Supported ruthenium-iron alloy catalyst for preparing ammonia through electro-catalysis of nitrate as well as preparation method and application of supported ruthenium-iron alloy catalyst

Abstract

The invention discloses a supported ruthenium-iron alloy catalyst for preparing ammonia through electro-catalysis of nitrate as well as a preparation method and application of the supported ruthenium-iron alloy catalyst, and belongs to the technical field of preparation of ammonia synthesis catalysts. The preparation method comprises the following steps: dispersing pyrrole in water, adding ferrous chloride tetrahydrate, and then adding hydrogen peroxide to polymerize pyrrole; stirring and drying to obtain a product; taking sodium chloride and zinc chloride as templates, adding the product and ruthenium chloride, stirring, and freeze-drying the solution to obtain a precursor; and annealing the precursor in an argon atmosphere, carbonizing under the protection of argon, pickling, and washing with water and ethanol to obtain a final product, namely the supported ruthenium-iron alloy catalyst. The supported ruthenium-iron alloy catalyst prepared by the invention has outstanding catalytic performance and stability when being used for electrocatalytic reaction of nitrate to produce ammonia; the preparation method is safe and simple, raw materials are cheap and easy to obtain, cost is low, and industrial production is easy to realize.

Description

Technical Field

[0001] The present application belongs to the technical field of synthetic ammonia catalyst preparation, and specifically relates to a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate ammonia production, a preparation method and an application thereof. Background Art

[0002] Ammonia, as one of the most important industrial chemicals, is a chemical raw material for many products and a clean energy carrier. However, the production of NH3 relies on the traditional Haber-Bosch process, which consumes a lot of energy and releases excess carbon dioxide under harsh operating conditions. As a potential alternative, the electrocatalytic reduction of nitrogen-containing small molecules to NH3 under mild conditions has attracted considerable attention. Despite long-term efforts, the ammonia yield and Faradaic efficiency of the electrochemical nitrogen reduction reaction still cannot meet commercial needs due to the low solubility of N2 in water, which is 0.66 mmol L under ambient conditions. -1 , the dissociation energy of the N≡N bond is 941 kJ mol -1 Compared with NRR, the electrochemical nitrate reduction reaction (NO3RR) has a higher reaction rate because NO3 - The solubility of N=O is higher, and the bond energy of N=O is 204kJ mol -1 In addition, NO3 - It is also a serious nitrogen-containing water pollutant produced by nitrogen fertilizer use, industrial wastewater discharge and fossil fuel combustion. Therefore, the NO3RR process will also contribute to environmental protection.

[0003] However, there is still considerable room for improvement in the NH3 yield and FE of the NO3RR system. - The electroreduction of is a complex eight-electron and nine-proton transfer process, which produces a large number of by-products, such as NO2, NO2 - , NO, N2O, N2, and NH2OH. In addition, the competitive hydrogen evolution reaction leads to the consumption of electrons and relatively low selectivity. Therefore, it is urgent to develop efficient NO3RR electrocatalysts to suppress the formation of by-products and promote NO3 -Selective reduction to NH3. In general, the selectivity of heterogeneous catalysts in hydrogenation reactions depends on the adsorption capacity of reaction intermediates on the catalyst surface, and sites with multiple metal atoms are crucial for the activation of reactants / intermediates. In this context, some advanced materials, such as single-atom catalysts, show excellent catalytic performance in certain reactions, but only have isolated metal active sites, which will not be able to achieve effective adsorption and activation of NO3RR reaction intermediates. Compared with SACs, metal nanoparticles with higher tunability in chemical composition and atomic arrangement of active sites can provide multiple adsorption sites for handling complex reaction systems. In addition, the introduction of a second metal will trigger the heteroatom group effect and provide the feasibility of changing the adsorption configuration of reactant molecules, which can help stabilize the reaction species, accelerate the reaction, and improve the NO3RR performance. Therefore, the in situ construction of a Ru-Fe bimetallic alloy on an Fe single-atom catalyst substrate can trigger the heteroatom group effect, optimize intermediate adsorption, and promote the electroreduction of nitrate to ammonia. Summary of the invention

[0004] In view of the problems existing in the prior art, the present invention provides a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate production of ammonia, a preparation method and application thereof.

[0005] A method for preparing a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate production of ammonia, the method comprising the following steps:

[0006] (1) dispersing pyrrole in water, adding ferrous chloride tetrahydrate, and then adding hydrogen peroxide to polymerize the pyrrole; stirring, drying, and obtaining a product;

[0007] (2) using sodium chloride and zinc chloride as templates, adding the above product and ruthenium chloride, stirring and freeze-drying the solution to obtain a precursor;

[0008] (3) The precursor is annealed in an argon atmosphere, then carbonized under argon protection, acid-washed, and then washed with water and ethanol to obtain the final product, a supported ruthenium-iron alloy catalyst.

[0009] Preferably, the stirring time of step (1) and step (2) is 1 to 48 hours.

[0010] Preferably, the molar ratio of sodium chloride to zinc chloride is 4:1.

[0011] Preferably, the freeze-drying time is 6 to 48 hours.

[0012] Preferably, the annealing temperature is 300-700° C., and the annealing time is 1-3 hours.

[0013] Preferably, the carbonization temperature is 300-700° C., and the carbonization time is 1-3 hours.

[0014] Preferably, the drying temperature is 65°C.

[0015] Preferably, the drying environment is a vacuum.

[0016] The supported ruthenium-iron alloy catalyst for electrocatalytic nitrate production of ammonia is prepared by the preparation method.

[0017] Application of the above-mentioned supported ruthenium-iron alloy catalyst for electrocatalytic nitrate production of ammonia in ammonia production.

[0018] The supported ruthenium-iron alloy catalyst for synthesizing ammonia in the present application has high ammonia yield, Faraday efficiency and ammonia selectivity. Compared with the prior art, the beneficial effects produced by the ruthenium-iron alloy catalyst provided in the present application include:

[0019] 1) The iron single atom carrier ruthenium iron alloy catalyst provided in the present application for electrocatalytic nitrate reduction to produce ammonia has achieved a high yield of 118.8 mg h -1 mg -1 The ammonia yield and Faraday efficiency of 92.2% are much higher than those of the comparative iron single atom (Faraday efficiency of 11.7% and ammonia yield of 5.1 mg h -1 mg -1 ) and ruthenium single-atom catalysts (Faraday efficiency of 58.6% and ammonia yield of 41.0 mg h -1 mg -1 ), which is at the leading level among the disclosed catalysts.

[0020] 2) The supported ruthenium-iron alloy catalyst for electrocatalytic nitrate reduction to produce ammonia provided in the present application has good stability, and its activity does not decrease significantly after six cycles.

[0021] 3) The preparation method of the supported ruthenium-iron alloy catalyst provided in the present application uses raw materials such as pyrrole, ferrous chloride tetrahydrate and hydrogen peroxide, which are commercial products with low cost and high economic benefits.

[0022] 4) The preparation method of the supported ruthenium-iron alloy catalyst for ammonia synthesis provided in the present application has the advantages of simple and safe synthesis process and is easy to realize industrial production. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, for ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0024] Figure 1These are scanning electron microscope and high-resolution transmission electron microscope images of the RuFe-FeNC catalyst in Example 1.

[0025] Figure 2 X-ray powder diffraction and Raman spectra of the FeNC catalysts in Example 1 and Comparative Example 1.

[0026] Figure 3 This is a high-resolution transmission electron microscopy image of the RuNC catalyst in Comparative Example 2.

[0027] Figure 4 It is a performance comparison chart of Example 1 and Comparative Example 1.

[0028] Figure 5 It is a performance comparison chart of Example 1 and Comparative Example 2.

[0029] Figure 6 The stability of the RuFe-FeNC catalyst in Example 1 for electrocatalytic nitrate reduction to ammonia at room temperature and pressure was measured. DETAILED DESCRIPTION

[0030] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the 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.

[0031] Example 1

[0032] This embodiment provides a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate reduction to produce ammonia and a synthesis method, specifically:

[0033] (a) 2 mL of pyrrole is fully dispersed in water, an excess of ferrous chloride tetrahydrate is added, and hydrogen peroxide is added dropwise to polymerize the pyrrole. The bright yellow solution obtained after stirring is dried to obtain a yellow-brown product.

[0034] (b) Using sodium chloride and zinc chloride as templates, the yellow-brown product and ruthenium chloride are added, stirred and freeze-dried for 48 hours. The dried material is ground into powder and carbonized at 500° C. for 2 hours in an argon atmosphere. After acid washing with hydrochloric acid, it is washed with a large amount of water and ethanol, and dried at 60° C. under vacuum to obtain the final product, a supported ruthenium-iron alloy catalyst.

[0035] Comparative Example 1

[0036] This comparative example uses a conventional nitrogen-doped carbon substrate supported iron single atom catalyst, specifically:

[0037] This comparative example is basically the same as Example 1, except that FeNC can be synthesized without adding ruthenium chloride.

[0038] Comparative Example 2

[0039] This comparative example adopts a metal-organic framework-assisted pyrolysis method, specifically:

[0040] (a) Zn(NO3)2·6H2O and Ru(acac)3 were dissolved in methanol and then added to methanol containing 2-methylimidazole. After ultrasonication for 15 minutes and standing at room temperature for 24 hours, the pink precipitate was centrifuged and washed three times with methanol.

[0041] (b) The pink product was dried in a vacuum at 65°C and annealed at 900°C for 2 hours in an argon stream. The obtained black powder was soaked in a 1.0M sulfuric acid solution for 5 hours, then washed with deionized water and dried in a vacuum at 65°C to obtain Comparative Example 2.

[0042] The test of the catalyst for electrocatalytic nitrate reduction to ammonia prepared in Example 1 and Comparative Example 1 was carried out in detail as follows:

[0043] (1) Typically, 1 mg of catalyst and 10 μL of Nafion solution (5 wt%) were dispersed in 990 μL of anhydrous ethanol and ultrasonicated for at least 1 hour to form a uniform ink. 100 μL of catalyst ink was applied to an area of ​​1×1 cm 2 on carbon paper and dried at room temperature to obtain a cathode;

[0044] (2) Platinum wire was used as the counter electrode and Ag / AgCl (4M KCl) as the reference electrode. The electrolyte in the cathode and anode chambers was 30 mL of 0.5 M potassium sulfate and 0.1 M potassium nitrate solution. Argon was bubbled into the electrolyte at a gas flow rate of 10 sccm before and during the electrochemical test. A gas absorption cell filled with 20 mL of 0.1 M HCl was connected to the end of the cathode chamber to avoid the loss of ammonia. After 1 hour of constant potential testing at -1.5 V, -1.4 V, -1.3 V, -1.2 V, -1.1 V and -1.0 V (vs. RHE), the iron single atom supported ruthenium iron alloy catalyst achieved a high energy density of 118.8 mg h -1 mg -1 The ammonia yield and Faradaic efficiency of 92.2% are much higher than those of the comparative iron single atom (Faraday efficiency of 11.7% and ammonia yield of 5.1 mg h -1 mg -1 ) and ruthenium single-atom catalysts (Faraday efficiency of 58.6% and ammonia yield of 41.0 mg h -1 mg -1 );

[0045] (3) Stability test of electrocatalytic nitrate reduction to ammonia by supported ruthenium-iron alloy catalyst: Cyclic constant potential test was carried out in 0.5M potassium sulfate and 0.1M potassium nitrate solution at voltages of -1.5V, -1.4V, -1.3V, -1.2V, -1.1V and -1.0V (vs. RHE) for 1 hour. Figure 6 It can be seen that RuFe-FeNC has good stability and its activity remains basically unchanged after six cycles.

[0046] In the description of this specification, the description with reference to the terms "one embodiment", "example", "specific example", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0047] The above shows and describes the basic principles, main features and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited to the above embodiments, and the above embodiments and descriptions are only for explaining the principles of the present invention. Without departing from the spirit and scope of the present invention, the present invention may have various changes and improvements, and these changes and improvements all fall within the scope of the present invention to be protected.

Claims

1. A method for preparing a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate to ammonia production, characterized in that: The method comprises the following steps: (1) dispersing pyrrole in water, adding ferrous chloride tetrahydrate, and then adding hydrogen peroxide to polymerize the pyrrole; stirring, drying, and obtaining a product; (2) using sodium chloride and zinc chloride as templates, adding the above product and ruthenium chloride, stirring and freeze-drying the solution to obtain a precursor; (3) The precursor is annealed in an argon atmosphere, then carbonized under argon protection, acid-washed, and then washed with water and ethanol to obtain the final product, a supported ruthenium-iron alloy catalyst.

2. The method for preparing a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate to ammonia production according to claim 1, characterized in that: The stirring time of step (1) and step (2) is 1 to 48 hours.

3. The method for preparing a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate to ammonia production according to claim 1, characterized in that: The molar ratio of sodium chloride to zinc chloride is 4:

1.

4. The method for preparing a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate to ammonia production according to claim 1, characterized in that: The freeze-drying time is 6 to 48 hours.

5. The method for preparing a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate to ammonia production according to claim 1, characterized in that: The annealing temperature is 300-700° C., and the annealing time is 1-3 hours.

6. The method for preparing a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate to ammonia production according to claim 1, characterized in that: The carbonization temperature is 300-700° C., and the carbonization time is 1-3 hours.

7. The method for preparing a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate to ammonia production according to claim 1, characterized in that: The drying temperature is 65°C.

8. The method for preparing a supported ruthenium-iron alloy catalyst for electrocatalytic nitrate to ammonia production according to claim 1, characterized in that: The drying environment is vacuum.

9. A supported ruthenium-iron alloy catalyst for electrocatalytic nitrate production of ammonia obtained by the preparation method according to any one of claims 1 to 8.

10. Use of the supported ruthenium-iron alloy catalyst for electrocatalytic nitrate production of ammonia as claimed in claim 9 in the production of ammonia.

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