Cobalt-nitrogen-oxygen composite modified lignin carbon catalyst as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of catalysts, and discloses a cobalt-nitrogen-oxygen composite modified lignin carbon catalyst as well as a preparation method and application thereof. The molecular formula is Co-Co3O4 (at) NC. The preparation method comprises the following steps: S1, dipping and stirring lignin powder, an N source and water at normal temperature to obtain a turbid solution; s2, after the turbid liquid is precipitated, evaporating to dryness, and drying to obtain a solid; s3, grinding the solid into powder, calcining for 1.5-2.5 hours at 700-900 DEG C in an inert atmosphere, grinding, washing with water, and drying to obtain NC; s4, after fully grinding NC, dipping and stirring NC together with cobalt acetate, zinc acetate and an alcohol solvent at normal temperature to obtain a turbid solution; s5, after the turbid liquid is precipitated, evaporating to dryness the alcohol solvent, and drying to obtain a solid; s6, grinding the solid into powder, and calcining the powder for 1.5-2.5 h at 890-950 DEG C in an inert atmosphere to obtain Co-coated NC; and S7, sufficiently grinding the Co-coated NC, paving the Co-coated NC, and carrying out heat preservation for 21-23 hours at the temperature of 150-250 DEG C in an air or oxygen atmosphere to obtain the Co-Co3O4-coated NC. The catalyst is low in preparation cost and high in catalytic activity, and the average rate of catalyzing NH3BH3 to hydrolyze and produce hydrogen reaches 3302 mL * min <-1 > * gCo <-1 >.

Description

Technical Field

[0001] The invention belongs to the technical field of catalysts, and specifically relates to a cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst and a preparation method and application thereof. Background Art

[0002] As a clean energy carrier, hydrogen has the advantages of high energy density and no pollution after combustion, and has the greatest potential for sustainable development. Ammonia borane has the advantages of high hydrogen content (19.6 wt%), low molecular weight (30.87 g / mol), stable performance and environmental sustainability, and is considered to be the most promising chemical hydride. Precious metal catalysts such as Pt, Pd, and Ru are ideal catalysts for the hydrolysis of borohydrides, but their application is hindered by high cost and scarcity. Therefore, it is urgent to prepare non-precious metal catalysts with high catalytic performance to catalyze the hydrolysis of ammonia borane.

[0003] As a representative of transition metals, Co has the ability to construct active sites to improve catalytic performance. During the pyrolysis process of the catalyst, Co nanoparticles tend to agglomerate, causing a decrease in catalytic activity; if carbon materials are introduced to prepare cobalt-based carbon composites, their agglomeration can be inhibited and catalytic hydrogen production performance can be promoted. At the same time, biomass energy is the only renewable carbon-containing energy in nature, consisting of cellulose, hemicellulose and lignin. Lignin is one of the main components of agricultural and forestry wastes and is the second largest biomass resource in the plant kingdom after cellulose. It has a carbon content of up to 60%, but it has not been fully utilized.

[0004] Therefore, it is very promising to develop a new type of catalyst for the hydrolysis of ammonia borane. Summary of the invention

[0005] In order to solve the problems existing in the prior art: ① Resource utilization of lignin from agricultural and forestry waste; ② The precious metal-based catalysts are expensive and resource-limited in the production of hydrogen by hydrolysis of ammonia borane; ③ Non-precious metals are prone to aggregation during the preparation process; ④ Non-precious metal catalysts have low activity in the production of hydrogen by hydrolysis of ammonia borane, the purpose of the present invention is to provide a cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst and its preparation method and application.

[0006] To achieve the above purpose, the technical solution adopted by the present invention is as follows: A cobalt-nitrogen-oxygen composite modified lignin carbon catalyst has a molecular formula of Co-Co3O4@NC, wherein NC represents nitrogen-doped carbon. The catalyst uses NC as a carrier, and Co3O4 nanoparticles wrap Co nanoparticles and are uniformly distributed on NC.

[0007] A method for preparing a cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst, comprising the following steps: S1: Immerse and stir lignin powder, N source and water at room temperature to obtain a turbid liquid; S2: After the precipitation of the turbid liquid obtained in S1 is completed, the water is evaporated and then dried to obtain a solid; S3: Grind the solid obtained in S2 into powder, calcine it at 700-900 °C for 1.5-2.5 h under an inert atmosphere, cool it naturally to room temperature, take it out, grind it, wash it with water, and dry it to obtain nitrogen-doped carbon NC; S4: After grinding NC sufficiently, NC is immersed and stirred with cobalt acetate, zinc acetate and alcohol solvent at room temperature to obtain a turbid liquid; S5: After the precipitation of the turbid liquid in S4 is completed, the alcohol solvent is evaporated and then dried to obtain a solid; S6: Grind the solid obtained in S5 into powder, calcine it at 890-950 °C for 1.5-2.5 h under an inert atmosphere, cool it naturally to room temperature and then take it out to obtain cobalt-modified nitrogen-doped carbon Co@NC; S7: Grind Co@NC thoroughly and flatten it (a thin layer is enough, the thinner the better), oxidize it at 150-250 °C for 21-23 h in air or oxygen atmosphere, cool it naturally to room temperature and then take it out to obtain the cobalt-nitrogen-oxygen composite modified lignin carbon catalyst Co-Co3O4@NC.

[0008] Preferably, in step S1, the N source includes but is not limited to urea, dicyandiamide or melamine, more preferably urea.

[0009] Preferably, in step S1, the mass ratio of lignin powder to N source is (1.8-2.2) g to (3.8-4.2) g, and the soaking and stirring treatment is performed for 5.5-6.5 h.

[0010] Preferably, in step S3, the solid obtained in S2 is ground into powder, washed with water until the pH value is neutral, and then dried and calcined.

[0011] Preferably, in step S4, the mass ratio of NC: cobalt acetate: zinc acetate = 1 g: (0.73-0.76) g: (1.63-1.66) g, and the immersion and stirring treatment is performed for 5.5-6.5 h.

[0012] Preferably, in step S4, the alcohol solvent is ethanol.

[0013] Preferably, in step S3 and step S6, the temperature is 4-6 °C·min -1 The heating rate is increased to the calcination temperature.

[0014] Application of a cobalt-nitrogen-oxygen composite modified lignin char catalyst in hydrogen production by ammonia borane hydrolysis.

[0015] In the present invention, the role of adding zinc acetate to the raw materials is: on the one hand, it can provide zinc and cobalt to compete and prevent the agglomeration of cobalt nanoparticles; on the other hand, it can volatilize during calcination (zinc will volatilize at about 900°C) to create a porous structure, both of which contribute to the improvement of the catalytic ability of the catalyst.

[0016] Beneficial effects: 1. Through the regulation of transition metal Co and heteroatoms N and O, two active sites, Co and Co3O4, were generated on NC made of lignin, which provided essential active substances for catalyzing the hydrolysis of ammonia borane to produce hydrogen, reduced the dissociation energy barrier between ammonia borane and water, optimized the dissociation route of ammonia borane hydrolysis to produce hydrogen, and improved the activity of ammonia borane hydrolysis to produce hydrogen; 2. An innovative catalyst with lignin as a carbon carrier loaded with transition metals was synthesized. The presence of nitrogen-doped lignin carbon carrier makes the metal nanoparticles uniform in size and evenly distributed, which can be used to efficiently catalyze the hydrolysis of ammonia borane to produce hydrogen, which is beneficial to the utilization of agricultural and forestry waste resources and the design and preparation of lignin-based carbon catalysts. 3. The catalyst of the present invention has low preparation cost and high catalytic activity. When the reaction temperature is 30 °C, the average rate of hydrogen production by catalyzing the hydrolysis of NH3BH3 reaches 3302 mL·min -1 ·g Co -1 . BRIEF DESCRIPTION OF THE DRAWINGS

[0017] Figure 1 : X-ray powder diffraction patterns of Co-Co3O4@NC (Example 1), Co@NC-700 (Comparative Example 1), Co@NC-800 (Comparative Example 2) and Co@NC-900 (Comparative Example 3).

[0018] Figure 2 :Co-Co3O4@NC (Example 1) ( Figure 2 d~f)、Co@NC-700(Comparative Example 1)( Figure 2 a), Co@NC-800 (Comparative Example 2) ( Figure 2 b) and Co@NC-900 (Comparative Example 3) ( Figure 2 c) TEM image.

[0019] Figure 3 : Catalytic hydrogen production performance diagram of Co-Co3O4@NC (Example 1), Co@NC-700 (Comparative Example 1), Co@NC-800 (Comparative Example 2) and Co@NC-900 (Comparative Example 3). DETAILED DESCRIPTION

[0020] The following is a clear and complete description of the technical solution of the present invention in conjunction with the specific embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0021] Example 1 A method for preparing a Co-Co3O4@NC catalyst, the preparation steps are as follows: S1: Weigh 2.0000 g of uniformly ground lignin powder, add it to 30 mL of aqueous solution of 4.0000 g of urea, immerse and stir for 6 h at room temperature to obtain a brown turbid liquid; S2: After the brown turbid liquid in S1 is precipitated, place it in a 60°C water bath to evaporate the water, and then place it in a 60°C oven to dry to obtain a brown solid; S3: The brown solid obtained in S2 was ground into powder using a mortar and placed in a 10 mL crucible. The crucible was placed in a muffle furnace under a nitrogen atmosphere at 5 °C min -1 The heating rate was raised to 800 °C and the mixture was kept at this temperature for 2 h. After the calcination, the mixture was taken out after being cooled to room temperature naturally, ground, washed with water and dried to obtain nitrogen-doped lignin charcoal, which was labeled as NC-800. S4: After grinding NC-800 sufficiently, weigh 0.2000 g and add it to 20 mL of anhydrous ethanol solution of 0.1492 g of cobalt acetate and 0.3294 g of zinc acetate, and immerse and stir for 6 h at room temperature to obtain a dark purple turbid liquid; S5: After the dark purple turbid liquid in S4 is precipitated, place it in a 40°C water bath until the ethanol is evaporated, and then place it in a 40°C vacuum drying oven to dry to obtain a black solid; S6: The black solid obtained in S5 was ground into powder using a mortar, placed in a magnetic boat, placed in a tube furnace, and heated at 5 °C min under a nitrogen atmosphere. -1 The heating rate was raised to 900 °C and the mixture was kept at this temperature for 2 h. After the calcination, the mixture was taken out after being cooled to room temperature naturally to obtain cobalt-modified lignin charcoal, which was labeled as Co@NC-800. S7: Weigh 0.2000 g of Co@NC-800 and spread it in a beaker, place it in a 200 °C oven, keep it warm for 22 h for oxidation, wait for it to cool down to room temperature naturally, and obtain the target catalyst, marked as Co-Co3O4@NC.

[0022] Comparative Example 1 The difference from Example 1 is that in step S3, the calcination temperature is 700°C, and step S7 is omitted.

[0023] The obtained product was labeled as Co@NC-700.

[0024] Comparative Example 2 The difference from Embodiment 1 is that step S7 is omitted.

[0025] The obtained product was labeled as Co@NC-800.

[0026] Comparative Example 3 The difference from Example 1 is that in step S3, the calcination temperature is 900°C, and step S7 is omitted.

[0027] The obtained product was labeled as Co@NC-900.

[0028] Catalyst structure characterization Figure 1 X-ray powder diffraction patterns of the prepared catalysts Co-Co3O4@NC (Example 1), Co@NC-700 (Comparative Example 1), Co@NC-800 (Comparative Example 2) and Co@NC-900 (Comparative Example 3). Figure 1 It can be seen that the diffraction peaks at 26.51°, 51.52° and 44.22° correspond to the (002), (200) and (111) crystal planes of Co (PDF#15-8006), and it can be concluded that all four catalysts contain Co. The diffraction peak at 36.85° corresponds to the (311) crystal plane of Co3O4 (PDF#42-1467), indicating that the target catalyst Co-Co3O4@NC can be successfully synthesized through the oxidation strategy.

[0029] Figure 2 The prepared catalyst Co-Co3O4@NC (Example 1) ( Figure 2 d~f)、Co@NC-700(Comparative Example 1)( Figure 2 a), Co@NC-800 (Comparative Example 2) ( Figure 2 b) and Co@NC-900 (Comparative Example 3) ( Figure 2 c) TEM image. Figure 2 It can be seen that: Figure 2 a~c As the temperature increases, the number of metal nanoparticles increases. When the temperature is too high ( Figure 2 c) Agglomeration occurred, resulting in decreased performance; heteroatom O was introduced at the most suitable temperature (800 °C), and Example 1 prepared ( Figure 2 df), the Co and Co3O4 heterostructures were successfully synthesized, which is consistent with the XRD results, and the metal nanoparticles were uniform in size and evenly distributed.

[0030] Catalyst performance test The prepared Co-Co3O4@NC (Example 1), Co@NC-700 (Comparative Example 1), Co@NC-800 (Comparative Example 2) and Co@NC-900 (Comparative Example 3) were used as catalysts for the hydrolysis of ammonia borane to produce hydrogen. An aqueous solution (5 mL) of sodium hydroxide (0.20 g) was prepared, 2.5 mL of the aqueous solution of sodium hydroxide and 10 mg of the catalyst were put into a 25 mL round-bottom flask and ultrasonically mixed evenly, 45 mg of ammonia borane was dissolved in the remaining 2.5 mL of the aqueous solution of sodium hydroxide and added to the above flask, and the hydrolysis and hydrogen production reaction was carried out in a water bath at 30 ° C, and the volume of hydrogen produced and the required time were recorded.

[0031] Figure 3 The graphs of hydrogen production from the hydrolysis of ammonia borane catalyzed by four catalysts Co-Co3O4@NC (Example 1), Co@NC-700 (Comparative Example 1), Co@NC-800 (Comparative Example 2) and Co@NC-900 (Comparative Example 3) at 30 °C are shown. Figure 3 It can be seen that the hydrogen production rate of Co-Co3O4@NC (Example 1) is 3302 mL·min -1 ·g Co -1 , the hydrogen production rate of Co@NC-700 (Comparative Example 1) is 1394 mL·min -1 ·g Co -1 , the hydrogen production rate of Co@NC-800 (Comparative Example 2) is 2710 mL·min -1 ·g Co -1 , the hydrogen production rate of Co@NC-900 (Comparative Example 3) is 1672 mL·min -1 ·g Co -1 The results show that the catalyst Co@NC-800 (Comparative Example 2) has a higher catalytic efficiency than the catalysts Co@NC-700 (Comparative Example 1) and Co@NC-900 (Comparative Example 3), and the catalytic hydrogen production rate of the catalyst Co-Co3O4@NC obtained by heating and activating the catalyst Co@NC-800 in an oven is directly increased by 21.8%.

Claims

1. A cobalt-nitrogen-oxygen composite modified lignin carbon catalyst, characterized in that: The molecular formula is Co-Co3O4@NC, NC represents nitrogen-doped carbon, the catalyst uses NC as a carrier, and Co3O4 nanoparticles wrap Co nanoparticles and are uniformly distributed on NC.

2. A method for preparing the cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst as claimed in claim 1, characterized in that: Here are the steps: S1: Immerse and stir lignin powder, N source and water at room temperature to obtain a turbid liquid; S2: After the precipitation of the turbid liquid obtained in S1 is completed, the water is evaporated and then dried to obtain a solid; S3: Grind the solid obtained in S2 into powder, calcine it at 700-900 °C for 1.5-2.5 h under an inert atmosphere, cool it naturally to room temperature, take it out, grind it, wash it with water, and dry it to obtain nitrogen-doped carbon NC; S4: After grinding NC sufficiently, NC is immersed and stirred with cobalt acetate, zinc acetate and alcohol solvent at room temperature to obtain a turbid liquid; S5: After the precipitation of the turbid liquid in S4 is completed, the alcohol solvent is evaporated and then dried to obtain a solid; S6: Grind the solid obtained in S5 into powder, calcine it at 890-950 °C for 1.5-2.5 h under an inert atmosphere, cool it naturally to room temperature and then take it out to obtain cobalt-modified nitrogen-doped carbon Co@NC; S7: Grind Co@NC thoroughly and flatten it, oxidize it at 150~250℃ for 21~23h in air or oxygen atmosphere, cool it to room temperature naturally and then take it out to obtain the cobalt nitrogen oxygen composite modified lignin carbon catalyst Co-Co3O4@NC.

3. The method for preparing the cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst according to claim 2, characterized in that: In step S1, the N source includes but is not limited to urea, dicyandiamide or melamine.

4. The method for preparing the cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst according to claim 2 or 3, characterized in that: In step S1, the mass ratio of lignin powder to N source is (1.8-2.2) g to (3.8-4.2) g, and the impregnation and stirring treatment is performed for 5.5-6.5 h.

5. The method for preparing the cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst according to claim 2, characterized in that: In step S3, the solid obtained in S2 is ground into powder, washed with water until the pH value is neutral, dried, and then calcined.

6. The method for preparing the cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst according to claim 2, characterized in that: In step S4, the mass ratio is NC: cobalt acetate: zinc acetate = 1 g: (0.73-0.76) g: (1.63-1.66) g, and the immersion and stirring treatment is performed for 5.5-6.5 h.

7. The method for preparing the cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst according to claim 2 or 6, characterized in that: In step S4, the alcohol solvent is ethanol.

8. The method for preparing the cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst according to claim 2, characterized in that: In step S3 and step S6, the temperature is 4-6 °C·min -1 The heating rate is increased to the calcination temperature.

9. Use of the cobalt-nitrogen-oxygen composite modified lignin charcoal catalyst as claimed in claim 1 in hydrogen production by hydrolysis of ammonia borane.

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