A composite catalyst containing a molybdenum oxide base and a preparation method and application thereof

Abstract

The application belongs to the technical field of catalyst preparation, and particularly relates to a composite catalyst containing molybdenum oxide and a preparation method and application thereof. The preparation method comprises the following steps: (1) mixing molybdate and a ligand to obtain a mixed solution; (2) soaking foamed nickel in the mixed solution to obtain a suspension; wherein the soaking time is not less than 1 h; and (3) performing hydrothermal reaction and calcination. The preparation method utilizes the etching effect of molybdate on foamed nickel, and the foamed nickel is immersed in a mixed solution containing molybdate and a ligand, so that the nickel in the foamed nickel is dissolved in the form of ions, and a nickel-molybdenum complex transition layer is grown in situ on the surface of the foamed nickel by the molybdate ions and the ligand; a nickel-molybdenum-based catalyst precursor is grown on the complex transition layer through hydrothermal reaction, and the composite catalyst is obtained after calcination, so that the catalyst is firmly anchored on the foamed nickel substrate, thereby improving the stability and impact resistance of the catalyst and avoiding the shedding of active components in the catalyst.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of catalyst preparation, and particularly relates to a composite catalyst containing molybdenum oxide and a preparation method and application thereof. BACKGROUND

[0002] Hydrogen energy, as a green energy, only produces water when burned, which can effectively reduce air pollution and climate change. Meanwhile, hydrogen has the characteristics of high energy density and renewability, and can be used as an energy storage medium. Hydrogen can be prepared by electrolysis of water, and hydrogen can be converted into electricity when needed, so as to realize efficient storage and utilization of energy. In recent years, the development of water electrolysis hydrogen production technology has brought more possibilities for efficient preparation of green hydrogen energy.

[0003] However, most of the water electrolysis hydrogen production catalysts are platinum-based catalysts, which have low stability and are scarce, greatly limiting the wide application of hydrogen energy in life and production. SUMMARY

[0004] Therefore, the technical problem to be solved by the present application is to overcome the problem that the water electrolysis hydrogen production catalysts in the prior art mostly use platinum-based catalysts with low stability and scarcity, so as to provide a composite catalyst containing molybdenum oxide and a preparation method and application thereof.

[0005] To this end, the present application provides the following technical solutions.

[0006] The present application provides a preparation method of a composite catalyst containing molybdenum oxide, comprising the following steps:

[0007] (1) mixing molybdate and a ligand to obtain a mixed solution;

[0008] (2) soaking the foamed nickel in the mixed solution to obtain a suspension; wherein the soaking time is not less than 1h;

[0009] (3) hydrothermal reaction and calcination.

[0010] In the step (2), the soaking temperature is 10-60℃;

[0011] Preferably, the soaking is carried out at room temperature.

[0012] Preferably, the soaking time is 1-5h.

[0013] The step (2) further comprises the steps of oscillation and / or stirring while soaking.

[0014] Preferably, the oscillation frequency is 50-200rpm.

[0015] The ligand is at least one of an oxygen-containing organic ligand, a nitrogen-containing organic ligand and a sulfur-containing organic ligand.

[0016] Preferably, the ligand is at least one of carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, sodium dodecyl sulfate, uric acid, p-phenylenediamine, terephthalic acid, and trimesic acid.

[0017] In the step (1), the mass concentration of the ligand in the mixed solution is 3-16 g / L.

[0018] In the step (1), the mass concentration of the molybdate in the mixed solution is 30-160 g / L.

[0019] Preferably, the molybdate is at least one of ammonium molybdate tetrahydrate, ammonium molybdate, and ammonium phosphomolybdate.

[0020] In the step (1), the mass ratio of the molybdate to the ligand is (5-15):1.

[0021] The temperature of the hydrothermal reaction is 100-180℃, and the time is 2-12 h.

[0022] Preferably, the calcination specifically comprises: heating at a heating rate of 4-10℃ / min to 350-600℃ for 0.5-8 h.

[0023] Preferably, the volume content of hydrogen in the atmosphere of the calcination is 4-10%.

[0024] In the preparation of the mixed solution, there is no specific requirement for the mixing order of the raw materials, as long as the mixture is uniform. In the preparation of the mixed solution, any of the following methods can be used:

[0025] (1) dissolving the molybdate and the ligand in water to obtain a clear mixed solution;

[0026] (2) dissolving the molybdate in water to obtain solution 1; dissolving the ligand in water to obtain solution 2; mixing solution 1 and solution 2 to obtain a clear mixed solution.

[0027] In the preparation of the composite catalyst, the ligand is added, and the foamed nickel is immersed in the mixed solution to obtain a suspension, which can dissolve the metal nickel in the foamed nickel and generate a nickel-molybdenum complex transition layer in situ on the surface of the molybdate ion and the ligand, so that the connection between the catalyst and the foamed nickel substrate is more firm.

[0028] The application further provides a molybdenum oxide-containing composite catalyst prepared by the above method.

[0029] The application further provides an application of the composite catalyst prepared by the above method in the electrolysis of water to produce hydrogen.

[0030] The technical scheme of the application has the following advantages:

[0031] 1. The preparation method of the composite catalyst containing molybdenum oxide provided by the present application, the preparation method comprising (1) mixing molybdate and ligand to obtain a mixed solution; (2) soaking the foamed nickel in the mixed solution to obtain a suspension; wherein the soaking time is not less than 1 h; (3) hydrothermal reaction and calcination. The composite catalyst prepared by the method has low cost, good stability and high activity. The preparation method utilizes the etching effect of molybdate on foamed nickel, immerses the foamed nickel in the mixed solution containing molybdate and ligand, makes the nickel in the foamed nickel dissolve in the form of ions, grows a nickel-molybdenum complex transition layer on the surface of the foamed nickel in situ with the molybdate ions and the ligand, grows a nickel-molybdenum-based catalyst precursor on the complex transition layer through hydrothermal reaction, and obtains the composite catalyst after calcination; the complex transition layer well connects the foamed nickel substrate and the catalyst, so that the catalyst is firmly anchored on the foamed nickel substrate, thereby improving the stability and impact resistance of the catalyst and avoiding the shedding of the active components in the catalyst. Since the catalyst does not contain noble metals, the raw material cost is greatly reduced. The present application has simple process and mild operating conditions in the preparation of the catalyst, and the obtained catalyst has uniform distribution, high catalytic activity, good stability and is easy to mass-produce.

[0032] In addition, the present application does not need to add a nickel source or platinum-based noble metal in the preparation of the catalyst.

[0033] 2. The preparation method of the composite catalyst containing molybdenum oxide provided by the present application, which immerses the foamed nickel in the mixed solution at room temperature and controls the soaking time to be 1-5 h, so that a nickel-molybdenum complex transition layer with appropriate thickness can be formed, further ensuring the connecting effect between the catalyst layer and the substrate, and effectively preventing problems such as excessive etching of the substrate, brittleness of the substrate, and influence on the subsequent preparation of the catalyst.

[0034] 3. The composite catalyst containing molybdenum oxide provided by the present application, which forms a sharp-knife-shaped catalyst layer with a size of 1-3 μm, and has the advantages of low cost, good stability and high activity. BRIEF DESCRIPTION OF DRAWINGS

[0035] In order to more clearly illustrate the specific embodiments of the present application or the technical solutions in the prior art, the drawings needed in the following specific embodiments or prior art description will be briefly introduced. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0036] Figure 1 is the scanning electron microscope image of the catalyst of Example 1 of the present application;

[0037] Figure 2is a scanning electron microscope image of the catalyst of Example 2 of the present application;

[0038] Figure 3 is a scanning electron microscope image of the catalyst of Comparative Example 1 of the present application;

[0039] Figure 4 is a scanning electron microscope image of the catalyst of Comparative Example 2 of the present application;

[0040] Figure 5 is an X-ray powder diffraction pattern of the catalyst of Example 1 of the present application;

[0041] Figure 6 is a transmission electron microscope image of the catalyst of Example 1 of the present application;

[0042] Figure 7 is a three-electrode long-time performance stability graph of the catalyst of Example 1;

[0043] Figure 8 is a linear sweep voltammetry curve of the catalyst of the example and comparative example. DETAILED DESCRIPTION

[0044] The following examples are provided to better further understand the present application, and are not limited to the best mode, and do not constitute a limitation on the content and scope of protection of the present application, and any person under the inspiration of the present application or the combination of the present application with other prior art features, any product identical or similar to the present application falls within the scope of protection of the present application.

[0045] The specific experimental steps or conditions are not indicated in the examples, and can be operated according to the conventional experimental steps described in the literature in the art or the operation or conditions. The reagents or instruments used are not indicated by the manufacturer, and are conventional reagent products that can be obtained by market purchase.

[0046] Example 1

[0047] The present embodiment provides a preparation method of a molybdenum oxide-containing composite catalyst, comprising the following steps:

[0048] (1) ammonium molybdate, polyvinylpyrrolidone and water are mixed to obtain a mixed solution, the mass concentration of ammonium molybdate in the mixed solution is 33 g / L, and the mass concentration of polyvinylpyrrolidone is 3 g / L.

[0049] (2) the foamed nickel and the mixed solution are placed in a shaker, so that the foamed nickel is soaked and shaken in the mixed solution for 2 h, the frequency of shaking is 150 rpm, and a white green suspension is obtained; wherein, the temperature of soaking and shaking is 25℃.

[0050] (3) The foamed nickel and the white-green suspension liquid are placed in a hydrothermal reaction at 150°C for 6h to obtain a catalyst precursor; then the temperature is raised to 500°C at a temperature raising rate of 5°C / min, and the catalyst precursor is calcined at 500°C for 2h to obtain a composite catalyst containing molybdenum oxide; wherein the volume ratio of hydrogen in the calcination atmosphere is 5%, and the rest of the gas is argon.

[0051] Example 2

[0052] The embodiment provides a preparation method of a composite catalyst containing molybdenum oxide, comprising the following steps:

[0053] (1) Ammonium molybdate, sodium dodecyl sulfate and water are mixed to obtain a mixed solution, and the mass concentration of ammonium molybdate in the mixed solution is 100g / L, and the mass concentration of sodium dodecyl sulfate is 15g / L.

[0054] (2) The foamed nickel and the mixed solution are placed in a shaker, so that the foamed nickel is soaked and shaken in the mixed solution for 2h, and the frequency of the shaking is 150rpm, to obtain a white-green suspension liquid; wherein the soaking temperature is 25°C.

[0055] (3) The foamed nickel and the white-green suspension liquid are placed in a hydrothermal reaction at 150°C for 6h to obtain a catalyst precursor; then the temperature is raised to 500°C at a temperature raising rate of 5°C / min, and the catalyst precursor is calcined at 500°C for 2h to obtain a composite catalyst containing molybdenum oxide; wherein the volume ratio of hydrogen in the calcination atmosphere is 5%, and the rest of the gas is argon.

[0056] Comparative Example 1

[0057] The comparative example provides a preparation method of a composite catalyst, comprising the following steps:

[0058] (1) Ammonium molybdate, polyvinylpyrrolidone and water are mixed to obtain a mixed solution, and the mass concentration of ammonium molybdate in the mixed solution is 33g / L, and the mass concentration of polyvinylpyrrolidone is 3g / L.

[0059] (2) The foamed nickel and the mixed solution are mixed, and a hydrothermal reaction is performed at 150°C for 6h to obtain a catalyst precursor; then the temperature is raised to 500°C at a temperature raising rate of 5°C / min, and the catalyst precursor is calcined at 500°C for 2h to obtain a composite catalyst; wherein the volume ratio of hydrogen in the calcination atmosphere is 5%, and the rest of the gas is argon.

[0060] Comparative Example 2

[0061] The comparative example provides a preparation method of a composite catalyst, comprising the following steps:

[0062] (1) Ammonium molybdate and water are mixed to obtain a solution, and the mass concentration of ammonium molybdate in the solution is 33g / L.

[0063] (2) The foamed nickel and the above solution were placed in a shaker, and the foamed nickel was soaked and shaken in the solution for 2 h at a frequency of 150 rpm, to obtain a blue clear solution; wherein the soaking temperature was 25°C.

[0064] (3) The foamed nickel and the above blue solution were placed in a hydrothermal reactor at 150°C for 6 h to obtain a catalyst precursor; then the temperature was raised to 500°C at a rate of 5°C / min, and the catalyst precursor was calcined at 500°C for 2 h to obtain a composite catalyst; wherein the volume ratio of hydrogen in the calcination atmosphere was 5%, and the rest of the gas was argon.

[0065] Test Example

[0066] The test example provides performance tests of the catalysts prepared in each of the examples and the comparative examples, as follows:

[0067] Test method for catalyst stability: A catalyst with a size of about 1 cm x 1 cm was taken, soaked in water, and then treated with ultrasound for 3600 s, to observe whether the catalyst fell off, and to compare the stability of the catalysts in the examples and the comparative examples. The frequency of the ultrasound was 53 KHz.

[0068] Polarization curve of the catalyst: A three-electrode test method was used, with the catalyst as the cathode (the catalyst was from each of the examples and the comparative examples), a platinum mesh as the counter electrode, and a saturated calomel electrode as the reference electrode, to measure in a glass electrolytic cell, with a potassium hydroxide solution with a molar concentration of 1 mol·L -1 -1 as the electrolyte, to obtain an overpotential of 1 A·cm -2 -1. A commercial platinum-carbon catalyst was used as a control group, with the manufacturer and model being Johnson Matthey, HISPEC10000; 60% Pt.

[0069] Table 1: Performance test results of the catalysts in the examples and the comparative examples

[0070] Example Stability of the catalyst Current density of 1 A-cm -2 Overpotential of 0.2 V Example 1 No peeling after the end of the ultrasound 81 Example 2 No peeling after the end of the ultrasound 102 Comparative Example 1 Peeling after about 60 s of ultrasound 305 Comparative Example 2 Peeling after about 300 s of ultrasound 320

[0071] Figure 1-4 The scanning electron microscope images of the catalysts in Example 1, Example 2, Comparative Example 1, and Comparative Example 2, respectively. As can be seen from Figure 1-4 , the catalysts in Examples 1-2 have a sharp knife-like structure, and the morphology is uniform; the catalyst in Comparative Example 1 is relatively broken and not uniform, and the catalyst in Comparative Example 2 has many cracks and is a spike-like structure, which is not uniform.

[0072] Figure 5 is the X-ray powder diffraction pattern of the catalyst in Example 1, and as can be seen from Figure 5 , the bulk structure of the catalyst is molybdenum dioxide.

[0073] Figure 6 is a transmission electron microscope image of Example 1. From Figure 6 It can be seen that the morphology of the catalyst presents a sharp knife structure; its bulk structure is molybdenum dioxide phase, and metal nickel nanoparticles are attached on the top.

[0074] Figure 7 is a three-electrode long-time performance stability diagram of the catalyst of Example 1, from which it can be seen that the catalyst has excellent stability.

[0075] Figure 8 is a linear sweep voltammetry curve of Example 1-2, Comparative Example 1-2 and the control group, from which it can be seen that the catalyst of Example 1-2 has excellent catalytic hydrogen evolution performance.

[0076] From the above results, it can be seen that the catalyst of Example 1-2 of the present application does not fall off after ultrasonic treatment for 3600s, indicating that the catalyst has good stability, further indicating that the catalyst has good mechanical strength and impact resistance, and can anchor the catalyst on the nickel foam substrate, avoiding the active component from falling off.

[0077] Further, by the overpotential of 1A·cm -2 , it can be seen that the catalyst of Example 1-2 of the present application has good catalytic activity. Further, Comparative Example 1 directly hydrothermally reacts the nickel foam and the mixed solution to obtain the catalyst, which is prone to falling off and has decreased activity; in Comparative Example 2, the ligand is removed during the preparation of the catalyst, and the catalyst obtained falls off after ultrasonic treatment for about 300s, and the catalyst activity is lower than that of the present application.

[0078] Obviously, the above examples are only examples for clearly illustrating, and do not limit the embodiments. For those skilled in the art, on the basis of the above description, other different forms of changes or variations can also be made. Here, it is not necessary and impossible to enumerate all the embodiments. The obvious changes or variations derived therefrom are still within the protection scope of the present application.

Claims

1. A method for producing a composite catalyst containing molybdenum oxide, characterized by, The method comprises the following steps: (1) mixing molybdate and ligand to obtain a mixed solution; (2) soaking the foamed nickel in the mixed solution to obtain a suspension; wherein the soaking time is not less than 1 hour; wherein the soaking is accompanied by a shaking and / or stirring step; (3) hydrothermal reaction and calcination.

2. The production method according to claim 1, characterized by, In the step (2), the soaking temperature is 10-60℃.

3. The production method according to claim 2, characterized by, The soaking is carried out at room temperature.

4. The production method according to claim 2, characterized by, The soaking time is 1-5 hours.

5. The method of any one of claims 1-4, wherein, The shaking frequency is 50-200 rpm.

6. The method of any one of claims 1-4, wherein, The ligand is at least one of oxygen-containing organic ligand, nitrogen-containing organic ligand and sulfur-containing organic ligand.

7. The production method according to claim 6, characterized by, The ligand is at least one of carboxymethyl cellulose, methyl cellulose, polyvinyl alcohol, sodium alginate, polyvinylpyrrolidone, sodium dodecyl sulfate, uric acid, p-phenylenediamine, terephthalic acid and trimesic acid.

8. The method of any one of claims 1-4, wherein, In the step (1), the mass concentration of the ligand in the mixed solution is 3-16 g / L.

9. The method of any one of claims 1-4, wherein, In the step (1), the mass concentration of the molybdate in the mixed solution is 30-160 g / L.

10. The method of any one of claims 1-4, wherein, The molybdate is at least one of ammonium molybdate tetrahydrate, ammonium molybdate and ammonium phosphomolybdate.

11. The method of any one of claims 1-4, wherein, In the step (1), the mass ratio of the molybdate to the ligand is (5-15):

1.

12. The method of any one of claims 1-4, wherein, The hydrothermal reaction temperature is 100-180℃ and the time is 2-12 hours.

13. The method of any one of claims 1-4, wherein, The calcination specifically comprises: heating at a heating rate of 4-10℃ / min to 350-600℃ and calcining for 0.5-8 hours.

14. The method of claim 13, wherein, The hydrogen content in the calcination atmosphere is 4-10%.

15. The molybdenum oxide-containing composite catalyst prepared by the method of any one of claims 1-14.

16. The use of the composite catalyst prepared by the method of any one of claims 1-14 in the electrolysis of water to produce hydrogen.

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