CN111408392A - Cobalt-nitrogen co-doped porous carbon material catalyst, preparation method and application thereof - Google Patents

Abstract

The invention discloses a cobalt-nitrogen co-doped porous carbon material catalyst, a preparation method thereof and application thereof in 2-hydroxymethylfurfural oxidation esterification reaction. The catalyst is prepared by taking chitosan as a precursor, stirring and mixing the chitosan with zinc salt and cobalt salt, and then pyrolyzing the mixture at high temperature. The cobalt-nitrogen co-doped porous carbon material is used as a catalyst, methanol is used as a solvent, an aldehyde group protection reagent and an esterification reagent, and oxygen at normal pressure is used as an oxidant, so that the conversion of HMF to furan-2, 5-methyl diformate can be realized at 50 ℃. The catalyst is cheap and easy to obtain, noble metal catalysts such as gold and palladium do not need to be added, the catalytic reaction condition is mild, the oxidation and esterification of HMF can be realized at low temperature and normal pressure in an oxygen atmosphere, the catalytic reaction can be carried out at high concentration, and the catalyst is suitable for industrial application.

Description

Cobalt-nitrogen co-doped porous carbon material catalyst, preparation method and application thereof

technical field

The invention belongs to the technical field of metal organic catalysis, and relates to a cobalt-nitrogen co-doped porous carbon material catalyst for oxidative esterification of 2-hydroxymethyl furfural and a preparation method thereof.

Background technique

Cobalt-nitrogen co-doped carbon materials are widely used in the fields of organic catalysis, electrocatalysis and energy storage. Common methods for synthesizing such materials generally use organic ligands to coordinate with cobalt salts, then add activated carbon support, and prepare them by high temperature pyrolysis (GreenChemistry 2018, 20(1), 266-273; ChemSusChem 2014, 7(12), 3334-3340.). However, the carbon material prepared by this method has a small specific surface area, and its metal active sites are covered by carbon, so the catalytic performance is poor. By adding sacrificial agents, such as SiO ₂ and inorganic metal salts in the preparation of carbon materials, porous carbon materials with high specific surface area can be prepared through the subsequent etching process, but the etching process is cumbersome and generally requires strong acid and alkali solutions (Science Advances 2018, 4(7), eaat0788). Using cobalt-zinc bimetallic ZIF materials as precursors, cobalt-nitrogen co-doped porous carbon materials can also be obtained by the self-sacrificial template method, but the ZIF precursors have low yield (<10%) and high cost and are not suitable for large-scale production. Scale production (Advanced Materials 2015, 27(34), 5010-5016.).

2-Hydroxymethylfurfural (HMF) is an important class of chemical substances generated from the dehydration of biomass such as glucose, fructose, and cellulose. It can be used to convert into a variety of commercial chemicals, which are oxidatively esterified by HMF. The resulting FDMC is an important unit for the synthesis of PEF plastics, and thus has received extensive attention from industry and academia. The common HMF oxidative esterification methods mainly include the following two: (1) HMF oxidative esterification reaction catalyzed by noble metals such as Pd and Au as catalysts (ChemSusChem2008,1,75-78; J.Catal.2015,326,1 -8; Green Chem. 2018, 20, 3050-3058.); (2) HMF oxidative esterification catalyzed by non-precious metals such as Co and Cu as catalysts (ChemSusChem 2014, 7, 3334-3340; ChemCatChem 2016, 8, 2907-2911; Catal. Commun. 2017, 90, 91-94.).

However, the above methods have some disadvantages. For example, the use of precious metal catalysts such as Pd and Au increases the reaction cost, which is not conducive to industrial application; the use of alkalis such as sodium methoxide and potassium carbonate will cause water pollution, which is not conducive to environmental protection; the reaction requires additional K- OMS-2 and other additives; the temperature and pressure required for the reaction are very high, which will cause side reactions and have potential safety hazards.

SUMMARY OF THE INVENTION

The purpose of the present invention is to provide a cobalt-nitrogen co-doped porous carbon material catalyst and a preparation method thereof. The catalyst has excellent catalytic performance for HMF oxidative esterification.

The technical scheme that realizes the object of the present invention is as follows:

The preparation method of a cobalt-nitrogen co-doped porous carbon material catalyst uses chitosan as a precursor to prepare a cobalt-nitrogen co-doped porous carbon material catalyst, and the specific steps are as follows:

Step 1, sequentially add zinc salt, cobalt salt and chitosan to the solvent, stir and mix well, remove the solvent by vacuum distillation, and dry, the solvent is any of methanol, ethanol, water, methanol and water mixed solution. One, the mass ratio of described zinc and cobalt is 4～16:1;

In step 2, the mixture obtained in step 1 is heated up to 700-900° C. under an argon atmosphere at a heating rate of 5-10° C./min, and then calcined to obtain a cobalt-nitrogen co-doped porous carbon material Co@CN-ZnX -Y.

Preferably, in step 1, the zinc salt is zinc acetate, zinc nitrate or zinc sulfate.

Preferably, in step 1, the cobalt salt is cobalt chloride, cobalt nitrate or cobalt acetate.

Preferably, in step 1, the mass ratio of zinc to cobalt is 8-12:1.

Preferably, in step 1, the drying is vacuum drying, the drying temperature is 80-100° C., and the drying time is 12-24 h.

Preferably, in step 1, the stirring and mixing temperature is 25-80° C., and the stirring time is 12-48 h.

Preferably, in step 2, the holding time during the calcination is 1-4h.

The present invention provides a cobalt-nitrogen co-doped porous carbon material catalyst prepared by the above preparation method.

The invention also provides the application of the above-mentioned cobalt nitrogen co-doped porous carbon material catalyst in HMF oxidative esterification, using the cobalt nitrogen co-doped porous carbon material as the catalyst, without adding alkali or noble metal, low temperature, normal pressure oxygen Catalytic HMF oxidative esterification, the concrete method is as follows:

Mix HMF, cobalt-nitrogen co-doped porous carbon material catalyst and methanol, react at 50-60 ℃ under normal pressure oxygen condition, cool down after the reaction, separate the catalyst and the reaction liquid, remove methanol by rotary evaporation of the organic phase, and obtain by recrystallization reaction product.

Preferably, the reaction time is 16-18h.

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

(1) the catalyst of the present invention uses cheap biomass chitosan as a precursor, the cost is low, the preparation process is simple, environmentally friendly, and has the possibility of enlarged production;

(2) Using the cobalt-nitrogen co-doped porous carbon material of the present invention as a catalyst to catalyze the oxidative esterification of HMF, the reaction conditions are mild, no alkali, strong oxidant or precious metal catalyst is required, the yield is high, the selectivity is good, and the product is easy Separation, the reaction can be carried out at high concentration (2M), with the possibility of scale-up production.

Description of drawings

FIG. 1 is a SEM image of the cobalt-nitrogen co-doped porous carbon material catalyst of the present invention.

Fig. 2 is a graph showing the effect of different heating rates on the specific surface area of cobalt-nitrogen co-doped porous carbon materials and the yield of HMF oxidative esterification.

Figure 3 is a graph showing the effect of the mass ratio of Zn and Co on the specific surface area of the cobalt-nitrogen co-doped porous carbon material and the yield of HMF oxidative esterification.

Detailed ways

The present invention will be described in further detail below in conjunction with the embodiments and the accompanying drawings.

Example 1: Preparation of cobalt-nitrogen co-doped porous carbon material

Add zinc acetate dihydrate (338mg), cobalt chloride hexahydrate (100mg) and chitosan (500mg) to the mixed solution of methanol and water (10g methanol, 10g water) respectively, stir and mix well at 50°C, reduce the pressure The solvent was distilled off and dried in a vacuum oven at 80°C for 12h. The obtained solid was calcined at 900 °C (the heating rate was 5 °C/min, and the holding time was 2 h) in an argon atmosphere in a tube furnace, and the obtained black powder was the cobalt-nitrogen co-doped porous carbon material Co@CN-Zn4- 5. By changing the mass ratio X of Zn and Co (where the mass of Co remains unchanged), and the heating rate Y of pyrolysis, a series of cobalt nitrogen-doped porous carbon materials Co@CN-ZnX-Y can be obtained.

Example 2: Oxidative Esterification of HMF

The reaction route is as follows:

0.3 mmol of HMF, 15 mg of Co@CN-ZnX-Y (Co 10 mol%), and 3 mL of methanol were added to the reaction vessel, and the reaction was carried out at 50 °C for 16 h under atmospheric oxygen conditions. After the reaction is completed and the temperature is lowered, the catalyst and the reaction solution are separated, the solvent is removed from the organic phase by rotary evaporation, and the reaction product is obtained by recrystallization. The specific surface area of the catalyst Co@CN-ZnX-Y can be adjusted by changing the mass ratio X of Zn and Co, and the heating rate Y of pyrolysis, and its specific surface area is proportional to the yield of HMF oxidative esterification. The specific results are shown in Fig. 2. Show. Among them, the catalyst Co@CN-Zn12-5 has the largest specific surface area of 658m ² /g, and the target product yield obtained by its catalytic reaction is also the highest (94%).

Example 3: Oxidative Esterification of High Concentration HMF (2M)

4 mmol HMF, 200 mg Co@CN-Zn12-5 (Co 10 mol%), and 2 mL methanol were added to the reaction vessel, and the reaction was carried out at 50 °C for 24 h under atmospheric oxygen conditions. After the reaction was completed and the temperature was lowered, the catalyst and the reaction solution were separated, the solvent was removed from the organic phase by rotary evaporation, and the reaction product was obtained by recrystallization, and the isolated yield was 85%.

Figure 1 is the SEM image of the cobalt-nitrogen co-doped porous carbon material catalyst, in which (a) Co@CN-Zn0-5 (b) Co@CN-Zn4-5 (c) Co@CN-Zn8-5 (d) Co@CN-Zn12-5. Figure 2 is a graph showing the effect of different heating rates on the specific surface area of the cobalt-nitrogen co-doped porous carbon material and the yield of HMF oxidative esterification. It can be seen from Figure 2 that when the heating rate is too low (2.5 °C/min) or the heating rate is too high (15 °C/min), the specific surface area of the prepared cobalt-nitrogen co-doped porous carbon material is lower, and the corresponding The yield of HMF oxidative esterification also decreased significantly. When the heating rate was 5-10 °C/min, the specific surface area of the prepared cobalt-nitrogen co-doped porous carbon material and the corresponding HMF oxidative esterification reaction yield were higher. Figure 3 is a graph showing the effect of the mass ratio of Zn and Co on the specific surface area of the cobalt-nitrogen co-doped porous carbon material and the yield of HMF oxidative esterification. It can be seen from Figure 3 that if the mass ratio of Zn and Co is too low (0 or 2), the specific surface area of the prepared cobalt-nitrogen co-doped porous carbon material is low, and the corresponding HMF oxidative esterification reaction yield is also low. significantly decreased. When the mass ratio of Zn to Co is 4-16:1, the specific surface area of the prepared cobalt-nitrogen co-doped porous carbon material and the corresponding HMF oxidative esterification reaction yield are higher, and when the mass ratio is 8-12 , the prepared cobalt-nitrogen co-doped porous carbon material has the highest specific surface area and corresponding HMF oxidative esterification reaction yield.

Claims (10)

1. the preparation method of cobalt nitrogen co-doped porous carbon material catalyst, is characterized in that, concrete steps are as follows: Step 1, sequentially add zinc salt, cobalt salt and chitosan to the solvent, stir and mix well, remove the solvent by vacuum distillation, and dry, the solvent is any of methanol, ethanol, water, methanol and water mixed solution. One, the mass ratio of described zinc and cobalt is 4～16:1; In step 2, the mixture obtained in step 1 is heated up to 700-900° C. under an argon atmosphere at a heating rate of 5-10° C./min, and then calcined to obtain a cobalt-nitrogen co-doped porous carbon material Co@CN-ZnX -Y. 2. preparation method according to claim 1 is characterized in that, in step 1, described zinc salt is zinc acetate, zinc nitrate or zinc sulfate, and described cobalt salt is cobalt chloride, cobalt nitrate or cobalt acetate . 3. The preparation method according to claim 1, wherein in step 1, the mass ratio of the zinc to cobalt is 8-12:1. 4 . The preparation method according to claim 1 , wherein in step 1, the drying is vacuum drying, the drying temperature is 80-100° C., and the drying time is 12-24 h. 5 . 5 . The preparation method according to claim 1 , wherein, in step 1, the stirring and mixing temperature is 25-80° C., and the stirring time is 12-48 h. 6 . 6 . The preparation method according to claim 1 , wherein, in step 2, the holding time during the calcination is 1 to 4 h. 7 . 7. The cobalt-nitrogen co-doped porous carbon material catalyst prepared by the preparation method according to any one of claims 1 to 6. 8. The application of the cobalt-nitrogen co-doped porous carbon material catalyst according to claim 7 in the oxidative esterification of HMF. 9. application according to claim 8, is characterized in that, concrete method is as follows: Mix HMF, cobalt-nitrogen co-doped porous carbon material catalyst and methanol, react at 50-60 °C under atmospheric oxygen conditions, cool down after the reaction, separate the catalyst and the reaction liquid, remove methanol by rotary evaporation of the organic phase, and obtain by recrystallization reaction product. 10 . The application according to claim 9 , wherein the reaction time is 16-18 h. 11 .

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