and high-pressure reactor;

[0116] b) Replace the air in the reactor with hydrogen three times, then fill the reactor with hydrogen until the initial pressure is 2 MPa, raise the temperature to 110°C, stir at a rate of 450 r / min, and react for 4 h.

[0117] c) After the reaction is complete, stop heating and stirring. After the reaction vessel has cooled to room temperature, release the pressure and open the vessel. Separate the liquid reaction products and catalyst. Use gas chromatography to perform qualitative and quantitative analysis on the liquid reaction products and calculate the conversion rate of 3-ethylphenol and the yield of 3-ethylcyclohexanol.

[0118] The reaction results are shown in Table 8.

[0119] Table 8 Results of the selective hydrogenation of 3-ethylphenol catalyzed by Co / Al2O3 catalyst at -250 ℃

[0120]

[0121] Example 12

[0122] Co / Al₂O₃ catalyst at 650 °C catalyzes the selective hydrogenation of 4-ethylphenol.

[0123] a) Add 0.12 g of the Co / Al2O3-650 ℃ catalyst obtained according to Example 3 and 10 mL of n-hexane solution containing 0.1527 g of 4-ethylphenol and 0.213 g of n-dodecane internal standard to a high-temperature and high-pressure reactor;

[0124] b) Replace the air in the reactor with hydrogen three times, then fill the reactor with hydrogen until the initial pressure is 4 MPa, raise the temperature to 130°C, stir at 550 r / min, and react for 8 h.

[0125] c) After the reaction is complete, stop heating and stirring. After the reaction vessel has cooled to room temperature, release the pressure and open the vessel. Separate the liquid reaction products and catalyst. Use gas chromatography to perform qualitative and quantitative analysis on the liquid reaction products and calculate the conversion rate of 4-ethylphenol and the yield of 4-ethylcyclohexanol.

[0126] The reaction results are shown in Table 9.

[0127] Table 9 Results of the selective hydrogenation of 4-ethylphenol catalyzed by Co / Al2O3 catalyst at -650 ℃

[0128]

[0129] The results of Examples 7-12 show that, under the catalysts and reaction conditions described in each example, the conversion rates of the six alkyl-substituted phenols were 89.1%-99.0%, and the corresponding yields of alkyl-substituted cyclohexanols were 79.5%-94.7%, indicating that the Co / Al₂O₃ catalyst can be used for the selective hydrogenation of methylphenol and ethylphenol with different substitution positions. Since the catalyst samples and reaction conditions used in Examples 7-12 were not entirely the same, the above results are used to illustrate the suitability of the catalyst for different aromatic phenol substrates and are not intended to directly compare the intrinsic activity of different catalysts or the ease of reaction of different substrates.

[0130] Example 13

[0131] Cyclic stability test of Co / Al2O3 catalyst for selective hydrogenation of phenol at 450 ℃

[0132] The catalyst from Example 4 was filtered and separated, washed three times with ethanol, and dried under vacuum at 60 °C for 6 h to obtain the recovered catalyst. The recovered catalyst was then used for the selective hydrogenation of phenol under the same conditions as in Example 4. The recovery and reaction were repeated a total of 10 times, and the results are shown in Table 10.

[0133] Table 10 Cyclic stability test results of Co / Al2O3 catalyst at -450 ℃ for selective hydrogenation of phenol

[0134]

[0135] As shown in Table 10, under the conditions of the cyclic stability test, the phenol conversion rate of the catalyst was still 99.9% after 10 cycles, and the cyclohexanol yield decreased from 99.8% in the first run of the cycle test to 94.5%, a decrease of 5.3 percentage points, indicating that the catalyst has good cyclic stability.

[0136] In summary, this invention introduces a Co precursor in situ during the formation of the aluminum-containing precursor, allowing for sufficient contact between the Co species and the aluminum-containing species during the hydrothermal treatment stage. This is beneficial for improving the distribution of Co species on the Al2O3 support and its contact state with the support. The resulting Co / Al2O3 catalyst can be used for the selective hydrogenation of the aromatic rings of phenol and alkyl-substituted phenols. Specifically, phenol undergoes selective hydrogenation of its aromatic ring to produce cyclohexanol, while methylphenol and ethylphenol undergo selective hydrogenation of their aromatic rings to produce the corresponding methylcyclohexanol and ethylcyclohexanol. The above reactions retain the CO bond corresponding to the phenolic hydroxyl group and the alkyl substituents on the aromatic ring, without involving methoxy group removal or hydrogenation deoxygenation. Examples 4-6 demonstrate that, under different catalyst compositions, preparation conditions, and reaction conditions specified in this invention, the obtained Co / Al2O3 catalyst can be used for the selective hydrogenation of phenol to produce cyclohexanol. Example 4 is a preferred embodiment of the present invention. The Co / Al₂O₃-450 °C catalyst, under conditions of 120 °C, initial hydrogen pressure of 3 MPa, reaction time of 6 h, and stirring rate of 500 r / min, achieved a phenol conversion rate of 99.9% and a cyclohexanol yield of 99.8%. Examples 7-12 further demonstrate that, under the catalyst and reaction conditions described in each example, the Co / Al₂O₃ catalyst can be used for the selective hydrogenation of the aromatic rings of methylphenol and ethylphenol with different substitution positions, indicating its good substrate applicability to alkyl-substituted aromatic phenols without methoxy groups. Since the catalyst samples and reaction conditions used in Examples 7-12 are not entirely the same, the above results are used to illustrate the applicability of the catalyst to different aromatic phenol substrates and are not used to directly compare the intrinsic activity of different catalysts or the ease of reaction of different aromatic phenol substrates. The cyclic stability test in Example 13 showed that after 10 cycles, the Co / Al2O3 catalyst at -450℃ still achieved a phenol conversion of 99.9% and a cyclohexanol yield of 94.5%, indicating that the catalyst has good cyclic stability. The key technical point of this invention is to improve the contact state between Co species and the Al2O3 support through hydrothermal in-situ construction, and to use the resulting Co / Al2O3 catalyst for the selective hydrogenation of aromatic rings without methoxy aromatic phenol substrates.

[0137] The technical solutions disclosed and proposed in this invention can be implemented by those skilled in the art by appropriately modifying the conditions and routes, etc. Although the methods and preparation techniques of this invention have been described through preferred embodiments, those skilled in the art can obviously modify or recombine the methods and technical routes described herein without departing from the content, spirit, and scope of this invention to achieve the final preparation technique. It should be particularly noted that all similar substitutions and modifications are obvious to those skilled in the art and are considered to be included within the spirit, scope, and content of this invention.

Claims

1. A hydrothermally in-situ constructed Co / Al2O3 single-metal catalyst, characterized in that, Co is the only added transition metal component, and Al2O3 is the support; the mass fraction of Co in the catalyst is 10-30 wt% of the total mass of the catalyst.

2. The method for preparing the hydrothermally in-situ constructed Co / Al2O3 monometallic catalyst according to claim 1, characterized in that, Includes the following steps: 1) Dissolve aluminum nitrate nonahydrate in deionized water at a concentration of 0.32–0.46 mol / L and stir until completely dissolved to obtain an aluminum-containing precursor solution; 2) Under room temperature and stirring conditions, add cobalt nitrate hexahydrate and urea to the aluminum-containing precursor solution in step 1), and continue stirring until the mixture is homogeneous to obtain a mixed solution; the molar ratio of cobalt nitrate hexahydrate to aluminum nitrate nonahydrate is 0.09 to 0.38:1, and the molar ratio of urea to aluminum nitrate nonahydrate is 1.37 to 1.60:1; 3) Transfer the mixed solution from step 2) to a hydrothermal reactor and perform hydrothermal treatment at 100~140 ℃ for 20~24 h to obtain a hydrothermal precursor containing Co-Al; 4) Filter the hydrothermal precursor from step 3) and wash it with deionized water, then dry it at 56-64 °C for 10-14 h to obtain the dried precursor; 5) The dried precursor from step 4) is calcined and then reduced in a hydrogen-containing atmosphere to obtain a Co / Al2O3 single metal catalyst with a Co mass fraction of 10-30 wt%.

3. The method for preparing the hydrothermally in-situ constructed Co / Al2O3 monometallic catalyst as described in claim 2, characterized in that, In step 5), the calcination temperature is 250~650 ℃, the calcination time is 4~6 h, and the heating rate is 4~6 ℃ / min.

4. The method for preparing the hydrothermally in-situ constructed Co / Al2O3 monometallic catalyst as described in claim 2, characterized in that, In step 5), the reducing atmosphere is a 2-8% H2 / N2 mixed gas, the reduction temperature is 250-650 ℃, the reduction time is 4-6 h, and the heating rate is 1-3 ℃ / min.

5. The application of the Co / Al2O3 single-metal catalyst of claim 1 in the hydrogenation of aromatic phenols to prepare cyclohexanol, comprising the following steps: a) Add the catalyst, aromatic phenol substrate and reaction solvent to a high-pressure reactor and mix thoroughly. After sealing, replace the gas in the reactor with hydrogen and fill with hydrogen until the initial pressure is 2-4 MPa. b) Heat the reactor to 110–130 °C and react for 4–8 h with stirring at 450–550 r / min. After the reaction is complete, stop heating and stirring, and after the reactor cools to room temperature, release the pressure and open the reactor to separate the liquid reaction products and catalyst.

6. The application as described in claim 5, characterized in that, The aromatic phenol substrate is an aromatic phenol that does not contain methoxy groups.

7. The application as described in claim 5, characterized in that, The aromatic phenolic substrate is one of phenol, 2-methylphenol, 3-methylphenol, 4-methylphenol, 2-ethylphenol, 3-ethylphenol, and 4-ethylphenol.

8. The application as described in claim 5, characterized in that, The reaction solvent was n-hexane, and n-dodecane was used as an internal standard for quantitative gas chromatography.

9. The application as described in claim 5, characterized in that, The mass ratio of catalyst to aromatic phenol substrate is 1: (0.9~2.0).

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