Ru / WO3-x heterojunction catalyst and application

Abstract

The invention relates to the technical field of catalysis, in particular to a Ru / WO3-x heterojunction catalyst, the chemical formula of the catalyst is Ru / WO3-x, and x represents oxygen vacancy; ru is loaded on the surface of a WO3-x support in the form of a metal simple substance, and the preparation method comprises the following steps: by taking tungstate as a tungsten source, ammonium sulfate as a morphology adjuvant and ruthenium trichloride as a ruthenium source, adjusting the pH value to 0-2, adding deionized water to prepare a hydrothermal reaction solution, performing hydrothermal reaction with a current collector, washing with deionized water, and drying, thereby obtaining the WO3-x support. And calcining in a reducing gas atmosphere to obtain the Ru / WO3-x heterojunction catalyst integrated electrode. Under the same test condition, nitrate can be effectively inhibited from being excessively hydrogenated into the final product ammonia, so that the product stays in the intermediate hydroxylamine.

Description

Technical Field

[0001] The present invention relates to the field of catalytic technology, and in particular to a Ru / WO 3-x Heterojunction catalysts and their applications. Background Art

[0002] Nowadays, nitrate wastewater has become one of the main factors leading to eutrophication of water bodies and decline in biodiversity. Traditional nitrate purification technologies, such as biological denitrifying bacteria technology and chemical oxidation-reduction technology, have disadvantages such as uncontrollable reaction rate and high cost. The nitrate electroreduction reaction is a continuous reaction of hydrogenation to generate nitrite, hydroxylamine and ammonia in sequence under the regulation of specific catalysts. 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 drug intermediates in the pharmaceutical industry, photolithography developers in the electronics industry, and corrosion inhibitors in the anti-corrosion industry, while the latter is mainly used as agricultural fertilizers, chemical raw materials and hydrogen storage carriers. At present, hydroxylamine is mainly synthesized in industry through the Raschig Process, catalytic reduction of nitro compounds and catalytic oxidation (HPO) method. Although they are mature in industrialization, they have disadvantages such as high cost and low yield of precious metal catalysts. The use of emerging electrocatalyst technology to convert nitrates into hydroxylamine in a targeted manner is more environmentally friendly, but there is currently a lack of electrocatalysts that can generate hydroxylamine with high selectivity. Summary of the invention

[0003] The present invention solves the problems in the related art and proposes a Ru / WO 3-x Heterojunction catalysts, Ru / WO with oxygen vacancies, were obtained by one-step hydrothermal synthesis of integrated electrodes and calcination. 3-x The integrated electrode can be used for the electroreduction of nitrate to produce hydroxylamine. Under the same test conditions, the catalyst can effectively inhibit the excessive hydrogenation of nitrate to the final product ammonia, so that the product remains as the intermediate hydroxylamine.

[0004] In order to solve the above technical problems, the present invention is implemented by the following technical solutions: a Ru / WO 3-x Heterojunction catalyst, 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 hydrothermal reaction solution: Use tungstate as tungsten source, ammonium sulfate as morphology auxiliary agent, ruthenium trichloride as ruthenium source, adjust pH to 0-2, add deionized water to prepare hydrothermal reaction solution, S2, preparation of Ru-WO3·yH2O integrated electrode: the hydrothermal reaction solution in S1 is subjected to hydrothermal reaction together with the current collector, the reaction temperature is 120-200°C, the reaction time is 1-24 h, after the reaction is completed, it is rinsed with deionized water and dried to obtain the Ru-WO3·yH2O integrated electrode, y is the number of crystal water; S3. Preparation of Ru / WO 3-x Heterojunction catalyst integrated electrode: Ru / WO can be obtained by calcining the Ru-WO3·yH2O integrated electrode in a reducing gas atmosphere. 3-x The heterojunction catalyst integrated electrode is characterized in that the reducing gas is a hydrogen / argon mixed gas or a hydrogen / nitrogen mixed gas, the volume ratio of hydrogen to the mixed gas 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 .

[0005] As a preferred embodiment, in step S1, the preparation method of the hydrothermal reaction solution is 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 uniform, and finally add ruthenium trichloride solution. In the hydrothermal reaction solution finally obtained, the concentration of sodium tungstate dihydrate ranges from 0.01 to 0.5 mol / L, the concentration of oxalic acid ranges from 0.01 to 0.5 mol / L, the concentration of ammonium sulfate ranges from 0.1 to 0.5 mol / L, and the concentration of ruthenium trichloride ranges from 0.1 to 10 mg / mL.

[0006] 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.

[0007] As a preferred embodiment, 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 shell, and place it in a forced air oven for hydrothermal reaction.

[0008] As a preferred solution, the Ru / WO 3-x The heterojunction catalyst integrated electrode can be applied to the electroreduction of nitrate to hydroxylamine. The specific steps are as follows: Ru / WO 3-x The integrated electrode is used as the cathode, commercial IrO2 is used as the anode, the cathode electrolyte is an acidic or neutral electrolyte containing nitrate, the anolyte is pure water, the proton exchange membrane is used to separate the cathode and cathode for electrolysis, the cell voltage applied to the electrolyzer is 0.8~3 V, and the current density is 0.1~600 mA / cm 2 , the electrolysis time is 0.1~24 h.

[0009] As a preferred embodiment, the acidic electrolyte is at least one of a sulfuric acid solution, a nitric acid solution, a hydrochloric acid solution, and a perchloric acid solution.

[0010] As a preferred embodiment, the neutral electrolyte is at least one of a sodium chloride solution, a potassium chloride solution, a sodium sulfate solution, and a potassium sulfate solution.

[0011] Compared with the prior art, the present invention has the following advantages: the present invention obtains Ru / WO with oxygen vacancies by one-step hydrothermal synthesis of an integrated electrode and calcination. 3-x Integrated electrode, under the same test conditions, the catalyst can effectively inhibit the excessive hydrogenation of nitrate into the final product ammonia, so that the product remains at the intermediate hydroxylamine. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 The Ru / WO of Example 1 of the present invention 3-x , WO 3-x and X-ray powder diffraction spectra of Ru catalysts; Figure 2 The Ru / WO of Example 1 of the present invention 3-x Element surface scan and line scan diagrams; Figure 3 The Ru / WO of Example 1 of the present invention 3-x Electron paramagnetic resonance spectrum with commercial WO3 standard sample; Figure 4 The present invention Ru / WO 3-x X-ray powder diffraction spectra at different calcination temperatures; Figure 5 The present invention Ru / WO 3-x Electron paramagnetic resonance spectra at different calcination temperatures; Figure 6 is a schematic diagram of an electrolysis device of the present invention; Figure 7 The present invention Ru / WO 3-x , WO 3-x Polarization curve of nitrate reduction at Ru integrated electrode, experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate; Figure 8 The present invention Ru / WO 3-x , WO 3-x Product selectivity distribution of nitrate reduction by Ru-integrated electrode, experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate, 25 mA / cm 2 Current density; Fig. 9 The Ru / WO with different Ru loading amounts in the present invention 3-xProduct selectivity distribution of nitrate reduction by integrated electrode, experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate, 25 mA / cm 2 Current density; Fig.10 The Ru / WO of different hydrothermal reaction times of the present invention 3-x Product selectivity distribution of nitrate reduction by integrated electrode, experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate, 25 mA / cm 2 Current density; Fig.11 The present invention Ru / WO 3-x Product selectivity distribution diagram of nitrate electroreduction at different current densities applied to the integrated electrode. Experimental conditions: 1 mol / L sulfuric acid, 0.1 mol / L sodium nitrate; Fig.12 The present invention Ru / WO 3-x Product selectivity distribution diagram of the integrated electrode in different nitrate concentration electrolytes. Experimental conditions: 1 mol / L sulfuric acid, 25 mA / cm 2 Current density. DETAILED DESCRIPTION

[0013] 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, rather than all the embodiments. The following description of at least one exemplary embodiment is actually only illustrative and is by no means intended to limit the present invention and its application or use. 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.

[0014] Example 1

[0015] A Ru / WO 3-x The heterojunction catalyst is prepared as follows: (1) A 2 cm × 2 cm carbon paper was ultrasonically cleaned in nitric acid, acetone, ethanol, and deionized water for 10 min in sequence; (2) Prepare the hydrothermal reaction solution: dissolve 1.23 g sodium tungstate dihydrate in 30 mL deionized water, adjust the pH of the solution to 1, add 0.94 g oxalic acid dihydrate, 3.75 g ammonium sulfate and 100 mg ruthenium trichloride in sequence, and stir evenly; (3) The carbon paper treated in step (1) is placed vertically in a polytetrafluoroethylene liner, the hydrothermal reaction solution in step (2) is added, and the carbon paper is placed in a stainless steel sealed shell, and the carbon paper is placed in a forced air oven for hydrothermal reaction at a temperature of 180°C for 12 h. After the hydrothermal reaction is completed, the current collector is removed, rinsed with deionized water, and dried to obtain a Ru-WO3·yH2O integrated electrode, where y is the number of crystal waters.

[0016] (4) The Ru-WO3·yH2O integrated electrode was calcined 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 was cooled, Ru / WO 3-x Integrated electrode, x represents oxygen vacancies, and the final ruthenium loading is about 1 mg / cm 2 .

[0017] The product obtained in Example 1 was characterized, and the X-ray powder diffraction spectrum showed that Ru / WO 3-x The integrated electrode contains hexagonal WO 3-x and Ru metal diffraction peaks ( Figure 1 ), the element surface scan and line scan show that the Ru element is evenly distributed in WO 3-x surface( Figure 2 ), the electron paramagnetic resonance spectrum shows that compared with the commercial WO3 standard sample, Ru / WO 3-x There are abundant oxygen vacancies in Figure 3 ), which proves that Ru / WO rich in oxygen vacancies was successfully synthesized 3-x Integrated electrode.

[0018] The parameters of other embodiments are shown in the following table (other parameters not listed are the same as those of embodiment 1):

[0019] Comparing the products obtained in Examples 1, 4, and 5, the X-ray powder diffraction spectrum shows that as the calcination temperature increases from 300°C to 500°C, the carrier WO3 crystal form changes from hexagonal to orthorhombic ( Figure 4 ), the electron paramagnetic resonance spectrum shows that as the calcination temperature increases from 300℃ to 500℃, the oxygen vacancy content in the carrier WO3 increases ( Figure 5 ).

[0020] Comparative Example 1 70 μL of ruthenium trichloride solution (concentration 100 mg / mL) was directly drop-coated on the carbon paper and calcined under the same conditions as step (4) in Example 1 to obtain a comparative Ru metal integrated electrode. The final Ru loading was about 1 mg / cm 2 .

[0021] Comparative Example 2 The WO3·yH2O electrode can be synthesized by carrying out a hydrothermal reaction in the same manner as step (3) of Example 1 in a hydrothermal solution without a Ru source, and then calcining conditions in the same manner as step (4) of Example 1 can be carried out to obtain a comparative WO3·yH2O electrode. 3-x Integrated electrode.

[0022] Hydroxylamine Selective Test: like Figure 6 As shown in the figure, 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 The Ru integrated electrode was used as the cathode, the commercial IrO2 integrated electrode was used as the anode, the anolyte was pure water, and the anode and cathode were separated by a proton exchange membrane. 2 The electrolysis was carried out for 12 h, and the product hydroxylamine was determined by UV-visible spectrophotometry reported by D.S. Frear and R.C. Burrell et al.; the polarization curve shows that the Ru / WO prepared in Example 1 3-x The integrated electrode was used as the cathode at the same current density (25 mA / cm 2 ) requires a cell voltage of 1.31 V, which is lower than that of Ru metal integrated electrode (1.56 V) and WO 3-x Integrated electrode (1.79 V) ( Figure 7 ), at this current density Ru / WO 3-x The intermediate hydroxylamine selectivity obtained by the integrated electrode can reach 18.01±2.93%, which is higher than that of the Ru metal integrated electrode (7.03±2.63%), while the WO 3-x The integrated electrode has no selectivity for hydroxylamine and only produces ammonia ( Figure 8 ).

[0023] Reduce the ruthenium loading to about 0.1 mg / cm 2 (Example 2), the hydroxylamine selectivity was reduced to 10.84±1.65%, and the ruthenium loading was increased to about 3 mg / cm 2 (Example 3), the selectivity of hydroxylamine was increased to 27.32±2.36% ( Fig. 9 ).

[0024] When the hydrothermal reaction time was reduced to 1 h (Example 6), the hydroxylamine selectivity was reduced to 9.32±2.14%, and when the hydrothermal reaction time was increased to 24 h (Example 7), the hydroxylamine selectivity was increased to 19.32±2.14% ( Fig.10 ).

[0025] The Ru / WO prepared in Example 1 was used 3-xIntegrated electrode test, increasing the current density to 100 mA / cm 2 and 600 mA / cm 2 , the hydroxylamine selectivity decreased to 12.03±2.54% and 3.65±1.52%, respectively ( Fig.11 ), the nitrate concentration was increased to 0.5 mol / L and 1 mol / L, respectively, and the hydroxylamine selectivity was increased to 36.84±3.74% and 41.28±4.02%, respectively ( Fig.12 ).

[0026] The above are preferred implementation modes of the present invention. Those skilled in the art to which the present invention belongs can also change and modify the above implementation modes. Therefore, the present invention is not limited to the above specific implementation modes. Any obvious improvements, substitutions or modifications made by those skilled in the art on the basis of the present invention belong to the protection scope of the present invention.

Claims

1. Ru / WO 3-x A heterojunction catalyst, characterized in that: 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 a hydrothermal reaction solution: use tungstate as a tungsten source, ammonium sulfate as a morphology auxiliary agent, ruthenium trichloride as a ruthenium source, adjust the pH to 0-2, and add deionized water to prepare a hydrothermal reaction solution; S2, preparation of Ru-WO3·yH2O integrated electrode: the hydrothermal reaction solution in S1 is subjected to hydrothermal reaction together with the current collector, the reaction temperature is 120-200°C, the reaction time is 1-24 h, after the reaction is completed, it is rinsed with deionized water and dried to obtain the Ru-WO3·yH2O integrated electrode, y is the number of crystal water; S3. Preparation of Ru / WO 3-x Heterojunction catalyst integrated electrode: Ru / WO can be obtained by calcining the Ru-WO3·yH2O integrated electrode in a reducing gas atmosphere. 3-x The heterojunction catalyst integrated electrode is characterized in that the reducing gas is a hydrogen / argon mixed gas or a hydrogen / nitrogen mixed gas, the volume ratio of hydrogen to the mixed gas 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. Ru / WO according to claim 1 3-x A heterojunction catalyst, characterized in that: In step S1, the preparation method of the hydrothermal reaction solution is 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 uniform, and finally add ruthenium chloride solution. In the hydrothermal reaction solution finally obtained, 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 chloride is 0.1-10 mg / mL.

3. Ru / WO according to claim 1 3-x A heterojunction catalyst, 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. Ru / WO according to claim 3 3-x A heterojunction catalyst, characterized in that: In step S2, the specific steps of the hydrothermal reaction are as follows: the treated current collector is vertically placed in a polytetrafluoroethylene liner, 30 mL of the hydrothermal reaction solution is added, and the current collector is placed in a stainless steel sealed housing, and placed in a forced air oven for hydrothermal reaction.

5. Ru / WO according to claim 1 3-x A heterojunction catalyst, characterized in that: The obtained Ru / WO 3-x The heterojunction catalyst integrated electrode can be used for nitrate reduction to hydroxylamine. 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 , the electrolysis time is 0.1~24 h.

6. Ru / WO according to claim 5 3-x A heterojunction catalyst, characterized in that: The acidic electrolyte is at least one of a sulfuric acid solution, a nitric acid solution, a hydrochloric acid solution, and a perchloric acid solution.

7. Ru / WO according to claim 5 3-x A heterojunction catalyst, characterized in that: The neutral electrolyte is at least one of a sodium chloride solution, a potassium chloride solution, a sodium sulfate solution, and a potassium sulfate solution.

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