阅读说明：本技术 CuCo-N/C纳米催化剂的制备方法及其催化氧化1,2-丙二醇制备乳酸的应用 (Preparation method of CuCo-N/C nano catalyst and application of CuCo-N/C nano catalyst in preparing lactic acid by catalytic oxidation of 1, 2-propylene glycol ) 是由 卢聪明 吕明俊 冯永海 王慧杰 于 2020-05-19 设计创作，主要内容包括：本发明属于催化技术领域,涉及CuCo-N/C纳米催化剂的制备方法及其催化氧化1,2-丙二醇制备乳酸的应用,采用蚕丝作为天然的富氮碳前驱体,碳化后形成氮掺杂碳材料,氮含量高达9.4％,在与活性元素Cu-Co的键合下形成CuCo-N活性位点,提高了催化剂的活性,同时由于碳层的包覆作用,具有良好的抗氧化性能,在催化氧化1,2-丙二醇制备乳酸的反应中,该催化剂表现出良好的催化活性和产物选择性,所制备的铜基纳米催化剂颗粒小且分散均匀,具有良好的催化寿命。(The invention belongs to the technical field of catalysis, and relates to a preparation method of a CuCo-N/C nano catalyst and an application of the CuCo-N/C nano catalyst in preparing lactic acid by catalytic oxidation of 1, 2-propylene glycol, wherein silk is used as a natural nitrogen-rich carbon precursor, a nitrogen-doped carbon material is formed after carbonization, the nitrogen content is up to 9.4%, a CuCo-N active site is formed under bonding with an active element Cu-Co, the activity of the catalyst is improved, and simultaneously, due to the coating effect of a carbon layer, the catalyst has good oxidation resistance, and in the reaction of preparing the lactic acid by catalytic oxidation of 1, 2-propylene glycol, the catalyst shows good catalytic activity and product selectivity, and the prepared copper-based nano catalyst has small particles, uniform dispersion and good catalytic life.)

A preparation method of a CuCo-N/C nano catalyst is characterized by comprising the following steps:

step 1, preparing a regenerated silk fibroin solution, and marking as RSF for later use;

step 2, preparing Cu-Co bimetal nanoparticle colloid:

adding a certain amount of copper salt and cobalt salt into the prepared regenerated fibroin solution, increasing the chelating capacity of the regenerated fibroin solution and Cu-Co bimetal by adjusting the pH value of the solution, and stirring at room temperature to react to obtain a Cu-Co bimetal nanoparticle colloid;

step 3, freeze-drying and carbonizing to prepare the CuCo-N/C doped bimetallic nano-catalyst:

and (3) freeze-drying a certain amount of the Cu-Co bimetal nanoparticle colloid prepared in the step (2), taking out, and then preserving heat at a certain carbonization temperature to obtain the CuCo-N/C doped bimetal nano catalyst.

2. The preparation method of CuCo-N/C nanocatalyst as claimed in claim 1, wherein in the step 1, the preparation step of the regenerated silk fibroin solution RSF is as follows: shearing silkworm cocoons into pieces with uniform size, adding the pieces into 0.02M anhydrous sodium carbonate solution, and boiling for 30 minutes to obtain regenerated silk fibroin; cleaning regenerated silk fibroin for three times by using deionized water, naturally drying for three days at room temperature, adding the dried regenerated silk fibroin into a 9.3M lithium bromide solution, preserving the heat in a 60 ℃ drying oven for 4 hours, dialyzing for three days to remove lithium bromide, and centrifuging to remove insoluble impurities to obtain a regenerated silk fibroin solution; wherein the mass concentration of RSF is 4-5%.

3. The method for preparing CuCo-N/C nanocatalyst of claim 1, wherein in step 2, the copper salt is Cu (NO)₃)₂·2H₂O, cobalt salts being Co (NO)₃)₂·6H₂The mass ratio of O, metal Cu and Co is 6: 4.

4. The method for preparing a CuCo-N/C nanocatalyst as claimed in claim 1, wherein in the step 2, the pH value of the solution is adjusted to be: and (3) adjusting the pH value of the reaction solution to 10.86-11.03 by using a 50% NaOH aqueous solution, and stirring for 24 hours.

5. The method for preparing a CuCo-N/C nanocatalyst according to claim 1, wherein in the step 3, the freeze-drying temperature is-85 ℃; the freeze-drying time is 3-5 days; the carbonization temperature is 800-1000 ℃, and the heat preservation time is 4 h.

The CuCo-N/C nano catalyst is characterized by being prepared by the preparation method of any one of claims 1-5, wherein the loading amount of Cu-Co bimetallic nanoparticles in the catalyst is 10% of the mass of carrier regenerated silk fibroin.

7. Use of the CuCo-N/C nanocatalyst of claim 6 for preparing lactic acid by catalytic oxidation of 1, 2-propanediol.

8. Use according to claim 7, characterized by the steps of:

firstly, adding sodium hydroxide into a prepared 1, 2-propylene glycol aqueous solution with a certain concentration to form a mixed solution, then adding a certain mass of CuCo-N/C nano catalyst, adding the reaction stock solution into a quick-open high-pressure reaction kettle, introducing oxygen to remove air in the reaction kettle, introducing oxygen with a certain pressure after checking the tightness, starting a stirring device and a heating device, starting timing after reaching a specified temperature, stopping the reaction after reacting for a certain time, filtering and acidifying the reaction product, analyzing by adopting a high performance liquid chromatography and a gas chromatography, and calculating the result.

9. The use according to claim 8, wherein in the mixed solution, 1, 2-propanediol is used in a concentration of 0.16-0.48mol/L and the ratio of the concentration of sodium hydroxide to the concentration of 1, 2-propanediol is 0.5-3: 2;

the oxygen pressure is 0.1-2MPa, the stirring speed is 800rpm, the catalytic reaction temperature is 80-160 ℃, the catalytic reaction time is 1-8h, and the dosage ratio of the mixed solution to the CuCo-N/C nano catalyst is 40 mL: 0.05-0.15 g.

Technical Field

The invention belongs to the technical field of catalysis, and relates to a preparation method of a CuCo-N/C nano catalyst and application of the CuCo-N/C nano catalyst in preparing lactic acid by catalytic oxidation of 1, 2-propylene glycol.

Background

Lactic acid, a commonly used biomass derivative, plays an important role in food processing, drug synthesis and cosmetic production, and is also used as a monomer for synthesizing polylactic acid in chemical industrial production, so the annual global consumption of lactic acid is increasing year by year. The existing method for synthesizing lactic acid mainly comprises chemical synthesis, biological fermentation and the like, wherein the biological fermentation mainly utilizes a proper microorganism to produce lactic acid in a proper environment, but is accompanied by a large amount of biological sludge, and has the advantages of low reaction rate and high cost; also, chemical synthesis, which involves reacting acetaldehyde with HCN and then hydrolyzing with sulfuric acid, is not environmentally friendly although it yields high yields. Therefore, a high-efficiency and environment-friendly path for preparing the lactic acid is researched and developed, and the method has important social and economic significance and environmental protection significance.

1, 2-propanediol is a carbon source believed to replace and regenerate high value acids from the oxidation of biomass polyols (e.g., glycerol, isopropanol, sorbitol, etc.). In recent years, researches on the preparation of important chemicals by a chemical conversion method using 1, 2-propanediol as a renewable carbon source have attracted strong attention of researchers to establish a "biomass-to-chemical value chain" of 1, 2-propanediol. Mainly along with a large amount of byproduct glycerin in the large-scale biodiesel production process, the upstream biomass raw material of the 1, 2-propylene glycol is rich, and along with the expansion of the scale of the coproduction of the dimethyl carbonate and the 1, 2-propylene glycol, the serious problem that the supply of the 1, 2-propylene glycol is greater than the demand in the aspect of the production of the organic solvent and the unsaturated polyester resin is caused. Therefore, it is a very significant subject to study the change of 1, 2-propanediol into valuable lactic acid under such circumstances.

In previous reports, most of the catalysts for researching 1, 2-propylene glycol are noble metal catalysts such as Au, Au-Pd, Au-Pt and the like, although the noble metal catalysts have high catalytic activity and lactic acid selectivity, the cost is high, the expansion application is limited, therefore, the development of a green and high-efficiency replaceable non-noble metal catalyst is still a huge challenge in the field!

Disclosure of Invention

The method comprises the steps of firstly degumming and dissolving silkworm cocoons to prepare a regenerated silk fibroin solution (RSF), adding Cu-Co bimetal, freeze-drying the solution, preparing a CuCo-N/C bimetal nano catalyst by carbonizing and reducing the Cu-Co at high temperature, and applying the CuCo-N/C bimetal nano catalyst to catalyze 1, 2-propylene glycol to prepare lactic acid. In the invention, the catalyst has the advantages of small usage amount, high catalytic activity, low temperature required by reaction, small pressure and longer service life.

The technical scheme of the invention is as follows:

the preparation method of the CuCo-N/C nano catalyst comprises the following steps:

step 1, preparing a regenerated silk fibroin solution, and marking as RSF for later use;

step 2, preparing Cu-Co bimetal nanoparticle colloid:

adding a certain amount of copper salt and cobalt salt into the prepared regenerated fibroin solution (RSF), increasing the chelating capacity of the regenerated fibroin solution and Cu-Co bimetal by adjusting the pH value of the solution, and stirring at room temperature for reaction to obtain a Cu-Co bimetal nanoparticle colloid;

step 3, freeze-drying and carbonizing to prepare the CuCo-N/C doped bimetallic nano-catalyst:

and (3) freeze-drying a certain amount of the Cu-Co bimetal nanoparticle colloid prepared in the step (2), taking out, and then preserving heat at a certain carbonization temperature to obtain the CuCo-N/C doped bimetal nano catalyst.

In step 1, the preparation of the regenerated silk fibroin solution (RSF) comprises the following steps: shearing silkworm cocoons into pieces with uniform size, adding the pieces into 0.02M anhydrous sodium carbonate solution, and boiling for 30 minutes to obtain regenerated silk fibroin; cleaning regenerated silk fibroin with deionized water for three times, naturally drying at room temperature for three days, adding into 9.3M lithium bromide solution, keeping the temperature in a 60 ℃ oven for 4 hours, dialyzing for three days to remove lithium bromide, and centrifuging to remove insoluble impurities to obtain regenerated silk fibroin solution (RSF); wherein the mass concentration of RSF is 4-5%.

In step 2, the copper salt is Cu (NO)₃)₂·2H₂O, cobalt salts being Co (NO)₃)₂·6H₂The mass ratio of O, metal Cu and Co is 6: 4.

In step 2, the pH value of the solution is adjusted to: and (3) adjusting the pH value of the reaction solution to 10.86-11.03 by using a 50% NaOH aqueous solution, and stirring for 24 hours.

In the step 3, the freeze-drying temperature is-85 ℃; the freeze-drying time is 3-5 days; the carbonization temperature is 800-1000 ℃, and the heat preservation time is 4 h.

In the step 3, in the prepared CuCo-N/C doped bimetallic nano-catalyst, the loading capacity of Cu-Co bimetallic nano-particles is 10% of the mass of carrier regenerated fibroin.

The application of the CuCo-N/C nano-catalyst prepared by the invention in preparing lactic acid by catalytic oxidation of 1, 2-propylene glycol comprises the following specific steps:

firstly, adding sodium hydroxide into a prepared 1, 2-propylene glycol aqueous solution with a certain concentration to form a mixed solution, then adding a certain mass of CuCo-N/C nano catalyst, adding the reaction stock solution into a quick-open high-pressure reaction kettle, introducing oxygen to remove air in the reaction kettle, introducing oxygen with a certain pressure after checking the tightness, starting a stirring device and a heating device, starting timing after reaching a specified temperature, stopping the reaction after reacting for a certain time, filtering and acidifying the reaction product, analyzing by adopting a high performance liquid chromatography and a gas chromatography, and calculating the result.

In the mixed solution, the concentration of 1, 2-propylene glycol is 0.16-0.48mol/L, the concentration ratio of sodium hydroxide to 1, 2-propylene glycol is 0.5-3:2, the oxygen pressure is 0.1-2MPa, the stirring speed is 800rpm, the catalytic reaction temperature is 80-160 ℃, the catalytic reaction time is 1-8h, and the dosage ratio of the mixed solution to the CuCo-N/C nano catalyst is 40 mL: 0.05-0.15 g.

Silkworm cocoon and Cu (NO) in the technical scheme₃)₂·2H₂O、Co(NO₃)₂·6H₂O, its function is to provide N, C, Cu²⁺And Co²⁺。

The invention has the beneficial effects that:

the CuCo-N/C nano catalyst provided by the invention belongs to a non-noble metal catalyst, can realize high-yield lactic acid at a low temperature of 80-160 ℃, saves energy sources and has higher application value compared with the catalysis temperature of more than 200 ℃ in the prior art.

Detailed Description

The CuCo-N/C bimetallic nano-catalyst prepared by the technical scheme is applied to catalyzing 1, 2-propylene glycol, and the invention is further explained by combining specific implementation examples.