Preparation method of catalyst and establishment of catalytic system for high-selectivity preparation of styrene from phenylacetylene
By preparing a catalyst composed of an N-heterocyclic carbene salt-modified metal-organic framework and palladium, the problem of low activity in the existing phenylacetylene semi-hydrogenation catalyst was solved, achieving highly selective and stable styrene preparation, inhibiting excessive hydrogenation of styrene, and improving the thermal stability and cycle life of the catalyst.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2025-12-15
- Publication Date
- 2026-03-24
AI Technical Summary
Existing phenylacetylene semi-hydrogenation catalysts have low activity, resulting in low styrene yield, low catalytic selectivity, and problems such as excessive hydrogenation of phenylacetylene to ethylbenzene.
Catalysts composed of N-heterocyclic carbene salt-modified metal-organic frameworks and palladium were prepared by ion exchange and impregnation methods to form N-heterocyclic carbene tetrafluoroborate-modified metal-organic frameworks, which supported palladium nanoparticles, thereby improving the thermal stability and selectivity of the catalyst.
It achieves highly selective preparation of styrene, with a selectivity of up to 99.9%, suppresses excessive hydrogenation of styrene, has a long catalyst cycle life, and good thermal stability.
Smart Images
Figure CN121715221A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of catalyst technology, and in particular to a method for preparing a catalyst and the establishment of a highly selective catalytic system for the preparation of styrene from phenylacetylene. Background Technology
[0002] Styrene, as the most widely used derivative of benzene and a fundamental aromatic chemical, is an important basic organic chemical raw material. Furthermore, styrene is the raw material for the synthesis of polystyrene, and is one of the important pathways in the modern chemical industry for the synthesis of coatings, dyes, and pharmaceuticals.
[0003] Currently, the main methods for styrene preparation include ethylbenzene dehydrogenation and extraction of styrene from the C8 fraction of ethylene cracking byproducts. However, both methods result in the presence of small amounts of phenylacetylene in the styrene obtained. The presence of phenylacetylene not only poisons the catalyst during polymerization but also degrades the styrene, causing discoloration, off-flavors, and degradation. Therefore, developing novel phenylacetylene semi-hydrogenation catalysts with high conversion rates, good selectivity, and excellent stability is of great significance. However, existing phenylacetylene semi-hydrogenation catalysts suffer from problems such as low activity leading to low styrene yields and low catalytic selectivity resulting in excessive hydrogenation of phenylacetylene to ethylbenzene. Summary of the Invention
[0004] Based on the technical problems existing in the background art, the present invention proposes a method for preparing a catalyst and establishes a catalytic system for the highly selective preparation of styrene from phenylacetylene. The catalyst of the present invention has good thermal stability, catalytic activity, selectivity and cycle life. When used with cesium salt in the semi-hydrogenation reaction of phenylacetylene, it can produce styrene with high selectivity of up to 99.9%, and can inhibit the over-hydrogenation of styrene.
[0005] This invention proposes a catalyst comprising: an N-heterocyclic carbene salt modified metal-organic framework and palladium, wherein the N-heterocyclic carbene is an imidazole derivative; and palladium is immobilized on the N-heterocyclic carbene salt modified metal-organic framework by coordination and deposition.
[0006] Preferably, the N-heterocyclic carbene salt is an N-heterocyclic carbene tetrafluoroborate.
[0007] Preferably, the metal-organic framework is composed of metal ions and organic ligands connected by coordination bonds.
[0008] Preferably, the organic ligand is 2-substituted terephthalic acid.
[0009] Preferably, the 2-substituent group is -(CH2). n -X, where X is a halogen and n≥0; more preferably n is 0, 1, 2, or 3.
[0010] The aforementioned 2-substituted terephthalic acid refers to terephthalic acid in which the 2-position of the benzene ring is substituted.
[0011] N-heterocyclic carbene refers to an intermediate with a nitrogen-containing cyclic structure and a lone pair of electrons.
[0012] Of the palladium mentioned above, a portion of the palladium is coordinated with the metal-organic framework modified with N-heterocyclic carbene tetrafluoroborate in a coordinated manner, while the other portion of the palladium is deposited atomically on the metal-organic framework modified with N-heterocyclic carbene tetrafluoroborate.
[0013] Preferably, the metal ion is a trivalent metal ion.
[0014] Preferably, the metal ion is Fe. 3+ Cr 3+ Al 3+ At least one of them.
[0015] Preferably, the imidazole derivative is one of N-methylimidazolium, N-ethylimidazolium, and N-propylimidazolium.
[0016] Preferably, the 2-substituted terephthalic acid is substituted by its 2-substituent group -(CH2). n The X in -X undergoes a substitution reaction with the N at the 3-position of the imidazole ring in the imidazole derivative to achieve N-heterocyclic carbene halide modification of the metal-organic framework.
[0017] Preferably, the N-heterocyclic carbene halide-modified metal-organic framework is formed by an ion exchange reaction with tetrafluoroborate to form an N-heterocyclic carbene tetrafluoroborate-modified metal-organic framework.
[0018] Preferably, the palladium content in the catalyst is 0.01-1 wt%.
[0019] Metal-organic frameworks (MOFs) possess unique porous structures, high specific surface areas, and extremely high gas storage capacity. They can serve as supports for palladium nanoparticles, promoting carrier separation and electron transfer, thereby improving thermocatalytic efficiency and hydrogenation catalytic activity. However, palladium nanoparticles are unstable on MOFs and are prone to leaching, leading to reduced catalyst cycle life. Furthermore, the poor thermal stability of MOFs reduces the catalyst's hydrogenation catalytic performance. This invention selects suitable organic ligands to react with imidazole derivatives to modify MOFs with N-heterocyclic carbene halide salts. Functional ion exchange allows the anions to form salts with the imidazole derivatives, improving the thermal stability of MOFs and enhancing their hydrogenation catalytic performance. Furthermore, selecting appropriately structured N-heterocyclic carbenes (NHCs) provides π-conjugated bonds and double-electron vacancies. The π-conjugated bonds coordinate with palladium, and the double-electron vacancies can be occupied by palladium electrons. After NHCs coordinate with palladium particles with small particle sizes, the catalyst exhibits better stability and reduces palladium leaching, thus improving the catalyst's thermal stability, catalytic activity, selectivity, and cycle life.
[0020] The present invention also proposes a method for preparing the above-mentioned catalyst, comprising the following steps: subjecting an N-heterocyclic carbene halide-modified metal-organic framework to an acid radical ion via an ion exchange reaction to obtain an intermediate; and impregnating the intermediate in a palladium precursor solution to obtain the catalyst.
[0021] After the above ion exchange reaction is completed, the solid and liquid are separated and dried to obtain the intermediate.
[0022] After the above impregnation is completed, the solid and liquid are separated and dried to obtain the catalyst.
[0023] Preferably, the metal-organic framework undergoes a substitution reaction with an imidazole derivative to obtain an N-heterocyclic carbene halide-modified metal-organic framework.
[0024] After the above substitution reaction was completed, the solid and liquid were separated, the solid was washed and dried to obtain the metal-organic framework modified with N-heterocyclic carbene halide.
[0025] The metal-organic frameworks described above are denoted as MOFs, and the metal-organic frameworks modified with the above N-heterocyclic carbene halide are denoted as MOFs-NHCs.
[0026] Preferably, the substitution reaction is carried out at a temperature of 20-90°C for 1-48 hours.
[0027] Preferably, the weight ratio of the metal-organic framework to the imidazole derivative is 1:0.02-0.5; more preferably, it is 1:0.2.
[0028] Preferably, the reaction solvent for the substitution reaction is at least one of N,N-dimethylformamide, diethyl ether, 1,4-dioxane, and tetrahydrofuran.
[0029] Preferably, the substitution reaction is carried out in an inert gas atmosphere.
[0030] Preferably, the anion is tetrafluoroborate.
[0031] Tetrafluoroborate ions can be provided by tetrafluoroboric acid or tetrafluoroborates; tetrafluoroborates can be silver tetrafluoroborate, sodium tetrafluoroborate, potassium tetrafluoroborate, etc.
[0032] Preferably, the ion exchange reaction is carried out at a temperature of 20-90°C for 1-8 hours.
[0033] Ion exchange reactions occur in water.
[0034] Preferably, the weight ratio of the N-heterocyclic carbene halide-modified metal-organic framework to the anion is 1:0.05-0.3; more preferably, it is 1:0.2.
[0035] Preferably, the ion exchange reaction is carried out in an inert gas atmosphere.
[0036] Preferably, the impregnation temperature is 20-80℃ and the time is 1-48h.
[0037] Preferably, the impregnation is carried out under normal pressure or negative pressure conditions.
[0038] Preferably, the vacuum degree during impregnation is 20-700 mbar.
[0039] Preferably, the palladium precursor is at least one of palladium chloride, palladium chloride, palladium acetate, palladium acetylacetonate, and tetra(triphenylphosphine)palladium.
[0040] The aforementioned chloropalladium salts can be sodium chloropalladium, potassium chloropalladium, etc.
[0041] Preferably, the solvent for the palladium precursor solution is at least one of water, 1,4-dioxane, tetrahydrofuran, N,N-dimethylformamide, and dilute hydrochloric acid.
[0042] Preferably, the weight ratio of the intermediate to the palladium precursor is 1:0.0001-0.05.
[0043] When the anion is tetrafluoroborate, the intermediate is an N-heterocyclic carbene tetrafluoroborate modified metal-organic framework, denoted as MOFs-NHCs-BF4, and its corresponding catalyst is denoted as Pd / MOFs-NHCs-BF4.
[0044] Preferably, the preparation method of metal-organic frameworks includes the following steps: hydrothermal reaction of organic ligands with metal ions to obtain metal-organic frameworks.
[0045] Preferably, the solvent for the hydrothermal reaction is at least one of N,N-dimethylformamide, water, methanol, and aqueous HF solution.
[0046] Preferably, the hydrothermal reaction temperature is 110-250℃ and the time is 4-24h.
[0047] Preferably, the molar ratio of the organic ligand to the metal ion is 1:0.5-4.
[0048] Preferably, after the hydrothermal reaction is completed, the solid and liquid are separated, and the solid is activated in an inert gas atmosphere to obtain a metal-organic framework.
[0049] Preferably, the activation temperature is 100-250℃ and the activation time is 1-24h.
[0050] The inert gas mentioned above can be nitrogen, etc.
[0051] This invention also proposes the application of the above-mentioned catalyst and the catalyst prepared by the above method in the selective catalytic preparation of styrene from phenylacetylene.
[0052] Preferably, cesium salt is added during the selective catalytic preparation of styrene from phenylacetylene.
[0053] Preferably, the cesium salt is cesium carbonate.
[0054] The present invention also proposes a method for highly selectively preparing styrene from phenylacetylene, comprising the following steps: in a hydrogen atmosphere, phenylacetylene and substance A undergo a hydrogenation reaction to obtain styrene, wherein substance A is a catalyst or substance A is a catalyst and a cesium salt, and the catalyst is the above-mentioned catalyst or a catalyst prepared by the above method.
[0055] This invention reveals that catalysts prepared with different modifying groups and other types of catalysts combined with cesium carbonate exhibit significant differences in their ability to inhibit further hydrogenation of styrene. The catalyst of this invention alone can produce styrene with high selectivity. When the catalyst of this invention is combined with a cesium salt in a catalytic system for the semi-hydrogenation of phenylacetylene, the selectivity of styrene can be further improved, reaching as high as 99.9%, effectively inhibiting further hydrogenation of styrene. Furthermore, even if the hydrogenation reaction time is extended after the phenylacetylene reaction is complete, styrene will not undergo excessive hydrogenation to form ethylbenzene, and styrene will still maintain high selectivity, reaching as high as 99%. The catalytic system of this invention combined with a cesium salt not only produces styrene with high selectivity but also inhibits excessive hydrogenation of styrene.
[0056] Preferably, the hydrogenation reaction is carried out under normal pressure.
[0057] Preferably, the hydrogenation reaction is carried out at a temperature of 10-50°C for 1-24 hours.
[0058] Preferably, the molar ratio of phenylacetylene to palladium in the catalyst is 1:0.0001-0.01.
[0059] Preferably, when substance A is a catalyst and a cesium salt, the molar ratio of phenylacetylene to cesium salt is 1:0.0001-0.3.
[0060] Preferably, the hydrogenation reaction is carried out in a solvent.
[0061] Preferably, the solvent is at least one selected from methanol, ethanol, tetrahydrofuran, and dimethyl sulfoxide.
[0062] This invention modifies metal-organic frameworks with N-heterocyclic carbene halide salts, introduces acid radicals for salt formation through functional ion exchange, and loads palladium to obtain a catalyst, thereby improving the catalyst's thermal stability, catalytic activity, selectivity, and cycle life. Using the catalyst of this invention in the semi-hydrogenation reaction of phenylacetylene can produce styrene with high selectivity. Using the catalytic system composed of the catalyst of this invention and cesium salt in the semi-hydrogenation reaction of phenylacetylene can further improve the selectivity of styrene to as high as 99.9%. Even after the phenylacetylene reaction is complete, if the hydrogenation reaction time is extended, styrene will not be over-hydrogenated to ethylbenzene, and styrene will still have high selectivity of up to 99%. Attached Figure Description
[0063] Figure 1 This is a SEM image of MOFs3 obtained in Example 3.
[0064] Figure 2 The image shows a SEM image of Pd / MOFs-NHCs-BF4-3 obtained in Example 3. Detailed Implementation
[0065] The technical solution of the present invention will now be described in detail through specific embodiments.
[0066] Example 1
[0067] A method for preparing a catalyst includes the following steps: 5.06 g (0.021 mol) of AlCl3·6H2O, 1.71 g (0.007 mol) of 2-bromoterephthalic acid, and 50 mL of methanol were ultrasonically mixed and transferred to a hydrothermal reactor. The mixture was then subjected to hydrothermal reaction at 145 °C for 8 h. The mixture was slowly cooled, filtered, and the filter cake was washed with water and ethanol in sequence. After drying, the mixture was activated at 120 °C for 4 h under a nitrogen atmosphere to obtain a metal-organic framework, denoted as MOFs1. 2.3 g of MOFs1 was added to a methanol solution of N-methylimidazole with a mass fraction of 5 wt% (1.2 g of N-methylimidazole was used). The substitution reaction was carried out under nitrogen atmosphere and stirred at 40 °C for 24 h. The solution was then filtered, washed with diethyl ether, and dried under vacuum to obtain MOFs-NHCs-1. 2.2 g of MOFs-NHCs-1 was added to an aqueous solution of silver tetrafluoroborate (0.18 g of tetrafluoroborate ion was used), and ion exchange was carried out by stirring at 60 °C for 5 h under a nitrogen atmosphere. Then, the mixture was filtered, washed, and vacuum dried to obtain MOFs-NHCs-BF4-1. Dissolve 0.021 g of palladium acetate in 100 mL of acetone, add 2 g of MOFs-NHCs-BF4-1, adjust the vacuum to 250-300 mbar, stir and impregnate at room temperature for 4 h, filter, wash, and dry to obtain the catalyst, denoted as Pd / MOFs-NHCs-BF4-1, wherein the Pd content in the catalyst is 0.5 wt%.
[0068] A method for the highly selective preparation of styrene from phenylacetylene includes the following steps: 1.1 mL (10 mmol) of phenylacetylene, 0.16 g (0.5 mmol) of cesium carbonate, and 15 mL of ethanol were added to a reaction tube and mixed. Then, the air was replaced with nitrogen and hydrogen in sequence. Then, 0.212 g (based on Pd, Pd is 0.01 mmol) of Pd / MOFs-NHCs-BF4-1 prepared in Example 1 was added. The reaction was carried out in a hydrogen atmosphere at 30 °C under normal pressure for 1.8 h. The phenylacetylene reacted completely to obtain styrene with a selectivity of up to 99.9%. After the reaction was extended for another 1 h, the selectivity of styrene still reached 99.7%.
[0069] Comparative Example 1 A method for the highly selective preparation of styrene from phenylacetylene includes the following steps: Without adding cesium carbonate, styrene was prepared using the Pd / MOFs-NHCs-BF4-1 catalyst obtained in Example 1 as the catalyst, following the method in Example 1. It was found that after reacting at 30°C for 2.3 h, the phenylacetylene reaction was complete, yielding styrene with a selectivity of up to 98.2%. After extending the reaction by 1 h, the selectivity of styrene was 65%, and the selectivity of ethylbenzene was 34%.
[0070] It can be seen that: styrene can be produced with high selectivity when the catalyst of the present invention is used alone; when the catalyst of the present invention is combined with cesium salt, the high selectivity of styrene can be maintained, and even if the hydrogenation reaction time is extended after the phenylacetylene reaction is complete, styrene will not be excessively hydrogenated to produce ethylbenzene.
[0071] Example 2
[0072] A method for preparing a catalyst includes the following steps: 4 g (0.01 mol) of Cr(NO3)3·9H2O, 3 g (0.01 mol) of 2-iodoterephthalic acid, 10 mL of 1 mol / L HF aqueous solution, and 50 mL of water were ultrasonically mixed and transferred to a hydrothermal reactor. The mixture was then hydrothermally reacted in a constant temperature chamber at 220 °C for 12 h. The mixture was then slowly cooled, filtered, washed with N,N-dimethylformamide, washed with ethanol by distillation, dried, and then activated at 200 °C for 6 h under a nitrogen atmosphere to obtain a metal-organic framework, denoted as MOFs2. 3g of MOFs2 was added to a methanol solution of N-methylimidazole with a mass fraction of 5wt% (0.45g of N-methylimidazole was used). The substitution reaction was carried out under nitrogen atmosphere and stirred at 40°C for 5h. The solution was then filtered, washed with diethyl ether, and dried under vacuum to obtain MOFs-NHCs-2. 2.8 g of MOFs-NHCs-2 was added to an aqueous solution of sodium tetrafluoroborate (0.3 g of tetrafluoroborate ion was used), and the mixture was stirred at 60 °C for 5 h under a nitrogen atmosphere for ion exchange. Then the mixture was filtered, washed, and vacuum dried to obtain MOFs-NHCs-BF4-2. 0.017 g of palladium chloride was dissolved in 200 mL of dilute hydrochloric acid, and 2 g of MOFs-NHCs-BF4-2 was added. The vacuum was adjusted to 30 mbar, and the mixture was stirred and impregnated at room temperature for 2 h. The mixture was then filtered, washed, and dried to obtain the catalyst, denoted as Pd / MOFs-NHCs-BF4-2, in which the Pd content was 0.5 wt%.
[0073] A method for the highly selective preparation of styrene from phenylacetylene includes the following steps: 1.1 mL (10 mmol) of phenylacetylene, 0.08 g (0.25 mmol) of cesium carbonate, and 15 mL of ethanol were added to a reaction tube and mixed. Then, the air was replaced with nitrogen and hydrogen in sequence. Then, 0.106 g (based on Pd, Pd is 0.005 mmol) of Pd / MOFs-NHCs-BF4-2 prepared in Example 2 was added. The reaction was carried out in a hydrogen atmosphere at 30 °C under normal pressure for 6 h. The phenylacetylene reacted completely to obtain styrene with a styrene selectivity of up to 99.9%. After extending the reaction by 1 h, the styrene selectivity still reached 97%.
[0074] When cesium carbonate is not added, and the Pd / MOFs-NHCs-BF4-2 prepared in Example 2 is still used as the catalyst, styrene is prepared according to the method of Example 2. It is found that after reacting at 30°C for 4.5 h, the phenylacetylene reaction is complete, and styrene is obtained. The selectivity of styrene is as high as 99.9%. After extending the reaction by 1 h, the selectivity of styrene is 67%, and the selectivity of ethylbenzene is 33%.
[0075] Example 3
[0076] A method for preparing a catalyst includes the following steps: 8.11 g (0.03 mol) of FeCl3·6H2O was ultrasonically dissolved in water, and 3 g (0.015 mol) of 2-chloroterephthalic acid was ultrasonically dissolved in 150 mL of N,N-dimethylformamide. The two solutions were then mixed and transferred to a hydrothermal reactor and reacted hydrothermally at 125 °C for 24 h. The mixture was then slowly cooled, filtered, and washed successively with hot N,N-dimethylformamide and hot ethanol. The mixture was then washed successively with hot water and ethanol by distillation, dried under vacuum at 70 °C, and activated at 120 °C for 8 h under a nitrogen atmosphere to obtain a metal-organic framework, denoted as MOFs3. 3g of MOFs3 was added to an ethanol solution containing 0.6g of N-ethylimidazole. The substitution reaction was carried out at 30°C for 8 hours under a nitrogen atmosphere and stirred. The solution was then filtered, washed with diethyl ether and methanol, and dried under vacuum to obtain MOFs-NHCs-3. 2.5 g of MOFs-NHCs-3 was added to 100 g of 0.3 wt% silver tetrafluoroborate aqueous solution. The ion exchange reaction was carried out by stirring at 60 °C for 5 h under a nitrogen atmosphere. The solution was then filtered, washed, and vacuum dried to obtain MOFs-NHCs-BF4-3. Take 100g of sodium chloropalladium aqueous solution (Pd mass fraction is 0.02wt%), add 2g of MOFs-NHCs-BF4-3, adjust the vacuum degree to 40mbar, stir and impregnate at room temperature for 8h, filter, wash and dry to obtain the catalyst, denoted as Pd / MOFs-NHCs-BF4-3, wherein the Pd content in the catalyst is 1wt%.
[0077] The catalyst Pd / MOFs-NHCs-BF4-3 comprises: a metal-organic framework modified with N-ethylimidazolium tetrafluoroborate and palladium, wherein palladium is immobilized on the metal-organic framework modified with N-ethylimidazolium tetrafluoroborate by coordination and deposition.
[0078] The MOFs1 and Pd / MOFs-NHCs-BF4-1 prepared in Example 3 were tested, and the results are as follows: Figures 1-2 As shown.
[0079] Figure 1 This is a SEM image of MOFs3 obtained in Example 3.
[0080] Figure 2 The image shows a SEM image of Pd / MOFs-NHCs-BF4-3 obtained in Example 3.
[0081] A method for the highly selective preparation of styrene from phenylacetylene includes the following steps: 1.1 mL (10 mmol) of phenylacetylene, 0.035 g (0.1 mmol) of cesium carbonate, and 30 mL of methanol were added to a reaction tube and mixed. Then, the air was replaced with nitrogen and hydrogen in sequence. Then, 0.053 g (based on Pd, Pd is 0.005 mmol) of Pd / MOFs-NHCs-BF4-3 prepared in Example 3 was added. The reaction was carried out in a hydrogen atmosphere at 40 °C under normal pressure for 3.8 h. The phenylacetylene reacted completely to obtain styrene with a selectivity close to 100%. After the reaction was extended for another 2 h, the selectivity of styrene still reached 99%.
[0082] After the above reaction is completed, the catalyst Pd / MOFs-NHCs-BF4-3 is recovered. The specific recovery steps are as follows: the liquid in the reaction tube is aspirated, the reaction tube is washed with methanol and water respectively, and then the catalyst Pd / MOFs-NHCs-BF4-3 in the reaction tube is placed in a vacuum drying oven and dried at 60°C for 24 hours to complete the recovery.
[0083] When repeating the experiment, simply add the reaction substrate directly to the reaction tube.
[0084] The Pd / MOFs-NHCs-BF4-3 from Example 3 was recovered, and styrene was prepared 6 times in the same manner as described above. The results are shown in Table 1.
[0085] Table 1. Loop Results
[0086] As shown in Table 1, the catalytic performance of the Pd / MOFs-NHCs-BF4-3 catalyst did not decrease significantly after 6 cycles, indicating that Pd / MOFs-NHCs-BF4-3 has a good cycle life.
[0087] When cesium carbonate is not added, and the Pd / MOFs-NHCs-BF4-3 prepared in Example 3 is still used as the catalyst, styrene is prepared according to the method of Example 3. It is found that after reacting at 40°C for 4.5 h, the phenylacetylene reaction is complete, and styrene is obtained with a selectivity of 98%. After continuing the reaction for another 2 h, the selectivity of styrene is 32%, and the selectivity of ethylbenzene is 67%.
[0088] Example 4
[0089] A method for preparing a catalyst includes the following steps: 7.88 g (0.021 mol) of Al(NO3)3·6H2O, 1.4 g (0.007 mol) of 2-chloroterephthalic acid, and 60 mL of methanol were ultrasonically mixed and transferred to a hydrothermal reactor. The mixture was then subjected to hydrothermal reaction at 160 °C for 13 h. The mixture was then slowly cooled, filtered, and the filter cake was washed with water and ethanol in sequence. After drying, the mixture was activated at 110 °C for 10 h under a nitrogen atmosphere to obtain a metal-organic framework, denoted as MOFs4. 3g of MOFs4 was added to a methanol solution of N-methylimidazole with a mass fraction of 5wt% (0.6g of N-methylimidazole was used). The substitution reaction was carried out under nitrogen atmosphere and stirred at 40°C for 20h. The solution was then filtered, washed with diethyl ether, and dried under vacuum to obtain MOFs-NHCs-4. 3g of MOFs-NHCs-4 was added to 100g of 0.5wt% tetrafluoroboric acid aqueous solution. The ion exchange reaction was carried out by stirring at 60℃ for 5h under a nitrogen atmosphere. Then, the mixture was filtered, washed, and vacuum dried to obtain MOFs-NHCs-BF4-4. Dissolve 0.042 g of palladium acetate in 100 mL of acetone, add 2 g of MOFs-NHCs-BF4-4, adjust the vacuum to 250-300 mbar, stir and impregnate at room temperature for 2 h, filter, wash, and dry to obtain the catalyst, denoted as Pd / MOFs-NHCs-BF4-4, wherein the Pd content in the catalyst is 1 wt%.
[0090] A method for the highly selective preparation of styrene from phenylacetylene includes the following steps: 1.1 mL (10 mmol) of phenylacetylene, 0.032 g (0.1 mmol) of cesium carbonate, and 20 mL of ethanol were added to a reaction tube and mixed. Then, the air was replaced with nitrogen and hydrogen in sequence. Then, 0.0106 g (based on Pd, Pd is 0.001 mmol) of Pd / MOFs-NHCs-BF4-4 prepared in Example 4 was added. The reaction was carried out in a hydrogen atmosphere at 30 °C under normal pressure for 6 h. The phenylacetylene reacted completely to obtain styrene with a selectivity of up to 99.9%. After the reaction was extended for another 2 h, the selectivity of styrene could still reach 99%.
[0091] When cesium carbonate is not added, and the Pd / MOFs-NHCs-BF4-4 prepared in Example 4 is still used as the catalyst, styrene is prepared according to the method in Example 4. It is found that when the reaction is carried out at 30°C for 6 hours, the phenylacetylene reaction is complete, and styrene is obtained. The selectivity of styrene is 88% and the selectivity of ethylbenzene is 11%. After the reaction is extended for another hour, the selectivity of styrene is 43% and the selectivity of ethylbenzene is 56%.
[0092] Comparative Examples 2-3 The catalyst was prepared according to the method of Example 1 by successively replacing N-methylimidazole with N-butylimidazole and N-isopropylimidazole. The obtained catalysts were then used to completely react phenylacetylene according to the method of Example 1 to prepare styrene, and the reaction was extended for another 1 hour to investigate the selectivity of styrene.
[0093] Comparative Example 4 The palladium acetate was replaced with palladium dichloroammonium, and a catalyst was prepared according to the method of Example 1. The obtained catalyst was then used to completely react phenylacetylene according to the method of Example 1 to prepare styrene, and the reaction was extended for another 1 hour to investigate the selectivity of styrene.
[0094] Comparative Example 5 The catalyst Pd / MOFs-NHCs-BF4-1 in Example 1 was replaced with a palladium on carbon catalyst (Pd was 0.01 mmol). The method for the high-selectivity preparation of styrene from phenylacetylene in Example 1 was followed, allowing the phenylacetylene reaction to be complete. The reaction was then extended for another 1 h to examine the selectivity of styrene.
[0095] Comparative Example 6 A method for preparing a catalyst includes the following steps: 0.042 g of palladium acetate was dissolved in 100 mL of acetone, and 1 g of MOFs-NHCs-4 prepared in Example 4 was added. The vacuum degree was adjusted to 250-300 mbar, and the mixture was stirred and impregnated at room temperature for 2 h. After filtration, washing, and drying, the catalyst was obtained and denoted as Pd / MOFs-NHCs-4, wherein the content of Pd in the catalyst was 2 wt%.
[0096] Following the method for highly selective preparation of styrene from phenylacetylene in Example 4, the phenylacetylene reaction was completed, and the reaction was extended for another 1 hour to examine the selectivity of styrene.
[0097] The styrene selectivity of Example 1 and Comparative Examples 2-6 was statistically analyzed, and the results are shown in Table 2.
[0098] Table 2 Test Results
[0099] As shown in Table 2, the present invention can improve the catalytic activity and selectivity of metal-organic frameworks by selecting appropriate N-heterocyclic carbene, palladium precursor, and acid radical ions for modification. Furthermore, the catalysts prepared with different modification groups and other types of catalysts combined with cesium carbonate have significantly different abilities to inhibit further hydrogenation of styrene. The catalytic system composed of the catalyst and cesium carbonate described in this invention, when used in the phenylacetylene semi-hydrogenation reaction, can not only produce styrene with high selectivity but also inhibit excessive hydrogenation of styrene.
[0100] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.
Claims
1. A catalyst, characterized in that, include: The metal-organic framework modified with N-heterocyclic carbene salt and palladium, wherein the N-heterocyclic carbene is an imidazole derivative; palladium is immobilized on the N-heterocyclic carbene salt modified metal-organic framework by coordination and deposition.
2. The catalyst according to claim 1, characterized in that, Preferably, the N-heterocyclic carbene salt is an N-heterocyclic carbene tetrafluoroborate; the metal-organic framework is composed of metal ions and organic ligands linked by coordinate bonds; preferably, the organic ligand is 2-substituted terephthalic acid; preferably, the 2-substituted group is -(CH2). n -X, where X is a halogen and n≥0; preferably, the metal ion is a trivalent metal ion; preferably, the metal ion is Fe. 3+ Cr 3+ Al 3+ At least one of the following; preferably, the imidazole derivative is one of N-methylimidazolium, N-ethylimidazolium, and N-propylimidazolium; preferably, the 2-substituted terephthalic acid is substituted through its 2-substituent group -(CH2). n The X in -X undergoes a substitution reaction with the N at the 3-position of the imidazole ring in the imidazole derivative to achieve N-heterocyclic carbene halide modification of the metal-organic framework; preferably, the metal-organic framework modified with N-heterocyclic carbene halide reacts with tetrafluoroborate to form an N-heterocyclic carbene tetrafluoroborate modified metal-organic framework through an ion exchange reaction.
3. The catalyst according to claim 1 or 2, characterized in that, The palladium content in the catalyst is 0.01-1 wt%.
4. A method for preparing the catalyst according to any one of claims 1-3, characterized in that, The process includes the following steps: ion exchange reaction of N-heterocyclic carbene halide-modified metal-organic framework with acid radical ions to obtain an intermediate; impregnation of the intermediate in a palladium precursor solution to obtain a catalyst.
5. The method for preparing the catalyst according to claim 4, characterized in that, A metal-organic framework is substituted with an imidazole derivative to obtain an N-heterocyclic carbene halide-modified metal-organic framework; preferably, the substitution reaction is carried out at a temperature of 20-90°C for a time of 1-48 h; preferably, the weight ratio of the metal-organic framework to the imidazole derivative is 1:0.02-0.5; preferably, the reaction solvent for the substitution reaction is at least one selected from N,N-dimethylformamide, diethyl ether, 1,4-dioxane, and tetrahydrofuran; preferably, the substitution reaction is carried out in an inert gas atmosphere.
6. The method for preparing the catalyst according to claim 4 or 5, characterized in that, The anion is tetrafluoroborate; preferably, the temperature of the ion exchange reaction is 20-90℃ and the time is 1-8h; preferably, the weight ratio of the N-heterocyclic carbene halide-modified metal-organic framework to the anion is 1:0.05-0.3; preferably, the ion exchange reaction is carried out in an inert gas atmosphere.
7. The method for preparing the catalyst according to any one of claims 4-6, characterized in that, The impregnation temperature is 20-80℃, and the time is 1-48h; preferably, impregnation is carried out under normal pressure or negative pressure conditions; preferably, the vacuum degree during impregnation is 20-700mbar; preferably, the palladium precursor is at least one of palladium chloride, palladium chloride, palladium acetate, palladium acetylacetone, and tetra(triphenylphosphine)palladium; preferably, the solvent of the palladium precursor solution is at least one of water, 1,4-dioxane, tetrahydrofuran, N,N-dimethylformamide, and dilute hydrochloric acid; preferably, the weight ratio of the intermediate to the palladium precursor is 1:0.0001-0.
05.
8. The method for preparing the catalyst according to any one of claims 4-7, characterized in that, The preparation method of metal-organic frameworks includes the following steps: hydrothermal reaction of organic ligands with metal ions to obtain metal-organic frameworks; preferably, the solvent for the hydrothermal reaction is at least one selected from N,N-dimethylformamide, water, methanol, and aqueous HF solution; preferably, the temperature of the hydrothermal reaction is 110-250℃ and the time is 4-24h; preferably, the molar ratio of organic ligands to metal ions is 1:0.5-4; preferably, after the hydrothermal reaction is completed, solid and liquid are separated, and the solid is activated in an inert gas atmosphere to obtain metal-organic frameworks; preferably, the activation temperature is 100-250℃ and the time is 1-24h.
9. The application of the catalyst as described in any one of claims 1-3, or the catalyst prepared by the method as described in any one of claims 4-8, in the selective catalytic preparation of styrene from phenylacetylene; preferably, a cesium salt is added during the selective catalytic preparation of styrene from phenylacetylene; preferably, the cesium salt is cesium carbonate.
10. A method for the highly selective preparation of styrene from phenylacetylene, characterized in that, The process includes the following steps: In a hydrogen atmosphere, phenylacetylene and substance A undergo a hydrogenation reaction to obtain styrene, wherein substance A is a catalyst or substance A is a catalyst and a cesium salt, and the catalyst is the catalyst described in any one of claims 1-3 or the catalyst prepared by the method described in any one of claims 4-8; preferably, the hydrogenation reaction is carried out at atmospheric pressure; preferably, the temperature of the hydrogenation reaction is 10-50°C and the time is 1-24 h; preferably, the molar ratio of phenylacetylene to palladium in the catalyst is 1:0.0001-0.01; preferably, when substance A is a catalyst and a cesium salt, the molar ratio of phenylacetylene to the cesium salt is 1:0.0001-0.3; preferably, the hydrogenation reaction is carried out in a solvent; preferably, the solvent is at least one selected from methanol, ethanol, tetrahydrofuran, and dimethyl sulfoxide.