CN113231103B - Cobalt Schiff base catalyst grafted by imine bond, preparation method and application thereof - Google Patents

Cobalt Schiff base catalyst grafted by imine bond, preparation method and application thereof Download PDF

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CN113231103B
CN113231103B CN202110586057.4A CN202110586057A CN113231103B CN 113231103 B CN113231103 B CN 113231103B CN 202110586057 A CN202110586057 A CN 202110586057A CN 113231103 B CN113231103 B CN 113231103B
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石国军
梁雨欣
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Abstract

Cobalt Schiff base catalyst grafted by imine bond, preparation method and application thereof, relating to the preparation technology and application field of cobalt Schiff base catalyst. Modification of carrier SiO with gamma-aminopropyl triethoxysilane 2 Surface to obtain surface ammoniated carrier SiO 2 APTES; then salicylaldehyde or derivatives thereof, cobalt (II) acetylacetonate and a surface ammoniation carrier SiO 2 APTES is dissolved in a solvent, and grafted cobalt Schiff base catalyst is prepared by imine covalent bond grafting, so that the grafted cobalt Schiff base catalyst with the grafting concentration of cobalt Schiff base complex of 0.09-0.16 mmol/g can be applied to solvent-free molecular oxygen oxidation reaction of toluene, active components of the catalyst are not lost in the catalytic reaction, the toluene oxidation activity is high, the stability is good, and the catalyst can be recycled.

Description

Cobalt Schiff base catalyst grafted by imine bond, preparation method and application thereof
Technical Field
The invention relates to a preparation technology and application field of cobalt Schiff base catalyst.
Background
Toluene is a typical aromatic compound, and catalytic oxidation of toluene plays a very important role in processing aromatic compounds, and main products of benzaldehyde, benzyl alcohol and benzoic acid are widely applied in industry. Benzaldehyde has received attention from the pharmaceutical, fragrance, pesticide industries and the like, and world-wide annual demand has exceeded 9 ten thousand tons (Catalysis Science & Technology,2019, volume 9, pages 4441-4450). Benzoic alcohol and benzoic acid are also important chemical raw materials, are commonly used for synthesis of fragrances, dyes, preservatives and the like, and have considerable market prospects (RSC Advance,2016, volume 6, pages 68170-6877). Toluene is difficult to oxidize in homologs, and thus, research on this reaction is of great instructive significance for the oxidation of its homologs and even the oxidation of other hydrocarbons. Liquid phase catalytic oxidation of toluene usually employs transition metal salts of cobalt, manganese, etc. as catalysts (Catalysis Letters,2014, volume 144, pages 333-339). However, the catalyst is difficult to separate from the reactants in a homogeneous system, which results in difficult recovery of the catalyst and poor recyclability. Research has shown that heterogeneous catalyst recovery and reuse can be achieved by immobilizing the homogeneous catalyst (Chemistry Select,2016, vol.1, 6797-6804). Grafting is also a common means of immobilization, simply by covalent bonding of the carrier to the active ingredient. The catalyst immobilized by the method has better dispersity of active components, more uniform distribution and relatively stable performance (Catalysis Today,2013, volume 204, pages 114-124). Schiff base compounds refer to organic compounds containing imine or azomethine (-RC=N) structures formed by substituting an imine for carbonyl groups of aldehydes or ketones. The Schiff base and the complex thereof have stronger coordination capability because N atoms in the molecular structure have lone pair electrons, and the special structure enables the Schiff base and the complex to be widely researched and applied in the field of catalysis. In many catalytic conversions, schiff base structures are able to stabilize different metals and influence the oxidation state of the metals, thus modulating the catalytic properties of the central atom (Chemical Society Reviews,2004, volume 33, pages 410-421). Salicylaldehyde derivatives are the most useful materials for preparing schiff base complexes, the structure of which is capable of affecting electron cloud density around metals. The charge density is closely related to the degree of molecular oxygen activation, that is, the reactivity can be affected by changing the structure of the salicylaldehyde derivative.
Disclosure of Invention
The invention aims to provide a cobalt Schiff base catalyst grafted by an imine bond, which can exist stably under the reaction condition, has good catalytic effect and can be recycled repeatedly.
The invention comprises SiO 2 Support and graft on SiO 2 Cobalt Schiff base complex on carrier, which is grafted on SiO through imine bond 2 And on the carrier, the grafting concentration of the cobalt Schiff base complex is 0.09-0.16 mmol/g.
It is another object of the present invention to provide a process for the preparation of the above grafted cobalt schiff base catalyst.
The invention comprises the following steps:
1) Modification of carrier SiO with gamma-aminopropyl triethoxysilane (APTES) 2 Surface to obtain surface ammoniated carrier SiO 2 -APTES；
2) Salicylaldehyde or derivatives thereof, cobalt (II) acetylacetonate and a surface ammoniation carrier SiO 2 APTES is dissolved in solvent, and grafted cobalt Schiff base is prepared through imine covalent bond graftingA catalyst.
Further, the surface ammoniated carrier SiO 2 The preparation method of APTES comprises the following steps:
SiO is firstly put into 2 And gamma-aminopropyl triethoxysilane APTES is dissolved in a dichloromethane solvent to obtain a reaction solution;
then, the reaction solution is refluxed for 24 h at 44 ℃ to react, so as to prepare suspension;
finally filtering and separating the suspension to obtain solid powder, washing the solid powder by using absolute ethyl alcohol, and drying the solid powder in a vacuum drying oven to obtain the surface ammoniated carrier SiO 2 -APTES。
The SiO is 2 And gamma-aminopropyl triethoxysilane in a feed molar ratio of 5:1, said SiO 2 The feed ratio with the dichloromethane solvent was 100 mmol:100 mL.
The salicylaldehyde or the derivative thereof in the step 2) is one of salicylaldehyde, o-hydroxyacetophenone, 4- (diethylamino) salicylaldehyde or 5-nitrosalicylaldehyde.
Step 2) comprises the steps of:
firstly, salicylaldehyde or derivatives thereof, cobalt (II) acetylacetonate and a surface ammoniation carrier SiO 2 Adding APTES into dichloromethane to obtain a reaction solution;
reflux-reacting the reaction solution at 44 ℃ for 24 h to prepare suspension;
and finally, filtering and separating the suspension to obtain solid powder, washing the solid powder with dichloromethane, and drying the solid powder in a vacuum drying oven to obtain the grafted cobalt Schiff base catalyst.
The surface ammoniation carrier SiO 2 The ratio of APTES mass to solvent feed volume is 1.6 g:100 mL, salicylaldehyde derivative to surface ammoniated carrier SiO 2 APTES is fed in a ratio of 5mmol to 1.6. 1.6 g and salicylaldehyde ligand to cobalt (II) acetylacetonate in a molar ratio of 5:0.32.
The catalyst which is most favorable for the solvent-free molecular oxygen selective oxidation reaction of toluene is preferably selected by modulating the substituent on the structure of the salicylaldehyde derivative.
It is a further object of the present invention to provide the use of the catalyst.
The grafted cobalt Schiff base catalyst is applied to the solvent-free molecular oxygen oxidation reaction of toluene as a recoverable catalyst.
The temperature of the solvent-free molecular oxygen oxidation reaction is 70-120 ℃, the pressure is 3MPa, the molar ratio between toluene and the catalyst is 1600-3400, and the reaction time is 0-5 h.
The synthesis principle of the invention: firstly, modifying SiO by using gamma-aminopropyl triethoxy silane APTES 2 Surface of SiO 2 Surface ammoniation to generate carrier SiO 2 APTES (APTES) for facilitating the next grafting of salicylaldehyde derivatives on carrier SiO (SiO) 2 On APTES, finally, metal cobalt coordinates with grafted salicylaldehyde or derivative thereof, and gamma-aminopropyl triethoxysilane APTES modifies SiO 2 The reaction is shown in the following formula:
Figure 818136DEST_PATH_IMAGE001
then the salicylaldehyde derivative is grafted on a carrier SiO through imine bond 2 On APTES, grafted salicylaldehyde derivatives are formed. Then, the metallic cobalt coordinates with the metallic cobalt to form a grafted cobalt Schiff base catalyst. The salicylaldehyde derivative comprises salicylaldehyde, O-hydroxyacetophenone, 4- (diethylamino) salicylaldehyde or 5-nitrosalicylaldehyde, all of which have carbonyl (-C=O), and are easy to aminate with surface of carrier SiO 2 APTES is dehydrated to prepare a grafted Schiff base complex, then cobalt (II) acetylacetonate is added, and the cobalt and the grafted Schiff base complex are coordinated to prepare a cobalt Schiff base catalyst, wherein the reaction is shown in the following formula (taking o-hydroxyacetophenone as a ligand for example):
Figure 557553DEST_PATH_IMAGE002
the prepared cobalt Schiff base catalyst grafted by the imine bond is subjected to solid-liquid separation after the selective oxidation reaction of the catalyst toluene without solvent molecular oxygen, the solid is obtained, the catalyst is pulped and washed by ethanol solvent, and the catalyst is placed into a vacuum drying oven for drying, so that the cobalt Schiff base catalyst grafted by the imine bond is obtained, and the cobalt Schiff base catalyst grafted by the imine bond can be repeatedly used for a plurality of times.
Compared with the prior art, the invention has the remarkable advantages that: 1. the catalyst has no loss of active components in the catalytic reaction and good stability; 2. the catalyst can be recycled, and can be used as a recyclable catalyst in the solvent-free molecular oxygen selective oxidation reaction of toluene; 3. the catalyst of the structure of salicylaldehyde derivative which is most favorable for the reaction is selected.
Drawings
FIG. 1 is a synthetic route diagram of example 1.
FIG. 2 is SiO in example 1 2 APTES and products, siO 2 Is a spectrum of infrared light of (a) is obtained.
FIG. 3 is SiO in example 1 2 APTES and products, siO 2 Ultraviolet-visible diffuse reflectance spectrum of (c).
FIG. 4 is a plot of the product of example 1 13 C solid nuclear magnetic spectrum.
FIG. 5 is Co (acac) 2 Co 2p narrow spectrum of (c).
FIG. 6 is SiO 2 Co 2p XPS narrow spectrum of APTES-HAP-Co.
FIG. 7 is SiO 2 -N1 s narrow spectrum of APTES-HAP-Co.
FIG. 8 is a Co 2p XPS narrow spectrum of the product of example 1.
FIG. 9 is a narrow spectrum of N1 s XPS of the product of example 1.
FIG. 10 is SiO in example 2 2 APTES and products, siO 2 Is a spectrum of infrared light of (a) is obtained.
FIG. 11 is SiO in example 3 2 APTES and products, siO 2 Is a spectrum of infrared light of (a) is obtained.
FIG. 12 is SiO in example 4 2 APTES and products, siO 2 Is a spectrum of infrared light of (a) is obtained.
Detailed Description
Example 1
The synthetic route of this example is shown in FIG. 1:
(1) Modification of SiO using gamma-aminopropyl triethoxysilane APTES 2 ：
6 g of SiO was charged into a 250 mL single neck round bottom flask 2 20 mmol of gamma-aminopropyl triethoxysilane APTES and 100 mL dichloromethane CH 2 Cl 2 Transferring the flask into oil bath, setting up reflux unit, stirring, heating to 44deg.C in oil bath, maintaining constant temperature, reacting, refluxing for 24 h, stopping heating and stirring, cooling to room temperature, removing reflux unit, filtering the reaction solution, pulping and washing the filter cake with 60 mL anhydrous ethanol for three times, and drying the obtained white solid powder in vacuum drying oven at 50deg.C for 24 h to obtain SiO 2 -APTES。
(2) The operation is a one-step preparation method, and the o-hydroxyacetophenone and SiO 2 Primary amine on APTES carrier reacts to generate grafted o-hydroxyacetophenone, and cobalt (II) acetylacetonate is coordinated with the o-hydroxyacetophenone to prepare a catalyst SiO 2 APTES-HAP-Co: into a 250 mL round bottom flask was added 1.6 g of the SiO obtained in the first step 2 APTES, 5mmol of o-hydroxyacetophenone, 0.32 mmol of cobalt (II) acetylacetonate and 100 mL methylene dichloride, transferring the flask into an oil bath, building a reflux device, stirring, heating the oil bath to 44 ℃ and keeping constant temperature, reacting, refluxing for 24 h, stopping heating and stirring, cooling to room temperature, removing the reflux device, filtering the reaction liquid, pulping a filter cake with 60 mL methylene dichloride, washing a dark field, putting the obtained green powder into a vacuum drying box at 50 ℃ for drying for 24 h later use, and obtaining the target catalyst SiO2-APTES-HAP-Co, wherein the grafting concentration of cobalt is 0.15mmol/g.
As shown in FIG. 2, siO 2 At 3683 cm –1 The absorption peak at the position is attributed to the surface hydroxyl stretching vibration peak at 1091 and 1091 cm –1 And 805 cm –1 、461 cm –1 Asymmetric stretching vibration peak, symmetric stretching vibration peak and bending vibration of Si-O respectively, at 958 cm –1 The absorption peak at this point is assigned to the SiO-H bending vibration peak. As can be seen by comparison, siO 2 APTES at 1530 cm –1 Flexural vibration at N-H bond, indicating NH 2 The presence of a group. SiO (SiO) 2 APTES at 2892, 2938 cm –1 1470 and 1470 cm -1 The peaks appearing are due to symmetrical stretching vibration peaks, asymmetrical stretching vibration peaks and bending vibration peaks of saturated C-H bonds, while 3683 cm –1 The absorption peak at the silicon hydroxyl group becomes weak, indicating that APTES was successfully grafted to SiO 2 A surface. SiO (SiO) 2 APTES-HAP-Co at 1610 cm –1 Characteristic absorption peak of c=n bond, 556 cm appears -1 The weak and sharp absorption peak that occurs is due to the characteristic absorption peak of Co-O1550 cm -1 Corresponds to the framework vibration of benzene rings, and 2892, 2938 and 2938 cm –1 1470 and 1470 cm -1 The stretching vibration peak of saturated C-H bond still exists, which indicates that the Schiff base structure is successfully formed.
As shown in FIG. 3, the carrier SiO 2 In the wavelength range of 200-800 nm, there is only one absorption peak at 220 nm. SiO (SiO) 2 The absorption peak of APTES at 220 nm is lost, probably due to SiO 2 The structure and the surface state of the (B) are changed, which shows that the silane coupling agent APTES successfully modifies SiO 2 。SiO 2 The absorption peaks of APTES-HAP-Co at 230 nm and 310 nm are caused by pi-pi and N-pi transitions, respectively, indicating the presence of c=n bonds. 390 nm is a typical metal-ligand charge transfer (MLCT) in which 540, 580 and 640 nm are related to the d-d transitions of complexes of metallic cobalt with amino groups, demonstrating that cobalt schiff bases have been successfully synthesized.
As shown in FIG. 4, the aliphatic regions 10.7, 22.1, 43.3 ppm correspond to the corresponding 3 carbon atoms on the aminopropyl group in the structure of the silane coupling agent gamma-aminopropyl triethoxysilane, respectively. Immobilizing metal Schiff base complex on carrier SiO 2 At 58.6 ppm of methylene carbon attributed to ethoxy groups, the appearance of this peak indicates that the ethoxy groups in the silane coupling agent are present in combination with SiO 2 The grafting process is not completely hydrolyzed to form Si-O-Si. Aromatic carbon atoms on the ligand were observed at 110-150 ppm, 165.3 ppm corresponding to carbon atoms on the imine bond (c=n) on the schiff base. The prepared cobalt Schiff base catalyst SiO is further prepared by identifying the peak on the solid nuclear magnetic spectrum 2 The structure of APTES-HAP-Co was confirmed and the signal of the imine bond of the characteristic structure and the remaining functions of the catalyst structure were foundThe signal of the carbon atoms on the clusters demonstrates that cobalt schiff base catalysts were successfully prepared.
As shown in FIGS. 5, 6 and 7, siO in FIG. 6 2 Co 2p XPS narrow spectrum findings of APTES-HAP-Co, co 2p appeared at 780.9 eV 3/2 Energy spectrum peak, and there was a distinct satellite peak at 784.7 eV. In Co 2p 3/2 Co 2p appears at 796.4 eV of 15.5 eV from energy spectrum peak 1/2 Energy spectrum peaks, and the occurrence of satellite peaks at 802.2 eV, indicate the catalyst SiO 2 Co in APTES-HAP-Co 2+ Dominant. FIG. 5 is Co (acac) 2 Co 2p narrow spectrum of (2) is compared with Co 2p narrow spectrum in a catalyst which forms cobalt Schiff base after coordination, co 2p after immobilization 3/2 The chemical shift is increased by 0.3 eV due to the cobalt acetylacetonate and SiO immobilization 2 The coordination environment of cobalt in the catalyst is changed, and it is presumed that, because a signal of N1 s is observed in the whole spectrum of the catalyst, from structural analysis of solid nuclear magnetism, two oxygen atoms in four oxygen atoms around the central cobalt atom structure are replaced by N atoms, the electronegativity of the N atoms is weaker than that of the oxygen atoms, and in the catalyst structure, the electron donating ability is lower than that of the oxygen atoms, so that the electron cloud density around cobalt is reduced, and the binding energy of cobalt is improved. FIG. 7 is SiO 2 N1 s narrow spectrum of APTES-HAP-Co, peak of spectrum at 401.6 eV corresponds to SiO 2 The two peaks at 399.9 eV and 399.0 eV of the N element in the N-H bond on APTES, ascribed to c=nh and the N element in the imine (c=n) structure on the catalyst on the cobalt schiff base formed, demonstrate successful grafting of the o-hydroxyacetophenone with the aminopropyl group.
SiO 2 Application of APTES-HAP-Co in toluene solvent-free molecular oxygen catalytic oxidation reaction: adding 80 mmol toluene, 2 mmol NHPI and 0.025 mmol catalyst into a reaction kettle, checking the air tightness of the reaction kettle device by using 2.0MPa high-purity oxygen, keeping a pressure gauge stable, using 2.0MPa high-purity oxygen to replace air in the reaction kettle for 5 times if no air leakage phenomenon is determined, transferring the reaction kettle into a heater provided with a magnetic stirring device after replacement, starting stirring, raising the temperature of the reaction kettle to 100 ℃, reacting for 1 h under 500 r/min magnetic stirring, and cooling the reaction kettle to a roomAnd (3) carrying out temperature and centrifugal separation, wherein the obtained liquid phase is a product mixture, analyzing the liquid mixture after reaction, and obtaining the conversion rate and selectivity of toluene, wherein the catalytic reaction result is shown in Table 1.
SiO 2 Recovery and regeneration of APTES-HAP-Co catalyst: pulping and washing the recovered catalyst with absolute ethanol for three times, wherein the concentration of the catalyst in the ethanol is about 0.004 g/mL, and drying the filtered solid sample in a vacuum drying oven at 50 ℃ for 24 h to obtain the regenerated immobilized cobalt Schiff base catalyst SiO 2 -APTES-HAP-Co-R1。
Example 2
The difference between this embodiment and embodiment 1 is that: in step 2, salicylaldehyde and SiO are used 2 Primary amine reaction on APTES carrier, followed by Co (acac) 2 Coordination is carried out to obtain SiO 2 APTES-SA-Co, wherein the grafting concentration of cobalt was 0.157 mmol/g.
As can be seen from FIG. 10, siO 2 At 3683 cm –1 The absorption peak at the position is attributed to the O-H stretching vibration peak in the surface hydroxyl group, and the absorption peak at 1091 and 1091 cm –1 And 805 cm –1 、461 cm –1 958 and 958 cm –1 Are all SiO 2 Is a characteristic peak of (2). Intermediate SiO 2 APTES compared to the support SiO 2 At 1530 cm –1 The signal at this point is attributed to bending vibrations of the N-H bond, as in 2892, 2938 cm –1 1470 and 1470 cm -1 The peaks appearing are due to symmetrical stretching vibration peaks, asymmetrical stretching vibration peaks and bending vibration peaks of saturated C-H bonds, indicating SiO 2 Is successfully ammonia functionalized. Catalyst SiO 2 APTES-SA-Co at 1604 cm –1 A characteristic absorption peak of c=n bond occurs, 570 cm -1 The absorption peak at this point was attributed to the characteristic absorption peak of Co-O, indicating successful formation of the Schiff base structure.
SiO 2 Application of APTES-SA-Co in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol toluene, 2 mmol NHPI and 0.025 mmol catalyst are added into a reaction kettle, the air tightness of the reaction kettle device is checked by using 2.0MPa high-purity oxygen, a pressure gauge is kept stable, the air in the reaction kettle is replaced by using 2.0MPa high-purity oxygen for 5 times when no air leakage phenomenon is determined, and after the replacement is finished, the reaction is carried outThe reaction kettle is moved into a heater equipped with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, after the reaction kettle is magnetically stirred at 500 r/min for reaction for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the liquid mixture after reaction is analyzed, the conversion rate and selectivity of toluene are obtained, and the catalytic reaction result is shown in Table 1.
SiO 2 Recovery and regeneration of APTES-SA-Co catalyst: pulping and washing the recovered catalyst with absolute ethanol for three times, wherein the concentration of the catalyst in the ethanol is about 0.004 g/mL, and drying the filtered solid sample in a vacuum drying oven at 50 ℃ for 24 h to obtain the regenerated immobilized cobalt Schiff base catalyst SiO 2 -APTES-SA-Co-R1。
Example 3
The difference between this embodiment and embodiment 1 is that: the salicylaldehyde derivative used in the step 2 is 4- (diethylamino) salicylaldehyde, 4- (diethylamino) salicylaldehyde and SiO 2 Primary amine reaction on APTES carrier, followed by Co (acac) 2 Coordination is carried out to obtain SiO 2 APTES-EASA-Co, wherein the grafting concentration of cobalt was 0.144 mmol/g.
From FIG. 11, it can be seen that SiO 2 At 3683 cm –1 The absorption peak at the position is attributed to the O-H stretching vibration peak in the surface hydroxyl group, and the absorption peak at 1091 and 1091 cm –1 And 805 cm –1 、461 cm –1 958 and 958 cm –1 Are all SiO 2 Is a characteristic peak of (2). Intermediate SiO 2 APTES compared to the support SiO 2 At 1530 cm –1 The signal at this point is attributed to bending vibrations of the N-H bond, as in 2892, 2938 cm –1 1470 and 1470 cm -1 The peaks appearing are due to symmetrical stretching vibration peaks, asymmetrical stretching vibration peaks and bending vibration peaks of saturated C-H bonds, indicating SiO 2 Is successfully ammonia functionalized. SiO (SiO) 2 Characteristic absorption peak of C=N bond in-APTES-EASA-Co structure appears 1609cm -1 ，564 cm -1 The absorption peak at this point was attributed to the characteristic absorption peak of Co-O, indicating successful formation of the Schiff base structure.
SiO 2 Application of APTES-EASA-Co in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene were taken upAdding 2 mmol NHPI and 0.025 mmol catalyst into a reaction kettle, checking the air tightness of the reaction kettle device by using high-purity oxygen of 2.0MPa, keeping a pressure gauge stable, replacing air in the reaction kettle by using high-purity oxygen of 2.0MPa for 5 times if no air leakage phenomenon is determined, after replacement, transferring the reaction kettle into a heater provided with a magnetic stirring device, starting stirring, raising the temperature of the reaction kettle to 100 ℃, magnetically stirring at 500 r/min for reaction for 1 h, cooling the reaction kettle to room temperature, centrifugally separating, taking the obtained liquid phase as a product mixture, taking the analysis of the liquid mixture after the reaction, and obtaining the conversion rate and selectivity of toluene, wherein the catalytic reaction result is shown in Table 1.
SiO 2 Recovery and regeneration of APTES-EASA-Co catalyst: pulping and washing the recovered catalyst with absolute ethanol for three times, wherein the concentration of the catalyst in the ethanol is about 0.004 g/mL, and drying the filtered solid sample in a vacuum drying oven at 50 ℃ for 24 h to obtain the regenerated immobilized cobalt Schiff base catalyst SiO 2 -APTES-EASA-Co-R1。
Example 4
The difference between this embodiment and embodiment 1 is that: the salicylaldehyde derivative used in the step 2 is 5-nitrosalicylaldehyde, 5-nitrosalicylaldehyde and SiO 2 Primary amine reaction on APTES carrier, followed by Co (acac) 2 Coordination is carried out to obtain SiO 2 APTES-NSA-Co, wherein the grafting concentration of cobalt is 0.144 mmol/g.
From FIG. 12, it can be seen that SiO 2 At 3683 cm –1 The absorption peak at the position is attributed to the O-H stretching vibration peak in the surface hydroxyl group, and the absorption peak at 1091 and 1091 cm –1 And 805 cm –1 、461 cm –1 958 and 958 cm –1 Are all SiO 2 Is a characteristic peak of (2). Intermediate SiO 2 APTES compared to the support SiO 2 At 1530 cm –1 The signal at this point is attributed to bending vibrations of the N-H bond, as in 2892, 2938 cm –1 1470 and 1470 cm -1 The peaks appearing are due to symmetrical stretching vibration peaks, asymmetrical stretching vibration peaks and bending vibration peaks of saturated C-H bonds, indicating SiO 2 Is successfully ammonia functionalized. SiO (SiO) 2 APTES-NSA-Co at 1601 cm –1 A characteristic absorption peak of c=n bond appears, 558 cm -1 The absorption peak at this point was attributed to the characteristic absorption peak of Co-O, indicating successful formation of the Schiff base structure.
SiO 2 Application of APTES-NSA-Co in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 2 mmol of NHPI and 0.025 mmol of catalyst are added into a reaction kettle, the air tightness of the reaction kettle device is checked by using high-purity oxygen of 2.0MPa, a pressure gauge is kept stable, the air in the reaction kettle is replaced by using the high-purity oxygen of 2.0MPa for 5 times when no air leakage phenomenon is determined, after the replacement is finished, the reaction kettle is moved into a heater provided with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, the reaction kettle is magnetically stirred at 500 r/min for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the analysis of the liquid mixture after the reaction is carried out, the conversion rate and the selectivity of toluene are carried out, and the catalytic reaction result is shown in Table 1.
SiO 2 Recovery and regeneration of APTES-NSA-Co catalyst: pulping and washing the recovered catalyst with absolute ethanol for three times, wherein the concentration of the catalyst in the ethanol is about 0.004 g/mL, and drying the filtered solid sample in a vacuum drying oven at 50 ℃ for 24 h to obtain the regenerated immobilized cobalt Schiff base catalyst SiO 2 -APTES-NSA-Co-R1。
Example 5
In this example, the SiO recovered in example 1 was used 2 Application of APTES-HAP-Co-R1 in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 2 mmol of NHPI and 0.025 mmol of catalyst are added into a reaction kettle, the air tightness of the reaction kettle device is checked by using high-purity oxygen of 2.0MPa, a pressure gauge is kept stable, the air in the reaction kettle is replaced by using the high-purity oxygen of 2.0MPa for 5 times when no air leakage phenomenon is determined, after the replacement is finished, the reaction kettle is moved into a heater provided with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, the reaction kettle is magnetically stirred at 500 r/min for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the analysis of the liquid mixture after the reaction is carried out, the conversion rate and the selectivity of toluene are carried out, and the catalytic reaction result is shown in Table 1.
Example 6
In this example, the SiO recovered in example 2 was used 2 Application of APTES-SA-Co-R1 in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 2 mmol of NHPI and 0.025 mmol of catalyst are added into a reaction kettle, the air tightness of the reaction kettle device is checked by using high-purity oxygen of 2.0MPa, a pressure gauge is kept stable, the air in the reaction kettle is replaced by using the high-purity oxygen of 2.0MPa for 5 times when no air leakage phenomenon is determined, after the replacement is finished, the reaction kettle is moved into a heater provided with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, the reaction kettle is magnetically stirred at 500 r/min for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the analysis of the liquid mixture after the reaction is carried out, the conversion rate and the selectivity of toluene are carried out, and the catalytic reaction result is shown in Table 1.
Example 7
In this example, the SiO recovered in example 3 was used 2 Application of APTES-EASA-Co-R1 in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 2 mmol of NHPI and 0.025 mmol of catalyst are added into a reaction kettle, the air tightness of the reaction kettle device is checked by using high-purity oxygen of 2.0MPa, a pressure gauge is kept stable, the air in the reaction kettle is replaced by using the high-purity oxygen of 2.0MPa for 5 times when no air leakage phenomenon is determined, after the replacement is finished, the reaction kettle is moved into a heater provided with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, the reaction kettle is magnetically stirred at 500 r/min for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the analysis of the liquid mixture after the reaction is carried out, the conversion rate and the selectivity of toluene are carried out, and the catalytic reaction result is shown in Table 1.
Example 8
In this example, siO recovered in example 4 was used 2 Application of APTES-NSA-Co-R1 in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol toluene, 2 mmol NHPI and 0.025 mmol catalyst are added into a reaction kettle, the air tightness of the reaction kettle device is checked by using 2.0MPa high-purity oxygen, a pressure gauge is kept stable, the air in the reaction kettle is replaced by using 2.0MPa high-purity oxygen for 5 times when no air leakage phenomenon is determined, and after the replacement is finished, the reaction is carried outThe reaction kettle is moved into a heater equipped with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, after the reaction kettle is magnetically stirred at 500 r/min for reaction for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the liquid mixture after reaction is analyzed, the conversion rate and selectivity of toluene are obtained, and the catalytic reaction result is shown in Table 1.
Example 9
In this example, siO prepared in example 3 was used 2 Application of APTES-EASA-Co in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 4 mmol of NHPI and 0.05mmol of SiO as catalyst 2 APTES-EASA-Co is added into a reaction kettle, high-purity oxygen of 2.0MPa is used for checking the air tightness of the reaction kettle device, a pressure gauge is kept stable, high-purity oxygen of 2.0MPa is used for replacing air in the reaction kettle for 5 times if no air leakage phenomenon is determined, after replacement is finished, the reaction kettle is moved into a heater provided with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, after the reaction kettle is magnetically stirred at 500 r/min for 1 h, a cooling kettle of the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the conversion rate and the selectivity of toluene are analyzed by taking the liquid mixture after the reaction, and the catalytic reaction result is shown in Table 1.
SiO 2 Recovery and regeneration of APTES-EASA-Co catalyst: pulping and washing the recovered catalyst with absolute ethanol for three times, wherein the concentration of the catalyst in the ethanol is about 0.004 g/mL, and drying the filtered solid sample in a vacuum drying oven at 50 ℃ for 24 h to obtain the regenerated immobilized cobalt Schiff base catalyst SiO 2 -APTES-EASA-Co-R11。
Example 10
The SiO recovered in example 9 was used in this example 2 Application of APTES-EASA-Co-R11 in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 4 mmol of NHPI and 0.05mmol of SiO as catalyst 2 APTES-EASA-Co-R11 is added into a reaction kettle, high-purity oxygen of 2.0MPa is used for checking the air tightness of the reaction kettle device, a pressure gauge is kept stable, the air in the reaction kettle is replaced by high-purity oxygen of 2.0MPa for 5 times when no air leakage phenomenon is determined, and the reaction kettle is replaced after the replacement is finishedTransferring into a heater equipped with a magnetic stirring device, starting stirring, raising the temperature of the reaction kettle to 100 ℃, reacting for 1 h under 500 r/min magnetic stirring, cooling the reaction kettle to room temperature, centrifugally separating to obtain a liquid phase which is a product mixture, analyzing the liquid mixture after reaction, and obtaining the conversion rate and selectivity of toluene, wherein the catalytic reaction result is shown in Table 1.
SiO 2 Recovery and regeneration of APTES-EASA-Co-R11 catalyst: pulping and washing the recovered catalyst with absolute ethanol for three times, wherein the concentration of the catalyst in the ethanol is about 0.004 g/mL, and drying the filtered solid sample in a vacuum drying oven at 50 ℃ for 24 h to obtain the regenerated immobilized cobalt Schiff base catalyst SiO 2 -APTES-EASA-Co-R12。
Example 11
The SiO recovered in example 10 was used in this example 2 Application of APTES-EASA-Co-R12 in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 4 mmol of NHPI and 0.05mmol of SiO as catalyst 2 APTES-EASA-Co-R12 is added into a reaction kettle, high-purity oxygen of 2.0MPa is used for checking the air tightness of the reaction kettle device, a pressure gauge is kept stable, high-purity oxygen of 2.0MPa is used for replacing air in the reaction kettle for 5 times when no air leakage phenomenon is determined, after replacement is finished, the reaction kettle is moved into a heater provided with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, after the reaction kettle is magnetically stirred at 500R/min for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the analysis of the liquid mixture after the reaction is taken, the conversion rate and the selectivity of toluene are shown in the table 1, and the catalytic reaction result is shown in the table 1.
SiO 2 Recovery and regeneration of APTES-EASA-Co-R12 catalyst: pulping and washing the recovered catalyst with absolute ethanol for three times, wherein the concentration of the catalyst in the ethanol is about 0.004 g/mL, and drying the filtered solid sample in a vacuum drying oven at 50 ℃ for 24 h to obtain the regenerated immobilized cobalt Schiff base catalyst SiO 2 -APTES-EASA-Co-R13。
Example 12
The SiO recovered in example 11 was used in this example 2 -APTES-EASThe A-Co-R13 is applied to toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 4 mmol of NHPI and 0.05mmol of SiO as catalyst 2 APTES-EASA-Co-R13 is added into a reaction kettle, high-purity oxygen of 2.0MPa is used for checking the air tightness of the reaction kettle device, a pressure gauge is kept stable, high-purity oxygen of 2.0MPa is used for replacing air in the reaction kettle for 5 times when no air leakage phenomenon is determined, after replacement is finished, the reaction kettle is moved into a heater provided with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, after the reaction kettle is magnetically stirred at 500R/min for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the analysis of the liquid mixture after the reaction is taken, the conversion rate and the selectivity of toluene are shown in the table 1, and the catalytic reaction result is shown in the table 1.
SiO 2 Recovery and regeneration of APTES-EASA-Co-R13 catalyst: pulping and washing the recovered catalyst with absolute ethanol for three times, wherein the concentration of the catalyst in the ethanol is about 0.004 g/mL, and drying the filtered solid sample in a vacuum drying oven at 50 ℃ for 24 h to obtain the regenerated immobilized cobalt Schiff base catalyst SiO 2 -APTES-EASA-Co-R14。
Example 13
The SiO recovered in example 12 was used in this example 2 Application of APTES-EASA-Co-R14 in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 4 mmol of NHPI and 0.05mmol of SiO as catalyst 2 APTES-EASA-Co-R14 is added into a reaction kettle, high-purity oxygen of 2.0MPa is used for checking the air tightness of the reaction kettle device, a pressure gauge is kept stable, high-purity oxygen of 2.0MPa is used for replacing air in the reaction kettle for 5 times when no air leakage phenomenon is determined, after replacement is finished, the reaction kettle is moved into a heater provided with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, after the reaction kettle is magnetically stirred at 500R/min for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the analysis of the liquid mixture after the reaction is taken, the conversion rate and the selectivity of toluene are shown in the table 1, and the catalytic reaction result is shown in the table 1.
SiO 2 Recovery and regeneration of APTES-EASA-Co-R14 catalyst: pulping the recovered catalyst with absolute ethanolWashing for three times, wherein the concentration of the catalyst in ethanol is about 0.004 g/mL, and drying the filtered solid sample in a vacuum drying oven at 50 ℃ for 24 h to obtain the regenerated immobilized cobalt Schiff base catalyst SiO 2 -APTES-EASA-Co-R15。
Example 14
The SiO recovered in example 13 was used in this example 2 Application of APTES-EASA-Co-R15 in toluene solvent-free molecular oxygen catalytic oxidation reaction: 80 mmol of toluene, 4 mmol of NHPI and 0.05mmol of SiO as catalyst 2 APTES-EASA-Co-R15 is added into a reaction kettle, high-purity oxygen of 2.0MPa is used for checking the air tightness of the reaction kettle device, a pressure gauge is kept stable, high-purity oxygen of 2.0MPa is used for replacing air in the reaction kettle for 5 times when no air leakage phenomenon is determined, after replacement is finished, the reaction kettle is moved into a heater provided with a magnetic stirring device, stirring is started, the temperature of the reaction kettle is raised to 100 ℃, after the reaction kettle is magnetically stirred at 500R/min for 1 h, the reaction kettle is cooled to room temperature, centrifugal separation is carried out, the obtained liquid phase is a product mixture, the analysis of the liquid mixture after the reaction is taken, the conversion rate and the selectivity of toluene are shown in the table 1, and the catalytic reaction result is shown in the table 1.
Comparative example 1
80 mmol of toluene was added to the reaction vessel and reacted under magnetic stirring at 500 r/min under reaction conditions of 100℃and an oxygen pressure of 2.5 MPa for 1 h. After the reaction is finished, cooling the reaction liquid to room temperature, adding acetone for dilution, and taking the diluted mixed reaction liquid to obtain the conversion rate and selectivity of toluene.
Comparative example 2
80 mmol of toluene and 4 mmol of NHPI are added to the reaction vessel and reacted under magnetic stirring at 500 r/min under reaction conditions of 100℃and 2.5 MPa of oxygen pressure for 1 h. After the reaction is finished, cooling the reaction liquid to room temperature, adding acetone for dilution, centrifuging the diluted mixed reaction liquid, and taking the reaction liquid obtained after centrifugation for analysis to obtain the conversion rate and selectivity of toluene.
Comparative example 3
80 mmol of toluene and 0.05mmol of SiO catalyst were introduced into a reaction vessel 2 APTES-EASA-Co reaction bars at 100℃and oxygen pressure of 2.5 MPaUnder the reaction conditions, the reaction was conducted under magnetic stirring at 500 r/min for 1 h. After the reaction is finished, cooling the reaction liquid to room temperature, adding acetone for dilution, centrifuging the diluted mixed reaction liquid, and taking the reaction liquid obtained after centrifugation for analysis to obtain the conversion rate and selectivity of toluene.
The following tables show the reaction results of examples 1-12 and comparative examples 1-3 for the catalytic toluene solvent-free molecular oxygen selective oxidation.
Figure 840766DEST_PATH_IMAGE003
As can be seen from the above table, in comparative example 1, in which no catalyst was added, toluene conversion was 0; comparative example 2 was under the same experimental conditions, with only NHPI added as catalyst, toluene conversion was 0.8%, and the products were benzaldehyde and benzyl alcohol; comparative example 3 addition of catalyst SiO alone 2 No product was detected with APTES-HAP-Co. When SiO is added at the same time 2 When APTES-HAP-Co and NHPI catalyze the oxidation of toluene, the ethylbenzene conversion was 20.0% and the selectivities of benzaldehyde, benzyl alcohol and benzoic acid were 14.7%, 9.9% and 71.0%, respectively, under the given test conditions (example 1). This means that under the reaction conditions SiO 2 APTES-HAP-Co can be used in cooperation with NHPI to catalyze toluene oxidation. Under the same experimental conditions, cobalt Schiff base catalysts prepared by using different salicylaldehyde or derivatives thereof as ligands all show the catalytic performance of the oxidation reaction of the p-toluene. According to the element analysis result after the reaction of the fresh catalyst, the second reaction without supplementing the fresh catalyst is carried out, so that the error caused by the catalytic oxidation activity of toluene generated by the metallic cobalt adsorbed on the surface of the catalyst possibly exists on the catalyst during the first reaction is avoided. The cobalt Schiff base catalyst with the substituent on the benzene ring being nitro has the lowest activity in four catalysts, the substituent is a catalyst of methyl or ethyl, the reactivity is relatively close, the catalyst with the aldehyde group para-diethylamino substituent on the benzene ring has the highest reactivity, and the activity of the cobalt Schiff base catalysts prepared by the four different ligands in toluene molecular oxygen catalytic oxidation is SiO in turn 2 -APTES-NSA-Co<SiO 2 -APTES-SA-Co<SiO 2 -APTES-HAP-Co<SiO 2 APTES-EASA-Co. From the results of these four catalytic reactions, it is assumed that in the reaction of molecular oxygen-catalyzed oxidation of toluene under solvent-free conditions, when the substituent on the ligand is an electron withdrawing group, the catalytic oxidation of toluene is inferior to that of electron donating groups, and the stronger the electron donating ability, the better the catalytic effect on the reaction. SiO (SiO) 2 During the recycling process of APTES-EASA-Co for 5 times, toluene conversion rate and selectivity of benzaldehyde, benzyl alcohol and benzoic acid are all kept stable. The catalyst has no loss of active components in the use process, and has excellent stability under the reaction condition.

Claims (7)

1. The application of cobalt schiff base catalyst grafted by imine bond includes cobalt schiff base catalyst, which is characterized in that: the cobalt Schiff base catalyst is cooperated with NHPI to be applied as a recoverable catalyst in the solvent-free molecular oxygen oxidation reaction of toluene;
cobalt schiff base catalyst comprises SiO 2 Support and graft on SiO 2 Cobalt Schiff base complex on carrier, which is grafted on SiO through imine bond 2 On the carrier, the grafting concentration of the cobalt Schiff base complex is 0.09-0.16 mmol/g;
the preparation method of the cobalt Schiff base catalyst grafted by the imine bond comprises the following steps:
1) Modification of carrier SiO with gamma-aminopropyl triethoxysilane 2 Surface to obtain surface ammoniated carrier SiO 2 -APTES；
2) Salicylaldehyde or derivatives thereof, cobalt (II) acetylacetonate and a surface ammoniation carrier SiO 2 APTES is dissolved in a solvent, and grafted cobalt Schiff base catalyst is prepared through imine covalent bond grafting.
2. The use of cobalt schiff base catalysts grafted with imine bonds according to claim 1, characterized in that the surface ammoniated support SiO 2 The preparation method of APTES comprises the following steps:
SiO is firstly put into 2 And gamma-aminopropyl triethoxysilane APTES in dichloromethaneSolvent to obtain reaction liquid;
then, the reaction solution is refluxed for 24 h at 44 ℃ to react, so as to prepare suspension;
finally filtering and separating the suspension to obtain solid powder, washing the solid powder by using absolute ethyl alcohol, and drying the solid powder in a vacuum drying oven to obtain the surface ammoniated carrier SiO 2 -APTES。
3. Use of cobalt schiff base catalysts grafted with imine bonds according to claim 2, characterized in that the SiO 2 And gamma-aminopropyl triethoxysilane in a feed molar ratio of 5:1, said SiO 2 The feed ratio with the dichloromethane solvent was 100 mmol:100 mL.
4. The use of cobalt schiff base catalyst grafted with imine bonds according to claim 1, characterized in that the salicylaldehyde or derivative thereof in step 2) is one of salicylaldehyde, o-hydroxyacetophenone, 4- (diethylamino) salicylaldehyde or 5-nitrosalicylaldehyde.
5. Use of a cobalt schiff base catalyst grafted with imine bonds according to claim 1, characterized in that step 2) comprises the following steps:
firstly, salicylaldehyde or derivatives thereof, cobalt (II) acetylacetonate and a surface ammoniation carrier SiO 2 Adding APTES into dichloromethane to obtain a reaction solution;
reflux-reacting the reaction solution at 44 ℃ for 24 h to prepare suspension;
and finally, filtering and separating the suspension to obtain solid powder, washing the solid powder with dichloromethane, and drying the solid powder in a vacuum drying oven to obtain the grafted cobalt Schiff base catalyst.
6. The use of cobalt schiff base catalyst grafted with imine bonds according to claim 5, characterized in that the surface ammoniated support SiO 2 APTES mass to solvent feed volume ratio of 1.6 g:100 mL, salicylaldehyde derivatives to TableSurface ammoniation carrier SiO 2 APTES is added in a ratio of 5mmol to 1.6: 1.6 g, and the molar ratio of salicylaldehyde ligand to cobalt (II) acetylacetonate is 5:0.32.
7. The use of a cobalt schiff base catalyst grafted with imine bonds according to claim 1, characterized in that: the temperature of the solvent-free molecular oxygen oxidation reaction is 70-120 ℃, the pressure is normal pressure to 3MPa, the molar ratio between toluene and the catalyst is 1600-3400, and the reaction time is 1-5 h.
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