Preparation method and application of a heat-treated modified palladium catalyst
By depositing non-metallic carbon on the surface of palladium catalysts through heat treatment technology, the valence state and coordination environment of palladium metal are changed, thus preparing modified palladium catalysts with high selectivity and stability. This solves the problems of low selectivity and conversion rate of existing catalysts and realizes the efficient and green production of cyclohexanone by hydrogenation of phenol.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Patents(China)
- Current Assignee / Owner
- QINGDAO INST OF BIOENERGY & BIOPROCESS TECH CHINESE ACADEMY OF SCI
- Filing Date
- 2022-10-11
- Publication Date
- 2026-06-19
AI Technical Summary
Existing catalysts for the hydrogenation of phenol to cyclohexanone exhibit low selectivity and conversion rates, and traditional modification methods affect the subsequent separation and purification process of cyclohexanone, which does not conform to the principles of green chemistry.
Non-metallic carbon was deposited on the surface of a palladium catalyst using a heat treatment technique. The valence state and coordination environment of palladium metal were changed by the small molecule volatile gases generated by the pyrolysis of polymers, thus preparing a modified palladium catalyst with high specific surface area and stability.
It achieves a phenol conversion rate of over 99% and a cyclohexanone selectivity of over 90%, simplifies the production process, reduces costs, and is suitable for green and efficient industrial production.
Smart Images
Figure CN117861650B_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of catalysts and relates to a method for preparing a heat-treated modified palladium catalyst, particularly its catalytic selective hydrogenation of phenol to cyclohexanone. Background Technology
[0002] The information disclosed in this background section is intended only to enhance understanding of the overall background of the invention and is not necessarily to be construed as an admission or in any way implying that such information constitutes prior art known to those skilled in the art.
[0003] Substances containing C=O are an important class of chemicals. Cyclohexanone, for example, is a crucial platform molecule and organic reagent in chemical production, and a key raw material for the preparation of caprolactam and adipic acid, critical intermediates in Nylon 6 and Nylon 66. Currently, the industrial production of cyclohexanone mainly employs two methods: cyclohexane oxidation and selective hydrogenation of phenol. The former requires high-temperature and high-pressure reaction conditions, resulting in high production costs and energy consumption, while also exhibiting low selectivity for the target product and significant challenges in the subsequent recovery and separation of cyclohexanone. Compared to cyclohexane oxidation, the one-step hydrogenation of phenol to produce cyclohexanone offers advantages such as simple production process, high atom economy, low energy consumption, and fewer byproducts, demonstrating greater industrial production potential and application prospects. Currently, the main problem with this production route is the instability of cyclohexanone, which easily leads to further reaction and the formation of the over-hydrogenation product cyclohexanol. Therefore, preparing catalysts with high phenol conversion and cyclohexanone selectivity is key to studying this process.
[0004] Supported palladium catalysts have been widely reported in the hydrogenation of phenol to cyclohexanone, exhibiting excellent activity and selectivity (CN110898853A). To further improve the selectivity of cyclohexanone, acid-base additives are added to the reaction system to alter the steric adsorption mode of cyclohexanone on the active component and inhibit excessive hydrogenation (CN101709027A). However, the catalytic reaction requires an organic reagent or CO2 system, and the addition of additives affects the subsequent separation and purification process of cyclohexanone, which does not conform to the principles of green chemistry. Patent CN103831099A discloses a method for modifying palladium catalysts using alkynes. The modified palladium catalyst exhibits good catalytic performance in the hydrogenation of styrene, but the inventors found that the selectivity and conversion rate of this modified palladium catalyst for the hydrogenation of phenol to cyclohexanone still need to be improved. Summary of the Invention
[0005] The purpose of this invention is to address the problems of complex processes and low yields in the hydrogenation of phenol to cyclohexanone by providing a method for synthesizing a heat-treated modified palladium catalyst, which exhibits excellent catalytic performance in the selective reduction of cyclohexanone by hydrogen. This invention utilizes a simple heat treatment technique, employing small-molecule volatile gases generated during polymer decomposition during pyrolysis to decompose, deposit, and infiltrate onto the surface of the palladium catalyst, thereby altering the valence state and coordination environment of the palladium metal. The heat-treated modified palladium metal catalyst obtained after subsequent activation and reduction treatment possesses advantages such as high specific surface area, high stability, and high selectivity in the hydrogenation of phenol to cyclohexanone.
[0006] To achieve the above objectives, the present invention adopts the following technical solution:
[0007] In a first aspect, the present invention provides a method for preparing a heat-treated modified palladium catalyst, comprising:
[0008] The palladium catalyst and the polymer that can be decomposed into volatile small molecules by heat, or by directly introducing a carbon-containing small molecule gas, are heat-treated together under an inert atmosphere to obtain product B.
[0009] Product B is activated, dried, and reduced to obtain the final product.
[0010] This invention proposes a process in which a palladium catalyst is mixed with a polymer that decomposes into volatile small molecules upon heating during a heat treatment process. Non-metallic carbon elements modify the surface and subsurface of the palladium metal crystals, altering the valence state and coordination environment of the active palladium particles. This regulates the adsorption of intermediate C=O groups and inhibits the formation of β-hydrides, achieving the goal of highly selective hydrogenation of phenol to prepare cyclohexanone. This catalyst uses non-metallic carbon as an electronic aid, which is widely available, inexpensive, and readily available. The process is simple and suitable for green, efficient, and large-scale production.
[0011] In a second aspect, the present invention provides a heat-treated modified palladium catalyst prepared by the method described above.
[0012] A third aspect of the present invention provides the application of the heat-treated modified palladium catalyst described above in the presence of multiple functional groups for the catalytic selective hydrogenation to obtain highly selective C=O products.
[0013] Beneficial effects of the present invention
[0014] (1) The present invention modifies the palladium catalyst by heat treatment vapor deposition technology, thereby achieving non-metallic carbon deposition / doping of the active sites of metal particles, which has the characteristics of uniform metal particle dispersion, multiple active sites, and good stability.
[0015] (2) When the heat-treated modified palladium catalyst of the present invention is applied to the hydrogenation of phenol to cyclohexanone, the phenol conversion rate reaches more than 99% and the cyclohexanone selectivity reaches more than 90%, realizing the one-step conversion of phenol. It has the advantages of simple production process, low cost, mild reaction conditions, and is easy to industrial production. Attached Figure Description
[0016] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0017] Figure 1 TEM image of palladium on carbon catalyst;
[0018] Figure 2 TEM image of the heat-treated modified palladium catalyst prepared in Example 1;
[0019] Figure 3 TEM image of the heat-treated modified palladium catalyst prepared in Example 2;
[0020] Figure 4 TEM image of the heat-treated modified palladium catalyst prepared in Example 3. Detailed Implementation
[0021] It should be noted that the following detailed description is illustrative and intended to provide further explanation of the invention. Unless otherwise specified, all technical and scientific terms used in this invention have the same meaning as commonly understood by one of ordinary skill in the art to which this invention pertains.
[0022] A catalyst for the hydrogenation of phenol to cyclohexanone, wherein the catalyst uses any catalyst containing zero-valent palladium as a precursor, the palladium metal loading being 1%-30%, and the specific surface area being 200-1000 m². 2 / g. The polymer is a substance that can decompose into volatile small-molecule low-chain alkanes, alkenes, and alkynes when heated.
[0023] Studies have shown that, compared with direct gas introduction, using polymer thermal decomposition has the advantages of cheaper and more readily available polymer raw materials, lower overall modification costs, and avoidance of potential dangers during gas transportation, making it safer and more convenient. The selectivity and conversion rate of catalytic hydrogenation of phenol to cyclohexanone are also improved.
[0024] Specifically, the synthesis method of a phenol hydrogenation catalyst for cyclohexanone prepared by the present invention includes the following steps: a palladium catalyst and a polymer that can be decomposed into volatile small molecules by heat treatment are placed together in a tube furnace to achieve in-situ deposition / doping of non-metallic carbon to prepare a modified palladium catalyst; then, the embedded metal active sites are appropriately stripped under oxidative conditions, and after subsequent thermal reduction, a heat-treated modified palladium catalyst with exposed active sites is obtained, which is applied in the one-step synthesis of cyclohexanone by phenol hydrogenation.
[0025] In some embodiments, the palladium catalyst is selected from all catalysts containing zero-valent palladium, and is not limited to supported or encapsulated catalysts with different support materials, structures and surface morphologies, such as commercial palladium on carbon catalysts and commercial palladium alumina catalysts.
[0026] In some embodiments, the palladium catalyst loading is selected from 1% to 30% by mass.
[0027] In some embodiments, the polymer is selected from substances that can decompose into volatile low-chain alkanes, alkenes, and alkynes when heated, such as resins, biomass molecules, and polymeric compounds.
[0028] In some embodiments, the carbon-containing small molecule is at least one of low-chain alkanes, alkenes, or carbon oxides.
[0029] In some embodiments, the mass ratio of the palladium catalyst to the polymer that can be decomposed into volatile small molecules upon heating is selected from 1:0.1 to 1:1.
[0030] In some embodiments, the heat treatment temperature is selected from 30-600°C, the heating rate is 0.5-5°C / min, and the treatment time is 5-300min.
[0031] In some embodiments, the heat treatment atmosphere is one or more of argon, nitrogen, or helium in any combination.
[0032] In some embodiments, the oxidant used in the activation process is selected from one or more of hydrogen peroxide, sodium hypochlorite, or perchloric acid in any proportion.
[0033] In some embodiments, the vacuum drying temperature is 50-80℃, the vacuum drying time is 0.5-10h, and the vacuum degree is -0.05 to -0.1MPa.
[0034] In some embodiments, the reduction treatment temperature is 100-300℃, the heating rate is 0.5-5℃ / min, and the reduction time is 0.5-8 hours.
[0035] In some embodiments, the reduction atmosphere is a hydrogen-argon mixture, with a hydrogen-argon ratio of 1:20 to 1:4.
[0036] The present invention also provides a heat-treated modified palladium catalyst prepared according to the above method.
[0037] This invention provides the application of the above-mentioned catalyst in the hydrogenation of phenol to prepare cyclohexanone.
[0038] In some embodiments, the catalytic solvent is one or more of water, ethanol, dichloromethane, cyclohexane, or n-heptane.
[0039] In some embodiments, the phenol hydrogenation reaction is carried out in a stainless steel high-pressure reactor at a temperature of 30-200°C, a hydrogen pressure of 0.1-4 MPa, a time of 0.5-9 hours, and a stirring rate of 200-400 rpm; the mass ratio of the catalyst to phenol is 1:10-1:1.
[0040] In some embodiments, after the catalytic hydrogenation reaction is completed, the cleaning agent for recycling the catalyst is water, ethanol, cyclohexane, or ethyl acetate.
[0041] The present invention will be further described in detail below with reference to specific embodiments. It should be noted that the specific embodiments are explanations of the present invention and not limitations thereof.
[0042] In the following examples, the palladium-on-carbon catalyst was a 10% commercial palladium-on-carbon catalyst purchased from Alam (Shanghai) Chemical Technology Co., Ltd.
[0043] Example 1
[0044] 100 mg of 10% palladium-on-carbon catalyst and 50 mg of resorcinol-formaldehyde resin (which decomposes into volatile small molecules upon heating) were placed together in a quartz boat-type tube furnace, with the polymer placed at the upper air inlet for gas passage and the palladium-on-carbon catalyst at the lower air inlet for gas passage. The reaction was carried out at 500°C for 2 hours under an inert argon atmosphere. 200 mg of the obtained material and 20 ml of hydrogen peroxide were weighed into a round-bottom flask and stirred at 60°C for 4 hours. After centrifugation and filtration, the material was vacuum-dried at 50°C for 2 hours and then reduced at 300°C for 6 hours under a 10% hydrogen-argon mixed atmosphere to obtain the heat-treated modified palladium catalyst.
[0045] 1 mmol of phenol and 50 mg of the heat-treated modified palladium catalyst were weighed and added to a 25 ml reaction vessel. 5 ml of deionized water was used as the solvent. Hydrogen gas was bubbled through the vessel three times to purge air, maintaining a hydrogen pressure of 1 MPa. The reaction was carried out at 160 °C for 3 hours. After cooling in an ice-water bath, the mixture was separated, extracted with ethyl acetate, and hexadecane was added as an internal standard. Gas chromatography was used to analyze the sample. The experimental results showed that the phenol conversion rate was 99%, and the selectivity for cyclohexanone was 93%. Under the same experimental conditions, the selectivity of cyclohexanone increased from 40% to 93% after heat treatment modification.
[0046] Example 2
[0047] 100 mg of 10% commercial palladium catalyst on carbon and 25 mg of cellulose, which decomposes into volatile small molecules upon heating, were placed together in a quartz boat-shaped tube furnace. The cellulose was placed at the upper air vent for gas passage, and the palladium catalyst at the lower air vent. The reaction was carried out at 400°C for 2 hours under an inert argon atmosphere. 200 mg of the obtained material and 20 ml of hydrogen peroxide were weighed into a round-bottom flask and stirred at 80°C for 4 hours. After centrifugation and filtration, the material was vacuum-dried at 50°C for 2 hours and then reduced at 300°C for 4 hours under a 10% hydrogen-argon mixed atmosphere to obtain the heat-treated modified palladium catalyst.
[0048] 2 mmol of phenol and 50 mg of the heat-treated modified palladium catalyst were weighed and added to a 25 ml reactor. 5 ml of the catalyst was used as solvent, and the reactor was purged three times with hydrogen gas to remove all air, maintaining a hydrogen pressure of 1 MPa. The reaction was carried out at 160 °C for 6 hours. After cooling in an ice-water bath, the mixture was separated, extracted with ethyl acetate, and hexadecane was added as an internal standard. Gas chromatography was used to analyze the sample. The experimental results showed that the phenol conversion rate was 99%, and the selectivity for cyclohexanone was 60%.
[0049] Example 3
[0050] 100 mg of 10% commercial palladium-on-carbon catalyst and 10 mg of polystyrene (which decomposes into volatile small molecules upon heating) were placed together in a quartz boat-type tube furnace, with the polystyrene placed at the upper air inlet for gas passage and the palladium-on-carbon catalyst at the lower air inlet for gas passage. The reaction was carried out at 300°C for 4 hours under an inert argon atmosphere. 200 mg of the obtained material and 20 ml of hydrogen peroxide were weighed into a round-bottom flask and stirred at 80°C for 4 hours. After centrifugation and filtration, the material was vacuum-dried at 50°C for 2 hours and then reduced at 300°C for 2 hours under a 10% hydrogen-argon mixed atmosphere to obtain the heat-treated modified palladium catalyst.
[0051] 1 mmol of phenol and 50 mg of the heat-treated modified palladium catalyst were weighed and added to a 25 ml reactor. 5 ml of a 1:1 volume ratio ethanol-water solvent was added, and the reactor was purged three times with hydrogen gas to remove all air, maintaining a hydrogen pressure of 1 MPa. The reaction was carried out at 160 °C for 6 hours. After cooling in an ice-water bath, the mixture was separated, extracted with ethyl acetate, and hexadecane was added as an internal standard. Gas chromatography was used to analyze the sample. The experimental results showed that the phenol conversion rate was 99%, and the selectivity for cyclohexanone was 83%.
[0052] Table 1 Catalytic hydrogenation activity of palladium on carbon catalyst before and after heat treatment modification for p-phenol
[0053]
[0054] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.
Claims
1. A method for preparing a thermally treated modified palladium catalyst, characterized in that, include: A palladium catalyst and a polymer that can decompose into volatile small molecules upon heating are heat-treated together under an inert atmosphere to obtain product B. Product B is activated, dried, and reduced to obtain the final product. The heat treatment temperature is 300-600°C, and the heating rate is 0.5-5°C / min; The reduction treatment temperature is 100-300°C, the heating rate is 0.5-5°C / min, the reduction time is 0.5-8 hours, and the reduction treatment atmosphere is a hydrogen-argon mixture with a hydrogen to argon ratio of 1:20-1:
4. The polymer is at least one of phenolic resin, cellulose, and polystyrene; the oxidant in the activation treatment is selected from at least one of hydrogen peroxide, sodium hypochlorite, or perchloric acid.
2. The method for preparing a thermal treatment modified palladium catalyst according to claim 1, characterized by, The mass ratio of the palladium catalyst to the polymer that can be decomposed into volatile small molecules upon heating is 1:0.1 to 1:
1.
3. The method for preparing a thermal treatment modified palladium catalyst according to claim 1, wherein The heat treatment time is 5-300 min.
4. The method for preparing a thermal treatment modified palladium catalyst according to claim 1, characterized by, The heat treatment atmosphere is at least one of argon, nitrogen, or helium.
5. The method for preparing a thermal treatment modified palladium catalyst according to claim 1, wherein The drying process is vacuum drying; the vacuum drying temperature is 50-80°C, the vacuum drying time is 0.5-10h, and the vacuum degree is -0.05~-0.1MPa.
6. The heat-treated modified palladium catalyst prepared by the method according to any one of claims 1-5.
7. The application of the heat-treated modified palladium catalyst according to claim 6 in the catalytic selective hydrogenation to obtain highly selective C=O products in the presence of multiple functional groups.