Cobalt supported nitrogen-doped porous carbon catalysts, methods of making and using the same

Abstract

The application belongs to the field of chemical catalysis technology, and particularly relates to a cobalt-loaded nitrogen-doped porous carbon catalyst and a preparation method and application thereof. A series of highly dispersed cobalt-based nitrogen-doped ordered porous carbon catalysts are synthesized by a sacrifice template method. In the catalyst, Co is used as an active component, porous carbon is used as a carrier, mesoporous molecular sieves are used as hard templates, and nitrogen-containing organic matter is used as a ligand. The catalyst has the characteristics of low price, simple operation, high conversion rate, good product selectivity and the like, and the catalyst is convenient to recover, so that the stability of the reaction and the economy of the process are greatly improved.

Description

Technical Field

[0001] This invention belongs to the field of chemical catalysis technology, specifically relating to a cobalt-supported nitrogen-doped porous carbon catalyst, its preparation method, and its application. Background Technology

[0002] In recent years, mesoporous materials have been recognized as a research hotspot and frontier in materials science. Among them, MCM-41 mesoporous molecular sieves possess a highly ordered hexagonal mesoporous structure that is uniform and controllable. Furthermore, their specific surface area and internal surface are easily modified with organic groups. Their unique properties include high loading capacity due to their large surface area and high thermal stability (over 900°C). o C) The large and uniform pore size is suitable for loading organic ligands and transition metals; MCM-41 mesoporous carbon materials have received considerable attention in the field of catalysis and are widely used in environmental applications, petrochemical industry and separation processes.

[0003] Methyl furoate is an important fine chemical product derived from biomass conversion, widely used in food flavoring, tobacco flavoring, and cosmetic flavoring industries. It is also an important chemical raw material and intermediate. The traditional synthesis method involves first oxidizing aldehydes or alcohols to prepare acids or acid derivatives, followed by esterification of the acid or acid derivatives. However, this process is complex and generates many toxic byproducts. Therefore, developing a simple, efficient, and low-cost synthesis method for methyl furoate has significant application value and sustainable development implications.

[0004] Patent CN 104650014 A discloses a supported nano-noble metal catalyst and its preparation method for one-step oxidative esterification of aldehydes. The supported nano-noble metal catalyst has high yield, strong stability, and is easy to recover, but often requires the addition of additives, making it neither environmentally friendly nor costly. Patent CN 109824634 A discloses a cobalt-based composite particle supported catalyst and its preparation method for one-step oxidative esterification of aldehydes. It offers mild catalytic conditions, good effect, long lifespan, and easy separation and recycling, but requires the addition of chloroauric acid, resulting in high cost. Patent CN 109574964 A discloses an N-oxygen radical initiator for one-step oxidative esterification of aldehydes. This method is simple to operate, low in cost, easy to separate, and environmentally friendly, but has low selectivity for methyl furoate. Patent CN 108148024 A discloses a method for preparing methyl furoate by furfural oxidative esterification. This method is green and pollution-free, but the reaction time is long, and the conversion rate is low when the reaction time is short. Patent CN 109433242... A discloses a nitrogen-doped supported porous molybdenum catalyst and its preparation method. The catalyst has a large specific surface area and high selectivity, but it is expensive and has a low conversion rate. At present, there is an urgent need to develop catalysts with high conversion rate, high selectivity, low cost and low energy consumption. The most effective way is to develop catalysts that are completely free of precious metals. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a cobalt-supported nitrogen-doped porous carbon catalyst; the porous carbon catalyst has the characteristics of low price, fast reaction rate, high conversion rate and good selectivity; the present invention also provides its preparation method and application.

[0006] The cobalt-supported nitrogen-doped porous carbon catalyst of the present invention uses cobalt as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 1-5%.

[0007] Cobalt-supported nitrogen-doped porous carbon catalysts have a specific surface area of ​​200–600 m². 2 / g, with a pore size of 3–7 nm.

[0008] in: Nitrogen-containing organic compounds are one or more of alkylpyridine, aminopyridine, vinylpyridine, 2,2'-bipyridine, or melamine.

[0009] The method for preparing the cobalt-supported nitrogen-doped porous carbon catalyst of the present invention comprises the following steps: (1) The hard template and ligand are dissolved in a mixed solution of ethanol and water, and the soluble salt of metallic cobalt is dissolved in ethanol. Then the two solutions are mixed and stirred to remove the solvent, and the solid is heated and calcined. (2) The calcined product obtained in step (1) is etched, centrifuged, washed and dried in an alkaline solution to obtain a cobalt-supported nitrogen-doped porous carbon catalyst.

[0010] in: The hard template mentioned in step (1) is a mesoporous molecular sieve, which is one or more of MCM-22, MCM-41, MCM-48 or ZSM-5.

[0011] The volume ratio of ethanol to water in step (1) is 0.2 to 3:1, and the mass ratio of hard template to ligand is 0.5 to 5:1.

[0012] The soluble salt mentioned in step (1) is one or more of acetate, nitrate, hydrochloride or sulfate; the volume ratio of the amount of soluble cobalt salt to ethanol is 0.01-5:50-2000, in mol / ml, preferably 0.01-5 mol of soluble cobalt salt dissolved in 50-2000 ml of ethanol.

[0013] The mixing temperature of the two solutions in step (1) is 50-120 °C, and the mixture is stirred for 12-16 h. The solvent is removed by rotary evaporation.

[0014] The solid obtained in step (1) is placed in a tube furnace and heated under nitrogen protection at a temperature of 2-10 °C. o The temperature is increased to 600–900 °C at a rate of C / min, and calcined for 1–5 h.

[0015] The alkaline solution mentioned in step (2) is either a sodium hydroxide solution or a potassium hydroxide solution; preferably, 2 to 8 mol of a 0.1 mol / L sodium hydroxide solution.

[0016] The etching time described in step (2) is 10 to 30 hours to remove the hard template.

[0017] The washing process described in step (2) involves a mixed solution of ethanol and water, performed under vacuum at 40–80 °C. o Dry at C for 12-15 hours.

[0018] The application of the cobalt-supported nitrogen-doped porous carbon catalyst of the present invention involves adding the cobalt-supported nitrogen-doped porous carbon catalyst, aldehydes, and alcohols to a reaction vessel under an oxygen atmosphere for one-step oxidative esterification of aldehydes and alcohols to generate esters.

[0019] Wherein: the aldehydes are saturated aldehydes, and the alcohols are saturated alcohols.

[0020] As a preferred technical solution, the application of the cobalt-supported nitrogen-doped porous carbon catalyst of the present invention involves reacting the cobalt-supported nitrogen-doped porous carbon catalyst, furfural, and methanol in a reaction vessel under an oxygen atmosphere of 0.1–3 MPa to prepare methyl furoate.

[0021] in: The reaction temperature is 40–120℃, and the reaction time is 1–3 h; the molar ratio of furfural to methanol is 1:10–100, and the mass of the cobalt-supported nitrogen-doped porous carbon catalyst is 0.1–2 g.

[0022] Compared with the prior art, the present invention has the following advantages: (1) The cobalt-supported nitrogen-doped porous carbon catalyst of the present invention uses Co as the active component and porous carbon as the support; it has the characteristics of low price, fast reaction rate, high conversion rate, good selectivity and long service life; the conversion rate and selectivity do not decrease significantly after the catalyst is recycled.

[0023] (2) The cobalt-supported nitrogen-doped porous carbon catalyst of the present invention has the effect of the doped nitrogen atoms on the spin density and charge distribution of adjacent carbon atoms, thereby generating more structural defects (such as nitrogen-containing functional groups) and active sites; the electronegativity of doped nitrogen can stabilize the deposited metal, increase the binding energy of cobalt carbon, thereby improving catalytic performance and stability.

[0024] (3) The cobalt-supported nitrogen-doped porous carbon catalyst of the present invention forms a core-shell structure of nitrogen-doped single-layer carbon, which can effectively prevent the loss of active metal.

[0025] (4) The cobalt-supported nitrogen-doped porous carbon catalyst of the present invention can effectively fix the substrate by doping nitrogen atoms and improve the adsorption performance of the substrate; the doped nitrogen atoms, especially lone pair nitrogen atoms, will increase the electron density of the metal, thereby promoting the oxidative addition of OH bonds or CH bonds, resulting in an increase in reaction rate and thus improving the activity of the catalyst.

[0026] (5) The cobalt-supported nitrogen-doped porous carbon catalyst of the present invention is prepared by the sacrificial template method, which is simple to operate, and the prepared catalyst has high conversion rate and good product selectivity.

[0027] (6) The cobalt-supported nitrogen-doped porous carbon catalyst described in this invention is used for the one-step oxidation esterification of aldehydes and alcohols to produce esters. It has the characteristics of high catalyst conversion rate and good product selectivity. Furthermore, the catalyst is easy to recover, which greatly improves the stability of the reaction and the economy of the process. Attached Figure Description

[0028] Figure 1This is a scanning electron microscope image of the cobalt-supported nitrogen-doped porous carbon catalyst prepared in Example 1; Figure 2 This is a transmission electron microscope (TEM) image of the cobalt-supported nitrogen-doped porous carbon catalyst prepared in Example 1. Detailed Implementation

[0029] The present invention will be further described below with reference to embodiments.

[0030] Example 1 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 1 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 2.7%.

[0031] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 532 m². 2 / g, with a pore size of 5.0 nm.

[0032] The preparation method of the cobalt-supported nitrogen-doped porous carbon catalyst described in Example 1 consists of the following steps: First, dissolve 5 g of MCM-41 and 4.68 g of 2,2'-bipyridine in a mixture of 20 ml of water and ethanol (V:V = 1:1), and heat at 80 °C. o Under vigorous stirring, 2.37 g of CoCl2·6H2O was dissolved in 50 ml of ethanol. The two solutions were mixed to form a yellow solution, and then heated at 80°C. o Stirred overnight at C for 12 h, then remove the solvent by rotary evaporation; the resulting solid was then placed in a tube furnace under nitrogen protection at 4°C. o Heating at a rate of C / min to 800 o The material was then calcined at 70°C for 2 hours; subsequently, it was etched in a 6 mol NaOH solution (0.1 mol / L) for 24 hours to remove the template. The material was collected by centrifugation and washed with a mixture of ethanol and water. Finally, the obtained catalyst was heated under vacuum at 70°C. o Dry at C for 12 hours.

[0033] The application of the cobalt-supported nitrogen-doped porous carbon catalyst described in Example 1 for the preparation of methyl furfurylate follows the steps below: The reaction was carried out in a 50 ml stainless steel jacketed depressurized batch reactor according to conventional procedures. 0.5 g of the catalyst, 0.01 mol of furfural, and 0.2 mol of methanol were added. A mass flow meter controlled a stable oxygen flow rate of 15 mol / min, and a distributor was used to maintain good gas distribution. A magnetic stirrer was used for heating and stirring to maintain good contact between the gas, liquid, and solid phases. The tail gas from the reaction outlet was cooled and refluxed using a condenser to prevent the volatilization of raw materials and reaction products. A pressure regulating valve was connected after the condenser to control the pressure in the reactor. After sealing the reaction apparatus, oxygen was first introduced to 0.5 MPa, and then a circulating water bath was started to heat the reactor at 80°C. Stirring was then started to initiate the reaction. After 2 hours of reaction, the gas inlet and stirring were stopped, the heating was turned off, circulating cold water was introduced for cooling, the gas was purged, and the sample was taken out for gas chromatography analysis. The detection data are shown in Table 1.

[0034] Example 2 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 2 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 1.7%.

[0035] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 258 m². 2 / g, with a pore size of 5.4 nm.

[0036] In Example 1, MCM-41 was replaced with ZSM-5, and the remaining steps for preparing the cobalt-supported nitrogen-doped porous carbon catalyst were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The detection results are shown in Table 1.

[0037] Example 3 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 3 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 2.5%.

[0038] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 468 m². 2 / g, with a pore size of 4.5 nm.

[0039] In Example 1, MCM-41 was replaced with MCM-22, and the remaining steps for preparing the cobalt-supported nitrogen-doped porous carbon catalyst were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The detection results are shown in Table 1.

[0040] Example 4 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 4 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 2.8%.

[0041] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 496 m². 2 / g, with a pore size of 4.9 nm.

[0042] In Example 1, MCM-41 was replaced with MCM-48, and the remaining steps for preparing the cobalt-supported nitrogen-doped porous carbon catalyst were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The detection results are shown in Table 1.

[0043] Example 5 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 5 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 2.7%.

[0044] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 468 m². 2 / g, with a pore size of 4.8 nm.

[0045] In Example 1, 2,2'-bipyridine was replaced with alkylpyridine, and the remaining steps for preparing the cobalt-supported nitrogen-doped porous carbon catalyst were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The detection results are shown in Table 1.

[0046] Example 6 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 6 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 2.7%.

[0047] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 456 m². 2 / g, with a pore size of 4.6 nm.

[0048] In Example 1, 2,2'-bipyridine was replaced with aminopyridine, and the remaining steps for preparing the cobalt-supported nitrogen-doped porous carbon catalyst were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The detection results are shown in Table 1.

[0049] Example 7 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 7 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 2.7%.

[0050] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 475 m². 2 / g, with a pore size of 4.7 nm.

[0051] In Example 1, 2,2'-bipyridine was replaced with vinylpyridine, and the remaining steps for preparing the cobalt-supported nitrogen-doped porous carbon catalyst were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The results are shown in Table 1.

[0052] Example 8 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 8 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 2.7%.

[0053] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 450 m². 2 / g, with a pore size of 3.9 nm.

[0054] In Example 1, 2,2'-bipyridine was replaced with melamine, and the remaining steps for preparing the cobalt-supported nitrogen-doped porous carbon catalyst were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The detection results are shown in Table 1.

[0055] Example 9 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 9 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 2.7%.

[0056] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 487 m². 2 / g, with a pore size of 4.8 nm.

[0057] The 2.37 g CoCl2·6H2O in Example 1 was replaced with 1.83 g Co(NO3)2, and the remaining steps for preparing the cobalt-supported nitrogen-doped porous carbon catalyst were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The detection results are shown in Table 1.

[0058] Example 10 The cobalt-supported nitrogen-doped porous carbon catalyst described in Example 10 uses Co as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 2.7%.

[0059] The specific surface area of ​​the cobalt-supported nitrogen-doped porous carbon catalyst is 512 m². 2 / g, with a pore size of 5.0 nm.

[0060] The 2.37 g CoCl2·6H2O in Example 1 was replaced with 2.81 g CoSO4·7H2O, and the remaining steps for preparing the cobalt-supported nitrogen-doped porous carbon catalyst were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The detection results are shown in Table 1.

[0061] Example 11 The steps were the same as in Example 1. The catalyst was recycled eight times to prepare methyl furoate, and the conversion rate and selectivity were tested. The test results are shown in Table 1.

[0062] Comparative Example 1 The catalyst was prepared by impregnation. 2.37 g of CoCl₂·6H₂O and 4.68 g of 2,2'-bipyridine were dissolved in 50 ml of ethanol and stirred for 4 h. Then, the support MCM-41 was added, and the water bath temperature was controlled at 45°C. o C, stir for 2 h, remove solvent by rotary evaporation, 80 o Dry at 4°C for 12 hours, then place the resulting solid in a tube furnace under nitrogen protection. o Heating at a rate of C / min to 800 o The porous carbon catalyst was calcined at C for 2 h and then used to prepare methyl furoate under the same conditions as in Example 1. The conversion rate of aldehyde and the selectivity of ester were tested, and the results are shown in Table 1.

[0063] Comparative Example 2 The 2.37 g CoCl2·6H2O in Example 1 was replaced with 2.70 g FeCl3·6H2O, and the remaining steps were the same as in Example 1. The obtained porous carbon catalyst was used to prepare methyl furoate under the same conditions as in Example 1, and the conversion rate of aldehyde and the selectivity of ester were detected. The detection results are shown in Table 1.

[0064] Table 1. Conversion and selectivity data for Examples 1-11 and Comparative Examples 1-2

Claims

1. The application of a cobalt-supported nitrogen-doped porous carbon catalyst, characterized in that: The cobalt-supported nitrogen-doped porous carbon catalyst uses cobalt as the active component, porous carbon as the support, and nitrogen-containing organic matter as the ligand; the cobalt loading is 1-5%; the nitrogen-containing organic matter is one or more of alkylpyridine, aminopyridine, vinylpyridine, 2,2'-bipyridine, or melamine. The method for preparing the cobalt-supported nitrogen-doped porous carbon catalyst comprises the following steps: (1) The hard template and ligand are dissolved in a mixed solution of ethanol and water, and the soluble salt of metallic cobalt is dissolved in ethanol. Then the two solutions are mixed and stirred to remove the solvent, and the solid is heated and calcined. (2) The calcined product obtained in step (1) is etched, centrifuged, washed and dried in an alkaline solution to obtain a cobalt-supported nitrogen-doped porous carbon catalyst. in: The hard template mentioned in step (1) is a mesoporous molecular sieve, which is one or more of MCM-22, MCM-41, MCM-48 or ZSM-5; In step (1), the mass ratio of the hard template to the ligand is 0.5 to 5:1; In step (1), the volume ratio of the amount of soluble cobalt salt to ethanol is 0.01–5: 50–2000, in mol / ml. Application of the cobalt-supported nitrogen-doped porous carbon catalyst: Under an oxygen atmosphere, the cobalt-supported nitrogen-doped porous carbon catalyst, aldehydes, and alcohols are added to a reactor for reaction, which is used for one-step oxidative esterification of aldehydes and alcohols to generate esters.

2. The application of the cobalt-supported nitrogen-doped porous carbon catalyst according to claim 1, characterized in that: In step (1), the volume ratio of ethanol to water is 0.2 to 3:

1.

3. The application of the cobalt-supported nitrogen-doped porous carbon catalyst according to claim 1, characterized in that: In step (1), the soluble salt is one or more of acetate, nitrate, hydrochloride or sulfate.

4. The application of the cobalt-supported nitrogen-doped porous carbon catalyst according to claim 1, characterized in that: In step (1), the mixing temperature of the two solutions is 50-120℃, and the mixture is stirred for 12-16 hours. The solvent is removed by rotary evaporation. The resulting solid is placed in a tube furnace and heated to 600-900℃ at a rate of 2-10℃ / min under nitrogen protection. The solid is then calcined for 1-5 hours.

5. The application of the cobalt-supported nitrogen-doped porous carbon catalyst according to claim 1, characterized in that: In step (2), the alkaline solution is either sodium hydroxide solution or potassium hydroxide solution; the etching time is 10-30 h; the washing is performed with a mixed solution of ethanol and water, and the solution is dried under vacuum at 40-80 °C for 12-15 h.

6. The application of the cobalt-supported nitrogen-doped porous carbon catalyst according to claim 1, characterized in that: Methyl furoate was prepared by reacting cobalt-supported nitrogen-doped porous carbon catalyst, furfural, and methanol in an oxygen atmosphere of 0.1–3 MPa in a reactor. The reaction temperature was 40–120 °C, the reaction time was 1–3 h, the molar ratio of furfural to methanol was 1:10–100, and the mass of the cobalt-supported nitrogen-doped porous carbon catalyst was 0.1–2 g.

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