Non-metallic heteroatom-doped carbon-supported zinc metal catalysts, their preparation and use

Abstract

This invention discloses a method for preparing a heteroatom-doped porous carbon-supported zinc catalyst. The catalyst is prepared by co-milling an organic carbon precursor containing one or more non-metallic elements (boron, nitrogen, oxygen, phosphorus, sulfur, etc.), silica sol, and zinc salt, followed by high-temperature calcination and etching with a template agent. It is a supported catalyst in which metal active centers are loaded onto a carbon support doped with various non-metallic heteroatoms. The active centers include non-metallic heteroatom active sites and zinc. The support is a carbon material doped with one or more non-metallic elements. The zinc loading in the catalyst is 0.5-5 wt%. The non-metallic element content in the support is 2-20 wt%. The specific surface area of ​​the catalyst can reach 1600-2200 m². 2 ·g ‑1 The preparation method used in this invention is simple, easy to operate, and has a low loading of active components. At the same time, it has excellent catalytic activity for the cross-coupling reaction of monohydric alcohols with α-H and primary amines, with high alcohol conversion and imine selectivity, making it suitable for industrial production.

Description

Technical fields:

[0001] This invention belongs to the field of catalyst preparation technology, specifically relating to a method for preparing a non-metallic heteroatom-doped porous carbon-supported metallic zinc catalyst and its application. Background technology:

[0002] Imines are an important class of nitrogen-containing organic intermediates, widely used in reduction, addition, cyclization, and aziridine reactions involved in their synthesis in fields such as biology, agriculture, and medicine. Traditional synthetic methods often involve unstable aldehydes and acid catalysts, which have significant drawbacks from both economic and environmental perspectives. In recent years, the synthesis of imines via alkanolamine coupling reactions has attracted considerable attention from researchers, primarily based on homogeneous catalysis and heterogeneous noble and non-noble metal catalysis, such as Mn, Fe, Co, and Cu. Homogeneous catalytic systems often require additional ligands, bases, or other additives, which greatly complicates the separation and purification of imine products. For heterogeneous catalytic systems, noble metal resources are scarce and expensive, limiting their practical application. Therefore, developing non-noble metal heterogeneous catalysts for imine synthesis is crucial. Currently, non-noble metal catalytic systems such as Mn, Fe, Co, and Cu exist in the field of imine synthesis, but the metal Zn-catalyzed imine synthesis process has not yet been reported. Summary of the Invention

[0003] To overcome the shortcomings of existing technologies, this invention provides a method for preparing a non-metallic heteroatom-doped porous carbon-supported zinc catalyst and its application. The catalyst preparation method is simple and convenient to operate, and it has excellent catalytic activity for the cross-coupling of primary amines with monohydric alcohols containing α-H to produce corresponding imines. Moreover, the catalyst is inexpensive and environmentally friendly.

[0004] This invention is achieved through the following technical solution:

[0005] This invention provides a non-metallic heteroatom-doped porous carbon-supported zinc catalyst, wherein the active center comprises non-metallic heteroatom active sites and metallic zinc; the zinc loading in the catalyst is 0.5-5 wt%; the dopant content in the support is 2-20 wt%; and the specific surface area of ​​the catalyst can reach 1600-2200 m². 2 ·g -1 ;

[0006] Based on the above technical solutions, preferably, the non-metallic element in the non-metallic carbon active center is one or more of B, N, O, P, and S.

[0007] Another aspect of this invention provides a method for preparing the above-mentioned heteroatom-doped porous carbon-supported zinc catalyst, characterized in that: a zinc precursor, a support precursor, and a silica sol aqueous solution are mixed and thoroughly ground to obtain a uniform colloidal mixture, and the mixture is then subjected to nitrogen atmosphere at 2-10 °C·min. -1 The heating rate was increased to 600-900℃ and maintained at this temperature for 1-6 hours; then the obtained black powder was immersed in SiO2 template etchant for etching treatment; after the template agent was removed, it was washed and filtered with a large amount of deionized water until the filtrate was neutral; the filtered cake was placed at 60-120℃ to dry thoroughly to obtain the catalyst.

[0008] Based on the above technical solutions, the preferred mass ratio of zinc precursor: carrier precursor: silica sol aqueous solution is 1-10:0.5-4:0.5-4.

[0009] Based on the above technical solutions, preferably, the mass fraction of the silica sol aqueous solution is 35-50 wt%.

[0010] Based on the above technical solutions, preferably, the carrier precursor is one or more of monosaccharides, polysaccharides, thiophene derivatives, sulfoxide compounds, organophosphorus compounds, and organoboronic acids; the non-metallic element in the carrier precursor is one or more of B, N, O, P, and S.

[0011] Based on the above technical solutions, preferably, the sulfoxide compound is one or two of diphenyl sulfoxide and benzene sulfoxide; the organophosphorus compound is one or two of triphenylphosphine and phytic acid; and the organoboronic acid is one or two of p-tolueneboronic acid and 2,2'-biphenyldiboronic acid.

[0012] Based on the above technical solutions, the preferred zinc precursor is one of ZnCl2, ZnSO4, ZnSO3, Zn(NO3)2, Zn(Ac)2, ZnC2O4, B2O6Zn3, or Zn3(PO4)2.

[0013] In another aspect, the present invention provides a method for producing a corresponding imine by cross-coupling a primary amine with a monohydric alcohol containing α-H, wherein the above-mentioned catalyst is used to synthesize the imine by one-pot oxidative catalysis using a primary amine and a monohydric alcohol containing α-H as raw materials.

[0014] Based on the above technical solution, the preferred method for synthesizing the imine is as follows: A primary amine, an α-H-containing monohydric alcohol, a base, a solvent, and a catalyst are added to a reactor; the reactor is sealed, 1-10 bar of air is provided, stirring is started, and the temperature is raised to 100-130°C; in the reaction mixture, the mass ratio of the α-H-containing monohydric alcohol to the primary amine in the reaction system is preferably 1:1-2; in the reaction mixture, with the α-H-containing monohydric alcohol as a reference, the volume of the solvent in the reaction system is preferably 1-4 mL / mmol; in the reaction mixture, the molar ratio of the α-H-containing monohydric alcohol to the base in the reaction system is preferably 1:0.1-0.5; in the reaction mixture, with the α-H-containing monohydric alcohol as a reference, the mass of the catalyst in the reaction system is preferably 20-80 mg / mmol; after the reaction proceeds for 6-24 hours, the reaction indicators obtained are: conversion rate of the α-H-containing monohydric alcohol ≥95%, and selectivity of the imine ≥92%.

[0015] Beneficial effects:

[0016] In this invention, the addition of silica template agent plays a pore-forming role, increasing the specific surface area of ​​the material and fully exposing the active centers, thus enabling them to better exert their catalytic effect. The introduction of metallic zinc serves two purposes: firstly, it forms pores, further endowing the material with a microporous structure; secondly, it serves as a metallic active site introduced into the catalyst. Therefore, the non-metallic heteroatom-doped porous carbon-supported metallic zinc catalyst prepared by this method exhibits outstanding performance in catalyzing the cross-coupling of primary amines with α-H-containing monohydric alcohols to produce corresponding imines.

[0017] The beneficial effects of this invention are as follows: In this invention, a non-metallic heteroatom-doped porous carbon-supported zinc catalyst is prepared by simple mixing, grinding, and calcination of the precursor. The active center of the catalyst includes non-metallic heteroatom active sites and metallic zinc. The zinc loading in the catalyst is 0.5-5 wt%. The non-metallic element content in the support is 2-20 wt%. The catalyst prepared by this method has low requirements for the precursor, allowing for a wide range of selections, and the catalyst specific surface area can reach up to 2200 m². 2 ·g -1 This greatly increases the mass transfer efficiency. In addition, the active sites of metallic zinc and non-metallic active sites in the catalyst form a synergistic catalysis, resulting in higher selectivity and conversion rate. When this catalyst is applied to the reaction of primary amine and monohydric alcohol containing α-H cross-coupling to produce the corresponding imine, the conversion rate of the monohydric alcohol containing α-H is ≥95% and the selectivity of imine is ≥92% after running for more than 6 hours. Moreover, it has excellent stability after more than 5 cycles.

[0018] The preparation method used in this invention is simple, easy to operate, and has a low loading of active components. At the same time, it has excellent catalytic activity for the cross-coupling reaction of monohydric alcohols with α-H and primary amines, with high alcohol conversion and imine selectivity, making it suitable for industrial production. Attached Figure Description

[0019] Appendix Figure 1 This is an electron microscope image of the catalyst prepared in Example 1;

[0020] Appendix Figure 2 The catalyst recovery and recycling performance is shown in Example 1;

[0021] Appendix Figure 3 These are the N2 adsorption-desorption isotherms of Example 1 and Comparative Example 1. Detailed Implementation

[0022] The present invention will be further described in detail below with reference to specific embodiments, so as to help those skilled in the art to have a more complete, accurate and in-depth understanding of the inventive concept and technical solution of the present invention. The scope of protection of the present invention includes, but is not limited to, the following embodiments. Any modifications made to the details and form of the technical solution of the present invention without departing from the spirit and scope of this application shall fall within the scope of protection of the present invention.

[0023] Example 1

[0024] 5.4 g zinc chloride, 1 g chitosan, 2 g phytic acid (70 wt%) solution, and 2 g silica sol (40 wt%) were mixed and thoroughly ground to obtain a homogeneous gel-like mixture. This mixture was then subjected to a nitrogen atmosphere at 5 °C / min. -1 The heating rate was increased to 800℃ and maintained at this temperature for 2 hours. Subsequently, the obtained black powder was immersed in hydrofluoric acid aqueous solution for etching treatment, and then washed and filtered with a large amount of deionized water until the filtrate was neutral. The filtered cake was dried thoroughly at 80℃ to obtain the catalyst m-Zn-NOPC-0.5%, wherein the zinc loading was 0.5wt% and the total content of non-metallic elements other than C was about 15wt%.

[0025] Example 2

[0026] The catalyst preparation conditions were the same as in Example 1, except that p-tolueneboric acid was used to replace phytic acid by an equal amount, resulting in catalyst m-Zn-NOBC-0.5%, with a total content of non-metallic elements other than C of approximately 15 wt%.

[0027] Example 3

[0028] The catalyst preparation conditions were the same as in Example 1, except that 1g of diphenyl sulfoxide was added during the preparation of the black powder to obtain catalyst m-Zn-NOPSC-0.5%, and the total content of non-metallic elements other than C was about 15wt%.

[0029] Example 4

[0030] The catalyst preparation conditions were the same as in Example 1, except that 10.8 g of zinc chloride was used to obtain the catalyst m-Zn-NOPC-2%, and the total content of non-metallic elements other than C was about 15 wt%.

[0031] Comparative Example 1

[0032] The catalyst preparation conditions were the same as in Example 1, except that the catalyst calcination temperature was replaced with 400℃, resulting in catalyst m-Zn-NOPC-400-0.5%, with a total non-metallic element content of approximately 15wt% excluding C.

[0033] Comparative Example 2

[0034] The catalyst preparation conditions were the same as in Example 1, except that the precursors chitosan and phytic acid were replaced with 3g of activated carbon to obtain catalyst m-Zn-OC-0.5%, with a total content of non-metallic elements other than C of about 10wt%.

[0035] Comparative Example 3

[0036] The catalyst preparation conditions were the same as in Example 1, except that zinc chloride was not added, and the catalyst m-NOPC was obtained, with a total content of non-metallic elements other than C of about 15 wt%.

[0037] Comparative Example 4

[0038] The catalyst preparation conditions were the same as in Example 1, except that no silica sol was added, and the resulting catalyst was Zn-NOPC-0.5%, with a total content of non-metallic elements other than C of approximately 15 wt%.

[0039] Example 5

[0040] The catalysts described in Examples 1-3 and Comparative Examples 1-4 were applied to the synthesis reaction of benzylidene under the same conditions:

[0041] 0.5 mmol of benzyl alcohol and 0.6 mmol of aniline were added to a 10 mL Schlenk tube, along with 40 mg / mmol of catalyst, 7.2 mg / mmol of lithium hydroxide, and 2 mL / mmol of n-heptane. The tube was then sealed with a magnetic stir bar, connected to an air bulb, and placed in an oil bath at 110 °C for stirring. After the reaction was completed, the tube was cooled to room temperature. Biphenyl was added as an internal standard and dissolved and diluted with 1,4-dioxane. The mixture was stirred for 3 min until homogeneous, then centrifuged. A suitable amount of the supernatant was collected and analyzed by gas chromatography to calculate the conversion rate of benzyl alcohol and the yield of benzyl aniline.

[0042] The results are shown in Table 1. As can be seen from the table, the catalyst of this invention exhibits good selectivity for benzylidene aniline. Increasing the calcination temperature helps improve catalyst activity and product selectivity; doping the carbon support with non-metallic elements promotes catalytic activity; zinc plays an important role in the synthesis of benzylidene aniline and exhibits a synergistic catalytic effect with the doped non-metallic elements; the use of a template agent is beneficial for improving catalyst activity.

[0043] Table 1. Screening of catalysts for the cross-coupling of benzyl alcohol and aniline to produce imine.

[0044]

[0045] Examples 6-13, Comparative Examples 5-10

[0046] Except for the differences in the amount of aniline used, reaction temperature, type of alkali, and type of solvent, the catalyst activity evaluation was the same as in Example 5. Specific conditions were:

[0047] 0.5 mmol of benzyl alcohol and 0.6 mmol of aniline were added to a 10 mL Schlenk tube, along with 40 mg / mmol of m-Zn-NOPC-0.5%, 0.3 mmol / mmol of inorganic base, and 2 mL / mmol of solvent, using the amount of benzyl alcohol as a standard. The tube was then sealed with a magnetic stir bar, connected to an air bulb, and placed in an oil bath at 110 °C for stirring. After the reaction was completed, the tube was cooled to room temperature, and biphenyl was added as an internal standard and dissolved and diluted with 1,4-dioxane. The mixture was stirred for 3 min to achieve homogeneity, then centrifuged. An appropriate amount of the supernatant was collected and analyzed by gas chromatography to calculate the conversion rate of benzyl alcohol and the yield of benzylene aniline.

[0048] The results are shown in Table 2. As can be seen from the table, the catalyst of this invention exhibits good selectivity for benzylide-aniline. Increasing the reaction temperature helps improve substrate conversion and imine yield. Air provides the oxygen required for the oxidation reaction, which requires a certain level of alkalinity.

[0049] Table 2. Experimental control of imine production via cross-coupling of benzyl alcohol and aniline.

[0050]

[0051]

[0052] Examples 14-24

[0053] Except for the differences in alcohol substrate, reaction temperature, alkali dosage, solvent, and result analysis method, the catalyst activity evaluation was the same as in Example 5. Specific conditions were:

[0054] 0.5 mmol of alcohol derivatives and 0.6 mmol of aniline were added to a 10 mL Schlenk tube, along with 40 mg / mmol of catalyst, 7.2 mg / mmol of lithium hydroxide, and 2 mL / mmol of n-heptane. The tube was then sealed with a magnetic stir bar, connected to an air bulb, and placed in an oil bath at 110 °C with stirring. After the reaction was complete, the tube was cooled to room temperature and evacuated to a vacuum level for 1 min at room temperature to remove the solvent. Benzyl benzoate was added as an internal standard, and 1 mL of CDCl3 was added as a solvent. After thorough mixing, the mixture was centrifuged, and a suitable amount of the supernatant was measured using a 400 MHz nuclear magnetic resonance spectrometer. 1 The yield of the imine product was calculated by 1H spectrum analysis, and the product structure was confirmed by gas chromatography-mass spectrometry.

[0055] The results are shown in Table 2:

[0056] Table 2. Cross-coupling of different alcohol substrates with aniline to produce imines

[0057]

[0058]

[0059] Examples 25-35

[0060] Except for the differences in amine substrate, base dosage, and analytical methods, the catalyst activity evaluation was the same as in Example 5. Specific conditions were as follows:

[0061] 0.5 mmol of benzyl alcohol, 0.6 mmol of an amine derivative (based on the amount of benzyl alcohol), 40 mg / mmol of catalyst, 7.2 mg / mmol of lithium hydroxide, and 2 mL / mmol of n-heptane were added to a 10 mL Schlenk tube. A magnetic stir bar was placed in the tube, which was then sealed and connected to an air bulb. The tube was placed in an oil bath at 110 °C and stirred. After the reaction was complete, the tube was cooled to room temperature and evacuated to a vacuum for 1 min at room temperature to remove the solvent. Benzyl benzoate was added as an internal standard, and 1 mL of CDCl3 was added as a solvent. After thorough mixing, the tube was centrifuged, and a suitable amount of the supernatant was measured using a 400 MHz nuclear magnetic resonance spectrometer. 1The yield of the imine product was calculated by 1H spectrum analysis, and the product structure was confirmed by gas chromatography-mass spectrometry.

[0062] The results are shown in Table 3:

[0063] Table 3. Cross-coupling of benzyl alcohol and different amine substrates to produce imines

[0064]

[0065]

[0066] The catalyst preparation method described in this invention is simple, has low requirements for precursors, high oxidation efficiency for alcohols, mild reaction conditions, high product yield, and wide substrate applicability; it uses air as an oxygen source, which is economical and environmentally friendly, and has good application prospects.

Claims

1. The application of a non-metallic heteroatom-doped carbon-supported zinc catalyst in the catalytic cross-coupling of a primary amine with an α-H-containing monohydric alcohol to produce the corresponding imine, characterized in that, Add the primary amine, α-H monohydric alcohol, base, solvent, and catalyst to the reactor; seal the reactor, supply air into the reactor at a pressure of 1-10 bar, start stirring, and raise the temperature to 100-130℃. ； In the reaction mixture, the mass ratio of α-H-containing monohydric alcohol to primary amine in the reaction system is 1:1~2; In the reaction mixture, using a monohydric alcohol containing α-H as a reference, the volume of the solvent in the reaction system is 1-4 mL / mmol α-H monohydric alcohol; In the reaction mixture, the molar ratio of the α-H-containing monohydric alcohol to the base in the reaction system is 1:0.1~0.5; In the reaction mixture, using a monohydric alcohol containing α-H as a reference, the mass of the catalyst in the reaction system is 20~80 mg / mmol α-H monohydric alcohol; The alkali is one or more of KOH, NaOH, LiOH, t-BuOK, t-BuONa, Li2CO3, K2CO3, and Na2CO3; The solvent is one or more of dioxane, n-heptane, and tert-amyl alcohol; the reaction time is 8-12 h. The specific steps of the preparation method of the catalyst are: mixing a metal zinc precursor, chitosan, another carrier precursor and a silicon sol aqueous solution, and sufficiently grinding to obtain a uniform colloidal mixture; raising the temperature of the mixture to 600-900 ℃ at a temperature raising rate of 2-10 ℃·min -1 under nitrogen, and keeping the temperature for 1-6 h; then, immersing the obtained black powder in a silicon oxide template etching agent for etching treatment; after the silicon oxide template is removed, washing and filtering with water until the filtrate is neutral; and drying the filtered filter cake at 60-120 ℃ to obtain the catalyst. The other carrier precursor is one or more of sulfoxide compounds, organophosphorus compounds, and organoboronic acids; The sulfoxide compounds are one or more of diphenyl sulfoxide and benzene sulfoxide; the organophosphorus compounds are one or two of triphenylphosphine and phytic acid; and the organoboronic acids are one or two of p-tolueneboronic acid and 2,2'-biphenyldiboronic acid.

2. The application according to claim 1, characterized in that, Add the primary amine, α-H monohydric alcohol, base, solvent, and catalyst to the reactor; seal the reactor, supply air into the reactor at a pressure of 2-4 bar, start stirring, and raise the temperature to 110-120℃. In the reaction mixture, the mass ratio of α-H-containing monohydric alcohol to primary amine in the reaction system is 1:1.2~1.4; In the reaction mixture, using a monohydric alcohol containing α-H as a reference, the volume of the solvent in the reaction system is 2-3 mL / mmol α-H monohydric alcohol; In the reaction mixture, using a monohydric alcohol containing α-H as a reference, the mass of the catalyst in the reaction system is 30-50 mg / mmol α-H monohydric alcohol; The reaction time is 9.5-10.5 h; The specific steps of the preparation method of the catalyst are: mixing a metal zinc precursor, chitosan, another carrier precursor and a silicon sol aqueous solution, and sufficiently grinding to obtain a uniform colloidal mixture; raising the temperature of the mixture to 750-850 ℃ at a temperature raising rate of 4-8 ℃·min -1 -1 under nitrogen, and keeping the temperature for 3-5 h; then, immersing the obtained black powder in a silicon oxide template etching agent for etching treatment; after the silicon oxide template is removed, washing and filtering with water until the filtrate is neutral; and drying the filtered filter cake at 60-120 ℃ to obtain the catalyst.

3. The application according to claim 1, characterized in that, In the process of preparing black powder in the method, the mass ratio of zinc precursor: carrier precursor: silica sol aqueous solution is 1~10:0.5~4:0.5~4.

4. The application according to claim 3, characterized in that, In the process of preparing black powder in the method, the mass ratio of zinc precursor: carrier precursor: silica sol aqueous solution is 2-4:0.8-1.2:1-2.

5. The application according to claim 1, characterized in that, The catalyst comprises a carbon support doped with non-metallic heteroatoms and metallic zinc supported on the support; the zinc loading in the catalyst is 0.5-5 wt%; the non-metallic element content in the carbon support is 2-20 wt%.

6. The application according to claim 5, characterized in that, The catalyst comprises a carbon support doped with non-metallic heteroatoms and metallic zinc supported on the support; the zinc loading in the catalyst is 0.5-1.5 wt%; and the non-metallic element content in the carbon support is 8-15 wt%.

7. The application according to claim 1, characterized in that, The zinc precursor is one of ZnCl2, ZnSO4, ZnSO3, Zn(NO3)2, Zn(OAc)2, ZnC2O4, B2O6Zn3, or Zn3(PO4)2.

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