A semiconductor phase MoS2 transition metal-based composite catalyst, its preparation method, and its application in the electrocatalytic synthesis of ammonia from N2O.

Abstract

The application belongs to the field of electrochemical catalysts, and particularly relates to a semiconductor phase MoS2 transition metal-based composite catalyst, a preparation method thereof and application of the semiconductor phase MoS2 transition metal-based composite catalyst in electrocatalytic synthesis of ammonia from N2O. The preparation method of the semiconductor phase MoS2 transition metal-based composite catalyst comprises the following steps: (1) dissolving molybdate and a sulfur-containing organic compound in water, then adding a soluble salt of a transition metal to form a uniform precursor solution by stirring; adding a phosphorization source into the precursor solution to uniformly disperse to obtain a mixed solution; (2) reacting the mixed solution in step (1) at 160-200 DEG C for 20-28 h, cooling to room temperature after the reaction is completed, and washing and drying the obtained product to obtain the semiconductor phase MoS2 transition metal-based composite catalyst. The application successfully constructs a close heterojunction of transition metal phosphide / sulfide and MoS2 in a MoS2-based composite structure through a one-pot hydrothermal-phosphorization synergistic preparation method.

Description

Technical Field

[0001] This invention relates to the field of electrochemical catalysts, specifically to a semiconductor phase MoS2 transition metal-based composite catalyst, its preparation method, and its application in the electrocatalytic synthesis of ammonia from N2O. Background Technology

[0002] [0002 Among many nitrogen-containing substances, nitrous oxide (N2O) is a potent greenhouse gas with a global warming potential far exceeding that of carbon dioxide, and it can lead to stratospheric ozone depletion, posing a serious threat to the environment. However, current electrochemical reduction of oxidized nitrogen (such as nitrogen gas N2 and nitrate NO3) is not feasible.] - In the research field of ammonia synthesis from nitrogen oxides (NO, etc.), studies on the electrochemical resource recovery of N2O, a specific pollutant, and its targeted conversion into harmless nitrogen gas (N2) and high-value-added ammonia (NH3), are very limited. This may be because the N2O molecule has a unique linear structure and N=NO bond sequence, making its activation and selective bond-breaking pathways more complex than other nitrogen oxides, thus placing higher demands on catalyst design. Therefore, developing electrocatalytic technologies that can synergistically achieve the harmless decomposition and value conversion of N2O is of significant necessity and has important application prospects.

[0003] Given the aforementioned challenges, the research community is actively exploring alternative pathways for the efficient synthesis of ammonia from more readily activated oxidized nitrogen sources. This strategy aims to bypass the fundamental bottleneck of N≡N bond activation. However, these alternative pathways still face numerous limitations in practical applications, such as raw material sources (fluctuations in nitrate concentration in wastewater), competing reactions (hydrogen evolution reaction HER), and product separation. It is noteworthy that within this research paradigm of converting "high-valence nitrogen" to "low-valence nitrogen," the value of another nitrogen-containing gas with a high oxidation state (+1 valence)—nitrous oxide (N₂O)—has not been fully explored. N₂O is not only a potent greenhouse gas, but the bond energies of the NO bond and N=N double bond in its molecular structure (N=NO) are significantly lower than those of the triple bond in N₂, theoretically resulting in a lower activation energy barrier. Therefore, expanding the research scope of electrochemical ammonia synthesis to N₂O reduction could not only open up a resource-based channel for this troublesome environmental pollutant, but also potentially provide a new chemical perspective for overcoming the kinetic limitations of nitrogen reduction reactions.

[0004] Although the electrochemical reduction of N2O to NH3 holds promise for both environmental protection and resource utilization, its practical implementation still faces significant scientific and technological challenges. Currently disclosed catalytic systems fall short of application requirements in terms of activity, selectivity, and stability, while the design of targeted, highly efficient catalysts is still in its early stages of exploration. This is particularly evident in existing patented technologies. For example, while patent CN119144987A directly proposes a technical solution of "transition metal-modified MoS2 catalyst for electrocatalytic N2O reduction to ammonia synthesis," its reported ammonia yield and Faradaic efficiency remain low, indicating significant deficiencies in key aspects such as N2O adsorption activation, selective NO bond cleavage, and suppression of side reactions. On the other hand, patent CN117587454A reports a method for preparing an "in-plane heterostructure of transition metal phosphide / metallic molybdenum disulfide (TMP / 1T-MoS2)"—this type of structure is similar to the transition metal-based catalytic material system of semiconductor phase MoS2 that this study focuses on, and theoretically, its catalytic performance can be optimized through interfacial electronic regulation. However, this patent has two limitations: firstly, its preparation process involves multiple steps of high-temperature phosphating and phase transition control, making the process complex; secondly, and more importantly, the material is applied to the water electrolysis reaction, without any testing of N2O reduction performance, and its key parameters such as the adsorption characteristics, reduction pathway, and selectivity of N2O molecules are all unknown. These two representative patents reflect the main dilemma in this field: the lack of effective strategies for catalyst design for N2O reduction (low performance), while heterostructure material systems with potential advantages are seriously disconnected from the research objectives (no N2O verification). Therefore, developing a novel catalyst system that is easy to synthesize, has a well-defined structure, and can efficiently and synergistically catalyze the selective reduction of N2O to ammonia has become a key breakthrough for promoting the development of this field. Summary of the Invention

[0005] To address the problems and shortcomings of existing technologies, this invention aims to provide a semiconductor phase MoS2 transition metal-based composite catalyst, its preparation method, and its application in the electrocatalytic synthesis of ammonia from N2O.

[0006] To achieve the objectives of this invention, the technical solution adopted is as follows: The first aspect of this invention provides a method for preparing a semiconductor phase MoS2 transition metal-based composite catalyst, comprising the following steps: (1) Dissolve molybdate and sulfur-containing organic compound in water, then add transition metal salt and stir to form a homogeneous precursor solution; add phosphating source to the precursor solution and disperse evenly to obtain a mixed solution; (2) The mixed solution from step (1) was reacted at 160-200℃ for 20-28 h. After the reaction was completed, it was cooled to room temperature. The resulting product was washed and dried to obtain a semiconductor phase MoS2 transition metal-based composite catalyst.

[0007] Preferably, in step (1), the molar ratio of molybdate to sulfur-containing organic compound is 1:(20-30); the molybdate is ammonium molybdate or sodium molybdate; and the sulfur-containing organic compound is thioacetamide or thiourea.

[0008] Preferably, in step (1), the transition metal is at least one of Cu, Ni, Mn, and Co, and the amount is calculated as 0.5% to 3.0% of the mass fraction of the transition metal element in the semiconductor phase MoS2 transition metal-based composite catalyst.

[0009] Preferably, the soluble salt of the transition metal is at least one of the acetate and nitrate of the corresponding metal.

[0010] Preferably, the phosphating source is at least one selected from ammonium hypophosphite, sodium hypophosphite, and calcium hypophosphite.

[0011] Preferably, in step (1), the mass ratio of phosphating source to molybdate is (2-3):6.

[0012] Preferably, in step (2), water and ethanol are used for washing in sequence; the drying temperature is 60-80℃ and the drying time is 2-4 h.

[0013] A second aspect of the present invention provides a semiconductor phase MoS2 transition metal-based composite catalyst prepared using the preparation method described in the first aspect.

[0014] The third aspect of this invention provides the application of the semiconductor phase MoS2 transition metal-based composite catalyst described in the second aspect in the electrochemical reduction of N2O to synthesize ammonia.

[0015] The fourth aspect of this invention provides a method for electrochemically reducing N2O to synthesize ammonia, comprising the following steps: uniformly dispersing the semiconductor phase MoS2 transition metal-based composite catalyst described in the second aspect in an ethanol solution and coating it onto the surface of carbon paper to form a working electrode, which is then assembled into a three-electrode system; in the three-electrode system, a 0.1 mol / L Na2SO4 solution is used as the electrolyte, Ag / AgCl is used as the reference electrode, and a glassy carbon electrode is used as the counter electrode; the three-electrode system is connected to an electrochemical workstation, and ammonia is synthesized by reacting under an N2O atmosphere of 10 mL / min and a voltage range of 0 to -1.2 V for 1 to 5 h.

[0016] Beneficial effects of this invention: 1. This invention successfully constructs a tight heterogeneous interface between transition metal phosphides / sulfides and MoS2 in a MoS2-based composite structure using a one-pot hydrothermal-phosphating synergistic preparation method. The construction of this multiphase composite structure is a hallmark feature of this catalyst. Unlike catalysts prepared by simple physical mixing or stepwise synthesis methods, it achieves uniform distribution and strong coupling of multiple active components at the atomic / nanoscale through a one-step in-situ reaction, fundamentally solving key bottlenecks such as the single active site and slow electron transfer in the electrocatalytic reduction of N2O.

[0017] 2. The composite structure of the catalyst in this invention brings about a synergistic improvement in activity and stability. On the one hand, the high conductivity and metal-like properties of transition metal phosphides (such as Ni2P and CoP) complement the semiconductor properties of MoS2, constructing an efficient charge transport channel and accelerating electron transfer during the reaction process. At the same time, the strong electronic interactions formed at the interface can optimize the adsorption configuration of linear N2O molecules at the active sites, effectively weakening NO bonds and significantly reducing their activation energy barrier. On the other hand, the chemical bonding between the in-situ generated transition metal sulfides and the MoS2 substrate, as well as the stable anchoring of the phosphide phase, together endow the catalyst with excellent structural stability, ensuring its performance durability during long-term electrocatalytic operation.

[0018] 3. The composite catalyst of this invention exhibits significantly enhanced catalytic activity, higher ammonia yield, and superior Faraday efficiency in the electrocatalytic reduction of N2O to ammonia. The catalyst preparation method is simple, efficient, and operates under mild conditions, demonstrating good reproducibility and scalability. It provides a high-performance catalyst solution with practical application potential for the efficient resource conversion of N2O, a potent greenhouse gas. Attached Figure Description

[0019] Figure 1 SEM and TEM images of NiS2 / Ni2P / MoS2 prepared in Example 1; Figure 2 The XRD pattern of NiS2 / Ni2P / MoS2 prepared in Example 1; Figure 3 Raman plot of NiS2 / Ni2P / MoS2 prepared in Example 1; Figure 4 The XRD pattern of CoS2 / Co2P / MoS2 prepared in Example 2; Figure 5 Raman plot of CoS2 / Co2P / MoS2 prepared in Example 2; Figure 6 The XRD pattern of NiS2 / Ni2P / MoS2 prepared in Comparative Example 1; Figure 7Raman plot of NiS2 / Ni2P / MoS2 prepared in Comparative Example 1; Figure 8 NH3 production and Faraday efficiency curves of NiS2 / Ni2P / MoS2 prepared in Example 1; Figure 9 LSV curves of NiS2 / Ni2P / MoS2 prepared in Example 1 under Ar and N2O atmospheres; Figure 10 NH3 production and Faraday efficiency curves of CoS2 / Co2P / MoS2 prepared in Example 2; Figure 11 LSV curves of CoS2 / Co2P / MoS2 prepared in Example 2 under Ar and N2O atmospheres; Figure 12 The NH3 yield and Faraday efficiency curves of NiS2 / Ni2P / MoS2 prepared for Comparative Example 1. Detailed Implementation

[0020] The embodiments described herein are merely illustrative of the technical content of the invention and are not intended to limit the scope of protection of the invention. The invention can be implemented in many forms and should not be construed as limited to the specific examples listed below.

[0021] Example 1 A method for preparing a semiconductor phase MoS2 transition metal-based composite catalyst, the specific steps of which are as follows: (1) Dissolve 1.8 g ammonium molybdate tetrahydrate and 2.4 g thioacetamide together in 30 mL of deionized water, then add 0.1 g nickel acetate tetrahydrate (Ni element mass is calculated as 1.0% of the final composite catalyst mass), and stir at room temperature for 45 minutes to form a homogeneous precursor solution; (2) Add 0.85 g of sodium hypophosphite as a phosphating source to the precursor solution in step (1), stir at room temperature for 15 minutes, and disperse evenly to obtain a mixed solution; (3) Transfer the mixed solution from step (2) into a 50 mL polytetrafluoroethylene liner, seal it in a stainless steel high-pressure reactor, and place it in an oven at 180°C for 24 h. (4) After the reaction is completed, the product is naturally cooled to room temperature. The black solid product is washed three times with deionized water and anhydrous ethanol, and then dried in an oven at 60°C for 4 hours. (5) The dried block material was ground into a uniform black powder in an agate mortar to obtain the MoS2 transition metal-based composite catalyst NiS2 / Ni2P / MoS2.

[0022] Example 2 A method for preparing a semiconductor phase MoS2 transition metal-based composite catalyst, the specific steps of which are as follows: (1) Dissolve 1.8 g ammonium molybdate tetrahydrate and 2.4 g thioacetamide together in 30 mL of deionized water, then add 0.2 g cobalt nitrate tetrahydrate (Co element mass is calculated as 2.7% of the final composite catalyst mass), and stir at room temperature for 45 minutes to form a homogeneous precursor solution; (2) Add 0.80 g of sodium hypophosphite as a phosphating source to the precursor solution in step (1), stir at room temperature for 15 minutes, and disperse evenly to obtain a mixed solution; (3) Transfer the mixed solution from step (2) into a 50 mL polytetrafluoroethylene liner, seal it in a stainless steel high-pressure reactor, and place it in an oven at 180°C for 24 h. (4) After the reaction is completed, the product is naturally cooled to room temperature. The black solid product is washed three times with deionized water and anhydrous ethanol, and then dried in an oven at 60°C for 4 hours. (5) The dried block material was ground into a uniform black powder in an agate mortar to obtain the MoS2 transition metal-based composite catalyst CoS2 / Co2P / MoS2.

[0023] Comparative Example 1 A method for preparing a MoS2 transition metal-based composite catalyst, the specific steps of which are as follows: (1) Dissolve 1.8 g ammonium molybdate tetrahydrate and 2.4 g thioacetamide together in 30 mL of deionized water, then add 0.1 g nickel acetate tetrahydrate (Ni element mass is calculated as 1.0% of the final composite catalyst mass), and stir at room temperature for 45 minutes to form a homogeneous precursor solution; (2) The precursor solution from step (1) was transferred to a 50 mL high-pressure reactor and reacted at 180 °C for 24 hours. After the reaction was completed, the product was washed, dried at 60 °C, and ground to obtain NiS2 / MoS2 precursor powder. (3) The NiS2 / MoS2 precursor powder prepared in step (2) and 0.85 g sodium hypophosphite were placed in the upstream and downstream regions of a tube furnace, respectively. Under a nitrogen atmosphere, the temperature was increased to 300℃ at 5℃ / min and kept at the temperature for 2 h for phosphating reaction. After the reaction was completed, the temperature was naturally cooled to room temperature, and the sample was collected to obtain the MoS2 transition metal-based composite catalyst NiS2 / Ni2P / MoS2.

[0024] Characterization tests: (1) Morphological characteristics The NiS2 / Ni2P / MoS2 composite catalyst prepared in Example 1 was characterized by scanning electron microscopy and transmission electron microscopy, and the results are as follows: Figure 1As shown in the figure. The results indicate that the one-pot hydrothermal-phosphating preparation induced in-situ recombination and structural reorganization of the MoS2 sheets as semiconductor phases (2H) and transition metal species, forming a composite catalytic system with rich interfaces and fine structures.

[0025] (2) Chemical composition and phase characterization To determine the chemical composition and phase composition of the composite catalysts, X-ray diffraction (XRD) and Raman spectroscopy analyses were performed on the composite catalysts of Examples 1, 2, and 1 (Comparative Example 1). The results are as follows: Figures 2-7 As shown.

[0026] The X-ray diffraction (XRD) and Raman spectra of the composite catalyst prepared in Example 1 are as follows: Figure 2 , Figure 3 As shown, the composite catalyst contains characteristic phases of NiS2, Ni2P, and MoS2, and these three phases form a tight composite structure, with MoS2 exhibiting a 2H semiconductor phase. The X-ray diffraction (XRD) and Raman spectra of the composite catalyst prepared in Example 2 are shown below. Figure 4 , Figure 5 As shown, the composite catalyst exhibits characteristic phases of CoS2, Co2P, and MoS2, forming a tight composite structure. MoS2 exhibits as a 2H semiconductor phase. The X-ray diffraction (XRD) and Raman spectra of the composite catalyst prepared in Comparative Example 1 are shown below. Figure 6 , Figure 7 As shown, the composite catalyst MoS2 sheets are formed through in-situ composite and structural recombination of the semiconductor phase (2H) and transition metal species, resulting in a composite catalytic system with rich interfaces and fine structures. Comparative analysis revealed that the catalyst prepared in Example 1 exhibited a wider half-maximum width of diffraction in XRD, indicating that the one-step hydrothermal method is beneficial for forming small-sized microcrystals, providing abundant catalytic activity edges; while Comparative Example 1, due to high-temperature phosphating at 300℃, showed a significant increase in phase crystallinity. In Raman spectroscopy, the characteristic peak shift of MoS2 in Example 1 was more pronounced, confirming that the in-situ one-step method can induce stronger interfacial electronic coupling between NiS2 / Ni2P and the MoS2 support. This tight interfacial structure is conducive to charge transfer, thereby improving catalytic performance.

[0027] (3) Electrocatalytic performance test 0.5 mg of the composite catalysts prepared in Examples 1, 2, and Comparative Example 1 were weighed, uniformly dispersed, and coated onto the surface of carbon paper to prepare working electrodes. An H-type electrolytic cell was used with 40 mL of 0.1 mol / L Na₂SO₄ solution as the electrolyte, an Ag / AgCl electrode as the reference electrode, and a glassy carbon electrode as the counter electrode. The cells were connected to an electrochemical workstation for performance characterization. After reacting for 1 hour at potentials of -0.6 V to -0.2 V (relative to the reference electrode), 2 mL of electrolyte was taken, and the concentration of generated NH₃ was detected using the indophenol blue method. The linear sweep voltammetry (LSV) curve of the composite catalyst was measured under an Ar or N₂O atmosphere at a flow rate of 10 mL / min, with a test voltage range of (-1.2) to 0 V.

[0028] The NH3 concentration and linear sweep voltammetry (LSV) curve results of the composite catalyst prepared in Example 1 are as follows: Figure 8 , Figure 9 As shown in Table 1, the GC-TCD analysis results of the cathode tail gas show that, apart from unreacted N2O, no byproducts such as NO or NO2 were detected. NH3 concentration results ( Figure 8 The results showed that at a potential of -0.5 V, the yield of NH3 reached 743.8 ug h. - 1 mg cat This potential represents the optimal condition for the electrocatalytic reduction of N₂O to NH₃, enabling efficient electron utilization and the synthesis of the target product. Linear sweep voltammetry (LSV) curve ( Figure 9 The solid line in the figure represents the current density measured in an N2O atmosphere, and the dashed line represents the current density measured in an Ar atmosphere. It can be seen that the current density measured in an N2O atmosphere is significantly higher than that in an Ar atmosphere. Combined with the detection results of NH3 production, it is confirmed that N2O resources can be converted into high-value-added product NH3 through an electrochemical pathway.

[0029] Table 1. Results of cathode exhaust gas detection The NH3 concentration and linear sweep voltammetry (LSV) curve results of the composite catalyst prepared in Example 2 are as follows: Figure 10 , Figure 11 As shown in Table 2, the GC-TCD analysis results of the cathode tail gas show that, apart from unreacted N2O, no byproducts such as NO or NO2 were detected. NH3 concentration results ( Figure 10 The results showed that at a potential of -0.5 V, the yield of NH3 reached 356.0 ug h. -1 mg catThis potential represents the optimal condition for the electrocatalytic reduction of N₂O to NH₃, enabling efficient electron utilization and the synthesis of the target product. Linear sweep voltammetry (LSV) curve ( Figure 11 The solid line in the figure represents the current density measured in an N2O atmosphere, and the dashed line represents the current density measured in an Ar atmosphere. It can be seen that the current density measured in an N2O atmosphere is significantly higher than that in an Ar atmosphere. Combined with the detection results of NH3 production, it is confirmed that N2O resources can be converted into high-value-added product NH3 through an electrochemical pathway.

[0030] Table 2. Results of cathode exhaust gas detection The NH3 concentration of the composite catalyst prepared in Comparative Example 1 is as follows: Figure 12 As shown, the NH3 yield reaches its maximum at a potential of -0.4 V, at only ~179.6 μg h. -1 mg cat This is significantly lower than the 743.8 ugh of the one-pot sample from Example 1. -1 mg cat The stepwise method involves high-temperature calcination and stepwise reactions, resulting in poor dispersion of active components (especially Ni2P) and weak interfacial bonding with the MoS2 substrate. This is not conducive to charge transport and reactant adsorption, and therefore the catalytic performance is significantly inferior to that of the one-pot method of one-step in-situ synthesis.

Claims

1. A method for preparing a semiconductor phase MoS2 transition metal-based composite catalyst, characterized in that, Includes the following steps: (1) Dissolve molybdate and sulfur-containing organic compounds in water, then add soluble salts of transition metals and stir to form a homogeneous precursor solution; A phosphating source is added to the precursor solution and dispersed evenly to obtain a mixed solution; (2) The mixed solution from step (1) was reacted at 160-200℃ for 20-28 h. After the reaction was completed, it was cooled to room temperature. The resulting product was washed and dried to obtain a semiconductor phase MoS2 transition metal-based composite catalyst.

2. The preparation method according to claim 1, characterized in that, Step (1) The molar ratio of molybdate and sulfur-containing organic compound is 1:(20-30); the molybdate is ammonium molybdate or sodium molybdate; the sulfur-containing organic compound is thioacetamide or thiourea.

3. The preparation method according to claim 1, characterized in that, Step (1) The transition metal is at least one of Cu, Ni, Mn and Co, and the amount is calculated as 0.5% to 3.0% of the mass fraction of the transition metal element in the semiconductor phase MoS2 transition metal-based composite catalyst.

4. The preparation method according to claim 3, characterized in that, The soluble salt of the transition metal is at least one of the acetate or nitrate of the corresponding metal.

5. The preparation method according to claim 1, characterized in that, The phosphating source is at least one of ammonium hypophosphite, sodium hypophosphite, and calcium hypophosphite.

6. The preparation method according to claim 5, characterized in that, Step (1) The mass ratio of phosphide source to molybdate is (2-3):

6.

7. The preparation method according to any one of claims 1 to 6, characterized in that, Step (2) Wash with water and ethanol in sequence; dry at 60-80℃ for 2-4 hours.

8. A semiconductor phase MoS2 transition metal-based composite catalyst prepared by any of the preparation methods described in claims 1 to 7.

9. The application of the semiconductor phase MoS2 transition metal-based composite catalyst according to claim 8 in the electrochemical reduction of N2O to synthesize ammonia.

10. A method for synthesizing ammonia by electrochemical reduction of N₂O, characterized in that, The process includes the following steps: uniformly dispersing the semiconductor phase MoS2 transition metal-based composite catalyst prepared according to claim 8 in an ethanol solution and coating it onto the surface of carbon paper to form a working electrode, which is then assembled into a three-electrode system; in the three-electrode system, a 0.1 mol / L Na2SO4 solution is used as the electrolyte, Ag / AgCl is used as the reference electrode, and a glassy carbon electrode is used as the counter electrode; the three-electrode system is connected to an electrochemical workstation, and ammonia is synthesized by reacting under a N2O atmosphere at a flow rate of 10 mL / min and a voltage range of 0 to -1.2 V for 1 to 5 h.

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