CN104069883A - Cobalt-based catalyst for generating ester by alcohol oxidation, and preparation method and application of cobalt-based catalyst - Google Patents

Abstract

The invention belongs to the technical field of liquid-phase oxidation, and discloses a cobalt-based catalyst used for the oxidation of alcohols to generate esters and its preparation method and application. The cobalt-based catalyst is mainly composed of cobalt, carbon and nitrogen elements, wherein the weight ratio of each element is It is: 27.0-50.0 wt% of cobalt, 45.0-60.0 wt% of carbon, and 0.5-20.0 wt% of nitrogen; the particle size of the cobalt nanoparticles in the cobalt-based catalyst is 5-40nm. The cobalt-based catalyst is prepared by using ZIF-67 as a precursor by pyrolysis in an inert atmosphere. In the presence of the cobalt-based catalyst, the ester compound can be prepared by reacting the two alcohols in an atmospheric environment at normal temperature and pressure without adding any basic additives. The cobalt-based catalyst of the present invention is easy to be synthesized in large quantities, and is magnetically recyclable; the method of using the cobalt-based catalyst to catalyze the oxidation of alcohols to generate esters has the advantages of low cost, simple operation, environmental protection, mild reaction conditions, easy separation of products, and the like.

Description

A kind of cobalt-based catalyst for alcohol oxidation to generate ester and its preparation method and application

technical field

The invention belongs to the technical field of liquid-phase oxidation, and relates to a cobalt-based catalyst, in particular to a cobalt-based catalyst used to oxidize alcohols to generate esters, a preparation method and application thereof. the

Background technique

As one of the most important functional groups in the field of organic chemistry, ester groups are widely found in various fine chemicals, natural chemicals, and polymers. They can be used as food additives or cosmetic additives, and some esters can be used in medicine and other fields. For example, methyl esters are widely used as flavoring agents, solvents, diluents and extractants, etc., and have very high commercial value. Aromatic esters are often used as intermediates in organic synthesis due to their versatility, and are widely used as microcrystalline polymers, cosmetics, and pharmaceuticals. the

At present, researchers mainly synthesize ester compounds through four routes. At the end of the last century, acid derivatives such as acid chlorides or acid anhydrides were mainly synthesized by reacting with alcohols, but this reaction pathway would generate some unwanted by-products, and cause waste of resources and environmental pollution (Larock R C, "Comprehensive organic transformations: a guide to functional group preparations”, New York: Wiley-VCH.1999). Around 2005, it was found that a more direct synthesis route is to use transition metal catalysts to catalyze the reaction of halogenated aromatic hydrocarbons and alcohols to form ester compounds, but this involves the carbonylation of halogenated aromatic hydrocarbons, and the reaction conditions are relatively harsh and require high temperature. CO atmosphere and high pressure, the reaction system is not environmentally friendly (halogenated aromatic hydrocarbons pollute the environment). Subsequently, researchers found that esters can be formed by the reaction of aldehydes and alcohols, but an equivalent amount of metal salt or metal oxide (such as potassium hydrogen sulfate or manganese dioxide) should be added as an oxidizing agent in the reaction system. In addition, the aldehyde in the reactant also needs to be oxidized by alcohol, which is time-consuming and labor-intensive (Xu B, Liu X, Haubrich J, "Vapour-phase gold-surface-mediated coupling of aldehydes with methanol", Nature Chemistry, 2010, 2,61). The synthesis routes of the above three esters are not simple enough and there are many by-products in the reaction, and the utilization rate of raw materials is not high. As one of the most basic chemicals that can be obtained in large quantities from nature, the direct synthesis of esters from alcohols is the most simple, economical and environmentally friendly synthesis route. the

At present, a large number of catalysts have been developed and applied to the oxidation of alcohol to ester as a single reactant, including two systems of homogeneous catalysis and heterogeneous catalysis. the

In terms of homogeneous catalytic systems, Lei et al. in 2011 used the noble metal bisacetonitrile palladium chloride as the catalyst, two equivalents of sodium tert-butoxide as the base, and silver fluoroboride as the additive to efficiently catalyze the formation of esters from alcohols in an oxygen atmosphere (Liu C, Wang J, Meng L, "Palladium‐Catalyzed Aerobic Oxidative Direct Esterification of Alcohols", Angew.Chem.Int.Ed., 2011, 123, 5250). the

From the viewpoint of sustainable development, the study of heterogeneous catalytic systems has attracted the attention of many researchers. The following mainly introduces the heterogeneous reaction catalytic systems that catalyze the oxidation of alcohols to esters in recent years, mainly using noble metal catalysts, such as Au, Pd, etc. In recent years, the most widely used catalyst for the heterogeneous catalysis of alcohol oxidation to ester is gold catalyst. Researchers almost disperse gold on the carrier to reduce the size of gold to improve the dispersion of gold. This is due to the smaller particles of gold catalysts. Higher activity. Under the condition of using a noble metal such as Au as a catalyst, most of the literatures still need to add a base to promote the alcohol dehydrogenation process, and almost all of them require an oxygen atmosphere, and the reaction temperature is relatively high. In 2010, Kobayashi et al. synthesized Au/Pt bimetallic catalysts to realize the reaction of alcohol oxidation to ester under three equivalents of potassium carbonate as base and oxygen atmosphere. After alcohols are oxidized to aldehydes, whether aldehydes are preferentially hydrated to form diols or hemiacetals are preferentially formed, and the author believes that the coordination effect of the Au/Pt bimetallic catalyst promotes the formation of hemiacetals from aldehydes, thereby promoting the reaction进行(Kaizuka K,Miyamura H,Kobayashi S,“Remarkable Effect of Bimetallic Nanocluster Catalysts for Aerobic Oxidation of Alcohols:Combining Metals Changes the Activities and the Reaction Pathways to Aldehydes/Carboxylic Acids or  Esters”,Journal of the American Chemical Society,2010 , 132, 15096). the

In addition, in 2013, Stahl et al. used Pd/charcoal (5wt%) catalyst to catalyze the alcohol oxidation reaction with palladium as the catalyst in the heterogeneous reaction for the first time under the coordinated action of Bi(NO ₃ ) ₃ and Te metal. Bi and Te can speed up the reaction rate, selectivity and yield of the target product. This catalytic system has good substrate applicability and can catalyze the esterification of most aromatic alcohols and difficult-to-react aliphatic alcohols, but this reaction also requires the addition of one equivalent potassium methoxide and requires a pure oxygen atmosphere (Powell A B, Stahl S S, "Aerobic Oxidation of Diverse Primary Alcohols to Methyl Esters with a Readily Accessible Heterogeneous Pd/Bi/Te Catalyst", Organic Letters, 2013, 15, 5072).

Although more and more literature reports have confirmed that the direct synthesis of esters from alcohol oxidation is a promising direction, but further improvements in the catalytic efficiency and practical performance of the catalysts are still needed. Homogeneously catalyzed oxidative esterification of alcohols often requires the addition of inorganic bases or inorganic acids, and the presence of noble metals or visible light to catalyze alcohols to form esters. The activity of the reaction system needs to be improved, and the separation after the reaction is complicated. Heterogeneously catalyzed alcohol oxidative esterification reactions mostly require precious metals as catalysts, need to add alkali to promote the alcohol dehydrogenation process, and mostly require to be carried out in a pure oxygen atmosphere, the required oxygen pressure is sometimes even as high as 1MPa, and the reaction temperature is relatively high . Due to the limited resources of precious metals and their high prices, finding economical and environmentally friendly cheap catalysts is the key to promote the industrial application of direct oxidation of alcohols to esters. For the reaction substrates, aromatic alcohols have higher activity due to the presence of active groups such as benzene rings, and the reactivity of aliphatic alcohols and heterocyclic alcohols is not ideal, and most of them require harsher conditions than aromatic alcohols to proceed. the

Contents of the invention

In order to overcome the shortcomings and deficiencies of the prior art, prepare a cheap metal catalyst with high activity, and apply it to alcohol oxidation under mild reaction conditions to directly generate ester, the primary purpose of the present invention is to provide a method for alcohol oxidation to generate Cobalt-based catalysts for esters;

Another object of the present invention is to provide the preparation method of above-mentioned cobalt-based catalyst;

Another object of the present invention is to provide the application of cobalt-based catalysts. the

The purpose of the present invention is achieved through the following technical solutions:

A cobalt-based catalyst used to oxidize alcohols to form esters, the cobalt-based catalyst is mainly composed of transition metal cobalt, carbon and nitrogen elements, wherein the weight ratio of each element is: cobalt 27.0-50.0wt%, carbon 45.0-60.0wt% , 0.5-20.0 wt% nitrogen; the cobalt nanoparticles in the cobalt-based catalyst have a particle size of 5-40nm. the

A kind of preparation method according to the above-mentioned cobalt base catalyst that is used for alcohol oxidation to generate ester, comprises the steps:

(1) Preparation and activation of metal-organic framework material ZIF-67: Weigh cobalt nitrate hexahydrate and 2-methylimidazole (abbreviation: Im) respectively and add to water, stir at room temperature to obtain a mixed solution; Centrifuge, filter to obtain the precipitate, wash the unreacted ligand in the precipitate with water, and then wash the precipitate with methanol solution; finally, vacuumize the precipitate to obtain the metal organic framework material ZIF-67;

(2) Preparation of the catalyst: use the metal-organic framework material ZIF-67 obtained in step (1) as a precursor, heat to the target temperature in an inert atmosphere, pyrolyze at a constant temperature, and then cool to room temperature to obtain a powdery product, which is The cobalt-based catalyst used for the oxidation of alcohols to generate esters. the

Preferably, the molar ratio of cobalt nitrate hexahydrate, 2-methylimidazole and water in step (1) is Co ²⁺ :Im:H ₂ O=1:58:1100.

Preferably, the time for stirring at room temperature in step (1) is 6-8 hours. the

Preferably, the vacuum treatment in step (1) is vacuumizing the precipitate at 80-200° C. for 12-36 hours. the

Preferably, the target temperature in step (2) is 400-1200°C. the

Preferably, the time for constant temperature pyrolysis in step (2) is 0.5-12 hours. the

The application of the above-mentioned cobalt-based catalyst for the oxidation of alcohols to generate esters in the atmosphere of normal temperature and pressure without adding alkali to catalyze the oxidation of alcohols to generate esters. the

The preferred scheme of the above application includes the following steps: put the cobalt-based catalyst and alcohol into a reactor, and carry out stirring reaction at normal temperature and pressure to produce the corresponding ester. the

Preferably, the alcohol is primary aromatic alcohol, aliphatic alcohol or diol; the control conditions for stirring reaction at normal temperature and pressure are reaction temperature 15-35°C, reaction pressure is normal pressure, stirring reaction time is 3-5 Day; The mol ratio of described alcohol and cobalt-based catalyst (calculated as cobalt) is 1～10;

Preferably, the cobalt-based catalyst can be recycled and reused after hydrogen reduction at 300-450° C. for 0.5-4 hours. the

Principle of the present invention:

The cobalt-based catalyst provided by the invention is prepared by using a metal-organic framework structure as a precursor and adopting a one-step pyrolysis method. The advantages that the selected catalyst precursor ZIF-67 of the present invention possesses are: one, the size of the synthesized ZIF-67 is smaller, and the material particles after pyrolysis are small and have a larger active surface; The high content can effectively hinder the agglomeration of cobalt nanoparticles during the pyrolysis process; and the nitrogen content of ZIF-67 is high, and the nitrogen doped in the catalyst after pyrolysis can promote the reaction. the

Compared with the prior art, the present invention has the following advantages and effects:

(1) The cobalt-based catalyst of the present invention is easy to synthesize in large quantities, and has magnetism. After the reaction, the catalyst and the reaction mixture are separated by magnetism, and the reaction operation is very simple. the

(2) The cobalt-based catalyst provided by the present invention adopts a heterogeneous catalytic system. Under normal temperature and pressure conditions, without adding alkaline additives, it can efficiently realize the oxidation of alcohols to generate esters, which solves the problem of catalyst activity under mild conditions. Low and alcohol oxidation to generate ester requires alkaline additives, avoiding the use of traditional precious metals (gold, palladium, etc.), harsh reaction conditions (such as higher temperature and pressure), with low cost, simple operation, environmental protection, The reaction conditions are mild and the product separation is simple. the

(3) The recycling performance of the cobalt-based catalyst of the present invention is good. The recovered cobalt-based catalyst is reduced with hydrogen at 300-450° C. for 0.5-4 hours, and the catalytic activity and selectivity of the reduced cobalt-based catalyst remain unchanged after repeated use for many times. the

(4) Utilize the catalytic system of the cobalt-based catalyst of the present invention to catalyze alcohol to produce ester, the reaction conditions are mild, efficient, high in selectivity and good in stability, and there are few by-products, no alkaline additives are needed, green and environmentally friendly, and environmentally friendly Friendly catalytic system for catalyzing the oxidation of alcohols to esters. the

(5) The cobalt-based catalyst of the present invention has good substrate applicability, and can efficiently catalyze the reaction of various alcohols to generate corresponding esters, and the yield of the esters can reach up to more than 99%. the

Description of drawings

Figure 1 is a high-magnification transmission electron microscope image of the cobalt-based catalyst of the present invention. the

Detailed ways

The present invention will be further described in detail below in conjunction with the embodiments and the accompanying drawings, but the embodiments of the present invention are not limited thereto. the

The metal-organic framework material ZIF-67 used in the present invention can be prepared according to the following examples 1 or 2:

Example 1

Weigh cobalt nitrate hexahydrate and 2-methylimidazole respectively and add them to deionized water, the molar ratio is Co2 ⁺ :Im: _H2O =1:58:1100, and stir at room temperature for 6 hours to obtain a purple mixed solution; Centrifuge the purple mixed solution, filter to obtain a purple precipitate, wash off the unreacted ligand with a large amount of deionized water, and then wash the purple precipitate with methanol solution for 3 times; finally vacuumize the collected purple precipitate at 80°C for 24 hours, The metal-organic framework material ZIF-67 was obtained.

Example 2

Weigh cobalt nitrate hexahydrate and 2-methylimidazole respectively and add them to deionized water, the molar ratio is Co2 ⁺ :Im: _H2O =1:58:1100, and stir at room temperature for 6 hours to obtain a purple mixed solution; Centrifuge the purple mixed solution, filter to obtain a purple precipitate, wash off the unreacted ligand with a large amount of deionized water, and then wash the purple precipitate with methanol solution for 3 times; finally vacuumize the collected purple precipitate at 200°C for 24 hours, The metal-organic framework material ZIF-67 was obtained.

The cobalt-based catalyst used for alcohol oxidation to generate ester according to the present invention can be prepared by the method described in any one of embodiments 3 to 10:

Example 3

Using ZIF-67 as the precursor, heated to the target temperature of 400°C in an inert atmosphere, then thermolyzed for 0.5h, and then cooled to room temperature; the collected black powder was the cobalt-based catalyst for the oxidation of alcohols to esters. the

Example 4

Using ZIF-67 as the precursor, heated to the target temperature of 400°C in an inert atmosphere, thermolyzed for 12 hours, and then cooled to room temperature; the collected black powder was the cobalt-based catalyst for the oxidation of alcohol to ester. the

Example 5

Using ZIF-67 as the precursor, heated to the target temperature of 1200°C in an inert atmosphere, then thermolyzed for 0.5h, and then cooled to room temperature; the collected black powder was the cobalt-based catalyst for the oxidation of alcohol to ester. the

Example 6

Using ZIF-67 as the precursor, heated to the target temperature of 1200°C in an inert atmosphere, then thermolyzed for 12 hours, and then cooled to room temperature; the collected black powder was the cobalt-based catalyst used to oxidize alcohols to form esters. the

Example 7

Using ZIF-67 as the precursor, heated to the target temperature of 600°C in an inert atmosphere, then thermolyzed for 8 hours, and then cooled to room temperature; the collected black powder was the cobalt-based catalyst for the oxidation of alcohol to ester. the

Example 8

Using ZIF-67 as the precursor, heated to the target temperature of 700°C in an inert atmosphere, then pyrolyzed at a constant temperature for 8 hours, and then cooled to room temperature; the collected black powder was the cobalt-based catalyst for the oxidation of alcohol to ester. the

Example 9

Using ZIF-67 as the precursor, heated to the target temperature of 800°C in an inert atmosphere, then thermolyzed for 8 hours, and then cooled to room temperature; the collected black powder was the cobalt-based catalyst for the oxidation of alcohol to ester. The high-magnification transmission electron microscope image of the cobalt-based catalyst used in the oxidation of alcohol to generate ester obtained in this example is shown in Figure 1, and B is a partial enlarged view in the box A. the

Example 10

Using ZIF-67 as the precursor, heated to the target temperature of 900°C in an inert atmosphere, then pyrolyzed at a constant temperature for 8 hours, and then cooled to room temperature; the collected black powder was the cobalt-based catalyst for the oxidation of alcohol to ester. the

The catalytic application of the cobalt-based catalyst used for alcohol oxidation to generate ester according to the present invention can be realized by the scheme in Examples 11-14:

Example 11

The raw material alcohol of reactant column shown in table 1, described cobalt-based catalyst, methyl alcohol and normal hexane (solvent) that are used for alcohol oxidation to generate ester are added in test tube and carry out the reaction that oxidation generates ester, and concrete reaction condition is as follows: The temperature is 25°C, the reaction pressure is normal pressure (0.1MP), the molar ratio of raw material alcohol:cobalt-based catalyst (calculated as cobalt) is 6, the reaction atmosphere is air atmosphere, and the reaction time is 4 days; after the reaction is completed, it is cooled naturally, and the magnetic The cobalt-based catalyst and the reaction mixture were separated, and the reaction products were detected by GC-MS. The results are shown in Table 1. the

Table 1. Raw materials, products and yields of cobalt-based catalysts for the oxidation of alcohols and methanol to the corresponding esters

The recovered cobalt-based catalyst was washed with methanol, and reduced in a hydrogen atmosphere at 400° C. for 0.5 h; the above steps were repeated for the reduced cobalt-based catalyst. The productive rate of described cobalt-based catalyst recycling is as shown in Table 2, as can be seen from Table 2, the cobalt-based catalyst is reused 5 times and the reaction effect is not reduced, indicating that this cobalt-based catalyst is very stable and can be reused many times of. the

Table 2. The recycling performance measurement results of the cobalt-based catalyst

Example 12

The raw material alcohol of the reactant column shown in Table 1, the cobalt-based catalyst, methyl alcohol and normal hexane (solvent) that are used to oxidize the alcohol to generate the ester are added in the test tube to carry out the reaction of oxidizing to generate the ester, and the specific reaction conditions are as follows : The reaction temperature is 15° C., the reaction pressure is normal pressure (0.1 MP), the molar ratio of raw material alcohol: cobalt-based catalyst (calculated as cobalt) is 1, the reaction atmosphere is air atmosphere, and the reaction time is 3 days. The product and the productive rate measured after the reaction finishes are close to the results in Table 1. the

Example 13

The raw material alcohol of reactant row shown in table 1, described cobalt-based catalyst, methyl alcohol and normal hexane (solvent) that are used for alcohol oxidation to generate ester are added in the test tube and carry out the reaction that oxidation generates ester, and specific reaction condition is as follows: The reaction temperature is 35°C, the reaction pressure is normal pressure (0.1MP), the molar ratio of raw material alcohol: cobalt-based catalyst (calculated as cobalt) is 1, the reaction atmosphere is air atmosphere, and the reaction time is 5 days. The product and the productive rate measured after the reaction finishes are close to the results in Table 1. the

Example 14

The raw material alcohol of reactant row shown in table 1, described cobalt-based catalyst, methyl alcohol and normal hexane (solvent) that are used for alcohol oxidation to generate ester are added in the test tube and carry out the reaction that oxidation generates ester, and specific reaction condition is as follows: The reaction temperature is 35°C, the reaction pressure is normal pressure (0.1MP), the molar ratio of raw material alcohol: cobalt-based catalyst (calculated as cobalt) is 10, the reaction atmosphere is air atmosphere, and the reaction time is 4 days. The product and the productive rate measured after the reaction finishes are close to the results in Table 1. the

Precursor ZIF-67 and the surface physicochemical property analysis of cobalt-based catalyst of the present invention:

The surface physicochemical properties of the ZIF-67 obtained in Example 1 and the cobalt-based catalysts obtained in Examples 7-10 were analyzed respectively. Firstly, the specific surface area and pore volume were measured: ZIF-67 and cobalt-based catalysts were vacuum-dried at 150°C for 12 hours, and nitrogen adsorption and desorption tests were carried out on the Micromeritics ASAP2020 analyzer at 77K to obtain the specific surface area and pore volume of the material . The analysis results are shown in Table 3. the

Table 3. Pore structure data of cobalt-based catalysts prepared at different carbonization temperatures

It can be seen from Table 3 that the cobalt-based catalyst of the present invention has a specific surface area of about 300 m ² g ^-1 and relatively concentrated pore diameters.

The above-mentioned embodiment is a preferred embodiment of the present invention, but the embodiment of the present invention is not limited by the above-mentioned embodiment, and any other changes, modifications, substitutions, combinations, Simplifications should be equivalent replacement methods, and all are included in the protection scope of the present invention. the

Claims (10)

1. A cobalt-based catalyst for alcohol oxidation to generate ester, characterized in that: the cobalt-based catalyst is mainly composed of transition metal cobalt and carbon, nitrogen, wherein the weight ratio of each element is: cobalt 27.0～50.0wt%, 45.0-60.0 wt% of carbon, 0.5-20.0 wt% of nitrogen; the particle size of cobalt nanoparticles in the cobalt-based catalyst is 5-40nm. 2. the preparation method for the cobalt-based catalyst that is used for alcohol oxidation to generate ester according to claim 1, is characterized in that comprising the steps: (1) Preparation and activation of metal-organic framework material ZIF-67: Weigh cobalt nitrate hexahydrate and 2-methylimidazole (abbreviation: Im) respectively and add to water, stir at room temperature to obtain a mixed solution; Centrifuge, filter to obtain the precipitate, wash the unreacted ligand in the precipitate with water, and then wash the precipitate with methanol solution; finally, vacuumize the precipitate to obtain the metal-organic framework material ZIF-67; (2) Preparation of the catalyst: use the metal-organic framework material ZIF-67 obtained in step (1) as a precursor, heat to the target temperature in an inert atmosphere, pyrolyze at a constant temperature, and then cool to room temperature to obtain a powdery product, which is The cobalt-based catalyst used for the oxidation of alcohols to generate esters. 3. The preparation method according to claim 2, characterized in that: the molar ratio of cobalt nitrate hexahydrate, 2-methylimidazole and water described in step (1) is Co ²⁺ : Im:H ₂ O=1 :58:1100. 4. The preparation method according to claim 2, characterized in that: the time for stirring at room temperature in step (1) is 6 to 8 hours; the vacuum treatment in step (1) is to place the precipitate at 80 to 200° Vacuumize for 12 to 36 hours. 5. The preparation method according to claim 2, characterized in that: the target temperature in step (2) is 400-1200°C. 6. The preparation method according to claim 2, characterized in that: the time for constant temperature pyrolysis in step (2) is 0.5-12 hours. 7. The application of the cobalt-based catalyst for the oxidation of alcohols to generate esters according to claim 1 in catalyzing the oxidation of alcohols to generate esters at normal temperature and pressure without adding alkali. 8. The application according to claim 8, characterized in that it comprises the following steps: putting the cobalt-based catalyst and alcohol into a reactor, and stirring and reacting at normal temperature and pressure to produce the corresponding ester. 9. The application according to claim 8, characterized in that: the alcohol is primary aromatic alcohol, aliphatic alcohol or diol; the control condition for the stirring reaction under normal temperature and pressure is that the reaction temperature is 15-35°C, and the reaction The pressure is normal pressure, and the stirring reaction time is 3-5 days; the molar ratio of the alcohol to the cobalt-based catalyst (calculated as cobalt) is 1-10. 10. The application according to claim 8, characterized in that the cobalt-based catalyst can be recycled and reused after hydrogen reduction at 300-450°C for 0.5-4 hours.