Boehmite catalysts enriched in flps for selective transfer hydrogenation of enals, mild preparation method and use thereof

Abstract

Boehmite catalyst rich in FLPs for olefinic aldehyde selective transfer hydrogenation, mild preparation method and application thereof belong to the field of nano-catalysis and are an AlOOH catalyst with FLPs.Step 1, ammonia solution is added into an aqueous solution of aluminum nitrate to obtain a mixed solution; step 2, urea and cetyltrimethylammonium bromide are added into the mixed solution, and the solution is stirred until a sol is formed; the sol is subjected to hydrothermal reaction at 80-120 DEG C to obtain a white powder; step 3, the white powder is calcined in air at 550-850 DEG C to obtain an aluminum oxide solid; step 4, the aluminum oxide solid is stirred in cyclohexane, deionized water is added dropwise, and the liquid is evaporated after being heated to obtain a boehmite catalyst. The catalyst is applied to realize selective hydrogenation of alpha, beta-unsaturated to generate unsaturated alcohol. The catalyst has the advantages of high catalytic activity, conversion rate > 95%, selectivity > 90%, simple preparation process, mild conditions and high stability.

Description

Technical Field

[0001] This invention belongs to the field of nanocatalysis and relates to a boehmite catalyst rich in FLPs for selective transfer hydrogenation of enaldehydes, a mild preparation method and its application. Specifically, it relates to a boehmite (AlOOH) catalyst rich in hindered Lewis acid-base pairs (FLPs) and its preparation method, which is applied to the efficient transfer hydrogenation of enaldehydes such as methacrolein to produce enols. Background Technology

[0002] Unsaturated alcohols are an important class of fine chemical intermediates, widely used in pharmaceuticals, pesticides, fragrances, coatings, surfactants, and food additives. Among them, methyl allyl alcohol can react with ethylene oxide to produce methyl allyl polyoxyethylene ether (HPEG), a core monomer in the modern concrete admixture industry, which has a crucial impact on the quality, construction efficiency, and engineering safety of high-performance concrete.

[0003] Selective hydrogenation can be further divided into direct hydrogenation using hydrogen gas as the hydrogen source and transfer hydrogenation using isopropanol, cyclohexanol, etc., as hydrogen sources. Compared to the significant safety risks associated with directly using molecular hydrogen, using liquid hydrogen donors such as alcohols has greater potential for industrial applications. While traditional homogeneous catalytic systems possess high activity, they generally suffer from difficulties in catalyst separation, poor stability, and high metal recovery costs, limiting their large-scale application. Therefore, developing recyclable heterogeneous catalytic systems has become an important research direction in this field.

[0004] In recent years, Cui et al. (Highly selective transfer hydrogenation of α, β-unsaturated aldehydes by frustrated Lewis pairs (FLPs) on oxygen-defect-rich Co3O4@NC. J. Catal, 2023, 428, 115126) prepared a Co3O4@NC catalyst. They constructed solid-state FLPs by coordinating unsaturated Co and N sites on the material surface for the selective hydrogenation of cinnamaldehyde, relying on the synergistic effect of FLPs to precisely activate the hydrogen donor and carbonyl group. However, for chain-like small molecule substrates such as methacrolein, due to their small steric hindrance and significant competitive activation of C=C and C=O bonds, non-selective hydrogenation is more likely to occur during catalysis, making the selective control of the target unsaturated alcohol still challenging. Therefore, it is necessary to further construct solid-state FLP active centers with high density distribution and synergistic enhancement effects to improve the preferential directional activation ability of C=O bonds, thereby achieving highly selective hydrogenation control of chain-like unsaturated aldehyde systems. Liu et al. (Solid surface frustrated Lewis pair constructed onlayered AlOOH for hydrogenation reaction. Nat. Commun., 2022, 13, 2320) constructed FLPs on the surface of AlOOH (boehmite), which interacted with adjacent unsaturated Al through surface hydroxyl vacancies. 3+ Site synergy forms Lewis acid-base pairs, enabling efficient hydrogenation of alkenes and alkynes. However, the high-temperature calcination required for preparation leads to significant loss of surface hydroxyl groups and low FLP content. Based on this, this patent synthesizes a boehmite catalytic material rich in FLPs through mild modification of the amorphous alumina surface, significantly improving the selective hydrogenation of C=O and achieving highly selective hydrogenation of unsaturated aldehydes such as methacrolein to prepare unsaturated alcohols. Summary of the Invention

[0005] To address the problems existing in the prior art, this invention provides a boehmite catalyst rich in FLPs for the selective transfer hydrogenation of enaldehydes, a mild preparation method, and its application. Specifically, it is a metal-free AlOOH catalyst with FLPs, its preparation method, and its application, used to achieve the selective hydrogenation of α,β-unsaturated aldehydes (methacrylaldehyde, cinnamaldehyde, furfural, and isopentenal) to unsaturated alcohols. This catalyst features high catalytic activity, high stability, and low cost.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows: A method for preparing an FLP-rich boehmite catalyst for selective transfer hydrogenation of enaldehydes includes the following steps: Step 1: At room temperature, aluminum nitrate Al(NO3)3·9H2O is placed in a flask, and deionized water is added and stirred to dissolve it to obtain an aqueous solution of aluminum nitrate. Concentrated ammonia water is diluted with deionized water to obtain an aqueous solution of ammonia, which is then added to the aqueous solution of aluminum nitrate. A large amount of white precipitate will be generated in the flask immediately after addition. The precipitate will disappear after stirring continuously until it becomes clear and transparent, resulting in a mixed solution.

[0007] Furthermore, in the aluminum nitrate aqueous solution, 10 to 20 g of aluminum nitrate is added for every 20 mL of deionized water.

[0008] Furthermore, in the ammonia solution, the sum of the volumes of deionized water and concentrated ammonia is equal to the volume of deionized water in the aluminum nitrate solution, and for every 20 mL of deionized water in the aluminum nitrate solution, there are 1 to 6 mL of concentrated ammonia with a mass concentration of 25%.

[0009] Step 2: At room temperature, slowly add urea and hexadecyltrimethylammonium bromide (CTAB) to the mixed solution obtained in Step 1. Continue stirring for 2-12 hours until a uniform and transparent sol is formed. Transfer the sol to a hydrothermal reactor with a polytetrafluoroethylene liner and place it in an oven at 80-120 °C for hydrothermal reaction for 12-48 hours. After the hydrothermal reactor cools down, wash it 2-5 times with deionized water to recover the white precipitate. Dry the precipitate in an oven at 80-120 °C overnight and grind it to obtain a white powder.

[0010] Furthermore, 5-10 g of urea and 2-5 g of hexadecyltrimethylammonium bromide are added to every 40 mL of the mixed solution.

[0011] Step 3: Place the white powder obtained in step 2 into a tube furnace and calcine it in air at 550~850 ℃ for 2~4 hours. The heating rate is 2~6 ℃ / min, and the gas flow rate is 20~100 mL / min. Finally, solid alumina is obtained.

[0012] Step 4: Add 20-50 mL of cyclohexane to Al2O3 in a flask and stir at room temperature for 2-5 hours. Then, add deionized water dropwise to the flask containing Al2O3, and then heat to 80-100 °C to evaporate the liquid in the flask to dryness. After evaporation, place the flask in an oven at 80-120 °C to dry overnight. After drying, transfer the solid to a mortar and grind it into a powder without obvious lumps to obtain the boehmite catalyst. In this step, the formation of Al2O3 + H2O → 2AlOOH at low temperature and normal pressure is not easy; cyclohexane plays a crucial role. The two-phase system of "hydrophobic reagent cyclohexane - hydrophilic reagent water" provides a locally water-rich environment for Al2O3 under vigorous stirring and evaporation conditions, creating conditions for the formation of boehmite crystal nuclei.

[0013] Furthermore, for every 0.2 to 1.0 g of Al2O3, add 20 to 50 mL of cyclohexane and 3 to 10 mL of deionized water.

[0014] A boehmite catalyst rich in FLPs for selective transfer hydrogenation of enaldehydes was prepared using the method described above. The catalyst was obtained by converting amorphous alumina into boehmite using a hydrophobic reagent and water at low temperature and ambient pressure, followed by the construction of hindered Lewis acid-base pairs on the boehmite. Specifically, it is an AlOOH catalyst with FLPs. The AlOOH catalyst is generally rod-shaped with a specific surface area of ​​100–160 m². 2 / g, pore volume 0.10~1.20 cm³ 3 / g, with an average pore size of 2~10 nm.

[0015] The application of FLP-rich boehmite catalysts for the selective transfer hydrogenation of enaldehydes is specifically for the efficient transfer hydrogenation of methacrolein to methacrolein alcohol. This involves the selective hydrogenation of α,β-unsaturated alcohols to unsaturated alcohols. Using a high-pressure reactor as the reaction vessel, boehmite catalyst (AlOOH catalyst), reaction substrate, and solvent were added sequentially into the reactor. After sealing the reactor, the air in the reactor was replaced with high-purity nitrogen. Then, nitrogen was introduced into the reactor to 1-2 MPa, and the reaction was carried out at 160-180℃ for 1.5-2.5 h. After the reaction, the substrate conversion rate reached over 95%, approaching 100%, and the selectivity of the target product reached over 90%, with a maximum of 94.3%.

[0016] Furthermore, 0.1 to 0.2 mL of reaction substrate and 0.075 to 0.175 g of AlOOH catalyst are added to every 5 to 25 mL of solvent.

[0017] Furthermore, the reaction substrate is selected from methacrolein, cinnamaldehyde, furfural, and isopentenal; the solvent is selected from isopropanol.

[0018] The beneficial effects of this invention are as follows: (1) The AlOOH catalyst prepared under mild conditions in this invention can avoid the defects such as the significant loss of hydroxyl groups caused by high-temperature calcination of alumina and the inability of isolated acid-base sites to form FLP sites, resulting in higher FLP site density, stronger accessibility, and significantly improved transfer hydrogenation activity.

[0019] (2) In the AlOOH catalyst of the present invention, the acid sites on the FLPs adsorb electron-rich oxygen atoms from the C=O bond, and the basic sites adsorb electron-deficient hydrogen atoms from the -OH group of isopropanol; simultaneously, the electron-deficient carbon atoms from the C=O bond adsorb electron-rich hydrogen atoms from the α-CH group of isopropanol, forming a six-membered ring transition state. Thus, hydrogen atoms from the -OH group and the α-CH group of isopropanol are transferred to the C=O bond, completing the hydrogenation reaction. In the efficient hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols, the catalyst exhibits high catalytic activity, with a conversion rate >95% and a selectivity >90%.

[0020] (3) The AlOOH of the present invention serves as a catalyst for the efficient transfer hydrogenation of α,β-unsaturated aldehydes to unsaturated alcohols. The preparation process is simple, the conditions are mild, and the raw materials used are inexpensive and readily available, which is beneficial for large-scale industrial production. The synthesized catalyst has high stability and can be stored in the environment for a long time. Attached Figure Description

[0021] Figure 1 XRD patterns of alumina prepared for the examples, as well as modified alumina treated with cyclohexane and water.

[0022] Figure 2 To conduct cycle stability tests on the catalyst prepared in Case 1.

[0023] Figure 3 This is a SEM image of the catalyst Al2O3 prepared in Example 1.

[0024] Figure 4 This is a SEM image of AlOOH prepared in Example 1. Detailed Implementation

[0025] The present invention will be further described in detail below with reference to specific implementation examples. Of course, the present invention is not limited to the specific implementation examples described below.

[0026] Example 1 Weigh 15 g of Al(NO3)3·9H2O into a flask, add 20 mL of deionized water and stir to dissolve. Measure 3 mL of 25% concentrated ammonia solution and dilute it to 20 mL with deionized water, then add it to the flask containing dissolved aluminum nitrate and stir. Subsequently, add 7.2 g of urea and 3.64 g of hexadecyltrimethylammonium bromide to the above solution. After stirring for 5 h, transfer the solution to a hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally heat it at 100 °C for 48 hours. Then wash it three times with deionized water, place the white precipitate in an oven and dry it overnight at 100 °C. After grinding, calcine it in a tube furnace at 550 °C for 4 hours in air atmosphere to obtain solid alumina.

[0027] Weigh 0.5 g of Al₂O₃ into a flask, add 30 mL of cyclohexane, and stir at room temperature for 3 hours. Measure 5 mL of deionized water and add it dropwise to the flask containing Al₂O₃. Heat to 90°C and evaporate the liquid in the flask to dryness. After evaporation, place the flask in an oven at 100°C and dry overnight. After drying, transfer the solid to a mortar and grind it until it becomes a powder without obvious lumps. Collect the white solid powder to complete the preparation, obtaining the AlOOH catalyst.

[0028] The catalyst used in this embodiment was as follows: 125 mg of the prepared AlOOH was added to the reactor, and 0.15 mL of methacrolein and 20 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After replacement, nitrogen gas at a pressure of 2 MPa was introduced, and the reaction was carried out at 180 °C for 2.5 h. GC analysis showed that the conversion rate of methacrolein was 100%, and the selectivity of methacrolein alcohol was 93.6%.

[0029] Figure 1 The XRD pattern shows that ordinary alumina is amorphous. The modified alumina treated with cyclohexane and water has sharp diffraction peaks at 14°, 28°, 38°, 49°, 55°, 64°, and 72°. After consulting the literature and the PDF card, we found that these are characteristic peaks of AlOOH. Figure 2 For the cyclic stability test of the catalyst, after 6 cycles, the conversion rate remained at 100% and the selectivity hardly decreased, indicating that the catalyst has good stability. Figure 3 and 4 The images show SEM images of catalysts Al2O3 and AlOOH, respectively. Amorphous alumina has a slender rod-like structure. After treatment with cyclohexane and water, it still has a rod-like structure, but the diameter increases and the length decreases. In addition, fine hairs grow around it. These hairs may be due to the change in the structure of Al2O3 caused by the evaporation of water that has penetrated into the interior of Al2O3.

[0030] Comparative Example 1 Considering that Al2O3 is hydrophilic, and the reagents used for treatment, cyclohexane and water, are respectively hydrophobic and hydrophilic, Comparative Example 1 replaces the hydrophilic reagent water in step 4 with methanol, and the rest of the preparation method is basically the same as in Example 1.

[0031] The catalyst used in this embodiment was as follows: 125 mg of prepared AlOOH was added to the reactor, and 0.15 mL of methacrolein and 20 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After replacement, nitrogen gas at a pressure of 2 MPa was introduced, and the reaction was carried out at 180 °C for 2.5 h. GC analysis showed that the conversion rate of methacrolein was 45%, and the selectivity of methacrolein alcohol was 52.2%.

[0032] The above experiments once again demonstrate that water is the key to improving the catalytic performance of Al2O3. Water acts as a reactant, reacting with alumina to form boehmite.

[0033] Comparative Example 2 Replace the hydrophobic reagent cyclohexane in step 4 with n-hexane, and the rest of the preparation method is basically the same as in Example 1.

[0034] The catalyst used in this embodiment was as follows: 125 mg of the prepared AlOOH was added to the reactor, and 0.15 mL of methacrolein and 20 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After replacement, nitrogen gas at a pressure of 2 MPa was introduced, and the reaction was carried out at 180 °C for 2.5 h. GC analysis showed that the conversion rate of methacrolein was 89.9%, and the selectivity of methacrolein alcohol was 76.4%.

[0035] Comparative Example 3 Replace the hydrophobic reagent cyclohexane in step 4 with n-heptane, and the rest of the preparation method is basically the same as in Example 1.

[0036] The catalyst used in this embodiment was as follows: 125 mg of prepared AlOOH was added to the reactor, and 0.15 mL of methacrolein and 20 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After replacement, nitrogen gas at a pressure of 2 MPa was introduced, and the reaction was carried out at 180 °C for 2.5 h. GC analysis showed that the conversion rate of methacrolein was 89.6%, and the selectivity of methacrolein alcohol was 80%.

[0037] Analysis of Comparative Examples 2 and 3 revealed that cyclohexane acts as an auxiliary reagent, amplifying the effect of water. The addition of cyclohexane forms a two-phase system of cyclohexane and water, creating localized water enrichment. Because cyclohexane and water are immiscible, two phases form within the flask. During vigorous stirring, the aqueous phase is dispersed into numerous tiny droplets. Amorphous alumina solids (especially nanoscale particles), due to their hydrophilic surface, preferentially accumulate at the oil-water interface or directly enter the aqueous droplets. Upon evaporation, cyclohexane evaporates first, and the alumina particles undergo a stage of being enveloped by a concentrated small amount of aqueous phase, effectively providing a localized water environment with a higher concentration than a simple water bath, creating a high supersaturation for boehmite nucleation. Secondly, the surface tension effect promotes contact between water and alumina. The surface tension of cyclohexane is much lower than that of water. The mixed system helps water more easily wet and penetrate the microporous structure of alumina. Stirring generates stronger shear forces and microturbulence, continuously renewing the water film on the alumina surface. After cyclohexane volatilizes, the remaining thin water film is "locked" around the particles, effectively subjecting each particle to localized hydrothermal treatment. In summary, the effect of cyclohexane is primarily kinetic: by improving mass transfer, creating localized water-rich zones, and reducing surface diffusion resistance, it significantly lowers the temperature and time thresholds required for the reaction.

[0038] Example 2 Weigh 10 g of Al(NO3)3·9H2O into a flask, add 20 mL of deionized water and stir to dissolve. Measure 6 mL of 25% concentrated ammonia solution, dilute to 20 mL with deionized water, and add to the flask containing dissolved aluminum nitrate, stirring. Then, add 10 g of urea and 2 g of hexadecyltrimethylammonium bromide to the above solution. Continue stirring for 12 h, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally heat at 120 °C for 36 hours. Next, wash five times with deionized water, place the white precipitate in an oven and dry overnight at 120 °C, grind, and then calcine in a tube furnace at 850 °C for 4 hours in air atmosphere to obtain solid alumina.

[0039] Weigh 0.5 g of Al₂O₃ into a flask, add 50 mL of cyclohexane, and stir at room temperature for 5 hours. Measure 10 mL of deionized water and add it dropwise to the flask containing Al₂O₃. Heat to 100℃ and evaporate the liquid in the flask to dryness. After evaporation, place the flask in an oven at 120℃ and dry overnight. After drying, transfer the solid to a mortar and grind it until it becomes a powder without obvious lumps. Collect the white solid powder to complete the preparation, obtaining the AlOOH catalyst.

[0040] The catalyst used in this embodiment was as follows: 75 mg of the prepared AlOOH was added to the reactor, and 0.2 mL of methacrolein and 25 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After replacement, nitrogen gas at a pressure of 2 MPa was introduced, and the reaction was carried out at 160 °C for 2.5 h. GC analysis showed that the conversion rate of methacrolein was 95.8%, and the selectivity of methacrolein alcohol was 94.3%.

[0041] Example 3 Weigh 20 g of Al(NO3)3·9H2O into a flask, add 20 mL of deionized water and stir to dissolve. Measure 1 mL of 25% concentrated ammonia solution and dilute it to 20 mL with deionized water, then add it to the flask containing dissolved aluminum nitrate and stir. Subsequently, add 5 g of urea and 5 g of hexadecyltrimethylammonium bromide to the above solution. Continue stirring for 12 h, then transfer to a hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally heat at 80°C for 12 hours. Next, wash twice with deionized water, place the white precipitate in an oven and dry overnight at 80°C, grind it, and then calcine it in a tube furnace at 650°C for 4 hours in air atmosphere to obtain solid alumina.

[0042] Weigh 0.5 g of Al₂O₃ into a flask, add 20 mL of cyclohexane, and stir at room temperature for 2 hours. Measure 10 mL of deionized water and add it dropwise to the flask containing Al₂O₃. Heat to 80°C and evaporate the liquid in the flask to dryness. After evaporation, place the flask in an oven at 80°C and dry overnight. After drying, transfer the solid to a mortar and grind it until it becomes a powder without obvious lumps. Collect the white solid powder to complete the preparation, obtaining the AlOOH catalyst.

[0043] The catalyst used in this embodiment was as follows: 175 mg of the prepared AlOOH was added to the reactor, and 0.25 mL of methacrolein and 5 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After replacement, nitrogen gas at a pressure of 1 MPa was introduced, and the reaction was carried out at 170 °C for 2.0 h. GC analysis showed that the conversion rate of methacrolein was 98.3%, and the selectivity of methacrolein alcohol was 94.1%.

[0044] Example 4 Weigh 20 g of Al(NO3)3·9H2O into a flask, add 20 mL of deionized water and stir to dissolve. Measure 5 mL of 25% concentrated ammonia solution and dilute it to 20 mL with deionized water, then add it to the flask containing dissolved aluminum nitrate and stir. Subsequently, add 7 g of urea and 4 g of hexadecyltrimethylammonium bromide to the above solution. After stirring for 5 h, transfer the solution to a hydrothermal reactor with a polytetrafluoroethylene liner and hydrothermally heat at 100 °C for 24 hours. Then wash four times with deionized water, place the white precipitate in an oven and dry at 90 °C overnight, grind it, and calcine it in a tube furnace at 600 °C for 4 hours in air atmosphere to obtain solid alumina.

[0045] Weigh 0.5 g of Al₂O₃ into a flask, add 40 mL of cyclohexane, and stir at room temperature for 2 hours. Measure 6 mL of deionized water and add it dropwise to the flask containing Al₂O₃. Heat to 80°C and evaporate the liquid in the flask to dryness. After evaporation, place the flask in an oven at 90°C and dry overnight. After drying, transfer the solid to a mortar and grind it until it becomes a powder without obvious lumps. Collect the white solid powder to complete the preparation, obtaining the AlOOH catalyst.

[0046] The catalyst used in this embodiment was as follows: 125 mg of prepared AlOOH was added to the reactor, and 0.15 mL of methacrolein and 20 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After replacement, nitrogen gas at a pressure of 1 MPa was introduced, and the reaction was carried out at 180 °C for 2.5 h. GC analysis showed that the conversion rate of methacrolein was 97.8%, and the selectivity of methacrolein alcohol was 93.4%.

[0047] Example 5 The preparation method is the same as in Example 1.

[0048] The catalyst used in this embodiment was as follows: 125 mg of prepared AlOOH was added to the reactor, and 0.15 mL of cinnamaldehyde and 20 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After replacement, nitrogen gas at a pressure of 2 MPa was introduced, and the reaction was carried out at 180 °C for 2.5 h. GC analysis showed that the conversion rate of cinnamaldehyde was 99.3%, and the selectivity of cinnamyl alcohol was 96.7%.

[0049] Example 6 The preparation method is the same as in Example 1.

[0050] The catalyst used in this embodiment was as follows: 125 mg of prepared AlOOH was added to the reactor, and 0.15 mL of furfural and 20 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After the replacement was completed, nitrogen gas at a pressure of 2 MPa was introduced, and the reaction was carried out at 180 °C for 2.5 h. GC analysis showed that the conversion rate of furfural was 100%, and the selectivity of furfural alcohol was 94.9%.

[0051] Example 6 The preparation method is the same as in Example 1.

[0052] The catalyst used in this embodiment was as follows: 125 mg of prepared AlOOH was added to the reactor, and 0.15 mL of isopentenal and 20 mL of isopropanol were placed in a high-pressure reactor. High-purity nitrogen was introduced to replace the air in the reactor. After replacement, nitrogen gas at a pressure of 2 MPa was introduced, and the reaction was carried out at 180 °C for 2.5 h. GC analysis showed that the conversion rate of isopentenal was 100%, and the selectivity of isopentenol was 93.6%.

[0053] The above embodiments are merely illustrative of the implementation methods of the present invention, but should not be construed as limiting the scope of the present invention. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of the present invention, and these modifications and improvements all fall within the protection scope of the present invention.

Claims

1. A mild method for preparing an FLP-rich boehmite catalyst for selective transfer hydrogenation of enaldehydes, characterized in that, The mild preparation method includes the following steps: Step 1: At room temperature, aluminum nitrate Al(NO3)3·9H2O is placed in a flask, and deionized water is added and stirred to dissolve it to obtain an aluminum nitrate aqueous solution; concentrated ammonia water is diluted with deionized water to obtain an ammonia aqueous solution, which is added to the aluminum nitrate aqueous solution and stirred until clear and transparent to obtain a mixed solution; Step 2: At room temperature, urea and hexadecyltrimethylammonium bromide (CTAB) are added to the mixed solution obtained in Step 1; stirring is continued until a uniform and transparent sol is formed. The sol is then transferred to a hydrothermal reactor and subjected to a hydrothermal reaction at 80-120 °C. After the hydrothermal reaction, post-treatment is performed to obtain a white powder. Step 3: Place the white powder obtained in Step 2 into a tube furnace and calcine it in air at 550~850 ℃ for 2~4 hours to obtain solid alumina; Step 4: At room temperature, add solid alumina to cyclohexane and stir, then add deionized water dropwise, then heat to evaporate the liquid, dry and grind to obtain boehmite catalyst.

2. The mild preparation method of the FLP-rich boehmite catalyst for selective transfer hydrogenation of enaldehydes according to claim 1, characterized in that, In step 1: In the aluminum nitrate aqueous solution, 10-20 g of aluminum nitrate is added for every 20 mL of deionized water; In the ammonia solution, the sum of the volumes of deionized water and concentrated ammonia is equal to the volume of deionized water in the aluminum nitrate solution, and for every 20 mL of deionized water in the aluminum nitrate solution, there are 1 to 6 mL of concentrated ammonia with a mass concentration of 25%.

3. The mild preparation method of the FLP-rich boehmite catalyst for selective transfer hydrogenation of enaldehydes according to claim 1, characterized in that, In step 2: For every 40 mL of mixed solution, add 5-10 g of urea and 2-5 g of hexadecyltrimethylammonium bromide. Stir for 2-12 hours until a uniform and transparent sol is formed. Transfer the sol to a hydrothermal reactor with a polytetrafluoroethylene liner. Place it in an oven at 80-120 ℃ for hydrothermal reaction for 12-48 hours.

4. The mild preparation method of the FLP-rich boehmite catalyst for selective transfer hydrogenation of enaldehydes according to claim 1, characterized in that, In step 2, the post-processing is as follows: after cooling the hydrothermal autoclave, wash with deionized water 2 to 5 times to recover the white precipitate, dry it overnight in an oven at 80 to 120 ℃, and then grind it to obtain a white powder.

5. The mild preparation method of the FLP-rich boehmite catalyst for selective transfer hydrogenation of enaldehydes according to claim 1, characterized in that, In step 3, the heating rate is 2 ~ 6 ℃ / min, and the gas introduction rate is 20 ~ 100 mL / min.

6. The mild preparation method of the FLP-rich boehmite catalyst for selective transfer hydrogenation of enaldehydes according to claim 1, characterized in that, In step 3: For every 0.2 to 1.0 g of Al2O3, add 20 to 50 mL of cyclohexane and 3 to 10 mL of deionized water; Stir for 2 to 5 hours; evaporate to dryness at 80 to 100 ℃; dry at 80 to 120 ℃.

7. A boehmite catalyst rich in FLPs for selective transfer hydrogenation of enaldehydes, characterized in that, The preparation method described in any one of claims 1-6 is used to obtain a boehmite catalyst by converting amorphous alumina into boehmite with hydrophobic reagent and water at low temperature and normal pressure, and constructing hindered Lewis acid-base pairs on the boehmite. Specifically, it is an AlOOH catalyst with FLPs. The AlOOH catalyst is rod-shaped with a specific surface area of ​​100-160 m². 2 / g, pore volume 0.10~1.20 cm³ 3 / g, with an average pore size of 2~10 nm.

8. The application of the FLP-rich boehmite catalyst of claim 7 for the selective transfer hydrogenation of enaldehydes, characterized in that, It is applied to achieve selective hydrogenation of α,β-unsaturated compounds to generate unsaturated alcohols.

9. The application of the FLP-rich boehmite catalyst according to claim 8 for the selective transfer hydrogenation of enaldehydes, characterized in that, The application is specifically for the efficient transfer hydrogenation of methacrolein to methacrolein alcohol: A high-pressure reactor was used as the reaction vessel. Boehmite catalyst, reaction substrate, and solvent were added to the reactor in sequence. After sealing the reactor, the air in the reactor was replaced with high-purity nitrogen. Then, nitrogen was introduced into the reactor. The reaction was carried out at 160-180℃ for 1.5-2.5 h. After the reaction, the substrate conversion rate reached more than 95%, and the selectivity of the target product reached more than 90%.

10. The application of the FLP-rich boehmite catalyst according to claim 9 for the selective transfer hydrogenation of enaldehydes, characterized in that, In the application: For every 5–25 mL of solvent, add 0.1–0.2 mL of reaction substrate and 0.075–0.175 g of AlOOH catalyst. The reaction substrate is selected from methacrolein, cinnamaldehyde, furfural, and isopentenal; the solvent is selected from isopropanol. Pour nitrogen gas into the reactor to 1-2 MPa; The substrate conversion rate after the reaction can approach 100%, and the highest selectivity of the target product is 94.3%.

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