Tungsten oxide-loaded ruthenium oxide catalyst, preparation method thereof and application of catalyst in thermoelectric catalytic synthesis of ammonia

Abstract

The invention provides a tungsten oxide loaded ruthenium oxide catalyst, a preparation method thereof and an application in thermoelectric catalytic synthesis of ammonia, the catalyst comprises an oxygen vacancy-rich WO3-x carrier and a RuO2 nanoparticle active component, RuO2 is anchored through oxygen vacancies in the WO3-x carrier to form a Ru-O-W interface structure, and the mass fraction of RuO2 in the catalyst is 0.05 wt.%-5wt.%. The WO3x carrier is impregnated with ruthenium salt, and high-temperature annealing treatment is performed under inert atmosphere protection. The active component Ru is firmly anchored through the electron capture effect of oxygen vacancies, and migration and agglomeration of metal nanoparticles in a high-temperature environment can be effectively inhibited through formed strong interface interaction; and meanwhile, by combining a high-temperature and high-pressure electrochemical reaction system, the solubility and activity of nitrogen in the electrolyte are remarkably improved. Under the conditions of high temperature and high pressure, the ammonia production rate reaches up to 319.45 mu gmg1h1, the Faraday efficiency is 15.53%, and the composite material has excellent structural stability and catalytic activity and provides a new technical approach for efficient electrocatalytic synthesis of ammonia.

Description

Technical Field

[0001] This invention belongs to the field of electrocatalytic ammonia synthesis technology, and relates to a tungsten oxide supported ruthenium catalyst, its preparation method and its application in thermoelectrocatalytic ammonia synthesis. Specifically, it relates to a method for preparing a tungsten oxide supported ruthenium oxide (RuO2 / WO3) catalyst with oxygen-rich vacancies, and the application of the catalyst in electrocatalytic nitrogen reduction (NRR) ammonia synthesis under high temperature and high pressure conditions. Background Technology

[0002] Ammonia, as one of the world's largest-produced chemical industrial products, plays an indispensable role in agricultural fertilizers, chemical raw materials, and clean energy carriers. Although the traditional Haber-Bosch process has been used for over a century, its harsh high-temperature and high-pressure conditions result in energy consumption accounting for 1%–2% of global total energy consumption and contributing approximately 1.5% of global greenhouse gas emissions, severely hindering the achievement of sustainable development. Therefore, developing green, low-energy-consumption ammonia synthesis technologies has become an urgent priority. Electrocatalytic nitrogen reduction (NRR) technology, due to its ability to achieve "zero-carbon" ammonia production using renewable energy under mild conditions, is considered a highly promising alternative technology.

[0003] However, conventional ambient temperature and pressure electrocatalytic NRR faces serious bottlenecks: First, nitrogen has extremely low solubility in aqueous solutions, resulting in insufficient N2 concentration at active sites and slow mass transfer kinetics; second, the hydrogen evolution reaction (HER) in aqueous electrolytes is highly competitive, leading to generally low Faradaic efficiency (FE) and yield in ammonia synthesis. Studies have shown that increasing reaction temperature and pressure can significantly increase nitrogen solubility and accelerate N≡N bond activation, but this places higher demands on catalyst stability. Ruthenium, as a recognized active metal for ammonia synthesis, is considered to effectively adsorb and activate nitrogen molecules, and is usually supported on tungsten oxide. However, in high-temperature hydrothermal environments (e.g., 250°C), supported metal catalysts face severe challenges: metal nanoparticles have extremely high surface energy, are prone to migration and aggregation under high-temperature conditions, and are easily oxidized to metal oxides, leading to loss of active sites and rapid degradation of catalytic performance. Traditional physical loading methods are insufficient to meet the stability requirements of high-temperature and high-pressure electrochemical processes. Therefore, developing a catalyst with a strong interaction interface, capable of locking active metal sites, and resistant to high temperature and high pressure shocks is a key challenge in the current exploration of high-temperature electrocatalytic ammonia synthesis. Summary of the Invention

[0004] To address the above problems, this invention provides a tungsten oxide-supported ruthenium oxide catalyst, its preparation method, and its application in thermoelectric catalytic ammonia synthesis. Oxygen vacancies are introduced in situ via an alcoholothermic method to anchor Ru, and combined with a subsequent high-temperature annealing process, WO3 is prepared. 3-x The RuO2 nanoparticle supported catalyst exhibits extremely high activity and stability under the high temperature and high pressure environment of thermoelectric catalytic ammonia synthesis.

[0005] To achieve the above objectives, the present invention adopts the following technical solution: A tungsten oxide-supported ruthenium oxide catalyst, comprising oxygen-rich vacancy WO3 3-x The carrier (x represents an oxygen vacancy) and RuO2 nanoparticles are active components, wherein the RuO2 nanoparticles are transported via WO3. 3-x Oxygen vacancies in the support are anchored to form a Ru-OW interface structure. The catalyst does not have an oxygen vacancy EPR signal. The mass fraction of RuO2 nanoparticles in the catalyst is 0.05 wt.%-5 wt.%.

[0006] The tungsten element in the carrier is in the hexavalent state.

[0007] This invention also provides a method for preparing a ruthenium catalyst supported on tungsten oxide, comprising the following steps: (1) Add the ruthenium salt solution dropwise to WO4. 3-x In the support, ruthenium is loaded by an equal-volume impregnation method, so that the ruthenium component is loaded onto the oxygen vacancy defect sites on the support surface; (2) The dried solid was placed in a tube furnace and subjected to high-temperature annealing under an inert atmosphere. The Ru-OW interface structure was constructed by utilizing the anchoring effect of oxygen vacancies to obtain RuO2 / WO. 3-x catalyst.

[0008] The ruthenium salt mentioned in step (1) includes one or more of ruthenium trichloride, ruthenium nitrosyl nitrate, and ruthenium acetylacetonate.

[0009] The concentration of ruthenium salt in step (1) is 0.02-0.4 mol / L.

[0010] The annealing temperature in step (2) is 300-500℃.

[0011] In step (1), WO 3-x The preparation method of the support includes dissolving tungsten salt in anhydrous ethanol, stirring until homogeneous, transferring to a hydrothermal reactor, and carrying out a solvothermal reaction; after the reaction, centrifugation, washing, and drying are performed to obtain deep blue oxygen-rich vacancy WO3. 3-x Carrier.

[0012] The ethanol is used as both a solvent and a reducing agent.

[0013] The mass-to-volume ratio of the tungsten salt to anhydrous ethanol is 0.1-5 g : 40 mL.

[0014] The solvothermal reaction conditions are 160~200℃ for 12~24h.

[0015] The tungsten salt includes one or more of tungsten hexachloride, sodium tungstate, and ammonium metatungstate.

[0016] The present invention also provides the application of the catalyst in thermoelectric catalytic synthesis of ammonia.

[0017] The reaction temperature is 100℃-250℃, and the reaction pressure is 10bar-50bar.

[0018] The beneficial effects of this invention are: (1) Strong metal-support interaction (SMSI): Oxygen vacancies are anchor points for Ru. High-temperature annealing ensures that Ru is firmly anchored near oxygen vacancies, enabling the Ru component to re-coordinate with O and W atoms in the water of crystallization to form chemical bonds, constructing a Ru-OW strong interaction interface, which makes Ru highly dispersed and anchored. By constructing the Ru-OW interface, the transformation of the Ru component from physical loading to chemical anchoring is realized, effectively inhibiting the migration and sintering of Ru nanoparticles during high-temperature electrolysis; at the same time, combined with the high-temperature and high-pressure electrochemical reaction system, the solubility and mass transfer efficiency of nitrogen in the electrolyte are significantly improved, and the activation kinetics of nitrogen molecules are accelerated.

[0019] (2) Significant performance improvement: The ammonia production rate of this catalyst under ambient conditions (normal temperature and pressure) is only 14.33 μg·mg. -1 ·h -1 The FE content was 6%; however, thanks to the stability and kinetic acceleration of the Ru-OW interface under high temperature and pressure, the ammonia production rate was significantly increased to 319.45 μg·mg at 250°C and 50 bar. -1 ·h -1 FE increased to 15.53%.

[0020] (3) Structural stability: After long-term operation under high temperature and high pressure, Ru nanoparticles still remain highly dispersed. After 12 hours of long-term electrolysis, the current density can still be maintained at more than 90% of the initial value, which fully demonstrates the decisive role of oxygen vacancy anchoring effect in maintaining the integrity of active sites. Attached Figure Description

[0021] Figure 1 For WO3 and WO 3-x SEM image.

[0022] Figure 2 For WO3 and WO 3-x XRD pattern.

[0023] Figure 3 HRTEM and EDX plots for RuO2 / WO3.

[0024] Figure 4 For WO3, WO 3-x RuO2 / WO3 and RuO2 / WO 3-x The ultraviolet-visible diffuse reflectance spectrum.

[0025] Figure 5 For WO3, WO 3-x RuO2 / WO3 and RuO2 / WO 3-x XPS graph.

[0026] Figure 6 For WO3, WO 3-x andRu / WO 3-x EPR diagram.

[0027] Figure 7 This is a diagram of a high-temperature and high-pressure reactor; where 1 is the cathode cell, 2 is the PBI membrane, 3 is the anode cell, and 4 is the outer shell.

[0028] Figure 8 The UV-Vis spectrum and standard curve for determining ammonia yield using the indophenol blue method.

[0029] Figure 9 For WO3 and WO under environmental conditions 3-x RuO2 / WO3 and RuO2 / WO 3-x ammonia yield and Faraday efficiency.

[0030] Figure 10 WO3 and WO3 under conditions of 200℃ and 45bar 3-x RuO2 / WO3 and RuO2 / WO 3-x ammonia yield and Faraday efficiency.

[0031] Figure 11 Ru / WO at 200℃ and 45 bar 3-x , RuO2 / WO3, RuO2 / WO3-A and RuO2 / WO 3-x The results of long-term electrolysis tests. Detailed Implementation

[0032] The present invention will be further described in detail below with reference to specific examples, but the present invention is not limited to the specific embodiments.

[0033] Example 1 (1) WO 3-x Preparation of the support: 0.1 g of tungsten hexachloride was dissolved in 40 ml of anhydrous ethanol and continuously stirred magnetically for 30 min at room temperature until completely dissolved, forming a deep blue transparent solution. The solution was transferred to a 50 ml hydrothermal reactor lined with polytetrafluoroethylene (PTFE) and subjected to a solvothermal reaction at 200 °C for 12 hours. After the reaction, the mixture was allowed to cool naturally to room temperature, and the blue precipitate was collected by high-speed centrifugation. The precipitate was washed three times alternately with deionized water and anhydrous ethanol, and then dried in a vacuum drying oven at 60 °C for 12 hours to obtain an oxygen-rich vacancy tungsten oxide support, denoted as WO₂.3-x .

[0034] (2) Will WO 3-x The carrier was annealed at 500°C in a muffle furnace to obtain yellow tungsten oxide without oxygen vacancies, denoted as WO3.

[0035] (3) WO 3-x Morphological characteristics: Figure 1 a is the SEM image of WO3. Figure 1 b is WO 3-x The SEM image shows that WO 3-x The material has a uniform nanostructure, and the surface exhibits a microscopic roughness due to the presence of oxygen vacancies. After calcination in air, the WO3 material undergoes significant sintering, resulting in a large number of nanoparticles.

[0036] Figure 2 For WO3 and WO 3-x The XRD pattern of WO. From the pattern, we can see that WO... 3-x The diffraction peaks are consistent with the standard card of monoclinic WO3, but the lattice distortion caused by oxygen vacancies hinders the growth of some crystal planes.

[0037] Example 2 (1)RuO2 / WO 3-x Catalyst preparation: Weigh 100 mg of WO3 prepared in Example 1 3-x The powder was placed in an impregnation flask. Then, an equal volume of 20 μL of ruthenium chloride (RuCl3) aqueous solution (containing 1 mg of metallic Ru) was added for impregnation. The mixture was stirred with an impregnation rod to ensure the Ru component was fully impregnated into the oxygen vacancies of the support. The flask was then placed in a 60 °C oven for 24 h to obtain a solid powder. This powder was then transferred to a ceramic boat and annealed at 400 °C at a heating rate of 5 °C / min for 2 h under an argon atmosphere. During this process, Ru... 3+ Oxidized and stably anchored at oxygen vacancies, a robust Ru-OW interface is constructed. After cooling to room temperature, the catalyst is removed, yielding the final catalyst, denoted as RuO2 / WO. 3-x .

[0038] (2) Same as step (1) for WO 3-x The carrier was changed to WO3, resulting in RuO2 / WO3.

[0039] (3) Same as step (1), replace the argon gas with a 5% H2 / 95% Ar mixture to obtain Ru / WO 3-x .

[0040] (4) Replace the argon gas with air in the same step (1) to obtain RuO2 / WO3-A.

[0041] (5) RuO2 / WO 3-x Interface representation: Figure 3 a is RuO2 / WO 3-x The HRTEM image shows that Ru nanoparticles are highly dispersed on the support surface. The lattice spacing shows that the (200) crystal plane of RuO2 is in close contact with the (200) crystal plane of WO3, proving the successful construction of the Ru-OW interface. Figure 3 b is RuO2 / WO 3-x The EDX plot shows that Ru is uniformly distributed in WO3 material.

[0042] Figure 4 For WO3, WO 3-x RuO2 / WO3 and RuO2 / WO 3-x The UV-Vis diffuse reflectance spectrum of WO3 is observed. WO3 annealed in air exhibits typical semiconductor characteristics with a band gap of 2.68 eV. In contrast, WO3 directly prepared by hydrothermal method... 3-x The band gap narrowed significantly to 2.57 eV, and a strong, broad absorption band appeared in the low-energy region. After loading the active component Ru, the absorption edge of the RuO2 / WO3 catalyst showed a significant red shift compared to the support.

[0043] Figure 5 For WO3, WO 3-x RuO2 / WO3 and RuO2 / WO 3-x XPS images. XPS results show that Ru is present in Ru on the vector. 4+ The oxygen-rich vacancy system RuO2 / WO3 exists; compared to the control sample RuO2 / WO3, the oxygen-rich vacancy system RuO2 / WO3... 3−x The binding energies of Ru 3d (280.75 eV) and W 4f (35.73 eV) in the catalyst showed a significant positive shift. This synergistic energy shift strongly demonstrates the existence of a powerful electron-sense interface (SMSI) between the Ru nanoparticles and the defective support, indicating a significant transfer of electrons from Ru to the support side through the Ru-OW interface. This results in a highly electron-deficient state at the Ru center, which not only helps suppress the competitive hydrogen evolution reaction (HER) but also confirms the successful regulation of the interfacial electronic structure by oxygen vacancies. This chemical bonding effect enhances the thermodynamic stability of the catalyst, enabling it to suppress the aggregation of the active component Ru even under harsh high-temperature and high-pressure conditions of 200 °C and 45 bar, thus maintaining extremely high ammonia synthesis activity and stability.

[0044] Figure 6 The microscopic defect structure of the catalyst was further characterized using electron paramagnetic resonance (EPR) spectroscopy. As shown in the attached figure, compared to WO3, the WO3 prepared in this invention...3-x The support exhibited a strong single-electron capture signal near g=2.002, confirming the presence of oxygen vacancies. When the active component Ru was loaded, the RuO2 / WO... 3-x The signal strength increased by an order of magnitude and broadened significantly, a phenomenon reflecting the interaction between the Ru component and WO. 3-x Strong electron exchange and coupling effects between oxygen vacancies in the carrier.

[0045] Example 3: Test Procedure for Electrocatalytic Nitrogen Reduction Synthesis of Ammonia (1) Performance Testing: Electrocatalytic nitrogen reduction (NRR) performance testing was conducted in a custom-designed high-temperature and high-pressure reactor. The reactor was equipped with a custom-designed PTFE liner and modified into an H-type double-compartment structure to isolate interference from metal ions in the reactor body. The working electrode was loaded with RuO2 / WO3. 3-x The reactor used hydrophobic carbon paper (0.25 cm²), a high-temperature, high-pressure Ag / AgCl electrode as the reference electrode, and platinum foil as the counter electrode. 60 mL and 20 mL of 0.1 M Na₂SO₄ electrolyte were injected into the cathode and anode chambers, respectively. The high-temperature, high-pressure reactor and its lining are as follows: Figure 7 As shown, the inner liner comprises a cathode cell 1, a PBI membrane 2, an anode cell 3, and an outer shell 4. Before testing, ultrapure nitrogen (6N grade) was introduced into the reactor and pressurized to the specified pressure, while the temperature was simultaneously raised to 250 °C via an external heating mantle. After reaching the set temperature and pressure, cyclic voltammetry was performed until the current stabilized, followed by a 1-hour constant potential test under different bias voltages. The stability test involved continuous electrolysis for 12 hours at the optimal potential.

[0046] (2) NH3 concentration detection: The indophenol blue method was used. Take 2 mL of the electrolyte after electrolysis, and add 2 mL of solution A (a mixture of 5 wt% salicylic acid, 5 wt% sodium citrate, and 0.1 mol / L sodium hydroxide), 1 mL of 0.05 mol / L sodium hypochlorite solution, and 0.2 mL of 1 wt% potassium nitrosoferricyanide solution sequentially. Let stand for 60 min to develop color. Measure the absorbance at 655 nm using a UV-Vis spectrophotometer. Calculate the ammonia concentration using a standard curve and convert the ammonia production rate and Faraday efficiency (FE).

[0047] Example 4 (1) The WO3 and WO3 prepared in Examples 1 and 2 3-x RuO2 / WO3 and RuO2 / WO 3-x The catalyst was compared in performance under ambient temperature and pressure and high temperature and high pressure (250 °C, 50 bar) conditions, following the method described in Example 3. Figure 9 and Figure 10 As shown, pure WO3 has the worst activity; WO 3-xThe activity was enhanced after the introduction of Ru due to the increased adsorption of N2 by oxygen vacancies; and after loading Ru and forming a Ru-OW interface, the performance was nearly twice that of the support. This indicates that Ru, as the main active center, produced a strong synergistic effect with the support. Specifically, the RuO2 / WO2 interface... 3-x Under environmental conditions, the ammonia production rate was only 14.33 μg·mg. -1 ·h -1 With an FE content of 6%, the ammonia production rate reached as high as 319.45 μg·mg under conditions of 200 ℃ and 45 bar. -1 ·h -1 The Faraday efficiency is close to 15.53%.

[0048] Example 5 The Ru / WO prepared in Example 2 3-x RuO2 / WO3, RuO2 / WO 3-x The RuO2 / WO3-A catalyst was subjected to long-term electrolysis tests at high temperature and high pressure (250 °C, 50 bar) according to the method in Example 3. Figure 11 As shown, Ru / WO 3-x RuO2 / WO3 and RuO2 / WO3-A both showed a significant current decay trend, while RuO2 / WO 3-x It exhibits excellent high-temperature hydrothermal electrolysis stability. This indicates that the Ru-OW interface constructed through lattice oxygen can adapt to high-temperature hydrothermal electrocatalytic reaction systems.

[0049] In summary, the advantages of this material are: 1. WO 3-x The abundant oxygen vacancies in the catalyst provide numerous metal anchoring sites, and the Ru-OW interface formed by annealing at 500 °C exhibits extremely high thermodynamic stability, preventing the migration and aggregation of active centers under high-temperature hydrothermal conditions. Secondly, the high-pressure environment (45 bar) significantly enhances the solubility of nitrogen in aqueous solution, overcoming the problem of limited mass transfer at room temperature. Thirdly, the high temperature (200 °C) accelerates the kinetics of N≡N bond breaking. Through the synergy of support defect engineering and the high-temperature, high-pressure reaction system, this catalyst achieves efficient and stable electrocatalytic ammonia synthesis under harsh conditions, with performance far superior to traditional room-temperature, ambient-pressure electrocatalytic systems.

Claims

1. A tungsten oxide-supported ruthenium oxide catalyst, characterized in that: Including WO 3-x The carrier and RuO2 nanoparticles are active components, wherein the RuO2 nanoparticles are transported via WO3. 3-x Oxygen vacancies in the support are anchored to form a Ru-OW interface structure. The catalyst does not have an oxygen vacancy EPR signal. The mass fraction of RuO2 nanoparticle active components in the catalyst is 0.05 wt.%-5 wt.%.

2. A method for preparing the tungsten oxide-supported ruthenium catalyst according to claim 1, characterized in that: Includes the following steps: (1) Add the ruthenium salt solution dropwise to WO4. 3-x In the support, ruthenium is loaded by impregnation, so that the ruthenium component is loaded onto the oxygen vacancy defect sites on the support surface; (2) The dried solid was placed in a tube furnace and subjected to high-temperature annealing under an inert atmosphere. The Ru-OW interface structure was constructed by utilizing the anchoring effect of oxygen vacancies to obtain RuO2 / WO. 3-x catalyst.

3. The preparation method according to claim 2, characterized in that: The ruthenium salt mentioned in step (1) includes one or more of ruthenium trichloride, ruthenium nitrosyl nitrate, and ruthenium acetylacetonate.

4. The preparation method according to claim 2, characterized in that: The concentration of ruthenium salt in step (1) is 0.02-0.4 mol / L.

5. The preparation method according to claim 2, characterized in that: The annealing temperature in step (2) is 300-500℃.

6. The preparation method according to claim 2, characterized in that: In step (1), WO 3-x The preparation method of the support includes dissolving tungsten salt in anhydrous ethanol, stirring until homogeneous, transferring to a hydrothermal reactor, and carrying out a solvothermal reaction; after the reaction, centrifugation, washing, and drying are performed to obtain deep blue oxygen-rich vacancy WO3. 3-x Carrier.

7. The preparation method according to claim 6, characterized in that: The mass-to-volume ratio of the tungsten salt to anhydrous ethanol is 0.1-5 g : 40 mL; and / or, The tungsten salt includes one or more of tungsten hexachloride, sodium tungstate, and ammonium metatungstate.

8. The preparation method according to claim 6, characterized in that: The solvothermal reaction conditions are 160~200℃ for 12~24h.

9. The application of the catalyst of claim 1 in thermoelectric catalytic synthesis of ammonia.

10. The application as described in claim 9, characterized in that: The reaction temperature is 100℃-250℃, and the reaction pressure is 10bar-50bar.

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