CN114345413A - Aromatic acid coordinated iron-cobalt nitrogen fixation catalyst and preparation method and application thereof - Google Patents
Aromatic acid coordinated iron-cobalt nitrogen fixation catalyst and preparation method and application thereof Download PDFInfo
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Abstract
The invention relates to the field of nitrogen fixation catalysts, and discloses an aromatic acid coordinated iron-cobalt nitrogen fixation catalyst, and a preparation method and application thereof. The nitrogen fixation catalyst comprises an aromatic acid organic ligand and an iron/cobalt-based composite carrier, wherein the aromatic acid organic ligand is combined with the iron/cobalt-based composite carrier through a coordination bond, and the preparation method comprises the following steps: mixing N, N-dimethylformamide and absolute ethyl alcohol, adding an aromatic acid organic ligand and a divalent cobalt salt, stirring for 10-15min, adding a trivalent ferric salt, and stirring for 30-40min to obtain a precursor; and (3) carrying out solvothermal reaction on the precursor, and separating a product after the reaction is finished to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst. The nitrogen fixation catalyst has high catalytic activity and low requirement on nitrogen fixation conditions, can convert nitrogen into ammonia under both light and no light conditions, and can be used for nitrogen fixation under the light condition at normal temperature and normal pressure.
Description
Technical Field
The invention relates to the field of nitrogen fixation catalysts, in particular to an aromatic acid coordinated iron-cobalt nitrogen fixation catalyst and a preparation method and application thereof.
Background
Nitrogen is one of the inert gases, because nitrogen is the highest content of gas in the earth environment, but the molecular bond energy of nitrogen is high, and large energy is required for immobilization. The Haber-Bosch process (300 ℃ C., 500 ℃ C., 15-25MPa) has been used for fixing nitrogen industrially, but the process requires a large amount of fossil fuel to provide heat and generates a large amount of greenhouse gases, so that the development of a new sustainable method for replacing the conventional nitrogen fixing method is urgently needed.
The photocatalytic nitrogen fixation technology utilizes solar energy to convert nitrogen into ammonia, has the advantages of mild conditions, energy conservation, environmental protection and the like, and is considered to be one of the best alternative methods of the traditional Haber-Bosch method. How to improve the nitrogen fixation efficiency of the photocatalyst is a main problem faced by the existing photocatalytic nitrogen fixation technology, and in the reported photocatalytic nitrogen fixation catalysts, the nitrogen fixation efficiency is low, and most of the nitrogen fixation efficiency is 10-50 mu mol.L-1·h-1. Among the usual photocatalytic media, the graphite phase carbon nitride (g-C)3N4) And modifications thereof are one of the most widely and extensively studied catalysts at present. But due to g-C3N4The solar energy collector has a wide energy gap (Eg is 2.77eV), only ultraviolet rays and near ultraviolet rays with high energy can be excited, and the content of ultraviolet radiation in sunlight is low (only accounts for about 3 percent), so that the solar energy utilization rate is low.
Transition metals contain d orbitals that are not completely filled with electrons to varying degrees and therefore have many potential properties. The organic ligand is coordinated on the transition metal, so that the performance of the organic ligand and the transition metal can be combined, and the forbidden bandwidth of the catalyst can be adjusted, so that the catalyst is adjusted towards the direction beneficial to nitrogen fixation, and a new idea is provided for the design of the nitrogen fixation catalyst. However, the nitrogen fixing effect of the organic ligand coordinated transition metal photocatalyst reported before is still limited, and the nitrogen fixing condition is harsh, for example, high temperature or low temperature needs to be applied in the nitrogen fixing process, or the wavelength of light is limited. For example, a nitrogen-fixing catalyst [ (TPB) Fe (N) Fe is disclosed in the literature, Catalytic conversion of Nitrogen to Ammonia by an iron model complex (Anderson, J.S.; Rittle, J.; Peters, J.C., Catalytic conversion of Nitrogen to Ammonia by an iron model complex, Nature 2013,501(7465),84-7.)2)][Na(12-crown-4)2]Having at-78 ℃ aHigher catalytic activity, so that the nitrogen fixation reaction must be carried out at low temperature to obtain higher nitrogen fixation efficiency.
Disclosure of Invention
In order to solve the technical problems, the invention provides an aromatic acid coordinated iron-cobalt nitrogen fixation catalyst and a preparation method and application thereof. The nitrogen fixation catalyst has high catalytic activity and low requirement on nitrogen fixation conditions, can convert nitrogen into ammonia under both light and no light conditions, and can be used for nitrogen fixation under the light condition at normal temperature and normal pressure.
The specific technical scheme of the invention is as follows:
an aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises an aromatic acid organic ligand and an iron/cobalt-based composite carrier; the aromatic acid organic ligand is combined with the iron/cobalt-based composite support through a coordination bond.
The mechanism of the nitrogen fixation catalyst for catalyzing the conversion of nitrogen into ammonia is as follows: first, nitrogen is adsorbed at catalyst oxygen vacancies; under the condition of light, the catalyst semiconductor is excited by light to generate electron-hole pairs, electrons are transferred from the aromatic acid organic ligand to oxygen holes on the surface of the catalyst and then transferred to nitrogen, N [ identical to ] N of the nitrogen is broken, and proton hydrogen in water is combined to generate reduction reaction. Meanwhile, a part of sacrificial reagent (such as sodium sulfite) used cooperatively consumes holes to generate oxidation reaction, and a part of Fe doped in the iron/cobalt-based composite carrier2+Also reacts with the holes and is converted into Fe3+The holes are eliminated better, so that the recombination of photogenerated electron-hole pairs is inhibited; final N is NH3Is dissociated from the catalyst active sites due to NH3Very soluble in water and therefore in NH4 +Is present in water. Under the condition of no light, the nitrogen fixation catalyst can absorb energy from the environment to generate electrons and holes, so that nitrogen fixation is realized.
The invention adopts aromatic acid and iron/cobalt-based composite carrier for coordination, and the reduction potential of the obtained nitrogen fixation catalyst is-0.5 eV to-1.5 eV which is higher than the potential required by nitrogen fixation (-0.092eV), so the nitrogen fixation catalyst has better nitrogen fixation catalysis effect, mild nitrogen fixation condition and mild light and dark lightThe nitrogen fixation can be effectively fixed under normal temperature and normal pressure under visible light, and the nitrogen fixation rate can reach 929 mu mol.L-1·h-1. The technical effect is realized under the coordination of aromatic acid, iron base and cobalt base, and when a single iron base is used as a carrier to coordinate the aromatic acid, the reduction potential of the catalyst cannot reach the potential required by nitrogen fixation; when a single cobalt base is adopted as a carrier to coordinate aromatic acid, the forbidden band width of the catalyst is narrow, the electron-hole pairs are easy to compound, and no nitrogen fixation effect exists; by adopting the organic ligand in the prior art to coordinate with the iron/cobalt-based composite carrier, the reduction potential equivalent to that of the invention can not be obtained.
Preferably, the aromatic acid organic ligand is one or more of 2,2' -biphenyldicarboxylic acid, 2,4, 6-trimethyl benzoic acid, 2, 4-dimethoxy benzoic acid, 2, 5-dipyridyl carboxylic acid, 2-iodobenzoic acid, 3-indole carboxylic acid, p-formyl benzoic acid, 4-bromobenzoic acid, 4-ethyl benzoic acid, p-methoxy benzoic acid, p-hydroxybenzoic acid, m-methyl benzoic acid, o-nitrophenylacetic acid and the like.
Further, the aromatic acid organic ligand is 2,4, 6-trimethyl benzoic acid.
Compared with other aromatic acid organic ligands, 2,4, 6-trimethyl benzoic acid is coordinated with the iron/cobalt-based composite carrier, so that the nitrogen fixation effect is better due to the following reasons: the steric hindrance of the 2,4, 6-trimethyl benzoic acid is larger, the special structure of the 2,4, 6-trimethyl benzoic acid enables the catalyst to exist stably after being coordinated with metal, and the reduction potential of the iron-cobalt catalyst modified by the ligand is-0.83 eV, which is higher than the reduction potential required by nitrogen fixation, so that the nitrogen fixation can be carried out efficiently.
Preferably, in the nitrogen fixation catalyst, the molar ratio of the aromatic acid organic ligand to the iron element to the cobalt element is 0.2-4:1: 0.1-10.
The relative content of the aromatic acid organic ligand and the iron and cobalt can influence the nitrogen fixation performance of the catalyst: if the relative content of the aromatic acid organic ligand is too small, electrons and holes are directly quenched due to too high photocatalytic activity of the iron/cobalt-based composite carrier, so that the nitrogen fixation efficiency is too low, and even the nitrogen fixation reaction cannot be catalyzed; if the relative content of the aromatic acid organic ligand is too large, the surface of the iron/cobalt-based composite carrier is covered by the organic ligand, and sufficient active sites are not available, so that the nitrogen fixation effect is also influenced, and even the nitrogen fixation reaction cannot be carried out.
The relative amounts of iron and cobalt also have a great influence on the nitrogen fixation effect: if the content of cobalt is too low or cobalt is not contained, the iron oxide is taken as a main substrate, and the reduction potential of the iron oxide is not enough to reduce nitrogen, so that the nitrogen fixation effect is low or even no nitrogen fixation effect is generated; if the iron content is too low or no iron is contained, the substrate is mainly cobalt oxide, and the forbidden band width is too narrow, so that the photo-generated electron-hole pairs are easy to recombine, and nitrogen fixation cannot be performed.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and absolute ethyl alcohol, adding an aromatic acid organic ligand, dissolving, adding a divalent cobalt salt, stirring for 10-15min, adding a trivalent iron salt, and stirring for 30-40min to obtain a precursor;
(2) and (3) carrying out solvothermal reaction on the precursor, and separating a product after the reaction is finished to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Preferably, in the step (1), the molar ratio of the aromatic acid organic ligand to the cobalt ions in the divalent cobalt salt to the iron ions in the trivalent iron salt is 0.2-4:1: 0.1-10.
Preferably, the divalent cobalt salt is Co (NO)3)2·6H2O。
Preferably, the ferric salt is FeCl3。
Preferably, in the step (1), the volume ratio of the N, N-dimethylformamide to the absolute ethyl alcohol is 1: 0.5-1.5.
Preferably, in the step (2), the temperature of the solvothermal reaction is 150-210 ℃ and the time is 15-18 h.
In the invention, the temperature of the solvothermal reaction needs to be controlled within a certain range, and if the temperature is too low, the catalyst is not completely crystallized, so that the nitrogen fixation performance of the catalyst is influenced; if the temperature is too high, the inner container of the reaction kettle is broken, the solvent is volatilized, and the catalyst cannot be synthesized.
A nitrogen fixation method using the nitrogen fixation catalyst, wherein the nitrogen fixation condition is dark or under visible light or natural light.
Preferably, the nitrogen fixation method comprises the following steps: and adding the nitrogen fixation catalyst into a reducing agent solution, dispersing uniformly, and then carrying out nitrogen fixation reaction under the conditions of light shielding, visible light or natural light.
Preferably, the reducing agent solution is 0.01-1mol/L sodium sulfite solution; the mass volume ratio of the nitrogen fixation catalyst to the reducing agent solution is 1mg:0.5-3 mL.
Compared with the prior art, the invention has the following advantages:
(1) the invention takes the aromatic acid organic ligand coordinated iron/cobalt-based composite carrier as the nitrogen fixation catalyst, has high catalytic activity and lower requirement on nitrogen fixation condition, can convert nitrogen into ammonia under both light and dark conditions, and can carry out the nitrogen fixation process under the light condition at normal temperature and normal pressure.
(2) According to the invention, the ratio of the aromatic acid to the iron and cobalt is controlled within a certain range, so that the aromatic acid organic ligand and the iron/cobalt-based composite carrier can better play a synergistic effect, and the nitrogen fixation effect of the catalyst is improved.
Detailed Description
The present invention will be further described with reference to the following examples.
General examples
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises an aromatic acid organic ligand and an iron/cobalt-based composite carrier; the aromatic acid organic ligand is combined with the iron/cobalt-based composite support through a coordination bond. The aromatic acid organic ligand is one or more of 2,2' -biphenyldicarboxylic acid, 2,4, 6-trimethyl benzoic acid, 2, 4-dimethoxy benzoic acid, 2, 5-dipyridyl carboxylic acid, 2-iodobenzoic acid, 3-indole carboxylic acid, p-formyl benzoic acid, 4-bromobenzoic acid, 4-ethylbenzoic acid, p-methoxy benzoic acid, p-hydroxybenzoic acid, m-methylbenzoic acid, o-nitrophenylacetic acid and the like. In the nitrogen fixation catalyst, the molar ratio of the aromatic acid organic ligand to the iron element to the cobalt element is 0.2-4:1: 0.1-10.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and absolute ethyl alcohol according to the volume ratio of 1:0.5-1.5, adding an aromatic acid organic ligand, dissolving, adding a divalent cobalt salt, stirring for 10-15min, adding a trivalent ferric salt, and stirring for 30-40min, wherein the molar ratio of the aromatic acid organic ligand to cobalt ions in the divalent cobalt salt to iron ions in the trivalent ferric salt is 0.2-4:1:0.1-10, so as to obtain a precursor;
(2) carrying out solvothermal reaction on the precursor at the temperature of 150-210 ℃, wherein the reaction time is 15-18 h; and after the reaction is finished, separating a product to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
A nitrogen fixation method using the nitrogen fixation catalyst comprises the following steps: adding the nitrogen fixation catalyst into 0.01-1mol/L sodium sulfite solution, wherein the mass volume ratio of the nitrogen fixation catalyst to the reducing agent solution is 1mg:0.5-3mL, and after uniform dispersion, carrying out nitrogen fixation reaction under the conditions of light shielding, visible light or natural light.
Example 1
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises a 2,4, 6-trimethyl benzoic acid organic ligand and an iron/cobalt-based composite carrier; the 2,4, 6-trimethyl benzoic acid organic ligand is combined with the iron/cobalt-based composite carrier through a coordination bond.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and anhydrous ethanol 10mL respectively, adding 0.5mmol 2,4, 6-trimethyl benzoic acid organic ligand, dissolving, adding 0.5mmol Co (NO)3)2·6H2O, stirring for 10min, and adding 0.5mmol FeCl3Stirring for 30min to obtain a precursor;
(2) transferring 20mL of the precursor into a 50mL polytetrafluoroethylene inner container, and carrying out solvothermal reaction at 200 ℃ for 15 h; and after the reaction is finished, washing and drying to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Example 2
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises an o-nitroacetoacetic acid organic ligand and an iron/cobalt-based composite carrier; the o-nitroacetophenone organic ligand is combined with the iron/cobalt-based composite carrier through a coordination bond.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and anhydrous ethanol each 10mL, adding 0.5mmol of o-nitroacetoacetic acid organic ligand, dissolving, and adding 0.5mmol of Co (NO)3)2·6H2O, stirring for 10min, and adding 0.5mmol FeCl3Stirring for 30min to obtain a precursor;
(2) transferring 20mL of the precursor into a 50mL polytetrafluoroethylene inner container, and carrying out solvothermal reaction at 200 ℃ for 15 h; and after the reaction is finished, washing and drying to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Example 3
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises a 2,2' -biphenyldicarboxylic acid organic ligand and an iron/cobalt-based composite carrier; the 2,2' -biphenyl dicarboxylic acid organic ligand is combined with the iron/cobalt-based composite carrier through a coordination bond.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and anhydrous ethanol each 10mL, adding 0.5mmol 2,2' -biphenyldicarboxylic acid organic ligand, dissolving, adding 0.5mmol Co (NO)3)2·6H2O, stirring for 10min, and adding 0.5mmol FeCl3Stirring for 30min to obtain a precursor;
(2) transferring 20mL of the precursor into a 50mL polytetrafluoroethylene inner container, and carrying out solvothermal reaction at 200 ℃ for 15 h; and after the reaction is finished, washing and drying to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Example 4
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises a 4-bromobenzoic acid organic ligand and an iron/cobalt-based composite carrier; the 4-bromobenzoic acid organic ligand is combined with the iron/cobalt-based composite support through a coordination bond.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and anhydrous ethanol each 10mL, adding 0.5mmol of 4-bromobenzoic acid organic ligand, dissolving, and adding 0.5mmol of Co (NO)3)2·6H2O, stirring for 10min, and adding 0.5mmol FeCl3Stirring for 30min to obtain a precursor;
(2) transferring 20mL of the precursor into a 50mL polytetrafluoroethylene inner container, and carrying out solvothermal reaction at 200 ℃ for 15 h; and after the reaction is finished, washing and drying to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Comparative example 1
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises a 2,4, 6-trimethyl benzoic acid organic ligand and an iron/cobalt-based composite carrier; the 2,4, 6-trimethyl benzoic acid organic ligand is combined with the iron/cobalt-based composite support through a coordination bond.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and anhydrous ethanol 10mL respectively, adding 0.5mmol 2,4, 6-trimethyl benzoic acid organic ligand, dissolving, adding 5mmol Co (NO)3)2·6H2O, stirring for 10min, and adding 5mmol FeCl3Stirring for 30min to obtain a precursor;
(2) transferring 20mL of the precursor into a 50mL polytetrafluoroethylene inner container, and carrying out solvothermal reaction at 200 ℃ for 15 h; and after the reaction is finished, centrifugally washing and drying to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Comparative example 2
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises a 2,4, 6-trimethyl benzoic acid organic ligand and an iron/cobalt-based composite carrier; the 2,4, 6-trimethyl benzoic acid organic ligand is combined with the iron/cobalt-based composite support through a coordination bond.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and anhydrous ethanol 10mL respectively, adding 0.5mmol 2,4, 6-trimethyl benzoic acid organic ligand, dissolving, adding 0.1mmol Co (NO)3)2·6H2O, stirring for 10min, and adding 0.1mmol FeCl3Stirring for 30min to obtain a precursor;
(2) transferring 20mL of the precursor into a 50mL polytetrafluoroethylene inner container, and carrying out solvothermal reaction at 200 ℃ for 15 h; and after the reaction is finished, washing and drying to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Comparative example 3
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises an aromatic acid organic ligand and an iron/cobalt-based composite carrier; the aromatic acid organic ligand is combined with the iron/cobalt-based composite support through a coordination bond.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and anhydrous ethanol 10mL respectively, adding 0.5mmol 2,4, 6-trimethyl benzoic acid organic ligand, dissolving, adding 0.5mmol Co (NO)3)2·6H2O, stirring for 10min, and adding 0.5mmol FeCl3Stirring for 30min to obtain a precursor;
(2) transferring 20mL of the precursor into a 50mL polytetrafluoroethylene liner, and carrying out solvothermal reaction at 120 ℃ for 15 h; and after the reaction is finished, washing and drying to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Comparative example 4
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises a 2,4, 6-trimethyl benzoic acid organic ligand and an iron/cobalt-based composite carrier; the 2,4, 6-trimethyl benzoic acid organic ligand is combined with the iron/cobalt-based composite carrier through a coordination bond.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and anhydrous ethanol 10mL respectively, adding 0.5mmol 2,4, 6-trimethyl benzoic acid organic ligand, dissolving, adding 0.95mmol Co (NO)3)2·6H2O, stirring for 10min, and then adding 0.05mmol FeCl3Stirring for 30min to obtain a precursor;
(2) transferring 20mL of the precursor into a 50mL polytetrafluoroethylene inner container, and carrying out solvothermal reaction at 200 ℃ for 15 h; and after the reaction is finished, washing and drying to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Comparative example 5
An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst comprises a 2,4, 6-trimethyl benzoic acid organic ligand and an iron/cobalt-based composite carrier; the 2,4, 6-trimethyl benzoic acid organic ligand is combined with the iron/cobalt-based composite carrier through a coordination bond.
A preparation method of the nitrogen fixation catalyst comprises the following steps:
(1) mixing N, N-dimethylformamide and anhydrous ethanol 10mL respectively, adding 0.5mmol 2,4, 6-trimethyl benzoic acid organic ligand, dissolving, adding 0.08mmol Co (NO)3)2·6H2O, stirring for 10min, and adding 0.92mmol FeCl3Stirring for 30min to obtain a precursor;
(2) transferring 20mL of the precursor into a 50mL polytetrafluoroethylene inner container, and carrying out solvothermal reaction at 200 ℃ for 15 h; and after the reaction is finished, washing and drying to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
Application example
A nitrogen fixation method using the nitrogen fixation catalyst comprises the following steps: 10mg of the nitrogen fixation catalyst prepared in the examples 1 to 4 and the comparative examples 1 to 5 was added to 15ml of 0.3mol/L sodium sulfite solution, after uniform dispersion, nitrogen gas was introduced, nitrogen fixation reaction was performed in the dark or in the visible light, the ammonium concentration was measured by a Naeser reagent, and the nitrogen fixation rate was calculated, and the results are shown in Table 1.
TABLE 1
From table 1 the following conclusions can be drawn:
(1) in examples 1 to 4, catalysts were prepared using different aromatic acids, respectively. The nitrogen fixation rate of the catalyst obtained in example 1 is significantly higher than that of examples 2-4, indicating that the use of 2,4, 6-trimethyl benzoic acid has a better nitrogen fixation effect than other aromatic acids, presumably because: the steric hindrance of the 2,4, 6-trimethyl benzoic acid is larger, the special structure of the 2,4, 6-trimethyl benzoic acid enables the catalyst to exist stably after being coordinated with metal, and the reduction potential of the iron-cobalt catalyst modified by the ligand is-0.83 eV, which is higher than the reduction potential required by nitrogen fixation, so that the nitrogen fixation can be carried out efficiently.
(2) In example 1, comparative example 1 and comparative example 2, an aromatic acid-based organic ligand and Co (NO)3)2·6H2O、FeCl3The molar ratio of the two is 1:1:1, 0.1:1:1 and 2:1:1 respectively. The nitrogen fixation rate of the catalyst prepared in the comparative example 1 and the comparative example 2 is smaller than that of the catalyst prepared in the example 1, which shows that the nitrogen fixation effect of the catalyst is influenced by the relative content of the aromatic acid organic ligand in the catalyst which is too large or too small, and the reason is presumed that: if the relative content of the aromatic acid organic ligand is too small, the photocatalytic activity of the iron/cobalt-based composite carrier is too high, so that electrons and holes are directly quenched, and the nitrogen fixation efficiency is too low; if the relative content of the aromatic acid organic ligand is too large, the surface of the iron/cobalt-based composite carrier is covered by the organic ligand, so that enough active sites are not available, and the nitrogen fixation effect is also influenced.
(3) In example 1 and comparative example 3, the solvothermal reaction temperatures were 200 ℃ and 120 ℃, respectively. The nitrogen fixation rate of the catalyst prepared in comparative example 3 is significantly lower compared to example 1, which indicates that the nitrogen fixation effect of the catalyst is affected by too low a solvothermal reaction temperature, presumably because: the catalyst crystallization is incomplete due to the fact that the solvothermal reaction temperature is too low, and the nitrogen fixation performance of the catalyst is affected.
(4) In example 1, comparative example 4 and comparative example 5, Co (NO)3)2·6H2O and FeCl3The molar ratio of the two is 1:1, 1:0.05 and 1:11.5 respectively. The nitrogen fixation rate of the catalyst prepared in the comparative example 4 and the catalyst prepared in the comparative example 5 are both smaller than that of the catalyst prepared in the example 1, and the nitrogen fixation effect of the catalyst is influenced by the relative content of iron and cobalt in the catalyst, which is presumed to be caused by that: if the content of cobalt is too small, the substrate is iron oxide, and the reduction potential of the iron oxide is not enough to reduce nitrogen, so that the nitrogen fixation effect is low or even no nitrogen fixation effect is generated; if the iron content is too low, the substrate is cobalt oxide, and the forbidden band width is too narrow, so that light is emittedThe electron-generating hole pairs are very easy to recombine, and nitrogen fixation is also impossible.
The raw materials and equipment used in the invention are common raw materials and equipment in the field if not specified; the methods used in the present invention are conventional in the art unless otherwise specified.
The above description is only a preferred embodiment of the present invention, and is not intended to limit the present invention, and all simple modifications, alterations and equivalents of the above embodiments according to the technical spirit of the present invention are still within the protection scope of the technical solution of the present invention.
Claims (10)
1. An aromatic acid coordinated iron-cobalt nitrogen fixation catalyst is characterized by comprising an aromatic acid organic ligand and an iron/cobalt-based composite carrier; the aromatic acid organic ligand is combined with the iron/cobalt-based composite support through a coordination bond.
2. The nitrogen-fixing catalyst as claimed in claim 1, wherein the aromatic acid organic ligand is one or more selected from 2,2' -biphenyldicarboxylic acid, 2,4, 6-trimethylbenzoic acid, 2, 4-dimethoxybenzoic acid, 2, 5-bipyridinecarboxylic acid, 2-iodobenzoic acid, 3-indolecarboxylic acid, p-formylbenzoic acid, 4-bromobenzoic acid, 4-ethylbenzoic acid, p-methoxybenzoic acid, p-hydroxybenzoic acid, m-methylbenzoic acid, o-nitrophenylacetic acid, etc.
3. The nitrogen-fixing catalyst according to claim 2, wherein the aromatic acid-based organic ligand is 2,4, 6-trimethylbenzoic acid.
4. The nitrogen-fixing catalyst according to claim 1, 2 or 3, wherein the molar ratio of the aromatic acid-based organic ligand to the iron element to the cobalt element in the nitrogen-fixing catalyst is 0.2-4:1: 0.1-10.
5. A method for preparing a nitrogen-fixing catalyst according to any one of claims 1 to 4, comprising the steps of:
(1) mixing N, N-dimethylformamide and absolute ethyl alcohol, adding an aromatic acid organic ligand, dissolving, adding a divalent cobalt salt, stirring for 10-15min, adding a trivalent iron salt, and stirring for 30-40min to obtain a precursor;
(2) and (3) carrying out solvothermal reaction on the precursor, and separating a product after the reaction is finished to obtain the aromatic acid coordinated iron-cobalt nitrogen fixation catalyst.
6. The method according to claim 5, wherein in the step (1), the molar ratio of the aromatic acid organic ligand to the iron ions in the divalent cobalt salt and the trivalent iron salt is 0.1-4:1: 0.1-10.
7. The method according to claim 5, wherein the temperature of the solvothermal reaction in step (2) is 150 ℃ to 210 ℃ for 15-18 h.
8. A method for fixing nitrogen by using the nitrogen-fixing catalyst as claimed in any one of claims 1 to 4, wherein the nitrogen-fixing condition is dark or visible light or natural light.
9. The method of claim 8, comprising the steps of: and adding the nitrogen fixation catalyst into a reducing agent solution, dispersing uniformly, and then carrying out nitrogen fixation reaction under the conditions of light shielding, visible light or natural light.
10. The method of claim 9, wherein the reducing agent solution is a 0.01-1mol/L sodium sulfite solution; the mass volume ratio of the nitrogen fixation catalyst to the reducing agent solution is 1mg:0.5-3 mL.
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