A tubular polyaniline-supported copper-selenium catalyst and its preparation method and use

Abstract

The invention discloses a tubular polyaniline-loaded copper-selenium catalyst in the field of aldoxime dehydration reaction catalysts and its preparation method and use. The catalyst is prepared by photocatalytic oxidation polymerization of aniline in the presence of copper salts and polymeric carbon nitride, and then impregnated in a sodium selenide solution. The method is simple to operate and raw materials are easily available. The obtained catalyst can be used for the dehydration reaction of adipaldehyde-1,6-dioxime. Polyaniline is used to form a unique tubular structure so that its internal selenium-copper material will not be over-oxidized, thereby being able to selectively catalyze the dehydration reaction of adipaldehyde-1,6-dioxime to generate adiponitrile, without deoximation to generate adipaldehyde or further oxidation to generate adipic acid due to an oxidation reaction. The reaction can be controlled to proceed under mild conditions.

Description

Technical Field

[0001] The invention belongs to the fields of material chemistry and catalytic chemistry, and particularly relates to a catalyst for aldoxime dehydration reaction. Background Art

[0002] Metal nanoparticles have been widely used in drug development, sensors, electrode materials, catalysis, and other fields. Polyaniline-loaded metal nanoparticles are particularly useful in these fields because aniline monomers are inexpensive and have abundant industrial applications. Although aniline is toxic, polyaniline is less toxic and safer for the environment. Furthermore, compared to inorganic supports, polyaniline has a variety of applications, and its properties can be tuned by controlling the material's structure, which is a very practical technology in laboratory and industrial production. Polyaniline-loaded metal catalysts are excellent catalysts for oxidation reactions.

[0003] On the other hand, aldoxime dehydration can produce nitrile. Since aldehydes are relatively easy to obtain and the deoximation reaction is also easy to occur, this reaction has great synthetic significance. More importantly, in some industrial transformations, aldoxime dehydration is a crucial step. For example, in the technology of preparing adiponitrile by selenium-catalyzed cyclohexene ammoxidative cleavage reaction discovered by our research group before, aldoxime dehydration is the key step that determines whether the reaction can successfully produce adiponitrile (ZL201810267865.2). The use of non-petroleum raw materials to prepare adiponitrile is of great significance. Our research group raised this issue in 2022 and it was successfully selected as one of the top ten industrial technology issues of the China Association for Science and Technology. A review article was published in Science Bulletin to introduce related progress (Science Bulletin, doi:10.1360 / TB-2023-0607).

[0004] However, the aldoxime dehydration reaction is a bottleneck in this step, primarily due to the conflict between catalyst activity and reaction selectivity: insufficient catalyst activity necessitates harsh conditions such as high temperature and pressure, while high catalyst activity can lead to severe side reactions due to overoxidation. For example, our group has previously reported that, under selenium catalysis, aldoxime can undergo oxidative deoximation to produce aldehydes rather than dehydration to nitriles (Adv. Synth. Catal. 2017, 359, 1194–1201). Although selenium-catalyzed aldoxime dehydration to nitriles is a dehydration reaction, it also requires certain oxidizing conditions, allowing the selenium species to be oxidized to the selenous acid state before catalyzing the dehydration reaction (Org. Lett. 2014, 16, 1346–1349). However, when the system is highly oxidizing, deoximation occurs (Adv. Synth. Catal. 2017, 359, 1194–1201). On the other hand, when selenium catalysts are used in conjunction with metals, a synergistic effect increases the activity of the catalyst system. The principle is that the metal can catalyze the oxidation of selenium by molecular oxygen to a high-valent active species (Chin. J. Chem. 2020, 38, 1045-1051). Therefore, how to prevent the excessive oxidation of the reducing organic functional groups in the catalyst active center, thereby ensuring the smooth and efficient dehydration of the aldoxime reaction, is a technical problem that needs to be solved urgently. Summary of the Invention

[0005] The present invention aims to provide a tubular polyaniline-supported copper-selenium catalyst, which can protect the active center of the catalyst from being over-oxidized, thereby ensuring that the aldoxime dehydration reaction proceeds smoothly and efficiently.

[0006] To this end, the technical solution of the present invention is as follows: a method for preparing a tubular polyaniline-supported copper-selenium catalyst, wherein the catalyst is prepared by photocatalytically oxidatively polymerizing aniline in the presence of a copper salt and polymeric carbon nitride, and then impregnating the aniline in a sodium selenide solution; the weight ratio of the polymeric carbon nitride to the volume ratio of the aniline is 1 to 7 mg / mL; the molar ratio of the copper salt to the volume ratio of the aniline is 0.011 to 0.035 mmol / mL; and the molar concentration of the sodium selenide solution used during the impregnation is 0.05 to 0.45 mol / L.

[0007] The present invention synthesizes polyaniline through photocatalytic oxidative polymerization. Under illumination, the oxidative polymerization reaction occurs, forming a tubular polyaniline structure that simultaneously absorbs copper from the solution. Utilizing the coordination effect between aniline nitrogen and copper, copper is embedded within the inner wall of the tubular polyaniline, producing a tubular polyaniline-loaded copper material (abbreviated as Cu@PANI-L). Taking advantage of the strong coordination bond between copper and selenium, the copper sites can be "plated" with selenium by immersion in a sodium selenide solution, resulting in a tubular polyaniline-loaded copper-selenium material (abbreviated as Cu-Se@PANI-L). The copper and selenium inside the tubular polyaniline are highly active, and thus can catalyze the dehydration of adipaldehyde-1,6-dioxime to produce adiponitrile under mild conditions. During the dehydration reaction, due to the tubular polyaniline structure, the active center of the catalyst is wrapped by reducing organic functional groups, so that the selenium and copper substances inside it will not be over-oxidized, thereby selectively catalyzing the dehydration reaction of adipaldehyde-1,6-dioxime to produce adiponitrile, without deoximation to produce adipaldehyde or further oxidation to produce adipic acid due to oxidation reaction. The reaction can be controlled to proceed under mild conditions.

[0008] Furthermore, the weight ratio of the polymeric carbon nitride to the volume ratio of aniline is 4 mg / mL. The amount of polymeric carbon nitride photocatalyst used is related to the speed of the photocatalytic aniline oxidative polymerization reaction, and thus to the material morphology. Forming the catalyst into a tubular shape, as pre-designed, effectively protects the selenium-copper catalytic sites and inhibits side reactions. Extensive parallel experiments have shown that when the ratio of polymeric carbon nitride to aniline is 4 mg / mL, the prepared catalyst material exhibits the optimal tubular morphology and the best catalytic activity.

[0009] Furthermore, the copper salt used is one of copper sulfate, copper nitrate, copper chloride, or copper acetate. Preferably, the copper salt used is copper acetate. The anions in the copper salt affect its adsorption to the inner wall of the polyaniline nanotubes. Copper acetate, because it carries organic anions, is more easily absorbed into the nanotube inner wall at predetermined locations, resulting in better activity.

[0010] In the present invention, the molar ratio of the copper salt to the volume of aniline is 0.011 to 0.035 mmol / mL, and the molar ratio of copper acetate to the volume of aniline is preferably 0.023 mmol / mL. At the above ratio, the amount of copper salt is sufficient. Further increasing the copper salt will cause the copper to stack into agglomerates, which on the one hand causes waste of copper, and on the other hand, the binding force between the upper copper and the inner copper is far less strong than the binding force between the bottom copper and the polyaniline nitrogen through coordination bonding, resulting in the upper copper easily falling off during the reaction along with its coordinated selenium, which reduces the catalyst activity.

[0011] Furthermore, the sodium selenide solution used during impregnation preferably has a concentration of 0.25 mol / L. This allows for sufficient coverage of the copper on the inner wall of the tubular polyaniline without causing overly high selenium concentrations to cause overlaying. The catalyst prepared under these conditions exhibits optimal activity.

[0012] The tubular polyaniline-supported copper-selenium catalyst obtained by the invention can be used for aldoxime dehydration reaction, preferably for adipaldehyde-1,6-dioxime dehydration reaction, and the ratio of the weight amount of the catalyst to the molar amount of adipaldehyde-1,6-dioxime is 1.5-3 g / mol. BRIEF DESCRIPTION OF THE DRAWINGS

[0013] Figure 1 This is the infrared spectrum of the prepared Cu@PANI-L.

[0014] Figure 2 Nitrogen adsorption-desorption curve of the prepared Cu@PANI-L.

[0015] Figure 3 This is the pore size distribution diagram of the prepared Cu@PANI-L.

[0016] Figure 4 This is the scanning electron microscopy image of the prepared Cu@PANI-L.

[0017] Figure 5 Transmission electron microscopy image of the prepared Cu@PANI-L.

[0018] Figure 6 High-resolution transmission electron microscopy image of the prepared Cu@PANI-L.

[0019] Figure 7 This is the electron diffraction pattern of the prepared Cu@PANI-L.

[0020] Figure 8 Energy dispersive X-ray spectroscopy (EDX) of the prepared Cu@PANI-L.

[0021] Figure 9 This is the X-ray photoelectron spectroscopy (XPS) diagram of Cu in Cu@PANI-L. DETAILED DESCRIPTION

[0022] Example 1:

[0023] 1. Preparation of Cu-Se@PANI-L material:

[0024] Synthesis of polymer carbon nitride (PCN): Take 20g of melamine, place it in a crucible, put it in a tube furnace, pass N2, and heat it to 550℃ at 2℃ / min. Then, maintain this temperature for 4h, and after cooling, 5.2g of original crude PCN material can be prepared. Subsequently, take the above 5.2g of original crude PCN material, add 20mL of deionized water, mix well, spread the material on the surface of a glass culture dish, and put it in an oven. Set the temperature to 60℃, dry it for 6h, and then take it out. After cooling, grind the obtained material into powder and pour it into the crucible. Put it into the tube furnace again, pass N2, and heat it at a rate of 2℃ / min. After it reaches 550℃, burn it at this temperature for 4h. After the material cools, take it out and grind it evenly to obtain 3.1g of PCN material, which is stored for later use.

[0025] Synthesis of Cu@PANI-L: 5 mL of aniline was dissolved in 50 mL of 1 mol / L hydrochloric acid. Simultaneously, 22.7 mg of copper acetate monohydrate (0.113 mmol, with a copper acetate to aniline ratio of 0.023 mmol / mL) was dissolved in another 50 mL of 1 mol / L hydrochloric acid. The two solutions were mixed, and 20 mg of the PCN material synthesized above was added. The mixture was irradiated with a 455 nm light source (10 W) at room temperature (25°C) for 24 hours, resulting in the formation of a black precipitate. After neutralization with a 1 mol / L aqueous sodium hydroxide solution, the precipitate was separated by centrifugation and washed with deionized water. The mixture was vacuum dried in a 65°C vacuum oven for 2 hours to obtain Cu@PANI-L.

[0026] Synthesis of Sodium Hydroselenide (NaHSe): 30 mmol of NaBH4 and 25 mmol of selenium powder were placed in a 250 mL three-necked round-bottom flask equipped with a spherical condenser. After cooling in an ice-water bath, the air was displaced with nitrogen and, under nitrogen protection, 40 mL of anhydrous ethanol was added. The reaction was vigorous, with bubbling. The released gas was piped out of the top of the condenser and vented to the outside (this gas is hydrogen; for large-scale production, combustion can be used to remove the tail gas). After the vigorous reaction, the ice-water bath was removed and the reaction was allowed to proceed at room temperature until colorless. The solution was then heated under reflux for 0.5 h to decompose the excess sodium borohydride, yielding a nearly colorless, transparent solution of sodium hydroselenide in ethanol. This solution was transferred to a 50 mL volumetric flask and brought to volume to a 0.5 mol / L sodium hydroselenide solution. Various sodium hydroselenide concentrations can be prepared by dilution for experimental purposes. A 0.25 mol / L sodium hydroselenide solution can be obtained by diluting the solution to half with ethanol.

[0027] Cu-Se@PANI-L Synthesis: Take 1 g of the Cu@PANI-L synthesized above and immerse it in 10 mL of 0.25 mol / L sodium selenide solution for 12 hours. Centrifuge and wash the precipitate with deionized water. Dry in a vacuum oven at 65°C for 2 hours to obtain Cu-Se@PANI-L.

[0028] 2. Material Characterization

[0029] The Cu@PANI-L prepared in Example 1 was subjected to infrared testing to obtain the Fourier transform infrared spectrum (FT-IR) of Cu@PANI-L. Figure 1 As shown, 2926cm -1 The peak at 1582cm reflects the stretching vibration of NH. -1 and 1222cm -1 The absorption peaks on the left and right are caused by the C=C stretching vibration of the quinone ring and the benzene ring, which are the basic molecular units of polyaniline. -1 The absorption peak at corresponds to the out-of-plane bending vibration of the monosubstituted CH in the benzene structure, and the peak is very strong and obvious, indicating that the polymerization of aniline is mainly para-polymerization.

[0030] The surface structure of the material can be detected from the N2 adsorption / desorption experimental results of Cu@PANI-L, such as Figure 2 As shown. Under high pressure, the material shows a type III isotherm, indicating that the material has strong micro-porosity. The calculated specific surface area of ​​Cu@PANI-L is 83.45m 2 / g, pore volume is 0.238cm 3 / g. The pore size distribution confirmed that the main mesopores were 31.04 nm, such as Figure 3 This unique porous structure, derived from controlled photooxidative synthesis, produces uniform polyaniline nanofibers containing stable mesopores. The regulated mesostructure provides a high density of active pores, which can accommodate substrate molecules through pore filling, thereby improving substrate adsorption capacity.

[0031] Figure 4 Scanning electron microscopy (SEM) images show that Cu@PANI-L is formed by an ordered fiber structure. The dense fiber structure contains a large number of pores, which facilitate the shuttle of substrate molecules and enable the loaded metal active centers to contact the substrate as much as possible, thereby improving the catalytic activity of the material.

[0032] Figure 5 Transmission electron microscopy (TEM) studies have shown that the Cu@PANI-L fibers are hollow and contain polyaniline channels with a diameter of about 30–40 nm. Figure 3The results obtained from the mesopore size distribution diagram are consistent with those obtained from the pore size distribution diagram.

[0033] exist Figure 6 No crystalline particles were observed in the high-resolution transmission electron microscopy (HR-TEM) image shown, indicating that copper metal exists in an amorphous state in Cu@PANI-L.

[0034] exist Figure 7 This is further confirmed by the electron diffraction pattern shown, which shows that copper metal exists in an amorphous state in Cu@PANI-L.

[0035] Figure 8 Energy dispersive X-ray spectroscopy (EDX) shown confirms the successful loading of copper, while carbon and nitrogen on the polyaniline were also observed.

[0036] exist Figure 9 The valence information of metallic copper in Cu@PANI-L was analyzed by X-ray photoelectron spectroscopy (XPS). From the Cu2p spectrum, it can be observed that there are Cu 2+ and Cu 1+ Two valence states. Among them, Cu 1+ The emergence of polyaniline is due to the reduction and photocatalytic reduction process. Through photocatalytic preparation, more Cu 1+ , Cu 1+ The increase in content also helps to improve the catalytic activity of the subsequently prepared Cu-Se / PANI-L.

[0037] 3. Application:

[0038] The Cu-Se@PANI-L material prepared in Example 1 above was applied to the dehydration reaction of adipaldehyde-1,6-dioxime (Hexanedial, 1,6-dioxime, CAS Registry Number: 40703-03-5) to generate adiponitrile.

[0039] Adipaldehyde-1,6-dioxime can be prepared by condensing adipaldehyde with hydroxylamine hydrochloride in the presence of a base. The specific method is as follows: In a 250 mL round-bottom flask, add 0.1 mol of adipaldehyde, 0.22 mol of sodium hydroxide, 0.22 mol of hydroxylamine hydrochloride, and a magnetic stirrer. Then, add 100 mL of water. Stir at 50°C for 3 hours. Concentrate the solution to 20 mL, and filter out the precipitated sodium chloride. Evaporate the solvent from the clear solution to obtain crude adipaldehyde-1,6-dioxime. This crude product is dissolved in 40 mL of anhydrous ethanol and heated to 60°C. Filter while hot to remove insoluble matter. Concentrate the solution to 10 mL and cool in an ice-water bath. Crystals precipitate. Filter and dry the crystals to yield 8.1 g of adipaldehyde-1,6-dioxime, a yield of 56%. The melting point was determined to be 177.2–178.3°C, which was consistent with the literature report (178°C, J. Org. Chem. 1962, 27, 2918).

[0040] In a 25 mL three-necked flask equipped with a reflux condenser, add 5 mmol of adipaldehyde-1,6-dioxime and 10 mL of acetonitrile. Then add 10 mg of Cu-Se@PANI-L. Insert an air tube so that it is below the liquid surface. Blow air (flow rate 1.0 cm 3 / S), utilize air flow to promote material mixing evenly, and make the catalyst uniformly suspended in the reaction solution.Under the condition of keeping air bubbling, the system is heated at 50 ℃ for 12 hours.After cooling, the reaction solution is transferred to a 100mL volumetric flask containing 0.5mmol biphenyl (internal standard) and fixed to volume with acetonitrile.Gas spectrum detection learns that this reaction produces adiponitrile with a gas spectrum yield of 92%.

[0041] Example 2:

[0042] Other conditions were the same as in Example 1, except that the amount of polymeric carbon nitride added during the Cu@PANI-L preparation stage was varied. The various Cu-Se@PANI-L catalysts prepared were then subjected to the dehydration reaction of adipaldehyde-1,6-dioxime, and the resulting adiponitrile gas spectrum yield was measured. The experimental results are shown in Table 1. Table 1. Comparison of the performance of Cu-Se@PANI-L materials prepared using different amounts of polymeric carbon nitride during the Cu@PANI-L preparation stage.

[0043]

[0044] From the above results, it can be seen that the best effect is achieved when the ratio of polymer carbon nitride dosage (mg) to aniline dosage (mL) is 4 mg / mL. The yield using Cu-Se@PANI-L catalysis is the highest, reaching 92%. When the carbon nitride dosage is too low or too high, the yield using Cu-Se@PANI-L catalysis is not ideal.

[0045] Example 3:

[0046] Other conditions were the same as in Example 1, with the exception of the type of copper salt used during the Cu@PANI-L preparation phase. The various Cu-Se@PANI-L catalysts prepared were then subjected to the dehydration reaction of adipaldehyde-1,6-dioxime, and the resulting adiponitrile yields were measured by gas chromatography. The experimental results are shown in Table 2.

[0047] Table 2 Effect of the type of copper salt used in the preparation of Cu@PANI-L on the properties of the final prepared Cu-Se@PANI-L:

[0048] serial number Types of copper salts Adiponitrile gas spectrum yield (%) 1 copper sulfate 28 2 Copper nitrate 42 3 Copper chloride 53 4 Copper acetate (Example 1) 92

[0049] The above results show that when copper acetate is used as the copper salt, the catalytic yield of the prepared Cu-Se@PANI-L is the highest, reaching 92%. Increasing the copper salt with other types does not improve the catalyst activity, but instead reduces the reaction yield.

[0050] Example 4:

[0051] Other conditions were the same as in Example 1, except that the molar ratio of copper salt to aniline was varied during the Cu@PANI-L preparation phase. Each of the prepared Cu-Se@PANI-L catalysts was subjected to the dehydration reaction of adipaldehyde-1,6-dioxime, and the resulting adiponitrile yield was measured by gas chromatography. The experimental results are shown in Table 3.

[0052] Table 3 Effect of the molar ratio of copper salt to aniline on the properties of the prepared Cu-Se@PANI-L material during the preparation stage of Cu@PANI-L:

[0053]

[0054]

[0055] The above results show that when the molar ratio of copper salt to aniline is 0.023 mmol / mL, the yield of Cu-Se@PANI-L catalysis is the highest, reaching 92%. Further increasing the amount of copper salt does not improve the catalyst activity.

[0056] Example 5:

[0057] Other conditions were the same as in Example 1. The effects of different sodium hydride selenide concentrations on material properties during the Cu@PANI-L impregnation phase were investigated. The various Cu-Se@PANI-L catalysts prepared were subjected to the dehydration reaction of adipaldehyde-1,6-dioxime, and the resulting adiponitrile yields were measured by gas chromatography. The experimental results are shown in Table 4.

[0058] Table 4 Effect of different sodium selenide concentrations on the properties of the prepared Cu-Se@PANI-L during the Cu@PANI-L impregnation stage:

[0059] serial number Sodium selenide solution concentration (mol / L) Adiponitrile gas spectrum yield (%) 1 0.05 36 2 0.10 62 3 0.15 77 4 0.20 88 5 0.25 (Example 1) 92 6 0.30 90 7 0.35 87 8 0.40 82 9 0.45 76

[0060] As can be seen from the above table, when the concentration of sodium selenide solution is 0.25 mol / L, the yield of Cu-Se@PANI-L catalysis is the highest, reaching 92%. When the concentration of sodium selenide solution increases, the catalytic activity of the catalyst cannot be improved, and the reaction yield decreases.

[0061] Example 6:

[0062] Based on the dehydration reaction of adipaldehyde-1,6-dioxime in Example 1, only the amount of catalyst was changed. The experimental results are shown in Table 5:

[0063]

[0064]

[0065] The results show that the ratio of the weight amount of the catalyst to the molar amount of adipaldehyde-1,6-dioxime can be selected as: 1.5-3 g / mol, and the optimal ratio is 2 g / mol.

[0066] The present invention is not limited to the above-mentioned embodiments. On the basis of the technical solutions disclosed in the present invention, those skilled in the art can make some substitutions and modifications to some of the technical features therein according to the disclosed technical content without creative labor, and these substitutions and modifications are all within the protection scope of the present invention.

Claims

1. A method for preparing a tubular polyaniline-supported copper-selenium catalyst, characterized in that: The catalyst is prepared by photocatalytically oxidizing and polymerizing aniline in the presence of a copper salt and polymeric carbon nitride, and then impregnating it in a sodium selenide solution. The weight ratio of the polymeric carbon nitride to the volume ratio of aniline is 1-7 mg / mL; the molar ratio of the copper salt to the volume ratio of aniline is 0.011-0.035 mmol / mL; and the molar concentration of the sodium selenide solution used during the impregnation is 0.05-0.45 mol / L.

2. The method for preparing a tubular polyaniline-supported copper-selenium catalyst according to claim 1, wherein: The weight ratio of the polymer carbon nitride to the volume ratio of aniline is 4 mg / mL.

3. The method for preparing a tubular polyaniline-supported copper-selenium catalyst according to claim 1, wherein: The copper salt used is one of copper sulfate, copper nitrate, copper chloride or copper acetate.

4. The method for preparing a tubular polyaniline-supported copper-selenium catalyst according to claim 1, wherein: The copper salt used was copper acetate.

5. The method for preparing a tubular polyaniline-supported copper-selenium catalyst according to claim 4, wherein: The molar ratio of copper acetate to aniline volume ratio is 0.023 mmol / mL.

6. The method for preparing a tubular polyaniline-supported copper-selenium catalyst according to claim 1, wherein: The concentration of the sodium selenide solution used during the immersion was 0.25 mol / L.

7. A tubular polyaniline-supported copper-selenium catalyst, characterized in that: Prepared according to the method according to any one of claims 1 to 6.

8. The use of a tubular polyaniline-supported copper-selenium catalyst according to claim 7, characterized in that: For the dehydration reaction of adipaldehyde-1,6-dioxime, the ratio of the catalyst weight to the molar amount of adipaldehyde-1,6-dioxime is: 1.5~3g / mol.

Images