A Ru / WO 3-x heterojunction catalyst and its application

Abstract

The present invention relates to the field of catalytic technology, and particularly relates to a Ru / WO 3‑x heterojunction catalyst, and the chemical formula of the catalyst is Ru / WO 3‑x , where x represents oxygen vacancies; Ru is loaded on the WO 3‑x support surface in the form of metallic element, and the preparation method is as follows: using tungstate as the tungsten source, ammonium sulfate as the morphology assistant, ruthenium trichloride as the ruthenium source, adjusting the pH to 0-2, adding deionized water to prepare a hydrothermal reaction solution, and performing a hydrothermal reaction together with the current collector, rinsing with deionized water and drying, and calcining in a reducing gas atmosphere to obtain the Ru / WO 3‑x heterojunction catalyst integrated electrode. Under the same test conditions, the present invention can effectively inhibit the over-hydrogenation of nitrate to the final product ammonia, and make the product stay at the intermediate hydroxylamine.

Description

Technical Field

[0001] The present invention relates to the field of catalytic technology, and particularly relates to a Ru / WO 3-x heterojunction catalyst and its application. Background Art

[0002] Nowadays, nitrate waste liquid has become one of the main factors leading to water eutrophication and the decline of biodiversity. Traditional nitrate purification technologies, such as biological denitrifying bacteria technology and chemical redox technology, all have disadvantages such as uncontrollable reaction rate and high cost. The nitrate electroreduction reaction is a continuous reaction of sequentially adding hydrogen to generate nitrite, hydroxylamine, and ammonia under the regulation of a specific catalyst. Current research mainly focuses on the directional generation of the final product ammonia rather than the intermediate hydroxylamine. The economic value and application prospects of the intermediate hydroxylamine are much higher than those of the final product ammonia. The former can be used in the synthesis of oxime pharmaceutical intermediates in the pharmaceutical industry, photolithographic developers in the electronics industry, and corrosion inhibitors in the anti-corrosion industry, etc., while the latter is mainly used as agricultural fertilizers, chemical raw materials, and hydrogen storage carriers, etc. Currently, in industry, hydroxylamine is mainly synthesized by the Raschig Process, catalytic reduction of nitro compounds, and catalytic oxidation method (HPO method). Although they are industrially mature, they have disadvantages such as high cost of noble metal catalysts and low yield. Using the emerging electrocatalyst technology to convert nitrate into hydroxylamine directionally is more environmentally friendly, but currently, there is a lack of electrocatalysts with high selectivity for generating hydroxylamine. Summary of the Invention

[0003] The present invention solves the problems in the related technologies and provides a Ru / WO 3-x heterojunction catalyst. By one-step hydrothermal synthesis of an integrated electrode and calcination, a Ru / WO 3-x integrated electrode with oxygen vacancies is obtained, which can be applied to the electroreduction of nitrate to hydroxylamine. Under the same test conditions, this catalyst can effectively inhibit the over-hydrogenation of nitrate to the final product ammonia, and make the product stay at the intermediate hydroxylamine.

[0004] To solve the above technical problems, the present invention is realized through the following technical solutions: A Ru / WO 3-x heterojunction catalyst, the chemical formula of the catalyst is Ru / WO 3-x , where x represents oxygen vacancies; in Ru / WO 3-x , Ru is loaded on the surface of WO 3-x support in the form of metallic Ru, and its preparation method is as follows:

[0005] S1. Prepare a hydrothermal reaction solution: Use tungstate as the tungsten source, ammonium sulfate as the morphology assistant, ruthenium trichloride as the ruthenium source, adjust the pH to 0 - 2, and add deionized water to prepare a hydrothermal reaction solution.

[0006] S2. Preparation of Ru-WO₃·yH₂O integrated electrode: Hydrothermally react the hydrothermal reaction solution in S1 with the current collector at a reaction temperature of 120-200 °C for 1-24 h. After the reaction, rinse with deionized water and dry to obtain the Ru-WO₃·yH₂O integrated electrode, where y is the number of crystal water molecules carried;

[0007] S3. Preparation of Ru / WO 3-x heterojunction catalyst integrated electrode: Calcinate the Ru-WO₃·yH₂O integrated electrode in a reducing gas atmosphere to obtain the Ru / WO 3-x heterojunction catalyst integrated electrode, where the reducing gas is a hydrogen / argon mixture or a hydrogen / nitrogen mixture, the volume fraction of hydrogen in the mixture is 5-10%, the calcination temperature is 300-500 °C, the time is 2-6 h, and the final ruthenium loading range is 0.1-3 mg / cm 2 .

[0008] As a preferred solution, in step S1, the hydrothermal reaction solution is prepared as follows: Dissolve sodium tungstate dihydrate in deionized water, adjust the pH of the solution to 0-2, add oxalic acid dihydrate and ammonium sulfate, stir until homogeneous, and finally add ruthenium trichloride solution. In the finally obtained hydrothermal reaction solution, the concentration range of sodium tungstate dihydrate is 0.01-0.5 mol / L, the concentration range of oxalic acid is 0.01-0.5 mol / L, the concentration range of ammonium sulfate is 0.1-0.5 mol / L, and the concentration range of ruthenium trichloride is 0.1-10 mg / mL.

[0009] As a preferred solution, in step S2, the current collector needs to be ultrasonically cleaned with nitric acid, acetone, ethanol, and deionized water before the hydrothermal reaction.

[0010] As a preferred solution, in step S2, the specific steps of the hydrothermal reaction are as follows: Vertically place the treated current collector in a polytetrafluoroethylene inner liner, add 30 mL of the hydrothermal reaction solution, put it into a stainless steel sealed shell, and place it in a forced-air oven for hydrothermal reaction.

[0011] As a preferred solution, the obtained Ru / WO 3-x heterojunction catalyst integrated electrode can be applied to the electroreduction of nitrate to hydroxylamine, and the specific steps are as follows: The Ru / WO 3-x integrated electrode is used as the cathode, commercial IrO₂ is used as the anode, the cathode electrolyte uses an acidic or neutral electrolyte containing nitrate, the anode electrolyte uses pure water, a proton exchange membrane separates the cathode and anode for electrolysis, the cell voltage applied to the electrolytic cell is 0.8-3 V, the current density is 0.1-600 mA / cm 2 , and the electrolysis time is 0.1-24 h.

[0012] As a preferred embodiment, the acidic electrolyte is at least one of sulfuric acid solution, nitric acid solution, hydrochloric acid solution, and perchloric acid solution.

[0013] As a preferred embodiment, the neutral electrolyte is at least one of sodium chloride solution, potassium chloride solution, sodium sulfate solution, and potassium sulfate solution.

[0014] Compared with the prior art, the beneficial effects of the present invention are as follows: By one-step hydrothermal synthesis of an integrated electrode and subsequent calcination, an Ru / WO 3-x integrated electrode with oxygen vacancies is obtained. Under the same test conditions, this catalyst can effectively inhibit the over-hydrogenation of nitrate to the final product ammonia, and make the product stay at the intermediate hydroxylamine. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is the X-ray powder diffraction pattern of the Ru / WO 3-x , WO 3-x and Ru catalysts in Example 1 of the present invention;

[0016] Figure 2 is the elemental surface scan and line scan diagram of the Ru / WO 3-x in Example 1 of the present invention;

[0017] Figure 3 is the electron paramagnetic resonance spectrum of the Ru / WO 3-x in Example 1 of the present invention and a commercial WO3 standard sample;

[0018] Figure 4 is the X-ray powder diffraction pattern of the Ru / WO 3-x at different calcination temperatures in the present invention;

[0019] Figure 5 is the electron paramagnetic resonance spectrum of the Ru / WO 3-x at different calcination temperatures in the present invention;

[0020] Figure 6 is the schematic diagram of the electrolysis device of the present invention;

[0021] Figure 7 is the polarization curve diagram of the nitrate electroreduction of the Ru / WO 3-x , WO 3-x and Ru integrated electrodes, experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate;

[0022] Figure 8 is the product selectivity distribution diagram of the nitrate electroreduction of the Ru / WO 3-x , WO 3-x and Ru integrated electrodes, experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate, 25 mA / cm2 Current density;

[0023] Figure 9 is the product selectivity distribution diagram of nitrate electroreduction on the Ru / WO integrated electrode with different Ru loadings of the present invention 3-x Experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate, 25 mA / cm 2 Current density;

[0024] Figure 10 is the product selectivity distribution diagram of nitrate electroreduction on the Ru / WO integrated electrode with different hydrothermal reaction times of the present invention 3-x Experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate, 25 mA / cm 2 Current density;

[0025] Figure 11 is the Ru / WO of the present invention 3-x Product selectivity distribution diagram of nitrate electroreduction with different current densities applied to the integrated electrode. Experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate;

[0026] Figure 12 is the Ru / WO of the present invention 3-x Product selectivity distribution diagram of electroreduction of the integrated electrode in electrolytes with different nitrate concentrations respectively. Experimental conditions: 1 mol / L sulfuric acid, 25 mA / cm 2 Current density. Detailed implementation manners

[0027] Next, the technical solutions in the embodiments of the present invention will be clearly and completely described in conjunction with the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are only a part of the embodiments of the present invention, rather than all the embodiments. The description of at least one exemplary embodiment below is actually only illustrative and in no way restrictive of the present invention and its application or use. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts belong to the scope of protection of the present invention.

[0028] Example 1

[0029] A Ru / WO 3-x heterojunction catalyst, and its preparation method is as follows:

[0030] (1) Ultrasonically clean a 2 cm×2 cm carbon paper in nitric acid, acetone, ethanol, and deionized water for 10 min each;

[0031] (2) Prepare the hydrothermal reaction solution: Dissolve 1.23 g of sodium tungstate dihydrate in 30 mL of deionized water, adjust the pH of the solution to 1, and successively add 0.94 g of oxalic acid dihydrate, 3.75 g of ammonium sulfate, and 100 mg of ruthenium trichloride, and stir evenly;

[0032] (3) Vertically place the carbon paper treated in step (1) in a polytetrafluoroethylene inner liner, add the hydrothermal reaction solution in step (2), put it into a stainless steel sealed outer shell, and place it in a blast drying oven for hydrothermal reaction. The reaction temperature is 180 °C and the time is 12 h. After the hydrothermal reaction is completed, take out the current collector, rinse it with deionized water and dry it to obtain the Ru-WO3·yH2O integrated electrode, where y is the number of crystal water molecules.

[0033] (4) Calcinate the Ru-WO3·yH2O integrated electrode in a hydrogen / argon reducing gas atmosphere with a hydrogen volume content of 10% at a constant temperature of 400 °C for 4 h. After the reaction cools down, the Ru / WO 3-x integrated electrode can be obtained, where x represents oxygen vacancies, and the final ruthenium loading is about 1 mg / cm 2 .

[0034] Characterize the product obtained in Example 1. The X-ray powder diffraction pattern shows that the Ru / WO 3-x integrated electrode contains two diffraction peaks of WO 3-x in the hexagonal crystal system and Ru metal ( Figure 1 ). The elemental surface scan and line scan maps show that the Ru element is evenly distributed on the surface of WO 3-x ( Figure 2 ). The electron paramagnetic resonance spectrum shows that compared with the commercial WO3 standard sample, Ru / WO 3-x has rich oxygen vacancies ( Figure 3 ). Thus, it can be proved that the Ru / WO 3-x integrated electrode rich in oxygen vacancies has been successfully synthesized.

[0035] The parameters of other examples are shown in the following table (the other parameters not listed are the same as those in Example 1):

[0036]

[0037] Compare the products obtained in Examples 1, 4, and 5. The X-ray powder diffraction pattern shows that as the calcination temperature increases from 300 °C to 500 °C, the crystal form of the carrier WO3 changes from the hexagonal crystal system to the orthorhombic crystal system ( Figure 4 ). The electron paramagnetic resonance spectrum shows that as the calcination temperature increases from 300 °C to 500 °C, the oxygen vacancy content in the carrier WO3 increases ( Figure 5 ).

[0038] Comparative Example 1

[0039] 70 μL of ruthenium(III) chloride solution (concentration 100 mg / mL) was directly drop-coated on carbon paper and calcined under the same conditions as in step (4) of Example 1 to obtain a comparative sample Ru metal integrated electrode, and the final Ru loading was about 1 mg / cm 2 .

[0040] Comparative Example 2

[0041] A hydrothermal reaction consistent with step (3) of Example 1 was carried out in a hydrothermal solution without a Ru source to synthesize a WO3·yH2O electrode, and then calcined under the same conditions as in step (4) of Example 1 to obtain a comparative sample WO 3-x integrated electrode.

[0042] Hydroxylamine selectivity test:

[0043] As Figure 6 shown, 1 mol / L sulfuric acid and 0.1 mol / L sodium nitrate were used as the cathode mixed electrolyte. Ru / WO 3-x , WO 3-x and Ru integrated electrodes were used as the cathode respectively, and a commercial IrO2 integrated electrode was used as the anode. The anode electrolyte was pure water, and a proton exchange membrane was used to separate the anode and cathode. Electrolysis was carried out at a constant current density of 25 mA / cm 2 for 12 h. The product hydroxylamine was determined by the ultraviolet-visible spectrophotometry reported by D. S. Frear and R. C. Burrell et al.; The polarization curve showed that the cell voltage required for the Ru / WO 3-x integrated electrode prepared in Example 1 as the cathode at the same current density (25 mA / cm 2 ) was 1.31 V, lower than that of the Ru metal integrated electrode (1.56 V) and WO 3-x integrated electrode (1.79 V) ( Figure 7 ). At this current density, the selectivity of the intermediate hydroxylamine obtained by the Ru / WO 3-x integrated electrode could reach 18.01±2.93%, higher than that of the Ru metal integrated electrode (7.03±2.63%), while the WO 3-x integrated electrode had no hydroxylamine selectivity and only produced ammonia ( Figure 8 ).

[0044] Reducing the Ru loading to about 0.1 mg / cm 2 (Example 2), the hydroxylamine selectivity decreased to 10.84±1.65%. Increasing the Ru loading to about 3 mg / cm 2 (Example 3), the hydroxylamine selectivity increased to 27.32±2.36% ( Figure 9 ).

[0045] The hydrothermal reaction time was reduced to 1 h (Example 6), and the selectivity of hydroxylamine was reduced to 9.32 ± 2.14%. When the hydrothermal reaction time was increased to 24 h (Example 7), the selectivity of hydroxylamine was increased to 19.32 ± 2.14% ( Figure 10 ).

[0046] The integrated electrode prepared in Example 1 was used for testing. When the current density was increased to 100 mA / cm 3-x and 600 mA / cm 2 respectively, the selectivity of hydroxylamine was reduced to 12.03 ± 2.54% and 3.65 ± 1.52% ( 2 ). When the nitrate concentration was increased to 0.5 mol / L and 1 mol / L respectively, the selectivity of hydroxylamine was increased to 36.84 ± 3.74% and 41.28 ± 4.02% ( Figure 11 ). Figure 12 ).

[0047] The above are the preferred embodiments of the present invention. Those skilled in the art to which the present invention pertains can also make changes and modifications to the above embodiments. Therefore, the present invention is not limited to the above specific embodiments, and any obvious improvements, substitutions or variations made by those skilled in the art on the basis of the present invention fall within the protection scope of the present invention.

Claims

1. An application of a Ru / WO 3-x heterojunction catalyst integrated electrode in the electroreduction of nitrate to hydroxylamine, characterized in that: The specific steps are as follows: The electrolyte uses an acidic or neutral electrolyte containing nitrate. The cell voltage applied to the electrolytic cell is 0.8 - 3 V, and the current density is 0.1 - 600 mA / cm 2 , and the electrolysis time is 0.1 - 24 h; The chemical formula of the catalyst is Ru / WO 3-x , x represents oxygen vacancy; Ru / WO 3-x Ru is loaded on WO in the form of metal element 3-x The support surface is prepared as follows: S1. Prepare the hydrothermal reaction solution: Use tungstate as the tungsten source, ammonium sulfate as the morphology assistant, ruthenium trichloride as the ruthenium source, adjust the pH to 0 - 2, and add deionized water to prepare the hydrothermal reaction solution; S2. Prepare the Ru-WO3·yH2O integrated electrode: Carry out hydrothermal reaction on the hydrothermal reaction solution in S1 together with the current collector at a reaction temperature of 120 - 200 °C and a reaction time of 1 - 24 h. After the reaction, rinse with deionized water and dry to obtain the Ru-WO3·yH2O integrated electrode, where y is the number of crystal water molecules; S3. Preparation of Ru / WO 3-x Heterojunction catalyst integrated electrode: The Ru-WO3·yH2O integrated electrode can be calcined in a reducing gas atmosphere to obtain Ru / WO 3-x Heterojunction catalyst integrated electrode, where the reducing gas is a hydrogen / argon mixture or a hydrogen / nitrogen mixture, the proportion of hydrogen gas in the mixture is 5-10%, the calcination temperature is 300-500 °C, the time is 2-6 h, and the final ruthenium loading range is 0.1-3 mg / cm 2 .

2. According to claim 1, Ru / WO 3-x The application of the integrated electrode of the heterojunction catalyst in the electroreduction of nitrate to hydroxylamine is characterized in that: In step S1, the hydrothermal reaction solution is prepared as follows: Dissolve sodium tungstate dihydrate in deionized water, adjust the solution pH to 0 - 2, add oxalic acid dihydrate and ammonium sulfate, stir until homogeneous, and finally add ruthenium trichloride solution. In the finally obtained hydrothermal reaction solution, the concentration range of sodium tungstate dihydrate is 0.01 - 0.5 mol / L, the concentration range of oxalic acid is 0.01 - 0.5 mol / L, the concentration range of ammonium sulfate is 0.1 - 0.5 mol / L, and the concentration range of ruthenium trichloride is 0.1 - 10 mg / mL.

3. According to claim 1, Ru / WO 3-x The application of the integrated electrode of the heterojunction catalyst in the electroreduction of nitrate to hydroxylamine is characterized in that: In step S2, the current collector needs to be ultrasonically cleaned with nitric acid, acetone, ethanol, and deionized water before the hydrothermal reaction.

4. According to claim 3, Ru / WO 3-x The application of the integrated electrode of the heterogeneous catalyst in the electroreduction of nitrate to hydroxylamine is characterized in that: In step S2, the specific steps of the hydrothermal reaction are as follows: Vertically place the treated current collector in a polytetrafluoroethylene liner, add 30 mL of the hydrothermal reaction solution, put it into a stainless steel sealed outer shell, and place it in a forced-air oven for hydrothermal reaction.

5. According to claim 1, Ru / WO 3-x The application of the Ru / WO The acidic electrolyte is at least one of sulfuric acid solution, nitric acid solution, hydrochloric acid solution, and perchloric acid solution.

6. According to claim 1, Ru / WO 3-x Application of the integrated electrode of the heterogeneous catalyst in electroreduction of nitrate to hydroxylamine, characterized in that: The neutral electrolyte is at least one of sodium chloride solution, potassium chloride solution, sodium sulfate solution, and potassium sulfate solution.

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