CN109603831B

CN109603831B - Cobalt and graphene composite nano material catalyst and preparation method thereof

Info

Publication number: CN109603831B
Application number: CN201811603520.6A
Authority: CN
Inventors: 周锦霞; 杨帆; 毛璟博; 李慎敏
Original assignee: Dalian University
Current assignee: Dalian University
Priority date: 2018-12-26
Filing date: 2018-12-26
Publication date: 2021-11-23
Anticipated expiration: 2038-12-26
Also published as: CN109603831A

Abstract

The invention relates to a cobalt and graphene composite nano-material catalyst and a preparation method thereof. The main components of the catalyst are cobalt and graphene; the preparation steps of the catalyst are as follows: loading cobalt salt on self-synthesized or commercially-purchased reduced graphene oxide by adopting an impregnation method, drying after impregnation to obtain a catalyst precursor containing the cobalt salt/graphene, roasting the precursor in a nitrogen atmosphere to decompose the cobalt salt, and simultaneously enabling cobalt species to generate strong interaction with the graphene to obtain the cobalt and graphene composite nanomaterial, wherein the catalyst simultaneously contains monatomic cobalt, cobalt clusters and cobalt oxide nanoparticles which are tightly combined with a graphene substrate.

Description

Cobalt and graphene composite nano material catalyst and preparation method thereof

Technical Field

The invention relates to a cobalt and graphene composite nano-material catalyst, a main component of the catalyst and a preparation method of the catalyst.

Background

The excellent catalyst is the key for improving the catalytic reaction performance. The performance of the catalyst is mainly determined by two aspects: one is the ingredient and the other is the method of preparation. The same ingredients, with different preparation methods, will have very different properties, and similarly, the same preparation methods with different ingredients will also produce catalysts with different effects. In recent years, catalysts containing monatomic and atomic clusters and nanoparticles with uniform particle size distribution are increasingly emphasized, and efficient catalysis can be realized by regulating and controlling the composition, structure and morphology and electronic state of the catalysts at a nanometer level. The preparation technique of the catalyst containing single atom mainly comprises the step-by-step reduction method (Zhang H., Kawashima K., Okumura M., et al., colloidal Au single-atom catalysts embedded on Pd nanocrusters [ J]Journal of materials Chemistry A,2014,2(33):13498.), dipping (Mosesdebusk M., Yoon M., Allard L.F., et Al₂O₃(010)surface.[J]Journal of American Chemical Society,2013,135(34):12634-12645.), atomic layer deposition (Xing J., Chen J.F., Li Y.H., et al.Stable Isolated metals as Active Sites for Photonic Hydrogen Evolution [ J.]Chemistry-AEuroplan Journal,2014,20(8): 2138-2144), anti-Ostward curing methods (Hu, P., Huang, Z., Amghouz, Z., Makkee, M., Xu, F., Kapteijn, F., Dikhtiarenko, A., Chen, Y., Gu, X.and Tang, X. (2014), Electronic Metal-Support Interactions in Single-Atom catalysts, Angew.Chem.int.Ed.,53:3418-3421.), etc. Although some methods can achieve a good metal loading effect, the preparation process is high in load and cost, and industrial popularization is difficult.

From the perspective of catalyst components, graphene (graphene) as an emerging material is very colorful in the field of catalysis due to its unique material structure and physicochemical properties. Graphite powder was used to prepare graphite Oxide by hummers method (William S. hummers Jr, Richard E. Offeman. preparation of graphite Oxide [ J ]]Journal of the American Chemical Society,1958,80(6): 1339) to Graphene Oxide (GO) and then reduced to reduced graphene oxide (rGO) by reduction, with the possibility of mass production, which enables graphene to be used as a bulk catalyst preparation material. Some researches find that the metal exists on the surface of the graphene in the form of Nanoparticles (NPs), clusters (clusters) or single atoms (single atoms), and the metal and the graphene generate excellent catalytic effect under the synergistic effect. However, the synthesis of catalysts containing a single atom is somewhat difficult, and the metal loading is made more difficult by the hydrophobicity of the graphene material. At present, the methods for loading metal particles on graphene mainly include the following methods: in the first method, preformed NPs and graphene are dispersed in a solvent, and attachment is driven by electrostatic or van der waals interactions and pi-pi bond interactions. The process allows better control of the characteristics of the NPs, but the catalyst is not stable; in the second method, the target NPs are formed in situ on the graphene-based material, and the functional group or aromatic ring structure of the graphene stabilizes the NPs. In this case, better interaction between NPs and the vector can be achieved, but control over NPs structure and morphology may be lost; in the third method, the formation of metal/metal compound NPs and the conversion from GO to rGO are carried out in situ at the same time, so that the interaction between the catalyst and the metal component can be strengthened; in the fourth method, NPs and graphene are formed in situ by small molecules through a bottom-up one-step method, so that synthesis is performedA more stable catalyst was obtained (Das VK, ShifranaZ B, Bronstein LM. graphene and graphene-like materials in biomass conversion: compressing the way to the future [ J ]]Journal of materials chemistry a,2017,5(48), which is costly, harsh in terms of conditions, and difficult to industrially synthesize on a large scale. In addition, the noble metal and transition metal catalysts synthesized by the above methods have metals and metal oxides generally existing in the form of NPs on the carrier, and single atoms rarely occur, and most of the metals are noble metals rather than transition metals. At present, few reports about the loading of the monoatomic transition metal on the graphene exist. (Deng D, Chen X, LiangY, et al. A single iron site defined in a graphene matrix for the catalytic oxidation of benzene at room temperature [ J]Science Advances,2015,1(11): e1500462-e1500462. taking graphene as a carrier, introducing a FeN component with iron phthalocyanine, combining Fe with four N atoms in the form of a single atom on the carrier, and grafting onto a graphene carbon skeleton. (Fei, H., Dong, J., Feng, Y., Allen, C.S., Wan, C., Volossky, B., et al. (2018) General synthesis and defined structural identification of MN₄C₄single-atom catalysts with tunable electrophoretic activities, nature catalysts, 1(1), 63-72) mixing Fe, Co, Ni chloride salt, graphene oxide and hydrogen peroxide, carrying out hydrothermal treatment, drying to obtain a catalyst precursor, reacting the catalyst precursor with ammonia gas in Ar gas flow at 900 ℃ to obtain a monatomic catalyst, and M-NHGFs (M ═ Fe, Co, Ni), wherein transition metal in the catalyst is connected with graphene through N atom, namely MN is used₄C₄The catalyst exists in the form of (M ═ Fe, Co and Ni), and has good application effect in oxygen evolution electrocatalytic reaction. So far, there is no report on a catalyst in which monoatomic cobalt, cobalt atom clusters, and cobalt oxide nanoparticle components are simultaneously supported on graphene by an impregnation-baking method.

Disclosure of Invention

In order to overcome the defects and shortcomings of the prior art, the invention synthesizes a novel catalyst containing cobalt in various forms on graphene by adopting a simple method, namely an impregnation-roasting method, and the catalyst is named as Co/rGO. The catalyst takes transition metal Co as activityThe component is reduced graphene oxide (rGO) as a carrier, and Co is prepared by various oxides (CoO, Co) on the carrier₂O₃、Co₃O₄) Nanoparticles, clusters of Co atoms and monoatomic Co forms.

The invention adopts the following technical scheme: the cobalt-graphene composite nano material catalyst mainly comprises the following components in percentage by weight: cobalt accounts for 1-50 wt% of the mass of the catalyst; preferably, the cobalt accounts for 5-10 wt% of the mass of the catalyst. The invention also discloses a preparation method of the cobalt-graphene composite nano-material catalyst, which comprises the following steps:

(1) impregnation

Loading cobalt salt on graphene by adopting an impregnation method, and drying after impregnation to obtain the graphene/cobalt salt/stone

A catalyst precursor of graphene;

(2) roasting

Roasting the catalyst precursor containing cobalt salt/graphene at the temperature of 700 ℃ in the nitrogen atmosphere at 400 ℃ to decompose the cobalt salt, and enabling cobalt to interact with graphene to obtain the cobalt-graphene composite nano material catalyst.

The cobalt salt is one or two of cobalt nitrate and cobalt acetate.

In the step (1), an ethanol water solution is used for preparing the cobalt salt solution, wherein the content of ethanol is 10-80%, and 20% is preferably adopted.

The impregnation method adopted in the step (1) can be equal-volume impregnation and excess impregnation, and equal-volume impregnation is preferentially adopted.

In the step (2), the roasting protective gas is high-purity nitrogen with the purity of 99.95 percent or more.

In the step (2), the calcination temperature is preferably 500-600 ℃.

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

the invention adopts cheap transition metal cobalt as the active component of the catalyst, and prepares the catalyst simultaneously containing the monatomic cobalt, the cobalt cluster and the cobalt oxide nano-particles which are tightly combined with the graphene substrate by a simple isometric dipping and roasting method.

Drawings

FIG. 1HAADF-STEM characterization and monatomic Co simulation.

Detailed Description

The present invention is described in further detail below with reference to examples of characterization and test reactions, but the embodiments of the present invention are not limited thereto.

The adopted graphene can adopt reduced graphene oxide (rGO) which is synthesized by self or purchased commercially; in this embodiment, reduced graphene oxide (rGO), abbreviated as graphene, for synthesizing the catalyst may be commercialized graphene or may be self-synthesized according to Hummers method. The rGO used in this example was self-synthesized with detailed steps: a dry 2.0L beaker was charged with 230mL of concentrated sulfuric acid and 5.0g of sodium nitrate (NaNO)₃) Stirring in ice bath, adding 10.0g natural crystalline flake graphite powder when the temperature T is less than or equal to 5 ℃, and continuing stirring for 2.5 hours; after mixing well, slowly add 30.0g potassium permanganate (KMnO)₄) During the period, the temperature of the system is controlled not to be higher than 20 ℃ (namely, when the temperature rises too fast, the filling speed is slowed down, the stirring speed is reduced, and ice blocks are added for cooling); then transferring the beaker to a constant-temperature water bath at 35 ℃, continuously stirring and reacting for 2.0 hours, and adding 460mL of deionized water; taking out the beaker, putting the beaker in an oil bath at the temperature of 98 ℃, timing when the temperature of the solution reaches 98 ℃, and stirring for 15 minutes; finally, 1.4L of deionized water was added to terminate the reaction, and 25mL of hydrogen peroxide (30% H) was added₂O₂) The solution was found to have a brownish black color to a bright yellow color and a metallic luster; and taking out the beaker, cooling to room temperature, centrifuging, washing with deionized water for 8-10 times (pH is approximately equal to 7), transferring to a brown reagent bottle, and sealing and storing for later use, namely the Graphene Oxide (GO) paste. Taking 1g of dry GO (taking a certain amount of GO paste, drying and dehydrating to obtain GO powder, and calculating to obtain the concentration of the GO paste) to disperse in 1000mL of deionized water, carrying out ultrasonic treatment for 30min, standing and aging for one night, then transferring to a round bottom flask (only taking upper brown solution, and taking bottom black solution as undispersed graphite oxide, discarding), adding 25mL of 30% ammonia water and 6mL of 80% hydrazine hydrate, refluxing in a water area at 95 ℃ under magnetic stirring at 2000rpm for 3h, and then carrying out ultrasonic treatmentAnd adding 4mL of 80% hydrazine hydrate, continuing to react for 30min, taking out the flask, dropwise adding 4% hydrochloric acid until a black solution generates a black flocculent precipitate, floating on the liquid surface, clarifying and transparent the solution, performing suction filtration while the solution is hot, washing with hot water until no ammonia smell exists, and freeze-drying to obtain loose rGO powder. 100mg of rGO is placed in a 50mL beaker, deionized water is sequentially added into the beaker by a 100uL liquid transfer gun, and the stirring is continued until the rGO is pasty and seeps water, and the water absorption capacity is measured to be 7 mL/g.

1. Catalyst preparation

The Co/rGO catalyst is prepared by adopting an isometric impregnation-roasting two-step method, and the specific steps are as follows:

(1) dipping:

preparation of salt solution: taking Co (NO)₃)₂·6H₂Dissolving 0.3mmol of O in deionized water to prepare 2.1mL of salt solution; putting 2.1mL of prepared salt solution into a 50mL beaker, adding 0.6mL of absolute ethyl alcohol, and shaking up; weighing 300mg rGO, quickly adding into a beaker, completely covering the solution, and continuously stirring for 30min clockwise by using a glass rod until the powder is pasty; sealing the beaker with tinfoil, perforating, standing at room temperature for 4h, and drying in a vacuum drying oven at 50 deg.C for 12 h;

(5) roasting:

taking out the catalyst in the beaker, grinding the catalyst by using an agate mortar to enable the catalyst to be powder, putting the prepared powdery sample into a quartz tube, putting the quartz tube into a tube furnace, raising the temperature from room temperature to 500 ℃ by a program of 10 ℃/min in the atmosphere of nitrogen, roasting the quartz tube at the constant temperature of 500 ℃ for 2 hours, taking out the sample when the temperature is reduced to the room temperature, and sealing and storing the sample.

2. Characterization results

The catalyst was characterized using a high angle annular dark field-scanning transmission electron microscope (HAADF-STEM): taking a very small amount of Co/rGO to be ultrasonically dispersed in an ethanol solution, preparing a sample by using a copper grid, and then placing the sample into an instrument for testing. The characterization results are shown in fig. 1, and it can be seen from fig. 1 that many Co oxide nanoparticles are uniformly loaded on rGO, and a large number of Co atomic clusters and monatomic Co.

The above description is only for the purpose of creating a preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any person skilled in the art can substitute or change the technical solution and the inventive concept of the present invention within the technical scope of the present invention.

Claims

1. The cobalt-graphene composite nano material catalyst is characterized in that the main components are cobalt and graphene, and the preparation method comprises the following steps:

(1) impregnation

Preparing a cobalt salt solution by using an ethanol aqueous solution, wherein the content of ethanol is 10-80%, loading cobalt salt on reduced graphene oxide by adopting an isometric impregnation or excess impregnation method, and drying after impregnation to obtain a catalyst precursor containing cobalt salt/graphene; the cobalt accounts for 5-10 wt% of the mass of the catalyst; the cobalt salt is one or two of cobalt nitrate and cobalt acetate;

(2) roasting

Roasting a catalyst precursor containing cobalt salt/graphene at the temperature of 400-700 ℃ in a nitrogen atmosphere to decompose the cobalt salt, and enabling cobalt to interact with graphene to obtain a cobalt-graphene composite nano material catalyst;

the catalyst is structurally characterized by simultaneously containing monatomic cobalt, cobalt clusters and cobalt oxide nanoparticles which are tightly combined with a graphene substrate.

2. The catalyst of claim 1, wherein the ethanol is present in an amount of 20%.

3. The catalyst of claim 1, wherein an isovolumetric impregnation method is used.

4. The catalyst according to claim 1, wherein in the step (2), the calcination protecting gas is a high-purity nitrogen gas having a purity of 99.95% or more.

5. The catalyst as claimed in claim 1, wherein the calcination temperature in the step (2) is 500-600 ℃.